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Sample records for central patagonian cordillera

  1. Continental underthrusting and obduction during the Cretaceous closure of the Rocas Verdes rift basin, Cordillera Darwin, Patagonian Andes

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    Klepeis, Keith; Betka, Paul; Clarke, Geoffrey; Fanning, Mark; Hervé, Francisco; Rojas, Lisandro; Mpodozis, Constantino; Thomson, Stuart

    2010-06-01

    The Patagonian Andes record a period of Cretaceous-Neogene orogenesis that began with the compressional inversion of a Late Jurassic rift called the Rocas Verdes basin. Detrital zircon ages from sediment that filled the southern part of the basin provide a maximum depositional age of ˜148 Ma, suggesting that the basin opened approximately simultaneously along its length during the Late Jurassic. Structural data and U-Pb isotopic ages on zircon from granite plutons near the Beagle Channel (55°S) show that basin inversion involved two stages of shortening separated by tens of millions of years. An initial stage created a small (˜60 km wide) thrust wedge that placed the basaltic floor of the Rocas Verdes basin on top of adjacent continental crust prior to ˜86 Ma. Structures and metamorphic mineral assemblages preserved in an exhumed middle to lower crustal shear zone in Cordillera Darwin suggest that this obduction was accompanied by south directed subduction of the basaltic crust and underthrusting of continental crust to depths of ˜35 km beneath a coeval volcanic arc. A subsequent stage of out-of-sequence thrusting, culminating in the Paleogene, shortened basement and Upper Jurassic igneous rock in the internal part of the belt by at least ˜50 km, forming a bivergent thrust wedge. This latter period coincided with the exhumation of rocks in Cordillera Darwin and expansion of the fold-thrust belt into the Magallanes foreland basin. This orogen provides an important example of how orogenesis initiated and led to continental underthrusting and obduction of basaltic crust during closure of a quasi-oceanic rift basin.

  2. La cordillera oriental colombiana no se desprende de la cordillera central

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    Ujueta, Guillermo

    2012-01-01

    Geologically the Central and Eastern Cordilleras depict different periods of genesis and different types of rocks which allow them to keep their identities and independence from Colombia to Bolivia; however, in the area of study are connected by a bridge formed by a recent geomorphollogical feature which is the result of combined tectonic and volcanic stresses which took place toward the end of the Pliocene. This bridge has a direction NW-SE and connects the Cutanga Volcanoe on the Central Co...

  3. Geochronology, geochemistry and tectonic evolution of the Western and Central cordilleras of Colombia

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    Villagómez, Diego; Spikings, Richard; Magna, Tomas; Kammer, Andreas; Winkler, Wilfried; Beltrán, Alejandro

    2011-08-01

    Autochthonous rocks of the pre-Cretaceous continental margin of NW South America (the Tahami Terrane) are juxtaposed against a series of para-autochthonous rock units that assembled during the Early Cretaceous. Allochthonous, oceanic crust of the Caribbean Large Igneous Province collided with and accreted onto the margin during the Late Cretaceous. We present the first regional-scale dataset of zircon U-Pb LA-ICP-MS ages for intrusive and metamorphic rocks of the autochthonous Tahami Terrane, Early Cretaceous igneous para-autochthonous rocks and accreted oceanic crust. The U-Pb zircon data are complemented by multiphase 40Ar/ 39Ar crystallization and cooling ages. The geochronological data are combined with whole rock major oxide, trace element and REE data acquired from the same units to constrain the tectonic origin of the rock units and terranes exposed in the Western Cordillera, Cauca-Patía Valley and the Central Cordillera of Colombia. The Tahami Terrane includes lower Paleozoic orthogneisses (~ 440 Ma) that may have erupted during the active margin stage of the Rheic Ocean. Basement gneisses were intruded by Permian, continental arc granites during the final assembly of Pangea. Triassic sedimentary rocks were subsequently deposited in rift basins and partially melted during high-T metamorphism associated with rifting of western Pangea during 240-220 Ma. Continental arc magmatism during 180-145 Ma is preserved along the whole length of the Central Cordillera and was followed by an Early Cretaceous out-board step of the arc axis and the inception of the Quebradagrande Arc that fringed the continental margin. Back-stepping of the arc axis may have been caused by the collision of buoyant seamounts, which were coeval with plateau rocks exposed in the Nicoya Peninsular of Costa Rica. Rapid westward drift of South America closed the Quebradagrande basin in the late Aptian and caused medium-high P-T metamorphic rocks of the Arquía Complex to exhume and obduct onto

  4. Recent (0-8 Ma) tectonics and exhumation processes in Cordilleras Blanca and Negra, Central Peru: Constraints from (U-Th)/He dating

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    Margirier, Audrey; Robert, Xavier; Gautheron, Cécile; Audin, Laurence

    2014-05-01

    The Central Andes are a classical example of topography building in front of an oceanic subduction. However, many first order questions are still debated: How do subduction processes and observed tectonic uplift interact along the Andean margin? What is the impact of tectonic, magmatism and climate on exhumation? The Cordilleras Blanca (6768 m) and Negra (5181 m), in north Central Peru, belong to the highest Andean reliefs. Both ranges trend parallel to the subduction zone and are separated by the NW-SE Rio Santa valley. The Cordillera Blanca pluton formed in an active subduction context at 8-5 Ma and renders an abnormal magmatic activity over a planar subduction. In contrast with the Cordillera Blanca, the Cordillera Negra is an older relief, which evolution and exhumation history has never been studied. A remarkable ~200 km-long normal fault system showing ~4500 m of vertical displacement since 5 Ma edges the western flank of the Cordillera Blanca. This region is a perfect target to study the impact of magmatism and subduction processes on exhumation. We perform a morphotectonic study on both cordilleras coupled with low-temperature thermochronology apatite (U-Th)/He dating to quantify these processes. Geomorphic parameters and altitude contrasts between these two ranges indicate a differential uplift. The Cordillera Negra displays a smooth and asymmetric relief from the West to the East whereas the Cordillera Blanca shows higher and sharper relief with North/South and East/West contrasts. We obtain apatite (U-Th)/He ages for twenty samples located along vertical and horizontal profiles at different latitudes of the Cordilleras Blanca and Negra. The (U-Th)/He ages range from 13.4 ± 1.3 to 5.6 ± 0.6 Ma in the Cordillera Negra and range from 11.8 ± 1.2 to 2.0 ± 0.2 Ma in the Cordillera Blanca. We use them as inputs in QTQt tools for time-temperature reconstructions and thus to constrain the exhumation history. Whole ages evidence a more regional exhumation than

  5. Petrographic and Geochemical Characterization of the Cambumbia STOCK in Andean Central Cordillera, Colombia

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    Rojas Lequerica, S.; Jaramillo Mejía, J.; Concha Perdomo, A.

    2012-12-01

    The Cambumbia Stock is located on the western flank of the Central Cordillera of the northern Andes. The goals of this study were to petrographic and geochemically characterize the Cambumbia igneous body and to establish its petrogenetic history. 41 samples were collected, 28 for petrographic analysis and 14 for elementary chemical determination by ICP-MS. Petrographically the samples were classified as hornblende and pyroxene-gabbros varying to diorites, gabbronorites and tonalites, the rock texture varies from medium to coarse granular grain, with local microporfiritic texture. It was concluded from the major elements analysis that the samples correspond to the sub-alkaline series with low K content, mainly in the calc-alkaline series, within the gabbros and diorites fields. By using the SiO2 vs TiO2 (Jaramillo, 1980), Th/Yb vs Ta/Yb (Pearce, 1984) (Fig. 1) and Zr/117-Th-Nb/16 (Wood, 1979) diagrams it was determined that these rocks were generated in two geotectonic environments: one type MOR (extension) and other island arc (subduction, compression). Petrographic and geochemical comparisons between the rocks of Cambumbia Stock and Diorite and Gabbro El Pueblito (Giraldo, 2009) (located about 25 km to the north-west) may postulate a possible genetic link between them. Recently, a U/Pb age was obtained by the Universidad de Caldas in zircon in 2009 (not published data), yielded an age of 233.41 ± 3.4 Ma (Middle Triassic). This age is consistent with the global event of the extension and fragmentation of Pangea supercontinent. In addition, the mantle nature of the source and the petrogenetic evolution of the magmatic system were established. References GIRALDO, M.I., (2009): Esquema geodinámica de la parte noroccidental de la cordillera Central de Colombia. (Thesis). p.56-68. Universidad Nacional de Colombia, Medellín. JARAMILLO, J.M. (1980): Petrology and geochemistry of the Nevado del Ruiz Volcano northern Andes, Colombia (Thesis). 167 p. University of Houston

  6. Three new species of Pristimantis (Lissamphibia, Anura from montane forests of the Cordillera Yanachaga in Central Peru

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    William E. Duellman

    2007-12-01

    Full Text Available We describe three additional new species of Pristimantis from the Cordillera Yanachaga, a part of the Andes in central Peru. Analyses of DNA sequences of the mitochondrial rRNA genes show that onespecies is a close relative of P. bipunctatus (P. conspicillatus Group, another is a close relative of P. stictogaster (P. peruvianus Group, and the third is related to several species in the P. unistrigatus Group. The first two species are morphologically similar to their closest relatives but occur at lower elevations. Twenty-nine species of Pristimantis and Phrynopus are known from the vicinity of the Cordillera Yanachaga. The number of species, especially of Pristimantis, is high in the humid montane forestin comparison with other sites in humid montane forests in Peru, but the number is lower than on the western slopes of the Andes in Ecuador.

  7. Un modelo de la historia de la vegetación de la Cordillera de La Costa de Chile central-sur: la hipótesis glacial de Darwin A model for the history of vegetation of the Coastal Range of central-southern Chile: Darwin's glacial hypothesis

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    CAROLINA VILLAGRÁN

    2001-12-01

    Andean and at high latitudes exist in south-central Chile, between 37 and 43° S. According to Darwin (1859, such "islands" are remnants of glacial populations, which were distributed at lower altitudes and latitudes during glacier advances. Also, in Chile there were expansions of the Andean and southernmost flora into the Longitudinal Valley of Los Lagos region during the last glaciation, which reversed during the Late-glacial (14, 600-10,000 14C years BP and Holocene (after 10,000 14C years BP. Considering this hypothesis, in this study we analyzed two palynological sequences from summits of the Coastal Range of Los Lagos region (Cordillera de Nahuelbuta and Cordillera de Sarao and both were correlated with published high and low altitude records from the Los Lagos and Los Canales regions. The records from the Coastal Range show the following chronological sequence: (1 at the lower and middle Holocene, after 9,040 14C years BP, the Cordillera de Sarao site documents the colonization of Magellanic moorlands and north-Patagonian forest elements, followed by north-Patagonian-Valdivian forest elements during the upper Holocene; (2 the Cordillera de Nahuelbuta site shows the development of conifer forest and Magellanic moorlands during the middle Holocene, ca. 5,430 14C years BP. Other palynological records from the Coastal Range (Cordillera Pelada and Cordillera de Piuchué show the development of both communities during the Late-glacial and lower Holocene. In contrast, the low altitude pollen records from the Los Lagos region indicate that conifers and magellanic moorland elements occupied the Longitudinal Valley during the Last Glacial Maximum (LGM, ca. 22,000 14C years BP. Various pollen profiles from Los Lagos and Los Canales regions evidenced for the late-glacial (14,600-10,000 14C years BP the rapid southern expansion of conifers and other north-Patagonian elements, following the deglaciation of these areas. During the Holocene, Valdivian forest elements invaded the

  8. Serpentinitas y cromititas de La Cabaña, Cordillera de la Costa, Chile central

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    Fernando Barra; Osvaldo M Rabbia; Guillermo Alfaro; Hubert Miller; Christine Höfer; Stefan Kraus

    1998-01-01

    RESUMEN Las serpentinitas del área de La Cabaña forman parte de la Serie Occidental del Basamento Metamórfico de la Cordillera de la Costa de la IX Región y corresponden a dunitas de grano grueso parcial a totalmente serpentinizadas. Contienen cromita como mineral accesorio, la que generalmente está alterada en grado variable a ferricromita. En cambio, las cromitas presentes en las cromititas de Centinela Bajo, preservan su composición original con un mínimo grado de alteración, lo que permit...

  9. A new colorful species of Pristimantis (Anura: Craugastoridae) from the eastern flank of the Cordillera Central in Colombia .

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    Rivera-Prieto, Diego A; Rivera-Correa, Mauricio; Daza, Juan M

    2014-01-01

    We describe a new species of Pristimantis from the humid forests on the eastern flank of the northern Cordillera Central in Colombia (6º 23' 19.3554" N, 75º 1' 24.0594" W; ca. 1150 m.a.s.l.). Pristimantis jaguensis sp. nov. is characterized by an extraordinary variation in color and is readily distinguished from congeneric species by lacking nuptial pads, discoidal fold and conical calcar tubercles; flanks and belly white to cream without blotches as well as iris yellow ocher to copper with thick brown reticulation and cream sclera. Molecular phylogenetic analyses recovered the new species in a clade with species mostly distributed in Ecuador. Our finding suggests that new taxa can still be discovered in the Middle Magdalena River valley of Colombia despite the extensive sampling this region has received during the last decades.  PMID:25543734

  10. Tithonian age of dinosaur fossils in central Patagonian, Chile: U-Pb SHRIMP geochronology

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    Suárez, Manuel; De La Cruz, Rita; Fanning, Mark; Novas, Fernando; Salgado, Leonardo

    2015-12-01

    Three Tithonian concordant U-Pb SHRIMP zircon ages of 148.7 ± 1.4, 147.9 ± 1.5 and 147.0 ± 1.0 from tuffs intercalated in a clastic sedimentary succession with exceptional dinosaur bones including the new taxon Chilesaurus diegosuarezi gen. et sp. nov. exposed in central Chilean Patagonia (ca. 46°30'S) are reported herein. The fossiliferous beds accumulated in a synvolcanic fan delta reaching a shallow marine basin as indicated by glauconite present in some of the beds, and coeval with the beginning of the transgression of the Aysén Basin.

  11. 40Ar/39Ar ages from blueschists of the Jambaló region, Central Cordillera of Colombia : implications on the styles of accretion in the Northern Andes

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    Bustamante, A.; Juliani, C.; C. M. Hall; Essene, E. J.

    2011-01-01

    This paper presents the first argon dating of blueschists from the Jambaló area (Cauca Department) in the Central Cordillera of the Colombian Andes. Step-heating 40Ar/39Ar spectra were obtained for mica from several lenses of blueschists including greenschist facies rocks. The blueschists are mainly constituted of preserved lenticular cores in strongly mylonitic rocks, which resulted from retrometamorphic processes that affected the high pressure rocks during their exhumation. The majority of...

  12. Petrological characteristics of Plio-Quaternary 'Sencca' Ignimbrites, Western Cordillera of the Central Andes in Peru

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    Çubukçu, H. E.; Gerbe, M.-C.; Thouret, J.-C.; de la Rupelle, A.; Boivin, P.

    2012-04-01

    Large-volume ignimbrite deposits have been emplaced between 24.6 and 1.37 Ma in the western Andean Cordillera of Southern Peru. The ignimbrites older than 9 Ma (Nazca, Alpabamba, Huaylillas and Caraveli ignimbrites) have formed plateaus, whereas the deep valleys incised in plateaus have been filled by younger Lower-Upper Sencca (~5- 2 Ma) and Las Lomas ignimbrites. Among the younger valley-filling units, Lower and Upper Sencca ignimbrites, with intercalated Upper Barroso lavas, have probably originated from a source beneath the Nevado Coropuna volcano. The unwelded-to-loose, crystal-poor pumice flows of Las Lomas unit (c.1.56-1.37 Ma) can be readily distinguished in the field from the rhyolitic Sencca ignimbrites. In contrast, discriminating Lower Sencca from Upper Sencca deposits in the field is difficult due to comparable lithofacies characteristics. Such a distinction is, however, essential in order to determine temporal constraints on valley incision. The Lower Sencca compound ignimbrite sheet is more widespread (~800 km2) than the Upper Sencca ignimbrite sheet (~600 km2). The Lower Sencca ignimbrites usually form terraces hanging on valley sides but Upper Sencca form deposits crop out near the present valley bottoms or in shallow valleys on high plateaus around Barroso volcanoes. The Lower Sencca ignimbrite is composed of multiple cooling units with a crystal- and fiamme-rich vitrophyric base, overlain by strongly welded, eutaxitic subunits towards the top. Uppermost subunits exhibit an indurated ash and pumice rich vapour-phase facies. The Upper Sencca ignimbrite sheet comprises two subunits only: (1) the basal, black vitrophyre, overlain by a fiamme- and crystal-rich, strongly welded, eutaxitic subunit; 2) the upper subunit with an indurated or slightly welded, crystal-poor, pumice-rich vapour phase facies The dominant mineralogy of Lower Sencca compound ignimbrites includes plagioclase (An13-68) + alkali feldspar (Or38-65) + biotite (XMg: Mg/Mg+Fe= 0

  13. Calculo Preliminar de la Tasa de Meteorización del Batolito Antioqueño, Cordillera Central, Colombia

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    Carolina Garcia

    2010-04-01

    Full Text Available Este trabajo es una estimación preliminar del tiempo necesario para generar la espesa capa de saprolito que caracteriza el perfil de meteorización actual de un batolito cuarzodiorítico cretácico que aflora en altiplanos de la Cordillera Central de Colombia, entre 5º50' y 7º00' de latitud Norte y 74º50' y 75º35' de longitud Oeste y a alturas entre 750 y 2700 m.Se utilizan datos obtenidos previamente mediante el análisis de la composición química de las aguas superficiales de cuatro cuencas con áreas diferentes, ubicadas sobre el Batolito Antioqueño, al este de Medellín. Los cáculos se hicieron con el método basado en la pérdida de componentes en solución utilizando diferentes valores de solutos. Al utilizar la pérdida de sílice se obtiene un tiempo de meteorización de unos 6 x 10 6 años, comparable con el obtenido mediante la datación de las cenizas volcánicas mas antiguas que recubren la topografía actual y que indican la fecha mínima de configuración de la superficie de erosión.A pesar de resultar de una serie de suposiciones simplificadoras, este resultado es interesante y justifica la realización de determinaciones mas detalladas. Confirma la larga preservación de superficies de erosión antiguas conformadas sobre un saprolito que desde hace varios millones de años no ha sido sometido a una erosión profunda, fenómeno poco común en una zona tectónicamente activa como la estudiada.

  14. Migración boyacense en la Cordillera Central, 1876-1945Del altiplano cundiboyacense a los espacios de homogeneización antioqueña*

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    Ramírez Bacca, Renzo; Tobasura Acuña, Isaías

    2014-01-01

    El artículo ofrece un enfoque histórico-sociológico sobre el proceso migracional cundiboyacense en la cordillera central colombiana. Explica la evolución histórica y las fases de la migración, sus procesos socioculturales, interpreta las determinantes del fenómeno, y explica el perfil de su contacto y consecuente adaptación e integración con el elemento de ascendencia antioqueña en la zona de asentamiento. El espacio andino escogido —municipios del Líbano y Murillo en el departamento del Toli...

  15. Unraveling an antique subduction process from metamorphic basement around Medellín city, Central Cordillera of Colombian Andes

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    Bustamante, Andres; Juliani, Caetano

    2011-10-01

    varies between 400 and 555 °C at pressures of 5-6 kbar in the retrograde metamorphic path. The El Retiro rocks evidence strong decompression with narrow variation in temperature, showing pressure values between 8.7 and 2.7 kbar at temperatures of 740-633 °C. These metamorphic fragments of the basement in the Central Cordillera of the Colombian Andes could represent a close relationship with an antique subduction zone.

  16. El caso del Outburst Flood histórico de la laguna Derrumbe, Cholila, Chubut: Colapso de dique Morénico en la Cordillera Norpatagónica The historic outburst flood of the laguna Derrumbe, Cholila, Chubut: Fast glacier retreat and moraine dam failure in North Patagonian Cordillera

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    Bruno Colavitto

    2012-09-01

    Full Text Available La laguna Derrumbe es un cuerpo de agua ubicado en los Andes Norpatagónicos en la provincia de Chubut, Argentina. Está contenida en un circo glaciario y endicada por una morena frontal del glaciar homónimo. A través del reconocimiento de campo se pudo describir a esta laguna y a un importante depósito rocoso que se halla aguas abajo de la misma, interpretado como un depósito de outburst flood. Estos depósitos son generados por procesos de alta energía relacionados con la rotura de un dique natural, en este caso un dique morénico. El estudio realizado permitió concluir que la morena frontal del glaciar Derrumbe sufrió una rotura parcial en tiempos históricos, desatando así una inundación súbita aguas abajo de la laguna, a través del valle del río Tigre, en la localidad de Cholila. En este trabajo se analizaron las posibles causas que dieron lugar a la rotura, la cual probablemente sea producto del rápido retroceso que el glaciar experimentó durante la década del ´50 y principios del ´60. Retroceso comparable con el ocurrido en muchos de los cuerpos glaciares de los Andes Patagónicos durante el último siglo.The Laguna Derrumbe is a body of water located in the North Patagonian Andes, in Chubut province, Argentina. This lake is contained in a glacial cirque and dammed by the terminal moraine of the namesake glacier. Through field survey it was possible to describe this lake and an important rocky deposit downstream of it, which is interpreted as an outburst flood deposit. These deposits are generated by high-energy processes related to the failure of a natural dam, in this case a moraine dam. The study made allowed to conclude that the frontal moraine of the Derrumbe glacier suffered a partial rupture in historic times, unleashing a flash flood downstream to the lake, through the Tigre river valley in the town of Cholila. In this work the possible causes that led to the failure are discussed, concluding that the main cause

  17. U-Pb La-ICP-ms geochronology and regional correlation of middle Jurassic intrusive rocks from the Garzon Massif, Upper Magdalena Valley and central cordillera, southern Colombia

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    New U-Pb zircon geochronology from four granitic units sampled along a southeast-northwest transect between the Garzon massif and the Serrania de las Minas (central cordillera), records a middle Jurassic magmatic activity with two different spatio-temporal domains at ca. 189 ma and 180-173 ma. Reconnaissance data suggest that the four granitoids are characterized by mineralogical and geochemical characteristics akin to a continental magmatic arc setting. The new results suggest that the southern Colombian continental margin includes remnants of tectonomagmatic elements formed by the subduction of the Farallon plate under the South American continental margin. This middle Jurassic arc magmatism is part of the broader Andean scale arc province, and is significant for understanding the tectonic and paleogeographic scenario that characterized the Mesozoic tectonic evolution of the northern Andes.

  18. The High Andean Cordillera of central Argentina and Chile along the Piuquenes Pass-Cordon del Portillo transect: Darwin's pioneering observations compared with modern geology

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    Laura Giambiagi

    2009-04-01

    Full Text Available The geological observations made by Darwin in 1835 during his crossing of the Andes from Santiago to Mendoza via the Piuquenes Pass and Cordón del Portillo are compared with the present geological knowledge of the Cordillera Principal and Cordillera Frontal at 33°-34°S. The analysis of the complex stratigraphy of the Cordillera Principal, the imbricated structure of the Aconcagua fold and thrust belt, as well as the stratigraphy and structure of the inter mountain foreland Tunuyán Basin, allows to assess the pioneer observations of Darwin. He recognized the old metamorphic basement and the granitoids and volcanic sequences of late Paleozoic to Triassic age of the Cordillera Frontal, established the Cretaceous age of the marine successions cropping out along the eastern Cordillera Principal and studied the conglomeratic deposits associated with the uplift of the Cordillera in the Alto Tunuyán Basin. Based on the study of clast provenance of the synorogenic deposits of the Alto Tunuyán Basin, Darwin recognized that the Cordillera Frontal was uplifted later than the Cordillera Principal. The present knowledge of this sector of the Andean Cordillera confirms his pioneer observations and show that Darwin was one of the first scientists ever in realizing that in an orogenic system the sequence of uplift and deformation proceeds from hinterland towards foreland, according to a process that is exceptionally well-illustrated along the Piuquenes-Cordón del Portillo transect.

  19. Depositación atmosférica de nitrógeno en un transecto valle longitudinal-cordillera de Los Andes, centro-sur de Chile Atmospheric deposition of nitrogen in a transect from the Central Valley to Cordillera de Los Andes, south-central Chile

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    CARLOS E. OYARZÚN

    2002-03-01

    Full Text Available El aumento de las actividades agrícolas y ganaderas en el centro-sur de Chile puede producir elevadas emisiones de nitrógeno hacia la atmósfera (mayormente NH3. El amoniaco es transportado por corrientes de aire y depositado en el suelo y vegetación. El presente estudio evalúa la depositación atmosférica de compuestos nitrogenados (NO3- y NH4+ en la química de las precipitaciones en un transecto altitudinal de 66 km, desde los alrededores de la ciudad de Osorno (40º 35' S, 72º 57' O, 55 m de altitud hasta la cordillera de Los Andes, Parque Nacional Puyehue (40º 46' S, 72º 11' O, 1.120 m de altitud. En siete sitios, durante el período anual junio-1999 hasta mayo-2000, se registró la precipitación y mensualmente se colectaron muestras de agua para determinar: pH, conductividad y las concentraciones de NO3- y NH4+. La precipitación anual se incrementó desde 1.103 mm en la zona de Osorno hasta 6.799 mm en el sector Antillanca, Parque Nacional Puyehue. Los valores promedio anual del pH registraron escasa variación desde 6,3 en el valle central hasta 5,8 en la cordillera de Los Andes. La conductividad presentó los máximos valores en la proximidad de Osorno (22,9 myS cm-1 para descender a través del transecto en zonas intermedias y alcanzar en la Cordillera de los Andes un valor de 11,3 myS cm-1. Las concentraciones promedio de NO3-Nen la lluvia fluctuaron entre 52,3 myg L-1 en la zona agrícola-ganadera y 6,9 myg L-1 en los bosques del Parque Nacional Puyehue. Las concentraciones de NH4-N variaron entre 699,4 myg L-1 en el sector de Osorno y 37,8 myL-1 en la cordillera de Los Andes. Los valores de N-inorgánico poseen una marcada tendencia estacional en el sector agrícola, con valores máximos en primavera-verano y los mínimos en invierno. Las tasas anuales de depositación atmosférica de NO3-N fluctuaron entre 0,53 y 0,57 kg ha-1 año-1 y las de NH4-N fueron entre 6,4 y 2,8 kg ha-1 año-1 para los sitios agrícola-ganaderos de

  20. Studies in Neotropical Paleobotany. XV. A Mio-Pliocene palynoflora from the Eastern Cordillera, Bolivia: implications for the uplift history of the Central Andes.

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    Graham, A; Gregory-Wodzicki, K M; Wright, K L

    2001-09-01

    An assemblage of 33 fossil pollen and spores, recovered from the 3600-m high Pislepampa locality of E. W. Berry, Eastern Cordillera, Bolivia, adds considerably to our knowledge of three aspects of the region in late Neogene time: (1) the paleovegetation, (2) the paleoclimate, and (3) the paleoelevation of the Central Andes. The plant microfossils recognized are Isoetes, Lycopodium (three types), Cnemidaria, Cyathea (three types), Grammitis, Hymenophyllum, Pteris, trilete fern spores (two types), Danaea, monolete fern spores (four types), Podocarpus, Gramineae, Palmae, Ilex, cf. Oreopanax, Cavanillesia, cf. Pereskia, Compositae (three types), Ericaceae, Tetrorchidium, and unknowns (three types). The diversity of the Compositae suggest that this flora has a maximum age around the Miocene-Pliocene boundary, that is, 6-7 million years. All members of the paleocommunity presently grow in the bosque montano húmedo (cloud forest) along the eastern slope of the Central Andes of Bolivia, which occurs between MATs (mean annual temperatures) of ∼10° and 20°C. The Pislepampa flora probably represents the lower limits of this forest because the fossil leaves collected by Berry from the same locality all have entire margins, suggesting that the flora grew near the cloud forest-tropical forest transition. Presently, the lower limit of the cloud forest forest has MATs of ∼20°C, a mean annual precipitation between 1000 and 1500 mm, and that part containing most of the identified genera of fossil pollen is found at elevations ∼1200-1400 m. These conditions are thus inferred for the Pislepampa flora; however, because of the uncertainty of the magnitude of global climate change and of possible changes in the ecological range of plant genera, we estimate an error of at least ±1000 m for the paleoelevation estimate. When the total uplift is corrected for probable amounts of erosionally driven isostatic rebound, the paleoelevation estimate suggests that from one-third to one

  1. Estado de conocimiento del orden Ephemeroptera en la Patagonia Current knowledge of Patagonian Ephemeroptera

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    Pablo Pessacq

    2009-06-01

    Full Text Available El conocimiento actual del orden Ephemeroptera en la Patagonia se debe en gran parte a la labor original y compilatoria de M.L. Pescador, W.L. Peters y E. Domínguez, llevada a cabo en la década del 80 del siglo pasado. Se suman a ésta, importantes contribuciones que han conducido a un adecuado conocimiento del grupo en la cordillera norte y centro de la Patagonia, aunque menor en la zona austral de esta región (Santa Cruz y Tierra del Fuego y las áreas de estepa. Merced al trabajo de campo realizado en 80 sitios de muestreo relevados en el marco del "Darwin Initiative Project" en el Parque Nacional Nahuel Huapi, se incluyen aquí nuevos registros para la Argentina (Hapsiphlebia anastomosis Demoulin, la región Andina (Apobaetis Day y la provincia de Río Negro (Chaquihua bullocki (Navás, Andesiops ardua (Lugo-Ortíz & McCafferty, Murphyella needhami Lestage y Dactylophlebia carnulenta Pescador & Peters. Con estos registros, la riqueza de Ephemeroptera de la Patagonia alcanza 43 especies y 24 géneros, de las cuales 33 (en 20 géneros se conocen para la Argentina.The current knowledge of the Patagonian Ephemeroptera is due to the original and compiling work by M.L. Pescador, W.L. Peters and E. Domínguez during last Century's 80´s . Besides, other previous publications exist that contributed to achieve a reasonable knowledge of its taxonomy for the norhtern and central Patagonian Andes, though poor for the southernmost mountain areas (Santa Cruz and Tierra del Fuego provinces and the steppe. From the field work carried in 80 collecting sites during the development of the "Darwin Initiative Project" in the Nahuel Huapi Nacional Park, some species are recorded for the first time in Argentina (Hapsiphlebia anastomosis Demoulin, the Andean region (Apobaetis Day and the province of Río Negro (Chaquihua bullock (Navás, Andesiops ardua (Lugo-Ortíz & McCafferty, Murphyella needhami Lestage, Dactylophlebia carnulenta Pescador & Peters. With

  2. Las bioconstrucciones de corales y sus facies asociadas durante el Malm en la Cordillera Ibérica Central (provincia de Zaragoza

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    Meléndez, A.

    1987-08-01

    Full Text Available The differents types of bioconstructions and associated facies in the Central Iberian Chain (Higueruelas Formation, Upper Kimmeridgian have been studied. Biohermes of different thickness (decimetric to metric and less lateral continuity are developped, highly colonized by corals, that are associated to oncolitic, bioclastic and oolitic of high energy facies, in marginal areas, near the litoral developpment. At the same time takes place an important set up of mud mounds, with a small coral colonisation, in protected arcas in a inner shelf, or in outer areas, where the action of the waves is not so effective. The environment protection is been generated in some places due to the appearance of oolitic barrier islands.Se estudian los diferentes tipos de bioconstrucciones de corales, y sus facies asociadas, presentes en el sector central de la rama aragonesa de la Cordillera Ibérica, en la Formación Higueruelas (Kimmeridgiense superior. Se desarrollan biohermos de potencias métricas a decimétricas y escasa continuidad lateral, intensamente colonizados por corales coloniales, que se encuentran asociados a facies oncolíticas, bioclásticas y oolíticas de alta energía en zonas marginales, próximas al desarrollo litoral. Al mismo tiempo tiene lugar una importante instalación de mud mounds, con escasa colonización de corales, en zonas protegidas dentro de la plataforma interna o en zonas más externas, donde la acción del oleaje no es efectiva. La protección del medio viene condicionada en algunos puntos por la aparición de islas barrera oolíticas.

  3. Caracterización de superficies de erosión mediante geomorfología cuantitativa, Altiplano Antioqueño, Cordillera Central de Colombia

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    Xavier Bustos

    2013-01-01

    Full Text Available En el presente trabajo se caracterizan treinta y cinco superficies de erosión (SE en la Cordillera Central de Colombia mediante geomorfología cuantitativa y análisis digital de terreno. Utilizando modelos digitales de elevación (MDE se derivaron las curvas hipsométricas para dichas superficies, y se comparan los resultados desde dos ópticas. Primero, mediante técnicas geoestadísticas utilizando subrutinas elaboradas bajo R, en combinación con el Lenguaje de Consulta Estructurado (SQL. Segundo, mediante sus respectivos valores de integral hipsométrica, lo que permitió discriminar el grado de madurez, juventud y vejez de las mismas. Desde un vista geomático este trabajo contribuye en el empleo de Bases de Datos Geográficas (Geodatabase lo que permite optimizar el tiempo y el número de cálculos en el procesamiento, todo esto fue integrado usando Sistemas de Información Geográfica (SIG. Los resultados obtenidos acá permiten caracterizar las superficies y relacionar su morfología con fenómenos físicos y climáticos tales como: levantamiento superficial del terreno, erosión, incisión de ríos y presencia de fallas. Adicionalmente, este enfoque multidisciplinario podría ser utilizado para caracterizar topo-formas remanentes a lo largo de Suramérica, las cuales son de vital importancia ya que contienen información de la interacción de procesos climáticos y tectónicos a lo largo del tiempo geológico.

  4. Present and future water resources supply and demand in the Central Andes of Peru: a comprehensive review with focus on the Cordillera Vilcanota

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    Drenkhan, Fabian; Huggel, Christian; Salzmann, Nadine; Giráldez, Claudia; Suarez, Wilson; Rohrer, Mario; Molina, Edwin; Montoya, Nilton; Miñan, Fiorella

    2014-05-01

    Glaciers have been an important element of Andean societies and livelihoods as direct freshwater supply for agriculture irrigation, hydropower generation and mining activities. Peru's mainly remotely living population in the Central Andes has to cope with a strong seasonal variation of precipitations and river runoff interannually superimposed by El Niño impacts. Direct glacier and lake water discharge thus constitute a vital continuous water supply and represent a regulating buffer as far as hydrological variability is concerned. This crucial buffer effect is gradually altered by accelerated glacier retreat which leads most likely to an increase of annual river runoff variability. Furthermore, a near-future crossing of the 'peak water' is expected, from where on prior enhanced streamflow decreases and levels out towards a new still unknown minimum discharge. Consequently, a sustainable future water supply especially during low-level runoff dry season might not be guaranteed whereas Peru's water demand increases significantly. Here we present a comprehensive review, the current conditions and perspectives for water resources in the Cusco area with focus on the Vilcanota River, Cordillera Vilcanota, Southern Peru. With 279 km2 the Cordillera Vilcanota represents the second largest glacierized mountain range of the tropics worldwide. Especially as of the second half of the 1980s, it has been strongly affected by massive ice loss with around 30% glacier area decline until present. Furthermore, glacier vanishing triggers the formation of new lakes and increase of lake levels and therefore constitutes determining hazardous drivers for mass movements related to deglaciation effects. The Vilcanota River still lacks more profound hydrological studies. It is likely that its peak water has already been or might be crossed in near-future. This has strong implications for the still at 0.9% (2.2%) annually growing population of the Cusco department (Cusco city). People mostly

  5. Diversidad florística y estructura de remanentes de bosque andino en la zona de amortiguación del parque nacional natural los nevados, cordillera central colombiana

    OpenAIRE

    Franco, Marcela; Betancur, Julio; Franco, Pilar

    2012-01-01

    Se caracterizó la diversidad, la composición fl orística y la estructura de los bosquesde la Reserva Torre Cuatro, la cual hace parte de la zona amortiguadora del ParqueNacional Natural Los Nevados, Cordillera Central de los Andes colombianos. Losremanentes de bosque se subdividieron en tres zonas de acuerdo a la altitud: baja(2650-2900 m), media (3000-3300 m) y alta (3400-3750 m), en cada una de las cualesse muestreó 0.1 ha y se censaron todos los individuos con DAP ≥ 2.5 cm. La riquezade es...

  6. Lichenometric dating using Rhizocarpon subgenus Rhizocarpon in the Patagonian Andes, Argentina

    Science.gov (United States)

    Garibotti, Irene Adriana; Villalba, Ricardo

    2009-05-01

    This study represents the first attempt to develop and apply lichenometric dating curves of Rhizocarpon subgenus Rhizocarpon for dating glacier fluctuations in the Patagonian Andes. Six glaciers were studied along the Patagonian Andes. Surfaces of known ages (historical evidences and tree-ring analyses) were used as control sites to develop indirect lichenometric dating curves. Dating curves developed for the studied glaciers show the same general logarithmic form, indicating that growth rate of subgenus Rhizocarpon decreases over time. The strong west-east precipitation gradient across the Andean Cordillera introduces statistically significant differences in the growth curves, with faster growth rates in the moist west sites than the drier eastern sites. Latitudinal difference among the studied glaciers does not appear to be a major factor regulating lichen growth rates. Therefore, we developed two lichenometric curves for dating glacier fluctuations in wetter and drier sites in the Patagonian Andes during the past 450 yrs. Application of the developed curves to moraine dating allowed us to complement glacial chronologies previously obtained by tree-ring analyses. A first chronosequence for moraine formation in the Torrecillas Glacier (42°S) is presented. Our findings confirm the utility of lichenometry to date deglaciated surfaces in the Patagonian Andes.

  7. Orogenesis at the southern tip of the Americas: the structural evolution of the Cordillera Darwin metamorphic complex, southernmost Chile

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    Cunningham, W. Dickson

    1995-04-01

    New, detailed lithologic and structural data are presented from three separately mapped areas along the southern boundary of the Cordillera Darwin metamorphic complex of southernmost Chile. Cordillera Darwin is a unique uplift because it exposes the highest grade rocks in the Andes south of Peru and averages 1 km higher in elevation than adjacent areas. The structural data indicate that Cordillera Darwin experienced mid-Late Cretaceous trans-pressional deformation with a partitioned strike-slip component localized along the Beagle Channel that forms the southern boundary to the range. Foliation, lineation and fold axis trends indicate NE-SW-directed contraction and NW-SE strike-slip shearing (present directions) during progressive {D1}/{D2} Andean deformation. D2 deformation is marked by outcrop-to 10 km-scale south-southwest-vergent folds. Late Cretaceous-Tertiary brittle-ductile and brittle left-lateral strike-slip faults and shear zones crosscut all {D1}/{D2} structures. Although limited structural evidence for extensional tectonics was documented in this study, apparent normal offsets across both arms of the Beagle Channel and previously documented field evidence for extension from other areas in Cordillera Darwin suggest that transtensional displacements also may have occurred in southern Cordillera Darwin during the Late Cretaceous-Early Tertiary. Cordillera Darwin's position within the evolving Patagonian Orocline adjacent to an evolving Mesozoic-Cenozoic left-lateral transform boundary between the South American and Antarctic plates, and later the South American and Scotia plates, necessitates consideration of the possible effects of regional counterclockwise rotation on development of structures. Regional counterclockwise rotation of Cordillera Darwin may have controlled the temporal and spatial transition of deformational regimes within Cordillera Darwin. Exhumation of the metamorphic core of Cordillera Darwin during the Late Cretaceous-Early Tertiary is

  8. Glacial areas, lakes areas, and snowlines from 1975-2012: Status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    Science.gov (United States)

    Hanshaw, Maiana Natania

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 144 multi-spectral satellite images spanning almost four decades, from 1975-2012, to obtain glacial and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. In a second step, we have estimated the snowline altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: First, since 1988 glacial areas throughout the Cordillera Vilcanota have been declining at a rate of 5.46 +/- 1.70 km2/yr (22-year average, 1988-2010, with 95 % confidence interval). The Quelccaya Ica Cap, specifically, has been declining at a rate of 0.67 +/- 0.18 km2/yr since 1980 (31-year average, 1980-2011, also with 95 % confidence interval); Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2011) as compared to the preceding decade (1990-2000); Third, the snowline of the Quelccaya Ice Cap is retreating to higher elevations as glacial areas decrease, by a total of almost 300 m between its lowest recorded elevation in 1989 and its highest in 1998; and fourth, as glacial regions have decreased, 61 % of lakes connected to glacial watersheds have shown a roughly synchronous increase in lake area, while 84 % of lakes not connected to glacial watersheds have remained stable or have declined in area. Our new and detailed data on glacial and lake areas over 37 years provide an important spatiotemporal assessment of climate variability in this area. These data can be integrated into further

  9. Glacial areas, lake areas, and snow lines from 1975 to 2012: status of the Cordillera Vilcanota, including the Quelccaya Ice Cap, northern central Andes, Peru

    Science.gov (United States)

    Hanshaw, M. N.; Bookhagen, B.

    2014-03-01

    Glaciers in the tropical Andes of southern Peru have received limited attention compared to glaciers in other regions (both near and far), yet remain of vital importance to agriculture, fresh water, and hydropower supplies of downstream communities. Little is known about recent glacial-area changes and how the glaciers in this region respond to climate changes, and, ultimately, how these changes will affect lake and water supplies. To remedy this, we have used 158 multi-spectral satellite images spanning almost 4 decades, from 1975 to 2012, to obtain glacial- and lake-area outlines for the understudied Cordillera Vilcanota region, including the Quelccaya Ice Cap. Additionally, we have estimated the snow-line altitude of the Quelccaya Ice Cap using spectral unmixing methods. We have made the following four key observations: first, since 1988 glacial areas throughout the Cordillera Vilcanota (1988 glacial area: 361 km2) have been declining at a rate of 3.99 ± 1.15 km2 yr-1 (22 year average, 1988-2010, with 95% confidence interval (CI), n = 8 images). Since 1980, the Quelccaya Ice Cap (1980 glacial area: 63.1 km2) has been declining at a rate of 0.57 ± 0.10 km2 yr-1 (30 year average, 1980-2010, with 95% CI, n = 14). Second, decline rates for individual glacierized regions have been accelerating during the past decade (2000-2010) as compared to the preceding decade (1988-1999) with an average increase from 37.5 to 42.3 × 10-3 km2 yr-1 km-2 (13%). Third, glaciers with lower median elevations are declining at higher rates than those with higher median elevations. Specifically, glaciers with median elevations around 5200 m a.s.l. are retreating to higher elevations at a rate of ~1 m yr-1 faster than glaciers with median elevations around 5400 m a.s.l. Fourth, as glacial regions have decreased, 77% of lakes connected to glacial watersheds have either remained stable or shown a roughly synchronous increase in lake area, while 42% of lakes not connected to glacial

  10. Osseous Metaplasia in a Free-living Snake (Patagonian Green Racer; Philodryas patagoniensis) in Brazil, 2012.

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    Nogueira, Carlos H O; Jerdy, Hassan L; Silveira, Leonardo S

    2016-04-28

    We describe an osseous metaplasia in a wild Patagonian green racer (Philodryas patagoniensis). The 5.5×1.5-cm lesion of irregular contour on the right dorsolateral surface proximal to the snake's cloaca was raised, hard, ulcerated centrally, and radiopaque and interfered with mobility. Microscopy revealed osseous metaplasia on skin and muscle. PMID:26981689

  11. Estratigrafía del Pérmico y Triásico en el sector central de la rama castellana de la Cordillera Ibérica.

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    Pérez-Arlucea, M.

    1985-08-01

    Full Text Available The main Permian and Triassic sequence in Molina de Aragón and South Albarracín is established. More than 45 sections have been studied, analysing the lateral changes and establishing 16 lithoestratigraphic Units. Part of these 1ithoestraigraphic Units were originally established by Ramos (1979 in the Molina de Aragon area, but this study prove that they can be followed to our arca. .
    The description, main characteristics, lateral changes and extension of each lithoestratigraphic Units are established here. .
    The paleogeography of this area with a large high located in the half north of Albarracín Sierra, is discussed here. That high was related with the tectonic movements contemporaneous to sedimentation during Upper Permian and Triassic.

    Se establece la sucesión estratigráfica tipo del Pérmico y Triásico de la región comprendida entre Molina de Aragón y el sur de Albarracín. Sobro la base do más de 45 columnas estratigráficas levantadas y del análisis de las variaciones que presentan los distintos tramos litológicos de que se compone la serie, se establecen 16 unidades litoestratigráficas, Aunque una parte de estas unidades fueron definidas originalmente en otros sectores de la Cordillera Ibérica, el estudio realizado demuestra que son también válidas en este área. Es el caso de las unidades definidas para parte del Pérmico y para las facies Buntsandstein por Ramos (1979, al oeste de Molina de Aragón.
    Se describen y analizan las principales características de cada una de las unidades litoestratigráficas establecidas. así como sus variaciones laterales y extensión superficial. .
    Por último, se discuten las implicaciones paleogeográficas que tuvo la existencia de un importante umbral situado en la mitad norte de la Sierra de Albarracín, Y se relaciona su presencia con la actividad tectónica contemporánea de la sedimentación del Pérmico superior y del Triásico.

  12. New KAr age determinations of intrusive rocks from the Cordillera Occidental and Altiplano of central Peru: Identification of magmatic pulses and episodes of mineralization

    Science.gov (United States)

    Soler, P.; Bonhomme, M. G.

    The post-Albian evolution of the Andes of central Peru is characterized by igneous activity, both effusive and intrusive, and by at least six distinct episodes of compressional tectonics. New KAr age determinations have been made of intrusive rocks from the Cajatambo-Oyón-Cerro de Pasco area. In conjunction with already published information, these new data permit a better estimate of the ages and the lateral extent of successive Cenozoic magmatic arcs. Metallogenetic implications of the 26.3-29.3 Ma age of mineralized Milpo-Atacocha intrusions are also discussed.

  13. The Patagonian toothfish: biology, ecology and fishery.

    Science.gov (United States)

    Collins, Martin A; Brickle, Paul; Brown, Judith; Belchier, Mark

    2010-01-01

    Patagonian toothfish (Dissostichus eleginoides) is a large notothenioid fish that supports valuable fisheries throughout the Southern Ocean. D. eleginoides are found on the southern shelves and slopes of South America and around the sub-Antarctic islands of the Southern Ocean. Patagonian toothfish are a long-lived species (>50 years), which initially grow rapidly on the shallow shelf areas, before undertaking an ontogenetic migration into deeper water. Although they are active predators and scavengers, there is no evidence of large-scale geographic migrations, and studies using genetics, biochemistry, parasite fauna and tagging indicate a high degree of isolation between populations in the Indian Ocean, South Georgia and the Patagonian Shelf. Patagonian toothfish spawn in deep water (ca. 1000 m) during the austral winter, producing pelagic eggs and larvae. Larvae switch to a demersal habitat at around 100 mm (1-year-old) and inhabit relatively shallow water (illegal, unreported and unregulated fishing (IUU). These problems have now largely been addressed, but continued vigilance is required to ensure that the species is sustainably exploited and the ecosystem effects of the fisheries are minimised.

  14. Utilización de recursos faunísticos y materias primas líticas durante el Holoceno tardío en la cordillera de Chile central: un enfoque integrador desde Caletón Los Queltehues Use of faunal resources and lithic raw materials during the late Holocene in the cordillera of central Chile: an integrative approach from Caletón los Queltehues

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    Rafael Labarca Encina

    2012-07-01

    Full Text Available Este trabajo evalúa, desde una perspectiva tecnológica y conductual, tendencias a largo plazo de cambio y continuidad en las estrategias de aprovechamiento de recursos faunísticos y líticos en contextos de cazadores-recolectores cordilleranos de Chile central. Para esto, tomamos los datos procedentes de un contexto ubicado en la cuenca superior del río Maipo: Caletón Los Queltehues, y escogimos, de su secuencia ocupacional, los componentes Arcaico IV y Alfarero temprano (5000 a 1000 AP. Los resultados de los análisis no arrojaron mayores variaciones entre ambos períodos en términos de taxones explotados, frecuencia de partes esqueletarias, modificaciones culturales y fragmentación de los restos óseos. De manera similar, las materias primas, las categorías morfofuncionales y los tipos de desechos líticos se observaron relativamente constantes. Sólo se registraron cambios en la tasa de la depositación, la frecuencia de modificaciones naturales y la diversidad de actividades de uso/descarte lítico, las que son interpretadas como una tendencia hacia una variación en la recurrencia e intensidad de la ocupación, pero no en cuanto a su funcionalidad.This article evaluates long-term trends in change and continuity of lithic and faunal use strategies in hunter-gatherer contexts in the central Chilean cordillera from technological and behavioral perspectives. The main objective of the analysis is to articulate both lines of evidence from a behavioral and technological perspective in order to infer unknown elements of the function and organization of activities in this kind of archaeological context. As an initial example, the Archaic IV and Early Ceramic (5000-1000 BP components from a classic site located in the upper valley of the Maipo river, Caletón Los Queltehues, were analyzed in detail. The results do not show significant variation between the periods in exploited taxa, skeletal part frequencies, cultural modifications, or

  15. The High Andean Cordillera of central Argentina and Chile along the Piuquenes Pass-Cordon del Portillo transect: Darwin's pioneering observations compared with modern geology La Alta Cordillera de los Andes del centro de Argentina y Chile a lo largo de la transecta del Paso Piuquenes-Cordón del Portillo: Las observaciones pioneras de Darwin comparadas con la geología moderna

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    Laura Giambiagi

    2009-04-01

    Full Text Available The geological observations made by Darwin in 1835 during his crossing of the Andes from Santiago to Mendoza via the Piuquenes Pass and Cordón del Portillo are compared with the present geological knowledge of the Cordillera Principal and Cordillera Frontal at 33°-34°S. The analysis of the complex stratigraphy of the Cordillera Principal, the imbricated structure of the Aconcagua fold and thrust belt, as well as the stratigraphy and structure of the inter mountain foreland Tunuyán Basin, allows to assess the pioneer observations of Darwin. He recognized the old metamorphic basement and the granitoids and volcanic sequences of late Paleozoic to Triassic age of the Cordillera Frontal, established the Cretaceous age of the marine successions cropping out along the eastern Cordillera Principal and studied the conglomeratic deposits associated with the uplift of the Cordillera in the Alto Tunuyán Basin. Based on the study of clast provenance of the synorogenic deposits of the Alto Tunuyán Basin, Darwin recognized that the Cordillera Frontal was uplifted later than the Cordillera Principal. The present knowledge of this sector of the Andean Cordillera confirms his pioneer observations and show that Darwin was one of the first scientists ever in realizing that in an orogenic system the sequence of uplift and deformation proceeds from hinterland towards foreland, according to a process that is exceptionally well-illustrated along the Piuquenes-Cordón del Portillo transect.Las observaciones geológicas efectuadas por Darwin en 1935 durante su cruce de la Cordillera de Los Andes entre Santiago y Mendoza realizado en 1835 a través de los pasos del Portillo y Piuquenes son examinadas y comparadas con el conocimiento actual existente de las Cordilleras Principal y Frontal entre los 33°-34°S. El análisis de la compleja estratigrafía de la Cordillera Principal, la estructura de las diferentes láminas imbricadas de la faja plegada y corrida del

  16. Análisis espectral de materiales geológicos en la Cordillera Volcánica Central de Costa Rica y su relación con la detección remota de anomalías

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    Rejas, J. G.

    2014-12-01

    Full Text Available The aim of this work is the comparative study of methods for calculating spectral anomalies from imaging spectrometry in several test areas of the Central Volcanic Range (CVR of Costa Rica. In the detection of anomalous responses it is assumed no prior knowledge of the targets, so that the pixels are automatically separated according to their spectral information significantly differentiated with respect to a background to be estimated, either globally for the full scene, either locally by image segmentation techniques. We used spectral ranges of visible-near infrared (VNIR, shortwave infrared (SWIR and thermal (TIR data cubes hiperepectrales from HyMAP airborne sensors and MASTER. We have designed experiments on natural scenes of the CVC, and semi-urban of different complexity, analyzing the behavior of the standard RX (Reed & Xiaoli, 1990 anomaly detector and different approaches based on imaging and dimensionality reduction. In this paper we propose a new technique for anomaly detection in hyperspectral data called DAFT (Detector de Anomalías de Fondo Térmico, as a Projection Pursuit (Malpica et al., 2008 variant, based on dimensionality reduction by projecting anomalies or targets with unknown spectral signature to the background, in a range thermal spectrum wavelengths. We discuss the results considering their implications on geological processes, as well as their use as terrestrial analogs for planetary exploration.El objetivo del presente trabajo es el estudio de bandas de absorción y reflexión de espectros de materiales geológicos presentes en distintas áreas de test de la Cordillera Volcánica Central (CVC de Costa Rica, y su correlación con el cálculo automático de anomalías a partir de espectrometría de imagen de alta resolución, también llamada teledetección hiperespectral. En la detección de respuestas anómalas se asume un no conocimiento previo de los objetivos. Los píxeles se separan automáticamente en funci

  17. Cambios latitudinales en la pesquería pelágica de merluza de cola (Macruronus magellanicus de la zona centro-sur (1986-2003 Latitudinal changes in the Patagonian grenadier (Macruronus magellanicus pelagic fishery off central-southern Chile (1986-2003

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    Luis A Cubillos

    2009-01-01

    Full Text Available Se analizaron los cambios espacio-temporales de las capturas de merluza de cola obtenidas por la flota industrial de cerco en la zona centro-sur de Chile (34°-41°30'S, para revisar la hipótesis de migración hacia el norte de la fracción juvenil de merluza de cola en primavera. Se utilizaron datos de bitácoras de pesca del periodo 1986-2003, y a partir de éstos se calcularon centros de gravedad de las capturas y su varianza. Se postula que si la flota sigue el comportamiento migratorio de la fracción juvenil, se esperaría que los centros de gravedad de las capturas migren latitudinalmente de sur a norte conforme la estación de pesca avanza. No obstante, sólo se encontró cuatro casos en que ocurrió una migración hacia el norte de los centroides. Más bien, los centros de gravedad se presentan estacionarios, al interior de cada temporada de pesca. Se postula que existe una fracción juvenil residente que sólo incrementa su accesibilidad y vulnerabilidad en aguas superficiales en primavera debido al régimen ambiental, que se caracteriza por la dominancia de eventos de surgencia y no a una migración de sur a norte.We analyzed spatio-temporal changes in Patagonian grenadier catches by the purse-seine fleet off central-southern Chile (34°-41°30'S in order to check the hypothesis that the juvenile fraction of the population migrates northward in spring. Log-book data from 1986 to 2003 were used to calculate the center of gravity of and variance of each catch. We proposed that, if the fleet follows the migratory behavior of the juvenile fraction, the centers of gravity of the catches will migrate from south to north as the fishing season progresses. Nevertheless, the centers of gravity migrated northward in only four cases. Unexpectedly, the centers of gravity remained stationary within each fishing season. Now we propose that, in spring, a resident juvenile fraction of Patagonian grenadier increases its accessibility and vulnerability

  18. Nueva especie de rana (atelopus) de los farallones de cali, cordillera occidental de colombia

    OpenAIRE

    Kattan, Gustavo

    2012-01-01

    Durante la realización de colecciones herpetológicas en el Departamento del Valle del Cauca, fue encontrada una especie no descrita de Atelopus (Anura: Bufonidae) en los farallones de Cali, a 2600 m de altura. Esta es la primera especie en este género que se encuentra a elevaciones superiores a 2000 m en la Cordillera Occidental. Se conocen varias especies de Atelopus en las Cordilleras Central y Oriental de Colombia y en los Andes ecuatorianos (COCHRAN y GOIN 1970; PETERS 1973; RIVERO 1963) ...

  19. Pleistocene refugia and polytopic replacement of diploids by tetraploids in the Patagonian and Subantarctic plant Hypochaeris incana (Asteraceae, Cichorieae).

    Science.gov (United States)

    Tremetsberger, Karin; Urtubey, Estrella; Terrab, Anass; Baeza, Carlos M; Ortiz, María Angeles; Talavera, María; König, Christiane; Temsch, Eva M; Kohl, Gudrun; Talavera, Salvador; Stuessy, Tod F

    2009-09-01

    We report the phylogeographic pattern of the Patagonian and Subantarctic plant Hypochaeris incana endemic to southeastern South America. We applied amplified fragment length polymorphism (AFLP) and chloroplast DNA (cpDNA) analysis to 28 and 32 populations, respectively, throughout its distributional range and assessed ploidy levels using flow cytometry. While cpDNA data suggest repeated or simultaneous parallel colonization of Patagonia and Tierra del Fuego by several haplotypes and/or hybridization, AFLPs reveal three clusters corresponding to geographic regions. The central and northern Patagonian clusters (approximately 38-51 degrees S), which are closer to the outgroup, contain mainly tetraploid, isolated and highly differentiated populations with low genetic diversity. To the contrary, the southern Patagonian and Fuegian cluster (approximately 51-55 degrees S) contains mainly diploid populations with high genetic diversity and connected by high levels of gene flow. The data suggest that H. incana originated at the diploid level in central or northern Patagonia, from where it migrated south. All three areas, northern, central and southern, have similar levels of rare and private AFLP bands, suggesting that all three served as refugia for H. incana during glacial times. In southern Patagonia and Tierra del Fuego, the species seems to have expanded its populational system in postglacial times, when the climate became warmer and more humid. In central and northern Patagonia, the populations seem to have become restricted to favourable sites with increasing temperature and decreasing moisture and there was a parallel replacement of diploids by tetraploids in local populations. PMID:19674310

  20. Phylogenetic analysis of Ostreococcus virus sequences from the Patagonian Coast.

    Science.gov (United States)

    Manrique, Julieta M; Calvo, Andrea Y; Jones, Leandro R

    2012-10-01

    A phylogenetic analysis of new Ostreococcus virus (OV) sequences from the Patagonian Coast, Argentina, and homologous sequences from public databases was performed. This analysis showed that the Patagonian sequences represented a divergent viral clade and that the rest of OV sequences analyzed here were clustered into six additional phylogenetic groups. Analyses of 18S gene libraries supported a close relationship of the Patagonian Ostreococcus host with clade A sequences described elsewhere, corroborating previous studies indicating that clade A strains are ubiquitous. Besides the Patagonian OV sequences, several phylogenetic groupings were linked to particular geographic locations, suggesting a role for allopatric cladogenesis in viral diversification. However, and in agreement with previous observations, other viral lineages included sequences with diverse geographic origins. These findings, together with analyses of ancestral trait trajectories performed here, are consistent with an evolutionary dynamics in which geographical isolation has a role in OV diversification but can be followed by rapid dispersion to remote places. PMID:22674355

  1. Mixed bird flocks: patterns of activity and species composition in a region of the Central Andes of Colombia Bandadas mixtas de aves: patrones de actividad y composición de especies en una región de la Cordillera Central de los Andes de Colombia

    Directory of Open Access Journals (Sweden)

    Enrique Arbeláez-Cortés

    2011-06-01

    Full Text Available Mixed bird flocks are groups of individuals from different species that travel and forage together. Such groups are common in several bird communities around the world. We present species composition and activity patterns of mixed bird flocks in a region of the Central Andes of Colombia. We compared the number of species per flock, as well as the number of flocks among 3 different habitats. We tested hypotheses concerning the flocks daily activity and the co-occurrences of species within them. We recorded 75 species, and the species number per flock varied from 4 to 21. Our data suggest that habitat affects the number of flocks but not their species number, and that the activity of flocks is similar throughout the day. In addition, the association of birds in flocks is affected by interspecific facilitation, with some species co-occurrences found more times than expected by chance. We hypothesize that some tanager species could have a role in flock cohesion. We witnessed 2 predator attacks upon flocks, a number of agonistic interactions among flock members, and squirrels following bird flocks. Our results meet some general patterns described for mixed bird flocks.Las bandadas mixtas de aves son grupos de individuos de diferentes especies que viajan y forrajean juntos, y son comunes en varias comunidades de aves alrededor del mundo. Presentamos la composición de especies y los patrones de actividad de las bandadas mixtas de aves en una región de la Cordillera Central de los Andes Colombianos. Comparamos el número de especies por bandada y el número de bandadas en 3 hábitats distintos. Evaluamos hipótesis relacionadas con la actividad de las bandadas durante el día y la presencia simultánea de especies en estos grupos. Observamos 75 especies, y el número de especies por bandada varió entre 4 y 21. Nuestros datos indican que el hábitat parece afectar el número de bandadas pero no su número de especies y que la actividad de las bandadas

  2. Can cosmic ray exposure dating reveal the normal faulting activity of the Cordillera Blanca Fault, Peru?

    Directory of Open Access Journals (Sweden)

    L.L. Siame

    2006-12-01

    Full Text Available The build-up of in situ-produced cosmogenic 10Be within bedrock scarps and escarpments associated to the Cordillera Blanca Normal Fault, Peru, was measured to evaluate, through Cosmic Ray Exposure dating, its normal faulting activity. The highest mountain peaks in Peru belong to the 210 km-long, NW- striking, Cordillera Blanca. Along its western border, the Cordillera Blanca Normal Fault is responsible for a vertical relief over 4.4 km, whose prominent 2 km high escarpment is characterized by ~1 km-high triangular facets corresponding to vertical displacements cumulated during the last 1-2 million years. At a more detailed scale, this fault system exhibits continuous geomorphic evidence of repeated displacements, underlined by 2 to 70 m-high scarps, corresponding to vertical displacements cumulated since Late Pleistocene and Holocene periods. Although microseismicity occurs along the Cordillera Blanca Normal Fault, no major historical or instrumental earthquake has been recorded since the beginning of the Spanish settlement in the 16th century. To evaluate the vertical slip rate along the major 90 km-long central segment of the Cordillera Blanca Normal Fault, the Quaternary fault escarpment (i.e., triangular facet, as well as the bedrock fault scarp, have been sampled for 10Be Cosmic Ray Exposure dating. Even if the uppermost part of the triangular facets have been resurfaced by the Last Glacial Maximum glaciers, our results allow to estimate a vertical slip-rate of 3±1 mm/yr, and suggest at least 2 seismic events during the last 3000 years.

  3. Late cenozoic magmatism in the South Patagonian batholith: SHRIMP U-Pb zircon age evidence

    International Nuclear Information System (INIS)

    The North Patagonian Batholith (NPB) has a zonal age pattern which includes a well defined belt of Miocene and Mio-Pliocene plutons in its central portion (Pankhurst et al., 1999) which are spatially, and probably genetically related to the Liquine-Ofqui Fault Zone. Previous geochronological studies in the Southern Patagonian Batholith (SPB), as summarized by Bruce et al. (1991), have yielded 9 late Cenozoic K-Ar or Ar-Ar ages out of a total of 116 age determinations. None of these young ages correspond to U-Pb determinations on zircons, and some of the young ages correspond to satellite plutons east of the SPB proper, such as the Torres del Paine intrusion. In this paper we present the first late Cenozoic SHRIMP U-Pb zircon ages in the area of the SPB. The morphology of the analysed zircon crystals is described and leads to some inferences on the methodology and on the geological interpretation of the obtained ages (au)

  4. Predator associated morphology in Galaxias platei in Patagonian lakes

    DEFF Research Database (Denmark)

    Milano, D.; Cussac, V.E.; Macchi, P.J.;

    2002-01-01

    Among 158 Galaxias platei individuals, collected from nine deep Andean lakes and from one shallow lake on the Patagonian steppe. morphological characters associated with caudal fin length ere negatively correlated with predation intensity as measured by the incidence of piscivory. Fish from lakes...

  5. Las áreas de filtración de metano constituyen zonas de agregación del bacalao de profundidad (Dissostichus eleginoides frente a Chile central? Do the methane seep areas constitute aggregation spots for the Patagonian toothfish (Dissostichus eleginoides off central Chile?

    Directory of Open Access Journals (Sweden)

    Javier Sellanes

    2012-11-01

    Full Text Available Se presenta los resultados de dos campanas (invierno y verano de pesca de bacalao de profundidad (Dissostichus eleginoides, realizadas sobre un área de filtración de metano (AFM y un sitio aledano utilizado como control. Estas fueron desarrolladas con el objetivo de determinar si las AFM constituyen sitios de agregación de D. eleginoides. Para cada área se registró la captura promedio, el rendimiento de pesca y se determinó índices de abundancia y diversidad incluyendo la fauna capturada incidentalmente. Los ejemplares de bacalao de profundidad capturados en ambos sitios fueron sexados, medidos y pesados. Adicionalmente, se presentan imágenes tomadas in situ, dentro del AFM, que documentan la presencia tanto de D. eleginoides como aparejos de pesca perdidos utilizados en su captura frente a la costa de Concepción. Las mayores capturas y rendimientos fueron observadas en el AFM, con valores promedio de 56,2 kg por lance de pesca y rendimientos promedios de 80,3 g/anzuelo, siendo significativamente mayores en comparación al sitio control. La campana de pesca realizada en invierno registra mayores capturas y rendimientos en ambas áreas. La composición faunística evaluada a través de los índices comunitarios, indica diferencias significativas entre sitios, registrándose un mayor número de especies de fauna acompanante en el AFM, en comparación con el sitio control (18 y 14 especies, respectivamente. Se hipotetiza que la mayor abundancia de bacalao de profundidad en el AFM, estaría relacionada tanto con la mayor heterogeneidad espacial, dada por la presencia de arrecifes de carbonatos autigénicos, como con la disponibilidad de presas, constituyendo estos sitios como zonas de alimentación. El presente trabajo entrega información tendiente a establecer el rol ecológico de las AFM y la fauna asociada a ellas en ambientes batiales frente a Chile.We report results of two seasons (winter and summer fishing for Patagonian toothfish

  6. Modeling the Glacial Buzzsaw in the Patagonian Andes

    Science.gov (United States)

    Brandon, M. T.; Tomkin, J. H.

    2006-12-01

    Modeling the Glacial Buzzsaw in the Patagonian Andes The concept of a "glacial buzzsaw" was spawned by Steve Porter's observation in 1977 and 1988 that the "equilibrium line altitude" (ELA) for alpine glaciation in the Andes parallels the summit elevations of the range. The modern ELA in the Patagonian Andes drops from about 4.5 km at 30 S to about 1 km at 50 S, due to colder temperatures at higher latitudes. The summit elevations decrease steadily by a similar amount over this 2200 km distance. The landscape of the western side of the Patagonian Andes clearly shows that it has long been dominated by glacial erosion. Locally preserved tills indicate that alpine glaciation was active at 7 to 4.6 Ma, if not earlier. The idea of a glacial buzzsaw is that erosion by alpine glaciers is aggressive enough to limit the height of a mountain range. Fission-track cooling ages indicate modest long-term erosion rates (~0.5 to 1 km/Ma) for the Patagonian Andes, which precludes the possibility that the range was trimmed down to size by Quaternary- age glaciations. Furthermore, the range shows clear evidence of growth by continental subduction and tectonic accretion along its eastern margin. Evidence for recent tectonic shortening is based on the observation that the range has an approximately constant taper, as expected for a critical wedge. The width of the range decreases southward in parallel with the decreasing summit elevations. We have developed a general analytical model for coupled wedge growth and glacial erosion that accounts for much of the tectonic evolution of the Patagonian Andes. The model is based on an actively accreting wedge that maintains a constant taper geometry. The size of the wedge is controlled by competition between accretion and glacial erosion. Recent work by one of us (JHT) and Gerard Roe shows that the erosional yield caused by alpine glaciation is approximately proportional to the local elevation difference between the summit of the range and the

  7. THE PAIPA VOLCANO, EASTERN CORDILLERA OF COLOMBIA, SOUTH AMERICA (PART II: PETROGRAPHY AND MAJOR ELEMENTS PETROLOGY

    Directory of Open Access Journals (Sweden)

    Cepeda Héctor

    2005-08-01

    Full Text Available Paipa volcano products are mainly pyroclastic pumice and ash flow tuffs, lava domes and pyroclastic block and ash flow tuffs. They are classified as alkaline rhyolites and trachytes and high-K calcalkaline rhyolites. Chemical data show SiO2 values between 68 and 72%, and alkalis (Na2O+K2O content of 7%-10%. Essential minerals are phenocrysts and glomerocrysts of anorthoclase, sanidine up to 1,5 cm and anorthoclase-mantled plagioclase; accessory minerals are red biotite, and hastingsite while trace minerals are augite, zircon, sphene and magnetite. Crystals have disequilibrium textures, such as dissolution embayments, corrosion and reabsortion borders, normal, inverse, oscillating and patchy zonation, together with fibrous borders intercalated with euhedral borders. In correlation with published data of Iza volcanic rocks, Paipa rocks chemical composition confirms that acid and alkaline magmas that have erupted in the Eastern Cordillera of Colombia during the Neogene are strongly different from the calc-alkaline magmas that erupt in the westward active arc (Central Cordillera. Detailed structural, geochemical and geophysical research has to be done in future research to establish the geodynamic framework that governs the volcanism of the Eastern Cordillera.

  8. Disentangling Topographic and Climatic Change during the Late Cretaceous and Cenozoic in the Western US Cordillera

    Science.gov (United States)

    Snell, K. E.; Eiler, J. M.; Wernicke, B. P.; Peppe, D. J.; Fox, D. L.; Fetrow, A. C.; Passey, B. H.

    2014-12-01

    A diverse suite of tectonic and climatic drivers influenced the topographic evolution of the western USA Cordillera. Despite years of study, considerable uncertainty remains about fundamentals of this evolution, such as the timing and magnitude of maximum average elevations for the different physiographic provinces; the drivers and topographic effects of different episodes of extension during the Cenozoic; and the relative relief of peaks and intermontane basins within the Cordillera at different times and in different places. Numerous tectonic models have been developed to explain the evolution of the Cordillera, and understanding these details is key for distinguishing between these different models. In addition, the topographic changes in the Cordillera have important implications for regional and local climate of the western US at different times in the past, and may drive important differences in local climatic responses to global climate changes through the Cenozoic. The majority of the tools that currently exist for quantitatively reconstructing changes in topography through time and space rely on paleoclimate proxy data. Thus it is also important to be able to disentangle climatic change from elevation change in terrestrial paleoclimate records. To address some of these outstanding questions, we have generated and compiled paleotemperature estimates from the Late Cretaceous through the Miocene of the western US. In this presentation, we will focus on the latest installment of the project, which utilizes Oligocene paleotemperature records from central Utah and South Dakota and Miocene-Holocene paleotemperature records from Kansas. The data are dominantly composed of mean annual temperature estimates from leaf margin analysis and summer temperature estimates from carbonate clumped isotope thermometry. We will discuss how these data compare to temperature data from the Paleogene from the western US, what general trends exist within all the data and how these

  9. Behavior, nutrition, and veterinary care of patagonian cavies (Dolichotis patagonum).

    Science.gov (United States)

    Kessler, David S; Hope, Katharine; Maslanka, Michael

    2009-05-01

    Patagonian cavies (Dolichotis patagonum) are large South American rodents well adapted for cursorial life (well adapted for running). They are monogamous but can live in groups of up to 70 individuals who maintain communal burrows. They are primarily herbivorous and may be maintained on commercially produced rodent or primate diets. Their long, thin legs and skittish nature make them difficult to restrain. Common medical problems include malocclusion of cheek teeth, gastrointestinal parasites, hypertrophic cardiomyopathy, and traumatic leg fractures. PMID:19341953

  10. Morphology of the lingual papillae in the Patagonian cavy.

    Science.gov (United States)

    Emura, Shoichi; Okumura, Toshihiko; Chen, Huayue

    2011-11-01

    We examined the dorsal lingual surfaces of an adult Patagonian cavy (Dolichotis patagonum) by scanning electron microscopy. The tongue of the Patagonian cavy is about 8 cm long and the lingual body had lingual prominence on the posterior third. There were no fungiform papillae in the lingual dorsal surface. The fungiform papillae were observed in both lateral sides of the lingual apex. The filiform papilla of the lingual body consisted of a large conical papilla. The connective tissue core of the filiform papilla showed many slender processes. The fungiform papillae were round in shape. The connective tissue core of the fungiform papilla was flower-bud shaped. Two vallate papillae were located on between lingual body and root, and insert in two grooves. The connective tissue core of the vallate papilla was covered with numerous small spines. Many foliate papillae were observed on the posterolateral regions of the tongue. After removing epithelium from the foliate papillae many vertical depressions became apparent. These findings suggest that in the structure of the lingual papillae of the Patagonian cavy there is similar to that of the capybara. PMID:22519071

  11. Spring northward juvenile migration of the Patagonian grenadier (Macruronus magellanicus from the Northwest Patagonian waters of Chile

    Directory of Open Access Journals (Sweden)

    Luis A Cubillos

    2015-11-01

    Full Text Available Important nursery grounds for Patagonian grenadier (Macruronus magellanicus are located mainly in the Northwest Patagonian Inner Sea (42ºS-44ºS, from which juvenile must to disperse or migrate offshore, then along the Chilean coast either northward or southward. The objective of this paper was to estimate northward spring juvenile migration of the Patagonian grenadier from nursery to feeding areas, which are located near Talcahuano (35º00’S-37º10’S. Length-frequency data (LFD were obtained from an acoustic survey carried out in November 1999, which covered from 35ºS to 47ºS. Generalized linear model was used to describe the presence of juvenile per latitude and depth, and to infer the origin and displacement of juveniles. Subsequently, LFD data were grouped according to latitudinal strata. Grouped LFD were decomposed into normal component groups, from which mean, standard deviation and proportion were estimated from the mixed LFD. The average length of the identified groups were sorted from south to north, and linked to compute significant increment in fish length and age per kilometers. The length increment per time was not due to growth, rather they was due to spatial displacement of juvenile from southern nursery grounds to northern feeding areas. Although homing to feeding areas and/or high residency (partial migration have been postulated, it seems that recruitment of juveniles to northern feeding areas are origintaed from NPIS nurseries. The West Wind Drift Current seems to be the main drive for dispersion of Patagonian grenadier to recruit northward in open waters along the continental shelf.

  12. Multi-temporal InSAR for Deformation Monitoring of the Granada and Padul Faults and the Surrounding Area (Betic Cordillera, Southern Spain)

    NARCIS (Netherlands)

    Sousa, J.J.; Ruiz, A.M.; Hooper, A.J.; Hanssen, R.F.; Perski, Z.; Bastos, L.C.; Gil, A.J.; Galindo-Zaldivar, J.; Sanz de Galdeano, C.; Alfaro, P.; Garrido, M.S.; Armenteros, J.A.; Gimenez, E.; Aviles, M.

    2014-01-01

    The quantification of low rate active tectonic structures is a major target of geodetic and geological studies to improve the knowledge of seismic hazards. The central Betic Cordillera (southern Spain) is affected by moderately active tectonic structures and seismicity. Part of this seismic activity

  13. Slope stability of moraines, Cordillera Blanca, Peru

    Science.gov (United States)

    Klimes, J.; Novotny, J.

    2012-12-01

    Landslides originating from inner slopes of moraine dams are often capable of producing glacial lakes outburst floods (GLOFs). Therefore assessing stability conditions of the moraines is important for predicting this potentially damaging phenomenon. Characteristics of the basic mechanical properties of the material and geophysical investigations were applied to collect necessary information for slope stability assessment of the Palcacocha Lake moraine dam, Peru. The lake is situated in the Cordillera Blanca Mts. at the altitude of about 4,500m asl and produced catastrophic GLOF in 1941. Another minor flood originated in 2003 due to landslide impact into the lake. Detailed investigations of this landslide site included geomorphological mapping, geophysical investigations and characterization of basic mechanical properties of the forming material. Geomorphological mapping identified dormant landslide with scarp up to 2m high which developed on the edge of the inner moraine slope. It is conditioned by set of parallel extension trenches which also affected the origin of 2003 landslide. Within its scarp area, significant water bearing layer was noticed around 10 m bellow the moraine surface. Three profiles were investigated using electric resistivity tomography performed on 4poing light instrument with 24 electrodes and with spacing ranging from 1 to 4m. Results helped to verify geometry of the main shear plane of the mapped landslide as well as the spacing and depth of extension trenches. Significant heterogeneity in the moraine resistivity characteristics was found. The high resistivity regions are explained by rock block accumulation whereas the low resistivity may represent wet layers within the moraine body. Grain size distribution of 33 disturbed soil samples originating from moraine material within the Cordillera Blanca Mts., Peru were determined and classified according to the UCSC classification system. The samples were taken from moraine dams and slopes

  14. Zoonotic parasites associated with felines from the Patagonian Holocene

    Directory of Open Access Journals (Sweden)

    Martín Horacio Fugassa

    2009-12-01

    Full Text Available Feline coprolites were examined for parasites with the aim of studying ancient infections that occurred in the Patagonian region during the Holocene period. Eggs compatible to Trichuris sp., Calodium sp., Eucoleus sp., Nematodirus sp., Oesophagostomum sp. (Nematoda, Monoecocestus sp. (Cestoda and Eimeria macusaniensis (Coccidia were recovered from faecal samples. The results obtained from the analysis provide evidence of consumption by felids of the viscera of both rodents and camelids. This knowledge allows for improved explanations as to the distribution of parasitism and its significance to the health of humans and animals inhabiting the area under study during the Middle Holocene.

  15. Patagonian and southern South Atlantic view of Holocene climate

    Science.gov (United States)

    Kaplan, M. R.; Schaefer, J. M.; Strelin, J. A.; Denton, G. H.; Anderson, R. F.; Vandergoes, M. J.; Finkel, R. C.; Schwartz, R.; Travis, S. G.; Garcia, J. L.; Martini, M. A.; Nielsen, S. H. H.

    2016-06-01

    We present a comprehensive 10Be chronology for Holocene moraines in the Lago Argentino basin, on the east side of the South Patagonian Icefield. We focus on three different areas, where prior studies show ample glacier moraine records exist because they were formed by outlet glaciers sensitive to climate change. The 10Be dated records are from the Lago Pearson, Herminita Península-Brazo Upsala, and Lago Frías areas, which span a distance of almost 100 km adjacent to the modern Icefield. New 10Be ages show that expanded glaciers and moraine building events occurred at least at 6120 ± 390 (n = 13), 4450 ± 220 (n = 7), 1450 or 1410 ± 110 (n = 18), 360 ± 30 (n = 5), and 240 ± 20 (n = 8) years ago. Furthermore, other less well-dated glacier expansions of the Upsala Glacier occurred between ~1400 and ∼1000 and ∼2300 and ∼2000 years ago. The most extensive glaciers occurred over the interval from ∼6100 to ∼4500 years ago, and their margins over the last ∼600 years were well within and lower than those in the middle Holocene. The 10Be ages agree with 14C-limiting data for the glacier histories in this area. We then link southern South American, adjacent South Atlantic, and other Southern Hemisphere records to elucidate broader regional patterns of climate and their possible causes. In the early Holocene, a far southward position of the westerly winds fostered warmth, small Patagonian glaciers, and reduced sea ice coverage over the South Atlantic. Although we infer a pronounced southward displacement of the westerlies during the early Holocene, these conditions did not occur throughout the southern mid-high latitudes, an important exception being over the southwest Pacific sector. Subsequently, a northward locus and/or expansion of the winds over the Patagonia-South Atlantic sector promoted the largest glaciers between ∼6100 and ∼4500 years ago and greatest sea ice coverage. Over the last few millennia, the South Patagonian Icefield has experienced

  16. Relationship between volcanism and marine sedimentation in northern Austral (Aisén) Basin, central Patagonia: Stratigraphic, U-Pb SHRIMP and paleontologic evidence

    Science.gov (United States)

    Suárez, M.; De La Cruz, R.; Aguirre-Urreta, B.; Fanning, M.

    2009-04-01

    The northernmost part of the oil-producing Austral Basin, known as Aisén Basin or Río Mayo Embayment (in central Patagonian Cordillera; 43-46°S), is a special area within the basin where the interplay between volcanism and the initial stages of its development can be established. Stratigraphic, paleontologic and five new U-Pb SHRIMP age determinations presented here indicate that the Aisén Basin was synchronous with the later phases of volcanism of the Ibáñez Formation for at least 11 m.yr. during the Tithonian to early Hauterivian. In this basin marine sedimentary rocks of the basal units of the Coihaique Group accumulated overlying and interfingering with the Ibáñez Formation, which represents the youngest episode of volcanism of a mainly Jurassic acid large igneous province (Chon Aike Province). Five new U-Pb SHRIMP magmatic ages ranging between 140.3 ± 1.0 and 136.1 ± 1.6 Ma (early Valanginian to early Hauterivian) were obtained from the Ibáñez Formation whilst ammonites from the overlying and interfingering Toqui Formation, the basal unit of the Coihaique Group, indicate Tithonian, early Berriasian and late Berriasian ages. The latter was a synvolcanic shallow marine facies accumulated in an intra-arc setting, subsequently developed into a retro-arc basin.

  17. Crustal deformation across the Southern Patagonian Icefield observed by GNSS

    Science.gov (United States)

    Richter, A.; Ivins, E.; Lange, H.; Mendoza, L.; Schröder, L.; Hormaechea, J. L.; Casassa, G.; Marderwald, E.; Fritsche, M.; Perdomo, R.; Horwath, M.; Dietrich, R.

    2016-10-01

    Geodetic GNSS observations at 43 sites well distributed over the Southern Patagonian Icefield region yield site velocities with a mean accuracy of 1 mm/a and 6 mm/a for the horizontal and vertical components, respectively. These velocities are analyzed to reveal the magnitudes and patterns of vertical and horizontal present-day crustal deformation as well as their primary driving processes. The observed vertical velocities confirm a rapid uplift, with rates peaking at 41 mm/a, causally related to glacial-isostatic adjustment (GIA). They yield now an unambiguous preference between two competing GIA models. Remaining discrepancies between the preferred model and our observations point toward an effective upper mantle viscosity even lower than 1.6 ṡ1018 Pas and effects of lateral rheological heterogeneities. An analysis of the horizontal strain and strain-rate fields reveals some complex superposition, with compression dominating in the west and extension in the east. This deformation field suggests significant contributions from three processes: GIA, a western interseismic tectonic deformation field related to plate subduction, and an extensional strain-rate field related to active Patagonian slab window tectonics.

  18. Landsat TM and ETM+ derived snowline altitudes in the Cordillera Huayhuash and Cordillera Raura, Peru, 1986–2005

    Directory of Open Access Journals (Sweden)

    J. Ramage

    2010-10-01

    Full Text Available The Cordilleras Huayhuash and Raura are remote glacierized ranges in the Andes Mountains of Peru. A robust assessment of modern glacier change is important for understanding how regional change affects Andean communities, and for placing paleo-glaciers in a context relative to modern glaciation and climate. Snowline altitudes (SLAs derived from satellite imagery are used as a proxy for modern (1986–2005 local climate change in a key transition zone in the Andes. Clear sky, dry season Landsat Thematic Mapper (TM and Enhanced Thematic Mapper (ETM+ satellite images from 1986–2005 were used to identify snowline positions, and their altitude ranges were extracted from an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER DEM. Based on satellite records from 31 glaciers, mean snowline altitudes (SLAs, an approximation for the equilibrium line altitudes (ELAs, for the Cordillera Huayhuash (13 glaciers and Cordillera Raura (18 glaciers were 5046 m a.s.l. and 5013 m a.s.l., respectively, from 1986–2005. The rate of SLA rise was 25 m/decade in the Cordillera Huayhuash and 62 m/decade in the Cordillera Raura.

  19. Landsat TM and ETM+ derived snowline altitudes in the Cordillera Huayhuash and Cordillera Raura, Peru, 1986–2005

    Directory of Open Access Journals (Sweden)

    J. Ramage

    2011-05-01

    Full Text Available The Cordilleras Huayhuash and Raura are remote glacierized ranges in the Andes Mountains of Peru. A robust assessment of modern glacier change is important for understanding how regional change affects Andean communities, and for placing paleo-glaciers in a context relative to modern glaciation and climate. Snowline altitudes (SLAs derived from satellite imagery are used as a proxy for modern (1986–2005 local climate change in a key transition zone in the Andes. Clear sky, dry season Landsat Thematic Mapper (TM and Enhanced Thematic Mapper (ETM+ satellite images from 1986–2005 were used to identify snowline positions, and their altitude ranges were extracted from an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER digital elevation model (DEM. Based on satellite records from 31 glaciers, average snowline altitudes (SLAs, an approximation for the equilibrium line altitude (ELA, for the Cordillera Huayhuash (13 glaciers and Cordillera Raura (18 glaciers from 1986–2005 were 5051 m a.s.l. from 1986–2005 and 5006 m a.s.l. from 1986–2002, respectively. During the same time period, the Cordillera Huayhuash SLA experienced no significant change while the Cordillera Raura SLA rose significantly from 4947 m a.s.l. to 5044 m a.s.l.

  20. Semidiurnal internal tides in a Patagonian fjord

    Science.gov (United States)

    Ross, L.; Pérez-Santos, I.; Valle-Levinson, A.; Schneider, W.

    2014-12-01

    The fjords of central Chilean Patagonia (47°S) receive fresh water from both precipitation and the Baker River. This buoyancy input generates a two layer hydrographic system characterized by strong salinity stratification (∼30 g kg-1 over a depth range of 7-15 m), which favors baroclinic conditions in the fjord. Hourly current velocity profiles were collected with an acoustic Doppler current profiler (ADCP) moored at a depth of 40 m during March-April 2009, and complemented by 11 CTD profiles and hourly sea level time series. These data allowed the detection of semidiurnal internal tidal waves for the first time in this region. Wavelength and horizontal phase speeds were determined by the dynamical mode 1 for internal waves. Maximum wavelength was 52 km, travelling at a horizontal phase speed of ∼1.16 m s-1. Wavelet, spectral and empirical orthogonal function (EOF) analysis techniques applied to the echo anomaly signal and to the baroclinic velocity showed largest semidiurnal amplitudes near the pycnocline. Out of three modes obtained from the EOF analysis, two modes displayed a two- or three-layer flow structure with flow direction reversing at the pycnocline. The semidiurnal internal waves were found as fluctuations near the pycnocline in sporadic packets correlated to high discharge pulses of the Baker River (r2 = 0.77). Additionally, internal Froude number calculations at the mouth of the Baker River indicated critical flow conditions, which allowed for generation of internal waves at the plume front. These waves are separated from the river plume after internal wave phase speeds surpassed frontal speeds. This suggests that the internal waves were modulated by pulses in high river discharge rather than the interaction of barotropic tide with bathymetry (a sill). An implication of these internal waves would be to increase vertical mixing of nutrients toward the surface, through shear instabilities, which would favor primary production.

  1. Complex brittle deformation pattern along the Southern Patagonian Andes (Argentina)

    Science.gov (United States)

    Barberón, Vanesa; Sue, Christian; Ronda, Gonzalo; Ghiglione, Matías

    2016-04-01

    The Southern Patagonian Andes is located in the southern extreme of the Pacific subduction zone, where the Antartic oceanic plate sinks underneath South America. The history of the area begins with compression during Paleozoic, Jurassic extension associated to the rift and opening of the South Atlantic Ocean, then a sag stage in the Lower Cretaceous followed by a foreland phase as a result of plate tectonics (Ghiglione et al., 2016). The kinematic study is concentrated in the Argentinean foothills, between 46°40' and 48° SL. We measured around 800 fault planes and their striaes with the sense of movement in order to characterize the stress field. The software used to make the stress inversion were Tensor (Delvaux, 2011) and Multiple Inverse Method MIM (Yamaji et al., 2011). The stress field map was built with the results of the MIM. We present new data from 48 sites located in the northern sector of the Southern Patagonian Andes. The measurements were made in several rocks from Paleozoic to Lower Cretaceous, even though most were taken in pyroclastic jurassic rocks from El Quemado Complex. Paleostress tensors obtained are mostly strike-slip, although a 25% is normal and there are a few compresional. The pattern of faults found is complex. In some sites the tensor can be locally linked to satellite images and observations from the field or be related to a major thrust front. There is no clear correlation between the age and/or lithology with the tensor since the youngest rocks measured are Lower Cretaceous. Probably there are several generations of family faults connected to different and recent tectonic phases then the paleostress tensors might correspond to the latest tectonic events.

  2. Mohorovicic discontinuity depth analysis beneath North Patagonian Massif

    Science.gov (United States)

    Gómez Dacal, M. L.; Tocho, C.; Aragón, E.

    2013-05-01

    The North Patagonian Massif is a 100000 km2, sub-rectangular plateau that stands out 500 to 700 m higher in altitude than the surrounding topography. The creation of this plateau took place during the Oligocene through a sudden uplift without noticeable internal deformation. This quite different mechanical response between the massif and the surrounding back arc, the short time in which this process took place and a regional negative Bouguer anomaly in the massif area, raise the question about the isostatic compensation state of the previously mentioned massif. In the present work, a comparison between different results about the depth of the Mohorovicic discontinuity beneath the North Patagonian Massif and a later analysis is made. It has the objective to analyze the crustal thickness in the area to contribute in the determination of the isostatic balance and the better understanding of the Cenozoic evolution of the mentioned area. The comparison is made between four models; two of these were created with seismic information (Feng et al., 2006 and Bassin et al., 2000), another model with gravity information (Barzaghi et al., 2011) and the last one with a combination of both techniques (Tassara y Etchaurren, 2011). The latter was the result of the adaptation to the work area of a three-dimensional density model made with some additional information, mainly seismic, that constrain the surfaces. The work of restriction and adaptation of this model, the later analysis and comparison with the other three models and the combination of both seismic models to cover the lack of resolution in some areas, is presented here. According the different models, the crustal thickness of the study zone would be between 36 and 45 Km. and thicker than the surrounding areas. These results talk us about a crust thicker than normal and that could behave as a rigid and independent block. Moreover, it can be observed that there are noticeable differences between gravimetric and seismic

  3. Spatio-temporal variability of snow water equivalent in the extra-tropical Andes Cordillera from distributed energy balance modeling and remotely sensed snow cover

    OpenAIRE

    E. Cornwell; Molotch, N. P.; McPhee, J

    2016-01-01

    Seasonal snow cover is the primary water source for human use and ecosystems along the extratropical Andes Cordillera. Despite its importance, relatively little research has been devoted to understanding the properties, distribution and variability of this natural resource. This research provides high-resolution (500 m), daily distributed estimates of end-of-winter and spring snow water equivalent over a 152 000 km2 domain that includes the mountainous reaches of central Chi...

  4. The magmatic history of the Vetas-California mining district, Santander Massif, Eastern Cordillera, Colombia

    Science.gov (United States)

    Mantilla Figueroa, Luis C.; Bissig, Thomas; Valencia, Víctor; Hart, Craig J. R.

    2013-08-01

    The Vetas-California Mining District (VCMD), located in the central part of the Santander Massif (Colombian Eastern Cordillera), based on U-Pb dating of zircons, records the following principal tectono-magmatic events: (1) the Grenville Orogenic event and high grade metamorphism and migmatitization between ˜1240 and 957 Ma; (2) early Ordovician calc-alkalic magmatism, which was synchronous with the Caparonensis-Famatinian Orogeny (˜477 Ma); (3) middle to late Ordovician post-collisional calc-alkalic magmatism (˜466-436 Ma); (4) late Triassic to early Jurassic magmatism between ˜204 and 196 Ma, characterized by both S- and I-type calc-alkalic intrusions and; (5) a late Miocene shallowly emplaced intermediate calc-alkaline intrusions (10.9 ± 0.2 and 8.4 ± 0.2 Ma). The presence of even younger igneous rocks is possible, given the widespread magmatic-hydrothermal alteration affecting all rock units in the area. The igneous rocks from the late Triassic-early Jurassic magmatic episodes are the volumetrically most important igneous rocks in the study area and in the Colombian Eastern Cordillera. They can be divided into three groups based on their field relationships, whole rock geochemistry and geochronology. These are early leucogranites herein termed Alaskites-I (204-199 Ma), Intermediate rocks (199-198 Ma), and late leucogranites, herein referred to as Alaskites-II (198-196 Ma). This Mesozoic magmatism is reflecting subtle changes in the crustal stress in a setting above an oblique subduction of the Panthalassa plate beneath Pangea. The lower Cretaceous siliciclastic Tambor Formation has detrital zircons of the same age populations as the metamorphic and igneous rocks present in the study area, suggesting that the provenance is related to the erosion of these local rocks during the late Jurassic or early Cretaceous, implying a local supply of sediments to the local depositional basins.

  5. Growth and gravitational collapse of a mountain front of the Eastern Cordillera of Colombia

    Science.gov (United States)

    Kammer, Andreas; Montana, Jorge; Piraquive, Alejandro

    2016-04-01

    The Eastern Cordillera of Colombia is bracketed between the moderately east-dipping flank of the Central Cordillera on its western and the gently bent Guayana shield on its eastern side. It evolved as a response to a considerable displacement transfer from the Nazca to the Southamerican plate since the Oligocene break-up of the Farallon plate. One of its distinctive traits refers to its significant shortening by penetrative strain at lower and folding at higher structural levels, approximating a wholesale pure-shear in analogy to a vice model or a crustal welt sandwiched between rigid buttresses. This contrasting behavior may be explained by the spatial coincidence between Neogene mountain belt and a forebulge that shaped the foreland trough during a Cretaceous subduction cycle and was very effective in localizing a weakening of the backarc region comprised between two basin margin faults. In this paper we examine a two-phase evolution of the Eastern mountain front. Up to the late Miocene deformation was restrained by the inherited eastern basin margin fault and as the cordilleran crust extruded, a deformation front with an amplitude similar the present structural relief of up to 10.000 m may have built up. In the Pliocene convergence changed from a roughly strike-perpendicular to an oblique E-W direction and caused N-S trending faults to branch off from the deformation front. This shortening was partly driven by a gravitational collapse of the Miocene deformation front, that became fragmented by normal faults and extruded E on newly formed Pliocene thrust faults. Normal faults display displacements of up to 3000 m and channelized hydrothermal fluids, leading to the formation of widely distributed fault breccias and giving rise to a prolific Emerald mineralization. In terms of wedge dynamics, the Pliocene breaching of the early formed deformation front helped to establish a critical taper.

  6. Las adakitas de la Cordillera Patagónica: Nuevas evidencias geoquímicas y geocronológicas The adakites of the Patagonian Cordillera: new geochemical and geochronological evidences

    Directory of Open Access Journals (Sweden)

    V.A. Ramos

    2004-12-01

    Full Text Available El origen de muchas adakitas consideradas como productos de la fusión de corteza oceánica subducida ha sido cuestionado ya que su formación puede ser atribuida a fusión de corteza continental engrosada o fusión de material procedente de la erosión cortical por subdución. Una de las mejores candidatas para adakitas formadas por fusión de una losa oceánica subducida son las Adakitas Cerro Pampa (47°55'SL en la Patagonia, que se emplazaron al este del arco volcánico andino inactivo cuando la dorsal de Chile colisionó con la trinchera oceánica hace unos 12 Ma. El origen de estas dacitas portadoras de hornblenda se infiere como producido por fusión de una losa oceánica subducida, basado en las altas concentraciones de Sr (1330-2300 ppm a 63-68% de SiO2, valores de 87Sr/86Sr similares al MORB (0,7028-0,7031, razones de 143Nd/144Nd > 0,5129, y sus diseños de tierras raras empinados, con empobrecimiento de tierras raras pesadas (La/Yb = 30-37, a pesar de haberse emplazado en una región de corteza delgada. Recientemente se han reconocido otras dos localidades con adakitas miocenas en Puesto Nuevo (48°59'°S y Chaltén (~49°25'°S - (65-66% SiO2, 1370-1440 ppm Sr, 87Sr/86Sr = 0,7032-7033, 143Nd/144Nd ~ 0,51289, La/Yb 28-30- que se encuentran al sudoeste de la anterior, y donde también colisionó la dorsal de Chile hace ~ 12 Ma. Estas adakitas afloran al este de las adakitas de arco pleistocenas y recientes de la Zona Volcánica Austral. Nuevas edades de plateau 40Ar/39Ar obtenidas mediante calentamiento incremental por laser en hornblendas muestran que las adakitas de Chaltén, Puesto Nuevo y Cerro Pampa decrecen en edad (14,50 ± 0,29 Ma, 13,12 ± 0,55 Ma, 11,39 ± 0,61 Ma, en forma consistente con la colisión de la dorsal que progresaba hacia el norte y con la fusión parcial del borde posterior de la placa de Nazca. Sus características geoquímicas contrastan con las andesitas miocenas de retroarco de la región de Cerro Moyano (~50°15'S, que no tienen características adakíticas, a pesar que se hallan ubicadas al este de donde la dorsal de Chile chocó alrrededor de los 14 Ma. En esta última región no hay importantes lavas basálticas miocenas de meseta relacionadas con ventanas astenosféricas entre la placa Antártica y la de Nazca. Los estudios de campo y las consideraciones petrológicas señalan que la fusión de corteza oceánica miocena en Patagonia requirió un aporte térmico desde el manto astenosférico tanto como de la subducción de una placa joven y caliente. Un caso similar puede ser observado entre las adakitas de arco de la Zona Volcánica Austral y los basaltos pliocenos a recientes del sector extrandino.The origin of many adakites ascribed to slab melting has been questioned with their formation being attributed to melting of thickened continental crust or forearc subduction erosion. Some of the best remaining candidates for a slab-melt origin are the Cerro Pampa adakites (47°55'SL in Patagonia that erupted east of the inactive volcanic arc as the Chile Ridge collided with the Chile Trench at ca. 12 Ma. Support for a slab-melt origin for these hornblende-bearing dacites comes from high Sr concentrations (1330-2300 ppm at 63-68% SiO2, MORB-like 87Sr/86Sr (0.7028-0.7031, 143Nd/144Nd > 0.5129, and steep (heavy depleted REE pattern (La/Yb = 30-37 in an area of thin crust. Two other adakite localities to the southwest that are also east of where the Chile ridge collided at ~ 12 Ma, have been recognized more recently (65-66% SiO2, 1370-1440 ppm Sr, 87Sr/86Sr = 0.7032-7033, 143Nd/144Nd ~ 0.51289, La/Yb 28-30. These Puesto Nuevo (48°59'°S and Chaltén adakites (~49°25'°S adakites are to the east of the Pleistocene to Recent adakites in the Austral Volcanic Zone arc. New 40Ar/39Ar plateau ages obtained via laser incremental heating of hornblendes show that the Chaltén, Puesto Nuevo, and Cerro Pampa adakites decrease nortwards in age (14.50 ± 0.29, 13.12 ± 0.55, 11.39 ± 0.61 Ma, consistent with melting of the trailing edge of the Nazca plate as ridge collision progressed to the north. Their chemistry contrasts with non-adakitic Miocene retroarc andesites in the Cerro Moyano (~50°15'S region, east of where the Chile ridge collided at ca. 14 Ma. A major difference in this southern region is the relative absence of large late Miocene plateau flows related to a slab window between the Nazca and Antarctic plates. This association suggests that Miocene slab melting in Patagonia required a thermal input from the asthenospheric mantle as well as a young, hot subducting plate. A similar case can be made between Austral Volcanic Zone adakites and extra-Andean Pliocene to Recent basalts.

  7. Surviving historical Patagonian landscapes and climate: molecular insights from Galaxias maculatus

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    Carrea Cecilia

    2010-03-01

    Full Text Available Abstract Background The dynamic geological and climatic histories of temperate South America have played important roles in shaping the contemporary distributions and genetic diversity of endemic freshwater species. We use mitochondria and nuclear sequence variation to investigate the consequences of mountain barriers and Quaternary glacial cycles for patterns of genetic diversity in the diadromous fish Galaxias maculatus in Patagonia (~300 individuals from 36 locations. Results Contemporary populations of G. maculatus, east and west of the Andes in Patagonia, represent a single monophyletic lineage comprising several well supported groups. Mantel tests using control region data revealed a strong positive relationship when geographic distance was modeled according to a scenario of marine dispersal. (r = 0.69, P = 0.055. By contrast, direct distance between regions was poorly correlated with genetic distance (r = -0.05, P = 0.463. Hierarchical AMOVAs using mtDNA revealed that pooling samples according to historical (pre-LGM oceanic drainage (Pacific vs. Atlantic explained approximately four times more variance than pooling them into present-day drainage (15.6% vs. 3.7%. Further post-hoc AMOVA tests revealed additional genetic structure between populations east and west of the Chilean Coastal Cordillera (coastal vs. interior. Overall female effective population size appears to have remained relatively constant until roughly 0.5 Ma when population size rapidly increased several orders of magnitude [100× (60×-190×] to reach contemporary levels. Maximum likelihood analysis of nuclear alleles revealed a poorly supported gene tree which was paraphyletic with respect to mitochondrial-defined haplogroups. Conclusions First diversifying in the central/north-west region of Patagonia, G. maculatus extended its range into Argentina via the southern coastal regions that join the Pacific and Atlantic oceans. More recent gene flow between northern

  8. Late Quaternary geomorphic history of a glacial landscape - new sedimentary and chronological data from the Cordillera de Cochabamba (Bolivia)

    Science.gov (United States)

    May, J.-H.; Preusser, F.; Zech, R.; Ilgner, J.; Veit, H.

    2009-04-01

    Throughout the Central Andes, glacial landscapes have long been used for the reconstruction of Late Quaternary glaciations and landscape evolution. Much work has focused on the Andes in Peru, Chile and the Bolivian Altiplano, whereas relatively little data has been published on glaciation history in the eastern Andean ranges and slopes. Even less is known with regard to the postglacial evolution of these glacial landscapes. In the Cordillera de Cochabamba (Bolivia), local maximum advances probably peaked around 20-25 ka BP and were followed by significant readvances between ~12-16 ka BP. This generally points to temperature controlled maximum glacial advances along the humid eastern slopes of the Central Andes, which is supported by glacier-climate-modelling studies. However, most studies include only marginal information with regard to the complex geomorphic and sedimentary situation in the Cordillera de Cochabamba. Furthermore, the chronological results are afflicted with several methodological uncertainties inherent to surface exposure dating and call for application of alternative, independent age dating methods. Therefore this study aims at i) documenting and interpreting the complex glacial geomorphology of the Huara Loma valley in the Cordillera de Cochabamba (Bolivia), ii) analyzing the involved units of glacial sediments, and iii) improving the chronological framework by applying optically stimulated luminescence (OSL) and radiocarbon dating (14C). For this purpose, geomorphic mapping was combined with field documentation of sedimentary profiles. The involved sediments were subject to geochemical and mineralogical analysis in order to deduce information on their erosional and weathering histories. In addition, the interpretation of OSL ages from glacial and proglacial sediments integrated several methodological procedures with regard to sample preparation and statistical analysis of the measurements in order to increase the degree of confidence. These

  9. A new species of salamander (Bolitoglossa: Plethodontidae from the Cordillera Oriental of the Colombian Andes

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    Andrés R. Acosta-Galvis

    2012-01-01

    Full Text Available Eight species of salamanders are recognized to Cordillera Oriental of Colombia. Here we describe a new species of the genus Bolitoglossa, named Bolitoglossa guaneae sp. nov. The highest number of species of this genus is found in the cloud forests located in the western flank of the Cordillera Oriental.

  10. Cowpoxvirus infection in the Patagonian cavy (Dolichotis patagonum) emerging disease in an educational animal park the first reported case.

    Science.gov (United States)

    Kik, M J L; Liu, P L; van Asten, J A M

    2006-06-01

    Generalized cowpox infection in the Patagonian cavy may represent a threat to the health of immunocompromised persons. We report the first case of cowpoxvirus infection in the Patagonian cavy in an educational animal park. The mara developed extensive pox lesions, shedding large amounts of viral particles. The ending of vaccination programmes against smallpox in the late 1970's may lead to an increase in susceptibility of humans to zoonotic poxviruses. PMID:16841565

  11. Estimation of overland flow metrics at semiarid condition: Patagonian Monte

    Science.gov (United States)

    Rossi, M. J.; Ares, J. O.

    2012-05-01

    Water infiltration and overland flow (WIOF) processes are relevant in considering water partition among plant life forms, the sustainability of vegetation and the design of sustainable hydrological management. WIOF processes in arid and semiarid regions present regional characteristic trends imposed by the prevailing physical conditions of the upper soil as evolved under water-limited climate. A set of plot-scale field experiments at the semi-arid Patagonian Monte (Argentina) was performed in order to estimate infiltration-overland descriptive flow parameters. The micro-relief of undisturbed field plots at z-scale events were video-recorded and the runoff speed was measured with ortho-image processing software. Antecedent and post-inflow moisture were measured, and texture, bulk density and physical properties of the soil at the upper vadose zone were estimated. Field data were used to calibrate a physically-based, time explicit model of water balance in the upper soil and overland flows with a modified Green-Ampt (infiltration) and Chezy's (overland flow) algorithms. Modelling results satisfy validation criteria based on the observed overland flow areas, runoff-speed, water mass balance of the upper vadose zone, infiltration depth, slope along runoff-plume direction, and depression storage intensity. The experimental procedure presented supplies plot-scale estimates of overland flow and infiltration intensities at various intensities of water input which can be incorporated in larger-scale hydrological grid-models of arid regions. Findings were: (1) Overland flow velocities as well as infiltration-overland flow mass balances are consistently modelled by considering variable infiltration rates corresponding to depression storage and/or non-ponded areas. (2) The statistical relations presented allow the estimation of theoretical hydrodynamic parameters (Chezy's frictional C, average overland flow depth d*) through measurable characteristics of the surface soil and

  12. Estimation of overland flow metrics at semiarid condition: Patagonian Monte

    Directory of Open Access Journals (Sweden)

    M. J. Rossi

    2012-05-01

    Full Text Available Water infiltration and overland flow (WIOF processes are relevant in considering water partition among plant life forms, the sustainability of vegetation and the design of sustainable hydrological management. WIOF processes in arid and semiarid regions present regional characteristic trends imposed by the prevailing physical conditions of the upper soil as evolved under water-limited climate. A set of plot-scale field experiments at the semi-arid Patagonian Monte (Argentina was performed in order to estimate infiltration-overland descriptive flow parameters. The micro-relief of undisturbed field plots at z-scale <1 mm was characterized through close-range stereo-photogrammetry and geo-statistical modelling. The overland flow areas produced by experimental runoff events were video-recorded and the runoff speed was measured with ortho-image processing software. Antecedent and post-inflow moisture were measured, and texture, bulk density and physical properties of the soil at the upper vadose zone were estimated. Field data were used to calibrate a physically-based, time explicit model of water balance in the upper soil and overland flows with a modified Green-Ampt (infiltration and Chezy's (overland flow algorithms. Modelling results satisfy validation criteria based on the observed overland flow areas, runoff-speed, water mass balance of the upper vadose zone, infiltration depth, slope along runoff-plume direction, and depression storage intensity. The experimental procedure presented supplies plot-scale estimates of overland flow and infiltration intensities at various intensities of water input which can be incorporated in larger-scale hydrological grid-models of arid regions. Findings were: (1 Overland flow velocities as well as infiltration-overland flow mass balances are consistently modelled by considering variable infiltration rates corresponding to depression storage and/or non-ponded areas. (2 The statistical relations presented

  13. Mesozoic fault systems, deformation and fault block rotation in the Andean forearc: a crustal scale strike-slip duplex in the Coastal Cordillera of northern Chile

    Science.gov (United States)

    Taylor, G. K.; Grocott, J.; Pope, A.; Randall, D. E.

    1998-12-01

    In this paper we discuss the evolution and tectonic significance of the Mesozoic trench-parallel fault systems which affected the Coastal Cordillera and their relation to magmatism and crustal rotation. The oldest, extensional, fault system separates basement from rift-related Late Triassic and younger sedimentary units. This system [I] subsequently developed into a wider extensional fault system which acted as the locus of magma ascent and emplacement of the Coastal Batholith during much of the Jurassic to earliest Cretaceous period. This extensional fault system defined the forearc sliver during this period and was the consequence of a retreating subduction boundary. During the Early Cretaceous (c. 132-125 Ma) the kinematics of this fault system changed to transtension [II] and accommodated a major component of left-lateral strike-slip motion, the principal fault being the Atacama Fault Zone along which plutons continued to be emplaced. The final phase of pluton emplacement within the Coastal Cordillera appears to be c. 106 Ma, after which this magmatic arc and fault system was abandoned. An Late Cretaceous arc and fault system [III] developed some 20 Ma later and located some 50 km to the east in what is now the Central Valley of northern Chile. This paper seeks to show that the Coastal Cordillera was deformed as a whole by this Late Cretaceous fault system [III] which formed a crustal-scale left-lateral transpressional duplex. During this deformation the thermally weakened crust was dissected into a series of large-scale blocks bounded by NW-trending left-lateral strike-slip faults which merge into a NNE-SSW fault zone which forms the eastern boundary to the duplex. We term this eastern boundary zone the Central Valley Fault Zone (CVFZ) and this together with the NW-trending faults defines the duplex system which we refer to as a whole as the Coastal Cordillera Fault System (CCFS) [III]. We have traced the CCFS duplex between 25°S and 29°S and suspect that it

  14. Slab flattening, dynamic topography and normal faulting in the Cordillera Blanca region (northern Peru)

    Science.gov (United States)

    Margirier, A.; Robert, X.; Laurence, A.; Gautheron, C.; Bernet, M.; Simon-Labric, T.; Hall, S. R.

    2015-12-01

    Processes driving surface uplift in the Andes are still debated and the role of subduction processes as slab flattening on surface uplift and relief building in the Andes is not well understood. Some of the highest Andean summits, the Cordillera Blanca (6768 m) and the Cordillera Negra (5187 m), are located above a present flat subduction zone (3-15°S), in northern Peru. In this area, both the geometry and timing of the flattening of the slab are well constrained (Gutscher et al., 1999; Rosenbaum et al., 2005). This region is thus a perfect target to explore the effect of slab flattening on the Andean topography and uplift. We obtained new apatite (U-Th)/He and fission-track ages from three vertical profiles located in the Cordillera Blanca and the Cordillera Negra. Time-temperature paths obtained from inverse modeling of the thermochronological data indicates a Middle Miocene cooling for both Cordillera Negra profiles. We interpret it as regional exhumation in the Cordillera Occidental starting in Middle Miocene, synchronous with the onset of the subduction of the Nazca ridge (Rosenbaum et al., 2005). We propose that the Nazca ridge subduction at 15 Ma and onset of slab flattening in northern Peru drove regional positive dynamic topography and thus enhanced exhumation in the Cordillera Occidental. This study provides new evidence of the impact subduction processes and associated dynamic topography on paleogeography and surface uplift in the Andes.

  15. Holocene denudation and landscape deformation in the Cordillera Blanca, Peru

    Science.gov (United States)

    Hodson, K. R.; Hall, S. R.; Michalak, M.; Farber, D.; Hourigan, J. K.

    2012-12-01

    Active orogenic systems are subject to a host of processes that influence their topographic and structural evolution. Broadly speaking, these processes can be divided into two general groups: tectonics and climate. Both are capable of inducing profound changes within an orogen, although many specifics regarding their forcings, interactions, and feedbacks remain unclear. Here, we address the evolution of the Cordillera Blanca Mountain Range of northern Peru: an elevated, high-relief, 200km long string of glaciated peaks along the spine of the Andes. The striking Cordillera Blanca Detachment Fault (CBDF) is actively facilitating the production of several kilometers of relief along the western flank of the range, and abundant records of past glaciations span from >440 ka to the present. Thus, tectonics (active faulting) and climate (glacial erosion) are operating in tandem to produce some of the highest topography in the western hemisphere, affording the opportunity to investigate their potential interactions. Through the use of cosmogenic 10Be, low temperature thermochronology and digital terrain analysis we characterize the rates of landscape change as well as the present morphology. Significant variation in range elevation (maximum, mean, modal and minimum), relief (local and within basins) and slope (maximum, mean and minimum) exist along the strike of the range, potentially reflecting variable displacement along the CBDF, varying degrees of glacial erosion along the mountain range, or some combination of the two. The morphology of the adjacent supradetachment basin varies as well, containing zones with distinct styles of faulting and basin growth likely defined by the segmentation history of the CBDF. New thermochronologic data extends the current dataset, which we combine with 10Be basin-averaged erosion rates from basins along the range. These two datasets constrain the exhumational and erosional history of the range-forming Cordillera Blanca Batholith from the

  16. Plant species richness and shrub cover attenuate drought effects on ecosystem functioning across Patagonian rangelands.

    Science.gov (United States)

    Gaitán, Juan J; Bran, Donaldo; Oliva, Gabriel; Maestre, Fernando T; Aguiar, Martín R; Jobbágy, Esteban; Buono, Gustavo; Ferrante, Daniela; Nakamatsu, Viviana; Ciari, Georgina; Salomone, Jorge; Massara, Virginia

    2014-10-01

    Drought is an increasingly common phenomenon in drylands as a consequence of climate change. We used 311 sites across a broad range of environmental conditions in Patagonian rangelands to evaluate how drought severity and temperature (abiotic factors) and vegetation structure (biotic factors) modulate the impact of a drought event on the annual integral of normalized difference vegetation index (NDVI-I), our surrogate of ecosystem functioning. We found that NDVI-I decreases were larger with both increasing drought severity and temperature. Plant species richness (SR) and shrub cover (SC) attenuated the effects of drought on NDVI-I. Grass cover did not affect the impacts of drought on NDVI-I. Our results suggest that warming and species loss, two important imprints of global environmental change, could increase the vulnerability of Patagonian ecosystems to drought. Therefore, maintaining SR through appropriate grazing management can attenuate the adverse effects of climate change on ecosystem functioning. PMID:25339654

  17. Infection of Myxobolus galaxii (Myxozoa) in Galaxias maculatus (Osmeriformes: Galaxiidae) from northwestern Patagonian Andean lakes (Argentina).

    Science.gov (United States)

    Flores, Verónica; Viozzi, Gustavo

    2007-04-01

    The infection of Myxobolus galaxii Szidat, 1953, from the musculature and abdominal organs of northwestern Patagonian Galaxias maculatus is described. Plasmodia are histozoic and intercellular. Spores are pyriform in valvar view and biconvex in sutural view, with 4-9 edge notches in the sutural line, varying in shape within the same plasmodium. Myxobolus galaxii was detected in fish from 7 of 17 Andean Patagonian lakes, with prevalences ranging between 2 and 17%. A repeating pattern of summer increment in prevalence was observed, which could be explained by the ontogenetic migratory movements of the fish in Lake Gutiérrez. Also, accumulation of plasmodia through the life span of fish was detected. PMID:17539428

  18. Nazca plate subduction, mantle flow and Cordilleras formation

    Science.gov (United States)

    Capitanio, Fabio A.

    2013-04-01

    The Nazca-South America convergence represents a unique natural laboratory to probe our understanding of subduction, mantle flow and stress coupling at Andean-type margins. Here, it is shown that the most fundamental balance of forces associated with the downgoing slab, the upper plates and the mantle can account for the Nazca plate motions, although it does not adequately explain the variations of the Cordilleran tectonics found along the ~6000 km wide margin. Using three-dimensional numerical models it is shown that trench-parallel gradients in both the driving and resisting forces are an essential component of the force balance, and necessary to reproduce the macroscopic features observed. When along-trench buoyancy variations similar to the Nazca plate's are included, the slab dips and upper plate deformations observed in the Nazca slab, in the Cordilleras and South American continent interiors can be reproduced. The models show that gradients in the resisting shear force along the trench can be as relevant, as they modulate the trench retreat to form the concave Bolivian Orocline. Pressure gradients in the mantle follow the Nazca buoyancy gradients, and effectively rearrange the flow introducing a trench-parallel component, similar to what suggested by seismic anisotropy in this area. Although they introduce only secondary variations to the primary subduction and mantle flow dynamics, the regional features of the Nazca and South American plates exert a primary control at the margin-local scale. This suggests that far-field forces, e.g. from spreading Atlantic or large-scale convection, should play a minor role in the formation of the Cordilleras.

  19. Antifungal steroidal glycosides from the patagonian starfish anasteriasminuta: structure-activity correlations.

    Science.gov (United States)

    Chludil, Hugo D; Seldes, Alicia M; Maier, Marta S

    2002-02-01

    Two new sulfated steroidal hexaglycosides, anasterosides A (2) and B (3), along with the known versicoside A (1) have been isolated from the Patagonian starfish Anasterias minuta. Their structures have been elucidated by spectroscopic analysis (NMR and FABMS) and chemical transformations. Compounds 1 and 2 and the synthetic pentaglycoside 1b derived from versicoside A showed antifungal activity against the plant pathogenic fungus Cladosporium cucumerinum. Desulfation of hexaglycoside 1 rendered a totally inactive saponin. PMID:11858747

  20. Fossil pollen records indicate that Patagonian desertification was not solely a consequence of Andean uplift

    Science.gov (United States)

    Palazzesi, L.; Barreda, V. D.; Cuitiño, J. I.; Guler, M. V.; Tellería, M. C.; Ventura Santos, R.

    2014-03-01

    The Patagonian steppe—a massive rain-shadow on the lee side of the southern Andes—is assumed to have evolved ~15-12 Myr as a consequence of the southern Andean uplift. However, fossil evidence supporting this assumption is limited. Here we quantitatively estimate climatic conditions and plant richness for the interval ~10-6 Myr based on the study and bioclimatic analysis of terrestrially derived spore-pollen assemblages preserved in well-constrained Patagonian marine deposits. Our analyses indicate a mesothermal climate, with mean temperatures of the coldest quarter between 11.4 °C and 16.9 °C (presently ~3.5 °C) and annual precipitation rarely below 661 mm (presently ~200 mm). Rarefied richness reveals a significantly more diverse flora during the late Miocene than today at the same latitude but comparable with that approximately 2,000 km further northeast at mid-latitudes on the Brazilian coast. We infer that the Patagonian desertification was not solely a consequence of the Andean uplift as previously insinuated.

  1. The Cordillera Blanca normal fault and its contribution to the Andean topographic evolution (northern Peru)

    Science.gov (United States)

    Margirier, Audrey; Robert, Xavier; Schwartz, Stéphane; Audin, Laurence

    2015-04-01

    Nature and localization of Quaternary tectonics remains largely unconstrained in Peruvian Andes as well as the mechanism driving rock uplift. The Cordillera Blanca normal fault accommodates extension in a convergent context. The fault system trends parallel to the subduction zone, just above the Peruvian flat-slab, and separate the Cordilleras Blanca and Negra. The Cordillera Blanca batholith (8-5 Ma) is an elongated pluton, emplaced at ~6 km depth in the Jurassic sedimentary country rocks. The Cordillera Blanca range (6768 m) that comprises the highest Peruvian peak built the footwall of the fault. The ~200 km-long fault has showed ~4500 m of vertical displacement since 5 Ma. This normal fault is described as active despite the lack of historical seismicity and constitutes a striking singularity within the prevailing compressional setting of the Andean orogeny. This region is a perfect target to explore the contribution of large normal fault in relief building. Our goals are to determine if the fault was pre-existing before the Cordillera Blanca batholith emplacement, when it has been reactivated and how does it interact with the batholith exhumation. For that purpose, we focus on brittle deformation analysis from a regional scale (faults trends) to outcrop scale (fault planes, striaes and kinematics). We present here new structural data and focal mechanisms indicating a senestral transtensive component on the Cordillera Blanca normal fault and a regional extensional regime in the Cordillera Negra area. We compare the paleotensors obtained from the inversion of the microstructural data and focal mechanisms with the exhumation history deduced from the thermochronological data to constrain the role of the normal fault in relation with relief building. We propose that the Cordillera Blanca normal fault is an inherited tectonic feature reactivated in transtension after the slab flattening at ~8 Ma. The differential exhumation of the Cordillera Blanca with respect to

  2. Constraining the crustal root geometry beneath the Rif Cordillera (North Morocco)

    Science.gov (United States)

    Diaz, Jordi; Gil, Alba; Carbonell, Ramon; Gallart, Josep; Harnafi, Mimoun

    2016-04-01

    The analyses of wide-angle reflections of controlled source experiments and receiver functions calculated from teleseismic events provide consistent constraints of an over-thickened crust beneath the Rif Cordillera (North Morocco). Regarding active source data, we investigate now offline arrivals of Moho-reflected phases recorded in RIFSIS project to get new estimations of 3D crustal thickness variations beneath North Morocco. Additional constrains on the onshore-offshore transition are derived from onland recording of marine airgun shots from the coeval Gassis-Topomed profiles. A regional crustal thickness map is computed from all these results. In parallel, we use natural seismicity data collected throughout TopoIberia and PICASSO experiments, and from a new RIFSIS deployment, to obtain teleseismic receiver functions and explore the crustal thickness variations with a H-κ grid-search approach. The use of a larger dataset including new stations covering the complex areas beneath the Rif Cordillera allow us to improve the resolution of previous contributions, revealing abrupt crustal changes beneath the region. A gridded surface is built up by interpolating the Moho depths inferred for each seismic station, then compared with the map from controlled source experiments. A remarkably consistent image is observed in both maps, derived from completely independent data and methods. Both approaches document a large modest root, exceeding 50 km depth in the central part of the Rif, in contrast with the rather small topographic elevations. This large crustal thickness, consistent with the available Bouguer anomaly data, favor models proposing that the high velocity slab imaged by seismic tomography beneath the Alboran Sea is still attached to the lithosphere beneath the Rif, hence pulling down the lithosphere and thickening the crust. The thickened area corresponds to a quiet seismic zone located between the western Morocco arcuate seismic zone, the deep seismicity area

  3. BANCO DE SEMILLAS EN UN BOSQUE DE ROBLE DE LA CORDILLERA CENTRAL COLOMBIANA SOIL SEED BANK IN AN OAK FOREST FROM THE COLOMBIAN CENTRAL CORDILLERA

    Directory of Open Access Journals (Sweden)

    Luz Bibiana Moscoso Marín

    2005-12-01

    Full Text Available El banco de semillas del suelo es importante para el funcionamiento del ecosistema, pues se constituye en un reservorio de especies listas a germinar cuando se presenta una perturbación o cuando las condiciones ambientales cambian para iniciar el proceso de sucesión. El objetivo principal de esta investigación fue evaluar la variación espacial del banco de semillas y su relación con la vegetación actual en un fragmento de bosque altoandino dominado por roble de tierra fría (Quercus humbodtii Bonpl. a 2.290 m.s.n.m. en la cuenca de la Quebrada Piedras Blancas, en el departamento de Antioquia, Colombia. Allí se estableció una parcela de 6.400 m², donde se eligieron 57 puntos de muestreo. En cada uno de ellos se colectó una muestra de hojarasca y una de suelo. Además se marcaron cinco subparcelas de 160 m²para hacer el muestreo de la vegetación. La determinación del banco de semillas se hizo por el método de germinación directa, evaluando la emergencia de plántulas. En total, se censaron 204 individuos pertenecientes a 25 familias y 41 géneros. Las especies con mayor representación fueron Alfaroa cf. colombiana, Myrcia popayanensis Rich. y Quercus humboldtii Bonpl. En el ensayo de germinación se obtuvieron 428 individuos en las muestras de suelo y 113 en las de hojarasca, pertenecientes a 20 morfoespecies. La composición de especies del banco de semillas de este fragmento de robledal, no reflejó la composición actual de la vegetación del bosque. El banco de semillas esta constituido principalmente por especies herbáceas y en menor proporción por arbustos. La hojarasca contiene poca cantidad de semillas (198 semillas m-2 y en los primeros 10 cm del suelo se acumula una gran cantidad de semillas viables (4.330 semillas m-2. Se presenta una variación espacial significativa en la densidad de semillas del suelo a través del bosque a escala de unos pocos metros.Soil seed banks are important for ecosystem functioning because they stores species ready to germinate when a perturbation occurs or when environmental conditions change to start the successional process. The main objective of this research was to evaluate the spatial variation of seed banks and its relation with the current vegetation in a highland Andean forest dominated by oak (Quercus humbodtii Bonpl. at 2.290 m.a.s.l. in the watershed of the Piedras Blancas stream, in the department of Antioquia, Colombia. We sampled 57 points in a 6.400 m² plot established in that forest. In each point we collected one sample each of litter and soil. We also established five subplots of 160 m²each for sampling vegetation. Seed banks were assessed by the method of direct germination. We obtained 204 trees belonging to 25 families and 41 genera. The most representative tree species were Alfaroa cf. colombiana, Myrcia popayanensis Rich. and Quercus humboldtii Bonpl. We obtained 428 individuals from soil samples and 113 individuals from litter samples in the germination trial, belonging to 20 morpho species. Species composition of the soil seed bank did not reflect the composition of the forest vegetation, and we found mainly herbaceous and shrub vegetation. Litter had 198 seeds m-2 and soil had 4.330 seeds m-2. There was large spatial variation in the amount of seeds in this forest fragment.

  4. Análisis de las características geométricas y desarrollo temporal de un sistema de díaclasas en las rocas triásicas del límite Cordillera Ibérica - Sistema Central

    OpenAIRE

    Sevillano, Ana; Gutiérrez Alonso, Gabriel; Gross, M.R.

    2000-01-01

    The mesozoic and tertiary rocks at the Iberian Range-Spanish Central System boundary in Guadalajara (Spain) depict a very important development of systematic joint sets. This study is focused on a detailed and systematic analysis of the orientations and lengths of the joints, and the relationship between both geometric parameters in two well exposed outcrops called Atance 1 and Atance 2. Both outcrops are located on two nearly horizontal beds of Muschelkalk dolomites and have been mapped in g...

  5. Active rollback in the Gibraltar Arc: Evidences from CGPS data in the western Betic Cordillera

    Science.gov (United States)

    Gonzalez-Castillo, L.; Galindo-Zaldivar, J.; de Lacy, M. C.; Borque, M. J.; Martinez-Moreno, F. J.; García-Armenteros, J. A.; Gil, A. J.

    2015-11-01

    The Gibraltar Arc, located in the western Mediterranean Sea, is an arcuate Alpine orogen formed by the Betic and Rif Cordilleras, separated by the Alboran Sea. New continuous GPS data (2008-2013) obtained in the Topo-Iberia stations of the western Betic Cordillera allow us to improve the present-day deformation pattern related to active tectonics in this collision area between the Eurasian and African plates. These data indicate a very consistent westward motion of the Betic Cordillera with respect to the relatively stable Iberian Massif foreland. The displacement in the Betics increases toward the south and west, reaching maximum values in the Gibraltar Strait area (4.27 mm/yr in Ceuta, CEU1, and 4.06 mm/yr in San Fernando, SFER), then progressively decreasing toward the northwestern mountain front. The recent geological structures and seismicity evidence moderate deformation in a roughly NW-SE to WNW-ESE compressional stress setting in the mountain frontal areas, and moderate extension toward the internal part of the cordillera. The mountain front undergoes progressive development of folds affecting at least up to Pliocene deposits, with similar recent geological and geodetical rates. This folded strip helps to accommodate the active deformation with scarce associated seismicity. The displacement pattern is in agreement with the present-day clockwise rotation of the tectonic units in the northern branch of the Gibraltar Arc. Our data support that the westward emplacement of the Betic Cordillera continues to be active in a rollback tectonic scenario.

  6. Cytotoxic and antifungal triterpene glycosides from the Patagonian sea cucumber Hemoiedema spectabilis.

    Science.gov (United States)

    Chludil, Hugo D; Muniain, Claudia C; Seldes, Alicia M; Maier, Marta S

    2002-06-01

    Two new sulfated triterpene glycosides, hemoiedemosides A (1) and B (2), have been isolated from the Patagonian sea cucumber Hemoiedema spectabilis. Their structures have been established by a combination of spectroscopic analysis (NMR and FABMS) and chemical transformations. Both glycosides present the same aglycon and differ in the degree of sulfation of the tetrasaccharide chain. Hemoiedemoside B (2) is a new example of a small number of trisulfated triterpene glycosides from sea cucumbers belonging to the family Cucumariidae. Glycosides 1 and 2 exhibit considerable antifungal activity against the phytopathogenic fungus Cladosporium cucumerinum, while the semisynthetic desulfated derivative 1a is less active. PMID:12088428

  7. Wing pattern variation in the Patagonian biting midge, Forcipomyia (Forcipomyia multipicta Ingram & Macfie (Diptera, Ceratopogonidae

    Directory of Open Access Journals (Sweden)

    Gustavo R. SPINELLI

    2012-01-01

    Full Text Available Examination of the type-series and non-type specimens of the Patagonian biting midge, Forcipomyia (Forcipomyia multipicta Ingram & Macfie (Diptera: Ceratopogonidae, revealed considerable variation in wing patterns of both sexes. One pattern includes several distinct light spot areas, whereas another pattern (e.g, in the holotype only features marginal light spots in cell r3, while other light spots are barely perceptible or absent. The cause(s of the differential lack of dark macrotrichia in certain areas of the wing membrane in specimens of some series could not be attributed either to their age, sex, or method of preservation.

  8. Patagonian and Antarctic dust as recorded in the sediments of Laguna Potrok Aike (Patagonia, Argentina)

    Science.gov (United States)

    Haberzettl, Torsten; Stopp, Annemarie; Lisé-Pronovost, Agathe; Gebhardt, Catalina; Ohlendorf, Christian; Zolitschka, Bernd; von Eynatten, Hilmar; Kleinhanns, Ilka; Pasado Science Team

    2010-05-01

    Although an increasing number of terrestrial paleoclimatic records from southern South America has been published during the last decade, these archives mostly cover the Lateglacial and/or the Holocene. Only little is known about the Patagonian climate before the Last Glacial Maximum. Here, we present a continuous, high-resolution magnetic susceptibility record for the past 48 ka from the maar lake Laguna Potrok Aike (51°58' S, 70°23' W, southern Patagonia, Argentina). Magnetic susceptibility serves as an excellent parameter for the parallelization of sediment cores all over Laguna Potrok Aike including sediment cores taken within the ICDP (International Continental Scientific Drilling Program) project PASADO (Potrok Aike maar lake Sediment Archive Drilling prOject). Additionally, magnetic susceptibility is assumed to be a proxy for dust deposition in this lake. Distinct similarities were found between the independently dated magnetic susceptibility record from Laguna Potrok Aike and the non-sea-salt calcium (nss-Ca) flux from the EPICA Dome C ice core record (75°06'S, 123°24'E) the latter being a proxy for mineral dust deposition in Antarctica [1]. Comparison of the two records and variations in grain size of the Laguna Potrok Aike sediment records indicate a relatively high aeolian activity in southern South America during the glacial period. During the Holocene climatic conditions driving sediment deposition seem to have been more variable and less dominated by wind compared to glacial times. Although the source of the dust found in Antarctic ice cores often has been attributed to Patagonia [2], we present the first evidence for contemporaneity of aeolian deposition in both the target area (Antarctica) and the major source area (Patagonia). Considering the similarities of the two records, magnetic susceptibility might yield the potential for chronological information: transfer of the ice core age model to a lacustrine sediment record. This would be important

  9. Investigation of a measles outbreak in Cordillera, Northern Philippines, 2013

    Science.gov (United States)

    Zapanta, Ma Justina; de los Reyes, Vikki Carr; Tayag, Enrique; Magpantay, Rio

    2016-01-01

    Introduction Measles is a highly infectious viral illness that remains one of the leading causes of death among children worldwide. In the Philippines, decreasing routine vaccination coverage from 2007 to 2011 led to local measles outbreaks. A team investigated a measles outbreak reported in Cordillera of the Philippines in May 2013. Methods Measles case data with symptom onset from 2 February to 27 May 2013 were obtained from official sources and verified on site. Data included age, sex, residential address, signs and symptoms and vaccination status. Active case-findings were also conducted for contacts of these cases. The living environments of the cases were investigated. A survey was conducted with the cases and caregivers to understand their knowledge and attitudes about measles. Results There were 50 measles cases identified with an age range from six months to 32 years (median: 16 years). Thirty-two were male (64%). Twenty (40%) were hospitalized with one death. Thirty-two (64%) cases were laboratory confirmed, and 36 (72%) received a single dose of measles vaccine. Overcrowded living environments were observed among many cases. The majority of respondents (46/48, 96%) knew about measles, but there were misconceptions about the cause of measles and how it can be prevented and managed. Conclusion This measles outbreak occurred in an area with low immunization coverage. Achieving 95% measles immunization coverage and strengthening routine immunization strategies to address high-risk populations are recommended. Also, we recommend health education campaigns to include components that address misconceptions about measles. PMID:27766180

  10. Investigation of a measles outbreak in Cordillera, northern Philippines, 2013

    Directory of Open Access Journals (Sweden)

    Paola Katrina Ching

    2016-07-01

    Full Text Available Introduction: Measles is a highly infectious viral illness that remains one of the leading causes of death among children worldwide. In the Philippines, decreasing routine vaccination coverage from 2007 to 2011 led to local measles outbreaks. A team investigated a measles outbreak reported in Cordillera of the Philippines in May 2013. Methods: Measles case data with symptom onset from 2 February to 27 May 2013 were obtained from official sources and verified on site. Data included age, sex, residential address, signs and symptoms and vaccination status. Active case-findings were also conducted for contacts of these cases. The living environments of the cases were investigated. A survey was conducted with the cases and caregivers to understand their knowledge and attitudes about measles. Results: There were 50 measles cases identified with an age range from six months to 32 years (median: 16 years. Thirty-two were male (64%. Twenty (40% were hospitalized with one death. Thirty-two (64% cases were laboratory confirmed, and 36 (72% received a single dose of measles vaccine. Overcrowded living environments were observed among many cases. The majority of respondents (46/48, 96% knew about measles, but there were misconceptions about the cause of measles and how it can be prevented and managed. Conclusion: This measles outbreak occurred in an area with low immunization coverage. Achieving 95% measles immunization coverage and strengthening routine immunization strategies to address high-risk populations are recommended. Also, we recommend health education campaigns to include components that address misconceptions about measles.

  11. Geology and micromammals of the Serra-1 site (Tabernas Basin, Betic Cordillera

    Directory of Open Access Journals (Sweden)

    Ruiz Bustos, A.

    1993-12-01

    Full Text Available A chronology is given for the alluvial fan deposits in the Tabernas Basin (Internal Zone, Betic Cordillera. Palaeontological and sedimentological data are used to establish a palaeoclimatic model for the Quaternary in southeastern Spain.La Cuenca de Tabernas está situada en la zona interna de la Cordillera Bética, se da una cronología para los depósitos formados por abanicos aluviales y se plantea a través de datos paleontológicos y sedimentológicos un modelo paleochmátlco para el Cuaternano en el sureste de España.

  12. Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation.

    Science.gov (United States)

    Metcalf, Jessica L; Turney, Chris; Barnett, Ross; Martin, Fabiana; Bray, Sarah C; Vilstrup, Julia T; Orlando, Ludovic; Salas-Gismondi, Rodolfo; Loponte, Daniel; Medina, Matías; De Nigris, Mariana; Civalero, Teresa; Fernández, Pablo Marcelo; Gasco, Alejandra; Duran, Victor; Seymour, Kevin L; Otaola, Clara; Gil, Adolfo; Paunero, Rafael; Prevosti, Francisco J; Bradshaw, Corey J A; Wheeler, Jane C; Borrero, Luis; Austin, Jeremy J; Cooper, Alan

    2016-06-01

    The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, with major phases coinciding with both human arrival and climate change around the world. The Americas provide a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame (~15 to 14.6 ka) but during contrasting temperature trends across each continent. Unfortunately, limited data sets in South America have so far precluded detailed comparison. We analyze genetic and radiocarbon data from 89 and 71 Patagonian megafaunal bones, respectively, more than doubling the high-quality Pleistocene megafaunal radiocarbon data sets from the region. We identify a narrow megafaunal extinction phase 12,280 ± 110 years ago, some 1 to 3 thousand years after initial human presence in the area. Although humans arrived immediately prior to a cold phase, the Antarctic Cold Reversal stadial, megafaunal extinctions did not occur until the stadial finished and the subsequent warming phase commenced some 1 to 3 thousand years later. The increased resolution provided by the Patagonian material reveals that the sequence of climate and extinction events in North and South America were temporally inverted, but in both cases, megafaunal extinctions did not occur until human presence and climate warming coincided. Overall, metapopulation processes involving subpopulation connectivity on a continental scale appear to have been critical for megafaunal species survival of both climate change and human impacts. PMID:27386563

  13. Deepening of the ocean mixed layer at the northern Patagonian continental shelf: a numerical study

    CERN Document Server

    Zanella, Juan; Pescio, Andres; Dragani, Walter

    2014-01-01

    A possible deepening of the ocean mixed layer was investigated at a selected point of the Patagonian continental shelf where a significant positive wind speed trend was estimated. Using a 1-dimensional vertical numerical model (S2P3) forced by atmospheric data from NCEP/NCAR I reanalysis and tidal constituents from TPXO 7.2 global model on a long term simulation (1979-2011), it was found that the mixed layer thickness presents a significant and positive trend of 10.1 +/- 1.4 cm/yr. Several numerical experiments were carried out in order to evaluate the impact of the different atmospheric variables (surface zonal and latitudinal wind components, air temperature, atmospheric pressure, specific humidity and cloud coverage) considered in this study. As a result it was found that an increase in the wind speed can be considered as the main responsible of the ocean mixed layer deepening at the selected location of the Patagonian continental shelf. A possible increasing in the mixed layer thickness could be directly ...

  14. Patagonian red wines: selection of Lactobacillus plantarum isolates as potential starter cultures for malolactic fermentation.

    Science.gov (United States)

    Bravo-Ferrada, Bárbara Mercedes; Hollmann, Axel; Delfederico, Lucrecia; Valdés La Hens, Danay; Caballero, Adriana; Semorile, Liliana

    2013-09-01

    The aim of this study was to evaluate fifty-three Lactobacillus plantarum isolates obtained from a Patagonian red wine, molecularly identified and typified using RAPD analysis, in order to select starter cultures for malolactic fermentation (MLF). The results obtained suggest a considerable genetic diversity, taking into account that all L. plantarum isolates were obtained from one cellar and one vintage. Based on the capacity to tolerate a concentration of 14 % ethanol in MRS broth for 2 days, eight isolates were selected for the subsequent analysis. The incidence of various wine stress factors (ethanol, acid pH, lysozyme and sulfur dioxide) on isolates growth was studied. Besides, glucosidase and tannase activities were evaluated, and the presence of genes involved in the synthesis of biogenic amines was examined by PCR. A previously characterized indigenous Oenococcus oeni strain was included with comparative purposes. Differences in technologically relevant characteristics were observed among the eight L. plantarum selected isolates, revealing an isolate-dependent behavior. Detectable glucosidase and tannase activities were found in all isolates. The presence of genes encoding histidine and tyrosine descarboxylases and putrescine carbamoyltransferase was not detected. The ability of L. plantarum isolates to grow and consume L-malic acid in simulated laboratory-scale vinifications revealed that two of them could be considered as possible MLF starter cultures for Patagonian red wines. These isolates will be subjected to further analysis, for a final winery technological characterization.

  15. Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation.

    Science.gov (United States)

    Metcalf, Jessica L; Turney, Chris; Barnett, Ross; Martin, Fabiana; Bray, Sarah C; Vilstrup, Julia T; Orlando, Ludovic; Salas-Gismondi, Rodolfo; Loponte, Daniel; Medina, Matías; De Nigris, Mariana; Civalero, Teresa; Fernández, Pablo Marcelo; Gasco, Alejandra; Duran, Victor; Seymour, Kevin L; Otaola, Clara; Gil, Adolfo; Paunero, Rafael; Prevosti, Francisco J; Bradshaw, Corey J A; Wheeler, Jane C; Borrero, Luis; Austin, Jeremy J; Cooper, Alan

    2016-06-01

    The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, with major phases coinciding with both human arrival and climate change around the world. The Americas provide a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame (~15 to 14.6 ka) but during contrasting temperature trends across each continent. Unfortunately, limited data sets in South America have so far precluded detailed comparison. We analyze genetic and radiocarbon data from 89 and 71 Patagonian megafaunal bones, respectively, more than doubling the high-quality Pleistocene megafaunal radiocarbon data sets from the region. We identify a narrow megafaunal extinction phase 12,280 ± 110 years ago, some 1 to 3 thousand years after initial human presence in the area. Although humans arrived immediately prior to a cold phase, the Antarctic Cold Reversal stadial, megafaunal extinctions did not occur until the stadial finished and the subsequent warming phase commenced some 1 to 3 thousand years later. The increased resolution provided by the Patagonian material reveals that the sequence of climate and extinction events in North and South America were temporally inverted, but in both cases, megafaunal extinctions did not occur until human presence and climate warming coincided. Overall, metapopulation processes involving subpopulation connectivity on a continental scale appear to have been critical for megafaunal species survival of both climate change and human impacts.

  16. Biodiversity and spatial distribution of medusae in the Magellan Region (Southern Patagonian Zone

    Directory of Open Access Journals (Sweden)

    Sergio Palma

    2014-11-01

    Full Text Available Epipelagic medusae collected in the Magellan Region (Southern Patagonian Zone during spring 2009 were analyzed. A total of 27 species of medusae were identified (25 hydromedusae and 2 scyphomedusae. Twelve medusae species were recorded for the first time in the Magellan region. Six dominant species were found: Clytia simplex (19.8%, Rhopalonema funerarium (16.2%, Aurelia sp. (15.9%, Bougainvillia muscoides (15.5%, Proboscidactyla stellata (8.9%, and Obelia spp. (6.0%. The horizontal distribution of all these species, except Obelia spp., showed the highest abundances to the south of 54°S, particularly in the Almirantazgo and Agostini fjords and in the Beagle Channel. Most of the dominant species were collected in shallow strata (0-50 m, with less saline waters (<30, except for R. funerarium, which was mainly collected above depths deeper than 25 m in more saline waters (30-33. These results confirm the success of several species in the colonization of the inland waters of the Southern Patagonian Zone.

  17. Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation

    Science.gov (United States)

    Metcalf, Jessica L.; Turney, Chris; Barnett, Ross; Martin, Fabiana; Bray, Sarah C.; Vilstrup, Julia T.; Orlando, Ludovic; Salas-Gismondi, Rodolfo; Loponte, Daniel; Medina, Matías; De Nigris, Mariana; Civalero, Teresa; Fernández, Pablo Marcelo; Gasco, Alejandra; Duran, Victor; Seymour, Kevin L.; Otaola, Clara; Gil, Adolfo; Paunero, Rafael; Prevosti, Francisco J.; Bradshaw, Corey J. A.; Wheeler, Jane C.; Borrero, Luis; Austin, Jeremy J.; Cooper, Alan

    2016-01-01

    The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, with major phases coinciding with both human arrival and climate change around the world. The Americas provide a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame (~15 to 14.6 ka) but during contrasting temperature trends across each continent. Unfortunately, limited data sets in South America have so far precluded detailed comparison. We analyze genetic and radiocarbon data from 89 and 71 Patagonian megafaunal bones, respectively, more than doubling the high-quality Pleistocene megafaunal radiocarbon data sets from the region. We identify a narrow megafaunal extinction phase 12,280 ± 110 years ago, some 1 to 3 thousand years after initial human presence in the area. Although humans arrived immediately prior to a cold phase, the Antarctic Cold Reversal stadial, megafaunal extinctions did not occur until the stadial finished and the subsequent warming phase commenced some 1 to 3 thousand years later. The increased resolution provided by the Patagonian material reveals that the sequence of climate and extinction events in North and South America were temporally inverted, but in both cases, megafaunal extinctions did not occur until human presence and climate warming coincided. Overall, metapopulation processes involving subpopulation connectivity on a continental scale appear to have been critical for megafaunal species survival of both climate change and human impacts. PMID:27386563

  18. Comparative flight morphology in queens of invasive and native Patagonian bumblebees (Hymenoptera: Bombus).

    Science.gov (United States)

    Polidori, Carlo; Nieves-Aldrey, José Luis

    2015-02-01

    Since its introduction in Chile, the European Bombus terrestris L. (Hymenoptera: Apidae) has progressively reduced the abundance of the native Patagonian bumblebee, Bombus dahlbomii Guérin. Because an important cause of successful invasion of a species may depend on a potentially advantageous phenotype, we studied morphologies related to flight performance (flight muscle ratio (FMR), wing loading (WL), excess power index (EPI, which integrates FMR and WL) and wing aspect ratio (AR)) in the queens of the two species. Previous empirical studies showed that greater FMR, AR and EPI, and lower WL increase flight performance. In the Patagonian Chilean fjord where the study was carried out, B. dahlbomii was 40% heavier than B. terrestris, a difference theoretically allowing the queens of the native species to take off with heavier loads, despite the fact that the two species have virtually identical FMRs. However, FMR negatively depended on body mass at the intra-specific level. The total wing area was 35% greater in B. dahlbomii, but the difference in forewing length was only of 16%. Once taken into account the effect of body size, WL, was significantly lower in B. terrestris. AR increased with body mass and did not differ between species. EPI was weakly but significantly higher in B. terrestris. Experiments formally linking such parameters with flight performance may help to explain the observed quick and wide spread of this alien species in Patagonia in the last few years. PMID:25499798

  19. Nautiloideos del Triásico Medio en la Cordillera Ibérica y en la parte oriental de las Cordilleras Béticas

    OpenAIRE

    Goy Goy, A.; Martínez, G.

    1996-01-01

    [ES] En el presente trabajo se dan a conocer las sucesiones de los nautiloideos obtenidos en cada una de las cuencas estudiadas, así como sus implicaciones biocronoestratigráficas. En la parte oriental de las Cordilleras Béticas existe el siguiente registro de nautiloideos: — Grypoceras cf? privatum (MOJSISOVICS). Parte inferior del Muschelkalk en Quipar (Murcia). — Germanonautilus bidorsatus (SCHLOTI-{EIM); Mojsvaroceras cf? kummeli PARNES; fudonautifus cf? awadi KUMM...

  20. Evaporite deposits of Bogota area, Cordillera Oriental, Colombia

    Science.gov (United States)

    McLaughlin, Donald H.

    1972-01-01

    Four evaporite-bearing stratigraphic zones are known in Cretaceous strata of the Cordillera Oriental of Colombia north and east of Bogota. The easternmost and oldest zone is probably of Berriasian to Valanginian age. The next oldest is probably late Barremian to early Aptian in age. The third appears to be Aptian. The westernmost and best known sequence in the Sabana de Bogota is Turonian to early Coniacian in age. This youngest sequence contains the thickest salt deposits known in Colombia and is probably the most widespread geographically. Most of the rock salt exposed in the three accessible mines (at Zipaquira, Nemocon, and Upin) has a characteristic lamination of alternating slightly argillaceous and highly argillaceous salt layers of varied but moderate thickness. Black, calcareous claystone, commonly very pyritic, is interbedded conformably with the laminated salt in many places throughout the deposits. Fragments of black claystone derived from the thinner interbeds are ubiquitous in all deposits, both as concordant breccia zones and as isolated clasts. Anhydrite is scarce at Zipaquira and apparently even rarer at Nemocon and Upin. Gypsum is produced at three small deposits in the oldest evaporite zone where it probably was concentrated by leaching of salt initially associated with it. The two intervening evaporite zones are not exposed, but their existence and distribution are indicated by brine springs and locally by "rute," a distinctive black, calcareous mud formed by the leaching of salt beds. Fossils show that the youngest salt-claystone zone, in the Sabana de Bogota, is contemporary with associated hematitic sandstone and siltstone, and with carbonaceous and locally coaly claystone. Although evidence is poor, this same facies relation probably exists within the other three evaporite zones. All salt deposits in this study probably are associated with anticlines, a relation best exemplified by the deposits on the Sabana de Bogota. Within these

  1. Feeding analysis of larvae and juveniles of the common hake Patagonian stock (Merluccius hubbsi) in relation to the zooplankton taxonomic composition, abundance and nutritional quality.

    OpenAIRE

    Temperoni, B.

    2015-01-01

    The trophic relationships among early life stages (larvae and age-0 juveniles) of Patagonian hake (Merluccius hubbsi) stock and the zooplanktonic community in the spawning (between Isla Escondida and Bahía Camarones) and nursery (Golfo San Jorge) areas in the Argentine Sea (SW Atlantic ocean) were investigated. The study took place in the north Patagonian region (42°-47° S) during hake reproductive season (December-March). The effect of environmental features, including frontal regions, up...

  2. Palynology of cushion bogs of the Cordillera Pelada, Province of Valdivia, Chile

    Science.gov (United States)

    Heusser, Calvin J.

    1982-01-01

    Fossil pollen identified in the earliest sediments of three cushion bogs in the Cordillera Pelada (40°10'S, 73°30'W) dated 10,425 14C yr B.P. includes the subantarctic species Dacrydium fonckii, Tetroncium magellanicum, Astelia pumila, Gaimardia australis, Donatia fascicularis, and Drosera uniflora. All grow today in the Cordillera Pelada and range poleward to the southernmost Province of Magallanes; one species, Drapetes muscosa, included with the pollen of these plants in the earliest record, is no longer a constituent of the flora but is limited only to subantarctic Chile. Available evidence indicates that plants survived the last glaciation north of the glacial border with the course of postglacial migration southward following the wastage of the glacier complex. Holocene climatic and vegetational changes in the Cordillera Pelada are interpreted in the context of regional reconstructions which show maximum warmth about 9000 yr ago with a pronounced dry period lasting from 9000 to 6500 yr B.P. Maximum precipitation was later reached around 4000 yr ago but has decreased overall since then. The regional decline of the endemic gymnosperm Fitzroya cupressoides, which today is extensively destroyed in the Cordillera Pelada, follows this decrease in precipitation. These climatic data suggest a net south ward shift in the zone of westerly winds that bring rainfall to the region over the past 4000 yr.

  3. GPS velocities and the construction of the Eastern Cordillera of the Colombian Andes

    Science.gov (United States)

    Mora-Páez, Héctor; Mencin, David J.; Molnar, Peter; Diederix, Hans; Cardona-Piedrahita, Leonardo; Peláez-Gaviria, Juan-Ramón; Corchuelo-Cuervo, Yuli

    2016-08-01

    GPS velocities across the northeast trending Eastern Cordillera of Colombia show oblique convergence at 8.8 ± 1.7 mm/yr, consisting of 8.0 ± 1.7 mm/yr of right-lateral strike-slip shear along the mountain range and 3.7 ± 0.3 mm/yr of northwest southeast shortening. Faster convergence occurs only at the northeast end of the Cordillera, where its eastern edge trends northwest and the highest mountains lie. The strike-slip shear corroborates geologic work suggesting such movement southwest and northeast of the range. Given the ~200 km width of the Eastern Cordillera, the ~100-150 km of crustal shortening inferred from balanced cross sections and implied by recent estimates of crustal thickness would require ~25-40 Myr of shortening at ~4 mm/yr. The present-day GPS measurements, therefore, are inconsistent with the inference, based on paleobotanical observations that the entire Eastern Cordillera rose 1500-2500 m since 3-6 Ma and called for a different interpretation of those data.

  4. Can cosmic ray exposure dating reveal the normal faulting activity of the Cordillera Blanca Fault, Peru? ¿Dataciones por exposición de rayos cósmicos revelan fallamiento activo normal en la falla de la Cordillera Blanca, Perú?

    Directory of Open Access Journals (Sweden)

    L.L. Siame

    2006-12-01

    Full Text Available The build-up of in situ-produced cosmogenic 10Be within bedrock scarps and escarpments associated to the Cordillera Blanca Normal Fault, Peru, was measured to evaluate, through Cosmic Ray Exposure dating, its normal faulting activity. The highest mountain peaks in Peru belong to the 210 km-long, NW- striking, Cordillera Blanca. Along its western border, the Cordillera Blanca Normal Fault is responsible for a vertical relief over 4.4 km, whose prominent 2 km high escarpment is characterized by ~1 km-high triangular facets corresponding to vertical displacements cumulated during the last 1-2 million years. At a more detailed scale, this fault system exhibits continuous geomorphic evidence of repeated displacements, underlined by 2 to 70 m-high scarps, corresponding to vertical displacements cumulated since Late Pleistocene and Holocene periods. Although microseismicity occurs along the Cordillera Blanca Normal Fault, no major historical or instrumental earthquake has been recorded since the beginning of the Spanish settlement in the 16th century. To evaluate the vertical slip rate along the major 90 km-long central segment of the Cordillera Blanca Normal Fault, the Quaternary fault escarpment (i.e., triangular facet, as well as the bedrock fault scarp, have been sampled for 10Be Cosmic Ray Exposure dating. Even if the uppermost part of the triangular facets have been resurfaced by the Last Glacial Maximum glaciers, our results allow to estimate a vertical slip-rate of 3±1 mm/yr, and suggest at least 2 seismic events during the last 3000 years.La acumulación in situ de 10Be cosmogénico en las rocas intrusivas de las escarpas de la falla normal de la Cordillera Blanca del Perú han sido medidas para evaluar, su actividad de fallamiento normal., con edades de exposición a los rayos cósmicos. Los más altos picos en el Perú conforman la Cordillera Blanca que se extiende con una longitud de 210 km según una orientación NO. A lo largo de su l

  5. New cystidicolid species (Nematoda) from Galaxias platei (Osmeriformes: Galaxiidae) in Patagonian freshwater environments.

    Science.gov (United States)

    Brugni, Norma L; Viozzi, Gustavo P

    2008-08-01

    During a parasitological survey of Galaxias platei Steindachner, 1898, from Patagonian Andean Lakes, a new species of Cystidicolidae was found in the stomach of fish. The new species was described using light and scanning electron microscopy; the species has characteristics of Ascarophis and is distinguishable from other species by a combination of the following features: well-developed pseudolabia with T-shaped inner extensions, bifurcate deirids, small ratio GE:ME, small left spicule, small ratio LS:RS, and larvigerous eggs with thick and fine filaments in both poles. Intraspecific variation in the morphology of larvigerous eggs was studied. This is the first species of Ascarophis described from freshwater fishes. PMID:18576739

  6. Estado actual del conocimiento del orden Odonata en la Patagonia Current knowledge of Patagonian Odonata

    OpenAIRE

    Javier Muzón

    2009-01-01

    El orden Odonata se encuentra representado en la Patagonia por 36 especies, reunidas en nueve familias y 18 géneros. El nivel de endemismo de esta taxocoenosis es alto, aproximadamente el 60% de las especies y casi el 40% de los géneros endémicos. La riqueza específica en la Patagonia decrece de Oeste a Este y de Norte a Sur, las áreas de mayor riqueza resultan ser las cordilleras de Nahuel Buta (Chile) y de los Andes entre 38° y 41° S, y la meseta de Somuncurá (Argentina) en la estepa. Se br...

  7. Strike-slip faults in the southernmost Andes and the development of the Patagonian orocline

    Science.gov (United States)

    Cunningham, W. Dickson

    1993-02-01

    The Patagonian orocline is the 90° bend in the southernmost Andes between 50°S and 56°S. Paleomagnetic and structural data indicate that the orocline is, at least in part, the product of tectonic rotation. Recent field work in the Beagle Channel region of southernmost Chile provides evidence for widespread left-lateral strike-slip faulting in the internal zones of the mountain belt. Both arms of the Beagle Channel are interpreted to be left-lateral strike-slip faults based on detailed study of mesoscale strike-slip faults (Riedel shears) observed in coastal outcrops. Although much of the evidence indicates Cenozoic brittle strike-slip faulting, other fabric data, including vertical foliation zones containing horizontal quartz stretching lineations and ductile left-lateral kinematic indicators, suggest that Mesozoic ductile strike-slip or oblique-slip shearing also occurred. The implication is that the mid-Cretaceous Andean orogeny involved the transpressional inversion of the Rocas Verdes marginal basin and that transpression has been the dominant deformational regime in the region for the last 120 Ma. Regional left-lateral strike-slip faults are now recognized in all lithotectonic provinces of the southernmost Andes. A statistical study of regional lineament trends using aerial photographs and satellite imagery suggests that many unstudied lineaments are also strike-slip faults. A new model is proposed that integrates the development of strike-slip faulting and the structural evolution and uplift of the southernmost Andes with the rotational development of the orocline. The Patagonian orocline appears to be the product of broad interplate shearing accommodated by strike-slip faulting, block rotation, and contraction and is probably continuing to evolve today.

  8. Seasonal change of phytoplankton (spring vs. summer) in the southern Patagonian shelf

    Science.gov (United States)

    Gonçalves-Araujo, Rafael; de Souza, Márcio Silva; Mendes, Carlos Rafael Borges; Tavano, Virginia Maria; Garcia, Carlos A. E.

    2016-08-01

    As part of the Patagonian Experiment (PATEX) project two sequential seasons (spring/summer 2007-2008) were sampled in the southern Patagonian shelf, when physical-chemical-biological (phytoplankton) data were collected. Phytoplankton biomass and community composition were assessed through both microscopic and high-performance liquid chromatography/chemical taxonomy (HPLC/CHEMTAX) techniques and related to both in situ and satellite data at spatial and seasonal scales. Phytoplankton seasonal variation was clearly modulated by water column thermohaline structure and nutrient dynamics [mainly dissolved inorganic nitrogen (DIN) and silicate]. The spring phytoplankton community showed elevated biomass and was dominated by diatoms [mainly Corethron pennatum and small (cells of Thalassiosira spp.], associated with a deeper and more weakly stratified upper mixed layer depth (UMLD) and relatively low nutrient concentrations, which were probably a result of consumption by the diatom bloom. In contrast, the phytoplankton community in summer presented lower biomass and was mainly dominated by haptophytes (primarily Emiliania huxleyi and Phaeocystis antarctica) and dinoflagellates, associated with shallower and well-stratified upper mixed layers with higher nutrient concentrations, likely due to lateral advection of nutrient-rich waters from the Malvinas Current. The gradual establishment of a strongly stratified and shallow UMLD as season progressed, was an important factor leading to the replacement of the spring diatom community by a dominance of calcifying organisms, as shown in remote sensing imagery and confirmed by microscopic examination. Furthermore, in spring, phaeopigments a (degradation products of chlorophyll a) relative to chlorophyll a, were twice that of summer, indicating the diatom bloom was under higher grazing pressure.

  9. Tracing dissolved organic matter (DOM) from land-based aquaculture systems in North Patagonian streams.

    Science.gov (United States)

    Nimptsch, Jorge; Woelfl, Stefan; Osorio, Sebastian; Valenzuela, Jose; Ebersbach, Paul; von Tuempling, Wolf; Palma, Rodrigo; Encina, Francisco; Figueroa, David; Kamjunke, Norbert; Graeber, Daniel

    2015-12-15

    Chile is the second largest producer of salmonids worldwide. The first step in the production of salmonids takes place in land-based aquacultures. However, the effects of the discharge from these aquacultures on stream dissolved organic matter (DOM) content, molecular composition and degradability are unknown. The aim of this study was thus to investigate the inputs of anthropogenic DOM from land-based aquaculture to the predominantly pristine river systems of North Patagonia. We hypothesized, that i) DOM exported from land-based aquaculture mainly consists of protein-like fluorescence (tyrosine and tryptophan) released from fish feces and food remains, and that ii) this DOM is highly degradable and therefore rapidly turned-over within the receiving streams. In the North Patagonian region we conducted a screening of ten land-based aquacultures and an intensive sampling campaign for one aquaculture. This was combined with longitudinal transects and a degradation experiment in order to couple the composition of DOM exported from land-based aquacultures to its degradability in streams. We measured dissolved organic carbon (DOC) concentration by high-temperature catalytic oxidation and DOM composition by fluorescence spectroscopy and parallel factor analysis. In the effluent of the ten screened aquacultures and in the repeated sampling of one aquaculture, we consistently found an increase of DOC concentrations and a dominance of protein-like fluorescence. The protein-like fluorescence rapidly disappeared downstream of the aquacultures, and in the degradation experiment. 21% of the DOC export from the repeatedly sampled aquaculture resulted from food addition and 76% from fish production. We conclude that large amounts of degradable DOM are exported from land-based aquacultures. This probably has strong effects on the ecological structure and function of North Patagonian streams, and similarly affected streams worldwide.

  10. Climate control on ancestral population dynamics: insight from Patagonian fish phylogeography.

    Science.gov (United States)

    Ruzzante, Daniel E; Walde, Sandra J; Gosse, John C; Cussac, Victor E; Habit, Evelyn; Zemlak, Tyler S; Adams, Emily D M

    2008-05-01

    Changes in lake and stream habitats during the growth and retreat of Pleistocene glaciers repeatedly altered the spatial distributions and population sizes of the aquatic fauna of the southern Andes. Here, we use variation in mtDNA control region sequences to infer the temporal dynamics of two species of southern Andean fish during the past few million years. At least five important climate events were associated with major demographic changes: (i) the widespread glaciations of the mid-Pliocene (c. 3.5 Ma); (ii) the largest Patagonian glaciation (1.1 Ma); (iii) the coldest Pleistocene glaciation as indicated by stacked marine delta(18)O (c. 0.7 Ma); (iv) the last southern Patagonian glaciation to reach the Atlantic coast (180 ka); and (v) the last glacial maximum (LGM, 23-25,000 years ago). The colder-water inhabitant, Galaxias platei, underwent a strong bottleneck during the LGM and its haplotype diversity coalesces c. 0.7 Ma. In contrast, the more warm-adapted and widely distributed Percichthys trucha showed continuous growth through the last two glacial cycles but went through an important bottleneck c. 180,000 years ago, at which time populations east of the Andes may have been eliminated. Haplotype diversity of the most divergent P. trucha populations, found west of the Andes, coalesces c. 3.2 Ma. The demographic timelines obtained for the two species thus illustrate the continent-wide response of aquatic life in Patagonia to climate change during the Pleistocene, but also show how differing ecological traits and distributions led to distinctive responses. PMID:18363661

  11. Freezing resistance in Patagonian woody shrubs: the role of cell wall elasticity and stem vessel size.

    Science.gov (United States)

    Zhang, Yong-Jiang; Bucci, Sandra J; Arias, Nadia S; Scholz, Fabian G; Hao, Guang-You; Cao, Kun-Fang; Goldstein, Guillermo

    2016-08-01

    Freezing resistance through avoidance or tolerance of extracellular ice nucleation is important for plant survival in habitats with frequent subzero temperatures. However, the role of cell walls in leaf freezing resistance and the coordination between leaf and stem physiological processes under subzero temperatures are not well understood. We studied leaf and stem responses to freezing temperatures, leaf and stem supercooling, leaf bulk elastic modulus and stem xylem vessel size of six Patagonian shrub species from two sites (plateau and low elevation sites) with different elevation and minimum temperatures. Ice seeding was initiated in the stem and quickly spread to leaves, but two species from the plateau site had barriers against rapid spread of ice. Shrubs with xylem vessels smaller in diameter had greater stem supercooling capacity, i.e., ice nucleated at lower subzero temperatures. Only one species with the lowest ice nucleation temperature among all species studied exhibited freezing avoidance by substantial supercooling, while the rest were able to tolerate extracellular freezing from -11.3 to -20 °C. Leaves of species with more rigid cell walls (higher bulk elastic modulus) could survive freezing to lower subzero temperatures, suggesting that rigid cell walls potentially reduce the degree of physical injury to cell membranes during the extracellular freezing and/or thaw processes. In conclusion, our results reveal the temporal-spatial ice spreading pattern (from stem to leaves) in Patagonian shrubs, and indicate the role of xylem vessel size in determining supercooling capacity and the role of cell wall elasticity in determining leaf tolerance of extracellular ice formation. PMID:27217529

  12. NEW GEOLOGICAL AND GEOPHYSICAL CONTRIBUTIONS IN THE SECTION IBAGUÉ – ARMENIA, CENTRAL CORDILLERA - COLOMBIA

    Directory of Open Access Journals (Sweden)

    Vargas Carlos A.

    2005-08-01

    Full Text Available Ha sido interpretada la sección geológica entre las ciudades de Ibagué y Armenia basada en observaciones geofísicas y estructurales en busca de establecer el estilo estructural dominante y la configuración del basamento en profundidad. Inicialmente se realizaron mediciones gravimétricas y magnetométricas levantadas cada 500 m entre estas ciudades, las cuales permitieron soportar el desarrollo del experimento sísmico "Armenia-Quake". El alcance del experimento sísmico permitió detectar reflectores hasta aproximadamente 17 km de profundidad en un área de influencia de aproximadamente 25 km. La interpretación integral de la información geológica y geofísica permite concluir que el Complejo Cajamarca define una estructura sinclinal amplia cerca al Municipio de Cajamarca. Partiendo de dicha información se pudo reconocer la presencia de un basamento compuesto por cuñas de rocas basálticas y sedimentarias asociadas a las formaciones Quebradagrande y Arquía. Igualmente se reconoce la existencia de una gran flexión de la paleo-placa oceánica relacionada a la formación Barroso, la cual se encuentra limitada al occidente por la falla Cauca-Almaguer. La estructura en flexión y la evolución compresiva del estado de esfuerzos en esta región de América del Sur podrían ser las responsables del depósito y posterior plegamiento de la formación Cinta de Piedra que constituye en gran medida la Serranía de Santa Bárbara.

  13. [Biomass recovery through secondary succession in the Cordillera Central de los Andes, Colombia].

    Science.gov (United States)

    del Valle, Jorge Ignacio; Restrepo, Héctor Iván; Londoño, Mónica María

    2011-09-01

    Estimations on biomass recovery rates by secondary tropical forests are needed to understand the complex tropical succession, and their importance on CO2 capture, to offset the warming of the planet. We conducted the study in the Porce River Canyon between 550 and 1 700m.a.s.l. covering tropical and premontane moist belts. We established 33 temporary plots of 50m x 20m in secondary forests, including fallows to succesional forests, and ranging between 3 and 36 years old; we measured the diameter at breast height (D) of all woody plants with D > or = 5cm. In each one of these plots we established five 10m x 10m subplots, in which we measured the diameter betweem 1cm woody plants. We estimated the biomass of pastures by harvesting 54 plots of 2m x 2m, and of shrubs in the fallows by harvesting the biomass in 18 plots of 5m x 2m. We modeled Bav (above ground live biomass of woody plants) and Brg (coarse root biomass) as a function of succesional age (t) with the growth model of von Bertalanffy, using 247t/ha and 66t/ha as asymptote, respectively. Besides, we modeled the ratios brg/bav = f(D) and Brg/Bav = f(t). The model estimated that 87 years are required to recover the existing Bav of primary forests through secondary succession, and 217 years for the Brg of the primary forest. The maximum instantaneous growth rate of the Bav was 6.95 t/ha/yr at age 10. The maximum average growth rate of the Bav was 6.26 t/ha/yr at age 17. The weighted average of the absolute growth rate of the Bav reached 4.57t/ha/yr and the relative growth rate 10% annually. The ratio brg/bav decreases with increasing D. The ratio Brg/Bav initially increases very rapidly until age 5 (25%), then decreases to reach 25 years (18%) and increases afterwards until the ratio reaches the asymptote (26.7%). PMID:22017137

  14. Regional Analysis of the Hazard Level of Glacial Lakes in the Cordillera Blanca, Peru

    Science.gov (United States)

    Chisolm, Rachel E.; Jhon Sanchez Leon, Walter; McKinney, Daene C.; Cochachin Rapre, Alejo

    2016-04-01

    The Cordillera Blanca mountain range is the highest in Peru and contains many of the world's tropical glaciers. This region is severely impacted by climate change causing accelerated glacier retreat. Secondary impacts of climate change on glacier retreat include stress on water resources and the risk of glacial lake outburst floods (GLOFs) from the many lakes that are forming and growing at the base of glaciers. A number of GLOFs originating from lakes in the Cordillera Blanca have occurred over the last century, several of which have had catastrophic impacts on cities and communities downstream. Glaciologists and engineers in Peru have been studying the lakes of the Cordillera Blanca for many years and have identified several lakes that are considered dangerous. However, a systematic analysis of all the lakes in the Cordillera Blanca has never before been attempted. Some methodologies for this type of systematic analysis have been proposed (eg. Emmer and Vilimek 2014; Wang, et al. 2011), but as yet they have only been applied to a few select lakes in the Cordillera Blanca. This study uses remotely sensed data to study all of the lakes of the Glacial Lake Inventory published by the Glaciology and Water Resources Unit of Peru's National Water Authority (UGRH 2011). The objective of this study is to assign a level of potential hazard to each glacial lake in the Cordillera Blanca and to ascertain if any of the lakes beyond those that have already been studied might pose a danger to nearby populations. A number of parameters of analysis, both quantitative and qualitative, have been selected to assess the hazard level of each glacial lake in the Cordillera Blanca using digital elevation models, satellite imagery, and glacier outlines. These parameters are then combined to come up with a preliminary assessment of the hazard level of each lake; the equation weighting each parameter draws on previously published methodologies but is tailored to the regional characteristics

  15. Sedimentary cyclicity in early Pleistocene, evaporitic, playa-lake lacustrine deposits in the Guadix-Baza basin (Betic Cordillera, Spain)

    International Nuclear Information System (INIS)

    The Guadix-Baza basin (Betic Cordillera, southern Spain) contains in its eastern sector an early Pleistocene (Gelasian and lowermost Calabrian) sedimentary unit that was deposited in a shallow lacustrine environment. Given that the chronological limits of this unit lie between 2.5 and 1.6 Ma BP, the thickness of its preserved sediments (400 m) and high sedimentation rate (44.4 cm/ka) are remarkable. Numerous sedimentary cycles marked by an alternation of marls and sands are commonly found in the marginal sectors and marls and gypsum in the central sector, which would owe their origins to permanent flooding and evaporation/ re-flooding phases due to global climatic changes. Spectral analyses carried out using Fourier transform have revealed the existence of temporary frequencies associated with sedimentary cycles of between 0.2 and 5.2 ka. The origin of these cycles may be associated with variations in solar radiation and oscillations in the Moons orbital position, which would induce global climatic changes resulting in the rise and fall of the water table of the lake. Autocorrelation analyses conducted separately on the marly and evaporitic levels support this conclusion, as they indicate the existence of significant direct correlations between about 4 to 12 sedimentary cycles, which would correspond to repetitions of the stratigraphic series over a time span of 1.3 to 4 ka. (Author)

  16. Heat-shock response and antioxidant defense during air exposure in Patagonian shallow-water limpets from different climatic habitats

    OpenAIRE

    Pöhlmann, Kevin; Koenigstein, Stefan; Alter, Katharina; Abele, Doris; Held, Christoph

    2011-01-01

    Climate warming involves not only a rise of air temperature means, but also more frequent heat waves in many regions on earth, and is predicted to intensify physiological stress especially in extremely changeable habitats like the intertidal. We investigated the heat-shock response (HSR) and enzymatic antioxidant defense levels of Patagonian shallow-water limpets, adapted to distinct tidal exposure conditions in the sub- and intertidal. Limpets were sampled in the temperate Northern Patagonia...

  17. Understanding the transport of Patagonian dust and its influence on marine biological activity in the South Atlantic Ocean

    OpenAIRE

    Johnson, M. S.; Meskhidze, N.; Kiliyanpilakkil, V. P.; Gassó, S.

    2010-01-01

    The supply of bioavailable iron to the high-nitrate low-chlorophyll (HNLC) waters of the Southern Ocean through atmospheric pathways could stimulate phytoplankton blooms and have major implications for the global carbon cycle. In this study, model results and remotely-sensed data are analyzed to examine the horizontal and vertical transport pathways of Patagonian dust and quantify the effect of iron-laden mineral dust deposition on marine biological productivity in the surface waters o...

  18. Understanding the transport of Patagonian dust and its influence on marine biological activity in the South Atlantic Ocean

    OpenAIRE

    Johnson, M. S.; Meskhidze, N.; Kiliyanpilakkil, V. P.; Gassó, S.

    2011-01-01

    The supply of bioavailable iron to the high-nitrate low-chlorophyll (HNLC) waters of the Southern Ocean through atmospheric pathways could stimulate phytoplankton blooms and have major implications for the global carbon cycle. In this study, model results and remotely-sensed data are analyzed to examine the horizontal and vertical transport pathways of Patagonian dust and quantify the effect of iron-laden mineral dust deposition on marine biological productivity in the surface waters of the S...

  19. Taxonomic review of the species of Helina R.-D. (Diptera: Muscidae) from Andean-Patagonian forests.

    Science.gov (United States)

    Patitucci, Luciano Damián; Mulieri, Pablo Ricardo; Mariluis, Juan Carlos

    2016-01-01

    Helina Robineau-Desvoidy, 1830 is the second genus of Muscidae in terms of richness. This genus includes several species collected at high altitudes and high latitudes, and is poorly studied in the Neotropical region. Only 12 species of Helina have been recorded in the southern limit of South America in the Andean-Patagonian forests. In the present work, we studied all the species known from the Andean-Patagonian forests, with the exception of H. viola Malloch, 1934, present three new species, H. araucana sp. nov., H. dorada sp. nov., and H. ouina sp. nov., and provide the first description of the females of H. australis Carvalho & Pont, 1993 and H. rufoapicata Malloch, 1934. We also propose four new synonymies: H. nigrimana basilaris (Carvalho & Pont, 1993) and H. nigrimana grisea (Malloch, 1934) as new junior synonyms of H. nigrimana (Macquart, 1851); and H. fulvocalyptrata Malloch, 1934 and H. simplex Malloch, 1934 as new junior synonyms of H. chilensis Malloch, 1934. Finally, we provide a generic diagnosis and a new key for the Helina species of the Andean-Patagonian forests, as well as notes on the biology and distribution maps of each specimen, and discuss a preliminary contruction of groups of species. PMID:27515658

  20. Understanding the Transport of Patagonian Dust and Its Influence on Marine Biological Activity in the South Atlantic Ocean

    Science.gov (United States)

    Johnson, Matthew; Meskhidze, Nicholas; Kiliyanpilakkil, Praju; Gasso, Santiago

    2010-01-01

    Modeling and remote sensing techniques were applied to examine the horizontal and vertical transport pathways of Patagonian dust and quantify the effect of soluble-iron- laden mineral dust deposition on marine primary productivity in the South Atlantic Ocean (SAO) surface waters. The global chemistry transport model GEOS-Chem, implemented with an iron dissolution scheme, was applied to evaluate the atmospheric transport and deposition of mineral dust and bioavailable iron during two dust outbreaks originating in the source regions of Patagonia. In addition to this "rapidly released" iron, offline calculations were also carried out to estimate the amount of bioavailable iron leached during the residence time of dust in the ocean mixed layer. Model simulations showed that the horizontal and vertical transport pathways of Patagonian dust plumes were largely influenced by the synoptic meteorological patterns of high and low pressure systems. Model-predicted horizontal and vertical transport pathways of Patagonian dust over the SAO were in reasonable agreement with remotely-sensed data. Comparison between remotely-sensed and offline calculated ocean surface chlorophyll-a concentrations indicated that, for the two dust outbreaks examined in this study, the deposition of bioavailable iron in the SAO through atmospheric pathways was insignificant. As the two dust transport episodes examined here represent typical outflows of mineral dust from South American sources, our study suggests that the atmospheric deposition of mineral dust is unlikely to induce large scale marine primary productivity and carbon sequestration in the South Atlantic sector of the Southern Ocean.

  1. Resolving the tectonic transition between ancestral North America and the northern Cordillera

    Science.gov (United States)

    Schaeffer, A. J.; Audet, P.; Lebedev, S.

    2015-12-01

    The northern Cordillera, situated in the Canadian northwest, is one of the most actively deforming regions in Canada and host to the highest earthquake activity in the country. Furthermore, it presents a largely contiguous snapshot through almost 4 Gyr of Earth's history across a zone Mackenzie Mountains Experiment, new studies will leverage these datasets enabling more detailed imaging of the structure and seismicity across the region. Here we present a new high-resolution, vertically polarized shear speed and azimuthal model of northwestern Canada and Alaska, constrained by vertical component seismogram fits computed using the Automated Multimode Inversion of Surface, S, and multiple-S waveforms. With this new model, we aim to address key questions relating to the dynamics of the northern Cordillera, including how far west the craton edge extends at depth, in addition to the crustal thickness, velocity structure, and pattern of crustal fabrics around major faults throughout the region.

  2. Identificación, caracterización y dinámica de las geoformas glaciales y periglaciales en la Cordillera de los Andes a través de sensores remotos

    OpenAIRE

    Falaschi, Daniel

    2015-01-01

    El presente trabajo de Tesis Doctoral tuvo el objetivo de estudiar los glaciares y glaciares de escombros en tres regiones montañosas a lo largo de la Cordillera de los Andes Argentina: Monte San Lorenzo (Provincia de Santa Cruz), Volcán Domuyo (Provincia de Neuquén), y Nevados de Cachi (Provincia de Salta). Cada uno de estos sitios presenta características climáticas propias, representativas de tres porciones particulares de los Andes: Andes Patagónicos Meridionales, Andes Centrales Meridion...

  3. Lichenometry in the Cordillera Blanca, Peru : "Little Ice Age" moraine chronology

    OpenAIRE

    O. Solomina; Jomelli, Vincent; Kaser, G.; Ames, A; Berger, B; Pouyaud, Bernard (dir.)

    2007-01-01

    This paper is a comparison and compilation of lichenometric and geomorphic studies performed by two independent teams in the Cordillera Blanca, Peru, in 1996 and 2002 on 66 "Little Ice Age" moraines of 14 glaciers. Using eleven new control points, we recalibrated the initial rapid growth phase of the previously established Rhizocarpon subgenus Rhizocarpon growth curve. This curve was then used to estimate the age of "Little Ice Age" moraines. The time of deposition of the most prominent and n...

  4. Cretaceous Exhumation of the North American Cordillera Measured through Mineral Multi-Dating: Insights into Basin Filling Models and Orogenic Architecture

    Science.gov (United States)

    Painter, C. S.; Carrapa, B.; DeCelles, P. G.; Gehrels, G. E.; Thomson, S. N.

    2015-12-01

    exhumation rates is observed in South America in the central Andean arc, Puna-Altiplano, and eastern Cordillera zones.

  5. The 2008 Emiliania huxleyi bloom along the Patagonian Shelf: Ecology, biogeochemistry, and cellular calcification

    Science.gov (United States)

    Poulton, Alex J.; Painter, Stuart C.; Young, Jeremy R.; Bates, Nicholas R.; Bowler, Bruce; Drapeau, Dave; Lyczsckowski, Emily; Balch, William M.

    2013-12-01

    blooms are significant contributors to the global production and export of calcium carbonate (calcite). The Patagonian Shelf is a site of intense annual coccolithophore blooms during austral summer. During December 2008, we made intensive measurements of the ecology, biogeochemistry, and physiology of a coccolithophore bloom. High numbers of Emiliania huxleyi cells and detached coccoliths (>1 × 103 mL-1 and >10 × 103 mL-1, respectively), high particulate inorganic carbon concentrations (>10 mmol C m-2), and high calcite production (up to 7.3 mmol C m-2 d-1) all characterized bloom waters. The bloom was dominated by the low-calcite-containing B/C morphotype of Emiliania huxleyi, although a small (30%, similar to estimates for E. huxleyi and indicative of a significant role for this diatom in bloom biogeochemistry. Cell-normalized calcification rates, when corrected for a high number of nonactive cells, were relatively high and when normalized to estimates of coccolith calcite indicate excessive coccolith production in the declining phase of the bloom. We find that low measures of calcite and calcite production relative to other blooms in the global ocean indicate that the dominance of the B/C morphotype may lead to overall lower calcite production. Globally, this suggests that morphotype composition influences regional bloom inventories of carbonate production and export and that climate-induced changes in morphotype biogeography could affect the carbon cycle.

  6. Charles Darwin and the firstscientific observations on the patagonian shingle formation (Rodados Patagónicos

    Directory of Open Access Journals (Sweden)

    Oscar A. Martínez

    2009-04-01

    Full Text Available TheRodados Patagónicos is one of the most intriguing lithostratigraphic unitsin the Late Cenozoic of Patagonia. Charles Darwin named these gravels as the "PatagonianShingle Formation", when he discovered them during his trip toPatagonia on board HMS Beagle in 1832. According to the prevailing paradigm ofthe time, he assigned these deposits to a giant transgression during the GreatUniversal Déluge epoch, considering that their formation was related to waveaction along the beach in ancient times. The name of Rodados Patagónicos,as they are generally known in the Argentine geological literature, is usuallyconfusing since it has been applied to a wide number of geological units ofmultiple origin and age. Many authors have discussed the nature and origin ofthese gravels, considering them to have been formed by piedmont, alluvial,colluvial, glaciofluvial, and/or marine processes. Today, it is accepted thatthe term Rodados Patagónicos includes gravel deposits of varied nature and age,perhaps with a prevalence of piedmont genesis in northern Patagonia andglaciofluvial dynamics in southern Patagonia and Tierra del Fuego.

  7. Ecological Status of a Patagonian Mountain River: Usefulness of Environmental and Biotic Metrics for Rehabilitation Assessment.

    Science.gov (United States)

    Laura, Miserendino M; Adriana, M Kutschker; Cecilia, Brand; La Ludmila, Manna; Cecilia, Prinzio Y Di; Gabriela, Papazian; José, Bava

    2016-06-01

    This work evaluates the consequences of anthropogenic pressures at different sections of a Patagonian mountain river using a set of environmental and biological measures. A map of risk of soil erosion at a basin scale was also produced. The study was conducted at 12 sites along the Percy River system, where physicochemical parameters, riparian ecosystem quality, habitat condition, plants, and macroinvertebrates were investigated. While livestock and wood collection, the dominant activities at upper and mean basin sites resulted in an important loss of the forest cover still the riparian ecosystem remains in a relatively good status of conservation, as do the in-stream habitat conditions and physicochemical features. Besides, most indicators based on macroinvertebrates revealed that both upper and middle basin sections supported similar assemblages, richness, density, and most functional feeding group attributes. Instead, the lower urbanized basin showed increases in conductivity and nutrient values, poor quality in the riparian ecosystem, and habitat condition. According to the multivariate analysis, ammonia level, elevation, current velocity, and habitat conditions had explanatory power on benthos assemblages. Discharge, naturalness of the river channel, flood plain morphology, conservation status, and percent of urban areas were important moderators of plant composition. Finally, although the present land use in the basin would not produce a significant risk of soil erosion, unsustainable practices that promotes the substitution of the forest for shrubs would lead to severe consequences. Mitigation efforts should be directed to protect headwater forest, restore altered riparian ecosystem, and to control the incipient eutrophication process. PMID:26961305

  8. The impact of predation by marine mammals on patagonian toothfish longline fisheries.

    Directory of Open Access Journals (Sweden)

    Marta Söffker

    Full Text Available Predatory interaction of marine mammals with longline fisheries is observed globally, leading to partial or complete loss of the catch and in some parts of the world to considerable financial loss. Depredation can also create additional unrecorded fishing mortality of a stock and has the potential to introduce bias to stock assessments. Here we aim to characterise depredation in the Patagonian toothfish (Dissostichus eleginoides fishery around South Georgia focusing on the spatio-temporal component of these interactions. Antarctic fur seals (Arctocephalus gazella, sperm whales (Physeter macrocephalus, and orcas (Orcinus orca frequently feed on fish hooked on longlines around South Georgia. A third of longlines encounter sperm whales, but loss of catch due to sperm whales is insignificant when compared to that due to orcas, which interact with only 5% of longlines but can take more than half of the catch in some cases. Orca depredation around South Georgia is spatially limited and focused in areas of putative migration routes, and the impact is compounded as a result of the fishery also concentrating in those areas at those times. Understanding the seasonal behaviour of orcas and the spatial and temporal distribution of "depredation hot spots" can reduce marine mammal interactions, will improve assessment and management of the stock and contribute to increased operational efficiency of the fishery. Such information is valuable in the effort to resolve the human-mammal conflict for resources.

  9. Effects of future sea-level rise on tidal processes on the Patagonian Shelf

    Science.gov (United States)

    Carless, Stacey J.; Green, J. A. Mattias; Pelling, Holly E.; Wilmes, Sophie-Berenice

    2016-11-01

    The response of tidally driven processes on the Patagonian Shelf to sea-level rise (SLR) is revisited using large but realistic levels of change in a numerical tidal model. The results relate to previous studies through significant differences in the impact, depending on how SLR is implemented. This is true for how the boundary at the coastline is treated, i.e., if we allow for inundation of land or assume flood defences along the coast, but also for how the sea-level change itself is implemented. Simulations with uniform SLR provide a different, and slightly larger, response than do runs where SLR is based on observed trends. In all cases, the effect on the tidal amplitudes is patchy, with alternating increases and decreases in amplitude along the shelf. Furthermore, simulations with a realistic future change in vertical stratification, thus affecting tidal conversion rates, imply that there may be a small but significant decrease in the amplitudes along the coast. Associated processes, e.g., the location of mixing fronts and potential impacts on biogeochemical cycles on the shelf are also discussed.

  10. Preference for different inorganic nitrogen forms among plant functional types and species of the Patagonian steppe.

    Science.gov (United States)

    Gherardi, Laureano A; Sala, Osvaldo E; Yahdjian, Laura

    2013-11-01

    We have explored species-specific preferences for nitrate (NO3(-)) and ammonium (NH4(+)) as an alternative niche separation in ecosystems where nitrogen (N) is present mostly in inorganic forms. The Patagonian steppe is dominated by shrubs and grasses. Shrubs absorb water and nutrients from deep soil layers, which are poor in N, while grasses have the opposite pattern, absorbing most of their water and nutrients from the upper layers of the soil. We hypothesized that the preferences of shrub and grass for inorganic N forms are different and that the rate of potential N uptake is greater in shrubs than in grasses. To test this hypothesis, we grew individuals of six dominant species in solutions of different NH4(+):NO3(-) concentration ratios. Nitrate uptake was found to be higher in shrubs, while ammonium uptake was similar between plant functional types. The NH4(+):NO3(-) uptake ratio was significantly lower for shrubs than grasses. Shrubs, which under field conditions have deeper rooting systems than grasses, showed a higher N absorption capacity than grasses and a preference for the more mobile N form, nitrate. Grasses, which had lower N uptake rates than shrubs, preferred ammonium over nitrate. These complementary patterns between grasses and shrubs suggest a more thorough exploitation of resources by diverse ecosystems than those dominated by just one functional type. The loss of one plant functional group or a significant change in its abundance would therefore represent a reduction in resource use efficiency and ecosystem functioning. PMID:23812108

  11. Ecological Status of a Patagonian Mountain River: Usefulness of Environmental and Biotic Metrics for Rehabilitation Assessment

    Science.gov (United States)

    Laura, Miserendino M.; Adriana, M. Kutschker; Cecilia, Brand; La Ludmila, Manna; Cecilia, Prinzio Y. Di; Gabriela, Papazian; José, Bava

    2016-06-01

    This work evaluates the consequences of anthropogenic pressures at different sections of a Patagonian mountain river using a set of environmental and biological measures. A map of risk of soil erosion at a basin scale was also produced. The study was conducted at 12 sites along the Percy River system, where physicochemical parameters, riparian ecosystem quality, habitat condition, plants, and macroinvertebrates were investigated. While livestock and wood collection, the dominant activities at upper and mean basin sites resulted in an important loss of the forest cover still the riparian ecosystem remains in a relatively good status of conservation, as do the in-stream habitat conditions and physicochemical features. Besides, most indicators based on macroinvertebrates revealed that both upper and middle basin sections supported similar assemblages, richness, density, and most functional feeding group attributes. Instead, the lower urbanized basin showed increases in conductivity and nutrient values, poor quality in the riparian ecosystem, and habitat condition. According to the multivariate analysis, ammonia level, elevation, current velocity, and habitat conditions had explanatory power on benthos assemblages. Discharge, naturalness of the river channel, flood plain morphology, conservation status, and percent of urban areas were important moderators of plant composition. Finally, although the present land use in the basin would not produce a significant risk of soil erosion, unsustainable practices that promotes the substitution of the forest for shrubs would lead to severe consequences. Mitigation efforts should be directed to protect headwater forest, restore altered riparian ecosystem, and to control the incipient eutrophication process.

  12. A tectonically controlled basin-fill within the Valle del Cauca, West-Central Colombia

    Energy Technology Data Exchange (ETDEWEB)

    Rine, J.M.; Keith, J.F. Jr.; Alfonso, C.A.; Ballesteros, I.; Laverde, F.; Sacks, P.E.; Secor, D.T. Jr. (Univ. of South Carolina, Columbia (United States)); Perez, V.E.; Bernal, I.; Cordoba, F.; Numpaque, L.E. (Ecopetrol, Bogota (Colombia))

    1993-02-01

    Tertiary strata of the Valle del Cauca reflect a forearc/foreland basin tectonic history spanning a period from pre-uplift of the Cordillera Central to initiation of uplift of the Cordillera Occidental. Stratigraphy of the Valle del Cauca begins with Jurassic-Cretaceous rocks of exotic and/or volcanic provenance and of oceanic origin. Unconformably overlying these are Eocene to Oligocene basal quartz-rich sandstones, shallow marine algal limestones, and fine-grained fluvial/deltaic mudstones and sandstones with coalbeds. These Eocene to Oligocene deposits represent a period of low tectonic activity. During late Oligocene to early Miocene, increased tectonic activity produced conglomeratic sediments which were transported from east to west, apparently derived from uplift of the Cordillera Central, and deposited within a fluvial to deltaic setting. East-west shortening of the Valle del Cauca basin folded the Eocene to early Miocene units, and additional uplift of the Cordillera Central during the later Miocene resulted in syn-tectonic deposition of alluvial fans. After additional fold and thrust deformation of the total Eocene-Miocene basin-fill, tectonic activity abated and Pliocene-Quaternary alluvial and lacustrine strata were deposited. Within the framework of this depositional and tectonic history of the Valle del Cauca, hydrocarbon exploration strategies can be formulated and evaluated.

  13. Los deslizamientos de la cordillera neuquina al sur delos 38° S: suinducción

    OpenAIRE

    Emilio F González Díaz; Andrés Folguera

    2009-01-01

    Las conclusiones sobre losdeslizamientos individualizados en la cordillera neuquina (36°-38°S), (suinducción sísmica; rechazo de la consideración de sus depósitos como till),indujo a proyectar su estudio al sur de los 38°S. Se distinguieron inéditaszonas de deslizamientos, cuya promoción y contexto sismotectónico difieren delos reconocidos entre los 36°-38°S. Su estudio regional, que abarcó trescomarcas (Aluminé, Chapelco y Arroyo Limay Chico), comprobó el predominio delas corrientes de tierr...

  14. Towards an annually-resolved record of Lateglacial Patagonian ice sheet dynamics using glaciolacustrine varves

    Science.gov (United States)

    Bendle, Jacob; Palmer, Adrain; Thorndycraft, Varyl

    2016-04-01

    Proglacial sedimentary archives, in particular, glaciolacustrine varve sequences, offer the potential for detailed reconstructions of past ice sheet dynamics. Specifically, glaciolacustrine varves (i) allow reconstructions of sediment (and thus meltwater) influx at annual and even sub-annual resolution; and (ii) provide a continuous, annually-resolved chronology to estimate rates of change and/or the duration of significant events in the deglaciation of a basin. In South America, glacial geologists have relied heavily on cosmogenic nuclide exposure dating to construct chronologies for palaeoglaciological activity. Whilst effective, the typical uncertainties associated with boulder dating methods (±10%) preclude the investigation of short-term (e.g. ≤ centennial-scale) glacier and/or climatic change(s), which are shown to be important at modern ice-margins. Moreover, moraine chronologies are fragmentary, and inherently biased towards episodes of positive glacier mass balance (i.e. moraine construction), and thus limit our understanding of ice sheet retreat dynamics. By contrast, long, continuous, high-resolution (i.e. varve) palaeolimnological records have the potential to significantly refine models of ice sheet deglaciation. In this talk, we present data from Valle Fenix Chico, in the Lago Buenos Aires (LBA) basin (-46.57°S -71.07°W), in which ice-contact Glacial Lake Buenos Aires formed as the LBA ice lobe of Patagonian ice sheet withdrew from its innermost LGM moraine (~17.2 ± 0.9 ka). Thick (>40m) sequences of laminated glaciolacustrine sediment were deposited in the palaeolake, and are now exposed in a sub-aerial canyon that was cut when the lake drained. We report on the detailed macro- and micro-facies of the LBA sediments. In particular, we: (1) develop a process model for the formation of silt and clay couplets, which suggests an annual (varve) origin; (2) present varve series for the initial phase (~1kyr) of LBA ice lobe deglaciation.

  15. A Paleomagnetic Test of the Patagonian Orocline, Thirty Years Later: New Data, New Insights, New Problems.

    Science.gov (United States)

    Rapalini, A.; Herve, F.; Calderon, M.; Singer, S.; Lippai, H.; Tassone, A.; Cordani, U.

    2005-05-01

    The Andean Chain undergoes a 90 degrees bend at around 52 S, from N-S to the north to E-W to the south. This feature is called the Patagonian orocline and its origin and evolution have been much debated. Since the first paleomagnetic test performed by Dalziel et al. in the early seventies that suggested a secondary bend, several paleomagnetic studies have been carried out in the region. However, density of studies is still very low compared to other oroclines. Despite numerous uncertainties, including in cases experimental reliability, ages of magnetization and paleohorizontal control, some preliminary conclusions can be drawn from the available distribution of paleomagnetic declinations along the curved orogen. A systematic pattern of ccw rotation is apparent along the orogen that in a broad sense is consistent with a secondary origin for the bend. Largest values of rotation, 90 or more degrees, on the ocean side of the inverted Rocas Verdes marginal basin, suggest that its closure was probably an important event in the development of the orocline. To the foreland, rotations are smaller, with ca. 30 degrees in the Fueguian Andes (south of 52 S), which suggest either magnetization ages younger than most of the oroclinal bending or a complex development with local patterns of rotations. To the north, anomalous ccw rotations of ca. 50 degrees have been observed along the front of the Magallanes thrust and fold belt and an identical declination anomaly has been found along the whole Sarmiento ophiolite, although in the latter case an alternative explanation to crustal block rotation around a vertical axis is possible.

  16. The Patagonian Orocline: New paleomagnetic data from the Andean magmatic arc in Tierra del Fuego, Chile

    Science.gov (United States)

    Cunningham, W. Dickson; Klepeis, Keith A.; Gose, Wulf A.; Dalziel, Ian W. D.

    1991-09-01

    The Hardy Formation is a 1300-m-thick succession of Upper Jurassic-Lower Cretaceous volcaniclastic sedimentary rocks interbedded with lava flows on Hoste Island at the southernmost tip of South America (55.5°S, 291.8°E). The strata are gently folded and metamorphosed to the prehnite-pumpellyite grade. A well-defined characteristic direction of magnetization, carried by magnetite, was readily identified in 95 samples from seven sites. At a given site, the directions group slightly better without structural correction. However, the means of the seven sites cluster better without tilt correction at the 99% significance level, implying that the magnetization postdates the folding event. It is most likely that the magnetization was acquired during the mid- to Late Cretaceous Andean orogeny that involved the folding and emplacement of the Patagonian Batholith. The fact that all samples are normally magnetized supports this age assignment. The pole position of 42.9°N, 156.6°E, α95=3.3° implies that the sampling area has rotated counterclockwise relative to cratonic South America by 90.1±11.9° with no significant flattening of inclination (F=1.9 ± 3.7°). Geologic considerations indicate that the rotation involved the entire Andean magmatic arc in Tierra Del Fuego. The results support interpretation of the Hardy Formation as part of the Andean magmatic arc deposited on the Pacific side of the Late Jurassic-Early Cretaceous Rocas Verdes marginal basin. Oroclinal bending of the arc in southernmost South America accompanied inversion of the marginal basin and the development of a Late Cretaceous-Cenozoic left-lateral transform system (South America-Antarctica) that later developed into the North Scotia Ridge.

  17. Early and mid-Holocene age for the Tempanos moraines, Laguna San Rafael, Patagonian Chile

    Science.gov (United States)

    Harrison, Stephan; Glasser, Neil F.; Duller, Geoff A. T.; Jansson, Krister N.

    2012-01-01

    Data about the nature and timing of Holocene events from the Southern Hemisphere, especially in southern South America, are required to provide insight into the extent and nature of past climate change in a region where land-based records are restricted. Here we present the first use of single grain Optically Stimulated Luminescence (OSL) dating of a moraine sequence recording glacial advance along the western side of the Patagonian Icefields. Dates from the Tempanos moraines at Laguna San Rafael (LSR) show that the San Rafael Glacier (SRG) advanced to maximum Holocene positions during the period 9.3 to 9.7 ka and at 5.7 ka. Outwash lying beneath the moraine in its northern portion, dated to 7.7 ka, indicates that the glacier front was also advanced at this time. Since these advances span both the regional early Holocene warm-dry phase (11.5 ka to 7.8 ka) and the subsequent cooling and rise in precipitation in the mid-late Holocene (since 6.6 ka) we infer that the advances of the SRG are not simply climate-driven, but that the glacier has also probably responded strongly to non-climatic stimuli such as internal ice dynamics and the transition between calving and non-calving. Many westwards-flowing glaciers in Patagonia were probably calving during much of the Late Pleistocene and Holocene, so we conclude that establishing robust glacial chronologies where climatic and non-climatic factors cannot be distinguished is likely to remain a challenge.

  18. Spectral attenuation of solar radiation in Patagonian fjord and coastal waters and implications for algal photobiology

    Science.gov (United States)

    Huovinen, Pirjo; Gómez, Iván

    2011-03-01

    The spectral attenuation of solar irradiation was measured during summer in two types of coastal waters in southern Chile, a north Patagonian fjord (Seno Reloncaví) and open coast (Valdivia). In order to relate the light availability with the light requirements of upper subtidal seaweeds, the saturating irradiance for photosynthesis ( Ek) from P- I curves was measured. In addition the UV risk was assessed. Based on the z1% of PAR, the lower limit of the euphotic zone in the studied systems averaged 21 m ( Kd 0.24 m -1) in Seno Reloncaví and 18 m ( Kd 0.27 m -1) in the coast of Valdivia. Photosynthesis of the studied seaweeds was saturated at markedly lower irradiances than found in their natural depths at the time of the study. Solar radiation penetrating into these depths at both locations largely supports the light requirements for the photosynthesis of subtidal species: 50-160 μmol m -2 s -1 for seaweeds from Seno Reloncaví (7 m tidal range) and 20-115 μmol m -2 s -1 for Valdivia assemblages (2 m tidal range). Optimal light conditions to saturate photosynthesis ( Ek) were present at 10-16 m water depth. The attenuation of solar irradiation did not vary significantly between the fjord and coastal sites of this study. However, the underwater light climates to which seaweeds are exposed in these sites vary significantly because of the stronger influence of tidal range affecting the fjord system as compared with the open coastal site. The patterns of UV-B penetration in these water bodies suggest that seaweeds living in upper littoral zones such as the intertidal and shallow subtidal (<3 m) may be at risk.

  19. How much is too much? Assessment of prey consumption by Magellanic penguins in Patagonian colonies.

    Science.gov (United States)

    Sala, Juan E; Wilson, Rory P; Quintana, Flavio

    2012-01-01

    Penguins are major consumers in the southern oceans although quantification of this has been problematic. One suggestion proposes the use of points of inflection in diving profiles ('wiggles') for this, a method that has been validated for the estimation of prey consumption by Magellanic penguins (Spheniscus magellanicus) by Simeone and Wilson (2003). Following them, we used wiggles from 31 depth logger-equipped Magellanic penguins foraging from four Patagonian colonies; Punta Norte (PN), Bahía Bustamente (BB), Puerto Deseado (PD) and Puerto San Julián (PSJ), all located in Argentina between 42-49° S, to estimate the prey captured and calculate the catch per unit time (CPUT) for birds foraging during the early chick-rearing period. Numbers of prey caught and CPUT were significantly different between colonies. Birds from PD caught the highest number of prey per foraging trip, with CPUT values of 68±19 prey per hour underwater (almost two times greater than for the three remaining colonies). We modeled consumption from these data and calculate that the world Magellanic penguin population consumes about 2 million tons of prey per year. Possible errors in this calculation are discussed. Despite this, the analysis of wiggles seems a powerful and simple tool to begin to quantify prey consumption by Magellanic penguins, allowing comparison between different breeding sites. The total number of wiggles and/or CPUT do not reflect, by themselves, the availability of food for each colony, as the number of prey consumed by foraging trip is strongly associated with the energy content and wet mass of each colony-specific 'prey type'. Individuals consuming more profitable prey could be optimizing the time spent underwater, thereby optimizing the energy expenditure associated with the dives. PMID:23251554

  20. How much is too much? Assessment of prey consumption by Magellanic penguins in Patagonian colonies.

    Directory of Open Access Journals (Sweden)

    Juan E Sala

    Full Text Available Penguins are major consumers in the southern oceans although quantification of this has been problematic. One suggestion proposes the use of points of inflection in diving profiles ('wiggles' for this, a method that has been validated for the estimation of prey consumption by Magellanic penguins (Spheniscus magellanicus by Simeone and Wilson (2003. Following them, we used wiggles from 31 depth logger-equipped Magellanic penguins foraging from four Patagonian colonies; Punta Norte (PN, Bahía Bustamente (BB, Puerto Deseado (PD and Puerto San Julián (PSJ, all located in Argentina between 42-49° S, to estimate the prey captured and calculate the catch per unit time (CPUT for birds foraging during the early chick-rearing period. Numbers of prey caught and CPUT were significantly different between colonies. Birds from PD caught the highest number of prey per foraging trip, with CPUT values of 68±19 prey per hour underwater (almost two times greater than for the three remaining colonies. We modeled consumption from these data and calculate that the world Magellanic penguin population consumes about 2 million tons of prey per year. Possible errors in this calculation are discussed. Despite this, the analysis of wiggles seems a powerful and simple tool to begin to quantify prey consumption by Magellanic penguins, allowing comparison between different breeding sites. The total number of wiggles and/or CPUT do not reflect, by themselves, the availability of food for each colony, as the number of prey consumed by foraging trip is strongly associated with the energy content and wet mass of each colony-specific 'prey type'. Individuals consuming more profitable prey could be optimizing the time spent underwater, thereby optimizing the energy expenditure associated with the dives.

  1. Hydroacoustical evidence of the expansion of pelagic swarms of Munida gregaria (Decapoda, Munididae) in the Beagle Channel and the Argentine Patagonian Shelf, and its relationship with habitat features

    Science.gov (United States)

    Diez, Mariano J.; Cabreira, Ariel G.; Madirolas, Adrián; Lovrich, Gustavo A.

    2016-08-01

    Squat lobsters are highly diversified and widespread decapods, of which only three species form pelagic swarms. Here we infer the expansion of Munida gregaria populations in the Beagle Channel and the Argentine Patagonian Shelf by means of acoustic surveys of pelagic swarms. We also describe the habitat characteristics in which these swarms occur. Acoustic data was collected during three multidisciplinary scientific cruises on board of the R/V Puerto Deseado during 2009, 2012 and 2014. Despite differences in the environmental conditions between the two surveyed areas, between 2009 and 2014 pelagic swarms increased their occurrence and abundance both in the Beagle Channel and on the Argentine Patagonian Shelf. Towards the end of the studied period, pelagic swarms of M. gregaria occurred in new locations, supporting the notion of a population expansion. Within the Beagle Channel swarm expansions were more marked than on the Patagonian Shelf. We here postulate that M. gregaria expansions occur in association with productive areas of the Argentine continental shelf, such as frontal zones, favoured by the squat lobster phenotypic plasticity that permit to exploit resources in both the neritic and benthic environments. At a regional scale on the Patagonian Shelf, three main groups of pelagic swarms of M. gregaria were clearly associated to respective frontal zones. The information presented here is necessary to understand fluctuations in both distribution and abundance patterns of a key species on the Argentine continental shelf. These fluctuations could be direct or indirect indicators of changes in the ecosystem.

  2. Long-lasting concentrations of cefovecin after subcutaneous and intramuscular administration to Patagonian sea lions (Otaria flavescens).

    Science.gov (United States)

    García-Párraga, D; Gilabert, J A; García-Peña, F J; Álvaro, T; Ros-Rodríguez, J M; Valls, M; Encinas, T

    2016-02-01

    Cefovecin is a third-generation cephalosporin developed as an aqueous solution for use by the subcutaneous route in dogs and cats. This study evaluated the duration of cefovecin plasma concentrations after single intramuscular (IM) or subcutaneous (SC) injection at different doses in 10 Patagonian sea lions (Otaria flavescens). Blood samples were collected serially from the day of the injection up to 60-90 days post-injection. Plasma drug concentrations were determined by high performance liquid chromatography-UV detection and pharmacokinetic parameters were calculated by non-compartmental analysis. No reactions or side effects associated with the drug were observed in any of the studied animals. Both routes showed very similar pharmacokinetic behaviour. Elimination half-life (11.3-21.6 days, SC; 13.1-15.9 days, IM) and mean residence time (17.6-36.8 days SC; 16.5-25.4 days IM) were, in all cases and doses, considerably longer than those previously reported for any other species. Based on these findings, and preliminary data on specific pathogen sensitivity, cefovecin was found to be a very promising antimicrobial for Patagonian sea lions, in particular those that are difficult to access or that are under certain rehabilitation conditions.

  3. Metabolic and molecular characterization of bacterial community associated to Patagonian Chilean oligotrophic-lakes of quaternary glacial origin.

    Science.gov (United States)

    Leon, Carla; Campos, Víctor; Urrutia, Roberto; Mondaca, María-Angélica

    2012-04-01

    The Patagonian Lakes have particular environmental conditions with or without intermittent disturbances. The study of the microorganisms present in aquatic ecosystems has increased notably because they can be used as micro-scale bioindicators of, among others, anthropogenic pollution and climatic change. The aim of the work was to compare the composition of the bacterial communities associated with sediments of three Patagonian Lakes with different geomorphologic patterns and disturbances. The lake sediments were characterized by molecular techniques, physiology profiles and physico-chemical analyses. The metabolic and physiological profiles of the microbial community demonstrated that non-impacted Tranquilo Lake is statistically different to impacted Bertrand and Plomo Lakes. Similar results were detected by DGGE profiles. FISH results demonstrated that betaproteobacteria showed the highest count in the Tranquilo Lake while gammaproteobacteria showed the highest counts in the Bertrand and Plomo Lakes, indicating that their sediments are highly dystrophic. The results demonstrate differences in the metabolic activity and structural and functional composition of bacterial communities of the studied lakes, which have different geomorphological patterns due to disturbances such as volcanic activity and the climatic change.

  4. Overland flow from plant patches: Coupled effects of preferential infiltration, surface roughness and depression storage at the semiarid Patagonian Monte

    Science.gov (United States)

    Rossi, María J.; Ares, Jorge O.

    2016-02-01

    The objective of this study is to characterize and quantify the overland flow generated from the plant patch areas of spotted vegetation toward the immediate surrounding bare ground including the coupled effects of preferential infiltration, surface roughness and depression storage. To this aim a series of overland flow plot experiments were designed in areas of the Patagonian Monte where evidence of patch-to-soil overland flow was observed. The experiments produced data on the plot micro-topography and physical properties of the soil, root density and the frictional parameters of the overland flow as well as the extent of the areas of water depression storage. The obtained data were used to calibrate a spatial-explicit (CREST) hydrological model of the flows and pathways generated by stemflow and throughfall during characteristic storms in the area. Good agreement between the model estimates and the measured data was found. This work provides physically-based metrics of runoff redistribution from the plant patch areas toward the immediate surrounding bare soil areas, including the effect of plant roots and depression storage as influenced by various shapes of the plant patch slopes. It is concluded that water transport can result from stemflow and throughfall at the patch areas during typical rainfall events at the semiarid Patagonian Monte. Implications of this phenomenon in the surface distribution of water, nutrients and seeds may feasibly follow.

  5. Subduction system and flat slab beneath the Eastern Cordillera of Colombia

    Science.gov (United States)

    Chiarabba, Claudio; De Gori, Pasquale; Faccenna, Claudio; Speranza, Fabio; Seccia, Danilo; Dionicio, Viviana; Prieto, Germán. A.

    2016-01-01

    Seismicity at the northern terminus of the Nazca subduction is diffused over a wide area containing the puzzling seismic feature known as the Bucaramanga nest. We relocate about 5000 earthquakes recorded by the Colombian national seismic network and produce the first 3-D velocity model of the area to define the geometry of the lithosphere subducting below the Colombian Andes. We found lateral velocity heterogeneities and an abrupt offset of the Wadati-Benioff zone at 5°N indicating that the Nazca plate is segmented by an E-W slab tear, that separates a steeper Nazca segment to the south from a flat subduction to the north. The flat Nazca slab extends eastward for about 400 km, before dip increases to ˜50° beneath the Eastern Cordillera, where it yields the Bucaramanga nest. We explain this puzzling locus of intermediate-depth seismicity located beneath the Eastern Cordillera of Colombia as due to a massive dehydration and eclogitization of a thickened oceanic crust. We relate the flat subducting geometry to the entrance at the trench at ca. 10 Ma of a thick - buoyant oceanic crust, likely a volcanic ridge, producing a high coupling with the overriding plate. Sub-horizontal plate subduction is consistent with the abrupt disappearance of volcanism in the Andes of South America at latitudes > 5°N.

  6. Isotopic evolution of the idaho batholith and Challis intrusive province, Northern US Cordillera

    Science.gov (United States)

    Gaschnig, R.M.; Vervoort, J.D.; Lewis, R.S.; Tikoff, B.

    2011-01-01

    The Idaho batholith and spatially overlapping Challis intrusive province in the North American Cordillera have a history of magmatism spanning some 55 Myr. New isotopic data from the ???98 Ma to 54 Ma Idaho batholith and ???51 Ma to 43 Ma Challis intrusions, coupled with recent geochronological work, provide insights into the evolution of magmatism in the Idaho segment of the Cordillera. Nd and Hf isotopes show clear shifts towards more evolved compositions through the batholith's history and Pb isotopes define distinct fields correlative with the different age and compositionally defined suites of the batholith, whereas the Sr isotopic compositions of the various suites largely overlap. The subsequent Challis magmatism shows the full range of isotopic compositions seen in the batholith. These data suggest that the early suites of metaluminous magmatism (98-87 Ma) represent crust-mantle hybrids. Subsequent voluminous Atlanta peraluminous suite magmatism (83-67 Ma) results primarily from melting of different crustal components. This can be attributed to crustal thickening, resulting from either subduction processes or an outboard terrane collision. A later, smaller crustal melting episode, in the northern Idaho batholith, resulted in the Bitterroot peraluminous suite (66-54 Ma) and tapped different crustal sources. Subsequent Challis magmatism was derived from both crust and mantle sources and corresponds to extensional collapse of the over-thickened crust. ?? The Author 2011. Published by Oxford University Press. All rights reserved.

  7. New isotopic ages and the timing of orogenic events in the Cordillera Darwin, southernmost Chilean Andes

    Science.gov (United States)

    Hervé, F.; Nelson, E.; Kawashita, K.; Suárez, M.

    1981-10-01

    The Cordillera Darwin, a structural culmination in the Andes of Tierra del Fuego, exposes an orogenic core zone that has undergone polyphase deformation and metamorphism. Some of the classic problems of orogenic zones have remained unanswered in the Cordillera Darwin: the age of deformed plutonic rocks, the distinction of structurally reactivated basement and metamorphosed cover rocks, and the timing of orogenic events. This study addresses and partially answers these questions. A well-constrained Rb-Sr isochron age of157±8m.y. and an initial 87Sr/ 86Sr ratio of 0.7087 obtained from a pre-tectonic granitic suite suggest a genetic relation between this suite and Upper Jurassic silicic volcanic rocks in the cover sequence (Tobifera Formation), and also suggest involvement of continental crust in formation of these magmas. A poorly constrained Rb-Sr isochron age of240±40m.y. obtained from supposed basement schists is consistent with field relations in the area which suggest a late Paleozoic/early Mesozoic metamorphism for these pre-Late Jurassic rocks. However, because of scatter in the data and the uncertainties involved in dating metasedimentary rocks, the significance of the isotopic age is dubious. Compilation of previously published ages in the area [9] with new mineral ages reported here indicate that "early Andean" orogenic events occurred between 100 and 84 m.y. ago, and that subduction-related magmatism has contributed, probably discontinuously, to the crustal evolution of the region throughout the Mesozoic.

  8. Estado actual del conocimiento del orden Odonata en la Patagonia Current knowledge of Patagonian Odonata

    Directory of Open Access Journals (Sweden)

    Javier Muzón

    2009-06-01

    Full Text Available El orden Odonata se encuentra representado en la Patagonia por 36 especies, reunidas en nueve familias y 18 géneros. El nivel de endemismo de esta taxocoenosis es alto, aproximadamente el 60% de las especies y casi el 40% de los géneros endémicos. La riqueza específica en la Patagonia decrece de Oeste a Este y de Norte a Sur, las áreas de mayor riqueza resultan ser las cordilleras de Nahuel Buta (Chile y de los Andes entre 38° y 41° S, y la meseta de Somuncurá (Argentina en la estepa. Se brinda una actualización del estado de conocimiento y un análisis de los principales patrones de distribución.The Odonata order is represented in Patagonia by 36 species belonging to nine families and 18 genera. The endemicity level is high being approximately 60% of the species and 40% of genera endemic. The specific richness in Patagonia decreases from West to East and from North to South, being Nahuel Buta (Chile and Andes mountains between 38° and 41° S on the forest area, and the Somuncurá plateau (Argentina on the steppe the richest areas. An update of its records and an analysis of the main distribution patterns are provided in this paper.

  9. The Patagonian Orocline: Paleomagnetic evidence of a large counter-clockwise rotation during the closure of the Rocas Verdes basin.

    Science.gov (United States)

    Poblete, Fernando; Roperch, Pierrick; Herve, Francisco; Ramirez, Cristobal; Arriagada, Cesar

    2014-05-01

    The southernmost Andes of Patagonia and Tierra del Fuego present a prominent arc-shaped structure, the Patagonian Orocline. Despite the fact that this major structure was already described by Alfred Wegener in his famous textbook in 1929, few paleomagnetic studies have been attempted to describe the rotations associated with the formation of the Patagonian Orocline. In this study we present a paleomagnetic and anisotropy of magnetic susceptibility (AMS) study from more than 130 sites obtained from the Ultima Esperanza region (NS structures at ~51°S) to Península Hardy, south of the Beagle Channel at ~55°S. 45 sites were sampled in early-cretaceous gabbros (gabbro complex), mid-cretaceous tonalites and granodiorites (Canal Beagle group) and Paleocene intrusive rocks (Seno Año Nuevo group) from the South Patagonian batholith, 4 sites from the late Jurassic Hardy formation, a volcanic succession outcropping in Hardy Peninsula and Stewart Island, 9 sites were drilled in the lower cretaceous sedimentary infill of the Rocas Verdes Basin, 3 sites from the Tortuga ophiolite, a quasi-oceanic crust related to the opening of the Rocas Verdes basin. 80 sites were sampled in Cretaceous to Miocene sedimentary rocks from the Magallanes fold and thrust belt and Magallanes Basin. Characteristic Remanent Magnetizations (ChRMs) obtained from the Rocas Verdes Basin tectonic province correspond to secondary magnetizations postdating the early phase of folding. Pyrrhotite is the main magnetic carrier in some of these sites. ChRMs from the South Patagonian Batholith correspond to a primary magnetization. These rocks record about 90° counterclockwise rotations south of the Beagle channel. Few sites from sediments of the Magallanes fold and thrust belt have stable ChRM. The available paleomagnetic results show that no rotation has occurred in the Provincia of Ultima Esperanza (51.5°S), at least, for the last 60 Ma. In the southern part of Provincia de Magallanes and Tierra del Fuego

  10. Stable isotope evidence for multiple pulses of rapid surface uplift in the Central Andes, Bolivia

    OpenAIRE

    Leier, Andrew; McQuarrie, Nadine; Garzione, Carmala; Eiler, John

    2013-01-01

    Paleoelevation histories from mountain belts like the Central Andes of Bolivia provide important constraints on the timing and geodynamic mechanisms associated with surface uplift. We present new oxygen and carbon isotope data (δ^(18)O, δ^(13)C, and Δ_(47)) from Oligocene–Miocene strata exposed in the Eastern Cordillera of the Bolivian Central Andes in order to reconstruct both the deformation and paleoelevation history of the region prior to late Miocene time. Paleosol carbonate in strata >2...

  11. Drainage reorganization during mountain building in the river system of the Eastern Cordillera of the Colombian Andes

    Science.gov (United States)

    Struth, Lucía; Babault, Julien; Teixell, Antonio

    2015-12-01

    The Eastern Cordillera of Colombia is a thick-skinned thrust-fold belt that is characterized by two topographic domains: (1) the axial zone, a high altitude plateau (the Sabana de Bogotá, 2500 masl) with low local relief and dominated by longitudinal rivers, and (2) the Cordillera flanks, where local relief exceeds 1000 m and transverse rivers dominate. On the basis of an analysis of digital topography and river parameters combined with a review of paleodrainage data, we show that the accumulation of shortening and crustal thickening during the Andean orogeny triggered a process of fluvial reorganization in the Cordillera. Owing to a progressive increase of the regional slope, the drainage network evolves from longitudinal to transverse-dominated, a process that is still active at present. This study provides the idea of progressive divide migration toward the inner part of the mountain belt, by which the area of the Sabana de Bogotá plateau is decreasing, the flanks increase in area, and ultimately transverse rivers will probably dominate the drainage of the Cordillera.

  12. Strong lateral strength contrasts in the mantle lithosphere of continents: A case study from the hot SW Canadian Cordillera

    NARCIS (Netherlands)

    Hardebol, N.J.; Beekman, F.; Cloetingh, S.A.P.L.

    2013-01-01

    This study aims at quantifying the 3-D variability in lithosphere strength of the south-eastern Canadian Cordillera and adjacent craton to the east. Strength is calculated in a forward manner, starting from rheological laws of brittle and ductile deformation. The work flow calculates a temperature m

  13. The South Patagonian batholith: 150 my of granite magmatism on a plate margin

    Science.gov (United States)

    Hervé, F.; Pankhurst, R. J.; Fanning, C. M.; Calderón, M.; Yaxley, G. M.

    2007-09-01

    A new database of 70 U-Pb zircon ages (mostly determined by SHRIMP) indicates that the South Patagonian batholith resulted from the amalgamation of subduction-related plutons from the Late Jurassic to the Neogene. Construction of the batholith began with a voluminous, previously undetected, Late Jurassic bimodal body mainly composed of leucogranite with some gabbro, emplaced along its present eastern margin within a restricted time span (157 to 145 Ma). This episode is, at least in part, coeval with voluminous rhyolitic ignimbrites of the Tobífera Formation, deposited in the deep Rocas Verdes Basin east of the batholith; this was the last of several southwestward-migrating silicic volcanic episodes in Patagonia that commenced in an Early Jurassic extensional tectonic regime. The quasi-oceanic mafic floor of the basin was also contemporaneous with this Late Jurassic batholithic event, as indicated by mutually cross-cutting field relationships. Changes in subduction parameters then triggered the generation of earliest Cretaceous plutons (Cretaceous 1: 144-137 Ma) west of the Late Jurassic ones, a westward shift that culminated at 136-127 Ma (Cretaceous 2) along the present western margin of the batholith. Most mid- to Late Cretaceous (Cretaceous 3: 126-75 Ma) and Paleogene (67-40 Ma) granitoids are represented by geographically restricted plutons, mainly emplaced between the previously established margins of the batholith, and mostly in the far south; no associated volcanic rocks of similar age are known at present in this area. During the final Neogene stage of plutonism (25-15 Ma) a recurrence of coeval volcanism is recognized within and east of the batholith. Typical ɛNdt values for the granitoids vary from strongly negative (- 5) in the Late Jurassic, to progressively higher values for Cretaceous 1 (- 4), Cretaceous 2 (- 0.7), Cretaceous 3 (+ 2) and the Paleogene (+ 5), followed by lower and more variable ones in the Neogene (- 1 to + 5). These variations may

  14. Lichenometric Dating of Little Ice Age Moraines in the Cordillera Vilcabamba, Southern Peruvian Andes

    Science.gov (United States)

    Taggart, J. R.; Licciardi, J. M.

    2008-12-01

    Lateral and end moraines deposited by two valley glaciers were mapped on the south side of Nevado Tucarhuay (5910 m asl) and on the east side of Nevado Salcantay (6271 m asl) in the Cordillera Vilcabamba in the southern Peruvian Andes (~13°S latitude). The geomorphic expression of outer and inner moraine sequences in these two drainages mimics that of a previously studied pair of moraines in the upper Rio Blanco valley on the south side of Nevado Salcantay. Cosmogenic 10Be surface exposure dating has yielded ages of 9.0 ± 0.3 ka and 195 ± 24 years, respectively, for these outer and inner Rio Blanco moraines. In all three valleys, prominent outer moraines occur ~3-5 km from headwalls and inner moraine ridges are found ~2.5-3 km from headwalls. Recessional moraines found exclusively on the east side of Salcantay indicate multiple early- to late-Holocene glacier pauses, rather than continuous retreat, prior to the latest Holocene glacier readvance. Diameters of the lichen Rhizocarpon subgenus Rhizocarpon were measured on moraine boulders from the inner moraines in all three valleys. Lichen diameters on the two undated inner moraines are consistent with diameters on the inner 10Be-dated Rio Blanco moraine, which signifies similar lichenometric ages and supports synchronous glacier culminations in all three drainages during the Little Ice Age. The new lichen measurements and age estimates provide a critical link between previous lichen studies in the Cordillera Blanca to the north and in the Cordillera Real to the south, thereby increasing spatial coverage of terrestrial paleoclimate information. Moreover, the extensive lichen measurements gathered on the inner 10Be-dated Rio Blanco moraine define a new control point for the Rhizocarpon subgenus Rhizocarpon growth curve in the tropical Peruvian- Bolivian Andes, which will increase the accuracy of lichenometric age estimates in this region. 10Be exposure dating of the inner moraines in adjacent valleys is underway

  15. Tectonic Evolution of the Patagonian Orocline: New Insights from a Paleomagnetic Study in Southernmost America

    Science.gov (United States)

    Roperch, P. J.; Poblete, F.; Arriagada, C.; Herve, F.; Ramirez de Arellano, C.

    2015-12-01

    One of the most noteworthy features of the Southern Andes is its bend, where the orogenic trend and main tectonic provinces change from Andean N-S oriented structures to W-E orientations in Tierra del Fuego. Few paleomagnetic studies have been carried out, and whether the bending is a primary curvature or a true orocline is still matter of controversy; also the mechanism of its formation. We have conducted a paleomagnetic study between 50°S to ~56°S, where 146 sites were drilled. Paleomagnetic data were obtained in 44 sites. Results in Early Cretaceous sediments and volcanics rocks confirm a remagnetization event during the mid-Cretaceous and record ~90° of counterclockwise rotation. Paleomagnetic results in mid-Cretaceous intrusives rocks record large counterclockwise rotation (>90°) while Late Cretaceous-Early Eocene intrusive rocks only record ~45° to ~30°. The paleomagnetic results reveal a systematic pattern of rotation—the Fueguian rotation pattern—suggesting that the curvature of Patagonia would have occurred in two stages: the first stage during the collapse and obduction of the Rocas Verdes basin in the mid-Cretaceous and a second stage between the Late Cretaceous and the Paleocene, concomitant with exhumation of Cordillera Darwin and propagation of the fold and thrust belt into the Magallanes foreland. Integrating this result in plate reconstructions shows the Antarctic Peninsula as a prolongation of Patagonia and would have acted as a non-rotational rigid block, facilitating the development of the Patagonia Bend. This land bridge could be a dispersal mechanism for fauna between Australia and South America and would have restricted deep ocean water circulation.

  16. Tectónica neógena en el extremo sur de la Cordillera Patagónica Septentrional: Cuenca de los lagos la Plata y Fontana (45°S Neogene tectonics in the southernmost extreme of the Northern Patagonian Cordillera: La Plata-Fontana lakes basin (45°S

    Directory of Open Access Journals (Sweden)

    A. Folguera

    2003-06-01

    Full Text Available Nuevos datos acerca de la anisotropía del manto, debajo de los Andes entre los 45° y los 46°S han revelado un rasgo sorprendente: un eje de polarización con orientación NO coincide con la segmentación estructural, derivada de la geometría de la cuenca cretácica inferior a estas latitudes. La geometría de la litosfera inferior induciría flujo astenosférico, en forma no paralela al tren andino. Adicionalmente se relaciona este mismo, con el desarrollo de una serie de pequeños depocentros extensionales en el retroarco de edad neógena a cuaternaria, los cuales se encuentran alineados con la estructura extensional cretácica. ¿Fue la reactivación transtensional de estructuras de basamento, durante el Neógeno, la que modificó la geometría de la litosfera inferior, a través de la actividad de un antiguo detachment, induciendo corrientes convectivas en el manto superior? ¿O simplemente la actividad de este detachment se relacionó con los efectos de arrastre que produjera la apertura de una ventana astenosférica, en la litosfera inferior, provocando la ruptura de la corteza a través de discontinuidades fósiles?New anisotropic seismic data below the Andes at 45°- 46°S have revealed a striking feature: a fast polarization NW axis coinciding with the Lower Cretaceous segmentation derived from basin geometry. The geometry of the lower lithosphere would induce astenospheric flux which is not parallel to the Andean trend. Moreover, a series of Quaternary-Neogene small basins in the retro-arc are aligned with the Cretaceous extensional structure. Did transtensional reactivation of basement structures during the Neogene modify lower lithosphere geometry through activity of ancient detachments, inducing convective cells in the upper mantle? Or would the activity of the ancient detachment be linked to the opening of a slab astenospheric window and to its drag in the lower lithosphere, making the crust yield through fossilized discontinuities?

  17. Tides and lake-level variations in the great Patagonian lakes: Observations, modelling and geophysical implications.

    Science.gov (United States)

    Marderwald, Eric; Richter, Andreas; Horwath, Martin; Hormaechea, Jose Luis; Groh, Andreas

    2016-04-01

    -level time series from Lagos Argentino and Viedma yields the amplitudes and phases of the lake tides for the four major tidal constituents M2, S2, O1 and K1. The maximum amplitude, corresponding to the semi-diurnal moon tide M2 in Lago Argentino, amounts to 3 mm. For the four lakes under investigation the theoretical amplitudes and phases of seven constituents (Q1, O1, P1, K1, N2, M2 and S2) are modelled accounting for the contributions of both the solid earth's body tides and the ocean tidal loading (Marderwald 2014). Both contributions involve a deformation of the earth surface and of the equipotential surfaces of the gravity field. For the load tide computation the global ocean tide model EOT11a (Savcenko and Bosch, 2012) and the Gutenberg-Bullen A earth model (Farrell, 1972) was applied and the conservation of water volume is taken into account. The comparison of the tidal signal extracted from the lake-level observations in Lagos Argentino and Viedma with the lake tide models indicates a phase shift which is most likely explained by an 1 hour phase lag of the employed global ocean tide model in the region of the highly fragmented Pacific coast. REFERENCES: Farrell, W. E., (1972). Deformation of the Earth by Surface Loads. Rev. Geophy. Space Phy., 10(3):761-797. Ivins, E., James, T., 2004. Bedrock response to Llanquihue Holocene and present-day glaciation in southernmost South America. Geophys. Res. Lett. 31 (L24613). Doi:10.1029/2004GL021500. Klemann, V., E. R. Ivins, Z. Martinec, and D. Wolf (2007), Models of active glacial isostasy roofing warm subduction: Case of the South Patagonian Ice Field, J. Geophys. Res., 112, B09405, doi: 10.1029/2006JB004818. Lange, H., Casassa, G., Ivins, E. R., Schröder, L., Fritsche, M., Richter, A., Groh, A., Dietrich, R., (2014). Observed crustal uplift near the Southern Patagonian Icefield constrains improved viscoelastic Earth models. Geophysical Research Letters, DOI: 10.1002/2013GL058419. Marderwald ER, 2014. Modelado de las mareas

  18. Remains of early Ordovician mantle-derived magmatism in the Santander Massif (Colombian Eastern Cordillera)

    Science.gov (United States)

    Mantilla Figueroa, Luis C.; Bissig, Thomas; Cottle, John M.; Hart, Craig J. R.

    2012-10-01

    An Early Ordovician magmatic event has been documented in the Santander Massif (north-Eastern Cordillera, Colombia). Three U/Pb laser ablation ages of 477 ± 2 Ma (Arenig), were obtained from metamorphosed and foliated calc-alkaline diorites. The 176Hf/177Hf values in zircons from these meta-diorites, yielded epsilon Hf values (ɛHft) > 0 (Mean = 2 ± 1, at 477 Ma). These data allow interpretation of the origin of these zircons from a radiogenic initial Hf isotope source, which is characteristic of the Earth's mantle. This, together with the fact that the rocks have been affected subsequently by tectonometamorphic processes, suggests that the early Ordovician diorites have been emplaced in a supra-subduction tectonic setting, related to onset of the Iapetus Ocean closure.

  19. Precambrian crust beneath the Mesozoic northern Canadian Cordillera discovered by Lithoprobe seismic reflection profiling

    Science.gov (United States)

    Cook, Frederick A.; Clowes, Ronald M.; Snyder, David B.; van der Velden, Arie J.; Hall, Kevin W.; Erdmer, Philippe; Evenchick, Carol A.

    2004-04-01

    The Cordillera in northern Canada is underlain by westward tapering layers that can be followed from outcrops of Proterozoic strata in the Foreland belt to the lowermost crust of the orogenic interior, a distance of as much as 500 km across strike. They are interpreted as stratified Proterozoic rocks, including ˜1.8-0.7 Ga supracrustal rocks and their basement. The layering was discovered on two new deep seismic reflection profiles in the Yukon (Line 3; ˜650 km) and northern British Columbia (Line 2; ˜1245 km in two segments) that were acquired as part of the Lithoprobe Slave-Northern Cordillera Lithospheric Evolution (SNORCLE) transect. In the Mackenzie Mountains of the eastern Yukon, the layering in Line 3 is visible between 5.0 and 12.0 s (˜15 to 36 km depth). It is followed southwestward for nearly 650 km (˜500 km across strike) and thins to less than 1.0 s (˜3.0-3.5 km thickness) near the Moho at the Yukon-Alaska international boundary. In the northern Rocky Mountains of British Columbia, the upper part of the layering on Line 2 correlates with outcrops of Proterozoic (1.76-1.0 Ga) strata in the Muskwa anticlinorium. At this location, the layering is at least 15 km thick and is followed westward then southward into the middle and lower crust for ˜700 km (˜300 km across strike). It disappears as a thin taper at the base of the crust ˜150 km east of the coast of the Alaskan panhandle. The only significant disruption in the layering occurs at the Tintina fault zone, a late to postorogenic strike-slip fault with up to 800 km of displacement, which appears as a vertical zone of little reflectivity that disrupts the continuity of the deep layering on both profiles (˜300 km apart). The base of the layered reflection zone coincides with the Moho, which exhibits variable character and undulates in a series of broad arches with widths of ˜150 km. In general, the mantle appears to have few reflections. However, at the southwest end of Line 3 near the Alaska

  20. Holocene Paleoglacier History of Glaciar Dalla Vedova, Cordillera DARWIN, Tierra del Fuego, Chile

    Science.gov (United States)

    Reynhout, S.

    2015-12-01

    Southernmost South America is unique in its position immediately north of the present-day Antarctic Convergence, making it ideally suited for the evaluation of Antarctic influences on terrestrial paleoclimate. Here we present a glacial geomorphic interpretation of the paleoglacial history of Glaciar Dalla Vedova in Bahía Blanca, Cordillera Darwin, Chile (53°S). This interpretation is further constrained by radiocarbon dating, cosmogenic dating, dendrochronology, and historical photogrammetry. Preliminary field work suggests that Holocene glacier fluctuations have been constrained to within 3 km of the present glacier boundary, punctuated by rapid recent glacier retreat over the past century. By comparing the observed chronology with the record contained further north in Patagonia, we will evaluate possible mechanisms of regional climate variability over the Holocene across southernmost South America.

  1. Timing and Style of Deformation in the Floresta Massif, Axial Eastern Cordillera, Colombia

    Science.gov (United States)

    Saylor, J.; Stockli, D. F.; Mora, A.

    2009-12-01

    The Floresta Massif is one of the largest exposures of Paleozoic and Pre-Cambrian rocks in the Eastern Cordillera. Estimates for the age of onset of shortening-related deformation in the Eastern Cordillera range from late Cretaceous to late Miocene (e.g., Hoorn et al., 1995; Bayona et al., 2008; Parra et al., 2009). The massif is typically interpreted as being exhumed along a high-angle reverse fault (the Soapaga fault) that reactivated Mesozoic extensional structures (e.g., Kammer and Sanchez, 2006). We examined these dual linked issued with new zircon U/Th-He (ZHe) data, new geological mapping and previously published apatite fission track (AFT) data from the Floresta Massif and the associated footwall strata. Previously, an overturned Paleozoic - Cretaceous sequence was mapped emplaced on Tertiary strata along the Soapaga fault. However, new geologic mapping identifies two previously unrecognized thrusts which place, from west to east, Paleozoic strata on Jurassic strata (Fault 3), Jurassic strata on Cretaceous strata (Fault 2) and Cretaceous strata on Tertiary strata (along the previously identified Fault 1). These results are confirmed by AFT and ZHe data. ZHe ages show no resetting in the Tertiary footwall strata, but show partial resetting in the Cretaceous strata and full resetting in the Jurassic and Paleozoic strata. Similarly, AFT data show older ages in the Cretaceous strata than in the Jurassic or Paleozoic strata. Fully reset ZHe ages from Jurassic strata show that exhumation of the Floresta Massif was ongoing by at least the early Oligocene (~ 30 Ma). However, this deformation post-dates an older episode of deformation associated with partially reset ZHe ages in the Cretaceous strata. Based on a decrease in lag time in detrital ZHe data, we infer that the earlier episode of deformation occurred in the mid - late Eocene (45 - 35 Ma).

  2. Ethno-botanical survey of edible wild fruits in Benguet, Cordillera administrative region, the Philippines

    Institute of Scientific and Technical Information of China (English)

    Racquel Tan Chua-Barcelo

    2014-01-01

    Objective: To conduct a survey on the common name/s, traditional uses and cultural importance of the edible wild fruits in different municipalities of Benguet, Cordillera administrative region. Methods: Interviews using questionnaires with barangay leaders and indigenous people were conducted with 176 key informants from June 2011 to July 2013. Results: A total of 36 fruit species were found in different municipalities of Benguet. These fruit species belong to 27 genera and 20 families. Among the 13 municipalities of Benguet, Kibungan has the highest number of species. There are many uses of wild fruits which ranged from food (snack/dessert/table food), forage (especially for birds, monkeys and wild animals such as cloud rat and grass eaters), offertory, processed/preserved (as jam, jellies, candies, juice and wine), condiment or ingredient (for cooking), source of dye or ink, decoration (to garnish food) and as medicine to common ailments or health problems. Based on the inventory and calculated cultural importance index, Garcinia binucao (balokok) belonging to Clusiaceae is the most abundant fruit, hence it is the commonly used fruit for various purposes such as food, forage, processing/preservation and condiment/ingredient; Vaccinium myrtoides (ayusip) for offerings and as source of dye/ink; Saurauia elegans (uyok) for decoration, and, Antidesma bunius (bugnay) for medicine. Conclusions: Benguet province in the Cordillera region provides a diversity of edible wild fruits. The data gathered from the study signifies that collection, processing and utilization of edible wild fruits are still part of the daily activities of the people in Benguet.

  3. Graptolitos ordovícicos en el Sur de la Cordillera frontal de Mendoza

    Directory of Open Access Journals (Sweden)

    Hugo Tickyj

    2009-04-01

    Full Text Available En el flanco sudoriental de la Cordillera Frontal mendocina aflora un conjunto plegado de metasedimentitas conocido como Formación Las Lagunitas, cuyos afloramientos se extienden entre los ríos Diamante por el sur y Tunuyán por el norte, alcanzando un ancho máximo de 15 km a la latitud del volcán Maipo. El perfil estudiado en el arroyo Cortaderas (34º23'S está compuesto por una secuencia silicoclástica marina integrada por tres conjuntos litológicos, que de este a oeste son: a areniscas gruesas a medias, bien seleccionadas, y areniscas conglomerádicas, b vaques de grano grueso a fino y c areniscas finas a medias, con intercalaciones de pelitas negras laminadas. En la última unidad fueron colectados graptolitos en regular estado de preservación. Su estudio sistemático permitió definir una asociación correspondiente a la Biozona de Climacograptus bicornis, por lo que la Formación Las Lagunitas es asignada al Ordovícico Superior (Sandbiano o Caradociano. La completa extensión cronoestratigráfica de la Formación Las Lagunitas no ha sido establecida, debido a que en el perfil estudiado no es clara la relación entre la unidad portadora de graptolitos y el resto de la secuencia. Este registro de graptolitos en el sur de la Cordillera Frontal mendocina constituye un aspecto novedoso para el análisis del Ordovícico, con implicancias en el contexto de la evolución tectónica de las cuencas sedimentarias ordovícicas del oeste argentino.

  4. Crustal structure of the western transect of the Rif Cordillera from broadband magnetotelluric data

    International Nuclear Information System (INIS)

    Complete text of publication follows. Within the frame of the Topo-Iberia project, the magnetotelluric method has been applied for first time in the western transect of the Rif Cordillera to delineate the electrical crustal structure. Data acquisition has been done in 18 MT measurement sites, with ADU-07 Metronix equipment, including vertical magnetic records. Frequencies range from 4Hz to 32 kHz and acquisition time on each site was from two to three days. The profile extends approximately 110 km in NE-SW trend orthogonal to the main regional geological structures, crossing from the Alboran Sea coast through the major alpine units of the western Rif Cordillera up to the foreland Gharb basin. We have performed a dimensionality analysis using the Wal's and the Bahr's methods, both based on the rotational invariants. The data obtained show variable dimensionalities ranging from 1D to 3D. Predominant strikes suggest NW-SE orientations. Therefore several 2D models have processed using Winglink software with different rotations. The model with N145 deg E rotation shows a good correlation between the resistive structures and the surface geology, as well as their continuity in depth. The Internal Zones corresponds generally to resistive rocks (metamorphic rocks) including a significant conductive body that probably corresponds to the nearby outcropping Beni Boussera peridotites. The External Zones and the foreland basin are characterized by shallow heterogeneous conductive structures. In depth, the most relevant feature corresponds to a large resistive body located below the frontal part of the Rif. The presence of exotic gneiss blocks in the front of the External Zones suggests that this large deep body may correspond to a gneissic or granitic basement surrounded by metapelitic rocks. The deep structure of this transect contributes to highlight the recent evolution and development of the southern part of the Gibraltar Arch in the frame of the Eurasian-African convergent

  5. SHRIMP U-Pb zircon geochronology of Mesozoic granitoids from the Bariloche region (Argentina): Implications for the Middle-Late Jurassic evolution of the North Patagonian batholith.

    Science.gov (United States)

    Castro, Antonio; Vujovich, Graciela; Fernández, Carlos; Moreno-Ventas, Iñaki; Martino, Roberto; Corretgé, Guillermo; Díaz-Alvarado, Juan; Heredia, Nemesio; Gallastegui, Gloria

    2010-05-01

    A detailed U-Pb geochronological study has been carried out on granitoids of the North Patagonian batholith in the region of Bariloche (Argentina), between 40°30' S and 41°45' S. In this region, the calc-alkaline, subduction-related, granitic bodies of the North Patagonian batholith intruded an Early Jurassic volcano-sedimentary sequence contemporary with the intrusion of the Subcordilleran Patagonian batholith (J1 magmatism), and unconformably overlying a metamorphic Gondwanan basement. All these rocks were affected by the Andean compressional phases during the Cenozoic. U-Pb SHRIMP dating of zircon crystals from 11 samples (109 spots) of diorites, tonalites, granodiorites and granites yielded dates ranging from 173 ± 3 Ma to 150 ± 2 Ma (Aalenian to Tithonian). No significant age differences have been identified among the distinct lithological types. Also no spatial trend emerges from these results, although ages tend to be younger westward in the traverse of the Manso River (≈ 41° 35' S). Two peaks appear in the probability density plot of zircon ages. Most of the dated zircons are Bajocian-Bathonian (Middle Jurassic, ≈169 Ma, J2 magmatism), while a secondary peak is observed at the boundary Oxfordian-Kimmeridgian (Late Jurassic, ≈ 156 Ma, J3 magmatism). The J2 magmatic period is coeval to the main stage of effusive activity (V2) in the huge volcanic Chon Aike Province, while J3 coincides with the lesser V3 period of volcanism in Chon Aike. These new geochronological data strongly contribute to the knowledge of the first stages of tectonic evolution of the Andean subduction margin in southern South America. Contrary to previous models, it can be proposed that the subduction-related Mesozoic magmatism started well before the Late Jurassic, and that a continuous supply of calc-alkaline magmas dominated the active margin of South America during at least 190 Ma, from the Early Jurassic to nowadays. Therefore, no dramatic time gap can be observed between

  6. An Alternative Interpretation of Plasma Selenium Data from Endangered Patagonian Huemul Deer ( Hippocamelus bisulcus )

    International Nuclear Information System (INIS)

    The prevalence of osteopathology in 57% in the endangered adult Patagonian huemul deer (Hippocamelus bisulcus), malformed antler development, and general lack of recovery were previously suggested to possibly be related to mineral imbalances like selenium (Se) deficiency, and not to stem from fluorosis. From recent bone analyses of these diseased huemul, fluoride levels averaged 58 ppm (SE=10.7), thus eliminating fluorosis as a causal factor for the osteopathology reported in huemul. In contrast, when analyzing high-elevation sites commonly used by extant populations, we found soils deficient in Se. Ashes from recent volcanism also were very low in Se. As Se-responsive diseases in livestock have been documented in Chile, we reclassified recently published Se levels in huemul and determined that 73% were deficient and 18% marginal. Together with these several lines of indirect evidence, we conclude that Se deficiency plays a role in the lack of recovery of huemul populations.

  7. Marine effect of introduced salmonids: Prey consumption by exotic steelhead and anadromous brown trout in the Patagonian Continental Shelf

    Science.gov (United States)

    Ciancio, J.; Beauchamp, D.A.; Pascual, M.

    2010-01-01

    On the basis of stable isotope analysis, we estimated the marine diet of the most abundant anadromous salmonid species in Patagonian Atlantic basins. The results were coupled with bioenergetic and population models to estimate the consumption of food by salmonids and was compared with that by seabirds, the most abundant top predators in the area. Amphipods were the main salmonid prey, followed by sprat, silversides, squid, and euphausiids. The total consumption, even assuming large anadromous salmonid populations, represented <5% of the total consumption by seabirds. We also identified the particular seabird colonies and artisanal fisheries with which salmonid trophic interactions at a more local scale could be significant. ?? 2010, by the American Society of Limnology and Oceanography, Inc.

  8. An Alternative Interpretation of Plasma Selenium Data from Endangered Patagonian Huemul Deer ( Hippocamelus bisulcus )

    Energy Technology Data Exchange (ETDEWEB)

    Flueck, Werner T. [National Council of Scientific and Technological Research (CONICET), Bariloche (Argentina); Univ. of Basel (Switzerland). Swiss Tropical and Public Health Inst.; ETH Zurich (Switzerland). Inst. of Biogeochemistry and Pollutant Dynamics; Smith-Flueck, Jo Anne M. [Univ. Atlantida Argentina, Bariloche (Argentina). Inst. of Natural Resources Analysis; Mincher, Bruce J. [Idaho National Lab. (INL), Idaho Falls, ID (United States). Aqueous Separations and Radiochemistry Dept.; Winkel, Lenny H. H.E. [Swiss Federal Inst. of Aquatic Science and Technology, Dubendorf (Switzerland). Eawag; ETH Zurich (Switzerland). Inst. of Biogeochemistry and Pollutant Dynamics

    2014-10-01

    The prevalence of osteopathology in 57% in the endangered adult Patagonian huemul deer (Hippocamelus bisulcus), malformed antler development, and general lack of recovery were previously suggested to possibly be related to mineral imbalances like selenium (Se) deficiency, and not to stem from fluorosis. From recent bone analyses of these diseased huemul, fluoride levels averaged 58 ppm (SE=10.7), thus eliminating fluorosis as a causal factor for the osteopathology reported in huemul. In contrast, when analyzing high-elevation sites commonly used by extant populations, we found soils deficient in Se. Ashes from recent volcanism also were very low in Se. As Se-responsive diseases in livestock have been documented in Chile, we reclassified recently published Se levels in huemul and determined that 73% were deficient and 18% marginal. Together with these several lines of indirect evidence, we conclude that Se deficiency plays a role in the lack of recovery of huemul populations.

  9. Fluctuations of Glaciar Esperanza Norte in the North Patagonian Andes of Argentina during the past 400 yr

    Directory of Open Access Journals (Sweden)

    L. Ruiz

    2011-11-01

    Full Text Available The number of studies of Little Ice Age (LIA glacier fluctuations in Southern South America has increased in recent years but is largely biased towards sites in the South Patagonian Andes. In this paper we present a detailed record of length and areal fluctuations of Glaciar Esperanza Norte (GEN, in the North Patagonian Andes of Argentina, during the past four centuries. The GEN record was reconstructed through the dendro-geomorphological dating of moraines and the analysis of satellite imagery, aerial photographs and documentary material complemented with extensive field surveys. The maximum LIA extent at GEN was associated with an outer moraine dated to the mid 17th century. At least 19 subsequent readvances or standstills evidenced by morainic ridges were identified inside the most extensive LIA moraine. The dating and spacing of these moraines and the additional information available indicate that the ice front retreated much more rapidly during the 20th century than during earlier centuries. Comparison with the record of LIA fluctuations of Glaciar Frías, an ice mass of similar characteristics located 110 km to the north of GEN, shows a similar pattern of recession over the past 400 yr. Both glacier records have the peak LIA event occurring roughly during the same interval and show a minor readvance during the 1970s, but there are still a few discrepancies in the dating of some inner moraines. These differences may be due to local, specific factors or associated with the inherent uncertainties in the dating of the moraines. The chronologies of GEN and Frías are among the most detailed currently available in Patagonia, but a larger number of study sites is needed to develop robust, regionally representative glacier chronologies. Detailed glaciological, geomorphological and meteorological data are also needed to understand the glacier-climate relationships in this region and develop reliable paleoclimatic reconstructions.

  10. In Search of Patagonian Dust: Atmospheric Deposition of Micronutrients to the Southern Atlantic

    Science.gov (United States)

    Chance, R.; Baker, A. R.; Jickells, T. D.

    2012-12-01

    Atmospheric inputs constitute a low but variable source of micronutrients to the south Atlantic and Southern Ocean, the magnitude and spatial distribution of which remains poorly constrained. In particular, dust arising from the arid parts of southern South America has been identified as a potentially significant source of micronutrients. Ice core records indicate large fluctuations in Patagonian dust supply over glacial-interglacial timescales, but little is known about modern day fluxes. As part of the UK-GEOTRACES program, atmospheric aerosol was simultaneously sampled in the eastern and western basins of the southern Atlantic downwind of Patagonia. Specifically, a new time-series station for monitoring atmospheric aerosol in the western south Atlantic was established at Carcass Island (51o15' S, 60o35' W) in the Falkland Islands, in September 2010, and shipboard aerosol and rain samples were collected in the region between Cape Town, South Africa, and 40oS, 5oW in November and December 2010 (cruise D357). Sampling at Carcass Island continued during the austral summer of 2011-2012, and in January 2012 a second shipboard transect across the Atlantic at 40oS was completed (cruise JC068). Here we compare atmospheric concentrations and wet and dry deposition fluxes for trace metals and major nutrients in the two basins are compared, and use principal component analysis to investigate qualitative differences in the overall composition of aerosol from different sources. Concentrations of aerosol nitrogen were higher at Carcass Island than in the eastern Atlantic. During cruise D357, median concentrations of 1.7 nmol m-3 nitrate and 2.0 nmol m-3 ammonium were observed, consistent with remote south Atlantic air, while on Carcass Island corresponding concentrations were 2.3 and 6.3 nmol m-3 during the first year of sampling. Differences in the isotopic composition of aerosol nitrate from the two campaigns are discussed. "Soluble" trace metals were operationally defined

  11. Patagonian Glacier Advances in Concert with those in Western North America

    Science.gov (United States)

    Maurer, M. K.; Menounos, B.; Clague, J. J.; osborn, G.

    2012-12-01

    The question of whether Holocene glacier advances in the Northern and Southern hemispheres are synchronous remains open. Here we report on the evidence for late Holocene advances at Stoppani Glacier (54.78° S, 68.98° W), 50 km west of Ushuaia, Argentina, and compare this record to glacier fluctuations in western North America. The glacier is an outlet glacier of the Darwin Cordillera icefield, has an area of 92 km2 and descends to 80 m asl. Wood mats containing stumps in growth position are separated by units of till in a 100-m-high section through the northeast lateral moraine. Radiocarbon ages on the wood mats and stumps decrease up-section, demonstrating that Stoppani Glacier advanced successively farther over the past 3800 years. The earliest of the advances is recorded by a till overlying peat containing wood that returned a calibrated radiocarbon age of 3.83-3.64 ka (kilo calendar years BP). This advance coincides with a well documented glacier advance in western Canada, the so-called '4.2 ka event' [4.2-3.8 ka]. Stoppani Glacier further thickened and overran stumps in growth position at 3.16-2.95 and at 2.86-2.76 ka; both of these events are contemporaneous with widespread advances of alpine glaciers in British Columbia and Alberta. A fourth advance of Stoppani Glacier at about 2.30-2.01 ka coincides with advances of Deming Glacier on Mount Baker, Washington, USA [2.35-2.15 ka], and several glaciers in the Coast Mountains of British Columbia, Canada. The final advance of Stoppani Glacier began about 0.29 ka when the glacier thickened, overran a vegetated surface, and deposited till that forms the crest of the moraine. This advance coincides with the maximum, classical, Little Ice Age advance of nearly all glaciers in western North America. Collectively, our data indicate that Stoppani Glacier advanced in step with glaciers in western North America during the late Holocene. The most parsimonious explanation is that century-scale climate forcing

  12. Tectonic styles and crustal shortening of the Central Andes "Pampean" flat-slab segment in northern Chile (27-29°S)

    Science.gov (United States)

    Martínez, Fernando; Arriagada, César; Peña, Matías; Deckart, Katja; Charrier, Reynaldo

    2016-01-01

    The Andean orogenic belt, located in the Central Andes "Pampean flat-slab" segment in northern Chile (27-29°S), is composed of two major tectonic regions: the Coastal Cordillera and the Frontal Cordillera. To understand their internal tectonic styles, history of growth and the shortening absorbed by the upper crustal structure of this segment, we combined regional geological mapping data, new ages obtained from radiometric U-Pb dating, and a semibalanced and restored cross-section 225.18 km in length. The results as shown in the previous Mesozoic extensional fault systems, established in northern Chile by the Gondwana breakup, have played a fundamental role in the orogenic buildup. The central structure is characterized by an asymmetric basin (Upper Cretaceous-Paleocene) confined by a doubly vergent fault system composed of inverted faults related to the edges of the Mesozoic Chañarcillo and Lautaro Basins. The U-Pb geochronological data obtained from synorogenic volcano-sedimentary deposits and the angular unconformities recorded between the Cenozoic geological units have revealed that the compressive deformation in this segment started at around ~ 80 Ma by tectonic inversion in the eastern Coastal Cordillera and western Frontal Cordillera, however, the presence of Paleocene and Miocene synorogenic successions at the footwall of the basement reverse faults of the Frontal Cordillera suggests a migration of Andean deformation from the west to the east during the Paleocene-Miocene by propagation of ramps involving inherited basement highs. The pre-compression restoration makes it possible to estimate 40.94 km of minimum shortening, concentrated by inversion anticlines and fault-controlled basement highs across the Frontal Cordillera.

  13. Crustal-thickness variations in the central Andes

    Science.gov (United States)

    Beck, Susan L.; Zandt, George; Myers, Stephen C.; Wallace, Terry C.; Silver, Paul G.; Drake, Lawrence

    1996-05-01

    We estimated the crustal thickness along an east-west transect across the Andes at lat 20°S and along a north-south transect along the eastern edge of the Altiplano from data recorded on two arrays of portable broadband seismic stations (BANJO and SEDA). Waveforms of deep regional events in the downgoing Nazca slab and teleseismic earthquakes were processed to isolate the P-to-S converted phases from the Moho in order to compute the crustal thickness. We found crustal-thickness variations of nearly 40 km across the Andes. Maximum crustal thicknesses of 70 74 km under the Western Cordillera and the Eastern Cordillera thin to 32 38 km 200 km east of the Andes in the Chaco Plain. The central Altiplano at 20°S has crustal thicknesses of 60 to 65 km. The crust also appears to thicken from north (16°S, 55 60 km) to south (20°S, 70 74 km) along the Eastern Cordillera. The Subandean zone crust has intermediate thicknesses of 43 to 47 km. Crustal-thickness predictions for the Andes based on Airy-type isostatic behavior show remarkable overall correlation with observed crustal thickness in the regions of high elevation. In contrast, at the boundary between the Eastern Cordillera and the Subandean zone and in the Chaco Plain, the crust is thinner than predicted, suggesting that the crust in these regions is supported in part by the flexural rigidity of a strong lithosphere. With additional constraints, we conclude that the observation of Airy-type isostasy is consistent with thickening associated with compressional shortening of a weak lithosphere squeezed between the stronger lithosphere of the subducting Nazca plate and the cratonic lithosphere of the Brazilian craton.

  14. The reconstruction and climatic implication of an independent palaeo ice cap within the Andean rain shadow east of the former Patagonian ice sheet, Santa Cruz Province, Argentina

    Science.gov (United States)

    Wolff, Ingo W.; Glasser, Neil F.; Hubbard, Alun

    2013-03-01

    This paper describes the reconstruction of the previously undocumented Meseta Cuadrada palaeo ice cap on south-west Meseta del Lago Buenos Aires, Santa Cruz Province, Patagonia. Based on theoretical surface profiles the reconstruction of the Meseta Cuadrada Palaeo Ice Cap indicates an ice mass covering at least 78 km2 with a total ice volume around 9.2 km3. The inferred equilibrium line altitude (ELA) of the palaeo ice cap (2031 m asl) represents a drop of 286 m compared to the ELA of the current Meseta Cuadrada glacier (~ 2317 m asl). We explain this small change in ELA with reference to the flat hypsometry of the palaeo ice cap and an enhanced aridity to the west of the Patagonian Andes caused by the existence of the Last Glacial Maximum (LGM) Patagonian ice sheet. Calculated annual accumulation values of ca. 402 to 957 mm/a at the ELA of the Meseta Cuadrada palaeo ice cap derived by a degree day model (DDM) during the last local glacial maximum extent are low compared with estimations of the current accumulation at the ELA of the remaining glacierized area of around 3789 mm/a. This strongly supports the existence of increased aridity and seasonality east of the Patagonian Andes during the Last Glacial Maximum, provided both maximum extents were synchronous.

  15. Further Studies on the Physical and Biogeochemical Causes for Large Interannual Changes in the Patagonian Shelf Spring-Summer Phytoplankton Bloom Biomass

    Science.gov (United States)

    Signorini, Sergio R.; Garcia, Virginia M.T.; Piola, Alberto R.; Evangelista, Heitor; McClain, Charles R.; Garcia, Carlos A.E.; Mata, Mauricio M.

    2009-01-01

    A very strong and persistent phytoplankton bloom was observed by ocean color satellites during September - December 2003 along the northern Patagonian shelf. The 2003 bloom had the highest extent and chlorophyll a (Chl-a) concentrations of the entire Sea-viewing Wide Field-of-view Sensor (SeaWiFS) period (1997 to present). SeaWiFS-derived Chl-a exceeded 20 mg/cu m in November at the bloom center. The bloom was most extensive in December when it spanned more than 300 km across the shelf and nearly 900 km north-south (35degS to 43degS). The northward reach and the deep penetration on the shelf of the 2003 bloom were quite anomalous when compared with other years, which showed the bloom more confined to the Patagonian shelf break (PSB). The PSB bloom is a conspicuous austral spring-summer feature detected by ocean color satellites and its timing can be explained using the Sverdrup critical depth theory. Based on high-resolution numerical simulations, in situ and remote sensing data, we provide some suggestions for the probable mechanisms responsible for that large interannual change of biomass as seen by ocean color satellites. Potential sources of macro and micro (e.g., Fe) nutrients that sustain the high phytoplankton productivity of the Patagonian shelf waters are identified, and the most likely physical processes that maintain the nutrient balance in the region are discussed.

  16. Four New Species of Nepenthes L. (Nepenthaceae from the Central Mountains of Mindanao, Philippines

    Directory of Open Access Journals (Sweden)

    Thomas Gronemeyer

    2014-06-01

    Full Text Available Together with the islands of Sumatra (Indonesia and Borneo (Indonesia, Malaysia, the Philippines are the main center of diversity for carnivorous pitcher plants of the genus, Nepenthes L. Nepenthes are the largest of all carnivorous plants, and the species with the biggest pitchers are capable of trapping and digesting small amphibians and even mammals. The central cordillera of Mindanao Island in the south of the Philippines is mostly covered with old, primary forest and is the largest remaining cohesive, untouched area of wilderness in the Philippines. In a recent field exploration of two areas of the central cordillera, namely Mount Sumagaya and a section of the Pantaron range, four new taxa of Nepenthes were discovered. These four remarkable new species, N. pantaronensis, N. cornuta, N. talaandig and N. amabilis, are described, illustrated and assessed.

  17. Four New Species of Nepenthes L. (Nepenthaceae) from the Central Mountains of Mindanao, Philippines.

    Science.gov (United States)

    Gronemeyer, Thomas; Coritico, Fulgent; Wistuba, Andreas; Marwinski, David; Gieray, Tobias; Micheler, Marius; Mey, François Sockhom; Amoroso, Victor

    2014-01-01

    Together with the islands of Sumatra (Indonesia) and Borneo (Indonesia, Malaysia), the Philippines are the main center of diversity for carnivorous pitcher plants of the genus, Nepenthes L. Nepenthes are the largest of all carnivorous plants, and the species with the biggest pitchers are capable of trapping and digesting small amphibians and even mammals. The central cordillera of Mindanao Island in the south of the Philippines is mostly covered with old, primary forest and is the largest remaining cohesive, untouched area of wilderness in the Philippines. In a recent field exploration of two areas of the central cordillera, namely Mount Sumagaya and a section of the Pantaron range, four new taxa of Nepenthes were discovered. These four remarkable new species, N. pantaronensis, N. cornuta, N. talaandig and N. amabilis, are described, illustrated and assessed. PMID:27135505

  18. DISTRIBUCIÓN DEL AGUA LLUVIA EN TRES BOSQUES ALTOANDINOS DE LA CORDILLERA CENTRAL DE ANTIOQUIA, COLOMBIA RAINFALL DISTRIBUTION IN THREE HIGH ANDEAN FORESTS IN THE CENTRAL CORDILLERA OF COLOMBIA

    Directory of Open Access Journals (Sweden)

    Juan Diego León Peláez

    2010-06-01

    Full Text Available Se estudió la distribución del agua lluvia durante tres años en un bosque climácico de roble (Quercus humboldtii y dos plantaciones forestales, de pino (Pinus patula y ciprés (Cupressus lusitanica ubicados en los Andes colombianos. Los principales ingresos de agua al bosque ocurrieron por la lluvia, cuyo valor medio anual fue 1.700 mm año-1. La precipitación interna tuvo la mayor participación de los flujos hídricos del bosque, siendo máxima en el cipresal (1.486 mm a-1, 90 % y mínima en el pinar (1.389 mm a-1, 81 %, mientras que el escurrimiento cortical fue muy bajo en los tres bosques (1-3 mm a-1, 0,1-0,2 %. La máxima intercepción se presentó en el pinar (329 mm a-1, equivalente al 19 % de la lluvia. A diferencia de estos flujos hídricos del dosel los flujos hídricos del suelo sí mostraron diferencias significativas entre coberturas (P Rainfall distribution was assessed for three years in a mature oak forest (Quercus humboldtii, pine (Pinus patula and cypress (Cupressus lusitanica plantations in the northern part of the colombian Andean mountains. An annual average of 1700 mm was the main water input in the forests, which came from the bulk precipitation. The higher water flows were represented by throughfall, which showed a maximum value in the cypress (1486 mm y¹, 90% and a minimum one in the pine (1389 mm y¹, 81% plantations, respectively. Stemflow was very low in the three forest types (1-3 mm y¹, 0.1-0.2%. The maximum amount of water intercepted by forest crowns was found in the pine plantation (329 mm y¹, which accounted for 19% out of the total rainfall. In opposition to the patterns found for throughfall and stemflow, soil hydric flows did show significant differences among forest types (P<0.05. In the oak forest water infiltration inversely decreased with soil depth; this forest type showed the lowest water losses by deep drainage (2 mm y¹. Finally, throughfall and stemflow were significantly correlated with the amount and intensity of rainfall. In conclusion, oak forests showed the highest rainfall regulation capacity, followed by the pine plantation. In contrast, the cypress plantation had a very low rainfall regulation potential once that this forest type was characterized by high and fast water losses by deep drainage.

  19. CO2-rich thermomineral groundwater in the Betic Cordilleras, southeastern Spain: Genesis and tectonic implications

    Science.gov (United States)

    Cerón, J. C.; Martín-Vallejo, M.; García-Rossell, L.

    The CO2-rich thermal groundwater in the Betic Cordilleras in Spain has been studied with regard to the geological and hydrogeological setting, physical and chemical characteristics, and 13C-isotope content. The study area is about 60km northeast of Almería city, in southeastern Spain. The thermomineral waters are plentiful and are related to regional geothermal anomalies. Temperatures of 20 -41°C, high bicarbonate concentrations (183-1824mg/L), and high amounts of PCO2 (Resumen Las aguas termales con elevados contenidos en CO2 de las Cordilleras Béticas han sido estudiadas en relación con los aspectos geológicos e hidrogeológicos, sus características físicas y químicas, y sus contenidos en 13C. El área de estudio se encuentra aproximadamente a 60km al noreste de la ciudad de Almería, en el sureste de España. Las aguas termominerales son numerosas y están relacionadas con anomalías geotermales regionales. El agua subterránea tiene una temperatura comprendida entre 20-41°C, alta concentración de bicarbonatos (entre 183-1824mg/L) y elevada PCO2 (<1.1bares). Las variaciones espaciales de CO2 están relacionadas con la proximidad de los sistemas de fallas de Carboneras, Palomares y Guadalentín, y puede ser la manifestación en superficie de una zona de adelgazamiento cortical. Los datos de δ13C indican un posible aporte de origen profundo de CO2, posiblemente del manto y/o de las rocas carbonatadas presentes en el sustrato metamórfico. Las elevadas concentraciones de CO2 en el agua subterránea origina problemas en los sondeos y en el uso del agua. El carácter hidrotermal de este área estaría relacionado con su actividad neotectónica.

  20. Downscaling reanalysis data to high-resolution variables above a glacier surface (Cordillera Blanca, Peru)

    Science.gov (United States)

    Hofer, Marlis; Mölg, Thomas; Marzeion, Ben; Kaser, Georg

    2010-05-01

    Recently initiated observation networks in the Cordillera Blanca provide temporally high-resolution, yet short-term atmospheric data. The aim of this study is to extend the existing time series into the past. We present an empirical-statistical downscaling (ESD) model that links 6-hourly NCEP/NCAR reanalysis data to the local target variables, measured at the tropical glacier Artesonraju (Northern Cordillera Blanca). The approach is particular in the context of ESD for two reasons. First, the observational time series for model calibration are short (only about two years). Second, unlike most ESD studies in climate research, we focus on variables at a high temporal resolution (i.e., six-hourly values). Our target variables are two important drivers in the surface energy balance of tropical glaciers; air temperature and specific humidity. The selection of predictor fields from the reanalysis data is based on regression analyses and climatologic considerations. The ESD modelling procedure includes combined empirical orthogonal function and multiple regression analyses. Principal component screening is based on cross-validation using the Akaike Information Criterion as model selection criterion. Double cross-validation is applied for model evaluation. Potential autocorrelation in the time series is considered by defining the block length in the resampling procedure. Apart from the selection of predictor fields, the modelling procedure is automated and does not include subjective choices. We assess the ESD model sensitivity to the predictor choice by using both single- and mixed-field predictors of the variables air temperature (1000 hPa), specific humidity (1000 hPa), and zonal wind speed (500 hPa). The chosen downscaling domain ranges from 80 to 50 degrees west and from 0 to 20 degrees south. Statistical transfer functions are derived individually for different months and times of day (month/hour-models). The forecast skill of the month/hour-models largely depends on

  1. Past peak water in Peru's Cordillera Blanca: diagnosing the demise of glacier influence on stream discharge

    Science.gov (United States)

    Baraer, M.; Mark, B. G.; McKenzie, J. M.

    2011-12-01

    In conditions of continuous retreat, glaciers generate a temporary increase in stream runoff as they lose mass. Yet as the extant glacier volume diminishes, the annual runoff reaches a peak and is followed by a persistent decrease. In the present study we explore historical and modern discharge measurements measured between 1952 and 2010 at nine stations across the upper Rio Santa watershed, the basin that drains most of the western Cordillera Blanca, Peru, and situate the regional stream hydrology within this glacier influence change sequence. The relation between glacial retreat and stream discharge is investigated by the use of a simple water balance model that simulates glacier retreat influence on the annual and dry-season discharge, as well as on the annual discharge variability, permitting distinction between four phases of glacier retreat hydrological impact. The link between the modeled synthetic time series and the Cordillera Blanca discharge records is assessed using polynomial regressions and the Mann-Kendall non-parametric statistical test on daily discharge series for three hydrograph parameters: the yearly average, the dry season discharge and the variability coefficient. The glacial retreat for the same period is estimated using existing historical data of glacial coverage from an analysis of composite ASTER imagery that shows accelerating glacier recession in the upper Rio Santa watershed, with the overall glacierized area decreasing annually by 0.81 % between 1990 and 2009. The results provide statistically significant evidence that seven of the nine discharge time series have crossed a critical transition, and now exhibit a decreasing trend related to glacier retreat. La Balsa station measures discharge from the entire upper Rio Santa before entering a major hydro-electrical power plant, and it is undergoing a decline in dry season flow that probably began during the 1970s. Our results predict that if the glaciers completely melt, stream

  2. Revisiting mountain-building in the Andes of Central Chile: constraints from structural geology and thermochronology.

    Science.gov (United States)

    Riesner, M.; Lacassin, R.; Simoes, M.; Armijo, R.; Carrizo, D.

    2015-12-01

    The Andes, one of the most significant reliefs on Earth, is the case example of a subduction-type mountain belt. In central Chile and western Argentina, the particular east-vergent structure of the Aconcagua fold-and-thrust belt (AFTB) is found atop a huge basement high with elevations > 4000 m, the Frontal Cordillera. Classical conceptual models consider the Andes as an east-vergent orogen, opposite to the Nazca subduction, and describe the exhumation of the Frontal Cordillera as an eastward in-sequence event that occurred late in the andean deformation (by ~10My). An alternative model recently challenged this view by proposing that the Andes have mainly a primary westward vergence. Within this scheme, the exhumation of the Frontal Cordillera would have begun earlier, by ~25My, synchronous with formation of the AFTB on the western side of the basement high. Here we test these two models by revisiting structural cross-sections of the Andes at the latitude of Santiago de Chile and of the Aconcagua (~33°S). We provide thermochronological constraints on the timing of exhumation of the Frontal Cordillera by (U-Th)/He dating on apatites retrieved from paleozoic granitoids along a 2,3km high nearly vertical section in the core of the basement high. Preliminary results suggest that the Frontal Cordillera exhumation was not a late event and likely began around 25 Ma. Therefore it appears to be synchronous with deformation within the AFTB and the westernmost fold-and-thrust belt at this latitude. We discuss these results and their implications while building a crustal-scale cross section of the range at the latitude of Santiago de Chile.

  3. Four New Species of Nepenthes L. (Nepenthaceae) from the Central Mountains of Mindanao, Philippines

    OpenAIRE

    Thomas Gronemeyer; Fulgent Coritico; Andreas Wistuba; David Marwinski; Tobias Gieray; Marius Micheler; François Sockhom Mey; Victor Amoroso

    2014-01-01

    Together with the islands of Sumatra (Indonesia) and Borneo (Indonesia, Malaysia), the Philippines are the main center of diversity for carnivorous pitcher plants of the genus, Nepenthes L. Nepenthes are the largest of all carnivorous plants, and the species with the biggest pitchers are capable of trapping and digesting small amphibians and even mammals. The central cordillera of Mindanao Island in the south of the Philippines is mostly covered with old, primary forest and is the largest rem...

  4. Understanding the transport of Patagonian dust and its influence on marine biological activity in the South Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    M. S. Johnson

    2011-03-01

    Full Text Available The supply of bioavailable iron to the high-nitrate low-chlorophyll (HNLC waters of the Southern Ocean through atmospheric pathways could stimulate phytoplankton blooms and have major implications for the global carbon cycle. In this study, model results and remotely-sensed data are analyzed to examine the horizontal and vertical transport pathways of Patagonian dust and quantify the effect of iron-laden mineral dust deposition on marine biological productivity in the surface waters of the South Atlantic Ocean (SAO. Model simulations for the atmospheric transport and deposition of mineral dust and bioavailable iron are carried out for two large dust outbreaks originated at the source regions of northern Patagonia during the austral summer of 2009. Model-simulated horizontal and vertical transport pathways of Patagonian dust plumes are in reasonable agreement with remotely-sensed data. Simulations indicate that the synoptic meteorological patterns of high and low pressure systems are largely accountable for dust transport trajectories over the SAO. According to model results and retrievals from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO, synoptic flows caused by opposing pressure systems (a high pressure system located to the east or north-east of a low pressure system elevate the South American dust plumes well above the marine boundary layer. Under such conditions, the bulk concentration of mineral dust can quickly be transported around the low pressure system in a clockwise manner, follow the southeasterly advection pathway, and reach the HNLC waters of the SAO and Antarctica in ~3–4 days after emission from the source regions of northern Patagonia. Two different mechanisms for dust-iron mobilization into a bioavailable form are considered in this study. A global 3-D chemical transport model (GEOS-Chem, implemented with an iron dissolution scheme, is employed to estimate the atmospheric fluxes of soluble

  5. Understanding the transport of Patagonian dust and its influence on marine biological activity in the South Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    M. S. Johnson

    2010-11-01

    Full Text Available The supply of bioavailable iron to the high-nitrate low-chlorophyll (HNLC waters of the Southern Ocean through atmospheric pathways could stimulate phytoplankton blooms and have major implications for the global carbon cycle. In this study, model results and remotely-sensed data are analyzed to examine the horizontal and vertical transport pathways of Patagonian dust and quantify the effect of iron-laden mineral dust deposition on marine biological productivity in the surface waters of the South Atlantic Ocean (SAO. Model simulations for the atmospheric transport and deposition of mineral dust and bioavailable iron are carried out for two large dust outbreaks originated at the source regions of Northern Patagonia during the austral summer of 2009. Model-simulated horizontal and vertical transport pathways of Patagonian dust plumes are in reasonable agreement with remotely-sensed data. Simulations indicate that the synoptic meteorological patterns of high and low pressure systems are largely accountable for dust transport trajectories over the SAO. According to model results and retrievals from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO, synoptic flows caused by opposing pressure systems (a high pressure system located to the east or north-east of a low pressure system elevate the South American dust plumes well above the marine boundary layer. Under such conditions, the bulk concentration of mineral dust can quickly be transported around the low pressure system in a clockwise manner, follow the southeasterly advection pathway, and reach the HNLC waters of the SAO and Antarctica in ~3–4 days after emission from the source regions of Northern Patagonia. Two different mechanisms for dust-iron mobilization into a bioavailable form are considered in this study. A global 3-D chemical transport model (GEOS-Chem, implemented with an iron dissolution scheme, is employed to estimate the atmospheric fluxes of soluble

  6. Early and Middle Holocene evidence for plant use and cultivation in the Middle Cauca River Basin, Cordillera Central (Colombia)

    Science.gov (United States)

    Aceituno, Francisco J.; Loaiza, Nicolás

    2014-02-01

    This paper presents the latest results of research done in the Colombian Andean region known as Middle Cauca River Basin, an important location for the study of the origins of plant use and the dispersal of domesticates throughout the Americas due to its geographical position in northwest South America. We discuss human-environment interactions during Pleistocene/Holocene transition to middle Holocene (ca 10,000-4000 BP), specifically human-plant interaction and environmental factors that led to the adoption of horticultural practices. Three lines of evidence are analyzed: archaeological stratigraphy, lithic technology, and microbotanical remains. Our results suggest that early Holocene environmental stability allowed Middle Cauca settlers to use the diverse local resources for several millennia, altering the local vegetation, and leading to the development of horticultural practices that included the use of both local and foreign plants. These results inform the ongoing debate about the antiquity and nature of plant domestication and dispersals in the Americas.

  7. Estructura y riqueza de plantas arborescentes en Un Bosque de Niebla de la Cordillera Central (Tolima, Colombia

    Directory of Open Access Journals (Sweden)

    Campo Kurmen Juan Manuel

    2006-06-01

    Full Text Available Se presenta el estudio de la estructura, la riqueza y la composición florística del componente arborescente de un
    bosque entresacado, en la vereda Dantas, municipio de Ibagué, Tolima, Colombia, con base en el mues-treo de
    los individuos con DAP 2,5 cm en 0,1 ha. El bosque se caracteriza por la escasez de lianas y de hemiepífitas,
    ausencia de familias típicas de bosques de niebla colombianos entre los 2.000 y 2.500 msnm (Araceae, Ericaceae,
    Myrtaceae, Meliaceae y Aquifoliaceae y por un incremento en la riqueza de familias como Sabiaceae y Euphorbiaceae.
    Comparado con otros bosques de niebla de los Andes colombianos y del neotrópico, éste presenta una de las
    más bajas densidades de tallos (237 individuos con DAP ³ 2,5 cm por 0,1 ha y una proporción de árboles grandes
    muy alta (39,7% individuos con DAP 10 cm por 0,1 ha. Aparentemente, los efectos de la extracción selectiva
    de maderas sobre la riqueza, la estructura y la composición, son la disminución de la densidad y la riqueza de lianas, mayor riqueza de Sabiaceae y Euphorbiaceae y mayor densidad de especies secundarias como Hedyosmum goudotianum Slms-Laubach var. goudatianum, Miconia resima Naud. y Palicourea calophlebia Standl.

  8. Pre-collisional extensional tectonics in convergent continental margins: the cretaceous evolution of the central cordillera of the Colombian Andes

    OpenAIRE

    Zapata Henao, Sebastian

    2015-01-01

    Abstract: The Cretaceous tectonic evolution of the Northern Andes continental margin is characterized by continuous convergence that allowed the formation of continental volcanic arcs, back arc basins, extensional divergent tectonics and accretion of exotic terranes. Such a record, particularly the extensional phases, is commonly hidden by the overimposition of deformational events associated with evolution of the subduction configuration, collision of exotic terranes and strike slip fragment...

  9. Integrative taxonomy and conservation status of amphibians in western Panama with an emphasis on the highlands of the Cordillera Central

    OpenAIRE

    Hertz, Andreas

    2015-01-01

    Amphibien bevölkern die Erde seit über 300 Millionen Jahren und sind heute, mit über 7000 bekannten Arten und vielen weiteren die noch zu entdecken sind, eine der artenreichsten Wirbeltierklassen der Welt. Wie verschiedene Studien herausgefunden haben ist etwa ein Drittel der bekannten Amphibienarten unmittelbar vom Aussterben bedroht, was sie zur meist bedrohten Wirbeltierklasse macht. Panama hat im Verhältnis zu seiner relativ kleinen Landesfläche eine der artenreichsten Amphibienfaunen wel...

  10. Sedimentary cyclicity in early Pleistocene, evaporitic, playa-lake lacustrine deposits in the Guadix-Baza basin (Betic Cordillera, Spain); Ciclicidad sedimentaria en depositos lacustres evaporiticos tipo playa-lake del Pleistoceno inferior en la cuenca de Guadix-Baza (Cordillera Betica, Espana)

    Energy Technology Data Exchange (ETDEWEB)

    Garcia Aguilar, J. M.; Guera-Menchan, A.; Serrano, F.; Palmqvist, P.

    2013-06-01

    The Guadix-Baza basin (Betic Cordillera, southern Spain) contains in its eastern sector an early Pleistocene (Gelasian and lowermost Calabrian) sedimentary unit that was deposited in a shallow lacustrine environment. Given that the chronological limits of this unit lie between 2.5 and 1.6 Ma BP, the thickness of its preserved sediments (400 m) and high sedimentation rate (44.4 cm/ka) are remarkable. Numerous sedimentary cycles marked by an alternation of marls and sands are commonly found in the marginal sectors and marls and gypsum in the central sector, which would owe their origins to permanent flooding and evaporation/ re-flooding phases due to global climatic changes. Spectral analyses carried out using Fourier transform have revealed the existence of temporary frequencies associated with sedimentary cycles of between 0.2 and 5.2 ka. The origin of these cycles may be associated with variations in solar radiation and oscillations in the Moons orbital position, which would induce global climatic changes resulting in the rise and fall of the water table of the lake. Autocorrelation analyses conducted separately on the marly and evaporitic levels support this conclusion, as they indicate the existence of significant direct correlations between about 4 to 12 sedimentary cycles, which would correspond to repetitions of the stratigraphic series over a time span of 1.3 to 4 ka. (Author)

  11. Photogrammetric determination of spatio-temporal velocity fields at Glaciar San Rafael in the Northern Patagonian Icefield

    Directory of Open Access Journals (Sweden)

    H.-G. Maas

    2010-11-01

    Full Text Available Glaciar San Rafael in the Northern Patagonian Icefield, with a length of 46 km and an ice area of 722 km2, is the lowest latitude tidewater outlet glacier in the world and one of the fastest and most productive glaciers in southern South America in terms of iceberg flux. In a joint project of the TU Dresden and CECS, spatio-temporal velocity fields in the region of the glacier front were determined in a campaign in austral spring of 2009. Monoscopic terrestrial image sequences were recorded with an intervallometer mode high resolution digital camera over several days. In these image sequences, a large number of glacier surface points were tracked by subpixel accuracy feature tracking techniques. Scaling and georeferencing of the trajectories obtained from image space tracking was performed via a multi-station GPS-supported photogrammetric network.

    The technique allows for tracking hundreds of glacier surface points at a measurement accuracy in the order of one decimeter and an almost arbitrarily high temporary resolution. The results show velocities of up to 16 m per day. No significant tidal signals could be observed. Our velocities are in agreement with earlier measurements from theodolite and satellite interferometry performed in 1986–1994, suggesting that the current thinning of 3.5 m/y at the front is not due to dynamic thinning but rather by enhanced melting.

  12. Spatial Models of Abundance and Habitat Preferences of Commerson’s and Peale’s Dolphin in Southern Patagonian Waters

    Science.gov (United States)

    Dellabianca, Natalia A.; Pierce, Graham J.; Raya Rey, Andrea; Scioscia, Gabriela; Miller, David L.; Torres, Mónica A.; Paso Viola, M. Natalia; Schiavini, Adrián C. M.

    2016-01-01

    Commerson’s dolphins (Cephalorhynchus c. commersonii) and Peale’s dolphins (Lagenorhynchus australis) are two of the most common species of cetaceans in the coastal waters of southwest South Atlantic Ocean. Both species are listed as Data Deficient by the IUCN, mainly due to the lack of information about population sizes and trends. The goal of this study was to build spatially explicit models for the abundance of both species in relation to environmental variables using data collected during eight scientific cruises along the Patagonian shelf. Spatial models were constructed using generalized additive models. In total, 88 schools (212 individuals) of Commerson’s dolphin and 134 schools (465 individuals) of Peale’s dolphin were recorded in 8,535 km surveyed. Commerson’s dolphin was found less than 60 km from shore; whereas Peale’s dolphins occurred over a wider range of distances from the coast, the number of animals sighted usually being larger near or far from the coast. Fitted models indicate overall abundances of approximately 22,000 Commerson’s dolphins and 20,000 Peale’s dolphins in the total area studied. This work provides the first large-scale abundance estimate for Peale’s dolphin in the Atlantic Ocean and an update of population size for Commerson’s dolphin. Additionally, our results contribute to baseline data on suitable habitat conditions for both species in southern Patagonia, which is essential for the implementation of adequate conservation measures. PMID:27783627

  13. Emissions from potential Patagonian dust sources and associated biological response in the Atlantic sector of the Southern Ocean

    Science.gov (United States)

    Castagna, A.; Evangelista, H.; Tilstra, L. G.; Kerr, R.

    2014-07-01

    The effect of Patagonian dust over primary producers in the Southern Ocean has long been disputed. Here we present new remote sensing evidence in favour of dust mediated biological response and postulate a hypothesis to explain the spatial relation observed. A new remote sensing definition of dust source areas based on the Normalized Difference Vegetation Index (NDVI) and Absorbing Aerosol Index (AAI) correlation is presented and interannual variation in AAI is evaluated within the source regions as a proxy for dust activity. Correlation of this data with annual chlorophyll concentration, phytoplankton biomass, and diatom dominance reveals a spatially coherent latitudinal band of positive correlation concentrated between the Polar Front and the Subtropical Front. This pattern is restricted to western areas in the biomass correlation and extends toward Africa for the chlorophyll and diatom correlation. This region is equivalent to the area of the Subantarctic Mode Water formation, characterized by a ratio Si : N ≪ 1 in late summer, an unfavourable condition for diatom development, especially under iron limitation. Therefore, due to Si-Fe co-limitation, the positive correlation could be the consequence of an enhanced sensibility of this area to external iron addition for diatom growth. For the Argentinean shelf-break, is not clear whether direct dust input and/or wind stress driving water masses upwelling could be responsible for the positive correlation.

  14. Use of a hybrid external skeletal fixator for repair of a periarticular tibial fracture in a Patagonian cavy.

    Science.gov (United States)

    Joyner, Priscilla H; Rochat, Mark C; Hoover, John P

    2004-04-15

    An 8-week-old female Patagonian cavy was examined because of acute right hind limb lameness; radiography revealed a moderately displaced, comminuted fracture of the proximal third of the tibia. The fracture was stabilized with a hybrid external skeletal fixator. Two Kirschner wires were placed in the main proximal fragment, parallel to the tibial plateau and at right angles to each other. These wires were connected to a partial circular external fixator ring. Three half pins were placed in the distal fragment, and a straight connecting rod positioned on the medial side of the limb was connected to these pins and the fixator ring. A second connecting rod was positioned on the craniomedial side of the limb and was connected to the fixator ring and a fourth half pin in the distal fragment. The fracture healed without complications, and the fixator was removed 3 weeks after surgery. Hybrid external skeletal fixators combine the benefits of circular and linear external skeletal fixation methods, enabling rigid fixation of periarticular long bone fractures without adversely affecting mobility of the adjacent joint. PMID:15112778

  15. Emissions from potential Patagonian dust sources and associated biological response in the Atlantic sector of the Southern Ocean

    Directory of Open Access Journals (Sweden)

    A. Castagna

    2014-07-01

    Full Text Available The effect of Patagonian dust over primary producers in the Southern Ocean has long been disputed. Here we present new remote sensing evidence in favour of dust mediated biological response and postulate a hypothesis to explain the spatial relation observed. A new remote sensing definition of dust source areas based on the Normalized Difference Vegetation Index (NDVI and Absorbing Aerosol Index (AAI correlation is presented and interannual variation in AAI is evaluated within the source regions as a proxy for dust activity. Correlation of this data with annual chlorophyll concentration, phytoplankton biomass, and diatom dominance reveals a spatially coherent latitudinal band of positive correlation concentrated between the Polar Front and the Subtropical Front. This pattern is restricted to western areas in the biomass correlation and extends toward Africa for the chlorophyll and diatom correlation. This region is equivalent to the area of the Subantarctic Mode Water formation, characterized by a ratio Si : N ≪ 1 in late summer, an unfavourable condition for diatom development, especially under iron limitation. Therefore, due to Si–Fe co-limitation, the positive correlation could be the consequence of an enhanced sensibility of this area to external iron addition for diatom growth. For the Argentinean shelf-break, is not clear whether direct dust input and/or wind stress driving water masses upwelling could be responsible for the positive correlation.

  16. Clasificación de yeso mediante imágenes ASTER en la Cordillera Principal Mendocina Gypsum classification based on ASTER images in the Principal Cordillera of Mendoza

    OpenAIRE

    José F Mescua

    2010-01-01

    Se presenta una metodología para obtener el mapa de distribución de yeso con imágenes satelitales ASTER. Se utilizaron imágenes con nivel de procesamiento ASTERL3A correspondientes a dos áreas de la Cordillera Principal mendocina. La estratigrafía de las áreas de estudio se encuentra compuesta por una espesa sucesión sedimentaria mesozoica, volcanitas cenozoicas y depósitos cuaternarios. Dentro de los depósitos mesozoicos se encuentra la Formación Auquilco, integrada por yeso y anhidrita. El ...

  17. Dinámica e implicancia del aluvión de la laguna 513, Cordillera Blanca, Ancash, Perú Dinamics and implications of the laguna 513 Aluvion, Cordillera Blanca, Ancash Perú

    Directory of Open Access Journals (Sweden)

    Patricio Valderrama

    2012-09-01

    Full Text Available La Cordillera Blanca, al norte de Perú, es la zona con más actividad geodinámica externa en Perú. En ella ocurrieron grandes flujos de detritos de origen glaciar, varios de ellos fueron grandes desastres y cobraron miles de vidas. El 11 de abril del 2010, la laguna 513, ubicada en el centro de la Cordillera Blanca, sufrió un desembalse parcial por la caída de un gran bloque de hielo y rocas del nevado Hualcán (5500 m.s.n.m.. Este evento pese a ser de dimensiones considerables, no generó grandes pérdidas ni afectó alguna ciudad importante. Mediante simulaciones numéricas de flujo se estudió su dinámica, se determinó sus volúmenes y su turbulencia así como también explicamos e papel de la morfología de la zona en la desaceleración del flujo, su encausamiento en un valle fluvial y su posterior comportamiento como crecida de río. Las simulaciones realizadas mediante FLO2D se validan mediante comparaciones con imágenes de satélite post evento y datos de campo.The Cordillera Blanca in northern Peru is the most external geodynamics active areas in Perú. There have been occurred the biggest glacier source debris flow in the Peruvian history, most of them became on major disasters and claimed thousands of lives. On April 11th, 2010, the Laguna 513, located in the center of the Cordillera Blanca, suffered a partial GLOF due a massive rock and ice fall from Nevado Hualcán (5500 masl. This event, despite being of considerable size, did not generate large losses or affect any major city. Using numerical simulations we study the dynamics of the consequent GLOF and debris flow. We determined the volume and turbulence as well as also explained the role of the geomorphology of the area in the flow deceleration process and the river flood subsequent behavior. The FLO 2D simulations are validated with post event satellite image and field data.

  18. Temperaturas de formación en cataclasitas triásicas de la Cordillera Domeyko, Antofagasta, Chile Temperatures of formation in Triassic cataclasites of Cordillera Domeyko, Antofagasta, Chile

    OpenAIRE

    Hans Niemeyer; Héctor Berríos; María Dolores Ruiz Cruz

    2004-01-01

    Las cataclasitas, aquí estudiadas, representan antiguas zonas de falla exhumadas que afectan a macizos de rocas paleozoicas de la Cordillera Domeyko, conformando franjas largas, angostas y anastomosadas de orientación noroeste. Tanto las relaciones de contacto como dataciones radiométricas K-Ar (roca total), indican que la cataclasis se produjo durante el Triásico. Ésta se atribuye a una tectónica de 'rifts' intracontinentales ocurrida durante esa época en el borde suroccidental de Gondwana. ...

  19. Slope deformations in high-mountain regions as observed by InSAR: Examples from the Cordillera Blanca, Peru

    Science.gov (United States)

    Frey, Holger; Strozzi, Tazio; Caduff, Rafael; Huggel, Christian; Klimeš, Jan; Vilímek, Vít; Wiesmann, Andreas; Kääb, Andreas; Cochachin, Alejo; Plummer, Stephen

    2016-04-01

    Steep topography, the world's highest concentration of tropical glaciers, numerous glacial lakes and strong seismic activity combined with a densely populated valley bottom in the Rio Santa basin characterize the Cordillera Blanca in Peru. Besides glacier-related processes, a variety of landslide types and processes is present outside the glaciated areas, favoured by the steep terrain, geological conditions, sparse vegetation, intense precipitation, and strong seismicity. This combination of high hazard potentials and vulnerabilities results in a long list of natural disasters. Information on surface displacements is very valuable for early detection of emerging hazard potentials and their assessment. Interferometric processing of SAR data (InSAR) provides the possibility to remotely detect different types of surface displacement processes, also in remote locations where no other monitoring data are available. This contribution, developed under the ESA-funded S:GLA:MO project (sglamo.gamma-rs.ch), shows the potential of InSAR products for hazard assessments and glaciological investigations in high-mountain regions. We present a selection of different surface displacements as observed in the Cordillera Blanca based on InSAR data: a landslide zone near the Rampac Grande village, where in 2009 a landslide caused casualties and property loss; a landslide at the entry of the Santa Cruz Valley, northern Cordillera Blanca, where the displacement history could be reconstructed over five years; surface displacements at the interior moraine slopes surrounding Laguna Palcacocha, a major glacier lake above the city of Huaraz, which are compared to and complemented by geophysical investigations in the field; surface displacements at the moraine damming Laguna Safuna Alta, a glacier lake in the northern part of the Cordillera Blanca; glacier velocities across the entire Cordillera Blanca, revealing ice flow velocities of more than 200 m yr-1 at certain locations at the end of

  20. Structure of Sierra Blanca (Alpujarride Complex, west of the Betic Cordillera

    Directory of Open Access Journals (Sweden)

    Andreo, B.

    1995-04-01

    Full Text Available Sierra Blanca, situated in the SW of Málaga, forms part of the Blanca unit, belonging to the Alpujarride Complex of the Betic Cordillera. Its lithologic sequences are made up of a group of migmatites, gneisses and schists and an upper formation of marbles (white dolomitic and the bottom and blue calcareous towards the top, linked with a transitional contact. The structure of Sierra Blanca is comprised of folds, generally isoclinal, with reversed limbs and with important tectonic transpositions, the direction of which is approximately E-W in the eastern area and N-S and E-W in the West. In both areas the folds present opposing vergences, consistently towards the interior of the sierra. The origin of these structures is explained with a model of westerly movements of the Blanca unit, in relation to the Los Reales unit, with the formation of frontal and lateral folds. In its advancement, the western part of Sierra Blanca underwent an important anti-clockwise rotation responsible for the co-existence of folds in N-S and E-W directions. These structures occurred under ductile conditions, owing to the presence of important overthrusting peridotitic masses of the Los Reales unit. This model of westerly displacement is inserted in the process undergone by the Betic-Rif Internal Zones (with Blanca and Los Reales units included which occurred at the end of the Oligocene-Early Miocene when the Gibraltar arch began to be formed.Sierra Blanca, situada al SW de Málaga, forma parte de la unidad de Blanca que pertenece al complejo Alpujárride de la Cordillera Bética. Su secuencia litológica está compuesta por un conjunto inferior de migmatitas, gneises y esquistos, y por una formación superior de mármoles, blancos dolomíticos en la base y mármoles calizos azules hacia la parte superior, entre los que existe un tránsito gradual. La estructura de Sierra Blanca está formada por pliegues, generalmente isoclinales, con flancos invertidos que muestran

  1. Proglacial hydrology in the tropical Andes: lessons from the Cordillera Blanca, Peru (Invited)

    Science.gov (United States)

    McKenzie, J. M.; Mark, B. G.; Baraer, M.

    2009-12-01

    Understanding the complexities of tropical Andean hydrology is critical for managing modern water resources and interpreting paleohydrologic records. Glaciers are the most visible component of these systems, responding to global climate change and acting as critical hydrologic reservoirs. Tropical Andean glaciers are undergoing rapid retreat with complex impacts on the downstream hydrology. Groundwater is also an important component of the Andean regional hydrologic system, but its contribution is difficult to assess due to remote site access, minimal baseline data, and lack of continuous historical discharge and precipitation measurements. We have synthesized hydrochemical data from synoptically sampled glacial melt water, groundwater, precipitation, and stream discharge collected intermittently between 1998 and July 2008 throughout the Callejon de Huaylas, a 5000 km2 watershed that drains the western side of the Cordillera Blanca in northern Perú. Our data from 2004 to 2006 show systematic annual shifts in the isotopic ratios (δ18O and δ2H) of river water, indicating an increase in glacial melt water input, and we are able to use these changes across the Cordillera Blanca to estimate an average increase of 1.6 (± 1.1) % in the specific discharge of the glacierized basins. Enhanced total stream discharge in more glacierized catchments (>20% glacier area) is demonstrated by a significant positive trend in a 43-year discharge anomaly record. Our hydrochemical basin characterization method (HBCM) uses chemical mass balance mixing to quantify the contribution of glacial melt water, groundwater, and surface runoff to streams for different valleys and nested watersheds in the Callejon de Huaylas. The Yanamarey basin (7% glaciated) has been observed since 1998 and the HBCM results show good agreement with measured stream discharge (maximum R2 of 0.99) for monthly cumulative values. These results suggest that for most of the studied years groundwater is the main

  2. Los deslizamientos de la cordillera neuquina al sur delos 38° S: suinducción

    Directory of Open Access Journals (Sweden)

    Emilio F. González Díaz

    2009-06-01

    Full Text Available Las conclusiones sobre losdeslizamientos individualizados en la cordillera neuquina (36°-38°S, (suinducción sísmica; rechazo de la consideración de sus depósitos como till,indujo a proyectar su estudio al sur de los 38°S. Se distinguieron inéditaszonas de deslizamientos, cuya promoción y contexto sismotectónico difieren delos reconocidos entre los 36°-38°S. Su estudio regional, que abarcó trescomarcas (Aluminé, Chapelco y Arroyo Limay Chico, comprobó el predominio delas corrientes de tierra sobre los deslizamientos rotacionales, siendo laexcepción tipológica la avalancha de rocas de Chapelco, definida por sumagnitud y morfología. Se interpretó una íntima relación entre sus ocurrenciasy la presencia del Miembro Arroyo Limay Chico (Formación Caleufu. Su litología(con matriz de arcillas expansivas, su particular comportamientofísico-mecánico ante su saturación por precipitaciones y su disposiciónsubyacente a planicies estructurales lávicas o conglomerádicas, determinaron sucarácter de factor intrínseco condicionante. El inductor de las prehistóricascorrientes de tierra (y aun de las actuales, ha sido las precipitacionesintensas. La infiltración de sus aguas redujo la cohesión y fricción de losmateriales, incrementó la presión del agua de los poros y la hidrostáticanormal a las pendientes, haciéndolas proclives a su desestabilización. Losdeslizamientos rotacionales son genéticamente relacionados con el socavamientobasal en los valles por erosión lateral fluvial y adicionalmente con lasprecipitaciones. En ambos casos influyeron la orientación de las pendientes(>insolación, el debilitamiento de abruptas laderas (artesas por esfuerzoshorizontales (lateral release y la pérdida postglaciaria del soporte oapoyo (debutressing que brindaban las lenguas glaciarias. Eldesprendimiento de la avalancha de rocas del Chapelco, ha sido relacionado conintensas precipitaciones o prolongados períodos lluviosos. Se

  3. Documenting and describing the redox evolution of the Neoproterozoic ocean: lessons from the Canadian Cordillera (Invited)

    Science.gov (United States)

    Johnston, D. T.; Poulton, S. W.; Langmuir, C. H.; MacDonald, F. A.; Chen, Z.; Knoll, A.

    2009-12-01

    The geological record of the Neoproterozoic preserves evidence for large-scale perturbations in Earth’s climate and changes in tectonic configuration. During the terminal Proterozoic, and within the context of these changes, Earth’s fluid envelope achieved a level of oxygenation that allowed for the evolution and subsequent radiation of complex multi-cellular life. As such, better constraining the geochemical evolution of the oceans and atmosphere throughout the entire Neoproterozoic will allow for a more mechanistic understanding of the links between changing environmental chemistry and biological innovation. Further, it will provide information on the relative timing of these changes and, where robust dates are available, estimates on the absolute rates of change (both chemical and biological). To this end, our ongoing work has focused on constructing high stratigraphic resolution geochemical records through mixed lithological packages of sedimentary rocks from eastern Alaska and the Canadian Cordillera. Here, we present detailed chemostratigraphic reconstructions of redox sensitive proxies, including Fe-speciation and trace element budgets, that provide an integrated window into Neoproterozoic marine oxidant budgets. These oxidant budgets then allow for the modeling of the relative influence of different aerobic and anaerobic microbial processes on the overall carbon cycle. Taken together, it is this cascade of microbial processes that drives remineralization reactions, the sum of which serves to counter-act organic carbon export, which is ultimately responsible for the buildup of O2. This simple framework serves as the foundation for our interpretation of Neoproterozoic biogeochemistry and informs our view of late Precambrian marine ecosystems. This approach can be further applied to more specific, and perhaps even more anomalous intervals of Neoproterozoic Earth history, including the Cryogenian Bitter Springs event and the Ediacaran Shuram anomaly; both

  4. Paleontologic and stratigraphic relations of phosphate beds in Upper Cretaceous rocks of the Cordillera Oriental, Colombia

    Science.gov (United States)

    Maughan, Edwin K.; Zambrano O., Francisco; Mojica G., Pedro; Abozaglo M., Jacob; Pachon P., Fernando; Duran R., Raul

    1979-01-01

    Phosphorite crops out in the Cordillera Oriental of the Colombian Andes in rocks of Late Cretaceous age as strata composed mostly of pelletal carbonate fluorapatite. One stratum of Santonian age near the base of the Galembo Member of the La Luna Formation crops out at many places in the Departments of Santander and Norte de Santander and may be of commercial grade. This stratum is more than one meter thick at several places near Lebrija and near Sardinata, farther south it is locally one meter thick or more near the base of the Guadalupe Formation in the Department of Boyaca. Other phosphorite beds are found at higher stratigraphic levels in the Galembo Member and the Guadalupe Formation, and at some places these may be commercial also. A stratigraphically lower phosphorite occurs below the Galembo Member in the Capacho Formation (Cenomanian age) in at least one area near the town of San Andres, Santander. A phosphorite or pebbly phosphate conglomerate derived from erosion of the Galembo Member forms the base of the Umir Shale and the equivalent Colon Shale at many places. Deposition of the apatite took place upon the continental shelf in marine water of presumed moderate depth between the Andean geosyncline and near-shore detrital deposits adjacent to the Guayana shield. Preliminary calculations indicate phosphorite reserves of approximately 315 million metric tons in 9 areas, determined from measurements of thickness, length of the outcrop, and by projecting the reserves to a maximum of 1,000 meters down the dip of the strata into the subsurface. Two mines were producing phosphate rock in 1969; one near Turmeque, Boyaca, and the other near Tesalia, Huila.

  5. Recent evolution and mass balance of Cordón Martial glaciers, Cordillera Fueguina Oriental

    Science.gov (United States)

    Strelin, Jorge; Iturraspe, Rodolfo

    2007-10-01

    Past and present glacier changes have been studied at Cordón Martial, Cordillera Fueguina Oriental, Tierra del Fuego, providing novel data for the Holocene deglaciation history of southern South America and extrapolating as well its future behavior based on predicted climatic changes. Regional geomorphologic and stratigraphic correlations indicate that the last glacier advance deposited the ice-proximal ("internal") moraines of Cordón Martial, around 330 14C yr BP, during the Late Little Ice Age (LLIA). Since then glaciers have receded slowly, until 60 years ago, when major glacier retreat started. There is a good correspondence for the past 100 years between the surface area variation of four small cirque glaciers at Cordón Martial and the annual temperature and precipitation data of Ushuaia. Between 1984 and 1998, Martial Este Glacier lost 0.64 ± 0.02 × 10 6 m 3 of ice mass (0.59 ± 0.02 × 10 6 m 3 w.e.), corresponding to an average ice thinning of 7.0 ± 0.2 m (6.4 ± 0.2 m w.e), according to repeated topographic mapping. More detailed climatic data have been obtained since 1998 at the Martial Este Glacier, including air temperature, humidity and solar radiation. These records, together with the monthly mass balance measured since March 2000, document the annual response of the Martial Este Glacier to the climate variation. Mass balances during hydrological years were positive in 2000, negative in 2001 and near equilibrium in 2002. Finally, using these data and the regional temperature trend projections, modeled for different future scenarios by the Atmosphere-Ocean Model (GISS-NASA/GSFC), potential climatic-change effects on this mountain glacier were extrapolated. The analysis shows that only the Martial Este Glacier may survive this century.

  6. Infrared Imaging and Modeling of Proglacial Stream Temperature in the Cordillera Blanca, Peru

    Science.gov (United States)

    Baker, E. A.; Lautz, L.; McKenzie, J. M.; Aubry-Wake, C.; Somers, L. D.; Wigmore, O.; Glose, A.; Glas, R. L.; Mark, B. G.

    2015-12-01

    In the tropical Andes, glacial meltwater is an important water resource for downstream communities, especially during the dry season. Due to climate change, glacial retreat is accelerating and straining already limited water resources in the region. It is hypothesized that groundwater storage and discharge will play a critical role in sustaining future river flows. To improve our understanding of the hydrologic fluxes in proglacial valleys of the tropical Andes, we monitored a ~1.2 km reach of the Quilcayhuanca River, in the Cordillera Blanca, Peru, using a high resolution infrared (IR) camera and in-stream temperature sensors. We positioned the IR camera on the southern valley wall, 96 m above the valley floor, and collected >700 IR images at 10 minute intervals over 5 days. We deployed 40 temperature sensors along the stream at ~25 m intervals and 10 sensors at additional control points throughout the surrounding valley, recording temperature at 10 minute intervals. Groundwater temperature was recorded in 6 wells in the study area. The reach had diurnal temperature fluctuations from ~4 to 13°C, but did not exhibit large longitudinal temperature differences. Stream temperature profiles within the water column show stream water is well mixed, improving the ability of the IR camera to accurately observe the stream temperature at this research site. Temperature sensors in 4 reach tributaries recorded warmer temperatures than the main channel. The daily temperatures of one tributary fluctuated within the range of the groundwater temperature (~9 to 11°C), while another tributary exhibited a range of ~18°C. A weather station in the study area recorded climate data (air temperature, humidity, wind speed, solar radiation) at 10 minute intervals. We used this field data as input for a spatial and temporal energy balance model of the reach. Our model demonstrates the utility of IR imagery to monitor stream temperatures and improves our understanding of energy fluxes in

  7. Ensayo de zonación sismotectónica en la Cordillera Ibérica. Depresión del Ebro y borde sur Pirenáico

    Directory of Open Access Journals (Sweden)

    Simon, J. L.

    1987-12-01

    Full Text Available Spatial relations between recent (Pliocene and Quaternary structures and seismic activity in the Iberian Chain, Ebro Basin and Outer Pyrenean Sierras are analysed. Starting from these relations, a seismotectonic zonation defining four main regions (Eastern Iberian Chain, Middle Iberian Chain, Outer Pyrenean Sierras-Carneros-Demanda Massif and Central sector of the Ebro Basin is stablished. Several zones and subzones with homogeneous characteristics from the seismotectonic point of view are differenciated within each of these four main regions. This zonation is the basis of an attempt to calculate seismic risk with a deterministic criterion.Se analizan las relaciones espaciales entre estructuras recientes (pliocenas y cuaternarias y actividad sísmica en el área de la Cordillera Ibérica, Depresión del Ebro y Sierras Exteriores Pirenaicas. A partir de ellas se realiza una zonación sismotectónica, definiendo cuatro regiones principales (Ibérica Oriental, Ibérica central, Sierras Exteriores-Macizo de Cameros-Demanda y sector central de la Depresión del Ebro y, en cada una de ellas, diferentes zonas y subzonas con características homogéneas desde el punto de vista sismotectónico. Esta zonación constituye la base de un ensayo de cálculo de riesgo sísmico con criterio determinista.

  8. Constraining Subsurface Structure and Composition Using Seismic Refraction Surveys of Proglacial Valleys in the Cordillera Blanca, Peru

    Science.gov (United States)

    Glas, R. L.; Lautz, L.; McKenzie, J. M.; Mark, B. G.; Baker, E. A.; Aubry-Wake, C.; Somers, L. D.; Wigmore, O.

    2015-12-01

    As tropical glaciers rapidly recede in response to climate change, the storage and discharge of groundwater will play an increasing role in regulating river baseflow, particularly during the dry season, when stream flow is currently sustained predominantly by glacial melt. Little is understood regarding the hydrogeologic processes controlling base flow characteristics of low-gradient proglacial valleys of the Cordillera Blanca in Northwestern Peru, which has the world's highest density of tropical glaciers. To better understand the processes of groundwater storage and discharge in proglacial meadows, we completed seismic refraction surveys in three representative valleys of the Cordillera Blanca range: the Quilcayhuanca, Yanamarey, and Pachacoto valleys. The locations of survey transects were chosen based on locations of previous sediment core sampling, GPR lines, and quantification of groundwater-surface water interaction derived from dye and temperature tracing experiments. The seismic surveys consisted of 48 vertical component geophones with 2.5 m spacing. Across the three representative valleys a total of 15 surveys were conducted, covering a distance of 1800 m in cross, down, and oblique-valley directions. Preliminary interpretation of the seismic refraction data indicates a maximum imaging depth of 16 m below land surface, and a transition from glacio-lacustrine sediments to buried saturated talus at a depth of 6 m in the Quilcayhuanca valley. The organic-rich glacio-lacustrine sediments in the Yanamarey valley have seismic velocities ranging from 300 to 800 m/s and are >16 m in thickness at mid- valley. Weathered metasedimentary bedrock in the Pachacoto valley was imaged at ~5 m below the valley surface, exhibiting a p-wave velocity of 3400 m/s. The knowledge of hydrogeologic structure derived from seismic refraction surveys will provide crucial boundary conditions for future groundwater models of the valleys of the Cordillera Blanca.

  9. Spatio-temporal variability of snow water equivalent in the extra-tropical Andes Cordillera from distributed energy balance modeling and remotely sensed snow cover

    Science.gov (United States)

    Cornwell, E.; Molotch, N. P.; McPhee, J.

    2016-01-01

    Seasonal snow cover is the primary water source for human use and ecosystems along the extratropical Andes Cordillera. Despite its importance, relatively little research has been devoted to understanding the properties, distribution and variability of this natural resource. This research provides high-resolution (500 m), daily distributed estimates of end-of-winter and spring snow water equivalent over a 152 000 km2 domain that includes the mountainous reaches of central Chile and Argentina. Remotely sensed fractional snow-covered area and other relevant forcings are combined with extrapolated data from meteorological stations and a simplified physically based energy balance model in order to obtain melt-season melt fluxes that are then aggregated to estimate the end-of-winter (or peak) snow water equivalent (SWE). Peak SWE estimates show an overall coefficient of determination R2 of 0.68 and RMSE of 274 mm compared to observations at 12 automatic snow water equivalent sensors distributed across the model domain, with R2 values between 0.32 and 0.88. Regional estimates of peak SWE accumulation show differential patterns strongly modulated by elevation, latitude and position relative to the continental divide. The spatial distribution of peak SWE shows that the 4000-5000 m a.s.l. elevation band is significant for snow accumulation, despite having a smaller surface area than the 3000-4000 m a.s.l. band. On average, maximum snow accumulation is observed in early September in the western Andes, and in early October on the eastern side of the continental divide. The results presented here have the potential of informing applications such as seasonal forecast model assessment and improvement, regional climate model validation, as well as evaluation of observational networks and water resource infrastructure development.

  10. Soil charcoal analysis as a climato-stratigraphical tool: The key case of Cordillera Real, northern Andes

    Energy Technology Data Exchange (ETDEWEB)

    Di Pasquale, G. [Dipartimento di Arboricoltura Botanica e Patologia Vegetale, Universita di Napoli Federico II, Via Universita 100, 80055 Portici (Italy); Impagliazzo, S., E-mail: stefania.impagliazzo@unina.i [Dipartimento di Arboricoltura Botanica e Patologia Vegetale, Universita di Napoli Federico II, Via Universita 100, 80055 Portici (Italy); Lubritto, C. [CIRCE, Dipartimento di Scienze Ambientali, II Universita di Napoli, and INNOVA, via Vivaldi, 43, 81100 Caserta (Italy); Marziano, M. [Dipartimento di Arboricoltura Botanica e Patologia Vegetale, Universita di Napoli Federico II, Via Universita 100, 80055 Portici (Italy); Passariello, I. [CIRCE, Dipartimento di Scienze Ambientali, II Universita di Napoli, and INNOVA, via Vivaldi, 43, 81100 Caserta (Italy); Ermolli, E. Russo [Dipartimento di Arboricoltura Botanica e Patologia Vegetale, Universita di Napoli Federico II, Via Universita 100, 80055 Portici (Italy)

    2010-04-15

    The present study represents the first attempt of reconstructing fire history through soil charcoal dating. The investigated area is located in the Guandera Biological Reserve (western Cordillera Real, northern Ecuador). Six AMS radiocarbon dating, performed at the base of five soil profiles allowed a fire phase to be identified during the Pleistocene-Holocene transition. A strong correspondence was highlighted between the age of the Guandera fires and the El Abra stadial, which is considered the Younger Dryas equivalent in South America. This local evidence of fires contributes to define the geographic area in which the El Abra stadial was recorded and suggests a wider use of the soil charcoal analysis.

  11. Paleogeographic and tectonic controls on the evolution of Cenozoic basins in the Altiplano and Western Cordillera of southern Peru

    Science.gov (United States)

    Carlotto, Víctor

    2013-03-01

    Integrated studies of stratigraphy, sedimentology, paleogeography and tectonic controls on Cenozoic basins provide the basis for a series of time-slice reconstructions of basin evolution in the Andes of southern Peru. The Altiplano and adjacent margin of the Western Cordillera are characterized by several Paleocene-Miocene synorogenic continental basins with thicknesses locally exceeding 10 km. The evolution of these basins has been controlled by NW-trending tectonic features that mark the Altiplano-Western Cordillera and Altiplano-Eastern Cordillera boundaries and the Condoroma structural high. Sedimentary deposits of Paleocene age preserved in the Altiplano are the result of nonmarine sedimentation in a distal foreland basin. During the early Eocene, predominantly dextral strike-slip movements in the Altiplano between the Cusco-Lagunillas and Urcos-Ayaviri fault systems created the transpressional Kayra basin. The Soncco and Anta basins (middle Eocene-early Oligocene) are related to NE shortening (43-30 Ma) and represent proximal, wedge-top and foredeep basin environments preserved on the Altiplano. At ~ 29-28 Ma, a change to predominantly E-W shortening produced sinistral strike-slip motion along NW-striking faults, resulting in intermontane, transpressional basins. In the Altiplano, the Tinajani and Punacancha (29-5 Ma), and Paruro (12-6 Ma) basins were controlled by the Cusco-Lagunillas and the Urcos-Ayaviri fault systems. The Maure, Tincopalca-Huacochullo and Condoroma basins (22-5 Ma) of the Western Cordillera developed between the Condoroma high and the Cusco-Lagunillas fault system. Oligocene-Miocene sedimentation commonly evolved from proximal (alluvial) facies along the borders to distal (lacustrine) facies. These basins were linked to sinistral strike-slip faults that evolved into reverse-sinistral structures. Plate kinematics may play a role in Andean basin evolution, with deformation influenced by major preexisting faults that dictated paleogeographic

  12. Variabilidad espacial de los atributos de la capa arable de un inceptisol del piedemonte de la cordillera oriental (casanare, colombia)

    OpenAIRE

    Peña, Ricardo; Rubiano, Yolanda; Peña, Andrés; Chaves, Bernardo

    2009-01-01

    El objetivo de este trabajo fue estudiar la variabilidad espacial de los atributos del suelo, enfocado a optimizar futuros muestreos en suelos similares. El estudio se realizó en una superficie de 58 ha, ubicada en Tauramena, departamento de Casanare, Orinoquia colombiana. El suelo del estudio corresponde a un Oxic Dystrudept de textura franco arenosa a franco arcillosa, localizado sobre un abanico de terraza del piedemonte de la cordillera Oriental. A través del análisis del semivariograma y...

  13. A distinctive new subspecies of Scytalopus griseicollis (Aves, Passeriformes, Rhinocryptidae from the northern Eastern Cordillera of Colombia and Venezuela

    Directory of Open Access Journals (Sweden)

    Jorge Avendaño

    2015-06-01

    Full Text Available We describe a new subspecies of Pale-bellied Tapaculo Scytalopus griseicollis from the northern Eastern Cordillera of Colombia and Venezuela. This form differs diagnosably in plumage from described subspecies S. g. griseicollis and S. g. gilesi and from the latter in tail length. It is also differentiated non-diagnosably in voice from both these populations. Ecological niche modelling analysis suggests that the new subspecies is restricted to the Andean montane forest and páramo north of both the arid Chicamocha valley and the Sierra Nevada del Cocuy.

  14. A distinctive new subspecies of Scytalopusgriseicollis (Aves, Passeriformes, Rhinocryptidae) from the northern Eastern Cordillera of Colombia and Venezuela.

    Science.gov (United States)

    Avendaño, Jorge Enrique; Donegan, Thomas M

    2015-01-01

    We describe a new subspecies of Pale-bellied Tapaculo Scytalopusgriseicollis from the northern Eastern Cordillera of Colombia and Venezuela. This form differs diagnosably in plumage from described subspecies Scytalopusgriseicollisgriseicollis and Scytalopusgriseicollisgilesi and from the latter in tail length. It is also differentiated non-diagnosably in voice from both these populations. Ecological niche modelling analysis suggests that the new subspecies is restricted to the Andean montane forest and páramo north of both the arid Chicamocha valley and the Sierra Nevada del Cocuy. PMID:26085800

  15. Clasificación de yeso mediante imágenes ASTER en la Cordillera Principal Mendocina

    OpenAIRE

    José F Mescua

    2010-01-01

    Se presenta una metodología para obtener el mapa de distribución de yeso con imágenes satelitales ASTER. Se utilizaron imágenes con nivel de procesamiento ASTERL3A correspondientes a dos áreas de la Cordillera Principal mendocina. La estratigrafía de las áreas de estudio se encuentra compuesta por una espesa sucesión sedimentaria mesozoica, volcanitas cenozoicas y depósitos cuaternarios. Dentro de los depósitos mesozoicos se encuentra la Formación Auquilco, integrada por yeso y anhidrita. El ...

  16. An enigmatic frog of the genus Atelopus (Family Bufonidae) from Parque Nacional Chirripó, Cordillera de Talamanca, Costa Rica.

    Science.gov (United States)

    Savage, Jay M; Bolaños, Federico

    2009-01-01

    A distinctive new species of Atelopus is described from Parque Nacional Chirrip6 Grande, Cordillera de Talamanca (3,400-3,500 m). It closely resembles populations of the Atelopus ignescens complex from the Andes of northern Ecuador and southern Colombia. It differs most significantly from these frogs in the pattern of spiculae and coni development on the throat, chest, hands and feet. The Costa Rican species appears to be an outlier of the complex inexplicably separated geographically from its nearest allies by an over land distance of about 1,600 km. PMID:19637715

  17. Magnetic fabric and microstructures of Late Paleozoic granitoids from the North Patagonian Massif: Evidence of a collision between Patagonia and Gondwana?

    Science.gov (United States)

    López de Luchi, Mónica G.; Rapalini, Augusto E.; Tomezzoli, Renata N.

    2010-10-01

    Widespread Late Paleozoic magmatism in northern Patagonia is a target to test hypotheses on the long standing question over the origin of Patagonia. In recent years, a dispute over whether it is an accreted crustal block that collided with Gondwana in Paleozoic times or an autochthonous part of South America has taken place. As part of a multidisciplinary study, an integrated microstructural and magnetic fabric study was carried out on the Late Carboniferous Yaminué Complex and the Early Permian Navarrete Plutonic Complex, both exposed in the northeastern corner of the North Patagonian Massif (40.5°S, 67.0°W). Other investigated units are the Late Carboniferous Tardugno Granodiorite, the newly defined Cabeza de Vaca Granite and the Late Permian San Martin pluton. Over 300 oriented cores from 60 sites were collected for anisotropy of magnetic susceptibility (AMS) measurements. A systematic analysis of around 100 petrographic thin sections was performed to characterize the microstructures of the different magmatic units. Microstructures in the Yaminué Complex are indicative of a transition from magmatic to solid-state deformation. Microstructures of the orthogneiss of tonalitic composition suggest an early stage in the emplacement history of this complex. The Cabeza de Vaca Granite, intrusive in Yaminué Complex, is the most evolved unit and records less intense high-temperature solid-state deformation which suggests that the stress field that controlled the emplacement of the Yaminué Complex outlasted it. According to petrologic and structural considerations, the Navarrete Plutonic Complex has been subdivided into three facies, i.e. Robaina, Guanacos and Aranda, respectively. Microstructures of the Navarrete Plutonic Complex are mostly magmatic to submagmatic, versus the solid-state fabric that characterizes the Robaina facies at the contact with the Yaminué Complex. Combined analyses of AMS and microstructural data lead us to suggest that the Yaminué Complex

  18. Paleomagnetic evidence for a pre-early Eocene (˜ 50 Ma) bending of the Patagonian orocline (Tierra del Fuego, Argentina): Paleogeographic and tectonic implications

    Science.gov (United States)

    Maffione, Marco; Speranza, Fabio; Faccenna, Claudio; Rossello, Eduardo

    2010-01-01

    The southernmost segment of the Andes of southern Patagonia and Tierra del Fuego forms a ˜ 700 km long orogenic re-entrant with an interlimb angle of ˜ 90° known as Patagonian orocline. No reliable paleomagnetic evidence has been gathered so far to assess whether this great orogenic bend is a primary arc formed over an articulated paleomargin, or is due to bending of a previously less curved (or rectilinear) chain. Here we report on an extensive paleomagnetic and anisotropy of magnetic susceptibility (AMS) study carried out on 22 sites (298 oriented cores), predominantly sampled in Eocene marine clays from the external Magallanes belt of Tierra del Fuego. Five sites (out of six giving reliable paleomagnetic results) containing magnetite and subordinate iron sulphides yield a positive fold test at the 99% significance level, and document no significant rotation since ˜ 50 Ma. Thus, the Patagonian orocline is either a primary bend, or an orocline formed after Cretaceous-earliest Tertiary rotations. Our data imply that the opening of the Drake Passage between South America and Antarctica (probably causing the onset of Antarctica glaciation and global climate cooling), was definitely not related to the formation of the Patagonian orocline, but was likely the sole consequence of the 32 ± 2 Ma Scotia plate spreading. Well-defined magnetic lineations gathered at 18 sites from the Magallanes belt are sub-parallel to (mostly E-W) local fold axes, while they trend randomly at two sites from the Magallanes foreland. Our and previous AMS data consistently show that the Fuegian Andes were characterized by a N-S compression and northward displacing fold-thrust sheets during Eocene-early Miocene times (50-20 Ma), an unexpected kinematics considering coeval South America-Antarctica relative motion. Both paleomagnetic and AMS data suggest no significant influence from the E-W left-lateral Magallanes-Fagnano strike-slip fault system (MFFS), running a few kilometres south of our

  19. Egg masses of the Patagonian squid Doryteuthis (Amerigo gahi attached to giant kelp (Macrocystis pyrifera in the sub-Antarctic ecoregion

    Directory of Open Access Journals (Sweden)

    Sebastián Rosenfeld

    2014-11-01

    Full Text Available Egg masses of the Patagonian squid Doryteuthis (Amerigo gahi attached to giant kelp (Macrocystis pyrifera in the Magellanic channels of the sub-Antarctic ecoregion in southern South America is documented for the first time. Of seven egg masses observed between 2008 and 2011, one was taken to the laboratory to be analysed and photographed. Comprising long transparent capsules containing eggs, the masses were strongly attached to the stipes of M. pyrifera. This macroalgae is a potentially important economic resource due to its multiple industrial uses; this study shows that it also serves an important ecological role as a spawning substrate for D. gahi.

  20. Central Andean crustal structure from receiver function analysis

    Science.gov (United States)

    Ryan, Jamie; Beck, Susan; Zandt, George; Wagner, Lara; Minaya, Estela; Tavera, Hernado

    2016-07-01

    The Central Andean Plateau (15°-27°S) is a high plateau in excess of 3 km elevation, associated with thickened crust along the western edge of the South America plate, in the convergent margin between the subducting Nazca plate and the Brazilian craton. We have calculated receiver functions using seismic data from a recent portable deployment of broadband seismometers in the Bolivian orocline (12°-21°S) region and combined them with waveforms from 38 other stations in the region to investigate crustal thickness and crust and mantle structures. Results from the receiver functions provide a more detailed map of crustal thickness than previously existed, and highlight mid-crustal features that match well with prior studies. The active volcanic arc and Altiplano have thick crust with Moho depths increasing from the central Altiplano (65 km) to the northern Altiplano (75 km). The Eastern Cordillera shows large along strike variations in crustal thickness. Along a densely sampled SW-NE profile through the Bolivian orocline there is a small region of thin crust beneath the high peaks of the Cordillera Real where the average elevations are near 4 km, and the Moho depth varies from 55 to 60 km, implying the crust is undercompensated by ~ 5 km. In comparison, a broader region of high elevations in the Eastern Cordillera to the southeast near ~ 20°S has a deeper Moho at ~ 65-70 km and appears close to isostatic equilibrium at the Moho. Assuming the modern-day pattern of high precipitation on the flanks of the Andean plateau has existed since the late Miocene, we suggest that climate induced exhumation can explain some of the variations in present day crustal structure across the Bolivian orocline. We also suggest that south of the orocline at ~ 20°S, the thicker and isostatically compensated crust is due to the absence of erosional exhumation and the occurrence of lithospheric delamination.

  1. Landscape evolution within a retreating volcanic arc, Costa Rica, Central America

    Science.gov (United States)

    Marshall, Jeffrey S.; Idleman, Bruce D.; Gardner, Thomas W.; Fisher, Donald M.

    2003-05-01

    Subduction of hotspot-thickened seafloor profoundly affects convergent margin tectonics, strongly affecting upper plate structure, volcanism, and landscape evolution. In southern Central America, low-angle subduction of the Cocos Ridge and seamount domain largely controls landscape evolution in the volcanic arc. Field mapping, stratigraphic correlation, and 40Ar/39Ar geochronology for late Cenozoic volcanic rocks of central Costa Rica provide new insights into the geomorphic response of volcanic arc landscapes to changes in subduction parameters (slab thickness, roughness, dip). Late Neogene volcanism was focused primarily along the now-extinct Cordillera de Aguacate. Quaternary migration of the magmatic front shifted volcanism northeastward to the Caribbean slope, creating a new topographic divide and forming the Valle Central basin. Stream capture across the paleo Aguacate divide led to drainage reversal toward the Pacific slope and deep incision of reorganized fluvial networks. Pleistocene caldera activity generated silicic ash flows that buried the Valle Central and descended the Tárcoles gorge to the Orotina debris fan at the coast. Growth of the modern Cordillera Central accentuated relief along the new divide, establishing the Valle Central as a Pacific slope drainage basin. Arc migration, relocation of the Pacific-Caribbean drainage divide, and formation of the Valle Central basin resulted from slab shallowing as irregular, hotspot-thickened crust entered the subduction zone. The geomorphic evolution of volcanic arc landscapes is thus highly sensitive to changes in subducting plate character.

  2. Recent trends in annual snowline variations in the northern wet outer tropics: case studies from southern Cordillera Blanca, Peru

    Science.gov (United States)

    Veettil, Bijeesh Kozhikkodan; Wang, Shanshan; Bremer, Ulisses Franz; de Souza, Sergio Florêncio; Simões, Jefferson Cardia

    2016-03-01

    This paper describes the changes in the annual maximum snowlines of a selected set of mountain glaciers at the southern end of the Cordillera Blanca between 1984 and 2015 using satellite images. Furthermore, we analysed the existing glacier records in the Cordillera Blanca since the last glacial maximum to understand the evolution of glaciers in this region over a few centuries. There was a rise in the snowline altitude of glaciers in this region since the late 1990s with a few small glacier advances. Historical to the present El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) records were also analysed to understand whether there was a teleconnection between the glacier fluctuations in the region and the phase changes of ENSO and PDO. We also assessed the variations in three important climatic parameters that influence the glacier retreat—temperature, precipitation, and relative humidity—over a few decades. We calculated the anomalies as well as the seasonal changes in these variables since the mid-twentieth century. There was an increase in temperature during this period, and the decrease in precipitation was not so prominent compared with the temperature rise. There was an exceptionally higher increase in relative humidity since the early 2000s, which is relatively higher than that expected due to the observed rate of warming, and this increase in humidity is believed to be the reason behind the unprecedented rise in the snowline altitudes since the beginning of the twenty-first century.

  3. Tectonic and unroofing history of Neogene Manantiales foreland basin deposits, Cordillera Frontal (32°30'S), San Juan Province, Argentina

    Science.gov (United States)

    Pérez, Daniel J.

    2001-12-01

    The Miocene Manantiales foreland basin is located in Cordillera Frontal of San Juan, between 32°30' and 33°S. The unroofing study of the synorogenic Miocene deposits provides information about the structural evolution of Cordón de La Ramada fold-and-thrust belt. These Tertiary deposits are represented by the Chinches Formation and comprise seven members (Tc0-Tc6). They are the result of the uplift of Mesozoic sequences that crop out in La Ramada fold-and-thrust belt of the Cordillera Principal. Quaternary deposits unconformably overlying the Chinches Formation are composed of granitic and rhyolitic blocks, and represent the final uplift of the Cordón del Espinacito and a series of out-of-sequence thrusts. The unroofing studies also provide sufficient information to establish the out-of-sequence timing of the deformation at this latitude. Initial deposition of the Tertiary deposits can be dated at about 20 Ma, or early Miocene. Andesitic lavas dated in 9.2±0.3, 10.7±0.7, and 12.7±0.7 Ma unconformably overlie the structure of La Ramada fold-and-thrust belt. These facts constrain the uplift of the High Andes between 20 and 10 Ma at this latitude. The unconformity between Tertiary and Quaternary deposits suggests final uplift during Pliocene-Pleistocene times.

  4. Simultaneous batholith emplacement, terrane/continent collision, and oroclinal bending in the Blue Mountains Province, North American Cordillera

    Science.gov (United States)

    Žák, Jiří; Verner, Kryštof; Tomek, Filip; Holub, František V.; Johnson, Kenneth; Schwartz, Joshua J.

    2015-06-01

    The North American Cordillera is a classic example of accretionary orogen, consisting of multiple oceanic terranes attached to the western margin of Laurentia during the Mesozoic times. Although the Cordillera is linear for most parts, terrane boundaries are at a high angle to the overall structural grain in several segments of the orogen, which has been a matter of longstanding controversy as to how and when these orogenic curvatures formed. This paper discusses mechanisms, kinematics, and timing of initiation of one of these major curvatures, the Blue Mountains Province in northeastern Oregon. Here magmatic fabric patterns and anisotropy of magnetic susceptibility in the Wallowa batholith record three phases of progressive deformation of the host Wallowa terrane during Early Cretaceous. First is terrane-oblique ~NE-SW shortening, interpreted as recording attachment of the amalgamated oceanic and fringing terranes to the continental margin during dextral convergence at ~140 Ma. Deformation subsequently switched to pure shear-dominated ~NNE-SSW shortening associated with crustal thickening, caused by continued impingement of the amalgamated Blue Mountains superterrane into a presumed westward concave reentrant in the continental margin at ~135-128 Ma. Upon impingement (at ~126 Ma), the northern portion of the superterrane became "locked," leading to reorientation of the principal shortening direction to ~NNW-SSE while its still deformable southern portion rotated clockwise about a vertical axis. We thus propose oblique bending as the main mechanism of the orocline formation whereby horizontal compressive forces resulting from plate convergence acted at an angle to the terrane boundaries.

  5. Coupling data from U-series and 10Be CRN to evaluate soil steady-state in the Betic Cordillera

    Science.gov (United States)

    Schoonejans, Jerome; Vanacker, Veerle; Opfergelt, Sophie; Granet, Mathieu; Chabaux, François

    2015-04-01

    The regolith mantel is produced by weathering of bedrock through physical and biochemical processes. At the same time, the upper part of the regolith is eroded by gravity mass movements, water and wind erosion. Feedback's between production and erosion of soil material are important for soil development, and are essential to reach long-term steady-state in soil chemical and physical properties. Nowadays, long-term denudation rates of regolith can be quantified by using in-situ cosmogenic nuclides (CRN). If the soil thickness remains constant over sufficiently long time, soil production rates can be determined. However, the a priori assumption of long-term steady-state can be questionable in highly dynamic environments. In this study, we present analytical data from two independent isotopic techniques, in-situ cosmogenic nuclides and Uranium series disequilibrium. The disequilibrium of Uranium isotopes (238U, 234U, 230Th, 226Ra) is an alternative method that allows assessing soil formation rates through isotopic analysis of weathering products. Nine soil profiles were sampled in three different mountain ranges of the Betic Cordillera (SE Spain): Sierra Estancias, Filabres, Cabrera. All soils overly fractured mica schist and are very thin (analytical techniques is useful to further unravel the mechanisms of chemical and physical weathering in such dynamic environments. Bellin, N., Vanacker, V., and Kubik, P. W., 2014, Denudation rates and tectonic geomorphology of the Spanish Betic Cordillera: Earth and Planetary Science Letters, v. 390, p. 19-30.

  6. Genetic Structure in a Small Pelagic Fish Coincides with a Marine Protected Area: Seascape Genetics in Patagonian Fjords.

    Science.gov (United States)

    Canales-Aguirre, Cristian B; Ferrada-Fuentes, Sandra; Galleguillos, Ricardo; Hernández, Cristián E

    2016-01-01

    Marine environmental variables can play an important role in promoting population genetic differentiation in marine organisms. Although fjord ecosystems have attracted much attention due to the great oscillation of environmental variables that produce heterogeneous habitats, species inhabiting this kind of ecosystem have received less attention. In this study, we used Sprattus fuegensis, a small pelagic species that populates the inner waters of the continental shelf, channels and fjords of Chilean Patagonia and Argentina, as a model species to test whether environmental variables of fjords relate to population genetic structure. A total of 282 individuals were analyzed from Chilean Patagonia with eight microsatellite loci. Bayesian and non-Bayesian analyses were conducted to describe the genetic variability of S. fuegensis and whether it shows spatial genetic structure. Results showed two well-differentiated genetic clusters along the Chilean Patagonia distribution (i.e. inside the embayment area called TicToc, and the rest of the fjords), but no spatial isolation by distance (IBD) pattern was found with a Mantel test analysis. Temperature and nitrate were correlated to the expected heterozygosities and explained the allelic frequency variation of data in the redundancy analyses. These results suggest that the singular genetic differences found in S. fuegensis from inside TicToc Bay (East of the Corcovado Gulf) are the result of larvae retention bya combination of oceanographic mesoscale processes (i.e. the west wind drift current reaches the continental shelf exactly in this zone), and the local geographical configuration (i.e. embayment area, islands, archipelagos). We propose that these features generated an isolated area in the Patagonian fjords that promoted genetic differentiation by drift and a singular biodiversity, adding support to the existence of the largest marine protected area (MPA) of continental Chile, which is the Tic-Toc MPA. PMID:27505009

  7. Genetic Structure in a Small Pelagic Fish Coincides with a Marine Protected Area: Seascape Genetics in Patagonian Fjords.

    Science.gov (United States)

    Canales-Aguirre, Cristian B; Ferrada-Fuentes, Sandra; Galleguillos, Ricardo; Hernández, Cristián E

    2016-01-01

    Marine environmental variables can play an important role in promoting population genetic differentiation in marine organisms. Although fjord ecosystems have attracted much attention due to the great oscillation of environmental variables that produce heterogeneous habitats, species inhabiting this kind of ecosystem have received less attention. In this study, we used Sprattus fuegensis, a small pelagic species that populates the inner waters of the continental shelf, channels and fjords of Chilean Patagonia and Argentina, as a model species to test whether environmental variables of fjords relate to population genetic structure. A total of 282 individuals were analyzed from Chilean Patagonia with eight microsatellite loci. Bayesian and non-Bayesian analyses were conducted to describe the genetic variability of S. fuegensis and whether it shows spatial genetic structure. Results showed two well-differentiated genetic clusters along the Chilean Patagonia distribution (i.e. inside the embayment area called TicToc, and the rest of the fjords), but no spatial isolation by distance (IBD) pattern was found with a Mantel test analysis. Temperature and nitrate were correlated to the expected heterozygosities and explained the allelic frequency variation of data in the redundancy analyses. These results suggest that the singular genetic differences found in S. fuegensis from inside TicToc Bay (East of the Corcovado Gulf) are the result of larvae retention bya combination of oceanographic mesoscale processes (i.e. the west wind drift current reaches the continental shelf exactly in this zone), and the local geographical configuration (i.e. embayment area, islands, archipelagos). We propose that these features generated an isolated area in the Patagonian fjords that promoted genetic differentiation by drift and a singular biodiversity, adding support to the existence of the largest marine protected area (MPA) of continental Chile, which is the Tic-Toc MPA.

  8. Tectonic evolution of the North Patagonian Andes (41°-44° S) through recognition of syntectonic strata

    Science.gov (United States)

    Echaurren, A.; Folguera, A.; Gianni, G.; Orts, D.; Tassara, A.; Encinas, A.; Giménez, M.; Valencia, V.

    2016-05-01

    The North Patagonian fold-thrust belt (41°-44° S) is characterized by a low topography, reduced crustal thickness and a broad lateral development determined by a broken foreland system in the retroarc zone. This particular structural system has not been fully addressed in terms of the age and mechanisms that built this orogenic segment. Here, new field and seismic evidence of syntectonic strata constrain the timing of the main deformational stages, evaluating the prevailing crustal regime for the different mountain domains through time. Growth strata and progressive unconformities, controlled by extensional or compressive structures, were recognized in volcanic and sedimentary rocks from the cordilleran to the extra-Andean domain. These data were used to construct a balanced cross section, whose deep structure was investigated through a thermomechanical model that characterizes the upper plate rheology. Our results indicate two main compressive stages, interrupted by an extensional relaxation period. The first contractional stage in the mid-Cretaceous inverted Jurassic-Lower Cretaceous half graben systems, reactivating the western Cañadón Asfalto rift border ~ 500 km away from the trench, at a time of arc foreland expansion. For this stage, available thermochronological data reveal forearc cooling episodes, and global tectonic reconstructions indicate mid-ocean ridge collisions against the western edge of an upper plate with rapid trenchward displacement. Widespread synextensional volcanism is recognized throughout the Paleogene during plate reorganization; retroarc Paleocene--Eocene flare up activity is interpreted as product of a slab rollback, and fore-to-retroarc Oligocene slab/asthenospheric derived products as an expression of enhanced extension. The second stage of mountain growth occurred in Miocene time associated with Nazca Plate subduction, reaching nearly the same amplitude than the first compressive stage. Extensional weakening of the upper plate

  9. Genetic Structure in a Small Pelagic Fish Coincides with a Marine Protected Area: Seascape Genetics in Patagonian Fjords

    Science.gov (United States)

    Ferrada-Fuentes, Sandra; Galleguillos, Ricardo; Hernández, Cristián E.

    2016-01-01

    Marine environmental variables can play an important role in promoting population genetic differentiation in marine organisms. Although fjord ecosystems have attracted much attention due to the great oscillation of environmental variables that produce heterogeneous habitats, species inhabiting this kind of ecosystem have received less attention. In this study, we used Sprattus fuegensis, a small pelagic species that populates the inner waters of the continental shelf, channels and fjords of Chilean Patagonia and Argentina, as a model species to test whether environmental variables of fjords relate to population genetic structure. A total of 282 individuals were analyzed from Chilean Patagonia with eight microsatellite loci. Bayesian and non-Bayesian analyses were conducted to describe the genetic variability of S. fuegensis and whether it shows spatial genetic structure. Results showed two well-differentiated genetic clusters along the Chilean Patagonia distribution (i.e. inside the embayment area called TicToc, and the rest of the fjords), but no spatial isolation by distance (IBD) pattern was found with a Mantel test analysis. Temperature and nitrate were correlated to the expected heterozygosities and explained the allelic frequency variation of data in the redundancy analyses. These results suggest that the singular genetic differences found in S. fuegensis from inside TicToc Bay (East of the Corcovado Gulf) are the result of larvae retention bya combination of oceanographic mesoscale processes (i.e. the west wind drift current reaches the continental shelf exactly in this zone), and the local geographical configuration (i.e. embayment area, islands, archipelagos). We propose that these features generated an isolated area in the Patagonian fjords that promoted genetic differentiation by drift and a singular biodiversity, adding support to the existence of the largest marine protected area (MPA) of continental Chile, which is the Tic-Toc MPA. PMID:27505009

  10. Influence of oceanographic features on the spatial and seasonal patterns of mesozooplankton in the southern Patagonian shelf (Argentina, SW Atlantic)

    Science.gov (United States)

    Sabatini, M. E.; Reta, R.; Lutz, V. A.; Segura, V.; Daponte, C.

    2016-05-01

    Surveys conducted during spring, summer and late winter in 2005-2006 over the southern Patagonian shelf have allowed the seasonal distribution of mesozooplankton communities in relation to water masses and circulation to be investigated. In this system, most of the shelf is dominated by a distinct low salinity plume that is related to the runoff from the Magellan Strait (MSW), while the outer shelf is highly influenced by the cold and salty Subantarctic water (SAW) of the boundary Malvinas Current. Separating these two, the Subantarctic Shelf water mass (SASW) extends over the middle shelf. Correspondingly, the structure of the MSW and SAW mesozooplankton communities was found to be clearly different, while the former and the SASW assemblages were barely separable. This relatively fresh water mass is actually a variant of Subantarctic water that enters into the region from the south and the shelf-break, and hence its mesozooplankton community was not significantly different from that of the SAW water mass. Dissimilar species abundance, in turn associated with different life histories and population development, was more important than species composition in defining the assemblages. Total mesozooplankton abundance increased about 2.5-fold from the beginning of spring to late summer, and then decreased at least two orders of magnitude in winter. Across all seasons copepods represented > 70-80% of total mesozooplankton over most of the shelf. Copepod species best represented through all seasons, in terms of both relative abundance and occurrence, were Drepanopus forcipatus and Oithona helgolandica. Although seasonal differences in abundance were striking, the spatial distribution of mesozooplankton was largely similar across seasons, with relatively higher concentrations occurring mainly in Grande Bay and surroundings. The well defined spatial patterns of mesozooplankton that appear from our results in conjunction with the southward wide extension of the shelf and

  11. Transverse Zones in the Eastern Cordillera (Colombia): An example in the Zipaquira Anticline

    Science.gov (United States)

    Garcia Delgado, H. S.; Jimenez, G.

    2014-12-01

    model for the Eastern Cordillera. Our goal is related the ZA and the transverse zones using Anisotropy of Magnetic Susceptibility (AMS) and paleomagnetism to unraveal the kinematic evolution of the anticline and the temporal relationship between the transverse zones and the ZA.

  12. ZONIFICACIÓN AGROECOLÓGICA DE LA CORDILLERA DE GUANIGUANICO

    Directory of Open Access Journals (Sweden)

    F. Soto

    2007-01-01

    Full Text Available El desarrollo de un país necesita de una planificación de la actividad agrícola, que si se quiere que sea económicamente rentable, debe ceñirse a la realidad ecológica de las áreas de producción. En este sentido, la zonificación agroecológica es una de las principales herramientas para disminuir los riesgos a los que está sometida la agricultura. Teniendo en cuenta estos elementos, se procedió a realizar la zonificación agroecológica de la cordillera de Guaniguanico. Se tuvo información de ocho estaciones meteorológicas y 62 pluviómetros de la red del Instituto Nacional de Recursos Hidráulicos, con lo cual se llevó a cabo la zonificación climática; se estudiaron 371 000 ha, en las que se obtuvo información de más de 500 perfiles con planillas completas, lo que permitió caracterizar los suelos desde los puntos de vista físico, químico y mineralógico. Se utilizaron diferentes Sistemas de Información Geográfica (SIG, para establecer las relaciones entre los distintos parámetros estudiados y llegar a la zonificación agroecológica. A partir del análisis de la información sobre el comportamiento de los cultivos, se establecieron las bases para la zonificación, tomándose como elementos fundamentales del clima la temperatura y la lluvia; ambos se combinaron y se definieron los potenciales de rendimiento para cada condición. El otro elemento discriminante fue el suelo; en primer lugar, se tuvieron en cuenta los tipos de suelo y su aptitud para el cultivo y posteriormente se consideró la profundidad efectiva.

  13. Timing and paleoclimatic significance of Holocene glacier fluctuations in the Cordillera Vilcabamba of southern Peru

    Science.gov (United States)

    Licciardi, J. M.; Taggart, J. R.; Schaefer, J. M.; Lund, D. C.

    2009-12-01

    Past fluctuations in climatically sensitive tropical glaciers provide important insight into regional paleoclimatic trends and forcings, but well-dated chronologies are scarce, particularly during the Holocene. We have established precise cosmogenic 10Be surface exposure ages of moraine sequences in the Cordillera Vilcabamba (13°20’S latitude), located in the outer tropics of southern Peru. Results indicate the dominance of two major glacial culminations and associated climatic shifts in the Vilcabamba, including an early Holocene glacial interval and a somewhat less extensive glaciation late in the ‘Little Ice Age’ (LIA) period. Lichenometric measurements on the youngest moraines support the 10Be ages, but uncertainties in the lichen ages arise from the lack of a local lichen growth curve. The Peruvian glacier chronologies differ from a recently-developed New Zealand record but are broadly correlative with well-dated glacial records in Europe, suggesting climate linkages between the tropics and the North Atlantic region. For the latest Holocene, our leading hypothesis is that climate forcings involving southward migration of the Atlantic Intertropical Convergence Zone can explain concurrent glaciations in tropical South America and northern high latitudes, but the influence of other climate drivers such as the El Niño/Southern Oscillation may have also played a role. Estimated differences between equilibrium-line altitudes (ELAs) on modern glaciers and those inferred for expanded latest Holocene glaciers reveal an ELA rise of 165-200 m since the LIA, suggesting that temperatures 1.1-1.3°C cooler than present could have sustained glaciers at their LIA maximum positions if temperature was the only control, and thus providing an upper bound on temperature depression during the LIA. However, further work is required to constrain the likely role of precipitation changes. These new Peruvian glacier chronologies and ELA reconstructions complement ice core and

  14. Pollen-based 17-kyr forest dynamics and climate change from the Western Cordillera of Colombia: no-analogue associations and temporarely lost biomes

    NARCIS (Netherlands)

    C.A. Velásquez-R.; H. Hooghiemstra

    2013-01-01

    A 17 kyr long pollen record from the unexplored Western Cordillera of Colombia (Páramo de Frontino; 3460 m elevation) shows vegetation change and inferred climate dynamics at ~ 125 yr resolution. The cold and wet Lateglacial showed well-defined stadials and interstadials. At the transition to the Ho

  15. Glacier Changes in the Cordillera Blanca, Peru, Derived From SPOT5 Imagery, GIS and Field- Based Measurements

    Science.gov (United States)

    Racoviteanu, A.; Arnaud, Y.; Williams, M. W.; Singh Khalsa, S.

    2007-12-01

    There is urgency in deriving an extensive dataset for deriving glacier changes within the Cordillera Blanca, Peru, in a cost-effective and timely manner. Rapid glacial retreat during the last decades in this area poses a threat for water resources, hydroelectric power and local traditions. While there is some information on decadal changes in glacier extents, there still remains a paucity of mass balance measurements and glacier parameters such as hypsometry, size distribution and termini elevations. Here we investigate decadal changes in glacier parameters for Cordillera Blanca of Peru using data from Système Probatoire d'Observation de la Terre (SPOT) sensor, an old glacier inventory from 1970 aerial photography, field-based mass balance measurements and meteorological observations. Here we focus on: constructing a geospatial glacier inventory from 2003 SPOT scenes; mass balance estimations using remote sensing and field data; frequency distribution of glacier area; changes in termini elevations; hypsometry changes over time; glacier topography (slope, aspect, length/width ratio); AAR vs. mass balance for Artesonraju and Yanamarey benchmark glaciers; precipitation and temperature trends in the region. Over the last 25 years, mean temperatures increases of 0.09 deg.C/yr were greater at lower elevation than the 0.01 deg.C/yr at higher elevations, with little change in precipitation. Comparison of the new SPOT-based glacier inventory with the 1970 inventory shows that glaciers in Cordillera Blanca retreated at a rate of 0.6% per year over the last three decades, with no significant differences in the rate of area loss between E and W side. At lower elevations there is an upward shift of glacier termini along with a decrease in glacier area. Small glaciers are losing more area than large glaciers. Based on the relationship between specific mass balance (bn) and accumulation area ratio (AAR) for the two benchmark glaciers, we predicted a steady-state equilibrium line

  16. Tectonic and lithological controls on denudation rates in the central Bolivian Andes

    Science.gov (United States)

    Kober, F.; Zeilinger, G.; Hippe, K.; Marc, O.; Lendzioch, T.; Grischott, R.; Christl, M.; Kubik, P. W.; Zola, R.

    2015-08-01

    The topographic signature of a mountain belt depends on the interplay of tectonic, climatic and erosional processes, whose relative importance changes over times, while quantifying these processes and their rates at specific times remains a challenge. The eastern Andes of central Bolivia offer a natural laboratory in which such interplay has been debated. Here, we investigate the Rio Grande catchment which crosses orthogonally the eastern Andes orogen from the Eastern Cordillera into the Subandean Zone, exhibiting a catchment relief of up to 5000 m. Despite an enhanced tectonic activity in the Subandes, local relief, mean and modal slopes and channel steepness indices are largely similar compared to the Eastern Cordillera and the intervening Interandean Zone. Nevertheless, a dataset of 57 new cosmogenic 10Be and 26Al catchment wide denudation rates from the Rio Grande catchment reveals up to one order of magnitude higher denudation rates in the Subandean Zone (mean 0.8 mm/yr) compared to the upstream physiographic regions. We infer that tectonic activity in the thrusting dominated Subandean belt causes higher denudation rates based on cumulative rock uplift investigations and due to the absence of a pronounced climate gradient. Furthermore, the lower rock strength of the Subandean sedimentary units correlates with mean slopes similar to the ones of the Eastern Cordillera and Interandean Zone, highlighting the fact, that lithology and rock strength can control high denudation rates at low slopes. Low denudation rates measured at the outlet of the Rio Grande catchment (Abapo) are interpreted to be a result of a biased cosmogenic nuclide mixing that is dominated by headwater signals from the Eastern Cordillera and the Interandean zone and limited catchment sediment connectivity in the lower river reaches. Therefore, comparisons of short- (i.e., sediment yield) and millennial denudation rates require caution when postulating tectonic and/or climatic forcing without

  17. Effects of long-term grazing disturbance on the belowground storage of organic carbon in the Patagonian Monte, Argentina.

    Science.gov (United States)

    Larreguy, C; Carrera, A L; Bertiller, M B

    2014-02-15

    The objective of this study was to analyze the effect of grazing disturbance on the amount and the spatial distribution (vertical and horizontal) of root biomass and soil organic carbon (SOC) in order to evaluate whether grazing alters the belowground storage of organic carbon (C) in arid rangelands of the Patagonian Monte. We selected three representative sites (3 ha each) with low, moderate and high grazing disturbance located far, mid-distance and near the watering point, respectively, in rangelands submitted to sheep grazing for more than 100 years. We assessed the canopy structure and identified the four most frequent plant patch types at each site. We selected four replications of each patch type and extracted a soil sample (0-30 cm depth) underneath the canopy and in the middle of the nearest inter-patch bare soil area in winter and summer. We assessed the root and soil dry mass and the respective organic C concentration in each sample and then we estimated the total belowground organic C storage at each site. Total plant and perennial grass cover were lower with high than low grazing disturbance while the reverse occurred with dwarf shrub cover. High grazing disturbance led to the increase in total root biomass in the whole soil profile of patch areas and in the upper soil of inter-patch areas. SOC was higher in patch than in inter-patch areas at all sites but at both areas was reduced with high grazing disturbance. This was probably the result of the low total plant cover and the low and recalcitrant contribution of above and below-ground plant litter to soils at sites with high grazing disturbance. Accordingly, these changes did not result in variations in the total belowground organic C storage. We concluded that high grazing disturbance did not affect the total belowground organic C storage but led to changes in the spatial patterning of this organic C storage (i.e shifting from soil to roots).

  18. Patrones geográficos de diferenciación craneofacial entre poblaciones de la región central del país y otras de Argentina: aportes desde la genética del paisaje

    Directory of Open Access Journals (Sweden)

    Mariana Fabra

    2008-09-01

    Full Text Available In this study we analyze the patterns of spatial variation of a population sample from the pre-Hispanicinhabitants of the central territory of Argentina (Córdoba and San Luis provinces archaeologically known as«Sierras Centrales», and 13 other samples from different ecological and geographical regions from Argentina.Additionally, we searched for the existence of genetic barriers in the geographic landscape. The study is based on10 craniometric measurements. Results from principal component analysis reveal that the pre-Hispanic inhabitantsof the Central Mountains of Argentina were biologically more related to the Patagonian groups than to thenortheast, central western and northwestern populations. Monmonier`s algorithm reveals that the pre-Hispanicinhabitants of the Central Mountains of Argentina were biologically more related to the Patagonian groups thanto the central and northern populations. These results support our hypothesis that the peopling of the centralregion of Argentina most likely took place as a migratory wave proceeding from the northeast, and continuedsouthward to Patagonia and Tierra del Fuego.

  19. Recalibration of the yellow Rhizocarpon growth curve in the Cordillera Blanca (Peru) and implications for LIA chronology

    Science.gov (United States)

    Jomelli, V.; Grancher, D.; Brunstein, D.; Solomina, O.

    2008-01-01

    A new lichen dating method and new moraine observations enabled us to improve the chronology of glacier advances in the Cordillera Blanca (Peru) during the Little Ice Age (LIA). Our results reveal that an early LIA glacial advance occurred around AD 1330 ± 29. However, a second major glacial advance at the beginning of the 17th century overlapped the earlier stage for most glaciers. Hence, this second glacial stage, dated from AD 1630 ± 27, is considered as the LIA maximum glacial advance in the Cordillera Blanca. During the 17th-18th centuries, at least three glacial advances were recorded synchronously for the different glaciers (AD 1670 ± 24, 1730 ± 21, and 1760 ± 19). The moraines corresponding to the two first stages are close to the one in 1630 suggesting a slow recession of about 18% in the total length of the glacier. From the LIA maximum extent to the beginning of the 20th century, the 24 glaciers have retreated a distance of about 1000 m, corresponding to a reduction of 30% in their length. This rate is comparable to that observed during the 20th century. Estimates of palaeo-Equilibrium Line Altitudes show an increase in altitude of about 100 m from the LIA maximum glacial extension at the beginning of the 17th century to the beginning of the 20th century. Because long time series are not available for precipitation and temperature, this glacial retreat is difficult to explain by past climate changes. However, there is a fair correspondence between changes in glacier length and the δ18O recorded in the Quelccaya ice core at a century timescale. Our current knowledge of tropical glaciers and isotope variations leads us to suggest that this common tropical signal reflects a change from a wet LIA to the drier conditions of today. Finally, a remarkable synchronicity is observed with glacial variations in Bolivia, suggesting a common regional climatic pattern during the LIA.

  20. Coarse Grain Progradation in a Foreland basin: Application of Detrital Zircon Double Dating to Cenozoic Stratigraphy, Eastern Cordillera, Colombia.

    Science.gov (United States)

    Odoh, S.; Saylor, J. E.; Higuera-Diaz, C.; Lapen, T. J.; Copeland, P.

    2015-12-01

    Progradation of coarse clastic material into distal foreland basins has been attributed to both 1) enhanced sediment production during rapid tectonic exhumation and 2) sediment reworking during tectonic quiescence. The Floresta and Medina basins in the Eastern Cordillera record deposition of alternating coarse- and fine-grained clastic strata in medial and distal (respectively) Cenozoic foreland basins. The Medina Basin records the continued eastward progradation of the deformation front in the Neogene. We use detrital zircon U-Pb (ZPb) and (U-Th)/He (ZHe) analyses from the Paleogene Floresta Basin and the entire Cenozoic Medina Basin record to evaluate the effects of episodic thrust-belt exhumation and wide-spread deposition of coarse-grained sediments in the adjacent foreland basin. Both ZPb and ZHe systems are applied to individual grains (double dating) to constrain source area and up-section variations in exhumation rates. Changes in exhumation rate or introduction of new sediment sources are recorded as changes in lag time (ZHe age - depositional age). Analysis of 6 samples from the Floresta Basin shows a decrease in lag time during deposition of the coarse-grained middle Eocene Picacho Formation and upper Paleocene Socha Sandstone suggesting that Paleogene deposition of coarse-grained intervals in this medial location corresponds to an increase in exhumation rate. However, initial results from the Medina basin are less clear as there is evidence for Paleocene volcanic input but no clear evidence for thrust-belt related sediment until the Oligocene-early Miocene. We interpret the evidence for different sediment sources for Eocene strata in the axial Eastern Cordillera (Floresta) versus the Eastern foothills (Medina) as indicative of separation of these two regions by an emergent forebulge. Exhumation rate and granularity appear to be inversely correlated in post-Oligocene strata, though confirmation of initial interpretations awaits larger samples sizes

  1. Faults delineation and stress orientations from the microseismicity analysis of the Servita Fault System, Colombian Eastern Cordillera

    Science.gov (United States)

    Pedraza García, P.; Dimate, C.

    2014-12-01

    The Servita Fault System (SFS) is located in the eastern foothills of the Colombian Andes Eastern Cordillera. This region is a structurally complex area with high seismogenic potential. The refined analysis of the microseismicity registered by a portable seismic network allows to delineate the main active faults and to estimate the direction of the regional tectonic stress. We analyzed a high quality microearthquake data-set consisting of 890 events occurred during 2011-2012 with a local magnitude range between 0.1 and 3.2 and depths up to 40km. The refined locations of the events show a general SW-NE trend that follows the trace of the SFS. Selected focal mechanisms show predominantly right-lateral strike slip motion. Results show that seismicity to the northern sector of the SFS is distributed in two groups, one on the axial zone of the cordillera and the other on the eastern flank. Most of the microearthquakes are concentrated in the rupture zone of Quetame earthquake (2008, Mw=5.9). Alignment of hypocenters along the eastern flank and some focal mechanisms suggest a fault plane dipping to the west, which is interpreted as the Servita Fault plane. Southwards of the Rio Negro, seismicity decreases and loses continuity. This feature coincides with the trace of the WSW-ENE Rio Blanco Fault which possibly segments the Servita Fault. Southwards, seismicity is spread over a wider area and exhibits deeper hypocenters compared to the northern sector. Hypocenter distribution and focal mechanisms in this sector suggest two planes dipping to the west which we interpret as segments of the Algeciras Fault and another plane (northwards) steeply dipping to the southeast interpreted as the fault plane of the Altamira Fault.

  2. Secular Variation and Paleomagnetic Studies of Southern Patagonian Plateau Lavas, 46S to 52S, Argentina

    Science.gov (United States)

    Brown, L.; Gorring, M.; Mason, D.; Condit, C.; Lillydahl-Schroeder, H.

    2007-12-01

    Regional studies of paleosecular variation of the Earth's magnetic field can provide us with information beyond that available from one location. Southern Patagonia, Argentina (46S to 52S latitude and 68W to 72W longitude) is a place where numerous Plio-Pleistocene lava flows are available for such a study. Volcanic activity in this area is related to back arc volcanism due to slab window activity as the South Chile Ridge is subducted beneath western South America, producing Neogene volcanic centers capping Mesozoic basement extending far to the east of the active plate boundary. Published studies on young lavas from both the northern (Meseta del Lago Buenos Aires, Brown et al, 2004) and southern (Pali Aike Volcanic Field, Mejia et al, 2004) portions provide stable paleomagnetic data on nearly 70 lava flows. Paleosecular variation values for the two studies differ, with 17.1 degrees obtained from the Pali Aike field and 20.0 degrees from the Lago Buenos Aires field. Recent fieldwork in the plateau lavas between these two locations has provided some 80 new sites allowing us to better investigate secular variation and the time-averaged field over this entire region during the past 5 myr. Rock magnetic studies on selected new samples (isothermal remanent magnetization and hysteresis measurements) as well as optical observations indicate low titanium magnetite as the primary carrier of remanence. Hysteresis properties range from 0.1 to 0.4 for Mr/Ms and 1.4 to 3.0 for Hcr/Hc indicating psuedo-single domain behavior. Mean destructive fields for AF demagnetization average 40 to 60 mT. Thirty-three new sites, mostly from Gran Meseta Central (48°S), yield a mean direction of inclination -61.8, declination of 356.6 with an alpha-95 of 5.7 degrees. These directions, with additional sites recently collected from Meseta de la Muerte south to Rio Santa Cruz, will allow us to further investigate paleosecular variation over this wide region.

  3. Changes in vegetation and drainage density as controlling factors in the episodicity of Quaternary sediment flux: southwestern United States and Bolivian Eastern Cordillera

    Science.gov (United States)

    Barnes, J.; Pelletier, J. D.

    2001-12-01

    Piedmont geomorphic surfaces in the southwestern U.S. primarily represent cut-and-fill cycles resulting from variations in sediment supply from adjacent mountain catchments. Although sparse, precise age control supports the hypothesis that sediment supply in the southwestern U.S. can increase by an order of magnitude during Quaternary humid-to-arid transitions recognized in high-resolution paleoclimatic proxies. As an example, this episodicity is quantified with a time series of sediment flux for the central Gila Mountains, southwestern Arizona, where paleosurfaces outcrop in the modern channel bank, permitting an estimate of deposit volume in conjunction with high-resolution photogrammetric DEMs. Age control is provided by a new method of surface exposure dating based on 3D hillslope diffusion adjacent to gullies penetrating the surface. We propose that episodes of piedmont alluviation result from an increase in drainage density resulting from climatically-induced vegetative successions from mature woodland vegetation to desert shrubs that excavate large amounts of hillslope colluvium stored during the previous humid interval. Analogous vegetative shifts occur in the Bolivian Eastern Cordillera (EC). Field observations and analyses of topographic maps and LANDSAT images suggest that the longitudinal profiles of the major rivers of the EC are dominated by an order-of-magnitude increase in Plio-Quaternary hillslope erosion in the elevation zone between approximately 2.5 and 3.5 kilometers above sea level corresponding to glacial-interglacial vegetational successions from Andean forest (glacial) to Paramo grasslands (interglacial). These vegetation changes resulted in rapid fluctuations in drainage density responsible for a large increase in transport rates that alluviated major valleys and enhanced bedrock incision rates downstream. Areas above and below this elevation have perennial grassland and forest, respectively, whose long-term vegetational stability has

  4. Paleomagnetism and magnetic fabric of the Eastern Cordillera of Colombia: Evidence for oblique convergence and non-rotational reactivation of a Mesozoic intra-continental rift

    Science.gov (United States)

    Jiménez Díaz, G.; Speranza, F.; Faccenna, C.; Bayona, G.; Mora, A.

    2012-12-01

    The Eastern Cordillera of Colombia (EC) is a double-verging mountain system inverting a Mesozoic rift, and bounded by major reverse faults that locally involve crystalline and metamorphic Precambrian-Lower Paleozoic basement rocks, as well as Upper Paleozoic-Cenozoic sedimentary and volcanic sequences. In map view the EC is a curved mountain belt with a regional structural strike that ranges from NNE in the southern part to NNW in the northern part. The origin of its curvature has not been studied or discussed so far. We report on an extensive paleomagnetic and anisotropy of magnetic susceptibility (AMS) investigation of the EC, in order to address to test its non-rotational vs. oroclinal nature. Fifty-eight sites were gathered from Cretaceous to Miocene marine and continental strata, both from the southern and northern parts of the EC; additionally, we examined the southern Maracaibo plate, at the junction between the Santander Massif and the Merida Andes of Colombia (Cucuta zone). Twenty-three sites reveal no rotation of the EC range with respect to stable South America. In contrast, a 35°±9° clockwise rotation is documented in four post-Miocene magnetically overprinted sites from the Cucuta zone. Magnetic lineations from AMS analysis do not trend parallel to the chain, but are oblique to the main strike of the orogenic belt. By also considering GPS evidence of a ~1 cm/yr ENE displacement of central-western Colombia accommodated by the EC, we suggest that the late Miocene-recent deformation occurred by a ENE oblique convergence reactivating a NNE rift zone. Our data show that the EC is a non-rotational chain, and that the locations of the Mesozoic rift and the mountain chain roughly correspond. One possible solution is that the oblique shortening is partitioned in pure dip-slip shear characterizing thick-skinned frontal thrust sheets (well-known along both chain fronts), and by range-parallel right-lateral strike-slip fault(s), which have not been identified

  5. Detrital zircon SHRIMP U-Pb age study of the Cordillera Darwin Metamorphic Complex of Tierra del Fuego : sedimentary sources and implications for the evolution of the Pacific margin of Gondwana

    OpenAIRE

    Herve, F.; Fanning, C.M.; Pankhurst, R.J.; Mpodozis, C.; Klepeis, K.; Calderon, M.; S. N. Thomson

    2010-01-01

    The Cordillera Darwin Metamorphic Complex in the southernmost Andes includes a basement of probable Palaeozoic age, a mid-Jurassic and younger volcano-sedimentary cover, and a suite of Jurassic granites, all of which were jointly metamorphosed during the Cretaceous. Detrital zircon ages presented here show that some of the amphibolite-facies metamorphic rocks previously mapped as basement have a Jurassic protolith. Overall the detrital zircon age patterns for samples of the Cordillera Darwin ...

  6. Fajas oblicuas de deformación neotectónica en Precordillera y Cordillera Frontal (31° 30´ - 33° 30´ LS: controles paleotectónicos

    Directory of Open Access Journals (Sweden)

    J.M. Cortés

    2006-12-01

    Full Text Available La Precordillera Sur y las Cerrilladas Pedemontanas de Mendoza, son dos unidades morfotectónicas principales en la vertiente oriental de los Andes centrales, a los 31º30' - 33º30' de latitud sur. Allí, dos cinturones de deformación transpresiva y orientación noroeste, denominados fajas Barreal-Las Peñas y Río Mendoza-Tupungato, se desarrollaron como consecuencia de la gradual somerización de la placa de Nazca en los últimos 20 Ma. Su orientación y compleja geometría estructural resulta de la interferencia de la deformación andina tardío-cenozoica con la estructura de orientación noroeste del rift triásico de la cuenca Cuyana y antiguas zonas de sutura colisional de edad paleozoica. Este trabajo demuestra que los rasgos paleotectónicos del substrato triásico-paleozoico de la Precordillera Sur y del margen oriental de la Cordillera Frontal controlan la configuración morfotectónica y la distribución y reactivación de gran parte de la estructura neotectónica del margen andino a estas latitudes.

  7. Population dynamics of Philureter trigoniopsis (Monogenea: Ancyrocephalinae) from urinary organs of Galaxias maculatus (Osmeriformes: Galaxiidae) in a cold temperate Andean Patagonian lake (Argentina).

    Science.gov (United States)

    Viozzi, Gustavo P; Semenas, Liliana G; Gutiérrez, Pablo

    2005-12-01

    Philureter trigoniopsis parasitizes the ureters and urinary bladder of Galaxias maculatus in Patagonian Andean lakes. To investigate factors associated with variation in the prevalence and intensity of this monogenean, fish were sampled periodically over 2 yr in Lake Gutiérrez. Prevalence and mean intensity are higher in smaller fishes than in larger ones. A seasonal pattern was observed, with peak recruitment and peak mean intensity occurring in early spring (September), followed by lows in late summer (January-February). Galaxias maculatus length classes are spatially segregated due to seasonal migrations, so the annual infection cycle is characterized by higher prevalence and intensity from late winter to early summer in the smaller fish from the deep zone of the lake. PMID:16539018

  8. Paleomagnetism of Permian and Triassic rock, central Chilean Andes

    Science.gov (United States)

    Forsythe, Randall D.; Kent, Dennis V.; Mpodozis, Constantino; Davidson, John

    The first paleomagnetic data from Permian and Triassic formations west of the Andean divide are presented. Four formations of Permian or Triassic age in the central Chilean Andes have been investigated: two are located in the coastal ranges, and two are in the main cordillera. Of the formations in the main cordillera (Pastos Blancos and Matahuaico formations), only the Pastos Blancos Formation has yielded characteristic directions. While a fold test is absent, magnetizations are most likely secondary and yield pre-tilt corrected concordant inclinations, but yield declinations discordant 30° clockwise in comparison to the South American apparent polar wander path. Both formations from the coastal ranges (Cifuncho and Pichidangui formations) yielded stable directions. Postfolding magnetizations in the Cifuncho Formation also show declinations discordant 30° clockwise and concordant inclinations. The Pichidangui Formation has two stable components: one of postfolding age is concordant to apparent polar wander path data, and one of probable prefolding (Late Triassic) age is concordant in declination, but discordant in inclination. Further work is needed to better define the prefolding magnetizations in the Pichidangui Formation, but at present these preliminary results are the first paleomagnetic signs of displaced terranes along the Pacific margin of Chile. If correct, the results suggest that the Pichidangui Formation was some 15° of latitude farther south during the Late Triassic and had likely moved northward to its present latitudinal position with respect to cratonic South America by Middle to Late Jurassic.

  9. Deformation, deposition, and surface uplift in the hinterland of the Central Andes, Bolivia

    Science.gov (United States)

    Leier, A.; McQuarrie, N.; Garzione, C. N.; Eiler, J. M.

    2011-12-01

    Paleoelevation histories from mountain belts like the Central Andes of Bolivia provide important constraints on the timing and geodynamic mechanisms associated with surface uplift. New stable isotope data from paleosol carbonate nodules in the Altiplano and Eastern Cordillera of the Central Andes of Bolivia indicate a previously undocumented episode of surface uplift occurred in the region between ca. 24 and 17 Ma. Oxygen isotope and clumped-isotope thermometry values from paleosol carbonate in strata >24 Ma suggest paleoelevations as low as sea-level. Paleosol carbonate in strata ca. 17 Ma have oxygen isotope and clumped-isotope thermometry values, which using modern lapse rates, indicate an increase in elevation of approximately 3 km. Relatively undeformed Oligocene and Miocene strata overlap faulted Paleozoic rocks of the Bolivian Eastern Cordillera, indicating deposition and surface uplift post-dated and was decoupled from upper crustal deformation. Together, geological data from the area record an initial period of deformation and exhumation, a subsequent period of sediment deposition and overlap, and then an episode of surface uplift that was not accompanied by upper crustal deformation. We propose accommodation for the Oligocene-Miocene strata was associated with mantle and lowermost crustal processes, and the subsequent increase in surface elevation was an isostatic response to removal of dense material through delamination or drip. Combined with existing data sets in the Central Andes, these new data suggest multiple, regionally-variable, and diachronous periods of surface uplift occurred within the Central Andes during the Cenozoic Era.

  10. Late cenozoic tectonic and geomorphic evolution of the Patagonian Andes between 42oS and 52oS, southern Chile assessed using fission-track thermochronology

    International Nuclear Information System (INIS)

    Fission-track (FT) analysis has been applied in the Patagonian Andes of southern Chile to assess the late Cenozoic geomorphic and tectonic response of the overriding plate to subduction of the Chile rise active oceanic spreading centre (Thomson et al., 2001). The timing and nature of tectonic uplift and denudation along the southern parts of the major transpression intra-arc Liquine-Ofqui fault (LOF) system have also been investigated (Thomson, 2001, submitted). Results from 130 FT ages (72 zircon and 58 apatite ages) and 39 apatite track length measurements reveal initiation of rapid cooling and denudation at ca. 30 Ma at the western margin of southern continental South America. This was followed by a ca. 200km eastward migration of the locus of maximum denudation to the position of the present day topographic divide between ca. 30 Ma and ca. 12 to 10 Ma. East of the Andean divide less than 3 km of denudation has occurred since the Late Cretaceous. Enhanced denudation is interpreted to be the result of increased tectonic uplift driven by a large increase in convergence rates at ca. 28 to 26 Ma that triggered orographically enhanced precipitation on the west-side of the Patagonian Andes allowing increased erosion by fluvial incision and mass transport processes. The eastward migration of the locus of maximum denudation can be related to either coeval eastward migration of the retro-arc deformation front, the effects of subduction erosion in the overriding plate at the Peru-Chile trench or shallowing of the angle of subduction. Away from the influence of the LOF the process of spreading centre subduction and collision itself coincides with an overall slow-down in denudation rates in the overriding plate most likely caused by a major reduction in the main tectonic force driving tectonic uplift in the upper plate to subduction. In contrast to the Andes south of ca. 46oS, increased cooling and denudation related to transpression induced rock uplift and erosion along

  11. Current deformation of the Betic Cordillera from a new GPS observation of the southern sector of the IBERIA95 Zero-Order Geodetic Network

    Science.gov (United States)

    Gil, Antonio J.; Galindo, Jesús; Alfaro, Pedro; de Lacy, María. Clara; Jesús Borque, María.; Franco, Juan A. Armenteros (1), Oscar; Ruano, Patricia; García Tortosa, Francisco Juan; López Garrido, Angel Carlos; Pedrera, Antonio

    2010-05-01

    The Betic Cordillera, located at the convergent plate boundary between Africa and Eurasia, is subjected to an average NNW-SSE compression and an associated orthogonal extension. In order to quantify this deformation a GPS campaign in the Southern Sector of IBERIA95 Zero-Order Geodetic Network was done in December 2008. This network was observed in 1995 by the Spanish National Geographical Institute (IGNE) and the Portuguese Institute of Cartography and Cadastre (IPCC) for the establishment of a Three-dimensional Geodetic Network in Spain and Portugal. The comparison of results in 1995 and 2009 provides one of the first geodetic results of the short-term deformation in the Betic Cordillera.

  12. Flujos de detritos recientes en la cordillera frontal de Mendoza: Un ejemplo de riesgo natural en la ruta 7 Recent debris flows in the Frontal Cordillera of Mendoza: an example of natural risk on the Road 7

    Directory of Open Access Journals (Sweden)

    Emmanuel Wick

    2010-06-01

    Full Text Available Se expone un estudio sobre los flujos de detritos ocurridos en enero de 2005, en el km 1.118,5 de la ruta nacional 7 en la provincia de Mendoza. La zona se ubica en la Cordillera Frontal, próxima al límite con la Precordillera. Se realizó un mapa geomorfológico detallado, sobre la base de una imagen Quickbird del año 2006. Además, se hicieron cálculos de volúmenes, velocidades y caudales, con mediciones en el campo y con ayuda de un sistema de información geográfico (SIG. El estudio de la geomorfología permitió proponer tres escenarios para el caso de un nuevo evento, a partir de los cuáles se creó un mapa de susceptibilidad a los flujos de detritos para el tramo de ruta analizado. Finalmente, se proponen medidas de protección y de mitigación ante la posibilidad de recurrencia de estos eventos en el sector.In this paper is presented a study dealing with the debris flows that reached the national road 7 in January 2005, in the km 1,118.5, Mendoza province. The area is located in the Frontal Cordillera near the limit of the Precordillera. A detailed geomorphologic map has been realized for this study using a Quickbird satellite imagery of the year 2006. Various calculations of volumes, velocities and peak discharges have been performed with the field data and using a geographic information system (GIS. The geomorphologic survey has permitted to propose three propagation scenarios in case of a new event. These allowed creating a map of debris flows susceptibility for the stretch of the road that has been studied. Finally, it has been proposed protection and mitigation measures, based on the results of the study, to protect the road from a new event.

  13. A cosmogenic 10Be chronology for the local last glacial maximum and termination in the Cordillera Oriental, southern Peruvian Andes: Implications for the tropical role in global climate

    Science.gov (United States)

    Bromley, Gordon R. M.; Schaefer, Joerg M.; Hall, Brenda L.; Rademaker, Kurt M.; Putnam, Aaron E.; Todd, Claire E.; Hegland, Matthew; Winckler, Gisela; Jackson, Margaret S.; Strand, Peter D.

    2016-09-01

    Resolving patterns of tropical climate variability during and since the last glacial maximum (LGM) is fundamental to assessing the role of the tropics in global change, both on ice-age and sub-millennial timescales. Here, we present a10Be moraine chronology from the Cordillera Carabaya (14.3°S), a sub-range of the Cordillera Oriental in southern Peru, covering the LGM and the first half of the last glacial termination. Additionally, we recalculate existing 10Be ages using a new tropical high-altitude production rate in order to put our record into broader spatial context. Our results indicate that glaciers deposited a series of moraines during marine isotope stage 2, broadly synchronous with global glacier maxima, but that maximum glacier extent may have occurred prior to stage 2. Thereafter, atmospheric warming drove widespread deglaciation of the Cordillera Carabaya. A subsequent glacier resurgence culminated at ∼16,100 yrs, followed by a second period of glacier recession. Together, the observed deglaciation corresponds to Heinrich Stadial 1 (HS1: ∼18,000-14,600 yrs), during which pluvial lakes on the adjacent Peruvian-Bolivian altiplano rose to their highest levels of the late Pleistocene as a consequence of southward displacement of the inter-tropical convergence zone and intensification of the South American summer monsoon. Deglaciation in the Cordillera Carabaya also coincided with the retreat of higher-latitude mountain glaciers in the Southern Hemisphere. Our findings suggest that HS1 was characterised by atmospheric warming and indicate that deglaciation of the southern Peruvian Andes was driven by rising temperatures, despite increased precipitation. Recalculated 10Be data from other tropical Andean sites support this model. Finally, we suggest that the broadly uniform response during the LGM and termination of the glaciers examined here involved equatorial Pacific sea-surface temperature anomalies and propose a framework for testing the viability

  14. La sección Messiniense - Plioceno de Crevillente (Cordillera Bética oriental): expresión de la crisis de salinidad del Mediterráneo

    OpenAIRE

    Soria, Jesús M.; Yébenes, Alfonso; Caracuel, Jesús Esteban

    2001-01-01

    A composite stratigraphic section in Crevillente (eastern Betic Cordillera) is studied. It represent a complete stratigraphical and paleontological record of the Messinian and Lower Pliocene. Two discontinuity surfaces related to the Mediterranean salinity crisis are analysed: a intra-messinian surface which coincides with a sea-level fall leading to the emergence of this area far from marine influences; and an uppermost Messinian unconformity, with strong erosionaI character, overlied by mar...

  15. The Messinian–early Pliocene stratigraphic record in the southern Bajo Segura Basin (Betic Cordillera, Spain): Implications for the Mediterranean salinity crisis

    OpenAIRE

    Soria, J. M.; Departamento Ciencias de la Tierra y del Medio Ambiente, Universidad de Alicante, Apdo. 99, San Vicente del Raspeig, 03080 Alicante; Caracuel, J. E.; Departamento de Ciencias de la Tierra y del Medio Ambiente, Universidad de Alicante, Apdo. Correos 99, 03080 Alicante, Spain; Corbí, H.; Departamento de Ciencias de la Tierra y del Medio Ambiente, Universidad de Alicante, Apdo. Correos 99, 03080 Alicante, Spain; Dinarès-Turell, J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Lancis, C.; Departamento de Ciencias de la Tierra y del Medio Ambiente, Universidad de Alicante, Apdo. Correos 99, 03080 Alicante, Spain; Tent-Manclús, J. E.; Departamento de Ciencias de la Tierra y del Medio Ambiente, Universidad de Alicante, Apdo. Correos 99, 03080 Alicante, Spain; Viseras, C.; Departamento de Estratigrafía y Paleontología, Universidad de Granada, Campus de Fuente Nueva s/n, 18071 Granada, Spain; Yébenes, A.; Departamento de Ciencias de la Tierra y del Medio Ambiente, Universidad de Alicante, Apto. 99, 03080 San Vicente del Raspeig, Alicante, Spain

    2008-01-01

    The analysis of the Messinian and Pliocene stratigraphy of the southern Bajo Segura Basin (Betic Cordillera, Spain) has revealed three highstand sedimentary phases (Messinian I, Messinian II, and Pliocene) bounded by two lowstand erosional surfaces (intra-Messinian and end-Messinian unconformities). The Messinian I highstand phase is characterized by the progradation of coastal and shallow marine sandstones (La Virgen Fm) over slope and pelagic-basin marls (Torremendo Fm). After this first ph...

  16. Spatio-temporal variability of snow water equivalent in the extra-tropical Andes cordillera from a distributed energy balance modeling and remotely sensed snow cover

    OpenAIRE

    E. Cornwell; Molotch, N. P.; McPhee, J

    2015-01-01

    Seasonal snow cover is the primary water resource precursor for human use and environmental sustain along the extratropical Andes Cordillera. Despite its importance, relatively little research has been devoted to understanding the properties, distribution and variability of this natural resource. This research provides high-resolution distributed estimates of end-of-winter and spring snow water equivalent over a 152 000 km2 domain that includes the mountainous reaches of ...

  17. Contribution of groundwater to the outflow from ungauged glacierized catchments : a multi-site study in the tropical Cordillera Blanca, Peru

    OpenAIRE

    M. Baraer; McKenzie, J.; B. G. Mark; Gordon, R.; Bury, J.; Condom, Thomas; J. Gomez; S. Knox; S. K. Fortner

    2015-01-01

    The rapid retreat of the glaciers of the Cordillera Blanca is having a noticeable impact on the downstream hydrology. Although groundwater is a critical hydrologic component that sustains stream flows during the dry season, its characteristics and its contribution to downstream hydrology remain poorly understood. In this study, we analyse the hydrochemical and isotopic properties of potential hydrologic sources mixing in surface streams to characterize the proglacial hydrology in four glacial...

  18. La porosidad en las areniscas triásicas (Rama Aragonesa de la Cordillera Ibérica

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    Arribas, J.

    1984-12-01

    Full Text Available Triassic sandstone's porosity (Buntsandstein and Muschelkalk facies from the Aragonesa Branch of the Iberian Range are studied, firstly at the sediment primary porosity calculation and secondly the porosity-reducing processes are analyzed. Processes creating secondary sandstone porosity can be established (dissolution and fracturing by the textural and genetic caracterization of the sandstone's voids. The dissolution of potassium feldspar, carbonate cement and barite cement, is related with meteoric pore-water flow alloys to intramesozoic unconformities, Fracturing porosity is related to Iberian Range tertiary structuration. Finally, we concluded that the amount of the sandstone's secondary porosity depends mainly on the original composition of the sediments and also on the geochemical sedimentary environments that control the first diagenetic stages (eodiagenesis, This fact manifests itself in the amount and types of variating porosities along the stratigraphic section.

    Se estudia la porosidad en las areniscas triásicas (facies Buntsandstein y Muschelkalk de la Rama Aragonesa de la Cordillera Ibérica, partiendo del cálculo estimativo de la porosidad primaria del sedimento, para posteriormente analizar los distintos procesos diagenéticos que han intervenido en su destrucción (compactación mecánica, compactación química y cementación. La caracterización textural y genética de los poros en dichas areniscas permite establecer la existencia de procesos generadores de porosidad secundaria (disolución y fractura. La disolución del feldespato potásico, cemento carbonático y de baritina se relaciona con flujos de aguas meteóricas ligadas a discordancias intramesozoicas, mientras que la porosidad de fractura se asocia a la estructuración terciaria de la Cordillera Ibérica. Por ú1timo se concluye que la cantidad de porosidad secundaria en las areniscas estudiadas depende fundamentalmente de la composición original de los dep

  19. ARTE EN LA ZONA DE HISTÉRESIS: QUEBRADA. LAS CORDILLERAS EN ANDAS DE GUADALUPE SANTA CRUZ Art in the Zone of Hysteresis: Quebrada. Las cordilleras en andas, by Guadalupe Santa Cruz

    Directory of Open Access Journals (Sweden)

    Cecilia Ojeda

    2007-12-01

    Full Text Available Este libro de Guadalupe Santa Cruz plantea el problema del desmedrado estatus del arte en un horizonte cultural dominado por la industria del entretenimiento. De este reconocimiento y del diseño vanguardista del libro en sí -concebido como un puente entre el arte y la vida, o como un instrumento de conocimiento privilegiado de lo real- surge una tensión característica del arte contemporáneo. Dicha tensión ha sido definida como el punto de histéresis de la obra artística en la que ésta tiende a conservar una propiedad en ausencia del estímulo que la ha generado, tensión artística que se examina en este ensayo.Quebrada. Las cordilleras en andas examines the issue of the artwork’s diminished status within a landscape dominated by the entertainment industry. From this knowledge and the vanguard design of the book itself -as an instrument of the real-arises a tension that is characteristic of contemporary art. This tension has been compared to the point of hysteresis of an element, in which like a magnetic material it, the work of art, preserves one of its properties in the absence of its stimulus. This essay examines how this tension is produced in the work by Guadalupe Santa Cruz.

  20. Mantle to Surface Fluid Transfer Above a Flat Slab Subduction Zone: Isotopic Evidence from Hot Springs in the Cordillera Blanca, Peru

    Science.gov (United States)

    Newell, D. L.; Jessup, M. J.; Hilton, D. R.; Shaw, C. A.; Hughes, C. A.

    2015-12-01

    Thermal springs in the Cordillera Blanca, Peru, provide geochemical evidence for deeply circulated hydrothermal fluids that carry significant mantle-derived helium. The Cordillera Blanca is a ~200 km-long NNW-SSE trending mountain range in the Peruvian Andes located above an amagmatic flat-slab subduction segment. The west side of the range is bounded by the Cordillera Blanca detachment that preserves a progression of top to the west ductile shear to brittle normal faulting since ~5 Ma. We report aqueous and stable isotope geochemical results from fluid and gas samples collected in 2013 and 2015 from 13 hot springs emanating from the Cordillera Blanca detachment and associated hanging wall faults. Most springs are vigorously bubbling (degassing), and range in temperature, pH, and conductivity from 17-89 °C, 5.95-8.87, and 0.17-21.5 mS, respectively. The hottest springs issue directly from the northern segment of the detachment. Geochemically, springs are CO2-rich, alkaline-chloride to alkaline-carbonate waters, with elevated trace metal contents including Fe, Cu, As, Zn, Sb, and Tl. Notably, As contents are ≤11 ppm, indicating that thermal waters may be adversely impacting local water quality. Water δ18O and δD, trends in elemental chemistry, and cation geothermometry collectively demonstrate mixing of hot (200-260 °C) saline fluid with cold meteoric recharge along the fault. Helium isotope ratios (3He/4He) for dissolved gases in the hot springs range from 0.62 to 1.98 RC/RA, indicating the presence of ~25% mantle-derived helium, assuming mixing of an asthenospheric end-member with the crustal helium reservoir. CO2/3He and carbon stable isotope ratios indicate a carbon source derived from mixing of crustal sources with minor mantle carbon. Overall, the volatile signature overlaps with orogen-wide datasets where crustal overprinting has modified mantle contributions at active arc volcanoes. Given the long duration since active magmatism in the Cordillera

  1. A geomorphological approach to determining the Neogene to Recent tectonic deformation in the Coastal Cordillera of northern Chile (Atacama)

    Science.gov (United States)

    Riquelme, R.; Martinod, J.; Hérail, G.; Darrozes, J.; Charrier, R.

    2003-01-01

    The large (≈10000 km 2) and local-scale (Atacama Fault System (AFS) accommodated the relative uplift of the western side of the Chilean Coastal Cordillera of the Chañaral region (southern Atacama Desert). The mean regional altitude systematically decreases eastwards crossing the AFS, independent of the lithological characteristics of the substratum cut by this system of faults. Topographic analysis reveals a more incised landscape west of the AFS that, at the local scale, is reported by the distribution of the altitudes (hypsometric curves and integrals) of tributary basins and by the presence of terraces. In the Middle and Upper Miocene, a thick (>300 m) sedimentary succession was deposited east of the AFS. The succession fills previously deep paleovalleys. And it consists of gravel, so-called "Atacama Gravels", which passes laterally into fine-grained playa related deposits near the AFS. We interpret the deposition of this succession as a result of a blocking closure of the valley flowing from the Precordillera due to the activity on AFS. A pedimentation episode followed sediment deposition and is locally strongly re-incised by the main modern-day river valleys draining the Precordillera. Incision may result from either regional uplift of the forearc, and/or from more localized activity on the AFS. Furthermore, Recent (Quaternary?) tectonic activity on the AFS has been observed which is consistent with a localized relative uplift of the crustal block west of the AFS.

  2. On the lag time between internal strain and basement involved thrust induced exhumation: The case of the Colombian Eastern Cordillera

    Science.gov (United States)

    Mora, Andrès; Blanco, Vladimir; Naranjo, Julian; Sanchez, Nelson; Ketcham, Richard A.; Rubiano, Jorge; Stockli, Daniel F.; Quintero, Isaid; Nemčok, Michal; Horton, Brian K.; Davila, Hamblet

    2013-07-01

    Thrust sheets accumulate internal strain before they start moving along discrete fault planes. However, there are no previous studies evaluating the time difference between initiation of strain and fault displacement. In this paper we use observations from the Eastern Cordillera of Colombia to evaluate this interval. We utilize multiple thermochronometers and paleothermometers to refine the timing of deformation. Based on these new data we build time-temperature path estimates that together with geometric outcrop-based structural analysis and fluid inclusions allow us to assign relative timing to features associated with strain, such as cleavage, veins and certain types of fractures, and compare that with the timing of thrusting. We find that cleavage was only formed close to maximum paleotemperatures, almost coeval with the onset of thrust-induced denudation by the Late Oligocene. The corresponding structural level of fold-related veins suggest that they were formed later but still when the country rocks were at temperatures higher than 160 °C, mostly during the Early Miocene and still coexisted with the latest stages of cleavage formation. Our data show that the main period of strain hardening was short (probably a few million years) and occurred before first-order basement thrusting was dominant, but was associated with second-order folding.

  3. Snow water equivalent spatiotemporal variability estimation in the Andes Cordillera through distributed energy balance modeling and intensive-study catchments.

    Science.gov (United States)

    McPhee, J. P.; Cornwell, E.; Molotch, N. P.

    2015-12-01

    Seasonal snow cover is the primary water resource precursor for human use and environmental sustain along the extratropical Andes Cordillera. This research provides high-resolution distributed estimates of end-of-winter and spring snow water equivalent over a 152,000-km2 domain, based on remotely sensed snow cover and a simplified snowpack energy balance model. Important data for model validation was obtained through a sustained effort aimed at monitoring snow conditions throughout the domain from newly installed sensors and snow surveys. Peak SWE estimates show an overall coefficient of determination R2 of 0.61 compared to observations at 12 automatic snow water equivalent sensors distributed across the model domain between latitudes 30º S and 37º S, with R2 values between 0.32 and 0.88. Estimated patterns of snow accumulation reflect appropriately the dominant effect of elevation, and suggest that the current government operational snow observation network may be inadequate under future climate change scenarios. Several insights can be obtained by analyzing the shortcomings of the modeling results when compared with high-resolution time series of energy and mass balance, as well as with distributed SWE observations obtained at experimental catchments. The results presented here have the potential of informing applications such as seasonal forecast model assessment and improvement, regional climate model validation, as well as evaluation of observational networks and water resource infrastructure development.

  4. Flujos de detritos recientes en la cordillera frontal de Mendoza: Un ejemplo de riesgo natural en la ruta 7

    Directory of Open Access Journals (Sweden)

    Emmanuel Wick

    2010-06-01

    Full Text Available Se expone un estudio sobre los flujos de detritos ocurridos en enero de 2005, en el km 1.118,5 de la ruta nacional 7 en la provincia de Mendoza. La zona se ubica en la Cordillera Frontal, próxima al límite con la Precordillera. Se realizó un mapa geomorfológico detallado, sobre la base de una imagen Quickbird del año 2006. Además, se hicieron cálculos de volúmenes, velocidades y caudales, con mediciones en el campo y con ayuda de un sistema de información geográfico (SIG. El estudio de la geomorfología permitió proponer tres escenarios para el caso de un nuevo evento, a partir de los cuáles se creó un mapa de susceptibilidad a los flujos de detritos para el tramo de ruta analizado. Finalmente, se proponen medidas de protección y de mitigación ante la posibilidad de recurrencia de estos eventos en el sector.

  5. Space-time evolution of a growth fold (Betic Cordillera, Spain). Evidences from 3D geometrical modelling

    Science.gov (United States)

    Martin-Rojas, Ivan; Alfaro, Pedro; Estévez, Antonio

    2014-05-01

    We present a study that encompasses several software tools (iGIS©, ArcGIS©, Autocad©, etc.) and data (geological mapping, high resolution digital topographic data, high resolution aerial photographs, etc.) to create a detailed 3D geometric model of an active fault propagation growth fold. This 3D model clearly shows structural features of the analysed fold, as well as growth relationships and sedimentary patterns. The results obtained permit us to discuss the kinematics and structural evolution of the fold and the fault in time and space. The study fault propagation fold is the Crevillente syncline. This fold represents the northern limit of the Bajo Segura Basin, an intermontane basin in the Eastern Betic Cordillera (SE Spain) developed from upper Miocene on. 3D features of the Crevillente syncline, including growth pattern, indicate that limb rotation and, consequently, fault activity was higher during Messinian than during Tortonian; consequently, fault activity was also higher. From Pliocene on our data point that limb rotation and fault activity steadies or probably decreases. This in time evolution of the Crevillente syncline is not the same all along the structure; actually the 3D geometric model indicates that observed lateral heterogeneity is related to along strike variation of fault displacement.

  6. Plantas Fósiles del Grupo Choiyoi, Cordillera Frontal a la Latitud del río Mendoza

    Directory of Open Access Journals (Sweden)

    Magdalena Koukharsky

    2011-06-01

    Full Text Available En este trabajo se dan a conocer los primeros restos fósiles hallados en sedimentitas, cuyo componente clástico es de origen volcánico, intercaladas en la Formación Tambillos del Grupo Choiyoi, Cordillera Frontal de Mendoza. Los mismos consisten en abundantes improntas de Sphenophyta en estado de preservación regular a malo. En la zona estudiada, las rocas de la Formación Tambillos, que son dominantemente volcánicas ácidas y de edad pérmica temprana a media según correlaciones regionales, se depositaron sobre una discordancia erosiva labrada en lavas andesíticas intensamente propilitizadas que se atribuyen a la Formación Portezuelo del Cenizo. Los restos vegetales se encuentran a unos 23 metros de la base, contenidos en niveles de areniscas finas y pelitas depositadas en un ambiente fluvial (microdelta, en los bordes de un lago y fueron coetáneas con los primeros episodios de volcanismo riolítico en la región. Si bien la flora encontrada no permite definir la edad, las formas presentes son comunes en niveles del Carbonífero superior-Pérmico y Triásico de Argentina.

  7. Three-dimensional inversion of magnetotelluric data from the Central Andean continental margin

    Science.gov (United States)

    Kühn, Christine; Küster, Jonas; Brasse, Heinrich

    2014-12-01

    Magnetotelluric data were collected in the late 1990s in the Central Andes of Chile and Bolivia, with the aim to delineate the electrical conductivity distribution in the subsurface and its relations to subduction processes. In previous studies, these data were interpreted based on 2-D models. The principal result was a vast conductivity zone beneath the Altiplano high plateau at mid and lower crustal depths and a much smaller, though significant conductor associated with the Precordillera Fault System. However, there are some significant 3-D effects in the investigation area, in particular near the coast and on the eastern Altiplano. The aim of this work is to give a reinterpretation based on new 3-D inversion of these data. The 3-D inversion not only provides a better fit to the data compared to 2-D results but furthermore allows to include sites with strong telluric distortion which were ignored in previous studies. We are now able to explain anomalous phases above 90° and induction arrows pointing subparallel to the coast as observed at several sites in the Coastal Cordillera. These strongly distorted data are caused by highly conductive near-surface structures that are partly connected to the Pacific Ocean, forcing currents to flow around the sites. The lower crust beneath the Coastal Cordillera resembles a poorly conductive, nearly homogeneous half-space and is electrically unremarkable. Besides, we can now image the Precordillera conductor as a continuous, elongated feature. The volcanic arc of the Western Cordillera is highly resistive with the exception of a few conductive spots which may be associated with certain individual volcanoes or geothermal resources, respectively. The Altiplano conductor is again the dominant electrical feature in the Central Andes, indicating widespread melting of the middle and lower back-arc crust.

  8. A fuzzy multi-objective linear programming approach for integrated sheep farming and wildlife in land management decisions: a case study in the Patagonian rangelands

    Science.gov (United States)

    Metternicht, Graciela; Blanco, Paula; del Valle, Hector; Laterra, Pedro; Hardtke, Leonardo; Bouza, Pablo

    2015-04-01

    Wildlife is part of the Patagonian rangelands sheep farming environment, with the potential of providing extra revenue to livestock owners. As sheep farming became less profitable, farmers and ranchers could focus on sustainable wildlife harvesting. It has been argued that sustainable wildlife harvesting is ecologically one of the most rational forms of land use because of its potential to provide multiple products of high value, while reducing pressure on ecosystems. The guanaco (Lama guanicoe) is the most conspicuous wild ungulate of Patagonia. Guanaco ?bre, meat, pelts and hides are economically valuable and have the potential to be used within the present Patagonian context of production systems. Guanaco populations in South America, including Patagonia, have experienced a sustained decline. Causes for this decline are related to habitat alteration, competition for forage with sheep, and lack of reasonable management plans to develop livelihoods for ranchers. In this study we propose an approach to explicitly determinate optimal stocking rates based on trade-offs between guanaco density and livestock grazing intensity on rangelands. The focus of our research is on finding optimal sheep stocking rates at paddock level, to ensure the highest production outputs while: a) meeting requirements of sustainable conservation of guanacos over their minimum viable population; b) maximizing soil carbon sequestration, and c) minimizing soil erosion. In this way, determination of optimal stocking rate in rangelands becomes a multi-objective optimization problem that can be addressed using a Fuzzy Multi-Objective Linear Programming (MOLP) approach. Basically, this approach converts multi-objective problems into single-objective optimizations, by introducing a set of objective weights. Objectives are represented using fuzzy set theory and fuzzy memberships, enabling each objective function to adopt a value between 0 and 1. Each objective function indicates the satisfaction of

  9. Clasificación de yeso mediante imágenes ASTER en la Cordillera Principal Mendocina Gypsum classification based on ASTER images in the Principal Cordillera of Mendoza

    Directory of Open Access Journals (Sweden)

    José F Mescua

    2010-06-01

    Full Text Available Se presenta una metodología para obtener el mapa de distribución de yeso con imágenes satelitales ASTER. Se utilizaron imágenes con nivel de procesamiento ASTERL3A correspondientes a dos áreas de la Cordillera Principal mendocina. La estratigrafía de las áreas de estudio se encuentra compuesta por una espesa sucesión sedimentaria mesozoica, volcanitas cenozoicas y depósitos cuaternarios. Dentro de los depósitos mesozoicos se encuentra la Formación Auquilco, integrada por yeso y anhidrita. El reconocimiento y distribución areal de esta unidad es el objetivo de este trabajo. Se aplicaron dos métodos de procesamiento a las imágenes. Por un lado se utilizó el índice de cuarzo (Qi, uno de los índices de determinación de minerales definidos para el subsistema TIR de ASTER. Este índice puede usarse también para reconocer sulfatos, y en particular yeso, ya que estos minerales proporcionan una respuesta muy baja en el Qi. El segundo método consistió en la aplicación combinada de los cocientes de bandas 4/5 y 7/5. Este método permite identificar al yeso por su elevada respuesta en el cociente 4/5 y baja respuesta en el cociente 7/5. A fin de simplificar la metodología, se generó un nuevo cociente a partir de los dos mencionados: (4/5/(7/5, de manera de destacar el yeso con alta respuesta. A partir del relevamiento de campo se observó que en ambos métodos los errores por exceso fueron más importantes que los errores por defecto, y que los píxeles determinados como yeso erróneamente por cada método son diferentes. Este hecho permite la aplicación de la técnica de "Decision Tree" del programa ENVI 4.2 con el objetivo de eliminar estos errores. En cada una de las imágenes se determinaron los valores de umbral para los píxeles reconocidos como yeso. Luego se generó un "árbol de decisiones" combinando los umbrales de cada imagen, seleccionando en una nueva clase los píxeles determinados como yeso por ambos métodos y

  10. Evaluation of metasomatic changes in an interlayered blueschist-greenschist sequence (Coastal Cordillera, Chile) by combining geochemical data with equilibrium assemblage diagrams

    Science.gov (United States)

    Halama, Ralf; Konrad-Schmolke, Matthias

    2014-05-01

    In the Coastal Cordillera of Central Chile, a spectacular sequence of interlayered blueschists and greenschists occurs in coastal outcrops near Pichilemu. Three explanations are generally proposed to interpret the interlayering of metamorphic rocks that represent distinct metamorphic facies: 1. Differences in the pressure-temperature (P-T) conditions of equilibration and late-stage tectonic juxtaposition, 2. Chemical differences between the layers inherited from the protolith, and 3. Differences in the degree of metasomatic overprint during metamorphism. Investigations of such interlayered sequences can shed light on the mobility of elements and fluid-rock interaction during metamorphism. To identify the processes responsible for interlayering, geochemical analyses were combined with petrologic investigations involving the calculation of isothermal and isobaric binary phase diagrams using the THERIAK-DOMINO [1] software. Major mineral phases in blueschist and greenschist layers are amphibole, white mica, chlorite, and albite with subordinate amounts of titanite, epidote, hematite and apatite. The mineralogy of blueschist and greenschist layers is similar, albeit the modal proportions differ, causing the distinct colouring. Peak P-T conditions of blueschists reach 370±20 °C at 10±1 kbar [2]. The layering on a cm-to-dm scale and the similar mineralogy suggest that both blueschist and greenschist layers experienced a similar P-T evolution. For adjacent blueschist-greenschist pairs, blueschists have consistently higher Si and Na contents, whereas greenschists are relatively enriched in Al, Mg and total Fe. However, the observed major element geochemical trends are inconsistent with magmatic differentiation. For several blueschist-greenschist pairs, ratios of incompatible trace elements, which are indicative of the protolith composition and considered as relatively immobile during low-T metamorphism (Th/Yb, Nb/Yb), are near identical. These features point to

  11. Extensional Detachment faulting in melange rocks. Plurikilometres migration by W the External Zone (Cordillera Bética, Spain)

    Science.gov (United States)

    Roldán, Francisco Javier; Azañon, Jose Miguel; Rodríguez, Jose; Mateos, Rosa Maria

    2014-05-01

    The synthesis and correlation of units carried out in the continuous geological map (Roldán et al., 2012), has revealed a fragmentation of the carbonate outcrops belong to the Subbetic Domain (García-Hernández et al., 1980). Subbetic NW verging thrust and fold axial traces have not lateral continuity and Jurassic carbonate outscrops appear as klippes on the olistotromic unit. These ductile structures that can be observed in the internal structure of these jurassic blocks are unrelated to the brittle-ductile deformation bands observed at the basal pelitic levels. Basal detachments are rooted in: a) the Olistostromic unit, a Upper Langhian-Lower Serravallian breccia constituted by gypsum-bearing clay and marls; b) Cretaceous-Tertiary marly sedimentary rocks (Rodríguez-Fernández, et al., 2013) . In both kind of rocks, cataclastic structures allows to infer a top-to-the WSW displacement. Paleostress measurements, made on these detachments levels, are compatible with a extensional regime (Roldán et al., 2012). At the same time, the analysis and interpretation of subsurface data (seismic surveys and borehole testing) shows that the Subbetic Domain (External Subbetic, Molina 1987) are affected by westward low-angle normal faults. A balanced cross-section, based on morphological and cartographic data in the area between Sierra de Cabra and Sierra de Alta Coloma (Valdepeñas de Jaén), shows plurikilometric displacements which has been produced during Late Serravallian-Early Tortonian times. References: García-Hernández, M., López-Garrido, A.C., Rivas, P., Sanz de Galdeano, C., Vera, J.A. (1980): Mesozoic paleogeographic evolution of the zones of the Betic Cordillera. Geol. Mijnb. 59 (2). 155-168. Molina, J.M. (1987). Análisis de facies del Mesozoico en el Subbético. Tesis Doctoral, Univ. Granada. 518 p. Rodríguez-Fernández, J., Roldán, F. J., Azañón, J.M. y García-Cortés, A. (2013). El colapso gravitacional del frente orogénico a lpino en el Dominio Subb

  12. Ichnological analysis in high-resolution sequence stratigraphy: The Glossifungites ichnofacies in Triassic successions from the Betic Cordillera (southern Spain)

    Science.gov (United States)

    Rodríguez-Tovar, Francisco J.; Pérez-Valera, Fernando; Pérez-López, Alberto

    2007-06-01

    This study integrates ichnological and sedimentological data in order to refine sequence stratigraphy and interpretations of sea-level dynamics for the Ladinian (Middle Triassic), Muschelkalk succession (Siles Formation) in the Betic Cordillera (southern Spain). Facies analysis was integrated with a detailed ichnological study, focused on the middle part of the lower member of the Muschelkalk succession (transgressive systems tract), which is characterized by an abundant and conspicuous trace fossil assemblage. Seven lithofacies were recognized, recording sediment accumulation in tidal flat, and inner to outer marine carbonate ramp, depositional environments. Thin-bedded marly limestones with bioclastic shelly beds (Facies E: middle ramp, with storm influence), are characterized by Diplocraterion and Rhizocorallium. Diplocraterion is protrusive, usually eroded on top, and mainly recorded in the marly limestone intervals. Rhizocorallium preserves well defined scratch-marks, and is commonly emplaced in bioclastic, shelly beds. The assemblage represents the Glossifungites ichnofacies. Sedimentological and ichnological data are interpreted to record a complex transgressive context, associated with high-frequency sea-level dynamics that allowed formation of transgressive surfaces of erosion (TSE, i.e., ravinement surfaces) of different orders. Major TSE, associated with continuous bioclastic shelly beds, delimit parasequences; the absence of the Glossifungites suite reveals that there was little time between erosion and deposition. Intermediate TSE, associated with discontinuous shell beds, are related to comparatively less significant sea-level rises and occur within parasequences. The Glossifungites suite reveals colonization of firmgrounds during relatively prolonged times between erosion and deposition related to intermediate TSE. Minor order TSE, recorded between the intermediate TSE, are related to punctuated, highest frequency sea-level changes; phases of

  13. Investigating potential precipitation changes with impacts on small-scale farming in mountain villages, Cordillera Blanca, Peru

    Science.gov (United States)

    Gurgiser, Wolfgang; Hofer, Marlis; Juen, Irmgard; Schauwecker, Simone; Singer, Katrin; Neuburger, Martina; Kaser, Georg

    2015-04-01

    Small subsistence farmers on the slopes above the city of Huaraz in the Peruvian Cordillera Blanca assign recent challenges in agricultural production - beyond other factors - to decreasing precipitation during the early crop cultivation period in August and September. In general, local climate is characterized by low annual variation in air temperature but a strong seasonality in precipitation. While driest conditions prevail in June and July, precipitation increases gradually towards the October to April wet season with strong topographically induced gradients. Because seeding occurs soon after the core dry months, cultivation is highly vulnerable to potential alterations in the transition period from dry to wet conditions. Within this study we try to find "data-based" evidence for changes in precipitation patterns, even though the availability of meteorological information for proving precipitation trends is generally poor for this region. We currently investigate the respective potential of connecting approx. 10 years (2003-2013) of ground measurements (weekly resolution with some gaps) with ERA-interim total precipitation output (0.75 deg. resolution) by (1) selecting those adjacent model grid points that explain measured precipitation variability best and by (2) fitting the data from the selected grid points to the measurements with quantile mapping. Uncertainties arising from the transfer functions are assessed with a cross validation approach. Our preliminary results suggest that (1) ground measurements are fairly explained by ERA interim data (despite the very complex topography), that (2) no significant trends in precipitation at the end of the dry season (August, September) are detectable for the period 1979-2013, but relatively high year-to-year variability occurs and that (3) process based limited area modeling might be required to effectively assess specific requests of user groups related to local precipitation variability.

  14. Unraveling Tropical Mountain Hydroclimatology by Coupling Autonomous Sensor Observations and Climate Modeling: Llanganuco Valley, Cordillera Blanca, Peru.

    Science.gov (United States)

    Hellstrom, R. A.; Fernandez, A.; Mark, B. G.; Covert, J. M.

    2015-12-01

    Northern Peru will face critical water resource issues in the near future as permanent ice retreats. Much of current global and regional climate research neglects the meteorological forcing of lapse rates and valley wind dynamics on critical components of the Peruvian Andes' water-cycle. In 2004 and 2005 we installed an autonomous sensor network (ASN) within the glacierized Llanganuco Valley, Cordillera Blanca (9°S), consisting of discrete, cost-effective, automatic temperature loggers located along the valley axis and anchored by two automatic weather stations. Comparisons of these embedded atmospheric measurements from the ASN and climate modeling (CM) by dynamical downscaling using the Weather Research and Forecasting (WRF) model elucidate distinct diurnal and seasonal characteristics of the mountain valley winds and lapse rates. Wind, temperature, humidity, and cloud simulations by WRF suggest that thermally driven valley winds converging with easterly flow aloft enhance late afternoon and evening cloud development which helps explain detected nocturnal precipitation maxima measured by the ASN. We attribute sustained evapotranspiration (ET), as estimated by the FAO-56 Penman-Monteith model, to an abundance of glacial melt-water during the dry season and strong pre-noon solar heating during the wet season. Furthermore, the extreme diurnal variability of along-valley-axis lapse rates and valley wind detected from ground observations and confirmed by dynamical downscaling demonstrate the importance of realistic scale parameterizations of the boundary layer to improve regional CM projections in mountainous regions. Our findings portray ET as an integral yet poorly represented process in Andean hydroclimatology. We show that coupling ASN and CM can improve understanding of multi-scale atmospheric and associated hydrological processes in mountain valleys.

  15. Provenance through the limit: integrated provenance from the Devonian sedimentary and basement rocks from the northern segment of the Eastern Cordillera of the Colombian Andes

    Science.gov (United States)

    Cardona, Agustin; Valencia, Victor; Lotero, Andrea; Villafañez, Yohana; Augustsson, Carita; Bayona, German; Ibañez, Mauricio

    2013-04-01

    The provenance record of sedimentary rocks is sometimes the only available archive of the geological evolution in continuously active continental margins where continuous exhumation, erosion and along strike fragmentation of continental margins destroy geological evidences. New integrated provenance constraints from segmented exposures of Devonian rocks of the northern segment of the Eastern Cordillera of Colombia are used to reconstruct overimposed Paleozoic, Mesozoic and Cenozoic paleogeographic scenarios of the northern Andes. Sandstones from deltaic to platform environments are characterized by very high quartz contents, stable to ultrastable heavy minerals and mostly angular fragments. U-Pb detrital zircon geochronology reveals prominent Silurian to Ordovician and Mesoproterozoic (Grenvillian) age populations with minor Devonian zircons. Tourmaline geochemistry and detrital quarz characterization suggest prominent low grade metamorphic sources. These provenance fingerprints can be related to the erosion of the older metasedimentary basement exposed in the same region and record the transition from a terrane collisional event to the formation of a new subduction zone before the final Late Paleozoic events that end in the agglutination of Pangea. The U-Pb detrital record of the Devonian and basement rocks of the Eastern Cordillera are also comparable with Early to Middle Paleozic Paleozoic rocks form the Northern segment of the eastern Peruvian Andes re-inforcing the view of along strike terrane thousand of kilometer transport along the Mesozoic proto-Andean margin. Petrographic and heavy mineral petrofacies and stratigraphic correlation between Devonian localities are also used as piercing points to document Cenozoic ten of kilometers strike slip displacements along the northern termination of the Eastern Cordillera.

  16. Kinematic evolution of Andean fold-thrust structures along the boundary between the Eastern Cordillera and Middle Magdalena Valley basin, Colombia

    Science.gov (United States)

    SáNchez, Javier; Horton, Brian K.; Tesón, Eliseo; Mora, AndréS.; Ketcham, Richard A.; Stockli, Daniel F.

    2012-06-01

    Surface and subsurface data support a kinematic reconstruction of Cenozoic fold-thrust deformation along the Eastern Cordillera-Magdalena Valley transition in Colombia. The La Salina fault (LSF) marks the boundary between west-vergent Eastern Cordillera structures and hinterland deposits of the Middle Magdalena Valley basin. Apatite fission track and (U-Th)/He thermochronological results for the west-directed LSF reveal initial hanging wall exhumation during middle Eocene-early Oligocene (45-30 Ma) shortening, renewed exhumation in the early middle Miocene (18-12 Ma), and accelerated late Miocene-Pliocene (12-3 Ma) exhumation. Vitrinite reflectance data suggest maximum burial of 4-6 km, helping constrain Cenozoic basin architecture. Mapping of the LSF reveals hanging wall Cretaceous-Eocene rocks in a broad anticline-syncline pair with limited faulting and footwall Eocene-Quaternary basin fill in a complex series of tight thrust-related folds. Limited displacement along the westernmost (frontal) thrust suggests that shortening is largely accommodated by east-directed thrusting within a broader triangle zone of a passive-roof duplex (and probable minor strike-slip deformation). In the preferred kinematic restoration, the most recent phase of shortening to transpressional deformation represents out-of-sequence reactivation of the LSF consistent with irregular crosscutting relationships among footwall structures. Earliest exhumation by 45-30 Ma in the Eastern Cordillera fold-thrust belt is correlated with increased sedimentary lithic fragments and high compositional maturity in sandstones of the adjacent Magdalena Valley basin. Exhumation since ˜15 Ma coincided with decreased compositional maturity and elevated accumulation rates for the Real Group. The compositional provenance shifts are attributed to westward advance of fold-thrust deformation into the proximal (eastern) segments of the Magdalena Valley basin.

  17. Base litoestratigráfica de las facies Buntsandstein y Muschelkalk en la rama aragonesa de la Cordillera Ibérica (zona norte

    Directory of Open Access Journals (Sweden)

    Arribas, J.

    1985-04-01

    Full Text Available In order to complete the information about the Triassic in the Iberian Range, a description of Buntsandstein and Muschelkalk facies lithostratigraphy of the aragonesa branch has been made. In this way we have informaly defined six lithostratigraphic units. The presence of two Triassic lithotypes (Iberian Triassic and Mediterranean Triassic in the study area allows us to analyse the lithologic relationships between both of them. Finally. a first attempt of correlation between the informal units mentioned above and the Ramos' (1979 units of the Molina de Aragón area has been made, This correlation permits us to relate the Triassic of both branches in the Iberian Range.

    En este trabajo se realiza una descripción de la litoestratigrafía de las facies Buntsandstein y Muschelkalk en la rama aragonesa de la Cordillera Ibérica, con el fin de cubrir un vacío bibliográfico de gran importancia en el contexto global del Trias de la Cordillera Ibérica. Se han definido informalmente cuatro unidades litoestratigráficas correspondientes a las facies Buntsandstein y dos a las facies Muschelkalk. La presencia de dos litotipos triásicos (mediterráneo e ibérico en la zona de estudio, permite analizar en detalle las relaciones litológicas entre ellos. Por último, se realiza un intento de correlación entre las unidades definidas informalmente en este trabajo con las definidas por Ramos (1979 en las proximidades de Molina de Aragón, con el fin de relacionar el Trías de las dos ramas de la Cordillera Ibérica.

  18. Una especie nueva de rana arbórea del género Hyloscirtus (Amphibia: Anura: Hylidae de la Cordillera del Cóndor

    Directory of Open Access Journals (Sweden)

    Ana Almendáriz

    2014-01-01

    Full Text Available Las ranas ecuatorianas del género Hyloscirtus incluyen 16 especies descritas, de las cuales 11 pertenecen al grupo H. larinopygion. Su distribución se limita a los flancos de la Cordillera de los Andes, tanto al oriente como al occidente. Una evaluación de la herpetofauna en el sector meridional de la Cordillera del Cóndor (bosques montanos sobre mesetas de arenisca en la provincia de Zamora Chinchipe, Ecuador, condujo al descubrimiento de una especie nueva del grupo que describimos aquí como Hyloscirtus condor sp. nov.; se analizan los renacuajos, las llamadas de anuncio y se estima las relaciones filogenéticas de la especie nueva y de las especies relacionadas en base a nuevas secuencias de los genes mitocondriales 12S, tRNA Val y 16S, con un total de hasta 2508 bp. Los resultados muestran que el grupo H. larinopygion está conformado por dos clados, uno distribuido en los Andes norte y centro de Ecuador y el otro al sur. La nueva especie pertenece al clado sur y es hermana de H. tapichalaca y de una especie aparentemente no descrita de la Provincia Morona Santiago. La especie nueva difiere de sus congéneres por su patrón de coloración dorsal, que consiste de puntos amarillo obscuro en un fondo canela. Es la especie más grande del grupo H. larinopygion y comparte con H. tapichalaca la presencia de una espina prepólica grande y curvada y brazos hipertrofiados. La especie nueva habita un área remota y bien conservada de la Cordillera del Cóndor. El descubrimiento de ésta y otras especies nuevas del mismo lugar denota la importancia biológica del área y motivan al desarrollo de planes de conservación.

  19. Nivel de conocimiento de la nueva Ley de bosque nativo y fomento forestal: el caso de los pequeños propietarios forestales de la Cordillera de Nahuelbuta (Chile

    Directory of Open Access Journals (Sweden)

    Sergio Monrroy-Concha

    2013-06-01

    Full Text Available Se evaluó el nivel de conocimiento de la nueva Ley de bosque nativo y fomento forestal que poseen los pequeños propietarios forestales en dos territorios de la Cordillera de Nahuelbuta, en Chile. Para ello, se aplicó una encuesta a 53 personas (10% de las viviendas, que abordó cinco temas centrales: (1 uso del bosque nativo, (2 participación en redes sociales y acceso a la información, (3 conocimiento general de la Ley, (4 conocimiento respecto a la administración y (5 fomento de la Ley. Los resultados mostraron que: (1 el bosque nativo es usado para obtener productos madereros y no madereros, (2 las redes sociales y especialmente la radio son fundamentales para la transferencia de información, (3 tanto el conocimiento general de la Ley como (4 el nivel de conocimiento respecto de la administración de la Ley es insuficiente, y (5 se desconocen los trámites que deben efectuarse para obtener los beneficios de la Ley. Se concluye que: (1 el nivel de conocimiento de la Ley es insuficiente, (2 es fundamental estimular el uso de los instrumentos de esta Ley en la totalidad del territorio, de modo de garantizar el uso sustentable del recurso, y (3 la difusión de los beneficios de la Ley debe considerar las formas de comunicación tradicionales, el nivel de educación y la cultura de los espacios rurales

  20. Sedimentary evolution of Neogene continental deposits (Ñirihuau Formation) along the Ñirihuau River, North Patagonian Andes of Argentina

    Science.gov (United States)

    Paredes, J. M.; Giacosa, R. E.; Heredia, N.

    2009-07-01

    The sedimentary evolution of the Ñirihuau Formation (late Oligocene-middle Miocene) was studied along the southern margin of the Ñirihuau River, in the North Patagonian Andes. The 1300-m-thick section includes 15 epiclastic and volcaniclastic lithofacies which are grouped into five lithofacies associations: deep lacustrine, shallow lacustrine, fluvial channels, subaerial floodplains and volcaniclastic flows (lahar). Syn-eruptive and inter-eruptive stages are recorded along the Ñirihuau River section. The former consist of highly aggradational packages several tens of meters thick of ash-fall beds and lahar deposits. During inter-eruptive periods sedimentation took place mostly in shallow and deep lacustrine environments, with four cycles of lake expansion and contraction, and a minor proportion of fluvial deposits. Sedimentary supply originated from the northeast and northwest in the lower part of the unit through low to moderate sinuosity fluvial systems, flowing into a lake with high-gradient margins, and forming Gilbert-type deltas. The younger sections were sourced from the northeast, east and southeast, indicating changes in the basin morphology. Basic and intermediate volcanic rocks similar to those of the Ventana Formation (Oligocene) are interstratified at the beginning of the sedimentation. The syn-orogenic nature of the Ñirihuau Formation is evidenced by the changes in the basin shape, but mainly by the differences in styles and intensities of deformation between the Ñirihuau River section and the overlying outcrops of La Buitrera Hill, both separated by a folded unconformity.

  1. Andean evolution of the Aluminé fold and thrust belt, Northern Patagonian Andes (38°30‧-40°30‧S)

    Science.gov (United States)

    García Morabito, Ezequiel; Ramos, Víctor A.

    2012-10-01

    The Aluminé fold and thrust belt between 38°30' and 40°30'S is the result of two periods of progression of deformation toward the foreland. The chronology of deformation and its relationship with magmatism through time show spatially and temporally separated magmatic events closely linked to distinct deformational stages. Data presented here confirms a Late Cretaceous mountain-building phase that coexisted in space and time with an eastward arc-migration. During this stage, a belt of deformation expanded through the foreland where it produced the Southern Neuquen Precordillera. This eastern independent mountain grew separately from the main Andean axis through a combination of inversion of the old rift systems and interaction with a pre-Andean belt which acted as a foreland obstacle. On the basis of tectonostratigraphic controls we define the last Andean contractional phase between the Late Miocene and the Pliocene. This event induced the reactivation of both sectors of the fold and thrust belt with minor propagation toward the foreland, leading to the uplift of the Patagonian Andes and reshaping the Southern Neuquén Precordillera. Both intervals of shortening are separated by a period of localized extension that resulted in the development of the Collón Cura basin within this Andean segment. Here, large thicknesses of volcanosedimentary sequences accumulated contemporaneously with the extensional activity between the earliest Oligocene and the Early Miocene.

  2. Assessing the variability of glacier lake bathymetries and potential peak discharge based on large-scale measurements in the Cordillera Blanca, Peru

    Science.gov (United States)

    Cochachin, Alejo; Huggel, Christian; Salazar, Cesar; Haeberli, Wilfried; Frey, Holger

    2015-04-01

    Over timescales of hundreds to thousands of years ice masses in mountains produced erosion in bedrock and subglacial sediment, including the formation of overdeepenings and large moraine dams that now serve as basins for glacial lakes. Satellite based studies found a total of 8355 glacial lakes in Peru, whereof 830 lakes were observed in the Cordillera Blanca. Some of them have caused major disasters due to glacial lake outburst floods in the past decades. On the other hand, in view of shrinking glaciers, changing water resources, and formation of new lakes, glacial lakes could have a function as water reservoirs in the future. Here we present unprecedented bathymetric studies of 124 glacial lakes in the Cordillera Blanca, Huallanca, Huayhuash and Raura in the regions of Ancash, Huanuco and Lima. Measurements were carried out using a boat equipped with GPS, a total station and an echo sounder to measure the depth of the lakes. Autocad Civil 3D Land and ArcGIS were used to process the data and generate digital topographies of the lake bathymetries, and analyze parameters such as lake area, length and width, and depth and volume. Based on that, we calculated empirical equations for mean depth as related to (1) area, (2) maximum length, and (3) maximum width. We then applied these three equations to all 830 glacial lakes of the Cordillera Blanca to estimate their volumes. Eventually we used three relations from the literature to assess the peak discharge of potential lake outburst floods, based on lake volumes, resulting in 3 x 3 peak discharge estimates. In terms of lake topography and geomorphology results indicate that the maximum depth is located in the center part for bedrock lakes, and in the back part for lakes in moraine material. Best correlations are found for mean depth and maximum width, however, all three empirical relations show a large spread, reflecting the wide range of natural lake bathymetries. Volumes of the 124 lakes with bathymetries amount to 0

  3. The organic matter of the Potosi basin (Cordillera Oriental, Bolivia) during the Upper Cretaceous-Lower tertiary: stratigraphic and palaeogeographic data

    Energy Technology Data Exchange (ETDEWEB)

    Blanc-Valleron, M.M.; Rouchy, J.M. (Centre National de la Recherche Scientifique (CNRS), 75 - Paris (France)); Schuler, M.; Rauscher, R. (Strasbourg-1 Univ., 67 (France)); Camoin, G. (Aix-Marseille-1 Univ., 13 - Marseille (France))

    1994-12-01

    Palynological and Rock-Eval pyrolysis studies of the Chaunaca and El Molino Fm (Santonian to Thanetian, Cordillera Oriental, Bolivia) indicate that some facies have economic significance as potential oil source rocks. The occurrence of Pediastrum and Azolla testify a lacustrine environment. In the Upper Molino, the environmental interpretation of an almost monospecific association of dinocysts is discussed. The presence of Apectodinium quinquelatum indicates that the age of the upper part of the Upper El Molino Fm is likely to be Upper Thanetian. (authors). 22 refs., 5 figs.

  4. Las unidades litoestratigráficas del Pérmico y Triásico Inferior y Medio en el sector de la Cordillera Ibérica

    OpenAIRE

    López Gómez, José; Arche, Alfredo

    1992-01-01

    Se definen formalmente las unidades litoestratigráficas que constituyen el Pérmico y Triásico del SE de la Cordillera Ibérica representados en Facies Muschelkalk, Buntsandstein y Saxoniense. El rango definido para las unidades es de Formación, algunas de las cuales han sido a su vez subdivididas en Miembros. El conjunto total es de nueve Formaciones y catorce Miembros que constituyen dos Grupos subdivididos en dos Subgrupos cada uno. Los pasos seguidos para estas definiciones s...

  5. THE STRATIGRAPHY OF THE UPPER BATHONIAN TO MIDDLE OXFORDIAN SUCESSION OF THE ARAGONESE BRANCH OF THE CORDILLERA IBÉRICA (SPAIN AND ITS EUROPEAN CONTEXT

    Directory of Open Access Journals (Sweden)

    KEVIN N. PAGE

    2004-03-01

    Full Text Available The Upper Bathonian-Middle Oxfordian succession of the Aragonese branch of the Cordillera Ibérica is one of the most completely developed in Europe and includes localities of international importance for Jurassic bio- and chronostratigraphy. Of particular importance are a potential stratotype for the Upper Bathonian of North West Europe and reference sections for a number of Submediterranean Province Middle Oxfordian biostratigraphic units. The intervening Callovian sequence, albeit locally strongly condensed, also includes faunas of key stratigraphical importance. The sequence of stratigraphically important ammonite faunas for this interval is here reviewed and placed in its European context.

  6. X-ray color maps of the zoned garnets from Silgará Formation metamorphic rocks,SantanderMassif, Eastern Cordillera (Colombia

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    Takasu Akira

    2010-12-01

    Full Text Available

    The metamorphic rocks of the Lower Paleozoic Silgará Formation of the Santander Massif, Eastern Cordillera (Colombia, were affected by a Barrovian-type metamorphism under low to high temperature and medium pressure conditions. These rocks contain garnet porphyroblasts, which show several kinds of chemical zoning patterns. The garnet grains behave as closed systems with respect to the rock matrix. Most of the observed zoning patterns are due to gradual changes in physicochemical conditions during growth. However, some garnet grains show complex zoning patterns during multiple deformation and metamorphic events.

  7. A reassessment of the evidence for hydrothermal activity in the Neogene-Quaternary lacustrine environments of the Baza basin (Betic Cordillera, SE Spain) and its paleoecological implications

    Science.gov (United States)

    García-Aguilar, José Manuel; Guerra-Merchán, Antonio; Serrano, Francisco; Flores-Moya, Antonio; Delgado-Huertas, Antonio; Espigares, M. Patrocinio; Ros-Montoya, Sergio; Martínez-Navarro, Bienvenido; Palmqvist, Paul

    2015-03-01

    In a recent paper, García-Aguilar et al. (2014) reported on lithological, mineralogical and geochemical evidence of intense, tectonically-induced hydrothermal activity during the continental sedimentary infilling of the Baza basin, a postorogenic, intramontane area developed on the boundary between the Internal and External Zones of the Betic Cordillera, Southeast Spain (Fig. 1). This evidence includes the finding of sulfur contents, magnesium clays, fluorspar and celestine deposits, thermogene stromatolites and travertine growths in the latest Miocene (Turolian) to Middle Pleistocene lacustrine sediments and is particularly concentrated at certain stages and places (e.g. at Calabrian times in the Orce area).

  8. Una nueva especie de rana terrestre del género Pristimantis (Amphibia: Craugastoridae), de la Cordillera de Kutukú, Ecuador

    OpenAIRE

    Jorge Brito M.; Glenda Pozo-Zamora

    2013-01-01

    Describimos una especie nueva de mediano tamaño (LRC en la hembra 38.7 mm; en machos de 23.8 a 26.4 mm) de rana terrestre del género Pristimantis de los bosques sub-tropicales de la Cordillera de Kutukú, del sureste de Ecuador, a elevaciones de 1581-1820 m. Asignamos a Pristimantis almendariz sp. nov., al subgénero Hypodictyon, serie de especies ridens. La nueva especie difiere de otros miembros de la serie ridens por su patrón distintivo con manchas dorsales, membrana timpánica ausente, pres...

  9. Climate Change and Mountain Community Fire Management in the Cordillera Blanca, Peru

    Science.gov (United States)

    All, J.; Medler, M.; Cole, R. J.; Arques, S.; Schmitt, C. G.

    2014-12-01

    In the central Andes of Peru, climate change is altering fire risk through changes in local meteorology and fuel loading. Greater moisture and favorable growing conditions are increasing vegetative productivity, which in turn increases fuel loads. This process is accentuated during El Nino events and potentially results in increased fire occurrence and frequency during relatively dry La Nina events. Park officials are concerned about the ramification of the changes on local ecology and tourist use of the resources. However, using a time-series of two different products from the MODIS Terra and Aqua platforms (Active Fire and Burned Area), TRMM 3B43 precipitation data, and Multivariate ENSO Index data we document fire occurrence and extent from 2000 to 2010 and our analysis indicates that fires are burning exclusively during winter months when there are no natural ignition sources. Globally, fire is used in conjunction with grazing to improve the regeneration and yield of grasses. During our interviews, locals claimed to only set fires in the buffer zone outside of the park, but our analysis indicates that the buffer zone rarely burns and that most fires begin within the park and only occasionally move into the buffer zones. Additionally, we determined that although this is small-scale fire activity every year, overall fire is having a very minor effect on local systems. The park service must develop programs to work with local grazing stakeholders to better limit the impacts of fire, while also address the negative perceptions from tourists in the future. In this instance, fire perception and fire reality are not the same and the challenge for resource managers is how to reconcile these two factors in order to more effectively manage the parklands.

  10. Coal deposits in the front ranges and foothills of the Canadian Rocky Mountains, southern Canadian Cordillera

    Energy Technology Data Exchange (ETDEWEB)

    Bustin, R.M.; Smith, G.G. (University of British Columbia, Vancouver, BC (Canada). Department of Geological Sciences)

    1993-09-01

    Over one-third of Canada's coal resources occurs in the southern Canadian Rocky Mountains, with major deposits in the Front Ranges, Inner Foothills and Outer Foothills. In the Front Ranges, deposits of metallurgical and thermal, high-volatile bituminous to semi-anthracite coal occur in the Late Jurassic-Early Cretaceous Mist Mountain Formation. In the Inner Foothills of northeastern British Columbia and west-central Alberta, resources of metallurgical and thermal medium- and low-volatile bituminous coal occur in Early Cretaceous strata of the Gething and Gates Formations. In the Outer Foothills resources of thermal, high-volatile bituminous coal occur in Late Cretaceous and Paleocene strata of the Belly River Coalspur and Paskapoo Formations. The major deposits of the Front Ranges and Inner Foothills accumulated within the coastal plains of the Fernie and Moosebar-Clearwater seas. Shorelines prograded to the north and northeast into a foreland basin that evolved in advance of the evolving Colombian Orogen. In the Outer Foothills, coal deposits of the Belly River Formation originated within coastal plains during the withdrawal of the Pakowki Sea. The major coal deposits of the Coalspur and Paskapoo Formations accumulated in the alluvial plain of the foreland basin during the Laramide orogeny. Coal measures of the region were folded and faulted during the Laramide orogeny. Structural deformation has affected the mineability and quality of the coals. Shearing of the seams in adjacent strata has led to oxidation, resulting in weak coal pillars and roofs in underground mines. Faulting and folding has partitioned many coal deposits into discrete structural domains of varying style and complexity. The variation in coal rank in the southern Canadian Rocky Mountains reflects the preorogenic depth of burial. There is some evidence for syn-and post-orogenic coalification. 46 refs., 15 figs., 1 tab.

  11. Formación Río Foyel, oligoceno de la Cuenca de Ñirihuau: la transgresión pacífica en la Cordillera Norpatagónica The Río Foyel Formation, Oligocene- Ñiriuhau Basin: The Pacific Transgression in the Northern Patagonian Andes

    Directory of Open Access Journals (Sweden)

    Marcos A Asensio

    2010-05-01

    Full Text Available La fuerte tectónica extensional producida por el roll-back negativo de la zona de subducción entre las placas Farallón y Sudamericana, desde el Eoceno hasta el Oligoceno temprano, generó diversos depocentros que fueron inundados por el océano Pacífico, originando depósitos marinos con predominio de facies profundas. Las condiciones de circulación marina restringida, anóxicas hasta disóxicas, inferidas para la Formación Río Foyel serían consecuencia de la morfología de los mencionados depocentros. Moldes de yeso cristalino de ejemplares y de cámaras aisladas de Transversigerina cf. transversa en las muestras aparentemente basales de esta formación indicarían una conexión pacífica y profunda. Los niveles basales preservan escasos palinomorfos, pero en los niveles superiores la diversidad y abundancia de dinoquistes y el predominio de materia orgánica amorfa con abundante pirita framboidal sugieren ambientes marinos anóxicos, relativamente distales al área de aporte continental. Los esporomorfos denotan la presencia de bosques templado-húmedos con áreas abiertas subordinadas y gran aporte del ambiente costero.The strong extensive tectonics caused by the negative roll-back of the subduction zone between the Farallón and Southamerican plates due to their relative velocity of convergence, from the Eocene until the early Oligocene, generated diverse marine depocenters connected with the Pacific Ocean, originating marine deposits of dominant deep facies. The restricted circulation and the dysoxic and even anoxic prevailing conditions were a consequence of the morphology of these depocenters; these conditions are inferred for the Río Foyel Formation. Crystalline gypsum internal moulds, of both specimens and isolated chambers of the foraminifera Transversigerina cf. transversa, from apparent basal samples of this formation; suggest a Pacific connection and deep water settings. Palynomorphs are scarce in the basal levels; in the upper levels, the abundance and diversity of dinocysts and the predominance of amorphous organic matter with abundant framboidal pyrite suggest anoxic marine environments relatively distal from the continental source area. The sporomorphs indicate the presence of template-humid forest with subordinate open areas and a remarkable input from the coastal environment.

  12. Preliminary Results From the CAUGHT Experiment: Investigation of the North Central Andes Subsurface Using Receiver Functions and Ambient Noise Tomography

    Science.gov (United States)

    Ryan, J. C.; Ward, K. M.; Porter, R. C.; Beck, S. L.; Zandt, G.; Wagner, L. S.; Minaya, E.; Tavera, H.

    2011-12-01

    Jamie Ryan, Kevin M. Ward, Ryan Porter, Susan Beck, George Zandt, Lara Wagner, Estela Minaya, and Hernando Tavera The University of Arizona The University of North Carolina San Calixto Observatorio, La Paz, Bolivia IGP, Lima, Peru In order to investigate the interplay between crustal shortening, lithospheric removal, and surface uplift we have deployed 50 broadband seismometers in northwestern Bolivia and southern Peru as part of the interdisciplinary Central Andean Uplift and Geodynamics of High Topography (CAUGHT) project. The morphotectonic units of the central Andes from west to east, consist of the Western Cordillera, the active volcanic arc, the Altiplano, an internally drained basin (~4 km elevation), the Eastern Cordillera, the high peaks (~6 km elevation) of an older fold and thrust belt, the Subandean zone, the lower elevation active fold and thrust belt, and the foreland Beni basin. Between northwestern Bolivia and southern Peru, the Altiplano pinches out north of Lake Titicaca as the Andes narrow northward. The CAUGHT seismic instruments were deployed between 13° to 18° S latitudes to investigate the crust and mantle lithosphere of the central Andes in this transitional zone. In northwest Bolivia, perpendicular to the strike of the Andes, there is a total of 275 km of documented upper crustal shortening (15° to 17°S) (McQuarrie et al, 2008). Associated with the shortening is crustal thickening and possibly lithospheric removal as the thickening lithospheric root becomes unstable. An important first order study is to compare upper crustal shortening estimates with present day crustal thickness. To estimate crustal thickness, we have calculated receiver functions using an iterative deconvolution method and used common conversion point stacking along the same profile as the geologically based shortening estimates. In our preliminary results, we observed a strong P to S conversion corresponding to the Moho at approximately 60-65 km depth underneath the

  13. Sr-Nd isotope changes of late cretaceous to early miocene volcanic rocks in central Chile (33oS)

    International Nuclear Information System (INIS)

    A longitudinal depression, the Central Valley, separates the Coast Range from the Andean Cordillera in central Chile. It contains volcanic and volcaniclastic rocks of Late Cretaceous to Tertiary age deposited in a continental environment, and partly eroded Tertiary volcanic complexes. The age of the rocks at the northern end of the Central Valley and their grouping in formations have been a long-standing controversy in Chilean geology (Thomas, 1958; Aguirre, 1960; Drake et al., 1976; Vergara and Drake, 1979; Thiele, 1980; Moscoso et al., 1982; Gana and Wall, 1997; Lopez-Escobar and Vergara, 1997; Selles, 1999). Here, we report new 40Ar/39Ar data and Sr-Nd isotope ratios for lavas, pyroclastic flows and associated subvolcanic rocks from this part of central Chile (au)

  14. Subduction of the South Chile active spreading ridge: A 17 Ma to 3 Ma magmatic record in central Patagonia (western edge of Meseta del Lago Buenos Aires, Argentina)

    Science.gov (United States)

    Boutonnet, E.; Arnaud, N.; Guivel, C.; Lagabrielle, Y.; Scalabrino, B.; Espinoza, F.

    2010-01-01

    The Chile Triple Junction is a natural laboratory to study the interactions between magmatism and tectonics during the subduction of an active spreading ridge beneath a continent. The MLBA plateau (Meseta del Lago Buenos Aires) is one of the Neogene alkali basaltic plateaus located in the back-arc region of the Andean Cordillera at the latitude of the current Chile Triple Junction. The genesis of MLBA can be related with successive opening of slabs windows beneath Patagonia: within the subducting Nazca Plate itself and between the Nazca and Antarctic plates. Detailed 40Ar/ 39Ar dating and geochemical analysis of bimodal magmatism from the western flank of the MLBA show major changes in the back-arc magmatism which occurred between 14.5 Ma and 12.5 Ma with the transition from calc-alkaline lavas (Cerro Plomo) to alkaline lavas (MLBA) in relation with slab window opening. In a second step, at 4-3 Ma, alkaline felsic intrusions were emplaced in the western flank of the MLBA coevally with the MLBA basalts with which they are genetically related. These late OIB-like alkaline to transitional basalts were generated by partial melting of the subslab asthenosphere of the subducting Nazca plate during the opening of the South Chile spreading ridge-related slab window. These basalts differentiated with small amounts of assimilation in shallow magma chambers emplaced along transtensional to extensional zones. The close association of bimodal magmatism with extensional tectonic features in the western MLBA is a strong support to the model of Patagonian collapse event proposed to have taken place between 5 and 3 Ma as a consequence of the presence of the asthenospheric window (SCR-1 segment of South Chile Ridge) below the MLBA area.

  15. ESTADO DE LA POBLACIÓN DE MONOS AULLADORES ROJOS EN EL CAÑÓN DEL BARBAS, FRAGMENTO MONTANO, CORDILLERA CENTRAL, COLOMBIA

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    Gomez-Posada Carolina

    2010-04-01

    Full Text Available

    Los bosques de montaña en Colombia han sufrido fuerte degradación por causas antrópicas; en la actualidad la mayoría son remanentes aislados e inmersos en hábitats antropogénicos. Los aulladores rojos han persistido en estas condiciones pero poco se conoce sobre su biología y respuesta a la alteración de su ambiente. Evaluamos la densidad poblacional y estatus de esta especie en la cuenca del río Barbas (Quindío y Risaralda, fragmento de bosque montano bajo (790 ha. Estimamos la densidad empleando censos por transectos lineales repetidos. Adicionalmente seguimos tropas de aulladores y evaluamos variables de vegetación teniendo en cuenta los requerimientos de la especie. Estimamos una densidad de 11.7±6 grupos y 132.1±68 individuos por km2, para un tamaño poblacional de 1044 aulladores. El tamaño promedio por tropa fue 11, con elevado número de individuos en capacidad de reproducirse y pocos individuos inmaduros (lo cual indica posibles alteraciones sociales. En general el bosque ofrece buena disponibilidad de recursos estructurales y alimenticios para los aulladores. Esta población no se encuentra amenazada en la actualidad por actividades antrópicas, el bosque se encuentra en buen estado con pequeñas zonas en recuperación, la frontera agrícola se encuentra estable y no hubo evidencias de cacería. El fragmento ha sido recientemente protegido bajo la figura de Parque Regional Natural y se adelantan corredores de conexión con otros remanentes. Sin embargo, esta población de aulladores se encuentra aislada de otras poblaciones y por tanto es urgente desarrollar medidas de manejo del paisaje para atenuar los efectos del aislamiento.

  16. Dinámica e implicancia del aluvión de la laguna 513, Cordillera Blanca, Ancash, Perú

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    Patricio Valderrama

    2012-09-01

    Full Text Available La Cordillera Blanca, al norte de Perú, es la zona con más actividad geodinámica externa en Perú. En ella ocurrieron grandes flujos de detritos de origen glaciar, varios de ellos fueron grandes desastres y cobraron miles de vidas. El 11 de abril del 2010, la laguna 513, ubicada en el centro de la Cordillera Blanca, sufrió un desembalse parcial por la caída de un gran bloque de hielo y rocas del nevado Hualcán (5500 m.s.n.m.. Este evento pese a ser de dimensiones considerables, no generó grandes pérdidas ni afectó alguna ciudad importante. Mediante simulaciones numéricas de flujo se estudió su dinámica, se determinó sus volúmenes y su turbulencia así como también explicamos e papel de la morfología de la zona en la desaceleración del flujo, su encausamiento en un valle fluvial y su posterior comportamiento como crecida de río. Las simulaciones realizadas mediante FLO2D se validan mediante comparaciones con imágenes de satélite post evento y datos de campo.

  17. Descripción de las larvas de dos centrolénidos (Anura: Centrolenidae del noroccidente de la Cordillera Oriental, Colombia

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    Marco Rada

    2007-01-01

    Full Text Available Se describen las larvas de dos especies de la familia Centrolenidae (Hyalinobatrachium ibama y Cochranella daidalea procedentes del flanco occidental de la cordillera Oriental en el departamento de Norte de Santander, Colombia. En la descripción de las larvas, además de las características morfológicas tradicionales, se incorporaron nuevos elementos de juicio como la longitud del tubo cloacal, la forma del rostro, el patrón de color y la posición del espiráculo, los cuales resultaron ser informativos y muy útiles en la diferenciación de las especies. Se proporciona una discusión acerca de la validez taxonómica de algunos de los caracteres morfológicos empleados usualmente en las descripciones y comparaciones de los renacuajos de la familia Centrolenidae.We describe herein the larvae of two species of the family Centrolenidae (Hyalinobatrachium ibama and Cochranella daidalea from the Department of Norte de Santander on the western flank of the Cordillera Oriental, Colombia. In order to provide an adequate description, we incorporate new elements such as: vent-tube length, snout shape, color pattern and spiracle position. A discussion about the taxonomic validity of some tadpole morphological characteristics traditionally used in descriptions and comparisons of the family Centrolenidae is provided.

  18. Niche shifts and range expansions along cordilleras drove diversification in a high-elevation endemic plant genus in the tropical Andes.

    Science.gov (United States)

    Kolář, Filip; Dušková, Eva; Sklenář, Petr

    2016-09-01

    The tropical Andes represent one of the world's biodiversity hot spots, but the evolutionary drivers generating their striking species diversity still remain poorly understood. In the treeless high-elevation Andean environments, Pleistocene glacial oscillations and niche differentiation are frequently hypothesized diversification mechanisms; however, sufficiently densely sampled population genetic data supporting this are still lacking. Here, we reconstruct the evolutionary history of Loricaria (Asteraceae), a plant genus endemic to the Andean treeless alpine zone, based on comprehensive population-level sampling of 289 individuals from 67 populations across the entire distribution ranges of its northern Andean species. Partly incongruent AFLP and plastid DNA markers reveal that the distinct genetic structure was shaped by a complex interplay of biogeography (spread along and across the cordilleras), history (Pleistocene glacial oscillations) and local ecological conditions. While plastid variation documents an early split or colonization of the northern Andes by at least two lineages, one of which further diversified, a major split in the AFLP data correlate with altitudinal ecological differentiation. This suggests that niche shifts may be important drivers of Andean diversification not only in forest-alpine transitions, but also within the treeless alpine zone itself. The patterns of genetic differentiation at the intraspecific level reject the hypothesized separation in spatially isolated cordilleras and instead suggest extensive gene flow among populations from distinct mountain chains. Our study highlights that leveraging highly variable markers against extensive population-level sampling is a promising approach to address mechanisms of rapid species diversifications.

  19. Origin of gem corundum in calcite marble: The Revelstoke occurrence in the Canadian Cordillera of British Columbia

    Science.gov (United States)

    Dzikowski, Tashia J.; Cempírek, Jan; Groat, Lee A.; Dipple, Gregory M.; Giuliani, Gaston

    2014-06-01

    The calcite marble-hosted gem corundum (ruby, sapphire) occurrence near Revelstoke, British Columbia, Canada, occurs in the Monashee Complex of the Omineca Belt of the Canadian Cordillera. Corundum occurs in thin, folded and stretched layers with green muscovite + Ba-bearing K-feldspar + anorthite (An0.85-1) ± phlogopite ± Na-poor scapolite. Other silicate layers within the marble are composed of: (1) diopside + tremolite ± quartz and (2) garnet (Alm0.7-0.5Grs0.2-0.4) + Na-rich scapolite + diopside + tremolite + Na,K-amphiboles. Non-silicate layers in the marble are either magnetite- or graphite-bearing. Predominantly pink (locally red or purple) opaque to transparent corundum crystals have elevated Cr2O3 (≤ 0.21 wt.%) and variable amounts of TiO2; rare blue rims on the corundum crystals contain higher amounts of TiO2 (≤ 0.53 wt.%) and Fe2O3 (≤ 0.07 wt.%). The associated micas have elevated Cr, V, Ti, and Ba contents. Petrography of the silicate layers show that corundum formed from muscovite at the peak of metamorphism (~ 650-700 °C at 8.5-9 kbar). Because the marble is almost pure calcite (dolomite is very rare), the corundum was preserved because it did not react with dolomite to spinel + calcite during decompression. The scapolite-bearing assemblages formed during or after decompression of the rock at ~ 650 °C and 4-6 kbar. Gem-quality corundum crystals formed especially on borders of the mica-feldspar layers in an assemblage with calcite. Whole rock geochemistry data show that the corundum-bearing silicate (mica-feldspar) layers formed by mechanical mixing of carbonate with the host gneiss protolith; the bulk composition of the silicate layers was modified by Si and Fe depletion during prograde metamorphism. High element mobility is supported by the homogenization of δ18O and δ13C values in carbonates and silicates for the marble and silicate layers. The silicate layers and the gneiss contain elevated contents of Cr and V due to the volcanoclastic

  20. EXPERIENCIAS DE CORDILLERA, ECOS DE FRÍO: RELATOS CRUZADOS ENTRE CHILE Y QUITO EN EL SIGLO XVI

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    Alejandra Vega

    2011-11-01

    Full Text Available La narración de la secuencia de la conquista del Perú nos enfrenta con la fijación de dos episodios diferentes aunque articulados: la jornada a Quito de Pedro de Alvarado en 1534 y la expedición a Chile de Diego de Almagro, entre 1535 y 1536, que incluyen, ambas, una travesía cordillerana. El presente artículo discute los ecos que pueden rastrearse de los relatos acerca de estas expediciones en un conjunto de obras redactadas en torno a 1550 (Gonzalo Fernández de Oviedo, Francisco López de Gómara, Pedro Cieza de León y Agustín de Zárate. A partir de convergencias y diferencias inesperadas en estos textos, se discute la importancia de la circulación oral de historias entre los conquistadores del Perú. Se plantea que la práctica social de la conversación oral permitió fijar, además de estas historias, una temprana conceptualización cristiana de los límites del Tawantinsuyu. En ella se concibió a Quito y Chile como las marcas fronterizas del espacio recién conquistado, permitiendo que ambos territorios se superpusieran al caracterizarse a partir a un mismo conjunto de imágenes sobre la experiencia de la cordillera.In the Hispanic narrative of the conquest of Peru, we can identify two different yet related episodes: Pedro de Alvarado's journey to Quito in 1534 and the expedition to Chile commanded by Diego de Almagro in 1535-1536. This article discusses the echoes than can be pinpointed in the accounts of both experiences in a corpus of texts written or printed around 1550 (Gonzalo Fernández de Oviedo, Francisco López de Gómara, Pedro Cieza de León and Agustín de Zárate. By tracing unexpected similarities and differences, this proposal discusses the importance of oral circulation of histories amongst Peruvian conquistadors. The features of conversation, as a social practice, allowed the register ofan early Christian conceptualization of the Tawantinsuyu territory. Here Quito and Chile became frontier marks of the

  1. Modelling cascading and erosional processes for glacial lake outburst floods in the Quillcay catchment, Huaraz, Cordillera Blanca, Peru

    Science.gov (United States)

    Baer, Patrick; Huggel, Christian; Frey, Holger; Chisolm, Rachel; McKinney, Daene; McArdell, Brian; Portocarrero, Cesar; Cochachin, Alejo

    2016-04-01

    Huaraz as the largest city in Cordillera Blanca has faced a major disaster in 1941, when an outburst flood from Lake Palcacocha killed several thousand people and caused widespread destruction. Recent studies on glacial lake outburst flood (GLOF) modelling and early warning systems focussed on Lake Palcacocha which has regrown after the 1941 event, from a volume of half a million m3 in 1974 to a total volume of more than 17 million m3 today. However, little research has been conducted so far concerning the situation of other lakes in the Quillcay catchment, namely Lake Tullparaju (12 mill. m3) and Cuchillacocha (2.5 mill. m3), which both also pose a threat to the city of Huaraz. In this study, we modelled the cascading processes at Lake Tullparaju and Lake Cuchillacocha including rock/ice avalanches, flood wave propagation in the lake and the resulting outburst flood and debris flows. We used the 2D model RAMMS to simulate ice avalanches. Model output was used as input for analytical 2D and 3D calculations of impact waves in the lakes that allowed us to estimate dam overtopping wave height. Since the dimension of the hanging glaciers above all three lakes is comparable, the scenarios in this study have been defined similar to the previous study at Lake Palcacocha. The flow propagation model included sediment entrainment in the steeper parts of the catchment, adding up to 50% to the initial flow volume. The results for total travel time as well as for inundated areas and flow depth and velocity in the city of Huaraz are comparable to the previous studies at Lake Palcacocha. This underlines the importance of considering also these lakes within an integral hazard analysis for the city of Huaraz. A main challenge for modelling GLOFs in the Quillcay catchment using RAMMS is the long runout distance of over 22 km combined with the very low slope gradient of the river. Further studies could improve the process understanding and could focus on more detailed investigations

  2. Microstructures and Petrology of Melt Inclusions in the Anatectic Sequence of Jubrique (Betic Cordillera, S Spain): Implications for Crustal Anatexis

    Science.gov (United States)

    Acosta-vigil, A.; Barich, A.; Garrido, C. J.; Cesare, B.; Tajčmanová, L.; Bartoli, O.

    2014-12-01

    We report a new occurrence of melt inclusions in polymetamorphic granulitic gneisses of the Jubrique unit, a complete though thinned crustal section located above the Ronda peridotite slab (Betic Cordillera, S Spain). The gneissic sequence is composed of mylonitic gneisses at the bottom and porphyroblastic gneisses on top. Mylonitic gneisses are strongly deformed rocks with abundant garnet and rare biotite. Except for the presence of melt inclusions, microstructures indicating the former presence of melt are rare or absent. Upwards in the sequence garnet decreases whereas biotite increases in proportion. Melt inclusions are present from cores to rims of garnets throughout the entire sequence. Most of the former melt inclusions are now totally crystallized and correspond to nanogranites, whereas some of them are partially made of glass or, more rarely, are totally glassy. They show negative crystal shapes and range in size from ≈5 to 200 micrometers, with a mean size of ≈30-40 micrometers. Daughter phases in nanogranites and partially crystallized melt inclusions include quartz, feldspars, biotite and muscovite; accidental minerals include kyanite, graphite, zircon, monazite, rutile and ilmenite; glass has a granitic composition. Melt inclusions are mostly similar throughout all the gneissic sequence. Some fluid inclusions, of possible primary origin, are spatially associated with melt inclusions, indicating that at some point during the suprasolidus history of these rocks granitic melt and fluid coexisted. Thermodynamic modeling and conventional thermobarometry of mylonitic gneisses provide peak conditions of ≈850 ºC and 12-14 kbar, corresponding to cores of large garnets with inclusions of kyanite and rutile. Post-peak conditions of ≈800-850 ºC and 5-6 kbar are represented by rim regions of large garnets with inclusions of sillimanite and ilmenite, cordierite-quartz-biotite coronas replacing garnet rims, and the matrix with oriented sillimanite. Previous

  3. Recurrencia en el desarrollo de cuencas de intraarco.: Cordillera Neuquina (37°30´- 38°S

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    A. Folguera

    2003-03-01

    Full Text Available Los Andes entre 36° y 39°S están caracterizados por la superposición de tres cuencas de intraarco a lo largo de los últimos 25 millones de años, de las cuales las primeras dos han sido separadas entre sí por fenómenos de inversión tectónica. El rasgo orogénico resultante de esta fase de deformación colapsó parcialmente durante los últimos dos ciclos de extensión. El primer evento extensional corresponde a la cuenca de Cura Mallín que se desarrolló entre 25 y 12 millones de años atrás (Oligoceno superior al Mioceno inferior-medio, fue invertida entre 12 y 8 Ma (Mioceno superior, con una cordillera resultante de poco más de 2000 metros de altura. El segundo ciclo se corresponde con la cuenca de Cola de Zorro, la cual comenzó a subsidir hace 5 millones de años (Plioceno inferior. La unidad correspondiente a la Formación Cola de Zorro se ha depositado desde su comienzo sobre la estructura compresiva del orógeno formado a partir de la inversión de la cuenca de Cura Mallín, como consecuencia de un colapso extensional del mismo o quizás de un relajamiento extensional de la estructura compresiva, que deprimió este rasgo por debajo de la cota de 1200 metros sobre el nivel del mar. A lo largo del límite internacional, existen aún remanentes de la estructura orogénica del Mioceno superior que fueron conservados como altos estructurales de la cuenca pliocena inferior. Estos altos facilitan el estudio de la estructura original. La recurrencia en la formación de cuencas de intraarco durante los últimos 25 millones de años estaría ligada a la migración promedio hacia la trinchera del frente volcánico durante el Terciario, como consecuencia del empinamiento de la placa de Nazca y a inestabilidades de la estructura orogénica derivadas de reorganizaciones mayores en el sistema subductivo entre las placas vecinas.

  4. Spatio-temporal assessment of WRF, TRMM and in situ precipitation data in a tropical mountain environment (Cordillera Blanca, Peru

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    L. Mourre

    2015-07-01

    Full Text Available The estimation of precipitation over the broad range of scales of interest for climatologists, meteorologists and hydrologists is challenging in high altitudes of tropical regions, where the spatial variability of precipitation is important while in situ measurements remain scarce largely due to operational constraints. Three different types of rainfall products – ground based, satellite derived, RCM outputs – are compared here during the hydrological year 2012/13 in order to retrieve rainfall patterns at time scales ranging from sub-daily to annual over a watershed of approximately 10 000 km2 in Peru. It is a high altitude catchment, located in the region of the Cordillera Blanca, with 41 % of its area above 4000 m a.s.l. and 340 km2 glaciated. Daily in situ data are interpolated using a kriging with external drift (KED algorithm; the satellite product is TRMM 3B42, which incorporates monthly gauge data; RCM outputs are obtained from WRF run with a Thompson microphysical scheme at three nested resolutions: 27, 9 and 3 km. The performances of each product are assessed from a double perspective. A local comparison with gauge data is first carried out when relevant (diurnal and seasonal cycles, statistics of rainfall occurrence; then the ability of each product to reproduce some well-known spatial features of rain fields at various time scales (from annual down to daily is analysed. WRF simulations largely overestimate the annual totals, especially at low spatial resolution, while reproducing correctly the diurnal cycle and locating the spots of heavy rainfall more realistically than either the ground-based KED or the TRMM products. The main weakness of the KED data is the production of annual rainfall maxima over the summit rather than on the slopes, induced by a lack of in situ data above 3800 m a.s.l. One main limitation of the TRMM product is its poor performance over ice-covered areas because ice on the ground behaves in a similar way as

  5. Controls on the isotopic composition of surface water and precipitation in the Northern Andes, Colombian Eastern Cordillera

    Science.gov (United States)

    Saylor, Joel E.; Mora, Andrés; Horton, Brian K.; Nie, Junsheng

    2009-12-01

    Empirical datasets provide the constraints on the variability and causes of variability in stable isotope compositions (δD or δ 18O) of surface water and precipitation that are essential not only for models of modern and past climate but also for investigations of paleoelevation. This study presents stable isotope data for 76 samples from four elevation transects and three IAEA GNIP stations in the Eastern Cordillera of Colombia and the northern Andean foreland. These data are largely consistent with theories of stable isotope variability developed based on a global dataset. On a monthly basis, the precipitation-amount effect exerts the dominant control on δD p and δ 18O p values at the IAEA GNIP stations. At the Bogotá station (2547 m), the δD p and δ 18O p values vary seasonally, with isotopic minima correlating with maxima in precipitation-amount. Although surface water samples from Eastern Cordilleran streams and rivers fall on the Global Meteoric Water Line, samples from three of four lakes (2842-3459 m) have evaporatively elevated δD sw and δ 18O sw values. The IAEA GNIP station data averaged over multiple years, combined with stream and river water data, define vertical lapse rates of -1.8‰ km -1 for Δδ 18O and -14.6‰ km -1 for ΔδD, and are a close fit to a common thermodynamically based Rayleigh distillation model. Elevation uncertainties for these relationships are also evaluated. Comparison of this Colombian dataset with the elevation uncertainties generated by the thermodynamically based model shows that the model underestimates uncertainty at high Δδ 18O and ΔδD values while overestimating it for low Δδ 18O and ΔδD values. This study presents an independent, empirical assessment of stable isotope-based elevation uncertainties for the northern Andes based on a dataset of sufficient size to ensure statistical integrity. These vertical lapse rates and associated uncertainties form the basis for stable isotope paleoelevation studies

  6. The Formation of a Retroarc Fold-Thrust Belt by the Closure and Inversion of a Back-Arc Basin; Patagonian-Fuegian Fold-Thrust Belt, Chile

    Science.gov (United States)

    Betka, P.; Klepeis, K. A.; Mosher, S.

    2012-12-01

    The Late Cretaceous closure and inversion of the Late Jurassic Rocas Verdes back-arc basin (RVB) defines the onset of the Andean orogeny and the development of the Patagonian retroarc fold-thrust belt (FTB) between 50°-54.5° S. Back-arc extension in the RVB led to the generation of new oceanic crust that was coeval with the deposition of syn-rift silicic volcanoclastic rocks on the continental margin. A > 500 m thick succession of mudstone and distal turbidite deposits accumulated in the RVB (post-rift). New maps and line-balanced cross-sections from three transects across the FTB show a transition through time from thin-to thick-skinned structural styles that is controlled by the inherited stratigraphic architecture and structure of the RVB. The closure of the RVB and development of the FTB occurred in two stages. During the initial stage, mafic schist, gabbro, basalt, and hemipelagic mudstone of the RVB floor were imbricated and thrust onto the continental margin resulting in the formation of the Magallanes foreland basin and underthrusting of the continental crust to depths of ~ 35 km. Displacement from the obduction of the RVB was transferred along two decollement levels into the FTB by ~85 Ma. Each decollement level formed at a rheological boundary within the syn- and post-rift stratigraphy. The lower decollement formed in quartz-chlorite schist (basement) > 1 km beneath the top-basement contact with relatively strong syn-rift volcanoclastic deposits. The lower decollement is defined by a ~1 km thick ductile shear zone. C-S fabrics, C-C' shear bands and prominent SW plunging quartz stretching lineations that occur within the shear zone indicate a top-NE transport direction. Isoclinal recumbent F2 folds and inclined tight F3 folds refold the S1/L1 surface. The decollement cuts up-section through the syn-rift volcanoclastic deposits to join a structurally higher decollement that formed within weak, post-rift mudstone and turbidite deposits on the continental

  7. Tectonic control on rock uplift, exhumation, and topography above an oceanic ridge collision: Southern Patagonian Andes (47°S), Chile

    Science.gov (United States)

    Georgieva, Viktoria; Melnick, Daniel; Schildgen, Taylor F.; Ehlers, Todd A.; Lagabrielle, Yves; Enkelmann, Eva; Strecker, Manfred R.

    2016-06-01

    The subduction of bathymetric anomalies at convergent margins can profoundly affect subduction dynamics, magmatism, and the structural and geomorphic evolution of the overriding plate. The Northern Patagonian Icefield (NPI) is located east of the Chile Triple Junction at ~47°S, where the Chile Rise spreading center collides with South America. This region is characterized by an abrupt increase in summit elevations and relief that has been controversially debated in the context of geodynamic versus glacial erosion effects on topography. Here we present geomorphic, thermochronological, and structural data that document neotectonic activity along hitherto unrecognized faults along the flanks of the NPI. New apatite (U-Th)/He bedrock cooling ages suggest faulting since 2-3 Ma. We infer the northward translation of an ~140 km long fore-arc sliver -- the NPI block -- results from enhanced partitioning of oblique plate convergence due to the closely spaced collision of three successive segments of the Chile Rise. In this model, greater uplift occurs in the hanging wall of the Exploradores thrust at the northern leading edge of the NPI block, whereas the Cachet and Liquiñe-Ofqui dextral faults decouple the NPI block along its eastern and western flanks, respectively. Localized extension possibly occurs at its southern trailing edge along normal faults associated with margin-parallel extension, tectonic subsidence, and lower elevations along the Andean crest line. Our neotectonic model provides a novel explanation for the abrupt topographic variations inland of the Chile Triple Junction and emphasizes the fundamental effects of local tectonics on exhumation and topographic patterns in this glaciated landscape.

  8. Spatial overlap of Black-browed albatrosses with longline and trawl fisheries in the Patagonian Shelf during the non-breeding season

    Science.gov (United States)

    Copello, Sofía; Seco Pon, Juan Pablo; Favero, Marco

    2014-05-01

    Incidental mortality in fisheries is the main at-sea threat albatrosses are facing nowadays. In this study we used remote sensing techniques to model the degree of spatial overlapping between the Black-browed albatross (Thalassarche melanophris) and Argentine fisheries, assuming this as a proxy of risk for albatrosses. Eleven tags were deployed on albatrosses during the non-breeding seasons 2011 and 2012 in the Patagonian Shelf. Their distribution overlapped to different extents with the two coastal trawl, three offshore trawl and one demersal longline fisheries. The overlap index showed highest values with both coastal fleets, followed by the ice-chilling trawl fleet. These intersections were located in the Argentinean-Uruguayan Common Fishing Zone, in coastal areas of the SE of Buenos Aires province, El Rincón estuary and over the shelf break. The analysis of intersections of focal areas from albatrosses and all fisheries allowed the identification of thirty-four fishing management units (1° by 1° grid within the Argentine EEZ) classified as of medium, high or very high conservation priority. Very high priority units were placed between 35 and 38°S in the external mouth of Rio de la Plata, and between 45 and 47°S in neighboring waters East to the hake fishing closure. Although there were possible biases due to the limited number of tracked birds and the locations where albatrosses were captured and instrumented, the information presented in this study provides a comprehensive picture of important areas of overlapping during winter that could be used by the fishery administration to prioritize conservation actions under limited resource scenarios.

  9. Combined impact of ultraviolet radiation and increased nutrients supply: A test of the potential anthropogenic impacts on the benthic amphipod Amphitoe valida from Patagonian waters (Argentina

    Directory of Open Access Journals (Sweden)

    Macarena S. Valiñas

    2014-08-01

    Full Text Available Experiments were conducted during the Austral Summer of 2014 to determine the effects of increased nutrient input and ultraviolet radiation (UVR on the food consumption rate (FCR and food preference in the amphipod Amphitoe valida. We collected specimens from the Patagonian coast (Argentina, from beaches close (Barrancas Blancas; BB and further away (Cangrejales; C from the Chubut River, which constitutes the potential source of eutrophication. Organisms were exposed to different radiation regimes (full radiation vs. PAR only and fed with different macroalgae diets (i.e., from different geographical location and with different quality in terms on nutrient content. Males collected from C showed food compensation, consuming more food under low-nutrient diets, while no compensation was observed in males from BB. Regardless of their origin, UVR decreased the FCR when males where fed on ambient nutrient diets, but not when males fed on high-quality diets indicating that in the former case, individuals were in worse physiological conditions to cope with UVR; food quality, however, significantly counteracted the deleterious effects of UVR on FCR. Females collected from the two beaches showed similar FCR under high-nutrient diet and had no food compensation when fed in low-nutrient diets. Females were more vulnerable to UVR, since their FCR were lower when exposed to UV radiation independent of the diet. Our results show that under anthropogenic eutrophication and high solar UVR levels an increase in the nutrient input could favor only males of A. valida, by reducing the negative effects of UVR on their FCR. Nevertheless, these nutrient inputs might cause additional problems like anoxia, as a result of an unusual macroalgal growth, thus affecting amphipod’s survival.

  10. Did Patagonia collide against Gondwana in the Late Paleozoic? Some Insights From Magnetic Fabrics of Granitoids in the North Patagonian Massif.

    Science.gov (United States)

    Rapalini, A. E.; Lopez de Luchi, M. G.; Tomezzoli, R. N.

    2008-05-01

    The Paleozoic tectonic evolution of Patagonia has been a matter of much debate in the last two decades. There is no consensus on whether the North Patagonian Massif (NPM) was accreted by a frontal collision to Gondwana in the Late Paleozoic or if it shared a similar paleotectonic evolution with other Gondwana blocks during the Paleozoic. Different geologic, geochronologic, geophysical and structural data have been interpreted either as supporting or refuting the collisional model. Paleomagnetic data obtained so far is consistent with an authochtonous evolution since the Devonian, but it does not rule out relative displacements of up to 1500 km between Patagonia and Gondwana.Therefore, a Late Paleozoic frontal collision cannot be definitely ruled out on the basis of paleomagnetic data alone. As part of a muldisciplinary research project a magnetic fabric study, by means of the anisotropy of magnetic susceptibility (AMS), was carried out on Late Paleozoic granitoids exposed in northeastern NPM. Two main composite units were studied, the highly to variably foliated Yaminue Complex, poorly dated as Late Carboniferous and ranging in composition from tonalite to leuco-granite, and the much less deformed granodiorites to monzoganites of the Early Permian (283 Ma) Navarrete complex. While the former is composed of both ferro and paramagnetic units, with a dominance of the latter; the Navarrete plutons are basically ferromagnetic. Directional and scalar AMS results joined with meso and microstructural studies permitted the characterization of the deformational and magmatic fabric of the different units. An evolutionary picture of the succesive intrusive events in NPM emerged which confirms an important NNE-SSW contractional event associated with intrusion of the different units that compose the Yaminue Complex. This event ended before the intrusion of the Navarrete Complex, which is governed by a different stress regime. Our results fit the hypothesis of a collisional event

  11. Genetic variation in seedling water-use efficiency of Patagonian Cypress populations from contrasting precipitation regimes assessed through carbon isotope discrimination

    Energy Technology Data Exchange (ETDEWEB)

    Pastorino, M. J.; Aparicio, A. G.; Marchelli, P.; Gallo, L. A.

    2012-11-01

    Water-use efficiency (WUE) is a physiological parameter that plays a significant role in the evolutionary dynamics of many forest tree species. It can be estimated indirectly through carbon isotope discrimination (A). In general, plants of more arid origins have lower values of A. In order to study the degree of genetic control of this parameter and the genetic variation in A of Patagonian Cypress seedlings, three Argentinean natural populations chosen to represent two contrasting precipitation regimes were sampled in a common garden trial. The dry situation was represented by two neighboring marginal forest patches from the steppe, while the humid condition was represented by a population with 1,200 mm higher mean annual precipitation. Height (H) and A were measured in 246 five-year-old seedlings from 41 open-pollinated families. The factor family had a significant effect on both variables; however heritability for A was found not to be significant in two out of the three populations. This could be explained by low sample size in one of them and by a real evolutionary effect in the other. An inverse association between H and A was verified, which is interpreted as evidence of an adaptation process at the intra-population level. The studied populations were not shown to discriminate carbon isotopes differently; hence evidence of adaptation to current environmental conditions could not be obtained. On the other hand, the arid populations proved to be quite different in terms of genetic variation, which seems to be the consequence of genetic drift and isolation. (Author) 49 refs.

  12. What controls millennial-scale denudation rates across the Central Andes?

    Science.gov (United States)

    Zeilinger, Gerold; Korup, Oliver; Schlunegger, Fritz; Kober, Florian

    2015-04-01

    Sustainable planning of erosion control measures in the Central Andes requires robust knowledge about natural denudation rates. We explore a large dataset combining new and published 10Be (and 26Al) catchment-wide denudation rates from a swath at 17 to 19° S spanning the Western Cordillera that rises from sea level to 5500 m elevation; the Altiplano at ~4000 m; the Eastern Cordillera with elevations up to 6500 m; the Interandean Zone; the Subandean Zone; and the Chaco Plain at 300 m. The selected catchments span a large spread regarding morphometric and climate properties where mean slope angles range from 1 to 31°, and mean precipitation from 100 to 3900 mm/a. The denudation rates (0.0036 to 1.93 mm/a) are averaged over millennia, and reveal two to three magnitudes difference across the Central Andes. The regional distribution of denudation rates clearly demonstrates a more complex interaction of geomorphological, geological and meteorological parameters with the dominant geomorphological processes. In order to elucidate the key controls on denudation, we use multivariate statistics such as principal component analysis in order to remove potentially redundant predictors of denudation in the studied catchments. These predictors include catchment elevation, topographic relief, hillslope inclination, mean precipitation, tree cover, specific stream power, channel steepness indices, sinuosity, drainage density and hypsometric index that we derived from the SRTM 90 m Digital Elevation Database, the Tropical Rainfall Measuring Mission (TRMM) data, and the Terra MODIS Vegetation Continuous Fields dataset. Additionally, the rock strength index (PLI) was estimated based on geological units. Preliminary results allow distinguishing five different longitudinal domains of denudation on the basis of climatic regime, hillslope steepness, and the degree of accumulated crustal deformation. We find that the pattern of 10Be catchment-wide denudation rates in the Central Andes

  13. Comments to Middle Miocene closure of the Central American Seaway

    Science.gov (United States)

    Coates, A.G.; Stallard, Robert F.

    2016-01-01

    In a recent paper proposing an early (mid-Miocene) closure of the Central American Seaway (CAS), Montes et al. 2015 (1) disregard existing paleogeographic data that invalidate Panama as a source for zircons, and inappropriately ignore the evidence for trans-isthmian marine connections until 4-3 Ma. They also fail to cite previous work (2, 3), that had reconstructed the Central American arc already docked with South America by 12 Ma. Montes et al. 2015 (1) (Fig. 1) disregard the Atrato-San Juan sedimentary basin (3), a shallowing Oligocene to Pliocene, Pacific to Caribbean seaway (3, 4, 5). This deep graben (6) is filled with thousands of meters of Pre-Pliocene marine sediments (3, 5, 6) that now occupy a lowland between the Baudo uplift to the west and the Western Cordillera to the east. The Mande Batholith and numerous Eocene and younger volcanic rocks (4), the most proximal source of the zircons, are situated to the east of this seaway and would have shed zircons eastward towards the Cordillera Central. There is no evidence for any rivers crossing the seaway (3, 5), and thus no Panamanian source of zircons. Instead this seaway is evidence of a significant marine connection between the Pacific and Atlantic oceans into the Pliocene. The authors assume that the middle Miocene closure of the CAS effectively creates a continuous land bridge connecting North and South America and separating the Atlantic from the Pacific. They acknowledge, but then discount, marine connections across the Isthmus until 4-3 Ma even though these satisfactorily explain (Coates and Stallard, 2014 (6)) the oceanographic, molecular and Great American Biological Interchange events ignore unexplained by Montes et al. 2015. Only by conspicuously ignoring these events can they imply that the Isthmus was formed at 15-13 Ma. References 1. C. Montes et al., Middle Miocene closure of the Central American Seaway. Science 348, 226-229 (2015). 2. A. G. Coates, R. F. Stallard, How old is the Isthmus of

  14. Infection patterns of Tylodelphys barilochensis and T. crubensis (Trematoda: Diplostomatidae) metacercariae in Galaxias maculatus (Osmeriformes: Galaxiidae) from two Patagonian lakes and observations on their geographical distribution in the southern Andean region, Argentina.

    Science.gov (United States)

    Flores, Verónica; Liliana, Semenas

    2002-12-01

    In the Patagonian Andean region, 2 species of diplostomatids parasitize the brains of Galaxias maculatus. The purpose of this study was to evaluate seasonal variation, spatial variation, and association with host age in the transmission of Tylodelphys barilochensis and T. crubensis in several oligotrophic lakes in Argentinian Patagonia. Fishes were captured monthly in Lake Gutiérrez and bimonthly in Lake Escondido. One summer or autumn sample was also taken in several other Patagonian lakes. Infection parameters were calculated and compared using nonparametric tests. The 2 species co-occurred in most of the sampled lakes, with high values of prevalence and mean intensity. In Lake Gutiérrez and Lake Escondido, the intensity of both diplostomatid species did not show significant differences between sexes and co-varied with host length. All age classes were infected; maximum prevalence values were reached before maximum mean intensity values in the 1-yr age class. A seasonal pattern of prevalence and mean intensity of the 2 parasite species with autumn mean intensity values differing significantly from those of the other seasons was evident only in Lake Gutiérrez. PMID:12537107

  15. Evolución de las cuencas sinorogénicas de la Cordillera Principal entre 35°- 36° S, Malargüe Evolution of the foreland basins in the Cordillera Principal, at 35º - 36º S. Malargüe

    OpenAIRE

    Silvestro, J.; P. Kraemer; Achilli, F.; W. Brinkworth

    2005-01-01

    La faja plegada y corrida de Malargüe se encuentra localizada en el extremo sur de la Cordillera Principal a los 35°-36° S. Los estratos de crecimiento preservados en cuencas sintectónicas registraron la cinemática de plegamiento de la faja plegada durante el Cenozoico. La cuenca Pinchera-Ventana, ubicada en el sector oeste del área, está rellena por dos secuencias volcaniclásticas cubiertas por basaltos. En el sector occidental de esta cuenca, las secuencias se adelgazan hacia los anticlinal...

  16. New Constraints on the Timing and Magnitude of Deformation and Basin Exhumation in the Eastern Cordillera of NW Argentina.

    Science.gov (United States)

    Trimble, J. D.; Carrapa, B.; Stockli, D. F.; Stutz, J.

    2008-12-01

    The Angastaco Basin is a ~20km wide and ~6km thick intramontane basin within the Eastern Cordillera (EC) of NW Argentina. The basin is bounded to the east and west by reverse faults that put basement rocks of the Paleozoic Puncoviscana and Cretaceous Santa Barbara Group on top of the Cenozoic sequence. Numerous faults and folds disrupt the basin internally. Some, if not most, of these structures seem to be the result of reactivation of previous normal faults related to the Salta Rift (Carrera et al. , 2006). Recent structural and thermochronological data from the EC of Argentina suggest tectonic deformation in the Eocene-Miocene (e.g., Coutand et al., 2006; Hogn et al., 2007). Data from the EC in Bolivia suggest that deformation ceased by ca. 10.7 Ma (McQuarrie et al., 2005). Therefore, different challenging questions remain open such as: (1) Are all the structures observed in the basin and along its margin a result of reactivation? (2) When was the timing and what was the magnitude of deformation within the basin and surrounding region? New detailed mapping and cross-sections in the Angastaco Basin reveal a number of faults and folds never before documented, including several km-scale west vergent folds interspersed with a complex arrangement of smaller, more angular, east-vergent faults and folds. Clear influence from both east and west-vergent deformation within the basin suggests interplay between the eastward propagation of EC related structures and westward reactivation of Santa Barbara System structures. A lack of structural continuity across the roughly E-W trending portions of Rio Calchaqui suggests that the river follows one or more unexposed strike- slip faults as it cuts across the Tertiary section from W to E. Minor offsets and lack of lateral continuity suggest that these faults are likely tear-faults coeval with deformation in the basin, although they may have been active during multiple pulses of tectonism. With an east-west trend, these structures

  17. Clasificación de yeso mediante imágenes ASTER en la Cordillera Principal Mendocina

    Directory of Open Access Journals (Sweden)

    José F Mescua

    2010-06-01

    Full Text Available Se presenta una metodología para obtener el mapa de distribución de yeso con imágenes satelitales ASTER. Se utilizaron imágenes con nivel de procesamiento ASTERL3A correspondientes a dos áreas de la Cordillera Principal mendocina. La estratigrafía de las áreas de estudio se encuentra compuesta por una espesa sucesión sedimentaria mesozoica, volcanitas cenozoicas y depósitos cuaternarios. Dentro de los depósitos mesozoicos se encuentra la Formación Auquilco, integrada por yeso y anhidrita. El reconocimiento y distribución areal de esta unidad es el objetivo de este trabajo. Se aplicaron dos métodos de procesamiento a las imágenes. Por un lado se utilizó el índice de cuarzo (Qi, uno de los índices de determinación de minerales definidos para el subsistema TIR de ASTER. Este índice puede usarse también para reconocer sulfatos, y en particular yeso, ya que estos minerales proporcionan una respuesta muy baja en el Qi. El segundo método consistió en la aplicación combinada de los cocientes de bandas 4/5 y 7/5. Este método permite identificar al yeso por su elevada respuesta en el cociente 4/5 y baja respuesta en el cociente 7/5. A fin de simplificar la metodología, se generó un nuevo cociente a partir de los dos mencionados: (4/5/(7/5, de manera de destacar el yeso con alta respuesta. A partir del relevamiento de campo se observó que en ambos métodos los errores por exceso fueron más importantes que los errores por defecto, y que los píxeles determinados como yeso erróneamente por cada método son diferentes. Este hecho permite la aplicación de la técnica de "Decision Tree" del programa ENVI 4.2 con el objetivo de eliminar estos errores. En cada una de las imágenes se determinaron los valores de umbral para los píxeles reconocidos como yeso. Luego se generó un "árbol de decisiones" combinando los umbrales de cada imagen, seleccionando en una nueva clase los píxeles determinados como yeso por ambos métodos y

  18. Reducing risks from hazardous glacier lakes in the Cordillera Blanca (Peru): Six decades of experience and perspectives for the future

    Science.gov (United States)

    Portocarrero, Cesar; Cochachin, Alejo; Frey, Holger; González, Cesar; Haeberli, Wilfried; Huggel, Christian

    2016-04-01

    Outbursts from glacier lakes at various spatial and temporal scales have had marked geomorphological effects in many mountain ranges. In many glacierized Andean mountain regions substrates of human settlements made out of flood and debris-flow deposits are testimonies of such events. Examples in the Cordillera Blanca, Peru, are the towns of Caraz, Carhuaz or parts of Huaraz. Continued glacier shrinking since the end of the Little Ice Age caused the formation or enlargement of numerous lakes. The outburst of Laguna Palcacocha, destroying the centre of Huaraz and causing more than 1800 losses of life in December 1941, marked the beginning of systematic risk reduction work in Peru. Corresponding efforts included glacier and lake inventories, hazard assessments, definition of high-risk situations, and completion of engineering work for lake-level lowering in more than 30 cases. The latter comprises outlet reinforcements on morainic dams as well as artificial tunnels in bedrock thresholds. This work has been remarkably efficient as documented in the latest case of the Laguna Huallcacocha (Carhuaz-Ancash), where the earlier made installations withstood the erosive power of an impact wave from an ice avalanche in 2015. In the case of the Laguna 513, the impact wave and far-reaching flood caused by a rock/ice avalanche from Nevado Hualcán in April 2010 showed that the risk had been essentially reduced by the preventive lake-level lowering in the early 1990s but not to zero. Risk assessments, planning, construction and non-structural risk reduction efforts continue. Work is in progress to increase the safety of Laguna Palcacocha where extensive assessments and model calculations had been carried out. Risks related to rock/ice avalanches into lakes from steep icy slopes and related to de-buttressing processes as well as long-term permafrost degradation increases. Based on morphological indications and numerical modelling (GlabTop) an inventory of possible future lakes

  19. Reactivation episodes of the romeral fault system in the northwestern part of central andes, colombia, through 39ar-40ar and k-ar results

    OpenAIRE

    VINASCO VALLEJO, CESAR JAVIER; Cordani, Umberto

    2013-01-01

    Direct dating of reactivation of the San Jerónimo Fault (SJF), easternmost limit of the Romeral fault system (RFS), is presented through 39Ar-40Ar and K-Ar results in neo-formed micas and mylonitic bands of strongly hidrothermalized gabbros. Published cooling and crystallization ages from sin-tectonic magmatic rocks exposed in the western fl ank of the Central Cordillera have suggest that tectonic evolution of the paleo-fault system began since Triassic and Lower Jurassic before the installat...

  20. Una nueva especie de rana terrestre del género Pristimantis (Amphibia: Craugastoridae, de la Cordillera de Kutukú, Ecuador

    Directory of Open Access Journals (Sweden)

    Jorge Brito M.

    2013-01-01

    Full Text Available Describimos una especie nueva de mediano tamaño (LRC en la hembra 38.7 mm; en machos de 23.8 a 26.4 mm de rana terrestre del género Pristimantis de los bosques sub-tropicales de la Cordillera de Kutukú, del sureste de Ecuador, a elevaciones de 1581-1820 m. Asignamos a Pristimantis almendariz sp. nov., al subgénero Hypodictyon, serie de especies ridens. La nueva especie difiere de otros miembros de la serie ridens por su patrón distintivo con manchas dorsales, membrana timpánica ausente, presencia de tubérculos cónicos agrandados en el párpado, tubérculo inter-orbital prominente, e iris plateado con reticulaciones negras.

  1. Levelling profiles and a GPS network to monitor the active folding and faulting deformation in the Campo de Dalias (Betic Cordillera, southeastern Spain).

    Science.gov (United States)

    Marín-Lechado, Carlos; Galindo-Zaldívar, Jesús; Gil, Antonio José; Borque, María Jesús; de Lacy, María Clara; Pedrera, Antonio; López-Garrido, Angel Carlos; Alfaro, Pedro; García-Tortosa, Francisco; Ramos, Maria Isabel; Rodríguez-Caderot, Gracia; Rodríguez-Fernández, José; Ruiz-Constán, Ana; de Galdeano-Equiza, Carlos Sanz

    2010-01-01

    The Campo de Dalias is an area with relevant seismicity associated to the active tectonic deformations of the southern boundary of the Betic Cordillera. A non-permanent GPS network was installed to monitor, for the first time, the fault- and fold-related activity. In addition, two high precision levelling profiles were measured twice over a one-year period across the Balanegra Fault, one of the most active faults recognized in the area. The absence of significant movement of the main fault surface suggests seismogenic behaviour. The possible recurrence interval may be between 100 and 300 y. The repetitive GPS and high precision levelling monitoring of the fault surface during a long time period may help us to determine future fault behaviour with regard to the existence (or not) of a creep component, the accumulation of elastic deformation before faulting, and implications of the fold-fault relationship. PMID:22319309

  2. Levelling Profiles and a GPS Network to Monitor the Active Folding and Faulting Deformation in the Campo de Dalias (Betic Cordillera, Southeastern Spain

    Directory of Open Access Journals (Sweden)

    Carlos Marín-Lechado

    2010-04-01

    Full Text Available The Campo de Dalias is an area with relevant seismicity associated to the active tectonic deformations of the southern boundary of the Betic Cordillera. A non-permanent GPS network was installed to monitor, for the first time, the fault- and fold-related activity. In addition, two high precision levelling profiles were measured twice over a one-year period across the Balanegra Fault, one of the most active faults recognized in the area. The absence of significant movement of the main fault surface suggests seismogenic behaviour. The possible recurrence interval may be between 100 and 300 y. The repetitive GPS and high precision levelling monitoring of the fault surface during a long time period may help us to determine future fault behaviour with regard to the existence (or not of a creep component, the accumulation of elastic deformation before faulting, and implications of the fold-fault relationship.

  3. Características físicas de la población prehispánica de la cordillera oriental: implicaciones etnogenéticas

    Directory of Open Access Journals (Sweden)

    José Vicente Rodríguez Cuenca

    2010-03-01

    Full Text Available Se recurre al análisis estadístico para examinar el grado de similitud o afinidad entre las series de cráneos de la cordillera oriental y otras muestras comparativas de Colombia y América. Se sugiere microevolución en esta región a partir de sus primeros pobladores, con tendencia a la braquicefalización; se plantea deriva genética como mecanismo evolutivo explicativo de la especificidad morfológica de la población de la Mesa de los Santos. No se corroboran las tesis de migraciones tardías hacia el territorio que ocuparon los Muiscas.

  4. Spatiotemporal variability and differentiation between anthropogenic and natural contamination of heavy metals of surface water: a case study in the Cordillera Blanca, Peru

    Science.gov (United States)

    Guittard, A.; Baraer, M.; McKenzie, J. M.; Mark, B. G.; Fernandez, A.; Walsh, E.; Santos Perez, A.

    2015-12-01

    The Rio Santa, Peru, drains the western slopes of the glacierized Cordillera Blanca and provides water resources at almost all levels of the watershed. As it flows away from the valleys of the Cordillera Blanca, the Rio Santa takes out pollution from numerous sources, including acid mine drainage and natural sulfide oxidation by-products. The Rio Santa dry season discharge decline that is projected to be a consequence of glaciers retreat will probably have implications for the evolution of water pollution. This threat makes the characterization of the actual contamination mechanisms of primary importance. The present study focuses, first, on the spatiotemporal variability of heavy metal contamination across the entire Rio Santa Watershed and secondly on differentiating anthropogenic and natural contaminated sites. First, a macroscale sampling has been done during the summer 2013 to provide an overview of the contamination by trace metal, in water, suspended sediments and riverbed sediments. In addition, 30 water samples were taken from a point next to the city of Huaraz at a frequency of once every 2 weeks and analyzed for trace metals. Secondly, in order to identify hydrochemical contaminant origin dependant signatures in the Rio Santa watershed, 5 areas of known contamination origins were sampled during the summer 2014.Spatially speaking, we observed that most pollution is located in the south of the watershed, and that a large part of the arsenic that reaches the Santa in an aqueous phase does not make it to the outlet but remains trapped in the riverbed. Annual variation in water shows a very unusual fluctuation in Mn compare to other trace metal which are relatively stable. By differencing anthropogenic and natural sites and by considering glaciers melt and decrease water in future what would be the impact of the part of natural contaminated sites versus anthropogenic, mining and cities, on the water quality? Preliminary results show that anthropogenic sites

  5. Cenozoic uplift of the Central Andes in northern Chile and Bolivia - reconciling paleoaltimetry with the geological evolution.

    Science.gov (United States)

    Lamb, S. H.

    2015-12-01

    The Cenozoic geological evolution of the Central Andes, along two transects between ~17.5°S and 21°S, is compared with paleo-topography, determined from published paleo-altimetry studies. Surface and rock uplift are quantified using simple 2-D models of crustal shortening and thickening, together with estimates of sedimentation, erosion and magmatic addition. Prior to ~25 Ma, during a phase of amagmatic flat-slab subduction, thick skinned crustal shortening and thickening was focused in the Eastern and Western Cordilleras, separated by a broad basin up to 300 km wide and close to sea level, which today comprises the high Altiplano. Surface topography in the Eastern Cordillera appears to be ~1 km lower than anticipated from crustal thickening, which may be due to the pull-down effect of the subducted slab, coupled to the overlying lithosphere by a cold mantle wedge. Oligocene steepening of the subducted slab is indicated by the initiation of the volcanic arc at ~27 - 25 Ma, and widespread mafic volcanism in the Altiplano between 25 and 20 Ma. This may have resulted in detachment of mantle lithosphere and possibly dense lower crust, triggering 1 - 1.5 km of rapid uplift (over Altiplano and western margin of the Eastern Cordillera and establishing the present day lithospheric structure beneath the high Andes. Since ~25 Ma, surface uplift has been the direct result of crustal shortening and thickening, locally modified by the effects of erosion, sedimentation and magmatic addition from the mantle. The rate of crustal shortening and thickening varies with location and time, with two episodes of rapid shortening in the Altiplano, lasting < 5 Myrs, that are superimposed on a long term history of ductile shortening in the lower crust, driven by underthrusting of the Brazilian Shield on the eastern margin.

  6. Structural inheritance and selective reactivation in the central Andes: Cenozoic deformation guided by pre-Andean structures in southern Peru

    Science.gov (United States)

    Perez, Nicholas D.; Horton, Brian K.; Carlotto, Victor

    2016-03-01

    Structural, stratigraphic, and geochronologic constraints from the Eastern Cordillera in the central Andean plateau of southern Peru (14-15°S) demonstrate the existence and position of major pre-Andean structures that controlled the accumulation of Triassic synrift fill and guided subsequent Cenozoic deformation. The timing of initial clastic deposition of the Triassic Mitu Group is here constrained to ~ 242-233 Ma on the basis of detrital and volcanic zircon U-Pb geochronology. Regionally distinct provenance variations, as provided by U-Pb age populations from localized synrift accumulations, demonstrate Triassic erosion of multiple diagnostic sources from diverse rift-flank uplifts. Stratigraphic correlations suggest synchronous initiation of extensional basins containing the Mitu Group, in contrast with previous interpretations of southward rift propagation. Triassic motion along the NE-dipping San Anton normal fault accommodated up to 7 km of throw and hanging-wall deposition of a synrift Mitu succession > 2.5 km thick. The contrasting orientation of a non-reactivated Triassic normal fault suggests selective inversion of individual structures in the Eastern Cordillera was dependent on fault dip and strike. Selective preservation of a ~ 4 km thick succession of Carboniferous-Permian strata in the down-dropped San Anton hanging wall, beneath the synrift Mitu Group, suggests large-scale erosional removal in the uplifted footwall. Field and map observations identify additional pre-Andean thrust faults and folds attributed to poorly understood Paleozoic orogenic events preserved in the San Anton hanging wall. Selective thrust reactivation of normal and reverse faults during later compression largely guided Cenozoic deformation in the Eastern Cordillera. The resulting structural compartmentalization and across-strike variations in kinematics and deformation style highlight the influence of inherited Paleozoic structures and Triassic normal faults on the long

  7. central t

    Directory of Open Access Journals (Sweden)

    Manuel R. Piña Monarrez

    2007-01-01

    Full Text Available Dado que la Regresión Ridge (RR, es una estimación sesgada que parte de la solución de la regresión de Mínimos Cuadrados (MC, es vital establecer las condiciones para las que la distribución central t de Student que se utiliza en la prueba de hipótesis en MC, sea también aplicable a la regresión RR. La prueba de este importante resultado se presenta en este artículo.

  8. Environmental and biological factors controlling the spring phytoplankton bloom at the Patagonian shelf-break front - Degraded fucoxanthin pigments and the importance of microzooplankton grazing

    Science.gov (United States)

    Carreto, José I.; Montoya, Nora G.; Carignan, Mario O.; Akselman, Rut; Acha, E. Marcelo; Derisio, Carla

    2016-08-01

    The aim of this study was to investigate the biotic and abiotic factors controlling the spring phytoplankton blooms at the Patagonian shelf-break front (PSBF). Using a CHEMTAX analysis of HPLC pigment data and other methods, the biomass and spatial variability of plankton communities were studied in four sections (39-48°S) across the PSBF during October 2005. Environmental factors and the biomass and composition of plankton communities exhibited a marked spatial heterogeneity. The latitudinal and cross-shelf progression in the timing of the spring bloom initiation and the nutritive properties of the water masses (Subantarctic Shelf Waters and Malvinas Current Waters) seemed to be the key factors. Three plankton regions were distinguished: (a) Outer shelf (OS), (b) Shelf-break front (SBF) and (c) Malvinas Current (MC). At the highly stratified OS region, the post-bloom community showed low-biomasshigh-phytoplankton diversity formed mainly by small cells (haptophytes 30-62%, diatoms 17-49%, chlorophytes 0-34%, and prasinophytes 0-21% of total Chl a). High amounts of degraded fucoxanthin were found associated with the heterotrophic dinoflagellate, Protoperidinium capurroi. Grazing by this microheterotroph on the diatom population seemed to be the most important factor for the spring bloom decay at the OS. A remarkable quasi monospecific bloom (∼90%) of a nanodiatom (Thalassiosira bioculata var. raripora) associated with high Chl a (up to 20 mg m-3) occurred along (∼1000 km) the SBF and in the most northern extension of the MC. In the southern region, the bloom was developed under absent or incipient density stratification, increasing solar irradiance, high nitrate and phosphate availability, and low numbers of phytoplankton grazers. The average mixedlayer PAR irradiance (iron-rich sediments. The upwelling along the SBF provides a large source of macronutrients and probably the dissolved iron needed to sustain the intense diatom bloom, but also diatom resting

  9. Reproductive aspects of the Patagonian toothfish (Dissostichus eleginoides off southern Chile Aspectos reproductivos del bacalao de profundidad (Dissostichus eleginoides en el extremo austral de Chile

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    Patricio Arana

    2009-01-01

    Full Text Available We present the results for the reproductive biology of Patagonian toothfish (Dissostichus eleginoides caught off southern Chile from January to March and June to November 2006. A total of 10,896 specimens were measured (55-220 cm total length, TL and sexed (7,049 males, 64.7%; and 3,847 females, 35.3%. Macroscopic observations showed that gonad maturation begins at 60 cm TL in both sexes, with an average maturation size of 81 cm TL in males and 89 cm TL in females. This species appears to have an ampie spawning period that occurs only off the far southern region of Chile. To date, no evidence indicates that this resource reproduces in any other areas of the Pacific Ocean off the coasts of South América, where no specimens were observed with mature gonads, percentages of atresia were high, and juvenile fish were not caught in trawl fishing operations targeting other commercial species.Se dan a conocer resultados sobre la biología reproductiva del bacalao de profundidad (Dissostichus eleginoides capturado en el extremo sur-austral de Chile, entre enero y marzo y de junio a noviembre de 2006. En dicho período se midió y determinó el sexo a 10.896 ejemplares, comprendidos entre 55 y 220 cm de longitud total (LT, de los cuales 7.049 correspondieron a machos (64,7% y 3.847 a hembras (35,3%. Mediante la observación macroscópica de las gónadas se determinó que en machos y hembras se observa el comienzo de la maduración gonádica a partir de 60 cm de LT, con una talla media de maduración (TMS50% en machos a 81 cm y en hembras a 89 cm. Se sugiere que esta especie presenta un período amplio de desove y que este proceso se efectuaría únicamente en la región austral de Chile, destacándose que hasta ahora no se cuenta con evidencias que este recurso se reproduzca en otra zona del océano Pacífico frente a la costa de Sudamérica en atención a la ausencia de ejemplares maduros en las capturas, altos porcentajes de atresia y ausencia de peces

  10. Subduction of the South-Chile active spreading ridge: a 17 Ma to 3 Ma magmatic record in central Patagonia (western edge of Meseta del Lago Buenos Aires, Argentina)

    Science.gov (United States)

    Boutonnet, Emmanuelle; Arnaud, Nicolas; Guivel, Christèle; Lagabrielle, Yves; Scalabrino, Bruno; Espinoza, Felipe

    2010-05-01

    The Chile Triple Junction is a natural laboratory to study the interactions between magmatism and tectonics during the subduction of an active spreading ridge beneath a continent. The MLBA plateau (Meseta del Lago Buenos Aires) is one of the Neogene alkali basaltic plateaus located in the back-arc region of the Andean Cordillera at the latitude of the current Chile Triple Junction. The genesis of MLBA can be related with successive opening of slabs windows beneath Patagonia: within the subducting Nazca Plate itself and between the Nazca and Antarctic plates. Detailed 40Ar/39Ar dating and geochemical analysis of bimodal magmatism from the western flank of the MLBA show major changes in the back-arc magmatism which occurred between 14.5 Ma and 12.5 Ma with the transition from calc-alkaline lavas (Cerro Plomo) to alkaline lavas (MLBA) in relation with slab window opening. In a second step, at 4- 3 Ma, alkaline felsic intrusions were emplaced in the western flank of the MLBA coevally with the MLBA basalts with which they are genetically related. These late OIB-like alkaline to transitional basalts were generated by partial melting of the subslab asthenosphere of the subducting Nazca plate during the opening of the South Chile spreading ridge-related slab window. These basalts differentiated with small amounts of assimilation in shallow magma chambers emplaced along transtensional to extensional zones. The close association of bimodal magmatism with extensional tectonic features in the western MLBA is a strong support to the model of Patagonian collapse event proposed to have taken place between 5 and 3 Ma as a consequence of the presence of the asthenospheric window (SCR-1 segment of South Chile Ridge) below the MLBA area.

  11. Caracterización física, química y mineralógica de suelos con vocación forestal protectora región andina central colombiana / physical chemical and mineralogical characterization of soils with a protective forest vocation, central andean region of colombia

    OpenAIRE

    Leyder Echeverri Tafur; Jaime Vicente Estévez Varón; Juan Guillermo Bedoya Patiño

    2014-01-01

    Resumen. En la Reserva Forestal Protectora Bosques de la CHEC, ubicada sobre la vertiente occidental de la cordillera central colombiana, municipios de Manizales y Villamaría, departamento de Caldas, se hizo la caracterización física, química y mineralógica de dos perfiles de suelos, descritos sobre dos laderas, con un manejo actual correspondiente a una plantación de aliso (Alnus acuminata) y un bosque secundario. Los resultados permitieron establecer,desde el punto de vista físico, el domin...

  12. Geology, structure and age of the Nahuel Niyeu Formation in the Aguada Cecilio area, North Patagonian Massif, Argentina

    Science.gov (United States)

    Greco, Gerson A.; González, Pablo D.; González, Santiago N.; Sato, Ana M.; Basei, Miguel A. S.; Tassinari, Colombo C. G.; Sato, Kei; Varela, Ricardo; Llambías, Eduardo J.

    2015-10-01

    The low-grade Nahuel Niyeu Formation in the Aguada Cecilio area (40°50‧S-65°53‧W) shows ultramafic to felsic metaigneous rocks forming a sill swarm intercalated in the metasedimentary sequence and a polyphase deformation which permit an integrated study of the magmatic and tectonometamorphic evolution of this geological unit. In this paper we present a geological characterization of the Nahuel Niyeu Formation in the Aguada Cecilio area combining mapping, structural and metamorphic analysis with a SHRIMP U-Pb age and geochemical data from the metaigneous rocks. The metasedimentary sequence consists of alternating metagreywackes and phyllites, and minor metasandstones and granule metaconglomerates. The sills are pre-kinematic intrusions and yielded one SHRIMP U-Pb, zircon crystallization age of 513.6 ± 3.3 Ma. Their injection occurred after consolidation of the sedimentary sequence. A syn-sedimentary volcanic activity is interpreted by a metaandesite lava flow interlayered in the metasedimentary sequence. Sedimentary and igneous protoliths of the Nahuel Niyeu Formation would have been formed in a continental margin basin associated with active magmatic arc during the Cambrian Epoch 2. Two main low-grade tectonometamorphic events affected the Nahuel Niyeu Formation, one during the Cambrian Epoch 2-Early Ordovician and the other probably in the late Permian at ˜260 Ma. Local late folds could belong to the final stages of the late Permian deformation or be even younger. In a regional context, the Nahuel Niyeu and El Jagüelito formations and Mina Gonzalito Complex show a comparable Cambrian-Ordovician evolution related to the Terra Australis Orogen in the south Gondwana margin. This evolution is also coeval with the late and early stages of the Pampean and Famatinian orogenies of Central Argentina, respectively. The late Permian event recorded in the Nahuel Niyeu Formation in Aguada Cecilio area is identified by comparable structures affecting the Mina Gonzalito

  13. Depositación atmosférica de nitrógeno en un transecto valle longitudinal-cordillera de Los Andes, centro-sur de Chile Atmospheric deposition of nitrogen in a transect from the Central Valley to Cordillera de Los Andes, south-central Chile

    OpenAIRE

    Oyarzún, Carlos E; ROBERTO GODOY; SERGIO LEIVA

    2002-01-01

    El aumento de las actividades agrícolas y ganaderas en el centro-sur de Chile puede producir elevadas emisiones de nitrógeno hacia la atmósfera (mayormente NH3). El amoniaco es transportado por corrientes de aire y depositado en el suelo y vegetación. El presente estudio evalúa la depositación atmosférica de compuestos nitrogenados (NO3- y NH4+) en la química de las precipitaciones en un transecto altitudinal de 66 km, desde los alrededores de la ciudad de Osorno (40º 35' S, 72º 57' O, 55 m d...

  14. A Constrained 3D Density Model of the Upper Crust from Gravity Data Interpretation for Central Costa Rica

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    Oscar H. Lücke

    2010-01-01

    Full Text Available The map of complete Bouguer anomaly of Costa Rica shows an elongated NW-SE trending gravity low in the central region. This gravity low coincides with the geographical region known as the Cordillera Volcánica Central. It is built by geologic and morpho-tectonic units which consist of Quaternary volcanic edifices. For quantitative interpretation of the sources of the anomaly and the characterization of fluid pathways and reservoirs of arc magmatism, a constrained 3D density model of the upper crust was designed by means of forward modeling. The density model is constrained by simplified surface geology, previously published seismic tomography and P-wave velocity models, which stem from wide-angle refraction seismic, as well as results from methods of direct interpretation of the gravity field obtained for this work. The model takes into account the effects and influence of subduction-related Neogene through Quaternary arc magmatism on the upper crust.

  15. Tectonomorphic evolution of the Eastern Cordillera fold-thrust belt, Colombia: New insights based on apatite and zircon (U-Th)/He thermochronometers

    Science.gov (United States)

    Ghorbal, B.; Stockli, D. F.; Mora, A.; Horton, B. K.; Blanco, V.; Sanchez, N.

    2010-12-01

    The Eastern Cordillera (EC) of Colombia marks the eastern boundary of Cenozoic fold-thrust deformation in the northern Andes. It is a classic example of an inversion belt formed in the retro-arc region, in this case superimposed on a Triassic/Jurassic to Cretaceous intracontinental rift system of northern South America. Ongoing thrust reactivation (inversion) in this contractional orogen provides an excellent opportunity to study the patterns of deformation and influence of preexisting anisotropies (Mora et al., 2006). The objective of this detailed (U-Th)/He study is to unravel the tectonic and thermal evolution of the EC from the Magdalena Valley basin in the west to the Llanos foreland basin in the east and reconstruct the temporal and spatial progression of deformation in the EC fold-thrust belt. Furthermore, the Subandean or foothills zone of Colombia is key for understanding the petroleum systems in the complex frontal zone of the inverted fold-thrust belt. We present detailed apatite and zircon (U-Th)/He thermochronometric data from surface samples along a ~220 km WNW-ESE transect across the EC from the frontal fold-thrust belt at the edge of the Llanos basin to the western edge of the EC, the Magdalena basin. Surface and borehole zircon and apatite (U-Th)/He data, integrated with structural data, show that the EC fold-thrust belt propagated foreland-ward from the axial zone to the modern edges of the fold-thrust belt from at least the early Oligocene to the early Miocene. Detailed apatite and zircon (U-Th)/He data from surface samples and borehole samples in the foothills-Llanos transition zone and the Middle Magdalena Valley basin, between the large-displacement Guaicaramo and Pajarito-Chámeza thrusts in the east and the La Salina fault system in the west show a temporally complex evolution. The frontal fold-thrust belt was characterized by continued progressive foreland-ward migration of deformation and an apparent phase of major out-of-sequence motion

  16. El Paleozoico inferior y medio de la región de Los Colorados, borde occidental de la Cordillera Oriental (provincia de Jujuy

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    Ricardo A. Astini

    2004-06-01

    Full Text Available La estratigrafía de la región de Los Colorados, situada en el borde occidental de la Cordillera Oriental argentina, inicia con una sucesión de arenitas cuarzosas rosadas y limolitas varicolores cámbricas pertenecientes al Grupo Mesón, cubiertas por una sucesión dominantemente pelítica que abarca parte de los pisos tremadociano y arenigiano correspondientes al Grupo Santa Victoria. En la base del perfil, este último remata con ciclos progresivamente más arenosos de la Formación Acoite. Le siguen la Formación Alto del Cóndor (nom. nov., la Formación Sepulturas (emend. y el horizonte glacial de Zapla, las últimas dos unidades pertenecientes al Ordovícico Medio y Superior, respectivamente. A continuación, se ubica un primer horizonte ferrífero de menos de 1 metro de espesor seguido de la Formación Lipeón que, aunque de reducido espesor, abarcaría gran parte del Silúrico. Por encima se ubica un segundo nivel ferrífero (de hasta 4m de espesor seguido de una unidad areno-limosa con restos de fauna siluro-devónica, comparable con la presente en la Formación Arroyo Colorado de las Sierras Subandinas o su equivalente, la Formación Baritú, de mejor registro en subsuelo. La estratigrafía paleozoica de la sección está truncada erosivamente por depósitos continentales rojos del Grupo Salta (Cretácico desconociéndose el espesor eliminado por erosión. El registro estratigráfico relativamente completo preservado en esta región del oeste de la Cordillera Oriental argentina obliga a replantear algunos presupuestos clásicos sobre la existencia de altos topográficos estructurados a partir del Ordovícico Temprano. La continuidad del relleno habría sido interrumpida periódicamente por fluctuaciones relativas del nivel del mar, de signatura más posiblemente eustática que puramente tectónica, que serían responsables de la mayor parte de los límites entre unidades y delimitación de secuencias y supersecuencias. La única

  17. Pedological and mineralogical investigations on a soil-paleosoil sequence within Andosols in the Western Cordillera of the Peruvian Andes (region Laramate, 14.5S)

    Science.gov (United States)

    Leceta Gobitz, Fernando; Mächtle, Bertil; Schukraft, Gerd; Meyer, Hans-Peter; Eitel, Bernhard

    2016-04-01

    An integrated research project of environmental sciences focuses on a group of four Andosol profiles in Western flank of the Peruvian southern Andes. Aim of this study is to contribute to the reconstruction of the paleo environmental conditions in the Western Cordillera of the Peruvian Andes. Standard pedological and sedimentological analysis has been conducted in order to identify morphological and geochemical features generated by climatic variations during the middle and late Holocene. Though a provenance analysis of sediments, all potential lithological sources around the town of Laramate are being examined under the scanning electron microscope, in order to find significant mineralogical associations downward the soil-profile. Preliminary results reveal two edaphic cycles within a soil-paleo soil-sequence: a relative poor developed "Ah" topsoil, mostly composed by fine grain sediments, is underlain by a well preserved "2Ah" paleo soil; a "2Bwt" subsoil exhibits signs of alteration and clay translocation; parent material in slight weathered statement at "2C" culminates the sequence. Mineralogical analytical data supports the premise, that materials in the uppermost horizons are relatable to distal geological units of the Western and Eastern Cordillera, therefore also related to other described aeolian archives from the region: "Desert Margin Loess" at the Andean foot-zone and "Mixed Loess" in the Puna grassland. The amphibole varieties Actinolite, Mg-Hornblende and Edenite could be only distinguished within the soil sediments. The fluvial transport to its current position is excluded, insofar mentioned varieties stem from the granodiorites of Coastal Batholite (downstream the study area), and the vulcanites of the Anta und Andahuaylas Formation (eastward the continental divide). References: Eitel, B., et al. (2005). "Geoarchaeological evidence from desert loess in the Nazca-Palpa region, southern Peru : Palaeoenvironmental changes and their impact on Pre

  18. Algunos aspectos de la estructura de la Zona Subbética (Cordilleras Béticas. España meridional

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    Hermes, Jacobus J.

    1985-08-01

    Full Text Available Analysis of sedimentation and tectonics of the Subbetic zone of the Betic Cordilleras leads to the conclusion that sedimentation and subsequent deformation are largely governed by a Wilson cycle (Wilson, 1966, 1968 that began the opening of the Tethyan rift in the Pangaea continent during the Pliensbachian, 180 Ma ago. The resulting ocean began to close again in the Cretaceous, a process that led to a collision between Iberia and African elements in the Burdigalian, which was followed by strike-slip movement along a shear zone between the two plates which continues to this day. It is argued that the collision led to general uplift of the Subbetic zone as shown by the termination of deep water pelagic and hemipelagic sedimentation in the entire zone, and that the subsequent strike-slip movements along a system of anastomosing faults loo to very intense deformation localized along separate fault zones, and to the opening of pull-apart basins with characteristic sedimentation sequences.

    El análisis de la sedimentación y la tectónica de la Zona Subbética (Cordilleras Béticas conduce a la conclusión de que la sedimentación y la deformación posterior han sido ampliamente determinadas por un ciclo de Wilson (Wilson, 1966, 1968; Mitchell y Reading, 1978 que comenzó con la apertura del Tethys en el continente de Pangaea durante el Pliensbaquiense, hace 180 ID. a. El océano resultante empezó a cerrarse de nuevo en el Cretácico. Este proceso condujo a la colisión entre Iberia y elementos africanos en el Burdigaliense y fue seguido por un movimiento de salto en dirección a favor de una zona de cizalla que aún continúa en la actualidad. La colisión provocó el levantamiento general del la Zona Subbética, como lo demuestra el cese de la sedimentación pelágica y hemipelágica profundas por toda ella. Los movimientos subsiguientes de salto en 'dirección a favor de un sistema de fallas anastomosadas produjeron una deformación muy

  19. Cenozoic foreland-basin evolution in the northern Andes : insights from thermochronology and basin analysis in the Eastern Cordillera, Colombia

    OpenAIRE

    Parra, Mauricio

    2009-01-01

    The modern foreland basin straddling the eastern margin of the Andean orogen is the prime example of a retro-arc foreland basin system adjacent to a subduction orogen. While widely studied in the central and southern Andes, the spatial and temporal evolution of the Cenozoic foreland basin system in the northern Andes has received considerably less attention. This is in part due to the complex geodynamic boundary conditions, such as the oblique subduction and accretion of the Caribbean plates ...

  20. Bioestratigrafía del Triásico de la zona Subbética (Cordillera Bética).

    OpenAIRE

    Pérez López, Alberto; Fernández, J.; Solé de Porta, N.; Márquez Aliaga, Ana

    1991-01-01

    Theree differents lithology can be differenciated basically in t he Triassic of the central sector of Betic: carbona­ tes (facies Muschelk alk), terrigenou s (facies Keuper) and evaporites (facies Keuper). The study of several ou t­ crops in this area allow to know better the paleoecologica ls aspects of Triassic, and to review the stratigraphic paleontology. In the carbonate section fosiil record is formed by molluscs and branchiopods. The occurrence of Costatoria goldfussi and Enantiostreon...

  1. Nd, Sr and Pb isotopic composition of metasomatised xenoliths from the backarc Patagonian Mantle Wedge: Insights into the origin of the uprising melts

    Science.gov (United States)

    Zanetti, Alberto; Mazzucchelli, Maurizio; Hemond, Christope; Cipriani, Anna; Bertotto, Gustavo W.; Cingolani, Carlos; Vannucci, Riccardo

    2010-05-01

    Information about the geochemical composition of metasomatic melts migrating through the Patagonian mantle wedge is provided by the ultramafic xenoliths occurrence of Tres Lagos (TL; lat. 49.13°S, long. 71.18°W), Argentina. Such a locality is placed at the eastern border of the Meseta de la Muerte backarc basaltic plateau, where a post-plateau volcanic diatreme contains mantle xenoliths in both pyroclastites and lavas. Its latitude corresponds with the Northern limit of the Austral Volcanic Arc (AVZ), which is separated from the Southern Volcanic Zone (SVZ) by a gap in the arc magmatism ranging between 49° and 46°30' latitude S. The analysed xenoliths have been distinguished into two groups (Group 1 & 2). Group 1 consists of lherzolites and harzburgites, whereas Group 2 is formed by harzburgites. The texture of the Group 1 lherzolites varies from protogranular to granoblastic to porphyroblastic, whereas Group 1 harzburgites have always granoblastic texture. Group 2 harzburgites have granular texture, which may change to porphyroblastic owing to the random concentration of large olivine and orthopyroxene crystals. The clinopyroxenes (Cpx) from Group 1 lherzolites have PM-normalised REE patterns ranging from LREE-depleted (LaN/SmN= 0.24-0.37), to LREE-enriched (LaN/YbN up to 4.08) and spoon-shaped: the latter have minimum at Pr and Pr-Yb concentrations similar to those shown by the LREE-depleted Cpx. The Cpx from Group 1 harzburgites have lower REE concentrations with respect to the lherzolite ones and their REE patterns vary from HREE-enriched, steadily fractionated, (LaN/YbN = 0.21-0.35, Ybn ~ 1-2) to spoon-shaped (LaN/SmN = 2.81; SmN/YbN = 0.89; YbN ~ 3. The Cpx from the Group 2 harzburgites have convex-upward (LaN/SmN = 0.31; SmN/YbN = 1.50) to LREE-enriched (LaN/YbN = 2.94) patterns. The Sr, Nd and Pb isotopic compositions of the Group 1 clinopyroxenes form arrays spanning from DM to the field delimited by the TL basaltic lavas, pointing to EMI end

  2. Late Quaternary Glaciations in the Central Peruvian Andes (10°-11°S) and Evidence for a Link to Heinrich Events

    Science.gov (United States)

    Smith, J. A.; Farber, D. L.; Finkel, R. C.; Rodbell, D. T.; Seltzer, G. O.

    2009-05-01

    Seven cosmogenic 10Be ages from a moraine in the Santuario Nacional Bosque de Piedras de Huayllay (BP) in the Western Cordillera of the central Peruvian Andes (10°59'S, 76°20'W, 4180-4200 masl) are consistent with 10Be ages on moraines in both the Eastern Cordillera (40-45 km to the east) and Nevado Jeulla Rajo (NJR) massif (10°00'S, 77°16'W) at the southern end of the Cordillera Blanca (150 km to the northwest). In the BP, 10Be ages are ~14-15 ka on four ignimbrite boulders, ~26 and ~20 ka on two quartz boulders, and ~45 ka on ignimbrite bedrock below the trimline in the valley wall. In the Eastern Cordillera bordering Lake Junin, the most extensive glaciations are >150 ka, but end moraines farther upvalley date to the local last glacial maximum (LLGM; 25-30 ka) and a late-glacial stillstand or readvance (14-18 ka). In NJR, 10Be ages indicate that the largest lateral moraines were deposited during similar intervals (27-32 ka and 14-18 ka). Avulsion of a glacial valley preserved an older, smaller pair of lateral moraines (56-65 ka) in NJR; correlative moraines were apparently not preserved in the Junin valleys. We have found no moraines in NJR that date to the global LGM (ca. 19-24 ka), but see some evidence for an advance ca. 40-48 ka. Outwash deposits (ca. 43-50 ka) located beyond the termini of NJR moraines are underlain by lodgement till that extends ca. 6 km across the Conococha Plain, suggesting that at least one older glaciation was far more extensive than any of the late Quaternary NJR advances dated by 10Be (ages calculated using CRONUS-Earth Online Calculator v. 2.2, Lal/Stone time-dependent scaling, and zero erosion). The timing of glacial advances in the central Peruvian Andes since 70 ka suggests a correlation to Heinrich events and associated southward shifts of the Intertropical Convergence Zone (ITCZ) in the Atlantic Ocean. We propose that Peruvian glaciers typically expanded when southward migration of the ITCZ resulted in increased

  3. Estratigrafía y facies volcánicas y volcaniclásticas de la Formación Valle del Cura: magmatismo paleógeno en la Cordillera Frontal de San Juan Stratigraphy and volcanic facies of the of the Valle del Cura Formation: Paleogene volcanism in the Frontal Cordillera of San Juan

    Directory of Open Access Journals (Sweden)

    V.D. Litvak

    2005-06-01

    Full Text Available En la región del Valle del Cura, Cordillera Frontal de San Juan, aflora una espesa secuencia de rocas volcánicas y volcaniclásticas, en facies piroclásticas y epiclásticas, que representa el desarrollo de un importante episodio volcano-sedimentario eoceno-oligoceno inferior. Esta unidad, la Formación Valle del Cura, incluye espesos paquetes de tobas, conglomerados gruesos, areniscas líticas medianas a gruesas, areniscas volcánicas y escasas pelitas. Los niveles volcánicos están formados por flujos lávicos e ignimbritas de alto grado de composiciones riolíticas, las cuales representan flujos piroclásticos de alta temperatura y alto grado de soldadura. La Formación Valle del Cura también incluye espesos niveles de flujos piroclásticos primarios formados por tobas cristalinas, líticas y/o vítreas, tobas lapillíticas e inclusive facies gruesas como aglomerados y brechas volcánicas. Vinculados a estos depósitos piroclásticos se interdigitan facies epiclásticas de composición dominante volcánica, que representan el retrabajo del material piroclástico primario. Los depósitos ignimbríticos muestran evidencias que indican su proximidad respecto al centro de emisión, el cual se encontraría en el extremo sur de la cordillera de la Brea. Esta secuencia se puede correlacionar con secuencias equivalentes que afloran hacia el norte en el río de la Sal y en las nacientes del río Blanco, en Macho Muerto, y cronológicamente, con los intrusivos mesosilíceos de la Unidad Bocatoma que afloran en territorio chileno -a la misma latitud- y que están emplazados a lo largo del frente magmático eoceno. En constraste, la Formación Valle del Cura representa una intensa actividad volcanodesimentaria sinorogénica depositada en una cuenca de retroarco.A thick volcanic and volcaniclastic sequence, which includes epiclastic and pyroclastic facies, was recognized in the Valle del Cura region in the Frontal Cordillera of San Juan. The Valle

  4. ESTATUS DE LA POBLACIÓN DE MONOS AULLADORES ROJOS EN EL CAÑÓN DEL BARBAS, FRAGMENTO MONTANO, CORDILLERA CENTRAL, Colombia Status of the red howler monkeys population in the Barbas canion, montane fragment, central mountains, Colombia

    Directory of Open Access Journals (Sweden)

    Jorge Mario Londoño

    Full Text Available Los bosques de montaña en Colombia han sufrido fuerte degradación por causas antrópicas y en la actualidad la mayoría son remanentes aislados e inmersos en hábitat antropogénicos. Los aulladores rojos han persistido en estas condiciones pero poco se conoce sobre su biología y respuesta a la alteración de su ambiente. Durante cinco meses en el 2005, evaluamos densidad y estatus poblacional de esta especie en la cuenca del río Barbas (Departamentos de Quindío y Risaralda, fragmento aislado de bosque montano bajo de 790 ha . Estimamos la densidad empleando censos por transectos lineales repetidos. Adicionalmente seguimos tropas de aulladores y evaluamos variables de vegetación teniendo en cuenta los requerimientos ecológicos de la especie. Estimamos una densidad de 11.7±6 grupos y 132.1±68 individuos/km2, superior a la usualmente reportada en bosques continuos. Esta alta densidad probablemente se deba al aislamiento del fragmento, que limita las posibilidades de dispersión de los aulladores. El tamaño promedio por tropa fue 11.3±2.5 individuos, con más de cinco machos y siete hembras adultas, y de uno a cuatro inmaduros. En general el bosque ofrece buena disponibilidad de recursos estructurales y alimenticios para los aulladores. Esta población no se encuentra amenazada en la actualidad por actividades antrópicas. El fragmento ha sido recientemente protegido bajo la figura de Parque Regional Natural y se adelantan corredores de conexión con otros remanentes cercanos. Sin embargo, esta población de aulladores se encuentra aislada de otras poblaciones y por tanto es urgente desarrollar medidas de manejo del paisaje para atenuar los efectos del aislamiento.The montane forests in Colombia have suffered strong degradation due to human activities; currently, most of them are remnants isolated and immersed in anthropogenic habitats. The red howler monkeys have persisted in these conditions but little is known on their biology and response to the alteration of their environment. During five months in 2005, we evaluated the population density and status of this species in the basin of the Barbas River (Quindío and Risaralda departments, a low montane isolated forest fragment of 790 ha . We estimated density by censuses for linear repeated transects. Additionally we followed troops of howlers and evaluated vegetation variables according to howler ecological requirements. We estimated a density of 11.7±6 groups and 132.1±68 individuals per km2, higher than what is usually reported for this species in continuous forests. This high density might be caused due to the isolation of the fragment that reduces the possibilities of dispersion of the howlers. The average troop size was 11±2.5 individuals, with more than five males and seven females, and one to four immature individuals. In general, the forest offers to the howlers, good availability of food and structural resources. Currently, this population is not threatened by anthropogenic activities. Recently, this fragment has been protected as a Regional Park , and it exists a project to develop corridors of connection with others remnants. Nevertheless, this howler population is isolated of other populations, and therefore urgent measures of landscape management are needed to attenuate the effects of the isolation.

  5. Episodios de reactivación del sistema de fallas del Romeral en la parte Nor-Occidental de los Andes Centrales de Colombia a través de resultados 39AR-40AR y K-AR.

    OpenAIRE

    Vinasco Vallejo, Cesar; Cordani, Umberto

    2012-01-01

    Direct dating of reactivation of the San Jerónimo Fault (SJF), easternmost limit of the Romeral fault system (RFS), is presented through 39Ar-40Ar and K-Ar results in neo-formed micas and mylonitic bands of strongly hidrothermalized gabbros. Published cooling and crystallization ages from sin-tectonic magmatic rocks exposed in the western fl ank of the Central Cordillera have suggest that tectonic evolution of the paleo-fault system began since Triassic and Lower Jurassic before the installat...

  6. Active tectonics and Quaternary landscape evolution across the western Panama block, Costa Rica, Central America

    Science.gov (United States)

    Marshall, Jeffrey Scott

    Three aspects of active tectonism are examined across central Costa Rica: (1) fault kinematics; (2) volcanic arc retreat; and (3) spatially variable coastal uplift. Diffuse faulting along the Central Costa Rica Deformed Belt (CCRDB) defines the western margin of the Panama block and aligns with the rough-smooth boundary (RSB) on the subducting Cocos plate. Sub-horizontal subduction of rough, hotspot thickened crust (Cocos Ridge and seamounts) shifts active shortening into the volcanic arc along the CCRDB. Mesoscale faults express variable kinematics across three domains: transtension in the forearc, transcurrent motion across the volcanic arc, and transpression in the back arc. Fault kinematics agree with seismicity and GPS data, and isotopic ages confirm that faulting postdates the late Neogene onset of shallow subduction. Stratigraphic correlation augmented by 40Ar/39Ar dating constrain the timing of Quaternary arc migration from the Neogene Aguacate range to the modern Cordillera Central. The Valle Central basin, between the cordilleras, filled with thick sequences of lavas, pyroclastic flows, and lahars. Middle Pleistocene drainage capture across the Aguacate arc linked the Valle Central with the Pacific slope and ash flows descended onto the coastal Orotina debris fan. Arc retreat reflects slab shallowing and enhanced tectonic erosion as rough crust entered the subduction zone. Differing subduction parameters across the RSB (crustal age, slab dip, roughness) produce marked contrasts in coastal tectonism. Varying uplift rates across coastal faults reflect sub-horizontal subduction of seamount roughness. Three groups (I--III) of fluvial terraces are correlated along the coast by isotopic ages and geomorphic characteristics. Base level fluctuations and terrace genesis reflect interaction between eustatic sea level and spatially variable rock uplift. Low uplift rates (north of RSB), yield one surface per terrace group, whereas moderate rates (south of RSB

  7. Upper plate deformation and seismic barrier in front of Nazca subduction zone: The Chololo Fault System and active tectonics along the Coastal Cordillera, southern Peru

    Science.gov (United States)

    Audin, Laurence; Lacan, Pierre; Tavera, Hernando; Bondoux, Francis

    2008-11-01

    The South America plate boundary is one of the most active subduction zone. The recent Mw = 8.4 Arequipa 2001 earthquake ruptured the subduction plane toward the south over 400 km and stopped abruptly on the Ilo Peninsula. In this exact region, the subduction seismic crisis induced the reactivation of continental fault systems in the coastal area. We studied the main reactivated fault system that trends perpendicular to the trench by detailed mapping of fault related-geomorphic features. Also, at a longer time scale, a recurrent Quaternary transtensive tectonic activity of the CFS is expressed by offset river gullies and alluvial fans. The presence of such extensional fault systems trending orthogonal to the trench along the Coastal Cordillera in southern Peru is interpreted to reflect a strong coupling between the two plates. In this particular case, stress transfer to the upper plate, at least along the coastal fringe, appears to have induced crustal seismic events that were initiated mainly during and after the 2001 earthquake. The seafloor roughness of the subducting plate is usually thought to be a cause of segmentation along subduction zones. However, after comparing and discussing the role of inherited structures within the upper plate to the subduction zone segmentation in southern Peru, we suggest that the continental structure itself may exert some feedback control on the segmentation of the subduction zone and thus participate to define the rupture pattern of major subduction earthquakes along the southern Peru continental margin.

  8. Geophysical Exploration of Disseminated and Stockwork deposits associated with plutonic intrusive: A Case study in the eastern flank of the western Cordillera, Colombia

    Science.gov (United States)

    Hernandez, O.; Alexander, G. C.; Pintor, I. M.

    2011-12-01

    Disseminated deposit exploration in the tropics suffers from difficult geological mapping due to thick vegetation, lack of rock outcrop, and extensive but variable saprolitic weathering. Geophysical exploration of these deposits normally includes magnetic, induced polarization and gamma ray spectrometry surveys. The largest RTP Total field magnetic anomaly highs are usually associated with the diorite porphyry intrusive bodies. Normally, diorites are less magnetic than the basaltic rocks. Therefore, where the magnetic anomaly highs are related to the intrusions they can be explained by the intensive mineralization of basic metals including magnetite that are associated with the porphyry intrusions. Regularly, the magnetic anomaly gradients help to delineate local discontinuities that can be interpreted as local faults and joints that can be mineralized. The gamma ray spectrometry is useful to determine the anomalous concentration of Potassium, Uranium and Thorium that can be interpreted in terms of alteration halos and linear discontinuities. The statistical analysis of the data also can determine the intermediate intrusive / extrusive nature of the porphyry intrusions. The use of gamma ray spectrometry helps to determine the concentration of elemental potassium, regardless of the associated potassium mineral species, enabling alteration mapping in a geological setting related to volcanic-associated massive sulphide base metals and gold. The induced polarization survey is useful in outlining sulphide distribution in porphyry deposits related to chargeability anomaly highs. The preliminary results of the geophysical exploration program of the eastern flank of the Western Cordillera in the Andes Mountains of Colombia are discussed.

  9. Time-scales of assembly and thermal history of a composite felsic pluton: constraints from the Emerald Lake area, northern Canadian Cordillera, Yukon

    Science.gov (United States)

    Coulson, Ian M.; Villeneuve, Mike E.; Dipple, Gregory M.; Duncan, Robert A.; Russell, James K.; Mortensen, James K.

    2002-05-01

    Knowledge of the time-scales of emplacement and thermal history during assembly of composite felsic plutons in the shallow crust are critical to deciphering the processes of crustal growth and magma chamber development. Detailed petrological and chemical study of the mid-Cretaceous, composite Emerald Lake pluton, from the northern Canadian Cordillera, Yukon Territory, coupled with U-Pb and 40Ar/ 39Ar geochronology, indicates that this pluton was intruded as a series of magmatic pulses. Intrusion of these pulses produced a strong petrological zonation from augite syenite, hornblende quartz syenite and monzonite, to biotite granite. Our data further indicate that multiple phases were emplaced and cooled to below the mineral closure temperatures over a time-scale on the order of the resolution of the 40Ar/ 39Ar technique (˜1 Myr), and that emplacement occurred at 94.3 Ma. Simple thermal modelling and heat conduction calculations were used to further constrain the temporal relationships within the intrusion. These calculations are consistent with the geochronology and show that emplacement and cooling were complete in less than 100 kyr and probably 70±5 kyr. These results demonstrate that production, transport and emplacement of the different phases of the Emerald Lake pluton occurred essentially simultaneously, and that these processes must also have been closely related in time and space. By analogy, these results provide insights into the assembly and petrogenesis of other complex intrusions and ultimately lead to an understanding of the processes involved in crustal development.

  10. Evidence of a large deep conductive body within the basement of the Guadalquivir foreland Basin (Betic Cordillera, S-Spain) from tipper vector modelling: Tectonic implications

    Science.gov (United States)

    González-Castillo, L.; Galindo-Zaldívar, J.; Junge, A.; Martínez-Moreno, F. J.; Löwer, A.; Sanz de Galdeano, C.; Pedrera, A.; López-Garrido, A. C.; Ruiz-Constán, A.; Ruano, P.; Martínez-Martos, M.

    2015-11-01

    The Betic Cordillera is an Alpine belt formed by the interaction of the Eurasian and African plates and the westward motion of the Alboran Domain. Long Period Magnetotelluric observations at 26 sites in its westernmost part provide induction arrows that have been compared with 3D forward models including bathymetry and major geological bodies. The results highlight the presence of a major conductive body (0.05 Ω m) unknown to date and located within the basement of the Guadalquivir foreland basin. Aeromagnetic and field magnetic measurements further support the occurrence of magnetic anomalies related to the top of this anomalous body. This major structure is interpreted as an intermediate or basic igneous rock, with a high proportion of metallic mineralization. Its origin is discussed in the framework of the regional geological setting, possibly produced in the southern Iberian Variscan Massif by a huge concentration of volcanogenic massive sulphide (VMS) in the prolongation of the Iberian Pyrite Belt during Devonian-early Carboniferous times. Another possibility is that the conductive anomaly is due to magmatic intrusions associated with the Mesozoic fragmentation of Southern Iberia and the opening of the Tethys.

  11. Are scale detrital zircon age spectra from modern sands representative of their catchment sources? : An empirical test from the Eastern Cordillera of Colombia

    Science.gov (United States)

    Knowles, J.; Bande, A.; Ramirez, J. C.; Mora, A.; Horton, B. K.; Nie, J.; Saylor, J.

    2010-12-01

    Despite potential pitfalls, detrital zircon U-Pb geochronology remains a widely used method to determine provenance and age, and conduct tectonic reconstructions. Potential problems include whether the zircon populations from sandstone samples accurately capture both the presence and relative abundances of zircon populations within the catchment. Sand and sandstone samples were collected and analyzed from two rivers, the Rio Cravo Sur and Rio Cusiana, and the various Cretaceous-Cenozoic formations present in their respective catchments (areas= XX, YY km2, respectively). Using digital watershed delineation, mapped surface geology, the areal extent of each formation, and the measured detrital zircon U-Pb age spectrum for each formation, model zircon populations were generated to represent each catchment. We compared this to the measured river data using both qualitative and statistical analysis methods in order to determine whether sampled formations yield representative populations. Statistical tests including the coefficient of determination (R-squared), overlap-similarity comparison, and the Chi-square test support the conclusion that populations reflect their contributors. Modern river sediments sampled in the Eastern Cordillera of the Colombian Andes reveal U-Pb age spectra that are representative of the contributing formations. Significantly, not only do river samples accurately reflect the presence of zircon populations, they also closely reflect the relative abundance of those populations. We attribute deviations between model and measured spectra to differences in zircon concentration, or erosion.

  12. Hypoxia in Chilean Patagonian Fjords

    Science.gov (United States)

    Silva, Nelson; Vargas, Cristian A.

    2014-12-01

    Chilean Patagonia is one of the largest estuarine systems in the world. It is characterized by a complex geography of approximately 3300 islands, a total surface area of 240,000 km2, and 84,000 km of coast line, including islands, peninsulas, channels, fjords, and sounds. The Chilean Patagonia Interior Sea is filled with a mixture of sea, estuarine, and fresh waters, and is characterized by a two layer vertical general circulation. Dissolved oxygen (DO) conditions in these fjords were analyzed based on historic salinity, dissolved oxygen and nutrient data from 1200 oceanographic stations. Horizontal advection of adjacent well oxygenated Subantarctic Waters (5-6 mL L-1) was the mayor source of DO in the deep layers of the Interior Sea. Incoming DO was consumed by the respiration of autochthonous and allochthonous particulate organic matter, as ocean water flows towards the continental fjord heads, reaching near-hypoxic (2-3 mL L-1) or hypoxic levels (2 mL L-1) and four hypoxic (<2 mL L-1), but only at their heads. None were found to be anoxic (0 mL L-1). We found these DO conditions to be permanent features of the Chilean Patagonia Interior Sea.

  13. Geological and structural setting, age, and geochemistry of the orogenic gold deposits at the Pataz Province, Eastern Andean Cordillera, Peru

    OpenAIRE

    Haeberlin, Yves; Fontboté, Lluis; Moritz, Robert

    2004-01-01

    La province de Pataz au Nord-Pérou est la plus septentrionale des ceintures paléozoïques d'or, antimoine et tungstène orogéniques (mésothermales) de la Cordillère Orientale des Andes Centrales. Longue de plus de 160 km, elle est connue pour ses veines épigénétiques de quartz aurifères riches en sulfures (ressource: 40 millions d'onces d'or). Les minéralisations, datées à ~314 Ma, sont localisées dans des fractures inverse-décrochantes dextres et d'extension le long des marges et à l'intérieur...

  14. Geological and structural setting, age, and geochemistry of the orogenic gold deposits at the Pataz Province, Eastern Andean Cordillera, Peru

    OpenAIRE

    Haeberlin, Yves

    2001-01-01

    La province de Pataz au Nord-Pérou est la plus septentrionale des ceintures paléozoïques d'or, antimoine et tungstène orogéniques (mésothermales) de la Cordillère Orientale des Andes Centrales. Longue de plus de 160 km, elle est connue pour ses veines épigénétiques de quartz aurifères riches en sulfures (ressource: 40 millions d'onces d'or). Les minéralisations, datées à ~314 Ma, sont localisées dans des fractures inverse-décrochantes dextres et d'extension le long des marges et à l'intérieur...

  15. Central Pain Syndrome

    Science.gov (United States)

    ... Enhancing Diversity Find People About NINDS NINDS Central Pain Syndrome Information Page Table of Contents (click to ... being done? Clinical Trials Organizations What is Central Pain Syndrome? Central pain syndrome is a neurological condition ...

  16. Central venous line - infants

    Science.gov (United States)

    CVL - infants; Central catheter - infants - surgically placed ... plastic tube that is put into a large vein in the chest. WHY IS A ... central catheter (PICC) or midline central catheter (MCC). A CVL ...

  17. The Bolivian Orocline and its implications for the origin of the central Andes

    Science.gov (United States)

    Arriagada, C.

    2015-12-01

    The tectonic evolution of the Central Andes includes a complex combination of thrusting, wrenching and block rotation leading progressively to the curvature of the orogenic system of the South American continental margin at 18ºS (Bolivian Orocline). Tectonic deformation in the Bolivian Orocline cannot be realistically restored using information from balanced cross sections alone, as the deformation includes an important component of block rotation, associated to counterclockwise block rotation in southern Peru and clockwise rotation in northern Chile. Recent work shows that block rotations in the forearc are essentially pre-early Miocene, predating the onset of Neogene shortening in the Sub Andean zone. Most rotations in the forearc of northern Chile where acquired through a single tectonic event during the Paleogene-early Miocene which probably coincides with the Eocene orogen-wide Incaic event which affected large regions of the central Andes between ca. 50 and 40 Ma. Results from 2D restoration experiments support the hypothesis of the Paleogene formation of the Bolivian Orocline, as a consequence of differential shortening, concentrated in the Eastern Cordillera of Bolivia, southern Peru and northwestern Argentina. Within the southern central Andes four additional curvatures including striking changes in the pattern of rotations have been discovered. From north to south these are the Antofagasta-Calama Lineament, Vallenar, Maipo and Arauco oroclines. However, an important part of rotation needs to be balanced, in the forearc region, by two major conjugate oblique shear zones (Abancay Deflection and Antofagasta-Calama Lineament). These structural features are probably related to inherited lithospheric discontinuities associated with the accretion of basement terranes which could be responsible for producing and delimitating significant and abrupt changes in the magnitude of the Central Andean Rotation Pattern along the margin. While shortening and crustal

  18. Insights from analyzing and modelling cascading multi-lake outburst flood events in the Santa Cruz Valley (Cordillera Blanca, Perú)

    Science.gov (United States)

    Emmer, Adam; Mergili, Martin; Juřicová, Anna; Cochachin, Alejo; Huggel, Christian

    2016-04-01

    Since the end of Little Ice Age, the Cordillera Blanca of Perú has experienced tens of lake outburst floods (LOFs), resulting in the loss of thousands of lives and significant material damages. Most commonly involving glacial lakes, such events are often directly or indirectly related to glacier retreat. Here we analyze an event on 8th February 2012 involving four lakes and affecting two valleys (Santa Cruz and Artizón) in the northern part of the Cordillera Blanca. Using the combination of field data, satellite images, digital elevation model (DEM) and GIS-based modelling approaches, the main objectives are: (i) to better understand complex multi-lake outburst flood and related foregoing and induced geomorphological processes; and (ii) to evaluate and discuss the suitability, potentials and limitations of the r.avaflow model for modelling such complex process chains. Analyzing field geomorphological evidence and remotely-sensed images, we reconstruct the event as follows: a landslide from the recently deglaciated left lateral moraine of Lake Artizón Alto (4 639 m a.s.l.), characterized by steep slopes and a height of more than 200 m produced a displacement wave which overtopped the bedrock dam of the lake. The resulting flood wave breached the dam of the downstream moraine-/landslide-dammed Lake Artizón Bajo (4 477 m a.s.l.), decreasing the lake level by 10 m and releasing 3 x 105 m3 of water. Significant amounts of material were eroded from the steeper parts of the Artizón Valley (mean slope >15°) and deposited further downstream in the flatter part of the Santa Cruz Valley (mean slope <2°; confluence of the two valleys at 3 985 m a.s.l.). The flood affected two debris cone-dammed lakes (Jatuncocha and Ichiccocha) in the Santa Cruz Valley. Some minor damages to the dam of Lake Jatuncocha were documented. Geomprohological evidence of the event was observed more than 20 km downstream from Lake Artizón Alto. The described multi-LOF event was employed as a

  19. Arquitectura precerámica en la cordillera de los Andes, Piruru frene a la diversidad de los datos

    Directory of Open Access Journals (Sweden)

    Elisabeth Bonnier

    1988-12-01

    Full Text Available Los datos sobre la arquitectura precerámica en la cordilleraandina provienen de cinco sitios: La Galgada, Piruru, Huaricoto, Shillacotoy Kotosh. Contexto arqueológico y rasgos arquitectónicos específicos permitenidentificar la función ceremonial de esta arquitectura. La descripciónde las construcciones religiosas pone en evidencia un conjunto pertinente decaracteres comunes. El espacio ceremonial, construido y sin construir, se articulaalrededor del doble elemento arquitectónico fundamental, el fogón yel piso. Para analizar el piso a dos niveles, dos neologismos, pericausto y epicaustohan sido creados. El análisis arquitectónico muestra que el piso es elespacio sagrado por excelencia. Los fechados 14C de los sitios estudiadosdestacan la larga duración del Precerámico Final con arquitectura. A la luz delos últimos trabajos en Piruru y de los cambios arquitectónicos perceptiblesen este sitio, la hipótesis, formulada a principios de este decenio, sobre ·taexistencia de una tradición religiosa única propia de los Andes Centrales, seestá reconsiderando.

  20. Flora y vegetación de suelos crioturbados y hábitats asociados en la Cordillera Blanca, Ancash, Perú

    Directory of Open Access Journals (Sweden)

    Asunción Cano

    2011-05-01

    Full Text Available Entre los años 2006 y 2008, se llevaron a cabo estudios florístico y de vegetación de los suelos crioturbados y hábitats asociados en cuatro localidades de la Cordillera Blanca (Ancash, Perú localizadas por encima de los 4500 m. Se realizaron recolectas botánicas además de transectos de intersección-línea, en los cuales se midió el espacio (en cm ocupado por cada especie. Fueron determinadas 136 especies de plantas vasculares, agrupadas en 65 géneros y 26 familias. Las Magnoliópsida (dicotiledóneas fueron las más diversas con 97 especies, seguidas de las Liliópsidas (Monocotiledóneas con 36. La mayor diversidad está concentrada en las familias Asteraceae y Poaceae (40,63%. Los géneros con mayor riqueza de especies fueron Senecio (18 y Calamagrostis (12. Se registraron 76 especies (54,82% en suelos crioturbados y hábitats asociados; mientras que 60 especies (44,11% fueron colectadas en la vegetación adyacente. El 95,56% de las especies reportadas fueron hierbas perennes. Se caracterizaron cuatro tipos de comunidades vegetales: a comunidad de suelos crioturbados propiamente dicha, b comunidad de suelos crioturbados asociada a pajonal, c comunidad de suelos crioturbados asociada a roquedal seco y d comunidad de suelos crioturbados asociadas a roquedal húmedo. Se indícan las especies características de cada comunidad.

  1. Deformación cenozoica de la faja plegada y corrida del Aconcagua y Cordillera Frontal: entre los 33°30' y 33°45'S

    Directory of Open Access Journals (Sweden)

    L. B. Giambiagi

    2003-03-01

    Full Text Available Este trabajo presenta nuevos datos sobre la evolución tectónica de los Andes entre los 33º30´ y 33º45´S, los cuales han sido obtenidos a partir del estudio de la estructura de la faja plegada y corrida del Aconcagua y la evolución de la cuenca de antepaís del Alto Tunuyán. La deformación en la faja plegada y corrida comenzó durante el Mioceno temprano a medio con la inversión de antiguas estructuras de rift. Durante el Mioceno medio la deformación migró progresivamente hacia el este, involucrando a las secuencias mesozoicas. Esto generó una cuña orogénica adelgazada hacia el este. Esta faja fue sujeta a períodos de deformación en su sector frontal y períodos de deformación en su sector interno de manera tal de restaurar su ángulo crítico. La discordancia que separa a distintas unidades sinorogénicas neógenas, el cambio en las direcciones de paleocorrientes desde el oeste hacia el nordeste y la presencia de clastos derivados de zonas proximales aportaron evidencias del levantamiento de la Cordillera Frontal a partir de los 9 Ma. Este levantamiento continuó hasta los 6 Ma, luego del cual la faja plegada y corrida y la cuenca de antepaís continuaron deformándose. Las rocas volcánicas pliocenas inferiores a pleistocenas que cubren discordantemente la faja deformada indican que la principal deformación de la zona ocurrió antes del Plioceno bajo.

  2. The Early Andean Magmatic Province (EAMP): 40Ar/ 39Ar dating on Mesozoic volcanic and plutonic rocks from the Coastal Cordillera, northern Chile

    Science.gov (United States)

    Oliveros, Verónica; Féraud, Gilbert; Aguirre, Luis; Fornari, Michel; Morata, Diego

    2006-10-01

    The Early Andean Magmatic Province (EAMP), consists of about 150 000 km 3 of volcanic and plutonic units in the Coastal Cordillera of northern Chile and southern Peru and represents a major magmatic Mesozoic event in the world, for which the precise age of the thick volcanic series was unknown. Thirty 40Ar/ 39Ar analyses were carried out on primary mineral phases of volcanic and plutonic rocks from northern Chile (18°30'-24°S). Reliable plateau and "mini plateau" ages were obtained on plagioclase, amphibole and biotite from volcanic and plutonic rocks, despite widespread strong alteration degree. In the Arica, Tocopilla and Antofagasta (700 km apart) regions, the ages obtained on lava flows constrain the volcanic activity between 164 and 150 Ma and no N-S migration of volcanism is observed. The uppermost lava flows of the volcanic sequence at the type locality of the La Negra Formation extruded at ca. 153-150 Ma, suggesting the end of the volcanic activity of the arc at that time. The oldest volcanic activity occurred probably at ca. 175-170 Ma in the Iquique area, although no plateau age could be obtained. The plutonic bodies of the same regions were dated between ca. 160 and 142 Ma, indicating that they were partly contemporaneous with the volcanic activity. At least one volcanic pulse around 160 Ma is evidenced over the entire investigated reach of the EAMP, according to the ages found in Arica, Tocopilla, Michilla and Mantos Blancos regions. The episodic emplacement of huge amounts of subduction related volcanism is observed throughout the whole Andean history and particularly during the Jurassic (southern Peru, northern Chile and southern Argentina). These events probably correspond to periodic extensional geodynamic episodes, as a consequence of particular subduction conditions, such as change of obliquity of the convergence, change in the subduction angle, slab roll back effect or lower convergence rate, that remain to be precisely defined.

  3. Evidencias de deformación pleistocena en el sistema de falla de La Carrera (32º40'-33º15'ls, Cordillera Frontal de Mendoza

    Directory of Open Access Journals (Sweden)

    Casa Analía Laura

    2010-08-01

    Full Text Available Entre los 32º25' y 33º15' LS, el frente de levantamiento cenozoico de la Cordillera Frontal, muestra signos de reactivación pleistocena y está representado por el sistema de falla de La Carrera. En el margen oriental del cordón del Plata, la distribución de la deformación cuaternaria no es homogénea. A la latitud de la localidad de El Salto, dichas evidencias se concentran en un tramo comprendido entre los 32º55' y 33º05' LS, tanto en el frente serrano como en el piedemonte adyacente. En la montaña, la actividad neotectónica está asociada a la falla Río Blanco, que delimita el frente. En el piedemonte una ramificación de esta falla afectó un pedimento rocoso y su cobertura aluvial pleistocena, mientras que una segunda falla cuaternaria (falla El Salto ascendió tres niveles de pedimentos cuaternarios. Se presentan asimismo escarpas pedemontanas en el aluvio. En ese tramo montañoso, las cuencas de drenaje están poco desarrolladas; allí se han calculado bajos valores del índice de sinuosidad del frente (Smf y de la relación ancho del piso-alto del valle (Vf, y altos valores del índice de longitud-gradiente de cursos (SL. Este conjunto de evidencias sugiere una persistente actividad tectónica cuaternaria a lo largo de segmentos estructurales en el frente montañoso del cordón del Plata y en el área pedemontana asociada. Las evidencias identificadas a la latitud de El Salto, parecen ser la continuación norte de la falla La Aguadita y amplían el alcance de la deformación cuaternaria dentro del sistema de falla de La Carrera.

  4. Geología y controles estructurales de las áreas de alteración del portezuelo de las Burras (Cordillera Frontal, San Juan

    Directory of Open Access Journals (Sweden)

    Constantino Karkanis

    2004-03-01

    Full Text Available Se describen las características estratigráficas, petrográficas y estructurales de la comarca del portezuelo de las Burras, localizada en la Cordillera Frontal (San Juan, Argentina. Está constituida por un basamento de sedimentitas de la Formación La Puerta (Carbonífero superior - Pérmico inferior y grandes espesores volcánicos y sedimentarios subordinados del Grupo Choiyoi (Pérmico - Triásico, niveles lávicos andesíticos de la Andesita Las Vizcachas (Mesozoico superior ? - Terciario ?, volcanitas de carácter más ácido de la Formación Arroyo de las Chinches (Oligoceno - Mioceno y de volcanitas andesíticas de la Formación Entrecordilleras (Mioceno superior - Pleistoceno. En relación intrusiva se ha identificado al Plutón Entrecordilleras (Neógeno y a otros cuerpos dacíticos pertenecientes presumiblemente a otra facies del mismo plutón. Los cursos del río Manantiales y arroyo Las Burras se disponen sobre una zona de fallamiento transcurrente senestral principal expresado por fallas sintéticas y antitéticas, donde el sector próximo al portezuelo de las Burras constituye un resalto de alivio de transferencia tectónica con características dilatantes. Éste habría controlado la circulación y emplazamiento de fluidos hidrotermales mineralizantes, responsables de las anomalías cromáticas, mineralógicas y geoquímicas detectadas, asociadas a alteraciones hidrotermales de tipo arcillosa y silícea, que alientan un interés sobre la posibilidad de alumbrar acumulaciones económicas de minerales preciosos.

  5. Estructura duplex plegada en el frente montañoso de la Cordillera Principal, río Atuel, provincia de Mendoza

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    L.V. Dimieri

    2005-12-01

    Full Text Available El objetivo de este trabajo es obtener una reconstrucción estructural de los afloramientos del alto valle del Río Atuel, al sudoeste de la provincia de Mendoza. Esta región forma parte del frente montañoso de la Cordillera Principal que fue construido por medio de sistemas de corrimientos. Cercano a la localidad de El Sosneado, entre los arroyos Blanco y La Manga, la secuencia estratigráfica está compuesta por rocas Mesozoicas que van desde la Formación Auquilco hasta la Formación Malargüe. Esta pila sedimentaria es afectada por sistemas de corrimientos que se despegan de la Formación Auquilco (yeso cuya disposición en la zona de trabajo es moderadamente buzante al este. Este despegue está dirigido hacia el antepaís con sistemas de fallas y plegamiento asociado que se desarrollan encima del mismo. Estos sistemas de fallas parecen conectados con despegues de techo localizados principalmente en la Formación Huitrín y en la Formación Diamante, por lo tanto generando una geometría duplex. El frente de este duplex, que aflora en la margen occidental del Ao. La Manga, muestra a los estratos Mesozoicos invertidos. Esto sugiere que se trata de una estructura con características de un duplex antiformal que ha sido plegado. Una cuña tectónica basamental, que se propaga hacia el antepaís con retrocorrimientos en su frente y que está localizada en el subsuelo de esta región, es la responsable del volcado final de las estructuras descriptas.

  6. Hydrothermal activity and its paleoecological implications in the latest Miocene to Middle Pleistocene lacustrine environments of the Baza Basin (Betic Cordillera, SE Spain)

    Science.gov (United States)

    García-Aguilar, José Manuel; Guerra-Merchán, Antonio; Serrano, Francisco; Palmqvist, Paul; Flores-Moya, Antonio; Martínez-Navarro, Bienvenido

    2014-07-01

    The continental sedimentary record of the Baza Basin (Guadix-Baza Depression, Betic Cordillera, SE Spain) shows six sedimentary units of lacustrine origin deposited from the latest Miocene to the Middle Pleistocene. Depending on the interval considered, the lacustrine deposits are mainly composed of marls, carbonates or gypsiferous evaporites, showing lithological, mineralogical and geochemical features (i.e., magnesium, strontium and sulfur contents, celestine deposits and travertine growths) that are evidence of intense, tectonically-induced hydrothermal activity. According to the high concentrations of strontium and sulfur as well as the abundance of travertines and magnesium clays, the supply of hot waters was greater during the Zanclean, the Gelasian and the Calabrian, as a result of tectonic activity. Hydrothermal activity has continued until the present time and is responsible of the hot springs that are nowadays active in the Guadix-Baza Depression. The paleoenvironmental consequences of these sublacustrine hot springs were that during some intervals the lakes maintained a relatively permanent water table, not subject to periodic desiccations in the dry season, and warmer temperatures throughout the year. This resulted in a high level of organic productivity, especially for the Calabrian, which allowed the development of a rich and well diversified mammalian community, similar to those of modern African savannas with tree patches. In this mild environment, the permanent water sheet favored the presence of drought intolerant megaherbivores such as the giant extinct hippo Hippopotamus antiquus. The high standing crop biomass of ungulates resulted in the availability of abundant carcasses for scavengers such as hyenas and hominins, which explains the very high densities of skeletal remains preserved in the sediments distributed along the lake surroundings.

  7. New insights into the North American Cordillera forearc: Cretaceous to Eocene tectonic evolution of the Leech River Schist, Southern Vancouver Island, Canada

    Science.gov (United States)

    Jakob, Johannes; Johnston, Stephen

    2015-04-01

    The Leech River Complex on southern Vancouver Island is a part of the Pacific Rim Terrane of the North American Cordillera and comprises a series of fault-bounded slices of mainly meta-sedimentary and meta-igneous rocks of Triassic to Cretaceous age. The tectono-metamorphic history of this unit provides important constraints on the history of terrane accretion and the paleogeographic and tectonic evolution of the western North American forearc region. Our focus is on the structures and tectonic fabrics that developed within the western most part of the Leech River Schist from ~88 Ma through ~37 Ma. Similar syn- and post-instrusive structures that developed during emplacement of the ~88 Ma Jordan River meta-granodiorite and the ~51 Ma Walker Creek Intrusions respectively, indicate a consistent stress field during >35 m.y. of northward translation of the outboard Cordilleran terranes. A regional high temperature, Staurolite-Andalusite-grade metamorphic event is recorded in the meta-sedimentary rocks. Subcretion of the Crescent terrane beneath the Leech River Schist at ~51 Ma caused folding of the metamorphic rocks, the development of a system of dextral and sinistral brittle shears, and normal faulting. Related extension to the northwest resulted in the opening of Barkley Sound and the more westerly marine Tofino basin. These multi-faceted deformational structures are most likely a direct consequence of the subcretion of the Crescent terrane and the linked development of the Southern Vancouver Island Orocline. The deposition of sandstones and conglomerates of the Sooke Formation began at ca. 37 Ma. This siliciclastic sequence unconformably overlies the Leech River Schist, records rapid subsidence of the forearc following a preceding uplift and exhumation event, and may be a record of a younger subcretion event.

  8. Zircon (U-Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

    Science.gov (United States)

    Powell, Jeremy; Schneider, David; Stockli, Daniel; Fallas, Karen

    2016-03-01

    Sedimentary strata of the Neoproterozoic Mackenzie Mountains Supergroup (MMSG) and Windermere Supergroup (WSG) occupy the cores of anticlines in the Mackenzie Mountains of the Canadian Cordilleran Foreland Belt. Stratigraphic and structural evidence suggest that these rocks have undergone several episodes of burial and unroofing relatively intact. We report single-grain detrital muscovite 40Ar/39Ar and zircon (U-Th)/He (ZHe) data from a suite of samples across the fold-thrust belt and the Neoproterozoic stratigraphic record. The strata have not reached high enough temperatures to reset the muscovite 40Ar/39Ar system, and instead our detrital muscovite data refine Tonian-Cryogenian depositional ages. Single-crystal ZHe dates range from 432 ± 35 to 46 ± 4 Ma, indicating that MMSG and WSG strata have not been heated sufficiently to fully reset the ZHe system. These factors make the Neoproterozoic strata an attractive natural laboratory to test the utility of the zircon radiation damage and annealing model on the quantification of thermal histories from detrital zircon populations that have accumulated radiation damage over long geologic timescales. Thermal modeling reveals that (1) a substantial sedimentary package was deposited following the Devonian and removed during Permo-Triassic cooling, and (2) the Cordilleran deformation front propagated through the study area from the Albian to the Paleocene, with a moderate increase in cooling rates between 75-67 Ma in the southwest and 60-55 Ma at the deformation front. Ultimately, relationships between radiation damage and helium diffusion kinetics in zircon explain substantial ZHe date dispersion and elucidate the temperature-time history of the northern Canadian Cordillera.

  9. Dynamics of the Central American Pacific

    Science.gov (United States)

    Vieytez, Begonia; Marrero-Díaz, Ángeles; José Machín, Francisco; José Gavidia, Francisco; Castro, Mi

    2014-05-01

    The Central American Pacific (CAP) is the area located in front of the Central America coast, within the Eastern Tropical Pacific region (ETP). The CAP dynamic is strongly influenced by the NE and SE trade winds, also this area is characterized by the presence of coastal wind jets at Gulf of Papagayo and Gulf of Panama, which are product of wind pulses blowing through the mountain gaps of the central cordillera, generating important eddies as the cyclonic eddy of Costa Rica Dome (CRD). Nevertheless, the implications of the topography of the continental margin of Central America in the determination of the dynamic processes in the area related to the action of winds and currents are still unknown. Between November and December 2010 (dry season), onboard the R/V Miguel Oliver, oceanographic parameters were measured in the CAP area, which despite its importance, has been poorly investigated until date. Available oceanographic information was processed in order to describe the dynamic along the Pacific coast of Central America, which is notable for its particularly strong stratification in the water column and the distribution of properties, as response to the presence of areas with high temperatures (above 28° C) and other areas with salinity minimum (less than 24). In this study was possible to distinguish three hydrographic zones: PM, south, in the adjacent region to Gulf of Panama, PY, in the center, in the adjacent region to Gulf of Papagayo, and FC, to the north, in the adjacent region to Gulf of Fonseca. The surface transformations of the water bodies, from south to north, observed in these zones could be indicting the presence of Costa Rica current. The prevailing wind system is the main force of variations in the surface distribution of the temperature in the area, and they are responsible of important structures as the anticyclonic eddy in front Gulf of Fonseca, eddies derived from the wind pulses of Gulf of Papagayo, and the relatively low temperatures in

  10. Geochemistry and tectonic setting of the «ophites» from the external zones ofthe Betic Cordilleras (S. Spain

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    Aguirre, L.

    1997-08-01

    Full Text Available Mesozoic basic magmatism in the External Zones of the Betic Cordilleras (S. Spain is represented by small tectonic bodies (ophites in Triassic formations, and submarine flows with abundant pillow-lavas interbedded with Jurassic sediments. Both basic igneous manifestations suffered very low- to low-grade metamorphism, more intense in the case of the ophites. Two types of ophites are distinguished on the basis of their primary mineralogy. In the first type, orthopyroxene is present in the less differentiated products. Clinopyroxene and Ca-plagioclase are the main primary phases and quartz appears in the more evolved rocks. In the second type, olivine is present in the less differentiated products. Ti-rich augite and Ca-plagioclase are also important primary minerals, but quartz is absent. Whole-rock chemistry (major and trace elements, including REE also allows us to discriminate between these two groups. The first group has higher SiO2, and lower TiO2, P2O5 and lower Na2O/K2O ratios than the second. Normative quartz is almost invariably present in this first group, whereas normative nepheline (lower than 5% is characteristic of the second group. Both groups are Sr, K, Ba, Rb, Th, Nb and Ce enriched with respect to normal MORB, but the first group has higher K, Rb, Ba, Th and lower Nb, Ce contents than the alkaline group. Nb/Y and Ti/V ratios are also different and show a tholeiitic affinity for the first group and transitional to alkaline for the second. Chondrite-normalised REE patterns in both groups are similar and characterized by LREE enrichment with respect to HREE. LREE/HREE ratios are, however, slightly higher in the transitional to alkaline group. Various discriminant tectonic diagrams indicate a continental intraplate setting for both ophite groups. This magmatism is related to the first extensional period of the Betic Cordilleras, during the Triassic-Jurassic. Geochemical differences between the two groups could evidence different

  11. Andesita Cerro Bola: Nueva unidad vinculada al magmatismo mioceno de la Cordillera de Olivares, San Juan, Argentina (30°35´S; 69°30´O Cerro Bola Andesite: New unit linked to the Miocene magmatism of the Olivares Cordillera, San Juan (30°35' S ; 68°30' W

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    A.F. Wetten

    2005-03-01

    Full Text Available El área de estudio se halla en la zona de Tocota, inmediatamente al este de la Cordillera de Olivares, en el borde oriental de la Cordillera Frontal, provincia de San Juan. En ella se encuentran unidades ígneas y sedimentarias del ciclo gondwánico, las que fueron intruidas y cubiertas en relación discordante por cuerpos subvolcánicos y volcánicos asignados anteriormente al ciclo ándico en sentido amplio, los cuales constituyen el principal objeto del presente estudio. Estos cuerpos han sido mapeados a fin de poder caracterizarlos adecuadamente, en el contexto estratigráfico de la región. Los afloramientos de interés han sido reconocidos en el cerro Bola y alrededores, donde se observan distribuidos irregularmente, cubriendo un área superior a 5 km². Las rocas, de coloración gris clara y composición andesítica - fenoandesítica, presentan estructuras de domo y colada. Estos afloramientos serían correlacionables con la unidad volcánica Pircas (Mioceno, la que aflora al oeste, y conformarían un evento magmático posterior al de pórfidos de diferente composición situados tanto en el arroyo Chita como en el cerro Divisadero. La extensión del área involucrada, la uniformidad litológica, el bajo grado de alteración y una edad radimétrica obtenida por el método K/Ar, fueron considerados para proponer a estas volcanitas como una unidad litoestratigráfica de edad miocena superior, con la denominación de Andesita Cerro Bola.The study area is located in the region of Tocota Creek, close to the Cordillera Olivares, eastern border of the Frontal Range, San Juan province. In this place, igneous and sedimentary units belonging to the Gondwanic cycle, were recognized. These units were intruded and unconformably covered by subvolcanic and volcanic bodies, which were commonly referred to the Tertiary or Andean cycle. The study of these bodies is the main proposal of this work. These bodies had been mapped in order to characterize them

  12. Los deslizamientos de la cordillera neuquina al sur delos 38° S: suinducción Mass wasting in the Neuquén Cordillerasouth of 38º: its trigger factors

    OpenAIRE

    Emilio F González Díaz; Andrés Folguera

    2009-01-01

    Las conclusiones sobre losdeslizamientos individualizados en la cordillera neuquina (36°-38°S), (suinducción sísmica; rechazo de la consideración de sus depósitos como till),indujo a proyectar su estudio al sur de los 38°S. Se distinguieron inéditaszonas de deslizamientos, cuya promoción y contexto sismotectónico difieren delos reconocidos entre los 36°-38°S. Su estudio regional, que abarcó trescomarcas (Aluminé, Chapelco y Arroyo Limay Chico), comprobó el predominio delas corrientes de tierr...

  13. El Transporte Terrestre a través de la Cordillera Cantábrica en Tiempos de Felipe II. Un Estudio a partir de la Correspondencia de Simón Ruiz con Laredo

    OpenAIRE

    Oscar LUCAS VILLANUEVA

    2012-01-01

    El presente trabajo analiza las condiciones y costes del transporte terrestre en tiempos de Felipe II en el ámbito de las relaciones comerciales entre Castilla y el espacio atlántico septentrional, a partir de la información proporcionada por las cartas comerciales del mercader Simón Ruiz. Los datos nos indican que las dificultades geográficas no fueron tan determinantes para el tráfico a través de la Cordillera Cantábrica como se había pensado hasta ahora. El artículo también aborda la cuest...

  14. Cuantificación del acortamiento alpino y estructura en profundidad del extremo sur-occidental de la Cordillera Ibérica (sierras de Altomira y Bascuñana)

    OpenAIRE

    Muñoz Martín, Alfonso; Vicente Muñoz, Gerardo de

    1998-01-01

    En este trabajo se describe la estructura en profundidad del extremo sur-occidental de la Cordillera Ibérica, a partir de la integración de datos estructurales, sísmicos y gravimétricos. Estos datos han permitido la construcción de dos mapas de isobatas, uno para el techo del basamento, y otro para el techo del Cretácico superior, así como la construcción de seis cortes geológicos equilibrados transversales a las principales estructuras de la cobertera. La estructura del basamento está defini...

  15. Caracterización de las unidades litoestrafigráficas del Triásico en el subsuelo del tercio noroccidental de la Cordillera Ibérica y áreas adyacentes

    OpenAIRE

    Muñoz, A.; Ramos, Amparo; Sánchez Moya, Yolanda; Sopeña, Alfonso

    1995-01-01

    [ES] En este trabajo se realiza un estudio de los sedimentos pérmicos y triásicos que se localizan principalmente en el subsuelo de la Cuenca de Almazán, borde E de la Cuenca dcl Duero y borde NW de la Cuenca del Ebro, mediante el análisis detallado de los sondeos y líneas sísmicas que existen en estas áreas. Esto ha permitido establecer una serie de correlaciones con los materiales equivalentes que afloran en superficie en áreas próximas de ambas ramas de la Cordillera Ibér...

  16. Ammonoideos y bioestratigrafía del Triásico Medio (Anisiense superior-Ladiniense) en la sección de Calasparra (sector oriental de la Cordillera Bética, Murcia, España)

    OpenAIRE

    Pérez Valera, Juan Alberto

    2005-01-01

    [ES] Se ha realizado el estudio paleontológico y bioestratigráfico de los ammonoideos del Anisiense superior y del Ladiniense en el SE de Calasparra (sector oriental de la Cordillera Bética). Los materiales corresponden a la facies Muschelkalk y están constituidos por dolomías y calizas fosilíferas, que tienen un espesor de 89 m. El análisis taxonómico efectuado ha permitido identificar 5 géneros y 9 especies, algunas de las cuales se han citado en España por primera vez, como Par...

  17. Ammonoideos y bioestratigrafía del Triásico Medio (Anisiense superior-Ladiniense) en la sección de Calasparra (sector oriental de la Cordillera Bética, Murcia, España)

    OpenAIRE

    Pérez Valera, Juan Alberto

    2005-01-01

    Se ha realizado el estudio paleontológico y bioestratigráfico de los ammonoideos del Anisiense superior y del Ladiniense en el SE de Calasparra (sector oriental de la Cordillera Bética). Los materiales corresponden a la facies Muschelkalk y están constituidos por dolomías y calizas fosilíferas, que tienen un espesor de 89 m. El análisis taxonómico efectuado ha permitido identificar 5 géneros y 9 especies, algunas de las cuales se han citado en España por primera vez, como Paraceratitoides ...

  18. Paleontología y ambientes del Triásico Medio en el sector noroccidental de la cordillera ibérica (provs. de Soria y Guadalajara, España)

    OpenAIRE

    Márquez Aliaga, Ana; García Gil, S.

    1991-01-01

    El Triásico Medio del sector noroccidental de la Cordillera Ibérica está compuesto por dos formaciones carbonáticas, que se corresponden con la unidad carbonática superior del Muschelkalk, y que hacia el NW pasan lateralmente a una formación terrígena. El registro fósil se encuentra en ambos tipos de formaciones. Tanto el estudio tafonómico como sedimentológico, permiten inferir la presencia de elementos acumulados que podrían corresponder a asociaciones autóctonas, compuestas ...

  19. 'El león de la cordillera'. Primo Capraro y el desempeño empresario en la región del nahuel Huapi, 1902-1932

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    Méndez Laura

    2009-01-01

    Full Text Available La historia económica de la Patagonia Norte vivió cambios radicales en el período 1902-1932. Bariloche, un pequeño pueblo de frontera sobre la cordillera de los Andes, se convirtió en un centro turístico internacional. Este artículo pretende explicar el proceso de transformación económica de este espacio social, a través del comportamiento empresario de Primo Capraro, un inmigrante italiano que se convirtió en el empresario más importante de la región.

  20. El sistema aluvio-travertínico de Frailes (Cuenca Neógeno-Cuaternaria de Alcalá la Real, provincia de Jaén, Cordillera Bética)

    OpenAIRE

    García García, Fernando; Nieto, Luis M.

    2004-01-01

    On study an alluvial-travertine complex system located near to Frailes village (Betic Cordillera, Jaén province). It is made up of two steps with their flat top located at 930 and 1026 m a.s.l. The lower one prograding to N130ºE is mainly formed by allochthonous travertine facies. The upper step consists of alluvial and travertine facies. There are two detrital facies associations, characteristic of alluvial fan, and three carbonate facies associations consisting of allochthonous ...

  1. To centralize or not to centralize?

    OpenAIRE

    Campbell, Andrew; Kunisch, Sven; Müller-Stewens, Günter

    2011-01-01

    The CEO's dilemma-were the gains of centralization worth the pain it could cause?-is a perennial one. Business leaders dating back at least to Alfred Sloan, who laid out GM's influential philosophy of decentralization in a series of memos during the 1920s, have recognized that badly judged centralization can stifle initiative, constrain the ability to tailor products and services locally, and burden business divisions with high costs and poor service.1 Insufficient centralization can deny bus...

  2. Ecosistemas presentes y pasados en la Quebrada Benjamín Matienzo (32º 35' - 32º 50' L. S. y 70º 06' L. O., Cordillera de Los Andes, Mendoza, Argentina Present and past ecosystems in the quebrada Benjamín Matienzo (32º 35' - 32º 50'S and 70º 06'W, cordillera de Los Andes, Mendoza, Argentina

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    Mónica C Wingenroth

    2012-09-01

    Full Text Available Los sedimentos de un perfil en la quebrada Benjamín Matienzo, cordillera de Los Andes (32º 35' - 32º 50' L. S. y 70º 06' L. O., aproximadamente a 3400 m de altura, fueron datados en 6400 años AP a los 572 cm de profundidad. El polen identificado en 174 eventos (capas hallados en dicho perfil se relacionó con el polen presente (1980-1981 / 1981-1982. Un total de siete ambientes se definieron en la quebrada, en base a las diferencias registradas entre la cantidad y calidad del polen local, sugiriendo cambios de la vegetación y/o producción de polen, en respuesta a las variaciones en la disponibilidad del agua y la temperatura. A partir de las diferencias detectadas entre la cantidad y calidad del polen alóctono, se infirieron las direcciones predominantes de los vientos que llegaron a Matienzo en cada evento pasado. A su vez para los eventos incluidos en los mencionados ambientes se sugirieron balances acumulativos de la masa de hielo positivos y negativos, derretimiento de las áreas periglaciales congeladas y los correspondientes ciclos solares y su actividad.Sediments from a profile in the quebrada Benjamín Matienzo, cordillera de Los Andes (32º35'-32º50'S and 70º06'W, 3400 m asl, were dated at the bottom of a 572 cm-depth core to 6400 years B.P. The pollen identified in 174 events (layers of the profile was related to the present pollen assemblage (1980-1981 / 1981-1982. Differences between the quantity and quality of the local pollen defined a total of seven environments in the quebrada Benjamín Matienzo and suggested changes in vegetation and/or pollen production due to water availability and temperature variations. In turn, differences between the quantity and quality of the allochthonous pollen were used to infer the predominant wind directions reaching the quebrada Benjamín Matienzo during each past event. In addition, positive and negative cumulative ice mass balance, melting of frozen periglacial areas and correspondence

  3. Tectonomagmatic characteristics of the back-arc portion of the Calama-Olacapato-El Toro Fault Zone, Central Andes

    Science.gov (United States)

    Acocella, V.; Gioncada, A.; Omarini, R.; Riller, U.; Mazzuoli, R.; Vezzoli, L.

    2011-06-01

    Post-20 Ma magmatism in the Central Andes is either localized in the magmatic arc or distributed east of it, on the Altiplano-Puna Plateau. Here there is a distinct concentration of magmatic centers on NW-SE trending lineaments, such as the Calama-Olacapato-El Toro (COT), that extends into the Eastern Cordillera to the east of the Puna. Understanding the possible genetic relationship between prominent structures and magmatic centers on these lineaments is important to elucidate the tectonomagmatic evolution of the Central Andes. We investigated the back-arc area of the COT using remote sensing, geological, structural, and petrochemical data. Our study demonstrates that this portion of the COT consists of NW-SE striking faults, formed under overall left-lateral transtension that decreases in activity toward the COT termini. Deformation on the COT occurred during and after activity of prominent N-S striking transpressive fault systems and is coeval with magmatism, which is focused on the central COT. The most evolved magmatic rocks, with an upper crustal imprint, are exposed on the central COT, whereas more primitive, mantle-derived mafic to moderately evolved magmatic rocks, are found toward the COT termini. This points to a genetic relationship between upper crustal deformation and magmatic activity that led to enhanced magma storage in the central COT. COT magmas may result either from slab steepening or episodic delamination of the asthenospheric mantle.

  4. The nature of orogenic crust in the central Andes

    Science.gov (United States)

    Beck, Susan L.; Zandt, George

    2002-10-01

    The central Andes (16°-22°S) are part of an active continental margin mountain belt and the result of shortening of the weak western edge of South America between the strong lithospheres of the subducting Nazca plate and the underthrusting Brazilian shield. We have combined receiver function and surface wave dispersion results from the BANJO-SEDA project with other geophysical studies to characterize the nature of the continental crust and mantle lithospheric structure. The major results are as follows: (1) The crust supporting the high elevations is thick and has a felsic to intermediate bulk composition. (2) The relatively strong Brazilian lithosphere is underthrusting as far west (65.5°W) as the high elevations of the western part of the Eastern Cordillera (EC) but does not underthrust the entire Altiplano. (3) The subcrustal lithosphere is delaminating piecemeal under the Altiplano-EC boundary but is not completely removed beneath the central Altiplano. The Altiplano crust is characterized by a brittle upper crust decoupled from a very weak lower crust that is dominated by ductile deformation, leading to lower crustal flow and flat topography. In contrast, in the high-relief, inland-sloping regions of the EC and sub-Andean zone, the upper crust is still strongly coupled across the basal thrust of the fold-thrust belt to the underthrusting Brazilian Shield lithosphere. Subcrustal shortening between the Altiplano and Brazilian lithosphere appears to be accommodated by delamination near the Altiplano-EC boundary. Our study suggests that orogenic reworking may be an important part of the "felsification" of continental crust.

  5. Climate change and permafrost stability in the eastern Canada Cordillera:The results of 33 years of measurements

    Institute of Scientific and Technical Information of China (English)

    Stuart; A.Harris

    2009-01-01

    Over the last 33 years,a network of climate stations has been set up at high altitude mountain permafrost sites from Plateau Mountain near Claresholm,Alberta,north to Sheldon Lake on the North Canol Road in the Yukon.Taken together with the data from the US National Weather Service and the Canadian Atmospheric Environment Service,the results indicate a cooling of mean annual air temperature south of Calgary,no significant change in Calgary,a slight warming at Jasper,and a major warming at Summit Lake,west of Fort Nelson.In contrast,the south eastern and central Yukon show only a minor warming trend that lies well within the limits of a sixty-year record measured by the Canadian Atmospheric Environment Service.Along the Mackenzie valley and on the North Slope of Alaska,the mean annual air temperature is rising.Permafrost is aggrading on Plateau Mountain,degrading at Summit Lake,and appears to be stable in southern Yukon and southern Alaska.This is in contrast to the warming occurring on the Arctic coastal plain and along the Mackenzie valley.It therefore appears that changes in climate vary considera-bly from place to place,and even where warming may occur,it may not continue indefinitely.There has been a northward shift of the arctic front due to a weakening of air pressure in the Yukon and Alaska relative to the continental tropical(cT) and maritime polar(mT) air masses to the south.Any actual changes that may be occurring appear to undergo amplification along the Mackenzie valley and Arctic coastal plain and reduction by buffering in the interior Yukon and Alaskan mountains,a result of mi-cro-environmental factors.Continued,careful monitoring of the climate is required and needs to be expanded in the National Parks in the mountains in order to provide data on the changes that may be taking place.Such measurements can provide a sound basis for interpreting ecological and other climate-related data.The existing climate models are not working satisfactorily because

  6. Climate change and permafrost stability in the eastern Canada Cordillera: The results of 33 years of measurements

    Institute of Scientific and Technical Information of China (English)

    Stuart A. Harris

    2009-01-01

    Over the last 33 years, a network of climate stations has been set up at high altitude mountain permafrost sites from Plateau Mountain near Claresholm, Alberta, north to Sheldon Lake on the North Canol Road in the Yukon. Taken together with the data from the US National Weather Service and the Canadian Atmospheric Environment Service, the results indicate a cooling of mean annual air temperature south of Calgary, no significant change in Calgary, a slight warming at Jasper, and a major warming at Summit Lake, west of Fort Nelson. In contrast, the south eastern and central Yukon show only a minor warming trend that lies well within the limits of a sixty-year record measured by the Canadian Atmospheric Environment Service. Along the Mackenzie valley and on the North Slope of Alaska, the mean annual air temperature is rising. Permafrost is aggrading on Plateau Mountain,degrading at Summit Lake, and appears to be stable in southern Yukon and southern Alaska. This is in contrast to the warming occurring on the Arctic coastal plain and along the Mackenzie valley. It therefore appears that changes in climate vary considerably from place to place, and even where warming may occur, it may not continue indefinitely. There has been a northward shift of the arctic front due to a weakening of air pressure in the Yukon and Alaska relative to the continental tropical (cT) and maritime polar (mT) air masses to the south. Any actual changes that may be occurring appear to undergo amplification along the Mackenzie valley and Arctic coastal plain and reduction by buffering in the interior Yukon and Alaskan mountains, a result of micro-environmental factors. Continued, careful monitoring of the climate is required and needs to be expanded in the National Parks in the mountains in order to provide data on the changes that may be taking place. Such measurements can provide a sound basis for interpreting ecological and other climate-related data. The existing climate models are not

  7. The low-grade Canal de las Montañas Shear Zone and its role in the tectonic emplacement of the Sarmiento Ophiolitic Complex and Late Cretaceous Patagonian Andes orogeny, Chile

    Science.gov (United States)

    Calderón, M.; Fosdick, J. C.; Warren, C.; Massonne, H.-J.; Fanning, C. M.; Cury, L. Fadel; Schwanethal, J.; Fonseca, P. E.; Galaz, G.; Gaytán, D.; Hervé, F.

    2012-02-01

    The Canal de las Montañas Shear Zone (CMSZ), southern Patagonian Andes (51-52°S), is a low-grade mylonite belt generated from felsic ignimbritic, pelitic and basaltic protoliths of the Late Jurassic-Early Cretaceous Rocas Verdes basin. The different types of rock fabrics across the CMSZ are thought to be associated with relatively intermediate and high strain conditions, characterized by the development of a narrow western belt of S-Ć-type mylonites and phyllonites interpreted as the metamorphic sole thrust of the Sarmiento Ophiolitic Complex. Highly strained rocks of the CMSZ display a reverse, continent-ward tectonic transport, with a minor dextral component of shearing. Transitional pumpellyite-actinolite and upper greenschist facies metamorphic conditions at ca. 5-6 kbar and 230-260 °C indicate that the primary shearing event occurred in a subduction zone setting. In-situ 40Ar/39Ar laserprobe chronology yielded ages of ca. 85 Ma on syntectonic phengite which are interpreted as representing cooling synchronous with mica crystallization during the main compressive deformational event. The 78-81 Ma U-Pb zircon crystallization ages of cross-cutting plutonic and hypabyssal rocks and 40Ar/39Ar amphibole age of ca.79 Ma from lamprophyric dikes within the fold-thrust belt constrain an upper age limit of the ophiolite tectonic emplacement deformation.

  8. By-catch composition of the Patagonian scallop fishery: the fishes Composición de la captura incidental en la pesquería de vieira patagónica: los peces

    Directory of Open Access Journals (Sweden)

    Laura Schejter

    2012-11-01

    Full Text Available An inventory of 24 fish species incidentally caught by the Patagonian scallop fleet in the SW Atlantic Ocean is provided for the first time. The most frequent species were Psammobatis spp. (81.4%, Bathyraja brachyurops (75.1%, B. macloviana (73.5%, Patagonotothen ramsayi (66.1%, Merluccius hubbsi (53.7% and B. albomaculata (50.3%. Many of the recorded chondrichthyes are considered vulnerable or endangered species. The number of taxa (fishes + invertebrates that conforms the by-catch of the fishery was increased and updated to nearly 200 species.Este estudio presenta por primera vez un inventario con 24 especies de peces registradas en la captura incidental de la pesca de la vieira patagónica en el Océano Atlántico sudoccidental por la flota pesquera comercial. Las especies más frecuentes fueron Psammobatis spp. (81,4%, Bathyraja brachyurops (75,1%, B. macloviana (73,5%, Patagonotothen ramsayi (66,1%, Merluccius hubbsi (53,7% y B. albomaculata (50,3%. Muchos de los condrictios registrados se encuentran actualmente considerados como especies vulnerables o en peligro. El número de taxa (peces + invertebrados que conforman la captura incidental de esta pesquería se incrementó y actualizó con estos resultados a aproximadamente 200 especies.

  9. Regional Permafrost Probability Modelling in the northwestern Cordillera, 59°N - 61°N, Canada

    Science.gov (United States)

    Bonnaventure, P. P.; Lewkowicz, A. G.

    2010-12-01

    and Radburn, 1992; Heginbottom et al., 1995) but is several orders of magnitude more detailed. It also exhibits some significant differences, including the presence of an area of valley-floor continuous permafrost around Beaver Creek near the Alaskan border in the west, as well as higher probabilities of permafrost in the central parts of the region near the boundaries of the sporadic and extensive discontinuous zones. In addition, parts of the northernmost portion of the region would be classified as sporadic discontinuous permafrost because of inversions in the terrestrial surface lapse rate which cause permafrost probabilities to decrease with elevation through the forest. These model predictions are expected to of direct use for infrastructure planning and northern development and can serve as a benchmark for future studies of permafrost distribution in the Yukon. References Heginbottom JR, Dubreuil MA and Haker PT. 1995. Canada Permafrost. (1:7,500,000 scale). In The National Atlas of Canada, 5th Edition, sheet MCR 4177. Ottawa: National Resources Canada. Heginbottom, J.A. and Radburn, L.K. 1992. Permafrost and ground ice conditions of northwestern Canada; Geological Survey of Canada, Map 1691A, scale 1:1,000,000. Digitized by S. Smith, Geological Survey of Canada.

  10. SHRIMP U-Pb dating of the Antucoya porphyry copper deposit: new evidence for an Early Cretaceous porphyry-related metallogenic epoch in the Coastal Cordillera of northern Chile

    Science.gov (United States)

    Maksaev, Victor; Munizaga, Francisco; Fanning, Mark; Palacios, Carlos; Tapia, José

    2006-10-01

    The Antucoya porphyry copper deposit (300 Mt at 0.45% total Cu) is one of the largest deposits of a poorly known Early Cretaceous porphyry belt in the Coastal Cordillera of northern Chile. It is related to a succession of granodioritic and tonalitic porphyritic stocks and dikes that were emplaced within Jurassic andesitic rocks of the La Negra Formation immediately west of the N-S trending sinistral strike-slip Atacama Fault Zone. New zircon SHRIMP U-Pb data indicate that the porphyries of Antucoya crystallized within the time span from 142.7 ± 1.6 to 140.6 ± 1.5 Ma (±2 σ), and late, unmineralized, NW-SE trending dacite dikes with potassic alteration and internal deformation crystallized at 141.9 ± 1.4 Ma. The Antucoya porphyry copper system appears to be formed after a change of stress conditions along the magmatic arc from extensional in the Late Jurassic to transpressive during the Early Cretaceous and provides support for an Early Cretaceous metallogenic episode of porphyry-type mineralization along the Coastal Cordillera of northern Chile.

  11. Tectono-magmatic response to major convergence changes in the North Patagonian suprasubduction system; the Paleogene subduction-transcurrent plate margin transition

    NARCIS (Netherlands)

    Aragón, E.; D'Eramo, F.; Castro, A.; Pinotti, L.; Brunelli, D.; Rabbia, O.; Rivalenti, G.; Varela, R.; Spakman, W.; Demartis, M.; Cavarozzi, C.E.; Aguilera, Y.E.; Mazzucchelli, M.; Ribot, A.

    2011-01-01

    The southern and central Andes reflect significant along-strike differences of tectonic activity, including shortening, alternating flat-to-normal subduction styles and magmatism. In northern Patagonia, the subduction/supra-subduction system, fore arc, arc and back arc basins developed in an extensi

  12. Benthic foraminiferal biostratigraphy of the Aalenian-Bajocian (Middle Jurassic) boundary in the Barranco de Agua Larga section (Betic Cordillera, southern Spain)

    Science.gov (United States)

    Silva, Sílvia; Canales, María Luisa; Sandoval, José; Henriques, Maria Helena

    2016-04-01

    This work describes the benthic foraminiferal assemblages recorded across the Aalenian - Bajocian boundary in the Barranco de Agua Larga section (Betic Cordillera, SE of Spain), where the ammonite record has enabled the recognition of the Gigantea Subzone in the Bradfordensis Zone (Middle Aalenian), the Concavum and Limitatum subzones in the Concavum Zone (Upper Aalenian) and the Discites Zone (Lower Bajocian). This reference section is characterized by an alternation of limestones and marly limestones corresponding to distal marine environmental conditions, where a total of 17 samples have been collected. They have provided abundant and diverse foraminiferal assemblages, constituted by well-preserved specimens displaying close similarities to those already described for the Jurassic carbonate platforms of the Boreal Realm. From the study of the samples, a total of 3139 specimens have been obtained, corresponding to 5 suborders, 11 families, 25 genus and 80 species. The representatives of the Suborder Lagenina are the most abundant, Vaginulinidae is the most abundant family and Lenticulina is the most abundant genus. From a specific level, the most abundant species are Thurammina jurensis (Franke), Lenticulina muensteri (Roemer) and Prodentalina pseudocommunis (Franke). The occurrence of Astacolus dorbignyi (Roemer) in the Gigantea Subzone has enabled the recognition of the Astacolus dorbignyi Zone. The first occurrence of Lenticulina quenstedti (Gümbel) in the Concavum Subzone has allowed the recognition of the Lenticulina quenstedti Zone. In Barranco de Agua Larga section this species co-occur with Ramulina spandeli Paalzow, the index fossil used in the establishment of the Ramulina spandeli Zone. This zone was defined in the lower part of the Discites Zone in the Murtinheira section (the Bajocian GSSP) and related to distal platform conditions. In the Iberian Basin the Ramulina spandeli Zone was recognized in the Hontoria del Pinar section, but not in the

  13. The Messinian marine to nonmarine gypsums of Jumilla (Northern Betic Cordillera, SE Spain): Isotopic and Sr concentration constraints on the origin of parent brines

    Science.gov (United States)

    Rossi, Carlos; Vilas, Lorenzo; Arias, Consuelo

    2015-10-01

    The origin of the Messinian Hoya de la Sima (HS) gypsum (Betic foreland) is constrained using 87Sr/86Sr, δ34S, Sr concentration, and petrographic data. The Lower and Middle HS units consist of subaqueous vertically-aligned and stromatolitic selenites, the latter containing unusual microbial depositional textures. The Upper Unit consists of very-shallow-water bioturbated lenticular gypsum with Paracamelus ichnites. 87Sr/86Sr and δ34S indicate precipitation from predominantly marine waters, with upward increasing continental influence. Mixing models between Messinian seawater and continental water that dissolved Triassic evaporites show that the percentages of seawater required to explain the measured 87Sr/86Sr are analogous to the percentages obtained using δ34S, supporting precipitation from such mixtures. 87Sr/86Sr and δ34S of Lower HS selenites resemble those of the Primary Lower Gypsum (PLG) of the Messinian Salinity Crisis (MSC), in both cases indicating precipitation from seawater-continental water mixtures in which most Sr and SO4 were supplied by Messinian seawater. In the Lower HS selenites, Sr concentrations indicate contributing continental waters with Sr/Ca ratios similar to seawater. However, Sr concentrations of PLG selenites from other Betic basins (Bajo Segura, Sorbas indicate parent waters with Sr/Ca ratios lower than seawater. If the Sr contents of the betic PLG selenites are representative, it is unlikely that the Lower HS selenites represent the PLG. However, we cannot completely discard that option since different LPG subbasins could have had variable Sr/Ca. The HS gypsums formed coevally to diapirism of Triassic evaporites, in a restricted lagoonal basin developed during or slightly after a phase of strike-slip faulting in the Betic Cordillera. More general implications of this work are that Sr concentrations, combined with 87Sr/86Sr and δ34S data, provide key constraints on the origin of parent brines, and using Sr concentrations as

  14. Using nanogranitoids and phase equilibria modeling to unravel anatexis in the crustal footwall of the Ronda peridotites (Betic Cordillera, S Spain)

    Science.gov (United States)

    Bartoli, Omar; Acosta-Vigil, Antonio; Tajčmanová, Lucie; Cesare, Bernardo; Bodnar, Robert J.

    2016-07-01

    Anatexis in the crustal footwall of Ronda peridotites (Betic Cordillera, S Spain) is apparently related to the hot emplacement of this mantle slab over metasedimentary rocks. In this study, we combine the analysis of melt inclusions (MI) and phase equilibria calculations on quartzo-feldspathic mylonites (former migmatites) occurring at the contact with the mantle rocks, in the region of Sierra Alpujata (Ojén unit). The goal is to better characterize anatexis in these rocks and to provide new constraints on the geodynamic evolution of the crustal footwall. Such data are important for understanding the mechanisms of crustal emplacement of the mantle slice. The quartzo-feldspathic mylonites are characterized by the mineral assemblage Qtz + Pl + Kfs + Sil + Grt + Ilm + Bt ± Ap ± Gr. Clusters of MI are observed both at the core and toward the rim of peritectic garnet. In each cluster, MI range from totally glassy to nanogranitoids, consisting of Qtz + Kfs + Bt + Ms + Pl aggregates. The trapped melt is leucogranitic and peraluminous with variable Na2O/K2O values and low H2O contents (≈ 2-4 wt%). Phase equilibria modeling in the MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2-TiO2-O2-C (MnNCaKFMASHTOC) system with graphite-saturated fluid constrains the P-T conditions of melting at ≈ 6 kbar, ≈ 820 °C. MI data support the fluid-absent character of melting. The investigated MI represent the primary anatectic melts produced during prograde anatexis of the host rocks via biotite dehydration melting. Field, compositional, and textural observations indicate that mylonitic migmatites represent strongly deformed former diatexites. The comparison between the new data and some recently published information on migmatites located further from the contact with the peridotites and toward the bottom of the crustal footwall, raises some important issues which question the previously proposed geodynamic models for this region. Among them, (i) the crustal footwall at Sierra Alpujata

  15. Seismic investigations of the Earth's lithosphere and asthenosphere in two unique convergent margin settings: The Carpathians, Romania, and U.S. Cordillera, Idaho-Oregon

    Science.gov (United States)

    Stanciu, Adrian Christian

    Proposed mechanisms for the unusual seismicity ~100 km southeast of the contact between the Transylvanian Basin and the Eastern Carpathians in Romania have included tearing and rollback of a subducted slab of oceanic lithosphere and gravitational instability and delamination of continental lithosphere. We examined the upper mantle fabrics using shear wave splitting of SK(K)S phases recorded at four broadband seismic stations in the Transylvanian Basin. Our results indicate a regional NW-SE splitting trend, with measurements that reflect an abrupt change from this regional flow field in the vicinity of the Vrancea body to a NE-SW trend that is consistent with redirection of mantle flow. Crustal thickness measurements show 28-30 km in the western part of the Transylvanian Basin, 34-39 km at the contact with the Eastern Carpathians, and 40-45 km further east. These results, along with previous estimates, constrain the locus of the inferred Miocene suture between the southeastern-most portion of the Tisza-Dacia terrane and the East European Platform. The second convergent margin system represented here is in the North American Cordillera in Idaho and Oregon, where subduction and accretion of exotic terranes have modified the western margin of North America. We used teleseismic receiver functions from 85 broadband stations to analyze the geometry of the Salmon River suture zone, the western Idaho shear zone, and the Grouse Creek-Farmington zone boundary. Results show a clear break in crustal thickness from ~28 km beneath the accreted terranes to 36 km east of the surface expression of the WISZ. A strong mid-crustal converter at ~20 km depth is consistent with tectonic wedging during accretion of the Blue Mountains terranes. An eastern Moho offset of ~6 km is consistent with the Archean Grouse Creek-Farmington zone boundary. We used deep converted phases generated beneath the study area to image the mantle transition zone. We observe a continuous high amplitude P410s

  16. Evolución de las cuencas sinorogénicas de la Cordillera Principal entre 35°- 36° S, Malargüe

    Directory of Open Access Journals (Sweden)

    J. Silvestro

    2005-12-01

    Full Text Available La faja plegada y corrida de Malargüe se encuentra localizada en el extremo sur de la Cordillera Principal a los 35°-36° S. Los estratos de crecimiento preservados en cuencas sintectónicas registraron la cinemática de plegamiento de la faja plegada durante el Cenozoico. La cuenca Pinchera-Ventana, ubicada en el sector oeste del área, está rellena por dos secuencias volcaniclásticas cubiertas por basaltos. En el sector occidental de esta cuenca, las secuencias se adelgazan hacia los anticlinales de La Valenciana y Torrecillas en el oeste y hacia los retrocorrimientos de La Brea en el este, desarrollando discordancias progresivas observadas en el campo. En el sector oriental de la cuenca, el arreglo de facies, la composición de los clastos y la presencia de discordancias sugieren una proveniencia desde el anticlinal Bardas Blancas en el oeste. Dataciones radimétricas de los niveles andesíticos basales (15,1 Ma y de los basaltos al techo (6,7 Ma limitan la edad de esta cuenca al Mioceno medio y superior. La cuenca Malargüe desarrollada en el sector oriental del área de estudio, está rellena por dos secuencias sintectónicas volcaniclásticas, cubiertas por una secuencia postectónica. El análisis sísmico de las secuencias de crecimiento muestra un arreglo divergente relacionado al levantamiento del anticlinal Malargüe en el oeste de la cuenca y un triángulo de crecimiento hacia el este relacionado al levantamiento del anticlinal Chacay. La datación de niveles andesíticos basales en 5,04 Ma y la secuencia postectónica al tope, limitan la edad de la cuenca entre el Mioceno superior y Cuaternario. Estas observaciones indican que los depocentros sedimentarios migraron hacia el antepaís conjuntamente con el avance de la faja plegada en igual sentido.

  17. NIDDK Central Repository

    Data.gov (United States)

    U.S. Department of Health & Human Services — The NIDDK Central Repository stores biosamples, genetic and other data collected in designated NIDDK-funded clinical studies. The purpose of the NIDDK Central...

  18. Central and peripheral demyelination

    OpenAIRE

    Man Mohan Mehndiratta; Natasha Singh Gulati

    2014-01-01

    Several conditions cause damage to the inherently normal myelin of central nervous system, perepheral nervous system or both central and perepheral nervous system and hence termed as central demyelinating diseases, perepheral demyelinating diseases and combined central and perepheral demyelinating diseases respectively. Here we analysed and foccused on the etiology, prevalance, incidence and age of these demyelinating disorders. Clinical attention and various diagnostic tests are needed to ad...

  19. Isotopic and fluid-inclusion constraints on the formation of polymetallic vein deposits in the central Argentinian Patagonia

    Science.gov (United States)

    Dejonghe, Léon; Darras, Benoît; Hughes, Guillermo; Muchez, Philippe; Scoates, James S.; Weis, Dominique

    2002-03-01

    The lead isotope compositions of galena and the fluid-inclusion systematics of nine barite-bearing polymetallic (Au, Ag, Pb, Zn) deposits of the central Argentinian Patagonia (Chubut and Rio Negro provinces) have been investigated to constrain the compositions and sources of the mineralizing fluids. Most of the deposits occur as veins, with less common wall-rock disseminations and/or stockworks, and are low-sulfidation epithermal deposits hosted in Jurassic volcanic rocks. Fluid-inclusion homogenization temperatures (Th) from quartz and sphalerite from the deposits fall within the range of 100-300 °C, with the highest measured average temperatures for the most eastern deposits (Mina Angela - 298 °C; Cañadón Bagual - 343 °C). The salinities of the hydrothermal fluids at all deposits were low to moderate (≤10.4 equiv. wt% NaCl). Three groups of ore deposits can be defined on the basis of 206Pb/204Pb ratios for galena and these show a general decrease from west to east (from 18.506 to 18.000). The central Argentinian Patagonia deposits have distinctly less radiogenic lead isotope compositions than similar deposits from Peru and Chile, except for the porphyry copper deposits of central and southern Peru. Galena from the Mina Angela deposit is characterized by very low radiogenic lead isotope compositions (18.000Precambrian basement. The geographic trend in lead isotope compositions of both galena and whole rocks indicates a crustal contribution which increases eastwards, also reflected in the strontium-neodymium isotope systematics of the host lavas. Finally, due to the lack of precise age determinations for the central Patagonian polymetallic deposits, a potential link with Andean porphyry copper systems remains an open question.

  20. Evolución geoquímica y temporal del magmatismo básico mesozoico en las Zonas Externas de las Cordilleras Béticas

    Directory of Open Access Journals (Sweden)

    Aguirre, L.

    1995-08-01

    Full Text Available The Mesozoic basic magmatism found in the External Zones of the Betic Cordilleras (ZECB is represented either as «ophites» forming small dimension tectonic blocks intercalated in the Keuper gypsum-rich, clay sediments, or also as lava ilow bodies, most of them with pillow structures, within the Jurassic sedimentary rocks. Geochemical characteristics of these rocks indicate sorne differences between these two magmatic series. Two different chemical affinities have been carried out within the «ophites»: a with modal orthopyroxene and tholeiitic affinity; and b with modal olivine and transitionalalkaline affinity. Chemical characteristics of this last group are similar to those of the volcanic rocks from the Jurassic sediments. The field relationships found in sorne «ophite» outcrops al!ow us to deduce that the tholeiitic rocks are mostly present as extrusive rocks. However, their older whole-rock K-Ar ages range between 182 ± 9 and 187 ± 4 M.a., and do not correctly represent Upper Triassic ages. Transitional-alkaline «ophites» occur as subvolcanic rocks and their older obtained radiometric age is 137 ± 4 M.a. Al! these radiometric ages obtained may be intepreted as a result of the hybridization between the age of the Triassic magmatism and the very low- to low-grade metamorphism present in these rocks. This metamorphism is responsable for the new formed secondary paragenesis, made of prehnite + pumpel! yite + sericitie + mafic phyl!osicates. Radiometric age obtained in sorne intra-Jurassic volcanic rocks range between 155 ± 3 to 166 ± 4 M.a. These new radiometric data and field relationships are used to define the Mesozoic magmatic evolution in the ZECB. Tholeiitic magmatism was generated during an initial Triassic distensive stage. After this magmatic event, and as a consequence of an increment of the distensive regime, with important continental crust thickening, transitionalalkaline magmatism occurS. This

  1. Phylogeographic Diversity of the Lower Central American Cichlid Andinoacara coeruleopunctatus (Cichlidae

    Directory of Open Access Journals (Sweden)

    S. Shawn McCafferty

    2012-01-01

    Full Text Available It is well appreciated that historical and ecological processes are important determinates of freshwater biogeographic assemblages. Phylogeography can potentially lend important insights into the relative contribution of historical processes in biogeography. However, the extent that phylogeography reflects historical patterns of drainage connection may depend in large part on the dispersal capability of the species. Here, we test the hypothesis that due to their relatively greater dispersal capabilities, the neotropical cichlid species Andinoacara coeruleopunctatus will display a phylogeographic pattern that differs from previously described biogeographic assemblages in this important region. Based on an analysis of 318 individuals using mtDNA ATPase 6/8 sequence and restriction fragment length polymorphism data, we found eight distinct clades that are closely associated with biogeographic patterns. The branching patterns among the clades and a Bayesian clock analysis suggest a relatively rapid colonization and diversification among drainages in the emergent Isthmus of Panama followed by the coalescing of some drainages due to historical connections. We also present evidence for extensive cross-cordillera sharing of clades in central Panama and the Canal region. Our results suggest that contemporary phylogeographic patterns and diversification in Lower Central American fishes reflect an interaction of historical drainage connections, dispersal, and demographic processes.

  2. Orogénesis y drenaje en la región del Valle de Lerma (cordillera oriental, Salta, Argentina durante el Pleistoceno Tardío Orogeny and drainage in the Lerma Valley region (Eastern Cordillera, Salta, Argentina during the late Pleistocene

    Directory of Open Access Journals (Sweden)

    Gustavo González Bonorino

    2012-03-01

    Full Text Available En el Pleistoceno tardío, luego de la incipiente elevación de las serranías subandinas, la contracción retornó al interior del orógeno. En aquel tiempo un piedemonte conectaba los contrafuertes occidentales de la Cordillera Oriental (sierras de Lesser y Obispo con la llanura subandina, a través de la región que hoy7 ocupan el valle de Lerma y la serranía Mojotoro-Castillejo. La contracción dio origen a las elevaciones interiores en la sierra de Vaqueros y los Cerrillos de San Miguel, y luego se propagó al este una falla que derivó en el desarrollo de la serranía Mojotoro-Castillejo y el cierre del valle de Lerma. Algunos ríos incidieron a través de las nacientes barreras topográficas mientras que otros fueron a una cuenca endorreica inundada por un antiguo lago Lerma. La capacidad de incisión fue mayor en el valle de Lerma septentrional, donde los ríos llegaban con gradientes de cauce elevados a los sitios de ascenso topográfico, y donde el río Mojotoro persistió como cauce antecedente. En el sur, el lago Lerma colmató la cuenca hasta un punto de derrame por bajos estructurales en capas del Grupo Salta, y el agua labró el cauce subsecuente del actual río Juramento a través de la sierra de Castillejo. Más de 800 m de sedimento (aquí denominado Grupo Valle de Lerma se acumularon en el valle de Lerma durante el Pleistoceno tardío. Información de subsuelo permite hacer una revisión crítica de la estratigrafía de este relleno y proponer una subdivisión más detallada. En particular se acota la extensión geográfica de la Formación Tajamar y se revisan las extrapolaciones que de ella se han hecho.In the late Pleistocene, following uplift of the first subandean ranges, contraction returned to the orogen interior. At the time, a wide piedmont connected the western ramparts of the Eastern Cordillera (Lesser and Obispo ranges to the subandean plain, spanning the zone presently occupied by the Lerma Valley and the

  3. Regeneración Natural del Roble Negro (Colombobalanus excelsa, Fagaceae en Dos Poblaciones de la Cordillera Oriental de los Andes, Colombia Natural Regeneration of Black Oak (Colombobalanus excelsa, Fagaceae in Two Populations from the Cordillera Oriental of the Colombian Andes

    Directory of Open Access Journals (Sweden)

    César Augusto Parra Aldana

    2011-12-01

    Full Text Available Colombobalanus excelsa es una especie endémica de la zona andina de Colombia, con cuatro poblaciones aisladas que forman rodales homogéneos denominados robledales negros. Se encuentra en categoría vulnerable de amenaza, debido principalmente a la conversión del bosque para usos agropecuarios; observaciones en campo indican que la regeneración natural bajo su propia cobertura es escasa. Se propone responder las siguientes preguntas: 1. ¿La estructura del bosque evidencia deficiencias en la regeneración natural de dos poblaciones de roble negro localizadas en la cordillera oriental de los Andes? 2. ¿El reclutamiento de fhmoreno@unal.edu.co está limitado por la disponibilidad y viabilidad de las semillas en las dos poblaciones estudiadas? Con este objetivo se establecieron 16 transectos permanentes de 0,1 ha para evaluar la estructura de adultos (DAP>10 cm y de la regeneración natural. Durante un año se realizó monitoreo sobre las épocas de fructificación, lluvia de semillas, germinación y banco de semillas. Los resultados muestran un suministro extremadamente bajo de renuevos y propágulos de roble negro, lo cual potencialmente puede poner en riesgo la persistencia de estos bosques. Esta situación obedece a diversos factores involucrados en el proceso de regeneración: desde baja producción de semillas de los árboles adultos, altos niveles de depredación pre-dispersión, alta proporción de semillas vacías, baja viabilidad de las semillas sanas, hasta alta mortalidad de las semillas sanas y viables que llegan al suelo. Si bien todos estos factores actúan en cascada, el último de ellos es quizás el que ejerce un efecto más dramático en el bajo éxito reproductivo de esta especie.Colombobalanus excelsa is an endemic species of the Andean region of Colombia, with four isolated populations, forming pure stands called black oak forests. It has been classified in the threat category ''Vulnerable'', mainly due to conversion of

  4. Evolución de las cuencas sinorogénicas de la Cordillera Principal entre 35°- 36° S, Malargüe Evolution of the foreland basins in the Cordillera Principal, at 35º - 36º S. Malargüe

    Directory of Open Access Journals (Sweden)

    J. Silvestro

    2005-12-01

    Full Text Available La faja plegada y corrida de Malargüe se encuentra localizada en el extremo sur de la Cordillera Principal a los 35°-36° S. Los estratos de crecimiento preservados en cuencas sintectónicas registraron la cinemática de plegamiento de la faja plegada durante el Cenozoico. La cuenca Pinchera-Ventana, ubicada en el sector oeste del área, está rellena por dos secuencias volcaniclásticas cubiertas por basaltos. En el sector occidental de esta cuenca, las secuencias se adelgazan hacia los anticlinales de La Valenciana y Torrecillas en el oeste y hacia los retrocorrimientos de La Brea en el este, desarrollando discordancias progresivas observadas en el campo. En el sector oriental de la cuenca, el arreglo de facies, la composición de los clastos y la presencia de discordancias sugieren una proveniencia desde el anticlinal Bardas Blancas en el oeste. Dataciones radimétricas de los niveles andesíticos basales (15,1 Ma y de los basaltos al techo (6,7 Ma limitan la edad de esta cuenca al Mioceno medio y superior. La cuenca Malargüe desarrollada en el sector oriental del área de estudio, está rellena por dos secuencias sintectónicas volcaniclásticas, cubiertas por una secuencia postectónica. El análisis sísmico de las secuencias de crecimiento muestra un arreglo divergente relacionado al levantamiento del anticlinal Malargüe en el oeste de la cuenca y un triángulo de crecimiento hacia el este relacionado al levantamiento del anticlinal Chacay. La datación de niveles andesíticos basales en 5,04 Ma y la secuencia postectónica al tope, limitan la edad de la cuenca entre el Mioceno superior y Cuaternario. Estas observaciones indican que los depocentros sedimentarios migraron hacia el antepaís conjuntamente con el avance de la faja plegada en igual sentido.The Andean fold-and-thrust belt of Malargüe is located in the foothills of Cordillera Principal at 35º-36º S. The geometry and age of the growth strata preserved in syntectonic

  5. Geología y controles estructurales de las áreas de alteración del portezuelo de las Burras (Cordillera Frontal, San Juan Geology and structural controls on areas of alteration of Portezuelo de las Burras (Cordillera Frontal, San Juan, Argentina

    Directory of Open Access Journals (Sweden)

    Constantino Karkanis

    2004-03-01

    Full Text Available Se describen las características estratigráficas, petrográficas y estructurales de la comarca del portezuelo de las Burras, localizada en la Cordillera Frontal (San Juan, Argentina. Está constituida por un basamento de sedimentitas de la Formación La Puerta (Carbonífero superior - Pérmico inferior y grandes espesores volcánicos y sedimentarios subordinados del Grupo Choiyoi (Pérmico - Triásico, niveles lávicos andesíticos de la Andesita Las Vizcachas (Mesozoico superior ? - Terciario ?, volcanitas de carácter más ácido de la Formación Arroyo de las Chinches (Oligoceno - Mioceno y de volcanitas andesíticas de la Formación Entrecordilleras (Mioceno superior - Pleistoceno. En relación intrusiva se ha identificado al Plutón Entrecordilleras (Neógeno y a otros cuerpos dacíticos pertenecientes presumiblemente a otra facies del mismo plutón. Los cursos del río Manantiales y arroyo Las Burras se disponen sobre una zona de fallamiento transcurrente senestral principal expresado por fallas sintéticas y antitéticas, donde el sector próximo al portezuelo de las Burras constituye un resalto de alivio de transferencia tectónica con características dilatantes. Éste habría controlado la circulación y emplazamiento de fluidos hidrotermales mineralizantes, responsables de las anomalías cromáticas, mineralógicas y geoquímicas detectadas, asociadas a alteraciones hidrotermales de tipo arcillosa y silícea, que alientan un interés sobre la posibilidad de alumbrar acumulaciones económicas de minerales preciosos.The main stratigraphical, petrographical and structural features of the Portezuelo de Las Burras altered area, located in the Cordillera Frontal (San Juan Province, Argentina, are described. The area is composed of the La Puerta Formation (Upper Carboniferous - Lower Permian, thick volcanic and subordinate sedimentary layers of the Choiyoi Group (Permian - Triassic, levels of andesitic lava of Andesita Las Vizcachas (Upper

  6. Unidades tectónicas y estructura general de la Sierra de Gádor y zonas adyacentes (Cordillera Bética, provincia de Almería: implicaciones paleogeográficas

    Directory of Open Access Journals (Sweden)

    Delgado Salazar, F.

    2007-06-01

    Full Text Available In the Sierra de Gádor (Almeria province terrains belonging to the Internal Betic Zone crop out. According to stratigraphic, structural and petrologic features we have recognised five tectonic units. These units are called, from bottom to top, Gádor-Turón, Laujar, Murtas, Felix and Chirán unit. The lower fourth are ascribed to the Alpujárride Complex, whilst the last one is ascribed to the Maláguide Complex. We also discuss if the Felix unit may be included in the Intermediate Units. The Felix unit represents the Triassic palaeogeographic transition between the Alpujárride and the Maláguide, and it was located between both complexes during the alpine tectono-metamorphic evolution of the Betic Cordillera.En la Sierra de Gádor (provincia del Almería afloran rocas pertenecientes a la Zona Interna de la Cordillera Bética. En este sector hemos reconocido un total de cinco unidades tectónicas, en función de sus características estratigráficas, estructurales y petrológicas. Estas unidades se denominan, de abajo a arriba, unidad de Gádor-Turón, unidad de Laujar, unidad de Murtas, unidad de Felix y unidad de Chirán. Las cuatro más bajas las asignamos al Complejo Alpujárride, mientras que la más alta la asignamos al Complejo Maláguide. Se discute además la posible inclusión de la unidad de Felix dentro de las denominadas Unidades Intermedias. La unidad de Felix representa el tránsito paleogeográfico durante el Triásico entre el dominio Alpujárride y el Maláguide, y estaría situada entre ambos complejos durante la evolución tectono-metamórfica alpina de la Cordillera Bética.

  7. GRANDE SERTÃO: Cordilleras

    OpenAIRE

    Bairon Oswaldo Vélez Escallón

    2012-01-01

    Grande Sertão: Veredas (1956) y Pedro Páramo (1955) crean, en la misma instancia que interrumpen, figuraciones totalizadoras del ser y del mundo: así operan sus ficciones. Esa participación encuentra su máxima paradoja en la apropiación que, sobre esas obras, ha ejercido la crítica latinoamericana: como precursoras de obras posteriores o como consolidaciones de una literatura latinoamericana madura. ¿Esas obras aceptan sin tensiones o resistencias esa filiación? Este trabajo explora estos ...

  8. Multiple glacial culminations from the Lateglacial to the late Holocene in central and southern Peru (Invited)

    Science.gov (United States)

    Licciardi, J. M.; Schaefer, J. M.; Rodbell, D. T.; Stansell, N.; Schweinsberg, A.; Finkel, R. C.; Zimmerman, S. R.

    2013-12-01

    Fluctuations in small tropical mountain glaciers serve as sensitive indicators of variations in past and present-day climate. Most of the world's modern tropical glaciers reside in the Peruvian Andes, where a growing number of well-dated glacial records have recently been developed. As additional records are documented, regional patterns of late Pleistocene to Holocene glacial activity have begun to emerge. Here we present a compilation of new and previously obtained 10Be surface exposure ages from boulders on well-preserved moraine successions in two glaciated Andean ranges: the Cordillera Vilcabamba of southern Peru (13°20'S, 72°32'W) and the Huaguruncho massif (10°32'S, 75°56'W), located in central Peru ~450 km northwest of the Vilcabamba. A high-resolution composite chronology that merges >100 10Be measurements on moraine sequences in five glaciated drainages of the Cordillera Vilcabamba reveals the occurrence of at least five discrete glacial culminations from the Lateglacial to the late Holocene. At the Huaguruncho massif, >20 10Be exposure ages obtained from moraine sequences in a south-facing cirque indicate at least three major glacial stages spanning the Lateglacial to the Little Ice Age. The moraine ages at Huaguruncho are broadly correlative with the Vilcabamba moraine chronologies, with some dated moraine belts exhibiting geomorphic expressions that closely resemble those of their coeval counterparts in the Vilcabamba. A recurring finding in both field areas is a mismatch between basal radiocarbon ages from bog and lake sediments and 10Be exposure ages on outboard moraines, which enclose the depositional basins. These age discrepancies suggest that cosmogenic 10Be production rates scaled to high altitudes in the tropics are substantially lower than previous estimates. While we anticipate that future refinements to scaled isotope production rates may significantly affect correlation of 10Be exposure ages in the high Andes with ages derived from

  9. Hypericum species in the Páramos of Central and South America: a special focus upon H. irazuense Kuntze ex N. Robson

    Science.gov (United States)

    Crockett, Sara; Eberhardt, Marianne; Kunert, Olaf; Schühly, Wolfgang

    2010-01-01

    Knowledge about members of the flowering plant family Clusiaceae occurring in the tropical mountain regions of the world is limited, in part due to endemism and restricted distributions. High altitude vegetation habitats (Páramos) in Central and South America are home to numerous native Hypericum species. Information related to the phytochemistry of páramo Hypericum, as well as ecological factors with the potential to influence chemical defenses in these plants, is briefly reviewed. Results of the phytochemical analysis of Hypericum irazuense, a species collected in the páramo of the Cordillera de Talamanca in Costa Rica, are presented. Lastly, guidelines for the viable and sustainable collections of plant material, to facilitate future investigations of these interesting plants, are given. PMID:21151765

  10. Glacial and periglacial geomorphology and chronology around the Nevado de Chañi (Cordillera Oriental of Jujuy): implication for past climate in NW Argentina

    Science.gov (United States)

    Martini, M. A.; Strelin, J. A.; Kaplan, M. R.; Schaefer, J. M.

    2012-12-01

    steep active eroding valley walls. The minimum altitude and the local topographic context suggest that changes in the activity of rock glaciers correspond with local conditions (e.g., debris or talus supply) rather than climatic changes (e.g., temperature) around Chañi. Our geomorphological-based findings allow us to propose a preliminary correlation with other glaciated areas in the arid Andes and the northern Cordillera Oriental and with lake transgression phases recorded on the southern Bolivian Altiplano, during the late Pleistocene. The paleo-equilibrium line altitudes rise from east to west across the region indicating that the source of moisture came from the east and northeast during the past glaciations, which is similar to the present-day circulation scenarios along the north side of the Arid Diagonal.

  11. Relating geodynamic setting to periods of crustal growth and reworking as illustrated by the Phanerozoic granitoids of the Eastern Cordillera of South Peru

    Science.gov (United States)

    Reitsma, M.; Schaltegger, U.; Spikings, R.; Ulianov, A.; Gerdes, A.; Chiaradia, M.

    2012-04-01

    The granitoids that form the backbone of the Eastern Cordillera of Peru between 12 and 14°S, are the ideal material for a case study to relate geodynamic setting to crustal growth over the period of a Wilson cycle. Extension related plutons were emplaced in the back-arc region of the Western Gondwana margin during the Ordovician, Permo-Carboniferous, Triassic and Early Jurassic. With the onset of the Andean cycle in the Middle Jurassic the South American margin was under compression, the plutonic record of this period is in the study area restricted to the Eocene and Miocene. The Ordovician to Triassic back-arc related plutons share many geochemical characteristics that point to dominant crustal reworking as the main process during their formation. These are 1) their mainly felsic and peraluminous nature; 2) the similarity of whole rock REE and trace element compositions compared to those of average continental crust; 3) the presence of negative Nb-Ta anomalies only in the more evolved samples which indicates that these excursions have been obtained by crustal melting rather than from a slab fluid and 4) the presence of significant amounts of xenocrystic cores in zircon. According to the literature the last major episode of juvenile crust formation was during the Grenvillian age Sunsas event (1.2 - 0.9 Ga) related to the collision of Laurentia and south-western Amazonia during the assembly of Rodinia. Hf-isotopes on zircons from the Ordovician, Permo-Carboniferous and Triassic plutons confirm their origin as mainly crustal melts generated by reworking of Sunsas-age crust. Under these geodynamic conditions it is mainly the crust that melts due to an elevated geothermal gradient as the result of crustal thinning. However, data from Jurassic nepheline bearing syenite and Eocene hornblende diorite and monzonite have epsilon Hfi values well above those of Sunsas crust, indicating an important mantle component in the melts. The Jurassic geodynamic setting is interpreted

  12. Central Laboratories Services

    Data.gov (United States)

    Federal Laboratory Consortium — The TVA Central Laboratories Services is a comprehensive technical support center, offering you a complete range of scientific, engineering, and technical services....

  13. Metamorfismo y deformación de la Formación Tobífera en la cordillera Riesco, región de Magallanes, Chile: evidencias para su evolución tectónica

    Directory of Open Access Journals (Sweden)

    G. Galaz

    2005-12-01

    Full Text Available La Formación Tobífera (150 Ma se deposita en parte contemporánea al Complejo Ofiolítico Sarmiento durante un ambiente geodinámico de rifting de la cuenca de Rocas Verdes. Posteriormente se depositan en concordancia sobre ella las unidades cretácicas de las Formaciones Zapata, Punta Barrosa y Cerro Toro. En Cordillera Riesco está compuesta por tobas silíceas, tobas soldadas silíceas, limolitas negras cuarcíferas y lutitas cuarcíferas, afectadas por una deformación milonítica, que desarrolla indicadores cinemáticos dúctiles inversos, con menor componente dextral, que sugiere un movimiento dextral-inverso para la zona de falla. La mineralogía metamórfica y la aplicación de geotermobarómetros reflejan que esta zona milonítica alcanzó condiciones P-T de 6,37 ± 1,1 kb y 399 ± 64°C, respectivamente. Esto sugiere que estas rocas alcanzaron una profundidad entre 19-26 km, posiblemente producto de un evento de subducción reversa que afectó a estas rocas. Además, determinan una facies esquistos verdes para asociaciones minerales en la matriz y facies prehnita-actinolita para asociaciones minerales en vetillas. Este último evento metamórfico sería de carácter retrógrado. Clastos deformados de la Formación Tobífera en brechas de la Formación Cerro Toro, evidencian que ésta se exhumó antes del Cretácico superior. La configuración actual de las estructuras en Cordillera Riesco posiblemente se debe a rotaciones hacia el oeste, producidas dentro del desarrollo de la faja plegada y corrida de Magallanes.

  14. Andesita Cerro Bola: Nueva unidad vinculada al magmatismo mioceno de la Cordillera de Olivares, San Juan, Argentina (30°35´S; 69°30´O

    Directory of Open Access Journals (Sweden)

    A.F. Wetten

    2005-03-01

    Full Text Available El área de estudio se halla en la zona de Tocota, inmediatamente al este de la Cordillera de Olivares, en el borde oriental de la Cordillera Frontal, provincia de San Juan. En ella se encuentran unidades ígneas y sedimentarias del ciclo gondwánico, las que fueron intruidas y cubiertas en relación discordante por cuerpos subvolcánicos y volcánicos asignados anteriormente al ciclo ándico en sentido amplio, los cuales constituyen el principal objeto del presente estudio. Estos cuerpos han sido mapeados a fin de poder caracterizarlos adecuadamente, en el contexto estratigráfico de la región. Los afloramientos de interés han sido reconocidos en el cerro Bola y alrededores, donde se observan distribuidos irregularmente, cubriendo un área superior a 5 km². Las rocas, de coloración gris clara y composición andesítica - fenoandesítica, presentan estructuras de domo y colada. Estos afloramientos serían correlacionables con la unidad volcánica Pircas (Mioceno, la que aflora al oeste, y conformarían un evento magmático posterior al de pórfidos de diferente composición situados tanto en el arroyo Chita como en el cerro Divisadero. La extensión del área involucrada, la uniformidad litológica, el bajo grado de alteración y una edad radimétrica obtenida por el método K/Ar, fueron considerados para proponer a estas volcanitas como una unidad litoestratigráfica de edad miocena superior, con la denominación de Andesita Cerro Bola.

  15. Central centrifugal cicatricial alopecia

    OpenAIRE

    Collin Blattner; Dennis C Polley; Frank Ferritto; Elston, Dirk M

    2013-01-01

    Central centrifugal cicatricial alopecia is a common cause of progressive permanent apical alopecia. This unique form of alopecia includes entities previously know as “hot comb alopecia,” “follicular degeneration syndrome,” “pseudopelade” in African Americans and “central elliptical pseudopelade” in Caucasians. The etiology appears to be multifactorial and the condition occurs in all races.

  16. Optimal Central Bank Transparency

    NARCIS (Netherlands)

    van der Cruijsen, C.A.B.; Eijffinger, S.C.W.; Hoogduin, L.H.

    2008-01-01

    Should central banks increase their degree of transparency any further? We show that there is likely to be an optimal intermediate degree of central bank transparency. Up to this optimum more transparency is desirable: it improves the quality of private sector inflation forecasts. But beyond the opt

  17. Optimal central bank transparency

    NARCIS (Netherlands)

    C.A.B. van der Cruijsen; S.C.W. Eijffinger; L. Hoogduin

    2008-01-01

    Should central banks increase their degree of transparency any further? We show that there is likely to be an optimal intermediate degree of central bank transparency. Up to this optimum more transparency is desirable: it improves the quality of private sector inflation forecasts. But beyond the opt

  18. Optimal central bank transparency

    NARCIS (Netherlands)

    C.A.B. van der Cruijsen; S.C.W. Eijffinger; L.H. Hoogduin

    2010-01-01

    Should central banks increase their degree of transparency any further? We show that there is likely to be an optimal intermediate degree of central bank transparency. Up to this optimum more transparency is desirable: it improves the quality of private sector inflation forecasts. But beyond the opt

  19. Central pontine myelinolysis

    Science.gov (United States)

    ... from one nerve to another. The most common cause of central pontine myelinolysis is a quick change in the body's sodium ... The nerve damage caused by central pontine myelinolysis is usually ... The disorder can cause serious long-term (chronic) disability.

  20. Central Diffraction at ALICE

    CERN Document Server

    Lämsä, Jerry W

    2011-01-01

    The ALICE experiment is shown to be well suited for studies of exclusive final states from central diffractive reactions. The gluon-rich environment of the central system allows detailed QCD studies and searches for exotic meson states, such as glueballs, hybrids and new charmonium-like states. It would also provide a good testing ground for detailed studies of heavy quarkonia. Due to its central barrel performance, ALICE can accurately measure the low-mass central systems with good purity. The efficiency of the Forward Multiplicity Detector (FMD) and the Forward Shower Counter (FSC) system for detecting rapidity gaps is shown to be adequate for the proposed studies. With this detector arrangement, valuable new data can be obtained by tagging central diffractive processes.

  1. Central diffraction at ALICE

    Energy Technology Data Exchange (ETDEWEB)

    Laemsae, J W; Orava, R, E-mail: risto.orava@helsinki.fi [Helsinki Insitute of Physics, and Division of Elementary Particle Physics, Department of Physics, PL 64 (Gustaf Haellstroeminkatu 2a), FI-00014 University of Helsinki (Finland)

    2011-02-01

    The ALICE experiment is shown to be well suited for studies of exclusive final states from central diffractive reactions. The gluon-rich environment of the central system allows detailed QCD studies and searches for exotic meson states, such as glueballs, hybrids and new charmonium-like states. It would also provide a good testing ground for detailed studies of heavy quarkonia. Due to its central barrel performance, ALICE can accurately measure the low-mass central systems with good purity. The efficiency of the Forward Multiplicity Detector (FMD) and the Forward Shower Counter (FSC) system for detecting rapidity gaps is shown to be adequate for the proposed studies. With this detector arrangement, valuable new data can be obtained by tagging central diffractive processes.

  2. Organizational centralization in radiology.

    Science.gov (United States)

    Aas, I H Monrad

    2006-01-01

    Traditionally, hospitals have a radiology department, where images are taken and interpretation occurs. Teleradiology makes it possible to capture images in one location and transmit them elsewhere for interpretation. Organizational centralization of radiology interpretations is therefore of interest. Empirical data have been collected in qualitative interviews of 26 resource persons with substantial experience with picture archiving and communication systems and teleradiology, from 12 departments of radiology in Norway. The response rate was 90%. A total of 21 theoretically possible types of centralization of image interpretation were identified, representing combinations of three categories of geographical centralization, and seven categories of centralization according to function. Various advantages and disadvantages of centralization were identified. Organizational changes may be decisive for the future of teleradiology, but it may be wise to plan for change in small steps, since we know little about how broad future organizational changes based on teleradiology will be, or what will decide how far particular organizations will go. PMID:16438776

  3. The time-space distribution of Eocene to Miocene magmatism in the central Peruvian polymetallic province and its metallogenetic implications

    Science.gov (United States)

    Bissig, Thomas; Ullrich, Thomas D.; Tosdal, Richard M.; Friedman, Richard; Ebert, Shane

    2008-07-01

    Eocene to late Miocene magmatism in the central Peruvian high-plain (approx. between Cerro de Pasco and Huancayo; Lats. ˜10.2-12°S) and east of the Cordillera Occidental is represented by scattered shallow-level intrusions as well as subaerial domes and volcanic deposits. These igneous rocks are calc-alkalic and range from basalt to rhyolite in composition, and many of them are spatially, temporally and, by inference, genetically associated with varied styles of major polymetallic mineralization. Forty-four new 40Ar- 39Ar and three U/Pb zircon dates are presented, many for previously undated intrusions. Our new time constraints together with data from the literature now cover most of the Cenozoic igneous rocks of this Andean segment and provide foundation for geodynamic and metallogenetic research. The oldest Cenozoic bodies are of Eocene age and include dacitic domes to the west of Cerro de Pasco with ages ranging from 38.5 to 33.5 Ma. South of the Domo de Yauli structural dome, Eocene igneous rocks occur some 15 km east of the Cordillera Occidental and include a 39.34 ± 0.28 Ma granodioritic intrusion and a 40.14 ± 0.61 Ma rhyolite sill, whereas several diorite stocks were emplaced between 36 and 33 Ma. Eocene mineralization is restricted to the Quicay high-sulfidation epithermal deposit some 10 km to the west of Cerro de Pasco. Igneous activity in the earliest Oligocene was concentrated up to 70 km east of the Cordillera Occidental and is represented by a number of granodioritic intrusions in the Milpo-Atacocha area. Relatively voluminous early Oligocene dacitic to andesitic volcanism gave rise to the Astabamba Formation to the southeast of Domo de Yauli. Some stocks at Milpo and Atacocha generated important Zn-Pb (-Ag) skarn mineralization. After about 29.3 Ma, magmatism ceased throughout the study region. Late Oligocene igneous activity was restricted to andesitic and dacitic volcanic deposits and intrusions around Uchucchacua (approx. 25 Ma) and felsic

  4. Geodynamic controls on the contamination of Cenozoic arc magmas in the southern Central Andes: Insights from the O and Hf isotopic composition of zircon

    Science.gov (United States)

    Jones, Rosemary E.; Kirstein, Linda A.; Kasemann, Simone A.; Dhuime, Bruno; Elliott, Tim; Litvak, Vanesa D.; Alonso, Ricardo; Hinton, Richard

    2015-09-01

    Subduction zones, such as the Andean convergent margin of South America, are sites of active continental growth and crustal recycling. The composition of arc magmas, and therefore new continental crust, reflects variable contributions from mantle, crustal and subducted reservoirs. Temporal (Ma) and spatial (km) variations in these contributions to southern Central Andean arc magmas are investigated in relation to the changing plate geometry and geodynamic setting of the southern Central Andes (28-32° S) during the Cenozoic. The in-situ analysis of O and Hf isotopes in zircon, from both intrusive (granitoids) and extrusive (basaltic andesites to rhyolites) Late Cretaceous - Late Miocene arc magmatic rocks, combined with high resolution U-Pb dating, demonstrates distinct across-arc variations. Mantle-like δ18O(zircon) values (+5.4‰ to +5.7‰ (±0.4 (2σ))) and juvenile initial εHf(zircon) values (+8.3 (±0.8 (2σ)) to +10.0 (±0.9 (2σ))), combined with a lack of zircon inheritance suggests that the Late Cretaceous (∼73 Ma) to Eocene (∼39 Ma) granitoids emplaced in the Principal Cordillera of Chile formed from mantle-derived melts with very limited interaction with continental crustal material, therefore representing a sustained period of upper crustal growth. Late Eocene (∼36 Ma) to Early Miocene (∼17 Ma) volcanic arc rocks present in the Frontal Cordillera have 'mantle-like' δ18O(zircon) values (+4.8‰ (±0.2 (2σ) to +5.8‰ (±0.5 (2σ))), but less radiogenic initial εHf(zircon) values (+1.0 (±1.1 (2σ)) to +4.0 (±0.6 (2σ))) providing evidence for mixing of mantle-derived melts with the Late Paleozoic - Early Mesozoic basement (up to ∼20%). The assimilation of both Late Paleozoic - Early Mesozoic Andean crust and a Grenville-aged basement is required to produce the higher than 'mantle-like' δ18O(zircon) values (+5.5‰ (±0.6 (2σ) to +7.2‰ (±0.4 (2σ))) and unradiogenic, initial εHf(zircon) values (-3.9 (±1.0 (2σ)) to +1.6 (±4.4 (2

  5. The Glacier Inventory of the Central Andes of Argentina (31°-35°S)

    Science.gov (United States)

    Ferri Hidalgo, L.; Zalazar, L.; Castro, M.; Pitte, P.; Masiokas, M. H.; Ruiz, L.; Villalba, R.; Delgado, S.; Gimenez, M.; Gargantini, H.

    2015-12-01

    The National Law for protection of glaciers in Argentina envisages the development of a National Inventory of Glaciers. All glaciers and periglacial landforms which are important as strategic water resource must be properly identified and mapped. Here we present a detailed and complete glacier and rock glacier inventory of the Central Andes of Argentina between 31° and 35°S. This semi-arid region contains some of the highest mountains of South America and concentrates the second most glacierized area in Argentina after the Patagonian Andes. To develop the inventory, we used remotely sensed data and related techniques complemented with field surveys. Clean ice and perennial snowfields were identified applying an automatic extraction method on medium spatial-resolution images. Debris-covered and rock glaciers were manually digitized on higher spatial-resolution images. With minor modifications, the present digital inventory is consistent with GLIMS standards. For each glacier, we derived 38 database fields, adding five specific attributes for rock glaciers, which are not included in the original GLIMS database. In total we identified 8069 glaciers covering an area of 1768 km2. Debris-covered ice and rock glaciers represent 57% of the total inventoried area. In this region, rock glaciers are a common feature in the arid landscape and constitute an important water reserve at regional scale. Many glaciers were characterized by gradual transition from debris-covered glaciers, in the upper part, to rock glaciers, in the lower sector. The remaining 43% includes clean ice glaciers and permanent snowfields. These are mostly mountain and valley-type glaciers with medium-to-small sizes. This detailed inventory constitutes a valuable contribution to the ongoing global efforts (e.g. WGI, RGI and GLIMS) to map the world's glaciers. It is also the base for ongoing glaciological, climatological and hydrological studies in this portion of southern Andes.

  6. Cryptic speciation in a benthic isopod from Patagonian and Falkland Island waters and the impact of glaciations on its population structure

    Directory of Open Access Journals (Sweden)

    Kop Anna

    2008-12-01

    Full Text Available Abstract Background The Falkland Islands and Patagonia are traditionally assigned to the Magellan Biogeographic Province. Most marine species in Falkland waters are also reported from southern Patagonia. It remains unclear if relatively immobile, marine benthic, shallow-water species maintain gene flow, and by what mechanism. Recurrent fluctuations in sea level during glacial cycles are regarded as a possible mechanism that might have allowed genetic exchange between the regions. However, the realized genetic exchange between the Falkland Islands and Patagonia has never been estimated. Results This study analyses the genetic structure of three populations of the marine shallow-water isopod Serolis paradoxa (Fabricius, 1775 from the Falkland Islands and southern Patagonia (central Strait of Magellan and the Atlantic opening applying seven nuclear microsatellites and a fragment of the mitochondrial 16S rRNA gene. Both marker systems report highest genetic diversity for the population from the central Strait of Magellan and lowest for the Falkland Islands. The estimated effective population sizes were large for all populations studied. Significant differentiation was observed among all three populations. The magnitude of differentiation between Patagonia and the Falkland Islands (16S: uncorrected p-distance 2.1%; microsatellites: standardized F'ST > 0.86 was an order of magnitude higher than between populations from within Patagonia. This indicates that there is currently no effective gene flow for nominal S. paradoxa between these two regions and it has been absent for time exceeding the last glacial maximum. We argue that specimens from the Strait of Magellan and the Falkland Islands very likely represent two distinct species that separated in the mid-Pleistocene (about 1 MY BP. Conclusion The results of this study indicate limited gene flow between distant populations of the brooding isopod Serolis paradoxa. The patterns of genetic diversity

  7. MATERIAL ASSIMILATION IN A SHALLOW DIAPIRIC FORCEFUL INTRUSION: EVIDENCE FROM MICROSTRUCTURES AND CSD ANALYSIS IN A PORPHYRITIC INTRUSIVE BODY, “LA LÍNEA” TUNNEL, CENTRAL CORDILLERA, COLOMBIA

    Directory of Open Access Journals (Sweden)

    Rayo Lorena

    2008-06-01

    Full Text Available The contact between the unit Porphyry Andesite and the Cajamarca Group is observed in the "Túnel de la Linea" section. The integration of petrographic, geochemical and textural (crystal size distribution, CSD analysis allows description of physical and chemical processes that took place in the contact zone in order to propose a model for the intrusion. Material assimilation produced quartz enrichment towards pluton's boundaries associated to a simple process of melt injection. The difference between host rock and hot melt rheologies causedshear stress that produced crystal breaking, folding and foliation rotation.

  8. Cenozoic stratigraphic development in the north Chilean forearc: Implications for basin development and uplift history of the Central Andean margin

    Science.gov (United States)

    Hartley, Adrian J.; Evenstar, Laura

    2010-11-01

    Analysis of the Cenozoic stratigraphic development of the forearc of northern Chile between 18°S and 23°30'S, allows constraints to be placed on the timing and nature of basin formation and the uplift history of the Central Andes. Chronostratigraphic charts have been constructed from 20 lithostratigraphic sections distributed throughout the forearc. Sections were taken from the Longitudinal Valley, Central Depression, Calama Basin, Salar de Atacama, Precordillera and the western flank of the Western Cordillera. Correlation and timing of events is largely based on the presence of dated volcanic horizons in all the studied sections. Three chronostratigraphic units are defined based upon the presence of regional unconformities. Deposition of the Late Eocene to Early Miocene chronostratigraphic unit (38-19 Ma) commenced across an irregular unconformity surface between ˜ 38 and 30 Ma with alluvial fan and fluvial sediments derived from the east interbedded with rhyolitic ignimbrites. Aggradation after 25 Ma resulted in development of a large broad basin over much of northern Chile that expanded eastwards through onlap onto basement. Deposition terminated around 19 Ma with the development of an angular unconformity over much, but not all of the study area. During deposition of the Early to Late Miocene chronostratigraphic unit (18-10 Ma) emergent volcanic source areas to the east provided catchments for large fluvial systems that drained westwards into endorheic ephemeral lacustrine basins. Fold growth affected sedimentation restricting accommodation space to small intra-thrust basins in the Precordillera and localised disruption and unconformity development in the Longitudinal Valley. The Late Miocene to present day chronostratigraphic unit (10-0 Ma) followed the development of a regional angular unconformity at 10 Ma. Sedimentation was restricted to a series of thrust-bounded endorheic basins in both the Central Depression and the Precordillera sourced from the east

  9. Ailinella mirabilis gen. n., sp. n. (eucestoda: pseudophyllidea) from Galaxias maculatus (Pisces: Galaxiidae) in the Andean-Patagonian region of Argentina.

    Science.gov (United States)

    de Pertierra, Alicia A Gil; Semenas, Liliana G

    2006-12-01

    Ailinella gen. n. (Pseudophyllidea: Triaenophoridae) is proposed to accommodate Ailinella mirabilis sp. n. from Galaxias maculatus (Jenyns, 1842), a freshwater fish inhabiting the Andean lakes in Argentinean Patagonia. Ailinella belongs to the Triaenophoridae because it has a marginal genital pore, a follicular vitelline gland, and a ventral uterine pore. The new genus can be distinguished from other triaenophorids by the following combination of characters: a small body size, a low number of proglottides, which are longer than wide, a truncated pyramidal to globular scolex, a rectangular apical disc, presence of the neck, lack of internal longitudinal musculature separating the cortex from the medulla, testes distributed in one central field surrounding the ovary laterally and posteriorly, the vagina predominantly anterior to the cirrus sac, vitelline follicles circum-medullary, the genital pores post-equatorial, a saccate uterus, and operculate eggs. Blade-like spiniform microtriches were present on all tegument surfaces, and tumuli on all surfaces of the scolex and the anterior surface of the neck. Microtriches were characterized according to their size and density, and tumuli according to their size, inter-tumulus distance and density. Ailinella mirabilis is the first cestode described from G. maculatus and the second triaenophorid species recorded from a South American freshwater fish. PMID:17256203

  10. Imaging central pain syndromes.

    Science.gov (United States)

    Veldhuijzen, Dieuwke S; Greenspan, Joel D; Kim, Jong H; Coghill, Robert C; Treede, Rolf-Detlef; Ohara, Shinji; Lenz, Frederick A

    2007-06-01

    Anatomic, functional, and neurochemical imaging studies have provided new investigative tools in the study of central pain. High-resolution imaging studies allow for precise determination of lesion location, whereas functional neuroimaging studies measure pathophysiologic consequences of injury to the central nervous system. Additionally, magnetic resonance spectroscopy evaluates lesion-induced neurochemical changes in specific brain regions that may be related to central pain. The small number of studies to date precludes definitive conclusions, but the recent findings provide information that either supports or refutes current hypotheses and can serve to generate new ideas.

  11. Diatoms and dinoflagellates macroscopic regularities shaped by intrinsic physical forcing variability in Patagonian and Fuegian fjords and channels (48°-56°S)

    Science.gov (United States)

    Paredes, María Alejandra; Montecino, Vivian; Anic, Vinka; Egaña, Miguel; Guzmán, Leonardo

    2014-12-01

    The distribution of planktonic organisms remains a central focus of research due to the fact that physical and biological interactions affect the marine pelagic ecosystem in different ways and at different scales. Therefore, different patterns in the structure of phytoplankton community emerge according to the observation scale. In the Chilean fjords systems, suggested to be autotrophic and showing neither a nitrate nor a phosphate deficit, we studied the phytoplankton structures from data sets obtained in four seasonal cruises across a large geographical region in Patagonia and Tierra del Fuego, including the biogeographic Magellan District and a portion of the Fuegian District (48-55°S) separated in three sectors. We also processed a database from a spring cruise at a sub-regional spatial scale, which covers a portion of the central and southern Magellan sectors (52-55° S) separated in seven areas with distinctive geographic characteristics. More defined patterns of microphytoplankton at large spatial scales were predicted, with greater heterogeneity and differences between assemblages at a smaller scale. Therefore, at a smaller scale particular local zones with characteristic phytoplankton assemblage are expected as a result of particular environmental conditions of the different geographical areas. In order to evaluate the phytoplankton community structure in both data bases, statistical tools such as multidimensional scaling (MDS), analysis of similarities (ANOSIM), Similarity Percentages (SIMPER) and Cluster Analysis were used when required. At a sub-regional mesoscale, principal component (PCA) and factor analysis were used for environmental data in order to determine if their distribution patterns influences the formation of local zones with similar microphytoplankton assemblages. A Canonical Correspondence Analysis (CCA) was performed to find the relationship between environmental variables and diatom and dinoflagellate grouped by genera. At the regional

  12. Central nervous system

    Science.gov (United States)

    The central nervous system is composed of the brain and spinal cord. Your brain and spinal cord serve as the main "processing center" for your entire nervous system. They control all the workings of your body.

  13. Central Station Design Options

    DEFF Research Database (Denmark)

    2011-01-01

    The purpose of EDISON Work Package 4.1 is the evaluation of possible Central (charging) Stations design options for making possible the public charging of Electric Vehicles (EVs). A number of scenarios for EVs are assessed, with special emphasis on the options of Fast Charging and Battery Swapping....... The work identifies the architecture, sizing and siting of prospective Central Stations in Denmark, which can be located at shopping centers, large car parking lots or gas stations. Central Stations are planned to be integrated in the Danish distribution grid. The Danish island of Bornholm, where a high.......g. due to vandalism, the charge supply circuit is disconnected. More electrical vehicles on the market are capable today of quick charging up to 50 kW power level. The feasibility of Central Stations with fast charging/swapping option, their capacity, design, costs and grid impact, as well as battery...

  14. Central Data Exchange

    Data.gov (United States)

    U.S. Environmental Protection Agency — The Central Data Exchange (CDX) enables fast, efficient and more accurate environmental data submissions from state and local governments, industry and tribes to...

  15. "Central Station" Londonis

    Index Scriptorium Estoniae

    2000-01-01

    Londoni galeriis Milch seitsme läti, leedu ja eesti kunstniku projekt "Central Station". Kuraatorid Lisa Panting, Sally Tallant. Eestist osalevad Hanno Soans (Catarina Campinoga koostöös valminud video), Kiwa, Kai Kaljo

  16. Central Asian Republic Info

    Data.gov (United States)

    US Agency for International Development — CAR Info is designed and managed by the Central Asian Republic Mission to fill in the knowledge and reporting gaps in existing agency systems for that Mission. It...

  17. Central nervous system resuscitation

    DEFF Research Database (Denmark)

    McIntosh, T K; Garde, E; Saatman, K E;

    1997-01-01

    Traumatic injury to the central nervous system induces delayed neuronal death, which may be mediated by acute and chronic neurochemical changes. Experimental identification of these injury mechanisms and elucidation of the neurochemical cascade following trauma may provide enhanced opportunities...

  18. Centralization and political accountability

    OpenAIRE

    Hindriks, Jean; Lockwood, Ben

    2004-01-01

    In this paper we abstract from the usual gains and costs of decentralization (e.g. preference matching, spillovers and economies of scale). Instead we compare the political accountability of decentralized governments relative to centralized ones when there is a risk of "bad" governance. We study both the selection and incentive effects of accountability. A key aspect of centralization is to make the politician answerable to multiple constituencies subject to a common budget constraint. Our ma...

  19. Central Bank independence

    OpenAIRE

    Vasile DEDU; Tiberiu STOICA

    2012-01-01

    In this paper we present the key aspects regarding central bank’s independence. Most economists consider that the factor which positively influences the efficiency of monetary policy measures is the high independence of the central bank. We determined that the National Bank of Romania (NBR) has a high degree of independence. NBR has both goal and instrument independence. We also consider that the hike of NBR’s independence played an important role in the significant disin...

  20. Outsourcing central banking

    DEFF Research Database (Denmark)

    Khoury, Sarkis Joseph; Wihlborg, Clas

    2005-01-01

    The literature on Currency Boards (CB) stops at the water edge in terms of dealing with the totality of the functions of a central bank. Monetary policy, and banking supervisioncan be "outsourced" in an open economy with substantial foreign direct investment (FDI)in the banking sector if political...... the feasibility of, and constraints on, outsourcing of central bank functions. A brief discussion of the Argentinian experience is used for contrast.Key words: Currency Board, Foreign Banks, Supervision, Regional Integration,outsourcing....

  1. Caracterización y evolución metamórfica de las rocas ultramáficas de la faja del río de las Tunas, Cordillera Frontal de Mendoza Characteristics and metamorphic evolution of the ultramafic rocks from Río de Las Tunas Belt, Frontal Cordillera of Mendoza.

    Directory of Open Access Journals (Sweden)

    M. Florencia Gargiulo

    2011-12-01

    Full Text Available Se presenta el estudio petro-mineralógico y químico de metaperidotitas y serpentinitas de la faja máfica-ultramáfica del río de Las Tunas, Cordillera Frontal de Mendoza. Las metaperidotitas preservan relictos de Ol, Cpx, Spls.l. (castaño-rojizo y escaso Opx con diferentes proporciones modales, que permiten inferir protolitos de dunitas, dunitas espinélicas, dunitas clinopiroxénicas, wehrlitas, clinopiroxenitas olivínicas y clinopiroxenitas. La secuencia de cristalización observada en los minerales de reemplazo de las fases primarias: Srp+Mgt(±Brc±Chl→àTr±Tlc→�}Ath→à±Spls.s./Ple(verde±Opx, evidencia el proceso de serpentinización inicial seguido de aumento del grado metamórfico hasta alcanzar condiciones equivalentes a la transición entre la facies de anfibolita de alto grado y la facies de granulita. Un segundo evento de serpentinización manifestado por texturas pseudomórficas según Amp y Chl y texturas no pseudomórficas y de recristalización, junto con las secuencias a FeChr→àCrMgtà→Mgt y b Spls.s./Ple(verdeà→Mgt, indican condiciones posteriores de bajo grado vinculadas a la etapa retrógrada del ciclo de metamorfismo regional. Durante esta etapa también se desarrollan zonas de reacción entre los cuerpos ultramáficos y su roca de caja, como consecuencia de un proceso metasomático entre las litologías en contacto. De manera relativamente simultánea, se genera también la carbonatización penetrativa de cuerpos ultramáficos cercanos a los niveles carbonáticos del Complejo Guarguaráz. Durante el estadío final del ciclo metamórfico, se emplazan cuerpos ígneos gondwánicos en el área de estudio, que aportan las condiciones físico-químicas que favorecen la movilización de elementos y la concentración de minerales, además de potenciar el desarrollo de los procesos metasomáticos. Un nuevo evento de serpentinización restringido en zonas de cizalla, concentra la alteración extrema y

  2. Vegetation, Fire and Climate Over the Last 2000 Yrs in Central West Patagonia (45°S)

    Science.gov (United States)

    Villa-Martinez, R. P.; Simi, E. I.; Moreno, P. I.

    2014-12-01

    We report high-resolution pollen and charcoal records from lake sediments obtained from Lago Mellizas and Lago Churrasco to reconstruct the history of vegetation, fire and past variations of the southern westerly winds (SWW) over the last 2000 years. Both sites are located near to the climate-modulated forest-steppe ecotone in central west Patagonia. In this region the SWW are the only source of precipitation and is ideal for reconstructing past changes in atmospheric circulation. This is facilitated by the marked west-east precipitation gradient across the Patagonian Andes that induces a zonation of the regional vegetation which can be used for inferring past changes in precipitation regimes based on fossil pollen records. Furthermore, the Chilean-European colonization process in central west Patagonia started early in the 20th century, allowing characterization of natural vegetation and climate variability in the absence of human disturbance until the end of the 19th century. The pollen records shows dominance of Nothofagus deciduous forests with minor fluctuations and low herb and aquatics abundances, which suggest humid climate conditions. We detect a major change in the pollen stratigraphy at 200 cal yr BP, when started a sustained decreasing trend in Nothofagus, along with increases of Poaceae and aquatics plants (Cyperaceae, Myriophyllum). We interpret these changes as a forest opening and centripetal expansion of littoral environments toward the lake center driven by lake-level lowering in response to lowered precipitation brought by the SWW. Pinus, Rumex, Plantago, which indicate human perturbation, increase in 1900 AD. Macroscopic charcoal increases at 1750, 1400, 850-700, 500, and 200 cal yr BP, suggesting local fires, followed by sharp increases during the last 100 years. We interpret the pre-20th century charcoal peaks as dry intervals with lowered SWW influence. Acknowledgement: Fondecyt 1121141, Fondap 15110009, and ICM grants P02-51 and NC120066.

  3. An evaluation of methods for modelling distribution of Patagonian insects Una evaluación de los métodos para modelizar la distribución de insectos patagónicos

    Directory of Open Access Journals (Sweden)

    MARCELO F TOGNELLI

    2009-01-01

    Full Text Available Various studies have shown that model performance may vary depending on the species being modelled, the study área, or the number of sampled localities, and suggest that it is necessary to assess which model is better for a particular situation. Thus, in this study we evalúate the performance of different techniques for modelling the distribution of Patagonian insects. We applied eight of the most widely used modelling methods (artificial neural networks, BIOCLIM, classification and regression trees, DOMAIN, generalized additive models, GARP, generalized linear models, and Maxent to the distribution of ten Patagonian insect species. We compared model performance with five accuracy measures. To overeóme the problem of not having reliable absence data with which to evalúate model performance, we used randomly selected pseudo-absences located outside of the polygon área defined by taxonomic experts. Our analyses show significant differences among modelling methods depending on the chosen accuracy measure. Maxent performed the best according to four out of the five accuracy measures, although its accuracy did not differ significantly from that obtained with artificial neural networks. When assessed on per species basis, Maxent was also one of the strongest performing methods, particularly for species sampled from a relatively low number of localities. Overall, our study identified four groups of modelling techniques based on model performance. The top-performing group is composed of Maxent and artificial neural networks, followed closely by the DOMAIN technique. The third group includes GARP, GAM, GLM, and CART, and the fourth best performer is the BIOCLIM technique. Although these results may allow obtaining better distributional predictions for reserve selection, it is necessary to be cautious in their use due to the provisional nature of these simulations.Varios estudios han mostrado que el desempeño de los modelos de distribución puede

  4. Arc-oblique fault systems: their role in the Cenozoic structural evolution and metallogenesis of the Andes of central Chile

    Science.gov (United States)

    Piquer, Jose; Berry, Ron F.; Scott, Robert J.; Cooke, David R.

    2016-08-01

    The evolution of the Main Cordillera of Central Chile is characterized by the formation and subsequent inversion of an intra-arc volcano-tectonic basin. The world's largest porphyry Cu-Mo deposits were emplaced during basin inversion. Statistically, the area is dominated by NE- and NW-striking faults, oblique to the N-striking inverted basin-margin faults and to the axis of Cenozoic magmatism. This structural pattern is interpreted to reflect the architecture of the pre-Andean basement. Stratigraphic correlations, syn-extensional deposits and kinematic criteria on fault surfaces show several arc-oblique structures were active as normal faults at different stages of basin evolution. The geometry of syn-tectonic hydrothermal mineral fibers, in turn, demonstrates that most of these structures were reactivated as strike-slip ± reverse faults during the middle Miocene - early Pliocene. Fault reactivation age is constrained by 40Ar/39Ar dating of hydrothermal minerals deposited during fault slip. The abundance and distribution of these minerals indicates fault-controlled hydrothermal fluid flow was widespread during basin inversion. Fault reactivation occurred under a transpressive regime with E- to ENE-directed shortening, and was concentrated around major plutons and hydrothermal centers. At the margins of the former intra-arc basin, deformation was largely accommodated by reverse faulting, whereas in its central part strike-slip faulting was predominant.

  5. Snakes of an urban-rural landscape in the central Andes of Colombia: species composition, distribution, and natural history

    Directory of Open Access Journals (Sweden)

    Julián Andrés Rojas-Morales

    2012-12-01

    Full Text Available From 2005 to 2011, I studied the composition, distribution and natural history of an Andean urban-rural snake assemblage at the Cordillera Central of Colombia, based on three data sources: (1 examination of specimens in the MHN-UC [Museo de Historia Natural, Universidad de Caldas], (2 incidental encounters by author, and (3 collection of data by other researchers. Additionally, I provide natural history notes for the species involved. A total of 14 species, including two subspecies of snakes, belonging to 12 genera and four families, have been found in the studied area (municipality of Manizales, Caldas. Taking into account this total, 10 had atleast one record in the urban area, 13 in the rural area and 14 in forested areas. Only Liophis epinephelus bimaculatus was found exclusively in forest environment. Three species (21.4% are apparently endemic to the region, six species (42.8% correspond to afauna representative of the Tropical–Andean range of South America, four species (28.5% are distributed from Central America to the tropical Andes, and only one species is widely distributed in the whole continent. The snake assemblage in Manizales is mostly terrestrial, and in general, the species tend to be more active in the rainy periods of the year (mainly from October–December, and most of them may occasionally be found in urban areas, mainly close to areas of vegetation such as crops and pastures.

  6. CENTRAL PLATEAU REMEDIATION

    Energy Technology Data Exchange (ETDEWEB)

    ROMINE, L.D.

    2006-02-01

    A systematic approach to closure planning is being implemented at the Hanford Site's Central Plateau to help achieve the goal of closure by the year 2035. The overall objective of Central Plateau remediation is to protect human health and the environment from the significant quantity of contaminated material that resulted from decades of plutonium production in support of the nation's defense. This goal will be achieved either by removing contaminants or placing the residual contaminated materials in a secure configuration that minimizes further migration to the groundwater and reduces the potential for inadvertent intrusion into contaminated sites. The approach to Central Plateau cleanup used three key concepts--closure zones, closure elements, and closure process steps--to create an organized picture of actions required to complete remediation. These actions were merged with logic ties, constraints, and required resources to produce an integrated time-phased schedule and cost profile for Central Plateau closure. Programmatic risks associated with implementation of Central Plateau closure were identified and analyzed. Actions to mitigate the most significant risks are underway while high priority remediation projects continue to make progress.

  7. ESTRUCTURA, DIVERSIDAD Y DINÁMICA DE LA VEGETACIÓN EN EL ECOTONO BOSQUE-PÁRAMO: REVISIÓN DE LA EVIDENCIA EN LA CORDILLERA DE MÉRIDA

    Directory of Open Access Journals (Sweden)

    Luis Daniel LLAMBÍ

    2015-07-01

    Full Text Available En los Andes tropicales, el límite altitudinal de los bosques corresponde a una compleja zona de transición entre el bosque paramero y el páramo andino. En el límite inferior de esta zona ocurre a su vez una transición gradual entre el bosque y las selvas nubladas. La ordenación del territorio en estos ecosistemas se ha convertido en un tema prioritario en virtud de la creciente amenaza que representan para su conservación las actividades agropecuarias y la minería. En este trabajo se revisaron las investigaciones realizadas en la Cordillera de Mérida (Venezuela sobre los cambios en la estructura, diversidad y respuesta a disturbios de la vegetación a lo largo del ecotono bosque-páramo. Los resultados de estas investigaciones documentan la alta riqueza de especies y formas de vida que caracterizan la vegetación del ecotono, así como una alta tasa de recambio de especies a lo largo del gradiente de elevación. Así mismo, estudios sobre la dinámica sucesional de la vegetación en áreas intervenidas por la agricultura en diferentes posiciones a lo largo de la transición, indican que las leñosas del bosque muestran una capacidad mucho menor de colonización de las áreas perturbadas que las especies dominantes del páramo. Con base en la evidencia disponible, se discuten elementos estructurales que pueden servir de base para la delimitación de los ecosistemas presentes en la zona de transición y se enfatiza la necesidad de diseñar estrategias de conservación y restauración asistida que partan de interpretar el ecotono bosque-páramo como una unidad dinámica integrada.Vegetation Structure, Diversity and Dynamics in the Forest-Paramo Ecotone: A Review of the Evidence in the Cordillera de MéridaIn the tropical Andes, the mountain treeline corresponds to a complex transition zone between páramo forests and páramos. In the lower limit of this ecotone there is a more or less gradual transition between mountain cloud forests and

  8. Colloquium on Central Asia

    International Nuclear Information System (INIS)

    This colloquium on Azerbaijan was organized by the direction of international relations of the French Senate and the French center of foreign trade (CFCE). This document gathers the interventions of the participants and the debates with the audience following these interventions. The topics treated concern: - the present day political-economical situation of Central Asia countries (problem of borders, relations with Russia and China); - the economies of Central Asia countries: short term problems and medium-term perspectives; - the relations with the European Union (political, economical, trade and investments, perspectives); - the European energy stakes of Caspian sea (oil and gas reserves, development of hydrocarbon resources, exploitation and transport constraints, stakes for Europe and France); - TotalFinaElf company in Central Asia (Kazakhstan, Azerbaijan, enclavement problem); - the economical impacts of the TRACECA pathway (Transport Corridor Europe Caucasus Asia). (J.S.)

  9. SOCRATES Invades Central Europe

    Directory of Open Access Journals (Sweden)

    Joseph Slowinski

    1998-04-01

    Full Text Available The objective of this article is to explore the current reality faced by higher education students in Central and Eastern Europe and to draw out the implications of this current reality for policy makers in the future. In the article, I explore the influence of transnational corporations' training programs on education as it currently pertains to Central and Eastern European higher education and employment. In addition, multinational corporate entities exercise influence on European Union policy through the role of lobby organizations and activities. I explore the influence of these practices on education with an emphasis on the emerging importance of Western language skills. In addition, I focus on the European Union and its efforts to expand into Central and Eastern Europe in order to provide a focal point for analysis.

  10. The Naive Central Banker

    Directory of Open Access Journals (Sweden)

    Marcelo de Carvalho Griebeler

    2015-09-01

    Full Text Available There has been in some countries a trend of assigning other functions to central banks besides price stability. The most suggested function to be added to monetary authority’s obligations is to pursue economic growth or full employment. In this paper we characterize the behavior and analyse the optimal monetary policy of, what we call, a naive central banker. We describe the naive behavior as one that does face the inflation-unemployment trade-off, but it tries to minimize both variables simultaneously. Our findings, both under discretion and commitment, indicate that the naive central banker delivers lower expected inflation and inflation variance than the benchmark behavior whenever the economy is rigid enough. However, the degree of conservativeness also affects this result, such that the less conservative the naive policymaker, the more rigidity is necessary.

  11. Las unidades litoestratigráficas del Pérmico y Triásico inferior y medio en el sector SE de la Cordillera Ibérica

    Directory of Open Access Journals (Sweden)

    Arche Miralles, A.

    1992-08-01

    Full Text Available The lithostratigraphic units of the Permian and Triassic SE Iberian Ranges represented in Muschelkalk, Buntsandstein and Saxonian Facies are formally described. The range of definition for the units is the Formation and sorne of these have been also subdivided into Members. The whole of these units constitute two Groups subdivided into two Subgroups each one. This work has followed for the definitions the suggestions of the International Stratigraphic Guide published by the International Subcommission on Stratigraphic Classification (ISSC, 1976. The evolutive study of each unit (formation or member include their sedimentary and tectonic context and a general and extensive bibliographical review for the Permian and Triassic of the SE Iberian Ranges. Finally, it is included a discussion of sorne of the main stratigraphical, sedimentological and tectonical problems resolved until now as well as others not solved up to now.Se definen formalmente las unidades litoestratigráficas que constituyen el Pérmico y Triásico del SE de la Cordillera Ibérica representados en Facies Muschelkalk, Buntsandstein y Saxoniense. El rango definido para las unidades es de Formación, algunas de las cuales han sido a su vez subdivididas en Miembros. El conjunto total es de nueve Formaciones y catorce Miembros que constituyen dos Grupos subdivididos en dos Subgrupos cada uno. Los pasos seguidos para estas definiciones se han basado en las sugerencias de la Guía Estratigráfica Internacional redactadas por la Subcomisión Internacional de Clasificación Estratigráfica (ISSC, 1976. Se incluye en este trabajo una extensa revisión bibliográfica general para el Pérmico y Triásico del SE de la Cordillera Ibérica así como individualmente para cada formación, haciéndose un estudio de la evolución de cada unidad en su contexto sedimentario y tectónico. Finalmente, se realiza una discusión donde se exponen algunos de los principales problemas estratigr

  12. Hale Central Peak

    Science.gov (United States)

    2004-01-01

    19 September 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows some of the mountains that make up the central peak region of Hale Crater, located near 35.8oS, 36.5oW. Dark, smooth-surfaced sand dunes are seen to be climbing up the mountainous slopes. The central peak of a crater consists of rock brought up during the impact from below the crater floor. This autumn image is illuminated from the upper left and covers an area approximately 3 km (1.9 mi) across.

  13. Central Bank independence

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    Vasile DEDU

    2012-08-01

    Full Text Available In this paper we present the key aspects regarding central bank’s independence. Most economists consider that the factor which positively influences the efficiency of monetary policy measures is the high independence of the central bank. We determined that the National Bank of Romania (NBR has a high degree of independence. NBR has both goal and instrument independence. We also consider that the hike of NBR’s independence played an important role in the significant disinflation process, as headline inflation dropped inside the targeted band of 3% ± 1 percentage point recently.

  14. Several Centuries of Centrality

    OpenAIRE

    Roth, Dana L.

    2015-01-01

    As Carolyn Bertozzi mentioned in her inaugural editorial, the relationship of “Central Science” to “Chemistry” became popularized over 40 years ago with the publication of the first edition of Brown and LeMay’s Chemistry: The Central Science, now in its 13th edition. Yet as late as 2003, Prof. Sason Shaik at The Hebrew University claimed “popularization of chemistry remains scant.” He goes on to share [his] “own experience of popularizing chemistry by delivering the following universal messag...

  15. ORIC central region calculations

    International Nuclear Information System (INIS)

    The central region for the K = 100 Oak Ridge Isochronous Cyclotron, ORIC, will be modified to provide better orbit centering, focusing of orbits in the axial direction, and phase selection, in order to improve extraction efficiency, and reduce radioactive activation of cyclotron components. The central region is specifically designed for the acceleration of intense light ion beams such as 60 MeV protons and 15--100 MeV alphas. These beams will be used in the production of radioactive atoms in the Radioactive Ion Beam Project at Oak Ridge National Laboratory

  16. Efecto del Compost de Biosólidos en la producción de plantines de Austrocedrus Chilensis (ciprés de la cordillera Effect of Biosolids Compost on seedling production of Austrocedrus Chilensis (ciprés de la cordillera

    Directory of Open Access Journals (Sweden)

    Gustavo Basil

    2009-06-01

    Full Text Available La utilización de compost de residuos urbanos como sustrato en contenedores es una alternativa interesante a nivel económico y ambiental, dado que reduciría el uso de turba y «tierra negra» en la producción de plantines, y la disposición de residuos en vertederos. En el presente trabajo se estudió el efecto de 0, 30 y 50% de compost de biosólidos en el crecimiento inicial (primer año de ciprés de la cordillera, y el efecto durante los dos años siguientes de un tratamiento único con 50% de compost en el crecimiento posterior y el estado nutricional de los plantines. Se determinó diámetro y altura a 18, 25 y 37 meses, biomasa aérea y radicular a 25 y 37 meses, y concentración foliar de C, N, P, K, Ca y Mg a 37 meses. A pesar de que los tres tratamientos iniciales fueron homogeneizados al año en un único tratamiento con 50% de compost, se encontraron diferencias significativas de diámetro, altura y biomasa aérea y radicular entre los tratamientos originales en todas las fechas analizadas, correspondiendo los mayores valores a los tratamientos con compost. Al finalizar el ensayo, las concentraciones foliares de nutrientes fueron muy similares en todos los plantines, excepto Mg que fue mayor en el tratamiento original con 50% de compost. Los resultados muestran la importancia de los primeros meses de crecimiento en el desarrollo posterior de los plantines de ciprés y el valor potencial de los compost de biosólidos como sustrato para la producción de esta especie en contenedores.Using composts of urban waste, including biosolids, as substrates for containerized plant production is a sound economic and environmental alternative, since it could reduce the use of peat- and «black earth»-based media, and the disposal of organic wastes in landfills. The objectives of this work were to study the effect of 0, 30 and 50% biosolids compost on the initial growth (first year of cypress (Austrocedrus chilensis D. Don, and the effect

  17. Evolución tectónica, paleogeográfica y metalogénica durante el Cenozoico en los Andes de Chile norte y central e implicaciones para las regiones adyacentes de Bolivia y Argentina Tectonic, paleogeographic, and metallogenic evolution during the Cenozoic in the Andes of Central and Northern Chile and implication for the adjacent regions of Bolivia and Argentina

    Directory of Open Access Journals (Sweden)

    Reynaldo Charrier

    2009-10-01

    Full Text Available La orogenia incaica dio origen a un importante relieve en el Eoceno Medio, el que se concentró en el ámbito del arco magmático precedente, la Cordillera Incaica. Este relieve positivo de orientación NNE se extendió desde el sur de Perú hasta la región central de Chile y separó dos dominios paleogeográficos que tuvieron evoluciones diferentes durante el resto del Cenozoico. El dominio occidental se caracterizó por el predominio de procesos de erosión y sedimentación. En el dominio oriental también existieron importantes episodios de erosión que originaron depósitos que se encuentran en la vertiente oriental de la cadena en la actualidad y presentan una cronología comparable con la de los depósitos del dominio occidental. Sin embargo, la evolución se caracterizó por presentar, a partir del Eoceno Tardío, diferencias al norte y sur de los ~27ºS. Al norte de esa latitud, en el ámbito del Altiplano-Puna, el arco magmático se mantuvo aproximadamente en la misma posición, coincidente con la del arco actual, y estuvo bordeado por una cuenca de antepaís de retroarco; mientras que, al sur de ~27ºS, se desarrollaron sucesivos arcos magmáticos con una marcada migración hacia el este. El arco magmático del Eoceno Tardío al Oligoceno Tardío - Mioceno Temprano se caracterizó por el desarrollo de una amplia cuenca extensional de intra-arco, la cuenca de Abanico. En esta cuenca se acumularon hasta 3.000 m de rocas volcánicas, volcaniclásticas y, subordinadamente, sedimentarias. A partir del límite oligoceno-mioceno, tuvo lugar un nuevo evento compresivo a lo largo de todo el orógeno que rejuveneció el núcleo de la Cordillera Incaica e invirtió la cuenca de Abanico permitiendo la generación de abundantes depósitos sintectónicos a ambos lados de los nuevos relieves. El inicio de este evento coincide con la orogenia pehuenche, los pulsos compresivos se mantuvieron hasta el Plioceno Temprano. En el Mioceno Temprano a Medio

  18. Retiring the central executive.

    Science.gov (United States)

    Logie, Robert H

    2016-10-01

    Reasoning, problem solving, comprehension, learning and retrieval, inhibition, switching, updating, or multitasking are often referred to as higher cognition, thought to require control processes or the use of a central executive. However, the concept of an executive controller begs the question of what is controlling the controller and so on, leading to an infinite hierarchy of executives or "homunculi". In what is now a QJEP citation classic, Baddeley [Baddeley, A. D. (1996). Exploring the central executive. Quarterly Journal of Experimental Psychology, 49A, 5-28] referred to the concept of a central executive in cognition as a "conceptual ragbag" that acted as a placeholder umbrella term for aspects of cognition that are complex, were poorly understood at the time, and most likely involve several different cognitive functions working in concert. He suggested that with systematic empirical research, advances in understanding might progress sufficiently to allow the executive concept to be "sacked". This article offers an overview of the 1996 article and of some subsequent systematic research and argues that after two decades of research, there is sufficient advance in understanding to suggest that executive control might arise from the interaction among multiple different functions in cognition that use different, but overlapping, brain networks. The article concludes that the central executive concept might now be offered a dignified retirement.

  19. Ecodesign in Central America

    NARCIS (Netherlands)

    Crul, M.R.M.

    2003-01-01

    This PhD thesis describes and analyses the change process started by the Ecodesign project in Central America, executed between 1998 and 2002. The project started using the concept and praxis developed in Europe. Nine ecodesign projects were performed in industry, and ecodesign was introduced to cou

  20. Retiring the central executive.

    Science.gov (United States)

    Logie, Robert H

    2016-10-01

    Reasoning, problem solving, comprehension, learning and retrieval, inhibition, switching, updating, or multitasking are often referred to as higher cognition, thought to require control processes or the use of a central executive. However, the concept of an executive controller begs the question of what is controlling the controller and so on, leading to an infinite hierarchy of executives or "homunculi". In what is now a QJEP citation classic, Baddeley [Baddeley, A. D. (1996). Exploring the central executive. Quarterly Journal of Experimental Psychology, 49A, 5-28] referred to the concept of a central executive in cognition as a "conceptual ragbag" that acted as a placeholder umbrella term for aspects of cognition that are complex, were poorly understood at the time, and most likely involve several different cognitive functions working in concert. He suggested that with systematic empirical research, advances in understanding might progress sufficiently to allow the executive concept to be "sacked". This article offers an overview of the 1996 article and of some subsequent systematic research and argues that after two decades of research, there is sufficient advance in understanding to suggest that executive control might arise from the interaction among multiple different functions in cognition that use different, but overlapping, brain networks. The article concludes that the central executive concept might now be offered a dignified retirement. PMID:26821744

  1. Testing for central symmetry

    NARCIS (Netherlands)

    Einmahl, John; Gan, Zhuojiong

    2016-01-01

    Omnibus tests for central symmetry of a bivariate probability distribution are proposed. The test statistics compare empirical measures of opposite regions. Under rather weak conditions, we establish the asymptotic distribution of the test statistics under the null hypothesis; it follows that they a

  2. Central areolar choroidal dystrophy.

    NARCIS (Netherlands)

    Boon, C.J.F.; Klevering, B.J.; Cremers, F.P.M.; Zonneveld-Vrieling, M.N.; Theelen, T.; Hollander, A.I. den; Hoyng, C.B.

    2009-01-01

    OBJECTIVE: To describe the clinical characteristics, follow-up data and molecular genetic background in a large group of patients with central areolar choroidal dystrophy (CACD). DESIGN: Retrospective case series study. PARTICIPANTS: One hundred three patients with CACD from the Netherlands. METHODS

  3. The Bolivian and Maipo Oroclines: Two first scale structural features of the Central Andes

    Science.gov (United States)

    Arriagada, C. A.

    2013-05-01

    Two remarkable curvatures of the orogenic system of the Central Andes are the Bolivian and the Maipo Oroclines. While the former has been widely studied, the latter in central Chile, where few, geographically restricted, paleomagnetic studies have been carried out, knowledge about vertical-axis rotations is scarce. Here we show the results of the paleomagnetic studies carried out in the last years along the Central Andes within the Bolivian and Maipo Oroclines. Along-strike variations in horizontal shortening in the back- arc provided an efficient mechanism to explain the Bolivian Orocline and block rotations of the forearc region in northern Chile and southern Peru. As a first approximation, it appears reasonable that the arcuate shape of the Maipo Orocline could be accompanied by a significant pattern of rotations about a vertical axis in the forearc region and by a progressive decrease of crustal shortening and the resulting topography from north to south in the back-arc region. Furthermore, although the Maipo Orocline is located more than 1000 km south of the axial zone of the Central Andes, south of 30, clockwise rotations of up to 20 could have occurred during the evolution of the Bolivian Orocline. While the northern segment of the Maipo orocline corresponds with the ongoing subduction of the Pampean flat slab segment which proceeds nearly horizontally beneath the South American lithosphere, the southern segment coincides with the normal subduction segment developed to the south of 33S. The Maipo Orocline is thought to be result of collision of the Challenger Fracture Zone and Juan Fernández Ridge with the continent since 25 Ma. The southern flank of the Maipo Orocline can be traced along strike to around 38S. North of 33S, previous studies show no evidence for significant tectonic rotations. In contrary, south of 33S, both in the Coastal Cordillera and High Andes, clockwise block rotations have been observed and attributed to in situ block rotations in

  4. Intraseasonal variability of organized convective systems in the Central Andes: Relationship to Regional Dynamical Features

    Science.gov (United States)

    Mohr, K. I.; Slayback, D. A.; Nicholls, S.; Yager, K.

    2013-12-01

    The Andes extend from the west coast of Colombia (10N) to the southern tip of Chile (53S). In southern Peru and Bolivia, the Central Andes is split into separate eastern and western cordilleras, with a high plateau (≥ 3000 m), the Altiplano, between them. Because 90% of the Earth's tropical mountain glaciers are located in the Central Andes, our study focuses on this region, defining its zonal extent as 7S-21S and the meridional extent as the terrain 1000 m and greater. Although intense convection occurs during the wet season in the Altiplano, it is not included in the lists of regions with frequent or the most intense convection. The scarcity of in-situ observations with sufficient density and temporal resolution to resolve individual storms or even mesoscale-organized cloud systems and documented biases in microwave-based rainfall products in poorly gauged mountainous regions have impeded the development of an extensive literature on convection and convective systems in this region. With the tropical glaciers receding at unprecedented rates, leaving seasonal precipitation as an increasingly important input to the water balance in alpine valley ecosystems and streams, understanding the nature and characteristics of the seasonal precipitation becomes increasingly important for the rural economies in this region. Previous work in analyzing precipitation in the Central Andes has emphasized interannual variability with respect to ENSO, this is the first study to focus on shorter scale variability with respect to organized convection. The present study took advantage of the University of Utah's Precipitation Features database compiled from 14 years of TRMM observations (1998-2012), supplemented by field observations of rainfall and streamflow, historical gauge data, and long-term WRF-simulations, to analyze the intraseasonal variability of precipitating systems and their relationship regional dynamical features such as the Bolivian High. Through time series and

  5. Elevation-dependent changes in n-alkane δD and soil GDGTs across the South Central Andes

    Science.gov (United States)

    Nieto-Moreno, Vanesa; Rohrmann, Alexander; van der Meer, Marcel T. J.; Sinninghe Damsté, Jaap S.; Sachse, Dirk; Tofelde, Stefanie; Niedermeyer, Eva M.; Strecker, Manfred R.; Mulch, Andreas

    2016-11-01

    Surface uplift of large plateaus may significantly influence regional climate and more specifically precipitation patterns and temperature, sometimes complicating paleoaltimetry interpretations. Thus, understanding the topographic evolution of tectonically active mountain belts benefits from continued development of reliable proxies to reduce uncertainties in paleoaltimetry reconstructions. Lipid biomarker-based proxies provide a novel approach to stable isotope paleoaltimetry and complement authigenic or pedogenic mineral proxy materials, in particular outside semi-arid climate zones where soil carbonates are not abundant but (soil) organic matter has a high preservation potential. Here we present δD values of soil-derived n-alkanes and mean annual air temperature (MAT) estimates based on branched glycerol dialkyl glycerol tetraether (brGDGT) distributions to assess their potential for paleoelevation reconstructions in the southern central Andes. We analyzed soil samples across two environmental and hydrological gradients that include a hillslope (26-28°S) and a valley (22-24°S) transect on the windward flanks of Central Andean Eastern Cordillera in NW Argentina. Our results show that present-day n-alkane δD values and brGDGT-based MAT estimates are both linearly related with elevation and in good agreement with present-day climate conditions. Soil n-alkanes show a δD lapse rate (Δ (δD)) of - 1.64 ‰ / 100 m (R2 = 0.91, p < 0.01) at the hillslope transect, within the range of δD lapse rates from precipitation and surface waters in other tropical regions in the Andes like the Eastern Cordillera in Colombia and Bolivia and the Equatorial and Peruvian Andes. BrGDGT-derived soil temperatures are similar to monitored winter temperatures in the region and show a lapse rate of ΔT = - 0.51 °C / 100 m (R2 = 0.91, p < 0.01), comparable with lapse rates from in situ soil temperature measurements, satellite-derived land-surface temperatures at this transect, and

  6. Deterioro ambiental y micromamíferos durante el Holoceno en el nordeste de la estepa patagónica (Argentina Environmental deterioration and micromammals during the Holocene in northeastern Patagonian steppe (Argentina

    Directory of Open Access Journals (Sweden)

    ULYSES F. J. PARDIÑAS

    2000-03-01

    analysis of frequency and corrosive marks on the skeletal remains indicates that the material was probably deposited during winter time by a strigiform bird, possibly Tyto alba, which explains the low level of bone corrosion. Comparison with a recent sample of pellets from Tyto alba from the same locality, in which Calomys cf. C. laucha-C. musculinus accounted for 95% of the total micromammals, shows a marked loss in today's species diversity. Comparison with modern samples of owl pellets from different Patagonian phytogeographic districts, together with paleoenvironmental evidence from the Late Holocene, indicate that human activities are probably the most important agent of the modification of the environment. Activities like overgrazing by sheep and expansion of agriculture may have aided both the dispersal as well as the increased present-day abundance of Calomys on account of another micromammals.

  7. Alterations in the intestine of Patagonian silverside (Odontesthes hatcheri) exposed to microcystin-LR: Changes in the glycosylation pattern of the intestinal wall and inhibition of multidrug resistance proteins efflux activity.

    Science.gov (United States)

    Bieczynski, Flavia; Torres, Walter D C; Painefilu, Julio C; Castro, Juan M; Bianchi, Virginia A; Frontera, Jimena L; Paz, Dante A; González, Carolina; Martín, Alejandro; Villanueva, Silvina S M; Luquet, Carlos M

    2016-09-01

    Accumulation and toxicity of cyanobacterial toxins, particularly microcystin-LR (MCLR) have been extensively studied in fish and aquatic invertebrates. However, MCLR excretion mechanisms, which could reduce this toxin's effects, have received little attention. The Patagonian silverside, Odontesthes hatcheri, is an omnivorous-planktivorous edible fish, which has been shown to digest cyanobacterial cells absorbing MCLR and eliminating the toxin within 48h without suffering significant toxic effects. We studied the effects of MCLR on glycoconjugate composition and the possible role of multidrug resistance associated proteins (Abcc) in MCLR export from the cells in O. hatcheri intestine. We treated O. hatcheri with 5μg MCLRg(-1) body mass administered with the food. Twenty four hours later, the intestines of treated and control fish were processed for lectin-histochemistry using concanavalin A (ConA), Triticum vulgaris agglutinin (WGA), and Dolichos biflorus agglutinin (DBA). MCLR affected the distribution of glycoconjugates by augmenting the proportion of ConA-positive at the expense of WGA-positive cells. We studied MCLR effects on the transport of the Abcc-like substrates 2,4-dinitrophenyl-S-glutathione (DNP-SG) and calcein in ex vivo intestine preparations (everted and no-everted sacs and strips). In treated preparations, CDNB together with MCLR (113μg MCLRg(-1) intestine, equivalent to 1.14μmolL(-1) when applied in the bath) or the Abcc inhibitor, MK571 was applied for one hour, during which DNP-SG was measured in the bath every 10min in order to calculate mass-specific DNP-SG transport rate. MCLR significantly inhibited DNP-SG transport (pintestine (47 and 24%, for luminal and serosal transport, respectively). In middle intestine strips, MCLR and MK571inhibited DNP-SG transport in a concentration dependent fashion (IC50 3.3 and 0.6μmolL(-1), respectively). In middle intestine strips incubated with calcein-AM (0.25μmolL(-1)), calcein efflux was inhibited by

  8. Estratigrafía y geoquímica del volcanismo de composición intermedia (Mioceno Superior-Plioceno en el extremo oriental de la cordillera de San Buenaventura (Puna Austral

    Directory of Open Access Journals (Sweden)

    María Carolina Montero López

    2010-08-01

    Full Text Available La cordillera de San Buenaventura está integrada por unidades volcánicas de composición ácida e intermedia que abarcan un lapso entre el Mioceno superior y el Holoceno y se apoyan sobre un basamento neoproterozoico-paleozoico inferior, que incluye metamorfitas de grado variable y plutones, además de sedimentitas con intercalaciones volcánicas del Ordovícico bajo a medio. En el extremo oriental de la sierra, el volcanismo de composición intermedia está representado por el Complejo Volcánico La Hoyada, donde se agrupan términos efusivos y explosivos, de afinidad calcoalcalina rica en K, que corresponden a andesitas-traquiandesitas y dacitas. En base a los estudios de campo sumado a los resultados petrográficos, geoquímicos y geocronológicos se presenta una columna estratigráfica simplificada para este complejo, donde se distinguen dos grandes eventos volcánicos en un lapso entre ca. 7-2,5 Ma. A partir de las similitudes geoquímicas con las rocas calcoalcalinas del arco volcánico frontal que se encuentran entre los 25º y 27º S, se interpreta un origen semejante a partir de magmas mantélicos los cuales ya estaban enriquecidos con una componente cortical.

  9. Ecosistemas presentes y pasados en la Quebrada Benjamín Matienzo (32º 35' - 32º 50' L. S. y 70º 06' L. O., Cordillera de Los Andes, Mendoza, Argentina

    Directory of Open Access Journals (Sweden)

    Mónica C Wingenroth

    2012-09-01

    Full Text Available Los sedimentos de un perfil en la quebrada Benjamín Matienzo, cordillera de Los Andes (32º 35' - 32º 50' L. S. y 70º 06' L. O., aproximadamente a 3400 m de altura, fueron datados en 6400 años AP a los 572 cm de profundidad. El polen identificado en 174 eventos (capas hallados en dicho perfil se relacionó con el polen presente (1980-1981 / 1981-1982. Un total de siete ambientes se definieron en la quebrada, en base a las diferencias registradas entre la cantidad y calidad del polen local, sugiriendo cambios de la vegetación y/o producción de polen, en respuesta a las variaciones en la disponibilidad del agua y la temperatura. A partir de las diferencias detectadas entre la cantidad y calidad del polen alóctono, se infirieron las direcciones predominantes de los vientos que llegaron a Matienzo en cada evento pasado. A su vez para los eventos incluidos en los mencionados ambientes se sugirieron balances acumulativos de la masa de hielo positivos y negativos, derretimiento de las áreas periglaciales congeladas y los correspondientes ciclos solares y su actividad.

  10. Petroglifos en rocas de la Cordillera de la Costa así como en los raudales de los ríos de la selva virgen venezolana. La interpretación por Alejandro de Humboldt y observaciones actuales

    Directory of Open Access Journals (Sweden)

    Ursula Thiemer-Sachse

    2003-04-01

    Full Text Available Article in Spanish, Abstracts in English, German and Spanish.Indian Petroglyphs on rocks of the Venezuelan Cordilleras mountain chain as well as Región de los Raudales, the tropical forest headwaters. A. v. Humboldt’s petroglyph interpretations and present observations. Throughout the world the interpretation of petroglyphs and other prehistoric rock art is a difficult endeavor. Some of the factors contributing to these puzzles include, among others: a lack of knowledge about the circumstances (such as rituals and the concomitant ideas that played key roles in the creation of the petroglyphs. Even the famous nineteenth-century German explorer Alexander von Humboldt, who first saw South American petrogpyphs while mapping the river system connecting the Amazon and Orinoco rivers in Venezuela, ventured to decipher and analyze the complicated artwork as part of his interest in ancient civilizations. Since the time of Humboldt numerous other researchers have attempted to decode and provide a culturally-situated analysis of petroglyph’s meanings.

  11. El Transporte Terrestre a través de la Cordillera Cantábrica en Tiempos de Felipe II. Un Estudio a partir de la Correspondencia de Simón Ruiz con Laredo

    Directory of Open Access Journals (Sweden)

    Oscar LUCAS VILLANUEVA

    2012-12-01

    Full Text Available El presente trabajo analiza las condiciones y costes del transporte terrestre en tiempos de Felipe II en el ámbito de las relaciones comerciales entre Castilla y el espacio atlántico septentrional, a partir de la información proporcionada por las cartas comerciales del mercader Simón Ruiz. Los datos nos indican que las dificultades geográficas no fueron tan determinantes para el tráfico a través de la Cordillera Cantábrica como se había pensado hasta ahora. El artículo también aborda la cuestión de los costes que comportaban las operaciones de traslado de mercancías desde los puertos a los mercados del interior peninsular. Las fuentes nos permiten un detallado análisis de los mismos así como un cálculo de su cuantía en proporción a la suma total de la operación, relativizando la importancia de los mismos, lo que favorecería los traslados de mercancías por vía terrestre para distancias relativamente grandes.

  12. Geodynamic Drivers of Vertical Crustal Motion: Integrating Paleoaltimetry with Basin Development in the Central Andean Plateau of Southern Peru

    Science.gov (United States)

    Sundell, K. E., II; Saylor, J. E.; Lapen, T. J.; Villarreal, D. P.; Styron, R. H.; Horton, B. K.; Cardenas, J.

    2015-12-01

    Determining the spatial and temporal relationships betwee