Sample records for ROCAS CARBONATADAS (carbonate rocks)
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1

Estudio petrográfico de los xenolitos corticales y mantelares presentes en las lavas del cerro atravesado, falcón central, venezuela/ Petrograhy of crustal and mantle xenoliths present in the lava of cerro atravesado, central falcón, venezuela

Grande, Sebastián
2009-03-01

Resumen en español En la parte central de la cuenca de Falcón se recolectaron muestras de lava basanítica de la chimenea de brecha norte del cerro Atravesado, uno de los más antiguos cuerpos subvolcánicos alcalino-máficos intrusivos del Mioceno de Falcón (edad Ar-Ar: 23-21 Ma). Estas rocas contienen abundantes xenolitos que han sido agrupados petrográficamente como sigue: nódulos mantelares de lherzolita (o harzburgita) con Cr-espinela; xenocristales de ortopiroxeno serpentinizado, (mas) basamento precámbrico de alto grado (mármol con diópsido y flogopita, granulita máfica y anortosita); cuarcita y cuarcita micácea de bajo grado, caliza con foraminíferos pláncticos cretácicos, chert negro y otras rocas sedimentarias de proveniencia incierta. Los xenolitos muestran una intensa alteración hidrotermal a carbonato-clorita debido a que el ascenso rápido del magma no permitió el pirometamorfismo, pero su intrusión en sedimentos pelíticos hidro-saturados desató una intensa circulación hidrotermal, que afectó a todas las rocas. En este trabajo ha sido comprobada la presencia de un basamento posiblemente del Proterozoico tardío de afinidad grenvilliana, de los orógenos del Paleozoico tardío o del Mesozoico, y de rocas sedimentarias cretácicas de la cuenca occidental de Venezuela, provenientes de las Napas de Lara subyacentes. Esto permite concluir que el basamento de la cuenca de Falcón central consta probablemente de napas imbricadas que involucran rocas formadas por al menos a cuatro ciclos o eventos tectónicos: de alto grado (grenvilliano), de bajo grado (caledoniano-apalache o de la cordillera del Caribe), proto-caribeño (margen pasivo Cretácico al norte de Sudamérica) y falconiano (retro-arco con actividad ígnea intraplaca asociada). Resumen en inglés Samples of basanitic lava were collected from North Cerro Atravesado breccia pipe, one of the oldest alkali-mafic subvolcanic bodies intrusive in the Miocene in Central Falcon Basin (Ar-Ar age: 23-21 Ma). These rocks contain abundant xenoliths which have been petrographically grouped as follows: lherzolite (or harzburgite) mantle nodules, serpentinized orthopyroxene xenocrysts, grenvillian high grade basament (marble with diopside and phlogopite, mafic granulite and anort (mas) hosite); low grade quartzite and mica-quartzite; limestone containing Cretaceous planctic foraminifera, black chert and other sedimentary clastic rocks of uncertain origin. The xenoliths show intense carbonate-chlorite hydrothermal alteration since the rapid magma ascent did not allow for pyrometamorphism, but being intruded in water-saturated pelitic sediments unleashed an intense hydrothermal circulation which affected all the rock units. In this work, we prove the presence of a basement of probable Late Proterozoic and Grenvillian affinity, of Late Paleozoic or Mesozoic orogens, and of Cretaceous sedimentary rocks from the Venezuelan Western Basin present in the underlying Lara Nappes. It can be concluded that the basement of the Central Falcon Basin is probably formed by imbricated nappes that involve rocks pertaining to al least four tectonic cycles or events: high grade (Grenvillian), low grade (Caledonian-Appalachian or cordillera del Caribe), proto-Caribbean (Cretaceous passive margin in Northern South America), and Falconian (back-arc basin with intraplate igneous activity).

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2

El protolito siliciclástico de las Ectinitas El Jagüelito, provincia de Río Negro/ The siliclastic protolith of the El Jagüelito ectinites Río Negro provimce

Dalla Salda, LH; Aragón, E; Benialgo, A; Abre, P; Pezzotti, C
2003-09-01

Resumen en español Mediante el análisis del protolito se determinó el carácter de los sedimentos madre de las Ectinitas El Jagüelito, localizadas en la secuencia de metamorfitas del basamento cristalino del este del Macizo Norpatagónico. Se realizaron estudios que incluyeron petrografía, análisis con conteo de granos, relaciones y composición del bandeado y rayos X. Las rocas investigadas derivaron de grauvacas y arenitas líticas, principalmente de grano psamítico y pelítico, dep (mas) ositadas en una cuenca marina profunda por corrientes de alta densidad, provenientes de un arco magmático cercano. Escasas rocas ricas en cuarzo y otras de bajo contenido en carbonato de calcio, pueden representar ambientes más neríticos. El sistema químico de las muestras analizadas no parece haberse modificado por alteración, transporte o metamorfismo. El comportamiento de muchos elementos relevantes en el estudio de protolitos, sugiere que el metamorfismo fue isoquímico. Los diagramas de discriminación de ambientes tectónicos, apuntan a un margen activo como fuente de procedencia de los sedimentos. Recientes datos geocronológicos parecen indicar que el arco continental y la sedimentación del protolito, ocurrieron durante el Cámbrico. Resumen en inglés The sedimentary character of the El Jagüelito ectinites, within the classic sequence of the crystalline basement of eastern North Patagonian Massif has been established by protolith analysis. A range of studies from hand specimen to trace elements analysis and including micro section, single grain, banding relations and X-ray analysis were performed. The rocks are derived from pre-existing greywacke and lithic sandstone, of shale to sandy grain size. They were deposited (mas) within a deep-sea basin, as high-density current deposits coming from a magmatic arc. Sparse quartz- rich rocks and calcium-poor carbonate rocks may represent a more neritic environment. Weathering, transportation and diagenesis seem not to modify the HFS elements. The behaviour of chemical elements, which are relevant to protoliths, suggests that metamorphism was isochemical. Discriminate tectonic diagrams indicate an active margin as the source of the sediments. Recent data from the region seem to indicate a Cambrian age for the continental arc and protolith sedimentation.

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3

Rasgos Geoquímicos de las Calizas de la Formación Arroyo Verde (Eoceno), en Punta Colorada. Provincia de Río Negro. Argentina: Reconstrucción Paleoambiental/ Geochemical features of limestones in Arroyo Verde Formation (Eocene) in Punta Colorada. Río Negro Province. Argentina: Palaeoenvironmental reconstruction

Luna, Liliana; Schillizzi, Roberto; Bonuccelli, Renzo
2008-12-01

Resumen en español El creciente desarrollo de la industria cementera ha reactivado la exploración de los yacimientos de calizas en el sur de Argentina. En la zona de Punta Colorada, a 36 km de Sierra Grande, Prov. de Río Negro, se encuentra un depósito de estas rocas pertenecientes a la Formación Arroyo Verde, del Eoceno inferior, originada por una ingresión marina ocurrida el Cretácico superior-Terciario inferior. A través de un estudio técnico se cubicaron 14.806.106 tn de reserva (mas) s medidas y 1.799.174 tn de reservas indicadas en carbonato de calidad menor al 4 % MgO. Se estudió un área de 800 Ha, dividida en 2 zonas ubicadas al norte y al sur de Punta Colorada, separadas por el Arroyo Las Palmas, en el litoral marítimo atlántico. Se determinó una potencia media de 10 m de calizas por medio de perforaciones y perfiles. El análisis de los perfiles permitió establecer 4 niveles compuestos por calizas masivas a granulares, con estratificación entrecruzada, fosilíferas. Microscópicamente se observan bivalvos, equinodermos, corales, foraminíferos y algas. La fracción clástica terrígena, tamaño arena-limo, está compuesta principalmente por cuarzo, feldespato y concreciones arcillosas verdosas. Se analizaron los tenores de CaO, MgO y se calcularon las relaciones Mg/Ca observándose variaciones verticales con aumento del MgO hacia los niveles superiores del yacimiento. Sobre la base de los porcentajes de estos óxidos se clasifica a las rocas en caliza, caliza dolomítica y dolomita calcítica. Se analizaron además Al, Fe, K, Mg, Mn, Na, P, S y Ti, observándose variaciones geoquímicas laterales y verticales que se relacionarían con cambios morfológicos, paleoambientales y de evolución de la cuenca. Se concluye que las calizas están constituidas principalmente por calcita con cantidades variables de MgO. Estas rocas se habrían formado en lagunas costeras de aguas cálidas, con alto contenido en fósforo. En otros sectores de la cuenca se habrían formado áreas pandas, con alimentación intermitente de aguas marinas, que quedaron aisladas temporalmente del ambiente marino dominante idea apoyada por el aumento en el contenido de Na y K. El contenido de Al, Fe, Mn y Ti estaría relacionado con la presencia de material terrígeno; sin embargo, el escaso aporte a la cuenca indicaría condiciones climáticas de aridez con bajo régimen pluvial. La estratificación entrecruzada en el nivel 2 se asocia a corrientes marinas. La abundancia de fósiles fragmentados revelaría la alta energía del medio. Sobre las planicies de marea las trazas de bioturbación de poco espesor, marcarían condiciones de inestabilidad, además de estadios de energía moderada a relativamente baja con tasa de sedimentación de igual calificación. En la etapa final las condiciones de depositación son marinas costeras, someras, con presencia de conchillas enteras dispersas, estratificación entrecruzada y aumento en el contenido de Fe y Mn. Mientras que en otras áreas el aumento en el contenido de azufre como yeso, señalaría una sostenida regresión del mar en dirección SO-NE. Resumen en inglés The fast growing cement industry has reactivated the exploration for calcareous materials in southern Argentina.A carbonatic deposit is found in Punta Colorada, located 36 km from the town of Sierra Grande, Río Negro Province. These rocks, deposited during a Late Cretaceous - Early Tertiary marine ingression, belong to Arroyo Verde Formation (Early Eocene). These coastal deposits have been studied since 1927 by Wichmann, Arnolds (1952), de Alba (1964), Weber (1983) and B (mas) usteros et al. (1998). Rossi de García and Levy (1982) assigned these rocks to the Eocene; Spalletti et al. (1993) located them within the Roca Formation (Rocanense ingression) and Gelós et al. (1992) correlated these rocks with Arroyo Verde Formation (Malvicini and Llambías, 1974). Arroqui Langer et al. (2006) from sedimentologic, geochemical and lithologic data in carbonatic rocks of the Precordillera Argentina established an exploration and exploitation pattern. Bonuccelli (2006) made a similar technical study in Punta Colorada, where 14,806,106 tn of measured reserves and 1,799,174 tn of indicated reserves were determined in a carbonate of less than 4% MgO grade. The study area comprise 800 Ha divided in two zones separated by Arroyo Las Palmas gully and located at the north and at the south of a basement outcrop denominated Punta Colorada, in the atlantic marine coast (Fig. 1). By means of 12 drills cores and 8 stratigraphic profiles, a thickness of 10 m was determined for the limestone. Major and minor chemical elements were determined by ICP-MA in 100 ml with two replicas in Alex Steward laboratories, Mendoza. The criterion of Tucker (1981) was used to classify the limestones by the dolomite percentage. From stratigraphic profiles four levels composed of cross-bedded massive to granular fosiliferous limestones were determined. Microscopically they are composed of a fossiliferous limestone (bioclastic packstone) with bivalves, equinoderms, corals, foraminifera and algae, being algal buildups more abundant in level three. The clastic sand to silt fraction is mainly composed of quartz, feldspar and green clay concretions. CaO and MgO contents and the relationships Mg/ Ca (Tables 1 and 2) in the stratigraphic profiles and drills cores show vertical variations with increasing MgO values toward the upper levels of the sequence. Based on the percentages of these oxides the rocks are classified as limestone, dolomitic limestone and calcitic dolomite. In drill cores Al, Fe, K, Mg, Mn, Na, P, S and Ti contents, indicate lateral and vertical variations that would be related to geomorphological and paleoenvironmental changes and to the basin evolution as well (Fig. 2, Tables 1-3). It is concluded that the limestones are mainly composed of calcite with variable quantities of MgO. These rocks would have been formed in warm lagoons with high P content. At the same time shallower areas with intermittent influx of marine waters would have been developed in other sectors. The increase in the content of Na and K in these sectors would support the idea that these evaporitic deposits were temporarily isolated from the dominant marine environment. Al, Fe, Mn and Ti concentrations would be related to the presence of terrigenous material; however, the scarce contribution to the basin would indicate climatic conditions of aridity with low pluvial regimen. Crossbedding in level 2 is associated to marine currents. The abundance of broken fossils would indicate a highly energy environment. On the tidal flat, the presence of rather thin bioturbation traces (Thalassinoides) would indicate conditions of instability during the development of this ichnofacies, as well as a rather moderate energy with low sedimentation rates. At the final stage, shallow marine, coastal, sedimentation prevail, marked by the abundance of entire shells, cross-bedding and an increment in the Fe and Mn concentration. At the same time in other sectors, the increase in the sulfur content as gypsum, would indicate a sustained SW-NE sea regression.

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4

Petrográfica y Geoquímica de la dolomía hospedante de una mineralización de Zn y Pb. Puesto Gregor, Neuquén, Argentina/ Petrography and geochemistry of a Zn- Pb mineralization hosted in a dolostone, Puesto Gregor, Neuquen, Argentina

Gómez, M. Cristina; Garrido, Mirta; Cesaretti, Nora; Domínguez, Eduardo
2008-07-01

Resumen en español En la Cuenca Neuquina (Argentina) y asociada a la Formación Lajas (Jurásico) se mencionó por primera vez una mineralización de esfalerita y galena asociada a carbonatos. En el área del yacimiento Puesto Gregor, ésta Formación está constituida por una secuencia clástico carbonática. Para caracterizar el ambiente de depositación de la dolomía hospedante de la mineralización de Zn y Pb se realizaron estudios petrográficos y geoquímicos. Entre los últimos los (mas) más utilizados son los análisis e interpretación de isótopos estables (O, C), elementos mayoritarios y trazas e inclusiones fluidas. En el horizonte dolomítico de 0,90 m de espesor y 300 m de corrida se distinguen petrográficamente dos tipos de dolomita: el primer tipo es penetrativo, sin preservación de la fábrica sedimentaria original y es anterior a la mineralización, el segundo tipo está vinculado a la precipitación de sulfuros y consiste en una dolomita de tipo silla de montar (saddle). El estudio de las inclusiones fluidas en la dolomita penetrativa indica la presencia de fluidos orgánicos y fluidos acuosos. Determinaciones microtermométricas sobre inclusiones fluidas acuosas revelaron temperaturas de 140º C. Geoquímicamente la capa presenta proporciones casi estequiométricas y promedios de CaCO3 y MgCO3 iguales al 52 y 48% molar, respectivamente. En cuanto a los elementos trazas, el Sr varió entre 79 y 159 ppm y el Na entre 74 y 225 ppm. Los contenidos de Mn y Fe son mucho más altos que los valores determinados para estos elementos en rocas carbonáticas. El contenido en ETR es bajo y los diagramas de ETR muestran una anomalía negativa de Ce y de Eu. Se determinaron valores de isótopos de C y O. Los valores de ä13 C (VPDB) entre -2,9 y -9 0/00 no son coherentes con los datos informados para calizas marinas de edad jurásica mientras que los valores de ä18O(VPDB) entre -2,6 y -4 0/00 coinciden con los valores informados para carbonatos de igual edad. Los datos de ä18O indican que la interacción entre el fluido y la roca de caja fue baja. Los valores del ä18O del fluido en equilibrio con la dolomía a temperaturas de 140ºC indican que este fluido corresponde a una salmuera de cuenca. Por otro lado, los isótopos de carbono indican un aporte de carbono procedente de la diagénesis de la materia orgánica causada por un aumento de temperatura vinculada al soterramiento de la cuenca. Los resultados petrográficos y geoquímicos son consistentes con la dolomitización de un carbonato de origen marino que sufrió soterramiento. Resumen en inglés In Neuquen Basin, Argentina, a Zn-Pb mineralization was first reported by Garrido et al. (2000). The ore occurs in a carbonatic level located in Puesto Gregor, 50 km SSE from the city of Zapala at 39°11'34'' S, 69° 59'18'' W (Fig. 1). The hosting bed, a dolostone, belongs to a carbonatic-siliciclastic sequence of Lajas Formation, which is part of the Cuyo Group, Jurassic age. In the mineralization of Pb-Zn deposits associated to dolostones, the fluids that were involved (mas) in the ore precipitation process were also related to the dolomitization of the carbonatic rock (Warren, 2000). In this contribution, field, petrographic and geochemical studies were carried out in order to determine the temperature and composition of the dolimitizing fluids. The obtained results were then compared to those obtained from Carbon and Oxygen isotopes (Garrido et al., 2001) to discuss the dolimitization process. The mineralized bed, 0.90 m thick, outcrops for about 300 m along the strike (W-E) and 60 m in the dip direction (Fig. 2). This bed pinches out toward the east and toward the west it is no longer visible, it is cover by scours. Petrographic studies determined that the host rock is a dolostone with a breccia texture that becomes more siliciclastic towards the east grading thus to a fine sandstone with carbonatic cement. The hypogenic mineralization, mainly sphalerite, low quantities of galena, pyrite and marcasite is found within the small fractures. Some ghosts of fossils are still visible, but pervasive dolomitization characterizes the horizon. Two distinct dolomites are recognized by crosscutting relationships: a fine to medium grained crystalline dolomite, and a coarse grained crystalline dolomite related to the mineralization. The fomer shows dark-orange and white crystals which occur as patches or partially filled vugs. These crystals are 120-400 mm in size and exhibit subhedral to anhedral shapes (Fig. 3). According to Sibley and Gregg (1987), the texture is no planar -a- unimodal to polimodal. The latter dolomite presents well developed crystals (> 5 mm); they are translucent with pink color and pearl shine and have crystal faces that look like a pavement and is referred as "saddle" dolomite according to Radke and Mathis (1980). This "saddle" dolomite is found into dissolution cavities or as clusters of crystals located on the wall fractures; it is always associated to the mineralization. Chemical analysis of major, traces and rare earth elements are homogeneous throughout the bed. Mean values are 15% MgO, 29,66% CaO and 40,43 % CO2, with high MnO and Fe2O3 contents. The molar percentages of CaCO3 and MgCO3 indicate near stoichiometric ratio (52% and 48%) with a light excess of Ca (Table 1, Fig. 4). The trace elements Sr, Na, Fe and Mn are used to constrain dolomite evolution. Sr values varies from 79 to 159 ppm and Na from 74 to 225 ppm; Mn and Fe contents are higher than the values determined for carbonatic rocks (Turekian and Wedepohl, 1961). ÓREE and LREE contents are low, and the diagram normalized to chondrite shows a negative anomaly of Eu and a great negative anomaly of Ce. The 13C (VPDB) and 18O (VPDB) values vary from -2,9 to -9(0)/00 and from -2,6 to -4 0/00 respectively (Table 2). The 13C are incoherent with the data recorded for Jurassic marine carbonates (near 0 0/00) while 18O values can be correlated with carbonates of the same age (Veizer et al., 1999). Petrography and chemical analysis allow characterizing the depositional environment of the Zn- Pb mineralized dolostone. The xenotopic texture of the dolomite with no planar crystals, gives evidence that the temperatures of deposition should have been higher than 50-60°C (Gregg and Sibley, 1984). On the other hand, the chemical composition, near ideal dolomites (stoichiometric ratio), indicates slow crystallization at high temperature (Morrow, 1982). Morover, the destructive fabric and the homogeneous composition suggest a high temperature dolomitization (Machel, 2004). Trace element values, mainly Na and Sr, agree with burial dolomites, as well as the fluid inclusions reported for these samples by Cesaretti et al. (2002). The negative Ce anomaly indicates that these rocks were formed in a marine environment. Two different processes of carbonate precipitation can produce negative Ce anomaly (Möller, 1989; Bau and Möller, 1992): deposition from seawater or from hydrothermal solutions equilibrated with highly oxydized sediments. The latter is discarded because of the presence of framboidal pyrite and organic matter, which, along with the Eu negative anomaly indicates that the dolimitization were generated under euxinic conditions. This dolostone is in contact with anoxic mudstones (Los Molles Formation, Cuyo Group). Petrographic and geochemical criteria reflect that the dolomitization were caused by normal or modified sea water in a burial environment at temperatures above 140ºC. In burial or altered dolostones, the oxygen isotopes reflect temperature of precipitation and isotope composition of the dolomitizing fluids. The oxygen isotope values of this dolomitized bed are compatible with the isotope composition of carbonates precipitated from sea water at 25°C. The narrow range in the obtained values indicates that there was no influence of meteoric water during this process (Allan and Mathews, 1982). The homogeneous values of 18O isotope suggest that the physic-chemical conditions remained constant during dolomitization, what is in agreement with the textural and geochemical homogeneity found in the study samples. The 18O isotope values of a fluid equilibrated with carbonate at 140°C indicate that the fluid belongs to a basinal fluid. The 13C isotopes reflect an organic origin for the carbon. This carbon came from the diagenesis of organic matter caused by an increase in temperature during the burial of the basin (Garrido et al., 2001; Cesaretti et al., 2002). In contrast with other MVT deposits of the world, in Puesto Gregor, the dolomitization was slow process acting at high temperatures, what has been confirmed by the homogeneity of the fabric and the narrow range in the isotope and trace elements composition. These conditions were reached during burial of the basin where the rocks interact with the basin fluids associated to the ore minerals.

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Lutitas negras lacustres cercanas al límite Paleógeno-Neógeno en la región noroccidental de la provincia del Neuquén: Evidencias palinológicas/ Lacustrine black shales near to the Paleogene - Neogene boundary in north-western Neuquén Province: palynological evidence

Leanza, H. A.; Volkheimer, W.; Hugo, C. A.; Melendi, D. L.; Rovere, E. I.
2002-09-01

Resumen en español Se muestrearon con fines palinológicos sedimentitas lacustres referidas a la Formación Lileo nov. aflorantes en las cercanías de la localidad de Los Miches, en el noroeste de la provincia del Neuquén, República Argentina. Sobre la base del análisis microflorístico las capas portadoras de palinomorfos pueden asignarse al Oligoceno Tardío - Mioceno Temprano. Las rocas muestreadas se caracterizan por lutitas negras, gris verdosas, gris oscuras y castaño claras, alte (mas) rnando con niveles delgados, a veces oolíticos de calizas gris claras, con superficie de meteorización blanco amarillenta. Entre estas sedimentitas se intercalan andesitas, tobas y aglomerados volcánicos de composición mesosilícica. En los afloramientos del área del río Guañacos se observan capas irregulares de carbonato fibroso tanto como baritina nodular con estructura fibroradial, junto con bivalvos indeterminados de agua dulce. La asociación microflorística muestra relativamente baja diversidad. En general, el género Nothofagidites domina la asociación. Los componentes principales de la microflora consisten en granos de polen pertenecientes a varios taxones de angiospermas, tales como Baumannipollis sp. cf. B. variaperturatus, Corsinipollenites atlantica, Milfordia sp., Nothofagidites saraensis, Smilacipites sp. cf. S. echinatus and Tricolpites asperamarginis junto con granos de polen de angiospermas de Araucariacites australis, Equisetosporites notensis y Podocarpidites spp. Los elementos de Pteridophyta/Bryophyta están representados por Cyatheacidites annulatus, Cicatricosisporites sp., Deltoidospora sp., Lycopodiumsporites austroclavatidites, Ricciaesporites sp. y Laevigatosporites ovatus, mientras que entre los taxones lacustres se reconocieron Azolla sp. y Botryococcus sp. (Chlorophyta). Resumen en inglés Lacustrine sedimentary rocks referred to the Lileo Formation nov. cropping out near Los Miches locality, northwestern Neuquén Province, Argentine Republic, were sampled for palynological study. On the basis of the microfloristic analysis, the palynomorph-bearing beds can be ascribed a Late Oligocene to Early Miocene age. The sampled rocks are black, grey-green, dark grey and light brown shales alternating with thin,locally oolithic, light grey limestones, with yellowish (mas) white weathering. Among these rocks are interbedded andesites, tuffs, and volcanic agglomerates of mesosilicic composition. In the outcrops of the Guañacos river area, some irregular beds of fibrous carbonate have been observed as well as fibroradial nodular barite, together with some indeterminate fresh-water. The microfloristic assemblages have a relatively low diversity. In most of them the genus Nothofagidites dominates the association. The components present in the microflora are pollen grains corresponding to several angiosperm taxa, such as Baumannipollis sp. cf. B. variaperturatus, Corsinipollenites atlantica, Milfordia sp., Nothofagidites saraensis, Smilacipites sp. cf. S. echinatus and Tricolpites asperamarginis together with gymnosperm pollen grains of Araucariacites australis, Equisetosporites notensis and Podocarpidites spp. The Pteridophyta/Bryophyta elements are represented by Cyatheacidites annulatus, Cicatricosisporites sp., Deltoidospora sp., Lycopodiumsporites austroclavatidites, Ricciaesporites sp. and Laevigatosporites ovatus, whereas among the lacustrine taxa Azolla sp. and Botryococcus sp. (Chlorophyta) were recognized.

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Travertinos y jasperoides de Manantial Espejo, un ambiente Hot Spring Jurásico: Macizo del Deseado, Provincia de Santa Cruz, Argentina/ Travertines and jasperoids of the Manantial Espejo, a Jurassic hot spring environment: Macizo del Deseado, Santa Cruz Province, Argentina

Echeveste, Horacio
2005-07-01

Resumen en español En este trabajo se analiza el origen y las relaciones entre travertinos y jasperoides intercalados en rocas volcaniclásticas jurásicas en el distrito argento-aurífero Manantial Espejo, ubicado en el borde sur-occidental del Macizo del Deseado, provincia de Santa Cruz, Argentina. Los cuerpos de travertino constituyen estratos delgados de hasta 60 cm de espesor de calcita micrítica finamente laminada, en ocasiones con estratificación rítmica de calcita y ópalo, asoci (mas) ados a depósitos de tobas de caída y tufitas de ambiente lacustre. En algunos afloramientos, los morfotipos reconocidos revelan que la precipitación del carbonato correspondía a sectores proximales relacionados a geisers y conductos de vapor, los cuales se orientaban a los largo de las fracturas que constituyeron los canales de circulación de fluidos. La posterior silicificación de los niveles carbonáticos produjeron jasperoides que se presentan como cuerpos tabulares subverticales y subhorizontales, estos últimos con características texturales similares a aquellas de sinters. La silicificación se originó tardíamente, posiblemente durante la etapa principal del régimen hidrotermal que generó las vetas portadoras de plata y oro. Los travertinos se formaron en un ambiente de hot spring, relacionado con fracturas de un sistema de cizalla conjugado orientadas entre N 20° a 45° E y N 20° a 40° O y constituyen las evidencias más tempranas de la presencia de un régimen epitermal asociado al proceso volcánico jurásico, en un régimen tectónico distensivo, en Manantial Espejo. Resumen en inglés In the last few years, an intense mining prospecting activity for gold and silver epithermal deposits has been carried out in the Deseado Massif, Argentina. As a result, many hot spring related deposits, of possible Jurassic age, have been detected. This paper describes the mineralogical and textural characteristics as well as the facies of a group of travertine and jasperoid outcrops occurring near the silver-gold carrying lodes in the Manantial Espejo prospect (Schalamu (mas) k et al., 1998). A genetic interpretation of the deposits is done on the basis of their structural, textural, and emplacement characteristics. Their possible relationship with the epithermal mineralization is also considered. The Manantial Espejo district is located on the southwestern area of the Deseado Massif, in the middle of the province of Santa Cruz (Fig.1). The area is almost entirely covered by andesitic and rhyolithic rocks of the Bajo Pobre and Chon Aike Formations, the product of a strong, bimodal volcanic activity of Jurassic age. This volcanic event developed in a back-arc tectonic environment linked to the opening of the Atlantic Ocean (Uliana et al., 1985; Riley et al., 2001). Acidic rocks prevail in the area, consisting on high-grade ignimbrites with ash fall tuffs, tuffites, and hydroclastic breccias (Fig. 2). Among them, the chemical and biogenic carbonate and silica deposits, are present (Fig.3). The travertine mantles can be up to 0.5 m thick and, in most of cases, they overlie tuffite layers. Typically, the rock is laminated in millimetrical to submillimetrical laminae of dense, hard, non porous micritic carbonate, displaying three types of lamination: parallel sub-horizontal; stromatolithic; and, «en echelon» (possibly, a terrace facies, Fig. 4). Sometimes, the laminated structure consists of a rhythmic deposit of calcium carbonate and opal (Figs. 5 a, b), unusual association in hot spring deposits, both recent and fossil (Jones et al., 2000a; Campbell et al., 2002; Canet et al., 2005). A variety of porous travertine, dominated by small, sub-spherical and columnar growths, of the microstromatolithic or the oncoid types. The travertine layers grade laterally to siliceous laminated jasperoids (sensu Spur, 1898 and Lovering, 1972), which make sub-horizontal mantles, 0.5 to 2.0 m thick, with identical sedimentary structures as those of travertines, although they are entirely formed of chalcedony, which is interpreted as the product of replacement of calcite into silica (Fig. 6a, b). Silicification occurred at a later stage, during the intense hydrothermal alteration accompanying the formation of the quartz veins carrying gold and silver. Some jasperoid outcrops show grossly stratified, rounded surfaces with domical structures, forming banks 0.2 to 0.4 m thick, and showing a more or less concentric layout which could correspond to the silicification of bio-built algal structures (Fig. 6b). The occurrence of small vents (Fig. 6e) show the water and steam outlets. Vertical, tabular, laminated bodies, filling fractures of NE-SW strike and slip up to 1,000 m, and 3 m thick (Fig. 6f, h). They are formed of chalcedony, displaying a vertical, banded and, at times, diffuse (Fig. 6g) or breccia like structure. The morphology of the travertines and associated jasperoids in the Manantial Espejo district are compared with travertines or hot spring deposits in general, of Quaternary or Recent (Guo and Riding, 1999; Chafetz and Guidry, 2003; Hancock et al., 1999). The analogies founded allowed to reconstruct, at least in part, the depositional environment of the studied rocks (Fig. 8). The sub-vertical, tabular bodies of banded silica, would correspond to subsurface levels of fissure ridges, where erosion has generally eliminated the surface deposits with sub-horizontal stratification overlying the faults. The northernmost end of the Ayelen Oeste «vein» (Fig. 6h) would correspond to the proximal zone of the discharge channel, very close to the fissure, since part of the sub-horizontal stratification next to the fracture (zone B in Fig. 8). This area represents the most active depositional environment, where the carbonate precipitation rate is higher. Figure 6e shows a fluid outlet vent in a spring zone (zone C, in Fig. 8). The «en echelon» stratification shows very similar characteristics to those of terraces and micro-terraces occurring in modern hot springs. Micro-terraces shown in Figure 5e, found near one of the fissure crests, could correspond to those formed laterally to the outlet channels (D, in Fig. 8). As to that shown in Figure 5f, associated to travertine with sub-horizontal, parallel lamination, could correspond to that formed in the edges of pools. With regard to the parallel lamination of micritic carbonate, occurring in most of the outcrops, it may correspond to the lacustrine rims (sensu Pentecost, 1995). This type of thin lamination, forming laterally extended banks, several tens of decimeters thick, would have formed on depressed surfaces, with a distal position relative to the spring zones. The rhythmic intercalation of thin opal laminae between the calcite layers occurring in some outcrops, reveals temporary changes in the physical-chemical conditions of the mineral precipitation, possibly seasonal temperature fluctuations. Finally, the observed stromatolites and microstromatolites (Fig. 5c, g, h) indicate the presence of microorganisms in the geothermal environment. Although there is no agreement among researchers about the organic or inorganic origin of these morphotypes in geothermal environments, it is admitted that algae and bacteria induce the precipitation of calcium carbonate. The stratigraphic position of the calcareous levels identified in Manantial Espejo show that the hot spring environment began to develop early in the district, associated to an extensional tectonic regime coincident with the La Frisia or Zanjón del Pescado System (Reimer et al., 1996) which caused fracturing (direct faults) N 20° to 45º E, and N 20º to 40° W, as a consequence of aó1 located around 0°. The produced faults, made the main hydrothermal fluid circulation channels (barren) which, after reaching the surface and losing the dissolved CO2, precipitated the calcium carbonate. The migration of the maximum stress (anti clockwise, at 315°) produced a new stress field, the Bajo Grande System (Panza, 1982, 1984) generating direct faulting combined with dextral movement, at a 110° azimuth, cutting and displacing the subvertical travertine bodies. These new fluid circulation channels end up lodging the quartz veins carrying silver and gold.

Scientific Electronic Library Online (Spanish)

7

The weathering action of saxicolous lichens in maritime Antarctica

Ascaso, Carmen; Sancho, Leopoldo G.; Rodríguez Pascual, C.
1990-01-01

Digital.CSIC (Spain)

8

The Drama basin water: quality and peat/lignite interaction

Georgakopoulos, Andreas; Fernandez-Turiel, J. L.; Christanis, K.; Kalaitzidis, S.; Kassoli-Fournaraki, Anna; Llorens, J. F.; Filippidis, Anestis; Gimeno, D.
2001-01-01

Digital.CSIC (Spain)

11

Structural characterization of kerogen in 3.4 Ga Archaean cherts from the Pilbara Craton, Western Australia

Marshall, Craig P.; Love, Gordon D.; Snape, Colin E.; Hill, Andrew C.; Allwood, Abigail C.; Walter, Malcolm R.; Van Kranendonk, Martin J.; Bowden, Stephen A.; Sylva, Sean P.; Summons, Roger E.
2007-05-05

Digital.CSIC (Spain)

12

Soil characteristics on varying lithological substrates in the South Shetland Islands, maritime Antarctica

Navas Izquierdo, Ana; López-Martínez, Jerónimo; Casas Sáinz de Aja, José; Machín Gayarre, Javier; Durán, Juan José; Serrano, Enrique; Cuchí, J. A.; Mink, Sandra
2008-03-15

Digital.CSIC (Spain)

15

Sandstone petrofacies in the northwestern sector of the Iberian Basin

Arribas, J.; Ochoa, M.; Mas, R.; Arribas, Mª E.; González-Acebrón, L.
2007-01-01

Digital.CSIC (Spain)

17

Role of fluid mixing in deep dissolution of carbonates

Corbella, M. ; Ayora, Carlos

The presence of cavities filled with new minerals in carbonate rocks is a common feature in oil reservoirs and lead-zinc deposits. Since groundwater equilibrates rapidly with carbonates, the presence of dissolution cavities in deep carbonate host rocks is a paradox. Two alternative geochemical proce...

DRIVER (Spanish)

20

Perfiles paleokársticos en el techo de la unidad intermedia del mioceno de la cuenca de Madrid

Cañaveras, J. C.; Sánchez-Moral, S.; Ordóñez, S.; Calvo Sorando, J. P.
2003-08-30

Digital.CSIC (Spain)

23
25

Neogene structures overprinting Palaeozoic thrust systems in the Andean Precordillera at 30°S latitude

Alvarez-Marrón, Joaquina; Rodriguez-Fernandez, Luis Roberto; Heredia, Nemesio; Busquets, Pedro; Colombo Piñol, Ferrán; Brown, Dennis
2006-12-01

Digital.CSIC (Spain)

26
28

Mesozoic palaeogeographic evolution of the External Zones of the Betic Cordillera

García-Hernández, M.; López-Garrido, A. C.; Rivas, Pascual; Sanz de Galdeano, Carlos; Vera, Juan Antonio
1980-01-01

Digital.CSIC (Spain)

33

Las Orogénesis del Paleozoico Inferior en el margen protoandino de América del Sur, Sierras Pampeanas, Argentina.

Pankhurst, R. J.; Galindo, C.; Baldo, Eduardo G.; Casquet, C.; Dahlquist, J.; Rapela, C.W.; Saavedra Alonso, Julio
2001-01-01

Digital.CSIC (Spain)

34

Las Orogénesis del Paleozoico Inferior en el margen protoandino de América del Sur, Sierras Pampeanas, Argentina.

Pankhurst, Robert J.; Galindo, Carmen; Baldo, Eduardo G.; Casquet, C.; Dahlquist, J.; Rapela, Carlos W.; Saavedra Alonso, Julio
2001-01-01

Digital.CSIC (Spain)

35

Ladinian carbonates of the Cabo Cope Unit (Betic Cordillera, SE Spain): a tethys-maláguide palaeogeographic gateway.

Pérez-López, Alberto; López-Garrido, A. C.; Márquez-Aliaga, Ana; Sanz de Galdeano, Carlos; García-Tortosa, Francisco Juan
2003-12-01

Digital.CSIC (Spain)

36

La Plataforma de Tortosa (Cuenca Catalana) durante el Jurásico Medio: unidades litoestratigráficas, paleogeográficas y ciclos ambientales

Aurell, Marcos; Fernández-López, S. R.; García-Joral, F.; Gómez Fernández, J. J.; Henriques, M. H. P; Martínez, G.; Meléndez, Guillermo; Suárez Vega, L. C.
1998-01-01

Digital.CSIC (Spain)

37

In situ evaluation of the biodeteriorating action of microorganisms and the effects of biocides on carbonate rock of the Jeronimos Monastery (Lisbon)

Ascaso, Carmen; Wierzchos, Jacek; Souza-Egipsy, Virginia; Ríos, Asunción de los; Delgado Rodrigues, J.
2002-01-01

Digital.CSIC (Spain)

38

Improvements in soil quality and performance of mycorrhizal Cistus albidus L. seedlings resulting from addition of microbially treated sugar beet residue to a degraded semiarid Mediterranean soil

Alguacil García, María del Mar; Caravaca Ballester, María Fuensanta; Azcón González de Aguilar, Rosario; Pera, J.; Díaz, G.; Roldán Garrigos, Antonio
2003-09-01

Digital.CSIC (Spain)

39

Igneous Origin of CO2 in Ancient and Recent Hot-Spring Waters and Travertines from the Northern Argentinean Andes

Gibert, Roger O.; Taberner, Conxita; Sáez, Alberto; Giralt, Santiago; Alonso, Ricardo N.; Edwards, R. Lawrence; Pueyo Mur, Juan José
2009-01-01

Digital.CSIC (Spain)

40

Gypsum, a Tricky Material

Herrero Isern, Juan; Artieda, Octavio; Hudnall, W. H.
2009-09-01

Digital.CSIC (Spain)

41

Gypsum, a Tricky Material

Herrero Isern, Juan; Artieda, Octavio; Hudnall, W. H.
2009-11-01

Digital.CSIC (Spain)

42

Glauconite and phosphate peloids in Mesozoic carbonate sediments (eastern Subbetic Zone, Betic Cordilleras, SE Spain)

Jiménez-Millán, Juan; Molina, José Miguel; Nieto, F.; Nieto, L. M.; Ruiz-Ortiz, P. A.
1998-12-01

Digital.CSIC (Spain)

46

Estudios mineralógénicos en el borde granítico de Linares de Riofrio-Fuentes de Bejar (Salamanca)

Saavedra Alonso, Julio; Pellitero Pacual, E.; Egido Manzano, Moises; Sánchez Hernández, M.
1975-01-01

Digital.CSIC (Spain)

51

El Jurásico de Mallorca (Islas Baleares)

Álvaro, M.; Barnolas, A.; Cabra, P.; Comas-Rengifo, M. J.; Fernández-López, S. R.; Goy Goy, A.
1989-01-01

Digital.CSIC (Spain)

55

Deteriorating effects of lichen and microbial colonization of carbonate building rocks in the Romanesque churches of Segovia (Spain)

Ríos, Asunción de los; Cámara, Beatriz; García del Cura, M.ª Ángeles; Rico, Víctor J.; Galván, Virginia; Ascaso, Carmen
2009-01-15

Digital.CSIC (Spain)

59

Cinética de carbonatación de morteros experimentales de cal de tipo romano

Sánchez-Moral, S.; García Guinea, Javier; Luque, L.; González-Martín, R.; López-Arce, Paula
2004-09-30

Digital.CSIC (Spain)

60

Caracterización de los lignitos garumnienses del Pirineo Central catalán.

García-Vallés, M.; González-Prado, J.; Vendrell-Sanz, M.
1993-01-01

Digital.CSIC (Spain)

61

Cambrian small shelly fossils from the Çal Tepe Formation, Taurus Mountains, Turkey | «Small shelly fossils» del Cámbrico en la Formación Çal Tepe, Montes Taurus, Turquía

Sarmiento, Graciela N. ; Fernández-Remolar, David ; Göncüoglu, M. Cemal

[EN] Lower and Middle Cambrian carbonate rocks of the Çal Tepe Formation, cropping out in the western Taurus Mountains, yieldeda large number of microfossil remains. Small shelly fossils from a single level in the upper Lower Cambrian represent a high diversitybiota that could be related to the «C...

DRIVER (Spanish)

62

Cambrian small shelly fossils from the Çal Tepe Formation, Taurus Mountains, Turkey

Sarmiento, Graciela N.; Fernández-Remolar, David; Göncüoglu, M. Cemal
2001-01-01

Digital.CSIC (Spain)

64

Análisis y distribución de facies del Cretácico inferior del Prebético en la provincia de Alicante

Company, M.; García-Hernández, M.; López-Garrido, A. C.; Vera, Juan Antonio; Wilke, H.
1982-01-01

Digital.CSIC (Spain)