Sample records for MEDIO AMBIENTES DEL SUBSUELO (subsurface environments)
from WorldWideScience.org

Sample records 1 - 12 shown.



1

Very high-resolution seismo-acoustic imaging of seagrass meadows (Mediterranean Sea): Implications for carbon sink estimates

Lo Iacono, Claudio; Mateo, Miguel Angel; Gràcia i Mont, Eulàlia; Guasch, Lluis; Carbonell, Ramón; Serrano, Laura; Serrano, Oscar; Dañobeitia, Juan José
2008-09-01

Digital.CSIC (Spain)

2

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)

3

Sísmica de reflexión de alta resolución en el estudio del Cuaternario de áreas de pie de monte/ Shallow, high-resolution seismic reflection in the study of the Quaternary in foothill areas

González Bonorino, G.; Boyce, J. I.; Koseoglu, B. B.
2003-03-01

Resumen en español Se realizaron varias pruebas piloto con sísmica de reflexión de baja profundidad en depósitos de abanicos aluviales distales en la provincia de Salta, Argentina. Las pruebas incluyen dos áreas con características de subsuelo contrastantes. En el sector nororiental de la provincia, los depósitos del extenso abanico aluvial del Bermejo son arenosos y macizos, casi sin intercalaciones arcillosas; la napa se encontraba a más de 40 m de profundidad al tiempo del estudio (mas) . La otra zona de prueba se ubica al sur de la ciudad de Salta, donde coalescen abanicos aluviales pequeños que rellenan el valle de Lerma con depósitos de arena y grava, los cuales en los tramos distales se interdigitan con potentes capas arcillosas; la napa en esta área se hallaba a una profundidad mayor de 20 m al momento del estudio. La operación sísmica empleó un sismógrafo Geometrics R24 con 24 canales activos que se aumentaron a 48 mediante un "roll-over switch", alcanzando un máximo de cobertura de 1200%. Se probaron dos fuentes de sonido: una masa de 5 kg y una escopeta calibre 12. Principalmente por razones operativas se eligió como fuente la masa. Las pruebas en el abanico del Bermejo dieron registros de baja calidad, probablemente debido a la rápida pérdida de energía en las areas poco consolidadas y secas. Localmente, sin embargo, pudieron distinguirse tres unidades sísmicas y el techo del Terciario posiblemente fue detectado. Las pruebas en eje del valle de Lerma dieron registros sísmicos de excelente calidad. Se distinguieron cuatro unidades sísmicas. Un reflector débil a aproximadamente 220 mseg coincide con un cambio de las velocidades a unos 2500 m/seg y puede corresponder con el techo del sustrato terciario. Una potente capa de arcilla a una profundidad de 25 a 50 m puede claramente mapearse como un acuitardo. Los resultados de este estudio piloto demuestran que la sísmica de reflexión de poca profundidad puede ser aplicada con provecho en el noroeste de la Argentina para obtener imágenes del subsuelo en ambientes de abanicos aluviales distales. Resumen en inglés Several trial shallow seismic reflexion surveys were carried out in distal alluvial fan settings in Salta Province, Argentina. The tests span two areas with contrasting subsurface characteristics. In the north-eastern sector of the province, the extensive Bermejo alluvial fan deposits are sandy and massive, with almost no clay intercalations; the water table in this area was located below a depth of 40 m at the time of the survey. The other survey area is located south of (mas) Salta City, where small, coalescing alluvial fans fill the Valle de Lerma with sandy and gravelly deposits that in the distal, axial reaches interfinger with thick clayey beds; the water table in this area was located below a depth of 20 m at the time of the survey. Seismic operation involved a Geometrics R24 seismograph with 24 active channels that were incremented to 48 using a roll-over switch, providing a maximum 1200% subsurface coverage. Two seismic source types were tested: a 5 kg sledge hammer and a 12-gauge down-hole seismic gun. Mainly due to operational considerations the hammer source was finally chosen. Tests on the Bermejo fan generally resulted in poor quality seismic records, likely due to rapid loss of energy through the unconsolidated, dry sands. Locally, however, three seismic units could be distinguished and the top of the Tertiary bedrock was possibly mapped. Tests along the axis of the Valle Lerma resulted in excellent quality seismic records. Four seismic units were distinguished. A weak reflector at about 220 msec marks a shift to velocities of around 2500 m/s and may correspond with the top of Tertiary bedrock. A thick clay unit at 25-50 m depth can be clearly mapped and acts as an aquitard. The results of this pilot study show that shallow seismic reflection can be applied profitably in NW Argentina for subsurface imaging in distal alluvial fan environments.

Scientific Electronic Library Online (Spanish)

7

Seafloor characterization and backscatter variability of the Almería Margin (Alboran Sea, SW Mediterranean) based on high-resolution acoustic data

Lo Iacono, Claudio; Gràcia, Eulàlia; Díez, Susana; Bozzano, Graziella; Moreno, Ximena; Dañobeitia, Juan José; Belén, Alonso
2008-04-21

Digital.CSIC (Spain)

8

MedArgo: a drifting profiler program in the Mediterranean Sea

Poulain, P. M.; Barbanti, R.; Font, Jordi; Cruzado, Antonio; Millot, C.; Gertman, I.; Griffa, A.; Molcard, A.; Rupolo, V.; Le Bras, S.; Petit de la Villeon, L.
2007-08-08

Digital.CSIC (Spain)

9

Management of Alluvial Aquifers in Two Southern African Ephemeral Rivers: Implications for IWRM

Benito, Gerardo; Rohde, Rick; Seely, M.; Kulls, C.; Dahan, O.; Yehouda, Enzel; Todd, Simon; Botero, Blanca; Morin, Efrat; Grodek, T.; Roberts, Carole
2009-05-26

Digital.CSIC (Spain)

10

Geología y fracturas en la estructura San Pedro, sierra del Alto Río Seco, Sierras Subandinas, provincia de Salta/ Geology and fractures in the San Pedro Structure, Sierra Alto del Río Seco, Sierras Subandinas, Province of Salta

Di Marco, L.
2005-12-01

Resumen en español La estructura San Pedro se encuentra en el sector central-septentrional de la unidad morfo-estructural de Sierras Subandinas. Su columna estratigráfica esta caracterizada por una compleja historia geológica en la que se superponen varias cuencas sedimentarias con distinto origen, con un relleno total de más de 10.000 m de espesor y desarrolladas en diferentes edades geológicas y bajo distintos ambientes. El yacimiento San Pedrito (niveles devónicos), ubicado en el bl (mas) oque Acambuco de la cuenca de Tarija puede ser estudiado en principio como un reservorio naturalmente fracturado por el carácter del fracturamiento y fallamiento que presentan las rocas reservorio. Siguiendo esta dirección de pensamiento, se realizó un estudio de fracturas, concentrando la atención en las Formaciones Las Peñas y San Telmo para luego intentar una posible vinculación con las unidades de subsuelo que componen las rocas reservorios del yacimiento San Pedrito. El solapamiento de las zonas de mayor intensidad de fracturas en superficie con las que presentan los mayores valores de producción acumulada del yacimiento San Pedro (niveles carboníferos) demuestra que la deformación sufrida por todo el carbonífero como un solo paquete unitario fue desarrollada en forma coherente. Y que si bien los depósitos carboníferos pueden presentar discontinuidades menores, la deformación tectónica no llego a desacoplar mecánicamente los depósitos del Carbonífero superior e inferior. Las fracturas perpendiculares a la estructura (Tipo I) hallan sus valores de mayor intensidad en las secciones crestales, y las paralelas a la estructura (Tipo II) lo hacen en las secciones del limbo frontal. Este último juego guarda una próxima relación con la curvatura modelada y con los datos de producción acumulada de los pozos pertenecientes al yacimiento San Pedro. Resumen en inglés The San Pedro structure is located at the north-central section of the Subandean Ranges morphostructural unit. Its stratigraphic column is characterized by a complex geologic history and a over position of a different origins sedimentary basins , with a total backfill of more than 10,000 m developed at different geological ages and under different environments. The San Pedrito reservoir (Devonian levels) located at the Acambuco Block of the Tarija Basin can be studied lik (mas) e a naturally fractured reservoir due to the fracturing and faulting features present in the the anticline core. A fracture study has been done, focused on Las Peñas and San Telmo Formations outcrops to analyze the links with subsurface units (Carboniferous basal levels) which compose the reservoir rocks of the San Pedro field. The overlap of major zones of intense fractures on surface with high accumulated production values permit to postulate that the deformation affected all Carboniferous deposits like a single package developed in a consistent way. The Carboniferous deposits may show minor discontinuities but the tectonic stress does not decouple the upper and lower Carboniferous deposits. The orthogonal fractures (type I) have their major intensity values at the ridge sections and the parallel fractures (type II) have their mayor intensity values at the forelimb sections. This last set keeps a close relationship with the bend fold model and to the accumulated production of the San Pedro Oil field.

Scientific Electronic Library Online (Spanish)

11

Fraccionamiento químico de carbono en Acrisoles con hori­zontes sómbricos del Sur de Brasil/ Chemical fractionation of carbon on Acrisols with sombric horizon from South Brazil

Velasco-Molina, M.; Almeida, J.A.; Vidal-Torrado, P.; Macías, F.
2010-01-01

Resumen en español Los horizontes sómbricos (subsuperfi­ciales, oscuros y con mayor contenido de C) tienen una génesis escasamente cono­cida, pudiendo funcionar como sumideros de C en condiciones subtropicales. En dos Acrisoles del Estado de Santa Catarina (S-Brasil) se ha comprobado que la máxima acumulación de formas de C ligadas a Fe y Al extraíbles con pirofosfato y oxalato se presenta en horizontes sómbricos, pero que ésta no está relacionada con procesos de podsolización, a (mas) ndosolización, solodi­zación o acumulación de C por condicio­nes de hidromorfía subóxica. La mayor parte de su C se presenta en formas de oxidabilidad intermedia (oxidable con K2Cr2O7, en frío, pero no con KMnO4 0,2 M). Los porcentajes de C recalcitrante (no oxidable o díficilmente oxidable) son sig­nificativos (20-45%) pero variables a pe­queñas distancias. Procesos ligados a cambios de uso del suelo con diferente lo­calización del aporte de necromasa y efec­tos de incendios de la vegetación parecen ligados a su formación. Resumen en inglés Sombrics horizons (subsurface, dark and with a high content of C) have a genesis poorly understood and can be conceived as a potential sink of C in subtropical envi­ronments. The maximum accumulation of C bound to Fe and Al extracted by pyrophos­phate and oxalate solution was observed in sombric horizons of two Acrisols of Santa Catarina State (S-Brazil), but this is not in­dicative of podzolisation, andosolisation or solodisation processes or accumulation of C due hyd (mas) romorphy conditions. Most of its C was found at intermediate wet oxidisable fraction (oxidisable with K2Cr2O7, cold, but not by KMnO4). Recalcitrant C (non­oxidisable and difficult oxidisable) was an important pool (20-45%), but variable into profile. Changes on land use with different input of necromass and vegetations fire ef­fects seem to be involved in its formation.

Scientific Electronic Library Online (Spanish)

12

Factors affecting linear alkylbenzene sulfonates removal in subsurface flow constructed wetlands

Huang, Yuming; Latorre Fernández, Anna; Barceló, Damià; García, Joan; Aguirre, Paula; Mujeriego, Rafael; Bayona Termens, Josep María
2004-03-20

Digital.CSIC (Spain)