Structural interpretation of the northern flatslab zone from magnetic data. Precordillera of San Juan and La Rioja [Interpretación estructural del sector norte del flatslab pampeano a partir de datos magnéticos. Precordillera de San Juan y La Rioja]
Sanchez M.A.,CONICET |
Folguera A.,Institute Estudios Andinos Don Pablo Groeber |
Martinez M.,CONICET |
Geoacta (Argentina) | Year: 2016
The Andean region between -28° to -31° of latitude included the transition of geological provinces: Front Range, Western Sierras Pampeanas and Precordillera in the provinces of San Juan and La Rioja. The geological evolution and the compressive tectonic regime in the area could have made its mark in areas where micro-continents collided and amalgamated, identified as suture zones. From a base of magnetic data collected from different types (air and land) sources and acquired at different times, a series of geophysical reductions in order to obtain a single homogeneous database was applied. At the map of Total Magnetic Anomaly obtained, we applied two different methods of filtering: Analytic Upward Continuation and Frequency. Finally, on cross sections toward East - West, solutions from 2D Werner deconvolution - with results consistent with the existing models for Precordillera and it structure - were calculated. We have interpreted the arrangement of units with different magnetic susceptibility correlating these with the configuration of Paleozoic "terranes" amalgamated in this region. The location of Werner solutions allowed us to recognize the behavior in depth of the exposed structures. © 2015 Asociación Argentina de Geofísicos y Geodestas.
Comerio M.,Institute Estudios Andinos Don Pablo Groeber |
Comerio M.,CONICET |
Morosi M.E.,CONICET |
Tunik M.,National University of Rio Negro |
And 3 more authors.
Canadian Mineralogist | Year: 2014
We report the occurrence of dawsonite, NaAlCO3(OH)2, in volcaniclastic rocks of the Albian hydrocarbon reservoir Castillo Formation, Golfo San Jorge Basin, neighboring the Cañadón Asfalto Basin in Patagonia; this is the first known occurrence in Argentina. Dawsonite replaces crystals pseudomorphically, and can also be found as a cement together with other carbonates, which induced a loss in the porosity of the host rock. Previous studies reported incomplete chemical reactions which suggested that oligoclase and analcime were dawsonite precursors. In the present work we document either totally achieved or incomplete chemical reactions which led to the transformation of analcime into kaolinite and dawsonite into kaolinite, respectively. These facts allowed us to deduce that the transformation of analcime into kaolinite was via dawsonite, minerals formed during different stages under a telogenetic regime. Dawsonite values of δ13C PDB (-0.1 to 1.5‰) are consistent with a magmatic source of CO2 provided by hypabyssal, basic alkaline igneous rocks of regional importance starting in the Eocene. We identify both internal and external sources of Na and Al used in the formation of dawsonite.
Chapori N.G.,Institute Estudios Andinos Don Pablo Groeber |
Laprida C.,Institute Estudios Andinos Don Pablo Groeber |
Watanabe S.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia |
Totah V.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia |
Violante R.A.,Servicio de Hidrografia Naval
Micropaleontology | Year: 2014
In the Atlantic sector of the Southern Ocean up to 35°S, Neogene benthic foraminiferal faunal changes have been interpreted, alternatively, as changes in deep water-masses distribution and organic matter availability, in surface, the Southwestern South Atlantic presents a highly dynamic frontal zone and exhibits large spatial and temporal variability in primary productivity that influences the export of organic carbon from the euphotic zone. However, below ∼1000 meters depth, it is characterized by the interaction of several water masses. For this reason, the western sector of the South Atlantic is a natural laboratory to test the benthic foraminifera's response to changes in both, the deep water-masses distribution and the exported productivity, in order to define which was the main factor controlling the benthic foraminiferal assemblages structure during a glacial Mid-Late Pleistocene event, abundance analysis of organic matter content, oxygen availability and water masses marker species, and Q-mode factor analysis were carried out on core SP1251 (3400m; ∼3S°S - 54°W). Our results indicate that the benthic foraminiferal assemblages are mainly composed of high organic matter and oxygen availability-associated species revealing that productivity has been the main factor in determining the stracture of the assemblages' composition. These results also reflect that surface productivity regime would have not been uniform as a result of variations in the shelfbreak up welling of Patagonia as a consequence of variations in the Antarctic upwelling.
Gonzalez P.D.,CONICET |
Gonzalez P.D.,National University of Rio Negro |
Tortello M.F.,CONICET |
Damborenea S.E.,CONICET |
And 3 more authors.
Geological Journal | Year: 2013
In South America, autochthonous archaeocyathan faunas preserved in Early Cambrian limestones have not been found yet. Nevertheless, a few well-documented occurrences of these fossils in clasts contained in coarse-grained rocks of a wide age range have been discovered in recent years. Erratic limestone blocks from the Late Carboniferous-Early Permian Fitzroy Tillite Formation in the Falkland/Malvinas Islands yielded three archaeocyath taxa. Also, seven taxa were reported from archaeocyathan limestone clasts in a metaconglomerate of the Cambro-Ordovician El Jagüelito Formation in northern Patagonia. In addition, a new record from the Late Carboniferous-Early Permian Sauce Grande Formation diamictites in Sierras Australes, Buenos Aires Province, Argentina, is presented herein. Preservation of this scarce new material is poor, but at least three different taxa can be distinguished. The most likely source of all archaeocyathan limestone clasts found in southern South America is the Shackleton Limestone from the Transantarctic Mountains in East Antarctica. The new record from the Sauce Grande Formation and the inferred clast provenance reinforce the correlation between this unit, the Dwyka Tillite (South Africa) and the Fitzroy Tillite Formation (Falklands/Malvinas), suggesting a very wide distribution of these Antarctic occurrences during the Late Carboniferous-Early Permian Gondwana glaciation (Episode III). Thus, even though being allochthonous, archaeocyaths are emerging as a new key biological feature for Gondwana palaeogeographic reconstructions. © 2012 John Wiley & Sons, Ltd.
Torres Carbonell P.J.,CONICET |
Guzman C.,Institute Estudios Andinos Don Pablo Groeber |
Yagupsky D.,Institute Estudios Andinos Don Pablo Groeber |
Tectonophysics | Year: 2016
Tectonic models for the evolution of the Patagonian orogenic curve were evaluated using analog experiments that considered either a rotational or a non-rotational orogenic backstop, combined with a basement promontory on the foreland cratonic margin. Five different kinematic configurations were used, aiming to evaluate the influence of the Río Chico Arc as a rigid obstacle on the evolution of the Fuegian thrust-fold belt. Rotations, strains and displacement fields obtained from each analog experiment were compared with the structural geology known from the Fuegian thrust-fold belt, in order to appraise the tectonic models that are more consistent with the natural structure. The push of a counterclockwise rotational backstop, combined with the buttressing effect of a foreland promontory, seem of major importance in controlling the final structure and map-view shape of the thrust wedge. © 2016 Elsevier B.V.
Lazo D.G.,Institute Estudios Andinos Don Pablo Groeber |
Damborenea S.E.,Museo de Ciencias Naturales de La Plata
Journal of Paleontology | Year: 2011
The Cretaceous Huitrín Formation in west-central Argentina records the final connection of the Neuquén Basin to the Pacific Ocean. This formation is comprised of a variety of continental to marginal-marine sediments deposited behind an Andean volcanic arc under warm, arid paleoclimatic conditions. Here we focus on a bivalve fauna from carbonate ramp deposits within the Barremian La Tosca Member of the Huitrín Formation. This fauna is very abundant and widely distributed within the basin but, surprisingly, it has not yet been studied in detail. In addition, paleoenvironmental affinities remain unresolved, with the fauna variously interpreted as having freshwater, brackish, and marine affinities. We studied the fauna's taxonomy and paleoecology based on more than 500 specimens collected at ten fossil localities in combination with new field observations. The bivalve assemblage was recorded from middle to outer carbonate ramp deposits and is composed of five taxa of marine affinity: Phelopteria huitriniana n. sp., Isognomon cf. I. nanus (Behrendsen), Placunopsis? pichi n. sp., Anthonya jarai n. sp., and Argenticyprina mulensis n. gen. n. sp.; the first three may be regarded as eurytopic and/or opportunistic. Reduced diversity, low evenness, overall small size (length <4 cm), thin shells, eurytopic or opportunistic life strategies, and high endemism point to a restricted marine setting for the La Tosca Member. The most important limiting factors likely were low primary productivity and fluctuating salinity and temperature, as conditions inferred for the unit include high evaporation rates combined with low continental runoff and reduced rainfall. Thick evaporite deposits below and above La Tosca Member and thin intercalated gypsum beds support a restricted, hypersaline setting. © 2011 The Paleontological Society.
Luci L.,Institute Estudios Andinos Don Pablo Groeber |
Cichowolski M.,Institute Estudios Andinos Don Pablo Groeber
Palaios | Year: 2014
Despite many advances in the study of the paleoecology of nautiloids and amonoids, there is still much ground to cover. Study of their encrusters provides information on their paleoecology and taphonomy. In this work the encrusting fauna of abundant material of the nautilid Cymatoceras perstriatum (Steuer) is statistically and taxonomically analyzed in order to infer paleoecological and taphonomic features of the fossil organism. The available material of C. perstriatum consists mainly of phragmocone fragments, with rare cases in which the body chamber was preserved. Nine encrusting taxa, evenly distributed across the nautilid shell (cementing bivalves, serpulids, sabellids, cyclostome bryozoans, and agglutinated foraminifers), were observed in and on C. perstriatum. Of these taxa, oysters are dominant. Encrusters are abundant, with a mean of 12 encrusters per shell. Internal encrustation is common, especially inside the body chamber. The orientation of encrusters is variable. Intensity of encrustation varies, with some shells heavily colonized while others remained clean. The encrusting fauna is interpreted as mainly postmortem. Encrusters are distributed across the shell in a uniform way, lack particular orientation, and are common on the inside of the body chamber, suggesting that encrustation occurred both during necroplanktonic drift and as the shell rested on the sea bottom. A few encrusters were trapped between shell whorls, indicating that less extensive in vivo encrustation took place. Some differences in encrustation parameters were found among localities, corresponding to minor paleoenvironmental differences. Variable encrustation intensity suggests moderate to prolonged duration of exposure of the shells. However, those collected from an exceptional concentration at the El Salado locality were probably buried shortly after death. Copyright © 2014, SEPM (Society for Sedimentary Geology).
Geophysical characterization of the upper crust in the transitional zone between the Pampean flat slab and the normal subduction segment to the south (32-34°S): Andes of the Frontal Cordillera to the Sierras Pampeanas
Sanchez M.,National University of San Juan |
Lince Klinger F.,National University of San Juan |
Martinez M.P.,National University of San Juan |
Alvarez O.,National University of San Juan |
And 3 more authors.
Geological Society Special Publication | Year: 2015
The Nazca Plate subducting beneath the South American Plate has strongly influenced Cenozoic mountain growth in western Argentina and Chile sectors (32-34°S; 70-66°W). At these latitudes, the Pampean flat slab has induced the development of prominent mountain systems such as the Frontal Cordillera, the Precordillera, and the associated Sierras Pampeanas in the eastwards foreland region. Through a gravity study from the Frontal Cordillera to the Sierras Pampeanas region between 32 and 34°S, we delimit a series of geological structures that are accommodating shortening in the upper crust and others of regional and subsurface development, without any clearly defined mechanics of deformation. Additionally, through an isostatic residual anomaly map based on the Airy-Heiskanen local compensation model, we obtain a decompensative gravity anomaly map that highlights anomalous gravity sources emplaced in the upper crust, related to known geological structures. In particular, by applying the Tilt method which enhances the gravity anomalies, the NW-trending Tunuyan Lineament is depicted south of 33.4°S following previous proposals. Using the decompensative gravity anomaly, two profiles were modelled through the northern sector of the study area using deep seismic refraction lines, borehole data and geological information as constraints. These density models of the upper crust of this structurally complex area accurately represent basin geometries and basement topography and constitute a framework for future geological analysis. © 2015 The Geological Society of London.
Luci L.,Institute Estudios Andinos Don Pablo Groeber |
Lazo D.G.,Institute Estudios Andinos Don Pablo Groeber
Ameghiniana | Year: 2012
The genus Steinmanella Crickmay is recorded in several Lower Cretaceous marine units of the Neuquen Basin. It is particularly abundant at the transition between the Vaca Muerta and Mulichinco formations. This paper presents a taxonomic revision of this fauna, discusses the stratigraphic range of each species, and describes and interprets the associated lithofacies based on detailed field sections, newly collected specimens and revision of previous fossil collections. Four sections were measured in northern Neuquen comprising the upper beds of the Vaca Muerta Formation and the lower ones of the Mulichinco Formation. The Steinmanella fauna was dated accurately on the basis of a precise ammonoid zonation. The species were found in the Neocomites wichmanni and Lissonia riveroi zones of early Valanginian age. Specimens were collected in situ from dark grey shales, alternating siltstones, wackestones and mudstones, and rudstones. Three species were identified: Steinmanella curacoensis (Weaver), S. quintucoensis (Weaver), and S. subquadrata sp. nov. Steinmanella curacoensis has an oval outline, poor demarcation of carinae, flank and corselet ribs partially intercalated at the median part of the valve, and oval escutcheon. Steinmanella quintucoensis has a furrow below the marginal carina, subrectangular outline, robustly tuberculated flank ribs, and lanceolate escutcheon. Steinmanella subquadrata sp. nov. has a subquadrate outline, well-marked carinae, and oval escutcheon ornamented with thin ribs and small elongated tubercles.