CONICET | Buscador de Institutos y Recursos Humanos

Continental carbonates are rich in paleoclimatic, paleoenvironmental, and paleontologic information. While carbonate sedimentation-precipitacion mechanisms have been described for different continental environments and in extensional basins there are still uncertainties that existing facies models fail to answer. The Triassic Cerro de las Cabras and Cerro Puntudo Formations are alluvial-fluvial-lacustrine sequences that represent a part of the sedimentary infilling in two sub-basins of the Cuyana basin during the early stages of the Triassic rift in west-central Argentina. Previous work has provided absolute dates, confirming that deposits are coeval (Anisian) allowing a comparative study of carbonate sedimentation in an extensional tectonic context. The research addresses the description and origin of freshwater carbonate deposits and their surrounding siliciclastic sediments therefore identifying the major factors that controlled carbonate precipitation in specific areas of the Cuyana rift, the characterization of the paleohydrology, and an understanding of the evolution in space and time of the carbonate sedimentary systems. Sedimentologic studies of the Cerro de las Cabras Formation reveal an ephemeral, playa-lake depositional system with subaerial exposure and pedogenesis. The unit is an aggradational succession that corresponds to the evaporative facies association type, diagnostic of underfilled lake basins. However, the lakes model links underfilled lakes with persistently closed surface hydrology, though groundwater supply may be open in this case. In the Cerro de las Cabras Formation evidence for biota in the microbialitic limestones indicates microbially-induced precipitation of carbonate. Sedimentologic studies of the Cerro Puntudo Formation reveal an alkaline playa-lake system fed by groundwater and ephemeral surface-water input. The unit is an aggradational-minor progradational succession, pointing to a fluctuating profundal facies association suggesting a balanced-filled lake type. The Cerro Puntudo paleolake contains a microbialite assemblage that reflects an aquatic paleoecosystem with a simple trophic network. These two synchronous, lacustrine depositional systems were influenced by tectonics (synrift geography and lithology of drainage area) and climate (surface water and groundwater input). Provenance and hydrology are key controls in carbonate accumulation in continental rift basins that must be included in future models. Comparison with successions of different rift basins suggest that application of these concepts to other rift basins will aid in developing new carbonate sedimentation models for freshwater limestones in extensional settings.