INSTITUTO DE GEOCRONOLOGIA Y GEOLOGIA ISOTOPICA
Unidad Ejecutora - UE
congresos y reuniones científicas
New U-Pb ages on a pyroclastic level from the Fosatti depocenter of the Jurassic Cañadon Asfalto basin, Chubut, Argentina
HAUSER, NATALIA; MATTEINI, MASSIMO; CABALERI, NORA; VOLKHEIMER, WOLFGANG; ARMELLA, CLAUDIA; GALLEGO, OSCAR F.; MONFERRAN, MATEO
Simposio; VIII South American Simposium on Isotope Geology; 2012
The Early Jurassic Cañadón Asfalto basin represents a NW oriented rift structure related to the separation of Africa and South America during the dismemberment of Gondwana. The Cañadón Asfalto Basin located in the central area of Extraandean Patagonia, Argentina (Silva Nieto et al., 2002b), at the centre of Chubut province (between 42º 05´ and 44º 30´ S and 68° 33´ and 70º W) possesses the most important records of the continental Jurassic sedimentation from South America. This basin is constituted by three depocenters, namely: Fossati depocenter, Portezuelo-Llanquetrus depocenter, and Cerro Cóndor depocenter. Each depocenter constitutes an isolated and single sub-basin with its own evolution history, not necessarily contemporary but diachronous. The sub-basins present different depositional sedimentary sequences, generally with lacustrine systems that prograde to fluvial systems. The Cañadón Asfalto Formation in the Fossati depocenter consists of two Members, Las Chacritas (Aalenian-Bajocian) and Puesto Almada (Oxfordian-Thitonian). Las Chacritas Mb. presents carbonate, siliciclastic and pyroclastic facies interpreted as a lacustrine system related to a subtropical climate with a dry season. The Puesto Almada Mb. presents facies of lacustrine, alluvial fan and fluvial paleoenvironments with pyroclastic levels, and it represents the silting of the basin where a regional tendency towards climatic aridity is observed. New U-Pb dating on zircons from a pyroclastic level of the Puesto Almada Mb in the Fosatti depocenter were obtained. Analyses were carried out using LA-MC-ICP-MS Neptune at the Laboratory of Geochronology of the Geosciences Institute at the University of Brasilia. The obtained age of 158±1 Ma permits to correlate the studied pyroclastic level from the Fossati depocenter with a pyroclastic level (161±3 Ma) at the base of the Puesto Almada Mb in the Cerro Condor depocenter.