CONICET | Buscador de Institutos y Recursos Humanos

Despite the large interest in terms of their geodynamic significance, the stratigraphy and paleoenvironments of the Miocene clastic deposits that are genetically related to subduction-driven lithospheric processes are poorly known. These beds, located south of Lago Buenos Aires at the foothills of the Southern Patagonian Andes, are included in the marine Centinela Formation, transitionally covered by the continental Río Zeballos Group. The aim of this work is to present an integrated stratigraphic section and discuss tectonicdrivers for the paleoenvironmental evolution that includes the passage from extensional faulting at the base to the main event of basement uplift during continentalization. We measured a 980 m-thick succession which was subdivided into three facies association, representing paleoenvironments. At the base of the column, FA I is dominated by shallow marine, bioturbated sandstones and heterolithic deposits. Above, FA II is a fluvial system dominated by interbedded medium to pebbly cross-stratified sandstones and mudstones, interpreted as fluvial channels and floodplains with incipient paleosols. Finally, to the upper part, FA III is composed of conglomerates with tractive and massive structures, interbedded with coarse sandstones, interpreted as channel and sheet-flood deposits of an alluvial fan. The whole coarsening upward trend, suggests these deposits were influenced by a progressive reduction in accommodation space, until total basin abandonment and generation of a bypass surface. Based on our results and the thermochronological data available, we relate depositional evolution to changes from punctuated extensional tectonic to a synchronous contraction-related eastward migration of the deformation front of the Andean orogenic belt during Miocene times.