Tectonostratigraphic significance of the Miocene sedimentary record of the northwestern Austral Basin, Patagonia

ARAMENDÍA, INÉS; CUITIÑO, JOSÉ I.; GHIGLIONE, MATÍAS C.; BOUZA, PABLO

Congreso; XVI Reunión Argentina de Sedimentología; 2018

Asociación Argentina de Sedimentología

Despite the large interest in terms of theirgeodynamic significance, the stratigraphy and paleoenvironments of the Mioceneclastic deposits that are genetically related to subduction-driven lithosphericprocesses are poorly known. These beds, located south of Lago Buenos Aires atthe foothills of the Southern Patagonian Andes, are included in the marineCentinela Formation, transitionally covered by the continental Río ZeballosGroup. The aim of this work is to present an integrated stratigraphic sectionand discuss tectonic-drivers for the paleoenvironmental evolution that includesthe passage from extensional faulting at the base to the main event of basementuplift during continentalization. We measured a 980 m-thick succession whichwas subdivided into three facies association, representing paleoenvironments.At the base of the column, FA I isdominated by shallow marine, bioturbated sandstones and heterolithic deposits.Above, FA II is a fluvial system dominated by interbedded medium topebbly cross-stratified sandstones and mudstones, interpreted as fluvialchannels and floodplains with incipient paleosols. Finally, to the upper part, FAIII is composed of conglomerates with tractive and massive structures,interbedded with coarse sandstones, interpreted as channel and sheet-flooddeposits of an alluvial fan. The whole coarsening upward trend, suggests thesedeposits were influenced by a progressive reduction in accommodation space,until total basin abandonment and generation of a bypass surface. Based on ourresults and the thermochronological data available, we relate depositionalevolution to changes from punctuated extensional tectonic to a synchronouscontraction-related eastward migration of the deformation front of the Andeanorogenic belt during Miocene times.