MOREIRAS Stella Maris
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Glacial chrono-stratigraphy constrained by rock avalanches along the Mendoza river valley, Argentine Central Andes (32º S).
Congreso; INQUA; 2019
Huge rock avalanches clustered in the northern extreme of the Cordon del Plata range (32ºS) stratigraphically related to Pleistocene glacial drifts and valley fill deposits were chrono-stratigraphically studied. Cosmogenic dating (TCN) on surficial blocks of the rock avalanche deposits and optically stimulated luminescence dating (OSL) of paleo-lakes dammed by these rock avalanches were performed. These dates (17 TCN and 4 OSL) determine Middle-Late Pleistocene ages contrasting with the previously glacial chronology of Mendoza river valley that was established based on relative dating techniques, paleontological context, and tephrochronology. Hence, the previously dated ash layers were geochemically analyzed by ICP spectrometry to clarify if indeed those tephra relate to a single event.TCN dating technique opens the possibility of dating landslide directly constituting the most useful tool for Quaternary studies for the Arid Central Andes where tephrochronology is limited to relative ages, and thermoluminescence techniques (TL/OSL) are limited to fine sediments. Late-Middle Pleistocene age obtained by TCN for rock avalanches clustered in the Cordón del Plata range is significantly confident and consistent with stratigraphic studies. Besides, new findings throw light on the regional neotectonic as the studied rock avalanches, presumably triggered by M>6 earthquakes, are gathered along the active Carrera Fault System. As well, obtained cosmogenic dates adjust the ages for the first horse (Hippidion devillei) remains found in the province of Mendoza, initially assigned to the Middle Pleistocene by stratigraphic relationships. Clearly, our findings help to redefine the geomorphological evolution of the Mendoza river valley. Especially indicate that the glacial stratigraphy earlier proposed must be reconsidered. In addition, our data suggest that the Carrera Fault system bounding the valleys of the Cordillera del Plata has been more recently active than earlier proposed.