CONICET | Buscador de Institutos y Recursos Humanos

Our work reports on new results of Cenozoic paleowater isotope records from basins in the Central Patagonian ~50 °S to Southern/Central Andes ~35 °S. In this talk we emphasize an interesting observation that geochemical records indicate that paleotopography in this region was established before 55 Ma and has remained relatively steady since this time, despite changes in sediment fluxes and deposition rates. Numerous studies have quantified the spatiotemporal evolution of this range using different approaches, yet there remains considerable debate over the timing and magnitude of topographic change along the length of the orogen and how topographic change relates to sediment export and deposition. A number of datasets suggest that the Andes grew to their current size from the Miocene onwards. However others suggest the range may have formed early, during Late Cretaceous shortening. We analyzed the hydrogen isotopic composition of inorganic volcanic glass and plant-derived organic molecular biomarkers from Malargüe Basin (~35°S) and multiple Cenozoic Basins at ~47 °S and ~50 °S in southern Chile and Argentina, to reconstruct spatiotemporal changes in precipitation isotopes on the eastern margin of the range. Precipitation isotopes are strongly related to the topography of the orogen through isotopic distillation during rainout and changes in temperature with elevation. Biomarker and glass isotope data indicate persistent and similar isotopic fractionation from the Eocene to present. This result stands in contrast with sedimentologic data, which suggest a change in the timing and magnitude of sediment fluxes along the orogen from the Miocene to recent. These data suggest that temporal shifts in the rates of exhumation and erosion could produce ?steady state? topography for much of the Cenozoic.