EMES Colloquium Speaker: Sarah George

Impacts of the Miocene Climate Optimum on the Central Andes

Climate exerts critical controls on the behavior of orogenic systems by regulating erosion which influences fold-thrust belt behavior. We investigate the stratigraphic and orogenic response to pronounced climatic warming during the Miocene Climatic Optimum (ca. 17-14 Ma) in the southern Central Andes.  We present stratigraphic and geochronologic data from a series of basins at ~25-35°S that occupied both high and low elevation positions during basin filling. Regionally ubiquitous eolianite deposition from 23-17 Ma supports arid conditions on the eastern flank of the Central Andes leading up to the Miocene Climatic Optimum. A rapid and regional shift from eolian dune fields to fluvial-lacustrine conditions occurs near the onset of the Miocene Climatic Optimum over 1000 km along-strike. These results support a change from arid to more seasonal and humid conditions during the Miocene Climatic Optimum. Stratigraphic constraints are corroborated by climate models which indicate increased seasonality and moisture availability on the eastern flank of the Andes during increasing pCO2, likely driven by an intensification of the South American Monsoon. We compare our results with published sequentially restored, regional cross-sections to explore linkages between the climatic shift and orogenic growth.