INTENSIFICATION OF THE SOUTH AMERICAN MONSOON AT THE START OF THE MIDDLE MIOCENE CLIMATIC OPTIMUM IN THE CENTRAL ANDES AS A MODULATOR OF OROGENIC SHORTENING (Invited Presentation)

Climate exerts critical controls on the behavior of orogenic systems by regulating erosion, which in turn influences fold-thrust belt behavior. We investigate the stratigraphic and orogenic response to pronounced climatic warming during the Middle 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 Middle Miocene Climatic Optimum. A rapid and regional shift from eolian dune fields to fluvial-lacustrine conditions occurs near the onset of the Middle Miocene Climatic Optimum over 1000 km along-strike. These results support a change from arid to more seasonal and humid conditions during the Middle 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.