The stratigraphic and orogenic response to the Middle Miocene Climatic Optimum in the southern Central Andes

Abstract

Changes in precipitation can drive major shifts in stratigraphy and 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.  New and compiled stratigraphic and geochronologic data come from depocenters at ~25-35°S; these basins would have occupied both high and low elevation positions during the middle Miocene. Regionally ubiquitous eolianite deposition from ca. 22-17 Ma supports arid conditions on the eastern flank of the Central Andes preceding the Middle Miocene Climatic Optimum. Eolian facies are replaced by fluvial-lacustrine strata 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. New climate models also support increased seasonality and moisture availability on the eastern flank of the Andes during the Middle Miocene Climatic Optimum, which we attribute to 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. A more seasonal climate should drive increased erosion, which in turn should drive the wedge into sub-critical state as predicted by critical taper theory.