THE FORELAND BASIN RECORD OF CENOZOIC CLIMATE FROM THE CENTRAL ANDES (Invited Presentation)

The Central Andes preserve a well dated continental record of paleodepositional environments which record the effects of paleoclimate change on sedimentary processes and ecology throughout the Cenozoic. We analyze patterns of geochemical and sedimentological changes in basins from the Central Andes which suggest that key climatic intervals such as the Eocene, Middle Miocene Climate Optimum (MMCO) and the Late Miocene Cooling (LMC) leave recognizable imprints in the sedimentary record. Data show that warm, humid, and more variable – monsoonal like - climatic conditions result in flashier depositional systems characterized by fluvial megafans in the Eocene. Drier conditions in the lower to middle Miocene (~21-17 Ma) are recorded by extensive eolian deposits preserved at high and low paleoelevations. A regional shift from eolian to fluvio—lacustrine deposition is recorded across the MMCO and is interpreted to represent an increase in precipitation possibly associated with the South American monsoon. A shift from fluvial to alluvial fan dominated systems corresponds to the late Miocene cooling (LMC). This is consistent with increased aridification, intensification of the Hadley circulation and the C₃ to C₄ ecological shift across the LMC. Increased aridification in the Pliocene resulted in widespread alluvial fan deposition and an apparent decrease in sedimentation rates, which is at odds with increasing global erosion proposed for the Pliocene. Overall, these variable responses have implications for our ability to recognize the record of climate change from continental deposits.