TECTONIC AND CLIMATIC INFLUENCES ON OLIGOCENE-MIOCENE ARIDIFICATION DURING ANDEAN FORELAND BASIN EVOLUTION, WEST-CENTRAL ARGENTINA

Cenozoic aridification in the Andean foreland basin of western Argentina was recorded by widespread eolian conditions that coincided with accelerated Andean shortening and tectonic loading in the southern central Andes. A persistent eolian dune system, which is rare in most foreland basins, indicates an arid climate and specific conditions of atmospheric circulation, orography, sediment dispersal, and subsidence. Detrital zircon U-Pb geochronological results for eolian sandstones spanning 20 foreland localities in western Argentina, from 22°S to 36°S, reveal relatively local Andean (western) sources rather than regional cratonic (eastern) sources. Clastic detritus was derived chiefly from Phanerozoic igneous and sedimentary rocks of the Andean magmatic arc and retroarc fold-thrust belt during initial shortening and uplift of hinterland regions in the west (Western Cordillera, Principal Cordillera, and Frontal Cordillera). This provenance record provides the earliest evidence for major westerly winds, transporting Andean detritus broadly eastward to the foreland basin (with axial northward or southward deflections) during a climate shift marked by the latest Oligocene-earliest Miocene establishment of arid conditions. In addition to the climatic implications, independent stratigraphic data provide the basis for a compilation of sediment accumulation histories showing that eolian deposition was synchronous with accelerated subsidence and accommodation generation attributable to enhanced Andean shortening. We propose that accelerated Andean uplift during the latest Oligocene-early Miocene generated rain-shadow conditions contemporaneous with increased subsidence and sediment accumulation in the foreland basin, highlighting the importance influence of tectonic processes on regional climate conditions.