The late miocene climatic change -: persistence of a climatic signal through the orogenic stratigraphic record in northwestern Argentina

From the analysis of stratigraphic sections located in different areas of northwestern Argentina, an important climatic change was defined. This change, which took place during the late Miocene, is widely represented in the whole region (and in other latitudes). It is best displayed in the Calchaqui Valley, across the contact between the Angastaco and Palo Pintado Formations. The Angastaco Formation is composed of sandstones and conglomerates deposited in alluvial, fluvial, and eolian environments, under extremely and climatic conditions, with practically no fossil content. Conversely, the Palo Pintado Formation was deposited in lacustrine and fluvial settings, under wetter climatic conditions, comparable with the present prevailing conditions in the Andean eastern foothills and in the 'Chaco Salteno' (foreland Chaco Plains,). Matching this climatic amelioration, the Palo Pintado Formation supports an important fossil content (vertebrates, plants, and palinomorphs'). The persistence of this climatic change (although not so clear) in other parts of NW Argentina remarks its importance and shows that the climatic signal in question was strong enough to avoid being masked by the facial variations linked to the important tectonic signature that characterizes the Cenozoic orogenic successions. (C) 2001 Elsevier Science Ltd. All rights reserved.