MORPHOSTRATIGRAPHIC EVOLUTION OF THE NORTHWESTERN MARGIN OF THE SALAR-DE-ATACAMA BASIN (23-DEGREES-S-68-DEGREES-W)

The 2,500 km2 Salar de Atacama forms the center of a large Cenozoic de positional basin in the Andes of northern Chile. The stratigraphy and geomorphology of the western uplifted margin of this basin correlates well with the stages of the piedmont evolution resulting from the main Andean uplift. These uplifting/erosional processes produced the accum ulation of sediments which infill the basin. Major NNE oriented morpho structural features largely controlled the distribution of the sedimen tary units in this part of the basin. The sediments include red sandst ones, siltstones, conglomerates and evaporites. Evaporites were mainly deposited to the center of the basin, whereas the piedmont deposits a ccumulated closer to the basin margin. The basin was originated during the Oligocene and deposition is still active. A pediment-type planati on which produced a gravel veneer matches well with the Atacama pedipl ain. It is suggested that the Oligo-Miocene morphostratigraphic evolut ion of the Salar de Atacama basin, which is correlated with the Andean piedmont, is closely related to the rates of convergence and geodynam ic effects on the southeastern Pacific region.