The Quaternary lake of Angastaco, Valle Calchaquí, Salta, Argentina

Abstract

Evidence has been found of the existence of Quaternary lacustrine sediments in the central part of Valle Calchaquí, Salta, Argentina. The lake dam was formed as a consequence of folding and faulting of thick Neogene foreland, non-marine successions (Payogastilla Group), during the last Andean diastrophism (Diaguita orogeny, post 1.3 Ma). The Diaguita orogeny was, in turn, the late event of tectonic inversion processes on the western faulting edge of the Cretaceous Salta Group rift basin. The lake extended along the NNW strike, as does the current depression of Valle Calchaquí, north of  the village of Angastaco. The lacustrine sediments lie in angular unconformity on Neogene folded deposits and underlie with distinctive discontinuity fluvial and piedmont accumulations. The pelitic lacustrine deposits, at least 25 m thick, show lateral interfingering facies with coeval sandy and conglomerate fluvial strata, whose provenance was from the east and west of the lacustrine basin. There is not enough available information yet to specify the age of this lacustrine episode during Quaternary times, although it surely took place after the folding and faulting of the Payogastilla Group in Early Pleistocene.