Upper Devonian and Carboniferous of the Altiplano of Bolivia: Stratigraphy, sedimentology and paleogeographic evolution

Upper Devonian and Carboniferous rocks of the Bolivian Altiplano represent the partial filling of a foreland retroarc basin occupying most of the Central Andes during the Mid and Late Paleozoic. Based on a revised lithostratigraphic subdivision and on the sedimentological (lithofacies and provenance) analysis of the Upper Devonian and Carboniferous sedimentary rocks in the Altiplano basin of Bolivia, a general outline of its paleogeographic and paleoclimatic evolution is proposed. Upper Devonian and Lower Carboniferous deposition took place in a wave- and storm-dominated shallow marine clastic shelf, with glacial-marine deposition (Cumana Formation) during late Famennian marking the base of a complex thickening-coarsening sequence resulting from coastal progradation (Ambo Group). This sequence includes the gradual progradation of a fluvial- and wave-dominated braid deltaic plain (upper member of the Kasa Formation), as a result of tectonic and glacial activity to the east. This temporary local source is interpreted as a foreland transpressive uplift or a forebulge developed between the Altiplano and the Subandean region of Bolivia. The overlying deposits of the Siripaca Formation mark an important change in fluvial style to a higher-sinuosity deltaic plain and distal alluvial system. This unit records the final retreat of the sea during a Mid-Carboniferous regression, as well as an increased influence of a magmatic arc provenance from an unknown source, under conditions of less sediment influx and lower depositional slope. The Siripaca Formation marks the end of the Ambo Group, followed by an erosional period which removed all or part of the Lower Carboniferous and Upper Devonian deposits in some areas. During the Kasimovian, a transgression from the north began, accompanied by migration of fluvial and coastal deposits into the Altiplano (Yaurichambi Formation). Development of a shallow carbonate ramp followed, which persisted into the Permian (Copacabana Formation).; The evolution of the Altiplano basin during the Late Devonian and Carboniferous records important climatic changes related to the latitudinal shift of this part of Gondwana towards lower latitudes. Interaction among global climatic and eustatic changes and regional tectonism influenced Upper Devonian and Carboniferous sedimentation in the Altiplano.