The Barreiras Group in the northeastern coast of the State of Bahia, Brazil: depositional mechanisms and processes

The Barreiras Group is a Miocene to Lower Pleistocene continental terrigeno us sedimentary deposit exhibiting a large occurrence along the Brazilian co ast. In the Conde region, located in the northeastern part of the State of Bahia, the sedimentological characteristics of these sediments are indicati ve of a deposition as gravelly and sandy bed load in braided fluvial system s, related to alluvial fans, under an and to semi-arid climate. The basal p ortion of the group is dominated by a gravelly-sandy lithofacies deposited by debris flows and pseudoplastic debris flows, with lesser occurrences of subaqueous deposits, characterizing a proximal fluvial system deposition. T he upper portion is made up of gravelly-sandy sediments that include subaqu eous, debris flows and pseudoplastic debris flows deposits. They suggest de position in a more distal zone as indicated by the larger occurrence of sub aqueous deposits and the presence, though rare, of downstream-accretion mac roforms. Besides the climate control, deposition of the Barreiras Group was strongly influenced by the intraplate tectonism, which has been affecting the South America Platform since the Middle Miocene, when neotectonism bega n in Brazil.