Faciologia e análise tectônica preliminar da Formação Barreiras no litoral sul do estado da Bahia, Brasil

Abstract

Many researchers have asserted that the Barreiras Formation sediments are the result of gravitational flows because of the almost complete absence of hydrodynamic sedimentary structures. These studies have also suggested a non-tectonic origin for this unit. This paper deals with the lithofacies association and structural features of the Barreiras Formation along the southern coast of the State of Bahia, Brazil. Outcrop analysis revealed that the Barreiras Formation lithofacies are typically fluvial and are associated with braided channels. Immaturity of the sediments indicates that temporary small rivers in hyperconcentrated flows and playa lakes predominated in the initial stages of deposition. Transportation and deposition during the middle to final stages of the Barreiras Formation were characterized by well-developed braided channels, with larger rivers. Field work revealed a large number of NW-SE oriented joints and a relatively small number of NE-SW oriented joints. Preliminary tectonic stress determination, based on measurements of coeval-joints, indicated that the neotectonic stress field presents a NW-SE-trending horizontal maximum compression, which is similar to the present-day stress field determined by breakout analyses. Analysis of modern drainage patterns indicates that crustal blocks limited by major fault zones have been tilted in several directions.