Fácies Sedimentares E Modelo De Sedimentação Do Grupo Paraguaçu Na Região De Rio De Contas, Borda Ocidental Da Chapada Diamantina, Bahia

Abstract

· SEDIMENTARIES FACIES AND SEDIMENTATION MODEL FOR THE PARAGUA<;U GROUP IN RIO DE CONTAS REGION, WESTERN BORDER OF CHAPADA DIAMANTINA, BAHIA. The Middle Proterozoic metasediments of the Paraguacu Group, outcropping in the Rio de Contas region, on the western border of the Chapada Diamantina (Bahia), consist of three terrigenous sedimentary facies displaying characteristic features of eolian-, coastal-, and shelf-type depositional environments. The facies I, which occupies the basal portion of the sequence, is made up of quartzites and laminated metasandstones interpreted as transgressive in nature, and deposited over as extensive. shallow marine platform, showing storm effects. The intermediate facies 2 is composedof quartzites with large scale high-angle cross-bedding defined as eolian is origin, accumulated on vast coastal dune fields, Facies 3, which constitutes the top of the group, starts with transgressive, fine. and laminated metasandstones (sub-facies 3A) deposited in a shoreface environment, under moderate energy conditions. This is overlain by muddy deposits (sub-facies 3B), also transgressive in nature and accumulated in a shelf environment submitted to hydraulic regimes of alternating calm and stormy periods. The uppermost facies of the Paraguacu Group (sub-facies 3C) consists of metasiltstones and metasendstones deposited in a shoreface zone, prograding over a muddy shelf.