Aptian sedimentation in the Reconcavo-Tucano-Jatoba Rift System and its tectonic and paleogeographic significance

Abstract

This study, based on detailed sedimentologic and stratigraphic analysis of the Aptian succession preserved in the Reconcavo-Tucano-Jatoba Rift System (RTJ), present new elements for biostratigraphic correlation and paleogeographic reconstruction in the mid-Cretaceous South Atlantic realm, supporting novel interpretations on the tectonic and sedimentary evolution related to the W-Gondwana breakup. The Aptian sedimentary succession in the RTJ has been referred to as Marizal Formation, and interpreted as post-rift deposits. Detailed sedimentologic and stratigraphic studies of these deposits enabled the recognition and individualization of two distinctive sedimentary units that can be traced in the entire RTJ. These units are here described and named Banzae and Cicero Dantas members of the Marizal Formation. Their contact is locally marked by the fossiliferous successions of the here proposed Amargosa Bed, lying at the top of the Banzae Member. Both members of the Marizal Formation record large river systems captured by the Tucano Basin with the local development of eolian dune fields and fault bounded alluvial fans. The Amargosa Bed represents a regional-scale base level change preserved between the Aptian fluvial successions along the RTJ. Hence, the studied sedimentary record presents important implications for the timing and direction of marine ingressions affecting NE-Brazil interior basins during the Aptian. A remarkable contrast in preserved fluvial architecture between the Banzae Member, characterized by connected channel bodies, and the Cicero Dantas Member, characterized by isolated channel bodies within overbank fines, is here reported. The main interpreted control for the observed contrast in fluvial stratigraphy is sedimentary yield variation. The interval is also subject to the interpretation of a regional shift in the mechanism responsible for the subsidence of the basins formed during the Cretaceous break-up of the Central South Atlantic. This view is challenged by our results which reveal that basin forming extension continued throughout the Aptian. As a conclusion, the detailed stratigraphy of the Marizal Formation forward alternative geodynamic interpretations for the Aptian successions in northeastern Brazil, bringing new elements to the mid-Cretaceous biogeographical, paleogeographical and tectonic reconstructions of western Gondwana. (C) 2017 Elsevier Ltd. All rights reserved.