Arquitetura deposicional da Formação Serraria, bacia de Sergipe-Alagoas

Abstract

Accommodation rates in rift basins are mainly controlled by tectonics. However, during early rift stages, normal faults activity is dispersed and incipient, which makes the definition of the rift onset a difficult task. The sedimentary stacking pattern of rift-related depositional environments can be decisive to solve this question. This paper aimed to evaluate the stratigraphic record of the Tithonian-Berriasian (?) Serraria Formation (Sergipe-Alagoas Basin, Brazil), which was deposited in the Afro-Brazilian Depression, as a result of the early extension of the South Atlantic rifting. 14 lithofacies were described, interpreted and grouped into 7 facies associations of fluvial, aeolian and fluvio-deltaic origin. These genetic units were quantified in order to provide a more accurate depositional system interpretation. At the base of the formation occur bars and sand sheets within small channels, which are on top of lacustrine mudstones of the Bananeiras Formation. There is a change in stratigraphic architecture by the intermediate section, where fluvial channels become deeper due to increasing discharge, promoting greater rates of sand and gravel bar stacking. Crevasse channels and restricted aeolian dune fields could occur adjacent to fluvial channel belts. Upwards, the Serraria Formation becomes dominated by delta front and delta plain deposits. Fluvial and aeolian facies associations represent a progressive decrease in accommodation, while the upper fluvio-deltaic interval means an increase in accommodation, pointing to the early rift stage climax. The fluvial “Caioba” sandstone on top of the Serraria Formation indicate reestablishment of fluvial drainage due to the decreasing tectonism. Thus, the sedimentary stacking pattern of Serraria Formation represents higher frequency cycles within an early rift tectonic system tract.