Facies distribution as a response to early rift tectonic activity in the Sergipe-Alagoas Basin, northeastern Brazil

Abstract

Accommodation rates in rift basins are mainly controlled by tectonics. However, during early rift stages, normal fault activity is dispersed and incipient, which makes it difficult to recognize the effects of early crustal extension. The sedimentary stacking pattern of rift-related depositional environments can be decisive to address 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 West Gondwana. In total, 14 lithofacies were described, interpreted and arranged into 7 facies associations. At the base of the formation, bars and sand sheets were deposited by low discharge braided channels, which were deposited on top of lacustrine mudstones of the Bananeiras Formation. There is a change in stratigraphic architecture in the middle of the section, where fluvial channels become deeper due to increasing discharge, promoting an increase in grain size of the transported bedload and greater rates of coarse sand and gravel bar stacking. Rare crevasse channels and restricted aeolian dune fields occur adjacent to braided channel belts. Upwards, the Serraria Formation becomes dominated by delta front and delta plain deposits. The 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 indicates reestablishment of fluvial drainage either due to decreasing tectonism or due to low accommodation at the time of deposition. Thus, the sedimentary stacking pattern of Serraria Formation represents higher frequency cycles within an early rift tectonic system tract. (C) 2019 Elsevier B.V. All rights reserved.