Análise sismoestratigráfica dos depósitos sinrifte da Formação Coqueiro Seco (Aptiano inferior a médio), Bacia de Sergipe-Alagoas

Seismic stratigraphic analysis of sinrift deposits of the Coqueiro Seco Formation (lower to middle Aptian), Sergipe-Alagoas Basin

Abstract

The study interval comprises the early-middle Aptian sinrift deposits of the Coqueiro Seco Formation of the Sergipe-Alagoas Basin. The interval is composed mainly by clastic rocks which are distributed from the northern part of the Sergipe sub-basin to the northeastern sector of the Alagoas Sub-basin, where it reaches thicknesses up to 3.000m. The proposed stratigraphic framework was based on the identification of T-R (transgressive-regressive) sequences, characterized by distinct sedimentary stacking patterns and key surfaces. It could be divided in at least in three sequences and their respective systems tracts, limited by erosional unconformities. The non differentiation of tracts of high and low sea levels in the available well and seismic data make it difficult to consider usual models of Sequence Stratigraphy. This interval is particularized by its strongly conditioning tectonic source, which is mainly characterized by the peculiar influence of an important depositional low, named Varrela Low. In seismic terms, the reflection patterns related to the target interval are mainly composed by plane-parallel and diverging events in a typical ramp feature. The use of a seismic pattern recognition software provided useful results for better identification and characterization of the proposed seismic stratigraphic sequences. In general, a strong tectonic influence is assumed for the sedimentation, which is mainly characterized as a braided delta system, where fluvial-deltaic and lacustrine sediments are laterally associated with alluvial fan systems related to the faulted border. In this way, half-grabens were infilled with a prevailing progradational character.