High Resolution Sequence Stratigraphy In a Rift Section: Climatic Control and Sedimentation of Maceio Formation, Sergipe-Alagoas Basin, Brazil : ABSTRACTS

Abstract

This work deals with the Aptian rift section of Maceio Formation, Alagoas Basin, northeastern Brazil, using outcrops and 16 wells (718 meters of cores). Detailed facies descriptions were performed to characterize turbidites, with individualized channel/overbank deposits and lobes/interlobes deposits. High-resolution stratigraphy, was applied to identify the main stratigraphic sequences and to determine lateral and vertical continuity of the deposits. Using stratigraphic analysis techniques, the section was divided into three sequences of 4th order: Alpha, Beta and Gamma. The Alpha Sequence was divided into 6 sequences of 5th order, the Beta Sequence into 4 sequences of 5th order and the Gamma Sequence into 8 sequences of 5th order. In wells with cores, 5th order sequences were subdivided into 6th order sequences. The use of standard sequence stratigraphy concepts proved difficult for rift-section analysis. An alternative approach using "climatic systems tracts", resulted in excellent correlation between deposit types and climatic conditions. Transgressive system tracts, related to humid periods, represent phases of high siliciclastic input into the basin, resulting on sandstone turbidite sequences, typically enriched on continental organic matter. In contrast, later highstand system tracts, corresponding to arid conditions, are dominated by muddy lacustrine deposits, enriched on algalic organic matter and showing mudcracks. Locally, lowstand system tracts dominated by evaporites are found in restricted areas. Climate and tectonic were the main controlling factors of the architecture and frequency of the sequences. This study showed that an integrated approach, using outcrops and subsurface data, is a powerful tool to quantify and calibrate the geometry. and continuity of continental-rift deposits.