Arcabouço estratigráfico da Formação Sergi (Jurássico Superior) na Bacia de Almada, Bahia

Abstract

This study analyzed the fluvial and aeolian deposits of Sergi Formation (pre-rift section) in the Almada Basin, aiming at supplying a stratigraphic framework for this interval, based on concepts of sequence stratigraphy. Sergi Formation was deposited in a wide intracratonic basin during the Neo-Jurassic and Eo-Cretaceous periods. By using outcrops and well data, it was possible to subdivide The Sergi Formation into three distinct depositional sequences. Sequences I and II correspond to the Sergi Formation lithostratigraphic interval and Sequence III encompasses the top of the Sergi Formation plus the Itaípe Formation. The criterion used to define this framework was the abrupt shift of the facies association along correlated surfaces in a basin scale, in well logs, and also in a regional correlation with adjacent basins. Sequence I is composed of braided fluvial channel belt facies association, with paleochannels flowing to the NW quadrant and by aeolian dunes and interdunes facies association, with paleocurrents indicating aeolian palaeodunes migrating to the SE quadrant. Sequence II is made up of braided fluvial channel belt facies association, with paleochannels flowing northeast. At its base, the Sequence III is composed of aeolian sand sheets facies association and at the top of lacustrine facies association. The development of these depositional sequences and their boundary surfaces is a consequence of variations in the rates of accommodation space (A)/and sedimentary supply (B), which are triggered by tectonic rearrangements and climatic oscillations in the basin.