A geological and geophysical study of the Sergipe-Alagoas Basin

Extensional stresses caused Africa and South America to break up about 130 Million Years. When Africa rifted away from South America, a large onshore triple junction began at about 13? S and propagated northward. This triple junction failed and created the Reconcavo-Tucano-Jupato rift (R-T-J), located in northeastern Brazil (north of Salvador). The extensional stress that created this rift was caused by a change in the force acting on the plate during the Aptian. A series of offshore rifts also opened at this time, adjacent to the R-T-J rift; this series of basins are referred to as Jacuipe, Sergipe, and Alagoas (J-S-A). The basins are separated by bathymetric highs to the north and the south of the Sergipe-Alagoas basin. The Sergipe-Alagoas basin has a Bouguer gravity anomalies more negative than -35 mGal, and the other two basins have values more negative than -100 mGal; the total magnetic intensity is also about 60-80 nT higher in the Sergipe-Alagoas basin than the surrounding basins. The gravity and magnetic values in the Sergipe-Alagoas basin, when compared to the Jacuipe and the Sergipe-Alagoas basins, indicate that the depositional history and/or the formation of the Sergipe-Alagoas basin is different from the other two basins. This study was done by analyzing the gravity and magnetic anolamies in the region, and comparing these anomalies to the stratigraphy of the basin. This research has allowed the stratigraphy and structures of the Sergipe-Alagoas basin to be better understood - the location of the Sergipe fracture zone will also be outlined. This study provides a comprehensive view of the Sergipe-Alagoas basin and outlines a method for using Gravity and Magnetics to better understand the stratigraphy and structure of the Sergipe-Alagoas basin.