Cenozoic uplift of the Fátima Basin, NE Brazil

Abstract

The Fátima Basin is a small Cretaceous interior basin that was formed within the continental Borborema Province in northeastern Brazil. Its formation was related to the opening of the southern Atlantic Ocean. This study investigates the hypothesis of post-rift tectonic reactivation within this basin through an integrated set of geophysical (aeromagnetic), surface (outcrops), and subsurface (boreholes) data to model the tectono-stratigraphic framework of the basin. An analysis of several morphometric parameters, including the slope index, relief aspect, stream profiles, asymmetry factor (AF), stream-gradient index (SL), and valley floor width-to-height ratio (VF) was used to identify possible tectonic adjustments related to post-rift stress fields. The integration of geophysical and subsurface data showed that the basin possesses a half-graben geometry with the main basin axis trending NE-SW. Two families of topographic lineaments were identified: 1) NE-SW, corresponding to the main shear zones and faults of the Pre-Cambrian basement, and 2) NW-SE, representing faults and fractures in the adjacent basement and the sedimentary cover. A digital elevation model revealed that the maximum topographic elevation was 950 m, associated with deposits of the Paleozoic Tacaratu Formation located over the hinge line of the flexural margin of the basin. The AF values in the basin ranged between 25 and 76, and first- and second-order SL index anomalies were frequent, especially in the faulted border, the southeast sector, and the northeast sector. Analyses of the main river channels revealed VF values of around 1, which indicate active incisions in the river valleys. We suggest that the basin was subjected to differential uplift during the Cenozoic, which strongly affected the southeast and northeast sectors. Based on the exhumation of the Tacaratu Formation deposits, we estimate that the basin experienced approximately 500 m of uplift that influenced the erosion of Cretaceous deposits and adjacent basement rocks.