Multi-scale tectono-stratigraphic analysis of pre- and syn-rift sequences in the Rio do Peixe Basin, NE Brazil

Abstract

Intracratonic rift basins developed in Northeastern Brazil during the Early Cretaceous, recording the continental rifting stage that preceded the development of the passive margins along the South Atlantic. The Rio do Peixe Basin is a remarkable example of this set of basins. It comprises four well-exposed NE-to E-W-trending half-grabens, the larger of which, the Brejo das Freiras and Sousa Half-grabens, being connected by a complex rift-related structural high, the Santa Helena Step. The basin also represents a unique case in the region where Lower Devonian strata underlies the Lower Cretaceous Rift Sequence, as a remnant pre-rift Paleozoic basin. This work covers part of the Sousa Half-graben and the Santa Helena Step, combining outcrop, wells and 3D seismic data to improve analysis of the tectono-stratigraphic framework of both the pre- and syn-rift sequences. The Lower Devonian Sequence comprises a deltaic system, which delta front to prodeltaic deposits characterize a transgressive systems tract, followed by delta plain deposits of a regressive systems tract. The base of the Lower Cretaceous Rift Sequence is defined by a low-angle unconformity recognizable at both surface and subsurface. This sequence displays interfingered contacts between its coeval units and is subdivided into four tectonic systems tracts related to the beginning of extension and periods of high and low tectonic activity. The southern termination of the Brejo das Freiras Fault performs an important depositional control in the Santa Helena Step, which at this place didn't developed high escarpments and acted as source area for fluvial fans. In the strike ramp and flexural margin of the Sousa Half-graben, fluvial distributary systems predominate and the basement contact is characterized by NE- and E-W-trending oblique slip normal faults. Finally, our study emphasizes the association of the structural framework with the Neocomian NW-SE rifting extension responsible for the South Atlantic opening.