Evolução tectono-estratigráfica da Bacia do Rio do Peixe, NE do Brasil: porção NW do semi-gráben de Sousa

Abstract

During the South Atlantic opening, in the Early Cretaceous, interior rift basins were developed in Northeastern Brazil, recording the continental rifting stage that predated the development of the passive margins along the South Atlantic. The Rio do Peixe Basin belongs to this set of basins whose sedimentary fill is related to the rift stage. Recently, Lower Devonian strata were identified underneath the Rift Sequence, making the Rio do Paixe Basin a differentiated example among rift basins in this region. Using data from 160 outcrops, 3 exploratory wells and 3D seismic data, this work aims to analyze the tectono-stratigraphic aspects of the surface and subsurface of the pre- and syn-rift sequences of the basin, applying field methods, seismic interpretation, structural techniques and sequence stratigraphy. The study area includes the western border of Sousa half-graben, as well as the eastern portion of the Santa Helena Step. Regarding the tectono-stratigraphic setting of the area, it was found that the basement contact with the sedimentary package, on the strike ramp and on the flexural margin of the Sousa halfgraben is established by faults. It was also observed in surface and subsurface that the contact between the pre- and syn-rift sequences corresponds to a low angle unconformity. In the tectono-structural analysis, it was interpreted faults and propagation folds, which are related to the rift event, characterized by a NW-SE extension. As a minor expression, a second set of structures is observed, including faults of directional displacement, related to the opening of the Equatorial Margin, in a transtensional dextral regime. It was found that the Lower Devonian Sequence developed a deltaic system, being divided into a transgressive system tract, with delta front deposits and transition to prodelta, and a regressive system tract, with delta plain deposits. The lithofaciological and seismic stratigraphic characterization of the region allowed to establish a new suggestion for stratigraphic delimitation for the Paleozoic remnant. In the Rift Sequence, the interdigitation relation between its units was attested. This sequence was subdivided into tectonic systems tracts, which both in the region of Santa Helena Step and in Sousa half-graben, are related to the moments of initial tectonics of the rift event and to episodes of high and low tectonic activities. In this characterization, the initial system tracts of these two structural sectors are correlated, thus sharing the same depositional system.