Architectural framework of the NW border of the onshore Potiguar Basin (NE Brazil): an aeromagnetic and gravity based approach

Abstract

On the basis of qualitative and quantitative geophysical interpretations, studies on tectonostratigraphic evolution were carried out in NW onshore Potiguar basin. Airborne magnetic and terrestrial gravity data were acquired in order to investigate tectonostratigraphic relationships in a poorly studied area of this oil-bearing Early Cretaceous basin. The present integrated study determined the main geophysical lineaments, basin internal geometry and depth of intra-basement magnetic and gravity sources, characterizing geological domains in terms of lithostructural elements. The depth of geophysical sources was estimated using 2D and 3D Euler deconvolution. 2D forward gravity modeling was also performed along three transects. The results unravel crustal partitioning, characterized by NE-SW lineaments with local E-W to NW-SE inflexions. The geophysical patterns are directly related to basement grain, which is Brasiliano in age. In fact, the Jaguaribe shear zone, that is not clearly marked on the surface, appears much more pronounced in the various geophysical maps and gravity models. The Ponta Grossa and Fazenda Belém shear zones show similar geophysical signatures to the Jaguaribe shear zone and appear to limit a low-related gravity features. Another important magnetic lineament was revealed by 2D Euler deconvolution and was named Retiro shear zone. 2D gravity modeling shows the basin geometry in depth, which presents shallow depocenters that may be associated with hydrocarbon reservoirs to the east, such as the Fazenda Belém oil field. An evolutionary tectonic model of this reservoir is proposed comparing our results and previous geological studies. This study indicates that a few faults, which occur in the NW edge of Potiguar Basin and form depocenter boundaries, oblique to the main transform continental margin in NE Brazil, have the orientation, kinematics and geometry as the main rift faults. Thus, our final model suggests that the grabenlike depocenter could be the westernmost expression of the NE Brazilian Rift System that generated a series of rift basins along the Borborema Province in the Early Cretaceous. The still unknown deposition of rift-related sequences to the west of Fazenda Belém oil field is probably associated with raised area that remained active when the eastern sector of the Potiguar basin presented overall subsidence. It is likely this basement structural configuration is topographic highs and lows, keeping geodynamics relationships with strike-slip fault regimes installed in the Atlantic Equatorial Margin during Aptian.