3D Crustal Modeling of the Barreirinhas and Ceara Basins of Northeastern Brazil



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The Barreirinhas and Ceara Basins, offshore northeastern Brazil, cover a combined area of approximately 105,000 km^2 and formed north and south of the Romanche Fracture Zone (RFZ) respectively. The RFZ is a 4,500 km-long, 10-40 km-wide oceanic fracture zone that extends from offshore northeastern Brazil to offshore Ghana-Togo/Benin. During Aptian times, northeastern Brazil rifted from the continental margin of West Africa. Questions remain regarding northeastern Brazil’s crustal structure, its reconstructed fit with NW Africa, and its exploration potential. To address these questions, a 3D model was created by integrating industry quality 2D seismic reflection and well log data with open-file gravity, sediment thickness, topography, and seismic refraction data (including wide-angle lines and individual stations). Additionally, a sediment thickness grid was produced by interpreting 13,171 km of modern 2D seismic profiles to constrain the inversion. The Barreirinhas and Ceara basins 3D model was constructed with five horizons, which separated six layers: air, water, sedimentary rocks, upper crystalline crust, lower crystalline crust, and upper mantle. A 3D gravity structural inversion on the Moho horizon was performed, the total thickness of the crystalline crust based on the new Moho horizon was calculated, and a continent-ocean transition zone (COTZ) based on the new crustal thickness was defined. The width of the transition zone in the Barreirinhas basin ranged from 5 to 25 km and in the Ceara from 5 to 100 km. Landward of the COTZ, the continental crust thickness ranged from 14 km near the COTZ to 40 km, whereas seaward of the COTZ, the oceanic crust thickness ranged from 5 to 10 km. These thicknesses support the idea that the equatorial South Atlantic Ocean opened as a series of right-lateral, pull-apart basins with varying degrees of obliquity to the South Atlantic opening direction. The Romanche Fracture Zone does not extend as far west as previously thought, but appears to have formed in-line with intracontinental pre-existing zones of weakness. The new sediment thickness map better defines the major depocenters offshore equatorial Brazil while the model-derived crustal thickness map and COTZ, may provide insights for source rock maturity within the Barreirinhas and Ceara basins.



Barreirinhas Basin, Ceara Basin, Romanche Fracture Zone, Equatorial Brazil, Equatorial South Atlantic, Gravity inversion, Crustal structures, 3D Gravity Model, Pull-apart, Conjugate Margin