New Insights into South Atlantic Rifting from the Santos and Campos Basins, Offshore Brazil—a Tale of Two Basins

Scot I. Fraser and Mike Lentini
Shell International E&P Inc, Houston, TX

The Santos and Campos Basins resulted from the Cretaceous break-up of Gondwanaland. South Atlantic plate reconstruction models propose uniform, east-west extension and rift-basin symmetry is thus inferred with the conjugate margin. This implies that half-graben development and planar faults would characterise the structural style of the Santos and Campos syn-rift basins. PSDM 2D-seismic data has revealed, important structural relationships previously obscured by Aptian salt. A more complex rift-margin evolution is inferred. Inherited basement lineaments, imparted mechanical anisotropy to South Atlantic crust. Contrasting crustal rheology differentiates deformation styles in the Santos and Campos Basins, with the Santos Basin margin evolution more consistent with oblique extension and asymmetric rifting. Crustal heat flow has had a primary influence on brittle versus more ductile rift-kinematics. The interpretation challenges a simple symmetric rift model and can explain the distribution of tectonic versus thermal-sag subsidence patterns observed. Reconstruction of the continent/ocean boundary, along the basin margins and consideration of their conjugate African basins demonstrates clear asymmetry. The structural expression of the transition from continental to oceanic crust in the Campos and Santos Basins is distinctive and is related to the primary rifting mechanism inferred for each. The conspicuous remnant, intra-basinal Sao Paolo Plateau/ridge however, does suggest that the loci of oceanic crust formation in the Santos Basin may have experienced a dynamic basinward translation as a response to continued asymmetric lithosphere extension. The Cabo-Frio Arch structurally partitions contrasting Campos and Santos syn-rift basin architectures and the new interpretation has fundamental implications for their respective petroleum systems.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005