Structural modeling based on sequential restoration of gravitational salt deformation in the Santos Basin (Brazil)

Abstract

The structural restoration of two parallel cross-sections in the central portion of the Santos Basin enables a first understanding of existent 3D geological complexities. Santos Basin is one of the most proliferous basins along the South Atlantic Brazilian margin. Due to the halokinesis, geological structures present significant horizontal tectonic transport. The two geological cross-sections extend from the continental shelf to deep waters, in areas where salt tectonics is simple enough to be solved by 2D restoration. Such crosssections display both extensional and compressional deformation. Paleobathymetry, isostatic regional compensation, salt volume control and overall aspects related to structural stylewere used to constrain basic boundary conditions. Several restoration algorithms, such as simple shear, flexural slip and free methods, were used to restore the sedimentary deformation, including salt gravity gliding. The results of the 2D restoration are consistent with five major sequences of sedimentary evolution: (1) the brittle pre-salt deformation, (2) the significant and fast salt deposition, (3) the initial post-salt deformation with predominant rafting tectonics, (4) the Late Cretaceous progradational deposition and coeval development of compressional minibasins, and (5) the Cenozoic sedimentary deposition, with less intense salt tectonics. A 1D subsidence analysis based on the 2D restored results is shown as a useful restoration control tool. The 1D results indicate that an initially proximal infill evolves towards distal regions under salt tectonics control. The 1D diagrams also record the history of the overburden movements through lateral depocenter migration in minibasins areas, submitted to large horizontal salt spreading. The results highlight an important isostatic movement during salt deposition, large but not enough to eliminate a needed depression to accommodate the thick evaporites. By quantifying the halokinetic lateral deformation through time, the results suggest less intensity of the phenomenon throughout the Paleogene, with minor impacts on the petroleumsystemin this period.