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International audienceThe structural restoration of two parallel cross-sections in the central portion of the Santos Basin enablesa first understanding of existent 3D geological complexities. Santos Basin is one of the most proliferousbasins along the South Atlantic Brazilian margin. Due to the halokinesis, geological structures presentsignificant horizontal tectonic transport. The two geological cross-sections extend from the continental shelfto deep waters, in areas where salt tectonics is simple enough to be solved by 2D restoration. Such crosssectionsdisplay both extensional and compressional deformation. Paleobathymetry, isostatic regionalcompensation, salt volume control and overall aspects related to structural stylewere used to constrain basicboundary 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 2Drestoration are consistent with five major sequences of sedimentary evolution: (1) the brittle pre-saltdeformation, (2) the significant and fast salt deposition, (3) the initial post-salt deformation with predominantrafting tectonics, (4) the Late Cretaceous progradational deposition and coeval development ofcompressional minibasins, and (5) the Cenozoic sedimentary deposition, with less intense salt tectonics. A1D subsidence analysis based on the 2D restored results is shown as a useful restoration control tool. The 1Dresults indicate that an initially proximal infill evolves towards distal regions under salt tectonics control. The1D diagrams also record the history of the overburden movements through lateral depocenter migration inminibasins areas, submitted to large horizontal salt spreading. The results highlight an important isostaticmovement during salt deposition, large but not enough to eliminate a needed depression to accommodatethe thick evaporites. By quantifying the halokinetic lateral deformation through time, the results suggest lessintensity of the phenomenon throughout the Paleogene, with minor impacts on the petroleumsystemin thisperiod

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The hypothesis that Kohout thermal convection may have induced the massive dolomitization of the 60 m thick lowest more reefal unit in well Unda [top of Great Bahama Bank (GBB)] is evaluated through numerical modelling. A twodimensional (2-D) section, including lithological and petrophysical data, together with datings for the sediments of the GBB, was used in the basin model TEMISPACK to reconstruct the history of the whole platform, with a focus on the reef unit.Simulations showed that during high sea-level periods, Kohout convection is a valid mechanism in the settings of the GBB, although the convection cell remains¯at in most cases because of high permeability anisotropy. This mechanism induces rapid¯uid¯ow in the super®cial as well as in the deeper parts of the platform, with velocities of at least two orders of magnitude higher than with compaction alone. Lithology appears as a strong control of¯uid circulations at the margin scale through the permeability anisotropy, for which a critical value lies between values of 10 and 100. The reefal unit in Unda is part of a larger area determined by the lithologic distribution, in which¯ow velocities are signi®cantly higher than in the rest of the platform. These velocities are high enough to bring the magnesium necessary to precipitate the observed amounts of dolomite, within durations in agreement with the available time of post-reef deposition high sea level(s). However, neither¯uid¯ow pattern nor¯ow velocities are able to explain the preferential massive dolomitization of the lower reef unit and the complete absence of dolomite in the upper one.

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