Abstract
Recent important discoveries of gas and oil fields during the last few years have called attention to the Santos Basin, offshore Southeast Brazil. The basin is located south of the Campos Basin, the most prolific Brazilian oil province. The Cabo Frio Arch is the frontier between them, but the two basins present many similarities in their structural and stratigraphic evolution. Meanwhile, the Upper Cretaceous record is significantly more preserved in the Santos Basin, being characterized by thick Santonian to Maastrichtian progradational siliciclastic clinoforms. The accommodation space was generated by salt basinward withdrawal, which in consequence caused the rafting of the Albian Guaruja carbonate sequences and of the deposition of Cenomanian to Turonian marine shales and Ilhabela turbidites. Because of the withdrawal of Aptian transitional evaporites and rafted younger sequences, the deltaic clastic wedges downlap the pre-Aptian unconformity, placing in contact Upper Cretaceous reservoirs with Lower Cretaceous rift source-rocks. Progradation was not simultaneous along the basin and resulted from migration of sediment input along the Brazilian margin. In order to understand the way of depocenter migration, a sequence stratigraphic analysis was carried out using available seismic lines and well data. The sequence boundaries were traced in 60 wells, and isopach and several lithologic ratio maps were produced for each sequence. The maps show clearly a depocenter migration towards northeast during the Late Cretaceous along the Santos Basin into the Campos Basin, where the Tertiary section is well developed. Early Tertiary section is well developed in the north portion of the Santos Basin, represented by prominent deltaic progradation and associated turbidite systems. Another important Tertiary depocenter is placed in the southmost portion of the Santos Basin, where deep-water systems were recognized in seismic sections. The recognition of the pathway of depocenter migration is an important guide to oil and gas exploration, since it support interpretation concerning the relation between the formation of reservoir rocks and the timing of petroleum generation and migration.
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