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Regional Case Studies |
Amerada Hess Limited, 33 Grosvenor Place, London SW1X 7HY, UK
Salt movements have dominated the post-Aptian tectonic process of the West Africa Salt Basin, which extends from northern Namibia to southern Cameroon. The thick salt layer was deposited during the Aptian within the shallow rift basins of the proto-South Atlantic and was overlain by an extensive carbonate platform. As a result of the basinward tilt of the margin, the carbonate platform and the overlying Upper Cretaceous sequence slid on the salt layer and broke up into smaller blocks. This process caused a mobilization of the salt and the formation of salt rollers, salt diapirs and a whole suite of raft tectonics structures such as turtlebacks, carbonate rafts and severe folding at the toe of the salt basin. Although this process is seen throughout the Angola Salt Basin, the areal distribution of the salt movement-induced structures shows a significant differentiation. Burial history curves also show important differences along the margin in the post-Aptian subsidence. Analysis of recent seismic data suggests that the thin-skinned extension needed for salt and raft tectonics is accommodated basinward by folding of the overburden up to a point where all the extension has been taken up. From there to the toe of the salt layer, the overburden is largely undisturbed. The salt and raft tectonics in the Angola Basin was the main factor that influenced the distribution of oil reserves in the region and its understanding is very important for hydrocarbon exploration there.
