Abstract

A seismic-stratigraphic investigation integrated with the structural modeling of the southern part of the Orange Basin passive margin, South Africa, demonstrates that a single tectonic event resulted in a significant alteration to both the location and style of sediment accumulation during its postrift evolution. This alteration to the margin has a significant effect on the hydrocarbon system of the area, we predict that it increased the hydrocarbon potential of the area. The evolution of the margin can be divided into two principal phases; the first comprised an overall aggradational shelf margin with little or no deformation during the Cretaceous. Deposition during the Late Cretaceous was punctuated by an episode of margin tilting that resulted in significant erosion of the inner margin and alteration of the margin architecture. The second phase of deposition, during the Tertiary, occurred to the west of the Cretaceous shelf margin and was characterized by significant margin instability and the development of a coupled growth fault and toe-thrust system. This change in passive-margin configuration and the associated switch in the location of overburden accumulation is likely to have increased the petroleum prospectivity of the deep-water part of the margin. We predict that the rapid western (seaward) migration of sediment accumulation resulted in the maturation of the high-quality distal source interval, whereas the resulting toe-thrust geometry provides suitable structural traps for the hydrocarbons.

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