Comparison of depositional sequences and tectonic styles among the West African deepwater frontiers of western Ivory Coast, southern Equatorial Guinea, and northern Namibia

Abstract

The recent success of Tertiary plays in the deepwater offshore central West Africa has generated exploration interest in underexplored Upper to Middle Cretaceous plays along the margin. Three areas are examined in this article, including: the upper slopes of western Ivory Coast, southern Equatorial Guinea, and northern Namibia. Depositional sequences in the three areas have similar development but differ in depositional character and form. Initial identification of sequences is based on unconformity bound units seen on 3D seismic data. There are 6–7 major seismic sequences identified in each area. Each seismic sequence is correlated to well control for age and approximate lithologic calibration using 2D seismic data sets. The central West African margin includes offshore territories from the transform-bounded Gulf of Guinea to the north, down to a southern limit just north of Walvis Ridge (Figure 1). The areas considered in this study include the offshore areas of western Ivory Coast, southern Equatorial Guinea, and northern Namibia. The Ivorian margin is bound by two transform zones—the St. Paul to the north and the Romanche to the south. The Ivory Coast data consist of a 1200-km2 3D seismic survey offshore the westernmost edge of the country. The data were acquired and processed in 2000. The area is approximately 150–200 km west of, and along trend, with the discoveries in a present-day shelf to upper slope position. The second, centrally located study area overlies the Ascension Transform Zone in southernmost Equatorial Guinea. A 3120-km2 3D seismic survey forms the basis of the interpretation in this area. A prestack time migration was applied to the data, which were acquired and processed in 2001. The data are 20–30 km south of the Rio Muni Basin discoveries and extend to the northern edge of the Gabonese salt basin. The third, most southerly study …