Stratigraphical nature of the Top Albian surface, from seismic and wells data analyses, in the south Sanaga area (Cameroon Atlantic margin): Palaeogeographical significance and petroleum implications

Abstract

The study area is located at the southern part of the Cameroon Atlantic Margin (CAM) in the Gulf of Guinea. This work analyses 20 wells and 02 Cameroon Span seismic lines to re-examine the stratigraphical nature of the Top Albian surface of the CAM for a better understanding of the basin evolution. The results obtained by wells analysis show that, from the Douala sub-basin (Dehane) onshore to the Kribi-Campo continental slope, the Top Albian surface has an erosive shape. The seismic analysis reveals that this surface has two characters: erosive from the continental shelf to continental slope and concordant in the deep basin. This observation indicates that the Top Albian surface corresponds to an unconformity (u/c) on shallow waters with its correlative conformity (cc) in deep basin. The erosive form was amplified by erosion caused by the margin uplift. The combination of seismic and wells data reveals that in shallow waters, the Top Albian u/c erodes Aptian-Albian deposits. These sediments mainly consist of sandstones, shales and evaporitic unit. The occurrence of dark shales before late Albian epoch, suggests that the Douala/Kribi-Campo (DKC) Basin was already transgressed by marine sediments at this time. Hence, the Top Albian surface resulted probably from a relative sea-level fall, mainly caused by the tectonic uplift. The 3D modeling carried out provides a better resolution of its distribution in the study area. This surface boundary has regional extension on the DKC Basin. Furthermore, the Top Albian surface seals both good sandstones reservoir rocks and dark shales source-rocks in the studied basin.