Tectonic Setting of the Niger Delta
The Niger delta is situated on the Gulf of Guinea on the west coast of central Africa (Figure 1). During the Tertiary it built out into the Atlantic Ocean at the mouth of the Niger-Benue river system, an area of catchment that encompasses more than a million square kilometers of predominantly savannah-covered lowlands. The delta is one of the world’s largest, with the subaerial portion covering about 75,000 km2 and extending more than 300 km from apex to mouth (Figure 1). The regressive wedge of clastic sediments which it comprises is thought to reach a maximum thickness of about 12 km.
Accumulation of marine sediments in the basin probably commenced in Albian time, after the opening of the South Atlantic Ocean between the African and South American continents. True delta development, however, started only in the late Paleocene/Eocene, when sediments began to build out beyond troughs between basement horst blocks at the northern flank of the present delta area. Since then, the delta plain has prograded southward onto oceanic crust, gradually assuming a convex-to-the-sea morphology.
Throughout the geological history of the delta, its structure and stratigraphy have been controlled by the interplay between rates of sediment supply and subsidence. Important influences on sedimentation rate have been eustatic sea-level changes and climatic variations in the hinterland. Subsidence has been controlled largely by initial basement morphology and differential sediment loading on unstable shale. The delta sequence is extensively affected by synsedimentary and postsedimentary normal faults, the most important