Two principal Upper Cretaceous sedimentary successions in Nigeria show considerable hydrocarbon prospects, especially in parts of southeastern Nigeria.

The first succession, of Albian to Santonian age, is restricted to the eastern half of Nigeria and is comprised mainly of shale, limestone, and sandstone. The basal sandy sediments possibly were deposited in a rift valley genetically related to opening of the South Atlantic. Advanced denudation and subsequent thinning of the crust may have favored the eastern part of Nigeria as the locus of rifting and early basin development. Marine Albian to Santonian sedimentary rocks are present in the southern parts of eastern Nigeria, but the succession is less complete in the north.

The pre-Santonian beds underwent a major tectonic deformation in Santonian--early Campanian time.

The second succession, of Campanian-Maestrichtian age, is present mainly in the western half of Nigeria. The basins are filled with a variety of sedimentary rocks: marine/non-marine shale and ironstone, sandstone, siltstone, and lignite.

The ancient "Guinea sea" and the Tethys sea probably merged twice across Nigeria in the Late Cretaceous, as indicated by faunal and lithologic evidence.