Cretaceous cyclic sedimentation in the southern Benue trough, together with unconformities, provide a tripartite subdivision of the sedimentary succession into (1) the Albian Asu River Group, (2) the late Cenomanian to early Santonian Cross River Group (new name) comprising the marine Nkalagu Formation (new name) and interfingering marginal marine sandstones, and (3) the post-Santonian coal measures sequence.

Most of the Albian to Eocene marine shales in the Benue trough and the Turonian shales in the southern Chad basin contain well over 0.5% total organic carbon, with values of up to 7.4% in Turonian anaerobic shales. Based on the high content of soluble organic matter, thermal maturity, and the predominantly terrigenous character of the Late Cretaceous shales, mostly natural gas was probably generated in both basins. The late Santonian folding and uplift would have disrupted petroleum reservoirs. Also, crude oil accumulations which were not dissipated by tectonism would be relocated at relatively shallow depths and hence become accessible to invading meteoric waters.