The Calabar Flank sedimentary basin that extends from the southern margin of the is Oban Basement complex to the boundary with the e Niger Delta. Here, sudden sediment thickening e demarcates the Niger Delta Basin that formed as the latest of a series of basins in the Benue Trough, diagonally crossing Nigeria from the southwest to ir the northwest.
Northwest-southern trending basement structures underlie the Calabar Flank and e define the ltu High and the lkang Trough, thus relating the Calabar Flank to the South Atlantic Cretaceous marginal basins with similar horst-and-graben structures in Angola and Gabon. The sedimentary succession on the Calabar Flank is mostly of Cretaceous age, comprising an ancient river-borne sandstone, the Awi Formation; and the overlying marine Odukpani Group of Albian to Late Cretaceous age.
The Odukpani Group comprises the Mfamosing Limestone, the Ekenkpon Shale and the New Netim Marl, which :h are all exposed near the Odukpani local government area headquarters. This is unconformably covered by the Nkporo Shale. Tertiary marine shales and regressive sandstones overlie the Cretaceous succession. The total sediment thickness in the surfaces of the Calabar Flank is over 3500m.