Lithofacies and depositional environment of the Amasiri Sandstone, southern Benue Trough, Nigeria

Eight lithofacies typical of mass flow, turbidity current and tidal shelf were identified. The sandstone outcrop sections exhibit pronounced Bouma sequences. A shelf to deep water depositional model is proposed for the Amasiri Sandstone. Eight lithofacies typical of tidally-influenced shelf, mass flow and turbidity current processes characterize the Amasiri Sandstone (Cenomanian - Turonian) in the southern Benue Trough, Nigeria. The cross bedded sandstone lithofacies (Sxm) in Afikpo area were deposited in tidally influenced, shallow sandy shoreline environment while similar lithofacies associated with the conglomeratic lithofacies (Sfc) in Akpoha are proximal canyon-fill deposits. The conglomeratic lithofacies with rip-up clasts together with the massive, horizontal-bedded lithofacies (Smm) and parallel-laminated sandstone lithofacies (Sfl) in Akpoha were deposited in confined channels in proximal submarine canyon setting. The wavy/ripple-laminated sandstone lithofacies (Sfw) and very fine grained bioturbated sandstones lithofacies (Sfb) represent weakly confined distributary splay and unconfined associations in proximal to distal submarine canyon settings. The bioturbated mudstone lithofacies (Msb) and parallel-laminated mudstones lithofacies (Msl) comprise the bypass/levees association in the inner to outer shelf and in the distal canyon settings. Overall, these lithofacies indicate deposition in shelf to deep water depositional environments.