STRATIGRAPHY AND STRUCTURE OF THE CRETACEOUS GONGOLA BASIN, NORTHEASTNIGERIA

The N-S aligned Gongola Basin links Nigeria's Benue Trough with the Bo rnu (Chad) Basin forming part of the West African Rift System. Its lit hostratigraphical sequence begins with thick Lower Cretaceous continen tal clastics, the Bima Group. Basically fining-upwards, these clastics are divisible into the ''Lower'', ''Middle'' and ''Upper Bima'' forma tions. The continental to marine Yolde Formation lies above. The Pindi ga Formation represents the greater part oi the dominantly marine Uppe r Cretaceous Series. II is divisible into three units: the Kanawa Memb er, Upper Cenomanian to Lower Turonian shales and limestones; the Gula ni, Deba Fulani and Dumbulwa members, sands deposited during a Middle Turonian regression; and the Fika Member, marine and mainly argilllace ous, at the top. The Gombe Formation, a Maastrichtian coarsening-upwar d deltaic unit, which infilled a sea closed to the south, completes th e Cretaceous sequence. The basin structure was controlled by NE-SW (st rike-slip), N-S (strike-slip) and NW-SE (normal) trending faults. Fold axes have variable trends, dominantly N-S and E-W, resulting from str ess patterns produced in association with the strike-slip movements. M ajor deformations occurred during the Maastrichtian. Several earlier t ectonic episodes occurred locally, notably along the Gombe fault and i n the positive block of the ''Dumbulwa-Bage High'' which forms the nor thern boundary of the basin. Regional compression may have occurred du ring the Santonian.