Jornal de Geologia e Geofísica
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New Lithostratigraphic Data and Depositional Pattern of the Mamfe Sedimentary Basin, Cameroon, West Africa

OA Njoh, EU Essien, ME Udofia, GM Agyingi, JA Taku, M Bessonge

As part of the West Central African Rift System and the southeastern extension of the Benue Trough that straddles the Nigeria/Cameroon territorial boundary, the Mamfe Basin also holds the history of the opening of the South Atlantic Ocean. It has become so strategic because of its hydrocarbon and solid mineral potentials. However, ever since geologic studies began in this basin, no concerted efforts have ever been made toward harmonizing and standardizing its stratigraphic framework. Consequently, several frameworks exist in literature wherein, no two authors agree on the ranking, number of units or their nomenclature, and none presents designated type sections or type localities of units described. Research activities have however recently intensified with the involvement of international hydrocarbon companies. In order to guarantee its unambiguous intelligibility, an urgent need to review, amend and erect a new standardized and harmonized lithostratigraphic column for the Mamfe Basin is compelling. Preliminary data from on-going basin-wide studies have confirmed its tripartite depositional pattern which typifies most Cretaceous tropical lacustrine basins comprising: a basal alluvial and fluvial, a middle deep to shallow lacustrine, an upper fluvio-deltaic setting. Sequences studied present different units with unique facies characteristics, lithofacies associations, depositional environment and processes, and lateral extent. Palynological analyses revealed non-marine sediments of Aptian-Cenomanian-Turonian ages. Guided by the international stratigraphic code, a type-section and type-locality were described for each unit and the most appropriate names re-assigned. Each unit was shown to be mappable and exhibits peculiar internal homogeneity. Accordingly, they have now been reviewed from the rank of members (as in previous literature) to formations, from bottom to top as follows: • Okoyong Formation, type section: Awatu hill outcrop, • Manyu River Formation, a composite type-section: Satom bridge and Nfaitok outcrops, • Akwen Formation, type section: The Akwen and Ndebayang outcrops. A new lithostratigraphic column and depositional pattern have been proposed for the basin