Shallow Marine Cretaceous Sequences and Petroleum Geology of the Onshore Portion Rio del Rey Basin, Cameroon, Gulf of Guinea

Abstract

Extensive thickly folded sedimentary sequences are exposed onshore of the Rio del Rey Basin contrary to previous reports of their rarity. Shales predominate, frequently intercalated by marl- stones, sandstones, mudstones, limestones and marls and have been intruded in places by vol- canic rocks of the Cameroon Volcanic Line (CVL). An integration of lithostratigraphic, paleon- tologic, granulometric and petrographic data generated from field and laboratory studies, per- mitted the identification of eleven (11) lithofacies which were subsequently grouped into three facies associations to facilitate the reconstruction of the paleo-depositional environment. Graphic logs constructed from the different outcrops studied revealed general coarsening upward se- quences. Mega body fossils recovered from these sediments include severely altered, ferruginized fish and turtle-like heads, bivalve shells and moulds. Two bivalve taxa were identified: Exogyra ponderosa (Roemer) and members of the Venericardiinae sub-family. Textural and mineralogical details were obtained from granulometric and thin sections (microscopy). Interpretation of these data inferred an open relatively deeper marine, probably middle neritic to near shore transitional intertidal environments into which these sediments previously dated as Lower to Upper Cretaceous were deposited. Elements of a possible petroleum system: source and reservoir rocks, migratory pathways and trapping conditions, have been pointed out and thought to exist in space and time.