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

Agbor Junior Taku,Olivier Anoh Njoh

doi:10.4236/ojms.2016.62014

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 marlstones, sandstones, mudstones, limestones and marls and have been intruded in places by volcanic rocks of the Cameroon Volcanic Line (CVL). An integration of lithostratigraphic, paleontologic, granulometric and petrographic data generated from field and laboratory studies, permitted 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 sequences. 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 theVenericardiinae 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.

Highlights

The Rio del Rey Basin occupies the extreme south-western part of Cameroon (Figure 1), in the Gulf of Guinea.How to cite this paper: Njoh, O.A. and Taku, A.J. (2016) Shallow Marine Cretaceous Sequences and Petroleum Geology of the Onshore Portion Rio del Rey Basin, Cameroon, Gulf of Guinea
The shales comprise of thick beds that are intercalated in places by limestones, marlstones, sandstones and concretions
The simple bedsets or cosets represented by alternating beds of shale and sandstones as in the MS and Sandstone-Mudstone Couplets (SM) facies characterizes repetitions of genetically related conditions in a given depositional environment, while the composite bedsets or cosets represent repeated alternations of two sets of conditions occurring in a given sedimentary environment [44] [45]

Summary

Introduction

The Rio del Rey Basin occupies the extreme south-western part of Cameroon (Figure 1), in the Gulf of Guinea. (2016) Shallow Marine Cretaceous Sequences and Petroleum Geology of the Onshore Portion Rio del Rey Basin, Cameroon, Gulf of Guinea. The Rio del Rey Basin accounts for over 70% of Cameroon’s hydrocarbon production with the oilfields located exclusively offshore and within the Tertiary strata for which this basin is known. Apart from the recent deltaic sands that are loose and widespread probably as overbank flow deposits, the Tertiary sediments of this basin occur exclusively offshore [2] [8] To these early studies, [4] and many others have revealed that northward, away from the swamps and towards the edge of the basin, thick sedimentary strata occur and have been folded, uplifted and are well exposed along deeply incised river channels. Heavy rainfall, high rate of weathering, thick tropical evergreen forest, extensive mangrove swamps and the many rivers at their third stage, characterize this region and partly account for the stagnation of geologic field studies

Geologic Setting

Materials and Methods

Facies Descriptions

Facies Associations and Depositional Environments

Petrographic and Granulometric Analyses

Petroleum Potential

Reservoirs

Trapping Mechanisms

Petroleum System

Conclusions

Conflict of Interest