Facies Analysis and Depositional Environment of Cretaceous Sediments Exposed Along Enugu–Agbogugu Road, Anambra Basin, Nigeria

Abstract

This study focuses on facies distribution in Cretaceous outcrops along Enugu-Agbogugu axis of the Anambra Basin, south-eastern Nigeria. It is aimed at unravelling the depositional environments of the sedimentary successions and reconstructing the paleogeographic setting. Six well-exposed outcrops were methodically studied with six lithofacies identified, namely: lateritic claystone, bioturbated sandy heteroliths, carbonaceous shale, coal seam, ironstone beds and cross-bedded sandstones. The lithofacies diagnostic features were flaser and lenticular bedding, herringbone cross-stratification; planar and trough crossbedding and an assemblage of ichnofossils including Planolites, Skolithos, and Asterosoma. The lithofacies were grouped into four genetically correlated facies associations, viz: flood plain, distributary channel, prodelta and open marine or offshore that together defined a deltaic system dominated by fluvial processes and associated tidal overprint. The vertical successions and lateral correlations of lithofacies reveal a stratigraphic architecture indicating a complex history of delta progradation influenced by relative sea-level fluctuations and high sediment supply. The outcrops are generally structurally deformed by joints, fractures, syn-depositional normal faults and folds. The folds are effect of compressive stress believed to be associated with the post-Santonian tectonic events. This outcrop-scale study enhances the understanding of heterogeneity in deltaic reservoir under the strong influence of fluvial and tidal processes, as well as the potential for petroleum stratigraphic and structural traps in Anambra basin and others with similar tectonic and stratigraphic settings.