Original scientific paper
Petrographic and stratigraphic analyses of Palaeogene Ogwashi-Asaba formation, Anambra Basin, Nigeria
Clement Bassey
; Department of Geosciences, Akwa Ibom State University, Mkpat Enin, Nigeria
Oboho Eminue
; Department of Geosciences, Akwa Ibom State University, Mkpat Enin, Niger
Abstract
An integrated analytical approach comprising petrographic, geochemical, and sedimentological studies was carried out in thirteen outcrop and four subsurface samples of the Pakaeogene Ogwashi-Asaba Formation in the Anambra Basin. The goal was inferring about source rock, transport history, tectonic setting, depositional environment and hydrocarbon potentials. Sandstones are coarse to medium grained, moderately to poorly sorted, fine to nearly symmetrically skewed. Bivariate plots of skewness against sorting and sorting against mean size indicate a fluvial depositional environment. Most of the sandstone exhibit bimodality, which indicated more than one source. Those are lithic arenites comprising 64% rock fragment, 31% quartz, 5% feldspar which suggest that they are mineralogically immature sands. The ternary plot of the framework elements revealed that they are derived from an orogen which is taken to be a molasse trough formed between basin and craton. Geochemical analysis showed the prevalence of SiO2 (5.84-84.57%) and total Fe (12.69-92.07%) over all other oxides. This points to an oxidizing, sub aerial environment, which favours the formation of hematite. SiO2/A2O3 ratio indicates chemical immatureness. Organic analysis in lignite gave TOC 1.60-3.13%. Vitrinite dominated maceral suggested has the source potential for gas. Scatter plots (tissue preservation vs. gelification index) indicated on swamps as depositional environment of lignite.
Keywords
Ogwashi-Asaba Formation; Anambra Basin; Palaeogene; sandstone lithofacies; Nigeria
Hrčak ID:
86221
URI
Publication date:
31.8.2012.
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