Integrated Sedimentology, Organic Geochemistry, and Depositional Environment of the Ogwashi–ASABA Formation at Mgbiligba Spring, Southern Nigeria

Abstract

Despite the hydrocarbon significance of the Ogwashi–Asaba Formation in the Niger Delta Basin, integrated sedimentological and organic geochemical investigations of the Mgbiligba Spring exposure remain limited, resulting in an incomplete understanding of its depositional history and petroleum source-rock potential. This study integrates sedimentological, micropaleontological, and organic geochemical analyses to reconstruct the depositional environment and evaluate the hydrocarbon generation potential of the Ogwashi–Asaba Formation exposed at Mgbiligba Spring, southern Nigeria. Granulometric analysis of the sandstone and conglomerate facies indicates deposition under predominantly continental fluvial-to-deltaic conditions, characterised by moderate sediment maturity and variable depositional energy. The occurrence of benthic foraminifera, including Ammobaculites, Fursenkoina, and Anomalina, within shale intervals provides evidence of intermittent shallow-marine incursions, suggesting deposition within a transitional marginal-marine setting. Total Organic Carbon (TOC) values range from 1.36% in lignite to 1.66–3.71% in shale, indicating fair to good organic-matter enrichment and appreciable source-rock potential. Organic petrographic analysis reveals the dominance of huminite macerals, with subordinate liptinite and inertinite, reflecting organic-matter accumulation in humid, waterlogged swamp environments. The organic matter is interpreted as predominantly Type II/III kerogen, indicating mixed terrestrial and marine organic inputs with the potential to generate oil and gas where sufficient thermal maturity is attained. These findings provide new insights into the depositional evolution of the Ogwashi–Asaba Formation at Mgbiligba Spring and contribute to an improved evaluation of its petroleum system and hydrocarbon exploration potential within the Niger Delta Basin.