Foraminiferal Distribution in the Tertiary Ewekoro Formation, Dahomey Basin, Southwestern Nigeria: Implications for Paleoenvironmental Interpretation and Age Assessment

Abstract

The Ewekoro Formation, a key stratigraphic unit in Nigeria's Dahomey Basin, is renowned for its rich paleontological record, particularly its diverse foraminiferal assemblages. This study aims to investigate foraminiferal assemblages in the Ibese region of the Dahomey Basin to understand paleoenvironmental conditions, by characterizing species diversity and abundance, reconstructing paleoenvironmental parameters, establishing biostratigraphic relationships, interpreting depositional environments, and correlating paleontological data with existing geological information. This study analyzed twenty-nine core samples from PET-1 well in Ibese region, Ewekoro Formation, Dahomey Basin, Nigeria, employing standard lithologic description and foraminiferal preparation techniques, including kerosene treatment, wet and dry sieving, and microscopic examination, to investigate the formation's microfossil content and sedimentological characteristics. Among these twenty-nine (29) cores samples, only two planktonic species, Acarinina soldadoensis and Morozovella conicotruncata, were identified. The quantitative analysis yielded a total count of 933 benthic foraminifera across 10 species which include Anomalina plummerae, Anomalinoides midwayensis, Anomalinoides umbonifera, Cibicides haperi, Cibicides succedens, Eponides pseudoelevatus, Gavelinella spp., Gavelinella guineana, Florilus spp., and Pararotalia tuberculifera and other Marine Microfauna which include ostracods, gastropods, pelecypods and so on. The foraminiferal assemblages from the PET-1 well, including key species like Acarinina soldadoensis, Gavelinella guineana, and Anomalinoides species, indicate a Paleocene-Eocene age. The Anomalinoides Biozone provides a robust biostratigraphic marker for global correlation. The diverse fossil assemblage, comprising benthic and planktonic foraminifera, bryozoans, ostracods, and echinoids, suggests a shallow to middle neritic marine environment with normal salinity and good oxygenation. This assemblage indicates a warm, humid tropical to subtropical climate and a productive marine ecosystem in an offshore or coastal setting during the Paleocene-Eocene period.