Biostratigraphy and Palaeoecological Studies of the Late Cretaceous-Tertiary Sediments in the Dahomey Basin, Nigeria

The Maastrichtian–Eocene sediments (mainly shales and limestones) penetrated by the Itori borehole and Ilaro boreholes in the Dahomey Basin were investigated for foraminiferal biostratigraphy and palaeoecological interpretation. These boreholes penetrated Araromi, Ewekoro, and Oshosun formations at varying depths. Selected shale sediments were subjected to foraminiferal analysis and many planktonic and benthic species of foraminifera (agglutinated and calcareous) were recovered from the Cretaceous interval of the penetrated boreholes. Twelve species of planktic foraminifera (Globalomalina planocompressa, G. pseudomenardii, Globigerina inaequispira, Acarinina cf.coalingenis, Acarinina nitida, Chiloguembelina cretacea, chiloguembelina subtriangularis, Orthokasrstenia sp., Hedbergella holmdelensis, Globigerina sp., Globigerinelloids asperus, Morozovella formosa formosa) and thirteen species of benthic i.e Bolivina sp., B. Crassicostata, , E. africana, Eponides psuedoelevatus, Gavelinella cf. guineana, Gavelinella pachysuturalis, Haplophragmiodes sp., Lenticulina cyprina, L. inornata, L. olokuni, L. psuedomamilligera, L. taylorensis, Nonionella communis, N. spissa, N. panamensis, Orthokarstenia sp., Planulina oyae) were identified. In general, benthic species of infauna deposit feeder and epifauna dominate the population. These species occupy a range of environments from dyoxic to anoxic, brackish water to marsh environment down to upper bathyal depth. Based on the abundant and stratigraphical distribution of the foraminiferal species, four biostratigraphic zones were recognized: Afrobolivina afra zone of late Maastrichtian, Globigerina zone of early Paleocene, Globalomalina pseudomenardii zone of late Paleocene and Morozovella formosa formosa zone of the early Eocene.