Paleoecologic implications of foraminiferal assemblages in the Upper Cretaceous-Paleogene strata, eastern Dahomey (Benin) Basin, southwestern Nigeria

Abstract

The paleoecologic conditions of eastern Dahomey (Benin) Basin during Late Campanian-Eocene were investigated using foraminifera as proxies. Twenty-four (24) samples obtained from four (4) exploration boreholes and three (3) exposed outcrop sections were subjected to conventional micropaleontological processing techniques. Thirty-one (31) species of foraminifera (25 benthic and 6 planktic species) were identified from the samples. The recovered assemblages consist predominantly of Paleocene calcareous benthic species such as Anomalinoides midwayensis, Anomalinoides umboniferus, Eponides pseudoelevatus, Gavellina guineana, and Cibicides succedens. Sparse occurrence of Late Cretaceous agglutinated benthic species comprising Ammobaculites coprolithiformis and Textularia hockleyensis was also recorded. The Upper Cretaceous strata are either devoid of microfauna or contain few agglutinated taxa suggestive of continental to brackish water settings. The development of calcareous benthic foraminiferal assemblages in Paleogene strata of the study area signaled the incursion of open marine neritic conditions. Influx of sandy sediments at some horizons in the studied boreholes resulted into increased pore-water oxygenation leading to poor preservation of benthic foraminifera at these horizons. Planktic/benthic (P/B) ratio analysis of the foraminiferal assemblages suggests paleo-water depth not exceeding 65 m.