Cretaceous-Tertiary Foraminifera and Palynomorphs from Djega Section and Inferred Paleodepositional Environments Rio Del Rey Basin Cameroon West Africa

摘要

Late Cretaceous-Paleocene foraminiferans and palynomorphs were recovered from the upper section of the Djega outcrop in the Rio del Rey Basin. Only a few planktonic foraminiferan species of the genera Heterohelix and Hedbergella were recovered among an assemblage dominated by calcareous and agglutinated benthonics. Marine dinocysts are curiously absent from among the palynomorph assemblage, which consists dominantly of pollen grains from land plants (angiosperms and gymnosperms) and pteridophytic spores, together with a few fungal remains. Two benthonic foraminiferal assemblages that include the Campanian-Maastrichtian Bolivina afra-Haplophragmoides talokensis and the Paleocene Anomalinoides umboniferus-Eponides pseudoelevatus are well established at this outcrop. The palynomorphs include a few typical Late Cretaceous and typical Paleogene species, while the majority are long ranging forms that straddle the Cretaceous-Tertiary boundary. The foraminiferal and palynomorph biostratigraphic distributions permitted us to recognize the succession of Campanian-Maastrichtian and Paleocene strata and the Cretaceous-Tertiary boundary for the first time in this basin. Lithofacies change from a monotonous thick pile of shales below, succeeded by sandstones, frequently alternating with mudstone, above. This indicates a general fall in sea level during the Early Paleocene earlier reported within this subregion, and the boundary marks the start of the out building of the Niger Delta which the Tertiary Rio del Rey Basin is part of. Both microfossils and lithofacies analyses aided the reconstruction of an open marine, probably middle to inner neritic shallow and transitional intertidal paleodepositional environments for the sediments exposed at this outcrop.