Campano–Maastrichtian foraminifera from onshore sediments in the Rio del Rey Basin, Southwest Cameroon

Abstract

Campanian–Maastrichtian marine sediments outcrop in five genetically linked sedimentary basins along the West African coast in the Gulf of Guinea, from the Douala Basin in Cameroon to the Anambra Basin in Nigeria. These sediments in the more centrally located Rio del Rey Basin have been the least studied. Therefore, the geologic history of this region has merely been speculative. The Rio del Rey Basin like the adjacent Niger Delta is producing hydrocarbon from the offshore Tertiary sedimentary interval in which all studies have been focused, neglecting the onshore Cretaceous sediments. Outcrops in the basin are rare, small and highly weathered. Samples from some of these sediments have yielded a few Planktonic and dominantly benthonic foraminiferal assemblages. The long-ranging heterohelix and hedbergellids characterized the planktics while the species Afrobolivina afra which is a well known diagnostic taxon for Campanian–Maastrichtian sediments in West African basins clearly dominate the benthic assemblage. Its occurrence in association with other Upper Cretaceous forms such as Bolivina explicata, Praebulimina exiqua, Gabonita lata, Ammobaculites coprolithiformis amongst others, formed the basis on which this age was assigned to the sediments sampled from the Rio del Rey Basin. Hence, this work has undoubtedly established the much needed link in this regional geologic history and correlates these sediments with the Logbaba and Nkporo Formations in the Douala Basin in Cameroon and the southeastern Nigerian Sedimentary Basins. Thus, these units were all deposited during this same geologic period and probably controlled by the same geologic event.