Foraminifera Biostratigraphy and Paleoenviroment Of The Etop Well,Deep Offshore,Niger Delta,Nigeria

Abstract

lithostratigraphic and foraminiferal biostratigraphic study has been carried out on ditch cutting samples from Bonga-Etop well located in the offshore area of the Niger delta. An attempt was made to determine the relative age and depositional environment of the section.  A lithologic analysis of the section shows that the samples are made up of shale, claystone and siltstone which are grey to dark grey and brown in colour with intercalations of medium to fine grained sandstone beds. The dark coloured shale are also characteristics of environments with fluctuating salinities and limited circulation formed under anaerobic conditions. From the lithofacies analysis, varying percentages of Quartz, Rock fragments, rootlets, fecal pellets and fossils were recorded. The section yielded planktonic and benthonic forms with significant variations in abundance and diversity. The depth to depth foraminifera assemblage suggests the fossil Orbulina universa as the index fossil hence assigning the age as Middle Miocene. Planktic percentage was found to be higher infering a deep marine depositional environment for the section. The abundance of planktonic foraminifera also indicates salinity and clarity of waters during deposition of the section. Based on composition of North pacific planktonic foraminifera faunas after Bradshaw (1959), Orbulina universa, Globorotalia menardii, Globigernoides

conglobactus, Globigerina ruber and Pulleniatina sp. are all indicative of warm water conditions.