Upper-Cretaceous and Paleocene Biostratigraphy of Nkporo Shales, Calabar Flank, Southern Benue Trough

Abstract

The present study Biostratigraphic (foraminiferal and palynological), paleoenvironment and paleoecological evaluations are aimed at interpreting the lithology, age, paleoenvironmental as well as the paleoecological condition of the deposited sediments newly exposed along Ikot Okpara Otopy, Southeastern Nigeria. Lithological descriptions of the samples reveal that this section is predominantly shale. This shale is dark grey to light brown, fossiliferous with minor occurrence of silts and sandstones. Foraminiferal analysis reveals a Paleocene interval within the Nkporo Formation for the first time. The sediments have low to moderate number of taxa with 96% benthic and 4% planktics, while a total of 196 microflora were recovered and identified. The microfloral species contain 60% of continental plants with 40% of marine counterparts. Key foraminiferal taxa used in this study include Bolivina afra, Bolivina explicata, Globigerina fringe and Haplophragmoides talokaense, while their microfloral counterparts encountered within the section include Cingulatisporites ornatus, Auriculidites reticulates Ephedripites ambonoides, Retidiporites magdalenensis, Synolocolporites marginatus, Constructipollenites ineffectus, Foveotriletes margaritae, Buttinia andreevi, Proxapertites operculatus, Zlivisporis blanensis and Paleocystodinium sp. These assemblages (Foraminiferal and Palynological) depict the deposition of these sediments during the Maastrichtian Paleocene age. The combination of lithologic and biostratigraphic data reveal paleoenvironment interpretation of the study section to range from marginal - shallow to Middle neritic paleo-water depths, while the paleoecological studies depicts a fluctuation in the salinity from brackish to marine settings deposited within a tropical to subtropical warm and humid climate.