Morphological Description of Calcareous Nannofossils Assemblage of a Middle-Miocene to Late-Miocene Section in the Niger-Delta, Nigeria

摘要

Forty four (44) different forms of nannofossils recovered from the middle-Miocene to late-Miocene sediments of a section ((8900 - 11,000) ft (2713 - 3353 m)) of a well in the prolific oil producing Niger delta, Nigeria were described and grouped into twelve, though not on phylogenetic relationship, for documentation purpose. The standard strewn-slide technique was used to recover the fossils. The aim is to present the distinguishing morphological features of each of the nannofossils group. Of the recovered forms Genus, Discoaster, was found prominent and divisible into six sub-groups: 6-rayed discoaster with bifurcations, 6-rayed discoasters without bifurcation, 5-rayed discoasters, 5-rayed discoaster with acute bifurcations, 5-rayed nannolith and the indeterminate forms. Genus Sphenolithus recovered is also divisible into two: species without prominent apical spines and species with prominent, monocrystalline apical spines. Other genera found and described are Catinaster, Cyclicargolithus, Coccolithu, Minylitha, Syracosphaera, Helicosphaera, Pontosphaera, Calcidiscus and Reticulofenestra. All the nannofossils fall within NN11, NN10, NN9, NN8 and NN5 zones belonging to the Middle-Late Miocene age.