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, Ponto sphaera, Calcidiscus and Reticulofenestra . All the nannofossils fall within NN11, NN10, NN9, NN8 and NN5 zones belonging to the Middle-Late Miocene age.