| Popis: |
Biostratigraphy investigation of Nsukka Formation was carried out by subjecting well cutting samples obtained from Nzam-1 well to palynological studies with the view towards determining the relative geologic age and palaeoenvironment of deposition of the sediments. Samples were treated in the laboratory through digestion with hydrofluoric acid, sieving with 5 μm, oxidation with Nitric acid and mounting of the slides into sections with DPX mountant. A fairly high abundance and diversity of miospores were recovered, while the interval (847–1372 m) contains distinctive and diagnostic palynomorphs which are stratigraphically important. A Spinizonocolpites baculatus assemblage zone was established based on the basal occurrence of S. baculatus, Spinizonocolpites echinatus, Constructipollenites ineffectus, Periretisyncolpites sp. Periretisyncolpites giganteus, Monocolpites sp 1, Foveotriletes margaritae, Syncolporites marginatus, and Longapertites marginatus. The upper part of the interval is marked by association of Anacolosidites luidonisis (at top), Mauritiidites crassibaculatus, Retistephanocolpites williamsi, Proteacidites dehaani, Echitriporites trianguliformis, Proxapertites cursus, Retidiporites magdalenensis, S. baculatus, Retitricolpites gigeonetti, F. margaritae and Araucariacites sp. The Nsukka Formation is dated as Late Maastrichtian based on the co-occurrence of recovered index fossils. Importantly, Cretaceous–Tertiary (K/T) boundary is marked by high fossil content in the Maastrichtian sediments compared to paucity in palynomorph that characterise the overlying Paleocene facies. Palaeoenvironment of the analyzed section varies alternately from marginal marine to continental setting based on the presence of land-derived miospores and dinoflagellates. |
