Palynostratigraphy, palynofacies and thermal maturation of the Nsukka Formation from an excavation site in Okigwe, Southeastern Nigeria
Date
2016-03
Authors
Durugbo, Ernest Uzodimmaa
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Abstract
There is a dire need to assess the petroleum generating potential of the Nigerian inland basins. The Nigerian Federal Government has in the last few years demarcated the inland basins, of which little is known palynologically, for oil and gas exploration activities. An input from Nigeria concerning events of the Cretaceous -Paleogene boundary would broaden our knowledge of the global event. This palynological study of the Nsukka Formation from an excavation site in Okigwe, Southeastern Nigeria, revealed abundant records of pollen, spores and dinoflagellate cysts. Palm pollen Longapertites marginatus, L. vaneendenburgi, L. microfoveolatus, Spinizonocolpites echinatus, S. baculatus and Foveomonocolpites bauchiensis dominated the microfloral assemblage with common dinoflagellate cysts, especially Ifecysta spp., Cordosphaeridium spp., Fibrocysta spp., Senegalinium spp., Cerodinium spp., Phelodinium spp., Spiniferites spp. and Hafniasphaera spp., indicating alternating shallow to marginal marine depositional environments. The already published ranges of the palynostratigraphically important taxa such as Buttinia andreevi, Monocolpopollenites sphaeroidites, Rugulatisporites caperatus, Zlivisporis blanensis, Cingulatisporites ornatus, and the earliest Danian dinoflagellate cyst markers Damassadinium californicum, Carpatella cornuta, Hafniasphaera septate and Senegalinium bicavatum, enabled the delineation of the age as Late Maastrichtian-Middle Paleocene. The studied Nsukka sequences consist of alternating successions of fine grained sandstones, well bedded dark and sandy shales. The samples were dominated by terrestrial organic components, especially structured phytoclasts, black debris and unstructured phytoclasts/degraded wood elements, indicating deposition in predominantly nearshore environments, coupled with the dominance of peridinoids over gonyaulacoids. However, the basal samples were characterized by common amorphous organic matter co-occurring with dinoflagellate cysts suggesting brief periods of marine transgressions. Using Deltoidospora adriennis as an index, the spore colouration index (SCI), ranged from 4 (golden yellow) to 4.5 (deep yellow) which correlates to vitrinite reflectance values of 0.4 - < 0.5, indicating that the sediments were immature for oil and gas generation.
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Keywords
Nsukka Formation, Okigwe, palynomorphs, spore colouration, phytoclasts