Palynological Study of OSE 1 Well in Offshore Niger Delta Basin: Implications for Age, Paleoclimate and Depositional Paleoenvironment

Palynological study of 45 ditch samples from sedimentary successions penetrated by OSE 1 well located offshore western Niger Delta Basin was undertaken to determine the age of the sediment and reconstruct the paleoclimate and depositional paleoenvironment. All the analyzed samples were composited at 30 ft from stratigraphic depth interval of 6330 to 9010 ft. The lithologic composition comprised mainly of brownish grey or light grey, fine-grained shales with a gypsiferous horizon near the bottom. Palynological slides were prepared following standard palynological preparation procedures of sample maceration with hydrochloric (HCl) and hydrofluoric (HF) acids. The samples yielded moderately well-preserved, low to high diversity palynomorph assemblages of 58 taxa comprising 29 pollen grains, 9 pteridophic spores, 17 dinoflagellates, one acritarch, one freshwater algae and a fungi spore. The stratigraphic distribution of microflora assemblages was highly variable. The assemblage abundance was dominated by pollen and spores. The retrieved pollen grains included Monoporites annulatus, Sapotaceoidaepollenites sp. Psilatricolporites crassus, Psilatricolporites sp., Zonocostites ramonae, Retitricolporites irregularis, Monocolpites marginatus, Monocolpites sp., Pachydermites diederixi, Proxapertites cursus, Verrutricolporites rotundiporus, Striatopollis catatumbus, Retistephanocolpites gracilis, Echiperiporites estalae, Echiperiporites sp. and Inaperturopollenites sp. The retrieved spores included Magnastriatites howardi, Acrostichum aureum, Laevigatosporites sp., Polypodiaceoisporites sp., Verrucatosporites sp., Crassoretitriletes vanraadshooveni and Stereisporites sp. The recorded dinoflagellates included Achomosphaera sp., Andalusiella sp., Polysphaeridium zoharyi, Selenopemphix nephroides and Spiniferites sp. Leiosphaeridia sp. was the only acritarch present in the assemblage. The freshwater algae was Botryococcus braunii. Fungi spore was present but not in significant amount. The stratigraphic interval was dated Early to Late Miocene (Burgidalian-Messinian) based on the occurrence and distribution of some stratigraphic fossil marker species including Magnatriatites howardi, Crassoretitriletes vanraadshooveni and Retistephanocolpites gracilis The abundant occurrence of pollen and spores typical of rain forest and freshwater swamp communities in the assemblage indicated tropical paleoclimatic conditions. The distribution pattern of Monoporites annulatus (Poaceae) and Zonocostites ramonae (Rhizophora) suggested seasonal fluctuations between dryer and wetter climatic conditions. The sediments were deposited in a wide range of environments including brackish lagoons, open salt water swamps, freahwater and nearshore to inner neritic settings.

Geochemistry of Maastrichtian Clastic Sedimentary Rocks from Western Flank of Anambra Basin, Nigeria: Implications for Provenance, Tectonic Setting, Paleoclimate and Depositional Paleoenvironment

The geochemistry, provenance, tectonic setting, paleoclimate and depositional paleoenvironment of Maastrichtian clastic sedimentary rocks from the western flank of Cretaceous-Tertiary intracratonic Anambra Basin, Nigeria have been studied through major and trace element geochemical analysis. Ten (10) representatives outcrop samples collected from two stratigraphic sections in the study area were analyzed chemically using Inductively Coupled Plasma Atomic Emission Spectroscopy, ICP-AES (Lithium Borate Fusion). The geochemical data shows that the sediments are enriched in major oxides including SiO2, Al2O3, Fe2O3 and TiO2 but depleted in other major element oxides. Also, the sandstones have higher concentrations in SiO2, CaO and Na2O compared to the associated mudrocks whereas the mudrocks are more enriched in Al2O3, Fe2O3, MgO, K2O, TiO2 and P2O5 compared to the sandstones. The mudrock samples have higher concentration of Ba, Ni, Sr, Y, Nb, Sc in comparison to sandstones. However, sandstone samples have higher concentration in Zr (1098.50 ppm) than the mudrocks (1038 ppm). The sandstones are classified as litharenites, sublitharenites, Fe-rich sandstones, while the mudrocks are labeled as shale and Fe-rich shale based on chemical composition. Analysis of the data shows a dominantly felsic igneous to intermediate igneous and quartzose sedimentary provenances of mixed granite and granodiorite composition as indicated by various discriminant plots. The inferred provenance is corroborated by the low concentrations of Cr, Ni and Sc in the samples and other proxies. On the basis of various tectonic setting discriminant function diagrams, the Maastrichtian sediments from the study area were deposited on passive margin tectonic setting that developed consequent to the breakup of Gwandana supercontinent but was later affected by tectonism in Santonian times. The alteration feldspars to smectite and kaolinite as depicted by the A-CN-K ternary diagram alongside the high values of chemical index of alteration (CIA, 87.38 - 98.09) and chemical index of weathering (CIW, 89.22 - 99.90) indicates paleogeographic setting characterized by warm and humid/tropical paleoclimatic condition where there was prevalence of intense chemical weathering. The low values of Sr/Ba ratio (0.31 - 0.70) suggest sediment deposition in continental to deltaic paleoenvironment.