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

Abstract

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.