Jornal de Geologia e Geofísica
Acesso livre

Abstrato

Palynostratigraphy, Paleoclimate and Paleoenvironment of a Segment of GBO-04 Well, Onshore Western Niger Delta Basin, Nigeria

Ogbahon OA, Fola-Dara AO, Enweliku DS

Palynological study of 50 ditch samples from a segment of GBO-04 well located onshore western Niger Delta Basin was carried out determine the age of the sediment and reconstruct the paleoclimate and paleodepositional environments. All the analyzed samples were composited at 60 ft. from stratigraphic depth interval of 3010 to 6030 ft. The lithology was made of shale and friable sandstone. Palynological slides were prepared following standard palynological preparation procedure involving sample maceration with hydrochloric (HCl) and hydrofluoric (HF) acids. The samples yielded well preserved, moderately diversified palynomorph assemblages comprising 72 taxa and belonging to pollen, spores, dinoflagellates, acritarch, algae and fungi spores. The stratigraphic distribution of floristic assemblage was highly variable. The assemblage was dominated by pollen and spores. The pollen included Monoporites annulatus, Brevicolporites guinetii, Sapotaceoidaepollenites spp., Psilatricolporites crassus, Psilatricolporites spp., Zonocostites ramonae, Retitricolporites irregularis, Monocolpites marginatus, Monocolpites spp., Pachydermites diederixi, Proxapertites cursus, Verrutricolporites spp., Ctenolophonidites spp., Arecipites exilimuratus, Arecipites cf. crassimuratus, Striatricolporites catatumbus, Canthiumidites spp., Chenopodiacaea spp., Clavainaperturites clavatus, Crototricolporites crotonoisculptus, Echiperiporites icacinoides, Echiperiporites spp. and Inaperturopollenites spp. The retrieved spores included Magnastriatites howardi, Acrostichum aureum, Laevigatosporites spp., Polypodiaceoisporites spp., Verrucatosporites spp., Crassoratitriletes vanraadshooveni and Verrucatosporites usmensis, Charred graminae curticle, Cyathidites spp. and Foveotriletes margaritae. The dinoflagellates included Achmosphaera spp., Andulusiella polymorpha, Batiacasphaera spp., Selenopemphix nephroides and Spiniferites spp. Leiosphaeridia spp. was the only acritarch recovered in the assemblage. The algae were Botryococcus braunii and Pediastrum spp. Fungi spores and hyphae and charred curticle constituted minor components of the assemblage. The stratigraphic interval was dated Early Miocene (Burgidalian-Langhian) based on the occurrence and distribution of Pachydmies diederixi, Praedopollis flexibilies, Crassoretitrilete vanraadshoodveni, Psilatricolporites crassus and Laevigasporites spp. The abundant occurrence of pollen and spores typical of low land rain forest in the assemblage indicated tropical paleoclimatic conditions. The distribution pattern of Monoporites annulatus (Poaceae) and Zonocostites ramonae (Rhizophora) suggested cyclical fluctuations of paleoclimate between wetter and drier phases. The sediments were laid down in lagoons, delta swamps and shallow marine nearshore paleoenvironments.