Palynostratigraphy and Palaeoenvironmental Interpretation of AA-1 Well, 4329-5892 Feet, Niger Delta Basin, Nigeria

Abstract

Twenty ditch cutting samples composited and prepared at 80 ft from interval 4329 to 5892 ft of AA-1 Well in the Niger Delta Basin, Nigeria was studied and analyzed through the use of palynoflora assemblage of important diagnostic palynomorphs as well as their stratigraphic distribution with respect to a reference zonation scheme. This is to unravel the biostratigraphic and palaeoenvironmental reconstruction of the studied section. A total of 226 palynomorph species were identified of which 31 represent spores, 153 pollen, 22 dinoflagellate cysts, 13 fungal spores while 7 are microforaminifera test wall linings. The diagnostic forms recovered permitted the zonation and dating of the analyzed section. The result of the section has been broadly assigned to the P520, P480 and P470 palynological zones. The upper boundary of P520 subzone was cautiously placed at 4300 ft, the depth of the first sample analyzed while its base is marked by Last Downhole Occurrence of Racemonocolpites hians at 4800 ft. Important species in this subzone are Racemonocolpites hians Retitricolporites irregularis, Verrutricolporites usmensis, Psilatricolporites crassus, Monoporites annulatus, Praedapollis flexibillis and Striatopollis catatumbus. The top of P480 is marked by base occurrence of Racemonocolpites hians at 4800 ft while the base is defined by the base occurrence of Cinctiporipollis mulleri at 5200 ft. The diagnostic species within this subzone are Proxapertites cursus, Spinizonocostites echinatus, Grimsdalea polygonalis, Polypodiaceiosporites gracillimus and Gemmamonoporites sp. The top of P470 is marked by the base occurrence of Cinctiporipollis mulleri at depth of 5200 ft which is the top occurrence of Verrutricolporites usmensis, while the base is tentatively placed 6000 ft. The diagnostic palynomorphs in this subzone are Psilatricolporites crassus, Striatopollis catatumbus, Retitricolporites irregularis, Retibrevitricolporites protrudens and Verrutricolporites usmensis. Based on the result from palynostratigraphy of the studied section, the Well interval has been dated Late Eocene to Early Oligocene. The depositional environment deciphered in this study range from transitional inner to outer neritic marine.