Palynostratigraphy and Paleobathymetric Studies of XAD-1 Well Niger Delta Basin, Nigeria

Abstract

Palynological analysis was carried out on one hunderd and sixty-two (162) ditch cutting samples of XAD-1 well within the depth interval of 1373 – 4300 m with the aim of interpreting the palynostratigaphy and paleobathmetry. The well is located in Offshore depobelt of Niger Delta Basin, on Latitude 4°47′ N and Longitude 5°50′ E. Lithologic description of the samples shows that the lithologies of the studied section consist majorly of thick shale/mudstone, sandy mudstone and thin sandstone lithologic units, indicating lower part of the Agbada Formation. Standard procedures of acid method for recovery of palynomorph from samples were followed. The ditch cuttings samples yielded one hundred and twenty-three palynomorph species which occurred abundantly throughout the studied section of the well. These included diagnostic marker species like Zonocostites ramonae, Praedapolis africanus, Cicatricosisporites dorogensis, Retibrevitricolporites protrudens/obodoensis. Middle Eocene to Early Miocene was assigned to the studied section using age diagnostic marker species. Five palynostratigraphic zones were established based on the stratigraphic range of palynormorphs present in the studied section. The biozones include Monoporites annulatus – Margocolporites rauvolfii, Pachydermites diederixi – Doualaidites laevigatus, Racemonocolpites hians – Numulipollis neogenicus, Cicatricosisporites dorogensis – Praedapollis africanus and Grimsdalea polyonalis – Striatricolpites catatumbus Zone. These are useful for correlation of middle Eocene to early Miocene stratigraphic succession. Paleobathymetic interpretation was done using palynomorphs such as algae, dinoflagellate cysts, bissacate pollen, spores and pollens. The paleobathymetric ranges inferred from the studied section are estuarine (littoral) – inner neritic (0 – 40 m) and inner neritic – outer neritic (40 – 200 m) in the marine environments. This is an indication of significant depth of burial of deposited micro fauna and flora in the sediments, necessary for hydrocarbon accumulation and generation.