Biostratigraphic Study And Paleoenvironmental Reconstruction Of Cores From Offshore South Western Niger Delta Nigeria

Abstract Biostratigraphic and lithologic analysis were carried out on core samples from three wells of two fields in offshore depositional belt and one onshore well in coastal swamp depositional belt in southwestern Niger delta namely Bongo-ST-1 Bongo -4 Ngolo and Opukushi-25 respectively. A total of 99 samples are examined 35 samples for Bongo ST-1 23 for Bongo -4 16 for Ngolo and 25 samples for Opukushi -25 well with total thickness of 2421feet 526feet 5563feet respectively.Biostratigraphic analyses established Early- Middle Miocene age of Bongo ST -1 Ngolo and Opukushi 25 wells and Early Miocene for Bongo -4 well based on the First Appearance Datum FAD and last Appearance Datum LAD of diagnostic faunal and floral makers such as Globorotalia obesaGlobigerinoides bisphericusG. obliguus Globigerinoides immaturus Orbulina universa and Orbolina suturalis and their suite of Early-Middle Miocene benthic foraminiferal assemblage which include Bolivina mioceniaLenticulina rotulata Alveolephragmium crassium Bolivina beyrichi Saccammina complanata and Cyclammina minima. Some of the diagnostic flora makers encountered in this study include Magnastriatites howardii Verrutricolporites retundiporus Praedapollis africanus Crassoretitriletes vanraandshooveni Raccmonocolpites hians. Echiperiporites estalae Pachydermites diedeixi Grimsdalea magnaclavata and Echitricolporites spinosus The depositional environment and paleobathymetric ranges of the four wells are determine and interpreted with the use of depth sensitive benthics floral and associated accessories such as glauconite mica faecal pellets foraminiferal test linings pediastrum and fugal spores within each wells. The paleodepositional environment established marginal marine to shallow marine littoral-middle neritic corresponding to onshore to offshore within the continental plain to the continental shelf.