This study presents the Cenozoic foraminiferal biostratigraphy in the deep offshore of the Niger Delta and the Nigerian sector of the Sokoto Basin. The study areas lie between 4°–5°02′N and 3°–9°E in the Oil Mining Lease (OML) 65 and 13°–13°50′N and 5°10′–5°50′E respectively (Figures 1a, b). The geology, structures, depositional environments, source rocks, and hydrocarbon potentials of these basins have been intensively studied and well documented. The earliest geological work on
these basins have been reported by the following authors (Addeh and Duze, 1988; Adegoke, 1969; Adegoke et al., 1975, 1976; Reyment, 1959, 1960, 1963, 1965; Allen, 1964, 1965; Parkinson, 1967). They proposed an estuarine to freshwater palaeoenvironment of deposition for the sediments; microfauna and the geology of the Sokoto Basin have been studied. Other workers (Carter, 1960; Parker 1964; Kogbe 1976) studied the Cretaceous and Tertiary sediments of the Sokoto Basin. These workers have suggested several geological successions. The age of these deposits have been controversial. Gwandu Formation forms a part of the ‘Continental Terminal’. Amongst the workers that have worked on foraminferal evaluation in the Niger Delta are Seglie et al. (1982) and Adeniran (1997) amongst others. Boboye and Adeleye (2009) identified four condensed sections for the foraminiferal assemblages and four zones for the calcareous nannofossil in the Niger Delta which was correlated to the NN13, NN11, NN10 and NN9 of Global Cycle Chart (Boboye and Adeleye, 2009). Other workers with diverse reports on biostratigraphy of this basin include Ogbe (1982), Ozumba (1995), Salard-Cheboldaeff and Dejax (1991), Salami (1984) amongst others. However, planktonic biostratigraphy of the Neogene in the basins is limited to few references. Detailed work on the subsurface stratigraphy,
sedimentation and structures of the Tertiary Niger Delta Basin has been done and reviewed by Short and Stauble (1967), Asseez (1976), Hospers (1971), Merki (1972) and Weber and Daukoru (1975). Okosun (1999) studied the taxonomy and biostratigraphy of Ostracods and foraminifera of two boreholes in Sokoto Basin and these were based on palaeoecological and interpretation of the depositional environments. Petters (1978) reported that the Dange Formation contains a rich diversity of agglutinated foraminifera.