Calcareous Nannofossil Biozonation Scheme for the Deep Offshore Niger Delta

Lawrence S. Fadiya¹ and Babajide M. Salami²
(1) Global Energy Company Limited, Lagos, Nigeria
(2) Obafemi Awolowo University, Ile-Ife, Nigeria

A high resolution calcareous nannofossil biostratigraphic study has been carried out on eight wells from the deep offshore Niger Delta with the aim of subdividing the sequences penetrated into local zones and subzones. High to moderate diverse and abundant calcareous nannofossils were recorded in the eight wells. This facilitated precise zonal delineation and recognition of dated events using the Martini, Okada & Bukry and Berggren et al. zonation schemes. The zones encountered in this study range from the early Miocene NN1 (CN1a) to early Pliocene NN13 (CN10c).

Five major zones NN1, NN2, NN4, NN5 & NN11 has been subdivided into subzones based on First and Last Occurrences of marker species as well as their relative abundance. Several new criteria have been thrown up for delineating newly and previously recognized zones. The Miocene/Pliocene boundary is easily inferred with the consistent occurrence of Ceratolithus acutus and Cr. armatus in the Niger Delta deepwater.

Calcareous nannofossils in the middle Miocene Serravalian age of the deep offshore Niger Delta have been found to be weakly developed. This is probably due to the cooling climatic conditions prevalent at the time. -

The resulting zonation scheme has further helped to subdivide the deep offshore Niger Delta Miocene-Pliocene sequence into easily recognizable biostratigraphic units. This will no doubt enhance the application of this discipline in exploration activities in the deepwater region and the entire Gulf of Guinea areas.