Foraminiferal Biozonation of Late Eocene - Early Oligocene sediments of BC-1 well, Onshore, Western Niger Delta Basin, Nigeria

Abstract

Foraminiferal analysis was carried out on forty (40) ditch cutting samples from BC-1 well in the Onshore, Western Niger Delta at depth intervals of 5590 ft. - 8300 ft. Lithologic description of the samples together with the gamma ray log analytical data indicated the presence of four lithostratigraphic units composed of shale, sandstone, sandy shale and shaly sand corresponding to the continental Benin and paralic Agbada Formations. A total of twelve (12) species defined into eleven (11) genera, six (6) subfamilies and eleven (11) families were recovered. Benthonic and planktonic foraminiferal species constitute approximately 82 % and 18 % respectively. The calcareous benthics make up 44.4 % while the arenaceous benthics representing 37.7% of the total foraminiferal assemblages.  Foraminiferal index marker species - Globorotalia opima nana, Nonion oyae, Cassigerinella chipollensis and Spiroplectammina wrightii
revealed that the age of the studied well is from Late Eocene - Early Oligocene epoch. This indicated that both the planktonic and benthonic foraminiferal recovered from the well contained the transition between the Priabonian and the Rupelian age. Three (3) informal foraminiferal zone were established - Nonion oyae zone, Cassigerinella chipollensis zone and undiagnostic zone. The zones compares with foraminiferal markers species whose stratigraphic ranges are well established in the Niger Delta and globally.

Keyword: Lithostratigraphic units, Agbada Formation, Eocene, Oligocene and Biozone.