Foraminifera biostratigraphy and paleoenvironmental studies of two wells from offshore western Niger delta

Abstract

Biostratigraphic analysis was carried out on two wells from the deep offshore western Niger Delta Basin of Nigeria. The maximum flooding surfaces encountered were dated in both wells with foraminifera data at different horizons from the top to the total depths. Five foraminiferal zones were recognized in both wells. These are (i) Globorotalia acostaensis/ Uvigerina subperegrina zone, (9.5Ma and older); (ii) Globorotalia merotumida/plesiotumida/Ammobaculites agglutinans zone (7.4Ma); (iii) Globoquadrina dehiscens/Haplophragmoides narivaensis zone (the base of this zone is defined by the 7.4 Ma maximum flooding surface and the top bounded by an unconformity dated 6.7Ma); (iv) Globorotalia tumida/ Cyclammina minima zone (the top and base of this zone are defined by the 5.0 Ma maximum flooding surface and 6.7 Ma sequence boundary) and (v) Globigerina nepenthes/ Haplophragmoides compressa zone. The paleobathymetry for the two wells ranges from Inner Neritic to Upper bathyal as confirmed by the benthonic foraminifera assemblage. Most of the documented benthonic foraminifera recovered from the two wells such as Heterolepa, Globocassidulina, Florilus, Lenticulina among others, are normal marine benthonic foraminifera. It can therefore be inferred that the sediments were of normal salinity and Early-Pliocene to Late-Miocene in age.

Keywords: Foraminifera, Biostratigraphy, Maximum Flooding Surface, Neritic, Bathyal.