Abstract:
Over the years, various biostratigraphic approaches (foraminifera, pollen and spores)
have been used for determining age and biozonation which are useful for exploration
and production activities in the Niger Delta. However actual age determination and
refined zonation of the deep offshore Niger Delta area have not been achieved. Hence
the need to determine the litho-stratigraphic sequence, age of the strata and a sequence
stratigraphic frame work for the Paleogene – Neogene section of the Niger Delta.
This study was therefore designed to establish absolute age using calcareous
nannofossils for the sediments penetrated by three Wells 1, 2 and 3 in Northwest
offshore Niger Delta.
Five hundred and ninety nine ditch cuttings (599) from three wells (1, 2, 3) offshore
Niger Delta were lithologically examined and lithofacies delineated. Slides from the
ditch cuttings were prepared using standard procedures and studied using light
microscopy. The abundance and diversity of the markers of the calcareous
nannofossils were identified using standard procedures and were used for precise zonal
delineation and recognition of dated events.
Greyish to brownish shale, silt and mudstone intercalated with coarse to medium and
fine-grained sand beds were identified. Forty-one calcareous nannofossil species
identified confirmed Early Paleocene to Early Pliocene age (NP3-NN15 zones) for the
three wells. Well 1 penetrated Middle Miocene to Early Pliocene (NN7-NN15 zones);
Well 2 was restricted to Early to Late Miocene age (NN3-NN11), while Well 3
encountered the Early Paleocene (NP3-NN4 zones). Established on the first and last
appearances of the marker species as well as their relative abundances three major
zones (NN7-NN8, NN9-NN10, NN10 and Younger) four major zones (NN3-NN4,
NN7, NN8-NN10, NN11) and three major zones (NP3-NP6, NP14-NP21, NN4) were
identified for well 1, 2 and 3 respectively. The acme events of Discoaster
prepentaradiatus, Catinaster coalithus, Discoaster kugleri, Helicosphaera
ampliaperta, Helicosphaera scissura, Pemma basquensis and Chiasmolithus daniscus
were associated with the 8.80, 9.50, 12.18, 14.20, 15.60, 32.47 and 64.75 Ma
maximum flooding surfaces, respectively. The correlation of the three wells showed
basin-ward younging direction and two zones recognized in wells 1 and 2 (NN7 and
NN8) belonging to the Late Miocene age was confirmed.
The established zonation scheme for Wells 1, 2 and 3 subdivided the offshore Niger
Delta Paleocene to Pliocene sequence into zones, subzones and lithostratigraphic
sequences and hence the absolute age determined
