Foraminifera biostratigraphy and paleoenvironment of sediments from Well AM-2, Niger Delta

Abstract

Ditch cutting samples from depth interval 1440 – 2720 metres in Well AM-2, onshore Niger Delta were studied for their lithology and foraminiferal content with the aim of determining the age and paleoenvironment of the strata penetrated by the well. Standard foraminiferal preparation technique involving sample disaggregation and
washing through a 63 micron mesh sieve, drying and picking of the foraminifera and accessory fauna were employed. The well sequence penetrated the alternating sand and shale sequence of the Agbada Formation at the upper part, while the predominantly shaly lower part corresponded to the Akata Formation. A Middle - Late Eocene age was assigned to the strata penetrated by the well based on age diagnostic planktic foraminifera species including Globigerina eocaena, Pseudohastigerina micra, Hastigerina cf bolivariana, T. cerroazulensis cerroazulensis, T. pseudomayeri and T. cerroazulensis pomeroli. The occurrence of the benthic foraminiferal species – Hopkinsina hourqi and Nonion oyae which were characteristic species for the Middle to Late Eocene in the Niger Delta also supported the assigned age to the well section. Four informal benthonic foraminferal assemblage zones - Altistoma tenuis zone, Eponides africana zone, Uvigerina  peregrina/Lenticulina grandis zone, Bolivina ihuoensis/Hopkinsina hourqi zone corresponding to the P12, P13/P14, P15 and P16 and younger planktic foraminiferal zones were erected for the studied interval of the well. The four major Condensed Sections identified had been dated 35.9 Ma, 36.8 Ma, 38.0 Ma and 39.4 Ma. Paleoenvironmental interpretation based on recovered benthic foraminiferal association revealed that the sequences were deposited in the Inner to Middle Neritic environments.

Keywords: Foraminifera, Eocene, Neritic, Paleoenvironment, Niger Delta.