Paleo-environmental reconstruction of oligocene to early miocene sediments of Greater UghelliDepobelt, Niger Delta Basin

F.a Lucas ,T.J Fregene

doi:10.4314/jasem.v22i1.18

Abstract

Paleoenvironmental study of Oligocene to Early Miocene sediments of Greater UghelliDepobelt Niger Delta Basin were carried outusing foraminiferal micropaleontology as geologic tools.Fifty (50) ditch cutting samples ranging from 20ft.-11,820ft (6.09m-3603.7m) was used with the aim of establishing thepaleo-environment of the well. A total of twenty six (26) foraminiferal species were recorded, most of the species recorded are calcareous and arenaceous benthic foraminiferal species while planktonic foraminiferal species are generally scarce in the well. The non-recovery of planktonic and the general poor recovery of foraminiferal species might be due to environmental factor. The foraminiferal abundances revealed two varying depositional environment which are Continental to Marginal Marine and Proximal to distal Inner Neritic environment. These deductions were based primarily on benthic foraminiferal assemblage, their abundance and diversity. The presence or absence of planktonic foraminifera also helped in deciphering open ocean environments.The Continental to Marginal Marine setting range from 1640ft to 11,100ft due to non-recovery to rare foraminiferal species recorded within this interval while the Proximal to Distal Inner Neritic ranges from 11,160ft to 11,760ft with the presence of few foraminiferal species consisting of rare benthic foraminiferal species and scarcity of planktonics foraminiferal species indicating deposition in a shallow water, suggesting sediments deposition is fluctuating between proximal to distal Inner Neritic. Keywords: foraminiferal; Proximal to Distal Inner Neritic;Paleoenvironment; Niger Delta Basin; Depobelt

Highlights

The Niger Delta is the most significant hydrocarbon province on the West African continental margin
The Cenozoic Niger Delta is situated at the intersection of the Benue Trough and the South Atlantic Ocean where a triple junction developed during the separation of South America and Africa in the Late Jurassic (Whiteman, 1982)
Allmon, (1993) stated that paleontology is still a necessary geologic tool because the geologic time scale is based on fossils, fossils are still the primary tool for dating sedimentary rocks and fossils records the history of life and environmental changes

Summary

Introduction

The Niger Delta is the most significant hydrocarbon province on the West African continental margin. The Cenozoic Niger Delta is situated at the intersection of the Benue Trough and the South Atlantic Ocean where a triple junction developed during the separation of South America and Africa in the Late Jurassic (Whiteman, 1982) It is found in the Tertiary period in the geologic column. Biostratigraphy is an essential tool for dating rocks and identifying the biotic record through time and is necessary for establishing temporal correlation, reconstructing paleogeography, paleoenvironmental reconstruction as well as recognition of oil and gas deposits and intervals. Niger delta stratigraphy: The Tertiary Niger delta complex is divided into three formations, representing prograding depositional facies that are distinguished mostly on the basis of sand-shale ratios They are the Akata, Agbada and Benin Formations.

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