Sedimentology and Paleogeographic Synthesis of Cretaceous Sediments in Auchi Area of Anambra Basin

O.A Ilegieuno,R.O Sunny,E.J Ighodaro

doi:10.4314/jasem.v24i5.32

Abstract

The sedimentary rock in the Auchi area of Edo State constitutes part of the Upper Cretaceous Deposits of the Anambra Basin, which has its depocentre in Eastern Nigeria. Lithostratigraphic and Sedimentological studies carried out on twenty eight (28) selected samples from a section of a road–cut show that the sediments range from fine through medium to coarse grained. Sorting is poor to moderate. Grain size analysis shows that the sediments are strongly fine skewed and they exhibit mesokurtic to platykurtic kurtosis. These coupled with the various colours observed in the sediment, ranging from whitish sand through yellowish brown, pink and reddish brown possibly indicate a non–marine environment and a fluviatile to deltaic environment of sedimentation is suggested. The sediments might have been transported in a fairly high energy medium and deposited under a slightly fluctuating velocity. Keywords: Sedimentology, Cretaceous, Paleogeography, Grain size, Anambra Basin

Highlights

The sedimentary rock in Auchi area form parts of the Upper Cretaceous sediments of the Anambra Basin
Lithostratigraphic observation of a sedimentary rock section reveals that the rock unit which is about 20m thick at the representative section consist dominantly of partially indurated sandstone with occasional occurrence of sandy – clay at intervals
Paleogeography reconstruction of the Cretaceous sequence has been attempted by several workers among whom are: Adegoke (1969, 1978); Reyment (1965), Murat (1972); Adeleye (1975) and the Peters (1972)

Summary

Introduction

Based on physical attributes such as colour, grain size and sorting, representative samples were taken from each distinct lithologic unit and were carefully described. Graphic mean values of the analysed samples ranged from minimum 0.27Ø to a maximum 2.71Ø recorded for a coarse grained sand and a fine grained sand respectively within an average value of about 1.17Ø.

Results

Conclusion