Paleo-environmental deduction from pebble morphometry and textural studies of sandstone deposits of Isuochi and Environs, Anambra Basin, South Eastern Nigeria

Ejiofor C Ezike,Emmanuel C Iyi,Henry I Okonkwo

doi:10.4314/gjgs.v18i1.3

Abstract

Textural analysis and pebble morphomentric were carried out on the sandstone deposits of Isuochi area in Anambra Basin, in an attempt to reconstruct the paleoenvironment of deposition. Field observation shows that the sandstone samples, collected from various locations were analyzed for sieve analysis, while two hundred fresh quartz pebbles that are greater than 2.00mm in diameter were collected for pebble morphomentric. Morphomentric parameters include; elongation ratio, flatness index, oblate index, and maximum projection sphericity were computed. Bivariate plots of Maximum Projection Sphericity against Oblate Prolate Index show that about 69% of the pebbles are of fluvial origin,while 31% is surf, bivariate plots of Flatness Index against Maximum Projection Sphericity show that about 57% is of fluvial origin, while 43% show surf; these imply that the associated pebbles are of fluvial origin. Bivariate plots of sandstone textural parameters such as skewness against standard deviation also suggest that the sediments are more of fluvial origin while multivariate parameter shows partly shallow marine environment. Keywords: Pebble Morphometry, Oblate-Prolate Index, Paleoenvironment.

Highlights

Sedimentation in the south eastern Nigeria started during the middle Albian which led to the deposition of the oldest sediment in the Southern Benue Trough mainly around Abakaliki; some pyroclastics of Aptian Early Albian ages have been sparingly reported
The high amount of equiaxial pebbles compared to the oblate, prolate and bladed pebbles (38%) shows a greater tendency towards sphericity, which decreases from rivers to beaches
SUMMARY AND CONCLUSION On the basis of pebble form indices, it is evident that the pebbles were shaped in fluvial environment

Summary

Introduction

Sedimentation in the south eastern Nigeria started during the middle Albian which led to the deposition of the oldest sediment in the Southern Benue Trough mainly around Abakaliki; some pyroclastics of Aptian Early Albian ages have been sparingly reported. Ojoh, (1990). Sedimentation in the south eastern Nigeria started during the middle Albian which led to the deposition of the oldest sediment in the Southern Benue Trough mainly around Abakaliki; some pyroclastics of Aptian Early Albian ages have been sparingly reported. Isuochi and environs, which is the study area is composed of sediments of Ezeaku Shale, Nkporo Shale, Mamu. Major area covers includes: Umuokwu, Amuda, Ngodo, Lekwesi, Ugwueme and Lomara, with major outcrops being exposed along stream channels, quarries, Enugu-Port. Harcourt express way and road cuts (figure 1). It lies between latitudes 05° 561 011N and 06° 011 0011N, and longitudes 07° 221 011E and 07° 271 011E.

Methods

Findings

Conclusion