Pebble morphometry and sieve analysis: tools in determining the depositional environments of sediments in oron and environs

Abstract

Pebble morphometry and grain size analysis were carried out in parts of Benin Formation exposed along Oron and environs to determine the depositional environment of the sediments. Quartz pebbles (900 pebbles) collected from 60 different locations around stream channels and quarries were subjected to axial measurement of long (L), short (S) and intermediate (I) axis. Fifteen (15) sediments were further subjected to sieve analysis. Results from morphometric studies shows that the pebbles are dominantly compact-bladed (CB) and elongate (E) with mean values for flatness ratio (FR), elongation ratio (ER), maximum projection sphericity index (MPSI), oblate-prolate index (OPI) and braided ratio (BR) as 0.48, 0.61, 0.67, 3.54 and 0.63 respectively with mean roundness value of 32%. Sieve analysis revealed that the sediments are dominantly medium-grained, well sorted, skewed to near symmetrical and leptokurtic to mesokurtic. Bivariate Plots of roundness versus elongation ratio, sphericity versus OP index, FI versus MPSI, and skewness versus sorting indicates deposition of the sediments predominantly in the fluvial environment. Thus, this study showed that the sediments in Benin Formation were deposited by fluvial depositional processes.