Morphometric Studies of Pebbles from Ewen Area, Calabar Flank, Southeastern Nigeria: Implications for Paleoenvironmental Reconstruction

Abstract

Morphometric parameters of unbroken quartz pebbles recovered from the basal section of Awi Formation exposed around Ewen area, southeastern Nigeria were studied for paleoenvironmental reconstruction. The study involved the determination of the roundness and measurement of the three orthogonal axes (long, short and intermediate) for about 200 pebbles. The pebbles were selected from 20 points across four exposed sections of the Awi Formation around Ewen village. The roundness was determined using the standard roundness chart. The results show that the pebbles are sub-rounded to sub-angular and predominantly compact-bladed. The mean values for the following morphometric parameters: Flatness index, elongation ratio, maximum projection sphericity index and oblate-prolate (OP) index are 0.57, 0.78, 0.74 and 15.65 respectively. These values are in agreement with those of modern fluvial pebbles. This result was integrated with the deductions from bivariate plots of roundness against elongation ratio and sphericity against OP index and they all inferred the deposition of the conglomeratic sandstones in a fluvial setting with subordinate transitional setting.