Pebble morphometric analysis as signatures of the fluvial depositional environment of the Katberg Formation near Kwerela River around East London, Eastern Cape Province, South Africa.

Abstract

Pebbles were collected along the Katberg Formation sandstone beds next to Kwerela River (R63) near East London. During the study of pebble morphology, calculations were made to derive values that were used for bivariate plots to confirm the depositional environment of the Katberg Formation. Bivariate plots of MPs against OP showed that 79% of pebbles fall in fluvial environment, whereas 21% of pebbles fall in the beach environment. The plot of flatness index versus sphericity index shows that 87% of pebbles have a sphericity of greater than 0.65 falling into fluvial environment and 13% falling into a beach environment. The average morphometric indices indicated the dominance of river pebbles with an average sphericity of 0.73, which is above 0.65 and considered the limit of sphericity belonging to fluvial environment. The occurrence of a small proportion of beach pebbles suggests that the river reached the marginal marine environment during its flow. The river pebbles have the lowest roundness, highest sphericity index, and neutral Oblate-Prolate Index. Based on calculated indices, it is evident that the pebbles of the Katberg formation were shaped in fluvial environment. Majority of the pebbles yielded a bladed compact shape with a dominating sphericity index symptomatic of fluvial sediments. All the bivariate plots illustrate fluvial depositional environment for the sediments of the Katberg Formation.