Paleoenvironmental Analysis of Sandstone Deposits within ESUT Agbani Campus, Enugu State, Nigeria, using Pebble Morphometry and Textural Analysis

Abstract

Pebble morphometric and textural analysis were carried out on the sandstone deposits within the Agbani Campus of Enugu State University of Science and Technology (ESUT) in an attempt to reconstruct the paleoenvironment of deposition. The area has four major lithological units which include: Coarse Sandstone, Medium Sandstone, Clayey Shale and Very Fine to Fine Sandstone. A total of ninety fresh Quartz pebbles (fifteen each from six locations) were collected for Pebble analysis and five sandstone samples were collected for sieve analysis. Morphometric parameters such as size, flatness ratio, elongation ratio, maximum projection sphericity, form geometry and oblate index were computed. Bivariate scattergrams of roundness versus oblate-prolate index were also plotted.Results show that the coefficient of flatness for the area range from 45.76 to 226.6    while mean values of sphericity and oblate prolate index ranges from 0.061 to 7.615 and 0.746 to 18.872 respectively. These values suggest fluvial origin for the pebbles. Scatter plots of coefficient of flatness versus sphericity and sphericity versus oblate-prolate index suggests that the pebbles were formed in a fluvial environment. Bivariate plots of sand-textural parameters such as simple skewness against simple standard deviation also suggest that the sediments are more of a fluvial and partly shallow marine environment. The widespread of Orphiomopha, Skolitus and Rhizocolarium in the area supports the idea of a near shore depositional environment.

Keywords: Pebble Morphometry, Paleoenvironment, Coefficient of Flatness, Oblate-prolate Index, Roundness