Granulometric and Pebble Morphometric Analyses of Sandstone Lithofacies of the Ameki Formation in Northeastern Part of Akwa Ibom State, Niger Delta, Nigeria

Sandstone lithofacies of the Ameki Formation outcrop extensively in the northeastern part of Akwa Ibom State, Niger Delta Basin, Nigeria. The aim of this study is to reconstruct the depositional milieu of the sandstone lithofacies. Granulometric and pebble morphometric analyses were used to achieve this. Pebble morphometry analysis of 200 unbroken quartz pebbles indicates that the mean values of the various morphometric parameters ranged as follows: flatness ratio (S/L = 0.31 – 0.67), elongation ratio (I/L = 0.58 -0.78), maximum projection sphericity (Ψp = 0.54 – 0.73), Oblate-Prolate index (ŌP̄ = -0.73 – 5.41) and coefficient of flatness (31.49 – 53.15). These values are in agreement with those of modern beach pebbles, which are recommended for characterizing such a depositional environment. Bivariate plots of coefficient of flatness versus maximum projection sphericity and maximum projection sphericity versus oblate-prolate index also support beach environment of deposition. Granulometric analysis of 25 sandstone samples showed the samples to be well sorted and negatively skewed with sorting values ranging from 0.1 to 0.39 phi, which suggests a beach depositional environment. Bivariate plots of skewness versus sorting and mean grain size versus sorting also show the majority of the samples plotted within the beach depositional realm. Interpretation of granulometric and pebble morphometric analyses data indicate that the sandstone lithofacies of the Ameki Formation in northeastern part of Akwa Ibom State was deposited in a beach environment.