Grain Size Characterization and Depositional Environment of Exposed Rocks of the Ise Formation, Eastern Dahomey Basin, Southwest Nigeria

This study investigates the depositional setting, transportation mechanism, and provenance of newly exposed rocks of the Ise Formation in the Eastern Dahomey Basin, southwestern Nigeria, using granulometric techniques. Four rock exposures, namely OB, IJ, ER, and OK, were mapped, and 50 sediment samples were collected systematically, with three points logged at each outcrop. Granulometric analysis was carried out using 11 sieve meshes of varying sizes to understand the grain size distribution of each sample. The sediments’ mean grain size (Mz), skewness (SK), standard deviation (r), and kurtosis (KG) were analyzed and classified according to the Folk and Ward scheme. In addition, bivariate plots of the textural parameters were plotted, and linear discriminant functions were used to distinguish between different paleo-environmental settings. The results show that the basal units of the outcrops consist mainly of sandstones with varying colors and clast sizes, while the uppermost units are lateritic. The sediments were predominantly sandy gravel or gravelly sand to sandy gravel, with an average grain size ranging from 0.05 f to 0.66 f, indicating the predominance of coarse- to very coarse-grained sediments. The sediments were also largely platykurtic to mesokurtic, poorly sorted, and texturally immature. Our conceptual model shows that the sediments were transported in a high-energy environment by river channels and longshore drift and deposited close to their source areas, predominantly in a shallow marine setting.