Granulometric and Petrographic Assessment of the Textural, Minerological and Paleoenvironment of Deposition of Gulma Sandstone Member, Gwandu Formation, Sokoto Basin, Northwestern Nigeria

Abstract

Granulometric analysis was carried out on sandstone samples collected from the Gulma Area, a suburb of Argungu town, Kebbi State, Nigeria. The sandstone facies were investigated to determine textural characteristics, transportation history, maturity, and paleoenvironment of deposition of the sediments. Heavy mineral analysis and mineral point count were carried out to determine the sandstone’s mineralogical and textural maturity. The standard sieve analysis method was employed by arranging sieves in order of size with the coarsest at the top and the finest size at the bottom with a basal attached pan. The sieve shaker was allowed to operate for fifteen minutes to allow separation of various grain sizes. Field observation revealed that the lithostratigraphic section is composed of nine repetitive layers. The main lithofacies are purplish, moderately bioturbated, liesegang ring structure sandstone, yellowish nodular claystone, and continental massive reddish claystone. The topmost beds are continental massive reddish mudstone and ferruginized granules stone as the capping facies which is different from the commonly oolitic ironstone that characterized the top of the Gwandu Formation. A characteristic liesegang ring structure is present in the Gulma Sandstone Member which is a unique appearance in Gwandu Formation. Cumulative frequencies were plotted whereby textural statistical parameters such as mean, standard deviation (sorting), skewness and kurtosis were calculated. The mean values of the samples vary from 2.2-2.26 with an average of 1.86, indicative of fine sand class. The sorting values range between 1.2-1.216 with an average value of 1.196, indicative of poorly sorted particles, characterized by tidal current deposits of high energy. The skewness values vary between -0.447 to -0.1 (ave. 0.198), which is negatively skewed. Kurtosis values range from 0.7-1.82, classified into very leptokurtic, platykurtic and leptokurtic classes. The paleoenvironment of deposition was deduced using multivariate values which range from -9.07 to -5.90; suggestive of marginal marine setting of a tidal and tidal shelf deposition. The Gulma Sandstone Member of the Gwandu Formation is a texturally and mineralogically submatured sediment.