Geology and sedimentology of Mulke and environs, Northern Benue Trough, Northeastern Nigeria.

Abstract

This paper investigates the geological and sedimentological characteristics of Mulke and its environs within the Yola Arm of the Northern Benue Trough, northeastern Nigeria. The study involved field mapping, petrographic and granulometric analysis to assess depositional processes and the sedimentary environment. Geological field mapping identified the Bima Sandstone as the main lithologic unit. This sandstone exhibits a variety of sedimentary structures, including parallel bedding, planar cross-bedding, massive bedding, graded bedding, and ripple marks, all of which are consistent with tractional depositional processes. A petrographic analysis of five thin sections revealed that the sandstone is predominantly composed of quartz, with minor amounts of feldspar and clay minerals. The grains are mostly angular to sub-rounded, and the intergranular contacts indicate that it can be classified as quartz arenite, reflecting a high degree of textural and compositional maturity. Granulometric analysis of twelve (12) representative samples showed grain sizes ranging from very coarse to medium sand (−0.48 to 1.45 Φ), with sorting values between 0.81 and 1.39 Φ, suggesting a moderate to poor sorting. The skewness values vary from 0.03 to 0.34, indicating distributions that are nearly symmetrical to fine-skewed, while kurtosis values range from 0.27 to 1.49, which corresponds to very platykurtic to leptokurtic sand. Bivariate plots and log-probability curves indicate that sediment transport is mainly driven by traction and saltation under different flow conditions. Based on the gathered data, the study concludes that the sandstone in the area was deposited in a fluvial environment.