Depositional environment of the Gombe Formation in the Gongola sub-basin of the northern Benue trough: Using grain size parameters

Abstract

The depositional environment of the Gombe Formation was determined using grain size parameters in which sixteen sandstone samples and ninety nine pebbles were subjected to granulometric and pebbles morphometric analysis respectively. The granulometric analysis for the sixteen (16) samples of the Gombe Formation show an average graphic mean of 2.51ϕ (fine grained sandstone), mean standard deviation of 0.58ϕ (moderately well sorted sandstone), mean skewness value of 0.09ϕ (nearly symmetrical) and mean kurtosis value of 0.89ϕ (platykurtic). The Bivariate plot of standard deviation vs. skewness indicated dominance of fluvial environment. While the probability curves plots showed a dominance of three sand populations  indicating influence of marine processes. Environmental discrimination formulae for Y1, Y2 and Y3 indicated dominance of Aeolian, shallow agitated marine environment and shallow marine environment respectively. The plots of Y2 vs.Y1 and Y3 vs. Y2 showed a dominance shallow marine environment. The morphometric analysis indicates both fluvial and beach environment with dominance of fluvial environment.

Keywords: Gombe Formation, Gongola Sub-Basin, Pebbles Morphology,  Granulometric analysis, grain size