Lithostratigraphy and Geochemistry of Gombe Formation around Pindiga and Futuk Areas, Gongola Basin, Northern Benue Trough, North Eastern Nigeria

Abstract

The Lithostratigraphy and geochemistry of the Gombe Formation around Pindiga and Futuk areas were carried out. Twenty (20) sandstone samples were subjected to granulometric analysis, three (3) mudstones samples were subjected for geochemical analysis and twelve (12) Sandstone samples were subjected for petrographic analysis. The result of the granulometric analysis shows the graphic mean size for the various samples ranging from 1.77ϕ to 3.5ϕ, which indicate medium to very fine grained, Inclusive Standard deviation ranging from 0.28ϕ to 0.57ϕ, this indicates very well sorted to moderately sorted, Inclusive Skewness values for various samples range from -0.36ϕ to 0.54ϕ which indicate negatively skewed to positively skewed, kurtosis ranging from 0.94ϕ to 3.48ϕ which indicate mesortic to extremely leptokurtic. The Bivariate plot of standard deviation vs. skewness indicated dominance of fluvial environment. While, the probability plots show 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 geochemical results indicate the SiO2/ Al2O3 ratio fluctuate between 3.0 and 3.7 showing textural immaturity, the Al2O3/ TiO2 ratio varies from 5.92 to 6.13 indicating derivation from mafic rocks, the values of Sr/Cu ranging from 0.51 to 0.63 with an average of 0.58, which shows deposition under humid climatic condition, an average Index Compositional Variability (ICV) value of 0.45 was recorded showing high degree of weathering processes. The discrimination plots indicate the tectonic a continental rift of passive margin setting for the Gongola basin. The Petrographic analysis of these sandstones tends to show that sorting ranges from poorly to well sorted but moderate sorting predominates. The grain shape ranges from sub angular to well-rounded with sub-angular dominating, and the sphericity varies from low-high. Quartz predominates in the framework grains of the sandstones. Monocrystalline quartz is dominant, while polycrystalline quartz occurs in very few samples.