Abstract:
Sedimentological characteristics exhibits by sediment penetrated by a shallow in Lagos Mainland we're studied. The aim is to carry out the sedimentological studies of a section of the Alluvium deposits/ Coastal Plain sand of Southwestern Nigeria with a view to determining the possible lithofacies constituting the Alluvium deposits. The methods employed are: heavy mineral analysis using ImageJ point, grain size analysis, and petrographic study of thin section prepared from the sediment. The heavy mineral analysis reveals the presence of minerals such as tourmaline, Zircon, staurolite, with opaque minerals dominating suggesting metamorphic and igneous origin. The sand grains have low sphericity and range from sub- augular to sub- rounded. Histograms of the sediments exhibit both unimodal, bimodal and polymodal trends suggesting sediments derived from many sources. The grain size ranges between 2.894 φ and 0.985 φ (fine grained to coarse) while the standard deviation values from 0.881 φ and 1.493 φ (poorly sorted to moderately sorted). The skewness values varied between 0.022 φ and 0.379 φ (near symmetrical- strongly fine skewed) and the graphic kurtosis ranged from 0.806 φ and 1.097 φ (llatykurtic - mesokurtic peaked). The preponderance of fine sands suggests moderate energy conditions of deposition. The moderately sorted nature of the sediments is probably due to rapid back and forth flow of the depositing medium. The bivariate plot of moment skewness vs. moment standard deviation shows the samples plotting in the river sand Zone, indicating fluvial environment. From petrographic studies, the sediments are texturally mature based on the amount of quartz with rare occurrence of orthoclase feldspar content in them. The sediments can be defined as one lithofacies on the basis of their general sedimentological characteristics. Also based on the location of the well, the sediments were likely deposited by ancient River Ogun along what now constitutes the Ewekoro depression
