Sedimentology and Depositional Environment of part of Lokoja Formation Exposed at Felele Junction, Southern Bida Basin

Abstract

The exposed Campanian sedimentary sequence at Felele junction around Lokoja has been mapped, logged and sampled. The total thickness of the section is approximately 21.48m. The sediments consist of conglomeratic sandstones, coarse sandstones and mudstones. Grain size analysis performed on nineteen sandstone samples revealed the average values of mean, sorting, skewness and kurtosis as 0.6, 1.03, 0.53 and 0.76 respectively. These results show that the sandstones are coarse grained, poorly sorted, strongly fine skewed and platykurtic. This characteristic is typical of fluvial depositional environment. The plots of skewness against sorting, sorting versus kurtosis and mean against sorting suggest a fluvial depositional environment. Petrographic analysis of selected sandstones reveals the presence of quartz, feldspars (plagioclase and microcline) and mica (biotite and muscovite). Quartz (especially monocrystalline) dominates followed by feldspar with minor muscovite and biotite. Heavy mineral study revealed the presence of non-opaque mineral suites suggesting that the sediments are derived from the basement complex of igneous and metamorphic rocks. The heavy minerals observed include staurolite, rutile, kyanite, zircon and sphene. The samples are dominated by stauronite which signifies low grade metamorphism in the area. Integration of sedimentological and petrographical characteristics in this study suggest that the sandstone samples are derived from mixed origin and deposited in fluviatile environment under high energy setting not too far from the source. Hence it is a proximal deposit.