Analysis Of The Sedimentology And Paleodepositional Environment Of The Basal Conglomeratic Unit Of Lokoja Formation, Southern Bida Basin, Nigeria

This research work focuses on detailed analysis of the sedimentology, mineralogy and paleodepositional environment of the outcropping basal conglomeratic unit of the Lokoja Formation, Southern Bida Basin. The methods employed are petrographic, sieve and pebble morphometric (particle size) analysis. Result from the petrographic analysis shows that the minerals contained in the samples of sandstone are largely feldspar and quartz with quartz having the majority composition. This indicated the provenance of the sediments as volcanic-plutonic rock or preexisting sedimentary rock. The grains exhibit angular to sub-angular shapes; suggesting short transportation history and closeness to source area. The sieve analysis result showed that the sediments are mostly coarse grained, poorly sorted, platykurtic and negatively skewed. This implies that the coarse sandstone component of the basal conglomeratic sandstone in the study area probably occurred as a result of sediment being carried by forceful fast-moving water. In poor sorting there is poor porosity which may infer poor reservoir characteristics of the sandstone sediments. The morphometric analysis revealed the paleoenvironment of the pebbles was a river environment based on the scatter plot of MPSI against OPI and plot of FI versus MPSI for the analyzed pebbles.