Determination of origin and granulometric analysis of river channel sediments of Osi, southwestern Nigeria

Abstract

Osi is located within the south-western part of the Nigerian Basement Complex and plays a host to unconsolidated deposits and major examples of Precambrian – Paleozoic crystalline rocks in the region. Detailed geological mapping revealed the area to comprise essentially of migmatite – banded gneiss complex and diorites and minor rock types that include pegmatite and quartz veins. Superficial stream sediments occur abundantly and proximally along channels in the vicinity. These river channels host considerable amount of loose deposits that are useful for sedimentological and provenance study. While efforts have been committed to regional mapping, petrography and geochemistry of rocks in the region, little attention was paid to the associated stream sediments. This study adopted geological mapping of the crystalline rocks and sieve analysis of the stream sediments, as well as the use of XRF and inductively coupled plasma Mass spectrometry (ICP – MS) to establish some relationship between the basement geology and the surrounding deposits in the area. Migmatites are abundant in the south-west and parts of the north-west, while granite gneisses with isolated occurrence of diorite are confined to the north-east of the study area. Granulometry of the sediments revealed a predominantly medium – coarse grained, poorlysorted leptokurtic sands, indicating products of in-situ weathering of host rocks. Geochemical analysis supports a strong correlation between the rocks and the sediments. The study is applicable to enhanced understanding of grai -size distribution and in regional mapping and geochemical method of exploration.

Keywords: Basement complex, migmatite – gneiss complex, stream sediments, grai -size analysis, elemental abundance, south-western Nigeria