Geochemical Detection of Soil Discontinuities in a Relatively Stable Terrain: Wonu, South-West Nigeria

Offiong I Akpanika

doi:10.7176/jnsr/9-3-02

Abstract

Movement of soil materials resulting in transported overburden occur in relatively stable terrains as described from the Wonu area of South-West Nigeria. The effect of such transported soils may be serious in pedogeochemical studies as they could lead to false anomalies, masked anomalies and incorrect bedrock identification during geological mapping in highly weathered terrains. Several techniques and parameters have been successfully used to detect discontinuities in soil. A lot of these are based on ‘abrupt changes’ expressed by a departure in depth trends mostly physical between zones of otherwise relative uniformity. This study shows that plots of bases/alumina versus silica/alumina from geochemical analysis can be used to separate the transported soil material from that of the soil formed in-situ. Keywords: Lithologic discontinuities, pedogeochemistry, bedrock, anomalies, profile DOI : 10.7176/JNSR/9-3-02

Highlights

Modern methods of soil studies as exploration tool in prospecting for economic deposits was first used in USSR in the search for tin in the early 1930’s
Geochemical studies of soils have become a tool for geologic mapping of bed rock in areas with few or no outcrops and a high degree of weathering (Webb 1970, Matheis 1980, Laming and Gibbs 1982)
The major problem posed in the use of this technique is the possibility of the displacement of geochemical anomalies either as a result of seasonal wash (Chowdhury 1982) or mass movement of soil resulting in ‘transported overburden’ (Michie et al 1972)

Summary

Introduction

Modern methods of soil studies as exploration tool in prospecting for economic deposits was first used in USSR in the search for tin in the early 1930’s. Geochemical studies of soils have become a tool for geologic mapping of bed rock in areas with few or no outcrops and a high degree of weathering (Webb 1970, Matheis 1980, Laming and Gibbs 1982). The principles underlying the use of soil as a geochemical sampling medium are based on the fact that during the process of soil formation, chemical components of the bed-rock become incorporated in the soil so that the elemental content of the near-surface soil reflects that of the parent rock (Bradshaw and Thompson 1982). Weathering of sub-outcropping mineralization results in metals being retained in the overlying soil and the formation of a residual soil anomaly. The major problem posed in the use of this technique is the possibility of the displacement of geochemical anomalies either as a result of seasonal wash (Chowdhury 1982) or mass movement of soil resulting in ‘transported overburden’ (Michie et al 1972)

Objectives

Discussion

Conclusion