Trace and rare earth elements geochemistry of Oshosun sediments of Dahomey basin, Southwestern Nigeria

Abstract

Geochemical data of two borehole samples that penetrated Oshosun formation in Oja-Odan area located in the western part of the Dahomey basin of SW Nigeria were studied. A total of twenty-nine elements, comprising three major, twenty trace and six rare earth elements were considered with the objective of determining the distribution pattern, source rocks and the environment of deposition of the sediments. The results showed that the mean concentrations for Fe, Na and K are 3.725, 0.073 and 0.683 wt.%, respectively. The relatively high Fe content is attributed to accumulation of goethite in the phosphatic shales of the formation. The absolute REE concentrations are in the order of clay>grey shale>black shale. On the average, the patterns indicate that the sediments were derived from granite and grey gneiss of nearby basement rocks but their accumulation was strongly controlled by mechanical and chemical processes of sedimentation. Trace element data on Cr and Co shows that the sediments of Oshosun formation are argillaceous and were deposited in a shallow oxygen poor environment consistent with the model of structural framework of a series of horst and grabens of the Dahomey basin. © 2006 Asian Network for Scientific Information.