Study of Rock Weathering Profiles and Their Influence on Soil Formation in Ekiti State

Rock weathering processes in the basement complex terrain of Ekiti State, South West Nigeria, produce lateritic and saprolitic profiles that exert fundamental control on soil physical and chemical properties, agricultural land capability, and building material availability. This study investigates the characteristics of weathering profiles developed on gneissic and granitic basement rocks at three localities in Ekiti State, with the objective of documenting profile structure, mineralogical transformation, and geochemical evolution with depth. Weathering profiles were exposed in road cuts and borrow pits and described from top to bottom, with distinct weathering zones designated using the Geological Society Engineering Group Working Party classification. Representative samples were collected from each zone for X-ray diffraction mineralogy, X-ray fluorescence geochemistry, and particle size distribution analysis. The chemical index of alteration and the plagioclase index of alteration were computed to quantify weathering intensity at each horizon. Pedogenic processes including ferrallitisation, ferruginisation, and kaolinisation were documented and interpreted in relation to prevailing climate and drainage conditions. The study establishes depth-dependent geochemical trends consistent with advanced tropical weathering, with complete destruction of primary silicates above the saprolite zone. Findings contribute to understanding of laterite formation in Ekiti State and support rational soil fertility management and earthwork planning. Keywords: rock weathering, laterite, chemical index of alteration, Ekiti State, soil formation.