GEOCHEMISTRY OF CALCIC HORIZONS IN RELATION TO HILLSLOPE PROCESSES, SOUTHERN INDIA

The study concerns chemical and mineralogical properties of calcic hor izons in relation to their physical environment such as position in th e soil profile and the terrain, The carbonates were calcitic in upslop e positions but dolomite was abundant in valley sites. The content of fluorine increased downslope. The distribution of the composition in t he terrain indicates a sequential precipitation of calcite, dolomite a nd fluorite from soil water and groundwater as the water flows downslo pe to discharge areas. Carbonates in Vertisols formed from the more ba sic charnockites were of the low-Mg calcite type, while dolomite occur red only in Entisols and Alfisols formed from biotite-hornblende gneis ses. Manganese in calcic horizons increased as the groundwater level w as approached. Black intercalations in laminated petrocalcic horizons contained elevated concentrations of Mn, K, Al and Si, This may indica te periods of higher soil moisture and clay formation. The presence of low-Mg calcitic carbonates overlying dolomitic ones in valley sites i s likely to be due to deposition of calcite-rich material from upslope . The amount of soil eroded from upslope positions was between 0.2 and 2 m in four investigated profiles.