Characterization and Genesis of Saprolite Derived from Gneissic Rocks of Virginia

Abstract Saprolite is the most prevalent soil parent material in the Piedmont and Blue Ridge Highlands regions of Virginia. Soil‐saprolite‐land‐scape associations were examined in these regions in order to describe and characterize saprolite formed from gneissic rocks, and to study saprolite genesis on these landscapes. Three representative landscape associations were chosen as study sites, and soil and saprolite were examined at the summit, backslope, and footslope positions of each. Saprolite thickness decreased from summit to footslope. Greater thicknesses of saprolite at summits are apparently related to the relative stability of this position compared with associated backslopes and footslopes. Reconstruction results indicate that between 20 and 36% of the mass of the partially weathered rock, which is the precursor of saprolite, is lost during saprolite formation. From 73 to 82% of these losses are Al or Si. Initial soil formation occurs at a faster rate than saprolite formation. As profile development increases, the rate of soil formation and consequent increase in solum thickness is reduced. After soil formation is reduced to a rate below that of saprolite formation, and chemical weathering controls the rate at which the thickness of the regolith increases, saprolite begins to accumulate below the solum.