Stone distribution in a stony tableland soil

Abstract

Texture-contrast profiles on a stony tableland showed concentration of stone in the A horizon, very little stone in the B horizon, and marked recurrence of stone below. The stone was identical with that in an underlying silcrete duricrust. There had been only slight lowering of the soil surface to form the present pavement, and no other stone appears ever to have been exposed. The contours of the surface soil are inconsistent with stone derivation from a higher-lying siliceous horizon. Heavy minerals indicate that the profiles are residual and that the stone-free clay B horizon is not a depositional layer. Upward displacement of stone within the profile by swelling and shrinkage of the clay subsoil alone explains the consistent relationship between soil horizons and the distribution of stone. There appears to have been little or no associated gilgai formation, probably owing to the mulching effect of a thick, coarse textured, stony surface soil. A bleached A2 horizon and a horizon of salt accumulation developed after stone displacement, and indicate cessation of subsoil movement and withdrawal of the wetting front with change to a drier climate.