Clay Illuviation in Weathered Regolith

The role of clay illuviation is seen to be an important one. Clay will go into suspension in the soil solution when soil is saturated, particularly if the clay is dispersive. Consequently the clay is transported by mass flow through macropores (usually fissures in this case) in the soil. Wetting fronts represent the end of mass flow and clay is deposited on the surface of macropores as the residual water is absorbed into the soil matrix.

Because clay shrinks and swells, the fissures where clay has been deposited can be enlarged or enhanced. This becomes a preferential path for water movement and hence further clay accumulation. The accumulated clay acts as a throttle to water movement and the soil close to the clay remains wet for longer than the rest of the soil mass. Reducing conditions are therefore more common near the clay-filled fissures. Over time this results in strong differentiation of redox conditions and ultimately a fragmentation of the remaining (not reduced) ferricrete mass.