Tutorial:Soil Eluviation

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Clay eluviation
Clay eluviation (or lessivage as it is sometimes known) is the process whereby clay is washed down through the profile suspended in the soil water. Fine organic matter and fine silt can also be washed down through the profile. The clay is deposited as coatings around sand grains, aggregates (peds) and pores lower down in the profile. This leads to the formation of an argillic (UK and USDA), or argic (World Reference Soils Base) soil horizon below the topsoil.

An argillic horizon has an appreciably higher clay content than those overlying it, and contains clay coatings and cappings. Clay coatings can be identified as segregations of clay with a slightly metallic sheen, coating aggregates, grains, and pores. Grooved coatings on aggregates may be slickensides and are not indicative of clay eluviation.

Argillic soils are an important source of environmental information, and in some instances can provide evidence of past land clearance and cultivation.

The effects of post-depositional clay eluviation are often seen in archaeological sediments and can lead to the overprinting of stratigraphy by soil horizons, and in sever cases the loss of fine material can remove evidence of previous stratigraphy.

Clay eluviation seems to be particularly prevalent in soils prone to periods of drying out, and in soils containing a mixture of sand and clay particles (sandy clays and sandy clay loams). Disturbance, such as cultivation, earth moving, and colluviation may also initiate clay eluviation.

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