Illuvial processes

Argilluviation is the formation of an argillic illuviation horizon, as a result of translocation of clay from the surface soil to the depth of accumulation. It is the dominant process in the Alfisol order of soils. The process consists of three essential phases ... 

Genetic soil formed by the soil-forming processes. Horizons of illuviation, residual ... 

Fig. 1. Hypothetical soil profile chat has all principal horizons. Not all horizons shown are present in any given profile, but every profile has some of them. Terms used in diagram Eluviation is the downward movement of soluble or suspended material in a soil from the A horizon to the B horizon by groundwater percolation. The term refers especially, but not exclusively, lo the movement of colloids, whereas the term leaching refers lo the complete removal of soluble materials. Illuviation is the accumulation of soluble or suspended material in a lower soil horizon that was transported from an upper horizon by the process of eluviation. Gleying is soil mottling, caused by partial oxidation and reduction of its constituent ferric iron compounds, due to conditions of intermittent water saturation. Process is also called gleizalion (Adapted from USD A diagram)...

Illuvial. Pertaining to the deposition of dissolved or particulate soil material into one area or horizon of the soil from another. This material is transported by the process of eluviation. 

The natural radioactivity of soils depends particularly on the origin and composition of the parent rock, on the degree of weathering, and on the prevalent types of the soil formation process (particularly leaching). For example, the soils obtained by weathering of acid rocks contain higher amounts of radioactive elements as compared to those produced from basic rocks. Heavy soils contain higher amounts of radioactive elements than sandy soils. The distribution of radioactive isotopes in the soil profile is usually fairly uniform, and only in certain soils is it possible to observe an increased accumulation in illuvial horizons. 

The most noticeable pedogenic processes in the field are organic carbon accumulation and calcium carbonate leaching in the upper centimeters of the soils, and illuviation further down the profile a few decimeters below. The calcium carbonate accumulations are very intensive in the Holocene soils. 

---