Characteristic of the impure clay coatings occurring in chernozem of Romania

The impure clay coatings can be found from the surface to the deeper layers of the investigated profiles of calcic and luvic chemozems. This type of coatings cannot be seen macromorphologically in the field but they can be observed micromorphologically in the thin sections. The main characteristics of these coatings are: a faint contrast against the fine material of the groundmass; a high content of organic matter; a darker chroma in plain polarized light; a redder hue and a weak optical orientation of clay between crossed polarizers; only seldom they are microlaminated. The formation of the impure clay coatings is the result of a higher mobility of the fine fraction induced by the passage of the groundmass material throughout the faunal body (faunal pedofeatures). In time these faunal pedofeatures are integrated in the groundmass. Due to its high mobility the fine fraction either migrates along the profile, leaving depleted sites, or migrates locally. This local migration results in fine fraction enriched sites. Thus, the fine material which forms the impure clay coatings originates in the depleted sites previously described. An other cause which also accelerates the migration is the new conditions created in soil by irrigation During their development, the impure clay coatings lose part of the organic matter and become (more or less) limpid clay coatings as the typical coatings in a Bt horizon. For this reason in the profiles of luvic chernozems occur both types of clay coatings: impure clay coatings (which we suggest as being recent) and limpid clay coatings (which are older). Impure clay coatings do not concentrate in (neither form) a continuous specific horizon, they can oe found along the whole profile (Ap, Am, A/C, A,/B, By, Bt, Cca).