Clay materials in the soils of the Baraba Steppe and the Priobskoe Plateau

The composition and the regularities of the profile distribution of the clay minerals in the solods of the Baraba Steppe (ground moistening) and the Priobskoe Plateau (atmospheric moistening) were studied. The two profiles have the distinct eluvial-illuvial distribution of the clay fraction. The composition of the clay fraction in the eluvial layer is dominated by illite. The content of chlorite and labile minerals of the montmorillonite group increases downwards in the profile. The revealed regularities in the profile distribution of the clay fraction and some groups of clay minerals are explained by the joint influence of the mineral dissolution under the influence of the gleying and alkaline hydrolysis, as well as the processes of illitization and lessivage. The major differences in the content and distribution of the clay minerals between the solods and the podzolic soils are the following. The solods have a clear illuvial layer in the clay, while the majority of podzolic soil profiles have the eluvial distribution of the silty fraction. The solods in the eluvial part of the profile and sometimes in even the bottom layers have an unusually high content of the illite minerals in the clay fraction due to illitization. The podzolic layers of the solods do not contain soil chlorites common for the eluvial layers of the podzolic soils, which is due here to a less acidic medium that can not provide the proper conditions of aluminum mobilization and migration needed for the development of chloritization.