PROFILE DISTRIBUTION OF MINERALS IN TEXTURAL FRACTIONS OF DIFFERENT DIMENSIONS IN THE SOLONETS IN DRY STEPPE ZONE OF RUSSIA

Abstract

Mineralogical composition of different texture fractions of Solonetz (Calcic Gypsic Endosalic Solonetz (Columnic Cutanic differentic) was studied. Inves-tigated object was located on the Borsi key plot in the northern part of the Caspian lowland (absolute height of the territory about 48 m) and developed on Early Khvalynian deposits. The profile of Solonetz is formed on coarsesilty clays and is characterized by depletion of silt in the upper 5cm horizon. The modern pedogenesis causes eluvial-illuvial distribution of silt fraction along the profile and the different ratio of mineral phases: 1) trioctahedral illites prevail in the SEL horizon, which indicates the process of illitization; 2) the upper natric horizon differs from the underlying ones by the predominance of labile minerals with the segregation of smectite packages. This pattern is associated with the process of lessivage, which occurs as the forming of clayey coatings. According to the mineralogical composition, some stratification of the soil-forming material is noted: in the upper part of the profile there was an increased content of illite of tridioctahedral type and mixed-layer minerals in comparison with the lower horizons. Comparing to the accumulative-calcareous horizons BCA and BSN3s the calcareous (Cca,s) horizon has a higher content of chlorite and kaolinite with perfect structure. The distribution of clastogenic minerals along the Solonetz profile in silt fractions and ≥ 10 μm has a weak disordered variation. With the increase of fractions sizes, an increase in the content of quartz, feldspars, plagioclases was marked. Also, the decrease of micas due to their more active disintegration during the pedogenesis was revealed.

Keywords

• mineralogical composition
• particle-size fractions
• lessivage
• illitization