Mineralogy and Geochemistry of Granulometric Fractions As a Tool for Studying Transformations of Solid Phase of Soils

A detailed study of mineralogy and chemical composition of bulk samples and granulometric fractions <2, 2–5, 5–10, 10–50, and 50–250 μm of typical chernozem (Stavropol krai) was conducted using a complex of methods, including X-ray diffraction analysis and Mössbauer and X-ray fluorescence spectroscopy, as an example of the development of instrumental approaches to studying the transformation and accumulation of different solid-phase products of soil functioning. Mineralogical analysis of fractions records the distribution of mineral phases in different dimensions. Thus, quartz and feldspars are predominant in the fraction of coarse and medium silt, smectite is registered in the fine silt fraction, and the content of hydromica increases. Smectite predominates in the clay fraction; kaolinite, illite, and quartz are also present. Unlike in the case of the soil-forming rock, a decrease in the degree of crystallization of the smectite lattice is noted for the soil horizon, no formation of mixed layering is observed, Fe hydroxide (lepidocrocite) was additionally found in trace amounts. A detailed analysis of the state of iron compounds and distribution of iron oxides by granulometric fractions was conducted, and the contribution of χ granulometric fractions to the total specific magnetic susceptibility was determined. A change in geochemical indices by granulometric fractions was analyzed. Such approach is aimed at the development of a system of mineralogical and geochemical indices of biogenic-abiogenic interactions in soils to reach a maximal significance of possible paleoreconstructions based on the solid-phase soil memory.