V.N. Konishchev (1981) studied the distribution of different minerals by particle-size fractions for sediments subjected to weathering under different climatic conditions. On this basis, he suggested an index to estimate the conditions of weathering and called it the coefficient of cryogenic contrast (CCC).
CCC = (Quartz / Feldspars (0.01 – 0.05 mm)) : (Quartz / Feldspars (0.1 – 0.05 mm))
The CCC values above 1.0 attest to the formation of sediments under strongly cryogenic (permafrost) conditions; the values below 1.0 suggest that these sediments were formed under warm humid conditions (without cryogenesis). For permafrost environments, a linear negative correlation exists between the CCC value and the mean annual temperature at the soil surface.
The specificity of mineral distribution by particle-size fractions in the permafrost-affected soils can be used as a diagnostic feature of the Gelic material. It is suggested that the mineralogical composition and specificity of soil microfabric should be taken into account in the definition of Gelic material. The CCC values in this material should exceed 1.0.
The notion of a polygenetic character of Holocene soils in the Russian Plain should also be taken into account in analyses of the mineralogical composition of coarse fractions. Different stages of the development of these soils and their parent materials — the Pre-Holocene cryogenic stage and the Holocene noncryogenic humid stage — are characterized by different directions of weathering processes. The Holocene soils on mantle loams can be considered the soils developing from the previous cryogenic weathering mantle.
The cryogenic stage is marked by the enrichment of the coarse silt fraction in quartz; the recent weathering processes delete the results of the cryogenic weathering, as quartz grains of this size are partly dissolved. The dissolution of quartz in the coarse silt fraction is comparable in intensity with the involvement of silica into the biological turnover and its hydrochemical discharge with river flows.
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