ИСТИНА

Cryogenic soils (Cryosols and long season frozen soils) are formed in extreme environments, when pedogenesis is limited to a very short period with positive temperatures, and soil horizonation is influenced by cryogenic processes. The study of paleosols leads to the development of a new research area – paleocryogenic studies. Cold biospheres in duration do not exceed 4% of the geologic history of the Earth. Nevertheless plate tectonics and shifting of the poles result in expansion of paleocryogenic soils in the geological record of all thermal belts of the Earth, including tropical ones. During cold biospheres the glaciers could occupy up to one third of the Earth terrain with periglacial zones even wider. Frost features in paleosols could be correlated with similar features in soils of modern cryolithozone and for this reason paleocryogenic soils are one of the most reliable indicators of cold environments. Frost features in soils helps to reconstruct the former land surface (especially when paleosol profile is truncated), position of permafrost table and the depth of seasonal freezing. So paleocryogenic soils are important for stratigraphy and paleoenvironmental reconstructions. Like in modern soils, frost features in paleosols appear at all morphological levels - soilscape, macro-, meso-, micro- and sub-micro levels. Frost impact also influences chemical features of paleosols. Frost features may be syngenetic to pedogenesis. However quite often features of temperate pedogenic and cryogenic features in paleosols are in a complex relationships, preceding each other. So that frost features could affect temperate soils and temperate pedogenesis could be superimposed on frost features appeared in the preceding cold period. The evolution of the pedosphere in the geologic record is a succession of extreme cryogenic and non-cryogenic stages. Paleocryogenic soils are currently recorded starting from Paleo-proterozoic, they are described in Neo-proterozoic, Upper Ordovician and at the time of Permo-Carboniferous glaciations. Paleocryogenic features are widely spread in soils formed in the Quaternary glacial and periglacial sediments and could often influence surface soils of the Upper Pleistocene glacial and periglacial areas.