Soils of Chalk Polygons of the Sub-Ural Plateau: Morphology, Properties, and Classification

Unique soils of the chalk polygons in the steppe zone of Obshchii Syrt and the Sub-Ural Plateau have been studied. They are characterized by a combination of uneven-aged features formed in contrasting environments. Modern features are the result of biogenic-accumulative processes, structuring, salinization, and crust formation. Relict features are associated with paleocryogenesis and include paleo-permafrost block–pseudomorph complexes, cryoturbations, paleo-permafrost wedges, accumulations and sorting of coarse fraction, etc. The good conservation of relict cryogenic features and modern cryogenic processes determine the uniqueness of these steppe soils. Such horizons and profile formula are not found in the existing diagnostic scheme for the classification and diagnostics of soils in Russia (CDSR). In order to represent the features, modern image, and genesis of these soils in the terminology of CDSR, a new diagnostic BCM cryostructural-metamorphic horizon was proposed. The soils were diagnosed as cryostructural-metamorphic on microhighs, protohumic and light-humus cryostructural-metamorphic on microslopes, and light-humus and light-humus cryometamorphic in microdepressions of the chalk polygons. Relict cryogenic features are proposed to be taken into account in the classification of these soils at the level of soil genus with the prefix ‘paleo’. According to the WRB, soils were classified as Rendzic Endoleptic Calcaric Phaeozems (Relictiturbic, Tonguic) in microdepressions, Skeletic Calcaric Regosols (Relictiturbic, Ruptic, Nudiyermic) on microhighs, and (Relictiturbuc, Raptic, Ochric) on microslopes.