Soils of Karst Sinkholes of the Polar Urals: Morphology, Genesis, and Classification

A slope series of karst sinkhole soils in the Subarctic zone of the eastern macroslope of the Polar Urals (67°13′ N) was studied and compared with the background soil. The genesis and taxonomic position of poorly studied soils of the altitudinal belt of mountain tundra (230 m above sea level) were clarified for the first time on the basis of macro- and micromorphological diagnostics and the analysis of soil chemical properties and the vegetation cover. The parent rocks are represented by loose boulder-free coarse-silty heavy loams, overlying karst rocks (marbled limestones). Iron-illuvial svetlozems (Skeletic Albic Podzols (Neocambic)) are formed in the inter-funnel surface and on the slopes of sinkholes and are replaced by soddy-cryometamorphic soils (Calcaric Skeletic Cambisols (Loamic)) in the bottom of funnels. The main differences in the surface horizons are associated with the composition of organic matter: different ratios of weakly decomposed and carbonized tissues and weakly and highly decomposed plant residues with traces of their biogenic processing and cryogenic fragmentation. A common macro- and micromorphological feature for the middle and lower parts of the profile of all the studied soils is the specific structural organization in the form of thin-platy, lens-type layered, angular-granular, angular-rounded, and rounded microaggregates. It is shown that the conditions of long-term seasonal freezing along with the aggregation of finely dispersed mass and fragmentation of plant residues result in the destruction of iron-containing minerals with the release of amorphous iron compounds and with the formation of nodules and ferruginated plant residues.