Gypsiferous Gazha Soils of the Subboreal Zone of Eurasia.

Gypsiferous soils (gazha soils—soils formed from loose powdery gypsum sediments) under bioclimatic conditions of forest-steppe, steppe, semidesert, and desert of the subboreal zone are analyzed. Their morphological, micromorphological, mineralogical, and chemical properties are described. Gazha horizons of these soils may have different geneses: sedimentation, in situ weathering of hard gypsum rocks, and hydrogenic precipitation from groundwater. Despite the different origins of the gazha horizon, its morphology and properties have much in common: the gypsum content >50%, its powdery character with crystal size of <0.25 mm, and the presence of calcium carbonates and soluble salts with a predominance of sodium and magnesium sulfates. However, in some cases, the identification of the gazha horizon in the field and the chemical determination of gypsum give incorrect information about its presence; mineralogical analysis is necessary to determine the composition of the salts. An analysis of the micromorphological structure clearly demonstrates the genesis of gypsum: under hydrogenic conditions, when gypsum precipitates from groundwater or from lake and river water, gypsum material predominates and displays a subparallel microstructure, while in the in situ gazha or gazha originated from the lateral (colluvial) processes, gypsum crystals are deposited together with silicate plasmic material. [ABSTRACT FROM AUTHOR]