Gypsiferous Gazha Soils of the Subboreal Zone of Eurasia

Abstract

Gypsiferous soils (gazha soils – loose powdery gypsum) developed underdifferent bioclimatic conditions–forest-steppe, steppe, semidesert, and desertof 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 gazhahorizon of these soils, its morphology and properties have much in common: the gypsum content of 50%, its powdery character with crystal size of 0.25 mm, the presence of calcium carbonates and soluble salts with a predominance of sodium and magnesium sulfates. However, in some cases, the field determination of the gazhahorizon 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 hydrogenous conditions, when gypsum precipitates from groundwater or from lake and river water, the predominantly gypsum material with subparallel microstructure is formed, while in the in situ gazha or gazha originated from the lateral (colluvial) processes, gypsum is deposited together with plasmic material.