The origin of sulfate salts in soils developed on Maikop clays in the North Caucasus region (According to data of the isotope composition of sulfur)

The ratio of ³²S/³⁴S stable isotopes was determined for soils developed on the Maikop clay sediments in the North Caucasus region in order to study the salt geochemistry in the soils. The soil sulfates were proved to be polygenetic. Three groups (generations) of sulfates of different geneses were distinguished according to their isotopic composition (³⁴S). In the underlying deposits and, partially, in the salt-bearing horizons of the soils, secondary sulfates originated from the oxidation of sulfides contained in the marine clay predominate. In the soil profiles, the sulfates inherited from the parent material (marine clay) are mixed with sulfates arriving with the atmospheric precipitation. The portion of the latter reaches about 30% of the total amount of sulfates in the soils. The salt (gypsum)-bearing horizons were formed in the course of the eluvial-illuvial redistribution of salts to the depth of seasonal wetting. The mobilization of sulfate salts from the underlying deposits and their transport to the upper parts of the soil profile with ascending water flows in the course of evaporation from the soil surface did not play a significant role in the accumulation of sulfates in the studied soils.