Mineralogy of solods in the estuary at the Dzhanybek stationary site of the Institute of Forestry of the Russian Academy of Sciences

The structure of the soil cover of the Northern Caspian region includes the interdepression solonetz complex, soils of depressions and estuaries. Permanent elements of the microrelief of the estuary bottom are closed rounded microdepressions up to 9 m in diameter. The soil combination of microdepressions is represented by meadow-steppe solods with different thickness of the solodized horizon, the largest on the periphery and the smallest in the bottom. Two soil profiles were studied: in the bottom of the microdepression – medium-thick solod, and on the flat part of the estuary bottom on the edge of the microdepression – deep solod. Less solodization thickness in the bottom of the microdepression is accompanied by a higher content of silt particles with the same thickness of textural and accumulative-carbonate horizons. In both soils, the same type of qualitative composition of clay and clastogenic minerals was established. A uniform differentiation was revealed by the profiles of clastogenic minerals, but the degree of their expression is not the same. The more contrasting differentiation was established in the solod of the microdepression. The content of feldspars increases in the lower horizons and quartz, on the contrary, in the upper horizons. Differentiation of clay minerals also occurs. Illite accumulates in the upper horizons, and the content of chlorite increases in the lower horizons. In the textural horizons of the profiles, an increase in mixed-layer mica-smectite formations is noted and insignificant kaolinite minerals are fixed in a superdispersed state. A decrease in the role of the smectite phase in the upper horizons is associated with its illitization in both solods. In the solod of the microdepression, superdispersion is associated with the reverse transformation of illite into smectite layers, which is ensured by a periodically stagnant water regime of atmospheric nutrition, in which the products of chemical weathering are mobilized within the soil profile in the form of various mixed-layer formations.