Morphology, mineralogical composition and genesis of vertisols in liman Bolshoi (Volgograd region)

The morphological structure of the profiles of two vertisols on microelevations of the gilgai complex of the Bolshoi liman (Svetloyarsk district of the Volgograd region) was studied. Despite the same microrelief position and equal relative heights of microelevations, morphological differences in the profiles at the subtype level were revealed. In one of the profiles, due to the higher humidity, the signs of vertisol genesis were less pronounced. Whereas in the second, more pronounced signs of vertic processes were described – slickensides with 15–30 cm length, smaller slickensides up to 10 cm, wedge-shaped aggregates. The proportion of the clay fraction in the mixed horizons, obtained by the Gorbunov method, was 45– 52%. Analysis of the qualitative mineralogical composition of the clay (<1μm) fractions showed that the smectite phase is represented mainly by disordered and mixed-layered smectite-illite formations. Individual illite belongs to the biotite variety according to the filling of the octahedral layer. Analysis of the ratio of the main mineral phases showed the predominance of illite (53–87%) in all soil samples. In the first pit an increase in the proportion of the smectite component with depth (from 1 to 35%) is noted. In the second pit, there are no regularities in the distribution of mineral phases (fluctuations within 24–37%), which may be associated with the involvement of chocolate clays layers in the profile during soil formation. Mineralogical analysis of chocolate clays (parent rocks) showed their high heterogeneity depending on the depth of the studied layer. No correlation was found between the severity of the signs of vertic processes and the proportion of the swelling component. Illustration of the stages of the formation of the soil cover on the investigated plot of the liman is given. The main reasons that led to the formation of different soils on microelevations are the unevenness of the “squeezing out” of soil blocks upward in the process of microrelief formation in combination with local erosion.