SOIL FABRIC OF DRY-STEPPE SOLONETZ COMPLEXES OF THE CASPIAN LOWLAND UNDER CONDITIONS OF CHANGING CLIMATE

The northern part of the Caspian Lowland developed in a close connection with the Caspian Sea shoreline dynamics. The sea transgressions and regressions have resulted in changes in the lithological composition of sediments. Subarid soils of the Caspian Lowland are sensitive to climatic fluctuations and, therefore, it is possible to identify consecutive pedogenetic stages based on characteristics of solid phase of such soils. We identified changes in soil characteristics along catenas (solonetz, light chestnut soils and meadow chestnut soils) within the Dzhanybek Plain, based on a combined mineralogical-micromorphological analysis of soils and calculations of the coefficient of cryogenic contrast (CCC).

The data obtained were indicative of current levelling of microrelief due to the surface subsidence, especially, around areas with a hollow microtopography and disturbances by soil fauna. We suggest that sinking of the modern microrelief is caused by moistening of lower saline horizons due to the groundwater table rising (from 7 to 4-5 m depths over the last 30-40 years) and dissolution of sodium sulfate (tenardite), which results in an increase in soil density, i.e., suffosion processes. Subsidence tends to occur in those soils, where the lower horizons have high values of interpedal porosity and cryoarid aggregation, but it is untypical in cases where shallow stratified sediments are underlain by chocolate clays (ChC).

It was shown that a 70-year-long development of solonetz within a sunken area resulted in leaching of soluble salts, humus accumulation and changes in microforms of organic matter within humus horizons. However, its upper 0-50 cm layer retained microfeatures of the former solonetzization and a solonetz-type structural organization, which developed within closed drainage basins of the study region during the interval of 3500-3000 BP. Below the depth of 50(60) cm, we discovered features of cryoarid pedogenesis (ooidal peds) dating back to the Late Pleistocene based on the presence of ChC particles (0.01-0.25 mm) and high (≥1.2) CCC values.

Thus, the present study revealed that soils of dry-steppe solonetz complexes combined pedogenic and lithogenic features of different ages.

This work was supported by the Russian Science Foundation, grant №21-74-20121.