Salt neoformations in the soils of the Aral Sea dried bottom

Abstract

Salt neoformations in sandy and silty loam soils of the Aral Sea dried bottom in the south-western part were studied by X-ray fluorescence, electron microscopic, sedimentation methods of analysis and laser diffractometry. The surface layers of soils are significantly saline and enriched with CaCO₃. The distribution of CaCO₃ over the area is quite uniform, which indicates relatively close conditions of its formation during desiccation. The salt content varies from 0.4 to 1.2% in sands and from 3.1 to 5.8% in silty loam. The latter are characterized by the highest salinity, when, in addition to gypsum and halite, readily soluble salts are formed: eugsterite (2Na₂SO₄^.CaSO₄.2H₂O), astrakhanite (Na₂SO₄^.MgSO₄^.4H₂O), and mirabilite (Na₂SO₄^.10H₂O). Precipitation of calcite upon drying leads to the formation of CaCO₃-ooids in sands and CaCO₃- microaggregates from clay and silty particle in silty loam. The reason for the increased activity of easily soluble salts in the processes of aeolian transport has been established. This transport and, correspondingly, the salinization of adjacent territories are facilitated by the blocking of adsorption centers in clays by calcite, which prevents the binding of easily soluble salts in clay-salt microaggregates.