Saline lakes of Northern Kazakhstan: Geochemical correlations of elements and controls on their accumulation in water and bottom sediments

This paper is a review of the saline endorheic lakes of the Northern Kazakhstan, with the provided data on chemical composition of their waters and sediments, diversity/uniformity, mineral precipitation sequences and brine evolution. Study saline lakes are located in the Ishim steppe geographical unit of the southern Western Siberia and are ancient closed basins. The lakes are of Cl-Na and Cl-Na-Mg chemical types (the most saline Zhalauly lake (428 g/L) is Cl-Mg type), their pH values vary from 6.0 (Kalibek lake) to 9.1 (Shureksor Lake). The common trend for the lakes chemical state is a low calcium concentration with high values of sodium, i.e. calcium < magnesium < sodium (with three exceptions). The Na/Cl, Cl/SO4 and Mg/Ca ratios were calculated for the solutions from the lakes in order to reveal their primary trends of geochemical evolution. The geochemical indexes of enrichment and pollution (EF and I-geo) of the bottom sediments show that enrichment is low or absent in comparison with the geochemical background for the lakes of Western Siberia. We imply four main stages of lake evolution indicated by precipitation of different secondary minerals: calcite and Mg-carbonates, gypsum, halite, thenardite and bischofite. We suggest the onset of crystallization of each mineral as a tipping point of the water evolution that resulted in the complete removal of a certain chemical element consistent with the solubility constant of corresponding mineral.