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GEOCHEMICAL PROCESSES CONTROLLING THE WATER CHEMISTRY OF SALINE LAKES IN THE NORTH KAZAKHSTAN REGION

Olga Gaskova, Marina Kolpakova, Olga Naymusgina, Sergey Krivonogov

Abstract

Ishim steppe (plain) is the southern part of Western Siberia, situated between the Irtysh and Tobol rivers. The plain is composed chiefly of sand and clay deposits of the Neocene era, covered with loess-like loams. In the lowlands and valleys there are many fresh, bitter, and salt lakes, including investigated B.Tarangul, Shaglyteniz, Zhamantuz, Kishikaroy and Kalibek lakes. This paper gives a recent study of the water lakes chemistry to show their diversity despite a close arrangement, the similar hydrogeological, landscape and climatic conditions. We also noted a variation in the evaporite mineral assemblages. This is confirmed by the mineralogical analysis of bottom sediments and thermodynamic calculations of the water saturation indices. The lake characteristics are given in the following order - the type of salinity, TDS (g/L), pH. They are B.Tarangul (Cl-HCO3-Na, 0.9, 8), Shaglyteniz (Cl-Na, 2.5, 8), Zhamantuz (Cl-Na, 99.3, 8.5), Kishikaroy (Cl-Na, 201.4, 6-7) and Kalibek (Cl-Na, 307.2, 6.5). Major minerals with respect to which lakes water is supersaturated and which may appear during evaporation are: Shaglyteniz and B.Tarangul (CaCO3), Zhamantuz (CaCO3, NaCl), Kishikaroy (CaCO3, NaCl, Na2SO4?CaSO4), Kalibek (CaMg(CO3)2, NaCl, CaSO4?2H2O). Halite is the most important chloride mineral and it dominates in the littoral zone and deeper horizons. So the evaporation of solutions doesnпїЅt exceed the halite saturation stage. Despite the linear correlation coefficient for Cl-Br-B-Li, the ratios of these anions are quite different for the lakes named above. It is known that high level of Br and B indicates a possible chemical interaction of ground water and surface water. Thermodynamic calculations using computer code пїЅHChпїЅ allowed us to show their influence on the elements distribution between surface waters and bottom sediments. If coupled with other proxies like sedimentological analysis, this may have important implications for paleoclimatic fluctuations in the Ishim steppe.

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DOI resolver: doi.org/10.5593/sgem2017/31/s12.041

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