ABSTRACT

Possible origins of lake water, salts dissolved in water of a saline lake, Lake Vanda, those contained in cored sediments of the lake and those distributed on the ground surface in the adjacent area were investigated on the basis of the stable isotope compositions, ¹³C/¹²C, ¹⁸O/¹⁶O and ³⁴S/³²S. The lake water is concluded to be neither marine nor volcanic in origin but surface fresh water such as glacial melt water, because of the low δ¹⁸O values ranging from -30.3 to -31.9‰. On the other hand, sulfate in lake water and in cored sediments from Lake Vanda shows δ³⁴S values similar to that of sea water sulfate. Therefore, it is supposed to be marine in origin. Salts distributed on the ground surface near the lake consist mainly of calcite, gypsum, thenardite, sodium niter and halite. The isotopic compositions of carbonate and sulfate minerals range from -14.4 to +17.6‰ for δ¹³C and from -0.4 to +22.3‰ for δ¹⁸O of calcite and from +14.1 to +20.3 ‰ for δ³⁴S of gypsum. From the isotopic compositions of calcite and gypsum, three different origins, hydrothermal, marine and marine aerosol are considered according to their occurrences and localities. Salts distributed in this area, however, do not constitute the source for those contained in Lake Vanda. The genesis and historical events of the saline lake also were examined. The lake was once a fjord containing sea water and was isolated from the ocean by glaciation after the Tertiary. After the isolation of the lake from the ocean, evaporation of lake water in cold climate and supply of glacial melt water in warm climate have alternately taken place several times.