Abiogenic reduction of sulfate by acetic acid has been conducted at temperatures ranging from 241 to 340°C. The sulfides produced and the remaining sulfates have been chemically and isotopically quan tified. The reaction of the aqueous sulfate reduction obey first-order kinetics. The rate constants are strongly dependent on temperature. The temperature dependence of the reaction rate (min-') is given by the following rate law: log k=-10.3 x 103/T+15.1. The activation energy for the reaction of sulfate reduction is 208 kJ mol-1.

No abstract

No abstract

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, 180/160 and 34S/325 .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 8180 values ranging from -30.3 to -31.9%0. On the other hand, sulfate in lake water and in cored sediments from Lake Vanda shows 834S 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%o for 813C and from -0.4 to +22.3%o for 81,10 of calcite and from +14.1 to +20.3 %o for 834S 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.

No abstract