Physicochemical model for the generation of the isotopic composition of the carbonate travertine produced by the Tokhana spring, Mount Elbrus area, northern Caucasusстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:The isotopic composition of calcite from travertine deposits of the Tokhana-Verkhnii hot spring in the Elbrus area shows broad variations in delta C-13 and delta O-18 ( from + 3.8 to + 16.3 parts per thousand and from + 24.6 to + 28.1 parts per thousand, respectively). The delta C-13 and delta O-18 values increase toward the sole of the travertine dome. The isotopically heaviest carbonates (delta C-13 of up to + 16.3 parts per thousand) were found near the bottom of the dome and composed ancient travertine, which are now not washed by mineral water. The scatter of the delta C-13 values of the fresh sample is slightly narrower: from + 3.8 to + 10 parts per thousand. Calculations indicate that all carbonates of the Tokhana dome were not in equilibrium with spontaneous carbon dioxide released by the spring (delta C-13(CO2) = - 8 parts per thousand). To explain the generation of isotopically heavy travertine, a physicochemical model was developed for precipitation of Ca carbonates during the gradual degassing of the mineral water. The character of variations in the calculated delta C-13 values ( from +5.5 to + 13 parts per thousand) is in good agreement with the tendency in the variations of the delta C-13 in the carbonate samples. The calculated and measured pH values are also consistent. Our results demonstrate that the isotopic composition of large travertine masses can be heterogeneous, and this should be taken into account during paleoclimatic and paleohydrogeological reconstruction.