Temperature and salinity effects on 18O fractionation for rapidly precipitated carbonates:: Laboratory experiments with alkaline lake water -: Perspective

An important factor involved in determining the isotopic composition of precipitating lake minerals is their mineralogy. In the Dead Sea (Israel) the aragonite-calcite ratio of lake carbonate sediments can be correlated with delta(13)C and delta(18)O fractionation increasing aragonite concentration conforms to an increase in the heavier carbon and oxygen isotopes. The enrichment of the heavier isotopes is explained by strong evaporation during the formation of aragonite, when the lighter isotopes are preferentially removed as part of Got. Calcite was formed as a result of degradation of gypsum through the activity of bacteria which preferentially use lighter isotopes from their carbon source.In a hypersaline lake at Salt Flat, Texas (US), layers of isotopically-heavy and isotopically-light carbonate sediments alternate in beds similar to those of the Dead Sea. As in the Dead Sea, the light layers are composed for the most part of calcite which has resulted from the bacterial decomposition of gypsum. At Salt Flat the isotopically heavy carbonate is dolomite, and not aragonite as in the Dead Sea.