Oxygen Isotope Fractionation in the System Dolomite-Calcite-Carbon Dioxide

Oxygen isotopes were equilibrated between carbon dioxide and calcite at four temperatures in the range 350° to 610°C and between carbon dioxide and dolomite at 350° and 400°C. Carbon of unusual isotopic composition was used as a tracer to demonstrate the nature and extent of the exchange process. Extrapolation of these data at lower temperatures indicates that at 25°C dolomite is enriched in oxygen-18 by 6.8 per mil with respect to calcite. This result indicates that those natural dolomite-calcite assemblages which show very small fractionations were not formed in isotopic equilibrium