Dear all, I've been asked by a student (Dirk Sachse,[log in to unmask]) to forward this question to the list, Jens Dear list members, I analysed d18O and d13C of a dolomite core (lagoonal, southern margin of the Zechstein basin, E-Germany). The data show quite clearly that the isotopic values are derived from initial water isotopic composition (controlled by evaporation and freshwater inflow; correlate with lithology, high d18O in anhydrit bearing horizons, low d18O in shales; d13C shows opposite behaviour) . So I'd like to calculate the initial isotopic composition of the lagoonal water (assuming a temperature range). I found several equations for the fractionation of d18O in water vs. dolomite (Land, 1983). They seem to give reasonable values (0 to 4 ‰ VSMOW) for temperatures around 30°C. But, since the sediment was deposited as calcite first (assuming the brine reflux model) these equations don't give me information about the initial water but about the dolomitizing fluids. So, what exactly happens especially to oxygen isotopes during dolomitization of calcite by hypersaline brines? Are there any references? Thank you, Dirk.