The origin of platform dolomites: new evidence.

A sequence of Cretaceous dolomites from the Judean Mountains in Israel displays the following petrographic, chemical, and isotopic features: most of the rocks are thinly bedded to laminar, calcite-free dolomites, the dolomite containing up to 5% excess calcium. Chemical analysis of these dolomites for (H₂O non-leachable) Mg, Ca, Sr, and Na, and stable isotope analysis reveals significant positive correlations between excess calcium, Sr/Ca and Na/Ca ratios, and a weaker positive correlation between the Na/Ca ratio, delta¹⁸O, and delta¹³C. It is proposed that the composition of the dolomites is original, and that it reflects changes in salinity, ionic, and isotopic ratios which prevailed in the solutions during the penecontemporaneous dolomitization process. The geochemical and stratigraphic data presented are in disaccord with the 'evaporitic' as well as with the 'brackish' dolomitization models. In view of the renewed controversy on the 'dolomite problem', we suggest that some of the concepts of this study may be extended to other ancient platform dolomites.-Authors