Stable chlorine isotopes in Phanerozoic evaporites

Modern seawater has a uniform δ 37Cl value (0.0 per mille ), with an exception in the upper current of the Bosphorus (0.4 per mille ). Marine halite ranging in age from Cambrian to Miocene has δ 37Cl values of 0.0 ± 0.9 per mille , with most of the data in the range 0.0 ± 0.5 per mille . Mean δ 37Cl values differ measurably between basins, with no evident relationship to basin size or to age. Smaller evaporite bodies have the largest δ 37Cl ranges. Potash facies halite has mean δ 37Cl values lower than those of halite facies salt in the East Siberia and Zechstein basins. The bulk δ 37Cl of bedded halite preserving sedimentary textures cannot be shifted measurably after deposition under plausible natural conditions. During the Phanerozoic, a detectable change in the δ 37Cl values of the oceans is unlikely as a result of Cl fluxes to and from the mantle and evaporites. In halite, the values of δ 37Cl that cannot be explained by fractionation occurring on crystallization are best explained by the addition of non-marine Cl with δ 37Cl ≠ 0.0 per mille to evaporite brine