Stable chlorine isotopes in Phanerozoic evaporites

Modern seawater has a uniform δ37Cl value (0.0‰), with an exception in the upper current of the Bosphorus (0.4‰). Marine halite ranging in age from Cambrian to Miocene has δ37Cl values of 0.0 ± 0.9‰, with most of the data in the range 0.0 ± 0.5‰. Mean δ37Cl values differ measurably between basins, with no evident relationship to basin size or to age. Smaller evaporite bodies have the largest δ37Cl ranges. Potash facies halite has mean δ37Cl values lower than those of halite facies salt in the East Siberia and Zechstein basins. The bulk δ37Cl of bedded halite preserving sedimentary textures cannot be shifted measurably after deposition under plausible natural conditions. During the Phanerozoic, a detectable change in the δ37Cl values of the oceans is unlikely as a result of Cl fluxes to and from the mantle and evaporites. In halite, the values of δ37Cl that cannot be explained by fractionation occurring on crystallization are best explained by the addition of non-marine Cl with δ37Cl ≠ 0.0‰ to evaporite brine.