Stable chlorine isotopes in Phanerozoic evaporites

Modern seawater has a uniform delta Cl-37 value (0.0 parts per thousand), with an exception in the upper current of the Bosphorus (0.4 parts per thousand). Marine halite ranging in age from Cambrian to Miocene has delta Cl-37 values of 0.0 +/- 0.9 parts per thousand, with most of the data in the range 0.0 +/- 0.5 parts per thousand. Mean delta Cl-37 values differ measurably between basins, with no evident relationship to basin size or to age. Smaller evaporite bodies have the largest delta Cl-37 ranges. Potash facies halite has mean delta Cl-37 values lower than those of halite facies salt in the East Siberia and Zechstein basins. The bulk delta Cl-37 of bedded halite preserving sedimentary textures cannot be shifted measurably after deposition under plausible natural conditions. During the Phanerozoic, a detectable change in the delta Cl-37 values of the oceans is unlikely as a result of Cl fluxes to and from the mantle and evaporites. In halite, the values of delta Cl-37 that cannot be explained by fractionation occurring on crystallization are best explained by the addition of nonmarine Cl with delta Cl-37 not equal 0.0 parts per thousand to evaporite brine. (c) 2006 Elsevier Ltd. All rights reserved.