BRINE INCLUSIONS IN HALITE AND THE ORIGIN OF THE MIDDLE DEVONIAN PRAIRIE EVAPORITES OF WESTERN CANADA

Brines were extracted from fluid inclusions in Lower Salt halite of th e Middle Devonian Prairie Formation in Saskatchewan, Canada, The brine s were analyzed by ion chromatography and were found to be of the Na-K -Mg-Ca-Cl type, They do not fall along a simple evaporation trend, Bri nes from clear, diagenetic halite are significantly lower in Na+ and h igher in Mg2+, Ca2+, and Cl- than brines-from cloudy, subaqueously for med halite with che c-ron structures, The isotopic composition of stro ntium and sulfur in anhydrite associated with the halites was found to be the same as that of Middle Devonian sea water, The composition of the inclusion brines can be derived from that of modern seawater by ev aporation, extensive dolomitization of limestone, and albitization of clay minerals, Other evolution paths are, however, also feasible, and it is impossible to rule out effects due to the addition of nonmarine waters (hydrothermal solutions, surface runoff, and groundwater), or d issolutional recycling of existing evaporites within the Prairie evapo rite basin. Our analyses and published data on brine inclusions in hal ite from a number of Phanerozoic evaporite deposits show that the Na-K -Mg-Ca-Cl type brine is more common than the Na-K-Mg-Cl-SO4 type, whic h is expected from evaporation of modern seawater.