Halite-bearing evaporites occur to substantial depths in 3 arid closed-basins in the western U.S. and preserve a record of paleoclimate for more than 2 million years. This project will examine the paleoclimate record in salt deposits from these basins over the last 3 glacial-interglacial cycles (approximately 300,000 years) using existing samples and materials from 2 boreholes to be drilled to depths of 100 m. Emphasis will be on chemical analyses of fluid inclusions in crystals of primary halite and other evaporite minerals to obtain: activity of H2O and the major element chemistry (microthermometry and leachate analysis), hydrogen and oxygen isotopic composition of fluid inclusion waters (Mass spectrometry), and atmospheric gas composition, for those crystals which contain trapped air (quadrupole mass spectrometry). Fluid inclusions and supplementary data (sedimentology, mineralogy, petrography) may potentially be used to interpret paleoclimates, in terms of: (1) basin aridity, (2) relative temperatures, (3) atmospheric chemistry, (4) lacustrine water chemistry and brine evolution, and (5) closed-basin depositional settings. Local and global influences on paleoclimate will be distinguished by comparing data with the record from a fourth closed-basin (Searles Lake), Great Basin vein calcites, polar ice cores, and the marine oxygen isotope record. Possible local influences of hydrothermal fluids on the hydrologic record will be examined at Bristol Dry Lake, where Holocene volcanic activity is well documented. Dating of halite will done using U-series methods and 36Cl, and will be supplemented by tephrachronology. Long term records of the hydrosphere and atmosphere are needed to document continental paleoclimates and how such climates have been influenced by global and local processes. Nonmarine evaporites and associated closed-basin sediments, because of the special climatic and hydrologic conditions necessary for their formation, hold great promise for understanding ancient continental climates.
