POST-LAKE BONNEVILLE DEPOSITIONAL RECORDS OF THE BONNEVILLE SALT FLATS, UTAH

The Bonneville Salt Flats, Utah, is a large saline pan that is used for potash mining and recreational activities, such as land-speed racing. Radiocarbon dating of pollen from salt flat cores reveals that, contrary to previous assumptions, the salt flats are not remnants of Lake Bonneville. Sediment from Lake Bonneville is locally eroded in the area surrounding the salt flats. Following deflation, gypsum deposition began at ~8 cal ka and persisted to 5.5 cal ka. Gypsum deposition corresponds with a hot, dry climatic period, while halite deposition occurred during wetter, cooler periods. Up to 1.5 m of sediment has been deposited at the salt flats since ~8 cal ka, but only ~8 cm of halite were deposited in the past ~600 cal years. Halite deposition occurred during wetter, cooler periods, and gypsum deposition occurred during hotter, drier periods. Strontium isotope measurements of gypsum from the Bonneville Salt Flats indicate it differs in source from gypsum in the surrounding Great Salt Lake Desert. This depositional record provides an important saline record of Holocene change in the Great Basin. Additionally, it provides important context for recent declines in the area and volume of the Bonneville Salt Flats, which have been of great concern to its land managers and recreational users.