Radiocarbon chronology of Lake Bonneville, Eastern Great Basin, USA

Lake Bonneville occupied a series of connected topographically-closed structural basins in the eastern Great Basin from about 30 ka to 12 ka. The following synthesis of Lake Bonneville history is based on a critical evaluation of the stratigraphic and geomorphic contexts of 83 radiocarbon ages of a variety of samples, including wood, charcoal, dispersed organic matter, mollusk shells, and tufa. The lake began to rise from levels close to average Holocene levels after about 28 ka. By 22 ka it had transgressed approximately 100 m; between 22 and 20 ka it regressed about 45 m in the Stansbury oscillation and the Stansbury shoreline was formed. Transgression after 20 ka proceeded in two phases—a rapid phase from 20 to 18 ka, and a slower phase from 18 to 15 ka. The lake overflowed intermittently at its highest level (the Bonneville shoreline) from about 15 to 14.5 ka, then catastrophically dropped 100 m during the Bonneville Flood to the level of the Provo shoreline, which it occupied until about 14 ka. Subsequent closed-basin regression was rapid and complete by 12 ka, and was followed by a modest transgression to form the Gilbert shoreline between 10.9 and 10.3 ka. The Lake Bonneville record is an accurate proxy of the changing water balance in the Bonneville basin during the late Pleistocene, although the nature of the climatic changes during this period are still uncertain.