LATE QUATERNARY HISTORY OF GREAT SALT LAKE AND LAKE BONNEVILLE FROM SEDIMENT CORES

New analyses of sediment cores from Great Salt Lake illuminate the lacustrine history of the basin during the late Quaternary. These cores have allowed us to 1) apply new methods to interpret the stratigraphic record of changes in lakes in the Bonneville basin; 2) apply advances in knowledge in radiocarbon dating and tephrochronology to refine the chronology of paleolimnological changes over the past 40,000 years; and 3) directly compare results from cores collected from different parts of the basin with the shoreline record. Coring sites were selected based on previous coring and seismic surveying of the lake floor. We sampled the cores at 1-cm and 0.5-cm contiguous intervals, and analyzed the samples for total inorganic carbon (TIC), carbonate mineralogy (calcite, aragonite, dolomite), carbon and oxygen stable isotopes, AMS radiocarbon, ostracodes, and magnetic susceptibility. AMS radiocarbon ages of bulk organic carbon samples appear to be approximately 1800 ¹⁴C yr too old compared with ages associated with the Mazama tephra and radiocarbon ages of other materials. Pre-Bonneville sediments (older than approximately 26,000 radiocarbon years ago) are dominated by low-carbonate, fine-sandy laminated mud with brine-shrimp fossils and few ostracodes; Bonneville sediments (ca. 26,000 to 13,000 radiocarbon years ago) are dominated by massive calcareous mud with abundant ostracodes. Holocene sediments are dominated by dense, laminated and organic-rich calcareous mud that grades into brine-shrimp fecal-pellet aragonitic mud. These changes in sedimentology mark key events in the history of the lake system, including: 1) the initial transgression of Lake Bonneville, 2) its long closed-basin transgressive phase, 3) the Bonneville flood (which catastrophically dropped the lake level about 100 m), 4) the development of the Provo shoreline, 5) the rapid regression from the Provo shoreline to low lake levels, 6) the development of the Gilbert shoreline, and 7) the evolution of Holocene Great Salt Lake.