ROCK MAGNETISM AS A CHRONOLOGICAL TOOL AND ROCK FLOUR PROXY IN THE LATE PLEISTOCENE SEDIMENTS OF MONO LAKE, CALIFORNIA

Mono Lake, California, is a large perennial lake occupying a basin at the Sierra Nevada range front, and forms a collection basin for water and sediments from the Sierra. Spectacular moraines extending from the mountain canyons indicate the dominance of glacial erosion during the last glaciation, with rock flour eroded from the Sierran plutons and roof pendants forming the dominant clastic input to the late Pleistocene Wilson Creek Formation. We have developed a high-resolution GISP2-based chronology for the Wilson Creek Formation, suitable for correlation of paleoclimate records from Mono Lake to global abrupt climate changes, based on correlation of a record of NRM/IRM (Natural Remnant Magnetization/Isothermal Remnant Magnetization) from Mono Lake to the global relative paleointensity reference curve. Here we use the IRM record as a proxy for rock flour input to the lake silts of the Wilson Creek Formation. IRM acquisition curves, along with results of previous studies, indicate the dominance of the magnetic remanence by fine-grained, unweathered magnetite, carried in the rock flour fraction. Similarity of the high-resolution IRM record to a low-resolution geochemical rock flour proxy developed in neighbouring Owens Lake and applied to Mono Lake strengthens our inference that the IRM records input of rock flour. Comparison of the Mono Lake IRM record to the high-resolution geochemical rock flour record from Owens Lake (Bischoff and Cummins, 2001; Quat. Res. 55:14-24) shows good agreement, indicating that both records preserve a regional glacial signal.