2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 10
Presentation Time: 10:50 AM

Rock Magnetic Studies of Glacial Lake Missoula Flood Sediments

HANSON, Michelle A.1, ENKIN, Randolph J.2, BARENDREGT, René3 and CLAGUE, John1, (1)Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada, (2)Paleomagnetism, Geological Survey of Canada - Pacific, 9860 West Saanich Road, POB 6000, Sidney, BC V8L 4B2, Canada, (3)Department of Geography, University of Lethbridge, 4401 University Drive, Lethbridge, AB T1K 3M4, Canada, mhanson@sfu.ca

During the late Wisconsinan, the Purcell Trench lobe of the Cordilleran Ice Sheet advanced south into Idaho where it dammed the Clark Fork River to create glacial Lake Missoula in western Montana. Concurrently, the Okanogan Lobe, farther west, dammed the Columbia River creating glacial Lake Columbia in northeastern Washington. Between approximately 17,200 and 11,300 14C years ago, glacial Lake Missoula repeatedly filled and emptied catastrophically through its dam. The floodwaters flowed initially into glacial Lake Columbia before spilling across the Channeled Scablands in eastern Washington. At least 46 separate floods are recorded in exposures of glacial Lake Columbia sediments. Detailed rock magnetic studies were carried out on samples from three flood and intervening lacustrine beds at the Manila Creek site in northeastern Washington and on three lacustrine units from glacial Lake Missoula sediments at the Ninemile Creek site, Montana. The sediments record strong and stable magnetic remanence. Temperature-dependent measurements of the saturation magnetization indicate that glacial Lake Missoula sediments are dominated by hematite and glacial Lake Columbia sediments are dominated by titanium-poor magnetite. The S-ratio, which reflects the presence of high-coercive minerals, varies systematically throughout flood and interbedded lacustrine units at the Manila Creek site. These data indicate that the coarser flood sediments are dominated by local material, whereas the finer grain sizes that settle out at the end of the flood are dominated by sediments of a glacial Lake Missoula provenance, over 200 kilometres away.