HR: 1340h
AN: GP43A-0927    [Abstracts]
TI: Stratigraphic and Paleomagnetic Study of Glacial Lake Missoula Lacustrine and Flood Sediments
AU: * Hanson, M A
EM: mhanson@sfu.ca
AF: Department of Earth Sciences Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
AU: Barendregt, R
EM: barendregt@uleth.ca
AF: Faculty of Arts and Science University of Lethbridge, 4401 University Drive, Lethbridge, AB T1K 3M4, Canada
AU: Clague, J J
EM: jclague@sfu.ca
AF: Department of Earth Sciences Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
AU: Enkin, R J
EM: renkin@nrcan.gc.ca
AF: Paleomagnetism, Geological Survey of Canada - Pacific, 9860 West Saanich Road, Sidney, BC V8L 4B2, Canada
AB: During the late Wisconsinan, the Purcell Trench lobe of the Cordilleran Ice Sheet advanced south into Idaho where it dammed the Clark Fork River and formed glacial Lake Missoula in western Montana. The lake repeatedly filled and emptied through its dam between about 16,000 and 12,500 ¹⁴C yr ago. The floodwaters entered glacial Lake Columbia, Washington, and spilled across the plateaux of eastern Washington. Repeated floods excavated the Channeled Scablands and deposited slackwater sediments in several valleys in Washington and in the Willamette Valley in Oregon. Stratigraphic study of the flood and slackwater sediments in Washington and Oregon, and of glacial Lake Missoula sediments near Missoula, Montana, provide evidence for at least 46 glacial Lake Missoula floods. Paleomagnetic analyses were done on oriented samples of (1) glacial Lake Missoula sediments at the Ninemile section and at a section in Missoula (348 samples); (2) interstratified flood and lacustrine sediments at the Manila Creek site in the Sanpoil Valley, Washington (615 samples); and (3) backwater sediments in the Yakima, Walla Walla, and Willamette valleys (813 samples). The sediments record strong and stable magnetic remanence carried by either magnetite or hematite. Magnetic remanence directions of flood beds and of interbedded lacustrine units show secular variation over a time span of hundreds to a few thousands of years, consistent with deposition by many tens of floods separated on average by several decades. Rock magnetic properties of the flood deposits give insight into depositional processes involved and the source of the floodwaters. We are now attempting to date the floods using radiocarbon and optically stimulated luminescence techniques, to correlate the paleomagnetic records between our study sites, which are up to 750 km apart, and to correlate them with well dated paleomagnetic records from Fish Lake, Oregon, and Mono Lake, California.
DE: 1522 Paleomagnetic secular variation
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting