HR: 1340h
AN: PP33B-0920    [Abstracts]
TI: A Glacial Chronology for the Fish Creek Drainage of Boulder Mountain, Utah
AU: * Marchetti, D W
EM: dwmarche@mines.utah.edu
AF: University of Utah, Department of Geology & Geophysics 135 South 1460 East Room 719, Salt Lake City, UT 84112 United States
AU: Cerling, T E
EM: tcerling@mines.utah.edu
AF: University of Utah, Department of Geology & Geophysics 135 South 1460 East Room 719, Salt Lake City, UT 84112 United States
AU: Lips, E
EM: elips@geog.utah.edu
AF: University of Utah, Department of Geology & Geophysics 135 South 1460 East Room 719, Salt Lake City, UT 84112 United States
AB: The Colorado Plateau physiographic province has several mountain ranges and high plateaus that supported valley glaciers and small ice caps during the late Quaternary. Although the glacial deposits in these ranges have been studied to some degree, there are only three quantitative age determinations for glacial deposits from all of the ranges on the Colorado Plateau. The timing of late Pleistocene glacial advance for this large and unique physiographic province remains largely unknown. Boulder Mountain, located on the western edge of the Plateau in south central Utah, has a well-preserved record of late Pleistocene glaciation. The mountaintop is a relatively flat volcanic upland $\sim$180 km$^{2}$ in area at an elevation of $\sim$3300 m. Glacial evidence on the summit surface in the form of freshly polished and striated bedrock outcrops, sculpted whaleback ridges and massive rouches moutonn‚es indicate that a thick ice cap occupied the mountaintop sometime in the recent past. Several reentrants around the mountaintop have deeply carved glacial valleys and steep sided latero-terminal moraine sets that were deposited by outlet glaciers spilling off the main ice cap. Using $^{3}$He exposure age dating and a correction for non-cosmogenic $^{3}$He, we determined corrected $^{3}$He exposure ages for pyroxenes from basaltic-andesite boulders on the most well preserved moraines in the Fish Creek drainage of Boulder Mountain. $^{3}$He exposure ages indicate a last glacial maximum (LGM) advance at 21,800 to 20,600 $^{3}$He years and a later and smaller advance at 16,500 to 15,400 $^{3}$He years. Our chronology is similar to other cosmogenic records from mountain ranges in the western U.S. (e.g. Wind River Range, Wyoming; Wallowa Mountains, Oregon) and is consistent with previous suggestions of a regional synchroneity of mountain glacier fluctuations during the LGM and associated deglaciation for ranges significantly south of the Laurentide margin.
DE: 3344 Paleoclimatology
DE: 1827 Glaciology (1863)
DE: 1035 Geochronology
DE: 1045 Low-temperature geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting