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Master of Science (MS)
Babcock, R. Scott (Randall Scott)
Easterbrook, Don J., 1935-
Gosse, John C.
Multiple post-last glacial maximum (LGM) moraines occur in the Sawtooth Range of the Rocky Mountains in central Idaho. Although relative ages of the moraines have been studied, few numerical ages exist for these moraine sequences. In this study, the ages of LGM and late glacial (Younger Dryas) moraines in the Redfish Lake drainage of Idaho are constrained with 23 new, cosmogenic, 10Be dates. Results of this study include developing a new chronology for the Redfish Lake late Pleistocene moraines that are consistent with regional morainal ages.
New cosmogenic 10Be data from boulders on Bull Lake moraines at Redfish Lake are consistent with other dates obtained from Bull Lake moraines elsewhere in the Rocky Mountains. Ages of 107 to 206 ka and 238 to 323 ka suggest synchroniety with other Bull Lake glacial advances in the Wind River Range, Tetons, and Yellowstone.
New cosmogenic 10Be data from boulders on terminal moraines in Redfish Lake valley, Idaho, show a LGM at 18.5 ± 0.9 ka to 15.6 ± 0.8 ka, recessional (or minor readvance) moraines deposited between 15.4 ± 0.7 ka and 14.2 ± 0.7 ka; and a Younger Dryas (YD) phase at 11.4-11.7 ± 0.5 ka. Boulders on an LGM moraine at Alturas Lake, Idaho were 10Be dated in order to supplement and test the existing concepts of glaciation there. Ages of 17.2 ± 1.0 ka and 16.8 ± 0.8 ka indicate that this moraine is late Pinedale, not mid-Pinedale as previously suggested by Thackray et al. (2004).
The late Pleistocene ice chronology at Redfish Lake is consistent with the glacial chronology in the Wind River Range, WY (LGM 24 ka to l8 ka; recessional deposits 18 ka to 16 ka and YD 11.5 ka); Yellowstone, WY (LGM advances: 29.5-22.5 ka, and 19.5- 5.5 ka); Wallowa Mountains, OR (two 10Be dated LGM advances: 21.1 ± 0.4 ka and 17.0 ± 0.3 ka, and YD advance: 10.2 ± 0.6 ka); Crowfoot Lake, Canada (YD advance: 11,330 ± 220-10,100 ± 70 14C yrs B.P.); and many other places throughout western North America. This research provides chronological constraints on Pinedale LGM (~18.5 ka) moraines, Pinedale recessional (between 18.5 and 14.2 ka) moraines, and Younger Dryas (~11.4 ka) moraines in the Sawtooth Range of the Rocky Mountains, and assists in determining the areal extent of the late Pleistocene cold period in the Western United States.
Dating moraines, Pleistocene glacial changes
Western Washington University
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Sherard, Cody, "Regional Correlations of Late Pleistocene Climatic Changes Based on Cosmogenic Nuclide Exposure Dating of Moraines in Idaho" (2006). WWU Graduate School Collection. 664.