The age of glacier peak tephra in west-central Montana |
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| Authors: | Peter J Mehringer John C Sheppard Franklin F Foit |
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| Institution: | 1. Department of Anthropology, Washington State University, Pullman, Washington 99164 USA;2. Department of Geology, Washington State University, Pullman, Washington 99164 USA;3. Department of Chemical Engineering, Washington State University, Pullman, Washington 99164 USA;4. Department of Anthropology, Washington State University, Pullman, Washington 99164 USA;5. Department of Geology, Washington State University, Pullman, Washington 99164 USA |
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| Abstract: | At Sheep Mountain Bog, near Missoula, Montana, a late-glacial tephra, that probably fell in late summer, is preserved as an 8-mm-thick graded bed overlain by another 8 mm of redeposited ash mixed with lake deposits. Sediment surrounding the ash was 14C dated to about 11,200 yr B.P. Electron-microprobe analyses of the volcanic glass and hornblende phenocrysts from this ash layer indicate that they are similar in major-element chemistry to those of Glacier Peak layer G previously considered to be about 12,000 yr old or older. |
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