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Recurring middle Pleistocene outburst floods in east-central Alaska |
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| Authors: | Duane G Froese Derald G SmithJohn A Westgate Thomas A AgerShari J Preece Amanjit SandhuRandolph J Enkin Florence Weber |
| Institution: | a Department of Earth Sciences, Simon Fraser University Burnaby, British Columbia, V5A 1S6 Canada b Department of Geography, University of Calgary, 2500 University Drive, Calgary, Alberta T2N 1N4 Canada c Department of Geology, University of Toronto, Toronto, Ontario, M5S 3B1, Canada d United States Geological Survey, Mail Stop 980, Box 25046 Federal Center, Denver, CO 80225, USA e Geological Survey of Canada, 9860 West Saanich Road, Sidney, British Columbia, V8L 4B2, Canada f United States Geological Survey, P.O. Box 80586, Fairbanks, AK 99708, USA |
| Abstract: | Recurring glacial outburst floods from the Yukon-Tanana Upland are inferred from sediments exposed along the Yukon River near the mouth of Charley River in east-central Alaska. Deposits range from imbricate gravel and granules indicating flow locally extending up the Yukon valley, to more distal sediments consisting of at least 10 couplets of planar sands, granules, and climbing ripples with up-valley paleocurrent indicators overlain by massive silt. An interglacial organic silt, occurring within the sequence, indicates at least two flood events are associated with an earlier glaciation, and at least three flood events are associated with a later glaciation which postdates the organic silt. A minimum age for the floods is provided by a glass fission track age of 560,000 ± 80,000 yr on the GI tephra, which occurs 8 m above the flood beds. A maximum age of 780,000 yr for the floods is based on normal magnetic polarity of the sediments. These age constraints allow us to correlate the flood events to the early-middle Pleistocene. And further, the outburst floods indicate extensive glaciation of the Yukon-Tanana Upland during the early-middle Pleistocene, likely representing the most extensive Pleistocene glaciation of the area. |
| Keywords: | Glacial chronology Tephra Early-middle Pleistocene Yukon River Outburst floods |
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