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Age of Sheep Creek Tephra (Pleistocene) in Central Alaska from Thermoluminescence Dating of Bracketing Loess

Published online by Cambridge University Press:  20 January 2017

Glenn W. Berger ,
Troy L. Péwé ,
John A. Westgate  and
Shari J. Preece
Glenn W. Berger
Affiliation:
Quaternary Sciences Center, Desert Research Institute, Reno, Nevada, 89506-0220
Troy L. Péwé
Affiliation:
Department of Geology, Arizona State University, Tempe, Arizona, 85287
John A. Westgate
Affiliation:
Department of Geology, University of Toronto, Toronto, Ontario, M5S 3B1, Canada
Shari J. Preece
Affiliation:
Geology Department, Miami University, Oxford, Ohio, 45056
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Abstract

The age of the Sheep Creek tephra (SCt), a widespread marker ash bed in eastern Alaska and western Yukon Territory, has been ambiguous and controversial. We have obtained three reliable thermoluminescence age estimates from bracketing loess near Fairbanks that imply a deposition age of about 190,000 ± 20,000 yr for SCt. Three of six loess samples near and closely bracketing the SCt beds near Fairbanks yielded younger age estimates (∼117,000 and ∼135,000 yr), most likely (based on field aspects) because of reworking and contamination by translocated grains. The new, reliable age assignment of 190,000 yr confirms independent stratigraphic evidence of a pre-last interglaciation age, and stratigraphic evidence from one site (Upper Eva Creek) that SCt is older than the more-widespread 140,000-yr-old Old Crow tephra. The SCt age also has implications for regional correlations of glacial and nonglacial deposits. In particular, it supports the stratigraphic and geomorphic interpretation that the Delta Glaciation in the east-central Alaska Range and the Reid Glaciation in western Yukon Territory are older than the last interglaciation (isotope substage 5e).

Type
Research Article
Information
Quaternary Research , Volume 45 , Issue 3 , May 1996 , pp. 263 - 270
Copyright
University of Washington

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