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Trace-element geochemistry of individual glass shards of the Old Crow tephra and the age of the Delta glaciation, central Alaska

Published online by Cambridge University Press:  20 January 2017

James E. Begét  and
Mary J. Keskinen
James E. Begét*
Affiliation:
Department of Geology and Geophysics, University of Alaska, Fairbanks, AK 99775-0760, USA
Mary J. Keskinen
Affiliation:
Department of Geology and Geophysics, University of Alaska, Fairbanks, AK 99775-0760, USA
*
*Corresponding author. Fax: +1-907-474-5163. E-mail address:ffjeb1@uaf.edu (J.E. Begét).
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Abstract

Two widespread tephra deposits constrain the age of the Delta Glaciation in central Alaska. The Old Crow tephra (ca. 140,000 ± 10,000 yr), identified by electron microprobe and ion microprobe analyses of individual glass shards, overlies an outwash terrace coeval with the Delta glaciation. The Sheep Creek tephra (ca. 190,000 yr) is reworked in alluvium of Delta age. The upper and lower limiting tephra dates indicate that the Delta glaciation occurred during marine oxygen isotope stage 6. We hypothesize that glaciers in the Delta River Valley reached their maximum Pleistocene extent during this cold interval because of significant mid-Pleistocene tectonic uplift of the east-central Alaska Range.

Keywords

TephrochronologyGlaciationNeotectonicsAlaska
Type
Research Article
Information
Quaternary Research , Volume 60 , Issue 1 , July 2003 , pp. 63 - 69
Copyright
University of Washington

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