Identification of last interglacial deposits in eastern Beringia: a cautionary note from the Palisades, interior Alaska

Journal of Quaternary Science
By: , and 

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Abstract

Last interglacial sediments in unglaciated Alaska and Yukon (eastern Beringia) are commonly identified by palaeoecological indicators and stratigraphic position ~2-5m above the regionally prominent Old Crow tephra (124 + or - 10ka). We demonstrate that this approach can yield erroneous age assignments using data from a new exposure at the Palisades, a site in interior Alaska with numerous exposures of last interglacial sediments. Tephrochronology, stratigraphy, plant macrofossils, pollen and fossil insects from a prominent wood-rich organic silt unit are all consistent with a last interglacial age assignment. However, six 14C dates on plant and insect macrofossils from the organic silt range from non-finite to 4.0 14C ka BP, indicating that the organic silt instead represents a Holocene deposit with a mixed-age assemblage of organic material. In contrast, wood samples from presumed last interglacial organic-rich sediments elsewhere at the Palisades, in a similar stratigraphic position with respect to Old Crow tephra, yield non-finite 14C ages. Given that local permafrost thaw since the last interglaciation may facilitate reworking of older sediments into new stratigraphic positions, minimum constraining ages based on 14C dating or other methods should supplement age assignments for last interglacial sediments in eastern Beringia that are based on palaeoecology and stratigraphic association with Old Crow tephra.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Identification of last interglacial deposits in eastern Beringia: a cautionary note from the Palisades, interior Alaska
Series title Journal of Quaternary Science
DOI 10.1002/jqs.1464
Volume 26
Issue 3
Year Published 2011
Language English
Publisher John Wiley & Sons
Publisher location Hoboken, NJ
Contributing office(s) Geology and Environmental Change Science Center
Description 8 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Journal of Quaternary Science
First page 345
Last page 352
Country United States;Canada
State Alaska;Yukon
Other Geospatial Eastern Beringia