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

• Published in: Journal of Quaternary Science
• Main Authors: REYES, ALBERTO V., ZAZULA, GRANT D., KUZMINA, SVETLANA, AGER, THOMAS A., FROESE, DUANE G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2011
• Subjects: Palisades; The Palisades; Yukon; Old Crow; permafrost; Alaska; Beringia
• Online Access: http://dx.doi.org/10.1002/jqs.1464; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjqs.1464; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jqs.1464

Abstract Last interglacial sediments in unglaciated Alaska and Yukon (eastern Beringia) are commonly identified by palaeoecological indicators and stratigraphic position ∼2–5 m above the regionally prominent Old Crow tephra (124 ± 10 ka). 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 14 C dates on plant and insect macrofossils from the organic silt range from non‐finite to 4.0 14 C 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 14 C 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 14 C 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. Copyright © 2011 John Wiley & Sons, Ltd.