New evidence for a 179 ka age of the Old Crow tephra

Yeo, Desmond; Huang, Yongsong; Guo, Fei; Vachula, Richard; Wang, Karen; O'Donnell, Jonathan; Clemens, Steven; Russell, James

Accurate age control is a prerequisite for paleoclimate and paleoenvironmental research but remains a persistent challenge for Arctic lake sediment cores. Well-dated regional tephrochronologies can provide robust stratigraphic markers in sediments. In Arctic Eastern Beringia, the Old Crow tephra (OCt) is one of the most widely distributed late Quaternary tephras and serves as an important stratigraphic anchor beyond the radiocarbon range (>50 ka BP). However, the age of the OCt remains debated and has undergone numerous revisions, with studies using different dating methodologies to ascribe ages ranging from 124 ka to 203 ka. While the commonly reported age of the OCt based on fission track dating is 124 ± 10 ka, a recent study using uranium-thorium/ helium ((U-Th)/He) dating of zircon placed the OCt at 202.9 ± 9.5 ka. Here, we independently find an age of 179.0 ± 4.6 ka for the OCt from a lacustrine sediment record in Alaska (Imuruk Lake) with confirmation using the marine benthic δ18O chronology. This revises the current tephrostratigraphic framework in this region. We also report a previously undocumented mafic tephra layer (IM#1), which is likely a local eruption on the Seward Peninsula, with an age of 157.2 ± 4.7 ka, providing a new tephrostratigraphic marker for this region.

New evidence for a 179 ka age of the Old Crow tephra

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