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Tephrostratigraphy and paleoenvironments of the late Quaternary in eastern Beringia Open Access


Other title
Type of item
Degree grantor
University of Alberta
Author or creator
Jensen, Britta J.L.
Supervisor and department
Froese, Duane (Earth and Atmospheric Sciences)
Examining committee member and department
Lowe, David (Earth and Ocean Sciences, Waikato University)
Schweger, Charles (Anthropology)
Stachel, Thomas (Earth and Atmospheric Sciences)
Rutter, Nathaniel (Earth and Atmospheric Sciences)
Department of Earth and Atmospheric Sciences

Date accepted
Graduation date
Doctor of Philosophy
Degree level
In this dissertation, tephrostratigraphy is used as the central method to address issues of chronology in the late Quaternary sedimentary record of eastern Beringia (non-glaciated Yukon and Alaska) at a variety of spatial and temporal scales. The Palisades, central Alaska, preserves paleoenvironmental records thought to span, with major unconformities, the Holocene to early Pleistocene (~2 Ma). Two paleomagnetic transects of normal polarity and tephrostratigraphic data show the Palisades are Middle to Late Pleistocene in age, with no major unconformities. Of 19 tephra beds identified, nine are Middle Pleistocene beds known from other sites. The Variegated (VT) tephra has a known distribution second only to the Old Crow tephra. Reference samples from Fairbanks, Alaska, are correlated by glass major and trace-element geochemistry, Fe-Ti oxide geochemistry, stratigraphy, and age data to eight other sites in eastern Beringia. A new infrared stimulated luminescence age of 106 ± 10 ka, stratigraphy, paleoenvironmental data, and independent ages from other sites place VT within Marine Isotope Stage (MIS) 5, likely MIS 5d. Halfway House, an exposure of primary loess west of Fairbanks, is one of the most studied exposures in Alaska, but has little chronologic control. A new tephrostratigraphic framework shows Halfway House contains a relatively complete MIS 6 to Holocene record, dated by the Old Crow (124 ± 10 ka), VT (106 ± 10 ka), Sheep Creek-Klondike (ca. 80 ka), Dominion Creek (77 ± 8 ka) and Dawson (ca. 30 cal ka BP) tephra beds. The Skalamælifell/post-Blake paleomagnetic excursion (94.1 ± 7.8 ka) provides independent age control, and adds to the increasing body of evidence that III Alaskan loess can record subtle variations in the Earth’s geomagnetic field. This framework places high-resolution magnetic susceptibility profiles into context and shows loess accumulation is highly variable, casting doubt on the validity of correlating Alaskan susceptibility records to global δ18O curves. The Alaskan White River Ash, eastern lobe (WRe; ~AD 840), is correlated to the European cryptotephra known as AD 860B. This correlation means WRe is present in northeastern Pacific marine cores, across the North American continent, in the NGRIP ice core from Greenland, and northern Europe.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Jensen, B.J.L., Preece, S.J., Lamothe, M., Pearce, N.J.G., Froese, D.G., Westgate, J.A., Schaefer, J., Begét, 2011. The variegated (VT) tephra: A new regional marker for middle to late marine isotope stage 5 across Yukon and Alaska. Quaternary International 246, 312–323.Jensen, B.J.L., Reyes, A.V., Froese, D.G., Stone, D.B. The Palisades is a key reference site for the middle Pleistocene of eastern Beringia: new evidence from paleomagnetics and regional tephrostratigraphy. Quaternary Science Reviews, accepted for publication November 2012

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