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  • http://hdl.handle.net/10402/era.29409
  • Tephrostratigraphy and paleoenvironments of the late Quaternary in eastern Beringia
  • Jensen, Britta J.L.
  • English
  • tephra
    loess
    Yukon
    Alaska
    Beringia
    Pleistocene
    Paleomagnetic
  • Nov 20, 2012 3:13 PM
  • Thesis
  • English
  • Adobe PDF
  • 54913439 bytes
  • 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.
  • 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
  • Doctoral
  • Doctor of Philosophy
  • Department of Earth and Atmospheric Sciences
  • Spring 2013
  • Froese, Duane (Earth and Atmospheric Sciences)
  • Stachel, Thomas (Earth and Atmospheric Sciences)
    Rutter, Nathaniel (Earth and Atmospheric Sciences)
    Schweger, Charles (Anthropology)
    Lowe, David (Earth and Ocean Sciences, Waikato University)