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Refining the geochronology and paleoenvironmental significance of key tephra beds in Yukon and Alaska
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- Author / Creator
- Buryak, Serhiy D.
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Developing precise analytical tools for dating young volcanic deposits (under 3 million years old) is essential for constructing Quaternary chronological frameworks. This dissertation presents an improved method for determining eruption ages of volcanic ash (tephra) deposits in the ice-age sediments of unglaciated Yukon and Alaska (eastern Beringia). These regions, largely unglaciated during the Quaternary Period (last 2.6 million years), preserve a unique sedimentary record crucial for reconstructing past climate and environmental changes. Abundant tephra beds in these sediments are key to dating past climate changes, evaluating megafauna extirpation hypotheses, and understanding climate-landscape linkages.
However, radiometric dating of these relatively young tephra deposits is difficult. Some tephra can be directly dated with glass fission-track techniques, but relatively low precision of this technique has hindered progress in deciphering the sedimentary record of eastern Beringia. In the last decade, major improvements in instrumentation and other methodological advances are offering new opportunities to revisit this outstanding problem. Here a combination of U-Pb and/or U-series zircon dating via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is used to resolve eruption age uncertainty for important Quaternary tephra deposits. U-Pb zircon dating is commonly used to date much older geological materials, but there is a pressing need to adapt these techniques for application to more recent periods of time that are directly relevant to issues of global environmental change.
The enhanced tephrochronological framework, combined with paleoenvironmental and paleobiological data, offers a better understanding of eastern Beringian sediment deposition over the last 3 million years. This research presents zircon ages for 14 key tephra layers providing critical temporal anchors for Marine Isotope Stages 5 to 8 and older sediments in eastern Beringia. This includes improved dates for Old Crow, Sheep Creek - Fairbanks, HP, Gold Run, PA, Quartz Creek, Lost Chicken, GI tephra, and new chronology for Woodchopper Creek, Snag, Biederman PAL, and 80 Pup tephra. The dissertation also addresses statistical challenges in evaluating complex zircon populations and proposes refined age calculation methods. Additionally, it examines the preservation of volcanogenic zircon grains in sediment, highlighting the relationship between age, grain morphology, and recovery methods, thus improving the identification of syn-depositional grains in detrital sediments. This research revises the chronology of volcanism in Alaska and Yukon and refines methods for dating young volcanic deposits. -
- Subjects / Keywords
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- Graduation date
- Fall 2024
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.