Characterization of Lower and Middle Pleistocene tephra beds in the southern plains of western Canada
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Date
2022
Authors
Westgate, John A.
Naeser, Nancy D.
Barendregt, René W.
Pearce, Nicholas J. G.
Journal Title
Journal ISSN
Volume Title
Publisher
Canadian Science Publishing
Abstract
Wellsch Valley tephra, near Swift Current, southwestern Saskatchewan, and Galt Island tephra, near Medicine Hat, southeastern Alberta, have been referenced in the literature since the 1970s, but little is available on their physical and chemical attributes — necessary information if they are to be recognized elsewhere. This study seeks to remedy this situation. Both have a calc-alkaline rhyolitic composition with hornblende, biotite, plagioclase, pyroxene, and Fe–Ti oxides being dominant. They have a similar composition but are not the same. Wellsch Valley tephra has a glass fission-track age of 0.75 ± 0.05 Ma, a reversed magnetic polarity, and was deposited at the close of the Matuyama Chron. Galt Island tephra has an age of 0.49 ± 0.05 Ma, a normal magnetic polarity, and was deposited during the early Brunhes Chron. Rich fossil vertebrate faunas occur in sediments close to them. Major- and trace-element concentrations in their glass shards indicate a source in the Cascade Range of the Pacific Northwest, USA, but differences in trace-element ratios suggest they are not consanguineous.
Description
Accepted author manuscript
Keywords
Tephra , Glass shards , Fission-track dating , Paleomagnetism , Major and trace elements , Western Canada
Citation
Westgate, J. A., Naeser, N. D., Barendregt, R. W., & Pearce, N. J. G. (2022). Characterization of Lower and Middle Pleistocene tephra beds in the southern plains of western Canada. Canadian Journal of Earth Sciences, 59(6), 360-370. https://doi.org/10.1139/cjes-2021-0073