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TitleLegacy radiocarbon ages and the MIS 3 dating game: a cautionary tale from re-dating of pre-LGM sites in western Canada
AuthorReyes, A V; Dillman, T; Kennedy, K; Froese, D; Beaudoin, A B; Paulen, R CORCID logo
SourceGSA 2020 Connects Online - Geological Society of America Annual Meeting; Geological Society of America, Abstracts With Programs vol. 52, no. 6, 2020 p. 1,
Alt SeriesNatural Resources Canada, Contribution Series 20200502
PublisherGeological Society of America
MeetingGSA 2020: Geological Society of America Annual Meeting 2020; October 26-30, 2020
Mediaon-line; digital
File formathtml; pdf
ProvinceAlberta; Yukon
Subjectsgeochronology; surficial geology/geomorphology; paleontology; Nature and Environment; Science and Technology; radiometric dating; radiocarbon dates; fossils; paleoclimates; interstadial deposits; mass spectrometer analysis; analytical methods; sample preparation; Beringia; Cordilleran Ice Sheet; Standards; Phanerozoic; Cenozoic; Quaternary
ProgramGEM2: Geo-mapping for Energy and Minerals Mackenzie Corridor, Southern Mackenzie Surficial Mapping
Released2020 10 01
AbstractMeta-analyses that include compilations of thousands of radiocarbon dates are becoming more abundant in the contemporary geoscience literature. However, there can be pitfalls with the uncritical use of dates near the temporal limits of radiocarbon dating, and even minute amounts of 'younger' carbon can cause a sample that is actually beyond the limit of radiocarbon dating to give a misleading finite age. We present a cautionary note on the use of pre-LGM radiocarbon dates (both conventional and AMS) compiled from earlier literature, based on case studies at four purportedly MIS 3 sites in both glaciated and unglaciated western Canada. In unglaciated central Yukon Territory, a spruce stump previously dated to ~26 14C ka BP yielded non-finite and ~50 14C ka BP dates by AMS (n=3), with implications for hypotheses on full-glacial boreal forest refugia in eastern Beringia. In southeast Yukon, sub-till plant macrofossils originally dated to ~24 14C ka BP were re-dated to ~45 14C ka BP (n=5) and thus no longer provide reliable constraints for the timing of Cordilleran ice-sheet advance near its northeast limit. Two sites in Alberta, with previously published MIS 3 radiocarbon dates on sub-till organics, similarly returned AMS ages (n=6) that were either non-finite or almost indistinguishable from the background standard. We were not able to replicate the MIS 3 radiocarbon dates that constrain the ages of any of these four purportedly interstadial sites. Our results suggest that substantial caution should be exercised when relying on MIS 3 radiocarbon dates compiled from the literature, including careful manual vetting of published ages; consideration of the stratigraphic and taphonomic context; and judicious re-dating using stringent sample preparation, modern AMS techniques, and suitable secondary standards.
Summary(Plain Language Summary, not published)
A re-analysis was done with key sites in western Canada to make researchers aware of the use of radiocarbon dates that were analyzed several decades ago. This is especially true with older (MIS3) ages, and we recommend that samples be either re-analyzed or interpreted with caution.

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