| Titre | Legacy radiocarbon ages and the MIS 3 dating game: a cautionary tale from re-dating of pre-LGM sites in western Canada |
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| Auteur | Reyes, A V; Dillman, T; Kennedy, K; Froese, D; Beaudoin, A B; Paulen, R C |
| Source | GSA 2020 Connects Online - Geological Society of America Annual Meeting; Geological Society of America, Abstracts With Programs vol. 52, no. 6, 2020 p. 1, https://doi.org/10.1130/abs/2020AM-360064 |
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| Année | 2020 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20200502 |
| Éditeur | Geological Society of America |
| Réunion | GSA 2020: Geological Society of America Annual Meeting 2020; Octobre 26-30, 2020 |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.1130/abs/2020AM-360064 |
| Media | en ligne; numérique |
| Formats | html; pdf |
| Province | Alberta; Yukon |
| Sujets | datation radiométrique; datations au radiocarbone; fossiles; paléoclimats; dépôts interstadiaires; analyse par spectromètre de masse; méthodes analytiques; preparation d'échantillons; Beringie; Calotte
glaciaire de la Cordillère; Norme; géochronologie; géologie des dépôts meubles/géomorphologie; paléontologie; Nature et environnement; Sciences et technologie; Phanérozoïque; Cénozoïque; Quaternaire |
| Programme | GEM2 : La géocartographie de l'énergie et des minéraux Cartographie des dépôts meubles du sud du Mackenzie du corridor de Mackenzie |
| Diffusé | 2020 10 01 |
| Résumé | (disponible en anglais seulement)
Meta-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. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Une nouvelle analyse a été effectuée auprès de sites clés de l'Ouest canadien pour sensibiliser les chercheurs à l'utilisation de datations au
radiocarbone analysées il y a plusieurs décennies. Cela est particulièrement vrai avec les âges plus anciens (MIS3), et nous recommandons que les échantillons soient ré-analysés ou interprétés avec prudence. |
| GEOSCAN ID | 327413 |
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