Résumés
Abstract
Superimposition and intersection of preglacial and postglacial valley systems on the Canadian plains indicates that some of the recovered Quaternary vertebrate fossils may be redeposited. To test this proposition, an accelerator mass spectrometer (AMS) date was obtained on bone from a previously described helmeted muskox skull from near Fort Saskatchewan, Alberta. The specimen, identified as Bootherium bombifrons = Symbos cavifrons was previously thought to be Late Pleistocene (postglacial) in age but showed evidence of transport. A date of 30 570 ± 250 14C yrs BP indicates that it is of Middle Wisconsinan (pre-Last Glacial Maximum) age and therefore was ultimately derived from the Empress Formation (Saskatchewan Gravels and Sands) in the Edmonton area. Other vertebrate fossils must be assessed carefully in this light and direct dating is recommended wherever possible to facilitate both stratigraphic and paleontological studies.
Résumé
La surimposition et l’entrecroisement des réseaux fluviatiles pré- et postglaciaires dans les Prairies indiquent que certains fossiles de vertébrés du Quaternaire pourraient avoir fait l’objet d’un remaniement. Pour tester l’hypothèse, nous avons daté, à l'aide d'un accélérateur de particules (SMA), un os provenant d'un crâne d'ovibos casqué (antérieurement décrit) trouvé près de Fort Saskatchewan. Identifié comme un Bootherium bombifrons = Symbos cavifrons, le spécimen, qu'on avait daté du Pléistocène supérieur (postglaciaire), portait des traces de transport. La date de 30 570 ± 250 ans 14C BP obtenue par SMA, indique qu'il daterait plutôt du Wisconsinien moyen (avant le dernier maximum glaciaire) et qu'il proviendrait, par conséquent, de la Formation d’Empress (Graviers et Sables de la Saskatchewan), dans la région d'Edmonton. À la lumière de ce résultat, d'autres fossiles de vertébrés devraient être réétudiés et, dans la mesure du possible, faire l'objet d'une datation directe, afin de favoriser les études stratigraphiques et paléontologiques.
Parties annexes
References
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