1. Be ages of flood deposits west of Lake Nipigon, Ontario: evidence for eastward meltwater drainage during the early Holocene Epoch
- Author
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Kelly, Meredith A., Fisher, Timothy G., Lowell, Thomas V., Barnett, Peter J., and Schwartz, Roseanne
- Subjects
Drainage -- Natural history ,Sediments (Geology) -- Natural history ,Earth sciences - Abstract
The Nipigon channels, located to the west and northwest of Lake Nipigon, Ontario, are thought to have enabled the eastward drainage of meltwater from glacial Lake Agassiz during the last deglaciation. Here we present the first direct ages of flood deposits in two of these channels using [sup.10]Be surface exposure dating. Five [sup.10]Be ages of a coarse- grained deposit near the Roaring River in the Kaiashk channel complex indicate deglaciation and cessation of water flow by ~11070 ± 430 years. To test for inherited nuclides in boulder samples, we also measured the [sup.10]Be concentrations of the undersides of two boulders at the Roaring River site. Five [sup.10]Be ages of boulders atop a large bed form near Mundell Lake in the Pillar channel complex indicate deglaciation and cessation of water flow by ~10 770 ± 240 years. Two [sup.10]Be ages of nearby bedrock are slightly younger (10 340 ± 260 and 9860 ± 270 years). The [sup.10]Be ages from the two sites are statistically indistinguishable and indicate that Laurentide Ice Sheet recession occurred rapidly in the region. We used clast diameters and channel dimensions at the Mundell Lake site to estimate paleodischarge and evaluate the possibility that meltwater drainage influenced climate conditions. We estimate a large maximum discharge of 119 000-159 000 [m.sup.3] x [s.sup.-1] at the site. However, the timing of meltwater discharge at both Roaring River and Mundell Lake is not contemporaneous with abrupt climate events. Les chenaux de Nipigon, situes a l'ouest et au nord-ouest du lac Nipigon (Ontario) auraient permis la vidange vers l'est de l'eau de fonte issue du lac glaciaire Agassiz durant la derniere deglaciation. Nous presentons les premiers ages directs de depots d'inondation dans deux de ces chenaux, obtenus par datation au [sup.10]Be de l'exposition en surface. Cinq ages [sup.10]Be d'un depot a grains grossiers situe pres de la riviere Roaring, dans le complexe de chenaux de Kaiashk, indiquent que la deglaciation et la cessation de l'ecoulement de l'eau avaient deja eu lieu vers 11070 ± 430 ans. Pour verifier la presence de nucleides herites dans des echantillons de bloc, nous avons egalement mesure les concentrations de [sup.10]Be des faces inferieures de deux blocs au site de la riviere Roaring. Cinq ages [sup.10]Be de blocs au sommet d'une grande forme de fond pres du lac Mundell dans le complexe de chenaux de Pillar indiquent que la deglaciation et la cessation de l'ecoulement de l'eau avaient deja eu lieu vers 10 770 ± 240 ans. Deux ages [sup.10]Be du substrat rocheux a proximite sont legerement plus jeunes (10 340 ± 260 et 9860 ± 270 ans). Les ages [sup.10]Be obtenus des deux sites sont statistiquement identiques et indiquent que le recul de la calotte glaciaire des Laurentides s'est effectue rapidement dans cette region. Nous avons utilise les diametres des clastes et les dimensions des chenaux au site du lac Mundell pour estimer les paleodebits et evaluer la possibilite que la vidange de l'eau de fonte ait influence les conditions climatiques. Nous estimons un important debit maximum au site, de l'ordre de 119 000 a 159 000 [m.sup.3] x [s.sup.-1]. Le moment de la vidange de l'eau de fonte tant a la riviere Roaring qu'au lac Mundell ne correspond toutefois pas a des evenements climatiques brusques. [Traduit par la Redaction], Introduction It has long been thought that channels in the areas located west of Thunder Bay and west and northwest of Lake Nipigon, Ontario (Fig. 1), served as eastern outlets [...]
- Published
- 2016
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