The Omar Story: The Role of Omars in Assessing Glacial History of West-Central North America
The direction of Wisconsinan glacial dispersion of distinctive Proterozoic erratics derived from the Belcher Group in southeastern Hudson Bay is shown to have been northwestward, westward and southward for hundreds of kilometres across Hudson Bay, Northern Ontario, western Canada, and several adjoin...
| Published in: | Géographie physique et Quaternaire |
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| Main Authors: | , , |
| Format: | Text |
| Language: | English |
| Published: |
Les Presses de l'Université de Montréal
2000
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| Subjects: | |
| Online Access: | http://id.erudit.org/iderudit/005654ar https://doi.org/10.7202/005654ar |
| Summary: | The direction of Wisconsinan glacial dispersion of distinctive Proterozoic erratics derived from the Belcher Group in southeastern Hudson Bay is shown to have been northwestward, westward and southward for hundreds of kilometres across Hudson Bay, Northern Ontario, western Canada, and several adjoining northern States. The most distinctive of these erratics, termed "omars", are composed of massive siliceous wacke characterized by buff-weathering calcareous concretions; these erratics were derived from the Omarolluk Formation of the Belcher Group, exposed in the Belcher Islands of eastern Hudson Bay, and probably underlying much of the southern part of this inland sea. Far less common but equally distinctive are erratics of red oolitic jasper that were derived from the Kipalu Formation of the Belcher Group. In parallel with the now widely accepted field term "omar", we introduce the term "kipalu" for such erratics of oolitic jasper. A map showing the distribution of the distinctive erratics, in relation to indicators of Wisconsinan glacier movement, provides the basis for inferring at least two discrete glaciations that produced several major ice lobes. This paper summarizes the field observations of numerous Canadian and American earth scientists, traces the evolution of thought on provenance of the distinctive erratics, and outlines the criteria for distinguishing "true" omars from erratics derived from other bedrock sources of concretion-bearing wackes. Des erratiques de roches protérozoïques du Groupe de Belcher du sud-est de la baie d'Hudson, montrant certaines caractéristiques particulières, ont été transportés vers le nord-ouest, l'ouest et le sud, sur des centaines de kilomètres au cours du Wisconsinien, à travers la baie d'Hudson, le nord de l'Ontario, jusque dans l'Ouest canadien et dans plusieurs états voisins du nord des États-Unis. Le plus abondant de ces erratiques, l'« omar », est un grauwacke silicieux et massif contenant, dans les cas d'altération, des concrétions calcaires de couleur chamois. ... |
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