Calcareous Till Facies North of Lake Superior, Ontario: Implications for Laurentide Ice Streaming
In the Geraldton and Hemlo areas distantly-derived carbonate tills lie between slightly to non-calcareous tills and can be distinguished by textural, carbonate, and clast compositions. Their occurrence and uniform character over large areas of the Shield attest to high sediment flux by rapid movemen...
| Published in: | Géographie physique et Quaternaire |
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| Main Author: | |
| Format: | Text |
| Language: | English |
| Published: |
Les Presses de l'Université de Montréal
1988
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| Subjects: | |
| Online Access: | http://id.erudit.org/iderudit/032719ar https://doi.org/10.7202/032719ar |
| Summary: | In the Geraldton and Hemlo areas distantly-derived carbonate tills lie between slightly to non-calcareous tills and can be distinguished by textural, carbonate, and clast compositions. Their occurrence and uniform character over large areas of the Shield attest to high sediment flux by rapid movement of distal debris within the southern part of the Laurentide Ice Sheet. This is consistent with low surface profiles reconstructed for the Superior and Michigan lobes which were likely fed by ice north of Superior and probably affected by ice streaming. Till deposition in the Geraldton and Hemlo areas can be explained with one southwestward glacial advance. A broad ice stream probably issued out of James Bay and up the Albany conduit between zones of normal ice velocity within the Laurentide marginal area. It may have split to flow down the Drowning and Kenogami troughs. Eventually, zones of ice streaming reached the Geraldton and Hemlo areas where Shield uplands induced lee side extending flow, downward transport, and lodgment of calcareous englacial debris on local tills. Following the glacial maximum much of the distal englacial debris was laid down by subglacial meltout. However, a glacial reactivation occurred which moulded drumlins in the carbonate tills near Geraldton and deposited an upper calcareous lodgment till at Hemlo. Final Laurentide decay resulted in meltout of supraglacial debris that had been sheared up to or near the glacier surface from the stoss sides of the uplands. Dans les régions de Geraldton et de Hemlo, des tills carbonates transportés sur de longues distances s'intercalent entre des couches de tills non calcaires ou très légèrement calcaires; ils se distinguent par leur texture, leur teneur en carbonate et la composition lithologique de la fraction grossière. Leur présence et leur uniformité sur de grandes étendues du Bouclier témoignent d'un important transport de sédiments grâce à un apport rapide de débris dans la partie méridionale de l'Inlandsis laurentidien. Cette hypothèse ... |
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