Deformation till in the Great Lakes region: implications for rapid flow along the south-central margin of the Laurentide Ice Sheet
Structural and lithologic data indicate that, while deposited under actively moving ice, considerable portions of three muddy calcareous subglacial tills in the Great Lakes region probably experienced some component of ductile deformation. Viscous till flow and ductile shear are invoked to explain a...
Published in: | Canadian Journal of Earth Sciences |
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Language: | English |
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Canadian Science Publishing
1992
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Online Access: | http://dx.doi.org/10.1139/e92-123 http://www.nrcresearchpress.com/doi/pdf/10.1139/e92-123 |
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crcansciencepubl:10.1139/e92-123 2024-09-15T18:12:31+00:00 Deformation till in the Great Lakes region: implications for rapid flow along the south-central margin of the Laurentide Ice Sheet Hicock, Stephen R. Dreimanis, Aleksis 1992 http://dx.doi.org/10.1139/e92-123 http://www.nrcresearchpress.com/doi/pdf/10.1139/e92-123 en eng Canadian Science Publishing http://www.nrcresearchpress.com/page/about/CorporateTextAndDataMining Canadian Journal of Earth Sciences volume 29, issue 7, page 1565-1579 ISSN 0008-4077 1480-3313 journal-article 1992 crcansciencepubl https://doi.org/10.1139/e92-123 2024-08-22T04:08:45Z Structural and lithologic data indicate that, while deposited under actively moving ice, considerable portions of three muddy calcareous subglacial tills in the Great Lakes region probably experienced some component of ductile deformation. Viscous till flow and ductile shear are invoked to explain a combination of features such as recumbent isoclinal folds, unlithified sediment clasts, mixed ostracode shells, reversed stone lee ends, girdle and transverse fabrics, irregular stone pavements, fine striae following stone curves, and inconsistent stone striae and a-axes. Deforming, fine-textured subglacial till is considered as a subhorizontal shear zone, rheologically layered with associated structures (in descending order): ductile (e.g., isoclinal folds), brittle–ductile (e.g., fissility), and brittle (e.g., till wedges). Rheology would be controlled mainly by till pore water content, matrix texture, and stone content. Spatial and temporal superposition of rheologies and subglacial processes probably occurred while some fine tills were forming. Fine deformation till may be especially common around areas of the Great Lakes region where proglacial mud and weak bedrock were remoulded as ice travelled along major basins and troughs. In such areas, under a wet-based glacier, resulting till would have been too weak to sustain a large shear stress or inhibit rapid ice flow over it. Instead, in these places, the till was probably water saturated, accounting for most of the glacial flow, and protected the substrate from extensive deformation while effectively acting as a lubricant to overriding ice. Areas of fine deformation till probably represent areas of former low subglacial fluid conductivity and rapid glacial flow. In other areas, subglacial sheet flow of meltwater may have accelerated glacial flow. These two types of areas may have been connected at times under zones of ice streaming and (or) surging. Article in Journal/Newspaper Ice Sheet Canadian Science Publishing Canadian Journal of Earth Sciences 29 7 1565 1579 |
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Open Polar |
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Canadian Science Publishing |
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crcansciencepubl |
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English |
description |
Structural and lithologic data indicate that, while deposited under actively moving ice, considerable portions of three muddy calcareous subglacial tills in the Great Lakes region probably experienced some component of ductile deformation. Viscous till flow and ductile shear are invoked to explain a combination of features such as recumbent isoclinal folds, unlithified sediment clasts, mixed ostracode shells, reversed stone lee ends, girdle and transverse fabrics, irregular stone pavements, fine striae following stone curves, and inconsistent stone striae and a-axes. Deforming, fine-textured subglacial till is considered as a subhorizontal shear zone, rheologically layered with associated structures (in descending order): ductile (e.g., isoclinal folds), brittle–ductile (e.g., fissility), and brittle (e.g., till wedges). Rheology would be controlled mainly by till pore water content, matrix texture, and stone content. Spatial and temporal superposition of rheologies and subglacial processes probably occurred while some fine tills were forming. Fine deformation till may be especially common around areas of the Great Lakes region where proglacial mud and weak bedrock were remoulded as ice travelled along major basins and troughs. In such areas, under a wet-based glacier, resulting till would have been too weak to sustain a large shear stress or inhibit rapid ice flow over it. Instead, in these places, the till was probably water saturated, accounting for most of the glacial flow, and protected the substrate from extensive deformation while effectively acting as a lubricant to overriding ice. Areas of fine deformation till probably represent areas of former low subglacial fluid conductivity and rapid glacial flow. In other areas, subglacial sheet flow of meltwater may have accelerated glacial flow. These two types of areas may have been connected at times under zones of ice streaming and (or) surging. |
format |
Article in Journal/Newspaper |
author |
Hicock, Stephen R. Dreimanis, Aleksis |
spellingShingle |
Hicock, Stephen R. Dreimanis, Aleksis Deformation till in the Great Lakes region: implications for rapid flow along the south-central margin of the Laurentide Ice Sheet |
author_facet |
Hicock, Stephen R. Dreimanis, Aleksis |
author_sort |
Hicock, Stephen R. |
title |
Deformation till in the Great Lakes region: implications for rapid flow along the south-central margin of the Laurentide Ice Sheet |
title_short |
Deformation till in the Great Lakes region: implications for rapid flow along the south-central margin of the Laurentide Ice Sheet |
title_full |
Deformation till in the Great Lakes region: implications for rapid flow along the south-central margin of the Laurentide Ice Sheet |
title_fullStr |
Deformation till in the Great Lakes region: implications for rapid flow along the south-central margin of the Laurentide Ice Sheet |
title_full_unstemmed |
Deformation till in the Great Lakes region: implications for rapid flow along the south-central margin of the Laurentide Ice Sheet |
title_sort |
deformation till in the great lakes region: implications for rapid flow along the south-central margin of the laurentide ice sheet |
publisher |
Canadian Science Publishing |
publishDate |
1992 |
url |
http://dx.doi.org/10.1139/e92-123 http://www.nrcresearchpress.com/doi/pdf/10.1139/e92-123 |
genre |
Ice Sheet |
genre_facet |
Ice Sheet |
op_source |
Canadian Journal of Earth Sciences volume 29, issue 7, page 1565-1579 ISSN 0008-4077 1480-3313 |
op_rights |
http://www.nrcresearchpress.com/page/about/CorporateTextAndDataMining |
op_doi |
https://doi.org/10.1139/e92-123 |
container_title |
Canadian Journal of Earth Sciences |
container_volume |
29 |
container_issue |
7 |
container_start_page |
1565 |
op_container_end_page |
1579 |
_version_ |
1810450110452072448 |