Nunataks of the last ice sheet in northwest Scotland
High‐level weathering limits separating ice‐scoured topography from an upper zone of frost‐weathered detritus were identified on 17 mountains in NW Scotland at altitudes of <600 m to< 900 m, and a further 6 peaks were found to support evidence of ice scouring to summit level. Weathering limits...
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crwiley:10.1111/j.1502-3885.1995.tb00782.x 2024-09-15T18:12:21+00:00 Nunataks of the last ice sheet in northwest Scotland McCARROLL, DANNY BALLANTYNE, COLIN K. NESJE, ATLE DAHL, SVEIN‐OLAF 1995 http://dx.doi.org/10.1111/j.1502-3885.1995.tb00782.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1502-3885.1995.tb00782.x https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1502-3885.1995.tb00782.x en eng Wiley http://onlinelibrary.wiley.com/termsAndConditions#vor Boreas volume 24, issue 4, page 305-323 ISSN 0300-9483 1502-3885 journal-article 1995 crwiley https://doi.org/10.1111/j.1502-3885.1995.tb00782.x 2024-07-25T04:20:31Z High‐level weathering limits separating ice‐scoured topography from an upper zone of frost‐weathered detritus were identified on 17 mountains in NW Scotland at altitudes of <600 m to< 900 m, and a further 6 peaks were found to support evidence of ice scouring to summit level. Weathering limits are most clearly defined on Torridon Sandstone, which is resistant to frost shattering, but can also be mapped on Cambrian Quartzite, Lewisian Gneiss and Moine Schist. Contrasts in degree of rock surface weathering above and below the weathering limits were evaluated using measurements of joint depth and rock surface hardness, and through X‐ray diffraction analyses of clay mineral assemblages. The results indicate significantly more advanced rock and soil weathering above the weathering limits. Widespread persistence of gibbsite above the weathering limits suggests that they represent the upper limit of Late Devensian glacial erosion, and the regularity of the decline in weathering limit altitude along former flowlines eliminates the possibility that it represents a former thermal boundary between protective cold‐based and erosive warm‐based ice. The weathering limits are therefore interpreted as periglacial trimlines defining the maximum surface altitude of the last ice sheet around former nunataks. Calculated basal shear stresses of 50–78 kPa are consistent with this interpretation. The altitude of the trimlines implies that the former ice shed lay at 900–930 m in the Fannich Mountains and descended gently northwards, and that the ice surface descended NW from the ice shed to >500 m over the extreme NW tip of Scotland and to 700–730 m at the head of Little Loch Broom. Article in Journal/Newspaper Ice Sheet Wiley Online Library Boreas 24 4 305 323 |
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Wiley Online Library |
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crwiley |
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English |
description |
High‐level weathering limits separating ice‐scoured topography from an upper zone of frost‐weathered detritus were identified on 17 mountains in NW Scotland at altitudes of <600 m to< 900 m, and a further 6 peaks were found to support evidence of ice scouring to summit level. Weathering limits are most clearly defined on Torridon Sandstone, which is resistant to frost shattering, but can also be mapped on Cambrian Quartzite, Lewisian Gneiss and Moine Schist. Contrasts in degree of rock surface weathering above and below the weathering limits were evaluated using measurements of joint depth and rock surface hardness, and through X‐ray diffraction analyses of clay mineral assemblages. The results indicate significantly more advanced rock and soil weathering above the weathering limits. Widespread persistence of gibbsite above the weathering limits suggests that they represent the upper limit of Late Devensian glacial erosion, and the regularity of the decline in weathering limit altitude along former flowlines eliminates the possibility that it represents a former thermal boundary between protective cold‐based and erosive warm‐based ice. The weathering limits are therefore interpreted as periglacial trimlines defining the maximum surface altitude of the last ice sheet around former nunataks. Calculated basal shear stresses of 50–78 kPa are consistent with this interpretation. The altitude of the trimlines implies that the former ice shed lay at 900–930 m in the Fannich Mountains and descended gently northwards, and that the ice surface descended NW from the ice shed to >500 m over the extreme NW tip of Scotland and to 700–730 m at the head of Little Loch Broom. |
format |
Article in Journal/Newspaper |
author |
McCARROLL, DANNY BALLANTYNE, COLIN K. NESJE, ATLE DAHL, SVEIN‐OLAF |
spellingShingle |
McCARROLL, DANNY BALLANTYNE, COLIN K. NESJE, ATLE DAHL, SVEIN‐OLAF Nunataks of the last ice sheet in northwest Scotland |
author_facet |
McCARROLL, DANNY BALLANTYNE, COLIN K. NESJE, ATLE DAHL, SVEIN‐OLAF |
author_sort |
McCARROLL, DANNY |
title |
Nunataks of the last ice sheet in northwest Scotland |
title_short |
Nunataks of the last ice sheet in northwest Scotland |
title_full |
Nunataks of the last ice sheet in northwest Scotland |
title_fullStr |
Nunataks of the last ice sheet in northwest Scotland |
title_full_unstemmed |
Nunataks of the last ice sheet in northwest Scotland |
title_sort |
nunataks of the last ice sheet in northwest scotland |
publisher |
Wiley |
publishDate |
1995 |
url |
http://dx.doi.org/10.1111/j.1502-3885.1995.tb00782.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1502-3885.1995.tb00782.x https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1502-3885.1995.tb00782.x |
genre |
Ice Sheet |
genre_facet |
Ice Sheet |
op_source |
Boreas volume 24, issue 4, page 305-323 ISSN 0300-9483 1502-3885 |
op_rights |
http://onlinelibrary.wiley.com/termsAndConditions#vor |
op_doi |
https://doi.org/10.1111/j.1502-3885.1995.tb00782.x |
container_title |
Boreas |
container_volume |
24 |
container_issue |
4 |
container_start_page |
305 |
op_container_end_page |
323 |
_version_ |
1810449933903331328 |