Cosmogenic 10 Be and 36 Cl geochronology of cryoplanation terraces in the Alaskan Yukon-Tanana Upland
ABSTRACT Cryoplanation terraces are prominent but enigmatic landforms found in present and past periglacial environments. Geomorphologists have debated for more than a century over processes involved in the formation of these elevated, step-like, bedrock features. Presented here are the first numeri...
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crcambridgeupr:10.1017/qua.2020.25 2024-09-09T20:03:17+00:00 Cosmogenic 10 Be and 36 Cl geochronology of cryoplanation terraces in the Alaskan Yukon-Tanana Upland Nyland, Kelsey E. Nelson, Frederick E. Figueiredo, Paula M. 2020 http://dx.doi.org/10.1017/qua.2020.25 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033589420000253 en eng Cambridge University Press (CUP) https://www.cambridge.org/core/terms Quaternary Research volume 97, page 157-166 ISSN 0033-5894 1096-0287 journal-article 2020 crcambridgeupr https://doi.org/10.1017/qua.2020.25 2024-08-07T04:04:34Z ABSTRACT Cryoplanation terraces are prominent but enigmatic landforms found in present and past periglacial environments. Geomorphologists have debated for more than a century over processes involved in the formation of these elevated, step-like, bedrock features. Presented here are the first numerical surface exposure ages and scarp retreat rates from cryoplanation terraces in the Yukon-Tanana Upland (YTU) in Alaska, part of unglaciated eastern Beringia, obtained from terrestrial cosmogenic nuclides (TCN) in surface boulders. Ages comprise six 10 Be TCN ages from two terrace treads near Eagle Summit and six 36 Cl ages from two treads on Mt. Fairplay. Based on these exposure ages, scarps at both locations were last actively eroding from 49 to 22.4 ka. Both locations exhibit time-transgressive development, particularly near scarp-tread junctions. Boulder exposure ages and distances between sampled boulder locations were used to estimate scarp retreat rates of 0.11 to 0.56 cm/yr. These numerical exposure ages presented here demonstrate that the cryoplanation terraces in the YTU are diachronous surfaces actively eroding during multiple cold intervals. With these results, hypotheses for cryoplanation terrace formation are discussed and evaluated for the YTU, including those based on geologic structure, nivation, and the influence of permafrost. Article in Journal/Newspaper permafrost Alaska Beringia Yukon Cambridge University Press Yukon Quaternary Research 97 157 166 |
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Open Polar |
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Cambridge University Press |
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crcambridgeupr |
language |
English |
description |
ABSTRACT Cryoplanation terraces are prominent but enigmatic landforms found in present and past periglacial environments. Geomorphologists have debated for more than a century over processes involved in the formation of these elevated, step-like, bedrock features. Presented here are the first numerical surface exposure ages and scarp retreat rates from cryoplanation terraces in the Yukon-Tanana Upland (YTU) in Alaska, part of unglaciated eastern Beringia, obtained from terrestrial cosmogenic nuclides (TCN) in surface boulders. Ages comprise six 10 Be TCN ages from two terrace treads near Eagle Summit and six 36 Cl ages from two treads on Mt. Fairplay. Based on these exposure ages, scarps at both locations were last actively eroding from 49 to 22.4 ka. Both locations exhibit time-transgressive development, particularly near scarp-tread junctions. Boulder exposure ages and distances between sampled boulder locations were used to estimate scarp retreat rates of 0.11 to 0.56 cm/yr. These numerical exposure ages presented here demonstrate that the cryoplanation terraces in the YTU are diachronous surfaces actively eroding during multiple cold intervals. With these results, hypotheses for cryoplanation terrace formation are discussed and evaluated for the YTU, including those based on geologic structure, nivation, and the influence of permafrost. |
format |
Article in Journal/Newspaper |
author |
Nyland, Kelsey E. Nelson, Frederick E. Figueiredo, Paula M. |
spellingShingle |
Nyland, Kelsey E. Nelson, Frederick E. Figueiredo, Paula M. Cosmogenic 10 Be and 36 Cl geochronology of cryoplanation terraces in the Alaskan Yukon-Tanana Upland |
author_facet |
Nyland, Kelsey E. Nelson, Frederick E. Figueiredo, Paula M. |
author_sort |
Nyland, Kelsey E. |
title |
Cosmogenic 10 Be and 36 Cl geochronology of cryoplanation terraces in the Alaskan Yukon-Tanana Upland |
title_short |
Cosmogenic 10 Be and 36 Cl geochronology of cryoplanation terraces in the Alaskan Yukon-Tanana Upland |
title_full |
Cosmogenic 10 Be and 36 Cl geochronology of cryoplanation terraces in the Alaskan Yukon-Tanana Upland |
title_fullStr |
Cosmogenic 10 Be and 36 Cl geochronology of cryoplanation terraces in the Alaskan Yukon-Tanana Upland |
title_full_unstemmed |
Cosmogenic 10 Be and 36 Cl geochronology of cryoplanation terraces in the Alaskan Yukon-Tanana Upland |
title_sort |
cosmogenic 10 be and 36 cl geochronology of cryoplanation terraces in the alaskan yukon-tanana upland |
publisher |
Cambridge University Press (CUP) |
publishDate |
2020 |
url |
http://dx.doi.org/10.1017/qua.2020.25 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033589420000253 |
geographic |
Yukon |
geographic_facet |
Yukon |
genre |
permafrost Alaska Beringia Yukon |
genre_facet |
permafrost Alaska Beringia Yukon |
op_source |
Quaternary Research volume 97, page 157-166 ISSN 0033-5894 1096-0287 |
op_rights |
https://www.cambridge.org/core/terms |
op_doi |
https://doi.org/10.1017/qua.2020.25 |
container_title |
Quaternary Research |
container_volume |
97 |
container_start_page |
157 |
op_container_end_page |
166 |
_version_ |
1809935217130995712 |