Late Quaternary loess in northeastern Colorado: Part II—Pb isotopic evidence for the variability of loess sources
A new application of the Pb isotopic tracer technique has been used to determine the relative importance of different silt sources for late Wisconsin loess in the central Great Plains of eastern Colorado. Samples of the Peoria Loess collected throughout the study area contain K-feldspar derived from...
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1999
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ftunivnebraskali:oai:digitalcommons.unl.edu:usgsstaffpub-1156 2023-11-12T04:17:58+01:00 Late Quaternary loess in northeastern Colorado: Part II—Pb isotopic evidence for the variability of loess sources Aleinikoff, John N Muhs, Daniel R. Sauer, Rebecca R Fanning, C. Mark 1999-01-01T08:00:00Z application/pdf https://digitalcommons.unl.edu/usgsstaffpub/157 https://digitalcommons.unl.edu/context/usgsstaffpub/article/1156/viewcontent/Muhs_GSAB_1999_Late_Quaternary_loess_part_2.pdf unknown DigitalCommons@University of Nebraska - Lincoln https://digitalcommons.unl.edu/usgsstaffpub/157 https://digitalcommons.unl.edu/context/usgsstaffpub/article/1156/viewcontent/Muhs_GSAB_1999_Late_Quaternary_loess_part_2.pdf USGS Staff -- Published Research Earth Sciences text 1999 ftunivnebraskali 2023-10-30T10:37:35Z A new application of the Pb isotopic tracer technique has been used to determine the relative importance of different silt sources for late Wisconsin loess in the central Great Plains of eastern Colorado. Samples of the Peoria Loess collected throughout the study area contain K-feldspar derived from two isotopically and genetically distinct sources: (1) glaciogenic material from Early and Middle Proterozoic crystalline rocks of the Colorado province, and (2) volcaniclastic material from the Tertiary White River Group exposed on the northern Great Plains. Pb isotopic compositions of K-feldspar in loess from two dated vertical sections (at Beecher Island and Last Chance, Colorado) vary systematically, implying climatic control of source availability. We propose a model whereby relatively cold conditions promoted the advance of Front Range valley glaciers discharging relatively little glaciogenic silt, but strong winds caused eolian erosion of White River Group silt due to a decrease in vegetation cover. During warmer periods, valley glaciers receded and discharged abundant glaciogenic silt, while surfaces underlain by the White River Group were stabilized by vegetation. Isotopic data from eastern Colorado loess sections record two warm-cold-warm cycles during late Wisconsin time between about 21,000 and 11,000 radiocarbon yr B.P., similar to results from other studies in the United States and Greenland. Text Greenland University of Nebraska-Lincoln: DigitalCommons@UNL Greenland Peoria ENVELOPE(-118.286,-118.286,55.617,55.617) |
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Open Polar |
collection |
University of Nebraska-Lincoln: DigitalCommons@UNL |
op_collection_id |
ftunivnebraskali |
language |
unknown |
topic |
Earth Sciences |
spellingShingle |
Earth Sciences Aleinikoff, John N Muhs, Daniel R. Sauer, Rebecca R Fanning, C. Mark Late Quaternary loess in northeastern Colorado: Part II—Pb isotopic evidence for the variability of loess sources |
topic_facet |
Earth Sciences |
description |
A new application of the Pb isotopic tracer technique has been used to determine the relative importance of different silt sources for late Wisconsin loess in the central Great Plains of eastern Colorado. Samples of the Peoria Loess collected throughout the study area contain K-feldspar derived from two isotopically and genetically distinct sources: (1) glaciogenic material from Early and Middle Proterozoic crystalline rocks of the Colorado province, and (2) volcaniclastic material from the Tertiary White River Group exposed on the northern Great Plains. Pb isotopic compositions of K-feldspar in loess from two dated vertical sections (at Beecher Island and Last Chance, Colorado) vary systematically, implying climatic control of source availability. We propose a model whereby relatively cold conditions promoted the advance of Front Range valley glaciers discharging relatively little glaciogenic silt, but strong winds caused eolian erosion of White River Group silt due to a decrease in vegetation cover. During warmer periods, valley glaciers receded and discharged abundant glaciogenic silt, while surfaces underlain by the White River Group were stabilized by vegetation. Isotopic data from eastern Colorado loess sections record two warm-cold-warm cycles during late Wisconsin time between about 21,000 and 11,000 radiocarbon yr B.P., similar to results from other studies in the United States and Greenland. |
format |
Text |
author |
Aleinikoff, John N Muhs, Daniel R. Sauer, Rebecca R Fanning, C. Mark |
author_facet |
Aleinikoff, John N Muhs, Daniel R. Sauer, Rebecca R Fanning, C. Mark |
author_sort |
Aleinikoff, John N |
title |
Late Quaternary loess in northeastern Colorado: Part II—Pb isotopic evidence for the variability of loess sources |
title_short |
Late Quaternary loess in northeastern Colorado: Part II—Pb isotopic evidence for the variability of loess sources |
title_full |
Late Quaternary loess in northeastern Colorado: Part II—Pb isotopic evidence for the variability of loess sources |
title_fullStr |
Late Quaternary loess in northeastern Colorado: Part II—Pb isotopic evidence for the variability of loess sources |
title_full_unstemmed |
Late Quaternary loess in northeastern Colorado: Part II—Pb isotopic evidence for the variability of loess sources |
title_sort |
late quaternary loess in northeastern colorado: part ii—pb isotopic evidence for the variability of loess sources |
publisher |
DigitalCommons@University of Nebraska - Lincoln |
publishDate |
1999 |
url |
https://digitalcommons.unl.edu/usgsstaffpub/157 https://digitalcommons.unl.edu/context/usgsstaffpub/article/1156/viewcontent/Muhs_GSAB_1999_Late_Quaternary_loess_part_2.pdf |
long_lat |
ENVELOPE(-118.286,-118.286,55.617,55.617) |
geographic |
Greenland Peoria |
geographic_facet |
Greenland Peoria |
genre |
Greenland |
genre_facet |
Greenland |
op_source |
USGS Staff -- Published Research |
op_relation |
https://digitalcommons.unl.edu/usgsstaffpub/157 https://digitalcommons.unl.edu/context/usgsstaffpub/article/1156/viewcontent/Muhs_GSAB_1999_Late_Quaternary_loess_part_2.pdf |
_version_ |
1782334704274374656 |