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Isotopic evidence for the diversity of late Quaternary loess in Nebraska: Glaciogenic and nonglaciogenic sources

GSA Bulletin

By:
, , , , , and
DOI: 10.1130/B26222.1

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Abstract

Pb isotope compositions of detrital K-feldspars and U-Pb ages of detrital zircons are used as indicators for determining the sources of Peoria Loess deposited during the last glacial period (late Wisconsin, ca. 25–14 ka) in Nebraska and western Iowa. Our new data indicate that only loess adjacent to the Platte River has Pb isotopic characteristics suggesting derivation from this river. Most Peoria Loess in central Nebraska (up to 20 m thick) is non-glaciogenic, on the basis of Pb isotope ratios in K-feldspars and the presence of 34-Ma detrital zircons. These isotopic characteristics suggest derivation primarily from the Oligocene White River Group in southern South Dakota, western Nebraska, southeastern Wyoming, and northeastern Colorado. The occurrence of 10–25 Ma detrital zircons suggests additional minor contributions of silt from the Oligocene-Miocene Arikaree Group and Miocene Ogallala Group. Isotopic data from detrital K-feldspar and zircon grains from Peoria Loess deposits in eastern Nebraska and western Iowa suggest that the immediate source of this loess was alluvium of the Missouri River. We conclude that this silt probably is of glaciogenic origin, primarily derived from outwash from the western margin of the Laurentide Ice Sheet. Identification of the White River Group as the main provenance of Peoria Loess of central Nebraska and the Missouri River valley as the immediate source of western Iowa Peoria Loess indicates that paleowind directions during the late Wisconsin were primarily from the northwest and west, in agreement with earlier studies of particle size and loess thickness variation. In addition, the results are in agreement with recent simulations of non-glaciogenic dust sources from linked climate-vegetation modeling, suggesting dry, windy, and minimally vegetated areas in parts of the Great Plains during the last glacial period.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Isotopic evidence for the diversity of late Quaternary loess in Nebraska: Glaciogenic and nonglaciogenic sources
Series title:
GSA Bulletin
DOI:
10.1130/B26222.1
Volume
120
Issue:
11-12
Year Published:
2008
Language:
English
Publisher:
Geological Society of America
Publisher location:
Boulder, CO
Contributing office(s):
Geology and Environmental Change Science Center
Description:
16 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
GSA Bulletin
First page:
1362
Last page:
1377
Country:
United States
State:
Nebraska