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

Authors

John N. Aleinikoff, U.S. Geological Survey
Daniel R. Muhs, U.S. Geological SurveyFollow
E. Arthur Bettis III, University of IowaFollow
William C. Johnson, University of Kansas
C. Mark Fanning, Australian National University
Rachel Benton, U.S. National Park Service

Date of this Version

2008

Comments

Published in GSA Bulletin; November/December 2008; v. 120; no. 11/12; p. 1362–1377.

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.