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Optical ages on loess derived from outwash surfaces constrain the advance of the Laurentide Ice Sheet out of the Lake Superior Basin, USA

Published online by Cambridge University Press:  20 January 2017

Randall J. Schaetzl ,
Steven L. Forman  and
John W. Attig
Randall J. Schaetzl*
Affiliation:
Department of Geography, 128 Geography Bldg, Michigan State University, East Lansing, MI 48824-1117, USA
Steven L. Forman
Affiliation:
Luminescence Dating Research Laboratory, Dept. of Earth and Environmental Sciences, 845 W. Taylor Street (m/c 186), 2440 Science and Engineering South, Univ. of Illinois at Chicago, Chicago, IL 60607-7059, USA
John W. Attig
Affiliation:
Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison, WI 53705-5100, USA
*
*Corresponding author. Fax: + 1 517 432 1671. E-mail address:[email protected] (R.J. Schaetzl).
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Abstract

We present textural and thickness data on loess from 125 upland sites in west-central Wisconsin, which confirm that most of this loess was derived from the sandy outwash surfaces of the Chippewa River and its tributaries, which drained the Chippewa Lobe of the Laurentide front during the Wisconsin glaciation (MIS 2). On bedrock uplands southeast of the widest outwash surfaces in the Chippewa River valley, this loess attains thicknesses > 5 m. OSL ages on this loess constrain the advance of the Laurentide ice from the Lake Superior basin and into west-central Wisconsin, at which time its meltwater started flowing down the Chippewa drainage. The oldest MAR OSL age, 23.8 ka, from basal loess on bedrock, agrees with the established, but otherwise weakly constrained, regional glacial chronology. Basal ages from four other sites range from 13.2 to 18.5 ka, pointing to the likelihood that these sites remained geomorphically unstable and did not accumulate loess until considerably later in the loess depositional interval. Other OSL ages from this loess, taken higher in the stratigraphic column but below the depth of pedoturbation, range to nearly 13 ka, suggesting that the Chippewa River valley may have remained a loess source for several millennia.

Keywords

WisconsinLoessChippewa RiverOutwash surfacesMAR OSLLuminescence dating
Type
Research Article
Information
Quaternary Research , Volume 81 , Issue 2 , March 2014 , pp. 318 - 329
Copyright
University of Washington

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