T143 The Status of the Laurentide Ice Sheet during MIS-3 I

Tuesday, 11 October 2022
8:00 AM - 12:00 PM
603

RECYCLING OLD IDEAS: THE IOWAN, THE ALTONIAN AND THE MIS 3 SHELDON CREEK FORMATION IN IOWA

Paper number: T143-13
Program: Technical Sessions
Time: 10:55 AM – 11:10 AM

Authors

  • Charles Rovey Presenting Author
    Missouri State University, Springfield, MO

Abstract

Evidence for an MIS 3 ice advance into the midwestern U.S. has been recognized for over a century but was largely discounted. The loess record offers some of the most compelling, albeit indirect, evidence for such an advance. The widespread Roxana Silt and equivalents are constrained stratigraphically to a time interval between development of the subjacent Sangamon Geosol (Sangamon interglacial) and deposition of the overlying Peoria Silt (Late Wisconsinan). Eventually, radiocarbon dates gave ages for the Roxana spanning MIS 3; thus, the loess implied derivation from valley-train outwash sourced from an early Wisconsinan advance, dubbed the Altonian Substage. The Altonian displaced the Iowan as the oldest Wisconsin glacial substage, but both of these time-stratigraphic units, compatible with today’s MIS 3, were soon discarded: the Altonian, because till deposits in northern Illinois, thought to be of this age, turned up missing. In Iowa, the Iowan surface east of the Des Moines Lobe was shown to be a regional erosion surface above older pre-Illinoian tills, not undissected topography of a younger “Iowan” glaciation.

Meanwhile, quarry excavations on the Des Moines Lobe (DML) in Iowa had exposed two tills (Sheldon Creek Formation) below the Peoria Silt and the surficial till of the DML. The Sheldon Creek tills are separated by a weakly developed weathering profile and give radiocarbon ages of ~43 and 30 ka, respectively: a nice fit with MIS 3. These two tills are easily recognized by their matrix properties, and tracing shows that they extend beneath the DML and become the surface deposit in small areas east of the lobe and over an extensive area to the west.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-382731

© Copyright 2022 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.