Date of Degree
Access restricted until 08/31/2019
MS (Master of Science)
Bettis, E. A., III
First Committee Member
Cramer, B. D.
Second Committee Member
Dorale, J. A.
Third Committee Member
Schaetzl, R. J.
Data from new subsurface studies, lithologic analyses, radiocarbon dating, and geologic mapping demonstrate that an early middle Wisconsinan (MIS 3) to late Wisconsonan (MIS2) till sheet is more widespread in northcentral Iowa than previously assumed. This till had been mapped to the west of and beneath the late Wisconsinan (MIS 2) Des Moines Lobe (DML); this thesis research has shown that the boundary of that till sheet extends 40 to 50 km east of the DML margin. Sediments deposited by the MIS 3 glacier are termed the Sheldon Creek Formation; they share many lithologic properties with DML Dows Formation deposits. Some of these shared properties, such as clasts of Pierre Shale, suggest a similar northwesterly provenance and glacial flow from the Keewatin Dome of the Laurentide Ice Sheet during both glaciations. Radiocarbon ages of organic materials within and beneath the Sheldon Creek Formation, as well as stratigraphic relationships in cores and outcrops, suggest that the unit accumulated during two distinct advances, herein named the Ft. Dodge Advance (ca. 46-40 ka) and the Lehigh Advance (ca. 34-29 ka).
The presence of ice in Iowa before the regional Last Glacial Maximum has important implications for modeling buildup of the Laurentide Ice Sheet (LIS) and understanding the regional variability of ice sheet extent during the last glacial period. Existing models the LIS buildup are challenged by the pre-MIS 2 chronology reported here, which puts the ice sheet much farther south during MIS 3b than had previously been reported. This points to a much earlier buildup of the Keewatin Dome than previously assumed. The timing of the Sheldon Creek advances appear to coincide with Heinrich events 3 and 5 in the North Atlantic, indicating that both the Keewatin and Laurentian Domes of the ice sheet were large at this time. Further work needs to be done to determine if the MIS 3b and early MIS 2 Sheldon Creek Formation deposits in Iowa are unique, or if there are other unrecognized deposits from these time periods.
Glaciation, Iowa, Middle Wisconsin, MIS 3, Quaternary, Sheldon Creek
xii, 99 pages
Includes bibliographical references (pages 90-99).
Copyright © 2018 Phillip James Kerr
Kerr, Phillip James. "Middle to early-late Wisconsin glaciation in north central Iowa: timing, distribution, and implications for reconstructions of the Laurentide Ice Sheet during MIS 3." MS (Master of Science) thesis, University of Iowa, 2018.
Available for download on Saturday, August 31, 2019