DOI

10.17077/etd.5q52vfji

Document Type

Thesis

Date of Degree

Summer 2018

Access Restrictions

Access restricted until 08/31/2019

Degree Name

MS (Master of Science)

Degree In

Geoscience

First Advisor

Bettis, E. A., III

First Committee Member

Cramer, B. D.

Second Committee Member

Dorale, J. A.

Third Committee Member

Schaetzl, R. J.

Abstract

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.

Keywords

Glaciation, Iowa, Middle Wisconsin, MIS 3, Quaternary, Sheldon Creek

Pages

xii, 99 pages

Bibliography

Includes bibliographical references (pages 90-99).

Copyright

Copyright © 2018 Phillip James Kerr

Available for download on Saturday, August 31, 2019

Included in

Geology Commons

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