IS THE MARSHALL MORAINE A MORAINE?

The Marshall Moraine, as mapped by Leverett (1932), extends from Roberts County, SD southeastward into Watonwan County, MN. Subsequent to Leverett's work, Matsch (1972), Hobbs and Goebel (1982), and Patterson (1996) have all disregarded the idea of a "Marshall Moraine" and instead labeled the features in the area "outwash channels." The goal of this project was to determine if a portion of Leverett's Marshall Moraine in western Brown County, is or is not a moraine.

To determine whether or not the western Brown County feature was a moraine, I had to decide: A) If this was a moraine, what were the depositional environments? Or, B) if this was not a moraine, what was the origin of the topography in the area?

Air photos were used to locate and map different geomorphic landforms. Exposures were located and sediments were described and interpreted. Depositional environments (specifically whether or not sedimentary features were ice contact) were determined. Finally, till samples were collected for point counts to determine provenance.

Fieldwork showed that ice-contact stratified drift and collapse features are present. Two distinct till units, both deposited by the Des Moines Lobe, were differentiated on the basis of color. Finally, unique soft sediment clasts composed of the underlying Cretaceous lithologies within a constructional landform indicate an ice marginal environment.

In conclusion, Leverett's designation of The Marshall Moraine in western Brown County has merit, but more evidence is required. Future work will include mapping to the northwest in search of morainic topography and additional exposures.

Research for this study was funded by a grant from the National Science Foundation Research Experiences for Undergraduates (REU) Program (NSF-EAR 9820249).