ANALYSES AND CORRELATION OF PRE-WISCONSINAN AGE GLACIAL TILLS, YELLOW MEDICINE AND CHIPPEWA COUNTIES, WEST CENTRAL MINNESOTA

Multiple Pre-Wisconsinan tills were analyzed in the river cuts of Hawk Creek and Yellow Medicine River, two tributaries of the Minnesota River. Up to five Pre-Wisconsinan tills have been distinguished in the study area (Patterson 1999). However, the age and the extent of these tills are unknown. Additionally, few Pre-Wisconsinan tills have been correlated over long distances. The goal of this project was to describe, and correlate these Pre-Wisconsinan tills using provenance analysis, field descriptions, and plant macrofossils in an attempt to develop a local Pre-Wisconsinan stratigraphy.

All till units studied were described and traced in the field. A cobble unit consistently cropped out above the youngest Pre-Wisconsinan till and older tills were occasionally separated by sand lenses or silts. However, tills often varied in outcrop thickness, color, and texture.

Till samples were analyzed for provenance and macrofossil content. Provenance analyses of the tills and sand horizons did not differentiate source. Thus, this was not an effective tool for correlation. The Pre-Wisconsinan till samples were nearly devoid of macrofossils.

Research for this study was funded by grants for the National Science Foundation-Research Experiences for Undergraduate program (NSF-EAR 9820249), the Geological Society of America (North-Central Section), and the Iowa College Foundation/Maytag.