SEARCHING FOR WARREN UPHAM'S POCKET WATCH: A CHRONOLOGY FOR GLACIAL LAKE AGASSIZ UPPER SHORELINES ALONG THE NAMESAKE TRANSECT

Testing temporal relationships between lake level changes in Lake Agassiz and climate change events requires a direct chronology of shoreline occupation. This study focuses on the four major strandlines of the Lake Agassiz southern basin named by Warren Upham in his 1895 USGS monograph. His “type section” followed a portion of the Great Northern Railway line, which is paralleled by present day Minnesota Highway 9. Shoreline complexes were assigned the names of the closest towns. They are, in order of decreasing elevation, Herman, Norcross, Tintah and Campbell. These names as well as a sparse, sporadic, and often internally inconsistent radiocarbon chronology have been extended around large portions of Lake Agassiz’s margin, however, ages have never been determined for sites along the namesake transect. Optically Stimulated Luminescence (OSL) dating has had recent success in determining depositional ages for glacial Lake Agassiz shoreline deposits. In this presentation we report OSL ages from 11 field sites encompassing all four shoreline complexes along the namesake transect. Three criteria were used to select sampling locations for this study; proximity to the type section, topographic expression in the field, and soil composition. All samples were dated using single-aliquot regenerative dose data collection (SAR) procedures as well as dose distribution analysis methods. Our results can be used to add a chronometric identity to the major shorelines of Lake Agassiz’s southern basin, thereby increasing confidence in long-range correlation of the shoreline segments around the basin and enhancing our understanding of the relationship between lake level changes in Lake Agassiz and global climate change.