ISGS geologists participated in updating 36 maps depicting the receding margin of the Laurentide Ice Sheet of North America starting from the last global glacial maximum about 18,000 radiocarbon years ago to the present at 500-year snapshot intervals (Dalton et al., 2020). The maps update the classic work of Dyke et al. (2003). Of the 1,541 new radiocarbon ages added to the database, about 200 are from Illinois, primarily from samples collected by ISGS geologists.
In the map of the last global glacial maximum (18,000 radiocarbon years ago) above, the southeastern part of the ice sheet is shown, with Illinois providing seven new datum constraints for this time slice. The ice margin as previously mapped in 2003 is shown by the dotted line; our contributions move the boundary north about 150 km.
The dotted line remains the last local glacial maximum for the Lake Michigan lobe, but it dates from about 20,000 radiocarbon years ago. The difference between the local and global conditions likely reflects the rapid response of the southern margin of the Laurentide Ice Sheet to favorable conditions for expansion of continental ice.
The updated paleogeographic maps will be used by earth systems modelers and other researchers interested in glacial dynamics and history.
Dalton, A., and 71 others, 2020. An updated radiocarbon-based ice margin chronology for the last deglaciation of the North American Ice Sheet Complex. Quaternary Science Reviews, v. 234, https://doi.org/10.1016/j.quascirev.2020.106223.
Dyke, A.S., Moore, A., and Robertson, L., 2003. Deglaciation of North America. Geological Survey of Canada, Open File 1574, https://doi.org/10.4095/214399.