Constraining Early and Middle Pleistocene Laurentide Ice Sheet advances with 10Be-26Al burial dating

Throughout the Quaternary, cyclical variations in global ice volume are recorded by benthic marine δ¹⁸O fluctuations. This signal is dominated by the waxing and waning of Northern Hemisphere ice sheets, particularly the Laurentide Ice Sheet (LIS) in North America, which builds periodically into the largest of all ice sheets on Earth. At such times, the LIS advanced southward into the American Midwest where glacial deposits emplaced prior to Marine Isotope Stage (MIS) 6 are known from just a handful of securely-dated sites. Consequently, current understandings of LIS extent and volume through time are incomplete and poorly constrained.

Here, we focus on tills bearing putative pre-MIS 6 depositional ages along the southern and southwestern margins of the LIS. We combine single-grain sedimentary provenance analyses with cosmogenic ¹⁰Be-²⁶Al burial dating in an aim to better resolve till chronology and provenance, using P-PINI and CosmoChron numerical models to calculate burial ages.

Building on existing magneto-, tephro-, and lithostratigraphic correlations, our new burial ages will significantly improve knowledge of the timing and extent of the LIS and its sediment source areas feeding different ice sheet sectors along the southern and southwestern margins. Our findings will improve reconstructions of LIS configurations through time, and yield new insights into Early–Middle Pleistocene global ice volume variability linked directly to the terrestrial record.