Collaborative Research: An Absolute Chronology of the Southernmost Advances of the Laurentide Ice Sheet

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Work under this collaborative will provide key information to address a long-standing issue in North American Quaternary geology: correlating continental physical evidence of repeated glaciations with the marine oxygen isotope record.To a great extent, what we know about the glaciations of the last several million years has been deduced from a proxy - rhythmic variations in d18O that reflect the balance between seawater and freshwater locked up in ice. These variations can be dated by relating them to changes in the Earth's inclination towards the Sun, and the eccentricity of the orbit - both factors which change how much energy the surface receives. However, there is little to no information on the distribution of that ice over the continental surfaces, and little information on why there are changes in ice periodicity not explained by orbital changes.Dating of glacial advances by the mapping of tills on the continent has been extremely difficult until the advent of a cosmogenic nuclide technique pioneered by this team. Beryllium-10/Aluminium-26 dating is a technique that provides resolution not provided by other chronometers. Dating of tills from Missouri northwards into Iowa will yield direct dates for at least five of the southernmost advances of the Laurentide Ice Sheet. The team will be able to provide data for questions about the role of ice sheets in Plio-Pleistocene climate, and their role in abrupt climate change.Through extensive collaboration with state geological surveys, the team will be able to transfer the technique into areas of geohydrological mapping that are interested in correlating different tills. In addition, the team has received extensive coverage for previous work on dating of fossil bearing sediments as well as the continent's oldest dated till, and expects to continue this public interest in the applications of cosmogenic nuclide dating techniques.