Keeping time with past ice sheets: progress on dating the late Pleistocene history of the Laurentide and Cordilleran ice sheets

Dr Alberto Reyes, U. Alberta

23 mars 2021

Despite decades of research and thousands of age determinations, there is still much to learn about the Late Pleistocene history of Canada’s ice sheets. The timing and spatial pattern of ice sheet advance and deglaciation are important variables for assessing linkages between Quaternary climate change, ice volume, and sea-level change. In this talk, I will present new results from three projects dealing with the challenges of ice-sheet geochronology, both prior to and after the last glacial maximum. I will first present a cautionary tale on interpreting legacy radiocarbon dates that, in part, have been used to support recent proposals for a “small” Laurentide Ice Sheet during the interstadial period prior to the last glacial maximum. I will then turn to lessons learned for using cosmogenic exposure ages on erratic boulders to date the deglacial history of the northwest Laurentide Ice Sheet, which currently has few reliable constraints on ice-margin retreat across much of inland Northwest Territories. I will close with a discussion of new exposure ages from six sites that provide direct chronology for the separation of the Cordilleran and Laurentide ice sheets along the length of their suture zone, with implications for abrupt deglacial climate and sea-level change.