GSA Connects 2022 meeting in Denver, Colorado

Paper No. 47-2
Presentation Time: 1:50 PM

RAPID RETREAT OF THE SOUTHWESTERN LAURENTIDE ICE-SHEET DURING THE BØLLING-ALLERØD INTERVAL (Invited Presentation)


NORRIS, Sophie, Dalhousie University, Department of Earth and Environmental Sciences, Halifax, AB B3J 3J5, CANADA, TARASOV, Lev, Department of Physics and Physical Oceanography, Memorial University, St. John's, NF A1C 5S7, Canada, MONTEATH, Alistair, Geography and Environmental Science, University of Southampton, Southampton, AB SO17 1BJ, United Kingdom, GOSSE, John, Department of Earth and Environmental Sciences, Dalhousie University, Halifax, NS B3J 3J5, Canada, HIDY, Alan J., Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, MARGOLD, Martin, Department of Geography, Durham University, Lower Mountjoy South Road, Durham, DH1 3LE, United Kingdom and FROESE, Duane, Earth & Atmospheric Science, University of Alberta, 1-26 Earth Sciences Bldg, Edmonton, AB T6G 2E3, Canada

The timing of Laurentide Ice Sheet deglaciation, along its southwestern margin, controls the evolution and drainage of large glacial lakes and has implications for the migration of early humans into the Americas. Accurate reconstruction of the ice sheet’s retreat also constrains glacial isostatic adjustment models and is imperative for our understanding of ice sheet sensitivity to climate forcings. Despite its importance, much of the retreat history of the southwestern Laurentide Ice Sheet is still poorly constrained by minimum limiting 14C data. Here, we present a database of 26 10Be surface exposure ages from glacial erratics spanning southwestern Alberta to northwestern Saskatchewan, Canada. Using a Bayesian framework, we combine these data with geomorphic mapping, 10Be, and high-quality minimum-limiting 14C ages to provide an updated chronology. This dataset presents an internally consistent retreat record and indicates that the initial detachment of the SWLIS from its convergence with the Cordilleran Ice Sheet began by ca. 15.0 ka, concurrent with or slightly prior to the onset of the Bølling-Allerød interval (14.7–12.9 ka) and retreated >1200 km to its Younger Dryas (YD) position in ∼2500 yr. Ice-sheet stabilization at the Cree Lake Moraine facilitated a meltwater drainage route to the Arctic from glacial Lake Agassiz within the YD, but not necessarily at the beginning. Our record of deglaciation and new YD constraints demonstrate deglaciation of the Interior Plains was ∼60% faster than suggested by minimum 14C constraints alone. Numerical modelling of this rapid retreat estimates a loss of ∼3.7 m of sea-level equivalent from the SWLIS during the Bølling-Allerød interval.