Dating the last deglaciation: Geochronologic methods used to assign temporal constraints to the retreat of late pleistocene ice sheets

Assignment of a temporal scale to deglaciation events is elemental to the understanding of processes involved during and subsequent to the retreat of continental ice sheets. Dating the recession of ice sheets, however, is complicated by the fact that ice sheets cease to exist following deglaciation, leaving behind no tangible remnants of the ice itself that can directly be analyzed. Hence, dating exercises essentially aim to place constraints on ice sheet recession by examining proxy records that resulted from or are associated with the former existence of ice sheets. A deglaciation timescale enables rates of postglacial geomorphic processes as well as the pace of environmental evolution to be determined. Additionally, such chronologies facilitate the analysis of variations in the distribution of biotic communities over time, in conjunction with changes in climatic conditions and other aspects of the environment. In areas where isostatic rebound occurred following glacial unloading, accurate dating allows geophysical models of viscoelastic responses to be calibrated, including changes in sea level. This chapter provides a review of dating methods that have been used to constrain the retreat of Late Pleistocene ice sheets from formerly glaciated regions following the Last Glacial Maximum, with a focus on North America. Chronological methods explored include cosmogenic-nuclide exposure, luminescence, radiocarbon and varve dating techniques. In each instance, the principles behind the dating technique and the types of material that can be dated are examined. The chapter concludes with a brief outline of a case study conducted in western Canada to constrain the Late Pleistocene retreat of the Laurentide Ice Sheet from the region.