Timing of advance and basal condition of the Laurentide Ice Sheet during the last glacial maximum in the Richardson Mountains, NWT

Abstract

This study presents new ages for the northwest section of the Laurentide Ice Sheet (LIS) glacial chronology from material recovered from two retrogressive thaw slumps exposed in the Richardson Mountains, Northwest Territories, Canada. One study site, located at the maximum glacial limit of the LIS in the Richardson Mountains, had calcite concretions recovered from aufeis buried by glacial till that were dated by U/Th disequilibrium to 18,500 cal yr BP. The second site, located on the Peel Plateau to the east yielded a fossil horse (Equus) mandible that was radiocarbon dated to ca. 19,700 cal yr BP. These ages indicate that the Peel Plateau on the eastern flanks of the Richardson Mountains was glaciated only after 18,500 cal yr BP, which is later than previous models for the global last glacial maximum (LGM). As the LIS retreated the Peel Plateau around 15,000 cal yr BP, following the age of the Tutsieta phase, we conclude that the presence of the northwestern margin of the LIS at its maximum limit was a very short event in the western Canadian Arctic.

Deglaciation of the Laurentide Ice Sheet from the Last Glacial Maximum

“…Its extent during MIS 3 is uncertain (Dredge and Thorleifson, 1987;Stokes et al, 2012;Dalton et al, 2016), but it grew rapidly to its Local Last Glacial Maximum, which was attained around 26-25 ka (e.g. Dyke, 2002;Clark et al, 2009), although with some regions advancing much later, such as in the far north-west (Lacelle et al, 2013). After over a century of debate, a consensus has emerged that it existed as an extensive, multi-domed ice sheet that extended to the edge of the continental shelf at its marine margins, but that it was thinner (~3000 m) than some earlier work had suggested and consumed a sea-level equivalent of around 50 m (Clark et al, 1996).…”

“…More recently, a number of studies have shown that ice sheet margin in the far north-west, in the vicinity of the Mackenzie River delta and along the Richardson Mountains, attained its maximum position relatively late and certainly less than 20 ka (e.g. Murton et al, 2007;Kennedy et al, 2010;Lacelle et al, 2013), possibly as a short-lived advance between 17 and 15 ka .…”

“…at the far north-west (Kennedy et al, 2010;Lacelle et al, 2013;Murton et al, 2007Murton et al, , 2015. Dyke et al (2002) pointed out that there is little evidence of regional recession prior to 17 ka (14 14 C ka), with the exception of the Atlantic Provinces, the Lake Michigan basin, the Mackenzie Lobe in the far north-west (cf.…”

“…It is also interesting that whilst the southern margin was beginning to retreat, there is strong evidence that the margin in the far north-west was still advancing and likely attained its maximum position after 18.5 ka (e.g. Murton et al, 2007;Kennedy et al, 2010;Lacelle et al, 2013). It is not clear why the northwest margin advanced to its maximum position a few millennia after the global LGM (sensu Clark et al, 2009), but Lacelle et al (2013) suggested that sea-level rise and the opening of the Arctic Ocean along the Beaufort Sea coastline may have provided a local source of moisture and increased precipitation that enabled an advance of the LIS in this region.…”

“…Murton et al, 2007;Kennedy et al, 2010;Lacelle et al, 2013). It is not clear why the northwest margin advanced to its maximum position a few millennia after the global LGM (sensu Clark et al, 2009), but Lacelle et al (2013) suggested that sea-level rise and the opening of the Arctic Ocean along the Beaufort Sea coastline may have provided a local source of moisture and increased precipitation that enabled an advance of the LIS in this region. They also pointed out that the abundance of deformable sediments in the region may also have facilitated a rapid advance of the Mackenzie Lobe (ice stream) (cf.…”