Coalescence of late Wisconsinan Cordilleran and Laurentide ice sheets east of the Rocky Mountain Foothills in the Dawson Creek region, northeast British Columbia, Canada

Abstract

Geomorphic, stratigraphic and geochronological evidence from northeast British Columbia (Canada) indicates that, during the late Wisconsinan (approximately equivalent to marine oxygen isotope stage [MIS] 2), a major lobe of western-sourced ice coalesced with the northeastern-sourced Laurentide Ice Sheet (LIS). High-resolution digital elevation models reveal a continuous 75 km-long field of streamlined landforms that indicate the ice flow direction of a major northeast-flowing lobe of the Cordilleran Ice Sheet (CIS) or a montane glacier (>200 km wide) was deflected to a north-northwest trajectory as it coalesced with the retreating LIS. The streamlined landforms are composed of till containing clasts of eastern provenance that imply that the LIS reached its maximum extent before the western-sourced ice flow crossed the area. Since the LIS only reached this region in the late Wisconsinan, the CIS/montane ice responsible for the streamlined landforms must have occupied the area after the LIS withdrew. Stratigraphy from the Murray and Pine river valleys supports a late Wisconsinan age for the surface landforms and records two glacial events separated by a non-glacial interval that was dated to be of middle Wisconsinan (MIS 3) age.Peer reviewedCordilleran ice sheet; Laurentide ice sheet; Ice sheet coalescence; Ice free corridor; LiDAR; Stratigraphy; Optical dating; OSL; Ice flow; Till geochemistr

The pattern and style of deglaciation at the Late Wisconsinan Laurentide and Cordilleran ice sheet limits in northeastern British Columbia

“…9; Table 2), and give a weighted mean age of 13.0 ± 0.5 ka. They are significant, since they provide a northern extension to, and are consistent in age with, the existing chronology of dune activity in British Columbia and Alberta (e.g., Wolfe et al 2004;Hickin et al 2015Hickin et al , 2016. …”

“…The glacial history of the region outlined here is constrained by 14 C ages of organic material, 230 Th/ 234 U isotopic ages of speleothems, cosmogenic ages of glacial erratics, and optical ages of dune fields in adjacent areas of British Columbia, Yukon, and Northwest Territories (e.g., Ford 1976;Mathews 1980;Rampton 1987;Rutter et al 1993;Lemmen et al 1994;Duk-Rodkin and Lemmen 2000;Smith 2000Smith , 2002Bednarski and Smith 2007;Bednarski 2008;Hartman and Clague 2008;Trommelen and Levson 2008;Demchuk 2010;Huntley et al 2011;Hickin et al 2015Hickin et al , 2016. Radiocarbon ages are converted to approximate corresponding calendar years BP (ka) using the calibration model of Reimer et al (2009).…”

“…As deglaciation progressed, large proglacial lake systems formed along retreating margins of the Cordilleran and Laurentide ice sheets in northwestern Canada (Mathews 1980;Smith 1992Smith , 1994Lemmen et al 1994;Teller et al 2002Teller et al , 2005Dyke et al 2003;Zazula et al 2004;Bednarski 2008;Hickin et al 2015Hickin et al , 2016Figs. 2B-2F).…”

“…8A) are indicative of initial advance of ice margins over sand and clay-rich bed materials containing permafrost (cf. Dyke and Prest 1987;Johnson 1990;Kleman and Borgström 1994;Bennett et al 1998;Boulton et al 1999;Ó Cofaigh et al 2005;Bednarski 2008;Evans et al 2008;Hartman and Clague 2008;Hickin et al 2008;Trommelen and Levson 2008;Benediktsson et al 2009;Lajeunesse 2014;Hickin et al 2016).…”

“…Surficial geology mapping and fieldwork in northeastern British Columbia over the last 50 years have established that meltwater spillways and glacial lakes formed along retreating margins of the Late Wisconsinan (Late Pleistocene Marine Isotope Stage 2) Cordilleran and Laurentide ice sheets (Mathews 1980;Smith 1992Smith , 1994Lemmen et al 1994;Duk-Rodkin et al 1996;Teller et al 2002Teller et al , 2005Dyke et al 2003;Zazula et al 2004;Bednarski and Smith 2007;Bednarski 2008;Hartman and Clague 2008;Trommelen and Levson 2008;Hickin et al 2015Hickin et al , 2016. In the context of landsystem models of past ice sheets and observations of modern dynamic ice sheet behaviour, outstanding questions remain regarding (1) the limits of Laurentide and Cordilleran ice sheets in the region, (2) patterns and relative timing of ice retreat, (3) the sources and influences of meltwater on ice sheet dynamics during deglaciation, (4) evolution of meltwater drainage routes, and (5) elevation limits and extent of proglacial lake formation.…”