Late Wisconsinan Cordilleran and Laurentide glaciation of the Peace River Valley east of the Rocky Mountains, British Columbia

Abstract

In the past, researchers have disagreed over the maximum extent of the Cordilleran Ice Sheet in the Peace River valley during the Late Wisconsinan. Some workers argued that Cordilleran ice reached beyond the Rocky Mountains and briefly coalesced with the Laurentide Ice Sheet on the westernmost Interior Plains. In contrast, others asserted that Cordilleran ice did not reach beyond the eastern front of the Rocky Mountains. Stratigraphic interpretation of three sections within a Middle Wisconsinan paleovalley and re-examination of a previously published regional stratigraphic framework show that western-sourced ice (likely the Cordilleran Ice Sheet) extended east of the mountain front during the Late Wisconsinan, prior to the incursion of the Laurentide Ice Sheet into the area. This conclusion has implications for Cordilleran Ice Sheet reconstruction and modelling, and provides insight into the interactions between the Cordilleran and Laurentide ice sheets during the last glaciation.

Using10Be dating to determine when the Cordilleran Ice Sheet stopped flowing over the Canadian Rocky Mountains

“…The coalescence of the CIS and LIS east of the Rocky Mountains is now well established (Atkinson et al, 2016; Hartman et al, 2018; Margold et al, 2018), with this study providing further evidence for ice flow over the Rocky Mountains at the lLGM. In contrast, the timing and style of deglaciation in the interior of the ice sheet is very poorly constrained with the mountainous topography thus far impeding the reconstruction of ice sheet-wide glacial retreat patterns.…”

“…The interaction between the Cordilleran and Laurentide ice sheets east of the Rocky Mountains at the LGM has been debated for many decades, with some researchers arguing for the coalescence of the two ice sheets on the westernmost Interior Plains (e.g., Mathews, 1978;Dyke and Prest, 1987;Stumpf et al, 2000;Dyke et al, 2003;Dyke, 2004;Bednarski and Smith, 2007), while others argue that the CIS did not extend over the Rocky Mountains at the local LGM (lLGM) (e.g., Bobrowsky and Rutter, 1992;Catto et al, 1996). Recently, empirical evidence supporting the coalescence of the two ice sheets has grown (Atkinson et al, 2016;Hickin et al, 2016;Hartman et al, 2018), and it is now generally accepted that they coalesced at the lLGM (Fig. 1).…”

“…3a), (3) geomorphological evidence of ice drainage through a system of broad mountain cols located between 54.5°N and 55°N (Fig. 3b), (4) eastwardly transported glacial erratics along the Rocky Mountain Foothills (Bednarski and Smith, 2007), and (5) the presence of volcanic-rich Cordilleran till east of the Rocky Mountains (Mathews, 1978;Bednarski and Smith, 2007;Hartman et al, 2018). Margold et al (2018Margold et al ( , 2019 incorporated ice flow over the Hart Ranges into a broader, regional picture of the ice sheet configuration, showing the ice drainage pattern at, and shortly after, the lLGM.…”

The age of the opening of the Ice-Free Corridor and implications for the peopling of the Americas

“…To directly date the opening of the IFC with century-scale precision, we collected multiple samples for 10 Be surface exposure dating from each of six sites ( SI Appendix , Figs. S1 and S2 ) along a 1,200-km-long, south–north transect (∼50 to 59°N) where mapping identified the confluence of the Cordilleran and Laurentide Ice Sheets ( 42 – 44 ) ( Fig. 1 ).…”