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

Abstract

This paper reports on the landform assemblages at the northern confluence of the Late Wisconsinan Laurentide and Cordilleran ice sheets with montane and piedmont glaciers in the northern Rockies and southern Mackenzie Mountains. Recent observations in northeastern British Columbia refine our knowledge of the pattern and style of ice sheet retreat, glacial lake formation, and meltwater drainage. At the onset of deglaciation, confluent Laurentide and Cordilleran terminal ice margins lay between 59°N, 124°30=W and 60°N, 125°15=W. From this terminal limit, ice sheets retreated into north-central British Columbia and Yukon Territory, with remnant Cordilleran ice and montane glaciers confined to mountain valleys and the Liard Plateau. Distinctive end moraines are not associated with the retreat of Cordilleran ice in these areas. Laurentide ice retreated northeastward from uplands and the plateaus; then separated into lobes occupying the Fort Nelson and Petitot river valleys. Ice-retreat landforms include recessional end moraines (sometimes overridden and drumlinized), hill-hole pairs, crevasse-fill deposits, De Geer-like ribbed till ridges, hummocky moraines, kames, meltwater features, and glacial lake deposits that fall within the elevation range of glacial Lake Liard and glacial Lake Fort Nelson (ca. 840-380 m). Meltwater and sediment transport into glacial lakes Fort Nelson, Liard, Nahanni, and Mackenzie was sustained by remnant ice in the Liard River and Fort Nelson River drainage basins until the end of glaciation. Optical dating of sand from stabilized parabolic dunes on the Liard Plateau indicates that proglacial conditions, lake formation, and drainage began before 13.0 ± 0.5 ka (calendar years). The Petitot, Fort Nelson, and Liard rivers all occupy spillways incised into glacial deposits and bedrock by meltwater overflow from glacial lakes Peace and Hay.Résumé : L'article rend compte des assemblages de formes de relief au confluent septentrional des inlandsis Laurentidien et de la Cordillère, d'âge wisconsinien tardif, avec des glaciers de montagne et de piémont dans le nord des montagnes Rocheuses et le sud des monts Mackenzie. Des observations récentes dans le nord-est de la Colombie-Britannique peaufinent les connaissances sur le motif et le style du retrait des inlandsis, la formation de lacs glaciaires et l'évacuation des eaux de fonte. Au début de la déglaciation, les marges terminales confluentes des inlandsis Laurentidien et de la Cordillère se trouvaient entre 59°N, 124°30=O et 60°N, 125°15=O. De cette limite terminale, les inlandsis ont retraité vers le centre-nord de la Colombie-Britannique et le Yukon, les restes de l'inlandsis de la Cordillère et des glaciers de montagne étant confinés à des vallées et au plateau de la Liard. Des moraines frontales distinctes ne sont pas associées au retrait de l'inlandsis de la Cordillère dans ces régions. L'inlandsis Laurentidien s'est retiré vers le nord-est à partir de hautes-terres et des plateaux, pour ensuite se diviser en lobes occupant les vall...

Current evidence allows multiple models for the peopling of the Americas

“…A series of 76 10 Be surface exposure cosmogenic nuclide ages reveal that intermediate and high elevation sites in the Peace River Corridor bottleneck were ice-free between 15,000 and 14,000 years ago, while 22 luminescence dates on eolian sand indicate that a broad subaerially exposed landscape was present by at least ~15,000 years ago (and possibly earlier) and that glacial lakes had already substantially drained ( Fig. 3 ) ( 37 , 55 – 57 ). Figure 1 illustrates the locations of these key late Pleistocene (and pre-Clovis) geological and paleoecological samples.…”

Deglaciation of the Cordillera of Western Canada at the end of the Pleistocene

“…Clague, 1989). Also shown are places referred to in the text; CR -Cascade Range, CV -Coquitlam Valley, DE -Dixon Entrance, HS -Hecate Strait; MAPP -Mount Assiniboine Provincial Park, WLNPWaterton Lakes National Park. To the east, glaciers flowed from the British Columbia interior and the Rocky Mountains, and locally coalesced with the Laurentide Ice Sheet over the Rocky Mountain Foothills (Clague, 1989;Dyke, 2004;Bednarski and Smith, 2007;Atkinson et al, 2016;Huntley et al, 2017). These ice masses, however, joined only briefly at the maximum of the last glaciation 18,000 years ago (Jackson et al, 1999).…”

Sea level fingerprinting of the Bering Strait flooding history detects the source of the Younger Dryas climate event

“…4, circles), and cosmogenic dating (Fig. 4, triangles) have established minimum ages of ice retreat in this region (17)(18)(19)(20). While there is evidence for ice-free conditions within the former saddle region by 15 ka (19), details of the timing, rate, and geometry of the saddle disintegration require refinement to understand the history of global mean sea level (GMSL) sourced from the eastern CIS and western LIS over the deglaciation.…”