Recognizing order in chaotic sequences of Quaternary sediments in the Canadian Cordillera

Abstract

Episodic growth and decay of the Cordilleran ice sheet during the Pleistocene has imposed order on Quaternary stratigraphies in British Columbia and southern Yukon Territory. Although Quaternary deposits in this region are inherently complex, thick valley and lowland "lls consist of discrete packages of glacial sediments separated by unconformities or by generally thin, patchy interglacial deposits. Some unconformities de"ne former valley and lowland landscapes of similar relief to the present. Each package of glacial sediments displays stratigraphic order: distinctive #uvial and lacustrine units, deposited during the early stage of a glaciation and later overridden and eroded by glaciers, are overlain by retreat phase and interglacial #uvial, lacustrine, and marine sediments. Packages of glacial sediments contain one or more unconformities produced by glacial erosion; commonly the unconformities are better stratigraphic markers than tills, which are not always present, especially in valleys. The Quaternary stratigraphic record in the Canadian Cordillera becomes less complete with age, owing to repeated erosion during both interglaciations and glaciations. The most complete glacial sequence is the youngest, deposited during the late Wisconsin Fraser Glaciation. Deposits of the penultimate glaciation are common but generally incomplete. Only sporadic remnants of older, apparently Middle and Early Pleistocene glacial deposits are present in the Cordillera.

Late-glacial lakes in the Thompson Basin, British Columbia: paleogeography and evolution

“…Fluvial and glacial erosion have dissected the Thompson Plateau resulting in deep valleys (up to -1500 m relief), today filled with thick (up to -800 m) Quaternary deposits (Fulton 1965;Ryder 1976;Eyles and Mullins 1997). High (>100 m) cliffs of glaciolacustrine silt dominate the South Thompson and Thompson valleys and are by far the dominant Quaternary fill (Fulton and Armstrong 1965;Fulton and Smith 1978;Ryder 1976Ryder , 1981Clague 2000;Clague and Evans 2003). West of Kamloops Lake to Spences Bridge, numerous fluvial terraces dominate the valley-sides and record up to 150 m of river incision.…”

A post-glacial sea level hinge on the central Pacific coast of Canada

“…5 (also see Luternauer and Murray, 1983;Mathews, 1991;Barrie and Conway, 2002b). By 11,400 calendar years ago, the extent of glacial ice cover in the Coast Mountain was similar to that of today (Clague, 1981(Clague, , 2000. Tidewater glaciers are still present to the north in southeast Alaska.…”

A 14,500-year record of landscape change from Okpilak Lake, northeastern Brooks Range, northern Alaska

“…River aggradation could take place in response to a number of environmental and landscape changes. For example, during alpine glacial advances, aggradation can occur as the sediment stored within and beneath glaciers is delivered to fluvial systems (Clague 2000;Marren 2002;Wilkie and Clague 2009). On the other hand, retreating glaciers expose large areas of erodible sediment that when contributed to rivers can cause alluviation and changes in channel planform (Gottesfeld and Johnson -Gottesfeld 1990;Brooks 1994;Clague et al 2003).…”