The formation and draining of late Wisconsinan superglacial lakes on the Riding Mountain Uplands, Manitoba

Abstract

The late Wisconsinan deglaciation of the Riding Mountain Uplands was associated with the Lockhart Phase of glacial Lake Agassiz (11,600-10,800 B.P.). During the waning stages of the Falconer ice advance (post 11,400 B.P.) a large area of glacial ice stagnated on the Riding Mountain Uplands. Subsequent downwasting generated a drainage network consisting of several superglacial lakes, spillways and meltwater channels. Many of these glacial rivers eroded their ice beds and incised into the substratum. Glaciofluvial sediments were deposited as sandurs, eskers and kames. Subaqueous fans were deposited in the superglacial lakes and a major delta was built into the north end of glacial Lake Hind. During this time an advance of the Valley River Sublobe created the Mears kame moraine.
 
 Following this advance. Northeastern ice (the Assiniboine Sublobe) retreated from the Rivers - Rapid City Endmoraine to the Brookdale position. As downwasting of the stagnant ice on the uplands continued, the superglacial lakes drained and an entrenched drainage system developed on the stagnant ice moraine complex.
 
 RÉSUMÉ
 La déglaciation du Wisconsinien tardif du plateau de Riding Mountain était associée à la phase Lockhart du lac glaciaire Agassiz (11,600-10,800 B.P.). À la fin de l'avancée glaciaire Falconer (après 11.400B.P.), une vaste étendue de glace est resiée stagnante sur le plateau de Riding Mountain. L'ablation subséquente a laissé un réseau de drainage composé de plusieurs lacs supraglaciaires ainsi que des canaux de débordement et de fonte. Plusieurs de ces rivières glaciaires ont érodé leur lit de glace et le substrat. Les sédiments fluvio-glaciaires ont été déposés sous formé de sandurs, d'eskers et de kames. Des cônes subaqueux ont été déposés dans les lacs supraglaciaires et un delta important a été formd à l'extremité nord du lac glaciaire Hind. Pendant ce temps, une avancde du lobe secondaire de la rivière Valley a cté é la moraine à kames Mears.
 
 Après cette avancée, la partie nord-est du glacier (le lobe secondaire Assiniboine) à reculé, dépuis la moraine frontale de Rivers - Rapid City jusqu'à la position de Brookdale. Pendant l'ablation du glacier stagnant sur le plateau, les lacs supraglaciaires se sont drained et un réseau de drainage encaissé s'est développé sur le complexe de moraine associé au glacier stagnant.
 
 [Traduit par le journal]

Optically stimulated luminescence ages from the Lake Agassiz basin in Manitoba

“…The elevation of the point bar surface at the inner bend of the 180° forced meander is higher than the eastern rim of the valley meander and substantially higher than the two stream valleys that have captured modern runoff. Relative ages of the now-abandoned glacial spillways on Riding Mountain have been proposed by McGinn (e.g., 1991, 2002) and McGinn et al (2007, 2009).…”

“…9). In places, active ice was thrust up onto these upland “islands,” and this also became stagnant (McGinn, 1991, 1997). Meltwater ponded over the stagnant ice on Riding Mountain, creating small supraglacial lakes, and later an integrated network of ice-walled lakes and drainage channels formed (McGinn, 1991).…”

“…In places, active ice was thrust up onto these upland “islands,” and this also became stagnant (McGinn, 1991, 1997). Meltwater ponded over the stagnant ice on Riding Mountain, creating small supraglacial lakes, and later an integrated network of ice-walled lakes and drainage channels formed (McGinn, 1991). McGinn (1991) established that the supraglacial lakes drained eastward over stagnant ice into the McFadden Valley–Polonia Trench (MVPT) and deposited a large subaqueous fan (Bethany Fan) at its southern end (Fig.…”

“…McGinn (1991, 2002) and McGinn et al (2009) mapped the extent of superglacial Lake Proven on Riding Mountain (Fig. 3), located to the west of Lake Agassiz and more than 200 m above its highest level.…”

“…The elevation of the upland areas above the Lake Agassiz lowland ranges from <100 m in the south to ~425 m along Duck Mountain. On the uplands to the west of the escarpment in Manitoba, the landscape is hummocky and is covered by glaciogenic sediments such as till, glaciofluvial and glaciolacustrine deposits, and locally derived fluvial, lacustrine, and peaty sediments of Holocene age (Klassen, 1979; McGinn, 1991, 2000, 2002; Fullerton et al, 2000; McGinn and Zaniewski, 2004; McGinn et al, 2007, 2009). The upland is underlain by Cretaceous bedrock of the Pierre Shale Formation and is capped by the resistant siliceous Odanah shale (Bannatyne, 1970).…”