Sedimentation in Ice-Damned Glacial Lake Assiniboine, Saskatchewan, and Catastrophic Drainage Down the Assiniboine Valley

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Ice-dammed glacial Lake Assiniboine covered approximately 1500 km<jats:sup>2</jats:sup>in eastern Saskatchewan at about 11,000 BP. Lithofacies in two cores from the lake basin were identified, correlated, and linked to paleolake strandlines and inflow and outflow channels discerned from aerial photos and surface mapping. Deeper lake stages are reflected by silt and clay varve deposition in the deepest part of the basin, whereas shallower stages are represented by fluctuating grain size and current-generated sedimentary structures in sediments nearer to where influxes of melt-water occurred. The stratigraphie record revealed six lake phases, beginning with a shallow period when water collected in the interlobate area between ice on the Duck Mountain Upland to the east and the Assiniboine Ice Lobe to the west. A rise in lake level to about 495 m occurred as the southern outlet was dammed by ice. After about 85 varve years, waters from the Porcupine Hills Upland to the north flooded into glacial Lake Assiniboine, perhaps as a result of the drainage of an ice marginal lake, causing erosion at the lake's southern outlet and a drop in lake level. A second major influx of water from the Porcupine Hills area, at least 20 varve years later, led to downcutting of the outlet and draining of Lake Assiniboine. Shallow and deep channels, streamlined hills, and scattered boulders adjacent to the now-entrenched Assiniboine valley at the former outlet of glacial Lake Assiniboine suggest that the lake drained catastrophically. Similar geomorphic features at sites downstream along the Assiniboine valley are also indicative of catastrophic flow, although only those areas north of the Qu'Appelle River spillway junction are predominantly attributed to outbursts from glacial Lake Assiniboine.</jats:p>

A multi-proxy study of changing environmental conditions in a Younger Dryas sequence in southwestern Manitoba, Canada, and evidence for an extraterrestrial event

“…The sandy siliciclastic sediments of Unit C reflect times of higher flow of the rivers feeding the Lake Hind lowland, perhaps normal annual floods or those related to flood outbursts from the headwaters of the Assiniboine-Qu'Appelle watersheds to the northwest (Fig. 13) associated with the numerous flood features that lie adjacent to the Assiniboine River, including along the northern margin of the Lake Hind basin, as described by others (Sun, 1993; Sun and Fulton, 1995; Wolfe and Teller, 1995). As can be seen in Figure 2, major rivers lie along both the southern and northern sides of the Glacial Lake Hind basin, and smaller rivers such as Pipestone Creek feed into the basin from the west.…”

“…13), which have been interpreted to have abruptly released their waters and eroded the downstream valley in a few years. Kehew (1982), Kehew and Clayton (1983), Kehew and Lord (1986, 1987), Kehew and Teller (1994a, 1994b), Sun (1996), Sun and Teller (1997), and Wolfe and Teller (1995) have described various late-glacial floods and the resultant channels in the drainage basin to the west of Lake Hind.

Figure 12.(color online) Aerial photograph showing scoured surface along margin of channel in southeastern Saskatchewan eroded by catastrophic floodwaters released from proglacial lakes.

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“…During its life, Lake Hind covered ~4000 km 2 , and was impounded by the LIS, receiving water directly from the ice and from proglacial rivers that drained into the lake. Some of this inflow may have included outbursts from a number of short-lived, ice-marginal lakes that drained catastrophically (e.g., Kehew and Clayton, 1983; Kehew and Teller, 1994a; Wolfe and Teller, 1995). Finer-grained and increasingly organic-rich sediment was deposited in the Lake Hind basin as the LIS retreated and drainage systems were rerouted.…”

The drainage of Lake Ojibway in glaciolacustrine sediments of northern Ontario and Quebec, Canada

“…Such a lowering of the water column would have caused the rhythmites to be reworked by traction currents, thereby causing most fine-grained particles (clay) to be washed away, leaving the coarser (silt) particles behind (e.g. Wolfe & Teller 1995). Reworking is supported by the fact that ostracod valves present in this unit are rarely pristine, being commonly broken or dislocated.…”

“…Wolfe & Teller 1995). Such a lowering of the water column would have caused the rhythmites to be reworked by traction currents, thereby causing most fine-grained particles (clay) to be washed away, leaving the coarser (silt) particles behind (e.g.…”