Conclusion Landsystem

The ability to identify former surging glaciers is crucial for reconstruction and interpretation of the dynamics of former ice sheets. However, no individual landform, except probably concertina eskers which are difficult to identify in the ancient landform record, can be unequivocally labelled as the product of glacier surging. The surging glacier landsystem presented in this chapter combines observations on the geomorphology, sedimentology and glaciology of surging glaciers in Iceland, Svalbard, the USA and Canada, integrating the suite of landforms and sediments known to be produced by surging glacier margins. The model is designed to assess the dynamics of palaeo-glaciers and ice sheets by identification of an integrated landform-sediment assemblage. For example, across large parts of the southwest margin of the Laurentide Ice Sheet the occurrence of numerous large thrust-block moraine arcs and associated mega-flutings, hummocky moraine tracts, areas of transverse (crevasse-squeeze?) ridges, and stratigraphic sequences comprising glacitectonized multiple tills/glacitectonites have been used to suggest that surging behaviour was characteristic during ice recession (e.g. Boulton et al., 1985; Clayton et al., 1985; Fisher et al, 1985; Clark, 1994b). Application of a comprehensive landsystems model to an area of east-central Alberta corroborates the proposed palaeo-surging activity and indicates that further assessments of regional glacial geomorphology are warranted in order to identify large scale ice mass dynamics.

Figure 11.18 Evidence of palaeo-surging in east-central Alberta, Canada. A) Location map of the Lac la Biche palaeo-ice stream (only the geomorphic features relating to the ice stream are presented). Sections used in Fig. 11.18d are marked by asterisk and double cross symbols. B) The geomorphology of the east-central part of NTS map area 73E, east central Alberta, Canada (boxed area on Fig. 11.18a), showing all ice flow-parallel and flow-transverse ridges. TM = major thrust-block moraines breached by most recent surge. The last surge in the area produced the dense network of crevasse-squeeze ridges in the eastern half of the map, which grade into the southernmost flutings of the former Lac La Biche ice stream in the northern half of the map. Hummocky moraine and kame and kettle topography occurs at the southernmost edge of the map. L = the town of Lloydminster. C) Aerial photograph mosaic of the area represented in Figure 11.18 B, illustrating the major geomorphic features. D) selected, representative stratigraphic exposures from the region, showing (upper) interbedded tills and rafted sands overlying sandstone bedrock (after Andriashek and Fenton, 1989; see asterisk symbol on Fig. 11.18 A), and (lower) glacitectonized bedrock, faulted and folded stratified sediments and associated diamictons (tills) at the core of a thrust-block moraine (a = folded bedrock, b = massive diamicton, c = laminated diamicton with sand lenses, d = faulted and folded sands, e = massive diamicton with bedrock rafts, f = faulted and folded interbeds of laminated fines and gravels; after Mougeot, 1995; see double cross symbol on Fig. 11.18 A).

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