Surficial geology mapping at a scale of 1:50 000, cosmogenic dating, and detailed stratigraphic and sedimentological logging of 86 cliff-bank exposures and more than 3000 roadcuts and hand-driven auger borings have resolved the century-old controversy as to the
number and timing of continental glaciations in the Rocky Mountain Foothills of southwestern Alberta.
The stratigraphy shows a consistent succession repeated throughout much of the area: one to several montane tills are always topped by either one continental till or a complex of continental tills, or a gravel unit containing Canadian Shield lithologies where a continental till has been eroded.
Exceptions only occur along the Rocky Mountain Front, at the mouths of major valleys where no continental till is present.
There is no evidence of subaerial erosion or soil-forming processes that would represent long hiatuses between glacial advances responsible for continental till deposition. The same holds true for montane tills, with the exception of those found in the subsurface of Cloudy Ridge and the sediments
capping Mokowan Butte. The drift units underlying paleosols at these two sites clearly predate the last interglaciation. The upper elevation limits of glacial erratics from the Canadian Shield and their abrupt western limit indicate that montane glaciers prevented penetration of continental glacial
ice up major Rocky Mountain Foothills valleys, hence continental and montane glaciers coalesced during the culmination of the maximum continental ice advance.
Paleomagnetic sampling of the oldest tills infilling buried valley systems shows that all deposition occurred during the Brunhes chron (<0.78 Ma). Cosmogenic 36Cl exposure dating of the foothills erratics train and the former limits of the continental ice-sheet cover constrains the single
continental glaciation to the Late Wisconsinan. The area was deglaciated by ca. 11 200 radiocarbon years before present.
In southwestern Alberta, Canada, a westward‐rising last‐glacial‐maximum continental ice limit has been identified. This limit is defined by the upper elevation of Canadian Shield erratics deposited by last‐glacial‐maximum continental ice along the flanks of prominent ridges and buttes within the region. The interpolation between ice‐limit data points has produced two distinct slope profiles: 2.9 m/km to the east, and 4.2 m/km to the west of Mokowan Butte. Three hypotheses are proposed to explain this westward rise of the last‐glacial‐maxi ‐mum continental ice limit: (1) regional tectonic uplift, (2) glacioisostatic uplift, and (3) continental ice‐flow convergence due to topographic obstacles and interaction with montane ice. Inferred long‐term rates of tectonic uplift and glacioisostati c modelling show that these two mechanisms account for less than 25% of the observed absolute elevation increase of the limit between the Del Bonita uplands and Cloudy Ridge in southwestern Alberta. The remaining rise in elevation of the continental ice‐sheet margin in this region is thought to result from continental ice‐flow convergence due to the combined effects of the regional topography and interaction with montane glaciers to the west. The steeper rise in the former continental ice surface west of Mokowan Butte can be explained by the tographic obstruction and interaction with montane glaciers in the area of the Rocky Mountain front.
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