ABSTRACT

It is well known that the evolution of the Alberta Foreland Basin was influenced by extrinsic and intrinsic factors operating at different scales. It is widely believed that on a continental scale the Alberta Foreland Basin was influenced by the mechanical properties of the lithosphere and the tectonic events that telescoped the Rocky Mountain Fold-Thrust Belt along the basin's western margin. This geological scenario has been modelled by Beaumont (1981) using thin plate theory. His models indicate clearly that, as progressively increasing and advancing loads deform the lithosphere along the margin of the plate, a forebulge develops and migrates within the basin. This particular model has been widely accepted and has found application in sedimentological studies that have attributed a forebulge origin to the localization of the "shelf sandstone ridges" of the Albian-Campanian seaway (Tankard, 1986). However, the stratigraphy of the Alberta Foreland Basin does not support the existence of a forebulge. If such a forebulge exists, it must lie farther east of the basin. It will be shown that in order to explain the observed stratigraphy, a lithosphere that thickens eastward to more than 250 km beneath the North America Craton is required. This thick "Root" is also required by the post-glacial rebound data and is supported by recent seismic data. The notion of a deep, strong "root" that travels coherently with the continents, however, challenges some of the basic tenets of plate tectonic theory and forces us to rethink the evolution of continents.

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