R. Rae Teal, 1983. "The Triangle Zone at Cabin Creek, Alberta", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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The seismic line presented in this paper lies approximately 300 km (190 mi) west of Edmonton, in the Cabin Creek area, Alberta, Canada (Figure 2). Based on the excellent seismic data of this line and the well control provided by Shell Cabin Creek 4-9-55-3 W6M, a depth converted version of the line and a balanced structural cross section are constructed to show the geometry, at this location, of the transition between the disturbed belt of the Alberta Foothills and the undisturbed strata of the Alberta basin.
For the past 20 years, the term "Triangle Zone" was frequently applied in an informal fashion to the leading edge of the disturbed belt of the Southern Canadian Foothills. The name was originally derived from the triangular arrangement of surface dips and seismic reflections found in early seismic profiles (Figure 1). Subsequent seismic collection and drilling have shown that the arrangement of reflections arises from the cross-sectional shape of a large wedge of rock bounded by two planes of discontinuity: a lower one dipping to the southwest, and an upper one dipping to the northeast (Figure 5). These two planes are the expression of one and the same thrust (that is, they are the bounding surfaces of a northeastward facing wedge forced into the adjacent rock package to the northeast). The emplacement, or injection, of the wedge displaces the sediments above the wedge only in a vertical sense; in a lateral sense these sediments can be regarded as still autochthonous.