Throughout most of its length, the Cordilleran front in Alberta is characterized by east-dipping Mesozoic and Cenozoic sediments overlying an east-dipping detachment surface that consists of one or more low-angle underthrust faults. More than 5,000 sq mi (13,000 sq km) of deformed sediments containing several major oil and gas fields are concealed beneath the detachment. East-dipping underthrusts of the detachment outcrop along east flanks

Figure

of quasi-anticlinal structures sometimes called "triangle zones" because of their overall appearance in cross section. Oil and gas fields in triangle zones occur in Paleozoic carbonate and Mesozoic clastic reservoir rocks. Because of their complexity, triangle zones have also been the sites of some very expensive dry holes. Surface and subsurface data can be used to determine the geometry of a triangle zone and create an idealized model. The model can be adapted to structural problems both within and beyond the limits of the triangle zone, suggesting a new perspective on the tectonic development of the entire Foothills belt.

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