ABSTRACT

Three cross-sections through the area were obtained by the TRIPOD Structural Geological Information System. After balancing, the sections show between 27 and 35 per cent shortening. The major structures of the area are, from north to south: the Pedley Thrust, Coalspur Triangle Zone (formerly called Coalspur Anticline), Entrance Syncline, Mercoal Thrust, Brazeau Flats, Brazeau Thrust, Brazeau Syncline, Grave Flats Thrust, Cadomin Syncline, and Nikanassin Thrust. The Pedley Thrust appears to have at least 1 km of southwest-directed displacement. This fault defines the Coalspur Triangle Zone. The Mercoal Thrust may have about 2 km of southwest-directed displacement and defines a triangle zone that probably formed before the Coalspur Triangle Zone. The Brazeau Thrust shows at least 3 km of northeast-directed movement and places Blackstone shale on top of the Brazeau Formation. The Brazeau Syncline has an overturned southwest limb and is a tight fold. The Nikanassin Thrust forms the boundary with the Front Ranges.

The economic coal seams of the Tertiary Coalspur Formation are of high volatile C rank and are present in three parallel bands in the Entrance Syncline and the Coalspur Triangle Zone. The Mercoal band is the southern-most and dips about 30 degrees to the northeast. The Coalspur band is in the middle and dips generally to the southwest. The Robb band is the northern-most band, contains northeast-dipping strata, and is less deformed than the Coalspur band. In the Entrance Syncline, the Coalspur coals are buried at various depths (up to 1 km) and may form exploration targets for coal-bed methane. The Lower Cretaceous coals of the Luscar Group are exploited in the Cadomin-Luscar Coalfield. The rank of these coals ranges from high volatile A to low volatile bituminous. Where buried (for example, underneath the town of Cadomin), they form exploration targets for coal-bed methane.

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