The Triangle Zone and foothills structures in the Grease Creek syncline area, Alberta

Abstract

The Triangle Zone structure is a deformed wedge inserted along a delaminated horizon in the basal Upper Brazeau Formation. This structure has an en echelon geometry in the Grease Creek area with a 20 kilometre strike length; this geometry implies structural trap closure along strike. A composite model of the Triangle Zone is presented; important features include a unified terminology system, distal merging of the upper and lower detachments, and an upper detachment with a ramp and flat geometry. The duplex geometry of the intercutaneous wedge is hinterland-dipping, but in general any duplex geometry may be present. An abandoned or relict Triangle Zone is interpreted beneath the west flank of the Grease Creek syncline. The study area was mapped at a scale of 1:24000. Map data, combined with the subsurface borehole and available seismic data, were used to construct regional balanced cross-sections from the McConnell Thrust, through the study area, to the Plains.