Folded Faults and Sequence of Thrusting in Alberta Foothills

Abstract

Thrust faults in the Alberta Foothills were folded by development of step-thrusts and other thrust-generated structures beneath them. Because step-thrusting is a pattern of faulting found in layered rocks of varying competence, folded faults may be expected in any thrust belt where the stratigraphic sequence is in-homogeneous and higher thrusts are emplaced before underlying ones. By invoking folded faults, several structures in the Alberta Foothills can be reinterpreted without the geologic and geometric inconsistencies inherent in existing interpretations. Although a west-to-east sequence of thrust emplacement in the Alberta Foothills is implicit in the mechanics of folding of thrusts, some structural relations indicate an east-to-west sequence. The apparent contradiction may be resolved by the proposition that the time taken for a thrust to form, spreading both across and along strike, is greater than the time interval between initiation of successive thrusts.