Geology of Rocky Mountain Front Ranges Near Bow River, Alberta

Abstract

The front ranges of the Rocky Mountains near the Bow River, Alberta, are a fine example of the thrust-fault type of structure which characterizes the eastern Canadian Rockies. The ranges consist largely of repeated sequences of Paleozoic strata dipping 40° W. and separated by subsequent valleys eroded in Mesozoic or Upper Paleozoic beds. Cambrian to Upper Cretaceous strata are exposed. The map area is traversed by the Calgary-Banff highway and the main line of the Canadian Pacific Railway and, although visited by many geologists since the 1880's, it has not heretofore been mapped. The map area, which consists of three fault blocks that repeat most of the Paleozoic section, is bounded on the east by a major folded thrust fault which throws Middle Cambrian rocks over Upper Cretaceous strata. This fault marks the boundary between the Rocky Mountains and the Foothill belt. The Cascade Coal Basin is the westward limit of mapping. Middle Cambrian strata along the mountain front are overlain unconformably by the Ghost River formation of questionable Devonian age. This is overlain conformably by Upper Devonian dolomites and limestones and these are followed by Lower, Middle, and Upper Mississippian shales and limestones, Pennsylvanian quartzitic and dolomitic sandstones, Permian (?) chert and quartzite Triassic shaly siltstone, Jurassic black shale, and Lower Cretaceou or Jurassic sandstones, shales, and coal. No igneous rocks are exposed in this part of the Rocky Mountains. The great thrust faults, displacements on which are measured in miles, in some places develop drag folds, but the fault planes are clean breaks with little or no gouge, and the strata on both sides approach parallelism with the fault planes.