UPPER PROTEROZOIC TO MIDDLE CAMBRIAN HISTORY OF THE PEACE RIVER ARCH - EVIDENCE FROM THE ROCKY-MOUNTAINS

The stratigraphic record exposed in the Rocky Mountains provides important information on the early uplift history of the Peace River Arch that is unavailable from the subsurface. Thickness and facies changes in Upper Proterozoic, Lower Cambrian and Middle Cambrain strata show that the arch was a positive tectonic feature from the latest Upper Proterozoic (sub-Gog Group) through Middle Cambrain. No evidence of a two-sided arch was found in the Upper Preterozoic Windermere Supergroup: the "Mt. Vreeland High" is not the Cordilleran expression of the Peace River Arch, but part of a more proximal facies of the Windermere Supergroup that extends from what subsequently became the south margin of the Arch to well north of the Arch area (58-degrees-N). In the Rocky Mountains the south margin of the Arch follows important transverse, basement-involved structure(s) that formed during Late Proterozoic (Windermere) rifting. Similar structures may extend into the subsurface where they could have been reactivated during episodic tectonism associated with the uplift and subsidence of the Peace River Arch. During the Cambrian, the south margin of the Arch was a fundamental tectonic feature and the stratigraphic changes associated with this feature subsequently caused the formation of anomalous east-west trending faults and folds during the Cretaceous-Eocene deformation that formed the Rocky Mountains.