TECTONIC EVOLUTION OF THE MACKENZIE ARCH, A MAJOR CONTROL ON CAMBRIAN DEPOSITIONAL PATTERNS IN THE WESTERNMOST NORTHWEST TERRITORIES, CANADA

Distribution of Cambrian depocentres in northern mainland Canada was controlled by a network of positive tectonic elements (arches and domes). Recent studies on the Mackenzie Arch, a northwest-trending feature in the present-day eastern Mackenzie Mountains of the Northwest Territories, clarify its history and influence on regional stratigraphic patterns. Mackenzie Arch originally was recognized as a region where Guzhangian (upper Middle Cambrian) strata lay with angular unconformity upon lower Neoproterozoic strata, whereas to the northeast and southwest a more complete Terreneuvian (lowest Cambrian) to Cambrian Series 3 (Middle Cambrian) succession is present. The position of the Arch may have been controlled in part by an antecedent arch or anticline developed within the Neoproterozoic Mackenzie Mountains Supergroup. The western flank of the Arch also marks the northeastern preservational limit of Cryogenian-Ediacaran strata (Windermere Supergroup) in the Mackenzie Mountains. However, the earliest definitive evidence for the existence of the Arch is the presence of flanking facies belts to the northeast and southwest during deposition of Cambrian Series 2. During deposition, the inner detrital belt was sourced from sandstone of the Katherine Group (Neoproterozoic) that was exposed on the crest of the Arch. Uplift of the Arch (and possibly other features) during deposition of Cambrian Stage 5 (lower Middle Cambrian) bevelled earlier Cambrian strata along its flank and produced a regional unconformity. The uplifted Arch contributed to the restricted circulation that established an evaporitic basin extending northeastward to the Canadian Shield. The basin was characterized by well-developed facies belts along the eastern flank of Mackenzie Arch. Although age constraints are poor, this basin may have endured through much of the Drumian and Guzhangian (mid- to late Middle Cambrian). The deposits of this basin were affected by normal faulting but the faults do not offset overlying late Guzhangian (latest Middle Cambrian) carbonates, deposited following final inundation of the Arch. Although the basal beds of the carbonate succession are sand-rich above the former position of the Arch, the Arch had ceased to exert significant control on depositional patterns by the end of the Cambrian.