Reconnaissance studies of proterozoic and cambrian stratigraphy, lower Mackenzie river area (operation norman), District of Mackenzie
Authors: Aitken J D , Macqueen R W , Usher J L 
Published: March 2017

Proterozoic rocks of the interior part of the Mackenzie Mountains are divisible into two successions of probable Helikian and Hadrynian ages. Probable Helikian rocks, from 5,000 to over 15,000 feet in thickness (~ 1,500- 4,500 metres), include in ascending
sequence: unnamed map-unit H1 - dolomite and chert; Tsezotene Formation - shale, dolomite, quartzite; Katherine Group, lower and upper parts - quartzite, minor shale and dolomite; unnamed map-unit H5 - dolomite, shale, limestone, gypsum, stromatolitic reefs; and Little Dal Formation - massive,
varied limestones and dolomites. This succession is overlain unconformably by a succession of probable Hadrynian age, up to 8,000 feet thick (~ 2,400 metres), including the Rapitan Group - conglomerates, sandstones, shale, iron formation; Keele Formation - dolomite, sandstone/quartzite, shale;
and Sheepbed Formation - shale. The Helikian formations are present on both sides of the north-trending Mackenzie Arch, but more thickly and completely developed on the west side. The Hadrynian units, on the other hand, are confined to the area west of the Mackenzie Arch. Striking changes in the
Proterozoic succession are observable across the Mackenzie Arch and on the east side of the arch, along the Mackenzie Mountain front. In the latter area Paleozoic rocks lie directly upon Helikian rocks belonging to unnamed map-unit H5, and the Katherine Group. The intervening Little Dal (Helikian)
to Sheepbed (Hadrynian) sequence is missing on the crest and the east flank of the arch. These changes are attributable in part to eastward depositional thinning in the platform wedge sequence, but erosion associated with sub-Rapitan, sub-Cabrian and sub-Upper Cambrian unconformities has had a
dominant effect. Paleozoic rocks of the Mackenzie Mountain interior include the Lower Cambrian Backbone Ranges Formation - sandstone, dolomite, mudstone; and Sekwi Formation - limestone, varicolpured dolomite. Together these units may reach 4,000 feet ( ~ 1,20 metres). In the Operation Norman
are they are overlain by the Rond River Formation of Middle Cambrian to Early Ordovician age, consisting of shale and thin-bedded limestone up to 4,000 feet in thickness (~1,200 metres); this unit is probably
the "deep-water" equivalent of the Saline River and Franklin Mountain Formations developed further east. Along the frontal Mackenzies the Lower and Middle Cambrian Mount Cap Formation is only locally present beneath the sub-Upper Cambrian unconformity. The Upper Cambrian sequence there consists of
the Saline River Formation - shale, evaporites, sandstone; and the lower part of the Franklin Mountain Formation - carbonates. The type Macdougal Group, located in the frontal Mackenzies, contains rocks of Proterozoix probably Helikian age in the lower part, and equivalents of the Mount Cap and
Saline River formations in the upper part, and accordingly the name is abandoned. Within the Franklin Mountains, Proterozoic rocks are known only near Wrigley (south of the Operation Norman area), where 6,000 feet ( ~ 1,800 metres) of shales, carbonates, and quartzites are tentatively assigned
to the Helikian. Elsewhere, the oldest rocks seen in the Franklins are the Lower Cambrian Mount Clark Formation of quartzite and sandstone, and the overlying Mount Cap, Saline
River, and Franklin Mountain Formations. Sub-Franklin Mountain Paleozoic units may reach 2,000 feet in thickness ( ~ 600 metres) in the Franklins. Lowermost Paleozoic rocks of the Interior platform include the Old Fort Island Formation of orthoquartzitic sandstone, and the Mount Cap, Saline
River, and Franklin Mountain Formations. Sub-Franklin Mountain Paleozoic rocks may reach 1,000 feet in thickness (~ 300 metres). Interior Plains Proterozic rocks of the Shaler Group were not studied in detail.