Early Neoproterozoic strata (Sequence B) of mainland northern Canada and Victoria and Banks islands: a contribution to the Geological Atlas of the Northern Canadian Mainland Sedimentary Basin

Abstract

Sequence B is the second of three unconformity-bounded, post-Hudsonian Proterozoic sequences in northern Canada. Its deposition postdated the Grenvillian orogeny (ca. 1200-1000 Ma) and ended prior to the break-up of Rodinia (ca. 780-720 Ma). Sequence B crops out: in the Mackenzie Mountains, Wernecke Mountains, and Ogilvie Mountains of the northern Canadian Cordillera; south of Amundsen Gulf on the northern mainland; and on Victoria Island and Banks Island. Exposures in the eastern Northwest Territories and western Nunavut are part of the Amundsen Basin. Sequence B is present also in the subsurface in all these regions, as well as beneath the northern interior plains. Lithostratigraphic nomenclature of Sequence B is well developed in the Amundsen basin (Shaler Supergroup), partly formalized in the Mackenzie Mountains (Mackenzie Mountains supergroup), and largely informal elsewhere. Formations encompass a wide variety of siliciclastic, carbonate, and evaporite lithofacies. Deposition of Sequence B is interpreted to have taken place in an epicratonic basin (epeiric sea) that was episodically restricted during its evolution. Net depositional thickness of Sequence B was roughly twice as thick in the Mackenzie Mountains as in the Amundsen Basin, probably reflecting greater syndepositional crustal extension in the former area. Recognition of five, regional-scale subsequences with Sequence B permits correlation between the northern Cordillera and the Amundsen Basin but the subsequences cannot be recognized at present beneath the interior plains. Correlation charts and isopach maps presented in this report aid in reconstructing the tectonostratigraphic evolution of Sequence B. Sequence B has known potential for sediment-hosted base-metal deposits and red-bed-type stratiform Cu-Ag-Co deposits. In the Amundsen Basin, carving stone is obtained from Sequence B and some gypsum deposits may be of industrial value. Hydrocarbon potential is low to absent.