Sedimentology and stratigraphy of the Husky Creek Formation, Nunavut, CanadaWednesday, November 21, 2018 - 11:40 to 11:59 Theatre 1
The Mesoproterozoic Husky Creek Formation lies within the gently, northward-dipping Coppermine Homocline, 30-60 km south of the hamlet of Kugluktuk, Nunavut. Across northwestern Canada, thick Mesoproterozoic-Neoproterozoic sedimentary and volcanic successions record the amalgamation and break-up of supercontinent Rodinia. These rocks are subdivided, from oldest to youngest, into three-unconformity bounded successions: A, B, and C. The boundary between successions A and B is exposed in the Coppermine Homocline, where rocks of the Rae Group (Succession B; <1151 ± 13 Ma, U/Pb detrital zircon) unconformably overlie the Husky Creek Formation of the Coppermine River Group (Succession A; <1230 ± 15 Ma, U/Pb detrital zircon). Exceptional exposures of the Husky Creek Formation occur along steep-walled canyons of the Coppermine River and its tributaries, which make it suitable for the 3D depositional architectural analysis. It has a composite thickness of ca. 1900 m and is dominated by planar and cross-stratified red sandstone and siltstone that is interlayered with 20-100 m thick basalt flows. The Husky Creek Formation overlies the Copper Creek Formation, a ca. 2.5 km thick, regionally extensive basaltic plateau linked to the 1.27 Ga Mackenzie Igneous Event. Petrographic analysis indicates that sandstones are dominated by mafic lithic detritus, suggesting provenance mainly from the basalts. Planar and cross-bedded sandstones with abundant desiccation cracks, adhesion structures and pedogenic nodules indicate a temperate to arid terrestrial paleo-environment that includes fluvial channel belts and floodplains subject to local eolian winnowing. U/Pb dating of detrital zircon grains collected from four stratigraphic levels (base to top) of the Husky Creek Formation reveal three main age groupings: (i) a 1270 Ma peak attributed to the Mackenzie Igneous Event; (ii) 1750 Ma -2700 Ma zircons, possibly recycled from the Hornby Bay Group, which underlies the Coppermine River Group and is exposed to the south; and (iii) >2700 Ma zircons attributed to the Archean Slave Province. An up-section decrease in ca. 1270 Ma zircon grains and a relative increase in Paleoproterozoic and Archean grains is interpreted to reflect expansion of the drainage basin as the Husky Creek Formation was being deposited. Paleoflow patterns indicate dominant south-southwestward transport, which is from the direction of the interpreted focal point of the Mackenzie Igneous Event. We conclude that the Husky Creek Formation was deposited in the waning stages of the Mackenzie Igneous Event by rivers flowing in a geographically restricted, possibly endorheic basin, carved into an extensive mafic volcanic plateau.