Open AccessNeoproterozoic-Cambrian stratigraphy of the Mackenzie Mountains, northwestern Canada, part IV: a stratigraphic reference section for the Ediacaran-Cambrian transition in NTS 95-M (Wrigley Lake map area)
Author(s) -
Robert B. MacNaughton,
K M Fallas
Publication year - 2021
Language(s) - English
Resource type - Reports
DOI - 10.4095/329217
Subject(s) - siltstone , dolostone , geology , ichnofacies , diamictite , arenite , paleontology , carbonate , clastic rock , stratigraphic unit , unconformity , sedimentary depositional environment , carbonate rock , geochemistry , facies , sedimentary rock , structural basin , materials science , metallurgy
A composite reference section for the upper Ediacaran and lower Cambrian is documented for a location near Moose Horn River in Wrigley Lake map area (NTS 95-M), Mackenzie Mountains, Northwest Territories. Four measured stratigraphic sections cover, in ascendingorder: the uppermost Sheepbed Formation; the informal Sheepbed carbonate; the lower, middle, and upper members of the Backbone Ranges Formation; the Sekwi Formation; and the lowermost beds of the Rockslide Formation. The uppermost Sheepbed Formation is dominated by dark-weathering shale andsiltstone. The Sheepbed carbonate (440 m) lies conformably on the Sheepbed Formation and consists of limestone, dolostone, and dolomitic siltstone, including several horizons of rudstone with clasts up to boulder size. The upper surface of the Sheepbed carbonate has been eroded and the unit thins toa zero edge to the east. The lower member of the Backbone Ranges Formation (253 m) is heterolithic, including interbedded quartzose siltstone and quartzose sandstone, quartz arenite (locally with horizons of quartz pebbles), and dolostone to dolomitic sandstone. The middle member of the BackboneRanges Formation (93 m) consists mainly of pink to grey-weathering limestone with red mudstone partings. The upper member (501.5 m) is dominated by quartz arenite, but also contains intervals of siltstone. Partway through the upper member there is a marker unit of dolostone to dolomitic sandstonethat previous work suggests is a tongue of the Ediacaran Risky Formation. Based on regional correlations, the top of this marker may approximate the Ediacaran-Cambrian boundary in this section. The Sekwi Formation lies abruptly upon the Backbone Ranges Formation. The contact is unconformable at thislocality and mapping in the area indicates eastward erosional removal of the upper member of the Backbone Ranges Formation beneath the Sekwi Formation. The Sekwi Formation here consists of variegated siltstone with lesser dolostone, limestone, and quartz sandstone. An abrupt contact with nodularlimestone and grey shale of the overlying Rockslide Formation approximates the base of Cambrian Series 3.