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TitleSubsurface sedimentology, ichnology and sequence stratigraphy of Cambrian Mount Clark and Mount Cap formations beneath the Colville Hills, Northwest Territories
AuthorSommers, M J; Gingras, M K; MacNaughton, R BORCID logo; Fallas, K MORCID logo
SourceCore Conference 2019, proceedings; 2019 p. 1-6 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesNatural Resources Canada, Contribution Series 20190098
PublisherCanadian Society of Petroleum Geologists
MeetingCore Conference 2019; Calgary, AB; CA; May 16-17, 2019
DocumentWeb site
Mediaon-line; digital
File formatpdf
ProvinceNorthwest Territories
NTS95J; 95K; 95M; 95N; 95O; 96B; 96C; 96D; 96E; 96F; 96G; 96J; 96K; 96L; 96M; 96N; 96O; 97A; 97B; 106A; 106G; 106H; 106I; 106J; 106O; 106P; 107A
AreaColville Hills
Lat/Long WENS-132.0000 -122.0000 69.0000 62.0000
Subjectsstratigraphy; sedimentology; paleontology; Science and Technology; Nature and Environment; systematic stratigraphy; stratigraphic analyses; ichnology; trace fossils; bedrock geology; lithology; sedimentary rocks; sandstones; shales; carbonates; mudstones; dolostones; wells; core samples; facies analyses; sedimentary structures; Northern Interior Plains; Mount Clark Formation; Mount Cap Formation; Union Mobil Colville D-45 Well; Tweed Lake A-67 Well; Phanerozoic; Paleozoic; Cambrian
Illustrationslocation maps; tables
ProgramGEM2: Geo-mapping for Energy and Minerals Mackenzie Corridor, Shield-to-Selwyn geo-transect, Mackenzie-Selwyn sub-activity
Released2019 05 01
The Series 2 and Miaolingian (Lower and Middle) Cambrian succession in the Colville Hills region, Northwest Territories consists (ascending order) of the Mount Clark, Mount Cap and Saline River formations, all of which were deposited in an epicontinental basin, herein named the Colville Basin. Mount Clark Formation consists of a sandstone-dominated succession with a prominent shale package near the middle of the unit. Mount Cap Formation is divided into an informal lower member (shale with prominent dolostone and sandy dolostone markers) and upper member (shale with carbonates). A high-resolution study of all ten available industry cores used process sedimentology and ichnology to delineate fifteen lithofacies in the Mount Clark and Mount Cap Formations: six sandstone dominated; three mudstone dominated; four heterolithic sandstone and mudstone; and one each of dolostone and glaucony. The facies can be grouped into four facies associations (FAs). FA1 consists of sandstone with well-preserved, wave-formed sedimentary structures, recording deposition in storm-influenced shoreface settings. Bioturbation is minimal to absent, suggesting that wave energy exerted a major stress on burrowing organisms. FA2 consists of sandstone in which bioturbation is strongly developed and trace-fossil diversity is high, including local development of Skolithos 'pipe-rock', but with poor preservation of physical sedimentary structures. Deposition thus is interpreted to have been in fairweather shoreface settings. FA3 contains varying volumes of mudstone, generally recording deposition in more offshore settings. Absence of bioturbation in some successions of FA3 may reflection stresses due to seawater chemistry, possibly low oxygen levels. FA4 encompasses bioturbated, locally sandy carbonates deposited in relatively shallow water. Core and wireline log data permitted delineation of three transgressive-regressive (T-R) sequences in the Mount Clark and lower Mount Cap formations, which can be traced over an area of approximately 300,000 km2. The base of the Cambrian is a regional-scale disconformity and sequence boundary (sub-Cambrian unconformity). Based on archival trilobite collections, T-R Sequence 1 is of Bonnia-Olenellus Zone age or older, but unlikely to be older than early Cambrian. T-R Sequence 2 contains Bonnia-Olenellus Zone trilobites in its uppermost part, though its base may be older. The base of T-R Sequence 3 is within the Bonnia-Olenellus Zone, and the lowest trilobites of the Glossopleura Zone are present just above its top, although fossil collections from much of the sequence are equivocal as to age. The upper member of the Mount Cap Formation has not been subdivided into sequences, but contains a prominent maximum flooding surface near its base and is capped by an unconformity at the base of the Saline River Formation. The upper member is mainly of Glossopleura Zone age. As noted by previous workers, syndepositional extension during deposition of the Mount Cap Formation was pronounced in the Mackenzie Trough but more subdued beneath the Colville Hills.
Summary(Plain Language Summary, not published)
During the early and middle Cambrian Period, the region beneath Canada's northern interior plains was covered by an ancient sea. Today, rocks deposited in that sea are buried and contain accumulations of natural gas and oil. This manuscript uses industry drill cores and geophysical well logs to reconstruct the early history of the basin within which the ancient sea formed. The oldest deposits of the sea consist mainly of sandstone (Mount Clark Formation), whereas the younger deposits are dominated by mudstone with some carbonate rocks (Mount Cap Formation). We document three packages ("sequences") of rock that record rising and falling sea levels. Combined with age controls from previously documented trilobites, these three packages provide a means to correlate these rocks with greater precision across the north than previously was possible. The ancient basin in which these rocks accumulated currently is unnamed. It is suggested to name it the Colville Basin, after the Colville Hills and the community of Colville Lake, which today are roughly in its centre.

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