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TitleSubsurface analysis and correlation of Mount Clark and lower Mount Cap formations (Cambrian), Northern Interior Plains, Northwest Territories
AuthorSommers, M J; Gingras, M K; MacNaughton, R BORCID logo; Fallas, K MORCID logo; Morgan, C A
SourceBulletin of Canadian Petroleum Geology vol. 68, no. 1, 2020 p. 1-29,
Alt SeriesNatural Resources Canada, Contribution Series 20190098
PublisherCanadian Society of Petroleum Geologists
Mediapaper; on-line; digital
File formatpdf; html
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; geoscientific sketch maps; stratigraphic charts; tables; geophysical logs; photographs; block diagrams; stratigraphic cross-sections; fence diagrams; lithologic sections; biostratigraphic charts
ProgramGEM2: Geo-mapping for Energy and Minerals Mackenzie Corridor, Shield-to-Selwyn geo-transect, Mackenzie-Selwyn sub-activity
Released2020 03 01
AbstractThe 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. The Mount Clark Formation is sandstone-dominated with a shale package near the middle of the unit. The Mount Cap Formation is divided into an informal lower member (shale with dolostone and sandy dolostone beds) and upper member (shale with mixed limestone and dolostone). 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 of 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 extensively developed and trace-fossil diversity is high, including local development of Skolithos 'pipe-rock', but with poor preservation of physical sedimentary structures. Deposition is interpreted to have been in fairweather shoreface settings. FA3 contains varying amounts of mudstone, generally recording deposition in more distal environments. Absence of bioturbation in some successions of FA3 may reflect stresses due to seawater chemistry, possibly low dissolved oxygen contents. FA4 encompasses bioturbated, locally sandy carbonates deposited in relatively shallow water. Three transgressive-regressive (T-R) sequences in the Mount Clark and lower Mount Cap Formation can be traced over an area of approximately 300,000 km2. The base of the Cambrian is a regional unconformity and sequence boundary. T-R Sequence 1 is entirely within the Mount Clark Formation. Based on archival trilobite collections, it is of Bonnia-Olenellus Zone age or older, but unlikely to be older than early Cambrian. T-R Sequence 2 spans the Mount Clark-Mount Cap Formation contact and has Bonnia-Olenellus Zone trilobites in its uppermost part, though its base may be older. T-R Sequence 3 is entirely within the Mount Cap Formation and its top corresponds to the boundary between the informal lower and upper members of the formation. The base of the sequence is within the Bonnia-Olenellus Zone, its maximum flooding surface is within the Plagiura-Poliella Zone, and the lowest trilobites of the Glossopleura Zone are present just above its top. The upper member of the Mount Cap Formation could not be subdivided into sequences, but contains a prominent maximum transgressive 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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