Blairmore Group

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Blairmore Group
Stratigraphic range: Early Cretaceous
Type Group
Sub-units Cadomin Formation, Gladstone Formation, Beaver Mines Formation, Ma Butte Formation
Underlies Crowsnest Formation, Alberta Group
Overlies Kootenay Group
Thicknessup to 2,000 m (6,560 ft) [1]
Lithology
Primary Sandstone, siltstone, mudstone
Other Conglomerate, limestone
Location
RegionFlag of Alberta.svg  Alberta Flag of British Columbia.svg  British Columbia
CountryCanada
Type section
Named for Blairmore, Alberta
Named byW.W. Leach, 1914 [2]

The Blairmore Group, originally named the Blairmore Formation, is a geologic unit of Early Cretaceous age in the Western Canada Sedimentary Basin that is present in southwestern Alberta and southeastern British Columbia. [1] [3] It is subdivided into four formations: Cadomin Formation, Gladstone, Beaver Mines and Ma Butte , all of which are defined by type sections, most of which contain plant fossils. [4] In some areas the Blairmore contains significant reservoirs of natural gas.

Contents

Lithology

The Blairmore group includes the conglomerate and quartzose sandstones of the Cadomin Formation at the base, and grades to sandstone, siltstone, mudstone, and limestone in the overlying formations. [1]

The Cadomin Formation has beds of quartzose sandstone and, in some sections, especially in the eastern foothills, is totally quartzose sandstone. [4] It is normally a very durable, siliceous pebble conglomerate. [4] A sequence of interbedded, highly variable-proportioned grey mudstone to sandstone layers makes up the bottom portion of the underlying Gladstone Formation. [4] Sandstones, whose grain size rarely exceeds fine, frequently show a noticeable upward decline in grain size. Dark grey, argillaceous limestone and fossiliferous calcareous shale make up the top Gladstone Formation. Limestone deposits are few or nonexistent north of the Clearwater River (52°N). [4]

Both the Beaver Mines Formation in the south and the Mountain Park Formation in the north are made up of interbedded mudstone to very fine-grained sandstone with minor but noticeable thicker and coarser sandstone units that have abrupt bases and fining upward grain size. [4] Conglomerate beds make up a small portion. The marine mudstone Moosebar Member of the Malcolm Creek Formation, which is restricted to the region north of Waiparous Creek (51°20'N), is overlain by the notable sandstone-dominated Torrens Member and the coal-bearing Grande Cache Member. Mudstone to very fine-grained sandstone, as well as layers of conglomerate and coarser sandstone, make up the Ma Butte Formation. [4]

The Beaver Mines and Ma Butte formations in the upper part of the group also include minor beds of bentonite and tuff. [1]

In the type area, tuffaceous mudstones are widespread in the top portion of the formation, but they vanish to the northwest along the foothills. North of the Clearwater River, the structure is completely missing. [4] Various shades of red and green, frequently speckled south of the Bow River, are particularly prevalent. Except in the Mountain Park Formation, where greenish grey predominates in more southerly areas and is increasingly prominent higher, grey prevails to the north. [4] In the Smoky River region, the uppermost part of the formation, the proportion of the section with a conspicuously greenish tint is restricted to a subtle shade of greenish-grey as it declines northward. [4]

Stratigraphy

The Blairmore Group is subdivided into the following formations from top to base:

Formation Age LithologyMax
Thickness		Reference
Ma Butte Formation Early Cretaceous mudstone, siltstone, very fine-grained sandstone, bentonite and tuff 120 m (390 ft) [1]
Beaver Mines Formation Early Cretaceousgreenish grey sandstone and mudstone; minor conglomerate, bentonite and tuff 455 m (1,490 ft) [1]
Gladstone Formation Early Cretaceous argillaceous limestone and calcareous shale 180 m (590 ft) [1]
Cadomin Formation Early Cretaceous conglomerate, sandstone 170 m (560 ft) [1]

Some early workers included the Crowsnest Formation, which overlies the Ma Butte Formation, at the top of the Blairmore Group, but that practice has been abandoned. [1]

Distribution and Thickness

The name Blairmore Group is applicable in the foothills and mountains of southwestern Alberta and southeastern British Columbia, from the Canada–United States border northward to the Clearwater River. The equivalent strata north of the Clearwater River, which were originally assigned to the Blairmore Group, differ in that they contain major coal deposits and they have therefore been reassigned to the Luscar Group. [5]

The Blairmore Group has a maximum thickness of about 2,000 m (6,560 ft). [1] The Ma Butte portion has a thickness of 635 m (2,080 ft) The Fernie Basin's maximum reported thickness is estimated to be 2,000 m (6,560 ft). [4] The easternmost foothills have reported thicknesses of roughly 300 m (980 ft), indicating a clear west to east thinning. [4] In the northwest, thicknesses of 400 to 600 m (1312 to 1968 ft) are common in the foothills. [4]

Relationship to other units

The Blairmore Group unconformably overlies the Kootenay Group and is gradationally overlain by the Crowsnest Formation or, where the Crowsnest Formation is absent, is disconformably overlain by the Alberta Group. It is equivalent to the Luscar Group north of the Clearwater River [5] and to the Mannville Group in the plains to the east. [1]

In northwestern Montana the Cut Bank Sandstone correlates with the Cadomin Formation; the lower Kootenai Formation, including the Draney Limestone with the Beaver Mines Formation; and the lower Blackleaf Formation with the Ma Butte Formation. [4]

Environment of deposition and paleontology


The Blairmore Group is a westward-thickening clastic wedge of clastic sediments derived from the erosion of newly uplifted mountains to the west. [6] The sediments were transported eastward by river systems and deposited in a variety of braided stream, river channel, floodplain, and coastal plain environments along the western edge of the Western Interior Seaway. Its formations include a variety of plant fossils, trace fossils, bivalves, and microfossils.

See also

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<span class="mw-page-title-main">Nikanassin Formation</span>

The Nikanassin Formation is a stratigraphic unit of Late Jurassic (Portlandian) to Early Cretaceous (Barremian) age. It is present along the western edge of the Western Canada Sedimentary Basin in western Alberta and northeastern British Columbia. Its name was first proposed by D.B. Dowling in 1909 (Coal Fields South of Grand Trunk Pacific Railway, in the foothills of the Rocky Mountain, Alberta Page 140 paragraph 4 " to this it is proposed to give the name Nikanassin, from the Cree word meaning outer range" Also it is noted on the map by D.B. Dowling.(Geological Survey of Canada. Incorrect info follows: It was named by B.R. MacKay in 1929 for the Nikanassin Range of the front-central ranges of the Canadian Rockies. Mackay did not designate a type locality for the formation, although he described outcrops near the hamlet of Brûlé, north of the Yellowhead Highway outside of Jasper National Park.

<span class="mw-page-title-main">Cadomin Formation</span>

The Cadomin Formation is a stratigraphic unit of Early Cretaceous age in the western part of the Western Canada Sedimentary Basin. It is extends from southeastern British Columbia through western Alberta to northeastern British Columbia, and it contains significant reservoirs of natural gas in some areas. It was named after the mining town of Cadomin, which is an acronym of "Canadian Dominion Mining".

<span class="mw-page-title-main">Bluesky Formation</span>

The Bluesky Formation is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin. It takes the name from the hamlet of Bluesky, and was first described in Shell's Bluesky No. 1 well by Badgley in 1952.

Gething Formation is a stratigraphic unit of Lower Cretaceous (Aptian) age in the Western Canada Sedimentary Basin. It is present in northeastern British Columbia and western Alberta, and includes economically important coal deposits.

Bullhead Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin of northeastern British Columbia and western Alberta. It was first defined by F.H. McLearn in 1918 as the Bullhead Mountain Formation, but later was upgraded to group status. It consists of the Cadomin and Gething Formations, although some early workers included the Bluesky Formation and others in the group.

The Fort St. John Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin. It takes the name from the city of Fort St. John, British Columbia and was first defined by George Mercer Dawson in 1881.

The Alberta Group is a stratigraphical unit of Cenomanian to early Campanian age in the Lewis overthrust in the Western Canadian Sedimentary Basin.

The Joli Fou Formation is a allostratigraphicalunit of middle Albian age in the Western Canadian Sedimentary Basin. It takes the name from the Joli Fou Rapids on the Athabasca River, and was first described in an outcrop along the river, 8 kilometers (5.0 mi) downstream from Joli Fou Rapids, by RTD Wickenden in 1949.

The Mist Mountain Formation is a geologic formation of latest Jurassic to earliest Cretaceous age in the Western Canada Sedimentary Basin that is present in the southern and central Canadian Rockies. It was named for outcrops along the western spur of Mist Mountain in Alberta by D.W. Gibson in 1979. The Mist Mountain Formation contains economically important coal seams that have been mined in southeastern British Columbia and southwestern Alberta.

<span class="mw-page-title-main">Morrissey Formation</span>

The Morrissey Formation is a stratigraphic unit of Late Jurassic (Portlandian) age in the Western Canada Sedimentary Basin. It is named for outcrops on Morrissey Ridge, 16 kilometres (10 mi) southeast of Fernie, British Columbia, and is present in southeastern British Columbia and southwestern Alberta.

The Elk Formation is a stratigraphic unit of the Western Canada Sedimentary Basin that is present in southeastern British Columbia and southwestern Alberta. It is probably of Early Cretaceous age, but in some areas its strata could be as old as Late Jurassic. It includes minor thin coal beds and was named for outcrops near the now-abandoned Elk River coal mine east of Fernie, British Columbia.

The Monach Formation is a geologic formation of Early Cretaceous (Valanginian) age in the Western Canada Sedimentary Basin that consists primarily of sandstone. It is present in the northern foothills of the Canadian Rockies and the adjacent plains in northeastern British Columbia.

The Monteith Formation is a geologic formation of Early Cretaceous (Valanginian) age in the Western Canada Sedimentary Basin that consists primarily of sandstone. It is present in the northern foothills of the Canadian Rockies and the adjacent plains in northeastern British Columbia and west-central Alberta.

The Beaver Mines Formation is a stratigraphic unit of Early Cretaceous (Albian) age in the Western Canada Sedimentary Basin that is present in southwestern Alberta and southeastern British Columbia, Canada. It was established by G.B. Mellon in 1967 who named it for the hamlet of Beaver Mines, Alberta. It contains a variety of plant fossils.

The Gorman Creek Formation is a geologic formation of Early Cretaceous (Valanginian) age in the Western Canada Sedimentary Basin that consists primarily of nonmarine sediments. It is present in the northern foothills of the Canadian Rockies and the adjacent plains in northeastern British Columbia. Plant fossils and dinosaur tracks have been described from its strata.

The Bickford Formation is a geologic formation of Early Cretaceous (Valanginian) age in the Western Canada Sedimentary Basin that consists primarily of nonmarine sediments. It is present in the northern foothills of the Canadian Rockies in northeastern British Columbia.

The Luscar Group is a geologic unit of Early Cretaceous age in the Western Canada Sedimentary Basin that is present in the foothills of southwestern Alberta. It is subdivided into a series of formations, some of which contain economically significant coal deposits that have been mined near Cadomin and Luscar. Coal mining in those areas began in the early 1900s and continues near Luscar as of 2016.

The Gladstone Formation is a stratigraphic unit of Early Cretaceous (Aptian) age in the Western Canada Sedimentary Basin. It is present in the foothills of southwestern Alberta and is named for outcrops along Gladstone Creek, a tributary of the Castle River south of the Crowsnest Pass.

The Ma Butte Formation is a stratigraphic unit of Early Cretaceous (Albian) age in the Western Canada Sedimentary Basin. It was named for Ma Butte, a mountain north of Coleman, Alberta, by J.R. McLean in 1980. It is present in the foothills of southwestern Alberta and it contains plant fossils.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 Glass, D.J. (editor) 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba. Canadian Society of Petroleum Geologists, Calgary, 1423 p. on CD-ROM. ISBN   0-920230-23-7.
  2. ↑ Leach, W.E. 1914. Blairmore map-area, Alberta. Geological Survey of Canada, Summary Report 1912, Map 107A.
  3. ↑ Canadian Society of Petroleum Geologists and Alberta Geological Survey (1994). "The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 19: Cretaceous Mannville Group of the Western Canada Sedimentary Basin". Compiled by Mossop, G.D. and Shetsen, I. Archived from the original on 1 July 2016. Retrieved 20 June 2016.
  4. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Lexicon of Canadian stratigraphy (4 ed.). Canadian Society of Petrologists. 1981. p. 74-75.
  5. 1 2 Langenberg, W.C. and McMechan, M.E. 1985. Lower Cretaceous Luscar Group (revised) of Alberta's northern and north-central foothills. Bulletin of Canadian Petroleum Geology, v. 33, p. 1-11.
  6. ↑ McCarthy, Paul J.; Martini, I. Peter; Leckie, Dale A. (1997). "Pedosedimentary history and floodplain dynamics of the Lower Cretaceous upper Blairmore Group, southwestern Alberta, Canada". Canadian Journal of Earth Sciences. 34 (5): 598–617. Bibcode:1997CaJES..34..598M. doi:10.1139/e17-048.
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