Cadomin Formation

Cadomin Formation
Stratigraphic range: Early Cretaceous

A photomicrograph of Cadomin sandstone
Type Geological formation
Unit of Bullhead Group, Blairmore Group
Underlies Gething Formation
Overlies Kootenay Group, Nikanassin Formation, Minnes Group and Fernie Group
Thickness 1 to more than 170 m[1]
Lithology
Primary Conglomerate, sandstone
Other shale, coal
Location
Coordinates 53°00′N 117°19′W / 53.000°N 117.317°WCoordinates: 53°00′N 117°19′W / 53.000°N 117.317°W
Region Western Canada Sedimentary Basin
Country  Canada
Type section
Named for Cadomin, Alberta
Named by B.R. Mackay[2]

The Cadomin Formation is a stratigraphic unit of Early Cretaceous (Barremian to Aptian) age in the western part of the Western Canada Sedimentary Basin.[3] It is present in western Alberta and northeastern British Columbia, and it contains significant reservoirs of natural gas. It was named after the mining town of Cadomin, itself an acronym of "Canadian Dominion Mining".[4]

Stragtigraphy

The Cadomin Formation is of Early Cretaceous (Barremian to Aptian) age. It is the basal unit of the Bullhead Group in northeastern British Columbia and of the Blairmore Group in Alberta.[3] The formation is a distinctive marker horizon, and it was sometimes called the "coal conglomerate" because it was useful as a reference point for locating coal seams in the underlying Kootenay Group and the overlying Gething Formation.[5]

Lithology

The formation consists primarily of conglomerate, although at some localities there are minor interbeds of coarse-grained sandstone, shale, and coal. The conglomerate is typically massive and consists of well-rounded pebbles, cobbles and boulders of white, grey and green chert, and white and grey quartzite, in a matrix of quartzose sand. In some areas there are also minor pebbles, cobbles and boulders of limestone, dolostone, black argillite and, rarely, greenish volcanics. The conglomerate and sandstone beds are cemented with silica, making them very hard and resistant to erosion, so they tend to form prominent outcrops.[1][6]

Environment of deposition

Deposition of the Cadomin Formation marked the renewal of subsidence and sedimentation following a long period of uplift, exposure and erosion of older strata.[3] The Cadomin sediments were derived from sources in the mountains to the west, and were deposited across the pediment surface by systems of alluvial fans and braided streams. It is postulated that the streams flowed generally northeastward, turning northwestward at the Fox Creek Escarpment.[5]

Distribution

Outcrops near Cadomin are the type locality. The formation is exposed at the surface in the foothills of the Canadian Rockies, extending from the United States-Canada border in western Alberta to the Peace River region in northeastern British Columbia, a distance of more than 1,000 kilometers (620 mi). It is also recognizable in the subsurface east of the foothills. It thickens from west to east, with thicknesses ranging from 1 meter (3.3 ft) to more than 170 meters (560 ft).[1][7]

Relationship to other units

The Cadomin Formation overlies a major regional unconformity caused by pre-Cadomin erosion, although little or no evidence of the angular nature of that unconformity is apparent in most outcrops.[6] It rests unconformably on the Fernie Formation, the Nikanassin Formation, the Minnes Group or the Kootenay Group, depending on the location and the extent of the erosion. It is conformably overlain by the Gladstone Formation in Alberta and Gething Formation in northeastern British Columbia, and it is equivalent to the base of the Mannville Group.[3]

Hydrocarbon production

Natural gas is produced from the Cadomin Formation in the Deep Basin of western Alberta in the Hinton-Grande Cache-Grande Prairie area, as well as in the Cutbank area in northeastern British Columbia.[8]

Gallery

References

  1. ↑ 1.0 1.1 1.2 Lexicon of Canadian Geologic Units. "Cadomin Formation". Retrieved 2009-02-05.
  2. ↑ Mackay, B.R., 1930. Stratigraphy and structure of bituminous coal fields in the vicinity of Jasper Park, Alberta. Can. Inst. Min. and Metall., Trans., v. 33, p. 473-509.
  3. ↑ 3.0 3.1 3.2 3.3 Mossop, G.D. and Shetsen, I., (compilers), Canadian Society of Petroleum Geologists and Alberta Geological Survey (1994). "The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 19: The Cretaceous Mannville Group of the Western Canada Sedimentary Basin". Retrieved 2013-08-01.
  4. ↑ Alberta Speleological Society. Cadomin Cave
  5. ↑ 5.0 5.1 McLean, J.R. 1977. The Cadomin Formation: Stratigraphy, sedimentology, and tectonic implications. Bulletin of Canadian Petroleum Geology 25: 792-827.
  6. ↑ 6.0 6.1 Stott, D.F. 1965. Lower Cretaceous Bullhead and Fort St John Groups, between Smoky and Peace Rivers, Rocky Mountain foothills, Alberta and British Columbia. Geological Survey of Canada, Bulletin 152, 279 p. ISBN 0-660-10208-0.
  7. ↑ 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.
  8. ↑ Varley, C.J. 1984. The Cadomin Formation: A model for the Deep Basin type gas trapping mechanism. In: Stott, D.F. and Glass, D.J. (editors), Mesozoic of Middle North America; Canadian Society of Petroleum Geologists, Memoir 9, p. 471-484.