Fort St. John Group

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Fort St. John Group
Stratigraphic range: Lower Cretaceous
Type Geological formation
Sub-units Cruiser Formation, Goodrich Formation, Hasler Formation, Gates Formation, Moosebar Formation, Shaftesbury Formation, Peace River Formation, Spirit River Formation, Bluesky Formation, Sully Formation, Sikanni Formation, Lepine Formation, Scatter Formation, Garbutt Formation, Buckinghorse Formation
Underlies Dunvegan Formation
Overlies Bullhead Group
Thickness up to 2,000 metres (6,560 ft)[1]
Lithology
Primary Shale
Other Sandstone, siltstone and conglomerates
Location
Region Northeast  British Columbia
Northwest  Alberta
Southern  Yukon
Southern  Northwest Territories
Country  Canada
Type section
Named for Fort St. John
Named by George Mercer Dawson, 1881

The Fort St. John Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin.[2] It takes the name from the city of Fort St. John, British Columbia and was first defined by George Mercer Dawson in 1881.

Lithology[edit]

The Fort St. John Group is mostly composed of dark shale deposited in a marine environment. Bentonite is present in the shale, and it is interbedded with sandstone, siltstone and conglomerates.

Distribution[edit]

The Fort St. John Group occurs in the subsurface in the Peace River Country of northeastern British Columbia and north-western Alberta, in southern Yukon and southern Northwest Territories. It has a thickness of 700 metres (2,300 ft) to 2,000 metres (6,560 ft).

Relationship to other units[edit]

The Fort St. John Group is conformably overlain by the Dunvegan Formation and conformably underlain by the Bullhead Group or may rest disconformably on older units.

Subdivisions[edit]

The Fort St. John Group is subdivided into the following formations:

Canadian Rockies foothills of British Columbia[edit]

Sub-unit Age Lithology Max.
Thickness
Reference
Cruiser Formation Albian - Cenomanian marine shale, argillaceous siltstone and fine grained marine sandstone 230 m (750 ft) [3]
Goodrich Formation late Albian fine-grained, laminated sandstone, mudstone partings 400 m (1,310 ft) [4]
Hasler Formation middle to late Albian marine shale and siltstone, minor sandstone and pebble conglomerate 265 m (870 ft) [5]
Commotion Formation early to middle Albian sandstone, shale and conglomerate 490 m (1,610 ft) [6]
Gates Formation early Albian massive well-sorted sandstone, carbonaceous sandstone, mudstone, siltstone, coal 263 m (860 ft) [7]
Moosebar Formation early Albian marine shale and siltstone 289 m (950 ft) [8]

Peace River Country[edit]

Sub-unit Age Lithology Max. Thickness Reference
Shaftesbury Formation Albian friable shale, fish scale siltstone, bentonite, ironstone 400 m (1,310 ft) [9]
Peace River Formation middle Albian Paddy Member - greywacke, coal
Cadotte Member - coarse to fine marine sandstone
Harmon Member - dark, fissile, non-calcareous shale
60 m (200 ft) [10]
Spirit River Formation middle Albian Notikewin Member - fine to medium grained argillaceous sandstone, dark shale, ironstone
Falher Member - greywacke, shale, siltstone, coal
Wilrich Member - dark shale thin sandstone and siltstone stringers
348 m (1,140 ft) [11]
Bluesky Formation early Albian brown, fine to medium grained, glauconitic, porous sandstone 46 m (150 ft) [12]

Liard River and Fort Liard Area[edit]

Sub-unit Age Lithology Max
Thickness
Reference
Sully Formation early to Late Cretaceous marine shale and siltstone 300 m (980 ft) [13]
Sikanni Formation early Cretaceous fine-grained, calcareous, glauconitic sandstone, argillaceous siltstone and shale 240 m (790 ft) [14]
Lepine Formation* middle to late Albian silty mudstone, sideritic concretions 900 m (2,950 ft) [15]
Scatter Formation* early to middle Albian Bulwell Member - glauconitic sandstone
Wildhorn Member - silty mudstone
Tussock Member - glauconitic sandstone, silty mudstone
375 m (1,230 ft) [16]
Garbutt Formation* early Aptian Lower Garbutt - mudstone, siltstone, siderite, bentonite
Upper Garbutt - mudstone, sideritic weathering, argillaceous siltstone, laminated sandstone
290 m (950 ft) [17]
Chinkeh Formation Barremian to early Albian sandstone with marine shale, conglomeratic base discontinuous [18]

*Buckinghorse Formation is equivalent to the sum of Lepine Formation, Scatter Formation and Garbutt Formation. It occurs north-east of the Canadian Rockies foothills in British Columbia, between the Halfway River and Muskwa River. It is composed of silty marine mudstone with fine grained marine sandstone interbeds.

References[edit]

  1. ^ Lexicon of Canadian Geologic Units. "Fort St. John Group". Retrieved 2009-02-11. 
  2. ^ 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: Cretaceous Mannville Group of the Western Canada Sedimentary Basin". Archived from the original on 2013-08-14. Retrieved 2013-08-01. 
  3. ^ Lexicon of Canadian Geologic Units. "Cruiser Formation". Retrieved 2009-02-11. 
  4. ^ Lexicon of Canadian Geologic Units. "Goodrich Formation". Retrieved 2009-02-11. 
  5. ^ Lexicon of Canadian Geologic Units. "Hasler Formation". Retrieved 2009-02-11. 
  6. ^ Lexicon of Canadian Geologic Units. "Commotion Formation". Retrieved 2009-02-11. 
  7. ^ Lexicon of Canadian Geologic Units. "Gates Formation". Retrieved 2009-02-11. 
  8. ^ Lexicon of Canadian Geologic Units. "Moosebar Formation". Retrieved 2009-02-11. 
  9. ^ Lexicon of Canadian Geologic Units. "Shaftesbury Formation". Retrieved 2009-02-11. 
  10. ^ Lexicon of Canadian Geologic Units. "Peace River Formation". Retrieved 2009-02-11. 
  11. ^ Lexicon of Canadian Geologic Units. "Spirit River Formation". Retrieved 2009-02-11. 
  12. ^ Lexicon of Canadian Geologic Units. "Bluesky Formation". Archived from the original on 2012-07-09. Retrieved 2009-02-11. 
  13. ^ Lexicon of Canadian Geologic Units. "Sully Formation". Retrieved 2009-02-11. 
  14. ^ Lexicon of Canadian Geologic Units. "Sikanni Formation". Retrieved 2009-02-11. 
  15. ^ Lexicon of Canadian Geologic Units. "Lepine Formation". Retrieved 2009-02-11. 
  16. ^ Lexicon of Canadian Geologic Units. "Scatter Formation". Retrieved 2009-02-11. 
  17. ^ Lexicon of Canadian Geologic Units. "Garbutt Formation". Retrieved 2009-02-11. 
  18. ^ Lexicon of Canadian Geologic Units. "Chinkeh Formation". Retrieved 2010-01-09.