Fort St. John Group

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.

Fort St. John Group
Stratigraphic range:
TypeGeological formation
Sub-unitsCruiser 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
UnderliesDunvegan Formation
OverliesBullhead Group
Thicknessup to 2,000 metres (6,560 ft)[1]
Lithology
PrimaryShale
OtherSandstone, siltstone and conglomerates
Location
RegionNortheast  British Columbia
Northwest  Alberta
Southern  Yukon
Southern  Northwest Territories
Country Canada
Type section
Named forFort St. John
Named byGeorge Mercer Dawson, 1881

Lithology

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

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

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

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

Canadian Rockies foothills of British Columbia
Sub-unitAgeLithologyMax.
Thickness		Reference
Cruiser FormationAlbian - Cenomanianmarine shale, argillaceous siltstone and fine grained marine sandstone230 m (750 ft) [3]
Goodrich Formationlate Albianfine-grained, laminated sandstone, mudstone partings400 m (1,310 ft) [4]
Hasler Formationmiddle to late Albianmarine shale and siltstone, minor sandstone and pebble conglomerate265 m (870 ft) [5]
Commotion Formationearly to middle Albiansandstone, shale and conglomerate490 m (1,610 ft) [6]
Gates Formationearly Albianmassive well-sorted sandstone, carbonaceous sandstone, mudstone, siltstone, coal263 m (860 ft) [7]
Moosebar Formationearly Albianmarine shale and siltstone289 m (950 ft) [8]

Peace River Country
Sub-unitAgeLithologyMax. ThicknessReference
Shaftesbury FormationAlbianfriable shale, fish scale siltstone, bentonite, ironstone400 m (1,310 ft) [9]
Peace River Formationmiddle AlbianPaddy Member - greywacke, coal
Cadotte Member - coarse to fine marine sandstone
Harmon Member - dark, fissile, non-calcareous shale		60 m (200 ft) [10]
Spirit River Formationmiddle AlbianNotikewin 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 Formationearly Albianbrown, fine to medium grained, glauconitic, porous sandstone46 m (150 ft) [12]

Liard River and Fort Liard Area
Sub-unitAgeLithologyMax
Thickness		Reference
Sully Formationearly to Late Cretaceousmarine shale and siltstone300 m (980 ft) [13]
Sikanni Formationearly Cretaceousfine-grained, calcareous, glauconitic sandstone, argillaceous siltstone and shale240 m (790 ft) [14]
Lepine Formation*middle to late Albiansilty mudstone, sideritic concretions900 m (2,950 ft) [15]
Scatter Formation*early to middle AlbianBulwell Member - glauconitic sandstone
Wildhorn Member - silty mudstone
Tussock Member - glauconitic sandstone, silty mudstone
375 m (1,230 ft) [16]
Garbutt Formation*early AptianLower Garbutt - mudstone, siltstone, siderite, bentonite
Upper Garbutt - mudstone, sideritic weathering, argillaceous siltstone, laminated sandstone		290 m (950 ft) [17]
Chinkeh FormationBarremian to early Albiansandstone with marine shale, conglomeratic basediscontinuous [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
  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.{{cite web}}: CS1 maint: multiple names: authors list (link)
  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". Archived from the original on 2012-07-08. 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.
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