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Fort St. John Group
Stratigraphical unit of the Western Canadian Sedimentary Basin

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.

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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.ThicknessReference
Cruiser FormationAlbian - Cenomanianmarine shale, argillaceous siltstone and fine grained marine sandstone230 m (750 ft)2
Goodrich Formationlate Albianfine-grained, laminated sandstone, mudstone partings400 m (1,310 ft)3
Hasler Formationmiddle to late Albianmarine shale and siltstone, minor sandstone and pebble conglomerate265 m (870 ft)4
Commotion Formationearly to middle Albiansandstone, shale and conglomerate490 m (1,610 ft)5
Gates Formationearly Albianmassive well-sorted sandstone, carbonaceous sandstone, mudstone, siltstone, coal263 m (860 ft)6
Moosebar Formationearly Albianmarine shale and siltstone289 m (950 ft)7

Peace River Country

Sub-unitAgeLithologyMax. ThicknessReference
Shaftesbury FormationAlbianfriable shale, fish scale siltstone, bentonite, ironstone400 m (1,310 ft)8
Peace River Formationmiddle AlbianPaddy Member - greywacke, coalCadotte Member - coarse to fine marine sandstoneHarmon Member - dark, fissile, non-calcareous shale60 m (200 ft)9
Spirit River Formationmiddle AlbianNotikewin Member - fine to medium grained argillaceous sandstone, dark shale, ironstoneFalher Member - greywacke, shale, siltstone, coalWilrich Member - dark shale thin sandstone and siltstone stringers348 m (1,140 ft)10
Bluesky Formationearly Albianbrown, fine to medium grained, glauconitic, porous sandstone46 m (150 ft)11

Liard River and Fort Liard Area

Sub-unitAgeLithologyMaxThicknessReference
Sully Formationearly to Late Cretaceousmarine shale and siltstone300 m (980 ft)12
Sikanni Formationearly Cretaceousfine-grained, calcareous, glauconitic sandstone, argillaceous siltstone and shale240 m (790 ft)13
Lepine Formation*middle to late Albiansilty mudstone, sideritic concretions900 m (2,950 ft)14
Scatter Formation*early to middle AlbianBulwell Member - glauconitic sandstoneWildhorn Member - silty mudstoneTussock Member - glauconitic sandstone, silty mudstone375 m (1,230 ft)15
Garbutt Formation*early AptianLower Garbutt - mudstone, siltstone, siderite, bentoniteUpper Garbutt - mudstone, sideritic weathering, argillaceous siltstone, laminated sandstone290 m (950 ft)16
Chinkeh FormationBarremian to early Albiansandstone with marine shale, conglomeratic basediscontinuous17

*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. 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) https://web.archive.org/web/20130814133127/http://www.ags.gov.ab.ca/publications/wcsb_atlas/a_ch19/ch_19.html ↩

  2. Lexicon of Canadian Geologic Units. "Cruiser Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  3. Lexicon of Canadian Geologic Units. "Goodrich Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  4. Lexicon of Canadian Geologic Units. "Hasler Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  5. Lexicon of Canadian Geologic Units. "Commotion Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  6. Lexicon of Canadian Geologic Units. "Gates Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  7. Lexicon of Canadian Geologic Units. "Moosebar Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  8. Lexicon of Canadian Geologic Units. "Shaftesbury Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  9. Lexicon of Canadian Geologic Units. "Peace River Formation". Archived from the original on 2012-07-08. Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  10. Lexicon of Canadian Geologic Units. "Spirit River Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  11. Lexicon of Canadian Geologic Units. "Bluesky Formation". Archived from the original on 2012-07-09. Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  12. Lexicon of Canadian Geologic Units. "Sully Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  13. Lexicon of Canadian Geologic Units. "Sikanni Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  14. Lexicon of Canadian Geologic Units. "Lepine Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  15. Lexicon of Canadian Geologic Units. "Scatter Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  16. Lexicon of Canadian Geologic Units. "Garbutt Formation". Retrieved 2009-02-11. /wiki/Lexicon_of_Canadian_Geologic_Units ↩

  17. Lexicon of Canadian Geologic Units. "Chinkeh Formation". Retrieved 2010-01-09. /wiki/Lexicon_of_Canadian_Geologic_Units ↩