Fort St. John Group

Template:Short description Template:Infobox Rockunit 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.

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 to .

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-unit	Age	Lithology	Max. Thickness	Reference
Cruiser Formation	Albian - Cenomanian	marine shale, argillaceous siltstone and fine grained marine sandstone
Goodrich Formation	late Albian	fine-grained, laminated sandstone, mudstone partings
Hasler Formation	middle to late Albian	marine shale and siltstone, minor sandstone and pebble conglomerate
Commotion Formation	early to middle Albian	sandstone, shale and conglomerate
Gates Formation	early Albian	massive well-sorted sandstone, carbonaceous sandstone, mudstone, siltstone, coal
Moosebar Formation	early Albian	marine shale and siltstone

Peace River Country

Sub-unit	Age	Lithology	Max. Thickness	Reference
Shaftesbury Formation	Albian	friable shale, fish scale siltstone, bentonite, ironstone
Peace River Formation	middle Albian	Paddy Member - greywacke, coal Cadotte Member - coarse to fine marine sandstone Harmon Member - dark, fissile, non-calcareous shale
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
Bluesky Formation	early Albian	brown, fine to medium grained, glauconitic, porous sandstone

Liard River and Fort Liard Area

Sub-unit	Age	Lithology	Max Thickness	Reference
Sully Formation	early to Late Cretaceous	marine shale and siltstone
Sikanni Formation	early Cretaceous	fine-grained, calcareous, glauconitic sandstone, argillaceous siltstone and shale
Lepine Formation*	middle to late Albian	silty mudstone, sideritic concretions
Scatter Formation*	early to middle Albian	Bulwell Member - glauconitic sandstone Wildhorn Member - silty mudstone Tussock Member - glauconitic sandstone, silty mudstone
Garbutt Formation*	early Aptian	Lower Garbutt - mudstone, siltstone, siderite, bentonite Upper Garbutt - mudstone, sideritic weathering, argillaceous siltstone, laminated sandstone
Chinkeh Formation	Barremian to early Albian	sandstone with marine shale, conglomeratic base	discontinuous

*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.