The Fort St. John Group is a

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostra ...

unit of

Lower Cretaceous Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eig ...

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone or something has been alive or has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

in the Western Canada Sedimentary Basin. It takes the name from the city of Fort St. John,

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

and was first defined by

George Mercer Dawson George Mercer Dawson (August 1, 1849 – March 2, 1901) was a Canadian geologist and surveyor. Biography He was born in Pictou, Nova Scotia, the eldest son of Sir John William Dawson, Principal of McGill University and a noted geologis ...

in 1881.

Lithology

The Fort St. John Group is mostly composed of dark shale deposited in a marine environment.

Bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-m ...

is present in the shale, and it is interbedded with

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

, siltstone and conglomerates.

Distribution

The Fort St. John Group occurs in the subsurface in the

Peace River Country The Peace River Country (or Peace Country; french: Région de la Rivière-de-la-paix) is an aspen parkland region centring on the Peace River in Canada. It extends from northwestern Alberta to the Rocky Mountains in northeastern British Columbia ...

of northeastern

and north-western

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

, in southern

Yukon Yukon (; ; formerly called Yukon Territory and also referred to as the Yukon) is the smallest and westernmost of Canada's three territories. It also is the second-least populated province or territory in Canada, with a population of 43,964 as ...

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 Bullhead Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin of northeastern British Columbia and western Alberta. It was first defined by F.H. McLearn in 1918 as the Bullhead Mountain Formation, but later ...

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 British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

Peace River Country The Peace River Country (or Peace Country; french: Région de la Rivière-de-la-paix) is an aspen parkland region centring on the Peace River in Canada. It extends from northwestern Alberta to the Rocky Mountains in northeastern British Columbia ...

Liard River and
Fort Liard Fort Liard (Slavey language: ''Echaot'l Koe'' "people from the land of the giants" or ''Acho Dene Kue'') is a hamlet in the Dehcho Region of the Northwest Territories, Canada. It is located north of the British Columbia border. It became acces ...
Area

*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

, between the

Halfway River The Halfway River is a tributary of the Peace River in northeastern British Columbia, Canada. The river originates in the Muskwa Ranges at an elevation of . It flows from Robb Lake, between Mount Kenny and Mount Robb, then flows east to Pink Moun ...

and

Muskwa River The Muskwa River flows through northern British Columbia, Canada. It is a major tributary of the Fort Nelson River - part of the Mackenzie River system. The river rises at Fern Lake in the Bedaux Pass in the Northern Rocky Mountains. From the ...

. It is composed of silty marine mudstone with fine grained marine

interbeds.

References

{{Western Canadian Sedimentary Basin, Northwest_Plains=yes, Fort_Nelson=yes, Liard_River=yes Lower Cretaceous Series of North America Cretaceous Alberta Cretaceous British Columbia Cretaceous Northwest Territories Cretaceous Yukon Stratigraphy of Alberta Stratigraphy of British Columbia Stratigraphy of the Northwest Territories Stratigraphy of Yukon

Lithology

Distribution

Relationship to other units

Subdivisions

Canadian Rockies foothills of British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

Peace River Country The Peace River Country (or Peace Country; french: Région de la Rivière-de-la-paix) is an aspen parkland region centring on the Peace River in Canada. It extends from northwestern Alberta to the Rocky Mountains in northeastern British Columbia ...

Liard River and Fort Liard Fort Liard (Slavey language: ''Echaot'l Koe'' "people from the land of the giants" or ''Acho Dene Kue'') is a hamlet in the Dehcho Region of the Northwest Territories, Canada. It is located north of the British Columbia border. It became acces ... Area

References

Canadian Rockies foothills of
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

Liard River and
Fort Liard Fort Liard (Slavey language: ''Echaot'l Koe'' "people from the land of the giants" or ''Acho Dene Kue'') is a hamlet in the Dehcho Region of the Northwest Territories, Canada. It is located north of the British Columbia border. It became acces ...
Area