Big Snowy Group

Big Snowy Group Stratigraphic range: Chesterian PreЄ Є O S D C P T J K Pg N
Type	Geological formation
Underlies	Tyler Formation Watrous Formation
Overlies	Madison Group
Area	51,800 square kilometres (20,000 sq mi)
Thickness	up to 135 metres (440 ft)^[1]
Lithology
Primary	Shale, limestone, sandstone
Location
Region	Williston Basin WCSB
Country	United States Canada
Type section
Named for	Big Snowy Mountains
Named by	H.W. Smith, 1935

The Big Snowy Group is a stratigraphical unit of Chesterian age in the Williston Basin.

It takes the name from Big Snowy Mountains in Montana, and was first described on the north slopes of the mountain by H.W. Smith in 1935.

Lithology

Subdivisions

The Big Snowy Group is composed of three subdivisions, from top to base: ^[1]

Heath Formation: black shale with sandstone lenses.
Otter Formation: limestone and grey to green shale
Kibbey Formation: shaly sandstone

Distribution

The Big Snowy Group reaches a maximum thickness of 135 metres (440 ft) in the Williston Basin.^[1] It is exposed in outcrop in the Big Snowy Mountains, Little Belt Mountains, Castle Mountains and Lombard Hills of central Montana. It occurs in the sub-surface throughout the central part of the Williston Basin and into a limited area of south-central Saskatchewan.

Relationship to other units

The Big Snowy Group is unconformably overlain by the Tyler Formation in Montana, and by the Watrous Formation in Saskatchewan; It disconformably overlays the Madison Group.^[1]

References

1 2 3 4 Lexicon of Canadian Geologic Units. "Big Snowy Group". Retrieved 2010-02-03.

Western Canadian Sedimentary Basin

Hydrocarbon history	Oil sands and heavy oil Frontier exploration and development Natural gas liquids Natural gas

Depositional Regions	Southern Alberta Central Alberta Northwestern Alberta Plains South-central Canadian Rockies foothills North-east Plains North-central foothills Liard River Fort Nelson Northern Rocky Mountains Fort St. John Saskatchewan Western Manitoba

Saskatchewan	Cypress Hills FM Ravenscrag FM Frenchman FM Whitemud FM Eastend FM Bearpaw FM Judith River GRP Belly River FM Oldman FM Foremost FM Lea Park FM Pakowki FM Milk River FM Colorado GRP Viking FM Mannville GRP Pense FM Cantuar FM Success FM Vanguard FM Ellis GRP Swift FM Rierdon FM Sawtooth FM Shaunavon FM Piper FM Gravelbourg FM Gypsum Springs FM Watrous FM Big Snowy GRP Madison GRP Charles FM Poplar Ratcliffe Midale Mission Canyon FM Kisbey SS Alida Tilston Lodgepole FM Souris Valley Three Forks GRP Bakken FM Big Valley FM Torquay FM Saskatchewan GRP Birdbear FM Duperow FM Manitoba GRP Souris River FM Elk Point GRP Davson Bay FM Prairie FM Winnipegosis FM Ashern FM Interlake FM Stonewall FM Stony Mountain FM Herald FM Yeoman FM Winnipeg FM Deadwood FM Canadian Shield

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