Type Geological formation Named by H.W. Smith, 1935 Named for Big Snowy Mountains Underlies Watrous Formation | Country United States
Canada Area 51,800 km² Overlies Madison Group | |
Thickness up to 135 metres (440 ft) Regions Williston Basin, Western Canadian Sedimentary Basin Primary Slate, Limestone, Sandstone | ||
The Big Snowy Group is a stratigraphical unit of Chesterian age in the Williston Basin.
Contents
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.
Subdivisions
The Big Snowy Group is composed of three subdivisions, from top to base:
Distribution
The Big Snowy Group reaches a maximum thickness of 135 metres (440 ft) in the Williston Basin. 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.