Arctomys Formation

The Arctomys Formation is a stratigraphic unit of late Middle Cambrian age. It is present on the western edge of the Western Canada Sedimentary Basin in the Canadian Rockies of Alberta and British Columbia.^[3] It was named for Arctomys Peak near Mount Erasmus in Banff National Park by Charles Doolittle Walcott in 1920. Outcrops of the Arctomys can be seen in Banff and Jasper National Parks.^[4]

Arctomys Formation
Stratigraphic range: Middle Cambrian ~509–500 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Formation
Underlies	Waterfowl Formation
Overlies	Pika Formation
Thickness	Up to 336 metres (1,100 ft)[1]
Lithology
Primary	Shale
Other	Dolomite, limestone
Location
Coordinates	51°57′35″N 116°55′16″W
Region	Canadian Rockies
Country	Canada
Type section
Named for	Arctomys Peak
Named by	Charles Doolittle Walcott[2]

Lithology and deposition

The Arctomys was deposited along the western shoreline of the North American Craton during late Middle Cambrian time.^[3][5] It consists primarily of red, grey, and green platy shale. Sedimentary structures include mudcracks, ripple marks, and casts of salt crystals.^[1][3] Environments of deposition may have included shallow lakes, lagoons, and sheet-flood deposits on dry mud flats.^[6]

Distribution and stratigraphic relationships

The Arctomys Formation is present in the Rocky Mountains of Alberta and British Columbia. It thickens northward from White Man Mountain to a maximum of 336 metres (1,100 ft) at Mount Robson.^[1] It is overlies the Pika Formation and is overlain by the Waterfowl Formation.^[7] Both contacts are gradational.^[1]