The Southesk Formation is a stratigraphic unit of Late Devonian (late Frasnian) age. It is present on the western edge of the Western Canada Sedimentary Basin in the Rocky Mountains and foothills of Alberta and southeastern British Columbia. It was named for the Southesk River in Jasper National Park by D.J. McLaren in 1955.^[2]

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Southesk Formation
Stratigraphic range: late Frasnian PreꞒ Ꞓ O S D C P T J K Pg N
Type	Formation
Unit of	Fairholme Group
Sub-units	Ronde Member Arcs Member Grotto Member Peechee Member
Underlies	Sassenach Formation, Alexo Formation, Palliser Formation, or Crowfoot Formation
Overlies	Cairn Formation, or Borsato Formation
Thickness	Up to about 300 m (1000 feet)[1]
Lithology
Primary	Dolomite
Other	Limestone
Location
Coordinates	52°38′00″N 116°58′00″W
Region	Alberta  British Columbia
Country	Canada
Type section
Named for	Southesk River
Named by	D.J. McLaren, 1955.[2]

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The formation consists primarily of dolomite^[1] and it preserves fossils of marine animals such as stromatoporoids and rugose corals.^[2]

The Southesk Formation was deposited in reefal environments.^[3] It is commonly between 150 and 260 m (490 and 850 feet) thick, and reaches a maximum of about 300 m (1000 feet) in the Flathead area of southeastern British Columbia.^[1] It has been subdivided into four members, shown in descending order below.^[1]

The Southesk Formation is discontinuously present in the Canadian Rockies from Jasper National Park to the Flathead area of southeastern British Columbia. It is also present in the subsurface beneath the adjacent plains to the east. It conformably overlies the Cairn Formation or, in the Crows Nest Pass area, the Borsato Formation. At its margins it may interfinger with the Perdrix and Mount Hawk Formations. In the mountains it is unconformably overlain by the Sassenach, the Alexo or, rarely, the Palliser Formation. It is overlain by the Crowfoot Formation in the plains.^[1][4]

• List of fossiliferous stratigraphic units in Alberta