Southesk Formation


The Southesk Formation is a stratigraphic unit of Late Devonian 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.
The formation consists primarily of dolomite and it preserves fossils of marine animals such as stromatoporoids and rugose corals.

Lithology and thickness

The Southesk Formation was deposited in reefal environments. It is commonly between 150 and 260 m thick, and reaches a maximum of about 300 m in the Flathead area of southeastern British Columbia. It has been subdivided into four members, shown in descending order below.
MemberLithologyMax. ThicknessFossilsReference
Ronde Memberlimestone & silty limestone; present only in limited areasnot fossiliferousGlass, p. 1006
Arcs Memberlight grey, medium-bedded, medium-crystalline dolomiteminor branching stromatoporoids, foraminifera, & algaeGlass, p. 62
Grotto Memberthick- to thin-bedded, dark brown to grey, variably argillaceous dolomitebranching stromatoporoids; tabulate coralsGlass, p. 533
Peechee Membermassive, light grey, medium- to coarse-crystalline dolomite; minor limestone & anhydritebulbous & branching stromatoporoids; tabulate coralsGlass, p. 915

Distribution and relationship to other units

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.