Southesk Formation

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]

Southesk Formation
Stratigraphic range:
TypeFormation
Unit ofFairholme Group
Sub-unitsRonde Member
Arcs Member
Grotto Member
Peechee Member
UnderliesSassenach Formation, Alexo Formation, Palliser Formation, or Crowfoot Formation
OverliesCairn Formation, or Borsato Formation
ThicknessUp to about 300 m (1000 feet)[1]
Lithology
PrimaryDolomite
OtherLimestone
Location
Coordinates52°38′00″N 116°58′00″W
Region Alberta
 British Columbia
Country Canada
Type section
Named forSouthesk River
Named byD.J. McLaren, 1955.[2]

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

Lithology and thickness

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]

MemberLithologyMax. ThicknessFossilsReference
Ronde Memberlimestone & silty limestone; present only in limited areas55 m (180 ft)not fossiliferous Glass, p. 1006[1]
Arcs Memberlight grey, medium-bedded, medium-crystalline dolomite74 m (240 ft)minor branching stromatoporoids, foraminifera, & algae Glass, p. 62[1]
Grotto Memberthick- to thin-bedded, dark brown to grey, variably argillaceous dolomite67 m (220 ft)branching stromatoporoids; tabulate corals Glass, p. 533[1]
Peechee Membermassive, light grey, medium- to coarse-crystalline dolomite; minor limestone & anhydrite300 m (980 ft)bulbous & branching stromatoporoids; tabulate corals Glass, p. 915[1]

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.[1][4]

See also

References

  1. Glass, D.J. (editor) 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba, p. 1094. Canadian Society of Petroleum Geologists, Calgary, 1423 p. on CD-ROM. ISBN 0-920230-23-7.
  2. Devonian formations in the Alberta Rocky Mountains between Bow and Athabasca rivers. Geological Survey of Canada, Bulletin 35.
  3. Weissenberger, J.A.W. and McIlreath, I.A. 1989. Southesk Cairn reef complex, Upper Devonian (Frasnian), Alberta. In: Reefs: Canada and adjacent areas, H.H.J. Geldsetzer, N.P. James and G.E. Tobbutt (eds.), Canadian Society of Petroleum Geologists, Memoir 13, p. 535-542.
  4. Alberta Geological Survey. "Alberta Table of Formations, May 2019" (PDF). Alberta Energy Regulator. Retrieved 24 March 2020.
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