Elk Point Group

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Elk Point Group
Stratigraphic range: Early to Middle Devonian
Type Geological formation
Sub-units Upper and Lower Elk Point Group
Underlies Beaverhill Lake Group, Manitoba Group
Overlies Precambrian to Silurian formations[1]
Thickness up to 610 metres (2,000 ft)[2][3]
Lithology
Primary Dolomite, halite, anhydrite
Other Limestone, shale, potash
Location
Coordinates 53°54′19″N 110°37′49″W / 53.9053°N 110.6304°W / 53.9053; -110.6304 (Elk Point Group)Coordinates: 53°54′19″N 110°37′49″W / 53.9053°N 110.6304°W / 53.9053; -110.6304 (Elk Point Group)
Region Northern plains
Country  Canada  United States
Type section
Named for Elk Point
Named by J.R. McGehee[4]

The Elk Point Group is a stratigraphic unit of Early to Middle Devonian age in the Western Canada and Williston sedimentary basins. It underlies large area that extends from southern boundary of the Northwest Territories in Canada to North Dakota in the United States. It has been subdivided into numerous formations,[5] many which host major petroleum and natural gas reservoirs.[6]

Lithology[edit]

The formations of the Elk Point Group are composed primarily of carbonate rocks (dolostone and limestone) and evaporitic rocks (halite, anhydrite and potash), with lesser amounts of dolomitic mudstone and shale. [2] [3]

Paleontology[edit]

Some of the carbonate formations of the Elk Point Group contain rich assemblages of marine invertebrate fossils, including many species of brachiopods, gastropods, bivalves, cephalopods, crinoids, ostracods and corals. The evaporitic formations are unfossiliferous or contain a few spores and algal remains.[2][3]

Environment of Deposition[edit]

The formations of the Elk Point Group were deposited in a marine embayment that stretched from an open ocean in the present-day Northwest Territories of Canada to North Dakota in the United States, covering an area roughly half as large as that covered by today's Mediterranean Sea. At times of low water levels and excessive evaporation, halite and other evaporite minerals were deposited in sabkha, supratidal flat and coastal lagoon environments, and at times of higher water levels carbonate platform sedimentation and reef growth were dominant.[1][5]

Distribution and Thickness[edit]

The Elk Point Group extends from the southern boundary of the Northwest Territories through northwestern British Columbia, Alberta, Saskatchewan, and southwestern Manitoba in Canada, and continues into eastern Montana and North Dakota in the United States.[1] It reaches a maximum thickness of about 610 metres (2,000 ft) in eastern Alberta.[2][3]

Stratigraphy[edit]

The Elk Point Group was named for the town of Elk Point, Alberta by J.R. McGehee in 1949.[4] Core from a well that was drilled near Elk Point has been designated as the type section (Anglo-Canadian Elk Point No. 11, 2-11-57-5W4).[1] The group is subdivided into the Lower and Upper Elk Point Group, each of which is further subdivided into formations according to the dominant lithologies,[1][2][3] as shown in the tables below.

The Lower Elk Point Group comprises all strata lying below the Winnipegosis Formation (in the south) or the Keg River Formation (in the north) and is present only in the deepest parts of the basin. The Upper Elk Point Group, which is present throughout the basin, includes those formations and all overlying formations to the base of the Manitoba Group (in the south) or the Beaverhill Lake Group (in the north).[1]

Subdivisions[edit]

In northern Alberta and central Alberta, the Elk Point Group contains the following subdivisions, from top to base:

Sub-unit Age Lithology Max.
Thickness
Reference
Watt Mountain Formation Givetian red and green shale, sandstone, anhydrite, dolostone, limestone 74.4 m (240 ft) [7]
Gilwood Member Givetian coarse quartz and feldspathic sandstone 15.2 m (50 ft) [8]
Presqu'ile Formation Givetian crystalline dolostone 300 m (980 ft) [9]
Sulphur Point Formation Givetian fossiliferous limestone, green shale 106 m (350 ft) [10]
Muskeg Formation Givetian anhydrite, salt, dolostone, limestone 270 m (890 ft) [11]
Zama Member Givetian sucrosic dolostone 24 m (80 ft) [12]
Keg River Formation Givetian porous dolostone, wackestone limestone, includes the Rainbow Member (dolomitized reef) 300 m (980 ft) [13]
Contact Rapids Formation Eifelian to Givetian argillaceous dolostone, dolomitic shale 48.8 m (160 ft) [14]
Chinchaga Formation Eifelian to Givetian anhydrite, crystalline dolostone, quartz sandstone, dolomitic shale, halite 76 m (250 ft) [15]
Cold Lake Formation Eifelian halite, dolomitic shale 117 m (380 ft) [16]
Ernestina Lake Formation Eifelian red shale (base), carbonates, anhydrite (top) 23 m (80 ft) [17]
Lotsberg Formation Eifelian halite, calcareous shale 229 m (750 ft) [18]
Basal red beds Eifelian red dolomitic or calcareous shales, silty or sandy, quartzose sandstone   [19]
In southern Alberta

The Elk Point Group is dolomitic and is not differentiated.

In Saskatchewan, Manitoba and Montana
Sub-unit Age Lithology Max.
Thickness
Reference
Dawson Bay Formation Givetian dolomitic mudstone, crystalline limestone, argillaceous carbonate, bituminous limestone, dolostone, anhydrite, halite 50 m (160 ft) [20]
Prairie Evaporite Formation Givetian halite, anhydrite, dolostone, dolomitic mudstone, limestone, potash 218 m (720 ft) [21]
Winnipegosis Formation Givetian dolostone, bituminous carbonates, anhydrite 100 m (330 ft) [22]
Ashern Formation Eifelian to Givetian argillaceous dolostone and dolomitic shale and siltstone; minor anhydrite 55 m (180 ft) [23]
Meadow Lake Formation Eifelian dolostone with mudstone interbeds, limestone and sandstone at base 56 m (180 ft) [24]

Relationship to Other Units[edit]

The Elk Point Group is conformably overlain by the Manitoba Group in Manitoba and Saskatchewan, and by the Beaverhill Lake Group in Alberta. It rests unconformably on Precambrian basement rocks in northern Alberta, on Cambrian strata in northeastern Alberta and in Saskatchewan, and on Ordovician[2] to Silurian[1] formations in western Alberta, Saskatchewan and southwestern Manitoba.[2] In the Northwest Territories, some of its uppermost units are exposed at surface or are unconformably overlain by Cretaceous strata.[1]

The Lower Elk Point Group is equivalent to the Stone Formation and its equivalents, and the Headless and Nahanni Formations, in northerneastern British Columbia and the southwestern Northwest Territories. In the same areas, the Upper Elk Point includes the Pine Point Group, and is equivalent to parts of the Horn River Formation, Besa River Formation, and others.[2][3]

Petroleum and Natural Gas[edit]

The porous carbonate rocks of the Elk Point Group host major petroleum and natural gas reservoirs. As of 1994, the Initial Established Recoverable Petroleum Reserves and the Cumulative Petroleum Production for the group were estimated at 339.3 and 240.4 million cubic metres, respectively. For natural gas, the Initial Established Marketable Reserves and the Cumulative Production were estimated at 142.7 and 79.5 billion cubic metres, respectively.[6]

References[edit]

  1. ^ a b c d e f g h Meijer Drees, N.C. 1986. Evaporitic deposits of western Canada. Geological Survey of Canada, paper 85-20.
  2. ^ a b c d e f g h Lexicon of Canadian Geologic Units. "Elk Point Group". Retrieved 2009-03-01. 
  3. ^ a b c d e f Glass, D.J. (editor) 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba. Canadian Society of Petroleum Geologists, Calgary, 1423 p. on CD-ROM. ISBN 0-920230-23-7.
  4. ^ a b McGehee, J.R., 1949. Pre-Waterways Paleozoic stratigraphy of Alberta Plains. Bull. American Association of Petroleum Geologists, 33:4, p. 603-613.
  5. ^ a b Mossop, G.D. and Shetsen, I. (compilers). Canadian Society of Petroleum Geologists and Alberta Geological Survey (1994). "The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 10: Devonian Elk Point Group of the Western Canada Sedimentary Basin". Retrieved 2014-10-17. 
  6. ^ a b Mossop, G.D. and Shetsen, I., (compilers), Canadian Society of Petroleum Geologists and Alberta Geological Survey (1994). "The Geological Atlas of the Western Canada Sedimentary Basin, Chapter 32: Oil and Gas Resources of the Western Canada Sedimentary Basin". Retrieved 2013-08-01. 
  7. ^ Lexicon of Canadian Geologic Units. "Watt Mountain Formation". Retrieved 2010-01-09. 
  8. ^ Lexicon of Canadian Geologic Units. "Gilwood Member". Retrieved 2010-01-09. 
  9. ^ Lexicon of Canadian Geologic Units. "Presqu'ile Formation". Retrieved 2009-12-26. 
  10. ^ Lexicon of Canadian Geologic Units. "Sulphur Point Formation". Retrieved 2010-01-09. 
  11. ^ Lexicon of Canadian Geologic Units. "Muskeg Formation". Retrieved 2009-12-26. 
  12. ^ Lexicon of Canadian Geologic Units. "Zama Member". Retrieved 2010-01-09. 
  13. ^ Lexicon of Canadian Geologic Units. "Keg Rive Formation". Retrieved 2010-01-09. 
  14. ^ Lexicon of Canadian Geologic Units. "Contact Rapids Formation". Retrieved 2009-12-26. 
  15. ^ Lexicon of Canadian Geologic Units. "Chinchaga Formation". Retrieved 2009-12-26. 
  16. ^ Lexicon of Canadian Geologic Units. "Cold Lake Formation". Retrieved 2009-12-26. 
  17. ^ Lexicon of Canadian Geologic Units. "Ernestina Lake Formation". Retrieved 2009-12-26. 
  18. ^ Lexicon of Canadian Geologic Units. "Lotsberg Formation". Retrieved 2009-12-26. 
  19. ^ Lexicon of Canadian Geologic Units. "Basal red beds". Retrieved 2009-12-26. 
  20. ^ Lexicon of Canadian Geologic Units. "Dawson Bay Formation". Retrieved 2009-12-26. 
  21. ^ Lexicon of Canadian Geologic Units. "Prairie Evaporite Formation". Retrieved 2009-12-26. 
  22. ^ Lexicon of Canadian Geologic Units. "Winnipegosis Formation". Retrieved 2009-12-26. 
  23. ^ Lexicon of Canadian Geologic Units. "Ashern Formation". Retrieved 2010-01-09. 
  24. ^ Lexicon of Canadian Geologic Units. "Meadow Lake Formation". Retrieved 2010-01-09.