Woodbend Group

The Woodbend Group is a stratigraphical unit of Frasnian age in the Western Canadian Sedimentary Basin.

Woodbend Group
Stratigraphic range:
TypeGeological group
Sub-unitsCooking Lake Formation
Duvernay Formation
Leduc Formation
Ireton Formation
UnderliesWinterburn Group
OverliesBeaverhill Lake Group
Thicknessup to 700 metres (2,300 ft)[1]
Lithology
PrimaryLimestone, dolomite
OtherShale
Location
Coordinates53.34507°N 113.6949°W / 53.34507; -113.6949 (Woodbend Group)
Region Alberta
 British Columbia
 Saskatchewan
 Manitoba
 Northwest Territories
 Yukon
Country Canada
Type section
Named byImperial Oil
Year defined1950

It was first described in the British American Pyrcz No. 1 well by Imperial Oil geological staff in 1950.[2]

Lithology

The Formation is composed of crystalline and dolomitized limestone (Cooking Lake Formation) in off-reef areas, bituminous shale and argillaceous limestone, detrital limestone (reef fallout), stromatoporoid calcarenite (Duvernay Formation), gray shale, argillaceous limestone, argillaceous dolomite, crystalline dolomite (Ireton Formation). In reef build-ups, it consists of massive limestone and dolomite with porosity (Leduc Formation). [1]

Hydrocarbon production

Oil is produced from the Leduc Formation in central Alberta since the early 1950s. Shale gas and liquids are extracted from the Duvernay Formation using horizontal drilling and multi-stage hydraulic fracturing.[3] Several project test the economic viability of extracting bitumen from the Grosmont Formation.

Distribution

The Woodbend Group reaches a maximum thickness of 700 metres (2,300 ft) in northern Alberta (where reefs were developed), and has typical thickness of 300 metres (980 ft) in southern and central Alberta.[1] It extends laterally from north-eastern British Columbia through Alberta and into southern Saskatchewan and southern Manitoba. Reef build-ups range in size from small mounds to pinnacle reefs and large atoll size reefs and bank developments.

Subdivisions
Central Alberta

In central Alberta the following formations are recognized, from top to bottom:

Sub-unitAgeLithologyMax.
Thickness		Reference
Ireton FormationFrasnianupper: calcareous shale and argillaceous limestone
middle: fissile grey-green shale with calcirudite beds
lower: massive and banded limestone with shale partings		250 m (820 ft) [4]
Leduc FormationFrasnianshallow water reef deposits: Stromatoporoid limestone, skeletal mudstone, boundstone, floatstone, packstone and wackestone, mostly dolomitized300 m (980 ft) [5]
Duvernay FormationFrasnianbituminous shale, calcareous shale, argillaceous limestone with disseminated pyrite250 m (820 ft) [6]
Cooking Lake FormationFrasnianlimestone (dolomite in the Rimbey-Meadowbrook reef trend)90 m (300 ft) [7]
Northeast Alberta

In northeast Alberta the following formations are recognized, from top to bottom:

Sub-unitAgeLithologyMax.
Thickness		Reference
Grosmont FormationFrasnianlimestone and dolomite, minor argillaceous dolomite, limestone, siltstone and shale230 m (750 ft) [8]
Ireton FormationFrasnianupper: calcareous shale and argillaceous limestone
middle: fissile grey-green shale with calcirudite beds
lower: massive and banded limestone with shale partings		250 m (820 ft) [4]
Cooking Lake FormationFrasnianlimestone: fossiliferous mudstone and wackestone, grainstone, stromatoporoid rudstone and floatstone90 m (300 ft) [7]

Relationship to other units

The Woodbend Group is conformably overlain by the Winterburn Group and conformably overlays the Beaverhill Lake Group.[1] It is transgressive in the Peace River Arch and Tathlina uplift. Newer deposits rest on the Woodbend group upon an erosional surface in eastern Alberta, south-central Saskatchewan and Manitoba.

It is equivalent to the Birdbear Formation and Duperow Formation in northern Montana, southern Saskatchewan and southwestern Manitoba, as well as parts of the Fort Simpson Formation and Muskwa Formation of northeastern British Columbia and southern Yukon, while it corresponds to the Tathlina Formation, Twin Falls Formation and Hay River Formation in the Northwest Territories.

References
  1. Lexicon of Canadian Geologic Units. "Woodbend Group". Retrieved 2009-03-01.
  2. Imperial Oil Limited, Geological Staff, Western Division, 1950. Devonian nomenclature in Edmonton area, Alberta, Canada. Bull. American Association of Petroleum Geologists, v. 34, p. 1807-1825
  3. "The Duvernay Shale". Retrieved 2012-03-04.
  4. Lexicon of Canadian Geologic Units. "Ireton Formation". Retrieved 2009-12-27.
  5. Lexicon of Canadian Geologic Units. "Leduc Formation". Retrieved 2009-12-27.
  6. Lexicon of Canadian Geologic Units. "Duvernay Formation". Retrieved 2009-12-27.
  7. Lexicon of Canadian Geologic Units. "Cooking Lake Formation". Retrieved 2009-12-27.
  8. Lexicon of Canadian Geologic Units. "Grosmont Formation". Retrieved 2011-06-25.
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