Woodbend Group

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

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

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).

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. Several project test the economic viability of extracting bitumen from the Grosmont Formation.

Distribution

The Woodbend Group reaches a maximum thickness of in northern Alberta (where reefs were developed), and has typical thickness of in southern and central Alberta. 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-unit	Age	Lithology	Max. Thickness	Reference
Ireton Formation	Frasnian	upper: calcareous shale and argillaceous limestone middle: fissile grey-green shale with calcirudite beds lower: massive and banded limestone with shale partings
Leduc Formation	Frasnian	shallow water reef deposits: Stromatoporoid limestone, skeletal mudstone, boundstone, floatstone, packstone and wackestone, mostly dolomitized
Duvernay Formation	Frasnian	bituminous shale, calcareous shale, argillaceous limestone with disseminated pyrite
Cooking Lake Formation	Frasnian	limestone (dolomite in the Rimbey-Meadowbrook reef trend)

Northeast Alberta

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

Sub-unit	Age	Lithology	Max. Thickness	Reference
Grosmont Formation	Frasnian	limestone and dolomite, minor argillaceous dolomite, limestone, siltstone and shale
Ireton Formation	Frasnian	upper: calcareous shale and argillaceous limestone middle: fissile grey-green shale with calcirudite beds lower: massive and banded limestone with shale partings
Cooking Lake Formation	Frasnian	limestone: fossiliferous mudstone and wackestone, grainstone, stromatoporoid rudstone and floatstone

Relationship to other units

The Woodbend Group is conformably overlain by the Winterburn Group and conformably overlays the Beaverhill Lake Group. 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.