Blairmore Group


The Blairmore Group, originally named the Blairmore Formation, is a geologic unit of Early Cretaceous age in the Western Canada Sedimentary Basin that is present in southwestern Alberta and southeastern British Columbia. It is subdivided into a series of formations, most of which contain plant fossils. In some areas it contains significant reservoirs of natural gas.

Lithology

The Blairmore group includes the conglomerate and quartzose sandstones of the Cadomin Formation at the base, and grades to sandstone, siltstone, mudstone, and limestone in the overlying formations. The Beaver Mines and Ma Butte Formations in the upper part of the group also include minor beds of bentonite and tuff.

Stratigraphy

The Blairmore Group is subdivided into the following formations from top to base:
FormationAgeLithologyMax
Thickness		Reference
Ma Butte FormationEarly Cretaceousmudstone, siltstone, very fine-grained sandstone, bentonite and tuff
Beaver Mines FormationEarly Cretaceousgreenish grey sandstone and mudstone; minor conglomerate, bentonite and tuff
Gladstone FormationEarly Cretaceousargillaceous limestone and calcareous shale
Cadomin FormationEarly Cretaceousconglomerate, sandstone

Some early workers included the Crowsnest Formation, which overlies the Ma Butte Formation, at the top of the Blairmore Group, but that practice has been abandoned.

Distribution and Thickness

The name Blairmore Group is applicable in the foothills and mountains of southwestern Alberta and southeastern British Columbia, from the Canada–United States border northward to the Clearwater River. The equivalent strata north of the Clearwater River, which were originally assigned to the Blairmore Group, differ in that they contain major coal deposits and they have therefore been reassigned to the Luscar Group.
The Blairmore Group has a maximum thickness of about and thins from west to east.

Relationship to other units

The Blairmore Group unconformably overlies the Kootenay Group and is gradationally overlain by the Crowsnest Formation or, where the Crowsnest Formation is absent, is disconformably overlain by the Alberta Group. It is equivalent to the Luscar Group north of the Clearwater River and to the Mannville Group in the plains to the east.

Environment of deposition and paleontology

The Blairmore Group is an eastward-thinning wedge of clastic sediments derived from the erosion of newly uplifted mountains to the west. The sediments were transported eastward by river systems and deposited in a variety of braided stream, river channel, floodplain, and coastal plain environments along the western edge of the Western Interior Seaway. Its formations include a variety of plant fossils, trace fossils, bivalves, and mircofossils.