Tunnel Mountain Formation


The Tunnel Mountain Formation is a geologic formation that is present on the western edge of the Western Canada Sedimentary Basin in the Canadian Rockies of western Alberta. Named after Tunnel Mountain near Banff, it was deposited during the Early Pennsylvanian sub-period of the Carboniferous period.

Lithology and stratigraphy

The Tunnel Mountain Formation consists of quartzose sandstone, interbedded with lesser amounts of dolomite, dolomitic sandstone in the lower part, and minor beds of quartzite in the upper part. In areas where they can be differentiated, the formation is subdivided into the three formations shown below in ascending order. Where they cannot be differentiated, the name Tunnel Mountain Formation is applied to the entire sequence.
The dolomite beds of the Tunnel Mountain sequence include scattered brachiopods and foraminifera.

Thickness, distribution, and relationship to other units

The Tunnel Mountain Formation is present in the front ranges of the Canadian Rockies of western Alberta, and reaches a maximum thickness of about 200 metres. It unconformably overlies the Etherington Formation or the Todhunter Formation of the Mississippian Rundle Group, and is conformably overlain by the Late Pennsylvanian Kananaskis Formation. In areas where the Kananaskis is not present, it is unconformably overlain by the Permian Ishbel Group.