The black shales of the Exshaw Formation are rich in organic matter and are one of the most important petroleum source rocks of the Western Canada Sedimentary Basin.

The lower shales are dark grey to black, thin-bedded to laminated, and rich in organic matter, with scattered sulphide and phosphate nodules.

[1][5] The upper member consists of brown-weathering, medium- to thick-bedded, calcareous and dolomitic siltstones with subordinate silty limestones.

[1][6] Bioturbation by burrowing marine organisms is common and indicates that they were deposited in an oxygenated environment, closer to the paleocoastline than the lower black shales were.

It is a widespread unit that can be seen in outcrop at many locations in the Canadian Rockies, and it is present in the subsurface from the prairies of northern Montana to southern Northwest Territories.