At the proposed type section near Mount Costigan in Banff National Park, the carbonates of the Palliser Formation are more than 255 m thick and include, in the upper part, a subtle, erosional unconformity. This unconformity is correlated with the sub-Big Valley unconformity of the Alberta plains. A subdivision of the Morro and Costigan members in lower and upper parts is proposed to accommodate two new units: A basal dolostone unit (the lower Morro sub-member) and an upper, fossiliferous unit which overlies the unconformity (the upper Costigan sub-member). The dolomitic, lower Morro sub-member is 34.4 m thick and includes a basal, intertidal facies. It does not contain diagnostic fossils. The marine, shallow water carbonates of the upper Morro sub-member are 94.5 m thick and include brachiopods of the Basilicorhynchus Zone and conodonts of the Lower crepida to Lower marginifera zones. The peritidal and evaporitic carbonates of the lower Costigan are about 34 m thick and do not contain diagnostic fossils. The upper Costigan ranges in thickness between 6 and 8 m and is composed of marine, shallow water limestones that include minor depositional discontinuities. It is characterized by brachiopods of the Gastrodetoechia Zone and conodonts of the trachytera to Lower expansa zones.