Following deposition of the Success Formation, a high-relief (100 m) erosional surface developed on uplifted structural blocks. The paleotopography was highest in the southwest. From there, valleys radiated to the north, northeast and east across Jurassic and Mississippian strata before turning north and northwest across Devonian rocks. The thickness of Cantuar and Pense formation (Mannville Group) rocks which were deposited on this surface is therefore very variable, ranging from less than 30 m to more than 100 m locally and 240 m regionally. [Upper Cretaceous isopach map]
Regionally, rocks of the Cantuar Formation are products of a marine invasion that extended from the Arctic to the Williston Basin. In Saskatchewan, the seaway was relatively narrow and more estuarine in nature. Provenances were the Cordillera in the west, older strata forming topographic interfluves, and the Precambrian Shield to the north and northeast. Three major facies are recognized in Saskatchewan: a green biotite-chlorite facies in the southwest (Dimmock Creek and Atlas members)and in west-central Saskatchewan (Grand Rapids Formation); these grade eastward into the centrally distributed Clearwater facies of marine repeated sequences of black mudstones, bioturbated sandstones, grey mudstones and argillaceous sandstones, and well sorted sandstones interrupted by fluviatile and deltaic marine channel sandstones, lagoonal mudstones and thin coals; this facies grades eastward into kaolinitic quartzose sandstones feathering in from the Precambrian Shield and also characterizes the underlying McMurray-Dina Member deposited in fluviatile to estuarine conditions.
The unconformably overlying Pense Formation is of marine origin. Where fully developed, it contains four upward-coarsening sequences of mudstone, bioturbated mudstone-sandstone, and clean sandstone.
Rocks of the Colorado Group overlie those of the Mannville Group. They thicken from their eastern edge to about 500 m in the southwest, and are mostly dark grey to black marine shales. Subordinate sandstone units are sourced from the Rocky Mountain foreland in the west and from the Precambrian Shield in the north and east. For example, the Viking Formation of burrowed, poorly sorted and pebbly sandstone thins from about 55 m in the southwest to about 10 m towards the north, and shales out eastwards, whereas the Spinney Hill and St. Walburg sandstone units tongue in from the north and the Newcastle from the southeast. The Upper Colorado subgroup is made up of a lowermost calcareous shale known as the Second White Specks Formation in the west and as the Favel Formation in the east, overlain by noncalcareous shales of the Carlile Formation (west) and Morden Shale (east), with, at the top, the calcareous Niobrara Formation. Subordinate sandstone units (for example, the Medicine Hat sandstone) are present.
The Montana Group rests with slight unconformity on the Colorado Group, and also thickens to the southwest where it reaches a maximum of almost 400 m. The basal Milk River Formation of argillaceous siltstones and sandstones is host to Saskatchewan's main source of natural gas. It is overlain by interdigitating shales and sandstones named, from oldest to youngest, the Lea Park (marine shales), Judith River (fluviomarine to continental sandstones and shales) and Bearpaw Formations (marine shales). The Bearpaw Formation is succeeded, apparently conformably, by the Eastend, Whitemud, and Battle Formations, all predominantly of continental origin.
The youngest Cretaceous rocks disconformably overlie the Montana Group. They make up about 60 m of fluviatile and lacustrine sandstone, bentonitic shale and muddy siltstone of the Frenchman Formation, and contain dinosaur fauna.
The Frenchman Formation is conformably overlain by the Ravenscrag Formation of interbedded claystones, feldspathic sandstones, siltstones shales and coals of fluviatile to lacustrine origin. The Ravenscrag is Paleocene in age and is up to about 245 m thick.
Resting unconformably upon the Ravenscrag Formation in southwestern Saskatchewan are more than 170 m of conglomerates and sandstones of the Cypress Hills Formation (Oligocene). In places, up to about 15 m thicknesses of conglomerates and sandstones of the Upper Eocene Swift Current Formation and of the Miocene Wood Mountain Formation cap the Ravenscrag Formation.