Middle Albian to Santonian detrital sediments were deposited in a shallow sea east of the Rocky Mountain geosyncline. Two transgressive phases of dominant mud deposition were separated by a major regressive phase, represented by a north-eastward-thinning wedge incorporating conglomerate and sandstone.

The transgressive Joli Fou Formation is represented on the east by the Spinney Hill Sandstone, comprising cosets of planar sandy foresets and subordinate mudstone intercalations (proximal fluviomarine deposits). These grade westward into a succession of vertically repeated, sandy, fining-upward sequences (distal fluviomarine deposits) overlain by and passing laterally into mudstone. The fining-upward sequences comprise, in ascending order, planar sandy foresets, bioturbated sandstone, alternating sandstone and mudstone, and mudstone. The sequence probably reflects lateral migration of the tidal channels of an estuarine delta.

The regressive Viking Formation gave rise to deposits in which size fractionation through increase in the proportion of admixed mud northeastward is accompanied by progressive change in assemblages of sedimentary structures. A thick sequence of planar sandy foresets and subordinate mudstone intercalations (nearshore deposits) is replaced by clinobeds composed of coarsening-upward sequences (proximal shelf deposits), which northeastward grade to bioturbated, muddy sandstone (distal shelf deposits) and mudstone (shelf muds). The Flatten Lake sand displaying southwestward diminution of grain size along the erosional edge of the Colorado succession is referable to the regressive phase.

The pre-Cenomanian (Big River Formation) of the late transgressive phase is predominantly mudstone, replaced northeastward by fine-grained, horizontally laminated and micro-crosslaminated sandstone and bioturbated sandstone, with abundant discontinuous mudstone intercalations (St. Walburg Sandstone). These beds are succeeded by a thick mudstone incorporating northeastward-thinning units rich in bioclastic debris: a basal unit rich in fish remains (fish-scale marker) and 2 main calcareous units containing coccolith aggregates and pelecypod debris (Greenhorn and Niobrara equivalents). The bioclastic debris commonly is in thin, graded layers passing upward into mudstone. Lateral size fractionation within the units occurs by progressive decrease in proportion of sand and silt and concomit nt increase in mud content.

The principal agents of sediment transportation recognized are tidal currents occasionally augmented by storm-surge waves giving rise to both laterally migrating channels and large-scale sand ridges. Mass movement of sand downslope apparently was confined to local salt-solution sinks.

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