The Jurassic rocks of northern Yukon and westernmost Northwest Territories are entirely marine sedimentary strata deposited in a somewhat unstable epicratonic shelf setting at what was then the northwestern corner of the North American continent. The eastern and southeastern facies comprise a series of superposed sandstone and shale sequences which are thicker, more argillaceous, and more complete (in terms of the time they represent) to the west and northwest. They comprise the Bug Creek Group, and the Husky and Porcupine River formations. Disconformities between these sequences increase in number and magnitude toward the stable craton to the southeast and east. Thickness and facies trends suggest point sources for the introduction of sediment supply to the marine shelf environment, and redistribution on the shelf by marine currents. The sediment sources migrated southward through the Jurassic, in association with increased southward and southeastward episodic transgression of the craton. Equivalent strata to the west and northwest are in an entirely siltstone and shale facies, the Kingak Formation. Every stage of the Jurassic, and 33 fossil zones, are indicated by diagnostic ammonites or bivalves.