Of the Triassic-Jurassic Systems, only Lower Triassic was deposited in southern Saskatchewan, North Dakota, and southern Montana. Thicknesses in excess of 700 ft are present in western North Dakota reflecting the depocenter of restricted salt basins. On the basis of lithologic correlation, the lower Watrous Formation in Saskatchewan is considered to be equivalent to the upper part of the Spearfish Formation in North Dakota. Lower Middle and Upper Triassic rocks in western Alberta are of marine origin, attain thicknesses in excess of 4,000 ft, and produce oil and gas.
Jurassic rocks are widespread throughout the map area as a result of Jurassic seas transgressing from the northwest along the Eastern Cordillera, then spreading east across Montana into the Williston basin. Lower Jurassic formations in the map area are restricted to southwestern Alberta. Middle Jurassic formations are the most widespread, and are thicker than 500 ft in a depocenter in southeast Saskatchewan and northwest North Dakota. Similar thicknesses are present in the Alberta trough. Upper Jurassic sediments also are widespread, reaching thicknesses of 7,000 ft in the Eastern Cordillera of Alberta and more than 700 ft in eastern Montana.
Economic deposits of coal, gypsum, oil, and gas occur in Middle and Upper Jurassic formations. Oil is the most significant, particularly in southwestern Saskatchewan where 20 fields are estimated to have ultimate production of 347 million bbl. These fields produce in stratigraphic traps, primarily from sandstone associated with shoreline facies.