In southern Saskatchewan and Manitoba the interval between the late Paleozoic and late Jurassic epeirogenies is represented in stratigraphic order by continental redbeds, evaporites, carbonates, and clastics. The sequence is in excess of 1,400 feet thick in south-central Saskatchewan and thins north, west, and east. Depositional and erosional thinning are complementary and the northern limits are determined by late to post-Jurassic truncation.

The system was divided (Milner and Thomas, 1954) into the Watrous, Gravelbourg, Shaunavon, and Vanguard formations, each representing widely recognizable lithologic units.

Proof of Jurassic age is available for the Gravelbourg, the Shaunavon, and Vanguard formations. These formations together appear to represent the Bajocian to Kimmeridgian time interval. The evaporites of the Watrous formation possibly represent the lower Bajocian or earlier Jurassic stages. Recent findings, still unpublished (Peterson, 1955), indicate that rocks of Triassic age may be included in the lowermost continental sediments of the Watrous.

A minor unconformity of Middle Jurassic age is indicated by the occurrence of chert on top of marine carbonates of the Gravelbourg. The evidence for this unconformity is strongest in central and southeast Saskatchewan. There the anhydrite of the Watrous formation thickness markedly and the evaporite conditions appear to have lasted into a higher stratigraphic level than in western Saskatchewan. In the same area the marine sediments above the unconformity thin and gradually change facies. The carbonates to the west are substituted by clastics, and coarse clastics appear in increasing

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amounts in an easterly direction. It would appear that a separate basinal area existed toward the end of Middle Jurassic time in Manitoba, receiving clastic sediments from the north and east.

The Shaunavon formation can not be traced lithologically in this facies district but approximately equivalent picks can be made from electric and radiation logs. The lithologic character of the uppermost Gravelbourg, Shaunavon, and Vanguard formations in Manitoba resembles closely that of the Sundance formation in North and South Dakota.

Callovian time is represented by the lower part of the Vanguard formation. During this time uniform basinal conditions were established across the entire area. A slight unconformity, recognizable in western Saskatchewan, marks a change from marine to brackish conditions which must have taken place in middle Oxfordian time. In the center of the basin 150 feet of marine middle Vanguard represent the Oxfordian interval. The upper Vanguard is partly marine, partly brackish and contains Kimmeridgian fauna. The lithologic character of the upper Vanguard, and the fact that it contains reworked fragments of older Jurassic faunas, indicate redeposition of material from the truncated basin flanks into the center.

The hiatus between Kimmeridgian and Lower Cretaceous is represented by a major unconformity which marks the top of the Jurassic system in Saskatchewan.

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