Jurassic and Cretaceous sediments form a northward-thinning wedge of 5,000 ft maximum thickness that occupies 125,000 sq mi in south Saskatchewan. Significant petroleum production began in the 1940s. New reservoirs were located each year to total, by the end of 1969, 73 main pools in 6 principal producing units, yielding 337,089,144 bbl of crude oil and 435,851,579 Mscf of natural gas from depths of 750 to 4,700 ft.

Middle Jurassic beach and channel-fill, marine sandstones and carbonates, enclosed in less permeable carbonates and fine-grained clastic rocks yield medium-gravity oil in southwestern Saskatchewan and are prospective both west of the oil-field trend and in southeastern Saskatchewan. Medium-gravity oil also is produced in southwestern Saskatchewan from Upper Jurassic marine sandstones forming updip mesas, buttes, and interfluves beneath a basal Cretaceous cover of locally permeable and productive continental deposits. Production of heavy oil and nonassociated natural gas is obtained where deltaic sandstones of the Cretaceous interdigitate with marine shales. The sequence is prospective throughout central Saskatchewan, particularly where sandstone-body trends may be related to major str ctural features. In west-central Saskatchewan, light oil and nonassociated gas are produced from sandstone bodies of good economic potential. These sandstones are hydraulically isolated within a thick sequence of Lower Cretaceous marine shales and exhibit structural features that closely reflect the texture of the dissected

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pre-Cretaceous surface. Nearshore marine and continental-fluviomarine sandstone bodies of Late Cretaceous age yield nonassociated natural gas in western Saskatchewan; the best prospects appear to be at the base of this sequence in southwestern Saskatchewan.

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