ABSTRACT

The Middle Devonian Prairie Evaporite, comprising up to 215 m of halite and potash minerals, and no more than 3200 m deep, overlies the Winnipegosis Formation in southeastern Saskatchewan. Numerous Winnipegosis reef-like accumulations up to 110 m thick have been found surrounded and covered by salt. The main structural pattern of the Williston Basin's northeastern flank is a homocline moderately deformed by faults, hinge lines and folds. Elongate trough and sub-circular (chimneylike) salt-collapse structures and structural depressions over the Winnipegosis reefs are superimposed on the main homocline structure. The structures have been generated as a result of multistage collapse, reflecting salt solution. The elongate trough structures have been initiated by Laramide faults and hinge lines, reflecting rejuvenation of basement linear features, or differential subsidence in the Williston Basin. The subcircular collapse structures and the structural depressions over the Winnipegosis reefs have been initiated by salt flowage. The salt compressed between the Winnipegosis reefs and the Dawson Bay carbonates flows laterally. The salt's lateral flow generates structural depressions over the reefs and salt pillows next to the reefs. Consequently, some of the salt pillows are developed as sub-circular collapse structures. The salt movement and the features of the Williston Basin's salt structures generated by salt flowage have some similarities to the salt structures of the southern British Sea.

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