ABSTRACT

Subsurface dissolution of the Middle Devonian Prairie Evaporite is a major structure-forming process in south-central Saskatchewan. The dissolution phenomenon is a multistage process of salt removal that entails collapse of the overlying sedimentary column and accelerated sedimentation into surface depressions produced during collapse. The process is important because it affects the sedimentation and diagenesis of younger strata and may produce structures suitable for petroleum entrapment.

Linear dissolution trends which migrate laterally with time occur within the South Regina and Hummingbird Troughs. Analysis of structure contour, isopach and residual maps has yielded a chronology of dissolution events. Salinities (TDS) increase and hydraulic heads decrease as one moves eastward from a large salt-free area into the main salt body. Both composition of subsurface waters and fluid pressures suggest an upwelling of formation waters within the Hummingbird Trough.

Within the map-area, two differing situations appear to affect salt dissolution. In the northeast, salt removal appears to be localized above porous and permeable Winnipegosis mounds of the Elk Point Basin. In the southwestern part of the study-area, underlain by the Winnipegosis marginal carbonate shelf, it seems likely that dissolution was localized by fracturing associated with diastrophic (deep-seated) structures.