Sedimentary depositional environment of the Prairie Evaporite Formation, Saskatoon region, Saskatchewan

Abstract

This thesis attempts to reconstruct the environments in which the potashbearing, Prairie Evaporite Formation (Middle Devonian) of the Elk Point Basin was deposited, using preserved primary sedimentary features. Evidence from cores, thin sections and mine obsetvations indicates that sedimentation was not continuously subaqueous, but episodic, with periods of desiccation recorded throughout the formation. Deposition of the Prairie Evaporite Formation began with a major drop of the sea-level, leaving most of the basin desiccated and the carbonate mounds of the underlying Winnipegosis Formation exposed. Fed by seepage through barriers, the region became a carbonate mudflat environment with patchy brine pools between the carbonate mounds, and this was succeeded by a salt-pan environment. The Whitkow Member, which was deposited under these conditions, filled approximately half of the original relief of the intermound depressions. Subsequently, sea-level rose sufficiently high to flood the area episodically, resulting in sedimentation of the Shell Lake Member in intertidal to supratidal environments. The filling of the basin and concomitant regression of the sea brought the area under a more continental influence during the Leofnard Member deposition. Except for the northernmost part, where salt-pan environments persisted, most of the study area developed into a pericontinental salt lake environment. A considerable amount of potash may have been deposited with halite syndepositionally, probably during the peak of the evaporative conditions, and was prone to early diagenetic alteration under periodic subaerial conditions. The model presented provides a more dynamic and more realistic picture of the changing depositional environments. This not only leads to a better understanding of the deposit itself, but also may help to overcome some of difficulties in potash mining that relate directly to the conditions during the time of deposition. Note:This thesis contains maps that have been sized to fit the viewing area. Use the zoom in tool to view the maps in detail or to enlarge the text.