The Williston basin lies within the so-called stable cratonic interior and would not be expected to have had the same intensity of tectonic activity as is generally considered to be characteristic of cratonic margin sedimentary basins. Local paleotectonic controls on sedimentation are much more subtle, thus sediment distribution patterns are commonly related to major regional structural elements such as the ancestral Williston basin and the Sweetgrass arch. From time to time, however, other structural features appear to have been effective controls on sediment distribution patterns. In southern Saskatchewan, one of the most active of these was the Swift Current platform. This feature appears to have been sufficiently positive during early Paleozoic time to have caused a d stinct thinning of those sediments over it. But it is in early Middle Devonian time that it plays a more prominent role. During the time the Winnipegosis Formation was being deposited, the platform acted as a core for an accreting carbonate wedge that forms the southwestern margin of the Elk Point basin. Progressive inundation of the platform during the remainder of the Devonian made it a part of a broad, shallow shelf sea. However, it was a site of active local salt solution during that time, and may have been as well the locale for repeated accumulations of anhydrite deposits, particularly during the time the Duperow Formation was being laid down. The platform was mildly positive during other periods of sedimentation, as well as during periods of erosion. It was a site of widespread sa t solution during Mesozoic time, which was also its time of major tectonic fluctuation, as well as being the period when it had the most significant influence on sedimentation.

Southeastern Saskatchewan is the locale for some significant regional gravity and magnetic anomalies which appear related to exposed structural zones in the Precambrian Shield. A major gravity anomaly on the extreme eastern side of the province is on trend with the Nelson River zone of Manitoba and a magnetic anomaly (Camfield-Gough conductor zone) can be traced to the Wollaston trend in north-central Saskatchewan. The existence of these two trends suggests that the regions proximal to them may have been tectonically active during various geologic periods. The Camfield-Gough zone is particularly significant in that it lies along the axis of the Hummingbird trough, an area affected by basement-controlled early salt solution, and it extends southward into the United States, where it is lanked by a number of local multizone oil-producing structures in North Dakota and Montana. The proximity of these structures to that conductor, which is thought to be a suture between two Proterozoic plates, suggests there is a relationship between them. Isopach and isochron maps have been used to show that these structures have been active during various geologic periods. Similar mapping techniques may show that similar structures are present in southeastern Saskatchewan.

End_of_Article - Last_Page 1345------------