| Abstract | From l ate 1967 to early 1969, the Duval Corporation sank two s hafts, 20 feet in diameter and 3, 500 feet deep, near Saskatoon, Saskatchewan. The object was to recover the sylvite ore of potash from
the Middle Devonian Prairie Evaporite Formation, a unit within the Middle and Upper Devonian carbonate sequence. The Devonian succession is overlain unconformably by elastic Cretaceous strata which, in turn, are overlain by Pleistocene till.
The
thick Prairie Evaporite salt represents the culmination of an early cycle in a success ion of clastic-carbonate-evaporite cycles that become successively thinner upward in the sequence and disappear entirely at the end of Middle Devonian time.
The overlying Dawson Bay Formation comprises a second cycle. The formation consists of basal dolomitic red beds, a middle marine limestone, and an upper evaporite composed of anhydrite with a trace of halite.
The Souris River Formation,
composed of three members, overlies the Dawson Bay. The lower or Davidson Member consists of a basal elastic unit ("First Red Beds"), a middle argillaceous limestone unit, and an upper intertidal and supratidal sequence preceding the final beds of
halite. The overlying Harris and Hatfield Members each contain several incomplete cycles interrupted by evaporitic supratidal phases. An anhydrite in the lower part of the Hatfield Member contains inclusions of chert.
The Upper Devonian Duperow
Formation is distinguished by alternating argillaceous and non-argillaceous limestones that form the basis for subdivision into the Saskatoon, Elstow, Wymark and Seward Members. A solution cavity occurs in interbedded carbonate and elastic strata of
the Wymark Member. The Birdbear Formation, at the top of the Devonian is truncated by the sub-Cretaceous unconformity.
The Cretaceous sequence evolves, in ascending order, from the aggrading nonmarine, basal (Cantuar Formation) sandstones above
the unconformity; through transgressive intertidal and subtidal (Pense Formation) shaly sandstones; to shallow marine (Ashville) shale; and, in the basal part of the Upper Cretaceous, kerogenous ("white-speckled") oil s hales. Cordilleran silt and
fine sand modify the overlying thick Upper Cretaceous (Lea P ark) shale sequence and dominate the youngest beds composed of non-marine sandstones of the Belly River Formation.
Unoxidized till is covered by a mantle of outwash material.
A
detailed lithologic log (Appendix I) of the succession in the shaft above the Prairie Evaporite is keyed to fossil localities as well as to induction, radiation and sonic wireline logs. Appendix II illustrates the mineralogy of the insoluble
components of the upper part of the evaporite as determined by X-ray diffraction. The stratigraphic summary suggests new interpretations of contact relationships, structure and sedimentation, and contains reports on paleontology including
correlations and age determinations. |