ABSTRACT

The names Whitkow Salt, Shell Lake Gypsum and Quill Member were introduced informally by Jordan (1967, 1968) for rock-stratigraphic units within the Middle Devonian Prairie Evaporite Formation of Saskatchewan. These rock units are present throughout central and south-central Saskatchewan, in a similar stratigraphic relationship to that depicted by Jordan. The Whitkow Salt and Shell Lake Gypsum are given member status and are considered to constitute the lower Prairie Evaporite Formation. The Quill Member of the Shell Lake Gypsum (Jordan, 1968), is re-named the Quill Lake marker beds of the Shell Lake Member.

The finely laminated carbonate mudstone and associated anhydrite, which is present between upper Winnipegosis banks, is here named the Ratner Member of the Winnipegosis Formation. The Ratner Member is the uppermost member of the Winnipegosis Formation in interbank positions, and is overlain by the Whitkow Member of the Prairie Evaporite Formation.

Basinal areas between carbonate banks of the upper Winnipegosis became the sites of accumulation of the lower Prairie Evaporite which reached thicknesses of 300 ft and more. The Whitkow Member, which consists mainly of halite in basinal positions, changes to anhydrite in a bankward direction and merges with anhydrite of the Shell Lake Member on the flanks of banks, where anhydrite, up to 244 ft thick, occurs. Thick anhydrite sequences have accumulated preferentially on the southeast sides of carbonate banks. Apparently the banks influenced deposition between them and may have been the cause of local marine restriction and evaporite formation.

A distinctive pisolite unit, 10 to 30 ft thick, is present on upper Winnipegosis banks and extends into the Shell Lake Member in basinal positions, where it is represented by the Quill Lake marker beds. Thus, there were two phases of carbonate-bank development, one before deposition of anhydrite and halite of the Whitkow Member, and one after. The Quill Lake marker beds are most fully developed on the south and southeast sides of carbonate banks, within thick sequences of anhydrite, and pinch out completely in basinal areas away from banks.

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