Abstract

The Ratner Member was previously included in the Middle Devonian Winnipegosis Formation of the Elk Point Basin. Recent studies, however, have demonstrated that the Ratner Member was not genetically related to the Winnipegosis Formation in terms of depositional environments and thus should not be part of the Winnipegosis Formation. In this paper we propose that the Ratner Member be raised to formational status. In the northern portion (Saskatoon–Quill Lake area) of the Saskatchewan sub-basin, the type section of the Ratner Formation comprises three vertically stacked brining-upward successions, each of which consists of a basal unit of carbonate laminite, a middle unit of interlaminated carbonate and anhydrite, and a capping unit of enterolithic bedded anhydrite. Compared to the type section, the Ratner Formation in the southern part of the Saskatchewan sub-basin has a number of distinct features, including: (1) a much darker grey colour because of its greater proportion of organic-rich partings, (2) more pervasive development of fine, crinkly lamination or cryptalgal structures, (3) considerably less common enterolithic anhydrite beds, (4) more common calcitization of anhydrite, whereby anhydrite laminae were altered to coarsely crystalline white dolomite, (5) less common occurrences of contorted, interlaminated dolomite and anhydrite caused by displacive anhydrite growth, and (6) predominance of single-cycled laminite succession. Most of these characteristics, especially the darker-grey colour and general lack of multiple cycles, are interpreted as the result of deposition of the laminite in a deeper-water setting in the southern part of the Saskatchewan sub-basin, where more frequent and prolonged plankton blooms and fewer desiccation episodes would have prevailed. The Ratner Formation is interpreted to have formed during the transitional phase of the Elk Point Basin from a reefal environment to a large intracratonic salina.

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