The stratigraphy, organic petrology, and depositional environments of the Middle Devonian Brightholme Member and Ratner Formation of south central Saskatchewan

The lithologies, lithofacies and organic facies of the Brightholme Member of the Winnipegosis Formation and the Ratner Formation of the Middle Devonian Elk Point Basin of south central Saskatchewan have been studied to interpret the paleoenvironment of this unique carbonate-evaporite sequence. 3D seismic data supplied by the Potash Corporation of Saskatchewan (PCS) provided spatial and geometric visualization models of the rock units such that a revised model has been developed for these units.; The Upper Member of the Winnipegosis Formation represents a complex network of small pinnacle reefs which collectively form a regional bank-like feature, rather than a "solid" true carbonate bank. The key difference from previous models is the complexity recognized within the inter-reef setting, previously interpreted to be a single bank feature (the "Quill Lake Bank") in the study area. This network of small pinnacle reefs had a major impact on wave energy, circulation, and water chemistry within this area of the Elk Point Basin, and as such controlled deposition and the resulting facies and distribution of the Brightholme Member and Ratner Formation.; The defining characteristics of the Brightholme Member are: (i) laminations of dark brown to black (organic rich) and yellowish brown carbonate, (ii) skeletal debris and calcareous algae-derived carbonate, dominantly wackestone to wackepackstone with some grainstone intervals, (iii) abundant structured organic macerals, dominated by the alginite Tasmanites. Thin section and organic petrology observations indicate the sediment is primarily pelagic, with both the carbonate and organic components likely being sourced by algal productivity. Secondary sediment in the Brightholme Member is derived from the associated mounds as previously interpreted.; The defining characteristics of the Ratner Formation include: (i) laminated texture made distinct by colour variation and organic material at the partings, (ii) distinct brining upward cycles consisting of laminated dolomite, interbedded dolomite/anhydrite, and bedded-nodular or mosaic anhydrite, (iii) the total absence of skeletal debris, (iv) limited to inter-reef, basinal areas. The proposed depositional model for the Ratner Formation is a network of shallow water (10-40 m depth) salinas with varying degrees of connection, circulation, and brine concentrations. Distribution and sediment type of the Ratner Formation is interpreted as being controlled by local variations in water chemistry within the Elk Point Basin created by circulation patterns and the influence of the Upper Winnipegosis mounds, rather than variations in sea level.; Reflected light fluorescent microscopy of the Brightholme Member and Ratner Formation was used to characterize and classify the dispersed organic matter into 5 different organic facies. There is excellent correlation between the paleosetting based on organic facies and the paleosedimentary environment interpreted from the lithology and facies of the carbonates and evaporites of the two units. Previous organic facies models for petroleum source rocks in the Western Canada Sedimentary Basin have been revised to accommodate the steep-sided nature of the Upper Winnipegosis buildups and rapid transition from near shore to basinal environments.