The Nisku Formation in the Alberta subsurface consists of bank facies, reefal facies, and basinal/slope facies along the Outer Shelf. The bank facies was not previously recognized, and is here designated the Dismal Creek Member. Most buildups are coral-bearing mudmounds. / The Nisku Formation was affected by more than twenty diagenetic processes, most notably by dolomitization and anhydritization. The buildups were partially lithified in shallow phreatic environments, and some were subaerially exposed. Dolomitization took place at depths of about 300 to 1000 m by fluids that were derived mainly from the underlying Ireton Formation. Most of the anhydrites formed during the last stages of and/or after dolomitization. After oil emplacement, thermochemical redox reactions between hydrocarbons and sulfates resulted in partial removal of anhydrite in the deepest buildups, and the formation of 'dead' oil, sour gas, replacive calcite, saddle dolomite, celestite, and native sulfur. Diagenetic changes after maximum burial were very minor.

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