Sedimentology and diagenesis of middle devonian winnipegosis reef complexes Dawson Bay, Manitoba

Winnipegosis reef complexes probably consist of coalesced buildups, 75 to 100 m thick. They occur on a platform, 10 to 15 m thick. Basin sediments, 10 m thick, surround the complexes.Six facies are identified: (1) platform (lower and upper platform subfacies); (2) buildup interior; (3) buildup flank (laminated, bioturbated, cemented subfacies); (4) organic rim; (5) stromatolite cap; (6) basin (Brightholme, Ratner Members).Diagenesis occurred in four diagenetic environments: (1) open marine; (2) subaerial/meteoric; (3) restricted marine/shallow subsurface; (4) deeper subsurface. Fibrous cements occur in the cemented subfacies. Calcrete horizons with pendant cements formed in the stromatolite cap facies. All sediments are dolomitized.Isotopic data suggest that dolomitization occurred in the restricted marine and shallow burial environments in fluids derived from normal to slightly hypersaline Middle Devonian marine waters. Dolomitizing fluids derived from either the mechanical compaction of encasing evaporites or deeper formation waters were probably funnelled into the buildups.Minor fracturing and calcite cementation occurred in the deeper subsurface. Dedolomitization and calcitization of evaporites probably occurred at greater depths