In this study, we present a detailed investigation of C-O-S-Sr isotope systematics and elemental analysis of secondary sulfates and associated host rock carbonates of Cambrian to Devonian sedimentary successions along the eastern flank of the Michigan Basin, Ontario. This study evaluates the diagenetic evolution of pore fluids and their sources in fracture-fill and replacement sulfate minerals within low-permeability carbonate units in the Michigan Basin. Secondary sulfates, represented by gypsum and anhydrite, contain various petrographic types, represented by vug- and fracture-filling fibrous anhydrite in the Cambrian (δ18O vary between 16.8 to 17.6 permil VPDB and δ 34S 28.3 to 29.0 permil CDT, 87Sr/86Sr ratios vary from 0.70834 to 0.70991, respectively) and Ordovician fibrous anhydrite (δ18O 16.8 permil, δ 34S 28.2 permil, 87Sr/86Sr ratios 0.70829). These phases display mainly uniform REE patterns with Y/Ho and Zr/Hf ratios, flat La*, Gd*, and Y* and enriched LREEs. Idiotopic satin-spar δ18O values vary between 4.0 and 8.3 permil, δ 34S 23.4 and 31.4 δ with 87Sr/86Sr ratios 0.70816-0.70866), xenotopic porphyroblast gypsum δ18O value vary between 4.5 and 13.3 permil, δ34S 22.6 to 33.1 permil with 87Sr/86Sr ratios of 0.70850-0.70880, alabastrine gypsum δ18O values vary between 4.2 and 11.7 permil, δ34S 23.1 to 26.9 permil with 87Sr/86Sr ratios of 0.70816-0.70876) and felted anhydrite δ18O values of 11.1 permil, δ 34S 27.4 permil with 87Sr/86Sr ratio of 0.70849). These geochemical proxies suggest a comparable sulfate-rich source for both age groups under similar geochemical conditions. Gypsum in the Silurian Salina Group display a wide range of REE values with Y/Ho, and Zr/Hf ratios, Nd/YbN and Pr/YbN, flat to strong Ce/Ce*, and flat to strong Eu/Eu* anomaly, Gd/LaN and Tb/LaN, Sm/LaN). These sulfates formed at burial from fluids of variable isotopic, chemical composition and temperatures. The sources of these fluids range from brines migrating from a deeper part of the basin forming anhydrite in the Cambrian and Ordovician sequences which were also affected by dolomitization and later hydrothermal fluid influx, to rehydration of gypsum at shallower burial depths and affected by salt dissolution and incursion of meteoric water during and following the Alleghenian orogeny.

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