Petrographic And Geochemical Attributes Of Silurian And Devonian Dolomitized Formations In The Huron Domain, Michigan Basin

This study provides a thorough examination of dolomitization and other related diagenetic processes in Silurian and Devonian carbonates of the eastern side of the Michigan Basin. Core samples from multiple deep boreholes were analyzed for petrographic, stable and Sr isotopes, fluid inclusions microthermometry and major, trace and rare-earth elements (REE) to characterize the nature of dolomitizing fluids, the paragegenesis of different types of dolomite, and the evolution of diagenetic pore fluids. Petrographic analysis indicates that both age groups are characterized by the presence of a pervasive replacive fine-crystalline (50-100µm) dolomite matrix (RD2 and RD3, respectively). In addition to these types, a coarse crystalline (\u3e500 µm) saddle dolomite cement (SD) filling fractures and vugs is observed only in the Silurian rocks. Geochemical and fluid inclusion data suggest that the diagenesis of Silurian and Devonian formations can be attributed to two distinct fluid systems: (1) an earlier Silurian system with a marked negative shift in δ18O and δ13C values (dolomite δ18O average: -6.72‰ VPDB; dolomite δ13C average: 1.12‰ VPDB), Sr isotopic composition slightly more radiogenic than coeval seawater, high temperatures (dolomite Th average: 110 ⁰C) and hypersaline signature (dolomite average: 26.8 wt.% NaCl eq); and (2) a later Devonian fluid system characterized by a less pronounced negative shift in δ18O and δ13C values (dolomite δ18O average: -5.74‰ VPDB; dolomite δ13C average: 2.99‰ VPDB), Sr isotopic composition in range with the postulated values for coeval seawater, lower temperatures (dolomite Th average: 83 ⁰C) and less saline signature (dolomite average: 20.8 wt.% NaCl eq)