Chemical and isotopic constraints for recrystallization of sedimentary dolomites from the Western Canada Sedimentary Basin

Mississippian shoal carbonates of Western Canada Sedimentary Basin are important hydrocarbon hosts. Dolomitization plays a major role in the evolution of reservoir porosity in these carbonates. This process varies across the basin and reflects, in part, divergent sources and chemistry of pore fluids. Dolomites from several petroleum reservoirs were analyzed for mineralogical, geochemical and isotopic variation. The data clearly demonstrate the progressive and complex recrystallization of dolomite during shallow and deep burial in modified marine, meteoric and burial fluids. These data include: change in crystal size, stoichiometry, cathodoluminscence characteristics, stable oxygen and carbon isotopic shifts and changes in radiogenic Sr isotopic composition. However, regional geology, tectonic history and fluid flow evolution play important roles in the diagenetic imprints and the degree of recrystallization. Early microcrystalline dolomite formed in normal marine and evaporative conditions in Mississippian carbonates from Western Canada Sedimentary Basin have undergone variable degrees of recrystallization, from pristine dolomite akin to Holocene sabkha dolomite with preserved mineralogical and chemical attributes to highly recrystallized mesodolomite, however still nonstoichiometric, but with highly altered chemical signatures. Careful attention should be made to local geology, hydrodynamics and fluid flow when investigating dolomite recrystallization in sedimentary basins.