Fe-poor dolomite and anhydrite form a mineralogical succession of replacement after detrital quartz, lesser amounts of potassium feldspar, and, rarely, plagioclase, in a dolomitized carbonate platform margin (Leduc Formation, Frasnian in age) in the Peace River Arch region, Alberta. Preferential, pronounced dolomite replacement occurs within the platform in areas in which fractures controlled migration of deep burial (>700) fluids. Two types of dolomite replacement are common. Type 1 differs little from the host microcrystalline dolomite; with alteration, a grain is transformed into domains surrounded by dolomite and the definition of the original grain boundary is lost. Type 2 replacement occurs where microfractures (<20 mum) filled with brightly luminescent dolomite intersect silicate grains, and where fluid from these fractures moved laterally into the adjacent host rock. In context of the known paragenetic sequence of diagenesis in the platform, Type 1 alteration occurred at temperatures less than about 60-degrees-C, possibly in the presence of fluids carrying early-stage, aqueous-phase hydrocarbons. Type 2 replacement appears to have formed at greater burial depths (> 1 km) in the presence of warmer fluids (> 100-degrees-C). The extent of alteration (absent to greatly decreased) by dolomite in other parts of the platform suggests that lateral temperature and chemical gradients may have been established during lateral migration of fluids from fracture zones. The change from dolomite to anhydrite as replacement mineralogy required a change in bulk saturation of pore waters as the platform was further buried; an association with fractures remains uncertain. Inter- and intraparticle variation of the extent of silicate alteration reflects differences in particle microstructure as well as force of crystallization. Complete alteration by Type 1 dolomite locally camouflages the original distribution of silicate detritus. This type of diagenesis should be expected in other carbonate platforms, especially those containing variable amounts of mixed siliciclastic and carbonate sediments. If not recognized, this type of diagenesis could add considerable bias to interpretations of carbonate platform aggradation given the geological significance of sand-size detritus in carbonate platform margin settings with respect to controls on across-shelf transport of sediment during changes in sea level and climate.