Most Precambrian dolostones are considered here to represent replacement of original limestone or calcareous sediment. The sequential development of dolomite is recorded in a middle Precambrian carbonate-clastic platform succession in the Belcher Islands. The timing of dolomitization ranges from penecontemporaneous (eogenetic) to late burial (mesogenetic). The platform sequence has three distinctive megacycles: I) a siliciclastic-dominated phase, wherein pisolitic tufas formed in the upper reaches of a supratidal flat and II) a mixed clastic-carbonate and stromatolitic carbonate phase, where penecontemporaneous dolomite formed under conditions of high evaporation rates and high salinity, and III) a stromatolite buildup-slope-basin phase where incipient dolomitization may have taken place within a mixed seawater-freshwater aquifer system. However, pervasive dolomitization of the platform sequence did not occur until a later stage of burial diagenesis, and postdated the main stage of silica diagenesis. Recrystallization resulted in only minor crystal enlargement; stylolitization produced local crystal growth but was not responsible for pervasive dolomitization. Fracture-filling dolomite accumulated as a result of deformation and uplift during the Hudsonian Orogeny.--Modified journal abstract.