Increasing dolomite abundance with age (relative to limestone) has long been accepted as one of the general truisms of sedimentary geology, a relationship which suggests that dolomitization is a cumulative process occurring slowly over the full burial history of a carbonate sequence. However, reevaluation of data in support of this assumption indicates that, although relative dolomite abundances do change significantly throughout Phanerozoic carbonate sequences, no data set demonstrates any direct correlation between dolomite content and age, whereas tabulation of available data does suggest greater amounts of dolomite formation during periods of continental flooding. Global mass balance calculations of potential magnesium sources also indicate that most dolomite has formed from marine or marine-derived fluids at the Earth's surface. This conclusion is indirectly supported by significant short-term (period scale) changes in Phanerozoic dolomite abundance, a variation which would be more attenuated if dolomitization were dominantly a burial process. Dolomitization may be enhanced during times of global transgression, higher atmospheric pCO 2 , and lower calcite saturation state in shallow-marine settings.