Which of the following is a dolomitization model?

• A. Metamorphic
• B. Evaporative
• C. Sedimentary
• D. Igneous

Answer: (B)

Dolomitization is the diagenetic replacement of calcite by dolomite minerals when magnesium-rich fluids interact with carbonate rocks. In the evaporative model, this process is driven by brines formed as seawater evaporates in coastal, arid environments like sabkhas and tidal flats. As water evaporates, magnesium becomes concentrated in the remaining brine, which then circulates through porous carbonate rocks and slowly replaces calcium with magnesium to form dolomite (CaMg(CO3)2). This setting—Mg-rich evaporative fluids driving replacement—best explains many coastal dolostones and their textures. Metamorphic or igneous routes require high-temperature or deep-fluid conditions not typical of shallow diagenesis, and a vague sedimentary description doesn’t specify the fluid source needed for dolomite formation.