Abstract
Dolomitic carbonate rock units from a variety of Phanerozoic localities and depositional environments throughout North America were evaluated with respect to their dolomite content and dolomite composition by X-ray diffraction analysis. Dolomite compositions range from 48 to 57 mole% $$CaCO_{3}$$ with well-defined modes at 51% (nearly stoichiometric dolomite) and 55% (distinctly calcian dolomite) $$CaCO_{3}$$. Values of percentage of dolomite also exhibit a pronounced, albeit less well-defined, bimodal distribution with modes at 97% (dolostones) and 20% (dolomitic limestones) dolomite. Similar distributions characterize most other published data on Phanerozoic dolomitic carbonates. These data suggest that two separate processes may lead to two distinct populations of sedimentary dolomite: (1) dolomitic limestones originate in diagenetically closed systems during magnesian calcite dissolution-calcite and dolomite precipitation reactions, and (2) dolostones originate in diagenetically open systems during th...
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