Marine Diagenesis of Shallow Marine Lime-Mud Sediments: Insights from dgrO18 and dgrC13 Data.
Shallow marine lime-mud sediments of the Ste. Genevieve Formation (Mississippian), in part of the Illinois Basin, underwent at least three diagenetic changes: (i) local dolomitization in seawater or a brine, producing dolostone having average deltaC(13) of +2.5 per mille and deltaO(18) of +1.9 per mille (versus PDB-1); (ii) more usually cementation of unreplaced CaCO(3), in intrasediment seawater, yielding isotopically marine lime mudstone mainly composed of calcite, 4-micron or finer, with deltaO(18) of from -1 to +1 per mille; (iii) later partial alteration of CaCO(3), in permeable dolomitic rocks, by isotopically "lighter" waters, to calcite with an estimated deltaO(18) of -10 per mille or less. Isotope data appraised by petrographic analysis thus suggest "submarine" cementation of these carbonates in shallow marine conditions.
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