STRATIGRAPHIC CONTEXT OF DOLOMITE IN THE STE GENEVIEVE LIMESTONE OF SOUTH CENTRAL KENTUCKY

It is well known that secondary (or diagenetic) dolomite is common in the early Paleozoic rock record. The majority of interest in dolomitic reservoir rocks has focused naturally on where it is prevalent such as in classic Cambrian-Ordovician sections (e.g., Ellenberger Group and Knox Group). Middle to Late Paleozoic rocks in contrast, have been studied less but where they have been studied, focus has been on diagenetically altered carbonates associated with MVT (Mississippi Valley Type) ores. The Mississippian-aged Ste Genevieve Limestone of south central Kentucky is not known to contain significant MVT ores but nonetheless is a focus of study for dolostone and baroque dolomite that may aid us in better understanding the constraints or controls on dolomitization.

Exposures provided by road cuts approaching one kilometer in length near Bowling Green provide excellent stratigraphic, textural and petrographic context documenting the nature and distribution of vugular dolomite, dolostone, and dolomitic limestone intervals. Our field work documents dolomitic vugs occurring in rocks possessing depositional textures that range widely from mudstone-wackestone to packstone-grainstone units. Generalized sedimentological and stratigraphic commonalities appear to be that dolomitizing fluids migrated in relatively high permeability rocks and such units are dolomite rich where they are capped by or in facies contact with relatively low permeability units. Vuggy dolomite however is not limited to “fluid carrier” beds but is present in muddy to grainy carbonates. A preliminary model suggests dolomitization of texturally diverse units is possible but only because significant carrier beds provided the means for such calcite-to-dolomite transformation. Additional work incorporating isotopic studies could provide for better understanding the nature of dolomite mineralization in these Mississippian carbonates.