Cross-bedded oolitic grainstones in the Ste. Genevieve Limestone (Mississippian) of the Illinois basin have generally been considered to be shallow marine. However, fine- to medium-grained cross-bedded grainstones of mixed clast type in the Ste. Genevieve of Harrison County, southern Indiana, are here interpreted to be of eolian dune origin on the basis of small-scale sedimentary structures, particularly climbing-wind-ripple structures. In addition, subaerial exposure of surfaces at the tops and bases of the eolian units is indicated by pedogenic features such as in-situ breccias and rhizoliths. Associated skeletal and oolitic grainstones of marine origin are distinguished from the eolian grainstones by the presence of pebble-sized fossils. The presence of several intervals of eolian deposits in the Ste. Genevieve is probably a result of eustatic sea level fluctuations.
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Mississippian Oolites and Modern Analogs
A coincidence of tectonic, eustatic, and geochemical conditions resulted in substantial deposits of oolitic limestone during later Mississippian time in the continental United States. These oolitic limestones have formed petroleum reservoirs with favorable primary and secondary recovery characteristics. Significant potential reserves in stratigraphic traps remain to be discovered and developed in these reservoirs.