Oolitic calcarenite of the Ste. Genevieve Limestone was deposited in shallow water along the southwestern margin of the Illinois basin northeast of the Ozark shoal. Considerable divergence in shelf current patterns is indicated by the large variance (6,363) for azimuths of cross-bed sets of oolitic calcarenite and by outcrop polymodal windrose diagrams. Tidal current deposition is suggested locally by 180° reversals in sequences of cross-bed sets. The dominant currents flowed northwestward, as evidenced by the 326° vectorial mean for cross-bed azimuths and the northwestward migration of the thicker (40-90 in.) cross-bed sets.

During early diagenesis of the carbonate sand, aragonite in fossils and in ooid laminae was dissolved by low-Mg water to form extensive moldic porosity within insoluble micrite envelopes. Earlier precipitation of thin calcite crusts around the grains prevented collapse of most micrite envelopes. Intergranular and moldic pores were subsequently filled by mosaic calcite cement.

Ooids with calcite spar interiors and off-center nuclei are explained by (1) solution of aragonitic ooid laminae within an insoluble micrite envelope, (2) gravitative settling of the nucleus to the bottom of the mold, and (3) filling of the mold by calcite cement that displaced the nucleus to a nongeopetal position. Ferroan calcite spar of (Ca_.990 Mg_.006 Fe_.004) CO₃ composition (electron microprobe analyses) was precipitated within the ooid molds in some beds. The presence of ferroan calcite reflects concentration of iron in the water inside the molds derived from dissolution of iron-bearing ooid laminae.

Postlithification chert, chalcedony, calcite, ferroan calcite, and dolomite formed along joint and solution openings by precipitation and/or replacement processes.

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