Petrology, paleoecology, and depositional environments of a micritic limestone in Cave Hill Member of Kinkaid Formation (Mississippian, Chesterian), southern Illinois

The Cave Hill Member of the Kinkaid Formation (Mississippian, Chesterian) contains a skeletal-lime mud buildup that is a thin lenticular unit which crops out in Johnson County in southern Illinois. The skeletal-lime mud buildup is characterized by a series of biofacies which are laterally correlatable throughout the buildup. These biofacies-the sponge spicule biofacies, the crinoid biofacies, the Composita-Fenestella biofacies, and the Composita biofacies-represent a series of different communities. In addition, a poorly fossiliferous lime mud facies is present. In the two lower biofacies, the sponge spicule and crinoid biofacies, the skeletal constituents are fragmented and abraded owing to bioturbation. The upper biofacies, the Composita and Composita-Fenestella biofacies, contain more distinct and well-preserved grains. Brachiopods, such as Composita, and bryozoans, such as Fenestella and Archimedes, are present as whole specimens, some in life position. The thicker, upper biofacies probably accumulated as a result of the baffling action of fenestrate bryozoans. Some of these biofacies display distinct zoning or concentration of shelly material interpreted to be the result of intermittent storm waves and suggesting that the depth of deposition was below normal wave base not yet below storm wave base. The skeletal-lime mud buildup indicates deposition on a shallow sloping shelf of the Chester sea. The quiet water marine conditions were favorable for a localized concentration of fauna, some of which had been abraded by bioturbation, and which were intermittently affected or concentrated by storm waves not yet largely fragmented or abraded.