Facies analysis depositional environments and sequence stratigraphy of the Ste. Genevieve Limestone in Johnson Union Franklin and Williamson counties southern Illinois

In the Illinois Basin, the Mississippian age (early Chesterian) Ste. Genevieve Limestone consists of shallow marine carbonates deposited in a carbonate ramp platform. Sequence stratigraphic classification of these sediments has proved challenging due to low gradients, heterogeneous facies distribution and variable thermal related basin subsidence.;The purpose of this study is facies analysis and recognition of important stratigraphic surfaces and facies trends to sub-divide the Ste. Genevieve succession into transgressive-regressive cycles (sequences) of various orders in outcrop (Johnson and Union Counties) and subsurface (southwest Franklin and Williamson County) of Southern Illinois.;Following careful compilation of several datasets which include outcrop observations, facies descriptions, benthic fossil assemblage, thin-section analysis, and well log correlations, it was determined that the Ste. Genevieve Limestone encompasses 2 shallow marine facies belts including tidal channel barrier shoals and subtidal open marine facies. In the study area, the Ste. Genevieve Limestone forms 2 third order sequences that are composed of several 4th to 5th order parasequences. The sequences are comprised of a transgressive and highstand systems tract (sequence 1), and a transgressive systems tract (sequence 2), which formed during the Mississippian by tectonically associated thermal subsidence and global eustasy.