The Bluefield Formation (Chesterian, Upper Mississippian) of the Appalachian Basin is a lithologically variable unit, composed of mudstones lithofacies with subordinate amounts of sandstone and limestone. By analyzing sedimentology and the prominence of ostracodes, an ostracode biofacies model was generated that provides a large-scale paleoenvironmental framework for the Bluefield Formation. Three ostracode assemblages were defined in an effort to identify environmental conditions during deposition of the Bluefield: Assemblage I - Polytylites Assemblage; Assemblage II - Sansabella Assemblage; and Assemblage III - Whipplella Assemblage. The assemblage distributions indicate that nearshore transitional marine environments were common and normal open marine conditions were very rare. The variable units and upward-shallowing sequences in the Bluefield reflect changes in the influx of freshwater that caused salinity fluctuations. Within the depositional environments of the Bluefield Formation, salinity was the most important controlling factor in the ostracode distribution.

Pterotocrinus is an echinoderm of the class Crinoidea that is restricted to the Chesterian Series (Chestnut and Ettensohn, 1988; Sutton, 1934). The most identifiable and best preserved remains of Pterotocrinus are the wing plates (Welsh, 1978). These wing plates are specialized tegmen plates that give Pterotocrinus its name (from pteron, Greek for "wing") (Welsh, 1978). This study questions whether or not wing plates can be used for biostratigraphy throughout the Chesterian Series, as well as what the functions of the wing plates were. New morphologies of Pterotocrinus found within the Menard Limestone during this study bring into question the biostratigraphical usefulness of many of the morphologies of Pterotocrinus wing plates. Certain species of Pterotocrinus appear to remain valuable index fossils within the Menard Limestone and the Kinkaid Formation. Four new morphologies were collected within the Menard Limestone during this study. These new finds draw questions about our knowledge of this genus. This study also attempted to explain the function of the wing plate, and how it may have changed over time. Pterotocrinus wing plates evolved rapidly during the Chesterian Series developing vastly different morphologies from the time the Menard Limestone was deposited to the time when the Kinkaid Formation was deposited. This study suggests a functional shift over time, with the wing plates of the Menard Limestone acting as rudders to orient the calyx to either assist in feeding or reduce stress on the calyx, and the wing plates of the Kinkaid Formation acting as an antipredatory defense mechanism. This study presents new conclusions and new questions regarding the wing plates of Pterotocrinus.

The purpose of this study is to document and describe newly observed marine fossils from the upper part of the Degonia Sandstone and to infer the depositional setting of this horizon. Previous studies have shown that the Degonia Sandstone (Elviran Stage, Chesterian Series, Mississippian Subsystem) contains sedimentological evidence of several depositional environments (i.e. terrestrial, fluvial, nearshore deltaic, tidal, and possible marine zones); however, no body fossils had been observed. The only fossils identified in the Degonia are non-diagnostic trace fossils and Carboniferous plant remains such as Lepidodendron trunks and Stigmaria casts, suggesting a terrestrial environment. In 2010, Mary Seid and Joseph Devera of the Illinois State Geological Survey found marine fossils in the upper Degonia Sandstone in a stream bed located within the Wolf Creek Fault Zone. They associated these fossils with a marine environment, contradicting earlier assessments. Four study localities were found throughout the study, one each in the Gorham, Cobden, Glendale, and Raddle Quadrangles of southern Illinois. Sampling localities were found using geologic maps to locate the Degonia-Kinkaid contact, specifically areas where large stream valleys cut through the Kinkaid Formation and into the Degonia Sandstone throughout southern Illinois. The boundaries between the Degonia Sandstone and the overlying Kinkaid Formation were walked in order to find indicators of the marine zone (i.e. the presence of the shaly layer of the upper Degonia Sandstone). The reference section (the Gorham locality) contains the largest diversity of fossils and represents a storm deposit. The Cobden locality appears to contain a zone of dwarfed specimens and a zone of normal sized specimens, and represents a storm deposit. The Glendale locality is dominated by a single bivalve and represents brackish water conditions. The Raddle locality is non-fossiliferous, but was within the intertidal zone. The fauna identified by this study consists of four Phyla: Arthropoda, Brachiopoda, Bryozoa, and Mollusca. The only Arthropoda observed was a burrowing barnacle (Acrothoracica). The Brachiopoda observed consist of Diaphragmus nivosus, Orthotetes kaskaskiensis, Anthracospirifer occiduus, and Composita sp. The Bryozoa observed include Fenestrate and Trepostome. The Mollusca are the most diverse phyla observed, consisting of bivalves (Wilkingia walkeri, ?Edmondia sp., Aviculopecten winchelli, Promytilus illinoisensis, Myalina sp., ?Septimyalina sp., Myalinella meeki, ?Sphenotus monroensis, and four species of unknown bivalves), cephalopods (Reticycloceras sp., Endolobus sp., Liroceras sp., Metacoceras sp., and Domatoceras sp.), and gastropods (Euconospira sturgeoni, ?Eotrochus cf. marigoldensis, and an unknown gastropod). Other fossils observed were crinoid stem molds and plant material. The characterization of invertebrate fossils occurring in the upper Degonia supports the previous suggested marine sedimentological features of the Degonia Sandstone.

The Big Clifty (Jackson) Sandstone Member of the Golconda Formation is the most important of the Mississippian (Chesterian) heavy-oil reservoirs in the southeastern Illinois Basin. Heavy oil reservoirs, or asphalt rock deposits, have been studied extensively in south central and western Kentucky, and ~2 billion barrels of original oil in place (OOIP) have been proposed to occur in the Big Clifty Sandstone. Despite high OOIP estimates, heterogeneities in the reservoir negatively impact the production of heavy oil deposits. Heterogeneities related to depositional facies changes are poorly understood in the Big Clifty Sandstone of Kentucky, where it has been mostly described as a 60-120 feet thick sandstone unit. In some locations, the Big Clifty occurs as two distinct sand bodies with intercalated mud-rich units and, most typically, with the greatest clay- and silt-rich units present between sandstone bodies. Questions exist as to how such muddy facies occur in the reservoir. This study couples sedimentary facies analysis with sequence stratigraphy to assess how lithological factors affect the occurrence of petroleum in Big Clifty reservoirs. Multiple datasets were integrated to develop a depositional model for lithologic facies observed in this study. Datasets include core, exposure descriptions, petrographic analysis, bitumen concentrations, electrical resistivity tomography (ERT), and borehole geophysical analysis. This study occurred in Logan, Warren, and Butler counties, with emphasis on an active asphalt-rock mine in Logan County. Surface geophysical methods aided in demarcating Chesterian limestones, sandstone bodies and, in particular, highly resistive heavy-oil laden Big Clifty channel bodies. In Warren County, located E-NE of the Stampede Mine, the Big Clifty coalesces into a single amalgamated sandstone channel or a series of superimposed stacked channels as observed in outcrop along Indian Creek at McChesney Field Station and at Jackson’s Orchard. In these locations, the tidal influence is subtle with large-scale trough cross bedding dominating, and the contact on the Beech Creek Limestone is sharp. Facies changes related to the environment of deposition greatly impact the quality of heavy-oil reservoirs and must be taken into consideration during exploration and siting of asphalt rock mines.