Anthraconaiasp. occurs in the thin nonmarine interval that lies between the Upper Millersburg Coal Member and the Lower Millersburg Coal Member (Pennsylvanian, Desmoinesian) in Warrick County, Indiana. Specimens ofAnthraconaiasp. resembleAnthraconaiathat occur in Pennsylvanian and Permian rocks of the Appalachian Basin, but they differ slightly in size, form ratios, or both. Specimens were found in massive, nonfissile gray mudstone; buff-colored, laminated limestone (ostracodal biomicrite, wackestone); and platy black shale. The only statistically significant variation between shells from these different lithologies is that shells recovered from the limestone tend to be more ovate than shells from the other two lithologies. This contradicts the findings of previous investigations in which more ovateAnthraconaiawere found in the more organic-rich sediments of a given stratigraphic sequence. This difference is probably caused by the lack of discernible change in energy level through the depositional history of the interval and suggests that changing energy levels may be more important to the control of the morphology ofAnthraconaiathan the level of organic carbon in the sediment.
Joint patterns in coal, black shale, gray shale and mudrock, and limestone and dolomite in the Appalachian Basin
