Type area and synonyms: The term Springfield was first applied by Worthen (1883, p. 6) to a coal mined near Springfield, Sangamon County, Ill. Sec. 16, T. 16 N., R. 4 W., was later designated as the type area (Wanless, 1956, p. 10), and still later the use of this term was extended into Indiana (Wier, 1961, 1965; Wayne, Johnson, and Keller, 1966). This coal had been called the Main Newburg Coal by Owen (1839, p. 11) and later Coal V by Ashley (1899, p. 90, 843 1909, p. 56). The terms Petersburg Coal and the coal at Alum Cave have also been used for this coalbed (Cumings, 1922, fig. 2).
Description: The widespread Springfield coal of the Petersburg Formation is Indiana's most important economic coal. It is thickest near three contemporaneous channels in south-western Indiana, the Galatia, Leslie Cemetery, and Terre Haute Channels, where it may reach thicknesses of 13 feet (4 m) in places. In several areas in Gibson, Pike, Knox, and Sullivan Counties, a gray silty shale as much as 90 feet (27 m) thick, similar in lithology to the Dykersburg Shale Member of Illinois, overlies the coal and thins and pinches out distally from the Galatia Channel. Adjacent to this channel the coal may be split in places by shale. This split has been designated the Folsomville Member (Eggert, 1982) in south-eastern Gibson County and northwestern Warrick County, where the Springfield is split into at least two thinner coalbeds separated by as much as 65 feet (20 m) of clastic Folsomville rocks. The Terre Haute Channel in Vigo County is also associated with areas of split Springfield coal and a zone of nondeposition (Friedman, 1956, 1960).
Where the Springfield coal adjacent to channels is overlain by 20 feet (6 m) or more of gray silty freshwater shale, it is commonly lower in sulfur than in areas where it is overlain by black fissile marine shale. Black fissile shale and the Alum Cave Limestone Member (Dugger Formation) commonly overlie the Springfield away from the channels, but these units thin and pinch out over the gray shale associated with the Galatia Channel and over areas where the Folsomville is thick. The coal is generally underlain by silty clay or by shale or sandstone in some places. Away from the contemporaneous channels the Springfield ranges from 2.5 to 6 feet (0.8 to 1.8 m) in thickness and has an average thickness of about 4 feet (1.2 m). As described by Neavel (1961) and Hower and Wild (1982), the Springfield is a bright coal that dulls upward, and as shown by Guennel (1952) and Peppers (1970), it has a distinctive spore content.
Correlation: The Springfield is now the recognized name for this coal in Illinois, Indiana, and western Kentucky, where it had been known by several names (Shaver and others, 1985 Jacobson and others, 1985). The Springfield is believed to be similar in age to the Middle Kittaning and Princess No. 7 Coals of the Appalachian Basin (Peppers, 1970; Kosanke, 1973).