Blue River Group,
Type locality, principal reference section, and history of nomenclature: The Paoli Limestone was named by Elrod (1899, p. 259) for Paoli, Orange County, near which are many exposures of the formation. A type section was not designated, but an excellent exposure of the formation is in an abandoned quarry north of the now abandoned Monon Railroad on the west side of Paoli (SW¼SE¼SE¼ sec. 35, T. 2 N., R. 1 W.). This may be the exposure referred to as the type section by Malott and Esarey (1940, p. 5), and it is here designated the principal reference section.
As currently defined, the Paoli comprises the rocks between the Ste. Genevieve Limestone (below) and the Bethel Formation, but the Paoli of Elrod (1899) included the rocks above the Lost River Chert Bed, in the lower part of the Ste. Genevieve, and below the lowest Chesterian sandstone, which at that time was incorrectly thought to be what is now the Sample Formation. In later use (Cumings, 1922, p. 515), the Paoli was defined essentially as it is now and was considered to be the lowest Chesterian unit. The Paoli of Malott (1952, p. 12), however, excluded the lower sandy and shaly rocks, assigned here to the Popcorn Member of the Paoli, that Malott (1945, p. 1180 1946, p. 322-323) had correlated with Keyes's (1892, p. 296) Aux Vases Sandstone of Missouri. Stating that these rocks do not correspond either to the classic Aux Vases Sandstone or to the Aux Vases Formation of subsurface usage in the Illinois Basin, Gray, Jenkins, and Weidman (1960, p 49) rejected the name Aux Vases and reassigned these rocks to the lower part of the Paoli.
Description and distribution: Much of the exposed Paoli is characterized by four principal lithologies, which are here designated as members, in descending order: (1) gray to light-gray medium-grained thin- to thick-bedded skeletal and oolitic limestone, the Downeys Bluff Member; (2) gray or greenish-gray calcareous shale and thin discontinuous beds of skeletal and micritic limestone, the Yankeetown Member; (3) gray to greenish-gray skeletal, oolitic, and micntic limestone, the Shetlerville Member; and (4) gray calcareous sandstone, dark shale, and impure limestone, which in places grade without apparent break into the overlying member and which are called the Popcorn Member. (See the articles on these members.)
The Paoli ranges from about 20 to 35 feet (6 to 11 m) in thickness throughout most of its outcrop (Carr, Leininger, and Golde, 1978, p. 18), and it has a maximum subsurface thickness of 65 feet (20 m) in Posey County. It rests on the Ste. Genevieve Limestone with little evidence of more than a minor break in sedimentation (Perry and Smith, 1958, p. 32-33 Gray, Jenkins, and Weidman, 1960, p. 50), and it is associated with that formation in the outcrop belt extending from Crawford and Harrison Counties, on the Ohio River, to central Owen County, where rocks of the West Baden clastic belt (see under "Elwren Formation") in places cut out the Paoli (Malott, 1952, p. 45-49), and to west-central Putnam County, where Pennsylvanian rocks disconformably overlap the Paoli.
Correlation: The Paoli Limestone is correlated with the middle and upper parts of the Renault Formation of subsurface usage in western Indiana (Pinsak, 1957; Gray, Jenkins, and Weidman, 1960, table 5) and in the Illinois standard section with the ascending sequence consisting of the Shetlerville Limestone Member of the Renault, the Yankeetown Sandstone, and the Downeys Bluff Limestone (Pinsak, 1957, p. 17-18; Swann, 1963, p. 32-34, 51, 77). It is precisely equivalent, therefore, to the Cedar Bluff Group of Swann (1963). Shetlerville-equivalent rocks extend to the middle shale break, a determination borne out by conodont ratios of Cavusgnathus, Gnathodus, and Spathognathodus (Rexroad and Liebe, 1962).
The Paoli of Indiana contains the crinoid Talarocrinus (Malott, 1952, p. 12), and on this basis it has been correlated with the lower part of presumably post-Platycrinites penicillus rocks in the Talarocrinus Range Zone of other areas, for example, with a part of the Gasper Oolite of Butts (1917, p. 64) in Kentucky. (See Cumings, 1922, p. 515, 518 Perry and Smith, 1958, p. 30-31 and Swann, 1963, p. 33, 83). The Paoli correlates with rocks within North American foraminiferal Zone 16i of Mamet and Skipp (1971) and within the Visean Series (approximately Zone V3ci) of European usage. The formation is within the middle part of the Gnathodus bilineatus-Cavusgnathus charactus Assemblage Zone of conodonts (Collinson, Rexroad, and Thompson, 1971).