Mississippian System

Type section and description: The Reelsville Limestone was named by Malott (1919, p. 10-11) for exposures of gray, biomicritic, somewhat ferruginous, and locally sandy limestone about 3 feet (1 m) thick near Reelsville, Putnam County, Ind. Malott (1952, p. 26-27) later designated a type section on the south bluff of Walnut Creek immediately south of Reelsville. This section is somewhat isolated from the major area of distribution of the Reelsville Limestone.

The somewhat erratic distribution of the Reelsville is best understood by reference to the West Baden clastic belt (see under "Elwren Formation"), an elongate area that extends from Owen and Greene Counties southwestward (Sullivan, 1972). In the clastic belt the Beaver Bend and Reelsville Limestones are absent, and much of the West Baden Group is made up of sandstone that is indivisible into formations. Along the edges of the belt the limestones are anomalously thick and sandy, apparently the result of dilution by terrigenous clastic material from the belt.

North and west of the clastic belt, in an area that includes the type locality as well as the northern part of its outcrop, the Reelsville occurs only in isolated small areas. Few outcrops are known, therefore, from Putnam County southward to Lawrence County (Malott, 1952). South and east of the clastic belt the Reelsville is more continuous, and in many places two or more limestone beds are recognized in this general stratigraphic position. As concluded by Ross (1962) in an outcrop study from Martin County to Crawford County, only the lowermost of these beds is correctly assigned to the Reelsville; the others belong within the overlying Elwren Formation.

Characteristically the Reelsville Limestone is a single bed of skeletal limestone 2 to 7 feet (0.5 to 2 m) thick, but in some small areas it is as thick as 20 feet (6 m). The Reelsville conformably overlies the Sample Formation and is overlain conformably by the Elwren Formation or disconformably by the Mansfield Formation (Morrowan).

Correlation: The Reelsville Limestone was considered by Malott (1931, p. 222) to be equivalent to the lower part of the Paint Creek Formation of southwestern Illinois; it was later shown instead to represent the upper part of the Paint Creek (Swann and Atherton, 1948). The term Paint Creek (as the Paint Creek Group) is now restricted to western Illinois use (Willman and others, 1975, p. 153), and the name Reelsville has been adopted with member status for the upper part of the Ridenhower Formation of the standard Chesterian section (Swann, 1963, p. 35; Willman and others, 1975, p. 155).

The Reelsville Limestone correlates with rocks within North American foraminiferal Zone 16s of Mamet and Skipp (1971) and within Zone V3cs of the type Visean Series of European usage. On the basis of its conodont fauna, the Reelsville has been assigned to the Gnathodus bilineatus-Cavusgnathus charactus Assemblage Zone of the North American standard (Collinson, Rexroad, and Thompson, 1971).