Type locality and history of name in Indiana: The name Big Clifty Sandstone is generally credited to Norwood (1876), who, however, did not specifically indicate the source of the name. Presumably it derives from Big Clifty Creek in Grayson County, Ky. (Butts, 1917, p. 87; Willman and others, 1975, p. 157). The formation was described as a buff to cream heavy-bedded and cross-laminated fine-grained friable sandstone 60 to 130 feet (18 to 40 m) thick that passes westward into shale.
A major part of the Big Clifty Formation on the outcrop in Indiana is a prominent cliff-forming sandstone that for many years was referred to as the Cypress Sandstone (Malott, 1931, 1952), a result of miscorrelation as explained below. Above the sandstone is a gray shale and mudstone that was for a time called the Indian Springs Shale (Malott and Thompson, 1920; Malott, 1931, p. 224) but that was later assigned to the Golconda Formation (Malott and Esarey, 1940; Malott, Esarey, and Bieberman, 1948).
When the name Big Clifty was adopted for use in Indiana, it was modified to the present form (Gray, Jenkins, and Weidman, 1960, p. 40-41), and the unit was redefined to include the gray shale and mudstone that are now designated the Indian Springs Shale Member. An exposure that shows both aspects of the formation is in a railroad cut about 3 miles (4 km) east of Shoals, in sec. 28, T. 3 N., R. 3 W., Martin County (Gray and others, 1957, p. 14-16). This exposure and an equally representative core from sec. 32. T. 2 N., R. 2 W., Orange County (Gray, Jenkins, and Weidman, 1960, p. 75-77), are here designated principal reference sections of the Big Clifty Formation in Indiana.
Description: In many places the Big Clifty Formation is composed in descending order of 3 to 14 feet (1 to 4 m) of gray fossiliferous shale and interbedded limestone, 3 to 10 feet (1 to 3 m) of varicolored mudstone and siltstone, 25 to 40 feet (8 to 12 m) of thin-bedded fine-grained sandstone, and in places as much as 6 feet (2 m) of black pyritiferous shale at the base. The two upper units are assigned to the Indian Springs Shale Member. On the outcrop the sandstone member of this formation is a conspicuous cliff former of great lateral extent (Gray, Jenkins, and Weidman, 1960, p. 40-41), but down dip in the subsurface of southwestern Indiana the formation is primarily shale, and the sandstone, sometimes referred to by drillers as the Jackson Sand, occurs as isolated lenses.
The Big Clifty Formation is recognized on the surface from Owen County southward to the Ohio River and in the subsurface from central Clay County southwestward. The formation conformably overlies the Beech Creek Limestone (Barlow Lime of some subsurface usage) and is overlain conformably by the Haney Limestone or disconformably by the Mansfield Formation (Morrowan).
Correlation: Butts (1917, p. 86-90) was possibly the first to mistakenly equate the Big Clifty Sandstone of western Kentucky with the Cypress Sandstone of southern Illinois. This view was shared by Malott (1919, p. 17; 1952, p. 16), who adopted the name Cypress Sandstone for use in Indiana. The Cypress, however, is equivalent to an older unit, the Elwren Formation (Swann and Atherton, 1948; McFarland and others, 1955). The Big Clifty Formation of Indiana usage is equivalent to the Fraileys Shale of the standard Chesterian section, but in Illinois the term Big Clifty is applied to a sandstone member of the Fraileys Shale (Swann, 1963; Willman and others, 1975, p. 156-157).
The fossiliferous shale and limestone of the Indian Springs Member at the top of the Big Clifty contain wing plates of the crinoid Pterotocrinus, which elsewhere in the Illinois Basin is restricted to the Golconda Group and is especially characteristic of the Fraileys Shale and Haney Limestone (Welch, 1978). The Big Clifty corresponds to rocks within North American foraminiferal Zone 16s of Mamet and Skipp (1971) and within Zone V3cs of the type Visean sequence in Belgium. The Big Clifty is within the conodont-based Gnathodus bilineatus-Cavusgnathus altus Assemblage Zone of Collinson, Rexroad, and Thompson (1971).