Pennsylvanian System

Type locality, use of name, and synonyms: The limestone exposed in the high banks of the Ohio River at West Franklin, Posey County, was first mentioned in the literature by Owen (1839, p. 8) and later by Lesquereux (1862, p. 296-297), who described the units exposed along the river and referred to them informally as the lower bank of the West Franklin Limestone. Wilmarth (1938, p. 2307), however, gave credit for first use of the name to Collett (1884, p. 61-62), who also used the term West Franklin Limestone. Wier and Gray (1961) and Wier (1961, 1965) reduced the rank of this limestone to that of member, uppermost in the Shelburn Formation, and Wier (1961, 1965, 1970) stated that the exposure at West Franklin in the SE¼SE¼ sec. 24, T. 7 S., R. 12 W., was the type locality, but the correct locality is in the NE¼SE¼ sec. 24. The bedrock outcrop of the West Franklin was mapped by Gray, Wayne, and Wier (1970), Gray and others (1979), and Gray, Ault, and Keller (in preparation).

Synonyms of the West Franklin are the terms Somerville Formation, used in Gibson County by Fuller and Clapp (1904, p. 2), and Maria Creek Limestone, used in Sullivan County by Malott (1948, p. 125).

Description and correlation: The West Franklin Limestone Member generally consists of limestone beds separated by shale. In Gibson County three beds of limestone are found, but northward only the upper two are present and in places only one limestone bed can be seen. The lowest bed is sparsely fossiliferous, ranges from 1 to 4 feet (0.3 to 1.2 m) in thickness, and is overlain by 1 to 25 feet (0.3 to 7.6 m) of tan, blue-gray, or variegated nonfossiliferous shale that in some places has an intercalated shale. The middle limestone is a massive light-gray to tan argillaceous fossiliferous limestone ranging from 4 to 10 feet (1.2 to 3 m) in thickness at the south end of the outcrop and thinning northward to 0.5 to 3.8 feet (0.2 to 1.2 m) of flaggy nodular limestone in Sullivan County. In Posey County it contains large colonies of the coral Chaetetes. Gray shale, 0.1 to 3 feet (< 0.1 to 0.9 m) thick, separates the middle limestone from the upper, more cherty limestone, which is gray to brown, dense, crystalline, argillaceous, and fossiliferous. The upper limestone is 1 to 6 feet (0.3 to 1.8 m) thick in Gibson, Vanderburgh, and Posey Counties and attains a maximum thickness of 10 feet (3 m) in Sullivan County.

In parts of the subsurface in Posey and Gibson Counties any one or more of the above three beds are not present, and drilling records indicate that some thin limestone beds are present in the shale, sandy shales, and sandstones 100 feet (30 m) or more beneath the normal stratigraphic interval of the West Franklin. This variation in the presence and the location of the limestone beds makes definition of the base of the West Franklin arbitrary in places.

The West Franklin is recognized in Illinois, and the term West Franklin Limestone Member (in the Sturgis Formation) has been proposed for Kentucky use by Jacobson and others (1985).