Branchville Formation


Buffalo Wallow Group,

Mississippian System

Type and reference sections and description: The Branchville Formation was named by Gray (1978, p. 8) for a small settlement in Perry County, Ind. A section near Branchville, earlier described by Malott (1925, p. 125-126), was designated as the type section, but because this section was much overgrown, several reference sections were specified. The most important of these is Indiana Geological Survey drill hole 132, near Oriole, Perry County (Gray, 1978, appendix 2). In this hole the Branchville Formation is 92 feet (28 m) thick and consists mainly of mudstone, shale, siltstone, and sandstone, and in relatively thin beds. At its base is the Vienna Limestone Member, and marking its top is the Leopold Limestone Member. Both of these members are thin.

The Branchville Formation crops out from the Ohio River northward to southwestern Orange County. Where the entire formation is present, it is 85 to 105 feet (26 to 32 m) thick. It conformably overlies the Tar Springs Formation and is clearly distinguishable from that formation only where the Vienna Limestone Member is present. It is conformably overlain by the Tobinsport Formation, and this distinction can commonly be made only where the Leopold Limestone Member is present. Along the north edge of its extent, the Branchville Formation is truncated and disconformably overlain by the Mansfield Formation (Morrowan).

The Branchville Formation is restricted to outcrop use, but the basal key member, the Vienna, is widely recognized in the subsurface, where it has formation rank as the Vienna Limestone. The upper key member, the Leopold, is a tongue of the Menard Limestone of subsurface usage.

Correlation: The Branchville Formation is equivalent to the lower part of the Buffalo Wallow Formation of Kentucky usage and to the Vienna Limestone, the Waltersburg Formation, and some part of the Menard Limestone of the standard Chesterian section. The Branchville equates with rocks within North American foraminiferal Zone 17 of Mamet and Skipp (1971) and within Zone E1 of the Namurian Series of European usage. On the basis of contained conodonts, the Branchville belongs to the Kladognathus primus Assemblage Zone and the lower part of the overlying Kladognathus-Cavusgnathus naviculus Assemblage Zone of North American standard usage (Collinson, Rexroad, and Thompson, 1971).

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