Mississippian System

Type locality and use of name in Indiana: The Sample Formation was originally named the Sample Sandstone Member of the Gasper Oolite by Butts (1917, p. 70-73), who designated a type locality at Sample Station, Breckinridge County, Ky. As exposed in that area, the formation consists of 20 to 40 feet (6 to 12 m) of massive thick-bedded and crossbedded sandstone, flaggy sandstone, and shale.

Equivalent rocks in Indiana were originally given the name Brandy Run Sandstone (Malott, 1919, p. 10). This name was abandoned when equivalence to the Sample Sandstone was recognized (Cumings, 1922, p. 515-516). Dominance of sandstone on natural outcrops gives a false impression of the lithology of the unit, as is also true for other Chesterian clastic units, and for this reason Gray and Perry (1956) changed the name to Sample Formation. A railroad cut near Huron, Lawrence County (Gray and others, 1957, p. 10-14; Malott, 1952, p. 103-105), is here designated a reference section for the Sample Formation in Indiana.

Description: The Sample Formation in Indiana is 15 to 50 feet (5 to 15 m) thick and consists of varicolored shale and thin-bedded and crossbedded sandstone (Gray and others, 1957, pl. 2). Shale dominates in the northern part of the outcrop area from Putnam County southward through Orange County, but sandstone becomes more conspicuous southward to the Ohio River (Malott, 1952, p. 13). The formation is present in the subsurface from Parke County southwestward, but in much of this area it is indistinguishable from formations above and below because the limestone formations that define its upper and lower boundaries are absent (Sullivan, 1972, p. 19; see also the discussion of the West Baden clastic belt under "Elwren Formation") .

The Sample Formation conformably overlies the Beaver Bend Limestone and is overlain conformably by the Reelsville Limestone. Where the Reelsville is depositionally absent, clastic rocks that would normally be assigned to the Elwren Formation directly overlie clastic rocks that would normally be assigned to the Sample, and to place a contact between them is difficult or impossible. At a few localities a disconformity appears to separate the two formations (Malott, 1919, p. 11; 1952, p. 56-57), but Gray and Perry (1956) considered this feature to be of local significance only, a manifestation of what later came to be understood as the West Baden clastic belt. Where higher Chesterian rocks are missing as a result of pre-Pennsylvanian erosion, the Sample Formation is disconformably overlain by the Mansfield Formation (Morrowan).

Correlation: The Sample Formation has been considered equivalent to part of the Paint Creek Formation of former Illinois usage (Swann and Atherton, 1948, p. 270). The name Paint Creek has been replaced in the standard Chesterian section, however, and the Sample is now designated as the middle member of the Ridenhower Formation (Swann, 1963, p. 35; Willman and others, 1975, p. 154).