Mississippian System

Type locality and description: The Beaver Bend Limestone was named by Malott (1919, p. 9-10 1952, p. 103-105) for exposures near Huron, Lawrence County, Ind., where Beaver Creek makes a conspicuous bend. A gray skeletal to oolitic to biomicritic limestone, the unit is generally 10 to 14 feet (it to 4 in) thick (Malott, 1952, p. 13) but is as thin as 1 foot (0.3 m) (Malott, 1952, p. 27) and as thick as 30 feet (9 in) (Sullivan, 1972, p. 17). Anomalously thick sections commonly are along the edge of linear areas in which the Beaver Bend and Reelsville Limestones are missing and in which much of the West Baden Group is made up of sandstone. Sullivan (1972) referred to these linear areas, which trend down dip toward the axis of the Illinois Basin, as the West Baden clastic belt and noted reeflike buildups of limestone along their margins. (See discussion of the West Baden clastic belt under Elwren Formation.)

The Beaver Bend Limestone conformably overlies the Bethel Formation and is overlain conformably by the Sample Formation or disconformably by the Mansfield Formation (Morrowan). It is known on the outcrop from central Putnam County southward to the Ohio River and can be recognized in the subsurface from Parke County southwestward.

Correlation: Although other correlations have seen suggested, the Beaver Bend Limestone is now thought to be equivalent to the lower part of the Ridenhower Formation of the Illinois standard section and is recognized as the basal member of that formation (Swann, 1963, p. 35; Willman and others, 1975, p. 154). In the subsurface of the lower Wabash Valley area, the Beaver Bend has commonly been called the Lower Paint Creek Limestone, but this assignment is incorrect, and Sullivan (1972, p. 10) has recommended that the latter term be suppressed in favor of the more precise name Beaver Bend.

As reported by Pohl (1970), the coral Caninia veryi (Greene) in Kentucky is restricted to the Beaver Bend Limestone. This coral has not been reported in Indiana, but typical forms of the blastoid Pentremites godoni (Defiance), common in the Paint Creek Group in Illinois, are present (Galloway and Kaska, 1957). The Beaver Bend corresponds to rocks in the lower part of North American foraminiferal Zone 16s of Mamet and Skipp (1971) and within Zone V3cs of the type Visean sequence in Belgium. On the basis of its conodont fauna, the Beaver Bend is assigned to the Gnathodus bilineatus-Cavusgnathus charactus Assemblage Zone of North American usage (Collinson, Rexroad, and Thompson,1971).