Mississippian System

Type area, characteristic section, and use of name: The name Lost River Chert was given by Elrod (1899, p. 259) to rocks exposed along the dry bed of Lost River in Orange County. It is particularly well exposed in Wesley Chapel Gulf (called Elrod Gulf on the French Lick topographic quadrangle map), one-half mae (0.8 km) south of Wesley Chapel Church in the SW¼NE¼ sec. 9, T. 2 N., R. 1 W., and near Orangeville in the SE¼ sec. 6, T. 2 N., R. 1 W. Elrod considered the Lost River Chert to be an interformational marker between his Paoli Limestone and his Mitchell Limestone, but Cumings (1922, p. 507) included it rn the St. Louis Limestone, as did Woodson (1982) more recently. Especially through the work of Malott (1952, for example), the Lost River is now assigned to the lower part of the Ste. Genevieve Limestone and given the rank of bed. (See Smith, 1970, p. 96-97.)

Description and distribution: The Lost River Chert Bed consists of one stratum or more of very fossiliferous and siliceous limestone distributed through a stratigraphic interval as much as 6 feet (1.8 m) thick. It contains abundant bryozoans and is oolitic in places. Commonly the chert is bluish gray, but in places it is light brownish gray and blends with the host limestone. The bryozoan limestone is differentially silicified, so that weathered surfaces from which the carbonate has been leached have a distinctive aspect.

The Lost River Chert Bed is an important stratigraphic marker 15 to 40 feet (4.6 to 12.2 m) above the base of the Fredonia Member and of the Ste. Genevieve Limestone. It is especially persistent in and south of Lawrence County, but northward the bed is mostly absent, although it has been reported as far north as Greencastle, Putnam County (Malott, 1952, p. 8, 23). The Lost River is probably present in the subsurface of western Indiana (Pinsak, 1957, p. 20), and it has been suggested that it correlates with a similar zone of chert in southeastern Kentucky and northern Tennessee (McGrain, 1969, p. 1506-1507).

Correlation: The Lost River Chert Bed and the immediately overlying beds contain conodonts of the Apatognathus scalenus-Cavusgnathus Assemblage Zone (Collinson, Rexroad, and Thompson, 1971) and so correlates with the upper part of the St. Louis Limestone of the Mississippi Valley. (See also just above the statement on distribution and correlation.)