Floyds Knob Limestone Member

Image showing IGS seal and the words Indiana Geological Survey, a research institute of Indiana University. Click to go to the home page.

Click for information about these images.

Floyds Knob Limestone Member,

(CBR)

Edwardsville Formation,

Mississippian System

Type section and use of name: The Floyds Knob Limestone Member was originally named as a formation for exposures along U.S. Highway 150 through the Knobstone Escarpment at Floyds Knobs in the center of sec. 21, T. 2 S., R. 6 E., three-fourths of a mile east of Floyds Knobs post office in Floyd County, Ind. (Stock dale, 1929a, p. 170 1931, p. 195-196). The unit was reduced to the rank of member of the Muldraugh Formation by Smith (1965) and was re-assigned to the Edwardsville Formation by Nicoll and Rexroad (1975, p. 3). (See "Borden Group" for a discussion of obsolete terms that have been applied to this stratigraphic interval.)

Description: The Floyds Knob is primarily a limestone as far north in Indiana as Jackson County but is "expressed by a peculiar light buff to ocherous zone of slightly calcareous, shaly and arenaceous rock with many variations" north of there (Stockdale, 1931, p. 197). In its type area and southern extent the Floyds Knob approximates 5 feet (1.5 m) in thickness. From Monroe County northward bioherms and lenticular limestone beds are locally prominent in the Edwardsville; however, these generally appear to be somewhat above the Floyds Knob stratigraphically. The Floyds Knob is conformable within the Borden Group, although there is some reworked material in its basal part and a bed of glauconite in many places marks the base of the overlying part of the Edwardsville.

Correlation: Conodonts recovered from the type section of the Floyds Knob (Gates and Rexroad, 1970 Whitehead, 1978) show that the Floyds Knob is correlative with part of the Keokuk Limestone of the upper Mississippi Valley.