Mississippian System

Type area and use of name: The Spar Mountain Sandstone Member of the Ste. Genevieve Limestone was named by Tippie (1945, p. 1657) for Spar Mountain, a topographic feature in Hardin County, Ill. There the member consists of 8 to 15 feet (2.4 to 4.6 m) of light-gray to greenish-gray calcareous and glauconitic sandstone and siltstone that grade to sandy limestone. Use of the name was extended into Indiana by Swann (1963, p. 27-28) to replace the term Rosiclare Sandstone Member, which had been introduced into Indiana by Malott (1945, p. 1180 1946, p. 323) for a calcareous sandstone in the middle part of the Ste. Genevieve Limestone at Cataract Falls, Owen County, but which had been improperly correlated (Pinsak, 1957, p. 22). The name presently used in Indiana, the Spar Mountain Member, was adopted in recognition of the mixed lithologic character of the unit where exposed along the outcrop (Carr, Leininger, and Golde, 1978, p. 16).

Description: Along the outcrop in Indiana, the Spar Mountain Member is traceable from central Putnam County to the Ohio River and commonly ranges from 8 to 15 feet (to 4.6 m) in thickness. In the subsurface it is thicker. In many places the unit consists of crossbedded lenticular arenaceous carbonate sand bodies that are erratic in thickness. But for the most part it consists of thin beds of detrital, micritic, and oolitic limestone that contain as much as 40 percent silt- and sand-size quartz in places the micritic limestone is conglomeratic or brecciated. In some places the limestone is interbedded with calcareous shale and sandstone, generally quartzose but cherty in some places, but these clastic lithologies generally constitute less than 18 percent of the unit in other places silty dolomite is present.

Correlation: The Spar Mountain Member can be traced across the Illinois Basin to its type section, where conodonts of the Gnathodus bilineatus-Cavusgnathus charactus Assemblage Zone are found in both overlying and underlying rocks. The Spar Mountain, therefore, is securely assigned to that zone.