Chesterian Series

Mississippian System

Type locality and description: The name West Baden was originally proposed as a group name in 1920 by E. R. Cumings in a letter to Stuart Weller (Cumings, 1922, p. 514). The term received no subsequent use, however, until it was revived in a slightly modified sense by Gray, Jenkins, and Weidman (1960, p. 44-48). The group is named for West Baden, Orange County, Ind., and consists in descending order of the Elwren Formation (the Cypress Formation in the subsurface), the Reelsville Limestone, the Sample Formation, the Beaver Bend Limestone, and the Bethel Formation. It consists dominantly of gray to varicolored shale and mudstone and thin-bedded to crossbedded sandstone lime-stone in beds of variable thickness is an important but lesser constituent (Gray, 1962, table 2 and fig. 4). Total thickness along the outcrop ranges from 100 to 140 feet (30 to 43 m). Known on the surface from Putnam County southward to the Ohio River, the West Baden Group is also recognized in the subsurface from Parke County southwestward. Maximum reported subsurface thickness is 260 feet (80 m) in western Gibson County (Sullivan, 1972, p. 11 and pl. 3).

A major feature of the West Baden Group is a southwestward-trending belt about 6 miles (10 km) wide across which the limestones were not deposited and in which sandstone dominates the entire thickness of the group. (See the description of the clastic belt under "Elwren Formation.") The West Baden overlies the Blue River Group (Valmeyeran and Chesterian) conformably except at a few localities along the clastic belt where basal sandstone of the West Baden Group lies disconformably as deep as 50 feet (15 m) below the normal position of the top of the Blue River Group (Malott, 1952, p. 49). The West Baden Group is overlain conformably by the Stephensport Group (Chesterian) or disconformably by the Mansfield Formation (Morrowan).

Correlation: The West Baden Group correlates with rocks within the lower part of the North American foraminiferal Zone 16s of Mamet and Skipp (1971) and within the Visean Series (V3cs) of European usage. On the basis of its conodont faunas, the West Baden was assigned to the upper part of the Gnathodus bilineatus-Cavusgnathus charactus Assemblage Zone of standard North American usage by Collinson, Rexroad, and Thompson (1971).

Naming of groups in upper part of Mississippian System in Indiana: Rocks that are now considered to belong to the Chesterian Series in Indiana previously went by a variety of names, most of which originated elsewhere. Among these names are Ferruginous Sandstone, Kaskaskia Limestone, Archimedes Limestone, Pentremital Limestone, and Chester Limestone, most of which were originally used in early reports on the geology of the region surrounding Ste. Genevieve, Mo., and Chester, Ill,

Hopkins (1902, 1904) first applied an indigenous name to these rocks in Indiana. He included in his Huron Group, named for a village in southwestern Lawrence County, all rocks from the top of the Mitchell Limestone (see the discussion under "Blue River Group") to the base of the Mansfield Formation. The name Huron was used for a time, but it was preoccupied, and when equivalence to the Chester Group of southern Illinois became clear, Greene (1911, p. 269) suggested that the name Chester be substituted. He then casually and without explanation used the name Solsberry Formation for these rocks (Greene, 1911, p. 275, 281) .

As the term Chester came into common use and formational names became accepted, subdivision of the series into groups became possible. These subdivisions were called "lower," "middle," and "upper Chester" (Cumings, 1922, p. 408, 515) and were used as groups, sometimes with capital letters, but were commonly not expressly called groups. "Chester" became "Chesterian," a time and time-rock name that is appropriately designated a series or epoch but that is inappropriate as a group name; principally for this reason Gray, Jenkins, and Weidman (1960, p. 44) adapted two group names earlier suggested by Cumings (1922, p. 514), West Baden and Stephensport, to replace with some modification the former usage, lower and middle Chester. The Kentucky name Buffalo Wallow was adopted by Gray (1978) in a group sense and in somewhat modified scope for outcropping upper Chesterian rocks.