Type locality, names, and reference sections: The name Borden Series was proposed by Cumings (1922, p. 487) to replace the older non geographic term Knobstone. Borden in Clark County, Ind., which was the site of the Borden Institute that W. W. Borden founded, was formerly called New Providence and is unique in that the same town serves as the source of the names for the Borden Group and for one of its formations, the New Providence Shale. The type and standard reference sections of the formations constituting the Borden Group, which are in ascending order the New Providence Shale and the Spickert Knob and Edwardsville Formations, provide key sections for understanding the group. See these units for locations of the sections.
Stockdale (1931) named four facies of the New Providence Shale, four of his Locust Point Formation, eight of his Carwood Formation, three of his Floyds Knob Formation, and six of his Edwardsville Formation. He also named two members in his Carwood and five in his Edwardsville. These minor names of Stockdale have remained virtually unused, but a listing can be found in Stockdale (1931) and Shaver and others (1970). (Stockdale's Locust Point and Carwood Formations are treated here as parts of the Spickert Knob Formation, and his Floyds Knob Formation is considered here as a member of the Edwardsville Formation.)
Description: The Borden Group is composed dominantly of gray argillaceous siltstone and of shale. Fine-grained sandstone is common. Interbedded limestones form discontinuous lenses and facies that are minor except for the interval of the Floyds Knob Limestone Member at the base of the Edwardsville Formation. The three formations of the Borden represent three major deposition settings. The New Providence Shale resulted from prodelta deposits, the Spickert Knob Formation from delta-slope deposits, and the Edwardsville from delta-platform deposits. It is convenient, therefore, to summarize the lithology of the Borden in terms of these three units. Descriptions are given for individual formations elsewhere in the compendium.
The New Providence Shale consists dominantly of greenish-gray shale and of minor amounts of red shale, sandstone, ironstone, me stone, and silty dolomite. The lower part of the Spickert Knob Formation includes siltstone, silty shale, and mixtures of these in a complex of discontinuous lenses and facies. Very silty shale is common. Upward the formation includes more massive siltstone and since amounts of sandstone and limestone, which are argillaceous. Ironstone nodules and geodes are irregularly distributed in the formation. Next above the Spickert Knob, the Floyds Knob Limestone Member of the Edwardsville is dominantly limestone, but the rest of the Edwardsville above includes siltstone, sandstone, and sandy shale in varying intermixtures and only minor amounts of limestone, which is biohermal in places.
The Borden outcrop belt, in places as much as 36 miles (58 km) wide, extends in Indiana from the Ohio River in southern Harrison County northward and northwestward to Benton County. The Borden ranges from about 485 to 800 feet (138 to 244 m) in thickness on outcrop (Stockdale, 1939, p. 27). The group consists of a series of lobate deltaic pods of sediment that in total thin in a southwesterly direction, so that the group is represented only by very thin time-equivalent shale in the subsurface of the southwestern-most part of the state. North of Putnam and Parke Counties, however, thinning of the group is the result of the Mississippian-Pennsylvanian erosional unconformity (Pinsak 1957, p. 30).
The Borden Group rests on the Rockford Limestone or, where that is absent, on the New Albany Shale. It is unconformable at the base except in northwestern Indiana, where it is apparently conformable with the Rockford (Rexroad and Scott, 1964, p. 19). The Borden is overlain with apparent disconformity by the Ramp Creek Formation and the laterally equivalent Muldraugh Formation. Along the northern part of the Borden outcrop area in central western Indiana, the Mississippian-Pennsylvanian unconformity truncates younger Mississippian rocks down to the New Albany Shale, so that the Mansfield Formation (Morrowan) overlies the Borden Group in part of that area.
Correlation: The Borden Group is termed the Borden Formation in Kentucky and there includes the Muldraugh Member, which is a postdeltaic equivalent of the Ramp Creek Formation. The Muldraugh was deposited in the topographic basin left after cessation of Borden sedimentation and is not time correlative with any part of the Borden Group of Indiana. In Illinois the group is represented in the subsurface by the Borden Siltstone, and according to Shaver and others (1985), it correlates with the Springville and Warsaw Shales, the Fern Glen Formation, and the Meppen, Burlington, and Keokuk Limestones. Rexroad and Scott (1964, p. 19) showed that the base of the Borden Group in Benton County was in the Bactrognathus-Polygnathus communis Assemblage Zone (conodonts) and correlated with the lower part of the Burlington Limestone of the upper Mississippi Valley. In part of southern Indiana the base belongs in the younger Bactrognathus-Taphrognathus Assemblage Zone and is no older than late Burlington in age. Indeed, a number of workers (for example, Kammer, Ausich, and Lane, 1983; Kammer, 1984; and Butts, 1915) correlated the lower interval with the Keokuk Limestone. Conodonts recovered from the Floyds Knob Limestone Member of the Edwardsville Formation indicated correlation with part of the Keokuk Limestone of the upper Mississippi Valley (Gates and Rexroad, 1970; Whitehead, 1978), as did crinoids from the upper part of the group in Montgomery County (Van Sant and Lane, 1964).