The Borden Group: Ancient and modern perspectives from the Knobs Overlook, Indiana
One of many remarkable exposures of the Borden Group (lower Middle Mississippian) is on either side of a nearly continuous 1.5-mi (2.4-km) road cut along U.S. 50 leading downthrough the Knobstone Escarpment from the Knobs Overlook (aconvenient parking area for field-trip groups) in the northernthird of section 10 and central western part of section 14, T.5N., R.3E. (Medora and Kurtz 7½-minute Quadrangles), JacksonCounty, Indiana (Fig. 1). From the time of its earliest scientificnote by one of America’s great pioneer geologists (David DaleOwen in 1838), the wedge of Borden rocks, as much as 700 ft(210 m) thick in an area extending from central Illinois eastwardand southeastward into north-central Tennessee, has been intensivelystudied by scores of geologists.
Perhaps the two most significant of the earlier, pioneeringIndiana studies were conducted by Borden (1874) and Stockdale (1931). These and other studies of the time were preoccupiedwith descriptive explorations and with establishing ages of theBorden divisions within the Subcarboniferous Group, a term thatOwen had correctly applied about 150 years ago. Only during amodern period of intensive study in the broader area noted abovedid geologists come to realize that the Borden Group is a sperbexample of a vast ancient delta system complete with bottomset, foreset, and topset beds together with many sedimentologic faciesand ecologic niches afforded by prodelta, delta-slope, deltaplatform, distributary-channel, and interdistributary-flat environments.(See, for example: Swarm and others, 1965; Lineback, 1966;Suttner and Hattin, 1973; Kepferle, 1977; Gray, 1979