Ordovician System

Type area, former names, and use of name in Indiana: Weiss and Sweet (1964) proposed the name Kope Formation for 240 feet (75 m) of shale and minor interbedded limestone that "lies between the Point Pleasant formation and shaly limestones equivalent to the Fairmount and MacMillan formations" m the Maysville area of Kentucky and Ohio. This formation includes the lowermost Cincinnatian rocks of that area, rocks that were formerly for the most part assigned to the Eden Shale or the Eden Group. Those terms have acquired a chronostratigraphic connotation, however, and the present name, which was taken from Kope Hollow north of Levanna, Ohio, is intended to be strictly lithographic .

Brown and Lineback (1966, p. 1020) extended the use of the name Kope Formation into Indiana, in part to replace several names that had been applied more in the sense of biostratigraphic zones than as lithostratigraphic units. The former names (Patton, Perry, and Wayne, 1953) included the Eden Group and its component formations, in descending order, the McMicken, Southgate, and Economy Formations. Brown and Lineback (1966) and later Gray (1972b) also expanded the concept of the Kope to include shale below the classic Eden, as explained below.

Description: The Kope Formation includes not only the bluish- to brownish-gray shale that is exposed at many places in the classic outcrop area in southeastern Indiana but also a thick basal dark-brown to nearly black shale that is known only in the subsurface, the Utica Shale of drillers' old terminology. As illustrated and described by Gray (1972b), more than 95 percent of the formation is shale, and in places as much as two-thirds of the shale is brown.

The upper contact of the Kope Formation is apparently conformable but is picked at different horizons in different places because the criterion that distinguishes the Kope from the overlying Dillsboro Formation is the dominance of shale in the Kope as contrasted to a significant, though not dominant, amount of limestone in the Dillsboro. In many places this contact must be arbitrarily placed in a transitional sequence. The basal contact of the Kope is more complex. In southeastern most Indiana the Kope conformably overlies the Lexington Limestone, but limestone of that formation gives way northwestward and interfingers with dark shale of the basal Kope (Gray, 1972b, fig. 9). In a narrow linear area that extends from southern Franklin County to northern Harrison County, basal dark shale of the Kope Formation overlies the Plattin Formation of the Black River Group (Keith, 1985). Northwest of that area, and to the limit of its recognition, the Kope Formation overlies the Trenton Limestone along a time-transgressive discontinuity (Brian D. Keith, oral communication, 1984).

These contact relationships make a statement regarding thickness of the Kope Formation difficult to formulate. Because there is a tendency to step the upper contact of the Kope Formation upward in a northwesterly direction, reflecting a corresponding westward diminution in limestone content of the overlying Dillsboro Formation (Gray, 1972b, fig. 5), the Kope might be expected to thicken northwestward counteracting this trend, however, is a general westward thinning of all parts of the Maquoketa Group. Over most of the area in which it can be recognized, therefore, the Kope Formation is 300 to 400 feet (90 to 120 m) thick. At its southeastern most extent, however, where the basal dark shale is missing and the Kope rests conformably on the Lexington Limestone, the Kope is about 200 feet (60 m) thick and contains more limestone and less shale than it does elsewhere (Gray, 1972b, fig. 9).

As presently defined, the Kope Formation is restricted in Indiana to the area in which the overlying Dillsboro Formation can be discriminated. Thus the Kope can be identified only in the outcrop area of southeastern Indiana and in the near subsurface in core holes and other drill holes for which excellent records were kept, so that the upward increase in limestone content, which is the basis for determination of the Kope-Dillsboro contact, can be adequately evaluated.

Correlation: The greater part of the body of rocks now assigned to the Kope Formation was once explicitly assigned to the Eden Group this part of the formation is now considered to be Edenian in age. The dark shale that forms the basal part of the Kope, however, is in part late Champlainian in age (Sweet and Bergstrom, 1971, fig. 2), and to the extent that the upper contact of the formation steps upward to the northwest, some of the Kope in that area may be Maysvillian in age.

The Kope Formation is laterally continuous with part of the Scales Shale of central and western Indiana, but a boundary between areas of application of these names has not been defined. The age equivalent of the Kope, however, is at least in part found in the Trenton Limestone in western Indiana and Illinois, a consequence of the time-transgressive nature of the boundary between these formations, as explained above.