Devonian System

Type locality and reference sections: The North Vernon Limestone was named (Borden, 1876, p. 148, 160) for North Vernon, Jennings County, Ind., where blue and gray limestone was exposed below the New Albany Shale and above the Jeffersonville Limestone (then called the Corniferous Limestone) in quarry exposures. Three reference sections were designated by Burger and Patton (1970, p. 120) as follows: (1) Scott County Stone Co. quarry near Scottsburg, Ind. (center N2 sec. 20, T. 3 N., R. 8 E.), about 19 feet (5.8 m) of the formation exposed; (2) Louisville Cement Co. quarry 1 mile northeast of Speed, Clark County, lnd. (Clark Military Grants 131 and 132), about 21 feet (6.4 m) exposed; and (3) Sellersburg Stone Co., Inc., quarry at Sellersburg, Clark County, Ind. (Clark Military Grant 90), about 21 feet (6.4 m) exposed .

History of nomenclature: Although Borden (1876) related type North Vernon rocks to what was then called the Hydraulic Limestone (now the Silver Creek Member) in the Clark County area, much confusion in nomenclature has attended studies of the North Vernon and equivalent rocks in Indiana and Kentucky. In 1899 the name Sellersburg Beds was given by Kindle (p. 8, 23, and 110) to nearly the same section that was named by Borden, that is, to the limestones directly underlying the New Albany Shale and extending down to the lowest beds mined in the cement quarries of Clark County. The New York term Hamilton Group was also used for these Indiana rocks at about this same time, for example, by Blatchley and Ashley (1898, p. 19). In 1901 Siebenthal (1901b, p. 345-346) named the Cement Rock the Silver Creek Hydraulic Limestone and restricted the Sellersburg to bioclastic rocks that lie above the Hydraulic Limestone and that had been called the Crinoidal (Encrinital, Encrinai) Limestone (presently the Beechwood Member of the North Vernon). Butts (1915, p. 120) later restored the original definition of the Sellersburg and named the upper crinoidal beds the Beechwood Limestone Member and the lower beds the Silver Creek Limestone Member. As recorded by Wilmarth (1937, p. 1952), Butts's scheme was adopted by the U.S. Geological Survey.

In this same period, however, additional facies (mostly faunal) of North Vernon (= Sellersburg) rocks were studied. Among them are: the New Chapel Chert Bed, named by Whitlatch and Huddle (1932, p. 3671 for a cherty interval in the upper part of the Silver Creek; the Speeds Member of the Sellersburg (= North Vernon) as named by Sutton and Sutton (1937, p. 326) for shaly fossiliferous (identified as Hamilton fossils) limestone exposed below the cement beds in Clark County; and the Deputy and Swanville Formations as named by Campbell (1942) for faunal facies of already named units or combinations of units. Campbell also changed the rank of the Speeds, the Silver Creek, and the Beechwood from member to formation.

Fossiliferous North Vernon rocks exposed in the upper Wabash Valley in northern Indiana are a matter of historical record of probably more than 120 years, but not by that name. "Jeffersonville Limestone" was one of the names used along with these newer names: Logansport Limestone named by Cooper and Warthin (1941), Little Rock Creek Limestone also named by Cooper (1941), and Miami Bend Formation named by Cooper and Phelan (1966). Still later, Orr (1969) referred these same rocks in Cass and Carroll Counties to the Traverse Formation (corresponds to the North Vernon). (See Shaver and others, 1971, p. 52-53; Orr, 1971, p. 9; Thornbury and Deane, 1955, p. 18-19; and Doheny, Droste, and Shaver, 1975, p. 4-5, for summaries of the nomenclatural history of the North Vernon and related rocks in northern Indiana, including an assessment of the newer names as being rather strictly described on faunal bases.)

Since about 1960 the Indiana Geological and Water Survey has taken a consistent stand (as recorded in Shaver and others, 1970) on use of the term North Vernon Limestone in place of the later published name Sellersburg Limestone; furthermore, since the 1970 mapping of Schneider and Keller, the term North Vernon Limestone has been applied to the appropriate rocks south of the structural crest in northern Indiana, whereas the term Traverse Formation has been used for the corresponding rocks north of the structural crest. Moreover, the members, where recognizable, have been called the Speed and Silver Creek Members in the lower part and the Beechwood Member in the upper part, which in these exact spellings and combinations are slight variations from historical uses.

Nevertheless, in the modern period of study, James E. Conkin and associates have used in southern Indiana and adjacent Kentucky not only the names used here in southern Indiana but also all, or nearly all, the names of southern Indiana derivation not recommended here or by the Kentucky Geological Survey. These uses include formation and group ranks not in accord with the ranks given here. (For example, see Conkin and Conkin, 1972, p. 15-16, and Conkin, Conkin, and Lipchinsky, 1976, fig. 10, and 1980, figs. 5 and 6, for the many names, for variations in ranks and surnames, and for a member, the Carey Member of the Beechwood Formation (and Limestone) not mentioned above. Compare such schemes with the official positions of the Indiana and Kentucky Geological Surveys as recorded in Shaver and others, 1985.)

Description: Although basically a limestone, the North Vernon has many lateral and vertical facies. In its type area and southward along outcrop the formation has been described in three parts. Two lower parts consist variably of gray dense massive argillaceous dolomitic limestone called the Silver Creek Member (the Cement Beds of older literature) and of gray granular to shaly thin-bedded very fossiliferous limestone called the Speed Member. These members are in facies relationship with one another. (See articles here.) The upper part, called the Beechwood Member, consists of gray and dark-gray medium-grained to very coarse grained thin- to thick-bedded crinoidal limestone containing glauconite and, in its basal part, black phosphate grains and pebbles.

These lithologies are not identified as separate members far northward along this Devonian outcrop area or in the subsurface, however, where the formation now has widespread recognition. (See Thornbury and Deane, 1955, p. 18-20; Shaver, 1974a, p. 5; Beeker, 1974, p. 42-43; and Doheny, Droste, and Shaver, 1975, p. 84-86.) In this northern area the North Vernon is generally light colored (tan, gray, white). Granularity varies from very fine grained in dense, earthy, shaly, or argillaceous rocks, including some sublithographic limestone, to fine grained (calcisiltite), to very coarse grained (biocalcarenite). Some tan limestones consist of very fine grained earthy, chalky matrix hosting coarser carbonate sand grains consisting of fossil fragments. Chert, glauconite, and phosphate are fairly common but not simply in the stratigraphic order noted above for the classic southern Indiana outcrop area. Dark-brown granular vuggy dolomite, as well as interbedded dark shale in the upper part of the formation, is present far northward. Many of these limestones are conspicuously fossiliferous .

The North Vernon overlies unconformably both the Jeffersonville Limestone (Middle Devonian) and the Wabash Formation (Upper Silurian). It underlies the New Albany Shale both conformably and unconformably. (See Shaver and others, 1985, for areas and magnitude of these changing relations.)

By complementary definition with the Traverse Formation as noted above, the North Vernon is limited in its Indiana distribution to the Devonian outcrop area southwest and west of the Kankakee and Cincinnati Arches and to the subsurface in the Illinois Basin. In this distribution the formation ranges in thickness from an erosional zero to an average of about 25 feet (7.2 m) where uneroded near the outcrop and to 120 feet (37 m) or more in Posey County (Becker, 1974, fig. 22). In the area of Jasper County, northwestern Indiana, where upper rocks of the Muscatatuck extend physically across the Kankakee Arch in thicknesses of 20 to 25 feet (6.1 to 7.6 m), the North Vernon Limestone and the Traverse Formation may be considered as having a mutual vertical cutoff boundary.

Correlation: On the basis of its many macrofossils, the North Vernon has been correlated approximately with the Hamilton Group (upper Middle Devonian) of New York for more than a hundred years. The more recent conodont work reaffirms this correlation. The upper part of the Silver Creek (lower North Vernon), as well as the Skaneateles Formation (upper lower Hamilton) of New York (see Rickard, 1975, pl. 3), is in the Icriodus latericrescens latericrescens Zone (early Givetian, global standard) (Orr and Pollock, 1968). (See, however, the discussion under "Speed Member" for other opinion on age.) The Beechwood (upper North Vernon), as well as the Ludlowville Formation of the lower upper Hamilton, lies in the lower part of the Polygnathus varcus Zone (middle Givetian) (Orr, 1971, p. 17).

In the midwestern area the North Vernon correlates approximately or very closely with: the Lingle Formation, Illinois (see North, 1969); the Traverse Formation, northern Indiana; much of the section ranging from the Dundee Limestone through the Traverse Group (Limestone), Michigan; the section ranging possibly from the uppermost part of the Columbus Limestone through the Traverse Group (Formation), central to northwestern Ohio; and the Sellersburg Limestone, central Kentucky. (See Shaver and others, 1985.)