Devonian System

Type area and use of name in Indiana: First designated the Detroit River Series (Lane and others, 1909, p. 555), the rocks exposed along the Detroit River in southeastern Michigan are now referred to the Detroit River Group and constituent formations in that state. In Indiana the name Detroit River Formation was first adopted by Schneider and Keller (1970), following the outlines of Pinsak and Shaver (1964), and has since been used for ail Middle Devonian rocks that lie between Silurian rocks (below) and the Traverse Formation (above) and that are north of the Kankakee and Cincinnati Arches. (See the historical review of the study of Middle Devonian rocks in northern Indiana by Doheny, Droste, and Shaver, 1975, p. 4-7.)

Description: The Detroit River Formation of northern Indiana exhibits three basic lithologies or mixtures of lithologies that respectively characterize three named members and that are partial facies of one another. The generally lower interval of Detroit River rocks begins at its base with sandy dolomicrite that grades up into a series of cyclically deposited light-colored fine-grained dolomite and evaporate rocks. These are, in ascending order in a typical cycle, light-gray massive dolomite mudstone, pale-blue anhydrite and white crystalline gypsum, pale-yellowish-brown massive dolomite mudstone, and dark-yellowish-brown laminated dolomite mudstone. This range in lithology characterizes the Grover Ditch Member.

In a generally middle position, the Detroit River consists of dolomite that is richly colored tan and brown, fine grained, saccharoidal, vuggy, and characteristic of the Milan Center Dolomite Member. Oolitic and pelletoidal rocks and grainstones and packstones, some obviously fossiliferous, are included. In a generally upper position, the formation consists of gray to dark-brown sublithographic and lithographic dolomite (evaporitic dolomite?) and limestones and massive to thin beds of gypsum and anhydrite. Some carbonate sections are brecciated, and a few are cherty. These lithologies characterize particularly the Cranberry Marsh Member.

A metabentonitic shale, 1 to a few inches (0.03 to 0.15 m) thick and called the Tioga Bentonite Bed, is present in some subsurface sections and quarry exposures. It has been found in all three facies described above.

The Detroit River Formation unconformably overlies Silurian rocks of the Salina Group as low as the Mississinewa Shale Member (Wabash Formation) in regionally truncative fashion. It is overlain unconformably by the Traverse Formation in an overlapped manner. Detroit River rocks extend from an eroded edge (zero thickness) along the north flank of the Kankakee and Cincinnati Arches, through a northeastward-thickening wedge that ranges in thickness along the Michigan-Indiana line from about 80 feet (24 m) to more than 160 feet (49 m). Nearly all this distribution is in the subsurface because there are thick Quaternary materials in that area and because the Traverse generally overlaps the Detroit River southward, although along much of the southernmost distribution of these rocks post-Middle Devonian erosion has removed the proof of overlap.

Correlation: Because much of the Detroit River Formation of northern Indiana was deposited in penesaline to hypersaline conditions, normal-marine fossils of the kind used for interregional correlation in the age sense are scarce. Statements on correlation, therefore, rely mostly on physical tracing and position in the stratigraphic sequence. Nevertheless, a few conodont determinations, the Tioga Bentonite Bed, and some intertonguing of Detroit River rocks with normal-marine rocks in western Ohio and in southern Indiana (speculative; before erosion) provide keys that allow close correlations.

Much of the Detroit River of Indiana is an up dip extension of the much thicker Lucas Formation (Detroit River Group) in the deeper part of the Michigan Basin. In Steuben County, far northeastern Indiana, the lowest Detroit River interval may correspond to parts of the Sylvania Sandstone and the Amherstburg Formation of adjacent Michigan and Ohio (Shaver and others, 1985). And according to Rooney (1965), the upper Detroit River evaporate section of northwestern Indiana correlates with the so-called Reed City Anhydrite of western Michigan.

The Detroit River of Indiana extends directly into most of a northwestern Ohio sequence that begins at its base with the Sylvania and the Amherstburg and extends upward through the Lucas and thence into a westward-transgressive body of normal-marine rocks made up of the Columbus and Dundee Limestones. In this relationship, therefore, an upper part (lithographic carbonate rocks) of the Detroit River of Indiana extends into Ohio as a middle to lower part of the Dundee Limestone of Janssens (1970, figs. 1 and 7) and Sparling (1983, fig. 9 and p. 839).

Although Detroit River rocks are now physically separated (because of erosion) from the Jeffersonville Limestone of central and southern Indiana, similar lithologic sequences in each formation suggest close, almost member-by-member correlation (Droste and Shaver, 1973 and 1975a).

Conodonts have been found only sparingly in the Detroit River of Indiana and in LaPorte County include species assignable to the Polygnathus costatus (P. "webbi") Zone and that came from well below the Tioga bed. The Tioga elsewhere in the northeaster United States is known to occur at or just below the base of the Icriodus angustus Zone of Orr's (1971, p. 19-20) usage and equivalent biostratigraphic levels in the northeastern United States. (See Shaver and others, 1971, p. 54-55; Droste and Orr, 1974; and Sparling, 1983, p. 839.)

All these interrelated circumstances strongly suggest that the oldest Detroit River rocks of Indiana are as old as late Early Devonian (Emsian, global standard) and that the youngest Detroit River rocks are middle Middle Devonian (late Eifelian) in age. Close, but not necessarily exact, correlative include, therefore, the units already mentioned for Michigan, western Ohio, and southern Indiana; the Onondaga Formation of New York; the Grand Tower Limestone of Illinois; and the Jeffersonville Limestone of western Kentucky. Also, small, lower parts of the Lingle Formation of Illinois, the North Vernon Limestone of southern Indiana, the Sellersburg Limestone of western Kentucky, and the Marcellus Shale of New York may be correlatives of the uppermost Detroit River rocks as defined in Indiana.