Type and reference sections and use of name: The Muscatatuck Group was named for its many exposures along the forks and tributaries of the Muscatatuck River particularly in Jefferson and Jennings Counties, southeastern Indiana (Shaver, 1974a, p. 3-6). It was defined to include in Indiana ail the so-called Middle Devonian carbonate rocks or the Middle Devonian limestone (Limestone) of common usage, which meant all the rocks stratigraphically between the New Harmony Group (Lower Devonian) and the Upper Devonian black shale units above.
The type section was designated as the exposure along the north bluff of Big Camp Creek, Jefferson County (NE¼NE¼SW¼ sec 13, T. 4 N., R. 8 E.), there embracing the Jeffersonville and North Vernon Limestones. Three reference sections were designated, including two in northern Indiana, where the group consists of the Detroit River Formation below and the Traverse Formation above. One of these sections is both cored and exposed in the Woodburn Quarry of May Stone and Sand, Inc., Allen County (NW¼SE¼NE¼ sec. 23, T. 31 N., R. 14 E.).
Description: Several kinds of carbonate and evaporite lithologies make up the Muscatatuck Group. The most common are: drab-colored fine-grained sandy dolomite or dolomitic quartz sandstone, which is generally found lowest in the group but in other positions in some places; (2) brown granular vuggy dolomite, concentrated in, but not confined to, the Geneva and Milan Center Dolomite Members; (3) light-colored to dark limestones that are shaly to pure and granular and conspicuously fossiliferous and that exhibit features generally ascribed to normal-marine depositional regimes, these rocks typifying parts of the Jeffersonville Limestone and much of the North Vernon Limestone and the Traverse Formation; (4) variously colored dense, including lithographic, to fine-grained, commonly laminated dolomites and dolomitic limestones that exhibit other sedimentary features generally ascribed to penesaline or hypersaline depositional regimes and that especially typify parts of the Jeffersonville Limestone and much of the Detroit River Formation; and (5) white to pale-blue cryptocrystalline to coarsely granular and fibrous anhydrite and gypsum, which are found in lower and upper Detroit River rocks. (See several other articles for fuller details and for the complex interrelationships of these lithologies.)
In a few southwesternmost Indiana counties in the deeper part of the Illinois Basin, the Muscatatuck overlies carbonate rocks of the New Harmony Group (Lower Devonian) conformably. Elsewhere the Muscatatuck has mostly an overlapping, truncating relationship with Silurian rocks that range stratigraphically downward from the youngest rocks in the Salina Group (Wabash Formation) to within the Salamonie Dolomite (middle Niagaran). The magnitude of truncation increases in a southeasterly direction.
Except where affected by post-Devonian erosion, the Muscatatuck is overlain by the dark
shales of the New Albany Shale (southern Indiana) and of the Antrim Shale (northern Indiana). In places the contact is conformable, but the absence of a part or the whole of the lower black shale member from some places denotes modest unconformity for those places. The Muscatatuck has two principal areas of exposure in Indiana flanking either side of the Cincinnati and Kankakee Arches the rest of its distribution is subsurface in the Illinois and Michigan Basins. The thickness, therefore, ranges from an erosional zero to more than 250 feet in each of the basins (Shaver, 1974a, fig. 1). (See also Lazor, 1971; Shaver and others, 1971; Becker, 1974; Droste and Shaver, 1975a; and Doheny, Droste, and Shaver, 1975.)
Correlation: The Muscatatuck Group is mostly Middle Devonian in age (Erian, North American standard Eifelian and Givetian, global standard) as shown by different groups of index fossils and as keyed in part by the relationships of the Tioga Bentonite Bed. The lowest part of the Muscatatuck is very likely Early Devonian (Emsian, global standard Ulsterian, North American standard). (See discussions under "Detroit River Formation" and "Jeffersonville Limestone.")
Foremost among the index fossils are the name givers to several conodont zones that have been described by Orr (1964, 1969, 1971), Orr and Pollock (1968), Shaver and others (1971), Droste and Orr (1974), and Sparling (1983), among others. Other zonal indices include especially the brachiopods and corals that define the oft-cited biostratigraphic zones at the Falls of the Ohio. (See Perkins, 1963; Stumm, 1964; Boucot and Johnson, 1968; Powell, 1970; Oliver, 1976; and Conkin and Conkin, 1980.)
As noted in the Jeffersonville and Detroit River articles, the lowest Muscatatuck rocks in basinal positions are possibly late Early Devonian in age.
The closest correlatives of the Muscatatuck Group are: the Grand Tower Limestone and the Lingle Formation, Illinois; the Detroit River and Traverse Groups, Michigan Basin; most of the Detroit River Group through the Silica Formation and the Ten Mile Creek Dolomite, northwestern Ohio; equivalent rocks including the Columbus and Delaware Limestones, central Ohio; and the Jeffersonville and Sellersburg Limestones, western Kentucky .