Devonian System
Type and reference sections: The Grover Ditch Member was named for the lower dolomite and evaporate rocks of the Detroit River Formation that are exposed in the Woodburn Quarry of May Stone and Sand, Inc., and that were cut in Indiana Geological Survey drill hole 188, eastern Allen County, Ind (NE¼ sec. 23, T. 31 N., R. 14 E.). The name was taken from the drainage ditch that empties into the Maumee River alongside the quarry (Doherty, Droste, and Shaver, 1975, p. 24-25). Three other representative sections were designated, including the principal reference section consisting of rocks cored in the Northern Public Service Co. A. Tubbs No. 1 well in Steuben County, Ind. (SW¼ sec. 27, T. 36 N., R. 12 E.).
Description: The Grover Ditch consists of light-colored fine-grained dolomite, cryptocrystalline anhydrite, coarsely crystalline fibrous gypsum, and in its basal part gray fine-grained sandy dolomite. Above the upward-grading (decrease in quartz sand) basal rocks that average 10 to 15 feet (3.0 to 4.6 m) in thickness, yellowish laminated to thick-bedded dolomite mudstones are interbedded with massive dolomite mudstones. Brecciation and interbedded anhydrite and gypsum are common in this interval. Some thick sections show repeated sedimentary cycles consisting in ascending order of (1) dark-yellowish-brown laminated dolomite mudstone, (2) pale-yellowish-brown massive dolomite mudstone, (3) pale-blue anhydrite and white gypsum, and (4) light-gray massive dolomite mudstone. As many as 12 to 15 of these 5-foot (1.5-m) cyclothems have been noted in LaPorte and Steuben Counties.
The Tioga Bentonite Bed, consisting of an inch to a few inches (0.03 to 0.15 m) of metabentonite, is found in the Grover Ditch in part of its northern Indiana distribution.
The Grover Ditch Member rests unconformably on the Wabash Formation of Silurian age and is generally overlain conformably by other Detroit River rocks assigned to the Milan Center Dolomite Member. In some places, however, the Traverse Formation (Middle Devonian) overlies the Grover Ditch in an unconformable, overlapping relationship. The Grover Ditch is generally limited in its distribution to the northern three tiers of Indiana counties north of the crest of the Cincinnati and Kankakee Arches. There it increases from zero along its south and west eroded edge to thicknesses ranging from 20 to 140 feet (6 to 43 m) from west to east along the Michigan state line (Doherty, Droste, and Shaver, 1975, pl. 2C).
Correlation: The Grover Ditch represents a restricted marine environment and therefore mostly lacks faunas useful for interregional correlation. Nevertheless, the oldest Devonian conodont described by Orr (1971, p. 15) in his northern Indiana study come from the Grover Ditch and indicate a middle Eifelian age (early Erian, North American standard). Also, in accord with evidence and principles discussed in the Detroit River article, these general correlations may be stated: Geneva Dolomite Member of the Jeffersonville Limestone, southern Indiana; lower parts of the Grand Tower Limestone, Illinois, and of the Lucas Formation, Michigan; Lucas Formation, Ohio; and the Moorehouse Member and the lowest part of the Seneca Member of the Onondaga Formation, New York.
The Grover Ditch is in partial facies relationship with the other Detroit River members, the Milan Center and Cranberry Marsh, and therefore in a complex sedimentary pattern that has a rather variable age range among the different areas of occurrence. Also, the lowest Detroit River (Grover Ditch) rocks in Indiana may be late Early Devonian (Emsian) in age. (See the Detroit River article.) These circumstances suggest other, partial Grover Ditch correlations: upper parts of the Sylvania Sandstone and the Amherstburg Formation, adjacent Michigan and Ohio in the Michigan Basin, and the Dutch Creek Sandstone Member (Jeffersonville and Grand Tower Limestones), Indiana, Kentucky, and Illinois.