Type and reference section: The Cranberry Marsh Member was named by Doheny, Droste, and Shaver (1975, p. 32-33) for pertinent rocks that were cored in the Northern Public Service Co. August Taelman No. 1 well, eastern LaPorte County, Ind. (NE¼ sec. 16, T. 36 N., R. 1 W.), and that were assigned as the upper member to the Detroit River Formation. A principal reference section was designated as rocks that are exposed in the Woodburn Quarry of May Stone & Sand, Inc., eastern Allen County, lnd. (NE¼ sec. 23, T. 31 N., R. 14 E.), and that have been cored in Indiana Geological Survey drill hole 188.
Description: The Cranberry Marsh consists of a series of inter bedded gray to dark-brown lithographic to sub lithographic limestones, dolomite, and evaporate rocks. Some dolomitic grainstones and packstones are included, but micritic texture is a dominating character for this upper member of the Detroit River Formation. Brecciated intervals (due to evaporate solution?), shaly partings, and thin lamination are other features of note. As much as 30 feet (9 m) of massive gypsum is found in the lowest part of this member in eastern LaPorte County and western St. Joseph County.
The Cranberry Marsh conformably overlies the Milan Center Dolomite Member of the Detroit River Formation, probably in a partial facies relation. Where the Milan Center is absent from parts of northeastern Indiana, the Cranberry Marsh overlies the Grover Ditch Member, probably conformably. The Cranberry Marsh is overlain unconformable by the Traverse Formation (Middle Devonian) in an up dip overlapped, truncated manner.
The known Cranberry Marsh distribution is mainly in the subsurface of northern Indiana north of the Cincinnati and Kankakee Arches. From an eroded edge extending from Allen County to Pulaski and Lake Counties, the unit thickens toward northernmost LaPorte County to 60 feet (18 m) or more. Recognition is poor in northeastern Indiana, which may be due to two circumstances: truncation by the overlapping Traverse Formation and the facies relationship of the Cranberry Marsh and the Milan Center with the Grover Ditch Member. As the latter thickens, the other two members thin.
Correlation: No index fossils are known from the Milan Center, but the presumably isochronous Tioga Bentonite Bed is found in the Milan Center in part of the distribution of the member. Therefore, much of what is said elsewhere about correlation of the upper parts of the Detroit River and of the Grover Ditch applies to the Cranberry Marsh. (See articles on the Detroit River and the Grover Ditch.)
The Cranberry Marsh correlates physically with the lithologically similar Vernon Fork Member of the Jeffersonville Limestone, southern Indiana, specifically the upper part: with the Cooper Member (fine-grained to lithographic rocks) of the Grand Tower Limestone, central and southern Illinois (Meets and Swann, 1965, p. 7): and with part of the Dundee Limestone, northwestern Ohio. (See Janssens, 1970, and Sparling, 1983.) The Cranberry Marsh has also been correlated (Rooney, 1965, p. 270) with the so-called Reed City Anhydrite of Ells (1958, figs. 8 and 9), which Ells assigned to the upper part of the Detroit River Group but which Gardner (1974) assigned to the lower Dundee, southern Michigan.
The basal Cranberry Marsh gypsum unit in LaPorte and St. Joseph Counties has been confused with evaporate rocks in the Grover Ditch (Rooney, 1965), but that identification is no longer tenable.