Ellsworth Member

Devonian and Mississippian Systems

Type section and history of name in Indiana: The name Ellsworth Shale was first used by R. B. Newcombe in 1932 (p. 156) and then formally proposed (Newcombe, 1933, p. 49-51) for 30 to 40 feet (9 to 12 m) of greenish-gray shale exposed in the Petoskey Portland Cement quarry in the NE¼NE¼ sec. 26, T. 32 N., R. 8 W., 12 miles (2.4 km) south of Ellsworth, Antrim County, Mich. This exposure constitutes the type section. The name is used here with formation rank for the coextensive section in the area north of the Kankakee and Cincinnati Arches in Indiana and as the Ellsworth Member of the New Albany Shale south of the arches (Lineback, 1970; Hasenmueller and Bassett, 1981). Use of the name Ellsworth Member (of the New Albany Shale) in the northern part of the Illinois Basin was established by Lineback in 1970. At that time tongues of greenish-gray shale that Lineback believed occupied the same stratigraphic position as the upper part of the Ellsworth were noted in southwestern and west-central Indiana. The name Hannibal Member was later applied by Becker (1974) to these tongues and to much of the shale that had been called the Ellsworth Member by Line back. The name Hannibal Member was also applied in 1979 by Lechler and others to the body of dominantly greenish-gray shale lying stratigraphically beneath the Rockford Limestone and above the brownish-black shale that constitutes most of the New Albany. Still later, however, the name Ellsworth Member (of the New Albany Shale) was reapplied by Hasenmueller and Bassett (1981) to the rocks that Becker (1974) had called the Hannibal Member.

Description: The lower part of the Ellsworth Shale consists of alternating beds of gray-green shale and brownish-black shale the number of brownish-black shale beds diminish upward. The upper part is a grayish-green shale bearing light-greenish limestone or dolomite lenses and in some places dark-gray, thinly laminated dolomite. The Ellsworth Shale is overlain in northeastern most Indiana by the Sunbury Shale and is generally not differentiated from the Coldwater Shale (Kinderhookian and Valmeyeran) beyond the limit of the Sunbury Shale in western Lagrange County (Hasenmueller and Bassett, 1981). The Ellsworth overlies the Antrim Shale, and the Antrim-Ellsworth boundary is generally placed at the base of the lowest greenish-gray shale bed. The thickness of the Ellsworth ranges from less than 40 feet (12.2 m) in northern DeKalb County to more than 200 feet (61 m) in Lagrange County. Much of this change in thickness is attributed to the lower part of the Ellsworth grading into the Antrim (Hasenmueller and Bassett, 1981).

The Ellsworth Member contains both brownish-black and greenish-gray shales, although volumetrically greenish-gray shale is the dominant lithology. The upper part of the member consists predominantly of greenish-gray shale, and the lower part consists of greenish-gray shale inter bedded with brownish-black shale. The interbedded lithology occurs in the extreme northern part of the Illinois Basin in Indiana. In cores the Henryville and Jacobs Chapel Beds are recognized in the upper part of the Ellsworth (Hasenmueller and Bassett, 1981) as far north as Hendricks County.

The Ellsworth Member is present throughout much of the Illinois Basin in Indiana. It cannot be recognized in areas where both the Rockford Limestone and the Henryville Bed are absent, and it is not recognized in parts of west-central and south-central Indiana Bassett and Hasenmueller, 1980 Hasenmueller and Bassett, 1981). In Morgan County in central Indiana the Ellsworth Member, including the Henryville Bed, is about 27 feet (8 m) thick. In Sullivan and Vigo Counties the Ellsworth is as much as 22 feet (7 m) thick, and in Posey County in southwestern Indiana it is as much as 48 feet (15 m) thick. In the northernmost part of the Illinois Basin the Ellsworth Member thickens rapidly and is as much as 83 feet (25 m) thick in northwestern Benton County.

Correlation: The Ellsworth Member is equivalent to the Hannibal and Saverton Shales, the Louisiana Limestone, and the Horton Creek Formation of Illinois (Cluff and others, 1981). The upper part of the unit is equivalent to the Bedford Shale, the Berea Sandstone, and the Sunbury Shale of eastern Michigan and western Ohio (Keller and Burger, 1970 Shaver and others, 1985).