Sherwood Member

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Lithostratigraphy: Ottawa Limestone Megagroup >>Galena Group >>Kimmswick Subgroup >>Dunleith Formation >>Sherwood Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Trentonian Stage
Allostratigraphy: Tippecanoe Sequence

Primary source

Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.

Contributing author(s)

H. B. Willman and T. C. Buschbach


Original description

The Sherwood Member of the Dunleith Formation (Templeton and Willman, 1963, p. 123).


Named for Sherwood Street in East Dubuque, Jo Daviess County, near the type section.

Other names


Type section

Type location

The type section of the Sherwood Member is part of the Dunleith Formation type section (in an exposure in the Mississippi River bluffs on the north side of East Dubuque (SE 19, 29N-2W))(fig. O-2B), where the Sherwood Member is 13.6 feet thick.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The Sherwood Member of the Dunleith Formation overlies the Rivoli Member.

Extent and thickness

The Sherwood Member is 10 feet thick in central northern Illinois.


The Sherwood Member consists of relatively pure, vuggy dolomite with a strong argillaceous zone in the top 3.6 feet in the type section. Chert is erratic in occurrence, except for an almost continuous bed of chert just above the base in some areas. One of the most persistent bentonites, as much as 3 inches thick, occurs about 3 feet above the base, and another occurs locally at the base of the upper argillaceous zone.




Well log characteristics


Age and correlation

Environments of deposition

Economic importance



TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation