Beecher Member

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Lithostratigraphy: Ottawa Limestone Megagroup >>Galena Group >>Kimmswick Subgroup >>Dunleith Formation >>Beecher 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 Beecher Member of the Dunleith Formation (Templeton and Willman, 1963, p. 120).


Named for Beecher Street in East Dubuque, Jo Daviess County.

Other names


Type section

Type location

The type section of the Beecher 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)), where the Beecher Member is 6.3 feet thick.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The Beecher Member of the Dunleith Formation overlies the St. James Member.

Extent and thickness

The Beecher Member is commonly is about 8 feet thick in the northern outcrop area and 12 feet in the southern area.


In the type section the Beecher is lithographic to fine-grained, dolomite-mottled limestone, typical of the northern limestone facies, but in most of northern Illinois it is relatively pure, noncherty, mainly massive, vuggy dolomite. High purity and massiveness differentiate it from the cherty Eagle Point Member above and the more argillaceous St. James below. In the southern limestone facies it is coarse-grained, gray to pink, almost wholly massive, pure calcarenite.




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