Daysville Dolomite Member

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Lithostratigraphy: Ottawa Limestone Megagroup >>Ancell Group >>Glenwood Formation >>Daysville Dolomite Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Blackriveran 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 Daysville Dolomite Member of the Glenwood Formation (Templeton and Willman, 1963, p. 50).


Named for Daysville, Ogle County.

Other names


Type section

Type location

The type section of the Daysville Dolomite Member is located 3 miles northeast of Daysville, Ogle County, in a ravine (NWNW SW 6, 23N-11E) where is it 23.8 feet thick.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The Daysville Dolomite Member commonly overlies the Kingdom Sandstone Member of the Glenwood Formation.

Extent and thickness

The Daysville Dolomite Member is commonly 15-25 feet thick in the outcrop area but is about 45 feet thick, and locally 75 feet thick, in subsurface in an area extending from De Kalb County eastward to Lake Michigan. It thins rapidly northward, and southward it grades into the Starved Rock Member of the St. Peter Sandstone.


The Daysville is the only calcareous member of the Glenwood. It is largely argillaceous, silty, sandy, greenish gray to white, chalky to dense dolomite and occurs in irregular beds. Locally it is conglomeratic with intraformational dolomite pebbles, and, where it directly overlies the Tonti Sandstone Member of the St. Peter, the basal part contains interbedded layers of sandstone of the St. Peter type.




Well log characteristics


Worm borings are the only fossils known in the Daysville Dolomite Member.

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