Historical:Daysville Dolomite Member
H. B. Willman and T. C. Buschbach
The Daysville Dolomite Member of the Glenwood Formation (Templeton and Willman, 1963, p. 50), which commonly overlies the Kingdom Sandstone Member, is named for Daysville, Ogle County.
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.
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.
Worm borings are the only fossils known in the Daysville Dolomite Member.
TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.
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