H. B. Willman and T. C. Buschbach
The Rivoli Member of the Dunleith Formation (Templeton and Willman, 1963, p. 122) overlies the Mortimer Member and is named for Rivoli Street in East Dubuque, Jo Daviess County, near the type section.
The type section of the Rivoli 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 Rivoli Member is 19 feet thick.
Extent and Thickness
The Rivoli Member thins eastward from the type section and is 13 feet thick in central northern Illinois.
The Rivoli Member is the most argillaceous of the Dunleith members. The upper 5 feet is a persistent argillaceous zone that is very cherty in the type section. The lower 5-6 feet contains bands of large chert nodules. Corrosion surfaces are strongly developed in the Rivoli. Thin lenses of bentonite are locally present at or near the top and probably occur at other horizons, especially along sharp reentrants.
Receptaculites oweni is abundant in upper Rivoli strata and the overlying Sherwood Member- the Middle Receptaculites Zone.
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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