H. B. Willman and T. C. Buschbach
The Eldena Member of the Nachusa formation (Templeton and Willman, 1963, p. 89) is named for Eldena, Lee County, 6 miles southeast of the type section.
The type section of the Eldena Member is part of the type section of the Nachusa Formation (a quarry on the east edge of Dixon (SE SE SW 33, 22N-9E)) where it is 7.5 feet thick.
The Eldena Member is equivalent to the Leray Member of the Chaumont Formation in New York.
Extent and Thickness
The Eldena Formation is commonly 5-10 feet thick in the northern outcrop area and in Calhoun County, but south of there it thickens to 14 feet in Ste. Genevieve County, Missouri, and to 40 feet at Cape Girardeau, Missouri.
The Eldena Member has the typical Nachusa lithology, except that the lower part has thin partings of blue-gray to gray-green or brown shale, and it is slightly more argillaceous than the Everett Member. In the southern area it contains finely conglomeratic and pseudo-oolitic beds, and a bentonite as much as 6 inches thick occurs at or near the top.
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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