H. B. Willman and John C. Frye
Paleocene means "ancient and recent."
South of Illinois, the two formations of the Paleocene (Clayton and Porters Creek) are classified as the Midway Group.
Extent and Thickness
In Illinois, the Paleocene Series occurs only in the extreme southern counties-- Alexander and Pulaski. Paleocene deposits there have a maximum thickness of about 170 feet and are well exposed along the Ohio River near Olmsted and along the Cache River near Unity.
The Paleocene Series (Schimper, 1874) was differentiated from the Eocene because the floras of the sediments were believed to be sufficiently different from those of the younger Eocene to merit establishing a separate series. The floras of the Paleocene bridge the gap between typical Cretaceous and Eocene floras. The Paleocene consists of the Clayton (below) and Porters Creek Formations. Both formations include marine clays, but the Clayton is sandy and strongly glauconitic. The clays are dominantly montmorillonite (Pryor and Glass, 1961). The heavy minerals in the Paleocene sediments are similar to those in the Cretaceous and indicate their source was the metamorphic rocks of the Piedmont region far to the east.
Paleocene rocks are fossiliferous, but most of the fossils are microfossils or poorly preserved macrofossils.
PRYOR, W. A., and H. D. GLASS, 1961, Cretaceous-Tertiary clay mineralogy of the upper Mississippi Embayment: Journal of Sedimentary Petrology, v. 31, p. 36-51; Illinois State Geological Survey Reprint 1961-M.
SCHIMPER, W. P., 1874, Traite de paleontologic vegetale: v. 3, p. 680-682.
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