Pliocene Series

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Lithostratigraphy: Embayment Megagroup
Chronostratigraphy: Cenozoic Erathem >>Tertiary System >>Pliocene Series

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 John C. Frye


Original description

Pliocene Series (Lyell, 1833).


The Pliocene Series, translated as "more recent," was so named because the major part of the invertebrate fossils are referable to modern species.

Other names

All of the Pliocene Series deposits were previously called "Lafayette", "Lafayette-type", or "Tertiary" gravel.


Type section

Type location

Type author(s)

Type status

Reference section

Reference location

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Stratigraphic relationships

Extent and thickness

The Pliocene Series is represented in Illinois by the widespread brown chert gravel deposits of southern Illinois-- the Mounds Gravel-- and the similar but scattered deposits in western Illinois-- the Grover Gravel.





Well log characteristics


Age and correlation

Both the Mounds and Grover Formations probably contain some deposits reworked during the early Pleistocene that are not readily differentiated from those deposited during the late Tertiary. Consequently, both the Mounds and Grover Formations are assigned a Pliocene-Pleistocene age (Willman and Frye, 1970).

Environments of deposition

Economic importance



LYELL, CHARLES, 1833, Principles of geology: v. 3, London, p. 52-55, 57-58.
WILLMAN, H. B., and J. C. FRYE, 1970, Pleistocene stratigraphy of Illinois: Illinois State Geological Survey Bulletin 94, 204 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation