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| Pecatonica Formation | |
|---|---|
| Stratigraphic range: Ordovician | |
| Type | Formation |
| Unit of | Black River Group |
| Underlies | Plattin Formation |
| Overlies | Joachim Dolomite |
| Lithology | |
| Primary | Limestone |
| Location | |
| Region | Illinois, Indiana, Iowa and Wisconsin |
| Country | United States |
The Pecatonica Formation is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.