A Geoscience Digital Image Library
A Geoscience Digital Image Library
| Title | Clay ironstone nodule, from near Mazon Creek, Illinois, USA |
|---|---|
| Description | This is a nodule (concretion) from Francis Creek Shale of the Carbondale Formation (Pennsylvanian) near Mazon Creek, Illinois. These concretions, which developed through action of groundwater after the shale was deposited, are made of ironstone, and are mineralogically siderite ( FeCO3 = iron carbonate) with minor clay. These nodules are famous because many of them, when broken, reveal spectacular plant and animal fossils, including many soft parts. The Mazon Creek Area is known as one of the prime “lagerstatten” of the world. Lagerstatten, a term invented in Germany, really means “fossil Mother Lode.” The fossils from this shale come neatly packaged in their own container – namely a nodule or concretion. The concretion protects the fossils and leads to their remarkable preservation. Ironstone concretions are rare, only occurring in certain Upper Carboniferous strata, and have been reported from England, France, Germany and the USA (Illinois, Indiana, Missouri and Oklahoma). This sample is about 7 cm across. |
| Chronostratigraphy | Pennsylvanian |
| Lithostratigraphy | Francis Cr. Shale, Carbondale Formation |
| Location | USA ▹ Illinois. Near Mazon Creek. |
| Photographer | Nessa Eull. 2001-05-21. |
| Collection | Ward’s University Rock Collection #164. |
| Key words | ironstone, Mazon Creek, Francis Creek Shale, lagerstatten |
| Tech details | 666 KB. Hand specimen. Fujifilm FinePix S1Pro digital camera, 60mm Nikon AF micro lens. |
| GeoDIL number | 497 |
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