Geological Time: Carboniferous (300 m.y.a.) Size: 15 mm in length on a 30 mm x 33 mm nodule; Pos/Neg specimen.
Fossil Site: Mazon Creek, Braidwood, Illinois The Mazon Creek fossils are conservation lagerstätten found near Chicago , Illinois . The fossils are found in ironstone concretions formed approximately 300 mya in the mid- Pennsylvanian epoch of the Carboniferous . These concretions frequently preserve both hard and soft tissues of animal and plant materials, as well as many soft-bodied organisms that do not normally fossilize. The quality, quantity, and diversity of fossils, known since the mid-nineteenth century, make the Mazon Creek lagerstätte important to paleontologists in attempting to reconstruct the paleoecology of the sites.
The Mazon Creek fossils are found in the Francis Creek Shale; the type locality is Mazon Creek , a tributary of the Illinois River near Morris, Grundy County, Illinois . The 25 to 30 meters of shale was formed approximately 300 mya, during the Pennsylvanian period. The fossiliferous concretions are usually found within the thickest deposits of Francis Creek. The concretions occur in locallized deposits within of silty to sandy mudstones in the lower four metres ... read more