일반명 : 단괴형식물화석( Fossil Leaf Imprint in Nodule)

학명(Name) : Neuropteris sp.

지질시대(Age) : Carboniferous (Pennsylvanian, 280 mya

지층명(Formation) : Francis Creek Shale

원산지(Location): Mazon Creek, Illinois

On the dumps of coal strip mines of northestern Illinois - some of them not far from downtown Chicago - collectors find curious rounded nodules of rock. These nodules are concretions of siderite, or iron carbonate, and naturally split along the middle. With a careful tap from a rock hammer, a split nodule may reveal a beautifully preserved seed-fern leaf, a shrimp or millipede, or even a Tully monster. This is the Carboniferous-age Mazon Creek locality (or more accurately a set of localities called the Francis Creek Shale, of which Mazon Creek itself is one) whose uniquely preserved fossils provide a glimpse of the history of many organisms that would otherwise have left little trace. Similar concretions are found over a wide area of northern and eastern Illinois, at several sites. However, all of these are collectively known as "Mazon Creek" fossils.

Some "Mazon Creek" localities are known for terrestrial fossils, including beautifully preserved plants and, rarely, insects, centipedes and millipedes, scorpions and other arachnids, and even small amphibians. Others, which formed under marine conditions, include jellyfish and other cnidarians, crustaceans, molluscs, worms, and rare fish. Shown here is a polychaete annelid, Fossundecima, preserved in a concretion that has been split open.