Mazon Creek fossil beds

Mazon Creek is a Carboniferous fossil locality in Illinois, renowned for ironstone concretions that preserve a diverse range of plants and animals, including soft-bodied organisms.

Ironstone concretion: A rounded mass of iron-rich sedimentary minerals formed around a nucleus within sediment. Many Mazon Creek fossils occur inside these mineral masses, which helped preserve their shapes.
Tullimonstrum: An enigmatic extinct animal known chiefly from fossils in the Mazon Creek region. Its distinctive body plan made it the locality’s best-known fossil.
Pennsylvanian (geology): The later subdivision of the Carboniferous Period, lasting roughly 323 to 299 million years ago. The fossil-bearing deposits formed during this interval.
Paleoecology: The study of relationships between ancient organisms and their environments. Mazon Creek’s varied fossils help reconstruct a Carboniferous ecosystem.
Burgess Shale: A Middle Cambrian fossil deposit in British Columbia famous for preserving soft-bodied marine animals. Both preserve soft tissues, but they formed in different periods and geological settings.
Fossilization: The processes by which remains or traces of organisms become preserved in geological materials. Mazon Creek fossils record an unusual route from burial to preservation.
Esconichthys: An extinct marine ray-finned fish known from Carboniferous fossils, including Mazon Creek specimens. Its fossils show that the locality preserves vertebrates as well as invertebrates.
Illinois Basin: A broad sedimentary basin underlying parts of Illinois, Indiana, and Kentucky. The Mazon Creek deposits lie within this basin’s Carboniferous strata.
Fossil Lagerstätte: A sedimentary deposit that preserves fossils with exceptional abundance, diversity, or detail. Mazon Creek is classified as a Lagerstätte because of its unusually rich preservation.
Solnhofen limestone: A Late Jurassic limestone deposit in Germany famous for exceptionally preserved fossils, including Archaeopteryx. Its fine-grained limestone contrasts with Mazon Creek’s ironstone concretions.

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