The Winneshiek Shale is a Middle Ordovician shale deposit exposed within an ancient meteorite impact crater near Decorah, Iowa, roughly four hundred and sixty million years old, preserving an unusual, isolated marine fauna that includes one of the oldest known eurypterids and a jawless fish found nowhere else, protected from open ocean conditions by the crater's semi-enclosed basin. The deposit's crater setting makes its fauna distinct from other Ordovician sites of similar age.
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Winneshiek Shale (Wikipedia)
In Discipline: Stratigraphy, Lead paragraphQuote, In Discipline: Stratigraphy, Lead paragraph
The Winneshiek Shale (originally the Winneshiek Lagerstätte) is a Middle Ordovician (Darriwilian-age) geological formation in Iowa
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