Here is an amazingly well preserved Pecopteris fossil fern Leaf. It is from the famous Mazon Creek Lagerstatte of Central Illinois. There are several species of Ferns found in the Mazon Creek Floral record.
A Lagerstatte is a German word meaning storage place and we have used it to describe this area that is a “storehouse” of exceptionally preserved flora and fauna. The Carboniferous Period of Illinois was mostly a hot steamy jungle and swamps. The plants and animals were buried in sediment without much Oxygen and began to fossilize. The fossils are found within “Ironstone” nodules. These nodules when broken open display these exceptionally preserved fossils.
Often the “Freeze-thaw” method is used to break them open. The natural cycle of freeze thaw allows water to infiltrate the rock along the line of the fossil. Then freezing breaks it open along that line. If that doesn’t work after a while, a gentle whack with a hammer can help.
Francis Creek Shale
Near Braidwood, Illinois