Friday, March 27, 2020

Calymene celebra Trilobite from the Joliet formation

Calymene celebra is the state fossil of Wisconsin and a somewhat common fossil in the white/light grey/tan Silurian aged dolostones that can be found across a number of midwest states. Rocks like this stretch from Wisconsin and Iowa down through Illinois and Indiana into Kentucky.  Below is a specimen of  Calymene celebra from the Joliet formation near Grafton Illinois. It was likely found in a quarry as productive exposures of the Joliet formation are not easy to find. 

This fossil is a cast of the interior of the trilobite exoskeleton so it's missing some of the details one would normally see.  I like this specimen due to the presence of black specks that are present. It kind of reminds me of a Dalmation dog's coat.  I think the black spots are oxidized Pyrite or Marcasite.

I've been fortunate enough to find one specimen of Calymene celebra myself. It comes from a breakwater along Lake Michigan in Milwaukee, Wisconsin where I spotted it among the rocks being used to stabilize the shoreline. It was in a small flat slab so I didn't have to smash anything to collect the specimen. You can see that it was exposed for a time as one side is smooth and some of the fossil detail has been lost.  Since the rocks had been moved from their original location, I am not sure what formation this fossil comes from.

These fossils come from the Silurian period, Llandovery stage (roughly 438-436 mya) which corresponds to the basal Niagaran series in the old N. American chronostratigraphy.

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