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Geobulletin
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News from the Geoblogosphere
by Stratigraphy.net
New from Snet:
Lithologs
, a new tool to create lithological/sedimentological logs online..
Blog post recommendation
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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