A visit to the Late Carboniferous



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Opal and Silicified Fossils

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The Paleozoic epicontinental seas consisted of the highest silica concentrations in comparison to the later geologic epochs of the Phanerozoic Eon. Studies show a transition from Cambrian carbonates to predominantly aragonitic marine skeletons beginning in the early Triassic Period as the ocean chemistry and earth's climate changed after the Permian Extinction. In a mutually beneficent relationship, marine organisms use the silica in oceanic waters to build their skeletal shells. Siliceous ooze forms as organisms die and sink to the seafloor. When opal silica accumulates faster than it dissolves, the skeletal fragments are recrystallized and cemented forming chert.  Pictured here is a beautiful fossil coral I found along the Niagara Escarpment near Sturgeon Bay, Wisconsin. The Silurian rocks have resisted glacial meltwaters and erosion as evidenced by the extensive outcroppings, picturesque rocky beaches, and archeological ship wrecks along the peninsula. A first glance an...
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A rare find in the Pennsylvanian Black Shales

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On August 17th, I went on a group trip to the Starved Rock Clay Pit. I was specifically looking for some Listracanthus parts, and upon splitting open a large septarion nodule measuring roughly 2ft across, came upon what looked at first like a poorly preserved denticle. Upon returning home and examining more closely, it appeared to have segmentation. After showing photos of the specimen to Dave Carlson and Jack Wittry of ESCONI, it was identified as a rare  Tyrannophontes theridion Shram, 1969. From Wittry's book, The Mazon Ceek Fossil Fauna, "First discovered at Pit 11,  Tyrannophontes theridion was figured and described in 1969 by Shram. Subsequently, similar species were found preserved in the Pennsylvanian black shales of Iowa and Nebraska." Interestingly, nothing is mentioned of the black shales in Illinois. On a side note regarding the mysterious spiny, eel-shaped  Listracanthus that has eluded paleontologists for 150 years ,  a complete specimen has...
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A Test on Silurian Corals Stained with Alizarin Red S

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I've been slicing up Silurian corals in order to experiment with some histological carbonate staining techniques and analysis, mostly just to have fun following crystal diagenesis, observe morphological changes through coral life/death, mineralogy, etc.. I still have a lot of learning and work to do. This is just a first test using Alizarin Red S diluted with hydrochloric acid. For photos, I used my old Canon PowerShot SX120IS 10MP. Favosites sp. with Alizarin Red staining. Bridgeport Quarry, Chicago, IL Zoom I need to fix lighting! Above is an unknown specimen found at Hawthorne Quarry, Cicero, IL. It could be Alveolites sp or possibly a Chaetitid sponge. Above is another Favosites slice from the same coral, vertical slice. from Bridgeport showing corallites. Dolomite slice with echinoderm skeletal fragments. From Hawthorne. Zoom Mostly need to figure out a different lighting set up and timing of staining. These were all stained at the sa...
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