L Roebuck
Technical Support
Caving
^V^ Just a caver
Posts: 2,023
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Post by L Roebuck on Jun 15, 2007 8:36:27 GMT -5
;D Yes that pesky rock is in the way! It is hard for me to tell if there is a thin shell or not. But Maybe? Sure you can email Dr. Manger the picture.
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Post by Azurerana on Jun 15, 2007 17:23:50 GMT -5
Pesky geology schoolmarm butts in: Ord-O-vician... Ordovician-- from the Ordovicies-- name of a Celtic tribe.
Thanks for taking a look, Gillip. *|:-)
BTW-- It's probably not that relevant what the fossil is made of -- I've got plenty of siliceous fossils which were carbonates in their former lives. The reimmersion chertification of the whole known world....I'll never be certified, but there is great hope some day I could be chert!
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Post by gillip on Jun 16, 2007 21:36:29 GMT -5
I should write Ordovician 50 times so I remember how to spell it. Although a major spelling mistake is nothing new for me. I am sure that the editor at work cringes every time I hand her a report, mainly because of all the spelling errors. And sentence fragments. I guess that I should have clarified what I meant about the acid. If the rock is carbonate, and only the fossil is silicious, it may be the original material. In the picture, it looks like the rock is carbonate, so I assumed it is in limestone. You know what happens when you assume something. Most of the time when calcite or aragonite of a fossil are replaced by silica, the carbonate in the rock is replaced as well. I have seen some exceptions, where the calcite or aragonite of a fossil were dissolved and silica crystals form a vug inside the fossil's mold. I have also found a silicified fossil reworked into a younger carbonate formation. I have a ton, or at least several hundred pounds, of chert with various fossils. Corals, brachiopods, trilobites, crinoids, blastoids, etc. In north west Arkansas, it is nearly impossible to get away from the Boone Formation. I think it is the Reed Springs Formation in Missouri.
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Post by Azurerana on Jun 17, 2007 21:27:46 GMT -5
The Boone grades grades into the Elsey, Reeds Spring and even the Burlington up here.
And all three are chock full of fossils. Give me the Mississippian Period any old day for critters!
Of course a fair amount of our Cambrian and Ordovician is dolomitized. Sometimes it dissolves the fossils like the textbooks say. And sometimes not. (Even though the rock won't fizz in cold HCl).
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Post by gillip on Jun 19, 2007 6:30:28 GMT -5
Lynn, your fossil has been identified. Dr. Manger replied: "Your paloentology is still active, and It is a nautiloid. You are correct in questioning the sepatal arrangement. This is the siphuncular region of an endoceratoid nautiloid; remember the picture of the section I took in the men's room? [ed: This is not what it seems. The stalls in Ozark Hall are made from Ordovician Limestone. As a general rule don't look for nautiloids in the mens room] You've got the endocones preserved here. The septa and septal necks would be inserted into the depressions. Septa of endoceratoids are very thin and fragile, so many times you have only the siphunular regions preserved."
So there it is. The siphunculare region of an endoceratoid nautiloid. This would be only the pink area in the diagram jonsdigs posted. As soon as I read this, I could clearly see what he was talking about.
He also mentioned that the department is lacking in specimens of endoceratoid nautiloids, so if anyone out there has spare specimens of endoceratoid nautiloids they are willing to part with for educational purpose, it would be appreciated.
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L Roebuck
Technical Support
Caving
^V^ Just a caver
Posts: 2,023
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Post by L Roebuck on Jun 19, 2007 7:46:18 GMT -5
Thanks Gillip, so it is a nautiloid, afterall. I appreciate you taking the time to get the identification. No doubt that's an interesting mens room in Ozark Hall.
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