Silurian/Devonian Tube of Uncertain Affinity - Tentaculite?

[electricshaman]

Found this specimen all by itself, neatly embedded in the surface of the limestone-bedded creek that runs alongside Big Canyon Road to the south of the White Mound site in southern Oklahoma. Geological maps confirm the site is Hunton Group, the same formation group as White Mound, although this matrix is much harder and more crystalline than the limestone at White Mound. This group ranges in age from Early Silurian to Early Devonian.

The whole specimen was extracted along with some of the matrix. You might also notice the fossil looks like it's been somewhat dissolved. This is one of the very first fossils that I found and I made the rookie mistake of soaking it in vinegar, thinking it would clean up nicely. Instead it mostly dissolved away the smooth surface features, but the overall structure was preserved. The original state of the fossil (which I should have taken a picture of) was much the same, but less bumpy. I won't be making that mistake again.

The tube has multi-layered walls with symmetric rings. It might be hard to see in the photo but the inner walls also have rings. The closest thing I can find in the Audubon book which is the right age is tentaculites. Their picture doesn't really match (their example is much more conical shaped with larger ringlets) but the description is pretty close (except for the "coarse" rings and the width) and the age is appropriate. Here's what they have to say about tentaculites:

Description: "60 mm long, 44 mm wide. Small, narrow, straight cone, with coarse rings more uniform toward apex. Area between rings usually has concentric ringlets or lines. Inner wall of cone also has rings. Walls thick, multi-layered, pierced by tiny radiating canals. Interior toward apex has slightly concave septa sealing off sections of tube. Apex closed and bluntly pointed."

They also add: "The apex ends either in a point or a small bulb."

Age: "Lower Silurian through Upper Devonian (possibly also in the Lower Ordovician)"

[FossilDAWG]

The size is much too large for a tentaculitid. Although it is hard to be certain due to the extensive coarse silicification, the size and remaining surface features suggest a crinoid stem to me.

Don

[Rockwood]

The size is much too large for a tentaculitid. Although it is hard to be certain due to the extensive coarse silicification, the size and remaining surface features suggest a crinoid stem to me.

Don

I agree with crinoid stem. Photo #2 shows good casts of the lumen spaces between columnals.

I'm curious, if hesitant to question your wisdom, why you went with silicification over calcite though ?

[abyssunder]

I agree with the others. Crinoid columnal.

According to your other find, the Lobolith, I suppose it could belong to a Scyphocrinitid, Scyphocrinites. http://www.thefossilforum.com/index.php?/topic/36079-lobolite-from-scyphocrinites-morocco/

Edited December 9, 2015 by abyssunder

[FossilDAWG]

I'm curious, if hesitant to question your wisdom, why you went with silicification over calcite though ?

I'm not sure about the "wisdom" part. However, the fossil is clearly highly resistant compared to the matrix it is in, which appears to be limestone (and electricshaman says the bedrock is limestone). If the fossil was calcitic it would have the same chemical composition as the limestone, and so would not be so differentially resistant to erosion. The appearance is quite similar to many coarsely silicified fossils I have collected. Of course we are dealing with a photo here and so any notion of the chemical composition of the fossil is just a hypothesis, which we could test (if we had the specimen in hand) experimentally. I'd predict with a high degree of confidence that the matrix will fizz in dilute acetic acid, and the fossil will not.

Don

[Auspex]

...notice the fossil looks like it's been somewhat dissolved. This is one of the very first fossils that I found and I made the rookie mistake of soaking it in vinegar...

Sounds to me like the fossil was strongly etched by the acid.

[Archimedes]

heavily weathered silicified crinoid stem segment

Edited December 10, 2015 by Archimedes