Ordovician in Tennessee (Help!)

[Terri]

There seems to be similarities between your fossils and some of those in the Frey paper from that wikipedia page. I'm having a little trouble with the age and stratigraphy though. Generic IDs may be close as they all seem to be fairly long lived taxa, still... need more research.

I'll have to read the paper again too. But we had decided upper Ordovician, Sandbian stage right?

 

[DWhatley]

One more question on this one. Upper right again, just above the solid dark grey out cropping there are several darker grey, almost black bands forming a cone shape (more or less). How do you know this is not a cephalopod fossil?



I am still trying to work out in my mind how to tell an internal mold from an outside one. The main one in this is clearly internal since the section with the siphuncle is resting within the grooves but without that how would you determine that this mold was the inside and not the outside?

 

[Cuddlycuttlefsh]

I've been a member there for a couple of years, but I mostly just enjoy browsing the id. forum. I play a game and try to figure out what the fossil is before I read the responses. Fun!

Heh lol, I do the same thing except with octopus species.

 

[Terri]

D, I really want Kevin (please) to read over your questions in post #508 and my answers in #510, just to
make sure I'm giving you correct information, I think I'm wrong on the 2nd question that I thought was a gastropod mold, after looking at the rock in hand I don't think it's a fossil at all.

darker grey, almost black bands forming a cone shape (more or less).

If your referring to the flatish black form(?) I believe it's a brachiopod you can see the ribs, little fine lines and that straight edge along the bottom, I think would be the hinge line.

I am still trying to work out in my mind how to tell an internal mold from an outside one.

If you imagine the fossil before the shell wore away laying in the sediment on the sea bed, the matrix hardens and the shell wears away and leaves the mold (cast?) of the shell. It can be confusing, but again my answers need to be subject to Kevin's perusal. Maybe he would do an annotation for us.

 

[Architeuthoceras]

Annotated copy of the photo in post #498

The violet outlines what I believe to be an Estwing 22oz. Rock Hammer.

Red outlines brachiopod shells, for some reason they are preserved more often than mollusk shells. I don't know if this is original shell material or if they have been replaced with silica or another form of calcite.

The blue inside the top right brachiopod outlines something that looks like ribs of a large ribbed brachiopod or spines of an echinoid or crinoid columns, more would have to be exposed to find out for sure.

light yellow circles something of unknown affinity, something obviously discolored the rock and made it weather differently, but what it was is a mystery.

The dark yellow outlines the external mold of an orthoconic nautiloid ornamented with transverse annuli.

The green inside the dark yellow outlines what is left of the internal mold, sediment that filled the inside of the shell, and actually has an external mold of the siphuncle, and technically external molds of the septa, but since these were inside the shell we will still call it all an internal mold. Looking close you can see the gap the shell left after it dissolved.

Hope this helps, I will try to get to some of your other questions asap.

 

[Terri]

Awesome! Thanks Kevin, good catch on the hammer . Nice to know I mostly got things right, your explanations are a lot better than mine. There's a little horn coral just to the left of the orthocone..shows a little better in this photo though..

 

[DWhatley]

I understand the difference between internal and external molds mentally, I just don't know how to tell the difference visually but see if this works. A mold that is more or less concave (for a conical shaped object) is formed from the external part of the shell and a casting would produce would you would have seen when you observed the animal. Conversly a fossil that is convex is made from filling a shell and shows the internal design (that may look like the external) and a plaster casting would create the inner body chamber.

Unfortunately, it appears our lated upgrade broke picture enlarging so I will have to return see the marked up copy closely. It is the blue inside the red with the ribs showing that I was wondering about.

 

[Architeuthoceras]

There's a little horn coral just to the left of the orthocone..

A mold that is more or less concave (for a conical shaped object) is formed from the external part of the shell and a casting would produce would you would have seen when you observed the animal. Conversly a fossil that is convex is made from filling a shell and shows the internal design (that may look like the external) and a plaster casting would create the inner body chamber.

Correct

 

[Terri]

Unfortunately, it appears our lated upgrade broke picture enlarging

I think it's just the one picture that's not enlarging.

It is the blue inside the red with the ribs showing that I was wondering about

I think they are probably crinoid bits(?) could even be trilobite, or brachiopod parts. I think the only way to say for sure is if I can uncover them a little.( I dream of proper tools!)

In your defence Kevin, it really didn't show in the first pic.

 

[Terri]

Correct

Love it when Kevin says that...Good job D.

 

[Terri]

I think it's just the one picture that's not enlarging

Weird... some are enlarging and some are not.

 

[DWhatley]

So in my extreme laymen's terms, an outy is an internal mold and an inny is an external

 

[Terri]

Hey Kevin, just a nudge to remind you to look at post #496, It seems a little different than any others at this site, I don't quite know what to make of it.

 

[Terri]

Here's another (I have several more from the last ime out). My first thought was a badly crushed coiled nautiloid OR just a mish mash of ceph parts, the third pic. is the bottom of the fossil, bottom center you can see where a few septa wrap around the side of the rock.

 

[Terri]

There seems to be similarities between your fossils and some of those in the Frey paper from that wikipedia page. I'm having a little trouble with the age and stratigraphy though. Generic IDs may be close as they all seem to be fairly long lived taxa,

What do you mean," having trouble with the age and stratigraphy"? That the site these fossils are coming from are not Sandbian like we thought?