Colour banding in ammonoids

[Hajar]

I now have this confirmed as a nautilid.

 

[Hajar]

..but the specimen can stay in the ammonoid area since there's an ammonoid just next to the nautilid (I'm exposing it slowly and carefully). Having seen the Lituites I now wonder if the colour bands are the edges of the septa showing through.

 

[Architeuthoceras]

Nice to see that ammonoid

Why or how would the septa make a color band? It seems it would just make the shell a little thicker with the mural part of the septum (if it had some), and if the septa were sutured to the shell without a mural part there would be very little shell thickening. Would that form of preservation also cause color bands on the thick parts and sutures of the ammonoid, bivalves and brachiopods?

(That is a lingulid isn't it? )

 

[Hajar]

Yes, it'll be good to see what that is when it finally shows itself.

I'd look to diagenesis for an explanation of how a septum could make an apparent colour band, i.e. mineral precipitation. Mineralization of septa can be spectacular in some ammonites (e.g. those from Scunthorpe in the northern UK), but not visible when the opaque shell is present. In the Lituites case I'd guess the thin stripes of colour are iron oxides or hydrated iron oxides and they are visible because the shell is translucent.

No lingulids in this rock (that I've seen at least): there are several examples of Promyalina, a Claraia off to the left and a Eumorphotis with a Promyalina sticking out of the body chamber of that cephalopod. It's a wonderful hand specimen of "life just after the catastrophe".

 

[Architeuthoceras]

"life just after the catastrophe".

See Also THIS

(I can get you a copy )

 

[Terri]

What an interesting "rock" you picked up on that field trip Hajar, really fun watching your progress with it. I don't quite understand the significance of the color banding yet, but am reading all the links and papers you and Kevin provide and the discussion is priceless . What process are you using to prep your speciman?

Aren't fossils great, just like reading a good mystery novel before the end of the story is written! (except for the re-reading and looking up of big words).

 

[Hajar]

Thanks kevin! I saw the talk last year and would like a copy.

I agree Terri. I've picked up a lot of new knowledge from that short trip and this one rock, with all the trails of inquiry it provokes. I don't have any sophisticated prep tools, so it's just a Dremel.

 

[Hajar]

Very slow progress, but here comes that little ammonoid...

 

[DWhatley]

If I was not worried about ruining a really nice speciment, working down through the surrounding rock with a dremel seems like a fun set of afternoons. Keep posting your progress. The vicarious "work" is fun

 

[Hajar]

Shall do! Here's this evening's progress.

 

[Terri]

Very nice Hajar, do you know what the fossils are just below the ammonoid?

 

[Architeuthoceras]

That one between the nautiloid and the ammonoid looked like a Lingulid brachiopod to me... from a different angle now I can see it's not.

 

[Terri]

Hmmm, maybe Hajar will pop in and give us his thoughts...

 

[Hajar]

Yup, bivalves. I've looked over the rock for lingulids, but none that I can see. It's becoming quite fiddly working down through the rock behind that pair of bivalves. When the battery is recharged I'll take some more photos.

 

[Hajar]

Here it is this evening ..