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BenWorrell

Iowa Trace Fossils???

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BenWorrell

Hey all,

 

I found this slab of rock in a Linn County, IA creek this spring and I'm not sure how these patterns might have formed. Are they trace fossils from something? Did they form for normal geological processes? It's hard to pin down age of rocks in a creek like this, but most of our exposures are Devonian or Silurian. 

 

Thanks!

Trace Fossils Contrasted.jpg

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ynot

Look like feeding traces to Me.

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BenWorrell
4 minutes ago, ynot said:

Look like feeding traces to Me.

Any ideas what critters would make those?

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ynot
7 minutes ago, BenWorrell said:

Any ideas what critters would make those?

Most trace fossils can not be credited to any particular species.

Maybe @abyssunder can be a little more specific.

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MeargleSchmeargl

Creek name?

 

There are known exposures from the Silurian, Devonian, Carboniferous, Cretaceous and Pleistocene in the area. Knowing what creek it is would at least help with age.

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Rockwood

 

17 minutes ago, ynot said:

Look like feeding traces to Me.

They look like the finished product to me.

Coprolites

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ynot
2 minutes ago, Rockwood said:

 

They look like the finished product to me.

Coprolites

Could be, but aren't those feeding traces also.

Maybe @GeschWhat or @Carl can chime in on this.

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Rockwood
2 minutes ago, ynot said:

Could be, but aren't those feeding traces also.

Not at my table. :(

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MeargleSchmeargl
4 minutes ago, ynot said:

Could be, but aren't those feeding traces also.

Maybe @GeschWhat or @Carl can chime in on this.

*shudders* that reminds me a little too much about my dogs that eat linkin' logs. :wacko:

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DPS Ammonite

Something else to consider: echinoid spines. Better up close photos will help. If they are are straight segments and do not branch, trace fossils are less likely. 

 

@BenWorrell Can you get a better photo? If not, describe the structures. Are they straight, do they branch? Are they connected to each other? What type of ornamentation do they have?

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Rockwood

A photo of them dry would be best in my experience.

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BenWorrell

Here is a closer dry photo...

 

I can't make out any substructures, just the bigger shapes.

 

Trace Fossils 2 Cropped.jpg

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ynot

Thanks for the additional picture.

I still think they are feeding trace fossils.

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DPS Ammonite

Probable not echinoid spines; too curvy. 

 

They look segmented. Could they be parts of crinoids other than stems? 

 

Do these fizz in acid? Do they scratch with a knife blade? I am trying to see if they might be limestone.

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Rockwood

I was surprised to read that they are referred to as rods. Dry I can more easily envision them being feeding traces as ynot suggests.

The mention of stromatolite sheets would seem to support the idea.

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BenWorrell
16 minutes ago, Al Dente said:

It is probably a piece of “Anamosa Stone”. The rods are a common feature. Here’s another thread that talks about them- http://www.thefossilforum.com/index.php?/topic/58618-could-someone-help-me-to-id-these-small-fossils/&tab=comments#comment-624301

I think you're onto something Al Dente, those do look very similar. Sounds like maybe coprolite or worm tunnels, but nobody really knows in those "Anamosa Stones". Thanks!

 

I don't have concentrated acid on hand, but it didn't fizz with apple cider vinegar. 

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ynot
3 hours ago, BenWorrell said:

, but it didn't fizz with apple cider vinegar. 

This indicates that the stone is not calcium carbonate (limestone).

 

Edit - missed the didn't

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GeschWhat

I was paging through the Treatise on Invertebrate Paleontology (W), but my copy is very old (1975). "Unilobal feeding structures," are a possibility, but I don't know if that is even a legitimate type of trace fossil now. If they were coprolites, I would generally expect their composition to differ from the matrix. However, that isn't always the case with things like worms, nudibranchs (sea slugs), and the like that feed on nutrients in sediment.  Check out this guy:

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GeschWhat

Maybe there were a bunch of acorn worms like this guy...expl5008.jpg

 

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DPS Ammonite
1 hour ago, Al Dente said:

It is probably a piece of “Anamosa Stone”. The rods are a common feature. Here’s another thread that talks about them- http://www.thefossilforum.com/index.php?/topic/58618-could-someone-help-me-to-id-these-small-fossils/&tab=comments#comment-624301

By Jove I think you've got it. Anamosa, Iowa, where the stone was quarried, is just east of Linn County. Anamosa stone is a Silurian dolomitic limestone. Dolomites do not fizz much in household vinegar.

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abyssunder

Sometimes, it's extremely difficult to assign an ichnofossil to its maker, as Tony said it before in an elegant manner. Geological settings would be important for any ID, especially in the realm of traces, also the ichnofacies might be on help.
Unfortunately, I don't know the "Anamosa Stone", but the features of the specimen in question reminds me of Lockeia or appropriate.

 

DevonianLockeia121911_585.jpg.eefee306b07c7b040e765c9aae04a6d4.jpg

 

Similar to the OP's specimen might be the one below, from the Bright Angel Shale.

 

4748971457_7bc4eb1ca7_b.jpg.281ad3b518cc79ceb98795b55c150d9d.jpg

picture from here

 

 

 

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MeargleSchmeargl

Intruiging...

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Carl
20 hours ago, ynot said:

Could be, but aren't those feeding traces also.

Maybe @GeschWhat or @Carl can chime in on this.

I'm thinking not coprolites here.

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BenWorrell

@abyssunder Those Lockeia are strikingly similar! Thank you very much!

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