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Iowa Trace Fossils???


BenWorrell

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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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4 minutes ago, ynot said:

Look like feeding traces to Me.

Any ideas what critters would make those?

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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.

Darwin said: " Man sprang from monkeys."

Will Rogers said: " Some of them didn't spring far enough."

 

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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.

Every single fossil you see is a miracle set in stone, and should be treated as such.

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17 minutes ago, ynot said:

Look like feeding traces to Me.

They look like the finished product to me.

Coprolites

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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.

Darwin said: " Man sprang from monkeys."

Will Rogers said: " Some of them didn't spring far enough."

 

My Fossil collection - My Mineral collection

My favorite thread on TFF.

 

 

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2 minutes ago, ynot said:

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

Not at my table. :(

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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:

Every single fossil you see is a miracle set in stone, and should be treated as such.

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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?

My goal is to leave no stone or fossil unturned.   

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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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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.

My goal is to leave no stone or fossil unturned.   

See my Arizona Paleontology Guide    link  The best single resource for Arizona paleontology anywhere.       

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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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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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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

Darwin said: " Man sprang from monkeys."

Will Rogers said: " Some of them didn't spring far enough."

 

My Fossil collection - My Mineral collection

My favorite thread on TFF.

 

 

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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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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.

My goal is to leave no stone or fossil unturned.   

See my Arizona Paleontology Guide    link  The best single resource for Arizona paleontology anywhere.       

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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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Intruiging...

Every single fossil you see is a miracle set in stone, and should be treated as such.

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