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Inspired concretion


Rockwood

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I think the answer to what inspired this concretion became obvious in the photo that I included for context. I figured it might make a good example if this checks out.

The crinoid columnal mold at its very edge indicates that the shapes were most likely more pieces of crinoid that left only ghosts ?

:fingerscrossed:

IMG_4791.JPG

IMG_4793a.jpg

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Looks like weathered trace burrows(?) in first picture. I do not see the segmentation I would excpect fron crinoids.

It does look like there is a cross section view of a shell in the second picture. I also see a shell print on the darker grey seam (upper right of picture).

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More context.

IMG_4795a.jpg

IMG_4796a.jpg

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Tidgy's Dad

I agree with ynot. 

Those look like trace fossils of burrows, or feeding trails to me. 

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6 hours ago, Tidgy's Dad said:

I agree with ynot. 

Those look like trace fossils of burrows, or feeding trails to me. 

I just can't picture a critter digging these. I still think it's a concretional phenomenon. 

They are mostly thin voids with discrete columnal like shapes in concretion that is associated with a highly fossiliferous layer.

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5 hours ago, Rockwood said:

They are mostly thin voids with discrete columnal like shapes 

The fill of the trace seems to be slightly softer than the base rock. This has caused a slight erosional difference that makes the burrow look like a shallow channel.

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3 hours ago, ynot said:

The fill of the trace seems to be slightly softer than the base rock. This has caused a slight erosional difference that makes the burrow look like a shallow channel.

So the digs of this little creature became the nucleus of concretion ?

That was my first thought, but I thought it less likely after spotting the columnal.

It is the more interesting explanation. It's just that most of my more interesting explanations are wrong. :)

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35 minutes ago, Rockwood said:

So the digs of this little creature became the nucleus of concretion ?

Not necessarily, they could have been preserved because of the concretion. I do see other biologics in the piece.

 

37 minutes ago, Rockwood said:

It's just that most of my more interesting explanations are wrong. :)

Really, I had not noticed.

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abyssunder

In my opinion, there might be a bivalve steinkern with remnant of traces made by worms, sponges or other critters specialized in penetrating the hard substrates (shells, rocks, sediments). So, they may be ichnofossils. I compare them with the ones from the specimens below. :)

 

IMG_4791.JPG.07222599ed3638c9d7f8ee85abd5e365.thumb.JPG.0c6d555f5de2c8d8697d29a217d7447d.JPG5b16fb09d2198_2016NovembermeetingTomCucullaea.jpg.21e6246a95d4e6022944484375ac7092.jpg

comparative picture from here

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25 minutes ago, abyssunder said:

In my opinion, there might be a bivalve steinkern with remnant of traces made by worms, sponges or other critters specialized in penetrating the hard substrates (shells, rocks, sediments). So, they may be ichnofossils.

 I have found poorly preserved fossils that seemed like evidence of larger, thick shelled bivalves in glacial material in the area. There is a layer of semi blob, semi geometric, concretion that this came from though.

This from an Emsian formation.

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Here is an example.

IMG_4798a.jpg

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abyssunder

I know they are from different geological ages (my first post), but I would eliminate crack patterns for the traces visible on the surface of your specimen having the same color as the sediment under them -  compared to the ones below, having a lighter color in the cracks, although I'm not convinced that all the surface marks in the comparative specimen are cracks. Some of them, especially on the upper part in the comp. picture below, have no sign of cracks, so I conclude that the cracks were formed later, in the already weakened / altered substrate.

 

5b171f84cf4cc_Modiolopsisleightonivarquadrata.SilurianLeightonFormationUSNM58975scale-goldbar6mm..thumb.jpg.54c1cff84c00ff3ad84d412012e782d2.jpg

 

 

For the last example (" Here is an example."), I think the ferrugious alteration might be proper (trying to form liesegang patterns). They could be corals or sponges, I don't know which one. We are dealing with diagenetically transformed materials. :)

 

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7 hours ago, abyssunder said:

We are dealing with diagenetically transformed materials. :)

Shaked, baked, shocked, and tumbled for sure.;)

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