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Jim K

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With winter finally over we took a drive over to Lake Michigan to look along the beach. We found a many of the typical corals. I spotted this interesting looking fossil in the surf and quickly retrieved it. As I looked at it more closely and saw the details I became more unsure of what it is. I'll add some closeups in the next post. Thanks.

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2 minutes ago, Rockwood said:

Natural casts of colonial rugose coral ?

I believe so.  Nifty pattern

'Those who cannot remember the past are condemned to repeat it.'

George Santayana

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55 minutes ago, Rockwood said:

Natural casts of colonial rugose coral ?

Thanks. That was what I was thinking it had to be but the way some ran in a different direction from the others it was different from most that I find. Thanks again.

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1 hour ago, Jim K said:

the way some ran in a different direction from the others it was different from most that I find

Easy to imagine an epic tale of how that came to be.

Think paleozoic reality show. :)

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57 minutes ago, Rockwood said:

Easy to imagine an epic tale of how that came to be.

Think paleozoic reality show. :)

Not so loud!  Hollywood is so desperate for something new, your idea might be on next season's line up. ;)

 

 

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6 hours ago, Rockwood said:

Natural casts of colonial rugose coral ?

Could you explain how these would have been formed? Thanks!

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I agree it's a colonial rugose but it's not a cast - it's normal calcite and/or silica preservation that's weathered a bit proud of the matrix. A fine and attractive specimen. :) 

  • I found this Informative 1

Tarquin

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This is an interesting and unique pattern. Some of the shapes looked like horn coral to me. Cool find!

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Very nice. I used to have a lot of corals from Wisconsin when I was a kid. Nothing that looked like this, though. Definitely would have made my day.

 

 

Mark.

 

Fossil hunting is easy -- they don't run away when you shoot at them!

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Thanks everyone! This piece really stood out. When I first spotted it in the water, with the sun shining, it almost glowed a blue color. Never know what will show up.

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6 hours ago, TqB said:

but it's not a cast

 

6 hours ago, TqB said:

normal calcite and/or silica preservation

Would there not be a certain amount of overlap in normal preservation ? This example being perhaps a bit heavy on the infill ?

I want a thin section. :) 

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7 hours ago, Bronzviking said:

Could you explain how these would have been formed? Thanks!

Argument aside; If the original coral body were to be dissolved away and the cavity be refilled by a different mineral,  from solution, or colloidally, it would be considered a natural cast.

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I don't think it is a cast of all these corals in one stone; seems unlikely. Could it be Rugose Coral Lithostrotion?

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16 hours ago, Rockwood said:

Think paleozoic reality show. :)

Talk about being dead in the ratings.. That would probably have some of history's oldest pickup lines & jokes in it. :wacko:

Accomplishing the impossible means only that the boss will add it to your regular duties.

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6 hours ago, Bronzviking said:

I don't think it is a cast of all these corals in one stone; seems unlikely. Could it be Rugose Coral Lithostrotion?

 

8 hours ago, Rockwood said:

Argument aside; If the original coral body were to be dissolved away and the cavity be refilled by a different mineral,  from solution, or colloidally, it would be considered a natural cast.

The confusing world of casts and moulds! (Where usages vary around the world. :) )

This one is "normal" coral preservation, probably with at least some recrystallisation and/or chemical replacement of the skeleton, with the voids filled in with crystallisation from solution as Rockwood says

.

So you'd see an internal mould if the skeletal bits were then dissolved (which they're not), though it indeed quite often happens with weathered specimens when the skeleton is calcite and the infill silica.

 

If the whole thing was dissolved and the entire skeleton replaced with sediment infill, you'd obviously have a cast which wouldn't preserve any internal structure. I don't remember seeing this though it must happen sometimes - external moulds without the cast are quite common of course, especially as negatives in sandstone.

 

@Bronzviking If Carboniferous, it could be a lithostrotionid - Diphyphyllum is a possibility but doesn't look quite right, it should have obvious dissepiments. But there are similar looking things in the Devonian and earlier that aren't related and I don't know much about those - something like Thamnophyllum (Devonian) looks closer maybe.

 

  • I found this Informative 2

Tarquin

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