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Stone from Yahara River, Dane County, Wisconsin


karstic

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An acquaintance of mine found this material in a river bed here in Dane County, Wisconsin. Most of the locality bedrock is Ordovician or Cambrian limestone, sandstone or dolomite. This area is also glaciated, although you don't see a lot of till or erratics right around here. 

 

Any suggestions what this might be? It was initially suspected as fossilized wood, although that seems unlikely. 

289311931_704483917311496_273768460256116251_n.jpg

289493257_193057919714548_7145626796467083478_n.jpg

289497093_1075853230031674_8259405055142261286_n.jpg

Edited by karstic
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Welcome to TFF from Austria!

 

Is this rock greenish or green? If so, it could be greenschist or serpentinite with slickensides (link to wikipedia), very vaguely mimicking macro wood texture.

 

Franz Bernhard

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1 hour ago, Rockwood said:

It does look like the structure seen in slickensides.

It may be glacial striation. The area has experienced glaciation after all.

 

 

Mark.

 

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

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1 minute ago, Mark Kmiecik said:

It may be glacial striation. The area has experienced glaciation after all.

With as many layers as this ?

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Just now, Rockwood said:

With as many layers as this ?

Nope. You're right. Not likely. That first photo also whacks my hypothesis.

 

 

Mark.

 

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

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9 hours ago, FranzBernhard said:

Welcome to TFF from Austria!

 

Is this rock greenish or green? If so, it could be greenschist or serpentinite with slickensides (link to wikipedia), very vaguely mimicking macro wood texture.

 

Franz Bernhard

 

Thanks very much.

 

This rock is tan or grey in color. The green in the second and third photos is algae from the river. 

 

Thanks for that link. I was unfamiliar with slickenslides. That explanation, however, seems unlikely. You don't see much evidence of metamorphosis, orogeny etc. in the rocks here. I think it is most likely some kind of sedimentary rock feature or marine fossil. Given the location, a man-made building material or industrial waste my also be possible. 

Edited by karstic
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9 hours ago, karstic said:

This area is also glaciated,

You can't really rule it out on a 'supposed to be there' then.

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Well it looks like slickenslides might be a possibility in the bedrock right around here and areas nearby. Apparently their formation doesn't necessarily require such active or deep conditions and they can form right in Silurian dolomite. See page 5...

 

https://wgnhs.wisc.edu/pubshare/GS12.pdf

 

County bedrock map...

 

https://wgnhs.wisc.edu/catalog/publication/000913/resource/wofr201301plate01

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11 hours ago, karstic said:

sedimentary rock feature

Ok, its not green, so more probably a sedimentary rock. Limestone or sandstone?

If limestone, stylolites (link to wikipedia) are also a possibility.

Franz Bernhard

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3 hours ago, FranzBernhard said:

Ok, its not green, so more probably a sedimentary rock. Limestone or sandstone?

If limestone, stylolites (link to wikipedia) are also a possibility.

Franz Bernhard

 

It seems like it's most likely slilckenslides. Slickenslides is is described for dolomite bedrock not very far from this area and the photographs look just like it. 

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