Unknown Fossil, Aquatic?

[Katy2319]

Hi All! I'm trying to identify this fossil for a local museum, but I've never seen anything like it. We're not sure where it was found exactly, but definitely in Berrien County, MI. Our fossil record is heavily Devonian aquatic fossils, with later records of Pleistocene fauna. I'd be grateful for any help or tips anyone can give!

 

Thanks!

Katy

[Fossildude19]

The round item looks like a concretion or nodule of some sort.

The other item may be as well, but images of the ends of the longer piece may be helpful.

 

[Katy2319]

I'll see if the museum can send me some pictures with other angles, and measurements too, since I don't have those either.

[Mahnmut]

two possibilities that come to my mind are speleothem or stromatholite.

Best Regards,

J

[Rockwood]

It's tempting to try to imagine this being a poorly preserved orthocone. The actual evidence is weak though. 

[TqB]

Speleothem was my first thought, or maybe concretion.

[Coco]

You’d have to see the ends of the object long to see if there’s a hole all the way through, which reminds me of a stalactite.

 

Coco

[Katy2319]

I was able to get some more photos of the museum specimens, as well as a few more pieces as well! There appears to be a pith or potentially what used to be an open hole that runs through the center of all but the flat one (last two images) I've also done some research into speleothems, as was suggested by Mahnmut and TqB, and learned that there is one cave in the area, although its fairly removed from where these pieces were found. If they did come from the cave, perhaps they were picked up there and brought to the settlement by one of the missionaries.

[Coco]

Hi,

 

Stalactite, recognizable by the holes through which the water drained.

 

Coco

[supertramp]

I'm in the concretion camp for both, since the lateral cylindrical surface of the second find does not resemble that of a speleothem; many concretions do have a central hole

ciao

[Coco]

Hi,

 

Never seen a concretion like that, but the second photo seems odd for a stalactite.

 

How do we explain the hole in the concretions ?

 

Coco

[westcoast]

Are they calcite? Do they react with HCl..

[supertramp]

Hi Coco;

my colleagues and I from an Italian geology forum once came across concretions of this type and, rather interestingly, we had the opportunity to observe recent examples of their formation process;

 

 

 

 

 

when you try to immerse these formations in water to measure their mass after imbibition, very thin columns of air bubbles develop from the small holes in the center of the concentric rings, which last about ten minutes: evidently these are not simple holes, as they appear to radially drain the interior of the object;

perhaps this sheds light on the mechanism of formation: leakage of gas (CO2?) from the sediment --> decrease in the solubility of calcium carbonate --> precipitation of calcareous cement --> formation of concentric laminae?

[Al Dente]

They look like rhizoliths.