Multiple mazon creek pectin

[TheRocksWillShoutHisGlory]

In the freeze that process it is common for concretions to flake, on a piece of the flaked off rock I came across multiple pectin fossils including a couple that are about 1mm and am asking for help identifying the species.

 

[Fossildude19]

Cropped, rotated, and brightened:

 

[connorp]

Are you sure this is a concretion? The picture you posted is not very clear, but these look like brachiopods on a piece of limestone.

[connorp]

The big one in the middle could maybe be Hesperorthis, common in the Platteville Group in northern Illinois.

[westcoast]

Dunbarella is found in the Mazon Creek concretions 

[TheRocksWillShoutHisGlory]

58 minutes ago, connorp said:

Are you sure this is a concretion? The picture you posted is not very clear, but these look like brachiopods on a piece of limestone.

This was found in the bottom of a freeze thaw bin, in the broken bits of concretions and shale like pieces.  I'm not 100% sure but I'm pretty sure it is a part of a concretion or shale.  It is not as hard as limestone, and the edges have the more familiar redish color.

[Mark Kmiecik]

The overall shape I'm seeing is not typical of the species found in MC concretions. The color you mentioned around the edges may be due to association in a bucket full of siderite and may be staining. Try some vinegar or other mild acid just on the edge where the coloration is present. If the color remains the same after treatment then it is part of a concretion -- if not, then it's probably limestone that took on some surface color from its surroundings. I have seen some small pectens in MC nodules, down to about 7mm, but none quite this small. I can't determine from the photo if any of them are complete or fragments. A bit of judicious prep work might answer this question and others. Maybe some "prep" work on the back side can help positively determine the nature of the matrix. I'm getting a limestone vibe from this specimen as well, although I admit that it's hard to be sure by merely observing a photo.

 

 

 

Edited June 11, 2022 by Mark Kmiecik
fix typo

[TheRocksWillShoutHisGlory]

I took some new images of each individual with a microscope camera.  Unfortunately it looks like much of the smallest shell was broken.  The image of the apex of the shell also shows the red hue of the side of the rock.  I did the vinegar test Mark mentioned and the red does not wash away.

[Mark Kmiecik]

That doesn't look typical of the preservation within concretions. There wouldn't normally be any matrix between the ribs of the pecten or fading away like it does around the edge. There is usually a cleaner separation of the two surfaces. It just doesn't look right. I think it's part of another material associated with the Francis Creek Shale member and most probably one of the species found in Mazon Creek material, but it's not part of a concretion. Either way, though, it's a neat find and I would include it in my MC collection as an example of another type of preservation found in association with the member in which the concretions are found.