Oddball Mazon Nodule

[minnbuckeye]

My bucket of mazon nodules collected this summer have been sitting outside in the sub zero temperatures all winter. I was finally able to fetch the bucket and thaw them out recently. The nodule presented split completely different than other nodules that have opened. This one is a heptagon prism, VERY geometric, not split on a horizontal plane like I am used too . Is there a fossil present on the upper surface  and  have others experienced nodules opening up geometrical  like this one?

 

 Thanks for looking

 Mike

 

Front view

 

 

Back view.

 

[Runner64]

Afraid I’m not seeing a fossil in it. Although if you really want to be sure, you could soak it in a diluted water-vinegar mixture for an hour or so to remove the calcium.

 

Ive had some break in very odd ways before but am unsure what causes it as well.

[Mark Kmiecik]

That's not a nodule. It is Francis Creek Shale. The brown depression surrounded by the white mineral is where a nodule was in contact with the shale. If you ever get to see the concretions in situ, as is common in the banks of Mazon Creek, you'll see exactly what I mean. Actually, if you look at my avatar, the entire bank from the water to that ledge that's sticking out about eight or nine feet above the water is the shale member. If you google Mazon Creek and click on images you can find a larger photo of it in which it you can see more detail. 

 

Note: Google "mazon river illinois" instead for more and better photos.

Edited February 16, 2022 by Mark Kmiecik
added info

[minnbuckeye]

@Mark Kmiecik, Thanks for your explanation. After researching Francis Creek Shale, it has left me a bit confused. First of all, are nodules and concretions the same? Then my time spent in the creek this summer allowed me to examine the banks of the creek. I saw a grey layered shale  and within that, what I assumed were nodules/concretions. What I brought home from the creek bed resembled what was in the bank. Here is  the reassembled specimen that I had brought home. The red dots mark where my example yesterday popped out. So this is not a nodule or just shale?? Thanks for clarifying this for me.

 

[Mark Kmiecik]

1 hour ago, minnbuckeye said:

@Mark Kmiecik, Thanks for your explanation. After researching Francis Creek Shale, it has left me a bit confused. First of all, are nodules and concretions the same? Then my time spent in the creek this summer allowed me to examine the banks of the creek. I saw a grey layered shale  and within that, what I assumed were nodules/concretions. What I brought home from the creek bed resembled what was in the bank. Here is  the reassembled specimen that I had brought home. The red dots mark where my example yesterday popped out. So this is not a nodule or just shale?? Thanks for clarifying this for me.

 

In reference to MC fossils the words nodule and concretion are used interchangeably and refer to the same thing. If you look at your nodule you'll notice layering that is identical to the Francis Creek shale you saw in the banks of the creek. Now that I can see the whole nodule it makes more sense. This nodule is one that began forming but never completed the "transformation". It's a nodule want-to-be. The rusty layer is the iron siderite just beginning to form around the organic matter, that was interrupted for some reason before it could form completely. Perhaps the organic matter was dissolved or eaten by bacteria -- who knows? It just didn't finish the cycle. There may be a fossil somewhere in one of those layers. Is it worth cracking open to find out? Maybe -- maybe not. I would keep it as is in my collection as a classic example of what it is, an incomplete concretion. I've seen lots of them, but not many this good that opened so nicely. The chances of it containing a fossil are somewhere between "slim" and "none", and even if it does it will be poorly preserved because of the coarse grain of the shale. The siderite as it formed around the organic matter is much finer grained and if you look at concretions in situ you will notice that the forming nodules actually deformed the shale member's layers, pushing them apart as it formed. You can see how the brown layer is "domed" and the center of the nodule may be a fully formed concretion. I'm sure when you take the 3D jigsaw puzzle apart you can see if this is so. As I mentioned, even if it does contain a concretion, I would leave it the way it is as an example of how the nodules were formed. Technically, your specimen is half-way growth stage between shale and concretion.

 

I hope this helps you understand a small portion of the complicated process of iron siderite concretion formation. You can find more complete info in MC literature and online. The photos are of concretionary strata in China. I looked for a photo of MC strata but couldn't find one. My deformation statement refers to photo e, but if you look at the orange lines and arrows you'll get the idea.