Adventures in the Marmaton

[Titan]

I was fortunate to be able to take two trips recently to the Marmaton group in Northern Missouri and wanted to share my trip report with the forum.

 

It's hard to find information on the Marmaton in Missouri, and I struggled with the geology and understanding what members within the Marmaton I was seeing, but I had a great time non the less. I grew up in this region and have some ‘insiders’ information on a few spots I wanted to check out just from spending time running around the countryside as a kid. The first was in a local creek in the township I grew up in that contains concretions we called ‘dragon eggs.’  I was curious if they would contain fossils so on my first trip in early September I committed to breaking one open. First, here are a few pictures of the site:

 

I was able to break this one open, and it did contain fossils! The blue line on the lower left marks a very thin layer of limestone that the concretions seem to form right above.

Here are a few more pictures of the concretions for reference.

A particularly large one:

And one that is just cracked:

 

Unfortunately for me only the very first one I broke had any fossils. I spent several hours hoping another would reveal some but luck was against me at that point I guess and I failed to find a single one. Frustrated I spent the remainder of the evening searching through the fallen limestone exposures.

 

The next post will contain some of the specimens from the single fossiliferous concretion and the limestone.

[Titan]

One of my favorites from the single concretion that did contain specimens was this Orbiculoidea sp.

 

I was also surprised by this fish fin (actually a Listracanthus dermal denticle - Thanks Connorp!) because I've only found them in slate so far:

 

I also really like this unknown even though it's tiny at under a cm wide:

 

Here's a few more unknowns:

 

And lastly I found a dobsonfly (family Corydalidae) which is really cool as I hadn't ever found one in this stream before. I didn't know they could live for up to five years as a larva. They seem like something that would be right at home in the Carboniferous!

 

And here are a few of the specimens I kept from the limestone:

A Neospirifer sp.

 

An unknown brachiopod:

 

and one more I kept just cause it reminded me of stained glass:

 

I will do another post in the next day or two on the remainder of the adventure which consisted of exploring a slate exposure.

[connorp]

1 hour ago, Titan said:

This is a dermal denticle of the chondrichthyan Listracanthus hystrix. Not a fin, but definitely looks like one.

 

Maybe a gastropod, some more angles would help.

 

Gastropod, a platyceratid I think.

 

Quote

Gastropod as well I think, although it could be an ammonoid, I'm not positive. It's pretty faint.

 

Quote

I would guess some kind of bivalve, looks like more is buried.

 

Mesolobus would be my guess.

Great finds!

[Titan]

@connorp Thanks for the ID's! I've never seen a Listracanthus denticle so short so I figured it might be a fin

[connorp]

6 minutes ago, Titan said:

@connorp Thanks for the ID's! I've never seen a Listracanthus denticle so short so I figured it might be a fin

It's just a fragment. Looks like the base, or close to the base, of the denticle.

[Missourian]

Here are some maps of the Cherokee Group - Cabiness Subgroup (red) and Marmaton Group (blue) in northern Missouri. I hope this helps a little.

 

 

[Missourian]

Mesolobus is a reliable index fossil for identifying rocks as Demoinesian, at least in Missouri.

[Titan]

@Missourian Thanks for the maps and info! From the maps it's got to be Marmaton -the site is right in the blue. However deciding on the actual formation is really challenging to me. I think this site may be the Excello Shale member.

 

[Titan]

I think this next site is the Anna shale of the Pawnee limestone fm. and the Lexington coal from the Labette shale fm.

I don't know what it is, but collecting from slate is one of my favorite forms of hunting. Splitting slate is a bit like opening a 300 mya book.

Here is the beginning of the site with the first slate exposure. The stream is spring fed and runs year round. According to the landowner the nearest townsfolk used to have to walk to this spring for water and also used the coal beneath the slate.

Here's a closer picture just down the stream where you can see the coal member beneath the slate.

The difficulty with this site is that nature has thoroughly invaded all the easy to access exposures with roots.

 

The slate here is also very unproductive compared to the slate I split out of the Stark member in Kansas City but I was able to find a few things. The preservation is also poorer, but that may be in part from the nature/water action on the exposed slate. 

 

Here's a Listracanthus dermal denticle:

 

 

 

[Titan]

The most bizarre find was three of these unknown two inch blobs on a single layer.

#1

#2

#3

 

I wish the preservation were better but it was a really fun trip regardless. Thanks for coming along!

[deutscheben]

Great finds! I always love seeing new Pennsylvanian material, those giant concretions are fascinating. Could those last ones be some kind of thylacocephalan, like Concavicaris? They have the right shape and I know they are found in Pennsylvanian shale, I think @RCFossils has found some.

[connorp]

32 minutes ago, deutscheben said:

Great finds! I always love seeing new Pennsylvanian material, those giant concretions are fascinating. Could those last ones be some kind of thylacocephalan, like Concavicaris? They have the right shape and I know they are found in Pennsylvanian shale, I think @RCFossils has found some.

That was my thought as well.

[Missourian]

1 hour ago, Titan said:

@Missourian Thanks for the maps and info! From the maps it's got to be Marmaton -the site is right in the blue. However deciding on the actual formation is really challenging to me. I think this site may be the Excello Shale member.

 

The Excello did come to mind. I've found an ammonoid in a similar carbonaceous limestone in the Excello in Henry County after seeing one found in the same area. The apparent absence of the overlying Blackjack Creek Limestone gave me doubts here. However, it is possible the thin, fossiliferous limestone is a poorly developed/lithified Blackjack Cr.

 

If possible, I would thoroughly check through the black limestone. At the Henry Co. site, I hammered through a very modest bit of the stuff and came out with one goniatite. No guarantees at your site, though.

 

Finally, was the fossiliferous concretion from that outcrop, or was it lying loose? If loose, there could be more to find upstream. The outcrop gives me more of a Cherokee Group 'vibe'.

[Missourian]

I'll also cast a vote for carapace of Concavicaris or something similar. Very nice!

[Missourian]

For comparison, some carapaces from black shales of the Missourian Stage....

 

Stark Shale:

 

Muncie Creek Shale:

 

Eudora Shale:

 

[Titan]

Thank you all for weighing in on the identification.
@deutscheben Thanks! Happy to contribute something Also thank you for the ID as Concavicaris! The giant concretions are pretty exciting however only finding one that had fossils was a little disapointing. But I will be going back to open more when I get the chance.
 

@Missourian When I get a chance I will go through some of it as I'd love to find one of those. The fossiliferous concretion was from the outcrop and hadn't fallen out yet. There were more upstream and down stream for a few yards but mainly just appear at this area. I've spent countless hours at this creek and I know of only one other spot a few miles upstream that has a similar exposure with the same concretions. When I get back up there I'll check out the other outcrop and give a report.

Additionally thanks for posting the specimens you have! I love your muncie creek specimens. The preservation is much better on yours but they do have a similarity. I wasn't going to post this as the picture quality is bad but this assortment was also on the same plate as the Concavicaris just a few inches apart. I originally thought it might be nothing, but now I'm wondering if it's a assortment of appendages.

The positive:

and negative:

The outcrop could very well be in the Cherokee Group. I really don't have enough experience yet to deduce them accurately and your vibe is probably dead on

[Tidgy's Dad]

Interesting reports.

That Orbiculoidea looks stunning. 

[Missourian]

39 minutes ago, Titan said:

@Missourian When I get a chance I will go through some of it as I'd love to find one of those. The fossiliferous concretion was from the outcrop and hadn't fallen out yet. There were more upstream and down stream for a few yards but mainly just appear at this area. I've spent countless hours at this creek and I know of only one other spot a few miles upstream that has a similar exposure with the same concretions. When I get back up there I'll check out the other outcrop and give a report.

Additionally thanks for posting the specimens you have! I love your muncie creek specimens. The preservation is much better on yours but they do have a similarity. I wasn't going to post this as the picture quality is bad but this assortment was also on the same plate as the Concavicaris just a few inches apart. I originally thought it might be nothing, but now I'm wondering if it's a assortment of appendages.

 

The positive:

and negative:

The outcrop could very well be in the Cherokee Group. I really don't have enough experience yet to deduce them accurately and your vibe is probably dead on

 

The last two specimens are quite interesting. The granular texture resembles that of shark cartilage.

 

As for the stratigraphic level, it can be exceedingly difficult to pin it down unless some marker bed can be id'd. Fortunately, platy black shales can help to narrow down the possibilities a bit. The nice thing about Missourian strata is that the limestones adjacent to black shales typically have some unique character that allows for relatively easy identification.