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Missourian

Mystery Fossils (Pennsylvanian)

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Missourian

For nearly twenty years, I've collected some strange fossils from a unique Pennsylvanian deposit in northeast Kansas. I've been pondering them to this day, and I'm still drawing a blank.

 

I first found this slab:

 

post-6808-0-84337600-1323856781_thumb.jpg

 

The bold segments caught my eye. I then noticed that they have a branching habit.

 

I assumed they were sponges, but then I found this:

 

post-6808-0-42091700-1323856695_thumb.jpg

 

This one is also segmented and bifurcated, but it forms a nearly continuous surface. Perplexed, I looked at them up close. They seem to form thin (0.5 mm), leaf-like sheets (i.e. thalli).

 

I nicknamed these 'pahoeids', because they resemble pahoehoe lava flows.

 

Some appear to be featureless sheets. This one, with an attached Coelocladia sponge, was fractured. This may give a clue to its original consistency:

 

post-6808-0-14648400-1323856829_thumb.jpg

 

Here, the tips of some 'pahoeids' seem to be present:

 

post-6808-0-69075000-1323856858_thumb.jpg

 

(For scale, the squares on the couch cushion are 18 mm across. I took the photo after I found the rock back in October.)

 

Here's the same piece from the side:

 

post-6808-0-13384800-1323856895_thumb.jpg

 

This chunk demonstrates how the 'pahoeids' bind the sediment. They are so abundant, they actually form beds and lenses of limestone within a shaly matrix.

The few 'pahoeids' I've found in situ were on the undersides of slabs. The top surfaces of the organisms are never cleanly exposed; they are always locked in matrix. Also, encrusting bryozoans and brachiopods are often attached to the surface. All of this tells me the 'pahoeid' thalli were once suspended above the substrate.

 

Some more specimens....

 

Here's another bifurcated sheet:

 

post-6808-0-30961000-1323856944_thumb.jpg

 

And another:

 

post-6808-0-04856100-1323856972_thumb.jpg

 

These seem to be 'juveniles':

 

post-6808-0-33165700-1323857014_thumb.jpg

 

These form long, parallel branches:

 

post-6808-0-93219900-1323857051_thumb.jpg

 

This limestone nodule contains what are possibly undeformed 'pahoeid' thalli:

 

post-6808-0-40280500-1323857098_thumb.jpg

 

Note how the orangish sediment seems to 'fill' the little 'cups'.

 

An underlying limestone bed seems to contain fragmented 'pahoeids' as well as several Amblysiphonella sponges:

 

post-6808-0-24548200-1323857138_thumb.jpg

 

As to the nature of 'pahoeids', the only thing I can think of is some form of red algae, perhaps similar to present-day Mesophyllum or Peyssonnelia. It's possible they could be something akin to the Pennsylvanian Archaeolithophyllum. So far, I've been unable to discern any fine internal structure. If they indeed are phylloid algae, this will be the only example I know of where they are preserved in shale, let alone left with readily observable morphology.

 

For the sake of this post, I'm lumping all these thalli forms together as 'pahoeids'. They very well may represent a number of different organisms.

 

Here's a stratigraphic chart based on my sketches and observations in the field:

 

post-6808-0-50958100-1323980919_thumb.png

 

Going by the lithology, I've guessed that the 'pahoeids' lie in the Frisbie Limestone (which is, stratigraphically, a transgressive limestone). As far as I know, the beds could, instead, belong to the upper Liberty Memorial Shale.

 

The 'pahoeid' beds are a complex bundle of shale and impure limestone beds and lenses. At the top, there is limestone made up of fine fossil debris. There is pyrite and glauconite present througout the unit.

 

Below the Frisbie is the Liberty Memorial Formation, which is a typical shallow marine/non-marine shale. It is medium gray, sandy, and contains thin beds of sandstone in places. Trace fossils, including Conostichus, are present.

 

Above the 'pahoeid' beds is the Quindaro, a deeper-water shale. Fossils include profusely abundant sponges (Heliospongia ramosa, Maeandrostia, and especially Fissispongia), as well as some small crinoids, bryozoans, and brachiopods.

 

The thick limestone above the Quindaro appears to be typical Argentine (which is regressive, for those taking notes :) ), but the strata in the area are anything but routine. These sponge-'pahoeid' deposits are near the edge of a large algal reef build-up in the Wyandotte Formation. Less than a half mile away in either direction, fossils at this horizon are sparse to absent.

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Terry Dactyll

I have no idea.... Too consistent for casts of any kind and too uniform and directional to be trace fossils I would of thought... I hope someone knows something to expand on your theory....

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Missourian

I should mention that all of them are calcified.

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Indy

You said "Some appear to be featureless sheets"

post-6417-0-45684900-1323868319_thumb.jpg

I have seen many such examples of what initially appeared to be "featureless sheets"

in the shale at my Pennsylvanian research locality here in St. Louis.

I have discovered many to be compressed fragments of either a large gastropod

IE Stobeus or a coiled cephalopod IE Domatoceras

I believe I see a small feature in your specimen...that might point to cephalopod

(boxed area in the edited photo)

You have the specimen in hand...I would be Interested in your comments

regarding possible gastropod or cephalopod

Barry

Edited by Indy

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Mr.Scaphite

Dont know if my expertise is of any merit on the topic, but I have seen like features in marine deposits of the Sundace Fm. of Wyoming. My interpretation was they were trace ichnofacies, perhaps a reworking by an anilid, mollusk or the like. However there may have been algal mats that compositionally changed their substrate, not so much as stromatolite would have.... Think thinner, leaching mineral content from the substrate leaving a distinctive foot print, then being so weak that decomposition erases any relateable material.

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Auspex

Some of my thoughts exactly, Mr .Scaphite (I just couldn't organize them into a coherent idea).

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Terry Dactyll

I did consider the reworking idea but the 'arrangement' of the traces seem to be too uniform...

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Missourian

For what it's worth, here is an enlarged image of the 'pahoeids' with the long, parallel branches with encrusting organisms:

 

post-6808-0-92580900-1323893264_thumb.jpg

 

Green arrows point to tiny brachiopods, probably Leptalosia.

 

The blue arrows points to the bryozoan Fistulipora.

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Auspex

Do we know the up/down orientation to the bedding plane? These just look so much like ichno-traces...

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Missourian
On 12/14/2011 at 2:46 PM, Auspex said:
Do we know the up/down orientation to the bedding plane? These just look so much like ichno-traces...

 

The ones I've found in place were face down.

 

But then how would encrusting brachs and bryozoans end up on them? The only thing I can think of is that they were once upright, or were suspended just above the sea floor like low plants as the little encrusters lived a sheltered life on the undersides of the thalli.

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Auspex

These are a first-class mystery, for sure!

The ID arrows are pointed every which way...

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Rob Russell

I've found several cephalopod plates with overlapping dawsonoceras. And some cephalo's with encrusted little critters too. Even in my own mind it seems a stretch due to the mass and symmetry happening here, but these look like lobocyclendoceras to me. Just a thought

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Missourian

The ID arrows are pointed every which way...

:)

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Missourian

D'oh.... I forgot to mention that there are many Chondrites-like burrows that run through the mud between the 'pahoeids'.

 

Some can be seen as holes on the sides of beds. The ones shown above all have little holes in them.

 

I have others that are exposed on bedding surfaces. I'll try to get photos of some when I have the chance.

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Missourian
On 12/14/2011 at 10:14 AM, Mr.Scaphite said:

Dont know if my expertise is of any merit on the topic, but I have seen like features in marine deposits of the Sundace Fm. of Wyoming. My interpretation was they were trace ichnofacies, perhaps a reworking by an anilid, mollusk or the like. However there may have been algal mats that compositionally changed their substrate, not so much as stromatolite would have.... Think thinner, leaching mineral content from the substrate leaving a distinctive foot print, then being so weak that decomposition erases any relateable material.

 

Taking what you're saying, perhaps it's possible that:

 

1. some invertebrate created the segmented traces,

2. then some organism (eg. encrusting algae) lined the traces with a mineralized layer,

3. and then the substrate was somehow removed, exposing a thin calcite mold,

4. which provided a surface for little critters to attach to.

5. Eventually, sediment covers and compresses the fossils.

 

Here's a quick drawing of such a process :) :

 

post-6808-0-82503000-1323918229_thumb.png

 

Encrusting algae is quite prevalent in these beds. The sponges are often covered with the stuff.

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Wrangellian

Fascinating... I would think if they were just traces there would be no thickness to the fossil in cross-section as you see in pics 10 and 11, assuming these are the same thing as the ripply structures you see on a flat surface.. right?

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Missourian
On 12/15/2011 at 0:46 AM, Wrangellian said:

Fascinating... I would think if they were just traces there would be no thickness to the fossil in cross-section as you see in pics 10 and 11, assuming these are the same thing as the ripply structures you see on a flat surface.. right?

 

Right. All specimens shown are 'body' fossils. In the first image, at the top center of the slab, there is one ripply structure that is raised a bit above the rest and is broken off. I have a hard time visualizing how a trace could be preserved like that unless it was lined with calc algae. In the 'long, parallel' specimen, you can see where the calcite membrane has weathered off, exposing the lighter matrix beneath.

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Wrangellian

I think I see it. My uneducated guess is you've got some kind of algae, tho I know that's not very helpful. Very cool specimens anyway, I have seen nothing like them.

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Missourian

Since I mentioned Mesophyllum above, I should show an example:

 

post-6808-0-81939100-1323939623_thumb.jpg

 

(No, I didn't take the picture, but I would love the opportunity to do so in its natural habitat.... :) )

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Missourian

As mentioned before, there are Chondrites traces throughout the beds. Here are a few:

 

post-6808-0-85743700-1323947011_thumb.jpg

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Missourian

As a bonus, a bed just above the 'pahoeids' contains these mound-like structures:

 

post-6808-0-17044200-1323947533_thumb.jpg

 

Unfortunately, I haven't yet found any in situ.

 

Depending on the orientation, they could be something akin to algal mounds, or they could be filled burrows.

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cgodwin37

They kind of remind me of spreiten of trace fossils, the concentric grooves or tubes formed as an organism systematically grazes, but I have never seen any quite like that. The last pic in the original post definitely looks like there are some phylloid algae fragments in there. cool sample, is right at the contact? If so what does the top of the underlying unit look like?

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Mr.Scaphite

I have also seen some trilobite ichnofacies in the Deadwood Fm. in SD and WY that have a similar look. Mind you I am just taking shots in the dark. The trilo tracks due to the reworking of material sometimes are better indurated then the surrounding matrix. However it would take lots of trilobites to make what I see in the images. Perhaps it is some other filter feeder critter? I do however stand my my algal/microbial mat hypothesis. Particularly due to the lack of further physical evidence. Thank you Missourian for so nicely illustrating what I was getting at.

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Missourian
On 12/15/2011 at 6:15 AM, cgodwin37 said:

The last pic in the original post definitely looks like there are some phylloid algae fragments in there. cool sample, is right at the contact? If so what does the top of the underlying unit look like?

 

Do you mean the underlying unit of the rock in the last pic, or beneath the thalli in general?

 

The contacts below all specimens are shale, which range from feather-edge to thin. This is what allows the 'pahoeids' to become exposed in the first place. As you can imagine, the shale had disintegrated by the time I found them.

 

Most specimens shown here were lying loose on the surface. The 'pahoeids' are very difficult to recognize in the outcropping. But then I keep looking.... :)

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Missourian

For the sake of completeness, here are some sponges from the overlying Quindaro Shale....

 

Heliospongia:

 

post-6808-0-77019500-1320830795_thumb.jpg

 

Maeandrostia:

 

post-6808-0-08499100-1320831127_thumb.jpg

 

Fissispongia:

 

post-6808-0-96796900-1320831463_thumb.jpg

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