Recrystallized Fossil From The Permian Park City Fm. (Phosphoria), Central Wy

[dazzle]

Hi folks,

I found these specimens in a Permian dolomud/wackestone in central WY (Fremont County). It is from the Park City Fm. (Phosphoria equivalent). I've attached photos of two different specimens which were found about 10-15 meters from each other in the same bed. I found a few other examples, and they were typically spaced about that distance apart from one another (in other words, they don't seem to form colonies), and they were by no means common. These appear to be recrystallized (see macro images). As I said, I think this is a dolowackestone "matrix" and there appear to be some silicified (chert) burrows nearby to the specimens, for what that's worth. Up is stratigraphic up in the photos (photos are perpendicular to bedding, i.e. cross-section view). I can't find anything like this described in the literature on the Park City/Phosphoria, and I was hoping that someone with a little more experience in Permian fauna (e.g. the Capitan reef builders) or other might have some insight. I was able to collect one specimen, which I plan on cutting and polishing, and also making a thin section for a closer look. In the meantime, any thoughts on what I might be looking at??

Thanks very much in advance!

[Rockwood]

Don't take this an expert opinion. I know nothing about the formation. The second pic. from the left seems to show features in the surrounding rock that resemble those within the primary feature. I wonder if this could be an indication that this is more likely a nodule than a body fossil.

[mikeymig]

It looks like a plant (Cycad) to me but I'm no expert on the Permian. http://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Cycadeoidea_sp.jpg/216px-Cycadeoidea_sp.jpg

Mikey

[dazzle]

Thanks for your input, Rockwood and Mikey!

Rockwood- I agree with you that it could just be some odd nodule rather than a fossil. The way the specimen just kind of stands upright in the rock and thickens up gives me the impression of some sort of sponge or horn-coral-like animal. It also has these "disc" like layers with what I'll call "prismatic" calcite in the center of those discs (see rightmost photo). Makes me think there was some kind of pre-existing structure that got recrystallized. The features in the surrounding rock that I think you are referring to (the white-ish zones) are halos around what I think are chertified burrows. The intraclasts in the borrows are slightly coarser than the surrounding sediment. But you are right, it is quite possible that I am just looking at a recrystallized burrow.

Mikey- Interesting idea! I agree that it really looks similar to that Cycad photo you included. We are definitely subaqueous here, as I don't see any evidence for subareal exposure, so I don't know that it would necessarily be a terrestrial plant.

I still can't shake the feeling that I'm dealing with a sponge. There really wasn't much in the way of corals building reefs in the Permian, at least compared to other periods, and it has the "look" of a sponge (for example, http://www.bumblebee.org/invertebrates/images/synconoid.jpg).

Can any Porifera enthusiasts weigh in??

[Auspex]

There were certainly a bunch of reef-building calcareous sponges in the Permian; given the size of the specimen, though, the structure strikes me as a bit coarse for a sponge. Also, the frequency of occurrence doesn't really jibe with it's having been a reef builder. Still, it is something, and sponges seem like a good rout to follow up on.