Sunday, June 4, 2023

Uŋčí Makhá Park Revisited, Part 2: Further Fossils

We're now up to the fourth entry in a completely unexpected series on the Platteville–Decorah rocks and fossils of Uŋčí Makhá Park. We've already seen the common fossils from the site, so for this go-round I'm focusing on rarities.


I had no photos of bryozoans in the previous post, but this time I have returned with evidence of bryozoans, albeit in the Carimona Member of the Decorah rather than the more prominent Magnolia Member of the Platteville. One of the questions I had from the visits in the fall was whether there were more exposures of fossiliferous Carimona beds. It turns out there are, but are distributed sporadically (one horizon in particular).

Persistence is rewarded with twiggy bryozoans.


Practically all of the brachiopods that can be seen at the park are articulate forms. In one of the Magnolia landscaping blocks, though, I noticed this lingulid brachiopod.

The fossil is in the side of a block; a vertical orientation is actually life position for these brachiopods.

Then there's this. I initially interpreted the large shell impression in the following photo as a bivalve with a deep bulbous shell, but after further consideration, the symmetric shape of the shell plus the clarity and style of preservation of the growth lines lead me to interpret it as another lingulid (perhaps Pachyglossella [aka Lingula] elderi or something along the same lines). A much smaller true bivalve impression is visible in the lower right, and a couple of gastropod steinkerns are also present. There is also an odd bit of corduroy near the center; it's poorly exposed and could be anything from a slice of warped ribbed brachiopod to a strongly textured gastropod (see also the third-to-last photo in this post).

Plus the usual strophomenids.


I don't usually have a lot of bivalve photos. Here's a couple of shells in side view:

Well, technically steinkerns, as usual. They look kind of like soft hats.


The seasonals picked out a couple of interesting nautiloid fossils:

This is probably Beloitoceras pandion.

It's hard to tell from the photo, but this is a half-circle void with fragments of chamber walls. I'm interpreting it as the coiled nautiloid Plectoceras.

Later, I spotted this one in a block:

Your typical orthocone mold, surrounded by brachs. There's also a horn coral (corduroy acorn) sticking out of the side near the lower right corner.


We saw a number of gastropods last time, so there's no need to go over that ground again, but here's a parade of snail steinkerns.


One of the nicer fossils we saw is this piece of Isotelus cheek.

Fine structural features are apparent when you zoom in. Note also the Hesperorthis just below and to the right.

The Kentucky Geological Survey has a good page covering this trilobite of unusual size.


Last time I mentioned that I wasn't sure if I had an ostracode. This time I'm pretty sure.

Eoleperditia fabulites (again with the wonky color balance).


Below is the coolest fossil found by the seasonals: a partial crinoid stem a few inches long.

They always cut out just as they're getting interesting.

Trace Fossils

Either I was paying more attention to burrows this time, or a season of weathering had brought a few more to the surface, but the burrows were outstanding and included a variety of forms.

Nothing of particular scientific import, I just liked this vertical reverse mark of Zorro.

A winding vertical burrow.

There were also lumps of various origins associated with some of the burrows.

This is in a Carimona landscaping block. I suspect the lumps are shell traces and the block is upside down.

This one is in the Magnolia. The large lump on the left is clearly a brachiopod, but the whole underlying structure is intriguingly irregular, perhaps representing a collapsed lining.

The wrinkled surface of the irregular Magnolia burrow is reminiscent of a couple of other traces I observed at the site.

Note the wrinkles along the top margin of the burrow.

This is not the greatest photo, but a leaf-like pattern of surficial marks is visible on the darkened surface.

These examples put me in mind of the wrinkled object included in this post, albeit not quite as well-preserved. I'm still leaning to some kind of lined burrow akin to Palaeosynapta.


Finally, here are a few more that I couldn't quite place firmly, although I do have ideas.

I think I need to take a toothbrush for this one. There is clearly something beneath the Carimona mud here; what I hope it is is a Carabocrinus calyx, although if it is I don't think I want to fully expose it.

I'm pretty sure this is just one of our more ornate snails.

I saw something kind of like this back in November, albeit more strongly ridged. My first instinct again is a warped piece from a large trilobite (i.e., Isotelus).

This is probably just a steinkern of a steep-sided low-coiled snail (think like Maclurites), but it's also reminiscent of some kinds of crinoid holdfasts (of course, it would then be an awfully big crinoid for the Platteville).

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