Hunting For Chaetetid Sponges

[Missourian]

I've always been fascinated with the chaetetid sponge reefs that dominate the limestone beds of the Pennsylvanian Marmaton Group. Since these strata outcrop thirty to fifty miles east of the Kansas City metro, I don't have many opportunities to find them.

 

This weekend, we drove out to a family event in southeast Missouri. I took the opportunity to check out a road cut in the Pawnee Formation near Holden, Missouri that I had read about in a publication. The chaetetids are present in the Coal City Limestone member of the Pawnee.

 

At the expected spot, I encountered the black Anna Shale and a thick limestone that could be the Coal City:

 

 

The limestone was basically barren. When I stepped back, I noticed that there are actually two limestones in the cut:

 

 

Yeah, now I remember. The lower ledge is the Myrick Station Limestone. The one I'm looking for is on top. Up close, it appears to be an impenetrable wall. No fossils could be seen on the weathered joint surface or in the rubble:

 

[Missourian]

I crossed the road to some Coal City on the other side:

 

 

Chaetetids are well displayed on the side:

 

 

The one on top resembles a large hubcap in size and shape:

 

 

Fine detail can be seen when examined up close:

 

 

Unfortunately, there were no collectible pieces.

[Missourian]

On a previous trip, I picked up several chunks of chaetetids. Here are a few....

 

Detail. Note the frond-like growth pattern on the right:

 

 

Same piece, opposite side:

 

 

Another piece. The pit just right of center may be a boring:

 

 

A rounded fragment:

 

 

The same piece, from the top:

 

 

Chaetetes milleporaceus (genus 'Chaetetes' may no longer be valid for these)

Coal City Limestone

Warrensburg, Missouri

[Wrangellian]

Fascinating... You've got a nose for the unusual things that interest me but most people seem unaware of or uninterested in. Of course it helps living in a Paleozoic area...

Could you not pry up that slab that you said was not collectible and prep it down from the top (or get someone to do this - if it's possible I don't even know, but where there's a will there's a way)?

[Missourian]

On 10/29/2012 at 5:53 PM, Wrangellian said:

Could you not pry up that slab that you said was not collectible and prep it down from the top (or get someone to do this - if it's possible I don't even know, but where there's a will there's a way)?

 

That's possible, but I would prefer to find more easily collectible pieces in other outcrops. I plan on returning to the Warrensburg spot mentioned above if I can find an excuse to make the 100-mile round trip. There, I collected many large chunks in the road cut, so I don't know how much is left to find. On my recent road trip, I noticed an outcrop almost hidden from view on the other side of the highway. I'd like to find some more exposures, but there seems to be precious few in the mostly flat area.

 

Quote

Fascinating... You've got a nose for the unusual things that interest me but most people seem unaware of or uninterested in. Of course it helps living in a Paleozoic area...

 

It's nice to be interested in such 'uninteresting' things. You don't have to worry about competition or legal matters.

[Bullsnake]

You don't have to worry about competition...

...

[thair]

That is interesting. You are the first person I have seen collecting these odd sponge/coral specimens. I have a couple spots I hunt here in central Texas that I have collected those. I have one piece outside next to my driveway that weighs about 200 pounds that I picked up because it was close to the road. Thought I might polish one end of it to reveal the pattern and roll it to my back porch.

[thair]

Here is a picture of a couple of the column structures I have found at one of the sites.

[Missourian]

On 10/30/2012 at 11:47 AM, thair said:

Here is a picture of a couple of the column structures I have found at one of the sites.

 

Those are cool. I'd like to find some columnar forms that aren't locked in matrix.

[thair]

This is my idea of what the structures may have looked like based on my finds.

[Missourian]

On 10/30/2012 at 0:16 PM, thair said:

This is my idea of what the structures may have looked like based on my finds.

 

Very nice. Those sponges seem to have taken on a stromatolite-like growth habit.

[Missourian]

Since I was going to a Halloween party in a far-flung suburb, I took the opportunity to drive the extra distance to the Pawnee Formation outcrop near Warrensburg, Missouri mentioned above.

 

Again, this is the Coal City Limestone. The base of the Bandera Shale lies above it:

 

 

Chaetetids are abundant in this outcrop. I've been here before, but I don't remember seeing so many. They tend to occur as reef-like masses every twenty feet or so in the rock faces. Here is one such cluster:

 

 

The sponges stand out as gray in the reddish matrix.

 

Unlike the sheet-like forms I observed a few weeks ago, most of these took on the form of mounds. A few formed columns:

 

 

Many of the sponges in the rock face displayed some fine detail:

 

 

There was a beautiful cross section of a mound that I would have taken home, but it wouldn't budge. I couldn't even get a decent photo. I did collect several others that were lying loose in the talus. I'll post some pics when I get the opportunity.

[Wrangellian]

It's nice to be interested in such 'uninteresting' things. You don't have to worry about competition or legal matters.

I know, but I'm surprised how popular the oddball things can be on ebay for instance... used to think everyone was just into dino bones and shark teeth (and trilobites), but....

Anyway, keep it coming.

[squalicorax]

nice stuff missourian

often under appreciated critters

[Missourian]

More photos, as promised....

 

I brought a few chaetetid mounds home. They are quite large:

 

 

The one on the left is sectioned. It displays some nice structure:

 

 

Another sectioned sponge:

 

 

Yet another section. This one has some prominent growth lines:

 

[Missourian]

The mounds start out as relatively flat sheets. I found this one in two pieces:

 

 

Intact, it looks like an unremarkable slab of limestone. I prefer it broken:

 

 

Another flat piece is embedded in matrix:

 

 

Besides the chaetetids, crinoid fragments are by far the most common fossils in the Coal City. Some crinoid stems are quite remarkable in size:

 

 

These are the largest I've ever found.

 

Other fossils I've notice are a few brachiopods, fusulinids and coral.

[Missourian]

Many chaetetid pieces display odd spherical structures:

 

 

These tend to be about the size of large peas. I first thought they're some form of budding that was the start of a new layer of growth, but these show up on all sides of the fragments. I now think these are concretions that grew through the sponge framework.

 

This large chunk displays many of these spherules on its bottom side:

 

 

The spherules up close:

 

 

The growth of Syringopora coral on the other side of the piece was helpful in determining which side is up:

 

[Bullsnake]

So, you're implying coral on bottom?

[Missourian]

I believe the coral grew on top, though there is always the possibility they attached up-side-down in a sheltered area.

[Missourian]

These chaetetids are sclerosponges, otherwise known as coralline sponges. These consist of living crusts that secrete skeletons of calcium carbonate. The style of growth appears to be similar to that of stromatolites. Over time, these skeletons can become quite large. Some build-ups may take 1000 years to grow, according to some sources. As far as I know, the larger chaetetid mounds shown above could very well have been centuries old before death and burial.

Here are some examples of living sclerosponges for comparison:

(All pics snatched from Google images.)

[Missourian]

On a road trip from Kansas City to Branson, Missouri, we saw many interesting highway cuts in rocks ranging through the Ordovician, Mississippian and Pennsylvanian. A few cuts were within the outcrop belt of the chaetetid-bearing Marmaton Group.

 

This one near Urich is probably in the Higginsville Limestone:

 

 

The Higginsville is known to have chaetetids in varying degrees of abundance. I walked the exposure to see if any were present. Nothing showed up except for this nice little specimen:

 

 

There didn't seem to be any way to extract it from the rock face without a lot of work, so I left it in place. Intriguingly, it appears to be partially silicified. Some chaetetids could be amazing if they could be cleaned up in a bath of muriatic acid.

[squalicorax]

I hope it is silicified

looks neat

[Missourian]

I cleaned up the large mound shown in a post above. It's hard to get a decent photo, but here goes:

 

 

This is a complete chaetetid mound that somehow broke free from the limestone and remained intact. Normally, the larger ones break up upon weathering of the limestone.

 

A view of the side shows how the mound grew over time. Starting out with a low, shield-like form, the mound narrowed somewhat as it grew vertically. Cracks on the surface of the sheets indicate they broke off at times:

 

 

It's also possible that these cracks formed during compression of the sediments after burial. Some cracks close up:

 

 

A close-up of pores on the basal 'shield':

 

 

The piece reminds me of old, weathered travertine deposits around hot springs:

 

 

Its pattern of growth may have been similar.

 

It also reminds me of a loaf of bread and a small dog.

[astron]

Yes, Missourian, it's always a pleasure to follow your smoothly running and teaching reports

Thanks for all this

[Missourian]

On 11/23/2012 at 1:23 PM, astron said:

Yes, Missourian, it's always a pleasure to follow your smoothly running and teaching reports

Thanks for all this

 

Thanks much. And your online museum ('A Cretan Fossils Collection' and other threads) is a pleasure to 'walk' through.