Hunting For Chaetetid Sponges

[midesti]

I am an archaeologist in Wyoming who grew up in Crawford County, KS. Growing up, we would always find stone tool debris made from some weird silicified coral. My dad recently found a farm field with large cobbles of the stuff laying around in it. After doing some quick question-asking to geologists, I was put on the trail of chaetetids. I'm pretty certain that the silicified coral I'm dealing with is a chaetetid. I sawed some up with a rock saw, but I need to figure out how to polish the slabs in an inexpensive manner. Really pretty stuff.

[Missourian]

On 12/11/2012 at 8:25 PM, midesti said:

I am an archaeologist in Wyoming who grew up in Crawford County, KS. Growing up, we would always find stone tool debris made from some weird silicified coral. My dad recently found a farm field with large cobbles of the stuff laying around in it. After doing some quick question-asking to geologists, I was put on the trail of chaetetids. I'm pretty certain that the silicified coral I'm dealing with is a chaetetid. I sawed some up with a rock saw, but I need to figure out how to polish the slabs in an inexpensive manner. Really pretty stuff.

 

The Marmaton Group ('Pm' on the map) cuts straight through Crawford County, so it's a safe bet they are chaetetids:

 

 

Do you have any pics?

[Missourian]

Of course I'd be happy to volunteer to help remove chaetetid float from fields, considering that chert is hard on farm equipment.

[midesti]

I'm not completely sure where this particular nodule and the one that I sawed up were recovered. I found them laying around my folks' place. There are varying grades of the silicified form, which range from brownish/white to gray/violet and a more calciferous white variety. Most of what I've seen was in the form of archaeological artifacts, so I don't have a definite source of the fossils. These ones probably came out of some gravel from a creek.

Here is one nodule:

The one I sawed into. Vertical cross-section:

A Close-up of the horizontal cross-section:

[Missourian]

Nice pieces. I like the banding in the second one.

[Wrangellian]

Nice stuff for sure! (Pick some up for me while you're at it! ) I'll bet rockhounds have a '_____ Agate' name for that stuff.

[Missourian]

On 12/13/2012 at 5:03 PM, Wrangellian said:

Nice stuff for sure! (Pick some up for me while you're at it! ) I'll bet rockhounds have a '_____ Agate' name for that stuff.

 

I have plenty of the calcite stuff. I'm still looking for the silicified ones....

[midesti]

I've been speaking to a number of geologists and paleontologists, and I think I've found a consensus that the silicified examples in my photos are residual and alluvial pieces that have eroded from the base of the Houx-Higginsville limestone. I have also heard reports of silicified chaetetids coming out of the Laberdie limestone member of the Pawnee limestone and the Amoret limestone member of the Altamont limestone.

[midesti]

Missourian wanted me to post more photos, but I keep forgetting. Here they we go:

Vertical cross-section. Thin section (2-3 mm thick):

Half of a silicified chaetetid fossil, vertical cross-section:

[midesti]

Polished vertical cross-section:

Polished vertical cross-section:

[Missourian]

Beautiful!

 

Thanks for sharing.

[midesti]

This is a stone tool dating to approximately 3500 years ago made from a silicified chaetetid fossil:

[Wrangellian]

Interesting! Paleo and Archeo in one piece.

The slices are nice too - new one on me. If I had found these in a box of random lapidary pieces I would have assumed they were some type of pet wood.

[trilobiteruss]

Some cool info, thanks all for sharing, I always learn from your posts!

[Missourian]

On 1/13/2013 at 2:01 AM, midesti said:

This is a stone tool dating to approximately 3500 years ago made from a silicified chaetetid fossil:

 

Very cool. Was it found near an area that would have the sponges?

[midesti]

Very cool. Was it found near an area that would have the sponges?

Yes, it was. From what I've observed, it was probably a supplementary toolstone that prehistoric folks were picking up out of the local creekbeds. Most of their toolkit was made from Mississippian-age silicates from the Ozarks. Only rarely have I seen finished tools made from the local silicified chaetetid fossils in local archaeological sites; mostly it's just flakes and cores. And I rarely see it used outside of a very localized area.

[midesti]

I recently went hiking around Bone Creek Lake in northeastern Crawford County, KS. The Higginsville limestone member, Little Osage shale member, and Blackjack Creek limestone member of the Fort Scott limestone were clearly evident, as were very, very abundant chaetetid samples. Unfortunately, I only saw a couple fragments of fully silicified examples, but I would characterize most as partially-silicified. Some mining of the Summit Coal bed was also evident in the area. There were tons of very large phosphate nodules weathering from the Little Osage shale.

This is a stone fence that is constructed almost entirely of fossilized chaetetids:

This photo shows the Higginsville limestone at the top of the profile, the Little Osage shale (with the Summit Coal bed) in the middle, and the Blackjack Creek limestone at creek level:

Edited February 28, 2013 by midesti

[Missourian]

Two great walls.

 

That cut bank is spectacular. For me, it is a thrill to walk around a bend in a creek and encounter something like that. It's even better when fossils litter the area below.

[Keeper]

Amazing stuff. Love the pictures and the information. I'm so new to all this I don't know what I collect most of the time. I've come across what has been pictured here many many times. Might keep a nice piece but would move on looking for what I thought were the real fossils. Boy was I wrong!!! Going back soon as the snows gone to get me some sponge!!!

[nemocoral]

Thank you for the quick response. Like you mentioned that they come in mound types, Here are a few photos of one that I found. I greatly appreciate the identification information. Ours was not found in the area that the others shown were but that is ok.