Ordovician Micro Mystery - Foram or Something Else

[GeschWhat]

I was out hunting near Spring Valley, Minnesota with @Bev and @minnbuckeye the last couple of days. As always, I was looking for coprolites. Mike came across this first piece, sitting loose in a piece of weathered matrix. While we were splitting rocks, we found a virgin layer of the source matrix. When we got back to Bev's fossil barn (everyone should have one), I took a peak under the microscope at two of the loose, irregular objects but couldn't really see much because of the powdery iron oxide coating. When I lightly rinsed them, they revealed these microscopic (calcareous) jack-shaped objects. Similar inclusions were in both objects loose objects. You can see from the broken spine on the inclusion in the lower right that they are hollow. In the other loose piece and those still embedded in the matrix, I can also see random straw-like spines of the same material.

 

I'm not sure if these are coprolites, algal masses or something else. I have seen coprolites covered in powdery iron oxide before. Eventually I would like to free more of these from the matrix so that I can sacrifice one to get a look at the interior. Can anyone identify the little jack-shaped inclusions? The spines may have been quite a bit longer. The only things I can think of are forams or perhaps diatoms.

 

Bev and Mike - What was the name of that cliff again? Decorah Shale?

 

@Carl

[GeschWhat]

Here is what the host matrix looks like.

 

[Tidgy's Dad]

I think the 'jack' objects are sponge spicules so the main fossils could be sponges. 

[piranha]

Rigby, J.K., & Bayer, T.N. 1971

Sponges of the Ordovician Maquoketa Formation in Minnesota and Iowa.

Journal of Paleontology, 45(4):608-627

 

[GeschWhat]

 

1 minute ago, Tidgy's Dad said:

I think the 'jack' objects are sponge spicules so the main fossils could be sponges. 

 

1 minute ago, piranha said:

Rigby, J.K., & Bayer, T.N. 1971

Sponges of the Ordovician Maquoketa Formation in Minnesota and Iowa.

Journal of Paleontology, 45(4):608-627

 

Bingo! You guys are amazing! So these would be hexactines? Can you tell the species of sponge based on the shape of the spicules? Are sponges high in iron?

[Tidgy's Dad]

Yes, hexactinellid sponges. 

Someone very clever could maybe tell the species based on the spicules, but not me.

The spicules are primarily silica hence the nickname 'Glass sponges' but i doubt there's much iron in there before preservation. 

 

[minnbuckeye]

Bev may have a different opinion of the strata these came from. But it was in the area where we found the Isotelus parts. That in combo with the density and color of the rock there, I would say Maquoketa of the Ordovician. This I see correlates to what @piranha has posted.

[ynot]

Just a thought...

In the pictures of sponges I have seen on TFF the spicules are laid down in an organized pattern.  Your picture shows them randomly placed and disorganized.

Could the larger masses be coprolite from a sponge eating fish critter?

 

Thanks @minnbuckeye

Edited June 2, 2018 by ynot

[minnbuckeye]

1 hour ago, ynot said:

Just a thought

Could the larger masses be coprolite from a sponge eating fish?

 

No  fish in our  Ordovician

[ynot]

3 minutes ago, minnbuckeye said:

 

No  fish in our  Ordovician

Whoops.

[minnbuckeye]

maybe sponge eating cephalopod or trilobite instead??

[GeschWhat]

I plan on busting some more free and get a look at the innards. I bet they are the sponges. I have noticed in other posts that sponges often look like coprolites. The iron oxide does seem kind of weird though. Thanks again for all your help @minnbuckeye - best rock splitter ever (well, next to Axle).  I'll save you some of the sponges if you are interested in adding them to your collection.

[minnbuckeye]

best rock splitter ever (well, next to Axle)

 

I thought @Kane was top dog?? Actually, @GeschWhat, I will probably revisit the site looking through that trilobite shelf and pick up a bucket of those goofy rocks too. Without a scope, it is hard to appreciate them though. Xmas is only 7 months away. Actually, my birthday is only 1 month away. I better research scopes then drop a hint to everyone I know!!! It was a pleasure hunting with you!!  For everyone's information, Geschwhat is looking for trilobite poo. I suggest inviting her along on a hunt sometime. She will give you the trilos, or anything else she finds, with the understanding anything "coprolite like" is HERS!!!! I think it is a win win for anyone hunting with her.

[GeschWhat]

17 minutes ago, minnbuckeye said:

She will give you the trilos, or anything else she finds, with the understanding anything "coprolite like" is HERS!!!!

I don't know if I would quite go that far...if the trilos are associated with the coprolites, I keep at least one of those too! 

[Spongy Joe]

Nice..! Thanks to Adam, for pointing me over here. I'll confirm straight off that these are hexactine sponge spicules (noun: hexactin; adjective: hexactine; yes, I've been writing it wrong for years! ), very like the Rigby & Bayer paper. Isolated spicules like this (i.e. any with generic forms that lack real distinguishing features) really aren't identifiable - they might not even be hexactinellids, as hexactins go back quite a long way in their evolution.

 

Complete sponges are another matter, but I don't think these are; at least, not quite. I suspect what's going on here is that you have little calcite concretions (possibly centred on articulated sponge remains, possibly just on spicule-rich sediment) that have weathered out to give you the iron-oxide stained, spiculitic rubble. I'm intrigued by the preservation, though: are they really made of calcite..?

 

They should be silica, but of course can be replaced diagenetically. However, replaced spicules usually lose the axial canals, which are a feature of hexactinellids (and demosponges), but not calcareans. Another option is that these were biminerallic, with calcite wrapped around a silica core. That would be interesting, hence this thread:

   Looking at the middle of the 'sponge', I can see what may be different spicules too, but we'd need more magnification to check. Can you see any heteractins there as well..?

[GeschWhat]

1 hour ago, Spongy Joe said:

I suspect what's going on here is that you have little calcite concretions (possibly centred on articulated sponge remains, possibly just on spicule-rich sediment) that have weathered out to give you the iron-oxide stained, spiculitic rubble. I'm intrigued by the preservation, though: are they really made of calcite..?

I'm sorry, I only assumed the spicules were calcite (thinking they were some sort of foram). I broke a bunch out of the little concretions out of the matrix shown above this afternoon. The sponge/concretion that I posted first was weathered out. Those shown still in the matrix were not (below). Those were exposed when we started splitting/cracking the limestone. The thicker piece of limestone that entombed these didn't have a real fracture plain. I put one small specimen in vinegar and it fizzed revealing this spicule, which did not react to the vinegar. Pictures to follow. There are long tubular spicules, and probably others.

 

 

[Spongy Joe]

Thanks for that, Lori - that makes a lot of sense, and is a lot more what I'd have expected!

 

Will look forward to seeing the spicules... look out for microscleres: really, really tiny ones with interesting shapes!

[GeschWhat]

Here is the spicule that was revealed after exposure to vinegar for about 3 minutes. It is still soaking, so I will be checking on it again shortly.

[GeschWhat]

After soaking in vinegar for about an hour, the fizzing has all but stopped. The cross-shaped spicule is barely attached to the host concretion and appears to have a slight curve to it. Two additional spicule fragments are now exposed.

[GeschWhat]

While perusing the net for possible glass sponge predators, I came across THIS.  Perhaps these could be coprolites afterall. I have contacted the author for more info...stay tuned!