Solved: Stromatoporoid Sponge not Horn Coral on Jasper

[Pippa]

I picked up this jasper for its banding. Only later, when checking the rock through my hand lense did I discover what I think are a bunch of little rugose colonial corallites at the top and bottom of this rock.

 

If these are indeed corals, all but one lack most detail in the center.  If septa are faintly visible, they look differently preserved than on any of my other coral specimens. Mostly it's just circle after circle here, and areas full of "pores". 

Now that I'm looking at them on my larger screen, the "pores" themselves seem to be corallites - microscopic ones. The black dots are in the center of honeycomb like shapes.

I'm confused now, are these the fossilized remains of one or two type of corals, or maybe a colonial coral and a bryozoan?  

 

Sorry about the bad quality and distortion of the pictures taken through a microscope lens on my phone.

Please help me ID these tiny hurricane look-alikes. 

As always, thanks in advance.

 

 

Here a couple of them in various states of preservation. Lots of them have a vug where the center of the corallite would be. Here the circles look like growth rings and in some areas the "pores" are clearly visible. 

 

#1:  This one is the only one with detail in the center. Septa? 

 

#2:  a vug at the center seems all that's left here.

 

#3: Just pores in the center, and in between the circles, maybe the faintest lines that could have been septa?  

 

#4:

 

Area in between corals, with faintly visible honeycomb shapes:

 

 

Detail of the above:

 

Another area in between, looking somewhat different again:

 

 

 

    

 

 

 

 

 

[Al Dente]

The side view reminds me of a stromatoporoid. Maybe it grew around some coral. Some of the mound shaped structures could be mamelons.

[Shamalama]

Agreed, Stromatoporid that had some rugose corals that intergrew. I've seen it before on other specimens.  My initial reaction was a lake agate but the micro pics convince me of what @Al Dente said.

[Pippa]

23 hours ago, Al Dente said:

The side view reminds me of a stromatoporoid. Maybe it grew around some coral. Some of the mound shaped structures could be mamelons.

 

20 hours ago, Shamalama said:

Agreed, Stromatoporid that had some rugose corals that intergrew. I've seen it before on other specimens.  My initial reaction was a lake agate but the micro pics convince me of what @Al Dente said.

Al Dente and Shamalama, thank you very much!

I think you are so right! 

How could I not think of sponge?  Looking up stromatoporoids online, I've found photos and illustrations that look as if they could have been taken from my rock.  To think, that I've been looking for sponges at the beaches for such a long time now and then not recognizing one when I finally do find one...   

I guess I've expected sponges to look similar to the ones some people on this forum have found in their backyards or in abandoned quarries etc., which look very similar to vesicular volcanic rocks and nothing like the fossil on this jasper.

Anyway, i think the single well preserved marmelon is what made me think coral. And, I'm still not really sure what the different "features" on this rock are and the functions they fulfilled for the living sponge. I guess I will have to look at more than images and take the time to read up on stroms.  

When you say: "Maybe it grew around some coral."  and  "had some rugose corals that intergrew"   What parts are you suspecting to be coral?  The little "hurricanes?" The ones with little to no detail in the center? I'm asking because I'm now inclined to think that they all used to have mamelons too, but which have been broken off/eroded and some may have been filled by calcite or dolomite? No? 

 

Mamelons on this graph look just like the one on my rock:

 

 

 

 

 

[Al Dente]

1 hour ago, Pippa said:

When you say: "Maybe it grew around some coral."  and  "had some rugose corals that intergrew"   What parts are you suspecting to be coral?

I was thinking one of your photos showed coral septa but looking closer I think it might be another mamelon.

[Shamalama]

Yes, I thought that your #1 photo was septa as well. I'm not versed in Stromatoporoids well enough to know what a mamelon cross section looks like though.

[Pippa]

5 hours ago, Al Dente said:

I was thinking one of your photos showed coral septa but looking closer I think it might be another mamelon.

 

1 hour ago, Shamalama said:

Yes, I thought that your #1 photo was septa as well. I'm not versed in Stromatoporoids well enough to know what a mamelon cross section looks like though.

 

It is difficult to find any photos of stromatoporoids on the web that show much if any detail of the mamelons. 

Actually, my one little mamelon shows much better detail than anything I've found on the web so far. It's illustrations, most of them black and white, that show them better.  I'll keep looking.

 

I haven't even found a second mamelon on this rock yet. They are so tiny, that by eye, I can't differentiate between them and the focus of the microscope lens cannot be adjusted, so anything that's located on an incline or in the slightest depression just looks like mush and I cannot make them out. Actually, now that the photos of the whole rock are blown up on this thread, I think I'm seeing more and more of the little circular features.  I'll have to take another tour of the rock, see if I can find a second mamelon.

 

Anyway, thanks so much for your help in identifying my first sponge. You guys rock!

 

P.S.: I think I will rename the thread title along with the tags to reflect what this is, so it will pop when people are searching for sponges or stromatoporoids.

 

[TqB]

4 hours ago, Pippa said:

 

 

It is difficult to find any photos of stromatoporoids on the web that show much if any detail of the mamelons. 

Actually, my one little mamelon shows much better detail than anything I've found on the web so far. It's illustrations, most of them black and white, that show them better.  I'll keep looking.

 

I haven't even found a second mamelon on this rock yet. They are so tiny, that by eye, I can't differentiate between them and the focus of the microscope lens cannot be adjusted, so anything that's located on an incline or in the slightest depression just looks like mush and I cannot make them out. Actually, now that the photos of the whole rock are blown up on this thread, I think I'm seeing more and more of the little circular features.  I'll have to take another tour of the rock, see if I can find a second mamelon.

Search for stromatoporoid astrorhizae instead - there are a few helpful images, such as this:

 

 

[Pippa]

4 hours ago, TqB said:

Search for stromatoporoid astrorhizae instead - there are a few helpful images, such as this:

 

Yes, now I'm finding some images of beautifully preserved astrorhizae. Very cool! So the astrorhizal columns 

Good photos of well preserved details such as these are so helpful to me when I'm trying to ID a fossil.

And it always does come down to using the correct terminology when googling or doing any kind of research, the right term will get the most relevant results. 

Thanks so much for sharing your knowledge, TqB, I really do appreciate it.  

 

[Pippa]

[Pippa]

Well, it's been three years since I posted this thread. Here is finally the promised image of the best preserved mameloid / stromaporoid astrorhizae on this rock.