Stromatoporids

[Shamalama]

I was photographing some Stromatoporid fossils I have lying around my yard for my friend at the Louisville Fossil Blog <-- Click here! and thought I'd post the pics here. Stromatoporids are algal structures similar to modern formations found in Shark Bay, Australia. The build up column shaped formations by trapping sediment and then growing over it. The fossils below come from a Quarry not far from my Parents house and I try to visit it each time I visit them. Within the Quarry the exposed rocks are inclined very slighty to the northwest and contain a dense layer about three to five feet thick of mixed Stromatoporids and Favosite corals. The formation is the Silurian-Devonian Keyser which occurs just below the Helderberg group of Devonian and above the Silurian Tolonoway. Most studies have decided that the boundary between the two periods occurs somewhere in the upper portion of the Keyser but it's not marked by a sharp change in fauna. The fact that the layer is composed of nothing but Stromatoporids that then grade into small Favosite colonies with occasional Aulopora, that get larger the farther up you go, shows that this was probably a shallow tidal lagoon that was gradually deepened due to rising sea levels or regional settling. In either case they are a great example of Silurian non-coral reefs and you can occasionally find a stray Brachiopod or Gastropod in the layer that may have found a home within the densely packed Stromatoporids. Farther up in the column a more diverse fauna appears with Calymene trilobites, Crinoids, Tentaculites as well as Leptanea, Leptostrophia and Cupulorostrum Brachiopods.

These Stromatoporids form generally round to oval shaped mounds that when cracked open reveal the many layers that they are composed of. The best are found with the original top layer still intact that shows the bumps of individual colonies. Others can get very large or column like or even quite twisted looking as the different mounds fought for space in the sunlight filtering through the water. Some parts of the layer are just chock full of Stromatoporids to the point that they seem to form the limestone themselves. As fossils they are fairly mundane and don't attract much attention beyond an interesting garden rock. The larger of the two pictured below is just that, but is one of my favorite fossils. I collected it as a kid about 20 years ago and thought I had a fossil stump until an elder peer corrected my error. I just like the fact that it's an intact colony. It's missing the top but the exposed and weathered center gives it a nice look. The core part weathers orange but the outer rind weathers gray probably due to different mineralization during fossilization and the fact that the center was a solid core of layered sediment while the outer part was softer. Most of the outer bumps have weathered away but there is a small patch that remains. This rock gives my flower garden some interest in winter when the flowers are all dormant.

Small hand sized specimen

Large Garden rock

Bumps

Internal texture

[mommabetts]

Very interesting, thanks for sharing.

[Guest solius symbiosus]

Just a clarification(I noticed it on his blog, too). Stromatolites are algal mounds; stromotoporoids are sponges(Porifera). What you have is a stromotoporoid.

[Shamalama]

Oh! So it's a sponge? That I did not know and shows I need to do some more research. Very cool then, I have my first sponge!

[Phoenixflood]

Yes, I at first thought you meant stromatolites but the more I look and then read the following post I realized it was something completely different. Very nice!

You get some cool things SL.