Stromatolite or stromatoporoid?

I was going to write something clever about this nice and very “organic looking” stromatolite I found on Gotland this spring, but then I started to question if it really is a stromatolite and not a stromatoporoid? What do you think it is? I think its damn hard sometimes to tell the difference from these two fossils. Anyhow, its def Silurian if thats any help to experts out there. Im quite sure someone knows it better than me and I would appreciate the help with identification.

Stromatolite or Stromaporoid – I really like the details on it. Not just the color and the fine laminae, but all those small attached remains of bryozoans, brachiopods and roots of what nots.

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6 Responses to Stromatolite or stromatoporoid?

  1. Chris says:

    It looks to me like a stromatoporoid. It looks like it has encrustations of net bryozoans which wouldn’t have been able to survive in hypersaline stromatolite environs.

    I might be wrong though ;-) Still, a superbly well preserved fossil. Love it.

  2. Daniel says:

    Chris: But could it be possible that those encrustations came to be much later perhaps and therefor not indicate the environment?

  3. Chris says:

    @Daniel
    Yep – that is entirely possible, though unlikely, considering the environmental stability required for stromatolitic communities to build such large-scale structures. Again, this doesn’t rule out a change in environment, it just makes it much less likely.

  4. Daniel says:

    Chris: Ah yes. I see.

  5. steve says:

    You have shown only the side view of this fossil. It could be a tabulate coral. Can you show the side that is facing down in the table? (it is actually the top). Which locality on Gotland is it from? I know Gotland, stromatoporoids, stromatolites & may be able to ID it with more photos.

  6. steve says:

    You have shown only the side view of this fossil. It could be a tabulate coral. Can you show the side that is facing down in the table? (it is actually the top). Which locality on Gotland is it from? I know Gotland, stromatoporoids, stromatolites & may be able to ID it with more photos.

    By the way, in the Silurian, there are loads of normal marine stromatolites, which are not an indicator of hypersaline conditions in the absence of sedimentary facies information

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