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275 Views 3 Replies Last post: Feb 12, 2014 10:26 PM by MikeHardman RSS
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Feb 10, 2014 12:20 PM

Jelly Fish fossils??

lilly fossil 077.JPGlilly fossil 086.JPGlilly fossil 087.JPGlilly fossil 081.JPGlilly fossil 088.JPG

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    Feb 10, 2014 1:57 PM (in response to kate)
    Re: Jelly Fish fossils??

    Kate,

     

    No jelly fish.

     

    1. The circles: tricky... Perhaps alteration haloes around particular mineral grains/clasts (similar in principle to the concretions I have mentioned in recent replies today). The dark lumps: perhaps clasts of a dark mineral, though possibly also plant or other fragments. Would need to look mich closer, preferably with a microscope...

     

    2. Perhaps a mould where a piece of fossil wood fell away (leaving some of its discolouration in the rock).

     

    3 & 5. Concretionary colouration in sandstone. Notice how the banding is parallel to the edges of the block. That's probably because the block as you now see it was defined by a network of fractures in a much larger mass of rock at an earlier time. Later, those fractures were natural places for the outcrop to break-up into smaller pieces during weathering. But back a while: when your piece was just part of the much larger mass of rock, ground water would have used those fractures to circulate, transporting minerals as it went. As the concentrations of minerals in the water changed, your part of the rock soaked-up different concentrations at different times, permeating-in from the fractures, causing the zoning you see today.

    Well, that's one theory. It is perhaps strange, but for such a common phenomenon, there is still a lot of debate about how these phenomena actually occur - in what physical and chemical conditions, how soon after lithification, at what rate, etc.

     

    4. This is the most interesting rock, for me.

    I think you may have trace fossils, but closer inspection would be necessary. I'm not sure which ones.

    Google 'trace fossil' or 'ichnofossil'. You'll find there's another whole world of fossils out there.

     

    Mike

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      Feb 12, 2014 9:22 PM (in response to MikeHardman)
      Re: Jelly Fish fossils??

      Hi Mike

      The first image is interesting because I am at my 'whit's' end trying to answer it.

      I remember attending a nite class at out local geological society with similar specimens on show, but I am finding it hard to remember what was said about them.

      Mineral radiating away from an atom???? I know I am wrong but I think I am not far off.

      Don't know but very interesting.

       

      Tabfish

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