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835 Views 5 Replies Last post: Nov 2, 2013 9:21 PM by MikeHardman RSS
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Apr 23, 2013 4:46 PM

Fossil identification

Hi,

    Me and my little daughter poppy found this at a gravel pit site near the great ouse river in cambridgeshire, can anyone tell us if it is a fossil and what it might be?

 

Thanks

 

matt & poppy

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    Apr 24, 2013 4:43 PM (in response to matalode)
    Re: Fossil identification

    This looks like a piece of orange coloured flint, including some bivalve shells (the large one on the left perhaps a bit like Inoceramus, but there is not enough to get further than a guess on that).

     

    The subject of your question is more enigmatic, however. Various 'string of beads' fossils crop up on this forum and they usually cause some head scratching. For instance: http://www.nhm.ac.uk/natureplus/message/5416.

     

    There is a 'string of beads' fossil called Horodyskia (http://en.wikipedia.org/wiki/Horodyskia), but that is too old for your specimen, I am fairly sure.

    A foram is also possible, but I think the beads in your specimen are too large (http://www.bgs.ac.uk/discoveringGeology/time/Fossilfocus/foraminifera.html.

     

    So - I am not sure, but the possibilites discussed in http://www.nhm.ac.uk/natureplus/message/5416 could apply.

    Also http://www.nhm.ac.uk/natureplus/thread/9143.

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        Apr 25, 2013 4:15 PM (in response to matalode)
        Re: Fossil identification

        Matt,

        Yes. And the 'something' is almost definitely fossil (as opposed to mineral).

        There's always a chance you or anybody else might stumble upon the real answer, in which case please post here - we'd like to know!

        Mike

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    Nov 2, 2013 5:08 PM (in response to matalode)
    Re: Fossil identification

    Matt & Mike,

     

    Your enigmatic fossil (from the post back in June) is indeed a bivalve shell, as Mr. Hardman supposed. Specifically, the "chain of beads" is the LIGAMENT insertion pits along the hinge of the two molluscan shells. However, because they stick out (a bit like pearls on a string) those would be the sediment casts of the actual calcite shell (that has been dissolved or otherwise eroded away). There is actual shell material in your specimen, both near the hinge in cross-sectional view (the rows of wee prisms you can see) and also the outer surface of onwe of the valves below the hinge area.

     

    Now, as to the identification:  that is a specimen from the now-extinct bivalve family INOCERAMIDAE. They thrived during the Jurassic and Cretaceous periods, but became extinct almost at the same time as the last ammonites and also (on land) the dinosaurs and flying reptiles at the end of the Mesozoic.

     

    Dr. James Crampton, also a Kiwi, would no doubt be able to be of further assistance.

    He's in Lower Hutt and may be reached at:

     

    http://www.gns.cri.nz/who/staff/1870.html

     

    Cheers & good luck,

    CHRISTOPHER COLLOM

    Calgary, Alberta, Canada

    cjcollom@shaw.ca

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      Nov 2, 2013 9:21 PM (in response to cjcollom)
      Re: Fossil identification

      Christopher,

       

      Thank you very much for your input, confirmation of Inoceramid, and especially for IDing the string-of-beads!

       

      Please could you unravel a point of confusion in my head...

      You write of the beads being pits (ie. recesses in the original animal) yet also refer to them as casts (ie. the same shape as the original animal). I can't rationalize that. I can see the beads being moulds of the pits (ie. volumetric complements, if you like), or the gaps between them being casts (though not so pit-shaped in that case). I hope I've expressed my thoughts well enough!

       

      Do you think the prismatic layer is also a cast?

      If so, it seems unlikely the internal structure would be preserved (unless it is the edge of a shell that was broken before being cast).

      If not, it seems suprising that the shell is not a cast while the string-of-beads is a cast (I know some bivalves are composed of both calcite and aragonite, but in that sort of arrangement??)

       

      Lastly, in some string-of-beads specimens we see, the string-of-beads loops around and crosses over itself (example). Presumably such instances have a different explanation?

      Note that in many cases, the string-of-beads is rather isolated in the sediment (on the scale of centimetres, at least); ie. they are not found as part of a larger fossil. The first photo in this thread is an example of that. Also, this type of string-of-beads often seems to occur on the (curved) surfaces of pebbles - hinting at a modern origin, such as seaweed holdfast solution sockets.

       

      Any comments gratefully received!

       

      Mike

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