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1572 Views 8 Replies Last post: Aug 23, 2013 6:11 AM by MikeHardman RSS
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Aug 20, 2013 9:59 PM

Dino Dung????

Can anybody identify these large rocks? I found them when digging out a deep soakaway in my garden, about 2.5m deep! My garden being in Faringdon Oxfordshire! The largest measures about 520mm x 420mm and weigh roughly 25kgs, probably more! Would really appreciate an opinion on these! Thanks Steven

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    Aug 21, 2013 7:42 AM (in response to Sdb1)
    Re: Dino Dung????

    Steven,

     

    Intriguing...

    And well done for lugging them up and out.

     

    I need to ask some questions:

     

    Are those three holes indicental, where bits of the cream surface fell off?

    Do they have the same cream cracked surface all over (ie. on the underside, too)?

    Did they all come up intact? It would be very useful to see one in cross section.

    What type of rock/sediment did you dig them out of (eg. clay)?

    Did you see any fossils in it (if so, what?; photos?)?

    Whereabouts in Oxfordshire (town will do)?

     

    Mike

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        Aug 22, 2013 12:23 AM (in response to Sdb1)
        Re: Dino Dung????

        Thanks Steven.

         

        So they ar from the Jurassic, and probably the Oxford clay.

         

        I think thay are septarian nodules (a type of concretion), but I'd want to see a cut and polished cross section (or at least cut and wetted) to be sure of that - to see the internal structure properly. I make that ID based on your photos, but also bearing in mind that some old works mention lenticular beds of septaria in the area (a fair match for your specimens), and some more recent research includes concretions, eg.

        - Hudson, J.D. (1978) 'Concretions, isotopes, and the diagenetic history of the Oxford Clay (Jurassic) of central England'. Sedimentology, 25, 339–370.

        - Hudson, J.D., Coleman, M.L., Barreiro, B.A. and Hollingworth, N.T.J. (2001) 'Septarian concretions from the Oxford Clay (Jurassic, England, UK): involvement of original marine and multiple external pore fluids'. Sedimentology, 48, 507–531

        and

        - Hendry, J.P., Pearson, M.J., Pearson N.H., Trewin, N.H., Fallick, A.E. (2006) 'Jurassic septarian concretions from NW Scotland record interdependent bacterial, physical and chemical processes of marine mudrock diagenesis'. Sedimentology, 53, 537–565

        which is available here

        -http://funnel.sfsu.edu/students/balukasd/Courses/Students/Nick%20Aiello/concretions%20thesis/thesis%20sources/septarian%20concretions.pdf

        and which shows some septarian nodules externally and in cross section (to give you an idea what I would be looking for in a polished cross section of yours).

         

        If you were to cut through one of your specimens with an angle grinder using a stone-cutting disc, then wash and wet the surface, you might see something similar (though not as nicely as if sawn on a riock saw then polished). Obviously that would be at your own risk; do take care.

         

        Locality reference

        - http://www.ocv.org.uk/sites.php?id=68

         

        You can search for 'septarian nodule' in this forum and you'll see they crop up fairly often. Here's a link that'll do it for you -

        http://www.nhm.ac.uk/natureplus/search.jspa?peopleEnabled=true&userID=&containerType=&container=&spotlight=true&q=septarian+nodule

        ...Just one way to learn more about them.

         

        Mike

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            Aug 23, 2013 6:11 AM (in response to Sdb1)
            Re: Dino Dung????

            Steven,

             

            You're welcome.

             

            I understand about not wanting to wreck your nodules.

             

            The easiest person/place would be a local funereal stonemason. They are used to dealing with reasonablly-sized pieces of rocks (you might have an architectural stonemason nearby but they'd be less amenable to helping you out because of how they're geared-up to work). If you're lucky you might have another option - a local university earth science department/faculty, where (if you ask nicely) you might be able to find somebody to do it for you.

             

            Think about not just cutting and polishing it to see the inside; think about not so much losing a nodule as gaining a pair of bookends or doorstops...

            That is, design your cuts so:

            - you get two peices that match (roughly speaking)

            - you can use them somewhere they get displayed (if making doorstops, put self-adhesive clear plastic 'bumpers' on the door-facing faces to protect the doors; bumpers like you'd use on cupboard doors) (if making bookends, don't make them too easy to topple)

            And aim to keep some of the offcuts (might warrant polishing also) as more-conveniently-sized specimens.

            Having designed your cuts, you may find the stonemason has difficulty doing them (because of how the rock needs to be clamped during cutting), so you may have to make some modifications.

            Also, since we don't know how strong the rock is, be prepared for some breakage, and give the stonemason guidance on what to do if breakage occurs (eg. "call me!").

             

            Keep us posted!

            If you do manage to get it cut and polished (or even cut and varnished), we'd like to see it. We really don't know if it will prove to be boring or spectacular.

             

            Mike

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