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512 Views 6 Replies Last post: Mar 27, 2014 10:26 PM by MikeHardman RSS
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Mar 27, 2014 3:32 PM

What is this.

I took this photograph in Cornwall on rocks uncovered by recent storms. Is it a rock formation or a fossil? Either way its very interesting.

edithh t

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    Mar 27, 2014 4:18 PM (in response to edith t)
    Re: What is this.

    Edith,

     

    Bizarre!

    Never seen anything like it in all my geologizing years!

     

    Could you be exact about the location?...

    If so, I might be able to find some info.

     

    Mike

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        Mar 27, 2014 9:36 PM (in response to edith t)
        Re: What is this.

        Hi

         

        Interesting, my thoughts ,

         

        the right hand side of the picture is lower than the left

         

        Some of the markings are symetrical aligning on a crack, almost contours, it appears to me they represent different water levels and as a consequence evaperated salt deposits

         

        Alternatively the rock is composed of very thin different coloured layers which have been eroded /dissolved by running water,

        how hard is it

         

        Any other suggestions like Mike  I never seen anything like it

         

        Steve

         

        Steve

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        Mar 27, 2014 9:37 PM (in response to edith t)
        Re: What is this.

        Edith,

         

        Thanks.

        So we are in the Mylor Slate Formation (Devonian) - composed of slate and siltstone.

        But those have been subject to hydrothermal metamorphism, which may be a factor in your particular rocks.

        However, the structures appear at least partly sedimentary to me.

         

        I have found nothing in the literature to explain it.

        I think we need some local knowledge.

         

        So may I suggest you contact the Royal Geological Society of Cornwal (200 years old this year)

        - http://en.wikipedia.org/wiki/Royal_Geological_Society_of_Cornwall

        - http://geologycornwall.com/contact

        And please let us know if they give you an explanation!

         

        Mike

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          Mar 27, 2014 9:47 PM (in response to MikeHardman)
          Re: What is this.

          I think this is the right orientationP1050592.JPG

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            Mar 27, 2014 10:26 PM (in response to basquesteve)
            Re: What is this.

            Jessica Winder has posted on her Nature Blog re post-storm newly-exposed rocks nearby at Mewslade Bay on The Gower

            - http://natureinfocus.wordpress.com/tag/gower-geology/

             

            The connection is tenuous, but I thought she'd be interested anyway.

            So I've given her a gentle nudge to look at this discussion to see if she has seen anything like this.

             

            Seeing as the the thought is going through my mind, I might as well share it...

            I could imagine these structures to have been formed by soft-sediment deformation. Some sand/silt volcanoes arise from sand/silt dykes (the effusion tending to change from being dyke-wide to discrete vents upwards). I have seen this in the Namurian on the west coast of County Clare, Ireland. The symmetry of the layering either side of what are now dark lines goes along with an effusive process (on a much smaller scale somewhat like the mirrored magnetic striping in the lavas either side of the mid-atlantic ridge).

            The photos show some other hints that support that idea (rather difficult to explain without pointing an gesticulation).

            There are aspects that I have not seen before: primarily, the mirroring and aspects of the geometry.

            Just to be clear: the processes I am writing about took place before the sediment was lithified, and probably not long after its initial deposition.

             

            Mike

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