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1281 Views 13 Replies Last post: Mar 23, 2014 10:18 PM by MikeHardman RSS
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Mar 11, 2014 10:58 PM

Unknown fossilised impressions.....

Hi folks

I have this rock in the loft, I think it was found a good 20 years ago and it has what we thought might be small insect like footprint impressions on it, there are a few scattered about. Any ideas what they could be?

Cheers

Pies

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    Mar 12, 2014 9:28 AM (in response to Pies)
    Re: Unknown fossilised impressions.....

    Curious...

     

    I cannot tell what type of rock it is from the photo, but it looks like the surface shown is not a bedding plane (in a sedimentary rock). Therefore, the fact that the holes occur as triplets suggests either:

    - deepish parallel holes, made through thr rock, either modern, or ancient (representing a fossil)

    - shallow holes not parallel, made on that (recent) surface

     

    In neither case, do I recognize it.

    My gut reaction is that it is modern. There are many little gastropods and bivalves that bore holes into rocks, but none that make triplet holes, AFAIK. Some seaweeds' holdfasts dissolve rock to make pockets to help with anchoring, but I don't think it is that either. I await for a marine biologist to enlighten me/us.

     

    The other marks have me baffled, too, though I can see hints of fossil in them.

     

    Meanwhile...

    Did you find the rock on a beach, a riverside, or away from water?

     

    Mike

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      Mar 12, 2014 8:59 PM (in response to MikeHardman)
      Re: Unknown fossilised impressions.....

      Hello Pies

      Nice interesting find.

       

      Tabfish

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        Mar 15, 2014 12:32 PM (in response to Pies)
        Re: Unknown fossilised impressions.....

        Being from a beach, bivalves, gastropods, polychaete worms and seaweed would be around.

        ...Which is marginally helpful, but doesn't actually get us closer to an explanation.

         

        I guess I am leaning towards polychaete worms, which sometimes give rise to paired holes. But the triplet-holes still leave me scratching my head.

         

        I have asked Jessica Winder for her opinion

        http://natureinfocus.wordpress.com/2011/04/12/pebbles-with-holes-made-by-tube-worms/#comment-8124

         

        Mike

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        Mar 16, 2014 2:57 PM (in response to Pies)
        Re: Unknown fossilised impressions.....

        I asked Jessica Winder to look at this (Jessica's Nature Blog).

         

        Please see her reply

        - http://natureinfocus.wordpress.com/2011/04/12/pebbles-with-holes-made-by-tube-worms/#comment-8129

         

        Note especially her:

        - request for a higher-resolution photo

        - "My best suggestion at the moment is to contact NERC’s British Geological Survey which compiled the reports on the fossils from the Falklands (downloadable as pdf files on-line). BGS also holds house collections of Falklands fossils and rocks."

         

        Mike

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          Mar 16, 2014 9:18 PM (in response to MikeHardman)
          Re: Unknown fossilised impressions.....

          I tend to agree with these being impressions, but more likely to be of plant remains  than insect footprints. I found the nora.nerc.ac pdf by googling "Lafona formation", & it mention several episodes of sandstone & mudstone,& eg of the 2nd Bluff Cove Formation said "the presence of rare plant traces shows the nearby land mass was vegetated". Also after the bibliography a geological map of the falklands & 14 photos preceded by captions, which give some idea of the rock

          (the pdf is http://nora.nerc.ac.uk/10862/1/DepositsArticle-FI.pdf ) (which is different from yours mike)

           

          Message was edited by: rhossilian

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            Mar 16, 2014 8:35 PM (in response to rhossilian)
            Re: Unknown fossilised impressions.....

            Pies,

            Thanks for those further photos - much better (if still enigmatic).

             

            rhossilian,

            Thanks for looking into this.

            Could I trouble you for a link to the ref you found, please (my Googling seems to be missing it).

             

            Our guesses are the moment:

            - plant fossil (which could include seeds, BTW))

            - trace fossils (there are similarities to Arenicolites (that image is from http://www.cprm.gov.br/geossit/geossitios/ver/181, the photo indicates the marks in pairs), but I have found no references in triplet-holes with arenicolites); Chondrites also has some similarities; but it is only bifurcated; I don't think it has trifurcations, as would be necessary to explain the marks in your specimen)

            - polychaete or similar worms (modern)

            - seweed holdfast marks (modern)

             

            With the trace fossils, bear in mind that we don't know the animals that made the traces; the names relate to the traces themselves.

             

            To pick up on a comment of Jessica's (pondering it there are signs of a 4-fold arrangement, which I can see), one could imagine a vertebrate with three toes and a 'palm'. This photo shows what I have in mind, albeit with a different number of toes - http://en.wikipedia.org/wiki/File:Cheirotherium_prints_possibly_Ticinosuchus.JPG (from http://en.wikipedia.org/wiki/Trace_fossil).

            I don't think that leads us anywhere, however, since vertebrate feet/walking traces should be arranged to form a track, not randomly scattered and differently-oriented individual marks.

             

            Pies,

            While your photos are lit well (obliquely) to show the marks, I can't see into the individual holes/depressions. Please could you tell us what they are like: shallow or deep / gradually tapered or blunt-ended / variable or consistent / etc. Also, from the photos, I get the impression that the individual marks have straight (though not necessarily parallel) sides radiating somewhat from the centre of the triplet. Is that true or just an illusion?

             

            Mike

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              Mar 16, 2014 11:51 PM (in response to MikeHardman)
              Re: Unknown fossilised impressions.....

              Rhossilian - it's OK - I've found the PDFs now - including the bioturbated black mustone .

               

              Oh - that paper included mention of Glossopteris, a tree which had microsporangia in small clusters

              http://www.plantasyhongos.es/gimnospermae/Pteridospermopsida.htm

              I wonder if those were prone to break-up into threes? But low preservtion potential, methinks, even if so.

              ...Clutching at straws, still.

               

              Pies,

              Please can we have a photo of the other side, and the edges.

              Also, to help us get an idea what sort of rock it is:

              - Put a drop of vinegar on it, and tell us if you get any (even a smidge) of fizzing (limestone test)

              - Scratch it with a glass bottle: which gets scratched: the glass or the rock? Ditto a knife.

               

              Jessica has added some thoughts on her blog.

               

              Mike

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                Mar 21, 2014 7:33 AM (in response to MikeHardman)
                Re: Unknown fossilised impressions.....

                I wish my PhD supervisor, Pete Crimes, was still with us; ichnology was his speciality.

                I emailed another of his students, Liam Herringshaw (Durham), also into ichnology, to see if he can shed any light. Liam doesn't know, but he suggested asking on the Ichnology group on Facebook, which I have done - https://www.facebook.com/groups/415851935172452/

                 

                We are also awaiting answers to the questions I recently put to the original poster, most importantly whether the marks are just on this side, or all round.

                Hello Pies...

                 

                Mike

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                      Mar 23, 2014 10:18 PM (in response to Pies)
                      Re: Unknown fossilised impressions.....

                      Pies,

                       

                      Thanks for the further info.

                       

                      I see the rock is a finely laminated siltstone, possibly micaceous, judging by the bright flecks.

                      As you say, the marks in question do not appear as such on the underside or the edges. Because the underside is not as weathered as the top, any bioturbation has not been picked-out there (though there are vague signs of small vertical burrows). So unfortunately this tells us little definitively. That is: if the marks had been present on the sides or base, I would have been confident they are modern; their absence there is ambiguous.

                       

                      I think the relative softness suggests weak cementation rather than being limestone; limestone is also counter-indicated by the lack of fizzing.

                       

                      Micaceous siltstones certainly can be good rocks for finding trace fossils.

                       

                      This is definitely still a mystery.

                       

                      There have been a couple of comments on the Facebook page (link earlier), but no answer as such yet.

                       

                       

                      Mike

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