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696 Views 4 Replies Last post: Jun 2, 2013 10:11 AM by Thanasis RSS
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Jun 1, 2013 9:57 PM

Are these ammonites?

Hello to everyone!

I am new here and i have a question,which i hope is not silly!

 

Near my house on the West Coast of Greece,i was walking by a beach with an almost vertical clif of 5-6 metres.

As you can see in the photo,there is a lot of red ground until the layers beggin.

These layers have a lot of shell fossils of many kinds.

Then at the bottom,there is a grey-dark blue layer of thick mud,which gradually is rising the last years,was not so visible before.

So as i searched digging on that mud,i found these three 'ammonites' or kind of ammonites. I want your help for that.

The thing for me is that,since the 'ammonites' were burried in the mud,they have been preserved and they are not fossils.

I saw also other kind of sea shells and small part of woods etc.

I know i am not an expert,but i am not a completely begginer either.If the multiple layers above the grey mud,contain fossils of shells,corals,etc, then the mud layer should be really older!

 

So my question is:  a)Are these ammonites? 

                             b)Could it be possible to find non fossil ammonite or whatever it is from that old geological period?

                             c)Are there findings of non fossil ammonites?

 

Thank you in advance and i hope you help me!

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  • Currently Being Moderated
    Jun 1, 2013 10:33 PM (in response to Thanasis)
    Re: Are these ammonites?

    Thanasis,

     

    These are gastropods not ammonites.

     

    Ammonites died out during the Cretaceous–Paleogene extinction event.

    Modern Nautilus look superficially like ammonites, but actually, ammonites' closest relations are octopuses, squid, and cuttlefish.

     

    You are correct in thinking that deeper layers (strata) are usually older.

    See the geological law of superposition.

    But you should be aware that there are numerous exceptions. When rocks become involved in mountain building, the folding that occurs can result in the original sedimentary layering being turned upside down. Also, but much more rarely, an inversion of primary layering can occur around meteorite impact craters.

     

    The layers in your cliff seem to be relatively modern (from tens of thousands of years to a few million years). That may or may not be long enough for fossilization to occur; it all depends on the history of the sediments in terms of burial conditions. There are sediments in Cyprus, where I live, that are five million years old but only slightly lithified - they are not very different from when they were deposited. Some of them contain fossils, but they, too, tend to be rather fragile (poorly cemented).

    it seems your specimens are very early in their burial history, and have undergone little by way of chemical change (including one retaining its blue colour) - meaning they are barely fossilized or not fossilized at all.

     

    Mike

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      • Currently Being Moderated
        Jun 2, 2013 8:47 AM (in response to Thanasis)
        Re: Are these ammonites?

        Let me add another question, so we have:

        Q1. How old are the youngest fossils?

        Q2. How old are the oldest non-fossils?

         

        Before answering those questions, we have to ask when does a biological specimen become a fossil?

        In theory, the answer is when none of the original material remains - when it has all been replaced by other minerals, ie. when it is totally rock.

         

        That's all very well, but the process of fossilization can take a long time - thousands to hundreds of thousands of years. It is all about stability and entropy. Things commonly form in one environment and there they are stable. In the case of living organisms, it is a metastability - maintained only by life processes. As soon as an organism dies, that stability is lost and it starts to change. The biological decay of soft tissue is a complicating factor, and since soft tissue is rarely fossilized, we can focus on the hard tissue - the bones, teeth, scales, exoskeleton/shells, etc. As bones become buried in soil or sediment, they find themselves in a different chemical and physical environment, which makes their chemical and physical make-up prone to change - to change towards something different that is stable in the new environment. For the bones that survive scavenging and erosion and other destructive processes, gradually increasing depths of burial (affecting pressure and heat) and changes in ground water chemistry, cause the original calcium phosphate in bones and calcium carbonate in shells (eg.) to change chemical and perhaps physical form (eg. aragonite may change to calcite). The various types of biological specimen may alter in different ways, for instance wood may become fossilized under different conditions, which result in its tissue being replaced by silica. When talking about such replacement, it may be almost molecule-by-molecule, or it may entail dissolution of the original then filling of the cavity by new mineral. Eventually, there is nothing left of the original specimen: it has become a fossil.

         

        How quickly/slowly that happens depends on many factors. (And it may not happen at all - there is a thing called preservation potential. Many potential fossils never become fossils because they are too delicate, too prone to being eaten, or because they occur in environments not conducive to fossilization.)

         

        So, if a specimen is not a fossil until all the original material is gone, what is it?

        It is a subfossil.

         

        Let's re-state the questions:

        Q1. How old are the youngest fossils? (this excludes subfossils)

        Q2. How old are the oldest non-fossils? (this includes subfossils)


         

        A1.

        "The youngest fossils are about 10,000 years old"

        http://www.thescienceforum.com/biology/9307-questions-fossils-ive-always-wondered-about.html

        But this is at least partly a convention (a conveniently round-numbered age) rather than a reflection of the age of particular specimens.

         

        A2.

        There are various related answers one can find on the internet, eg. "The oldest subfossil to yield DNA is between 100,000 and 30,000 years"

        http://www.councilforresponsiblegenetics.org/genewatch/GeneWatchPage.aspx?pageId=222

        But since this question includes consideration of specimens that have only just begun to fossilize, the answer has to be very vague though much smaller - perhaps hundreds of years.

         


        One last complicating factor (for now at any rate):

        Fossils include trace fossils - fossils of marks made by living organisms. Dinosaur footprints are an obvious example, but there are actually many types of trace fossil, made by such animals as sea urchins, trilobites, and bivalves. Because these contain no essential biological material (there may be some incidental biological material such as faeces), they merely require the sediment to become rock in order for them to be considered fossils. That can happen more quickly - simple cementation of sediment grains can happen in a few years.

         

         

        Mike

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