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Fossil In/ Under Flint - Plant Matter?


mango5

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Hi Everyone, I found this fossil a couple of years back, and it's unlike any other fossil I've found. I was just walking down an unmade road through woodland, and this flint was part of the rubble that had been used to build up the surface, and so it was not originally from that area. It is 7.5cm long and almost 5cm wide. At first I thought the striations had been created where the flint had broken unusually, and picked it up for that reason. On closer inspection, however, it became clear that the striations were the fine impressions left by a shell (at points there is cracking in the shell where the striations mis-align). It also seems likely that the flecks of material in raised relief are fragments of shell that remained in situ. On the surface of the shell are two features indicative of other life forms there at the time of fossilisation - the first is some species of sea worm similar to those found today, which leaves a chalky tunnel in it's wake on the surface of the shell and then creates a coiling caste in which it lives. The second is more of a mystery - there is a small area of tessellating scale-like shapes that just seems to fade/blur at the peripheries rather than forming a distinct shape. At first this reminded me of reptilian or fish scales, but if either had been pressed to the shell in a fossilisation event they would be clearly outlined. Therefore, is this some kind of seaweed or film of plant cells/fluid filled bladders?

I would be interested in any insight into the latter, and verification of what I believe I know as described. Also as I have little experience of flint fossils, are they rare or common?

Thanks and Best wishes, Andrew

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Edited by mango5
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Looks more like some kind of encrusting lace like bryozoan or coral, ... that may have been attached to the shell.

That is more likely than some kind of plant.

Regards,

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I see the radiating ornamentation of an incomplete mollusk like Inoceramus with a couple of radial worm epibionts, bryozoan and some borings by gastrochaenids?

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Thank you both of you for your insights - it had not occurred to me that it could be wood - I suppose I associate flint with marine environments and the coasts of Kent. I looked up toredo bored wood, and was interested to read that marine worms bored into wood where woodland met water, and coral/ bryozoa as the tessellating section makes perfect sense.

Thanks again, best wishes, Andrew

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Hi Plax - so you think this is the pattern created by the liquid volcanic rock going over Inoceramus, a large clam - that was my thinking originally (a shell), and I thought the irregular fragments, many of which line seeming cracks, were remnants of actual shell. Looking at both Inceramus and bored wood comparisons, both seem possible. Looking very closely at the striations they do seem to 'step up' (from left to right as per the big picture) rather than being on a level with each other, though the increments are minute.

Edited by mango5
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I don't see volcanaic rock, what you originally saw and described was (in my opinion) a mollusk shell. Picture a modern thin shelled clam with all the little critters attached to its shell. Your flint shell is just a broken piece of a fairly round shell. Keep in mind that whatever information you receive on the forum is the opinion of the person answering your inquiry. If someone sees something they are familiar with they will opine in that direction.

One of your small encrustors looks like the modern (and ancient) spiral shelled worm spirorbis.

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Hi Plax, thanks for your replies - I've been trying to upload more photos taken in a natural light, but the uploader keeps freezing - I'm not sure if I'm allowed to add more photos to the original ones. The white dots across the surface of the fossil are all raised relief rather than depressions/holes, though this is not clear from the original photos - the photos I just took in natural light without flash show this nicely as well as the step-ups of the striations. The side of the fossil is solid yellow/orange flint with no features, and I'm pretty sure this is an inverse fossil or a fossil impression (I'm not sure if there's a proper word for that!). The new photos I'm trying to upload also reveal what looks like cracking more clearly - in the case of a clam being covered by molten flint (that's what I meant when I said volcanic rock) the heat might well crack the shell I suppose. The shape of the surface is also gently curving as a shell would - like the inside of a plate/dish. I'm thinking the white flecks may well be part of the actual shell that left the fossil impression. Is it straightforward to add more photos - the uploaded said 2mb, or is the total 2mb for the whole thread? It may be my internet's just being a bit slow!

Edited by mango5
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can't help with the upload problem, flint doesn't form volcanically, it forms within limestone or chalk, googling "flint" will probably give you better information than I can get from my head, guess my guess of boring sponge wasn't good if the white dots are positive, although some of the shell may have been leached leaving them in relief

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I just want to tidy up a few loose ends on this thread...

“Flint consists of extremely small crystals of quartz (silica) tightly packed together. In the flint of the Chalk the silica has come sponges. The familiar bath sponge is the skeleton of a sponge with a flexible protein skeleton containing no mineral matter. However, many sponges have skeletons made of tiny silica rods called spicules. Such sponges were very common in the chalk sea and their skeletons were preserved in the Chalk. This was subsequently buried under later deposits, together with some of the water contained in it, and the conditions of higher pressure and temperature which accompanied this burial the water dissolved many of the spicules. Flint nodules were formed subsequently by the redeposition of this silica, generally replacing some of the calcium carbonate which forms the Chalk. The silica that forms chert may have come from sponge spicules but also from other organisms with siliceous parts such as single-celled diatoms or Radiolaria.”

- Source: Chert - NHM London

More info can be found on this PDF: (None, not the same document the above information was quoted)

Chert and Flint Fossils.pdf

The semi-circular lines on your specimen are the ridges of an Inoceramus shell - not rings from a tree or formed in a volcanic way. On the Inoceramus shell are some worm tubes, potentially Rotularia which has attached itself to the bivalve. The “honeycomb” structure is a bryozoan. I think the “positive” white lumps on the specimen are what is left of the calcite shell - if you look closely you should be able to see faint lines running perpendicular to the rest of the flint specimen.

It has a nice colour, not the typical blacky-grey fresh flint so I think that it has been exposed for some time, weathered and stained a bit by elements in the soil to which it was deposited - most likely before or around the last Ice Age.

You can upload up to 2MB of files per post (not per topic); you may wish to re-size your photos if they are too large. I think I can recall some problems with particular internet browsers.

All the best,

Thomas

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Thanks Plax and Thomas - I had always though flint was volcanic, so that information helps me understand the formation of the fossil - I had previously thought it was a rapid event.

Thank you for your analysis Thomas - I have studied the white flecks closely and only one has a faint line on it, and that's at about 75 degrees to the lines on the flint. I think that possibly as the shell is of a less durable material than the flint is has worn on exposure losing some detail. Thanks also for the attached document - It was Dover flint nodules and their fluid appearance as though a liquid had filled a chalk cavity, that led to my mistaken belief that flint had been volcanic or in liquid form to do so.

The 4 photos I have uploaded so far come to less than 1mb together - I've sized down the two I want to add to 400kb each, so I'll try and upload them again,

Best wishes, Andrew

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This photo shows a cross section of an Inoceramus fragment in flint. Having been exposed on the beach and suffering from erosion the majority of the fracture lines have been worn down but the red lines show where they can be just about seen in good light.

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I would recommend the publication "Fossils of the Chalk" by The Palaeontological Association which has a section dedicated to flint.

All the best,

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Thanks Thomas - the picture you have posted is very interesting - I'm sure I've seen white almost rectangular lines embedded in flint before but I never realised they were fossils - I'll have to have a look for some next time I'm at the beach.

Best wishes, Andrew

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I agree with Thomas.

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