BREAKING NEWS: Giant ammonite discovery

Phil

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Just found this out from the BBC television text pages. So far there seem to be no web pages, but I will post details as I can find them.

Rare Fossil Discovered in Coastal Cliff

"A Margate archaeologist has found a fossil measuring 1.5 meters in a cliff face in Thanet-the intact ammonite is 80 million years old.

Dr Alastair Bruce says the council and English Nature will now dictate whether to move it or leave it in position.

He says he knows of only three other ammonites which are intact. [....er, not sure about this bit]

He added
Parapuzosia leptophyla could be left where it is as an educational resource, but could then be at risk of erosion during the winter'

Margate is about 12 miles from me so if I can I will try and arrange a trip up and photograph it for the site, it's practically on my doorstep after all. If anyone is interested, there is a small photo of Parapuzosia here at the pages of the Bournemouth Natural Science Society
 

Tintenfisch

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...And now over to Phil, our man in the field, arriving at the death scene a mere 80 million years after the incident... Phil, is is possible to speculate within such a short time-frame on the circumstances and significance of this event? ;)

:ammonite:
 

Clem

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Tintenfisch said:
Phil, is is possible to speculate within such a short time-frame on the circumstances and significance of this event? ;)
Global warming. Definitely global warming.
 

Phil

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Tintenfisch said:
.Phil, is is possible to speculate within such a short time-frame on the circumstances and significance of this event? :
Very difficult at the moment as depite exhausting trawls through the net, there is nothing to be seen yet. Luckily BBC 1 and ITV (two of our amazing total of five channels) both covered it in their regional news bulletins this evening. Unfortunately I missed both as I was at work at the time. Typical.

However, luckily a good friend of mine taped both for me and hopefully I should borrow the tapes off her. If all else fails I will try and get a few photos off the screen using the digi-camera, it might work. I'll let you know.

Southern UK was a shallow sea 80million years ago in the Late Cretaceous with Wales and Scotland forming two gigantic islands with the whole plate heading northwards. I believe that the UK was situated at a similar latitude to southern Italy/North Africa at the time (have to confirm this....) so would have had a warm oceanic Mediterranean climate. I think that examples of Parapuzosia are known from Hampshire, a couple of hundred miles to thewest of Margate, and from Germany. Therefore I imagine that this ammonite was probably not uncommon in European seas at that time.

However, I'm speculating too much here and am not 100% sure of my facts, so I'll report back after I have seen the broadcast.
 

Phil

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It transpires that this rare example of Parapuzosia leptophyla is, perhaps fortunately, somewhat inaccessible. According to Dr Alasdair Bruce, who runs geological tours of the Thanet coast for the public, this is only the third intact ammonite to be discovered in the chalk at Thanet, the other two are in Maidstone museum. English Nature are currently debating as to whether the fossil should be left to be seen by the public in situ for the time being, or whether it should be excavated to protect it from the elements. As can be seen from the photos below, only a third or so of the ammonite is actually protruding from the cliff face, with the bulk of the animal remaining buried, if it is truly intact. The trouble is, the Kent coast is regularly battered by storms in the winter and it is only a matter of time before the cliff collapses. As can be seen, the ammonite is high up in the cliff which will make excavation difficult, but on the other hand, will protect it from fossil hunters.

It is estimated that the chalk was laid down at a depth of 300ft or so 80million years or so. It is probably unwise to assume that Parapuzosia may have lived at that depth as the shell could have had drifted down to the sea-bed following the creatures' death in the upper waters. Having said that, it seems obvious that this animal was clearly robustly built, and should have had no difficulties coping with those pressures. (This is roughly the depth that the modern Nautilus tends to inhabit during the day).

Here are a few photos of the ammonite in the cliff face. I apologise for the poor quality of the photographs, these had to taken directly from the television using the digital camera, hence the interference lines. (Thanks for taping this, Mandy!). Still I think they do give an impression of the size and setting of this discovery.

If anyone is wondering where Margate and Thanet are, think of the SE corner of England, the closest point to France. Margate is fifteen miles or so to the north of Dover and the cliffs there are pretty much the same geological formation as the much-more famous White Cliffs of Dover though are somewhat less impressive.


 

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Phil

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Dr Bruce has kindly donated a much clearer photograph of the specimen for posting on this site; anyone reading this, please don’t steal it!

It seems that Parapuzosia leptophyla is not as rare as it has been reported in the press, though what is rare is that it still lies in context and has not been eroded out of the cliff. It is important to examine specimens in context if possible as the surrounding rock can contain data about the seabed life in association with the ammonite. For example, Dr Bruce has informed me that it is thought that the Upper Chalk was deposited at a rate of 25mm per 1000 years. With an ammonite of this size lying on the sea bed exposed for so many years it would have formed an important part of the Cretaceous reef community for, in all probability, centuries. The specimen can be examined for traces of other organisms that would have attached themselves to it after death. Normally this form of surface detail would be worn off the surface of the specimen if it is exposed to the elements, which is why it is important to try and collect this specimen before too much is exposed.

As an example of this, I have attached a photo of a fossil sea urchin (Echinocorys?) that I found last year at the chalk cliffs at Dover which are practically the same date as those containing the ammonite at Margate a few miles to the north. Interestingly, there appears to be a tube worm (serpulid?) attached that would have grown on the shell of the animal following its death. One may well expect to see similar attachments on the upper surface of this ammonite when it is, hopefully, recovered.


 

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Phil

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A Question for Dr Monks,

Neale,

This is more about the process of fossilisation than the animal itself.

In my ignorance there is one particular aspect of this fossil I cannot quite understand. When the ammonite died and had sunk to the sea-bed then obviously it would have begun to decay. If the chalk surrounding the ammonite had built up at a rate of just 25mm per 1000 years then the ammonite would have been exposed to the elements for something approximating to 10,000 years or more as the silt built up around it. This clearly could not be the case. If the shell had formed part of a reef system then surely animals attached to the upper surface of the shell would have hastened the decay.

How quickly do you think the shell could have mineralised in such a context, and why would such an animal not decay quickly? Do you think the animal could have been buried quickly in a shallow mud/silt slide?

Thanks!

Phil
 

Clem

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Phil,

What kind of aquatic environments are associated with chalk deposition? Also, are soft-body fossils ever found in chalk deposits?

Clem
 

Phil

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Clem,

That’s quite an interesting question. I’ve often wondered the same thing as I have a stunning view of the White Cliffs of Dover every day! After investigating I’ve found the answer is much more complicated than I had thought. It’s basically down to a change in the chemical composition of the seas at that time.

As I’m sure you know, chalk is composed of the skeletons of microscopic marine creatures. If you scrape a thin slice of chalk or reduce it to a powder, apparently these nanoplankton can be seen quite easily under the microscope. The origin of the chalk cliffs deposited in the Cretaceous is the mystery, something must have happened to the seas for the nanoplankton population to have suddenly exploded. A recent theory proposed by Lawrence Hardie suggests that there may have been higher levels of calcium in the waters at that time, thus fuelling the nanoplankton. This calcium is believed to have originated from hot brine springs, with calcium-rich seawater being pumped out having been transported from the mid ocean ridges.

At the mid-ocean ridges where the continental plates are being born and pushed apart, water from the sea-floor seeps into cracks in the earths crust, via convection cells generated from the heat of the lava. En route to the hot brine springs, magnesium and sulfates tend to be removed and calcium and potassium added. It seems likely that in the Cretaceous there must have been a change in the rate of seafloor spread with a consequent change in the number of these underwater brine springs. For whatever reason the amount of calcium-rich seawater erupting from the springs pumped much higher levels of calcium into the sea thus causing the nanoplankton to explode in population size. With the deaths of these tiny creatures, the seafloor was formed, and the lovely view across the English Channel.

In a manner of speaking chalk deposits could be viewed as shrimp dung! The nanobacteria, i.e coccoliths, were eaten by copepods. The indigestible skeletons of these creatures was passed through the digestive system and deposited as excreta, sinking to the sea floor. Not a very romantic image!

I don’t think that the chalk is particularly good at preserving soft-bodied fossils. Sea-urchins are very common (I have a few crushed examples of Micraster I can post if you like), and in Europe the chalk contains some of the very last belemnites. I have an ammonite preserved in chalk too; I’ll post a picture of it here tomorrow, though I’m afraid it is nothing special.

There is an interesting article here explaining this process in more detail:

http://unisci.com/stories/20014/1210012.htm

I'll see if I can find out some information on the aquatic environment itself tomorrow.

As a side-note, did you know ‘Cretaceous’ is Latin for Chalk? !!!!
'Cretaceously'...'in a chalky manner'.
 

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