A Nice Gault Clay Ammonite

Phil

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Thank you Neale for another fascinating post. I'll have to reexamine my heteromorph fragments and see if I have any items of interest to post here.

Thanks pocketmoon!

Here's a picture or two of the beach. Can you see yourself? Was the factsheet useful?
 

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I have a question about the Hoplitidae, or at least the Hoplitinae.

Is there any sign of sexual dimorphism or polymorphism? I have not had a real good look, but they all seem to have the same basic sculpture, just different amounts of sculpture strength and conch compression. Are the different shapes found at different horizons, or beds, is the difference biostratigraphical? Has this something to do with Lumpers and Splitters?

An example, and I am not saying it is right, is the Early Triassic ammonoid Anasibirites. It was divided into two or three different genera with about 35 different species based on different amounts of sculpture strength and conch compression. Then they were all put in synonomy with one nominal specie. These were not all from a single bed, but they were from a single horizon.

Just wondering if the same thing could or should or should not be done with the Hoplitids :?:
 

Phil

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Kevin,

I'm really sorry but I do not have any literature specific enough to answer those questions, unfortunately. You might find this short extract of some interest as an overview of Gault Ammonoidea:

Introduction to the Gault Ammonoidea.

One I can answer is, yes, the Gault is divided into sub-zones based on specific ammonite species. The zonation system, mostly via Hoplitid ammonites, is viewable at the links at the bottom of the page:

Gault Stratigraphy.
 

Phil

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Re: the large ammonite in the clay bed that started this thread, Robert has now cleaned up the specimen and identified it as Hoplites spathi. This places it in the lowest bed, i.e Bed I of the Middle Albian Gault which is dominated by Hoplites dentatus, such as the example pictured at the top of this thread.

Here are a couple more pictures of the ammonite in situ and cleaned up shots including a close up where one can see crystals on the surface of the ammonite (thanks, Robert):
 

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Thanks Phil, that answered alot. It shows how collecting fossils from deposits of differing sedimentation rates can skew your perception of things. In your outcrop you have several biozones in a 100 meter thick outcrop, some places over here I have collected fossils from one sub-zone in about the same thickness.

That is a very nice fossil, Robert should be very happy with it. What kind of crystals are they, and will they be left on the fossil or cleaned off?

and :welcome: to Pocketmoon
 

pocketmoon

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Architeuthoceras said:
and :welcome: to Pocketmoon
Chears :D


A quick Q, many of the fragments from Folkestone have this wonderful pink patina. What's the best way to protect this ?
 

Phil

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Kevin,

Architeuthoceras said:
What kind of crystals are they, and will they be left on the fossil or cleaned off?
Robert has just informed me that the crystals are calcite and the ammonite appears to be (famous last words) fairly stable. I'd imagine they will be left on.

pocketmoon said:
A quick Q, many of the fragments from Folkestone have this wonderful pink patina. What's the best way to protect this ?
The patina is the original mother-of-pearl coating and you can still find it on some of the ammonites and bivalves. What I tend to do is soak the fossils in water for a few days to remove the salts, leave them to fully dry and then coat them in a thin layer of varnish (I tend to use Satin Humbrol modelling varnish). Maybe this is not the best approach but has certainly worked for me, though if anyone has a better method I'd like to hear from you.

The fossils preserved in the black phosphate will be OK to be left untreated, but any preserved in pyrites will decay to a form of 'rocky fluff' within a couple of years. I've learned this to my cost!

Thanks,

Phil
 

pocketmoon

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Phil said:
The fossils preserved in the black phosphate will be OK to be left untreated
Would this be black phosphate (propped against a coaster) ?



I'm using 1 part PVA to 4 parts water for the others so I'll keep a close eye on them over the coming months.
 

Phil

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Yep, thats the stuff Pocketmoon. I've heard other people use mixtures of PVA and water before. If it works, please let me know and I'll try it myself.

By the way, if any readers were wondering what that strange-upturned pot drum-shaped building is in the photo Pocketmoon posted above is, it's a Martello Tower. This is just one of a chain of 75 or so towers that were erected all along the SE coast of Britain during the Napoleonic Wars, I think about 1810ish. They had a canon located on a pivot on top to watch over the coast and a small detachment of soldiers stationed inside. As you can see the entrance is high up in the wall and would have been accessed with a rope ladder, this made it easier to defend should the French army come knocking!
 

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hi guys only me, sorry I'm late & nice finds BTW.
3rd photo shows how quickly Gault fossils shrink in the wind !! :D

Poor Rob, another lamb to the slaughter & welcome & if you want a good book on your new obsession try Ammonites by Neal Monks :notworth: jsut finished reading my copy - top read !

Moi
 

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