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Anon88

85EE8F17-3188-4BB1-AEC7-E68C1CBB1798.jpeg  C71EA6FE-71D1-42AF-80A7-018404474276.jpeg  E6B58EF7-300E-4DCC-A476-96F2E7202FBA.jpeg  9CA9BA95-8C7F-43CF-BA4C-827E3DCB83CF.jpeg  Hi all,

I’m working on construction sites and one of the site lads handed this in to me from one of the trenches. Just thought to share it as I really appreciate this one.


He knows I look out for fossils, he insisted I take it (I gave him a bottle of wine and lots of thanks) 

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hoodie07
Really nice one!
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Barrow Museum
This septarian concretion has enclosed at least two ammonites.  The evidence of their identity is:
The larger one (fragment) appears to have falciform ribs (sickle-shaped) and a compressed whorl cross-section (can I see a keel?)  which suggests Toarcian or Aalenian/Bajocian stages of the Lower to Middle Jurassic.
The one next to it (impression of the centre) may be the same species as again, it looks as if the sickle-shaped ribs are present.
Grafham Water is in the middle of Oxford Clay country, but there is a thick plaster of glacial till on top and I am fairly sure that your specimen is from this upper, superficial geology layer.  As with some of your other finds, the glacially transported material from the north and northeast is the likely culprit.
So, as we cannot necessarily use the local geology as a clue, I'd suggest that your ammonite lived in the late Early Jurassic sea in which the Whitby Mudstone Formation ("Upper Lias") was being deposited and in which septarian concretions are the norm.  Unlike the Yorkshire coast preservation, to the south I have seen that attractive iridescent shell preservation on ammonites from the same age strata in Lincolnshire, (strata which extend out into the North Sea) which is the most likely origin of your specimen in my opinion.  Putting a name to this without handling the piece is tentative, but Harpoceras would be close.
Definitely worth searching for more.
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Anon88

Thanks for the response, really interesting. We were excavating a trench for drainage which is where this was found (3m - 5m depth) and the soil investigation showed that we were in a deep section of glacial till (at least 8m thick) as you alluded.

I didn’t spot the second one, so that’s a nice surprise!
image.jpg 
I have also been given another ammonite imprint from the security guard for the site! This one is soon the be ‘found’ by my niece.
image.jpg 
Thanks for taking the time to respond with the info, it’s really appreciated!

 

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Barrow Museum
I think I am going to have to swallow my words.  In the second photo, just added, I can see clearer what you have and I would now call this Amoeboceras ?serratum, from the Ampthill Clay (Oxfordian).  Just shows how difficult identification can be from photos sometimes.  The serrated keel is the distinguishing feature but the forward curve on the bifurcating ribs is a bit more accentuated than I would expect.  The type specimen of this species was actually from the Pleistocene till and they turn up regularly in the east Midlands.

The second imprint is again from a photo difficult, but I reckon it might be Arnioceras and the smooth inner whorls would make it A. semicostatum, from the "Lower Lias".  Without a complete whorl, the characteristic cross section is not visible.

Attached is a photo of a juvenile and adult Amoeboceras in my collection, both derived from the Ampthill Clay but found in the glacial till. Amoeboceras.jpg 
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nomadiclifeguide
and that everyone is a perfect example of how to baffle a newbie.
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Anonymous

Lol Definitely 🙂 

I had to google what the terms keel and whorl was after the first response... So I can say I’ve a long way to go to be able to understand what just happened. 

To be fair, the photos I posted were rubbish.

Thanks as always Barrow museum for the ongoing education. Any book suggestions will be welcome.

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Dirty Pete
Keep it coming BM or I might give up and take up stamp collecting.........apologies to any philatelists out there...

Pete.
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