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Charmouth Gault echinoid

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Cambrian Rockhound
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    Posted: 02 Jun 2011 at 7:39pm
And I was sure it was chertEmbarrassed - thanks again, Meg.
 
edit - Just checked my 30 year old file card and it says "?Micraster sp., Upper Chalk - drift" so my memory's going too... 

Edited by TqB - 02 Jun 2011 at 7:48pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rab7ies Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2011 at 7:28pm
i should have stuck with what i put first! but got talked outa it..sigh!
down amongst the stones.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote flintband Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2011 at 7:18pm
Targuin,
 
Just done some checking around and found good pictures of Pliotoxaster  on the Echinoid Directory. Click on pictures to enlarge them. Not quite the same species, but similar with good detail on the ambulacra.
On Micraster there is a groove running down the centre of each ambulacrum. There is no groove on Pliotoxaster.
Similar detail on Echinologia, for Pliotoxaster paqueri, another similar species.
 
Good hunting !!!!!!!!!!!!!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote flintband Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2011 at 7:03pm
Oh no it isn't !!!!!!!!!!
 
This one is Micraster coranguinum, from the glacial deposits which slump down and become mixed up with the Greensand material.
 
Pliotoxaster wrighti has much wider and shallower ambulacra and considerably more pore pairs.
 
No coconut this time, please try again !!!!!!!!!!!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rab7ies Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2011 at 1:35pm
hi,yep ive just had a look at pliotoxaster and its pretty much spot on!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TqB Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2011 at 1:30pm
Hi Rab - it does a bit but it's from the Upper Greensand -  to my inexpert eye it looks like a Hemiaster  and I was wondering if it's Pliotoxaster as mentioned by Flintband.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rab7ies Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2011 at 1:24pm
hi tarquin..that looks like a micraster(but im no expert)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TqB Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2011 at 11:24am
Thanks again, Meg; how about this one? -35mm long:
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Post Options Post Options   Thanks (0) Thanks(0)   Quote flintband Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2011 at 10:45am
No problem Tarquin, glad to be able to help.
 
If you collect the chert echinoids from Black Venn, look out for a hemiaster-like species which occurs with them. This is Pliotoxaster wrighti and it is rather more interesting than the various species of Pseudholaster.   Cheers,  Meg.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TqB Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jun 2011 at 8:51pm
Flintband, thanks very much!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote flintband Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jun 2011 at 7:51pm
The echinoid in question occurs in the top of the Gault Clay but is more often found as chert specimens from the Upper Greensand. This specimen is Pseudholaster latissimus and equally common are P. bicarinatus and P. suborbicularis.
 
The similar species from the Aptian Folkstone Beds is P. cantianus.
 
Next ................................................?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TqB Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jun 2011 at 6:04pm
Thanks, Thomas, I'd like to see those. There isn't a Lower Greensand equivalent at Charmouth - everything's missing between the Lias and the Gault. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ThomasM Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jun 2011 at 5:33pm

That’s very interesting Tarquin, thanks, in the Gault at Folkestone the preservation and fauna seem very different. The reason I suggested it was from the Greensand is that I know similar ones from the Lower Greensand are sometimes found at Folkestone. They’re smaller than yours and come from the Lower not the Upper Greensand, but worth comparing to. I don’t know the species offhand (I’m more into the Gault fauna than the Greensand) but I will try and find it out.

Thanks

Thomas
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TqB Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jun 2011 at 4:56pm
Richard, thanks - that's a beauty, I do have a couple of those (not as good!) in chert but my Gault ones are chert-free, I think it only occurs further up.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TqB Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jun 2011 at 4:50pm
Hi Thomas,
 
These are definitely from the Gault in that they are from well below the Cowstone band which marks the base of the Upper Greensand.
The facies is a lot sandier  than the Gault further east but is still siltier than the purer greensand above it - it's also not often exposed or accessible, I haven't looked for years and don't know if there's anything to be seen at the moment. 
 
Thanks for asking, definite IDs still pending!
 
  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richard Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jun 2011 at 4:49pm
Tarquin and Thomas, you may like to have a look at this urchin from Charmouth.....


I don't think that it is the same species, but the preservation may be similar i.e. chert on the outside??
Richard
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ThomasM Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jun 2011 at 3:29pm
Sorry for resurrecting a "dead" topic here, but I was going through some of the old posts and I missed this...

Tarquin - are you sure this is from the Gault? Seems much more akin to the preservation you get in the Greensand, in the Gault there is no internal mould as such, just clay with a crushed test on top.

Also this specimen does not appear to be match for any of the Gault species.

Thanks
Thomas
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TqB Quote  Post ReplyReply Direct Link To This Post Posted: 25 Sep 2010 at 6:00pm
Thank you; Andrasz, I believe you're right about the preservation, I always liked its appearance.
Dibbs, it's a bit crushed but here are profile views.
Also some shots of the other specimen which is incomplete but less distorted.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dibbs Quote  Post ReplyReply Direct Link To This Post Posted: 24 Sep 2010 at 4:58pm
Nice that the plate outlines are still visible between the ambulacra. Whats it's profile like from the rear and side?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote andrasz Quote  Post ReplyReply Direct Link To This Post Posted: 24 Sep 2010 at 2:44pm
That is a very nice and unusual echinoid preservation, never come accross anything like that. It is not quite an internal mold, because the external features of the shell are clearly visible. Probably the dissolving shell left a void, which was then replaced by a mineral infill. Lovely find, sorry cannot help on the species level.
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