Houlgate (Vaches Noires)

[ortho]

Though I've found plenty of info to help me identify what I collected at Vaches Noires I haven't sat down to get it all straightened out, and I thought I 'd post these images of a few items found during 2-3 hours walking on the beach from Houlgate to Villers-sur-Mer. I'll see if I can't give it a go during the holidays and add a few tags, but I thank any of your suggestions :-). 

Of these #17 is not a fossil and include it as a comparison to #14-16 which are equally sized but much thiner and blue/black in colour. Also not sure whether #8 and #27 are fossils. Just at the beginning of the cliffs there are large numbers of rusty fragments among the large limestones and I am not sure to what extent these are remnants from shells of the military type or from boats or other harbour equipment (not that there is much of a harbour to speak of) or metal refuse. I didn't get a chance to inform myself during my short stay about this and haven't found hints online, but the Germans put a battery on top of the hill by Houlgate which was heavily shelled. The info regarding the geology of the site was swipped from the French and is only an indication of the geology of the beach where one is allowed to pick fossils, not the cliffs themselves which release fossils as they are eroded. I don't include any Griphaea dilatata which have a truly impressive heft. I wouldn't be surprised if these were used as hoes or tools and weapons back in the stone age.

Cheers

 

[Ludwigia]

Looks like mostly recent gastropod shells, a few Rastellum or Arctostrea oysters (left:5,7,10. right:4,5,7,10), one partial fossilized gastropod steinkern (left:23) and a beat up ammonite (right: 12). The last 2 photos show weathered stones.

[Coco]

Hi,

 

14 to 17 look like recent Nassarius... What is the size ?

 

Coco

[ortho]

Thanks for the comments :-)

 

The ammonite (#12) needs some cleaning, I didn't remove the matrix. Sorry about that. I fret about damaging it if I am not careful and wanted to read on how to do this properly, preferably without having to borrow a dentists office.

There are enough rocks such as #3 around Paris to suspect its just a rock :-) but the shape made me suspect it's a piece of coral or similar.

On the other hand the quartz inclusion in #25 reminded me of orthoceras I have found before which is why I thought it might be something more interesting. I believe the rock is sandstone rather than limestone. Between rock and quartz is a thin iron layer.

#24 seemed like #25 but with the inclusion weathered away.
#27 was just weird. I realize it's probably not a fossil but thought to include it to ask about all the rusty iron bits near Houlgate. I can imagine it being a piece of an artillery shell. On the other hand other pieces (#8) might be rusting pyritized fossils.

Sure triggers your fantasy, but that's part of the fun.
 

#14-17 are all ~25 mm long. The shells are thinner in those that turned blue/white. The modern shells (Nassarius , thank you Coco) accumulate in Villers-sur-Mer.

#21-22 show mineral deposition/weathering.

#20 is different, it seems to have a steinkern (hardened clay) - thanks Ludwigia for teaching the proper nomenclature.

#18 and #19 are nothing like the tons of shells otherwise found on the beaches of Houlgate and Villiers, so I suspected they may be fossils. They are extremely worn and partly bleached. But they may of course just be really worn and partly bleached holocene shells :-)

[Coco]

2,5 cm is the size of most of my Nassarius reticulatus. May I have a close-up of aperture please and of the "back"  ?

 

Coco

[Pixpaleosky]

14 to 22, except 20 are all contemporary shells

 

4, 7 and 10 are lopha gregarea

 

9 is a part of myophorella

[Ludwigia]

It's still debateable as to whether the oysters at Houlgate are called Lopha or Arctostrea. Rastellum are also in these beds, but it's not always easy to distinguish between the two.

[ortho]

@CocoSome closeups of the Nassarius .

The worn shells (blue/black) were found at the foot of the cliffs whereas the intact ones (yellow/white) are from the beach on front/near Villers .

I am a little curious about what might cause the blue/black discoloration. Is it wearing of the shell exposing a darker layer, or a chemical process?

 

 

Edited November 26, 2017 by ortho
clarification

[Coco]

I think they are recent Nassarius reticulatus. The blue shells were able to remain some time buried in a little bit muddy sand of the beach, which can modify the color of the shell. I noticed that shells found in the mud are more darkened.

 

Coco

 

[ortho]

Thanks Coco. Whether a chemical and physical process is involved is interesting, and the order and progression of events. One problem is that the surf at Vaches Noires is quite rough and some modern shells can get mixed into the mud by the action of the waves. However I found the shells away from the immediate cliff face.