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Prepping in Graywacke


Spoons

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Hi All! I live in Northern California, in the middle if the Fransician Complex, and a lot of the fossils that I encounter here are contained within very hard greywacke matrix. This stuff is incredibly well cemented together, and only becomes harder in concretions. 

 

This hard stone has prevented me from prepping these fossils. 

 

I'm unsure if an ascribe will work on greywacke, I've only seen references on this forum to use soft limestones and shales. 

 

Any advice would be greatly appreciated. 

-Nick

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I can provide pictures of the specimens I’m trying to prepare if that would help at all. It’d have to be in the morning though.

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4 hours ago, Spoons said:

I can provide pictures of the specimens I’m trying to prepare if that would help at all. It’d have to be in the morning though.

That would be necessary for opinions.

 

Greetings from the Lake of Constance. Roger

http://www.steinkern.de/

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That looks difficult, particularly with the siltstone. I'd leave that as is. You could have a go with the airscribe on the grauwacke, at least the first piece, but I'd move very slowly and surely. It could also be that the stone is "married" with the fossils.

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Greetings from the Lake of Constance. Roger

http://www.steinkern.de/

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Yeah. I haven’t actually bought an air scribe yet. I didn’t want to spend the money only to have it not work.

 

These fossils are coming from a ways inland from the coast. They’ve been transported there via a VERY complex system of faults, that pretty much jumbles everything around on the accretionary wedge. I.e. ocean sediments get scrapped off oceanic plate at subduction zone and accreted to continent .

 

It seems that stuff metamorphoses pretty quickly around here.

 

 

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53 minutes ago, Ludwigia said:

That looks difficult, particularly with the siltstone. I'd leave that as is. You could have a go with the airscribe on the grauwacke, at least the first piece, but I'd move very slowly and surely. It could also be that the stone is "married" with the fossils.

Do you think a dremel might work?

 

I should also state that I am a complete beginner when it comes to fossil preparation.

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19 hours ago, Spoons said:

D2FE6CE3-B946-4BE5-906A-6822DD824CD6.jpeg

I just want to say: That´s a stunning specimen! Very, very nice!! Thanks for sharing!
Franz Bernhard

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35 minutes ago, FranzBernhard said:

I just want to say: That´s a stunning specimen! Very, very nice!! Thanks for sharing!
Franz Bernhard

 Thank you! I do believe that they’re Scutellaster major. Price Creek Formation. Late Miocene in Age.

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6 hours ago, FranzBernhard said:

I just want to say: That´s a stunning specimen! Very, very nice!! Thanks for sharing!

I echo Franz - beautiful specimen.  I think I'd leave this one as is.  It needs no enhancement.

 

I have similar looking matrix material encasing fossils  from the Eocene that I found in an E. Tx. quarry.  My efforts at mechanical prep of the fossils in the matrix have met with frustration and loss of the specimens.  So, I quit trying and now enjoy the specimens in matrix, as-is.  They are lovely as-is, just as your fossils are.

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Different turn ;):

 

19 hours ago, Spoons said:

5E2BC5B8-BF18-4273-B230-5ADDB920DF36.jpeg
back sides

There are pebbles/clasts in this specimen! What they are composed of? Some look volcanic, some cherty? Are some of them fossil-bearing? I am asking because of this thread:

Reworked Fossils

 

16 hours ago, Spoons said:

Price Creek Formation. Late Miocene in Age.

Based on the specimen above, this formation seems to have potential in this way! Did you find any specimens with fossils in pebbles/clasts?

BTW, I am only finding info about a Dino-bearing Upper Cretaceous Pri(n)ce Creek formation in northern Alaska - ?

Thanks!
Franz Bernhard

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some of you may like:

aalto_1982_franciscan_complex_sedimentation_tectonics.pdf

ProhoroffEtAl2012.pdf

Sandstone matrix olistostrome deposited on intra-subduction complex serpentinite,Franciscan Complex, western Marin County, California
Rachel Prohoroff , John Wakabayashi, Trevor A. Dumitru

Tectonophysics 568–569 (2012) 296–305

Being a "practioner"(=believer in the importance of) of comparative subductology,it's imperative that i have indepth knowledge of the geodynamics of California

edit: all PDF's recommended,BTW

edit two: being a huge Hendrix fan: amazing avatar

Platt 2014 San Simeon.pdf

International Geology Review, 2014

Origin of Franciscan blueschist-bearing melange at San Simeon, central California coast

John.P.Platt

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Hi,

 

11 hours ago, Spoons said:

I do believe that they’re Scutellaster major. Price Creek Formation. Late Miocene in Age.

Or Dendraster. See the 2nd pic.

 

Coco

----------------------
OUTIL POUR MESURER VOS FOSSILES : ici

Ma bibliothèque PDF 1 (Poissons et sélaciens récents & fossiles) : ici
Ma bibliothèque PDF 2 (Animaux vivants - sans poissons ni sélaciens) : ici
Mâchoires sélaciennes récentes : ici
Hétérodontiques et sélaciens : ici
Oeufs sélaciens récents : ici
Otolithes de poissons récents ! ici

Un Greg...

Badges-IPFOTH.jpg.f4a8635cda47a3cc506743a8aabce700.jpg Badges-MOTM.jpg.461001e1a9db5dc29ca1c07a041a1a86.jpg

 

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7 hours ago, FranzBernhard said:

Different turn ;):

 

There are pebbles/clasts in this specimen! What they are composed of? Some look volcanic, some cherty? Are some of them fossil-bearing? I am asking because of this thread:

Reworked Fossils

 

Based on the specimen above, this formation seems to have potential in this way! Did you find any specimens with fossils in pebbles/clasts?

BTW, I am only finding info about a Dino-bearing Upper Cretaceous Pri(n)ce Creek formation in northern Alaska - ?

Thanks!
Franz Bernhard

I’m finding it difficult to find any info either. It seems that the formation has gone through various names through the years. Carlotta Formation and Rio Dell Formation are pretty much synonymous at this point. 
 

The clasts are made up of Some colorful cherts, and maybe Diorite? It looks like it had visible crystals of horneblende. 
 

No Fossils though.

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I agree.  Scuttilaster major.   Here is one I cleaned up with a dremel.  Please understand that I used to find hundreds of these and some were in super hard rock and so decided to polish some.  

 

RB

Ech025B.JPG

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@RJBI like the way that looks. I think this specimen, and those picture above would really benefit from a shine like yours. May I ask how you did this? 
 

Type of Dremel, and heads, speed and whatnot. I’m a complete novice when it comes to preparing fossils and the like.
 

@FranzBernhard I should say that the chert may be fossiliferous, if your into radiolaria or the like, I have no way to tell exact age though or to prep those out for viewing. 

75D29C22-BD24-4070-B15D-6A820BC464CC.jpeg

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41 minutes ago, Spoons said:

if your into radiolaria or the like

Not macrofossils, but fossils at least :)!

 

41 minutes ago, Spoons said:

I think this specimen

This could benefit from a polish, but its also nice as it is. If you have many of them - polish it. If this is the only one, I would not polish it.

 

41 minutes ago, Spoons said:

those picture above

This seems to have nice contrast between matrix and fossils, so cutting and polishing could be an option.

Franz Bernhard

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