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FranzBernhard

Some Fossil Hunting in the Plabutsch-Formation of the Palaeozoic of Graz, Styria, Austria (Devonian – Eifelian)

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Wrangellian

Yes, those 3D specimens must have been exposed to the elements for a long time. I can see how that limestone bedrock would be difficult to work.

You find fossils in schist?

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FranzBernhard
3 hours ago, Wrangellian said:

You find fossils in schist?

I think I used the wrong word, shale would be more appropriate. Coaly bits have the reflectance of anthracite; Conodont Alteration Index and Illite Crystallinity point to high diagenetic to anchimetamorphic conditions in the Rannach nappe, including the Plabutsch-formation.

 

Concering shale within the Plabutsch-formation:

- Some shale layers in this formation are relatively extensive and few of them contain imprints of brachiopods ("Chonetenschiefer").

- Other shale layers and shale pods to not contain fossils itself, but fossils at the contact between limestone and these layers can be easily set free by weathering, at least at the shale side. So you get somewhat 2.5D samples ;).

- And there are some layers and lenses of a somewhat shaley limestone; if these are fossiliferous and mother nature has already done its work - you may hit the jackpot!

Franz Bernhard

 

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Wrangellian

Ah, shale makes more sense! I collected some samples of (unfossiliferous) schist recently from the small Pacific Rim Terrane which collided with Wrangellia about 55mya.  :)

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Echinoid

Stunning finds! And the woodland is so beautiful! Thanks for sharing

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FranzBernhard
9 hours ago, Wrangellian said:

Ah, shale makes more sense!

Problem is german language. Nearly everything is "Schiefer" here:

"Tonschiefer" = "clay schist" = slate. Hard clay with layering or foliation, diagenetic or slightly metamorphic, around 200°-300°C.

See also discussion of modern definition and historic usage below.

"Glimmerschiefer" = mica schist = medium grade metamorphic rock with garnet etc., about 500°-600°C. And in between is "Phyllite", low grade metamorphic rock, around 400°C... And all of these can have the same precursor sediment (clay). Confusing, isn´t it? ;)

 

5 hours ago, Echinoid said:

Stunning finds! And the woodland is so beautiful! Thanks for sharing

Thanks, you are welcome!
Franz Bernhard

 

Edited by FranzBernhard

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doushantuo

Franz: those temperatures:are they peak metamorphic temperatures?:ninja::D

pelitic schist,anyone?

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FranzBernhard
2 minutes ago, doushantuo said:

Franz: those temperatures:are they peak metamorphic temperatures?

Yes.

3 minutes ago, doushantuo said:

pelitic schist,anyone?

Thats a good one! :headscratch:

Franz Bernhard

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DPS Ammonite
23 minutes ago, FranzBernhard said:

Problem is german language. Nearly everything is "Schiefer" here: "Tonschiefer" = "clay schist" = hard clay with some layering or incipient foliation, diagenetic, around 200°C. 

 

Is tonschiefer what is known as slate in English: the grade between shale and phyllite?

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FranzBernhard
3 hours ago, DPS Ammonite said:

Is tonschiefer what is known as slate in English: the grade between shale and phyllite?

Yes. Direct translation according to wikipedia (very good german entry!): Tonschiefer = slate. Something between diagenetic and metamorphic, can be considered as sedimentary rock or metamorphic rock, as you like. Important is the perfect cleavage along cleavage planes, that are produced by tectonic stress. Thats the modern, petrographic definition.

Historic usage also includes lower grade, non-tectonized rocks. Classic example is "Ölschiefer" = Oilshale.

The siliciclastic layers of the Plabutsch-formation are something between shale and slate; tectonic deformation is often quite strong, sometimes weak (Brachiopod imprints!).

Franz Bernhard

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