Chonetid impressions in slate - Devonian Plabutsch-formation, Palaeozoic of Graz, Styria, Austria

[FranzBernhard]

Chonetid impressions in slate (“Chonetenschiefer”) from the Plabutsch-formation, Palaeozoic of Graz, Styria, Austria (Devonian – Eifelian)

The classic occurrence at Gaisbergsattel, west of Graz

 

The Eifelian Plabutsch-formation – mostly fossiliferous limestones – of the Palaeozoic of Graz, Styria, Austria, contains locally beds of slates of various colors. Some of these beds contain abundant limonitic imprints of brachiopods and bivalves (“Chonetenschiefer”). The locality first mentioned in the literature (1871) is that at Gaisbergsattel west of Graz:

Austrian map with "classic" occurrence of “Chonetenschiefer” at Gaisbergsattel (red x).

 

Part of geological map of Kuntschnig (1937) with “Chonetenschiefer” between the two red x east of Gaisbergsattel.

 

Here, the slate layer is up to 2 m thick, grey like mice and splits easily in flat pieces (Hanselmayer, 1957). The fauna was first listed in Heritsch (1935):

Chonetes subquadrata

Chonetes sarcinulata

Chonetes oblonga

Chonetes nova species (most abundant!)

Spirifer aculeatus

Pterinea fasciculata

Pterinea cf. bifida

Pterinea cf. costata

 

More than 10 years ago, my first attempt looking for these rocks was not successful. A few days ago (03/29/2019), however, I stumbled over this rock by pure serendipity. A small piece of it was lying on a rather busy hiking trail (“Mariazeller Weg 06”) east of Gaisbergsattel.

Relief map with my first find of “Chonetenschiefer” at the hiking trail (red x) and supposed outcrop area of this rock after the geologic map of Kuntschnig (1937).

Hiking trail “Mariazeller Weg 06”, where I found my first specimen. Pic from 04/01/2019.

 

I was able to split the rock with my fingernail – and there they were, the limonitic brachiopod imprints! A faint radial ripping is visible. No other specimen was found on the trail.

 

Now I looked closely at the geologic map, the text of Hanselmayer (1957), and the relief map and decided to explore the area around the red line (see above), where the outcrop of this rock is supposed to be. It’s a forested area with dense undergrowth, among the undergrowth many spiky blackberry bushes… No outcrop was found, but fallen trees have exposed some rock fragments: Abundant limestones, light brownish slates and, yes, some grey slate, mostly small pieces. I split only the largest of them – and again some brachiopod imprints were found...

[FranzBernhard]

“Outcrop” situation below a fallen tree. Note the freshly split specimen in the middle of the pic. 04/01/2019.

 

Freshly split slate specimen with chonetid impressions. Width of specimen 12 cm, Nr. 4228a, 04/01/2019.

 

Opposite sides of one split with chonetid impressions. Fine radial rips are barely visible, and you can discern a median line at least in one of them, I think.

 

So, nothing spectacular was found, only some limonitic blotches . But I am really satisfied, that I have finally found this rock and its fossils. The circumstances, why I was walking on this trail, were somewhat sad, but that’s a story not to be told here.

Thanks for looking!
Franz Bernhard

 

Literature:

Hanselmayer, J. (1957): Beiträge zur Sedimentpetrographie der Grazer Umgebung IX. Die Chonetenschiefer des Grazer Paläozoikums. Sitzungsberichte der Akademie der Wissenschaften, mathematisch-naturwissenschaftliche Klasse, Abt. 1, 166, 19-42.

Heritsch, F. (1935): Oberstes Unterdevon und unteres Mitteldevon bei Graz. Sitzungsberichte der Akademie der Wissenschaften, mathematisch-naturwissenschaftliche Klasse, Abt. 1, 144, 187-197.

Kuntschnig, A (1937): Geologische Karte des Bergzuges Plabutsch-Kollerkogel. Mitteilungen des naturwissenschaftlichen Vereines für Steiermark, 74, 114-132.

[Fossildude19]

Wow!  
Lovely detail in these, Franz! 
Absolutely beautiful! 

Informative report and great pictures, friend.  

Thanks for posting them. 

[Tidgy's Dad]

Super report and nice finds and photos. 

And it's about brachiopods!

Yaaaaaaaaaaaaaaaaaaayyyyyyyyyyyyyyyyy!!!!!!!!!!!!!!!!!!!!!!!!

[Al Tahan]

What a great report!! I felt like I was reading a research paper! Very detailed. 

 

Thanks for posting  

[doushantuo]

Nice one,Franz!!

[FranzBernhard]

3 hours ago, Fossildude19 said:

Thanks for posting them. 

 

3 hours ago, Tidgy's Dad said:

Super report and nice finds and photos.

 

42 minutes ago, Al Tahan said:

Thanks for posting

 

17 minutes ago, doushantuo said:

Nice one,Franz!!

Thanks for all your appreciation!

 

 

43 minutes ago, Al Tahan said:

Very detailed.

That was easy with only 3 specimens .

 

Franz Bernhard

[Monica]

Congratulations on the new finds!  Very exciting!!! 

[Wrangellian]

Again Monica is on at the same time as me and looking at the same things!

Nice find, Franz. It always surprises me to see things come out of spots I wouldn't think to look for fossils, with barely any rock exposed.