Coral hunting in the Weißenegg-formation, Styria, Austria (Langhian/Badenian, Miocene) – 10/17/2019

[FranzBernhard]

Hello!

Finally, I have some time to post this fossil hunting trip from a warm and sunny day in October, 2019.

 

Introduction

The Miocene Styrian basin in Austria is mostly filled with various clastic sediments, e.g. fossil-rich “Florianer Schichten” around St. Josef. The “Mittelsteirische Schwelle”, a north-south trending high-zone of palaeozoic, slightly metamorphic rocks, however, is, in a very literal sense, the base of various biogenic carbonate rocks (“Leithakalk”). The individual carbonate bodies are of slightly different age – spanning the whole Badenian (about three Million years) - and composition. The younger ones to the north around Wildon are characterized by coralline algae and often oncoidic limestones, corals are extremely rare there. To the south, corals became locally an important part of the limestones, besides the coralline algae. No really big coral reef structures have developed, though; coral carpets and small coral batch reefs are characteristic.

 

Various maps from the internet and literature of the visited area. 1 = Kittenberg; 2 = Hötzlweg

 

Depositional scheme of the Weißenegg-formation around the “Mittelsteirische Schwelle”. Within the green rectangle the area of interest.

 

Relief map of the area north of Heimschuh. Note the many very small to medium-sized quarries. Some cliffs are also visible.

 

These corals are witness of tropical to subtropical temperatures in this area about 15 Million years ago. Coral development is considered to depend on local factors like sediment input or (non-)exposure to severe wave action during storms. Coral diversity is relatively high, with at least a dozen of genera described or mentioned.

 

About four years ago, I have prospected the area north of Heimschuh several times for corals. My goal was to find some good coral sites. Fossils in the wild are not super-abundant in this formation, but I succeeded to find a few good spots. Corals are by far the most abundant fossil group, bivalves etc. are much rarer.

(Note: there is a very large, active quarry for portland cement fabrication in Retznei nearby, that is famous for all kind of marine stuff, incl. Meg teeth and other large vertebrates.)

 

I will present two sites that I have visited again at 10/17/2019, but already also four years ago. One is at Kittenberg in the woods (1), the other one is a small outcrop along a minor road called “Hötzlweg” (2).

 

Continued...

[FranzBernhard]

Kittenberg

Typically, the limestone forms low cliffs in the woods. Only rarely you can observe fossils in these outcrops. The rocks are usually covered by some kind of “patina”:

 

 

I took a random specimen from these outcrops and made a polished slab. Fossil detritus is set in a fine-grained matrix:

 

The situation is a little bit better in the scree below the outcrops. Some boulders are indeed composed of coral colonies. These two boulders, side by side, show quite different modes of preservation:

 

 

 

Overturned trees are always good. Here is a small imprint of a bivalve, the only one I have found that day:

 

And this nice specimen was just waiting to be picked up (this was submitted to FOTM October 2019):

 

Thats all from this site, lets go to Hötzlweg...

[FranzBernhard]

Hötzlweg

This site was a real surprise that day. A small road was re-routed in 2015, this work exposed some limestone on both sides of the road:

 

 

I found several corals there in 2015 and directed a friend to this site a little later, who was also successful. This day, I just planned to check out, how overgrown it is nowadays. No, no, the site has barely changed. Instead, more fossils than ever were just lying around. Various colonial corals:

 

 

 

Especially impressive to me was this accumulation of individual corallites of a yet to be determined phacelloid colonial coral:

 

 

For detailed pics of this coral see:

Unknown coral - Weißenegg formation

 

There are several other sites with corals in this small area north of Heimschuh. The limestone was mined in several quarries some time ago (see relief map), and in most of them you can find some corals. But the best spot is still that at “Hötzlweg”.

 

Continued with a "Geo-Bonus"...

[FranzBernhard]

As a "Geo-Bonus", there are also many very special quarries in this area, usually very, very small, sometimes partly underground:

 

 

These quarries exploited a breccia-member of the Weißenegg-formation (see geo map, "Fastlkogel-member"). The breccia is composed of mostly quartz and phyllite clasts of the Paleozoic basement, set in a carbonatic matrix. The quarry walls have characteristic half-cylindric, vertical hollow forms, indicative of the quarrying of millstones. Some of the quarries have only one and very short of these half cylinders, so only very few millstones where extracted at some sites. If you see the rock in person, you would not think about making millstones out of it. But it was the “best” rock for this purpose several tens of km around.

 

Finally, some landscape.

Pernitschkogel (Leithakalk) to the left, and Silberberg area (phyllitic schist) with some vineyards to the right, pic taken from the Sulm valey towards northeast:

 

And a higher part of the Sausal mountains (phyllitic schist) with some very steep vineyards:

 

That’s all !

Thanks for looking and your interest.

...No more hunting trip reports in the pipeline, waiting for better fossil hunting weather...

Franz Bernhard

[Tidgy's Dad]

Great report as always, Franz, and I love some of those colonial coral colonies. 

Very nice indeed.

[FossilDAWG]

Excellent report, as usual.

I wish we had sites like that for corals around here.

 

Don

[Kasia]

Very informative description and adorable specimens

[Monica]

Nice corals, Franz!  I especially like the specimens with the septa of the corallites clearly visible - they are exquisite!

[Shamalama]

Very interesting sites and a good Geology lesson as well. Thank you!

[FranzBernhard]

@Tidgy's Dad, @FossilDAWG, @Kasia, @Monica, @Shamalama,

Thank your very much for all your kind words!
Franz Bernhard