Ammonites from the Zone of Cyrtopleurites bicrenatus, Nor/Alaunium1 of the Hallstatt limestone
Written by Andreas Spatzenegger
The „Hohe Dachstein"
mountain with fresh fallen snow in spring;
The Dachstein is the highest mountain in the Salzkammergut area and the so called Dachstein limestone is named after this mountain.
Below the glacier, the partly forest covered mountain is named „Hirlatz". This is the type locality of the liassic „Hirlatz limestone". Down below the Hirlatz mountain, not visible on the picture, lays the small town Hallstatt on the lake of the same name. A period of the Bronze Age is named after this town with its old salt mines above on the "Salzberg". The Hallstatt limestone is named after this town too. Two old historical locations exist there above the salt mines. These are the historical location of the Sommeraukogel and the Steinbergkogel from where the first description of this limestone and its ammonoids come.
Dear Fossil Forum members
A long lasting search for a new outcrop in which the very scarce bicrenatus Zone/Alaun 1 is exposed came to an end a few years ago. Of course there are several old historical locations where this zone was exposed but after 150 years of exploration, there is not really much to find there at present. I was happy to find a new location where this scarce zone was exposed, but I had never dreamed of finding such a good one.
It all started very unspectacularly and unexpectedly.
Years ago I walked downhill from another fossil location in this area with a heavy rucksack on my back.
It was a beautiful day and I wanted to take some landscape pictures of this area. I put down my rucksack and walked a few steps beside the path.
As I was taking the pictures I looked down on the rock on which I stood. A very small cross-section of an orthicone ammonoid and a shell part of a bigger ammonite was visible. Both very unspectacular like other common cross-sections I often saw in this limestone.
My hammer was in the rucksack but I was too lazy to go back to the path and fetch it.
So I went further downwards and then drove home.
One week later I was in this area again. At noon my rucksack was full and I went prospecting for the rest of the day. My first way was to this ominous block which had been haunting my thoughts the whole week long.
I put the chisel on the block, one blow with my hammer and I recognised with one look that I had found something really special.
The ammonoid shell was a part of the weathered body chamber of a Clydonautilus noricus 30cm in diameter.
But this wasn't the best part of this block. I recognised that this block was a part of a 20 cm thick layer full of ammonites. The discovery of such a big spot I knew only from reports of the historical locations around the 19th century. The layer was totally undisturbed and untouched when I found it. No old traces of working were visible.
Nevertheless Mojsisovics has pictured ammonites from this area, fitting to this facies and layer, in his work "Das Gebirge um Hallstatt". I assumed that the in Mojs. pictured Ammonites either originated from a fallen block or that this layer had a second outcrop in this area hitherto unknown to me. If this layer would have been known in the time of Mojsisovics it would have been totally exploited like the outcrop on the Sommeraukogel where former collectors exploit the fossil bearing limestone up to a height of 6m.
„Corner stone of this location", Clydonautilus noricus
with a partly strongly weathered body chamber. The mossy crack on the picture is the last Septum.
Dug out block with ammonites of this outcrop. The glove shows the natural size. The weight is 30-40 kg roughly all in all a full rucksack.
The whole fossil layer consists of several intern layers which are dissected by manganese crusts.
These crusts have strongly condensated origin. This explains also the frequent ammonoids shells. Also visible is a current parallel alignment of the ammonoid shells.
The blocks shown are 10-15cm thick and bear Ammonites also inside the limestone.
I whistled for my colleague who was also collecting near to me in this area. Together we did a first examination of the whole outcrop. Stratigraphically we weren't sure at this moment what time this layer belonged to because we had only found ammonites without sculpture.
At this time we had only scratched a little on this location but we did already have a presumption at that moment about what stratigraphic time it may have been .
The most frequent ammonite on this location is Placites sp. in for this genus, enormous sizes up to 10cm.
Our next tour was directed at this location to collect there professionally. After a while the first Cyrtopleurites part occurred and we got confirmation of our former presumption. The other tours of this year brought us if at all possible to this location to collect some more at this outcrop.
If anyone should think that we have tons of material from this location at home, one and a half hours walking up to this location and a same long way down restricted the material to one rucksack a trip.
It makes no sense to carry more than 50 kg downhill in this wilderness. Everybody who has carried 40-50 kg down on his back for one and a half hours knows what I mean and knows where his physical limit is. After preparation, one third of this weight is left over. The other material is thumb stone and halves or badly preserved ammonites.
Now some ammonoids from this location
Cyrtopleurites cf. socius as found, 7cm in diameter
Cyrtopleurites altissimus as found. The orange circle is the cap of my drinking bottle.
Prepared block with C. altissimus. From 15cm thickness prepared down to 6cm and roughly 5 to 6 badly preserved ammonites destroyed by prepping.
Detail view of Cyrtopleurites altissimus, 9cm
Remarkable are crinoid roots on some ammonite shells. This leads to the presumption that the sedimentation rate was very low. The ammonoids shells lay on the seafloor for a long time without being covering by sediments and were settled by crinoid larvae.
On the hardgrounds, now indicated by manganese crusts, such roots are also visible. Ossicles of these small crinoids are visible frequently inside the red limestone.
The average diameter is 5mm. This is well visible on picture 7 and 8.
It is also visible that the Palaeo current comes from upper right in relation to the picture. The ammonites on the left side of the picture overlap each other and on the venter of the Cyrtopleurites a crinoid root stem settled with its well visible central channel.
Maybe current whirls, which occur on the sloping embedded ammonoids shells, helped the crinoid larvae to settle down preferably on such places in the shadow of the current.
Visible is a Crinoid root on the last septa of a big Cladiscites neortus. Diameter of the root is 3 mm.
This shows us forensic evidence of the settlement of the crinoid larvae after the death of this ammonite. Rhacophyllites sp. is frequent with two different species. Big specimens are mostly preserved without body chamber.
Rhacophyllites neojurensis, 14cm Diameter
Rhacophyllites debilis HAUER, 13cm.
More evolute and less thick than R. neojurensis. The yellow colour is due to the preparation of this ammonite from its underside. Generally this is the better preserved side but it isn't prepareable often.
Didymites cf. subglobus with Rhacophyllites neojurensis and Placites sp.
Diameter of the big Didymites is 7cm. On the left side is shown a Didymites of the same species in Venter view. Didymites occurs only in this Zone in the Hallstatt limestone and is very easy to confuse, in Form and shape, with Arcestes sp. But it has a very typical suture line which excludes confusion.
Arcestes cf. dicerus, Diameter 6cm
Items after rough preparation
The preparation of these ammonoids is only possible mechanically. I work with rough and fine air chisels. After preparation I finish the ammonites with stone fluat to protect them against the acid. Then I remove drops of the stone fluat from the mother rock and treat the rock with acid until it shows its natural colour again. Then, if necessary, cover the ammonites a second time and then it's finished.
Slab with Drepanites hyatti MOJS. (7cm), Rhacophyllites neojurensis and Arcestes sp.
Provisional list of Ammonoids and Nautiloids:
Arcestes cf. didymus MOJSISOVICS.
Arcestes dicerus MOJS.
Stenarcestes cf. diogenis MOJS.
Cyrtopleurites bicrenatus (HAUER1846)
C. altissimus MOJS.
C. socius MOJS. 1893
Cladiscites neortus MOJS.
C. beyrichi WELTER1914
C. quadratus MOJS.
Didymites tectus MOJS.
D. globus QUENSTEDT
D. subglobus MOJS.
D. quenstedti MOJS.
Drepanites hyatti MOJS.
Heraclites robustus (HAUER 1855)
Hauerites cf. rarestriatus HAUER
Pinacoceras cf. parma MOJS.
Placites oxyphyllum MOJS.
Clydonautilus noricus MOJSISOVICS
Gonionautilus quenstedti HAUER
Nautilus. sp. (2) undet.
Rhacophyllites neojurensis (QUENSTEDT)
R. debilis HAUER
I thank Mister Michael Henz member of the German "steinkern forum" for working (dissolving, sorting and identification), on the conodonts of this fossil layer.
The internet community makes it possible that collectors of the alpine Triassic and collectors of the German „Muschelkalk" can both work together very easily. I am very glad to have this contact.
For the future I hope for a further collaboration, maybe in more interesting stratigraphic levels to both sides, like the Anisium or lower Ladinium.
We do not know for sure if our conodont nomenclature is up to the latest scientific level. The conodonts were identified through the works of Kozur and Huckriede.
Material was dissolved only from the main fossil layer.
Because of the lack of Neogondolella hallstattensis we presume that there is no part of the stratigraphic lower Juvavites magnus zone in our fossil layer condensed in too. The result of the stratigraphic occurrence of both, ammonites and conodonts fit perfectly to the ammonoid-zone of the Cyrtopleurites bicrenatus/Alaunian I.
1a: Metapolygnathus spatulatus spatulatus, side view.
1b: Metapolygnathus spatulatus spatulatus, down side.
1c: Metapolygnathus spatulatus spatulatus, upper side.
2a: Metapolygnathus spatulatus spatulatus, upper side.
2b: Metapolygnathus spatulatus spatulatus, down side.
2c: Metapolygnathus spatulatus spatulatus, side view.
3a: Metapolygnathus spatulatus spatulatus, upper side.
3b: Metapolygnathus spatulatus spatulatus, side view.
4a: Metapolygnathus abneptis abneptis, down side.
4b: Metapolygnathus abneptis abneptis, upper side view.
4c: Metapolygnathus abneptis abneptis, side view.
1a: Metapolygnathus spatulatus spatulatus, juvenile, upper side.
1b: Metapolygnathus spatulatus spatulatus, juvenile, upper side.
1c: Metapolygnathus spatulatus spatulatus, juvenile, side view.
2a: Metapolygnathus spatulatus spatulatus, juvenile, lower side.
2b: Metapolygnathus spatulatus spatulatus, juvenile, upper side.
2c: Metapolygnathus spatulatus spatulatus, juvenile, side view.
3a: Metapolygnathus spatulatus spatulatus, lower side.
3b: Metapolygnathus spatulatus spatulatus, upper side.
3c: Metapolygnathus spatulatus spatulatus, side view.
4a: Neogondolella navicula, upper side.
4b: Neogondolella navicula, lower side.
4c: Neogondolella navicula, side view.
5a: Metapolygnathus spatulatus spatulatus, upper side.
5b: Metapolygnathus spatulatus spatulatus, upper side.
5c: Metapolygnathus spatulatus spatulatus, side view.
Drilling holes for magneto-stratigraphic aims, drilled most probably by the University of Vienna.
At the end I should mention that work on this location has ended long ago. Good material can be gained only by very great efforts because the layer runs steep into solid mother rock.
I hope you enjoyed this report and that I was able to give you a small insight into my special regional collecting field, the pelagic Triassic ammonites of the Alps.
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KOZUR, H. & MOCK, R. (1972): Neue Conodonten aus der Trias der Slowakei und ihre stratigraphische Bedeutung. — Geol. Paläont. Mitt. Innsbruck, 2, 1—20, Innsbruck
KOZUR, H(1973): Die Bedeutung der Conodonten für stratigraphische und paläogeographische Untersuchungen in der Trias. — Mitt. Ges. Geol. Bergbaustud., 212, 777—810, Innsbruck.
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TATZREITER, F. 1981, Ammonitenfauna und Stratigraphie im höheren Nor(Alaun, Trias) der Tethys aufgrund neuer Untersuchungen in Timor, Denkschr. Österr. Akad. Wiss., math.-naturwiss. KI., 121, Wien 1981, Springer Verlag
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TATZREITER,F. 1984: Bericht über paläontologische Untersuchungen in Hallstätterkalken auf Blatt 76 Wr. Neustadt und 96 Bad Ischl. - Jb. Geol. B.-A., 128/2, Wien 1985
TOZER, E. T. 1994. Canadian Triassic ammonoid faunas. Geological Survey of Canada Bulletin, 467, 1–663.