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Fossil snails of the genus Trochactaeon from Kainach near Voitsberg, Styria, Austria (Gosau-Group of Kainach, upper Cretaceous) - Summary of this years prospection Introduction Snails of the extinct genus Trochactaeon (formerly part of the genus Actaeonella) are among the most familiar fossils of the upper Cretaceous Gosau-Group of the Austrian Alps. The rather large size of some species (>10 cm), their intriguing spiral pattern in transverse sections and plenty supply, based on many mass occurrence, make them particularly popular. Some well known occurrences in Austria, distributed over several 100 km, are Brandenberg in Tyrol, “Schneckenwand”/Rußbach in Salzburg, Waaggraben near Hieflau in Styria and “Schneckengartl”/Dreistetten in Lower Austria; all of these are located within the Northern Calcareous Alps, mainly composed of Mesozoic rocks, especially Triassic platform carbonates. The most extensive occurrence of Gosau-Group sediments in Austria, the Kainach Gosau, however, is resting on sediments of the Palaeozoic of Graz. The Gosau-Group of Kainach consists mainly of coarse- to fine-grained clastic sediments (conglomerates to siltstones, Geistthal-formation, Afling-formation), some bituminous marls (St. Pankrazen-formation) and some hydraulic marls (St. Bartholomä-formation). The age of the whole group is considered to be mostly Campanian, but stretches into the Santonian and possibly into the Maastrichtian (Ebner & Rantitsch, 2000). In contrast to many other Gosau-Group occurrences, the Kainach Gosau is considered to be rather poor in fossils. Noticeable fossil occurrences are rudists of the St. Bartholomä-formation, some plant fossils and accumulations of small gastropods within the St. Pankrazen-formation and a few scattered ammonite concentrations within the Afling-formation. All of these fossils are already known since the 1850ies. This is also the case for the Trochactaeon snails. Transverse section of Trochactaeon giganteus from the Kainach Gosau. Generalized geological map of Styria with Trochactaeon occurrences in the northern part of the Kainach Gosau. Location of the Waaggraben site is also indicated. Brief history of Trochactaeon in the Kainach Gosau Trochactaeon snails were first mentioned in a footnote by Morlot (1850), thereby proofing the Cretaceous age of these sediments. Only two years later, their existence was already doubted (Peters, 1852). However, in 1871, Stur was able to prove the occurrence of Trochactaeon in the Kainach Gosau with museum specimens already submitted by Morlot (Locality “Am Sengsenwerk `in der Eben´, Kainach, Nord”). Indicative was the host rock of the snails, which is different to the host rocks of Trochactaeon snails within the Gosau sediments of the Northern Calcareous Alps. It took about 100 years, before several occurrences of this snail within actual outcrops were discovered by systematic investigations of a local teacher and collector in the 1960ies. But the in-situ occurrences where never described, only briefly mentioned in mapping reports and summaries of the regional geology (Gräf, 1975). The only exception is a large outcrop at the main road in Gallmannsegg north of Kainach, where some of these snails are very firmly embedded in a very hard, conglomeratic sandstone and can therefore be observed “permanently”. This site is featured in a recent excursion guide (Hubmann & Gross, 2015) and very interestingly, this is also the discovery locality of Morlot (1850), though highly modified during later road construction. Discovery site of Morlot (1850), highly modified during road construction (red X). Römaskogel Mt. (1006 m) to the upper right. Field work and results Already since several years on my wish list, it took two events in March 2020 which allowed me to prospect efficiently for this snails: First was a hint from Hans Eck (Voitsberg), who pointed out some occurrences to me, some very detailed hints, some quite general. Their distribution enabled me to restrict the prospecting area to a rather small stretch of land in the northwestern part of the Kainach Gosau, namely from Gschmurgraben/Anesbach to the east to Eckwirt to the west. The second incident was the C-thing, which allowed me to make for several day trips in this area, walking along forest roads and other paths some whole days long... Excerpts of the geological maps 1:50.000 Köflach (left) and Voits-berg (right) with the investigated area. All Trochactaeon occurrences are located within the red rectangle. Anesbach to the upper right, Eckwirt to the lower left, size of squares is 2x2 km. This prospection resulted in more than 10 “new” occurrences of Trochactaeon snails. They range from a few snails stuck within the driveways of forest roads to up to a 0.5 m thick bed tightly packed with snails. They are situated in the uppermost Geistthal-formation or the lowermost Afling formation; the literature gives ambiguous attribution of the snail-bearing zone. The especially good exposures along a forest road in the area of Breitenbach allowed the recognition of at least 6 Trochactaeon-bearing beds within a sediment thickness of about 20 m. About 100-200 higher in the sedimentary column, another Trochactaeon bed occurs. The host rock of the snails is a rather hard, dark grey to dark brown, mostly slightly conglomeratic sandstone, firmly enclosing the snails. Adjoining rocks of the snail beds are grey to greenish grey siltstones and sandstones, sometimes containing plant debris. Coarse-grained conglomerates are also abundant. Bedding planes dip generally with 20°-60° toward southeast to south. Rather surprising was the discovery of nearly black, up to 1 m thick limestone lenses with abundant fragments of radiolitid rudists near the snail beds in several spots. Continued...
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Hello, again I would like to ask for your kind help. I have two sectioned fossils from the Campanian Gosau basin of Kainach, Styria, Austria (St. Bartholomä-Formation). They are accompanied by radiolitid rudists (R), but I don´t think that they are rudists by itself. Could these be some kind of sponges? But I can not see any spicules. Frist specimen is 13.5 cm high, sections are ca. 3 mm apart. Second specimen is 11.5 cm wide, sections are ca. 16 mm apart. There is nothing visible on the wheatered surface, except some Radiolitid fragments. I know this website: http://www.cretaceous.de/ But I have not found anything definitive about sponges of the Austrian Gosau formations. Maybe someone can give me a hint? Thank you very much for your help! Franz Bernhard Specimen 1 Specimen 2
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Hello, this time a very mysterious fossil from the Gosau basin of Kainach, Styria, Austria (Campanium). A piece of limestone full of tubes with diameter up to 7 mm. There seem to be a variation of longidutinal ribs on the outside of the tubes. They are associated with one (lowest left) or two Hippuritids. I think these are serpulid worms, maybe genus Pyrgopolon, maybe something near to P. voigti Jäger, 2004. P. regia and P. macropus don´t fit 100%. What do you think? Problem is, I can not find any reference about serpulids from the Austrian gosau basins - ? Thank you very much for your help! Franz Bernhard
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Hello! I am currently looking for the rudists of the Upper Cretaceous Gosau basin of Kainach, Styria, Austria, around St. Bartholomae. So far, I have found one determinable specimen. I think, it could be Vaccinites vesiculosus (Woodward 1855). From this area, beside other rudists, Hippurites styriacus Hilber 1902, Hippurites carinthiacus Redlich 1899 and Hippirutes oppeli santoniensis Kühn 1954 are described in the literature, which seem to be all synonyms of V. vesiculosus, according to various sources. The first photo shows the outer surface of the specimen, which is not very distinctive. Height of the specimen is 13 cm, maximum diameter about 7 cm. A saw cut is indicated by a green arrow. The second picture shows the two polished, cut surfaces of the "rock". The diamater of the large rudist is 7 cm, it seems to be intergrown with a Radiolites sp. and there is also a small Hippurites sp. nearby. The third picture is an enlargement of the V. vesiculosus in question. What do you think, could my determination as V. v. be correct? Thank you very much for your help! Franz Bernhard Picture 2
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