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Some Fossil Hunting in the Plabutsch-Formation of the Palaeozoic of Graz, Styria, Austria (Devonian – Eifelian)
FranzBernhard posted a topic in Fossil Hunting TripsAs there are some polished fossil-rock specimens from this formation in the Christmas auction, I would like to present some background info with (mostly) some field photographs, so I have put this in “Fossil Hunting Trips”. The Palaeozoic of Graz is a thrust sheet within the Eastern Alps, composed of Silurian to Pennsylvanian sediments. It consists of three separate nappes, the most fossiliferous formation is the Plabutsch-formation within the Rannach nappe. This Devonian formation is of Eifelian age (ca. 395 Ma), about 100 m thick and mostly made up of a very dark, gray-blueish to black, fine-grained, thickly bedded limestone. Superficially, it weathers to a medium to light grey color. Geological map of Styria with the Palaeozoic of Graz situated north of Graz. Stratigraphic column of the Rannach nappe of the Palaeozoic of Graz, Plabutsch-formation is Nr. 4. From Hubmann & Gross, 2015. Thicknesses of formations are not to scale! The Plabutsch-formation crops out at various places to the west and north of Graz and more than 100 fossil sites are known within this formation. The most abundant fossils are corals, brachiopods, stromatoporids and crinoid fragments. Other fossils like gastropods, bivalves or trilo-bits are very rare. In a paper from 1975, about 50 coral species are listed, but less than 10 are abundant: Tabulata: Favosites styriacus Penecke, 1894 Pachycanalicula barrandei (Penecke, 1887) Thamnopora boloniensis (Gosselet, 1877) Thamnopora reticulata (Blainville, 1830) Striatiopora? suessi Penecke, 1894 Rugosa: Thamnophyllum stachei Penecke, 1894 Zelophyllia cornuvaccinum (Penecke, 1894) Do you feel that there is something strange with this list? Yes, it is! Most species have their type locality within this formation and were first described by Penecke, except T. boloniensis (T. reticulata was also erected by Penecke as Pachypora orthostachys and later synonymized with an earlier described species). In my opinion, this does not reflect a high degree of endemism, but an urgent need for revision… The most abundant fossil is Favosites styriacus, which can form massive colonies up to 0.5 m in size. Here is an example from Hohe Rannach Mt. (1018 m) north of Graz, photo 05/26/2018, Col-Nr. 4093, length of pocket knife is 9 cm: As most fossils in this formation, it was found in scree and float in a wooded area. Nr. 4093 is waiting near the pocket knife toward the lower right corner… Another Favosites styriacus, north of Fürstenstand Mt. (754 m), northwest of Graz, photo 10/30/2015, not in collection. Tabulae are very well visible, weathering is usually your friend there!