Rattendorf group

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The Rattendorf Group is a lithostratigraphic group that was deposited in the outgoing Upper Carboniferous and Lower Permian in the Carnic Alps .

designation

View from the Rattendorfer Alm to the east to the Gartnerkofel. The foot of the upstream Reppwand is built up by the layers of the Rattendorf group.

The Rattendorf Group, formerly also Rattendorfer Klassen , was named after its type locality , the Rattendorfer Alm in the municipality of Rattendorf .

stratigraphy

The 450-meter-mighty Rattendorf group, belonging to the Pontebba super group, follows the underlying Pramollo group . In turn, it is covered by the Trogkofel group . The group can be divided into three or four formations (from hanging to lying ):

Lithology

The 140 to 175 meter thick shoulder kofel formation represents a predominantly carbonate series of rocks and consists of banked, massive limestone . The thin siliciclastic inclusions of the beach area in the form of sandstones and rare conglomerate layers are only subordinate . Overall, the shoulder kofel formation is made up of an alternation of banked limestone, massive limestone and five thin sandstone- siltstone interconnections. The banked limes are consistently very rich in fossils and mostly micritic , ie the base material consists of solidified lime sludge.

In the 125-meter-thick borderland formation, siliciclastic rocks and limestone also alternate. The blue-gray carbonate banks / lenses are only a few meters thick and also relatively rare. The limestones are characterized by the massive occurrence of oncoids and large spherical fusulinids ( pseudo-sister-in-law ). The Zweikofel formation is 150 to 170 meters thick, is dark blue-gray and well banked, often with bulbous, wavy strata and dolomitized in places . Particularly noticeable are large onkoids, which can reach up to 20 centimeters in diameter, and very large, spherical, loosely rolled up fusulinids, the cells . With the exception of the basal transition to the borderland banks, the Zweikofel Formation is purely calcareous and developed without siliciclastic inclusions. The Zottachkopf Formation, which is restricted to the area around the Zottachkopf , is a 75-meter-thick, well-banked succession of neritic shallow-water limestones with algae mounds and reddish, silty carbonates. The last 10 meters are built up from a mediocre banked sequence of red bioclastic wackestones / packstones , which show an accumulation of oncoids locally.

Facies

The Rattendorf group is made up of siliciclastic / carbonate sediment packages that represent a transgressive / regressive cycle.

Hochwipfel and shoulder kofel

Similar to the underlying Pramollo group, up to four of these cyclothemes can be distinguished in the shoulder kofel formation , whereby their recognizable asymmetry can be attributed to the relief formed by the algae mounds. In contrast to the cycles of the Pramollo group, however, the cyclothemes of the shoulder kofel formation are overall more uniform and have the following structure: calcareous sandstones and siltstones at the base (interpreted as siliciclastic tempestites ), overlaid by banked limestone with fusulinides and, in places, oncoids. This is followed by calcareous-clayey algae mounds, calcareous algae thickets and other shallow water limestone, which are covered by black, banked limestone with pebbles . Banked, bioclastic limestone with processed organisms from the subsoil form the end.

Overall, the fossil content and micritic matrix indicate relatively calm sedimentation conditions on a flat shelf below the intertidal zone ( subtidal ). However, there are also higher-energy, better-washed, fossil-rich limestone banks ( grainstones ) whose base consists of diagenetically formed carbonate cement. In certain horizons the banked limestones are strongly micritic, dark in color and contain chert lumps. These limestones also contain pebble spicules and silicified ostracode shells, which point to somewhat deeper water up to possibly 50 meters. The algae mounds had grown in the warm still water below the wave base. The banked, pebbly limestone covering them indicates the respective high level of the cycle, which may have been a few tens of meters water depth and thereby ended the growth of the algae mounds, which "drowned" in the deeper water.

Boeckelmann (1985) interprets the deposit area of ​​the borderland formation as an inter- / subtidal area near the beach with increased water energies.

The deposits of the Zweikofel Formation , however, are viewed by Flügel (1974) as shallow water sediments far from the coast , which were deposited on a steadily sinking, poorly structured shelf.

Schaffhauser and colleagues (2015) see a return to shallow water sediments of the inner shelf area in the bank limestone of the Zottachkopf Formation .

Environmental conditions

The Rattendorf group was deposited in a warm aragonite sea near the paleo equator . The prevailing tropical climate made it possible for a significant terrigenous sediment input via river networks. The resulting increased nutrient supply prevented both the development of larger coral reef structures and pure carbonate separation during the Upper Carboniferous and Lower Permian. This conclusion is based on the remarkable poverty of corals coupled with an abundance of microbial oncoids and the presence of oolites and calcareous green algae .

Fossils

On fossils found in Rattendorf Group algae ( green algae and Phylloidalgen ), bivalves , brachiopods (mainly Productiden and spiriferids - Isogramma paotechowensis , Martinia incerta , Neospirifer cameratus , sp Productus. , Spirifer fasciger , nikitini S. , wynnei S. , Spiriferina holzapfeli and Spiriferella kei ), bryozoans , crinoids (stem), foraminifera (mostly Fusuliniden, Milioliden and benthic small forms), gastropods ( Bellerophontiden ), coral (single coral), ostracods ( Bairdia , Bairdiocypris and Knightina ), sponges (calcareous), sea urchins ( Spines) and trilobite remains . Plant residues such as homannisiphon also rarely occur . Worm structures are to be mentioned as trace fossils .

Among the algae with more than 30 species following taxa are to lead: Anchicodium , Calcitornella , Calcivertella , Claracrusta , Connexia , Efluegelia , Ellesmerella , Epimastopora , Eugenophyllum , Girvanella , Globuliferoporella , Gyroporella , Mizzia , Neoanchicodium catenoides , Pseudomastopora , Ramovsia , Tubiphytes and Ungdarella .

The fusulinids (large foraminifera) are very species-rich, they also enable a division into biozones . The key fossil Pseudoschwagerina ( Zellia ) is represented by many taxa - P. aequalis , P. alpina , P. carniolica , P. confinii , P. extensa , P. geyeri , P. heritschi , P. pulchra and P. turbida . More Fusuliniden are Biwaella , Boultonia willsi , Chalaroschwagerina incomparabilis and C. Solita flocosa , Daixina , Darvasites deminuatis , Leeina pseudodivulgata , Occidentoschwagerina alpina , Paraschwagerina inflate and P. nitida , Perigondwania forkii , Pseudochusenella cushmanni and P. havana , Robustoschwagerina nucelolata , Rugosochusenella , Rugosofusulina , Sakmarella fluegeli , S. lubenbachensis and S. moelleri , Schagonella , Schubertella australis , Tricitites , Zellia colanii , Z. cf. mira , Z. heritschi heritschi and Z. heritschi nicolia .

The small foraminifera are diversified with legal Climacammina , Diplosphaerina , Earlandia , Endothyra , Geinitzina , Girvanella , Globivalvulina , Hemidiscus , Hemigordius , Nodosinelloides , pseudo Vida Lina , Syzrania and Tuberitina .

The corals are indeed present with many taxa, but less important in the sediment volume Total Allotriophyllum Carnicum , zeliae Amandophyllum , Amplexocarinia heimoi and A. ruedemanni , Carinthiaphyllum kahleri , Corwenia , Linophyllum pendulum , Lophocarinophyllum major , profundum Lophophyllidium , Palaeosmilia ampfereri , Parachaetetes , Pseudovermiporella , Stylidophyllum arminiae , S. floriforme , S. volzi , Wentzelella stillei and Zeliaphyllum suessi .

Age

Originally the Rattendorf group only covered the outgoing Gzhelium and the Asselium , whereby the Carbon / Permian border was drawn with the fusulin species Occidentoschwagerina alpina . Recently the Zweikofel formation has also been placed in the sacmarium . A revision by Davydov and colleagues (2013) even rejuvenated the Rattendorf group. These authors assign the frontier formation entirely to the sacmarium (295 to 290 million years BP ). The Zweikofel formation with the final Zottachkopf formation are now in the Artinskium (290 to 282 million years BP). The Rattendorf group was therefore sedimented approximately in the period 300 to 282 million years BP.

Occurrence

The Ernesto Lomasti bivouac box on Rudnigsattel , underlain by the Rattendorf group. In the background the Trogkofel .

The occurrences of the Rattendorf group are limited to the central Carnic Alps in the Austrian-Italian border area and the southern Karawanken . In addition to the type locality near the Rattendorfer Alm, the following occurrences are known:

  • Garnitzenbach
  • Hüttenkofel (2013 m)
  • Rattendorfer Schneid (border with Italy)
  • Reppwand
  • Curtain wall
  • Rudnigsattel
  • Shoulder kofel (2091 m) - west face
  • Treßdorfer Höhe (1875 m)
  • Trogkofel (2280 m) - south side
  • Zottachkopf (2046 m)
  • Zweikofel (2059 m)

Individual evidence

  1. ↑ Karl Krainer: Short report on sedimentological-stratigraphic investigations in the Upper Palaeozoic (Auernig and Rattendorfer layer group) of the Carnic Alps . In: Yearbook of the Federal Geological Institute . l38. Vienna 1995, p. 687-690 ( PDF on ZOBODAT ).
  2. ↑ a b Vladimir Davydov, Karl Krainer, Valery Chernykh: Fusulinid biostratigraphy of the Lower Permian Zweikofel Formation (Rattendorf Group; Carnic Alps, Austria) and Lower Permian Tethyan chronostratigraphy . In: Geological Journal . tape 48 , 2013, p. 57-100 .
  3. ^ Maria Schaffhauser, Karl Krainer, Diethard Sanders: The Zottachkopf Formation: A new formation in the Lower Permian Rattendorf Group (Carnic Alps, Austria) . In: Pangeo 2010 abstracts, Journal of Alpine Geology . tape 52 , 2010, p. 218-219 .
  4. ↑ Klaus Boeckelmann: Microfaces of the Auernig layers and borderland banks west of the Rudnig saddle (Karbon-Perm, Carnic Alps) . In: Facies . tape 13 . Erlangen 1985, p. 155-174 .
  5. ↑ Erik Flügel: Facies interpretation of the sub-permic sediments in the Carnic Alps . In: Carinthia II . tape 84 . Klagenfurt 1974, p. 43–62 ( PDF on ZOBODAT ).
  6. ↑ Maria Schaffhauser, Karl Krainer and Diethard Sanders: Early Permian carbonate shelf margin deposits: the type section of the Trogkofel Formation (Artinskian / Kungurian), Carnic Alps, Austria / Italy . In: Austrian Journal of Earth Sciences . Volume 108/2. Vienna 2015, doi : 10.17738 / ajes.2015.0026 .
  7. ^ Mariangela Manzoni, Corrado Venturini, Luigi Vigliotti: Paleomagnetism of Upper Carboniferous limestones from the Carnic Alps . In: Tectonophysics . tape 165 , 1989, pp. 73-80 .
  8. ↑ Steven M. Stanley, Lawrence A. Hardie: Secular oscillations in the carbonate mineralogy of reef-building and sediment-producing organisms driven by tectonically forced shifts in seawater chemistry . In: Palaeogeography Palaeoclimatology Palaeoecology . tape 144 , 1998, pp. 3-19 .
  9. ↑ Holger C. Forke: Biostratigraphy (Fusuliniden; Conodonten) and microfaces in Unterperm (Sakmar) of the Carnic Alps (Naßfeld region, Austria) . In: Jb. Geol. B.-A. tape 138 . Vienna 1995, p. 207-297 .
  10. ↑ Franz Kahler, Karl Oskar Felser : The geology of Rattendorfer Alm (Carnic Alps) . In: Carinthia II . tape 153/73 . Klagenfurt 1963, p. 72–90 ( PDF on ZOBODAT ).