Trogkofel group

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The carbonate Trogkofel group is a lithostratigraphic group from the Permian of the Carnic Alps . It is often dolomitized and closes the permocarbonic Pontebba supergroup - the first alpine sediment cycle of the Southern Alps . Their lithology consists essentially of massive, biogenic reef limestone , which emerged from encrusting algae such as Archaeolithoporella , Bryozoa , Fusulinids and the taxon Tubiphytes .

The Trogkofel with the Trogkofel formation, seen from the direction of Sonnleiten (northeast)

designation

The Trogkofel group was named after its type locality - the 2280 meter high Trogkofel in the central Carnic Alps.

stratigraphy

The Trogkofel Group, which is a maximum of 825 meters thick, consists of the following four formations (from hanging wall to lying ):

The Trogkofel group forms the end of the Pontebba super group and follows the underlying Rattendorf group . In turn, it is covered by the Val Gardena formation .

Forni Avoltri limestone is also part of the Trogkofel group . A clastic development is also counted towards the Trogkofel group, the Košna series . It is only developed in Slovenia and Croatia . Their stratigraphic relationship to the Trogkofel Limestone is unclear.

The Tarvisian breccia begins the second alpine sediment cycle of the Southern Alps after a hiatus and lies discordantly over the first cycle. The layer gap was caused by Horst-und-Graben fracture tectonics and is associated with the Saalic phase . Strictly speaking, the Tarvisian breccia therefore no longer belongs to the Trogkofel Group, as it overlays them discordantly and partially processes their layered elements. Rather, it forms the horizontal part of the Val Gardena Formation and normally follows the Goggau Formation with a layer gap, but can reach down to the Trogkofel Formation as on the Trogkofel.

The Treßdorfer Kalk, the Goggau Formation and the Limes of Forni Avoltri are all tectonically isolated deposits and are not part of any stratigraphic association with the Trogkofel Limestone. Equivalents of the Trogkofel group only occur in tectonically isolated form in the South Karawanken. The thick-banked, light gray to whitish limestones and breccias of Javorniški Rovt and Kranjska Gora correlate with the Goggau limestone based on their fusulinid fauna from the late Artinsian period .

Lithology

The Trogkofel from the north

The 480-meter-thick Trogkofel formation consists of predominantly light gray, massive limestone , which can rarely be a little darker and banked. The mass limestone is predominantly a boundstone cemented with Tubiphytes and Archaeolithoporella . The limestones contain peloids , grains of bark, oncoids and rarely ooids as components . At the type locality of the Trogkofel reef limestone form a good two thirds of the sequence, in the upper third the deposit area flattened and was then covered by bioclastic grainstones .

The Treßdorfer Kalk is so far only known in the form of small, isolated deposits with a maximum thickness of about 15 meters in the vicinity of the Treßdorfer Alm . It is a Kalkbrekzie whose components consist of different Kalktypen. The Goggau formation is about 130 meters thick. The Tarvisian breccia reaches almost 200 meters at its type locality near Tarvisio , but is only reduced to a few meters at the Trogkofel. The breccia consists predominantly of angular, light gray Trogkofel limestone pebbles, which are embedded in a fine-grained, carbonate, reddish or gray colored ground mass . The individual rolls are usually only a few centimeters, rarely over 20 centimeters.

Facies

The Tarvisio breccia of Dovžanova soteska, Slovenia

The Trogkofel Formation is developed in different facies : as shelf edge reef facies on the Trogkofel (comparable to the Permian reefs in New Mexico and Texas ) or as pure shelf facies at Forni Avoltri. Clastic Trogkofel layers occur in the Karawanken .

The extent of the calcareous algae and probably also the fusulinids in the Tubiphytes / Archaeolithoporella reefs suggests a water depth of more than ten meters for the lower two thirds of the Trogkofel Formation of the type locality - in the photic zone probably below the fair-weather wave base. The bioclastic grainstones from the upper part can be viewed as platform deposits. However, they may also represent lime sands of the shelf edge that had been deposited due to higher-energy episodic events.

The limestone breccia of the Treßdorfer Kalk probably originated in tidal channels on the shelf. The Goggau formation was deposited on the edge of the shelf. The Tarvisio breccia is a polymictic, carbonate stylobreccia and is interpreted as debris fan deposition in the form of debris flows along fracture faults , with freshwater cements and pedogenic structures at least partially indicating subaeric deposition conditions. Reddish silt and clay stones that are carried along and contain caliche speak in favor of a coastal sabcha environment with vaporite formation .

Fossils

The limestone of the Trogkofel group contains the following fossils: algae ( calcareous algae ), ammonoids (rarely - Medlicottia artiensis var. Carnica ), brachiopods , bryozoa , conodonts ( Diplognathodus expansus , Neostreptognathodus cf. pequopensis , Sweet Rognathus whitei ), Echinoderms ( Crinoid stalk limbs ), cyanobacteria ( Koivaella ), foraminifera (small foraminifera and fusulinids ), gastropods , calcareous sponges , corals , shell remains , ostracods and trilobites (very rare shell remains). Agglutinated worm structures act as ego fossils .

From the limestone of the Trogkofel group, a total of 46 calcareous algae from the following groups have been described so far: Ancestral Corallinaceae , Cyanobacteria , Dasycladaceae , Epimastopore , Gymnocodiaceae , phylloid algae , Rhodophyceae , Solenoporaceae and Ungdarellaceae . The algae include: Archaeolithoporella hidensis , Connexia , Epimastopora , Globuliferoporella , Gyroporella , Mizzia , Neoanchicodium , Tubiphytes carinthiacus and T. obscurus .

The Brachiopodentaxa are quite numerous: Echinoconchus elegans , Geyerella distorta , Marginifera carniolica , Meekella depressa , Productus gratiosus , P. semireticulatus , Reticularia dieneri , R. stachei , Scacchinella gigantea and several spiriferids .

Among the bryozoa there should be mentioned Alternifenestella subquadratopora , Carnocladia fasciculata , Penniretepora sp. , P. trapezoida , Rhombopora sp. and Streblascopora germana .

About 70 Fusulinid species from the following groups are known: Acervoschwagerina ( A. stachei ), Boultonia ( B. willsi ), Chalaroschwagerina ( C. globularis ), Darvasites ( D. fornicatus ), Eoparafusulina ( Mccloudia ), Leeina ( L. pseudogruperaensis ) , Minojapanella ( M. elongata , M. wutuensis ), Misellina ( M. aliciae , M. claudiae ), Nagatoella ( N. orientis ), Nankinella , Pamirina ( P. darvasica ), Perigondwania ( P. oingaronica , P. sera , P. . tersa , P. zigarica ), Praeparafusulina ( P. lutugini ), Pseudofusulina ( P. ambigua , P. fusiformis , P. moelleri , P. Tschernyschewi , P. vulgaris ), Pseudofusulinoides ( P. regularis ), Pseudoichelina ( P. darvasica ), Pseudoschwagerina ( P. lata ), Quasifusulina ( Q. magnifica ), Robustoschwagerina ( R. geyeri , R. schellwieni , R. spatiosa , R. tumida ) and Triticites .

Benthic foraminifera are Lasiodiscus tenuis , Spireitlina tokmovensis , Tetrataxis and Tuberitina .

Corals are rare, so far Amplexocarinia muralis , Caninophyllum gortanii , Palaeosmilia hammeri , Parafusalina carnica , Tachylasma aster and Wentzelella yokohamai have been found .

tectonics

The Trogkofel slab sliding in from the northwest, seen from the Bivacco Ernesto Lomasti . In the foreground the squashed layers of the Rattendorf group.

The Trogkofel group and the strata surrounding it were affected by the Alpidic orogeny . Two competent partial ceilings were created that moved against each other. The ceiling on the Roßkofel (2239 m) with its Devonian reef limestone moved northwards, whereas the ceiling on the Trogkofel together with its underlay made of the rocks of the Rattendorfer group pushed over to the southeast. Thus, the deeper was Pramollo group squeezed vise-like and down slightly by the sliding of the Trogkofeldecke südvergent in east-west direction verfaltet . These conditions can be observed very nicely on the Rudnigsattel .

Age

The Trogkofel Group begins at the end of the Artinsian Era and survives the entire Kungurian Era - that is, the group was deposited in the period between 277 and 271 million years BP .

The biostratigraphic classification of the limestone of the Trogkofel group was carried out with the help of the Fusulinid fauna : The deeper part of the Trogkofel formation was placed in the lower sacmarium due to the occurrence of Pseudofusulina moelleri , the Treßdorfer limestone with Praeparafusulina lutugini in the lower Artinskium and the Goggauer limestone Pseudofusulina vulgaris and Pamirina darvasica in the upper Artinskium. The limestones of the Trogkofel group were therefore deposited in the Sakmarium-Artinskium period.

The Tarvisio breccia follows with a shift gap , its exact age is not known. Due to the fusulin fauna contained in the reclaimed limestone rubble, the Tarvisian breccia is generally classified under the Kungurium, but it is probably even younger.

This biostratigraphic classification, which had given the Trogkofel group an age of around 285 to 277 million years BP, was, however, significantly rejuvenated by Schönlaub and Forke (2007), since for the authors the Trogkofel group only begins in the upper Artinskium.

Occurrence

In addition to the type locality of the Trogkofel in the Pramollo basin , the occurrences of the Trogkofel group extend from Sexten and Forni Avoltri ( Forni Avoltri basin ) in the west over the Pramollo basin and the Tarvisio basin to the Karavanken of Slovenia in the east.

Individual evidence

  1. ^ A b Maria Schaffhauser, Karl Krainer, 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 .
  2. ↑ Matevz Novak, Holger C. Forke: Updated fusulinid biostratigraphy of Late Paleozoic rocks from the Karavanke Mts. (Slovenia) . In: Bernhard Hubmann, Werner E. Piller, 75th Annual Meeting of the Palaeontological Society, Graz, Aug. 27 –2. Sept. 2005: Contribution abstracts (Ed.): Reports of the Institute for Earth Sciences Karl-Franzens-Universität Graz . tape 10 . Institute for Earth Sciences, Geology and Paleontology, Karl-Franzens-University, Graz 2005, p. 90-91 .
  3. ^ Erik Flügel: Lower Permian Tubiphytes / Archaeolithoporella buildups in the southern Alps (Austria and Italy) . In: SEPM, Spec. Publ. Volume 30 . Tulsa 1981, p. 143-160 .
  4. ↑ Erik wing, Erentraud wing-Kahler: Algae from the limestone of the Trogkofel layers of the Carnic Alps . In: Erik Flügel, The Trogkofel stage in the Lower Permian of the Carnic Alps (Ed.): Carinthia II . Special issue 36th Natural Science Association for Carinthia, 1980, p. 113-182 .
  5. ^ Anton Ramovš: Biostratigraphy of the Trogkofel stage in Yugoslavia . In: New Yearbook Geology and Palaeontology, monthly books . 1963, p. 382-388 .
  6. ↑ Erik Flügel: Microfacies of Carbonate Rocks . Springer-Verlag, Berlin 2004, p. 976 .
  7. ^ A b Hans-Peter Schönlaub, Holger C. Forke: The post-Variscan sequence of layers of the Carnic Alps - Explanations of the geological map of the Young Paleozoic of the Carnic Alps 1: 12500 . In: Abhandlungen Geologische Bundes-Anstalt . tape 61 , 2007, p. 3–157 ( PDF on ZOBODAT ).
  8. ^ Karl Krainer: The Permian in Carinthia . In: Carinthia II . 183./103. Vintage. Klagenfurt 1993, p. 133–180 ( PDF on ZOBODAT ).
  9. ^ V. Kober: On the genesis of the Tarvisio breccia in the Karawanken, northwestern Yugoslavia . In: special publ. Geol. Inst. Univ. Cologne . tape 56 , 1984, pp. 1-155 .
  10. ^ Franz Kahler, Gustava Kahler: Fusulinids from the limestone of the Trogkofel layers of the Carnic Alps . In: Erik Flügel: The Trogkofel stage in the Lower Permian of the Carnic Alps (Ed.): Carinthia II . Special issue 36. Klagenfurt 1080, p. 183-254 .