Tarvisio breccia

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The Tarvisio Breccia is a geological formation that was deposited in the Permian of the Southern Alps . With it the second tectono-sedimentary cycle begins in the Southern Alps.

designation

The Tarvisio breccia of Dolžanova Soteska in Slovenia
Tarvisian breccia in Potokbach, Karawanken
Tarvisian breccia in Potokbach, Karawanken

The Tarvisio Breccia, with a maximum thickness of 200 meters, in Italian Breccia di Tarvisio , was named after its type locality , the northern Italian municipality of Tarvisio ( German : Tarvis). However, the actual type profile is located near Coccau (German: Goggau) southeast of the local church.

stratigraphy

After a layer gap, the Tarvisio breccia lies discordantly over rocks of the Trogkofel group , to which it is usually included. Strictly speaking, however, this is not correct, as it belongs to a different tectono-sedimentary cycle and reprocesses the sediments of the first cycle. The hiatus is associated with the tectonic movements of the Saalic phase . The Tarvisio Breccia usually transgresses over the Goggau Formation , but can also reach deeper and then lies on the Treßdorfer Kalk or the Trogkofel Formation - to be observed at the summit of the Trogkofel , where it is only several meters thick. Between the Passo del Cason di Lanza and the Straniger Alm it can even be found discordant over sediments of the Pramollo group . The Tarvisio breccia then merges into the Val Gardena formation in the hanging wall or interlocks with it. Stratigraphically equivalent are the Val Daone conglomerate (Italian: Conglomerato di Val Daone ) and the Sexten conglomerate (Italian: Conglomerato di Sesto ).

Lithology

In lithological terms, the Tarvisio breccia, which is usually only several tens of meters thick, is a coarse to fine-grained rudite , which is primarily formed as a macro- breccia , breccia or, more rarely, as a conglomerate . Most of the components consist of carbonate , more rarely quartz and arenitic clasts . They come from the Trogkofel group , occasionally also from the Rattendorf group .

To the east of the Straniger Alm, the only 10-meter-thick sequence consists of gray dolomite breccias alternating with red siltstones , solid dolomite and Rauhwacke . This is in contrast to the occurrence on the Trogkofel , the so-called Trogkofel breccia , which is mainly composed of angular, light gray carbonate clasts of the reclaimed Trogkofel limestone and a negligible proportion of siliciclastics. The clasts are between 2 and 8, rarely more than 20 centimeters, and are cemented together either by a fine-grained dolomite matrix or a reddish or gray colored, massive and homogeneous base mass . Fusulinides can be present in the basic mass, which is practically less fossilized . Other fossil remains have been reprocessed.

Facies

The Tarvisio breccia - a polymictic, carbonatic stylobreccia - was created by tectonic elevation of the upper carbonic / subpermic sediment sequence of the first cycle, which was exposed to severe karstification due to the prevailing dry climate . It corresponds to facially subaeric debris fan deposits , which were bound as debris flows to synsedimentary faults and therefore show strong fluctuations in thickness. Reddish silt and clay stones that are carried along and contain caliche speak for a coastal abkha environment with vaporite formation . It is believed that the Tarvisio breccia, like the equivalent Sexten conglomerate, was formed on an eyrie of the first sediment sequence. The trough in between was filled by the interlocking Val Gardena formation.

Age

Absolute radiometric dating of the age of the Tarvisian breccia is not available, so the formation can only be delimited stratigraphically. Since it merges into the Val Gardena formation, it can be seen as its base. The timing of the Val Gardena formation is also quite uncertain, but it has recently been placed in the lower Wuchiapingium . The Tarvisio breccia is therefore at the beginning of the Wuchiapingium or at the exit of the Capitanium and is therefore around 260 million years old. How much time the shift gap to the underlying Goggau formation represents cannot be estimated.

distribution

The Trögener Bach leads, among other things, debris from Tarvisio Breccia, seen in the foreground

The distribution area of ​​the Tarvisio breccia extends from Sexten in the west over the Carnic Alps and the Karawanken to Slovenia in the east. The occurrences in detail:

Individual evidence

  1. ↑ Werner Buggisch, Erik Fluegel, Friedrich Leitz, Gerd-Friedrich Tietz: The facial and palaeogeographical development in the Permian of the Carnic Alps and in the peripheral areas . In: Geologische Rundschau . tape 65 . Stuttgart 1976, p. 649-691 .
  2. ^ Karl Krainer: The Permian in Carinthia . In: Carinthia II . 183./103. Vintage. Klagenfurt 1993, p. 133–180 ( PDF on ZOBODAT ).
  3. ^ 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 .
  4. ^ Corrado Venturini: Evoluzione geologica delle Alpi Carniche - un viaggio attraverso il tempo . Publicazione n.48. Edizioni del Museo Friulano di storia naturale, Udine 2006.
  5. ↑ Marco Avanzini, Massimo Bernardi, Umberto Nicosia Avanzani: The Permo-Triassic tetrapod faunal diversity in the Italian Southern Alps . Ed .: Imran Ahmad Dar, Mithas Ahmad Dar, Earth and Environmental Sciences. Tech. Rijeka 2011, p. 591-608 .

Coordinates: 46 ° 30 ′ 49 ″  N , 13 ° 36 ′ 41 ″  E