Weyerer arches

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Sketch of the Weyerer arches

The Weyerer arches are the most important tectonic transverse structure in the Northern Limestone Alps , in the border area between Upper Austria , Lower Austria and Styria . The east-west running chains of the northern Limestone Alps are bent in a southerly direction in this area and pushed onto the units to the west of it.

Location and description

The Weyerer arches, named after the town of Weyer , start south of Waidhofen an der Ybbs and describe an approximately 40 km long arch over Großraming and run out in a south-southeast direction near St. Gallen in Styria. The ceilings and folds coming from the west are submerged under the eastern arches, which are turned counterclockwise and increasingly thinned towards the south. The sediments of the Gosau group lying on the eastern edge of the Reichraminger ceiling are also submerged under the eastern wing. The arching is so distinctive that it can also be clearly seen on satellite images.

The tectonic nappes and faults west and east of the Weyerer Arches can be largely parallelized, even if they do not have the same names for the most part. The postponement of the Mollner line to the west corresponds to the arches of the Weyer line to the east of it. The Ternberg ceiling west of the Weyerer arches corresponds to the Frankenfels ceiling in the arches and east of it. The Reichraminger ceiling has its counterpart in the arches and to the east of it in the Lunzer ceiling . Only the name Cenoman rim scale is the same on this side and on the other side of the arches. However, there are lithological differences. According to Alexander Tollmann , this transition in lithology from the rigid Wetterstein limestone block of the North Tyrolean facies in the west to the more plastic Lunz facies with, among other things, Reiflinger limestone , Lunz strata and Opponitz strata of the Middle and Upper Triassic in the east could also cause the tearing when the arches were formed to have.

In the eastern part of the northern Limestone Alps, Tollmann mentions two other, similar but much smaller arches: The Reinsberg arches southeast of Gresten in southwest Lower Austria and in Micheldorfer Bucht in southeast Upper Austria.

Age of arcing

Since the twisted wing has passed over Gosau sediments , which here extend up to the Paleocene, the arching must be more recent. On the basis of structural geological analyzes, the age can be narrowed down to the Eocene to Miocene range, i.e. to the time range between 55.8 and 5.3 million years.

Research history

Until today there is no clear clarity about the origin of the Weyerer arches. However, many geologists have dealt with the striking arch structure and its formation. The geologist Georg Geyer , from whom the first geological map of the area around Weyer originates, assumed that the Weyerer arches were created autochthonously at the beginning of the 20th century. First he assumed suitably shaped sediment troughs in the crystalline subsoil, later he suspected a fjord-like indentation as the cause of the arch structure. Otto Ampferer saw a strain in an east-west direction and subsequent compression as the cause of the arches. Other geologists, on the other hand, suspected an underground spur of the Bohemian Massif , on which the limestone Alps dammed up. The argument for this thesis was the granite of the monument to Leopold von Buch in the Pechgraben near Großraming. However, these granite rocks turned out to be rootless miners. The Viennese geologist Alexander Tollmann saw the Weyerer arches as the result of a space problem during the north thrust of the Northern Limestone Alps at the transition from the convex Alpine arch to the concave arch of the Carpathians . The rocks were pushed from the larger inner concave segment into the smaller outer segment and thus had to evade.

Individual evidence

  1. ↑ Alexander Tollmann: Tectonic map of the Northern Limestone Alps. In: Communications from the Geological Society in Vienna. Vol. 59, No. 2, 1966, ISSN  0072-1123 , pp. 231-253 .
  2. ↑ Christoph Janda: Geological-facial studies in the Lunzer ceiling southwest of Weyer (Upper Austria). Vienna 2000, p. 10 ff., P. 16, (Vienna, University, diploma thesis, 2000; digital version (PDF; 4.96 MB) ).
  3. ↑ Benno Plöchinger : The Northern Limestone Alps. In: Rudolf Oberhauser (Red.): The geological structure of Austria. Springer, Wien et al. 1980, ISBN 3-211-81556-2 , pp. 218–264, here p. 254 ( limited preview in the Google book search).
  4. ↑ Benno Plöchinger: To clarify the geological situation at the southern end of the Weyerer arches (Styria). In: Yearbook of the Federal Geological Institute. Vol. 130, No. 1, 1987, ISSN  0016-7800 , pp. 93-108, ( digital version (PDF; 5.1 MB) ).
  5. ↑ a b Alexander Tollmann: Basic principles of alpine tectonics. A system analysis using the example of the Northern Limestone Alps (= monograph of the Northern Limestone Alps. 1). Franz Deuticke, Vienna 1973, ISBN 3-7005-4398-0 , p. 352 ff.
  6. ↑ Christoph Janda: Geological-facial studies in the Lunzer ceiling southwest of Weyer (Upper Austria). Vienna 2000, p. 85, (Vienna, University, diploma thesis, 2000; digital version (PDF; 4.96 MB) ).
  7. ↑ Christoph Janda: Geological-facial studies in the Lunzer ceiling southwest of Weyer (Upper Austria). Vienna 2000, p. 10 ff., (Vienna, University, diploma thesis, 2000; digitized version (PDF; 4.96 MB) ).

Coordinates: 47 ° 49 ′ 7.3 ″  N , 14 ° 34 ′ 19.2 ″  E