Rocky slope on Lochbachstrasse

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Rock wall on Lochbachstrasse

The rocky slope on Lochbachstrasse is a geotope south of Obermaiselstein in the Oberallgäu district . Over a length of 200 meters not far from Kreisstraße OA 5 rock units from the Lower to Upper Cretaceous of the Helveticum are exposed .

Banked Schrattenkalk

geology

In the course of the Alpweg Lochbachtal , which is closed to public traffic, the Cretan layer sequence of the Helvetic ceiling is cut into a rock face up to 25 m high . The profile with the rock layers dipping south at an average of 30 degrees forms the south wing of the Schwarzenberg anticline . The oldest rocks are located at the beginning of Lochbachstrasse and are formed from the gray, banked, fossil debris-bearing Schrattenkalk limestone of the Lower Cretaceous, which is also exposed further south in the Breitachklamm and in the Helvetikum outcrop on Breitachstrasse . The Drusberg Formation below was not developed in the course of the profile, but the marls at the base of the profile indicate the border area.

By microfacies studies have shown that in the mid to upper parts of the Schrattenkalkes also reef formations - bioherms and biostromes are stored, which have a diameter up to 50 meters -. The stored fossils show that the reefs were deposited in a shallow area of ​​the sea in calm water. A: A total of three Biostrom horizons in the profile were detected oysters - coral - stromatoporoids , -Biostrom a coral-stromatoporoids bioelectricity and a rudists -Biostrom. The mussels lived as first settlers on the sandy bottoms in shallow water and formed hard grounds, which were then overgrown by the corals.

In parts, thin, clastic , terrestrial deposits are embedded in the Schrattenkalke . The Schrattenkalk Formation in this outcrop has an average thickness of 90 m.

The Schrattenkalke are discordantly overlaid in the course of the road by a glauconite-bearing sandstone sequence of the Garschella formation. The base of the Garschella sandstone is formed by a thin conglomerate processing horizon in which phosphorite nodules are embedded in parts . In the further course of the profile, the Garschella sandstones are overlaid by the marl stones of the Upper Cretaceous Amden strata .

The stratiform sequences exposed here, which were deposited in a predominantly flat sea on the shelf on the southern edge of the European continental plate, cover a period of around 35 million years - from the Aptium to the Coniacium . The tectonic deformation and thrusting of the Helveticum onto the northern Alpine foothills began in the early Tertiary .

The geotope rock slope on Lochbachstrasse has been classified by the Bavarian State Office for the Environment as a geoscientifically valuable geotope (geotope no. 780A004), with a suitability as a geotouristic object. Apart from microfacial and tectonic differences, the profile shows similarities with the Helvetikum profile on Breitachstrasse .

See also

Individual evidence

  1. ↑ Herbert Scholz: Bioherme and Biostrome in the Allgäu Schrattenkalk (Helvetikum, Lower Cretaceous) . In: Yearbook of the Federal Geological Institute . tape 127 , volume 3. Vienna 1984, p. 471-499 .
  2. ↑ a b Geotope data sheet of the Bavarian State Office for the Environment: Geotope no. 780A004 Rock slope on Lochbachstrasse , accessed on February 7, 2016
  3. ^ A b Ulrich Lagally, Stefan Glaser, Elisabeth Jobe, Georg Loth, Andreas Murr, Hubert Schmid, Wolfgang Schmid, Klaus Schwerd, Stephan Sieblitz and Ulrich Teipel: Geotope in Schwaben . In: Bavarian State Office for the Environment (Ed.): Earth science contributions to nature conservation . tape 7 . Augsburg 2009, ISBN 978-3-936385-34-2 , pp. 160 .

literature

  • Dieter Richter : Allgäu Alps . - Geological Guide Collection 77, Stuttgart 1984
  • Herbert Scholz: Paleontology, development and distribution of the Bioherme and Biostromes in the Allgäu Schrattenkalk (Helvetikum, Lower Cretaceous) . Dissertation, Technical University of Munich, Munich 1979, 133 pp.
  • Herbert Scholz: Bioherme and Biostrome in the Allgäu Schrattenkalk (Helvetikum, Lower Cretaceous) . Yearbook of the Federal Geological Institute, Volume 127, Issue 3, Vienna 1984, pp. 471–499
  • W. Zacher: The Helvetic between the Rhine and Iller (Allgäu-Vorarlberg) . Geotectonic research, volume 44, Stuttgart 1973, pp. 1-74

Web links

Commons : Geotop Lochbachstraße  - Collection of images, videos and audio files

Coordinates: 47 ° 25 ′ 45.3 "  N , 10 ° 14 ′ 14.4"  E