Cement marl bowl

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A cement marl bowl is an irregular hollow as a result of the different weathering resistance of mass limestone and embedded, banky marl limestone . The mass limestones were deposited from algae sponge reefs in the White Jura (160 to 150 million years (Ma)). Their erosion relics , the cement marl bowls, still form morphologically distinctive terrain forms in the Swabian Alb .

Demarcation

Cement marl bowls are to be distinguished from the karst tubs of the Swabian Alb, which may appear morphologically similar, but are rather smaller and, as a phenomenon of advanced karstification, extremely much younger (at most Pleistocene age, i.e. younger than 2.6 million years).

genesis

Block diagram of cement marl bowls, originated in the upper Jurassic period

In the upper section of the White Jura, mainly from the lying bank limestone formation (formerly White Jura sita 2 or ki 5), the formation of reefs took place on almost the entire Alb plateau. In the then, flat, tropical- marine facies area, mainly conical reef complexes developed and in between irregular hollow shapes with mostly flat bottom. The morphology of the Alb plateau is still determined today in the northern part ( Kuppenalb ) by these mass limestone rocks . In the course of the further history of the earth, gray cement marl sediments were deposited in the hollow forms , but in banky layers . The marly sediments were softer and more compact than the harder reef limestone. The "thickness of the cement marl formation was measured in the center of some cement marl bowls up to 170 meters."

For the area of ​​the Eastern Alb and the Eastern Middle Alb, from the western edge of the Nördlinger- Ries up to and including the Münsinger Zementmergelschüssel, the previous formations of the lying bank limestone and the cement marl are combined into a single formation, the “Mergelstetten Formation”. In the rest of the Swabian Alb area, the formation names used since then are still used.

Erosion by tectonic influences

Cement Marble Bowls, Swabian Alb . South of the cliff line morphologically more pronounced, as yet tertiary layers ablate were

Since the Alb plateau was exposed to more severe erosion , weathering and other erosion processes in the higher areas due to uplift and tilting (from northwest to southeast and layer traps to S) , the Alb surface is preserved in the direction of the layer falling to S into increasingly younger stratigraphic areas. On the Kuppenalb and the witness mountains of the Middle Alb ( Kornbühl , Monkberg, Köbele and Aufberg) the mass limestone reefs have been exposed, on the layered alb already eroded. The younger strata formations ( hanging bank limestone formation , cement marl formation, lying bank limestone formation ) are therefore hardly present north of the cliff line . This means that the cement marl bowls are often further eroded morphologically.

Erosion through time

In the middle part of the Alb , as well as on almost the entire Eastern Alb, there are still numerous bowls of cement marl. They are partly north and partly south of the Miocene cliff line - so partly also on the Kuppenalb. In places they are covered (protected) by limestone hanging over them .

In today's morphology of the Alb plateau, however, the cement marls are completely or “more or less” cleared out in almost all cement marl bowls. If the (cement) marl layers are not completely removed, the water-retaining properties of the marl have a beneficial effect on the otherwise arid agriculture of the Alb.

Occurrence

GeoMap Middle Swabian Alb . Gammertingen cement marl bowl marked in green

Similar to the reef limestone from the time of the Upper Jurassic of the Alb are also those from Switzerland, France, Spain, Poland and Romania. Despite the widespread distribution, it has not yet been possible to find recent sponge reefs that could be compared with the fossils from the Jurassic period .

Marl as clayey mixtures with a chalk content of 85% to 10% can be found in all karst areas worldwide. Mass limestone formations are predominant in the northern Swabian Alb as Kuppenalb. Cement marl bowls as relics of cleared marl banks between mass limestone, on the other hand, only occur on the southern areas of the Franconian Alb and predominantly on the southern Swabian Alb. Cement marl bowls on the Swabian East Alb are particularly large and still determine the geomorphology today .

Several bowls lie between Heidenheim and Sontheim, north and south of the cliff line and on both sides of the Brenz valley. North of the cliff line are the bowls of Böhmenkirch -Söhnstetten (sheet 7325), Härtsfeld (W Neresheim ) and the Hörvelsinger bowl (also around Langenau ).

The large Mergelstetter bowl ( type locality Mergelstetten ), which is rare because it has hardly been cleared, has a vertical thickness of 120 m. At its eastern edge - on the east side of the Brenz - there is a quarry that has been designated as a geotope and opens up the lower marl deposit, intermediate limestone and upper marl deposit.

The Lauchert still flows directly through the two bowls of Gammertingen and Jungnau . The basin of Gammertingen with a diameter of approx. 2 km has largely been cleared, but outlines are marked in the geological map, sheet 7721 Gammertingen. In the southwest of Gammertingen the cement marl rock is still pending. Here it was found again and again in building pits of residential buildings and in the cut of the Gammertingen- Neufra railway line at the station “Gammertingen-Europastr.” It is still open. In the marly sediments, important silicified fossils were found for dating , particularly sea ​​urchin spines and sponge needles , but no key fossils .

The bowl around the Blauen nature reserve (north of the Nollhof- Winterlingen road ) extends on both sides of the western break zone of the Lauchertgraben .

There are also two large bowls on the Kuppenalb near Münsingen and Gächingen (St. Johann) (geological map, sheet 7522 Urach ). The Münsinger bowl extends over 12 km². It is surrounded by a soaring wreath of mass limestone mountains and only partially cleared.

Cleared cement marl bowl; cut by the Danube
Danube valley near Bronnen Castle , behind: cement marl bowl

A beautiful example, clearly visible from the button maker rock , is the cleared bowl at Bronnen Castle on the Upper Danube between Fridingen and Beuron Abbey . Immediately on the steep edge of the valley, the strong late Miocene / Pliocene erosion of the Danube cut the funnel-shaped bowl. The two mass limestone rocks on the high edge of the valley - remnants of sponge reefs - depict the relief of the seabed of the Jura at that time.

See also

credentials

  1. ↑ Eberle (2007), front cover, inside
  2. ↑ Karst tubs (Uvala) are still considerably larger than sinkholes . Some sinkholes that have grown together to form karst tubs are larger than 2x1.2km
  3. ↑ According to recent research, about 70% of the reefs ( mass limestone ) are "particle limestone facies". “ Mud mounds ” of sponges , stromatolites and other faunal elements interlocked in different microfacial areas within the mass limestone, but also at its edges; Koch (2011), p. 78f
  4. ↑ Gwinner (1968), p. 37; Dietl & Schweigert (2001), p. 25ff
  5. ↑ Villinger (2008), p. 12
  6. ↑ The " Mergelstetten-Formation " reached almost nowhere on the Alb as continuous flatness as the other banky layers.
  7. ↑ Geyer & Gwinner (2011), p. 288
  8. ^ German Stratigraphic Commission, (STD 2002); Schweigert & Franz (2003)
  9. ↑ Gwinner (1968), p. 37
  10. ↑ On the southern part of the area Alb of the Middle and Eastern Alb tertiary sediments have only been removed so that the removal of the bowl morphologies may be less. In addition, even today larger tertiary residual areas (including Tautschbuch , Landgericht, Hochsträß ) cover bowls and the White Jura on the southern Alb
  11. ↑ Schweigert (1998)
  12. ↑ Geotopes North Württemberg (2007)
  13. ↑ Gwinner (1962), p. 172; also: Erl. GeoKarte 7721 Gammertingen (1993) p. 16
  14. ↑ Gwinner (1962). In this so-called Nollhof facies of the bowl, there are also no key fossils
  15. ↑ Gwinner (1968), p. 37
  16. ↑ Schweigert (1998) with photo; also Gwinner (1968), p. 37

literature

  • Gwinner (1962), Gwinner, MP, Geology of the White Jura of the Alb plateau (Württemberg), in: Neues Jahrb. Für Geol. U. Paleont. Abhandl., 115, Stuttgart 1962
  • Gwinner (1968), Gwinner, MP, Palaeogeography + Landscape Development in the White (Upper) Jura of the Swabian Alb, in: Geologische Rundschau, 58, Heidelberg 1968
  • GeoKarte Gammertingen (1974), Geological map of Baden-Württemberg 1: 25000, 7721 Gammertingen, Hrgb: Geological State Office Baden-Württemberg, Freiburg 1974
  • Erl. GeoMap 7721 Gammertingen (1993), Geological map 1: 25000 of Baden-Württemberg, explanations for sheet 7721 Gammertingen, Hrgb: Geological State Office Baden-Württemberg, Freiburg 1993
  • Schweigert (1998): Schweigert, G., Reefs in the White Jura of the Swabian Alb, in: Profil, 13, 1998, pp. 49–55
  • Dietl & Schweigert (2001), Dietl., G & Schweigert, G., In the realm of the sea angels, the Nusplinger Plattenkalk and its fossils, Munich 2001
  • German Stratigraphic Commission, (STD 2002): see web links
  • Geotopes North Württ. (2002), Geotopes in the Stuttgart administrative region, profile, publisher: State Institute for the Environment, Measurements and Nature Conservation Baden-Württemberg (LUBW), Karlsruhe 2002
  • Schweigert & Franz (2003), Schweigert, G. & Franz, M. The Mergelstetten Formation, a new rock unit in the Upper Jura of the eastern to central Swabian Alb, annual books and communications of the Upper Rhine Geological Association, Stuttgart 2003
  • Eberle (2007): Eberle, J .; Eitel, B .; Blümel, WD; Wittmann, S. Germany's South from the Middle Ages to the Present, Heidelberg 2007
  • Geotopes in the four administrative districts of Baden-Württemberg, protected area directory, full texts, LfU, Baden-Württemberg, 2000, 2003, 2005, 2007. See web links
  • Villinger (2008): Villinger, E., The Swabian Alb - a geological picture book landscape, in: Rosendahl (2008)
  • Rosendahl (2008): Rosendahl, W., et al., (Hrgb), Walks in der Erdgeschichte (18), Schwäbische Alb München 2008
  • Geyer & Gwinner (2011), Geology of Baden-Württemberg, 5th, completely revised edition, Stuttgart 2011
  • Koch (2011), Koch, R., Dolomite and Dolomite Decay in the Malm of Southern Germany - Distribution, Educational Models, Dolomite Karst; in: Laichinger Höhlenfreund, 46, Laichingen 2011

Web links