Tufa

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Moss, encrusted with freshly precipitated lime, continues to grow on this base

Tufa , also Quellkalk , Quelltuff called or Bachtuff, is a young, porous, secondary sediment . It is a secondary rock because primary calcareous sediments of an geological age were re-sedimented after chemical carbonic acid - solution weathering and precipitation.

In Europe, this type of limestone occurs in favorable circumstances in karst areas of the humid, temperate warm climate zone . Some occurrences on and on the edge of the Swabian and Franconian Alb and in the Alpine foothills are particularly known and investigated in Germany .

Demarcation

The Seeburg power plant (built in 1920) shows with its joint design and stone-sightedness a typical appearance of houses in the area of Seeburg , in which the Seeburg limestone tuff was broken up and built.

Limestone tuffs are "highly porous to cavernous and alternately solidified, non-marine carbonate rocks". Conceptual confusion arises when the term lime sinter and its sub-terms tuff and travertine are used synonymously.

Limestone tuffs have no clear stratification, show partially uniform surfaces, partially also have large cavities and partially contain fossilized plants and small animals such as snails. Limestone tuffs sometimes form cauliflower-like surface structures and are not banded. They are often loosened and only partially solidified, so they cannot be polished. In break damp condition they can be shaped by hand saws or knives and cure it.

In contrast, travertines are clearly layered, firm and polishable. If they are sawn against their storage direction, their cut shows clear banding. In the natural stone processing trade in Germany, a tuff of lime is called travertine, provided it is firm and can be polished. It cannot be shaped with a knife. One such natural stone is Gauingen travertine .

There is often misunderstanding that there are also volcanic tuffs . In contrast to the limestone tuffs, these are weakly consolidated volcanic ashes . All of the above rocks are soft rocks .

Before the emergence

Karstification

During karstification , in addition to processes of physical weathering, primarily chemical processes of carbonic acid weathering take place. Carbonated water in the brittle limestone ( limestone , chalk , marble and other calcium carbonates) of a more or less developed karst system absorbs the carbonates in solution until they are saturated. If the dissolved lime transported under different ambient conditions, it can be deposited again through chemical precipitation . The two processes can be viewed as two different states of equilibrium of a reversible chemical process (cf. calcium hydrogen carbonate ).

Precipitation of the dissolved lime

Interactions between karst water and carbon dioxide - underground or when it emerges back to the surface - can trigger the process of lime precipitation. Especially in karst caves and after karst springs, considerable amounts of lime can sediment because the dissolved lime precipitates again under various chemical and physical constellations of conditions. The products of this secondary sedimentation are counted as sintering in the geologies .

Formation of tufa

Extensive soaking and moss assimilation from the karst water favor precipitation and deposition

The sedimentation of lime (CaCO 3 ) as tufa occurs primarily behind cold layer springs in the karst. Such deposits have existed in some karst areas of the humid, temperate warm climate zone since the last warm period (see Worm Ice Age ) and are still present today. Whether it can lead to precipitation of limestone from karst water and in what amounts generally depends on the climatic and geological conditions, especially on other physical and chemical constellations of conditions that must be regional or local. The most favorable climatic conditions existed during the roughly two thousand years of the post-glacial Atlantic . During this time (approx. 8000–6000 years ago) the average temperatures in Central Europe were approx. 2 degrees higher than today, and there was more rain at that time. If these general requirements are met, the necessary conditions for failure also include the following factors:

  • a relatively small discharge of the respective source,
  • a relatively large evaporation surface,
  • a favorable corridor of water temperatures,
  • a change in the pressure conditions and
  • certain ion concentrations.

If karst water flows over moss carpets , algae carpets or colonies of cyanobacteria , a larger amount of lime can be precipitated if the organisms remove carbon dioxide from the karst water for their assimilation ( photosynthesis ). Cyanobacteria, formerly classified as blue-green algae , like mosses and algae, have the ability to photosynthesize, i.e. to absorb CO 2. By removing carbon dioxide, the pH value of the water rises and the solubility of lime decreases, the lime precipitates. The lime sediments can grow at rates of 0.01 mm / year for inorganic and up to 20 mm / year for organically induced precipitation.

The precipitated lime is deposited as a fine crystalline crust around all relatively dormant small material (sand, stones, twigs, leaves, ferns, mosses, algae slime). Overgrowth creates structures that grow upwards and forwards or cushions on small waterfalls or steps in brook terraces. Mosses grow fresh beyond their encrusted part and act like small traps and form a supporting structure. In this way, larger, fragile pendants ("noses") can also be created. Biotic contamination from algae and bacteria form relatively fine structures. The structures are more porous and lighter if mosses could withstand the flow energy. This tufa is often still moist and has a crumbly consistency. In the best of times, after a few centuries it had grown into mighty structures, so-called " Tufa limestone bars " (see below: "Special appearance factors").

Differentiation of the various names for precipitated lime

The solid sediments are often referred to as calcareous sinter, travertine and tufa, even if they have a similar morphology . the terms are even used synonymously. The more general term sinter , on the other hand, also subsumes those materials that are not counted among the geologically determined phenomena (e.g. wall sinter and boiler stone), or those that are formed with the substantial participation of other elements. (e.g. silica or sulfur sinter). In addition to the designation of the geological phenomena in the Karst, there are also regional, country-specific or language-related uses that have historically resulted from local occurrences, such as the regional name " Duckstein " in eastern Lower Saxony. The term tuff limestone is useful for a more precise definition (although “tuff” as a volcanic phenomenon is rather misleading). It is still in use in German-speaking countries and in German-language literature - probably also because of the relatively frequent occurrence and the good scientific mapping of this karst phenomenon. See the scientific and environmental mapping as geotopes . Uniform designation has not yet established itself in geologies either.

Tufa, travertine and sintered lime can be differentiated according to their decreasing proportion of free and bound water. They can be further differentiated according to their density or porosity (due to foreign bodies) and according to their strength (due to drying out and internal pressure).

Lime sinter can be viewed as a substance of high purity and / or dense stratification, like the stalactites in caves. Travertine is the sediment that remains more or less porous due to abiotic, possibly also biotic "impurities" and is changed by constant stratification and thus increasing intrinsic pressure and decreasing moisture. Such processes are called diagenesis .

Towers at Mono Lake , Tufa ( California ) - no tufa

en: Tufa , the generic term commonly used in America, which is also often translated as tufa, is not tuff! The z. B. In Mono Lake in the bank areas "Tufa columns" are towers that were created underground in alkaline water (salty water) by mixing with Ca-rich spring water (thermogenic Ca sources), are a completely different material than described here .

After California permanently withdrew large amounts of water from the entire country up to and including the Mono Lake Basin for drinking water, the water level of Mono Lake sank so much that the towers protruded from it. The English scientist A. Pentecost, an expert on all carbonate-containing sediments worldwide, says about Mono Lake tufa: “This formation does not arise from evaporated carbon dioxide (CO 2 ); strictly speaking, such deposits are not travertines, but are classified as epigenic forms because of their similarity. "

Petrified tufa: building material

Lower castle gate, Hohentübingen Castle , tufa-lime cuboid from 1606 (probably either Gönninger Kalktuff or Honauer Kalktuff)
400 year old tufa bricks

Tufa in the hardened state has been used as a high-quality building material for centuries and well into the 20th century: it is light, remains weather-resistant, abrasion-resistant, is good insulating and fire-resistant. The extraction in the quarry was technically easy - in a relatively fresh condition (freshly broken), porous cuboids can also be easily sawn and processed. They then harden further. Numerous abandoned quarries and the local development prove its local economic importance. As a locally occurring building block, tufa-lime was used almost as the only building material in many representative buildings, such as the Lower Castle Gate in Baden-Württemberg (built in 1606) and in Bavaria for the Burghauser Castle from the 13th century on, with sufficient material-specific load capacity and weather resistance ; Most of the churches, monasteries and older buildings in the town of Burghausen and many similar towns in the foothills of the Alps are also made of tufa. In other buildings such as the Ulm Minster and the old Stuttgart Castle , tufa-lime was used in small amounts, in Stuttgart in the 20th century during repair work.

Occurrence

"Eselstrog" at the foot of the Ludolfsklinge near Mosbach -Diedesheim on Bundesstrasse 37

In side valleys, valley fillings or amphitheater-like valley ends of the Albtrauf and the Franconian Alb, in the Eifel , the Alpine foothills, as well as in the Limestone Alps, there are fresh and old deposits of tufa, the older ones already completely hardened to rock. A recent tufa deposits exist at the entrance to the Ludolfsklinge near Diedesheim am Neckar .

On occurrences (e.g. in France, in England, in the Dinaric Alps or in Indiana (USA)) or spring limes of completely different conditions and climatic zones (e.g. large limestone deposits from thermal springs in Turkey and the Yellowstone National Park)

Special manifestations

Tufa ingots

At the foot of the hillside of the Albtrauf, many streams have created tufa-lime bars. On all seven slope-side streams that flow into the upper Fils between Wiesensteig and Geislingen an der Steige there are one or more extensive old, partly still active limestone deposits. The multiple limestone bars of the Echaz , the Wiesaz (former Gönninger quarries) and the Rohrbach near Geislingen / Steige are outstanding . The first and largest of seven tufa limestone bars behind the Echaz spring is the largest bar in the Swabian and Franconian Jura, with an area of ​​900 × 400 m and a thickness of at least 24 m. In the upper Ermstal (south of Bad Urach ) there are seven considerable tufa limestone bars, the largest of which originally blocked the entire width of the valley near Seeburg and thus dammed the Fischbach into a so-called bottomless lake (until 1821).

The proximity of the high-quality building material of such tufa-lime bars was certainly a reason for the preferred settlement there. In some cases the places (Honau, Seeburg) and cities (old town of Geislingen / Steige) grew directly on a bar. The morphology of the bars is easy to see on exposed slopes and abandoned quarries. The sediments reach thicknesses between 5 m and 40 m.

Tufa noses, tufa cushion

Limestone nose, side view, Gütersteiner waterfall. A gully on the nose ridge sprinkles the moss coating

These extraordinary structures rarely arise and only when tufa-lime moss cushions form in the running water on steep slopes, which can grow into "noses" upwards and forwards if there is increased lime precipitation. If, on the other hand, the gradient is not steep, the development of tufa dominates to the front and the " stone gutters " are created. Interesting geotopes are the Dreimühlen-Wasserfall in the Eifel, the Gütersteiner waterfall on the Albtrauf of the Maisental valley southwest of Bad Urach and near the Bavarian Isar the Growing Rocks of Landau / Usterling . Since the noses are extremely porous, made of moist, unhardened lime and therefore fragile, the nose of the Neidlingen waterfall , for example, collapsed half a century ago and has not yet grown up again. Large terraced rubble heaps, which are covered with old and fresh tufa and moss cushions, lie below the noses of the waterfalls ( Urach waterfall and the Güterstein waterfall 1.5 km to the north). They testify to repeated breaks in the nose. In the Mühltal Seeburgs, the headwaters of the Erms, six huge petrified limestone slopes (in one case a typical limestone tuff "nose") are preserved on the rubble of the northern flank of the Kerbtal (the backward erosion also affects the Albtrauf ) over a distance of only 600 m ), which arose when in an earlier karst with higher precipitation, less fissured springs emerged in layers above the valley floor.

Stone gutters

The stone channel of Erasbach

The geotopes of the stone gutters are rare . Narrow karst water rivulets meander down behind small springs on gentle slopes - following all the unevenness of the terrain. At the edge of the rivulet, the mosses grow, which in the manner described, depending on the flow speed of the rivulet water, develop their limestone frameworks into saddle-shaped dams more forwards than upwards. The gully grows upwards in a dense sinter layer, the irrigation of the sides allows the mosses to grow into limestone tuff moss structures. Depending on the slope and the accumulating lime sediment, loft beds up to 500 cm and lengths up to 600 m are observed. Their development is not continuous and not certain. Some specimens are no longer authentic due to irresponsible interference.

During an environmental mapping in Bavaria, around 20 stone gullies were recorded. The most important stone channel in Germany is the approx. 5000 year old, 40 m long and approx. 5.5 m high "growing rock of Usterling" ; There, in the nearby village church of St. Johannes von Usterling, there is also a Gothic picture depicting the baptism of Christ near this channel, a curiosity from the cultural and historical point of view. A very important natural example is the approximately 80-meter-long stone channel near Erasbach . The channel follows the undulating, slightly inclined terrain on an old, flat limestone tufa deposit in the loosened mixed forest. In Baden-Württemberg there is an inconspicuous stone channel near Lenningen (Swabian Alb, Esslingen district ) and below a former impact slope of the Jagst near Krautheim ( Hohenlohe district ).

View terraces

Fresh moss cushions over old tufa. The CO 2 consumption of the moss increases the lime precipitation enormously. Gütersteiner waterfall

Beneath the limestone tuff noses, on their rubble heaps and on the low-flow upper reaches of brooks in the Franconian and Swabian Alps and in the entire foothills of the Alps, there are numerous, sometimes unspectacular small terraces made of tufa in a staircase-like arrangement. The terraces of the Lillach in Franconian Switzerland are an imposing, but not natural geotope . There are distinct brook terraces around Seeburg (near the Erms source), above Bad Ditzenbach (on the tributary Ditz der Fils) and on the Zwiefalter Ach after the Wimsener Höhle . The Plitvice Lakes in Croatia were formed from a number of relatively large cascades with walls made of tufa , similar to the Band-e-Amir chain of lakes in Afghanistan. The pure white sintered terraces of Pamukkale , Turkey are also world-famous .

Primary caves / tuff caves

When pouring overlay upwards and forwards or when overhangs break off, more or less large cavities up to (semi) caves arise in larger limestone tufa deposits. If the cavities in the deposits are largely or completely developed, one speaks of so-called primary caves or tuff caves - primarily because they were formed at the same time as the rock. Since they were not created along the course of a waterway, they are usually only discovered when a limestone deposit breaks, it is dismantled or if something else is interfered with, as in the case of the Olga Cave .

Tufa formation with caves at the source of the Dard (French Jura)

Natural stone types

A relatively dense and roughly sanded sample board of Gönninger limestone tuff (size approx. 25 × 18 cm)

See also

literature

  • Alfons Baier: The "stone channel" on the mountain south of Erasbach / Opf. An investigation into the hydrogeology and chemistry of the Shallow Karst . In: Geologische Blätter NO-Bayerns , Vol. 52 (2002), Issue 1/4, pp. 139–194, 17 figs., 2 tab., 3 tab., ISSN  0016-7797 (cf. also the link Seichter Karst ).
  • Norbert Frank, Margarethe Braum, Ulrich Hambach, Augusto Mangini, Günther A. Wagner: Warm Period Growth of Travertine during the Last Interglacial in Southern Germany (PDF; 325 kB) . In: Quaternary Research. A interdisciplinary research , Vol. 54 (2000), pp. 38-48, ISSN  0033-5894 .
  • Allen Pentecost: Travertines. Springer-Verlag, Berlin Heidelberg 2005, 445 pages, (English)
  • Wilfried Rosendahl, Dorothee Sahm-Stotz (eds.): “Bottomless Lake” and Schickhardt-Stollen. Natural and cultural events in the limestone tuff of Seeberg near Bad Urach . Staatsanzeiger-Verlag, Stuttgart 2005, ISBN 3-929981-57-2 .
  • Rainer Schreg: Water in the Karst. Medieval hydraulic engineering and the interaction between humans and the environment . In: Communications of the German Society for Archeology of the Middle Ages and the Modern Times, Vol. 21 (2009), pp. 17–30. doi: 10.11588 / dgamn.2009.1.17287

Web links

Commons : Kalktuff  - album with pictures, videos and audio files
Commons : Steinerne Rinne (Krautheim)  - Collection of images

Individual evidence

  1. ↑ a b Wolfgang Werner, Roman Koch: Kalktuffe . In: Natural stone from Baden-Württemberg - occurrence, procurement and use . P. 317, ed. State Office for Geology, Raw Materials and Mining. Rüsselsheim 2013, ISBN 978-3-00-041100-7 .
  2. ↑ See link "Hydrogeology ..."
  3. ↑ Stephan Kempe, Wilfried Rosendahl (Ed.): Höhlen. Hidden worlds . Scientific Book Society, 2008, p. 39 ff
  4. ↑ see literature "Warm Period Growth ..."
  5. ↑ The Karst + Cave Glossaries of UNESCO from 1972 and EPA, Washington, DC from 2002 (links UNESCO and EPA) have only been able to systematize the references between names within a language and between languages.
  6. ^ Allen Pentecost, see literature
  7. ↑ Travertines are chosen as a generic term for all types of carbonate sediments. Tufa is not a "meteogenic", but a "thermogenic" product, Pentecost Travertine, p. 53.
  8. ↑ see literature, "Bodenloser See ...", p. 45ff
  9. ↑ See the link "Frankenalb, distribution of tufa in the northern Franconian Alb ..."
  10. ↑ Natural monuments in the administrative district of Karlsruhe . (PDF; 5.8 MB) 2nd edition. 2000. State Geological Institute for Environmental Protection Baden-Württemberg (LfU)
  11. ↑ See literature, "Bottomless Lake ..."
  12. ↑ Such views can be found on the Albtrauf in Seeburg, Honau / Lichtenstein, Gönningen. See link "Geotopes in the RGB Tübingen ..."
  13. ↑ 36 m in Seeburg, according to a geological study by Rosendahl / López Correa (2003); see literature, "Bottomless Lake ...", p. 22
  14. ↑ See link “Distribution of stone gutters in Bavaria” (Fränk. Alb and Alpenvorland).
  15. ↑ See link "The stone channel near Erasbach ..."
  16. ↑ See link "Geotopes in the RGB Stuttgart ..."