Kamenitza

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Kamenitzas are second order cart structures . They arise from solution weathering in karst rocks .

To the subject

The term Kamenitza is of Slavic origin (eg in the Slovenian kamenica , in Slovak and Czech kamenice ) extending from were derived (gravel, pebbles). In the early days of karst research, there was the wrong view that these bowl-like structures were caused by pebbles or boulders left on the limestone pavement, such as scour or glacier mills (this view was still held by Jovan Cvijić in 1924 , but is probably only a rare exception).

Kamenitzas, often in the real sense as Napfkarren or solution pans , English solution cups , solution basins , solution pans referred were scientifically processed for the first time by Jovan Cvijić 1924th He was followed by many other authors such as JF Smith and CC Albritton 1941, Alfred Bögli 1961, PW Williams 1966, DC Lowry and JN Jennings 1974. A recently published work is by Franco Cucchi,

Bowl carts are one of the possible explanations for cup stones , and are therefore also called sacrificial kettles .

description

Kamenitza or sacrificial cauldron in the lime near Alto de Brenas in Cantabria

Kamenitzas form on flat or only slightly sloping, sometimes slightly undulating rock surfaces in the karst. These are local depressions that are periodically moist or filled with water . The bowl-like basins are usually 10 to 40 inches wide and 1 to 10 inches deep. In rare cases, they can be up to 3 meters wide and 50 centimeters deep. Extreme shapes reach 6 meters in diameter, from the Paleocarst even an example with 7 meters is known. Their ground plan is usually circular to oval. Larger Kamenitzas often emerged from smaller basins that grew together.

Viewed in profile, a gently sloping, slightly convex slope usually leads from the edge to the flat ground. The edges can, however, also be vertical or inclined outwards and then often show a bead-like overhang. Circular to oval edges and rounded profiles usually characterize basins containing floors . However, the edges can also be embossed in a centimeter range by small, scallops , from which rounded grooves extend and run over the side slope to the flat floor. This grooved type is generally free from the ground, but can occasionally contain mosses and algae as well as rich flora and fauna in the coastal area.

Occurrence

Kamenitzas usually arise on limestone , on very lime-rich sandstones and on Dolomites , mostly on the mainland. On the coast they can be found in the intertidal area (splash water zone ).

Similar or analogous structures ( pseudo carts ) can be found on weathered granites and syenites , on basalts , on olivindolerites and on some sandstones (the Elbe sandstone may serve as an example ). The depressions can also sit on steeper parts in these rocks and contain soil and vegetation . Often they form groupings that are arranged like stairs.

So-called pseudokamenitzas occur in rhyolites and ignimbrites . Their formation is directly linked to bulbous, mafic concentrations in the volcanic rocks, which are more susceptible to solution corrosion and therefore weather out more quickly. In this case, the resulting round shapes are mapped out by the petrological texture of the rock.

Emergence

Kamenitzas in the Fier gorge near Lovagny

Kamenitzas or bowl carts are the result of superficial solution weathering , caused by unevenness or depressions in the rock, filling water. The extent to which organic, biological processes are involved is still controversial. Some authors still take the point of view of purely inorganic dissolution processes, others, however, that of a purely biochemical process linked to endolithic algae. The question of whether and to what extent Kamenitzas were formed under cover is also not completely clarified. Some researchers see them as half-covered geomorphological structures whose development began when they were still covered by shreds of earth and fragments of rock. This assumption is supported by the fact that Kamenitzas are very often found on smooth rock surfaces, the current undulations of which were inherited from a previously covered karst. Erosion and exposure of the protective soil then leads to the formation of Kamenitzas via static corrosion and dynamically to structures such as Gutter Carts and Groove Carts .

Solution corrosion on the sides of the structures usually occurs at a faster rate than it does downward. The limited vertical dissolution speed is explained by the insoluble residues such as rock flour, dust blown by the wind and organic compounds that have accumulated on the bottom of the bowls. An exception, however, are the cylindrical to conical solution cups in predominantly dolomitic rocks, the development of which progresses mainly towards the depths. This is explained by the increased, organic carbon dioxide production in an undersaturated solution near the ground. The solution cups are very similar in appearance to the sacrificial kettles and solution tubs in granitic rocks.

The explanation of the Kamenitzas covered with secondary grooved carts is problematic, since the creation of grooved carts is tied to flowing / moving water. Convection cells due to temperature differences , a Taylor-Görtler instability on the concave side slope or small waves generated by the wind may be generated in the stagnant basins .

Development scheme

Kamenitzas usually follow a development scheme that goes through the following phases:

  • Exposure of the surface and formation of the structure
  • growth
  • Demotion and disappearance

The static corrosion accentuates existing unevenness after the surface is exposed. Water can accumulate in them and then the corrosion process can continue in width, the structure grows. Often at this stage there is an overflow and the formation of a gutter, which will ultimately reach the ground level of the Kamenitza. During the widening and deepening of the gutter, the water level in the Kamenitza gradually lowers and a micro-notch is formed on the edge. This increases until the edge overhangs in a bead shape. The development ends when the edges collapse and the drainage channel becomes wider. The same thing happens if a crevice or crevice is encountered within the Kamenitza that allows the standing water to drain inwards.

The ground plan of the developing Kamenitzas is dependent on discontinuities (such as fissures, fractures, cracks, mineralized veins, etc.) in the rock. A more or less circular shape is only realized in very homogeneous rocks (such as micrites). Oval, elongated and elongated forms develop when fractures are present or when dominant or intersecting fissures are created (inhomogeneities in the rock structure thus control selective corrosion ). A higher porosity arises in fracture zones , which in turn results in an increased permeability of the corrosive solution. This means that the lateral erosion progresses faster along the direction of these areas. Another factor that cannot be overlooked is the depth of penetration of the discontinuity surfaces mentioned. The structure of the respective rock thus has a very large influence on the final design of the Kamenitzas; complex, sometimes multi-phase shapes can result.

Corrosion rates

Experimental studies on the rate of evolution of Kamenitzas are rare. Measurements in the classical karst area by F. Cucchi et al. (1990) showed a subsidence rate of the soil of 0.02 to 0.03 mm / year - ie it takes 1670 to 2500 years to form a 5 cm deep Kamenitza. With a rainfall of 1350 mm / year, Cucchi et al. in a later study in the classical karst area a somewhat broader spread of subsidence rates between 0.01 and 0.04 mm / year (i.e. 1250 to 5000 years in the above example). A very similar located estimate in the Lancashire Karst comes from Rose & Vincent, who put a value of 1630 years for 5 centimeters of subsidence.

The corrosion rates are both lithology and grain size dependent . They are high for micrites ( mudstones ), sparites ( rudstones or grainstones ) occupy a middle position and low for dolomitic limestone and calcareous dolomites .

See also

literature

  • JRL Allen: Sedimentary structures - their character and physical basis . Elsevier, 1984, ISBN 0-444-42232-3 .

Individual evidence

  1. ^ A. Cvijić: Geogr. Rev. Volume 14 , 1924, pp. 26-49 .
  2. ↑ A. Bögli: Karrentische, a contribution to karst morphology . In: Journal of Geomorphology . tape 5, 3 , 1961, pp. 185-193 .
  3. ^ PW Williams: Limestone pavements with special reference to western Ireland . In: Transactions of the British Geographers . tape 40 , 1966, pp. 155-172 .
  4. ^ Franco Cucchi: Kamenitzas . In: Angel Gines, Martin Knez, Tadej Slabe, Wolfgang Dreybrodt (eds.): Karst Rock Features, Karren Sculpturing .
  5. ↑ K. Bryan: Origin of Rock Tanks and Charcos . In: American Journal of Science . tape 50, 4 , 1920, pp. 163-174 .
  6. ↑ SE Humbert, SG Driese: Phased development of a subaerial paleokarst plane in upper Pennington Formation limestones (upper Mississippian) and associated paleokarst features . In: M. Sc. Thesis . 2001.
  7. ↑ MM Sweeting: Karst Landforms . Macmillan, London 1972.
  8. ↑ Emery, KO: J. Geol. Volume 54 , 1946, pp. 209-228 .
  9. ^ J. Avias: Karst . Ed .: M. Merak, VT Springfield. Elsevier, Amsterdam 1972, p. 129-188 .
  10. ^ F. Coetzee: Trans. Geol. Soc. S. Afr. tape 78 , 1975, p. 323-333 .
  11. ↑ S. Dzulynski, A. Kotarba: Journal of Geomorphology . tape 23 , 1979, pp. 172-191 .
  12. ↑ JA Bartrum, AP Mason: NZJ Sci. Technol. tape 30 , 1948, pp. 166-172 .
  13. ↑ DL Reynolds: J. Geol. Volume 69 , 1961, pp. 110-117 .
  14. ^ M. Mainguet: Le Modèle des Grès . Ed .: Institut Géographique National. 2 volumes. Paris 1972.
  15. ^ F. Forti: Le “vaschette di corrosione” . In: Atti e memorie della Commissione Grotte “Eugenio Boegan” . tape 11 , 1972, p. 37-65 .
  16. ^ G. Perna, U. Sauro: Atlante delle microforme di dissoluzione carsica sùperficiale del Trentino e del Veneto . In: Memorie del Museo Tridentino di Scienze Naturali . tape 22 . Trento 1978.
  17. ↑ CA Kaye: US Geol. Sur. Prof. Pap. 317-B, 1959, p. 49-140 .
  18. ^ P. Forti, et al .: Le "marmitte de corrosione" de la Grotta Perolas (San Paolo, Brazil) . In: Le Grotte d'Italia . tape 3.2 , 2001, p. 15-24 .
  19. ↑ F. Cucchi, N. Radovich, U. Sauro: I Campi solcati di Borgo Grotta Gigante nel Carso Triestino . In: International Journal of Speleology . tape 18 , no. 3-4 , 1990, pp. 125-138 .
  20. ^ F. Cucchi, F. Forti, F. Marinetti: Surface degradation of carbonate rocks in the karst of Trieste (Classical Karst, Italy) . In: JJ Fornós, A. Ginés (Ed.): Karren Landforms . Universitat de los Illes Baleares, Palma de Mallorca, p. 41-51 .
  21. ^ L. Rose, PJ Vincent: The Kamenitzas of Gait Barrows National Nature Reserve, north Lancashire, England . In: K. Patersen, MM Sweeting (Ed.): New Directions in Karst . Geobooks, Norwich 1986, pp. 473-495 .