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KARST IN THE CZECH REPUBLIC

Karst form of the Czech republic are developed nearly exclusively in different types of limestones and less frequently also in dolomitic limestones belonging to main geological and geomorphological units of the Bohemian Massif and Outer Western Carpathians.

The most important karst areas, i.e. Moravian Karst, Bohemian Karst and the prevailing part of karst areas of the northern Moravia, are developed in Devonian limestones and less frequently in Silurian limestones and dolomitic limestones. They are unmetamorphosed or only weakly metamorphosed, but they are strongly faulted and folded during orogenies. 

The major part of small karst areas was developed in crystalline limestones metamor-phosed in different intensity in the Moldanubian, Lugic (West Sudeten) and Moravo-Silesian units, in central Bohemian metamorphic islets, etc. Limestone/dolomite lenses occur also in other metamorphic units. Carbonate rocks are mostly of Lower Paleozoic age.

Jurassic limestones show limited karstification in the Lugicum (Lužický Ridge). Larger karst areas are developed in the Klippen Belt of the Outer Western Carpathians in the eastern part of the republic.

Cretaceous limestones belong to limited facies development of the Bohemian Cretaceous Basin. Distinct karstification is traceable to the west of Kutná Hora City.

Karst areas of the Czech republic represent mostly small islands with imperfectly developed karst morphology and with existing limited variety of karst forms. Also larger karst areas, i.e. Bohemian Karst, are composed of discontinuous mosaic of limestone strips isolated and interrupted by non-karst rocks. Only the Moravian Karst represents more developed karst area with abroad variety of karst phenomena including free underground water streams.

Type of karst. Owing to dominant lithology of karst rocks, our karst areas represent carbonate karst belonging to the Central European Type of polycyclic and polygenetic karst (PANOŠ V., 1964). It is isolated (scattered) type of karst which developed by repeating karstification during changing climatic and geomorphological conditions. Hydrothermal karst, firstly described from Zbrašov Aragonite Caves (KUNSKÝ J., 1957), represents a special type of karst. It developed by activity of penetrating thermomineral waters through a limestone massif.

The specificity of karst areas reflects e.g. their differentiated geomorphological evolution. Owing to small area of carbonate outcrops, the variety of karst forms is highly limited, in places. Karst areas have mostly identical geomorphological evolution with the geomorphological unit to which they belong. Except the Moravian Karst and several other karst areas, their expression in the relief is not distinct. They usually form elevations or short ridges, eventually morphological depressions. The dominant part of surface of carbonate rocks is covered by weathering products and other sedimentary covers of variable age and genesis. The sedimentary cover accelerates karst process, in limited places, or on the contrary it decelerates karst evolution, turning the karst into fossilised state. Evidences of previous karstifications are usually preserved under sediments.

Evolution of karst in our republic can be divided into several more distinct periods of karstification interrupted by orogenic processes and/or marine transgressions. The oldest proved period of karstification took place during the deposition of Lower Paleozoic carbonate rocks, and it is composed of several local phases of karstification. The next period of karstification is connected with final stages of the Variscan Orogeny ad it lasted until the beginning of Upper Cretaceous marine transgression in Cenomanian. A number of fossil karst forms resulted from this period hidden under Cretaceous cover in Bohemian and Moravian Karsts. The youngest period of karstification has been lasting from sea retreat in Upper Cretaceous until the present time. It is subdivided into numerous phases connected to reflections of the Alpine Orogeny in the foreland of the Bohemian Massif and separated either by short marine ingressions (eastern margins of the Bohemian Massif) and/or by expressive phases of accumulation of continental sediments (Neogene coal-bearing basins, Tertiary to Quaternary terraces). The most important underground cave systems developed during Tertiary in the Bohemian, Moravian and North Moravian Karsts, and in some of other isolated karst islands. Above mentioned phases of karstification produced typologically different karst forms in the dependence to tectonic, climatic and hydrological conditions. The evolution of karst areas differed also in different regions.

PSEUDOKARST IN THE CZECH REPUBLIC

Pseudokarst phenomena often occur in the Czech Republic. They are represented by karst and morphologically similar forms developed in non-karst rocks. They are especially rich in thick sequences of Upper Cretaceous sandstones of the Bohemian Cretaceous Basin. Caves developed along fissures, bedding planes and in blocky screes are common, as well as fissure shafts and niches. A number of those natural forms was changed by man. Features developed in calcareous spongilites, marlstones and calcareous sandstones of the Bohemian Cretaceous Basin are often classified as transitional or karst forms. 

The most extensive systems of pseudokarst fissure and scree caves and shafts are developed in sandstones and marlstones of the flysh zone of Western Carpathians.

Processes connected with young relief originated fissure caves in volcanic rocks of the Èeské støedohoøí Mts. Syngenetic inhomogeni-ties probably represent the basis of cavities in volcaniclastic rocks of the Doupovské hory Hills.

Pseudokarst cavities, i.e. mostly covered open fissures, fissures and cavities in scree in isolated rocks and rocky cliffs, occur in places within the whole territory of our republic. They are developed in solid rocks with blocky disintegrations, especially in magmatic and metamorphic rocks.

 
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