Veress Márton: A Bakony természettudományi kutatásának eredményei 23. - Covered karst evolution... (Zirc, 2000)

CONCLUSIONS

karst, at older syngenetic chimneys or at older karstic passages or cavities exposed by denudation. 6. Unconsolidated cover sediments are of decisive influence on the formation of covered karst depressions (and on the nature of covered karst development) since they govern chimney formation and its stages. At the same time, unconsolidated cover sediments also favour the rapid removal of karstic landforms; partly through the plugging of chimneys with the large amounts of inwashed deposits and, thus, covered karst features fill up rapidly and partly through the truncation of depressions as a consequence of rapid denudation. (The latter process is favoured by the formation of chimneys in higher parts of the karstic basement.) The small dimensions of karstic landforms in the mountains, however, is not caused by the young age of recent karstification but because the individual karst objects are young. Karstic features have fossilised and new features developed. The karst depressions are neither dolines nor true ponors. Although they receive water from their background areas, they are not formed by true bathycapture. The chimneys cannot develop into erosion systems because they function for a short period and there are no water courses of proper competence on the surface and debris and gravels for corrasion are also missing. The background areas are small (because of the block structure, the nature of topography and because depressions develop in each other's immediate vicinity) and, thus, small amounts of water are collected in the passages. Ponors cannot develop along the superimposed-antecedent valley sections either. Here intensive incision may destry or exposed the passages and cavities of flowing karst water. 7. Caves and cavities of no

> ponor origin develop in the zone of flowing karst water. Cavernation occurs close to the surface of karstic rock (particularly in nummulitic limestone if it is underlain by a Triassic carbonate rock) with moderate or great thickness (particularly in dolomite) or at greater depth. If the block is of low position, cavernation is at subsurface levels and the resulting valleys on the block are not superimposed or only at a later date (postgenetic valley) into the karstic rock (perhaps no valley develops). Cavities are not destroyed but cave in (collapse doline). Terrains like this are typical of buried horsts in summit position. The superimposed valley may further incise and reach the zone of cavernation. If it is gradually inactivating or cuts through the cavernation zone of moderate thickness, no bathycapture happens; the cavities of the zone are partly destroyed and partly exposed in valley sides. With the exception of cryptopeneplains, any block type may have such a terrain. If the inheritence of the valley on an isolated block occurs at an early stage (syngenetic valley) and is prolonged, valley evolution through cavity exposure takes place. A necessary condition to such an evolution is that the block should be enclosedd by non-karstic terrain and that cavernation should take place in a relatively great depth below the surface of the karstic rock or the cavernation zone should be continuous from the surface to a great depth. Cavernation and valley evolution are in a positive feedback relation and a gorge of karstic origin develops. The caves in the valley sides are not spring caves since no tapping of karst water occurred here; the water was conducted away instead. The exposure of cavities explains the small size and relatively high frequency as well as the location in valley sides of these caves. The distribution and three-dimensional shapes of cavities are controlled by the rate of uplift, the nature of uplift (cyclical or continuous) and possible intercalations in the karstic rock by impermeable strata.