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

KARSTIFICATION

- Covered karst landforms do not result from the bathycapture of surface water-courses. The lack of bathycapture is proved by the fact that depressions not located on the valley floor - even if they have channels - are neither crossed by channels nor associated with blind valleys. The channels of covered karst depressions are much younger than the depressions themselves. Since from the margin regressional channels are created, the development of channels is associated with that of the covered karst depressions. - True bathycapture cannot happen either at covered karst depressions on the valley floor. Where it takes place in superimposed karst valleys, the retreat of valley rock boundary makes the site of bathycapture in the direction of the head valley (JAKUCS 1971). The ponors of former sites of bathycapture develop into ponors (JAKUCS 1971; HEVESI 1980, 1986) and only the ponor closest to the head valley is active. The covered karst depressions aligned on the valley floors in the mountains this regularity is not observed. It often occurs that if there are several karst depressions on the valley floor, more than one or even all of them can be active. This also applies to the situation when inside the karst depressions there are accumulations of cover sediments of considerable depth. Mostly this does not mean fossilization proved by the generation of further partial depressions on the basement with cover sediments. In some valleys all covered karst depressions are active, while in other valleys active and inactive fossilized depressions alternate. It is also common that fossilized karst depression occur right along the upper sections of valleys, while along the lower sections all karst features are active. For their origin, the covered karst depressions of the mountains are different from all the mentioned covered karst doline types and, therefore, the introduction of a new terminology seems to be necessary. The differences are summarized in the following: - In the study area cover sediments play a decisive part in the development of chimneys. - While in the case of subjacent dolines cavities of various shape cave in and in the case of subsidence dolines the surface of the carbonate rock is affected by solution, in the study area vertically developed chimneys open to the surface. - Both for subsidence dolines and for subjacent dolines depressions form in the cover sediments and are hardly observed in the basement. Syngenetic and postgenetic karstification and its forms In the karstic rocks of the mountains there are numerous corrosional or even erosional passages formed at various dates. The reason for this is the abundance of paleokarsts and also the faulted structure and variable topography, which allowed multiple redeposition of cover sediments. The unconsolidated rock (loess) is also suitable from this respect. Thus, in the same site the conditions of chimney development (hidden rock boundary) could have existed in several subsequent periods. Therefore, the ages of chimneys, passages or surface depressions in their prolongation are not the same. Accordingly, the surface karst features of the mountains are classified to syngenetic and postgenetic karst features. The processes producing them are called syngenetic and postgenetic karstification. Syngenetic karstification takes place when the chimney and the associated depression form simultaneously. The surface karst landforms originates from the upward extension of the chimney in the karstic rock.