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

KARSTIFICATION

munierian clay alternate on the surface. In this case, in Requienian limestone but along the contact between the two rocks, as a consequence of karstification on hidden rock boundary, a range of karst landforms may develop (VERESS-SAJTOS-FUTÓ 1990). The amount of solvent arriving at the rock boundary also depends on the geomorphological conditions prevailing on the covered karst terrain. With the same cover sediment, the larger surfaces (eg. valley sides) slope towards hidden rock boundaries , the more solvent could arrive to these sites. Therefore, geomorphic evolution prior to karstification and the resulting assemblage of landforms are of decisive role in the activation of potential hidden rock boundaries. The covered karst landforms developed on hidden rock boundary, however, do not have distinct catchments since they have not been formed through bathycapture of surface water-courses. After their development, there are no major changes in the slope conditions of the surface (the only exception is presented by depression formation) and part of rainwater runoff takes place on the surface bypassing covered karst depressions. The terrains where permeable cover sediments are sufficiently thin but carbonate rocks do not outcrop yet are symmetric hidden rock boundaries, while those with carbonate outcrops are asymmetric rock boundaries (Fig. 3). At the same time, the uncovered smaller portions of carbonate terrain elevated above their environs are hardly affected by karstification, disregarding karren development (VERESS 1989, 1991; VERESS-FUTÓ 1990). The local thinning of cover sediments (primarily loess or its reworked varieties) are caused by unevenness of deposition, erosion or accumulation. Unevenness of deposition depends on the topography of the basement surface of the underlying carbonate rock. The variation of basement may be casued by tectonic impacts (basement dismembered by fault scarps) or paleokarstification (basement dissection with cones and enclosed depressions - Pict. 1 - VERESS 1991; VERESS-FUTÓ 1990). The strikes, lengths and degrees of dismemberment of various hidden rock boundaries and thus the sizes of areas capable of karstification, the surface pattern and frequency of sites suitable for karstification primarily depend on the unevenness of deposition of cover sediments, ie. from the topography of the carbonate basement. The unevenness of deposition is not permanent, but changes with the balance of erosion and accumulation. Therefore, during erosion the hidden symmetric and then the hidden asymmetric rock boundary develops gradually over the dissected basement. With further erosion of cover sediments the rock boundary and thus the site of karstification is shifting. The steeper slopes border the landforms of the carbonate basement, the more vertical is this shift. During exhumation rock boundary and thus karstification is shifting upwards and during accumulation downwards (Figs. 3, 46). During exhumation, over terrain fragments higher lying than the neighbouring ones covered by cover sediments karstic features are truncated (Pict. 2; Fig. 7) or fossilized with accumulation. During accumulation, the already existing karst landforms are first fossilized and then buried. Truncated, fossilized or buried karst landforms may be suitable for the reconstruction of geomorphic evolution and tectonic events in the area (VERESS 1991). In covered karst areas of the mountains surface karstification is associated with chimney formation (VERESS 1982a; VERESS-PÉNTEK 1995a,b). Where chimneys open to the surface, covered karst depressions are created. Chimney formation can expand in the rock mass. The present-day primary chimneys may have developed into secondary chimneys only partially. Therefore, chimneys are formed by solution (Pict. 3). Along the hidden rock boundaries of the carbonate basement, because of the increasingly impermeable character of loess and sloping surfaces, infiltration locally intensifies. This favours the penetration of solution several metres deep along water conduit lines (fractures, faults, bedding planes Fig. 4). Cracks of small width and chimneys of small diameter develop (primary chimneys).