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

KARSTIFICATION

studied recent bathycaptures happened on hidden rock boundaries. The thus created karst features are the covered karst ponors (Pict. 11). If chimney exposure does not involve bathycapture, a doline-with-ponor (VERESS 1982a) develops. Dolines-with-ponor are surface karst landforms with no catchment but with water conduit (ie. the exposed chimney). The portion of sloping terrain around the dolines-withponor from which water reaches the depression and through passages the karst is the background area of the depression. They may occur on valley floors (Pict. 13), in valley sides (Pict. 14) or on a terrain non-dissected by valleys. Dolines-with-ponor are found in isolation or twinned (Pict. 12), without channels or with subsequently formed channels. Most of the covered karst depressions of the Northern Bakony are dolines-with-ponor. Dolines-with-ponor form along symmetric or asymmetric rock boundaries or in old fossilized dolines. In the latter case the floor should be lined with permeable sediment. Chimney formation is generated by water collected in the fossilized doline and infiltrating from there. It is probable that the complete filling of the doline marks the end of chimney formation since then part of the rainwater runs off on the surface and partly reaches the karstic basement uniformly distributed over the area of the whole depression without concentration to a point. Within the fossilized doline one or more dolines-with-ponor can form. The karst landform is a composite one. The outer part is constituted by the slope and floor of the fossilized doline and the inner part by the doline-with-ponor developed on the floor. Morphologically, such dolines-with-ponor are similar to partial depressions. In the background area surface erosion (sheet wash or stream erosion) cna be so effective that an independent catchment may took shape there. Such varieties of dolines-withponor are called dolines with dolines-with-ponor-like features or pseudoponors (Pict. 15; Fig. 52). In cover sediments depressions of interior drainage form if cover sediments are transported through the older but cleared or just forming passages into the karst (VERESS 1998). The surface erosion of cover sediments (a precondition of karstification) lasts until the karstic rock, resistent to non-karstic ways of denudation, outcrops. The depressions of variable size and shape, which have interior drainage and form through material transport to depth from cover sediments between patches of carbonate outcrops are called exhumation depressions. The existence of exhumation depressions in the mountains are evidenced by the following facts. (These properties allow the easy identification of depressions.) - The uneven thickness of cover sediments points to the dissection of the carbonate basement. This is a direct evidence to the fact that lower-lying terrains with cover sediments are surrounded by carbonate outcrops. An indirect evidence is that the thickness of cover sediments is variable (as it appears in borehole data) and the changes do not correlate with the distribution of surface karst features (Fig. 45). - Since the surface of the spot with cover sediment lies lower than the environs without cover sediments, this can only be the result of transport to depth. Transport to depth is indicated by the gradient of the floors of the depressions towards the partial depressions inside them, from where regressional channels deepen into the sediment. - The one-time higher position of depression floors is proved by the now inactive karst depressions above the present-day floors. They were active recipients of sediment once. Their altitudinal position marks the elevation of the depression floor during its active stage. (Fossilization was due to the subsidence of the floor.) The depression may form during syngenetic (Figs. 16, 17) or postgenetic karstification (Fig. 18).