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

KARSTIFICATION

formed on interfluvial ridges cave in, collapse dolines are produced. (Some collapse dolines are inherited over loess cover sediments.) As a consequence, circular collapse dolines occur where the Eocene limestone is thinner (on the boundary between Middle Eocene limestone and „Hauptdolomit") and elongated and wide or elongated and narrow collapse dolines develop where it is thicker. This subtype of karstification is typical of terrains W of Hódos-ér (eg. around Dörgő Hill and on Szent László-erdő). Karstification of terrains with valley development simultaneous with cavernation With relatively early uplift of the block, valley incision and superimposition may take place at an early stage. However, karst water table lowers before superimposition (Fig. 58). Increasingly rapid valley incision into the karstic rock follows the subsidence of karst water table. No bathycapture takes place since - although percolating waters increase the rate of cavernation under the valleys - incision destroys the potential water conduits. Cavernation is concentrated under the floors of incising valleys as the percolating waters from the water-course are mixed with flowing karst water. Valley evolution is promoted by the already existing and exposing cavities (valley evolution through cavity exposure). The here outlined evolution of a superimposed valley may be prolonged by the catchment of considerable size on covered surfaces beyond the block (examples are the Cuha, the Gerence and the Ördög-árok streams). As a consequence, the process is still active in the valleys. The above suggest that valley evolution through cavity exposure is characteristic of syngenetic valleys. Postgenetic valleys only expose cavities, their water-courses do not contribute to the evolution. Therefore, with valley evolution through cavity exposure, the rate of mixing corrosion is highest under valley floors. The frequency of spherical cauldrons and cavity size are highest there. Moving laterally from the valley floors the frequency of spherical cauldrons and cavity size decrease. Incising postgenetic valleys may reach down to the zone of cavernation and cavities may be exposed. In this case, moving away from the valley axis, the assemblage of solution landforms (eg. the frequency of spherical cauldrons) remains the same. (Mixing corrosion was not limited to the zone under the channel.) It may occur that the water percolating from water-courses dissolves rocks. The resulting vertical cavities are virtually the same as the chimneys described under the heading surface karstification. The percolation may cause mixing corrosion in deeper levels and, thus, valley evolution through cavity exposure may gradually develop also for postgenetic valleys. If the valley is active for a sufficiently long time, cavities formed in greater depths may also be exposed. In the case of similar valleys, moving towards the valley floor, the frequency of spherical cauldrons may increase in the exposed cavities and cavity dimensions may also grow. Valley evolution through cavity exposure (VERESS 1980a,b, 1981a, 1982b) may accompany both superimposed-regressional and superimposed-antecedent valley evolution. In the sides of gorge sections of superimposed-antecedent valleys, cave ruins of vertical position may also occurs (eg. Kerteskő Gorge). The reason behind this is that antecedent valley evolution more probably takes place if block uplift is slow but continuous, accompanied by a similar trend in karst water table. If block uplift is rapid but cyclical, horizontal cavernation or cavity formation at several levels result also in antecedent valley sections (but more typically in superimposed valleys) and with impermeable (marl) intercalations.