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

KARSTIFICATION

accumulational surface. The here accumulating sediments derive from the neighbouring valley sides and floors. At the same time, the sediments were reworked by sheet wash and streams into postgenetic ponors and transported further to depth. The walls of postgenetic dolines-with-ponor are steep surfaces in unconsolidated sediments with collapses. Where there are more postgenetic dolines-with-ponor in the depressions, several old conduit passages may activate. They may develop through the formation of branches in the unconsolidated cover sediment and their exposure to the surface in various sites. Postgenetic dolines-with-ponor may lack a channel or may have regressional channels (streams). The channels may meander (indicating the low energy of their water) or sometimes reach over the edge of the internal part of the depression. Mostly, however, their catchment is restricted to some part of the depression area. They may acquire a blind valley character. Bedrock may outcrop on the channel and doline floors of postgenetic dolines-withponor and channels. Sites of pseudobathycapture may occur. Postgenetic landforms without depression are small basins of steep walls (outer an inner parts are not distinguishable) with no or hardly any background. The carbonate basement does not lie deeper than the surroundings. Such basins may lack a conduit passage (pseudodoline above passage) or have a passage. In the unconsolidated sediments of the floor erosion exposes secondary passages and partial depressions of variabled life-time may form (doline-with-pseudoponor above passage). On terrains where cover sediments are sufficiently thin or entirely removed chimney formation is replaced by the surface corrosion of carbonate rock. On terrains with a thin veneer subsidence dolines, while on terrains with only soil cover solution dolines may also come about. Fossilized covered karst features Fossilization begans if sediment transport from a karst depression to the karst stops or falls remarkably below the amount of sediment influx (VERESS 1995a). The conditions are favourable for fossilization if the water conduit is poorly developed and fine-grained material arrives from the background. (The grain size of sediments in the background area should be fine and the slopes of the background or the catchment area should be gentle.) The reduction of water influx also favours fossilization (although it involves the drop of sediment influx). It can be caused, for instance, by the loss of part of the background area. In the area of the infilled and fossilized karst landform a secondary depression may form through the compaction of sediments. The transport of some material to the depth in solution may also contribute to this process. A further factor is that the void ratio of precipitated matter is lower than before dissolution. The interior of such depressions is waterlogged and swampy for most of the year („wallow"). The permanently waterlogged ponds are locally called „kálistó", „förtés" or „wallow". Such localities are regarded karst features by HUNFALVY (1864). Waterlogged places probably do not only form in sites of impounded fossilized covered karst landforms. The evidence for the karst origin of wallows is summarized below. - One of the basins of some twinned karst depressions contains a wallow, while the other is still an active karst feature. - There are enclosed types of wallow of basin character. - In some explored wallows filling sediments dip from the edges towards the centre.