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

KARSTIFICATION

Fig. 25. Deposition in long-term ponds (modified after VERESS 1987a) Legend: 1. limestone; 2. unconsolidated sediment; 3. water conduit; 4. partially plugged conduit; 5. water table of intermittent pond at any date; 6. deposition; 7. plant detritus sequence of uniform appearance; 8. plant detritus rings with colloid coatings; 9. sequence of plant detritus rings; 10. colloid coating or plant detritus coating on tree trunk; 11. inflow into karst depression (length of arrow proportional to amount of water inflow per unit time); 12. water conducting (length of arrow proportional to amount of conducted water per unit time); 13. water table dropping (length of arrow proportional to sediment subsidence per unit time); 14. subsidence rate of plant detritus; A. water table dropping always exceeds subsidence of plant detritus; B. water table dropping always slower than subsidence of plant detritus; C. water table dropping sometimes exceeds subsidence of plant detritus; D. water table dropping 0 and then sometimes exceeds subsidence of plant detritus detritus in the same pond (reflecting the fluctuation of water table and its droping rate) does not point to the fluctuation of conduit capacity but of water recharge (during repeated rainfalls or snow-melt of variable intensity). A series with plant detritus, however, forms if water transfer into the karst is retarded, large sections of the conduit are partly filled or short sections are totally plugged. From ponds of longer existence colloids also deposit. The colloids from pond water adhere to tree-trunks and herbaceous plants in the karst depression. The colloid coating is also uniform if the rate of water table dropping is uniform and of annular form (Pict. 32) if the rate of water table dropping fluctuates. The upper margin of colloid rings is markedly distinct from the surface on which they formed (slow dropping) then it is gradually fading downwards because of the increasing speed of water table dropping. The various colloid rings and plant detritus zones are in the same level for a given depression. The uppermost colloid rings and the plant detritus or the series with plant detritus marks the maximum water table of the pond. - The sediment coarser than the colloids transported into long-term ponds is deposited, while the colloids are retained - after the evaporation of water - as gel. From every intermittent pond a pair of sediment strings (laminite) form. The occurrence of laminitic series indicates the plugging of conduits and water transfer into karst only through seepage. Sedimentation accompanying fossilization The complete fossilization of a karstic feature (VERESS 1995) results in the complete infilling of the depression. (On the floor of the depression waterlogging becomes ever more enduring.) The plant detritus transported in are gradually buried. In an environment without oxygen, a fill of high organic matter content with fragments variably carbonized accumulates (carbonic series with plant detritus). From the upper, soil-filled parts of the depression, infiltrating water carries iron to the lower levels. Iron precipitates in oxidic or limonite form. Fe-oxides precipitate at high pH in the presence of charcoal (which binds organic acids). Limonite precipitates in oxygen-free environment, resulting from the occurrence of groundwater. Consequently, the limone produced may point to the occurrence of groundwater and to the a complete cessation of water transfer, even by seepage, into the karst. Because of the transport of iron, a secondary depression may form. Therefore, the accumulation of the series with charcoal and plant detritus may continue or be repeated. The lime concretions in the fill of the fossilized depression originate when the pH of seeping