IV2 MECHANISM OF KARST PROCESS
Elena Marcenko1 , Dusan Srdoc1 , Stjepko Golubic2
Joze Pezdic3 and M J Head4
1 Ruder Boskovic Institute , Zagreb , Yugoslavia
2 Department of Biology , Boston University ,
Boston , Massachusetts
3 Institut Jozef Stefan , Ljubljana , Yugoslavia
4 Radiocarbon Dating Research Laboratory ,
Australia National University , Canberra , Australia
d 13C and 14C activity measurements were made on terrestrial , marsh and aquatic plants growing in their natural habitat of the Plitvice Lakes in northwest Yugoslavia.d13C values were ca -47‰ for aquatic mosses , which indicate that the carbon source was dissolved inorganic carbon ( DIC) from alkaline karst waters , following a C3 pathway ,and -25 ‰ for marsh plants ,indicating the carbon source was atmospheric CO2. 14C activity of true aquatic plants and submerged parts of helophytes was close to 14C activity of DIC ,whereas that of emergent parts of helophytes and terrestrial plants was similar to atmospheric CO2 activity. Aquatic plants which use DIC in freshwater for their photosynthesis are not suitable for 14C dating ,unless the initial activity of incorporated carbon is known. d13C values of plant material also depend on the carbon source and cannot be used for 14C age correction.
Arthur N. Palmer and Margaret V. Palmer
Department of Earth Sciences , State University of
New York College at Oneonta , New York
Every carbonate rock formation contains examples of replacement among carbonate minerals , sulfates , and silica .Although the net geomorphic effect is rarely significant , porosity and permeability can be greatly modified in this way. Recognition of these processes is also a powerful tool for interpreting past geochemical conditions. Examples can be observed in many areas of the Appalachians: in caves , paleokarst zones , and carbonate oil reservoirs. Some mechanisms are well known , but their recognition in the geologic record is not. Replacement of sulfates by carbonates usually involves common--ion effects , e.g. ,where dissolution of gypsum by calcite-saturated water causes precipitation of calcite .Evidence for former evaporites includes sutured , lath-shaped , double-terminated and lozenge-shaped calcite crystals , scimitar and anastomotic veins , multi-stage breccias , boxwork , nodular or cauliform textures , and authigenic carbonate sediment .Dolomitization and dedolomitization depend on the relative solubilities of calcite vs. dolomite. Below 23°C, dolomite is more soluble than calcite , but the relationship is reversed at higher temperatures.The sluggish kinetics of dolomite near saturation make it unlikely for dedolomitization to be a major karst process , except in sulfate- rich solutions , which greatly boost the solubility of dolomite .Dedolomitization ,recognized by scattered rhombs of calcite , is therefore another hint of former sulfates.
Silica easily replaces carbonates and sulfates .Carbonates and silica dissolve and precipitate under the opposite conditions: rising pH and temperatures increase the solubility of silica but decrease the solubility of limestone and dolomite .Silica replacement of either carbonate or sulfate minerals is usually very selective , so it is unlikely that such abroad-scale process as cooling of high-temperature fluids could be the main mechanism .Closed-system dissolution of carbonates isolated from carbon dioxide sources can raise the pH well above 9 , allowing much silica to dissolve . Aeration , evaporation , and exposure to local acidity cause silica to precipitate. These conditions are common in aerated caves and in zones rich in sulfates or organics.
Shopov Y. Y.
University of Sofia , Section Speleology; Fac. of Physics
The spectra of luminescence of 150 samples of 10 cave minerals from Bulgarian caves are investigated. The luminescence of vaterite and purpurite is investigated for first time and that of hydromagnesite , brucite , quartz and hydrozincite firstly in caves. 22 different spectra of luminescence of cave minerals are obtained.
It is shown that the luminescence of the infiltration cave minerals is due mainly to biogenic organic compounds. Those compounds had been absorbed on the surface of the speleothem during its growth.Therefore the investigation of their content along the growth axis of the flowstones can give important information for conditions of life of plants and heir vegetation population during the formation of corresponding layer of the flowstone.
Shopov Y. Y., Petrov1 S. L., Nenova2 P. I.,
Burin Kl. I., Tsankov L. T. Sofia University ,
Section Speleology; Faculty of Physics , A. Ivanov 5
1 Geologo-Geographycal Faculty, Dept. Mineralogy and Crystalography
2 Geol. Research Laboratory of Government Committee of Geology
A pseudokarstic cave in gneisses , placed at 4400 m altitude in the Din Gad River Valley in Garhwal Himalaya is investigated. The minerals plagioclase ,pottasium feldspar ,quartz , FeOOH , and alusite , tremolite and zircon were determined in the gneiss country rock of the cave. We determined that this cave has been formed by a tectonic fracture along a hydrothermal vein of quartz and calcite. Spectra of luminescence of quartz and calcite were determined. It allows us to determine that the calcite is of low-temperature hydrothermal origin and has admixtures of Mn2+ and Pb2+ . Luminescence of Fe3+ and FeO in quartz was found.
It was found one corrosional-erosion cave in amphibole-biotite- pyroxenic gneiss intersected by up to 0.5 m thick migmatite veins. This gneiss contained 3-30% calcite, which slowly dissolves in water , that is why the vein have even surface formes of dissolution (karstification). The cave is developed along a slopping tectonic fracture. The lower wall ( along which the water has flowed ) of the fracture is karstified , as calcite from the bedrock dissolves and other minerals eroded physically. Therefore the inclusions of the minerals stable to weathering ,as turmaline and garnet remained to stick out of the wall. The higher wall of the cave has no tracks of dissolution , but was covered with speleothems of secondary calcite and gypsum.
It was determined an unknown centrum of luminescence (phosphorescence) with maximum at 595nm , which is probably due to characteristic for tropics , organic compound of the soil solutions. Lines of luminescence of Mn2+ and Fe3+ was determined in the spectra of luminescence of gypsum.
SPELEOGENESIS IN AEOLIAN CALCARENITE:
A CASE STUDY IN WESTERN VICTORIA , AUSTRALIA
Department of Science , Deakin University: Rusden Campus , Australia
Most studies of karst landscapes and their processes have been concerned with consolidated ,often well jointed limestones. There are particular problems involved in the study of karst processes in softer less compact limestones such as chalk ,coral reefs and aeolian calcarenite. Previous studies in aeolian calcarenite indicated these problems and Jennings 1968 ,developed a scheme of speleogenesis in aeolian calcarenite.A study of karst processes in aeolian calcarenite at Bats Ridge in western Victoriahas developed this scheme further.The karst features and processes at BatsRidge are an integral part of the landscape of a middle Pleistocene calcarenite dune system. (White , 1989). This paper aims to synthesis the known karst features of the ridge and relate these to the other geological and geomorphological attributes of the area , and thereby resolve problems of the rapid subaerial speleogenesis in the area.
The dunes are presumed to have been deposited in the middle Pleistocene(Boutakoff , 1963; Kenley , 1976) after the Tertiary beds had been exposed and available as source material for dune building. The climate is thought to have become cooler and wetter before 40,000 years B.P., and became drier at about 32,000 years B.P. In the very late Pleistocene the sea cliffs at Bridgewater Lakes are thought to have formed during the Andara high sea level (4.6-6.1 m high sea level). The dunes would be by then vegetated and stable and the cap rock sufficiently developed for cave development to proceed at the top of a raised water table due to the higher sea level , in the late Pleistocene and early Holocene. These caves would be above the water table when it lowered as sea level dropped and the sea retreated .However any period of raised water table during the early Holocene to the present would lead to reactivation of such active cave formation Cave modification by collapse and speleothem development could continue above the water table.
The processes of syngenetic karst are delineated and explained in the context of Western Victorian aeolian calcarenite dune ridges and their karst features. Karst development on this aeolianite ridge is dependent on several conditions: lithological conditions such as the purity of the limestone , its porosity and its ability to support a cavity as well as the availability of aggressive water capable of solution. Firstly the dune ridge must have a sufficiently high proportion of soluble material , pure enough for the solution processes not to be impeded by insoluble residues left after solution has occurred. The higher the proportion of carbonate ,the more likely the karst features will develop. As the dunes have a high primary permeability and porosity the percolation of water is not dependent on the presence of joints , although the dune bedding planes may also be important as percolation routes for water.The development of under groundkarst forms , is dependent on the ability of the limestone to support a cavity. Insufficient tensional and compressive strength in the limestone will result in solutional cavities collapsing before they are very large .It is necessary also that there be a suitable climate with sufficient water available for solutional processes. The Cape Bridgewater area has an average of 850 mm p.a.of rainfall and climatic conditions in the past are not greatly different from the present climate. The percolating water is made more aggressive by CO2 enrichment from soil air and this is enhanced by the vegetation covering the dunes. Adaquate moisture is available for karst processes to be operative.
The lithification of the calcarenite is an important factor in the development of karst landforms. As the dune ridges are deposited during the early Pleistocene and the caves were initially excavated during the middle Pleistocene ,the higher water tables of this period , the dates of the dunes combined with the limited lithification in the dunes indicate that diagenesis of the calcarenite is occurring now and must have been occurring by the mid Pleistocene. This simultaneous nature of the lithification of the carbonate dunes into aeolian calcarenite rock and the development of solutional karst features in the dunes is the characteristic feature of this area and can be explained in terms of precipitation of carbonate in the dunes. The lithification process involving solution by CO2 enriched percolating water and redeposition of calcium carbonate has resulted in the formation of a hardened kankar layer in the dunes. This feature has been termed cap rock (Jennings , 1968).It is necessary for the formation of many karst forms , especially caves as it gives the otherwise relatively unconsolidated calcarenite structural strength. It is the formation of this caprock of sufficient compressive and tensile strength to support cavities ,which is the result of the interrelated factors of purity of limestone ,water chemistry conditions and position of the watertable that has resulted in the formation of karst features.