Geomorphological characteristics of karst on contact between limestone and dolomite in Slovenia
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Contact karst is a type of karst formed where allogenic waters from the surface influence the karst geomorphic system. Contact karst may be considered in both a strict sense and in a wide sense. In a strict sense, contact karst is the karst phenomena and forms influenced by the contact between a karstifiable rock and a non-karstifiable rock. In a wide sense, contact karst may also be the karst phenomena and forms influenced by the contact between two different karstifiable rocks, for example limestone and dolomite. This thesis focuses on the geomorphological characteristics of contact karst on limestone-dolomite contacts in Slovenia. The purpose of the research was to determine which processes contribute to the development of contact karst on the contact between limestone and dolomite, to define their dynamics, and to identify which surface and underground landforms are developed.
The spatial distribution of contacts between limestone and dolomite in Slovenia was determined in a GIS. Using existing lithological data as a data layer, the extent of carbonate rock cover in Slovenia was calculated. Carbonate rocks cover 47 % of Slovenia’s territory (27 % limestone, 14 % dolomite, and 6 % clastic carbonate or impure carbonate rocks). And, there are 1,353 limestone-dolomite contact lines in the country, totalling a length of 2,625 km.
Study areas were selected based on GIS analysis of the limestone-dolomite contacts. A total of 17 areas in Slovenia were studied in detail. Fieldwork at the study areas consisted of the collection and analysis of rock, sediment, and water samples, allowing each study area to be geomorphologically mapped.
General factors contributing to contact karst development on the lithological contact between limestone and dolomite were determined. The most important factor appears to be the characteristics of the inflow part, formed on the dolomite. Where dolomite functions as a karst rock, the water is dispersedly drained into the karst. In that case, the limestone-dolomite contact does not function as contact karst. Alternatively, where the dolomite functions as fluviokarst, a point recharge, or sinking stream, is formed. In that case, contact karst may be formed. The fluviokarstic character of the dolomite depends on its chemical and mechanical properties. The dolomite bedrock must be positioned at a higher elevation than the neighbouring limestone bedrock. To meet this requirement, dolomite beds, which in Slovenia are generally older than limestone and hence stratigraphically positioned below the limestone beds, need to be positioned above limestone by either folding that leads to inverse stratification, overthrusting, or by displacement along faults. Along faults, the dolomite is more prone to mechanical weathering due to tectonic crushing in addition to its chemical properties. Hence, contact karst is more likely to form at thrust contacts between thrust limestone and dolomite. Limestone-dolomite contact karst develops predominately at higher elevations due to increased precipitation (where allogenic inflow is higher) and greater frost action due to lower temperatures. Intense mechanical weathering of dolomite over limestone directly affects contact karst processes and significantly contributes to the spatial distribution of these types of surfaces. The location of the water table close to the surface is also a leading factor in limestone-dolomite contact karst formation due to enhanced border corrosion.
Landforms typical of contact karst were identified in the study areas during geomorphological analyses. However, they are not as clearly recognizable as those on contact between carbonate and non-carbonate rocks. The reason for this is the fact that allogenic waters from dolomitic catchment areas are by far not as corrosive as those from non-carbonate catchment areas.Cite
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The many karst types widely distributed in the regions of Kweichow,Kwangsi,western Hupeh,Hunan,eastern Yunnan and eastern Szechwan in South China haveformed special karst topography and morphology. The intensity of the karst development is closed related to the nature of carbonaterocks,that may be classified into seven kinds according to their chemical nature.Gen-erally,at temperature of 20°—30℃ and pressure of 1 atm.,the degree of the karstdevelopment of the limestone class is more stronger than the other classes.The solu-bilities of dolomites are always lower from 30—70 per cent than that of the limestones orcalcites.But in consequence of weathering the solubilities of marls or dolomites some-time are higher than that of the limestones. The texture of carbonate rocks also may be divided into six categories (see thechinese text).The intensity of the karst development in the coarse-grained carbonaterocks ordinarily is more powerful than that of the aphanitic varieties. The composite classification of the carbonates,being divided into six groups by theauthor has a close relationship with the karst development.Great karst phenemennons,for example caverns,sink holes,funnels,stone forest,poljes,karst basins,karst mountainpeaks,etc.are growing numerous in the first composite class of the carbonates(I),whichare thick beds of the coarse-grained limestones such as the Yangsin,the Maping,theHuanglung and the like formations.As a striking contrast to the first class,the sixthclass(VI)with alternations of thin beds of limestone,dolomite,marl,and shale reflectsfeebly on karst development. Another important factor controlling the karst development is hydromachanical condi-tion,which is examplified by twelve types in South China.The first four types are themost important ones.
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The karst geomorphology of the White Limestone Group of Jamaica is reviewed. The lithological and structural characteristics of the White Limestone Group are examined in relation to its karstification, specifically material properties such as purity, petrology, porosity and mechanical strength, which have been regarded as important in the development of karst landforms. The structural setting and palaeogeography during the deposition of the White Limestone, together with subsequent block faulting, are considered in relation to the origin and evolution of the karst topography. The phenomenon of case-hardening is examined as are the dissolution processes and influences related to the presence of a soil cover. The karst features on the White Limestone Group are considered in two categories; small-scale dissolution sculpturing phenomena, collectively termed karren, and larger scale landforms. The latter can be further divided into karst landform assemblages comprising doline, cockpit and tower karst. Cockpit karst is the most common landform unit on the White Limestone Group, and occurs on the harder crystalline limestones, dolostones and where case-hardening is important. Tower karst occurs on similar lithologies, but has a more restricted distribution. Doline karst is largely restricted to the chalky Montpelier Formation. The geomorphological characteristics of each landform type are described and their origin discussed. Other karst landforms include poljes, ridge karst, glades and a range of fluviokarst, each of which are described. The cave systems and underground rivers are also considered. Karst morphometric studies and theories of landform evolution are reviewed.
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Calcarenite
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The landscape of the Cumberland Valley of South Central Pennsylvania is dominated by karst topography. A study was initiated to determine if the development of karst was controlled primarily by geologic structure or by lithologic differences. Existing data concerning the geographic locations of karst features, the hydrogeologic characteristics of the Cumberland Valley, and the chemistry of the eleven carbonate formations within the 518 km[sup 2] study area were compiled. Data concerning 366 mapped sinkholes and over 9,000 additional karst features and their relations to the structural, lithological and spatial characteristics of the study area were collected and compiled into the database. Other factors contributing to karst development such as groundwater flow, soil and colluvium characteristics, and geographic distribution were considered. The data suggest that structure dominates lithology in the development of karst features within the study area. Structural features such as fractures, joints and folds, which create secondary porosity, are prerequisite for solution of the carbonate bedrock. Joint systems, fold axes, igneous intrusions, caves, springs and groundwater flow have a significant impact on the development of karst features. The presence of faults proved inconclusive. There are a greater number of karst features per unit area in areas of purer limestonesmore » (units with a lower percentage of acid insoluble residue). Lithological variations impact karst development only when structural features are present to provide secondary porosity that enhances chemical weathering. The distribution of karst features and the geologic factors governing their development and distribution should be taken into account when land-use decisions in karst terrains are made.« less
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In the Dagang region, the Ordovician is 600～800 m thick and mainly consists of limestones and dolostones. Karst reservoirs are developed. The main controls on karst reservoirs are : lithology, depositional environments, hydrology, ancient landform, fractures and weathering time and so on. The lithology composed of dolostones and gypsum is favorable for the development of karst reservoirs. Tidal flat environments are favorable facies to develop karst reservoirs. Karst reservoirs are mainly developed 20 to 200 m beneath the unconformity. Beofore the Carboniferous, the land surface of the study area inclined from southwest to northeast, and the ground water flew from southwest to northeast. Karst reservoir belt formed in this time also trends southwest northeast. The karst slope and karst depression with no standing water are favorable for the karst reservoir development, especially the karst slope. Karst reservoirs tend to develop in the place where fractures and faults are abundant, and the trend of fractures and faults controls the trend of karst reservoir belts The longer the weathering time, the better the karst willbe developed.
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Anticline
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The delimitation of a drainage area together with the accurate estimation of it’s surface area represents an important problem in dealing with karst springs. Water gushing from the fractured karst identifies the Gradole spring as a typical karst well of the rising type. The spring never runs dry, the ratio of minimal and maximal discharge being 1:15 to 1:20 or more. The surface of the drainage area and its spatial distribution have been defined on the basis of geological data; tectonics, morphology, photo-geological interpretation, hydrogeological characteristics of the rocks, the karst morphology (sinkholes, pits) and underground water tracing data. The drainage area is predominantly composed of carbonate rocks, mainly limestone, but there is also a lesser flysch component - marls and sandstones. The karst area is without any surface waterflows, in contrast to the flysch area where a hydrographic network of intermittent surface streams is developed. There are no real barriers to underground flow within the carbonate rocks. Nevertheless, the direction of flow is influenced by structural elements, the position of layers, the appearance of rocks - thin layers, shows of some less permeable rocks - dolomites, fissured and marly limestones. The confirmation of an underground connection of Cize swallow hole with the Gradole spring shows the possibility of supplementing low waters through the swallow holes from Butoniga accumulation lake.
Flysch
Sinkhole
Drainage system (geomorphology)
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The ancient karst landform of the Maokou formation in Shunan region controls the facture-cavern system's development.According to the thickness distribution of the Maokou formation in the region,the surface erosion on weathering crust and sediment properties as well as the degree of preservation of the Maokou formation,the ancient karst landforms in the Maokou formation can be recognized as or divided into three 2nd grade landform units as karst platform,karst slope(further divided into the western steep slope and northeastern gentle slope belt) and karst basin.Then the relationship of geomorphic unit and the cave system is studied.The results show that: water in karst platform seeps mainly vertically,weathering is strong,vertical solution fissure and cave is often filled with clay;the karstification is the strongest in the karst steep slope and the transition zone of karst steep slope to karst platform where pore and cave are developed,filling rate is low,fissure-cavity system develops best,and is favorable for exploration;the speed of water flow in karst gentle slope is slow,karst cycle is long and fissure-cavity system is easy to be filled,which does not conducive to fissure-cavity reservation;the erosional space in karst basin is less,and the reservoir performance is poor,which makes the area unfavorable for exploration.
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Fissure
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