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1.
Morphogenesis of the Postojna Basin karst periphery : dissertation
Astrid Švara, 2023, doktorska disertacija

Opis: This thesis represents a karstological study on the drainage of the Postojna Basin. It focuses on a multidisciplinary approach, based on fieldwork, computer analyses and dating. The northern study area has the highest: doline density of 108 dolines/km2, number of contact karst features (i.e. 9), and number of collapse dolines (i.e. 19). It has three catchments. The Lokva cuts into the flysch ridges and sinks in the Predjama Cave System at the lowest point of the basin (i.e. 474 m a.s.l.). Between 37 selected caves, 14 were longer than 150 m. The Predjama Cave System was developed in 3 levels and the Postojna Cave System was developed in 2 levels. The vertical passages connecting them are deepest in the Predjama cave, where the vadose zone is up to 250 m deep. By the favourable ponor steepheads and 140 m deep vadose passages, the Hrušica Plateau shows a major uplift phase. The Postojna Cave System, Risovec blind valley and 17 collapse dolines indicate significant past hydrological changes. First, Nanoščica formed the Risovec blind valley, followed by Otoška jama, Tartarus, Male jame, and Artificial tunnel toward E/NE, forming the Vodni dol. At the same time, the ponor of Pivka shifted in the Postojnska jama (at present “Stara jama”), flowing towards N, forming Jeršanove doline. The successive subsidence of the erosional base and the Postojna karst uplift redirected the Nanoščica in Pivka. Now they sink into active parts of the Postojna cave at 511 m a.s.l. The eastern study area has the Unroofed cave Kriva dolina as a former ponor of Pivka. At present the area has springs and favourable (sub)vertical passages. The southern study area has the highest variety of contact karst features (i.e. 5). The Prestranški ravnik represents an aquifer with ponors and springs. It is separated from the Slavinski ravnik, by a flysch belt. In the southern study area, 10 caves were longer than 150 m among 49 selected caves. The Loza Cave System, a case study in Slavinski ravnik, is developed in 3 epiphreatic levels that followed two phases of tectonic uplift with a successive formation of diversion routes through 30-40 m deep vadose passages. The oldest upper cave level has sediments from at least the Gilbert Chron with CW rotations. U-Th dates from speleothems prove vadose speleogenesis before the cave ceiling denudation and collapse from 210 ka to 550 ka (≤1.2 Ma). The middle cave level has epiphreatic sediments at least in the Gauss Chron (i.e. 2.59-3.59 Ma) and reveals 35-38° CCW rotations. The allogenic sediments in the lower cave level show Brunhes and Matuyama Chrons (i.e. <0.78-2.58 Ma). We generally discussed ponor steepheads that develop on steepest slopes on the thrust/fault contact, while blind valleys and border depressions develop on normal stratigraphic contact with mildest slopes. The speleogenesis was mainly driven by relatively quick tectonic uplift, followed by vadose speleogenesis, with intermediate speleogenesis in the epiphreatic zone. Speleogenesis and contact karst features follow the subsidence of the water table, evidenced by cave levels, and active and relict features. Allogenic sediments are followed by speleothems as shift of caves between hydrological zones. The sequence of events repeated 2-3 times. The main local source of allogenic sediments is in the Postojna Basin, represented by the erosion of flysch rocks and alluvium. The mineralogical composition between catchments is similar with no significant change. The regional compressional-tectonic regime has significantly influenced the changes in the drainage of the Postojna Basin during the last 7 Ma, with different uplifts and drop of the karst water table. The major uplift was reflected by the change in the Nanoščica course from the Slavinski ravnik to the Postojna karst from S to N, presumably between 3.59 Ma and >1.77 Ma and represented the last important general shift in the drainage of the Postojna Basin.
Ključne besede: karst, contact karst, regional tectonic uplift, cave levels, shift from epiphreatic to vadose speleogenesis, Loza Cave System, Postojna drainage basin
Objavljeno v RUNG: 05.12.2023; Ogledov: 549; Prenosov: 40
.pdf Celotno besedilo (29,89 MB)

2.
CO2 dynamics and dissolutional processes in the karst vadose zone
Lovel Kukuljan, 2022, doktorska disertacija

Opis: The dynamics and distribution of carbon dioxide (CO2) in karst systems are crucial for understanding fundamental karst processes, namely precipitation and dissolution, which drive karst development both at the surface and underground. The study of CO2 transport provides valuable insights into the role of karst systems in the global carbon cycle and the impact on present climate, but also into the growth of speleothems, which are one of the most reliable terrestrial archives for palaeoclimate reconstruction. Due to the complexity of karst systems, long-term monitoring and high-resolution analyses of cave air and water geochemistry are essential to better understand the controlling factors that affect these processes and their outcomes. In the framework of this dissertation, cave climate and water hydrochemistry monitoring was established in a side-passages of the renowned Postojna Cave in Slovenia during 2017–2021. In the Pisani Passage, high CO2 concentrations, large temporal variations and a heterogeneous distribution of CO2, as well as extreme dissolution features, have already been detected in previous studies. The aim of the present study was to investigate these observations in depth and to find the reasons for their occurrence. This led to creating of a conceptual model for CO2 transport in karst systems that would be valid not only in this case but in karst areas worldwide. The first focus of the study is dedicated to understanding the spatio-temporal dynamics of the partial pressure of CO2 (pCO2) in the Pisani Passage, which is mainly transported by advection (i.e., cave ventilation). Continuous measurements of airflow velocity, air temperature and pCO2 showed (1) that airflow through the karst massif is driven by both the action of the chimney effect and external winds, and (2) that the relationship between the direction of airflow, the configuration of airflow pathways and the connection to the outside explains the observed variations in pCO2. Due to the particular configuration of the airflow pathways, the terminal chamber of Pisani Passage accumulates high levels of CO2 (>10,000 ppm) and forms high vertical gradients of up to 1000 ppm/m. The pCO2 is low and uniform during updraft when outside air flows into the cave chamber through open, unobstructed passages (i.e., high-flow, low-pCO2 pathways). When the airflow reverses direction to downdraft, the chamber is fed by low-flow, high-pCO2 pathways that enter the cave passage through a CO2-rich fracture network embedded in a vadose zone. The spatial distribution of inlets and outlets results in minimal mixing between the low and high pCO2 pathways, leading to high and persistent pCO2 gradients. In addition to the chimney effect driving the seasonal ventilation of the cave, the specific signs of a secondary wind-driven effect were also found; which is the second focus of this study. Wind flow over irregular topography leads to near-surface air pressure variations, and thus, pressure differences between cave entrances at different locations. Pressure differences depend on wind speed and direction and their relationship to surface topography and the location of cave entrances. Winds can act in the same or opposite direction as the chimney effect, either enhancing, diminishing or even reversing the direction of density-driven airflows. In the case of Postojna Cave, north and northeast winds enhance the downdraft and limit updraft, while the opposite is true for south winds, which enhance the updraft and limit downdraft. To investigate the importance of wind-driven flow, a computational fluid dynamics model was used to calculate the wind pressure field over Postojna Cave and the pressure differences between selected points for different configurations of wind speed and direction. These values were compared with those obtained from airflow measurements in the cave and from simple theoretical considerations. Despite the simplicity of the approach and the complexity of the ca
Ključne besede: cave climate, cave ventilation, carbon dioxide, dripwater geochemistry, speleothem corrosion, Postojna Cave, Slovenia
Objavljeno v RUNG: 22.06.2022; Ogledov: 1681; Prenosov: 66
.pdf Celotno besedilo (8,45 MB)

3.
Speleogenetic factors and processes in the karst conduits of Zagorska Mrežnica Spring Cave (Croatia)
Petra Kovač Konrad, 2018, doktorska disertacija

Opis: Zagorska Mrežnica spring cave is in the Desmerice village, 7.59 km SW from the town of Ogulin. The coordinates of the entrance are X: 399563 m, Y: 5006974 m, and Z: 314 m (HTRS96). The cave system is positioned in the contact zone of Jurassic limestone and the thrust front composed of Triassic Dolomite. The karst drainage system has elements of point recharge through a set of ponors in the hinterland karst poljes and diffuse infiltration through numerous dolines on Velika Kapela Mountain. The karst of Ogulinsko Zagorje area and its epiphreatic and phreatic cave systems have been intensively explored for the last eight years, resulting in the mapping of 1134 m of submerged passages of the Zagorska Mrežnica spring cave. Until 2014 it was the longest mapped submerged system in Croatia explored by cave diving techniques only. Altogether, over 3.5 km of submerged passages in seven caves of Ogulinsko Zagorje (Zagorska Mrežnica spring cave, Spring of Rupečica, Ponor of Rupečica, Cave system Pećine-Veliko vrelo, Spring of Bistrac, Cave Zagorska Peć and Pit Klisura) were explored during 500 hours of diving over a ten-year period. The goal of the research was to determine speleogenetic factors and processes in phreatic conditions. A new methodology for mapping of cave cross-sections, microrelief forms, and structural elements was developed, sediment and petrographic analysis were done, hydrological analysis before and after the building of the accumulation lake Sabljaci, 48 cross-sections of the cave passaged and a 3D model of the cave system was created, water chemistry as well as geomorphological analysis was carried out. In the end, a simplified (modified) vulnerability assessment was also done. The results of my research showed that the distribution of the cave passages is a result of complex tectonic activities that are reflected in the orientation of cave passages. The general orientation of the measured fissures, measured during cave diving, show a dominance of a NWW-SEE direction but also the pattern of cave passages shows a significant dominance of the NE-SW orientation indicating the existence of multiple secondary traverse faults originating from main NW-SE faults. The morphology of the cave passages shows a transition between epiphreatic (possibly vadose) and phreatic phases as well as the presence of paragenetic developments in the ceiling. This indicates the existence of several epiphreatic (possibly vadose) and phreatic speleogenetic phases. The initial shape of the cross-sections was identified by sub-horizontal beds and bedding planes. The mapping of microrelief forms showed that the mechanical erosion was a very intensive process shaping the morphology of the cave passages. The sediment mineralogy coincides with the lithology of the catchment area, and the sub- angular grains reveal relatively short transport distances. Further analysis of the catchment area’s geomorphology and its relevance for the speleogenesis of Zagorska Mrežnica cave show influence of relief structures that have a Dinaric orientation (NW-SE) with cave structures and passage orientations, great relative relief, steep slopes on Velika Kapela, and flat areas of karst poljes dictate the allogenic and autogenic hydrological regime of the cave. A 3D model of the cave system reveals a relationship between the cave system and the landscape, as well as a possible connection with the nearby Zagorska Peć cave. The modified karst vulnerability assessment shows that the catchment area of Zagorska Mrežnica spring cave has a high vulnerability ranking, mainly due to high doline density and the potential large diffuse capacity of infiltration of pollutants.
Ključne besede: Ogulin Zagorje, karst, spring, speleogenesis, Zagorska Mrežnica spring cave
Objavljeno v RUNG: 02.03.2018; Ogledov: 4851; Prenosov: 196
.pdf Celotno besedilo (5,26 MB)

4.
Hydrogeological and speleological research of the spring cave Slatinski Izvor and its recharge are (Republic of Macedonia)
Biljana Gichevski, 2016, doktorska disertacija

Opis: This thesis represents a comprehensive study, giving first extensive information on the hydrogeological and speleological characteristics of the spring cave Slatinski Izvor and its catchment area. The researched spring is located in the Poreče basin of West-Central Macedonia, in the river valley of Slatinska Reka. The wider area around the spring belongs to two tectonic units. The Slatinski Izvor spring is situated on the Pelagonian horst anticlinorium, which is composed of carbonate rocks. The second is the Western Macedonian zone, and it is composed of non-carbonate rocks. The spring represents a significant potential for water supply for the settlement Slatina. Prior to this research only some basic information about the karst aquifer in Precambrian dolomite marbles was available. Therefore, my goal was to ensure better understanding of the functioning of the karst system in the recharge area of the spring, assessment of its vulnerability to various pollution sources, as well as study of karst development of the area. Because karst aquifers have unique hydrogeological characteristics and specific nature, they also require specifically adapted investigation methods. In order to reach the main goal, speleological investigations, hydrological methods, hydrochemical methods and tracer test were used. A monitoring network was combined with regular samplings for major and trace elements analysis, which enabled considerable advances in understanding the functioning of the karst system. The data from two-year period (December 2011 – November 2013) was compared and analyzed. The controlling of the karst development in the study area mostly depends on the tectonic and geologic conditions. Incision of Slatinska Reka is the main controlling factor in cave development by lowering the base level of karst terrains. All investigated caves (Gorna Slatinska, Slatinska II, Ovčarska Peštera, Puralo, Slatinski Izvor) have “normal” epigenic karst development. Slatinski Izvor is the youngest cave. The Slatinski Izvor spring serves as a cave entrance for the same cave and, represents the outflow of groundwater from the karst system. A conceptual model of the karst system of the study area was developed. The Slatinski Izvor spring has typical karst hydrological regime. The karst system is well developed by conduits and rains infiltrated into vadose zone flow rapidly towards the spring. The travel time of low mineralized water within the system corresponds well with the results from an artificial tracer test. Performed artificial tracer test confirmed that the Slatinski Izvor spring is recharged by allogenic stream. The dominant apparent flow velocity of 250 m/h, a single peak of the tracer breakthrough curve and more than 87% of tracer recovered indicate a rapid conduit flow and high vulnerability of the observed drinking water source. Analysis of spatial and temporal variations of physical and chemical parameters show that waters in the study area had different origin and were transmitted along different flow paths. The origin of the water of the Slatinski Izvor spring is from non-carbonate area, but the influence of mixed limestone-dolomite sequence in the carbonate area is significant. The results point out to short residence time of the water in the karst aquifer. The anthropogenic impact in the study area is insignificant which is reflected in the good water quality. In order to preserve it, land surface zoning was performed in terms of groundwater and spring water vulnerability to pollution according to the hydrogeological research. A comprehensive research with a combined use of various research tools presents an innovative approach and a new contribution to the Macedonian karstological science. Applied methods proved to be successful for to study of the karst system. Finally, the results of the study have clear applicative significance in terms of drinking water management.
Ključne besede: karst hydrology, cave, speleological investigation, hydrochemistry, tracer test, spring Slatinski Izvor
Objavljeno v RUNG: 14.10.2016; Ogledov: 30140; Prenosov: 158
.pdf Celotno besedilo (11,01 MB)

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