Roded et al 2024. Hypogene speleogenesis in carbonates by cooling, confined hydrothermal flow: The case of Mt. Berenike caves, Israel (original) (raw)
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Author's personal copy Morphogenesis of hypogenic caves
Hypogenic speleogenesis is the formation of solution-enlarged permeability structures by waters ascending to a cave-forming zone from below in leaky confined conditions, where deeper groundwaters in regional or intermediate flow systems interact with shallower and more local groundwater flow systems. This is in contrast to more familiar epigenic speleogenesis which is dominated by shallow groundwater systems receiving recharge from the overlying or immediately adjacent surface. Hypogenic caves are identified in various geological and tectonic settings, formed by different dissolutional mechanisms operating in various lithologies. Despite these variations, resultant caves demonstrate a remarkable similarity in patterns and meso-morphology, which strongly suggests that the hydrogeologic settings were broadly identical in their formation. Hypogenic caves commonly demonstrate a characteristic suite of cave morphologies resulting from rising flow across the cave-forming zone with distinct buoyancydissolution components. In addition to hydrogeological criteria (hydrostratigraphic position, rechargedischarge configuration and flow pattern viewed from the perspective of the evolution of a regional groundwater flow system), morphogenetic analysis is the primary tool in identifying hypogenic caves. Cave patterns resulting from ascending transverse speleogenesis are strongly guided by the permeability structure in a cave formation. They are also influenced by the discordance of permeability structure in the adjacent beds and by the overall hydrostratigraphic arrangement. Three-dimensional mazes with multiple storeys, or complex 3-D cave systems are most common, although single isolated chambers, passages or crude clusters of a few intersecting passages may occur where fracturing is scarce and laterally discontinuous. Large rising shafts and collapse sinkholes over large voids, associated with deep hydrothermal systems, are also known. Hypogenic caves include many of the largest, by integrated length and by volume, documented caves in the world. More importantly, hypogenic speleogenesis is much more widespread than it was previously presumed. Growing recognition of hypogenic speleogenesis and improved understanding of its peculiar characteristics has an immense importance to both karst science and applied fields as it promises to answer many questions about karst porosity (especially as deep-seated settings are concerned) which remained poorly addressed within the traditional epigenetic karst paradigm.
Morphogenesis of hypogenic caves
Geomorphology, 2009
Hypogenic speleogenesis is the formation of solution-enlarged permeability structures by waters ascending to a cave-forming zone from below in leaky confined conditions, where deeper groundwaters in regional or intermediate flow systems interact with shallower and more local groundwater flow systems. This is in contrast to more familiar epigenic speleogenesis which is dominated by shallow groundwater systems receiving recharge from the overlying or immediately adjacent surface.Hypogenic caves are identified in various geological and tectonic settings, formed by different dissolutional mechanisms operating in various lithologies. Despite these variations, resultant caves demonstrate a remarkable similarity in patterns and meso-morphology, which strongly suggests that the hydrogeologic settings were broadly identical in their formation. Hypogenic caves commonly demonstrate a characteristic suite of cave morphologies resulting from rising flow across the cave-forming zone with distinct buoyancy-dissolution components. In addition to hydrogeological criteria (hydrostratigraphic position, recharge–discharge configuration and flow pattern viewed from the perspective of the evolution of a regional groundwater flow system), morphogenetic analysis is the primary tool in identifying hypogenic caves.Cave patterns resulting from ascending transverse speleogenesis are strongly guided by the permeability structure in a cave formation. They are also influenced by the discordance of permeability structure in the adjacent beds and by the overall hydrostratigraphic arrangement. Three-dimensional mazes with multiple storeys, or complex 3-D cave systems are most common, although single isolated chambers, passages or crude clusters of a few intersecting passages may occur where fracturing is scarce and laterally discontinuous. Large rising shafts and collapse sinkholes over large voids, associated with deep hydrothermal systems, are also known.Hypogenic caves include many of the largest, by integrated length and by volume, documented caves in the world. More importantly, hypogenic speleogenesis is much more widespread than it was previously presumed. Growing recognition of hypogenic speleogenesis and improved understanding of its peculiar characteristics has an immense importance to both karst science and applied fields as it promises to answer many questions about karst porosity (especially as deep-seated settings are concerned) which remained poorly addressed within the traditional epigenetic karst paradigm.
Communications Earth & Environment, 2023
Karst systems, comprising interconnected voids and caves, are ubiquitous in carbonate formations and play a pivotal role in the global water supply. Accumulating evidence suggests that a significant portion of the global karst is hypogenic, formed via rock dissolution by groundwater ascending from depth (rather than by infiltration from the surface), yet the exact formation mechanism remains unclear. Here we show that cooling of carbon dioxiderich geothermal fluids, which turns them into highly corrosive agents due to their retrograde solubility, can dissolve and sculpt large caves on short geological timescales. A conceptual hydro-thermo-geochemical scenario is numerically simulated, showing cave formation by rising hot water discharging into a confined layer. Our models predict field observations characteristic of hypogenic caves, including enigmatic locations of the largest passages and intricate maze-like networks. Finally, we suggest that deep-seated carbon dioxide consumption during karst formation may constitute a link to the global carbon cycle.
Hypogene Karst Regions and Caves of the World
Hypogene Karst Regions and Caves of the World, 2017
This book illustrates the diversity of hypogene speleogenetic processes and void-conduit patterns depending on variations of the geological environments by presenting regional and cave-specific case studies. The cases include both well-known and newly recognized hypogene karst regions and caves of the world. They all focus on geological, hydrogeological, geodynamical and evolutionary contexts of hypogene speleogenesis. The last decade has witnessed the boost in recognition of the possibility, global occurrence, and practical importance of hypogene karstification (speleogenesis), i.e. the development of solutional porosity and permeability by upwelling flow, independent of recharge from the overlying or immediately adjacent surface. Hypogene karst has been identified and documented in many regions where it was previously overlooked or misinterpreted. The book enriches the basis for generalization and categorization of hypogene karst and thus improves our ability to adequately model hypogene karstification and predict related porosity and permeability. It is a book which benefits every researcher, student, and practitioner dealing with karst.
Acta Carsologica, 2015
UDC 551.435.84 Philippe Audra & Arthur N. Palmer: Research frontiers in speleogenesis. Dominant processes, hydrogeological conditions and resulting cave patterns Speleogenesis is the development of well-organized cave systems by fluids moving through fissures of a soluble rock. Epigenic caves induced by biogenic CO 2 soil production are dominant, whereas hypogenic caves resulting from uprising deep flow not directly connected to adjacent recharge areas appear to be more frequent than previously considered. The conceptual models of epigenic cave development moved from early models, through the "four-states model" involving fracture influence to explain deep loops, to the digital models demonstrating the adjustment of the main flow to the water table. The relationships with base level are complex and cave levels must be determined from the elevation of the vadose-phreatic transitions. Since flooding in the epiphreatic zone may be important, the top of the loops in the epiphreatic zone can be found significantly high above the base level. The term Paragenesis is used to describe the upward development of conduits as their lower parts fill with sediments. This process often records a general baselevel rise. Sediment influx is responsible for the regulation of long profiles by paragenesis and contributes to the evolution of profiles from looping to water table caves. Dating methods allow identification of the timing of cave level evolution. The term Ghost-rock karstification is used to describe a 2-phase process of speleogenesis, with a first phase of partial solution of rock along fractures in low gradient conditions leaving a porous matrix, the ghost-rock, then a second phase of mechanical removing of the ghost-rock mainly by turbulent flow in high gradient conditions opening the passages and forming maze caves. The first weathering phase can be related either to epigenic infiltration or to hypogenic upflow, especially in marginal areas of sedimentary basins. The vertical pattern of epigenic caves is mainly controlled by timing, geological structure, types of flow and base-level changes. We define several
Speleogenesis, geometry, and topology of caves: A quantitative study of 3D karst conduits
Geomorphology
Karst systems are hierarchically spatially organized three-dimensional (3D) networks of conduits behaving as drains for groundwater flow. Recently, geostatistical approaches proposed to generate karst networks from data and parameters stemming from analogous observed karst features. Other studies have qualitatively highlighted relationships between speleogenetic processes and cave patterns. However, few studies have been performed to quantitatively define these relationships. This paper reports a quantitative study of cave geometries and topologies that takes the underlying speleogenetic processes into account. In order to study the spatial organization of caves, a 3D numerical database was built from 26 caves, corresponding to 621 km of cumulative cave passages representative of the variety of karst network patterns. The database includes 3D speleological surveys for which the speleogenetic context is known, allowing the polygenic karst networks to be divided into 48 monogenic cave samples and classified into four cave patterns: vadose branchwork (VB), water-table cave (WTC), looping cave (LC), and angular maze (AM). Eight morphometric cave descriptors were calculated, four geometrical parameters (width-height ratio, tortuosity, curvature, and vertical index) and four topological ones (degree of node connectivity, α and γgraph indices, and ramification index) respectively. The results were validated by statistical analyses (Kruskal-Wallis test and PCA). The VB patterns are clearly distinct from AM ones and from a third group including WTC and LC. A quantitative database of cave morphology characteristics is provided, depending on their speleogenetic processes. These characteristics can be used to constrain and/or validate 3D geostatistical simulations. This study shows how important it is to relate the geometry and connectivity of cave networks to recharge and flow processes. Conversely, the approach developed here provides proxies to estimate the evolution of the vadose zone to epiphreatic and phreatic zones in limestonesfrom the quantitative analysis of existing cave patterns.
Hypogene speleogenesis in dolomite host rock by CO2 -rich fluids, Kozak Cave (southern Austria)
A growing number of studies suggest that cave formation by deep-seated groundwater (hypogene) is a more common process of subsurface water–rock interaction than previously thought. Fossil hypogene caves are identified by a characteristic suite of morphological features on different spatial scales. In addition, mineral deposits (speleothems) may provide clues about the chemical composition of the paleowater, which range from CO 2-rich to sulfuric acid-bearing waters. This is one of the first studies to examine hypogene cave formation in dolomite. Kozak Cave is a fossil cave near the Periadriatic Lineament, an area known for its abundance of CO 2-rich springs. The cave displays a number of macro-, meso-and micromorphological elements found also in other hypogene caves hosted in limestone, marble or gypsum, including cupolas, cusps, Laughöhle-type chambers and notches. The existance of cupolas and cusps suggests a thermal gradient capable of sustaining free convection during a first phase of speleogenesis, while triangular cross sections (Laughöhle morphology) indicate subsequent density-driven convection close to the paleowater table. Notches mark the final emergence of the cave due to continued rock uplift and valley incision. Very narrow shafts near the end of the cave may be part of the initial feeder system, but an epigene (vadose) overprint cannot be ruled out. Vadose speleothems indicate that the phreatic phase ended at least about half a million years ago. Drill cores show no evidence of carbon or oxygen isotope alteration of the wall rock. This is in contrast to similar studies in limestone caves, and highlights the need for further wall-rock studies of caves hosted in limestone and dolomite.
Geomorphology, 2014
The vertical organisation of karst conduit networks has been the focus of speleogenetic studies for more than a century. The four state model of , which still is considered as the most general, relates the geometry of caves to the frequency of permeable fissures. The model suggests that the 'water table caves' are common in areas with high fissure frequency, which is often the case in natural settings. However, in Alpine karst systems, water table caves are more the exception than the rule. Alpine speleogenesis is influenced by high uplift, valley incision rates and irregular recharge. To study the potential role of these processes for speleogenesis in the dimensions of length and depth, we apply a simple mathematical model based on coupling of flow, dissolution and transport. We assume a master conduit draining the water to the spring at a base level. Incision of the valley triggers evolution of deeper flow pathways, which are initially in a proto-conduit state. The master conduit evolves into a canyon following the valley incision, while the deep pathways evolve towards maturity and tend to capture the water from the master conduits. Two outcomes are possible: a) deep pathways evolve fast enough to capture all the recharge, leaving the master conduit dry; or b) the canyon reaches the level of deep pathways before these evolve to maturity. We introduce the Loop-to-Canyon Ratio (LCR), which predicts which of the two outcomes is more likely to occur in certain settings. Our model is extended to account for transient flow conditions. In the case of an undulating master conduit, floodwater is stored in troughs after the flood retreat. This water seeps through sub-vertical fractures ('soutirages') connecting the master conduit with the deep pathways. Therefore, the loops evolve also during the dry season, and the LCR is considerably increased. Although the model is based on several approximations, it leads to some important conclusions for vertical organisation of karst conduit networks and stresses the importance of base-level changes and transient recharge conditions. It therefore gives an explanation of speleogenesis that relies much more on the dynamic nature of water flow than on the static fracture density.
The initial stages of cave formation: Beyond the one-dimensional paradigm
Earth and Planetary Science Letters, 2011
The solutional origin of limestone caves was recognized over a century ago, but the short penetration length of an undersaturated solution made it seem impossible for long conduits to develop. This is contradicted by field observations, where extended conduits, sometimes several kilometers long, are found in karst environments. However, a sharp drop in the dissolution rate of CaCO 3 near saturation provides a mechanism for much deeper penetration of reactant. The notion of a "kinetic trigger" -a sudden change in rate constant over a narrow concentration range -has become a widely accepted paradigm in speleogenesis modeling. However, it is based on one-dimensional models for the fluid and solute transport inside the fracture, assuming that the dissolution front is planar in the direction perpendicular to the flow. Here we show that this assumption is incorrect; a planar dissolution front in an entirely uniform fracture is unstable to infinitesimal perturbations and inevitably breaks up into highly localized regions of dissolution. This provides an alternative mechanism for cave formation, even in the absence of a kinetic trigger. Our results suggest that there is an inherent wavelength to the erosion pattern in dissolving fractures, which depends on the reaction rate and flow rate, but is independent of the initial roughness. In contrast to one-dimensional models, two-dimensional simulations indicate that there is only a weak dependence of the breakthrough time on kinetic order; localization of the flow tends to keep the undersaturation in the dissolution front * Corresponding author