BACTERIA, FUNGI AND BIOKARST IN LECHUGUILLA CAVE, CARLSBAD-CAVERNS-NATIONAL-PARK, NEW-MEXICO, 1995, Cunningham Ki, Northup De, Pollastro Rm, Wright Wg, Larock Ej,

Lechuguilla Cave is a deep, extensive, gypsum- and sulfur-bearing hypogenic cave in Carlsbad Caverns National Park, New Mexico, most of which (> 90%) lies more than 300 m beneath the entrance. Located in the arid Guadalupe Mountains, Lechuguilla's remarkable state of preservation is partially due to the locally continuous Yates Formation siltstone that has effectively diverted most vadose water away from the cave. Allocthonous organic input to the cave is therefore very limited, but bacterial and fungal colonization is relatively extensive: (1) Aspergillus sp. fungi and unidentified bacteria are associated with iron-, manganese-, and sulfur-rich encrustations on calcitic folia near the suspected water table 466 m below the entrance; (2) 92 species of fungi in 19 genera have been identified throughout the cave in oligotrophic (nutrient-poor) ''soils'' and pools; (3) cave-air condensate contains unidentified microbes; (4) indigenous chemoheterotrophic Seliberius and Caulobacter bacteria are known from remote pool sites; and (5) at least four genera of heterotrophic bacteria with population densities near 5 x 10(5) colony-forming units (CFU) per gram are present in ceiling-bound deposits of supposedly abiogenic condensation-corrosion residues. Various lines of evidence suggest that autotrophic bacteria are present in the ceiling-bound residues and could act as primary producers in a unique subterranean microbial food chain. The suspected autotrophic bacteria are probably chemolithoautotrophic (CLA), utilizing trace iron, manganese, or sulfur in the limestone and dolomitic bedrock to mechanically (and possibly biochemically) erode the substrate to produce residual floor deposits. Because other major sources of organic matter have not been detected, we suggest that these CLA bacteria are providing requisite organic matter to the known heterotrophic bacteria and fungi in the residues. The cavewide bacterial and fungal distribution, the large volumes of corrosion residues, and the presence of ancient bacterial filaments in unusual calcite speleothems (biothems) attest to the apparent longevity of microbial occupation in this cave

Occurrence of hypogenic caves in a karst region: examples from central Italy., 1995, Galdenzi S. , Menichetti M.

OCCURRENCE OF HYPOGENIC CAVES IN A KARST REGION - EXAMPLES FROM CENTRAL ITALY, 1995, Galdenzi S, Menichetti M,

The caves of the Umbria and Marche regions in central Italy are made up of three-dimensional maze systems that display different general morphologies due to the various geological and structural contexts. At the same time, the internal morphologies of the passages, galleries, and shafts present some similarity, with solutional galleries characterized by cupolas and blind pits, anastamotic passages, roof pendants, and phreatic passages situated at different levels. Some of these caves are still active, as is the case for Frassassi Gorge, Parrano Gorge, and Acquasanta Terme, with galleries that reach the phreatic zone, where there is a rising of highly mineralized water, rich in hydrosulfydric acid, and with erosion of limestone walls and the formation of gypsum. Elsewhere there are fossil caves, such as Monte Cucco and Pozzi della Piana, where large speleothems of gypsum are present 500 m or more above the regional water table. In all of these important karst systems it is possible to recognize basal input points through fracture and intergranular porosity networks at the base of the oxidizing zone in the core of the anticline, where mineralized water rises up from the Triassic evaporitic layers in small hydrogeological circuits. Different underground morphologies can derive from the presence of a water table related to an external stream or from the confined setting of the carbonate rocks, underlying low permeable sedimentary cover, where artesian conditions can occur

The initiation of hypogene caves in fractured limestone by rising thermal water: investigation of a parallel series of competing fractures, 1999, Dumont K. A. , Rajaram H. , Budd D. A.

Integrated cave systems can either form at or near the surface of the earth (epigenic) or at some depth below the earth's surface (hypogenic)For caves that form in fractured limestone, the two most common types of cave-system morphologies are branchwork and mazeworkBranchwork caves are composed of tributaries that coalesce in the downstream direction, similar to surface streamsMazework caves exhibit two or more sets of parallel passages intersecting in a grid-like patternThe majority of epigenic caves exhibit branchwork morphologies, which represent the dominance of individual flow pathsIn contrast, mazework caves develop when dissolution occurs along numerous flow pathsWhereas most epigenic caves are related to surficial meteoric flow systems, some mazework caves are thought to have formed in hypogene environments where rising thermal water cools in response to the geothermal gradientOur objective is to examine the fundamental cause for the difference in morphology between epigenic and thermal hypogenic cave systems using numerical modelsIn particular, we are examining the competition between different flow paths in fractured limestone undergoing dissolutional enlargementAs noted in previous numerical studies, epigenic systems are characterized by the dominance of a single flow path, which is consistent with the structure of epigenic cavesSo, in order to explain the structure of maze caves, one has to explain why no single flow path attains dominanceThe retrograde solubility of calcite coupled with heat transfer from the fluid to the rock is hypothesized to provide the mechanism by which dissolutional power is distributed among all competing flow pathsNumerical models of fluid flow, heat transfer, and calcite dissolution chemistry are integrated to develop a model of hypogene cave initiation in fractured limestoneFlow is assumed to occur in the presence of a spatially variable rock temperature field that is constant through timePreliminary numerical modeling results for a system of parallel fractures demonstrate the differences in the nature of competition between flow paths in epigenic (constant temperature) and hypogenic systems (flow in the presence of a negative thermal gradient)Differences in results using various kinetic models for calcite dissolution are also presentedThe role of aperture variation and distribution in a parallel set of fractures is also examined

Bedrock Features of Lechuguilla Cave, Guadalup Mountains, New Mexico, 2000, Duchene, H. R.

Lechuguilla is a hypogenic cave dissolved in limestones and dolostones of the Capitan Reef Complex by sulfuric acid derived from oil and gas accumulations in the Delaware Basin of southeast New Mexico and west Texas. Most of the cave developed within the Seven Rivers and Capitan Formations, but a few high level passages penetrate the lower Yates Formation. The Queen and possibly Goat Seep formations are exposed only in the northernmost part of the cave below -215 m. Depositional and speleogenetic breccias are common in Lechuguilla. The cave also has many spectacular fossils that are indicators of depositional environments. Primary porosity in the Capitan and Seven Rivers Formations was a reservoir for water containing hydrogen sulfide, and a pathway for oxygenated meteoric water prior to and during sulfuric acid speleogenesis. Many passages at depths >250 m in Lechuguilla are in steeply dipping breccias that have a west-southwest orientation parallel to the strike of the shelf margin. The correlation between passage orientation and depositional strike suggests that stratigraphy controls these passages.

Microbiology and geochemistry in a hydrogen-sulphide-rich karst environment, 2000, Hose Louise D. , Palmer Arthur N. , Palmer Margaret V. , Northup Diana E. , Boston Penelope J. , Duchene Harvey R. ,

Cueva de Villa Luz, a hypogenic cave in Tabasco, Mexico, offers a remarkable opportunity to observe chemotrophic microbial interactions within a karst environment. The cave water and atmosphere are both rich in hydrogen sulphide. Measured H2S levels in the cave atmosphere reach 210 ppm, and SO2 commonly exceeds 35 ppm. These gases, plus oxygen from the cave air, are absorbed by freshwater that accumulates on cave walls from infiltration and condensation. Oxidation of sulphur and hydrogen sulphide forms concentrated sulphuric acid. Drip waters contain mean pH values of 1.4, with minimum values as low as 0.1.The cave is fed by at least 26 groundwater inlets with a combined flow of 200-300 l/s. Inlet waters fall into two categories: those with high H2S content (300-500 mg/l), mean PCO2=0.03-0.1 atm, and no measurable O2; and those with less than 0.1 mg/l H2S, mean PCO2=0.02 atm, and modest O2 content (up to 4.3 mg/l). Both water types have a similar source, as shown by their dissolved solid content. However, the oxygenated water has been exposed to aerated conditions upstream from the inlets so that original H2S has been largely lost due to outgassing and oxidation to sulphate, increasing the sulphate concentration by about 4%. Chemical modelling of the water shows that it can be produced by the dissolution of common sulphate, carbonate, and chloride minerals.Redox reactions in the cave appear to be microbially mediated. Sequence analysis of small subunit (16S) ribosomal RNA genes of 19 bacterial clones from microbial colonies associated with water drips revealed that 18 were most similar to three Thiobacilli spp., a genus that often obtains its energy from the oxidation of sulphur compounds. The other clone was most similar to Acidimicrobium ferrooxidans, a moderately thermophilic, mineral-sulphide-oxidizing bacterium. Oxidation of hydrogen sulphide to sulphuric acid, and hence the cave enlargement, is probably enhanced by these bacteria.Two cave-enlarging processes were identified. (1) Sulphuric acid derived from oxidation of the hydrogen sulphide converts subaerial limestone surfaces to gypsum. The gypsum falls into the cave stream and is dissolved. (2) Strongly acidic droplets form on the gypsum and on microbial filaments, dissolving limestone where they drip onto the cave floors.The source of the H2S in the spring waters has not been positively identified. The Villahermosa petroleum basin within 50 km to the northwest, or the El Chichon volcano [small tilde]50 km to the west, may serve as source areas for the rising water. Depletion of 34S values (-11.7[per mille sign] for sulphur stabilized from H2S in the cave atmosphere), along with the hydrochemistry of the spring waters, favour a basinal source

The hypogenic caves: a powerful tool for the study of seeps and their environmental effects, 2002, Forti P, Galdenzi S, Sarbu Sm,

Research performed in caves has shown the existence of significant effects of gas seeps, especially CO2 and H2S, within subterranean voids. Carbon dioxide causes important corrosive effects and creates characteristic morphologies (e.g., bell-shaped domes, bubble's trails), but is not involved in the deposition of specific cave minerals. On the other hand, in carbonate environments, hydrogen sulfide when oxidized in the shallow sections of the aquifer generates important corrosion effects and is also responsible for the deposition of specific minerals of which gypsum is the most common.Studies performed in the last few years have shown that H2S seeps in caves are associated with rich and diverse biological communities, consisting of large numbers of endemic species. Stable isotope studies (carbon and nitrogen) have demonstrated that these hypogean ecosystems are entirely based on in situ production of food by chemoautotrophic microorganisms using energy resulting from the oxidation of H2S.Although located only 20 m under the surface, Movile Cave does not receive meteoric waters due to a layer of impermeable clays and loess that covers the Miocene limestone in which the cave is developed. In the Frasassi caves, where certain amounts of meteoric water seep into the limestone, the subterranean ecosystems are still isolated from the surface. As the deep sulfidic waters mix with the oxigenated meteoric waters, sulfuric acid limestone corrosion is accelerated resulting in widespread deposition of gypsum onto the cave walls.Both these caves have raised a lot of interest for biological investigations regarding the chemoautotrophically based ecosystems, demonstrating the possibility of performing such studies in environments that are easily accessible and easy to monitor compared to the deep-sea environments where the first gas seeps were discovered

Hypogenic caves in Provence (France). Specific features and sediments, 2002, Audra Philippe, Bigot Jeanyves, Mocochain Ludovic

Two dry caves from French Provence (Adaouste and Champignons caves) were until now considered as "normal" caves having evolved under meteoric water flow conditions. A new approach gives evidence of a hypogenic origin from deep water uprising under artesian conditions. Specific morphologies and sediments associated with this hydrology are discussed.

Gypsum deposits in the Frasassi Caves, central Italy, 2003, Galdenzi, S. , Maruoka, T.

The Frasassi Caves are hypogenic caves in central Italy, where H2S-rich groundwater flows in the lowest cave level. Near the water table, the H2S is converted to sulfuric acid by biotic and abiotic processes, which have enhanced cave development. The sulfate generally deposits above the water table as a replacement gypsum crust coating limestone walls or as large gypsum crystals. Although the oxidation of sulfide also occurs below the water table, sulfate saturation is not achieved, therefore, sulfate does not precipitate below the water table. In the upper dry levels of the cave, three main types of ancient gypsum deposits occurs: (1) replacement crusts, similar to the presently forming deposits of the active zone, (2) microcrystalline large and thick floor deposits, and (3) euhedral crystals inside mud. The study of the depositional setting and the analysis of sulfur isotopes in the gypsum and groundwater clearly demonstrate that all the sampled gypsum in the cave formed by H2S oxidation above the water table. Some fraction of small sulfur isotopic differences between H2S in the water and gypsum can be explained by isotopic fractionation during abiotic and/or biotic oxidation of H2S.

Hypogenic caves in Provence (France): Specific features and sediments, 2003, Audra Ph, Bigot J. Y, Mocochain L.

Two dry caves from French Provence (Adaouste and Champignons caves) were until now considered as “normal” caves, evolved under meteoric water flow conditions. A new approach gives evidence of a hypogenic origin from deep water uprising under artesian conditions. Specific morphologies and sediments associated with this hydrology are discussed.

On feasibility of condensation corrosion in caves (Comment to the paper: ''Hypogenic caves in Provence (France): Specific features and sediments'' by Ph. Audra, J.Y. Bigot and L. Mocochain), 2003, Dreybrodt, W.

In Fig. 6 of this paper the authors suggest how condensation corrosion could shape ceiling cupolas. Hot water containing high concentration of carbon dioxide rises to a lake filling the lower part of the cave room. Degassing of CO2 creates a CO2-containing atmosphere, which is heated by the warmer water below and becomes saturated with vapor, which condenses to the cooler wall of the cave, dissolves limestone and flows back to the lake.
If this process would continue in time it would be perfect to shape large cupolas. However, it does not because condensation stops when the temperature of the cave walls approaches that of the heated air. The reason is that condensation of water at the cave wall releases heat of condensation of 2.45 kJoule/g. This corresponds to an energy flux of 28 Watt/square-meter if a film of 1 mm depth would condensate to the wall in one day. In addition there is also a flux of heat from the warm air to the cave wall. Since the thermal conductivity of limestone (1.3 Watt/m°K) and its thermal diffusivity (5.6 x 10-7 m2/s) are low this heat cannot be rapidly transported into the bedrock, and consequently the temperature of the cave wall rises. Therefore the amount of condensation is reduced. 

One further comment should be given. There have been attempts to measure the effect of condensation corrosion by suspending gypsum plates freely in the air and determining weight loss after a defined time. For the reasons stated above the heat of condensation and the heat flux from the air raise the temperature of such samples much quicker than that of the cave walls. Reliable measurements can only be performed when such samples are fixed to the cave walls by using a high thermal conductivity glue.

A further suggestion to prove condensed water on cave walls is to take samples and analyse them for Ca-concentration and 13 carbon isotopic ratio. Since CO2 comes from the atmosphere exclusively should be below or close to zero, and Ca-concentration should be about 0.6 mmol/liter, when the pCO2 of the cave atmosphere is atmospheric.

The influence of bedrock-derived acidity in the development of surface and underground karst: Evidence from the Precambrian carbonates of semi-arid northeastern Brazil, 2003, Auler As, Smart Pl,

Very extensive cave systems are developed in Precambrian Una Group carbonates in the Campo Formoso area, eastern Brazil. In contrast, the area is largely devoid of significant surface karst landforms, as would be expected given its semi-arid climate. The caves in the area display many morphological features characteristic of deep-seated hypogenic caves, such as lack of relationship with the surface, ramiform/network pattern, abrupt variations of passage cross-sections and absence of fluvial sediments, but do not show evidence of vertical passages marking the ascending path of acidic water nor present extensive gypsum or acid clay mineral deposits. Hydrochemical analyses of present-day ground water indicate that oxidation of bedrock sulphide is an active process, and sulphuric acid may be the main agent driving carbonate dissolution in the area. A shallow mode of speleogenesis is thus proposed, in which sulphuric acid produced through the oxidation of sulphide beds within the carbonates controls cave initiation and development. Moreover, the geological situation of the area in an ancient stable passive margin precludes the possibility of deep-seated sources of acidity. Under dry climate, due to the absence of recharge, solutional landforms will be largely subdued in the surface. Hypogenic processes, if present, are likely to predominate, producing a landscape characterized by a marked disparity in the comparative degree of development between surface and underground landforms. Rates of karst landform development have traditionally been analysed through a climatic perspective, runoff being the main controlling factor in promoting karst development. This view needs to be reassessed in the light of the growing awareness of the importance of climate-independent processes related to hypogenic sources of acidity.

A hypogenic cave formed by ''connate'' water from the Craven Basin? [Arthur's Cave, Bowland], 2004, Hunt Barry M.

Rates of condensation corrosion in speleothems of semi-arid northeastern Brazil, 2004, Auler A. S. , Smart P. L.

Condensation corrosion is a little studied, but important dissolutional process that occurs within caves in many karst settings around the world (for a review see Dublyansky and Dublyansky, 2000). Condensation corrosion occurs when air equilibrates with the cave atmosphere, becomes acidic and dissolves the bedrock and speleothems. It is a later vadose process that apparently depends on air circulation patterns, number of entrances and general configuration (vertical range, presence of ponded water, passage shape, etc) of the cave. Both bedrock and speleothems can be affected by the process, resulting in weathered outer surfaces. Condensation corrosion in speleogenesis has been regarded as responsible for dissolutional modification during later stages of cave development of coastal (Tarhule-Lips and Ford, 1998) and hypogenic caves (Hill, 1987; Palmer and Palmer, 2000).
Condensation corrosion is a little studied, but important dissolutional process that occurs within caves in many karst settings around the world (for a review see Dublyansky and Dublyansky, 2000). Condensation corrosion occurs when air equilibrates with the cave atmosphere, becomes acidic and dissolves the bedrock and speleothems. It is a later vadose process that apparently depends on air circulation patterns, number of entrances and general configuration (vertical range, presence of ponded water, passage shape, etc) of the cave. Both bedrock and speleothems can be affected by the process, resulting in weathered outer surfaces. Condensation corrosion in speleogenesis has been regarded as responsible for dissolutional modification during later stages of cave development of coastal (Tarhule-Lips and Ford, 1998) and hypogenic caves (Hill, 1987; Palmer and Palmer, 2000).
The Campo Formoso Karst area of northeastern Brazil holds very extensive cave systems, such as Southern Hemisphere’s longest cave, the 97 km long Toca da Boa Vista. These caves show remarkable features of condensation corrosion such as cupolas, weathered cave walls yielding dolomitic sand, “air scallops” and corroded speleothems. Weathering rinds up to 5 cm thick occur in both dolomite bedrock and speleothem surfaces. Unlike the dolomite, speleothems usually do not disintegrate but change to a milky white opaque porous calcite that is in marked contrast with the fresh crystalline calcite. The area is presently under semi-arid climate and the cave atmosphere is characterised by high internal temperatures (2729 °C) and low relative humidity (mean of 73% for sites away from entrances).
Despite being such a widespread process, rates of condensation corrosion have so far been reported only from caves in the coastal area of the Caribbean (Tarhule-Lips and Ford, 1998). In this study, rates of condensation corrosion in speleothems were derived by determining thickness of weathering rind and age of last unaltered calcite. These rates represent minimum rates because speleothem growth ceased later than age obtained, and also condensation corrosion may not be continuous in time. Due to variable thickness of weathering layer (usually thicker at the top and thinner at sides of stalagmites), maximum and minimum thickness were obtained for each sample. Dating was performed through the alpha spectrometric U-series method in the first unaltered calcite layer beyond the weathering rim. 
The rates obtained vary over two orders of magnitude. They appear to be highly site specific, and are probably heavily dependent on the local atmospheric conditions, although more sampling is needed to confirm this relationship. The data shows that rates are dependent primarily on thickness measured, as range of ages is quite small. Tarhule-Lips and Ford (1998), in the very different littoral caves of the Caribbean, have estimated condensation corrosion rates based on experiments using gypsum tablets. Their reported mean value of 24 mm/ka, much higher than observed in the Campo Formoso caves, suggest that the process may be episodic in the area, not occurring during speleothem growth phases associated with wetter periods.
Although the rates reported by Tarhule-Lips and Ford (1998) indicate that condensation corrosion may actually enlarge cave passages in the normal (10 4 – 10 6 ka) time range of speleogenesis, in the Campo Formoso caves the process appears to play a minor speleogenetic role, being responsible for later modification of cave walls and speleothems.

Hypogene Speleogenesis: Hydrogeological and Morphogenetic Perspective., 2007, Klimchouk A. B.

This book provides an overview of the principal environments, main processes and manifestations of hypogenic speleogenesis, and refines the relevant conceptual framework. It consolidates the notion of hypogenic karst as one of the two major types of karst systems (the other being epigenetic karst). Karst is viewed in the context of regional groundwater flow systems, which provide the systematic transport and distribution mechanisms needed to produce and maintain the disequilibrium conditions necessary for speleogenesis. Hypogenic and epigenic karst systems are regularly associated with different types, patterns and segments of flow systems, characterized by distinct hydrokinetic, chemical and thermal conditions. Epigenic karst systems are predominantly local systems, and/or parts of recharge segments of intermediate and regional systems. Hypogenic karst is associated with discharge regimes of regional or intermediate flow systems.

Various styles of hypogenic caves that were previously considered unrelated, specific either to certain lithologies or chemical mechanisms are shown to share common hydrogeologic genetic backgrounds. In contrast to the currently predominant view of hypogenic speleogenesis as a specific geochemical phenomenon, the broad hydrogeological approach is adopted in this book. Hypogenic speleogenesis is defined with reference to the source of fluid recharge to the cave-forming zone, and type of flow system. It is shown that confined settings are the principal hydrogeologic environment for hypogenic speleogenesis. However, there is a general evolutionary trend for hypogenic karst systems to lose their confinement due to uplift and denudation and due to their own expansion. Confined hypogenic caves may experience substantial modification or be partially or largely overprinted under subsequent unconfined (vadose) stages, either by epigenic processes or continuing unconfined hypogenic processes, especially when H2S dissolution mechanisms are involved.

Hypogenic confined systems evolve to facilitate cross-formational hydraulic communication between common aquifers, or between laterally transmissive beds in heterogeneous soluble formations, across cave-forming zones. The latter originally represented low-permeability, separating units supporting vertical rather than lateral flow. Layered heterogeneity in permeability and breaches in connectivity between different fracture porosity structures across soluble formations are important controls over the spatial organization of evolving ascending hypogenic cave systems. Transverse hydraulic communication across lithological and porosity system boundaries, which commonly coincide with major contrasts in water chemistry, gas composition and temperature, is potent enough to drive various disequilibrium and reaction dissolution mechanisms. Hypogenic speleogenesis may operate in both carbonates and evaporites, but also in some clastic rocks with soluble cement. Its main characteristic is the lack of genetic relationship with groundwater recharge from the overlying or immediately adjacent surface. It may not be manifest at the surface at all, receiving some expression only during later stages of uplift and denudation. In many instances, hypogenic speleogenesis is largely climate- independent.

There is a specific hydrogeologic mechanism inherent in hypogenic transverse speleogenesis (restricted input/output) that suppresses the positive flow-dissolution feedback and speleogenetic competition in an initial flowpath network. This accounts for the development of more pervasive channeling and maze patterns in confined settings where appropriate structural prerequisites exist. As forced-flow regimes in confined settings are commonly sluggish, buoyancy dissolution driven by either solute or thermal density differences is important in hypogenic speleogenesis.

In identifying hypogenic caves, the primary criteria are morphological (patterns and meso-morphology) and hydrogeological (hydrostratigraphic position and recharge/flow pattern viewed from the perspective of the evolution of a regional groundwater flow system). Elementary patterns typical for hypogenic caves are network mazes, spongework mazes, irregular chambers and isolated passages or crude passage clusters. They often combine to form composite patterns and complex 3- D structures. Hypogenic caves are identified in various geological and tectonic settings, and in various lithologies. Despite these variations, resultant caves demonstrate a remarkable similarity in cave patterns and meso-morphology, which strongly suggests that the hydrogeologic settings were broadly identical in their formation. Presence of the characteristic morphologic suites of rising flow with buoyancy components is one of the most decisive criteria for identifying hypogenic speleogenesis, which is much more widespread than was previously presumed. Hypogenic caves include many of the largest, by integrated length and by volume, documented caves in the world.

The refined conceptual framework of hypogenic speleogenesis has broad implications in applied fields and promises to create a greater demand for karst and cave expertise by practicing hydrogeology, geological engineering, economic geology, and mineral resource industries. Any generalization of the hydrogeology of karst aquifers, as well as approaches to practical issues and resource prospecting in karst regions, should take into account the different nature and characteristics of hypogenic and epigenic karst systems. Hydraulic properties of karst aquifers, evolved in response to hypogenic speleogenesis, are characteristically different from epigenic karst aquifers. In hypogenic systems, cave porosity is roughly an order of magnitude greater, and areal coverage of caves is five times greater than in epigenic karst systems. Hypogenic speleogenesis commonly results in more isotropic conduit permeability pervasively distributed within highly karstified areas measuring up to several square kilometers. Although being vertically and laterally integrated throughout conduit clusters, hypogenic systems, however, do not transmit flow laterally for considerable distances. Hypogenic speleogenesis can affect regional subsurface fluid flow by greatly enhancing initially available cross- formational permeability structures, providing higher local vertical hydraulic connections between lateral stratiform pathways for groundwater flow, and creating discharge segments of flow systems, the areas of low- fluid potential recognizable at the regional scale. Discharge of artesian karst springs, which are modern outlets of hypogenic karst systems, is often very large and steady, being moderated by the high karstic storage developed in the karstified zones and by the hydraulic capacity of an entire artesian system. Hypogenic speleogenesis plays an important role in conditioning related processes such as hydrothermal mineralization, diagenesis, and hydrocarbon transport and entrapment.

An appreciation of the wide occurrence of hypogenic karst systems, marked specifics in their origin, development and characteristics, and their scientific and practical importance, calls for revisiting and expanding the current predominantly epigenic paradigm of karst and cave science.