Sulfuric acid caves of the world: A review De Waele, Jo; D'Angeli, Ilenia M.; Audra, Philippe ...
Earth-science reviews,
March 2024, 2024-03-00, Letnik:
250
Journal Article
Recenzirano
In soluble rocks such as limestone and dolostone there are two main types of cave genesis (speleogenesis); (i) epigenic speleogenesis, in which the aggressiveness that forms caves is derived from the ...surface, and (ii) hypogenic speleogenesis where upwelling gases and fluids acquire their aggressiveness at depth dissolving carbonate rocks to form caves. Whereas epigenic (surface) waters can be undersaturated respect to carbonates obtaining their aggressiveness mainly from soil CO2, hypogenic (deep rising) fluids can obtain their carbonate-dissolving capacity at depth from various processes and mechanisms. Hypogenic speleogenesis that involves dissolution of carbonate rocks by sulfuric acid, mainly derived by oxidation of upwelling hydrogen sulfide, is called sulfuric acid speleogenesis (SAS). Although this type of process has been described during the early 19th century, the first elaborated theories are rather recent, and a detailed model was proposed only in the mid-1970s. Only a few cave areas were known to host sulfuric acid caves, but studies were boosted with the discovery and understanding of the inactive Lechuguilla Cave in New Mexico (USA), and the still active Movile Cave in Romania, both discovered in 1986.
Today 84 areas globally are known to contain sulfuric acid caves, offering a wide variety of environments. This review gives a historical overview of studies concerning these caves, explains the chemistry behind the formation of the dissolving fluids and their interaction with the carbonate host rock, and describes the chemical, mineralogical, geomorphological, and microbiological signatures typical of sulfuric acid dissolution. The significance of SAS caves in landscape evolution and their possible role in deep karstification, and thus hydrocarbon reservoirs and deep hydrogeology, is also briefly analyzed.
Within numerical models of karst development, geochemical and hydrological boundary conditions are typically assumed to be constant. However, rates of calcite dissolution in natural karst systems can ...vary substantially in time. In particular, variation in carbon dioxide (CO2) concentrations has been shown to produce time variability in dissolution rates in karst streams, but controls on CO2 variation within karst systems are relatively poorly quantified. Here we analyze hourly in-situ measurements of dissolved CO2, discharge, and specific conductance at a pair of karst underflow-overflow springs and examine potential drivers of variability in CO2 and dissolution rates. The springs display strong seasonal variability in CO2 and saturation state as well as moderate variation during storm events. Though both springs have elevated CO2 concentrations in the summer season, the overflow spring experiences a substantial decrease in dissolved CO2 below a critical discharge threshold. We hypothesize that this decrease results from ventilation within the overflow portion of the system as segments of the flow path transition from full pipe to open channel flow. The overflow spring experiences substantially lower average dissolution rates than the underflow spring, despite larger discharge and chemical variability during high flow events at the overflow spring. Though open systems are frequently presumed to have higher dissolution rates, because of their ability to replenish CO2 that is consumed in the dissolution process, these data suggest that dissolution rates within the closed portion of the system may in some cases be higher due to the inability of closed flow paths to ventilate excess CO2 to the atmosphere. Such conditions are likely to occur in conduits where CO2 concentrations are elevated above atmospheric levels and average flow through times are short compared to the time scale over which water reaches equilibrium with respect to calcite.
Morphogenesis of hypogenic caves Klimchouk, Alexander
Geomorphology (Amsterdam, Netherlands),
05/2009, Letnik:
106, Številka:
1
Journal Article
Recenzirano
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.
We documented the deformation in the southeastern domain of the Majella anticline (Central Apennines, Italy) to highlight timing and structural characteristics of different fracture sets affecting ...the outcropping Cretaceous-Miocene ramp carbonates. An isolated and inactive hypogene karst system produced by sulfuric acid (Cavallone-Bove cave system) was studied following a multidisciplinary approach. Our findings suggest that deep-rooted, sub-vertical strike-slip fault zones reaching the H2S source rocks were the main vehicle for ascending acidic fluid flow. Linkage and intersection of these faults by splays in extensional stepovers and pre-orogenic normal faults permitted ascending fluids to reach multiple recharge points (feeders) near the paleo water-table. In proximity to the oxygenated groundwater, where H2SO4 was produced, lateral dissolution focused along bedding planes and zones of localized deformation (fracture clusters) characterizing the hinge of the anticline. We conclude that structural position in the anticline and large-offset, vertically extended strike-slip fault zones control the localization of efficient permeability pathways and represent first order controlling features for fluid flow in the fold-and-thrust belt. This study provides insights into the understanding of time-space evolution, geometry, and pattern of sulfuric hypogene karst systems in folded carbonates, whose prediction is critical for fractured and karstified reservoirs.
•Deformation in the Majella anticline is critical for sulfuric acid speleogenesis.•Vertically extended strike-slip faults allow cross-formational H2S flow from depth.•Damage zones form high-permeability domains and act as feeders of acidic fluids.•Fracture cluster zones along the anticline hinge control karst macro-scale porosity.
The paper presents a detailed study demonstrating the hypogenic origin of the Corona 'e Sa Craba quartzite cave in SW Sardinia (Italy). Although the quartzite host-rock of this cave derived from ...silicification of Cambrian dolostones and dissolution of carbonate remnants could have had a role in the speleogenesis, detailed morphologic and petrographic investigation revealed clear evidence of quartz dissolution without signs of mechanical erosion by running waters. Thin section microscopy and scanning electron microscope (SEM) images show pervasive dissolution morphologies, such as pits and notches on quartz crystals causing the deep arenization of the cave walls, suggesting that the dissolution of quartz had a primary role in the formation of the void. The study of secondary cave minerals and the sulfur isotopic composition of sulfates and sulfides, coupled with data on fluid inclusions, allowed reconstruction of the peculiar speleogenetic history of this hypogenic hydrothermal quartzite cave. The cave formed by reduced hydrothermal fluids, probably under basic–neutral pH in phreatic conditions. The presence of abundant cations of Ba2+ in reduced Cl-rich fluids enhanced the quartz dissolution rate, allowing the formation of the voids in deep settings. During the Late Oligocene uplift of the area, the hydrothermal fluids in the cave reached oxygen-rich conditions, thus a minerogenetic phase started with the deposition of barite when the temperature of the fluid was ≤50°C. The presence of cinnabar crusts in the lower part of the cave walls and on the boulders suggests a later volcanic phase with Hg-rich vapors ascending from below. Other minerals such as alunite, basaluminite, gypsum and halloysite (typical of an acid sulfate alteration environment), and phosphates were formed in a final, much more recent stage. The δ34S values of the cave sulfate minerals indicate that S is derived from the remobilization of original Precambrian Pb–Zn Mississippi Valley Type ores. These last two stages did not significantly affect the morphology of the cave. The Corona 'e Sa Craba appears to be the world's first example of a hypogenic cave in quartzite where the speleogenetic mechanisms have been studied and reconstructed in detail, using a variety of modern methods. This study confirms that dissolution of quartz by thermal alkaline fluids at depth can produce large dissolutional voids in the apparently poorly soluble quartzite rocks.
•Corona 'e Sa Craba cave formed by quartz dissolution in phreatic deep settings.•The cave formed by reduced hydrothermal fluids at temperatures above 130°C.•The presence of BaCl2 in solution enhanced the dissolution of quartz.•Secondary sulfate minerals have deposited in a later acid and oxidative stage.•Quartz dissolution by hot alkaline fluids can form deep-seated hypogenic voids.
Cave studies enable us to unravel valuable information on landscape evolution. In glacial settings, the glacial cycles induced fluctuations in the underground hydraulic regime, sediment availability ...and base level in adjacent caves. Here, we present our work on the Grønli-Seter cave system in Northern Norway, which comprises >8 km of passage length at an elevation between 250 m and present sea level. By linking cave morphology and deposits to shifting glacier configurations and external base level changes during the last deglaciation and the Early Holocene, we establish how the hydraulic conditions in the cave system shifted in pace with glacier fluctuations. Maze sections and phreatic loops appear in a hydraulic confined setting close to the interface between the calcite marble and the overlying mica schist. Scallops in the cave walls demonstrate slow, ascending water flow, evidence of subglacial speleogenesis under wet-based, topographically constrained glaciers with a gentle surface slope. Moreover, cave morphology and clastic deposits indicate various hydrological phases of descending water flow, stagnant conditions, and excessive flow rates. Our work establishes that the last glaciation and deglaciation had an insignificant effect on the cave system's solutional development. In contrast, the cave sediments reveal diverse hydraulic conditions that may be related to shifting glacier configurations. This research offers valuable insights into glacier ice-contact speleogenesis and landscape development in glacial terrains.
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•Reveal the relationship between cave morphology, deposits and glacier fluctuations.•Relate ice-contact speleogenesis to the glacial valley development.•Identify shifting hydrological conditions in the caves during the last deglaciation.
Fort Stanton Cave in central New Mexico, USA has all the appearances of a Mammoth-Cave-style epigene stream passage type of cave and not a hypogene cave like Carlsbad Cavern and Lechuguilla Cave. Its ...~72 km of passages are located in the Permian San Andres Formation between two small rivers fed by snow melt and rainfall on nearby Sierra Blanca, the highest mountain peak in the region, all of which are pertinent to Fort Stanton Cave's origin. Radiometric dates of vadose speleothems within the cave and a bedrock calcite vein narrow down the timing of speleogenesis. We measured a uranium‑lead age of 12 My for the bedrock vein calcite, that speleogenesis of the Main Corridor has dissected, that provides a maximum age of the cave. The oldest vadose speleothems are >0.5 and <1 Ma, providing a minimum age for the cave. Using reasonable canyon incision rates for the two small rivers and these endmember age constraints, we show that Fort Stanton Cave is relatively young and that most of the cave likely formed 1 to 2 Ma. Cold water from Sierra Blanca and thicker soils/vegetation during glacial cycles of the Pleistocene provided conditions of cold CO2-charged groundwater with higher flow rates, the ingredients needed to form this large cave in soluble limestone units of the San Andres Formation.
•Fort Stanton Cave is a large epigene cave located in arid central New Mexico, USA.•This epigene cave with >71 km of passages is an anomaly in the southwestern USA.•Its origin is related to rivers, creeks, and groundwater from nearby mountains.•Radiometric dating constrains its age between 12 and 1 Ma.•Reasonable models of hypothesized river incision rates suggest it formed 1–2 Ma.
•Tectonics triggered speleogenesis by surface–subsurface connection.•The biodiversity in the hypogene cave environment is largely unknown.•The spatial homogeneity of goethite reveals both ...quantitative and qualitative changes.•Changes on goethite may result from the metabolic signature of the microbes.
We report the first detailed geological description of the hypogene Mavros Vrachos Quarry cave close to Sidirokastro in N. Greece. This study includes experimental results obtained using an arsenal of chemical, biological, and scattering techniques on a crust deposit that covers the cave’s interior. The major element involved in this study is iron. The crust deposit consists mainly (about 90 wt%) of goethite crystals. The typical crystallite size of goethite is between 15 and 21 nm. The goethite crystallites form a network of filaments in the shape of needle-like macrostructures arranged in spherical aggregates, resembling biologically induced structures. The crust deposit microflora is studied in detail using DNA sequencing. Proteobacteria and Firmicutes followed by Acidobacteria and Bacteriodetes are the most represented bacteria in the cave. Although the DNA sequencing of the crust deposit microflora is fully recorded, a large group of unclassified operational taxonomic units prevent us from fully identifying the biodiversity in the hypogene cave. Distinct places in goethite show secondary phases that might be related with distinct events in the life cycle of microbes. We claim that this study is a precursor relevant to the metabolic signature of microbes in a hypogene cave.
The thermal spring of Fetida Cave, a still active sulfuric acid cave opening at sea level and located in Santa Cesarea Terme, southeastern Salento (Apulia region, Southern Italy) hosts abundant ...floating white filaments. The white filaments were mainly composed of sulfur crystals surrounded by microbial mass of the phyla Epsilonbacteraeota, Proteobacteria, Bacteroidetes, and Patescibacteria. The most abundant genus in the white filaments collected from the waters in the innermost part of the cave dominated by sulfidic exhalations was Arcobacter. This abundance can be related to the higher concentration of sulfide dissolved in water, and low oxygen and pH values. Conversely, lower Arcobacter abundances were obtained in the filaments collected in the entrance and middle part of the cave, where sulfidic water mixes with seawater, as the cave is subjected to tides and the mixing of fresh (continental) with marine water. The geochemical analysis of water and atmospheric gases confirmed these environmental constraints. In fact, the highest concentrations of H2S in the air and water were recorded closest to the spring upwelling in the innermost part of the cave, and the lowest ones near the cave entrance. The metabolic versatility of Arcobacter might provide a competitive advantage in the colonization of water bodies characterized by high sulfide, low oxygen, and dynamic fluid movement.
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•Fetida Cave, Italy, is an active sulfuric acid cave opening at sea level.•The innermost part of the cave is highly influenced by sulfide exhalations.•The cave hosts abundant floating white filaments.•The filaments are dominated by Arcobacter (Epsilonbacteraeota).•Sulfide dissolved in water, low oxygen and acidic pH promote Arcobacter growth.
