SULFURIC ACID SPELEOGENESIS IN GREECE SPELEOGENEZA ŽVEPLOVE KISLINE V GRČIJI Georgios LAZARIDIS1, Vasilios MELFOS2, Lambrini PAPADOPOULOU2, Bogdan P. ONAC3,4, Christos L. STERGIOU1, Angelos G. MARAVELIS1, Panagiotis VOUDOURIS5, Despoina DORA6, Michalis FITROS7,8, Haritakis PAPAIOANNOU9 & Konstantinos VOUVALIDIS6 Abstract UDC 551.44:546.226-325(495) Georgios Lazaridis, Vasilios Melfos, Lambrini Papadopoulou, Bogdan P. Onac, Christos L. Stergiou, Angelos G. Maravelis, Panagiotis Voudouris, Despoina Dora, Michalis Fitros, Hari- takis Papaioannou & Konstantinos Vouvalidis: Sulfuric acid speleogenesis in Greece Manifestations of sulfuric acid speleogenesis (SAS) document- ed in several caves in the areas of Aghia Paraskevi, Konitsa, W. Peloponnese, Elassona, Lavrion and Kammena Vourla in Greece are examined and discussed in this work. Carbonate and sulfate samples collected from caves in Aghia Paraskevi and western Peloponnese areas were investigated using methods, such as flu- id inclusion, scanning electron microscopy, carbon, sulfur and oxygen stable isotopes, X-ray powder diffraction, and chemical analysis. The examined caves are mainly developed at or in the proximity of the local water table and they are related to hydro- thermal springs and geothermal fields. In addition to the docu- mentation of SAS in one case study from Aghia Paraskevi, calcite spar with a homogenization temperature peak at 280°C, indi- cates an early speleogenetic stage that involves meteoric-origin hydrothermal fluids under deep-seated settings. Sulfur isotope composition of sulfates (–4‰) is indicative for pyrite oxida- tion. The Konitsa caves represent a system developed at multiple altitudes that is related to the evolution of Sarantaporos River. The caves in West Peloponnese are located in two different geo- tectonic units. However, the caves in both units are active and share common characteristics, such as their development near Izvleček UDK 551.44:546.226-325(495) Georgios Lazaridis, Vasilios Melfos, Lambrini Papadopoulou, Bogdan P. Onac, Christos L. Stergiou, Angelos G. Maravelis, Panagiotis Voudouris, Despoina Dora, Michalis Fitros, Hari- takis Papaioannou & Konstantinos Vouvalidis: Speleogeneza žveplove kisline v Grčiji V tem delu so proučeni in obravnavani znaki speleogeneze žveplove kisline, dokumentirani v več jamah na območjih zahodnega Peloponeza, Aghia Paraskevi, Konica, Elasona, Lavrion in Kamena Vourla v Grčiji. Karbonatne in sulfatne vzorce, zbrane v jamah na območjih zahodnega Peloponeza in Aghia Paraskevi, smo raziskali z metodami, kot so študija z vključevanjem tekočin, vrstična elektronska mikroskopija, stabilni izotopi ogljika, žvepla in kisika, rentgenska praškovna difrakcija in kemijska analiza. Proučevane jame so nastale večinoma na gladini lokalne podtalnice ali v njeni bližini ter so povezane s hidrotermalnimi izviri in geotermalnimi polji. Po- leg dokumentiranja speleogeneze žveplove kisline v eni študiji primera z območja Aghia Paraskevi kalcitni spar z vrhom tem- perature homogenizacije pri 280°C kaže na zgodnjo speleogen- etsko stopnjo, ki vključuje hidrotermalne meteorne tekočine v globokem okolju. Izotopska sestava žvepla v sulfatih (–4  ‰) kaže na oksidacijo pirita. Jame Konica so sistem, ki se je razvil na več nadmorskih višinah in je povezan z razvojem reke Sa- rantaporos. Jame na zahodnem Peloponezu so v dveh geotek- tonskih enotah. Vendar so jame v obeh enotah aktivne in imajo skupne značilnosti, na primer vse nastale blizu morske gladine, ACTA CARSOLOGICA 53/2-3, 127-144, POSTOJNA 2024 1 Department of Geology, Faculty of Geology, Aristotle University, Thessaloniki, GR-54124, Greece, geolaz@geo.auth.gr 2 Department of Mineralogy, Faculty of Geology, Petrology and Economic Geology, Aristotle University, Thessaloniki, GR-54124, Greece 3 School of Geosciences, University of South Florida, 4202 E. Fowler Ave., Tampa, FL 33620, USA 4 Emil G. Racoviţă Institute, Babeș-Bolyai University, Clinicilor 5, 400006, Cluj-Napoca, Romania 5 Department of Mineralogy and Petrology, Faculty of Geology & Geoenvironment, National and Kapodistrian University of Athens, Greece 6 Department of Physical and Environmental Geography, Faculty of Geology, Aristotle University, Thessaloniki, School of Geology 7 Hellenic Survey of Geology and Mineral Exploration (HSGME), Olympic Village, Acharnae - Athens, Greece 8 Mineralogical Museum of Lavrion, Attica, Greece 9 Vikos-Aoos UNESCO Geopark, Greece Prejeto/Received: 8. 2. 2024 DOI: https://doi.org/10.3986/ac.v53i2-3.13668 Georgios Lazaridis, Vasilios Melfos, Lambrini Papadopoulou, Bogdan P. Onac, Christos L. Stergiou, Angelos G. Maravelis, Panagiotis Voudouris, Despoina Dora, Michalis Fitros, Haritakis Papaioannou & Konstantinos Vouvalidis: 1. INTRODUCTION Sulfuric acid speleogenesis (SAS) denotes caves formed in carbonate rocks dissolved by sulfuric acid. It is mainly attributed to the type of “hypogene karstification in un- confined/confined aquifers, partly incised by the erosional network, or side-open to the sea” (Klimchouk, 2017). This category includes the subtype of “sulfuric acid speleogen- esis, where deep H2S bearing fluids rise to an unconfined carbonate aquifer and the water table (Klimchouk, 2017). However, there are also a few examples of sulfuric acid speleogenesis that are explained by epigene processes (D'Angeli et al., 2019; Webb, 2021; De Waele et al., 2024). Active speleogenesis is quite common among SAS caves, since they are formed at the water table, where the oxi- dation of hydrogen sulfide is favored. In a thorough re- view of SAS caves of the world the following definition is suggested “sulfuric acid speleogenetic caves form through the oxidation of sulfides beneath the land surface, primar- ily resulting from the interaction between sulfuric acid- rich water and the host rock (mainly carbonates), leading to void creation” (De Waele et al., 2024). Compared to ordinary caves formed in carbonates by carbonic acid, SAS caves usually contain “exotic” minerals (Polyak and Provencio, 2001; Onac et al., 2009) and gypsum (e.g. Hill, 1995; Swezey et al., 2002). Only a small percentage of caves in carbonates are formed by SAS. In Italy, the country with the most SAS occurrences there is a cave system per ~13.000 km2 (D'Angeli et al., 2019). Another interesting aspect of these caves is their relation to hydrocarbon reservoirs that provide hydrogen sulfide, and ore deposits that are formed in phreatic reductive setting (Hill, 1995). Other processes such as microbial or thermochemical sulfate reduction (MSR and TSR, respectively) provide hydrogen sulfide to SAS; mantle degassing in volcanic areas, volcanic activity, and sul- fide oxidation may be responsible for hydrogen sulfide enrichment of waters (e.g., Auler and Smart, 2003, De Waele et al., 2024). In Greece, the best-known SAS cave system is Aghia Paraskevi (Lazaridis et al., 2011), which is the cave type locality of orpiment (Onac and Forti, 2011). Kounoupeli and Anigridon Nimfon caves of western Peloponessus have been described in the exploration report of Merdenisianos (1994). Konitsa and Kammena Vourla caves included in this paper are newly described. Furthermore, there are a few more cases that have been presumed as SAS caves (e.g., Lazaridis, 2017 and refer- ences therein). In this paper, morphological studies of these caves along with mineralogical and geochemical analysis provide further evidence on their speleogenetic setting. 2. GEOLOGICAL SETTING Greece is geologically subdivided into several geotec- tonic, encompassing external zones (pre-Apulian, Ioni- an, Gavrovo, Pindos and Parnassos zones) and internal Hellenides zones (Pelagonian, sub-Pelagonian, Attic- Cycladic, Axios, Circum-Rhodope, Serbomacedonian and Rhodope). The investigated SAS cave systems are situated as follow: Kounoupeli, Anigridon Nimfon, and Konitsa (Western Peloponessus) are in the external Hel- lenides, whereas the Aghia Paraskevi, Kammena Vourla, Peristeri, Psoroneria, Lavrion and Melissotripa are part of the internal Hellenides (Figure 1). External Hellenides record the shift in geotectonic regime, from an initial extensional (Triassic - early to middle Eocene) to a following compressional (since mid- dle Eocene) setting (Karakitsios, 1995; Zoumpouli et al., 2022). During the extensional phase, external Hellenides experienced crustal stretching and fault-related subsid- ence that resulted in extensive carbonate sedimentation in a rift-type setting (e.g., Zelilidis et al., 2015; Bourli et al., 2019a, b). The following compressional phase is relat- ed to the evolving Pindos Orogen and records siliciclastic sedimentation in a foreland basin system (Botziolis et al., sea level, morphology and fracture-guided pattern, and the pres- ence of gypsum with δ34S values (average –26‰) that are plausi- bly related to hydrocarbons and bacterial activity. Morphological and geochemical aspects of the caves in these two regions suggest long-lasting, multiphase speleogenetic systems. Keywords: sulfuric acid speleogenesis, Greece, hydrothermal karst, hypogene caves, cave mineralogy. imajo podobno morfologijo in prelomni vzorec, poleg tega je v vseh sadra z vrednostmi δ34S (povprečno –26 ‰), ki so verjetno povezane z ogljikovodiki in aktivnostjo bakterij. Morfološki in geokemijski vidiki jam v teh dveh regijah kažejo na dolgotrajne, speleogenetske sisteme, ki so se razvijali v več fazah. Ključne besede: speleogeneza žveplene kisline, Grčija, hidro- termalni kras, hipogene jame, jamska mineralogija. GEORGIOS LAZARIDIS, VASILIOS MELFOS, LAMBRINI PAPADOPOULOU, BOGDAN P. ONAC, CHRISTOS L. STERGIOU, ANGELOS G. MARAVELIS, PANAGIOTIS VOUDOURIS, DESPOINA DORA, MICHALIS FITROS, HARITAKIS PAPAIOANNOU & KONSTANTINOS VOUVALIDIS: 128 ACTA CARSOLOGICA 53/2-3 – 2024 SULFURIC ACID SPELEOGENESIS IN GREECE Figure 1: Geotectonic zones of Greece and the distribution of both verified and presumed caves formed by sulfuric acid speleogenesis. 1. Aghia Paraskevi; 2. Konitsa; 3. Kounoupeli; 4. Anygridon Nymfon; 5. Melissotripa; 6. Kammena Vourla and Psoroneria; 7. Lavrion; 8. Peristeri. ACTA CARSOLOGICA 53/2-3 – 2024 129 2021, 2023). The rock masses of the internal Hellenides include Mesozoic, Paleozoic and older metamorphic rocks that were mainly deformed by the Alpine orogeny and associated tectonics during the Jurassic-Cretaceous. The boundary between internal and external Hellenides is tectonic, with internal Hellenides being overthrusted over the external Hellenides. Geochemical data from the Palaeozoic basement rocks point at a subduction-zone setting, suggesting an active continental margin setting (Pe-Piper et al. 1993; Anders et al. 2005). 3. ANALYTICAL METHODS Microthermometric data were obtained using a LINKAM THM-600/TMS 90 heating-freezing stage coupled to a Leitz SM-LUX-POL microscope, housed at the Depart- ment of Mineralogy, Petrology, Economic Geology of the Aristotle University of Thessaloniki (AUTh). Calibration of the stage was achieved using organic standards with known melting points (chloroform −63.5˚C, naphthalene 80.35˚C, Merck 135 135˚C, saccharine 228˚C, Merck 247 247˚C), and ice (H2O). The precision of the heating and freezing measurements was ±1°C and ±0.2˚C, respec- tively. Fluid inclusion shapes and sizes, spatial relation- ships among inclusions and minerals, and phases within inclusions were observed. The BULK computer package (Bakker 2003) was used to process the fluid inclusion data for calculating salinities and densities. Mineral inspection and chemical analyses were car- ried out in the Scanning Electron Microscopy Labora- tory, using a JEOL JSM840A Scanning Electron Micro- scope (SEM) equipped with an Energy Dispersive Spec- trometer (EDS) with 20 kV accelerating voltage and 0.4 mA probe current. For SEM observations, the samples were coated with carbon, to an average thickness of 200 Å, using a vacuum evaporator JEOL-4X. Major element composition was determined by X- Ray Fluorescence (XRF) at the Laboratories of Mineralo- gy and Petrology of Hellenic Survey of Geology and Min- eral Exploration (H.S.G.M.E.), using a S4 Pioneer Bruker AXS (for SiO2, TiO2, Al2O3, MnO, MgO, CaO, Na2O, K2O, P2O5, Fe2O3 and SO3). Calcite samples were analyzed for oxygen and car- bon isotope ratios in CO2 expelled after reacting the carbonate powder for 24 hours with H3PO4 at 25˚C. The analyses were performed on a Thermo Delta V isotope ratio mass spectrometer at the Stable Isotope Labora- tory, School of Geosciences, University of South Florida (USA). The results are expressed in delta (δ) notation using the following formula: δ = (Rsample/Rstd – 1)·1000, reported in ‰, where Rsample is the ratio of 13C/12C or 18O/16O of carbonates and Rstd are the same ratios of the international reference standard Vienna PDB (VPDB). Sample δ-value was normalized to the VPDB scale using two reference materials (NBS-18 and NBS-19). Duplicate measurements of the reference materials show that the reproducibility for δ13C and for δ18O values is better than ± 0.08‰ and ± 0.06‰ (1σ), respectively. The sulfur (δ34S) isotope value of sulfate samples was determined following the protocols outlined by Grass- ineau et al. (2001) and Onac et al. (2011). The analyses were conducted in the Stable Isotope Lab at the School of Geosciences (University of South Florida, USA) using an Elemental Analyzer Costech ECS 4100 and a Temperature Conversion Elemental Analyzer, coupled to a Thermo Fisher Delta V IRMS. The results were normalized to Ca- ñon Diablo Troilite (CDT) based on the δ34S values of the IAEA standards S-2 and S-3. The reproducibility between replicate standards in each run was better than ±0.1 ‰ (1σ). 4. SULFURIC ACID CAVES OF GREECE 4.1 THE AGHIA PARASKEVI CAVE SYSTEM Explorations in the Aghia Paraskevi area have uncovered a total of eight small caves, each with its unique charac- teristics. The first comprehensive study focused on one of these caves, where active sulfuric acid speleogenesis was observed by Sotiriadis in 1969 (Figure 2F), who docu- mented the thermal spring and water chemistry in this cave. Subsequently, Sotiriadis et al. (1982) described an- other small cave in the area, examining it from the per- spective of epigene speleogenesis. Lazaridis et al. (2011), expanded the speleological evidence in the area, referencing six additional caves GEORGIOS LAZARIDIS, VASILIOS MELFOS, LAMBRINI PAPADOPOULOU, BOGDAN P. ONAC, CHRISTOS L. STERGIOU, ANGELOS G. MARAVELIS, PANAGIOTIS VOUDOURIS, DESPOINA DORA, MICHALIS FITROS, HARITAKIS PAPAIOANNOU & KONSTANTINOS VOUVALIDIS: 130 ACTA CARSOLOGICA 53/2-3 – 2024 SULFURIC ACID SPELEOGENESIS IN GREECE Figure 2: SAS manifestations in Aghia Paraskevi caves. Aerial view of the Aghia Paraskevi area with the locations of the water table (WTG), breakdown (BRCG), and the quarry (QG) group caves. B. Passage in WTG1 Cave with the paragenesis of orpiment (orp), tamarugite (tam), pickeringite (pick), and gypsum (g) on the highest parts and a notch at the water level fluctuation zone. C. View of the QG1 Cave with alunite (alun). D. Entrance of the feeder-like QG2 Cave. E. Phreatic hydrothermal calcite (cal) in QG2 cave. F. Sulfuric acid corrosion on the limestone of Aghia Paraskevi caves. G. Gypsum crust (g) in the deepest part of QG3 Cave. H. Typical passage produced by condensa- tion corrosion in WTG1 Cave, related to notches at the water table and sulfuric karren and the zone of water fluctuation. I. Replacement pockets on the limestone ceiling of QG3 Cave. ACTA CARSOLOGICA 53/2-3 – 2024 131 and detailing a rare mineral paragenesis that includes orpiment As2S3, tamarugite NaAl(SO4)2 · 6H2O, picker- ingite MgAl2(SO4)4·22H2O, and gypsum CaSO4·2H2O. Notably, all the caves in Aghia Paraskevi are a result of hypogene processes and can be categorized into three distinct groups based on their characteristics (Figure 2A). The first group, designated as the Water Table Group (WTG), comprises three caves situated near the water table along the steep seacoast, featuring thermal water. WTG1 (Figure 2B and 2H), the principal cave housing a thermal spring, spans approximately 15 m in length and 10 m in width, oriented along the N-S and E-W directions, respectively. An unexplored area is situated in its northeast part, mostly covered by a ther- mal water lake. The cave’s ground plan has a ramifying maze pattern, with fracture-guided dissolution form- ing pillar-like structures in cupola-shaped chambers (Lazaridis et al., 2011, Figure 2A). Notches are visible in various locations, and cm-size wide vertical karren of sulfuric acid origin can be observed in the water fluc- tuation zone (Figure 2H). Located about 10 m above the steep seacoast and southeast of WTG1, the vertical entrance to WTG2 cave primarily features an elongated chamber ~15 m long, developed along NNE-oriented fractures. In 2006, thermal water was confined to two small lakes within the cave. To facilitate the operation of the hy- drotherapy facility located within the cave, an artificial water recycling system was implemented, directing water from WTG1 to WTG2. Over time, this system caused the water level to rise, eventually covering the entire cave floor. WTG3 (Figure 2G) is the smallest cave in this group and is located southeast of the other two. It con- tains small occurrences of the aforementioned sulfate paragenesis. Additionally, several small cavities and vertically developed half-tubes can be found in the proximity of the caves of this group, with sea sand ob- served at about 10 m above present sea level (mapsl). The Breakdown Cave Group (BRCG) encompasses two caves positioned at a higher elevation of approxi- mately 40-45 mapsl compared to the others. Both caves are accessible through vertically developed openings: one results from a collapsed sinkhole, while the other is a small cave partially filled with clastic sediments and speleothems. Notably, the latter cave was described by Sotiriadis et al. (1982). The final group, known as the Quarry Group (QG), comprises three caves discovered during commercial quarry operations. QG1 (Figure 2C) is a sediment-filled cavity primarily containing clastic sediments, and an alunite KAl3(SO4)2(OH)6 layer has been identified in this cave. QG2 is a shaft that spiral downward, featur- ing a circular cross-section (Figure 2D). Its deepest part is obstructed by rocks. Within the cave passage, fine- grained clastic sediments can be found, with sections lined with phreatic calcite crystals (Figure 2E), a few centimeters in length. These crystals are also present just above the cave entrance. QG3 is a pothole that hosts water ponds at its deepest part. The uppermost part, near the artificial entrance, exhibits chains of cupolas. Gypsum crusts (Figure 2G) occur on the lower parts of the passage, along with replacement pockets (Figure 2I) and cupolas on the ceiling. In specific locations within the clastic sediments, we have observed rounded clasts approximately 10 cm in diameter. These clasts are com- posed of gypsum and are believed to have replaced the original limestone. 4.2 WESTERN PELOPONNESE: KOUNOUPELI AND ANIGRIDON NIMFON CAVES In the western region of the Peloponnese, two caves characterized by active thermal springs and SAS are noteworthy. The Anigridon Nymfon Cave is situated within the limestone formations of the Gavrovo Zone (Figure 1). This relatively small cave, measuring ap- proximately 70 m in length and covering an area of around 340 m2, is documented in a study by Merdeni- sianos (1994). The cave is primarily a single passage extending in a NNW-SSE direction. A thermal water lake, rich in hydrogen sulfide, extends to the entire cave area. Towards its deepest point, the passage’s size gradu- ally decrease to the point of becoming impassable. An analysis of gas seepage in NW Peloponnese by Etiope et al. (2006) revealed that the thermal springs are nota- bly abundant in thermogenic methane originating from deep Mesozoic limestone reservoirs, and the hydrogen sulfide is most probably of TSR origin; in which sulfur compounds, particularly sulfate minerals, undergo re- duction at high temperatures. The Kounoupeli Cave (Figure 3) is situated in the Late Triassic to Eocene carbonates, lying above the Tri- assic evaporites and beneath the Oligocene flysch of the Ionian Zone (Figure 1). These rock formations appear to give rise to mega-synclines and anticlines. Located at sea level and just a few meters from the coastline, this active sulfuric acid cave is ~50 m in length. It con- sists of a fracture-guided corridor with segments ori- ented along the N–S and E–W directions (Figure 3A). Gypsum crust partially covers side walls (Figs. 3B and 3C). Morphologically, the passage features a triangu- lar cross-section with a flat floor and a central channel (Figs. 3D; 3E and 3F). Moreover, water-table notches can be observed on the cave walls (Figs. 3D and 3F). GEORGIOS LAZARIDIS, VASILIOS MELFOS, LAMBRINI PAPADOPOULOU, BOGDAN P. ONAC, CHRISTOS L. STERGIOU, ANGELOS G. MARAVELIS, PANAGIOTIS VOUDOURIS, DESPOINA DORA, MICHALIS FITROS, HARITAKIS PAPAIOANNOU & KONSTANTINOS VOUVALIDIS: 132 ACTA CARSOLOGICA 53/2-3 – 2024 4.3 KONITSA Numerous caves related to SAS have been explored in Konitsa region, with the most striking ones being as- sociated with the evolution of the Sarantaporos River. These caves have been developed within the limestone formations on both sides of the riverbanks in the locali- ties of Pixaria Loutra and Skordyli Bridge (Figure 1). In the latter location, a series of small caves are distributed at different elevations, representing successive stages of speleogenesis that extending up to several tens of meters above water level. Presently, these caves are mostly inac- tive and undergoing recession due to erosion. However, Skordyli Cave is the largest in the area and is still active. It has a spacious main gallery (Figure 4A) that display multiple notches (Figure 4B) and dome-shaped cham- bers (Figs. 4C and 4D). A flat corroded stream bed with gypsum deposits featuring a thermal spring abundant in hydrogen sulfide that support the formation of whitish stream biofilms (Figure 4E). Along with multiple notch- es, clastic sediment banks can be seen in some cave areas (Figure 4F). Within the large cave, eroded clastic sediments and notches have formed concurrently with a drop in the local water level. Hydrogen sulfide concentrations up to 2 ppm has been detected in the deeper sections of the cave. Pixarias Cave is located in close proximity to Pixaria SULFURIC ACID SPELEOGENESIS IN GREECE Figure 3: SAS manifestations in the Kounoupeli Cave. Α. Plan of Kou- noupeli Cave (letters indicate posi- tion of photos). Β. Gypsum deposits identified as light-colored patches on the wall. C. Close up view of gypsum sample Sp49. D. View of the N-S gallery. E. Corrosion table and sulfuric feeder that form the floor of the cave. F. Underwater photo (courtesy of Vasilis Atha- nassopoulos) of the flat floor that forms a corrosion table. ACTA CARSOLOGICA 53/2-3 – 2024 133 thermo-mineral spring and has a maze pattern (Figure 5A). The cave passages follow structural discontinuities along joints and are relatively uniform in size, extending in various directions that interconnect at multiple points. In cross-section, they show multiple distinctive characteris- tics of SAS (Figure 5B). These passages exhibit bilateral symmetry, with the vertical axis aligning with the joint that guides the dissolution process by providing hydro- gen sulfide. The lower section of the passage narrows into a ver- tical crevice, where the width diminishes with depth. At the end of this central channel, an approximately hori- zontal floor forms. This floor is marked by numerous grooves, a few centimeters in width, transversely orient- ed concerning the passage. These grooves connect with smaller channels, creating a small-scale hydrographic network that correspond to sulfuric acid-derived karren. Above the floor, notches can be observed in both side-walls (Fig 5B). The upper part of the passage is nota- bly wider than the portion below the floor level and may contain gypsum deposits in several locations (Figure 5C). The cave has a mostly flat floor with a subtle inclina- tion of approximately 1° towards the Sarantaporos River (Figure 5D). It is worth noting that the limestone beds Figure 4: SAS manifestations in the Skordyli Cave. A. Entrance area of the Skordyli Cave. Note the sulfur-rich water that floods the en- tire chamber. Notches can be seen in both sides, along with eroded consolidated clastic sediments. Β. Detail of the close-spaced notches and the consolidated sediments. C. View of the deepest part of the cave. D. Part of the main corridor at its widest point; the sulfuric stream flows at lower altitude at the right side of the passage. E. Whitish fila- mentous microbial structure in the sulfuric stream. F. A narrow part of the main passage where the stream flows in the middle of eroded clastic sediments. GEORGIOS LAZARIDIS, VASILIOS MELFOS, LAMBRINI PAPADOPOULOU, BOGDAN P. ONAC, CHRISTOS L. STERGIOU, ANGELOS G. MARAVELIS, PANAGIOTIS VOUDOURIS, DESPOINA DORA, MICHALIS FITROS, HARITAKIS PAPAIOANNOU & KONSTANTINOS VOUVALIDIS: 134 ACTA CARSOLOGICA 53/2-3 – 2024 dip 20° towards SW, so the flat cave floor is a result of dis- solution processes rather than structural control. In the Pixaria Cave, several elliptical pond-like areas exist, all with a coarse surface on the floor. The central portion of these areas is influenced by sulfuric feeders. The surface of the ponds exhibits smaller depressions and sulfuric acid-formed karren. We examined two specific cases, each displaying variations in morphology. The first sulfuric pond (Figure 6A) is characterized steep walls, suggesting that it is a result of simultaneous SULFURIC ACID SPELEOGENESIS IN GREECE Figure 5: SAS manifestations in the Pixarias Cave. A. Ground-plan. B. Typical passage morphology with a medial discharge feeder, a flat floor that corresponds to the corrosion table overprinted by sulfuric karren and a pair of notches formed just above that table. C. Gypsum deposits on the cave walls. D. NW-SE profile on which limited dissolution below the corrosion table can be seen and the level of springs and Sarantaporos River. Figure 6: Origin of sulfuric karren in Pixaria Cave by: A. Simultane- ous dissolution from various feed- ers. B. Water level drop. ACTA CARSOLOGICA 53/2-3 – 2024 135 dissolution from multiple feeders. Its surface is charac- terized by sulfuric karren with concentric arrangement. This form reflects the interplay of sulfuric processes in shaping its morphology. The other pond (Figure 6B) is delimited by steep walls and has a stair-like floor surface dominated by small-sized few centimeters wide depressions. It is sug- gested to have formed due to a drop in the water level, leading to the concentration of sulfuric water in the low- est central part of the passage. This process results in a distinct morphology, marking a different origin for this particular pond. 4.4 KAMENA VOURLA CAVE A cave-spring is situated along the escarpment of the ac- tive Kamena Vourla fault zone, as documented in studies by Ganas et al. (1997) and Cundy et al. (2010). The cave passage is flooded (Figure 7), and the presence of hydro- gen sulfide is detectable in the cave atmosphere. Explora- tion of this cave has been limited, reaching only the first chamber, located approximately 10 m from the entrance. Figure 7: Entrance passage of Kammena Vourla spring-cave. 4.5 THE PERISTERI CAVE IN METHANA PENINSULA This cave is located in Methana Peninsula in the eastern part of Peloponnese and comprises the westernmost part of the south Aegean volcanic arc (Figure 1:8). Its entrance is formed due to ceiling collapse (Petrocheilou, 1974). Al- though it has been referred as related to SAS (Lazaridis, 2017), further investigation is needed to verify the con- tribution of sulfuric acid speleogenesis in the formation of the cave. 4.6 PSORONERIA CAVES Some small inactive caves (Figure 8) that occur next to the thermal sulfuric water spring of Psoroneria, in the vicinity of Kamena Vourla. They lack typical morpho- logical indicators and gypsum deposits and they need further research to interpret their origin. 4.7 LAVRION CAVES Recently, some natural dissolution caves cut by mining galleries in Lavrion mines (see 7 in Figure 1 for location) have been identified and are under investigations from a speleogenetic and ore deposit perspective. One of these cavities discovered in the Paleokamariza #18 Mine, displays morphologies with cupola- related features, gypsum and dolomite with quartz, celestine, opal-AN, cinnabar, gorceixite BaAl3[(PO3(O,OH)]2(OH)6, coronadite Pb(Mn 4+ 6Mn 3+ 2) O16, iron hydro/oxides, as well as a number of supergene uranium minerals: andersonite Na2Ca(UO2) (CO3)3·6H2O, bayleyite Mg2(UO2)(CO3)3·18H2O, boltwoodite (K0.56,Na0.42)(UO2)(SiO3OH)·1.5H2O, chadwickite (UO2) H(AsO3), lanthinite (non-uranium) La2(CO3)3·8H2O, nováčekite Mg(UO2)2(AsO4)2·10H2O, sklodowskite Mg(UO2)2(SiO3OH)2·6H2O, uranospinite Ca(UO2)2(AsO4)2.10H2O, uranophane Ca(UO2)2[SiO3OH]2·5H2O, uraninite UO2 (Rieck et al., 2018; Ottens and Voudouris, 2018; Vourlakos and Fitros, 2019). The deposition of gypsum and all associated minerals could be related to SAS of either hypogene, but most probably epigene processes. Figure 8: Morphology of Psoroneria caves with large voids and wide entrances. GEORGIOS LAZARIDIS, VASILIOS MELFOS, LAMBRINI PAPADOPOULOU, BOGDAN P. ONAC, CHRISTOS L. STERGIOU, ANGELOS G. MARAVELIS, PANAGIOTIS VOUDOURIS, DESPOINA DORA, MICHALIS FITROS, HARITAKIS PAPAIOANNOU & KONSTANTINOS VOUVALIDIS: 136 ACTA CARSOLOGICA 53/2-3 – 2024 4.8 THE MELISSOTRIPA CAVE IN ELASSONA Melissotripa encompasses a total passage length of ap- proximately 2.1 km, with large galleries forming a maze area (Figure 9A). It has developed within a carbonate unit right beneath the schists-gneisses of the Pelagonian massif (Figure 1). The largest chambers within the cave have undergone significant modifications due to exten- sive breakdown, while the section formed beneath the caprock primarily exhibits a two-dimensional maze-like pattern. This cave has been proposed as a hypogene cave with SAS in confined conditions, attributed to the pres- ence of phreatic cupolas, gypsum in blister speleothems, and the detection of hydrogen sulfide in a small wa- ter pond believed to be connected to the local aquifer (Vaxevanopoulos, 2006). However, we interpret the pres- ence of cupola morphology in the cave as the result of condensation corrosion. Lazaridis (2017) documented sulfuric karren (Figs. 9B and 9C) and replacement pock- ets (Figure 9D) within the cave, including it among Greece's hypogene caves. The cave's two-dimensional maze section and the schists-gneisses overlaying the car- bonates acting as a caprock, suggest a hydrological set- ting conducive to hosting hypogene processes. The cave extends to an elevation of 251.7 mapsl, whereas the average water table elevation was approxi- mately 256 mapsl for the period 1988-1992 (Manakos, 1999; Vasileiou & Koumantakis, 2013). This indicates that the small lakes within the cave are linked to the lo- cal karst aquifer, primarily developed in the carbonate formations of Krania, with no significant sulfur content. In fact, higher concentrations of sulfate ions (SO₄²-) were detected in surface water samples when compared to groundwater samples (Manakos et al., 2018). The karst water in the region is of Mg-HCO3 – type and discharges at a contact spring along a fault that also intersects the cave entrance. Given the absence of sulfur in the aquifer and con- sidering well-documented instances of epigene-based SAS processes elsewhere (e.g., Angeli et al., 2019; Webb, 2021), the origin of SAS in Melissotripa is subject of fur- ther investigation. 5. MINERALOGICAL AND GEOCHEMICAL RESULTS Mineralogy and geochemistry have been studied in two distinct areas with SAS. The first area of Aghia Paraskevi belongs to the Internal Hellinides and the second one in western Peloponessus belongs to the External Hellinides. They are both located in coastal areas and therefore they have been considered as comparable examples. Through their analysis it is attempted to interpret their evolution and to identify differences depending on the geological setting. Fluid inclusions data were obtained from a calcite sampled from the QG2 Cave. The results are presented in SULFURIC ACID SPELEOGENESIS IN GREECE Figure 9: SAS manifestations in Melissotripa Cave. A. Ground- plan pattern of the cave. B–C. Sul- furic karren formed by dripping- seeping water. D. Replacements pockets on the limestone walls. E. Intersected cupolas. ACTA CARSOLOGICA 53/2-3 – 2024 137 Figure 10. At room temperature, only two phase liquid- vapor inclusions were identified. Inclusions that were analyzed, ranged in diameter between 5 and 70 μm and display homogenization into the liquid state. Vapor to liquid ratio is 1–20 vol % μm with some exceptions that exceed 50%. The variability in homogenization tempera- ture data may be due to real variability in the fluid inclu- sion assemblages or to post-entrapment processes such as thermal re-equilibration or undetectable necking- down (Goldstein, 2003). Homogenization temperature ranges from 183 to 380 °C with a peak at ~280 °C (n=67). The initial melting temperature (Tfm) is approximately –21.2 °C, indicating that the main components of the fluid are H2O and NaCl. The salinity ranges from 1.91 to 3.39 wt% NaCl. Isotopic composition of calcite and gypsum sam- ples, and chemical analysis from the caves of Aghia Para- skevi are given in Supplementary Information (Tables 1 and 2). The calcite display traces of Fe, Mn, K, Na, S, P, Ti, As, Rb, and Sr. The gypsum is characterized by a high arsenic content (1754 ppm). Investigations were conducted on gypsum samples Sp47 and Sp 49-51 from Anigridon Nymphon and Kou- noupeli caves in the Peloponnese. SEM was used to ex- amine samples Sp49, Sp50, and Sp51. The Sp49 sample was found to consist of small gypsum crystals, ranging Figure 11: Scanning Electron Mi- croscope (SEM) images of gypsum samples from the cave at Kou- noupeli. A. and B. The images showcase the size and shape of gyp- sum crystals (G); C. some alumino- silicate minerals (indicated as A-S) in the Sp50 sample; D. gypsum of sample Sp51. Figure 10: Histogram of homogeni- sation temperatures measured in the fluid inclusions of Sp9/PAR(B) sample from QG2 Cave in Aghia Paraskevi. GEORGIOS LAZARIDIS, VASILIOS MELFOS, LAMBRINI PAPADOPOULOU, BOGDAN P. ONAC, CHRISTOS L. STERGIOU, ANGELOS G. MARAVELIS, PANAGIOTIS VOUDOURIS, DESPOINA DORA, MICHALIS FITROS, HARITAKIS PAPAIOANNOU & KONSTANTINOS VOUVALIDIS: 138 ACTA CARSOLOGICA 53/2-3 – 2024 in size from 5 to 50 μm (Figure 11). Both Sp50 and Sp51 contain gypsum along with aluminosilicate minerals (as shown in Figure 11), but Sp50 is particularly iron-rich. Semiquantitative SEM-EDS chemical analysis of the Kounoupeli aluminosilicate minerals found in sample Sp51 and the XRF chemical analysis of gypsum are given in Supplementary Information (Tables 3 and 4). Isotopic composition of gypsum samples from the caves of W. Peloponnese are included in Supplementary Information (Table 5). 6. DISCUSSION Among the cave examples discussed here, Aghia Para- skevi and Konitsa caves in Northern Greece, Kounoupeli and Anigridon Nimfon caves in western Peloponnese, stand out as regions in Greece with the best-documented instances of hypogene sulfuric acid speleogenesis. In oth- er areas, either SAS has not been fully confirmed yet (as in the cases of Peristeri and Psoroneria), or its role in the cave formation remains unclear, as is the case with Melis- sotripa Cave and the Paleokamariza #18 Mine. Moreover, some caves remain unexplored, including the Kamena Vourla spring-cave. 6.1 STAGE OF CAVE EVOLUTION The Aghia Paraskevi caves are categorized into three groups based on their stage of development, resulting in distinctive morphologies. It appears that the caves’ eleva- tion corresponds to their age, with higher caves being older. The WTG, primarily hosting active SAS caves, ex- hibits a unique orpiment-bearing paragenesis (Lazaridis et al., 2011). The Quarry Group caves contain calcite spar with high homogenization temperatures, as well as alunite and gypsum related to SAS development. The high calcite ho- mogenization temperature and the passage morphology indicative of formation in phreatic conditions, suggest a deep-seated speleogenetic setting. The homogenization temperature and salinity of the fluid inclusions in the cal- cite, compare well with data from basinal, seawater, me- teoric, metamorphic, and magmatic hydrothermal ore- forming fluids (Kesler, 2005). A meteoric origin for the fluids is suggested due to their increased homogenization temperature and relatively low salinity. The calcite bear- ing passages in Aghia Paraskevi caves are formed in depth as indicated by the homogenization temperature and then they have been uplifted. A similar succesion can be found in the Provalata Cave in North Macedonia, which shows an early phase of carbonic acid speleogenesis followed by SAS (Temovski et al., 2013, 2018). Azerou hydrothermal and sulfuric karst in Algeria is another example of these successive speleogenetic events (Audra, 2017). The positive δ13C value of the calcite suggests that the isotopic composition of the bedrock rather than soil CO2 dominate the δ 13C record. This is likely related to a pyrite oxidation process that drives the acidity needed for bedrock dissolution. An additional evidence of py- rite oxidation could be the δ34S values (–4‰) measured in sulfate crusts from several caves in this area. Further- more, gypsum crusts in QG3 Cave, associated with SAS at or near the water level, contain a high concentration of arsenic (1754 ppm), commonly found in the thermal waters of the region and in the orpiment paragenesis ob- served in the water table caves of the area (Lazaridis et al., 2011). Similarly, the hydrothermal calcite that more difficult incorporates arsenic (e.g. Fernandez-Martinez et al., 2006), displays a concentration of 10 ppm. Likewise Aghia Paraskevi caves, the cave system in Konitsa includes multiple cavities at different elevations. Those at river level are still active, representing another example of SAS with a complex geological history influ- enced by the uplift rates of the area and the downcutting rate of the Sarantaporos River. The genesis of caves in W. Peloponnese is closely tied to sea level fluctuations. However, the existence of submerged inactive SAS cave passages in these regions cannot be ruled out, as they have not yet been explored. In fact, the mean sulfur isotopic composition (~ –26‰; see Table 5 in Supplementary Information) suggests the presence of SAS, with H2S sourced from low-temperature microbial sulfate reduction. Comparable δ34S values have been reported from numerous SAS caves worldwide (for a review, see De Waele et al., 2024). In conclusion, we can distinguish three major stages of evolution for these cave systems: • Initial hydrothermal speleogenesis: characterized by carbonic acid-driven processes in deep settings, with the possible co-occurrence of SAS at the water table. • Active SAS caves: associated with the water table. • Inactive SAS caves: occur due to relative water table drop caused by uplift and denudation, leading to the formation of tiered cave levels and remnants of SAS above the water table. The rise of the water table may have submerged already formed SAS caves. SULFURIC ACID SPELEOGENESIS IN GREECE ACTA CARSOLOGICA 53/2-3 – 2024 139 6.2 CONTROL OF TECTONOSTRATIGRAPHIC SETTING ON THE FORMATION OF SAS SYSTEMS The density of hypogene SAS caves in Greece is one per ~26.000 km2. This high density is only second to Italy, where about 25% of the worldwide known SAS caves have been discovered (D’Angeli et al., 2019). This abun- dance of SAS systems in Greece could be associated with the regional tectonostratigraphic setting. The caves in W. Peloponnese (Kounoupeli Cave and Anigridon Nimfon) and Konitsa are situated in west- ern Greece, a region that was under extension through- out the Mesozoic and under compression since Early to Middle Eocene due to modifications in the motion of the Apulian and Pelagonian plates (e.g., De Graciansky et al., 1989; Doutsos et al., 1993). The extensional period dis- plays the ongoing evolution of a rift-type setting, from the pre- to syn-rift stage, and is characterized by the sedimentation of carbonates (Karakitsios, 1995; Bourli et al., 2019a, b). As such, Upper Triassic to Lower Juras- sic shallow marine limestones are deposited over Trias- sic evaporates. The Late Eocene shift in tectonic regime, from extensional to compressional, occurred because of the Pindos Orogen and is accompanied by a shift in sedi- mentation, from carbonate to siliciclastic. Such deposits are intensively deformed by contractional tectonics dur- ing the upbuilding and westward migration of the Pindos fold and thrust belt (Botziolis et al., 2021; 2023). Within this tectonic framework, a network of deep faults (both normal and reverse) cut across the entire regional stratigraphic succession. These faults serve(d) as potential pathways for the ascent of deep-seated sul- fidic fluids through the stratigraphic column, reaching shallow levels and forming the studied caves in western Peloponnesus. As these solutions ascended sulfate re- duction led to the formation of hydrogen sulfide, which subsequently oxidized near the surface, triggering the development of sulfuric acid caves. A similar mechanism has been invoked by D’Angeli et al. (2019) to explain the abundance of SAS systems in Italy. Likewise Italy, Greece shares similar geotectonic evolution since Mesozoic, thus, the source of sulfidic fluids might have been the Triassic evaporates. Another possible scenario that could form SAS systems is the in- teraction of hydrocarbons with evaporitic rocks in the lithological successions. The External Hellenides in the western Greece, share geological similarities with the Ex- ternal Albanides in the neighboring region of Albania. A study by Klimchouk et al. (2022) in Albania's External Albanides, relate SAS with geothermal reservoirs and hy- drocarbons discovered at a depth of 3,000 m. This sug- gests that the geological conditions supporting hydrocar- bons in Albania may extend into western Greece (e.g., Maravelis et al., 2012). The formation of these features is thought to be connected to the geotectonic evolution of the region from the Upper Miocene to Pleistocene. This period witnessed the uplift and erosion of the flysch cov- er, which in turn triggered artesian water flow through carbonate rocks, concurrently initiating hypogene spe- leogenesis. Similar consideration has been proposed for the caves of the Guadalupe Mountains that developed when upward moving H2S originating from the oil fields of the Delaware Basin, oxidized to sulfuric acid close to the water table (Hill, 1995). 6.3 CAVE MORPHOLOGY Fracture-guided cave morphology: In their entirety, the investigated caves exhibit single fracture-guided passages (e.g., Kounoupeli Cave), ramifying mazes (e.g., WTG1 in Aghia Paraskevi), network mazes (e.g., Pixarias Cave), conduits with sizable chambers affected by breakdown (e.g., Skordyli Cave), and vertically developed feeders (e.g., QG2 in Aghia Paraskevi). These feeders are pre- dominantly linear and tectonically guided. Sulfuric acid-induced dissolution contributes to speleogenesis in both subaqueous and subaerial condi- tions near the water table (e.g., De Waele et al., 2016). The latter is more dominant, particularly under specific con- ditions involving the flow of H2S-rich waters (Jones et al., 2015). A number of meso- and micro-scale dissolutional features observed in the studied caves are considered SAS morphologies. These include notches, corrosive table, dome-shaped pockets, floor elongated feeders, and sul- furic karren. All these features are susceptible to changes during later phases of cave development. In the caves of western Peloponnese, particularly in Kounoupeli Cave, where one level of lateral notches is present, the dissolved bedrock volume above the notches is considerably higher than that below the water table. This is indicative of significant subaerial SAS. From a few cross-sections in Pixarias Cave, we estimate that the notch level is about 10% of the cross- section, the feeder is 20%, and the domes represent 70%. The maximum width of the subaerially dissolved cross- section part is 40% wider than the notch level and more than four times the width of the feeder. This implies that dissolution above the water table is favored. However, in larger passages, like those in Skordyli Cave, where break- down plays a significant role in its development, the sub- aerial portion becomes even more extensive. The extensive morphology of SAS caves includes cupolas and a variety of speleogens that result from the interconnection of several cupolas, such as megascallops, cusps, windows, bridges, and more. While these features are found in most known examples of this cave type, they are polygenetic (e.g., Plan et al., 2012; Dublyansky, 2013; De Waele et al., 2016). Notches, although possibly unre- GEORGIOS LAZARIDIS, VASILIOS MELFOS, LAMBRINI PAPADOPOULOU, BOGDAN P. ONAC, CHRISTOS L. STERGIOU, ANGELOS G. MARAVELIS, PANAGIOTIS VOUDOURIS, DESPOINA DORA, MICHALIS FITROS, HARITAKIS PAPAIOANNOU & KONSTANTINOS VOUVALIDIS: 140 ACTA CARSOLOGICA 53/2-3 – 2024 lated to cupolas, also exhibit polygenetic characteristics in terms of chemical reactions (sulfuric and carbonic ac- ids can create notches) and erosion sensu lato processes (e.g., paragenesis; Farrant and Smart, 2011). However, when formed as pairs of identical notches at the same level, they serve as markers for the water table. Subaerial and subaqueous sulfuric karren and other small-scale forms such as drip tubes, pendant drip holes, and cups are mentioned in other case studies (Audra et al., 2009; De Waele et al., 2016). Notably, karren is a col- lective term that includes dissolutional features of various morphologies and sizes. In this work we described both subaqueously and subaerial karren. Subaerial sulfuric kar- ren corresponds to the drip tubes described by Audra et al. (2016), whereas the subaqueously ones can be found in caves such as WTG1 (Figure 2H) and Pixarias (Figure 6), where they form in the zone influenced by water level fluctuations, appearing on lower walls sections and cor- rosion tables. Another type of sulfuric karren reported in Melissotripa Cave (Lazaridis, 2017), consist of a dense network of channels originating from drip holes, ap- proximately 1 cm in diameter and running downward on inclined surfaces for several decimeters; they indicate a subaerial origin. Given that dripping points are unrelated to pendants or cusps, an additional factor contributing to dense dripping points should be considered and further investigated. A reasonable hypothesis would assume that biofilms would have been existed and were able to supply strong acid drips, referred as snottite (Barton et al., 2007). Although these forms are highly distinctive, they have not been observed in other caves included in this study. Replacement gypsum pockets are prominent features in SAS caves, that are easily recognizable and morphologi- cally they strictly define this type of speleogenesis. 6.4 GEOMORPHOLOGICAL CONTROL In the vicinity of and above the water table, the presence of high oxygen levels enables the oxidation of hydrogen sulfide, making SAS caves remarkable indicators of pre- vious water table levels (e.g. Hill, 1995; Audra et al., 2015; De Waele et al., 2016). Greece highlights notable exam- ples of SAS in locations linked to hydrothermal springs. These areas involve the mixing of water with seawater, discharging at or near sea level, or combining with me- teoric water and discharging in an incised valley. While inactive SAS caves at higher elevations than their active counterparts have not yet been documented in western Peloponnese, Aghia Paraskevi presents a unique case. It features relict caves displaying distinct SAS mineralogi- cal and morphological characteristics, suggesting a com- plex evolutionary history involving sea-level changes, climatic variations, and tectonic uplift. 7. CONCLUSIONS In the systematic investigation of Greek cave systems orig- inating from SAS, several key observations and conclu- sions emerge. The study highlights the widespread occur- rence of SAS systems in Greece, attributed to the dynamic geotectonic settings of the region. The cave systems in Greece are intrinsically linked to an ever-changing inter- play of factors, including environmental conditions, geo- logical uplift, and sea-level fluctuations. These dynamic variables influence the positioning of the water table and, consequently, the formation of these caves. The presence of deep faults, hydrothermal activity, volcanism, ore-forming processes, and potentially hydrocarbon reservoirs, make Greece ranking as the second-highest country in terms of SAS distribution per square kilometer. Based on their geological origin and historical evo- lution we identified: caves formed by deep-seated car- bonic acid and later modified by SAS, active, and inactive SAS caves. While the morphological characteristics of the dis- solutional features within these caves may exhibit poly- genetic origins, they also display unique characteristics that are indicative of SAS. These include replacement pockets, particular passage cross sections with dissolu- tion forms below the water table markers, floor ponds, and subaerial sulfuric karren. Despite the limited data available, the isotopic values of sulfate minerals within the investigated caves can be divided into two distinct groups: In the Aghia Paraskevi caves the δ34S values suggest pyrite oxida- tion, whereas the in W. Peloponnese the values indi- cate microbial sulfate reduction of gypsum hosted in the sedimentary sequence in the presence of hydro- carbons. The relationship between these caves and the water table makes them excellent markers for tracking past wa- ter table levels. Given the constant changes in the water table in the studied cases due to uplifting, down-cutting, and sea-level changes, the formation of sulfuric acid dis- solved cave passage at various levels is anticipated to have been occurred rapidly. In summary, the systematic exploration of SAS- driven cave systems in Greece sheds light on the complex interplay of geological, environmental, and hydrogeolog- ical factors shaping these unique underground environ- SULFURIC ACID SPELEOGENESIS IN GREECE ACTA CARSOLOGICA 53/2-3 – 2024 141 ments. The presence of distinct morphological features and mineralogical compositions further highlights the exceptional nature of these cave systems and their utility in understanding geological processes. ACKNOWLEDGMENTS Sampling and research in the studied caves were con- ducted after the permissions of the Ephorate of Paleoan- thropology and Speleology of Greece. The cavers Manolis Diamantopoulos and Prodromos Koulelis are thanked for their valuable assistance during fieldwork in Konitsa area. Ilias Lampropoulos is thanked for his assistance during the fieldwork in Kounoupeli. Konstantinos Ba- kolitsas is thanked for sampling gypsum deposits in Kaia- fas Cave. 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