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Chemical deposits inside evaporite (gypsum, anhydrite and halite) caves are far less common than those developed within limestone or volcanic cavities. Moreover they exhibit a lower scarce mineralogical variability due to several reasons, the most important of which are: 1) calcium sulfate and sodium chloride are by far less reactive than calcium carbonate; 2) evaporite outcrops normally have a low mineralogical variability within the cave recharge areas. Therefore these karst environments were less investigated from this point of view in the past: no general paper exists on speleothems developing in halite and anhydrite caves until present, while the last printed one on gypsum (and anhydrite) karst appeared around 20 years ago. Several mineralogical studies were carried out in the last decades in caves from different evaporite areas proving that some of them host peculiar minerogenetic mechanisms, which are, at the moment, exclusive for these areas, and sometimes also brought to light to rare or even new cave minerals. In the present paper, together with an overview on all the actually known minerogenetic mechanisms active within the evaporite caves, the related chemical deposits and speleothems are shortly described. Far from being exhaustive, the recent mineralogical research on evaporite caves puts in evidence their unexpected richness in peculiar hosted speleothems and rare cave deposits. Seven out of the fifty known evaporite cave minerals, and around 10 speleothem types/subtypes are exclusive to these environments. Taking into account that only a few evaporite areas have been, so far, studied, it is highly probable that in the near future many more new cave deposits will be discovered, thus increasing the mineralogical interest of these unique caves.

15 páginas.- 5 figuras.- 85 referencias.- The following are available online at http://www.mdpi.com/2079-6412/10/11/1134/s1 .- This article belongs to the Special Issue Biofilms on Cultural Heritage, The Galapagos Islands (Ecuador) have a unique ecosystem on Earth due to their outstanding biodiversity and geological features. This also extends to their subterranean heritage, such as volcanic caves, with plenty of secondary mineral deposits, including coralloid-type speleothems and moonmilk deposits. In this study, the bacterial communities associated with speleothems from two lava tubes of Santa Cruz Island were investigated. Field emission scanning electron microscopy (FESEM) was carried out for the morphological characterization and detection of microbial features associated with moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves. Microbial cells, especially filamentous bacteria in close association with extracellular polymeric substances (EPS), were abundant in both types of speleothems. Furthermore, reticulated filaments and Actinobacteria-like cells were observed by FESEM. The analysis of 16S rDNA revealed the presence of different bacterial phylotypes, many of them associated with the carbon, nitrogen, iron and sulfur cycles, and some others with pollutants. This study gives insights into subsurface microbial diversity of the Galapagos Islands and further shows the interest of the conservation of these subterranean geoheritage sites used as show caves, This research was funded by the Ecuadorian Ministry of Environment (Project PC-65-14 National Park Galapagos), by the Spanish project MINECO CGL2016-75590-P with European Regional Development Fund and the Portuguese Foundation for Science and Technology (Fundação para a Ciência e a Tecnologia-FCT) under the project UID/Multi/04449/2019 for HERCULES/UE. AMGS was supported by a FPU fellowship of the Spanish Ministry of Education, Culture and Sport (AP2010-2052). AZM was supported by a Marie Curie Intra-European Fellowship of the European Commission’s 7th Framework Programme (PIEF-GA-2012-328689-DECAVE) and a CEECIND/01147/2017 contract from FCT. MLC was supported by a CEECIND/00349/2017 contract from FCT. FG was financially supported by the “HIPATIA” research program of the University of Almeria.

The “espada” speleothems of Cueva de las Espadas (Naica Mine, Chihuahua, Mexico) comprise a high-purity selenite core overlain by successive deposits of calcite, gypsum and aragonite. Gypsum precipitated under water from a hydrothermal solution (~ 58°C) when the water table was above the cave level ca. 57 ka, during the last glaciation, and some intervals during deglaciation and the Holocene. Aragonite was deposited at lower temperatures (~ 26°C) in a perched lake occupying the cave bottom, when the water table dropped below the cave level during brief dry intervals during deglaciation and the early Holocene. The isotopic composition of gypsum water of crystallization shows that the deglaciation–Holocene aquifer water was enriched in deuterium by 12.8–8.7‰ relative to water from the last glaciation. This is attributed to an increased relative moisture contribution from the Gulf of Mexico during deglaciation and the Holocene compared to the last glaciation. This indicates that drier conditions occurred in the Naica area during the Holocene than around 57 ka. Furthermore, trace element analyses of gypsum served to deduce the circulation regime of the Naica aquifer during the past 60,000 yr, and also suggest that higher aquifer recharge occurred during the last glaciation.

The caves of Naica (Chihuahua, Mexico) have been known since the beginning of the nineteenth century, when they were intersected by mines. They became world famous in 2000 when the mining activities intersected three small caves, which hosted gigantic gypsum crystals. Their genesis and evolution is strictly related to rising thermal fluids induced by Tertiary intrusive magmatic activity, giving rise to polysulfide deposits. Speleogenesis began about 1.5 Myr BP, induced by rising thermal water. This process lasted for a relatively short time. Later evolutionary stages varied from cave to cave, reflecting alternately deep-seated phreatic, epiphreatic, and vadose environments. Deposition of the giant gypsum crystals began ~400–350 Kyr BP, when the water temperature dropped below 58 °C. Their growth suddenly ceased in 1985, when mine dewatering dried up the caves. Besides the giant gypsum crystals, Naica caves contain a wide variety of other cave minerals (over 40), ten of which are new for the cavern environment. In addition, they include fossil pollen trapped in the gypsum lattice, which allow reconstruction of the external climate of 350 Kyr BP, and microorganisms new to science, which were preserved in the fluid inclusions of the gypsum crystals for tens or even hundreds of thousands of years. In 2015, mining intercepted a major thermal water source, which flooded the mine, and the Cueva de los Cristales and other caves at −290 m were flooded by more than 160 m of hot water.

In Sardinia, no active hypogenic caves have yet been discovered or described. Although there are a few thermal springs, mostly correlated to Quaternary volcanic activity, none of these thermal waters have interacted with carbonate rocks. Nevertheless, in the SW of the Island many metal ore deposits hosted in Cambrian limestones have been exploited over the last two centuries, allowing the discovery of so-called mine caves, some of which are clearly of hypogenic origin. These caves formed by thermal waters in a phreatic setting and are now located far above the water table and are no longer active, apart from some recent dripstone formation. The mine tunnels in Mount San Giovanni, near Iglesias and Gonnesa towns, have cut most of these caves: among them the well-known Santa Barbara cave, covered with barite crystals, Santa Barbara 2 cave, with its unique oxidation vents, and Crovassa Ricchi in Argento. Other hypogenic caves have been discovered in the mines of Campo Pisano and Monteponi (Iglesias), Mount Onixeddu (Gonnesa), and especially Masua (Iglesias). A very special case of hypogenic cave is the Corona ’e Sa Craba quartzite system, known for its barite crystals and rich in many mineral species. This chapter summarizes these known inactive hydrothermal and sulfuric acid caves.

none 16 si Although outcropping rarely in Italy, evaporite (gypsum and anhydrite) karst has been described in detail since the early 20th century. Gypsum caves are now known from almost all Italian regions, but are mainly localised along the northern border of the Apennine chain (Emilia Romagna and Marche), Calabria, and Sicily, where the major outcrops occur. Recently, important caves have also been discovered in the underground gypsum mines in Piedmont. During the late 80s and 90s several multidisciplinary studies were carried out in many gypsum areas, resulting in a comprehensive overview, promoting further research in these special karst regions. More recent and detailed studies focused on the gypsum areas of Emilia-Romagna and Sicily. Sinkholes related to Permian-Triassic gypsum have been studied in Friuli Venezia Giulia. This article reviews the state of the art regarding different aspects of evaporite karst in Italy focusing on the main new results. open De Waele, J.; Piccini, L.; Columbu, A.; Madonia, G.; Vattano, M.; Calligaris, C.; D’Angeli, I.M.; Parise, M.; Chiesi, M.; Sivelli, M.; Vigna, B.; Zini, L.; Chiarini, V.; Sauro, F.; Drysdale, R.; Forti, P. De Waele, J.; Piccini, L.; Columbu, A.; Madonia, G.; Vattano, M.; Calligaris, C.; D’Angeli, I.M.; Parise, M.; Chiesi, M.; Sivelli, M.; Vigna, B.; Zini, L.; Chiarini, V.; Sauro, F.; Drysdale, R.; Forti, P.

The study area of Tang sorkh Aquifer is located on the northern flank of the Derak anticline, a part of the Zagros Mountain Range, in the central-south of Iran. The study area is limited to undifferentiated non-salt Gachsaran Formation (NSGF), mainly composed of alternative layers of marl and marlstone, and gypsum. This paper is focused on the hydrogeological and hydrochemistry characteristics of the NSGF. A detailed geological cross section, perpendicular to the strike of the GF was prepared by detailed field surveying. The thickness of GF is 1,268 m, with 82 alternative units of marl, marlstone, gypsum, sandstone and limestone. The sub-aquifers are limited to four limestone, five gypsum, and one gypsum-halite units. The waters of these sub-aquifers emerge as springs or seepage into the Tang sorkh River (TR). The average discharge of springs emerging from limestone and gypsum units ranges between 0.3–8.4 and 0.5–0.75 l s−1, respectively. The source for sub-aquifers is mainly recharge from precipitation or river water. Marly layers disconnect the hydraulic connection between the sub-aquifers, directing the general flow parallel to the strikes. The lack of sinkholes and caves in the gypsum units is due to the small thickness of sub-aquifers, and consequently, low amounts of recharge water. The springs are classified into four groups based on their lithology, electrical conductivity, type of water, and trend of ion-concentration. The type of water in most of the springs is calcium-sulfate. The electrical conductivity is the main parameter to differentiate the hydrochemistry of the groups. The hydrochemistry of springs depends on the recharge from the TR, and the lithology of sub-aquifers and their adjacent units.

Ojo de la Reina is the first and the smallest cave intersected at the -290 level in the Naica Mine (Mexico), therefore it was the first cavity in which the lowering of temperature induced by mine ventilation caused condensation over crystals’ surface since 2005. The consequent dissolution of the gypsum crystals and subsequent condensed water evaporation lead to the deposition of several new minerals, among which some highly soluble Mg/Na compounds (bloedite, epsomite, halite, hexahydrite, kieserite, starkeyite). The single available source of Mg and Na ions in this minerogenetic environment is represented by the huge fluid inclusions widespread within the crystals. The condensation occurs mainly along the widened principal exfoliation (010) planes, and allows to an easy and fast opening of the fluid inclusions that consequently drip Mg-rich fluids stored inside them. Finally the evaporation of the relatively small volumes of involved water allows to the development of the high soluble Mg and Na compounds.

Poiano is the largest karst spring of the Emilia Romagna region (northern Italy). It drains an aquifer of unique properties composed of anhydrite with halite lenses at depth and gypsum at the surface (both with high NaCl content). Hydrogeological research has been undertaken using automatically recorded hourly data on temperature, electrical conductivity, and water level. Water feeding the Poiano spring is restricted within the gypsum/anhydrite outcrop between the Lucola, Sologno and Secchia rivers. Karstification in the Upper Secchia Valley only concerns the gypsum rocks mainly present along the border and in the shallower parts of the sulfate outcrop and does not appear to occur at depth. Data strongly support the hypothesis that the salt content in the spring water derives from active halokinetic movements. For the first time, the fundamental hydrogeological importance of the anhydrite part inside the sulfate rocks is demonstrated. If gypsum prevails over anhydrite the karst drainage network can extend deep into the rocks following a network of fractures and fissures. Instead, if in the deep parts of the aquifer anhydrite prevails over gypsum, the karst evolution cannot take place at depth and the structure of the underground drainage paths only follows near-surface paths in gypsum.

Three hypogenic caves within the Naica mine of Mexico (Cueva de los Cristales — CLC, Ojo de la Reina — OR, and Cueva de las Velas — CLV) host spectacular gypsum crystals up to 11 m in length. These caves are close to another shallow cave of the area (Cueva de las Espadas — CLE), with which they cover a 160 m-deep vertical section of the local drainage basin. Similar to other hypogenic caves, all these caves lack a direct connection with the land surface and should be unrelated with climate. A record of multi-technique fluid inclusion data and pollen spectra from cave and mine gypsum indicates surprisingly that climatic changes occurring at Naica could have controlled fluid composition in these caves, and hence crystal growth. Microthermometry and LA-ICP-Mass Spectrometry of fluid inclusions indicate that the shallow, chemically peculiar, saline fluid (up to 7.7 eq. wt.%NaCl) of CLE could have formed from evaporation, during a dry and hot climatic period. The fluid of the deep caves was instead of low salinity (∼ 3.5 eq. wt.% NaCl) and chemically homogeneous, and was poorly affected by evaporation. We propose that mixing of these two fluids, generated at different depths of the Naica drainage basin, determined the stable supersaturation conditions for the gigantic gypsum crystals to grow. Fluid mixing was controlled by the hydraulic communication between CLE and the other deep caves, and must have taken place during cycles of warm-dry and fresh-wet climatic periods, which are known to have occurred in the region. Pollen grains from a 35 ka-old gypsum crystal of CLC corresponds to a fairly homogenous catchment basin made of a mixed broadleaf wet forest, which suggests precipitation during a fresh-wet climatic period and confirms our interpretation of the fluid inclusion data. The unusual combination of geological and geochemical factors of Naica suggests that other hypogenic caves found elsewhere may not host similar crystals. However, this work shows that fluid inclusions and pollen spectra represent a useful tool for cave studies in general, and if used in future studies might be essential to unravel the mechanisms of hypogenic deposition.

This article highlights the relationship between speleothems growing inside gypsum caves and the particular climate that existed during their development. Speleothems in gypsum caves normally consist of calcium carbonate (calcite) or calcium sulphate (gypsum) and the abundance of such deposits greatly differs from zone to zone. Observations carried out over the last 20 years in gypsum caves subjected to very different climates (Italy, Spain, New Mexico, northern Russia, Cuba, Argentina) highlight wide variation in their cave deposits. In arid or semi-arid climates, the speleothems are mainly composed of gypsum, whilst in temperate, humid or tropical regions, carbonate formations are largely predominant. In polar zones no speleothems develop. These mineralogical details could be useful paleoclimatic indicators of climate change. The interpretation proposed is based on the fact that in gypsum karst the kind of speleothems deposited is determined by competition between the two principal mechanisms that cause precipitation of calcite and gypsum. These mechanisms are completely different: calcite speleothem evolution is mainly controlled by CO2 diffusion, while gypsum deposits develop mostly due to evaporation. Therefore, the prevalence of one kind of speleothem over the other, and the relationship between the solution–precipitation processes of calcite and gypsum, may provide evidence of a specific paleoclimate. Additionally, other non-common deposits in gypsum caves like moonmilk, cave rafts and dolomite speleothems can be used as markers for the prevalence of long, dry periods in humid areas, seasonal changes in climate, or rainfall trends in some gypsum areas. Moreover, the dating of gypsum speleothems could contribute paleoclimatic data relating to dry periods when calcite speleothems are not deposited. In contrast, the dating of calcite speleothems in gypsum caves could identify former wet periods in arid zones.

2 páginas.-- 2 figuras, Coralloid-type speleothems were found in Ana Heva lava tube from Easter Island (Chile). The ceiling of the lava tube presents light to dark brown speleothems with globular coral-like shape. To appraise their internal structure and composition, optical microscopy (OM) of cross-sections, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDS) and X-Ray micro-computed tomography ( CT) were performed. The latter is a non-destructive method (NDM), performed to assess physical and compositional heterogeneities of the coralloids. The internal structure of these speleothems comprises a succession of thin layers, ranging from white to brown, with vitreous to resinous luster (Fig. 1A). According to their color and texture, four major layers are easily distinguishable, from the surface to their inner part: a superficial dark brown to black coating, with approximately 0.1 mm thick (L1); a 0.1-1 mm thick semi-transparent grayish layer (L2); a 0.1-1 mm thick white layer (L3), and a heterogeneous honey brown layer, with 1-5 mm thick and shades ranging from yellowish to honey brown (L4). FESEM-EDS microanalyses performed on the internal layers of longitudinally cut coralloid samples (Fig. 1B) showed systematic differences in chemical composition of the different color inner layers. In general, they contain variable proportions of Si, Mg and Ca (Fig. 1C-G). According to a previous study [1], the thin dark brown to black coating of the coralloid surfaces is probably derived from the weathering of the overlying volcanic rock and microbial activity [1]. The semi-transparent grayish layer (L2) is composed of low crystalline silica (opal-A), whereas the whitish layers (L3) are calcium carbonate (calcite). In contrast, the honey-brown layers (L4) present an unusual composition characterized by high levels of Mg, corresponding to an amorphous Mg hydrate silicate. Significant content of organic carbon was also found in these layers [1]. The CT study allowed us to confirm the existence of internal zoning in the studied coralloids (Fig. 2), and between them and the basaltic substrate. The brighter domains in the reconstructed images (Fig. 2D,E) correspond to the vacuolar basaltic. The other opaque domains, comprising thin spheroidal precipitates or dispersed spots within the coralloids (Fig. 2F-I), are calcium rich phases. According to mineralogical data and FESEM-EDS analysis, the inner/older spots correspond to apatite and the outer/more recent spots correspond to calcite. In contrast, the Si, Mg and C enriched domains are more transparent to X-ray radiation, combining at least two main phases (siliceous and magnesium silicate compounds). The proposed methodology was considered adequate for studying coralloid samples, by combining a NDM (μCT) with other microanalytical techniques. Investigations of speleothems using the potentialities of μCT provide general morphological and compositional information, suggesting the best approach for selecting and sectioning the samples. The FESEM-EDS provides characteristic information on the morphological, mineral and chemical composition., The authors acknowledge FCT for PEst-OE/CTE/UI0098/2011, AZM (SFRH/BPD/63836/2009) grant, and Spanish Ministry of Science and Innovation (Project CGL2011-2569) and CSIC 210230E125.

Kenya is one of the few countries in which karst cavities are scarce with respect to volcanic ones, which are widespread throughout the whole country. The great variability in lava composition allowed the evolution of very different cavities, some of which are amongst the largest lava tubes of the world. As normal for such a kind of cave, the hosted speleothems and cave minerals are scarce but important from the minerogenetic point of view. Anyway up to present no specific mineralogical research have been carried out therein. During the 8th International Symposium on Volcanospeleology, held in Nairobi in February 1998, some of the most important volcanic caves of Kenya have been visited and their speleothems and/or chemical deposits sampled: most of them were related to thick guano deposits once present inside these cavities. Speleothems mainly consisted of opal or gypsum, while the deposits related to guano often resulted in a mixture of sulphates and phosphates. The analyses confirmed the great variability in the minerogenetic mechanisms active inside the volcanic caves, which consequently allow the evolution of several different minerals even if the total amount of chemical deposit is scarce. Among the observed minerals kogarkoite, phillipsite and hydroxyapophyllite, must be cited because they are new cave minerals not only for the lava tubes of Kenya, but also for the world cave environment. The achieved results are compared with the available random data from previous literature in order to allow an updated overview on the secondary cave minerals of Kenya.

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 situprodu ction 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. r 2002 Elsevier Science Ltd. All rights reserved.

During a fi eld trip in November 2007 at San Pedro de Atacama (Chile) several centimetre- scale white rims and blisters were observed on the salt crust fl oor in the famous Valle de la Luna (moon valley). Th ese curious features are composed entirely of pure white salt and have been encountered in a limited area of about 15,000 m 2 . A total of 35 of these small structures, named here "salt rims" and "salt blisters", have been located and measured. Th eir average plan dimensions are 6.5 x 5.5 cm for a mean height of 3.6 cm. Almost 60% of these structures have an opening on top (salt rims), sometimes on their fl anks, typically smaller than their diameters. Th e biggest features always have an opening, being the closed structures, named blisters, normally less than 3 cm in diameter. A tube-like opening continuing underground for at least a decimetre, mostly deeper than 20 cm, is clearly visible in the inside of the salt rims. Th e rims perfectly match the edges of these holes. In some cases salt crystals grow on the inner walls of the rims forming curving fi laments. Th e salt blisters and rims are very similar to homonymous (sam-name) speleothems and form by condensation-evaporation processes after very sporadic rainy episodes. Rainfall (average annual rain- fall is < 20 mm), occurs very rarely and enables infi ltration of salty water through openings in the salt crusts. Th is water is conveyed underneath the impervious salt crust presumably in a network of inter- connected fi ssures and underground cavities containing airborne fi

In the morning of February 15th 2005, during excavation works in an underground gypsum quarry at Moncalvo (Monferrato area, Asti, Northern Italy), a water-bearing fracture was intercepted at level 134 m a.s.l. During the night a large amount of water (approximately 60,000 m3) and mud invaded the quarry tunnels reaching a height of 139 m a.s.l. the morning of the day after. Meanwhile a large sinkhole (20 m wide and 10 m deep) formed on the surface. Hydrogeological surveys were immediately carried out to follow the quickly evolving situation, while speleological and geomorphological fieldwork was made possible only seven months later. Two important caves were discovered both showing clear evidence of a hypogenic origin with sculpted morphologies due to slowly flowing water under pressure. The sinkhole formed by the collapse of one of the main chambers of the biggest of these caves, when buoyant support provided by the water started to decrease due to lowering of the virtual water table. The recharge of this karst system is from below and only very minor quantities of infiltration water come from the above lying surface, as has also been confirmed by hydrochemical analysis. This hypogene karst is completely invisible at the surface and develops entirely underground showing no relation whatsoever with the surface. Its presence is therefore extremely difficult to reveal and such types of karst can thus make up extremely dangerous situations. This is the first example of hypogene gypsum cave related to ascending waters in Italy.