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Genesis and microstratigraphy of calcite coralloids analysed by high resolution imaging and petrography

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Abstract

The genesis of calcite coralloid speleothems from Lamalunga cave (Southern Italy) is here investigated from a purely petrographic perspective, which constitutes the basis for any subsequent chemical investigation. Lamalunga cave coralloids formed on bones and debris on the floor of the cave. They consist of elongated columnar crystals whose elongation progressively increases from the flanks to the tips of the coralloid, forming a succession of lens-shaped layers, which may be separated by micrite or impurity-rich layers. Organic molecules are preferentially concentrated toward the centre of convex lenses as highlighted by epifluorescence. Their occurrence on cave floor, lens-shaped morphology and concentration of impurities toward the apex of the convex lenses supports the hypothesis that their water supply was hydroaerosol, generated by the fragmentation of cave drips. Evaporation and degassing preferentially occurred on tips, enhancing the digitated morphology and trapping the organic molecules and impurities, carried by the hydroaerosol, between the growing crystals which became more elongated. Micrite layers, that cap some coralloid lenses, likely identify periods when decreasing in hydroaerosol resulted in stronger evaporation and higher supersaturation with respect to calcite of the parent film of fluid. This interpretation of coralloid formation implies that these speleothems can be used to extract hydroclimate information.

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... Coralloid structures in natural limestone caves consist almost entirely of calcite or alternatively a combination of calcite and aragonite. Because calcite coralloid deposition processes in the natural cave environment are not directly related to dripping water, various morphogenetic interpretations have been proposed to account for the external appearance of these grape cluster-like botryoidal forms (Hill and Forti 1997;Self and Hill 2003;Vanghi et al. 2017). Recognized processes can be summarized as deposition from aerosols generated by splashing drops to source irregular distribution of nucleation sites on stalagmites (Dredge et al. 2013;Vanghi et al. 2017). ...
... Because calcite coralloid deposition processes in the natural cave environment are not directly related to dripping water, various morphogenetic interpretations have been proposed to account for the external appearance of these grape cluster-like botryoidal forms (Hill and Forti 1997;Self and Hill 2003;Vanghi et al. 2017). Recognized processes can be summarized as deposition from aerosols generated by splashing drops to source irregular distribution of nucleation sites on stalagmites (Dredge et al. 2013;Vanghi et al. 2017). An alternative process suggests that thin capillary driven water films move outward along crystalline boundaries to the surfaces of micro-protuberances, expanding the area of deposition as strong degassing occurs at the surface in combination with evaporation (Caddeo et al. 2015). ...
... Hydro-aerosols as a growth mechanism are not consistent with botryoidal deposits on calthemite soda straws from the study area. Such a mechanism would be more likely associated with floor deposition, not along a ceiling (Caddeo et al. 2015;Vanghi et al. 2017). In contrast, water flows as capillary driven thin films are outward from the central canal, directed along micro-cracks and networks of crystalline micro-porosity. ...
Article
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Distributions of calcareous calthemite deposits have been widely documented, but depositional processes and the architecture of their internal fabrics are not well understood. These concrete degradation products from a case study area in western Canada have external morphologies comparable to calcite speleothems formed in natural limestone caves, but the internal microstructural architecture and mineralogy are markedly different. The mineralogy consists of mostly calcite with secondary halite and minor percentages of trona and portlandite. A novel morphogenetic model explains depositional processes resulting in calcareous crusts that follow fractures of an overlying concrete surface, and how sufficient structural integrity provided by the internal architecture supports attachment areas of tubular soda straws. Interiors of these multi-cm crusts consist of curvilinear calcite laminae arrayed as sub-parallel walls, compartmentalizing water–gas interfaces along variously interconnected conduits and basin-form chambers. Overall porosities of 40–60% or more are prevalent, in contrast to < 1% associated with externally similar drapery-form crusts deposited within natural limestone caves. Several calcite fabrics new to calthemite deposits are described, including dendritic shrubs that coalesce into concentric growth rings along central canals of soda straws.
... However, in some cases, these are the most common speleothem type available, because they can also grow in semiarid settings, when the water supply inside a cave is relatively low whereas other speleothems, like stalagmites, require an active drip. Coralloids are a type of speleothem characterized by botryoidal morphology and curved internal structure (Thrailkill, 1965;Hill & Forti, 1997;Vanghi et al., 2017). Their formation is linked to: (i) hydroaerosols (Gadoros & Cser, 1986;Dublyansky & Pashenko, 1997;Vanghi et al., 2017), originating from drip-water sprays via splash and drop fragmentation, which transport and distribute particulate and dissolved chemicals onto the coralloid surface; (ii) seeping water combined with capillary forces that move the film of water upward through intercrystalline porosity (Maltsev, 1996;Cuevas-Gonz alez et al., 2010;Merino et al., 2014) or, externally, from the base towards the top of the coralloid (Caddeo et al., 2015); and (iii) enhanced evaporation on the curved surfaces of the coralloids, which increases the supersaturation with respect to calcite (SIcc) of the solution and leads to CaCO 3 precipitation on the protruding surfaces (Caddeo et al., 2015;Vanghi et al., 2017). ...
... Coralloids are a type of speleothem characterized by botryoidal morphology and curved internal structure (Thrailkill, 1965;Hill & Forti, 1997;Vanghi et al., 2017). Their formation is linked to: (i) hydroaerosols (Gadoros & Cser, 1986;Dublyansky & Pashenko, 1997;Vanghi et al., 2017), originating from drip-water sprays via splash and drop fragmentation, which transport and distribute particulate and dissolved chemicals onto the coralloid surface; (ii) seeping water combined with capillary forces that move the film of water upward through intercrystalline porosity (Maltsev, 1996;Cuevas-Gonz alez et al., 2010;Merino et al., 2014) or, externally, from the base towards the top of the coralloid (Caddeo et al., 2015); and (iii) enhanced evaporation on the curved surfaces of the coralloids, which increases the supersaturation with respect to calcite (SIcc) of the solution and leads to CaCO 3 precipitation on the protruding surfaces (Caddeo et al., 2015;Vanghi et al., 2017). If strong evaporation controls coralloid growth (Caddeo et al., 2015;Vanghi et al., 2017) this might imply that their stable isotopic composition is kinetically modified, compromising the use of d 18 O and d 13 C as climate proxies (Caddeo et al., 2015). ...
... Coralloids are a type of speleothem characterized by botryoidal morphology and curved internal structure (Thrailkill, 1965;Hill & Forti, 1997;Vanghi et al., 2017). Their formation is linked to: (i) hydroaerosols (Gadoros & Cser, 1986;Dublyansky & Pashenko, 1997;Vanghi et al., 2017), originating from drip-water sprays via splash and drop fragmentation, which transport and distribute particulate and dissolved chemicals onto the coralloid surface; (ii) seeping water combined with capillary forces that move the film of water upward through intercrystalline porosity (Maltsev, 1996;Cuevas-Gonz alez et al., 2010;Merino et al., 2014) or, externally, from the base towards the top of the coralloid (Caddeo et al., 2015); and (iii) enhanced evaporation on the curved surfaces of the coralloids, which increases the supersaturation with respect to calcite (SIcc) of the solution and leads to CaCO 3 precipitation on the protruding surfaces (Caddeo et al., 2015;Vanghi et al., 2017). If strong evaporation controls coralloid growth (Caddeo et al., 2015;Vanghi et al., 2017) this might imply that their stable isotopic composition is kinetically modified, compromising the use of d 18 O and d 13 C as climate proxies (Caddeo et al., 2015). ...
Article
Synchrotron high‐resolution and micro‐X‐ray fluorescence elemental mapping of two coeval coralloid speleothems from Lamalunga Cave (Italy) are complemented with petrographic, morphological and microstratigraphic studies. The importance of these speleothems relies on their direct and indirect association with a complete Neanderthal skeleton (‘Altamura Man’) found inside the cave. The coralloids grew discontinuously between 64·6 ka and the Holocene and reveal exceptionally high concentrations of Mg, Sr and Si, particularly on convex surfaces, where evaporation is more intense. The incorporation of trace elements depends on several factors including location, shape and geometrical evolution during their growth, as well as climate and environmental parameters. This resulted in calcite precipitation with Sr compositions from 100 to 1200 ppm and an average concentration of 7000 ppm Mg. An unusually high Si content (up to 16%) is possibly derived from volcanic ash transported as particulate and in solution inside the cave. The most common fabrics observed consist of non‐fluorescent elongated columnar calcite forming clean isopachous bands and fluorescent fibre‐like crystals associated with laminated, lenticular bands high in Sr, Mg and Si. Variability in Sr, Mg and Si concentrations appears to induce fabric changes in the coralloids. Elongation and lattice distortion of the crystals was found to coincide with high Mg concentrations. The transition from compact elongated to open to fibre‐like, is here interpreted as due to high concentrations of Si and Sr, which are preferentially incorporated in the speleothem at crystal boundaries and intra‐laminae. It is here inferred that coralloid fabric changes and their elemental content potentially record local rainfall variations through time, with the clean compact calcite marking high infiltration and open fibre‐like and micrite fabrics recording dry periods. This article is protected by copyright. All rights reserved.
... Au niveau macroscopique, une de leurs caractéristiques est leur développement en amas coalescents (Self et Hill 2003, Sallstedt et al. 2014). Face à la littérature abondante concernant le mondmilch, nous pouvons constater qu'il y a bien moins de publications entièrement dédiées aux coralloïdes, bien que récemment quelques études viennent combler ce manque (Caddeo et al. 2015, Vanghi et al. 2017. Il existe toutefois de nombreux travaux qui s'intéressent de façon plus générique aux spéléothèmes retrouvés dans les cavités, et dans ces travaux, il n'est pas rare de noter une mention ou référence plus ou moins détaillée de ce type de faciès (Cañaveras et al. 2001, Chaykovskyi et al. 2014, Bahadorinia et al. 2016. ...
... -Les couples aragonite/calcite qui traduisent des processus complexes, et qui sont assez rares (voir par exemple Railsback et al. 1994) -Les lamines dues aux éléments traces comme Sr ou Mg (voir par exemple Borsato et al. 2007). Fairchild et al. (2001) (Vanghi et al. 2017). ...
... En effet, le dépôt des aérosols peut avoir un impact durant les arrêts de croissance des spéléothèmes et peut potentiellement favoriser l'activité des microorganismes, en venant les alimenter. Dernièrement, Vanghi et al. (2017), émirent l'hypothèse que les coralloïdes de la grotte de Lamalunga en Italie sont formés par hydroaérosols, générés par effet 'splash' des égouttements environnants. Cette étude, basée uniquement sur des observations pétrographiques, sera détaillée lors du chapitre 6. ...
Thesis
La conservation du patrimoine constitué par les grottes ornées paléolithiques, fragile car très ancien, est un enjeu capital. Dans ce cadre, une approche taphonomique de l’état de surface des parois est envisagée à travers l’étude des concrétions qui recouvrent les parois de grottes. Ceci est primordial pour la compréhension de leurs mécanismes de genèse et de développement qui s’opèrent à l’échelle d’une grotte, d’une salle, d’une paroi ou d’un panneau orné. En effet, ces concrétions peuvent recouvrir de manière partielle ou totale des peintures ou gravures sous-jacentes. L’étude réalisée ici porte sur la caractérisation multiphysique et la variabilité spatiale de deux types de concrétions calcitiques, le mondmilch et les coralloïdes, qui sont fréquemment retrouvés dans les grottes ornées. Elle a été menée principalement dans une grotte laboratoire, la grotte de Leye, à Marquay (Dordogne, France), dépourvue d’intérêt archéologique et située dans la vallée de la Vézère, l’une des régions les plus riches en grottes ornées de France. La composition chimique et la structure des revêtements calcitiques ont été déterminées par l’utilisation conjointe de méthodes de caractérisation physico-chimique comme la spectroscopie sur plasma induit par laser (LIBS) et la spectroscopie Raman, couplées à des observations morphologiques en microscopies optique et électronique. Les coralloïdes, qui ont été très peu étudiés jusqu’à aujourd’hui, ont fait l’objet d’une attention particulière. La mise en perspective des résultats des analyses physico-chimiques portant sur les concrétions, avec d’une part des données concernant l’environnement souterrain telles que le comportement climatique et hydrologique de la cavité, la présence de micro-organismes, et d’autre part des données relatives à l’isotopie et à la datation de la calcite, permet de discuter les hypothèses de formation des faciès. Enfin, l’analyse statistique d’une base de données de cavités constituée à l’échelle de la vallée de la Vézère contribue à alimenter la réflexion sur les paramètres corrélés à la présence des concrétions.
... The observed coralloid calcite is associated with increased airflow, evaporation and condensation processes resulting in higher calcite saturations (Hill and Forti, 1997, pp. 59-60;Vanghi et al., 2017), in agreement with a smaller stalagmite diameter, indicating lower water availability or decreased carbonate saturation (Dreybrodt, 1999). The succession of detrital layers and coralloid calcite therefore suggests a climatically unstable period with successive mudflows and floods, followed by drier conditions towards~170 ka. 3. From~170 ka onward, a more regular larger stalagmite indicates more favourable conditions, although not reaching full interglacial conditions as indicated by the rather high detrital (clay) content. ...
Article
The Balkan Peninsula represents one of the most important human pathways into and out of Europe during the Pleistocene. Mishin Kamik cave, located in the karst region of Western Stara Planina, has a rich faunal content and shows promising features indicating a human occupation site with the discovery of potential bone artefacts and an intriguing accumulation of bear skulls and bones. Petrographic study and U-series dating of a stalagmite and other calcite deposits in the cave provide an absolute chronological frame for the detrital infillings and their archaeological content and inform the environmental and climatic context of the cave evolution. Most detrital deposits in the cave were probably deposited before Marine Isotope Stage (MIS) 5 and the cave morphology and sedimentary deposits display current morphologies since~135 ka. Consequently, the palaeontological and archaeological findings are older than~135 ka. Calcite dated on and under the accumulation of bear skulls and bones suggests deposition during MIS 7. A first depositional contextualization of the bone accumulation does not allow us to discriminate between a natural or anthropogenic origin. The study emphasizes the added value of speleothem studies in archaeological sites and particularly in bringing a well-constrained chronological and environmental framework.
... Crucial for speleothem crystallization are the routes taken by their feeding water, the water's chemical composition and the rate of carbon dioxide degassing. Straightforward growth mechanisms of conventional speleothems, such as stalagmites and flowstones, differ from the more complex crystallization mechanisms of some unusual speleothems (Moore, 1954;Hill and Forti, 1997;Caddeo et al., 2015;Vanghi et al., 2017). Despite the plethora of studies on speleothem growth mechanisms, the crystallization manner of some speleothems has not yet been fully explained. ...
Article
Healed speleothems, sparsely mentioned in literature, have been noted in one of the side passages of the Demänová Cave System in Slovakia. Speleothem healing commonly proceeds in columns and flowstones after their brittle deformation. Crystallization of calcium carbonate in fractures and along their mouths results in formation of various outgrowths: subvertical ridges, subhorizontal ridges, and helictites. Morphology of the subvertical ridges and helictites indicates that they were supplied by water migrating through the fractures, while the subhorizontal ridges resulted from gravity-controlled water flow down the speleothem surface. Stable isotope composition of the outgrowths suggests that they crystallized as a result of CO2 degassing, like most speleothems. Since speleothem damages in the DCS are directly linked to fault reactivation, the healed speleothems appear to be advantageous objects for seismotectonic analysis of karst terrains.
... In the case of caves accessible to the public, visitors can be a source of pollution as well [63]. Particles can also be formed by natural processes inside the cave such as the dispersion of drip water to form a very fine aerosol [64]. This aerosol is characterized by a high calcium content, which according to some studies [65] may have a positive effect of speleotherapy. ...
Article
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A total of 152 aerosol and spider web samples were collected: 96 spider’s webs in karst areas in 4 European countries (Czech Republic, France, Italy, and Slovakia), specifically from the surface environment (n = 44), photic zones of caves (n = 26), and inside (aphotic zones) of caves (n = 26), 56 Particulate Matter (PM) samples from the Sloupsko-Sosuvsky Cave System (speleotherapy facility; n = 21) and from aerosol collected from the nearby city of Brno (n = 35) in the Czech Republic. Nontuberculous mycobacteria (NTM) were isolated from 13 (13.5%) spider’s webs: 5 isolates of saprophytic NTM (Mycobacterium gordonae, M. kumamotonense, M. terrae, and M. terrae complex) and 6 isolates of potentially pathogenic NTM (M. avium ssp. hominissuis, M. fortuitum, M. intracellulare, M. peregrinum and M. triplex). NTM were not isolated from PM collected from cave with the speleotherapy facility although mycobacterial DNA was detected in 8 (14.3%) samples. Temperature (8.2 °C, range 8.0–8.4 °C) and relative humidity (94.7%, range 93.6–96.6%) of air in this cave were relatively constant. The average PM2.5 and PM10 mass concentration was 5.49 µg m−3 and 11.1 µg m−3. Analysed anions (i.e., F−, Cl−, NO2−, SO42−, PO43− and NO3−) originating largely from the burning of wood and coal for residential heating in nearby villages in the surrounding area. The air in the caves with speleotherapy facilities should be monitored with respect to NTM, PM and anions to ensure a safe environment.
... Crucial for speleothem crystallization are the routes taken by their feeding water, the water's chemical composition and the rate of carbon dioxide degassing. Straightforward growth mechanisms of conventional speleothems, such as stalagmites and flowstones, differ from the more complex crystallization mechanisms of some unusual speleothems (Moore, 1954;Hill and Forti, 1997;Caddeo et al., 2015;Vanghi et al., 2017). Despite the plethora of studies on speleothem growth mechanisms, the crystallization manner of some speleothems has not yet been fully explained. ...
Article
Multiphase cave conduit offset and related speleothem damage in the Demänová Cave System (DCS; the Low Tatra Mts, Central Western Carpathians) were dated with U-series methods, revealing five events: (1) 570 (442)–417 ka, (2) 306–291 ka, (3) 184–130 ka, (4) ~19 ka, and (5) 2.56–2.3 ka. To decipher the cause of the damage, we combined geochronological data with structural, geomorphological, and seismological research. Gravity sliding as a probable source of damage is unlikely since the Demänová Valley has deepened only to a small extent for the past 550 ka and the steep fissure guiding the studied parts of the DCS extends below the recent valley. However, coseismic block sliding cannot be unambiguously excluded, as Newmark displacement analysis revealed that any >M7 earthquake in the 25 km range could have produced a 10-cm pseudostatic displacement. The studied offsets were accompanied by shaking, as inferred from fallen stalagmites and stalactites; hence, distant earthquakes are plausible damage sources. We applied ground-motion models and compared them with seismicity and scant prehistoric and historical data to identify and quantify the probable seismic source, which is most likely the Sub-Tatric Fault located 17.5 km from the cave. As inferred from the applied ground-motion models, a >M7 event on the Sub-Tatric Fault would generate a PGA >4 m/s2 in the cave despite the attenuation, which is above the threshold horizontal ground acceleration forcing the majority of speleothems to break. Although the mechanism that leads to cave passage offsets remains unclear we consider them as an off-fault damage caused by secondary faulting related to postseismic surface vertical movements, or less likely but not out of the realm of possibility distributed rupturing.
... The observed coralloid calcite is associated with increased airflow, evaporation and condensation processes resulting in higher calcite saturations (Hill and Forti, 1997, pp. 59-60;Vanghi et al., 2017), in agreement with a smaller stalagmite diameter, indicating lower water availability or decreased carbonate saturation (Dreybrodt, 1999). The succession of detrital layers and coralloid calcite therefore suggests a climatically unstable period with successive mudflows and floods, followed by drier conditions towards~170 ka. 3. From~170 ka onward, a more regular larger stalagmite indicates more favourable conditions, although not reaching full interglacial conditions as indicated by the rather high detrital (clay) content. ...
Article
ABSTRACT: The Balkan Peninsula represents one of the most important human pathways into and out of Europe during the Pleistocene. Mishin Kamik cave, located in the karst region of Western Stara Planina, has a rich faunal content and shows promising features indicating a human occupation site with the discovery of potential bone artefacts and an intriguing accumulation of bear skulls and bones. Petrographic study and U‐series dating of a stalagmite and other calcite deposits in the cave provide an absolute chronological frame for the detrital infillings and their archaeological content and inform the environmental and climatic context of the cave evolution. Most detrital deposits in the cave were probably deposited before Marine Isotope Stage (MIS) 5 and the cave morphology and sedimentary deposits display current morphologies since ~135 ka. Consequently, the palaeontological and archaeological findings are older than ~135 ka. Calcite dated on and under the accumulation of bear skulls and bones suggests deposition during MIS 7. A first depositional contextualization of the bone accumulation does not allow us to discriminate between a natural or anthropogenic origin. The study emphasizes the added value of speleothem studies in archaeological sites and particularly in bringing a well‐constrained chronological and environmental framework. KEYWORDS: Karst; Middle Palaeolithic; Neanderthal; MIS 6; speleothem
... An important portion of the local economy relies on this cave, because of tickets profit and employment, as well as the touristic flux attracted by the underground landscape. More or less in the same area, ~ 50 km west nearby the town of Altamura, there is Lamalunga Cave, which is worldwide famous for hosting the remnants of the so called 'Altamura Man', a pristine skeleton of an ancient Neanderthal man covered by calcite crusts (Vanghi et al. 2017). Indeed, Apulia is a hot spot for cave-based anthropological studies because of the multiple findings. ...
Article
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The concept of geoheritage is related to places of geological interest, generally of aesthetic, cultural, socioeconomic and/ or scientific value. Many geosites are of karstic nature, because of their intrinsic beauty, their singularity and high geodi-versity. Caves are among the most visited and economically exploited geological landforms. They constitute geosites as a whole, with their scenic landscapes, hydrogeological importance and the presence of bewildering natural rock and mineral formations including stalactites, stalagmites, flowstones and many other bizarre speleothem shapes. In some cases, a single speleothem, and the palaeoclimate record it contains, can be on its own of extraordinary importance to science. Once studied , these samples are often stored in research institution collections, rarely accessible to the wide public. In this paper, we report on the museumization of a stalagmite that has delivered a unique and exceptionally long glacial climate record from southern Italy, shedding light on the causes that led to the Neanderthal contraction and Modern Human expansion in this mild Mediterranean climate between 45 and 42 thousands years ago. The proposed museumization aims to demonstrate the potential of speleothems, after scientific application, in terms of educational and tourist resources. This approach allows to highlight the scientific importance of karst and cave geosites to the wide public, promoting their conservation and the valorisation of the studied cave-material.
... A conceivable problem with the U-series dating method is that calcium carbonate accretions can behave as an open system for uranium, whereby the element can be leached out of the accretions or remobilized [see, e.g., (40,41)]. In such instances, the calculated ages will be too old because the dating method relies on the accurate measurement of uranium versus its decay product 230 Th. ...
Article
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Indonesia harbors some of the oldest known surviving cave art. Previously, the earliest dated rock art from this region was a figurative painting of a Sulawesi warty pig (Sus celebensis). This image from Leang Bulu' Sipong 4 in the limestone karsts of Maros-Pangkep, South Sulawesi, was created at least 43,900 years ago (43.9 ka) based on Uranium-series dating. Here, we report the Uranium-series dating of two figurative cave paintings of Sulawesi warty pigs recently discovered in the same karst area. The oldest, with a minimum age of 45.5 ka, is from Leang Tedongnge. The second image, from Leang Balangajia 1, dates to at least 32 ka. To our knowledge, the animal painting from Leang Tedongnge is the earliest known representational work of art in the world. There is no reason to suppose, however, that this early rock art is a unique example in Island Southeast Asia or the wider region.
... This proves that evaporation can indeed take place in the cave and may have been more pronounced in the past, when other climatic conditions or different air circulation patterns may have prevailed . Evaporation and degassing can be particularly significant in moonmilk, crusts and coatings on frostwork due to the high surface-to-volume ratio of the main mineral textures (Vanghi et al., 2017) and the fact they form by capillary water (Hill and Forti, 1997;Caddeo et al., 2015). Another important factor contributing to the elevated Mg/Ca ratios that enable the precipitation of Mg minerals seems to be the removal of Ca 2+ in solution by prior precipitation of CaCO 3 in the speleothems (Lippmann, 1973;Fairchild and McMillan, 2007). ...
Article
In Castañar Cave (Cáceres, Spain), Mg-Si phases forming fibres and films occur associated with aragonite, magnesite, huntite and spheroidal dolomite in moonmilk, coatings and crust speleothems. A detailed study of bulk and carbonate-removed samples allowed us to identify the Mg-Si phases as kerolite (Mg3Si4O10(OH)2·nH2O) and sepiolite Mg4Si6O15(OH)2·6(H2O) of variable “crystallinity” and very pure composition. Under the scanning electron microscope, kerolite appears as gelatinous, smooth masses or films, showing some desiccation features. Sepiolite mostly occurs as isolated fibres 50 to 200 nm thick and up to 50 μmlong and mats of interwoven fibres of several shapes. Analytical pyrolysis (Py-GC/MS) of the organic matter associated with these minerals in the moonmilk speleothems shows a compound assemblage lacking carbohydrates, nitrogen-bearing molecules and fatty acids, indicating no microbial activity. Kerolite and sepiolite most probably formed abiotically by direct precipitation in the cave waters, in conditions of high silica and magnesium activity and relatively high pH. These conditions were attained by local CO2 degassing taking place in extremely slow drips and capillary waters in speleothems with a large surface area, in a dynamic system where the renovation of infiltrated waters and diagenetic transformations of carbonates and silicates also contributed to significant hydrochemical variability at the microscale.
... Les plus importantes se situent au niveau de l'os maxillaire gauche, deux lacunes circulaires se trouvent juste sous le bord orbitaire. Leurs localisations pourraient faire penser à des foramens infra-Il s'agit plus certainement de concrétions calcaires pouvant être liées à un séjour à l'air libre d'une partie du crâne à un moment(Vanghi et al. 2017). La partie droite de la face est partiellement manquante. ...
Thesis
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Au Levant, le Paléolithique moyen (environ 200-50 Ka B.P.) correspond à une période cruciale pour la compréhension des mécanismes évolutifs et la dispersion des Homo sapiens hors d’Afrique. Le site de Qafzeh (Basse Galilée), au croisement des trois grandes aires géographiques de l’ancien monde, comprend des niveaux archéologiques chronologiquement situés au cœur de cette période (92 ± 5 ka BP). Il est exceptionnel en raison à la fois d’une riche documentation anthropologique comprenant des individus de toutes les classes d’âges (du périnatal à l’adulte) et de la présence de pratiques funéraires uniques (sépulture double, dépôt funéraire). Si de nombreuses études ont déjà été publiées sur cette documentation fossile, les progrès technologiques récents de la Paléoimagerie permettent d’extraire des données inédites. Ainsi grâce à des outils 2D (radiographies, coupes CT) et 3D (reconstructions virtuelles à partir de données photogrammétriques ou de [micro]CT-scan) des analyses sont réalisées sur la tête osseuse de trois individus (Qafzeh 6, 9 et 25). Deux types d’analyses sont menés : une étude morphométrique de structures internes (i.e. labyrinthe osseux) et une étude paléopathologique. L’examen de l’oreille interne dévoile ainsi une diversité inattendue pour la population présente à Qafzeh ; par ailleurs des rapprochements au sein des échantillons de comparaison, entre quelques individus classiquement considérés comme archaïques et d’autres modernes, se dégagent. L’étude paléopathologique quant à elle révèle sur Qafzeh 9 la présence de troubles de la croissance osseuse et dentaire, qui font écho aux anomalies du développement précédemment décrites sur des fossiles immatures du site. Ces données nous permettent de mieux appréhender la variabilité individuelle normale et pathologique documentée à Qafzeh et de replacer ces chasseurs-cueilleurs nomades dans le contexte plus large des groupes locaux et eurasiatiques associés au contexte archéologique Moustérien.
... The Lamalunga cave opens in the limestone of the Murgia plateau at an elevation of 508 m a.s.l., near the town of Altamura (Puglia, Italy). It represents the upper part of a large karstic complex where stalactites, stalagmites, and flowstones occur together with coralloid formations, which mostly represent the last phase of calcite precipitation caused by spray/aerosol phenomena (Agostini, 2011;Lari et al., 2015;Vanghi et al., 2017). This karstic system consists mainly of sub-horizontal galleries that developed at a shallow depth from the surface, intercepted by at least three pits clogged by detritus. ...
Article
The exceptionally well-preserved Neanderthal skeleton discovered in October 1993 within the Lamalunga cave near Altamura (Puglia, Italy) has been recently dated to a late Middle Pleistocene chronology, bracketed between 128.2 and 187.0 ka. Although the skeleton is still sealed in situ, in 2009 and 2015 a large part of its fragmentary right scapula was removed from the cave in three pieces, following a protocol aimed at preventing any biological contamination prior to aDNA extraction and analysis. The three fragments taken together preserve the glenoid fossa, the roots of both the coracoid and acromial processes, the superior two-thirds of the axillary border, portions of the spine, and part of the supraspinous fossa. This scapula is described here in detail for the first time. Morphological analyses show that it falls within the range of Neanderthal variability and also approaches the Mid-Pleistocene sample from Atapuerca Sima de los Huesos. However, the scapula from Altamura exhibits a bisulcate/ventral pattern of the axillary border: a feature that is uncommon for a Neanderthal and, more in general, among the European archaic humans of the Middle and Late Pleistocene. The scapula from Altamura expands our knowledge of the postcranial variability along the Neanderthal lineage.
... Under evaporative conditions, it is known that the parent fluid may reach growth sites 'per ascensum', via capillary flow. This has obvious influence on the SI C of the parent solution and on crystal fabrics (see Caddeo et al., 2015;Vanghi et al., 2017). When excited by 470 nm incident light the sparite crystal fans of this facies are nonluminescent, which suggests that the minerals do not contain organic compounds (Fig. 6H) and so are likely to have grown abiotically. ...
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Recent studies of continental carbonates revealed that carbonates with similar fabrics can be formed either by biotic, biologically‐induced, biologically‐influenced or purely abiotic processes, or a combination of all. The aim of this research is to advance knowledge on the formation of carbonates precipitated (or diagenetically altered) in extreme, continental environments by studying biotic versus abiotic mechanisms of crystallization, and to contribute to the astrobiology debate around terrestrial analogues of Martian extreme environments. Both fossil (upper Pleistocene to Holocene) and active carbonate spring mounds from the Great Artesian Basin (South Australia) have been investigated. These carbonates consist of low‐Mg to high‐Mg calcite tufa. Four facies have been described: (i) carbonate mudstone/wackestone; (ii) phytohermal framestone/boundstone; (iii) micrite boundstone; and (iv) coarsely crystalline boundstone. The presence of filaments encrusted by micrite, rich in organic compounds, including ultraviolet‐protectants, in phytohermal framestone/boundstone and micrite boundstone is clear evidence of the existence of microbial mats at the time of deposition. In contrast, peloidal micrite, despite commonly being considered a microbial precipitate, is not directly associated with filaments in the Great Artesian Basin mounds. It has probably formed from nano‐crystal aggregation on colloid particulate. Thus, where biofilms have been documented, it is likely that bacteria catalyzed the development of fabrics. It is less certain that microbes induced calcium carbonate precipitation elsewhere. Trace elements, including rare earth element distribution from laminated facies, highlight strongly evaporative settings (for example, high Li contents). Carbon dioxide degassing and evaporation are two of the main drivers for an increase in fluid alkalinity, resulting in precipitation of carbonates. Hence, although the growth of certain fabrics is fostered by the presence of microbial mats, the formation of carbonate crystals might be independent from it and mainly driven by extrinsic factors. More generally, biological processes may be responsible for fabric and facies development in micritic boundstone whilst micrite nucleation and growth are driven by abiotic factors. Non‐classical crystallization pathways (aggregation and fusion of nanoparticles from nucleation clusters) may be more common than previously thought in spring carbonate and this should be carefully considered to avoid misinterpretation of certain fabrics as by‐products of life. It is proposed here that the term ‘organic‐compound catalyzed mineralization’ should be used for crystal growth in the presence of organic compounds when dealing with astrobiological problems. This term would account for the possibility of multiple crystallization pathways (including non‐classical crystallization) that occurred directly from an aqueous solution without the direct influence of microbial mats.
... Samples BSP4 and BSP5 each display a single data point with a slightly younger age (on the order of a few hundred years) ( Table 1). We attribute these inversions to the calcite deposits having accumulated in ring-like formations rather than roughly flat and parallel to the pigment layer (as in typical flowstones) 42 . Alternatively, some coralloid speleothems have complex internal morphologies that reflect their origin as aggregates of a cluster of cylindrical, mound-like calcite structures 42 , leaving overhanging features with gaps between older material that are infilled by carbonate materials of younger age. ...
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Humans seem to have an adaptive predisposition for inventing, telling and consuming stories¹. Prehistoric cave art provides the most direct insight that we have into the earliest storytelling2–5, in the form of narrative compositions or ‘scenes’2,5 that feature clear figurative depictions of sets of figures in spatial proximity to each other, and from which one can infer actions taking place among the figures⁵. The Upper Palaeolithic cave art of Europe hosts the oldest previously known images of humans and animals interacting in recognizable scenes2,5, and of therianthropes6,7—abstract beings that combine qualities of both people and animals, and which arguably communicated narrative fiction of some kind (folklore, religious myths, spiritual beliefs and so on). In this record of creative expression (spanning from about 40 thousand years ago (ka) until the beginning of the Holocene epoch at around 10 ka), scenes in cave art are generally rare and chronologically late (dating to about 21–14 ka)⁷, and clear representations of therianthropes are uncommon⁶—the oldest such image is a carved figurine from Germany of a human with a feline head (dated to about 40–39 ka)⁸. Here we describe an elaborate rock art panel from the limestone cave of Leang Bulu’ Sipong 4 (Sulawesi, Indonesia) that portrays several figures that appear to represent therianthropes hunting wild pigs and dwarf bovids; this painting has been dated to at least 43.9 ka on the basis of uranium-series analysis of overlying speleothems. This hunting scene is—to our knowledge—currently the oldest pictorial record of storytelling and the earliest figurative artwork in the world.
... White, 1988;Ford and Williams, 2007). Specifically, Caddeo et al. (2015) explains the formation of coralloids as the result of degassing, evaporation and diffusion, and Vanghi et al. (2017) proposed that hydroaerosols produced by dripping water and evaporation played a key role in their formation. Coralloids also occur in shallow hydrothermal karst environments formed from saturated water vapor in subaerial environments and from ascending warm water saturated with respect to calcite in low hydrodynamic subaqueous conditions (Bakalowicz et al., 1987;Audra et al., 2002;Gradziński et al., 2011;Leél-Őssy et al., 2011;Dublyansky, 2012). ...
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We provide first insights into the speleogenesis of Ejulve cave (Teruel province, Iberian Range, NE Spain) by studying cave morphologies and cave deposits, combined with regional geomorphological and hydrothermal observations. Three main hydrogeomorphic evolutionary stages can be distinguised to explain the origin and evolution of the Ejulve endokarstic system. Cave pattern and cave solutional features (calcite vein fillings, tubes with rising ceiling cupolas, pendants and cusps, spongework and micro-corrosion features) suggest that the cave generated in a phreatic environment by ascending water. Cave morphologies and regional hydrothermal springs in this region suggest, but not prove, the involvement of thermal waters and related convection and condensation-corrosion mechanisms in the origin of the cave. Subsequently, the cave underwent a change to epigenic conditions driven by denudation, as a result of regional uplift. Once the karstic system was exhumated, carbonate speleothems formed in a vadose environment. Mineralogical, petrographic, isotopic and chronological (U-series dating) analyses of carbonate speleothems (i.e. stalagmites, flowstones, botryoids, spars, acicular crystals and farmed carbonate) are provided. Calcite, high-Mg calcite and aragonite are the most common minerals, whereas columnar, dendritic, micrite, mosaics and fans are the main fabrics. Mean δ¹⁸O values of − 7.3‰ and δ¹³C values of − 9.1‰ indicate carbonate precipitation from meteoric waters without a hydrothermal origin. Carbonate deposits formed at least since 650 ka BP. Our study suggests that hydrothermal fluid flow may explain, although the evidences are not fully conclusive, the speleogenesis of this cave.
Chapter
In this chapter, the authors deal with the physical, organic, and chemical deposits found in the dark or semi‐dark areas of caves, excluding those found in cave entrances or rock shelters. Clastic sediments in caves, excluding those found at entrances, have been the subject of numerous studies, mainly during the last 60 years. Phosphorite is a chemical deposit that can be deposited in caves. Speleothems are secondary mineral deposits that form in caves by flowing, dripping, ponded, or seeping water and take on a typical shape. They are mostly composed of minerals such as calcite, aragonite, or gypsum, but other minerals can also form entirely or partially speleothems. Speleothem texture and fabrics are increasingly used to support the interpretation of the geochemical signals (stable isotopes and trace elements) in the paleo‐environmental and paleoclimatic reconstructions based on speleothem archives.
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Atmosphere inside caves used for speleotherapy are microenvironments influenced by ventilation and human activities inside. In this context, particulate matter with an aerodynamic diameter from 15 nm to 10 μm was collected with an electrical low-pressure impactor ELPI+ in the Císařská Cave in the northern part of the Moravian Karst (Czech Republic) and 33 elements were determined with inductively coupled plasma tandem mass spectrometry (ICPMS/MS). To see the effect of ventilation, samples were collected with closed and opened entrances. Nucleation mode particles (particles with aerodynamic diameter less than 10 nm) were dominant in particle number concentrations at both cave ventilation regimes. Aitken mode particles (10–100 nm) differed in the content of sulphur, calcium, iron, chromium, magnesium and nickel for different ventilation regimes. Accumulation mode particles (100–1000 nm) consisted predominantly of sulphur and calcium, also chromium, copper, arsenic, molybdenum, selenium, cadmium and lead were mainly present in this particle size range. Coarse mode particles (larger than 1000 nm) contained predominantly calcium, in addition to common earth crust elements, originating by mechanical abrasion of cave floor. It is suggested that ventilation as well as children activities in the cave influence the elemental composition of particulate matter, which might have an impact on speleotherapy.
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The network of lava tubes is one of the most unexploited natural wonders of the Galapagos Islands. Here, we provide the first morphological, mineralogical, and biogeochemical assessment of speleothems from volcanic caves of the Galapagos to understand their structure, composition, and origin, as well as to identify organic molecules preserved in speleothems. Mineralogical analyses revealed that moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves were composed of calcite, opal-A and minor amounts of clay minerals. Extracellular polymeric substances, fossilized bacteria, silica microspheres and cell imprints on siliceous minerals evidenced microbe-mineral interactions and biologically-mediated silica precipitation. Alternating depositional layers between siliceous and carbonate minerals and the detection of biomarkers of surface vegetation and anthropogenic stressors indicated environmental and anthropogenic changes (agriculture, human waste, cave visits) on these unique underground resources. Stable isotope analysis and Py-GC/MS were key to robustly identify biomarkers, allowing for implementation of future protection policies.
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Parmi les ossements découverts à Regourdou figurait un calcanéus droit, Regourdou 2, trouvé hors contexte sépulcral. Cet ossement exhumé en 1963 est régulièrement cité dans la littérature concernant les os du pied des Néandertaliens, sans avoir fait l’objet d’une étude approfondie. Dans cette contribution, nous proposons une analyse complète de cette pièce incluant une étude taphonomique, morphologique et une étude métrique et multivariée. L’ensemble de ces données permettra de discuter de son insertion dans la variabilité néandertalienne. Si les résultats des analyses morphométriques confirment le caractère néandertalien de ce vestige, ils mettent aussi en évidence des particularités anatomiques inédites pour ce groupe (dimensions générales, proportions, morphologie des surfaces articulaires et robustesse). Cette étude apporte donc de nouvelles données sur la variabilité morphologique connue jusqu’alors pour cet ossement et ce groupe fossile. De plus, la description taphonomique apporte des informations inédites quant à son histoire et sa découverte. Enfin, du fait de son appartenance au côté droit, comme le calcanéus Regourdou 1, cet os démontre la présence d’un deuxième individu adulte dans ce site. __________________________________________________________________________________ The calcaneus "Regourdou 2": comparative morphometric study and discussion about its position in the neanderthalian variability. Among the numerous bones uncovered in the site of Regourdou, lied a right calcaneus, Regourdou 2, found out any funeral context. This remain discovered in 1963 is regularly cited in the literature regarding the Neanderthals foot bones, but it never has been precisely studied. In this paper, we propose a taphonomic, morphologic as well as a metric and multivariate analysis of this bone remain to discuss its inclusion in the Neanderthal variability. If the morphometric results confirmed this piece belongs to a Neanderthal individual, they highlight new characters for this group (general dimensions, proportions, morphology of the articular surfaces and robusticity). This study contributes to extend the morphological variability actually known for this fossil bones and this group. The taphonomic description also helps to bring unknown data and assumptions about its history and its discovery. Moreover, according to its affiliation to the right side, as the calcaneus Regourdou 1, this foot bone demonstrates the presence of a second adult individual in this site.
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Subaqueous flowstones have been studied in two resurgence caves in Slovak Karst (southern Slovakia), namely Krásnohorská and Drienovská Caves. The flowstones litter streambeds within the distance of several hundred meters upstream from resurgences. They form laminated crusts within channels of the underground streams flowing through the caves. Layers composed of columnar sparry calcite alternate with those composed of microcrystalline calcite. The latter are enriched in fine, detrital, non-carbonate components, which resulted in crystallization of microcrystalline calcite instead of sparry calcite. The growth rate of the studied flowstones reaches 0.96 mg/cm²/day, which corresponds to ca. 0.3 mm per year. Seasonal observations conducted between November 2010 and September 2012 reveal that deposition of subaqueous flowstones in the studied caves significantly depends on the local hydrological conditions. During the periods of low flow, SIcalc. values of underground stream increase and columnar sparry calcite grows. Conversely, during peak flow periods SIcalc. values decrease and subaqueous flowstones are subjected to destruction, both by mechanical erosion and corrosion. The decreasing discharge, just after peak flows, causes deposition of fine-grained particles, which results in precipitation of microcrystalline layers. Subaqueous flowstones grow in complete darkness and in atmosphere with elevated CO2 content, similarly to typical speleothems, but they are fed with turbulent stream water, similarly to calcareous tufas. Their growth rate is higher than those of ‘normal’ flowstones fed with a film of water seeping down; it falls within a range of growth rate of calcareous tufas, though near the lower limit of this range. Therefore, subaqueous flowstones represent an intermediate link between other speleothems and tufas deposited outside the cave environment.
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Phosphorus (P) is potentially a very important environmental proxy in speleothem palaeoclimate reconstructions. However, the transfer of P to a speleothem seems to vary between cave sites. Therefore, it is important to investigate the source of P and the way it is incorporated into a speleothem on a site-by-site basis before it can be used as a robust palaeoclimate proxy. In this paper, the distribution of P in one modern and two Early Pliocene speleothems formed in coastal caves on Christmas Island (Indian Ocean) and the Nullarbor Plain (southern Australia) is investigated using microscopy and ultra-high resolution chemical mapping. Phosphorus has been found to be both incorporated in the lattice and present as diverse P-rich phases. Monitoring data from Christmas Island suggest that co-precipitation of P-rich phases occurs when "prior calcite precipitation" decreases following recharge, even if the drip rate decreases. Microbial mediation may also play a role, which complicates a direct climate relationship between P and hydrology. We find that some P-enriched layers contain dissolution features, with possible involvement of microbial mats which colonise pores during reduced drip rates associated with prolonged dry spells. In the two Early Pliocene speleothems the relationship between P and microbial laminae is clearer. Both petrographic and chemical data suggest that phosphorus-rich phases in the microbial laminae mark intervals of reduced drip rates, which may indicate dry intervals during the otherwise wet palaeoclimate of the Early Pliocene. We develop a speleothem distribution coefficient for phosphorus (SK<sub>P</sub>) rather than the thermodynamic partition coefficient (K<sub>P</sub>) to account for the presence of crystalline phosphate inclusions. SK<sub>P</sub> describes P enrichment in speleothems regardless of the process, as similar mechanisms of phosphate co-precipitation may be in operation in biotic and abiotic conditions. The most important implication of our study is that variability in P concentration may be related to diverse processes which can be recognized through petrographic observations and chemical mapping. In particular, there may not be a direct relation between an increase in P concentration and seasonal infiltration as has been found in some previous studies, especially if the source of this element is not the labile phosphate released through leaching during seasonal vegetation dieback in temperate climates.
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Despite the paleoclimatic relevance of primary calcite to aragonite transitions in stalagmites, the relative role of fluid Mg/Ca ratio, supersaturation and CO32- concentration in controlling such transitions is still incompletely understood. Accordingly, we have monitored the hydrochemistry of 50 drips and 8 pools that are currently precipitating calcite and/or aragonite in El Soplao and Torca Ancha Caves (N Spain), investigating the mineralogy and geochemistry of the CaCO3 precipitates on the corresponding natural speleothem surfaces. The data reveal that, apart from possible substrate effects, dripwater Mg/Ca is the only obvious control on CaCO3 polymorphism in the studied stalagmites and pools, where calcite- and aragonite-precipitating dripwaters are separated by an initial (i.e. at stalactite tips) Mg/Ca threshold at ≈ 1.1 mol/mol. Within the analyzed ranges of pH (8.2-8.6), CO32- concentration (1-6 mg/L), supersaturation (SIaragonite: 0.08-1.08; SIcalcite: 0.23-1.24), drip rate (0.2-81 drops/min) and dissolved Zn (6-90 μg/L), we observe no unequivocal influence of these parameters on CaCO3 mineralogy. Despite the almost complete overlapping supersaturations of calcite- and aragonite-precipitating waters, the latter are on average less supersaturated because the waters having Mg/Ca above ∼1.1 have mostly achieved such high ratios by previously precipitating calcite. Both calcite and aragonite precipitated at or near oxygen isotopic equilibrium, and Mg incorporation into calcite was consistent with literature-based predictions, indicating that in the studied cases CaCO3 precipitation was not significantly influenced by strong kinetic effects. In the studied cases, the calcites that precipitate at ∼11°C from dripwaters with initial Mg/Ca aproaching ∼1.1 incorporate ∼5 mole% MgCO3, close to the published value above which calcite solubility exceeds aragonite solubility, suggesting that aragonite precipitation in high-relative-humidity caves is favored from a solubility viewpoint. We also show that unaccounted CaCO3 precipitation in intermediate sampling containers and splash effects may in cases result in underestimating dripwater Ca concentration and alkalinity, potentially leading to incorrect conclusions regarding the role of fluid Mg/Ca ratio and supersaturation on CaCO3 mineralogy. A simple way to elude the first effect is by taking water samples directly from stalactites and by titrating alkalinity in the same containers used to collect dripwaters.
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Ana Heva lava tube (Easter Island, Chile): Preliminary characterization of the internal layers of coralloid-type speleothems - Volume 21 Issue S6 - A.Z. Miller, M.F.C Pereira, J.M. Calaforra, P. Forti, A. Dionísio, C. Saiz-Jimenez
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In Snežna Jama cave, Slovenia, extensive speleothems composed of dolomite, aragonite and hydromagnesite have been found, occurring as 5 cm thick globular crusts coating the host rock. Arborescent aragonite constitutes the skeleton of the crust, whereas dolomite is cementing, coating and replacing the aragonite. The dolomite displays two distinctive fabrics: coarse rounded to spheroidal crystals, frequently showing fibrous radial and concentric patterns, and microcrystalline aggregates. Dissolution of the dolostone host rock has provided Mg, which is the main control on the precipitation of arago-nite, dolomite and hydromagnesite. Dolomite precipitation could be promoted by increased Mg/Ca ratios due to the prior precipitation of calcite and aragonite and by forced degassing due to ventilation caused by the existence of shafts cutting the main cave passage and a former entrance to the cave. However, in many caves such conditions do not lead to the formation of dolomite and so we discuss other mechanisms which might promote dolomite precipitation, like the possible contribution of microbes, or the transformation of precursor phases such as amorphous Ca-Mg carbonates, or hydromagnesite.
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Condensation in karst occurs over a wide range of natural settings, at latitudes from 25° to 70° and altitudes from sea level to 2600 m. In summer (April through September), condensation introduces a significant amount of water into the karst massifs (from 0.1% to as much as 20% of the total dry-season runoff). Contrary to common belief, in winter evaporation does not withdraw appreciable amounts of water from the massifs. Evaporating at depth, the water condenses near the surface within the epikarstic zone or on the snow cover and flows back. Condensation can sustain springs during prolonged dry periods (such as summer and winter) when there is no recharge by liquid precipitation. Condensation can play a significant role in speleogenesis, and many forms of cave macro-, meso-, and micromorphologies are attributable to condensation corrosion. It can be particularly efficient in the latter stages of hydrothermal cave development (during partial dewatering) when the temperature and the humidity gradients are highest. Coupled with evaporation, air convection, and aerosol mass transfer, condensation can play a crucial role in the formation of a number of speleothems, as well as create peculiar patterns of cave microclimate.
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The isotopic and cation chemistry of meteoric waters changes in response to the effects of rock—water interaction, uptake of organically derived CO2, and primary mineralogic differences among carbonate terranes. Moreover, variations in the dominance of these factors produce diverse chemical conditions within the meteoric systems which allow the sub- environments of vadose-phreatic, mixed-water, and spelean diagenesis to be distinguished. Therefore, geochemical patterns within the meteoric water system are examined to provide criteria for recognition of these subenvironments of meteoric diagenesis in ancient carbonate sequences.
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Electron backscattered diffraction (EBSD) applied to crystal fabric research in speleothems aids in our understanding of the origin of those fabrics. A significant advantage of this approach is the three dimensional data set of crystal c-axes. Here, we show a rare case of both convergent (radiaxial-fibrous) and divergent (fascicular-optic) orientations of the c-axes in pool calcites. The seemingly defective structure of the calcite lattice resulting in radiaxial- fibrous crystal orientations is probably caused by differential incorporation of Mg during crystal growth. The observation that radiaxial-fibrous and fascicular-optic fabrics co-exist in the same pool environment is remarkable and documents the complexity of the system.
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The systematic documentation of calcite fabrics in stalagmites and flowstones provides robustness to palaeoclimate interpretation based on geochemical proxies, but it has been neglected because it is difficult to transform crystal morphologies into numerical values, and construct fabric time series. Here, general criteria that allow for coding fabrics of calcite composing stalagmites and flowstones is provided. Being based on known models of fabric development, the coding ascribes sequential numbers to each fabric, which reflect climaterelated parameters, such as changes in drip rate variability, bio-mediation or diagenetic modifications. Acronyms are proposed for Columnar types, Dendritic, Micrite, Microsparite and Mosaic fabrics, whose use could then render possible comparison of calcite fabrics in stalagmites and flowstones from diverse latitudinal and altitudinal settings. The climatic and environmental significance of similarities in the geochemical signals and trends analysed in coeval stalagmites and flowstones (or differences in the signals and trends) will be more robust when compared with fabric time series. This is particularly true where, such as in the Holocene, changes in geochemical values may be subtle, yet fabrics may show changes related to variations in supersaturation, drip rate or input of detrital particles or organic compounds. The proposed microstratigraphic logging allows recognition of changes in stable isotope ratio or trace element values that can be ascribed to hydrology and diagenesis, with considerable improvement of reconstructions based on the chemical proxies of stalagmites and flowstones composed of calcite.
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Archaeologists have long been puzzled by the appearance in Europe ∼40-35 thousand years (kyr) ago of a rich corpus of sophisticated artworks, including parietal art (that is, paintings, drawings and engravings on immobile rock surfaces) and portable art (for example, carved figurines), and the absence or scarcity of equivalent, well-dated evidence elsewhere, especially along early human migration routes in South Asia and the Far East, including Wallacea and Australia, where modern humans (Homo sapiens) were established by 50 kyr ago. Here, using uranium-series dating of coralloid speleothems directly associated with 12 human hand stencils and two figurative animal depictions from seven cave sites in the Maros karsts of Sulawesi, we show that rock art traditions on this Indonesian island are at least compatible in age with the oldest European art. The earliest dated image from Maros, with a minimum age of 39.9 kyr, is now the oldest known hand stencil in the world. In addition, a painting of a babirusa ('pig-deer') made at least 35.4 kyr ago is among the earliest dated figurative depictions worldwide, if not the earliest one. Among the implications, it can now be demonstrated that humans were producing rock art by ∼40 kyr ago at opposite ends of the Pleistocene Eurasian world.
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Peculiar calcite speleothems developed in fissures in the Cergowa Sandstones were found in the Kle{ogonek}czany Quarry (Polish Western Carpathians). They represent flowstone and stalactites, rafts and various sparry crusts. Such speleothems, especially phreatic ones, are uncommon in the Outer Carpathians that are composed mainly of siliciclastic rocks of flysch type, with only limited calcium carbonate content. The speleothems analysed grew in vadose and phreatic conditions as well as at the air-water interface. Phreatic speleothems and thin rafts comprise calcite crystals of eccentric morphology. Based on their stable isotope composition the majority of the speleothems form two clusters. The first is characterized by δ18O values between -9.8 and -8.5‰ and of d13C values between -5.7 and -0.6‰ whereas the second cluster of samples yields δ18 O values between -9.4 and -7.3‰ and d13C values from -11.5 to -9.7‰. Speleothems grew between 230+14-13 ka and Holocene time. Phreatic speleothems, including massive rafts, precipitated from ascending water of deep circulation whereas vadose and water table speleothems crystallized from local infiltration water charged with soil CO2. Mixing of both waters in the shallow phreatic zone is plausible.
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Annually laminated stalagmites deposited over the last 30–160 years are analysed to determine their growth rate. Three natural and artificial cave sites in England, France, and Belgium were chosen for their wide range of variability in growth rate determining variables, and multiple samples were taken from each site. The annual nature of laminae deposition within the stalagmite calcite was confirmed by comparison to the date of cave/void opening, 14C analyses, or by using dated event horizons. Measured stalagmite growth rate was determined from annual laminae thickness measurements and compared to that theoretically predicted from the chemical kinetics of the calcite precipitation reaction. A good agreement is observed between empirical observations and theoretical predictions, although two complicating factors, variations in calcite porosity, and seasonal cessation of the water supply to the samples, both affect the growth rate. Implications for the extraction of palaeoclimate information from stalagmite growth rate are discussed.
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The abundance and variety of speleothems are undoubtedly among the remarkable features of Cova des Pas de Vallgornera, the longest cave system in Mallorca Island developed in the eogenetic karst of its southern coast. Due to the monotonous carbonate lithology of the area, most of the speleothems are composed of calcite and in a few cases aragonite, although other minerals are also represented (e.g., gypsum, celestine, barite). However, in spite of the rather common mineralogy of the speleothems, its distribution results strongly mediated by the lithologic and textural variability linked to the architecture of the Upper Miocene reefal rocks. Apart from a vast majority of speleothem typologies that are ubiquitous all along the cave system, some particular types are restricted to specific sections of the cave. In its landward inner passages, formed in the low permeability back reef facies, a great variety of speleothems associated to perched freshwater accumulations stands out, as well as some non frequent crystallizations like for example cave rims. On the other hand, the seaward part of the cave (developed in the very porous reef front facies) hosts conspicuous phreatic overgrowths on speleothems (POS), which are discussed to show their applications to constrain sea level changes. The factors controlling the distribution of speleothems found in Cova des Pas de Vallgornera are discussed along the paper, focusing the attention on the lithologic, hydrogeologic, and speleogenetic conditionings; at the same time some uncommon speleothems, not found in any other cave in Mallorca, are also documented from this locality. Finally, a cognizant effort has been undertaken to illustrate with photographs the most remarkable speleothem types represented in the cave.
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Karst environments are regions where sparingly soluble rocks outcrop and efficient acid hydrolysis creates spectacular dissolution landforms. The release of CO<sub>2</sub> from karst waters to the atmosphere causes precipitation of calcium-carbonate deposits, which, in caves, are collectively known as speleothems. Karst carbonate deposits capture climate and environmental signals in their macro- and micro-morphological characteristics, their mineral composition, and their chemical properties. They can be precisely dated with radiometric techniques and, thus, constitute an archive of climate change for millions of years. Karst carbonate formation is a product of both inorganic and organic processes. The influence of bacteria appears to be particularly important in the formation of calcareous tufa, deposits which commonly dam flowing water at both surface and subsurface. Bacteria also play a role in favouring the growth of mineral fibres in cave moonmilk, a plastic and powdery deposit consisting mostly of water and calcite. The most typical products of deposition in the subsurface karst environment are speleothems consisting of a rigid and relatively fragile arrangement in successive layers of calcium-carbonate crystals, which are here referred to as sparitic speleothems. Stalagmites, stalactites and flowstones mostly consist of calcite, and less commonly of aragonite or other minerals, which reflect events that occurred at the surface in their fabrics, trace-element composition, stable-isotope ratio and organic chemistry. The focus of this chapter is on issues related to the formation of karst deposits and their significance as palaeoclimate archives. © 2010 Elsevier B.V. All rights reserved.
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The distribution of phosphorous (P) in one modern and two Early Pliocene speleothems formed in low-lying, Christmas Island and the coastal Nullarbor caves wet settings in Australia is here investigated by microscopy and ultra-high resolution chemical mapping. Monitoring data in the modern setting suggest that co-precipitation of P with calcite occurs when the drip rate decreases, the aquifer is progressively drained and microbial mats possibly aid in the formation of concentrating phosphates. A bulk partition coefficient is proposed, which indicates that the P enrichment in the speleothem could be accounted for by inorganic processes. Our interpretation of the hydrological significance of P incorporation in wet, tropical speleothems is then used to interpret P peaks associated with micritic and stromatolithic layers in the two Early Pliocene stalagmites from the Nullarbor. From these observations it is speculated that dry periods may have interrupted the wet climate regime at ca. 4 Myr ago, hinting at a possible early onset of the Pleistocene climate mode.
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There is developing interest in cave aerosols due to the increasing awareness of their impacts on the cave environment and speleothem; this paper provides the first attempt to synthesize the issues. Processes of cave aerosol introduction, transport, deposition, distribution and incorporation are explored, and reviewed from existing literature. Key issues of specific aerosol processes of distribution and production as well as cave location and morphology effects are highlighted through the presentation of preliminary monitoring data. This study identifies the strong relationship between cave ventilation, cave aerosols and their consequent spatial distribution.The contribution of cave aerosol deposition to speleothem geochemistry is modelled and evaluated using a mass balance framework. As an example, speleothem trace element data from Obir Cave (Austria) are compared with aerosol inputs to evaluate their significance. The mass balance study demonstrates that generally, under normal continuous growth and environmental conditions aerosol deposition will be of only minor importance. However, it highlights specific scenarios in which aerosol contributions will be significant: speleothem hiatuses (or slow growth), high aerosol deposition, and secondary microbiological feedback.
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Two complementary image-based microanalysis methods, digital autoradiography of radioactive elements and X-ray fluorescence microspectroscopy (micro-XRF), were used to study the geochemistry of a speleothem from Eastern Siberia. Our objective was to show the interest of these micro-chemical methods to investigate the distribution of U and some other elements as Ca, Sr, and Si in speleothems. The sample studied was a corallite concretion that formed slowly by the precipitation of minerals from moisture that had condensed underground. Polished sections of the sample revealed alternating laminas of gray calcite and white aragonite. The concretion, which is older than 400 Kyr (U/Th-TIMS), showed no signs of detrital contamination (230Th/232Th > 10,000). Digital autoradiography and XRF analyses indicated exceptionally high uranium contents, ranging from 3–10 to more than 1300 μg ∙ g− 1 in different areas of the sample. Element maps for calcium (Ca), uranium (U), strontium (Sr) and silicon (Si) showed inverse correlations between Ca and U and between Ca and Si, but there is a strong correlation between Si and U. Under the optical microscope, the low Ca appears as corrosion voids, which were found to contain uranium-enriched amorphous silica replacing areas of aragonite and, in some cases, calcite. This postgenetic amorphous and uraniferous silica is composed of two kinds of opal: opal A formed by large microspheres of 30–40 μm in diameter and a gray opal CT with irregular lepispheres. This late opal, dated around 385–412 Kyr, is probably due to a special volcanic event formed by uraniferous glass ashes easily soluble by meteoric waters, as suggested by the presence of volcanic suite in the fine fraction of the opal. Opal precipitated after speleothem crystallization by evaporation or cryogenic supersaturation. The study of this exceptional concretion shows the value of direct chemical imaging methods, as they easily revealed the presence and distribution of U in the concretion, and allowed an unusual case of opal diagenesis in a carbonate speleothem to be described. Given the value of speleothems as geo-chronometers and recorders of environmental changes at different time scales, from season to isotopic stage, this methodology opens new perspectives in understanding the geochemical system and consequently the validity of radiometric datings, U/Th and U/Pb, especially in speleothem samples.
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Perhaps man’s first motivation to explore caves, beyond using them as shelter, was the search for substances that were not available elsewhere: most of them were minerals. However, for a long time it was believed that the cave environment was not very interesting from the mineralogical point of view. This was due to the fact that most cave deposits are normally composed of a single compound: calcium carbonate. Therefore, the systematic study of cave mineralogy is of only recent origin. However, although only a limited number of natural cavities have been investigated in detail, about 350 cave minerals have already been observed, some of which are new to science. The presence of such unexpected richness is a direct consequence of the variety of rocks traversed by water or other fluids before entering a cave and the sediments therein. Different cave environments allow the development of various minerogenetic mechanisms, the most important of which are double exchange reactions, evaporation, oxidation, hydration-dehydration, sublimation, deposition from aerosols and vapors, and segregation. The cave temperature and pH/Eh strictly control most of them, although some are driven by microorganisms. The cave environment, due to its long-term stability, can sometimes allow for the development of huge euhedral crystals, such as those found in the Naica caves (Mexico), but the presence of extremely small yet complex aggregates of different minerals is far more common. Future development in the field of cave mineralogy will likely be focused mainly on hydrothermal and sulfuric-acid caves and on the role played by micro-organisms in controlling some of the most important minerogenetic processes in caves.
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Five fabrics were identified in Alpine and Irish caves on the basis of morphological and microstructural characteristics, and related to growth mechanisms and growth environment. Columnar and fibrous fabrics grow when speleothems are continuously wet, and from fluids at near equilibrium conditions (low supersaturation; SIcc < 0.35), through the screw dislocation mechanism. The highly defective microcrystalline fabrics form at the same supersaturation range as columnar fabric but under variable discharge and the presence of growth inhibitors. Dendritic fabrics, which have the highest density of crystal defects, develop in disequilibrium conditions (high supersaturation) under periodic very low-flow-regime periods that result in prolonged outgassing. Cave calcareous tufa forms in disequilibrium conditions. Only the calcite crystals of fabrics formed at low supersaturation seem to precipitate near-isotopic-equilibrium conditions.
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To determine if microbial species play an active role in the development of calcium carbonate (CaCO3) deposits (speleothems) in cave environments, we isolated 51 culturable bacteria from a coralloid speleothem and tested their ability to dissolve and precipitate CaCO3. The majority of these isolates could precipitate CaCO3 minerals; scanning electron microscopy and X-ray diffractrometry demonstrated that aragonite, calcite and vaterite were produced in this process. Due to the inability of dead cells to precipitate these minerals, this suggested that calcification requires metabolic activity. Given growth of these species on calcium acetate, but the toxicity of Ca ions to bacteria, we created a loss-of-function gene knock-out in the Ca ion efflux protein ChaA. The loss of this protein inhibited growth on media containing calcium, suggesting that the need to remove Ca ions from the cell may drive calcification. With no carbonate in the media used in the calcification studies, we used stable isotope probing with CO2 to determine whether atmospheric CO2 could be the source of these ions. The resultant crystals were significantly enriched in this heavy isotope, suggesting that extracellular CO2 does indeed contribute to the mineral structure. The physiological adaptation of removing toxic Ca ions by calcification, while useful in numerous environments, would be particularly beneficial to bacteria in Ca-rich cave environments. Such activity may also create the initial crystal nucleation sites that contribute to the formation of secondary CaCO3 deposits within caves.
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Aragonite and calcite speleothems were sampled in the cave of Pierre Saint-Martin (Pyrénées-Atlantiques, France). These speleothems contain significant amounts of uranium and strontium, which were measured spatially and chemically by nuclear microprobe analysis. Sr and U distributions are highly varied, with a marked contrast between aragonite and calcite because the aragonite concentrates Sr and U. On the other hand, Zn is preferentially located in calcite and in layers of organic matter trapped in CaCO3. Sr contents ranged from 440 to 1100 μg/g in the calcite and 4900 to 18,500 μg/g in the aragonite. U concentrations show remarkably high values from 11 to 19 μg/g in the calcite and 89 to 350 μg/g in the aragonite. These U and Sr concentrations are amongst the highest measured in supergene speleothems deposited by infiltrating meteoric waters. X-ray absorption experiments with synchrotron radiation suggested that uranium was incorporated in its hexavalent oxidation state in both aragonite and calcite. Recrystallization from aragonite into calcite was indicated by micromorphological observations for some of the samples. This recrystallization process may explain the uranium loss in neogenic calcite deposits and consequently the opening of the geochemical system, which can lead to errors in age dating with the U-series dating method. Uranium loss in recrystallized calcite is one of the important aspects to be considered in U-series dating and more generally for U geochemical stability in CaCO3.
Book
Txtbook on cave minerals and speleothems
Article
Carbonate stalagmites have become increasingly attractive to Quaternary paleoclimate research, as they can be accurately dated by radiometric methods and concurrently yield high-resolution multi-proxy records of past climate conditions. Reliable series however require the precise characterization of stalagmite internal micro-stratigraphy, a task too often poorly accomplished despite the recent advances in speleothem research. This weakness is due to the lack of a robust integrative methodological framework capable of integrating the wide range of petrographical and micro-stratigrafical methods currently used in speleothem characterization. For covering this need, this review introduces the Speleothem Architectural Analysis (SAA), a holistic approach inspired in well-established stratigraphic procedures such as the architectural element analysis and the sequence stratigraphy, commonly used by geoscientists for categorizing internal stratigraphic heterogeneities in sedimentary deposits. The new approach establishes a six-fold hierarchy of speleothem architectural elements and their bounding surfaces: individual crystallites (1st order), single growth layers (2nd order), speleothem fabrics (3rd order), stacking patterns sets (4th order), morphostratigraphic units (5th order), unconformity-bounded units and major unconformities (6th order). Each category of architectural element is formed in a different range of time, from intervals as short as a year/season to others of centuries or millennia. The SAA, which has the capability of incorporating any petrographic or stratigraphic classification, provides a useful, systematic, and versatile tool for unraveling the complexities of speleothem growth, and thus for genetically interpreting stalagmites in a multi-temporal scale. A detailed speleothem stratigraphy must be the basis for performing robust reconstruction of paleoclimate series. They should precede and accompany any work focused in absolute age dating or in reconstructing paleoclimate by means of any geochemical proxy.
Article
This study comprises an innovative approach based on the combination of chromatography (analytical pyrolysis and pyrolysis compound-specific isotope analysis (Py-CSIA)), light stable isotopes, microscopy and mineralogy analyses to characterize the internal layering of coralloid speleothems from the Ana Heva lava tube in Easter Island (Chile). This multidisciplinary proxy showed that the speleothems consist of banded siliceous materials of low crystallinity with different mineralogical compositions and a significant contribution of organic carbon. Opal-A constitutes the outermost grey layer of the coralloids, whereas calcite and amorphous Mg hydrate silicate are the major components of the inner whitish and honey brown layers, respectively. The differences found in the mineralogical, elemental, molecular and isotopic composition of these distinct coloured layers are related to environmental changes during speleothem development. Stable isotopes and analytical pyrolysis suggested alterations in the water regime, pointing to wetter conditions during the formation of the Ca-rich layer and a possible increase in the amount of water dripping into the cave. The trend observed for delta N-15 values suggested an increase in the average temperature over time, which is consistent with the so-called climate warming during the Holocene. The pyrolysis compound-specific isotope analysis of each speleothem layer showed a similar trend with the bulk delta C-13 values pointing to the appropriateness of direct Py-CSIA in paleoenvironmental studies. The delta C-13 values for n-alkanes reinforced the occurrence of a drastic environmental change, indicating that the outermost Opal layer was developed under drier and more arid environmental conditions.
Article
In this study, multi-block analysis was applied for the first time to LIBS spectra provided by a portable LIBS system (IVEA Solution, France) equipped with three compact Czerny-Turner spectrometers covering the spectral ranges 200–397 nm, 398–571 nm and 572–1000 nm. 41 geological samples taken from a laboratory-cave situated in the “Vézère valley”, an area rich with prehistoric sites and decorated caves listed as a UNESCO world heritage in the south west of France, were analyzed. They were composed of limestone and clay considered as underlying supports and of two types of alterations referred as moonmilk and coralloid. Common Components and Specific Weights Analysis (CCSWA) allowed sorting moonmilk and coralloid samples. The loadings revealed higher amounts of magnesium, silicon, aluminum and strontium in coralloids and the saliences emphasized that among the three spectrometers installed in the LIBS instrument used in this work; that covering the range 572–1000 nm was less contributive. This new approach for processing LIBS data not only provides good results for sorting geological materials but also clearly reveals which spectral range contains most of the information. This specific advantage of multi-block analysis could lead for some applications to simplify the design and to reduce the size of LIBS instruments.
Article
Speleothems (mineral deposits that formed in caves) are currently giving us some of the most exciting insights into environments and climates during the Pleistocene ice ages and the subsequent Holocene rise of civilizations. The book applies system science to Quaternary environments in a new and rigorous way and gives holistic explanations the relations between the properties of speleothems and the climatic and cave setting in which they are found. It is designed as the ideal companion to someone embarking on speleothem research and, since the underlying science is very broad, it will also be invaluable to a wide variety of others. Students and professional scientists interested in carbonate rocks, karst hydrogeology, climatology, aqueous geochemistry, carbonate geochemistry and the calibration of climatic proxies will find up-to-date reviews of these topics here. The book will also be valuable to Quaternary scientists who, up to now, have lacked a thorough overview of these important archives. Additional resources for this book can be found at: www.wiley.com/go/fairchild/speleothem.
Article
Calcite speleothems are typically coarsely crystalline, colored various shades from brown through orange and white, and strongly luminescent. For most speleothems, the color is due to higher molecular weight humic substances incorporated in the calcite crystal structure, while the luminescence is mainly due to lower molecular weight fulvic acids. The fine scale banding of luminescence intensity has importance as a climatic indicator. A suite of eighteen speleothems spanning a range of geologic and climatic settings and a range of colors from deep brown to nearly white were selected for detailed characterization and spectroscopic measurements. Spectra were measured on solid samples and on solutions prepared by dissolving the speleothems in dilute HCl. The luminescent emission appears as a single broad band with peak wavelength varying from 390 to 450 nm. The excitation spectra are typically more complicated, with several maxima, and show more locality-to-locality variation. The emission bands shift to longer wavelengths as the excitation bands move to longer wavelengths, indicating that a mixture of molecular species is being selectively excited. The spectra of the solutions are similar but not identical to the spectra of the crystalline solids. The decay time of the luminescence (phosphorescence) is in the range of 0.5 to 0.7 second. Comparison of speleothem spectra from caves in different climatic settings and of speleothem spectra from the same cave indicate that each speleothem produces spectra characteristic of specific overlying soils and pathways through the epikarst and the vadose zone. No features were discovered that characterize regional scale geologic or climatic settings.
Article
Many speleothems can be assigned to one of two morphological groups: massive speleothems, which consist of compact bulks of material, and coralloids, which are domal to digitate in form. Faster growth on protrusions of the substrate occurs in the typical growth layers of coralloids (where those layers are termed “coralloid accretions”), but it is not observed in the typical layers of massive speleothems, which in contrast tend to smoothen the speleothem surface (and can therefore be defined as "smoothing accretions"). The different growth rates on different areas of the substrate are explainable by various mechanisms of CaCO3 deposition (e.g., differential aerosol deposition, differential CO2 and/or H2O loss from a capillary film of solution, deposition in subaqueous environments). To identify the causes of formation of coralloids rather than massive speleothems, this article provides data about δ13C and δ18O at coeval points of both smoothing and coralloid accretions, examining the relationship between isotopic composition and the substrate morphology. In subaerial speleothems, data show an enrichment in heavy isotopes both along the direction of water flow and toward the protrusions. The first effect is due to H2O evaporation and CO2 degassing during a gravity-driven flow of water (gravity stage) and is observed in smoothing accretions; the second effect is due to evaporation and degassing during water movement by capillary action from recesses to prominences (capillary stage) and is observed in subaerial coralloids. Both effects coexist in smoothing accretions interspersed among coralloid ones (intermediate stage). Thus this study supports the origin of subaerial coralloids from dominantly capillary water and disproves their origin by deposition of aerosol from the cave air. On the other hand, subaqueous coralloids seem to form by a differential mass-transfer from a still bulk of water towards different zones of the substrate along diffusion flux vectors of nutrients perpendicular to the iso-depleted surfaces. Finally, this isotopic method has proved useful to investigate the controls on speleothem morphology and to obtain additional insights on the evolution of aqueous solutions inside caves.
Article
Paucity of understanding mechanisms relevant to the generation of subsurface mobile colloids is a major limitation to our current knowledge of colloid-facilitated contaminant transport. To evaluate the roles of natural organic materials and pore water velocity on mobile colloid generation, colloids generated from 14-m³ lysimeters containing reconstructed soil profiles were collected and characterized. Colloids generated during low flow rates were 1030% less abundant, contained at least 65% more iron oxides and gibbsite, were 80% smaller, and had 40% greater electrophoretic mobility than colloids generated during higher flow rates. Quartz, kaolinite, and hydroxy-interlayered vermiculite were enriched by at least 32% in colloids generated during faster flow rates. Mobile colloid surface charge was greatly enhanced by organic carbon (OC) coatings. Concentrations of OC associated with mobile colloids were higher than or equal to the OC concentrations existing in the bulk soils from which the mobile colloids were derived. The profound effects of pore water flow rate and OC on mobile colloid generation introduces complexity to this potentially critical, yet poorly understood, component of subsurface contaminant transport. 41 refs., 8 figs., 1 tab.
Article
Host-rock, speleothems, and rock art paintings from Altamira and Tito Bustillo Caves (northern Spain) are coated by dense biofilms of phototrophic microorganisms (cyanobacteria and algae) and networks of heterotrophic bacteria (mainly actinomycetes). These microorganisms induce constructive (calcification, crystalline precipitates) and destructive fabrics (irregular etching, spiky calcite). To assess the microbial impact on both caves - which contain valuable rock art paintings - mineralogical, petrographical, hydrochemical, microenvironmental, and microbiological studies were carried out. The identified damage includes: (1) covering (scattered colored spots, whitish powdery patinas)of paintings by the microbial communities themselves and/or by their metabolic activity (including biofilms and 'bioinduced' precipitates); (2) chemical alteration, such as microbially mediated dissolution; and (3) mechanical alteration, such as substratum breakdown and scaling. In addition, some types of speleothems, such as hydromagnesite coatings, traditionally attributed to inorganic precipitation, can be considered to be a product of microbial activity, as this activity could foster the precipitation of Ca–Mg-carbonates by creating conditions of high alkalinity with low PCO2 values. Hydrochemical, geochemical, and microenvironmental data exclude an inorganic process in the precipitation of hydromagnesite and huntite in Altamira Cave.
Article
The vast majority of speleothems are composed of calcium carbonate, but this paper focuses on a suite of less-commonly reported speleothems, those formed almost entirely of silica, and on a quartzose rather than carbonate base rock. On the quartz sandstones of the Sydney region of southeastern Australia, small branched coralline silica stalactites, up to 10 mm in diameter and 80 mm in length, frequently are found. These stalactites have not been described in detail before and are clear evidence of the solution of silica (including quartz) from within the sandstones, and its transport and redeposition at the rock surface. Detailed analysis using SEM, XRD, and thin-section techniques revealed layered composition of both amorphous opal-A and crypto-crystalline chalcedony. Calcite forms no part of these stalactites. The internal structure also shows that they do not form in a manner similar to calcite stalactites. While the growth rate of these silica stalactites remains unknown, it is believed to be quite slow. But they clearly are not relict features and are forming under present-day temperate-climatic conditions, not the tropical conditions demanded by some authors for silica stalactites elsewhere. Further detailed study of these and other silica speleothems is continuing, as they have the potential to be used as important records of palaeoclimatic and land-use change. [Key words: silica karst, speleothem, coralline silica, silica stalactite, opal-A, chalcedony, quartz, silica solution.]
Article
High-resolution records of carbon isotope composition and grey level were analysed from a stalagmite, BW-1, from Beijing, China, deposited between c. 14 and 10.5 ka BP, the δ18O profile of which has been used to discuss the timing and structure of the Younger Dryas (YD) event in north China. The high grey level and low δ13C match the milk-white coloured locations on the polished stalagmite surface and coincide with enhanced luminescent bands within which the concentration of both impurities and the total organic carbon (TOC) are high. Additionally, the fluorescence of speleothems was derived from organic acids that have been flushed onto the stalagmite surface along with impurities from the overlying soil by heavy summer rain and co-precipitated with the speleothem calcite. Thus, predominantly low δ13C and high grey level values indicate increased summer precipitation that supports abundant vegetation and robust biological productivity. Consequently, three distinct time intervals are defined by the palaeoenvironmental conditions expressed in the δ13C and grey level records of stalagmite BW-1: (i) a warm-humid stage (Pre-YD, 13.97 to 12.85 ka BP, including a hiatus from 12.99 to 13.21 ka BP reported before); (ii) a cool-arid stage (YD, 12.85 to 11.56 ka BP); and (iii) a warm-humid stage (Post-YD, 11.56 to 10.39 ka BP). The inferences based on our research are generally consistent with other regional vegetation and climatic records.
Article
High-resolution isotopic and geochemical analyses in a modern (1990–2008) Soreq Cave stalagmite are com-pared to instrumental records of rainfall and dripwater from the cave, with the aim of determining how seasonal-resolution climate information is transmitted to speleothem geochemistry. In situ, micron-scale analysis of oxygen isotope ratios (δ 18 O) and trace elements by ion microprobe in combination with a continuous, linear traverse of trace element concentrations by laser-ablation ICP-MS (LA-ICP-MS) allow the definition of geochem-ical pathways within the cave. Fluorescent banding, imaged by confocal laser fluorescent microscopy (CLFM), as well as δ 18 O and trace element variations is used to define 18 annual growth increments. Reduced intensity of fluorescent banding and a change in trace element variability reflect the decrease in average rainfall from 628 mm/yr (1990–1998) to 433 mm/yr (1999–2008). During the wetter period before 1998, Pearson (r-value) and Spearman (ρ-value) correlation coefficients are N 0.5 for ion microprobe analyses of the element pairings Sr–Y, Y–P, and Mn–Si. After the transition to the drier period in 1999, a different set of geochemical pairings have r-and ρ-values N0.5, including Mg–δ 18 O, Mg–Sr, and Sr–Ba. Principal component analysis of data from the adjacent LA-ICP-MS traverse identifies two primary underlying modes of trace element variability. Based on the ion microprobe correlations and principal component analyses, we suggest that a greater seasonal influx of particulate material into the cave during the wetter period (1990–1998) brought about greater P, Cu, Sr, Na, and U variability in the stalagmite. The co-variability of δ 18 O, Mg, Sr, and Ba is characteristic of the trace element pattern from the drier period (1999–2008) of growth when particulate transport is reduced. These findings sup-port a two-reservoir model of Soreq Cave dripwaters. One reservoir displays a well-mixed "baseline" with a de-cadal residence time that supplies water to the cave year-round, probably from fine pores or grain-boundary films in the vadose zone. The second reservoir is seasonal rainwater enriched in organic acids, colloids, and small particles and is rapidly transmitted to the cave. Finally, the similar patterns of fluorescence intensity, P, and Cu concentrations support the hypothesis that fluorescent bands in Soreq Cave speleothems are caused by the influx of organic colloids.
Article
With the discovery of the József-hegy Cave, a cave of hydrothermal origin with an abundance of minerals unknown so far in Hungary came to light. Diversity and the frequency of the occurrence of crystals make this cave similar to the Lechuguilla Cave, even if the dimensions of the mineral precipitations and the passages do not compare in scale. The variety and mass of carbonates and sulphates are surprising. This paper describes the minerals and speleothems of the József-hegy Cave, their occurrence and genesis, including determined ages. The 41 U/Th measurements suggest that speleothems begun to develop in the upper level of the cave more than 350 ka ago. Some of these dated old speleothems were developing in dry passages, thus the uppermost passages of the József-hegy Cave have been dry at least for 350 ka. The karst water level was still at the main passage 200 ka ago and dropped to 120 m asl by the time of ~100 ka before present.
Article
Information concerning the bacterial and archaeal communities present on calcite speleothems in carbonate caves is of interest because the activity of these microbes has been implicated as a potential biogenic component in the formation of secondary mineral deposits. In addition, these speleothems may harbor unique, previously unidentified microbes. The current study presents a comparative analysis of the superficial bacterial and archaeal community structure of multiple stalactites from two different cave formations located in close proximity to each other in a nonhuman-impacted area of Kartchner Caverns, Arizona, USA. PCR-denaturing gradient gel electrophoresis analysis (PCR-DGGE) revealed that microbial communities sampled from stalactites of a single speleothem are more similar to each other than to the communities sampled from stalactites of an adjacent speleothem, suggesting that both bacterial and archaeal communities are speleothem-specific. SR-XRD analysis confirmed that both speleothems sampled were primarily calcite, but subtle differences were detected in the elemental composition profiles obtained from ICP-MS analysis indicating that substrate geochemistry was also speleothem-specific. PhyloChip analysis of composite samples from both speleothems revealed a broad diversity of phyla represented in the bacterial communities, while bacterial and archaeal bands sequenced from the DGGE profiles confirmed the presence of unique phylotypes not closely related (< 96% similarity) to any sequences deposited in the GenBank database.
Article
A 4-yr study of spatial and temporal variability in the geochemistry of vadose groundwaters from caves within the Edwards aquifer region of central Texas offers new insights into controls on vadose groundwater evolution, the relationship between vadose and phreatic groundwaters, and the fundamental influence of soil composition on groundwater geochemistry. Variations in Sr isotopes and trace elements (Mg/Ca and Sr/Ca ratios) of dripwaters and soils from different caves, as well as phreatic groundwaters, provide the potential to distinguish between local variability and regional processes controlling fluid geochemistry, and a framework for understanding the links between climatic and hydrologic processes.
Article
A previously unreported, coarsely crystalline calcite fills pores and is composed of crystals that possess inclusion-patterns and lattice-curvatures mimetic after bundled acicular carbonate cements. This calcite fabric, named 'fascicular-optic' because of the characteristic divergent optic-axis pattern within each crystal, is possibly widely distributed in certain limestones. It has been found within both shallow-marine and deep-water (pelagic) limestones. The replacement mechanism responsible for generating fascicular-optic calcite is believed to involve the lateral joining together (coalescence) of the former acicular crystals, either directly if the original cement had a low-Mg calcite mineralogy, or by coalescence of acicular aragonite or high Mg-calcite crystals, followed by subsequent stabilization (calcitization or magnesium loss).
Article
The Mississippian-Pennsylvanian unconformity in northwestern Arkansas contains pedogenically altered regolith preserved in low-lying areas on paleokarst on the Chesterian Pitkin Limestone. The regolith is succeeded by transgressive rocky-shore deposits of the Cane Hill Member, Hale Formation. Pitkin cements reflect extensive, meteoric, phreatic diagenesis prior to karstification. The overlying, pedogenically altered regolith contains calcretized lithoclasts in clay matrix, suggesting a shift from ever-wet conditions to more seasonal rainfall prior to the Pennsylvanian transgression. Basal Cane Hill strata consist of high-energy, shoreface, boulder-cobble conglomerate containing reworked Pitkin clasts. The conglomerate contains an unequivocal rocky-shore community. Preservation of poorly indurated paleosol beneath high-energy transgressive deposits suggests very rapid transgression consistent with a glacio-eustatic mechanism. Truncated Pitkin strata were removed by karstification and sub-aerial erosion during the hiatus and not by erosion during transgression. -from Author
Article
Recent explorations in Cueva Charles Brewer, a large cave in a sandstone tepui, SE Venezuela, have revealed silica biospeleothems of unprecedented size and diversity. Study of one — a sub-spherical mass of opaline silica — reveals a complex, laminated internal structure consisting of three narrow dark bands alternating with two wider light bands. Uranium–thorium dating has produced 3 stratigraphically correct dates on the light bands from 298±6 (MIS 9) to 390±33ka (MIS 11). U concentration is only 30–110ppb. Initial 234U/238U ratios are high and increase over time from 1.8 to 5.3. Growth rate is very low, the fastest, at 0.37±0.23mm/ka, in MIS 9. Trace element and heavy metal content of the dark bands is distinctly higher than that of the light bands. It is hypothesized that the dark and light bands correlate with drier/glacial and wetter/interglacial periods, respectively, and that this sample probably began to grow in MIS 13. The cave is in a region that straddles a regionally important ecotone: the speleothem isotopic and trace element variations may preserve a useful paleoclimatic signal. This is the first published suite of U–Th dates from a single silica speleothem and the longest Quaternary record for this region.
Article
When favorable conditions occur for carbonate precipitation (physicochemical processes) in tufas and travertines, organisms intervene either directly (the framework created by organisms acts as a crystal support) or indirectly (organic products influencing the mineralogy, nucleation, growth and habit of primary crystals). In the literature, fluvial and travertine crystalline sparite crusts with palisadic or prismatic crystals are generally interpreted as the result of early recrystallization of micrite in algal buildups (mostly composed of Schizothrix). Therefore, biological mediation is essential for the construction of continental bioherms and biostromes, even if organic remains are frequent in micrite and primary sparites, and rare or totally absent in secondary sparites.