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Simplified topographic map of Lebanon (A) – inset map showing the position of Lebanon in the Levant Region. (B) Geological map showing
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The Kanaan cave is situated at the coastal zone, north of Beirut City (capital of Lebanon). The cave is located within the upper part of the Jurassic Kesrouane Formation (Liassic to Oxfordian) which consists mainly of micritic limestone. Twenty seven cave pearls were subjected to petrographic (conventional and scanning electron microscopy) and geoc...
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... covers 10452 km 2 of surface area and stretches along the central eastern coast of the Mediterranean Sea (Fig. 1A). Geomorphologically, it consists of two mountain chains (Mount-Lebanon and Anti-Lebanon) separated by a high inland plain (the Bekaa; Fig. 1A). The western chain (Mount- Lebanon) borders the Mediterranean Sea, displaying relatively gentle slopes on its western flanks and steeper ones on its eastern flanks. The highest point in Lebanon ...
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... covers 10452 km 2 of surface area and stretches along the central eastern coast of the Mediterranean Sea (Fig. 1A). Geomorphologically, it consists of two mountain chains (Mount-Lebanon and Anti-Lebanon) separated by a high inland plain (the Bekaa; Fig. 1A). The western chain (Mount- Lebanon) borders the Mediterranean Sea, displaying relatively gentle slopes on its western flanks and steeper ones on its eastern flanks. The highest point in Lebanon is located in the northern part of this mountain chain; i.e. the Qornet es Saouda, 3083 m above sea level (asl). Precipitation (rain and snow) ...
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... Kanaan cave is located in the Kassarat area to the east of the coastal town of Antelias, a few kilometers north of Beirut City (capital of Lebanon; Fig. 1B). The cave is located within the deeply and intensively karstified rocks of the Kesrouane Formation (Fig. 1B). The deepest known sinkholes (Houet Fouar ed Dara, -622 m and Houet Qattine Azar, -450 m) as well as the longest cave in Lebanon (Magharet Jeita, 9 km) are found within this rock unit. The Kanaan cave was discovered in 1997, ...
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... Kanaan cave is located in the Kassarat area to the east of the coastal town of Antelias, a few kilometers north of Beirut City (capital of Lebanon; Fig. 1B). The cave is located within the deeply and intensively karstified rocks of the Kesrouane Formation (Fig. 1B). The deepest known sinkholes (Houet Fouar ed Dara, -622 m and Houet Qattine Azar, -450 m) as well as the longest cave in Lebanon (Magharet Jeita, 9 km) are found within this rock unit. The Kanaan cave was discovered in 1997, when its entrance became exposed during rock-quarrying. The entrance is situated at around 100 m above sea- ...
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... higher Na and Sr values could be related to sea-water incursions into that coastal cave. Figure 10 is a crossplot featuring the δ 18 O versus δ 13 C values for the cortical lamina from different cave pearls collected from the Kanaan cave (Table 2). The data show clearly a decreasing trend for both δ 18 O and δ 13 C from inner to outer cortical layers. ...
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... calcite; out of which several scenarios could also work for the Kanaan cave pearls -e.g. inorganic precipitation from cave water, formation of destructive coatings, and/or formation of constructive envelopes. The role of bacteria in the genesis of the Kanaan cave is refuted based on: (1) the cave pearls were found in splash-pools where water Fig. 11. Graphical display of the oxygen isotopic equilibrium relationship between water, temperature of precipitation and calcite minerals (Woronick & Land, 1985). Estimation of the δ 18 O composition of the water from which the cave pearls precipitated for temperatures between 18 and 20°C. The bar on the horizontal axis represents the ...
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... Degassing of CO 2 may also result in a depletion in δ 13 C values (Given & Wilkinson, 1985), this is further supported by the trigonal crystalline pattern observed at the outer part of the pearls (see above). The approach of Woronick & Land (1985) was used in order to estimate the δ 18 O SMOW of the fluid from which the cave pearls precipitated (Fig. 11). The temperature was set between 18 and 20°C and the δ 18 O PDB of the calcite was measured between -5.33 and -4.94‰. This resulted in δ 18 O SMOW around -4.2‰. Note that the δ 18 O of the meteoric water in the eastern Mediterranean region ranges between -6 and -4‰ V-SMOW (Emery & Robinson, ...
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... is somehow supported by the corresponding lower δ 18 O values. Figure 12 shows two cut-faces of two distinct cave pearls and a sketch presenting a tentative model explaining the formation of the cave pearls and their related recrystallization. After the precipitation of the nucleus and impurity- rich, inner micrite cortical laminae, the surrounding spar laminae (length-fast calcite) were formed in water highly saturated with Ca with enhanced CO 2 degassing. ...
Citations
... Ford and Williams 2007;Parise and Lollino 2011). Researchers have mainly focused on describing karst cave forms (Hill and Forti 2007;Nader 2007;Onac and Forti 2011) or modelling underground geomorphology (Kaufmann 2009). De Waele et al. (2011) or Parise (2015a summarized natural hazards related to karst environment. ...
We conducted one of the first complex geomorphological investigations of underground abandoned slate mines in Czechia, Central Europe. Sixty types of subterranean geomorphic forms were described from 114 abandoned underground slate mines in the Nízký Jeseník Upland. The forms, evaluated according to their type, scale, frequency, and fragility, are independent of each other or embedded. Their cascades occur in large multilevel mines affected by fluvial and gravitational processes. Analysis of the microforms revealed mine pearls enriched with titanium, calcareous soda-straw stalactites, amorphous calcareous-sulphurous piles, and quartz veins. Forty-seven of the identified mines were affected by gravitational failures. Four-year measurements of cracks revealed both negligible oscillations and distinct displacement of rock blocks up to 4 mm. The range of described geomorphic forms together with identified cascades and measured crack displacement point to rich geodiversity and high dynamics within the abandoned mines. Compared to other subterranean geosystems, the geomorphology of abandoned underground slate mines remains poorly investigated, although knowledge of subterranean geomorphic systems is crucial for future natural evaluation, risk assessment, remediation, or tourist management of abandoned mining sites. The recent results are applicable to other types of abandoned mines in the world. However, we should expect new findings and investigation of as yet undescribed geomorphic forms.
... Geralmente possui diâmetro em torno de milímetros a poucos centímetros. São também conhecidas como pisoides e/ou ooides e têm sido descritas na literatura desde o início do século XX (Hess 1929, Baker & Frostik 1951, Black 1952, Donahui 1969, Jones & MacDonalds 1989, Hill & Forti 1996, Gradziòski 2001, Silva et al. 2003, Nader 2007, Meldim & Spilde 2018. Os pré-requisitos para a sua formação são a presença de um núcleo para o crescimento do grão, uma solução saturada a supersaturada em CaCO3 e água disponível no meio ambiente para o seu desenvolvimento (Gradziòski 2001). ...
The Lapa D' Água is one of dozens caves of the Lapa Grande State Park, in the municipality of Montes Claros, northern Minas Gerais. The cave was formed in limestones of the Lagoa do Jacaré Formation, middle floor of the Bambuí sequence, deposited on a platform dominated by storms and tidal currents. It has 1,234 meters of development in horizontal projection in a NW-SE meandering linear pattern, with 20 meters of depth. The floor of the hall near the entrance, in the first 70 meters of the cave, is largely occupied by large pisoid structures known as cave pearls. They are embedded and concreted into old travertine dams, and are exposed in natural erosion ridges and more recent excavations. The genesis of the giant pearls of Lapa D' Água of Montes Claros is not fully unraveled; a genetic model is proposed from morphological and paleohydrological aspects specific to the cave, where the pearls was formed by the precipitation of CaCO3 around seeds available within the travertine basins, from the saturated carbonate solutions under flowing conditions, that promotes rotation of the forming structures. Due to the abundance, atypical dimensions and potential for geochronological and paleoenvironmental studies, it is proposed that Lapa D' Água be considered a geosite of international scientific importance, according to the application of the quantitative evaluation method established in the GEOSSIT platform, of the Geological Survey of Brazil. According to the same application, the geosite also has potential educational and tourist use, with national relevance, and low risk of degradation, since it is located in a nature conservation unit of full protection, under controlled use.
... In addition to the layering, questions remain regarding the importance of microbial activity in the growth of cave pearls (Jones & MacDonald, 1989;Jones, 2009;Melim & Spilde, 2018) and other speleothems (Jones, 2011;Pacton et al., 2013). Early views of caves as sterile settings where microbes could be safely ignored have been replaced with a more nuanced awareness that microbes are likely important in some cave pearls, but not all cave pearls (Donahue, 1969;Jones & MacDonald, 1989;Nader, 2007;Jones, 2009;Gradziñski et al., 2012;Zak et al., 2013;Melim & Spilde, 2018). Research is still needed on the conditions that lead to more or less microbial involvement in cave pearls. ...
... Recrystallization, however, can also occur without changing the mineralogy. Recrystallization of calcite to calcite has been found in some natural cave pearls (Gradziñski & Radomski, 1967;Kirchmayer, 1969Kirchmayer, , 1987Nader, 2007;Melim & Spilde, 2011 but not in other cave pearls (Jones, 2009). Recrystallization has also been recognized, using careful geochemical analysis, in a coarsely crystalline calcite stalagmite without obvious fabric changes (Bajo et al., 2016;Frisia et al., 2018). ...
... Layering in cave pearls is often very complicated (Donahue, 1969;Nader, 2007;Jones, 2009;Melim & Spilde, 2018), but lack of time control makes understanding the origin of these intricacies difficult. Are the different layers due to climatic changes (Mackin & Coombs, 1945;Kirchmayer, 1969;Jones & MacDonald, 1989;Jones, 2009), or are smaller scale variations in local conditions responsible (Jones & Renaut, 1994;Melim & Spilde, 2011)? ...
Speleothems form layered archives of the climate and local cave conditions during their formation. The origin of layering in cave pearls, however, is not well‐understood. Cave pearls grown in two adjacent mine sites between 2006 and 2014 elucidate the complexity of speleothem growth and recrystallization. Site A cave pearls grew under an active drip, while Site B cave pearls grew in small rimstone‐dam pools that filled with reverse‐graded fitted pearls between about 2009 and 2014. Despite the variation in pool setting, all samples are layered in grey and/or brown laminations and dendrites. The order and number of these layers varies widely, even between pearls growing millimetres apart in the same pool. However, stable isotope values reflect homogenized local precipitation. The variability between adjacent samples supports control by very local factors within each pool, likely related to CO2 degassing at the water–air interface and water flow within the confined space of each pool. Recrystallization of calcite to calcite occurs resulting in triangular microspar patches and much less obvious bladed calcite. Laminations of brown or grey 1 to 5 µm calcite crystals recrystallize to bladed calcite up 100 µm long, all the while retaining a memory of the original layers in the form of ‘ghost’ layers, as revealed by gentle acid etching. Pearls at the top of rimstone‐dam pools grew faster than those just a few millimetres deeper, resulting in reverse grading. This model is applicable to reverse grading in marine and lacustrine pisolites. This study suggests cave pearls in active flow regimes (drips or currents) are similar and largely abiogenic, in contrast to other locations with less flow, where more biological input is common. Recrystallization of calcite to calcite proceeds not only to equant spar (classic Ostwald ripening), but also to bladed calcite. Thus, bladed calcite in speleothems needs to be carefully evaluated for recrystallization even when aragonite is absent.
... First, the force of crystallization is widely invoked in carbonates to physically move adjacent grains or matrix, creating space for crystals to grow while shallowly buried (Weyl 1959;Assereto and Kendall 1977;Wallace and Hood 2018). Force of crystallization is used to explain the formation of ''cave pearls,'' which develop millimeter-scale isopachous carbonate cements that fully encircle grains despite a stationary growth habit and contact with neighboring grains (Emmons 1928;Davidson and McKinstry 1931;Bathurst 1972;Nader 2007;Melim and Spilde 2018). These ''cave pearls'' can appear strikingly similar to ooids examined here. ...
In modern ooid-forming environments in the Caribbean, aerobic respiration of organic matter below the sediment–water interface drives an increase in pCO2 and a corresponding decrease in carbonate saturation state (Ω) that creates shallow sediment porewater that is neutral or slightly caustic to carbonate. The locus of ooid growth, therefore, is presumed to be in the water column during suspension, where supersaturation with respect to calcium carbonate is the norm. In the past, however, during conditions of low aqueous O2, high Ω, or low organic-matter input, the shallow sub-sediment marine burial environment was conducive to carbonate precipitation.
Here we present petrographic and electron probe microanalyzer (EPMA) data from exquisitely preserved oolites through time that suggests that some ancient ooids may have grown within the sediment pile. We propose that each increment of ooid cortical growth originated as incipient isopachous marine cement formed during shallow burial within migrating ooid dunes. After a period of burial (∼ weeks to months), ooids were remobilized and rounded during bedload transport.
This “bedform model” for ooid growth explains: 1) why ancient ooids are not limited by the precipitation–abrasion balance that appears to prohibit modern tangential Caribbean ooids from achieving grain sizes larger than coarse sand, 2) the radial crystal fabric that defines the internal structure of many ancient ooids, and 3) the first-order correlation of the abundance of large and giant ooids in the rock record to periods with predicted high porewater Ω. This model implies that photosynthetic microbes were unimportant for growth of large and giant ooid but it remains agnostic to the effect of other microbes. The physical and chemical milieu of modern marine ooid-forming environments is perhaps not the best analogue for ancient ooid-forming environments; this should be considered when using ancient ooids to reconstruct secular trends in ocean chemistry.
... Cave pearls are spheroidal or subprolate grains which are formed by concentric growth of calcium carbonate layers around a nucleus (e.g. Gradziñski and Radomski, 1967;Donahue, 1969;Nader, 2007;Jones, 2009;Melim and Spilde, 2018). In modern karst cave systems, they usually form in two types of settings: low energy shallow pools bordered by rimstone dams and high energy shallow splash pools (Jones and Kahle, 1986;Jones and MacDonald, 1989;Hill et al., 1997;Spilde, 2011, 2018). ...
To extend the range of materials that can be used to provide chronological constraint in archaeological and palaeontological settings, we explore the use of cave pearls that form in shallow pools. Here, we present U-series dating results of cave pearls found in cave sediments with mammal fossils collected from systematic excavations at the Diaozhongyan Cave (“DZY”), located in Guangxi Zhuang Autonomous Region, southern China. Similar to soda straw stalactites, cave pearls can be transported after formation and subsequently incorporated into sediments. Thus, the U-series ages of the outermost layers of cave pearls are expected to be older than their host sediments and associated archaeological and paleontological materials. In conjunction with U-series dating of mammal teeth, which can provide a reliable minimum age, U-series ages of cave pearls can provide a maximum age limit of the deposits. Thus, dating of the mammal teeth and cave pearls from DZY reasonably constrains the first occurrence of the DZY Ailuropoda-Stegodon fauna to a period between 205.6 ± 1.4 ka and 231.0 ± 12.8 ka. These age constraints agree well with previous estimates for the time range of the late Middle Pleistocene Ailuropoda-Stegodon fauna in southern China. We propose that greater attention should be paid to cave pearls, which are commonly found in cave deposits that were laid down at least in part due to fluvial activity, and can be used for U-series dating to better constrain the age of the associated cave deposits.
... In contrast with the spherulites, the shape of these aggregates is poorly rounded and their textures is cataclastic and lacks banding; thus, their genetic mechanism must be distinct from that of the spherulites. By contrast, spherulites are really similar to pisolite or cave pearls (Nader, 2007), related to vadose groundwater circulation or to oolite/pisolite deposits related to hydrothermal circulation (Sant'Anna et al., 2004;Wu et al., 2014). ...
... In addition, changes in mineralogy, with concurrent changes in fabric, also produce layering (e.g., aragonite or clays; this study). Complicating the issue, varying levels of recrystallization obscures depositional layers in some locations (Gradziñski and Radomski 1967;Donahue 1969;Kirchmayer 1969;Nader 2007; Melim and Spilde 2011, this study) but not others (Jones 2009, this study). Although time constraints are usually absent for cave samples, recrystallization in mines has been shown to occur in very short time spans of years (Kirchmayer 1969) or even months . ...
... While a number of studies have documented the presence of a microbial community (Cacchio et al. 2003(Cacchio et al. , 2004Baskar et al. 2005Baskar et al. , 2009Gradziñski et al. 2012;Ortiz et al. 2014), only a few have shown growth layers with a microbial signature (Jones 2009(Jones , 2011Pacton et al. 2013;this study). Cave pearls, like other speleothems, show a range of microbial involvement from nearly absent (Nader 2007;Melim and Spilde 2011;this study) to major contributors to laminae (Jones 2009; this study). However, the microbial community is not independent from the cave system or from climate factors. ...
Although long thought to be largely the result of physicochemical processes, speleothems are now recognized as potentially including a microbial component. Cave pearls, a type of speleothem, are coated grains that form in caves and mines. Three diverse cave pearl sites in Carlsbad Cavern, New Mexico, U.S.A., provide insight into physicochemical and microbial controls on cave pearl formation and, by analogy, other speleothems. Pearl growth beneath active drips in the classic pearl nests of The Rookery was largely abiologic with autochthonous nuclei coated by laminae of columnar low-Mg calcite (LMC) alternating with laminae of LMC, high-Mg calcite (HMC), and aragonite. Changing mineralogy likely reflects a changing Mg/Ca ratio during evolution of the pool water during mineral precipitation, degassing, and evaporation. Pearls in Lower Cave, in contrast, grew on detrital nuclei in shallow pools from water that slowly evolved while flowing across a large, relatively flat cave floor. The pearl layers are variable amounts of LMC, authigenic clay mixed with biofilm (EPS), and aragonite with episodes of erosion and truncation. Here, abiologic precipitation dominated most precipitation but episodes of biofilm development aided precipitation of authigenic Mg clay, likely sepiolite. The third location, Secondary Stream Passage, had faster throughput of water, such that only LMC precipitated. Periodic influx of detrital Mg-Al clay, likely a trioctahedral smectite, supported a microbial community, including abundant reticulated microbial filaments. Combining these results with previous work on cave pearls allows development of a unified model for cave-pearl formation. Required elements include 1) saturated water entering a cave (present in most caves); 2) an available detrital or autochthonous crystal to act as a nucleus (again, readily available); 3) the water must enter into a relatively flat floor in a cave or mine, either as drips from the ceiling or as water slowly flowing across the floor; 4) a shallow pool must form, generally , 3 cm but up to 6 cm deep to allow agitation of the pearls; 5) conditions in the pool must change so as to create layers; and 6) additional chemicals or particles may enter with the groundwater to feed a microbial community and/or add detrital or authigenic clays to the cave pearls. It appears that the most restrictive control is the slope of the cave floor: pearls do not occur without at least a small area of nearly horizontal floor. In addition, the documentation of microbial and authigenic clay laminae in cave pearls suggest any dark and/or organic-rich layer in a speleothem should be thoroughly evaluated for possible authigenic and/or microbial origins and not be assumed to represent detrital, washed-in material.
... En los dos sistemas estudiados, el aragonito es el mineral principal (>80%) en las zonas proximales y disminuye distalmente, conforme aumenta la proporción de calcita. Los principales factores que favorecen la precipitación de aragonito en lugar de calcita son (a) temperaturas superiores a 40-45 ˚C (Jones y Renaut, 2010), o (b) relaciones Mg/Ca superiores a 1 (Nader, 2007). ...
Resumen: En este trabajo se compara un travertino de un sistema activo (El Saladillo, Murcia) con uno fósil (Azuaje, Las Palmas) posiblemente Holoceno. Los dos presentan facies y mineralogías similares. En ambos el mineral dominante en las zonas cercanas a las surgencias es el aragonito (agregados esferulíticos) que disminuye distalmente, a favor de la calcita (morfologías trigonales). Las facies características son: shrubs, burbujas calcificadas, costras laminares, granos con cubiertas y micríticas con diatomeas. En conjunto ambos depósitos corresponden a un sistema de pozas y cascadas. El fuerte desequilibrio químico que caracteriza la zona de surgencia y su tendencia a equilibrarse aguas abajo son los responsables de la mineralogía, las facies, y de la variación de ambas a lo largo del sistema. Palabras clave: aragonito, esferulitos, temperatura, calcita. Abstract: An active travertine (El Saladillo, Murcia) and a fossil travertine (Azuaje, Las Palmas) have been compared in the present work. Both travertines show similar facies and mineralogy despite their formed under different geological settings (sedimentary and volcanic respectively). Aragonite, usually as spherulitic crystal aggregates, is the dominant mineral phase close to the spring. Aragonite content diminishes distally to spring, whereas trigonal calcite crystals become to be the dominant mineral phase. Characteristic facies found in both deposits are: shrubs, coated bubbles, laminated crusts, coated grains, and micrite deposits containing abundant diatoms. These deposits correspond to spring-fed pool-cascade systems. Strong chemical disequilibrium close to spring and downflow trend to chemical equilibrium control facies, mineralogy, and their variations along the system.
... In addition to the layering, questions remain regarding the importance of microbial activity in the growth of cave pearls (Jones & MacDonald, 1989;Jones, 2009;Melim & Spilde, 2018) and other speleothems (Jones, 2011;Pacton et al., 2013). Early views of caves as sterile settings where microbes could be safely ignored have been replaced with a more nuanced awareness that microbes are likely important in some cave pearls, but not all cave pearls (Donahue, 1969;Jones & MacDonald, 1989;Nader, 2007;Jones, 2009;Gradziñski et al., 2012;Zak et al., 2013;Melim & Spilde, 2018). Research is still needed on the conditions that lead to more or less microbial involvement in cave pearls. ...
... Recrystallization, however, can also occur without changing the mineralogy. Recrystallization of calcite to calcite has been found in some natural cave pearls (Gradziñski & Radomski, 1967;Kirchmayer, 1969Kirchmayer, , 1987Nader, 2007;Melim & Spilde, 2011 but not in other cave pearls (Jones, 2009). Recrystallization has also been recognized, using careful geochemical analysis, in a coarsely crystalline calcite stalagmite without obvious fabric changes (Bajo et al., 2016;Frisia et al., 2018). ...
... Layering in cave pearls is often very complicated (Donahue, 1969;Nader, 2007;Jones, 2009;Melim & Spilde, 2018), but lack of time control makes understanding the origin of these intricacies difficult. Are the different layers due to climatic changes (Mackin & Coombs, 1945;Kirchmayer, 1969;Jones & MacDonald, 1989;Jones, 2009), or are smaller scale variations in local conditions responsible (Jones & Renaut, 1994;Melim & Spilde, 2011)? ...
Cave pearls are coated grains that form in caves and mines. Cave pearls forming in an underground limestone mine, Quincy, Illinois were monitored from 2005-2014. A classic splash pool (“pearl nest”) accumulated >20 cm of pearls and pool spar during this period, while a new area filled shallow rimstone dam pools with 1-3 cm cave pearls between 2008 and 2014. Regardless of pool, cave pearls are layered with four main fabrics: 1) dendrite layers of porous branching crystals; 2) v. dark brown to pale tan laminated layers; 3) microspar to fine bladed spar layers with poorly defined lamina; and 4) coarse radiating bladed spar. XRD of pearl components (N = 25) show only low-magnesium calcite (LMC). Stable isotope values (N = 18) of these components show no differences (δ13C = -9.7± 0.6; δ18O = -5.7 ± 0.2).
Petrography combined with SEM examination of etched thin sections and chips reveals multiple recrystallization styles. Previous work showed recrystallization of laminated layers by cross-cutting microspar advancing as reaction fronts starting in dendrite layers. New work has shown that the brown to tan laminated layers are also internally recrystallized. The darkest laminae are composed of 1 µm crystals defining 1-3 µm laminae. While some dark laminae go all the way around a pearl, more commonly they transition laterally to progressively lighter layers with darkest laminae preferentially on outside corners. In SEM, the petrographic transition to lighter tan is matched by a gradual increase in crystal size from ≤1 µm to >10 µm. The 1-3 µm laminae are destroyed in the process, but often can be traced in SEM as etch lines within coarser spar. The microspar to fine bladed spar layers may also be recrystallized but conclusive proof is elusive. Discontinuous laminae may be remnants of better defined layers, but the transition is not preserved.
While recrystallization is well known from ancient carbonates, it is rarely identified in modern carbonates. Here cave pearls only a few years old are recrystallizing without changing mineralogy (LMC to LMC) or apparently water chemistry (isotopic values are constant). The only obvious change is crystal size, suggesting Ostwald ripening. Similar processes are likely operating in modern carbonate muds.
... Their origin is debatable. Some authors consider that they are due to microbial activity (Chafetz and Meredith, 1983;Jones, 2009;Jones and Renaut, 2010), whereas an abiotic origin of precipitation from supersaturated waters in pools has also been invoked (Nader, 2007). ...
The Azuaje travertines in the north of Gran Canary Island crop out in the Azuaje Gorge, which is incised into Miocene volcanic breccias of the Roque Nublo Formation. This travertine is interesting because of the scarcity of travertines in the Canary Islands and its close relationship with recent volcanic events. Part of the travertine overlies a lava flow, dated at 2420 ± 40 years BP. The travertine is composed mainly of aragonite in both perched systems on the gorge walls and in gorge bottom deposits parallel to the present stream. Perched systems include deposits from the feeder conduits within the Roque Nublo Formation that spilled out through waterfalls and over barriers. The gorge (valley) bottom system includes barrier and pool deposits. The main laminated facies are composed mostly of large fibrous aragonite crystals, while there are also common micritic and porous microfabrics. Shrubs, coated grains, coated bubbles and rafts are present in many of the deposits. Detailed study of the microfacies shows the presence of sparsely distributed biogenic features. The δ13C values are between + 4.0 and + 11.0‰, and the δ18O values range between − 11.0 and − 2.0‰ VPDB. These δ13C values lie within the range of those of thermogene travertines fed by thermal waters that cooled downstream, as indicated by the increase of the carbon and oxygen isotope values in that direction. The common occurrence of fibrous radial fabrics is interpreted to be due to disequilibrium conditions during aragonite precipitation. Disequilibrium was likely caused by rapid CO2 degassing of the thermal waters that led to a rapid increase in the degree of aragonite saturation. Thus, the morphology of the aragonite crystals and the isotopic composition indicate that the formation of the Azuaje travertine was mostly due to abiogenic processes induced by rapid degassing of thermal waters, linked to the presence of a recent lava flow within the Gorge. In short, the Azuaje travertine shows the important role of volcanic activity in travertine deposition, in the facies distribution as well as in the geochemical signatures of the deposits, and so can be used as a recent analogue for ancient travertine deposits in volcanic settings.
