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Speleology in Kazakhstan

Shakalov on 04 Jul, 2018
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

Speleology in Kazakhstan

Shakalov on 04 Jul, 2018
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

Speleology in Kazakhstan

Shakalov on 11 Jul, 2012
Hello everyone!   I pleased to invite you to the official site of Central Asian Karstic-Speleological commission ("Kaspeko")   There, we regularly publish reports about our expeditions, articles and reports on speleotopics, lecture course for instructors, photos etc. ...

New publications on hypogene speleogenesis

Klimchouk on 26 Mar, 2012
Dear Colleagues, This is to draw your attention to several recent publications added to KarstBase, relevant to hypogenic karst/speleogenesis: Corrosion of limestone tablets in sulfidic ground-water: measurements and speleogenetic implications Galdenzi,

The deepest terrestrial animal

Klimchouk on 23 Feb, 2012
A recent publication of Spanish researchers describes the biology of Krubera Cave, including the deepest terrestrial animal ever found: Jordana, Rafael; Baquero, Enrique; Reboleira, Sofía and Sendra, Alberto. ...

Caves - landscapes without light

akop on 05 Feb, 2012
Exhibition dedicated to caves is taking place in the Vienna Natural History Museum   The exhibition at the Natural History Museum presents the surprising variety of caves and cave formations such as stalactites and various crystals. ...

Did you know?

That dissolution zone is a laterally extensive zone where extensive dissolution of bedrock has occurred.?

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Geochemical and mineralogical fingerprints to distinguish the exploited ferruginous mineralisations of Grotta della Monaca (Calabria, Italy), Dimuccio, L.A.; Rodrigues, N.; Larocca, F.; Pratas, J.; Amado, A.M.; Batista de Carvalho, L.A.
Karst environment, Culver D.C.
Mushroom Speleothems: Stromatolites That Formed in the Absence of Phototrophs, Bontognali, Tomaso R.R.; D’Angeli Ilenia M.; Tisato, Nicola; Vasconcelos, Crisogono; Bernasconi, Stefano M.; Gonzales, Esteban R. G.; De Waele, Jo
Calculating flux to predict future cave radon concentrations, Rowberry, Matt; Marti, Xavi; Frontera, Carlos; Van De Wiel, Marco; Briestensky, Milos
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Your search for saturation (Keyword) returned 131 results for the whole karstbase:
Showing 16 to 30 of 131
Lithification of peritidal carbonates by continental brines at Fisherman Bay, South Australia, to form a megapolygon/spelean limestone association, 1982, Ferguson J, Burne Rv, Chambers La,
Lithification, which commenced less than 3000 yrs BP is still active, and has formed a cavernous limestone containing megapolygons, tepees, and speleothems including pisoliths, floe aragonite, and aragonite pool deposits. The emerging waters evolved from low alkalinity waters of Pleistocene sand and clay coastal plain aquifers which passed through an underlying Tertiare marine carbonate aquifer, have high P CO2 , total carbonate, Ca, and sulfate concentrations. They are close to saturation with respect to aragonite, and their mMg (super 2) /mCa (super 2) ratios approach or exceed the critical aragonite precipitation value. Features which diagnose ancient examples of this process: primary aragonitic cements with high mSr (super 2) /mCa (super 2) values; nonmarine delta 34 S values in gypsum; two superimposed networks of surface polygons, one delineated by extensional boundaries, the other by tepees; high-water vadose-zone isopachous grain cements; interconnected, speleothem-lined cavities; and the presence of evaporites only in surface sediments. Possible ancient examples are recognized in West Texas, Lombardy, and the Atlas Mountains. The areal extent of each of these deposits suggests that the process may be a geologically important feature, and its products may be diagnostic of semi-arid or arid-zone paralic sedimentation.--Modified journal abstract

A Preliminary Survey of Water Chemistry in the Limestone of the Buchan Area Under Low Flow Conditions, 1984, Ellaway Mark, Finlayson Brian

Water samples from selected sites in the Buchan area were collected on two different occasions (survey 1 and survey 2) in an preliminary attempt to characterise the samples taken in terms of chemical composition. Chemical constituents such as Ca++, Mg++, and titration alkalinity (as mg/l CaCO3) varied considerably and ranged from 9.0 - 187.0 mg/l, 2.5 - 43.3 mg/l and 27 - 417 mg/l (survey 1) and 3.5 - 188.7 mg/l, 3.5 - 40.0 mg/l and 44 - 424 mg/l (survey 2) respectively. This range in values is attributed to the differing lithology of the sample sites chosen and reflects the geological control on water chemistry of karst landscapes. A computer program for determining equilibrium speciation of aqueous solutions was used to calculate partial pressure of carbon dioxide and saturation indices with respect to calcite and dolomite.


Deposition of Tufa on Ryans and Stockyard Creeks, Chillagoe Karst, North Queensland: The Role of Evaporation, 1987, Dunkerley, D. L.

A spring which feeds Ryans and Stockyard Creeks west of Cillagoe, was examined in order to understand the circumstances producing extensive deposits of tufa in the stream channels. The spring water was found to be of considerable hardness (300 ppm total carbonates) and to emerge only very slightly supersaturated with respect to calcium carbonate, but undersaturated with respect to dolomite. Both saturation levels rose very rapidly during the first 150 m of subaerial flow, as did pH and water temperature. In contrast to the reported behaviour of other limestone springs, carbonate hardness at this site does not decrease monotonically downstream, but rather locally undergoes significant increases. In particular, magnesium hardness at 1 km downstream is more than 4 times its value at the spring. These phenomena are explained in terms of evaporative concentration of the dissolved carbonates and in terms of possible chemical changes associated with the mixture of waters having contrasting characteristics at channel and pool sites along the streams.


An Investigation of the Mechanisms of Calcium Carbonate Precipitation on Straw Speleothems in Selected Karst Caves - Buchan, Victoria., 1988, Canning, E.

The relative significance of straw speleothem growth from evaporation and from CO2 degassing was determined in Lilli-Pilli and Moons Caves (Buchan, Victoria) from a seven-month study of cave climate and water chemistry. The relative importance of these two mechanisms was inferred from the calculation of the straw growth rates according to a degassing model and an evaporation model. The modelled straw growth rates from the carbon dioxide degassing model were on hundred to one thousand times those attributable to evaporation. A third model was used to calculate straw growth rates from the overall supersaturation of the water. Growth rates were found to be within the range of 0.01 to 0.07mm per annum.


ORIGIN AND MORPHOLOGY OF LIMESTONE CAVES, 1991, Palmer A. N. ,
Limestone caves form along ground-water paths of greatest discharge and solutional aggressiveness. Flow routes that acquire increasing discharge accelerate in growth, while others languish with negligible growth. As discharge increases, a maximum rate of wall retreat is approached, typically about 0.01-0.1 cm/yr, determined by chemical kinetics but nearly unaffected by further increase in discharge. The time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width, discharge, gradient, and P(CO2). Most caves require 10(4) - 10(5) yr to reach traversable size. Their patterns depend on the mode of ground-water recharge. Sinkhole recharge forms branching caves with tributaries that join downstream as higher-order passages. Maze caves form where (1) steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or (2) discharge or renewal of undersaturation is uniform along many alternate routes. Flood water can form angular networks in fractured rock, anastomotic mazes along low-angle partings, or spongework where intergranular pores are dominant. Diffuse recharge also forms networks and spongework, often aided by mixing of chemically different waters. Ramiform caves, with sequential outward branches, are formed mainly by rising thermal or H2S-rich water. Dissolution rates in cooling water increase with discharge, CO2 content, temperature, and thermal gradient, but only at thermal gradients of more than 0.01-degrees-C/m can normal ground-water CO2 form caves without the aid of hypogenic acids or mixing. Artesian flow has no inherent tendency to form maze caves. Geologic structure and stratigraphy influence cave orientation and extent, but alone they do not determine branch-work versus maze character

DISSOLUTION OF ARAGONITE-STRONTIANITE SOLID-SOLUTIONS IN NONSTOICHIOMETRIC SR(HCO3)2-CA(HCO3)2-CO2-H2O SOLUTIONS, 1992, Plummer L. N. , Busenberg E. , Glynn P. D. , Blum A. E. ,
Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO2-saturated nonstoichiometric solutions of Sr(HCO3)2 and Ca(HCO3)2 at 25-degrees-C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in Ca(HCO3)2 solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In Sr(HCO3)2 solutions the reactions usually become incongruent, precipitating a Sr-rich phase before reaching stoichiometric saturation. Dissolution of mechanical mixtures of solids approaches stoichiometric saturation with respect to the least stable solid in the mixture. Surface uptake from subsaturated bulk solutions was observed in the initial minutes of dissolution. This surficial phase is 0-10 atomic layers thick in Sr(HCO3)2 solutions and 0-4 layers thick in Ca(HCO3)2 solutions, and subsequently dissolves and/or recrystallizes, usually within 6 min of reaction. The initial transient surface precipitation (recrystallization) process is followed by congruent dissolution of the original solid which proceeds to stoichiometric saturation, or until the precipitation of a more stable Sr-rich solid. The compositions of secondary precipitates do not correspond to thermodynamic equilibrium or stoichiometric saturation states. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of solid solutions on surfaces of aragonite and strontianite single crystals immersed in Sr(HCO3)2 and Ca(HCO3)2 solutions, respectively. In Sr(HCO3)2 solutions, the XPS signal from the outer approximately 60 angstrom on aragonite indicates a composition of 16 mol% SrCO3 after only 2 min of contact, and 14-18 mol% SrCO3 after 3 weeks of contact. The strontianite surface averages approximately 22 mol% CaCO3 after 2 min of contact with Ca(HCO3)2 solution, and is 34-39 mol% CaCO3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer approximately 25 angstrom (as much as 26 mol% SrCO3 on aragonite and 44 mol% CaCO3 on strontianite). The results indicate rapid formation of a solid-solution surface phase from subsaturated aqueous solutions. The surface phase continually adjusts in composition in response to changes in composition of the bulk fluid as net dissolution proceeds. Dissolution rates of the endmembers are greatly reduced in nonstoichiometric solutions relative to dissolution rates observed in stoichiometric solutions. All solids dissolve more slowly in solutions spiked with the least soluble component ((Sr(HCO3)2) than in solutions spiked with the more soluble component (Ca(HCO3)2), an effect that becomes increasingly significant as stoichiometric saturation is approached. It is proposed that the formation of a nonstoichiometric surface reactive zone significantly decreases dissolution rates

EXPLORATION AND DEVELOPMENT OF GROUND-WATER FROM THE STONE FOREST KARST AQUIFERS OF SOUTH CHINA, 1992, Huntoon P. W. ,
Stone forest aquifers are the most widely exploited sources for ground water in the vast south China karst belt. These aquifers occupy a thin epikarst zone that has been infilled with clastic sediments. The aquifers are characterized by large lateral permeabilities and small reservoir capacities owing to their thinness. The carbonate rocks which comprise the framework for the aquifers are usually buried under the karst plains and large karst depressions where development is desired. The stone forest aquifer exploration procedure must first locate saturated zones. Second, those parts of the saturated zone having the greatest dissolution porosity must be identified because the infilled dissolution voids contain the water. The best indicators of saturation include the combination of low topography and the presence of active karst features such as springs, karst windows (natural openings exposing the water table), and live surface streams. These elements are readily observed on intermediate scale (1:20,000) aerial photography. The depth and degree of carbonate dissolution porosity is a function of several geologic and hydrologic factors including carbonate rock type, carbonate purity, fracture density, specific discharge, age of the circulation system, etc. These variables cannot be measured directly because the carbonate rocks are usually buried under a thin mantle of clastic sediments. However, if it is recognized that the ground-water system has already exploited the most favorable geology and that dissolution is an ongoing process, a simple indirect method can be used to identify the areas having the greatest porosity. The presence of karst depressions and recent sinkholes are indicative of the most intensely karstified and hydraulically active parts of the epikarst zone. Mapping of these surface features from stereo aerial photography is a simple geomorphology exercise that can be used to directly identify the most favorable well sites. Current well construction practices in the south China karst belt involve both dug and drilled wells. Dug wells are preferred in many locations owing to both cost-effectiveness associated with cheap labor and lack of available drilling equipment. The dug wells look and function identically to karst windows and thus conform to timeless water use traditions in the region

Carbonate chemistry of surface waters in a temperate karst region: the southern Yorkshire Dales, UK, 1992, Pentecost Allan,
A detailed study of surface water chemistry is described from an important limestone region in northern England. Major ions and pH were determined for 485 sites (springs, seeps, streams, rivers and lakes) during summertime. The saturation state of the waters with respect to calcite was determined as the calcite saturation ratio ([Omega]). An unexpectedly large number of samples were found to be supersaturated (65.5% of the 268 km of watercourses surveyed). As a consequence, several streams entering major cave systems were incapable of further limestone solution, at least during periods of low flow. Many waters were supersaturated from their source and some deposited travertine. A significant negative correlation was found between spring discharge and both ([Omega]) and pH. Supersaturation was caused primarily by atmospheric degassing, with some contribution from aquatic plant photosynthesis.The median total dissolved inorganic carbon and Ca concentrations were 2.49 and 1.35 millimoles 1-1 respectively. Calcium originated exclusively from limestone, and carbon dioxide mainly from the soil and dissolved limestone. South facing catchments provided springwaters with significantly higher levels of TDIC and Ca when compared with north facing catchments. The study suggests that acid rain made a measurable contribution to limestone dissolution.Carboniferous limestone denudation rates were estimated as 54 to 63 m3 km-2 a-1 (54 to 63 mm 1000 years-1). About 50% of the Mg came from limestone and the remainder, together with most K, Na, SO4 and Cl from precipitation.Concentrations of dissolved nutrients were low, medians for NO3, NH4, total PO4 and SiO3 were 24 [mu]mol, 1.4 [mu]mol, 0.64 [mu]mol and 15.5 [mu]mol 1-1 respectively. The concentration of a further 23 trace elements was determined

PALUSTRINE CARBONATES AND THE FLORIDA EVERGLADES - TOWARDS AN EXPOSURE INDEX FOR THE FRESH-WATER ENVIRONMENT, 1992, Platt N. H. , Wright V. P. ,
Palustrine carbonates are shallow fresh-water deposits showing evidence of subaqueous deposition and subaerial exposure. These facies are common in the geological record. The intensity of modification is highly variable depending on the climate and the length of emergence. Palustrine limestones have previously been interpreted as marginal lacustrine deposits from fluctuating, low-salinity carbonate lakes, but several problems remain with existing facies models: 1) palustrine carbonates possess a lacustrine biota but commonly display fabrics similar to those of calcretes and peritidal carbonates; 2) the co-occurrence of calcrete horizons and karst-like cavities is somewhat unusual and appears to indicate contemporaneous carbonate precipitation and dissolution in the vadose zone; 3) the dominance of gray colors indicates water-saturation, apparently inconsistent with the evidence for strong desiccation overprint; 4) profundal lake deposits are generally absent from palustrine sequences, and sublittoral facies commonly make up only a small proportion of total thicknesses; 5) no good modem analogue has been identified for the palustrine environment. Analogy with the Florida Everglades suggests a re-interpretation of palustrine limestones, not as pedogenically modified lake margin facies but as the deposits of extensive, very shallow carbonate marshes. The distribution of environments in the Everglades is determined by the local hydrology, reflecting the control of seasonal water-level fluctuations and topography. Climate and topography were the main controls on deposition of ancient palustrine carbonates. As in peritidal sequences, aggradational cycles are capped by a range of lithologies (evaporites, desiccation and microkarst breccias, calcretes, lignite or coal horizons etc.), permitting interpretation of the climate. Careful analysis of lateral facies variations may permit reconstruction of subtle topography. Consideration of the Florida Everglades as a modem analogue for the palustrine environment has suggested the development of an exposure index for fresh-water carbonates

MICROBIAL DECOMPOSITION OF ELM AND OAK LEAVES IN A KARST AQUIFER, 1993, Eichem Ac, Dodds Wk, Tate Cm, Edler C,
Dry Chinquapin oak (Quercus macrocarpa) and American elm (Ulmus americana) leaves were placed in four microcosms fed by groundwater springs to monitor changes in dry mass, ash-free dry mass, and microbial activity over a 35-day period. Oxygen microelectrodes were used to measure microbial activity and to estimate millimeter-scale heterogeneity in that activity. Oak leaves lost mass more slowly than elm leaves. Generally, there was a decrease in total dry weight over the first 14 days, after which total dry weight began to increase. However, there were consistent decreases in ash-free dry mass over the entire incubation period, suggesting that the material remaining after initial leaf decomposition trapped inorganic particles. Microbial activity was higher on elm leaves than on oak leaves, with peak activity occurring at 6 and 27 days, respectively. The level of oxygen saturation on the bottom surface of an elm leaf ranged between 0 and 75% within a 30-mm2 area. This spatial heterogeneity in O2 saturation disappeared when the water velocity increased from 0 to 6 cm s-1. Our results suggest that as leaves enter the groundwater, they decompose and provide substrate for microorganisms. The rate of decomposition depends on leaf type, small-scale variations in microbial activity, water velocity, and the length of submersion time. During the initial stages of decomposition, anoxic microzones are formed that could potentially be important to the biogeochemistry of the otherwise oxic aquifer

GROUNDWATER GEOCHEMISTRY OF THE CARBONATE KARST AQUIFER, SOUTH-CENTRAL KENTUCKY, USA, 1993, Hess J. W. , White W. B. ,
Analyses of 441 water samples from 15 sample sites, mainly springs and sinking creeks in the southcentral Kentucky karst, were used to determine hardness, P(CO2), and state of saturation with respect to calcite and dolomite. Most of the waters are undersaturated with respect to calcite and more undersaturated with respect to dolomite, in agreement with recent kinetic models. Time series data revealed chemical fluctuations on both weekly and seasonal time scales. Much of the short-term variation and some of the seasonal variation in the hardness and saturation index parameters can be accounted for by dilution effects from storm and seasonal runoff. Seasonal cycles in CO2 partial pressure arise from a dependence of soil CO2 on temperature and the growing season. Waters from different locations in the aquifer system are chemically distinct and fit into the concept of a hydrochemical facies

Hydrology and denudation rates of halite karst, 1994, Frumkin A,
Salt karst terrains exist mainly in arid climates where rock salt outcrops may escape complete destruction by dissolution. Such is the case with Mount Sedom, on the SW shore of the Dead Sea, one of the most arid parts of Israel. Many small catchments developed over the relatively insoluble cap rock which overlies the highly soluble rock salt. The catchments were surveyed and classified. Some 57% of the surface area is drained by an underground karst system. Water samples from various points in the system were analysed, and water development was inferred. Waters in cave conduits do not reach saturation during flood flow, unless the water is ponded for at least several hours. Based on the available evidence, regional karst denudation is tentatively estimated to be about 0.5-0.75 mm year-1, occurring mainly within the rock salt

HYDRODYNAMIC CONTROL OF INORGANIC CALCITE PRECIPITATION IN HUANGLONG RAVINE, CHINA - FIELD-MEASUREMENTS AND THEORETICAL PREDICTION OF DEPOSITION RATES, 1995, Liu Z. H. , Svensson U. , Dreybrodt W. , Yuan D. X. , Buhmann D. ,
Hydrochemical and hydrodynamical investigations are presented to explain tufa deposition rates along the flow path of the Huanglong Ravine, located in northwestern Sichuan province, China, on an altitude of about 3400 m asl. Due to outgassing of CO2 the mainly spring-fed stream exhibits, along a valley of 3.5 km, calcite precipitation rates up to a few mm/year. We have carried out in situ experiments to measure calcite deposition rates at rimstone dams, inside of pools and in the stream-bed. Simultaneously, the downstream evolution of water chemistry was investigated at nine locations with respect to Ca2 Mg2, Na, Cl-, SO42-, and alkalinity. Temperature, pH, and conductivity were measured in situ, while total hardness, Ca-T, and alkalinity have been determined immediately after sampling, performing standard titration methods. The water turned out to be of an almost pure Ca-Mg-HCO3 type. The degassing of CO2 causes high supersaturation with respect to calcite and due to calcite precipitation the Ca2 concentration decreases from 6 . 10(-3) mole/l upstream down to 2.5 . 10(-3) mole/l at the lower course. Small rectangular shaped tablets of pure marble were mounted under different flow regimes, i.e., at the dam sites with fast water flow as well as inside pools with still water. After the substrate samples had stayed in the water for a period of a few days, the deposition rates were measured by weight increase, up to several tens of milligrams. Although there were no differences in hydrochemistry, deposition rates in fast flowing water were higher by as much as a factor of four compared to still water, indicating a strong influence of hydrodynamics. While upstream rates amounted up to 5 mm/year, lower rates of about 1 mm/year were observed downstream. Inspection of the marble substrate surfaces by EDAX and SEM (scanning electron microscope) revealed authigeneously grown calcite crystals of about 10 mu m. Their shape and habit are indicative of a chemically controlled inorganic origin. By applying a mass transfer model for calcite precipitation taking into account the reaction rates at the surface given by Plummer et al. (1978), slow conversion of CO2 into H and HCO3-, and diffusional mass transport across a diffusion boundary layer, we have calculated the deposition rates from the hydrochemistry of the corresponding locations. The calculated rates agree within a factor of two with the experimental results. Our findings confirm former conclusions with respect to fast flow conditions: reasonable rates of calcite precipitation can be estimated in reducing the PWP-rate calculated from the chemical composition of the water by a factor of about ten, thus correcting for the influence of the diffusion boundary layer

HYDROGEOCHEMISTRY OF GRAND-CAYMAN, BRITISH-WEST-INDIES - IMPLICATIONS FOR CARBONATE DIAGENETIC STUDIES, 1995, Ng K. C. , Jones B. ,
Groundwater in the dolostone aquifers of the Bluff Group (Oligocene-Miocene) on Grand Cayman is divided into fresh, lightly and highly brackish, and saline (Type I and II) zones according to chemical characteristics that were determined during a 3 year (1985-1988) monitoring program. Brackish and Type I saline waters display the greatest variation in chemical properties whereas the Type II saline water has the most stable chemical characteristics. Most groundwaters from these dolostone aquifers are thermodynamically capable of precipitating calcite and/or dolomite. The saturation indices for these minerals, however, vary through time and space even in the context of small water lens. Simple mixing of fresh and sea water cannot explain the chemistry of the water found in the joint and karst controlled dolostone aquifers of Grand Cayman. Deviation from a simple mixing model is due to variations caused by tidal fluctuation, the rate of rain water recharge, influx of Ca-rich groundwater from the surrounding limestone aquifers, influx of CO2-rich surface water from sinkholes and swamps, and water-rock interactions (dissolution and precipitation of calcite and dolomite). Sustained groundwater abstraction from a lens can significantly alter the hydrochemistry of the water lens. This suggests that hydrochemical characterization of small fresh water lenses, like those on Grand Cayman, cannot be based on spot or short-term sampling. Interpretation of such fluids in terms of calcite-dolomite precipitation and/or dissolution must be treated with caution if the data base has not been derived from long-term monitoring

Geochemistry of submarine warm springs in the limestone cavern of Grotta Azzurra, Capo Palinuro, Italy: evidence for mixing-zone dolomitisation, 1996, Stuben Doris, Sedwick Peter, Colantoni Paolo,
Subtidal springs in and around the submarine limestone cavern of Grotta Azzurra, at Capo Palinuro, Italy, discharge fluids which are warm (-, Na and Mg2, and enriched in Si, alkalinity, Ca2, Sr2, Mn, NH4, PO43- and H2S, relative to surrounding seawater. The compositions of the warm fluid samples collected in and around the cave define mixing lines which suggest dilution of a single thermal fluid (T >= 23[deg]C) by cool overlying seawater (T= 17-17.6[deg]C). The chemical data suggest that the proposed thermal fluid contains two components, one derived from seawater ( 10%). Excess Si, alkalinity, Ca2, Sr2 and Mn relative to seawater are likely derived from the groundwater component or dissolution/hydrothermal alteration of the host rocks. Magnesium has been removed from the seawater component in exchange for Ca2, due to dolomitisation of the limestone and/or hydrothermal alteration reactions. Saturation-state calculations suggest that the vented fluids are near saturation with respect to calcite and supersaturated with respect to dolomite. This and the presence of dolomite in the host rocks and cave-floor sediments suggest that 'mixing-zone' dolomitisation of the limestones is occurring, perhaps kinetically assisted by elevated temperature and/or bacterial mediation in the reducing subseafloor zone. One possible 'end-member' condition is considered for the thermal fluid -- zero-Mg -- which suggests an end-member temperature of 50.5[deg]C and a fluid composition derived from ~ 38% seawater and ~ 62% groundwater. The heat source for the circulating fluids is uncertain, but may involve warm underlying igneous rocks or heating via the geothermal gradient. A continuous in-situ record of vent-fluid temperature, salinity, pH and O2 concentration collected within the cavern is consistent with our interpretation of the fluid origin, and suggests that tidal forcing affects circulation and venting of the warm fluids

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