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Recent investigations of drinking water quality related to the spring Mrzlek near Solkan, Slovenia are described. Multielemental analyses of 66 elements and anions such as nitrate, nitrite, sulphate, chloride, phosphate, bromide and fluoride in water from the spring Mrzlek and the river Soča, as well as determination of trihalomethanes in chlorinated water, were carried out to reveal eventual impacts of environmental pollution on the quality of drinking water from spring Mrzlek. It was observed that the pollution of the river Soča with heavy metals is recently decreasing, while the concentrations of trihalomethanes in drinking water are relatively low and have not increased during the last five years. At present the quality of drinking water from the spring Mrzlek meets all the standards. Higher concentrations of nitrate in the spring, however, indicate potential pollution from farming on the Banjšice plateau. In general, quite similar concentrations of most elements and anions were observed in the spring Mrzlek and the river Soča. Higher concentrations of Ca, Fe, Zn, nitrate and chloride were observed in the spring, while concentrations of Mn, Mg, Ba, As, and sulphate were significantly higher in the river.
The Mississippian Madison Formation contains abundant fracture zones and breccias that are hydrothermal in origin based on their morphology, distribution, and geochemical signature. The hydrothermal activity is related to crustal shortening during the Laramide orogeny. Brecciation is accompanied by dedolomitization, late-stage calcite precipitation, and porosity occlusion, especially in outcrop dolomites. The tectonic-hydrothermal late-stage calcite reduces permeability in outcrops and, potentially, high-quality subsurface reservoir rocks of the subsurface Madison Formation, Bighorn Basin. The reduction of permeability and porosity is increased along the margins of the Bighorn Basin but not predictable at outcrop scale. The destruction of porosity and permeability by hydrothermal activity in the Madison Formation is unique in comparison to studies that document enhanced porosity and permeability and invoke hydrothermal dolomitization models. Hydrothermal breccias from the Owl Creek thrust sheet are classified into four categories based on fracture density, calcite volume, and clast orientation. Shattered breccias dominate the leading edge of the tip of the Owl Creek thrust sheet in the eastern Owl Creek Mountains, where tectonic deformation is greatest, whereas fracture, mosaic, and chaotic breccias occur throughout the Bighorn Basin. The breccias are healed by calcite cements with d18O values ranging between _26.5 and _15.1xPeedee belemnite (PDB), indicating that the cements were derived from isotopically depleted fluids with elevated temperatures. In the chaotic and mosaic breccia types, large rotated and angular clasts of the host rock float in the matrix of coarse and nonzoned late-stage calcite. This appearance, combined with similar d18O values across even large calcite veins, indicates that the calcite precipitated rapidly after brecciation. Values for d13C(_5–12xPDB) from the frontal part of the Owl Creek thrust sheet indicate equilibrium between methane and CO2-bearing fluids at about 180jC. Fluid inclusions from the eastern basin margin show that these cements are in equilibrium with fluids having minimum temperatures between 120 and 140jC and formed from relatively low-salinity fluids, less than 5 wt.% NaCl. Strontium isotope ratios of these hydrothermal fluids are more radiogenic than proposed values for Mississippian seawater, suggesting that the fluids mixed with felsic-rich basement before migrating vertically into the Madison Formation. We envisage that the tectonic-hydrothermal late-stage calcitecemented breccias and fractures originated from undersaturated meteoric ground waters that migrated into the burial environment while dissolving and incorporating Ca2+ and CO3 2_ and radiogenic Sr from the dissolution of the surrounding carbonates and the felsic basement, respectively. In the burial environment, these fluids were heated and mixed with hypersaline brines from deeply buried parts of the basement. Expulsion of these fluids along basementrooted thrust faults into the overlying strata, including the Madison Formation, occurred most likely during shortening episodes of the Laramide orogeny by earthquake-induced rupturing of the host rock. The fluids were injected forcefully and in an explosive manner into the Madison Formation, causing brecciation and fracturing of the host rock, whereas the subsequent and sudden decrease in the partial pressure of CO2 caused the rapid precipitation of calcite cements. The explosive nature of hydrothermal fluid migration ultimately produces heterogeneities in reservoir-quality carbonates. In general, flow units in the Madison Formation are related to sequence boundaries, which create vertical subdivisions in the porous dolomite. The late-stage calcite cement surrounds hydrothermal breccia clasts and invades the dolomite, reducing porosity and permeability of the reservoir-quality rock. As a consequence, horizontal flow barriers and compartments are established that are locally unpredictable in their location and extent and regionally predictable along the margins of the Bighorn Basin.
Precipitation and dissolution reactions within fractures alter apertures, which in turn affects their flow and transport properties. Different aperture alteration patterns occur in different flow and reaction regimes, and they are also influenced by preferential flow resulting from spatial variations in the aperture. We consider the alteration of variable-aperture fractures in gradient reaction regimes, where fluids are in chemical equilibrium with a mineral everywhere but precipitation and dissolution are driven by solubility gradients associated with temperature variations. The temperature field is defined by a geothermal gradient corresponding to a conduction-dominated heat transfer regime. Monte Carlo simulations on computer-generated aperture fields vividly illustrate pattern formation resulting from two-way feedback between fluid flow and reactive alteration. In dissolution-controlled systems, distinct dissolution channels develop along the dominant flow direction, while elongated precipitate bodies form perpendicular to the mean flow direction in precipitation-controlled systems. Aperture variability accelerates the increase and decrease of effective transmissivity by dissolution and precipitation, respectively. The dominance of precipitation versus dissolution is determined by the angle between the mean hydraulic gradient and solubility/temperature gradient. Development of pronounced anisotropy with oriented elongate features is the key feature of aperture alteration in gradient reaction regimes. A stochastic analysis is developed, which consistently predicts general trends in the aperture field during reactive alteration, including the mean, variance, and spatial covariance structure. Our results are relevant to understanding the long-term diagenetic evolution of fractures in conduction-dominated heat transfer regimes and related problems such as emplacement of ocean bed methane hydrates.
Documenting the source and processes controlling dissolved sulfur (S) mineralization in thermo-mineral waters of the Cerna Valley, Romania is important to understanding speleogenesis in this karst region, in addition to understanding hydrogeological controls, therapeutic qualities and sustainability of the region's historic spas. Stable S and carbon (C) isotopic results reported here elucidate controls on redox processes, the source of dissolved S mineralization, and sulfur-bearing mineral precipitation in this unique karst hydrothermal system. At reservoir temperatures that occur in the Cerna Valley aquifers, it is likely that thermochemical sulfate reduction (TSR) is the dominant S reduction pathway. However the apparent isotope enrichment that we observed between coexisting dissolved sulfate and sulfide is higher than normally associated with TSR—a fact that likely reflects rapid redox cycling at low grade hydrothermal temperatures. δ13C values of dissolved inorganic carbon (DIC) are consistent with TSR using methane as an electron donor. δ34S values of total dissolved S (sum of sulfide and sulfate) in all springs sampled and particularly in those for which closed-system conditions can be demonstrated, is greater than + 16‰, consistently pointing to dissolved S that derives from marine-derived sulfate mineral sources. To this combined S–C isotope data set, we apply a model of Rayleigh distillation which describes exponentially increasing δ34S values of a diminishing sulfate reservoir during TSR, and linearly decreasing δ13C values of DIC indicating mixing of C from the electron donor involved in TSR. Comparison of our results to this model shows two distinct stages of TSR during transport of fresh water from karst aquifers towards the local geothermal anomaly. In an up-gradient group of springs and wells, incomplete TSR progress that is limited by energy from electron donors is evident from: low concentrations of dissolved sulfide with low δ34S values (as low as − 21.9‰), a large balance of remaining as SO42− similar in isotopic composition to its source ( + 17.4‰), and δ13C values showing little methane-derived DIC. Conversely, in a downstream group of springs and wells, excess concentration of methane provides abundant energy for near-complete TSR, and this near complete reaction progress is evident from: high δ34S values of remaining SO42− (up to + 71.8‰), high dissolved sulfide concentrations (> 32 mg/L as S2−) with δ34S values that take on the approximate isotopic signature of the total dissolved S (mean + 17.4‰), and low δ13C values of additional DIC derived from methane (as low as − 30‰). Thus the unique hydrogeology of the Cerna Valley allows the observation of two end-members of TSR (energy- and sulfate-limited) demonstrating wide boundary conditions of stable isotopic composition of dissolved S and C produced by TSR in a single natural system.
Zoloushka Cave is characterized by relatively high (1-5%) content of ÑÎ2 in its underground atmosphere. The source of ÑÎ2 is the oxidation of organic matter and methane by ammonifying and methane-oxidizing bacteria. The accumulation of carbon dioxide in the cave air is caused by slow air exchange with the surface. The distribution of ÑÎ2 through the cave space has been investigated in August 2008 and 2009 and compared with the CO2 distribution in 1982. The main regularities of ÑÎ2 distribution in the cave are region-by-region increase in CO2 concentrations in the direction from the entrance into depth of cave and the vertical stratification – increase of carbon dioxide content in depressions of cave bottom and shafts. The influence of ÑÎ2 on the working conditions in the cave, on the human body and his mind, is also analyzed. The integral table of safety precautions is proposed, which should be followed when doing of research in the cave
In order to reliably distinguish between different genetic processes of cave sulfate formation and to quantify the role of thermo-mineral waters on mineral deposition and cave morphology, it is critical to understand sulfur (S) sources and S transformations during hydrological and speleogenetic processes. Previous work has shown that sulfuric acid speleogenesis (SAS) often produces sulfate deposits with 34S-depleted isotopic signatures compared to those of the original source of S in sulfate rocks. However, 34S-depleted isotopic composition of S-bearing minerals alone does not provide enough information to clearly distinguish SAS from other speleogenetic processes driven by carbonic acid, geothermal heat, or other processes. The isotopic composition (δ18O and δ34S) of sulfate minerals (mainly gypsum) from seven caves of the Cerna Valley (Romania) defines three distinct populations, and demonstrates that the δ34S values of SAS-precipitated cave sulfates depend not only on the source of the S, but also on the H2S:SO4 2− ratio during aqueous S species reactions and mineral precipitation. Population 1 includes sulfates that are characterized by relatively low δ34S values (−19.4 to −27.9‰) with δ18O values between 0.2 and 4.3‰ that are consistent with oxidation of dissolved sulfide produced during methane-limited thermochemical sulfate reduction (TSR) that presently characterizes the chemistry of springs in the upper Cerna Valley. Population 2 of cave sulfates has 34S enriched δ34S values (14.3 to 19.4‰) and more 18O-depleted δ18O values (from −1.8 to −10.0‰). These values argue for oxidation of dissolved sulfide produced during sulfate-limited TSR that presently characterizes the chemistry of springs further downstream in the Cerna Valley. The δ18O values of cave sulfates from Population 1 are consistent with oxidation under more oxic aqueous conditions than those of Population 2. δ34S values of cave sulfates within Population 3 (δ34S: 5.8 to 6.5‰) may be consistent with several scenarios (i.e., pyrite oxidation, oxidation of dissolved sulfide produced during methane-limited TSR coupled with O2-limited oxidation during SAS). However, comparatively 18O-enriched δ18OSO4 values (11.9 to 13.9‰) suggest the majority of this sulfate O was derived from atmospheric O2 in gas-phase oxidation prior to hydration. Thus, the combined use of oxygen- and sulfur-isotope systematics of sulfate minerals precipitated in a variety of cave settings along Cerna Valley may serve as an example of how more complex cave systems can be deconvoluted to allow for more complete recognition of the range of processes and parameters that may be involved in SAS.
Jordan is a country with a large area of limestone. Nevertheless, only a few limestone caves are known. Here we report about two caves along Wwadi Sirhan Graben of Jordan that appear to have formed by stoping upward of collapsed deep-seated hypogene cavities along breccia pipes. The first one, Uwaiyed Cave, is a small breakdown-dominated chamber in basalt of the Naslet Al-Dhirwa volcano; the second, Beer Al-Malabeh, is a large, bell-shaped sinkhole that has geologically recently opened up to the surface. Wwe discuss the possible processes that led to their formation. The review of the existing stratigraphy as obtained by oil well drilling suggests that no salt layers occur below the caves. Gypsum layers seem to be limited to 4 m in thickness, probably not enough to form the observed features. The remaining process is dissolution caused by ascending gas (H2S or CH4) -rich waters from the underlying oil and oil-shale fields. Wwhen such solutions reach the water table, bacterial oxidation may create enough dissolutional power to form localized and large cavities. Their collapse could lead to the observed collapse structures and would explain the paucity of other cave structures throughout southeastern Jordan.
The middle Miocene Badenian basin of the Carpathian Foredeep is characterized by complex sedimentary and diagenetic carbonate-evaporite transitions. Six locations have been selected to evaluate the controls on the carbonand oxygen isotopic composition of the Badenian gypsum-associated limestones of the Tyras Formation in WestUkraine. At three locations marine limestones overlie the gypsum, at one location (Anadoly) the gypsum-associatedlimestones are polygenic, and at two localities (Pyshchatyntsi and Lozyna) gypsum deposits are lacking. Thestudied limestones have originated as primary, mostly peloidal carbonates as well as secondary carbonates formed by hypogene sulphate calcitisation. They show a wide range of δ13C (from from -0.9‰ to -39.8‰) and δ18O values(from 0.9‰ to -12.2‰). The Badenian limestones formed in marine environments (either as deposits accumulatedat the bottom of the sea or forming the infillings of solution cavities within gypsum) have less negative δ18O values compared to predominantly diagenetic formations. Wide ranges and usually very negative δ13C values andlow δ18O values of those limestones indicate that they suffered important meteoric diagenesis as supported bycommon sparitic fabrics. In addition, a large range of δ13C values even in the group of samples characterized byless-negative δ18O values shows that bacterial sulphate reduction and methane oxidation were active processes inthe pore fluids of the Tyras Formation. Very low carbon isotopic compositions (δ13C values from -22 to -40‰) of some sparitic limestones in the studied sections indicate the occurrence of oxidized methane within the diagenetic environment. Accordingly, the isotopic signatures of the studied limestones are a combination of both primary and secondary processes, the latter having a primordial importance. The common occurrence of similar negative δ13Cand δ18O values in evaporite-related carbonates in other Miocene evaporite basins suggest that extensive dissolution-reprecipitation in diagenetic or vadose-phreatic environments were common in evaporite-related carbonates.
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