CHEMICAL EVOLUTION OF GROUNDWATER NEAR A SINKHOLE LAKE, NORTHERN FLORIDA .1. FLOW PATTERNS, AGE OF GROUNDWATER, AND INFLUENCE OF LAKE WATER LEAKAGE, 1995,
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Katz B. G. , Lee T. M. , Plummer L. N. , Busenberg E. ,

Leakage from sinkhole lakes significantly influences recharge to the Upper Floridan aquifer in poorly confined sediments in northern Florida. Environmental isotopes (oxygen 18, deuterium, and tritium), chlorofluorocarbons (CFCs: CFC-11, CCl3F; CFC-12, CCl2F2; and CFC-113, C2Cl3F3), and solute tracers were used to investigate groundwater flow patterns near Lake Barco, a seepage lake in a mantled karst setting in northern Florida. Stable isotope data indicated that the groundwater downgradient from the lake contained 11-67% lake water leakage, with a limit of detection of lake water in groundwater of 4.3%. The mixing fractions of lake water leakage, which passed through organic-rich sediments in the lake bottom, were directly proportional to the observed methane concentrations and increased with depth in the groundwater flow system. In aerobic groundwater upgradient from Lake Barco, CFC-modeled recharge dates ranged from 1987 near the water table to the mid 1970s for water collected at a depth of 30 m below the water table. CFC-modeled recharge dates (based on CFC-12) for anaerobic groundwater downgradient from the lake ranged from the late 1950s to the mid 1970s and were consistent with tritium data. CFC-modeled recharge dates based on CFC-11 indicated preferential microbial degradation in anoxic waters. Vertical hydraulic conductivities, calculated using CFC-12 modeled recharge dates and Darcy's law, were 0.17, 0.033, and 0.019 mid for the surficial aquifer, intermediate confining unit, and lake sediments, respectively. These conductivities agreed closely with those used in the calibration of a three-dimensional groundwater flow model for transient and steady state flow conditions

Oxidation of organic matter in a karstic hydrologic unit supplied through stream sinks (Loiret, France), 1998,
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Alberic P, Lepiller M,

The aim of this paper is to appraise the ability of the oxidation of riverine organic matter in the control of limestone dissolution, in a karst network. Biogeochemical processes during infiltration of river water into an alluvial aquifer have already been described for an average flow velocity of 4-5 m d(-1) (Jacobs, L. A., von Gunten, H. R., Keil, R, and Kuslys, M. (1988) Geochemical changes along a river-groundwater infiltration flow path: Glattfelden, Switzerland. Geochim. Cosmochim. Acta 52, 2693-2706; Von Gunten, H. R., Karametaxas, G., Krahenbuhl, U., Kuslys, M., Giovanoli R., Hoehn E. and Keil R. (1991) Seasonal biogeochemical cycles in riverborne groundwater. Geochim. Cosmochim. Acta 55, 3597-3609; Bourg, A. C. M. and Bertin, C. (1993) Quantitative appraisal of biogeochemical chemical processes during the infiltration of river water into an alluvial aquifer. Environ. Sci. Technol. 27, 661-666). Karstic drainage networks, such as in the River Loire-Val d'Orleans hydrologic system (Fig. 1), make possible flow velocities up to 200 m h(-1 a) and provide convenient access to different water samples several tens of km apart, at both extremities of the hydrologic unit (Chery, J.-L. (1983) Etude hydrochimique d'un aquifere karstique alimente par perte de cours d'eau (la Loire): Le systeme des calcaires de Beauce sous le val d'Orleans. These, Universite d'Orleans; Livrozet, E. (1984) Influence des apports de la Loire sur la qualite bacteriologique et chimique de l'aquifere karstique du val d'Orleans. These, Universite d'Orleans). Recharge of the karstic aquifer occurs principally from influent waters from stream sinks, either through coarse alluvial deposits or directly from outcrops of the regional limestone bedrock (Calcaires de Beauce). Recharge by seepage waters From the local catchment basin is small (Zunino, C., Bonnet, M. and Lelong, F. (1980) Le Val d'Orleans: un exemple d'aquifere a alimentation laterale. C. R. somm. Soc. Geol. Fr. 5, 195-199; Gonzalez R. (1992) Etude de l'organisation et evaluation des echanges entre la Loire moyenne et l'aquifere des calcaires de Beauce. These, Universite d'Orleans) and negligible in summer. This karstic hydrologic: system is the largest in France in terms of flow (tens to hundreds of m(3)/s) and provides the main water resource of the city of Orleans. Chemical compositions of influent waters (River Loire) and effluent waters (spring of the river Loiret) were compared, in particular during floods in summer 1992 and 1993 (Figs 2-4). Variation of chloride in the River Loire during the stream rise can be used as an environmental tracer of the underground flow (Fig. 2). Short transit times of about 3 days are detectable (Fig, 2) which are consistent with earlier estimations obtained with chemical tracers (Ref. in Chery, J.-L. (1983) These, Universite d'Orleans). Depending on the hydrological regime of the river, organic carbon discharge ranges between 3-7 and 2-13 mg/l for dissolved and particulate matter respectively (Fig. 3). Eutrophic characteristics and high algal biomasses are found in the River Loire during low water (Lair, N. and Sargos, D. (1993) A 10 year study at four sites of the middle course of the River Loire. I - Patterns of change in hydrological, physical and chemical variables in relation to algal biomass. Hudroecol. Appl. 5, 1-27) together with more organic carbon rich suspended particulate matter than during floods (30-40 C-org % dry weight versus 5-10%). Amounts of total organic carbon and dissolved oxygen (Fig. 3) dramatically decrease during the underground transport, whereas conversely, dissolved calcium, alkalinity and inorganic carbon increase (Fig. 4). Anoxia of outflows map start in April. Dissolution of calcium carbonates along the influent path outweighs closed system calcite equilibrium of inflow river waters (Table 3). The impact of organic matter oxidation on calcite dissolution may be traced by variations of alkalinity and total carbonates in water. Following, Jacobs, L. A., von Gunten, H. R., Keil, R. and Kuslys, M. (1988) Geochemical changes along a river-groundwater infiltration flow path: Glattfelden, Switzerland. Geochim. Cosmochim. Acta 52, 2693-2706), results are shown graphically (Fig. 5). Extent of reactions is controlled by the consumption of dissolved O-2 and nitrate for organic matter oxidation and by the release of Ca2 for calcite dissolution (Table 2). The karstic network is considered to behave like a biological reactor not exchanging with the atmosphere, with steady inhabitant microbial communities (Mariotti A., Landreau A, and Simon B. (1988) N-15 isotope biogeochemisrry and natural denitrification process in groundwater: Application to the chalk aquifer of northern France. Geochim. Cosmochim. Acta 52, 1869-1878; Gounot, A.-M. (1991) Ecologie microbienne des eaux ei des sediments souterrains. Hydrogeologie, 239-248). Thus, energy requirements only are considered, not carbon assimilation. Moreover, there is no necessity to invoke any delay for nitrification enhancement, as observed elsewhere, after waste water discharge into the river (Chesterikoff, A., Garban, B., Billen, G. and Poulin, M. (1992) Inorganic nitrogen dynamics in the River Seine downstream from Paris (France). Biogeochem. 17, 147-164). Main microbial processes are assumed to be aerobic respiration, nitrification and denitrification. Reactions with iron and manganese, real but not quantitatively important, were neglected. Sulphate reduction and methane formation, certainly not active, were not considered. Denitrification, which is suggested by low nitrate and ammonium concentrations and anoxia in the outflow, is known to be rapid enough to be achieved in a short time (Dupain, S. (1992) Denitrification biologique heterotrophe appliquee au traitement des eaux d'alimentation: Conditions de fonclionnement et mise au point d'un procede. These, Universite Claude Bernard, Lyon). Reaction are somewhat arbitrary but conform to general acceptance (Morel, M. M. and Hering, J. G. (1993) Principles and Applications of Aquatic Chemistry. Wiley, New York). Anaerobic ammonium oxidation (Mulder A., van de Graaf, A. A., Robertson, L: A. and Kuenen, J. G. (1995) Anaerobic ammonium oxidation discovered in a denitrifying fluidized bed reactor. FEMS Microbiol. Ecol. 16, 177-184). although possible, was not considered. In fact, C/N ratio of the reactive organic matter has only mild repercussions on the results; i.e. in the same range as the analytical errors for alkalinity and total carbonates. The objective was simply to roughly confront characteristics of outflowing waters and the calculation. Respective roles of aerobes and denitrifiers, for instance, are not certain. Several periods during low water or floods were selected with various ranges for calcium dissolution or nitrate and oxygen concentrations. The result is that in most cases simulation and data are in reasonable accordance (Fig. 5). Amounts of organic matter in River Loire are generally sufficient to sustain the process (Table 3. Particulate organic matter is probably the most reactive. The balance of oxidation of organic matter indicates that about 65 mu g C-org/l.h are oxidized during the transport without much variation with the river regime or organic discharge. It is concluded that limestone dissolution is directly dependent on organic matter oxidation, but variation occurs (7-29 mg CuCO3/l) with the level of bases that can be neutralized in the River Loire water. (C) 1998 Elsevier Science Ltd. All rights reserved

Hydrochemical Interpretation of Cave Patterns in the Guadalupe Mountains, New Mexico, 2000,
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Palmer, A. N. , Palmer, M. V.

Most caves in the Guadalupe Mountains have ramifying patterns consisting of large rooms with narrow rifts extending downward, and with successive outlet passages arranged in crude levels. They were formed by sulfuric acid from the oxidation of hydrogen sulfide, a process that is now dormant. Episodic escape of H2S-rich water from the adjacent Delaware Basin, and perhaps also from strata beneath the Guadalupes, followed different routes at different times. For this reason, major rooms and passages correlate poorly between caves, and within large individual caves. The largest cave volumes formed where H2S emerged at the contemporary water table, where oxidation was most rapid. Steeply ascending passages formed where oxygenated meteoric water converged with deep-seated H2S-rich water at depths as much as 200 m below the water table. Spongework and network mazes were formed by highly aggressive water in mixing zones, and they commonly rim, underlie, or connect rooms. Transport of H2S in aqueous solution was the main mode of H2S influx. Neither upwelling of gas bubbles nor molecular diffusion appears to have played a major role in cave development, although some H2S could have been carried by less-soluble methane bubbles. Most cave origin was phreatic, although subaerial dissolution and gypsum-replacement of carbonate rock in acidic water films and drips account for considerable cave enlargement above the water table. Estimates of enlargement rates are complicated by gypsum replacement of carbonate rock because the gypsum continues to be dissolved by fresh vadose water long after the major carbonate dissolution has ceased. Volume-for-volume replacement of calcite by gypsum can take place at the moderate pH values typical of phreatic water in carbonates, preserving the original bedrock textures. At pHs less than about 6.4, this replacement usually takes place on a molar basis, with an approximately two-fold volume increase, forming blistered crusts.

Recent measurements of water quality in Mrzlek spring, 2000,
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Jug Tjaš, A, Vudrag Marko, Franko Mladen

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.

Geomicrobiology and redox geochemistry of the karstified Miocene gypsum aquifer, western Ukraine: The study from Zoloushka Cave, 2001,
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Andrejchuk Vn, Klimchouk Ab,

The gypsum karst of the western Ukraine developed largely under artesian conditions. The Miocene aquifer is presently entrenched and dewatered over much of the territory, while it remains confined in the zone adjacent to the Carpathian Foredeep. The most prominent geochemical features of the Miocene aquifer system in the confined karst zone are: (1) the almost universal presence of a bioepigenetic calcite bed, enriched in the light carbon isotope, at the top of the gypsum (the 'Ratynsky Limestone'), (2) the widespread sulfur mineralization associated with the above calcite bed (the region is one of the world's largest sulfur-bearing basins), and (3) high H2S and CO2 in the groundwater. Intense microbial sulfate-reduction processes occur in the gypsum in this zone. Zoloushka Cave is the third longest (92 km) and the largest by volume (more than 7 x 10(5) m(3)) gypsum cave in the world. It is a unique example of a young artesian cave that only during the Holocene became partly drained and during the last 50 years progressively dewatered due to a quarry operation. These rapid changes have induced a number of transitional geochemical processes, some of which appear to be bacterially mediated. Six groups of microorganisms have been identified in the cave. Our article discusses the aquifer geochemistry during the transitional stage in the light of the microbiological studies

Tropical response to the 8200 yr B.P. cold event? Speleothem isotopes indicate a weakened early Holocene monsoon in Costa Rica, 2004,
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Lachniet Matthew S. , Asmerom Yemane, Burns Stephen J. , Patterson William P. , Polyak Victor J. , Seltzer Geoffrey O. ,

A {delta}18O monsoon rainfall proxy record from a U-Th-dated Costa Rican stalagmite (8840-4920 yr B.P.) documents an early Holocene dry period correlative with the high-latitude 8200 yr B.P. cold event. High {delta}18O values between ca. 8300 and 8000 yr B.P. demonstrate reduced rainfall and a weaker monsoon in Central America. A relatively wetter and more stable monsoon was established ca. 7600 yr B.P. The early Holocene dry event suggests a tropical-extratropical teleconnection to the 8200 yr B.P. cold event and a possible association of isthmian rainfall anomalies with high-latitude climate changes. The likely source of such a tropical anomaly is a decrease in Atlantic thermohaline circulation and atmospheric perturbations associated with drainage of proglacial lakes and freshwater discharge into the North Atlantic. A weaker monsoon at 8200 yr B.P. may be linked to wetland contraction and a decrease in methane observed in Greenland ice cores

Methane discharge into the Black Sea and the global ocean via fluid flow through submarine mud volcanoes, 2006,
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Wallmann Klaus, Drews Manuela, Aloisi Giovanni, Bohrmann Gerhard,

During the MARGASCH cruise M52/1 in 2001 with RV Meteor we sampled surface sediments from three stations in the crater of the Dvurechenskii mud volcano (DMV, located in the Sorokin Trough of the Black Sea) and one reference station situated 15[no-break space]km to the northeast of the DMV. We analysed the pore water for sulphide, methane, alkalinity, sulphate, and chloride concentrations and determined the concentrations of particulate organic carbon, carbonate and sulphur in surface sediments. Rates of anaerobic oxidation of methane (AOM) were determined using a radiotracer (14CH4) incubation method. Numerical transport-reaction models were applied to derive the velocity of upward fluid flow through the quiescently dewatering DMV, to calculate rates of AOM in surface sediments, and to determine methane fluxes into the overlying water column. According to the model, AOM consumes 79% of the average methane flux from depth (8.9 [middle dot] 10 6[no-break space]mol a- 1), such that the resulting dissolved methane emission from the volcano into the overlying bottom water can be determined as 1.9 [middle dot] 10 6[no-break space]mol a- 1. If it is assumed that all submarine mud volcanoes (SMVs) in the Black Sea are at an activity level like the DMV, the resulting seepage represents less than 0.1% of the total methane flux into this anoxic marginal sea. The new data from the DMV and previously published studies indicate that an average SMV emits about 2.0 [middle dot] 10 6[no-break space]mol a- 1 into the ocean via quiescent dewatering. The global flux of dissolved methane from SMVs into the ocean is estimated to fall into the order of 10 10[no-break space]mol a- 1. Additional methane fluxes arise during periods of active mud expulsion and gas bubbling occurring episodically at the DMV and other SMVs

Lower Eocene carbonate cemented chimneys (Varna, NE Bulgaria): Formation mechanisms and the (a)biological mediation of chimney growth?, 2006,
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De Boever E, Swennen R, Dimitrov L,

In the area of Pobiti Kamani (Varna, northeast Bulgaria), massive carbonate cemented columns ('chimneys', up to 1.5 m diameter and 8 m high) and horizontal interbeds (2 within loose Lower Eocene sands. Field observations and petrographical and stable isotope geochemical characterisation of four studied locations reveal a relationship between these structures and processes of ancient hydrocarbon seepage. Column and interbed structures both consist of similar well-sorted silt- to sand-sized nummulitic host sediments, predominantly cemented by early diagenetic, low-magnesium calcite. Filamentous textures, about 10 [mu]m in diameter and 80-650 [mu]m long, are only locally detected within interparticle calcite cement of columns. Column samples from two sites reveal a similar, linear and inverse covariant trend of [delta]13C-[delta]18O values, which was interpreted as a mixing trend between two end member fluid/precipitation conditions, i.e. (1) a methane- and/or higher hydrocarbon-derived carbon member characterised by [delta]13C values as low as -[no-break space]43[per mille sign] and marine controlled precipitation conditions with [delta]18O of - 1 0.5[per mille sign] V-PDB and (2) a member with less contribution of methane which was mixed most likely with less depleted carbon sources explaining [delta]13C values ranging up to - 8[per mille sign] V-PDB. The corresponding, depleted [delta]18O values, with many samples clustering around - 8[per mille sign] V-PDB, are interpreted in terms of precipitation at elevated temperatures. This suggests the venting system was not a true 'cold' seep, sensu stricto. Furthermore, column cross-transects often document an internal pattern consisting of (concentric) zones with distinct isotopic signatures, which vary between the two end members. The mixing and internal pattern of column isotopic data, together with petrographical observations, are qualitatively interpreted as evidence of alternating precipitation conditions, controlled by varying seepage rates of a single fluid source at depth, during build-up of individual chimney pipes near the sediment surface. Based on several field observations, migration of the hydrocarbon-charged fluids in Lower Eocene times was possibly channelled along NE oriented faults. Isotopic signatures of calcite cemented horizontal interbeds, with depleted [delta]18O ratios as low as - 8.88[per mille sign] V-PDB and variable [delta]13C (- 1[per mille sign] to - 16[per mille sign], mainly around - 5[per mille sign] to - 7[per mille sign]) suggest that ascending fluids contributed to their cementation or resetted the calcite cement isotopic signature, predominantly during periods of active seepage of warmer fluids. Only few petrographical (and preliminary lipid-biomarker) evidence has been found, pointing to the presence or possibly former activity of microbiota, involved in carbon cycling and calcite precipitation, typical of cold seep settings. This may result from diagenetic alteration of organic components. However, considering the processes of chimney formation, a cementation process, governed by the inorganic oxidation of hydrocarbons in which interstitial oxygen is rapidly consumed without bacterial mediation, is considered

Tectonic-hydrothermal brecciation associated with calcite precipitation and permeability destruction in Mississippian carbonate reservoirs, Montana and Wyoming , 2006,
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Katz D. A. , Eberli G. P. , Swart P. K. , Smith Jr. L. B.

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. 

Alteration of fractures by precipitation and dissolution in gradient reaction environments: Computational results and stochastic analysis, 2008,
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Chaudhuri A. , Rajaram H. , Viswanathan H.

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.

Sulfur isotopic composition and the source of dissolved sulfur species in thermo-mineral springs of the Cerna Valley, Romania, 2010,
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Wynn Jonathan G. , Sumrall Jonathan B. , Onac Bogdan P.

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.

Spatial-dynamic peculiarities of CO2 distribution in the air of Zoloushka Cave, 2011,
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Andreychouk V. , Teleshman I. , Kouprich P.

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

Tracing the sources of cave sulfates: a unique case from Cerna Valley, Romania, 2011,
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Onac Bogdan P. , Wynn Jonathan G. , Sumrall Jonathan B.

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.

Hypogene Point Karstification along Wadi Sirhan Graben (Jordan): A Sign of Oilfield Degassing? , 2012,
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Almalabeh Ahmad, Kempe Stephan

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.

Carbon and oxygen isotopic composition of the Middle Miocene Badenian gypsum-associated limestones of West Ukraine, 2012,
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Peryt T. M. , Durakiewicz T. , Peryt D. , Poberezhskyy A.

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.