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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 potentiometer is an instrument used to measure voltage differences [16].?

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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 sulfate reduction (Keyword) returned 19 results for the whole karstbase:
Showing 1 to 15 of 19
Sulfate reducing bacteria in microbial mats: Changing paradigms, new discoveries, 0000, Baumgartner Lk, Reid Rp, Dupraz C, Decho Aw, Buckley Dh, Spear Jr, Przekop Km, Visscher Pt,
Sulfate reducing bacteria (SRB) have existed throughout much of Earth's history and remain major contributors to carbon cycling in modern systems. Despite their importance, misconceptions about SRB are prevalent. In particular, SRB are commonly thought to lack oxygen tolerance and to exist only in anoxic environments. Through the last two decades, researchers have discovered that SRB can, in fact, tolerate and even respire oxygen. Investigations of microbial mat systems have demonstrated that SRB are both abundant and active in the oxic zones of mats. Additionally, SRB have been found to be highly active in the lithified zones of microbial mats, suggesting a connection between sulfate reduction and mat lithification. In the present paper, we review recent research on SRB distribution and present new preliminary findings on both the diversity and distribution of [delta]-proteobacterial SRB in lithifying and non-lithifying microbial mat systems. These preliminary findings indicate the unexplored diversity of SRB in a microbial mat system and demonstrate the close microspatial association of SRB and cyanobacteria in the oxic zone of the mat. Possible mechanisms and further studies to elucidate mechanisms for carbonate precipitation via sulfate reduction are also discussed

Sulfate reduction and sulfur deposition in the Lower Fars Formation, northern Iraq, 1977, Alsawaf Fds,

DISLOCATION OF THE EVAPORITIC FORMATIONS UNDER TECTONIC AND DISSOLUTION CONTROLS - THE MODEL OF THE DINANTIAN EVAPORITES FROM VARISCAN AREA (NORTHERN FRANCE AND BELGIUM), 1993, Rouchy J. M. , Groessens E. , Laumondais A. ,
Within the Franco-Belgian segment of the Hercynian orogen, two thick Dinantian anhydritic formations are known, respectively in the Saint-Ghislain (765 m) and Epinoy 1 (904 m) wells. Nevertheless, occurrences of widespread extended breccias and of numerous pseudomorphs of gypsum/anhydrite in stratigraphically equivalent carbonate deposits (boreholes and outcrops), suggest a larger extent of the evaporitic conditions (fig. 1, 2). The present distribution of evaporites is controlled by palaeogeographical differentiation and post-depositional parameters such as tectonics and dissolution. These latter have dissected the deposits formerly present in all the structural units. By using depositional, diagenetic and deformational characters of these formations, the article provides a model for the reconstruction of a dislocated evaporitic basin. This segment of the Hercynian chain is schematically composed of two main units (fig. 1, 3) : (1) the autochthonous or parautochthonous deposits of the Namur synclinorium, (2) the Dinant nappe thrusted northward over the synclinorium of Namur. The major thrust surface is underlined by a complex fault bundle (faille du Midi) seismically recognized over more than 100 km. A complex system of thrust slices occurs at the Hercynian front. Except for local Cretaceous deposits, most of the studied area has been submitted to a long period of denudation since the Permian. Sedimentary, faunistic and geochemical data argue for a marine origin of the brines which have generated the evaporites interbedded with marine limestones. Sedimentary structures. - The thick evaporitic formations are composed of calcium-sulfates without any clear evidence of the former presence of more soluble salts (with the exception of a possible carbonate-sulfate breccia in the upper part of the Saint-Ghislain formation). As in all the deeply buried evaporitic formations, the anhydrite is the main sulfate component which displays all the usual facies : pseudomorphs after gypsum (fig. 4A, B), nodular and mosaic (fig. 4C), laminated. The gypsum was probably an important component during the depositional phase despite the predominant nodular pattern of the anhydrite. Early diagenetic nodular anhydrite may have grown during temporary emersion of the carbonates (sabkha environments), but this mechanism cannot explain the formation of the whole anhydrite. So, most of the anhydrite structures result from burial-controlled gypsum --> anhydrite conversion and from mechanical deformations. Moreover, a complex set of diagenetic processes leads to various authigenic minerals (celestite, fluorite, albite, native sulfur, quartz and fibrous silica) and to multistaged carbonate <> sulfate replacements (calcite and dolomite after sulfate, replacive anhydrite as idiomorphic poeciloblasts, veinlets, domino-like or stairstep monocrystals...). These mineral transformations observed ill boreholes and in outcrops have diversely been controlled during the complex evolution of the series as : depositional and diagenetic pore-fluid composition, pressure and temperature changes with burial, bacterial and thermochemical sulfate reduction, deep circulations favored by mechanical brecciation, mechanical stresses, role of groundwater during exhumation of the series. Deformational structures. - A great variety of deformational structures as rotational elongation, stretching, lamination, isoclinal microfolding, augen-like and mylonitic structures are generated by compressive tectonic stresses (fig. 4D to J). The similarities between tectonic-generated structures and sedimentary (lamination) or diagenetic (pseudo-nodules) features could lead lo misinterpretations. The calcareous interbeds have undergone brittle deformation the style and the importance of which depend of their relative thickness. Stretching, boudins, microfolds and augen structures F, H. I) affect the thin layers while thicker beds may be broken as large fractured blocks dragged within flown anhydrite leading to a mylonitic-like structure (fig, 4G). In such an inhomogeneous formation made of interlayered ductile (anhydrite) and brittle (carbonate) beds, the style and the intensity of the deformation vary with respect to the relative thickness of each of these components. Such deformational features of anhydrite may have an ubiquitous significance and can result either from compressive constraints or geostatic movements (halokinesis). Nevertheless, some data evidence a relation with regional tangential stresses: (1) increase of the deformation toward the bottom of the Saint-Ghislain Formation which is marked by a deep karst suggesting the presence of a mechanical discontinuity used as a drain for dissolving solutions (fig. 3, 4); (2) structural setting (reversed series, internal slidings) of the Epinoy 1 formation under the Midi thrust. However, tectonic stresses also induce flowing deformations which have contributed to cause their present discontinuity. It can be assumed that the evaporites played an active role for the buckling of the regional structure as detachment or gliding layers and more specifically for the genesis of duplex structures. Breccia genesis. - Great breccia horizons are widely distributed in outcrops as well as in the subsurface throughout the greater part of the Dinant and Namur units (fig. 2). The wide distribution of pseudomorphosed sulfates in outcrops and the stratigraphical correlation between breccia and Saint-Ghislain evaporitic masses (fig. 2) suggest that some breccia (although not all) have been originated from collapse after evaporites solution. Although some breccia may result from synsedimentary dissolution, studied occurrences show that most of dissolution processes started after the Hercynian deformation and, in some cases, were active until recently : elements made of lithified and fractured limestones (Llandelies quarries) (fig. 5A), preservation of pseudomorphs of late replacive anhydrite (Yves-Gomezee) (fig. 5B, C), deep karst associated with breccia (Douvrain, Saint Ghislain, Ghlin boreholes) (fig. 3, 4, 5D)). Locally, the final brecciation may have been favored by a mechanical fragmentation which controlled water circulations (fig. 5E). As postulated by De Magnee et al. [19861, the dissolution started mostly after the Permian denudation and continued until now in relation with deep circulations and surface weathering (fig. 6). So, the above-mentioned occurrences of the breccia are logically explained by collapse after dissolution of calcium-sulfates interbeds of significant thickness (the presence of salt is not yet demonstrated), but other Visean breccia may have a different origin (fig. 5F). So, these data prove the extension of thick evaporitic beds in all the structural units including the Dinant nappe, before dissolution and deformation. Implications. - Distribution of Visean evaporites in northern France and Belgium is inherited from a complicated paleogeographic, tectonic and post-tectonic history which has strongly modified their former facies, thicknesses and limits (fig. IA, 6). Diversified environments of deposition controlled by both a palaeogeographical differentiation and water level fluctuations led to the deposition of subaqueous (gypsum) or interstitial (gypsum, anhydrite) crystallization. Nevertheless, most of the anhydrite structures can be interpreted as resulting from burial conversion of gypsum to anhydrite rather than a generalized early diagenesis in sabkha-like conditions. Deformation of anhydrite caused by Hercynian tangential stresses and subsequent flow mechanisms, have completed the destruction of depositional and diagenetic features. The tectonic deformations allow us to consider the role of the evaporites in the Hercynian deformations. The evaporites supplied detachment and gliding planes as suggested for the base of the Saint-Ghislain Formation and demonstrated by the structural setting of Epinoy 1 evaporites in reverse position and in a multi-system of thrust-slices below the Midi overthrust (fig. 7). So, although the area in which evaporation and precipitation took place cannot be exactly delineated in geographic extent, all the data evidence that the isolated thick anhydritic deposits represent relics of more widespread evaporites extending more or less throughout the different structural units of this Hercynian segment (fig. 1B). Their present discontinuity results from the combination of a depositional differentiation, mechanical deformations and/or dissolution

THE OCCURRENCE AND EFFECT OF SULFATE REDUCTION AND SULFIDE OXIDATION ON COASTAL LIMESTONE DISSOLUTION IN YUCATAN CENOTES, 1993, Stoessell R. K. , Moore Y. H. , Coke J. G. ,
Dissolution of carbonate minerals in the coastal halocline is taking place in the karst terrain along the northeastern coast of the Yucatan Peninsula. The dissolution is being accelerated in cenotes (sinkholes) where sulfate reduction and oxidation of the produced sulfide is occurring. Hydrogen-sulfide concentrations ranged from 0.06 to 4 mmolal within the halocline in two sinkholes. Relative to concentrations expected by conservative mixing, fluids with high hydrogen-sulfide concentrations were correlated with low sulfate concentrations, high alkalinities, low pH values, and heavy sulfur isotope values for sulfate. Hydrogen-sulfide concentrations were less than those predicted from sulfate reduction, calculated from deficiencies in measured sulfate concentrations, indicating mobility and loss of aqueous sulfide. Fluids with low hydrogen-sulfide concentrations were correlated with very high calcium concentrations, high strontium and sulfate concentrations, slightly elevated alkalinities, low pH values, and sea-water sulfur isotope values for sulfate. Gypsum dissolution is supported by the sulfur isotopes as the major process producing high sulfate concentrations. However, oxidation of aqueous sulfide to sulfuric acid, resulting in carbonate-mineral dissolution is needed to explain the calcium concentrations, low pH values, and only slightly elevated alkalinities. The halocline may trap hydrogen sulfide that has been stripped from the underlying anoxic salt water. The halocline can act as a stable, physical boundary, holding some of the hydrogen sulfide until it is oxidized back to sulfuric acid through interaction with the overlying, oxygenated fresh water or through the activity of sulfide-oxidizing bacteria

CHEMICAL-REACTION PATH MODELING OF ORE DEPOSITION IN MISSISSIPPI VALLEY-TYPE PB-ZN DEPOSITS OF THE OZARK REGION UNITED-STATES MIDCONTINENT, 1994, Plumlee G. S. , Leach D. L. , Hofstra A. H. , Landis G. P. , Rowan E. L. , Viets J. G. ,
The Ozark region of the U.S. midcontinent is host to a number of Mississippi Valley-type districts, including the world-class Viburnum Trend, Old Lead Belt, and Tri-State districts and the smaller Southeast Missouri barite, Northern Arkansas, and Central Missouri districts. There is increasing evidence that the Ozark Mississippi Valley-type districts formed locally within a large, interconnected hydrothermal system that also produced broad fringing areas of trace mineralization, extensive subtle hydrothermal alteration, broad thermal anomalies, and regional deposition of hydrothermal dolomite cement. The fluid drive was provided by gravity flow accompanying uplift of foreland thrust belts during the Late Pennsylvanian to Early Permian Ouachita orogeny. In this study, we use chemical speciation and reaction path calculations, based on quantitative chemical analyses of fluid inclusions, to constrain likely hydrothermal brine compositions and to determine which precipitation mechanisms are consistent with the hydrothermal mineral assemblages observed regionally and locally within each Mississippi Valley-type district in the Ozark region. Deposition of the regional hydrothermal dolomite cement with trace sulfides likely occurred in response to near-isothermal effervescence of CO2 from basinal brines as they migrated to shallower crustal levels and lower confining pressures. In contrast, our calculations indicate that no one depositional process can reproduce the mineral assemblages and proportions of minerals observed in each Ozark ore district; rather, individual districts require specific depositional mechanisms that reflect the local host-rock composition, structural setting, and hydrology. Both the Northern Arkansas and Tri-State districts are localized by normal faults that likely allowed brines to rise from deeper Cambrian-Ordovician dolostone aquifers into shallower carbonate sequences dominated by limestones. In the Northern Arkansas district, jasperoid preferentially replaced limestones in the mixed dolostone-limestone sedimentary packages. Modeling results indicate that the ore and alteration assemblages in the Tri-State and Northern Arkansas districts resulted from the flow of initially dolomite-saturated brines into cooler limestones. Adjacent to fluid conduits where water/rock ratios were the highest, the limestone was replaced by dolomite. As the fluids moved outward into cooler limestone, jasperoid and sulfide replaced limestone. Isothermal boiling of the ore fluids may have produced open-space filling of hydrothermal dolomite with minor sulfides in breccia and fault zones. Local mixing of the regional brine with locally derived sulfur undoubtedly played a role in the development of sulfide-rich ore runs. Sulfide ores of the Central Missouri district are largely open-space filling of sphalerite plus minor galena in dolostone karst features localized along a broad anticline. Hydrothermal solution collapse during ore deposition was a minor process, indicating dolomite was slightly undersaturated during ore deposition. No silicification and only minor hydrothermal dolomite is present in the ore deposits. The reaction path that best explains the features of the Central Missouri sulfide deposits is the near-isothermal mixing of two dolomite-saturated fluids with different H2S and metal contents. Paleokarst features may have allowed the regional brine to rise stratigraphically and mix with locally derived, H2S-rich fluids

Groundwater Geochemistry of Isla de Mona, Puerto Rico, 1998, Wicks C. M. , Troester Jo. W.
In this study, we explore the differences between the hydrogeochemical processes observed in a setting that is open to input from the land surface and in a setting that is closed with respect to input from the land surface. The closed setting was a water-filled passage in a cave. Samples of groundwater and of a solid that appeared to be suspended in the relatively fresh region of saline-freshwater mixing zone were collected. The solid was determined to be aragonite. Based on the analyses of the composition and saturation state of the groundwater, the mixing of fresh and saline water and precipitation of aragonite are the controlling geochemical processes in this mixing zone. We found no evidence of sulfate reduction. Thus, this mixing zone is similar to that observed in Caleta Xel Ha, Quintana Roo, also a system that is closed with respect to input from the land surface.The open setting was an unconfined aquifer underlying the coastal plain along which four hand-dug wells are located. Two wells are at the downgradient ends of inferred flowpaths and one is along a flowpath. The composition of the groundwater in the downgradient wells is sulfide-rich and brackish. In contrast, at the well located along a flow line, the groundwater is oxygenated and brackish. All groundwater is oversaturated with respect to calcite, aragonite, and dolomite. The composition is attributed to mixing of fresh and saline groundwater, CO2 outgassing, and sulfate reduction. This mixing zone is geochemically similar to that observed in blue holes and cenotes.

Dolomitization of Holocene Shallow-Marine Deposits Mediated by Sulfate Reduction and Methanogenesis in Normal-Salinity Seawater, Northern Belize, 2000, Teal Chellie S. , Mazzullo S. J. , Bischoff William D. ,
Dolomite constitutes an average of 12% of the Holocene organic-rich sediments over a 15 km2 area of the Cangrejo Shoals mudbank in northern Belize. Although it defines a laterally persistent stratiform body that averages 3 m thick, it is present throughout the 7.6-m-thick sediment section. These transgressive sediments are less than [~]6400 years old and were deposited in shallow-marine environments of normal salinity. The dolomite is dominantly cement, and average crystal size is 7 m. There are no significant correlations among amount of dolomite vs. sediment texture, mineralogy, porosity, or mole % MgCO3 in associated particulate high-Mg calcite, depth, or location on the shoals. The dolomites are poorly ordered and calcic (39.5-44.5 mole % MgCO3), with low mean Mn (210 ppm) and relatively high mean Sr (1034 ppm) concentrations. There is no evidence of recrystallization or geochemical alteration of the dolomite. {delta}18O values of the dolomites range from 0.5 to 2.8{per thousand}PDB, and the mean value (2.1{per thousand}) suggests that the dolomite precipitated from normal-salinity pore water. Dolomite {delta}13C values range from -5.2{per thousand} to .6{per thousand}PDB (mean seawater {delta}13C = 0.5{per thousand}), which suggests dolomitization promoted by both bacterial sulfate reduction and methanogenesis in environments with anoxic pore water. Dolomitization attending these organodiagenetic reactions apparently was reversible over time, and episodic rather than continual precipitation is indicated. Requisite Mg and Ca were provided by seawater and by some dissolution of host sediments. The most rapid period of dolomitization may have been during early transgression, when relatively high sedimentation rates sustained high levels of organodiagenesis and pore-water alkalinities

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

Geology and Geochemistry of the Reocin Zinc-Lead Deposit, Basque-Cantabrian Basin, Northern Spain, 2003, Velasco Francisco, Herrero Jose Miguel, Yusta Inaki, Alonso Jose Antonio, Seebold Ignacio, Leach David,
The Reocin Zn-Pb deposit, 30 km southwest of Santander, Spain, occurs within Lower Cretaceous dolomitized Urgonian limestones on the southern flank of the Santillana syncline. The Reocin deposit is one of the largest known strata-bound, carbonate-hosted, zinc-lead deposits in Europe. The total metal endowment of the deposit, including past production and remaining reserves, is 62 Mt of ore grading 8.7 percent Zn and 1.0 percent Pb. The epigenetic mineralization consists of sphalerite and galena, with lesser marcasite and trace pyrite with dolomite as gangue. Microprobe analyses of different generations of dolomite revealed nonstoichiometric compositions with various amounts of iron (up to 14 mol % of FeCO3). Replacement of host dolomite, open-space filling of fractures, and cementation of breccias derived from dissolution collapse are the principal types of ore occurrence. Detailed cross-section mapping indicates a stratigraphic and structural control on the deposit. A stratiform morphology is present in the western part of the orebody (Capa Sur), whereas mineralization in the eastern part is highly discordant but strata bound (Barrendera). Stratigraphic studies demonstrate that synsedimentary tectonic activity, related to the rifting of the North Atlantic (Bay of Biscay), was responsible for variation in sedimentation, presence of unconformities (including paleokarsts), local platform emergence and dolomitization along the N60 fault trend. In the Reocin area, two stages of dolomitization are recognized. The first stage is a pervasive dolomitization of the limestone country rocks that was controlled by faulting and locally affected the upper part of the Aptian and the complete Albian sequence. The second dolomitization event occurred after erosion and was controlled by karstic cavities. This later dolomitization was accompanied by ore deposition and, locally, filling of dolomite sands and clastic sediments in karstic cavities. The circulation of hydrothermal fluids responsible for sulfide deposition and the infilling of karst cavities were broadly contemporaneous, indicating a post-Albian age. Vitrinite reflectance data are consistent with previously measured fluid inclusion temperatures and indicate temperatures of ore deposition that were less than 100{degrees}C. Carbon and oxygen isotopic data from samples of regional limestone, host-rock dolostone and ore-stage dolomite suggest an early hydrothermal alteration of limestone to dolostone. This initial dolomitization was followed by a second period of dolomite formation produced by the mixing of basinal metal-rich fluids with local modified seawater. Both dolomitization events occurred under similar conditions from fluids exhibiting characteristics of basinal brines. The{delta} 34S values of sulfides are between -1.8 and .5 per mil, which is consistent with thermochemical sulfate reduction involving organic matter as the main source of reduced sulfur. Galena lead isotope compositions are among the most radiogenic values reported for Zn-Pb occurrences in Europe, and they are distinct from values reported for galena from other Basque-Cantabrian deposits. This suggests that a significant part of the lead was scavenged from the local underlying Asturian sediments. The stratigraphic and structural setting, timing of epigenetic mineralization, mineralogy, and isotopic geochemistry of sulfide and gangue minerals of the Reocin deposit are consistent with the features of most of Mississippi Valley-type ore deposits

The Geomicrobiology of Ore Deposits, 2005, Southam G. , Saunders James A. ,
Bacterial metabolism, involving redox reactions with carbon, sulfur, and metals, appears to have been important since the dawn of life on Earth. In the Archean, anaerobic bacteria thrived before the Proterozoic oxidation of the atmosphere and the oceans, and these organisms continue to prosper in niches removed from molecular oxygen. Both aerobes and anaerobes have profound effects on the geochemistry of dissolved metals and metal-bearing minerals. Aerobes can oxidize dissolved metals and reduced sulfur, as well as sulfur and metals in sulfide minerals can contribute to the supergene enrichment of sulfide ores, and can catalyze the formation of acid mine drainage. Heterotrophic anaerobes, which require organic carbon for their metabolism, catalyze a number of thermodynamically favorable reactions such as Fe-Mn oxyhydroxide reductive dissolution (and the release of sorbed metals to solution) and sulfate reduction. Bacterial sulfate reduction to H2S can be very rapid if reactive organic carbon is present and can lead to precipitation of metal sulfides and perhaps increase the solubility of elements such as silver, gold, and arsenic that form stable Me-H2S aqueous complexes. Similarly, the bacterial degradation of complex organic compounds such as cellulose and hemicellulose to simpler molecules, such as acetate, oxalate, and citrate, can enhance metal solubility by forming Me organic complexes and cause dissolution of silicate minerals. Bacterially induced mineralization is being used for the bioremediation of metal-contaminated environments. Through similar processes, bacteria may have been important contributors in some sedimentary ore-forming environments and could be important along the low-temperature edges of high-temperature systems such as those that form volcanogenic massive sulfides

Sources and processes affecting sulfate in a karstic groundwater system of the Franconian Alb, southern Germany, 2005, Einsiedl F, Mayer B,
Chemical and isotope analyses on groundwater sulfate and H-3 measurements on groundwater were used to determine the sulfate sources and sulfur transformation processes in a heterogeneous karst aquifer of the Franconian Alb, southern Germany. Sulfate was found to be derived from atmospheric deposition. Young groundwater was characterized by high sulfate concentrations and delta(34)S values similar to those of recent atmospheric sulfate deposition. However,the delta(18)O values of groundwater SO42- were depleted by several per mil with respect to those of atmospheric deposition. This isotopic shift is indicative of mineralization of carbon-bonded S in the vadose zone of the karst system. In groundwater with mean residence times of more than 60 years, a trend of increasing delta(34)S values and 6180 values with decreasing sulfate concentrations was observed. This trend could not be solely explained by preindustrial atmospheric sulfate deposition with higher delta(34)S values, and hence, we conclude that bacterial (dissimilatory) sulfate reduction in the porous matrix of the karst aquifer must have occurred. This process has the potential to contribute to long-term biodegradation of contaminants in the porous rock matrix representing the dominant water reservoir of the fissured porous karst aquifer

The transition of a freshwater karst aquifer to an anoxic marine system, 2005, Garman Km, Garey Jr,
Jewfish Sink is located in the shallow seagrass flats of the Gulf of Mexico in west central Florida. Jewfish Sink was a submarine spring until the drought of 1961-1962 when it ceased flowing. Today, the sink is an anaerobic marine basin and provides the opportunity to study the implications of saltwater intrusion in coastal karstic areas. The biogeochemistry of Jewfish Sink was studied from summer 2001 through spring 2004. A distinct feature of the sink is the uniform cold temperature (16-17 degrees C) of the deeper anoxic water that does not match groundwater found nearshore or onshore (22-24 degrees C). There are four zones within the sink: oxic zone, transition zone, upper anoxic zone, and anoxic bottom water. The anoxic bottom water does not mix with water from above but may be linked to deep Gulf shelf water through ancient aquifer conduits. The other three zones vary seasonally in oxygen, salinity, and temperature because of limited mixing in the winter due to cooling and sinking of surface water. The walls of the anoxic zones have characteristic microbial mats that are found in other sulfidic karstic features in the area. Bacterial activity appears to be carbon limited in the anoxic zones where sulfate reduction appears to be the major metabolic process. The reduction of sulfate to sulfide appears to be driven by irregular influxes of organic matter including macroalgae, horseshoe crabs, and stingrays that become entrapped within the sink. Bacterial activity in the oxic zones appears to be phosphate limited. Although the system is partially isolated from the overlying marine ecosystem, organic input from above drives the bacterial anaerobic ecosystem, resulting in a sulfide pump. In this model, sulfide percolates up through the karst and removes oxygen from the overlying sediment, which has likely caused changes in the shallow benthic ecosystem. Jewfish Sink appears to be part of an extensive anoxic subterranean estuary that extends under parts of at least three coastal counties in Florida and can serve as a model for the effects of rising sea levels or aquifer mining

Australian Zn-Pb-Ag Ore-Forming Systems: A Review and Analysis, 2006, Huston David L. , Stevens Barney, Southgate Peter N. , Muhling Peter, Wyborn Lesley,
Zn-Pb-Ag mineral deposits are the products of hydrothermal ore-forming systems, which are restricted in time and space. In Australia, these deposits formed during three main periods at ~2.95, 1.69 to 1.58, and 0.50 to 0.35 Ga. The 1.69 to 1.58 Ga event, which accounts for over 65 percent of Australia's Zn, was triggered by accretion and rifting along the southern margin of Rodinia. Over 93 percent of Australia's Zn-Pb-Ag resources were produced by four ore-forming system types: Mount Isa (56% of Zn), Broken Hill (19%), volcanic-hosted massive sulfide (VHMS; 12%), and Mississippi Valley (8%). Moreover, just 4 percent of Australia's land mass produced over 80 percent of its Zn. The four main types of ore-forming systems can be divided into two 'clans,' based on fluid composition, temperature, and redox state. The Broken Hill- and VHMS-type deposits formed from high-temperature (>200{degrees}C) reduced fluids, whereas the Mount Isa- and Mississippi Valley-type deposits formed from low-temperature (<200{degrees}C), H2S-poor, and/or oxidized fluids. The tectonic setting and composition of the basins that host the ore-forming systems determine these fluid compositions and, therefore, the mineralization style. Basins that produce higher temperature fluids form in active tectonic environments, generally rifts, where high heat flow produced by magmatism drives convective fluid circulation. These basins are dominated by immature siliciclastic and volcanic rocks with a high overall abundance of Fe2. The high temperature of the convective fluids combined with the abundance of Fe2 in the basin allow inorganic sulfate reduction and leaching of sulfide from the country rock, producing reduced, H2S-rich fluids. Basins that produce low-temperature fluids are tectonically less active, generally intracratonic, extensional basins dominated by carbonate and variably mature siliciclastic facies with a relatively low Fe2 abundance. In these basins, sediment maturity depends on the paleogeography and stratigraphic position in an accommodation cycle. Volcanic units, if present, occur in the basal parts of the basins. Because these basins have relatively low heat flow, convective fluid flow is less important, and fluid migration is dominated by expulsion of basinal brines in response to local and/or regional tectonic events. Low temperatures and the lack of Fe2 prevent in-organic sulfate reduction during regional fluid flow, producing H2S-poor fluids that are commonly oxidized (i.e., {sum}SO4 > {sum}H2S). Fluid flow in the two basin types produces contrasting regional alteration systems. High-temperature fluid-rock reactions in siliciclastic-volcanic-dominated basins produce semiconformable albite-hematite-epidote assemblages, but low-temperature reactions in carbonate-siliciclastic-dominated basins produce regional K-feldspar-hematite assemblages. The difference in feldspar mineralogy is mostly a function of temperature. In both basin types, regional alteration zones have lost, and probably were the source of, Zn and Pb. The contrasting fluid types require different depositional mechanisms and traps to accumulate metals. The higher temperature, reduced VHMS- and Broken Hill-type fluids deposit metals as a consequence of mixing with cold seawater. Mineralization occurs at or near the sea floor, with trapping efficiencies enhanced by sub-surface replacement or deposition in a brine pool. In contrast, the low-temperature, oxidized Mount Isa- and Mississippi Valley-type fluids precipitate metals through thermochemical sulfate reduction facilitated by hydrocarbons or organic matter. This process can occur at depth in the rock pile, for instance in failed petroleum traps, or just below the sea floor in pyritic, organic-rich muds

Hydrocarbon Biomarkers in the Topla-Mezica Zinc-Lead Deposits, Northern Karavanke/Drau Range, Slovenia: Paleoenvironment at the Site of Ore Formation, 2006, Spangenberg Jorge E. , Herlec Ursos,
The Mississippi Valley-type zinc and lead deposits at Topla (250,150 metric tons (t) of ore grading 10 wt % Zn and 3.3 wt % Pb) and Me[z]ica (19 million metric tons (Mt) of ore grading 5.3 wt % Pb and 2.7 wt % Zn) occur within the Middle to Upper Triassic platform carbonate rocks of the northern Karavanke/Drau Range geotectonic units of the Eastern Alps, Slovenia. The ore and host rocks of these deposits have been investigated by a combination of inorganic and organic geochemical methods to determine major, trace, and rare earth element (REE) concentrations, hydrocarbon distribution, and stable isotope ratios of carbonates, kerogen, extractable organic matter, and individual hydrocarbons. These data combined with sedimentological evidence provide insight into the paleoenvironmental conditions at the site of ore formation. The carbonate isotope composition, the REE patterns, and the distribution of hydrocarbon biomarkers (normal alkanes and steranes) suggest a marine depositional environment. At Topla, a relatively high concentration of redox sensitive trace elements (V, Mo, U) in the host dolostones and REE patterns parallel to that of the North American shale composite suggest that sediments were deposited in a reducing environment. Anoxic conditions enhanced the preservation of organic matter and resulted in relatively higher total organic carbon contents (up to 0.4 wt %). The isotopic composition of the kerogen ({delta}13Ckerogen = -29.4 to -25.0{per thousand}, {delta}15Nkerogen = -13.6 to 6.8{per thousand}) suggests that marine algae and/or bacteria were the main source of organic carbon with a very minor contribution from detrital continental plants and a varying degree of alteration. Extractable organic matter from Topla ore is generally depleted in 13C compared to the associated kerogen, which is consistent with an indigenous source of the bitumens. The mineralization correlates with {delta}15Nkerogen values around 0 per mil, 13C depleted kerogen, 13C enriched n-heptadecane, and relatively high concentrations of bacterial hydrocarbon biomarkers, indicating a high cyanobacterial biomass at the site of ore formation. Abundant dissimilatory sulfate-reducing bacteria, feeding on the cyanobacterial remains, led to accumulation of biogenic H2S in the pore water of the sediments. This biogenic H2S was mainly incorporated into sedimentary organic matter and diagenetic pyrite. Higher bacterial activity at the ore site also is indicated by specific concentration ratios of hydrocarbons, which are roughly correlated with total Pb plus Zn contents. This correlation is consistent with mixing of hydrothermal metal-rich fluids and local bacteriogenic sulfide sulfur. The new geochemical data provide supporting evidence that Topla is a low-temperature Mississippi Valley-type deposit formed in an anoxic supratidal saline to hypersaline environment. A laminated cyanobacterial mat, with abundant sulfate-reducing bacteria was the main site of sulfate reduction

HYPOGENE KARST AND SULFATE DIAGENESIS OF THE DELAWARE BASIN: SOUTHEASTERN NEW MEXICO AND FAR WEST TEXAS, PhD Thesis , 2008, Stafford, Kevin Wayne

Hypogene speleogenesis is widespread throughout the Delaware Basin region as evidenced by intrastratal dissolution, hypogenic caves and suites of diagenetic minerals. The world famous carbonate caves of the Capitan reef facies of the Guadalupe Mountains have long been associated with sulfuric acid processes and recently have been associated with semi-confined, hypogene dissolution. However, evaporite karst within Permian backreef and basin-filling facies has been traditionally associated with surficial, epigene processes. On the eastern edge of the Delaware Basin cavernous porosity associated with oil reservoirs in Permian carbonates have been attributed to eogenetic karst processes.
Interbedded (evaporite / carbonate), backreef facies within the mid-Permian Seven Rivers Formation exhibit characteristics of hypogene karst associated with semi-confined dissolution controlled by the eastward migration and entrenchment of the Pecos River. Coffee Cave is a good example of hypogene dissolution, forming a multi-storey, rectilinear maze with abundant distinctive morphologic feature suites (i.e. risers, channels and cupolas) indicative of hypogene speleogenesis. Other caves within the Seven Rivers and Rustler Formations show similar patterns, although often less well developed.
Within the Delaware Basin, Castile Formation evaporites have been extensively modified by hypogene processes. Field mapping coupled with GIS analyses clearly shows that karst development and evaporite calcitization are highly clustered throughout the outcrop area. Individual caves commonly exhibit complex morphologies, including complete suites of morphologic features indicative of intrastratal dissolution. Clusters of hypogene caves are commonly associated with clusters of evaporite calcitization and often occurrences of secondary selenite bodies, suggesting all three are genetically related. Brecciated cores and associated native sulfur deposits indicate that calcitized evaporites are the result of semi-confined sulfate reduction in the presence of ascending hydrocarbons. Hypogene caves are currently being overprinted by epigene processes as surface denudation results in breaching of previously confined solutional conduits. However, calcitized evaporites stand as resistant masses attesting to the widespread importance of hypogene processes within the Castile Formation.
On the southern end of the Central Basin Platform, the spatial distribution of cavernous porosity, secondary mineralization and abundant karst fabrics within the Yates Field carbonate strata provide convincing evidence that karst porosity, at least locally, within the San Andres and overlying Permian strata is the result of hypogene speleogenesis. Porosity development appears to have been enhanced by high geothermal gradients and the addition of sulfuric acid-rich fluids, reminiscent of the same processes that have been proposed for the extensive carbonate caves of the Guadalupe Mountains.
Recognition of the widespread occurrence of hypogene speleogenesis throughout the Delaware Basin region indicates that the regional diagenetic evolution has been significantly affected by confined fluid migration, including not only the development of porosity but also the emplacement of many secondary mineral deposits. Therefore, future natural resource management plans must consider the nature of hypogene karst in site evaluations throughout the region in order to better predict geohazards, potential groundwater contamination and characterize mineral resources.


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