LA-ICP-MS geochemical studies of the Golden Mile pyrite nodules reveals differences between the nodules from each formation, but also consistent characteristics.
One of these, the Oroya Shale, contains diagenetic pyrite nodules with very similar textures to those from Lucky Bay, but the amount of Au and other trace elements contained in these nodules is significantly higher e. Chapter 2 appears to be the equivalent of a post-print version of an article published as: Steadman, J. Age, origin and significance of nodular sulfides in Ma carbonaceous black shale of the Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia, Precambrian research, , — Chapter 3 appears to be the equivalent of a post-print version of an article published as: Steadman, J.
Paragenesis and composition of ore minerals in the Randalls BIF-hosted gold deposits, Yilgarn Craton, Western Australia: Implications for the timing of deposit formation and constraints on gold sources, Precambrian research, , Chapter 5 appears to be the equivalent of a post-print version of an article published as: Steadman, J. Synsedimentary to early diagenetic gold in black shale-hosted pyrite nodules at the Golden Mile deposit, Kalgoorlie, Western Australia, Economic geology, 5 , User Menu Login Repository Statistics.
Open Access Repository. Download Statistics. Downloads Downloads per month over past year. Steadman, JA. Age, origin and significance of nodular sulfides in Ma carbonaceous black shale of the Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia, Precambrian research, , — Chapter 3 appears to be the equivalent of a post-print version of an article published as: Steadman, J.
Paragenesis and composition of ore minerals in the Randalls BIF-hosted gold deposits, Yilgarn Craton, Western Australia: Implications for the timing of deposit formation and constraints on gold sources, Precambrian research, , Chapter 5 appears to be the equivalent of a post-print version of an article published as: Steadman, J.
Publisher Publisher Publisher Publisher. To probe the micro-surface elemental content, an EDX line scans analysis from the upper surface to the interior subsurface is conducted on the vertical plane of samples Fig. In the original state, the elemental content at each point varies from the upper surface to the interior subsurface, among which the content of elemental Si, O and Al is relatively higher than other elements such as elemental C, S, Fe, Ca, K, and Mg Fig.
The elemental Si and O remains a relatively high proportion, but for other elements, such as the elemental Al, S, Fe, Ca, K, and Mg, their proportion decreases than the original state Fig. It is notably that, due to the special measure method, samples for original state measurement are not the experimental samples before treated, but obtained from the same parent rock. In spite of a little difference, it is reasonable to assume that this difference was same for three experimental groups and would not impact the conclusions.
The schematic diagram e indicates the scan direction of the sample. The mineral composition of each sample is demonstrated in Table 1 , the original samples mainly consist of quartz, plagioclase, muscovite, illite, calcite and pyrite. After treated by different solutions, the overall trend of minerals alteration is similar but the rate varies in three groups. The major minerals concentrations such as quartz, plagioclase, muscovite and calcite do not significantly change after reactions, but the pyrite content decreases by It can be seen that the jarosite only presents in G3 after treatment, which agrees with the SEM observations of numerals jarosite occurred on rocks micro-surface in G3.
The aqueous pH values moderately change with reaction time, the initial values of pH are 4. The aqueous ORP reflects the rate of oxidation-reduction reactions, which is higher in G2 and G3 than in G1 at the initial time.
Subsequently the ORP in three groups all increases, the G3 exhibits the highest increasing rate and reaches at the 2 nd day. However, the ORP gradually decreases during the 3—7 days in G3, in spite of a re-bounce at the 4 th day. In natural systems, the black shale oxidation process is usually involved in multiple factors, such as chemical and biological mechanisms 29 , Previous studies have shown an effective pyrite oxidation ability presented in biological system such as A.
Considering the oxidation process initiated at the rock surface, we assumed a correlation between rock micro-surface characteristics alteration and oxidation degree, especially at the initial stage. Therefore, in this study, a comparative experiment is designed and carried out on black shale slices, the pyrite oxidation rate is employed to the index for black shale oxidation degree, aim to reveal a core difference in chemical and biological oxidizing black shale at the initial stage.
Based on the micro-surface morphologies result, it can be seen that both the acid solution and A. In G1 and G3, the pyrite assemblage almost disappeared after reactions, whereas it remains on the rocks surface in G1 Fig. The XRD results indicate that the most reduction of pyrite content is presented in G3.
General speaking, the pyrite oxidation in black shale is accompanied by the microstructure decomposition associated with the damage of shale matrix cement 11 , However, this correlation seemed only occurred in abiolotic systems. The more robust pyrite oxidation led to the more clay minerals and irregular flocculent structures formed in G2 compared with that in G1. These results are consistent with previous findings 14 that the acidic environment is facilitated to black shale oxidation.
Whereas in the biolotic system, it is difficult to assess the micro-structure destruction, because of large amounts of jarosite covering on the rocks surface. Based on a field investigation, Liao et al. Therefore, the relationship between micro-surface morphologies and the pyrite oxidation rate is different in abiolotic and biolotic systems.
In the initial oxidation stage, we assume that the alterations of porosity and permeability would be limited to the micro-surface. However, the classic porosity measurement methods, such as nitrogen adsorption and high-pressure mercury intrusion tests seem unsuitable to the surface porosity measurement in this study.
By using a novel fluorescent staining method, the fluid distribution on the rock surface can be illustrated, since this fluorescent dye can be detected only when it occurred in aqueous. We suppose that rinsing with neutral PBS can remove the fluid not contained in the rocks surface pores, therefore, the fluid distribution images can be employed to reveal the porosity on the rocks surface. Another feature of this dye is the color dependence on aqueous pH, which is yellow in acidic environment but turned to green when approach to neutral solution.
Thus the MpH can also measure the pH of fluid distributed in the surface pores. As demonstrated in Fig. Although the total square of fluorescent density does not significantly change after reactions, the MpH is different to the original images and varies among groups.
The low MpH areas increase more in G2 than that in G1, indicating more acid solution contained in the rocks surface pores in G2. These results agree with the alterations of micro-surface morphologies, the more pyrite oxidation results in more increase of acid solution permeability. But this interpretation can not apply to G3, in regard of a similar aqueous pH and pyrite oxidation rate presents in G2 and G3.
The MpH does not significantly change in G3 by comparing with the original state, it probably since the surface jarosite coverage blocks the acid solution permeability. In addition, the carbonate also exists in the samples, its buffer ability may effect the MpH values, but considering the same experimental condition in all samples, this influence could be similar in three groups.
Nevertheless, the distinct MpH among groups suggests the alternation of micro-surface porosity and permeability is different in biolotic and abiolotic systems. Laboratory studies showed that the acid erosion could promote original matter oxidation and field investigations exhibited the organic matters nearly removed from the regolith 2 , 39 , these results indicated that the organic matters were depleted during black shale weathering process.
Although a biological mechanism for the oxidation of pyrite by A. Although the overall content of minerals shows a small variation in G1 and G2, a more obvious minerals dissolution may occur on the rocks micro-surface in G2 in accordance with a more significant micro-structure destruction.
Whereas in G3, which has a similar aqueous pH values with G2, the elemental C concentration increases after reactions. It may due to the attachment of A. Likewise, with the humidity climate of Pennsylvania, Jin et al.
Despite the EDX analysis just show the relative elemental C alterations, it can not equal to the total organic carbon TOC quantity, but for the micro-surface elemental C concentration, it shows depletion pattern in abiolotic system but addition pattern in biolotic system. Previous literature documented a more effective oxidation ability presented in A. If it assumed that the biological oxidation of black shale is much higher or even same the magnitude of the chemical effect, the overall rate of the biological oxidation processes should be re-estimated.
However, based on field observations, the biological effect is usually limit to the rock surface The underlying mechanisms may relate to the different micro-surface alternations in chemical and biological oxidizing black shale, especially at the initial stage.
In the proposed reactions at the initial oxidation stage, the pyrite embedded in black shale exhibited differential oxidation behavior in chemical and biological systems. In this regard, only effects of the first 7days are investigated in this study. Despite previous studies demonstrated a more obvious difference occurred in longer term experiments 22 , but which is not the focus of present study.
The pyrite oxidation rate is utilized as an index for black shale oxidation, which is higher in biolotic system at the initial 4 days. As shown in Table 1 and Fig. Based on the results of micro-surface charateristics, this decrease is primarily attributed to the jarosite formation and covering on the rock surface. The jarosite formation is a common problem of A. It is clear from above results that the jarosite formation is A. Initially, A. With the pyrite oxidation process ongoing, the ferric iron and sulfur concentrations increase, resulting in acceleration of jarosite formation 35 , Finally, the formed jarosite prefers to deposit on the rocks surface rather than dissolve in the biolotic aqueous systems Electro kinetic investigations have proposed that the changes in surface charge, such as a function of pH and ferric iron was the basis of pyrite oxidation 21 , 35 , however, the surface jarosite coating might passivate against this reaction.
Additionally, the accumulation of carbonates on the rocks surfaces could also make a contribution to inhibit further reactions.
Therefore, two phases of reactions may involve in A. Firstly, A. With the accumulation of ferric iron and sulfur, jarosite is formed and precipitated on the rocks surface, resulting in alteration of surface characteristics and inhibition of further reactions.
The schematic diagram of A. EPS, extracellular polymeric substances. It is notably that although a link between micro surface characteristics and black shale oxidation degree at the initial stage is founded in acid solution and A. For example, the pH in chemical system is at 2. Furthermore, there are multiple sources of microorganisms presented in local environment except for A.
Finally, given there are multiple minerals contained in black shale, the future work will be focused on their roles in the overall oxidation process of black shale. In this study, we investigated the correlation between micro surface characteristics and the oxidation degree of black shale under chemical and biological effects at the initial oxidation stage. The oxidize rate of pyrite was employed to the major index for evaluating the black shale oxidation degree and a comparative study of acid solution and A.
The results suggest,. Acidithiobacillus ferrooxidans A. After being cultivated to the logarithmic growth phase, the suspensed A. In two abiotic groups, the initial pH of the medium was different, where the Group 1 G1 was 4. In biotic Group 3 G3 , the initial pH of medium was adjusted to 2.
The polarized light microscopy Olympus, Tokyo, Japan was used for rock surface mineral observation before and after treatment.
Small dried fragments of samples before and after treatment were fixed onto aluminum stubs and sputter-coated with gold, then examined with a scanning electron microscopy SEM equipped with an energy dispersive X-ray spectroscopy EDX Zeiss, Heidenheim, Germany.
However, due to the special requirements of sample size and preparation methods, it is hard to conduct on same sample before and after experiments for SEM and EDX analysis, therefore, samples obtained from the same parent rock were employed to the original state measurement.
After rinsing by PBS pH 7. The images were analysed by Image J software. A Cu filament and Ni filter was performed for the qualitative mineral analysis. For the ferric and ferrous ions measurement, samples were firstly filtered by a cellulose acetate membrane 0.
Xu, J. Geochemistry of soils derived from black shales in the Ganziping mine area, western Hunan, China. Environmental Earth Sciences 70 , —90 Google Scholar. Wengel, M. Degradation of organic matter from black shales and charcoal by the wood-rotting fungus Schizophyllum commune and release of DOC and heavy metals in the aqueous phase. Sci Total Environ , —93 Wang, X. Chromium isotope fractionation during subduction-related metamorphism, black shale weathering, and hydrothermal alteration.
Chemical Geology , 19—33 Pi, D. Trace and rare earth element geochemistry of black shale and kerogen in the early Cambrian Niutitang Formation in Guizhou province, South China: Constraints for redox environments and origin of metal enrichments. Precambrian Research , —29 Peng, B. Environmental Geology 45 , —47 CAS Google Scholar. Parviainen, A. The soil chemistry and mineralogy data could not be reproduced without including the reactive gases. For example, pyrite remained in the soil even after 10, years if O2 was not continuously present in the soil column; likewise, chlorite remained abundant and porosity remained small with the presence of soil CO2.
The field observations were only simulated successfully when the specific surface areas of the reactive minerals were orders of magnitude smaller than surface area values measured for powdered minerals, reflecting the lack of accessibility of fluids to mineral surfaces and potential surface coating.
An increase in the water infiltration rate enhanced weathering by removing dissolution products and maintaining far-from-equilibrium conditions.
We conclude that availability of reactive surface area and transport of H2O and gases are the most important. Porosity evolution during weathering of Marcellus shale. Weathering is an important process that continuously converts rock to regolith. When cuttings are exposed at earth's surface, they can release toxic trace elements during weathering. In this study, we investigated the evolution of pore structures and mineral transformation in an outcrop of Marcellus shale - one of the biggest gas shale play in North America - at Frankstown, Pennsylvania.
A combination of neutron scattering and imaging was used to characterize the pore structures from nm to mm. The weathering profile of Marcellus shale was also compared to the well-studied Rose Hill shale from the Susquehanna Shale Hills critical zone observatory nearby. This latter shale has a similar mineral composition as Marcellus shale but much lower concentrations of pyrite and OC. The Marcellus shale formation in outcrop overlies a layer of carbonate at 10 m below land surface with low porosity shale samples above the carbonate layer are almost completely depleted in carbonate, plagioclase, chlorite and pyrite.
The porosities in the weathered Marcellus shale are twice as high as in protolith. In the nearby Rose Hill shale , the pyrite and carbonate are sharply depleted close to the water table m at ridgetop ; while chlorite and plagioclase are gradually depleted toward the land surface.
The greater weathering extent of silicates in the Marcellus shale despite the similarity in climate and erosion rate in these two neighboring locations is attributed to 1 the formation of micron-size pores increases the infiltration rate into weathered Marcellus shale and therefore promotes mineral.
During hydraulic fracturing, a technique often used to extract hydrocarbons from shales , large volumes of water are injected into the subsurface. Although the injected fluid typically contains various reagents, it can become further contaminated by interaction with minerals present in the rocks.
Pyrite , which is common in organic-rich shales , is a potential source of toxic elements, including arsenic and lead, and it is generally thought that for these elements to become mobilized, pyrite must first dissolve. Here, we use atomic force microscopy and environmental scanning electron microscopy to show that during fluid-rock interaction, the dissolution of carbonate minerals in Eagle Ford shale leads to the physical detachment, and mobilization, of embedded pyrite grains.
In experiments carried out over a range of pH, salinity, and temperature we found that in all cases pyrite particles became detached from the shale surfaces. On average, the amount of pyrite detached was equivalent to 6. This result suggests that mechanical detachment of pyrite grains could be an important pathway for the mobilization of arsenic in hydraulic fracturing operations and in groundwater systems containing shales.
The case for metamorphic base metal mineralization: pyrite chemical, Cu and S isotope data from the Cu-Zn deposit at Kupferberg in Bavaria, Germany. The stratiform Cu-Zn sulfide deposit at Kupferberg in Germany represents Bavaria's largest historic base metal producer.
The deposit is hosted by Early Paleozoic volcano-sedimentary strata at the margin of a high-grade allochthonous metamorphic complex.
The present paper reports on the first Cu and S isotope data as well as trace element analyses of pyrite from this unusual deposit. The new data point to syn-orogenic mineralization that was driven by metamorphic fluids during nappe emplacement.
Primary Cu ore occurs as texturally late chalcopyrite within stratiform laminated pyrite in black shale in two different tectonostratigraphic units of very low and low metamorphic grade, respectively, that were juxtaposed during the Variscan orogeny. In agreement with this model, Cu distribution in stream sediments in this region shows distinct enrichments bound to the margin of the allochthonous complex.
Thus, Kupferberg can be considered a rare example of a syn-orogenic Cu deposit with the Cu probably being derived from syn.
Reconnaissance examinations for uranium in 22 formations containing black shale were conducted in parts of Montana, North Dakota, Utah, Idaho, and Oregon during About samples from 80 outcrop localities and 5 oil and gas wells were submitted for uranium determinations.
Most of the black shale deposits examined contain less than 0. An eight-foot bed of phosphatic black shale at the base of the Brazer limestone of Late Mississippian age in Rich County, Utah, contains as much as 0. Commercial gamma ray logs of oil and gas wells drilled in Montana and adjacent parts of the Dakotas indicate that locally the Heath shale of Late Mississippian age contains as much as 0.
A reactive transport model for Marcellus shale weathering. As a first step toward understanding how Marcellus shale interacts with water in the surface or deep subsurface, we developed a reactive transport model to simulate shale weathering under ambient temperature and pressure conditions, constrained by soil and water chemistry data.
The simulation was carried out for 10, years since deglaciation, assuming bedrock weathering and soil genesis began after the last glacial maximum. Results indicate weathering was initiated by pyrite dissolution for the first years, leading to low pH and enhanced dissolution of chlorite and precipitation of iron hydroxides.
For example, pyrite remained in the soil even after 10, years if O2 was not continuously present in the soil column; likewise, chlorite remained abundant and porosity remained small if CO2 was not present in the soil gas. The field observations were only simulated successfully when the modeled specific surface areas of the reactive minerals were orders of magnitude smaller than surface area values measured for powdered minerals. Small surface areas could be consistent with the lack of accessibility of some fluids to mineral surfaces due to surface coatings.
In addition, some mineral surface is likely interacting only with equilibrated pore. The Marcellus Shale is currently the largest shale gas formation in play across the world.
The low-permeability formation requires hydraulic fracturing to be produced. In this process, millions of gallons of water are blended with chemical additives and pumped into each well to fracture the reservoir rock. The environmental properties of some of these additives have been studied, but their behavior under downhole conditions is not widely reported in the peer-reviewed literature.
These compounds and their reaction products may return to the surface as produced or waste water. In the event of a spill or release, this water has the potential to contaminate surface soil and water. Of these additives, biocides may present a formidable challenge to water quality.
Biocides are toxic compounds by design , typically added to the Marcellus Shale to control bacteria in the well. An assessment of the most frequently used biocides indicated a need to study the chemical dazomet under reservoir conditions. The Marcellus Shale contains significant deposits of pyrite.
This is a ubiquitous mineral within black shales that is known to react with organic compounds in both oxic and anoxic settings. Thus, the objective of our study was to determine the effect of pyrite on the hydrolysis of dazomet. Liquid chromatography-triple quadrupole mass spectrometry LC-QQQ was used to calculate the loss rate of aqueous dazomet.
Gas chromatography-mass spectrometry GC-MS was used to identify the reaction products. Our experiments show that in water, dazomet rapidly hydrolyses in water to form organic and inorganic transformation products. This reaction rate was unaffected when performed under anoxic conditions. However, with pyrite we found an appreciable increase in the removal rate of dazomet.
This was accompanied by a corresponding change in the distribution of observed. The origin of Cretaceous black shales : a change in the surface ocean ecosystem and its triggers. PubMed Central.
Black shale is dark-colored, organic-rich sediment, and there have been many episodes of black shale deposition over the history of the Earth. Black shales are source rocks for petroleum and natural gas, and thus are both geologically and economically important.
Here, we review our recent progress in understanding of the surface ocean ecosystem during periods of carbonaceous sediment deposition, and the factors triggering black shale deposition. The stable nitrogen isotopic composition of geoporphyrins geological derivatives of chlorophylls strongly suggests that N2-fixation was a major process for nourishing the photoautotrophs.
A symbiotic association between diatoms and cyanobacteria may have been a major primary producer during episodes of black shale deposition. The timing of black shale formation in the Cretaceous is strongly correlated with the emplacement of large igneous provinces such as the Ontong Java Plateau, suggesting that black shale deposition was ultimately induced by massive volcanic events.
However, the process that connects these events remains to be solved. A comparative study of selenium oxyanion sorption was carried out by means of batch sorption experiments on three argillaceous rocks that differ in their mineralogical compositions and textural properties.
The results show no selenate Se VI sorption onto the argillaceous rocks after 60 days, but clear sorption of selenite Se IV , the extent being closely related to the initial Se IV concentration. The Se IV sorption isotherms acquired for the three argillaceous rocks can be reproduced well by means of Langmuir formalism, particularly with a two-site Langmuir model.
The comparison of the Se IV sorption isotherms obtained for these three rocks led to identification of pyrite associated with natural organic matter NOM as one of the main phases involved in selenium retention. While the desorption results suggested a significant Se IV reduction in the Upper Toarcian samples, the reversible sorption shown on the Black Shales and OPA samples was correlated with a sulfate increase, symptomatic of surface oxidation of pyrite which could limit the Se IV reduction in favor of sorption.
Formation resistivity as an indicator of oil generation in black shales. Black , organic-rich shales of Late Devonian-Early Mississippi age are present in many basins of the North American craton and, where mature, have significant economic importance as hydrocarbon source rocks. Examples drawn from the upper and lower shale members of the Bakken Formation, Williston basin, North Dakota, and the Woodford Shale , Anadarko basin, Oklahoma, demonstrate the utility of formation resistivity as a direct in-situ indicator of oil generation in black shales.
With the onset of oil generation, nonconductive hydrocarbons begin to replace conductive pore water, and the resistivity of a given black-shale interval increases from low levels associated with thermal immaturitymore » to values approaching infinity. A resistivity of 35 ohm-m marks the boundary between immature and mature source rocks for each of the three shales studied. Thermal maturity-resistivity crossplots make possible a straightforward determination of thermal maturity at the onset of oil generation, and are sufficiently precise to detect subtle differences in source-rock properties.
In most black shales , such as the Chattanooga Shale and related shales of the eastern interior United States, increased metal and metalloid contents are generally related to increased organic carbon content, decreased sedimentation rate, organic matter type, or position in the basin.
In areas where the stratigraphic equivalents of the Chattanooga Shale are deeply buried and and the organic material is thermally mature, metal contents are essentially the same as in unheated areas and correlate with organic C or S contents. This paradigm does not hold for the Cambrian Alum Shale Formation of Sweden where increased metal content does not necessarily correlate with organic matter content nor is metal enrichment necessarily related to land derived humic material because this organic matter is all of marine source.
Tectonically disturbed and metamorphosed allochthonous samples of Alum Shale on the Caledonian front in western Sweden have even higher amounts for some metals V, Ni, Zn and Ba relative to the autochthonous shales in this area and those in southern Sweden. History of water-column anoxia in the Black Sea indicated by pyrite framboid size distributions.
A detailed study of size distributions of framboidal pyrite in Holocene Black Sea sediments establishes the timing of a change from deposition under an oxic water column to deposition under an anoxic and sulfidic water column. Late-stage sulfides and sulfarsenides in Lower Cambrian black shale stone coal from the Huangjiawan mine, Guizhou Province, People's Republic of China. The Ni-Mo Huangjiawan mine, Guizhou Province, People's Republic of China, occurs in Lower Cambrian black shale stone coal in an area where other mines have recently extracted ore from the same horizon.
Detailed electron microprobe EMPA and scanning electron microscope SEM analyses of representative thin sections have revealed a complex assemblage of sulfides and sulfarsenides. Early sulfidic and phosphatic nodules and host matrix have been lithified, somewhat fractured, and then mineralized with later-stage sulfides and sulfarsenides. Gersdorffite, millerite, polydymite, pyrite , sphalerite, chalcopyrite, galena, and clausthalite have been recognized.
EMPA data are given for the major phases. Pyrite trace-element distributions and coeval Ni-, As-sulfides indicate that in the main ore layer, the last sulfide deposition was Ni-As-Co-rich.
Mo and V deposition were early in the petrogenesis of these rocks. The assemblages gersdorffite-millerite-polydymite pyrite and millerite-gersdorffite pyrite and the composition of gersdorffite indicate a formation temperature of between ?? C suggesting that the last solutions to infiltrate and mineralize the samples were related to hydrothermal processes.
Environmentally sensitive elements such as As, Cd, and Se are hosted by sulfides and sulfarsenides and are the main source of these elements to residual soil. Crops grown on them are enriched in these elements, and they may be hazardous for animal and human consumption. Springer-Verlag Hydrocarbon potential of Upper Devonian black shale , eastern Kentucky. The gas-producing Upper Devonian black shales of eastern Kentucky represent cycles of organic units alternating with less-organic units that were dominated by an influx of clastics from a northeastern source.
This pattern of sedimentation is typical throughout the southern Appalachian basin in areas basinal to, yet still influenced by, the Catskill delta to the northwest. These black shales , which thin westward onto the Cincinnati arch, dip eastward into the Appalachian basin. To evaluate the future gas potential of Devonian shale , a data base has been compiled, consisting of specific geologic and engineering information from Devonian shale wells in Letcher,more » Knott, Floyd, Martin, and Pike Counties, Kentucky.
The first successful gas completion in eastern Kentucky was drilled in Martin County in Comparison of initial open-flow potential IP and long-term production data for these wells demonstrates that higher IP values generally indicate wells of higher production potential. Areas of higher IP are aligned linearly, and these lineaments are interpreted to be related to fracture systems within the Devonian shale.
These fractures may be basement influenced. Temperature log analyses indicate that the greatest number of natural gas shows occur in the lower Huron Member of the Ohio Shale.
Using both the temperature log to indicate gas shows and the gamma-ray log to determine the producing unit is a workable method for selecting the interval for treatment.
Black shale deposition during Toarcian super-greenhouse driven by sea level. One of the most elusive aspects of the Toarcian Oceanic Anoxic Event T-OAE is the paradox between carbon isotopes that indicate intense global primary productivity and organic carbon burial at a global scale, and the delayed expression of anoxia in Europe. During the earliest Toarcian, no black shales were deposited in the European epicontinental seaways, and most organic carbon enrichment of the sediments postdated the T-OAE defined by the overarching positive trend in the carbon isotopes.
In the present studied, we have attempted to establish a sequence stratigraphy framework for Early Toarcian deposits recovered from a core drilled in the Paris Basin using a combination of mineralogical quartz and clay relative abundance and geochemical Si, Zr, Ti and Al measurements. Combined with the evolution in redox sensitive elements Fe, V and Mo , the data suggest that expression of anoxia was hampered in European epicontinental seas during most of the T-OAE due to insufficient water depth that prevented stratification of the water column.
Only the first stratigraphic occurrence of black shales in Europe corresponds to the "global" event. Additionally, this first black shale occurrence is coeval with the record of the major negative Carbon Isotope Excursion CIE , likely corresponding to a period of transient greenhouse intensification likely due to massive injection of carbon into the Atmosphere-Ocean system. As a response to enhanced weathering and riverine run-off, increased fresh water supply to the basin may have promoted the development of full anoxic conditions through haline stratification of the water column.
In contrast, post T-OAE black shales were restricted to epicontinental seas higher Mo to TOC ratios during a period of relative high sea level, and carbon isotopes. The graphite black shale of Vendas de Ceira located in south of Coimbra Portugal , caused serious instability problems in recent road excavation slopes. The problems increased with the rain, transforming shales into a dark mud that acquires a metallic hue when dried.
The black shales are attributed to the Devonian or eventually, to the Silurian. At the base of the slope is observed graphite black shale and on the topbrown schist. Samples were collected during the slope excavation works. Undisturbed and less altered materials were selected. Further, sampling was made difficult as the graphite shale was covered by a thick layer of reinforced concrete, which was used to stabilize the excavated surfaces. The mineralogy is mainly constituted by quartz, muscovite, ilite, ilmenite and feldspar without the presence of expansive minerals.
The organic matter content is 0. The unconfined linear expansion confirms the higher expandability Due the shale material degradated with water, mercury porosimetry was used. The pores size vary between 0. In order to have a comparison term, a porosity test was carried out on the low weatherable brown shale , which is. A curious depletion of 13C in the organic matter of marine black shales has been widely recognized ever since the advent of carbon isotope measurements half a century ago.
Paleozoic and Mesozoic black shales commonly have del13C values between and permil, whereas modern marine organic matter has values between and permil. The black shale values mimic those of continental organic matter, yet sedimentary settings and Rock-Eval results indicate that the organic matter is marine in origin.
This presentation will overview and discuss hypotheses to explain the isotopically light values of the black shales. First, the preferential removal of isotopically heavier organic matter components such as carbohydrates by diagenesis will be examined and shown to be wanting. Second, the possible oxidation of isotopically light methane released from clathrates that would have altered the DIC pool available to phytoplankton will be considered and also be found unlikely.
A third possibility - that greater concentrations of CO2 in the greenhouse atmospheres that corresponded with deposition of many black shales allowed greater discrimination against 13C during photosynthesis - will be evaluated from del13C values of bulk carbon and of algal and land-plant biomarker molecules.
Finally, the possibility that stronger stratification of the surface ocean may have magnified photic zone recycling of organic matter and reincorporation of its isotopically light carbon into fresh biomass will be considered. Although the fourth possibility is contrary to the conditions of vertical mixing of nutrients that exist in modern upwelling systems and that are responsible for their high productivity, it is consistent with the strongly stratified conditions that accompanied the high productivity that produced the Pliocene-Pleistocene sapropels of the Mediterranean Sea.
Because the sapropels and most Phanerozic black shales share del15N values near 0 permil, nitrogen fixation evidently was. Distribution and variation of the inorganic fraction of Devonian to Bashkirian black shales in the north-western part of the Dniepr-Donets Basin, Ukraine. Mineralogical data of core samples from 12 wells are used to investigate lateral and vertical variations in the lithofacies of Devonian to Bashkirian black shales in the north-western part of the Dniepr-Donets-Basin.
Sulphur and carbonate contents as well as organic geochemical parameters, including TOC and Hydrogen Index have been determined on the same sample set within the frame of an earlier study Sachsenhofer et al. This allows the correlation of inorganic and organic composition of the black shales.
Aims of the study are to distinguish between detrital and authigenic minerals, to relate the lithofacies of the black shales with the tectono-stratigraphic sequences of the Dniepr-Donets Basin, to contribute to the reconstruction of the depositional environment and to relate diagenetic processes with the thermal history of the basin.
Mineral compositions were determined primarily using XRD-measurements applying several measurement procedures, e. Major differences exist in the mineralogical composition of the black shales.
Kaolinite contents are significantly higher in rocks with a Tournaisian or Early Visean age than in any other stratigraphic unit. This is also true for two Lower Visean coal samples from the shallow north-westernmost part of the basin. Chlorite contents reach maxima in uppermost Visean and overlying rocks. Quartz contents are often high in Upper Visean rocks and reach maxima in Bashkirian units.
Feldspar-rich rocks are observed in Devonian sediments from the north-western part of the study area and may reflect the proximity to a sediment source. Carbonate contents are typically low, but reach very high values in some Tournaisian, Lower Visean and Serpukhovian samples. Pyrite contents reach maxima along the basin axis in Tournaisian and Visean rocks reflecting anoxic conditions. Mixed layer. One of the most elusive aspects of the Toarcian oceanic anoxic event T-OAE is the paradox between carbon isotopes that indicate intense global primary productivity and organic carbon burial at a global scale, and the delayed expression of anoxia in Europe.
During the earliest Toarcian, no black shales were deposited in the European epicontinental seaways, and most organic carbon enrichment of the sediments postdated the end of the overarching positive trend in the carbon isotopes that characterises the T-OAE. In the present study, we have attempted to establish a sequence stratigraphic framework for Early Toarcian deposits recovered from a core drilled in the Paris Basin using a combination of mineralogical quartz and clay relative abundance and geochemical Si, Zr, Ti and Al measurements.
Combined with the evolution in redox sensitive elements Fe, V and Mo , the data suggest that expression of anoxia was hampered in European epicontinental seas during most of the T-OAE defined by the positive carbon isotope trend due to insufficient water depth that prevented stratification of the water column. Additionally, this first black shale occurrence is coeval with the record of the major negative Carbon Isotope Excursion CIE , likely corresponding to a period of transient greenhouse intensification likely due to massive injection of carbon into the atmosphere-ocean system.
In contrast, post T-OAE black shales during the serpentinum and bifrons Zones were restricted to epicontinental. Kiyokawa, S. The 3. These sequences formed coarsening and thickening upward black shale -BIF sequences. The Dixon Island Formation consists komatiite-rhyolite sequences with many hydrothermal veins and very fine laminated cherty rocks above them.
The Cleaverville Formation contains black shale , fragments-bearing pyroclastic beds, white chert, greenish shale and BIF. Especially, CL3 core, which drilled through the Iron formation, shows siderite-chert beds above black shale identified before magnetite lamination bed. The magnetite bed formed very thin laminated bed with siderite lamination. This magnetite bed was covered by black shale beds again.
Our preliminary result show that siderite and chert layers formed before magnetite iron sedimentation. The lower-upper sequence of organic carbon rich black shales are similar amount of organic content and 13C isotope around per mill. So we investigate that the Archean iron formation, especially Cleaverville iron formation, was highly related by hydrothermal input and started pre-syn iron sedimentation at anoxic oceanic condition.
To address the question of the redox state of the Precambrian atmosphere-hydrosphere system via sediments requires measurement of redox sensitive trace elements, and inter-element ratios, in deep water black shales with a chemical sedimentary "hydrogenic" component. This approach is endorsed by recent progress in research of redox-sensitive trace metals records in late Proterozoic and Phanerozoic sedimentary rocks, which has provided important clues to how the redox state of depositional environments has changed over time.
Many conventional studies, in contrast, have been on first cycle volcanogenic turbidites with a minimal hydrogenic input Taylor and McLennan, Accordingly, we have analyzed the redox-sensitive, trace element compositions of the 2. These pyrite -bearing black shales , which were originally argillaceous sediments containing organic matter and low in thermal maturity, were primarily deposited in the deep-sea pelagic environments.
Calculated U concentrations from hydrogenic component are between 0. The results are consistent with a locally to globally oxidized atmosphere-shallow hydrosphere pre Taylor, S. The geochemical evolution of the continental crust: Reviews of. Detachment of particulate iron sulfide during shale -water interaction. Hydraulic fracturing, a commonly used technique to extract oil and gas from shales , is controversial in part because of the threat it poses to water resources.
The technique involves the injection into the subsurface of large amounts of fluid, which can become contaminated by fluid-rock interaction.
The dissolution of pyrite is thought to be a primary pathway for the contamination of fracturing fluids with toxic elements, such as arsenic and lead. In this study, we use direct observations with atomic force microscopy to show that the dissolution of carbonate minerals in Eagle Ford shale leads to the physical detachment of embedded pyrite grains.
To simulate the way fluid interacts with a fractured shale surface, we also reacted rock samples in a flow-through cell, and used environmental scanning electron microscopy to compare the surfaces before and after interaction with water. Crucially, our results show that the flux of particulate iron sulfide into the fluid may be orders of magnitude higher than the flux of pyrite from chemical dissolution.
This result suggests that mechanical detachment of pyrite grains could be the dominant mode by which arsenic and other inorganic elements are mobilized in the subsurface. Thus, during hydraulic fracturing operations and in groundwater systems containing pyrite , the transport of many toxic species may be controlled by the transport of colloidal iron sulfide particles.
Pyrite footprinting of RNA. Schlatterer, Joerg C. Black -Right-Pointing-Pointer Repetitive experiments can be done in a powdered pyrite filled cartridge. Mapping the surface of RNA molecules with chemical and enzymatic probes has revealed invaluable information about structure and folding.
A crystal structure, molecular dynamics simulation and atomic mutagenesis studies suggest that nucleotides of an asymmetric bulge participate in the dynamic architecture of the ribozyme's active center. Here, we use powdered pyrite held in a commercially available cartridge to footprint the Diels-Alderase ribozyme with single nucleotide resolution. The loop's flexibility may contribute to substrate recruitment and product release.
In conjunction with horizontal drilling, hydraulic fracturing or fracking has enabled the recovery of natural gas from low permeable shale formations. In addition to water, these fracking fluids employ proppants and up to 38 different chemical additives to improve the efficiency of the process.
One important class of additives used in hydraulic fracturing is biocides. When applied appropriately, they limit the growth of harmful microorganisms within the well, saving energy producers 4. However, biocides or their harmful daughter products may return to the surface in produced water, which must then be appropriately stored, treated and disposed of. Little is known about the effect of mineral-fluid interactions on the fate of the biocides employed in hydraulic fracturing.
In this study, we employed laboratory experiments to determine changes in the persistence and products of these biocides under controlled environments. While many minerals are present in shale formations, pyrite , FeS2 s is particularly interesting because of its prevalence and reactivity.
Both of these surfaces have been shown to be reactive with organic compounds. Chlorinated compounds undergo redox reactions at the pyrite -fluid interface, and sulfur-containing compounds undergo exceptionally strong sorption to both pristine and oxidized pyrite. This mineral may significantly influence the degradation of biocides in the Marcellus Shale.
Thus, the overall goal of this study was to understand the effect of pyrite on biocide reactivity in hydraulic fracturing, focusing on the influence of pyrite on specific functional groups. The first specific objective was to demonstrate the effect of pyrite and pyrite reaction products on the degradation of the bromine-containing biocide, DBNPA.
On the addition of pyrite to DBNPA, degradation rates of the doubly brominated compound were found to increase. On the origin of a phosphate enriched interval in the Chattanooga Shale Upper Devonian of Tennessee-A combined sedimentologic, petrographic, and geochemical study.
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