首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Effective radium-226 concentration (ECRa) has been measured in soil samples from seven horizontal and vertical profiles of terrace scarps in the northern part of Kathmandu Valley, Nepal. The samples belong to the Thimi, Gokarna, and Tokha Formations, dated from 50 to 14 ky BP, and represent a diverse fluvio-deltaic sedimentary facies mainly consisting of gravelly to coarse sands, black, orange and brown clays. ECRa was measured in the laboratory by radon-222 emanation. The samples (n = 177) are placed in air-tight glass containers, from which, after an accumulation time varying from 3 to 18 days, the concentration of radon-222, radioactive decay product of radium-226 and radioactive gas with a half-life of 3.8 days, is measured using scintillation flasks. The ECRa values from the seven different profiles of the terrace deposits vary from 0.4 to 43 Bq kg?1, with profile averages ranging from 12 ± 1 to 27 ± 2 Bq kg?1. The values have a remarkable consistency along a particular horizon of sediment layers, clearly demonstrating that these values can be used for long distance correlations of the sediment horizons. Widely separated sediment profiles, representing similar stratigraphic positions, exhibit consistent ECRa values in corresponding stratigraphic sediment layers. ECRa measurements therefore appear particularly useful for lithologic and stratigraphic discriminations. For comparison, ECRa values of soils from different localities having various sources of origin were also obtained: 9.2 ± 0.4 Bq kg?1 in soils of Syabru–Bensi (Central Nepal), 23 ± 1 Bq kg?1 in red residual soils of the Bhattar-Trisuli Bazar terrace (North of Kathmandu), 17.1 ± 0.3 Bq kg?1 in red residual soils of terrace of Kalikasthan (North of Trisuli Bazar) and 10 ± 1 Bq kg?1 in red residual soils of a site near Nagarkot (East of Kathmandu). The knowledge of ECRa values for these various soils is important for modelling radon exhalation at the ground surface, in particular in the vicinity of active faults. Importantly, the study also reveals that, above numerous sediments of Kathmandu Valley, radon concentration in dwellings can potentially exceed the level of 300 Bq m?3 for residential areas; a fact that should be seriously taken into account by the governmental and non-governmental agencies as well as building authorities.  相似文献   

2.
Physical, physicochemical, and mineralogical-petrographic methods have been applied to samples of ophiolite-hosted chromite ore from different deposits and occurrences in the Urals. Temperature dependences of dielectric loss obtained for nine chromite ore samples consisting of 95–98% Cr spinel show prominent peaks indicating a relaxation origin of the loss. The analyzed samples have the loss peaks at different temperatures depending mainly on H = (FeO/Fe2O3)? : (FeO/Fe2O3)??, where (FeO/Fe2O3)? and (FeO/Fe2O3)?? are, respectively, the ferrous/ferric oxide ratios in the samples before and after heating to 800 °C, and H is thus the heating-induced relative change in the FeO/Fe2O3 ratio. These peak temperatures vary from 550 °C (sample 1, high-Cr chromium spinel with more than 52% Cr2O3) to 750 °C (sample 2, aluminous and magnesian spinel with less than 30% Cr2O3), and H ranges correspondingly from 1.61 to 5.49. The temperature of the loss peaks is related with H as H = 34.30 ? 11.52N + 1.20N2, with an error of σ = 0.19 (N = T · 10?2, T is temperature in °C).  相似文献   

3.
The solubility of synthetic ZnS(cr) was measured at 25–250 °C and P = 150 bars as a function of pH in aqueous sulfide solutions (~ 0.015–0.15 m of total reduced sulfur). The solubility determinations were performed using a Ti flow-through hydrothermal reactor. The solubility of ZnS(cr) was found to increase slowly with temperature over the whole pH range from 2 to ~ 10. The values of the Zn–S–HS complex stability constant, β, were determined for Zn(HS)20(aq), Zn(HS)3?, Zn(HS)42?, and ZnS(HS)?. Based on the experimental values the Ryzhenko–Bryzgalin electrostatic model parameters for these stability constants were calculated, and the ZnS(cr) solubility and the speciation of Zn in sulfide-containing hydrothermal solutions were evaluated. The most pronounced solubility increase, about 3 log units at m(Stotal) = 0.1 for the temperatures from 25 to 250 °C, was found in acidic solutions (pH ~ 3 to 4) in the Zn(HS)20(aq) predominance field. In weakly alkaline solutions, where Zn(HS)3? and Zn(HS)42? are the dominant Zn–S–HS complexes, the ZnS(cr) solubility increases by 1 log unit at the same conditions. It was found that ZnS(HS)? and especially Zn(HS)42? become less important in high temperature solutions. At 25 °C and m(Stotal) = 0.1, these species dominate Zn speciation at pH > 7. At 100 °C and m(Stotal) = 0.1, the maximum fraction of Zn(HS)42? is only 20% of the total Zn concentration (i.e. at pHt ~ 7.5), whereas at 350 °C and 3 <pHt <10, the fraction of Zn(HS)42? and ZnS(HS)? is less than 0.05% and 2.5% respectively, of the total Zn concentration and Zn(HS)20 and Zn(HS)3? predominate. The measured equilibrium formation constants were combined with the literature data on the stability of Zn–Cl complexes in order to evaluate the concentration and speciation of Zn in chloride solutions. It was found that at acidic pH, and in more saline fluids having total chloride > 0.05 m, Zn–Cl complexes are responsible for hydrothermal Zn transport with no significant contribution of Zn–S–HS complexes. The hydrosulfide/sulfide complexes will play a more important role in lower salinity (< 0.05 m chloride) hydrothermal solutions which are characteristic of many epithermal ore depositing environments. The value of ΔfG° (β-ZnS(cr)) = ? 198.6 ± 0.2 kJ/mol at 25 °C was determined via solubility measurements of natural low-iron Santander (Spain) sphalerite.  相似文献   

4.
Pure-iron end-member hibbingite, Fe2(OH)3Cl(s), may be important to geological repositories in salt formations, as it may be a dominant corrosion product of steel waste canisters in an anoxic environment in Na–Cl- and Na–Mg–Cl-dominated brines. In this study, the solubility of Fe2(OH)3Cl(s), the pure-iron end-member of hibbingite (FeII, Mg)2(OH)3Cl(s), and Fe(OH)2(s) in 0.04 m to 6 m NaCl brines has been determined. For the reactionFe2(OH)3Cl(s) + 3H+ ? 3 H2O + 2 Fe2+ + Cl?,the solubility constant of Fe2(OH)3Cl(s) at infinite dilution and 25 °C has been found to be log10 K = 17.12 ± 0.15 (95% confidence interval using F statistics for 36 data points and 3 parameters). For the reactionFe(OH)2(s) + 2H+ ? 2 H2O + Fe2+,the solubility constant of Fe(OH)2 at infinite dilution and 25 °C has been found to be log10 K = 12.95 ± 0.13 (95 % confidence interval using F statistics for 36 data points and 3 parameters). For the combined set of solubility data for Fe2(OH)3Cl(s) and Fe(OH)2(s), the Na+–Fe2+ pair Pitzer interaction parameter θNa+/Fe2+ has been found to be 0.08 ± 0.03 (95% confidence interval using F statistics for 36 data points and 3 parameters). In nearly saturated NaCl brine we observed evidence for the conversion of Fe(OH)2(s) to Fe2(OH)3Cl(s). Additionally, when Fe2(OH)3Cl(s) was added to sodium sulfate brines, the formation of green rust(II) sulfate was observed, along with the generation of hydrogen gas. The results presented here provide insight into understanding and modeling the geochemistry and performance assessment of nuclear waste repositories in salt formations.  相似文献   

5.
In this study we experimentally determine phlogopite/melt partition coefficients of Ra and other trace elements in a lamproitic system. This work was achieved using an analytical technique (LA-ICP-MS) with low detection limits (~ 0.01 fg) permitting the measurement of the very low Ra concentrations feasible in experiments (~ 1 ppb). DRaphlogopite/melt was determined to 2.28 ± 0.44 and 2.84 ± 0.47 in two experiments, the ratio DRa/DBa is around 1.6. The compatibility of Ra in phlogopite results from an ionic radius being close to the apex of the lattice strain parabola for earth alkalis in the large XII-coordinated interlayer site of phlogopite. A re-evaluation of DRa and DRa/DBa for magmatic minerals containing appreciable Ra, yields DRamineral/melt ranging from ~ 2.6 for phlogopite down to 2–3 ? 10? 5 for pyroxenes, and DRa/DBamineral/melt from ~ 4 for leucite to 2 ? 10? 2 for orthopyroxene. The influence of melt composition on DRa/DBa is less than 10%. All investigated minerals have different DRa/DBa, strongly fractionating Ra from Ba. Thus, for magmatic systems, (226Ra)/Ba in the various minerals is not constant, these minerals do not form a straight line in the (226Ra)/Ba–(230Th)/Ba system at the time of crystallization and thus, there is no (226Ra)/Ba–(230Th)/Ba isochron at t0. 226Ra–230Th–Ba mineral dating is thus applicable only to model ages calculated from mineral–glass pairs with known DRa.  相似文献   

6.
Over 300 samples for paleomagnetic analysis and K–Ar dating were collected from 27 sites at NW–SE and NE–SW trending dike swarms (herein, NW dikes and NE dikes, respectively) in the Koshikijima Islands, northern Ryukyu Arc. The NW dikes are Middle Miocene in age and have directions (D = ? 37.7°, I = 51.8°, α95 = 9.6°, and κ = 40.8) that are deflected westward relative to the stable eastern Asian continent. Conversely, the NE dikes, of Late Miocene age, have directions (D = 16.1°, I = 57.7°, α95 = 7.1°, and κ = 41.9) that show no such deflection. These differences are interpreted as indicating that the Koshikijima Islands underwent approximately 40° of counter-clockwise rotation during the Middle to Late Miocene. A synthesis of the paleomagnetic and structural data suggests a three-stage history of extensional deformation: (1) displacement upon normal faults (F1 faults) without vertical-axis block rotation, (2) strike-slip reactivation of F1 faults and oblique-normal displacement on NE–SW-trending faults (F2 faults) with vertical-axis block rotation, and (3) oblique-normal displacement on F2 faults without vertical-axis block rotation. Regional differences in the timing and amount of counter-clockwise vertical-axis block rotations indicate that the northern Ryukyu Arc rotated as several distinct rigid blocks.  相似文献   

7.
Uranium(VI) sorption onto kaolinite was investigated as a function of pH (3–12), sorbate/sorbent ratio (1 × 10?6–1 × 10?4 M U(VI) with 2 g/L kaolinite), ionic strength (0.001–0.1 M NaNO3), and pCO2 (0–5%) in the presence or absence of 1 × 10?2–1 × 10?4 M citric acid, 1 × 10?2–1 × 10?4 M EDTA, and 10 or 20 mg/L fulvic acid. Control experiments without-solids, containing 1 × 10?6–1 × 10?4 M U(VI) in 0.01 M NaNO3 were used to evaluate sorption to the container wall and precipitation of U phases as a function of pH. Control experiments demonstrate significant loss (up to 100%) of U from solution. Although some loss, particularly in 1 × 10?5 and 1 × 10?4 M U experiments, is expected due to precipitation of schoepite, adsorption on the container walls is significant, particularly in 1 × 10?6 M U experiments. In the absence of ligands, U(VI) sorption on kaolinite increases from pH ～3 to 7 and decreases from pH ～7.5 to 12. Increasing ionic strength from 0.001 to 0.1 M produces only a slight decrease in U(VI) sorption at pH < 7, whereas 10% pCO2 greatly diminishes U(VI) sorption between pH ～5.5 and 11. Addition of fulvic acid produces a small increase in U(VI) sorption at pH < 5; in contrast, between pH 5 and 10 fulvic acid, citric acid, and EDTA all decrease U(VI) sorption. This suggests that fulvic acid enhances U(VI) sorption slightly via formation of ternary ligand bridges at low pH, whereas EDTA and citric acid do not form ternary surface complexes with the U(VI), and that all three ligands, as well as carbonate, form aqueous uranyl complexes that keep U(VI) in solution at higher pH.  相似文献   

8.
《Comptes Rendus Geoscience》2007,339(14-15):872-884
Now extinct, short-lived radioactive nuclides, such as 7Be (T1/2 = 53 days), 10Be (T1/2 = 1.5 Ma), 26Al (T1/2 = 0.74 Ma), 36Cl (T1/2 = 0.3 Ma), 41Ca (T1/2 = 0.1 Ma), 53Mn (T1/2 = 3.7 Ma) and 60Fe (T1/2 = 1.5 Ma), were present in the protosolar nebula when the various components of meteorites formed. The presence of these radioactive isotopes requires a ‘last-minute’ origin, either nucleosynthesis in a massive star dying close in space and time to the nascent solar system or production by local irradiation of part of the protosolar disk by high-energy solar cosmic rays. In this review, we list: (i) the different observations indicating the existence of multiple origins for short-lived radioactive nuclides, namely 7Be, 10Be and 36Cl for irradiation scenario and 60Fe for injection scenario; (ii) the constraints that exist on their distribution (homogeneous or heterogeneous) in the accretion disk; (iii) the constraints they brought on the timescales of nebular processes (from Ca–Al-rich inclusions to chondrules) and of the accretion and differentiation of planetesimals.  相似文献   

9.
Phosphorite from the Meade Peak Phosphatic Shale member of the Permian Phosphoria Formation has been mined in southeastern Idaho since 1906. Dumps of waste rock from mining operations contain high concentrations of Se which readily leach into nearby streams and wetlands. While the most common mineralogical residence of Se in the phosphatic shale is elemental Se, Se(0), Se is also an integral component of sulfide phases (pyrite, sphalerite and vaesite–pyritess) in the waste rock. It may also be present as adsorbed selenate and/or selenite, and FeSe2 and organo-selenides.Se release from the waste rock has been observed in field and laboratory experiments. Release rates calculated from waste rock dump and column leachate solutions describe the net, overall Se release from all of the possible sources of Se listed above. In field studies, Se concentration in seepage water (pH 7.4–7.8) from the Wooley Valley Unit 4 dump ranges from 3600 µg/L in May to 10 µg/L by Sept. Surface water flow, Q, from the seep also declines over the summer, from 2 L/s in May to 0.03 L/s in Sept. Se flux ([Se] ? Q) reaches a steady-state of < 150 mg/day in 1–4 months, depending upon the volume of Q. Se release (mg/L) follows a first order reaction with a rate constant, k, = 1.35 – 6.35e?3 h? 1 (11.8–55.6 yr? 1).Laboratory experiments were performed with the waste shale in packed bed reactors; residence time varied from 0.09 to 400 h and outlet pH ～ 7.5. Here, Se concentration increased with increasing residence time and release was modeled with a first order reaction with k = 2.19e?3 h? 1 (19.2 yr? 1).Rate constants reported here fall within an order of magnitude of reported rate constants for oxidation of Se(0) formed by bacterial precipitation. This similarity among rate constants from both field and laboratory studies combined with the direct observation of Se(0) in waste shales of the Phosphoria Formation suggests that oxidation of Se(0) may control steady-state Se concentration in water draining the Wooley Valley waste dump.  相似文献   

10.
The main limiting factor in obtaining precise and accurate uranium-series (U-series) ages of corals that lived during the last few hundred years is the ability to constrain and correct for initial thorium-230 (230Th0), which is proportionally much higher in younger samples. This is becoming particularly important in palaeoecological research where accurate chronologies, based on the 230Th chronometer, are required to pinpoint changes in coral community structure and the timing of mortality events in recent time (e.g. since European settlement of northern Australia in the 1850s). In this study, thermal ionisation mass spectrometry (TIMS) U-series dating of 43 samples of known ages collected from living Porites spp. from the far northern, central and southern inshore regions of the Great Barrier Reef (GBR) was performed to spatially constrain initial 230Th/232Th (230Th/232Th0) variability. In these living Porites corals, the majority of 230Th/232Th0 values fell within error of the conservative bulk Earth 230Th/232Th atomic value of 4.3 ± 4.3 × 10?6 (2σ) generally assumed for 230Th0 corrections where the primary source is terrestrially derived. However, the results of this study demonstrate that the accuracy of 230Th ages can be further improved by using locally determined 230Th/232Th0 values for correction, supporting the conclusion made by Shen et al. (2008) for the Western Pacific. Despite samples being taken from regions adjacent to contrasting levels of land modification, no significant differences were found in 230Th/232Th0 between regions exposed to varying levels of sediment during river runoff events. Overall, 39 of the total 43 230Th/232Th0 atomic values measured in samples from inshore reefs across the entire region show a normal distribution ranging from 3.5 ± 1.1 to 8.1 ± 1.1 × 10?6, with a weighted mean of 5.76 ± 0.34 × 10?6 (2σ, MSWD = 8.1). Considering the scatter of the data, the weighted mean value with a more conservative assigned error of 25% (i.e. 5.8 ± 1.4 × 10?6) that encompasses the full variation of the 39 230Th/232Th0 measurements is recommended as a more appropriate value for initial 230Th corrections for U-series dating of most Porites samples from inshore regions of the GBR. This will result in significant improvement in both the precision and accuracy of the corrected 230Th ages related to those based on the assumed bulk Earth 230Th/232Th0 value of 4.3 ± 4.3 × 10?6. However, several anomalously high 230Th/232Th0 values reaching up to 28.0 ± 1.6 × 10?6 occasionally found in some coral annual bands coinciding with El Niño years imply high 230Th/232Th0 sources and highlight the complexities of understanding 230Th/232Th0 variability. For U-series dating of young coral samples from such sites where anomalous 230Th/232Th0 values occur, we suggest replicate dating of multiple growth bands with known age difference to verify age accuracy.  相似文献   

11.
Gold in the Sahinli and Tespih Dere intermediate sulfidation gold-base metal deposits in Western Turkey occurs in relatively deep epithermal quartz veins along with base metal minerals which have epithermal textures, including plumose quartz, vug infills, comb and cockade textures and matrix-supported milled breccias. The total sulfide content of the veins in the area is variable ranging from < 1% to 60% and is dominated by pyrite, galena, sphalerite and chalcopyrite. Sphalerite is Fe-poor (0.6 to 1.4 mol% FeS). Minor amounts of Ag-rich tetrahedrite are present. Primary hydrothermal alteration minerals include illite/muscovite, mixed-layer illite/smectite (11.6 Å) and clinochlore towards the east and, alunite, dickite/nacrite and pyrophyllite towards the west at Sahinli; major illite/muscovite and dickite occur at Tespih Dere and Sarioluk, respectively.Fluid inclusions in main-stage quartz at Sahinli are only liquid-rich, with homogenization temperatures ranging from 220 to 322 °C and the majority of Th values between 250 and 300 °C. Salinity ranges from 4.3 to 6.9 wt.% NaCl equiv. First ice-melting temperatures (Tmf) between ?24.5 and ?19.0 °C indicate that the fluids were dominated by NaCl – H2O during mineralization. The relatively higher average Th at the Tespih Dere deposit (295 °C) is attributed to a relatively deeper level of exposure.Calculated δ18O values indicate that ore-forming hydrothermal fluids in the study area had δ18OH2O ranging from + 1.1 to + 9.7‰ (average = 3.8‰), strongly 18O-enriched compared with present-day hydrothermal meteoric water in the area (δ18O = ?8.5‰). δD values of fluid inclusions in quartz range from ?58 to ?93‰ and δD values of clay minerals and alunite from ?40 to ?119‰. δD values from intermediate argillic alteration (average = ?68‰) in the study area are very similar to δD values of the present-day local geothermal system (average δD = ?54‰) whereas δD values from advanced-argillic alteration (average δD = ?33‰) are very different from the present-day local geothermal system.The δ34S values in samples from the Sahinli and Tespih Dere deposits average ?2.9‰ for pyrite; ?3.3‰ for chalcopyrite; ?5.4‰ for sphalerite and ?7.6‰ for galena. These data are consistent with derivation of the sulfur from either igneous rocks or possibly from local wallrock.  相似文献   

12.
Significant amounts of sulfuric acid (H2SO4) rich saline water can be produced by the oxidation of sulfide minerals contained in inland acid sulfate soils (IASS). In the absence of carbonate minerals, the dissolution of phyllosilicate minerals is one of very few processes that can provide long-term acid neutralisation. It is therefore important to understand the acid dissolution behavior of naturally occurring clay minerals from IASS under saline–acidic solutions. The objective of this study was to investigate the dissolution of a natural clay-rich sample under saline–acidic conditions (pH 1–4; ionic strengths = 0.01 and 0.25 M; 25 °C) and over a range of temperatures (25–45 °C; pH 1 and pH 4). The clay-rich sample referred to as Bottle Bend clay (BB clay) used was from an IASS (Bottle Bend lagoon) in south-western New South Wales (Australia) and contained smectite (40%), illite (27%), kaolinite (26%) and quartz (6%). Acid dissolution of the BB clay was initially rapid, as indicated by the fast release of cations (Si, Al, K, Fe, Mg). Relatively higher Al (pH 4) and K (pH 2–4) release was obtained from BB clay dissolution in higher ionic strength solutions compared to the lower ionic strength solutions. The steady state dissolution rate (as determined from Si, Al and Fe release rates; RSi, RAl, RFe) increased with decreasing solution pH and increasing temperature. For example, the highest log RSi value was obtained at pH 1 and 45 °C (−9.07 mol g−1 s−1), while the lowest log RSi value was obtained at pH 4 and 25 °C (−11.20 mol g−1 s−1). A comparison of these results with pure mineral dissolution rates from the literature suggests that the BB clay dissolved at a much faster rate compared to the pure mineral samples. Apparent activation energies calculated for the clay sample varied over the range 76.6 kJ mol−1 (pH 1) to 37.7 kJ mol−1 (pH 4) which compare very well with the activation energy values for acidic dissolution of monomineralic samples e.g. montmorillonite from previous studies. The acid neutralisation capacity (ANC) of the clay sample was calculated from the release of all structural cations except Si (i.e. Al, Fe, K, Mg). According to these calculations an ANC of 1.11 kg H2SO4/tonne clay/day was provided by clay dissolution at pH 1 (I = 0.25 M, 25 °C) compared to an ANC of 0.21 kg H2SO4/tonne clay/day at pH 4 (I = 0.25 M, 25 °C). The highest ANC of 6.91 kg H2SO4/tonne clay/day was provided by clay dissolution at pH 1 and at 45 °C (I = 0.25 M), which is more than three times higher than the ANC provided under the similar solution conditions at 25 °C. In wetlands with little solid phase buffering available apart from clay minerals, it is imperative to consider the potential ANC provided by the dissolution of abundantly occurring phyllosilicate minerals in devising rehabilitation schemes.  相似文献   

13.
The kinetics of forward extraction [AuCl4]? from aqua regia medium by diethylene glycol dibutyl ether (DBC) have been investigated by the Lewis cell (LC) technique. At first gold extraction has been carried out under different experimental conditions for achieving the stoichiometry coefficients and the value of the extraction equilibrium constant (K = 0.1). For kinetic data treatment, flux ‘F’ method has been applied. Reaction order with respect to DBC, pH and [AuCl4]? was determined and then the rate constant was calculated. The rate of gold extraction from 2 M chloride medium can be expressed as F = 100.88[AuCl4?]1.25 [DBC]0.4 [H+]?0.22. Kinetics data were treated by EVIEWS software and coefficients were obtained. The comparison of manual and software results indicated that the results had good conformity. Influence of temperature was studied and then activation energy, Ea, (11.17 kJ/mol), activation enthalpy (11.66 kJ/mol) and entropy (?187 J/mol K) were calculated by using Arrhenius and activation complex theory respectively. Ea value (< 20.9 kJ/mol) indicates that, the extraction of gold (III) in the investigated system is controlled by diffusion process.  相似文献   

14.
The distribution of glycerol dialkyl glycerol tetraethers (GDGTs) can reflect continental environmental changes. Recently, the distribution of branched GDGTs (bGDGTs) has been proposed as a novel tool for paleoelevation reconstructions. Here we report the variation in TEX86 (tetraether index of 86 carbon atoms) of isoprenoidal GDGTs (iGDGTs) and MBT (methylation of branched tetraether index) of bGDGTs along an altitudinal transect on Mt. Xiangpi, NE Qinghai-Tibetan Plateau. Both TEX86 and MBT values of surface soils showed significant linear decreases with altitude (TEX86: R2 = 0.65; n = 50; MBT: R2 = 0.69; n = 24). We suggest that the apparent relationships between the two indices and altitude may be related to temperature. Our preliminary investigation suggests that the TEX86 index can potentially be applied as a paleoelevation indicator in addition to the MBT index on the Qinghai-Tibetan Plateau.  相似文献   

15.
The organic geochemical methods of hydrocarbon prospecting involve the characterization of sedimentary organic matter in terms of its abundance, source and thermal maturity, which are essential prerequisites for a hydrocarbon source rock. In the present study, evaluation of organic matter in the outcrop shale samples from the Semri and Kaimur Groups of Vindhyan basin was carried out using Rock Eval pyrolysis. Also, the adsorbed low molecular weight hydrocarbons, methane, ethane, propane and butane, were investigated in the near surface soils to infer the generation of hydrocarbons in the Vindhyan basin. The Total Organic Carbon (TOC) content in shales ranges between 0.04% and 1.43%. The S1 (thermally liberated free hydrocarbons) values range between 0.01–0.09 mgHC/gRock (milligram hydrocarbon per gram of rock sample), whereas the S2 (hydrocarbons from cracking of kerogen) show the values between 0.01 and 0.14 mgHC/gRock. Based on the Tmax (temperature at highest yield of S2) and the hydrogen index (HI) correlations, the organic matter is characterized by Type III kerogen. The adsorbed soil gas, CH4 (C1), C2H6 (C2), C3H8 (C3) and nC4H10, (nC4), concentrations measured in the soil samples from the eastern part of Vindhyan basin (Son Valley) vary from 0 to 186 ppb, 0 to 4 ppb, 0 to 5 ppb, and 0 to 1 ppb, respectively. The stable carbon isotope values for the desorbed methane (δ13C1) and ethane (δ13C2) range between −45.7‰ to −25.2‰ and −35.3‰ to −20.19‰ (VPDB), respectively suggesting a thermogenic source for these hydrocarbons. High concentrations of thermogenic hydrocarbons are characteristic of areas around Sagar, Narsinghpur, Katni and Satna in the Son Valley. The light hydrocarbon concentrations (C1–C4) in near surface soils of the western Vindhyan basin around Chambal Valley have been reported to vary between 1–2547 ppb, 1–558 ppb, 1–181 ppb, 1–37 ppb and 1–32 ppb, respectively with high concentrations around Baran-Jhalawar-Bhanpur-Garot regions (Kumar et al., 2006). The light gaseous hydrocarbon anomalies are coincident with the wrench faults (Kota – Dholpur, Ratlam – Shivpuri, Kannod – Damoh, Son Banspur – Rewa wrench) in the Vindhyan basin, which may provide conducive pathways for the migration of the hydrocarbons towards the near surface soils.  相似文献   

16.
Small angle neutron scattering techniques have been applied to investigate the phase behavior of CO2 injected into coal and possible changes in the coal pore structure that may result from this injection. Three coals were selected for this study: the Seelyville coal from the Illinois Basin (Ro = 0.53%), Baralaba coal from the Bowen Basin (Ro = 0.67%), and Bulli 4 coal from the Sydney Basin (Ro = 1.42%). The coals were selected from different depths to represent the range of the underground CO2 conditions (from subcritical to supercritical) which may be realized in the deep subsurface environment. The experiments were conducted in a high pressure cell and CO2 was injected under a range of pressure conditions, including those corresponding to in-situ hydrostatic subsurface conditions for each coal. Our experiments indicate that the porous matrix of all coals remains essentially unchanged after exposure to CO2 at pressures up to 200 bar (1 bar = 105 Pa). Each coal responds differently to the CO2 exposure and this response appears to be different in pores of various sizes within the same coal. For the Seelyville coal at reservoir conditions (16 °C, 50 bar), CO2 condenses from a gas into liquid, which leads to increased average fluid density in the pores (ρpore) with sizes (r) 1 × 105 ≥ r ≥ 1 × 104 Å (ρpore ≈ 0.489 g/cm3) as well as in small pores with size between 30 and 300 Å (ρpore ≈ 0.671 g/cm3). These values are by a factor of three to four higher than the density of bulk CO2 (ρCO2) under similar thermodynamic conditions (ρCO2 ≈ 0.15 g/cm3). At the same time, in the intermediate size pores with r ≈ 1000 Å the average fluid density is similar to the density of bulk fluid, which indicates that adsorption does not occur in these pores. At in situ conditions for the Baralaba coal (35 OC, 100 bar), the average fluid density of CO2 in all pores is lower than that of the bulk fluid (ρpore / ρCO2 ≈ 0.6). Neutron scattering from the Bulli 4 coal did not show any significant variation with pressure, a phenomenon which we assign to the extremely small amount of porosity of this coal in the pore size range between 35 and 100,000 Å.  相似文献   

17.
Mafic xenoliths of garnet pyroxenite and eclogite from the Wajrakarur, Narayanpet and Raichur kimberlite fields in the Archaean Eastern Dharwar Craton (EDC) of southern India have been studied. The composition of clinopyroxene shows transition from omphacite (3–6 wt% Na2O) in eclogites to Ca pyroxene (<3 wt% Na2O) in garnet pyroxenites. Some of the xenoliths have additional phases such as kyanite, enstatite, chromian spinel or rutile as discrete grains. Clinopyroxene in a rutile eclogite has an XMg value of 0.70, which is unusually low compared to the XMg range of 0.91–0.97 for all other samples. Garnet in the rutile eclogite is also highly iron-rich with an end member composition of Prp26.5Alm52.5Grs14.7Adr5.1TiAdr0.3Sps1.0Uv0.1. Garnets in several xenoliths are Cr-rich with up to 8 mol% knorringite component. Geothermobarometric calculations in Cr-rich xenoliths yield different P–T ranges for eclogites and garnet pyroxenites with average P–T conditions of 36 kbar and 1080 °C, and 27 kbar and 830 °C, respectively. The calculated P–T ranges approximate to a 45 mW m?2 model geotherm, which is on the higher side of the typical range of xenolith/xenocryst geotherms (35–45 mW m?2) for several Archaean cratons in the world. This indicates that the EDC was hotter than many other shield regions of the world in the mid-Proterozoic period when kimberlites intruded the craton. Textural and mineral chemical characteristics of the mafic xenoliths favour a magmatic cumulate process for their origin as opposed to subducted and metamorphosed oceanic crust.  相似文献   

18.
Emission of phosphine, a gaseous form of P, is presently considered a potential pathway of the P biogeochemical cycle in aquatic sediments. This study investigated the emission fluxes of phosphine and its potential production mechanisms in the intertidal marshes of the Yangtze Estuary. It is shown that the relatively high emission fluxes of phosphine were measured in warm seasons, with the values of 3.85–24.9 ng m?2 h?1 and 4.21–36.5 ng m?2 h?1 in August and September, respectively. In contrast, lower fluxes of phosphine appeared in May (1.23–6.32 ng m?2 h?1) and January (0.21–0.91 ng m?2 h?1). Also, the fluxes of phosphine were generally higher in the freshwater marsh, compared with the brackish marsh. The spatio-temporal pattern of phosphine emissions was observed to be mainly associated with sediment structure, temperature and salinity. Meanwhile, the significant correlations of phosphine emissions with sedimentary P and alkaline phosphatase activities reflect that phosphine probably derives from the microbial transformations of PO4 and organic P. In addition, it is estimated that approximately 1.08 × 106 g of phosphine is released annually from sediments into the pelagic water of the Yangtze Estuary. Therefore, it is concluded that phosphine emissions may be an important internal source of P, making a significant contribution to the occurrence of algal blooms especially during warm seasons.  相似文献   

19.
This study was conducted on recent desert samples—including (1) soils, (2) plants, (3) the shell, and (4) organic matter from modern specimens of the land snail Eremina desertorum—which were collected at several altitudes (316–360 m above sea level) from a site in the New Cairo Petrified Forest. The soils and shellE. desertorum were analyzed for carbonate composition and isotopic composition (δ18O, δ13C). The plants and organic matterE. desertorum were analyzed for organic carbon content and δ13C. The soil carbonate, consisting of calcite plus minor dolomite, has δ18O values from −3.19 to −1.78‰ and δ13C values −1.79 to −0.27‰; covariance between the two values accords with arid climatic conditions. The local plants include C3 and C4 types, with the latter being dominant. Each type has distinctive bulk organic carbon δ13C values: −26.51 to −25.36‰ for C3-type, and −13.74 to −12.43‰ for C4-type plants.The carbonate of the shellE. desertorum is composed of aragonite plus minor calcite, with relatively homogenous isotopic compositions (δ18Omean = −0.28 ± 0.22‰; δ13Cmean = −4.46 ± 0.58‰). Most of the δ18O values (based on a model for oxygen isotope fractionation in an aragonite-water system) are consistent with evaporated water signatures. The organic matterE. desertorum varies only slightly in bulk organic carbon δ13C values (−21.78 ± 1.20‰) and these values suggest that the snail consumed more of C3-type than C4-type plants. The overall offset in δ13C values (−17.32‰) observed between shellE. desertorum carbonate and organic matterE. desertorum exceeds the value expected for vegetation input, and implies that 30% of carbon in the shellE. desertorum carbonate comes from the consumption of limestone material.  相似文献   

20.
LA–ICP–MS zircon U–Pb ages, geochemical and Sr–Nd–Pb isotope data are presented for mafic–ultramafic complexes from the southern Liaoning–southern Jilin area with the aim of determining the nature of the Mesozoic lithospheric mantle and to further constrain the spatial extent of destruction of the North China Craton (NCC). The complexes consist of olivine-websterite, gabbro, dolerite, and gabbro-diorite. Zircons from the complexes show typical zoning absorption, are euhedral–subhedral in shape, and yield high Th/U ratios (1.23–2.87), indicating a magmatic origin. Zircon U–Pb age data indicate that they formed in the Early Cretaceous (129–137 Ma). Geochemically, they have SiO2 = 44.3–49.8%, MgO = 6.8–26.5%, Cr = 102–3578 ppm, and Ni = 31–1308 ppm, and are characterized by enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs) and heavy rare earth elements (HREEs), as well as a wide range of Sr–Nd–Pb isotopic compositions [(87Sr/86Sr)i = 0.70557–0.71119; εNd (t) = ?5.4 to ?20.1; (206Pb/204Pb)i = 15.13–17.85; Δ7/4 = ?11.49 to 16.00; Δ8/4 = 102.64–203.48]. Compared with the southern Liaoning mafic–ultramafic rocks, the southern Jilin mafic–ultramafic rocks have high TiO2 and Al2O3 contents, high εNd (t) values, low (La/Yb)N values, low initial 87Sr/86Sr ratios, and low radiogenic Pb isotopic compositions. These findings indicate that the primary magmas of the southern Jilin complexes were derived from lithospheric mantle that was previously metasomatized by a melt derived from the delaminated ancient lower crust, whereas the primary magmas of the southern Liaoning complexes originated from partial melting of a lithospheric mantle source that was previously modified by melt derived from the broken-off Yangtze slab. Therefore, the lateral extent of the NCC destruction should include the southern Liaoning–southern Jilin area.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号