Characteristics of gas geochemistry in Yangbajing geothermal field, Tibet

CO 2 is a main component of gases in the Yangbajing geothermal field, usually higher than 85 in volume; others are N 2, H 2S, H 2, CH 4, etc. Helium R/R a ratios, ranging from 0.14 to 0.46, indicate a crustal component to be dominant in the gases. δ 13C-CO 2 values and δ 34S-H 2S values are in the range -7.72‰--11.33‰ and 0.2‰-8.3‰, respectively. The gases are inferred to mostly derive from the partial melting of the Nyainqentanglha core complex. The gases of shallow and deep reservoirs are distinctive in chemical compositions and δ 34S-H 2S values, which shows their different flowing paths and physical-chemical processes. Sulphur does not approach isotopic equilibrium between H 2S and SO 2- 4 species in both reservoirs. Significance of steam chemical monitoring is also discussed.     

Compound-specific carbon isotope compositions of individual long-chain n-alkanes in severe Asian dust episodes in the North China coast in 2002

Asian dust storms originating from the arid regions of central and eastern Asia and from the Loess Plateau in China frequently occur in spring [1,2]. Driven by the East Asian monsoon, Asian dust can be transported to northern Pacific Ocean[2―8]. Asian du…     

Variations of organic carbon isotopic composition and its environmental significance during the last glacial on western Chinese Loess Plateau

The last glacial period is characterized by a cold and dry climate with low atmospheric CO2 concentration. The relatively arid climate and low CO2 concentration are favorable to the growth of C4 plants, but the low temperature limits the development of th…     

Isotopic composition of organic carbon and elemental carbon in PM2.5 in Hangzhou, China

In order to identify the sources of organic carbon (OC) and elemental carbon (EC) in airborne PM2.5 in Hangzhou, OC and EC were oxidized to CO2 offline in two thermal steps, and their carbon isotope compositions were measured by mass spectrometer. Results showed that the average δ13COC values were -52.8‰, -48.1‰, -50.0‰ and -52.5‰ in spring, summer, autumn, and winter, respectively, and the annual average value was -50.9‰ (-85.0‰ to -35.6‰), whereas δ13CEC values were -26.4‰, -26.9‰, -26.7‰ and -25.9‰ in the four seasons, and its annual value was -26.5‰ (-30.5‰ to -23.8‰). Large differences were found between isotope compositions of the two types of carbon. δ13COC values were much smaller than those of δ13CEC, and varied in a large range, and the ratios in both spring and winter were the smallest. δ13CEC varied in a small range, and its mean values in four seasons were nearly the same. This suggests that the carbon isotope compositions of OC and EC in PM2.5 can provide useful information in distinguishing their sources.     

Preliminary study of microscale zircon oxygen isotopes for Dabie-Sulu metamorphic rocks： Ion probe in situ analyses

151 in situ analyses of oxygen isotopes were carried out by ion micro-probe for zircons from 8 localities of HP-UHP metamorphic rocks including eclogites in the Dabie-Sulu terrane. The results show significant heterogeneity in δ^18O values, with variation in different rocks from -8.5‰ to 9.7‰ and within one sample from 2‰ to 12‰. No measurable difference in δ^18O was observed between protolith magmatic (detrital) zircons and metamorphic recrystallized zircons within analytical uncertainties from the ion micro-probe measurements. This indicates that the metamorphic zircons have inherited the oxygen isotopic compositions of protolith zircons despite the HP to UHP metamorphism. According to their protolith ages from zircon U-Pb in situ dating by the same ion micro-probe, two groups of oxygen isotope composition are recognized, with one having δ^18O values of 6‰-7‰ for old protolith of 1.9-2.5 Ga ages and the other 0‰-2‰ for young protolith of 0.7-0.8 Ga ages. The latter anomalously low δ^18O values of zircons indicate that the magma has had the obvious involvement of meteoric water when forming the young protolith of high-grade metamorphic rocks. This may be correlated with the snowball Earth event occurring in South China and the world elsewhere during the Neoproterozoic.     

Southwest monsoon changes indicated by oxygen isotope of ostracode shells from sediments in Qinghai Lake since the late Glacial

The δ 18O records of ostracode shells in sediments of core QH-2000 from Qinghai Lake can be used as a better proxy to reflect monsoon changes. Low monsoon precipitation between 17.5 and 11 cal. ka BP is indicated by positive δ 18O values averaging 2.37‰. A fast shift in δ 18O from positive at 11 cal. ka BP to negative at 10 cal. ka BP indicates sharp increase of monsoon precipitation. An interval of generally high monsoon precipitation is observed between 10 and 6 cal. ka BP with δ 18O values averaging -2.15‰. Decrease of monsoon precipitation between 6 and 2.5 cal. ka BP is indicated by positive δ 18O values. δ 18O keeps positive values averaging 3.0‰ between 2.5 and 0 cal. ka BP suggesting low high monsoon precipitation. The climatic changes indicated by δ 18O records of ostracode shells in sedi- ments of core QH-2000 from Qinghai Lake and our broader regional comparison show that the climate in Qinghai Lake since the late Glacial is probably controlled by southwest monsoon other than southeast monsoon.     

Diet control on carbon isotopic composition of land snail shell carbonate

Carbon isotope compositions for both the carbonate shells and soft bodies (organic tissue) of living land snails collected mostly from the Loess Plateau, China have been measured. The result shows that δ 13C values range from -13.1‰ to -4.3‰ for the aragonite shell samples and from -26.8‰ to -18.0‰ for the soft body samples. Although the shells are enriched in 13C relative to the bodies averagely by 14.2(±0.8)‰, the shell δ 13Ca values are closely correlated to the body δ 13Corg values, expressed as δ 13Ca = 1.021 δ 13Corg 14.38 (R = 0.965; N = 31). This relationship indicates that δ 13Ca is primarily a function of the isotopic composition of the snail diets since previous studies have proved that the snail body is the same as their food in carbon isotope composition. In other words, carbon isotope compo-sition of the carbonate shell can be used as a proxy to estimate the dietary 13C abundance of the land snails. The data also support that the 13C enrichment of the carbonate shells results mainly from the equilibrium fractionations between the metabolic CO2, HCO3-in the hemolymph and shell aragonite, and partially from kinetic fractionations when snail shells form during their activity.     

Variation of δ13C in karst soil in Yaji Karst Experiment Site, Guilin

This study deals with δ₁₃ C variation in karst soil system of Yaji Karst Experiment Site, Guilin, a typical region of humid subtropical karst formations. Samples of near ground air, plant tissue, soil and water (soil solution and karst spring) were respectively collected on site in different seasons during 1996–1999. Considerable variation of δ₁₃ C values are not only found with different carbon pools of soil organic carbon, soil air CO₂ and soil water HCO₃⁻, but also with the soil depths and with different seasons during a year. The °₁₃ C values of CO₂ both of near ground air and soil air are lower in July than those in April by 1‰–4‰ PDB. Our results indicate that the δ₁₃ C values of carbon in the water and air are essentially dependent on interface carbon interaction of air-plant—soil-rock—water governed by soil organic carbon and soil CO₂ in the system.     

The biomarkers of 2,6,10,15, 19-pentamethylicosenes and their carbon isotopic composition in the sediments from the Gulf of Mexico

The methanogenic archaea and sulfate reduction bacteria are flourishing in the sediments associated with gas venting and gas hydrate settings on the sea floor, where the anaerobic oxidation of methane (AOM) me-diated by these bacteria is the dominant path…     

Variation of soil Δδ13C values in Xifeng loess-paleosol sequence and its paleoenvironmental implication

The carbon isotopic compositions of soil organic matter （SOM） and total carbonate （TC） in Xifeng Ioess-paleosol sequence have been studied. The δ^13CsoM values vary from -23.8‰ to -20.2‰, which are higher in interglacial than in glacial stages. Contrary to δ^13Csoi values, the δ^13CTc values vary from -8.5‰ to -3.6‰ and are lower in interglacial than in glacial stages. The differences （△δ^13C） between the δ^13CsoM and δ^13CTc values vary from 14.1‰ to 19.4‰. Our results from the Xifeng loesspaleosol sequence indicate that the △δ^13C values represent the ratio of primary carbonate （PC） to secondary carbonate （SC）. The △δ^13C values were high in the loess stages, and the maximal PC-to-SC ratio can reach 6：4. But in the paleosol stages, the △δ^13C values were low, with a small proportion of PC. The △δ^13C values in Ioess-paleosol sequence also indicate the contributions of the dust to the loess sediment in the Chinese Loess Plateau because the dust contains the PC.     

Foliar δ^13C and δ^15N values of C3 plants in the Ethiopia Rift Valley and their environmental controls

The foliar C and N stable isotopic compositions （δ^13C and δ^15N） and the relationships between these compositions and environmental factors of C3 plants in the Ethiopia Rift Valley were investigated. There were three distribution patterns for foliar δ^13C with mean values of -26.7‰±0.4‰, -29.7‰ ±0.6‰ , and -26.9‰± 1.2‰ in cold-moist, temperate-moist, and arid-hot environments, respectively. The δ^15N values ranged from -1.4‰ ±1.7‰ to 14.3‰ ± 0.1‰, with higher values under arid-hot conditions and the lowest values in plants growing at higher altitudes under cold-moist conditions. A strong negative relationship between mean annual precipitation and δ^15N explained more than half of the observed variation in the δ^15N values （r2= 0.54, P 〈 0.001）; a modest positive relationship was also found between δ^15N and temperature （r2 = 0.32, P 〈 0.01）. A weakly positive relationship existed between δ^13C and temperature, and changes in δ^13C values with precipitation and altitude followed quadratic curves. This suggests a shift in the effects of water and heat conditions caused by altitude on carbon isotopic discrimination.     

Molybdenum isotopic composition as a tracer for low-medium temperature hydrothermal ore-forming systems: A case study on the Dajiangping pyrite deposit,western Guangdong Province,China

Little is known about the range or controls on the molybdenum isotopic composition of low-medium temperature hydrothermal ore-forming systems. We present molybdenum isotope data from 12 hydrothermal syndepositional silicalite and carbonaceous slate samples from the Dajiangping pyrite deposit in western Guangdong Province, South China. The δ ^97/95 Mo values from Orebody III range from −0.02‰ to 0.29‰, with an average of 0.18‰. In contrast, the composition values from Orebody IV display a larger variation from −0.70‰ to 0.62‰. However, the five samples from the main ore bed all show strong negative values. This indicates that the significant variation in molybdenum isotopic composition supports different hydrothermal ore-forming metallogenesis and a metallogenic environment between the two orebodies. Orebody III is likely to have been deposited from submarine exhalative hydrothermal fluids under a relatively strong reducing environment and Orebody IV may have also been influenced by hydrothermal superimposition in a more oxidized disequilibrium condition. In addition, the δ ^97/95 Mo values of Orebody IV are clearly negative, together with the values increasing stratigraphically upward in the ore beds, suggesting that the metallogenic environment of Orebody IV is different from the open oceanic systems. There might be dynamic fractionation in this restricted environment. Therefore, the molybdenum isotope can be used as an effective tracer for the ore-forming fluid and metallogenic environment.     

Variability of snail growing season at the Chinese Loess Plateau during the last 75 ka

Knowledge of seasonal climate change is one of the key issues facing Quaternary paleoclimatic studies and estimating seasonal climate change is difficult,especially changes such as seasonal length on glacial-interglacial timescales.The stable isotope composition from seasonal land snail shells provides the potential to reveal seasonal climatic features.Two modern land snail species,cold-aridiphilous Pupilla aeoli and thermo-humidiphilous Punctum orphana,were collected from different climatic zones in 18 localities across the Chinese Loess Plateau,spanning 11 degrees of longitude and covering a range of 1000 km2.The duration of the snail growing season(temperature ≥10℃) was shorter(202 ± 6 d) in the eastern Loess Plateau compared with in the western Loess Plateau(162 ±7 d).The δ13C of P.aeoli shells was ?9.1‰ to ?4.7‰ and ?5.0‰ to 0.3‰ for δ18O.For P.orphana,the δ13C ranged from ?9.1‰ to ?1.9‰ and ?8.9‰ to ?2.9‰ for δ18O.Both the δ13C and δ18O differences between the two snail species were reduced from the east to the western Loess Plateau(2.8‰ to 0.2 ± 1.1‰ for δ13C and 4.7‰ to 2.9 ± 1.3‰ for δ18O).These isotopic differences roughly reflect the difference in the growing season lengths between the east and west Loess Plateau indicating that the duration of the snail growing season shortens by 15 d or 19 d if the difference decreases by 1‰ in δ13C or δ18O,respectively.Thus,the difference in δ13C and δ18O between both snail species can be used to reveal the length of the snail growing season in the past.Based on our investigation,the length of the snail growing seasons from the Xifeng region during the last 75 ka was reconstructed.During the mid-Holocene(8-3 ka),the mean isotopic difference from both snail species reached maximum values of 2.6 ± 0.7‰ and 2.1 ± 1.4‰ for δ13C and δ18O,respectively.This was followed by MIS 3 that ranged from 2.5 ± 0.4‰ for δ13C and 1.6 ± 0.8‰ for δ18O.The Last Glacial Maximum changed by only 0.2‰ and 0.4‰ for δ13C and δ18O,respectively.Therefore,we estimate that the duration of the snail growing seasons to be ～200 ± 10 d during the mid-Holocene,190 ± 6 d in MIS 3 and 160 ± 3 d during the last glacial period.     

A breakthrough of researching reservoir adsorption gas and its significance

GC-C-MS on linear isotope analysis equipment makes it possible to measure the hydrocarbon gases at the level of 10 -3-10 -2 μL- By applying this technique the carbon isotopes of C1-C3 of the adsorbed gas from the Triassic oil sand bed of the Aican-l Well in the Turpan-Hami basin were analysed. The δ13C values of C1-C3, are -55.1‰, -38.6‰ and -35.0‰ respectively. In terms of geochemical characteristics of natural gases and crude oils, in combination with basinal geological backgrounds, it is considered that the reservoir adsorbed gas was formed by crude-oil biodegradation, absorbed by reservoir rocks and its oil-gas source is related with the Permain (perhaps including the Carboniferous). The adsorbed gas is obviously different from the Jurassic coal-generated oil and gas.     

Preliminary Mo isotope data of Phanerozoic clastic sediments from the northern margin of the Yangtze block and its implication for paleoenvironmental conditions

Mo isotopes along with Nd isotopes and other geochemical characteristics of the Phanerozoic clastic sediments from the northern margin of the Yangtze block were analyzed by MC-ICP-MS and some other techniques, spanning the period from Cambrian to Jurassic. The δ 98Mo values and εNd(t ) in these sedimets were observed to exhibit a large range of variation (?0.65‰―+1.87‰, ?1.46―?10.90, respec-tively). Specifically, the sample from Late Permian Maokou Formation has relatively positive values in both δ 98Mo and...     

A reconnaissance of Cu isotopic compositions of hydrothermal vein-type copper deposit Jinman,Yunnan, China

The Jinman deposit is a low-temperature hydrothermal vein-type copper deposit, which occurs along faults and fractures within Middle Jurassic sandstone and mudstone units of the Lanping-Simao Mesozoic-Cenozoic basin of Yunnan Province. In this note, we report for the first time the Cu isotopic compositions of Cu-sulfides from the Jinman deposit. The data show large variations and low δ⁶⁵Cu values of -3.70‰ to +0.30‰, which are in sharp contrast to the δ⁶⁵Cu values of high-temperature magmatic-hydrothermal copper deposits (-0.62‰ to +0.40‰) and the modern ocean-floor massive sulfide deposits (-0.48‰ to +1.15‰). It is suggested that the Cu isotope fractionation at Jinman is affected mainly by the following factors, i.e. a low temperature of ore formation (150—286℃); a sedimentary source for ore materials; various stages of ore deposition; and involvement of organic matter in the ore-forming processes.     

Treatment efficiency of integrated vertical-flow constructed wetland for saline wastewater

The integrated vertical-flow constructed wetland(IVCW) was simulated with three suits of designed experiment columns planted with Kandelia candel.Units A,B and C were irrigated with sewage of different salinity(A:10‰ B:20‰,C:30‰),respectively.The removal rates of dissolved organic carbon(DOC),NH3-N and NO3--N dropped 90.4%-48.6%,80.2%-40.3% and 84.8%-60.9%,respectively,when salinity increases from 10‰ to 30‰.The removal rate of TP increased 14%-31.2%,oppositely.A 20-day inflow salinity drastic change shock affective trial was done on units D and E.Unit D was used as a control and irrigated with saline sewage(20‰).Unit E was irrigated with sewage with low salinity(5‰) as a salinity drastic change shock on the third and fourth days.DOC,NH3-N and NO3--N removal efficiency of unit E showed a three-stage process of change,"rapidly decrease,increase beyond the normal standard,and then back to the normal standard".TP removal value was negative during the 2-day shock period.     

Palaeodietary study of Sanxingcun Site, Jintan, Jiangsu

C and N stable isotope ratios of 19 human bones in Sanxingcun Site, Jintan, Jiangsu Province, were measured to explore the lifestyle and social economic structure. Although the bone collagen degraded to different extents, the atomic ratio of C/N was located in the range of 2.9-3.6, indicating that they were preserved very well. Average δ13C value (20.05±0.21‰), average δ 15N value (9.69 ±0.33‰) and poor positive correlation between each other suggested that rice agriculture was dominant with hunt-ing-fishing supplemented in human lifestyle. Poor negative correlation between δ 15N values and C3 percentages of foods implied relative independence of rice agriculture and hunting-fishing. Compared to Hemudu Site and Qingpu Site, rice agriculture was developed further, but hunting-fishing decreased. The mode for people in Sanxingcun Site to get the meat was still in the initial exploitation.     

Pure CO2 fluids in the Sarekoubu gold deposit at southern margin of Altai Mountains in Xinjiang, West China

Sarekoubu gold deposit occurs in metamorphosed acid volcanic rocks and volcaniclastic rocks of Devonian Kangbutiebao Formation along the southern margin of Altai Mountains in Xinjiang, West China. Pyritization, silicification and carbonatization are developed in wallrocks, and main gold mineralization stages are pyrite-quartz stage (Ⅱ)and polymetallic sulfide stage (Ⅲ). Primary fluid inclusions are often seen in main gold mineralization stages, which are almost pure CO2 liquid inclusions (Lco2) under room temperature with high densities of 0.85--1.07 g/cm^3. CO2-rich inclusions (Lco2-LH2O) and H2O-rich inclusions (LH2O-LCo2)are subordinate. Fluid inclusions in stage Ⅰ (polymetallic sulfide stage) are more complex than in stage Ⅱ, containing CO2-CH4 system with -78.1-61.9℃ of solid CO2 melting temperatures and -33.7-17.7℃ of partial homogenization temperatures. The trapping pressures of high densities are estimated to be 150-350 MPa. Laser Raman microprobe was used to confirm the composition of pure CO2 liquid inclusions. δ^13C values of CO2 inclusions range from -10.73‰ to -21.15‰, which are similar to some of fluids in the mantle-derived minerals that contain surface organic carbon by subduction recycling. These characteristics differ from many hydrothermal gold deposits. CO2 fluids have a regional source related to post-collisional orogeny.     

Stable carbon and hydrogen isotopic fractionations of alkane compounds and crude oil during aerobically microbial degradation

Petroleum-related environmental pollution has be-come a global concern with the industrial and economicaldevelopment, causing serious ecological risks and threat-ening natural resources and human health. Therefore, it isimportant to characterize contaminants and thereby iden-tify unambiguously the sources of contaminants, not onlyfor the purpose of settling disputes related to liability butmore importantly, for selecting appropriate responses andtaking effective cleanup precautions[1]. Chemica…