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1.
Sediments contain abundant lipid compounds in general, which are used as biomarker compounds to study organic matter sources and reconstruct the pa-laeoenvironments[1—7]. However, lipid compounds in sediments are generally a mixture of various genetic components so that it is difficult to correctly decouple their biological sources only by the results of bio-chemical researches. Carbon isotopic studies of indi-vidual sedimentary lipid compounds can discover their genetic information, which pr…  相似文献   

2.
Petroleum mainly comprises carbon and hydrogen elements. The stable carbon isotopic analysis for whole oil was undertaken as early as the 1930s. After decades, the stable carbon isotopic analytical methods have been developed from analysis for whole oil and oil fractions (e.g., saturated, aromatic and polar frac-tions) into compound-specific isotopic analysis with the emergence of the newly developed GC-C-IRMS analytical technique. Especially, by using com-pound-specific isotopic analytical…  相似文献   

3.
Source rock extracts and crude oils from the Songliao Basin were analyzed by high-temperature gas chromatography (HTGC), gas chromatography-mass spectrometry (HTGC-MS) and gas chromatography-isotope ratio-mass spectrometry (GC-IRMS), for high molecular-weight alkanes. The distributions of n-alkanes in the Nenjiang Formation extracts are in the C14―C63 range; a bimodal distribution occurs in the C-21 and C21―40 regions. The C30―C37 n-alkanes are accompanied by C29―C35 hopanes, whereas the high molecular-weight C45―C47 n-alkanes co-occur with abundant isoalkanes, alkylcyclohexanes and alkylcyclopentanes. The high δ 13C values of the n-alkanes and the microscopic maceral compositions indicate a highly diversified organic source input for the Nenjiang Formation source rocks, ranging from aquatic plants, blue alge-bacteria, to land plant material. In contrast, n-alkanes in the rock extracts of the Qingshankou Formation are characterized by a single modal distribution, with relatively low abundances of C29―C35 hopanes, but high molecular-weight isoalkanes, alkylcyclohexanes and alkylcyclopentanes. The relatively low δ 13C values of C22―C44 n-alkanes and organic material compositions indicate that the source rocks in the Qingshankou Formation contain dominantly type I algal organic matter. The relative abundance of C 40 compounds in source rocks changes little at low maturity stage, but decreases drastically at higher maturity levels, with a concurrent reduction in the odd/even carbon predominance. In crude oils, in contrast, the relative abundance of C 40 compounds appears to relate closely with the oil source and oil viscosity.  相似文献   

4.
The Luliang and Baoshan basins are two small ba- sins in Yunnan Province. In the recent ten years or so, there have been found a number of natural gas pools of commercial importance in the two basins. Although the gas pools are small in size, the natural …  相似文献   

5.
Nitrogen occupies a high content in crust and in atmospheric circle. It is one of the main elements in organism and an important element in sedimentary circle. Although nitrogen is little in crude oil, to a cer-tain degree, it influences the physical and chemical properties of oil, such as viscosity and density[1]. In reservoir the nitrogen-bearing compounds can form ion bonds or hydrogen bonds with substances on rock and form van der Vaals’ force among moleculae so they affect and alter the …  相似文献   

6.
During the 22nd Chinese Antarctic Research Expedition (CHINARE-22), the atmospheric gas samples above the oceanic surface and near the surface were collected on the track for the scientific ship “Xuelong” and on Millor Peninsula of eastern Antarctica, respectively, using the Tedlar gas bags. Every day the sampling times were 10:00 and 22:00 (local time), respectively. In the laboratory, high-precision measurement of the isotopic compositions for N2O in these gas samples was conducted using Thermo Finnigan MAT-253 Isotopic Mass Spectrometer with a fully automated interface for the pre-GC concentration (PreCon) of trace gases. The temporal and spatial variations of δ 15N and δ 18O in atmospheric N2O were analyzed. The mean δ 15N and δ 18O-N2O values above the oceanic surface were (7.21±0.50)‰ and (44.52±0.52)‰, respectively. From 30°N to Antarctica, the δ 15N (6.05‰–7.88‰) linearly increased with the rate of about 0.01‰ with the latitude while the δ 18O (43.05‰–48.78‰) showed a large fluctuation. The δ 15N negatively correlated with air temperature and N2O concentration, and slightly positively correlated with δ 18O. The summertime variations of δ 15N and δ 18O-N2O appeared the same trend on Millor Peninsula of eastern Antarctica. They significantly positively correlated with each other and negatively with N2O concentration. The δ 15N and δ 18O-N2O at different sites averaged (7.42±0.35)‰ and (44.69±0.49)‰, respectively, slightly higher than those above the oceanic surface, significantly higher than those of atmospheric N2O in the low-latitude regions of Northern Hemisphere. The predominant factors affecting the spatial variations of δ 15N and δ 18O values were also discussed. The isotopic data given in this study can help to investigate the global and regional N2O budgets. Supported by the National Natural Science Foundation of China (Grant Nos. 40676005 and 40406001)  相似文献   

7.
Serious interest has been directed toward natural gas hydrate as a potential energy resource; factor in global climate change, and submarine geohazard since naturally occurring gas-hydrate deposits were found in the 1960s. Hydrate Ridge, Cascadia convergent mar- gin, is characterized by abundant methane hydrates at and below the seafloor, active venting of fluids and gases, chemosynthetic communities, and some of the highest methane oxidation rates ever found in the ma-rine environment. All of…  相似文献   

8.
Carbon isotope ratios (δ 13C) of 89 C4 plant samples were determined from the loess area in North China. δ 13C values vary between −10.5‰ and −14.6‰ with a mean of −12.6‰. Along a precipitation gradient from the semi-moist area to the semiarid area, then to the arid area, the δ 13C values of C4 plants show a slight decreasing trend. The δ 13C values of C4 plants in the dry season are found lower than those in the wet season. These trends are opposite to those observed for C3 species.  相似文献   

9.
We describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic composition of CO2 in volcanic plumes. Data collected at Solfatara and Vulcano, where plumes are fed by fumaroles which are accessible for direct sampling, were first used to validate the technique. For both volcanoes, the plume-derived carbon isotopic compositions are in good agreement with the fumarolic compositions, thus providing confidence on the method, and allowing its application at volcanoes where the volcanic component is inaccessible to direct sampling. As a notable example, we applied the same method to Mount Etna where we derived a δ13C of volcanic CO2 between −0.9 ± 0.27‰ and −1.41 ± 0.27‰ (Bocca Nuova and Voragine craters). The comparison of our measurements to data reported in previous work highlights a temporal trend of systematic increase of δ13C values of Etna CO2 from ~ −4‰, in the 1970’s and the 1980’s, to ~ −1‰ at the present time (2009). This shift toward more positive δ13C values matches a concurrent change in magma composition and an increase in the eruption frequency and energy. We discuss such variations in terms of two possible processes: magma carbonate assimilation and carbon isotopic fractionation due to magma degassing along the Etna plumbing system. Finally, our results highlight potential of systematic measurements of the carbon isotopic composition of the CO2 emitted by volcanic plumes for a better understanding of volcanic processes and for improved surveillance of volcanic activity.  相似文献   

10.
Discrimination of abiogenic and biogenic alkane gases   总被引：5，自引：0，他引：5  
We have combined the analytical data of the carbon isotope distribution pattern, R/Ra and CH4/3He values of abiogenic and biogenic (referring to the thermogenic and bacterial or microbial) alkane gases in China with those of alkane gases from USA, Russia, Germany, Australia and other countries. Four discrimination criteria are derived from this comparative study: 1) Carbon isotopic composition is generally greater than -30‰ for abiogenic methane and less than -30‰ for biogenic methane; 2) Abiogenic alkane gases have a carbon isotopic reversal trend (δ 13C1> δ 13C2> δ 13C3> δ 13C4) with δ 13C1>-30‰ in general; 3) Gases with R/Ra >0.5 and δ 13C11 δ 13C2>0 are of abiogenic origin; 4) Gases (meth- ane) with CH4/3He≤106 are of abiogenic origin, whereas gases with CH4/3He≥1011 are of biogenic origin.  相似文献   

11.
Despite great achievements in the origins of domestic pigs made by the methods of zooarchaeology and molecular biology, how to scientifically distinguish the domesticated pigs from wild boars during the early stage of pig domestication is still poorly understood. Compared to wild boar’s diets which come from the natural environment, the diets of domestic pigs are more easily influenced by human feeding activities. Therefore, in principle, exploration of the dietary differences among pigs and under-standing the impact on pig diets fed by humans can have great potential to differentiate between wild boars and domesticated pigs. To reveal dietary differences among pigs and distinguish the domesticated pigs from wild boars based on comparison with the diets of humans and other animals, we analyzed the carbon and nitrogen stable isotopes of human bones from Xiaojingshan Site and animal bones from Yuezhuang Site, both of which belong to Houli Culture in Shandong Province and date to about 8500-7500 years ago. The mean δ13C value ((−17.8 ± 0.3)‰) and δ15N value ((9.0±0.6)‰) in human collagen indicate that although millet agriculture began it was not the main subsistence strategy as millets are typical of C4 plants and that humans made a living mainly by gathering, hunting or raising some domesticated animals. The δ13C value (−16.1‰) and δ15N value (6.9‰) in the bovine suggest that C3 plants were dominant in its diet with some C4 plants complemented. The fish has lower δ13C value (−24.9‰) and higher δ15N value (8.8‰) than the bovine, which is the characteristic of the isotopic values from Eurasian freshwater fish. Based on the differences in carbon and nitrogen isotope values, the pigs can be divided into three groups. A group, composed of two pigs, has low δ13C values (−18.1‰, −20.0‰) and low δ15N values (4.7‰, 6.0‰). B group, only one pig, has the highest δ13C value (−10.6‰) and mediate δ15N value (6.4‰). As for the C group, also only one pig, low δ13C value (−19.0‰) and the highest δ15N value (9.1‰) are observed. Previous studies on the stable isotopes from modern or ancient wild boars’ bones have suggested that C3 plants are predominated in their diets and that their δ15N values are close to those in herbivores and far from those in carnivores. Based on the comparison with the isotope values from humans, the wild boars and the domestic pigs from Xipo Site in Henan 6000-5500 years ago and Kangjia Site in Shaanxi 4500-4000 years ago, we conclude that A pig group belongs to wild boars while B and C groups can be attributed to domesticated pigs. Supported by Max-Planck Society and Chinese Academy of Sciences, Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX3.SYW.N12), National Natural Science Foundation of China (Grant No. 40702003) and President Funding of Graduate University of Chinese Academy of Sciences  相似文献   

12.
Although 1-alkyl-2,3,6-trimethylbenzenes and a high relative amount of 1,2,3,4-tetramethylbenzene have been detected in marine oils and oil asphaltenes from Tabei uplift in the Tarim Basin, their bio-logical sources are not determined. This paper deals with the molecular characteristics of typical ma-rine oil asphaltenes from Tabei and Tazhong uplift in the Tarim Basin and the stable carbon isotopic signatures of individual compounds in the pyrolysates of these asphaltenes using flash pyrolysis-gas chromatograph-mass spectrometer (PY-GC-MS) and gas chromatograph-stable isotope ratio mass spectrometer (GC-C-IRMS), respectively. Relatively abundant 1,2,3,4-tetramethylbenzene is detected in the pyrolysates of these marine oil asphaltenes from the Tarim Basin. δ 13C values of 1,2,3,4-tetrame-thylbenzene in the pyrolysates of oil asphaltenes vary from-19.6‰ to-24.0‰, while those of n-alkanes in the pyrolysates show a range from-33.2‰ to-35.1‰. The 1,2,3,4-tetramethylbenzene in the pyro-lysates of oil asphaltenes proves to be significantly enriched in 13C relative to n-alkanes in the pyro-lysates and oil asphaltenes by 10.8‰―15.2‰ and 8.4‰―13.4‰, respectively. This result indicates a contribution from photosynthetic green sulfur bacteria Chlorobiaceae to relatively abundant 1,2,3,4-tetramethylbenzene in marine oil asphaltenes from the Tarim Basin. Hence, it can be speculated that the source of most marine oil asphaltenes from the Tarim Basin was formed in a strongly reducing water body enriched in H2S under euxinic conditions.  相似文献   

13.
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14.
The carbon isotope compositions of high- and ultrahigh-pressure eclogite and apatite separate from Huangzhen and Shima in SE Dabie Mountains were analyzed by EA-MS online technique. The δ13C values of the eclogites cover a wide range of -30.7‰ - +1.5‰, whereas those of apatites only have a small range of -28.1‰--21.0‰. Some of the eclogites with the high δ13C values suffered retrogressive alteration by CO2-bearing fluids. The low δ13C values of the apatites indicate that the eclogites contain surficial carbon of organic origin. It is concluded that protoliths of the eclogites were exposed to the surface of the Earth, and that the carbon-bearing fluid was depleted in 13C during the eclogite-facies metamorphism.  相似文献   

15.
This paper presents systematic studies on the C—O and Sr—Nd isotopic compositions for Cretaceous Badou carbonatites, Fangcheng basalts, and Jiaodong lamprophyres and Paleozoic Mengyin kimberlites in Shandong Province, China. Paleozoic kimberlites have normal and uniform C—O isotopic compositions with δ13C and δ18O in the range of −4.8‰—−7.6‰ and +9.9‰—+13.2‰, respectively. However, Cretaceous three different types of mantlederived rocks have quite different C—O isotopic compositions, indicating that the mantle sources are probably partially contaminated with organic carbon-bearing crustal materials. These Cretaceous rocks show uniform and EMII-like Sr—Nd isotopic compositions and also indicate that the mantle sources were affected by recycled crustal materials. Comparative studies of C—O and Sr—Nd isotopes reveal that the lithospheric mantle beneath the eastern North China Craton had different isotope characteristics in the Paleozoic, the early Cretaceous, and the Tertiary time. This demonstrates that the lithospheric mantle beneath the region underwent at least twice reconstructions since the Paleozoic. Available data imply that the first reconstruction mainly happened during the Triassic-Jurassic time with gradual changes and the second in the Cretaceous with abrupt changes. Results also show that the early Cretaceous (especially at 120-130 Ma) was perhaps the key period leading to the dramatic change of the Mesozoic geodynamics on the eastern North China Craton.  相似文献   

16.
Geochemical and Pb-Sr-Nd isotopic compositions of five Indosinian granitoid intrusions from the western Qinling belt provide insights into basement nature and tectonic affinity. The results show that the western Qinling granitoids incline towards basic in their bulk chemical composition. The granitoids belong to high-K to shoshonitic series with K2O/Na2O=1.04-1.86 and are dominantly metaluminous with A/CNK=0.90-1.05 (most samples have A/CNK of <1.0). They have similar trace elemental compo- sitional patterns. In Sr-Nd isotopic compositions, they display some extent heterogeneity with Isr=0.70682-0.70845, εNd(t)=?4.85 to ?9.17 and TDM=1.26-1.66 Ga. They are characterized by high ra- diogenic Pb isotopic compositions. Their initial Pb isotopic ratios are 206Pb/204Pb=17.996-18.468, 207Pb/204Pb=15.565-15.677 and 208Pb/204Pb=38.082-38.587. Geochemical and Sr-Nd isotopic composi- tions reveal that magma for the granitoids was derived from partial melting of high-K (Rb) basaltic rocks, which might be formed in 900-1400 Ma. It is suggested that a large amount of the Proterozoic high-K (Rb) basaltic rocks, which underlie the Phanerozoic sedimentary cover, constitute the crustal basement of the western Qinling belt. Pb-Sr-Nd isotopic compositional comparison between the east- ern Qinling and the western Qinling Indosinian granitoids indicates that the crustal basement of the western Qinling is distinct from that of the eastern Qinling. The Baoji-Chengdu railway close to south-north orientation can be taken as an approximate boundary between both basements. The Pb-Nd isotopic compositional characteristics of the western Qinling granitoids suggest that the basement of the western Qinling belt has an affinity with the Yangtze block.  相似文献   

17.
2 and approximately 85% SO2 of the total sulfur gas. Relative amounts of He, Ar, and N2 show a distinct hot-spot signature ( ). The δ13C–CO2 is approximately −3.6‰ and δ34ST is approximately +3.3‰. The δD/δ18O of fumarole H2O indicates steam separation from local meteoric waters whose estimated minimum mean residence time from 3H analyses is ≤40 years. Fumarolic activity at Alcedo is controlled by a caldera-margin fault containing at least seven hydrothermal explosion craters, and by an intracaldera rhyolite vent. Two explosion craters which formed in 1993–1994 produce approximately 15 m3/s of steam, yet discharge temperatures are ≤97°C. Water content of the total gas is 95–97 mol.%, noncondensible gas is 92–98 mol.% CO2, and sulfur gas is dominated by H2S. Relative amounts of He, Ar, and N2 show extensive mixing between hot spot and air or air-saturated meteoric water components but the average . The δ13C–CO2 is approximately −3.5‰ and δ34ST is approximately −0.8‰. The δD/δ18O of fumarole steam indicates separation from a homogeneous reservoir that is enriched 3–5‰ in 18O compared with local meteoric water. 3H indicates that this reservoir water has a maximum mean residence time of approximately 400 years and empirical gas geothermometry indicates a reservoir temperature of 260–320°C. The intracaldera hydrothermal reservoir in Alcedo is probably capable of producing up to 150 MW; however, environmental concerns as well as lack of infrastructure and power users will limit the development of this resource. Received: 19 April 1999 / Accepted: 23 October 1999  相似文献   

18.
The relationship between the carbon isotopic composition of paleosols and pale-ovegetation on the Loess Plateau is still unclear. One of the main reasons is that we are short of knowledge about the characteristics of the carbon isotopic composition of modern soil in this area. A preliminary investigation of the carbon isotopic compositions of the modern soil and the loess/paleosol sequence on the Loess Plateau shows that the carbon isotopic composition of modern soil is consistent with the distribution of modern plants on the Loess Plateau, where the ecosystem is dominated by a mixture of C4 and C3 plants. Comparing the δ13C values of modern soil and loess-paleosol sequences from the Xunyi profile, we conclude that C3 plants dominated the landscape during loess sediment stages, while C4 plants expanded during paleosol stages.  相似文献   

19.
Two types of Hepialus larvae with different diets were distinguished in the Sejila Mountain, Tibetan Plateau based on the stable carbon isotope data of the host Hepialus larva of Cordyceps sinensis and its closely adjacent tender plant roots and humus fractions. Type I is the larva chiefly fed by soil humus, and characterized by the δ 13C values of −22.6‰ to −23.4‰, and more than −23.4‰ in its heads. Type II is the larva chiefly fed by tender plant roots, and characterized by the δ 13C values of −24.6‰ to −27.6‰, and less than −24.6‰ in its heads. Our result has exceeded the traditional understanding that their food sources only come from the tender plant roots, and may provide evidence for choosing cheap and high-quality foods and further establishing artificial habitats in their large-scale reproduction. Supported by the National Key Technology R & D Program (Grant No. 2007BAI32B05)  相似文献   

20.
Organic matter of the Sinian and early Cambrian black shales on the Yangtze Platform belongs to the light carhon group of isotopes with the δ13C values from - 27% to - 35 %, which are lower than those of the contempomneously deposited carbonates and phosphorites. A carbon isotope-stratified paleooceanographic model caused by upwelling is proposed, which can be used not only to interpret the characteristies of organic carbon isotopic compositions of the black shales, but also to interpret the paleogeographic difference in the organic carbon isotope compositions of various types of sedimentary rocks. Project supported by the National Natural Science Foundation of China (Grant No. 49472114) and the Open Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences.  相似文献   

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