Carbon and nitrogen stable isotope analyses of mammal bone fossils from the Zhongba site in the Three Gorges Reservoir region of the Yangtze River,China

Based on AMS ¹⁴C dating data, carbon and nitrogen isotope analyses were conducted on mammal bone collagen of deer, cattle and pigs from the Zhongba site in the Three Gorges Reservoir region of the Yangtze River. These analyses were conducted to reconstruct palaeodiets of mammals, palaeoecology, palaeoenviroment and previous human activities in the study area. Results show that the collagen loss of bone did not change the in vivo isotopic composition of carbon and nitrogen stable isotopes, and most of the bone fossils were well preserved. The bone collagen of samples from deer had a mean δ¹³C of -23.1‰ and a mean δ¹⁵N of 4.7‰, suggesting that deer subsisted in a closed habitat and fed on branches and leaves. The bone collagen of cattle had a mean δ¹³C of –19.6‰ and a mean δ¹⁵N of 5.2‰, which indicates that cattle subsisted in an open habitat and fed on grasses and stems. The δ¹³C values show that both deer and cattle fed on C₃ plants and lived in the same ecosystem, but the t-test results show that deer δ¹³C and δ¹⁵N values were both more negative than those of cattle, indicating that they inhabited different niches. The δ¹³C and δ¹⁵N values of cattle partially overlapped those of deer, suggesting some competition in diets between them. The t-tests show that the δ¹³C and δ¹⁵N values of pigs were more positive than those of cattle and deer, which signifies that pigs occupied a higher trophic level compared to cattle and deer. The wide range of pig δ¹³C values demonstrates that pig trading had been taking place from early Neolithic Age to late Bronze Age. There were no significant differences in deer δ¹³C and δ¹⁵N values among different archaeological periods, making it clear that climatic, ecological and environmental conditions were kept relatively stable from 2200 to 4200 a BP. This stability may have been responsible for the extensive and complete cultural layers at the Zhongba site. The minimum number of samples required to estimate the mean δ¹³C values of deer, pigs and cattle are 8, 73 and 16, respectively, and for mean δ¹⁵N values of deer, pigs and cattle, the minimum numbers are 4, 5 and 6, respectively.     

Stable isotopic analysis on sus bones from the Wanfabozi site, Tonghua, Jilin

In order to study the sus diets and explore the possibility to distinguish domestic pig from wild boar through dietary analysis, stable carbon and nitrogen isotopes of 28 pig bones from archaeological site of Wanfabozi in Tonghua City, Jilin Province were analyzed. The δ^13C and δ^15N values of uncontaminated bones show that the overall pigs in the site were generally herbivores and ate mainly C3 plants. Significant difference of δ^15N values was observed between wild boar and domestic pigs, which may result from the higher consumption of animal protein in domestic pigs other than from that in wild boar, possibly from human leftover or waste,. The dietary difference between wild boar and domestic pigs has great potential to differentiate wild boar and domestic pigs in the early stage of pig domestication.     

Relationship between climatic conditions and the relative abundance of modern C3 and C4 plants in three regions around the North Pacific

Using −24‰ and −14‰ as the endpoints of stable carbon isotopic composition of total organic carbon (δ¹³C_TOC) of surface soil under pure C₃ and C₄ vegetation, and surface soil δ¹³C_TOC data from eastern China, Australia and the Great Plains of North Amer- ica, we estimate the relative abundance of C₃/C₄ plants (i.e., the ratio of C₃ or C₄ biomass to local primary production) in modern vegetation for each region. The relative abundance of modern C₃/C₄ vegetation from each region is compared to the corresponding climatic parameters (mean annual temperature and precipitation) to explore the relationship between relative C₄ abundance and climate. The results indicate that temperature controls the growth of C₄ plants. However, even where temperature is high enough for the growth of C₄ plants, they will only dominate the landscape when precipitation declines as temperatures increase. Our results are consistent with those of other investigations of the geographic distribution of modern C₄ plant species. Therefore, our results provide an important reference for interpretation of past C₃/C₄ relative abundance records in these three regions.     

δ13CSC values of the loess-paleosol sequence in Dali area, Shaanxi Province, China, and paleoenvironmental implications

The carbon isotopic ratios of carbonate in the two profiles of the Dali area were analyzed and some new understandings on the influencing factors of the δ^13Csc value of the Iocss-paleosol sequence and its paleoenvironmental implications were discussed preliminarily in this report. The δ^13Csc value of the Dali Ioess-paleasol sequence is synchronizing with the variance of magnetic susceptibility basically and the negative peaks of the δ^13Csc curves are corresponding to the different developmental periods of the paleosol. It is believed that the intervention of the CO2 produced by plants will cause the decrease of the δ^13Csc value, the amplitude of which may be relevant to the paleovegetation density and the ancient humidity. The relative biomass of C4 plants in the vegetation will affect the sublevel change of the δ^13Csc. Low δ^13Csc value by and large indicates the environmental conditions of the relatively abundant vegetation and humid climate. During the last 250000 years, the period with the sparsest vegetation and the most arid climate is the phase of the loess in L2 depositing and the period with the most abundant vegetation and the most humid climate is the last interglacial period. The δ^13Csc curves of Dali also show that the High Temperature and Large Precipitation Event of the Qinghai-Tibetan Plateau during 40-30 kaBP had affected the Central Shaanxi Plain with relatively humid climate, and had apparent influence on the local vegetation and humidity.     

Carbon isotopic records in paleosols over the Pliocene in Northern China: Implication on vegetation development and Tibetan uplift

Carbon isotopic composition of pedogenic carbonate can be used to estimate the proportion of C₄ and C₃ plants. Here we present carbon isotopic data of carbonate in a red earth section at Xifeng, central Loess Plateau. Results show that C₄ vegetation increased in ∼4.4 Ma B.P., stabilized between 4.0 and 3.0 Ma B.P. The character and timing of C₄ expansion on the Loess Plateau are similar, but different with other localities, e.g. Pakistan and Africa, implying that regional climate changes were main factors driving the expansion of C₄ plants. This event is comparable in timing with increased aridity evidenced by Xifeng grain size and North Pacific eolian dust records. Therefore we argue that the Pliocene expansion of C₄ plants in northern China might have been caused by the increased aridity, which in turn might be related to rapid uplift of the Tibetan Plateau.     

Vegetation evolution on the central Chinese Loess Plateau since late Quaternary evidenced by elemental carbon isotopic composition

There are many controversial issues in loess studies such as natural vegetation types on the Chinese Loess Plateau during the historical periods and the spatial and temporal evolution of C3/C4 plants. Elemental carbon isotopic composition （δ^13Cec） in the loess section may offer new evidence for these problems. Elemental carbon （EC） is produced by incomplete combustion of vegetation, and its carbon isotopic composition has a very small difference from that of the formal vegetation, then δ^13Cec can be used as a record to recover the changes of vegetation. Elemental carbon was extracted by applying the oxidation method from the Ioess-paleosol sequence in the central Chinese Loess Plateau, and its car- bon isotope composition was analyzed by the isotope mass spectrometer. The results showed that the vegetation in this region was a mixed type of C3 and C4 plants, dominated with C3 plants in most of the time. Since late Quaternary, C3/C4 plants may not follow a simple glacial-interglacial cycle mode on the Chinese Loess Plateau, but showing fluctuations. C3 plants increased gradually in L4 period, and more C3 plants occurred during $3 period, and C4 plants increased again during L3-- L2 periods, after that, Cs plants dominated again during S1 --S0 periods. During periods of paleosol development, C3 plants were abundant in S3 and S1, and there were more Ca plants in S2 and SO. During periods of loess sedimen- tation, there were more C3 plants in L4 and L1, and there were more C4 plants in L3 and L2. On the orbital timescale, the vegetation variations revealed by δ^13Cec record are consistent with the results of pollen data and also similar to the results obtained by organic carbon isotopic composition since the last glacial period.     

Natural gas geochemistry of low evolutionary stage of medium- and small-sized basins in Yunnan Province, southwestern China

The biogenic gas and premature-low mature associated gases in some medium and small-sized basins of Yannan Province, such as Luliang, Yanglin, Baoshan and Jinggu basins, have beed researched. The results show that the biogenic-gas consists mainly of methane which is more than 99% in gasous hydrocarbons and of lighter carbon isotopic composition with δ13C1 values from -60.0‰ to - 75.4‰. The methane carbon isotopic compositions in the Baoshan Basin is relatively heavy (δ13C1 - 60‰- - 65‰), but those in Luliang and Yanglin basins are lighter (δ13C1, less than -70‰), which implies that the gas field of the Baoshan Basin formed earlier than the others. In the Jinggu Basin, where crude oil is premature-lower mature, the natural gas of associated oil relatively wet and the relative content of methane about 58%-95% in gasous hydrocarbons. Constituently the gas composition is much similar to associated one, but the methane carbon isotopic compositions from - 53.8‰ to - 57.8‰ are obviously richer in 12C than those of general oil fields and similarly characterize the biothermo-catalytic transitional zone gas. Their ethane carbon isotopic compositions from - 34.6‰ to -29.0‰ show that they may be derived from type Ⅰ or Ⅱ source rock. But for the associated gas from lower evolutionary stage, the heavier ethane carbon isotopic composition as well as the reversed order among the carbon isotopic composition of ethane, propylane and butane also implies that some gases from the type Ⅲ organic matter are mixed. The δ13CCo2 of the samples essentially less than - 10‰ may be generated from organic matter.     

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…     

Seasonal variations in the Sr-Nd isotopic compositions of suspended particulate matter in the lower Changjiang River: Provenance and erosion constraints

Suspended particulate matter samples were collected monthly for more than 2 years in Nanjing,China to examine seasonal changes in the Sr-Nd isotopic compositions of the lower Changjiang River(CR).The results indicate that the 87Sr/86Sr ratios of the samples ranges from 0.725352 to 0.738128,and the values ofεNd(0)ranges from-10.55 to-12.29.The Sr-Nd isotopic compositions show distinct seasonal variations.The samples had lower 87Sr/86Sr ratios and higherε Nd(0)values during the flood season than the dry seasons.The seasonal variations primarily reflect the controls of provenance rocks and erosion in different sub-catchments.The relative decrease in 87Sr/86Sr ratios and the increase inε Nd(0)values during the flood season may reflect an increasing in the mechanical erosion rate in the upper basin and the contribution of more sediment from the upper reaches.The end member values of 87Sr/86Sr andε Nd(0)of the samples were 0.728254 and?11.26,respectively.     

Hydrogen isotopic compositions and their environmental significance for individual n-alkanes in typical plants from land in China

Hydrogen isotopes of n-alkanes in grasses, tree leaves and reeds from six regions with latitudes of 20° to 39°N in China are measured by GC-TC-IRMS analytical technique in order to understand their hydrogen isotopic compositions and environmental significance. The results show that a difference in ° D values (from −42.1‰ to −66.6‰) of n-alkanes exists among the same kinds of plants from various regions. Hydrogen isotopic compositions of most even carbon numbered n-alkanes in every plant are slightly heavier than that of the odd homologues. A trend toward D-enrichment with increasing chain length of n-alkanes in most plant samples is observed. Mean ° D values of n-alkanes in the studied plants range from −202.6‰ to −130.7‰ and the reed from a salt marsh has the largest value. The mean ° D values of individual n-alkanes among the same kinds of plants from various regions have the characteristics of leaf > reed > grass. The hydrogen isotopic compositions of n-alkanes are apparently distinct among various kinds of plants from the same region and the mean ° D values exhibit a distribution of tree leaf > reed > grass. It is observed that the mean ° D values of n-alkanes and ° D values of C₂₇ and C₂₉ n-alkanes in the grasses and tree leaves from these studied regions correlate clearly negatively with latitude and positively with temperature, indicating that these values can be used as excellent indicators of environment and climate. These results provide important basic data for understanding the distributional law of hydrogen isotopes of individual n-alkanes and their applied research. Supported by National Natural Science Foundation of China (Grant Nos. 40642007 and 40772069), National Basic Research Program of China (Grant No. 2005CB422105) and Special Project for Winners of CAS President Award     

The Sr, Nd isotopic composition of lamprophyres in Laowangzhai gold orefield, Yunnan Province

Lamprophyres are widely spread over the Laowangzhai gold orefield in northern Mt. Ailao structure zone, Yunnan Province. Lamprophyres in the orefield are temporally and spatially related to gold mineralization. Lamprophyres in the orefield have anomalous Sr and Nd isotopic compositions, e.g. the 87Sr/ 86Sr ratios (0.706 665-0.707 960, the 87Sr/ 86Sr ratio of sample YLW-44 is 0.709 041) are higher than the modern value of the original mantle (0.704 5), the 143Nd/ 144Nd ratios (0.512 463-0.512 551) are lower than the modern value of the original mantle (0.512 638), and the calculated values ε Sr>0 (28.1-63.7) and ε Nd<0 (-1.34--3.07). The results of investigation indicate that lamprophyres in the Laowangzhai gold orefield with anomalous Sr and Nd isotopic compositions would not be produced as a result of contamination of the primary magma with the isotopic features of MORB by the crust materials high 87Sr/ 86Sr ratios and low 143Nd/ 144Nd ratios in the processes of rising or in the magma chamber, but the result of metasomatism of source mantle.     

Modern systematics and environmental significance of stable isotopic variations in Wanxiang Cave, Wudu, Gansu, China

This paper presents the stable isotopic compositions from the cave dripwater and actively forming soda straw stalactites collected from Wanxiang Cave, Wudu, Gansu, located on the Qinghai-Tibetan Plateau and Loess Plateau transition zone, China. The δ^18Odw and δDdw of dripwater samples in the cave plot directly on the local MWL, constructed by using GNIP data from 3 sites surrounding the cave regions (Lanzhou, Xi‘an, and Chengdu), the nearest site to the cave, suggesting that there is a close relationship be-tween the δ^18Odw of the cave water and the δ^18O of the pre-cipitations. Using the measured δ^18Odw and δ^18Omc values from the mid-farthest parts from the cave entrance and the carbonate paleotemperature equation, the calculated temperatures range from 8.9 to 12.4℃, with the mean value of 10.7℃ and the temperature calculated at 8 locations in the farthest part of the cave is in the range of 10.I--12.4℃, with the mean value of 11.5℃, being consistent with the survey value(10.99℃)in the cave, slightly lower than the mean annual temperature (14.4℃) in Wudu. This suggests that modern speleothems are forming under isotopic equilibrium and their isotopic composition accurately reflects the mean annual temperature at the surface, indicating that the isotopic composition of the modern speleothems records local temperature change with credibility.     

Different climatic controls of soil δ 13Corg in three mid-latitude regions of the Northern Hemisphere since the Last Glacial period

Paleoecological records of soil δ^13Corg from three regions in the middle latitudes of the Northern Hemisphere, including the Chinese Loess Plateau （CLP）, the Great Plains and adjacent areas of North America and northwestern Europe, showed different variations since the Last Glacial period. An attempt was made to evaluate the causes for the difference in δ^13Corg on the basis of the modern climatic data collected in these regions and of the modern C3 and C4 plant distributions. The analysis indicates that temperature, especially the growing season temperature, has a dominant control on the growth of C4 plants. When the mean annual or growing season temperatures are below the ＂threshold value＂, the growth of C4 plants is limited. When the temperature is above the ＂threshold value＂, C4 plants can grow under a wide range of precipitation. However, when the precipitation is high enough to favor the growth of trees, the proportions of C4 plants in local biomass will decline. The implicit control factor recovered by sedimentary records is consistent with the control factor on modern C3/C4 distribution. Pure C3 plants have been dominating the local biomass since the Last Glacial period in European loess region, mainly owing to the low local temperature. The increases in C4 plants from the late Pleistocene to the Holocene in the Chinese Loess Plateau, the Great Plains and adjacent areas, mainly reflect the influence of increasing temperature.     

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…     

Ch4-rich fluid inclusions in the Yushigou mantle peridotite and their implications, North Qilian Mountains, China

Studies were carried out on the early phase of fluid inclusions which occur in residual olivines in harzburgite from the Yushigou ophiolitic mantle peridotite, the North Qilian Mountains. Components of these inclusions, analyzed by micro laser Raman spectroscopy, are dominantly CH, (70%–95%) with minor H₂, N₂, H₂S, CO₂,C₂H₄, C₂H₆, and C₃H₆ but there are no H₂O,CO and SO₂. The highly CH₄-rich fluid was probably derived from an ancient deep mantle. This discovery plays an important role in all-round understanding of the fluid property of the upper mantle, especially the ancient oceanic upper mantle.     

The evidence of fossil carbon isotopes of the climatic event at the beginning of Quaternary

Tooth enamel of mammalian fossils can efficiently preserve the original carbon isotopic mposition when they lived. The ungulate fossils, especially equids in the early Early Pleistocene Bajiazui fauna from Qingyang, Gansu are studied. According to the enriched relation of carbon isotopes between mammalian tooth enamel and grass diets, the fractions of C₃ and C₄ plants in this region at that time are reconstructed, which indicates that C₃ grass occupied a dominant position. Because C₃ grass adapts itself to cold and clamp climates, cur analytic results show that the time of the Bajiazui fauna was in a critical state between a glacial stage beginning and a summer monsoon retreat, and it was a reflection to the turning cold event of the global climate at the beginning of the Quaternary.     

The specific carbon isotopic compositions of branched and cyclic hydrocarbons from Fushun oil shale

Various branched and cyclic hydrocarbons are isolated from the Fushun oil shale and their carbon isotopes are determined. The analytical results show that the branched and cyclic hydrocarbons are fully separated from n-alkanes by 5 A molecular-sieve adduction using long time and cold solvent. The branched and cyclic hydrocarbon fraction obtained by this method is able to satisfy the analytic requests of GC-IRMS. The carbon isotopic compositions of these branched and cyclic hydrocarbons obtained from the sample indicate that they are derived from photoautotrophic algae, chemoautotrophic bacteria (-33.4‰— -39.0‰) and methanotrophic bacteria (-38.4‰— -46.3‰). However the long-chain 2-methyl-branched alkanes indicate that their carbon isotopic compositions reflect biological origin from higher plants. The carbon isotopic composition of C30 4-methyl sterane (-22.1‰) is the heaviest in all studied steranes, showing that the carbon source or growth condition for its precursor, dinoflageilate, may be different from that of regular steranes. The variation trend of δ^13C ValUes between isomers of hopanes shows that ^13C-enriched precursors take precedence in process of their epimerization. Methanotrophic hopanes presented reveal the processes of strong transformation of organic matter and cycling of organic carbon in the water column and early diagenesis of oil shale.     

Spatial and temporal variations of C3/C4 relative abundance in global terrestrial ecosystem since the Last Glacial and its possible driving mechanisms

The primary factor controlling C 3 /C 4 relative abundance in terrestrial ecosystem since the Last Glacial has been widely debated. Now more and more researchers recognize that climate, rather than atmospheric CO 2 concentration, is the dominant factor. However, for a specific area, conflicting viewpoints regarding the more influential one between temperature and precipitation still exist. As temperature and precipitation in a specific area usually not only vary within limited ranges, but also covary with each other, it is difficult to get a clear understanding of the mechanism driving C 3 /C4 relative abundance. Therefore, systematic analysis on greater spatial scales may promote our understanding of the driving force. In this paper, records of C3/C4 relative abundance since the Last Glacial on a global scale have been reviewed, and we conclude that: except the Mediterranean climate zone, C3 plants predominated the high latitudes during both the Last Glacial and the Holocene; from the Last Glacial to the Holocene, C4 relative abundances increased in the middle latitudes, but decreased in the low latitudes. Combining with studies of modern process, we propose a simplified model to explain the variations of C3 /C4 relative abundance in global ecosystem since the Last Glacial. On the background of atmospheric CO2 concentration since the Last Glacial, temperature is the primary factor controlling C3/C4 relative abundance; when temperature is high enough, precipitation then exerts more influence. In detail, in low latitudes, temperature was high enough for the growth of C4 plants during both the Last Glacial and the Holocene; but increased precipitation in the Holocene inhibited the growth of C4 plants. In middle latitudes, rising temperature in the Holocene promoted the C4 expansion. In high latitudes, temperature was too low to favor the growth of C4 plants and the biomass was predominated by C3 plants since the Last Glacial. Our review would benefit interpretation of newly gained records of C3/C4 relative abundance from different areas and different periods, and has its significance in the understanding of the driving mechanisms of C3/C4 variations on longer timescales (e.g., since the late Miocene) with reliable records of temperature and atmospheric CO2 concentration.     

Carbon and hydrogen isotopic compositions and their evolutions of gases generated by herbaceous swamp peat at different thermal maturity stages

Coalbed methane (CBM) accumulation models include continuous gas accumulation and staged gas accumulation.However,studied on the geochemical characteristics and indices to evaluate staged accumulation CBM are lacking.This study for the first time obtained the carbon and hydrogen isotopic compositions of methane and ethane generated at different evolution stages using thermal simulation of samples prepared by treating an herbaceous swamp peat at different temperatures.The results showed that the carbon isotopic compositions of methane and ethane were obviously affected by the thermal evolution level of the starting sample,while the hydrogen isotopic compositions were closely related to the maturity of gases.The carbon and hydrogen isotopic compositions of gases generated by coal-forming organic matter with Ro values from 1.2%,1.7%,2.4%,3.2% and 3.7% to 5.2% were determinated.The relationship between Ro values and the carbon and hydrogen isotopic compositions of gases generated by coal-forming organic matter at different evolution stages as well as the carbon or hydrogen isotopic relationships between methane and ethane were established.The results provide a scientific basis for studying the genesis of CBM generated at different maturity intervals and understanding the geochemical characteristics of staged accumulation CBM.These results were applied to a case study on CBM from the southern Qinshui basin,and it was found that the CBM accumulated after the Middle Jurassic and was characteristic of staged gas accumulation.This is consistent with the result of geological studies,and further showed that the results of thermal simulation experiments are very important for evaluating the genesis of natural CBM.     

Ancient DNA sequences of rice from the low Yangtze reveal significant genotypic divergence

Rice (Oryza sativa) was first domesticated in the lower and middle Yangtze regions of China, and rice remains have been found in many Chinese archaeological sites. Until now, only phenotypic archeobotanical evidence, such as the spikelet bases of ancient grains, has been used to speculate on the domestication process and domestication rate of rice. In this study, we sequenced 4 genomic segments from rice remains in Tianluoshan, a site of the local Hemudu Neolithic culture in the low Yangtze and two other archaeological sites (??2400 and 1200 BC, respectively). We compared our sequences with those of the current domesticated and wild rice (O. rufipogon) populations. At least two genotypes were found in the remains from each site, suggesting a heterozygotic state of the rice seeds. One ancient genotype was not found in the current domesticated population and might have been lost. The rice remains belonged to the japonica group, and most if not all were japonica-type, suggesting that the remains might be at an early stage of indica-japonica divergence or an indica-japonica mixture. We also identified sequences with significant similarity to those from species of Sapindales, Zygophyllales, and Brassicales, which is consistent with the identification of other plant remains in the Tianluoshan site and the common rice field weeds such as mustards in southern China.