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Calcareous interbeds control the migration of oil and water in marine strata. However, in China, the origins of such calcareous interbeds have not been investigated in detail. In this paper, we present a study of calcareous interbeds in marine strata of the Zhujiang Formation in the Wenchang Oil Field, which is located in the southeast of Hainan Province, China. The lithological characteristics, types and features of diagenesis, and formation of the calcareous interbeds were investigated using core, thin-section, scanning electron microscopy, and cathodoluminescence observations, and stable carbon and oxygen isotope data. The calcareous interbeds consist of mixed sediments, which are dominated by bioclastic limestones containing terrigenous clasts, along with subordinate calcareous sandstone. The interbeds are densely cemented. The bioclasts are dominantly brachiopods, pleopods, and foraminifera, with minor amounts of echinodermata, bivalves, red algae, ostracods, and bryozoa. Diagenesis involved calcitic cementation, associated with relatively weak compaction. Carbon and oxygen isotopic data indicate the pore water that formed the carbonate cement was mostly sourced from seawater and minor amounts of meteoric water. The degree of carbonate cementation was significantly related to the bioclast content. On the basis of our study, a genetic model for the macroscopic and microscopic formation of calcareous interbeds is proposed. [ABSTRACT FROM AUTHOR]

Evaluating the effects of China's carbon emission trading scheme (ETS) is crucial for the coordinated development of Chinese cities. Therefore, based on the panel data of 242 cities in China from 2008 to 2019, this paper uses the multi-period difference-in-difference (DID) model to comprehensively evaluate the impact of carbon market on the coordinated development of cities from the perspectives of carbon market policy and carbon market efficiency, and then analyzes the mechanism and heterogeneity of the effect of carbon market efficiency. The results show that both carbon market policy and carbon market efficiency can promote the coordinated development of cities. Science and education expenditure plays a significant intermediary role in the impact of carbon market efficiency on the coordinated development of cities. The heterogeneity test finds that the stricter the performance penalty system, the higher the level of urban coordinated development, and the stronger the effect of carbon market efficiency. The findings of this paper provide policy recommendations for further improving the construction of China's pilot and national ETS and enhancing the coordinated development of Chinese cities. [ABSTRACT FROM AUTHOR]

The China government focuses on changes in carbon emission efficiency with establishing carbon emission trade exchange (CETE). It is meaningful to study whether the pilot CETEs can facilitate the betterment of carbon emission efficiency. Using the data of 283 cities in China within 2006–2019, this article gauges the carbon emission efficiency with the SBM-DEA model. This paper analyzes the impact of China's pilot CETEs, which was gradually launched from 2013 to 2014, on carbon emission efficiency through the time-varying difference-in-difference (DID) model. Finally, the mediating effect model is further used to analyze the impact mechanism of the pilot CETEs on carbon emission efficiency from the perspectives of innovation investment and pollution control investment. The results reveal that the carbon emission efficiency of each city from 2006 to 2019 is not very ideal. All cities have some room to facilitate the carbon emission efficiency. The pilot CETEs have increased the carbon emission efficiency and reduced carbon dioxide emission. The policy influences the carbon emission efficiency through innovation investment and pollution control investment, which represent long-run and short-run mechanism respectively. [ABSTRACT FROM AUTHOR]

Energy efficiency (EE) plays an important role in achieving the dual-carbon goal, and improving EE is thus indispensable. This paper evaluates the impact of carbon emission trading policy (CETP) on EE based on a difference-in-difference (DID) method, using 16-year data of 30 provinces and cities from 2005 to 2020. Conclusions are as follows: (1) CETP significantly promotes EE, and this conclusion still appears valid after robustness tests. (2) The positive impact of CETP on EE is more effective in regions of high foreign direct investment (FDI) and high government intervention (GOVI). (3) The positive impact of CETP on EE is through impact mechanisms of energy structure adjustment (ESA), green innovation (GI), and industrial structure upgrading (ISU). The findings in this paper may enrich current research in CETP and offer more pragmatic suggestions for policy advancement as well. [ABSTRACT FROM AUTHOR]

Industrial land is currently the main carrier and important source of global carbon emissions, and as the world's largest developing country, China's large-scale and diversified industrial land supply has made it the world's largest carbon emitter. Therefore, researching the impact of different supply methods of industrial land on carbon emissions and its impact paths in China can help provide a reference for other countries to reduce carbon emissions from the perspective of urban industrial land management, which is of great significance for effectively promoting global carbon reduction. Based on this, this paper analyses the impact of different supply methods of industrial land on carbon emissions and its urban heterogeneity using the SYS-GMM and chain-mediated effects models for 285 cities in China from 2008 to 2020. The study found that, in general, the impact of different industrial land transfer modes on carbon emission has hysteresis and persistence. Agreement and listing transfer with government intervention can significantly exacerbate carbon emissions, while more market-based bidding and auction transfer can dampen carbon emissions. In terms of intermediary effects, the transfer of industrial land by agreement and listing will inhibit the rationalization and advancement of industrial structure, thus aggravating carbon emissions. The transfer of industrial land by bidding and auction will create barriers to entry and a crowding-out effect, promote the rationalization of industrial structure and the transformation and upgrading of industrial structure and moderate carbon emissions. In terms of city heterogeneity, there is urban heterogeneity in the impact of industrial land transfer on carbon emissions in cities with different economic types. Bidding and auction transfer for industrial land in both economically developed and less developed cities can promote carbon pollution. While the more developed urban economy makes the intermediary effect of industrial structure not significant. In the future, it is necessary to strictly control the scale of industrial land supply; the whole process supervision mechanism of industrial land allocation and differentiated industrial land supply strategies will provide useful experience for many developing countries in allocating industrial land to mitigate carbon emissions, generating effective contributions to global carbon emission reduction. [ABSTRACT FROM AUTHOR]

Based on the theory of new economic geography, this paper used panel data from 284 cities in China from 2006 to 2019 to determine the effects of spatial spillover and heterogeneity of manufacturing agglomeration (MA) on urban total factor carbon productivity (TFCP) and the regulatory effect of fiscal decentralization on the outcome. The results showed that (1) MA shifted from the eastern region of China to the central and western regions, with the center of gravity moving towards the south. The spatial pattern of urban TFCP displayed the solidifying characteristics of "low-level agglomeration and high-level dispersion," with technological progress being the primary driver. (2) The MA had a significant U-shaped effect on the TFCP of local and nearby cities, promoting the improvement of urban TFCP through Jacobs' and Porter's externalities but not MAR externalities. (3) Regarding regional differences, MA had a significant U-shaped impact on urban TFCP in the eastern and central regions. At different levels of manufacturing development, there was an inverted U-shaped relationship in both manufacturing and non-manufacturing metropolitan areas. For varying degrees of manufacturing industry agglomeration, increasing the level of MA improved urban TFCP in low agglomeration areas, but inhibited it in high agglomeration areas. (4) The implementation of fiscal decentralization nationwide and in the eastern and central regions significantly weakened the impact of MA on TFCP. Furthermore, fiscal decentralization significantly enhanced the influence of MA on TFCP in cities exhibiting high levels of economic development, advanced industrial structure and strict environmental regulations. Therefore, based on the unique developmental characteristics of the manufacturing industry in various cities, fiscal policies ought to be tailored to local circumstances to support key areas. This strategy should facilitate the high-quality development of manufacturing industry and low-carbon development of cities. [ABSTRACT FROM AUTHOR]

The development of the digital economy is an effective way to mitigate the carbon emission problem in the broader setting of the significant data era and green development. Based on the panel data of 271 cities in China from 2011 to 2019, this paper constructs a bidirectional fixed model to analyze the nonlinear effect of the digital economy (DE) on carbon intensity (CI) and the moderating role of low-carbon regulation from theoretical and empirical perspectives. The results show that (1) DE has an enormous inverted U-shaped impact on CI. The findings remain after introducing instrumental variables to mitigate endogeneity and robustness tests. (2) Low-carbon regulation (CP) can strengthen the inverted U-shaped impact between the two and shift the inflection point to the left. (3) Heterogeneity analysis shows that the inverted U-shaped effect of DE on CI is more significant in the central and western regions, high human capital (HC) regions, and high urbanization regions. (4) The mediating effect of energy mix (EM) and green technology innovation (GTI) still hold after introducing instrumental variables to alleviate the endogenous effect of the intermediary effect. This study suggests that the adoption of carbon emission reduction strategies, which will more effectively lower carbon intensity CI, should go hand in hand with the development of DE. [ABSTRACT FROM AUTHOR]

To characterize the polyphase palaeokarst development of Wumishan formation in Jizhong depression, the data of outcrops, cores, thin sections, SEM, core plugs, drilling relief and leakage, and carbon isotope have been analyzed in this paper. The results reveal that the polyphase palaeokarst was petrography controlled of microbial dolostone and grain dolostone, and was identified as three phases: (1) poly-period eogenetic karst during Wumishan depositional environment, (2) two-period telogenetic karst in Triassic and Cretaceous, and (3) hydrothermal karst in Paleogene. The eogenetic karst was related to high frequent sea level fluctuations with development of vugs and selective dissolution porosities which distributed at the top of microbial dolostone and grain dolostone layers. The origin of the telogenetic karst was related to Indosinian and Yanshan orogeny which formed widespread fold belts and thrust faults, and provided the endokinetic force and a strong topography difference. Each period's telogenetic karst was characteristic of one-period fracture-cave system, and the Cretaceous telogenetic karst was stronger than the Triassic telogenetic karst in karst intensity. Moreover, the karst intensity increased downward in superimposed telogenetic karst zones. Hydrothermal karst was related to volcanic activities and provided the hydrothermal environment for its formation. It was featured by solution-enlarged porosities and new forming porosities. The microbial dolostone and grain dolostone layers with three-phase palaeokarst were the best exploration targets for high-quality reservoirs. This paper rebuilds a suitable karst model to show the palaeokarst evolution process. [ABSTRACT FROM AUTHOR]

Promoting green low-carbon development is an important task in the construction of ecological civilization of China. The leadership has proclaimed green low-carbon development as the top national priority for development. Green low-carbon economy has become the high point of global industrial competition. Green taxation, as a tool for environmental regulation, plays an important role in the construction of ecological civilization. Therefore, this paper investigates the impact of green taxation on green low-carbon development in the Yangtze River Delta (YRD) region of China, using data of 41 cities from 2011 to 2021 in the YRD region. We construct a green low-carbon development index with the combined weight CRITIC-entropy method, and employ a mediating effect model and a spatial Durbin model based on double fixed effects in this study, which intends to provide a theoretical basis for the establishment of a sound tax policy system that is conducive to the green low-carbon development. The results show that (1) there is an evident spatial dependence of green low-carbon development in the YRD region; (2) green taxation has a significant positive effect on green low-carbon development through rationalization of industrial structure and advance of industrial structure; and (3) the positive impact of green taxation on green low-carbon development in the region is characterized by spatial spillover and heterogeneity. Specifically, green taxation significantly promotes green low-carbon development in the core area, but such green taxation dividend has yet to be realized in the expansion area. [ABSTRACT FROM AUTHOR]

The advancement of electricity market reform highlights the need for China's photovoltaic (PV) industry to enter the stage of market competition. Under the carbon neutrality, what impacts electricity market reform has on China's PV industry is an important issue that needs to be considered. This paper analyzes the driving mechanism of the marketed on-grid price and constructs a system framework for the internal connection within the PV industry under the background of carbon neutrality. Then, two system dynamics (SD) models are built to perform the numerical simulation and analyze the evolution process. The results indicate that during the market competition stage, (i) the on-grid price will be stable at about 0.07 yuan/kWh by 2060; (ii) China's PV industry will go through three stages in the future: the first stage is the "rush to install" period for carbon peaking before 2030, followed by the "sluggish installation" period from 2030 to 2038. The third stage is the outbreak period of "PV + multi-scenarios."; (iii) under three scenarios by 2060, the proportion of PV power generation will account for 46%, 39%, and 32%, respectively, which are higher than those under the benchmark on-grid price; (iv) it is necessary for the government and enterprises to continue increasing support for research and development (R&D). Finally, we put forward corresponding policy recommendations. [ABSTRACT FROM AUTHOR]

The Upper Permian Changhsing Formation is one of the most important gas-bearing formations in the Eastern Sichuan Basin. Nonetheless, the primary factors controlling the reef-shoal gas reservoirs of different regions are diverse. Clarifying the controlling factors for the formation of intra-platform reef-shoal reservoirs will promote the exploration and development process of the Changhsing Formation. By using outcrop data, core observation, thin section identification, scanning electron microscope analysis, physical property study, and logging interpretation, this paper analyse the characteristics and factors controlling the reef-shoal reservoir in Dianjiang area of the Eastern Sichuan Basin. The results show that the reef cap and reef base microfacies fine-to-medium crystalline dolomite reservoir have the best physical properties, and the reservoir spaces are primarily composed of intercrystalline pores, intercrystalline solution pores, karst caves, and fractures. The main lithology of reservoir formation is reef-shoal facies. The results for the carbon and oxygen isotopes show that dolomites of different particle sizes are formed in three environments. Affected by regression in the late Changhsingian Age, the reef-shoal of the Changhsing Formation were subaerially exposed to meteoric water diagenesis environments, resulting in the highly dispersed particles in rocks that formed a honeycomb karst system, which greatly improved the physical properties of the reservoirs. After reflux dolomitization, the honeycomb karst system was well preserved due to strong resistance to pressure and dissolution of dolomite. Therefore, dolomitization in the Changhsing formation contributed to reservoir porosity. Later, tectonic fracturing has adjusted and modified the reef-shoal reservoir. In summary, penecontemporaneous karstification was the key to the formation of the reef-shoal reservoir. [ABSTRACT FROM AUTHOR]

In order to achieve the carbon peaking and carbon neutrality goals, energy-intensive industries in China, as the main sectors of energy consumption and carbon emissions, had huge pressure to reduce emissions. In addition, the reduction of vegetation area led to a decline in carbon sink capacity, which further exacerbated the imbalance of mutual penetration between carbon source and carbon sink. Therefore, this article considered the role of carbon source and carbon sink and defined and calculated the "carbon emission penetration" (CEP) of the six energy-intensive industries from 2001 to 2020. The KAYA formula and the LMDI method were used to decompose the driving factors of CEP in the three aspects of scale, intensity, and structure. The combined model of STIRPAT and the environmental Kuznets curve (EKC) was used to simulate and analyze the equilibrium points of energy-intensive industries in China from the perspective of factor driving. The analysis results indicated that there were differences in the fluctuation trend of CEP in the six energy-intensive industries, which can be divided into three types: "two-stage growth," "steady growth," and "single peak." Secondly, the driving factors from the three aspects of scale, intensity, and structure—emission intensity (CE), energy consumption intensity (EI), industrial structure (IS), economic scale (GP), and carbon sequestration scale (PCA)—had differences in industry and time dimensions. And the realization time of the CEP equilibrium points of six industries showed a three-level gradient feature significantly. This can provide some reference for the low-carbon transformation of six energy-intensive industries and optimization of China's environmental management under the carbon peaking and carbon neutrality goals. [ABSTRACT FROM AUTHOR]

The beginning of the Late Paleozoic Ice Age was characterized by localized events with small ice depocenters occurring in South America and a series of cyclic shallow-water limestones in far-field regions, in late Visean to Serpukhovian. This paper documents two topmost Visean–Serpukhovian sections in Guangxi, South China: a stromatolite-bearing deep-water succession in Helv village and a shallow-water succession in Dujie village. Seventeen microfacies types have been recognized and grouped into six microfacies associations. The vertical evolution of the microfacies associations from deep-water to shallow-water depositional environments in both sections indicate a major relative sea-level fall in the latest Visean. The repetitive successions comprising different morphological stromatolites in Helv section and the cyclic alternation of subtidal and peritidal facies in Dujie section imply high-frequency sea-level fluctuations during latest Visean to Serpukhovian, most likely eustatic in origin. The carbon isotope data of Dujie limestone exhibit a pronounced positive δ13C excursion with ± 4.3‰ in the peritidal deposits. This shift is interpreted as the result of enhanced organic carbon burial in other regions and depletion of the ocean in light carbon. The widespread coeval cyclicity occurring in settings in South China, Western Europe, and North America is most likely the results of glacio-eustatic sea-level fluctuations, possibly with local influences of tectonic movements. This pattern is interpreted to represent the expression of the onset of the major glaciation during the LPIA in low-latitudinal successions. [ABSTRACT FROM AUTHOR]

The stable carbon isotope composition (δ13C) of lacustrine sediments, which can record changes in past environmental conditions such as the C4/C3 terrestrial vegetation composition, has been widely used for the reconstruction of terrestrial ecosystems and global climate changes. It has also been widely used in paleolimnological studies in arid northwestern China. In recent years, however, an increasing number of studies have enriched the environmental significance reflected by the stable carbon isotope geochemistry of lakes; therefore, the interpretation of lake δ13C variations in paleoenvironmental reconstructions should be carefully evaluated from various aspects. In this paper, previous studies from the past several decades on the lacustrine δ13C variations in arid northwestern China were reviewed, and the possible mechanisms of the δ13C variations were discussed. Our study will provide a reference for the application of carbon isotope geochemistry in paleoenvironmental reconstructions. [ABSTRACT FROM AUTHOR]

High-resolution carbon and oxygen isotope records in stalagmites provide significant information for quantitative paleo-reconstructions of past temperature and precipitation. This paper describes results of isotopic analysis of dissolved inorganic carbon (DIC) in Panlong Cave water (from drips and shallow pools). Cave water was sampled monthly throughout 2012 and analyzed for δC composition. The values of δC in drip water were in the range of −10.42 to −16.07 ‰, while the values of δC in pool water were in the range of −1.88 to −6.94 ‰. Dissolved inorganic carbon isotope records showed a gradual stepwise negative excursion from January to August, and a gradual stepwise positive excursion from September to December. δC in cave water showed remarkable seasonal variations, which were negative excursion from 2 to 5 ‰ in rainy season than in dry season. A negative δC excursion in summer was not the result of vegetation types, which was contributed to enhance root respiration and decomposition of soil organic matter. A correlation between δC values of perennial drip water and pool water samples with air temperature and precipitation amount suggests that these negative excursions were caused by increasing air temperature during rainy season. Negative excursions in δC values of seasonal drip water were correlated with monthly precipitation, caused by the influx of soil organic matter into the cave. Hence, this paper provides an important framework and an empirical basis for reconstructing temperature from stalagmites and drip water in this region. [ABSTRACT FROM AUTHOR]

The archaeological culture found in Xiaohe Cemetery (1980-1450 BC) is one of the early Bronze Age cultures in Xinjiang, northwestern China. The material assemblages from Xiaohe culture display features with both eastern and western influences. These east-west cultural and dietary interactions may be observed via the diet of the Xiaohe population. This paper examined the stable carbon and nitrogen isotopes of human and animal bones and human hairs from the Xiaohe Cemetery and compared with those of human bones from the Gumugou Cemetery, another Xiaohe culture site. The results indicate that the diets of the peoples from the Xiaohe culture varied significantly over different periods. The unified diets of the earlier periods reflect that an admixed population first settled in the Lop Nur region and primarily engaged in animal husbandry. In the later periods, the transformations in the human diets in this region reflect that new immigrants constantly relocated here and promoted population complexity over time. Moreover, this population occasionally produced small quantities of domesticated wheat and millet. The complex population and diversified economy of the Xiaohe culture were due to the expansion of the coeval cultures in the Eurasian steppe and eastern immigrants. Additionally, the millet cereal was probably mainly used for ritual practices rather than for staple food in the later periods. [ABSTRACT FROM AUTHOR]

Three positive carbon isotope excursions are reported from Middle-Upper Ordovician in Tahe oil-gas field, northern Tarim Basin. Based on conodont biostratigraphy, the Middle Darriwilian Isotope Carbon Excursion (MDICE) and the Guttenberg Carbon Isotope Excursion (GICE) are identified from Darriwilian to Early Katian by the aid of whole-rock carbon isotope data from two well cores. Positive excursion within conodont Pygodus anserinus zone is developed in Early Sandbian, and the fluctuation range is no less than MDICE. Because the range of this excursion in the generalized global carbon isotope curve is short, previous studies paid little attention to it, and named Early Sandbian Isotope Carbon Excursion (ESICE) in this paper. Furthermore, these positive excursions are not directly related to sea level fluctuations and the MDICE and GICE identified in northern Tarim can be globally correlated to that in southern China, North America, South America, and Europe. The Saergan Fm. source rocks of Middle-Upper Ordovician in Kalpin Dawangou outcrop are in accord with the geologic time of MDICE and ESICE, and GICE have strong ties to the source rock of Lianglitag Fm. in basin. Abundant organic carbon burial is an important factor in genesis of positive isotope carbon excursions. Positive oxygen isotope excursion, conodont fauna turnover, decreased conodont total diversity, and the change of sedimentary facies indicated that dramatic changes of paleoceanographic environment of Early-Middle Ordovician in Tarim Basin started from the end of Darriwillian, and an obvious icehouse climate of Late Ordovician occurred in ESICE. [ABSTRACT FROM AUTHOR]

The crude oils typically from the Cambrian-Lower Ordovician source rocks of Tarim Basin, NW China, such as TD2Є and TZ62S, are C-enriched with the stable carbon isotopic ratios (VPDB) approaching −28 ‰. In this paper, the main research viewpoints on this issue are summarized, and combined with results from organic and inorganic carbon isotope stratum curves of the outcrop at the Ya'erdang Mountain in Tarim Basin. In addition, more alternative interpretations are discussed. On one hand, the inverse fractionation features of stable carbon and hydrogen isotopes of these crude oils may imply their protogenous nature. On the other hand, the anisotropy of source rocks and contribution from older stratum source rocks need verifying as well. For the sake of the final resolution of this issue, some further study topics are recommended. [ABSTRACT FROM AUTHOR]

Facing the double pressure of promoting economic growth and achieving the goal of "emission peak" by 2030, China must cut down the carbon emission intensity. Focusing on the typical characteristics of China's financial system arrangement, we theoretically analyze the mechanism of vertical fiscal asymmetry affecting carbon emission intensity and use a panel data from 30 Chinese provinces to conduct an empirical examination. The results show that (1) vertical fiscal asymmetry significantly increases the local carbon emission intensity. After a series of robust tests, such as replacement variables and sample data, the conclusion is still valid. (2) The analysis of regional heterogeneity shows that the influence of vertical fiscal asymmetry in carbon emission intensity is the largest in the central area of China, followed by the eastern provinces, and not evident in the western area. The rise in carbon emission intensity brought on by vertical fiscal asymmetry can be successfully reduced by the central transfer payment. The impact of vertical fiscal asymmetry on carbon emission intensity will be greatly lessened when the central transfer payment surpasses the threshold. (3) The mechanism test shows that vertical fiscal asymmetry increases the carbon emissions intensity by three paths: reducing the intensity of environmental regulation, strengthening local governments' dependence on land finance, and local government competition. The above analysis further enriches the relevant research on how China's vertical fiscal asymmetry system affects carbon emission intensity through land finance and local government competition while pointing out the role of transfer payment, and it can help to provide new ideas and empirical evidence for further improving the financial system and promoting the green development of the economy. [ABSTRACT FROM AUTHOR]

The analysis of household consumption carbon emissions (HCCEs), a significant source of CO2 emissions, is essential to achieving China's carbon peak before 2030 and carbon neutrality before 2060. Based on the calculation of urban and rural HCCEs during 2005–2019, the differences between urban and rural areas, spatial–temporal pattern and agglomeration characteristics of HCCEs were analyzed, and the panel quantile STIRPAT model was constructed to empirically test the influence of socioeconomic factors on urban and rural HCCEs at different quantile levels. The results indicate that, first, China's HCCEs are generally growing, indirect HCCEs are more than direct HCCEs, urban HCCEs are far more than rural, and the gap has a growing trend. Second, the urban and rural HCCEs have significant disequilibrium and agglomeration characteristics in space, and high-high and low-low agglomerations dominated the local region. Third, household size and the number of patent application authorizations increase the urban and rural HCCEs, while the consumption capacity and consumption structure inhibit the urban and rural HCCEs. In addition, the level of education also has an inhibitory effect on the rural HCCEs, while the aging degree of the population has a significant positive impact on the rural HCCEs when it is only at the 90th percentile. Finally, it is suggested to formulate differentiated emission reduction policies. [ABSTRACT FROM AUTHOR]

Secondary microbial gas accompanied by abnormally high CO2/N2 concentrations is widely developed in the southern Junggar Basin (SJB). However, the mechanism of nonhydrocarbon-enriched coalbed methane (CBM) remains unclear. Due to the close correlation between microbial gas and hydrogeology, the geochemical and microbial sequencing experiments were conducted to reveal hydrogeological controls on CBM geochemistry in this study. The results showed that CBM derives from thermogenic and biogenic genesis in SJB, and the biogenic genesis is mainly generated through CO2 reduction. CO2 is biogenic and N2 is of atmospheric and thermal genesis. CO2 concentration mainly depends on microbial production and consumption. The higher alkane-degrading bacterial abundance in As/V-enriched environments promotes CO2 generation, while high HCO3− contents inhibit CO2 dissolution in water and consumption by methanogens. Alkane-degrading bacteria enrichment and discontinuous CO2 consumption lead to the significantly high CO2 concentration. Atmospheric N2 concentration was negatively correlated with groundwater runoff intensity, while thermogenic N2 concentration showed a weak correlation with total dissolved solids (TDS). High atmospheric infiltration and thermogenic N2 replenishment lead to a N2 concentration exceeding 10%. Stable carbon isotopes are related to methanogens, and more methanogens in Li/Zn/Cu/Rb/Sn-enriched environments lead to decreasing δ13C–CH4. However, when TDS exceeds 15,000 mg/l, the inhibited methanogen production results in δ13C–CH4 higher than −55‰. Three CBM geochemistry distribution models were ultimately established: atmospheric mixed in the runoff–weak runoff area, reformation by shallow microbial gas migration in the weak runoff–stagnant area, and damping microbial gas generation with abundant alkane-degrading bacteria in the weak runoff–stagnant area. [ABSTRACT FROM AUTHOR]

The Maogongdong deposit is located in the giant Dahutang W-Cu-(Mo) ore field, northern Jiangxi Province, South China. It is mainly a vein-type deposit, characterized by early W and late Cu-Mo mineralization, and temporally and spatially associated with Late Mesozoic S-type muscovite granites emplaced into a Neoproterozoic granodiorite batholith and the Shuangqiaoshan Group metasedimentary rocks. Fluid inclusions and H–O isotopes suggest that the early ore-forming fluids of the Maogongdong deposit are mainly magmatic water with relatively high temperature (270–410 °C) and moderate-to-low salinity, while the late ore-forming fluids are mixed with meteoric water, with medium-to-low temperature (160–270 °C) and low salinity. Infrared and conventional microthermometric studies of fluid inclusions of the main tungsten mineralization stage show that the homogenization temperatures of primary fluid inclusion assemblages in wolframite (325 to 355 °C) are about 20 °C higher than those of coexisting scheelite and generally 40 °C higher than those in quartz. The δ34S values of sulfides (− 5.2 to − 1.3 ‰) in the sulfide stage are slightly lower than the magmatic sulfur (− 1.7 to 0.6 ‰) in the pre-ore stage, most likely due to an increase in oxygen fugacity. The low carbon isotope values (− 26.2 to − 15.5 ‰) of fluid inclusions in the tungsten mineralization stage show that a large amount of organic carbon was added before mineralization. Fluid cooling and pressure decrease are the main factors of tungsten ore precipitation, while local boiling may also make a contribution. Mixing of the different fluids led to the formation of copper and molybdenum ores. [ABSTRACT FROM AUTHOR]

The Early-Middle Permian δ13Ccarb variations are recorded by the marine carbonates of the Luduba section in the northern margin of the South China Block. The investigated interval (~ 300 m) spans the Chihsia and Maokou formations. Preservation of the investigated micritic carbonates was evaluated by multiple petrographic and geochemical screening tools. The δ13Ccarb and δ18O values of near-primary micrites range from 2.3 to 5.0‰ (VPDB) and from − 6.4 to − 3.4‰ (VPDB), respectively, showing insignificant correlation (R2 = 0.13). Similarly, the Mn/Sr ratios show insignificant correlation with δ13Ccarb or δ18O ratios. In addition, the Al and Sr concentrations exhibit insignificant correlation, which suggests preservation of at least near-primary δ13Ccarb signatures that can be utilized to construct a reliable C-isotope profile of the equatorial eastern Paleo-Tethys for global correlations. The C-isotope profile exhibits distinct short-time negative shifts superimposed on the general long-term trend of increase in δ13Ccarb values. The long-term trend likely reflects a consistent global sea-level rise during the Early Guadalupian, which was associated with one of the largest Permian transgressions. The general sea-level rise was disrupted by few minor short-term sea-level low-stands associated with negative δ13Ccarb shifts (~ 1–2 ‰) on the C-isotope profile, which are associated with similar minor positive 87Sr/86Sr shifts (~ 0.0005 each) on the Sr isotope profile and with Al enrichment, possibly caused by the combination of global eustasy and regional tectonics in South China. Two negative δ13Ccarb shifts have been recorded in the lower and upper Chihsia Formation that can be correlated with the Early Kungurian and the Kungurian/Roadian boundary, respectively. Also, the Maokou Formation records a middle negative shift that inferred correlates with the Early Wordian. These three negative δ13Ccarb shifts are globally comparable with those documented by both the eastern Paleo-Tethys and western Panthalassa Early-Middle Permian sedimentary records and can be utilized as chemostratigraphic markers. The general increase in the δ13Ccarb values peaks at ~ 5 ‰ near the top of the Maokou Formation that resembles the Kamura event recorded in Tethy but there are issues with the origin and timing of this positive δ13Ccarb excursion. The petrological characteristics of the Luduba section carbonates support the suggested scenario of the general long-term trend of sea-level rise. [ABSTRACT FROM AUTHOR]

Background and aims: Plant carbon (C), nitrogen (N), phosphorus (P) levels and their stoichiometry and N uptake strategies are important aspects influencing vegetation composition and C dynamics in boreal peatlands. However, C, N and P levels and N sources of different plants remain poorly understood, which prevents a better assessment of plant responses to projected increasing N availability in boreal ecosystems with climate warming and increasing N deposition. Methods: We investigated differences of leaf C, N and P concentrations and C and N isotopes (δ13C and δ15N) between graminoids and shrubs in 18 peatlands in northeastern China. Results: Ericoid mycorrhizal (ERM) and ectomycorrhizal (ECM) shrubs have higher C and P while lower C/N and C/P than nonmycorrhizal (NM) graminoids. Shrubs and graminoids have similar leaf N/P, mainly exhibiting N limitation or N and P co-limitation. ECM shrubs show higher N and lower δ15N than NM graminoids despite having similar rooting depths, indicating higher N availability and more uptake of 15 N-depleted organic N of ECM shrubs. However, deep-rooted ECM shrubs show slightly higher N than shallow-rooted ERM shrubs, and their δ15N differences are insignificant. Shallow-rooted ERM shrubs have higher N and lower δ15N than deep-rooted NM graminoids. Conclusions: Our results imply lower N and P use efficiencies of shrubs than graminoids, and the important role of mycorrhizal association in differentiating N availabilities and sources between shrubs and graminoids. These findings are useful for understanding peatland plant responses to environmental changes. [ABSTRACT FROM AUTHOR]

The occurrence of Precambrian stromatolites is closely related to the ancient seawater composition and the evolution of life. It is also a potential oil and gas reservoir. In what kind of environment the stromatolites of the upper Ediacaran Qigebulak Formation in the Tarim Basin developed, and whether they constitute potential hydrocarbon reservoirs, remained unclear. Stromatolites occur in 1–5 m thick layers, interbedded with thrombolites and dolostones. Distinct stromatolite morphologies were observed, including columnar, sinuous, short columnar, domal, and conical shapes. The δ13C values of the stromatolites (6.1‰ on average) are slightly lighter than those of the dolostones, and the δ18O values (− 1.4‰ on average) are significantly heavier than that of the dolostones. The stromatolites have a relatively high content of rare-earth elements and a minor Ce anomaly. The geochemical results imply that the stromatolites formed in an evaporative hypersaline lagoon environment. The presence of barrier dams near the coast led to the formation of lagoons, where hypersalinity was achieved when evaporation was greater than marine or freshwater input. High salinity conditions inhibited the growth of Ediacaran metazoans, allowing the buildup of stromatolites in the restricted lagoons. The stromatolites are rich in primary fenestral pores and sheet-like cavities along the laminae, and the secondary dissolution pores and vugs are related to meteoric karstification. The stromatolites, together with dolostones and thrombolites, constitute the majority of the hydrocarbon reservoirs in the Upper Ediacaran in the Tarim Basin. The results clarify the environment where the stromatolites could still flourish and be well preserved whereas they significantly declined globally throughout the Neoproterozoic elsewhere. The results imply that extensive stromatolites in the Proterozoic strata are potentially important reservoir rocks of Precambrian petroleum systems. [ABSTRACT FROM AUTHOR]

Based on a study of 49 conodont and 57 geochemical samples from the Upper Triassic, carbonate-dominated Dengdengqiao Formation, Qinling Basin, China, the Carnian conodonts and carbon isotope records are first reported. Two genera and four species have been identified amongst 87 conodont elements: Mosherella praebudaensis, Mo. longnanensis sp. nov., Mo. sp., and "Misikella" longidentata. The presence of Mo. praebudaensis indicates that the lower part (bed 2) of the formation is attributable to the Julian (lower Carnian) substage. A radiolarian fauna identified in a previous study belongs to the upper Carnian, but the sampling horizon is unclear. The δ13Ccarb curve shows a ∼1.8‰ negative excursion beginning from upper part of bed 3, but its stratigraphic location is uncertain. The Dengdengqiao Formation is clearly at least partly of Carnian age but could include younger strata. The abundant calcareous algae at the section is probably due to some transport rather than preserved in site. The unusual ecosystem with rare marine organisms may reflect long-term stressful and unfavorable conditions at Dengdengqiao. [ABSTRACT FROM AUTHOR]

Carbonate clumped isotope (Δ47) is a new and reliable geothermometer. Endogenic carbonates in lake sediments are good archives to reconstruct lake water temperature using clumped isotope thermometry. However, applications of carbonate clumped isotope thermometry to lacustrine carbonates are still scarce because the existed organic and/or sulfur contaminants in such samples interfere with clumped isotope analysis and cause notable temperature biases. Therefore, exploring an effective way to remove contamination is a prerequisite to widely applying carbonate clumped isotope thermometry to lake sediments. By pretreating fine-grained endogenic carbonates from Dali lake sediments with hydrogen peroxide of different concentrations for different lengths of time, we conducted a series of conditional experiments to seek the optimal pretreatment condition for clumped isotope analysis. Δ47, Δ48 offset and 49 parameter were obtained from clumped isotope measurements to assess the effect of contamination removal. Results showed that untreated samples ("0%–0") had a very high 49 parameter. After the treatment with hydrogen peroxide, the 49 parameter was significantly reduced while the Δ48 offset evidently increased. The Δ47, Δ48 offset and 49 parameter of samples pretreated under different conditions showed significant variability, even though the measured Δ47 temperatures changed within a relatively narrow range (i.e., from 17.0±1.3 to 22.8±1.6°C). Among various treated samples, the sample "3%–8" yielded a smaller Δ48 offset and 49 parameter, and lower Δ47 temperature of 17.0±1.3°C. Therefore, "reacting with 3% hydrogen peroxide for 8 h" was suggested to be the optimal condition for removing contaminants from lacustrine endogenic carbonates prior to clumped isotope analysis. At the time when the pretreatment condition was too intense (i.e., H2O2 concentration >3% and/or reaction time >8 h), secondary contaminants might have been generated in the closed reaction system, whose ultimately transformed state may interfere with masses 47, 48. Using the optimal pretreatment procedure, we obtained reasonable Δ47 temperature changes during the last deglaciation and found a temperature decrease of about 6°C in Northern China during the Younger Dryas period. Our study demonstrates a great potential of applying carbonate clumped isotope thermometry to lacustrine carbonates for paleo-temperature and paleo-elevation reconstructions in the future. [ABSTRACT FROM AUTHOR]

Background and aims: Land cover change (LCC) from natural forest (NF) to plantations (PF) has occurred worldwide over the past several decades. However, the different LCC effects on soil aggregate C and N turnover in various climatic zones remain uncertain. Methods: Soil samples were taken from both NF and PF at five sites along an approximately 4200 km north-south transect in eastern China. We measured soil aggregate C and N concentrations, and δ13C and δ15N. Results: The soil aggregate distribution is similar between NF and PF, except that the mass proportion of microaggregate is lower in NF. The impacts of LCC on soil C and N concentrations, and δ13C and δ15N vary among five climate zones. The changes in soil aggregate C and N concentrations and δ15N induced by LCC show nonlinear relationships with climatic factors (i.e., MAT and MAP), and there is a linear relationship between soil aggregate Δδ13C (calculated by subtracting PF from NF) and MAT and MAP. The soil aggregate C and N concentrations, and δ13C and δ15N show clear trends along the climatic transect. In addition, the impacts of LCC are more obvious in topsoil than in subsoil. Conclusion: Our findings highlight that the impacts of LCC on soil C and N concentrations are related to climatic factors. Specifically, that the increased decomposition of soil C in PF than NF can be compensated by higher C inputs with increasing MAT and MAP. [ABSTRACT FROM AUTHOR]

A large number of studies have analyzed the annual growth rings and environmental drivers in subtropical China. However, how environmental and physiological effects define the isotopic composition of the wood in this region is poorly understood. Here, we explored the potential of applying three components (whole wood, holocellulose, and α-cellulose) of stable carbon isotopes from Masson pine (Pinus massoniana Lamb.) to dendroclimatology. Sampling sites were covered at the northern, eastern, southern, and western margins of the Masson pine distribution in subtropical China. The results showed that the mean δ13C of holocellulose and α-cellulose both had more enriched values than whole wood, with differences of 1.261 ± 0.233‰ and 1.311 ± 0.189‰, respectively, within individual trees. The three components displayed uniform year-to-year variations and common significant climatic signals, indicating that the δ13C of whole wood from Masson pine was enough to reconstruct interannual paleoclimate information without cellulose isolation due to its high climate sensitivity and low time requirements. The mean δ13C record was significantly and negatively correlated with autumn hydroclimatic parameters (e.g., relative humidity and precipitation) in each study area. This study provides evidence of the influence of hydroclimatic variation on Masson pine forests at a large spatial scale and further enhances the interpretation of climate variations. [ABSTRACT FROM AUTHOR]

The Middle Permian Guadalupian witnessed significant environmental changes in the Phanerozoic such as large-scale sea-level drop, supercontinent Pangaea assembly, and transition from Early Permian glaciation to Late Permian non-glacial intervals. Carbonisotope tracers can provide insights for these environmental changes. The δ13C studies of the entire Guadalupian epoch are rare, and most of them has focused on near the end of Guadalupian and carbon isotopes of inoragnics. Here, we present carbon isotopic compositions of organic matters in the Guadalupian from two sections (Chaohu and Xiaolao) in the Lower Yangtze area, South China. Our results show that δ13Corg profiles in the Guadalupian show a peak in the Roadian and a gradual negative shift from the Roadian to the middle Capitanian. These trends can be matched by δ13C changes of carbonate rocks or organic matter in South China and other places in the world, representing a global carbon cycle signal. The Roadian positive peak was probably due to high productivity which was caused by upwelling during cooling time. The gradual negative shift of δ13C was caused mainly by a decrease of organic matter burial on land and in the ocean, resulting from global sea-level drop and anoxia-caused benthos decline, respectively. The less important causes for the gradual δ13C negative shift are volcanic-gases releasing, decreased mountain belts, and the resultant reduced silicate weathering-consumption of CO2. The gradual negative shift of δ13C coincides with the gradual extinction in the Guadalupian. Therefore, global sea-level drop and marine reducing conditions may be the main causes of the gradual extinction in the Guadalupian. [ABSTRACT FROM AUTHOR]

The Upper Neoproterozoic–Lower Cambrian section in the Olekma River basin is divided (from bottom to top) into the Dikimdia, Seralakh, Porokhtakh, and Pestrotsvetnaya formations, which are mainly composed of dolostones with a subordinate amount of sandstone, silty shales, gypsum, anhydrite, and native sulfur. The isotope data available allow one to substantially correct the stratigraphic units of the Olekma section, which is probably the most completed section on the Siberian Platform, including the transitional strata from the Vendian (Ediacaran) to the Cambrian. The Dikimdia Formation dolostones have typical Late Ediacaran values of 87Sr/86Sr = 0.70837–0.70843 and abnormally high δ13С values (up to 5.1‰), which gives reason to correlate this formation with the Ust'-Yudoma Formation (the stratotype area), the Dengying Formation in South China (548–550 Ma), the Uluntuy Formation of the Baikal Group, and the terminal Ediacaran sections in some other areas. The 87Sr/86Sr ratio decreases upward and reaches a minimum (0.70803–0.70818) near the Porokhtakh–Pestrotsvetnaya boundary. The lowermost part of the Porokhtakh Formation contains a negative carbon isotope excursion (δ13С = –4.4‰) marking the base of the Nemakit-Daldynian Stage, whereas ~8 m below the base of the Pestrotsvetnaya Formation the positive "pre-Tommotian" excursion (δ13С = 4.1‰) is located. There is a sharp decrease in Fe and Mn contents from ~3800 and ~300 ppm to ~2000 and ~130 ppm, respectively, in dolostones at the Ediacaran–Cambrian transition boundary which corresponds to the Seralakh–Porokhtakh boundary. High δ18О values (26.0 ± 1.2‰) do not provide reasons to associate the carbon isotope excursions, the 87Sr/86Sr trend, and variations of Fe and Mn contents with diagenetic alterations. [ABSTRACT FROM AUTHOR]

The Furongian Series of the Cambrian in the Tarim Craton (NW China) is mainly composed of crystalline dolostones, and is an important target for oil and gas exploration. The chronostratigraphic framework of the Furongian Series in the Tarim Craton has not yet been established due to the scarcity of fossils and the absence of the Steptoean Positive Carbon Isotope Excursion (SPICE), which is the primary global carbon isotope excursion of the Furongian Series. In this study, the SPICE was discovered by examining the carbon isotopes of the representative drilling wells in the West Platform and East Basin. A positive carbon isotope anomaly with δ13C values ranging from 1.5‰ to 1.9‰ (PDB), were found in the middle of the Xiaqiulitag Formation of the three drilling wells in the West Platform, and a positive excursion with δ13C values up to 4.0‰ (PDB), which is correlated with the SPICE, was found in the lower limestone of the Tuershaketag Formation in the East Basin. Based on the carbon isotopic data and chemostratigraphic correlation, the chronostratigraphic framework of the Furongian Series across different facies in the Tarim Craton is preliminarily established. The basal boundary of the Furongian Series was preliminarily defined by the occurrence of the SPICE. A weak positive anomaly of δ13C was observed at the base of the Penglaiba Formation of the three boreholes in the West Platform and the top of the Tuershaketag Formation of Tadong-2 well. We propose that the positive anomaly of the carbon isotope above the weak negative anomaly at the base of the Penglaiba Formation and the top of the Tuershaketag Formation can be used to define the Cambrian-Ordovician boundary in the Tarim Craton. [ABSTRACT FROM AUTHOR]

The placement of the Ediacaran-Cambrian boundary in deep-water realm in South China and the high-precision temporal framework for the Ediacaran-Cambrian transition in this region have not yet been completely solved. Recently, we have found two K-bentonite beds in the top of the Liuchapo Formation at the Pingyin section, Guizhou Province. It provides an opportunity for constructing the temporal framework of the transitional strata on the Yangtze Platform in South China and for determining the Ediacaran-Cambrian boundary in this area. In this study, we conducted high-precision CA-ID-TIMS U-Pb dating on zircons from the two K-bentonites. The ages of the two K-bentonites were precisely constrained at 536.40±0.47/1.1/1.2 Ma (2σ, n=7, MSWD=0.92) and 541.48±0.46/1.1/1.2 Ma (2σ, n=8, MSWD=1.3). Combining the geochronological results with organic carbon isotope data of chert in the topmost Liuchapo Formation from the section, we suggest that the EdiacaranCambrian boundary should be consistent with a significant negative organic carbon isotope excursion between the two K-bentonites. The scheme of the Ediacaran-Cambrian boundary in this study is of great significance for global correlation, and further for unravelling the information of the terminal Ediacaran-early Cambrian ocean. [ABSTRACT FROM AUTHOR]

The Permian–Triassic extinction was the largest Phanerozoic mass extinction event, yet its ultimate causes remain unresolved. Ocean redox conditions, global warming, and carbon cycle perturbations owing to massive volcanism and their inter-relationships are keys to resolve the origins of this event. We here assess such relationships using a method to obtain an instantaneous stratigraphic response from high-resolution (millennial-scale) records of carbonate-δ13C and pyrite framboid size distributions across the Permian–Triassic boundary (PTB) at Meishan, China. We report two gradual long-term negative δ13C shifts before and after the PTB. Late Permian ocean redox conditions varied through three successive oxic–dysoxic, dysoxic–euxinic, and high-frequency euxinic stages. Oxic and high-frequency euxinic events occurred in the early Griesbachian and middle Griesbachian, respectively. The short-term euxinia events were not associated with the negative δ13C excursions. Siberian volcanism could have produced large light-carbon inputs, global warming, and low-oxygen conditions at intermediate ocean depths, but it may not directly drive high-frequency euxinia across the PTB. Long-term dysoxia and occasional euxinia well before the PTB stressed mobile macroorganisms and caused gradual extinction before the major extinction event. High-frequency latest Permian euxinia reduced overall biotic adaptability, and caused the initial rapid mass extinction. Increasing temperatures and other deleterious environment factors then reinforced the extinction process. Oxic conditions contributed to biotic recovery immediately after the mass extinction in the early Griesbachian. Further millennial-scale dysoxic/euxinic alternations in the middle Griesbachian would have prolonged Early Triassic biotic recovery. [ABSTRACT FROM AUTHOR]

The Ediacaran-Cambrian succession in South China records dramatic biological, oceanic and geochemical changes, but it is not well constrained geochronologically. This study reports a new SIMS U-Pb date of 543.4±3.5 Ma (MSWD=1.2) from a tuffaceous layer in the Zhoujiaao Section, and carbonate C-O isotopes in both Zhoujiaao and Sixi sections, Three Gorges area. This tuffaceous layer is present in the upper Dengying Formation (i.e., the Baimatuo Member) which is characterized by a stable δ13Ccarb plateau and the beginning of a negative δ13Ccarb shift near its upper boundary. In accordance with the existing biostratigraphic and chemostratigraphic data, this new date corroborates that the upper boundary of the Dengying Formation in South China is approximately equivalent to the Ediacaran-Cambrian boundary (ca. 541 Ma). This age also provides the minimum age of the last appearance of the Shibantan biota in the Three Gorges area, indicating that the terminal Ediacaran index fossils (e.g., Cloudina, Sinotubulites) are not reliable stratigraphic markers for further subdivision of the uppermost Ediacaran. [ABSTRACT FROM AUTHOR]

The purpose of this study was to assess the water quality and variations in stable carbon and nitrogen isotopes of particulate organic matter (δ13CPOM and δ15NPOM), as well as to evaluate the sources of carbon and nitrogen that contribute to the POM pools in lakes and reservoirs located in the water-receiving area of the Eastern Route of South-to-North Water Transfer Project (SNWTP) in Northern China. During each season from October 2013 to July 2014, samples of POM from 14 lakes and reservoirs in Northern China were collected. The lakes and reservoirs were meso-eutrophic with considerably high brackish ions (SO42−, 173 mg/L; Cl−, 296 mg/L) in Yangtze River lake, and high total nitrogen: total phosphorus ratio (averaged with 772) or dissolved inorganic nitrogen: soluble reactive phosphorus molar ratios (averaged with 1077) in mountainous reservoirs. The δ13CPOM, δ15NPOM, carbon to nitrogen (C/N) ratios showed significant seasonal variation, with ranges of − 32.5 to − 17.4‰, − 3.6 to 13.5‰, and 5.1–13.2, respectively, while they were hard to be distinguished among types of water sources. Principal component analysis (PCA) indicated that brackish ions, nutrients, and their molar ratios were the main factors influencing variations in δ13CPOM and δ15NPOM. δ13CPOM and C/N ratios suggested autochthonous primary production mainly contributed to POM during from April to October, while exogenous organic matter might mainly contribute these carbon pools in January. The low values of δ15NPOM (< 0‰) and negative correlation between δ15NPOM and TN suggested discharge of agricultural waste water (e.g., fertilizers, irrigation tailwater) in Bailanghe, Xinan, and Taihe Reservoir during the fertilization season, while higher values indicated domestic sewage input to waterbodies (e.g., Mishan, Gengjing, Donghai Reservoir). Our results suggested that the aquatic ecosystem in water-receiving area of SNWTP would be potentially affected by the inter-basin water diversion, and thus, ecosystem-based strategies were also presented accordingly. [ABSTRACT FROM AUTHOR]

The fracture-cave reservoir of the Yingshan Formation is an important oil and gas producing zone in the Tarim Basin. Karstification occurs at the top surface of the carbonate rocks of the Yingshan Formation on the northern slope of the Tazhong area due to a short exposure, so abundant fracture-cave spaces are formed. On the basis of the data of nearly 49 samples obtained from 21 wells, the carbon and oxygen isotopes of the fracture-cave calcite were analyzed. The carbon and oxygen stable isotopic characteristics recorded during paleokarstification were discussed to provide geochemical evidence for predicting the distribution of the fracture-cave reservoirs, as well as to understand the genetic mechanism of karst fracture-caves and the fluid properties and paleo-hydrological conditions of paleokarstification. The fracture-cave calcite can be divided into three types based on its carbon and oxygen isotope values, which indicate three types of paleokarst environments with different fluid properties. Type I calcite has similar carbon and oxygen isotope values to the bedrock of the Yingshan Formation, with δ13C values of − 2.0 to 1.1‰ and δ18O values of − 5.76 to − 8.16‰. These values indicate that the calcite was precipitated in the eogenetic karst environment of the Yingshan Formation. Type II calcite has a δ13C value of − 2.13 to 1.0‰ and a δ18O value of − 12.41 to − 8.0‰. It has a similar δ13C value, but a significantly negative oxygen isotope value compared with values of the bedrock of the Yingshan Formation, indicating a buried karst environment. Type III calcite has an extremely negative δ18O value (δ18O value < − 14.50‰), indicating hypothermal karst genesis. Its formation is related to magma or deep hydrothermal fluids. No calcite with atmospheric freshwater genesis and significantly negative δ13C and δ18O values was found in the samples, indicating that the formation of fracture-caves is weakly affected by atmospheric freshwater. The main reservoir space of the Yingshan Formation is karst caves. The calcite in the karst cave fillings belongs to type I, indicating an eogenetic karstification environment. Therefore, the formation of the fracture-cave reservoirs of the Yingshan Formation in the Tazhong area is related to eogenetic karstification, which occurred during exposure and mainly contributed to the formation of the reservoir spaces. [ABSTRACT FROM AUTHOR]

Based on petrography and geochemistry, formation phases of carbonate cements and their sedimentary–diagenetic environments in Jurassic clastic rocks from the Lenghu V tectonic belt are determined. The results demonstrate that studied successions are mainly dark gray or black mudstone with interbedded thin gray siltstone and a few greywacke layers. Sandstones are lithic and feldspathic lithic greywacke with high kaolinite content. Calcite and ferrocalcite are the main carbonate cements. The carbon isotope values(δ13C) of the carbonate cements range from − 15.6 to 9.2‰ (average − 3.2‰) with a bimodal distribution. One peak is 4‰, which includes samples from the upper Xiaomeigou Formation (Fm) and the other one is − 12‰, which mainly represents the lower section. The oxygen isotope values(δ18O) have a wide range from − 18.5 to − 8.3‰ (average − 13.31‰). Combined with microscopic observations, two phases of carbonate cements are distinguished according to their isotopic characteristics. The earlier carbonate cements are mainly calcite and ferrocalcite, and they were precipitated in eodiagenesis stage. The carbon source of calcite was inorganic, and ferrocalcite was mixed with carbon from methanogenesis. This mixture led to a positive bias in the δ13C curve, which artificially inflated the paleosalinity. The later carbonate cements, formed in mesodiagenesis stage, were ferrocalcite. Decarboxylation of organic matters led to lower δ13C values. The major and trace elements data show that Sr, Ba, Fe and Mn have weak correlation with Al, Ti. So, they are effective to interpret the sedimentary environment. The Sr/Ba ratio < 1 indicates fresh water environment, Sr/Ca, Sr/Cu and Fe/Mn ratios suggest humid climate, and V/(V + Ni) ratio shows suboxic–anoxic environment. The carbon and oxygen isotopes, together with elemental geochemistry, show that the climate during the Early Jurassic was warm and wet and the studied successions were deposited in fresh water. The variations in elemental ratio curves indicate that climate became wetter and warmer later in the Early Jurassic. [ABSTRACT FROM AUTHOR]

Deep-water facies sections have advantages of recording complete information across the Permian-Triassic boundary (PTB). Here we present a detailed study on the conodont biostratigraphy and carbon isotope profile ranges from the Wuchiapingian-Changhsingian boundary (WCB) to the PTB of two deep-water facies sections at Zhuqiao and Shiligou in the Middle Yangtze region, western Hubei, South China. Fifteen species and three genera are identified. Eight conodont zones are recognized, in ascending order, they are the Clarkina orientalis, C. wangi, C. subcarinata, C. changxingensis, C. yini, C. meishanensis, Hindeodus parvus and Isarcicella isarcica zones. The onset of deposition of the deep-water siliceous strata of the Dalong Formation in western Hubei began in the Late Wuchiapingian and persisted to the Late Changhsingian. Carbon isotope negative excursions occur near both the WCB and PTB in both sections. The WCB δ13Ccarb negative excursion is in the C. orientalis and C. wangi zones. The PTB δ13Ccarb negative excursion began in the C. yini Zone and extended to the I. isarcica Zone. The absence of several Changhsingian zones may indicate the difficulty of extracting conodonts from siliceous strata or the presence of an intra-Changhsingian hiatus. [ABSTRACT FROM AUTHOR]

Biological carbon pumping (BCP) is a key process in which dissolved inorganic carbon in terrestrial aquatic ecosystems is utilized by aquatic autotrophs for photosynthesis and transformed into autochthonous organic matter (AOC). However, the mechanisms underlying BCP and the amount of generated AOC deposited effectively, are still poorly understood. Therefore, we conducted a systematic study combining modern hydrochemical monitoring and a sediment trap experiment in Fuxian Lake (Yunnan, SW China), the second-deepest plateau, oligotrophic freshwater lake in China. Temperature, pH, EC (electrical conductivity), DO (dissolved O2), [HCO3−], [Ca2+], SIc, partial CO2 (pCO2) pressure, and carbon isotopic compositions of HCO3− (δ13CDIC) in water from Fuxian Lake all displayed distinct seasonal and vertical variations. This was especially apparent in an inverse correlation between pCO2 and DO, indicating that variations of hydrochemistry in the lake water were mainly controlled by the metabolism of the aquatic phototrophs. Furthermore, the lowest C/N ratios and highest δ13Corg were recorded in the trap sediments. Analyses of the C/N ratio demonstrated that the proportions of AOC ranged from 30% to 100% of all OC, indicating that AOC was an important contributor to sedimentary organic matter (OC). It was calculated that the AOC flux in Fuxian Lake was 20.43 t C km−2 in 2017. Therefore, AOC produced by carbonate weathering and aquatic photosynthesis could potentially be a significant carbon sink and may have an important contribution to solving the lack of carbon sinks in the global carbon cycle. [ABSTRACT FROM AUTHOR]

Hydrocarbon migration mechanism in deep Ordovician reservoir of the Halahatang area, Tarim Basin, is investigated based on the analysis of the geological setting and geochemical parameters. The parameters successfully analyzed include oil–gas properties, crude oil maturity [Ts/(Ts + Tm) ratio], gas carbon isotopic ratios, and trace elements (B, V, Ni, and Cu) in crude oil. The results show that hydrocarbons migrate into the Ordovician of the Halahatang area from the Manjiaer Depression and the Halahatang area itself through unconformities and faults. The overall hydrocarbon migration orientation in the area is generally from south to north. The oil and gas migration process determine parameters vary regularly from south to north as follows: oil density, V/Ni ratio, Ni/Cu ratio, and concentrations of V, Ni and (Ni + B) in crude oil regularly increase, whereas Ts/(Ts + Tm), gas/oil ratio, and dryness coefficient gradually decrease, and methane show a trend toward depletion of heavy carbon isotopes. Additionally, there exist obvious anomalies of geochemical parameter values in the Repu3 well block, which indicates that a local fault intersection could provide a favorable hydrocarbon filling point. Based on these findings, further exploration activities in the deep Ordovician reservoir of the Halahatang area should be conducted in the southern part of the Halahatang area along the oil charging pathways, and fault intersection zones should be emphasized. [ABSTRACT FROM AUTHOR]

To date, few research have been reported on the evolution of C3/C4 vegetation in southern China, and the main mechanism influencing the evolution of C3/C4 vegetation is unclear. That makes it difficult for researchers to understand the competition mechanism of C3 and C4 plants under different climate environments and its relationship with the climate factors. It is also not conducive for researchers to assess the influence of future climate change on regional C3/C4 vegetation. Exactly, C3/C4 vegetation change in the regional-scale will have a significant impact on the global carbon cycle and agricultural production. Therefore, it is especially important to reconstruct the evolutionary history of C3/C4 vegetation in southern China and clarify the influencing mechanism of climate change. In this study, we systematically analyzed stable carbon isotope (δ13C) of the longchain n-alkanes in sediment samples from eight lakes and four peat profiles in southern China, to reconstruct the spatiotemporal evolution of C3/C4 vegetation in these regions since the Last Glacial Maximum (LGM) and to investigate the climate factors that affect the C4 plant abundance change in the research area. The integrated long-chain n-alkane (C27–C33) stable carbon isotope results of samples from Zhanjiang Huguangyan Maar Lake, Xingyun Lake, Lugu Lake and Dingnan peat showed that, from the LGM to the Early Holocene, C4 plant relative abundance exhibited a gradually increasing trend from 21% to 34%. In the Middle Holocene, the C4 plant abundance significantly declined and reached a lowest value of 10%. In space, the C4 plant abundance generally exhibited a gradually declining trend from south to north in the LGM and the Early Holocene, while it showed an opposite trend in the Holocene Climate Optimum (6.0 cal ka BP). It reflected that the main influencing factor on C4 plants spatial distribution was changing from temperature to precipitation. This study indicated that temperature was the dominant factor affecting C4 plant distribution in southern China, however, when the temperature condition was appropriate, an increase in precipitation (especially more spring precipitation) would reduce the competitive advantages of C4 plants. Therefore, the combination of temperature and seasonal precipitation was the important factor that determines the C3/C4 vegetation proportion change in the southern China. Under the premise that the temperature will rise and precipitation will increase in the future, the reduction of a competitive advantage for the C4 plants could affect agricultural production in China. [ABSTRACT FROM AUTHOR]

Hosted by volcaniclastics of the Carboniferous Dahalajunshan Formation, the Songhu iron deposit is located in the central segment of the Awulale metallogenic belt, Chinese Western Tianshan. Mineralization and alteration are structurally controlled by orogen-parallel NWW-striking faults. Integrating with mineralogical and stable isotopic analyses based on paragenetic relationships, two types of iron mineralization have been identified. The deuteric mineralization (Type I) represented by brecciated, banded, and disseminated-vein ores juxtaposed with potassic-calcic alteration in the inner zone, which was formed from a magmatic fluid generated during the late stages of regional volcanism. In contrast, the volcanic-hydrothermal mineralization (Type II) is characterized by hydrothermal features occurring in massive and agglomerated ores with abundant sulfides, and was generated from the magmatic fluid with seawater contamination. Two volcaniclastic samples from the hanging and footwall of the main orebody yield zircon U-Pb ages of 327.8 ± 3.1 and 332.0 ± 2.0 Ma, respectively, which indicate Middle Carboniferous volcanism. Timing for iron mineralization can be broadly placed in the same epoch. By reviewing geological, mineralogical, and geochemical features of the primary iron deposits in the Awulale metallogenic belt, we propose that the two types of iron mineralization in the Songhu iron deposit are representative regionally. A summary of available geochronological data reveals Middle-Late Carboniferous polycyclic ore-related volcanism, and nearly contemporaneous iron mineralization along the belt. Furthermore, petro-geochemistry of volcanic-volcaniclastic host rocks indicates that partial melting of a metasomatized mantle wedge under a continental arc setting could have triggered the continuous volcanic activities and associated metallogenesis. [ABSTRACT FROM AUTHOR]

The trophic relations of the red-crowned crane in Zhalong wetland, northeastern China may significantly be altered due to the rapid decrease in accessible food resources. To confirm this hypothesis, we determined the trophic status of this vulnerable species by using stable isotope (carbon (513C) and nitrogen (S15N) methods. The 513 Cand 15 Nsignatures in the red-crowned crane species were in the range of -- 17.8‰ to -- 18.5‰ and 6.9‰ to 8.1%, respectively. The majority of the ecosystem of Zhalong wetland has an average food-chain length of 3.9, and the trophic level of the examined species, i.e., red-crowned crane, was approximately 3.1. The trophic relations of red-crowned cranes have changed over the period of 2004 to 2014, as the biological species in the bottom trophic level significantly exhausted in the past years. The conflict of food demand by red-crowned cranes versus the livelihood demand of local wetland residents should be resolved to ensure sustainability of food supply sustainable for rare and extinguishable species. [ABSTRACT FROM AUTHOR]

Major elements and carbon isotopes of dissolved inorganic carbon (DIC) have been measured in the waters of Changbaishan mountain, a volcanic area in northeastern China, between June and September 2016 to decipher the origin of the CO involved in chemical weathering reactions. Spatial variations of major elements ratios measured in water samples can be explained by a change of the chemical composition of the volcanic rocks between the volcanic cone (trachytes) and the basaltic shield as evidenced by the variations in the composition of these rocks. Hence, DIC results from the neutralization of CO by silicate rocks. DIC concentrations vary from 0.3 to 2.5 mmol/L and carbon isotopic compositions of DIC measured in rivers vary from −14.2‰ to 3.5‰. At a first order, the DIC transported by rivers is derived from the chemical weathering's consumption of CO with a magmatic origin, enriched in C (−5%) and biogenic soil CO with lower isotopic compositions. The highest δC values likely result from C isotopes fractionation during CO degassing in rivers. A mass balance based on carbon isotopes suggest that the contribution of magmatic CO varied from less than 20% to more than 70%. Uncertainties in this calculation associated with CO degassing in rivers are difficult to quantify, and the consequence of CO degassing would be an overestimation of the contribution of DIC derived from the neutralization of magmatic CO by silicate rocks. [ABSTRACT FROM AUTHOR]

Neogene eolian successions are one of the most important terrestrial palaeoenvironmental archives in East Asia. However, they have received far less attention than Quaternary loess deposits, especially in the case of lipid biomarker analysis. In order to obtain a better insight into the early-middle Miocene palaeoenvironment, we conducted a study of n-alkane biomarkers from sediments of the QA-I section (Qinan) in the western Chinese Loess Plateau, and compared the results with those of previous n-alkane analyses of eolian and aquatic sediments of varying age. Our principal results are as follows: (1) All QA-I samples contain n-alkanes ranging from C to C, among which the relative content of short-chain n-alkanes (C-C) from microorganisms is significantly greater than that of long-chain n-alkanes (C-C) from the waxes of terrestrial higher plants; the main peak is at C-C. All samples have a relatively lower abundance of medium-chain n-alkanes (C21-C25) than that of long- and short-chain n-alkanes, similar to strongly weathered palaeosols in Quaternary loess and Late Miocene-Pliocene Hipparion Red-Earth; however, this distribution is significantly different from that in weakly-weathered loess of Quaternary loess and Late Miocene-Pliocene Hipparion Red-Earth, as well as from aquatic sediments. (2) Despite some odd-over-even carbon predominance of long-chain n-alkanes in the QA-I samples, the carbon preference index (CPI) values are significantly lower than those of most of the weakly-weathered sediments. Our results show that strong weathering and microbial processes have significantly altered the n-alkanes in the Miocene eolian deposits in Qinan, and led to a significant oxidation and degradation of long-chain n-alkanes and the predominance of short-chain n-alkanes from bacteria. Therefore, the contribution of microorganism to total organic carbon (TOC) and its resulting in carbon isotopic composition should be carefully assessed in future studies. [ABSTRACT FROM AUTHOR]

In order to explore subsistence patterns in northern Shaanxi Province around 4,000 yr BP, 28 human and 24 animal bones from the Shengedaliang site were sampled for stable carbon and nitrogen isotope ratio analysis. The results show that most people primarily subsisted on C resources, e.g. millet and millet-related animal products, despite the fact that there was some intake of C plants by some individuals. Stable nitrogen isotope values indicate that there were differences in meat consumption between individuals at the site. Pigs were mainly foddered with millet and millet byproducts, as well as some cattle, according to their high δ C values. However, most cattle and the sheep/goats consumed wild C plants at Shengedaliang. Our above findings indicates that subsistence patterns in northern Shaanxi around 4,000 yr BP were characterized by millet farming, while the grassland animal husbandry, e.g. cattle and sheep/goats raising, displayed very little contribution to local economy. The intensive millet farming in northern Shaanxi provided enough food for population growth, ensured the accumulation of wealth, and consequently accelerated social differentiation and complexity. [ABSTRACT FROM AUTHOR]

The Early Triassic was a period of ecological restoration for the earth's system after the end-Permian mass extinction. Geochemical records linked to the variations in marine ecosystems during this period have attracted the interest of geologists for many years. Based on petrographic analysis of samples and evaluations of their reliability as proxies for original seawater, this study investigated the carbon and oxygen isotopic compositions of 350 carbonate rock samples from the Lower Triassic (and adjacent strata) in the southern Longmenxia section of Guang'an, eastern Sichuan Basin. The results indicate that the Triassic carbonate rocks from the southern Longmenxia section favorably preserved the original seawater's δ C signal. Furthermore, carbon and oxygen isotopic compositions are found to be poorly correlated, with a determination coefficient as low as 0.0205 and only 44 rock samples show results of Mn/Sr>2 and/or δ O<-6.5‰. The complete carbon isotopic curve for the Lower Triassic is established using the data from the remaining 306 samples with Mn/Sr<2 and/or δ O>-6.5‰. This curve presents favorable comparability on a global scale, specifically in the δ C minima near the Permian-Triassic boundary, at the top of the Jia1 and within the the Jia3, as well as in the δ C maxima at the tops of the Ye1 and Ye4, at the base of the Jia2 and at the top of the Ye3. The peaks and troughs corresponding to these maxima and minima all reflect global signals. By comparing these results to previous research on coeval carbon isotopic curves established within the chronostratigraphic framework, the ages of these critical evolution points are determined. The results show that the Ye1 roughly corresponds to the Griesbachian substage; the Ye2 through Ye4 correspond to the Dienerian substage; Jia1 corresponds to the Smithian substage; from the Jia2 to the lower part of the Jia4 correspond to the Spathian substage; and the middle and upper parts of the Jia4 belongs to the Aegean Substage of the Middle Triassic. Around the boundary between the Jia1 and Jia2 (which represents the Smithian-Spathian boundary (SSB)), the value of δ C increases rapidly from -0.911‰ to 3.679‰. The span during which the seawater's carbon isotope experiences this drastic change may be less than 36 kyr. The oxygen isotope, which is more sensitive to sedimentary environmental changes, exhibits changes prior to the carbon isotope near the SSB, indicating a significant increase in the salinity of the seawater before a sharp rise in the carbon isotope; this event leads to the formation of evaporites and dolomites. [ABSTRACT FROM AUTHOR]

A preliminary isotopic evaluation using H and C dating based on a well-mixed reservoir model for groundwater in the arid irrigation zone in the upper reaches of the Peacock River, NW China was conducted in 2014 to reveal the renewal rate of the groundwater. The results show that the renewal rates are 0.004-1.9 and 0.01-0.7 % a for the unconfined water and confined water, respectively, which are very low and should be considered for sustainable development of groundwater in the study area. [ABSTRACT FROM AUTHOR]

To understand the effects of leaf physiological and morphological characteristics on δC of alpine trees, we examined leaf δC value, LA, SD, LNC, LPC, LKC, Chla+b, LDMC, LMA and N in one-year-old needles of Picea schrenkiana var. tianschanica at ten points along an altitudinal gradient from 1420 m to 2300 m a.s.l. on the northern slopes of the Tianshan Mountains in northwest China. Our results indicated that all the leaf traits differed significantly among sampling sites along the altitudinal gradient (P<0.001). LA, SD, LPC, LKC increased linearly with increasing elevation, whereas leaf δC, LNC, Chla+b, LDMC, LMA and N varied non-linearly with changes in altitude. Stepwise multiple regression analyses showed that four controlled physiological and morphological characteristics influenced the variation of δC. Among these four controlled factors, LKC was the most profound physiological factor that affected δC values, LA was the secondary morphological factor, SD was the third morphological factor, LNC was the last physiological factor. This suggested that leaf δC was directly controlled by physiological and morphological adjustments with changing environmental conditions due to the elevation. [ABSTRACT FROM AUTHOR]