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Urbanization and the release of carbon emission are two significant features of contemporary economic and social progress in China. However, there are few studies that consider how urbanization policy goals affect carbon emission. This paper aims to study the nonlinear effects of urbanization policy goals on carbon emission in 13 cities of the Beijing-Tianjin-Hebei region. In this paper, a multi-dimensional spatial disturbance grey model is proposed. Based on matrix perturbation theory, this paper explores the spatial perturbation bounds of the novel model and verifies that the spatial property of the model is consistent with the viewpoint of the First Law of Geography. Then, the novel model is used to predict the urban carbon emission under different urbanization policy goal scenarios. The results showed that the novel model has spatial regional correlation in spatial region prediction. With the development of urbanization level, carbon emissions show a downward trend in more than 50% of cities from 2022 to 2025. In addition, the improvement of urbanization policy goals will promote the carbon peak time of most cities. The carbon emission intensity will exhibit an inverted U-shaped trend distribution in space. The research results are conducive to providing scientific guidance for the formulation of new-type urbanization policies and helping to achieve the dual carbon goals. • A multi-dimensional spatial disturbance grey model is proposed. • The novel grey model is consistent with the viewpoint of the First Law of Geography. • The spatial distribution of carbon intensity showed an inverted U-shaped pattern. [ABSTRACT FROM AUTHOR]

Green finance is a financial innovation that directs capital allocation towards green industries. How will this affect regional carbon emissions? Based on the data on green finance and carbon emissions of 30 provinces in China from 2008 to 2019, this paper employs a multivariate linear regression model and a spatial econometric model to empirically study the impact of green finance on carbon emissions. The results find that (1) green finance significantly reduces provincial carbon emissions, specifically through promoting a cleaner energy structure and an advanced industrial structure, as well as improving the quality of green innovation. (2) Heterogeneity exists between regions. In eastern regions and areas characterized by high levels of marketization and minimal fiscal pressure, the role of green finance in promoting provincial carbon emission reduction is more pronounced. (3) Spatial econometric analysis found that green finance has a significant spatial spillover effect on carbon reduction in adjacent regions. Specifically, the flow of green resources and green ideas between provinces facilitates the formation of regional radiation, while green competition generates a siphon effect on neighboring regions. These findings provide some meaningful policy implications to achieve China's dual-carbon goal by promoting green finance. • Green finance has significantly reduced China's provincial carbon emissions. • The upgrading of energy structure and industrial structure is a positive channel to reduce carbon emissions. • Green innovation strengthens the carbon reduction effect of green finance, but reveals the potential "greenwashing". • Green finance has a significant spatial spillover effect on carbon reduction in adjacent regions. • Policymakers should develop flexible, dynamic and coordinated green finance development policies. [ABSTRACT FROM AUTHOR]

The Archaeocyathid Extinction Carbon Isotope Excursion (AECE) and Mingxinsi Carbon Isotope Excursion (MICE) are major events in the Early Cambrian sedimentary records but controversially heterogeneous in their magnitudes, as well as local and global correlations. This paper presents a high-resolution δ13C carb profile from the Shiliu section in the western Yangtze Platform (China) that spans the lower part of the Lower Cambrian. The investigated Lower Tianheban interval (∼110 m) is dominated by marine carbonates (lime mudstones) alternating occasionally with thinly-bedded black shale and mudstone interbeds. The investigated micritic carbonates were examined through a multi-technique protocol, combining petrographic and geochemical assessments, to evaluate the degree of sample preservation. The δ13C carb values (−2.4‰–1.8‰) show an insignificant correlation with the δ18O carb values (−12.6‰ to −8.7‰, R2 = 0.012), the Mn/Sr ratios (R2 = 0.001), and Al concentrations (R2 = 0.041). This supports the preservation of predominantly at least near-primary δ13C carb signatures, which can be utilized to reconstruct a reliable, high-resolution δ13C carb profile for chemostratigraphic correlations in the area and beyond. The profile displays a lower positive excursion of ∼3‰ overlain immediately by a negative excursion of ∼2.3‰. The archaeocyath zonation scheme suggests that the lower excursion is correlated with the global MICE event and the upper excursion with the AECE event. The results provide an alternative option for interpreting the carbon isotope excursions in the Lower Cambrian within the Yangtze Platform as well as other equivalent sections at a global scale. • δ13C carb composition of the Lower Cambrian carbonates in northwestern Yangtze Platform. • Distinct δ13C carb excursions correlated with the MICE and AECE events. • Alternative interpretation of the MICE and AECE events in the Yangtze Platform. • A useful C-isotope profile for chemostratigraphic correlations in Yangtze Platform and beyond. [ABSTRACT FROM AUTHOR]

[Display omitted] • The bitumen in wall rocks and the Danzhai paleo-oil reservoir both originate from the Lower Cambrian source rock. • The paleo-oil reservoir and the ore sulfur both derive from seawater sulfate in the strata. The metallogenic metals are mainly sourced from the underlying strata and basement. • Bitumen Re-Os and sphalerite Rb-Sr isotopes yield isochron ages of 424±160 Ma and 398±4.7 Ma, respectively. • Hydrocarbons supply a large amount of reduced sulfur for mineralization through TSR reaction. The Niujiaotang MVT Pb-Zn ore field is located at the southwestern end of the West Hunan-East Guizhou (WHEG) metallogenic belt, which overlaps spatially with the Majiang paleo-oil reservoir. The Pb-Zn mineralization is closely associated with oil-gas accumulation processes. However, the genetic link between the paleo-oil reservoir and the Pb-Zn deposits remains unclear. In this paper, we present new findings of bitumen (paleo-oil reservoir) and its features in the deposits, and apply various isotopic geochemical methods and 2D seismic data to elucidate the source rock and coupling relationship of the paleo-oil reservoir and the Pb-Zn deposits. This study reveals that the ore has a simple mineral composition, mainly comprising sphalerite, pyrite, and dolomite. Solid bitumen occurs widely in the ore and the host dolostone, and coexists with minerals from the mineralization stage. Laser Raman spectroscopy shows that the bitumen in the wall rocks of the Chengong deposit and the Danzhai paleo-oil reservoir are both overmature, and their carbon isotope compositions (δ13C PDB = –29.17 ‰ – –31.20 ‰, average –30.10 ‰, n = 6) and initial 187Os/188Os ratio (1.08±0.19) suggest that they have the Lower Cambrian source rock similar to the Majiang paleo-oil reservoir. The δ34S value of pyrite in the bitumen from the wall rocks in the Chengong deposit ranges from +28.15 ‰ to +44.12 ‰ (average +33.28 ‰, n = 18), which is consistent with the sulfur isotope composition of the ore sulfide reported previously, indicating that they both derived from sulfate in the Middle-Upper Cambrian strata. Bitumen Re-Os and sphalerite Rb-Sr isotopic dating indicate that oil reservoir accumulation in the ore-hosting strata preceded Pb-Zn mineralization, occurring at 424±160 Ma (MSWD = 1.3) and 398±4.7 Ma (MSWD = 0.66), respectively. The initial 87Sr/86Sr ratio of sphalerite is 0.709983±0.000027, which, after comparison and in combination with previous studies, suggests that the metallogenic metals mainly originated from the underlying strata and basement. 2D seismic data show that the Zaolou fault (F 2) that controls the mineralization is a deep fault that extends to the basin basement, and acts as a migration pathway for hydrocarbon fluids and ore-forming materials. We propose that liquid hydrocarbons played a significant role in Pb-Zn mineralization, acting as reductants to reduce sulfate through the thermochemical sulfate reduction (TSR) reaction and provide abundant reduced sulfur (H2S/HS−) for Pb-Zn mineralization. Finally, we present a comprehensive model of hydrocarbon accumulation and mineralization in the Niujiaotang ore field. [ABSTRACT FROM AUTHOR]

Under the background that China will achieve the goal of carbon neutrality by 2060, analyzing the impact of carbon neutral target constraints on the welfare of urban and rural residents is an important part of the design of a carbon emission reduction policy mechanism, in this paper, the dynamic recursive CGE(Computable general equilibrium) model is used to simulate the changes in welfare level, income consumption, and CO2 emissions of residents and their urban-rural heterogeneity under the policy of imposing a carbon tax on the fossil energy industry from 2022 to 2060. The results show that: compared with the BAU scenario, by 2060, first the income and consumption of residents will decrease slightly. Second, the target constraint of carbon neutrality makes the equivalent variation and compensate variation of urban and rural residents' welfare decrease slightly, and the equivalent variation and compensate variation of urban residents decrease more than those of rural residents. The following conclusions are drawn: first, the carbon-neutral target constraint makes the welfare of urban and rural residents decline slightly, but it will not have a strong impact on residents' income and consumption. Second, this constraint has a greater impact on the income, consumption and savings of urban residents than those of rural residents. [Display omitted] • A five-layer nested dynamic recursive CGE model is established to analyze residents' welfare. • Carbon taxes are incorporated into production decisions as a policy cost for energy companies. • The heterogeneity of the impact of carbon tax policy constraints on the welfare of urban and rural residents was analyzed. • The government needs to improve the intensive and diversified energy supply in rural areas to reduce the urban-rural gap. [ABSTRACT FROM AUTHOR]

Nitrogen isotope (δ15N) analysis has been used to evaluate depositional redox conditions in well-preserved sedimentary systems; however, fewer N-isotope studies have been performed to reconstruct the redox conditions in lacustrine shales. In this paper, we report the δ15N data from the Upper Triassic Chang 7 Shale of the Ordos Basin, North China. Sedimentary δ15N values are significantly higher in the Chang 7 3 and the lower part of the Chang 7 2 submembers (Zone A; average = 9.4 ± 1.3‰) than in the upper part of the Chang 7 2 and the Chang 7 1 submembers (Zone B; average = 5.4 ± 1.5‰). Previous geochemical measurements (i.e., U and TOC/P) of both zones show wide redox variation, however, the average values of these redox proxies are relatively higher in Zone A than those of Zone B. Combined with lithological aspects of the Chang 7 Shale, our study suggest that Zone A was mainly deposited under suboxic bottom water conditions, whereas Zone B deposits accumulated within an oxygenated water column. Stable organic carbon isotopes (δ13C org) and total nitrogen (TN) values of the two zones display little variation that could be attributed to changing organic matter sources and/or post-depositional alteration of δ15N. Thus, we suggest that variations in δ15N throughout the Chang 7 Shale primarily reflect differences in depositional redox conditions and δ15N values of the shale that can provide important details regarding the depositional history of unconventional resource plays. • Provide the first δ15N records of the Chang 7 Shale, Ordos Basin. • Differences in δ15N are primarily influenced by water column redox conditions. • Organic-rich intervals accumulated under suboxic conditions. • Tectonic events drove redox changes during deposition. [ABSTRACT FROM AUTHOR]

Paleo-altitude reconstructions using oxygen isotopes provide past surface elevation data that can constrain the topographic evolution of mountain belts. This paper presents oxygen and carbon stable isotopic compositions of gastropod fossils, carbonate cements, and shelly sandstones in the Anjihai and Shawan formations located in the Sikeshu drainage basin, northern Tianshan, western China. Correlations between the stable isotopic compositions and lithofacies suggest that the Sikeshu drainage basin was mainly an open hydrological depositional environment. Based on the oxygen isotopic compositions of the gastropod fossils and petrographic examination, the δ13C and δ18O values have not been reset by late-stage diagenesis. Paleo-altitudes were reconstructed using the corrected paleo-surface water δ18O psw values recovered from gastropod fossils, carbonate cements, and shelly sandstones. An empirical formula was developed to calculate the paleo-latitudes when the Anjihai and Shawan formations were deposited. The paleo-altitude of the Sikeshu drainage basin had attained an elevation exceeding 2000 m by 28 Ma, similar to the present-day elevation in this area. This conclusion contributes to our understanding of the extent of surface uplift in the Cenozoic of Tianshan and the climatic differences on either side of Tianshan during the Cenozoic. Unlabelled Image • This study is the first in Tianshan to provide quantitative evidence for uplift and exhumation. • δ18O date of gastropod fossil analyzed in situ by NanoSIMS rule out diagnetic reset. • Paleoelevation of the north of Tianshan have exceeded 2000 m at least before 28 Ma. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Paleoproterozoic Jingshan Group marble displays a pronounced positive δ13C V-PDB. • The positive excursion appears to have been a response to the Lomagundi-Jatuli event. • The carbon isotope anomaly appears most pronounced in shallow marine deposits. • BIF and graphite deposits formed coeval with increasing atmospheric oxygen levels. The North China Craton, one of the oldest continental blocks in the world, comprises Paleoproterozoic metamorphic sedimentary formations that record the effects of multiple major events in early Earth history, including the Great Oxidation Event (GOE) and its consequent Lomagundi-Jatuli carbon isotope event (LJE). The lack of focused research on the geological record of LJE-equivalent rocks of the Jiaodong Peninsula, Shandong Province, eastern China, has hindered our understanding of the Precambrian atmospheric oxygen evolution recorded by rocks of the North China Craton. This paper considers carbon and oxygen isotope and trace element geochemical data recovered from marble deposits of the Paleoproterozoic Jingshan Group (2.20–1.90 Ga) of the Jiaolai Basin. The investigated strata display a pronounced positive δ13C V-PDB excursion greater than 4.2 ‰. δ13C V-PDB and δ18O V-SMOW values range from −3.7 ‰ to 5.4 ‰ and 4.5 ‰ to 18.7 ‰, respectively. Positive co-variance of carbon and oxygen isotope values of the analyzed Jingshan Group samples is interpreted to reflect the effects of metamorphism and water–rock reactions. Marble deposits of the Jingshan Group experienced recrystallization, metamorphism, and silicification resulting in strong decarbonation. High amphibolite facies metamorphism may have reduced δ13C V-PDB by 3 ‰ to 5 ‰. Thus, estimated original sedimentary δ13C V-PDB values of as great as +8.4 ‰ suggest the existence of a strong positive anomaly that may reflect the global Lomagundi-Jatuli event. Rare earth and other trace element geochemical results of the present study suggest that banded iron formation (BIF) deposits associated with the Jingshan Group marble formed in a redox stratified ocean in the Jiaolai Basin dominated by ferruginous conditions. Moreover, our results suggest that positive carbon isotope anomaly associated with the LJE is largely constrained to sediment deposited in shallow and coastal marine environments. [ABSTRACT FROM AUTHOR]

Abstract: In their recent paper, ; Anti-phase oscillation of Asian monsoons during the Younger Dryas period: Evidence from peat cellulose δ13C of Hani, Northeast China, Palaeogeography, Palaeoclimatology, Palaeoecology 297, 214–222) discuss bulk peat sample cellulose δ13C data from a fen in northeast China as a proxy for East Asian summer monsoon intensity during the Late Glacial period. Based on their own results, cited papers, and an extensive re-interpretation of sedimentological and palynological data from nearby Lake Sihailongwan, construct a hypothesis of contrasting moisture conditions in northern and southern China, with wet conditions in the north during the Younger Dryas period and an anti-phase behaviour of Indian- and East Asian summer monsoon intensity. However, we do not approve of the re-interpretation of our Lake Sihailongwan data by and must strongly reject it. We show here that neither the fen data, nor the Lake Sihailongwan data or any other cited data allow for the sound assumption of an intensified East Asian summer monsoon in northeastern China during the Younger Dryas. The Late Glacial variability of the fen data found by can be easily explained by changes in the plant assemblage down core and thus by the composition of the peat. Furthermore, the use of bulk peat cellulose δ13C data as a precipitation proxy remains unproven for that area. Hence, there is no basis for a model contrasting Indian and East Asian summer monsoons during that period. [Copyright &y& Elsevier]

Abstract: Using the measured results of coalbed methane (CBM) δ13C1 of more 170 groups, the paper has analyzed the distribution characteristics and statistical regularity of δ13C1 in coal seam gas in China. The values of δ13C1 are between -73.3‰ ∼ -27.3, increasing with the coal rank in general, and after anthracite, the value of δ13C1 goes to be stably fluctuating around -35‰. Based on the variation relationship between carbon isotope of CBM and coal rank, using the Rmax of coal vitrinite in coal as index, the origin of the coal seam gas is divided into three categories: secondary biogenetic gas, mixed genetic gas and thermogenetic gas. In addition, the paper has pointed out the gas genetic types of partial coal mining areas in our country. [Copyright &y& Elsevier]

• Regional ecological benefits of developing forest carbon sequestration projects in carbon markets are empirically investigated. • The pilot policy of China's one regional offset mechanism (Guangdong PHCER) is used as a quasi-natural experiment. • The carbon market can effectively increase city greening by encouraging the development of forest carbon sequestration projects. • This effect does not crowd out arable resources.Thank you very much. This paper investigates the regional spillover effects of the project-based voluntary market under the carbon emissions trading scheme (ETS). By exploiting one local offset mechanism (China's PHCER) as a quasi-experiment, we detect the unintended causal effect of the carbon market on greening the city. Using the difference-in-differences (DiD) estimator, we find that the voluntary carbon market resulted in a 14.45% (14.34%) increase in city-year-level NDVI summary value (per capita). The primary mechanism is the expansion of forest carbon sequestration projects. Cities with lower carbon emissions and fewer carbon market participants experience a greater causal effect. More importantly, we find no evidence to support the crowding out of arable land by forest carbon sequestration projects. Finally, several policy implications for a more functional carbon market are discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

Under the influence of glacial-interglacial climate change and regional tectonic activities in the Quaternary, the sedimentary environments of the Bohai Sea changed greatly, providing significant information on transgression-regression events, East Asian monsoon changes and regional tectonic activities. This study analyzed the sedimentological characteristics of the BH1302 core (water depth of 12.3 m, length of 70.2 m) in the southern Bohai Sea based on grain size, foraminiferal assemblages, carbon and oxygen isotopes in foraminiferal shells and element geochemistry, and established a chronological framework based on AMS 14C, optically stimulated luminescence dating and Oxcal age-depth model using Bayesian modeling. The results showed that three interglacial transgressions and one interstadial transgression were revealed in BH1302 since the late Quaternary, corresponding to marine isotope stages (MIS) 7, 5, 3 and 1, and three subinterglacial transgressions were further identified during MIS 7. The sedimentary environments of Laizhou Bay transitioned from an estuary environment dominated by rivers to a neritic environment dominated by marine conditions because of subsidence of the Miaodao uplift in late MIS 7.1. Three subinterstadial transgressions occurred in both MIS5 with two subinterstadial in MIS 3, and the highstand sea level of MIS 3 reached approximately −18 ∼ −21 m. Under the influence of sea level fluctuations and the East Asian monsoon, the sedimentary environments of MIS 1 can be divided into a low salinity tidal-flat environment (12.0–7.0 kyr BP), a low salinity neritic environment (7.0–4.5 kyr BP) and a modern neritic environment (∼4.5 kyr BP). • The isotopes in the foraminifera shells have good indications to the impact of freshwater input on the neritic environments. • Except for 4 interglacial transgressions, the paper further identifies 3 sub-interglacial transgressions in the MIS7 period. [ABSTRACT FROM AUTHOR]

The South Qinling Belt is a key area for understanding the collisional history of the South China and North China blocks during the Lopingian (late Permian) and Triassic. This paper establishes the first integrated timescale based on conodont biostratigraphy and δ13C carb records from a continuous end Permian to the end-Early Triassic succession at Yiwagou, South Qinling Platform (SQP). Ten Early Triassic conodont zones are established. They are, in ascending order, Hindeodus parvus , H. postparvus , Neospathodus dieneri , Eurygnathodus costatus and E. hamadai , Novispathodus waageni - Scythogondolella mosheri , Pachycladina - Parachirognathus assemblage, Triassospathodus hungaricus , Ns. robustispinus and T. clinatus zones. Our record of δ13C carb fluctuations shows close correspondence to known Early Triassic carbon isotope fluctuations and, in combination with the conodont data, helps achieve a high-resolution age model for the region. The use of E. costatus as a good auxiliary marker for the Induan-Olenekian boundary (IOB), within palaeolatitudes of 40°N-40°S, is supported but it can not replace the use of Nv. waageni , because the former is absent in higher-latitude and cooler regions. The conodont faunas from the Palaeo-Tethyan Yiwagou section closely resemble those from the Northern Yangtze Platform (NYP), but they differ somewhat from the contemporaneous Nanpanjiang Basin at species level. Thus, the Qinling Sea was likely well connected with the NYP in the Early Triassic, but was more isolated from the Nanpanjiang Basin. The remarkable reappearance of Hindeodus fauna around the IOB at Yiwagou implies that the shallow-water Qinling Sea was a refuge area for this genus long after its disappearance elsewhere. • Conodont biostratigraphy and δ13C carb records from end Permian to the end-Early Triassic succession at Yiwagou, South Qinling Platform. • Discussion of index conodont for the Induan-Olenekian boundary. • Comparison of the conodont faunas between the eastern Paleo-Tethyan Yiwagou, South China and the western Paleo-Tethyan Europe. • The shallow-water Qinling Sea was a refuge area for Hindeodus fauna after Griesbachian. [ABSTRACT FROM AUTHOR]

[Display omitted] • The shale gas resource potential of the Longmaxi Formation was evaluated by using mud gas isotope logging technology. • The reservoir properties of shale were evaluated based on gas isotope fractionation effects. • The shale gas in the Changning area belongs to late kerogen cracking gas. • The lower part of the Longmaxi Formation has a better shale gas exploration potential. The Longmaxi Formation in the Sichuan Basin is one of the most important shale gas producing formations in China. Previous studies of shale gas were mostly carried out on based on laboratory analyses and did not provide effective guidelines for shale gas exploration. In this paper, we present a large amount of carbon isotopic data from mud gas isotope logging and rock-cutting headspace gas in wellsites. The δ13C 1 values showed a significant decrease at the bottom of the Longmaxi Formation. The δ13C 1 and δ13C 2 values in the Changning area were observed to be heavier than those in the Weiyuan and Jiaoshiba areas. The second half of the N216H27-3 horizontal well had obvious outgassing and carbon isotope fractionation effects. This indicates that the bottom of the Longmaxi Formation has better shale gas exploration potential. The shale gas of the Longmaxi Formation in the Changning area belongs to late kerogen cracking gas, where exploration prospects are poorer than those in the Weiyuan and Jiaoshiba areas. There were more oil cracking gas resources and better reservoir conditions at the end of the N216H27-3 horizontal well; therefore, drilling should be continued at this site. [ABSTRACT FROM AUTHOR]

Molecular parameters are both facies and maturity dependent. Source and maturity assessment remains a difficult task for oils which were derived from multiple source rocks at a wide range of maturities from the early to late oil generation window. In this paper, a new approach was presented to assess oil source on the basis of molecular facies parameters under maturity constraint using crossplots of one source parameter versus one maturity parameter. Concentrations of ΣC 29 steranes and C 30 hopane were tentatively used as maturity indicators. Quantitative GC, GC-MS and GC-IRMS analyses were performed on 52 oils from the southern and central Mahu sag of northwestern Junggar Basin, NW China. The 52 oils are first classified into three groups, i.e., groups I, II and III which were derived from source beds within the Lower Permian Fengcheng Formation (P 1 f), Middle Permian Lower Wuerhe Formation (P 2 w) and both, respectively on the basis of carbon isotopes of individual n -alkanes in combination with reservoir geological settings. These three oil groups, in particular groups I and II from different sources were further distinguished sufficiently using crossplots of ratios of pristane (Pr)/ n -C 17 and phytane (Ph)/ n -C 18 , β-carotane/ n -C 21 and concentrations of n -alkanes, Pr, Ph, β-carotane, Ts, C 29 Ts, C 30 diahopane, C 20 , C 21 and C 23 tricyclic terpanes versus concentrations of ΣC 29 steranes and C 30 hopane, respectively. Variation trends of isotopic reversal index (RI) and δ13C value of n -C 25 , the lowest among those of n -alkanes (n -C 12–34), with decreasing concentrations of ΣC 29 steranes and C 30 hopane demonstrate that carbon isotopes of n -alkanes were unlikely influenced significantly by oil maturities within oil generation window. Concentration of n -alkanes increases while concentrations of Pr, Ph, crotanes, terpanes and steranes generally decrease with decreasing concentrations of ΣC 29 steranes and C 30 hopane. Application of this approach provides numerous choices and opportunities to distinguish oil groups which were derived from different sources in combination with isotopic data and reservoir geological settings. • Molecular facies parameters were used to assess oil sources under maturity constraints. • Concentrations of n -alkanes and isoprenoids can be effective source and maturity indicators. • It is viable to assess oil source using concentration crossplots of biomarkers. • δ13C of individual n -alkanes are effective source indicator for the studied oils. [ABSTRACT FROM AUTHOR]

This paper describes numerous siderite occurrences from Nb-Zr-REY-Ga-enriched beds of tuffaceous mudstone from the Yujingshan borehole, eastern Yunnan, southwestern China. The mineral phases in the samples were identified and characterized through macroscopic observation, XRD (X-ray diffraction) analysis, optical microscopy, and FE-SEM (field emission-scanning electron microscopy). The results show that the siderite occurs in the drill core from depths of 664.07 to 729.21 m, where its content varies from 15.1 to 65.7%, 31.3% on average. Modes of occurrence of authigenic siderite include irregular banded or massive aggregates, discrete fine particles, oolitic aggregates, and double or multi-ring ellipsoid-shaped or rhombohedral aggregates. The mineralogical association with quartz, anatase, ilmenite, chromite, and zircon with sharp-edged outlines, high-temperature cracks and/or corroded embayments, and REE-bearing minerals and geochemical characteristics such as Al 2 O 3 /TiO 2 between 3 and 8, less commonly 8–23.77, indicate that abundant siderite was produced by hydrothermal alteration of airborne volcaniclastic materials. The δ 13C PDB , δ 18O PDB , and δ 18O SMOW values of siderite in the argillized tuff range from −12.56 to −1.32‰, −8.98 to −5.88‰, and 21.60 to 24.80‰, respectively. In the δ 13C PDB - δ 18O SMOW diagram, plots of the studied siderite are distributed between the fields of marine carbonate rocks, sedimentary organic matter, and carbonates of hydrothermal ores. Some siderite from the upper part of the studied borehole is isotopically close to REY carbonates from the Abramovka lignite deposit, Far Eastern Russia, which precipitated from evolved basinal waters mixed with CO 2 from a mantle source. In summary, this indicates a hybrid origin for the studied siderite including carbonate dissolution, dehydroxylation of sedimentary organic matter, and hydrothermal activity. Furthermore, the paleosalinity (Z) and paleotemperature (T) of the ore-forming fluids were calculated based on the age-corrected stable carbon and oxygen isotopic data in the samples. The Z values range from 96.65 to 121.5‰, suggesting the formation of siderite under brackish-water conditions. The T values vary from 19.47 to 47.12 °C, with some sharp fluctuations that may be due to ash falls and/or hydrothermal injections. Overall, our data support the model for critical-metal Nb(Ta)-Zr(Hf)-REY-Ga enrichment in tuffaceous deposits of southwest China including a combination of volcanic activity and terrestrial organic-rich sedimentation under warm and humid conditions, followed by low-temperature alteration evolved from acidic leaching, which is responsible for the Nb-Zr-REY-Ga enrichment, and, subsequently, formation of authigenic siderite with associated quartz, sulfide minerals, and phosphate minerals under reducing neutral/weakly alkaline conditions. • Abundant siderite is documented in the clay-altered tuffaceous horizons. • Fe was primarily derived from airborne pyroclastics. • C and O were sourced from carbonate, organic matter, and hydrotherm. • C-O isotopes show that siderite was affected by seawater and hot fluids. • A genetic model of siderite in Nb-Zr-REY-Ga deposits has been proposed. [ABSTRACT FROM AUTHOR]

Abstract: Whether there are terrestrial responses to the Oceanic Anoxic Events (OAEs) remain enigmatic. In this paper, we report a case study in the Lower Cretaceous continental and transitional sequences of coastal southeastern China. It may represent the first late Aptian to Albian terrestrial carbon isotope record from China. Several organic-rich black shale and grayish black mudstone horizons were found to develop widely in the coastal southeastern China during the period from 113±3Ma to 99±3Ma, when the Cretaceous OAEs were recorded primarily in marine sequences. Organic carbon isotope (δ13Corg), total organic carbon (TOC), and total nitrogen (TN) were analyzed for the black shales from two sections, i.e., the Shipu transitional and Chong'an continental sections. Five negative δ13Corg excursions can be recognized for both the sections, termed as SI–SV and CI–CV events for the Shipu (S) and Chong'an (C) sections, respectively. Correlations between δ13Corg, TOC and N/C ratio suggest that the SI–SIII and CI–CIII events might have been caused by global factors, i.e., the OAE1b event based on analogs to typical OAE1b reported in the Tethyan and Pacific basins. They archived the terrestrial carbon isotope response to the OAE1b accompanied with a disturbance of carbon isotope in carbon reservoir of the global ocean–atmosphere system under a warm and humid climate. [Copyright &y& Elsevier]

Abstract: With increasing collaboration between archeology and natural sciences, research on past human–environment interactions has received more attention in recent years. This paper uses nineteen radiocarbon and OSL dates from three profiles to explore environmental evolution of the Liyang Plain, investigate the spatial and temporal distributions of archaeological sites from the Paleolithic Age to the Shang–Zhou period and discuss relationships between human cultures and environmental changes. The results show that Paleolithic sites are mainly distributed in surrounding mountainous and hilly areas, changing to the plain in the late Paleolithic Age. Climatic cooling during the Last Glacial Maximum did not cause severe damage to the regional vegetation and ecosystem, which allowed the continuous development of the late Paleolithic culture in the Liyang Plain. Suitable environmental conditions and progression of human activities facilitated rice cultivation in the early Holocene, and rice agriculture as an important food resource provided a solid material foundation for social development. The number of archaeological sites increased continuously and their distribution expanded considerably into eastern low-lying plain areas during the Neolithic Age. These trends reversed in the late Shijiahe culture, and social development did not recover until the Shang–Zhou period. Variation of site distribution in the Liyang Plain was primarily influenced by hydrological and geomorphological changes as well as climate change. However, it might also have been affected by broader regional political situations, especially during the Shang–Zhou period. [Copyright &y& Elsevier]

Abstract: The present paper reports the recently discovered fossil teeth of Early Pleistocene Gigantopithecus blacki and associated mammalian fauna from Baeryan Cave, Bijie County in Guizhou Province, and also reviews briefly the known fossil sites of Gigantopithecus in south China of Pleistocene. In Early Pleistocene, Gigantopithecus had a wider distribution, but withdrew southward in Middle Pleistocene to a limited area mainly in South China, and it disappeared in the Late Pleistocene according to the present fossil records. Diet and habitat analysis from carbon isotope evidence is used to investigate the reasons for the extinction of Gigantopithecus, which fed on a pure C3 diet and lived in a forest habitat. It was clearly different from early hominins in South and East Africa, such as Australopithecus africanus, Paranthropus robustus and Paranthropus boisei, which had C4 diets. The extinction of Gigantopithecus was also related to the great changes of climate and environment of the Pleistocene, especially the last one million years, during which Homo became more and more prosperous and exerted great pressure on G. blacki. [Copyright &y& Elsevier]

Abstract: Carbonate minerals, oxygen and carbon isotopes, and Mg/Ca from surface sediments and soils were examined in Nam Co Lake, Central Tibet. This paper provides information of the irregular distribution and formation of monohydrocalcite, a metastable mineral. Carbonates of soils surrounding Nam Co Lake consist of calcite with minor dolomite. Carbonates in surface sediments in Nam Co Lake consist mainly of calcite and monohydrocalcite. All of the monohydrocalcite and most of the calcite in surface sediments are authigenic. The monohydrocalcite is distributed irregularly in Nam Co Lake because of inhomogeneous features of lake water, the variable micro-environment, high precipitation rate, and/or nucleation. Mg ions could play a greater role in the precipitation of monohydrocalcite than that of phosphate ions, because the amount of phosphate ions could be much lower than Mg ions in the 4781 m-altitude altiplano lake with poor nutrients. The presence of monohydrocalcite occurs at 2.1 ka BP, corresponding with the sharp increase of precipitation rate from 0.134 mm/y to 1.639 mm/y. High precipitation rate and/or nucleation is necessary for water molecule infiltration into the crystal lattice of monohydrocalcite. The δ18OV-PDB and δ13CV-PDB of carbonate minerals mixed with calcite and monohydrocalcite range from −5.3‰ to −8.0‰ with an average of −6.5‰, and from 2.8‰ to 4.5‰ with an average of 3.73‰, respectively. δ18OV-PDB and δ13CV-PDB of calcite range from −8.0‰ to −10.6‰ with an average of −8.09‰, and from 2.8‰ to 4.2‰ with an average of 3.25‰, respectively. Monohydrocalcite possibly has more positive values of δ18O and δ13C than those of calcite. [Copyright &y& Elsevier]

Abstract: The Xiangshan U deposit, the largest hydrothermal U deposit in China, is hosted in late Jurassic felsic volcanic rocks although the U mineralization post dates the volcanics by at least 20 Ma. The mineralization coincides with intrusion of local mantle-derived mafic dykes formed during Cretaceous crustal extension in South China. Ore-forming fluids are rich in CO2, and U in the fluid is thought to have been dissolved in the form of UO2 (CO3)2 2− and UO2 (CO3) 3 4− complexes. This paper provides He and Ar isotope data of fluid inclusions in pyrites and C isotope data of calcites associated with U mineralization (pitchblende) in the Xiangshan U deposit. He isotopic compositions range between 0.1 and 2.0Ra (where Ra is the 3He/4He ratio of air=1.39×10−6) and correlates with 40Ar/36Ar; although there is potential for significant 3He production via 6Li(n,α)3H(β)3He reactions in a U deposit (due to abundant neutrons), nucleogenic production cannot account for either the 3He concentration in these fluids, nor the correlations between He and Ar isotopic compositions. It is more likely that the high 3He/4He ratios represent trapped mantle-derived gases. A mantle origin for the volatiles of Xiangshan is consistent with the δ 13C values of calcites, which vary from −3.5‰ to −7.7‰, overlapping the range of mantle CO2. The He, Ar and CO2 characteristics of the ore-forming fluids responsible for the deposit are consistent with mixing between 3He- and CO2-rich mantle-derived fluids and CO2-poor meteoric fluids. These fluids were likely produced during Cretaceous extension and dyke intrusion which permitted mantle-derived CO2 to migrate upward and remobilize U from the acid volcanic source rocks, resulting in the formation of the U deposit. Subsequent decay of U within the fluid inclusions has reduced the 3He/4He ratio, and variations in U/3He result in the range in 3He/4He observed with U/3He ratios in the range 5–17×103 likely corresponding to U concentrations in the fluids <0.2 ppm. [Copyright &y& Elsevier]

Abstract: Carbon isotopic compositions of total organic carbon (TOC) or leaf waxes in soils have been used to reconstruct past changes in the relative abundance of C3 and C4 plants. However, TOC contains organic matter of different source organisms (plants, animals, fungi, bacteria etc.) and its isotopic ratios could be modified during diagenesis since different organic fractions (e.g., carbohydrates, proteins, lipids etc.) have different isotopic ratios and degradation rates. Leaf waxes, on the other hand, are transported by wind and hence represent vegetation input from a large geographic area. We report in this paper a new approach to extract in-situ paleovegetation information from late Quaternary paleosols by determining carbon isotopic compositions of biomarkers derived from aliphatic bio- and geopolymers of plant origin. We show that C9 to C17 n-alkenes derived from aliphatic bio- and geopolymers are the dominant compounds released by flash pyrolysis of insoluble organic matter isolated from the late Quaternary paleosols in the Chinese Loess Plateau. Because the aliphatic polymeric substances are mainly derived from plant leaves, bark and roots, the isotopic signatures of these alkenes, determined using pyrolysis–gas chromatography–isotopic ratio mass spectrometry, reflect in-situ vegetation changes. Our down-core δ 13C data from the Xifeng loess–paleosol profile show significant coherence among biopolymer-derived n-alkenes, leaf wax n-alkanes, and TOC for the past 40 kyr. However, the different amplitudes of the temporal isotopic changes among these data sets are indicative of variability in in-situ and regional vegetation dynamics, organic sources and effect of diagenesis. Our data also imply that below-ground biomass is a major source of soil organic matter in the central China loess sediment. [Copyright &y& Elsevier]

The late Paleozoic ice age (LPIA) during the Carboniferous and Permian (ca. 360–260 Ma) was vegetated Earth's only recorded icehouse-to-greenhouse transition and provides a deep-time perspective for climate-glaciation-environment coevolution and future climate change. During the LPIA, changes in glacial-interglacial cycles have been closely linked to atmospheric p CO 2. In this paper, we investigate the relationship between volcanism and glacial to interglacial climate cycles during the Pennsylvanian to earliest Cisuralian in the Liujiang Coalfield from the North China Plate (NCP). We use integrated data from Zircon U-Pb dating, Hg/TOC ratios and δ13C org to recover temporal trends in volcanic intensity and relate these to fluctuations in the global carbon cycle and atmospheric p CO 2. Four new radiometric dates from tuffaceous claystones provide a precision stratigraphic framework and constrain the succession to ~322 to 301 Ma. Results date the Benxi Formation to the Bashkirian–Moscovian stages of the Carboniferous, and the Taiyuan Formation ranging from the Kasimovian stage of the Carboniferous to the Asselian stage of the Permian. Results from Hg/TOC ratios record four peaks of volcanic intensity from the Bashkirian to the Carboniferous-Permian (C-P) transition period, and two low ebbs during the early-middle Bashkirian and the early-middle Moscovian. Peaks in volcanic intensity coincide with the four negative excursions of δ13C org and correlate with volcanism in the North China Plate and NW Europe, inferring volcanic drivers for the carbon isotope excursions and perturbations in the global carbon cycle. Periods of higher atmospheric p CO 2 correlate to interglacial intervals, the two lower ebbs in p CO 2 correlate with two positive isotope plateaus, while periods of lower atmospheric p CO 2 and cooling correlate with glacial intervals C3 and C4 recognized from other sections globally. Results suggest volcanism to be a significant driver for late Pennsylvanian to earliest Cisuralian shifts in global climates from glacial to interglacial through greenhouse gas emissions and changes to the global carbon cycle. Our results represent an important contribution to the development of an accurate chronostratigraphy for the continental facies of the NCP during the Pennsylvanian and earliest Permian, enabling correlation of volcanic and climate events including glacial and interglacial cycles. [ABSTRACT FROM AUTHOR]

The middle–late Cambrian is a key interval between the Cambrian Explosion and the Great Ordovician Biodiversification Event (GOBE) that marks a major biologic evolutionary transition in the geologic record. Diversity (i.e. richness) patterns in this interval show that macro-biota experienced evolutionary setbacks for the first time. However, relatively little attention has been paid to this interval in previous macroevolutionary studies and very different conclusions about the diversity patterns in coarse time-resolution have been documented. As a dominate group of marine benthic organisms in the Cambrian, trilobites provide insightful information to understand the history of biodiversity in the Cambrian marine ecosystem from the Cambrian Explosion to the GOBE. South China is a region with relatively good preservation of Cambrian fossil materials and sections, and 4 out of 6 Cambrian GSSPs were established in South China. In this paper, we use constrained optimization (CONOP) to correlate 19 sections from South China to reduce the Signor-Lipps effect and integrate the results with high-resolution chronostratigraphic data to evaluate the middle–late Cambrian trilobite diversity pattern in South China. This study, for the first time, constructs a high time-resolution (about 60 kyr) trilobite species-level richness curve with estimated time from Age 4 to the Paibian. A double-peaked species diversification is separated by a minor extinction in Stage 4; this is followed by a gradual decline of species diversity over the entire Wuliuan Age. A radiation of three times increase of species diversity in the Drumian and Guzhangian is exhibited and the diversity remains high for most of the Guzhangian Stage; this is followed by a great extinction at the end of the Guzhangian with around 50% species lost. Detailed comparison with previous composite studies and fossil material from single sections revealed that the Signor-Lipps effect could produce large biases in diversity pattern. In addition, a precise analysis of species evolution features compared with environmental indices provides a perspective about trilobite evolutionary mechanisms associated with environmental changes related to the carbon cycle and biotic competition. • Middle-late Cambrian trilobite diversity trajectory of South China is established. • High temporal resolution of diversity pattern is produced with CONOP method. • The results reveal two major diversity losses and a biodiversification event in Guzhuangian. • Signor-Lipps effect may affect diversity pattern significantly. • Major extinctions of trilobites are correlative with carbon isotope excursions. [ABSTRACT FROM AUTHOR]

This paper reports bulk organic carbon isotope data from a laboratory study designed to evaluate whether acid chromium reduction (ACR), commonly used to prepare rock/sediment samples for sulfur isotope analysis, significantly fractionates bulk organic carbon isotopes compared with the standard decarbonation (SD) method in Quaternary coastal plain incised valley sediments. In this study, 36 sediment samples obtained from a Quaternary sediment core from the Qiantang River incised valley on the East China coastal plain were tested. The results show differences in the δ13C org values between the ACR and SD methods for Quaternary incised valley sediments ranging from – 0.97‰ to +0.34‰, with most values (86%) showing a negative bias. Approximately half of the samples yield δ13C org values that differ by ≥ ± 0.3‰. The carbonate and total organic carbon (TOC) contents of the sediment samples have no significant effects on the bulk organic carbon isotopes derived by ACR. There is also no obvious correlation between the organic carbon loss by ACR and the difference of the δ13C org values. We believe that ACR loses more 13C-enriched labile organic carbon and/or volatile organic compounds (VOCs) than SD, which leads to a negative bias in the δ13C org values. The mineral composition was speculated to be related to a significant positive bias in the δ13C org values by ACR observed in two particular samples and requires further study. Consequently, ACR should be used with caution for sediments containing primarily young labile organic carbon with medium to high TOC contents (TOC ≥ 0.5 wt %), as it may cause a large offset of the δ13C org values compared with SD. However, ACR may be used for sediments containing organic matter primarily from terrestrial plants with relatively low TOC contents (TOC < 0.5 wt %). • Chromium reduction for analysis of bulk δ13C org values in Quaternary sediments were tested. • Chromium reduction significantly fractionated δ13C org values in Quaternary sediments. • Chromium reduction should be used with caution for analysis of δ13C org values in sediments. [ABSTRACT FROM AUTHOR]

The Northwestern Sichuan Basin is a hot spot for natural gas exploration, and in recent years, many wells have obtained high-yield commercial gas flows in the Qixia Formation. However, due to the influence of foreland orogeny, the oil and gas in the Qixia Formation often have the characteristics of multisource filling, multistage accumulation and multistage transformation, which results in an unclear understanding of the gas source and the accumulation process. This paper uses the concept of sub-block research through carbon isotope and biomarkers analyses, to carry out gas-gas, gas-source and bitumen-source rock comparisons in different structural belts to determine the natural gas sources. On this basis, basin simulation and fluid inclusion analysis technology are used to determine the stage of hydrocarbon accumulation, and then the accumulation process is determined. Studies have shown that the gas source of the Qixia Formation are different in the different structural belts: (1) The natural gas from the Qixia Formation in the thrust nappe belt mainly originates from the Qiongzhusi Formation source rock; (2) The natural gas from the Qixia Formation in the hidden fault belt is a mixture of the source rock of the Qixia Formation and the source rock of the Qiongzhusi Formation; and (3) The natural gas from the Qixia Formation in the gentle belt mainly originates from the Middle Permian source rock and the Upper Permian Longtan Formation source rock. The Indosinian, Yanshania, and Himalayan movements all have great influence on the formation of the Qixia Formation reservoir in northwestern Sichuan, and the accumulation process of the different structural belts is quite different, but generally, the accumulation process of the different structural belts have experienced three stages: a primary oil pool stage, gas pool stage and reformation and definition stage. • Through sub-block research, gas source of the foreland thrust belt is studied. • Different gas sources cause differences in carbon isotopes. • Accumulation process of each structural belt is distinct. • The results have implications for exploration in complex tectonic areas. [ABSTRACT FROM AUTHOR]

• The δ13C of different components of macrophytes in Taihu Lake were analysed. • The different components of δ13C exhibited significant differences in macrophytes. • The main influencing factor to the δ13C variability was the water pH. • The α-cellulose is more suitable as study carrier for study the evolution of lake. Understanding the fractionation mechanism and factors controlling carbon isotopes (δ13C) in macrophytes is significant for studying the biogeochemical carbon cycle and changes in nutrients within lakes. However, whether the environmental implications of δ13C are different in the different components (α-cellulose, holocellulose and whole sample) of macrophytes is unclear. In this paper, the δ13C composition of different macrophytes tissue components in Taihu Lake was analysed on spatial and temporal scales. The effects of aquatic environmental variables on the δ13C values of macrophytes were also explored. The results showed that emergent plants have the most negative stable carbon isotope signals, with a mean value (±SD) of −27.85‰ ± 0.95‰. Submerged macrophytes have large variations with significantly more positive δ13C values (−15.19‰ ± 3.08‰). The δ13C values of floating-leaved plants (−25.32‰ ± 1.02‰) fall between those of the two groups above. In the one-way analysis of variance (ANOVA), the different components (α-cellulose, holocellulose and whole sample) of δ13C exhibited significant differences (p-value <0.01) among the three groups of macrophytes. However, there was no significant seasonal difference in the δ13C of macrophytes. In addition, the δ13C of macrophytes in rivers were lighter than those in lakes. Correlation analyses indicated that the water pH was the main factor affecting δ13C variability in macrophytes. The δ13C values of α-cellulose showed stronger sensitivity to environmental variation than did those of the whole samples and holocellulose. Hence, it is necessary to extract α-cellulose when using the δ13C of aquatic macrophytes to study the changes in lake ecological environments. These results provided a theoretical reference and experimental data support for a modern process of using δ13C in macrophytes for palaeoenvironmental changes. [ABSTRACT FROM AUTHOR]

The Lower Paleozoic Ordovician Wufeng Formation and the Silurian Longmaxi Formation shale in the southeastern part of Sichuan Basin in China are the key strata for shale gas exploration. In this paper, based on a large number of outcrops, cores and natural gamma spectroscopy logs combined with scanning electron microscopy, geochemical parameter testing and mineral component analysis, the geological conditions and exploration potential of shale gas accumulation were studied in this area, and the relationship between structure and shale gas preservation is discussed. The vertical reduction in the U/Th ratio measured in the outcrop sandstone lenses and core horizontal bedding and observed in the energy spectrum logs indicates that the sedimentary water body transformed from a low-energy anoxic reducing environment to a high-energy oxidizing environment. The TI index and the kerogen carbon isotope indicate that the organic matter type of the shale is mainly type I kerogen. The TOC content of high-quality shale is generally above 2.50%, and the R o value is between 2.00% and 3.08%. High organic matter abundance, moderate thermal evolution and a large thickness of high-quality shale ensure an adequate supply of hydrocarbon resources. Multiple types of inorganic pores, primary organic pores and pores formed during hydrocarbon generation provide abundant reservoir space for the enrichment of shale gas. The tectonics have an important influence on the preservation of shale gas. Moderate fracture development, a late tectonic uplift time, small-scale tectonic uplift, and high formation pressure coefficient are conducive to the preservation of shale gas, and the gas content and productivity will be higher. Overall, a structural stability zone with a high formation pressure coefficient is a favorable area for shale gas exploration. • Comprehensive analysis the sedimentary environment based on three scales: outcrop, core and energy spectrum logging. • Later and small-scale tectonic uplift, moderate fracture development, good roof preservation are conducive to gas enrichment. • A structural stability zone with a high formation pressure coefficient is a favorable area for shale gas exploration. [ABSTRACT FROM AUTHOR]

Numerous studies have been conducted on the isotopic geochemical characteristics of shale gas. However, a systematic study of the relationship between the isotopic geochemical characteristics and gas content has not been addressed to date. In this study, we investigated the geochemical and isotopic compositions of shale gas samples, and the gas content of the Lower Silurian Longmaxi marine shale in the Huangjinba area, southern Sichuan Basin, China. In addition, we analyzed the quantitative relationship between the geochemical parameters and the gas content. The Longmaxi shale gas is a dry gas with a low wetness (0.12%–0.67%), dominated by methane (89.49%–99.00%) with a small amount of ethane (0.11%–0.61%). The average values of δ13C methane , δ13C ethane and δ13C propane are −29.8‰, −35.0‰, and −33.2‰, characterized by a partial isotopic reversal (δ13C methane > δ13C propane > δ13C ethane) with a maturity level (Ro ≈ 2.30%–2.51%). The total gas content of the Longmaxi shale varies widely from 0.42 m3/t to 3.88 m3/t. Correlation analyses revealed that the ethane isotope (δ13C ethane) and the magnitude of isotopic reversal (δ13C methane - δ13C ethane) exhibit strong correlations with the total gas content and the free gas content. This study demonstrates that carbon isotopic reversal of shale gas largely depends on the secondary cracking, and thermal maturity and residual liquid hydrocarbons content are important factors affecting the magnitude of carbon isotopic reversal. Based on the quantitative study conducted in this paper, we provide a new proxy for predicting the gas content of high maturity shale using an isotopic method. • Carbon isotopic reversal of shale gas largely depends on the secondary cracking. • Sufficient residual liquid hydrocarbon is necessary for the carbon isotopic reversal. • Wetness of 1.4% in high maturity shale gas indicates the peak of secondary cracking. • δ13C methane –δ13C ethane can be used to predict the gas content of high maturity shale. [ABSTRACT FROM AUTHOR]

• The methane in Weiyuan area comes from different hydrocarbon generation materials. • Nitrogen in Xiuwu basin is derived from atmosphere and deep crust-upper mantle. • The sealing capacity and the anticline are the reason for the high methane content. • The detachment layers, faults and volcanism are the reasons for the high nitrogen. Marine shale gas exploration in southern China has successes and failures. Under the condition of great hydrocarbon generation material basis, shale gas wells drilled from some shale gas blocks are rich in methane, while the wells in other shale gas blocks with high nitrogen and low hydrocarbon gas, which indicates that they have different accumulation mechanisms. Therefore, the study of gas composition in shale will help us to figure out the mechanism of shale gas accumulation and loss. In this paper, the Lower Cambrian shale from Wei-201 well in Upper Yangtze Weiyuan Block and Jiangye-1 well from Lower Yangtze Xiuwu Basin are selected as research object, and shale samples are used for tests and experiments including analysis of gas composition and nitrogen isotope, test of porosity and TOC content, overburden permeability test, permeability test before and after methane adsorption under different osmotic pressure, permeability test parallel and vertical to the bedding surface, FIB-SEM (Focus Ion Beam Scanning Electron Microscope) and FIB-HIM (Focused Ion Beam Helium Ion Microscope). Finally, the reasons for the difference in the gas components of the Lower Cambrian shale gas in Weiyuan Block and Xiuwu Basin are studied by means of seismic interpretation, core description and outcrop observation besides the tests and experiments. The results show that the gas components of the Lower Cambrian shale in Weiyuan Block, the Upper Yangtze, mainly consist of methane, derived from liquid hydrocarbon cracking. The sealing capacity of roof and floor, the great self-sealing of shale and the flat anticline structure contribute to the high methane content in shale gas. The Lower Cambrian shale gas in Xiuwu Basin, the Lower Yangtze, is mostly nitrogen, which is derived both from atmosphere and deep crust-upper mantle. The detachment layer at the bottom of the Lower Cambrian, the widely developed deep faults and the Jurassic volcanic activity are the reasons for the high nitrogen and low hydrocarbon of shale gas. Based on the above analysis, the patterns are summarized for shale gas accumulation in the simple anticline background and reservoir destruction in the complex syncline background. [ABSTRACT FROM AUTHOR]

Much of our existing knowledge of Middle Jurassic paleoclimate is based on well-dated marine isotopic records that show fluctuations between warm (greenhouse effected) and cool climates. In contrast, much less is known from contemporaneous terrestrial deposits that are often difficult to correlate stratigraphically with marine successions, and are typically considered as showing regional rather than global signals. In this paper we show that the carbon-isotopic, petrological and floral record through 20 m thick coals in the Northern Qaidam Basin (NW, China) represents a relatively comprehensive northern hemisphere Bajocian (Middle Jurassic) record for terrestrial climatic change. δ13C coal values for 88 samples from the Yuqia area in Northern Qaidam Basin range from–25.3‰ to –22.5‰, indicating that C3 plants were the main coal-forming vegetation in the region during the Middle Jurassic. This isotopic variation follows fluctuations in the composition of ferns and gymnosperms, where higher ratios correspond to more negative δ13C values. The similar carbon isotope values of gymnosperms and coal from the Yuqia area indicate that the coal comprises a high proportion of organic material derived from gymnosperm taxa, which is consistent with the very high abundance of diterpenoids in coal and especially pimarane and abietane that are produced primarily by gymnosperms. Results from the coal matrix provide an opportunity to record paleoclimate changes, showing several striking and regular coal-forming cycles with distinct long- and short-term variations. Trends of δ13C coal values changes coupled with the evolution of coal-forming plants may record a gradual increase in paleo-CO 2 (p CO 2) concentration, water-table level changes and the decrease in abundance of Classopollis conifer pollen through Bajocian. This result is in accordance with the published marine carbonate records for this time, with correlation enabled through matching carbon isotope curves from the terrestrial succession at Yuqia and marine records. The similarity of the terrestrial and marine geochemical and floral record is an indication that the observed paleoclimate signal is a global phenomenon. Furthermore, the high-frequency fluctuation of δ13C coal values, along with the coal petrologic variations may record short-term changes of environmental factors (e.g. temperature or humidity/precipitation), especially during intervals when palaeobotanical composition has not fluctuated intensely. • Paleoclimate trends evaluated from terrestrial Northern Qaidam Basin, NW China • Carbon-isotope, petrological and floral record of Bajocian age Yuqia coals revealed • Isotope value distribution indicate coals largely derived from gymnosperm plants • Variations in long- and short- peat deposition cycles record paleoclimate trends • Similarity of marine geochemical and terrestrial record supports global signal [ABSTRACT FROM AUTHOR]

Multiple lines of evidence revealed that enormous CO 2 was input into the ocean-atmosphere system during Oceanic Anoxic Event 1a (OAE 1a), which led to a series of environmental perturbations (e.g. temperature rising, enhanced weathering, promoted primary productivity and marine anoxia). Among them, increased carbon isotope fractionation (Δ13C carb-org) between the carbonate (δ13C carb) and organic carbon (δ13C org) in the sediments is one of the most important indicators to the enhanced atmospheric pCO 2. However, only a few research reported high-resolution paired carbon isotopes during OAE 1a, which were almost limited around the western Tethys. Here, we report new paired carbon isotopes of the Early Cretaceous sediments from the ODP site 866A in the western Pacific and the Lingshan Island section in the Sulu orogenic belt. The δ13C carb curves from both sections correlate well with OAE 1a, in which a positive δ13C carb excursion is identified between the C3–C6 segments. The Δ13C carb-org displays a ∼7–11‰ positive shift coinciding with the δ13C carb excursion, indicating a remarkable increase and a gradual decrease in CO 2 in water and atmosphere, which further support significant atmospheric pCO 2 changes during OAE 1a on a global scale. The sediments also show a few variations in carbon isotope records during OAE 1a between different locations, which may reflect different influences from local environments, and the deviations of stratigraphic correlation and diagenesis cannot be ruled out either. • The carbon isotopes from both sections correlate well with OAE 1a. • Atmospheric pCO 2 rose in early OAE 1a and fell in late OAE 1a on a global scale. • The atmospheric pCO 2 changes show a few variations between different locations. [ABSTRACT FROM AUTHOR]