Effects on global warming by microbial methanogenesis in alkaline lakes during the Late Paleozoic Ice Age (LPIA)

This work was jointly funded by the National Natural Science Foundation of China (Grant Nos . 42230808, 42203055 and 41830425) and PetroChina Science and Technology Major project (Grant No. 20 21DJ0108).Methane (CH4) is an important greenhouse gas, but its behavior and influencing factors over geological time scales are not sufficiently clear. This study investigated the Late Paleozoic Ice Age (LPIA), which is thought to have experienced an interval of rapid warming at ca. 304 Ma, that may have been analogous to modern warming. To explore possible causes of this warming event, we investigated ancient alkaline lakes in the Junggar Basin, northwestern China. Results show that microbial CH4 cycling here was strong, as evidenced by carbonate δ13C (δ13Ccarb) values of >5‰, ∼+0.6‰ offsets between pristane δ13C (δ13CPr) and phytane δ13C (δ13CPh) values, a 3β-methylhopane index of 9.5% ± 3.0%, and highly negative δ13C values of hopanes (−44‰ to −61‰). Low sulfate concentrations in the alkaline lakes made methanogenic archaea more competitive than sulfate-reducing bacteria, and the elevated levels of dissolved inorganic carbon promoted methanogenesis. Biogenic CH4 emissions from alkaline lakes, in addition to CO2, may have contributed to rapid climate warming.PostprintPeer reviewe

Breath-, air- and surface-borne SARS-CoV-2 in hospitals

The COVID-19 pandemic has brought an unprecedented crisis to the global health sector. When discharging COVID-19 patients in accordance with throat or nasal swab protocols using RT-PCR, the potential risk of reintroducing the infection source to humans and the environment must be resolved. Here, 14 patients including 10 COVID-19 subjects were recruited; exhaled breath condensate (EBC), air samples and surface swabs were collected and analyzed for SARS-CoV-2 using reverse transcription-polymerase chain reaction (RT-PCR) in four hospitals with applied natural ventilation and disinfection practices in Wuhan. Here we discovered that 22.2% of COVID-19 patients (n = 9), who were ready for hospital discharge based on current guidelines, had SARS-CoV-2 in their exhaled breath (~10⁵ RNA copies/m³). Although fewer surface swabs (3.1%, n = 318) tested positive, medical equipment such as face shield frequently contacted/used by healthcare workers and the work shift floor were contaminated by SARS-CoV-2 (3–8 viruses/cm²). Three of the air samples (n = 44) including those collected using a robot-assisted sampler were detected positive by a digital PCR with a concentration level of 9–219 viruses/m³. RT-PCR diagnosis using throat swab specimens had a failure rate of more than 22% in safely discharging COVID-19 patients who were otherwise still exhaling the SARS-CoV-2 by a rate of estimated ~1400 RNA copies per minute into the air. Direct surface contact might not represent a major transmission route, and lower positive rate of air sample (6.8%) was likely due to natural ventilation (1.6–3.3 m/s) and regular disinfection practices. While there is a critical need for strengthening hospital discharge standards in preventing re-emergence of COVID-19 spread, use of breath sample as a supplement specimen could further guard the hospital discharge to ensure the safety of the public and minimize the pandemic re-emergence risk

Preparation and properties of MDA-BAPP-BTDA copolyimide/18-crown ether-6 supramolecular films with inclusion structure and ultralow dielectric constants

In order to obtain polyimide composites with ultra-low dielectric constant, a series of MDA-BAPP-BTDA copolyimides/18-crown ether-6 (CPI/18-CE) supramolecular films with inclusion structure were prepared. The effects of 18-CE on CPI’s thermal, mechanical, dielectric and water absorption properties were investigated. The inclusion rate of 18-CE to CPI backbone was ∼50%. The introduction of 18-CE slightly reduced the thermal properties of CPI/18-CE supramolecular films, but greatly improved their mechanical, dielectric and hydrophobic properties. The tensile strength, young’s modulus and elongation at break of CPI/18-CE supramolecular films were maximally increased by 21.8%, 34.1% and 92.9% respectively. Meanwhile their dielectric constant, dielectric loss and water absorption were as low as 2.10, 0.007 and 0.63%, respectively. In summary, CPI/18-CE supramolecular films possess excellent dielectric properties and broad application prospect in the field of microelectronics

Carbon isotope and origin of the hydrocarbon gases in the Junggar Basin, China

The genetic type, source and distribution of hydrocarbon gases in the Junggar Basin were clarified through the carbon isotope analysis. Mature to post mature oil-type gas, mature to post mature coal-type gas, transition gas and biogas are identified in the Junggar Basin. Partly reversed order of carbon isotope of hydrocarbon gases in the Junggar Basin are attributed to one or several of the following reasons: mixing of oil-type and coal-type gases, mixing of coal-type gases of different source, mixing of coal-type gases of varied maturity, and microbial action. Three types of coal-type gases in the Junggar Basin are identified. The first type of coal-type gases characterized with high δ13C values of heavy hydrocarbon gases (δ13C2>−26.0‰) are the mature to high mature gases that are generated from Jurassic source rocks. The second type of coal-type gases characterized with low δ13C values of heavy hydrocarbon gases (δ13C2<−26.0‰) and wide maturity range, are generated from one or several source rocks in the Jurassic and the Wuerhe and Jiamuhe Formations of Permian. The third type of coal-type gases characterized with a wide δ13C value of heavy hydrocarbon gases and the high-post maturity are generated from the Carboniferous source rocks. Keywords: Carbon isotope, Hydrocarbon gas, Gas-source correlation, Junggar Basi

Deep-Buried Triassic Oil-Source Correlation in the Central Junggar Basin, NW China

Whether there is an effective deep-buried lacustrine Triassic petroleum system in the Junggar Basin, NW China, has been enigmatic and debated for a long time. Here we conduct an oil-source correlation to address this issue. Results show that the extracted bitumens from the Triassic mudstones in the central basin have distinctive stable carbon isotope and biomarker compositions compared to the Permian-sourced and Jurassic-sourced hydrocarbons, the other two recognized sources in the study area. These characteristics include δ13C value of -30.46~-26.30‰, β-carotane/maximum n-alkane of 0.22–0.41, Pr/Ph of 1.00–1.51, C24 tetracyclic terpane/C26 tricyclic terpane of 0.43–0.96, Ts/Tm of 0.34–0.64, gammacerane/C30 hopane of 0.10–0.14, and regular steranes C27 > C28 < C29 with C29 sterane in dominance (40–50%). These suggest that the Triassic mudstones in the study area host fresh lacustrine organic matters with high input of higher plants. The Triassic-reservoired crude oils and extracts can be divided into two types. Through oil-source correlation, we infer that both type A and type B oils are derived from mixed Permian and Triassic source rocks. Linear regression analysis shows that the contribution from Triassic mudstones to type A and B oils is 67% and 31%, respectively. This implies that the deep-buried Triassic lacustrine mudstones in the Junggar Basin may have some oil-generation potential and thus might represent a new case of Triassic petroleum systems in China and deserves a more detailed and thorough study in future exploration and exploitation

Diagenesis and pore evolution of Cretaceous Qingshuihe Formation reservoir in western section of southern margin of Junggar Basin

The Qingshuihe Formation in the western section of the southern margin of the Junggar Basin has excellent oil and gas exploration prospects. The systematic study of its diagenesis characteristics and pore evolution process will provide guidance for the later fine exploration and evaluation of oil and gas. Therefore, based on the analysis of ordinary thin sections, cast thin sections, whole rock X-ray diffraction, grain size, scanning electron microscopy, carbon and oxygen isotopes of carbonate cements and fluid inclusions, the diagenesis characteristics and pore evolution process of the Qingshuihe Formation in the western section of the southern margin of the Junggar Basin were systematically studied, and the differences of reservoir pore evolution process between different diagenetic facies were further discussed. The study shows that: (1)The reservoir of the Qingshuihe Formation in the studied area is dominated by glutenite. The content of rock debris is high, with an average of 65.97%, mainly tuff rock debris. The cement is mainly calcite. The average porosity of the reservoir is 6.2%, and the average permeability is 7.45×10-3 μm2. It is generally a tight reservoir of low porosity and low permeability, but high-quality reservoirs are still developed locally; (2)The reservoir burial mode of the Qingshuihe Formation in the southern margin of the Junggar Basin is characterized by long-term shallow burial and late rapid deep burial, and can be further divided into four evolutionary stages: long-term shallow burial, tectonic uplift to near surface, normal deep burial, and rapid deep burial. The diagenetic evolution of the reservoir was in early diagenetic stage A in the long-term shallow burial, tectonic uplift to near surface, and normal deep burial stages, while in the rapid deep burial stage, the reservoir was in early diagenetic stage B to middle diagenetic stage A; (3)The reservoir of the Qingshuihe Formation can be divided into four typical diagenetic facies types, namely, strong compaction facies, calcareous/iron argillaceous strong cementation facies, tuffaceous filling weak dissolution facies, and weak compaction pore development facies. The pore evolution model of the clastic rock reservoir of the Qingshuihe Formation in the southern margin of the Junggar Basin was established based on the constraints of diagenetic facies. The weak compaction pore development facies are high-quality reservoir diagenetic facies, followed by tuffaceous filling weak dissolution facies

Chemometric Classification and Geochemistry of Crude Oils in the Eastern Fukang Sag, Junggar Basin, NW China

Thirty oil samples collected from the eastern Fukang Sag were analyzed geochemically for their biomarkers and carbon isotopic compositions. The chemometric methods of principal component analysis and hierarchical cluster analysis, employed to thirteen parameters indicating source and depositional environment, classified the oil samples into three genetically distinct oil families: Family A oils were mainly derived from lower aquatic organisms deposited in a weakly reducing condition of fresh–brackish water, Family B oils came from a source containing predominantly terrigenous higher-plant organic matter laid down in an oxidizing environment of fresh water, and Family C oils received sources from both terrigenous and marine organic matter deposited in a weakly oxidizing to oxidizing environment of brackish water. Indirect oil–source correlations implied that Family A oils were probably derived from Permian source rocks, Family B oils originated mainly from Jurassic source rocks, and Family C oils had a mixed source of Carboniferous and Permian. Biomarker maturity parameters revealed that all three families of oils were in the mature stage. However, Family A oils were relatively less mature than Family B and Family C oils

Nitrogen isotope compositions and organic matter accumulation in terrestrial hydrocarbon source rocks in China

As an important biological element, nitrogen is causally linked with organic matter accumulation, but a systematic and regular understanding has not been developed. This paper discusses this issue by taking the widely developed Permian-Paleogene terrestrial (lacustrine) hydrocarbon source rocks in China as an example. The results show that the terrestrial source rocks in China can be classified into three groups according to the nitrogen isotope (δ15N) compositions and combined with the salinity and evaporative alkali mineral characteristics: the circum-neutral group 1 (average δ15N=4.0‰±1.5‰), the circum-neutral group 2 (average δ15N=7.1‰±1.6‰), and the alkaline group (average δ15N=18.4‰±3.3‰). In the circum-neutral group with δ15N 10‰, the organic matter types are good and shale oil potentials are higher, but the response relationship between δ15N of source rocks and organic matter accumulation is not as good as that of the circum-neutral group, reflecting that the organic matter accumulation in alkaline group is influenced by other comprehensive factors other than δ15N. Accordingly, the organic matter accumulation models of three types of lacustrine source rocks (10‰) classified on the basis of δ15N were established. The δ15N has the potential to trace organic matter accumulation and quality of source rocks. For example, low δ15N type (δ15N 5‰) is of good qualityin lacustrine source rocks. This paper enriches the biogeochemical and hydrocarbon source rock geochemical studies of nitrogen by exploring organic matter accumulation in source rocks from the new perspective of nitrogen isotope composition and nitrogen cycling