Vitrinite reflectance (Ro) is widely used to determine the thermal maturity of source rocks in petroleum exploration. Despite decades of investigation into the apparent suppression of vitrinite reflectance, the exact mechanisms underlying this phenomenon remain unclear. This study employed confined anhydrous thermal simulation experiments using a representative immature coal sample (Ro = 0.45 %), the solvent-extracted coal, and the extracted coal plus pure hydrocarbons (n-hexane, n-C-6, and n-triacontane, n-C-30), to investigate potential mechanisms for Ro suppression. The extracted coal plus pure n-C-6 and n-C-30 were used to create experimental systems with different hydrocarbon phases (gaseous or liquid) to investigate their specific influence on vitrinite maturation. The results show that the Ro value of the original coal is lower than that of the extracted coal under the same simulation conditions, with differences ranging from 0.25 % to 0.86 %. In addition, the Ro value of the extracted coal plus n-C-30 is lower than that of the extracted coal plus n-C-6, with variations between 0.01 % and 0.32 %. This disparity in Ro becomes more pronounced when gaseous hydrocarbons enter the main cracking stage (> 432 degrees C, Easy Ro > 1.69 %). The findings suggest that the direct release of short-chain compounds from vitrinite (< 432 degrees C, Easy Ro < 1.69 %) and the hydrogen transfer reactions between hydrocarbon gases and solid kerogen (> 432 degrees C, Easy Ro > 1.69 %) serve as two primary driving forces for Ro increase. The introduction of hydrocarbons (including gaseous and liquid fractions) retards vitrinite maturation rates, thereby inducing the Ro suppression effect. This study provides experimental evidence that liquid hydrocarbons can absorb on the surface of vitrinite and hinder the surface interaction between solid vitrinite and gaseous hydrocarbons. Meanwhile, the addition of gaseous hydrocarbons can further slow down the release of short-chain hydrocarbons from the vitrinite surface. These interactions reduce the release rate of hydrogen radicals from vitrinite, offering a possible mechanism for the observed suppression of reflectance.

The Ordovician reservoirs in both northern Halahatang (N-Halahatang) and western Lunnan (W-Lunnan) areas of the Tabei Uplift, Tarim Basin, experienced extensive biodegradation in the Late Hercynian (Permian). During the Late Himalayan (Neogene–Quaternary), the biodegraded reservoirs in N-Halahatang underwent intense burial-thermal maturation (>6,500 m depth; 1.02–1.22% Ro), whereas those in W-Lunnan experienced milder burial-thermal maturation (<5,800 m depth; 0.70–0.85% Ro). Despite similar δ13Coil values, biodegraded oils from these two areas display divergent biomarker profiles, complicating oil-oil correlations. To clarify whether the discrepancies in biomarker profiles can be attributed to variations in burial-thermal maturation, two relatively shallow-burial biodegraded oils from W-Lunnan (Wells LG40: slight to moderate biodegradation; LG7: heavy to severe biodegradation) were artificially pyrolyzed to various maturities. Subsequently, the biomarker profiles of pyrolyzed oils were compared with those of the naturally matured, deeply buried oils (heavy to severe biodegradation) from N-Halahatang. The results revealed that, when EasyRo exceeded 0.91% or 1.01%, deviations in biomarker parameters for oil-oil correlations exceeded 10%, diminishing their diagnostic utility. Notably, hopane-based parameters (e.g., gammacerane/C30 hopane) exhibited larger variability in the more severely biodegraded LG7 sequence. Furthermore, increased biodegradation severity also amplified variations in specific maturity-related parameters (e.g., diasteranes/regular steranes) during artificial maturation, highlighting the necessity of considering the synergistic effects of early-stage biodegradation and subsequent thermal maturation. Additionally, biomarker profiles of the N-Halahatang oils (1.05–1.15% Ro) matched those of the LG7 pyrolyzed oils at EasyRo = 1.00–1.15%, suggesting that the differences in biomarker profiles between the two areas could be attributed to differences in burial-thermal maturation.

The evolution of chain conformation in polymer glassy films under residual stress was investigated. Poly n-butyl methacrylate (PnBMA) was selected as the model polymer. The polymers were labeled at the two chain ends with a fluorescence donor and acceptor, separately. By measuring the fluorescence resonance energy transfer (FRET) efficiency between them, the end-to-end distance of the polymer chains was determined. Polymer thin films fabricated by spin-casting without thermal annealing were taken as the model sample with residual stress stored inside. It was found that the PnBMA chains are elongated as the molecular source of residual stress, as expressed by the increase in the scaling exponent, changing from 0.5 under zero residual stress to 0.8 at 8.5 MPa residual stress. Single-molecule fluorescence defocused microscopy was used to track the rotational motion of the fluorescent probes, revealing that the donor's rotation is suppressed in the presence of the acceptor, with larger suppression at shorter distance.

Sixteen previously undescribed furanolabdane diterpenoids, designated hypurpurins A-P (1-16), along with two known analogs, hypopurins B and C (17 and 18), were isolated from the aerial parts of Hypoestes purpurea. The chemical structures of 1-16 were elucidated through comprehensive spectroscopic analyses, including HR-ESI-MS, NMR, UV, and IR spectroscopy. The absolute configurations of these new compounds were further determined by electronic circular dichroism and single-crystal X-ray diffraction analysis. Structurally, compounds 1 and 2 are unprecedented furanolabdane diterpenoids bearing an 8,20:12,20-diepoxy unit; compounds 3 and 4 are unique furanolabdane diterpenoids featuring 12,20-epoxy and 19,20-lactone moieties; compounds 5 and 6 represent the first examples of furanolabdane diterpenoids possessing an 8,12-epoxy and 19,20-lactone ring. All isolated compounds were evaluated for their nitric oxide (NO) inhibitory effects and cytotoxicity against HPAC and ASPC-1 cancer cell lines. Among them, compounds 7 and 17 exhibited moderate inhibitory effects on lipopolysaccharide-induced NO release in RAW 264.7 cells, with IC50 values of 44.14 and 36.48 μM, respectively.

Aromatization occurs steadily during the petroleum evolution stage of light oil/condensate (LOC) formation, for which the composition and delta D of aromatics are of considerable geochemical significance. This paper presents a study on the composition and delta D of monomethyl aromatic compounds (toluene, methylnaphthalene, methylphenanthrene, and methyldibenzothiophene) and related hydrocarbon compounds in LOCs from the Tazhong uplift area of the Tarim Basin in China. Thermal maturity, the source rock of the LOCs, and the effect of gas washing on the oils are discussed. The calculated reflectance of the oils using methyldibenzothiophene and dimethylnaphthalene parameters is approximately 1.15%-1.5%. The thermal maturity of the oils in the Tazhong I fault-slope zone is slightly higher than that of the oils in the Tazhong 10 structural belt due to the more intense gas washing of the oils in the former. The varying degrees of gas washing also caused enrichment of low-carbon-number aromatic hydrocarbons and their H-2 isotopes in the oils of the Tazhong I fault-slope zone relative to those of the Tazhong 10 structural belt. In addition to the contributions from lower Cambrian and Middle-Upper Ordovician source rocks, these crude oils may have received contributions from upper Cambrian Furongian source rocks deposited within locally shielded environments. Crude oils such as TZ62(Silurian) and ZG432(Ordovician) contain heavy delta C-13 but light delta D isotopic compositions and may represent end member oils derived from Furongian source rocks.

Mercury (Hg) in sedimentary deposits has become a widely used proxy for reconstructing paleo-volcanic activity. However, a comprehensive understanding of Hg accumulation pattern and the isotope variation during early diagenesis is still lacking. A thorough diagenetic evaluation of sedimentary rocks is crucial prior to the interpretation of geochemical data, as diagenetic changes can lead to considerable differences between the original seawater signatures and the sedimentological records. We observed a Hg isotopic pattern characterized by a negative trend in S202Hg with a concurrent gradual positive shift in p199Hg throughout non-euxinic intervals in multiple marine sedimentary successions. We propose that the synchronous Hg mass dependent fractionation (MDF) and mass independent fractionation (MIF) were driven by diagenetic events. The release of organic-bound Hg and its subsequent diffusion downward to sites where it complexed with pyrite in early diagenetic stages may induce S202Hg shift towards more negative values in the Hg precipitate, and in turn, contribute to the concurrent positive shift of p199Hg observed in these sections.

Gaseous hydrocarbons (C1 − C5) are the primary components of shale gas. Their thermal degradation significantly impacts various aspects of shale gas reservoirs, including gaseous hydrocarbons composition and their carbon and hydrogen isotopes fractionation, H2 generation, reservoir overpressure, mineral dissolution and brittle mineral formation, changes in reservoir properties and storage space, as well as the formation and identification of resource sweet spots. This study reviews the experimental simulations of gaseous hydrocarbon cracking and the geochemical research on major global shale gas reservoirs conducted over the past few decades. In shale gas reservoirs, C5H12, C4H10, C3H8, C2H6 and CH4 initiate cracking at Ro values of approximately 1.0 %, 1.0 %, 1.3 %, 1.5 %, and 2.0 %, respectively, with main cracking stages occurring at Ro ranges of 1.7–2.4 %, 1.7–2.8 %, 1.8–3.2 %, 1.8–3.6 %, and 3.0–4.0 %. This cracking produces more gaseous molecules, significantly contributing to overpressure and H2 in high-overmature reservoirs. Wet gas cracking contributes carbon isotope rollover but CH4 cracking causes both carbon and hydrogen isotope reversals in shale gas. As CH4 cracking onset marks peak gas generation of shale, carbon isotope reversal serves as a key sweet-spot indicator. Furthermore, hydrous pyrolysis of gaseous hydrocarbons generates formic and acetic acids that enhance porosity and permeability by dissolving carbonate and feldspar minerals. Concurrent silica precipitation during feldspar dissolution promotes quartz formation, improving reservoir fracturability. This study advances our understandings of the formation, evolution and associated geological and geochemical anomalies of shale gas reservoirs, which holds significant implications for the exploration and exploitation of shale gas resources.

The natural gas resources in the Sichuan Basin are abundant and exhibit various phenomena, for example, mixed sources, mixed maturities and overlapping combinations, resulting in great difficulties in identifying natural gas sources. In this study, several groups of thermal simulation experiments were conducted on various types of kerogens using closed and/or semi‐open systems to investigate the characteristics of the carbon isotope compositions of light hydrocarbon gases derived from different typical kerogens. The results showed that the carbon isotope compositions and variation trends of methane and ethane are controlled by the kerogen type, thermal simulation system and thermal evolution degree. The carbon isotope compositions of light hydrocarbon gases derived from different types of kerogens exhibit some differences with increased thermal evolution degree. When the thermal simulation temperature increases from 320 to 550°C, the methane carbon isotope of typically marine source rocks, mainly type I and type II 1 kerogens, is slightly higher than or equivalent to that of ethane. However, the ethane carbon isotope of terrestrial source rocks, primarily types II 2 and III kerogens, is significantly heavier than methane. By comparison, the evolution trend of carbon isotope compositions of actual natural gas is well consistent with that of light hydrocarbon gases cracked from thermal simulation experiments with increased thermal evolution degree. These findings are of great importance to identify the source rock of actual natural gas with high thermal maturities, as well as to determine the sources of deep shale gas in the southern Sichuan Basin, the Yuanba gas field and the Puguang gas field. Finally, a fitting method of carbon isotope values of methane and ethane of light hydrocarbon gases can be used to more finely differentiate the sources of natural gas in complex areas with mixed sources, mixed maturities and overlapping combinations.

In this study, the geochemical significance of the delta C-13 and delta H-2 values of selected C-7 light hydrocarbons (nC(7) = n-heptane; MCH = methylcyclohexane; Tol = toluene) is investigated in 58 light oil/condensate (LOC) samples from the Kuqa Depression of the Tarim Basin, NW China. For most of the LOCs in the western region, the nC(7), MCH, and Tol exhibit systematic differences where delta C-13(n)C7 < delta C-13(MCH) < delta C-13(Tol) and delta H-2(Tol) < delta H-2(n)C7 < delta H-2(MCH). LOCs from the eastern area have higher delta C-13(oil), delta C-13(Tol), and delta C-13(MCH) values than those from the western area and their delta C-13 values for C-7 hydrocarbons are similar and delta H-2(n)C7 < delta H-2(MCH) < delta H-2(Tol). These organic geochemical differences indicate that the LOCs from the western and eastern areas of the Kuqa Depression were mainly derived from lacustrine and coaly parent materials, respectively. The LOC reservoirs generally received a late hydrocarbon charge of the high-maturity natural gas, and the LOCs from the western Kela-Keshen areas subsequently experienced gas leakage. Hierarchical cluster analysis indicates that the most important influencing factor on the LOCs of the Kuqa Depression is the sedimentary facies (coaly and lacustrine), followed by gas leakage and then parent organic type (lacustrine sapropel and humic organic matter). A cross-plot of the Delta delta H-2(Tol-MCH) versus Tol/MCH can distinguish the origins of continental facies parent materials and gas leakage of the LOCs.

Correlated molecular motion during the process of residual stress release in polymer glassy films is studied at the single-molecule level. Using poly(n-butyl methacrylate) (PnBMA) and poly(vinyl acetate) (PVAc) as the model polymers, thin films fabricated by spin-casting without thermal annealing were chosen as samples for investigation. Single-molecule fluorescence defocused microscopy was used to track the rotational motion of the fluorescent probes doped inside the polymer films. Under the activation effect of residual stress at experimental temperatures, the rotational motions of individual probes are discovered to be correlated a few degrees below the glass transition temperature (Tg), by analyzing the cross-correlation function of the rotational trajectories of different probes. Detailed investigations into the dependence on residual stress strength, intermolecular distance, probe-polymer interaction, and molecular orientation have been conducted. The results have revealed that the physical mechanism of the motion correlation is the randomization process from the state with preferred molecular orientation and presumably the polymer chain stretching.

Alkylnaphthalene homologues are important components of aromatic fraction in sedimentary organic matter and contain significantly geochemical information relative to formation and evolution of the host organic matter. They mainly originate from hydrocarbon aromatization reaction which involves the dehydrogenation of aliphatic rings resulting in the fractionation of stable hydrogen isotopes between aromatic hydrocarbons and their precursors. To examine these processes, this study thermally pyrolysed 1-n-butyldecalin (BD) at different time intervals under 360 degrees C/50 MPa to study the aromatization and hydrogen isotope fractionation during alkylnaphthalene formation and evolution. The relative content of aromatic products, such as naphthalene (N) and 1-methylnaphthalene (1-MN), increases with increasing aromatization. Sulfur enhanced the degree of aromatization during BD thermal evolution, resulting in greater N and 1-MN formation. For the compounds with the same carbon skeleton, i.e. tran-1-methyldecalin (1-MD), 5-methyltetraline (5-MT) and 1-MN, the H-2 enrichment follows the order S2H1-MD < S2H5-MT < S2H1-MN during the low thermal conversion of BD. However, the order was subsequently destroyed with increasing aromatization. The results indicate that hydrocarbon aromatization can enrich aromatic hydrocarbon in 2H, resulting in a higher S2H value of higher aromatic-ringnumber hydrocarbon than that of a lower aromatic-ring-number at low aromatization. However, 2H enrichment will decrease and even result in a reverse order with enhanced aromatization. Our findings are beneficial for understanding genetic mechanism and hydrogen isotope fractionation effect during the formation and evolution of aromatic hydrocarbons.

轮探 1(LT-1)井在 8000 m以下的寒武系中获得轻质油,是塔里木盆地超深层油气勘探的重大突破.对 LT-1 井寒武系轻质油的 δ13C、生物标志物地球化学特征开展分析,对 LT-1 井寒武系玉尔吐斯组干酪根开展催化加氢热解实验,以探讨寒武系轻质油与玉尔吐斯组烃源岩之间的油源关系.结果显示:LT-1 井轻质油的δ13C为?32.5‰;低碳数正构烷烃占优势,Pr/Ph值低,反映了其生烃母质还原的沉积环境;三环萜烷(TT)相对含量高,C19～31TT 分布完整,以 C23TT 为主峰,C24 四环萜烷丰度低;C27-C28-C29 规则甾烷的分布为C29>C27>C28.干酪根催化加氢产物、干酪根抽提物、烃源岩抽提物和原油的成熟度依次增加,体现了不同赋存状态有机质的演化差异,其中干酪根催化加氢产物由于受到干酪根大分子的保护作用而受到热演化的影响最小.综合分析 LT-1 井的地质背景、δ13C 对比关系、生物标志物分布特征及成熟度匹配关系等地质地球化学特征,推测LT-1井轻质油与玉尔吐斯组烃源岩具有亲缘关系,LT-1井8000 m以下轻质油藏的发现表明塔里木盆地超深层仍具有良好的油气勘探前景.

The Steptoean Positive Carbon Isotope Excursion (SPICE) event is extensively documented in globally distributed carbonate and organic-rich successions of slope and platform environments during the late Cambrian (ca. 497-494 Ma). Despite numerous studies, its regional manifestation remains controversial because of the major uncertainty of the redox conditions in sedimentary paleoenvironments and its effect on the changes in the biota. Biogeochemical processes that occurred during the SPICE event are important for assessing whether the excursion is associated with the co-evolution of organisms and environments. In this study, we investigated the changes in plankton and paleoenvironment at the molecular level by combining kerogen elemental analysis, catalytic hydropyrolysis (HyPy), and gas chromatography-mass spectrometry (GC-MS) analyses of saturates and aromatics with published carbon isotopic data. The three fluorene series, gammacerane/C30hopane (G/C30H) and pristine/phytane (Pr/Ph) ratios demonstrated that the shallow shelf seawater changed significantly from relatively reducing to oxidizing and back to reducing conditions during the SPICE interval coupled with a regression-transgression cycle. The phytoplankton during the rise of the SPICE were mainly organic-walled, such as cyanobacteria, various acritarchs, and algae, as evidenced by terpanes, hopanes, and steranes. Significant decreases in phytoplankton diversity and abundance coincided with the peak of the SPICE, corresponding to the most oxidized and hypersaline periods during the SPICE event in the eastern Tarim Basin. Plankton assemblages diversified significantly with increasing living space due to the rise of sea-level during the post-SPICE period. Therefore, this study supports the idea that plankton groups changed dramatically with the environment, and its revolution followed the SPICE into the Great Ordovician Biodiversification Event.

Generally, the low concentration and homogenisation of traditional biomarkers in light oil and condensate (LOC) lead to uncertainties in their indicative significance of the parental origin of crude oils. Here, we focus on the component and stable hydrogen isotope (δD) distribution of C7 light hydrocarbons, including n-heptane (nC7), methylcyclohexane (MCH) and toluene (Tol), to identify the source rocks of LOC. In total, 114 LOCs whose source rocks are believed to be marine, lacustrine or coal facies in the Tarim Basin, NW China, are selected for the case study. The results demonstrate that the δDMCH, δDTol and δDnC7 values in the LOCs from marine, lacustrine and coal facies exhibited strong, slight and inverse ‘V' distributions, respectively, on their Line Charts. By analysing the differences among these values, we found that the ΔδDnC7–Tol and ΔδDTol–MCH values in the LOCs show good linear correlation (R2 = 0.8) and have the potential to distinguish the sedimentary facies of the source rocks of these oils. The ΔδDnC7–Tol values for marine, lacustrine and coal-formed LOCs were ˃6‰, from −20‰ to 20‰, and < −20‰, respectively. Further, the ΔδDTol–MCH values in the marine, lacustrine and coal-formed LOCs are ˂ − 5‰, from −30‰ to ‰, and > 0‰, respectively. Thus, the plot of ΔδDnC7–Tol–ΔδDTol–MCH can effectively distinguish among marine, lacustrine and coal-formed LOCs.

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The composition of rare earth elements (REEs) in kerogen has long been hypothesized to preserve signatures of shallow seawater, assuming that kerogen primarily originates from biomass inhabiting the shallow photic zone. In this study, we examine the composition of REEs in kerogen samples obtained from the Ediacaran Dongkanshang and Fengtan sections in South China. Through a meticulous screening process, we provide evidence that kerogen samples exhibiting patterns of heavy rare earth element (HREE) enrichment are free from acid-insoluble mineral contamination and preserve unaltered REE signatures. This study reveals that kerogens display low total rare earth element (ΣREE) concentrations. As kerogen samples exhibit higher levels of HREE enrichment, the Ce/Ce*, Eu/Eu*, and Y/Ho ratios show an upward trend. Moreover, all the kerogen samples exhibit chondritic Y/Ho ratios (with an average of 32). These findings imply that REEs in kerogens are of diagenetic origin and influenced by the ambient redox conditions. Our results suggest that the distribution patterns of REEs in kerogens derive from porewater within methanogenic zones, as opposed to the oxic seawater photic zone. Consequently, the formation of kerogen could potentially occur within a similar domain as the methanogenic zones, where kerogens can assimilate REEs from pore fluids and incorporate them into their macromolecular structures.

The methoxyl group (-OCH3) is abundant in biomass containing lignin. The quantification and biogeochemical evolution features of -OCH3 in these materials are still a research focus. The quantification methods of -OCH3 available up to date overall have a large error range and/or are time consuming through the need for a series of treatments. The present work reports an anisole-based assessment method for -OCH3 quantification in biomass containing lignin, by applying an anisole standard reagent to react with hydroiodic acid to create an external quantification curve used for -OCH3 quantification in samples studied. In practice, 10-200 mu L of anisole and 0.2-1 g of lignite samples were reacted with surplus hydroiodic acid under 130 celcius for 30 min to quantitatively obtain the iodomethane (CH3I) produced in a 20 mL ampere vial. The headspace gas was subjected to GC-FID analysis to create an external calibration curve for -OCH3 quantification in the lignite samples. The results indicated that the external calibration curve had a fairly good correlative relationship (R-2 = 0.9523). Quantification of -OCH3 carbon in lignites by this method is well within the scope of previous reports. It seems likely that this simple and precise quantification method will have promising applications for methoxyl group quantification in lignin-rich biomass.