Organic Geochemistry最新文献

{"title":"Analytical inconsistencies in the measurement and reporting of IP25, IPSO25 and related biomarkers for paleo sea ice reconstruction","authors":"Simon T. Belt ,&nbsp;Lukas Smik","doi":"10.1016/j.orggeochem.2025.104989","DOIUrl":"10.1016/j.orggeochem.2025.104989","url":null,"abstract":"<div><div>IP₂₅ and related biomarkers are commonly used for Arctic and Antarctic sea ice reconstruction. With a growing number of laboratories performing their measurement, we reviewed many publications spanning the period 2007–2024 in order to assess analytical rigour. We found a number of common shortfalls in analytical protocols, or at least how they are reported, which may have important implications for future synthesis studies and meta-data analyses. Here, we outline some of these shortcomings and provide suggestions of how to improve both data acquisition and reporting.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"204 ","pages":"Article 104989"},"PeriodicalIF":2.6,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143724185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unraveling the origin and charge of Halahatang oils, Tarim Basin","authors":"Peng Sun ,&nbsp;Chunfang Cai ,&nbsp;Daowei Wang ,&nbsp;Yu Qi ,&nbsp;Chenlu Xu ,&nbsp;Paul F. Greenwood","doi":"10.1016/j.orggeochem.2025.104962","DOIUrl":"10.1016/j.orggeochem.2025.104962","url":null,"abstract":"<div><div>Uncertainty about the source of the oils from the Halahatang region of the Tabei Uplift, Tarim Basin (NW China) presents an ongoing challenge to exploration. Previous analyses of several Halahatang oils showed isotopic (δ¹³C &lt; –32 ‰) and aliphatic hydrocarbon distributions (e.g., V-shaped C₂₇-C₂₉ steranes) more typical of regional Ordovician source rocks than the Cambrian rocks that are the predominant source of petroleum of the Tarim Basin, supporting prospects for a second major regional oil source. In pursuit of a more definitive source assignment of Halahatang oils and further insight into their depositional environment and charge history, a detailed molecular appraisal of the aromatic hydrocarbon composition of 27 marine oils and complementary stable sulfur and carbon isotopic analyses were conducted. The oils were from different Halahatang wells resolved into three separate block groups, with variations to the extent molecular and isotopic data was influenced by secondary alteration (i.e., thermal maturity, biodegradation and, possibly, minor thermochemical sulfate reduction) evident among the groups. The major aromatic products of all oils were alkylated naphthalenes, phenanthrenes, dibenzothiophenes and trace levels of thiadiamondoids were detected in a few Group II and III oils. Aryl isoprenoids, typical biomarkers of an euxinic depositional environment, were also conspicuous in lower maturity Group I and II oils (Rc &lt; 0.9 %), but absent in higher maturity oils (Rc up to 1.02 %). Molecular evidence of severe biodegradation (e.g., unresolved complex matter, 25-norterpenoids) was evident in some Group I oils, although some of these also showed coincident non-biodegradation molecular features (e.g., low MW <em>n</em>-alkanes) implying a mixing of biodegraded and non-biodegraded charges. The δ³⁴S values of the bulk oil and their dibenzothiophene and alkyldibenzothiophene products were generally in the range +17 to +23 ‰,although some oils impacted by biodegradation showed slightly heavier δ³⁴S values (&gt;+26 ‰). The Group II oils were not significantly impacted by secondary processes and their aromatic signature (e.g., aryl isoprenoids), δ³⁴S data and whole oil δ¹³C values were closely correlated with regional Lower Cambrian source rocks and are atypical of Upper Ordovician source rocks. These results identify the Halahatang oils as a further representation of Lower Cambrian-derived oils of the Tabei Uplift.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"204 ","pages":"Article 104962"},"PeriodicalIF":2.6,"publicationDate":"2025-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143631874","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Clumped 13C–13C isotopes of ethane from laboratory pyrolysis of kerogen: Implications for intramolecular 13C distributions","authors":"Koudai Taguchi ,&nbsp;Yuichiro Ueno ,&nbsp;Alexis Gilbert ,&nbsp;Xiaoqiang Li ,&nbsp;Juske Horita","doi":"10.1016/j.orggeochem.2025.104951","DOIUrl":"10.1016/j.orggeochem.2025.104951","url":null,"abstract":"<div><div>The clumped isotope geochemistry of ¹³C–¹³C bonding offers a valuable tool for distinguishing the formation processes of ethane (C₂H₆) and its thermogenic and abiotic origins. Thermogenic ethane is characterized by isotope distributions that are nearly in thermodynamic equilibrium, whereas abiotic ethane is governed by kinetic isotope effects during C–C bond synthesis. ¹³C–¹³C ordering in thermogenic ethane varies with the source organic material, but limited studies on ethane clumped isotopes from natural gases restrict our understanding of these signatures. To address this, we performed pyrolysis experiments at 310–470 °C on various immature kerogens from the Eocene Green River Formation (Type I), Upper Devonian–Lower Mississippian Woodford Shale (Type II), and Pennsylvanian Springfield Coal Member (Type III). The ethane-clumped isotope compositions aligned with those of natural gas samples and varied based on the starting kerogen’s isotope composition. We propose a thermogenic model that describes isotopic systematics, including ¹³C–¹³C variations in the pyrolysis product ethane, driven by (i) combinatorial isotope effect during C–C bond breaking and (ii) intramolecular isotopic heterogeneity in the starting kerogen. Isotopic and clumped isotope variations suggest a zigzag isotopic pattern in kerogen alkyl chains, similar to that seen in biological fatty acids. We could extend the model to position-specific (PS) isotope signatures in propane, showing that intramolecular isotopic heterogeneity in kerogens also affect PS isotopes, alongside structural heterogeneity, such as isoprenoid versus alkyl. Overall, our findings demonstrate that ¹³C–¹³C clumping is a ubiquitous signature for thermogenic ethane, with variations reflecting isotopic information of the original organic matter.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"204 ","pages":"Article 104951"},"PeriodicalIF":2.6,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143631872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reforestation in northeastern China increased the soil microbial necromass carbon accumulation by influencing glomalin and enzyme activities","authors":"Li Pan ,&nbsp;Xiuwei Wang","doi":"10.1016/j.orggeochem.2025.104983","DOIUrl":"10.1016/j.orggeochem.2025.104983","url":null,"abstract":"<div><div>Farmland reforestation is a common measure aimed at improving soil properties and preventing soil carbon loss, with microbial necromass carbon (MNC) being a crucial component of soil organic carbon. The changes in soil MNC content are closely linked to microbial community structure and microbial metabolites. However, the precise impact of microbial community, enzyme activities, and glomalin-related soil protein (GRSP) on MNC accumulation following the conversion from farmland to forest remains incompletely understood. To address these knowledge gaps, soil samples were collected from a farmland and two adjacent forests in the black soil region of Northeast China, focusing on the 0–30 cm depth. By utilizing the microbial cell wall’s biomarker amino sugars, the study estimated MNC contents and investigated how reforestation influences MNC levels in farmland, along with exploring the underlying mechanisms. The results revealed a significant increase in soil MNC by 139–167% and soil organic carbon by 25–34% post-reforestation. Moreover, the contribution of MNC to the soil organic carbon pool was enhanced following reforestation. It was observed that GRSP content was predominantly influenced by microbial community composition, with β-1,4-N-acetyl-glucosaminidase and GRSP emerging as key indicators affecting soil MNC levels. Notably, compared to microbial community composition alone, GRSP and enzyme activities exerted a more substantial impact on MNC in soil. In conclusion, this study underscores the significance of GRSP and enzyme activities in shaping soil MNC accumulation, thereby enhancing our understanding of the implications of reforestation on soil carbon stocks and the microbial-driven mechanisms at play.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"204 ","pages":"Article 104983"},"PeriodicalIF":2.6,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143687784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sedimentary geochemical records of the palaeovegetation and palaeoclimate evolution in the Pinghu Formation, Western Slope Belt, Xihu Sag, East China Sea Basin","authors":"Yanan Wang ,&nbsp;Lin Wei ,&nbsp;Xiong Cheng ,&nbsp;Hui Diao ,&nbsp;Wenjun Li ,&nbsp;Dujie Hou ,&nbsp;Jiansheng Li","doi":"10.1016/j.orggeochem.2025.104973","DOIUrl":"10.1016/j.orggeochem.2025.104973","url":null,"abstract":"<div><div>The sedimentary development of source rocks in marine-continental transitional facies is controlled mainly by the synergistic evolution of palaeovegetation and palaeoclimate. A set of marine-continental transitional coal seams in Xihu Sag of the East China Sea Basin were discovered at the end of the last century, whose lithology is mainly fine-grained sedimentary, with significant non-homogeneity and complex developmental control factors. Although systematic geochemical evaluations and hydrocarbon potential studies have been carried out on the source rocks in the Xihu Sag, few studies have focused on the fine-grained characterization of the palaeovegetation and palaeoclimate evolution during the depositional period. In this study, the palaeovegetation and palaeoclimate of the Pinghu Formation in Xihu Sag have been reconstructed based on biomarkers, pollen abundance, and trace elements. The organic matter of the Pinghu Formation is mainly input from terrigenous higher plants. The biomarkers reveal that gymnosperms gradually increase from the early to late stages of the Pinghu Formation, whereas pteridophytes exhibit the opposite trend. The contribution of gymnosperms to organic matter in the Wuyunting area is higher than in the Pinghu area. Furthermore, the number of temperate deciduous broad-leaved angiosperms (<em>Alnipollenites</em>, <em>Ulmipollenites</em>, <em>Momipites</em>, and <em>Juglanspollenites</em>) and mountain coniferous gymnosperms (<em>Pinuspollenites</em>) increased from the early to late stages of the Pinghu Formation, while the abundance of tropical/subtropical plants (<em>Quercoidites</em>, <em>Taxodiaceaepollenites</em>, and <em>Salixipollenites</em>) decreased. The vegetation succession<!--> <!-->is characterized by gradually transforming from tall gymnosperms to low-growing pteridophytes from the northern Wuyunting area to the southern Pinghu area. In conclusion, palynological data (including pteridophytes, angiosperms, and gymnosperms) and trace element ratios indicate that from the early to late stages of the Pinghu Formation, the palaeoclimate gradually became colder, with humidity and water depth decreasing.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"203 ","pages":"Article 104973"},"PeriodicalIF":2.6,"publicationDate":"2025-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143578858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Preservation of archaeal core lipids in siliceous hot spring deposits: An experimental study","authors":"L. Weimann ,&nbsp;M. Reinhardt ,&nbsp;C. Ostertag-Henning ,&nbsp;J.-P. Duda ,&nbsp;V. Thiel","doi":"10.1016/j.orggeochem.2025.104974","DOIUrl":"10.1016/j.orggeochem.2025.104974","url":null,"abstract":"<div><div>Siliceous hot spring systems have been present on our planet since at least 3.5 Ga, often hosting diverse communities of Archaea. Isoprenoid core lipids are important biomarkers for these microorganisms, but these lipids have only been reported from modern and subrecent siliceous sinter settings, perhaps indicating a bias against their long-term preservation in such environments. We conducted closed-system maturation experiments with the archaeal core lipids archaeol and isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) at 250 °C and 300 bar for 14 days. Compounds were heated with artificial sea water, with and without silica, as single compounds, and as part of a lipid mixture from a microbial mat. The products were analyzed using gas chromatography-mass spectrometry, scanning electron microscopy, and X-ray diffraction. This allowed to assess the preservation potential of these biomarkers during simulated siliceous sinter formation and subsequent diagenesis. Amorphous silica gel transformed into small microspheres (∼10 µm) when heated with single organic compounds, but formed more irregularly shaped rounded grains when heated with the lipid mixture. The presence of silica led to an enhanced degradation of archaeol, most likely caused by hydroxyl radicals deriving from silica-fluid interactions. IsoGDGTs, in contrast, were less affected by silica and showed an enhanced stability when heated as part of the lipid mixture. The results indicate that (i) the silica matrix, (ii) the molecular structure, and (iii) the presence of other organic compounds play a critical role for the preservation of archaeal core lipids in siliceous hot spring systems.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"204 ","pages":"Article 104974"},"PeriodicalIF":2.6,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143631873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimized sample cleanup for compound-specific isotope analysis of polycyclic aromatic hydrocarbons in complex environmental samples","authors":"Md Samrat Alam ,&nbsp;Jason M.E. Ahad ,&nbsp;Colin A. Cooke","doi":"10.1016/j.orggeochem.2025.104966","DOIUrl":"10.1016/j.orggeochem.2025.104966","url":null,"abstract":"<div><div>Compound-specific isotope analysis (CSIA) using gas chromatography – isotope ratio mass spectrometry is a powerful tool to discriminate sources of polycyclic aromatic hydrocarbons (PAHs). However, interferences from co-eluting peaks often prevent accurate isotopic measurements in complex environmental samples. Purification of sample extracts is thus a crucial analytical step. In this study, we report a rapid and effective cleanup method using high-performance liquid chromatography (HPLC) that provides high integrity isolation of PAHs suitable for CSIA. The method reported here was effective at purifying both parent and alkylated PAHs from several highly complex matrices, including river sediments, bitumen, petroleum coke, and wildfire ash. HPLC separation removed much of the interfering aromatic unresolved complex mixture (UCM) and significantly improved chromatography, yielding well-resolved PAH peaks with high intensities and signal-to-noise ratios. Recoveries and purities of target compounds following HPLC separation were 70 ± 13% and 97 ± 5%, respectively. No noticeable differences (± 0.5‰) were observed in the carbon isotope values (δ¹³C) of standards subjected to extraction and HPLC purification steps, indicating negligible isotopic fractionation associated with the protocol. The δ¹³C values for individual PAHs in samples were comparable to those previously reported for the same sample types, further demonstrating this method’s high level of accuracy and precision. Additionally, this technique allows for isotopic characterisation of a larger number of 4- to 5-ring PAHs compared to many previous studies due to removal of much of the later-eluting UCM, potentially providing greater insight into source discrimination and understanding of PAH deposition and transformation processes. While the focus of this investigation was on PAHs, this technique could be adapted to other problematic compounds targeted for CSIA.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"203 ","pages":"Article 104966"},"PeriodicalIF":2.6,"publicationDate":"2025-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143511397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Diamondoids, biomarkers, and chemofacies: Uniting insights on hydrocarbon maturation and migration in the Cline Shale, Midland Basin","authors":"Maram AlSaif ,&nbsp;Ibrahim Atwah ,&nbsp;Mauro Becker ,&nbsp;J. Michael Moldowan ,&nbsp;Alex Zumberge ,&nbsp;Franco Marcantonio","doi":"10.1016/j.orggeochem.2025.104953","DOIUrl":"10.1016/j.orggeochem.2025.104953","url":null,"abstract":"<div><div>Basinal mudrocks within the Wolfcamp Group of the Midland Basin, including the Cline Shale (Wolfcamp-D) interval, have proven to be prolific producers of oil and gas. However, predicting hydrocarbon distribution within the Cline Shale remains challenging due to its complex lithological heterogeneity and geochemical variability. In this study, molecular techniques and chemometrics were applied to address this challenge by: (1) characterizing the chemo-stratigraphically distinct depositional units of the Cline Shale, (2) understanding the role of lithological facies in hydrocarbon distribution, and (3) correlating produced-oil samples with the most productive zones within the Cline Shale.</div><div>Results reveal that the Cline Shale is dominated by marine-derived organic matter, with minimal terrigenous input. The sediments, currently in the peak-to-late oil window, exhibit distinct variations in redox conditions, paleoproductivity, and organic matter preservation across the Upper, Middle, and Lower intervals. Biomarkers such as terpanes, hopanes, and steranes highlight these variations. Further analysis using Quantitative Diamondoid Analysis (QDA) indicates notable differences in maturity and hydrocarbon cracking that cannot be explained solely by burial depth (∼300 ft difference). The highly mature oil in the Upper Cline appears to have been generated locally, whereas condensate in the Lower Cline is likely the result of lateral migration from deeper, more mature intervals. Quantitative Extended Diamondoid Analysis (QEDA) supports this by correlating oil samples from a nearby well to extracts from siliceous mudstones in the Upper Cline.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"203 ","pages":"Article 104953"},"PeriodicalIF":2.6,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143508832","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sources of bacterial 3-hydroxy fatty acids in Liangzihu Lake from central China: Implications for paleoclimate reconstruction","authors":"Honghai Wang ,&nbsp;Yi Yang ,&nbsp;Canfa Wang ,&nbsp;Shucheng Xie","doi":"10.1016/j.orggeochem.2025.104949","DOIUrl":"10.1016/j.orggeochem.2025.104949","url":null,"abstract":"<div><div>Bacterial 3-hydroxy fatty acids (3-OH-FAs) derived proxies are new tools for paleoclimate reconstruction. However, their effectiveness in temperature reconstruction in lake environments remains unclear. We investigated the compositions of 3-OH-FA and bacterial community across a transect from nearshore soils to water column and surface sediments in the center of Liangzihu Lake (LZH), central China, to elucidate the origins of 3-OH-FA within the lake environments and to evaluate their potential as temperature proxies. The 3-OH-FA in lake center sediments was found to be produced in situ, which can be further supported by the 16S rRNA gene sequencing results. We quantified the input of soil organic matter (OM) in the lake using a δ¹³C_org based two-end member model. The contribution of soil OM ranged from above 50% in nearshore sediments to &lt; 20% in the lake center, reflecting a decreased influence of soil contribution offshore. Moreover, 3-OH-FA based temperature proxies, RAN₁₃ (the ratio of <em>anteiso</em> to <em>normal</em> C₁₃) and RIN₁₇ (the ratio of <em>iso</em> to <em>normal</em> C₁₇) were examined. The temperature estimates derived from the RAN₁₃ were close to the meteorological temperature, whereas the temperature estimates based on RIN₁₇ are lower than the measured temperature. Therefore, our study not only elucidates the sources of 3-OH-FAs within LZH but also evaluates the reliability of associated temperature indices, which provides insights into temperature reconstruction in lake sediment cores.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"203 ","pages":"Article 104949"},"PeriodicalIF":2.6,"publicationDate":"2025-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143474541","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structural properties of organic matter in marine-continental transitional shales and impacts on methane accumulation","authors":"Zhen Qiu ,&nbsp;Dongjun Song ,&nbsp;Jingyu Zhang ,&nbsp;Qin Zhang ,&nbsp;Wen Liu ,&nbsp;Weiliang Kong ,&nbsp;Guangyin Cai ,&nbsp;Wanli Gao ,&nbsp;Tianquan Qu","doi":"10.1016/j.orggeochem.2025.104946","DOIUrl":"10.1016/j.orggeochem.2025.104946","url":null,"abstract":"<div><div>The chemical structure characteristics of organic matter (OM) in marine-continental transitional (MCT) shales and the controls on shale gas accumulation were revealed through analysis of Raman spectroscopy, infrared spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and CO₂ adsorption tests on the Lower Permian Shan-2 shale OM samples from the eastern margin of the Ordos Basin. Organic matter in the high-mature shale is enriched in aromatic groups, with a noticeable condensation and polymerization of the chemical structure after ∼3.0 %R_mc (Raman-based R_o). As %R_mc increases from 2.30 to 3.42, the position of the (002) peak from the stacking of aromatic layers increases from 25.15° to 25.88° in XRD spectra, the spacing between aromatic layers (d₀₀₂) decreases from 0.3540 nm to 0.3444 nm, the calculated graphitization degree (level of OM transforming into graphite) gradually increases, and the carbon layers in the OM evolve from a chaotic shape to a better-oriented state in TEM images, directly indicating an elevated graphitized level. Release of heteroatoms from OM results in reduced average lateral size (L_a) and stacking height (L_c) of the aromatic layer, reaching minimum values at ∼3.0 to 3.2 %R_mc. The stacking of aromatic layers forms some organic micropores, as evidenced by similar micropore size distribution between OM and bulk shale samples, possibly favoring methane accumulation. These findings provide new insights into the factors that affect the gas accumulation characteristics in MCT shales.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"203 ","pages":"Article 104946"},"PeriodicalIF":2.6,"publicationDate":"2025-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143464518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}