Organic Geochemistry最新文献_第7页

Clumped 13C–13C isotopes of ethane from laboratory pyrolysis of kerogen: Implications for intramolecular 13C distributions 干酪根实验室热解中乙烷13C - 13C的团块同位素：对分子内13C分布的影响

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry

Pub Date : 2025-03-15 DOI: 10.1016/j.orggeochem.2025.104951

Koudai Taguchi , Yuichiro Ueno , Alexis Gilbert , Xiaoqiang Li , Juske Horita

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.

13C-13C键的团块同位素地球化学为区分乙烷（C2H6）的形成过程及其热源和非生物源提供了有价值的工具。热源乙烷的同位素分布基本处于热力学平衡状态，而非生物乙烷则受碳碳键合成过程中同位素的动力学影响。热成因乙烷中13C-13C的排序随有机质来源的不同而不同，但对天然气中乙烷团块同位素的有限研究限制了我们对这些特征的理解。为了解决这一问题，我们对始新世绿河组（I型）、上泥盆统-下侏罗统伍德福德页岩（II型）和宾夕法尼亚春田煤系（III型）的各种未成熟干酪根进行了310-470℃的热解实验，结果表明乙烷团块同位素组成与天然气样品一致，并根据起始干酪根的同位素组成而变化。我们提出了一个热成因模型来描述同位素系统，包括热解产物乙烷中13C-13C的变化，这是由(i) C-C键断裂过程中的组合同位素效应和（ii）起始干酪根中分子内同位素非均质性驱动的。同位素和团块同位素变化表明干酪根烷基链呈锯齿形同位素模式，类似于在生物脂肪酸中看到的。我们可以将该模型扩展到丙烷中的位置特异性（PS）同位素特征，表明干酪根中的分子内同位素非均质性也会影响PS同位素，以及结构非均质性，如类异戊二烯与烷基。总之，我们的发现表明13C-13C团块是热成因乙烷的普遍特征，其变化反映了原始有机质的同位素信息。

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引用次数: 0

Mid- to Late-Holocene branched GDGT-based air temperatures from a crater lake in Cameroon (Central Africa) 中非喀麦隆火山口湖的中至晚全新世分支gdg温度

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry

Pub Date : 2025-03-14 DOI: 10.1016/j.orggeochem.2025.104982

Guillemette Ménot , Salomé Ansanay-Alex , Valérie F. Schwab , Gilbert Todou , Olivier Séné , Jean-Michel Onana , Gerd Gleixner , Dirk Sachse , Yannick Garcin

African low-latitude regions tend to be underrepresented in global continental temperature reconstructions, limiting both our understanding and the reliability of predictions of past and future changes in temperature and precipitation in those parts of the world. The lack of continuous sedimentary archives and quantitative temperature proxies further complicates this issue, especially outside Eastern Africa. Here, we use data collected in Cameroon lakes to assess branched glycerol dialkyl glycerol tetraether (brGDGT)-based temperature proxies and examine potential confounding variables impacting temperature reconstructions. By analyzing GDGT distributions in soil watershed, water column, and surface sediment samples from a total of 11 Cameroon lakes, we could verify that the degree of methylation of brGDGTs (through the MBT′_5Me) can serve as a reliable indicator for reconstructing mean annual air temperatures. Additionally, we could confirm that surface water conductivity represents a controlling factor for the brGDGT assemblage in surface sediments of crater lakes. Moreover, we provide the first reconstruction of Mid- to Late-Holocene GDGT-based air temperatures for a crater lake in Cameroon (Central Africa), revealing a temperature decrease of 2.5 °C over the last 7000 years, which agrees with recently published records for East Africa but exceeds current model predictions. These discrepancies highlight the need for additional studies to focus on this geographically underrepresented area.

非洲低纬度地区在全球大陆温度重建中的代表性往往不足，这限制了我们对世界这些地区过去和未来气温和降水变化的了解以及预测的可靠性。缺乏连续的沉积档案和定量温度代用指标使这一问题更加复杂，尤其是在东非以外地区。在这里，我们利用在喀麦隆湖泊收集的数据来评估基于支链甘油二烷基甘油四醚（brGDGT）的温度代用指标，并研究影响温度重建的潜在混杂变量。通过分析总共 11 个喀麦隆湖泊的土壤流域、水体和表层沉积物样本中的 GDGT 分布，我们可以验证 brGDGT 的甲基化程度（通过 MBT′5Me）可以作为重建年平均气温的可靠指标。此外，我们还证实了地表水电导率是陨石坑湖地表沉积物中 brGDGT 组合的一个控制因素。此外，我们首次为喀麦隆（中非）的一个火山口湖重建了全新世中期到晚期的气温，显示在过去的7000年中气温下降了2.5°C，这与最近发表的东非记录一致，但超出了目前的模型预测。这些差异突出表明，有必要开展更多的研究，重点关注这一代表性不足的地理区域。

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引用次数: 0

Reforestation in northeastern China increased the soil microbial necromass carbon accumulation by influencing glomalin and enzyme activities 东北地区复林通过影响球囊素和酶活性增加土壤微生物坏死团碳积累

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry

Pub Date : 2025-03-13 DOI: 10.1016/j.orggeochem.2025.104983

Li Pan , Xiuwei Wang

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.

农田植树造林是一种旨在改善土壤性质和防止土壤碳流失的常见措施，而微生物坏死碳（MNC）是土壤有机碳的重要组成部分。土壤 MNC 含量的变化与微生物群落结构和微生物代谢物密切相关。然而，从农田到森林的转换过程中，微生物群落、酶活性和胶霉素相关土壤蛋白质（GRSP）对 MNC 积累的确切影响仍未完全了解。为了填补这些知识空白，研究人员从中国东北黑土区的一块农田和相邻的两片森林中采集了土壤样本，样本深度集中在 0-30 厘米。通过利用微生物细胞壁的生物标志物氨基糖，该研究估算了 MNC 的含量，并研究了植树造林如何影响农田中的 MNC 水平，同时探讨了其潜在机制。结果显示，植树造林后，土壤中的 MNC 明显增加了 139-167%，土壤中的有机碳增加了 25-34%。此外，植树造林后，MNC 对土壤有机碳库的贡献增加了。据观察，GRSP 含量主要受微生物群落组成的影响，β-1,4-N-乙酰-葡萄糖苷酶和 GRSP 是影响土壤 MNC 含量的关键指标。值得注意的是，与单纯的微生物群落组成相比，GRSP 和酶活性对土壤中 MNC 的影响更大。总之，这项研究强调了 GRSP 和酶活性在影响土壤 MNC 积累方面的重要作用，从而加深了我们对植树造林对土壤碳储量的影响以及微生物驱动机制的理解。

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引用次数: 0

Sedimentary geochemical records of the palaeovegetation and palaeoclimate evolution in the Pinghu Formation, Western Slope Belt, Xihu Sag, East China Sea Basin 东海盆地西湖凹陷西斜坡带平湖组古植被与古气候演化的沉积地球化学记录

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry

Pub Date : 2025-03-09 DOI: 10.1016/j.orggeochem.2025.104973

Yanan Wang , Lin Wei , Xiong Cheng , Hui Diao , Wenjun Li , Dujie Hou , Jiansheng Li

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 (Alnipollenites, Ulmipollenites, Momipites, and Juglanspollenites) and mountain coniferous gymnosperms (Pinuspollenites) increased from the early to late stages of the Pinghu Formation, while the abundance of tropical/subtropical plants (Quercoidites, Taxodiaceaepollenites, and Salixipollenites) 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.

海陆过渡相烃源岩的沉积发育主要受古植被和古气候的协同演化控制。上世纪末在东海盆地西湖凹陷发现了一套海陆过渡煤层，其岩性以细粒沉积为主，非均质性显著，发育控制因素复杂。虽然对西湖凹陷烃源岩进行了系统的地球化学评价和油气潜力研究，但对沉积期古植被和古气候演化的精细表征研究较少。根据生物标志物、花粉丰度、微量元素等指标，重建了西湖凹陷平湖组古植被和古气候。平湖组有机质主要由陆源高等植物输入。生物标志物显示，裸子植物在平湖组早期至晚期逐渐增多，而蕨类植物则相反。裸子植物对有机质的贡献在武云亭地区高于平湖地区。平湖组早期至晚期，温带落叶阔叶被子植物（全粉、乌粉、莫粉和菊粉）和山地针叶裸子植物（松粉）的数量呈增加趋势，热带/亚热带植物（栎属、红杉属和柳粉）的丰度呈下降趋势。从武云亭北部到平湖南部，植被演替呈现由高大裸子植物向低矮蕨类植物逐渐转变的特征。综上所述，孢粉（包括蕨类植物、被子植物和裸子植物）和微量元素比值表明，平湖组早期至晚期，古气候逐渐变冷，湿度和水深逐渐减少。

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引用次数: 0

Preservation of archaeal core lipids in siliceous hot spring deposits: An experimental study 硅质温泉沉积中古生物核心脂质的保存：实验研究

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry

Pub Date : 2025-03-04 DOI: 10.1016/j.orggeochem.2025.104974

L. Weimann , M. Reinhardt , C. Ostertag-Henning , J.-P. Duda , V. Thiel

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.

硅质温泉系统至少从3.5 Ga开始就存在于我们的星球上，经常容纳各种各样的古生菌群落。类异戊二烯核心脂质是这些微生物的重要生物标志物，但这些脂质仅在现代和亚近代硅质烧结环境中被报道，这可能表明它们在这些环境中长期保存存在偏见。我们用古菌核心脂质古醇和类异戊二烯甘油二烷基甘油四醚（isoGDGTs）在250°C和300 bar条件下进行了14天的封闭系统成熟实验。化合物用人工海水加热，含或不含二氧化硅，作为单一化合物，作为微生物垫的脂质混合物的一部分。产品使用气相色谱-质谱，扫描电子显微镜和x射线衍射分析。这可以评估这些生物标志物在模拟硅质烧结形成和随后的成岩作用期间的保存潜力。当与单一有机化合物一起加热时，无定形硅胶转变成小的微球（~ 10µm），但当与脂质混合物一起加热时，形成更不规则形状的圆形颗粒。二氧化硅的存在导致古酚的降解增强，这很可能是由二氧化硅与流体相互作用产生的羟基自由基引起的。相比之下，IsoGDGTs受二氧化硅的影响较小，并且在作为脂质混合物的一部分加热时表现出增强的稳定性。结果表明：(1)硅基基质，(2)分子结构，(3)其他有机化合物的存在对硅质温泉体系中古细菌核心脂质的保存起关键作用。

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引用次数: 0

Optimized sample cleanup for compound-specific isotope analysis of polycyclic aromatic hydrocarbons in complex environmental samples 复杂环境样品中多环芳烃化合物特异性同位素分析的优化样品清理

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry

Pub Date : 2025-02-28 DOI: 10.1016/j.orggeochem.2025.104966

Md Samrat Alam , Jason M.E. Ahad , Colin A. Cooke

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.

气相色谱-同位素比质谱法是鉴别多环芳烃（PAHs）来源的有力工具。然而，在复杂的环境样品中，来自共洗脱峰的干扰常常妨碍精确的同位素测量。因此，样品提取物的纯化是一个关键的分析步骤。在本研究中，我们报告了一种快速有效的高效液相色谱（HPLC）清除方法，该方法提供了适用于CSIA的高完整性分离多环芳烃。本文报道的方法在几种高度复杂的基质（包括河流沉积物、沥青、石油焦和野火灰烬）中纯化母体和烷基化多环芳烃都是有效的。高效液相色谱分离去除了大部分干扰芳香族未解析复杂混合物（UCM），并显著改善了色谱，得到了具有高强度和高信噪比的高解析多环芳烃峰。目的化合物经高效液相色谱分离后的回收率为70±13%，纯度为97±5%。经过萃取和HPLC纯化步骤的标准品的碳同位素值（δ13C）没有明显差异（±0.5‰），表明该方案相关的同位素分馏可以忽略不计。样品中单个多环芳烃的δ13C值与先前报道的相同样品类型的δ13C值相当，进一步证明了该方法具有较高的准确性和精密度。此外，与许多先前的研究相比，由于去除了大部分后期洗脱的UCM，该技术允许对更多数量的4至5环多环芳烃进行同位素表征，可能为多环芳烃的来源识别和沉积和转化过程的理解提供更深入的见解。虽然本研究的重点是多环芳烃，但该技术可以适用于CSIA靶向的其他问题化合物。

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引用次数: 0

Diamondoids, biomarkers, and chemofacies: Uniting insights on hydrocarbon maturation and migration in the Cline Shale, Midland Basin 金刚石类、生物标志物和化学相：对Midland盆地Cline页岩油气成熟和运移的统一认识

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry

Pub Date : 2025-02-26 DOI: 10.1016/j.orggeochem.2025.104953

Maram AlSaif , Ibrahim Atwah , Mauro Becker , J. Michael Moldowan , Alex Zumberge , Franco Marcantonio

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.

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.

米德兰盆地Wolfcamp组的盆地泥岩，包括Cline页岩（Wolfcamp- d）层段，已被证明是油气的高产产层。然而，由于Cline页岩具有复杂的岩性非均质性和地球化学变异性，预测其油气分布仍然具有挑战性。在这项研究中，分子技术和化学计量学应用于解决这一挑战，通过：(1)表征Cline页岩的化学地层不同沉积单元，(2)了解岩性相在油气分布中的作用，(3)将产油样品与Cline页岩内最高产带进行对比。结果表明，克莱因页岩以海相有机质为主，陆源有机质输入极少。目前，这些沉积物处于峰值至晚期的含油窗口，在上、中、下三个层段的氧化还原条件、古生产力和有机质保存方面表现出明显的差异。萜烷、藿烷和甾烷等生物标志物突出了这些变化。使用定量金刚石分析（QDA）进一步分析表明，成熟度和碳氢化合物裂解的显著差异不能仅仅用埋深（约300英尺的差异）来解释。上斜的高成熟油似乎是局部生成的，而下斜的凝析油可能是更深、更成熟层段侧向运移的结果。定量扩展金刚石分析（QEDA）通过将附近油井的石油样品与上克莱恩的硅质泥岩提取物进行对比，支持了这一观点。

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引用次数: 0

Sources of bacterial 3-hydroxy fatty acids in Liangzihu Lake from central China: Implications for paleoclimate reconstruction 梁子湖细菌3-羟基脂肪酸来源及其古气候重建意义

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry

Pub Date : 2025-02-24 DOI: 10.1016/j.orggeochem.2025.104949

Honghai Wang , Yi Yang , Canfa Wang , Shucheng Xie

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 < 20% in the lake center, reflecting a decreased influence of soil contribution offshore. Moreover, 3-OH-FA based temperature proxies, RAN₁₃ (the ratio of anteiso to normal C₁₃) and RIN₁₇ (the ratio of iso to normal 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.

细菌3-羟基脂肪酸（3-OH-FAs）衍生的代用物是古气候重建的新工具。然而，它们在湖泊环境温度重建中的有效性尚不清楚。研究了梁子湖中部从近岸土壤到水柱和表层沉积物的3-OH-FA的组成和细菌群落，以阐明3-OH-FA在湖泊环境中的来源，并评价其作为温度指标的潜力。湖心沉积物中的3-OH-FA是原位产生的，16S rRNA基因测序结果进一步支持了这一观点。采用基于δ13Corg的两端元模型定量分析了湖泊土壤有机质的输入量。土壤有机质在近岸沉积物中的贡献从50%以上到50%；湖中心为20%，反映近海土壤贡献的影响减小。此外，还检测了基于3-OH-FA的温度代用指标RAN13（前iso与正常C13之比）和RIN17 （iso与正常C17之比）。RAN13估算的温度接近气象温度，而RIN17估算的温度低于实测温度。因此，我们的研究不仅阐明了LZH内3-OH-FAs的来源，而且还评估了相关温度指标的可靠性，为湖泊沉积物岩心温度重建提供了新的思路。

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引用次数: 0

Structural properties of organic matter in marine-continental transitional shales and impacts on methane accumulation 海陆过渡页岩有机质结构特征及其对甲烷聚集的影响

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry

Pub Date : 2025-02-22 DOI: 10.1016/j.orggeochem.2025.104946

Zhen Qiu , Dongjun Song , Jingyu Zhang , Qin Zhang , Wen Liu , Weiliang Kong , Guangyin Cai , Wanli Gao , Tianquan Qu

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.

通过对鄂尔多斯盆地东缘下二叠统山2页岩有机质样品的拉曼光谱、红外光谱、x射线衍射（XRD）、透射电镜（TEM）和CO2吸附测试等分析，揭示了海陆过渡（MCT）页岩有机质的化学结构特征和页岩气成藏的控制因素。高成熟页岩有机质富含芳香基团，在~ 3.0% Rmc （raman -基Ro）后，化学结构发生了明显的缩聚和聚合。当%Rmc从2.30增加到3.42时，（002）峰在芳层堆积处的位置在XRD光谱中从25.15°增加到25.88°，芳层间距（d002）从0.3540 nm减小到0.3444 nm，计算出的石墨化程度（OM向石墨的转变程度）逐渐增加，OM中的碳层在TEM图像中从混沌形态演变为取向更好的状态，直接表明石墨化程度的提高。从OM中释放杂原子导致芳香层的平均横向尺寸（La）和堆积高度（Lc）降低，在~ 3.0 ~ 3.2% Rmc时达到最小值。芳烃层的堆积形成了一定的有机微孔，有机质与大块页岩样品的微孔大小分布相似，可能有利于甲烷的聚集。这些发现为研究影响MCT页岩天然气成藏特征的因素提供了新的思路。

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引用次数: 0

Chemodiversity of soil dissolved organic matter complementally improved by stepwise elution and electrospray ionization modes 阶梯式洗脱和电喷雾电离方式对土壤溶解有机质的化学多样性有互补作用

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Organic Geochemistry

Pub Date : 2025-02-22 DOI: 10.1016/j.orggeochem.2025.104965

Shasha Zhuo, Rong Qin, Qing-Long Fu

The chemodiversity of dissolved organic matter (DOM) molecules can affect the biogeochemical cycling of carbon and nitrogen in terrestrial and aquatic environments. In this study, the negative and positive ion modes of electrospray ionization (ESI(−) and ESI(+), respectively) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were employed to reveal the chemical composition of seven soil DOM isolates by stepwise elution using different methanol/water solvents. The intensity percentage of CHON molecules in soil DOM detected in the ESI(+) mode was 4.6%–47.3% higher than that for the ESI(−) mode. The O/C ratio, H/C ratio, and the nominal oxidation states of the carbon value of soil DOM molecules linearly correlated (R² > 0.8 for 72% number of stepwise eluted DOM isolates) with the increasing volume of methanol in the SPE elution solvents in dual ion modes, demonstrating the selective fractionation of oxygen-rich and highly polar molecules by methanol-poor solvents. This polarity-dependent fractionation is expected to be universal across different soils. These results suggest that combining the ESI(−) and ESI(+) modes with stepwise elution enables the comprehensive characterization of soil DOM composition, favouring the in-depth understanding of the critical roles of DOM in the biogeochemical cycles of carbon and nitrogen.

溶解有机质（DOM）分子的化学多样性影响着陆地和水生环境中碳氮的生物地球化学循环。本研究采用电喷雾电离的负离子模式(ESI（−）和正离子模式（ESI(+)）结合傅里叶变换离子回旋共振质谱（FT-ICR MS），通过不同的甲醇/水溶剂逐步洗脱，揭示了7种土壤DOM分离物的化学成分。ESI（+）模式下土壤DOM中检测到的CHON分子强度百分比比ESI（−）模式高4.6% ~ 47.3%。O/C比、H/C比与土壤DOM分子标称氧化态碳值呈线性相关(R2 >；在双离子模式下，随着固相萃取溶剂中甲醇体积的增加，DOM分离物的分离率为0.8(72%)，证明了贫甲醇溶剂对富氧和高极性分子的选择性分离。这种与极性有关的分馏可望在不同的土壤中普遍存在。上述结果表明，ESI（−）和ESI（+）模式与逐步洗脱相结合，可以全面表征土壤DOM的组成，有利于深入了解DOM在碳氮生物地球化学循环中的关键作用。

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引用次数: 0