Pub Date : 2025-01-06DOI: 10.1016/j.orggeochem.2025.104929
Yves Perrette , Hervé Vezin , Bernard Fanget , Julia Garagnon , Jérome Poulenard
The evolution of soil organic carbon (SOC) stocks is critical for both food production and climate change mitigation. This study uses advanced electron paramagnetic resonance (EPR) spectroscopy to investigate the spatial localisation and characterisation of organic carbon in speleothems, with a particular focus on methodological advances in recent decades. A speleothem sample from the Choranche cave in France was analysed using UV laser-induced fluorescence (LIF) and continuous wave EPR spectroscopy. The LIF analysis identified three main types of organic compounds − aromatic amino acids, aliphatic aromatics and larger aromatic compounds − distributed throughout the sample. EPR spectroscopy revealed the presence of Fe3+ and Mn2+ ions, along the entire sample for Fe3+ and more localised for Mn2+. When radical organic matter (ROM) is detected, first and second harmonic EPR imaging shows its collocation with Fe3+ and Mn2+, suggesting specific embedding conditions or source events. The study highlights a significant discrepancy between fluorescent organic matter (FOM) and ROM, challenging previous assumptions about their co-transfer from soil to speleothems. The results suggest that ROM is likely to be associated with specific soil redox conditions or high-energy events, whereas FOM represents a continuous background transfer. This distinction is crucial for accurate interpretations of soil organic carbon loss and its environmental implications. Future research should integrate detailed spectroscopic and isotopic analyses to better quantify organic carbon dynamics and their environmental proxies. Our results highlight the importance of distinguishing between different types of organic matter in speleothems to improve our understanding of soil organic carbon fluxes in relation to climate and human land use.
{"title":"Revisiting the fingerprint of organic matters in speleothem by Electron Paramagnetic Resonance","authors":"Yves Perrette , Hervé Vezin , Bernard Fanget , Julia Garagnon , Jérome Poulenard","doi":"10.1016/j.orggeochem.2025.104929","DOIUrl":"10.1016/j.orggeochem.2025.104929","url":null,"abstract":"<div><div>The evolution of soil organic carbon (SOC) stocks is critical for both food production and climate change mitigation. This study uses advanced electron paramagnetic resonance (EPR) spectroscopy to investigate the spatial localisation and characterisation of organic carbon in speleothems, with a particular focus on methodological advances in recent decades. A speleothem sample from the Choranche cave in France was analysed using UV laser-induced fluorescence (LIF) and continuous wave EPR spectroscopy. The LIF analysis identified three main types of organic compounds − aromatic amino acids, aliphatic aromatics and larger aromatic compounds − distributed throughout the sample. EPR spectroscopy revealed the presence of Fe<sup>3+</sup> and Mn<sup>2+</sup> ions, along the entire sample for Fe<sup>3+</sup> and more localised for Mn<sup>2+</sup>. When radical organic matter (ROM) is detected, first and second harmonic EPR imaging shows its collocation with Fe<sup>3+</sup> and Mn<sup>2+</sup>, suggesting specific embedding conditions or source events. The study highlights a significant discrepancy between fluorescent organic matter (FOM) and ROM, challenging previous assumptions about their co-transfer from soil to speleothems. The results suggest that ROM is likely to be associated with specific soil redox conditions or high-energy events, whereas FOM represents a continuous background transfer. This distinction is crucial for accurate interpretations of soil organic carbon loss and its environmental implications. Future research should integrate detailed spectroscopic and isotopic analyses to better quantify organic carbon dynamics and their environmental proxies. Our results highlight the importance of distinguishing between different types of organic matter in speleothems to improve our understanding of soil organic carbon fluxes in relation to climate and human land use.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"201 ","pages":"Article 104929"},"PeriodicalIF":2.6,"publicationDate":"2025-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143145154","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}
Pub Date : 2024-12-22DOI: 10.1016/j.orggeochem.2024.104920
Akanksha Singh , Sze Ling Ho , Min-Te Chen , Pei-Ling Wang , Martin Jakobsson , Richard Gyllencreutz , Ludvig Löwemark
Arctic sea ice affects Earth’s albedo, marine productivity and organic matter (OM) transport. Lipid biomarkers have been used to trace OM transport in the Arctic Ocean, but uncertainties remain regarding their spatio-temporal variations and sources over the last glacial cycle. Our study addresses these gaps by analyzing glycerol dialkyl glycerol tetraethers (GDGTs), n-alkanes, and total organic carbon (TOC) in nine central Arctic sediment cores spanning the Marine Isotope Stages (MISs) 3–1. Elevated IIIa/IIa values of branched GDGTs (brGDGTs) in the central Arctic throughout the studied interval suggest a marine origin, contrasting to the #ringstetra ratios which indicate a terrigenous brGDGT source. We propose that the IIIa/IIa ratio may be a more sensitive indicator of in situ brGDGT production in the central Arctic marine sediments. TOC and biomarker concentrations in the Central Lomonosov Ridge (CLR) cores were higher compared to those from the Lomonosov Ridge off Greenland (LRG) and Morris Jesup Rise (MJR) cores. Low productivity in the central Arctic, along with similarity in the spatial patterns of marine-derived brGDGTs and isoprenoid GDGTs, as well as terrestrial long-chain n-alkanes, suggests that these biomarkers are primarily transported to the central Arctic from the Siberian shelves. This spatial pattern persisted throughout MISs 3–1, suggesting continued sea ice drift during glacial periods, albeit with weakened intensities. Meanwhile, the spatiotemporal variations of the Branched Isoprenoid Tetraether (BIT) index in the region plausibly reflect the relative changes in the crenarchaeol and brGDGT production on the shelf and/or selective degradation of crenarchaeol during its transport.
{"title":"Spatial distribution of n-alkanes and GDGTs in the central Arctic Ocean during Marine Isotope Stages 1, 2 and 3","authors":"Akanksha Singh , Sze Ling Ho , Min-Te Chen , Pei-Ling Wang , Martin Jakobsson , Richard Gyllencreutz , Ludvig Löwemark","doi":"10.1016/j.orggeochem.2024.104920","DOIUrl":"10.1016/j.orggeochem.2024.104920","url":null,"abstract":"<div><div>Arctic sea ice affects Earth’s albedo, marine productivity and organic matter (OM) transport. Lipid biomarkers have been used to trace OM transport in the Arctic Ocean, but uncertainties remain regarding their spatio-temporal variations and sources over the last glacial cycle. Our study addresses these gaps by analyzing glycerol dialkyl glycerol tetraethers (GDGTs), <em>n</em>-alkanes, and total organic carbon (TOC) in nine central Arctic sediment cores spanning the Marine Isotope Stages (MISs) 3–1. Elevated IIIa/IIa values of branched GDGTs (brGDGTs) in the central Arctic throughout the studied interval suggest a marine origin, contrasting to the #rings<sub>tetra</sub> ratios which indicate a terrigenous brGDGT source. We propose that the IIIa/IIa ratio may be a more sensitive indicator of in situ brGDGT production in the central Arctic marine sediments. TOC and biomarker concentrations in the Central Lomonosov Ridge (CLR) cores were higher compared to those from the Lomonosov Ridge off Greenland (LRG) and Morris Jesup Rise (MJR) cores. Low productivity in the central Arctic, along with similarity in the spatial patterns of marine-derived brGDGTs and isoprenoid GDGTs, as well as terrestrial long-chain <em>n</em>-alkanes, suggests that these biomarkers are primarily transported to the central Arctic from the Siberian shelves. This spatial pattern persisted throughout MISs 3–1, suggesting continued sea ice drift during glacial periods, albeit with weakened intensities. Meanwhile, the spatiotemporal variations of the Branched Isoprenoid Tetraether (BIT) index in the region plausibly reflect the relative changes in the crenarchaeol and brGDGT production on the shelf and/or selective degradation of crenarchaeol during its transport.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"201 ","pages":"Article 104920"},"PeriodicalIF":2.6,"publicationDate":"2024-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143378488","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}
Pub Date : 2024-12-18DOI: 10.1016/j.orggeochem.2024.104919
Aaron F Diefendorf
This study compares different lipid extraction methods and solvents with a focus on reducing or eliminating the use of dichloromethane (DCM). DCM has high neurotoxicity and is carcinogenic. This study focuses on lake sediment extraction using accelerated solvent extraction (ASE), sonication, QuEChERS, and Soxhlet methods and compares the solvents DCM, ethyl acetate (EtOAc), methanol (MeOH), and hexanes. For ASE and sonication extractions, the replacement of DCM with EtOAc results in similar extraction efficiencies for n-alkanes, n-alkanols, and slightly lower extraction of n-alkanoic acids. For example, when using an ASE with recovery standards, switching from 9:1 DCM/MeOH to 9:1 EtOAc/MeOH results in a small decrease of 10% in the extraction of total hydrocarbons (mostly n-alkanes), the same recovery of the alcohols (mostly n-alkanols), and a decrease of 19% for the acids (mostly n-alkanoic acids). The QuEChERS method reduces the volume of DCM, but had poor recovery compared to ASE or sonication. Many labs could switch from using DCM to EtOAc with ASE or sonication and have minor to no changes in extraction efficiency. The use of 9:1 hexanes/EtOAc produced high recoveries of n-alkanes and n-alkanols with a cleaner extract that requires less post extraction cleanup. Sonication has the potential advantage of higher throughput and lower costs, although hands-on time is higher than ASE and recoveries were not always as high as with ASE. While this study focuses on the extraction of lake sediment, the results should be transferable to the extraction of soils, rocks, and other biological materials with minor method adjustments.
{"title":"Comparing lipid extraction methods on lake sediments without dichloromethane","authors":"Aaron F Diefendorf","doi":"10.1016/j.orggeochem.2024.104919","DOIUrl":"10.1016/j.orggeochem.2024.104919","url":null,"abstract":"<div><div>This study compares different lipid extraction methods and solvents with a focus on reducing or eliminating the use of dichloromethane (DCM). DCM has high neurotoxicity and is carcinogenic. This study focuses on lake sediment extraction using accelerated solvent extraction (ASE), sonication, QuEChERS, and Soxhlet methods and compares the solvents DCM, ethyl acetate (EtOAc), methanol (MeOH), and hexanes. For ASE and sonication extractions, the replacement of DCM with EtOAc results in similar extraction efficiencies for <em>n</em>-alkanes, <em>n</em>-alkanols, and slightly lower extraction of <em>n</em>-alkanoic acids. For example, when using an ASE with recovery standards, switching from 9:1 DCM/MeOH to 9:1 EtOAc/MeOH results in a small decrease of 10% in the extraction of total hydrocarbons (mostly <em>n</em>-alkanes), the same recovery of the alcohols (mostly <em>n</em>-alkanols), and a decrease of 19% for the acids (mostly <em>n</em>-alkanoic acids). The QuEChERS method reduces the volume of DCM, but had poor recovery compared to ASE or sonication. Many labs could switch from using DCM to EtOAc with ASE or sonication and have minor to no changes in extraction efficiency. The use of 9:1 hexanes/EtOAc produced high recoveries of <em>n</em>-alkanes and <em>n</em>-alkanols with a cleaner extract that requires less post extraction cleanup. Sonication has the potential advantage of higher throughput and lower costs, although hands-on time is higher than ASE and recoveries were not always as high as with ASE. While this study focuses on the extraction of lake sediment, the results should be transferable to the extraction of soils, rocks, and other biological materials with minor method adjustments.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"202 ","pages":"Article 104919"},"PeriodicalIF":2.6,"publicationDate":"2024-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143386988","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}
Pub Date : 2024-11-29DOI: 10.1016/j.orggeochem.2024.104901
Congsheng Bian , Shiju Liu , Wei Liu , Xiong Cheng , Xin Liu , Jin Dong , Rui Wang , Yongxin Li , Ming Guan , Qianhui Tian , Wenzhi Zhao
The Late Cretaceous Nenjiang Formation in the Songliao Basin presents a unique setting to examine how climate change and sea-level rise influenced organic matter accumulation. This study combines TOC analysis, Rock-Eval pyrolysis, GC–MS, GC–MS-MS, and elemental geochemistry on core samples from two wells to assess organic matter deposition before and after transgressive events. TOC values range from 0.18 to 14.63 wt%, with significant variations in hydrocarbon potential and thermal maturity. Periodic warm and cool climates triggered intermittent seawater intrusions that created anoxic conditions conducive to marine diatom and lacustrine dinoflagellate proliferation. Extended warm periods, however, suppressed dinoflagellate development and reduced paleo-productivity. The activity of methanogenic bacteria further contributed to the degradation of sedimentary organic matter, hindering its accumulation. While warm climates facilitated flood events that transported terrigenous nutrients, enhancing dinoflagellate blooms and expanding the oxygen minimum zone. These findings highlight the bio-environmental interactions that governed organic matter accumulation during transgressions, offering insights for exploration in similar sedimentary environments.
{"title":"Organic matter accumulation driven by land-sea interactions during the Late Cretaceous: A geochemical study of the Nenjiang Formation, Songliao Basin","authors":"Congsheng Bian , Shiju Liu , Wei Liu , Xiong Cheng , Xin Liu , Jin Dong , Rui Wang , Yongxin Li , Ming Guan , Qianhui Tian , Wenzhi Zhao","doi":"10.1016/j.orggeochem.2024.104901","DOIUrl":"10.1016/j.orggeochem.2024.104901","url":null,"abstract":"<div><div>The Late Cretaceous Nenjiang Formation in the Songliao Basin presents a unique setting to examine how climate change and sea-level rise influenced organic matter accumulation. This study combines TOC analysis, Rock-Eval pyrolysis, GC–MS, GC–MS-MS, and elemental geochemistry on core samples from two wells to assess organic matter deposition before and after transgressive events. TOC values range from 0.18 to 14.63 wt%, with significant variations in hydrocarbon potential and thermal maturity. Periodic warm and cool climates triggered intermittent seawater intrusions that created anoxic conditions conducive to marine diatom and lacustrine dinoflagellate proliferation. Extended warm periods, however, suppressed dinoflagellate development and reduced paleo-productivity. The activity of methanogenic bacteria further contributed to the degradation of sedimentary organic matter, hindering its accumulation. While warm climates facilitated flood events that transported terrigenous nutrients, enhancing dinoflagellate blooms and expanding the oxygen minimum zone. These findings highlight the bio-environmental interactions that governed organic matter accumulation during transgressions, offering insights for exploration in similar sedimentary environments.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"199 ","pages":"Article 104901"},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746085","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}
Pub Date : 2024-11-19DOI: 10.1016/j.orggeochem.2024.104884
Kun He , Xiaomei Wang , Chunlong Yang , Linfeng Xie , Shuichang Zhang
It is widely accepted that organic–inorganic interactions involving hydrogen-rich fluids (H2O and H2) play a significant role in hydrocarbon (HC) generation in sedimentary basins, and the effects of hydrogenation of organic matter (OM) by H2O/H2 on C/H isotope fractionation remain poorly understood. This study investigates these effects through a series of pyrolysis experiments conducted at 330–420 °C and 50 MPa, encompassing three groups: (1) anhydrous pyrolysis with kerogen only (Group 1), (2) kerogen and H2O (Group 2), and (3) kerogen, H2O, and Fe1-xS (Group 3). Groups 2 and 3 were designed to simulate hydrogenation of OM by H2O and H2, respectively. Results show that HC gas yields in Group 3 experiments are 1.8 to 3.2 times of those in Group 1, while yields in Group 2 are lower than Group 1. Moreover, hydrogenation by H2 produces HC gases with smaller 13C fractionation and more negative δ2H values compared to hydrogenation by H2O. These findings suggest distinct mechanisms for HC gas generation during H2-OM and H2O-OM reactions. Further analysis demonstrates that the equilibrium isotope effect (EIE) governs 13C and 2H isotope fractionation during hydrogenation of OM by H2. Importantly, the EIE for 2H isotope fractionation of H2O-H2, CH4-H2, and OM-H2 is evaluated under both experimental and geological conditions. This study provides crucial insights into the significant influence of hydrogenation of OM by H2 on the generation and C/H isotopic fractionation of HC gases, as well as the evolution and preservation of H2 in organic-rich shales.
{"title":"C/H isotope fractionation of hydrocarbon gases from hydrogenation of organic matter: Insights from hydrothermal experiments","authors":"Kun He , Xiaomei Wang , Chunlong Yang , Linfeng Xie , Shuichang Zhang","doi":"10.1016/j.orggeochem.2024.104884","DOIUrl":"10.1016/j.orggeochem.2024.104884","url":null,"abstract":"<div><div>It is widely accepted that organic–inorganic interactions involving hydrogen-rich fluids (H<sub>2</sub>O and H<sub>2</sub>) play a significant role in hydrocarbon (HC) generation in sedimentary basins, and the effects of hydrogenation of organic matter (OM) by H<sub>2</sub>O/H<sub>2</sub> on C/H isotope fractionation remain poorly understood. This study investigates these effects through a series of pyrolysis experiments conducted at 330–420 °C and 50 MPa, encompassing three groups: (1) anhydrous pyrolysis with kerogen only (Group 1), (2) kerogen and H<sub>2</sub>O (Group 2), and (3) kerogen, H<sub>2</sub>O, and Fe<sub>1-</sub><em><sub>x</sub></em>S (Group 3). Groups 2 and 3 were designed to simulate hydrogenation of OM by H<sub>2</sub>O and H<sub>2</sub>, respectively. Results show that HC gas yields in Group 3 experiments are 1.8 to 3.2 times of those in Group 1, while yields in Group 2 are lower than Group 1. Moreover, hydrogenation by H<sub>2</sub> produces HC gases with smaller <sup>13</sup>C fractionation and more negative δ<sup>2</sup>H values compared to hydrogenation by H<sub>2</sub>O. These findings suggest distinct mechanisms for HC gas generation during H<sub>2</sub>-OM and H<sub>2</sub>O-OM reactions. Further analysis demonstrates that the equilibrium isotope effect (EIE) governs <sup>13</sup>C and <sup>2</sup>H isotope fractionation during hydrogenation of OM by H<sub>2</sub>. Importantly, the EIE for <sup>2</sup>H isotope fractionation of H<sub>2</sub>O-H<sub>2</sub>, CH<sub>4</sub>-H<sub>2</sub>, and OM-H<sub>2</sub> is evaluated under both experimental and geological conditions. This study provides crucial insights into the significant influence of hydrogenation of OM by H<sub>2</sub> on the generation and C/H isotopic fractionation of HC gases, as well as the evolution and preservation of H<sub>2</sub> in organic-rich shales.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"199 ","pages":"Article 104884"},"PeriodicalIF":2.6,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142699708","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}
Pub Date : 2024-11-16DOI: 10.1016/j.orggeochem.2024.104897
Moazame Mesgar , Seyedahmad Kia , Paul R. Voroney , Andy Lo , Adam W. Gillespie
Research on soil organic matter (SOM) in its natural state is vital for comprehending the mechanisms governing soil stability and carbon cycling, crucial in addressing global climate change. We utilized solid-state 13C nuclear magnetic resonance (NMR) spectroscopy on HF treated samples, along with a 260-day laboratory mineralization experiment and thermal analysis-programmed pyrolysis (PP) to evaluate SOM biodegradability and thermal stability. To cover the potential range of organic carbon variability, we selected samples from three land uses and soil types, featuring total organic carbon levels from 1% to 39%. Our analysis confirmed the substantial contribution of non-protonated aromatic-carbon not bonded to oxygen to SOM’s biological and thermal stability, constituting approximately 14–21% of soil organic carbon. These components exhibited a strong correlation with SOM stability matrices, such as thermal stability and oxygen index determined by PP. Samples with a higher prevalence of these components also displayed the lowest cumulative carbon mineralization. These findings enhance our understanding of the stable SOM pool, aiding in the identification of sustainable soil management practices to mitigate climate change impacts on soil health and carbon dynamics.
{"title":"Role of aromatic and non-protonated aromatic carbon in the stability of soil organic matter","authors":"Moazame Mesgar , Seyedahmad Kia , Paul R. Voroney , Andy Lo , Adam W. Gillespie","doi":"10.1016/j.orggeochem.2024.104897","DOIUrl":"10.1016/j.orggeochem.2024.104897","url":null,"abstract":"<div><div>Research on soil organic matter (SOM) in its natural state is vital for comprehending the mechanisms governing soil stability and carbon cycling, crucial in addressing global climate change. We utilized solid-state <sup>13</sup>C nuclear magnetic resonance (NMR) spectroscopy on HF treated samples, along with a 260-day laboratory mineralization experiment and thermal analysis-programmed pyrolysis (PP) to evaluate SOM biodegradability and thermal stability. To cover the potential range of organic carbon variability, we selected samples from three land uses and soil types, featuring total organic carbon levels from 1% to 39%. Our analysis confirmed the substantial contribution of non-protonated aromatic-carbon not bonded to oxygen to SOM’s biological and thermal stability, constituting approximately 14–21% of soil organic carbon. These components exhibited a strong correlation with SOM stability matrices, such as thermal stability and oxygen index determined by PP. Samples with a higher prevalence of these components also displayed the lowest cumulative carbon mineralization. These findings enhance our understanding of the stable SOM pool, aiding in the identification of sustainable soil management practices to mitigate climate change impacts on soil health and carbon dynamics.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"201 ","pages":"Article 104897"},"PeriodicalIF":2.6,"publicationDate":"2024-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143145023","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}
Carbazoles in Ordovician ultra-deep marine oil from the FI17 fault zone in Fuman oilfield (Tarim Basin) were separated using a recently proposed silica gel column chromatographic method and the enriched fractions were analyzed by GC–MS. Biomarker and carbon isotope signatures revealed that all oil in the study area was produced from the same source rock and that compositional differences can be attributed to thermal maturation. The convergent ratios of N-H shielded isomers/N-H half shielded isomers and benzo[a]carbazole/(benzo[a]carbazole + benzo[c]carbazole) suggested that carbazoles in crude oil had not been affected by vertical migration. Therefore, thermal maturity was identified as the main controlling factor affecting chages of carbazole concentrations and ratios in crude oil. The concentrations of the total carbazole and its three isomers (N-H shielded isomers, N-H half shielded isomers and exposed isomers) in crude oil decreased sharply with increasing maturity. The 1,8-dimethylcarbazole/carbazole (1,8-MCa/Ca) and 1,8-dimethylcarbazole/2,4-dimethylcarbazole (1,8-MCa/2,4-MCa) ratios showed significant correlation with maturity expressed as %VRE (the vitrinite reflectance equivalent converted from MPI1 and MPR) when %VRE is <1.2 %. Similar trends were observed in the 1-methylcarbazole/3-methylcarbazole (1-MCa/3-MCa) as well as 1,8-dimethylcarbazole/2,6- dimethylcarbazole (1,8-DMCa/2,6-DMCa), (1,5- dimethylcarbazole + 3-ethylcarbazole)/2, 6-dimethylcarbazole ((1, 5-DMCa + 3-ECa)/2, 6-DMCa), and (1, 4-dimethylcarbazole + 4-ethylcarbazole)/2, 6-dimethylcarbazole ((1, 4-DMCa + 4-ECa)/2, 6-DMCa) when the %VRE of crude oil exceeds 1.0 %. This indicated that the concentrations and ratios of carbazole can be used to qualitatively evaluate crude oil maturity. The ratio of 1,8-dimethylcarbazole/1-ethylcarbazole (1,8-DMCa/1-ECa) showed a strict linear relationship with %VRE. The maturity of marine oil can be calculated using the formulas %Rc (the vitrinite reflectance equivalent calculated from MPI1) = −0.0335(1, 8-DMCa/1-ECa) + 1.2902 or %Rc1 (the vitrinite reflectance equivalent calculated from MPR) = −0.0405 (1, 8-DMCa/1-ECa) + 1.3418. The study can be helpful for exploring ultra-deep hydrocarbons and restoring the thermal history of source rocks in the Tarim Basin.
{"title":"Characteristics of carbazole compounds in ultra-deep marine oil from Fuman oilfield, Tarim Basin: Significance for thermal maturity assessment of crude oil","authors":"Zhongdeng Lu , Hongwei Ping , Honghan Chen , Zulin Chen , Yanqiu Zhang , Zhou Xie , Yintao Zhang , Xu Chen","doi":"10.1016/j.orggeochem.2024.104895","DOIUrl":"10.1016/j.orggeochem.2024.104895","url":null,"abstract":"<div><div>Carbazoles in Ordovician ultra-deep marine oil from the F<sub>I</sub>17 fault zone in Fuman oilfield (Tarim Basin) were separated using a recently proposed silica gel column chromatographic method and the enriched fractions were analyzed by GC–MS. Biomarker and carbon isotope signatures revealed that all oil in the study area was produced from the same source rock and that compositional differences can be attributed to thermal maturation. The convergent ratios of N-H shielded isomers/N-H half shielded isomers and benzo[<em>a</em>]carbazole/(benzo[<em>a</em>]carbazole + benzo[<em>c</em>]carbazole) suggested that carbazoles in crude oil had not been affected by vertical migration. Therefore, thermal maturity was identified as the main controlling factor affecting chages of carbazole concentrations and ratios in crude oil. The concentrations of the total carbazole and its three isomers (N-H shielded isomers, N-H half shielded isomers and exposed isomers) in crude oil decreased sharply with increasing maturity. The 1,8-dimethylcarbazole/carbazole (1,8-MCa/Ca) and 1,8-dimethylcarbazole/2,4-dimethylcarbazole (1,8-MCa/2,4-MCa) ratios showed significant correlation with maturity expressed as %<em>VRE</em> (the vitrinite reflectance equivalent converted from MPI<sub>1</sub> and MPR) when %<em>VRE</em> is <1.2 %. Similar trends were observed in the 1-methylcarbazole/3-methylcarbazole (1-MCa/3-MCa) as well as 1,8-dimethylcarbazole/2,6- dimethylcarbazole (1,8-DMCa/2,6-DMCa), (1,5- dimethylcarbazole + 3-ethylcarbazole)/2, 6-dimethylcarbazole ((1, 5-DMCa + 3-ECa)/2, 6-DMCa), and (1, 4-dimethylcarbazole + 4-ethylcarbazole)/2, 6-dimethylcarbazole ((1, 4-DMCa + 4-ECa)/2, 6-DMCa) when the %<em>VRE</em> of crude oil exceeds 1.0 %. This indicated that the concentrations and ratios of carbazole can be used to qualitatively evaluate crude oil maturity. The ratio of 1,8-dimethylcarbazole/1-ethylcarbazole (1,8-DMCa/1-ECa) showed a strict linear relationship with %<em>VRE</em>. The maturity of marine oil can be calculated using the formulas <em>%R</em>c (the vitrinite reflectance equivalent calculated from MPI<sub>1</sub>) = −0.0335(1, 8-DMCa/1-ECa) + 1.2902 or <em>%R</em>c<sub>1</sub> (the vitrinite reflectance equivalent calculated from MPR) = −0.0405 (1, 8-DMCa/1-ECa) + 1.3418. The study can be helpful for exploring ultra-deep hydrocarbons and restoring the thermal history of source rocks in the Tarim Basin.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104895"},"PeriodicalIF":2.6,"publicationDate":"2024-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652441","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}
Pub Date : 2024-11-10DOI: 10.1016/j.orggeochem.2024.104881
Bin Cheng , Zhiwei Wei , Yiman Zhang , Hanyu Deng , Yuxian Li , Haozhe Wang , Zewen Liao
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 °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 2H enrichment follows the order δ2H1-MD < δ2H5-MT < δ2H1-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 δ2H value of higher aromatic-ring-number 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.
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