Pub Date : 2025-12-01DOI: 10.1016/j.orggeochem.2025.105096
Daowei Wang , Chunfang Cai , Haijun Yang , Zicheng Cao , Qinghua Wang , Hao Zhang , Peng Sun , Weiquan Zhao , Wei Wang , Zhengzhong Liang , Haoyu Zhang , Qinghua Zheng
The origin of Paleozoic oils in the cratonic Tarim Basin, China, has long been debated, with previous studies attributing most oils to the Cambrian sources. However, the geochemical characteristics and distribution of the Ordovician-sourced oils remain poorly constrained. This study integrates biomarkers, carbon isotopes, and sulfur isotopes to identify the Ordovician-derived oils in the western part of the Shuntuoguole Low Uplift. Two oils (SHB7 and SHB71X) produced from the Ordovician exhibit distinct geochemical signatures, including the absence of aryl isoprenoids, high concentrations of C30 diahopane, elevated Pr/Ph ratios, and low DBT/P ratios, indicative of a clay-rich, suboxic depositional environment. Critically, these oils display significantly lighter bulk δ34S values (4.0‰ and –1.6‰), which closely match those of the Middle-Upper Ordovician kerogen (–6.7‰ to 5.6‰) and are distinctly lower than the Cambrian-sourced oils (15.8‰ to 23.2‰). Individual n-alkanes δ13C compositions further support a different genetic origin compared to the typical Cambrian-derived oils. These findings confirm the existence of a previously unrecognized Ordovician-sourced petroleum system in the basin. The distribution of such oils is likely controlled by migration from the Ordovician source kitchens in the Awati Depression or intra-platform depressions. This study underscores the superiority of sulfur isotopes over conventional biomarkers in resolving complex oil-source correlations in multi-source basins like Tarim.
{"title":"Definitive identification of Ordovician-sourced oils in the Tarim Basin: geochemical constraints from biomarkers and sulfur isotopes","authors":"Daowei Wang , Chunfang Cai , Haijun Yang , Zicheng Cao , Qinghua Wang , Hao Zhang , Peng Sun , Weiquan Zhao , Wei Wang , Zhengzhong Liang , Haoyu Zhang , Qinghua Zheng","doi":"10.1016/j.orggeochem.2025.105096","DOIUrl":"10.1016/j.orggeochem.2025.105096","url":null,"abstract":"<div><div>The origin of Paleozoic oils in the cratonic Tarim Basin, China, has long been debated, with previous studies attributing most oils to the Cambrian sources. However, the geochemical characteristics and distribution of the Ordovician-sourced oils remain poorly constrained. This study integrates biomarkers, carbon isotopes, and sulfur isotopes to identify the Ordovician-derived oils in the western part of the Shuntuoguole Low Uplift. Two oils (SHB7 and SHB71X) produced from the Ordovician exhibit distinct geochemical signatures, including the absence of aryl isoprenoids, high concentrations of C<sub>30</sub> diahopane, elevated Pr/Ph ratios, and low DBT/P ratios, indicative of a clay-rich, suboxic depositional environment. Critically, these oils display significantly lighter bulk δ<sup>34</sup>S values (4.0‰ and –1.6‰), which closely match those of the Middle-Upper Ordovician kerogen (–6.7‰ to 5.6‰) and are distinctly lower than the Cambrian-sourced oils (15.8‰ to 23.2‰). Individual <em>n</em>-alkanes δ<sup>13</sup>C compositions further support a different genetic origin compared to the typical Cambrian-derived oils. These findings confirm the existence of a previously unrecognized Ordovician-sourced petroleum system in the basin. The distribution of such oils is likely controlled by migration from the Ordovician source kitchens in the Awati Depression or intra-platform depressions. This study underscores the superiority of sulfur isotopes over conventional biomarkers in resolving complex oil-source correlations in multi-source basins like Tarim.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"210 ","pages":"Article 105096"},"PeriodicalIF":2.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145620421","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 : 2025-12-01DOI: 10.1016/j.orggeochem.2025.105095
Zongtang Yang , Biswaranjan Mohanty , Feike A. Dijkstra , Georg Guggenberger , Balwant Singh
Dissolved organic matter (DOM) is the most active and labile organic fraction in soils, participating in numerous biogeochemical processes. Comprehensive understanding of DOM composition at the molecular level remains a challenge due to limited or contrasting analytical data based on a single technique or limited analysis, which may be addressed using multiple complementary techniques. In this study, we utilized five prevalent and novel spectroscopic and spectrometric techniques, i.e., XPS, FTIR, NEXAFS, NMR, and FT-ICR-MS, coupled with multivariate analysis to decipher the complexity of DOM. We extracted DOM from four decomposed plant residues − pine, eucalyptus, pasture, and wheat. The organic carbon concentration in the DOM samples followed the order: pine > eucalyptus > wheat > pasture. Eucalyptus and pasture DOM exhibited similarities in aromatic compounds but differed in saturation and O-containing groups. Pine DOM was enriched in aromatic and carboxylic compounds, whereas wheat DOM contained more lipid and aliphatic compounds. The differences in the abundance of functional groups and compound families were attributed to the influence of both the original plant residues and microbial degradation. Chemical convergence of the four DOM samples, reflected by their broadly similar spectral composition was possibly due to similar biodegradation processes but in different stages. Multivariate analysis of multiple spectroscopic data comprehensively captured the DOM composition.
{"title":"Insights into the complex nature of dissolved organic matter from plant residues using multiple spectroscopic techniques","authors":"Zongtang Yang , Biswaranjan Mohanty , Feike A. Dijkstra , Georg Guggenberger , Balwant Singh","doi":"10.1016/j.orggeochem.2025.105095","DOIUrl":"10.1016/j.orggeochem.2025.105095","url":null,"abstract":"<div><div>Dissolved organic matter (DOM) is the most active and labile organic fraction in soils, participating in numerous biogeochemical processes. Comprehensive understanding of DOM composition at the molecular level remains a challenge due to limited or contrasting analytical data based on a single technique or limited analysis, which may be addressed using multiple complementary techniques. In this study, we utilized five prevalent and novel spectroscopic and spectrometric techniques, i.e., XPS, FTIR, NEXAFS, NMR, and FT-ICR-MS, coupled with multivariate analysis to decipher the complexity of DOM. We extracted DOM from four decomposed plant residues − pine, eucalyptus, pasture, and wheat. The organic carbon concentration in the DOM samples followed the order: pine > eucalyptus > wheat > pasture. Eucalyptus and pasture DOM exhibited similarities in aromatic compounds but differed in saturation and O-containing groups. Pine DOM was enriched in aromatic and carboxylic compounds, whereas wheat DOM contained more lipid and aliphatic compounds. The differences in the abundance of functional groups and compound families were attributed to the influence of both the original plant residues and microbial degradation. Chemical convergence of the four DOM samples, reflected by their broadly similar spectral composition was possibly due to similar biodegradation processes but in different stages. Multivariate analysis of multiple spectroscopic data comprehensively captured the DOM composition.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"210 ","pages":"Article 105095"},"PeriodicalIF":2.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145620424","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 : 2025-11-20DOI: 10.1016/j.orggeochem.2025.105090
Sanjukta Dhar, James M. Fulton
Porphyrin distributions were studied across 20 locations in the Western Canada Sedimentary Basin, particularly focusing on sediments deposited at the base of the Exshaw Shale, spanning the Devonian-Carboniferous boundary and contemporaneous with the Hangenberg mass extinction. Locations along a north–south transect represent thermally immature kerogen, while locations from east to west show a gradient of increasing thermal maturity. The study aimed to identify regional variability in syn-depositional environmental conditions and post-burial diagenesis influencing porphyrin preservation along the two transects. The relative abundance of three major categories of vanadyl porphyrins – cycloalkanoporphyrins, bicycloalkanoporphyrins, and etioporphyrins from the different sites exhibit notable spatial diversity, with the primary factor affecting their distribution being thermal maturity. Effects of paleoredox conditions and degree of organic matter decomposition were evaluated using trace element enrichments, thermal Rock Eval data, sterane and homohopane maturity indices.
{"title":"Paleoenvironmental and diagenetic effects on porphyrin distributions in the End-Devonian Exshaw Formation, Western Canada","authors":"Sanjukta Dhar, James M. Fulton","doi":"10.1016/j.orggeochem.2025.105090","DOIUrl":"10.1016/j.orggeochem.2025.105090","url":null,"abstract":"<div><div>Porphyrin distributions were studied across 20 locations in the Western Canada Sedimentary Basin, particularly focusing on sediments deposited at the base of the Exshaw Shale, spanning the Devonian-Carboniferous boundary and contemporaneous with the Hangenberg mass extinction. Locations along a north–south transect represent thermally immature kerogen, while locations from east to west show a gradient of increasing thermal maturity. The study aimed to identify regional variability in <em>syn</em>-depositional environmental conditions and post-burial diagenesis influencing porphyrin preservation along the two transects. The relative abundance of three major categories of vanadyl porphyrins – cycloalkanoporphyrins, bicycloalkanoporphyrins, and etioporphyrins from the different sites exhibit notable spatial diversity, with the primary factor affecting their distribution being thermal maturity. Effects of paleoredox conditions and degree of organic matter decomposition were evaluated using trace element enrichments, thermal Rock Eval data, sterane and homohopane maturity indices.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"210 ","pages":"Article 105090"},"PeriodicalIF":2.5,"publicationDate":"2025-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145575910","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}
The central Congo Basin is home to the world’s largest tropical peatland complex and is covered with swamp forest. In the face of climate change and future human activities in the region, it is important to understand the factors that determine the nature and dynamics of the peatland vegetation cover. One way to gain insight into these factors is to reconstruct the history of the central Congo Basin peatlands. Analysing lipid biomarkers extracted from peat cores such as plant wax n-alkanes enables past environmental and climatic conditions to be reconstructed. However, there is currently no information on how the production of plant waxes by different plant species influences the abundance and isotopic composition of n-alkanes in peat and other archives in the Congo Basin. In this study we analysed plant wax n-alkane abundances, δ13C and δD values according to photosynthetic pathways (C3 vs. C4), angiosperm subclasses (dicotyledons vs. monocotyledons), and source water δD values in the dominant plant types (trees, shrubs, and herbs) in the peatland area of the Cuvette Department in the Republic of the Congo. Our dataset enables the definition of a new n-alkane distribution index, named GRIND, that distinguishes between C3 (mostly dicotyledons) and C4 (monocotyledons) plants as follows: (n-C27 + n-C33 + n-C35)/(n-C25 + n-C27 + n-C29 + n-C31 + n-C33 + n-C35). This index may therefore be used to analyse Central African peat deposits and derive the relative abundance of C3 and C4 plant waxes in the past, independently of δ13C measurements. Furthermore, δ13C values from the central Congo Basin and other African sites suggest that environments with high relative humidity (> 80%) are characterised by very negative δ13C values (i.e., < –37‰) of n-C29 and n-C31 alkanes. This observation highlights the potential of n-alkane δ13C in deriving climatic information under high relative humidity conditions in Central African lowlands, and contribute to palaeo-climatic reconstructions. Finally, the δD values of n-C29 and n-C31 alkanes demonstrate that, despite contrasting apparent fractionation values associated with photosynthetic pathways and plant functional types — which can be accounted for using δ13C and pollen data in sedimentary deposits — they reliably reflect the δD of environmental water. This confirms that plant wax n-alkane δD values are effective tools for reconstructing palaeo-climatic changes in equatorial regions.
{"title":"Plant-wax n-alkanes from the central Congo Basin as palaeo-environmental and -climatic proxies","authors":"Mélanie Guardiola , Gaël U.D. Bouka , Carolia Abaye , Johanna Menges , Frauke Rostek , Guillaume Leduc , Edouard Bard , Enno Schefuß , Yannick Garcin","doi":"10.1016/j.orggeochem.2025.105092","DOIUrl":"10.1016/j.orggeochem.2025.105092","url":null,"abstract":"<div><div>The central Congo Basin is home to the world’s largest tropical peatland complex and is covered with swamp forest. In the face of climate change and future human activities in the region, it is important to understand the factors that determine the nature and dynamics of the peatland vegetation cover. One way to gain insight into these factors is to reconstruct the history of the central Congo Basin peatlands. Analysing lipid biomarkers extracted from peat cores such as plant wax <em>n-</em>alkanes enables past environmental and climatic conditions to be reconstructed. However, there is currently no information on how the production of plant waxes by different plant species influences the abundance and isotopic composition of <em>n-</em>alkanes in peat and other archives in the Congo Basin. In this study we analysed plant wax <em>n-</em>alkane abundances, δ<sup>13</sup>C and δD values according to photosynthetic pathways (C<sub>3</sub> vs. C<sub>4</sub>), angiosperm subclasses (dicotyledons vs. monocotyledons), and source water δD values in the dominant plant types (trees, shrubs, and herbs) in the peatland area of the Cuvette Department in the Republic of the Congo. Our dataset enables the definition of a new <em>n</em>-alkane distribution index, named GRIND, that distinguishes between C<sub>3</sub> (mostly dicotyledons) and C<sub>4</sub> (monocotyledons) plants as follows: (<em>n-</em>C<sub>27</sub> + <em>n-</em>C<sub>33</sub> + <em>n-</em>C<sub>35</sub>)/(<em>n-</em>C<sub>25</sub> + <em>n-</em>C<sub>27</sub> + <em>n-</em>C<sub>29</sub> + <em>n-</em>C<sub>31</sub> + <em>n-</em>C<sub>33</sub> + <em>n-</em>C<sub>35</sub>). This index may therefore be used to analyse Central African peat deposits and derive the relative abundance of C<sub>3</sub> and C<sub>4</sub> plant waxes in the past, independently of δ<sup>13</sup>C measurements. Furthermore, δ<sup>13</sup>C values from the central Congo Basin and other African sites suggest that environments with high relative humidity (> 80%) are characterised by very negative δ<sup>13</sup>C values (i.e., < –37‰) of <em>n-</em>C<sub>29</sub> and <em>n-</em>C<sub>31</sub> alkanes. This observation highlights the potential of <em>n-</em>alkane δ<sup>13</sup>C in deriving climatic information under high relative humidity conditions in Central African lowlands, and contribute to palaeo-climatic reconstructions. Finally, the δD values of <em>n</em>-C<sub>29</sub> and <em>n</em>-C<sub>31</sub> alkanes demonstrate that, despite contrasting apparent fractionation values associated with photosynthetic pathways and plant functional types — which can be accounted for using δ<sup>13</sup>C and pollen data in sedimentary deposits — they reliably reflect the δD of environmental water. This confirms that plant wax <em>n</em>-alkane δD values are effective tools for reconstructing palaeo-climatic changes in equatorial regions.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"212 ","pages":"Article 105092"},"PeriodicalIF":2.5,"publicationDate":"2025-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145659138","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 : 2025-11-17DOI: 10.1016/j.orggeochem.2025.105089
Tian Ao , Xianxin Meng , Hong Lu , Youping Zhou , Ping’an Peng
Trimethyl aryl isoprenoids (TMAIPs) provide significant insights into the biological and geochemical processes in modern and ancient aquatic environments. Obtaining carbon isotope (δ13C) data for these carotenoid-derived biomarkers can greatly enhance their interpretative value, as non-sulfur bacterial sources can be distinguished by their carbon isotope compositions from sulfur bacterial sources. However, δ13C measurement for individual TMAIPs is particularly challenging due to their low relative abundance in complex hydrocarbon mixtures. We present an argentated (with silver nitrate) silica gel column chromatography (Ag-CC)-based method for isolation of TMAIPs in the aromatic hydrocarbon fraction of crude oils. The effectiveness of the method was demonstrated by the successful isolation of the co-occurring 2,3,6- & 2,3,4- TMAIPs in two crude oil samples sourced from the hypersaline lacustrine environment of the Jianghan Basin in China, enabling reliable δ13C and δ2H analysis for the TMAIPs and other target biomarkers such as n-alkyl benzenes. The δ13C values of the 2,3,6-TMAIPs (−19.4‰ to −17.2‰) were found to be significantly higher than those of the 2,3,4-TMAIPs (−25.9‰ to −20.8‰), but the δ2H values of the 2,3,6-TMAIPs (−187.4‰ to −171.7‰) were significantly lower than those of the 2,3,4-TMAIPs (−140.3‰ to −106.7‰). Future work should be focused on the elucidation of the controlling factors of the TMAIPs isotopic compositions (promised by the new technique) and their broader geological implications.
{"title":"Isolation of 2,3,6- & 2,3,4-trimethyl aryl isoprenoids using argentation silica gel column chromatography for compound-specific isotopic analysis","authors":"Tian Ao , Xianxin Meng , Hong Lu , Youping Zhou , Ping’an Peng","doi":"10.1016/j.orggeochem.2025.105089","DOIUrl":"10.1016/j.orggeochem.2025.105089","url":null,"abstract":"<div><div>Trimethyl aryl isoprenoids (TMAIPs) provide significant insights into the biological and geochemical processes in modern and ancient aquatic environments. Obtaining carbon isotope (δ<sup>13</sup>C) data for these carotenoid-derived biomarkers can greatly enhance their interpretative value, as non-sulfur bacterial sources can be distinguished by their carbon isotope compositions from sulfur bacterial sources. However, δ<sup>13</sup>C measurement for individual TMAIPs is particularly challenging due to their low relative abundance in complex hydrocarbon mixtures. We present an argentated (with silver nitrate) silica gel column chromatography (Ag-CC)-based method for isolation of TMAIPs in the aromatic hydrocarbon fraction of crude oils. The effectiveness of the method was demonstrated by the successful isolation of the co-occurring 2,3,6- & 2,3,4- TMAIPs in two crude oil samples sourced from the hypersaline lacustrine environment of the Jianghan Basin in China, enabling reliable δ<sup>13</sup>C and δ<sup>2</sup>H analysis for the TMAIPs and other target biomarkers such as <em>n</em>-alkyl benzenes. The δ<sup>13</sup>C values of the 2,3,6-TMAIPs (−19.4‰ to −17.2‰) were found to be significantly higher than those of the 2,3,4-TMAIPs (−25.9‰ to −20.8‰), but the δ<sup>2</sup>H values of the 2,3,6-TMAIPs (−187.4‰ to −171.7‰) were significantly lower than those of the 2,3,4-TMAIPs (−140.3‰ to −106.7‰). Future work should be focused on the elucidation of the controlling factors of the TMAIPs isotopic compositions (promised by the new technique) and their broader geological implications.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"210 ","pages":"Article 105089"},"PeriodicalIF":2.5,"publicationDate":"2025-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145575909","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}
This study presents the results of an investigation into the distribution patterns of C3- and C4-alkylbenzenes in oils derived from hydrocarbon source rocks of varying geological age and origin. The study utilized analytical results from 515 oil samples collected from wells at 199 fields across various petroleum basins of Eurasia, most of which are located in Russia (including the West Siberian Basin, Siberian Platform (or Eastern Siberia), Northwestern Greater Caucasus, Middle Caspian, Sakhalin, Volga-Ural Basin, Timan-Pechora Basin, and the Baltic Basin (Kaliningrad), Belarus (Pripyat Trough), and Africa (Eastern Algeria). These samples cover a wide range of oil ages and genetic diversity. The obtained results significantly advance our understanding of the relationships between C3- and C4-alkylbenzene compositions in oils and the following factors: redox conditions during deposition of the source organic matter, photic zone anoxia in the depositional basin, type of primary producers, age of source rocks, and catagenesis. Linear discriminant analysis (LDA) was applied to characterize C3- and C4-alkylbenzene distributions in two variants based on: 1) genetic grouping of oils and 2) grouping by Pr/Ph values and tert-butylbenzene content. To enable global application of LDA models, we publish key foundational data − including analytical workflow, minimum/maximum relative concentration ranges, and discriminant function coefficients − enabling researchers to apply this framework to any petroleum basin worldwide. C4-alkylbenzenes are benzene derivatives of terpenoids and may have direct biological origins or originate from higher molecular weight components (e.g., aryl carotenoids). Consequently, they exhibit superior discriminative power for classifying oils into genetic groups compared to C3-alkylbenzenes. Oils with the most distinctive C4-alkylbenzene composition originate from (1) the Bazhenov Formation (West Siberia), (2) Domanik deposits of the Volga-Ural and Timan-Pechora basins, (3) non-marine Jurassic sequences in Western Siberia and the Greater Caucasus northwest, and (4) reservoirs of the Nepa-Botuoba Anteclise (Siberian Platform). The study revealed significant concentrations of tert-butylbenzene, which were detected in oils from: the Baikit Anteclise (Riphean age), Baltic Syneclise (Cambrian–Ordovician–Silurian), selected Algerian fields (Silurian–Devonian) and in isolated Palaeozoic-sourced oils of Western Siberia. Components that have a decisive influence on the position of the oils in the discriminant function coordinates were identified; these components can characterize source organic matter, its age, and redox conditions.
{"title":"Composition and distributional patterns of C3- and C4-alkylbenzenes in oils and source rocks from Meso–Neoproterozoic to Cenozoic","authors":"N.V. Oblasov , I.V. Eftor , I.V. Goncharov , S.V. Fadeeva","doi":"10.1016/j.orggeochem.2025.105091","DOIUrl":"10.1016/j.orggeochem.2025.105091","url":null,"abstract":"<div><div>This study presents the results of an investigation into the distribution patterns of C<sub>3</sub>- and C<sub>4</sub>-alkylbenzenes in oils derived from hydrocarbon source rocks of varying geological age and origin. The study utilized analytical results from 515 oil samples collected from wells at 199 fields across various petroleum basins of Eurasia, most of which are located in Russia (including the West Siberian Basin, Siberian Platform (or Eastern Siberia), Northwestern Greater Caucasus, Middle Caspian, Sakhalin, Volga-Ural Basin, Timan-Pechora Basin, and the Baltic Basin (Kaliningrad), Belarus (Pripyat Trough), and Africa (Eastern Algeria). These samples cover a wide range of oil ages and genetic diversity. The obtained results significantly advance our understanding of the relationships between C<sub>3</sub>- and C<sub>4</sub>-alkylbenzene compositions in oils and the following factors: redox conditions during deposition of the source organic matter, photic zone anoxia in the depositional basin, type of primary producers, age of source rocks, and catagenesis. Linear discriminant analysis (LDA) was applied to characterize C<sub>3</sub>- and C<sub>4</sub>-alkylbenzene distributions in two variants based on: 1) genetic grouping of oils and 2) grouping by Pr/Ph values and <em>tert</em>-butylbenzene content. To enable global application of LDA models, we publish key foundational data − including analytical workflow, minimum/maximum relative concentration ranges, and discriminant function coefficients − enabling researchers to apply this framework to any petroleum basin worldwide. C<sub>4</sub>-alkylbenzenes are benzene derivatives of terpenoids and may have direct biological origins or originate from higher molecular weight components (e.g., aryl carotenoids). Consequently, they exhibit superior discriminative power for classifying oils into genetic groups compared to C<sub>3</sub>-alkylbenzenes. Oils with the most distinctive C<sub>4</sub>-alkylbenzene composition originate from (1) the Bazhenov Formation (West Siberia), (2) Domanik deposits of the Volga-Ural and Timan-Pechora basins, (3) non-marine Jurassic sequences in Western Siberia and the Greater Caucasus northwest, and (4) reservoirs of the Nepa-Botuoba Anteclise (Siberian Platform). The study revealed significant concentrations of <em>tert</em>-butylbenzene, which were detected in oils from: the Baikit Anteclise (Riphean age), Baltic Syneclise (Cambrian–Ordovician–Silurian), selected Algerian fields (Silurian–Devonian) and in isolated Palaeozoic-sourced oils of Western Siberia. Components that have a decisive influence on the position of the oils in the discriminant function coordinates were identified; these components can characterize source organic matter, its age, and redox conditions.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"210 ","pages":"Article 105091"},"PeriodicalIF":2.5,"publicationDate":"2025-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145575911","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 : 2025-11-07DOI: 10.1016/j.orggeochem.2025.105085
Tharika Liyanage , Lennart M. van Maldegem , Janet Hope , Philippe Schaeffer , Pierre Adam , Hans Peter Nytoft , Dianne Edwards , Jochen Brocks
Tricyclic and tetracyclic terpane ratios are used as biomarker proxies for depositional environments and to classify crude oils and source rocks. However, the biological precursors and diagenetic drivers of these proxies are not well understood. This study reports on the discovery of tricyclic and tetracyclic breakdown products of pentacyclic hopanoids that co-elute with 14α-C19 and βα-C20–C22 cheilanthanes and C24 tetracyclic terpane in gas chromatograms. This includes hopanoid breakdown products (HBPs) that are identical to 14α-C19 cheilanthane and C24 tetracyclic terpane, biomarkers that are commonly used as indicators of terrigenous organic matter in source rocks and their derived hydrocarbon products. These HBPs were generated by pyrolysis of C30 diplopterol, a common compound found in the cell membranes of almost all hopanoid-producing bacteria, some lichens and higher plants. HBPs are common in rock-extracted bitumens and crude oils from the Neoproterozoic to the Cenozoic and across a wide range of thermal maturities. Comparison of the relative abundance of HBPs and cheilanthanes against commonly used tricyclic and tetracyclic terpane parameters shows that HBPs can drive or strongly influence terpane-based paleoenvironmental proxies. This study begins to rationalise why some of these parameters indicate specific depositional environments and proposes new ratios that quantify the impact of HBPs on biomarker proxies.
{"title":"Hopanoid breakdown products (HBPs) and their influence on tetracyclic and tricyclic terpane (cheilanthane) oil-source rock parameters","authors":"Tharika Liyanage , Lennart M. van Maldegem , Janet Hope , Philippe Schaeffer , Pierre Adam , Hans Peter Nytoft , Dianne Edwards , Jochen Brocks","doi":"10.1016/j.orggeochem.2025.105085","DOIUrl":"10.1016/j.orggeochem.2025.105085","url":null,"abstract":"<div><div>Tricyclic and tetracyclic terpane ratios are used as biomarker proxies for depositional environments and to classify crude oils and source rocks. However, the biological precursors and diagenetic drivers of these proxies are not well understood. This study reports on the discovery of tricyclic and tetracyclic breakdown products of pentacyclic hopanoids that co-elute with 14α-C<sub>19</sub> and βα-C<sub>20</sub>–C<sub>22</sub> cheilanthanes and C<sub>24</sub> tetracyclic terpane in gas chromatograms. This includes hopanoid breakdown products (HBPs) that are identical to 14α-C<sub>19</sub> cheilanthane and C<sub>24</sub> tetracyclic terpane, biomarkers that are commonly used as indicators of terrigenous organic matter in source rocks and their derived hydrocarbon products. These HBPs were generated by pyrolysis of C<sub>30</sub> diplopterol, a common compound found in the cell membranes of almost all hopanoid-producing bacteria, some lichens and higher plants. HBPs are common in rock-extracted bitumens and crude oils from the Neoproterozoic to the Cenozoic and across a wide range of thermal maturities. Comparison of the relative abundance of HBPs and cheilanthanes against commonly used tricyclic and tetracyclic terpane parameters shows that HBPs can drive or strongly influence terpane-based paleoenvironmental proxies. This study begins to rationalise why some of these parameters indicate specific depositional environments and proposes new ratios that quantify the impact of HBPs on biomarker proxies.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"210 ","pages":"Article 105085"},"PeriodicalIF":2.5,"publicationDate":"2025-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145474236","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 : 2025-11-06DOI: 10.1016/j.orggeochem.2025.105088
Aljasil Chirakkal , Ekaterina Kulakova , Calin C. Steindal , Jago J. Birk , Anton Anoikin , Redzhep Kurbanov , Petr Sosin , Peixian Shu , David K. Wright
This study presents a multi‑proxy investigation of loess–paleosol sequences from the Khovaling Loess Plateau (KLP) in Southern Tajikistan to explore long‑term human-environment interactions during the Middle Pleistocene. This region has been the focus of numerous archaeological projects since Soviet times, as it contains evidence of some of the oldest (∼0.9 Ma) hominin occupations in Central Asia and is one of the key regions connecting eastern Asia to centers of hominin evolution that lie to the west. Previous archaeological expeditions have discovered rich collections of stone tools from alternating non-pedogenically modified loess and paleosol sequences at the archaeological sites of Karatau, Lakhuti, Obi-Mazar, and Kuldura. We analyzed lipid biomarkers such as n‑alkanes, polycyclic aromatic hydrocarbons (PAHs), together with newly generated stable isotopes (δ13C, δ15N), magnetic susceptibility, and archaeological assemblages from three sites: Obi-Mazar/Lakhuti (on‑site), and non-artifact-bearing strata from Kuldara (near‑site) and Khonako‑II (off‑site), focusing on pedocomplexes (PCs) 4, 5, and 6 and their intercalated loess layers. High odd-over-even predominance (OEP) and average chain lengths (ACL) suggest that soil organic matter is predominantly derived from higher-order terrestrial plants, with better preservation in paleosols compared to loess layers. The inverse correlations of δ13C with TOC and C/N reflect organic matter degradation, while elevated δ15N in paleosols suggests enhanced nitrogen cycling under warmer and drier conditions. Magnetic susceptibility and δ13C trends reveal a progressive shift toward open grassland ecosystems since ∼0.8 Ma, with intensified pedogenesis during interglacial stages MIS 11, 13, and 15. The spatial distribution of PAH concentrations and lithic artifact densities further highlights human-environment interactions in the KLP locality. Obi-Mazar exhibits abundant lithic materials and high PAH levels, indicating repeated occupation and frequent burning in a resource‑rich riverine setting. Kuldara exhibits moderate PAHs but minimal artifacts, whereas Khonako-II records only a minimal level of signals, reflecting a decrease in human impact with distance from the water source. Together, these findings demonstrate that Early Paleolithic hominins preferentially occupied ecologically stable, pedogenically developed zones during interglacial phases, contributing to localized fire regimes and shaping their landscapes. This study provides a refined paleoenvironmental framework for understanding hominin adaptations in Central Asia during the Middle Pleistocene.
{"title":"Geochemical records from loess sediments provide insights into early hominin influence on the landscape in the Khovaling region of Southern Tajikistan, Central Asia","authors":"Aljasil Chirakkal , Ekaterina Kulakova , Calin C. Steindal , Jago J. Birk , Anton Anoikin , Redzhep Kurbanov , Petr Sosin , Peixian Shu , David K. Wright","doi":"10.1016/j.orggeochem.2025.105088","DOIUrl":"10.1016/j.orggeochem.2025.105088","url":null,"abstract":"<div><div>This study presents a multi‑proxy investigation of loess–paleosol sequences from the Khovaling Loess Plateau (KLP) in Southern Tajikistan to explore long‑term human-environment interactions during the Middle Pleistocene. This region has been the focus of numerous archaeological projects since Soviet times, as it contains evidence of some of the oldest (∼0.9 Ma) hominin occupations in Central Asia and is one of the key regions connecting eastern Asia to centers of hominin evolution that lie to the west. Previous archaeological expeditions have discovered rich collections of stone tools from alternating non-pedogenically modified loess and paleosol sequences at the archaeological sites of Karatau, Lakhuti, Obi-Mazar, and Kuldura. We analyzed lipid biomarkers such as <em>n</em>‑alkanes, polycyclic aromatic hydrocarbons (PAHs), together with newly generated stable isotopes (δ<sup>13</sup>C, δ<sup>15</sup>N), magnetic susceptibility, and archaeological assemblages from three sites: Obi-Mazar/Lakhuti (on‑site), and non-artifact-bearing strata from Kuldara (near‑site) and Khonako‑II (off‑site), focusing on pedocomplexes (PCs) 4, 5, and 6 and their intercalated loess layers. High odd-over-even predominance (OEP) and average chain lengths (ACL) suggest that soil organic matter is predominantly derived from higher-order terrestrial plants, with better preservation in paleosols compared to loess layers. The inverse correlations of δ<sup>13</sup>C with TOC and C/N reflect organic matter degradation, while elevated δ<sup>15</sup>N in paleosols suggests enhanced nitrogen cycling under warmer and drier conditions. Magnetic susceptibility and δ<sup>13</sup>C trends reveal a progressive shift toward open grassland ecosystems since ∼0.8 Ma, with intensified pedogenesis during interglacial stages MIS 11, 13, and 15. The spatial distribution of PAH concentrations and lithic artifact densities further highlights human-environment interactions in the KLP locality. Obi-Mazar exhibits abundant lithic materials and high PAH levels, indicating repeated occupation and frequent burning in a resource‑rich riverine setting. Kuldara exhibits moderate PAHs but minimal artifacts, whereas Khonako-II records only a minimal level of signals, reflecting a decrease in human impact with distance from the water source. Together, these findings demonstrate that Early Paleolithic hominins preferentially occupied ecologically stable, pedogenically developed zones during interglacial phases, contributing to localized fire regimes and shaping their landscapes. This study provides a refined paleoenvironmental framework for understanding hominin adaptations in Central Asia during the Middle Pleistocene.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"212 ","pages":"Article 105088"},"PeriodicalIF":2.5,"publicationDate":"2025-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145787553","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 : 2025-10-27DOI: 10.1016/j.orggeochem.2025.105086
Hatice Kara , Mehmet Ali Ertürk , Leyla Kalender , Cihan Yalçın , Mehmet Deniz Turan , Emine Cicioğlu Sütçü
This study examines the stable carbon (δ13C) and nitrogen (δ15N) isotope compositions of coal samples from the Upper Miocene–Pliocene (Neogene) Elbistan Basin, Turkey, to constrain the sources of organic matter and the depositional conditions of peat formation. A vertical sequence of samples collected from the Kışlaköy open-pit mine was analysed for total carbon and nitrogen contents, C/N ratios, and δ13C–δ15N values. The δ13C values range from −28.09 ‰ to −16.99 ‰, while δ15N values vary between 1.97 ‰ and 4.99 ‰. The carbon isotope data indicate a predominantly C3-type plant origin for the organic matter, with minor C4 contributions inferred from samples exhibiting enriched δ13C signatures. Although some δ13C enrichment may partly reflect microbial alteration of organic matter, the overall values remain consistent with a dominant C3 vegetation signal. Elevated δ15N values suggest fluctuating redox conditions and microbial nitrogen cycling during peat accumulation. In comparison with other Turkish lignite basins and global coal deposits, the Elbistan samples display a broader isotopic range, reflecting a more complex paleoenvironmental evolution. The data suggest that the coal beds formed mainly in freshwater mire settings, where fluctuating water tables, variable redox conditions, and occasional inputs from C4 plants influenced peat accumulation. These results provide new insights into the paleobotanical and geochemical history of the basin and demonstrate the value of stable isotope analysis for reconstructing depositional environments in coal-bearing successions.
{"title":"Isotopic signatures of organic matter in the Upper Miocene–Pliocene Elbistan coal seam (Turkey): Insights from δ13C and δ15N variability","authors":"Hatice Kara , Mehmet Ali Ertürk , Leyla Kalender , Cihan Yalçın , Mehmet Deniz Turan , Emine Cicioğlu Sütçü","doi":"10.1016/j.orggeochem.2025.105086","DOIUrl":"10.1016/j.orggeochem.2025.105086","url":null,"abstract":"<div><div>This study examines the stable carbon (δ<sup>13</sup>C) and nitrogen (δ<sup>15</sup>N) isotope compositions of coal samples from the Upper Miocene–Pliocene (Neogene) Elbistan Basin, Turkey, to constrain the sources of organic matter and the depositional conditions of peat formation. A vertical sequence of samples collected from the Kışlaköy open-pit mine was analysed for total carbon and nitrogen contents, C/N ratios, and δ<sup>13</sup>C–δ<sup>15</sup>N values. The δ<sup>13</sup>C values range from −28.09 ‰ to −16.99 ‰, while δ<sup>15</sup>N values vary between 1.97 ‰ and 4.99 ‰. The carbon isotope data indicate a predominantly C<sub>3</sub>-type plant origin for the organic matter, with minor C<sub>4</sub> contributions inferred from samples exhibiting enriched δ<sup>13</sup>C signatures. Although some δ<sup>13</sup>C enrichment may partly reflect microbial alteration of organic matter, the overall values remain consistent with a dominant C<sub>3</sub> vegetation signal. Elevated δ<sup>15</sup>N values suggest fluctuating redox conditions and microbial nitrogen cycling during peat accumulation. In comparison with other Turkish lignite basins and global coal deposits, the Elbistan samples display a broader isotopic range, reflecting a more complex paleoenvironmental evolution. The data suggest that the coal beds formed mainly in freshwater mire settings, where fluctuating water tables, variable redox conditions, and occasional inputs from C<sub>4</sub> plants influenced peat accumulation. These results provide new insights into the paleobotanical and geochemical history of the basin and demonstrate the value of stable isotope analysis for reconstructing depositional environments in coal-bearing successions.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"210 ","pages":"Article 105086"},"PeriodicalIF":2.5,"publicationDate":"2025-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145413424","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}
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