Pub Date : 2025-10-01Epub Date: 2025-09-01DOI: 10.1016/j.orggeochem.2025.105059
Weiqing Liu , Haiyang Li , Yu Qiao , Wei Wu , Jienan Pan , Chuanlong Mou , Jianxin Yao , Yao Chen , Changsong Lin
Shale gas geochemical characteristics are critical for genetic identification and enrichment mechanism analysis. Current research focuses predominantly on marine shale gas, whereas studies on transitional shale gas (particularly the Permian Longtan Formation in South China) remain relatively limited, which constrains our understanding of the geochemical characteristics and genesis of transitional shale gases. The geochemical characteristics of transitional shale gas from the upper Permian Longtan Formation in western Hubei Province indicate that the organic matter is predominantly sapropelic, with some humic organic matter. The gas composition of the Longtan Formation consists primarily of CH4, with a low content of C2H6. The δ13CCH4 values range from −25.40 ‰ to −21.70 ‰, the δ13CC2H6 values range from –32.00 ‰ to −27.02 ‰, and the δ2HCH4 values range from −124.01 ‰ to −119.46 ‰. These findings imply that shale gas is composed mainly of oil-type gas of thermal origin, with a potentially minor presence of mixed gas. Isotope analysis of the shale gas reveals that it has undergone reversal (δ13CCH4 > δ13CC2H6), which is attributed to the cracking of liquid hydrocarbons under overmature conditions. The CO2 content ranges from 0.21 % to 2.33 % and the δ13CCO2 values range from −21.80 ‰ to −19.00 ‰, suggesting that the CO2 in the study area is of organic thermal origin. Additionally, a geochemical evolution pattern suggests that the gas composition of different sedimentary phases is controlled by the type of kerogen and the degree of thermal evolution. The multistage cracking of organic matter thermal evolution products caused the dynamic changes in carbon isotopes.
{"title":"Geochemical characteristics of Longtan transitional shale gas in the western Hubei Basin, northwest Middle Yangtze Block: Implications for the origin and carbon isotopes","authors":"Weiqing Liu , Haiyang Li , Yu Qiao , Wei Wu , Jienan Pan , Chuanlong Mou , Jianxin Yao , Yao Chen , Changsong Lin","doi":"10.1016/j.orggeochem.2025.105059","DOIUrl":"10.1016/j.orggeochem.2025.105059","url":null,"abstract":"<div><div>Shale gas geochemical characteristics are critical for genetic identification and enrichment mechanism analysis. Current research focuses predominantly on marine shale gas, whereas studies on transitional shale gas (particularly the Permian Longtan Formation in South China) remain relatively limited, which constrains our understanding of the geochemical characteristics and genesis of transitional shale gases. The geochemical characteristics of transitional shale gas from the upper Permian Longtan Formation in western Hubei Province indicate that the organic matter is predominantly sapropelic, with some humic organic matter. The gas composition of the Longtan Formation consists primarily of CH<sub>4</sub>, with a low content of C<sub>2</sub>H<sub>6</sub>. The δ<sup>13</sup>C<sub>CH4</sub> values range from −25.40 ‰ to −21.70 ‰, the δ<sup>13</sup>C<sub>C2H6</sub> values range from –32.00 ‰ to −27.02 ‰, and the δ<sup>2</sup>H<sub>CH4</sub> values range from −124.01 ‰ to −119.46 ‰. These findings imply that shale gas is composed mainly of oil-type gas of thermal origin, with a potentially minor presence of mixed gas. Isotope analysis of the shale gas reveals that it has undergone reversal (δ<sup>13</sup>C<sub>CH4</sub> > δ<sup>13</sup>C<sub>C2H6</sub>), which is attributed to the cracking of liquid hydrocarbons under overmature conditions. The CO<sub>2</sub> content ranges from 0.21 % to 2.33 % and the δ<sup>13</sup>C<sub>CO2</sub> values range from −21.80 ‰ to −19.00 ‰, suggesting that the CO<sub>2</sub> in the study area is of organic thermal origin. Additionally, a geochemical evolution pattern suggests that the gas composition of different sedimentary phases is controlled by the type of kerogen and the degree of thermal evolution. The multistage cracking of organic matter thermal evolution products caused the dynamic changes in carbon isotopes.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105059"},"PeriodicalIF":2.5,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144923054","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 : 2025-10-01Epub Date: 2025-08-05DOI: 10.1016/j.orggeochem.2025.105054
Luke M. Brosnan , Stephen F. Poropat , Madison Tripp , Sebastian Stanley , Peter Hopper , Xiao Sun , William D.A. Rickard , Antônio Á.F. Saraiva , Renan A.M. Bantim , Juliana M. Sayão , Alexander W.A. Kellner , Kliti Grice
Paraloid® resins, particularly Paraloid® B-72, are widely used in palaeontological preparation to stabilise fossils. However, their presence may interfere with organic geochemical analyses. To evaluate this, standard biomarker extraction protocols were applied to pure Paraloid® B-72, to a fossil bone previously treated with the resin, and to commercial grade acetone commonly used as its solvent. The resin was mobilised by dichloromethane-containing solvent mixtures during extraction and fractionation. Despite this, saturated and aromatic biomarkers were successfully isolated since the polyacrylate resin is insoluble in non-polar solvents. Paraloid® B-72 predominately eluted into the aromatic and polar fractions, but did not significantly impact saturated biomarker profiles. Insoluble residues isolated from these fractions analysed by flash pyrolysis–gas chromatography–mass spectrometry revealed compounds mainly from the resin. Microwave assisted solvent extraction appears to effectively separate Paraloid® B-72 from fossils, as no resin-derived monomers were detected in the extracted fossil pyrolysate. This suggests that the insoluble organic fraction of resin-stabilised fossils can be reliably studied using biomarker techniques with minimal interference. Time-of-flight secondary ion mass spectrometry (ToF–SIMS) analysis produced abundant organic fragments from Paraloid® B-72, but mapping specific oxygen-bearing peaks associated with the resin may allow researchers to distinguish regions containing indigenous organics from those contaminated by the consolidant. These findings indicate that, with appropriate analytical approaches, both soluble and insoluble organic fractions of Paraloid®-treated fossils can yield valid biomarker data, enabling chemical analysis of specimens previously deemed unsuitable due to conservation treatments.
{"title":"Can useful biomarker information be obtained from museum fossil specimens treated with Paraloid® B-72 acrylic resin?","authors":"Luke M. Brosnan , Stephen F. Poropat , Madison Tripp , Sebastian Stanley , Peter Hopper , Xiao Sun , William D.A. Rickard , Antônio Á.F. Saraiva , Renan A.M. Bantim , Juliana M. Sayão , Alexander W.A. Kellner , Kliti Grice","doi":"10.1016/j.orggeochem.2025.105054","DOIUrl":"10.1016/j.orggeochem.2025.105054","url":null,"abstract":"<div><div>Paraloid® resins, particularly Paraloid® B-72, are widely used in palaeontological preparation to stabilise fossils. However, their presence may interfere with organic geochemical analyses. To evaluate this, standard biomarker extraction protocols were applied to pure Paraloid® B-72, to a fossil bone previously treated with the resin, and to commercial grade acetone commonly used as its solvent. The resin was mobilised by dichloromethane-containing solvent mixtures during extraction and fractionation. Despite this, saturated and aromatic biomarkers were successfully isolated since the polyacrylate resin is insoluble in non-polar solvents. Paraloid® B-72 predominately eluted into the aromatic and polar fractions, but did not significantly impact saturated biomarker profiles. Insoluble residues isolated from these fractions analysed by flash pyrolysis–gas chromatography–mass spectrometry revealed compounds mainly from the resin. Microwave assisted solvent extraction appears to effectively separate Paraloid® B-72 from fossils, as no resin-derived monomers were detected in the extracted fossil pyrolysate. This suggests that the insoluble organic fraction of resin-stabilised fossils can be reliably studied using biomarker techniques with minimal interference. Time-of-flight secondary ion mass spectrometry (ToF–SIMS) analysis produced abundant organic fragments from Paraloid® B-72, but mapping specific oxygen-bearing peaks associated with the resin may allow researchers to distinguish regions containing indigenous organics from those contaminated by the consolidant. These findings indicate that, with appropriate analytical approaches, both soluble and insoluble organic fractions of Paraloid®-treated fossils can yield valid biomarker data, enabling chemical analysis of specimens previously deemed unsuitable due to conservation treatments.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105054"},"PeriodicalIF":2.5,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144842815","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 : 2025-10-01Epub Date: 2025-05-27DOI: 10.1016/j.orggeochem.2025.105026
Keith F. O’Connor , Melissa A. Berke , Cindy De Jonge , Ellen C. Hopmans , Lori A. Ziolkowski , Darci Rush
Recently, the analysis of non-derivatised bacteriohopanepolyols (BHPs) by ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS2) revealed a broad structural diversity in this lipid class. Multiple unique BHPs with nucleoside-type polar head groups (Nu-BHPs) were identified in soils. Nu-BHPs had previously been identified in high abundances in soil organic matter, but only by analysing acetylated BHPs, which hindered their structural elucidation. In this study, we apply the UHPLC-HRMS2 analysis method for the first time to a soil transect to re-examine the distribution of Nu-BHPs, their environmental dependencies, and their proxy potential. The presence and distribution of Nu-BHPs was examined in 17 surface soils along a ∼800 km transect in northern Alaska. Our results indicate that certain Nu-BHPs show significant correlation with environmental parameters, such as temperature and soil pH. The variation in 9 Nu-BHPs is captured using a novel ratio, and a regional calibration for warmest quarter soil temperature (WQST) was developed using a linear regression approach (R2 = 0.72). Other calibrations developed for summer air and mean annual temperatures also show strong positive correlations. As BHPs are ubiquitous in soils globally, this study highlights the potential benefit of complementing established organic proxies for soil pH and temperature (e.g., branched tetraether lipids) with calibrations based on Nu-BHPs. Nevertheless, the mechanism behind the environmental dependencies of these BHPs remains unknown. Further work to explore the proxy potential as well as the bacterial sources of these lipids should be undertaken, for instance by sampling soils along relevant (soil pH and temperature) gradients.
{"title":"Occurrence of nucleoside-bacteriohopanepolyol in high latitude soils: evidence of environmental controls on bacterial lipid membrane distributions","authors":"Keith F. O’Connor , Melissa A. Berke , Cindy De Jonge , Ellen C. Hopmans , Lori A. Ziolkowski , Darci Rush","doi":"10.1016/j.orggeochem.2025.105026","DOIUrl":"10.1016/j.orggeochem.2025.105026","url":null,"abstract":"<div><div>Recently, the analysis of non-derivatised bacteriohopanepolyols (BHPs) by ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS<sup>2</sup>) revealed a broad structural diversity in this lipid class. Multiple unique BHPs with nucleoside-type polar head groups (Nu-BHPs) were identified in soils. Nu-BHPs had previously been identified in high abundances in soil organic matter, but only by analysing acetylated BHPs, which hindered their structural elucidation. In this study, we apply the UHPLC-HRMS<sup>2</sup> analysis method for the first time to a soil transect to re-examine the distribution of Nu-BHPs, their environmental dependencies, and their proxy potential. The presence and distribution of Nu-BHPs was examined in 17 surface soils along a ∼800 km transect in northern Alaska. Our results indicate that certain Nu-BHPs show significant correlation with environmental parameters, such as temperature and soil pH. The variation in 9 Nu-BHPs is captured using a novel ratio, and a regional calibration for warmest quarter soil temperature (WQST) was developed using a linear regression approach (R<sup>2</sup> = 0.72). Other calibrations developed for summer air and mean annual temperatures also show strong positive correlations. As BHPs are ubiquitous in soils globally, this study highlights the potential benefit of complementing established organic proxies for soil pH and temperature (e.g., branched tetraether lipids) with calibrations based on Nu-BHPs. Nevertheless, the mechanism behind the environmental dependencies of these BHPs remains unknown. Further work to explore the proxy potential as well as the bacterial sources of these lipids should be undertaken, for instance by sampling soils along relevant (soil pH and temperature) gradients.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105026"},"PeriodicalIF":2.6,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144272111","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 : 2025-10-01Epub Date: 2025-08-18DOI: 10.1016/j.orggeochem.2025.105056
Simon T. Belt , Lukas Smik , Katrine Husum , Jochen Knies
Two tri-unsaturated and isomeric (E/Z) highly branched isoprenoid (HBI) diatom lipid biomarkers were quantified in 228 water column samples collected from the English Channel, West Svalbard (Arctic), the Scotia Sea (Southern Ocean) and East Antarctica. We found that the relative amounts of the two HBIs correlate well with water temperatures taken at the time of sampling. Based on these findings and some other HBI data reported previously, we suggest that the proportion of the HBI E-isomer (termed EZ25) may serve as a new proxy for palaeo sea surface temperatures, including in the polar regions. Next steps will involve determination of EZ25 in surface and downcore sediments to ascertain whether the temperature response described herein translates well to the geological record.
对采集自英吉利海峡、西斯瓦尔巴群岛（北极）、斯科舍海（南大洋）和东南极洲的228个水柱样品进行了两种三不饱和异构（E/Z）高支化类异戊二烯（HBI）硅藻脂类生物标志物的定量分析。我们发现，两种hbi的相对量与采样时的水温有很好的相关性。基于这些发现和先前报道的其他一些HBI数据，我们认为HBI e -异构体的比例（称为EZ25）可能作为古海面温度的新代表，包括在极地地区。下一步将包括测定地表和核心沉积物中的EZ25，以确定本文描述的温度响应是否能很好地转化为地质记录。
{"title":"A potential new sea surface temperature proxy based on isomeric highly branched isoprenoid lipid biomarkers: EZ25","authors":"Simon T. Belt , Lukas Smik , Katrine Husum , Jochen Knies","doi":"10.1016/j.orggeochem.2025.105056","DOIUrl":"10.1016/j.orggeochem.2025.105056","url":null,"abstract":"<div><div>Two tri-unsaturated and isomeric (<em>E</em>/<em>Z</em>) highly branched isoprenoid (HBI) diatom lipid biomarkers were quantified in 228 water column samples collected from the English Channel, West Svalbard (Arctic), the Scotia Sea (Southern Ocean) and East Antarctica. We found that the relative amounts of the two HBIs correlate well with water temperatures taken at the time of sampling. Based on these findings and some other HBI data reported previously, we suggest that the proportion of the HBI <em>E</em>-isomer (termed EZ<sub>25</sub>) may serve as a new proxy for palaeo sea surface temperatures, including in the polar regions. Next steps will involve determination of EZ<sub>25</sub> in surface and downcore sediments to ascertain whether the temperature response described herein translates well to the geological record.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 105056"},"PeriodicalIF":2.5,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144908201","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 : 2025-09-01Epub Date: 2025-05-24DOI: 10.1016/j.orggeochem.2025.105025
Georg Scheeder, Christian Ostertag-Henning, Martin Blumenberg
Alkyl benzenes and toluenes are common in petroleum and shales. In addition to the series of n-alkylated benzenes and toluenes, the phytanyl toluene (and −benzene) is often abundant. In the present study, n-alkyl toluenes and phytanyl toluene were detected in more than 180 petroleum oils with different maturation histories and from two different source rocks, the Jurassic Posidonia Shale and the Cretaceous Wealden Shale (from the Lower Saxony Basin; Germany). A novel ratio of C22-C24meta-substituted n-alkyl (combined in the ratio as “n”) to phytanyl (“iso”) toluenes is proposed as a thermal maturity indicator. Our data show that the relative proportion of phytanyl toluene to n-alkyl toluenes systematically decreases with maturity and therefore the “n/(n + iso)” toluene index increases. The relative change is due to both the processes of catalytic formation of n-alkyl toluenes and destruction of phytanyl toluene. The applicability of this ratio was confirmed using closed gold capsule pyrolysis maturation experiments with Posidonia Shale (for a maturation range from EASY%Ro of 0.78 to 1.4 %). The correlation is most pronounced in petroleum produced from the Posidonia Shale. For oils from the Wealden shales, the correlation is less clear due to the generally low phytanyl toluene contents. Comparisons of the “n/(n + iso)” toluene index with maturity-dependent biomarker ratios indicated its potential to record thermal maturity over a wide range. The occurrence of phytanyl toluene also appears to record a poorly understood (microbial) source, which was more abundant in the marine-euxinic depositional system of the Posidonia Shale than that of the brackish-marine Wealden shales.
{"title":"Abundance of phytanyl and n-alkyl toluenes in petroleum from the Lower Saxony Basin (Germany) provides information on maturity, palaeosettings and sources","authors":"Georg Scheeder, Christian Ostertag-Henning, Martin Blumenberg","doi":"10.1016/j.orggeochem.2025.105025","DOIUrl":"10.1016/j.orggeochem.2025.105025","url":null,"abstract":"<div><div>Alkyl benzenes and toluenes are common in petroleum and shales. In addition to the series of <em>n</em>-alkylated benzenes and toluenes, the phytanyl toluene (and −benzene) is often abundant. In the present study, <em>n</em>-alkyl toluenes and phytanyl toluene were detected in more than 180 petroleum oils with different maturation histories and from two different source rocks, the Jurassic Posidonia Shale and the Cretaceous Wealden Shale (from the Lower Saxony Basin; Germany). A novel ratio of C<sub>22</sub>-C<sub>24</sub> <em>meta</em>-substituted <em>n</em>-alkyl (combined in the ratio as “<em>n</em>”) to phytanyl (“<em>iso</em>”) toluenes is proposed as a thermal maturity indicator. Our data show that the relative proportion of phytanyl toluene to <em>n</em>-alkyl toluenes systematically decreases with maturity and therefore the “<em>n</em>/(<em>n</em> + <em>iso</em>)” toluene index increases. The relative change is due to both the processes of catalytic formation of <em>n</em>-alkyl toluenes and destruction of phytanyl toluene. The applicability of this ratio was confirmed using closed gold capsule pyrolysis maturation experiments with Posidonia Shale (for a maturation range from EASY%Ro of 0.78 to 1.4 %). The correlation is most pronounced in petroleum produced from the Posidonia Shale. For oils from the Wealden shales, the correlation is less clear due to the generally low phytanyl toluene contents. Comparisons of the “<em>n</em>/(<em>n</em> + <em>iso</em>)” toluene index with maturity-dependent biomarker ratios indicated its potential to record thermal maturity over a wide range. The occurrence of phytanyl toluene also appears to record a poorly understood (microbial) source, which was more abundant in the marine-euxinic depositional system of the Posidonia Shale than that of the brackish-marine Wealden shales.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"207 ","pages":"Article 105025"},"PeriodicalIF":2.6,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144123964","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 : 2025-09-01Epub Date: 2025-05-05DOI: 10.1016/j.orggeochem.2025.105013
Francien Peterse , Klaas G.J. Nierop , Nicole J. Bale , Sarah J. Feakins , Chan-Mao Chen
Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are a suite of membrane lipids that are widely used as empirical proxies for past temperature and pH. Although the stereochemistry of their glycerol moiety suggests that they are produced by bacteria, the exact producers and the biosynthetic pathway of brGDGTs remain unclear. Here we report the occurrence of tetraester and mixed ester/ether membrane-spanning lipids with a backbone consisting of iso-diabolic acid (iso-DA) containing up to two additional methyl groups in high-elevation (>1900 masl), acidic (pH < 4.5) mineral soils from Nepal and Rwanda. These compounds are presumed intermediate products during brGDGT synthesis but had not been detected in cultures or the environment before. Interestingly, while acid hydrolysis of the GDGT fraction releases iso-DA in the soil from Nepal, monoalkyl glycerol ethers with iso-C15 and iso-C17 chains are released in the soil from Rwanda. Although speculative, these results could support both current hypotheses that brGDGT synthesis can occur via tail-to-tail condensation of two iso-C15 fatty acids to form iso-DA, as well as through the reduction of diesters to diethers and subsequent carbon–carbon linking as shown to occur during the synthesis of archaeal GDGTs.
{"title":"Occurrence of tetraester and mixed ether/ester-bound iso-diabolic acid membrane-spanning lipids in acidic, high-elevation mineral soils","authors":"Francien Peterse , Klaas G.J. Nierop , Nicole J. Bale , Sarah J. Feakins , Chan-Mao Chen","doi":"10.1016/j.orggeochem.2025.105013","DOIUrl":"10.1016/j.orggeochem.2025.105013","url":null,"abstract":"<div><div>Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are a suite of membrane lipids that are widely used as empirical proxies for past temperature and pH. Although the stereochemistry of their glycerol moiety suggests that they are produced by bacteria, the exact producers and the biosynthetic pathway of brGDGTs remain unclear. Here we report the occurrence of tetraester and mixed ester/ether membrane-spanning lipids with a backbone consisting of <em>iso</em>-diabolic acid (<em>iso</em>-DA) containing up to two additional methyl groups in high-elevation (>1900 masl), acidic (pH < 4.5) mineral soils from Nepal and Rwanda. These compounds are presumed intermediate products during brGDGT synthesis but had not been detected in cultures or the environment before. Interestingly, while acid hydrolysis of the GDGT fraction releases <em>iso</em>-DA in the soil from Nepal, monoalkyl glycerol ethers with <em>iso</em>-C<sub>15</sub> and <em>iso</em>-C<sub>17</sub> chains are released in the soil from Rwanda. Although speculative, these results could support both current hypotheses that brGDGT synthesis can occur via tail-to-tail condensation of two <em>iso</em>-C<sub>15</sub> fatty acids to form <em>iso</em>-DA, as well as through the reduction of diesters to diethers and subsequent carbon–carbon linking as shown to occur during the synthesis of archaeal GDGTs.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"207 ","pages":"Article 105013"},"PeriodicalIF":2.6,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144071340","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 : 2025-09-01Epub Date: 2025-05-21DOI: 10.1016/j.orggeochem.2025.105014
Xiaoyong Yang , Youjun Tang , Peng Sun , Yiming Hu , Haifeng Yang , Feilong Wang
Aryl isoprenoids (AIs), a series of aromatic carotenoid derivatives, have served as significant biomarkers for paleoecology reconstructions. However, the effect of biodegradation on AIs remains unclear to date. Here, a confirmed family of progressively biodegraded oils from the Miaoxi Depression, Bohai Bay Basin was analyzed to investigate the fate of these compounds during severe biodegradation under natural conditions. Two pseudohomologous series with carbon numbers ranging from 13 to 31 and 40 were identified as 2,3,6- and 2,3,4-AIs in the reference oil. The concentrations of total AIs showed a gradual decline with increasing biodegradation but AIs survive in the most severely biodegraded oil (with a PM rank of 8 and an M-MN2 of 983) in this study. The differential proximity of adjacent methyl groups on the benzene ring may result in 2,3,4-AIs being more resistant to biodegradation compared to 2,3,6-AIs. No preferential biodegradation of individual AIs is proceeded systematically by carbon number, which may result from competition of two biodegradation pathways and favor of specific microbial communities. Moreover, the AIs-bearing proxies, including aryl isoprenoid ratio (AIR) and concentrations of total AIs, 2,3,6-AIs and 2,3,4-AIs, exhibit a significant decrease with increasing microbial alteration. Therefore, these proxies must be employed with caution to reconstruct photic-zone euxinia (PZE) for crude oils with potential microbial degradation.
{"title":"Aryl isoprenoids in severe biodegradation oils from the Miaoxi Depression, Bohai Bay Basin","authors":"Xiaoyong Yang , Youjun Tang , Peng Sun , Yiming Hu , Haifeng Yang , Feilong Wang","doi":"10.1016/j.orggeochem.2025.105014","DOIUrl":"10.1016/j.orggeochem.2025.105014","url":null,"abstract":"<div><div>Aryl isoprenoids (AIs), a series of aromatic carotenoid derivatives, have served as significant biomarkers for paleoecology reconstructions. However, the effect of biodegradation on AIs remains unclear to date. Here, a confirmed family of progressively biodegraded oils from the Miaoxi Depression, Bohai Bay Basin was analyzed to investigate the fate of these compounds during severe biodegradation under natural conditions. Two pseudohomologous series with carbon numbers ranging from 13 to 31 and 40 were identified as 2,3,6- and 2,3,4-AIs in the reference oil. The concentrations of total AIs showed a gradual decline with increasing biodegradation but AIs survive in the most severely biodegraded oil (with a PM rank of 8 and an M-MN2 of 983) in this study. The differential proximity of adjacent methyl groups on the benzene ring may result in 2,3,4-AIs being more resistant to biodegradation compared to 2,3,6-AIs. No preferential biodegradation of individual AIs is proceeded systematically by carbon number, which may result from competition of two biodegradation pathways and favor of specific microbial communities. Moreover, the AIs-bearing proxies, including aryl isoprenoid ratio (AIR) and concentrations of total AIs, 2,3,6-AIs and 2,3,4-AIs, exhibit a significant decrease with increasing microbial alteration. Therefore, these proxies must be employed with caution to reconstruct photic-zone euxinia (PZE) for crude oils with potential microbial degradation.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"207 ","pages":"Article 105014"},"PeriodicalIF":2.6,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144105273","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 : 2025-08-01Epub Date: 2025-05-03DOI: 10.1016/j.orggeochem.2025.105012
Yang Qin , Chiyang Liu , Junfeng Zhao , Faqi He , Wei Zhang , Lihua Yang , Nan Du , Deyong Shao
The Hangjinqi gas field, a vital tight sandstone gas field on the northern Ordos Basin margin, exhibits a debatable gas origin and accumulation mechanism. Integrating geochemical analyses with gas field data for basin-wide comparisons allows us to resolve the origin of the reservoired gas. Results reveal that the Upper Paleozoic coal-measure source rocks in the Hangjinqi area share similar characteristics with those in other Upper Paleozoic gas fields, where coal seams constitute the primary effective source rocks. However, they exhibit limited hydrocarbon-generating potential coupled with low thermal maturity. Natural gas has a broad range of dryness coefficient values. The carbon-hydrogen isotopes mostly exhibit a positive carbon-hydrogen isotope series, yet 40% of the samples display ethane and propane carbon-hydrogen isotope reversals. The C5-7 and C7 light hydrocarbons are dominated by isoalkanes and methylcyclohexane, respectively. The natural gas data follow the aromatic curve in the cross-plot of the heptane and isoheptane values. The natural gas in the Hangjinqi field is typical coal-derived gas, which is derived primarily from the Carboniferous-Permian transitional facies of humic organic matter, similar to Daniudi and other gas fields. Notably, the natural gas in the Hangjinqi gas field has undergone migration and dissipation (mainly including escape and loss). The Hangjinqi gas field presents an apparent contradiction between low maturity source rocks and high maturity natural gas. Its methane carbon isotope values significantly exceed those of the Daniudi gas field but align closely with those of the Sulige and Wushenqi gas fields, which are mature-type gas fields. Natural gas migration-dissipation is not the controlling factor in regional isotopic signatures. Therefore, approximately 40–76 % of the natural gas in the Hangjinqi gas field is exogenous gas. Moreover, these exogenous gases are derived primarily from the Sulige-Wushenqi gas field to its south, indicating strong genetic affinity. Overall, most Upper Paleozoic gas fields in the Ordos Basin have short migration distances, whereas the Hangjinqi gas field represents mixtures of locally generated hydrocarbons with gases migrating longer distances.
{"title":"Unravelling the origin of gas in tight sandstones of the Hangjinqi gas field, Ordos Basin, China: New insights from natural gas geochemistry data","authors":"Yang Qin , Chiyang Liu , Junfeng Zhao , Faqi He , Wei Zhang , Lihua Yang , Nan Du , Deyong Shao","doi":"10.1016/j.orggeochem.2025.105012","DOIUrl":"10.1016/j.orggeochem.2025.105012","url":null,"abstract":"<div><div>The Hangjinqi gas field, a vital tight sandstone gas field on the northern Ordos Basin margin, exhibits a debatable gas origin and accumulation mechanism. Integrating geochemical analyses with gas field data for basin-wide comparisons allows us to resolve the origin of the reservoired gas. Results reveal that the Upper Paleozoic coal-measure source rocks in the Hangjinqi area share similar characteristics with those in other Upper Paleozoic gas fields, where coal seams constitute the primary effective source rocks. However, they exhibit limited hydrocarbon-generating potential coupled with low thermal maturity. Natural gas has a broad range of dryness coefficient values. The carbon-hydrogen isotopes mostly exhibit a positive carbon-hydrogen isotope series, yet 40% of the samples display ethane and propane carbon-hydrogen isotope reversals. The C<sub>5-7</sub> and C<sub>7</sub> light hydrocarbons are dominated by isoalkanes and methylcyclohexane, respectively. The natural gas data follow the aromatic curve in the cross-plot of the heptane and isoheptane values. The natural gas in the Hangjinqi field is typical coal-derived gas, which is derived primarily from the Carboniferous-Permian transitional facies of humic organic matter, similar to Daniudi and other gas fields. Notably, the natural gas in the Hangjinqi gas field has undergone migration and dissipation (mainly including escape and loss). The Hangjinqi gas field presents an apparent contradiction between low maturity source rocks and high maturity natural gas. Its methane carbon isotope values significantly exceed those of the Daniudi gas field but align closely with those of the Sulige and Wushenqi gas fields, which are mature-type gas fields. Natural gas migration-dissipation is not the controlling factor in regional isotopic signatures. Therefore, approximately 40–76 % of the natural gas in the Hangjinqi gas field is exogenous gas. Moreover, these exogenous gases are derived primarily from the Sulige-Wushenqi gas field to its south, indicating strong genetic affinity. Overall, most Upper Paleozoic gas fields in the Ordos Basin have short migration distances, whereas the Hangjinqi gas field represents mixtures of locally generated hydrocarbons with gases migrating longer distances.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"206 ","pages":"Article 105012"},"PeriodicalIF":2.6,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143899459","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 : 2025-08-01Epub Date: 2025-04-19DOI: 10.1016/j.orggeochem.2025.105010
Devika Varma , Yord W. Yedema , Francien Peterse , Gert-Jan Reichart , Jaap S. Sinninghe Damsté , Stefan Schouten
<div><div>Isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs) and hydroxylated isoGDGTs (OH-isoGDGTs) are widespread in marine, lacustrine, and terrestrial environments and serve as paleoenvironmental proxies. Several indices based on their distributions, such as <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span> (based on isoGDGTs), <span><math><mtext>RI-OH</mtext></math></span>, <span><math><mrow><mtext>RI-OH</mtext><mo>′</mo></mrow></math></span> (both based on OH-isoGDGTs), <span><math><mrow><mo>%</mo><mi>O</mi><mi>H</mi></mrow></math></span> and <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> (both based on isoGDGTs and OH-isoGDGTs), have been utilized as sea water temperature proxies. Although terrestrial organic matter (OM) input of isoGDGTs may affect the <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span> in coastal marine settings, relatively little is known on its consequences for OH-isoGDGT distributions and related proxies. Here, we studied the distributions of OH-isoGDGTs in soils, rivers, and coastal marine settings at three locations: the Kara Sea, the Iberian margin, and the northern Gulf of Mexico, receiving terrestrial OM through the Yenisei, the Tagus and the Mississippi Rivers, respectively. In general, we observe higher relative abundances of OH-isoGDGTs (<span><math><mrow><mo>%</mo><mi>O</mi><mi>H</mi></mrow></math></span>) in coastal marine environments compared to soils and rivers from the same area. Comparison of OH-isoGDGT distributions shows that, in particular, the abundance of OH-isoGDGT with one cyclopentane moiety relative to total OH-isoGDGTs was lower in terrestrial settings. In general, the <span><math><mtext>RI-OH</mtext></math></span> was higher in terrestrial settings, while such a consistent offset was not observed for <span><math><mrow><mtext>RI-OH</mtext><mo>′</mo></mrow></math></span>. The <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> index, exhibits a distinct difference between terrestrial and marine settings, similar to the pattern observed for the <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span>. This similarity is primarily attributed to the relatively minor influence of terrestrial OH-isoGDGTs compared to regular isoGDGTs in the <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> index. Despite these differences, only the coastal sediments of the Kara Sea showed indications of a potential bias of OH-isoGDGTs-based proxies caused by terrestrial OM input. However, these distributional variations may also be caused by the large salinity gradient in the Kara Sea, since it has bee
{"title":"Impact of terrestrial organic matter input on distributions of hydroxylated isoprenoidal GDGTs in marine sediments: Implications for OH-isoGDGT-based temperature proxies","authors":"Devika Varma , Yord W. Yedema , Francien Peterse , Gert-Jan Reichart , Jaap S. Sinninghe Damsté , Stefan Schouten","doi":"10.1016/j.orggeochem.2025.105010","DOIUrl":"10.1016/j.orggeochem.2025.105010","url":null,"abstract":"<div><div>Isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs) and hydroxylated isoGDGTs (OH-isoGDGTs) are widespread in marine, lacustrine, and terrestrial environments and serve as paleoenvironmental proxies. Several indices based on their distributions, such as <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span> (based on isoGDGTs), <span><math><mtext>RI-OH</mtext></math></span>, <span><math><mrow><mtext>RI-OH</mtext><mo>′</mo></mrow></math></span> (both based on OH-isoGDGTs), <span><math><mrow><mo>%</mo><mi>O</mi><mi>H</mi></mrow></math></span> and <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> (both based on isoGDGTs and OH-isoGDGTs), have been utilized as sea water temperature proxies. Although terrestrial organic matter (OM) input of isoGDGTs may affect the <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span> in coastal marine settings, relatively little is known on its consequences for OH-isoGDGT distributions and related proxies. Here, we studied the distributions of OH-isoGDGTs in soils, rivers, and coastal marine settings at three locations: the Kara Sea, the Iberian margin, and the northern Gulf of Mexico, receiving terrestrial OM through the Yenisei, the Tagus and the Mississippi Rivers, respectively. In general, we observe higher relative abundances of OH-isoGDGTs (<span><math><mrow><mo>%</mo><mi>O</mi><mi>H</mi></mrow></math></span>) in coastal marine environments compared to soils and rivers from the same area. Comparison of OH-isoGDGT distributions shows that, in particular, the abundance of OH-isoGDGT with one cyclopentane moiety relative to total OH-isoGDGTs was lower in terrestrial settings. In general, the <span><math><mtext>RI-OH</mtext></math></span> was higher in terrestrial settings, while such a consistent offset was not observed for <span><math><mrow><mtext>RI-OH</mtext><mo>′</mo></mrow></math></span>. The <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> index, exhibits a distinct difference between terrestrial and marine settings, similar to the pattern observed for the <span><math><msub><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mn>86</mn></msub></math></span>. This similarity is primarily attributed to the relatively minor influence of terrestrial OH-isoGDGTs compared to regular isoGDGTs in the <span><math><msubsup><mrow><mi>T</mi><mi>E</mi><mi>X</mi></mrow><mrow><mn>86</mn></mrow><mrow><mi>O</mi><mi>H</mi></mrow></msubsup></math></span> index. Despite these differences, only the coastal sediments of the Kara Sea showed indications of a potential bias of OH-isoGDGTs-based proxies caused by terrestrial OM input. However, these distributional variations may also be caused by the large salinity gradient in the Kara Sea, since it has bee","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"206 ","pages":"Article 105010"},"PeriodicalIF":2.6,"publicationDate":"2025-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143917858","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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