Organic Geochemistry最新文献

{"title":"African C3 grass n-alkane distributions & plant chemotaxonomy","authors":"Ruth R. Tweedy ,&nbsp;Caroline A.E. Strömberg ,&nbsp;Tammo Reichgelt ,&nbsp;Rahab N. Kinyanjui ,&nbsp;Mbaluka Kimeu ,&nbsp;Venanzio Munyaka ,&nbsp;Kevin T. Uno","doi":"10.1016/j.orggeochem.2025.104994","DOIUrl":"10.1016/j.orggeochem.2025.104994","url":null,"abstract":"<div><div>Reconstructing past vegetation can elucidate the timing, climate forcings, and biotic mechanisms of ecosystem change. Plant macro- and microfossils are traditionally used to study past vegetation but suffer from production and taphonomic biases, such as underrepresentation of important herbaceous vegetation components. Geochemical proxies can fill this gap, but carbon isotopes (δ¹³C) in isolation are unable to distinguish between structurally different C₃ habitats, such as forests and grasslands. Thus, new geochemical methods to identify grassy C₃ ecosystems are necessary. We present <em>n</em>-alkane chain length distributions of 209 plant specimens from two Kenyan C₃-dominated ecosystems, representing a wide range of plant functional types (PFTs). We find that C₃ PACMAD grasses produce exceptionally high abundances of long chain C₃₃ and C₃₅ <em>n</em>-alkanes (ACL = 32.7, mean C₃₃ + C₃₅ relative abundance = 0.69), unlike other C₃ PFTs which produce low abundances of C₃₃ and C₃₅ (ACL = 28.9–30.3, mean C₃₃ + C₃₅ relative abundance = 0.0–0.21). This finding highlights the importance of measuring and reporting the C₃₅ <em>n</em>-alkane. Our data further demonstrate that <em>n</em>-alkane distributions can serve as a proxy for some African C₃ PACMAD grasses, offering a new paleoecological tool for distinguishing C₃ vegetation types.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"208 ","pages":"Article 104994"},"PeriodicalIF":2.6,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144365586","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

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

{"title":"Geochemistry Articles – January 2025","authors":"","doi":"10.1016/j.orggeochem.2025.104984","DOIUrl":"10.1016/j.orggeochem.2025.104984","url":null,"abstract":"","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"204 ","pages":"Article 104984"},"PeriodicalIF":2.6,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143820774","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemistry Articles – February 2025","authors":"","doi":"10.1016/j.orggeochem.2025.104985","DOIUrl":"10.1016/j.orggeochem.2025.104985","url":null,"abstract":"","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"204 ","pages":"Article 104985"},"PeriodicalIF":2.6,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143820775","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

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

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

{"title":"Mid- to Late-Holocene branched GDGT-based air temperatures from a crater lake in Cameroon (Central Africa)","authors":"Guillemette Ménot ,&nbsp;Salomé Ansanay-Alex ,&nbsp;Valérie F. Schwab ,&nbsp;Gilbert Todou ,&nbsp;Olivier Séné ,&nbsp;Jean-Michel Onana ,&nbsp;Gerd Gleixner ,&nbsp;Dirk Sachse ,&nbsp;Yannick Garcin","doi":"10.1016/j.orggeochem.2025.104982","DOIUrl":"10.1016/j.orggeochem.2025.104982","url":null,"abstract":"<div><div>African low-latitude regions tend to be underrepresented in global continental temperature reconstructions, limiting both our understanding and the reliability of predictions of past and future changes in temperature and precipitation in those parts of the world. The lack of continuous sedimentary archives and quantitative temperature proxies further complicates this issue, especially outside Eastern Africa. Here, we use data collected in Cameroon lakes to assess branched glycerol dialkyl glycerol tetraether (brGDGT)-based temperature proxies and examine potential confounding variables impacting temperature reconstructions. By analyzing GDGT distributions in soil watershed, water column, and surface sediment samples from a total of 11 Cameroon lakes, we could verify that the degree of methylation of brGDGTs (through the MBT′_5Me) can serve as a reliable indicator for reconstructing mean annual air temperatures. Additionally, we could confirm that surface water conductivity represents a controlling factor for the brGDGT assemblage in surface sediments of crater lakes. Moreover, we provide the first reconstruction of Mid- to Late-Holocene GDGT-based air temperatures for a crater lake in Cameroon (Central Africa), revealing a temperature decrease of 2.5 °C over the last 7000 years, which agrees with recently published records for East Africa but exceeds current model predictions. These discrepancies highlight the need for additional studies to focus on this geographically underrepresented area.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"204 ","pages":"Article 104982"},"PeriodicalIF":2.6,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143760936","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

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

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

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