Organic Geochemistry最新文献

{"title":"Characteristics of carbazole compounds in ultra-deep marine oil from Fuman oilfield, Tarim Basin: Significance for thermal maturity assessment of crude oil","authors":"Zhongdeng Lu ,&nbsp;Hongwei Ping ,&nbsp;Honghan Chen ,&nbsp;Zulin Chen ,&nbsp;Yanqiu Zhang ,&nbsp;Zhou Xie ,&nbsp;Yintao Zhang ,&nbsp;Xu Chen","doi":"10.1016/j.orggeochem.2024.104895","DOIUrl":"10.1016/j.orggeochem.2024.104895","url":null,"abstract":"<div><div>Carbazoles in Ordovician ultra-deep marine oil from the F_I17 fault zone in Fuman oilfield (Tarim Basin) were separated using a recently proposed silica gel column chromatographic method and the enriched fractions were analyzed by GC–MS. Biomarker and carbon isotope signatures revealed that all oil in the study area was produced from the same source rock and that compositional differences can be attributed to thermal maturation. The convergent ratios of N-H shielded isomers/N-H half shielded isomers and benzo[<em>a</em>]carbazole/(benzo[<em>a</em>]carbazole + benzo[<em>c</em>]carbazole) suggested that carbazoles in crude oil had not been affected by vertical migration. Therefore, thermal maturity was identified as the main controlling factor affecting chages of carbazole concentrations and ratios in crude oil. The concentrations of the total carbazole and its three isomers (N-H shielded isomers, N-H half shielded isomers and exposed isomers) in crude oil decreased sharply with increasing maturity. The 1,8-dimethylcarbazole/carbazole (1,8-MCa/Ca) and 1,8-dimethylcarbazole/2,4-dimethylcarbazole (1,8-MCa/2,4-MCa) ratios showed significant correlation with maturity expressed as %<em>VRE</em> (the vitrinite reflectance equivalent converted from MPI₁ and MPR) when %<em>VRE</em> is &lt;1.2 %. Similar trends were observed in the 1-methylcarbazole/3-methylcarbazole (1-MCa/3-MCa) as well as 1,8-dimethylcarbazole/2,6- dimethylcarbazole (1,8-DMCa/2,6-DMCa), (1,5- dimethylcarbazole + 3-ethylcarbazole)/2, 6-dimethylcarbazole ((1, 5-DMCa + 3-ECa)/2, 6-DMCa), and (1, 4-dimethylcarbazole + 4-ethylcarbazole)/2, 6-dimethylcarbazole ((1, 4-DMCa + 4-ECa)/2, 6-DMCa) when the %<em>VRE</em> of crude oil exceeds 1.0 %. This indicated that the concentrations and ratios of carbazole can be used to qualitatively evaluate crude oil maturity. The ratio of 1,8-dimethylcarbazole/1-ethylcarbazole (1,8-DMCa/1-ECa) showed a strict linear relationship with %<em>VRE</em>. The maturity of marine oil can be calculated using the formulas <em>%R</em>c (the vitrinite reflectance equivalent calculated from MPI₁) = −0.0335(1, 8-DMCa/1-ECa) + 1.2902 or <em>%R</em>c₁ (the vitrinite reflectance equivalent calculated from MPR) = −0.0405 (1, 8-DMCa/1-ECa) + 1.3418. The study can be helpful for exploring ultra-deep hydrocarbons and restoring the thermal history of source rocks in the Tarim Basin.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104895"},"PeriodicalIF":2.6,"publicationDate":"2024-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrogen isotope fractionation during aromatization to form alkylnaphthalene: Insights from pyrolysis experiments of 1-n-butyldecalin","authors":"Bin Cheng ,&nbsp;Zhiwei Wei ,&nbsp;Yiman Zhang ,&nbsp;Hanyu Deng ,&nbsp;Yuxian Li ,&nbsp;Haozhe Wang ,&nbsp;Zewen Liao","doi":"10.1016/j.orggeochem.2024.104881","DOIUrl":"10.1016/j.orggeochem.2024.104881","url":null,"abstract":"<div><div>Alkylnaphthalene homologues are important components of aromatic fraction in sedimentary organic matter and contain significantly geochemical information relative to formation and evolution of the host organic matter. They mainly originate from hydrocarbon aromatization reaction which involves the dehydrogenation of aliphatic rings resulting in the fractionation of stable hydrogen isotopes between aromatic hydrocarbons and their precursors. To examine these processes, this study thermally pyrolysed 1-<em>n</em>-butyldecalin (BD) at different time intervals under 360 °C/50 MPa to study the aromatization and hydrogen isotope fractionation during alkylnaphthalene formation and evolution. The relative content of aromatic products, such as naphthalene (N) and 1-methylnaphthalene (1-MN), increases with increasing aromatization. Sulfur enhanced the degree of aromatization during BD thermal evolution, resulting in greater N and 1-MN formation. For the compounds with the same carbon skeleton, i.e. <em>tran</em>-1-methyldecalin (1-MD), 5-methyltetraline (5-MT) and 1-MN, the ²H enrichment follows the order δ²H_1-MD &lt; δ²H_5-MT &lt; δ²H_1-MN during the low thermal conversion of BD. However, the order was subsequently destroyed with increasing aromatization. The results indicate that hydrocarbon aromatization can enrich aromatic hydrocarbon in ²H, resulting in a higher δ²H value of higher aromatic-ring-number hydrocarbon than that of a lower aromatic-ring-number at low aromatization. However, ²H enrichment will decrease and even result in a reverse order with enhanced aromatization. Our findings are beneficial for understanding genetic mechanism and hydrogen isotope fractionation effect during the formation and evolution of aromatic hydrocarbons.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104881"},"PeriodicalIF":2.6,"publicationDate":"2024-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652442","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":"Porphyrin protonation induces decoupling of trace metals in petroleum","authors":"Jingkun Zhang ,&nbsp;Jian Cao ,&nbsp;Wenjun He","doi":"10.1016/j.orggeochem.2024.104878","DOIUrl":"10.1016/j.orggeochem.2024.104878","url":null,"abstract":"<div><div>The mechanism of migration of trace metals in petroleum systems is poorly understood, which limits our understanding of organic–inorganic interactions and their application in tracing oil sources. Based on a molecular model of metalloporphyrin, numerical simulations involving density functional theory have revealed that porphyrin protonation is associated with trace-metal decoupling in petroleum. Trace metals readily form covalent bonds with weakly protonated porphyrin N to form stable compounds. However, the metals may be decoupled at lower fluid pH owing to increased N protonation, which activates the formation of ionic bonds with O²⁻. The released metals may then be fixed in authigenic calcite cement (ACC) reservoirs through substitution of Ca. For Mg, Mn, and Fe, the decoupling order is Mg &gt; Fe &gt; Mn, whereas that for the substitution of Ca is Mn &gt; Fe &gt; Mg, reflecting the complexity of organic–inorganic interactions and indicating the potential application of metals in fingerprinting oil sources. This case study of the southern Junggar Basin, China, revealed that Mn, Fe, and Mg enrichment of ACC may provide indications of Paleozoic, Mesozoic, and Cenozoic petroleum systems, respectively, providing a potential new approach for the tracing of oil sources in petroleum basins.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104878"},"PeriodicalIF":2.6,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652438","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":"Characterisation of dissolved organic matter in two contrasting arsenic-prone sites in Kandal Province, Cambodia","authors":"Oliver C. Moore ,&nbsp;Amy D. Holt ,&nbsp;Laura A. Richards ,&nbsp;Amy M. McKenna ,&nbsp;Robert G.M. Spencer ,&nbsp;Dan J. Lapworth ,&nbsp;David A. Polya ,&nbsp;Jonathan R. Lloyd ,&nbsp;Bart E. van Dongen","doi":"10.1016/j.orggeochem.2024.104886","DOIUrl":"10.1016/j.orggeochem.2024.104886","url":null,"abstract":"<div><div>Aquifers throughout Asia are impacted by the release of geogenic arsenic (As) into groundwater by microbial reduction of As-bearing Fe(III) (oxy)hydroxide minerals, severely impacting water quality. Groundwater dissolved organic matter (DOM) is likely key to As release, mainly as electron donor or electron shuttles. This study used optical analyses and ultra-high resolution mass spectrometry to examine the sources and composition of groundwater DOM in the As-prone aquifers of Kandal Province, Cambodia, at boreholes with differing host lithology (clay- and sand-dominated). Groundwater and surface water DOM composition were related to As concentrations, to infer the potential role of DOM in promoting As release. Optical and molecular-level analyses indicated an overall dominance of terrestrial-derived DOM in the groundwater samples, with higher freshness index and relative abundance (RA) of aliphatic compounds in clay compared to sand-dominated lithology. Compared to surface water, groundwater DOM had relatively lower O/C ratios and nominal oxidation state of carbon (−0.19 to −0.13 compared to 0.04 for ground and surface water, respectively), with a lower %RA of aliphatic compounds and higher %RA of carboxyl-rich alicyclic molecules, suggesting microbial processing of DOM since percolation into the aquifer. Concentrations of As across both sites were negatively correlated with DOM tryptophan:fulvic-like fluorescence and the %RA of aliphatics, potentially indicating microbial degradation of biolabile DOM in connection with As release, which is consistent with its role as an electron donor source. Together these data support DOM composition as an important control on microbial mediated As release.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104886"},"PeriodicalIF":2.6,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652445","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":"Abiotic chlorination of organic matter in the soil environment: A simulation study","authors":"Fanfan Ju ,&nbsp;Liuzhu Chen ,&nbsp;Yaoyao Kong ,&nbsp;Teng Ma ,&nbsp;Chi Zhang ,&nbsp;Zhanqiang Chen","doi":"10.1016/j.orggeochem.2024.104877","DOIUrl":"10.1016/j.orggeochem.2024.104877","url":null,"abstract":"<div><div>Chlorination of organic matter occurs naturally and is an important part of the chlorine cycle. To investigate the likelihood that inorganic oxidants, (Fe(NO₃)₃, H₂O₂, and hydroxyl radicals (·OH), frequently present in soil environments, could promote the synthesis of chlorinated organic matter in the soil environment, litterfall, humus, and soil (0–20 cm) were collected and used in laboratory based simulation experiments. Results indicate that these inorganic oxidants might promote the synthesis of chlorinated organic matter, but their impact varied due to varying suitable reaction circumstances. Litterfall was the most sensitive to chlorination, likely caused by the presence of abundant amounts of labile organic matter, and the chlorination process was limited by its Cl⁻ level. Hydroxyl radicals showed a dual effect (producing or degrading chlorinated organic matter) on the three materials assessed, which was controlled by both ·OH concentration and the stability of organic matter, and the dual effect was evident in order of litterfall &gt; humus &gt; soil. The Fe(NO₃)₃-mediated chlorination of organic matter was only significant in litterfall due to its labile organic matter composition, while the peroxidative reaction caused by H₂O₂ in the producing chlorinated organic matter was only obvious in soil, most likely due to the presence of metals, facilitating the process. Combined this study sheds light on the chlorine cycle by verifying that inorganic oxidants might mediate abiotic chlorination of organic matter in a natural soil environment.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104877"},"PeriodicalIF":2.6,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652444","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":"Hydroxylated GDGTs-0 in marine methane seep environments: A putative indicator for archaeal methanogenesis","authors":"Hongxiang Guan ,&nbsp;Lei Liu ,&nbsp;Daniel Birgel ,&nbsp;Jörn Peckmann ,&nbsp;Dong Feng ,&nbsp;Sanzhong Li","doi":"10.1016/j.orggeochem.2024.104862","DOIUrl":"10.1016/j.orggeochem.2024.104862","url":null,"abstract":"<div><div>Marine methane seeps are environments with a high microbial diversity, but are known for one biogeochemical key process, the sulfate-driven anaerobic oxidation of methane (SD-AOM) performed by anaerobic methane-oxidizing archaea (ANME) and sulfate-reducing bacteria (SRB). SD-AOM is also the dominant process at methane seeps in the South China Sea based on the lipid biomarker inventory of authigenic seep carbonates characterized by crocetane, a high <em>sn</em>2-hydroxyarchaeol over archaeol ratio, low contents of glycerol dibiphytanyl glycerol tetraethers (GDGTs), and δ¹³C_{lipid-methane} offsets of −52 ± 4‰. Combined with the dominance of aragonite over other carbonate minerals, such pattern suggests high seepage intensity with a predominance of ANME-2/SRB consortia. Interestingly, the studied seep carbonates also yielded some uncommon biomarkers for these consortia, which may derive from methanogenic archaea. Methylotrophic methanogenesis has been shown to be the dominant mode of methanogenesis in seep environments where non-competitive substrates like methanol or trimethylamine are abundant. The presence of methylotrophic methanogens is possibly indicated by high contents (more than 50% of all GDGTs) of hydroxylated GDGTs-0 (OH-GDGT-0 and 2OH-GDGT-0) with extreme ¹³C-depletion (−128‰ to −116‰); this unique pattern is recognized in only some of the studied seep carbonates, while other carbonates are dominated by typical distributions of ANME-2 lipids, also comprising GDGTs with 0 to 4 rings, but lacking high contents of OH-GDGTs. The overall lack of crenarchaeol, the specific biomarker of planktonic Thaumarchaeota, agrees with the tentative assignment of the highly abundant OH-GDGTs-0 to methanogenic archaea. Such interpretation is necessarily circumstantial considering that the compound and carbon isotope composition of the membranes of ANME and methanogenic archaea is similar. Although production of OH-GDGTs has been previously reported for both planktonic Thaumarchaeota and ANME, OH-GDGT-0 as sole and highly abundant OH-GDGT has only been recognized in one culture of methanogenic archaea. Therefore, the high abundance of ¹³C-depleted hydroxylated GDGTs-0 compared to only minor contents of regular, ANME-derived GDGTs 1–4 with similar ¹³C-depletions can possibly be used as an indicator for methylotrophic methanogenesis in seep environments. Future experimental work is needed and should test if ¹³C-depleted hydroxylated GDGTs-0 are indeed biomarkers of methylotrophic methanogenesis at seeps.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104862"},"PeriodicalIF":2.6,"publicationDate":"2024-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652443","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":"Environmental controls on the distribution of GDGT molecules in Lake Höglwörth, Southern Germany","authors":"Sudip Acharya ,&nbsp;Roland Zech ,&nbsp;Paul Strobel ,&nbsp;Marcel Bliedtner ,&nbsp;Maximilian Prochnow ,&nbsp;Cindy De Jonge","doi":"10.1016/j.orggeochem.2023.104689","DOIUrl":"https://doi.org/10.1016/j.orggeochem.2023.104689","url":null,"abstract":"<div><p>Tetraether lipids, such as glycerol dialkyl glycerol tetraethers (GDGTs), are an increasingly used proxy for reconstructing paleoclimatic and paleoenvironmental dynamics. On a global scale, environmental drivers controlling the distribution of GDGTs in lake systems have been described extensively. However, the drivers that control down-core sedimentary GDGT composition within single lake systems are still poorly constrained. Here, we analysed GDGTs in a sediment core collected from Lake Höglwörth (Bavaria, Germany) covering the last ∼1100 years. The increase in ratio ΣIIIa/ΣIIa values (a ratio which captures the variation of 3 structural isomers of penta- and hexamethylated brGDGTs respectively) reflects a higher contribution of branched (br) GDGTs from aquatic sources after 1800 CE. This is synchronous with a high nutrient input as a result of increased local anthropogenic activities. The climate proxy methylation of branched tetraethers (MBT'_5ME) reveals a pattern that deviates from the anticipated temperature changes during the last millennium. Instead, high MBT'_5ME values from ∼880 to 1120 CE coincide with a period of increased soil input, resulting from lake damming and/or construction of the Höglwörth monastery. Decreased values after 1800 CE until present date correspond to a higher contribution of aquatic brGDGTs, with changes in the dependency between Ia and IIa suggesting a direct influence of bacterial community changes on the MBT'_5ME. The proxy cyclisation of branched tetraethers (CBT') shows a linear increase with time, and a stepwise increase at 1700 CE, when a creek stream inflow channel was rerouted. Over time, MBT’_5ME decreases gradually, while CBT’ and ΣIIIa/ΣIIa increase. This is hypothesized to be potentially caused by decreasing water depth over time and/or post- or <em>syn</em>-sedimentary production of GDGTs. The degree of cyclization (DC') shows variations on shorter timescales, possibly driven by the lake mixing regime and water column redox conditions. Our results indicate that caution must be taken when interpreting GDGTs for paleoclimate and paleoenvironmental reconstruction considering the possible influence of shifts in the provenance of brGDGTs. Further studies focusing on both sedimentary and intact polar lipids are highly recommended to constrain the source (water column, or sedimentary production) of GDGTs in lake sediments.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"186 ","pages":"Article 104689"},"PeriodicalIF":3.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41227933","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":"Constraining multi-stage and protracted oil generation of alkaline lacustrine source rocks by heteroatomic compounds","authors":"Jingkun Zhang ,&nbsp;Jian Cao ,&nbsp;Baoli Xiang ,&nbsp;Ni Zhou ,&nbsp;Wanyun Ma ,&nbsp;Dan He","doi":"10.1016/j.orggeochem.2023.104668","DOIUrl":"10.1016/j.orggeochem.2023.104668","url":null,"abstract":"<div><p>It is unclear whether source rocks deposited in ancient alkaline lakes undergo multiple stages of hydrocarbon generation, particularly of oils. In this study, the lower Permian Fengcheng Formation in the Junggar Basin, China, was investigated using the geochemistry of heteroatomic species, with a focus on N-containing compounds, by negative-ion electrospray high-resolution Fourier transform ion cyclotron resonance mass spectrometry. The maturity parameters based on N-containing compounds (e.g., C_0–5/C_15–35-DBE 12 N₁ and C_0–5/C_15–35-DBE 15 N₁) and aromatic hydrocarbons (TMNr) reveal progressive generation of mature to highly mature crude oils. The polymerization index P1 ([DBE 18 + DBE 15]/DBE 12_N₁), alkylation index R1 (<em>R</em>C₆₋₃₅/<em>R</em>C₀₋₅), and paleo-salinity index (β carotane/<em>n</em>C_max) of the Fengcheng Formation source rocks suggest that the high salinity inhibited molecular polymerization of organic matter and prolonged the oil generation peak, which produced highly mature crude oils in the late stages of hydrocarbon generation. Therefore, alkaline lacustrine source rocks undergo multiple stages of protracted oil generation, which results in a longer oil window and higher threshold for gas generation than in the case of the classic Tissot model. The results highlight the oil generation potential of deep basins containing alkaline lacustrine source rocks and highly mature organic matter, which also have a lower gas-generation potential than previously thought.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"184 ","pages":"Article 104668"},"PeriodicalIF":3.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41311817","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":"Advancing chemical lability assessments of organic matter using a synthesis of FT-ICR MS data across diverse environments and experiments","authors":"Juliana D'Andrilli ,&nbsp;Carlos M. Romero ,&nbsp;Phoebe Zito ,&nbsp;David C. Podgorski ,&nbsp;Robert A. Payn ,&nbsp;Stephen D. Sebestyen ,&nbsp;Andrew R. Zimmerman ,&nbsp;Fernando L. Rosario-Ortiz","doi":"10.1016/j.orggeochem.2023.104667","DOIUrl":"10.1016/j.orggeochem.2023.104667","url":null,"abstract":"<div><p>Patterns in Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) data provide perspective on how organic matter (OM) character is shaped by natural processes. Here, we reevaluate and update the molecular lability boundary (MLB) approach to assess OM lability using a synthesis of FT-ICR MS data. Now included are MLB_L (biolability) indices (i.e., the OM proportion of hydrogen-to-carbon ratios ≥ 1.5) of freshwaters, plant litter and biochar leachates, soils, and oils across the US, trends in OM and dissolved OM (DOM) lability from laboratory experiments examining isolated microbial, photochemical, and thermal degradation, and biogeochemical interpretations of biolability patterns across ecosystems influenced by human activity (e.g., fertilizer addition and agricultural management). Photo-processing increased the hydrogen saturation of OM, describing products of higher biolability (&gt;MLB_L values). DOM MLB_L values decreased during microbial and thermal degradation processes. Laboratory experiments with isolated treatments showed larger changes in MLB_L than exhibited by field samples from systems managed by humans. We interpret changes in N- and/or S-containing DOM above the MLB as the production or use of heterogeneously biolabile material. We interpret heterogeneously labile DOM composition to indicate autochthonous production, biomass growth, nutrient accumulation, or biological degradation in stream and soil samples. The most recent data in our synthesis suggest that the MLB approach should be reframed to provide lability indices for biotic, thermal, and photochemical processes. A broader perspective on lability provides a useful tool to decompose large, complex, and process-driven DOM data into more simple and informative indicators of trends in ecosystem form and function.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"184 ","pages":"Article 104667"},"PeriodicalIF":3.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0146638023001134/pdfft?md5=20dea096e3c5865ebbbc39655518a301&pid=1-s2.0-S0146638023001134-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44845762","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":"Impact of biodegradation on methyltrimethyltridecylchromans (MTTCs) in crude oils from the Bohai Bay Basin, China","authors":"Xiaoyong Yang ,&nbsp;Youjun Tang ,&nbsp;Yi Yang ,&nbsp;Haifeng Yang ,&nbsp;Feilong Wang ,&nbsp;Xiaoxia Lü","doi":"10.1016/j.orggeochem.2023.104669","DOIUrl":"10.1016/j.orggeochem.2023.104669","url":null,"abstract":"<div><p>Methyltrimethyltridecylchromans (MTTCs), a class of aromatic hydrocarbon molecular marker compounds, provide an assessment of paleosalinity and maturity in sediments and crude oils. However, little is known about the effect of biodegradation on MTTCs. In this study, the saturated and aromatic fractions of a suite of oils from the Neogene Guantao (N₁g) and Minghuazhen (N₁m) Formation in the Miaoxi Depression, Bohai Bay Basin, were analyzed. Distriubutions of the more bioresistive biomarker show that the oils are derived from similar organic matter (dominantly from higher plants) and depositional environments (low salinity), and have similar maturity (in the middle oil window). Two biodegradation scales, were used to evaluate the level of biodegration. The samples ranged from PM 1 to 8 and MN2 from 140 to 983 (slight to heavy-severe biodegraded).</p><p>MTTC concentrations decrease with the increasing biodegradation levels and are or almost completely removed at PM = 8. The degree of alkylation affect their relative susceptibilities to biodegradation: trimethyl-MTTC (α-MTTC) &gt; dimethyl-MTTCs (including β-MTTC, γ-MTTC and ζ-MTTC) &gt; monomethyl-MTTC (δ-MTTC). The relative susceptibilities of dimethyl-MTTC isomers are γ-MTTC &gt; β-MTTC &gt; ζ-MTTC. The β/γ-MTTC, a maturity indicator, is significantly impacted by biodegradation. Paleosalinity inidcators, α/δ-MTTC, α/γ-MTTC, MTTCI and a ternary diagram of the relative abundance in different degree of alkylation of MTTCs, consistently indicate the oils are derived from sources deposited in a low samility environment. Additional research is needed to determine if biodegradation perturbs MTTC distributions in oils from other source environments to influence the inferred paleosalinity assessment.</p></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"184 ","pages":"Article 104669"},"PeriodicalIF":3.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41360918","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}