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  • A new sea surface temperature proxy based on bacterial 3-hydroxy fatty acids
    Org. Geochem. (IF 3.120) Pub Date : 2020-01-13
    Yi Yang; Canfa Wang; James A. Bendle; Xiaoguo Yu; Chao Gao; Xiaoxia Lü; Xiaoyan Ruan; Ruicheng Wang; Shucheng Xie

    3-Hydroxy fatty acids (3-OH-FAs), derived from Gram-negative bacterial outer membranes, have received recent attention for their potential as new terrestrial pH and temperature proxies for palaeoclimate studies. However, it is not known whether 3-OH-FAs based proxies can be developed and applied to the marine environment. Here we analyze 3-OH-FAs from a latitudinal transect of marine surface sediments from the North Pacific Ocean (12 °N to 61 °N with a mean annual sea surface temperature (SST) range of 28.1 °C to 1.3 °C). The results show that distributions of 3-OH-FAs in marine sediments yield overall higher abundances of anteiso 3-OH-FA homologues compared to soils. Furthermore, 16S rRNA gene sequencing of the marine sediments and soils shows the Gram-negative bacterial community is dominated by Proteobacteria (ca. 94%) at the phylum level. In contrast, in regional soils the Gram-negative bacterial community is more diverse with significant contributions from Proteobacteria (ca. 50%), Acidobacteria (ca. 24%), Verrucomicrobia (6%), Bacteroidetes (6%) and other phyla. These distinct genomic and molecular differences suggest distinctly different aggregate compositions of bacteria that produce 3-OH-FA in the marine realm vs soils. Moreover, we find that the ratio of anteiso to normal C13 3-OH-FA (RAN13) measured in surface sediments is highly correlated with mean annual SST throughout the temperature transect (1.3–28.1 °C). When applied to a short sediment core from the East China Sea, the SST changes reconstructed by the RAN13 proxy are comparable to instrumental SST data. These findings demonstrate that RAN13 and potentially other, so far undiscovered, proxies based on 3-OH-FAs have potential for environmental and palaeoclimate applications in marine environments.

    更新日期:2020-01-13
  • Heterocyte glycolipid diketones: A novel type of biomarker in the N2-fixing heterocytous cyanobacterium Microchaete sp
    Org. Geochem. (IF 3.120) Pub Date : 2020-01-10
    Thorsten Bauersachs; Muriel Gugger; Lorenz Schwark

    The heterocyte (heterocyst) glycolipid (HG) content of heterocytous (heterocystous) cyanobacteria can principally be separated into two different types. In the first type, the aglycone moiety attached to the sugar headgroup exclusively contains hydroxyl functionalities resulting in the formation of HG diols and HG triols. In the second type, one of the hydroxyl groups is replaced by a ketone functionality giving rise to HG keto-ols and HG keto-diols. In the N2-fixing heterocytous cyanobacterium Microchaete sp. PCC 7126 both types of HGs were dominant and consisted primarily of two structural isomers each of the HG28 diol and HG28 keto-ol. In addition to these well-characterized HGs, Microchaete sp. PCC 7126 also contained a yet undescribed type of HG that based on comparison of retention times, molecular weight and mass spectrometry consisted of a hexose headgroup attached to an aglycone moiety with 28 carbon atoms at which two instead of one ketone functionalities were attached. Hence, the novel HG structure was identified as HG28 diketone. This study thus provides further evidence for the large structural diversity of HGs, which allows chemotaxonomic profiling of heterocytous cyanobacteria and in turn studying community composition of these important diazotrophs in the geological rock record.

    更新日期:2020-01-11
  • Identification of a novel undecamethylhenicosane and three oxygenated precursors in a Maoming Basin shale, China
    Org. Geochem. (IF 3.120) Pub Date : 2020-01-07
    Jing Liao; Hong Lu; Qiao Feng; Youping Zhou; Quan Shi; Ping'an Peng; Guoying Sheng

    Further to our recent identification of a C33 botryococcane, a C33 botryococcan-24-one and two C31 botryococcanes (2,3,6,7,10,12,15,16,19,20-decamethylhenicosanes: C31 DMHs) with a methyl group β-positioned to the sole quaternary carbon in the skeleton in a sediment sample from the Maoming Basin, we report the NMR-based structural identification of a new C32 botryococcane (2,3,6,7,10,10,12,15,16,19,20-undecamethylhenicosane: C32 UMH), and MS-based structural identification of a C32 botryococcanal (C32 UMH-al) and two C31 epimeric botryococcanols (C31 DMH-ols) in the same sediment sample after trimethylsilylation. These three oxygenated botryococcanoids are speculated to possess the same β-positioned methyl group (to the sole quaternary carbon). We propose that the C32 UMH-al and two epimeric C31 DMH-ols are degradation products of the C=C double bond in the ethenyl group connected to the sole quaternary carbon in their biological precursor C33 botryococcene with a unique β-positioned methyl group (to the quaternary carbon), and are geochemical precursors for the C32 UMH and previously identified C31 DMHs, respectively. Since it is known that abiotic degradation (photo-mediated or autoxidation) preferentially acts on the internal double bond while sedimentary bacteria preferentially degrade the terminal double bond, our finding of a degraded terminal C24-25 double bond and an intact internal double bond (at C11-12) is indicative of bacterially mediated degradation. A detailed bacterially mediated degradation pathway is proposed to explain the formation of C31–C33 botryococcanes and their oxygenated derivatives.

    更新日期:2020-01-07
  • Improving the extraction efficiency of sedimentary carbohydrates by sequential hydrolysis
    Org. Geochem. (IF 3.120) Pub Date : 2020-01-03
    Rong Zhu; Julie Tolu; Longhui Deng; Annika Fiskal; Lenny H.E. Winkel; Mark A. Lever

    Carbohydrates serve as structural materials, energy storage compounds, and energy carriers in organisms and provide insights into the dominant sources and the degradation state of organic matter (OM). Several studies have analyzed dissolved and/or particulate carbohydrates in the environment, often with the aim of studying particular carbohydrate groups of interest. These studies have often employed different acids and hydrolytic conditions, making comparisons across studies a challenge. Here, we introduce a sequential acid hydrolysis protocol for the comprehensive extraction, quantification and compositional investigation of carbohydrates in sediment samples. This protocol has four acid hydrolysis steps that sequentially increase in extraction strength, where each subsequent hydrolysis step is performed on the unextracted remains previously hydrolyzed. The four hydrolysis steps consist of 1 M HCl for 2 h at (1) room temperature, (2) 50 °C, and (3) 105 °C, followed by incubation for 8 h using (4) 6 M HCl and 105 °C. Based on tests using diverse carbohydrate standard compounds, the protocol recovers most di- and oligosaccharides and soluble polysaccharides during the initial hydrolysis steps, whereas the recovery of most insoluble polysaccharides is highest during the final extraction step. Applying this protocol to different sediment types shows that recoveries of neutral sugars, amino sugars and sugar alcohols are on average ∼60% higher than with a reference one-step extraction method using only hydrolysis with hot 6 M HCl. This sequential extraction protocol thus provides an important new tool for the quantitative and compositional analysis of carbohydrates in aquatic sediments.

    更新日期:2020-01-04
  • A novel PARAFAC model for continental hot springs reveals unique dissolved organic carbon compositions
    Org. Geochem. (IF 3.120) Pub Date : 2020-01-03
    Joshua Nye; Everett Shock; Hilairy Hartnett

    Dissolved organic carbon in hot springs reflects a range of sources and biogeochemical processes. We evaluated ∼200 continental hot spring samples, with a range in pH and temperature, collected from the Tengchong hydrothermal region, Yunnan Province, China and Yellowstone National Park, Wyoming, USA. Dissolved organic carbon concentrations ranged from 16.7 µM to 2.97 mM. Acidic springs displayed the highest values and widest range in carbon concentration. Alkaline springs had a narrower range and lower average concentrations. Carbon composition was evaluated using ultraviolet absorption and 3D fluorescence spectroscopy. Total fluorescence was correlated (p < 0.05) with dissolved organic carbon (DOC) concentration. Fluorescence excitation-emission matrices were deconvolved using parallel factor analysis. We validated a five-component model that represented >97% of the total fluorescence. Our model includes three humic-like components, one protein-like component, and one novel component exclusively observed in highly acidic springs. The closest spectral match to the novel component is an acid-soluble lignin produced during high-temperature, acid digestion of wood pulp. Humic-like components were dominant in mid-pH springs (4 < pH < 7) indicating these springs had greater terrestrial carbon input. Acidic springs also exhibited evidence for terrestrial carbon input. Alkaline springs, in contrast, consistently had low dissolved organic carbon content and low fluorescence intensity suggesting that these springs had little terrestrial input. This absence of terrestrial carbon implies a predominantly hydrothermal fluid source. A comparison of the traditional fluorescence indices with our five model components suggest that these indices may have limited utility in continental hot springs with multiple organic matter sources and alteration processes.

    更新日期:2020-01-04
  • Superimposed secondary alteration of oil reservoirs. Part I: Influence of biodegradation on the gas generation behavior of crude oils
    Org. Geochem. (IF 3.120) Pub Date : 2020-01-02
    Yuhong Liao; Weimin Liu; Yinhua Pan; Xiaofeng Wang; Yunpeng Wang; Ping'an Peng

    Due to multi-stage tectonic movements, many oil reservoirs in typical superimposed basins of China have undergone more than one secondary alteration. Typically, these oil reservoirs experienced biodegradation at an early stage followed by thermal alteration at a later stage. The extent of each secondary alteration can be variable. Here, the succession of biodegradation and subsequent thermal alteration is called superimposed secondary alteration. This study aims not only to show the superimposed secondary alteration process in the reservoir by laboratory simulations, but also to show how varying extents of biodegradation influence the gas generation behavior of crude oils under thermal stress. Hydrocarbon gas generation potential is significantly reduced at the low to moderate biodegradation stage because of the selective removal of normal and branched alkanes. Hydrocarbon gases generated from the more severely biodegraded oils are drier, attributable to the decreasing yields of C2–C5 gases relative to methane. In the oil-generative window, the methane generated from more severely biodegraded oils is relatively enriched in 13C. Kinetic modeling suggests that moderately and severely biodegraded oils are thermally less stable than the non-biodegraded and slightly biodegraded oils. The bulk hydrocarbon gas yields from the non-biodegraded oil do not exceed those from the moderately biodegraded oils until EasyRo > 1.6%. For EasyRo of 1.6–2.5%, pyro-bitumen yields from heavily to severely biodegraded oils were about 2–4 times that of non-biodegraded oil. That is, the gas yields normalized to the weight of pyro-bitumen from heavily to severely biodegraded oil is only 25–50% of the gas yield of non-biodegraded oil. Therefore, hydrocarbon gas resource potential based on pyro-bitumen content must be very carefully considered in cases of superimposed secondary alteration.

    更新日期:2020-01-02
  • Cadalenes and norcadalenes in organic-rich shales of the Permian Irati Formation (Paraná Basin, Brazil): tracers for terrestrial input or also indicators of temperature-controlled organic-inorganic interactions?
    Org. Geochem. (IF 3.120) Pub Date : 2019-12-17
    Laercio Lopes Martins; Hans-Martin Schulz; Hélio Jorge Portugal Severiano Ribeiro; Caroline Adolphsson do Nascimento; Eliane Soares de Souza; Georgiana Feitosa da Cruz

    Cadalene, isocadalene and a series of norcadalenes were identified in black shales of the Permian Irati Formation in the northeastern and central eastern Paraná Basin (Brazil). The origin of their α-isomers with an isopropyl substituent is potentially related to higher plants, and likely reflects the spreading of pteridophytes and gymnosperms after the glaciation of southern Gondwana. A general increase in the relative abundance of isocadalene (1,6-dimethyl-3-isopropylnaphthalene, the β-isomer) co-occurs in with increasing thermal maturity at the base of the Amaral Machado Quarry (northeastern basin), and refers to the acid-catalyzed rearrangement of cadalene (1,6-dimethyl-4-isopropylnaphthalene, the α-isomer) due to the presence of montmorillonite, via an organic-inorganic interaction. This localized and incipient maturation can be related to diabase sills of the Serra Geral Formation. Similar maturation due to heating also affected the distribution of the norcadalenes by thermally stabilizing their α-isomers with an isopropyl substituent, in addition to the formation of related compounds with an ethyl substituent. Based on this, a norcadalene ratio is proposed, which is the sum of the 1,6-dimethyl-4-ethylnaphthalene and 1,6-dimethyl-3-ethylnaphthalene over the sum of the 1-isopropyl-4-methylnaphthalene and 1-isopropyl-7-methylnaphthalene. The results of this ratio and the established cadalene ratio resemble each other whereas samples from the São Mateus do Sul Quarry (central eastern basin) were not affected by thermal maturation and are characterized by a uniform distribution of the cadalenes and norcadalenes.

    更新日期:2019-12-18
  • Aromatic hydrocarbons provide new insight into carbonate concretion formation and the impact of eogenesis on organic matter
    Org. Geochem. (IF 3.120) Pub Date : 2019-12-12
    C. Plet; K. Grice; A.G. Scarlett; W. Ruebsam; A.I. Holman; L. Schwark

    Investigation of aromatic biomarkers extracted from carbonate concretions can contribute to characterize the enhanced microbial activity that mediates carbonate concretion formation. This microbial footprint can be further inferred from the stable isotopic values of carbonate (δ13C) and pyrite (δ34S). Here, we used a combination of GC-MS and GC×GC-ToF-MS to compare the aromatic fractions of two Toarcian carbonate concretions from the H. falciferum ammonite zone of the Posidonia Shale (SW-Germany) and their host sediment. The results revealed that n-alkylated and phytanyl arenes were enhanced in the concretions relative to the host sediment. These findings support a very early diagenetic (eogenetic) microbial source for alkylated and phytanyl arenes derived from the microbial ecosystem mediating concretion formation. In contrast, aromatic compounds formed by thermal maturation (e.g. polycyclic aromatic hydrocarbons, aromatic steroids, organic sulphur compounds) remained invariant in host rock and concretion samples. When combined with bulk sediment and concretion properties, the distribution of aromatic compounds indicates that eogenetic microbial activity upon concretion growth does not diminish organic matter quality.

    更新日期:2019-12-13
  • Amino acids in surface sediments of the Zannone Island shelf (Western Mediterranean Sea): possible bioindicators of submarine hydrothermal activity
    Org. Geochem. (IF 3.120) Pub Date : 2019-12-09
    E. Sañé, M. Ingrassia, E. Martorelli, FL. Chiocci

    This study shows results from amino acid analysis of seafloor sediment sampled between ∼80 and ∼130 m depth, within an active hydrothermal field located off Zannone Island (Tyrrhenian Sea). The total hydrolysable amino acid (THAA) content was determined at eight stations, three located within the main hydrothermal depression (i.e. the Zannone Giant Pockmark, ZGP) and five located in the surrounding seafloor. THAA concentration ranged between ∼2 and ∼11 nmol mg-1 dw and the lowest THAA concentrations were found at stations located within the ZGP. Amino acids resistant to degradation or originating from bacteria (β-alanine, histidine, leucine, arginine and lysine) had higher relative abundances inside the ZGP, whereas amino acids susceptible to degradation or originating from cellular plasma (proline, phenylalanine and tyrosine) showed higher relative abundances outside the ZGP. Degradation and reactivity indices were calculated, and the sedimentary organic matter in the three outside ZGP stations B07, B08 and B09 was found to be the most labile and reactive. Together with THAA concentrations, sediment grain size and carbon percentages were measured at 12 stations, five located within ZGP and seven located outside the ZGP. At all stations, the percentage of sand was ∼75% or higher. Carbon percentages were lower in samples located inside the ZGP than in the surrounding stations. The southern outside ZGP station B12 was found to be similar in terms of amino acids composition to the three inside ZGP stations, suggesting the influence of the hydrothermal fluids at this station.

    更新日期:2019-12-11
  • Organic geochemical signals of controlling freshwater dynamics on salinity stratification in organic-rich shales in the Lower Permian Irati Formation (Paraná Basin, Brazil)
    Org. Geochem. (IF 3.120) Pub Date : 2019-11-18
    Laercio Lopes Martins, Hans-Martin Schulz, Hélio Jorge Portugal Severiano Ribeiro, Caroline Adolphsson do Nascimento, Eliane Soares de Souza, Georgiana Feitosa da Cruz

    The Lower Permian Irati Formation in the northeastern and central eastern Paraná Basin (southern Brazil) was investigated in terms of bulk and molecular organic geochemistry in order to enlighten the complex depositional paleoenvironment during deposition of Irati black shales. The geochemical data reflect temporal and spatial variations of freshwater incursions promoting salinity stratification and high primary productivity in surface waters with the establishment of photic zone euxinia. Overall, highly concentrated C17 long-chain alkylnaphthalenes point to algal blooms as a result of freshwater inflows into the Irati Sea, mostly in the central eastern basin segment, and resemble concentration variations of pristane, phytane and nC17. The freshwater inflows were also retraced by increasing chroman ratios toward the top of the investigated units along with the general decrease of further palaeosalinity indicators, e.g., gammacerane, tetracyclic (C24), β-carotane, and the herein suggested γ-carotane and lexane indexes. The existence of a water column stratification promoting organic matter preservation is supported by the detection of tetrahydrophenanthrene at high concentrations, in addition to the known prominent occurrence of gammacerane. The detection of C10 to C31 aryl isoprenoids in addition to C16 and C18 pseudohomologue aryl isoprenoids points to the presence of photic zone euxinia. In general, samples from the central eastern basin were deposited in a deeper marine setting with lower salinity than samples from the northeastern basin, which displays signals of a shallower marine environment with reducing bottom water conditions, both deposited under freshwater influxes.

    更新日期:2019-11-19
  • Black carbon as a significant component of aromatic carbon in surface soils and its importance is enhanced in volcanic ash soil profiles
    Org. Geochem. (IF 3.120) Pub Date : 2019-11-16
    Guan-Yang Lu, Hiroko Imai, Kosuke Ikeya, Hiroaki Sumida, Akira Watanabe

    Black carbon (BC) constitutes a refractory carbon (C) pool in soil and other environments. Estimating the amount and dynamics of BC in soil is important in terms of the global C cycle. The goal of this study was to characterize the contribution of BC to total and aromatic C in a variety of soils using the benzene polycarboxylic acid (BPCA) method and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Thirteen A-/Ap (plowed layer)-horizon soils that belong to widely distributed soil series (Humic Andosols, Dystric Cambisols, Gleyic Cambisols, Eutric Fluvisols, and Dystric Planosols) under typical land uses (forest, grassland, upland field, and paddy field) in Japan and two Andosol profiles were analyzed. Three humic acid samples that included the green fraction that includes 4,9-dihydroxyperylene-3,10-quinone (DHPQ) as a chromophore and has mycorrhiza as a possible source (referred to as Pg) were also subjected to the BPCA procedure. The BC content in the 13 A-/Ap-horizon soils was 0.3–53 g C kg-1 or 5.7–48% of the total soil C (BC%). The BC content correlated positively with the total C content and with aromatic C content, while the relationship between BC% and soil order or land use was not clear. An analysis of Pg suggested the potential contribution of DHPQ to the yield of benzenehexacarboxylic acid in the BPCA method. The variations in BC content and C composition of two Andosol profiles indicated a greater stability of BC than the other types of C, including monocyclic aromatic C. The contribution of BC to aromatic C in their lower layers was estimated to be ca. 55–70% based on a regression equation when assuming that 70–90% of the BC was aromatic C.

    更新日期:2019-11-18
  • Abiotic Formation of Dissolved Organic Sulfur in Anoxic Sediments of Santa Barbara Basin
    Org. Geochem. (IF 3.120) Pub Date : 2019-06-10
    Hussain A. Abdulla, David J. Burdige, Tomoko Komada

    Sulfurization has been found to enhance organic matter preservation and petroleum formation in marine sediments. However, we do not yet have a comprehensive understanding of sulfurization mechanisms. In this study, we investigated several possible mechanisms of dissolved organic sulfur (DOS) formation in the top 4.5 m of anoxic sediments of Santa Barbara Basin (SBB), California Borderland. Using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS), we identified chemical formulas of potential dissolved organic matter (DOM) precursors to these DOS compounds. We also examined how the formulas of abiotically formed DOS changed as a function of depth across a major redox gradient. Results show that abiotic nucleophilic addition reactions involving bisulfide (HS-) and polysulfide (HSx-) are the major sulfurization pathways that form DOS in anoxic pore waters of SBB sediments. We identified 2,124 unique DOS formulas that could be generated from the addition of HS- and HSx- to 2,203 DOM formulas, and this accounted for ∼70% of all DOS formulas detected in these pore waters. Examining the DOM formulas that served as reactants in the abiotic sulfurization reactions, we found that 64% contained only carbon, hydrogen, and oxygen (CHO formulas) while the remainder (34%) included nitrogen (DON formulas). Our results revealed high reactivity toward sulfurization among many of the CHO and DON formulas that have H/C and O/C elemental ratios that overlap with those of carboxyl-rich alicyclic molecules (CRAM). This specific class of formulas could play an important role in the formation of organic sulfur compounds in sulfidic marine ecosystems, and in the formation of sulfur-containing protokerogen in marine sediments. Our results further suggest that anoxic sediments are a source of DOS compounds to the oceans.

    更新日期:2019-11-18
  • Evaluation of environmental proxies based on long chain alkyl diols in the East China Sea
    Org. Geochem. (IF 3.120) Pub Date : 2019-10-31
    Linghui He, Manyu Kang, Dongrong Zhang, Guodong Jia

    Long chain alkyl diols (LCDs) in marine environments are useful indicators of source organisms, ambient temperature, upwelling and nutrient conditions. However, the distribution of LCDs in the western Pacific marginal seas has been rarely reported, where wide shallow continental shelves and huge freshwater input from many rivers occur. In this study, we analyzed LCDs in surface sediments distributed from the Changjiang River estuary (CRE) to the East China Sea shelf to evaluate their sources and associated environmental proxies. Our results showed that the fractional abundance of C32 1,15-diol (FC32 1,15-diol) was highest in coastal area close to the CRE, with FC32 1,15-diol > 15% implying significant freshwater input. The C28 and C30 1,13-diols showed a similar spatial distribution to the C32 1,15-diol, suggesting that the long chain diol index (LDI), a sea surface temperature (SST) proxy, may be biased by freshwater-derived diols. By excluding the freshwater-influenced samples (i.e., FC32 1,15-diol > 15%), LDI reflected the autumn SST, yielding minimum temperature residuals (0.2 ± 1.5 °C). The C28, C30 and C30:1 1,14-diols were abundant in the mid-depth (15–45 m) offshore environment that was affected only slightly by the Changjiang River plume, and decreased toward both the eutrophic estuarine and oligotrophic marine environments; whereas the C28:1 1,14-diol showed higher fractional abundances close to the CE. The spatial distribution of 1,14-diols is similar to that reported for Proboscia diatoms in this region, although the exact sources of 1,14-diol requires further study. Nutrient proxies based on 1,14-diols did not correlate well with nutrient concentrations in this river-dominated marginal sea, where nutrient supply is dominated by the Changjiang River input.

    更新日期:2019-11-01
  • Geochemical characterization and artificial thermal maturation of kerogen density fractions from the Eocene Huadian oil shale, NE China
    Org. Geochem. (IF 3.120) Pub Date : 2019-10-31
    Xiaomin Xie, Maowen Li, Jin Xu, Lloyd R Snowdon, John K Volkman

    Oil shale is an important alternative energy resource through retorting to produce liquid hydrocarbons. A key factor in determining the value of an oil shale resource is its hydrocarbon generation potential and particularly its maceral distribution. To examine this, single maceral concentrates were obtained from a 1 kg Eocene Huadian oil shale sample using float-sink separation of chemically demineralized kerogen. Nine different density fractions were separated: the Botryococcus fraction occurred in the lightest (<1.06 g/ml) material, lamalginite in the 1.06–1.23 g/ml fraction, while detrovitrinite dominated in a higher density fraction (1.26–1.36 g/ml), which also contained some lamalginite. The Rock-Eval S2 and hydrogen index parameters as well as the aliphatic compound peaks in Fourier transform infrared (FTIR) spectra all decreased with increasing kerogen density, whereas the Rock-Eval oxygen index and the aromatic compound peaks in FTIR spectra increased. The δ13C values show slight variation within the different density fractions. The δ13C value of parent shale kerogen is very close to that of the density fraction dominated by lamalginite (–25.1‰), because the sample is dominated by lamalginite macerals (>70%). The Botryococcus sp. fraction is isotopically enriched because Botryococcus sp. is typically significantly enriched in 13C (δ13C = –24.6‰). Artificial thermal maturation hydrocarbon generation results show that absolute hydrocarbon gas yields are similar among the different density fractions. The 1.06–1.12 g/ml fraction, dominated by lamalginite, generates nearly twice as much liquid hydrocarbon as the 1.26–1.30 g/ml fraction dominated by detrovitrinite. The maximum hydrocarbon yields correspond well with the Rock-Eval HI values. Calculated by the relationships among HI, detrovitrinite and alginite compositions, the HI is 909 and 177 mg HC/g TOC for the purified alginite and detrovitrinite fractions, respectively. Kinetics analysis shows that Ea (activation energy) is higher for the low-density fraction (1.06–1.12 g/ml) than that for the heavy fraction (1.26–1.30 g/ml), indicating that lamalginite not only has a much better hydrocarbon generation potential but also higher thermal stability. Therefore, this lamalginite-rich oil shale is well suited for exploitation by retorting, even though the retorting temperature would be higher than detrovitrinite-rich fractions.

    更新日期:2019-11-01
  • Two New Isoprenoidal Ketones Related to Botryococcus braunii in The Chinese Maoming Basin
    Org. Geochem. (IF 3.120) Pub Date : 2019-10-31
    Jing Liao, Xiangyun Zhang, Hong Lu, Youping Zhou, Quan Shi, Ping'an Peng, Guoying Sheng

    We report the spectroscopy-based (NMR, HRMS, IR) reassignment of the structures of two previously mis-identified saturated methyl ketones (C15 ketone: 5,9-dimethyl-6-isopropyl-2-decanone and C18 ketone: 4,9,11-trimethyl-6-isopropyl-2-dodecanone in Zhang et al., 2017) (Zhang, X.Y., Lu, H., Liao, J., Tang, C.M., Sheng, G.Y., Peng, P.A., 2017. Two new oxygen-containing biomarkers isolated from the Chinese Maoming oil shale by silica gel column chromatography and preparative gas chromatography., Journal of Separation Science 40, 813–818, now retracted) in Maoming oil shale to 5,6,9,10-tetramethylundecan-2-one and 4,7,8,11,12-pentamethyltridecan-2-one, respectively. A diagenetic pathway is proposed to explain the isotopic and structural closeness between these two methyl ketones and the recently identified saturated C31 alcohols, C32 aldehydes (Liao, J., Lu, H., Feng, Q., Zhou, Y.P., Shi, Q., Peng, P.A., Sheng, G.Y., 2019. Identification of a novel undecamethylhenicosane and three oxygenated precursors in a Maoming Basin shale, China. Organic Geochemistry, under review) and C33 ketones (all with a unique methyl group β to the sole quaternary carbon in their skeletons) obtained from the same Maoming Basin sediments. The pathway involves, firstly, epoxidation, hydration, oxidation and double decarboxylation of the C33 botryococcene to C31 botryococcene. Subsequent photo- or autoxidation of the internal double bond around the quaternary carbon in the C31 botryococcene in an oxic environment leads to the formation of a C31 hydroperoxy-alkene. A heterolytic (Hock-type) or homolytic cleavage of the hydroperoxy-alkene around the quaternary carbon then gives rise to the C15 and C18 unsaturated methyl ketones, respectively. The so-formed unsaturated ketones are then geochemically stabilized by hydrogenation in an anoxic environment.

    更新日期:2019-11-01
  • Sources and composition of organic matter for bacterial growth in a large European river floodplain system (Danube, Austria).
    Org. Geochem. (IF 3.120) Pub Date : 2009-03-01
    Katharina Besemer,Birgit Luef,Stefan Preiner,Birgit Eichberger,Martin Agis,Peter Peduzzi

    Dissolved and particulate organic matter (DOM and POM) distribution, lignin phenol signatures, bulk elemental compositions, fluorescence indices and microbial plankton (algae, bacteria, viruses) in a temperate river floodplain system were monitored from January to November 2003. We aimed to elucidate the sources and compositions of allochthonous and autochthonous organic matter (OM) in the main channel and a representative backwater in relation to the hydrological regime. Additionally, bacterial secondary production was measured to evaluate the impact of organic carbon source on heterotrophic prokaryotic productivity. OM properties in the backwater tended to diverge from those in the main channel during phases without surface water connectivity; this was likely enhanced due to the exceptionally low river discharge in 2003. The terrestrial OM in this river floodplain system was largely derived from angiosperm leaves and grasses, as indicated by the lignin phenol composition. The lignin signatures exhibited significant seasonal changes, comparable to the seasonality of plankton-derived material. Microbially-derived material contributed significantly to POM and DOM, especially during periods of low discharge. High rates of bacterial secondary production (up to 135 μg C L(-1) d(-1)) followed algal blooms and suggested that autochthonous OM significantly supported heterotrophic microbial productivity.

    更新日期:2019-11-01
  • All-cis hentriaconta-9,15,22-triene in microbial mats formed by the phototrophic prokaryote Chloroflexus.
    Org. Geochem. (IF 3.120) Pub Date : 2001-09-07
    M T van der Meer,S Schouten,D M Ward,J A Geenevasen,J S Sinninghe Damste

    All-cis hentriaconta-9,15,22-triene (I) has been isolated from Chloroflexus mats, Yellowstone National Park (USA), and identified by GC-(HR)MS analysis of I and its hydrogenated and DMDS-derivatized products and by 1H and 13C NMR spectroscopy.

    更新日期:2019-11-01
  • Carbon isotope effects associated with autotrophic acetogenesis.
    Org. Geochem. (IF 3.120) Pub Date : 1989-01-01
    J T Gelwicks,J B Risatti,J M Hayes

    The carbon kinetic isotope effects associated with synthesis of acetate from CO2 and H2 during autotrophic growth of Acetobacterium woodii at 30 degrees C have been measured by isotopic analyses of CO2, methyl-carbon, and total acetate. Closed systems allowing construction of complete mass balances at varying stages of growth were utilized, and the effects of the partitioning of carbon between CO2 and HCO3- were taken account. For the overall reaction, total carbonate --> total acetate, isotope effects measured in replicate experiments ranged from -59.0 +/- 0.9% to -57.2 +/- 2.3%. Taking into account all measurements, the weighted mean and standard deviation are -58.6 +/- 0.7%. There is no evidence for intramolecular ordering in the acetate. The carbon isotopic composition of sedimentary acetate, otherwise expected to be near that of sedimentary organic carbon, is likely to be depleted in environments in which autotrophic acetogenesis is occurring.

    更新日期:2019-11-01
  • The role of minerals in the thermal alteration of organic matter--III. Generation of bitumen in laboratory experiments.
    Org. Geochem. (IF 3.120) Pub Date : 1987-01-01
    B J Huizinga,E Tannenbaum,I R Kaplan

    A series of pyrolysis experiments, utilizing two different immature kerogens (from the Monterey and Green River Formations) mixed with common sedimentary minerals (calcite, illite, or Na-montmorillonite), was conducted to study the impact of the mineral matrix on the bitumen that was generated. Calcite has no significant influence on the thermal evolution of bitumen and also shows virtually no adsorption capacity for any of the pyrolysate. In contrast, montmorillonite and illite, to a lesser extent, alter bitumen during dry pyrolysis. Montmorillonite and illite also display strong adsorption capacities for the polar constituents of bitumen. By this process, hydrocarbons are substantially concentrated within the pyrolysate that is not strongly adsorbed on the clay matrices. The effects of the clay minerals are significantly reduced during hydrous pyrolysis. The strong adsorption capacities of montmorillonite and illite, as well as their thermocatalytic properties, may in part explain why light oils and gases are generated from certain argillaceous source-rock assemblages, whereas heavy immature oils are often derived from carbonate source rocks.

    更新日期:2019-11-01
  • Long-chain carboxylic acids in pyrolysates of Green River kerogen.
    Org. Geochem. (IF 3.120) Pub Date : 1986-01-01
    K Kawamura,E Tannenbaum,B J Huizinga,I R Kaplan

    Long-chain fatty acids (C10-C32), as well as C14-C21 isoprenoid acids (except for C18), have been identified in anhydrous and hydrous pyrolyses products of Green River kerogen (200-400 degrees C, 2-1000 hr). These kerogen-released fatty acids are characterized by a strong even/odd predominance (CPI: 4.8-10.2) with a maximum at C16 followed by lesser amounts of C18 and C22 acids. This distribution is different from that of unbound and bound geolipids extracted from Green River shale. The unbound fatty acids show a weak even/odd predominance (CPI: 1.64) with a maximum at C14, and bound fatty acids display an even/odd predominance (CPI: 2.8) with maxima at C18 and C30. These results suggest that fatty acids were incorporated into kerogen during sedimentation and early diagenesis and were protected from microbial and chemical changes over geological periods of time. Total quantities of fatty acids produced during heating of the kerogen ranged from 0.71 to 3.2 mg/g kerogen. Highest concentrations were obtained when kerogen was heated with water for 100 hr at 300 degrees C. Generally, their amounts did not decrease under hydrous conditions with increase in temperature or heating time, suggesting that significant decarboxylation did not occur under the pyrolysis conditions used, although hydrocarbons were extensively generated.

    更新日期:2019-11-01
  • Phenols in hydrothermal petroleums and sediment bitumen from Guaymas Basin, Gulf of California.
    Org. Geochem. (IF 3.120) Pub Date : 1996-01-01
    B R Simoneit,R N Leif,R Ishiwatari

    The aliphatic, aromatic and polar (NSO) fractions of seabed petroleums and sediment bitumen extracts from the Guaymas Basin hydrothermal system have been analyzed by gas chromatography and gas chromatography-mass spectrometry (free and silylated). The oils were collected from the interiors and exteriors of high temperature hydrothermal vents and represent hydrothermal pyrolyzates that have migrated to the seafloor by hydrothermal fluid circulation. The downcore sediments are representative of both thermally unaltered and thermally altered sediments. The survey has revealed the presence of oxygenated compounds in samples with a high degree of thermal maturity. Phenols are one class of oxygenated compounds found in these samples. A group of methyl-, dimethyl- and trimethyl-isoprenoidyl phenols (C27-C29) is present in all of the seabed NSO fractions, with the methyl- and dimethyl-isoprenoidyl phenols occurring as major components, and a trimethyl-isoprenoidyl phenol as a minor component. A homologous series of n-alkylphenols (C13-C33) has also been found in the seabed petroleums. These phenols are most likely derived from the hydrothermal alteration of sedimentary organic matter. The n-alkylphenols are probably synthesized under hydrothermal conditions, but the isoprenoidyl phenols are probably hydrothermal alteration products of natural product precursors. The suites of phenols do not appear to be useful tracers of high temperature hydrothermal processes.

    更新日期:2019-11-01
  • Carbon isotope systematics of individual hydrocarbons in hydrothermal petroleum from Escanaba Trough, northeastern Pacific Ocean.
    Org. Geochem. (IF 3.120) Pub Date : 1997-04-01
    B R Simoneit,M Schoell,K A Kvenvolden

    We submitted individual aliphatic and polycyclic aromatic hydrocarbons in samples of hydrothermal petroleum from Escanaba Trough to compound specific isotope analysis to trace their origins. The carbon isotope compositions of the alkanes and polycyclic aromatic hydrocarbons (means -27.5 and -24.7%, respectively) reflect a primarily terrestrial organic matter source.

    更新日期:2019-11-01
  • High molecular weight polycyclic aromatic hydrocarbons in hydrothermal petroleums from the Gulf of California and Northeast Pacific Ocean.
    Org. Geochem. (IF 3.120) Pub Date : 1996-10-01
    B R Simoneit,J C Fetzer

    Hydrothermal petroleums and heavy tars have been analyzed for polycyclic aromatic hydrocarbons (PAH) with molecular weights greater than that of coronene (300 da). Samples from the hydrothermal systems in the Guaymas Basin (Gulf of California) and in the Escanaba Trough and Middle Valley (Northeastern Pacific) were analyzed by gas chromatography-mass spectrometry and high pressure liquid chromatography with diode-array absorbance detection. Mass spectra and fluorescence spectra were used to characterize the compounds. Several large PAHs with six and more rings were identified among the heavy PAH. Production routes via one-ring build-up and Scholl-condensation are proposed to explain the observed structures. The variations in PAH concentrations and distributions between samples from different locales are a consequence of the hydrothermal conditions of generation, migration, and post-depositional alteration.

    更新日期:2019-11-01
  • Compound-specific isotopic analyses: a novel tool for reconstruction of ancient biogeochemical processes.
    Org. Geochem. (IF 3.120) Pub Date : 1990-01-01
    J M Hayes,K H Freeman,B N Popp,C H Hoham

    Patterns of isotopic fractionation in biogeochemical processes are reviewed and it is suggested that isotopic fractionations will be small when substrates are large. If so, isotopic compositions of biomarkers will reflect those of their biosynthetic precursors. This prediction is tested by consideration of results of analyses of geoporphyrins and geolipids from the Greenhorn Formation (Cretaceous, Western Interior Seaway of North America) and the Messel Shale (Eocene, lacustrine, southern Germany). It is shown (i) that isotopic compositions of porphyrins that are related to a common source, but which have been altered structurally, cluster tightly and (ii) that isotopic differences between geolipids and porphyrins related to a common source are equal to those observed in modern biosynthetic products. Both of these observations are consistent with preservation of biologically controlled isotopic compositions during diagenesis. Isotopic compositions of individual compounds can thus be interpreted in terms of biogeochemical processes in ancient depositional environments. In the Cretaceous samples, isotopic compositions of n-alkanes are covariant with those of total organic carbon, while delta values for pristane and phytane are covariant with those of porphyrins. In this unit representing an open marine environment, the preserved acyclic polyisoprenoids apparently derive mainly from primary material, while the extractable, n-alkanes derive mainly from lower levels of the food chain. In the Messel Shale, isotopic compositions of individual biomarkers range from -20.9 to -73.4% vs PDB. Isotopic compositions of specific compounds can be interpreted in terms of origin from methylotrophic, chemautotrophic, and chemolithotrophic microorganisms as well as from primary producers that lived in the water column and sediments of this ancient lake.

    更新日期:2019-11-01
  • Biological marker distribution in coexisting kerogen, bitumen and asphaltenes in Monterey Formation diatomite, California.
    Org. Geochem. (IF 3.120) Pub Date : 1986-01-01
    E Tannenbaum,E Ruth,B J Huizinga,I R Kaplan

    Organic-rich (18.2%) Monterey Formation diatomite from California was studied. The organic matter consist of 94% bitumen and 6% kerogen. Biological markers from the bitumen and from pyrolysates of the coexisting asphaltenes and kerogen were analyzed in order to elucidate the relationship between the various fractions of the organic matter. While 17 alpha(H), 18 alpha(H), 21 alpha(H)-28,30-bisnorhopane was present in the bitumen and in the pryolysate of the asphaltenes, it was not detected in the pyrolysates of the kerogen. A C40-isoprenoid with "head to head" linkage, however, was present in pyrolysates of both kerogen and asphaltenes, but not in the bitumen from the diatomite. The maturation level of the bitumen, based on the extent of isomerization of steranes and hopanes, was that of a mature oil, whereas the pyrolysate from the kerogen showed a considerably lower maturation level. These relationships indicate that the bitumen may not be indigenous to the diatomite and that it is a mature oil that migrated into the rock. We consider the possibility, however, that some of the 28,30-bisnorhopane-rich Monterey Formation oils have not been generated through thermal degradation of kerogen, but have been expelled from the source rock at an early stage of diagenesis.

    更新日期:2019-11-01
  • An isotopic biogeochemical study of the Green River oil shale.
    Org. Geochem. (IF 3.120) Pub Date : 1992-12-01
    J W Collister,R E Summons,E Lichtfouse,J M Hayes

    Thirty-five different samples from three different sulfur cycles were examined in this stratigraphically oriented study of the Shell 22x-l well (U.S.G.S. C177 core) in the Piceance Basin, Colorado. Carbon isotopic compositions of constituents of Green River bitumens indicate mixing of three main components: products of primary photoautotrophs and their immediate consumers (delta approximately -30% vs PDB), products of methanotrophic bacteria (delta approximately -85%), and products of unknown bacteria (delta approximately -40%). For individual compounds synthesized by primary producers, delta-values ranged from -28 to -32%. 13C contents of individual primary products (beta-carotane, steranes, acyclic isoprenoids, tricyclic triterpenoids) were not closely correlated, suggesting diverse origins for these materials. 13C contents of numerous hopanoids were inversely related to sulfur abundance, indicating that they derived both from methanotrophs and from other bacteria, with abundances of methanotrophs depressed when sulfur was plentiful in the paleoenvironment. gamma-Cerane coeluted with 3 beta(CH3),17 alpha(H),21 beta(H)-hopane, but delta-values could be determined after deconvolution. gamma-Cerane (delta approximately -25%) probably derives from a eukaryotic heterotroph grazing on primary materials, the latter compound (delta approximately -90%) must derive from methanotrophic organisms. 13C contents of n-alkanes in bitumen differed markedly from those of paraffins generated pyrolytically. Isotopic and quantitative relationships suggest that alkanes released by pyrolysis derived from a resistant biopolymer of eukaryotic origin and that this was a dominant constituent of total organic carbon.

    更新日期:2019-11-01
  • Molecular and bulk isotopic analyses of organic matter in marls of the Mulhouse Basin (Tertiary, Alsace, France).
    Org. Geochem. (IF 3.120) Pub Date : 1993-01-01
    D J Hollander,J S Sinninghe Damste,J M Hayes,J W de Leeuw,A Y Huc

    Contents of 13C in kerogens and carbonates in 21 samples from a core of the MAX borehole, Mulhouse Evaporite Basin, range from -27.3 to -23.5 and -3.7 to -1.8% vs PDB, respectively. Organic nitrogen in the same samples is enriched in 15N relative to atmospheric N2 by 12.2-15.7%. Hydrogen indices and delta values for kerogens vary systematically with facies, averaging 493 mg HC/g Corg and -25.7% in the most saline facies (dominated by inputs from aquatic sources) and 267 mg HC/g Corg and -23.7% in the least saline facies (50/50 aquatic/terrigenous). Values of delta were measured for individual aliphatic hydrocarbons from three samples representing three different organic facies. For all samples, terrigenous inputs were unusually rich in 13C, the estimated delta value for bulk terrigenous debris, apparently derived partly from CAM plants, being -22.5%. In the most saline facies, isotopic evidence indicates the mixing of 13C-depleted products of photosynthetic bacteria with 13C-enriched products of halotolerant eukaryotic algae. At lower salinities, a change in the producer community is marked by a decrease in the 13C content of algal lipids. The content of 13C in algal lipids increases in the least saline facies, due either to succession of different organisms or to decreased concentrations of dissolved CO2.

    更新日期:2019-11-01
  • The effect of aromatization on the isotopic compositions of hydrocarbons during early diagenesis.
    Org. Geochem. (IF 3.120) Pub Date : 1994-01-01
    K H Freeman,C J Boreham,R E Summons,J M Hayes

    Polycyclic aromatic hydrocarbons with varying degrees of aromatization were isolated from the Eocene Messel Shale (Rheingraben, Germany). The high abundances of these compounds and their structural resemblances to cyclic triterpenoid lipids are consistent with derivation from microbial rather than thermal processes. Compounds structurally related to oleanane contain from five to nine double bonds; those within a series of aromatized hopanoids contain from three to nine. All are products of diagenetic reactions that remove hydrogen or methyl groups, and, in several cases, break carbon-carbon bonds to open rings. Aromatized products are on average depleted in 13C relative to possible precursors by l.2% (range: l.5% enrichment to 4% depletion, n = 9). The dependence of 13C content on the number of double bonds is not, however, statistically significant and it must be concluded that there is no strong evidence for isotopic fractionation accompanying diagenetic aromatization. Isotopic differences between series (structures related to ursane, des-A-ursane, des-A-lupane, des-A-arborane, and possibly, des-A-gammacerane are present) are much greater, indicating that 13C contents are controlled primarily by source effects. Fractionations due to chromatographic isotope effects during HPLC ranged from 0.1 to 2.8%.

    更新日期:2019-11-01
  • Partial resolution of sources of n-alkanes in the saline portion of the Parachute Creek Member, Green River Formation (Piceance Creek Basin, Colorado).
    Org. Geochem. (IF 3.120) Pub Date : 1994-01-01
    J W Collister,E Lichtfouse,G Hieshima,J M Hayes

    Systematic variations in the 13C contents of individual extractable n-alkanes (C16-C29) can be modelled quantitatively and interpreted as indicating contributions from at least five distinct sources. These appear to be cyanobacterial (C16-C18, delta 13C = -37% vs PDB), phytoplanktonic (C16-C23, delta = -32%), chemoautotrophic bacterial (C20-C29, delta = -38%), phytoplanktonic or heterotrophic bacterial (C20-C29, delta = -30%), and vascular plants (C23-C29, delta = -29%). Hydrous pyrolysis of related kerogens yields large quantities of additional n-alkanes with different and much more uniform delta values. The latter materials are apparently derived from the thermolysis of aliphatic biopolymers whose presence in the Green River Oil Shale has been recognized visually.

    更新日期:2019-11-01
  • Predictive isotopic biogeochemistry: hydrocarbons from anoxic marine basins.
    Org. Geochem. (IF 3.120) Pub Date : 1994-01-01
    K H Freeman,S G Wakeham,J M Hayes

    Carbon isotopic compositions were determined for individual hydrocarbons in water column and sediment samples from the Cariaco Trench and Black Sea. In order to identify hydrocarbons derived from phytoplankton, the isotopic compositions expected for biomass of autotrophic organisms living in surface waters of both localities were calculated based on the concentrations of CO2(aq) and the isotopic compositions of dissolved inorganic carbon. These calculated values are compared to measured delta values for particulate organic carbon and for individual hydrocarbon compounds. Specifically, we find that lycopane is probably derived from phytoplankton and that diploptene is derived from the lipids of chemoautotrophs living above the oxic/anoxic boundary. Three acyclic isoprenoids that have been considered markers for methanogens, pentamethyleicosane and two hydrogenated squalenes, have different delta values and apparently do not derive from a common source. Based on the concentration profiles and isotopic compositions, the C31 and C33 n-alkanes and n-alkenes have a similar source, and both may have a planktonic origin. If so, previously assigned terrestrial origins of organic matter in some Black Sea sediments may be erroneous.

    更新日期:2019-11-01
  • Isotope-ratio-monitoring gas chromatography-mass spectrometry: methods for isotopic calibration.
    Org. Geochem. (IF 3.120) Pub Date : 1994-01-01
    D A Merritt,W A Brand,J M Hayes

    In trial analyses of a series of n-alkanes, precise determinations of 13C contents were based on isotopic standards introduced by five different techniques and results were compared. Specifically, organic-compound standards were coinjected with the analytes and carried through chromatography and combustion with them; or CO2 was supplied from a conventional inlet and mixed with the analyte in the ion source, or CO2 was supplied from an auxiliary mixing volume and transmitted to the source without interruption of the analyte stream. Additionally, two techniques were investigated in which the analyte stream was diverted and CO2 standards were placed on a near-zero background. All methods provided accurate results. Where applicable, methods not involving interruption of the analyte stream provided the highest performance (sigma = 0.00006 at.% 13C or 0.06% for 250 pmol C as CO2 reaching the ion source), but great care was required. Techniques involving diversion of the analyte stream were immune to interference from coeluting sample components and still provided high precision (0.0001 < or = sigma < or = 0.0002 at.% or 0.1 < or = sigma < or = 0.2%).

    更新日期:2019-11-01
  • Acquisition and processing of data for isotope-ratio-monitoring mass spectrometry.
    Org. Geochem. (IF 3.120) Pub Date : 1994-01-01
    M P Ricci,D A Merritt,K H Freeman,J M Hayes

    Methods are described for continuous monitoring of signals required for precise analyses of 13C, 18O, and 15N in gas streams containing varying quantities of CO2 and N2. The quantitative resolution (i.e. maximum performance in the absence of random errors) of these methods is adequate for determination of isotope ratios with an uncertainty of one part in 10(5); the precision actually obtained is often better than one part in 10(4). This report describes data-processing operations including definition of beginning and ending points of chromatographic peaks and quantitation of background levels, allowance for effects of chromatographic separation of isotopically substituted species, integration of signals related to specific masses, correction for effects of mass discrimination, recognition of drifts in mass spectrometer performance, and calculation of isotopic delta values. Characteristics of a system allowing off-line revision of parameters used in data reduction are described and an algorithm for identification of background levels in complex chromatograms is outlined. Effects of imperfect chromatographic resolution are demonstrated and discussed and an approach to deconvolution of signals from coeluting substances described.

    更新日期:2019-11-01
  • Molecular indicators for palaeoenvironmental change in a Messinian evaporitic sequence (Vena del Gesso, Italy). II: High-resolution variations in abundances and 13C contents of free and sulphur-bound carbon skeletons in a single marl bed.
    Org. Geochem. (IF 3.120) Pub Date : 1995-06-01
    F Kenig,J S Damsté,N L Frewin,J M Hayes,J W De Leeuw

    The extractable organic matter of 10 immature samples from a marl bed of one evaporitic cycle of the Vena del Gesso sediments (Gessoso-solfifera Fm., Messinian, Italy) was analyzed quantitatively for free hydrocarbons and organic sulphur compounds. Nickel boride was used as a desulphurizing agent to recover sulphur-bound lipids from the polar and asphaltene fractions. Carbon isotopic compositions (delta vs PDB) of free hydrocarbons and of S-bound hydrocarbons were also measured. Relationships between these carbon skeletons, precursor biolipids, and the organisms producing them could then be examined. Concentrations of S-bound lipids and free hydrocarbons and their delta values were plotted vs depth in the marl bed and the profiles were interpreted in terms of variations in source organisms, 13 C contents of the carbon source, and environmentally induced changes in isotopic fractionation. The overall range of delta values measured was 24.7%, from -11.6% for a component derived from green sulphur bacteria (Chlorobiaceae) to -36.3% for a lipid derived from purple sulphur bacteria (Chromatiaceae). Deconvolution of mixtures of components deriving from multiple sources (green and purple sulphur bacteria, coccolithophorids, microalgae and higher plants) was sometimes possible because both quantitative and isotopic data were available and because either the free or S-bound pool sometimes appeared to contain material from a single source. Several free n-alkanes and S-bound lipids appeared to be specific products of upper-water-column primary producers (i.e. algae and cyanobacteria). Others derived from anaerobic photoautotrophs and from heterotrophic protozoa (ciliates), which apparently fed partly on Chlorobiaceae. Four groups of n-alkanes produced by algae or cyanobacteria were also recognized based on systematic variations of abundance and isotopic composition with depth. For hydrocarbons probably derived from microalgae, isotopic variations are well correlated with those of total organic carbon. A resistant aliphatic biomacromolecule produced by microalgae is, therefore, probably an important component of the kerogen. These variations reflect changes in the depositional environment and early diagenetic transformations. Changes in the concentrations of S-bound lipids induced by variations in conditions favourable for sulphurization were discriminated from those related to variations in primary producer assemblages. The water column of the lagoonal basin was stratified and photic zone anoxia occurred during the early and middle stages of marl deposition. During the last stage of the marl deposition the stratification collapsed due to a significant shallowing of the water column. Contributions from anaerobic photoautotrophs were apparently associated with variations in depth of the chemocline.

    更新日期:2019-11-01
  • A molecular and carbon isotopic study towards the origin and diagenetic fate of diaromatic carotenoids.
    Org. Geochem. (IF 3.120) Pub Date : 1994-12-01
    W A Hartgers,J S Sinninghe Damsté,A G Requejo,J Allan,J M Hayes,Y Ling,T M Xie,J Primack,J W De Leeuw

    Pyrolysates of high-molecular-weight sedimentary fractions of the Duvernay Formation (Western Canada Basin) are dominated by 1,2,3,4- and 1,2,3,5-tetramethylbenzene, which, generated via beta-cleavage, indicate the presence of diaromatic carotenoids in the macromolecular aggregates. This was substantiated by desulphurization of sulphur-rich aggregates of the polar fraction, which released (partly) hydrogenated carotenoids. Furthermore, these components were important constituents of the aromatic hydrocarbon fractions and related oils. Apart from renieratane and isorenieratane, 1H NMR analysis established the aromatic substitution pattern of the most abundant component present, which was identified as a diaromatic compound with an unprecedented 2,3,6-/3,4,5-trimethyl aromatic substitution pattern. Molecular and isotopic analyses of both soluble and insoluble fractions of organic matter revealed relationships between diagenetically-derived carotenoids found in bitumen and related oils and their precursors incorporated into high-molecular-weight fractions. Aryl isoprenoids, important components in extracts and oils, were apparently derived from thermal cracking of bound diaromatic carotenoids rather than cleavage of free carotenoids as previously suggested. Furthermore, products derived from diaromatic carotenoids were substantially enriched in 13C relative to n-alkanes of algal origin. Together with the characteristic carotenoids, this isotopic enrichment provides evidence of significant contributions from photosynthetic green sulphur bacteria (Chlorobiaceae), which fix carbon via the reversed tricarboxylic acid (TCA) cycle. In spite of the prominence of these molecular signals, the overall isotopic composition of the organic matter indicated that only a very small portion of the preserved organic carbon was derived from the biomass of photosynthetic green sulphur bacteria.

    更新日期:2019-11-01
  • The combined application of organic sulphur and isotope geochemistry to assess multiple sources of palaeobiochemicals with identical carbon skeletons.
    Org. Geochem. (IF 3.120) Pub Date : 1992-12-01
    M E Kohnen,S Schouten,J S Sinninghe Damsté,J W de Leeuw,D Merrit,J M Hayes

    Five immature sediments from a Messinian evaporitic basin, representing one evaporitic cycle, were studied using molecular organic sulphur and isotope geochemistry. It is shown that a specific carbon skeleton which is present in different "modes of occurrence" ("free" hydrocarbon, alkylthiophene, alkylthiolane, alkyldithiane, alkylthiane, and sulphur-bound in macromolecules) may have different biosynthetic precursors which are possibly derived from different biota. It is demonstrated that the mode of occurrence and the carbon isotopic composition of a sedimentary lipid can be used to "reconstruct" its biochemical precursor. This novel approach of recognition of the suite of palaeobiochemicals present during the time of deposition allows for identification of the biological sources with an unprecedented specificity.

    更新日期:2019-11-01
  • Identification and quantification of polyfunctionalized hopanoids by high temperature gas chromatography-mass spectrometry.
    Org. Geochem. (IF 3.120) Pub Date : 2014-02-06
    Alex L Sessions,Lichun Zhang,Paula V Welander,David Doughty,Roger E Summons,Dianne K Newman

    Hopanoids are triterpenoids produced mainly by bacteria, are ubiquitous in the environment, and have many important applications as biological markers. A wide variety of related hopanoid structures exists, many of which are polyfunctionalized. These modifications render the hopanoids too involatile for conventional gas chromatography (GC) separation, so require either laborious oxidative cleavage of the functional groups or specialized high temperature (HT) columns. Here we describe the systematic evaluation and optimization of a HT-GC method for the analysis of polyfunctionalized hopanoids and their methylated homologs. Total lipid extracts are derivatized with acetic anhydride and no further treatment or workup is required. We show that acid or base hydrolysis to remove di- and triacylglycerides leads to degradation of several BHP structures. DB-XLB type columns can elute hopanoids up to bacteriohopane-tetrol at 350 °C, with baseline separation of all 2-methyl/desmethyl homologs. DB-5HT type columns can additionally elute bacteriohopaneaminotriol and bacteriohopaneaminotetrol, but do not fully separate 2-methyl/desmethyl homologs. The method gave 2- to 7-fold higher recovery of hopanoids than oxidative cleavage and can provide accurate quantification of all analytes including 2-methyl hopanoids. By comparing data from mass spectra with those from a flame ionization detector, we show that the mass spectromet (MS) response factors for different hopanoids using either total ion counts or m/z 191 vary substantially. Similarly, 2-methyl ratios estimated from selected-ion data are lower than those from FID by 10-30% for most hopanoids, but higher by ca. 10% for bacteriohopanetetrol. Mass spectra for a broad suite of hopanoids, including 2-methyl homologs, from Rhodopseudomonas palustris are presented, together with the tentative assignment of several new hopanoid degradation products.

    更新日期:2019-11-01
  • Xeropreservation of functionalized lipid biomarkers in hyperarid soils in the Atacama Desert.
    Org. Geochem. (IF 3.120) Pub Date : 2017-01-01
    Mary Beth Wilhelm,Alfonso F Davila,Jennifer L Eigenbrode,Mary N Parenteau,Linda L Jahnke,Xiao-Lei Liu,Roger E Summons,James J Wray,Brian N Stamos,Shane S O'Reilly,Amy Williams

    Our understanding of long-term organic matter preservation comes mostly from studies in aquatic systems. In contrast, taphonomic processes in extremely dry environments are relatively understudied and are poorly understood. We investigated the accumulation and preservation of lipid biomarkers in hyperarid soils in the Yungay region of the Atacama Desert. Lipids from seven soil horizons in a 2.5 m vertical profile were extracted and analyzed using GC-MS and LC-MS. Diagnostic functionalized lipids and geolipids were detected and increased in abundance and diversity with depth. Deeper clay units contain fossil organic matter (radiocarbon dead) that has been protected from rainwater since the onset of hyperaridity. We show that these clay units contain lipids in an excellent state of structural preservation with functional groups and unsaturated bonds in carbon chains. This indicates that minimal degradation of lipids has occurred in these soils since the time of their deposition between >40,000 and 2 million years ago. The exceptional structural preservation of biomarkers is likely due to the long-term hyperaridity that has minimized microbial and enzymatic activity, a taphonomic process we term xeropreservation (i.e. preservation by drying). The degree of biomarker preservation allowed us to reconstruct major changes in ecology in the Yungay region that reflect a shift in hydrological regime from wet to dry since the early Quaternary. Our results suggest that hyperarid environments, which comprise 7.5% of the continental landmass, could represent a rich and relatively unexplored source of paleobiological information on Earth.

    更新日期:2019-11-01
  • Weathering of pyrogenic organic matter induces fungal oxidative enzyme response in single culture inoculation experiments.
    Org. Geochem. (IF 3.120) Pub Date : 2016-02-01
    Christy Gibson,Timothy D Berry,Ruzhen Wang,Julie A Spencer,Cliff T Johnston,Yong Jiang,Jeffrey A Bird,Timothy R Filley

    The addition of pyrogenic organic matter (PyOM), the aromatic carbon-rich product of the incomplete combustion of plant biomass or fossil fuels, to soil can influence the rate of microbial metabolism of native soil carbon. The interaction of soil heterotrophs with PyOM may be governed by the surficial chemical and physical properties of PyOM that evolve with environmental exposure. We present results of a 36-day laboratory incubation investigating the interaction of a common white-rot fungus, Trametes versicolor, with three forms of 13C-enriched (2.08 atom% 13C) PyOM derived from Pinus ponderosa (450 °C): one freshly produced, and two artificially weathered (254 nm, UV light-water treatment and water-leaching alone). Analysis (FTIR, XPS) of the UV-weathered PyOM showed increased aliphatic C-H content and oxidation of aromatic carbon relative to both the original and water-leached PyOM. The addition of both weathered forms of PyOM stimulated (positively primed) fungal respiration of the growth media, while the unaltered PyOM mildly inhibited (negatively primed) respiration. Artificial weathering resulted in higher oxidative (laccase and peroxidase) enzyme activity than unaltered PyOM, possibly the result of a diminished capacity to bind reactive substrates and extracellular enzymes after weathering. However, and contrary to expectations, simple water-leached weathering resulted in a relatively higher enzyme activity and respiration than that of UV-weathering. The 13C content of respired CO2 indicated negligible fungal oxidation of PyOM for all treatments, demonstrating the overall low microbial reactivity of this high temperature PyOM. The increased enzymatic and positive priming response of T. versicolor to weathered PyOM highlights the importance of weathering-induced chemistry in controlling PyOM-microbe-soil carbon interactions.

    更新日期:2019-11-01
  • Betulin-related esters from birch bark tar: identification, origin and archaeological significance
    Org. Geochem. (IF 3.120) Pub Date : 2019-10-25
    J. Perthuison, P. Schaeffer, P. Debels, P. Galant, P. Adam

    Birch bark tar, an organic material frequently encountered during archaeological excavations, has been identified from its lipid composition on the cracks of a ceramic dated to the late Neolithic. Lipids of this black substance were dominated by a characteristic triterpenoid assemblage of lupane-related triterpenoids from birch bark together with their thermal degradation products formed during preparation of the tar. Among the latter, four main series of unusual triterpenoid esters have been detected and were postulated to correspond to esters of Δ 2-betulin and Δ2-dihydrobetulin based on their mass spectra and hydrolysis experiments. Their conclusive identification has been achieved by synthesis of reference compounds. These compounds most likely originate from the esterification between triterpenoid alcohols related to betulin and fatty acids from suberin formed upon heating of birch bark tar. They could be considered as markers of intense heating during birch bark tar preparation using the “single pot“ procedure.

    更新日期:2019-10-25
  • Kinetics of oil generation from brackish-lacustrine source rocks in the southern Bohai Sea, East China
    Org. Geochem. (IF 3.120) Pub Date : 2019-10-14
    Haoran Liang, Fanghao Xu, Kliti Grice, Guosheng Xu, Alex Holman, Peter Hopper, Deliang Fu, Qing Yu, Jiaju Liang, Deying Wang

    Oil generation (C14+ hydrocarbons) of three Type II kerogen samples isolated from brackish-lacustrine mudstones from Palaeogene strata (Ed3, Es1, Es3) in the southern Bohai Sea was simulated by closed-system gold tube experiments. In addition, a series of complementary analyses (Rock-Eval pyrolysis, total organic carbon, vitrinite reflectance, trace element, X-ray diffraction and flash pyrolysis-gas chromatography–mass spectrometry) were also performed to identify the bulk geochemistry, palaeo-environment and chemical composition of the kerogen. The aim of this study was to achieve a better understanding of the kinetics of oil generation from lacustrine source rocks in the southern Bohai Sea. The results show that the three samples are Type II source rocks deposited in similar palaeo-environments (hot and arid climates, anoxic conditions, and brackish water in shallow to semi-deep lakes) with consequent similarity in the chemical compositions of their kerogens. The organic matter inputs are predominantly composed of lacustrine microalgae, with a relatively small contribution from land plants. The activation energies of oil generation from these samples show a range of 44–52 kcal/mol, with a frequency factor varying from 1.116×1014 to 1.274×1014 s-1. Due to the similar palaeo-environments and chemical composition, samples in this study exhibit strong consistencies in kinetic parameters. Transformation ratio (TR) evolution curves of oil generation from the three samples, calculated under a linear heating rate (3 K/Ma), exhibit a slight difference, which varies within 4 °C at a given TR. Due to the great similarities of the three kinetic models, an average kinetic model for the Type II brackish-lacustrine source rocks in the southern Bohai Sea was established. This model integrates the characteristics of the three kinetic models and is still dominated by activation energy of 52 kcal/mol. The geological temperature of the oil generation phase for the average model in the southern Bohai Sea is from 92–137 °C.

    更新日期:2019-10-15
  • A comparison of n-alkane contents in sediments of five lakes from contrasting environments
    Org. Geochem. (IF 3.120) Pub Date : 2019-10-10
    Yongdong Zhang, Jinlei Yu, Yaling Su, Yingxun Du, Zhengwen Liu

    In paleolimnology studies, the trajectories of n-alkane abundances and distribution in dated sediments are widely used indicators of changing environmental and ecological status in the overlying water over time. However, the factors contributing to the variable n-alkane profiles of lake system are not yet fully understood. Here, a comparative study was conducted to examine natural and anthropogenic influences on sediment n-alkane profiles of five representative lakes in China, using core samples from the deep oligo- mesotrophic lakes Fuxian and Lugu (FX-1 and LG-1 cores), the shallow eutrophic lakes Taibai and Changdang (TB-1 and CD-1 cores) and the alpine Lake Heihai (HH-1 core). While there were striking differences in n-alkane abundances and distribution between the cores, the results suggested that the n-alkanes in all five studied lakes are derived mainly from biogenic sources rather than from petroleum contamination. The short-chain (< C20) even carbon n-alkanes, assumed to derive from non-photosynthetic bacteria, were especially prevalent in FX-1, reaching 158.3–284.4 ug/g TOC, which might be a result of high levels of bacterial productivity in the deep (average 89.6 m) water column of Lake Fuxian. The contribution of bacterial production has diminished in the other four lakes, with < C20 n-alkanes declining to between 21.4–60.5 ug/g TOC on average in the studied cores. In the two shallow lakes, abundances of short-chain (< C20) odd carbon n-alkanes were greatly elevated in sediments corresponding to the eutrophic phase, for example, with maximum values of 136.3 ug/g TOC recorded in TB-1. This nutrient-driven effect was less apparent in deep lakes. The > C21 n-alkane profiles of different cores varied significantly. Abundances of long-chain n-alkanes (C29, C31 and C33) in HH-1 were approximately 3–7 times greater than in other cores. Coupled with the lowest Paq (average 0.29) values recorded in the study, this indicates a predominantly terrestrial plant origin for the > C21 n-alkanes, most likely the dense alpine meadow which surrounds the lake. In other cores, however, aquatic macrophytes appear to be more important contributors of the n-alkanes, a result that corresponds with the relatively low density of terrestrial plants in those catchments.

    更新日期:2019-10-12
  • Photo- and autoxidation of unsaturated algal lipids in the marine environment: an overview of processes, their potential tracers, and limitations
    Org. Geochem. (IF 3.120) Pub Date : 2019-10-09
    Jean-François Rontani, Simon T. Belt

    The present paper provides an overview of results obtained in the course of recent studies dealing with abiotic degradation of algal lipids in the marine realm. In the first part, the photooxidation of the main lipid components (chlorophyll phytyl chain, carotenoids, Δ 5-sterols, unsaturated fatty acids, alkenones and unsaturated alkenes) in senescent phytoplanktonic cells is examined. Type II photosensitized oxidation processes (i.e. involving singlet oxygen) play a key role in the photooxidation of these compounds. The second part of the paper describes free radical oxidation of the main lipids in senescent phytoplanktonic cells. These processes, which are believed to be induced by homolytic cleavage of photochemically produced hydroperoxides, involve the direct reaction of molecular oxygen in its triplet ground state with organic compounds under relatively mild conditions. Particular attention is given to the characterisation of pathway-specific tracers of the individual abiotic reactions described. Some of these compounds appear to have the potential to provide qualitative or semi-quantitative information about photooxidation, autoxidation, or the total abiotic degradation state of individual or groups of organisms. On the other hand, some other primary oxidation products are likely too susceptible to further degradation to permit reliable quantitative estimates, but can, nonetheless, provide qualitative indication of photooxidation and autoxidation.

    更新日期:2019-10-10
  • Carbon stable isotope patterns of cyclic terpenoids: A comparison of cultured alkaliphilic aerobic methanotrophic bacteria and methane-seep environments
    Org. Geochem. (IF 3.120) Pub Date : 2019-10-01
    Alexmar Cordova-Gonzalez, Daniel Birgel, Andreas Kappler, Jörn Peckmann

    Aerobic methanotrophic bacteria are known to synthesize a variety of cyclic terpenoids which are typified by 13C-depleted, methane-derived carbon. This peculiarity facilitates identification of methanotroph biomarkers in natural samples. However, the current biomarker database does not always allow biomarker patterns of marine samples to be assigned to the different types of aerobic methanotrophs. To overcome this shortcoming, the carbon stable isotope composition of cyclic terpenoids of two strains of the Type I methanotroph genus Methylomicrobium was analyzed. Other than aerobic methanotrophs used for biomarker studies in the past, these two strains deriving from soda lake environments are able to tolerate the conditions typifying marine environments including high alkalinity and salinity. The cyclic terpenoid inventory of the two strains comprises 4-methyl steroids, 3-methyl- and desmethyl bacteriohopanepolyols (aminotetrol and aminotriol), and tetrahymanol, all of which are 13C-depleted. The average carbon isotope fractionation between methane and the respective lipid (Δδ13Cterpenoid-methane) is found to be −25‰ for M. kenyense and −16‰ for M. alcaliphilum. These data shed new light on the previously reported compound and carbon stable isotope patterns of cyclic terpenoids from methane-seep environments. Particularly, 13C-depleted tetrahymanol and gammacerane are reinterpreted as biomarkers of aerobic methanotrophic bacteria based on their occurrence in methane-seep deposits in association with other biomarkers of aerobic methanotrophs. The use of δ13C values of anaerobic methane-oxidizing archaea (ANME) lipids for the reconstruction of the isotopic composition of parent methane allows us to calculate the Δδ13Cterpenoid-methane even for ancient seep environments. With this calculation, Type I and Type II methanotrophs can be discriminated, representing a new approach to better characterize past methanotrophy at seeps and possibly other marine environments.

    更新日期:2019-10-02
  • Origin of deep oil accumulations in carbonate reservoirs within the north Tarim Basin: Insights from molecular and isotopic compositions
    Org. Geochem. (IF 3.120) Pub Date : 2019-09-24
    Bin Cheng, Hua Liu, Zicheng Cao, Xian Wu, Zhonghong Chen

    Large amounts of light oil have been produced from carbonate reservoirs at depths below 7 km in the recently discovered Shunbei and Yuecan oil fields within the north Tarim Basin. Eighteen samples were investigated for molecular and isotopic compositions to help understand the origin of these deep oil accumulations. Several ratios based on C6 and C7 hydrocarbons suggest that they were not affected by evaporative fractionation. Linear relationships between the carbon number and log of the mole fraction of n-alkanes support no fractionation alteration. The correlation between concentrations of methyldiamantanes and stigmastane indicates that these oils were not severely cracked and probably at the beginning or an early stage of intense oil cracking. C29 sterane isomerization ratios 20S/(20S + 20R) and ββ/(ββ + αα) have reached their equilibrium points while a good linear relationship between the concentrations of terpanes and steranes suggests variations in maturity. Calculated vitrinite reflectance of source rocks based on phenanthrene and diamondoid hydrocarbons shows different ranges, which may reflect multiple oil charges to these deep oil accumulations. A narrow range of δ13C values of whole oil and oil fractions suggest a genetic correlation of these oils. Triangular plots based on C6 and C7 hydrocarbons and diamantanes also indicate a very similar source. In addition, several ratios based on n-alkanes, isoprenoids, tri-, tetra-, and pentacyclic saturated hydrocarbons support a common source. However, oil SB7 seems to differ from the others in terms of source rock depositional environment, indicated by its much higher pristane/phytane ratio and lower dibenzothiophene/phenanthrene ratio as well as a much lower dibenzothiophenes concentration.

    更新日期:2019-09-25
  • Identification, distribution and geochemical significance of four rearranged hopane series in crude oil
    Org. Geochem. (IF 3.120) Pub Date : 2019-09-19
    Hong Xiao, Meijun Li, Wenqiang Wang, Bing You, Xiaoqiang Liu, Zhe Yang, Jiguo Liu, Qingyao Chen, Martin Uwiringiyimana

    Four rearranged hopane series were simultaneously detected in oils from the Muglad Basin, one of several rift basins on the Central African Shear Zone (CASZ). The series are identified as having the structure of 17α(H)-diahopane (D series), 18α(H)-neohopane (Ts series), early eluting rearranged hopane (E series) and 21-methyl-28-norhopanes (Nsp series). The four rearranged hopane series exhibit strong positive correlations. The slope and intercept of the linear equation in plots of C29D/C29H vs C30D/C30H are 1.10 and 0.003 respectively, possibly implying identical biological origins and formation mechanisms. The relatively low slope (<0.80) and intercept (<0.07) in both C30E/C30H vs C30D/C30H and C29Nsp/C29H vs C29D/C29H suggest that E and Nsp series have similar biological origins as D series, but form at a slower rate following different rearrangement mechanisms. Both the Nsp and E series require the shifting of two methyl groups from their precursors, whereas the D series have only one methyl migration from C-18 to C-17. The extremely high values of slope (1.42) and intercept (0.427) in a plot of C29Ts/C29H vs C29D/C29H probably indicates that the Ts series is more easily generated than other rearranged hopane series and possibly has multiple biological sources, such as contributions from diplopterol and/or diploptene. Furthermore, C30E, C30D, C29Nsp and Ts are enriched relative to regular hopanes in severely biodegraded oil samples owing to their greater resistance to microbial degradation, and/or additional sources of rearranged hopanes from bacterially reworked terrigenous organic matter. Based on relative Gibbs free energies (ΔG) calculated by density functional theory (DFT), the thermodynamic stabilities of C30 isomers follow the order C30D > C30H > C30E.

    更新日期:2019-09-20
  • Changes of composition and content of tricyclic terpane, hopane, sterane, and aromatic biomarkers throughout the oil window: A detailed study on maturity parameters of Lower Toarcian Posidonia Shale of the Hils Syncline, NW Germany
    Org. Geochem. (IF 3.120) Pub Date : 2019-09-18
    Ronghui Fang, Ralf Littke, Laura Zieger, Alireza Baniasad, Meijun Li, Jan Schwarzbauer

    A total of 30 core samples of organic matter-rich Lower Toarcian shale (Posidonia Shale) were geochemically analyzed to study systematic changes in the quantitative and qualitative composition of specific biomarkers at different thermal maturities ranging from 0.48 to 1.45% vitrinite reflectance (VRr). The samples are derived from 5 wells (Hils Syncline, NW Germany) each representing a different level of maturation (0.48, 0.68, 0.73, 0.88, 1.45 %VRr). In NW Germany, Posidonia Shale was deposited under marine, oxygen-deficient bottom water containing initially high amounts of TOC (above 10%) and marine type I-II kerogen. Upon maturation, organic carbon has been lost and hydrogen index values have decreased. Biomarker ratios reflecting this maturation very well include ratios of short over long-chain n-alkanes, ratios of pristane and phytane over nC17 and nC18, Ts/(Ts+Tm), C29Ts/(C29Ts+C29H), ratios based on DMDBTs, and TA(I)/TA(I+II) ratios (triaromatic steroids). The evolution of different steroid-, hopane-, naphthalene-, phenanthrene- and dibenzothiophene-related parameters is documented and compared to literature. Concentrations of individual hydrocarbons were measured in order to obtain quantitative data on biomarker abundance and their evolution upon maturation. Whereas there is a general trend of increasing biomarker content from immature (0.48 %VRr) to early mature (0.68 %VRr) conditions and of decreasing biomarker content with maturation from 0.68 to 0.88 %VRr, there are some exceptions from this trend, especially at low levels of maturity. Almost no polycyclic biomarkers were detected at the highest maturity level of 1.45 %VRr in well Haddessen, where n-alkanes and aromatic hydrocarbons are predominant. The overall pattern of polycyclic biomarker abundance is not only determined by isomerization and aromatization processes, but mainly by preferential degradation of thermally less stable biomarkers leading to the observed modifications of biomarker maturity parameters. Furthermore, outer and inner sections from the 10 cm wide cores were compared in order to find out, whether 40 years of dry storage in a core repository affected the biomarker parameters. No significant and systematic differences have been observed, with exception of the most mature Haddessen well, where low molecular weight n-alkanes (

    更新日期:2019-09-19
  • Composition of the dissolved organic matter produced during in situ burning of spilled oil
    Org. Geochem. (IF 3.120) Pub Date : 2019-09-05
    Aprami Jaggi, Jagoš R. Radović, Lloyd R. Snowdon, Stephen R. Larter, Thomas B.P. Oldenburg

    In situ burning is often used as a response method for oil slicks in the marine environment. This process however forms viscous tar-like residues that either float on the surface or sink through the water column, introducing organic species into the water phase. The interaction of this burn residue with the water phase also introduces dissolved organics into the water column. In this study, we conducted laboratory-scale experiments to characterize and compare the organic species entering the water phase from the petrogenic (fresh oil) and pyrogenic (burnt oil) input during oil spills. The oil and water-soluble organics were characterized using ultra-high-resolution mass spectrometry (FTICR-MS). The results show that burning strongly increases concentrations of oil-related constituents entering the water phase, due to transformation reactions producing oxidized organic species with higher water solubility. The pyrogenic water-soluble organics also showed a higher percentage of unsaturated compounds relative to the petrogenic fraction. The effect of these highly unsaturated and oxygenated organic species on oil spill fate and their ecosystem impacts is currently unknown.

    更新日期:2019-09-06
  • Preferential degradation of long-chain alkyl substituted hydrocarbons in heavy oil under methanogenic conditions
    Org. Geochem. (IF 3.120) Pub Date : 2019-09-05
    Lei Cheng, Sheng-bao Shi, Lu Yang, Yahe Zhang, Jan Dolfing, Yong-ge Sun, Lai-yan Liu, Qiang Li, Bo Tu, Li-rong Dai, Quan Shi, Hui Zhang

    Methanogenic crude oil degradation is a significant process in subsurface environments and degradation of crude oil n-alkanes has been well documented. However, little is known about the biodegradability of the resulting heavy oil. In this study, a methanogenic consortium enriched from Shengli oilfield could generate 1.3–1.9 mmol CH4/g of heavy oil at a rate of 2.9–8.8 μmol CH4/g of oil/day. Four SARA fractions (saturates, aromatics, resins and asphaltenes) of oils experienced a loss in linear aliphatic structures. n-Alkylcyclohexanes, methyl-n-alkylcyclohexane, n-alkyldecalin, n-alkylbenzenes, n-alkyltoluenes and n-alkylxylenes with alkyl side chains longer than 14 carbons were degraded over 50% compared to the undegraded oil. In addition, the extent of degradation of these hydrocarbons increased with increasing carbon length. Correspondingly, n-fatty acids and naphthenic acids with 1–3 naphthenic rings accumulated over time. 16S rRNA gene analysis revealed that aceticlastic Methanosarcina and Methanothrix dominated in the archaeal domain, and bacterial members related to Dehalococcoidia and Soehngenia were consistently present in the successive transfer cultures. However, neither assA/masD-like genes nor alkyl-substituted succinate metabolites were detected, indicating an alternative degradation pathway rather than addition to fumarate. This study provides novel insights into methanogenic degradation of long-chain alkyl substituted hydrocarbons in heavy oil, which also extend our understanding of anaerobic degradation of crude oil in subsurface sedimentary environments.

    更新日期:2019-09-06
  • Group I alkenones and Isochrysidales in the world’s largest maar lakes and their potential paleoclimate applications
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-31
    Karen J. Wang, Jonathan A. O'Donnell, William M. Longo, Linda Amaral-Zettler, Gaoyuan Li, Yuan Yao, Yongsong Huang

    The Espenberg maar lakes on the Seward Peninsula, Alaska, are the largest volcanic crater lakes in the world and contain the longest known lacustrine sedimentary archives in Alaska. The lack of glacial-aged marine sedimentary archives around the Bering Land Bridge due to exposure of the shelf during sea level low-stands makes these lakes highly valuable for understanding the region’s past climate and environmental changes. Located en route to humanity’s last colonized American continents, the Seward Peninsula’s climate and environments during the last glacial period bear major anthropological significance. However, a lack of quantitative proxies has so far hampered exploration of these lakes for paleoclimate reconstructions. Here we report, for the first time, the discovery of abundant Group I alkenones and Isochrysidales in surface sediments from three maar lakes: White Fish, North Killeak and Devil Mountain, using a combination of lipid biomarker and 18S rRNA gene sequencing analyses. Our discovery adds to the expanding list of oligotrophic freshwater lakes where Group I alkenones are found, and water chemistry data contribute to the understanding of the environmental controls on Group I Isochrysidales. Our results further confirm the use of the U37K index of Group I alkenones as a proxy for the mean temperature of the spring isotherm (MTSI) and RIK37 as a quantitative measurement for Isochrysidales group mixing. We also demonstrate the analytical challenges for analyzing alkenones in freshwater lakes and the effectiveness of eliminating coelution using silver thiolate chromatographic material (AgTCM).

    更新日期:2019-09-03
  • The Organic Signature of an Experimental Meat-cooking Fireplace: the Identification of Nitrogen Compounds and their Archaeological Potential
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-26
    Mathieu Lejay, Marie A. Alexis, Katell Quénéa, Christelle Anquetil, François Bon

    A better understanding of the operation and use of prehistoric fires is fundamental to interpreting the organization of living spaces. Following a previous study that focused on the organic signatures of fireplaces fueled with wood and/or bones, this study targeted the completion of an experimental reference database through the addition of a wood-fueled fireplace dedicated to the cooking of meat. Different sedimentary features of this experimental fireplace were visually identified (e.g. darkening, reddening), sampled, and subjected to geochemical analysis. Corg and N contents were quantified, samples were extracted with organic solvents and analyzed through GC-MS and bulk organic matter was characterized through py(TMAH)-GC-MS. Five different samples were studied and compared with a control sample, representative of the local background. A significant increase of Corg and N contents was measured for the three samples presenting darkened or charred caracteristics. The meat-cooking fireplace seems to be characterized by the strong contribution of nitrogen, which was visible in elementary analyses as well as in the molecular composition of solvent extracts, and bulk organic matter. More specifically, compounds containing nitrile functions, amides, N-heterocyclic and N-aromatic compounds could be detected in solvent extracts. Amines, amides, N-heterocyclic and N-aromatic compounds could be identified in py(TMAH)-GC-MS. Some of these compounds present a relative stability in soils and could therefore aid in our comprehension and functional interpretations of archaeological fireplaces, and may, more particularly, make it possible to highlight the use of fireplaces for the cooking of meat.

    更新日期:2019-08-27
  • Comparison of n-alkane concentrations and δD values between leaves and roots in modern plants on the Chinese Loess Plateau
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-19
    Jinzhao Liu, Zhisheng An, Huawu Wu, Yunlong Yu

    Sedimentary δDn-alkane values have been widely used as a valuable proxy for paleoenvironmental reconstruction. A number of studies have focused on δDn-alkane values that derived exclusively from leaves, while less attention has been paid to the root-derived n-alkanes and their impact on sedimentary δDn-alkane values. In this study, we sampled modern plant leaf and root materials from different growth contexts (slopes and seasons) on the Chinese Loess Plateau to compare leaf-derived n-alkanes with root-derived n-alkanes. Our results demonstrated that total n-alkane (C27-C33) concentrations varied substantially between leaf and root materials, with average values of 209 μg/g and 29.5 μg/g observed in leaves and roots respectively. The results suggest that ca. 12% of the n-alkane concentration in sediments derived from plant roots. Furthermore, leaf-derived δDn-alkane values for Stipa bungeana (grass), Artemisisa vestita (shrub) and Bothriochloa ischaemum (grass) averaged -184‰, -152‰ and -198‰, compared with their root-derived δDn-alkane values of -199‰, -179‰ and -163‰, respectively. These statistically significant differences in concentrations and δD values between leaf-derived and root-derived n-alkanes suggest that the contribution of n-alkanes derived from plant roots is important to evaluate the resultant n-alkane composition of sediments for paleoenvironmental reconstruction. Our finding indicates that the effects of root-derived n-alkanes on total sedimentary δDn-alkane values should be carefully considered in future paleoenvironmental reconstruction efforts.

    更新日期:2019-08-20
  • Changes in archaeal ether lipid composition in response to agriculture alternation in ancient and modern paddy soils
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-19
    Fengfeng Zheng, Yufei Chen, Xiaotong Tang, Jianqiang Su, Yongguan Zhu, Chuanlun Zhang

    Paddy soil is the consequence of human activity, which has exerted significant anthropogenic impacts on the global carbon cycle in recent earth history, particularly through the production of microbial methane from paddy soils. However, the anthropogenic impact of rice fields on the distribution of methanogenic archaea and methane emission during human history is poorly documented. Isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs) are unique biomarkers for archaea, which can be used to examine changes in climate and environment during human evolution. This study aimed to reconstruct archaeal communities and evaluate how they might have been impacted by human activities during the development of two paddy soil profiles that recorded a cultivation history of over 6300 years in Zhejiang Province, southeastern China. Variations in archaeol, GDGT-0 and crenarchaeol strongly suggest that archaeal ether lipids deeply buried in the ancient paddy soil profiles are mainly fossil records rather than contemporary signals. Cluster analysis based on GDGT compositions revealed two major groups of GDGTs corresponding to different soil types, reflecting the shift of archaeal communities from Thaumarchaeota to methanogens. The archaeal ether lipids-based proxies (MI, archaeol/crenarchaeol and GDGT-0/crenarchaeol) related to methane-producing archaea varied remarkably in different soil types associated with the anthropogenic management. These proxies had significantly higher values in the buried paddy soils than currently cultivated paddy soils, implying that the earlier anthropogenic flooding may have resulted in considerable methane emission from paddy soils in southeastern China.

    更新日期:2019-08-20
  • Radiolysis as a source of 13C depleted natural gases in the geosphere
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-13
    Renzo C. Silva, Lloyd R. Snowdon, Haiping Huang, Michael Nightingale, Veith Becker, Stephen Taylor, Bernhard Mayer, Jon H. Pedersen, Rolando di Primio, Steve Larter

    Is natural radioactivity a significant agent of hydrocarbon gas generation from sedimentary organic matter? Laboratory gamma radiation of dead crude oil (no solution gas) yields wet hydrocarbon gases depleted in 13C: δ13C CH4 (-75‰ to -65‰), δ13C C2H6 (-52‰ to -45‰), δ13C C3H8 (-42‰ to -37‰) and δ13C C4H10 (-35‰ to -32‰). Although laboratory irradiation dose rates are orders of magnitude higher than those in geological settings, radiolytic transformations occur at total radiation doses equivalent to those in natural geological settings over many millions of years. Radiolysis generates wet gases with isotopic signatures that might be interpreted as “biogenic” if only the methane carbon isotope ratio is considered. We examine situations where such gases may be quantitatively significant.

    更新日期:2019-08-14
  • Biodegradative production and destruction of norhopanes – an example from residual oil in a Paleogene paleomigration conduit on the Utsira High, Norwegian North Sea
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-12
    S.D. Killops, H.P. Nytoft, R. di Primio

    Biodegradation of the more resistant hopanoids was examined using residual stains in a Paleogene paleomigration conduit on the Utsira High, Norwegian North Sea, together with related less degraded oils. Under currently anoxic conditions, the most severely biodegraded samples contain 25-nor, 28-nor and 25,28-dinorhopanes, in addition to regular hopanes, neohopanes, diahopanes and didiahopanes [9,15-dimethyl-25,27-dinorhopanes]. The C27 member of the 25,28-dinorhopanes comprises closely eluting 17α,21β and 17β,21α isomers. A pair of C31 compounds eluting just after the 17α-homohopanes were tentatively identified as the 22S/R isomers of homo-18α-neohopane. The 28,30-dinorhopane peak seems to comprise 17α,21β and 17β,21α isomers, with relatively more of the less thermodynamically stable 17α,21β contributing under the most severe biodegradation. The approximate order of increasing susceptibility to biodegradation was: gammacerane ≈ triaromatic 23,24-dimethylcholesteroids ≈ triaromatic dinosteroids < C21–C22 C-ring-monoaromatic steroids ≈ C21–C22 steranes < C21–C22 diasteranes < C31 methylhopanes < 22,29,30-trinorneohopane (27Ts) < C30 TPPs ≈ diahopane ≈ didiahopane ≈ 22,29,30-trinorhopane (27Tm) < 30-norneohopane (29Ts) ≈ C28+ 28-norhopanes/moretanes < C29+ hopanes ≈ C27+ diasteranes < C27+ steranes. This information can inform the selection of correlation parameters for heavily biodegraded oils, although the sequence should not be considered universally applicable. Regular hopanes declined steadily with increasing biodegradation. The 25-norhopane homologues may be initially produced, but are then also degraded, although the C26 component appears stable. There is a relative increase in 25,28-dinorhopane abundance with increasing biodegradation, which is likely to result from demethylation of 25- and 28-norhopanes; if so, there must also be some shortening of the E-ring side-chain. Concentration estimates suggest that there is an overall loss of the hopanoid skeleton with increasing severity of biodegradation.

    更新日期:2019-08-13
  • Composition of lipids from the First Lusatian lignite seam of the Konin Basin (Poland): relationships with vegetation, climate and carbon cycling during the mid-Miocene Climatic Optimum
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-12
    Achim Bechtel, Marek Widera, Michał Woszczyk

    Samples of detrital lignite have been collected for detailed organic geochemical and carbon isotope analyses from the First Lusatian lignite seam at the Adamów, Jóźwin IIB and Tomisławice opencast mines, deposited after the last peak of the Mid-Miocene Climatic Optimum. Carbon isotopic compositions of biomarkers from Polish lignite are reported for the first time. The aim of the study is to improve the chemotaxonomic value of biomarkers by relating the results to existing paleobotanical data, and to gain information about the influencing factors on δ13C of lignite and lipids. Furthermore, biomarker and isotopic proxies are tested for their applicability in paleoclimate studies. The molecular composition of the extracted lipids is highly variable, including leaf-wax n-alkanes in the C23 to C31 range, diterpenoids, hopanoids, and angiosperm-derived triterpenoids, as well as saturated fatty acids, long-chain n-alkanols and n-alkan-2-ones. The relative abundances of mid-chain (C23, C25) n-alkanes and their 1–2‰ higher δ13C values compared to long-chain n-alkanes (C29, C31) argue for a minor contribution of macrophytes (graminoids, etc.) to peat formation, enhanced during periods of raised water level. The presence of ferruginol and dehydroferruginol testifies the contribution of Taxodiaceae. The abundances of pimarane-type diterpenoids and the presence of non-aromatic abietane-derivatives argue for the contribution of Pinaceae. Based on the presence of lupeol and lupane-type triterpenoids, an input of Betulaceae can be concluded. The contribution of further angiosperms cannot be specified based on the composition of pentacyclic triterpenoids. However, the results indicate mixed vegetation, and are in agreement with paleobotanical data highlighting abundant conifers of the Taxodiaceae/Cupressaceae and Pinaceae families, as well as angiosperms of various families (e.g., Nyssa, Quercus, Fagus), including Betulaceae (e.g., Alnus, Betula, Corylus). Based on the relationship between the carbon preference index of n-alkanes and mean annual air temperatures, obtained from a global database of peatlands, an average temperature of 24.5 °C is obtained. This value is significantly higher as estimated from paleobotanical data (15.7–19.7 °C), probably due to the influence of changes in vegetation on carbon preference index. The relative abundances of diterpenoids versus di- plus angiosperm-derived triterpenoids in detrital lignite samples revealed variable contributions of gymnosperms and angiosperms during the middle Miocene. Consistent with these results, a positive relationship exists between the di-/(di- + tri-) terpenoid biomarker ratios and δ13C of lignite samples, indicating the dominating role of varying gymnosperm/angiosperm contributions on the carbon isotopic composition of lignite. The C-isotope data of long-chain n-alkanes, diterpenoids, and angiosperm-derived triterpenoids co-vary within the profiles, arguing for an overall control of changes in δ13C of atmospheric CO2 on δ13C of plant lipids. Fluctuations in δ13C of individual compounds may also be related to changes in carbon cycling within the peat, humidity and air temperature. The influence of local variations in ambient CO2 (e.g., the canopy effect) cannot be excluded.

    更新日期:2019-08-12
  • Production of long-chain n-alkyl lipids by heterotrophic microbes: new evidence from Antarctic lakes
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-12
    Xin Chen, Xiaodong Liu, Yangyang Wei, Yongsong Huang

    Long-chain n-alkyl lipids are traditionally ascribed to an origin from terrestrial vascular plants because these compounds are major constituents of higher plant leaf waxes. Over the past half century, numerous studies have taken advantage of these sedimentary biomarkers and their isotopic ratios to reconstruct paleo-environmental and paleo-climatological changes at a variety of time scales. However, it is uncertain and extremely difficult to determine if these compounds can also derive from microbes because of the prevalence of higher plants in most environments around the globe. Here we show, for the first time from natural sediment samples, that long-chain n-alkyl lipids can predominantly originate from aquatic microbial sources at three high-latitude (>69°S latitude) Antarctic lakes, where no vascular plants are present in the surrounding land mass. The high carbon isotopic values (up to –12‰) of these long-chain n-alkyl lipids exclude the possibility that these compounds are transported by wind from adjacent vegetated land masses. Instead, these isotope values are similar to lipids produced by aquatic microbial mats with an average bulk δ13C value of –14.2±1.7‰, indicating heterotrophic microbes are the likely source of these long-chain n-alkyl lipids. For comparison, we also show that when even small amount of vascular plants and mosses are present in the study region, for instance at Long Lake (∼ 62°S latitude) in the Antarctic Peninsula, the carbon isotopic values of sedimentary long-chain n-alkyl lipids decline dramatically, suggesting a rapid proportional increase in the relative contribution of leaf wax sources to total long-chain n-alkyl lipid inventory in lake sediments.

    更新日期:2019-08-12
  • Identification of phenyldibenzothiophenes in coals and the effects of thermal maturity on their distributions based on geochemical data and theoretical calculations
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-12
    Zhili Zhu, Meijun Li, Youjun Tang, Ling Qi, Junying Leng, Xiaoqiang Liu, Hong Xiao

    All four phenyldibenzothiophene (PhDBT) isomers were unequivocally identified in coals for the first time by the co-injection of authentic standards and comparison of the retention indices with those reported in previous studies. Based on density functional theory (DFT) calculations, the relative thermodynamic stability order of the phenyldibenzothiophene isomers (PhDBTs) was determined to be 3-PhDBT > 2-PhDBT > 4-PhDBT > 1-PhDBT. All PhDBT isomers were observed in a suite of coals from the Junggar and Ordos basins, and the effects of thermal maturity on their distributions were systematically investigated. Based on geochemical data and theoretical calculations, two phenyldibenzothiophene maturity indicators, i.e., PhDR1 (2-PhDBT/4-PhDBT) and PhDR2 ((2-PhDBT + 3-PhDBT)/4-PhDBT), are proposed. For high maturity coals (≥ 0.96 %Ro), PhDR1 and PhDR2 increase gradually with increasing thermal maturity. Two preliminary calibrations of these parameters against measured %Ro were made: %Rc = 0.60 × PhDR1 + 1.00 (≥ 1.00 %Ro) and %Rc = 0.30 × PhDR2 + 1.00 (≥ 1.00 %Ro). Compared to their corresponding methylated counterparts, phenyldibenzothiophenes are particularly useful as molecular markers of maturity at higher levels of thermal stress and provide a molecular assessment for sedimentary rocks containing types II and III kerogens where few biomarker parameters are available. PhDBTs in coals are likely to be generated during diagenesis/catagenesis as intermediate products in the formation of more condensed heterocyclic polycyclic aromatic compounds, such as triphenyleno[1,12-bcd]thiophene and benzobisbenzothiophenes, which were detected in the highly mature samples. This study broadens the current understanding of the occurrence, distribution, geochemical significance, and origin of phenyldibenzothiophenes in sedimentary organic matter.

    更新日期:2019-08-12
  • Production of branched tetraethers in the marine realm: Svalbard fjord sediments revisited
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-10
    Emily Dearing Crampton-Flood, Francien Peterse, Jaap S. Sinninghe Damsté

    Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids thought to be predominantly produced on land. They are used as a terrestrial paleothermometer based on an empirical relation between their molecular composition and air temperature in surface soils worldwide. The proxy has been applied in continental margin sediments based on the assumption that all brGDGTs originate from land and are transported to marine sediments predominantly by rivers. However, this assumption has been challenged by the discovery of in situ brGDGT production in the coastal marine environment. To better understand marine brGDGT production, we examined newly collected marine surface sediments from the Krossfjorden and Kongsfjorden in Svalbard with a chromatography method to separate previously co-eluting 5- and 6-methylated brGDGT isomers. ‘Living’ intact polar lipid (IPL)-derived and ‘fossil’ core lipid (CL) brGDGTs were also studied for a subset of fjord sediments. The relative proportion of cyclopentane moieties in tetramethylated brGDGTs, used as indicator for brGDGT production in coastal marine settings, is much higher in the fjord sediments (#ringstetra = 0.65–0.93 for CL and 0.24–0.79 for IPL-derived brGDGTs) compared to those in nearby soils (#ringstetra = 0.00–0.37), and confirms the predominantly marine source of the brGDGTs in the fjord. Surprisingly, however, IPL-derived brGDGTs have a substantially lower #ringstetra (up to 0.52 offset) compared to that of CL-brGDGTs in the same sediment. This suggests that brGDGTs are produced in situ in different distributions throughout the year, of which the CL distribution in the sediment is an integrated signal. The offset in #ringstetra between IPL-derived and CL brGDGTs varies between 0.15–0.52 and increases towards the open ocean, possibly linking brGDGT production to the natural salinity gradient and associated microbial community changes.

    更新日期:2019-08-11
  • Biomarker signatures of Upper Cretaceous Latrobe Group petroleum source rocks, Gippsland Basin, Australia: Distribution and geological significance of aromatic hydrocarbons
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-08
    Lian Jiang, Simon C. George

    Aromatic hydrocarbons extracted from Upper Cretaceous (Maastrichtian and Campanian) Latrobe Group coaly shales and shales from the Gippsland Basin were investigated by gas chromatography–mass spectrometry. A variety of 2-ring to 6-ring aromatic hydrocarbons were identified, including both higher-plant-derived and combustion-derived polycyclic aromatic hydrocarbons (PAHs). These aromatic compounds indicate that the Upper Cretaceous coaly shales and shales were deposited in a fluvial/deltaic environment with significant higher plant input and are at a relatively low thermal maturity stage. Higher plant parameters and angiosperm/gymnosperm indices based on aromatic components suggest that higher land plants, including both angiosperms and gymnosperms, were an important part of the palaeovegetation in the Upper Cretaceous. The aromatic angiosperm/gymnosperm index that includes chrysene- and picene-type PAHs is not as reliable for evaluation of relative angiosperm and gymnosperm contributions as the aliphatic indices due to input of combustion-derived PAHs and the complexity of burning conditions altering the relative contributions. However, combustion-derived PAHs and aromatic angiosperm/gymnosperm indices supplement the information from aliphatic hydrocarbons and provide further evidence to support the hypothesis that palaeoclimate cooled from the Campanian to the Maastrichtian.

    更新日期:2019-08-09
  • Hydrogen isotopic ratios of long-chain diols reflect salinity
    Org. Geochem. (IF 3.120) Pub Date : 2019-08-05
    Julie Lattaud, Zeynep Erdem, Gabriella M. Weiss, Darci Rush, Sergio Balzano, David Chivall, Marcel T.J. van der Meer, Ellen C. Hopmans, Jaap S. Sinninghe Damsté, Stefan Schouten

    Long-chain diols (LCDs) are ubiquitous lipids produced by freshwater and marine algae. A combination of semi-preparative high performance liquid chromatography and gas chromatography isotope ratio monitoring mass spectrometry, allowed the measurement of δ2H of individual LCDs from cultures, which indicated a correlation with the hydrogen isotope composition of the growth water and a species-specific effect. Results from environmental samples along a salinity gradient indicated the potential of δ2H ratios of LCDs to trace the hydrogen isotopic composition of water and sea surface salinity.

    更新日期:2019-08-06
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