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1.
We have conducted the first systematic analyses of molecular distribution and δD values of individual compounds in pyrolysates of insoluble organic matter (IOM) from different carbonaceous chondrite groups, using flash pyrolysis coupled to gas chromatography-mass spectrometry and compound-specific D/H analysis. IOM samples from six meteorites of different classifications, Elephant Moraine (EET) 92042 (CR2), Orgueil (CI1), Allan Hills (ALH) 83100 (CM1/2), Murchison (CM2), ALH 85013 (CM2), and Tagish Lake (C2) were isolated and studied. Except for the pyrolysate of Tagish Lake IOM, pyrolysates of all five meteorite IOM samples were dominated by an extensive series of aromatic (C1 to C7 alkyl-substituted benzenes, C0 to C2 alkyl-substituted naphthalenes), with aliphatic (straight chain and branched C10 to C15 alkanes) hydrocarbons and several S- and O- containing compounds (C1 to C2 alkylthiophenes, benzothiophene, benzaldehyde) being also present. The strong similarity in the pyrolysates of different carbonaceous chondrites suggests certain common characteristics in the formation mechanisms of IOM from different meteorites. The Tagish Lake IOM sample is unique in that its pyrolysate lacks most of the alkyl-substituted aromatic hydrocarbons detected in other meteorite IOM samples, suggesting distinctively different formation processes. Both bulk δD values of meteorite IOMs and weighted-average δD values of individual compounds in pyrolysates show a decreasing trend: CR2 > CI1 > CM2 > C2 (Tagish Lake), with the EET 92042 (CR2) IOM having the highest δD values (∼2000‰ higher than other samples). We attribute the high D contents in the IOM to primitive interstellar organic sources.  相似文献   

2.
Flame coal (Janina Mine, Poland) was an object of geochemical analyses for changes caused by the process of microbial desulphurisation. Ash content, beryllium, chromium, zinc, cobalt, lithium, manganese, copper, molybdenum, nickel, lead and vanadium concentrations were investigated in coal extracts, its macromolecular part, semi-coke and polar compound fractions of extracts and pyrolysates of crude and biodesulphurised coal density fractions. The macromolecular part of extracted density fractions was pyrolysed giving semi-coke and pyrolysate. These were separated into aliphatic hydrocarbons, aromatic and polar compounds by thin layer chromatography (TLC). Distributions of aliphatic and aromatic hydrocarbons in pyrolysates of the crude and desulphurised coal density fractions were compared by gas chromatography-mass spectrometry (GC-MS). Extracts, extracted density fractions, semi-coke and polar compound fractions were analysed for concentrations of trace elements. In the crude coal their concentrations in the macromolecular part are related only to coke. However, in the desulphurised coal the participation of the particular trace element increases in pyrolysate polar compound fractions. Its values are in the range from 1% (Mn) to 100% (Cr and Mo). These changes are the best seen in the 1.80-2.30×103 kg/m3 density fraction. Very high concentrations of trace elements were found in pyrolysate of desulphurised coal density fraction. This can be explained by the partial decomposition of coal macromolecule resulting from desulphurisation. Significant side-cleavage of peripheral groups and lighter aromatic hydrocarbons is possible. The effects of bacterial influence were manifested by the increase of polar compounds contents both in pyrolysates and extracts of the desulphurised coal and changes in distribution of aliphatic and aromatic hydrocarbon as pyrolytical products. These effects increase with mineral substance contents. Moreover, the increase of trace element concentration in coal organic matter occurs. It is reflected by the increase of participation of coal pyrolysate polar fraction in the total concentration of analysed elements in the macromolecular part of a given density fraction. The presented results are a part of the larger research aimed to find an influence of desulphurisation on chemical and technological properties of coal.  相似文献   

3.
Solid-state 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopic experiments have been performed on isolated meteoritic Insoluble Organic Matter (IOM) spanning four different carbonaceous chondrite meteorite groups; a CR2 (EET92042), a CI1 (Orgueil), a CM2 (Murchison), and the unique C2 meteorite, Tagish Lake. These solid state NMR experiments reveal considerable variation in bulk organic composition across the different meteorite group’s IOM. The fraction of aromatic carbon increases as CR2 < CI1 < CM2 < Tagish Lake. The increases in aromatic carbon are offset by reductions in aliphatic (sp3) carbon moieties, e.g., “CHx,” and “CHx(O,N).” Oxidized sp2 bonded carbon, e.g., carboxyls and ketones grouped as “CO,” are largely conservative across these meteorite groups. Single pulse (SP) 13C magic angle spinning (MAS) NMR experiments reveal the presence of nanodiamonds with an apparent concentration ranking in the IOM of CR2 < CI1 < CM2 < Tagish Lake. A pair of independent NMR experiments reveals that, on average, the aromatic moieties in the IOM of all four meteoritic IOM fractions are highly substituted. Fast spinning SP 1H MAS NMR spectral data combined with other NMR experimental data reveal that the average hydrogen content of sp3 bonded carbon functional groups is low, requiring a high degree of aliphatic chain branching in each IOM fraction. The variation in chemistry across the meteorite groups is consistent with alteration by low temperature chemical oxidation. It is concluded that such chemistry principally affected the aliphatic moieties whereas the aromatic moieties and nanodiamonds may have been largely unaffected.  相似文献   

4.
Ruthenium tetroxide oxidation was used to examine the macromolecular insoluble organic matter (IOM) from the Orgueil and Murchison meteorites and especially to characterize the aliphatic linkages. Already applied to various terrestrial samples, ruthenium tetroxide is a selective oxidant which destroys aromatic units, converting them into CO2, and yields aliphatic and aromatic acids. In our experiment on chondritic IOM, it produces mainly short aliphatic diacids and polycarboxylic aromatic acids. Some short hydroxyacids are also detected.Aliphatic diacids are interpreted as aliphatic bridges between aromatic units in the chemical structure, and polycarboxylic aromatic acids are the result of the fusion of polyaromatic units. The product distribution shows that aliphatic links are short with numerous substitutions. No indigenous monocarboxylic acid was detected, showing that free aliphatic chains must be very short (less than three carbon atoms). The hydroxyacids are related to the occurrence of ester and ether functional groups within the aliphatic bridges between the aromatic units. This technique thus allows us to characterize in detail the aliphatic linkages of the IOMs, and the derived conclusions are in agreement with spectroscopic, pyrolytic, and degradative results previously reported.Compared to terrestrial samples, the aliphatic part of chondritic IOM is shorter and highly substituted. Aromatic units are smaller and more cross-linked than in coals, as already proposed from NMR data. Orgueil and Murchison IOM exhibit some tiny differences, especially in the length of aliphatic chains.  相似文献   

5.
The kerogen of a sample of Estonian Kukersite (Ordovician) was examined by spectroscopic (solid state 13C NMR, FTIR) and pyrolytic (“off-line”, flash) methods. This revealed an important contribution of long, linear alkyl chains in Kukersite kerogen. The hydrocarbons formed upon pyrolysis are dominated by n-alkanes and n-alk-1-enes and probably reflect a major contribution of selectivity preserved, highly aliphatic, resistant biomacromolecules from the outer cell walls of Gloeocapsomorpha prisca. This is consistent with the abundant presence of this fossilized organism in Kukersite kerogen. In addition high amounts of phenolic compounds were identified in the pyrolysates. Series of non-methylated, mono-, di- and trimethylated 3-n-alkylphenols, 5-n-alkyl-1,3-benzenediols and n-alkylhydroxybenzofurans were identified. All series of phenolic compounds contain long (up to C19), linear alkyl side-chains. Kukersite kerogen is, therefore, an aliphatic type II/I kerogen, despite the abundance of free phenolic moieties. This study shows that phenol-derived moieties are not necessarily associated with higher plant-derived organic matter.The flash pyrolysate of Kukersite kerogen was also compared with that of the kerogen of the Guttenberg Oil Rock (Ordovician) which is also composed of accumulations of fossilized G. prisca. Similarities in the distributions of hydrocarbons and sulphur compounds were noted, especially for the C1–C6 alkylbenzene and alkylthiophene distributions. However, no phenolic compounds were detected in the flash pyrolysate of the Guttenberg kerogen. Possible explanations for the observed similarities and differences are discussed.  相似文献   

6.
Eight interplanetary dust particles (IDPs) exhibiting a wide range of H and N isotopic anomalies have been studied by transmission electron microscopy, x-ray absorption near-edge structure spectroscopy, and Fourier-transform infrared spectroscopy. These anomalies are believed to have originated during chemical reactions in a cold molecular cloud that was the precursor to the Solar System. The chemical and mineralogical studies reported here thus constitute direct studies of preserved molecular cloud materials. The H and N isotopic anomalies are hosted by different hydrocarbons that reside in the abundant carbonaceous matrix of the IDPs. Infrared measurements constrain the major deuterium (D) host in the D-enriched IDPs to thermally labile aliphatic hydrocarbon groups attached to macromolecular material. Much of the large variation observed in D/H in this suite of IDPs reflects the variable loss of this labile component during atmospheric entry heating. IDPs with elevated 15N/14N ratios contain N in the form of amine (-NH2) functional groups that are likely attached to other molecules such as aromatic hydrocarbons. The host of the N isotopic anomalies is not as readily lost during entry heating as the D-rich material. Infrared analysis shows that while the organic matter in primitive anhydrous IDPs is similar to that observed in acid residues of primitive chondritic meteorites, the measured aromatic:aliphatic ratio is markedly lower in the IDPs.  相似文献   

7.
Hydrous pyrolysis (closed vessel autoclaving in the presence of excess water) of organic-rich rocks is said to generate oils which closely resemble natural crude oils in their broad characteristics and composition. However there are only a few accounts of the proportions and compositions of hydrocarbons in hydrous pyrolysates and none of these discuss the aromatic hydrocarbon composition in detail. The present paper presents some data on the latter.Hydrous pyrolysis (3 days) of a dolomitic siltstone (Permian, Marl Slate) at 280, 300,320, 340 and 360°C produced significant amounts of oils in which the aromatic hydrocarbons were one and a half to two times as abundant as the saturated hydrocarbons.The overall composition of the aromatic hydrocarbons was similar to most crude oils; the major components isolated by our methods from natural oils and from pyrolysates were C1–4 alkylnaphthalenes. At the lowest pyrolysis temperature (280°C) the distributions of the more minor components of the pyrolysates (e.g. alkylphenanthrenes, aromatic steroids) were also generally similar to those found in natural crudes. However, a number of components (e.g. methylanthracenes, Diels' hydrocarbon) which are not usually reported in crudes, were also detected and the relative proportions of these increased at the higher temperatures. Hydrous pyrolysis (340°C) of an organic-rich oil shale (Jurassic, Kimmeridge) and an asphaltic-material containing no minerals produced pyrolysates in which many of these unusual compounds were also present. In addition the pyrolysate of the oil-shale contained higher proportions of organic sulphur compounds. It appears that the formation of the unusual compounds is not simply a function of the type of organic matter or mineralogy but rather of the high temperatures or fast heating rates employed.  相似文献   

8.
Vegetative remains of three coalified Lower Devonian vascular plants (Zosterophyllum, Psilophyton, Renalia) were analyzed using flash pyrolysis-gas chromatography-mass spectrometry. The distributions of pyrolysis products are compared with those from younger vascular plant fossil xylem (Cordaixylon, Callixylon) and cuticle (Pachypteris). The likelihood of the chemical preservation of characteristic higher plant macromolecules (e.g., lignin and cutan) in the Lower Devonian plant fossils is considered in light of this comparison and associated thermal maturity assessments. Reflectance values from vitrinite-like macerals, which may not be vitrinite sensu stricto in the Lower Devonian host rocks for the fossils selected for this study, are shown to provide a reasonable assessment of the thermal maturity of these early vascular plant fossils. Although lignin altered through burial maturation is the most likely source of the prominent alkylphenols and aromatic hydrocarbons in the Lower Devonian tracheophyte flash pyrolysates, a contribution from thermally modified tannins cannot be ruled out. Comparison of the highly aliphatic pyrolysates from the Zosterophyllum and Psilophyton axes with that of a thermally mature fossil gymnosperm leaf revealed that cutan was an important component in the Devonian plant remains. This is the earliest chemical evidence for the presence of cutan in vascular plants.  相似文献   

9.
《Comptes Rendus Geoscience》2007,339(14-15):895-906
Carbonaceous chondrites are characterized by their enrichment in organic matter, mainly represented by insoluble organic matter (IOM), which consists of small aromatic units linked by short-branched aliphatic chains. Furthermore, IOM contains organic radicals heterogeneously distributed along with diradicaloids. These chemical features discriminate IOM from terrestrial counterparts. Isotopic compositions, especially the D/H isotopic ratio, are also distinct. IOM is highly enriched in D (D/H > 350 × 10−6), and the D/H isotopic ratio is heterogeneous. The isotopic composition is the result of interstellar-like processes that could have taken place during the first ages of the protosolar nebula. Chemical structure and isotopic composition clearly show that IOM is synthesized by an abiotic process and is subsequently affected by aqueous alteration or high-temperature metamorphism on the parent body.  相似文献   

10.
Conventional biomarker studies typically interpret the distribution, structure and stable isotopic (e.g. 13C, D) composition of sedimentary hydrocarbons and polar compounds. However, compound and compound class specific 14C analysis (CSRA) is becoming increasingly relevant for characterising millennial scale residence and mobilisation of sedimentary organic carbon (OC). Here, the 14C content of the aliphatic and bulk fractions from shallow cores from the hypersaline playa, Lake Tyrrell, southeast Australia were compared. The aliphatic hydrocarbon fractions (predominantly n-alkanes) were substantially older than the corresponding bulk fractions, indicating the presence of active reservoirs of ancient carbon, likely derived from aeolian reworking of sediments. The 14C ages of the aliphatic hydrocarbons in the core revealed two noticeable shifts in age and source of ancient OC that were not apparent using biomarker composition and sedimentology alone. The study shows that aliphatic hydrocarbons are relatively simple to isolate, even from organically lean (ca. 0.05% TOC) terrestrial sediments, and their 14C ages yield information about carbon mobilisation and preservation not amenable to conventional analysis.  相似文献   

11.
Chemical structure of Jurassic vitrinites isolated from the coals in basins in NW China have been checked using solid state 13C NMR and flash pyrolysis-GC/MS. Study shows some Jurassic collodetrinites are rich in aliphatic products in pyrolysates, consisting with the high amount of methylene carbon in 13C NMR spectra. In contrast, pyrolysates of Jurassic collotelinites are rich in phenols and alkylbenzenes. Also one Pennsylvanian and one Permian vitrinite selected from the Ordos basin, NW China have been checked for comparison. The proportion of aliphatics is low in pyrolysates, and aliphatic carbon peak in 13C NMR spectrum of Permian vitrinite is mostly composed of gas-prone carbons compared with collodetrinites in those Jurassic basins. But both pyrolysis and 13C NMR data shows the Pennsylvanian vitrinite is not only gas-prone but also oil-prone. Relatively high proportion of long chain aliphatic structure of some Jurassic vitrinite in Junggar, Turpan-Hami basins may be due to the contribution of liptodetrinites, which may be included during the formation of vitrinites. And it seems that suberinite is the most possible precursor of long chain aliphatics in the structure of Jurassic collodetrinite.  相似文献   

12.
Potassium permanganate oxidative degradations were conducted for kerogens isolated from Cretaceous black shales (DSDP Leg 41, Site 368), thermally altered during the Miocene by diabase intrusions and from unaltered samples heated under laboratory conditions (250–500°C).Degradation products of less altered kerogens are dominated by normal C4–C15 α,ω-dicarboxylic acids, with lesser amounts of n-C16 and n-C18 monocarboxylic acids, and benzene mono-to-tetracarboxylic acids. On the other hand, thermally altered kerogens show benzene di-to-tetracarboxylic acids as dominant degradation products, with lesser or no amounts (variable depending on the degree of thermal alteration) of α,ω-dicarboxylic acids. Essentially no differences between the oxidative degradation products of naturally- and artificially-altered kerogens are observed.As a result of this study, five indices of aromatization (total aromatic acids/kerogen; apparent aromaticity; benzenetetracarboxylic acids/total aromatic acids; benzene-1,2-dicarboxylic acid/benzenedicarboxylic acids; benzene-1,2,3-tricarboxylic acid/benzenetricarboxylic acids) and two indices of aliphatic character (Total aliphatic acids/kerogen; Aliphaticity) are proposed to characterize the degree of thermal alteration of kerogens.Furthermore, a good correlation is observed between apparent aromaticity estimated by the present KMnO4 oxidation method and that from the 13C NMR method (DENNIS et al., 1982).  相似文献   

13.
The molecular structural features of humic acid (HA) fractions isolated from recent sediments from the estuaries and continental platform along the Huelva littoral (SW Iberian Peninsula, Spain) were studied using complementary analytical tools. The approach included elemental analysis, solid state, 13C cross polarisation magic angle spinning nuclear magnetic resonance spectroscopy (13C CP-MAS NMR), pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) and stable C and N isotopic composition (δ13C, δ15N). The results point to the presence of vascular plant matter contributing to all the HAs, even those far from the coastal area. A contribution of lignocellulose material was detected from 13C NMR signals at 152 ppm (O-aryl C), 55 ppm (methoxyl C) and 33 ppm (alkyl chain) and confirmed by the presence of lignin derived structures (methoxy phenols) in the pyrolysis chromatograms. Nevertheless, the HAs from the westernmost part of the continental platform had the lowest aromatic and the highest C-alkyl abundance (13C NMR spectroscopy). These data, combined with low C/N and high H/C values, a relative enrichment in δ13C and the presence in the pyrolysates of conspicuous n-alkyl nitrile and amide series, together with n-alkane/ene homologues, pointed towards a relevant marine (autochthonous) contribution to this sedimentary organic matter (OM). In contrast, HAs from sediments collected from the Tinto-Odiel River mouth and Guadiana Estuary areas revealed a major input of terrestrial OM. In general, the data support the idea that the HAs still contain valuable information about the signature of aliphatic and aromatic biomacromolecules contributing to the deposited OM.  相似文献   

14.
《Applied Geochemistry》2000,15(2):157-169
Ground-water chemistry and the stable C isotope composition (δ13CDIC) of dissolved inorganic C (DIC) were measured in a sand aquifer contaminated with JP–4 fuel hydrocarbons. Results show that ground water in the upgradient zone was characterized by DIC content of 14–20 mg C/L and δ13CDIC values of −11.3‰ to −13.0‰. The contaminant source zone was characterized by an increase in DIC content (12.5 mg C/L to 54 mg C/L), Ca, and alkalinity, with a significant depletion of 13C in δ13CDIC (−11.9‰ to −19.2‰). The source zone of the contaminant plume was also characterized by elevated levels of aromatic hydrocarbons (0 μg/L to 1490 μg/L) and microbial metabolites (aromatic acids, 0 μg/L to 2277 μg/L), non-detectable dissolved O2, NO3 and SO4. Phospholipid ester-linked fatty acid analyses suggest the presence of viable SO4-reducing bacteria in ground water at the time of sampling. The ground-water chemistry and stable C isotope composition of ground-water DIC are interpreted using a chemical reaction model involving rainwater recharge, contributions of CO2 from soil gas and biodegradation of hydrocarbons, and carbonate dissolution. The major-ion chemistry and δ13CDIC were reconciled, and the model predictions were in good agreement with field measurements. It was concluded that stable C isotope measurements, combined with other biogeochemical measures can be a useful tool to monitor the dominant terminal electron-accepting processes in contaminated aquifers and to identify mineralogical, hydrological, and microbiological factors that affect δ13C of dissolved inorganic C.  相似文献   

15.
Biomarker distributions in a suite of asphaltenes and kerogens have been analysed by flash pyrolysis directly coupled to a GCMS system. Attention has been focussed on biomarkers of the sterane and triterpane types. The sample suite under investigation consists of sediments with different kerogen types and some crude oils. Biomarker distributions in the pyrolysates have been compared with the “free” biomarkers in the corresponding saturated hydrocarbon fractions.The analyses show significant differences between the distributions of the free biomarkers and those in the pyrolysates. The latter have lower amounts of steranes while diasteranes are absent or present at low concentrations only. In the triterpane traces a shift of maximum intensity from C30 (free compounds) to C27/C29 is observed. Furthermore, the pyrolysates contain a set of triterpenes (not present among the free compounds), and there is a selective loss of “non-regular” triterpanes that are present in the saturated hydrocarbon fractions. The observed differences between pyrolysates and free hydrocarbons can be explained partly by the processes occurring during pyrolysis such as bond rupture and subsequent stabilisation of primary pyrolysis products. To a certain extent these differences also show that maturation processes occurring in sediments have effects on free biomarker molecules different from those on molecules that are enclosed in a macromolecular matrix (kerogen or asphaltenes).Differences between biomarker distributions of asphaltene and kerogen pyrolysates are relatively small. A comparison with the pyrolysates from extracted whole sediments suggests that these differences are mainly caused by interactions between the organic material and the mineral matrix during pyrolysis.Oil asphaltenes behave differently from sediment asphaltenes as their pyrolysates are more similar to the corresponding saturated hydrocarbon fractions, i.e. the differences described above are observed to a much smaller extent. This different behaviour appears to be the result of coprecipitation of a part of the maltene fraction with the oil asphaltenes.  相似文献   

16.
The present study aims to establish the factors controlling the stable carbon isotopic compositions (δ13C) of individual aromatic hydrocarbons analysed by compound specific isotope analysis (CSIA) in crude oils from western Australian petroleum basins of varying age and facies type. This paper reports δ13C values of individual aromatic hydrocarbons, like alkylbenzenes, alkylnaphthalenes, alkylphenanthrenes and methylated biphenyls. The main aims are to confirm the origin (source) and age of these oils based on CSIA of selected aromatic compounds and to understand why the Sofer plot is ineffective in establishing the source of western Australian petroleum systems. The bulk δ13C of saturated and aromatic hydrocarbon fractions of crude oils have been previously used to differentiate sources, however, many Australian crude oils are not classified correctly using this method. The oils were classified as marine by the δ13C values of individual aromatic compounds and as terrigenous based on the bulk δ13C data (Sofer plot).The oils where the δ13C values of 1,6-DMN and 1,2,5-TMN isomers are most negative are indicative of a marine source, whereas oils with a less negative values for the 1,6-DMN and 1,2,5-TMN isomers are derived from marine source rocks that contain a significant terrigenous component. Similarly, oils with the least negative δ13C values for the 1-MP and 1,9-DMP isomers reflect varying inputs of terrigenous organic matter to the their marine source rocks. Plots of P/DBT and Pr/Ph concentration ratios versus δ13C values of DMP, 1,6-DMN, 1,2,5-TMN, 1-MP and 1,9-MP are constructed to establish the relative amount of terrigenous organic matter contributing to the source rock of a series of marine oils. The ratios of P/DBT and Pr/Ph plotted against the δ13C values of the aromatic isomers (such as 1,6-DMN, 1,2,5-TMN, 1-MP and 1,9-MP) provide a novel and convenient way to discriminate crude oils derived from different source rocks that contain varying amounts of marine and terrigenous organic matter.  相似文献   

17.
Simultaneous mass spectral detection and stable carbon isotope analysis was performed on individual indigenous n-alkanes isolated from single C4 and C3 plant species and on a series of aliphatic and polycyclic aromatic hydrocarbons (PAH) produced from the combustion of these same biomass materials. The analysis technique used a combined gas chromatograph-mass spectrometer/combustion/isotope ratio mass spectrometer (GC-MS/C/IRMS). Precision (2σ) for replicate measurements of individual compounds in standard solutions using this novel configuration ranged between 0.2 and 0.5‰ for n-alkanes and 0.3 and 0.8‰ for PAH. Accuracy of the n-alkane measurements ranged between 0.1 and 0.4‰ and that of the PAH measurements ranged between 0.2 and 0.9‰. Replicate GC-MS/C/IRMS measurements on the combustion-derived n-alkene/alkane pairs were performed to within a precision of between 0.1 and 1.1‰ and the precision for the combustion PAH was similar to the standard PAH solution. No notable isotopic effects were observed when altering the temperature of the combustion process from 900 to 700°C, or as a result of the individual n-alkenes/alkanes partitioning between the gaseous and condensate fractions. Combustion-derived n-alkenes/alkanes ranged from C11 to C31, and the C4-derived n-alkenes/alkanes were approx. 8‰ more enriched in 13C than the C3-derived compounds. Both the C4 and C3-derived n-alkenes/alkanes (C20-C30) were isotopically similar to the indigenous n-alkanes and were 2-3‰ more depleted in 13C than the lower mol. wt (C1111-C19) n-alkenes/alkanes, suggesting an independent origin for the lower mol. wt compounds. Combustion-generated C4 and C3-derived 2-, 3-, and 4-ring PAH were also isotopically distinct (Δδ = 10‰). Unlike the n-alkenes/alkanes, no compound-to-compound variations were observed between the low and high mol. wt PAH. This study demonstrates that the isotopic composition of original plant biomass material is mainly preserved in the aliphatic hydrocarbons and PAH generated by its combustion. Consequently, analyses of these compounds in sediments impacted by fire occurrences may provide useful information about paleo-fire activity that may help elucidate the impact biomass burning may have had and could have on climate-biosphere interactions.  相似文献   

18.
The significance and validity of integrating data obtained from a variety of analytical techniques to understand, elucidate and model kerogen's complex chemical structure is reported here using degradative (open and closed system pyrolysis, chemical oxidation), non-degradative (13C CP/MAS NMR) and optical (incident white light and blue light) methods. Seven Cambrian Alum Shale samples, ranging in maturity from immature to post-mature with respect to petroleum generation, were studied and were chosen for their simple geological history, uniform organic matter type and high organic carbon content. The Alum Shale kerogens, which primarily consist of algal organic matter, liberate low molecular weight gaseous and aromatic compounds on pyrolysis and give mostly branched dicarboxylic acids on chemical oxidation. 13C NMR spectroscopy shows that the Alum Shale kerogens are anomalously rich in oxygen-bearing functional groups (such as C = O, ArCO, CHO, CHxO), most of which apparently remain intact within the kerogen macro-molecule (KMM) through the diagenetic and catagenetic stages. Fragments released by different degradative techniques are quantified and the aromaticity (fa), O/C and relative proportions of various carbon types estimated by 13C NMR. A synthesis of these data has allowed us to better understand the chemistry of the Alum Shale kerogen.  相似文献   

19.
Concentration of aliphatic, aromatic, and chlorinated hydrocarbons were determined from 33 surface-sediment samples taken from the Tidal Basin, Washington Ship Channel, and the Anacostia and Potomac rivers in Washington, D.C. In conjunction with these samples, selected storm sewers and outfalls also were sampled to help elucidate general sources of contamination to the area. All of the sediments contained detectable concentrations of aliphatic and aromatic hydrocarbons, DDT (total dichlorodiphenyltrichloroethane), DDE (dichlorodiphenyldichloroethene), DDD (dichlorodiphenyldichloroethane), PCBs (total polychlorinated biphenyls) and total chlordanes (oxy-, α-, and γ-chlordane and cis + trans-nonachlor). Sediment concentrations of most contaminants were highest in the Anacostia River just downstream of the Washington Navy Yard, except for total chlordane, which appeared to have upstream sources in addition to storm and combined sewer runoff. This area has the highest number of storm and combined sewer outfalls in the river. Potomac River stations had lower concentrations than other stations. Total hydrocarbons (THC), normalized to the fine-grain fraction (clay + silt, < 63 μm), ranged from 120 μg g?1 to, 1,900 μg g?1 fine-grain sediment. The hydrocarbons were dominated by the unresolved complex mixture (UCM), with total polycyclic aromatic hydrocarbons (PAHs) concentrations ranging from 4 μg g?1 to 33 μg g?1 fine-grain sediment. Alkyl-substituted compounds (e.g., C1 to C4 methyl groups) of naphthalene, fluorene, phenanthrere + anthracene, and chrysene series dominated the polycyclic aromatic hydrocarbons (PAHs). Polycyclic aromatic hydrocarbons, saturated hydrocarbons, and the unresolved complex mixture (UCM) distributions reflect mixtures of combustion products (i.e., pyrogenic sources) and direct discharges of petroleum products. Total PCB concentrations ranged from 0.075 μg g?1 to 2.6 μg g?1 fine-grain sediment, with highest concentrations in the Anacostia River. Four to six C1-substituted biphenyls were the most-prevalent PCBs. Variability in the PCB distribution was observed in different sampling areas, reflecting, differing proportion of Arochlor inputs and degradation. The concentration of all contaminants was generally higher in sediments closer to known sewer outfalls, with concentrations of total hydrocarbon, PAHs, and PCBs as high as 6,900 μg g?1, 620 μg g?1, and 20 μg g?1 fine-grain sediment, respectively. Highest PCB concentrations were found in two outfalls that drain into the Tidal Basin. Concentrations of organic contaminants from sewers draining to the Washington Ship Channel and Anacostia River had higher concentrations than sediments of the mid-channel or river. Sources of PCBs appear to be related to specific outfalls, while hydrocarbon inputs, especially PAHs, are diffuse, and may be related to street runoff. Whereas most point-source contaninant inputs have been regulated, the importance of nonpoint source inputs must be assessed for their potential addition of contaminants to aquatic ecosystems. This study indicates that in large urban areas, nonpoint sources deliver substantial amounts of contaminants to ecosystems through storm and combined sewer systems, and control of these inputs must be addressed.  相似文献   

20.
Biomarker ratios, together with stable carbon (δ13C) and hydrogen (δD) isotopic compositions of individual hydrocarbons have been determined in a suite of crude oils (n = 24) from the East Sirte Basin to delineate their sources and respective thermal maturity. The crude oil samples are divided into two main families (A and B) based on differences in source inputs and thermal maturity. Using source specific parameters including pristane/phytane (Pr/Ph), hopane/sterane, dibenzothiophene/phenanthrene (DBT/P), Pr/n-C17 and Ph/n-Cl8 ratios and the distributions of tricyclic and tetracyclic terpanes, family B oils are ascribed a marine source rock deposited under sub-oxic conditions, while family A oils have a more terrigenous source affinity. This genetic classification is supported by the stable carbon isotopic compositions (δ13C) of the n-alkanes. Using biomarker maturity parameters such as the abundance of Pr and Ph relative to n-alkanes and the distribution of sterane and hopane isomers, family A oils are shown to be more thermally mature than family B oils. The contrasting maturity of the two families is supported by differences between the stable hydrogen isotopic compositions (δD) of Pr and Ph and the n-alkanes, as well as the δ13C values of n-alkanes in their respective oils.  相似文献   

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