首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Biodegraded oils are widely distributed in the Liaohe basin, China. In order to develop effective oil-source correlation tools specifically for the biodegraded oils, carbon isotopic compositions of individual n-alkanes from crude oils and their asphaltene pyrolysates have been determined using the gas chromatography–isotope ratio mass spectrometry technique. No significant fractionation in the stable carbon isotopic ratios of n-alkanes in the pyrolysates of oil asphaltenes was found for anhydrous pyrolysis carried out at temperatures below 340°C. This suggests that the stable carbon isotopic distribution of n-alkanes (particularly in the C16–C29 range) in the asphaltene pyrolysates can be used as a correlation tool for severely biodegraded oils from the Liaohe Basin. Comparison of the n-alkane isotopic compositions of the oils with those of asphaltene pyrolysates shows that this is a viable method for the differentiation of organic facies variation and post-generation alterations.  相似文献   

2.
Structures and carbon isotopic compositions of biomarkers and kerogen pyrolysis products of a dolomite, a bituminous shale and an oil shale of the Kimmeridge Clay Formation (KCF) in Dorset were studied in order to gain insight into (i) the type and extent of water column anoxia and (ii) changes in the concentration and isotopic composition of dissolved inorganic carbon (DIC) in the palaeowater column. The samples studied fit into the curve of increasing δ13C of the kerogen (δ13CTOC) with increasing TOC, reported by Huc et al. (1992). Their hypothesis, that the positive correlation between TOC and δ13CTOC is the result of differing degrees of organic matter (OM) mineralisation in the water column, was tested by measuring the δ13C values of primary production markers. These δ13C values were found to differ on average by only 1‰ among the samples, implying that differences in the extent of OM mineralisation cannot fully account for the 3‰ difference in δ13CTOC. The extractable OM in the oil shale differs from that in the other sediments due to both differences in maturity, and differences in the planktonic community. These differences, however, are not likely to have significantly influenced δ13CTOC either. All three sediments contain abundant derivatives of isorenieratene, indicating that periodically euxinia was extending into the photic zone. The sediments are rich in organic sulfur, as revealed by the abundant sulfur compounds in the pyrolysates. The prominence of C1-C3 alkylated thiophenes over n-alkanes and n-alkenes is most pronounced in the pyrolysate of the sediment richest in TOC. This suggests that sulfurisation of OM may have played an important role in determining the TOC-δ13CTOC relationship reported by Huc et al. (1992).  相似文献   

3.
Analysis of the molecular composition of the organic matter (OM) from whole sediment samples can avoid analytical bias that might result from isolation of components from the sediment matrix, but has its own analytical challenges. We evaluated the use of GC × GC-ToFMS to analyze the pyrolysis products of six whole sediment samples obtained from above, within and below a 1 million year old OM-rich Mediterranean sapropel layer. We found differences in pyrolysis products <n-C22 between the OM-rich sapropel samples and the OM-poor background marls. The presence of alkyl pyrroles, probably derived from chlorophyll, in pyrolysates of the sapropels but not in those of the marls suggests that higher marine productivity and greater OM preservation accompanied deposition of the sapropels. Detection of tetramethyl benzenes considered to be pyrolysis products of isorenieratene in the sapropel samples is evidence that nitrogen-fixing green sulfur bacteria contributed to the high productivity. Greater abundances of shorter chain aliphatic hydrocarbons, pyrroles, furans and alkyl aromatics in the pyrolysates of sapropel samples relative to the marls confirm better preservation of marine OM in the sapropels. In addition, the presence of greater amounts of thiophenes in the sapropels than in the marls is consistent with the existence of euxinic conditions during sapropel deposition. The combination of whole sediment pyrolysis and GC × GC-ToFMS is promising, but the procedure requires careful selection of its multiple analytical variables, particularly the pyrolysis temperature and the operational features of the GC columns.  相似文献   

4.
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   

5.
Ocean Drilling Program Leg 207 recovered thick sequences of Albian to Santonian organic-carbon-rich claystones at five drill-sites on the Demerara Rise in the western equatorial Atlantic Ocean. Dark-colored, finely laminated, Cenomanian–Santonian black shale sequences contain between 2% and 15% organic carbon and encompass Oceanic Anoxic Events 2 and 3. High Rock-Eval hydrogen indices signify that the bulk of the organic matter in these sequences is marine in origin. However, δ13Corg values lie mostly between −30‰ and −27‰, and TOC/TN ratios range from 15 to 42, which both mimic the source signatures of modern C3 land plants. The contradictions in organic matter source indicators provide important implications about the depositional conditions leading to the black shale accumulations. The low δ13Corg values, which are actually common in mid-Cretaceous marine organic matter, are consequences of the greenhouse climate prevailing at that time and an associated accelerated hydrologic cycle. The elevated C/N ratios, which are also typical of black shales, indicate depressed organic matter degradation associated with low-oxygen conditions in the water column that favored preservation of carbon-rich forms of marine organic matter over nitrogen-rich components. Underlying the laminated Cenomanian–Santonian sequences are homogeneous, dark-colored, lower to middle Albian siltstones that contain between 0.2% and 9% organic carbon. The organic matter in these rocks is mostly marine in origin, but it occasionally includes large proportions of land-derived material.  相似文献   

6.
Suberinite, and subereous components of amorphous nature, comprise largely unrecognized, proficient sources of liquid hydrocarbons. Due to difficulties in recognizing the presence of subereous components and suberinite in organic sediments, the contributions of these liptinitic components to the organic input of source rocks are easily underestimated. Severe chemical alterations of suberinite in the vitrinite reflectance range of Ro = 0.35–0.60% are demonstrated. Organic geochemical data, obtained from samples subjected to natural maturation, reveal that subereous components/suberinite undergoes early thermal degradation to generate large amounts of hydrocarbons below Ro = 0.60%. Data obtained from laboratory maturation of immature, suberinite-rich coals indicate that about 50% of the potential of suberinite for generating C12+ hydrocarbons has already been exhausted during natural maturation of the samples, prior to the onset of the traditionally defined “oil window”. The present data (a) contradict the assumption that suberinite is mainly sourced by selective preservation/enrichment of a stable, highly aliphatic biopolymer, i.e. “suberan” and (b) suggest that suberinite contains appreciable amounts of aliphatic and aromatic moieties which are released at low thermal stress.  相似文献   

7.
Micro-scale sealed vessel (MSSV) pyrolysis experiments have been conducted at temperatures of 150, 200, 250, 300, 330 and 350°C for various times on a thermally immature Type II-S kerogen from the Maastrichtian Jurf ed Darawish Oil Shale (Jordan) in order to study the origin of low-molecular-weight (LMW) alkylthiophenes. These experiments indicated that the LMW alkylthiophenes usually encountered in the flash pyrolysates of sulphur-rich kerogens are also produced at much lower pyrolysis temperatures (i.e. as low as 150°C) as the major (apart from hydrogen sulfide) sulphur-containing pyrolysis products. MSSV pyrolysis of a long-chain alkylthiophene and an alkylbenzene indicated that at 300°C for 72 h no β-cleavage leading to generation of LMW alkylated thiophenes and benzene occurs. In combination with the substantial production of LMW alkylthiophenes with a linear carbon skeleton at these conditions, this indicated that these thiophenes are predominantly formed by thermal degradation of multiple (poly)sulfide-bound linear C5–C7 skeletons, which probably mainly originate from sulphurisation of carbohydrates during early diagenesis. LMW alkylthiophenes with linear carbon skeletons seem to be unstable at MSSV pyrolysis temperatures of ≥330°C either due to thermal degradation or to methyl transfer reactions. LMW alkylthiophenes with a branched carbon skeleton most likely derive from both multiple (poly)sulfide-bound branched C5–C7 skeletons and alkylthiophene units present in the kerogen.  相似文献   

8.
A molecular study of linear, branched and isoprenyl alkylbenzene skeletons and alkenylbenzenes in the soluble fraction extracted from a sulfur-rich Utrillas coal was carried out using gas chromatography–mass spectrometry (GC–MS). The presence of C24–C28 diaromatic compounds, not previously reported in coals, suggests that photosynthetic green sulfur bacteria may have made an input of organic matter to these coals. The unsaturated linear alkenylbenzenes and isoprenyl (C15 and C20) alkylbenzene skeletons are also described for the first time in the soluble fraction of geological samples.  相似文献   

9.
Carbonates from the Keg River Formation, La Crete Basin, Alberta, western Canada were examined in order to define: (a) oil source rock potential; (b) bulk maceral composition; (c) extract yield; and finally (d) facies variations using PY-GC-MS. Thirty samples from 6 different wells were examined from the lower Keg River member and 4 from the upper Keg River member using conventional geochemical methods. As maturity differences are absent within the sample set, variations in TOC, Tmax, hydrogen index, organic petrography and extract yields are caused by variability in organic matter input, which is revealed by molecular characterisation using PY-GC-MS. Lower Keg River member bituminous wackestones are excellent potential source rocks containing Types I–II and Type II organic matter. Types I–II organic matter contains large well preserved (up to 200μm in diameter) thick-walled Tasmanites (10–15% of sample) and akinete algal cells indicative of algal blooms within an amorphous bituminite. Type II organic matter contains a higher proportion of degraded alginites/bituminite relative to well-preserved alginites. Extract yields (mg/g TOC) were seen to increase from Types I–II to Type II organic matter. PY-GC-MS revealed that 1,2,3,4-tetramethylbenzene was a major peak in most samples. This is a pyrolysis product arising from β-cleavage of C40 diaromatic carotenoids incorporated within the kerogen during diagenesis. The source of this compound is thought to be from an unknown diaromatic compound with a 2,3,6-/3,4,5-trimethyl substitution pattern and isorenieratene, which is specific to photosynthetic green sulphur bacteria (Chlorobiaceae) suggesting that the photic zone was at least partially anoxic during deposition of these samples. The relative abundance of this compound/n-C11-alkene and organic sulphur (calculated from the thiophene ratio) both increase from Types I–II to Type II organic matter. This trend was grossly similar to the trend seen in the variability of extract yield with hydrogen index. A similar trend for HI and Tmax indicates samples containing a higher proportion of degraded alginites/bituminite relative to well-preserved alginite are more labile than Type I–II organic matter. Upper Keg River member marls contain Type II organic matter, which is characterised by heavily degraded algal material within a bituminous groundmass. Pyrolysates of two of the marl samples contain only low amounts of 1,2,3,4-tetramethylbenzene, in contrast to the bituminous wackestones, indicating that the depositional environment/source input was different during deposition of the marl samples. Although both marls contain similar organic matter, their pyrolysates were significantly different. One marl (1141.9 m) was highly paraffinic containing dominantly short-chain alkene/alkane doublets, while the other marl (1137.6 m) contained a bimodal n-alkane/alkene distribution and high amounts of alkylphenols, which may be derived from preservation of resistant algal polyphenolic molecules or suggest a terrestrial input.  相似文献   

10.
Hydrocarbon mixtures too complex to resolve by traditional capillary gas chromatography display gas chromatograms with dramatically rising baselines or “humps” of coeluting compounds that are termed unresolved complex mixtures (UCMs). Because the constituents of UCMs are not ordinarily identified, a large amount of geochemical information is never explored. Gas chromatograms of saturated/unsaturated hydrocarbons extracted from Late Archean argillites and greywackes of the southern Abitibi Province of Ontario, Canada contain UCMs with different appearances or “topologies” relating to the intensity and retention time of the compounds comprising the UCMs. These topologies appear to have some level of stratigraphic organization, such that samples collected at any stratigraphic formation collectively are dominated by UCMs that either elute early- (within a window of C15–C20 n-alkanes), early- to mid- (C15–C30 n-alkanes), or have a broad UCM that extends through the entire retention time of the sample (from C15–C42 n-alkanes). Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC–MS) was used to resolve the constituents forming these various UCMs. Early- to mid-eluting UCMs are dominated by configurational isomers of alkyl-substituted and non-substituted polycyclic compounds that contain up to six rings. Late eluting UCMs are composed of C36–C40 mono-, bi-, and tricyclic archaeal isoprenoid diastereomers. Broad UCMs spanning the retention time of compound elution contain nearly the same compounds observed in the early-, mid-, and late-retention time UCMs. Although the origin of the polycyclic compounds is unclear, the variations in the UCM topology appear to depend on the concentration of initial compound classes that have the potential to become isomerized. Isomerization of these constituents may have resulted from hydrothermal alteration of organic matter.  相似文献   

11.
For a better understanding of siliciclastic shelf environments, correlation between sequence stratigraphy and organic geochemistry is used. Our study is focused on the Cretaceous deposits of Marcoule (Gard, France), particularly on a close-packed siltites layer (200–400 m thick), which is well characterized as a marine flooding facies of a single trangressive–regressive cycle. During the Uppermost Albian and the Lower Cenomanian, the stratigraphic data indicate a change in the depositional environment from offshore to shoreface. Organic geochemistry is used in order to characterize origin and variability of the organic matter in relation to the stratigraphic data. The study is carried out on core samples from 2 drill holes (MAR 203 and MAR 501). Analyses of the aliphatic and aromatic hydrocarbons were performed using GC–MS and focused on biomarker distributions. The biomarkers indicate a contribution of mixed terrestrial and marine organic matter. The changes in molecular signatures are related to variations in the source of organic matter (marine versus terrestrial), preservation conditions (largely influenced by clay and early diagenesis), environmental oxidation-reduction and acidic conditions as well as bioturbation. Various environmental zones, characterized by different molecular signatures, can be distinguished. Resin derived biomarkers can be assigned to higher plant material input and may reflect the evolution and diversity of Gymnospermae versus Angiospermae during the transgressive/regressive cycle. The relative sea-level variations are clearly correlated with the nature and the preservation of the organic matter. For example, the Pr/Ph and Pr/n-C17 ratios as well as the regular steranes distributions underline the maximum flooding surface evidenced by other studies. We observe a good correlation between the organic data and sequence stratigraphy: changes in geochemical signatures reflect the 3rd order depositional cycles.  相似文献   

12.
A mixture of C33–C37 botryococcenes and partially reduced derivatives was isolated from ca. 32,000 year old sediment from Lake Masoko, a freshwater crater lake in the Rungwe Range area (Tanzania). Botryococcenes and derivatives accounted for 246 μg/g dry sediment and for >92% of the hydrocarbon fraction; 1D and 2D nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry allowed the structure of the dominant botryococcene (43% of hydrocarbon fraction) to be established, after purification using high performance liquid chromatography (HPLC). The compound is a novel tetraunsaturated dicyclic C34 botryococcene and is named C34 masokocene. Overall, the structures of six other novel botryococcenes and four partially reduced derivatives were tentatively assigned. The structures of the new biomarkers, three dicyclic C34–C36 botryococcenes (or masokocenes) and seven monocyclic C34–C37 analogues are discussed along with their biosynthetic relationship. The high abundance of such polyunsaturated compounds preserved in 32,000 year old sediment from the lake indicates an aquatic ecosystem dominated at the time by the green alga Botryococcus braunii, as well very good preservation of the organic matter.  相似文献   

13.
The organic matter of recent deltaic sediments cored in the Mahakam delta, East Kalimantan, has been studied before and after physical fractionation into sands >50 μm, silts 5–50 μm and clays <5 μm. Both the lipid and non-lipid components have been investigated.Weight, carbon and nitrogen fractionation budgets were used to define three types of samples, depending on coarse particle contributions to the total amount of organic matter: a = a first type with more than 50% of the O.M. in the coarse particles, high C/N ratios and O.M. content, b = an intermediary type with medium C/N ratios and O.M. content, each fraction having quite the same O.M. content, c = a third type with less than 5% of the whole O.M. in the sands and the lowest C/N ratios and O.M. content.Concerning the global organic characteristics of the fractions, a systematic increase of C/N ratios occurs when going from clays to sands; the finer the fraction is, the more nitrogenous the compounds are. This enrichment in nitrogen is related to a persistent high rate of hydrolysable material either for argillaceous organic matter-poor sediments or for the clay fractions of all types of samples. Conversely, the type (a) coarse sediments, in particular the sandy components were resistant to acid hydrolysis with burial.Concerning the geochemical markers signatures of granulometric fractions, the distribution patterns of n-alkanes and n-fatty acids are characterized by the predominance of high molecular weight compounds >C22. Carbon preference index (CPI) values are higher in the sands and silts, reflecting their enrichment in continentally-derived vegetation debris. For type (c), the fractionation revealed markers of microbial activity within the clay fractions. For all types of samples, we observed an increase with burial of the n-alkane and n-fatty acid concentrations, particularly in the clay fractions, suggesting possibly a better preservation and/or affinity of lipids with the finest fractions.  相似文献   

14.
The degree of isotopic variation in fossil organic matter renders bulk δ13C signatures strongly influenced by molecular isotopic heterogeneity. For example, in fossil wood the relative abundance of less depleted 13C moieties, i.e. preserved 13C enriched polysaccharides versus the relatively 13C depleted lignin moieties, can be seen to significantly bias δ13Cfossil wood values. Moreover the variation in δ13C values of specific compounds within fossil material are themselves highly variable and reflect the heterogeneity in isotopic values of different carbon atoms within individual compounds. For studies using δ13C values of fossil plant material as proxies (e.g., for δ13Cpalaeoatmosphere, δ13Cbiomass) it is recommended that the biases introduced through molecular heterogeneity, preservation type and taxonomic status of the fossil material are determined initially. Biases inherent in the bulk signature can then be reduced, rendering this value more robust. Alternatively, compound specific stable carbon isotope measurements of individual moieties preserved through geological time might prove to be an alternative proxy for monitoring changes in the bulk δ13C value of the plant and might reveal atmospherically induced trends.  相似文献   

15.
A Pliocene oil shale (Pula, Hungary), a C3 plant Triticum aestivum and a C4 plant Zea mays were compared using isotopic composition of bulk organic matter, along with distributions and individual carbon isotope ratios of n-alkanes from organic extracts. The microalga Botryococcus braunii (A race) was thus shown to be the main source of the predominant 27, 29 and 31 n-alkanes of Pula sediment Therefore, the dominance of odd carbon-numbered n-alkanes in the range C25–35 in extracts from immature sediments shall not be systematically assigned to higher plant contribution but algal input is also possible. In fact, the long chain n-alkanes with an odd predominance previously observed in extracts of various immature sediments are likely to be derived at least partially, from algae.  相似文献   

16.
In this study, organic matter content, type and maturity as well as some petrographic and physical characteristics of the Jurassic coals exposed in the eastern Taurus were investigated and their depositional environments were interpreted.The total organic carbon (TOC) contents of coals in the Feke–Akkaya, Kozan–Gedikli and Kozan–Kizilinc areas are 24.54, 66.78 and 49.15%, respectively. The Feke–Akkaya and Kozan–Kizilinc coals have low Hydrogen Index (HI) values while the Kozan–Gedikli coals show moderate HI values. All coal samples display very low Oxygen Index (OI) values. The Kozan–Gedikli coals contain Type II organic matter (OM), the Feke–Akkaya coals contain a mixture of type II and type III OM; and the Kozan–Kizilinc coals are composed of Type III OM. Sterane distribution was calculated as C27 > C29 > C28 from the m/z 217 mass chromatogram for all coal samples.Tmax values for the Feke–Akkaya, Kozan–Gedikli and Kozan–Kizilinc coals are 439, 412 and 427 °C. Vitrinite reflectance values (%Ro) for the Feke–Akkaya and Kozan–Kizilinc coal samples were measured as 0.65 and 0.51 and these values reveal that the Feke–Akkaya and Kozan–Kizilinc coals are at subbituminous A or high volatile C bituminous coal stage. On the basis of biomarker maturity parameters, these coals have a low maturity.The pristane/phytane (Pr/Ph) ratios for the Feke–Akkaya, Kozan–Gedikli and Kozan–Kizilinc coals are 1.53, 1.13 and 1.25, respectively. In addition, all coals show a homohopane distribution which is dominated by low carbon numbers, and C35 homohopane index is very low for all coal samples. All these features may indicate that these coals were deposited in a suboxic environment.The high sterane/hopane ratios with high concentrations of steranes, low Pr/Ph ratios and C25/C26 tricyclic ratios > 1 may indicate that these coals formed in a swamp environment were temporarily influenced by marine conditions.  相似文献   

17.
Nine rock samples from three Jurassic stratigraphic units of a shallow core from NW Germany were analyzed by pyrolysis-gas chromatography. The units contain a mixed Type-II/III kerogen (Dogger-α), a hydrogen-rich Type-II kerogen (Lias-), and a hydrogen-poor Type-III kerogen (Lias-δ). All of the kerogen was immature (Ro = 0.5%). Two sets of kerogen concentrates (“AD”: HCl/HF followed by a density separation, and “A”: only acid treatment) prepared from the rock samples were also analyzed to make a detailed comparison of the pyrolysates of rock and corresponding kerogen-concentrates.Hydrogen-index (HI) values of the kerogen concentrates prepared from organic-carbon poor rock were nearly 200% higher than HI values of the rock samples. Changes in HI were minimal for the samples containing Type-II kerogen. The A and AD samples from the Corg-poor rock yielded pyrolysates with n-alkane series of very different molecular lengths. Pyrograms of the rock samples had n-alkane series extending to n-C14; the chromatograms of the A samples reached the n-C14-nC20 range. The AD samples from Corg-poor rock and all three sample types from the Corg-rich rock had n-alkane series up to n-C29. The benzene/hexane and toluene/heptane ratios for the Corg-poor rock and A samples were far higher than for the AD samples, which had ratios similar to those of all three sample types from the Corg-rich rocks. These results indicate that choice of kerogen preparation method is critical when Corg-poor samples are analyzed.  相似文献   

18.
Surface sediment samples were collected from the Squamish River Delta, British Columbia, in order to determine the role of sediment surface area in the preservation of organic matter (OM) in a paralic sedimentary environment. The Squamish Delta is an actively prograding delta, located at the head of Howe Sound.Bulk total organic carbon (TOC) values across the Squamish Delta are low, ranging from 0.1 to 1.0 wt.%. The carbon/total nitrogen ratio (Corg/N) ranges from 6 to 17, which is attributed to changes in OM type and facies variations. The <25-μm fraction has TOC concentrations up to 2.0 wt.%, and a Corg/N ratio that ranges from 14 to 16. The 53–106-μm fraction has higher TOC concentrations and Corg/N ratios relative to the 25–53-μm fraction. The Corg/N ratio ranges from 9 to 18 in the 53–106-μm fraction and 5.5–10.5 in the 25–53-μm fraction. Surface area values for bulk sediments are low (0.5–3.0 m2/g) due to the large proportion of silt size material. Good correlation between surface area and TOC in bulk samples suggests that OM is adsorbed to mineral surfaces. Similar relationships between surface area and TOC were observed in size-fractionated samples. Mineralogy and elemental composition did not correlate with TOC concentration.The relationships between surface area, TOC and total nitrogen (TN) can be linked to the hydrodynamic and sedimentological conditions of the Squamish Delta. As a result, the Squamish Delta is a useful modern analogue for the formation of petroleum source rocks in ancient deltaic environments, where TOC concentrations are often significantly lower than those in source rocks formed in other geological settings.  相似文献   

19.
The chemical structure, source(s), and formation pathway(s) of kerogen-like organic matter (KL) were investigated in recent sediments from the northwestern Black Sea, off the Danube delta. Three sections from a sediment core collected at the mouth of the Sulina branch of the delta, under an oxic water column, were examined: S0 (0–0.5 cm bsf), S10 (10–13 cm bsf), and S20 (20–25 cm bsf). The bulk geochemical features of these sediments (total organic carbon, organic C/N atomic ratio, δ13Corg) were determined. Thereafter, KL was isolated from the samples, as the insoluble residue obtained after HF/HCl treatment. KL chemical composition was investigated via spectroscopic (FTIR, solid state 13C and 15N NMR) and pyrolytic (Curie point pyrolysis–gas chromatography–mass spectrometry) methods, and the morphological features were examined by scanning and transmission electron microscopy. Similar morphological features and chemical composition were observed for the three KLs and they suggested that the selective preservation of land-plant derived material as well as of resistant aliphatic biomacromolecules (probably derived from cell walls of freshwater microalgae) was the main process involved in KL formation. Besides, some melanoidin-type macromolecules (formed via the degradation-recondensation of products mainly derived from proteinaceous material) and/or some encapsulated proteins also contributed to the KL chemical structure.  相似文献   

20.
Samples from two argillaceous formations (Opalinus Clay and Posidonia Shale) of near-identical maturity from northern Switzerland were subjected to a geochemical characterisation of organic matter and to confined-system pyrolysis experiments. Throughout the study area, the characteristics of organic matter are similar, indicating a spatially homogeneous sedimentary facies. Posidonia Shale contains marine organic matter deposited in a reducing environment, while a predominantly terrigenous source and a more oxidising environment of deposition was identified for Opalinus Clay. In the western and central parts of the study area, organic maturity is close to the onset of oil generation. In the easternmost part, a higher maturity has been reached due to a deeper burial below thick Tertiary Molasse deposits.Isothermal pyrolysis experiments were conducted at temperatures between 250 and 390 °C over 24 h. Bitumen yields increase along similar pathways for both Opalinus Clay and Posidonia Shale, but the maximum values are displaced by 10–20 °C. Data pertaining to maturity were determined from GC–MS analyses of saturated hydrocarbons, and specific attention was given to C29-sterane and C32-hopane isomerisation ratios. The evolution of these parameters with rising temperature is slightly different in the two formations, which is attributed to the contrasting organic facies. The pyrolysis data, together with literature data from natural basins, were used to calculate kinetic parameters for C29-sterane and C32-hopane, assuming a single-step isomerisation scheme according to the Arrhenius law. The resulting values based on pyrolysis data alone are very similar to those based on the combination of pyrolysis and natural data. Activation energies are similar in both formations, while the frequency factors are up to one order of magnitude higher for Posidonia Shale when compared to Opalinus Clay. For the Benken site, maximum temperature during Cretaceous burial was calculated on the basis of the kinetic data, using the TTI approach. The resulting temperatures of 75–80 °C are 5–10 °C below those derived in the literature from apatite fission-track analysis, vitrinite reflectance and basin modelling.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号