Kerogen Pyrolysis Research Articles

Thermogravimetry and pyrolysis—GC of chlorophyll-a: with a special emphasis on thermal behavior of its phytyl chain

The thermal alteration of chlorophyll-a (Chl-a) was examined by means of thermogravimetry (TG) and pyrolysis—gas chromatography (Py-GC). Py-GC/mass spectroscopy, gas chromatography and infrared spectrometry were also used as complementary methods. When pyrolyzed at 340 °C for 15 s, Chl-a produced virtually only C20-isoprenoid hydrocarbons (C20-ISOPs). This result indicates that the major decomposition reaction below 340 °C is the release of a phytyl (3,7,11,15-tetramethyl-2-hexadecenyl) chain. When the 340 °C-pyrolysis residue was pyrolyzed again at 470 °C for 15 s, notable amounts of isoprenoid hydrocarbons with carbon numbers of 19 or less (S-ISOPs) were produced and amounts of C20-ISOPs became smaller. We assume that these S-ISOPs are produced from a phytanylaromatic structure which may have been formed during the 340 °C pyrolysis. On heating Chl-a at 150 °C for a long time (504 h) resulted in the formation of a material barely soluble in many organic solvents. S-ISOPs produced from the barely soluble material upon pyrolysis at 470 °C are similar in molecular distribution to those obtained by the pyrolysis at 470 °C of the 340 °C-pyrolysis residue of Chl-a. This suggests that a phytanyl-aromatic structure is formed also on long-term 150 °C heating. The Chl-a-derived S-ISOPs were almost identical to those obtained upon flash pyrolysis of kerogens (insoluble organic matter in sedimentary rocks) in terms of molecular composition. Thus, it is supposed that Chl-a changes into a polycondensed material having a phytanyl-aromatic structure in sediments/sedimentary rocks and is finally incorporated into a kerogen assemblage in nature.

Alternative biological sources for 1,2,3,4-tetramethylbenzene in flash pyrolysates of kerogen

Pyrolysates of kerogens isolated from Indian Ocean surface sediments and from Black Sea Unit II contain abundant 1,2,3,4-tetramethylbenzene (1,2,3,4-TMB) suggesting the presence of macromolecularly-bound isorenieratane skeletons derived from isorenieratene biosynthesized by green sulphur bacteria (cf. Hartgers et al., 1994c). However, the 13C content of 1,2,3,4-TMB is identical to that of algal lipids, excluding an origin from green sulphur bacteria. The presence of 1,2,3,4-TMB in pyrolysates of stable residues of several marine algae indicates that it can also have an algal origin. Therefore, the assessment of photic zone anoxia on the basis of the abundant presence of 1,2,3,4-TMB in the pyrolysate is not possible without determination of its stable carbon isotopic composition and comparison with those of algal lipids.

Release of covalently-bound alkane biomarkers in high yields from kerogen via catalytic hydropyrolysis

Fixed-bed pyrolysis of kerogens at high hydrogen pressures (> 10 MPa, hydropyrolysis) in the presence of a dispersed sulphided molybdenum catalyst gives rise to extremely high yields of dichloromethane (DCM)-soluble oil (> 65%). To illustrate the potential of this approach, the yields and conformations of the hopanes, steranes and methyl steranes released from Göynük oil shale (a type I kerogen) by hydropyrolysis after prior sequential extraction of the shale with DCM and pyridine and batchwise hydrogenation at 300°C (cf 520°C for hydropyrolysis) are reported here. The total yield of aliphatic hydrocarbons from hydropyrolysis represented ca 30% w/w of the kerogen's organic matter with yields of the C 29–C 32 17β(H), 21β(H)-hopanes being between three and ten times greater than those from DCM extraction and the milder hydrogenation treatment. The yields of the C 33–C 35 17β(H), 21β(H)-hopanes, not found in the DCM extracts and only minor constituents in normal pyrolysis oil, were again typically at least three times higher than from hydrogenation.

Electron microscopy and pyrolysis of kerogens from the Kimmeridge Clay Formation, UK: Source organisms, preservation processes, and origin of microcycles

Recent studies revealed short-term cyclic variations (microcycles) in total organic carbon (TOC) and the hydrogen index (HI) in the Kimmeridge Clay Formation, an organic-rich deposit considered to be a lateral equivalent of the main source rocks of the North Sea. In addition, three different types of organic matter that all appear to be amorphous when observed by light microscopy (AOM) were recognized. Together, these AOM types account for over 80% of total kerogen and their relative abundances show large variations along each microcycle. In the present work, transmission electron microscopy (TEM) observations were carried out on samples (whole kerogens, kerogen subfractions only comprising a single type of AOM, selected rock fragments) corresponding to typical points within a microcycle and obtained via high resolution sampling. The nature and the relative abundances of the products generated by Curie-point Py-GC-MS and off-line pyrolyses of isolated kerogens were also determined for two selected samples corresponding to the beginning and the top of the microcycle. Combination of such ultrastructural observations, including some semiquantitative studies, and the analysis of pyrolysis products allowed (1) determination of the ultrastructural features of the three AOM types thus providing what we believe to be the first example of correlations between light microscopy (palynofacies, in situ maceral analysis) and TEM observations on “amorphous” fossil materials; (2) identification of the source organisms and elucidation of the mode of formation of the different AOM types in the Kimmeridge Clay; (3) explanation of the variations in their relative abundances taking place along a microcycle and establishment of tight correlations with TOC and HI changes; and (4) explanation of the origin of the microcyclic variations in kerogen quantity (TOC) and quality (III) occurring in the Kimmeridge Clay Formation. Interrelationships between primary productivity, sulphate reduction intensity, and lipid “vulcanization” likely played a major role in the control of such variations.

Geosynthesis of organic compounds: I. Alkylphenols

Methylation, isopropylation, and sec-butylation are proposed as geosynthetic processes to account for the alkylphenol compositions of crude oils with phenol distributions dominated by ortho and para substituted compounds.Phenol distributions in eleven crude oils and four kerogen pyrolysates were analysed using GC-MS (gas chromatography-mass spectrometry). Ten of the crude oils show high relative abundances of ortho and para substituted phenol isomers and some were also enriched in C3–C5 alkylphenols compared to the kerogen pyrolysates. Because the distributions of products obtained from the laboratory alkylation of cresols closely resemble those of phenols in these crude oils, we propose that similar alkylation processes occur in source rocks. Alkylation ratios reflecting the degree of methylation, isopropylation, and sec-butylation, which were based on the relative abundance of the dominant alkylation products compared to their likely precursor ortho-cresol, indicate that high levels of methylation occurred in crude oils over a wide range of maturities, whereas high levels of isopropylation and sec-butylation were observed only in mature samples. Dissolution of the phenols in crude oils by water contact was discounted as an explanation for the observed phenol distributions based on the relative distribution coefficients of phenols between a hydrocarbon phase and water.

Application of pyrolysis-gas chromatography to the study of thermal alteration of chlorophyll-a — effect of clay minerals

The effect of clay minerals (montmorillonite and kaolinite) on the thermal alteration of chlorophyll-a (Ch-a) was examined by means of pyrolysis-gas chromatrography. When preliminarily heated at 150 °C for a period ranging from 2 h to 504 h in the presence of montmorillonite or kaolinite, Ch-a produced a considerable amount of material which was insoluble in a 9:1 mixture of iso-octane/ethanol (I/E) but soluble in 3:1 benzene/methanol (B/M). The yield of I/E insoluble-B/M soluble fraction (B/M extract) increased with increased preheating time. Upon pyrolysis, the B/M extract produced isoprenoid hydrocarbons (ISOPs) of carbon number 20 or less. With increased preheating time, the yields of ISOPs of carbon number 20 (C20-ISOPs) dramatically decreased, compared to those of ISOPs of smaller carbon numbers (S-ISOPs). The S-ISOPs were mostly identical to those produced upon pyrolysis of kerogens (insoluble organic matter in sedimentary rocks). The trend in the decrease in the yields of C20-ISOPs with preheating time is similar to that observed for Ch-a preheated in the absence of clay minerals. Clay minerals seem to promote the formation of a structure which preferentially produces 1-pristene (2,6,10,14-tetramethyl-1-pentadecene, Pr-1), the most predominant compound in the ISOPs from kerogens, upon pyrolysis.

Rapid quantification of biomarkers during kerogen microscale pyrolysis

A rapid, reproducible method incorporating closed system microscale pyrolysis and thermal desorption-gas chromatography/mass spectrometry has been developed and applied to the quantification of sterane biomarkers released during pyrolysis of the Messel oil shale kerogen under confined conditions. This method allows a substantial experimental concentration-time data set to be collected at accurately controlled temperatures, due to the low thermal inertia of the microscale borosilicate glass reaction vessels, which facilitates kinetic studies of biomarker reactions during kerogen microscale pyrolysis

95/00960 Trace analysis of 3-hydroxybenzo[a]pyrene in urine for the biomonitoring of human exposure to polycyclic aromatic hydrocarbons

This paper presents isotopic, bulk geochemical and biomarker data measured on organic matter accumulated in a narrow extensional basin developed at the oceanward margin of the huge Triassic carbonate platform in the Alps–Appenines domain. The integration of isotope signatures, organic petrographical and biomarker evidence together with the composition of kerogen pyrolysates suggests immature organic matter predominantly of algal origin with a minor, but not negligible, higher plant derived and moderate bacterial contribution for the entire sequence. The mineral sources are dominated by platform-derived subtidal Dachstein limestone with a minor palaeosol input and a moderate contribution of autochtonous quartz. Nevertheless, parallel variations observed in the mineral content, as well as in the amount and the quality of the organic matter reflect variations in the palaeoenvironment. The increased humidity, existing in the period of the accumulation of the upper section of the sequence, led to the restriction of dolomitization. A slightly greater higher plant derived contribution, in this section, is evidenced by the composition of bitumen and the results on GC and GC/MS analyses on the non-aromatic hydrocarbon fraction of bitumen. Moreover, the climate-induced weathering enchanced the primary productivity and resulted in a pronounced increase in the TOC content. The average estimated value of the planktonic productivity is about three times higher for the calcite-rich sequence than the dolomite-rich one, being 44.2 and 15.3 tCorg/m2/Ma, respectively. The low to moderate planktonic productivity shows that anoxic conditions, observed for the entire succession, are a consequence of the stagnant water stratification rather than high planktonic productivity. Depth trends in the data measured on kerogens (HI, OI, δ13Corg values, composition of pyrolysate) together with the δ18O excursions and Δδ13C values appear to be controlled by sea-level fluctuations. Consistent with the high abundance of alkyltiophenes in kerogen pyrolysates, the high Sorg/C ratios (ranging between 0.05 and 0.10) suggest the importance of natural sulfurization in the formation of the sulfur-rich type-II-S kerogen occurring in all of the samples.

The origin of alkylbenzenes and thiophenes in pyrolysates of geochemical samples

Alkylbenzenes and thiophenes are common in pyrolysates of sulphur-rich oils, kerogens, coals and humic substances. The formation of alkylbenzenes and alkylthiophenes as artifacts during flash pyrolysis of triglycerides, or unsaturated fatty acids, in the presence of elemental sulphur is proved, which suggests that these alkylated cyclic and heterocyclic compounds may have at least two origins: as evaporation/pyrolysis products from the macromolecular matrix, and/or as artifacts. Therefore, inferences made from the presence of such homologous series of compounds in pyrolysates should be drawn with caution.

A practical approach to quantitative group type analysis of kerogens using non-dedicated pyrolysis-mass spectrometry equipment: applications and comparison with other methods

Pyrolysis-mass spectrometry (Py-MS), based on a slight modification of a non-dedicated MS, has been applied to the quantitative determination of different groups of hydrocarbons and non-hydrocarbons present in kerogen pyrolysates. The Py-MS experiments were carried out by using conventional pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) equipment where the pyrolysate enters the ion source directly via an expansion chamber. A suite of kerogens were flash pyrolysed at 700°C for 20 s and the mass spectral data of teh pyrolysates were acquired at low electron voltage (20 eV), scanning from m/ z 30 to 250. Elapsed analysis time is approximately 2–3 min for each kerogen sample. Medium resolution (2500 RP) was applied to reduce the nominal mass overlap and thus enhance the identification potential. Quantification of the pyrolysate compounds was achieved by adding an internal polymer standard to the samples, accompanied by the use of response factors for each compound class, established by analysis of reference compounds. The Py-MS results have been evaluated in comparison with data from other analytical methods (Rock Eval pyrolysis, combined microscale sealed vessel pyrolysis-gas chromatography (MSSV-Py-GC), elemental analysis, nuclear magnetic resonance spectroscopy, high resolution MS of pyrolysates). The Py-MS method appears to be a reproducible and rapid technique for evaluation of sedimentary organic matter. Py-MS data and results from conventional and other analyses mentioned above were correlated using multivariate analysis. Good correlations between pyrolysate yield parameters from Rock Eval pyrolysis, MSSV-Py-GC and atomic H/C content from elemental analyses of kerogens versus hydrocarbon yields measured by Py-MS, are observed. The Py-MS pyrolysate yields and the relative aromatic hydrocarbon content clearly differentiate between kerogens with the high (>1.4), intermediate (0.5–1.4) and low H/C ratios (<0.5), when multivariate processing was applied. Kerogens with atomic H/C ratios between 0.5–1.0 are separated from those with H/C ratios between 1.0–1.4, mainly by differences in the alkylthiophene and carbon dioxide yields as well as the relative amount of different classes of hydrocarbons. In addition, there was a good correlation between Py-MS parameters and a variety of parameters obtained by other pyrolysis techniques widely in use in the petroleum industry. Thus, gas to oil ratios determined by sealed vessel pyrolysis GC correlate negatively with e.g. the relative amount of cycloalkanes present in pyrolysates as measured by Py-MS. Finally, the mean alkyl chain length in the kerogens has been estimated from pyrolysate Py-MS data based on calibration of MS-fragmentation ratios ( m/z 43 85 ) againnst known alkyl chain lengths.

First indications of the formation of kerogen amorphous fractions by selective preservation. Role of non-hydrolysable macromolecular constituents of Eubacterial cell walls

Two marine kerogens supposed to contain an important bacterial component were analysed and their spectroscopic and pyrolytic features compared with those of the amorphous non-hydrolysable macromolecular materials (bacterans) isolated from extent bacteria. Examination by Transmissio Electron Microscopy revealed that Dontrien (Lower Toarcian Shales, Paris Basin) is essentially composed of amorphous organic matter and OSB3 (Marl Slate Formation, N.E. England) is exclusively amorphous. The formation upon kerogen pyrolysis of series of products (3-methylalkanes, dimethylalkanes, ethylesters and alcohols) characteristic of bacteran pyrolysates is consistent with the contribution of bacterans to the formation of these two kerogens. The nature and distribution of the acids of the pyrolysates indicate that bacterial biomass was implicated in OSB3 and Dontrien kerogen formation via two pathways: bacteran selective preservation and incorporation of partly degraded lipids. Comparison between Dontrien and OSB3 indicates a weaker contribution of the selective preservation pathway to OSB3 kerogen whereas bacteria lipid incorporation may have been more significant in OSB3 kerogen. The selective preservation pathway was so far considered as restricted to the formation of kerogens having retained some of the morphological features of the source organisms. An important point derived from this study is therefore the ability of this pathway to also contribute to the formation of amorphous kerogens.

Ketones in a Proterozoic dolerite sill

A dolerite sample from the Middle Proterozoic McArthur Basin in northern Australia has solid bitumen on fracture surfaces and liquid hydrocarbon fluid inclusions in secondary calcite mineralization. The extract of this sample is rich in polar compounds and contains an unusual and novel series of saturated ketone isomers, including homologous series of n-alkan-2-ones and n-alkan-3-ones, together with a complicated series of branched mid-chain ketones. These ketone isomers were identified by the monitoring of diagnostic mass chromatograms, including those due to rearrangement ions. n-Alkanes are only three to four times more abundant than the ketones. The n-alkan-2-ones have a similar distribution to the n-alkanes and may have been formed by the pyrolysis and β-oxidation of carboxylic acids, followed by decarboxylation of the resultant β-keto acids. The n-alkan-3-ones and the mid-chain isomers have a distribution which is biased towards the low molecular weight isomers, probably due to the pyrolysis of a different kerogen moiety, perhaps alkyl chains cross-linked by ether groups. Ketones are known to occur when oil shales are pyrolysed and in hydrothermal oil, so by analogy the natural pyrolysis of kerogen in the fine-grained sediments by the dolerite sill resulted in the generation of liquid products (predominantly n-alkanes and ketones) which were preserved as hydrocarbon-bearing fluid inclusions and as solid bitumen in a fracture.

Oxygen Groups and Oil Suppression during Coal Pyrolysis

Suppressing effects on oil genesis during coal and kerogen pyrolysis can be correlated with oxygen content. In the present work oil suppression has been tentatively corrected by modeling. A plot of the corrected oil yield vs rank was found to resemble a Van Krevelen's H/C vs O/C diagram, and mass balance was consistent with a loss of oil potential in the early stage of coalification. Selective modifications of the oxygen groups of a lignite and of a bituminous vitrain were performed to test the above computations. The decarboxylation and dehydroxylation before pyrolysis resulted in a substantial increase and acceleration of oil formation

Analysis of kerogens and kerogen precursors by flash pyrolysis in combination with isotope‐ratio‐monitoring gas chromatography‐mass spectrometry (irm‐GC‐MS)

AbstractThis study describes the application of isotope ratio monitoring gas chromatography‐ mass spectrometry (irm‐GC‐MS) for compound‐specific stable carbon isotopic analysis of aliphatic hydrocarbon and phenolic products from flash pyrolysis (800 °C, 20s) of natural biopolymers and sedimentary kerogens. As part of this work, we provide a detailed description of the analysis of complex samples, including approaches for peak integration, data handling and correction for derivative carbons. Several aliphatic and aromatic biopolymers are analyzed by irm‐GC‐MS in order to establish relationships between the isotopic signatures of pyrolysis products and those of their parent macromolecules. We also analyze a select group of kerogens and kerogen precursors of different ages and biopolymer compositions to evaluate the applicability of combined pyrolysis/irm‐GC‐MS to complex geochemical mixtures. Our findings suggest that, in spite of the wide degree of heterogeneity, the isotopic values of individual aliphatic and phenolic pyrolysis products determined by irm‐GC‐MS can be related to the isotopic composition of the total organic carbon in kerogens and used to trace its biological sources. This study also highlights the need for optimum chromatographic separation in order to fully realize the potential of compound specific isotope analyses.

Carbon isotopic evidence for the origin of macromolecular aliphatic structures in kerogen

This study describes compound-specific stable carbon isotopic analyses of aliphatic hydrocarbon products from flash pyrolysis (800°C, 20 s) of kerogens representing a range of depositional environments (marine, estuarine, lacustrine) and ages (Recent to Ordovician). The carbon isotopic measurements were obtained, using isotope-ratio-monitoring gas chromatography-mass spectrometry (irmGC-MS), for the major aliphatic pyrolysis products ( n-hydrocarbons, acyclic isoprenoids and hopanoids). While isotopic compositions of n-hydrocarbons varied substantially between samples (average values ranged from −35 to −14 0 00 ), δ-values of n-alkenes and n-alkanes generated from a given sample generally ranged over less than ±3 0 00 . This isotopic uniformity implies a common origin for n-hydrocarbons (probably from thermal dissociation of biopolymers), supporting the concept of selective preservation of highly resistant aliphatic structures in kerogens. There are notable exceptions to this general relationship, in which either mixed biopolymeric sources (e.g. Guttenberg Fm) or minor contributions from aliphatic biopolymers (e.g. Monterey) must be inferred. In several cases, average n-hydrocarbon values also closely match the corresponding total organic carbon (TOC) δ-value, indicating that the n-hydrocarbons in these samples are derived from structurally important, or at least isotopically representative, constituents of the kerogen. In other samples significant discrepancies were observed between the δ-values for these products and δ 13C TOC. In these cases the presence of additional components not yielding hydrocarbons on pyrolysis is indicated. Isotopic compositions of isoprenoid hydrocarbons varied non-systematically relative to those of n-hydrocarbons, whereas hopanoid hydrocarbons were consistently depleted in 13C relative to both TOC and n-hydrocarbons, with δ-values as low as −50 0 00 .

Partial resolution of sources of n-alkanes in the saline portion of the Parachute Creek Member, Green River Formation (Piceance Creek Basin, Colorado)

Systematic variations in the 13C contents of individual extractable n-alkanes (C 16–C 29) can be modelled quantitatively and interpreted as indicating contributions from at least five distinct sources. These appear to be cyanobacterial ( C 16– C 18, δ 13 C = − 37 0 00 vs PDB ), phytoplanktonic C 16–C 23, δ = −32 0 00 ), chemoautotrophic bacterial ( C 20– C 29, δ = −38 0 00 ), phytoplanktonic or heterotrophic bacterial ( C 20– C 29, δ = −30‰ ), and vascular plants ( C 23– C 29, δ = −29‰ ). Hydrous pyrolysis of related kerogens yields large quantities of additional n-alkanes with different and much more uniform δ 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.

Chemical, molecular and isotopic differentiation of organic facies in the Tertiary lacustrine Duaringa oil shale deposit, Queensland, Australia

Total organic matter, extractable organic matter (bitumen), and pyrolysates released on low-temperature sealed-tube pyrolysis of kerogen were analysed chemically and isotopically. Based on bulk bitumen and biomarker parameters, the sediments are immature to a depth of approx. 1300 m. Within the terrestrial and lacustrine depositional environments of the Tertiary Duaringa Basin, various organic facies have been classified according to inorganic input and maceral abundances of organic matter derived from land-plant and algal sources; the latter derived mainly from Pediastrum and with a varying Botryococcus content. The lacustrine upper lamosite is chemically and isotopically distinct from the lower lamosite due to a changing algal community, relative contributions from allochthonous land-plants and, for the lower lamosite, a slightly more saline and restricted lake environment. The lower lamosite is associated with the highest concentrations of C 28-C 30 4-methylsteranes and 13C depletion in TOC. In the upper lamosite, there is a strong positive correlation between Botryococcus content and 13C enrichment. The organically lean claystones have sources nearly identical to the lamosites, but the organic matter is diluted due to rapid influx of siliciclastics. The terrestrial facies, the cannel coal and carbonaceous shales, are mainly distinguished from the lacustrine facies by higher relative proportions of C 29 steranes, C 30 4-methylsteranes and δ 13C values for the pyrolysed hydrocarbons intermediate between the two lamosite facies. The carbonaceous oil shale has a composite geochemical signature intermediate between the two end-members, lamosite and cannel coal. Oleanane and ring-A-degraded triterpanes derived from lupane, arborane and oleanane skeletons are distributed throughout all organic facies, representing both autochthonous and allochthonous higher plant inputs. Higher concentrations of oleanane and des-A-lupane are associated with the terrestrial facies. Hopanes dominate over steranes in all organic facies and their concentration ranges are independent of facies. For the lamosites, the aliphatic biopolymer algaenan is implicated as the dominant source for n-alkanes from analysis of their yields, homologue abundances, and individual δ 13C values. In the terrestrial facies, resinites are paraffinic and are a major source for the n-alkanes released on pyrolysis. Compound Specific Analysis of extractable and pyrolysate hydrocarbons allowed deconvolution of different source inputs to free lipids and kerogen. For the lamosites, low-molecular-weight n-alkanes in the bitumen are derived mainly from a Pediastrum source while Botryococcus is associated with waxy n-alkanes. However, the situation is reversed in the kerogen; Pediastrum algeanan has a longer average alkyl chain-length than Botryococcus algaenan. The magnitude of the isotopic differences between single n-alkanes released at different temperatures is useful in determining multiplicity of sources.

Geochemical significance of alkylbenzene distributions in flash pyrolysates of kerogens, coals, and asphaltenes

The distribution of C0-C5 alkylbenzenes in flash pyrolysates of forty-seven immature kerogens and coals from different geographical locations and of different ages were studied using gas chromatography (GC) in combination with mass spectrometry (MS) in order to decipher the origin of aromatic moieties in macromolecular matter. All possible structural isomers of the alkylated benzenes were determined, and, in some cases, absolute yields were calculated. Sulphur-rich (Type II-S) kerogens yield higher absolute amounts of alkylbenzenes in comparison to Type I, II, and III kerogens. The variations in internal distribution patterns of C2-C4 alkylbenzenes were analyzed using multivariate analysis techniques (principal component analysis; PCA). Major variations in alkylbenzene distributions were due to an increased abundance of specific alkylbenzenes, which are related to specific precursor moieties in the macromolecular structure assuming that they are mainly formed via β-cleavage. Alkylbenzenes possessing “linear” carbon skeletons are enhanced in flash pyrolysates of Guttenberg and Estonian Kukersite kerogens (Type I) and are proposed to be derived from linear precursors which have undergone cyclization/aromatization. Relatively high amounts of 1,2,3,4- and 1,2,3,5-tetramethylbenzenes were found in flash pyrolysates of Womble and Duvernay kerogens (Type II) which are likely to be derived from macromolecularly bound diaromatic carotenoids. The relatively high abundance of 1,2,3-trimethylbenzene and 1,3-/1,4-dimethylbenzene in pyrolysates of Monterey kerogens (Type II-S) is proposed to be indicative of the presence of bound nonaromatic carotenoids (e.g., β,β-carotene) which have undergone aromatization and/or loss of methyl groups upon diagenesis. 1-methyl-4-isopropylbenzene, which appears in relatively high amounts in flash pyrolysates of Walcott Chuar kerogen (Type II) and Catalan coals (Type III), is thought to be derived from a heteroatom-bound precursor. These results demonstrate that the structure of monoaromatic moieties in kerogen is biologically controlled. The internal distribution patterns of alkylbenzenes of flash pyrolysates of kerogens and asphaltenes show a marked resemblance, the latter showing a slight enhancement of alkylbenzenes with longer carbon skeletons. These observations support the idea that asphaltenes are structurally related to kerogen and that aromatic moieties in asphaltenes are bound by fewer intermolecular bridges.

Chemical and microscopical characterization of inner seed coats of fossil water plants

Inner seed coat layers (tegmens) of four different species of fossil water plants have been analyzed using light microscopy, scanning- and transmission-electron microscopy, and Curie-point pyrolysis. Microscopical analysis of the tegmens show two layers both comparable with a cuticle. Furthermore, the pyrolysates revealed the presence of highly aliphatic macromolecules comparable with cutan. The resistant constituents in the tegmens of two of the species also contained tocopheryl units which may serve as an additional source for prist-1-ene in pyrolysates of kerogens or of pristane upon natural thermodegradation.

A molecular and isotopic study of the organic matter from the Paris Basin, France

Thirteen Liassic sedimentary rocks of increasing depth and three petroleums from the Paris Basin were studied for 13C 12C isotopic compositions and biological markers, including steranes, sterenes, methylphenanthrenes, methylanthracenes, and triaromatic steroids. The isotopic compositions of n-alkanes from mature sedimentary rocks and petroleums fall in a narrow range (2%.), except for the deepest Hettangian rock and the Trias petroleum, for which the short-chain n-alkanes are enriched and depleted in 13C, respectively. Most of the molecular parameters increase over the 2000–2500 m depth range, reflecting the transformation of the organic matter at the onset of petroleum generation. In this zone, carbonate content and carbon isotopic composition of carbonates, as well as molecular parameters, are distinct for the Toarcian and Hettangian source rocks and suggest a migration of organic matter from these two formations. Two novel molecular parameters were defined for this task: one using methyltriaromatic steroids from organic extracts; the other using 1-methylphenanthrene and 2-methylanthracene from kerogen pyrolysates. The anomalous high maturity of the Dogger petroleum relative to the maturitydepth trend of the source rocks is used to estimate the minimal vertical distance of migration of the organic matter from the source rock to the reservoir.