J.S. Sinninghe Damsté

Analysis, structure and geochemical significance of organically-bound sulphur in the geosphere : State of the art and future research

Abstract This paper reviews the developments of the 1980s in the characterisation of organically-bound sulphur in the geosphere and summarises the geochemical significance of the results obtained by these studies. The identification of more than 1500 novel OSC (organic sulphur compounds) with structures related to biochemical precursors in mostly immature sediments and crude oils has led to a better understanding of the process by which inorganic sulphur is incorporated into organic matter. The sulphur enrichment of organic matter probably takes place via “quenching” of functionalised lipids by sulphur at the early stages of sediment diagenesis or even in the water column. This results in the formation of OSC with specific structures which may be applied as palaeoenvironmental indicators. Hydrocarbon biological marker distributions may be heavily biased by diverting functionalised potential hydrocarbon precursors in OSC. Thermal evolution of sedimentary organic matter also affects the composition of OSC and when these changes are completely understood these compounds may be applied as maturity parameters as well. Recent developments in the characterisation of organically-bound sulphur present in macromolecular substances, i.e. kerogen, asphaltenes and high-molecular-weight fractions of crude oils and bitumens, show that the sulphur-containing moieties in these substances are formed in a similar way to the low-molecular-weight OSC. Sulphur incorporation into functionalised lipids in an intermolecular fashion should be considered as an important pathway for the formation of macromolecular substances. The abundance of organic sulphur in these substances also has a marked influence on their thermal evolution. Hiatuses in our present knowledge are numerous and stimulate future studies. Priorities are: the unravelling of the actual mechanisms of sulphur incorporation into organic matter and a better understanding of the diagenetic pathways of OSC and sulphur-containing macromolecular substances.

Characterization of Tertiary Catalan lacustrine oil shales: Discovery of extremely organic sulphur-rich Type I kerogens

Abstract The kerogens of three Tertiary Catalan lacustrine oil shales were analyzed by light microscopy, flash pyrolysis-gas chromatography-mass spectrometry, and bulk composition methods (elemental analysis, Rock Eval pyrolysis). Two of the three kerogens (Ribesalbes and Campins) are extremely rich in organic sulphur (atomic Sorg/C ratio > 0.04) and hydrogen (atomic ratio H C ratio > 1.5) and are, consequently, classified as Type I-S kerogens. Very characteristic distribution patterns of flash pyrolysis products (e.g., alkan-9- and -10-ones, alkadienes) of the Ribesalbes kerogen revealed that it is predominantly composed of fossilized organic matter of the freshwater alga Botryococcus braunii. These two findings demonstrate that sulphurization of organic matter may also occur in lacustrine sediments provided that sulphate is supplied by external sources. Data on the third kerogen sample (Cerdanya) suggest that the freshwater alga Pediastrum may contain a (partly) aromatic biomacromolecule that is selectively preserved upon diagenesis. These findings testify to the large variability in palaeodepositional conditions in lacustrine environments. A comparison of the biomarker composition of the extract of the Ribesalbes oil shale with the kerogen composition indicate that biomarkers often cannot be used to assess the major sources of organic matter in such settings. A similar conclusion can be drawn from a comparison of literature data concerning the Messel Oil Shale.

Unique distributions of hydrocarbons and sulphur compounds released by flash pyrolysis from the fossilised alga Gloeocapsomorpha prisca, a major constituent in one of four Ordovician kerogens

Abstract Kerogens isolated from four rocks of Ordovician age from North America have been analysed by combined pyrolysis-gas chromatography-mass spectrometry to compare and contrast the type and distribution of sulphur-containing compounds and aromatic and aliphatic hydrocarbons present in the pyrolysates. When pyrolysed, all of the kerogens released several series of heterocyclic sulphur compounds including alkylthiophenes, alkylthiolanes, alkylthianes and alkylbenzothiophenes together with n -alkanes, n -alklenes and alkylcyclohexanes as well as alkyl-substituted benzenes and naphthalenes. One of the kerogens, isolated from the Guttenberg oil rock, consisted predominantly of the alga Gloeocapsomorpha prisca , which produced sulphur compounds and hydrocarbons with fingerprint pyrograms that were different from those of the other three kerogens. The data provide prima facie evidence that these distributions may act as pseudo “biological markers” for this species of alga, namely that unsaturated kerogen moieties available for the uptake of sulphur, or which can cyclise to form hydrocarbons, distinguish Gloeocapsomorpha prisca from the contributing organisms of the other kerogens analysed.

Similar morphological and chemical variations of Gloeocapsomorpha prisca in Ordovician sediments and cultured Botryococcus braunii as a response to changes in salinity

Abstract Most Ordovician source rocks consist of accumulation of a colonial marine microorganism, Gloeocapsomorpha prisca (G. prisca) whose nature, ecology and affinity with extant organisms have been in dispute for years. Furthermore, recent studies have shown major differences in phenol moieties between two G. prisca-rich samples. Examination of five G. prisca-rich kerogens by electron microscopy and pyrolysis studies revealed (i) the occurrence of two markedly distinct “morpho/chemical” types: a “closed/phenol-rich” type (Baltic samples) and an “open/phenol-poor” one (North American samples) and (ii) the selective preservation of the resistant micromolecular material building up the thick cell walls in the original organism. Comparison with extant Botryococcus braunii (a widespread green microalga) grown on media of increasing salinity suggests that G. prisca is likely to be a planktonic green microalga related to B. braunii, which can adapt to large salinity variations which, in turn, control its polymorphism. The large differences in colony morphology and in the content of phenol moieties observed in fossil G. prisca and the resulting occurrence of two “morpho/chemical” types, should therefore reflect depositional environments with different salinities. The presence of thick, highly aliphatic, resistant walls in G. prisca selectively preserved during fossilization, accounts for the major contribution of this organism to Ordovician organic-rich sediments and for the resulting typical signature of Ordovician oils.

Characterization of Estonian Kukersite by spectroscopy and pyrolysis: Evidence for abundant alkyl phenolic moieties in an Ordovician, marine, type II/I kerogen

Abstract 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.

Organic geochemical studies of a Messinian evaporitic basin, northern Apennines (Italy)—II Isoprenoid and n-alkyl thiophenes and thiolanes

Abstract Series of n-alkyl and isoprenoid thiophenes and thiolanes, most of which have not been previously reported, have been identified in an extract from a Messinian (Upper Miocene) marl layer deposited under hypersaline, euxinic conditions. The identifications were based on mass spectra and Chromatographic data of synthesized reference compounds and on comparison of mass spectra, relative retention times and response on the FPD. Their specific structures and their distribution patterns show similarities with those of the alkanes. Inorganic sulphur is therefore considered to be incorporated into specific lipid moieties from (archae)bacterial and/or algal input during diagenesis. A biosynthetic origin of these compounds is also possible, however. The organic sulphur compounds encountered are thought to be indicators of a hypersaline depositional environment.

Identification of intermediates leading to chloroform and C-4 diacids in the chlorination of humic acid

The chlorination of terrestrial humic acid was studied at pH 7. 2 with varying chlorine to carbon ratios. The principal products are chloroform, di- and trichloroacetic acid, and chlorinated C-4 diacids. At a high chlorine dose many new chlorination products were detected, among them chlorinated aromatic acids. At a low chlorine dose a class of chlorinated compounds was found, which contained a trichloromethyl group. These compounds may be converted into chloroform and in most eases C-4 diacids by oxidation and hydrolysis reactions. Because these compounds are found mainly at low chlorine dosage, they may be regarded as intermediates in the reactions that give chloroform. The intermediates support the hypothesis of Rook that m-dihydroxybenzene moieties in humic acid are responsible for the formation of chloroform. A reaction scheme is proposed that explains the formation of the intermediates.

Identification of C2C4 alkylated benzenes in flash pyrolysates of kerogens, coals and asphaltenes☆

Abstract Pseudo-Kovats indices were determined for all positional isomers of C2C4 alkylated benzenes using a non-polar capillary column (CP Sil-5). These indices were applied in combination with mass spectral data to identify these compounds in complex mixtures of a relatively non-polar nature generated upon flash pyrolysis of macromolecular sedimentary organic matter (kerogens, asphaltenes and coals). Alkylbenzene distribution patterns were constructed by integration of appropriate mass chromatograms. Generally, toluene is the major pyrolysis product. Other specific alkylated benzenes (e.g. 1,2,3,4-tetramethylbenzene and 1-methyl-4-isopropylbenzene) were found to be enhanced in flash pyrolysates of different samples. Flash pyrolysates of asphaltene and kerogen fractions isolated from the same oil shale exhibit similar alkylbenzene distributions.

Molecular analysis of sulphur-rich brown coals by flash pyrolysis-gas chromatography-mass spectrometry: The type III-S kerogen

The molecular composition of five brown coals from three different basins (Maestrazgo, Mequinenza and Rubielos) in Spain was investigated by flash pyrolysis-gas chromatography and flash pyrolysis-gas chromatography-mass spectrometry. In these techniques, the macromolecular material is thermally degraded in an inert atmosphere and the compounds formed are on-line separated, identified and quantified. This information provided insight into the macromolecular structure of the coals which was inaccesible by other means. The composition of the pyrolysates is described in detail with emphasis on the distributions and relative abundance of n-alkanes, n-1-alkanes, (alkyl)phenols, sulphur compounds [(alkyl)thiophenes and (alkyl)benzenes and (alkyl)naphthalenes. These compound classes represent the major pyrolysis products of the samples analysed and were used to assess the contributions of specific biomacromolecules mainly originating from higher plants. One of the five brown coal samples investigated is so rich in organic sulphur (one sulphur atom for every 9-15 carbon atoms as determined by elemental analysis) that a new kerogen type (Type III-S) describing the kerogen contained in this coal is defined. Type III-S kerogen is defined as a kerogen with high atomic S org./C (0.04) and O/C (0.20) ratios. Two of the five brown coals samples investigated contain a series of long-chain alkylbenzenes with an unprecedented carbon number distribution pattern with a second maximum at C18. This unusual distrubution pattern is thought to originate from the presence of long-chain alkylbenzene moieties bound via a heteroatom(presumably an ether bond) to the macromolecular coal matrix preferentially at position 12 in the alkyl side-chain of these moieties.

Characterisation of highly branched isoprenoid thiophenes occurring in sediments and immature crude oils

Abstract A number of C 20 and C 25 highly branched isoprenoid thiophenes (HBIT) (i.e. thiophenes with 2,6,10-trimethyl-7-(3′-methylbutyl)dodecane and 2,6,10,14-tetramethyl-7-(3′-methylpentyl)pentadecane carbon skeletons) have been identified in sediments and immature oils from different geographical locations. Eight C 20 and two C 25 HBIT structural isomers were assigned on the basis of mass spectral characterisation, desulphurisation of isolated or mixtures of C 20 and C 25 HBIT and in some cases by comparison of mass spectral and relative retention time data with authentic compounds. Only a limited number of all theoretically possible isomers were present, indicating that these HBIT are probably formed by selective sulphur incorporation reactions into the widely occurring highly branched isoprenoid alkenes.