Phenylnaphthalenes and polyphenyls in Palaeozoic source
rocks of the Holy Cross Mountains, Poland
Leszek Marynowski
a,*, Franciszek Czechowski
b, Bernd R.T. Simoneit
caDepartment of Earth Sciences, Silesian University, 60 BeËdzinska St., 41-200 Sosnowiec, Poland bInstitute of Organic Chemistry, Biochemistry and Biotechnology, Wrocaw University of Technology,
27 Wybrzez.e WyspianÂskiego St., 50-370 Wrocaw, Poland
cEnvironmental and Petroleum Geochemistry Group, College of Oceanic and Atmospheric Sciences,
Oregon State University, Corvallis, OR 97331, USA
Received 24 January 2000; accepted 9 October 2000 (returned to author for revision 12 May 2000)
Abstract
Source rocks from a marine depositional setting from Palaeozoic formations in the Holy Cross Mountains region (Midlands, Poland) were analysed for aromatics using capillary gas chromatography±mass spectrometry (GC±MS). The occurrence of two novel series of aromatic hydrocarbons in these sediments, namely phenyl derivatives of fused ring polycyclic aromatic hydrocarbons (PhPAH) and polyphenyls (PPh), was established. Furthermore, the methyl derivatives of these compounds were also present. The chromatographic behaviour of the triaromatic members of the series, i.e. two isomers of phenylnaphthalene (1-PhN and 2-PhN) and three isomers of terphenyl (o-TrP, m-TrP and p-TrP) was evaluated using authentic standards. The isomeric composition of the phenylnaphthalenes (PhNs) and ter-phenyls (TrPs) was found to depend on thermal maturity. In the lower maturity samples abundances of 1-PhN and o-TrP are higher. Increase in sample maturity is indicated by an increase in the relative abundance of 2-PhN as well as m-TrP and p-TrP. Three thermal maturity parameters of the organic matter based on the relative abundances of the PhN and TrP isomers are proposed: PhNR=2-PhN/1PhN, TrP1=p-TrP/o-TrP, and TrP2=(m-TrP+p-TrP)/o-TrP. In general their values positively correlate with the vitrinite re¯ectance (Ro) and MDR, while correlation of the other biomarker maturity parameters such as theTs/Tmratio are less apparent. The compounds above are believed to be geochemical products from unknown precursors. A potential geochemical process of formation for the o-TrP is proposed, and involves initial preservation of carbohydrates in sediments through sulfur incorporation, further dehydration, cyclisa-tion and aromatisacyclisa-tion to respective furan and/or thiophene derivatives, and ®nally reductive eliminacyclisa-tion of oxygen and sulfur in the furan and thiophene products, respectively.#2001 Elsevier Science Ltd. All rights reserved.
Keywords:Palaeozoic source rocks; Phenyl-polyaromatic hydrocarbons; Polyphenyls; Phenylnaphthalenes; Terphenyls; Maturity indices
1. Introduction
Aromatic hydrocarbon distributions in coals and organic extracts of sedimentary rocks have received
much attention, mainly because of their usefulness as indicators of the thermal maturity of the sediments (Radke et al., 1982; Radke and Welte, 1983; Alexander et al., 1985, 1986; Chaee et al., 1986; Cumbers et al., 1986, 1987; Radke, 1987, 1988; Yawanarajah and Kruge, 1994; Willsch and Radke, 1995; Requejo et al., 1996). Biphenyl and alkylbiphenyls, as well as alkylaro-matics with fused aromatic rings are ubiquitous con-stituents of ancient sediments, as they occur in
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* Corresponding author.
comparable relative concentrations in various sediments of terrestrial and marine origin (White and Lee, 1980; Alexander et al., 1986; Radke, 1987; Fan Pu et al., 1991; Trolio et. al., 1999).
The occurrence and formation of phenyl derivatives of aromatic hydrocarbons have received much less attention than their methyl analogues. The presence of triaromatic members of these structures, i.e., phe-nylnaphthalenes (PhNs) and terphenyls (TrPs), in organic-rich sediments has already been documented. Phenyl substituted naphthalenes, i.e. 1-PhN and 2-PhN, have been found in extracts from rocks of the Permian Kupferschiefer Rote Fule zone (PuÈttmann et al., 1990) and in late Permian organic-rich marl from northen Italy (Sephton et al., 1999). Additionally, abundant dibenzothiophenes and dibenzofurans in these sedi-ments were noted. PhNs also are common aromatic constituents of the extracts from bituminous coals (White and Lee, 1980; Czechowski, unpublished data). The ®rst indication of the occurrence of terphenyls in high volatile bituminous coal was given by Bartle et al. (1975) who used toluene supercritical extraction to study coal liquefaction. Terphenyl (unidenti®ed isomer) was also a prominent constituent in products of cataly-tic liquefaction of South African coals (So®anos and Butler, 1989). The o-TrP in vitrinite from dull coal (Radke et al., 1982) and recently m-TrP and p-TrP were observed at comparable concentrations in higher rank bituminous coals (Willsch and Radke, 1995). Also, Chaee et al. (1986 and earlier references therein, p. 324) give tentative observation of p-TrP. However, no extractable TrPs were found in sediments from marine depositional environments.
Oxidation experiments have established that phenyl-polyaromatic hydrocarbons are common structural units in the macromolecular network of the coal matrix. Aqueous sodium dichromate oxidation of Pocahontas no. 3 coal produced a variety of aromatic hydrocarbons, where PhNs, phenylanthracenes and phenylphenan-threnes, as well as biphenyl, terphenyls and quaterphe-nyls represented a high proportion of the hydrocarbons released (Stock and Obeng, 1997). These authors sug-gested that linear polyphenyls are linkages in the coal matrix, as such units are particularly resistant to oxida-tion. Additionally, oxidation of coal (Hayatsu et al., 1975, 1982) and ¯ash pyrolysis of charcoal from the samples representing the Cretaceous±Tertiary boundary (Kruge et al., 1994) have revealed dibenzofurans in the bituminous coals and polyaromatic matrices, with structures related to phenyl-aromatics in the fossil charcoal. Dibenzofuran and dibenzothiophene moieties, from which biphenyl and its alkyl derivatives can be formed, are also present in organic-rich sediments in the unbound form, as they were extracted from Posidonia shale and a Permian marine sediment (Radke and Willsch, 1994; Sephton et al., 1999).
Due to the lack of an obvious natural product pre-cursor, no source has yet been proposed to account for the formation of more complex phenyl-polyaromatic and polyphenyl compounds, and their geochemical behaviour remains unrecognised.
The present paper reports the occurrence of other phenyl-polyaromatic and polyphenyl compounds in Palaeozoic sediments from the Holy Cross Mountains, as well as the occurrence, and a detailed analysis of the PhN and TrP isomeric composition for the assessment of maturity. Their potential synthesis via multiple ther-mal alteration steps from carbohydrates (cellulose) is suggested.
2. Geological setting
3. Analytical methods
3.1. Vitrinite re¯ectance and TOC determination
Vitrinite re¯ectance was measured on polished cross-sections of the rock according to the standard procedure used for coals (Davis, 1978).
A Leco carbon analyzer was used for the quantitation of TOC contents. Carbonates were removed from the samples by treatment with hydrochloric acid prior to analysis.
3.2. Sample extraction and extract fractionation
The ®nely ground rock samples were exhaustively Soxhlet-extracted in pre-extracted thimbles using di-chloromethane:methanol (7.5:1, v/v). Asphaltenes were removed from the extracts by precipitation inn-hexane. Then-hexane solubles were further separated using pre-parative pre-washed silica gel TLC plates (Merck, 20200.025 cm). Prior to separation the TLC plates were activated at 150C for 3 h. Plates loaded with ca. 50 mg of then-hexane soluble fraction were developed withn-hexane. Bands comprising aliphatic (Rf0.4±1.0), aromatic (Rf0.05±0.4) and polar (Rf0.0±0.05) fractions were collected and the organic material was recovered from the silica gel with dichloromethane.
3.3. Gas chromatography±mass spectrometry (GC±MS)
GC±MS analysis was carried out with a HP5890 II gas chromatograph equipped with a fused silica capil-lary column (30 m0.25 mm i.d.) coated with diphe-nylpolysiloxane phase (HP-5, 0.25 mm ®lm thickness). Helium was used as a carrier gas. The GC oven was programmed from 35 to 300C at 3C minÿ1. The gas chromatograph was connected to a HP 5971A mass spectrometer detector. The MS was operated at an ion source temperature of 200C, ionisation energy of 70 eV. Samples were analysed using full scan data acquisi-tion (mass rangem/z40±600 with cycle time of 1 s) and selected ion monitoring (SIM) modes. Phenylnaphtha-lenes and terphenyls were monitored using selective ion monitoring of the molecular ions m/z 204 and 230, respectively.
3.4. Arti®cial maturation of 1-PhN and o-TrP
A sample of 1-PhN or o-TrP (10 mg) mixed with ®nely ground aluminium montmorillonite (500 mg) was placed into a glass tube, and after evacuation was sealed. The sealed glass tubes were heated in a furnace for half an hour at temperatures of 200, 300, 400 and 500C for 1-PhN/montmorillonite and 300, 400 and 500C for o-TrP/montmorillonite, respectively. After the period of
heating at constant temperatures the ampules were removed from the furnace, cooled to room temperature, opened and extracted with dichloromethane for GC± MS analysis. Appropriate blank experiments were car-ried out without 1-PhN or o-TrP being present.
3.5. Pyrolysis of cellulose
Two samples of cellulose, pure Whatman cellulose and cellulose separated from a Tertiary xylitic brown coal using the procedure described elsewhere (Cze-chowski and Jezierski, 1997) were pyrolysed in an open-system consisting of an electrically heated horizontal quartz tube. A tablet (ca. 1 g) made from ®nely ground cellulose was placed in the quartz tube. A constant ¯ow of argon was passed through the tube to ensure rapid removal of the volatilized pyrolysis products from the heating zone. To further minimise secondary thermal reactions the sample was heated up to 600C by slow introduction of the sample tube into the heating zone from the argon inlet side. The volatile pyrolysis compo-nents carried out in the argon stream were absorbed into
n-hexane. The n-hexane solutions were then analysed using GC±MS.
4. Results and discussion
4.1. Samples
The locations of the sedimentary rock samples ana-lysed are shown in Fig. 1 while their geological ages and some selected characteristics are given in Table 1. Sam-ples analysed comprised carbonates (limestones and dolostones) and shales (except sandstone from Gru-chawka). They derived from boreholes (cores) as well as from active and inactive quarries. The later were col-lected from sites of the minimal weathering. To avoid contamination the samples, prior to powdering and extraction, were ultrasonically washed in methanol. Bitumens of the investigated rocks are autochtonous (Marynowski, 1999).
In the area investigated the total organic carbon (TOC) content ranges from 0.01 to 2%, and only in the case of two Kowala shales analysed is it higher (4.0 and 23.3%). The maturities of the samples were within the oil generation zone, viz. 0.5±1.2%Ro. The values of the extract yields are rather small, usually below 80 mg of extract per gram of TOC in the rock. The concentration of saturated hydrocarbons varies from 8 to 76% and the aromatic fraction usually makes up 9±40% of the total extractable organic matter (Table 1).
The data on the conodont color alteration index (CAI) of HCMts area are also listed in Table 1 (Belka, 1990), while the biomarker maturity indices were described ear-lier (Marynowski, 1997). Geothermal histories assessed
by evaluations of CAI and biomarker maturity indices revealed a temperature jump throughout the section from the Kowala to the Kostomloty series. These were assessed in the range of 40±60C for the Kowala and Panek series and a high increase to the range of 115± 160C for the Kostomoty section.
4.2. Composition of the aromatic hydrocarbon fraction
The characteristic feature of aromatic hydrocarbon fractions from samples of the Palaeozoic carbonate and clastic rocks from the Holy Cross Mountains is their uncommon molecular composition, compared to typical aromatic hydrocarbons of marine sources from another areas. An example of the aromatic hydrocarbon total ion current (TIC) from a low maturity Radkowice sample, illustrating the major identi®ed compounds, is shown in Fig. 2. The dominant compounds are phen-anthrene, chrysene and/or triphenylene. Other abundant compounds include polyphenyls (PPhs), as well as phenyl substituted fused-ring polycyclic aromatic hydrocarbons (PhPAHs) represented mainly by phenylnaphthalenes (PhNs), phenyl¯uorene and diphenyl¯uorene. The pre-sence of polyaromatic sulfur compounds (dibenzothio-phene, benzonaphthothiophenes and various benzobis-benzothiophenes, as well as their furan counterparts Ð Fig. 2) is common in samples with high concentrations of previously unreported PhPAHs and PPhs in the sol-vent extracts. The composition of the two novel groups of aromatic compounds is illustrated in the summed ion chromatograms characteristic for PhPAHs and PPhs (Fig. 3a Ðm/z154+204+254+304 and Fig. 3b Ðm/z
154+168+230+244+306+320+382+396+458+472). In the sample discussed the PhPAH are comprised of phenylnaphthalenes (PhNs), phenylphenanthrenes, bi-naphthyls, tetraphenylene and, while the PPh are com-prised of biphenyl, terphenyls (TrPs), quaterphenyls, quinquephenyls and sexiphenyls as well as their methy-lated derivatives, with the ortho substitution pattern dominant. Relatively abundant dibenzofuran is also shown in Fig. 3b. The identi®cation of all PhN, TrP and binaphthyls isomers as well as tetraphenylene was achieved by comparison of the retention times and mass spectra of representative peaks in the ion chromatograms with the data of the authentic standards (Aldrich). Binaphthyls were synthetized according to Copeland et al. (1960). Other described compounds are tentatively iden-ti®ed on the basis of chromatographic behaviour and mass spectral interpretation (Fig. 3b).
4.3. Maturity trends of PhNs and TrPs
Table 1
Geochemical characteristics of the samples from the Holy Cross Mountains and their extracts
No. Locality Lithology Age CAla Ro
(%) TOC (%)
EOM (mg/g TOC)
Aliph. (%)
Arom. (%)
NSO+ Asph (%)
1 WisÂnioÂwka Shale U. Cambrian ± ± 0.13 59 42 40 18
2 MoÂjcza Limestone Llanvirn 1 ± 0.11 37 35 28 37
3 Gruchawka Sandstone Siegenian ± nf 0.09 33 65 19 16
4 Bukowa GoÂra Shale Emsian ± nf 0.07 43 47 19 34
5 Zachemie Dolostone Eifelian ± nf 0.03 50 17 22 61
6 Doy Opacie Dolostone Eifelian ± nf 0.03 20 26 30 44
7 Radkowice Dolostone Eifelian 1 nf 2.30 37 22 13 65
8 Radkowice Green shale Eifelian 1 nf 1.13 10 51 26 23
9 Radkowice Black shale Eifelian 1 nf 9.80 29 8 17 75
10 Jurkowice Shale Eifelian 2 nf 0.26 38 27 35 38
11 SÂwieËtomarz Sandstone Eifelian 3.5 nf 0.05 240 30 18 52
12 abeËdzioÂw Dolostone Givetian ± nf 0.03 50 20 30 50
13 KarwoÂw Limestone Givetian 1 nf 0.01 100 36 22 42
14 Budy Limestone Givetian 2 nf 0.15 93 31 35 34
15 WymysoÂw Limestone Givetian ± 0.76 0.14 107 40 16 44
16 Laskowa GoÂra Dolostone Givetian ± 1.22 0.37 11 30 28 42
17 Panek Limestone Frasnian ± nf 0.14 21 25 22 53
18 GoÂra Zamkowa Limestone Frasnian 1 nf 0.03 233 29 27 44
19 DeËbska Wola Limestone Frasnian 1 nf 0.03 67 39 26 35
20 Kowala Quarry Shale Frasnian 1±1.5 0.55 4.00 30 10 25 65
21 Jaworznia Limestone Frasnian ± 0.63 0.01 200 16 18 66
22 SitkoÂwka Kowala Limestone Frasnian ± 0.63 0.25 68 18 24 58
23 JoÂzefka Limestone Frasnian 1.5 0.74 0.53 57 45 20 35
24 Wietrznia Limestone Frasnian ± 0.79 0.32 47 76 14 10
25 GoÂrno Limestone Frasnian 2 0.85 0.28 31 71 3 26
26 SÂluchowice Shale Frasnian 1.5 0.96 0.97 94 54 29 17
27 Kostomloty Shale Frasnian 3 1.2 0.53 94 55 9 36
28 TudoroÂw Limestone Famennian? nf 0.37 19 37 11 52
29 GoÂragawa Limestone Famennian 1 0.52 0.73 27 15 17 68
30 Kowala Quarry Shale Famennian 1±1.5 0.53 23.00 40 15 26 59
31 BesoÂwka Limestone Famennian 1±1.5 0.67 0.32 6 36 31 33
32 Kadzielnia Limestone Famennian 1.5 0.82 0.10 120 71 23 6
Kowala-1 borehole
33 - depth 39.8 m Shale Famennian ± 0.55 4.00 43 27 22 51
34 - depth 318.8 m Limestone Frasnian ± nf 0.01 300 35 31 34
35 - depth 633.2 m Dolostone Givetian ± 0.64 0.53 113 32 22 46
36 - depth 732.5 m Dolostone Givetian ± nf 0.08 75 42 25 33
37 - depth 955.5 m Dolostone Eifelian ± 0.73 0.20 65 45 28 27
Janczyce-1 borehole
38 - depth 73.7 m Limestone Famennian 1.5±2 0.85 0.75 97 35 23 42
39 - depth 229.7 m Limestone Famennian 1.5±2 0.86 0.38 155 52 21 27
40 - depth 705.1 m Dolostone Givetian ± 0.99 0.11 100 44 27 29
41 - depth 943.0 m Dolostone Givetian ± nf 0.03 200 49 9 40
42 - depth 951.5 m Dolostone Givetian ± nf 0.10 70 36 17 47
43 - depth 1239.3 m Shale Eifelian ± 1.15 0.30 30 30 20 50
44 Jabonna IG-1 borehole-depth 52.0
Shale Tournaisian 1±1.5 0.53 3.70 16 38 34 28
45 OstroÂwka Shale Visean 1.5±2 0.85 0.80 15 54 33 13
46 GaeËzice Limestone Zechstein ± 0.56 0.11 18 32 32 36
47 KajetanoÂw Limestone Zechstein ± 0.90 0.40 50 26 20 54
a characteristic group of two peaks in them/z204 ion chromatogram and TrP isomers as a group of three peaks in the m/z 230 ion chromatogram. Their mass spectra are similar and show intense molecular and doubly charged molecular ions. It was shown that 1-PhN elutes before 2-1-PhN, while the TrPs elute in the order: o-TrP, m-TrP and p-TrP. The retention beha-viour determined here for the PhNs and TrPs is in agreement with those reported for standard polycyclic aromatic hydrocarbons (Lee et al., 1979).
The isomeric ratios of these compounds vary with the level of thermal maturity, and the potential of their use as maturity indicators was explored. The maturation behaviour of the PhNs and TrPs is similar to their methylnaphthalene and methylbiphenyl analogues. Dis-tribution patterns of PhNs and TrPs for selected samples of increasing maturity (based on Ro) are presented in Fig. 4. In the lower maturity sample (Ro=0.52%) a marked predominance of 2-PhN over 1-PhN and o-TrP over the m-TrP and p-TrP isomers occurs. Systematic changes in isomer constitution are observed with increasing maturity of the samples. Isomerisation of the TrPs with increasing maturity is proposed to account for these eects and may be explained in terms of the relative thermodynamic stabilities of the respective isomers.
The isomers of TrP can be considered as phenyl-sub-stituted biphenyls and therefore the same maturity principle can be applied as to the methylbiphenyls.
Indeed, in the Palaeozoic rocks the observed high pre-dominance of o-TrP during early catagenesis decreases with increasing maturity on advanced stages of cata-genesis where m-TrP and p-TrP become gradually more abundant (Fig. 4). The driving force for such a shift is the reduction of steric hindrance of the o-TrP isomer. The observed maturity trend in the relative abundances of the isomers re¯ects the stability of the TrPs which appears to be in the order: m-TrP>p-TrP>o-TrP. This is in agreement with a general rule applied to substituted aromatic ring systems, where compounds with meta substituents are most stable, and those with ortho sub-stituents are least stable. Literature data of TrP isomer stabilities evaluated from the molar enthalpies of for-mation con®rm that m-TrP is thermodynamically the most stable isomer (Verevkin, 1997). The PhN iso-merisation is more advanced compared to that of the TrPs for a given level of maturity.
Both compound classes have been used to develop maturity indicators de®ned as the ratios of particular isomers of dierent stability. This is based on the experimental evidence that the initially formed thermo-dynamically least stable 1-PhN and o-TrP have under-gone further thermocatalytic isomerisation in more mature sediments to the higher stability isomers of PhNs and TrPs by phenyl shifts catalysed by Lewis acids (e.g. admixtures of clay constituents contained in the carbonate rocks). The proposed maturity indicator
for the PhNs, designated as PhNR, is expressed as the relative abundance of the more stable 2-PhN to the less stable 1-PhN:
PhNR2-PhN=1-PhN
A corresponding rearrangement of o-TrP to m-TrP and p-TrP, the thermodynamically more stable two isomers, allows the proposal of two maturity parameters for TrPs:
TrP1p-TrP=o-TrP
TrP2 m-TrPp-TrP=o-TrP
The respective values of the de®ned maturity indica-tors are presented in Table 2. The correlations of the PhNR and TrP1 indices are shown in Fig. 5 versus vitrinite re¯ectance (Ro) in a range of 0.5±1.4%, and the maturity indicators of other marker compounds: MDR (methyldibenzothiophene ratio, Radke et al., 1986) and
Ts=Tm ratio (pentacyclic terpanes). The trends of the illustrated correlations are generally similar and exhibit positive regressions, i.e. a steady increase with higher
Fig. 3. Partial summed mass chromatograms of the aromatic fraction isolated from a sample of Radkowice green shale: (a) biphenyl, phenylnaphthalenes, binaphthyls, indeno[2,3-b;3,4-c]¯uorene, phenylphenanthrenes, tetraphenylene and phenyltriphenylenes (m/z
154+ 204+ 254+ 304), (b) biphenyl, methylbiphenyls and dibenzofuran, terphenyls, (*) methylterphenyls, (&) phenyldibenzofur-ans, (!) quaterphenyls, (?) methylquaterphenyls, quinquephenyls, methylquinquephenyls, sexiphenyls and methylsexiphenyls (m/z
maturity. The isomerisation of the phenylaromatics, similarly as the alkylaromatic compounds, is catalysed by acids and therefore likely to be aected by variations in sediment components, such as clay minerals. It was recognised earlier that the lithology of source rocks may aect the distribution of aromatic sulfur compounds (Connan et al., 1986; Chakhmakhchev and Suzuki, 1995). This explains the wide scatter of the data points over the overall correlation zones shown in Fig. 5, par-ticularly high in the case of correlations with Ts=Tm
ratio (Fig. 5c and f), which is believed to be due to the variations in the mineral matrix assemblages of the Palaeozoic rocks from the HCMt formations. This factor is partly responsible for the deviations in relative abun-dances of the compounds used in the maturity para-meters. However, the in¯uence of the mineral matrix factor on the catalytic potential of the sediment is di-cult to assess and therefore the observed PhN and TrP isomeric compositions are the net result of more complex simultaneous processes. It should be noted, however,
that mature sediments from carbonate source rocks where clay components are not present, exhibit a higher proportion of 1-PhN and o-TrP isomers, whilst mature samples derived from sediments containing clay coponents have higher proportions of 2-PhN as well as m-TrP and p-m-TrP isomers.
4.4. Arti®cial thermal maturation of 1-PhN and o-TrP
To recognise the in¯uence of thermal maturity on the distributions of PhN and TrP isomers arti®cial matura-tion experiments in the presence of montmorillonite were carried out on the less stable isomers: 1-PhN and o-TrP. The in¯uence of the mineral matrix was eval-uated by performing the same experiments using dolo-mite. Isomerisation over montmorillonite of 1-PhN occurs at lower temperature (200C) than that of o-TrP which started at about 300C. Clay-catalysed iso-merisation reactions start at these temperatures result-ing in generation of higher abundances of the respective
Table 2
Biomarker maturity indicators of the bitumen in samples from the Holy Cross Mountains No. Locality Ts/Tm C29Ts/C29Ha Index
MB-MDFb
DMNc TrMNd MDRe DMDBTf TMDBTg PhNR TrP1 TrP2
1 WisÂnioÂwka ± ± 0.90 0.42 0.94 4.70 0.78 1.76 15.7 10.5 16.0 2 MoÂjcza 1.00 0.51 0.29 0.29 0.82 5.00 0.90 2.10 4.0 2.9 5.3 3 Gruchawka 0.21 0.20 0.12 0.21 0.54 2.27 0.61 1.90 3.3 0.45 1.45 4 Bukowa GoÂra ± ± 0.67 0.33 0.90 9.38 1.00 2.35 24.0 17.0 54.0 5 Zachemie 0.79 0.35 0.35 0.23 0.77 8.33 2.25 5.29 6.1 3.43 8.0 6 Doy Opacie 0.78 0.25 ± ± ± 2.17 ± ± 3.8 2. 9.17 7 Radkowice 0.47 0.43 0.24 0.17 0.45 1.07 0.25 0.54 1.4 0.46 1.61 8 Radkowice 0.50 0.30 0.37 0.25 0.53 0.64 0.12 0.49 1.9 0.10 0.31 9 Radkowice 0.51 0.46 0.27 0.13 0.41 0.73 0.18 0.44 2.3 0.31 0.95 10 Jurkowice 1.95 0.40 0.47 0.23 0.77 1.83 0.42 1.00 1.9 0.34 1.04 11 SÂwieËtomarz 0.26 0.15 0.17 0.20 0.70 2.27 0.54 1.25 4.0 2.27 8.36 12 abeËdzioÂw 0.26 0.12 0.10 0.20 0.67 1.44 0.46 1.30 3.8 0.92 2.72 13 KarwoÂw 0.74 ± 0.25 0.20 0.68 2.50 0.67 1.32 1.9 0.2 0.72 14 Budy 0.27 0.15 0.09 0.21 0.50 1.39 0.44 1.00 2.4 0.61 1.68 15 WymysoÂw 1.30 0.59 0.50 0.26 0.78 3.43 0.71 1.55 2.1 0.63 1.76 16 Laskowa GoÂra ± ± 0.62 0.48 0.96 25.00 3.00 8.10 15.7 28.0 101.0 17 Panek 0.65 0.30 0.18 0.25 0.47 1.46 0.29 1.14 2.8 0.73 1.73 18 GoÂra Zamkowa 0.55 0.22 ± 0.23 0.52 1.71 0.53 1.26 3.8 0.55 1.82 19 DeËbska Wola 0.35 0.09 0.09 0.28 0.72 1.92 0.45 1.12 2.3 0.96 2.48 20 Kowala 0.23 0.38 0.13 0.23 0.45 0.93 0.57 1.50 2.7 0.48 1.85 21 Jaworznia 1.29 0.63 0.32 0.24 0.72 2.27 0.77 0.60 3.5 0.34 0.88 22 SitkoÂwka Kowala 0.16 0.15 0.13 0.21 0.47 1.39 0.40 0.76 3.5 0.81 2.9 23 JoÂzefka 1.47 0.49 0.40 0.19 0.81 2.50 0.75 1.61 2.8 0.18 0.51 24 Wietrznia 2.51 1.08 0.22 0.30 0.90 3.57 0.74 4.11 3.2 0.56 1.56 25 GoÂrno 3.08 1.30 0.38 0.27 0.85 5.00 0.67 1.61 5.3 1.9 6.3 26 SÂluchowice ± ± 0.69 0.36 0.91 12.50 3.00 5.29 15.7 2.4 5.6 27 Kostomloty 6.56 1.78 0.90 0.51 0.97 6.25 2.02 4.30 10.1 2.5 4.3 28 TudoroÂw 0.45 0.73 0.06 0.22 0.62 1.79 0.53 1.37 1.7 0.28 0.63 29 GoÂragawa 0.10 0.14 0.13 0.16 0.44 1.47 0.28 0.70 2.2 0.19 0.81 30 Kowala 0.21 0.37 0.22 0.14 0.42 0.73 0.40 0.67 1.2 ± ± 31 BesoÂwka 0.67 0.33 0.20 0.24 ± 1.92 0.48 2.47 2.7 0.41 1.19 32 Kadzielnia 1.38 0.66 0.30 ± ± 2.78 0.76 1.73 6.7 1.11 3.42
Kowala-1 borehole
33 - depth 39.8 m 0.22 0.30 0.20 0.26 0.73 0.52 0.32 0.57 1.3 ± ± 34 - depth 318.8 m 0.34 0.22 0.21 0.27 0.66 2.27 0.63 1.54 3.3 0.71 2.1 35 - depth 633.2 m 0.26 0.17 0.26 0.26 0.60 1.50 0.44 0.92 2.2 0.57 1.14 36 - depth 732.5 m 0.60 0.23 0.24 0.25 0.58 2.27 0.56 1.32 2.3 0.43 1.22 37 - depth 955.5 m 0.72 0.45 0.53 0.24 0.65 1.79 0.52 0.85 3.2 1.14 4.21
Janczyce-1 borehole
38 - depth 73.7 m 1.72 0.53 0.27 0.21 0.83 1.79 0.52 1.06 1.9 0.81 1.48 39 - depth 229.7 m 2.84 1.11 0.45 0.31 0.89 4.17 0.83 1.54 5.7 1.56 4.31 40 - depth 705.1 m ± ± 0.48 0.32 0.89 8.33 1.69 3.36 4.3 1.37 2.83 41 - depth 943.0 m ± ± 0.51 0.20 0.69 4.17 0.70 2.39 6.1 1.04 2.59 42 - depth 951.5 m ± ± 0.77 0.42 0.91 8.33 1.82 5.00 4.6 1.00 2.25 43 - depth 1239.3 m ± ± 0.91 0.49 0.97 25.00 6.00 6.73 32.3 50.0 114.0 44 Jabonna IG-1
borehole- depth 52.0 m
0.69 0.29 0.38 0.25 0.72 0.76 0.34 0.70 0.6 0.13 0.5 45 OstroÂwka 2.51 0.97 0.33 0.33 0.84 3.13 ± ± 4.0 0.94 3.44 46 GaeËzice 0.21 0.15 0.09 0.21 0.61 2.00 0.60 1.19 2.6 0.3 0.81 47 KajetanoÂw 1.20 0.55 0.45 0.38 0.93 4.40 0.93 1.50 13.3 9.71 22.9
a C
29Ts/C29H- 18a(H)-30-norhopane/C2917a(H)-hopane (Peters and Moldowan, 1993).
b MB-MDF index- (3-MB+4-MB)/ (3-MB+4-MB+4-MDF+2 and 3-MDF+1-MDF);- MB- methylbiphenyl. MDF- methyldibenzofuran. c DMN-dimethylnaphthalene ratio (2,6- and 2,7-DMN)/ (2,6- and 2,7-+1,6-+1,4- and 2,3- and 1,5-+1,2-DMN) (Yawanarajah and Kruge, 1994). d TrMN- trimethylnaphthalene ratio (1,3,7-+1,3,6-+2,3,6-TMN)/(1,3,7-+1,3,6-+2,3,6-+1,2,5-TMN) (Yawanarajah and Kruge, 1994). e MDR- methyldibenzothiophene ratio: 4-MDBT/1-MDBT (Radke et al., 1986).
f DMDBT- dimethyldibenzothiophene ratio: 2.4-DMDBT/1.4-DMDBT (Chakhmakhchev et al., 1997).
thermodynamically more stable isomers (TIC traces of the reaction products are shown Fig. 6). The relative proportion of more stable PhN and TrP isomers to less stable isomers increases with increasing temperature. An increase of the heating temperature up to 500C in intervals of 100favours the gradual increase in abun-dance of more thermodynamically stable isomers: 2-PhN, m-TrP and p-TrP (Fig. 6), as appears to occur with increasing maturity in sediments (Fig. 4). At higher temperatures more side products are generated. From 1-PhN abundant decomposition and cyclisation products besides 2-PhN have formed: naphthalene, biphenyl, ¯uoranthene and in lesser amounts methylphenyl-naphthalenes and methyl¯uoranthenes. Similarly, from o-TrP the products consisted of m-o-TrP and p-o-TrP as well as naphthalene, biphenyl, ¯uorene, phenanthrene, tripheny-lene, methylterphenyls and phenyl¯uorenes. The cyclisa-tion of o-TrP to triphenylene, which occurs already at 300C, is consistent with the similar cyclisation of ortho -methylbiphenyl to ¯uorene (Kagi et al., 1990). Fluorene derivatives with additional phenyl substituent(s) are also found in the natural samples (Fig. 2). They are cyclisa-tion products of theortho-substituted methyl-TrP at the terminal phenyl ring. The high abundance of the
observed structures indicates that in the case of methyl-derivatives of TrP cyclisation through the methylene bridge to a ®ve membered ring proceeds preferentially compared with respective cyclisation between ortho -substituted phenyls resulting in formation of a six-membered ring. Also maturity-related trends in the dis-tribution of PhNs and TrPs evaluated from arti®cial maturation experiments (due to high temperature and short reaction time) can not be directly related to natural maturation of the organic sediments, how-ever, the observed trends are consistent to those in natural samples.
Acid-catalysed isomerisation results in an equilibrium mixture of the terphenyl isomers. Evidence for equili-brium in thermocatalytic isomerisation derives from laboratory heating experiments performed with p-TrP over montmorillonite at 400C, from which the same distributions were obtained as by heating of o-TrP. This is due to isomerisation reactions resulting in the inter-conversion of the isomers. However, it is important to note that no isomerisation of 1-PhN and o-TrP occurred with dolomite up to temperatures of 500C. This explains why in samples of carbonate matrix the relative con-centration of the less stable isomers, 1-PhN and o-TrP,
Fig. 5. Cross plots showing a correlation between the maturity indices, PhNR (plots a, b and c), TrP1 (plots d, e and f) vs. vitrinite re¯ectence,Ro, methyldibenzothiophene ratio, MDR, and pentacyclic triterpane,Ts/Tm, ratio. A logarithmic scale is used for both
is higher and is re¯ected by lower values of the PhNR, TrP1 and TrP2 maturity indices (Tables 1 and 2).
The lateral distribution of the MDR and TrP1 maturity indices over the investigated area of the HCMts is presented in Fig. 7. The values clearly indicate a much higher geothermal gradient in the NW part of the area, particularly around the Kostomloty, Laskowa, WisnioÂwka and Zachelmie locales.
4.5. Origin of the phenylnaphthalenes and terphenyls
The presence of PhPAH and PPh compounds as com-mon constituents in Palaeozoic HCMts strata inspired the search for a possible biological precursor source of these structures. As is well documented, only a minority of the PAH compounds present in fossil fuels inherited their structure directly from biosynthetic compounds, while
Fig. 6. Mass chromatograms revealing the distributions of PhNs and TrPs in the clay catalysed thermal rearrangement products of: (a) 1-PhN and (b) o-TrP. Legend: MePhN- methylphenylnaphthalenes, MeFl- methyl¯uoranthenes, PhF- phenyl¯uorenes, MeTrPh-methyltriphenylenes.
the vast majority of PAHs are the products of complex geochemical transformations of naphthenic and/or ole-®nic biological precursors (Radke, 1987, Simoneit, 1998). The skeletons of the PhPAH and PPh compounds dis-cussed here are not known to be synthesised by living organisms (Barton et al., 1999), and, therefore, cannot be attributed directly to known biological precursors without signi®cant structural changes. The lack of a simple structural relationship to speci®c natural product precursors has led us to suggest that these compounds are geochemical diagenetic products formed via geosyn-thetic processes involving the structural rearrangement of other biological compounds.
The literature describes few possibilities which could be considered for an origin of these structures observed in nature. Some examples are described. (i) Generation of phenyl substituted PAHs in ancient vegetation ®res. As established by Killops and Massoud (1992), pyr-olytic origin PAHs in Upper Jurassic strata contained more stable isomer of PhN i.e. 2-PhN. (ii) Shock wave synthesis of PAHs from benzene, which resembles a pyrolytic reaction of benzene at high temperatures, pro-duced higher-molecular weight PAHs, ranging from 128 (naphthalene) to 306 da (quaterphenyl) (Mimura, 1995), with phenylnaphthalenes and terphenyls of broadly similar isomeric composition as observed in more mature samples analyzed here. The relative concentration of the respective isomers was in the order: m-TrP>p-TrP>o-TrP and 2-PhN>1-PhN. Direct copyrolysis of benzene and naphthalene in vacuum at 530C resulted in forma-tion of isomeric phenylnaphthalenes, terphenyls (2-PhN and m-TrP dominant) with cyclodehydrogenation pro-ducts of 1-PhN and o-TrP, i.e., ¯uoranthene and tri-phenylene, respectively (Perez and Cristalli, 1991). However, free radical reactions in kerogen maturation occur at rather advanced stages of catagenesis. The processes above cannot be excluded as supplementary to the formation of PhPAH and PPh compounds during late catagenesis, but are excluded in these relatively immature samples where these compounds are already observed with a speci®c ortho isomeric prevalence. (iii) The low temperature formation of C±C bonds between two 6-membered and other polyaromatic rings could proceed via an oxidative coupling process with phenolic precursors (which are widespread in natural systems as revealed by pyrolysis, Senftle et al., 1986; Senftle and Larter, 1987), or by electrophilic substitution proceed-ing easily with phenolic compounds. These reactions might occur during the accumulation and diagenesis of sedimentary organic matter. (iv) Structures possessing unsaturated polyene chains are known to be present in recent sediments. Cyclisation and aromatisation of lin-ear polyene chains in some carotenoids, are considered as an alternative pathway. It is well established that among the numerous polyalkylaromatic diagenetic and catagenetic products from the diaromatic carotenoid
isorenieratene, also highly alkylated structures with additional aromatic rings are generated (via an intramo-lecular Diels±Alder cyclisation of the polyene isoprenoid chain followed by aromatisation), i.e., possessing biphe-nyl or phebiphe-nylnaphthalene moieties (Koopmans et al., 1996). In the samples analysed such structures are not observed and there is no indication for the occurrence of speci®c biomarkers derived from isorenieratene, which are characteristic of photic-zone anoxia in the deposi-tional settings (Koopmans et al., 1996, Sinninghe Damste and Koopmans, 1997). Because of the absence of aryl and diaryl isoprenoids in most of the samples, this pathway of PhN and TrP formation was excluded.
(Moers et al., 1988; Kok et al., 1997; Gelin et al., 1998), which resulted in sulfur incorporation yielding carbohy-drate (macro)molecules as non-extractable sulfurised resi-dues. Pyrolysis/evaporation products of this sulfurised residue yielded several thiophene compounds with a molecular ®ngerprint identical to that found in natural samples. In this way carbohydrates may be preserved in sediments in a form that is resistant to microbial attack, and thus have a greater potential for survival during diagenesis than the carbohydrate precursor itself.
A similar process may have occurred during the deposition of the Palaeozoic sediments from the HCMts. It is well documented that sulfurisation of sedimentary organic matter occurs predominantly in marine rather than in lacustrine sediments, where sulfate required by sulfate reducing bacteria to produce hydrogen sul®de is usually limiting. Polysaccharides are widely distributed in biota where they have both structural and energy storage roles. A possible source for the carbohydrates probably was carbohydrate-rich algal detritus, to which sulfur was incorporated from hydrogen sul®de produced by sulfate reducing bacteria resulting in low-tempera-ture sulfur cross-linked (``vulcanized'') insoluble mate-rial. Sulfurised macromolecular carbohydrates in carbonate sediments undergo multiple competitive structural rearrangements (early dehydration reactions yielding a variety of unsaturated products, then their
further cyclisation and aromatisation) during diagenesis in the presence of clay. This generates various aromatic hydrocarbon derivatives among which the furan and thiophene moieties are formed as intermediates.
A tentative mechanism for the formation of ortho-isomers of PPh via furan intermediates as for example o-TrP is presented in Fig. 8. It involves intramolecular dehydration of carbohydrate sub-units leading to the formation of a conjugated double bond system within a carbohydrate sub-unit, followed by reductive ring opening and further intramolecular cyclisation to six-membered cyclohexadienyl rings via Diels±Alder type reactions. Further dehydration between the six-mem-bered cyclohexadienyl rings and resultant aromatisation yields a benzofuran derivative, i.e. trihydroxybenzo[1,2-b:3,4-b0]bis[1]benzofuran. The ®nal step involves ther-mocatalytic removal of hydroxy groups and heteroatoms under more reducing conditions, i.e., the cleavage of the weaker C±O bonds in trihydroxybenzo[1,2-b:3,4-b0]bis[1]benzofuran giving o-TrP (generally molecules dominated by ortho-isomers of PPh compounds). Additional carbohydrate sub-units involved in the reac-tion would result in the formareac-tion of further ortho-PPh homologs: 1,10;20,100;200,1000-quaterphenyl, 1,10;20,100;200,1000; 2000,20000-quinquephenyl, etc., the same structures as observed in these sediments (Fig. 3). Similar reactions could take place when thiophene derivatives are formed
Fig. 9. Mass chromatogram (TIC) products from pyrolysis of cellulose isolated from a xylitic brown coal. Inserts ofm/z204 andm/z
as intermediate structures from sulfurised poly-saccharides. In that case the ®nal step could involve the cleavage of C±S bonds in benzo[1,2-b:3,4-b0 ]bis[1]benzo-thiophene, or more generally in polybenzopolythio-phene derivatives. Similarly, 1-PhN could be formed from benzo[b]naphtho[2,1-d]furan or benzo[b]naphtho [2,1-d]thiophene as intermediates via thermocatalytic reductive heteroatom removal. These furan and thio-phene intermediate structures indeed are present in less mature samples (Fig. 3). Thermal stress acting on the Kostomloty sample (Fig. 7) dramatically changed the distribution of the aromatic compounds, resulting in a total disappearance of thermodynamically unstable benzofuran and benzothiophene intermediates.
The processes above, which take place at low maturity (during diagenesis and early catagenesis, where aromati-sation to benzofuran and benzothiophene derivatives is completed), lead to the selective formation of a -sub-stituted PhPAHs and ortho-isomers of PPhs. During later catagenesis they undergo Lewis-acid catalysed merisation where the more stable PhPAH and PPh iso-mers are formed, as was discussed for 1-PhN and o-TrP earlier.
This interpretation of a proposed possible carbohy-drate source for the PhPAH and PPhs is supported by the analysis of cellulose pyrolysis products. The arti®cial thermal maturation of cellulose separated from xylitic brown coal was performed by pyrolysis (see Section 3). GC±MS analysis of the pyrolytic products has revealed the presence of the same furan derivatives as found in the natural samples. Furthermore, PhN and TrP iso-mers showing a 1-PhN and o-TrP prevalence (insets of
m/z 204 and m/z 230 mass chromatograms in Fig. 9) were present among the variety of pyrolysis products. The results obtained from the laboratory studies imply that PhPAH and PPh structures are indeed, at least partly, geosynthetic compounds originating from car-bohydrates via reactions described above.
5. Conclusions
The occurrence of the two new groups of aromatic hydrocarbons, namely PhPAHs and PPhs, as well as their methyl derivatives, has been established for the Palaeozoic, predominantly marine-derived sediments of the Holy Cross Mountains area.
The members of the compound groups with three aromatic rings, PhNs and TrPhs, are present in all Palaeozoic sediments from the HCMts region. The iso-meric compositions of the PhNs and TrPs are maturity dependent. 1-PhN and o-TrP are the dominant isomers in lower maturity sediments, and appear prior to the oil generation window. As the maturity of the sediments increases their relative abundances decrease at the expense of the thermodynamically more stable isomers,
2-PhN, m-TrP and p-TrP. This eect has been attrib-uted to thermally induced, clay catalysed, isomerisation reactions, where 1-PhN is converted to 2-PhN and o-TrP forms the meta and para isomers. Three new maturity parameters based on the isomeric composition of these compounds are proposed: the PhNR, the TrP1 and TrP2 ratios. The development of the PhNR, TrP1 and TrP2 indices was based on the assumption that 1-PhN and o-TrP are the primary geosynthetic products generated under depositional conditions and they undergo isomerisation upon further maturation. The newly proposed maturity indices PhNR, TrP1 and TrP2 show, however, only general correlation with theRoand MDR while correlation withTs=Tm ratio is not satis-factory. It can be partly explained by clay catalysis, which has been shown to be signi®cant in inducing the isomerization reactions of the phenylnaphthalenes and terphenyls.
A successful study of the product-precursor relation-ship has been achieved with evidence from laboratory pyrolysis of cellulose for carbohydrate alteration as a primary source of the PhNs and TrPs. This yielded a variety of PhN and TrP compounds with isomer dis-tributions similar to those found in the low maturity sedimentary rocks. A tentative formation mechanism for these aromatic structures via dehydration, cyclisa-tion and aromatisacyclisa-tion reaccyclisa-tions has been proposed. The data suggest that these compounds are geochemical products derived from carbohydrates as possible pre-cursors. Therefore, the presence of PhPAHs and PPhs in the HCMts Palaeozoic strata is related to the preserva-tion of carbohydrates in marine sediments by early diagenetic sulfurisation processes. Multiple rearrange-ments of the sulfurised carbohydrates result in forma-tion of aromatic furan and thiophene derivatives. This view is supported by the abundant presence of aromatic furans and thiophenes in the analysed sediments.
Acknowledgements
Financial support of this study by the Polish Research Committee (KBN, grant no. 6 P04D 051 12) and by the Silesian University (grant BW-28/99) is gratefully acknowledged. We thank Professor R.I. Kagi and Dr. M. Radke and Associate Editor Dr. J.S. Sinninghe Damste for useful comments which considerably improved the manuscript.
Associate EditorÐJ.S. Sinninghe DamsteÂ
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