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Effects of biodegradation on Australian Permian coals
Organic Geochemistry 30 (1999) 1311±1322
Eects of biodegradation on Australian Permian coals Manzur Ahmed*, J.W. Smith, Simon C. George CSIRO Petroleum, PO Box 136, North Ryde, NSW 1670, Australia
Abstract Permian coals from Blackwater, Poitrel and Moura (Bowen Basin, Queensland) have been extracted and characterised by detailed organic geochemical techniques. A variety of source-related aliphatic and aromatic biomarker parameters indicate that these coals from three dierent locations are similar in terms of organic matter type and palaeoenvironment of deposition. The hydrocarbons extracted from these coals appear to have been generated from predominantly plant-derived organic matter deposited in a ¯uvio-deltaic environment. Moderately high Pr/Ph ratios, the high proportion of C29 steranes and very low sterane to hopane ratios are indicative of their largely terrestrial source. Molecular maturity parameters derived from aliphatic and aromatic biomarkers corroborate a measured maturity of 1.0±1.1% Ro for these medium volatile bituminous coals. The aliphatic and aromatic hydrocarbon distributions in these coals also allow their dierentiation into two groups: biodegraded Moura coals and non-degraded Blackwater and Poitrel coals. Comparison of various compound ratios from the degraded and non-degraded coals indicate the dependence of susceptibility to biodegradation on precise molecular structures. Major aromatic compound classes in coals, generally regarded as being more resistant, may be microbially altered before branched/cyclic alkanes are aected and even before the nalkanes are completely removed. As reported in crude oils, susceptibility to biodegradation of aromatic hydrocarbons decreases with increasing number of aromatic rings and with increasing number of alkyl substituents. Furthermore, alkylnaphthalenes with 1,6-dimethyl substitution patterns are more susceptible to degradation than other alkylnaphthalene isomers. This study reveals that biodegradation may alter the hydrocarbon composition of coals in a similar way to that observed in crude oils or oil spills, except that aromatic hydrocarbons are altered relatively earlier than aliphatic hydrocarbons in coals compared to oils. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Biodegradation; Coal; Hydrocarbon; Biomarkers; Bowen Basin
1. Introduction The aerobic biodegradation of organic matter is a selective utilisation of certain types of hydrocarbons by
* Corresponding author. Tel.: +61-2-9490-8720; fax: +612-9490-8921. E-mail address: [email protected] (Manzur Ahmed)
microorganisms. This process is generally believed to be limited to low temperatures [<65±808C], shallow depths, and conditions where circulating ground-waters with dissolved oxygen are available to aerobic bacteria (e.g. Bailey et al., 1973; Tissot and Welte, 1984; Peters and Moldowan, 1993). Sediments, soils, sedimentary rocks and interstitial waters contain more than 30 genera and 100 species of various bacteria, fungi and yeast which can utilise hydrocarbons as a sole source of energy in their metabolism (Hunt, 1996). During
0146-6380/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 6 - 6 3 8 0 ( 9 9 ) 0 0 1 0 4 - 7
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M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
microbial degradation, n-alkanes are oxidised to ketones, acids and di-acids, while cyclic alkanes and aromatic hydrocarbons are oxidised to di-alcohols on the adjacent carbon atoms (Jobson et al., 1972). The eects of biodegradation on the composition of crude oils and oil spills are well-documented (e.g. Connan, 1984; Tissot and Welte, 1984; Peters and Moldowan, 1993; Hunt, 1996; Bence et al., 1996). Insights into the detailed eects of microbial action have been obtained both from studies of oils collected from reservoirs at dierent depths and from laboratory experiments using bacterial cultures (e.g. Bailey et al., 1973; Rubinstein et al., 1977). Various authors (Volkman et al., 1983, 1984; Peters and Moldowan, 1993; Fisher et al., 1998) compiled a `quasi-stepwise' sequence to describe the general order of susceptibility of various biomarker compound classes to biodegradation: n-alkanes most susceptible > acyclic isoprenoids
Fig. 1. Map of Queensland, Australia, showing the Bowen Basin (hatched) and sample locations.
> hopanes 25-norhopanes presentrsteranes > hopanes no 25-norhopanes0diasteranes > aromatic steroids least susceptible: The term quasi-stepwise is used to indicate that a higher-ranked compound class can be attacked before a lower-ranked class is completely destroyed. It has also been established for aromatic hydrocarbons (e.g. Volkman et al., 1984; Williams et al., 1986; Rowland et al., 1986) that the rate of biodegradation decreases with increasing number of aromatic rings and with increasing number of alkyl substituents, and that the rate is also in¯uenced by the position of the alkyl substituents. More recently, Fisher et al. (1996) suggested that polymethylnaphthalenes with a 1,6-dimethyl substitution pattern are more susceptible to biodegradation than those isomers that lack this feature. Earlier studies of biodegradation, as described above, were concentrated mainly on crude oils in natural and laboratory conditions. In one recent study Curry et al. (1994) found high concentrations of ¯uorenes and methyl¯uorenes in Permian coals from the Cooper Basin, Australia, and suggested these as indicators of an extensive alteration of primary organic matter by the eects of oxidation and bacterial/fungal action. However, so far as we are aware, there have been no other reports on the eects of microbial degradation on the molecular composition of coals. Indeed, coals are commonly regarded as being highly resistant to microbial attack (Couch, 1987) and are eective conduits for water ¯ow. In this paper, the molecular composition of aliphatic and aromatic hydrocarbons extracted from Permian coals from three dierent locations in the Bowen Basin, Queensland are deter-
mined. The main objectives were (1) to elucidate the eects of biodegradation on the geochemically signi®cant hydrocarbon content of coals and (2) to identify the relative susceptibility to biodegradation of individual isomers of speci®c compound classes in coals.
2. Samples and geology The Late Permian coal samples included in this study were collected from Blackwater, Moura and Poitrel coal ®elds of the Bowen Basin, located in the hinterland of Central Queensland, Australia (Fig. 1). The Bowen Basin is one of the major coal basins of the world and was an area of shallow water or terrestrial sedimentation for most of the Permian. Coals accumulated throughout almost all of this period, initially around the margins and in isolated sites, but extending to cover virtually the whole basin in the latest Permian. The coal geology of the Bowen Basin has been thoroughly described by Hawthorne (1975) and Mallett et al. (1995), so only salient points pertinent to the three coal-®elds are mentioned here. Blackwater and Poitrel coals are part of the Rangal Coal Measure Formation while the Moura coal seams form part of the Baralaba Coal Measure Formation. Both these formations are lateral equivalents of the Bandanna Formation and were deposited during latest Permian times (0250±248 Ma; Korsch et al., 1998). All three coals were deposited under ¯uvio-deltaic conditions. The geological structure of the Moura coal ®eld becomes progressively more complex and faulting
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
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Table 1 Aliphatic hydrocarbon parametersa Sample number
Pr/Ph CPI26±30 CPI28±30 n-C31/n-C19 Ts/(Ts+Tm) C29Ts/C29ab hopane C30/C29Ts C30/C30ab hopane C29 hopanes ab/(ab+ba) C30 hopanes ab/(ab+ba) C31ab homohopanes 22S/(22S+22R) C32 ab homohopanes 22S/(22S+22R) C35/(C35+C34) [22S+22R] homohopanes Regular steranes/ab hopanes C27:C28:C29aaa 20R steranes C30/(C27 to C30) aaa 20R steranes (%) C27:C28:C29 abb 20S+20R steranes C27:C28:C29 ba 20S+20R diasteranes C27+C28+C29 ba diasteranes/(aaa+abb) steranes C29 aaa steranes 20S/(20S+20R) C29 abb/(abb+aaa) steranes C29 ba diasteranes 20S/(20S+20R) a
Blackwater coals
Poitrel coals
94916
22684
97054
97055
94915
94919
4.8 1.3 1.0 0.04 0.20 0.11 0.86 0.05 0.92 0.94 0.59 0.59 0.19 0.02 6:16:78 2.8 5:18:77 8:21:71 0.37 0.45 0.55 0.71
5.0 1.2 1.0 0.03 0.23 0.12 1.07 0.07 0.91 0.93 0.59 0.58 0.18 0.02 6:16:78 2.6 6:17:77 10:22:68 0.36 0.45 0.52 0.71
2.5 1.2 1.0 0.01 0.59 0.61 1.11 0.27 0.86 0.93 0.52 0.54 0.25 0.60 13:16:71 4.6 11:27:62 14:28:58 0.26 0.47 0.47 0.48
3.4 1.2 1.0 0.01 0.51 0.58 1.28 0.34 0.84 0.94 0.52 0.51 0.23 0.18 12:18:70 5.5 9:22:69 14:21:65 0.20 0.50 0.57 0.45
2.4 1.2 1.1 0.49 0.39 0.26 1.18 0.13 0.89 0.95 0.57 0.56 0.20 0.42 5:17:78 3.5 4:17:79 8:19:73 0.25 0.46 0.54 0.55
4.5 1.2 1.0 0.07 0.41 0.27 1.33 0.15 0.89 0.95 0.57 0.58 0.20 0.03 7:17:76 4.6 5:19:76 12:21:67 0.29 0.46 0.52 0.59
All ratios were calculated from MRM data, except those marked
is more frequent towards the northern end. The proportion of sandstones in the Baralaba Coal Measure Formation is high in comparison to other coal mines in the Bowen Basin. The faulting and inter-bedded sandstones may have acted as conduits for the penetration of surface water, at least in some parts of the Moura coal seams. The depth from the surface to the top of the open cut Moura coal seam is approximately 50 m, but based on the vitrinite re¯ectance of 1.0% the coal seam was probably buried to a depth of more than 1.5 km before uplift to the present level. This paper presents the geochemical results for a total of six coal samples, two from each of the three coal®elds: Blackwater, Moura and Poitrel.
3. Experimental 3.1. Extraction and fractionation Coal samples were cleaned thoroughly to remove any external matter and then crushed into powder. Powdered coals were exhaustively extracted with an azeotropic mixture of dichloromethane and methanol (93:7) for 72 h. Asphaltenes were precipitated from the extracts using an excess of n-pentane. The isolated
Moura coals
which were calculated from SIM data.
maltenes were fractionated into aliphatic hydrocarbons, aromatic hydrocarbons and polar fractions on a silica:alumina column by standard geochemical procedures. 3.2. Gas chromatography±mass spectrometry (GC±MS) GC±MS analyses of the aliphatic and aromatic hydrocarbon fractions were performed on a Hewlett Packard 5890 gas chromatograph interfaced to a VG AutoSpecQ Ultima (electron energy 70 eV; electron multiplier 250 V; ®lament current 200 mA; source temperature 2808C) tuned to 1000 resolution. Chromatography was carried out on a fused silica column (60 m 0.25 mm i.d.) coated with DB5MS (modi®ed 5% phenyl 95% methyl silicone, 25 mm ®lm thickness), using a splitless injection technique. The oven was programmed in two ways for dierent GC± MS runs: (a) for an initial temperature of 408C for 2 min, followed by heating at 48C/min to 3108C, and (b) for an initial temperature of 408C for 2 min, followed by heating at 208C/min to 2008C and then a second heating ramp at 28C/min to 3108C. The samples were run using full scan, single ion monitoring (SIM) and metastable reaction monitoring (MRM) programmes.
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M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
Fig. 2. Plot of C31±C35 homohopane distributions.
4. Results and discussions Parameters and abbreviations used subsequently are de®ned in Appendix A. For the methylphenanthrene index a response factor was used to correct for the dierent responses of phenanthrene and methylphenanthrenes in m/z 178 and 192 mass chromatograms. 4.1. Source Blackwater, Moura and Poitrel coals have Pr/Ph ratios varying from 2.4 to 5.0 (Table 1), which are consistent with their origin from predominantly terrestrial higher plant organic matter deposited in a deltaic environment (Didyk et al., 1978). The presence of a signi®cant amount of 17a(H)-diahopane (C30) in these coals (Table 1) suggests a signi®cant terrestrial input under oxic conditions (Philp and Gilbert, 1986; Peters
and Moldowan, 1993). The line plots (Fig. 2) of C31± C35 homohopane distributions indicate that the six coals from three dierent locations are geochemically similar. Very low C35 homohopane indices are consistent with deposition of the coals in oxic/terrestrial environments (Peters and Moldowan, 1991). C27, C28 and C29 aaa 20R and abb 20S+20R regular sterane distribution patterns in Blackwater, Moura and Poitrel coals (Table 1) are indicative of their similarity in terms of organic matter type and paleoenvironment of deposition. The high relative amount of C29 steranes (62±79%) in these coals suggests higher plant organic matter deposited in a terrestrial environment (Huang and Meinschein, 1979), as do the relative distributions of C27, C28 and C29 aaa 20S steranes (not shown in the table) and ba diasteranes. The occurrence of signi®cant quantities of diasteranes may be due to the association of these coals with clay-rich sediments deposited in oxic conditions (Mello et al., 1988). Very low (<0.60) sterane/hopane ratios of Blackwater, Moura and Poitrel coals (Table 1) are indicative of the incorporation of high levels of bacterial inputs commonly associated with terrigenous organic matter (Tissot and Welte, 1984; Peters and Moldowan, 1993) in these coals. The presence of a small but signi®cant amount of C30 steranes is supportive of some marine in¯uence in these coals (Moldowan et al., 1985). Poitrel coals have a relatively higher amount of C27 and C30 steranes and lower Pr/Ph ratios compared to Blackwater and Moura coals, indicating an origin in a slightly more marine-in¯uenced depositional environment. The aliphatic and aromatic hydrocarbon biomarker parameters indicate that the solvent extracts from the Blackwater, Moura and Poitrel coals have similar geochemical characteristics and appear to be indigenous to the coals. The coals originated predominantly from
Table 2 Aromatic hydrocarbon parameters Sample number
TNR-1 TNR-2 MPI 1 MPDF MPR DPR MDR Calculated re¯ectance (Rc%) Vitrinite re¯ectance (Ro%)
Blackwater coals
Poitrel coals
Moura coals
94916
22684
97054
97055
94915
94919
0.82 0.89 1.1 0.51 1.3 0.29 4.8 1.1 1.0
0.93 0.94 1.2 0.53 1.4 0.33 5.1 1.1 1.0
1.21 1.11 1.2 0.54 1.5 0.30 9.0 1.1 1.1
1.12 1.01 1.3 0.56 1.8 0.40 9.8 1.2 1.1
0.90 1.11 1.4 0.50 1.9 0.32 4.1 1.3 1.0
0.97 1.10 1.5 0.54 1.7 0.34 5.1 1.3 1.0
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
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Fig. 3. Total ion chromatograms showing the aliphatic and aromatic hydrocarbon distribution patterns in three representative coal samples. Numbers refer to n-alkane chain length; A=cyclohexanes; B=C14 bicyclic sesquiterpane; C±E=C15 bicyclic sesquiterpanes; F=C16 bicyclic sesquiterpane. Aromatic hydrocarbon abbreviations are de®ned in Appendix A.
terrestrial organic matter deposited in a deltaic environment. 4.2. Thermal maturity The vitrinite re¯ectance of the Blackwater, Moura and Poitrel coals varies from 1.0 to 1.1% Ro (Table 2), a range equivalent to the peak oil generation stage of organic evolution. Maturity calculated from the methylphenanthrene index (MPI 1 of Radke et al., 1982a) using the calibration of Radke and Welte (1983) ranges from 1.1 to 1.3% Rc (Table 2). Calculated re¯ectance for the Blackwater and Poitrel coals is close to but slightly higher than the measured vitrinite re¯ectance, whereas Moura coals have a much higher calculated re¯ectance than the measured re¯ec-
tance. Such a large variation for Moura coals might be due to suppression of vitrinite re¯ectance (George and Smith, 1995), or might have been caused by the preferential removal of phenanthrene and 1-MP due to biodegradation. This is discussed later in this paper. The aliphatic and aromatic biomarker ratios (Tables 1 and 2) suggest the coals have similar maturities. Ratios calculated from C29±C32 hopanes, C29 steranes and diasteranes are at or close to thermal equilibrium (Seifert and Moldowan, 1986; Mackenzie et al., 1980), suggesting that all these coals are at a maturity level beyond the early stages of oil generation. The carbon preference indices (CPI), TNR-1 (Alexander et al., 1985), TNR-2 (Radke et al., 1986), MPDF (Kvalheim et al., 1987), MPR (Radke et al., 1982b), DPR (Radke et al., 1982b) and MDR (Radke et al., 1986) corrobo-
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M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
Table 3 Ratios of less over more susceptible compound classes and individual isomers Sample number
Non-degraded coals Blackwater
Aliphatic hydrocarbons Pr/n-C17 Ph/n-C18 F/(C+D+E) Drimane/homodrimane Aromatic hydrocarbons EN/MN EN/DMN TMN/DMN TeMN/TMN MF/F MPy/Py MDBT/DBT DMDBT/MDBT MP/P DMP/MP Py/P MP/MN DMP/DMN P/F MP/MF MF/MN MDBT/MN DBT/P MDBT/MP Py/DBT Isomers 2-EN/1-EN 1,2,4-TMN/167-TMN 1,2,7-TMN/1,3,6-TMN 2,3,6,7-TeMN/1,3,6,7-TeMN 1,2,3,7-TeMN/1,2,6,7-TeMN 2-MF/1-MF 4-MF/3-MF 9-MP/3-MP 9-MP/1-MP 4-MDBT/2+3-MDBT
Biodegraded coals Poitrel
Moura
94916
22684
97054
97055
0.66 0.16 0.15 1.2
0.34 0.10 0.15 1.1
0.08 0.06 0.16 2.7
0.10 0.05 0.12 2.1
3.83 1.16 0.15 1.9
1.86 0.35 0.18 1.9
0.20 0.02 3.8 0.52 7.6 1.9 3.8 0.97 4.2 1.0 0.38 77.1 6.5 10.7 6.0 12.9 3.7 0.05 0.05 7.1
0.19 0.03 2.9 0.45 6.9 2.1 4.1 0.88 4.3 0.9 0.39 40.0 4.6 9.4 6.0 6.7 2.1 0.06 0.05 7.0
0.24 0.04 3.6 0.27 4.5 2.3 3.5 0.95 4.3 0.5 0.24 33.4 2.6 4.4 4.2 8.0 2.1 0.07 0.06 3.3
0.17 0.02 2.6 0.23 4.1 1.6 4.1 0.88 4.9 0.8 0.23 29.0 3.3 3.1 3.7 7.8 3.6 0.15 0.12 1.5
2.8 0.21 37.4 1.20 64.8 2.6 17.0 1.31 26.5 1.4 2.16 1570.2 165.8 16.8 6.9 228.6 113.3 0.11 0.07 19.2
1.5 0.10 6.1 0.64 22.1 2.3 9.1 1.02 9.2 1.2 0.66 198.8 14.9 13.3 5.6 35.8 16.3 0.08 0.08 8.0
0.16 0.19 0.21 0.21 0.40 0.29 0.57 1.2 1.3 1.4
0.57 0.14 0.20 0.23 0.34 0.32 0.47 1.1 1.3 1.3
0.95 0.16 0.17 0.21 0.34 0.35 0.42 1.0 1.5 1.0
0.53 0.14 0.13 0.22 0.34 0.31 0.36 1.0 1.8 0.9
1.43 1.44 0.36 0.29 0.59 0.46 0.60 1.5 2.3 1.7
1.67 0.54 0.27 0.25 0.50 0.41 0.49 1.2 1.6 1.6
rate each other and are indicative of maturity equivalent to about 1.0% Ro. The internal consistency of the molecular maturity parameters and their agreement with vitrinite re¯ectance indicate that the solvent extracts of these coals are indigenous. 4.3. Biodegradation The total ion chromatograms (TIC) of the aliphatic and aromatic hydrocarbon fractions of representative Blackwater, Poitrel and Moura coals are shown in Fig.
94915
94919
3. Aliphatic hydrocarbons of Blackwater and Poitrel coals are characterised by C12±C33 n-alkanes with a smooth unimodal distribution consistent with the high thermal maturity of the coals (Fig. 3a, b). Blackwater coal has a n-alkane maxima at n-C21, whereas in Poitrel coal the maxima is at n-C17 which is consistent with the slightly higher maturity of Poitrel coal. Moura coal, on the other hand, exhibits a completely dierent aliphatic hydrocarbon distribution pattern that re¯ects its alteration by microbial degradation (Fig. 3c). n-Alkanes over C25 are depleted, revealing a
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
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Fig. 4. Variation of (a) MPs/P with DMPs/MPs and (b) MDBTs/DBTs with DMDBTs/MDBTs, showing relative susceptibility to biodegradation of these compounds.
relatively higher abundance of C30 ab hopane and other polycyclic alkanes, compared to the Blackwater and Poitrel coals (Fig. 3). C10±C20 n-alkanes are almost completely absent, leaving cyclohexanes, acyclic isoprenoids and bicyclic sesquiterpenoids as the only remaining compound classes in this region of the chromatogram. The TICs of Blackwater and Poitrel coals exhibit a very similar aromatic hydrocarbon distribution patterns (Fig. 3d, e). Alkylnaphthalenes and alkylphenanthrenes are the two most abundant classes of compounds in these coals, with appreciable amounts of alkyl-substituted biphenyls, ¯uorenes, dibenzothiophenes and pyrenes also present. Such a molecular composition may be considered as characteristic of unaltered bituminous coals. On the other hand, the aromatic hydrocarbon distributions in Moura coal exhibits clear signs of biodegradation (Fig. 3f). Alkylphenanthrenes are abundant but the relative amounts of alkylnaphthalenes, alkylbiphenyls, and alkyl¯uorenes are signi®cantly decreased in abundance, relative to the non-degraded Blackwater and Poitrel coals. Biphenyl, ¯uorene and phenanthrene are almost completely removed. Based on these aliphatic and aromatic hydrocarbon distribution patterns the coals were divided into two groups: biodegraded Moura coals and non-degraded Blackwater and Poitrel coals. The eects of biodegradation on the dierent compound classes in the coals were then assessed. 4.3.1. Eects of biodegradation on aliphatic hydrocarbons It is evident from the TIC that biodegradation has
removed substantial amounts of n-alkanes from the Moura coals, a change re¯ected in the relative increase in Pr/n-C17 and Ph/n-C18 ratios (Table 3). The higher abundances of pristane, phytane and alkylcyclohexanes suggest these compound classes have been resistant to the level of biodegradation experienced by this coal. Williams et al. (1986) found the bicyclic sesquiterpanes C, D and E to be more susceptible to degradation than F (Fig. 3c); they also observed homodrimane to be more susceptible than drimane. No signi®cant increase in the ratios of F/(C+D+E) and of drimane/ homodrimane for the Moura coals (Table 3) compared to the non-degraded coals indicate that bicyclic sesquiterpanes in Moura coals are also unaected. No eects of biodegradation on steranes, diasteranes and hopanes (Volkman et al., 1983, 1984; Peters and Moldowan, 1993) could be distinguished in the degraded Moura coals compared to non-degraded Blackwater and Poitrel coals. Furthermore, except for a trace amount of 29,30-bisnorhopane, demethylated hopanes (Volkman et al., 1983) could not be detected in this degraded coal. Thus, it appears that sterane, diasterane and hopane distributions were unaected by biodegradation of Moura coals. In summary, the extent of microbial degradation of the aliphatic hydrocarbons in Moura coal is very limited. Biodegradation has caused a general depletion of n-alkanes over the entire range, with n-alkanes containing less than 20 carbon atoms being almost completely removed, without visible depletion of branched or cyclic alkanes. This extent of biodegradation is equivalent to level 2 of Volkman et al. (1983, 1984) and level 1-2 of Fisher et al. (1998).
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M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
Fig. 5. Variation of (a) 1,2,7-TMN/1,3,6-TMN with 1,2,4-TMN/1,6,7-TMN and (b) 2,3,6,7-TeMN/1,3,6,7-TeMN with 1,2,3,7TeMN/1,2,6,7-TeMN, showing relative susceptibility to biodegradation of these isomers.
4.3.2. Eects of biodegradation on aromatic hydrocarbons Table 3 includes the ratios of less biodegradable over more biodegradable major aromatic compounds and classes. These ratios were calculated by using absolute peak areas of the respective compounds or group of compounds. Direct comparison of these ratios in the degraded vs non-degraded samples allows their relative susceptibilities to biodegradation to be determined. For example, with respect to alkyl substitution, higher EN/MN ratios (Table 3) for biodegraded Moura coals compared to non-degraded Blackwater and Poitrel coals indicate that MNs are more susceptible to microbial degradation than ENs. Similarly, DMNs are more susceptible than ENs and TMNs, TMNs are more susceptible than TeMNs, F is more susceptible than MFs and Py is more susceptible than MPys. The ratios also indicate that P is more susceptible than MPs which in turn are more susceptible than DMPs (Table 3, Fig. 4a) and DBT is more susceptible than MDBTs which in turn are more susceptible than DMDBTs (Table 3, Fig. 4b). These observations show the order of susceptibility to microbial alteration in coals to be: most susceptible 4 least susceptible MN>DMN>EN>TMN>TeMN F>MF P>MP>DMP DBT>MDBT>DMDBT Py>MPy With respect to the number of aromatic rings, relatively higher MP/MN and Py/P ratios (Table 3) for biodegraded Moura coals suggest that naphthalenes
(di-aromatics) are more susceptible than phenanthrenes (tri-aromatics) which in turn are more susceptible than pyrenes (tetra-aromatics). Similarly, higher MF/MN, P/F and slightly higher MP/MF ratios in the Moura coal reveal that naphthalenes are more susceptible than ¯uorenes, which in turn are more susceptible than phenanthrenes. Owing to the extreme volatility of naphthalene, MNs were used in susceptibility comparisons. Although one Poitrel coal sample is an exception, the higher DBT/P and MDBT/MP ratios in Moura coals suggests more susceptibility of phenanthrenes compared to DBTs. Relatively higher amounts of sulphur-containing compounds in Poitrel coals may have been inherited from its slightly more marine-in¯uenced depositional environment. Again, greater susceptibility of DBT compared to pyrene is indicated by higher Py/ DBT ratios for biodegraded Moura coals. These observations show the order of susceptibility to biodegradation to be: most susceptible 4 least susceptible N>F>P>DBT>Py Thus it is apparent that ¯uorenes (bridged aromatic compounds) are more resistant to microbial attack than naphthalenes but less resistant than phenanthrenes, and that sulphur containing DBTs are more resistant than phenanthrenes. Apart from the susceptibility dierences between F and MF, ¯uorenes and di-/ tri-aromatics, and between Py and MPy, these ®ndings corroborate the previously described observations of Volkman et al. (1984), Bayona et al. (1986) and Rowland et al. (1986) with regard to relative susceptibilities to biodegradation of aromatic hydrocarbons in petroleum.
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
Relative susceptibilities to biodegradation of individual isomers of dierent aromatic compound classes were similarly determined by calculation of ratios of less susceptible over more susceptible compounds. The susceptibility to biodegradation of alkylnaphthalene isomers in coals (Table 3, Fig. 5a, b) follows the order observed by Volkman et al. (1984) in crude oils and Fisher et al. (1996, 1998) in the petroleum extracts of coastal and sea ¯oor sediments: more susceptible 4 less susceptible 1-EN>2-EN 1,6,7-TMN>1,2,4-TMN 1,3,6-TMN>1,2,7-TMN 1,3,6,7-TeMN>2,3,6,7-TeMN 1,2,6,7-TeMN>1,2,3,7-TeMN These authors noted that polymethylnaphthalenes with 1,6-dimethyl substitution patterns are more susceptible to biodegradation than other isomers. The ratios of other aromatic isomers (Table 3) indicate the following order of relative susceptibilities to biodegradation: more susceptible 4 less susceptible 1-MF>2-MF 3-MF>4-MF 3-MP, 1-MP, 2-MP>9-MP 2+3-MDBT>4-MDBT The observation that 9-MP is more resistant to microbial attack than the other MP isomers supports the earlier ®eld and laboratory studies of Rowland et al. (1986) and the results from in vitro degradation experiments reported by Bayona et al. (1986). No explanations for the variation in the degradation rates of methyl¯uorene, methylphenanthrene and methyldibenzothiophene isomers are presented. Based on the eects of biodegradation on aliphatic and aromatic hydrocarbons, a six point scale has been compiled (Table 1 of Fisher et al., 1998) to rank condensate, spilled in coastal sediments, into dierent levels of biodegradation. Direct comparison of the distribution of aliphatic hydrocarbons in Moura coals to this scale indicates a biodegradation level of 1±2, but based on aromatic hydrocarbons a level of 5 or more is indicated (DMNs severely depleted, TMN, TeMN, MP and DMP altered; Fisher et al., 1998). Therefore, biodegradation of Moura coals shows that long before the n-alkanes are completely removed or branched/cyclic alkanes are aected, almost all the major aromatic compound classes in coals may be microbially altered. These data suggest that the general order of susceptibility to biodegradation, as has been determined for oils (Volkman et al., 1983, 1984; Peters and Moldowan, 1993; Fisher et al., 1998), is not directly applicable to coals. Furthermore, these observations also imply signi®cant limitations on the use of aromatic hydrocarbons as maturity parameters in biodegraded coals.
1319
In view of the vitrinite re¯ectance of these coals (Table 2), it seems probable that biodegradation is a comparatively recent event, which occurred after uplift of the coal and possibly due to episodic or erratic invasion of the Moura coal seam by oxygenated and microorganism-supporting aquifers.
5. Conclusions The aliphatic and aromatic hydrocarbons isolated from Blackwater, Moura and Poitrel coals by solvent extraction are similar in respect of organic matter type, maturity and palaeoenvironment of deposition. The extracts of Moura coal exhibit characteristics of biodegradation, but the other coals do not. These characteristics parallel features of biodegraded crudes, with the susceptibility to biodegradation of aromatic hydrocarbons decreasing with increasing number of aromatic rings and with increasing number of alkyl substituents. Dierences in susceptibility to biodegradation are also observed in terms of the position of certain isomers. The main feature of the biodegradation of aliphatic hydrocarbons is an increase in isoprenoid/n-alkane ratios due to preferential loss of n-alkanes. In addition to demonstrating the commonality in the chemistry of the biodegradation of crude oils, oil spills and coals, this study suggests that in coals, in contrast to the relative susceptibilities to biodegradation of the hydrocarbon components of crude oils, aromatic hydrocarbons may be altered relatively earlier than aliphatic hydrocarbons. These observations require that where biodegradation is suspected, caution be exercised in using aromatic hydrocarbons in the assessment of coal maturity. The proverbial resistance of coal to microbial attack is questioned by this evidence of in situ alteration of hydrocarbon components. In this respect it may be that uplifting to the near surface and invasion by meteoric water, as experienced by Moura coals, are essential requirements for biodegradation of coals. Certainly, alteration of parent hydrocarbons is ®rmly established but the precise nature and fate of low molecular weight microbial products remain in doubt.
Acknowledgements The authors are grateful to BHP Australia Coal Limited for providing the valuable samples and also to Mr Robinson Quezada for his expert assistance with the GC±MS analyses. We appreciate the helpful comments of Dr Chris Boreham and Dr Roger Summons on an earlier version of this manuscript.
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M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
Appendix A A.1. De®nition of parameters TNR-1
2, 3, 6 ÿ TMN 1, 3, 5 ÿ TMN 1, 4, 6 ÿ TMN
TNR-2
1, 3, 7 ÿ TMN 2, 3, 6 ÿ TMN 1, 3, 5 ÿ TMN 1, 3, 6 ÿ TMN 1, 4, 6 ÿ TMN 1:5 2 ÿ MP 3 ÿ MP P 1 ÿ MP 9 ÿ MP
MPI 1
Rc % 0:6 MPI 1 0:4 MPDF
2 ÿ MP 3 ÿ MP 2 ÿ MP 3 ÿ MP 1 ÿ MP 9 ÿ MP
MPR
2 ÿ MP 1 ÿ MP
MDR
4 ÿ MDBT 1 ÿ MDBT
DPR
2, 6 ÿ DMP 2, 7 ÿ DMP 3, 5 ÿ DMP 1, 3 ÿ DMP 1, 6 ÿ DMP 2, 5 ÿ DMP 2, 9 ÿ DMP 2, 10 ÿ DMP 3, 9 ÿ DMP 3, 10 ÿ DMP
A.2. Abbreviations of ratios TNR MPI MPDF MPR DPR MDR
Trimethylnaphthalene Ratio Methylphenanthrene Index Methylphenanthrene Distribution Fraction Methylphenanthrene Ratio Dimethylphenanthrene Ratio Methyldibenzothiophene Ratio
A.3. Abbreviations of compounds N MN EN DMN TMN TeMN C5N F MF Py MPy Bp
Naphthalene Methylnaphthalene Ethylnaphthalene Dimethylnaphthalene Trimethylnaphthalene Tetramethylnaphthalene C5-alkylnaphthalene Fluorene Methyl¯uorene Pyrene Methylpyrene Biphenyl
MBp DMBp DBT MDBT DMDBT P MP DMP
Methylbiphenyl Dimethylbiphenyl Dibenzothiophene Methyldibenzothiophene Dimethyldibenzothiophene Phenanthrene Methylphenanthrene Dimethylphenanthrene
References Alexander, R., Kagi, R.I., Rowland, S.J., Sheppard, P.N., Chirila, T.V., 1985. The eects of thermal maturation on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleums. Geochimica et Cosmochimica Acta 49, 385±395. Bailey, N.J.L., Jobson, A.M., Rogers, M.A., 1973. Bacterial degradation of crude oil: comparison of ®eld and experimental data. Chemical Geology 11, 203±211. Bayona, J.M., Albaiges, J., Solanas, A.M., Pares, R., Garrigues, P., Ewald, M., 1986. Selective aerobic degradation of methyl-substituted polycyclic aromatic hydrocarbons in petroleum by pure microbial cultures.
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322 International Journal of Environmental Analytical Chemistry 23, 289±303. Bence, A.E., Kvenvolden, K.A., Kennicutt, M.C., 1996. Organic geochemistry applied to environmental assessments of Prince William Sound, Alaska, after the Exxon Valdez oil spill Ð a review. Organic Geochemistry 24, 7± 42. Connan, J., 1984. Biodegradation of crude oils in reservoirs. In: Welte, D.H., Brooks, K. (Eds.), Advances in Petroleum Geochemistry, vol. 1. Academic Press, New York, pp. 299±335. Couch, G.R., 1987. Biotechnology and Coal. I.E.A. Coal Research, pp. 7±56. Curry, D.J., Emmett, J.K., Hunt, J.W., 1994. Geochemistry of aliphatic-rich coals in the Cooper Basin, Australia and Taranaki Basin, New Zealand: implications for the occurrence of potentially oil-generative coals. In: Scott A.C., Fleet, A.J. (Eds.), Coal and Coal-bearing Strata as Oilprone Source Rocks?, Geological Society Special Publication No. 77, London, pp. 149±182. Didyk, B.M., Simoneit, B.R.T., Brassell, S.C., Eglinton, G., 1978. Organic geochemical indicators of palaeoenvironmental conditions of sedimentation. Nature 272, 216±222. Fisher, S.J., Alexander, R., Kagi, R.I., 1996. Biodegradation of alkylnaphthalenes in sediments adjacent to an o-shore petroleum production platform. Polycyclic Aromatic Compounds 11, 35±42. Fisher, S.J., Alexander, R., Kagi, R.I., Oliver, G.A., 1998. Aromatic hydrocarbons as indicators of biodegradation in North Western Australian reservoirs. In: Purcell, P.G., Purcell, R.R. (Eds.), The Sedimentary Basins of Western Australia 2: Proceedings of Petroleum Exploration Society of Australian Symposium, Perth, WA, pp. 185±194. George, S.C., Smith, J.W., 1995. The in¯uence of depositional environment on the methylphenanthrene index. In: Pajares, J.A., Tascon, J.M.D. (Eds.), Coal Science and Technology V24, Coal Science, Proceedings of the Eight International Conference on Coal Science. Elsevier, Amsterdam, pp. 287±290. Hawthorne, W.L., 1975. Regional coal geology of the Bowen Basin. In: Traves, D.M., King, D. (Eds.), Economic Geology of Australia and Papua New Guinea, 2. Coal. The Australian Institute of Mining and Metallurgy, pp. 68±77. Huang, W.Y., Meinschein, W.G., 1979. Sterols as ecological indicators. Geochimica et Cosmochimica Acta 43, 739± 745. Hunt, J.M., 1996. Petroleum Geochemistry and Geology, 2nd ed. W.H. Freeman and Company, New York. Jobson, A., Cook, F.D., Westlake, D.W.S., 1972. Microbial utilization of crude oil. Applied Microbiology 23, 1082± 1089. Korsch, R.J., Boreham, C.J., Totterdell, J.M., Shaw, R.D., Nicoll, M.G., 1998. Development and petroleum resource evaluation of the Bowen, Gunnedah and Surat Basins, eastern Australia. APPEA Journal 38 (1), 199±237. Kvalheim, O.M., Christy, A.A., Telnñs, N., Bjùrseth, A., 1987. Maturity determination of organic matter in coals using the methylphenanthrene distribution. Geochimica et Cosmochimica Acta 51, 1883±1888. Mackenzie, A.S., Patience, R.L., Maxwell, J.R.,
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Vandenbroucke, M., Durand, B., 1980. Molecular parameters of maturation in the Toarcian shales, Paris Basin, France Ð I. Changes in the con®guration of acyclic isoprenoid alkanes, steranes, and triterpanes. Geochimica et Cosmochimica Acta 44, 1709±1721. Mallett, C.W., Pattison, C., McLennan, T., Balfe, P., Sullivan, D., 1995. Bowen Basin, In: Ward, C.R, Harrington, H.J, Mallett, C.W, Beeston, J.W. (Eds.), Geology of Australian Coal Basins, Geological Society of Australia Incorporated Coal Geology Group Special Publication No. 1, pp. 299±340. Mello, M.R., Telnñs, N., Gaglianone, P.C., Chicarelli, M.I., Brassell, S.C., Maxwell, J.R., 1988. Organic geochemical characterisation of depositional palaeoenvironments in Brazilian marginal basins. Organic Geochemistry 13, 31± 45. Moldowan, J.M., Seifert, W.K., Gallegos, E.J., 1985. Relationship between petroleum composition and depositional environment of petroleum source rocks. Bulletin of the American Association of Petroleum Geologists 69, 1255±1268. Peters, K.E., Moldowan, J.M., 1991. Eects of source, thermal maturity, and biodegradation on the distribution and isomerization of homohopanes in petroleum. Organic Geochemistry 17, 47±61. Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide. Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood Clis (363 pp). Philp, R.P., Gilbert, T.D., 1986. Biomarker distributions in Australian oils predominantly derived from terrigenous source material. Organic Geochemistry 10, 73±84. Radke, M., Welte, D.H., Willsch, H., 1982a. Geochemical study on a well in the Western Canada Basin: relation of the aromatic distribution pattern to maturity of organic matter. Geochimica et Cosmochimica Acta 46, 1±10. Radke, M., Willsch, H., Leythaeuser, D., Teichmuller, M., 1982b. Aromatic components of coal: relation of distribution pattern to rank. Geochimica et Cosmochimica Acta 46, 1831±1848. Radke, M., Welte, D.H., 1983. The methylphenanthrene index (MPI): a maturity parameter based on aromatic hydrocarbons. In: Bjorùy, M., et al. (Eds.), Advances in Organic Geochemistry 1981. John Wiley, Chichester, pp. 504±512. Radke, M., Welte, D.H., Willsch, H., 1986. Maturity parameters based on aromatic hydrocarbons: in¯uence of the organic matter type. Organic Geochemistry 10, 51±63. Rowland, S.J., Alexander, R., Kagi, R.I., Jones, D.M., Douglas, A.G., 1986. Microbial degradation of aromatic components of crude oils: a comparison of laboratory and ®eld observations. Organic Geochemistry 9, 153±161. Rubinstein, I., Stausz, O.P., Spyckerelle, C., Crawford, R.J., Westlake, D.W.S., 1977. The origin of the soil sand bitumens of Alberta: a chemical and microbiological simulation study. Geochimica et Cosmochimica Acta 42, 1341± 1353. Seifert, W.K., Moldowan, J.M., 1986. Use of biological markers in petroleum exploration. In: Johns, R.B. (Ed.), Biological Markers in the Sedimentary Record, Methods in Geochemistry and Geophysics, vol. 24, pp. 261±290.
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M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
Tissot, B.P., Welte, D.H., 1984. Petroleum Formation and Occurrence. Springer-Verlag, Berlin. Volkman, J.K., Alexander, R., Kagi, R.I., Woodhouse, G.W., 1983. Demethylated hopanes in crude oils and their applications in petroleum geochemistry. Geochimica et Cosmochimica Acta 47, 785±794. Volkman, J.K., Alexander, R., Kagi, R.I., Rowland, S.J.,
Sheppard, P.N., 1984. Biodegradation of aromatic hydrocarbons in crude oils from the Barrow Sub-basin of Western Australia. Organic Geochemistry 6, 619±632. Williams, J.A., Bjorùy, M., Dolcater, D.L., Winters, J.C., 1986. Biodegradation in South Texas Eocene oils Ð eects on aromatics and biomarkers. Organic Geochemistry 10, 451±461.
Eects of biodegradation on Australian Permian coals Manzur Ahmed*, J.W. Smith, Simon C. George CSIRO Petroleum, PO Box 136, North Ryde, NSW 1670, Australia
Abstract Permian coals from Blackwater, Poitrel and Moura (Bowen Basin, Queensland) have been extracted and characterised by detailed organic geochemical techniques. A variety of source-related aliphatic and aromatic biomarker parameters indicate that these coals from three dierent locations are similar in terms of organic matter type and palaeoenvironment of deposition. The hydrocarbons extracted from these coals appear to have been generated from predominantly plant-derived organic matter deposited in a ¯uvio-deltaic environment. Moderately high Pr/Ph ratios, the high proportion of C29 steranes and very low sterane to hopane ratios are indicative of their largely terrestrial source. Molecular maturity parameters derived from aliphatic and aromatic biomarkers corroborate a measured maturity of 1.0±1.1% Ro for these medium volatile bituminous coals. The aliphatic and aromatic hydrocarbon distributions in these coals also allow their dierentiation into two groups: biodegraded Moura coals and non-degraded Blackwater and Poitrel coals. Comparison of various compound ratios from the degraded and non-degraded coals indicate the dependence of susceptibility to biodegradation on precise molecular structures. Major aromatic compound classes in coals, generally regarded as being more resistant, may be microbially altered before branched/cyclic alkanes are aected and even before the nalkanes are completely removed. As reported in crude oils, susceptibility to biodegradation of aromatic hydrocarbons decreases with increasing number of aromatic rings and with increasing number of alkyl substituents. Furthermore, alkylnaphthalenes with 1,6-dimethyl substitution patterns are more susceptible to degradation than other alkylnaphthalene isomers. This study reveals that biodegradation may alter the hydrocarbon composition of coals in a similar way to that observed in crude oils or oil spills, except that aromatic hydrocarbons are altered relatively earlier than aliphatic hydrocarbons in coals compared to oils. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Biodegradation; Coal; Hydrocarbon; Biomarkers; Bowen Basin
1. Introduction The aerobic biodegradation of organic matter is a selective utilisation of certain types of hydrocarbons by
* Corresponding author. Tel.: +61-2-9490-8720; fax: +612-9490-8921. E-mail address: [email protected] (Manzur Ahmed)
microorganisms. This process is generally believed to be limited to low temperatures [<65±808C], shallow depths, and conditions where circulating ground-waters with dissolved oxygen are available to aerobic bacteria (e.g. Bailey et al., 1973; Tissot and Welte, 1984; Peters and Moldowan, 1993). Sediments, soils, sedimentary rocks and interstitial waters contain more than 30 genera and 100 species of various bacteria, fungi and yeast which can utilise hydrocarbons as a sole source of energy in their metabolism (Hunt, 1996). During
0146-6380/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 6 - 6 3 8 0 ( 9 9 ) 0 0 1 0 4 - 7
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M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
microbial degradation, n-alkanes are oxidised to ketones, acids and di-acids, while cyclic alkanes and aromatic hydrocarbons are oxidised to di-alcohols on the adjacent carbon atoms (Jobson et al., 1972). The eects of biodegradation on the composition of crude oils and oil spills are well-documented (e.g. Connan, 1984; Tissot and Welte, 1984; Peters and Moldowan, 1993; Hunt, 1996; Bence et al., 1996). Insights into the detailed eects of microbial action have been obtained both from studies of oils collected from reservoirs at dierent depths and from laboratory experiments using bacterial cultures (e.g. Bailey et al., 1973; Rubinstein et al., 1977). Various authors (Volkman et al., 1983, 1984; Peters and Moldowan, 1993; Fisher et al., 1998) compiled a `quasi-stepwise' sequence to describe the general order of susceptibility of various biomarker compound classes to biodegradation: n-alkanes most susceptible > acyclic isoprenoids
Fig. 1. Map of Queensland, Australia, showing the Bowen Basin (hatched) and sample locations.
> hopanes 25-norhopanes presentrsteranes > hopanes no 25-norhopanes0diasteranes > aromatic steroids least susceptible: The term quasi-stepwise is used to indicate that a higher-ranked compound class can be attacked before a lower-ranked class is completely destroyed. It has also been established for aromatic hydrocarbons (e.g. Volkman et al., 1984; Williams et al., 1986; Rowland et al., 1986) that the rate of biodegradation decreases with increasing number of aromatic rings and with increasing number of alkyl substituents, and that the rate is also in¯uenced by the position of the alkyl substituents. More recently, Fisher et al. (1996) suggested that polymethylnaphthalenes with a 1,6-dimethyl substitution pattern are more susceptible to biodegradation than those isomers that lack this feature. Earlier studies of biodegradation, as described above, were concentrated mainly on crude oils in natural and laboratory conditions. In one recent study Curry et al. (1994) found high concentrations of ¯uorenes and methyl¯uorenes in Permian coals from the Cooper Basin, Australia, and suggested these as indicators of an extensive alteration of primary organic matter by the eects of oxidation and bacterial/fungal action. However, so far as we are aware, there have been no other reports on the eects of microbial degradation on the molecular composition of coals. Indeed, coals are commonly regarded as being highly resistant to microbial attack (Couch, 1987) and are eective conduits for water ¯ow. In this paper, the molecular composition of aliphatic and aromatic hydrocarbons extracted from Permian coals from three dierent locations in the Bowen Basin, Queensland are deter-
mined. The main objectives were (1) to elucidate the eects of biodegradation on the geochemically signi®cant hydrocarbon content of coals and (2) to identify the relative susceptibility to biodegradation of individual isomers of speci®c compound classes in coals.
2. Samples and geology The Late Permian coal samples included in this study were collected from Blackwater, Moura and Poitrel coal ®elds of the Bowen Basin, located in the hinterland of Central Queensland, Australia (Fig. 1). The Bowen Basin is one of the major coal basins of the world and was an area of shallow water or terrestrial sedimentation for most of the Permian. Coals accumulated throughout almost all of this period, initially around the margins and in isolated sites, but extending to cover virtually the whole basin in the latest Permian. The coal geology of the Bowen Basin has been thoroughly described by Hawthorne (1975) and Mallett et al. (1995), so only salient points pertinent to the three coal-®elds are mentioned here. Blackwater and Poitrel coals are part of the Rangal Coal Measure Formation while the Moura coal seams form part of the Baralaba Coal Measure Formation. Both these formations are lateral equivalents of the Bandanna Formation and were deposited during latest Permian times (0250±248 Ma; Korsch et al., 1998). All three coals were deposited under ¯uvio-deltaic conditions. The geological structure of the Moura coal ®eld becomes progressively more complex and faulting
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
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Table 1 Aliphatic hydrocarbon parametersa Sample number
Pr/Ph CPI26±30 CPI28±30 n-C31/n-C19 Ts/(Ts+Tm) C29Ts/C29ab hopane C30/C29Ts C30/C30ab hopane C29 hopanes ab/(ab+ba) C30 hopanes ab/(ab+ba) C31ab homohopanes 22S/(22S+22R) C32 ab homohopanes 22S/(22S+22R) C35/(C35+C34) [22S+22R] homohopanes Regular steranes/ab hopanes C27:C28:C29aaa 20R steranes C30/(C27 to C30) aaa 20R steranes (%) C27:C28:C29 abb 20S+20R steranes C27:C28:C29 ba 20S+20R diasteranes C27+C28+C29 ba diasteranes/(aaa+abb) steranes C29 aaa steranes 20S/(20S+20R) C29 abb/(abb+aaa) steranes C29 ba diasteranes 20S/(20S+20R) a
Blackwater coals
Poitrel coals
94916
22684
97054
97055
94915
94919
4.8 1.3 1.0 0.04 0.20 0.11 0.86 0.05 0.92 0.94 0.59 0.59 0.19 0.02 6:16:78 2.8 5:18:77 8:21:71 0.37 0.45 0.55 0.71
5.0 1.2 1.0 0.03 0.23 0.12 1.07 0.07 0.91 0.93 0.59 0.58 0.18 0.02 6:16:78 2.6 6:17:77 10:22:68 0.36 0.45 0.52 0.71
2.5 1.2 1.0 0.01 0.59 0.61 1.11 0.27 0.86 0.93 0.52 0.54 0.25 0.60 13:16:71 4.6 11:27:62 14:28:58 0.26 0.47 0.47 0.48
3.4 1.2 1.0 0.01 0.51 0.58 1.28 0.34 0.84 0.94 0.52 0.51 0.23 0.18 12:18:70 5.5 9:22:69 14:21:65 0.20 0.50 0.57 0.45
2.4 1.2 1.1 0.49 0.39 0.26 1.18 0.13 0.89 0.95 0.57 0.56 0.20 0.42 5:17:78 3.5 4:17:79 8:19:73 0.25 0.46 0.54 0.55
4.5 1.2 1.0 0.07 0.41 0.27 1.33 0.15 0.89 0.95 0.57 0.58 0.20 0.03 7:17:76 4.6 5:19:76 12:21:67 0.29 0.46 0.52 0.59
All ratios were calculated from MRM data, except those marked
is more frequent towards the northern end. The proportion of sandstones in the Baralaba Coal Measure Formation is high in comparison to other coal mines in the Bowen Basin. The faulting and inter-bedded sandstones may have acted as conduits for the penetration of surface water, at least in some parts of the Moura coal seams. The depth from the surface to the top of the open cut Moura coal seam is approximately 50 m, but based on the vitrinite re¯ectance of 1.0% the coal seam was probably buried to a depth of more than 1.5 km before uplift to the present level. This paper presents the geochemical results for a total of six coal samples, two from each of the three coal®elds: Blackwater, Moura and Poitrel.
3. Experimental 3.1. Extraction and fractionation Coal samples were cleaned thoroughly to remove any external matter and then crushed into powder. Powdered coals were exhaustively extracted with an azeotropic mixture of dichloromethane and methanol (93:7) for 72 h. Asphaltenes were precipitated from the extracts using an excess of n-pentane. The isolated
Moura coals
which were calculated from SIM data.
maltenes were fractionated into aliphatic hydrocarbons, aromatic hydrocarbons and polar fractions on a silica:alumina column by standard geochemical procedures. 3.2. Gas chromatography±mass spectrometry (GC±MS) GC±MS analyses of the aliphatic and aromatic hydrocarbon fractions were performed on a Hewlett Packard 5890 gas chromatograph interfaced to a VG AutoSpecQ Ultima (electron energy 70 eV; electron multiplier 250 V; ®lament current 200 mA; source temperature 2808C) tuned to 1000 resolution. Chromatography was carried out on a fused silica column (60 m 0.25 mm i.d.) coated with DB5MS (modi®ed 5% phenyl 95% methyl silicone, 25 mm ®lm thickness), using a splitless injection technique. The oven was programmed in two ways for dierent GC± MS runs: (a) for an initial temperature of 408C for 2 min, followed by heating at 48C/min to 3108C, and (b) for an initial temperature of 408C for 2 min, followed by heating at 208C/min to 2008C and then a second heating ramp at 28C/min to 3108C. The samples were run using full scan, single ion monitoring (SIM) and metastable reaction monitoring (MRM) programmes.
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M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
Fig. 2. Plot of C31±C35 homohopane distributions.
4. Results and discussions Parameters and abbreviations used subsequently are de®ned in Appendix A. For the methylphenanthrene index a response factor was used to correct for the dierent responses of phenanthrene and methylphenanthrenes in m/z 178 and 192 mass chromatograms. 4.1. Source Blackwater, Moura and Poitrel coals have Pr/Ph ratios varying from 2.4 to 5.0 (Table 1), which are consistent with their origin from predominantly terrestrial higher plant organic matter deposited in a deltaic environment (Didyk et al., 1978). The presence of a signi®cant amount of 17a(H)-diahopane (C30) in these coals (Table 1) suggests a signi®cant terrestrial input under oxic conditions (Philp and Gilbert, 1986; Peters
and Moldowan, 1993). The line plots (Fig. 2) of C31± C35 homohopane distributions indicate that the six coals from three dierent locations are geochemically similar. Very low C35 homohopane indices are consistent with deposition of the coals in oxic/terrestrial environments (Peters and Moldowan, 1991). C27, C28 and C29 aaa 20R and abb 20S+20R regular sterane distribution patterns in Blackwater, Moura and Poitrel coals (Table 1) are indicative of their similarity in terms of organic matter type and paleoenvironment of deposition. The high relative amount of C29 steranes (62±79%) in these coals suggests higher plant organic matter deposited in a terrestrial environment (Huang and Meinschein, 1979), as do the relative distributions of C27, C28 and C29 aaa 20S steranes (not shown in the table) and ba diasteranes. The occurrence of signi®cant quantities of diasteranes may be due to the association of these coals with clay-rich sediments deposited in oxic conditions (Mello et al., 1988). Very low (<0.60) sterane/hopane ratios of Blackwater, Moura and Poitrel coals (Table 1) are indicative of the incorporation of high levels of bacterial inputs commonly associated with terrigenous organic matter (Tissot and Welte, 1984; Peters and Moldowan, 1993) in these coals. The presence of a small but signi®cant amount of C30 steranes is supportive of some marine in¯uence in these coals (Moldowan et al., 1985). Poitrel coals have a relatively higher amount of C27 and C30 steranes and lower Pr/Ph ratios compared to Blackwater and Moura coals, indicating an origin in a slightly more marine-in¯uenced depositional environment. The aliphatic and aromatic hydrocarbon biomarker parameters indicate that the solvent extracts from the Blackwater, Moura and Poitrel coals have similar geochemical characteristics and appear to be indigenous to the coals. The coals originated predominantly from
Table 2 Aromatic hydrocarbon parameters Sample number
TNR-1 TNR-2 MPI 1 MPDF MPR DPR MDR Calculated re¯ectance (Rc%) Vitrinite re¯ectance (Ro%)
Blackwater coals
Poitrel coals
Moura coals
94916
22684
97054
97055
94915
94919
0.82 0.89 1.1 0.51 1.3 0.29 4.8 1.1 1.0
0.93 0.94 1.2 0.53 1.4 0.33 5.1 1.1 1.0
1.21 1.11 1.2 0.54 1.5 0.30 9.0 1.1 1.1
1.12 1.01 1.3 0.56 1.8 0.40 9.8 1.2 1.1
0.90 1.11 1.4 0.50 1.9 0.32 4.1 1.3 1.0
0.97 1.10 1.5 0.54 1.7 0.34 5.1 1.3 1.0
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
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Fig. 3. Total ion chromatograms showing the aliphatic and aromatic hydrocarbon distribution patterns in three representative coal samples. Numbers refer to n-alkane chain length; A=cyclohexanes; B=C14 bicyclic sesquiterpane; C±E=C15 bicyclic sesquiterpanes; F=C16 bicyclic sesquiterpane. Aromatic hydrocarbon abbreviations are de®ned in Appendix A.
terrestrial organic matter deposited in a deltaic environment. 4.2. Thermal maturity The vitrinite re¯ectance of the Blackwater, Moura and Poitrel coals varies from 1.0 to 1.1% Ro (Table 2), a range equivalent to the peak oil generation stage of organic evolution. Maturity calculated from the methylphenanthrene index (MPI 1 of Radke et al., 1982a) using the calibration of Radke and Welte (1983) ranges from 1.1 to 1.3% Rc (Table 2). Calculated re¯ectance for the Blackwater and Poitrel coals is close to but slightly higher than the measured vitrinite re¯ectance, whereas Moura coals have a much higher calculated re¯ectance than the measured re¯ec-
tance. Such a large variation for Moura coals might be due to suppression of vitrinite re¯ectance (George and Smith, 1995), or might have been caused by the preferential removal of phenanthrene and 1-MP due to biodegradation. This is discussed later in this paper. The aliphatic and aromatic biomarker ratios (Tables 1 and 2) suggest the coals have similar maturities. Ratios calculated from C29±C32 hopanes, C29 steranes and diasteranes are at or close to thermal equilibrium (Seifert and Moldowan, 1986; Mackenzie et al., 1980), suggesting that all these coals are at a maturity level beyond the early stages of oil generation. The carbon preference indices (CPI), TNR-1 (Alexander et al., 1985), TNR-2 (Radke et al., 1986), MPDF (Kvalheim et al., 1987), MPR (Radke et al., 1982b), DPR (Radke et al., 1982b) and MDR (Radke et al., 1986) corrobo-
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Table 3 Ratios of less over more susceptible compound classes and individual isomers Sample number
Non-degraded coals Blackwater
Aliphatic hydrocarbons Pr/n-C17 Ph/n-C18 F/(C+D+E) Drimane/homodrimane Aromatic hydrocarbons EN/MN EN/DMN TMN/DMN TeMN/TMN MF/F MPy/Py MDBT/DBT DMDBT/MDBT MP/P DMP/MP Py/P MP/MN DMP/DMN P/F MP/MF MF/MN MDBT/MN DBT/P MDBT/MP Py/DBT Isomers 2-EN/1-EN 1,2,4-TMN/167-TMN 1,2,7-TMN/1,3,6-TMN 2,3,6,7-TeMN/1,3,6,7-TeMN 1,2,3,7-TeMN/1,2,6,7-TeMN 2-MF/1-MF 4-MF/3-MF 9-MP/3-MP 9-MP/1-MP 4-MDBT/2+3-MDBT
Biodegraded coals Poitrel
Moura
94916
22684
97054
97055
0.66 0.16 0.15 1.2
0.34 0.10 0.15 1.1
0.08 0.06 0.16 2.7
0.10 0.05 0.12 2.1
3.83 1.16 0.15 1.9
1.86 0.35 0.18 1.9
0.20 0.02 3.8 0.52 7.6 1.9 3.8 0.97 4.2 1.0 0.38 77.1 6.5 10.7 6.0 12.9 3.7 0.05 0.05 7.1
0.19 0.03 2.9 0.45 6.9 2.1 4.1 0.88 4.3 0.9 0.39 40.0 4.6 9.4 6.0 6.7 2.1 0.06 0.05 7.0
0.24 0.04 3.6 0.27 4.5 2.3 3.5 0.95 4.3 0.5 0.24 33.4 2.6 4.4 4.2 8.0 2.1 0.07 0.06 3.3
0.17 0.02 2.6 0.23 4.1 1.6 4.1 0.88 4.9 0.8 0.23 29.0 3.3 3.1 3.7 7.8 3.6 0.15 0.12 1.5
2.8 0.21 37.4 1.20 64.8 2.6 17.0 1.31 26.5 1.4 2.16 1570.2 165.8 16.8 6.9 228.6 113.3 0.11 0.07 19.2
1.5 0.10 6.1 0.64 22.1 2.3 9.1 1.02 9.2 1.2 0.66 198.8 14.9 13.3 5.6 35.8 16.3 0.08 0.08 8.0
0.16 0.19 0.21 0.21 0.40 0.29 0.57 1.2 1.3 1.4
0.57 0.14 0.20 0.23 0.34 0.32 0.47 1.1 1.3 1.3
0.95 0.16 0.17 0.21 0.34 0.35 0.42 1.0 1.5 1.0
0.53 0.14 0.13 0.22 0.34 0.31 0.36 1.0 1.8 0.9
1.43 1.44 0.36 0.29 0.59 0.46 0.60 1.5 2.3 1.7
1.67 0.54 0.27 0.25 0.50 0.41 0.49 1.2 1.6 1.6
rate each other and are indicative of maturity equivalent to about 1.0% Ro. The internal consistency of the molecular maturity parameters and their agreement with vitrinite re¯ectance indicate that the solvent extracts of these coals are indigenous. 4.3. Biodegradation The total ion chromatograms (TIC) of the aliphatic and aromatic hydrocarbon fractions of representative Blackwater, Poitrel and Moura coals are shown in Fig.
94915
94919
3. Aliphatic hydrocarbons of Blackwater and Poitrel coals are characterised by C12±C33 n-alkanes with a smooth unimodal distribution consistent with the high thermal maturity of the coals (Fig. 3a, b). Blackwater coal has a n-alkane maxima at n-C21, whereas in Poitrel coal the maxima is at n-C17 which is consistent with the slightly higher maturity of Poitrel coal. Moura coal, on the other hand, exhibits a completely dierent aliphatic hydrocarbon distribution pattern that re¯ects its alteration by microbial degradation (Fig. 3c). n-Alkanes over C25 are depleted, revealing a
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
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Fig. 4. Variation of (a) MPs/P with DMPs/MPs and (b) MDBTs/DBTs with DMDBTs/MDBTs, showing relative susceptibility to biodegradation of these compounds.
relatively higher abundance of C30 ab hopane and other polycyclic alkanes, compared to the Blackwater and Poitrel coals (Fig. 3). C10±C20 n-alkanes are almost completely absent, leaving cyclohexanes, acyclic isoprenoids and bicyclic sesquiterpenoids as the only remaining compound classes in this region of the chromatogram. The TICs of Blackwater and Poitrel coals exhibit a very similar aromatic hydrocarbon distribution patterns (Fig. 3d, e). Alkylnaphthalenes and alkylphenanthrenes are the two most abundant classes of compounds in these coals, with appreciable amounts of alkyl-substituted biphenyls, ¯uorenes, dibenzothiophenes and pyrenes also present. Such a molecular composition may be considered as characteristic of unaltered bituminous coals. On the other hand, the aromatic hydrocarbon distributions in Moura coal exhibits clear signs of biodegradation (Fig. 3f). Alkylphenanthrenes are abundant but the relative amounts of alkylnaphthalenes, alkylbiphenyls, and alkyl¯uorenes are signi®cantly decreased in abundance, relative to the non-degraded Blackwater and Poitrel coals. Biphenyl, ¯uorene and phenanthrene are almost completely removed. Based on these aliphatic and aromatic hydrocarbon distribution patterns the coals were divided into two groups: biodegraded Moura coals and non-degraded Blackwater and Poitrel coals. The eects of biodegradation on the dierent compound classes in the coals were then assessed. 4.3.1. Eects of biodegradation on aliphatic hydrocarbons It is evident from the TIC that biodegradation has
removed substantial amounts of n-alkanes from the Moura coals, a change re¯ected in the relative increase in Pr/n-C17 and Ph/n-C18 ratios (Table 3). The higher abundances of pristane, phytane and alkylcyclohexanes suggest these compound classes have been resistant to the level of biodegradation experienced by this coal. Williams et al. (1986) found the bicyclic sesquiterpanes C, D and E to be more susceptible to degradation than F (Fig. 3c); they also observed homodrimane to be more susceptible than drimane. No signi®cant increase in the ratios of F/(C+D+E) and of drimane/ homodrimane for the Moura coals (Table 3) compared to the non-degraded coals indicate that bicyclic sesquiterpanes in Moura coals are also unaected. No eects of biodegradation on steranes, diasteranes and hopanes (Volkman et al., 1983, 1984; Peters and Moldowan, 1993) could be distinguished in the degraded Moura coals compared to non-degraded Blackwater and Poitrel coals. Furthermore, except for a trace amount of 29,30-bisnorhopane, demethylated hopanes (Volkman et al., 1983) could not be detected in this degraded coal. Thus, it appears that sterane, diasterane and hopane distributions were unaected by biodegradation of Moura coals. In summary, the extent of microbial degradation of the aliphatic hydrocarbons in Moura coal is very limited. Biodegradation has caused a general depletion of n-alkanes over the entire range, with n-alkanes containing less than 20 carbon atoms being almost completely removed, without visible depletion of branched or cyclic alkanes. This extent of biodegradation is equivalent to level 2 of Volkman et al. (1983, 1984) and level 1-2 of Fisher et al. (1998).
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Fig. 5. Variation of (a) 1,2,7-TMN/1,3,6-TMN with 1,2,4-TMN/1,6,7-TMN and (b) 2,3,6,7-TeMN/1,3,6,7-TeMN with 1,2,3,7TeMN/1,2,6,7-TeMN, showing relative susceptibility to biodegradation of these isomers.
4.3.2. Eects of biodegradation on aromatic hydrocarbons Table 3 includes the ratios of less biodegradable over more biodegradable major aromatic compounds and classes. These ratios were calculated by using absolute peak areas of the respective compounds or group of compounds. Direct comparison of these ratios in the degraded vs non-degraded samples allows their relative susceptibilities to biodegradation to be determined. For example, with respect to alkyl substitution, higher EN/MN ratios (Table 3) for biodegraded Moura coals compared to non-degraded Blackwater and Poitrel coals indicate that MNs are more susceptible to microbial degradation than ENs. Similarly, DMNs are more susceptible than ENs and TMNs, TMNs are more susceptible than TeMNs, F is more susceptible than MFs and Py is more susceptible than MPys. The ratios also indicate that P is more susceptible than MPs which in turn are more susceptible than DMPs (Table 3, Fig. 4a) and DBT is more susceptible than MDBTs which in turn are more susceptible than DMDBTs (Table 3, Fig. 4b). These observations show the order of susceptibility to microbial alteration in coals to be: most susceptible 4 least susceptible MN>DMN>EN>TMN>TeMN F>MF P>MP>DMP DBT>MDBT>DMDBT Py>MPy With respect to the number of aromatic rings, relatively higher MP/MN and Py/P ratios (Table 3) for biodegraded Moura coals suggest that naphthalenes
(di-aromatics) are more susceptible than phenanthrenes (tri-aromatics) which in turn are more susceptible than pyrenes (tetra-aromatics). Similarly, higher MF/MN, P/F and slightly higher MP/MF ratios in the Moura coal reveal that naphthalenes are more susceptible than ¯uorenes, which in turn are more susceptible than phenanthrenes. Owing to the extreme volatility of naphthalene, MNs were used in susceptibility comparisons. Although one Poitrel coal sample is an exception, the higher DBT/P and MDBT/MP ratios in Moura coals suggests more susceptibility of phenanthrenes compared to DBTs. Relatively higher amounts of sulphur-containing compounds in Poitrel coals may have been inherited from its slightly more marine-in¯uenced depositional environment. Again, greater susceptibility of DBT compared to pyrene is indicated by higher Py/ DBT ratios for biodegraded Moura coals. These observations show the order of susceptibility to biodegradation to be: most susceptible 4 least susceptible N>F>P>DBT>Py Thus it is apparent that ¯uorenes (bridged aromatic compounds) are more resistant to microbial attack than naphthalenes but less resistant than phenanthrenes, and that sulphur containing DBTs are more resistant than phenanthrenes. Apart from the susceptibility dierences between F and MF, ¯uorenes and di-/ tri-aromatics, and between Py and MPy, these ®ndings corroborate the previously described observations of Volkman et al. (1984), Bayona et al. (1986) and Rowland et al. (1986) with regard to relative susceptibilities to biodegradation of aromatic hydrocarbons in petroleum.
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
Relative susceptibilities to biodegradation of individual isomers of dierent aromatic compound classes were similarly determined by calculation of ratios of less susceptible over more susceptible compounds. The susceptibility to biodegradation of alkylnaphthalene isomers in coals (Table 3, Fig. 5a, b) follows the order observed by Volkman et al. (1984) in crude oils and Fisher et al. (1996, 1998) in the petroleum extracts of coastal and sea ¯oor sediments: more susceptible 4 less susceptible 1-EN>2-EN 1,6,7-TMN>1,2,4-TMN 1,3,6-TMN>1,2,7-TMN 1,3,6,7-TeMN>2,3,6,7-TeMN 1,2,6,7-TeMN>1,2,3,7-TeMN These authors noted that polymethylnaphthalenes with 1,6-dimethyl substitution patterns are more susceptible to biodegradation than other isomers. The ratios of other aromatic isomers (Table 3) indicate the following order of relative susceptibilities to biodegradation: more susceptible 4 less susceptible 1-MF>2-MF 3-MF>4-MF 3-MP, 1-MP, 2-MP>9-MP 2+3-MDBT>4-MDBT The observation that 9-MP is more resistant to microbial attack than the other MP isomers supports the earlier ®eld and laboratory studies of Rowland et al. (1986) and the results from in vitro degradation experiments reported by Bayona et al. (1986). No explanations for the variation in the degradation rates of methyl¯uorene, methylphenanthrene and methyldibenzothiophene isomers are presented. Based on the eects of biodegradation on aliphatic and aromatic hydrocarbons, a six point scale has been compiled (Table 1 of Fisher et al., 1998) to rank condensate, spilled in coastal sediments, into dierent levels of biodegradation. Direct comparison of the distribution of aliphatic hydrocarbons in Moura coals to this scale indicates a biodegradation level of 1±2, but based on aromatic hydrocarbons a level of 5 or more is indicated (DMNs severely depleted, TMN, TeMN, MP and DMP altered; Fisher et al., 1998). Therefore, biodegradation of Moura coals shows that long before the n-alkanes are completely removed or branched/cyclic alkanes are aected, almost all the major aromatic compound classes in coals may be microbially altered. These data suggest that the general order of susceptibility to biodegradation, as has been determined for oils (Volkman et al., 1983, 1984; Peters and Moldowan, 1993; Fisher et al., 1998), is not directly applicable to coals. Furthermore, these observations also imply signi®cant limitations on the use of aromatic hydrocarbons as maturity parameters in biodegraded coals.
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In view of the vitrinite re¯ectance of these coals (Table 2), it seems probable that biodegradation is a comparatively recent event, which occurred after uplift of the coal and possibly due to episodic or erratic invasion of the Moura coal seam by oxygenated and microorganism-supporting aquifers.
5. Conclusions The aliphatic and aromatic hydrocarbons isolated from Blackwater, Moura and Poitrel coals by solvent extraction are similar in respect of organic matter type, maturity and palaeoenvironment of deposition. The extracts of Moura coal exhibit characteristics of biodegradation, but the other coals do not. These characteristics parallel features of biodegraded crudes, with the susceptibility to biodegradation of aromatic hydrocarbons decreasing with increasing number of aromatic rings and with increasing number of alkyl substituents. Dierences in susceptibility to biodegradation are also observed in terms of the position of certain isomers. The main feature of the biodegradation of aliphatic hydrocarbons is an increase in isoprenoid/n-alkane ratios due to preferential loss of n-alkanes. In addition to demonstrating the commonality in the chemistry of the biodegradation of crude oils, oil spills and coals, this study suggests that in coals, in contrast to the relative susceptibilities to biodegradation of the hydrocarbon components of crude oils, aromatic hydrocarbons may be altered relatively earlier than aliphatic hydrocarbons. These observations require that where biodegradation is suspected, caution be exercised in using aromatic hydrocarbons in the assessment of coal maturity. The proverbial resistance of coal to microbial attack is questioned by this evidence of in situ alteration of hydrocarbon components. In this respect it may be that uplifting to the near surface and invasion by meteoric water, as experienced by Moura coals, are essential requirements for biodegradation of coals. Certainly, alteration of parent hydrocarbons is ®rmly established but the precise nature and fate of low molecular weight microbial products remain in doubt.
Acknowledgements The authors are grateful to BHP Australia Coal Limited for providing the valuable samples and also to Mr Robinson Quezada for his expert assistance with the GC±MS analyses. We appreciate the helpful comments of Dr Chris Boreham and Dr Roger Summons on an earlier version of this manuscript.
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Appendix A A.1. De®nition of parameters TNR-1
2, 3, 6 ÿ TMN 1, 3, 5 ÿ TMN 1, 4, 6 ÿ TMN
TNR-2
1, 3, 7 ÿ TMN 2, 3, 6 ÿ TMN 1, 3, 5 ÿ TMN 1, 3, 6 ÿ TMN 1, 4, 6 ÿ TMN 1:5 2 ÿ MP 3 ÿ MP P 1 ÿ MP 9 ÿ MP
MPI 1
Rc % 0:6 MPI 1 0:4 MPDF
2 ÿ MP 3 ÿ MP 2 ÿ MP 3 ÿ MP 1 ÿ MP 9 ÿ MP
MPR
2 ÿ MP 1 ÿ MP
MDR
4 ÿ MDBT 1 ÿ MDBT
DPR
2, 6 ÿ DMP 2, 7 ÿ DMP 3, 5 ÿ DMP 1, 3 ÿ DMP 1, 6 ÿ DMP 2, 5 ÿ DMP 2, 9 ÿ DMP 2, 10 ÿ DMP 3, 9 ÿ DMP 3, 10 ÿ DMP
A.2. Abbreviations of ratios TNR MPI MPDF MPR DPR MDR
Trimethylnaphthalene Ratio Methylphenanthrene Index Methylphenanthrene Distribution Fraction Methylphenanthrene Ratio Dimethylphenanthrene Ratio Methyldibenzothiophene Ratio
A.3. Abbreviations of compounds N MN EN DMN TMN TeMN C5N F MF Py MPy Bp
Naphthalene Methylnaphthalene Ethylnaphthalene Dimethylnaphthalene Trimethylnaphthalene Tetramethylnaphthalene C5-alkylnaphthalene Fluorene Methyl¯uorene Pyrene Methylpyrene Biphenyl
MBp DMBp DBT MDBT DMDBT P MP DMP
Methylbiphenyl Dimethylbiphenyl Dibenzothiophene Methyldibenzothiophene Dimethyldibenzothiophene Phenanthrene Methylphenanthrene Dimethylphenanthrene
References Alexander, R., Kagi, R.I., Rowland, S.J., Sheppard, P.N., Chirila, T.V., 1985. The eects of thermal maturation on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleums. Geochimica et Cosmochimica Acta 49, 385±395. Bailey, N.J.L., Jobson, A.M., Rogers, M.A., 1973. Bacterial degradation of crude oil: comparison of ®eld and experimental data. Chemical Geology 11, 203±211. Bayona, J.M., Albaiges, J., Solanas, A.M., Pares, R., Garrigues, P., Ewald, M., 1986. Selective aerobic degradation of methyl-substituted polycyclic aromatic hydrocarbons in petroleum by pure microbial cultures.
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322 International Journal of Environmental Analytical Chemistry 23, 289±303. Bence, A.E., Kvenvolden, K.A., Kennicutt, M.C., 1996. Organic geochemistry applied to environmental assessments of Prince William Sound, Alaska, after the Exxon Valdez oil spill Ð a review. Organic Geochemistry 24, 7± 42. Connan, J., 1984. Biodegradation of crude oils in reservoirs. In: Welte, D.H., Brooks, K. (Eds.), Advances in Petroleum Geochemistry, vol. 1. Academic Press, New York, pp. 299±335. Couch, G.R., 1987. Biotechnology and Coal. I.E.A. Coal Research, pp. 7±56. Curry, D.J., Emmett, J.K., Hunt, J.W., 1994. Geochemistry of aliphatic-rich coals in the Cooper Basin, Australia and Taranaki Basin, New Zealand: implications for the occurrence of potentially oil-generative coals. In: Scott A.C., Fleet, A.J. (Eds.), Coal and Coal-bearing Strata as Oilprone Source Rocks?, Geological Society Special Publication No. 77, London, pp. 149±182. Didyk, B.M., Simoneit, B.R.T., Brassell, S.C., Eglinton, G., 1978. Organic geochemical indicators of palaeoenvironmental conditions of sedimentation. Nature 272, 216±222. Fisher, S.J., Alexander, R., Kagi, R.I., 1996. Biodegradation of alkylnaphthalenes in sediments adjacent to an o-shore petroleum production platform. Polycyclic Aromatic Compounds 11, 35±42. Fisher, S.J., Alexander, R., Kagi, R.I., Oliver, G.A., 1998. Aromatic hydrocarbons as indicators of biodegradation in North Western Australian reservoirs. In: Purcell, P.G., Purcell, R.R. (Eds.), The Sedimentary Basins of Western Australia 2: Proceedings of Petroleum Exploration Society of Australian Symposium, Perth, WA, pp. 185±194. George, S.C., Smith, J.W., 1995. The in¯uence of depositional environment on the methylphenanthrene index. In: Pajares, J.A., Tascon, J.M.D. (Eds.), Coal Science and Technology V24, Coal Science, Proceedings of the Eight International Conference on Coal Science. Elsevier, Amsterdam, pp. 287±290. Hawthorne, W.L., 1975. Regional coal geology of the Bowen Basin. In: Traves, D.M., King, D. (Eds.), Economic Geology of Australia and Papua New Guinea, 2. Coal. The Australian Institute of Mining and Metallurgy, pp. 68±77. Huang, W.Y., Meinschein, W.G., 1979. Sterols as ecological indicators. Geochimica et Cosmochimica Acta 43, 739± 745. Hunt, J.M., 1996. Petroleum Geochemistry and Geology, 2nd ed. W.H. Freeman and Company, New York. Jobson, A., Cook, F.D., Westlake, D.W.S., 1972. Microbial utilization of crude oil. Applied Microbiology 23, 1082± 1089. Korsch, R.J., Boreham, C.J., Totterdell, J.M., Shaw, R.D., Nicoll, M.G., 1998. Development and petroleum resource evaluation of the Bowen, Gunnedah and Surat Basins, eastern Australia. APPEA Journal 38 (1), 199±237. Kvalheim, O.M., Christy, A.A., Telnñs, N., Bjùrseth, A., 1987. Maturity determination of organic matter in coals using the methylphenanthrene distribution. Geochimica et Cosmochimica Acta 51, 1883±1888. Mackenzie, A.S., Patience, R.L., Maxwell, J.R.,
1321
Vandenbroucke, M., Durand, B., 1980. Molecular parameters of maturation in the Toarcian shales, Paris Basin, France Ð I. Changes in the con®guration of acyclic isoprenoid alkanes, steranes, and triterpanes. Geochimica et Cosmochimica Acta 44, 1709±1721. Mallett, C.W., Pattison, C., McLennan, T., Balfe, P., Sullivan, D., 1995. Bowen Basin, In: Ward, C.R, Harrington, H.J, Mallett, C.W, Beeston, J.W. (Eds.), Geology of Australian Coal Basins, Geological Society of Australia Incorporated Coal Geology Group Special Publication No. 1, pp. 299±340. Mello, M.R., Telnñs, N., Gaglianone, P.C., Chicarelli, M.I., Brassell, S.C., Maxwell, J.R., 1988. Organic geochemical characterisation of depositional palaeoenvironments in Brazilian marginal basins. Organic Geochemistry 13, 31± 45. Moldowan, J.M., Seifert, W.K., Gallegos, E.J., 1985. Relationship between petroleum composition and depositional environment of petroleum source rocks. Bulletin of the American Association of Petroleum Geologists 69, 1255±1268. Peters, K.E., Moldowan, J.M., 1991. Eects of source, thermal maturity, and biodegradation on the distribution and isomerization of homohopanes in petroleum. Organic Geochemistry 17, 47±61. Peters, K.E., Moldowan, J.M., 1993. The Biomarker Guide. Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood Clis (363 pp). Philp, R.P., Gilbert, T.D., 1986. Biomarker distributions in Australian oils predominantly derived from terrigenous source material. Organic Geochemistry 10, 73±84. Radke, M., Welte, D.H., Willsch, H., 1982a. Geochemical study on a well in the Western Canada Basin: relation of the aromatic distribution pattern to maturity of organic matter. Geochimica et Cosmochimica Acta 46, 1±10. Radke, M., Willsch, H., Leythaeuser, D., Teichmuller, M., 1982b. Aromatic components of coal: relation of distribution pattern to rank. Geochimica et Cosmochimica Acta 46, 1831±1848. Radke, M., Welte, D.H., 1983. The methylphenanthrene index (MPI): a maturity parameter based on aromatic hydrocarbons. In: Bjorùy, M., et al. (Eds.), Advances in Organic Geochemistry 1981. John Wiley, Chichester, pp. 504±512. Radke, M., Welte, D.H., Willsch, H., 1986. Maturity parameters based on aromatic hydrocarbons: in¯uence of the organic matter type. Organic Geochemistry 10, 51±63. Rowland, S.J., Alexander, R., Kagi, R.I., Jones, D.M., Douglas, A.G., 1986. Microbial degradation of aromatic components of crude oils: a comparison of laboratory and ®eld observations. Organic Geochemistry 9, 153±161. Rubinstein, I., Stausz, O.P., Spyckerelle, C., Crawford, R.J., Westlake, D.W.S., 1977. The origin of the soil sand bitumens of Alberta: a chemical and microbiological simulation study. Geochimica et Cosmochimica Acta 42, 1341± 1353. Seifert, W.K., Moldowan, J.M., 1986. Use of biological markers in petroleum exploration. In: Johns, R.B. (Ed.), Biological Markers in the Sedimentary Record, Methods in Geochemistry and Geophysics, vol. 24, pp. 261±290.
1322
M. Ahmed et al. / Organic Geochemistry 30 (1999) 1311±1322
Tissot, B.P., Welte, D.H., 1984. Petroleum Formation and Occurrence. Springer-Verlag, Berlin. Volkman, J.K., Alexander, R., Kagi, R.I., Woodhouse, G.W., 1983. Demethylated hopanes in crude oils and their applications in petroleum geochemistry. Geochimica et Cosmochimica Acta 47, 785±794. Volkman, J.K., Alexander, R., Kagi, R.I., Rowland, S.J.,
Sheppard, P.N., 1984. Biodegradation of aromatic hydrocarbons in crude oils from the Barrow Sub-basin of Western Australia. Organic Geochemistry 6, 619±632. Williams, J.A., Bjorùy, M., Dolcater, D.L., Winters, J.C., 1986. Biodegradation in South Texas Eocene oils Ð eects on aromatics and biomarkers. Organic Geochemistry 10, 451±461.