- Email: [email protected]
Polycyclic aromatic hydrocarbons in ancient sediments and their relationships to palaeoclimate
PII:
Org. Geochem. Vol. 29, No. 5±7, pp. 1721±1735, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain S0146-6380(98)00083-7 0146-6380/98 $ - see front matter
Polycyclic aromatic hydrocarbons in ancient sediments and their relationships to palaeoclimate CHUNQING JIANG1*, ROBERT ALEXANDER1, ROBERT I. KAGI1 and ANDREW P. MURRAY2 Australian Petroleum CRC/Centre for Petroleum and Environmental Organic Geochemistry, School of Applied Chemistry, Curtin University of Technology, G.P.O. Box U 1987, Perth, WA 6001, Australia and 2Australian Geological Survey Organisation, G.P.O. Box 378, Canberra, ACT 2601, Australia
1
AbstractÐCombustion-derived and land-plant-derived polycyclic aromatic hydrocarbons (PAHs) have been investigated for an Upper Triassic to Middle Jurassic sedimentary sequence from the Northern Carnarvon Basin, Western Australia. The former included ¯uoranthene, pyrene, benzo¯uoranthenes, benzo[e]pyrene and benzo[a]pyrene, and the latter included retene, cadalene and simonellite. Combustion-derived PAHs are most abundant in the Upper Triassic and late Lower Jurassic sediments. The abundances of land-plant-derived markers all maximise in the upper part of the Lower Jurassic section, but vary independently of one another through time. The changes in the relative abundances of these markers have been related to the variation of regional climatic conditions, especially the changes in humidity and seasonality during the Late Triassic to Middle Jurassic times. # 1998 Elsevier Science Ltd. All rights reserved Key wordsÐcombustion markers, aromatic plant markers, PAHs, palaeoclimate, Northern Carnarvon Basin
INTRODUCTION
PAHs have been investigated in a variety of modern geological settings including soils (Blumer and Youngblood, 1975; Youngblood and Blumer, 1975), recent lake sediments (Giger and Schaner, 1978; La¯amme and Hites, 1978; Wakeham et al., 1980a,b; Gschwend and Hites, 1981), recent marine sediments (Youngblood and Blumer, 1975; Hites et al., 1977; Gschwend and Hites, 1981), river sediments (Giger and Schaner, 1978; Hites et al., 1980; Brown and Maher, 1992) and river particulates (Giger and Schaner, 1978). Two types of PAHs in recent sediments have been proposed. One group comprises the combustion-derived or pyrolytic PAHs and includes pyrene, ¯uoranthene, benzo[a]anthracene, benzo[b]¯uoranthene, benzo[k]¯uoranthene, benzo[e]pyrene, benzo[a]pyrene, benzo[ghi]perylene and coronene (Youngblood and Blumer, 1975; Blumer, 1976; Hites et al., 1977; La¯amme and Hites, 1978; Wakeham et al., 1980a; Tan and Heit, 1981). Combustion of organic materials such as fossil fuels and plant materials has been proposed by these workers as the major source for this type of PAH in recent sediments. Their conclusions are mainly based on: (1) the qualitative similarities of their distributions worldwide; (2) that unsubstituted PAHs are dominant over their alkyl*To whom correspondence should be addressed. E-mail: [email protected]
ated derivatives in recent sediments and this is also a characteristic of PAHs produced from the combustion of fossil fuels and plant materials. Their presence in recent sediments is attributed to their sorption onto combustion-generated airborne particulate matter which are subsequently deposited into sediments (Blumer, 1976; La¯amme and Hites, 1978). The second group of PAHs abundant in Recent sediments includes retene and perylene. They have been considered to be derived from biological precursors during post-depositional diagenesis, with the former being diagenetic product of abietic acid, a common diterpenoid acid in conifer resins (La¯amme and Hites, 1978; Tan and Heit, 1981); however, there are still divergent opinions as to whether perylene is of terrestrial or marine origin (La¯amme and Hites, 1978; Wakeham et al., 1980b; Tan and Heit, 1981; Tan et al., 1996). Phenanthrene and chrysene may arise in recent sediments through both combustion and diagenetic processes. It has been reported that they can be produced during high temperature combustion of organic materials (Blumer, 1976; La¯amme and Hites, 1978; Hites et al., 1980; Gschwend and Hites, 1981) and they can also be formed during sedimentary diagenesis, probably from terpenoids (Wakeham et al., 1980b; Tan et al., 1996). Fewer reports of unsubstituted PAHs in ancient sediments and petroleums have been published although Radke (1987) pointed out that a back-
1721
1722
C. Jiang et al.
ground of combustion-derived PAHs exists in most ancient sediments. Venkatesan and Dahl (1989) provided the ®rst detailed organic molecular evidence for the global ®res at the K/T boundary, based on their observation that there are enhanced levels of PAHs in the K/T boundary sediments and that unsubstituted PAHs predominate over their alkylated homologues compared with sediments from above and below the boundary. Killops and Massoud (1992) investigated the distribution of PAHs in an Upper Jurassic sequence from the Korean Bay Basin. Based on the dominance of unsubstituted PAHs over their substituted derivatives and the dominance of highly peri-condensed structures in the PAH distribution, they concluded that, in the Upper Jurassic Korean Bay Basin succession, periodic vegetation combustion was the major source of PAHs with three or more rings. Only traces of perylene were found in these sediments; but retene was fairly abundant in samples with high concentrations of combustion-derived PAHs. Simoneit and Lonsdale (1982), Kawka and Simoneit (1990) and Simoneit and Fetzer (1996) reported the distribution of PAHs in hydrothermal petroleums produced from Guaymas Basin (Gulf of California) and Escanaba Trough and Middle Valley (Northeastern Paci®c). The PAHs in these hydrothermal petroleums are formed by the thermal alteration of organic matter by vent ¯uids at temperatures ranging from 260 to 3508C. Another geological condition which can also produce these unsubstituted PAHs is volcanic activity. Petrological and geochemical study conducted in the Midland Valley of Scotland by Murchison and Raymond (1989) shows that the close association of organic matter with both intrusive and extrusive igneous materials can result in a marked contribution of unsubstituted PAHs to sediments, due to the abnormal thermal stress on the sedimentary organic matter. Cadalene, retene and simonellite have been used as biomarkers for the input of higher plants into sediments (Simoneit, 1977, 1986; La¯amme and Hites, 1978; Wakeham et al., 1980b; Tan and Heit, 1981; Alexander et al., 1992; Tan et al., 1996; van Aarssen et al., 1996). Compounds with the cadalene molecular skeleton have been found in higher plants and appear to be the precursors of cadalene (van Aarssen et al., 1990, 1992). The carbon skeleton of simonellite and retene are common in resin acids occurring widely in conifer plants (Simoneit, 1977; Gijzen et al., 1992) and have been proposed as their biological precursors during sedimentary diagenesis (Simoneit, 1977; La¯amme and Hites, 1978; Alexander et al., 1992; Tan et al., 1996). Ramdahl (1983) proposed that retene could also be formed by thermal degradation of resin compounds during low temperature combustion of coniferous wood. Furthermore, retene has been detected in sediments
from several K/T boundary sites (Venkatesan and Dahl, 1989) which are thought to be the result of a global ®re event (Wolbach et al., 1985, 1988; Kruge et al., 1994). Abundant retene and alkyl dehydroabietate were reported in a Chinese Precambrian and Lower Palaeozoic carbonate formation where there is presumed to be no higher plant input (Jiang et al., 1995) and so potential microbial sources need to be kept in mind in interpretation. In this paper, we report the distributions and origins of selected PAHs in an Upper Triassic to Middle Jurassic sedimentary sequence from the Northern Carnarvon Basin of Western Australia and, based on other geological information, relate them to the regional palaeoclimate during this period. SAMPLES AND GEOLOGICAL SETTING
Rock samples are from the Delambre-1 exploration well located in the Northern Carnarvon Basin, Western Australia (Fig. 1). The depositional environment in this area during the Late Triassic was ¯uvio-deltaic (Bradshaw et al., 1988; Hocking, 1988; Blevin et al., 1994). Mudstone and sandstone are the major sediments, with occasional occurrence of coals (data from well completion report). Early Jurassic times saw deposition in mainly shallow marine environments. The Middle Jurassic section is a thick set of siltstones/sandstones with occasional occurrence of mudstones and is thought to be deposited under non-marine/¯uviatile conditions (Apthorpe, 1994). The Upper Triassic to Middle Jurassic sequence of Delambre-1 has experienced only mild thermal stress. Rock-Eval analyses for Delambre-1 showed that the values of Tmax are between 415 and 4508C, implying that the maturity of the sediments range from immature to marginally mature. Current borehole temperatures obtained during logging were 488C at 2128 m; 758C at 3839 m; 1108C at 4900 m and 1348C at 5491 m, consistent with a mild thermal history. EXPERIMENTAL
Finely ground shaly rock samples, in the form of drill cuttings which were taken from intervals with TOC values greater than 0.7%, were extracted ultrasonically for 2 h with dichloromethane. DiluteHCl activated copper was employed to remove elemental sulphur from the extracts. Column chromatography separation of the extract (15 to 90 mg) was performed using silica gel (6 g) activated at 1208C overnight. The extract dissolved in as little as possible dichloromethane was placed onto a drypacked column which had been rinsed with pentane. The saturate fraction was obtained with 35 ml of pentane and elution with 40 ml of pentane±dichloromethane mixture (9:1) aorded the aromatic frac-
PAHs and palaeoclimate
1723
Fig. 1. Location map of the study area.
tion. Mixture of dichloromethane and methanol (1:1) was then used to elute the polar faction. GC/MS analyses of the aromatic fractions were performed on a Hewlett-Packard 5890 Series II GC coupled to a Hewlett-Packard 5971 series mass selective detector (MSD) operating in total ion acquisition mode. Automatic cool-on-column injection was employed into a 50 m 0.25 mm 0.25 mm J&W BP-5 capillary column. Helium was used as the carrier gas at a constant linear velocity of 29.1 cm/s. The column temperature was held at 608C for 1 min, then programmed at 38C/min to 3008C and held for 30 min. Mass spectrometric conditions are: ion source temperature, 1858C; ionisation energy, 70 eV; scanning speed, 1.2 scans/s and electron multiplier voltage, 2200±2400 V. Compounds were identi®ed by matching retention times with reference compounds for phenanthrene, anthracene, ¯uoranthene, pyrene, benzo[a]anthracene, chrysene, triphenylene, benzo[b]¯uoranthene, benzo[j]¯uoranthene, benzo[k]¯uoranthene, benzo[e]pyrene, benzo[a]pyrene, perylene, indeno[123cd]pyrene, benzo[ghi]perylene and coronene and by comparison of retention times and mass spectra with literature and work done in this laboratory for alkyl naphthalenes, alkyl phenanthrenes, retene and cadalene. PAH recovery estimate and quanti®cation was achieved by using both internal standards and normalisation standards. Sediment samples were spiked with known amounts of a representative suite of 5 deuterated PAHs (acenaphthene-d10; chrysene-d12; naphthalene-d8; perylene-d12 and phenanthrened10) as internal standards before extraction. A
known amount of m-terphenyl was added to the aromatic fractions for GC/MS analyses as a normalisation standard in order to calculate the recovery of PAHs. By comparing with peak intensities of internal reference compounds, absolute abundances of selected unsubstituted PAHs were calculated. The relative quanti®cation of compounds was achieved using peak intensities on molecular ion chromatograms or characteristic mass chromatograms.
RESULTS AND DISCUSSION
Analysis A total of 31 aromatic fractions from sedimentary rocks were subjected to detailed GC/MS analyses. A variety of 2-ring to 7-ring aromatic compounds were identi®ed. Figure 2 is partial total ion chromatogram (TIC) of an aromatic fraction showing its GC behaviour. PAHs involved in this paper have been numbered in the TIC and their structures are also given in Fig. 2. In this paper, we have elected to use 1,3,6,7-tetramethylnaphthalene (1367-TeMN) as a reference for the purpose of measuring the relative abundances of PAHs in the sediments. We believe that 1367TeMN is mainly microbe-derived, since (1) tetramethylnaphthalenes occur in sediments and crude oils of all ages; (2) 1367-TeMN is abundant in both marine and terrestrial samples and (3) principal component analysis of PAHs from crude oils and sediments from the Northern Carnarvon Basin
Fig. 2. Partial total ion chromatogram from GC/MS analysis of an aromatic fraction and structures for selected PAHs (sample: 3817.5 m; Lower Jurassic).
1724 C. Jiang et al.
Fig. 3. Relative distribution of unsubstituted PAHs for the Upper Triassic to Middle Jurassic sediments from the Delambre-1 well (refer to Fig. 2 for name abbreviations).
PAHs and palaeoclimate 1725
M. Jurassic M. Jurassic M. Jurassic M. Jurassic M. Jurassic M. Jurassic M. Jurassic M. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic
2557.5 2632.5 2752.5 2827.5 2962.5 3052.5 3142.5 3277.5 3367.5 3457.5 3547.5 3637.5 3727.5 3817.5 3907.5 4042.5 4127.5 4222.5 4312.5 4447.5 4537.5 4627.5 4717.5 4807.5 4897.5 4987.5 5077.5 5212.5 5302.5 5392.5 5475.5
24.08 (0.125) 11.77 9.95 16.67 10.55 6.81 (0.068) 5.58 12.87 36.19 25.13 (0.515) 24.49 20.52 15.31 14.49 (0.519) 14.03 23.54 22.32 (0.538) 28.61 33.86 (0.579) 42.68 46.93 50.66 44.89 38.37 (1.342) 39.98 40.79 45.01 35.00 (0.534) 25.77 32.55 28.75 (0.493)
P m/z 178
9.68 (0.050) 1.57 1.11 8.42 1.48 0.99 (0.010) 1.33 2.77 15.52 7.50 (0.154) 7.30 4.10 3.58 3.26 (0.117) 2.81 5.80 7.78 (0.187) 5.86 7.34 (0.126) 7.68 8.15 9.10 8.21 6.29 (0.220) 6.95 12.99 13.36 5.51 (0.084) 6.18 5.32 3.56 (0.061)
Fla m/z 202
15.40 (0.080) 2.61 1.82 7.55 1.84 2.64 (0.026) 3.34 6.20 21.99 17.35 (0.355) 15.16 8.99 8.04 7.65 (0.274) 5.64 9.45 9.59 (0.231) 8.87 10.83 (0.185) 9.55 12.57 13.91 15.13 11.34 (0.397) 12.29 15.43 16.57 10.61 (0.162) 7.37 7.62 6.11 (0.105)
Pyr m/z 202 3.96 (0.030) 0.71 0.41 2.61 0.34 1.06 (0.014) 1.52 1.76 9.11 5.05 (0.112) 5.61 3.05 2.82 2.82 (0.136) 2.12 4.53 4.25 (0.119) 3.23 4.81 (0.087) 4.99 6.31 5.97 6.07 5.06 (0.224) 5.61 6.41 6.50 4.58 (0.068) 3.70 3.40 2.84 (0.052)
BaAn m/z 228 4.83 (0.037) 1.95 0.69 3.88 0.65 1.14 (0.015) 1.19 2.09 9.14 6.03 (0.134) 7.03 3.39 2.28 2.11 (0.102) 2.40 3.71 4.38 (0.122) 3.79 5.56 (0.101) 6.51 8.61 9.78 8.85 8.84 (0.391) 10.13 8.74 10.43 8.86 (0.131) 6.39 8.03 7.41 (0.135)
Chry + Tpn, m/z 228
BePy m/z 252
BaPy m/z 252
Pery m/z 252
InPy m/z 276
BPery m/z 276
2.38 (0.035) 1.93 (0.028) 1.87 (0.027) 1.03 (0.015) 0.41 (0.006) 2.45 (0.036) 1.63 1.06 0.47 1.34 0.68 2.54 0.53 0.58 0.54 1.92 0.20 2.75 2.83 1.71 1.44 2.34 0.74 2.84 0.47 0.51 0.38 0.92 0.12 1.88 3.52 (0.074) 2.51 (0.052) 2.49 (0.052) 11.69 (0.244) 2.44 (0.051) 11.76 (0.246) 2.32 2.09 2.13 6.30 0.57 6.16 1.93 2.93 2.42 12.15 0.51 9.34 11.06 9.87 12.19 28.29 2.61 16.60 5.50 (0.227) 7.16 (0.295) 8.06 (0.332) 16.23 (0.669) 0.96 (0.039) 9.18 (0.378) 10.90 6.86 8.87 19.10 2.71 11.26 1.69 2.34 4.02 5.11 0.16 2.44 1.35 1.51 2.96 3.91 0.20 2.83 1.32 (0.130) 1.56 (0.153) 2.68 (0.263) 3.25 (0.319) 0.14 (0.014) 2.83 (0.278) 1.65 1.78 2.07 2.18 0.44 4.04 3.71 3.42 4.62 2.60 0.43 4.75 3.91 (0.319) 3.82 (0.312) 4.07 (0.332) 1.97 (0.161) 0.61 (0.050) 6.45 (0.526) 1.45 2.92 3.55 1.20 0.10 3.80 5.00 (0.175) 7.40 (0.259) 6.30 (0.220) 2.92 (0.102) 0.94 (0.033) 10.26 (0.359) 6.01 9.06 6.40 1.83 1.00 9.22 7.98 13.02 8.70 2.34 1.33 11.41 4.54 12.01 8.07 1.30 0.39 8.02 5.69 11.35 6.47 1.48 0.90 9.15 4.71 (0.404) 12.00 (1.031) 5.56 (0.478) 0.69 (0.059) 0.47 (0.040) 7.16 (0.615) 7.96 13.53 5.90 0.84 1.18 8.74 4.29 8.57 5.66 0.82 0.46 5.83 5.55 11.97 6.10 1.01 0.83 8.67 5.13 (0.084) 11.27 (0.185) 5.27 (0.086) 0.61 (0.010) 0.68 (0.011) 8.24 (0.135) 5.14 6.15 3.29 0.54 1.05 4.05 2.25 5.85 3.23 0.19 0.22 3.13 2.86 (0.107) 6.99 (0.263) 2.93 (0.110) 0.21 (0.008) 0.34 (0.013) 4.80 (0.180)
B¯as m/z 252
Table 1. Relative abundances* of individual PAHs and carbon isotope composition for cadalene for Delambre-1 sequence
Refer to Fig. 2 for abbreviations for compound names. *Relative to 1367-TeMN; Values in ( ) are absolute quantity in ppm of sediments; N.A.: not available.
Age
Depth (m) 1.38 2.56 1.45 2.31 1.70 1.45 2.14 1.69 6.66 12.54 15.80 13.24 6.27 2.29 1.26 0.75 0.69 1.00 0.93 0.45 0.45 0.67 0.44 0.31 0.40 0.39 0.56 0.28 0.19 0.54 0.59
1.23 0.76 1.16 0.85 0.91 1.54 2.43 1.73 3.81 5.02 4.48 4.63 7.19 6.86 5.56 3.01 2.73 2.87 2.67 1.80 1.96 1.38 1.29 0.59 0.58 0.49 0.70 0.38 0.18 0.30 0.35
0.70 0.33 0.42 0.71 0.38 0.27 0.80 0.54 3.32 2.99 1.43 2.09 3.93 2.96 1.68 0.74 0.62 1.03 1.18 0.42 0.35 0.55 0.24 0.11 0.17 0.09 0.14 0.05 0.01 0.05 0.04
N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. ÿ25.48 N.A. ÿ24.88 ÿ26.11 ÿ26.64 ÿ25.68 ÿ23.78 ÿ24.68 N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A.
Retene Cadal Simone Cadal d13 C m/z 219 m/z 183 m/z 237 (-)
1726 C. Jiang et al.
PAHs and palaeoclimate
showed that 1367-TeMN is poorly correlated with land-plant related markers, implying a dierent source (van Aarssen et al., 1996). Relative abundances of selected PAHs are shown in Table 1. Among these samples, 9 representative samples were also chosen for absolute quanti®cation (Table 1) and PAH recovery estimation. Recoveries for the 5 internal standards were 70±90% for naphthalene-d8, 84±96% for acenaphthene-d10, 85± 95% for phenanthrene-d10, 85±98% for chrysened12 and 70±90% for perylene-d12. Based on the assumption that deuterated and non-deuterated PAHs have similar absorption/desorption behaviour between rock and solvent, the recoveries of individual PAHs from the rock are also in this range. PAH distributions An examination of the relative distribution of r3-ring unsubstituted PAHs in Delambre-1 samples via GC/MS analyses shows that dierent PAHs predominate in dierent depth intervals and a general similarity exists within each particular interval. Shown in Fig. 3 are the representative relative distributions of these PAHs for dierent depth intervals. In Upper Triassic samples (5475.5 to 4312.5 m), phenanthrene is the predominant PAH. Benzo[e]pyrene, pyrene and benzo[ghi]perylene are the next most prominent. Perylene, indeno[123cd]pyrene and coronene are minor components. Entering the Jurassic period, perylene and benzo[ghi]perylene become more and more abundant relative to phenanthrene until about 3000 m. In the interval 4222.5 to 3457.5 m, there is also an enhanced level of other PAHs relative to phenanthrene. Perylene and benzo[ghi]perylene predominate over phenanthrene and other unsubstituted PAHs in samples over the 3367.5 to 3052.5 m interval. Above 3000 m phenanthrene takes over the major component. Figure 4 and Table 1 show that the presence of ¯uoranthene, pyrene, benzo[a]anthracene, benzo¯uoranthenes, benzo[e]pyrene and benzo[a]pyrene change synchronously with depth and therefore appear to be related to one another, implying a similar source. They exhibit high relative abundances in the Upper Triassic and late Lower Jurassic sediments. Phenanthrene and chrysene also demonstrate this distribution pattern. There are some PAHs which behave dierently to those mentioned above in terms of changes in their relative concentrations with depth. Perylene is one of them. It remains low in Upper Triassic (ratio over 1367-TeMN being 0.20±2.9 for the 5475.5 to 4312.5 m interval) and early Lower Jurassic (1.20± 5.11 for the 4222.5 to 3637.5 m interval) sediments. Its relative concentration increases abruptly to 6.30±28.29 during the 3547.5 to 3052.5 m interval. It then decreases to a low level (0.92±1.92) for the above succession. Retene, cadalene and simonellite
1727
also show dierent distribution patterns to the unsubstituted PAHs. Only traces of retene exist in the sediments of 5475.5 to 4042.5 m (Upper Triassic to early Lower Jurassic) and 3277.5 to 2557.5 m (Middle Jurassic) sections; however, it becomes so abundant in the sedimentary samples of late Lower Jurassic section (3907.5 to 3367.5 m) that it is one of the most intense peaks on the TIC of aromatic fractions of 3457.5 and 3547.5 m. Cadalene remains at low abundance in the bottom samples (5475.5 to 4807.5 m), but it becomes more abundant upward and maximises around 3727.5 m, where it can be readily identi®ed from the TIC (Fig. 2). It then decreases to a low level for the rest of the sequence but is still more abundant than in the bottom section (5475.5 to 4807.5 m). Simonellite follows the distribution trend of cadalene for the whole sequence, but its relative concentration peaks at dierent depths to cadalene (Table 1 and Fig. 6). It seems from Fig. 3 and Table 1 that the distribution pattern of benzo[ghi]perylene is the combination of those of perylene and benzo[e]pyrene. The variation of its abundance follows that of benzo[e]pyrene for the Upper Triassic section when benzo[e]pyrene and other unsubstituted PAHs are abundant. In the 3547.5 to 3052.5 m interval where perylene reaches its maximum, benzo[ghi]perylene also maximises and its change is closely related to that of perylene. Coronene also demonstrates a similar pattern of abundance change throughout the sequence. Sources of PAHs in the sediments Combustion-derived PAHs. It is evident that unsubstituted PAHs with a well-established combustion source (e.g. pyrene, ¯uoranthene, benzo[a]anthracene, benzo¯uoranthenes, benzopyrenes and indeno[cd]pyrene) in modern geological settings are also mainly combustion-derived in the Upper Triassic to Middle Jurassic sediments of the Northern Carnarvon Basin. Their similar relative abundance vs depth pro®les (Fig. 4 and Table 1) suggest a common source. Also, the similarity with the distribution reported for combustion-derived PAHs from the Upper Jurassic sediments from the Korean Bay Basin (Killops and Massoud, 1992) is apparent from Fig. 5. A palynological study (Hos, 1981) has shown that there is abundant carbonised wood in the Upper Triassic sediments but a dearth of palynomorphs. This is a supporting evidence for the occurrence of extensive combustion during the Late Triassic in the study area, accounting for the presence of combustion-derived PAHs. Phenanthrene and chrysene may have a combustion origin but are also likely to be formed during diagenesis from biological precursors (Killops and Massoud, 1992; Tan et al., 1996). Consequently, phenanthrene and chrysene plus triphe-
Fig. 4. Depth pro®les of the abundances of selected PAHs relative to 1367-TeMN for Delambre-1 well (refer to Fig. 2 for name abbreviations).
1728 C. Jiang et al.
PAHs and palaeoclimate
1729
Fig. 5. Distributions of unsubstituted PAHs (m/z 178 + 202 + 228 + 252 + 276 + 300) for (A) recent sediments and U. Jurassic sediments, Korean Bay Basin (Killops and Massoud, 1992) and (B) U. Triassic to M. Jurassic sediments of this study (refer to Fig. 2 for name abbreviations).
nylene have not been used in this study as indicators for combustion. As in recent sediments where the distribution of combustion-derived PAHs can be dominated by ¯uoranthene and pyrene (Killops and Massoud, 1992; Wilcock and Northcott, 1995) as well as benzo¯uoranthenes (Fernandez et al., 1996), the dominant pyrolytic PAH in the distribution of combustion-derived products from the Ancient sediments also varies. In addition to ¯uoranthene, pyrene and benzo¯uoranthenes, benzo[e]pyrene is the major component in some samples (Figs 3 and 5). Type of combustion materials, combustion temperature and post-depositional processes account for these variations in both cases.
Among the combustion-derived PAHs, benzo[e]pyrene may be the best representative of the original combustion products. The original distribution of combustion-derived PAHs may be modi®ed by subsequent sedimentary alkylation procedures (Alexander et al., 1995; Smith et al., 1995). The most susceptible compounds will therefore be depleted by such processes. Examination of the proportions of alkylated and unsubstituted PAHs in the samples showed that benzo¯uoranthenes and benzopyrenes are relatively much less susceptible to these processes. Studies by Stein (1978), Stein and Fahr (1985) and Sullivan et al. (1989) indicate that benzo[e]pyrene is the most stable PAH among the 5-ring C20H12 PAHs. So benzo[e]pyrene might be the least susceptible to post-depositional modi®-
1730
C. Jiang et al.
Fig. 6. Combined geochemical record and geological information for the study area (*: ratios over 1367-TeMN; **: palaeoclimatic information from Parrish et al., 1996; palaeolatitude data form Boote and Kirk, 1989; Williamson et al., 1989; Baillie et al., 1994; Exon and von Rad, 1994).
cations. For this reason, we here take benzo[e]pyrene as the representative of combustion-derived PAHs for the purpose of measuring the input from forest ®res or peat ®res. Combustion-derived PAHs arise from combustion of vegetation. Two sources for the PAHs in ancient sediments are expected to be forest ®res and peat ®res. Forest ®res have been reported as a major source of PAHs in recent sediments (Youngblood and Blumer, 1975). Elevated concentrations of aromatic hydrocarbons have been observed for peat samples which experienced ®re events (Rollins et al., 1993). Both types of combustions take place in terrestrial environments. The PAHs produced due to incomplete combustion can be absorbed and stabilised by the particulates released from combustion (Blumer and Youngblood, 1975; Blumer, 1976) or the residuals of combustion. Particles released from ®res can be both airborne and waterborne, and transported for long distances to a depositional site in lacustrine or marine environments. In the case of Northern Carnarvon Basin, both forest ®res and peat/swamp ®res could have contributed to the high abundances of combustion-derived PAHs. The occurrence of forest ®res is supported by palynological study showing that carbonised woody materials are very abundant and palynomorphs are scarce in the sedimentary interval with high abundances of combustion-derived PAHs (Upper Triassic)(Hos, 1981). A possible contribution of peat/swamp ®res to the abundant com-
bustion-derived PAHs in the Upper Triassic sediments can not be disregarded. Firstly, the ¯uvio-deltaic depositional environment of the study area during the Late Triassic was an ideal site for the formation of swamps and peat bogs which can catch ®re easily under suitable climatic conditions (Cope, 1981; Rollins et al., 1993). Secondly, GC/ MS analyses of saturated biomarkers in these samples showed that isopimarane is the major diterpane. This is a feature of the Eocene Fitzgerald River lignite from S.W. Western Australia and Miocene Yallourn lignite from Gippsland, Australia (Noble, 1986). Although aeolian transport can't be discounted, ¯uvial transport of these PAHs by combustion residuals probably played a more important role since the relative concentrations of these PAHs decrease quickly with distance from shoreline as shown by two other wells (i.e. Brigadier-1 and Gandara-1). The presence of combustion-derived PAHs will re¯ect the conditions of the terrestrial hinterland. For example, the abundances of various PAHs in ancient sediments should depend on the frequency and extent of ®res. Two speci®c factors are expected to be involved: the availability of fuel and the weather condition. Two types of combustible fuels have been available through the geological time period of interest in this study: land plants and fossil organic materials like peat. Their availability is controlled by the climatic conditions. Most plants grow rapidly under warm and humid conditions and arid climates constitute a water stress on the
PAHs and palaeoclimate
plants. Extremely cold or hot conditions could disturb the water and nutrient transport as well as the biochemical reactions in the plants, hence reducing growth rates. In a seasonal climate, dry times would be favourable for the occurrence of combustion. It can be seen that the presence of these PAHs in the ancient sediments indicates not only the input of land sediments into the environment but also a favourable regional palaeoclimate, especially a humid and seasonal climate. PAH biomarkers for land-plants. Cadalene, retene and simonellite are well recognised land plant markers. Their occurrences in the sequence do not follow those of combustion-derived PAHs and they vary with depth independently of one another (Fig. 6). This implies that they are derived from dierent plant types and hence their presences in the sediments represent the inputs of dierent land plants. Retene probably represent Conifer plants which were widespread in this region during the Aalenian, late Early Jurassic (depth interval of 3800 to 3353 m), spanning about 10 million years. Land plants containing cadalene and simonellite biological precursors appeared as early as the latest Triassic (around 4730 m) and reached their peak population at about 3730 m (the Toarcian). After experiencing a decrease in population, they peaked again at about 3360±3460 m (the Aalenian) and then diminished abruptly. The abrupt decreases in the population of plants represented by retene, cadalene and simonellite all occurred at about 3353 m which is the boundary of the Early Jurassic and Middle Jurassic. PAHs of other sources. Compared with the Upper Jurassic sediments of the Korean Bay Basin (Killops and Massoud, 1992), sediments from the Northern Carnarvon Basin have more abundant perylene, especially for the Jurassic sediments (Fig. 5). Perylene has long been recognised as a diagenetic/biogenic marker based on the facts that its occurrence in Recent sediments does not follow those of combustion-derived PAHs and that its abundance relative to combustion-derived PAHs increases with burial depth in modern depositional setting (Gschwend and Hites, 1981; Wilcock and Northcott, 1995; Fernandez et al., 1996). In the Delambre-1 sedimentary sequence (Table 1), the occurrence of perylene also does not follow those of combustion-derived PAHs, implying a dierent origin, possibly a diagenetic one. Benzo[ghi]perylene has been regarded as combustion-derived PAH (Blumer and Youngblood, 1975; Killops and Massoud, 1992; Leeming and Maher, 1992; Simoneit and Fetzer, 1996). In the Delambre1 sequence, its distribution correlates with other combustion-derived PAHs when perylene is in low abundance and correlates with perylene when perylene becomes abundant in the sediments. It seems that there are two origins for benzo[ghi]perylene
1731
depending on the source of sediments and depositional environment. This also applies to coronene. Detailed discussion of the sources and relationship of perylene, benzo[ghi]perylene and coronene will be given elsewhere. PAHs in ancient sediments and palaeoclimate Figure 6 shows the pro®les of the abundances of aromatic higher plant markers, namely retene, cadalene and simonellite, as well as combustion markers represented by benzo[e]pyrene relative to 1367TeMN, for the Upper Triassic to Middle Jurassic sequence of Delambre-1 well. Shown together with these geochemical data in Fig. 6 are geological information including palaeoclimate information from Parrish et al. (1996), palaeolatitude data (Boote and Kirk, 1989; Williamson et al., 1989; Baillie et al., 1994; Exon and von Rad, 1994) and sedimentation rates. Based on the distribution patterns of aromatic plant markers and combustion markers, six dierent sedimentary intervals, e.g. A, B, C, D, E and F from bottom to top, can be identi®ed and related to dierent palaeoclimatic conditions. Interval A. This interval is from 5500 to 4604 m, spanning the Carnian and Norian of the Late Triassic. Very abundant combustion-derived PAHs occur in this interval of sediments, suggesting that frequent periodic forest ®res and/or swamp/peat ®res took place. This clearly shows that the climate during this time interval was favourable for plant growth on land and swamp/peat formation on the delta plains and that a dry season suitable for combustion existed. This inference is supported by palaeoclimate data. Condition in this region was suggested to be warm to hot, humid and seasonal (Parrish et al., 1996). Since the study area was positioned at 50±558S latitude (Baillie et al., 1994; Exon and von Rad, 1994), a cool±warm condition would be more likely. Rapid deposition of terrestrial sediments (062 m/ma) via a ¯uvio-deltaic system support the claim of a humid climate. Although there is an obvious increase in the relative abundances of cadalene and simonellite from 4717.5 m upward, the aromatic plant markers are generally low in this interval. This might suggest that the origin of the vegetation for combustion may have been peat rather than forests. Examination of the saturated plant-derived biomarkers revealed that isopimarane was the major component and this compound has been observed in peat samples (Noble, 1986). Another explanation for the dearth of aromatic plant markers in this interval is: the higher plants growing in the region during this period did not contain the biological precursors of retene, cadalene and simonellite and their speci®c aromatic biomarkers have not been identi®ed at present time, or alternatively, the biological precursors of these compounds had been
1732
C. Jiang et al.
destroyed during combustion due to high thermal stress (Ramdahl, 1983). Interval B. This sedimentary interval is from 4604 to 4287 m (the Rhaetian, Late Triassic). The abundances of combustion markers started decreasing steadily and reached low levels by the end of the Triassic, implying a decreasing frequency of forest ®res and/or swamp/peat ®res. This change correlates well with the trend of climate becoming less humid (Fig. 6). At this time, the Northwest Shelf of Western Australia moved northwards to a position of 25 to 308S latitude (Exon and von Rad, 1994). Climate in this zone was more hot and arid than previously. Although the seasonality still existed for the occurrence of ®res, less water precipitation constituted water stress for the plants and reduced the formation of swamp/peat, resulting in less fuels for combustion. Figure 6 shows continuing increases of cadalene and simonellite despite that all these aromatic plant markers are remaining at a low level. This suggests that plants yielding cadalene and simonellite precursors are more tolerant of water stress and can survive a relatively arid climate. Interval C. Interval C ranges from 4287 to 3964 m which was deposited during the earliest Jurassic. Combustion markers are at low levels, indicating sparse combustion in the terrestrial environment. This coincides with the arid climate during this time (Parrish et al., 1996) which is also supported by the very low sedimentation rate (014 m/ma). The palaeolatitude position of the area was between 25 and 308S, which is in the global arid zone (Trewartha, 1968; Frakes, 1979). Under this climatic condition, few plants can grow and little swamp/peat can form due to the lack of water precipitation, resulting in low amounts of combustion products in the sediments. Aromatic plant markers remain similar to the end of previous period, providing further evidence that land plants represented by cadalene and simonellite can survive an arid climate. It has been proposed that carbon isotope composition of plant materials become heavier with increasing aridity of the growing environment (Yakir et al., 1994; Lipp et al., 1996). Carbon isotope analyses for speci®c PAHs show that the isotope composition of cadalene (Table 1) is heavier for samples from this interval (ÿ23.78-, ÿ24.68-) than from the interval above (ÿ25.48-; ÿ24.88-; ÿ26.11-; ÿ26.64- for interval D), suggesting that this section was deposited under a more arid climatic condition than the sections above. This is consistent with the palaeoclimatological study by Parrish et al. (1996) (Fig. 6). A palynological study shows that sediments of this interval are very abundant with the Classopollis torosus (Hos, 1981). This is the pollen of the conifer family Cheirolepids, the members of which are tolerant of drought (Parrish et al., 1996). Whether or
not cadalene and simonellite can be used as biomarkers for the plants of this conifer family needs to be further investigated. Interval D. This interval ranges from about 3964 to 3600 m. Aromatic plant markers increase in relative abundance rapidly in the sediments of this section. Early part of this time interval mainly saw the expansion of plants containing cadalene and simonellite precursors. Later on, the conifer plants yielding retene became abundant rapidly while the abundances of the other two plant types decreased. Nevertheless, the population of these land plants was expanded rapidly at this time. This change in the plant habitat strongly suggests that the climate was becoming more favourable to the growth of plants, which is very likely a change from arid in the previous period to more humid. This inference ®ts into the climate changing trend shown by palaeoclimatological study (Parrish et al., 1996) although the climatic conditions were not clearly indicated (Fig. 6). The low abundances of combustion markers in the sediments may suggest the lack of a seasonality during this time, which was also not clearly shown by palaeoclimatological study by Parrish et al. (1996) (Fig. 6). Interval E. This is an interval (3600 to 3353 m) with high relative abundances of both aromatic plant biomarkers and combustion markers in the sediments, signifying that land plants were widespread and the occurrence of forest ®res was frequent during this time interval. This clearly indicates a climatic condition with sucient water precipitation and seasonality, which is supported by palaeoclimatological study by Parrish et al. (1996) (Fig. 6). The high sedimentation rates (064 m/ma) also show plenty of water precipitation in the region. It is noteworthy that conifer plants containing retene precursors became widespread during this period. They took over the prevalence of cadalene and simonellite plants in the early part of this period but gave way to them thereafter. It seems that plants represented by cadalene and simonellite contributed more to the combustion than those represented by retene since the changing pattern of combustion markers is closer to cadalene and simonellite than retene. Interval F. Interval F is from the depth of 3353 m upward. It was deposited during the Middle Jurassic times. Generally speaking, both combustion markers and aromatic plant markers come to low levels in the sediments of this section despite some ¯uctuations. The change in the input of these terrestrial markers is abrupt around the boundary between the Lower Jurassic and the Middle Jurassic. There was not much change in climatic conditions as shown by palaeoclimatological study, remaining warm±hot, humid and seasonal (Parrish et al., 1996). High rate sedimentation (070 m/ma) of non-marine/¯uviatile deposit provides evidence
PAHs and palaeoclimate
for high water precipitation in the terrestrial environment. The palaeolatitude position of the area was probably between 30 and 408S, a small southward move. It seems that these geological conditions should have resulted in high rather than low concentrations of both aromatic plant markers and combustion markers in the sediments. One explanation for this phenomenon is related to palaeoclimatic conditions. The population of the conifer plants represented by retene decreases rapidly from a depth of about 3630 m upward. At the same time, the drought-resistant plants containing cadalene and simonellite precursors became more abundant for a short time and then diminished rapidly when entering the Middle Jurassic times. This may indicate that the climate was becoming unfavourable to the growth of land plants by the end of the Early Jurassic, even though abundant water must have been available considering the high sedimentation rates. We suggest that this may have resulted from very heavy but irregular rainfall, a situation common in tropical and subtropical cyclonic zones. The latitude positions of climatic zones change with geological times (Perlmutter and Mattthews, 1990). For example, the tropical zone can shift from 15 to 358 latitude. Although today's tropical cyclones in Northwestern Australia mainly develop between 18±228S, the study area was probably located in the tropical cyclone zone during the late Early Jurassic and Middle Jurassic. As can be expected from today's climatic conditions in this area, the water precipitation in the region could have been extremely great in total, due to very high and irregular rainfall brought by cyclones, but the climatic conditions were still unsuitable for plant growth since there was little rainfall during the periods between each cyclones. Also, top soils suitable for plant growth could have been easily removed and transported by wind and water to coastal environment, resulting in high rates of sedimentation. CONCLUSIONS
Combustion-derived PAHs have been analysed in the Upper Triassic to Middle Jurassic sediments from the Delambre-1 well, Northern Carnarvon Basin, Australia. Their occurrences in the sediments has been related to the ancient vegetation ®res which, in turn, were related to palaeoclimatic conditions. These PAHs are abundant in the sediments which were deposited under warm±hot and humid climatic conditions with seasonality. Aromatic plant markers retene, cadalene and simonellite have also been investigated and related to the change of climatic conditions. They vary independently throughout the sedimentary sequence and are thought to represent dierent plant types which ¯ourished and diminished at dierent times.
1733
Conifer plants represented by retene ¯ourished for about 10 million years in the late Early Jurassic which was a time of warm and humid climatic condition. The population of plants represented by cadalene and simonellite became abundant in the latest Triassic and maximised in the Early Jurassic. The relatively high abundances of cadalene and simonellite in the early Lower Jurassic sediments suggests that these plants can survive arid climates. A combination of the combustion markers and aromatic plant markers can be used to indicate climatic conditions. High abundances of both combustion markers and aromatic plant markers indicate a humid and seasonal climate. A humid but non-seasonal climate is re¯ected by high abundances of aromatic plant markers but low amounts of combustion markers in the sediments. Low abundances of both plant and combustion markers in sediments shows either an arid climate when sedimentation rates are also low, or an extreme climate with high and irregular rainfall when sedimentation rates are high. AcknowledgementsÐAssistance and comments from Mr G. Chidlow, Dr B. G. K. van Aarssen and other sta and Ph.D. students at PEOG, Curtin University of Technology are acknowledged. C. J. thanks the University and Australian Petroleum CRC for ®nancial support of his Ph.D. study. This paper bene®tted from the thorough and critical reviews by Dr N. Jiang and Dr H. Budzinski.
REFERENCES
van Aarssen, B. G. K., Cox, H. C., Hoogendoorn, P. and de Leeuw, J. W. (1990) A cadinene biopolymer present in fossil and extant dammar resins as a source for cadinanes and bicadinanes in crude oils from South East Asia. Geochimica et Cosmochimica Acta 54, 3021±3031. van Aarssen, B. G. K., Hessels, J. K. C., Abbink, O. A. and de Leeuw, J. W. (1992) The occurrence of polycyclic sesqui-, tri- and oligoterpenoids derived from a resinous polymeric cadinene in crude oils from South East Asia. Geochimica et Cosmochimica Acta 56, 1231± 1246. van Aarssen, B. G. K., Alexander, R. and Kagi, R. I. (1996) The origin of Barrow Sub-basin crude oils: A geochemical correlation using land-plant biomarkers. The APPEA Journal 36, 465±476. Alexander, R., Larcher, A. V., Kagi, R. I. and Price, P. L. (1992) An oil-source correlation study using age-speci®c plant-derived aromatic biomarkers. In Biological Markers in Sediments and Petroleum, eds. J. M. Moldowan, P. Albrecht and R. P. Philp, pp. 201±221. Prentice-Hall, Englewood Clis, N.J. Alexander, R., Bastow, T. P., Fisher, S. and Kagi, R. I. (1995) Geosynthesis of organic compounds: II. Methylation of phenanthrene and alkylphenanthrenes. Geochimica et Cosmochimica Acta 59, 4259±4266. Apthorpe, M. (1994) Towards an Early to Middle Jurassic palaeogeography for the North West Shelf: A marine perspective. In The Sedimentary Basins of Western Australia, eds. G. and P. R. Purcell, pp. 201±210. Proceedings of the Western Australian Basins Symposium, Perth, Western Australia. Baillie, P. W., Powell, C. McA., Li, Z. X. and Ryall, A. M. (1994) The tectonic frame work of Western
1734
C. Jiang et al.
Australia's Neoproterozoic to recent sedimentary basins. In The Sedimentary Basins of Western Australia, eds. P. G. and P. R. Purcell, pp. 45±61. Proceedings of the Western Australian Basins Symposium, Perth, Western Australia. Blevin, J. E., Stephenson, A. E. and West, B. G. (1994) Mesozoic structural development of the Beagle Subbasin: Implications for the petroleum potential of the Northern Carnarvon Basin. In The Sedimentary Basins of Western Australia, eds. P. G. and P. R. Purcell, pp. 479±496. Proceedings of the West Australian Basins Symposium, Perth, Western Australia. Blumer, M. and Youngblood, W. W. (1975) Polycyclic aromatic hydrocarbons in soils and recent sediments. Science 188, 53±55. Blumer, M. (1976) Polycyclic aromatic compounds in nature. Scienti®c America 234, 35±45. Boote, D. R. D. and Kirk, R. B. (1989) Depositional wedge cycles on evolving plate margin, Western and North Western Australia. AAPG Bulletin 73, 216±263. Bradshaw, M. T., Yeates, A. N., Beynon, R. M., Brakel, A. T., Langford, R. P., Totterdell, J. and Yeung, M. (1988) Palaeogeographic evolution of the North West Shelf region. In The North West Shelf, Australia, eds. P. G. and P. R. Purcell, pp. 29±54. Proceedings of Petroleum Exploration Society Australia Symposium, Perth, 1994. Brown, G. and Maher, W. (1992) The occurrence, distribution and sources of polycyclic aromatic hydrocarbons in the sediments of the George River Estuary, Australia. Organic Geochemistry 18, 657±668. Cope, M. J. (1981) Products of natural burning as a component of the dispersed organic matter of sedimentary rocks. In Organic Maturation Studies and Fossil Fuel Exploration, eds. J. Brooks, pp. 89±109. Academic Press. Exon, N. F. and von Rad, U. (1994) The Mesozoic and Cainozoic sequences of the Northwest Australian Margin, as revealed by ODP Core Drilling and related studies. In The Sedimentary Basins of Western Australia, eds. P. G. and P. R. Purcell, pp. 181±199. Proceedings of the Western Australian Basins Symposium, Perth, Western Australia. Fernandez, P., Vilanova, R. and Grimalt, J. O. (1996) PAH distributions in sediments from high mountain lakes. Polycyclic Aromatic Compounds 9, 121±128. Frakes, L. A. (1979) Climate Throughout Geologic Time. Elsevier, Amsterdam, p. 16. Giger, W. and Schaner, C. (1978) Determination of polycyclic aromatic hydrocarbons in the environment by glass capillary gas chromatography. Analytical Chemistry 50, 243±249. Gijzen, M., Lewinsohn, E., Savage, T. J. and Croteau, R. B. (1992) Conifer monoterpenes, Biochemistry and bark beetle chemical ecology. In Bioactive Volatile Compounds From Plants, eds. R. Teranishi, R. G. Buttery and H. Sugisawa, ACS Syposium Series 525, pp. 8±22. American Chemical Society, Washington, D.C. Gschwend, P. M. and Hites, R. A. (1981) Fluxes of polycyclic aromatic hydrocarbons to marine and lacustrine sediments in the Northeastern United States. Geochimica et Cosmochimica Acta 45, 2359±2367. Hites, R. A., La¯amme, R. E. and Farrington, J. W. (1977) Sedimentary polycyclic aromatic hydrocarbons: the historical records. Science 198, 829±831. Hites, R. A., La¯amme, R. E., Windsor, J. G. Jr., Farrington, J. W. and Deuser, W. G. (1980) Polycyclic aromatic hydrocarbons in an anoxic sediment core from the Pettaquamscutt River (Rhode Island, U.S.A.). Geochimica et Cosmochimica Acta 44, 873±878.
Hocking, R. M. (1988) Regional geology of the northern Carnarvon Basin. In The North West Shelf, Australia, eds. P. G. and P. R. Purcell, pp. 97±114. Proceedings of Petroleum Exploration Society of Australia Symposium, Perth. Hos, D. P. C. (1981) Palynological report on Woodside Petroleum Development PTY LTD Delambre-1 Well. Open Files of Western Australian Department of Mining. Jiang, N., Tong, Z., Ren, D., Song, F., Yang, D., Zhu, C. and Gao, Y. (1995) The discovery of retene in Precambrian and Lower Paleozoic marine formations. Chinese Journal of Geochemistry 14, 41±51. Kawka, O. E. and Simoneit, B. R. T. (1990) Polycyclic aromatic hydrocarbons in hydrothermal petroleums from Guaymas Basin spreading Centre. Applied Geochemistry 5, 17±27. Killops, S. D. and Massoud, M. S. (1992) Polycyclic aromatic hydrocarbons of pyrolytic origin in ancient sediments: evidence for Jurassic vegetation ®res. Organic Geochemistry 18, 1±7. Kruge, M. A., Stankiewicz, B. A., Crelling, J. C., Montanari, A. and Bensley, D. F. (1994) Fossil charcoal in Cretaceous±Tertiary boundary strata: Evidence for catastrophic ®restorm and megawave. Geochimica et Cosmochimica Acta 58, 1393±1397. La¯amme, R. E. and Hites, R. A. (1978) The global distribution of polycyclic aromatic hydrocarbons in recent sediments. Geochimica et Cosmochimica Acta 42, 289± 303. Leeming, R. and Maher, W. (1992) Sources of polycyclic aromatic hydrocarbons in Lake Burley Grin, Australia. Organic Geochemistry 18, 647±655. Lipp, J., Trimborn, P., Edwards, T., Waisel, Y. and Yakir, D. (1996) Climatic eects on the d13 C and d18 O of cellulose in the desert tree Tamarix jordanis. Geochimica et Cosmochimica Acta 60, 3305±3309. Murchison, D. G. and Raymond, A. C. (1989) Igneous activity and organic maturation in the Midland Valley of Scotland. International Journal of Coal Geology 14, 47± 82. Noble, R. (1986) A geochemical study of bicyclic alkanes and diterpenoid hydrocarbons in crude oils, sediments and coals. Ph.D. Thesis. Curtin University of Technology. Parrish, J. T., Bradshaw, M. T., Brakel, A. T., Mulholland, S. M., Totterdell, J. M. and Yeates, A. N. (1996) Palaeoclimatology of Australia during the Pangean Interval. Palaeoclimates 1, 241±281. Perlmutter, M. A. and Mattthews, M. D. (1990) Global cyclostratigraphy: A model. In Quantitative Dynamic Stratigraphy, eds. T. A. Cross, pp. 233±260. Prentice Hall, Englewood Clis, N.J. Radke, M. (1987) Organic geochemistry of aromatic hydrocarbons. In Advances in Petroleum Geochemistry, eds. J. Brooks and D. Welte, pp. 141±207. Academic Press, New York. Ramdahl, T. (1983) Retene: a molecular marker of wood combustion in ambient air. Nature 306, 580±582. Rollins, M. S., Cohen, A. D. and Durig, J. R. (1993) Eects of ®res on the chemical and petrographic composition of peat in the Snuggedy Swamp, South Carolina. International Journal of Coal Geology 22, 101±117. Simoneit, B. R. T. (1977) Diterpenoid compounds and other lipids in deep-sea sediments and their geochemical signi®cance. Geochimica et Cosmochimica Acta 41, 463± 476. Simoneit, B. R. T. and Lonsdale, P. F. (1982) Hydrothermal petroleum in mineralised mounds at the seabed of Guaymas Basin. Nature 295, 198±202. Simoneit, B. R. T. (1986) Cyclic terpenoids of the geosphere. In Biological Markers in the Sedimentary
PAHs and palaeoclimate Record, ed. R. B. Johns, pp. 43±82. Elsevier, Amsterdam. Simoneit, B. R. T. and Fetzer, J. C. (1996) High molecular weight polycyclic aromatic hydrocarbons in hydrothermal petroleums from the Gulf of California and Northeast Paci®c Ocean. Organic Geochemistry 24, 1065±1077. Smith, J. W., George, S. C. and Batts, B. D. (1995) The geosynthesis of alkylaromatics. Organic Geochemistry 23, 71±80. Stein, S. E. (1978) On high temperature chemical equilibria of polycyclic aromatic hydraocarbons. Journal of Phyysical Chemistry 82, 566±571. Stein, S. E. and Fahr, A. (1985) High temperature stability of hydrcarbons. Journal of Phyysical Chemistry 89, 3714±3725. Sullivan, R. F., Boduszynski, M. M. and Fetzer, J. C. (1989) Molecular transformations in hydrotreating and hydrocarcking. Energy and Fuels 3, 603±612. Tan, Y. L. and Heit, M. (1981) Biogenic and abiogenic polynuclear aromatic hydrocarbons in sediments from two remote Adirondack lakes. Geochimica et Cosmochimica Acta 45, 2267±2279. Tan, Y. L., Kong, A. and Monetti, M. (1996) Biogenic polycyclic aromatic hydrocarbons in an Alaskan arctic lake sediment. Polycyclic Aromatic Compounds 9, 185± 192. Trewartha, G. T. (1968) An Introduction To Climate. McGraw-Hill Book Company, New York, p. 257. Venkatesan, M. I. and Dahl, J. (1989) Organic geochemical evidence for global ®res at the Cretaceous/Tertiary boundary. Nature 338, 57±60.
1735
Wakeham, S. G., Schaner, C. and Giger, W. (1980a) Polycyclic aromatic hydrocarbons in recent lake sediments. I. Compounds having anthropogenic origins. Geochimica et Cosmochimica Acta 44, 403±413. Wakeham, S. G., Schaner, C. and Giger, W. (1980b) Polycyclic aromatic hydrocarbons in recent lake sediments. II. Compounds derived from biogenic precursors during early diagenesis. Geochimica et Cosmochimica Acta 44, 415±429. Wilcock, R. J. and Northcott, G. L. (1995) Polycyclic aromatic hydrocarbons in deep cores from Mangere Inlet, New Zealand. New Zealand Journal of Marine and Freshwater Research 29, 107±116. Williamson, P. E., Exon, N. F., Haq, B. U. and von Rad, U. (1989) A Northwest Shelf Triassic reef play: results from ODP Leg 122. The APEA Journal 29, 328±341. Wolbach, W. S., Lewis, R. S. and Anders, E. (1985) Cretaceous extinctions: Evidence for wild®res and search for meteoritic material. Science 230, 167±170. Wolbach, W. S., Gilmour, I., Anders, E., Orth, C. J. and Brooks, R. R. (1988) Global ®re at the Cretaceous± Tertiary boundary. Nature 334, 665±669. Yakir, D., Issar, A., Gat, J., Adar, E., Trimborn, P. and Lipp, J. (1994) 13 C and 18 O of wood from the Roman Siege Rampart in Masada, Israel (AD 70±73): Evidence for a less arid climate for the region. Geochimica et Cosmochimica Acta 58, 3535±3539. Youngblood, W. W. and Blumer, M. (1975) Polycyclic aromatic hydrocarbons in the environment: homologous series in soils and recent sediments. Geochimica et Cosmochimica Acta 39, 1303±1314.
Org. Geochem. Vol. 29, No. 5±7, pp. 1721±1735, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain S0146-6380(98)00083-7 0146-6380/98 $ - see front matter
Polycyclic aromatic hydrocarbons in ancient sediments and their relationships to palaeoclimate CHUNQING JIANG1*, ROBERT ALEXANDER1, ROBERT I. KAGI1 and ANDREW P. MURRAY2 Australian Petroleum CRC/Centre for Petroleum and Environmental Organic Geochemistry, School of Applied Chemistry, Curtin University of Technology, G.P.O. Box U 1987, Perth, WA 6001, Australia and 2Australian Geological Survey Organisation, G.P.O. Box 378, Canberra, ACT 2601, Australia
1
AbstractÐCombustion-derived and land-plant-derived polycyclic aromatic hydrocarbons (PAHs) have been investigated for an Upper Triassic to Middle Jurassic sedimentary sequence from the Northern Carnarvon Basin, Western Australia. The former included ¯uoranthene, pyrene, benzo¯uoranthenes, benzo[e]pyrene and benzo[a]pyrene, and the latter included retene, cadalene and simonellite. Combustion-derived PAHs are most abundant in the Upper Triassic and late Lower Jurassic sediments. The abundances of land-plant-derived markers all maximise in the upper part of the Lower Jurassic section, but vary independently of one another through time. The changes in the relative abundances of these markers have been related to the variation of regional climatic conditions, especially the changes in humidity and seasonality during the Late Triassic to Middle Jurassic times. # 1998 Elsevier Science Ltd. All rights reserved Key wordsÐcombustion markers, aromatic plant markers, PAHs, palaeoclimate, Northern Carnarvon Basin
INTRODUCTION
PAHs have been investigated in a variety of modern geological settings including soils (Blumer and Youngblood, 1975; Youngblood and Blumer, 1975), recent lake sediments (Giger and Schaner, 1978; La¯amme and Hites, 1978; Wakeham et al., 1980a,b; Gschwend and Hites, 1981), recent marine sediments (Youngblood and Blumer, 1975; Hites et al., 1977; Gschwend and Hites, 1981), river sediments (Giger and Schaner, 1978; Hites et al., 1980; Brown and Maher, 1992) and river particulates (Giger and Schaner, 1978). Two types of PAHs in recent sediments have been proposed. One group comprises the combustion-derived or pyrolytic PAHs and includes pyrene, ¯uoranthene, benzo[a]anthracene, benzo[b]¯uoranthene, benzo[k]¯uoranthene, benzo[e]pyrene, benzo[a]pyrene, benzo[ghi]perylene and coronene (Youngblood and Blumer, 1975; Blumer, 1976; Hites et al., 1977; La¯amme and Hites, 1978; Wakeham et al., 1980a; Tan and Heit, 1981). Combustion of organic materials such as fossil fuels and plant materials has been proposed by these workers as the major source for this type of PAH in recent sediments. Their conclusions are mainly based on: (1) the qualitative similarities of their distributions worldwide; (2) that unsubstituted PAHs are dominant over their alkyl*To whom correspondence should be addressed. E-mail: [email protected]
ated derivatives in recent sediments and this is also a characteristic of PAHs produced from the combustion of fossil fuels and plant materials. Their presence in recent sediments is attributed to their sorption onto combustion-generated airborne particulate matter which are subsequently deposited into sediments (Blumer, 1976; La¯amme and Hites, 1978). The second group of PAHs abundant in Recent sediments includes retene and perylene. They have been considered to be derived from biological precursors during post-depositional diagenesis, with the former being diagenetic product of abietic acid, a common diterpenoid acid in conifer resins (La¯amme and Hites, 1978; Tan and Heit, 1981); however, there are still divergent opinions as to whether perylene is of terrestrial or marine origin (La¯amme and Hites, 1978; Wakeham et al., 1980b; Tan and Heit, 1981; Tan et al., 1996). Phenanthrene and chrysene may arise in recent sediments through both combustion and diagenetic processes. It has been reported that they can be produced during high temperature combustion of organic materials (Blumer, 1976; La¯amme and Hites, 1978; Hites et al., 1980; Gschwend and Hites, 1981) and they can also be formed during sedimentary diagenesis, probably from terpenoids (Wakeham et al., 1980b; Tan et al., 1996). Fewer reports of unsubstituted PAHs in ancient sediments and petroleums have been published although Radke (1987) pointed out that a back-
1721
1722
C. Jiang et al.
ground of combustion-derived PAHs exists in most ancient sediments. Venkatesan and Dahl (1989) provided the ®rst detailed organic molecular evidence for the global ®res at the K/T boundary, based on their observation that there are enhanced levels of PAHs in the K/T boundary sediments and that unsubstituted PAHs predominate over their alkylated homologues compared with sediments from above and below the boundary. Killops and Massoud (1992) investigated the distribution of PAHs in an Upper Jurassic sequence from the Korean Bay Basin. Based on the dominance of unsubstituted PAHs over their substituted derivatives and the dominance of highly peri-condensed structures in the PAH distribution, they concluded that, in the Upper Jurassic Korean Bay Basin succession, periodic vegetation combustion was the major source of PAHs with three or more rings. Only traces of perylene were found in these sediments; but retene was fairly abundant in samples with high concentrations of combustion-derived PAHs. Simoneit and Lonsdale (1982), Kawka and Simoneit (1990) and Simoneit and Fetzer (1996) reported the distribution of PAHs in hydrothermal petroleums produced from Guaymas Basin (Gulf of California) and Escanaba Trough and Middle Valley (Northeastern Paci®c). The PAHs in these hydrothermal petroleums are formed by the thermal alteration of organic matter by vent ¯uids at temperatures ranging from 260 to 3508C. Another geological condition which can also produce these unsubstituted PAHs is volcanic activity. Petrological and geochemical study conducted in the Midland Valley of Scotland by Murchison and Raymond (1989) shows that the close association of organic matter with both intrusive and extrusive igneous materials can result in a marked contribution of unsubstituted PAHs to sediments, due to the abnormal thermal stress on the sedimentary organic matter. Cadalene, retene and simonellite have been used as biomarkers for the input of higher plants into sediments (Simoneit, 1977, 1986; La¯amme and Hites, 1978; Wakeham et al., 1980b; Tan and Heit, 1981; Alexander et al., 1992; Tan et al., 1996; van Aarssen et al., 1996). Compounds with the cadalene molecular skeleton have been found in higher plants and appear to be the precursors of cadalene (van Aarssen et al., 1990, 1992). The carbon skeleton of simonellite and retene are common in resin acids occurring widely in conifer plants (Simoneit, 1977; Gijzen et al., 1992) and have been proposed as their biological precursors during sedimentary diagenesis (Simoneit, 1977; La¯amme and Hites, 1978; Alexander et al., 1992; Tan et al., 1996). Ramdahl (1983) proposed that retene could also be formed by thermal degradation of resin compounds during low temperature combustion of coniferous wood. Furthermore, retene has been detected in sediments
from several K/T boundary sites (Venkatesan and Dahl, 1989) which are thought to be the result of a global ®re event (Wolbach et al., 1985, 1988; Kruge et al., 1994). Abundant retene and alkyl dehydroabietate were reported in a Chinese Precambrian and Lower Palaeozoic carbonate formation where there is presumed to be no higher plant input (Jiang et al., 1995) and so potential microbial sources need to be kept in mind in interpretation. In this paper, we report the distributions and origins of selected PAHs in an Upper Triassic to Middle Jurassic sedimentary sequence from the Northern Carnarvon Basin of Western Australia and, based on other geological information, relate them to the regional palaeoclimate during this period. SAMPLES AND GEOLOGICAL SETTING
Rock samples are from the Delambre-1 exploration well located in the Northern Carnarvon Basin, Western Australia (Fig. 1). The depositional environment in this area during the Late Triassic was ¯uvio-deltaic (Bradshaw et al., 1988; Hocking, 1988; Blevin et al., 1994). Mudstone and sandstone are the major sediments, with occasional occurrence of coals (data from well completion report). Early Jurassic times saw deposition in mainly shallow marine environments. The Middle Jurassic section is a thick set of siltstones/sandstones with occasional occurrence of mudstones and is thought to be deposited under non-marine/¯uviatile conditions (Apthorpe, 1994). The Upper Triassic to Middle Jurassic sequence of Delambre-1 has experienced only mild thermal stress. Rock-Eval analyses for Delambre-1 showed that the values of Tmax are between 415 and 4508C, implying that the maturity of the sediments range from immature to marginally mature. Current borehole temperatures obtained during logging were 488C at 2128 m; 758C at 3839 m; 1108C at 4900 m and 1348C at 5491 m, consistent with a mild thermal history. EXPERIMENTAL
Finely ground shaly rock samples, in the form of drill cuttings which were taken from intervals with TOC values greater than 0.7%, were extracted ultrasonically for 2 h with dichloromethane. DiluteHCl activated copper was employed to remove elemental sulphur from the extracts. Column chromatography separation of the extract (15 to 90 mg) was performed using silica gel (6 g) activated at 1208C overnight. The extract dissolved in as little as possible dichloromethane was placed onto a drypacked column which had been rinsed with pentane. The saturate fraction was obtained with 35 ml of pentane and elution with 40 ml of pentane±dichloromethane mixture (9:1) aorded the aromatic frac-
PAHs and palaeoclimate
1723
Fig. 1. Location map of the study area.
tion. Mixture of dichloromethane and methanol (1:1) was then used to elute the polar faction. GC/MS analyses of the aromatic fractions were performed on a Hewlett-Packard 5890 Series II GC coupled to a Hewlett-Packard 5971 series mass selective detector (MSD) operating in total ion acquisition mode. Automatic cool-on-column injection was employed into a 50 m 0.25 mm 0.25 mm J&W BP-5 capillary column. Helium was used as the carrier gas at a constant linear velocity of 29.1 cm/s. The column temperature was held at 608C for 1 min, then programmed at 38C/min to 3008C and held for 30 min. Mass spectrometric conditions are: ion source temperature, 1858C; ionisation energy, 70 eV; scanning speed, 1.2 scans/s and electron multiplier voltage, 2200±2400 V. Compounds were identi®ed by matching retention times with reference compounds for phenanthrene, anthracene, ¯uoranthene, pyrene, benzo[a]anthracene, chrysene, triphenylene, benzo[b]¯uoranthene, benzo[j]¯uoranthene, benzo[k]¯uoranthene, benzo[e]pyrene, benzo[a]pyrene, perylene, indeno[123cd]pyrene, benzo[ghi]perylene and coronene and by comparison of retention times and mass spectra with literature and work done in this laboratory for alkyl naphthalenes, alkyl phenanthrenes, retene and cadalene. PAH recovery estimate and quanti®cation was achieved by using both internal standards and normalisation standards. Sediment samples were spiked with known amounts of a representative suite of 5 deuterated PAHs (acenaphthene-d10; chrysene-d12; naphthalene-d8; perylene-d12 and phenanthrened10) as internal standards before extraction. A
known amount of m-terphenyl was added to the aromatic fractions for GC/MS analyses as a normalisation standard in order to calculate the recovery of PAHs. By comparing with peak intensities of internal reference compounds, absolute abundances of selected unsubstituted PAHs were calculated. The relative quanti®cation of compounds was achieved using peak intensities on molecular ion chromatograms or characteristic mass chromatograms.
RESULTS AND DISCUSSION
Analysis A total of 31 aromatic fractions from sedimentary rocks were subjected to detailed GC/MS analyses. A variety of 2-ring to 7-ring aromatic compounds were identi®ed. Figure 2 is partial total ion chromatogram (TIC) of an aromatic fraction showing its GC behaviour. PAHs involved in this paper have been numbered in the TIC and their structures are also given in Fig. 2. In this paper, we have elected to use 1,3,6,7-tetramethylnaphthalene (1367-TeMN) as a reference for the purpose of measuring the relative abundances of PAHs in the sediments. We believe that 1367TeMN is mainly microbe-derived, since (1) tetramethylnaphthalenes occur in sediments and crude oils of all ages; (2) 1367-TeMN is abundant in both marine and terrestrial samples and (3) principal component analysis of PAHs from crude oils and sediments from the Northern Carnarvon Basin
Fig. 2. Partial total ion chromatogram from GC/MS analysis of an aromatic fraction and structures for selected PAHs (sample: 3817.5 m; Lower Jurassic).
1724 C. Jiang et al.
Fig. 3. Relative distribution of unsubstituted PAHs for the Upper Triassic to Middle Jurassic sediments from the Delambre-1 well (refer to Fig. 2 for name abbreviations).
PAHs and palaeoclimate 1725
M. Jurassic M. Jurassic M. Jurassic M. Jurassic M. Jurassic M. Jurassic M. Jurassic M. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic E. Jurassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic L. Triassic
2557.5 2632.5 2752.5 2827.5 2962.5 3052.5 3142.5 3277.5 3367.5 3457.5 3547.5 3637.5 3727.5 3817.5 3907.5 4042.5 4127.5 4222.5 4312.5 4447.5 4537.5 4627.5 4717.5 4807.5 4897.5 4987.5 5077.5 5212.5 5302.5 5392.5 5475.5
24.08 (0.125) 11.77 9.95 16.67 10.55 6.81 (0.068) 5.58 12.87 36.19 25.13 (0.515) 24.49 20.52 15.31 14.49 (0.519) 14.03 23.54 22.32 (0.538) 28.61 33.86 (0.579) 42.68 46.93 50.66 44.89 38.37 (1.342) 39.98 40.79 45.01 35.00 (0.534) 25.77 32.55 28.75 (0.493)
P m/z 178
9.68 (0.050) 1.57 1.11 8.42 1.48 0.99 (0.010) 1.33 2.77 15.52 7.50 (0.154) 7.30 4.10 3.58 3.26 (0.117) 2.81 5.80 7.78 (0.187) 5.86 7.34 (0.126) 7.68 8.15 9.10 8.21 6.29 (0.220) 6.95 12.99 13.36 5.51 (0.084) 6.18 5.32 3.56 (0.061)
Fla m/z 202
15.40 (0.080) 2.61 1.82 7.55 1.84 2.64 (0.026) 3.34 6.20 21.99 17.35 (0.355) 15.16 8.99 8.04 7.65 (0.274) 5.64 9.45 9.59 (0.231) 8.87 10.83 (0.185) 9.55 12.57 13.91 15.13 11.34 (0.397) 12.29 15.43 16.57 10.61 (0.162) 7.37 7.62 6.11 (0.105)
Pyr m/z 202 3.96 (0.030) 0.71 0.41 2.61 0.34 1.06 (0.014) 1.52 1.76 9.11 5.05 (0.112) 5.61 3.05 2.82 2.82 (0.136) 2.12 4.53 4.25 (0.119) 3.23 4.81 (0.087) 4.99 6.31 5.97 6.07 5.06 (0.224) 5.61 6.41 6.50 4.58 (0.068) 3.70 3.40 2.84 (0.052)
BaAn m/z 228 4.83 (0.037) 1.95 0.69 3.88 0.65 1.14 (0.015) 1.19 2.09 9.14 6.03 (0.134) 7.03 3.39 2.28 2.11 (0.102) 2.40 3.71 4.38 (0.122) 3.79 5.56 (0.101) 6.51 8.61 9.78 8.85 8.84 (0.391) 10.13 8.74 10.43 8.86 (0.131) 6.39 8.03 7.41 (0.135)
Chry + Tpn, m/z 228
BePy m/z 252
BaPy m/z 252
Pery m/z 252
InPy m/z 276
BPery m/z 276
2.38 (0.035) 1.93 (0.028) 1.87 (0.027) 1.03 (0.015) 0.41 (0.006) 2.45 (0.036) 1.63 1.06 0.47 1.34 0.68 2.54 0.53 0.58 0.54 1.92 0.20 2.75 2.83 1.71 1.44 2.34 0.74 2.84 0.47 0.51 0.38 0.92 0.12 1.88 3.52 (0.074) 2.51 (0.052) 2.49 (0.052) 11.69 (0.244) 2.44 (0.051) 11.76 (0.246) 2.32 2.09 2.13 6.30 0.57 6.16 1.93 2.93 2.42 12.15 0.51 9.34 11.06 9.87 12.19 28.29 2.61 16.60 5.50 (0.227) 7.16 (0.295) 8.06 (0.332) 16.23 (0.669) 0.96 (0.039) 9.18 (0.378) 10.90 6.86 8.87 19.10 2.71 11.26 1.69 2.34 4.02 5.11 0.16 2.44 1.35 1.51 2.96 3.91 0.20 2.83 1.32 (0.130) 1.56 (0.153) 2.68 (0.263) 3.25 (0.319) 0.14 (0.014) 2.83 (0.278) 1.65 1.78 2.07 2.18 0.44 4.04 3.71 3.42 4.62 2.60 0.43 4.75 3.91 (0.319) 3.82 (0.312) 4.07 (0.332) 1.97 (0.161) 0.61 (0.050) 6.45 (0.526) 1.45 2.92 3.55 1.20 0.10 3.80 5.00 (0.175) 7.40 (0.259) 6.30 (0.220) 2.92 (0.102) 0.94 (0.033) 10.26 (0.359) 6.01 9.06 6.40 1.83 1.00 9.22 7.98 13.02 8.70 2.34 1.33 11.41 4.54 12.01 8.07 1.30 0.39 8.02 5.69 11.35 6.47 1.48 0.90 9.15 4.71 (0.404) 12.00 (1.031) 5.56 (0.478) 0.69 (0.059) 0.47 (0.040) 7.16 (0.615) 7.96 13.53 5.90 0.84 1.18 8.74 4.29 8.57 5.66 0.82 0.46 5.83 5.55 11.97 6.10 1.01 0.83 8.67 5.13 (0.084) 11.27 (0.185) 5.27 (0.086) 0.61 (0.010) 0.68 (0.011) 8.24 (0.135) 5.14 6.15 3.29 0.54 1.05 4.05 2.25 5.85 3.23 0.19 0.22 3.13 2.86 (0.107) 6.99 (0.263) 2.93 (0.110) 0.21 (0.008) 0.34 (0.013) 4.80 (0.180)
B¯as m/z 252
Table 1. Relative abundances* of individual PAHs and carbon isotope composition for cadalene for Delambre-1 sequence
Refer to Fig. 2 for abbreviations for compound names. *Relative to 1367-TeMN; Values in ( ) are absolute quantity in ppm of sediments; N.A.: not available.
Age
Depth (m) 1.38 2.56 1.45 2.31 1.70 1.45 2.14 1.69 6.66 12.54 15.80 13.24 6.27 2.29 1.26 0.75 0.69 1.00 0.93 0.45 0.45 0.67 0.44 0.31 0.40 0.39 0.56 0.28 0.19 0.54 0.59
1.23 0.76 1.16 0.85 0.91 1.54 2.43 1.73 3.81 5.02 4.48 4.63 7.19 6.86 5.56 3.01 2.73 2.87 2.67 1.80 1.96 1.38 1.29 0.59 0.58 0.49 0.70 0.38 0.18 0.30 0.35
0.70 0.33 0.42 0.71 0.38 0.27 0.80 0.54 3.32 2.99 1.43 2.09 3.93 2.96 1.68 0.74 0.62 1.03 1.18 0.42 0.35 0.55 0.24 0.11 0.17 0.09 0.14 0.05 0.01 0.05 0.04
N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. ÿ25.48 N.A. ÿ24.88 ÿ26.11 ÿ26.64 ÿ25.68 ÿ23.78 ÿ24.68 N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A. N.A.
Retene Cadal Simone Cadal d13 C m/z 219 m/z 183 m/z 237 (-)
1726 C. Jiang et al.
PAHs and palaeoclimate
showed that 1367-TeMN is poorly correlated with land-plant related markers, implying a dierent source (van Aarssen et al., 1996). Relative abundances of selected PAHs are shown in Table 1. Among these samples, 9 representative samples were also chosen for absolute quanti®cation (Table 1) and PAH recovery estimation. Recoveries for the 5 internal standards were 70±90% for naphthalene-d8, 84±96% for acenaphthene-d10, 85± 95% for phenanthrene-d10, 85±98% for chrysened12 and 70±90% for perylene-d12. Based on the assumption that deuterated and non-deuterated PAHs have similar absorption/desorption behaviour between rock and solvent, the recoveries of individual PAHs from the rock are also in this range. PAH distributions An examination of the relative distribution of r3-ring unsubstituted PAHs in Delambre-1 samples via GC/MS analyses shows that dierent PAHs predominate in dierent depth intervals and a general similarity exists within each particular interval. Shown in Fig. 3 are the representative relative distributions of these PAHs for dierent depth intervals. In Upper Triassic samples (5475.5 to 4312.5 m), phenanthrene is the predominant PAH. Benzo[e]pyrene, pyrene and benzo[ghi]perylene are the next most prominent. Perylene, indeno[123cd]pyrene and coronene are minor components. Entering the Jurassic period, perylene and benzo[ghi]perylene become more and more abundant relative to phenanthrene until about 3000 m. In the interval 4222.5 to 3457.5 m, there is also an enhanced level of other PAHs relative to phenanthrene. Perylene and benzo[ghi]perylene predominate over phenanthrene and other unsubstituted PAHs in samples over the 3367.5 to 3052.5 m interval. Above 3000 m phenanthrene takes over the major component. Figure 4 and Table 1 show that the presence of ¯uoranthene, pyrene, benzo[a]anthracene, benzo¯uoranthenes, benzo[e]pyrene and benzo[a]pyrene change synchronously with depth and therefore appear to be related to one another, implying a similar source. They exhibit high relative abundances in the Upper Triassic and late Lower Jurassic sediments. Phenanthrene and chrysene also demonstrate this distribution pattern. There are some PAHs which behave dierently to those mentioned above in terms of changes in their relative concentrations with depth. Perylene is one of them. It remains low in Upper Triassic (ratio over 1367-TeMN being 0.20±2.9 for the 5475.5 to 4312.5 m interval) and early Lower Jurassic (1.20± 5.11 for the 4222.5 to 3637.5 m interval) sediments. Its relative concentration increases abruptly to 6.30±28.29 during the 3547.5 to 3052.5 m interval. It then decreases to a low level (0.92±1.92) for the above succession. Retene, cadalene and simonellite
1727
also show dierent distribution patterns to the unsubstituted PAHs. Only traces of retene exist in the sediments of 5475.5 to 4042.5 m (Upper Triassic to early Lower Jurassic) and 3277.5 to 2557.5 m (Middle Jurassic) sections; however, it becomes so abundant in the sedimentary samples of late Lower Jurassic section (3907.5 to 3367.5 m) that it is one of the most intense peaks on the TIC of aromatic fractions of 3457.5 and 3547.5 m. Cadalene remains at low abundance in the bottom samples (5475.5 to 4807.5 m), but it becomes more abundant upward and maximises around 3727.5 m, where it can be readily identi®ed from the TIC (Fig. 2). It then decreases to a low level for the rest of the sequence but is still more abundant than in the bottom section (5475.5 to 4807.5 m). Simonellite follows the distribution trend of cadalene for the whole sequence, but its relative concentration peaks at dierent depths to cadalene (Table 1 and Fig. 6). It seems from Fig. 3 and Table 1 that the distribution pattern of benzo[ghi]perylene is the combination of those of perylene and benzo[e]pyrene. The variation of its abundance follows that of benzo[e]pyrene for the Upper Triassic section when benzo[e]pyrene and other unsubstituted PAHs are abundant. In the 3547.5 to 3052.5 m interval where perylene reaches its maximum, benzo[ghi]perylene also maximises and its change is closely related to that of perylene. Coronene also demonstrates a similar pattern of abundance change throughout the sequence. Sources of PAHs in the sediments Combustion-derived PAHs. It is evident that unsubstituted PAHs with a well-established combustion source (e.g. pyrene, ¯uoranthene, benzo[a]anthracene, benzo¯uoranthenes, benzopyrenes and indeno[cd]pyrene) in modern geological settings are also mainly combustion-derived in the Upper Triassic to Middle Jurassic sediments of the Northern Carnarvon Basin. Their similar relative abundance vs depth pro®les (Fig. 4 and Table 1) suggest a common source. Also, the similarity with the distribution reported for combustion-derived PAHs from the Upper Jurassic sediments from the Korean Bay Basin (Killops and Massoud, 1992) is apparent from Fig. 5. A palynological study (Hos, 1981) has shown that there is abundant carbonised wood in the Upper Triassic sediments but a dearth of palynomorphs. This is a supporting evidence for the occurrence of extensive combustion during the Late Triassic in the study area, accounting for the presence of combustion-derived PAHs. Phenanthrene and chrysene may have a combustion origin but are also likely to be formed during diagenesis from biological precursors (Killops and Massoud, 1992; Tan et al., 1996). Consequently, phenanthrene and chrysene plus triphe-
Fig. 4. Depth pro®les of the abundances of selected PAHs relative to 1367-TeMN for Delambre-1 well (refer to Fig. 2 for name abbreviations).
1728 C. Jiang et al.
PAHs and palaeoclimate
1729
Fig. 5. Distributions of unsubstituted PAHs (m/z 178 + 202 + 228 + 252 + 276 + 300) for (A) recent sediments and U. Jurassic sediments, Korean Bay Basin (Killops and Massoud, 1992) and (B) U. Triassic to M. Jurassic sediments of this study (refer to Fig. 2 for name abbreviations).
nylene have not been used in this study as indicators for combustion. As in recent sediments where the distribution of combustion-derived PAHs can be dominated by ¯uoranthene and pyrene (Killops and Massoud, 1992; Wilcock and Northcott, 1995) as well as benzo¯uoranthenes (Fernandez et al., 1996), the dominant pyrolytic PAH in the distribution of combustion-derived products from the Ancient sediments also varies. In addition to ¯uoranthene, pyrene and benzo¯uoranthenes, benzo[e]pyrene is the major component in some samples (Figs 3 and 5). Type of combustion materials, combustion temperature and post-depositional processes account for these variations in both cases.
Among the combustion-derived PAHs, benzo[e]pyrene may be the best representative of the original combustion products. The original distribution of combustion-derived PAHs may be modi®ed by subsequent sedimentary alkylation procedures (Alexander et al., 1995; Smith et al., 1995). The most susceptible compounds will therefore be depleted by such processes. Examination of the proportions of alkylated and unsubstituted PAHs in the samples showed that benzo¯uoranthenes and benzopyrenes are relatively much less susceptible to these processes. Studies by Stein (1978), Stein and Fahr (1985) and Sullivan et al. (1989) indicate that benzo[e]pyrene is the most stable PAH among the 5-ring C20H12 PAHs. So benzo[e]pyrene might be the least susceptible to post-depositional modi®-
1730
C. Jiang et al.
Fig. 6. Combined geochemical record and geological information for the study area (*: ratios over 1367-TeMN; **: palaeoclimatic information from Parrish et al., 1996; palaeolatitude data form Boote and Kirk, 1989; Williamson et al., 1989; Baillie et al., 1994; Exon and von Rad, 1994).
cations. For this reason, we here take benzo[e]pyrene as the representative of combustion-derived PAHs for the purpose of measuring the input from forest ®res or peat ®res. Combustion-derived PAHs arise from combustion of vegetation. Two sources for the PAHs in ancient sediments are expected to be forest ®res and peat ®res. Forest ®res have been reported as a major source of PAHs in recent sediments (Youngblood and Blumer, 1975). Elevated concentrations of aromatic hydrocarbons have been observed for peat samples which experienced ®re events (Rollins et al., 1993). Both types of combustions take place in terrestrial environments. The PAHs produced due to incomplete combustion can be absorbed and stabilised by the particulates released from combustion (Blumer and Youngblood, 1975; Blumer, 1976) or the residuals of combustion. Particles released from ®res can be both airborne and waterborne, and transported for long distances to a depositional site in lacustrine or marine environments. In the case of Northern Carnarvon Basin, both forest ®res and peat/swamp ®res could have contributed to the high abundances of combustion-derived PAHs. The occurrence of forest ®res is supported by palynological study showing that carbonised woody materials are very abundant and palynomorphs are scarce in the sedimentary interval with high abundances of combustion-derived PAHs (Upper Triassic)(Hos, 1981). A possible contribution of peat/swamp ®res to the abundant com-
bustion-derived PAHs in the Upper Triassic sediments can not be disregarded. Firstly, the ¯uvio-deltaic depositional environment of the study area during the Late Triassic was an ideal site for the formation of swamps and peat bogs which can catch ®re easily under suitable climatic conditions (Cope, 1981; Rollins et al., 1993). Secondly, GC/ MS analyses of saturated biomarkers in these samples showed that isopimarane is the major diterpane. This is a feature of the Eocene Fitzgerald River lignite from S.W. Western Australia and Miocene Yallourn lignite from Gippsland, Australia (Noble, 1986). Although aeolian transport can't be discounted, ¯uvial transport of these PAHs by combustion residuals probably played a more important role since the relative concentrations of these PAHs decrease quickly with distance from shoreline as shown by two other wells (i.e. Brigadier-1 and Gandara-1). The presence of combustion-derived PAHs will re¯ect the conditions of the terrestrial hinterland. For example, the abundances of various PAHs in ancient sediments should depend on the frequency and extent of ®res. Two speci®c factors are expected to be involved: the availability of fuel and the weather condition. Two types of combustible fuels have been available through the geological time period of interest in this study: land plants and fossil organic materials like peat. Their availability is controlled by the climatic conditions. Most plants grow rapidly under warm and humid conditions and arid climates constitute a water stress on the
PAHs and palaeoclimate
plants. Extremely cold or hot conditions could disturb the water and nutrient transport as well as the biochemical reactions in the plants, hence reducing growth rates. In a seasonal climate, dry times would be favourable for the occurrence of combustion. It can be seen that the presence of these PAHs in the ancient sediments indicates not only the input of land sediments into the environment but also a favourable regional palaeoclimate, especially a humid and seasonal climate. PAH biomarkers for land-plants. Cadalene, retene and simonellite are well recognised land plant markers. Their occurrences in the sequence do not follow those of combustion-derived PAHs and they vary with depth independently of one another (Fig. 6). This implies that they are derived from dierent plant types and hence their presences in the sediments represent the inputs of dierent land plants. Retene probably represent Conifer plants which were widespread in this region during the Aalenian, late Early Jurassic (depth interval of 3800 to 3353 m), spanning about 10 million years. Land plants containing cadalene and simonellite biological precursors appeared as early as the latest Triassic (around 4730 m) and reached their peak population at about 3730 m (the Toarcian). After experiencing a decrease in population, they peaked again at about 3360±3460 m (the Aalenian) and then diminished abruptly. The abrupt decreases in the population of plants represented by retene, cadalene and simonellite all occurred at about 3353 m which is the boundary of the Early Jurassic and Middle Jurassic. PAHs of other sources. Compared with the Upper Jurassic sediments of the Korean Bay Basin (Killops and Massoud, 1992), sediments from the Northern Carnarvon Basin have more abundant perylene, especially for the Jurassic sediments (Fig. 5). Perylene has long been recognised as a diagenetic/biogenic marker based on the facts that its occurrence in Recent sediments does not follow those of combustion-derived PAHs and that its abundance relative to combustion-derived PAHs increases with burial depth in modern depositional setting (Gschwend and Hites, 1981; Wilcock and Northcott, 1995; Fernandez et al., 1996). In the Delambre-1 sedimentary sequence (Table 1), the occurrence of perylene also does not follow those of combustion-derived PAHs, implying a dierent origin, possibly a diagenetic one. Benzo[ghi]perylene has been regarded as combustion-derived PAH (Blumer and Youngblood, 1975; Killops and Massoud, 1992; Leeming and Maher, 1992; Simoneit and Fetzer, 1996). In the Delambre1 sequence, its distribution correlates with other combustion-derived PAHs when perylene is in low abundance and correlates with perylene when perylene becomes abundant in the sediments. It seems that there are two origins for benzo[ghi]perylene
1731
depending on the source of sediments and depositional environment. This also applies to coronene. Detailed discussion of the sources and relationship of perylene, benzo[ghi]perylene and coronene will be given elsewhere. PAHs in ancient sediments and palaeoclimate Figure 6 shows the pro®les of the abundances of aromatic higher plant markers, namely retene, cadalene and simonellite, as well as combustion markers represented by benzo[e]pyrene relative to 1367TeMN, for the Upper Triassic to Middle Jurassic sequence of Delambre-1 well. Shown together with these geochemical data in Fig. 6 are geological information including palaeoclimate information from Parrish et al. (1996), palaeolatitude data (Boote and Kirk, 1989; Williamson et al., 1989; Baillie et al., 1994; Exon and von Rad, 1994) and sedimentation rates. Based on the distribution patterns of aromatic plant markers and combustion markers, six dierent sedimentary intervals, e.g. A, B, C, D, E and F from bottom to top, can be identi®ed and related to dierent palaeoclimatic conditions. Interval A. This interval is from 5500 to 4604 m, spanning the Carnian and Norian of the Late Triassic. Very abundant combustion-derived PAHs occur in this interval of sediments, suggesting that frequent periodic forest ®res and/or swamp/peat ®res took place. This clearly shows that the climate during this time interval was favourable for plant growth on land and swamp/peat formation on the delta plains and that a dry season suitable for combustion existed. This inference is supported by palaeoclimate data. Condition in this region was suggested to be warm to hot, humid and seasonal (Parrish et al., 1996). Since the study area was positioned at 50±558S latitude (Baillie et al., 1994; Exon and von Rad, 1994), a cool±warm condition would be more likely. Rapid deposition of terrestrial sediments (062 m/ma) via a ¯uvio-deltaic system support the claim of a humid climate. Although there is an obvious increase in the relative abundances of cadalene and simonellite from 4717.5 m upward, the aromatic plant markers are generally low in this interval. This might suggest that the origin of the vegetation for combustion may have been peat rather than forests. Examination of the saturated plant-derived biomarkers revealed that isopimarane was the major component and this compound has been observed in peat samples (Noble, 1986). Another explanation for the dearth of aromatic plant markers in this interval is: the higher plants growing in the region during this period did not contain the biological precursors of retene, cadalene and simonellite and their speci®c aromatic biomarkers have not been identi®ed at present time, or alternatively, the biological precursors of these compounds had been
1732
C. Jiang et al.
destroyed during combustion due to high thermal stress (Ramdahl, 1983). Interval B. This sedimentary interval is from 4604 to 4287 m (the Rhaetian, Late Triassic). The abundances of combustion markers started decreasing steadily and reached low levels by the end of the Triassic, implying a decreasing frequency of forest ®res and/or swamp/peat ®res. This change correlates well with the trend of climate becoming less humid (Fig. 6). At this time, the Northwest Shelf of Western Australia moved northwards to a position of 25 to 308S latitude (Exon and von Rad, 1994). Climate in this zone was more hot and arid than previously. Although the seasonality still existed for the occurrence of ®res, less water precipitation constituted water stress for the plants and reduced the formation of swamp/peat, resulting in less fuels for combustion. Figure 6 shows continuing increases of cadalene and simonellite despite that all these aromatic plant markers are remaining at a low level. This suggests that plants yielding cadalene and simonellite precursors are more tolerant of water stress and can survive a relatively arid climate. Interval C. Interval C ranges from 4287 to 3964 m which was deposited during the earliest Jurassic. Combustion markers are at low levels, indicating sparse combustion in the terrestrial environment. This coincides with the arid climate during this time (Parrish et al., 1996) which is also supported by the very low sedimentation rate (014 m/ma). The palaeolatitude position of the area was between 25 and 308S, which is in the global arid zone (Trewartha, 1968; Frakes, 1979). Under this climatic condition, few plants can grow and little swamp/peat can form due to the lack of water precipitation, resulting in low amounts of combustion products in the sediments. Aromatic plant markers remain similar to the end of previous period, providing further evidence that land plants represented by cadalene and simonellite can survive an arid climate. It has been proposed that carbon isotope composition of plant materials become heavier with increasing aridity of the growing environment (Yakir et al., 1994; Lipp et al., 1996). Carbon isotope analyses for speci®c PAHs show that the isotope composition of cadalene (Table 1) is heavier for samples from this interval (ÿ23.78-, ÿ24.68-) than from the interval above (ÿ25.48-; ÿ24.88-; ÿ26.11-; ÿ26.64- for interval D), suggesting that this section was deposited under a more arid climatic condition than the sections above. This is consistent with the palaeoclimatological study by Parrish et al. (1996) (Fig. 6). A palynological study shows that sediments of this interval are very abundant with the Classopollis torosus (Hos, 1981). This is the pollen of the conifer family Cheirolepids, the members of which are tolerant of drought (Parrish et al., 1996). Whether or
not cadalene and simonellite can be used as biomarkers for the plants of this conifer family needs to be further investigated. Interval D. This interval ranges from about 3964 to 3600 m. Aromatic plant markers increase in relative abundance rapidly in the sediments of this section. Early part of this time interval mainly saw the expansion of plants containing cadalene and simonellite precursors. Later on, the conifer plants yielding retene became abundant rapidly while the abundances of the other two plant types decreased. Nevertheless, the population of these land plants was expanded rapidly at this time. This change in the plant habitat strongly suggests that the climate was becoming more favourable to the growth of plants, which is very likely a change from arid in the previous period to more humid. This inference ®ts into the climate changing trend shown by palaeoclimatological study (Parrish et al., 1996) although the climatic conditions were not clearly indicated (Fig. 6). The low abundances of combustion markers in the sediments may suggest the lack of a seasonality during this time, which was also not clearly shown by palaeoclimatological study by Parrish et al. (1996) (Fig. 6). Interval E. This is an interval (3600 to 3353 m) with high relative abundances of both aromatic plant biomarkers and combustion markers in the sediments, signifying that land plants were widespread and the occurrence of forest ®res was frequent during this time interval. This clearly indicates a climatic condition with sucient water precipitation and seasonality, which is supported by palaeoclimatological study by Parrish et al. (1996) (Fig. 6). The high sedimentation rates (064 m/ma) also show plenty of water precipitation in the region. It is noteworthy that conifer plants containing retene precursors became widespread during this period. They took over the prevalence of cadalene and simonellite plants in the early part of this period but gave way to them thereafter. It seems that plants represented by cadalene and simonellite contributed more to the combustion than those represented by retene since the changing pattern of combustion markers is closer to cadalene and simonellite than retene. Interval F. Interval F is from the depth of 3353 m upward. It was deposited during the Middle Jurassic times. Generally speaking, both combustion markers and aromatic plant markers come to low levels in the sediments of this section despite some ¯uctuations. The change in the input of these terrestrial markers is abrupt around the boundary between the Lower Jurassic and the Middle Jurassic. There was not much change in climatic conditions as shown by palaeoclimatological study, remaining warm±hot, humid and seasonal (Parrish et al., 1996). High rate sedimentation (070 m/ma) of non-marine/¯uviatile deposit provides evidence
PAHs and palaeoclimate
for high water precipitation in the terrestrial environment. The palaeolatitude position of the area was probably between 30 and 408S, a small southward move. It seems that these geological conditions should have resulted in high rather than low concentrations of both aromatic plant markers and combustion markers in the sediments. One explanation for this phenomenon is related to palaeoclimatic conditions. The population of the conifer plants represented by retene decreases rapidly from a depth of about 3630 m upward. At the same time, the drought-resistant plants containing cadalene and simonellite precursors became more abundant for a short time and then diminished rapidly when entering the Middle Jurassic times. This may indicate that the climate was becoming unfavourable to the growth of land plants by the end of the Early Jurassic, even though abundant water must have been available considering the high sedimentation rates. We suggest that this may have resulted from very heavy but irregular rainfall, a situation common in tropical and subtropical cyclonic zones. The latitude positions of climatic zones change with geological times (Perlmutter and Mattthews, 1990). For example, the tropical zone can shift from 15 to 358 latitude. Although today's tropical cyclones in Northwestern Australia mainly develop between 18±228S, the study area was probably located in the tropical cyclone zone during the late Early Jurassic and Middle Jurassic. As can be expected from today's climatic conditions in this area, the water precipitation in the region could have been extremely great in total, due to very high and irregular rainfall brought by cyclones, but the climatic conditions were still unsuitable for plant growth since there was little rainfall during the periods between each cyclones. Also, top soils suitable for plant growth could have been easily removed and transported by wind and water to coastal environment, resulting in high rates of sedimentation. CONCLUSIONS
Combustion-derived PAHs have been analysed in the Upper Triassic to Middle Jurassic sediments from the Delambre-1 well, Northern Carnarvon Basin, Australia. Their occurrences in the sediments has been related to the ancient vegetation ®res which, in turn, were related to palaeoclimatic conditions. These PAHs are abundant in the sediments which were deposited under warm±hot and humid climatic conditions with seasonality. Aromatic plant markers retene, cadalene and simonellite have also been investigated and related to the change of climatic conditions. They vary independently throughout the sedimentary sequence and are thought to represent dierent plant types which ¯ourished and diminished at dierent times.
1733
Conifer plants represented by retene ¯ourished for about 10 million years in the late Early Jurassic which was a time of warm and humid climatic condition. The population of plants represented by cadalene and simonellite became abundant in the latest Triassic and maximised in the Early Jurassic. The relatively high abundances of cadalene and simonellite in the early Lower Jurassic sediments suggests that these plants can survive arid climates. A combination of the combustion markers and aromatic plant markers can be used to indicate climatic conditions. High abundances of both combustion markers and aromatic plant markers indicate a humid and seasonal climate. A humid but non-seasonal climate is re¯ected by high abundances of aromatic plant markers but low amounts of combustion markers in the sediments. Low abundances of both plant and combustion markers in sediments shows either an arid climate when sedimentation rates are also low, or an extreme climate with high and irregular rainfall when sedimentation rates are high. AcknowledgementsÐAssistance and comments from Mr G. Chidlow, Dr B. G. K. van Aarssen and other sta and Ph.D. students at PEOG, Curtin University of Technology are acknowledged. C. J. thanks the University and Australian Petroleum CRC for ®nancial support of his Ph.D. study. This paper bene®tted from the thorough and critical reviews by Dr N. Jiang and Dr H. Budzinski.
REFERENCES
van Aarssen, B. G. K., Cox, H. C., Hoogendoorn, P. and de Leeuw, J. W. (1990) A cadinene biopolymer present in fossil and extant dammar resins as a source for cadinanes and bicadinanes in crude oils from South East Asia. Geochimica et Cosmochimica Acta 54, 3021±3031. van Aarssen, B. G. K., Hessels, J. K. C., Abbink, O. A. and de Leeuw, J. W. (1992) The occurrence of polycyclic sesqui-, tri- and oligoterpenoids derived from a resinous polymeric cadinene in crude oils from South East Asia. Geochimica et Cosmochimica Acta 56, 1231± 1246. van Aarssen, B. G. K., Alexander, R. and Kagi, R. I. (1996) The origin of Barrow Sub-basin crude oils: A geochemical correlation using land-plant biomarkers. The APPEA Journal 36, 465±476. Alexander, R., Larcher, A. V., Kagi, R. I. and Price, P. L. (1992) An oil-source correlation study using age-speci®c plant-derived aromatic biomarkers. In Biological Markers in Sediments and Petroleum, eds. J. M. Moldowan, P. Albrecht and R. P. Philp, pp. 201±221. Prentice-Hall, Englewood Clis, N.J. Alexander, R., Bastow, T. P., Fisher, S. and Kagi, R. I. (1995) Geosynthesis of organic compounds: II. Methylation of phenanthrene and alkylphenanthrenes. Geochimica et Cosmochimica Acta 59, 4259±4266. Apthorpe, M. (1994) Towards an Early to Middle Jurassic palaeogeography for the North West Shelf: A marine perspective. In The Sedimentary Basins of Western Australia, eds. G. and P. R. Purcell, pp. 201±210. Proceedings of the Western Australian Basins Symposium, Perth, Western Australia. Baillie, P. W., Powell, C. McA., Li, Z. X. and Ryall, A. M. (1994) The tectonic frame work of Western
1734
C. Jiang et al.
Australia's Neoproterozoic to recent sedimentary basins. In The Sedimentary Basins of Western Australia, eds. P. G. and P. R. Purcell, pp. 45±61. Proceedings of the Western Australian Basins Symposium, Perth, Western Australia. Blevin, J. E., Stephenson, A. E. and West, B. G. (1994) Mesozoic structural development of the Beagle Subbasin: Implications for the petroleum potential of the Northern Carnarvon Basin. In The Sedimentary Basins of Western Australia, eds. P. G. and P. R. Purcell, pp. 479±496. Proceedings of the West Australian Basins Symposium, Perth, Western Australia. Blumer, M. and Youngblood, W. W. (1975) Polycyclic aromatic hydrocarbons in soils and recent sediments. Science 188, 53±55. Blumer, M. (1976) Polycyclic aromatic compounds in nature. Scienti®c America 234, 35±45. Boote, D. R. D. and Kirk, R. B. (1989) Depositional wedge cycles on evolving plate margin, Western and North Western Australia. AAPG Bulletin 73, 216±263. Bradshaw, M. T., Yeates, A. N., Beynon, R. M., Brakel, A. T., Langford, R. P., Totterdell, J. and Yeung, M. (1988) Palaeogeographic evolution of the North West Shelf region. In The North West Shelf, Australia, eds. P. G. and P. R. Purcell, pp. 29±54. Proceedings of Petroleum Exploration Society Australia Symposium, Perth, 1994. Brown, G. and Maher, W. (1992) The occurrence, distribution and sources of polycyclic aromatic hydrocarbons in the sediments of the George River Estuary, Australia. Organic Geochemistry 18, 657±668. Cope, M. J. (1981) Products of natural burning as a component of the dispersed organic matter of sedimentary rocks. In Organic Maturation Studies and Fossil Fuel Exploration, eds. J. Brooks, pp. 89±109. Academic Press. Exon, N. F. and von Rad, U. (1994) The Mesozoic and Cainozoic sequences of the Northwest Australian Margin, as revealed by ODP Core Drilling and related studies. In The Sedimentary Basins of Western Australia, eds. P. G. and P. R. Purcell, pp. 181±199. Proceedings of the Western Australian Basins Symposium, Perth, Western Australia. Fernandez, P., Vilanova, R. and Grimalt, J. O. (1996) PAH distributions in sediments from high mountain lakes. Polycyclic Aromatic Compounds 9, 121±128. Frakes, L. A. (1979) Climate Throughout Geologic Time. Elsevier, Amsterdam, p. 16. Giger, W. and Schaner, C. (1978) Determination of polycyclic aromatic hydrocarbons in the environment by glass capillary gas chromatography. Analytical Chemistry 50, 243±249. Gijzen, M., Lewinsohn, E., Savage, T. J. and Croteau, R. B. (1992) Conifer monoterpenes, Biochemistry and bark beetle chemical ecology. In Bioactive Volatile Compounds From Plants, eds. R. Teranishi, R. G. Buttery and H. Sugisawa, ACS Syposium Series 525, pp. 8±22. American Chemical Society, Washington, D.C. Gschwend, P. M. and Hites, R. A. (1981) Fluxes of polycyclic aromatic hydrocarbons to marine and lacustrine sediments in the Northeastern United States. Geochimica et Cosmochimica Acta 45, 2359±2367. Hites, R. A., La¯amme, R. E. and Farrington, J. W. (1977) Sedimentary polycyclic aromatic hydrocarbons: the historical records. Science 198, 829±831. Hites, R. A., La¯amme, R. E., Windsor, J. G. Jr., Farrington, J. W. and Deuser, W. G. (1980) Polycyclic aromatic hydrocarbons in an anoxic sediment core from the Pettaquamscutt River (Rhode Island, U.S.A.). Geochimica et Cosmochimica Acta 44, 873±878.
Hocking, R. M. (1988) Regional geology of the northern Carnarvon Basin. In The North West Shelf, Australia, eds. P. G. and P. R. Purcell, pp. 97±114. Proceedings of Petroleum Exploration Society of Australia Symposium, Perth. Hos, D. P. C. (1981) Palynological report on Woodside Petroleum Development PTY LTD Delambre-1 Well. Open Files of Western Australian Department of Mining. Jiang, N., Tong, Z., Ren, D., Song, F., Yang, D., Zhu, C. and Gao, Y. (1995) The discovery of retene in Precambrian and Lower Paleozoic marine formations. Chinese Journal of Geochemistry 14, 41±51. Kawka, O. E. and Simoneit, B. R. T. (1990) Polycyclic aromatic hydrocarbons in hydrothermal petroleums from Guaymas Basin spreading Centre. Applied Geochemistry 5, 17±27. Killops, S. D. and Massoud, M. S. (1992) Polycyclic aromatic hydrocarbons of pyrolytic origin in ancient sediments: evidence for Jurassic vegetation ®res. Organic Geochemistry 18, 1±7. Kruge, M. A., Stankiewicz, B. A., Crelling, J. C., Montanari, A. and Bensley, D. F. (1994) Fossil charcoal in Cretaceous±Tertiary boundary strata: Evidence for catastrophic ®restorm and megawave. Geochimica et Cosmochimica Acta 58, 1393±1397. La¯amme, R. E. and Hites, R. A. (1978) The global distribution of polycyclic aromatic hydrocarbons in recent sediments. Geochimica et Cosmochimica Acta 42, 289± 303. Leeming, R. and Maher, W. (1992) Sources of polycyclic aromatic hydrocarbons in Lake Burley Grin, Australia. Organic Geochemistry 18, 647±655. Lipp, J., Trimborn, P., Edwards, T., Waisel, Y. and Yakir, D. (1996) Climatic eects on the d13 C and d18 O of cellulose in the desert tree Tamarix jordanis. Geochimica et Cosmochimica Acta 60, 3305±3309. Murchison, D. G. and Raymond, A. C. (1989) Igneous activity and organic maturation in the Midland Valley of Scotland. International Journal of Coal Geology 14, 47± 82. Noble, R. (1986) A geochemical study of bicyclic alkanes and diterpenoid hydrocarbons in crude oils, sediments and coals. Ph.D. Thesis. Curtin University of Technology. Parrish, J. T., Bradshaw, M. T., Brakel, A. T., Mulholland, S. M., Totterdell, J. M. and Yeates, A. N. (1996) Palaeoclimatology of Australia during the Pangean Interval. Palaeoclimates 1, 241±281. Perlmutter, M. A. and Mattthews, M. D. (1990) Global cyclostratigraphy: A model. In Quantitative Dynamic Stratigraphy, eds. T. A. Cross, pp. 233±260. Prentice Hall, Englewood Clis, N.J. Radke, M. (1987) Organic geochemistry of aromatic hydrocarbons. In Advances in Petroleum Geochemistry, eds. J. Brooks and D. Welte, pp. 141±207. Academic Press, New York. Ramdahl, T. (1983) Retene: a molecular marker of wood combustion in ambient air. Nature 306, 580±582. Rollins, M. S., Cohen, A. D. and Durig, J. R. (1993) Eects of ®res on the chemical and petrographic composition of peat in the Snuggedy Swamp, South Carolina. International Journal of Coal Geology 22, 101±117. Simoneit, B. R. T. (1977) Diterpenoid compounds and other lipids in deep-sea sediments and their geochemical signi®cance. Geochimica et Cosmochimica Acta 41, 463± 476. Simoneit, B. R. T. and Lonsdale, P. F. (1982) Hydrothermal petroleum in mineralised mounds at the seabed of Guaymas Basin. Nature 295, 198±202. Simoneit, B. R. T. (1986) Cyclic terpenoids of the geosphere. In Biological Markers in the Sedimentary
PAHs and palaeoclimate Record, ed. R. B. Johns, pp. 43±82. Elsevier, Amsterdam. Simoneit, B. R. T. and Fetzer, J. C. (1996) High molecular weight polycyclic aromatic hydrocarbons in hydrothermal petroleums from the Gulf of California and Northeast Paci®c Ocean. Organic Geochemistry 24, 1065±1077. Smith, J. W., George, S. C. and Batts, B. D. (1995) The geosynthesis of alkylaromatics. Organic Geochemistry 23, 71±80. Stein, S. E. (1978) On high temperature chemical equilibria of polycyclic aromatic hydraocarbons. Journal of Phyysical Chemistry 82, 566±571. Stein, S. E. and Fahr, A. (1985) High temperature stability of hydrcarbons. Journal of Phyysical Chemistry 89, 3714±3725. Sullivan, R. F., Boduszynski, M. M. and Fetzer, J. C. (1989) Molecular transformations in hydrotreating and hydrocarcking. Energy and Fuels 3, 603±612. Tan, Y. L. and Heit, M. (1981) Biogenic and abiogenic polynuclear aromatic hydrocarbons in sediments from two remote Adirondack lakes. Geochimica et Cosmochimica Acta 45, 2267±2279. Tan, Y. L., Kong, A. and Monetti, M. (1996) Biogenic polycyclic aromatic hydrocarbons in an Alaskan arctic lake sediment. Polycyclic Aromatic Compounds 9, 185± 192. Trewartha, G. T. (1968) An Introduction To Climate. McGraw-Hill Book Company, New York, p. 257. Venkatesan, M. I. and Dahl, J. (1989) Organic geochemical evidence for global ®res at the Cretaceous/Tertiary boundary. Nature 338, 57±60.
1735
Wakeham, S. G., Schaner, C. and Giger, W. (1980a) Polycyclic aromatic hydrocarbons in recent lake sediments. I. Compounds having anthropogenic origins. Geochimica et Cosmochimica Acta 44, 403±413. Wakeham, S. G., Schaner, C. and Giger, W. (1980b) Polycyclic aromatic hydrocarbons in recent lake sediments. II. Compounds derived from biogenic precursors during early diagenesis. Geochimica et Cosmochimica Acta 44, 415±429. Wilcock, R. J. and Northcott, G. L. (1995) Polycyclic aromatic hydrocarbons in deep cores from Mangere Inlet, New Zealand. New Zealand Journal of Marine and Freshwater Research 29, 107±116. Williamson, P. E., Exon, N. F., Haq, B. U. and von Rad, U. (1989) A Northwest Shelf Triassic reef play: results from ODP Leg 122. The APEA Journal 29, 328±341. Wolbach, W. S., Lewis, R. S. and Anders, E. (1985) Cretaceous extinctions: Evidence for wild®res and search for meteoritic material. Science 230, 167±170. Wolbach, W. S., Gilmour, I., Anders, E., Orth, C. J. and Brooks, R. R. (1988) Global ®re at the Cretaceous± Tertiary boundary. Nature 334, 665±669. Yakir, D., Issar, A., Gat, J., Adar, E., Trimborn, P. and Lipp, J. (1994) 13 C and 18 O of wood from the Roman Siege Rampart in Masada, Israel (AD 70±73): Evidence for a less arid climate for the region. Geochimica et Cosmochimica Acta 58, 3535±3539. Youngblood, W. W. and Blumer, M. (1975) Polycyclic aromatic hydrocarbons in the environment: homologous series in soils and recent sediments. Geochimica et Cosmochimica Acta 39, 1303±1314.