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Identification and occurrence of dihydro-ar-curcumene in crude oils and sediments
Org. Geochem. Vol. 23, No. 3, pp. 197-203, 1995
Pergamon
0146-6380(94)00130-8
Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0146-6380/95 $9.50 + 0.00
Identification and occurrence of dihydro-ar-curcumene in crude oils and sediments LEROY ELLIS*t, RAJ K. SINGH, ROBERT ALEXANDER and ROBERT I. KAGI Australian Petroleum CRC at Centre for Petroleum and Environmental Organic Geochemistry, Curtin University of Technology, Box U!987 G.P.O. Perth, WA 6001, Australia (Received 23 June 1994; returned for revision 12 September 1994; accepted 21 December 1994)
Abstract--A suite of crude oils and sediments with a range of locations, source types, palaeoenvironments and ages has been analysed for dihydro-ar-curcumene. The concentrations of dihydro-ar-curcumene in 16 crude oils and sediments ranged from < 5 to 700 #g/g. Dihydro-ar-curcumene in sediments is suggested to be derived from sesquiterpenoids of the bisabolane skeletal type. The widespread occurrence of this type of sesquiterpenoid in terrestrial plants, and the association of this compound with biomarkers of higher plant origin in sediments, suggests that dihydro-ar-curcumene in sediments is derived primarily from higher plants. Key words--an~osperrns, biomarkers, conifers, dihydro-ar-curcumene, sesquiterpenoids in oils and sediments
derived from an extinct New Zealand species of Podocarpaceae. More recently, van Aarssen et al. (1991, 1992) reported this compound as a minor component in a crude oil and a dammar resin pyrolysate and suggested that it may have formed from polycadinanes by cracking processes. The transformation of natural products into saturated and aromatic hydrocarbon biomarkers in which the carbon skeleton of the natural product is retained is well-recognized (Tissot and Welte, 1984; Mackenzie, 1984; Radke, 1987). Natural products such as bisabolene (VI) might therefore be expected to give rise to a biomarker in the form of the aromatic hydrocarbon, dihydro-ar-curcumene (V), by commonly observed geochemical reactions. In this paper we report the identification, using an authentic refer-
INTRODUCTION
Monocyclic sesquiterpenoids with the bisabolane (I) (Fig. 1) carbon skeleton are common constituents of essential oils derived from the wood and resins of extant higher plants (Dev, 1989; Connolly and Hill, 1991). Within this group, aromatic compounds have also been reported. Examples include curcumene (II) isolated from turmeric (Simonsen, 1952) and sandalwood oil (Adams et al., 1975); ar-turmerone (Ill) (at-indicates a methyl group substituent on the aromatic ring) from the essential oils of Cureuma domestica and nuciferal (IV) obtained from the wood oil of the kaya tree (Dev, 1989; Connolly and Hill, 1991). Compounds with this carbon skeleton are, however, not confined to higher plants as they have been reported from Laurencia algae and from coelenterates (Scheuer, 1978a, b, 1983). Aromatic compounds with the bisabolane (I) carbon skeleton, and with saturated side chains, such as dihydro-ar-curcumene (V) have not been reported as natural products from terrestrial plants, however, there are several reports of this compound in fossil materials. These reports are based on tentative identifications made by interpreting mass spectral data obtained using G C - M S techniques. For example, Mills et al. (1984) suggested that it was a component in the ether-soluble fraction of Baltic amber, and Grimalt et al. (1989) identified it as a minor component in a fossil resin of Eocene age, *Present address: Argonne National Laboratory, Chemistry Division, 9700 S. Cass Avenue, Argonne IL 60439-4831, U.S.A. tTo whom all correspondence should be addressed.
(I)
(If)
(III)
(iv)
(v)
(vl)
Fig. 1. Molecular structures of some natural products structurally related to dihydro-ar-curcumene.
197
Leroy Ellis et al.
198
ence c o m p o u n d , o f d i h y d r o - a r - c u r c u m e n e (V) in s e d i m e n t a r y organic m a t t e r a n d its occurrence in crude oils a n d s e d i m e n t s which have an association with higher p l a n t material.
EXPERIMENTAL
Samples T h e locations o f the s a m p l e s a n d their ages, or in the case o f crude oils the p r o b a b l e ages o f their source rocks, are s h o w n in Table 1. H C H 34 w a s a lignite o b t a i n e d as a core f r o m a d e p t h o f 24.6 m. Loy Y a n g a n d Collie s a m p l e s were lignite a n d s u b - b i t u m i n o u s coals respectively a n d were o b t a i n e d f r o m open-pit mines. T h e SSB ( S o u t h S u m a t r a Basin) coal s a m p l e was o b t a i n e d as c u t t i n g s f r o m a p e t r o l e u m explor a t i o n well. T h e K e r o s e n e Shale was o b t a i n e d f r o m the G l e n Davis m i n e site a n d is primarily c o m p o s e d o f fossilized Botryococcus braunii (Metzger et al., 1991; D e r e n n e , 1989). P D 130A was p r o v i d e d as a d i a m o n d drill core f r o m the depth o f 317 m ( G S W A No. 72525A).
Sample preparation R o c k s a m p l e s were air dried a n d c r u s h e d to a fine p o w d e r using a T e m a mill, and extracted ultrasonically with d i c h l o r o m e t h a n e / m e t h a n o l (95:5). T h e solvent extract was recovered by filtration a n d the solvent was carefully distilled off to yield the soluble o r g a n i c m a t t e r (SOM).
Isolation of monoaromatic and branched and cyclic fractions C r u d e oil, or soluble organic m a t t e r extracts, were dissolved in h e x a n e a n d filtered t h r o u g h a s h o r t c o l u m n o f activated a l u m i n a to r e m o v e very polar
c o m p o u n d s . T h e filtrate was then separated into alkane a n d a r o m a t i c fractions using a M e r c k - L o b a r G r o b e A (240-10) L i c h r o p r e p Si 60, 40-63/~m c o l u m n a t t a c h e d to a W a t e r s Millipore Model 510 double piston p u m p . U s i n g a flow rate o f 2 m l m i n t o f n - h e x a n e , an alkane fraction was collected between elution times o f 8-12 min. T h e a r o m a t i c c o m p o n e n t s were t h e n eluted by reversing the direction of flow o f the solvent for a further 25 min. T h e alkane comp o n e n t s were detected using a W a t e r s Millipore Series R-400 Differential R e f r a c t o m e t e r a n d the a r o m a t i c c o m p o n e n t s were detected using a W a t e r s Associates Series 440 U V a b s o r b a n c e detector set at a wavelength o f 254 n m . T h e a r o m a t i c c o m p o n e n t s were t h e n further fractionated into m o n o a r o m a t i c , diaromatic a n d t r i a r o m a t i c b a n d s using a l u m i n a thin layer c h r o m a t o g r a p h y with n - h e x a n e as eluent. T h e m o n o a r o m a t i c fraction was collected by scraping b a n d s f r o m the plate a n d extracting the a l u m i n a with d i c h l o r o m e t h a n e . T h e alkane fraction collected f r o m M P L C was analysed by G C MS, t h e n further treated with Z S M - 5 m o l e c u l a r sieves to r e m o v e the n - a l k a n e , m e t h y l a l k a n e a n d alkylcyclohexane c o m p o n e n t s before analysis again by G C MS.
Analysis and quantification of dihydro-ar-curcumene b7 crude oils and sediment extracts In a typical separation, a crude oil or sediment extract (approx. 10 rag) was placed o n a small c o l u m n p a c k e d with silica gel a n d eluted with 7 m l d i c h l o r o m e t h a n e / p e n t a n e (1:9) which afforded a h y d r o c a r b o n fraction c o n t a i n i n g b o t h alkane a n d aromatic compounds. Q u a n t i t a t i v e analysis was carried out on the crude oil (as received) a n d s e d i m e n t extracts (weight stabilized S O M ) using external a n d n o r m a l i z a t i o n standards. External s t a n d a r d s with c o n c e n t r a t i o n s o f 5,
Table l, Locations, source rock ages and geochemicaldata of samples
Sample Oils Baram-8 Iron Duke Shengli SSB A SSB B Safaniya Tuna-4 Kenmore-1 Moorari-4 SD
Country
Basin
Probable age of source rocks
Pr
20S
Q,9
Dia
Ph
20S + 20R
C27
CPI(2)
Ster
Sarawak Brunei China Indonesia Indonesia Saudi Arabia Australia Australia Australia Australia
--Zhanhua South Sumatran South Sumatran -Gippsland Eromanga Eromanga Carnarvon
Tertiary Tertiary Tertiary Tertiary Tertiary Cretaceous Cretaceous Jurassic Jurassic Jurassic
4.7 3.4 0.6 1.9 5.9 0.6 4.7 2.8 6.9 2.6
0.43 0.35 0.45 0.42 0.51 0.51 0.50 0.49 0.39 0.49
3.3* 1.7" 0.8 0.4* 0.7* 1.3 3.0 3.4 3.9 0.9
1.0 1.0 1.2 1.1 hi 1.0 1.I 1.0 1.3 I. I
0.4* 0.4* 0.2 1.4" 0.8* 0.3 3.0 2. l 2.2 1.2
Australia Indonesia Australia Australia Australia Australia
Bremer South Sumatran Gippsland Collie Sydney Canning
Miocene Miocene Late Cretaceous Permian Permian Devonian
0.7 5.7 2.1 0.6 0.5 0.3
-0.46 -0.19 0.38 0.32
-4.5" -5.8 3.8 4.5
3.0 1.3 5.8 2.6 0.9 1.2
-0.3* -0.2 0.6 0.2
Sediments
HCH 34 SSB Loy Yang Collie Kerosene Shale PD 130A
Definitions and methods of measurements: Pr/Ph, pristane/phytane (TIC); 20S/(20S+20R), 20S and 20R diasteromers of 5a(H),14~(H),17~(H)-ethylcbolestane (m/z 217); C29/C27. (20R)-5~(H),14~(H),17:c(H)-ethylcholestane/(20R)-5:~(H),14~(H),17:~(H)cholestane (m/z 217); CPI(2) calculated using n-alkanes (TIC) using carbon numbers from 23 to 29 ([(EC23+ C25 + C27) + (EC25 + C27 + C29)]/2 × (I~C24 + C26 + C28)) (Marzi el al., 1993); Dia/Ster, (20R)-13fl(H),17~(H)-ethyldiacholestane/(20R)-Sa(H),l,4a(H),17c~(H)-ethylcholestane(m/z 217); *possible bicadinane interference; --, absent or no data available.
Identification and occurrence of dihydro-ar-curcumene in crude oils and sediments
199
I00
50
.= O9 >
91 0
.I,~ 40
........ 60
77
j,, 80
105
p I. . . .
] i~
100
204
J,[i . 120
.
.
.
.
140
t,
. 160
180
200
m/z Fig. 2. Electron-impact mass spectrum (70eV) and suggested mass spectral cleavage patterns of ihydro-ar-curcumene (V).
50, 250, 1000 and 2500 pg/g of dihydro-ar-curcumene were prepared, n-Octadecene was used as a normalization standard and added to the samples in known concentration (250#g/g). Dihydro-ar-curcumene concentrations were calculated by measuring (using m/z 119 mass chromatograms) the abundances of dihydro-ar-curcumene in the samples relative to the abundance of dihydro-ar-curcumene in the external standards normalized to the abundance (using m/z 83 mass chromatograms) of n-octadecene. Replicate analyses of the samples gave results to + 10%.
Dihydro-ar-curcumene reference standard The Grignard reagent prepared from 4methylpentyl bromide (8mmol) and magnesium (10mmol) (Furniss et al., 1989) was added to 4-methylacetophenone (8 mmol) in ether. The resulting benzylic alcohol was extracted and subjected to hydrogenolysis using palladium/carbon (10%) as catalyst in glacial acetic acid with a hydrogen pressure of 1.5 atm for 36 h. The crude hydrocarbon product (70% yield) was further purified by chromatography using a column of activated alumina with n-hexane as solvent to afford dihydro-ar-curcumene (96% pure by capillary gas chromatography). The ~H- and 13C-NMR spectra confirm the structure of this compound to be dihydro-ar-curcumene (1-(1,5-dimethylhexyl)-4-methylbenzene): JH-NMR (200 MHz, CDCI3) ~ (ppm relative to TMS): 0.79, 0.80, 0.82, 0.83 (d, 6H, CH-(CH3)2), 1.10-1.20 (m, 4H, RCH2-CH2-CH:R'), 1 . 1 8 , 1.21 (6/, 3H, Ar-CHR-CH3), 1.43-1.58 (m, 3H, R-CH(CH3)2, RCH2-CH2-CH2 R'), 2.31 (s, 3H, A r - C H 3), 2.48-2.71 (m, 1H, A r - C H R R ' ) , 7.07 (s, 4H, Ar-H); ~3C-NMR (200MHz, CDC13) 6 (ppm relative to TMS): 20.94 (IC, Ar-CH3), 22.36, 22.54, 22.65 (3C, R-CH3), 25.43 (1C, RCHz-CH2-CH 2R'), 27.80
(1C, RCH-(CH3)2), 38.66, 39,01, 39.42 (3C, RCH2-CH2-CH2R', Ar-CHRR'), 126.77, 128.88 (4C, unsub-Ar), 135.03, 145.00 (2C, sub-Ar). The mass spectrum of this compound is shown in Fig. 2.
Gas chromatography-mass spectrometry (GC-MS) A Hewlett-Packard 5970 MSD system equipped with a model 7673A automatic cool on-column injector system, fused silica columns of 50 m × 0.22 mm i.d. coated with BP5 (SGE Australia) and a 60m x 0.25 mm i.d. DB1701 ( J & W Scientific) were used for all analyses. Helium was used as carrier gas at a linear gas velocity of 33 cm s- ~and the oven was programmed from 70 ° to 300°C at 3°C min -j. RESULTS AND DISCUSSION
Identification of dihydro-ar-curcumene in oils and sediment extracts Dihydro-ar-curcumene was identified in the hydrocarbon fractions of crude oil, and sediment extracts, using GC-MS and comparing the retention behaviour, and mass spectral characteristics, of the component in the hydrocarbon fractions with those of the authentic reference compound. The reference compound coeluted with the component from the crude oil, and sediment samples, on both capillary columns. A total ion chromatogram of a monoaromatic fraction of crude oil, obtained using the BP-5 capillary column, is shown in Fig. 3. In addition to the dominant dihydro-ar-curcumene peak this chromatogram also shows sets of peaks that represent series of isomeric alkyltoluenes (Ellis et al., 1992). Crude oils and sediments from a range of geographical locations, and derived from source rocks
L e r o y Ellis et al.
200
Dihydro-ar-curcumene(V)
C t~Alkyltoluenes i
i
C2oAlkyltoluenes i
C 2~Alkyltoluenes
e= o
03
30
40
50
I
7
I
60
70
80
Retention time (min)
----
Fig. 3. T o t a l ion c h r o m a t o g r a m s h o w i n g o c c u r r e n c e o f d i h y d r o - a r - c u r c u m e n e (V) in the m o n o a r o m a t i c f r a c t i o n o f K e n m o r e - 1 c r u d e oil.
ranging in age from Devonian to Tertiary, were analysed for dihydro-ar-curcumene. The samples used in this study in which dihydro-ar-curcumene was identified are from a variety of maturities, source types and depositional environments as indicated by the range of values for the biomarker parameters shown in Table I. Pristane/phytane values ranged from 0.6 to 6.9, the 20S/(20S + 20R) values from 0.1 to 0.5, the C29/C27 sterane values from 0.8 to > 10, the CPI values from 0.9 to 5.7 and diasterane/ sterane values from 0.1 to 3. From the values listed in Table 1, no relationships with dihydro-ar-curcum-
ene concentration and any of these source, facies or maturity indicators were apparent. Occurrence The abundance of dihydro-ar-curcumene in the crude oils and sediments was calculated using external and normalization standards. The concentrations ranged from 40 to 700 #g/g for the crude oils and from <5 to 410#g/g for the sediments (Table 2). The contribution of a higher plant input into the source rocks of the crude oils, or to the sediments, can
Table 2. Higher plant indicators and abundance of dihydro-ar-curcumene in samples Higher plant indicators
Sample
Olea Hop
Bicad Hop
Phyllo Hop
Pimar Hop
Retene 9-MP
Higher plant contribution
Dihydro-ar -curcumene concentration
Oils Baram-8 Iron Duke Shengli SSB A SSB B Safaniya Tuna-4 Kenmore-I Moorari-4 SD
0.1 1.5 <0,1 1.0 0.6 <0.1 <0.1 < 0.1 < 0.1 <0.1
1,0 0, I <0,1 0.1 0.8 <0,t <0.1 < 0. I < 0. I <0.1
<0.1 < 0.1 <0.1 <0.1 <0.1 <0.1 1.3 0.2 0.3 <0.1
<0.1 < 0.1 <0.1 <0.1 <0.1 <0.1 1.2 0.4 0.3 <0.1
<0.1 < 0. I 0.2 <0.1 <0.1 0.1 0.5 2.4 5.6 0.5
A A B A A B A A A B
(,ug/g Crude oil) 610 350 80 100 700 60 140 140 510 40
<0.1 0.1 <0.1 <0.1 <0.1 <0.1
<0.1 0.3 <0.1 <0.1 <0.1 <0.1
<0.1 <0.1 <0.1 <0.1 <0.1 <0.1
<0.1 <0.1 <0.1 <0.1 <0.1 <0.1
<0.1 <0.1 1.2 <0.1 0.1 <0.1
C A A C B C
Sediments
H C H 34 SSB Loy Yang Collie Kerosene Shale PD 130A
SOM) <5 410 <5 <5 30 15
(#g/g
Definitions and methods of measurements: Olea/Hop, 18ct(H)-oleanane/C30 17ct(H),21fl(H)-hopane (m/: 191); Bicad/Hop, trans-trans-trans bicadinane (T)/C30 17:t(H),21fl(H)-hopane (m/z 191); Phyllo/Hop, 16/3(H)-phyllocladane (m/: 123)/C30 17ct(H),21/~(H)-hopane (m/: 191); Pimar/Hop, isopimarane (m/: 123)/C30 17~t(H),21//(H)-hopane (m/z 191); Retene/9-MP, retene (m/: 219)/9-metbylphenanthrene (m/z 192); Higher plant contribution (Type A, B and C), refer to Table 3.
Identification and occurrence of dihydro-ar-curcumene in crude oils and sediments be assessed using higher plant biomarkers. The bicadinanes, oleanane, phyllocladane, pimarane and retene are derived from natural product plant resin precursors and have been used as indicators of higher plant input to sediments (Thomas, 1969; Alexander et aL, 1992; Peters and Moldowan, 1993). Parameters based on these biomarkers, which express the abundance of the higher plant markers relative to the ubiquitous C30 hopane or, in the case of the aromatic biomarkers, to 9-methylphenenthrene, have been used to indicate the input of higher plant material to the samples used in this study. The geochemical parameters given in Table 2 were used to classify the crude oils and sediments into Types A, B and C on the basis of the higher plant biomarkers being high, low or absent respectively as shown in Table 3. Type A samples show oleanane and/or retene parameters with values >0.5 and/or bicadinane, phyllocladane or pimarane parameters with values >0.2. Type B samples show intermediate values with oleanane and/or retene parameter values of 0.14).5 and/or bicadinane, phyllocladane or pimarane parameter values of 0.14).2. Type C samples contain no biomarkers or no higher plant input and show biomarker parameter values < 0.1. Although five parameters can be used to clasify each sample, only the parameter which achieves the higher classification, on the basis A>B>Cis used. The crude oils Baram-8, Iron Duke, SSB A and B, Tuna-4, Kenmore-1 and Moorari-4 are all classified Type A and have at least one of the parameters with values indicating a significant input of higher plant biomarkers. Shengli, Safaniya and SD crude oils have been classified Type B and have low values suggesting a minor contribution only. Crude oils classified as Type A are suggested to reflect terrestrially derived or sourced crude oils whilst Type B crude oils are indicative of predominantly, but not exclusively, marine and/or lacustrine derived or sourced crude oils. The dihydro-ar-curcumene concentrations in the crude oil samples classified as Type A were all greater than 100 pg/g. In contrast, all those crude oils classified as Type B have dihydro-ar-curcumene concentrations of less than 100pg/g. This shows that there is a strong association between the high abundance of dihydro-ar-curcumene and the presence of higher plant biomarkers. Table 3. Classification of crude oils and sediments with respect to higher plant input Classification Biomarker parameter Olea or Retene Hop 9-MP Bicad or Phyllo or Pimar Hop Hop Hop
Type A
Type B
Type C
>0.5
0.1M).5
<0.1
or
or
or
>0.2
0.1~).2
<0.1
Definitions and methods of measurements: Biomarker parameters, refer to Table 2.
201
The sediments used in the study were coals, with the exception of the Kerosene Shale which is a torbanite (Derenne, 1989; Metzger et al., 1991). The concentrations of dihydro-ar-curcumene in these samples ranged from < 5 to 410#g/g. The SSB and Loy Yang coals have been classified Type A and the Kerosene Shale as Type B. HCH 34, Collie and PD 130A had values <0.1 for the higher plant parameters and have been classified Type C. The occurrence of dihydro-ar-curcumene in the Type C coals suggests that dihydro-ar-curcumene may be a useful biomarker for higher plant input in samples in which commonly observed biomarkers, such as those described in Table 2, are absent. It is also interesting to note that the Loy Yang coal sample had a very low abundance of dihydro-ar-curcumene showing that a higher plant input to the sediments is not always associated with a high abundance of dihydroar-curcumene. Age distribution o f dihydro-ar-curcumene Information relating the presence of sourcespecific higher plant biomarkers in crude oils and sediments is useful in recognizing plant groups which contributed to the organic biomass from which the coals and crude oils were derived (Peters and Moldowan, 1993). The crude oil samples from the Gippsland and Eromanga basins (Tuna-4, Kenmore-I and Moorari-4) exhibited high levels of dihydro-ar-curcumene and were found to contain many higher plant biomarkers such as phyliocladane and pimarane, which are characteristic of gymnosperm conifer plant groups (Noble et al., 1985a, b, 1986). Conifer distributions assumed predominance during Jurassic and Cretaceous times and plant fossils and biomarkers belonging to the Araucariaceae and Podocarpaceae families, and the Cupressaceae families have been reported in the Eromanga and Gippsland basins respectively (Alexander et al., 1992; Philp et al., 1981, 1983). These conifer families may account for the high levels of dihydro-arcurcumene found in the crude oils from these basins. The Cretaceous period also saw the introduction of the flowering plants (angiosperms), which rapidly spread and exist worldwide today (Stewart, 1983; White, 1988). The angiosperm plants, and their resins, produce the characteristic oleanane and bicadinane biomarkers found in the Baram-8, Iron Duke, SSB A and SSB B samples (van Aarssen et al., 1992; Peters and Moldowan, 1993). The highest concentrations of dihydro-ar-curcumene were found in the Baram, Iron Duke, and SSB samples whose organic matter dates from times when angiosperms were abundant. Higher plants from angiosperm genera, which have existed since the Cretaceous, and conifers which have occurred widely since Jurassic times appear to contribute organic material containing high levels of dihydro-ar-curcumene precursors to the sediments.
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D i h y d r o - a r - c u r c u m e n e has not been found by us to occur in samples older than Devonian which coincides with the appearance o f vascular plants in the sedimentary record. Specifically, angiosperms and conifer plant species appear to contribute the highest concentrations o f d i h y d r o - a r - c u r c u m e n e to petroleums. Although bisabolene-type precursors for d i h y d r o - a r - c u r c u m e n e have been identified in some algae (Scheuer, 1978a, b, 1983), the largest numbers o f monocyclic sesquiterpenoids with the bisabolane c a r b o n skeleton, and their widespread occurrence in plants, suggests that plants are the main source o f precursor c o m p o u n d s for d i h y d r o - a r - c u r c u m e n e in sediments. CONCLUSIONS D i h y d r o - a r - c u r c u m e n e has been identified in crude oils and sediments ranging in age from the Devonian to Tertiary. The highest concentration o f d i h y d r o - a r - c u r c u m ene measured in the crude oils and sediments analysed was 700 #g/g. The presence o f d i h y d r o - a r - c u r c u m e n e in these samples is attributed to an input to the sediments o f higher plant material containing appropriate precursor natural products such as curcumene or bisabolene. Input into sediments o f organic matter containing natural product precursor sesquiterpenoids, such as bisabolene and curcumene, which can undergo aromatization and reduction respectively, during diagenesis, is p r o p o s e d to be the source o f d i h y d r o - a r curcumene found in crude oils and sediments. Associate E d i t o r - - B . R. T. Simoneit Acknowledgements--Mr Leroy Ellis gratefully acknowledges receipt of a Curtin University Postgraduate Research Scholarship. Thanks are due to Mr Trevor Bastow, Dr Mauro Mocerino and Dr Bob Botto for assistance with NMR analyses and interpretation.
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van Aarssen B. G. K., Horsfield B. and de Leeuw J. W. (1991) A comparative study of three different pyrolysis methods used to characterise a biopolymer isolated from fossil and extant dammar resins. J. Anal. Appl. Pyrol. 20, 125-139. 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 southeast Asia. Geochim. Cosmochim. Acta 56, 1231-1246. Adams D. R., Bhatnagar S. P. and Cookson C. (1975) Sesquiterpenoids of Santalum album and Santalum spicaturn. Phytochemistry 14, 1459-1460. Alexander R., Larcher A. V., Kagi R. I. and Price P. L. (1992) An oil-source correlation study using age-specific plant-derived biomarkers. In Biological Markers in Sediments and Petroleum (Edited by Moldowan J. M., Albrecht P. and Philp R. P.), pp. 201 221. Prentice-Hall, Engelwood Cliffs, NJ.
Augustine R. L. (1965) Catalytic Hydrogenation : Techniques and Applications in Organic Synthesis, pp. 59 60. Edward Arnold Publishers, London. Connolly J. D. and Hill R. A. (1991) Mono- and sesquiterpenoids. In Dictionary ofTerpenoids, Vol. I, pp. 180 198. Chapman and Hall, London. Derenne S., Largeau C., Casadevall E. and Berkaloff C. (1989) Occurrence of a resistant bipolymer in the L race of Botryococcus braunii. Phytochemistry 28, 1137 1142. Dev S. (1989) Terpenoids. In Natural Products ~?f Wooclv Plants 11 (Edited by Rowe J. W.), pp. 691 807. Springer-Verlag, Berlin. Ellis L., Kagi R. I. and Alexander R. (1992) Separation of petroleum hydrocarbons using dealuminated mordenite molecular sieve. I. Monoaromatic hydrocarbons. Org. Geochem. 18, 587 593. Furniss B. S., Hannaford A. J., Smith P. W. G. and Tatchell A. R. (1989) In Vogel's Textbook o[" Practical Organic Chemistry, 5th edn, 538 pp. Longman Group UK Limited, U.K. Grimalt J. O., Simoneit B. R. T. and Hatcher P. G. (1989) Chemical affinities between the solvent extractable and the bulk organic matter of fossil resin associated with an extinct Podocarpaceae. Phytochemistry 28, 1167 117I. Mackenzie A. S. (1984) Applications of biological markers in petroleum geochemistry. In Advances t)7 Petroleum Geoehemistrv Vol. 1 (Edited by Brooks J. and Welte D.), pp. 115-214. Academic Press, London. Marzi R., Torkelson B. E. and Olson R. K. (1993) A revised carbon preference index. Org. Geochem. 20, 1303 1306. Metzger P., Largeau C, and Casadevall E. (1991) Lipids and Macromolecular Lipids of the Hydrocarbon-rich Microalga Botryococcus braunii. Chemical Structure and Biosynthesis. Geochemical and Biotechnological Importance. In Progress in the Chemistry o/" Organic: Natural Products 57 (Edited by Herz W., Kirby W., Steglich W. and Tamm Ch.), pp. 1 70. Springer-Verlag, New York. Mills J. S., White R and Gough L. J. (1984) The chemical composition of Baltic amber. Chem. Geol. 47, 15 39. Noble R. A., Knox J., Alexander R. and Kagi R. I. (1985a) Identification of tetracyclic diterpane hydrocarbons in Australian crude oils and sediments. J. Chem. Soc., Chem Comm. 32 33. Noble R. A., Alexander R., Kagi R. I. and Knox J. (1985b) Tetracyclic diterpenoid hydrocarbons in some Australian coals, sediments and crude oils. Geochim. Cosmochim. Acta 49, 2141 2147. Noble R. A., Alexander R., Kagi R. I. and Knox J. (1986) Identification of some diterpenoid hydrocarbons in petroleum. Org. Geochem. 10, 825 829. Peters K. E. and Moldowan J. M. (1993) The Biomarker Guide: Interpreting Molecular Fossils in Petroleum and Ancient Sediments. Prentice-Hall Inc., Engelwood Cliffs, NJ. Philp R. P., Gilbert T. D. and Friedrich J. (1981) Bicyclic sesquiterpenoids and diterpenoids in Australian crude oils. Geachim. Cosmochim. Acta 45, 1173 1180. Philp R. P., Simoneit B. R. T. and Gilbert T. D. (1983) Diterpenoids in crude oils and coals of South Eastern Australia. In Advances in Organic Geochemistry, 1981 (Edited by Bj~roy M. et al.), pp. 698 704. Wiley, New York. Radke M. (1987) Organic Geochemistry of aromatic hydrocarbons. In Adrances in Petroleum Geochemist O' Vol. 2 (Edited by Brooks J. and Welte D.), pp. 141- 207. Academic Press, London. Scheuer P, J. (1978a) Marine Natural Products. Chemical and Biological Perspectives, Vol. 1. pp. 134 139. Academic Press, New York. Scheuer P. J. (1978b) Marine Natural Products, Chemical and Biological Perspectives, Vol. 2, pp. 144-149. Academic Press, New York.
Identification and occurrence of dihydro-ar-curcumene in crude oils and sediments Scheuer P. J. (1983) Marine Natural Products. Chemical and Biological Perspectives, Vol. 5, pp. 251-296. Academic Press, New York. Simonsen J. (1952) The Terpenes, Vol. III. p. 18. Cambridge University Press, Cambridge. Stewart W. N. (1983) Palaeobotany and the Evolution o f Plants, pp. 392-396. Cambridge University Press. Cambridge.
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Identification and occurrence of dihydro-ar-curcumene in crude oils and sediments LEROY ELLIS*t, RAJ K. SINGH, ROBERT ALEXANDER and ROBERT I. KAGI Australian Petroleum CRC at Centre for Petroleum and Environmental Organic Geochemistry, Curtin University of Technology, Box U!987 G.P.O. Perth, WA 6001, Australia (Received 23 June 1994; returned for revision 12 September 1994; accepted 21 December 1994)
Abstract--A suite of crude oils and sediments with a range of locations, source types, palaeoenvironments and ages has been analysed for dihydro-ar-curcumene. The concentrations of dihydro-ar-curcumene in 16 crude oils and sediments ranged from < 5 to 700 #g/g. Dihydro-ar-curcumene in sediments is suggested to be derived from sesquiterpenoids of the bisabolane skeletal type. The widespread occurrence of this type of sesquiterpenoid in terrestrial plants, and the association of this compound with biomarkers of higher plant origin in sediments, suggests that dihydro-ar-curcumene in sediments is derived primarily from higher plants. Key words--an~osperrns, biomarkers, conifers, dihydro-ar-curcumene, sesquiterpenoids in oils and sediments
derived from an extinct New Zealand species of Podocarpaceae. More recently, van Aarssen et al. (1991, 1992) reported this compound as a minor component in a crude oil and a dammar resin pyrolysate and suggested that it may have formed from polycadinanes by cracking processes. The transformation of natural products into saturated and aromatic hydrocarbon biomarkers in which the carbon skeleton of the natural product is retained is well-recognized (Tissot and Welte, 1984; Mackenzie, 1984; Radke, 1987). Natural products such as bisabolene (VI) might therefore be expected to give rise to a biomarker in the form of the aromatic hydrocarbon, dihydro-ar-curcumene (V), by commonly observed geochemical reactions. In this paper we report the identification, using an authentic refer-
INTRODUCTION
Monocyclic sesquiterpenoids with the bisabolane (I) (Fig. 1) carbon skeleton are common constituents of essential oils derived from the wood and resins of extant higher plants (Dev, 1989; Connolly and Hill, 1991). Within this group, aromatic compounds have also been reported. Examples include curcumene (II) isolated from turmeric (Simonsen, 1952) and sandalwood oil (Adams et al., 1975); ar-turmerone (Ill) (at-indicates a methyl group substituent on the aromatic ring) from the essential oils of Cureuma domestica and nuciferal (IV) obtained from the wood oil of the kaya tree (Dev, 1989; Connolly and Hill, 1991). Compounds with this carbon skeleton are, however, not confined to higher plants as they have been reported from Laurencia algae and from coelenterates (Scheuer, 1978a, b, 1983). Aromatic compounds with the bisabolane (I) carbon skeleton, and with saturated side chains, such as dihydro-ar-curcumene (V) have not been reported as natural products from terrestrial plants, however, there are several reports of this compound in fossil materials. These reports are based on tentative identifications made by interpreting mass spectral data obtained using G C - M S techniques. For example, Mills et al. (1984) suggested that it was a component in the ether-soluble fraction of Baltic amber, and Grimalt et al. (1989) identified it as a minor component in a fossil resin of Eocene age, *Present address: Argonne National Laboratory, Chemistry Division, 9700 S. Cass Avenue, Argonne IL 60439-4831, U.S.A. tTo whom all correspondence should be addressed.
(I)
(If)
(III)
(iv)
(v)
(vl)
Fig. 1. Molecular structures of some natural products structurally related to dihydro-ar-curcumene.
197
Leroy Ellis et al.
198
ence c o m p o u n d , o f d i h y d r o - a r - c u r c u m e n e (V) in s e d i m e n t a r y organic m a t t e r a n d its occurrence in crude oils a n d s e d i m e n t s which have an association with higher p l a n t material.
EXPERIMENTAL
Samples T h e locations o f the s a m p l e s a n d their ages, or in the case o f crude oils the p r o b a b l e ages o f their source rocks, are s h o w n in Table 1. H C H 34 w a s a lignite o b t a i n e d as a core f r o m a d e p t h o f 24.6 m. Loy Y a n g a n d Collie s a m p l e s were lignite a n d s u b - b i t u m i n o u s coals respectively a n d were o b t a i n e d f r o m open-pit mines. T h e SSB ( S o u t h S u m a t r a Basin) coal s a m p l e was o b t a i n e d as c u t t i n g s f r o m a p e t r o l e u m explor a t i o n well. T h e K e r o s e n e Shale was o b t a i n e d f r o m the G l e n Davis m i n e site a n d is primarily c o m p o s e d o f fossilized Botryococcus braunii (Metzger et al., 1991; D e r e n n e , 1989). P D 130A was p r o v i d e d as a d i a m o n d drill core f r o m the depth o f 317 m ( G S W A No. 72525A).
Sample preparation R o c k s a m p l e s were air dried a n d c r u s h e d to a fine p o w d e r using a T e m a mill, and extracted ultrasonically with d i c h l o r o m e t h a n e / m e t h a n o l (95:5). T h e solvent extract was recovered by filtration a n d the solvent was carefully distilled off to yield the soluble o r g a n i c m a t t e r (SOM).
Isolation of monoaromatic and branched and cyclic fractions C r u d e oil, or soluble organic m a t t e r extracts, were dissolved in h e x a n e a n d filtered t h r o u g h a s h o r t c o l u m n o f activated a l u m i n a to r e m o v e very polar
c o m p o u n d s . T h e filtrate was then separated into alkane a n d a r o m a t i c fractions using a M e r c k - L o b a r G r o b e A (240-10) L i c h r o p r e p Si 60, 40-63/~m c o l u m n a t t a c h e d to a W a t e r s Millipore Model 510 double piston p u m p . U s i n g a flow rate o f 2 m l m i n t o f n - h e x a n e , an alkane fraction was collected between elution times o f 8-12 min. T h e a r o m a t i c c o m p o n e n t s were t h e n eluted by reversing the direction of flow o f the solvent for a further 25 min. T h e alkane comp o n e n t s were detected using a W a t e r s Millipore Series R-400 Differential R e f r a c t o m e t e r a n d the a r o m a t i c c o m p o n e n t s were detected using a W a t e r s Associates Series 440 U V a b s o r b a n c e detector set at a wavelength o f 254 n m . T h e a r o m a t i c c o m p o n e n t s were t h e n further fractionated into m o n o a r o m a t i c , diaromatic a n d t r i a r o m a t i c b a n d s using a l u m i n a thin layer c h r o m a t o g r a p h y with n - h e x a n e as eluent. T h e m o n o a r o m a t i c fraction was collected by scraping b a n d s f r o m the plate a n d extracting the a l u m i n a with d i c h l o r o m e t h a n e . T h e alkane fraction collected f r o m M P L C was analysed by G C MS, t h e n further treated with Z S M - 5 m o l e c u l a r sieves to r e m o v e the n - a l k a n e , m e t h y l a l k a n e a n d alkylcyclohexane c o m p o n e n t s before analysis again by G C MS.
Analysis and quantification of dihydro-ar-curcumene b7 crude oils and sediment extracts In a typical separation, a crude oil or sediment extract (approx. 10 rag) was placed o n a small c o l u m n p a c k e d with silica gel a n d eluted with 7 m l d i c h l o r o m e t h a n e / p e n t a n e (1:9) which afforded a h y d r o c a r b o n fraction c o n t a i n i n g b o t h alkane a n d aromatic compounds. Q u a n t i t a t i v e analysis was carried out on the crude oil (as received) a n d s e d i m e n t extracts (weight stabilized S O M ) using external a n d n o r m a l i z a t i o n standards. External s t a n d a r d s with c o n c e n t r a t i o n s o f 5,
Table l, Locations, source rock ages and geochemicaldata of samples
Sample Oils Baram-8 Iron Duke Shengli SSB A SSB B Safaniya Tuna-4 Kenmore-1 Moorari-4 SD
Country
Basin
Probable age of source rocks
Pr
20S
Q,9
Dia
Ph
20S + 20R
C27
CPI(2)
Ster
Sarawak Brunei China Indonesia Indonesia Saudi Arabia Australia Australia Australia Australia
--Zhanhua South Sumatran South Sumatran -Gippsland Eromanga Eromanga Carnarvon
Tertiary Tertiary Tertiary Tertiary Tertiary Cretaceous Cretaceous Jurassic Jurassic Jurassic
4.7 3.4 0.6 1.9 5.9 0.6 4.7 2.8 6.9 2.6
0.43 0.35 0.45 0.42 0.51 0.51 0.50 0.49 0.39 0.49
3.3* 1.7" 0.8 0.4* 0.7* 1.3 3.0 3.4 3.9 0.9
1.0 1.0 1.2 1.1 hi 1.0 1.I 1.0 1.3 I. I
0.4* 0.4* 0.2 1.4" 0.8* 0.3 3.0 2. l 2.2 1.2
Australia Indonesia Australia Australia Australia Australia
Bremer South Sumatran Gippsland Collie Sydney Canning
Miocene Miocene Late Cretaceous Permian Permian Devonian
0.7 5.7 2.1 0.6 0.5 0.3
-0.46 -0.19 0.38 0.32
-4.5" -5.8 3.8 4.5
3.0 1.3 5.8 2.6 0.9 1.2
-0.3* -0.2 0.6 0.2
Sediments
HCH 34 SSB Loy Yang Collie Kerosene Shale PD 130A
Definitions and methods of measurements: Pr/Ph, pristane/phytane (TIC); 20S/(20S+20R), 20S and 20R diasteromers of 5a(H),14~(H),17~(H)-ethylcbolestane (m/z 217); C29/C27. (20R)-5~(H),14~(H),17:c(H)-ethylcholestane/(20R)-5:~(H),14~(H),17:~(H)cholestane (m/z 217); CPI(2) calculated using n-alkanes (TIC) using carbon numbers from 23 to 29 ([(EC23+ C25 + C27) + (EC25 + C27 + C29)]/2 × (I~C24 + C26 + C28)) (Marzi el al., 1993); Dia/Ster, (20R)-13fl(H),17~(H)-ethyldiacholestane/(20R)-Sa(H),l,4a(H),17c~(H)-ethylcholestane(m/z 217); *possible bicadinane interference; --, absent or no data available.
Identification and occurrence of dihydro-ar-curcumene in crude oils and sediments
199
I00
50
.= O9 >
91 0
.I,~ 40
........ 60
77
j,, 80
105
p I. . . .
] i~
100
204
J,[i . 120
.
.
.
.
140
t,
. 160
180
200
m/z Fig. 2. Electron-impact mass spectrum (70eV) and suggested mass spectral cleavage patterns of ihydro-ar-curcumene (V).
50, 250, 1000 and 2500 pg/g of dihydro-ar-curcumene were prepared, n-Octadecene was used as a normalization standard and added to the samples in known concentration (250#g/g). Dihydro-ar-curcumene concentrations were calculated by measuring (using m/z 119 mass chromatograms) the abundances of dihydro-ar-curcumene in the samples relative to the abundance of dihydro-ar-curcumene in the external standards normalized to the abundance (using m/z 83 mass chromatograms) of n-octadecene. Replicate analyses of the samples gave results to + 10%.
Dihydro-ar-curcumene reference standard The Grignard reagent prepared from 4methylpentyl bromide (8mmol) and magnesium (10mmol) (Furniss et al., 1989) was added to 4-methylacetophenone (8 mmol) in ether. The resulting benzylic alcohol was extracted and subjected to hydrogenolysis using palladium/carbon (10%) as catalyst in glacial acetic acid with a hydrogen pressure of 1.5 atm for 36 h. The crude hydrocarbon product (70% yield) was further purified by chromatography using a column of activated alumina with n-hexane as solvent to afford dihydro-ar-curcumene (96% pure by capillary gas chromatography). The ~H- and 13C-NMR spectra confirm the structure of this compound to be dihydro-ar-curcumene (1-(1,5-dimethylhexyl)-4-methylbenzene): JH-NMR (200 MHz, CDCI3) ~ (ppm relative to TMS): 0.79, 0.80, 0.82, 0.83 (d, 6H, CH-(CH3)2), 1.10-1.20 (m, 4H, RCH2-CH2-CH:R'), 1 . 1 8 , 1.21 (6/, 3H, Ar-CHR-CH3), 1.43-1.58 (m, 3H, R-CH(CH3)2, RCH2-CH2-CH2 R'), 2.31 (s, 3H, A r - C H 3), 2.48-2.71 (m, 1H, A r - C H R R ' ) , 7.07 (s, 4H, Ar-H); ~3C-NMR (200MHz, CDC13) 6 (ppm relative to TMS): 20.94 (IC, Ar-CH3), 22.36, 22.54, 22.65 (3C, R-CH3), 25.43 (1C, RCHz-CH2-CH 2R'), 27.80
(1C, RCH-(CH3)2), 38.66, 39,01, 39.42 (3C, RCH2-CH2-CH2R', Ar-CHRR'), 126.77, 128.88 (4C, unsub-Ar), 135.03, 145.00 (2C, sub-Ar). The mass spectrum of this compound is shown in Fig. 2.
Gas chromatography-mass spectrometry (GC-MS) A Hewlett-Packard 5970 MSD system equipped with a model 7673A automatic cool on-column injector system, fused silica columns of 50 m × 0.22 mm i.d. coated with BP5 (SGE Australia) and a 60m x 0.25 mm i.d. DB1701 ( J & W Scientific) were used for all analyses. Helium was used as carrier gas at a linear gas velocity of 33 cm s- ~and the oven was programmed from 70 ° to 300°C at 3°C min -j. RESULTS AND DISCUSSION
Identification of dihydro-ar-curcumene in oils and sediment extracts Dihydro-ar-curcumene was identified in the hydrocarbon fractions of crude oil, and sediment extracts, using GC-MS and comparing the retention behaviour, and mass spectral characteristics, of the component in the hydrocarbon fractions with those of the authentic reference compound. The reference compound coeluted with the component from the crude oil, and sediment samples, on both capillary columns. A total ion chromatogram of a monoaromatic fraction of crude oil, obtained using the BP-5 capillary column, is shown in Fig. 3. In addition to the dominant dihydro-ar-curcumene peak this chromatogram also shows sets of peaks that represent series of isomeric alkyltoluenes (Ellis et al., 1992). Crude oils and sediments from a range of geographical locations, and derived from source rocks
L e r o y Ellis et al.
200
Dihydro-ar-curcumene(V)
C t~Alkyltoluenes i
i
C2oAlkyltoluenes i
C 2~Alkyltoluenes
e= o
03
30
40
50
I
7
I
60
70
80
Retention time (min)
----
Fig. 3. T o t a l ion c h r o m a t o g r a m s h o w i n g o c c u r r e n c e o f d i h y d r o - a r - c u r c u m e n e (V) in the m o n o a r o m a t i c f r a c t i o n o f K e n m o r e - 1 c r u d e oil.
ranging in age from Devonian to Tertiary, were analysed for dihydro-ar-curcumene. The samples used in this study in which dihydro-ar-curcumene was identified are from a variety of maturities, source types and depositional environments as indicated by the range of values for the biomarker parameters shown in Table I. Pristane/phytane values ranged from 0.6 to 6.9, the 20S/(20S + 20R) values from 0.1 to 0.5, the C29/C27 sterane values from 0.8 to > 10, the CPI values from 0.9 to 5.7 and diasterane/ sterane values from 0.1 to 3. From the values listed in Table 1, no relationships with dihydro-ar-curcum-
ene concentration and any of these source, facies or maturity indicators were apparent. Occurrence The abundance of dihydro-ar-curcumene in the crude oils and sediments was calculated using external and normalization standards. The concentrations ranged from 40 to 700 #g/g for the crude oils and from <5 to 410#g/g for the sediments (Table 2). The contribution of a higher plant input into the source rocks of the crude oils, or to the sediments, can
Table 2. Higher plant indicators and abundance of dihydro-ar-curcumene in samples Higher plant indicators
Sample
Olea Hop
Bicad Hop
Phyllo Hop
Pimar Hop
Retene 9-MP
Higher plant contribution
Dihydro-ar -curcumene concentration
Oils Baram-8 Iron Duke Shengli SSB A SSB B Safaniya Tuna-4 Kenmore-I Moorari-4 SD
0.1 1.5 <0,1 1.0 0.6 <0.1 <0.1 < 0.1 < 0.1 <0.1
1,0 0, I <0,1 0.1 0.8 <0,t <0.1 < 0. I < 0. I <0.1
<0.1 < 0.1 <0.1 <0.1 <0.1 <0.1 1.3 0.2 0.3 <0.1
<0.1 < 0.1 <0.1 <0.1 <0.1 <0.1 1.2 0.4 0.3 <0.1
<0.1 < 0. I 0.2 <0.1 <0.1 0.1 0.5 2.4 5.6 0.5
A A B A A B A A A B
(,ug/g Crude oil) 610 350 80 100 700 60 140 140 510 40
<0.1 0.1 <0.1 <0.1 <0.1 <0.1
<0.1 0.3 <0.1 <0.1 <0.1 <0.1
<0.1 <0.1 <0.1 <0.1 <0.1 <0.1
<0.1 <0.1 <0.1 <0.1 <0.1 <0.1
<0.1 <0.1 1.2 <0.1 0.1 <0.1
C A A C B C
Sediments
H C H 34 SSB Loy Yang Collie Kerosene Shale PD 130A
SOM) <5 410 <5 <5 30 15
(#g/g
Definitions and methods of measurements: Olea/Hop, 18ct(H)-oleanane/C30 17ct(H),21fl(H)-hopane (m/: 191); Bicad/Hop, trans-trans-trans bicadinane (T)/C30 17:t(H),21fl(H)-hopane (m/z 191); Phyllo/Hop, 16/3(H)-phyllocladane (m/: 123)/C30 17ct(H),21/~(H)-hopane (m/: 191); Pimar/Hop, isopimarane (m/: 123)/C30 17~t(H),21//(H)-hopane (m/z 191); Retene/9-MP, retene (m/: 219)/9-metbylphenanthrene (m/z 192); Higher plant contribution (Type A, B and C), refer to Table 3.
Identification and occurrence of dihydro-ar-curcumene in crude oils and sediments be assessed using higher plant biomarkers. The bicadinanes, oleanane, phyllocladane, pimarane and retene are derived from natural product plant resin precursors and have been used as indicators of higher plant input to sediments (Thomas, 1969; Alexander et aL, 1992; Peters and Moldowan, 1993). Parameters based on these biomarkers, which express the abundance of the higher plant markers relative to the ubiquitous C30 hopane or, in the case of the aromatic biomarkers, to 9-methylphenenthrene, have been used to indicate the input of higher plant material to the samples used in this study. The geochemical parameters given in Table 2 were used to classify the crude oils and sediments into Types A, B and C on the basis of the higher plant biomarkers being high, low or absent respectively as shown in Table 3. Type A samples show oleanane and/or retene parameters with values >0.5 and/or bicadinane, phyllocladane or pimarane parameters with values >0.2. Type B samples show intermediate values with oleanane and/or retene parameter values of 0.14).5 and/or bicadinane, phyllocladane or pimarane parameter values of 0.14).2. Type C samples contain no biomarkers or no higher plant input and show biomarker parameter values < 0.1. Although five parameters can be used to clasify each sample, only the parameter which achieves the higher classification, on the basis A>B>Cis used. The crude oils Baram-8, Iron Duke, SSB A and B, Tuna-4, Kenmore-1 and Moorari-4 are all classified Type A and have at least one of the parameters with values indicating a significant input of higher plant biomarkers. Shengli, Safaniya and SD crude oils have been classified Type B and have low values suggesting a minor contribution only. Crude oils classified as Type A are suggested to reflect terrestrially derived or sourced crude oils whilst Type B crude oils are indicative of predominantly, but not exclusively, marine and/or lacustrine derived or sourced crude oils. The dihydro-ar-curcumene concentrations in the crude oil samples classified as Type A were all greater than 100 pg/g. In contrast, all those crude oils classified as Type B have dihydro-ar-curcumene concentrations of less than 100pg/g. This shows that there is a strong association between the high abundance of dihydro-ar-curcumene and the presence of higher plant biomarkers. Table 3. Classification of crude oils and sediments with respect to higher plant input Classification Biomarker parameter Olea or Retene Hop 9-MP Bicad or Phyllo or Pimar Hop Hop Hop
Type A
Type B
Type C
>0.5
0.1M).5
<0.1
or
or
or
>0.2
0.1~).2
<0.1
Definitions and methods of measurements: Biomarker parameters, refer to Table 2.
201
The sediments used in the study were coals, with the exception of the Kerosene Shale which is a torbanite (Derenne, 1989; Metzger et al., 1991). The concentrations of dihydro-ar-curcumene in these samples ranged from < 5 to 410#g/g. The SSB and Loy Yang coals have been classified Type A and the Kerosene Shale as Type B. HCH 34, Collie and PD 130A had values <0.1 for the higher plant parameters and have been classified Type C. The occurrence of dihydro-ar-curcumene in the Type C coals suggests that dihydro-ar-curcumene may be a useful biomarker for higher plant input in samples in which commonly observed biomarkers, such as those described in Table 2, are absent. It is also interesting to note that the Loy Yang coal sample had a very low abundance of dihydro-ar-curcumene showing that a higher plant input to the sediments is not always associated with a high abundance of dihydroar-curcumene. Age distribution o f dihydro-ar-curcumene Information relating the presence of sourcespecific higher plant biomarkers in crude oils and sediments is useful in recognizing plant groups which contributed to the organic biomass from which the coals and crude oils were derived (Peters and Moldowan, 1993). The crude oil samples from the Gippsland and Eromanga basins (Tuna-4, Kenmore-I and Moorari-4) exhibited high levels of dihydro-ar-curcumene and were found to contain many higher plant biomarkers such as phyliocladane and pimarane, which are characteristic of gymnosperm conifer plant groups (Noble et al., 1985a, b, 1986). Conifer distributions assumed predominance during Jurassic and Cretaceous times and plant fossils and biomarkers belonging to the Araucariaceae and Podocarpaceae families, and the Cupressaceae families have been reported in the Eromanga and Gippsland basins respectively (Alexander et al., 1992; Philp et al., 1981, 1983). These conifer families may account for the high levels of dihydro-arcurcumene found in the crude oils from these basins. The Cretaceous period also saw the introduction of the flowering plants (angiosperms), which rapidly spread and exist worldwide today (Stewart, 1983; White, 1988). The angiosperm plants, and their resins, produce the characteristic oleanane and bicadinane biomarkers found in the Baram-8, Iron Duke, SSB A and SSB B samples (van Aarssen et al., 1992; Peters and Moldowan, 1993). The highest concentrations of dihydro-ar-curcumene were found in the Baram, Iron Duke, and SSB samples whose organic matter dates from times when angiosperms were abundant. Higher plants from angiosperm genera, which have existed since the Cretaceous, and conifers which have occurred widely since Jurassic times appear to contribute organic material containing high levels of dihydro-ar-curcumene precursors to the sediments.
Leroy Ellis et al.
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D i h y d r o - a r - c u r c u m e n e has not been found by us to occur in samples older than Devonian which coincides with the appearance o f vascular plants in the sedimentary record. Specifically, angiosperms and conifer plant species appear to contribute the highest concentrations o f d i h y d r o - a r - c u r c u m e n e to petroleums. Although bisabolene-type precursors for d i h y d r o - a r - c u r c u m e n e have been identified in some algae (Scheuer, 1978a, b, 1983), the largest numbers o f monocyclic sesquiterpenoids with the bisabolane c a r b o n skeleton, and their widespread occurrence in plants, suggests that plants are the main source o f precursor c o m p o u n d s for d i h y d r o - a r - c u r c u m e n e in sediments. CONCLUSIONS D i h y d r o - a r - c u r c u m e n e has been identified in crude oils and sediments ranging in age from the Devonian to Tertiary. The highest concentration o f d i h y d r o - a r - c u r c u m ene measured in the crude oils and sediments analysed was 700 #g/g. The presence o f d i h y d r o - a r - c u r c u m e n e in these samples is attributed to an input to the sediments o f higher plant material containing appropriate precursor natural products such as curcumene or bisabolene. Input into sediments o f organic matter containing natural product precursor sesquiterpenoids, such as bisabolene and curcumene, which can undergo aromatization and reduction respectively, during diagenesis, is p r o p o s e d to be the source o f d i h y d r o - a r curcumene found in crude oils and sediments. Associate E d i t o r - - B . R. T. Simoneit Acknowledgements--Mr Leroy Ellis gratefully acknowledges receipt of a Curtin University Postgraduate Research Scholarship. Thanks are due to Mr Trevor Bastow, Dr Mauro Mocerino and Dr Bob Botto for assistance with NMR analyses and interpretation.
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