Alkylated phenanthrene distributions as maturity and origin indicators in crude oils and rock extracts

- Geochimica et Cosmochimica Acta, Vol. 59, No. IO, pp. 2043-2056, 1995

1 Pergamon Copyright 0 1995 Elsevier Science Ltd Printed in the USA. All rights reserved

0016.7037/95-$9.50 + .oo

0016-7037(95)00125-S

Alkylated phenanthrene distributions as maturity and origin indicators in crude oils and rock extracts

H. BUDZINSKI, ’ PH. GARRIGUES, ’ J. CONNAN,’ J. DEVILLERS,~ D. DOMINE, 3 M. RADKE,~ and J. L. OUDIN’

‘URA 348 CNRS, Universite de Bordeaux I 33405, Talence Cedex, France *Elf-Aquitaine, CSTJF, Avenue Larribau, 64018 Pau Cedex, France

%ZTIS, 21 Rue de la Banniere, 69003 Lyon, France %ZG 4, Research Centre (KFA), D-52425 Jiilich, Germany

5Total Centre Technique, Domaine de Beauplan, 78470 Saint Remy les Chevreuse, France

(Received June 28, 1994; accepted in revisedform March 2, 1995)

Abstract-Methylphenanthrene (MP), dimethylphenanthrene (DMP) , and trimethylphenanthrene (TMP) distributions have been determined in crude oils and rock extracts from different origins at various stages of thermal maturity. A methodological approach combining Correspondence Factor Analysis and Nonlinear Mapping (NLM) was used for extracting origin/maturity information from these data. It allowed to benefit from the advantages of both methods. The use of such a multivariate data analysis appeared much more efficient than the use of molecular ratios that can be too restrictive and mask specific distribution patterns.

This approach performed on the set of natural samples clearly demonstrated the discrimination between the samples through the presence of specific methyl-, dimethyl-, and trimethylphenanthrene isomers as origin/maturity markers. Based on MP, DMP, and TMP distributions, it is possible to distinguish the variations in organic matter type from the effects of thermal maturation. Some substituted phenanthrenes in each isomer series appear as characteristic of the two studied systems: The Aquitaine basin as representative of a marine carbonate environment and the Mahakam delta as representative of a terrestrial environment (higher plants). These compounds could be tentatively related to natural precursors such as triterpenoids or hopanoids.

INTRODUCTION

Alkylated aromatic hydrocarbons are common constituents of petroleums and ancient sediments and have received considerable attention as indicators of thermal maturity. It is now widely accepted that the thermal maturity level of source rocks and crude oils can be assessed from the isomer distribution of methyl-substituted naphthalenes and phenanthrenes (Radke et al., 1982; Alexander et al., 1985, 1986; Radke, 1987, 1988; Garrigues et al., 1988). In a general way, the compounds substituted in (Y positions are less stable than related isomers with b-substitution patterns. Consequently, when increasing the degree of thermal maturation, the values of the p/a concentration ratios for specific groups of compounds often exhibit regular variations. However, irregular trends in isomer abundances for methylphenanthrenes have been observed, particularly in the case of type II organic matter (Radke et al., 1986; Cassini et al., 1988). It is now important to understand how and to what extent the origin of the organic matter may influence the distributions of the aromatic isomers in petroleum samples.

In order to investigate this influence on phenanthrene compound distributions, methylphenanthrene (MP), dimethylphenanthrene (DMP), and trimethylphenanthrene (TMP) distributions have been determined in various type II-S crude oils and type III crude oils and source rocks. For this purpose, a graphical approach based on the nonlinear mapping (NLM) method (Sammon, 1969; Domine et al., 1993) was used to visualize and discuss the distribution patterns observed for each series. By this way the set of samples has been studied

2043

for a possible origin/maturity differentiation only phenanthrene distributions.

EXPERIMENTAL

Samples

based on

Nine crude oils, originating from type II-S kerogen of the Aqui- taine Basin, have been described elsewhere (Connan and Lacrampe- Couloume, 1993 ) The set of Indonesian coals (7) and crude oils (7 ) (type III kerogens) came from the Handil field and from the Kerbau basin (Kalimantan, Indonesia). Geological information on these ba- sins have been reported elsewhere (Oudin and Picard, 1982; Garrigues et al., 1988; Radke et al., 1990) All samples are described in Table 1.

Analytical Procedure

Crude oils and organic extracts of rocks were fractionated by high pressure liquid chromatography (HPLC) as described elsewhere (Budzinski et al., 1993a). The triaromatic fractions were analyzed by gas chromatography coupled to mass spectrometry (GC-MS) using an HP 5890 series II gas chromatograph equipped with a splitless injector (purge delay: 30 s; purge flow: 60 mL/min). The detector used was an HP 5970 Mass Selective Detector (MSD) (Electron Impact Ionization (EI): 70 eV; voltage 2200 V) in the selected ion monitoring (SIM) mode based on the molecular ions of the compounds at 2 scans/s. The column used was a SB smectic phase (Di- onex, Lee Scientific Division) 50 m x 0.22 mm x 0.1 pm, which has demonstrated to be very selective in the analysis of isomeric compounds (Budzinski et al., 1992a,b). Helium was employed as carrier gas with 2.5 bars as inlet pressure. The column was kept at 50°C during 2 min then programmed to 140°C at 1 O”C/min rate, kept at 140°C during 2 min then programmed to 250°C at a 2”C/min rate and kept at 250°C during 30 min, the injector and the detector were at 250°C.

2044 H. Budzinski et al.

(4

240000

200000 -

160000 -

120000 -

60000 -

40000 -

0 ."I.. 30 32

Abundance

@) -I

120000

1

100000

j

60000

i

60000

i

8-HP I-HP

36 38 40

Time--(min.

2. B-IMP

a-HP

9

I&o

10

% 0

1 (a) 5

4 2 <P)

3

4 42 44 46 46 50

1

44 48 52 56 60 Time (min.)

FIG. 1. Single Ion Monitoring (SIM) chromatograms of a triaromatic fraction of a crude oil on the smectic liquid crystalline phase for the detection of (a) methylphenanthrenes (m/z 192). (b) dimethylphenanthrenes (m/z 206) (c) trimethylphenanthrenes (m/z 220).

identifications of methylphenanthrenes (four MP isomers), dimethylphenanthrenes (fourteen DMP isomers) and trimethylphenanthrenes (eighteen TMP isomers) were based on previous studies (Budzinski et al., 1992b, and references wherein; Fig. 1).

Statistical Analyses

All the data were used as percentage of individual component in the three sets of isomeric compounds (MP, DMP, and TMP). Even

Alkylated aromatic hydrocarbons in petroleum 2045

40 44 46 52 56 60 Time (min.)

FIG. 1. (Continued)

- 64

if Correspondence Factor Analysis (CFA) was initially designed for contingency and frequency data tables, it is also the method of choice to analyze the kinds of matrices shown in Tables 2 to 4 (Greenacre, 1984; Devillers and Karcher, 1990; Devillers et al., 1991; Escofier and Pages, 1991). A comprehensive description of this method with the advantages and drawbacks can be found in Devillers and Karcher

( 1990). Briefly, CFA is a linear multivariate method allowing the display of the rows and columns of a data matrix as points in dual low-dimensional vector spaces. This method based on the x2- metric allows the comparison of profiles introducing a probability component. CFA is interpreted from the graphical display of the factorial planes. When most of the inertia is explained on the two first factorial

Table 1. Description of the samples

Locanon Oils

#I Aquitaine #2 Aquitaine

Z Aquitaine Aquitaine

J1.5 Mahakam delta #6 Mahakam delta #7 Mahakam delta

2 hIahakam delta Mahakam delta

#IO Mahakamdelta #18 Mahakam delta #19 Aquitaine #20 Aquitaine 1121 Aquitaine #22 Aquitaine #23 Aquitaine

Reservorr

Low Cretaceous Barremirin Barremian Barremian Miocene Miocene Miocene Miocene Miocene Miocene Miocene

Albian BalXmkul Barremiatl BallXmiall

Source Depth Kerogen (ml type

Barmmian-Jurassic 2000-2020 n-s Barremian-Jurassic 32763290 II-S Banemian-Jurassic 2247-2273 B-S Barremian-Jurassic TtWt3925 ES h4iocene Miccene 1355 Miocene 1865 : Miocene 2993-3170 El Miccene 2602-2612 JJJ hIioXne 1234-1236 IB Miocene 3932.50 JB Hettangian-Rhaetian 2964-3065 B-S Barremian-Jurassic 1908-1940 JJ-S Barremian-Jurassic 2258-2292 B-S Barremian-Jurassic 1350-1368 B-S Banemian-Jurassic 2905-2906 B-S

Location Geologtcal %C H/C G/C Tmax Depth Rm Kerogen Rocks Age ?C, (m) (%) type

#ll Mahakam delta Miocene 70.4 0.85 0.15 425 2250 0.52 BJ #12 Mahakamdelta Miocene 76.4 0.92 0.10 439 3015 0.64 III #13 Mahakam delta Miocene 75.5 0.87 0.08 450 3180 0.64 BJ #14 Mahakam delta Miocene 64.1 0.92 0.18 429 2600 0.55 JB #15 Mahakam delta Miocene 68.9 0.90 0.16 429 2925 0.59 BJ #16 Mahakam delta Miocene 76.7 0.85 0.09 441 3610 0.75 JJJ #17 Mahakam delta Miocene 82.6 0.83 0.05 457 4065 0.86 BJ


Table 2. Relative abundances (%) of the methylphenanthrenes in the samples and values of the MP13 index (a)

Samples 3-MP (%)

2-MP (%)

9-MP (%a)

I-MP (%)

MPI3 (a)

#l 15.10 19.70 47.40 17.80 0.53 #2 12.00 16.20 50.10 21.70 0.39 #3 15.70 20.40 45.30 18.60 0.56 #4 13.91 16.22 49.01 20.86 0.43 #5 21.30 26.45 31.60 20.65 0.91 #6 25.13 27.27 29.42 18.18 1.10 #7 27.32 28.29 28.78 15.61 1.25 #8 29.47 31.44 24.24 14.85 1.56 #9 27.21 33.04 22.43 17.32 1.52 #lO 27.56 32.08 23.16 17.20 1.48 #11 21.99 28.60 24.79 24.62 1.02 #12 22.48 28.96 23.39 25.17 1.06 #13 19.40 29.58 26.35 24.67 0.96 #14 20.36 31.66 19.04 28.94 1.08 #15 20.17 30.30 18.43 31.10 1.02 #I6 21.85 30.13 22.22 25.80 1.08 #17 20.29 31.66 18.79 29.26 1.08 #18 23.53 29.41 26.47 20.59 1.12 #I9 14.80 21.20 39.90 24.10 0.56 #20 18.20 23.50 38.60 19.70 0.72 #21 14.00 22.40 40.80 22.80 0.57 #22 15.70 20.40 45.40 18.50 0.56 #23 16.10 17.60 49.20 17.10 0.51

(a) MPI3 = (% 3-MP + %2-MP) / (%9-MP + %l-MP)

axes, the interpretation is very easy since a simple inspection of only one plane (i.e., Fl X F2) is sufficient. However, in many instances, the percentage of inertia on the first factorial axes is not sufficient to allow a straightforward interpretation of the results from the sole FlF2 plane. In these cases, it is necessary to consider several maps (e.g., Fl X F3, F2 X F3), and for all points, inspect the absolute and relative contributions which depict the goodness of fit of the points on the different planes. This does not present major problems unless one has some practical expertise in statistics. However, this is a long and tedious task and when performed by untrained people in statistics, it can lead to erroneous conclusions.

For a more practical use of CFA, we recently proposed to employ this multivariate approach in combination with the nonlinear mapping (NLM) method (Devillers and Domine, 1994; Domine et al., 1994). Indeed, NLM (Sammon, 1969; Zitko, 1986, Domine et al., 1993) presents the ability to summarize at best the information con- tained in a data table on a sole map. Therefore, it ideally complements CFA, when most of the inertia is not carried by the first two factorial axes. It was also shown that this approach allowed to benefit from the advantages of both statistical methods. Indeed, CFA provides a useful and adapted data treatment while NLM simplifies the exploi- tation of the results. In this study, the percentages of inertia explained on the first factorial pane (Fl X F2) were not sufficient to fully interpret the results obtained for the DMP (83.4% of the total inertia on Fl X F2) and the TMP (82.3% of the total inertia on FI X F2) data on a sole map. Moreover, the study of the absolute and relative contributions for all factorial axes showed that high order factorial axes carried nonnegligible information. For these two reasons nonlinear mapping (NLM) analysis was used to summarize the maxi- mum of information from the CFA coordinates on a plane. In all cases, the number of FCs (Factorial Components) kept accounted for at least 99.4% of the total inertia (i.e., 3, 9, and 10 FCs for MP, DMP, and TMP, respectively)

NLM represents a set of points defined in an n-dimensional space in a lower d-dimensional space (d = 2 or 3). It tries to preserve distances between points in the display space as similar as possible to the actual distances in the original space. Briefly, the procedure

for performing this transformation consists in calculating an error between the distances in the original space and the distances in the display space (i.e., nonlinear map). This error is used to modify the coordinates of points in the display space. This process is carried out iteratively by means of a minimization algorithm called “steepest descent procedure” until termination conditions are satisfied. The most widely used termination condition is a sufficiently low differ- ence between the error calculated at the step n and the one at the step n - 1 in the iteration process.

For a comprehensive presentation of the NLM method, one should refer to a recently published review (Domine et al., 1993).

Interpretation of the maps was performed by plotting the original data (relative abundance of each isomer) by means of squares and circles proportional to the magnitude of the parameters. For a better visual interpretation, percentage data were centered with the mean of each table before their graphical representation on the nonlinear maps. Therefore, the larger the square, the larger the percentage and the larger the circle, the smaller the percentage.

CFA and NLM analyses were performed with STATQSAR ( 1993) and the graphical interpretation with GraphMu (Thioulouse, 1990).

RESULTS

The analytical results are given for the twenty-three studied samples in Tables 2 (MP), 3 (DMP), and 4 (TMP) in the form of relative abundances of each isomer (% ) in each series (calculated from the GUMS area). Methylphenanthrene index (MP&) was calculated from analyses by GUMS in SIM mode (Table 2).

All mapping errors were sufficiently low to consider that all information is summarized on the nonlinear maps.

Identification of Phenanthrene Compounds

Four methylphenanthrenes are observed in all the samples (Fig. la). The 4-MP, which is sterically hindered and has


INDONESIAN CRUDE OILS AQUITAINE CRUDE OILS

Immature

Mature

3-MP

Immature

Mature

2-MP

METHYLPHENANTHRENES FIG. 2. Methylphenanthrene distributions in crude oils of various origin.

Table 3. Relative abundances (%) of the. dimethylphenaathnxs in all the samples

SMPlCl 3.6-DMP 3.10.DMP 29-DMP 3.9-DMP II-DMP 1.9-DMP 2.10DMP lb-DMP 2.3.DMP 2.6.DMP 1.8.DMP 1.7-DMP 2.7.DMP 1.2.DMP

Yl 1.62 9.56 12.71 8.92 6.05 8.75 7.68 4.33 2.38 12.74 3.43 12.85 3.56 5.42 w 1.32 11.91 14.10 11.M) 6.90 9.94 9.68 4.98 2.37 5.50 4.35 11.23 2.77 3.35 Y3 1.77 9.70 11.78 8.97 6.36 8.55 8.34 5.22 3.13 8.03 3.54 14.60 4.07 5.94 14 1.44 11.07 13.53 13.58 6.65 8.88 11.96 5.43 3.m 5.26 4.25 9.44 2.85 2.63 #5 5.79 9.07 8.49 7.73 5.41 5.21 8.68 6.37 3.67 16.22 2.51 12.35 6.76 1.74 Y6 633 6.12 9.03 7.22 5.87 5.86 8.13 5.86 3.62 17.15 2.26 12.63 7.66 2.26 Y7 7.33 9.05 8.63 6.89 5.61 6.03 7.33 5.61 3.44 16.81 1.72 12.07 7.33 2.15 Y8 5.96 9.09 8.23 8.24 5.68 5.39 9.08 5.97 3.69 16.19 1.43 12.51 6.83 1.71 y9 5.05 8.13 8.35 6.04 6.48 5.16 8.68 7.58 5.62 13.04 2.43 13.97 7.48 1.99 YlO 5.66 8.73 7.85 7.82 5.15 5.07 8.36 6.46 4.11 14.91 2.44 13.72 7.50 2.22 111 2.93 5.71 6.14 9.90 4.48 4.62 5.78 7.83 4.53 9.33 4.64 23.78 4.58 5.74 Y12 2.01 6.91 6.71 6.07 4.07 5.74 6.12 7.15 3.78 8.43 3.13 30.42 5.28 4.18 Y13 331 7.77 6.97 7.86 4.76 5.73 5.87 8.81 4.76 10.72 4.36 18.13 5.53 5.42 1114 1.93 4.33 5.91 3.24 4.58 3.73 4.46 10.12 4.33 11.68 6.03 26.87 5.07 7.72 w15 2.13 5.69 7.13 5.56 4.49 3.62 5.35 9.22 3.95 10.37 6.21 25.27 4.38 6.63 W16 3.03 6.85 7.38 4.78 6.32 5.22 6.24 10.53 5.82 10.88 4.17 18.34 5.47 4.97 Y17 2.33 4.85 7.23 2.75 6.81 4.05 3.98 10.58 4.78 12.03 5.94 23.32 4.25 7.09 #I8 3.82 3.47 9.27 7.82 5.45 7.45 9.45 7.45 4.37 12.91 2.73 16.19 6.54 3.08 Y19 1.47 10.38 11.53 7.44 6.82 8.38 7.23 5.55 3.98 4.52 5.66 20.02 3.25 3.77 #20 2.66 10.34 10.m 10.34 7.37 6.76 9.01 6.04 3.27 6.65 3.79 14.53 4.71 4.50 x21 1.59 9.63 11.43 8.99 7.41 7.31 8.57 6.45 4.55 5.92 3.82 14.81 3.81 5.71 Y22 1.81 10.78 11.52 10.15 5.71 7.50 7.93 5.28 2.85 7.29 3.81 15.86 3.80 5.71 l23 1.18 11.95 11.42 13.67 5.49 8.07 7.53 6.24 4.09 7.64 2.58 10.87 2.92 6.35


TABLE 4. Relative abundances (%) of the trimethylphenanthrenes for all the samples.

Sunplcl lJ.lO-TMP 1,3,&ThQ 1.3.9-TMP 1.6.9-T?@ 2.3.6-TMP 23,10-TMP 2.6.9-TMP ZBJO-TMP 1.7,9-TMP

1,3,afTMP I1 4.87 3.41 5.96 5.57 2.21 6.16 10.58 4.55 13.58 a2 5.57 4.13 7.87 7.48 2.03 4.29 10.91 5.53 15.28 13 4.66 4.25 7.30 6.18 2.06 4.19 10.22 4.60 12.84 #4 6.27 3.27 7.36 7.36 1.91 8.71 13.64 6.54 15.53 #S 9.53 6.43 4.09 4.43 5.16 5.43 12.19 8.09 11.85 #6 9.16 6.43 3.48 4.25 5.45 5.68 12.10 8.83 11.65 #I a.84 5.93 3.91 3.91 5.93 9.85 10.73 7.83 a.84 18 9.10 5.81 4.50 3.95 5.15 7.79 11.08 8.44 11.08 #9 1.22 5.09 3.55 6.00 5.09 2.94 11.18 7.22 11.58 110 7.83 5.46 3.71 4.84 5.25 6.99 10.92 7.41 11.23 Wll 4.29 3.71 3.70 4.22 4.94 1.95 7.67 5.00 10.72 112 4.72 3.92 4.33 4.55 4.81 1.64 9.05 5.45 9.63 w13 4.41 2.40 2.59 5.10 4.29 5.29 7.31 4.41 13.23 #14 1.71 2.05 2.39 4.67 3.41 1.60 7.50 2.95 a.98 115 3.92 2.83 2.94 5.23 3.71 3.71 10.14 3.51 9.48 1116 3.78 3.35 281 4.65 3.89 3.2A a.43 4.54 9.73 a17 2.28 2.28 2.78 5.05 1.64 1.51 7.71 3.66 9.86 (118 7.19 4.64 4.31 4.97 5.31 6.96 9.83 6.63 12.48 Y19 3.77 2.64 4.76 6.19 1.42 3.04 9.83 3.84 13.37 120 6.61 4.60 6.21 6.91 2.70 3.60 9.71 6.61 13.41 #21 4.80 3.40 5.10 6.71 2.30 3.90 8.21 5.10 12.21 I22 5.62 2.81 5.62 6.02 1.60 6.22 11.43 4.91 11.94 xx3 a. d. n. d. n. d. ( n. d. = not detemuned because not mesurcd)

n. d. n. d. n. d. n. Ct. n. d. a. d.

a high enthalpy of formation (Garrigues et al., 1990), is lacking.

Among the twenty-five possible DMPs, fourteen DMP isomers have been previously detected by Garrigues et al. ( 1987a), Radke et al. ( 1990), and recently confirmed by Budzinski et al. ( 1992b). Fourteen compounds were detected in this study: four flfl substituted DMP, eight cwp substituted

Terrestrial crude oils

Group II Terrestrial source rocks

FIG. 3. Nonlinear map of the twenty-three samples for the MP. See Table 1 for correspondence between samples and numbers. Group I = marine crude oils, group II = terrestrial source rocks and group III = terrestrial crude oils.

DMP, and two CKX type DMP (Fig. lb). Compounds with methyl substituents in positions 4 or 5 are missing like compounds with strong peri (9,10 DMP) or ortho ( 1,lO DMP) effects.

Trimethylphenanthrenes (56) exist as possible isomeric compounds. However, as in the previous series, compounds with peri and ortho substitution or compounds substituted in

r: 3-methylphenanthrene 9-methylphenanthrene

c]’ Group III .Q

0

8% 0. 0 0

9@ 4 t-methylphenanthrene 1-methylphenanthrene

ED @

fl9

& & 0 II!!7 ??‘: 0

0 Group II 0 0J

L! b) (4

FIG. 4. Plot of centered percentages of MP. Each map corresponds to the percentages of one MP in all the twenty-three samples. Squares (positive values) and circles (negative values) are proportional to the magnitude of the data.


TABLE 4. (Continued) Relative abundances (%) of the trimethylphenanthrenes for all the samples.

Sultpls 1.3.7-TMP 1.2,9-TMP X7,9-TMP 1.6,7-T!&’ 23.7-TMP 1,2&TMP 1,2.8-TM? 127-TMP

Wl 6.07 2.92 6.67 3.37 3.13 2.10 14.68 3.52 112 6.27 3.31 8.26 4.29 3.66 2.14 L3 6.14 3.13 7.27 3.83 3.21 2.61 #4 3.12 2.46 8.45 3.49 2.46 1.64 IS 6.16 1.00 8.43 3.43 4.43 2.66 M 7.40 0.00 8.39 2.93 5.11 2.51 WI 7.83 0.00 8.84 2.90 4.92 2.91 I8 7.13 1.20 9.10 3.29 5.15 3.29 b 7.12 1.10 8.33 3.86 7.12 3.86 #lo 6.49 1.54 7.52 3.51 6.07 3.51 111 4.81 2.60 4.22 3.23 1.21 5.12 #I2 4.23 3.02 4.87 3.80 6.45 10.31 R13 6.18 2.33 4.73 4.66 5.66 7.57 014 4.66 2.72 4.66 5.58 2.61 8.64 #15 3.82 0.00 4.25 3.93 4.25 9.16 116 4.43 2.48 5.73 4.21 3.78 12.43 117 4.55 2.66 4.92 5.69 2.53 8.85 #18 5.63 1.65 7.52 4.64 5.96 3.98 Y19 7.39 2.64 6.28 3.45 3.25 1.83 120 7.41 2.10 7.91 5.00 5.10 2.40 121 6.91 3.00 7.21 4.40 6.41 2.30 #22 5.62 4.11 6.42 4.11 2.91 2.11

6.44 13.87 3.55 3.43 3.81 3.91 1.97 4.98 4.43 14.94 12.27 8.51

22.53 19.19 14.37 21.73 3.98

20.27 7.01 14.31 14.04 n. d.

2.54 3.65 1.64 2.66 2.82 2.91 1.97 3.76 3.29 11.05 6.88 11.10 13.31 9.93 8.10 1226 4.32 3.45 2.70 3.70 3.11

$23 n. d. n. d. n. d. n. d. n. d. n. d. n d.

position 4 (or position 5) are lacking in the environment (Budzinski et al., 1992b; Fig. lc) Only eighteen TMP have been identified by comparison with standard compounds: two compounds coelute ( 1,7,9 TMP and 1,3,8 TMP) . Since these two compounds have a comparable thermodynamic stability (AH = resp. 29.3 kcal/mol and 29.4 kcal/mol; Budzinski et al., 1993b), it could be reasonably assumed that their respec- tive contribution to the GC peaks is similar.

Marine crude oils

Terrestrial crude oils

GroupD w Terrestrial source rocks

FIG. 5. Nonlinear map of the twenty-three samples for the DMP. See Table 1 for correspondence between samples and numbers. Groups identified as in Fig. 3.

DISCUSSION

On Fig. 2, a sequence of Indonesian crude oils of increasing thermal maturity have been reported for their MP distribution. The MP isomers are ordered on the horizontal axis according to their relative thermodynamic stability as calculated previously (Ganigues et al., 1990; Budzinski et al., 1993b). A classical and regular evolution of the distribution with increasing maturity is observed in this type III organic matter: increasing concentrations of 2-MP and 3-MP with parallel de- creasing amounts of 9-MP and l-MP. This is indicated by the increasing MPIi (Table 2) values according the ranking of the oils (oils #.5 to #8 ) Some Aquitaine crude oils estimated as marginally mature (for example oils #l, #2, or #3) or mature (for example oils #4 and #20) according to Connan ( 1993), present erratic MP distributions on which no maturity evalu- ation could be done (Fig. 2). The distributions are dominated by the 9-MP at any maturity stage. Particularly this high level of 9-MP induces low MPIs (Table 2) values which are not of any use for maturity assessment. These observations are con- sistent with previous studies indicating a regular evolution in type III organic matter while irregular trends are observed in type II organic matter (Radke et al., 1986; Cassini et al., 1988). MP distributions have been shown to be origin de- pendent: I-MP dominates in type III kerogen, particularly in resinite-rich coals (Heppenheimer et al., 1992); 9-MP dominates in type II and also type I kerogens (Isaksen, 1991) 2- MP and 3-MP usually are predominant compounds in highly mature type I/type II kerogen (Radke et al., 1986).

Such specific isomer contributions related to either origin or maturity of the organic matter could be also observed in DMP and TMP series for the studied samples (Tables 3, 4). For instance 2,6-DMP dominates in Indonesian crude oils, meanwhile DMP isomers bearing methyl groups in position

2050 H. Bud&ski et al.

3,6-DMP O,o

n0

LJ G-4

3,10-DMg %

(b)

2,9-DMP ??n 0

0-

(4

5,9-DMP ??oo

. q . 0.

0. 5 00

(4

1,3-DMP, .

0

. .; ??

0

0 00

00 ??-0

O0 0 0'

(e)

L,9-DMP no

00 0

(f)

!,lO-DMP of3 .

. 40 .

(9)

1,6-DMP. 0

0

0 aoo . 00

na .**o . .

h)

2,3-DMP O0

2,6-DMP 00

o 6.’

??o

5

??u r!i@

“00

t.0

l&DMP 00

.,7-DMP ??o”

2,7-DMP 00

0

1,ZDMP 00 .

0 e O0

Oo 0 . . .

m

FIG. 6. Plot of centered percentages of DMP. Each map corresponds to the percentages of one DMP in all the twenty- three samples. Squares (positive values) and circles (negative values) are proportional to the magnitude of the data.

9 (or in position 10) are more abundant in Aquitaine crude oils. However, due to the great number of isomers, the interpretation of DMP and TMP distributions based on complex barcharts becomes difficult. Multivariate analyses associated with graphical representation are preferred in this instance (Kvalheim et al., 1987; Irwin and Meyer, 1990; Yunker et al., 1991).

Methylphenanthrenes

The map of the samples is presented on Fig. 3. Three clusters of samples are observed. Group I located on the bottom

right part of the map corresponds to samples #l to #4 and #19 to #23 which are the marine crude oils. Group II is located on the upper left part and corresponds to the samples #l 1 to #17 which are the terrestrial source rocks. Group III is located in the middle upper part of the map and corresponds to samples #5 to #lO and #18 which are the terrestrial crude oils. There- fore, these three clusters appear as directly related to origin and thermal maturity characters of the samples.

The percentages after centering have been plotted on the sample map (Fig. 4) by means of squares (positive values) and circles (negative values) proportional to the original data.

Alkylated aromatic hydrocarbons in petroleum 205 1

Group II Terrestrial source rocks

Group III Terrestrial crude oils

6

Group I Marine crude oils

FIG. 7. Nonlinear map of the twenty-two samples for the TMP. See Table I for correspondence between samples and numbers. Groups identified as in Fig. 3.

The largest squares represent the highest abundances of individual MP while the largest circles represent the lowest abundances. As previously observed on the bar-charts, high abundances of 9-MP (cw-substitution pattern) (large squares in Fig. 4c) are obtained in marine crude oils (group I located on the bottom right). The marine crude oils (group I) appear as systematically depleted in 3- and 2-MP (b-substitution pattern) (Fig. 4a, b) when compared to the other samples (groups II, III) so they could be considered as less thermally mature than the other samples when considering the MP distributions because they present lower abundances of the most thermodynamically stable isomers substituted in p position. In contrast, high amounts of I-MP (a-substitution pattern) (Fig. 4d) are linked with the terrestrial source rocks (group II located on the left part of the map). The same observations could be done for the 2-MP (Fig. 4b) for which high abundances are observed both for terrestrial source rocks and for terrestrial crude oils. In this last case the 2-MP (Fig. 4b) is both an origin and thermal maturity indicator. The 3-MP (Fig. 4a) is associated to high maturity level since the highest concentrations are found with the terrestrial crude oils in group III.

Thus, the 9-MP could be stated as a marker of marine origin and on the contrary the I-MP appears as a terrestrial indicator (Alexander et al., 1987). Furthermore the strong depletion in the most stable MP isomers (p substituted, 2- and 3-MP) in the case of the Aquitaine crude oils could also be interpreted as characteristic of marine origin.

Dimethyiphenanthrenes

The map of the samples (Fig. 5) shows the same three sample groupings as in the case of the MP. The original per-

centages after centering were plotted on the map for a more convenient discussion and fourteen maps are obtained corre- sponding to each isomer (Fig. 6).

Two compounds, resp. 1,3- (Fig. 6e) and 2,3-DMP (Fig. 6i), show very narrow range of concentrations as demonstrated by the fact that circles are of the similar size. It means that these two compounds are not discriminant ones in the study of the samples. They will not give information on origin or thermal maturity. On the contrary the 1,7- (Fig. 61) and 2,6-DMP (Fig. 6j) show the most intense variations of abundances as pointed out by the wide variations in the size of squares and circles. The distributions for these two compounds are very contrasted. The 1,7-DMP dominates in the case of the terrestrial source rocks (large squares in group II) and is more abundant than in the case of the crude oils. This compound presents a unique behaviour as demonstrated by the comparison of its map with the other ones. The 1,7-DMP can characterize the terrestrial source rocks. This compound (called also pimanthrene) has been often claimed to be related to natural precursors like pimaric acid present in resin material (Simoneit, 1977; Laflamme and Hites, 1979). Recent studies on coals (Heppenheimer et al., 1992) and on Jurassic Austra- lian rocks (Alexander et al., 1992) have shown the predominance of 1,7-DMP over the other isomers, in conjunction with retene ( 1 -methyl-7-isopropyl-phenanthrene) and 1-MP. The correlation between high amounts of I-MP and high amounts of 1,7-DMP is also found in the present study. 1,7- DMP can be suggested as a marker of terrestrial input of organic matter.

The 2,6-DMP (Fig. 6j) is the major compound of the terrestrial crude oils. To a lesser extent these crude oils can also be characterized by higher amounts of 3,6-DMP (Fig. 6a) and 2,7-DMP (Fig. 6m) than in other types of oils. These three compounds are the three most thermodynamically stable isomers for DMP series (Budzinski et al., 1993b). The marine crude oils and the terrestrial source rocks appear as depleted in these isomers relative to the terrestrial crude oils (circles opposed to squares).

For the Aquitaine crude oils (group I), the DMP distributions are generally marked by a&substituted DMP bearing methyl groups in the 9 (or 10) position: 2,9-, 1,9-, 3,9-, 3,10- DMP (respectively, Fig. 6c,f,d, and b) and to a lesser extent 2,10-DMP (Fig. 6g). In comparison the terrestrial samples exhibit lower abundances of these compounds. Crude oil #19 slightly differs from the other Aquitaine crude oils for it presents lower amounts of 3,9-DMP and 2, IO-DMP. This could be related to its source. It is the only Aquitaine oil, in the set of samples, associated to a Hettangian-Rhaetian source rock.

The 1,6-DMP exhibits a slightly contrasted map. It is more abundant in the terrestrial source rocks than in the crude oils. The last two cY&substituted isomers, i.e., 1,8- and 1,2-DMP, present very similar maps. They are generally more abundant in the terrestrial source rocks than in the crude oils. These three isomers could be associated with a terrestrial origin.

The DMP substituted in position 9 (or in position 10) could be interpreted as marine indicators and correlated to the 9- MP. The 1,7-DMP is strongly related to a terrestrial origin and linked to the I-MP. As in the case of the MP, the strong


1,3,10-TMP 2,3,6-TMP

0 0 e’:” .

1,7,9-TMP + 1,6,7-TMP

0 0 CBO 0 w O ??u

OO m* 0 0

.

0 O” . 0

.

0

OO 00 .

.

00

,“s 0

Y

0) (4 (e) Cm)

:,3,6-TMP 1,3,7-TMP 2,3,7-TMP

OO . ?? . .

On 00

8

0 0

CP

??

0 0

0

(b) (i) O-4

.,3,9-TMP 2,6,9-TMP 1,2,9-TMP

OW 1,2,64-M

%0° OOO

.u

“b. ??

. 0

0 ??

0.

0 00

OO

8

00 @O 0 08

(4 (k) (0)

.,6,9-TMP 2,6,10-TMP 2,7,9-TMP 1,2,8-TMP 0 0

0 . 00 eQ 0 ????w

00 0’

o. O ?? “0 u Od

OO no 00 Q

??0 .

0 0 .

??

k4 :h)

I

(1)

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cl Cl

PI IP 0

0 w 0

*0

3 (4)

FIG. 8. Plot of centered percentages of TMP. Each map corresponds to the percentages of one TMP in all the twenty- two samples. Squares (positive values) and circles (negative values) are proportional to the magnitude of the data.


FIG. 9. A mono aromatic compound (A) identified by Bisseret et al. ( 1987) in an amoeba as a possible precursor of the 9-MP.

depletion of the most stable DMP in the Aquitaine crude oils has to be related to the marine origin of these oils.

Trimethylphenanthrenes

The map of the samples (Fig. 7) shows the same three groups as in the case of the MP and DMP studies. The percentages after centering were plotted on the map for a more convenient discussion and seventeen maps were obtained cor- responding to each isomer (Fig. 8).

The 1,6,7-TMP (Fig. 8m) and 1,2,9-TMP (Fig. 8k) exhibit very weakly contrasted maps. They will not be very inform- ative for thermal maturity or origin assessment.

The TMP which shows the most contrasted map is the 1,2,8-TMP (Fig. 8~). This compound contrasts very strongly the terrestrial crude oils (group III: large circles) to the marine crude oils and the terrestrial source rocks (respectively, groups I and II: large squares). It is much more abundant in terrestrial source rocks and in marine crude oils than in terrestrial crude oils. This isomer has been identified previously by Carruthers and Douglas ( 1957). It was suggested as a marker derived from higher plants by dehydrogenation of te- tracyclic triterpenoids and of diterpenoids present in higher plants (Carruthers and Douglas, 1957). It was found in very high amounts in a recent study (Budzinski et al., 1993b) in coals and crude oils from the Handil field (Mahakam delta), and its occurrence was tentatively linked to the degradation of &amyrin according to a reaction scheme proposed by LaFlamme and Hites (1979). De Mayo ( 1959) and Hayatsu et al. ( 1987) report the preferential production of trimethylphenanthrenes (without precise substitution assignment) by dehydrogenation of compounds within the ftiedelane group, while P-amyrin compounds yield naphthalene and picene compounds. The high amount of 1,2,8-TMP in the marine crude oils, while slightly lower than in the source rocks, raises a problem as regards its specificity as a terrestrial marker. Its ubiquitous occurrence may suggest a way of formation more general than the degradation of higher plant triterpenoids. Kil-

lops ( 1991) has detected in a Jurassic lacustrine sequence, several dominant alkylphenanthrene homologs. While the methyl substitution pattern of these phenanthrenes has not been established, he suggests 1,2,8-TMP as a possible can- didate. He proposes the 1,2,8-TMP may derive from the degradation of hopanoids. Moreover, tricyclic and pentacyclic hopanoid aromatic derivatives have been suggested to be associated with a marine environment (Ganigues et al., 1987b). If 1,2,8-TMP is derived from bacteria-hopanoid precursors, this could explain its high abundance in type II organic matter.

Revill et al. ( 1993) have also found huge amounts of 1,2,8- TMP in tasmanite oil shale. As possible precursors of this TMP, they have proposed, in that case, tricyclic terpanes. The unquestionable algal origin of the tasmanite confirms the non- specificity of the 1,2,8-TMP as a molecular indicator of origin. Indeed this compound can have bacterial, algal, or terrestrial origin.

One of the most striking characters of the terrestrial source rocks is the high amounts of 1,2,7- (Fig. 8q) and 1,2,6-TMP (Fig. 80) (large squares) opposed to their low concentrations in crude oils (circles). It may be envisaged that when the “triad”, 1,2,7-, 1,2,6-, and 1,2,8-TMP is present in very high quantities, this could be related to a terrestrial origin. In this case, the 1,2,8-TMP could derive from triterpene from higher plants and be rearranged under thermal maturation by methyl shifts (Ensminger et al., 1978; Radke, 1987; Budzinski et al., 1993b) to produce 1,2,6- and 1,2,7-TMP.

Six of the seven most stable TMP isomers (Budzinski et al., 1993b), i.e., a /3P&substituted TMP, the 2,3,6-TMP (Fig. 8e), and five @P-substituted TMP, the 2,6,9-, 2,6,10-, 2,7,9-, 1,3,6-, and 1,3,7-TMP (respectively, Fig. 8g,h,l,b, and j) are more abundant in terrestrial crude oils than in marine oils as demonstrated by the largest and most numerous squares for the terrestrial oils. The marine crude oils seem to be less thermally mature than the terrestrial crude oils when considering only the TMP distributions. This observation was also done in the case of the MP and the DMP distributions.

The least thermodynamically stable isomers bearing a methyl in position 9, i.e., 1,3,9-, 1,6,9-, 1,7,9- (+ 1,3,8-), and 1,2,9-TMP (respectively, Fig. 8c,d,i, and k), are generally more abundant in marine crude oils than in terrestrial ones. The terrestrial source rocks are also very poor in these five TMP. These isomers can be considered as specific of marine samples and thus taken as marine markers.

The 1,3,10- (Fig. 8a) and 2,3,10-Th4P (Fig. 8f) are more abundant in the case of the terrestrial crude oils than in source rocks or marine oils. But it is difficult in this case to contrast the marine oils and the terrestrial ones because the differences are very small. It is preferable to restrict the comparison to the oils and the rocks.

The TMP substituted both in position 1 and 9 could be suggested as marine indicators meanwhile the 1,2,7- (Fig. 8q), 1,2,6 (Fig. 80), and 1,2,8-TMP (Fig. 8p) (when together with the first two) can be considered as terrestrial markers. Again as in the case of MP and DMP, the most stable isomers are present in very low amounts in the marine crude oils which


Table 5. Summary of the predominance of phenanthrene compounds depending on origin or thermal maturity.

Immaturity Marinecharacter Terrestrialcharact~

3-m xx 2-MP xx 1-W xx xx 9-W xx xx

2,10-DhQ 1,3-DMP 3,9-DMP 2,9-Dh4P 3,10-DhP 1,9-DMP 1,8-DMP 1,2-DMP 1.7-DhP 1,6-DhP 2,3-DMP 2,6-DMP 3,6-DMF’ 2,7-DMP

X X X X

X

X X X X

X xx X

xx X xx X xx X

1,2,7-TMP I ,2,8-W I ,2,6-TMP 1.2.9-W I ,6,9-W 1,7,9-TMP+1,3,8-W : ,3,9-TMP !,7,9-TMP, !3,10-w !,6,10-W ,36-W ,3.7-ThP JJO-W !,3,7-w :,3,6-ThG’ ,6,9-W

X X xx X X X 0 X X X X X X

X X X

X gr) xx X X X

could suggest an apparent low thermal maturity to these oils when compared to the terrestrial ones.

The Aquitaine crude oils are characterized generally by high amounts of phenanthrene compounds substituted in position 9. The predominance of these isomers could be related to unknown precursors. As a possible example of such a mol- ecule, it can be cited (Fig. 9) as the monoaromatic compound which was identified by Bisseret et al. ( 1987) in an amoeba and which bears a methyl group in position 6 of the steroid skeleton (which corresponds to position 9 of the phenanthrene skeleton). All the crude oils from the Aquitaine basin appear

as much less thermally mature than the terrestrial ones due to predominance of the least stable phenanthrenes over the most stable ones. This is not in agreement with the thermal “real- ity” but certainly reflects the influence of the environment of deposition. Indeed. methyl group migration on aromatic nu- cleus has been ascribed to presence of catalyst (Ensminger et al., 1978). This has been demonstrated in laboratory experi- ments (Alexander et al., 1982; Bearez, 1985). In prevailing carbonaceous environments like in the case of the Aquitaine basin, there is a lack of clay catalysis, Thus, the molecular rearrangements could be inefficient and could occur at a very


slow rate. The fingerprints could always exhibit very immature profiles with predominance of thermodynamically unsta- ble phenanthrenes substituted in position 9. Moreover, an- other hypothesis could be a continuous generation of these compounds from the kerogen.

Bisseret P., Adam H., and Rohmer M. ( 1987) Structural elucidation of ring B aromatic sterols of the soil amoeba Acanthamoeba po- lyphaga. Chem. Commun., 693-695.

Budzinski H., Garrigues P., and Bellocq J. (1992a). Gas chromatographic retention behaviour of dibenzothiophene derivatives on a smectic liquid crystalline polysiloxane stationary phase. J. Chro- matogr. SW, 297-303.

CONCLUSION

MP, DMP, and TMP isomer distributions allow the similar differentiation of type II and type III material, according to their origin as summarized in Table 5. Moreover, by the ex- amination of the MP distribution, we can get access to a very complete information on the various characteristics of the samples which are also confirmed by DMP and TMP patterns.

The distributions of phenanthrenes are strongly influenced by the origin. If in the case of type III material, phenanthrenes can be used for thermal maturity assessments, in the case of type II material, they cannot be used for that purpose. This conclusion agrees with the work of Radke et al. ( 1986) and of Cassini et al. ( 1988).

Budzinski H., Radke M., Garrigues P., Wise S. A., and Bellocq J. ( 1992b) Gas chromatographic retention behaviour of alkylated phenanthrenes on a smectic liquid crystalline stationary phase: application to organic geochemistry. J. Chromatogr. 627, 227-239.

Budzinski H., Garrigues P., Connan J., and Bellocq J. ( 1993a) Chro- matographic fractionation of aromatic compounds from ancient and recent sediments for access to alkylated PAH by GC-FID and GC-MS. Quimica Analitica 12, 69-74.

Budzinski H., Garrigues P., Radke M., Connan J., and Oudin J. L. ( 3993b) Thermodynamic calculations on alkylated phenanthrenes: geochemical applications to maturity and origin of hydrocarbons. Org. Geochem. 20,9 17-926.

Moreover, the use of the phenanthrene ratios like MP13 can be too restrictive and mask specific distribution patterns. The use of multivariate data analyses appears as much more efficient.

Carruthers W. and Douglas A. G. (1957) The constituents of high boiling petroleum distillates. part IV. Some polycyclic aromatic hydrocarbons in a Kuwait oil. J. Chem. Sot., 278-281.

Cassini F., Gallangos 0.. Talukdar S., Vallejos C., and Ehrmann U. ( 1988) Methylphenanthrene maturity index of marine source rock extracts and crude oils from the Maracaibo Basin. Org. geochem. 13,73-89.

In this study some phenanthrene compounds appear as useful markers of origin: 1- and 9-substituted compounds, respectively, for the Mahakam delta (terrestrial origin) and for the Aquitaine basin (marine origin) (see, for recapitulation, Table 5). The 1,2,8-TMP, which is always the predominant form in the TMP series, reveals its particular ubiquitous char- acter. Its origin remains to be proven but its ubiquitous presence could suggest degradation pathways both from triterpen- oid or hopanoid skeletons.

Connan J. ( 1993) Elf Ayuitaine, Internul Report. Connan J. and Lacrampe-Couloume ( 1993) The origin of the Lacq

Superieur heavy oil accumulation and of the giant Lacq Inferieur gas field (Aquitaine Basin, SW France). In Applied Petroleum Geochemistry (ed. M. L. Bordenave), pp. 465-488. Editions Technip.

De Mayo P. ( 1959) The Higher Terpenoids. Interscience. Devillers J. and Domine D. ( 1994) Extracting SAR information from

drug patents by means of the combined use of linear and nonlinear multivariate methods. (submitted)

Devillers J. and Karcher W. ( 1990) Correspondence factor analysis as a tool in environmental SAR and QSAR studies. In Practical Applications of Quantitative Structure-Activity Relationships (QSAR) in Environmental Chemistry and Toxicology (ed. W. Karcher and J. Devillers), pp. 181- 195. Kluwer.

Acknowledgmenrs-SNEA( P) and TOTAL are acknowledged for Devillers J., Thioulouse J., Domine D., Chastrette M., and Karcher the gift of the samples and for allowing publication of these data. We W. ( 1991) Multivariate analysis of the input and output data in thank PROCOPE program for supporting the exchange of research- the fugacity model level I. In Applied Multivariate Analysis in SAR ers. Financial support, from both precited French petroleum compa- and Environmmtul Studies (ed. J. Devillers and W. Karcher), pp. nies, is also gratefully acknowledged. 281-345. Kluwer.

Editorial handling: M. C. Kennicutt II

Domine D., Devillers J., Chastrette M., and Karcher W. ( 1993) Non- linear mapping for structure-activity and structure-property mod- elling. J. Chemometrics 7, 227-242.

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Alkylated phenanthrene distributions as maturity and origin indicators in crude oils and rock extracts