A stable carbon isotope and biological marker study of Polish bituminous coals and carbonaceous shales

International Journal of Coal Geology 55 (2003) 73 – 94 www.elsevier.com/locate/ijcoalgeo

A stable carbon isotope and biological marker study of Polish bituminous coals and carbonaceous shales Maciej J. Kotarba a,*, Jerry L. Clayton b a

Faculty of Geology, Geophysics and Environmental Protection, University of Mining and Metallurgy, Al. Mickiewicza 30, 30-059 Cracow, Poland b U.S. Geological Survey, P.O. Box 25046, MS 977, Denver Federal Center, Denver, CO 80225, USA Received 25 July 2002; accepted 13 May 2003

Abstract Biological marker and carbon isotopic compositions of coals and carbonaceous shales from the Upper Carboniferous strata of the Upper Silesian (USCB), Lower Silesian (LSCB), and Lublin (LCB) coal basins were determined to assess depositional conditions and sources of the organic matter. n-Alkane, sterane, and isoprenoid distribution, and carbon isotope ratios are consistent with an origin from higher plants. In some cases, pristane/phytane (Pr/Ph) ratios of carbonaceous shales (roof and floor shales) are < 1.0, while the associated coals have high ratios (H1.0). This suggests that reducing conditions prevailed during deposition of the shales, but a period of oxidizing conditions accompanied deposition of the coals. Steranes present in coal extracts are dominated by the 14a(H)17a(H)20R C29 stereoisomers, typical, but not conclusive, of higher plant origin. Carbonaceous shales exhibit a wider range of sterane composition, suggesting local, significant input of algal organic matter. Significant amounts of benzohopanes and gammacerane are present in some coals. Although benzohopanes are present at least in small amounts in samples from many different environments, they have been reported to occur most commonly in marine environments. The present study seems to provide the first example where benzohopanes have been reported in significant amounts in terrestrial organic matter. Gammacerane is abundant in rocks or sediments deposited in carbonate or highly saline marine environments. The finding of high gammacerane concentrations in the coals expands the depositional settings in which it has been observed and questions its utility as an independent indicator of hypersaline carbonate environments. Stable carbon isotope composition of coals, and type III kerogen in carbonaceous shales as well as correlation of stable carbon isotope composition of saturated and aromatic hydrocarbons in carbonaceous shales from both the USCB and the LSCB indicate terrigenous origin. Bitumens are always co-genetic with associated coals and kerogens. Isotopic data reveal that Sofer’s genetic classification of oils is not applicable to organic matter in coals. D 2003 Elsevier B.V. All rights reserved. Keywords: Biomarkers; Stable carbon isotopes; Coal; Carbonaceous shales; Upper Carboniferous (Pennsylvanian); Polish coal basins

1. Introduction

* Corresponding author. Tel./fax: +48-617-24-31. E-mail address: [email protected] (M.J. Kotarba).

Major resources of bituminous (hard) coals in Poland are hosted in Upper Carboniferous (Pennsylvanian) strata (Fig. 1). In this study, depositional

0166-5162/03/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0166-5162(03)00082-X

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M.J. Kotarba, J.L. Clayton / International Journal of Coal Geology 55 (2003) 73–94

Fig. 1. (A) General map of Poland showing locations of bituminous coal basins (shared areas), and (B) geological sketch map of the Upper Silesian Coal Basin (Permian, Mesozoic, and Cenozoic subcrops) showing locations of coal sampling sites. Geology from Kotas (1995).

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conditions and sources of organic matter were discussed in coals and carbonaceous shales from the Upper Silesian (USCB), Lower Silesian (LSCB), and Lublin (LCB) coal basins, based upon biomarker composition and stable carbon isotope ratios. Detailed discussions of the hydrocarbon potential of coals and carbonaceous shales, and occurrence and origin of coalbed gases of the USCB, LSCB, and LCB, are presented in separate papers by Kotarba (1988, 1990, 2001), Kotarba et al. (2002), and Kotarba and Rice (2001).

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During the past 20 years, a number of studies have investigated the oil and gas generation potential of coals and shales containing type III kerogen (e.g. Boreham and Powell, 1993; Clayton, 1993; Clayton et al., 1991; Curry et al., 1994; Durand and Paratte, 1983). The last three decades have seen growing interest in the study of the origin of hydrocarbons and genetic correlation between oils and source rock (kerogen and/or coal) based on biomarker study (e.g. Brooks and Smith, 1969; Clayton, 1993; Curry et al., 1994; ten Haven et al., 1988; Mastalerz et al., 1997;

Fig. 2. Upper Carboniferous lithostratigraphic profile of the Upper Silesian Coal Basin showing locations of sampled coal seams. Din.: Dinantian; U.: Upper; B.: Beds; FM.: Formation.

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Palmer, 1984; Peters and Moldowan, 1993; Peters et al., 1986; Thompson et al., 1994) as well as on stable carbon isotope analyses of oils, bitumens, fractions (saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltenes), kerogens, and/or coals (e.g. Galimov, 1985; Schoell, 1984; Sofer, 1984; Peters et al., 1986; Curiale, 1994; Thompson et al., 1994).

2. Geological setting Coals in the USCB, LSCB, and LCB, Poland, are of Upper Carboniferous age (Fig. 1). The USCB was formed as a Variscan foredeep of the Moravo-Silesian fold zone (Kotas, 1990, 1995). Here, the Upper

Carboniferous coal-bearing succession forms a major part of the molasse fill of a flexural foreland basin and exceeds 8000 m in thickness (Doktor and Gradzin´ski, 2002). The lower part of Upper Carboniferous lithostratigraphic sequence (Namurian A) is of paralic type and comprises deposits of marine, shore, deltaic and fluvial systems, whereas the upper part (Namurian B to Westphalian D) consists exclusively of nonmarine deposits that were laid down in various fluvial systems (Kotas, 1995; Doktor and Gradzin´ski, 2002; Stopa, 1967) (Figs. 1B and 2). The LSCB is situated in the Intra-Sudetic Synclinorium which forms the easternmost part of the intramontane basin system of the Bohemian Massif. The Walbrzych and Nowa Ruda coal districts are relatively small subbasins located in the NW and SE

Fig. 3. Upper Carboniferous lithostratigraphic profile of (A) Walbrzych and (B) Nowa Ruda Districts of the Lower Silesian Coal Basin showing locations of sampled coal seams. Modified from Nemec et al. (1982) and Bossowski and Ihnatowicz (1994). FM.: Formation; M.: Member; G.M.: Gorce Member.

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parts of the LSCB, respectively. The Upper Carboniferous coal-bearing succession is part of a continental molasse sequence (Nemec et al., 1982; Bossowski and Ihnatowicz, 1994; Mastalerz and Prouza, 1995). The coal-bearing succession is diversified in both subbasins (Fig. 3) and comprises alluvial fans, fluvial, lacustrine, peat bog, deltaic, and fan-deltaic deposits (Mastalerz and Prouza, 1995). The LCB is an epiplatform molasse basin developed as a pericratonic depression within the EastEuropean Platform. The lower part of the coalbearing succession (Upper Visean and Namurian A) is of marine-paralic type, the middle part (Namurian B and C and Westphalian A) is of paralic type, and the upper part (Westphalian B to D) comprises the

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deposits of fluvial systems (Kotas and Porzycki, 1984; Porzycki, 1990; Porzycki and Zdanowski, 1995a,b) (Fig. 4).

3. Coal ranks and types in Polish basins In the exploited interval down to 1000 m depth, the ranks of coals in Polish basins are diversified and range from subbituminous to high volatile bituminous in the USCB and LCB, and from subbituminous to semianthracite and anthracite in the LSCB. Dominant are humic coals rich in vitrinites. Sporadically, sapropelic coals occur in the USCB and LCB. The ranks of coals and maceral group composition of coals from the Polish basins were determined by, e.g.

Fig. 4. Upper Carboniferous lithostratigraphic profile of the Lublin Coal Basin showing locations of sampled coal seams. Modified from Porzycki (1990) and Porzycki and Zdanowski (1995a,b). U.: Upper.

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Bula et al. (1983), Gabzdyl and Probierz (1987), Jurczak-Drabek (1996), Knafel (1983), Kruszewska (1983), Kotarba (1988, 1990), Kotarba et al. (2002), Kwiecin´ska and Nowak (1997), and Mastalerz and Jones (1988).

4. Experimental 4.1. Sampling procedure Channel coal samples were collected from each of the coal beds from that were sampled for gas (Kotarba, 2001; Kotarba and Rice, 2001). Locations of sampling sites are presented in Table 1 and Fig. 1. Sampling coal seams in the lithostratigraphic profiles of the USCB, LSCB, and LCB are displayed in Figs. 2– 4. When possible, samples of carbonaceous shales (claystones and/or mudstones) were collected from above (‘‘roof rock’’) and below (‘‘floor rock’’) the seams where coal samples were taken. In the USCB, 28 coal samples and 30 carbonaceous shale samples (15 roof and 15 floor samples) were collected. In the LSCB, 10 coal samples and 10 carbonaceous shale samples (6 roof and 4 floor) were collected. In the LCB, only two coal samples and five carbonaceous shale samples (three roof and two floor) were collected. 4.2. Analytical procedures The coal and carbonaceous shale samples were pulverized, and then extracted with CHCl3 using a Soxhlet apparatus. The extracts were separated into saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltenes by column and thin-layer chromatography. Alumina/silica gel (2:1, v/v) columns (0.8  25 cm) were eluted with petroleum ether (distillation range 40– 45 jC), benzene, and benzene/methanol (1:1 v/v) in order to obtain the first three fractions. Asphaltenes were precipitated with petroleum ether prior to the column separations. After the removal of carbonates and bitumen, coal and carbonaceous shale samples selected for stable carbon isotope analyses were combusted in sealed glass tubes (Sofer, 1980). Preparation of bitumens and fractions for stable carbon isotope analyses was conducted using the same procedure. Stable carbon

Table 1 Information on sample sites Sample Mine code

Seam no.

Upper Silesian Coal Basin A-5 Anna 718 B-5 Brzeszcze 510 B-7 Brzeszcze 356 H-1 Halemba 506 J-5 Jastrze˛bie 502/1 Kr-10 KrupinVski 348 Mi-1 Miechowice 509 Mk-3 Morcinek 406/2 Mk-5 Morcinek 404/2 Mo-1 Moszczenica 506/3 Mo-2 Moszczenica 510/1 Mo-13 Moszczenica 605 NM-1 Niwka-Mod. 510 Pa-1 Paskov 906 eq. Pn-1 Pnio´wek 363 S-10 Silesia 308 S-11 Silesia 214/1 We-1 Wesola 501 Z-4 Zofio´wka 404/4

Age Surface (meters above sea level) N-A N-B W-A N-B N-B W-A N-B W-A W-A N-B N-B N-A N-B N-A W-A W-B W-B N-B W-A

287 252 250 262 260 260 300 274 275 250 221 251 248 314 270 253 254 305 272

Depth (meters above sea level)

Depth (meters below surface)

462 359 308 658 300 310 511 588 544 253 236 214 474 442 402 384 264 365 339

749 611 558 920 560 570 811 862 819 503 457 465 722 756 672 637 518 670 611

Lower Pi-1 Sl-1 Sl-2

Silesian Coal Piast Slupiec Slupiec

Basin—Nowa Ruda District 415/2 W-A 455 284 301/2 W-B 499 397 412 W-A 428 263

739 896 691

Lower T-29 V-30 V-31 V-33 W-30 W-31 W-32

Silesian Coal Thorez Victoria Victoria Victoria Walbrzych Walbrzych Walbrzych

Basin—Walbrzych District 672 N-A 441 672 N-A 479 430 W-A 520 673/4 N-A 573 431/2 W-A 480 430 W-A 620 672 N-A 510

291 42 + 25 90 + 27 355 223

732 521 495 563 453 975 733

713 690

882 864

Lublin Coal Basin Bo-1 Bogdanka Bo-2 Bogdanka

382 382

W-B 169 W-B 174

N-A: Namurian A; N-B: Namurian B; W-A: Westphalian A; W-B: Westphalian B; U. Carb.: Upper Carboniferous; eq.: equivalent; Mod.: Modrzejo´w.

isotope analyses were conducted using Micromass MM 602C and MI-1201 mass spectrometers. The stable carbon isotope data are presented in the standard d-notation relative to PDB. Analytical precision is F 0.15x.

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Gas chromatographic separations of the C11 + saturated hydrocarbons (n-alkanes and isoprenoids) were performed on a Hewlett Packard 5890 Series II GC equipped with a 25 m  0.32 mm capillary column coated with HP-1 100% dimethylpolysiloxane gum

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phase. The oven was programmed from 110 to 310 jC at the rate of 5 jC/min. GC-MS analysis was conducted using a HewlettPackard 5890 Series II GC coupled to a VG 7035 double-focusing mass spectrometer. Determination of

Table 2 Vitrinite reflectance and stable carbon isotope composition of CHCl3 extracts, fractions, and coals Sample code

Rr (%)

Total CHCl3 extract (wt.%)

Fraction composition (wt.%)

d13C (x )

S.Hc

A.Hc

Res.

Asph.

Bit.

3.3 4.2 3.0 6.4 1.1 12.6 11.3 5.0 10.3 4.6 6.6 1.5 0.7 4.3 13.3 1.7 6.4 9.1 6.2 9.8 9.8 8.8

S.Hc

A.Hc

Res.

Asph.

Coal

Upper Silesian Coal A-5 0.82 B-5 0.80 B-7 0.83 H-1 0.98 J-5 1.17 Kr-10 0.90 Mi-1g 0.85 Mi-1d 0.91 Mk-3 1.07 Mk-5a 0.95 Mk-5b 0.94 Mo-1 1.20 Mo-2 1.16 Mo-13 1.22 NM-1 0.60 Pa-1 1.50 Pn-1 1.02 S-10a 0.70 S-10b 0.69 S-11 0.59 We-1 0.69 Z-4 1.09

Basin 0.937 0.857 0.600 0.410 0.628 1.554 0.831 0.923 0.488 0.871 0.788 0.616 0.620 0.406 0.710 0.441 0.945 0.701 0.429 0.710 0.490 0.557

11.1 16.3 9.2 17.3 5.6 13.1 13.4 9.7 15.7 10.8 11.8 7.5 5.2 14.5 23.4 10.5 10.4 11.4 12.2 9.2 14.2 13.9

1.8 5.3 3.3 3.8 0.8 7.2 7.6 5.4 3.7 2.2 2.1 0.8 0.9 2.7 11.9 1.4 1.4 9.0 8.3 17.6 7.4 5.5

83.8 74.2 84.5 72.5 92.5 67.1 67.7 79.9 70.3 82.4 79.5 90.2 93.2 78.5 51.4 86.4 81.8 70.5 73.3 63.4 68.6 71.8

24.7 24.4 23.8 24.3 24.0 25.1 24.9 24.3 24.8 24.2 24.1 23.7 24.0 24.2 25.1 24.0 24.5 25.1 24.7 25.4 24.7 24.6

27.2 26.6 26.2 25.3 25.5 27.6 26.5 25.3 27.8 26.3 26.3 26.1 26.2 25.6 26.1 24.0 26.3 28.6 28.8 28.3 26.1 27.6

25.0 23.8 23.8 23.6 23.8 24.5 24.8 24.6 24.2 23.7 24.3 23.3 23.6 23.1 25.1 23.2 24.2 25.6 25.6 26.1 24.4 23.7

24.1 24.1 23.9 24.0 23.7 24.4 24.7 24.3 24.8 23.5 23.8 24.4 24.0 24.2 24.7 24.6 23.8 24.6 24.4 26.0 24.0 24.8

24.9 24.4 24.1 24.3 24.0 24.9 24.9 24.4 24.6 23.8 24.0 23.9 23.8 24.2 25.2 23.9 24.2 25.0 24.5 24.8 24.2 24.5

24.3 23.7 23.7 24.0 24.1 24.0 24.0 24.0 23.9 23.2 23.6 23.7 23.4 23.8 24.5 24.0 24.2 23.6 23.2 24.3 23.9 23.7

Lower Silesian Coal Pi-1 1.34 Sl-1 1.11 Sl-2 1.08

Basin—Nowa Ruda District 0.608 2.2 12.6 1.249 4.0 9.4 0.965 8.0 16.7

2.0 3.5 3.6

83.2 83.1 71.7

23.6 24.0 23.8

25.1 25.5 25.0

23.1 24.0 23.6

23.9 24.2 23.8

24.0 24.4 23.9

23.2 23.8 23.4

Lower Silesian Coal T-29 1.37 V-30 1.95 V-31 1.82 V-33 4.28 W-30 1.11 W-31 1.99 W-32 1.98

Basin—Walbrzych District 0.481 1.6 9.4 0.030 4.1 19.4 0.186 0.8 9.8 0.035 19.1 8.4 0.336 9.4 17.5 0.049 3.7 10.9 0.092 1.9 10.7

2.0 8.1 1.6 14.6 3.7 8.4 3.3

87.0 68.4 87.8 57.9 69.4 77.0 84.1

23.9 24.4 23.7 27.8 24.1 25.3 24.4

26.6 27.7 27.3 29.3 25.9 28.4 27.9

23.4 23.1 22.9 27.3 23.5 23.7 23.4

23.9 26.0 24.6 27.4 24.0 26.6 25.1

24.1 24.5 23.9 26.9 24.1 24.9 24.2

23.9 23.7 23.6 24.1 23.4 23.8 23.7

11.2 14.1

58.3 47.1

25.0 25.3

27.6 27.7

25.1 25.9

24.9 25.1

24.7 24.8

23.4 23.3

Lublin Coal Basin Bo-1 0.67 Bo-2 0.71

1.058 0.886

15.6 19.6

14.9 19.2

Rr: mean random vitrinite (telocollinite) reflectance from Kotarba et al. (2002); S.Hc: saturated hydrocarbons; A.Hc: aromatic hydrocarbons; Res.: resins; Asph.: asphaltenes; Bit: bitumen.

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Table 3 Vitrinite reflectance and stable carbon isotope composition of CHCl3 extracts, fractions, and kerogen in carbonaceous shales Total CHCl3 extract (wt.%)

Fraction composition (wt.%)

d13C (x)

S.Hc

A.Hc

Res.

Asph.

Bit.

Upper Silesian Coal A-5r 0.74 A-5f 0.77 B-5f 0.80 B-7r 0.83 B-7f 0.78 H-1r 1.00 H-1f 0.91 J-5ar n.a. J-5bf n.a. Kr-10r 0.92 Kr-10f 0.94 Mi-1r 0.78 Mk-3r 1.04 Mk-3f 1.03 Mk-5br 0.91 Mk-5bf 0.91 Mo-1r 0.94 Mo-1f 0.96 Mo-2f 1.06 Mo-13r 1.21 Pa-1f 1.52 Pn-1r 0.91 Pn-1f 0.88 S-10r 0.70 S-10f 0.69 S-11r 0.60 S-11f 0.59 We-1r 0.63 We-1f 0.67 Z-4f n.a.

Basin 0.034 0.176 0.155 0.031 0.123 0.026 0.029 0.035 0.079 0.044 0.047 0.104 0.142 0.163 0.113 0.053 0.137 0.044 0.219 0.088 0.022 0.094 0.030 0.029 0.091 0.025 0.053 0.040 0.070 0.057

13.0 5.9 5.6 7.9 4.5 7.0 9.3 14.7 6.1 13.2 10.9 17.9 4.7 2.2 7.6 10.2 1.9 8.5 2.3 3.3 15.9 6.7 18.0 10.5 14 19.9 13.4 9.7 19.3 6.6

16.1 14.1 15.5 11.9 13.1 11.8 20.1 10.2 11.6 31.3 38.6 15.6 19.8 12.1 16.3 13.6 11.1 14.7 8.6 9.8 19.0 14.6 13.2 8.1 17.5 15.7 12.6 10.9 16.4 16.1

8.2 5.2 2.3 6.4 8.0 6.1 14.8 11.6 4.1 25.5 29.4 13.4 5.8 4.0 5.9 7.3 2.0 6.7 2.0 1.7 11.0 4.3 10.9 12.0 12.9 23.1 14.6 10.6 12.7 8.6

62.7 74.8 76.6 73.8 74.4 75.1 55.8 63.5 78.2 30.0 21.1 53.1 69.7 81.7 70.2 68.9 85.0 70.1 87.1 85.2 54.1 74.4 57.9 69.4 55.6 41.3 59.4 68.8 51.6 68.7

25.4 25.0 24.6 25.4 24.8 24.8 24.8 26.0 24.7 n.a. 26.2 25.5 24.8 24.7 24.6 24.4 24.4 25.2 23.9 24.4 n.a. 25.4 26.2 25.8 25.6 n.a. 26.4 24.4 24.6 24.9

27.9 27.4 27.0 28.2 28.5 26.9 28.0 29.3 27.7 27.3 28.7 28.2 27.6 26.9 26.8 27.3 27.1 28.6 27.1 27.0 28.4 28.0 28.9 28.9 28.7 29.7 29.3 27.3 26.8 27.1

25.1 24.8 24.4 25.6 25.0 23.7 23.7 25.8 23.3 25.0 26.9 25.3 24.4 24.0 24.5 24.0 23.8 24.1 23.5 23.7 24.1 24.4 26.0 26.3 25.8 27.2 26.6 24.5 24.4 23.8

24.9 25.3 24.6 25.2 24.7 24.4 24.8 25.5 24.6 25.9 26.4 24.8 24.9 24.7 24.5 24.7 24.1 24.8 24.0 24.8 25.9 25.1 26.3 25.6 25.0 26.7 25.6 24.5 24.3 24.4

24.8 25.0 25.2 25.2 24.6 24.6 24.5 25.1 24.4 24.8 25.0 24.9 25.0 24.5 24.4 24.4 24.4 24.9 23.9 24.4 24.6 25.0 25.1 25.3 25.0 25.2 25.7 24.1 24.4 24.6

24.2 23.9 23.5 23.7 23.5 22.9 22.4 24.1 23.1 24.0 23.5 23.1 24.1 23.6 23.9 23.6 24.0 24.0 23.4 23.7 23.7 23.8 23.6 23.4 23.7 23.8 23.7 22.4 22.9 23.9

Lower Silesian Coal Pi-1r 1.36 Sl-1f 1.02 Sl-2f 1.02

Basin—Nowa Ruda District 0.022 15.9 19.0 0.049 5.6 17.6 0.089 3.2 12.3

11.0 7.0 5.0

54.1 69.8 79.5

23.6 24.9 23.6

26.9 27.5 27.0

23.3 24.3 23.7

24.3 25.3 24.9

24.0 24.5 23.4

22.8 23.2 22.6

Lower Silesian Coal T-29r 1.33 V-30f 1.98 V-31r 1.98 V-33r 4.22 W-30f 0.97 W-31r 1.96 W-32r 1.95

Basin—Walbrzych 0.051 0.008 0.013 0.010 0.048 0.028 0.008

District 7.8 26.4 11.7 40.1 4.5 8.6 30.4

23.1 9.8 20.9 14.1 10.8 18.8 20.5

8.2 33.6 19.9 32.0 9.0 14.2 24.3

60.9 30.2 47.5 13.8 75.7 58.4 24.8

n.a. n.a. – n.a. 24.5 n.a. n.a.

28.7 n.a. 29.1 n.a. 27.0 29.4 n.a.

23.8 n.a. 24.7 n.a. 23.9 23.3 n.a.

25.1 n.a. 26.3 n.a. 24.6 26.2 n.a.

24.5 n.a. 24.6 n.a. 24.6 25.1 n.a.

23.4 23.4 22.9 23.1 23.6 23.6 23.6

Lublin Coal Basin Bo-1r1 0.66 Bo-1r2 0.66 Bo-1f 0.66 Bo-2r 0.68 Bo-2f 0.68

0.248 0.020 0.011 0.037 0.014

20.9 17.1 25.5 8.2 19.6

19.7 15.2 11.8 11.9 15.7

17.5 22.1 16.6 11.1 23.3

41.9 45.6 36.1 68.8 41.4

24.2 n.a. n.a. n.a. n.a.

25.7 29.1 29.4 28.9 29.2

23.7 26.2 27.6 25.9 26.7

23.7 25.6 26.5 25.5 26.6

23.8 24.8 25.2 25.4 25.5

23.1 23.4 23.6 23.5 23.4

Sample code

Rr (%)

S.Hc

A.Hc

Res.

Asph.

Ker.

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biological marker distributions in extracts from coals and carbonaceous shales was done using single-ion monitoring of characteristic ions (m/z) for various compound groups.

5. Results and discussion 5.1. Stable carbon isotope composition of bitumen, its fractions, coals, and kerogens from shales Bitumen content and fraction analyses in coals and carbonaceous shales as well as results of stable carbon isotope analyses of CHCl3 extracts (bitumens), fractions (saturated and aromatic hydrocarbons, resins, and asphaltenes), coals, and kerogen from carbonaceous shales are presented in Tables 2 and 3. Mean d13C values and standard deviations for coals from the USCB and the LSCB are 23.9 F 0.3x(13 samples) and 23.8 F 0.4x(69 samples), respectively (Table 2; Figs. 5 and 6). Similar d13C values for two samples ( 23.4xand 23.2x ; Table 2) were obtained for coals from the LCB. With increasing maturity of kerogens and coals, d13C values increase slightly in a few cases, but generally exhibit no correlation with coal rank. Similar findings were reported by Galimov (1985) and Monin et al. (1981). Mean d13C values and standard deviations for kerogens of carbonaceous shales from the USCB and LSCB are 23.6 F 0.5x (28 samples) and 23.2 F 0.3x(10 samples), respectively (Table 3; Figs. 5 and 6). Similar d13C values for five samples (from 23.6% to 23.1x , mean 23.4x ; Table 3) were obtained for carbonaceous shales from the LCB. A progressive increase is observed in d13C values in the order: bitumen – asphaltenes –coals (or kerogens from carbonaceous shales) (Tables 2 and 3). Moreover, the average values of isotopic composition of asphaltenes are only insignificantly more negative (0.5 –1.5x) than the average for coals or kerogens. These data suggest that bitumens are co-genetic with associated coals or kerogens. In the Illinois coal basin, the mean d13C value in kerogen from carbonaceous

Fig. 5. Histograms comparing stable carbon isotope composition of coaly organic matter from coals and kerogen of carbonaceous shales from (A) Upper Silesian and (B) Lower Silesian coal basins. Data for Upper Silesian coals and carbonaceous shales from Table 2, for Lower Silesian coals (69 samples) from Table 2 and Kotarba (1988, 1990), and for carbonaceous shales (10 samples) from Table 3. x¯: mean d13C value and standard deviation.

shales ( 21.4 F 2.1x , eight samples) is less negative than that for coals (about 25x) (Mastalerz et al., 1999), which could have been caused by different deposition conditions of organic matter in coals and carbonaceous shales and/or different types of its precursors. Kerogens of the carbonaceous shales both in the USCB and the LSCB (mean d13C values are

Note to Table 3: Rr: mean random vitrinite (telocollinite) reflectance from Kotarba et al. (2002); S.Hc: saturated hydrocarbons; A.Hc: aromatic hydrocarbons; Res.: resins; Asph.: asphaltenes; Bit.: bitumen; Ker.: kerogen; r.: overlying of roof of coal seam; f.: underlying of floor of coal seam; n.a.: not analysed.

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Fig. 6. Histograms comparing stable carbon isotope composition of (A) saturated hydrocarbons and (B) aromatic hydrocarbons from Upper Silesian coals and carbonaceous shales, and (C) saturated hydrocarbons and (D) aromatic hydrocarbons from Lower Silesian coals and carbonaceous shales. x¯: mean d13C value and standard deviation.

23.6% and 23.2x, respectively) are not significantly enriched in 13C compared to the coals (mean d13C 23.9% and 23.8x , respectively) (Fig. 5A and B). These isotope data indicate that the organic matter accumulated in both the coal seams and dispersed form in Upper Carboniferous formations of the USCB, the LSCB and the LCB is terrestrial (humic) in origin and that higher C3 plants were precursors for it. Differences between mean d13C values of saturated hydrocarbons from coals and carbonaceous shales are

much greater than those between mean d13C values of aromatics from coals and carbonaceous shales both in USCB (Fig. 6A and B) and LSCB (Fig. 6C and D). There are no differences in isotopic composition of bitumens, subfractions, and kerogens from the USCB carbonaceous shales both overlying (roof) and underlying (floor) the coal seams (Table 3; Fig. 7A). Correlation of stable carbon isotope composition of saturated hydrocarbons and aromatic hydrocarbons in carbonaceous shales from both the USCB and the

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Fig. 7. Stable carbon isotope composition of saturated versus aromatic fractions of bitumens from (A) Upper Silesian, Lower Silesian, and Lublin carbonaceous shales overlying (roof) and underlying (floor) the coal seams, and (B) from Upper Silesian, Lower Silesian, and Lublin coals. Compositional fields from Sofer (1984).

LSCB indicates that the bitumens from the shales are generated from terrigenous organic matter (Fig. 7A). However, the same correlation for coals (Fig. 7B) suggests that bitumens from the USCB and the LSCB coals are derived from terrigenious, algal nonmarine and even marine organic matter. Because both USCB and LSCB coals are typically humic, and bitumens are genetically related to the associated coals (see biomarkers discussion below, and Kotarba et al., 2002), occurrence of bitumens of marine origin is unlikely. Sofer’s (1984) genetic line was constructed based on

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the analyses of isotopic composition of oils generated from dispersed organic matter, and not from organic matter accumulated in seam coals. Thus, the Sofer genetic classification of oils is not applicable to classification of organic matter in coals. We conclude that the isotopic differences between saturates and aromatics both from coals and carbonaceous shales (Fig. 6A and C) and the isotopic shift of saturates in coals (Fig. 7B) can be explained by different mechanisms of hydrocarbon generation during maturation of organic matter in coals as compared with that of dispersed organic matter with in the carbonaceous shales. It is possible that, compared to carbonaceous shales, the microporous structure of coals provides a better trapping (sorption) of the aromatics than the saturates produced during successive steps of their coalification. This difference between hydrocarbon retention capacity of coals and dispersed kerogens might also have an influence on isotopic fractionation. In the case of dispersed organic matter in carbonaceous shales, the so-called ‘‘matrix effect’’ of clay minerals (Espitalie´ et al., 1985) might cause a relatively greater isotopic shift in saturated hydrocarbons compared to aromatic hydrocarbons. For other coal basins, the following mean d13C values were reported: (1) Permian bituminous coals, Australia, 24.4 F 1.4x(Smith et al., 1982); (2) Pennsylvanian (Upper Carboniferous) bituminous coals and anthracite, USA, 23.9 F 0.4x(Mastalerz and Schimmelmann, 2002); (3) Upper Carboniferous high volatile bituminous coals, Saar District, Germany, 24.4 F 1.4x (Colombo et al., 1970); and (4) Upper Carboniferous medium and high volatile bituminous coals and anthracites, Lower Rhine and Aachen districts, Germany, 23.9 F 0.4x (Colombo et al., 1970). Stable carbon isotope data for humic bituminous coals and anthracites do not differ significantly from values reported previously for continental C3 plants (e.g. Degens, 1969; Galimov, 1985). Coals of various coal ranks have approximately the same stable carbon isotope composition, as originally suggested by Wickman (1953). Homogeneity of stable isotope composition through the whole coalification process [peat –lignite (brown coal) – bituminous (hard) coal – anthracite] is presumably related to extent of intermolecular, thermodynamically ordered carbon isotope distribution (Galimov, 1985).

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Fig. 8. Examples of distribution of n-alkanes and isoprenoids in Upper Silesian, Lower Silesian, and Lublin coals.

M.J. Kotarba, J.L. Clayton / International Journal of Coal Geology 55 (2003) 73–94 Fig. 9. Examples of comparison of distribution of n-alkanes and isoprenoids between coals and carbonaceous shales overlying (roof) and underlying (floor) the coal seams from Upper Silesian Coal Basin. 85

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5.2. n-Alkanes and isoprenoids n-Alkanes and isoprenoids determined from gas chromatography for coal and carbonaceous shale extracts are compared in Figs. 8 and 9, and Tables 4 and 5 give normalized amounts of individual components determined from integration of peak areas. Pr/Ph ratios have been used in many studies to infer oxicity or anoxicity of depositional environments and source of organic matter. High Pr/Ph ratios are usually associated with depositional environments or organic matter that has undergone oxidation to the extent that the phytol side chain of chlorophyll or

related structures has been oxidized, a pathway that leads preferentially to formation of pristane. However, a number of studies have demonstrated that there are multiple possible sources of these isoprenoids (e.g. Blumer and Snyder, 1965; Michaelis and Albrecht, 1979; Chappe et al., 1980) and the relation between depositional environment and Pr/Ph ratio is not fully understood (ten Haven et al., 1987). Accordingly, considerable circumspection is required when interpreting redox conditions based solely on Pr/Ph ratios. In spite of the potential difficulties interpreting Pr/Ph data, humic coals often have very high ratios, as would be predicted for terrestrially derived organic

Table 4 Ratios calculated from n-alkanes and isoprenoids composition of CHCl3 extracts of coals Sample code

CPI(Total)

CPI(17 – 23)

CPI(25 – 31)

1.01 1.05 1.09 0.97 0.92 1.08 0.99 0.91 0.84 0.97 1.24 0.98 1.11 1.25 1.29

1.16 1.16 1.24 1.13 1.12 1.09 1.15 1.14 1.23 1.06 1.28 0.98 1.58 1.91 1.09

3.64 4.69 6.25 2.43 0.96 5.82 3.10 3.42 0.81 1.65 8.76 4.38 3.38 5.84 5.67

0.73 1.85 3.14 0.70 0.27 2.61 1.31 2.19 0.42 0.35 2.32 2.65 2.35 5.24 1.85

0.15 0.24 0.39 0.25 0.20 0.43 0.21 0.22 0.35 0.18 0.28 0.37 0.33 0.64 0.37

Lower Silesian Coal Basin—Nowa Ruda District Pi-1 0.90 0.84 Sl-1 1.00 0.96 Sl-2 0.95 0.91

1.04 1.07 1.04

0.96 2.32 2.93

0.39 0.38 0.55

0.26 0.14 0.14

Lower Silesian Coal Basin—Walbrzych District T-29 0.91 0.89 V-31 0.89 0.73 V-33 1.01 1.06 W-30 0.99 0.96 W-31 0.96 1.02 W-32 1.06 1.01

0.93 1.03 0.98 1.06 0.95 1.23

3.96 0.36 0.90 5.25 0.61 0.24

0.53 0.72 0.94 0.88 0.66 0.49

0.11 0.65 0.74 0.15 0.54 0.98

Upper Silesian Coal Basin A-5 1.05 B-5 1.08 B-7 1.14 H-1 1.03 J-5 0.97 Kr-10 1.09 Mk-5a 1.03 Mk-5b 0.99 Mo-1 0.94 Mo-13 1.01 NM-1 1.25 Pn-1 0.98 S-10b 1.29 S-11 1.53 We-1 1.20

Lublin Coal Basin Bo-1 Bo-2

Pristane/phytane

Pristane/n-C17

Phytane/n-C18

1.26 1.08 1.47 10.39 10.49 0.64 1.31 1.23 1.43 15.93 10.17 0.58 : : : : : : : : : CPI (Total) =[(C 17 + C 19 + + C 27 + C 29 )+(C 19 + C 21 + + C 29 + C 31 )]/2(C 18 + C 20 + + C 28 + C 30 ); CPI (17 – 23) = [(C 17 + C 19 + C 21 )+ (C19 + C21 + C23)]/2(C18 + C20 + C22); CPI(25 – 31)=[(C25 + C27 + C29)+(C27 + C29 + C31)]/2(C26 + C28 + C30).

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Table 5 Ratios calculated from on n-alkanes and isoprenoids composition of CHCl3 extracts of carbonaceous shales Sample code

Location

Upper Silesian Coal Basin A-5 roof A-5 floor B-5 floor B-7 roof B-7 floor H-1 roof J-5 roof J-5 floor Kr-10 roof Kr-10 floor Mk-5b roof Mk-5b floor Mo-1 floor Pn-1 roof Pn-1 floor S-10 floor S-11 roof S-11 floor We-1 roof We-1 floor

CPI(Total)

CPI(17 – 23)

CPI(25 – 31)

Pristane/phytane

Pristane/n-C17

Phytane/n-C18

1.05 1.03 1.06 1.13 1.12 1.03 1.00 0.95 1.01 0.93 1.00 1.00 1.29 0.98 1.07 1.38 1.36 1.54 1.07 1.15

0.95 1.00 1.02 1.08 1.11 1.03 0.96 0.86 1.00 0.86 0.96 0.94 0.89 0.94 0.97 1.21 1.14 1.35 0.99 1.17

1.26 1.19 1.14 1.20 1.13 1.05 0.96 1.40 1.04 1.05 1.15 1.11 2.63 1.15 1.26 1.66 1.53 1.88 1.29 1.17

1.58 3.27 3.14 2.71 3.96 2.18 0.91 0.91 0.88 0.62 2.20 1.25 0.78 1.50 1.03 4.91 1.08 0.83 2.11 5.19

0.56 0.56 1.54 2.69 2.77 0.34 0.66 0.46 0.76 0.51 0.50 0.58 0.97 0.40 0.59 3.15 1.08 1.20 1.49 2.89

0.18 0.14 0.22 0.52 0.38 0.15 0.53 0.39 0.54 0.45 0.17 0.24 0.63 0.16 0.40 0.46 0.43 0.38 0.53 0.68

Lublin Coal Basin Bo-1 roof

1.16 1.03 1.30 5.85 6.39 0.46 CPI (Total) =[(C 17 + C 19 + : : : + C 27 + C 29 )+(C 19 + C 21 + : : : + C 29 + C 31 )]/2(C 18 + C 20 + : : : + C 28 + C 30 ); CPI (17 – 23) = [(C 17 + C 19 + C 21 )+ (C19 + C21 + C23)]/2(C18 + C20 + C22); CPI(25 – 31)=[(C25 + C27 + C29)+(C27 + C29 + C31)]/2(C26 + C28 + C30).

matter. Similarly, oils derived from coals or type III organic matter in shales typically have ratios greater than 1.0, often greater than about 4.0 (Clayton, 1993). Pr/Ph ratios for the coals and carbonaceous shales in our study are from 0.6 to more than 15 (Tables 4 and 5). Several coal samples (J-5 and Mo-1 from USCB, and Pi-1, V-31, V-33, W-31, and W-32 from LSCB) have Pr/Ph ratios less than 1.0, which is somewhat unusual for humic coals. Some carbonaceous shale samples (J-5, Kr-10, and Mo-1) also have Pr/Ph ratios less than 1.0. It should be stressed that all these samples come from the continental coal-bearing formations. A-5 samples from paralic coal-bearing formations have Pr/Ph ratios 3.64 (coal, Table 4), and 3.27 and 1.58 (carbonaceous shales, Table 5). In Fig. 9, carbonaceous shales collected from immediately below the coal seams (‘‘floor’’ shale) and above the coal (‘‘roof’’ shale) are compared with the coals themselves. In a number of cases, the floor and roof shales have notably lower Pr/Ph ratios than the associated coal. For example, shale samples above

and below coal sample Kr-10 (Fig. 9) have Pr/Ph ratios of 0.88 and 0.62, while the coal bed has a ratio of 5.82. In some cases, however, the coal has similar Pr/Ph ratio to one or both of the bounding shale beds. For example, sample Mo-1 has Pr/Ph ratios of 0.78 and 0.81 for the floor shale and coal bed, respectively (Tables 4 and 5). Similarly, samples J-5 have Pr/Ph ratios of 0.91, 0.96, and 0.91 for the floor shale, coal seam, and roof shale, respectively (Fig. 9). The low Pr/Ph ratios (i.e. less than 1.0) in shales bounding either the upper or lower margin of the coals suggest that these rocks were deposited in a reducing environment and the organic matter contained within them did not undergo appreciable transport (i.e. was not exposed to oxidation) or that dilution of the existing pristane occurred by input of phytane from an independent source, such as archaebacteria (Michaelis and Albrecht, 1979). We did not perform quantitative gas chromatography, so it is not possible to distinguish between these possibilities with the data available. However, the lower-maturity coals have

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Fig. 10. Normalized amounts (percentages) of 14a(H)17(H)20R steranes (C27 – C29) in coals and carbonaceous shales from peak areas of m/z 217.

high Pr/Ph ratios (Tables 2 and 4). The low Pr/Ph ratios occur only in coals at ranks corresponding to vitrinite reflectance of about 0.9% or greater. To some extent, Pr/Ph ratios of coals may decrease with increasing thermal maturity at high ranks (Brooks and

Smith, 1969). On the other hand, many of the coals still have high Pr/Ph ratios at high vitrinite reflectances, for example, in samples Pn-1, Sl-1, Sl-2, T-29, and W-30 (Tables 2 and 4), so thermal maturity alone cannot account for the Pr/Ph ratios less than one observed in some of the coals. Supporting evidence for this interpretation is seen in the presence of very low Pr/Ph ratios in some of the carbonaceous shales, even at thermal maturities of only about 0.6% vitrinite reflectance (e.g. Pr/Ph = 0.83 in S-ll floor shale, Rr = 0.59%) (Fig. 9). The n-alkane distributions of many of the extracts from the coals and carbonaceous shales at low thermal maturity contain a marked predominance of long-chain molecules (C25 +) (Fig. 8). CPI(25 – 31) carbon preference indexes are as high as about 1.9 (S-11 coal) in the thermally least mature coals and shales (Rr < 0.7%), but generally decrease with increasing thermal maturity so that at a vitrinite reflectance value of about 0.9% or greater the CPI values approach 1.0. An exception to this is the Pn-1 roof shale sample which has a CPI of 1.26 at vitrinite reflectance 0.88% (Fig. 9). These high CPI values are typical of waxes derived from higher plants, and attest to the relative high input of higher plant organic matter in these coals and shales. These n-

Table 6 Selected hydrocarbon biological marker characteristics of coals Sample code

Hopane S/(S + R)

Sterane S/(S + R)

M/(M + T)

C27

C28

C29

Benzohop

GI

OI

Ts/Tm

C29Ts

Pr/Ph

1.00 0.10 0.05 0.32

27 34 18 29

29 24 31 28

44 42 51 43

0.04 0.44 0.04 0.11

11 51 42 47

0 1 1 0

0.18 0.03 0.02 0.03

0.31 0.09 0.13 0.04

5.8 8.8 5.8 5.7

Lower Silesian Coal Basin—Nowa Ruda District Sl-1 0.61 0.46 0.80 Sl-2 0.57 0.38 0.80

29 46

26 17

45 37

nd nd

18 16

0 0

0.53 1.55

2.45 2.08

2.3 2.9

Lower Silesian Coal Basin—Walbrzych District W-30 0.71 0.37 0.80

39

20

41

nd

21

0

0.88

1.03

5.3

Lublin Coal Basin Bo-2 0.61

15

45

40

0.22

39

1

0.02

0.06

15.9

Upper Silesian Coal Basin Kr-10 0.66 0.44 NM-1 0.56 0.18 S-11 0.46 0.08 We-1 0.63 0.33

0.33

0.21

Hopane S/(S + R): 17a(H)21h20S/(20S + 20R); Sterane S/(S + R): 14a(H)17a(H) 20S/(20S + 20R); M/(M + T): mono-/(mono- + triaromatic steroids); C27, C28, C29: refers to aaa20R stereochemistry; Benzohop: E-ring aromatic hopane(C32); GI: Gammacerane index=(gammacerane/ hopane)100; OI: Oleanane index=(oleanane/hopane)100%; Ts/Tm: 18a(H)-22,29,30-trisnorneohopane/17a(H)-22,29,30-trisnorhopane; C29Ts: C29 18a(H)norneohopane; Pr/Ph: pristane/phytane; nd: none detected, blank spaces or not determinated.

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alkane distributions are consistent with the sterane distributions discussed below.

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nances of the C29 sterols in higher plants and associated recent sediments and predominance of C 27 homologues in marine plants. Following on their work, Czochanska et al. (1988) used the relative amounts of steranes to infer biological source of organic matter in oils, and many other workers since have applied the 20R aaa sterane distributions to interpretations of organic matter source. However, this approach must be used with caution as noted by Volkman (1986). Steranes in coal extracts or oils derived from coal or type III organic matter typically

5.3. Steroid distributions Distributions of the 14a(H)17a(H) C27 – C29 steranes (cholestane, 24-methylcholestane, 24-ethylcholestane) were determined by GC-MS monitoring the m/z 217 ion. Normalized percentages of the C27 –C29 20R isomers are plotted on the ternary diagram of Fig. 10. Huang and Meinschein (1979) found predomi-

Table 7 Vitrinite reflectance and selected hydrocarbon biological marker characteristics of carbonaceous shales Sample code

Rr (%)

Sterane S/(S + R)

M/(M + T)

C27

C28

C29

Benzohop

GI

OI

Ts/Tm

C29Ts

Pr/Ph

0.43 0.44 0.44 0.43 0.46 0.49 0.45 0.45 0.46 0.47 0.42 0.39 0.50 0.44 0.49 0.34 0.29 0.23 0.13 0.36 0.35 0.41

0.80

43

21

36

21

0

0.64

0.23

0.77

22 20 41 26 16 28 24 28 34 20 28 26 34 19 25 25 38 21 24 23

43 53 39 32 33 29 49 25 31 29 26 29 28 40 45 46 41 41 50 35

24 27 26 22 20 16 26 22 2 18 19 20 18 20 41 36 40 39 34 20

0 0 0 0 0 4 0 1 4 5 0 0 0 1 2 0 3 0 6

0.04 0.11 0.04 0.99 0.26 0.82 0.08 1.93 1.61 1.07 0.61 1.60 1.26 1.04 0.66 0.04 0.04 0.10 0.04 1.31

0.10 0.20 1.00 0.29 0.13 0.28 0.07 1.87 1.25 1.26 0.54 0.72 0.53 0.44 0.14 0.07 0.14 0.11 0.08 0.82

1.6 3.3 3.1

0.80

35 27 20 42 51 42 27 47 34 51 46 45 38 41 31 29 22 38 25 42

nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd 0.02 0.05 0.03 0.14 0.11 nd

Lower Silesian Coal Basin—Nowa Ruda District Sl-1f 1.02 0.65 0.38 0.80 Sl-2f 1.02 0.69 0.52 0.80

41 51

21 21

38 29

nd nd

24 20

0 0

1.04 0.89

0.70 0.49

Lower Silesian Coal Basin—Walbrzych District W-30f 0.97 0.60 0.32 0.80

39

21

40

nd

25

0

0.69

0.49

Lublin Coal Basin Bo-1r 0.66

22

21

57

0.14

32

0

0.03

0.08

Upper Silesian Coal A-5r 0.74 A-5f 0.77 B-5f 0.80 B-7r 0.83 B-7f 0.78 J-5r 1.17 Kr-10r 0.92 Kr-10f 0.94 Mi-1r 0.78 Mk-3r 1.04 Mk-3f 1.03 Mk-5br 0.91 Mk-5bf 0.91 Mo-2f 1.06 Pn-1r 0.91 Pn-1f 0.88 S-10r 0.70 S-10f 0.69 S-11f 0.59 We-1r 0.63 We-1f 0.67 Z-4f 1.09

Hopane S/(S + R) Basin 0.65 0.62 0.62 0.67 0.59 0.64 0.70 0.69 0.60 0.58 0.56 0.63 0.61 0.69 0.65 0.70 0.60 0.49 0.39 0.67 0.65 0.61

0.57

0.28

0.68 0.80 0.80 0.52 0.80 0.80

0.80 0.80 0.80 0.07

0.26

4.0 0.9 0.9 0.6

2.2 1.3

4.9 0.8 2.1 0.8

5.9

Rr: mean random vitrinite (telocollinite) reflectance from Kotarba et al. (2002); Hopane S/(S + R): 17a(H)21h20S/(20S + 20R); Sterane S/ (S + R): 14a(H)17a(H) 20S/(20S + 20R); M/(M + T): mono-/(mono- + triaromatic steroids); C27, C28, C29: refers to aaa20R stereochemistry; Benzohop: E-ring aromatic hopane(C32); GI: Gammacerane index=(gammacerane/hopane)100; OI: Oleanane index=(oleanane/hopane)100%; Ts/Tm: 18a(H)-22,29,30-trisnorneohopane/17a(H)-22,29,30-trisnorhopane; C29Ts: C29 18a(H)norneohopane; Pr/Ph: pristane/phytane; nd: none detected, blank spaces or not determinated; r.: overlying of roof of coal seam; f.: underlying of floor of coal seam.

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Fig. 11. Isomerization of 14a(H)17(H) C29 sterane [20S/(20S + 20R)] versus vitrinite reflectance for coals and carbonaceous shales. Sterane isomerization reaches equilibrium at Rr about 0.8%.

plot of Fig. 10, no significant difference is evident between coals and carbonaceous shales for the regular sterane distributions. Notably, a few of the carbonaceous shale extracts actually contain a predominance of the C27 steranes, but the C29 steranes are present in relatively greater amounts than C29 steranes in all of the coal extracts, and the shale extracts exhibit a much greater range of sterane distributions than coals. The least mature coals and carbonaceous shales contain steranes with mainly the biological stereochemistry [14a(H)17a(H)20R]. In the least mature samples, the 20S/(20S + 20R) ratios are as low as about 0.1 (Fig. 11; Tables 6 and 7). With increasing thermal maturity, the ratio increases and reaches its equilibrium value of about 0.5 by vitrinite reflectance between about 0.8% and 0.9%. There is no significant difference between shales and coals in sterane isomerization ratios (Fig. 11; Tables 6 and 7). 5.4. Terpanes

contain a predominance of C29 steranes (Clayton, 1993). Most of the coal and carbonaceous shale extracts in our sample set contain a predominance of the C29 steranes (Fig. 10; Tables 6 and 7), consistent with an interpretation of mainly terrestrial organic matter precursors for the lipids preserved in these samples. This interpretation is supported by the n-alkane distributions discussed above. According to the ternary

Hopane isomerization [20S/(20S + 20R)] for C31 homohopane is compared with vitrinite reflectance in Fig. 12. Like the sterane isomerization, the hopanes show a good correlation between thermal maturity and degree of isomerization at low levels of thermal maturity. By vitrinite reflectance between about 0.7% and 0.8%, the hopanes reach equilibrium and do not show significant changes at higher maturity levels.

Fig. 12. Isomerization of C31 17a(H)21h(H)homohopane 22S/(22S + 22R) versus vitrinite reflectance for coals and carbonaceous shales.

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In several coal samples, significant amounts of benzohopane were found. Hussler et al. (1984) found benzohopanes in a number of rocks and oils worldwide, mostly in carbonate basins, although they also found it in trace amounts in terrestrial crude oils of Nigeria and New Zealand. Similarly, we found very large amounts of a series of benzohopanes (C32 – C35) in immature oils produced from carbonate reservoirs in the Pripyat Basin, Belarus (J.L. Clayton, unpublished data). However, the present study seems to provide the first example of benzohopanes reported in significant amounts from the terrestrial organic matter. Hussler et al. (1984) hypothesized that these benzohopanes were derived from diagenetic reaction of bacteriohopane, probably catalyzed by the mineral matrix at low thermal maturity, and that like the hopanes, are abundant in confined environments. Gammacerane is present in fairly high abundance in many of the coals and carbonaceous shales from the LSCB, USCB, and LCB. The gammacerane index (GI; gammacerane/hopane  100) ranges from 2 to 40 in the shales, and from 11 to 51 in the coals (Tables 6 and 7). GI is compared with Pr/Ph ratios in Fig. 13. Gammacerane, a C30 triterpane, is believed to be indicative of high-salinity marine and nonmarine depositional environments (Moldowan et al., 1985; Brassell et al., 1986; Fu et al., 1986; ten Haven et al., 1988). This compound is thought to be derived mainly through diagenetic alteration of tetrahymanol believed

91

to substitute for normal membrane steroids in certain protozoa (Nes and McKean, 1977; Ourisson et al., 1987). Peters and Moldowan (1993) show increasing GI associated with a decrease in Pr/Ph for lacustrine source rocks from Angola, due presumably to increasing gammacerane caused by increasing salinity coupled with lower Pr/Ph ratios caused by reduced oxygen content in bottom waters caused by density stratification at higher salinities. In a study of Tertiary oil and source rocks from Nevada, Palmer (1984) found gammacerane in oil shales but not in lignitic siltstone. In the present study, there is no independent geological or geochemical evidence to support an interpretation of high salinities during deposition of the USCB, LSCB, or LCB coals, or carbonaceous shales. Therefore, finding gammacerane in fairly high amounts relative to hopane is somewhat surprising. However, it should be noted that no attempt was made to quantify the biomarker data. It is possible that both gammacerane and hopane are present in low absolute amounts compared to rocks and oils associated with hypersaline environments. Nevertheless, the GI values would be considered somewhat unusual for coals even if the absolute amounts are low. These findings suggest that either there may be other unrecognized sources of gammacerane, or that the parent organisms may inhabit a wider range of depositional environments than previously believed.

6. Conclusions

Fig. 13. Gammacerane index (gammacerane/hopane  100) versus pristane/phytane ratio for coals and carbonaceous shales. Amounts of gammacerane and hopane calculated from peak areas of m/z 191.

Molecular distribution of n-alkanes, steranes, and isoprenoids, and carbon isotope data indicate that most of the organic matter contained in the coals and carbonaceous shales analyzed in our study was derived from higher plant (terrestrial) precursors. However, some notable exceptions to this are carbonaceous shales containing abundant C27 steranes and low Pr/ Ph ratios ( < 1.0). These shales were apparently deposited under more reducing conditions than the associated coals which typically have high Pr/Ph ratios (H1.0) and contain mainly C29 steranes. From these data, it is suggested that depositional conditions and sources of organic matter changed sharply between deposition of the coals and the shales, rather than solely a continuum in relative proportion as of organic

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carbon and mineral matter input between coal and shale accumulation. Stable carbon isotope composition of coals, and kerogen in carbonaceous shales as well as correlation of stable carbon isotope composition of saturated hydrocarbons and aromatic hydrocarbons in carbonaceous shales from both the USCB and the LSCB indicates that the bitumens from the shales are generated from terrigenous organic matter. A progressive increase is observed in d13C values in the order: bitumen –asphaltenes – coals (or kerogens from carbonaceous shales). Moreover, the average values of isotopic composition of asphaltenes are not significantly more negative than the average for coals or kerogens. These data suggest that bitumens are always co-genetic (indigenous) with associated coals or kerogens. Kerogens of the carbonaceous shales both the USCB and the LSCB are enriched in 13C compared to the coals. Moreover, differences between mean d13C values of saturates from coals and carbonaceous shales are much greater than between mean d13C values of aromatics from coals and carbonaceous shales. The Sofer’s (1984) genetic line was constructed based on the analyses of isotopic composition of oils generated from dispersed organic matter, and not from coals accumulated in form of seam. Our isotopic data reveal that the Sofer graph is useful for characterization of dispersed organic matter in carbonaceous shales but not for coals. It seems reasonable to conclude that the isotopic shift for coals on Sofer’s diagram is caused by different mechanisms of isotopic fractionation during coalification of organic matter in seams compared with that of dispersed organic matter in the carbonaceous shales. The microporous structure of coals probably better traps (sorbs) aromatics than saturates which formed during successive steps of coalification. Significant amounts of benzohopanes are present in some of the samples and gammacerane is present in all samples, in some cases in fairly high relative amounts (i.e. high gammacerane index). High amounts of benzohopanes, and particularly high gammacerane contents, have been reported most often in carbonate environments or highly saline marine or nonmarine environments. The high gammacerane content of our samples is surprising and suggests that the precursor organisms for gammacerane may be more widespread than previously recognized and

illustrates the importance of circumspection when interpreting depositional environments based on biomarkers which do not have a well-established link between the biological precursor(s) and the diagenetic product.

Acknowledgements The research has been undertaken as part of American – Polish geochemical studies of coalbed gases, coals and carbonaceous shales funded by the Joint Maria Sklodowska –Curie II Fund (grant no. MEN/USGS-91-62). M. Mastalerz and W. Kalkreuth gave very constructive reviews which greatly improved the discussion and the possible consequences of the hypotheses presented in the manuscript. Analytical work by J.D. King and A. Warden, U.S.G.S., Denver, and A. Kowalski, T. Kowalski, and Z. Stecko, University of Mining and Metallurgy, Krakow, is gratefully acknowledged. W. Wieclaw assisted in preparation of figures.

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