Petrologic and geochemical characteristics of Seam 9-3 and Seam 2, Xingtai Coalfield, Northern China

International Journal of Coal Geology 49 (2002) 251 – 262 www.elsevier.com/locate/ijcoalgeo

Petrologic and geochemical characteristics of Seam 9-3 and Seam 2, Xingtai Coalfield, Northern China Yuzhuang Sun a,*, W. Pu¨ttmann b, W. Kalkreuth c, B. Horsfield d a Hebei Institute of Architectural Science and Technology, Handan, Hebei 056038, PR China Johann Wolfgang Goethe-Universita¨t Frankfurt, FB 17 Geowissenschaften-Umweltanalytik, Georg-Voigt-Str. 14, D-60054 Frankfurt on the Main, Germany c Instituto de Geocieˆncias, Universidade Federal do Rio Grande do Sul, Av. Benito Goncßalves, 9500, 91501-970 Poˆrto Alegre, Rio Grande do Sul, Brazil d ICG-4, Forschungszentrum Juelich, Germany b

Received 21 February 2001; accepted 7 December 2001

Abstract Six samples of Carboniferous (Mississippian – Pennsylvanian) coal (Seam 9-3) and 11 samples of Permian coal (Seam 2) from the Xingtai Coalfield were studied by petrological and organic geochemical methods. Both seams show different petrological and geochemical compositions. In Seam 9-3 of the Carboniferous age, the predominant maceral is vitrinite (83%) whereas in Seam 2 of Permian age, inertinite predominates (45%). ‘‘Barkinite’’ was found with an average content 1% only in Seam 2. Sixty-four different aromatic compounds were identified by gas chromatography (GC)/mass spectrometry (MS) analysis of solvent extracts (Extr) of both seams. Abundant polyaromatic sulfur hydrocarbons (PASH) were determined in coal samples from Seam 9-3, while they are very low in samples from Seam 2. 1,2,5-Trimethylnaphthalene and 1,2,5,6-tetramethylnaphthalene contents are much higher in Seam 2, while 2-methylfluorene contents are higher in Seam 9-3. Cadalene was found in Seam 2 with a high content of 94 mg/kg coal but was not detected in samples from Seam 9-3. This might indicate a different floral contribution to the sedimentary organic matter. All petrologic and geochemical results indicate that Seam 2 formed in a more oxidized environment compared with Seam 9-3. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Xingtai Coalfield; Barkinite; Cadalene; Maceral; Biomarker; Permian

1. Introduction The Xingtai Coalfield is located in the Hebei province, northern China (Fig. 1). Geologically, it occurs in the northern part of the Sino – Korean Craton. During the Cambrian and Early Ordovician,

*

Corresponding author. Fax: +86-310-6025698. E-mail address: sun _ [email protected] (Y. Sun).

the Sino – Korean Craton was covered by an epicontinental sea. After the Middle Ordovician, the craton was uplifted and subjected to substantial erosion. The uplift was followed by a period of subsidence during the Middle Carboniferous that resulted in a major transgression event from the northeast by which the craton once again was covered by an epicontinental sea. The coal-bearing Taiyuan Formation (Upper Carboniferous) and the Shanxi Formation (Lower Permian) subsequently formed in this area (Han and

0166-5162/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 6 - 5 1 6 2 ( 0 1 ) 0 0 0 6 7 - 2

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Yang, 1980; Yang et al., 1988). The sediments from the Permian Shanxi Formation were deposited in a fluvial-dominated deltaic depositional environment. The Upper Carboniferous Taiyuan Formation was deposited in a predominantly paralic environment (Han and Yang, 1980; Sun and Kalkreuth, 2000). On the basis of the previous results from FourierTransform Infrared spectroscopy analyses, Lin et al. (1996) also concluded that in the Xingtai Coalfield, the Permian peat accumulated in a relatively oxidizing environment on the upper delta plain, whereas the Carboniferous peat accumulated under relatively anoxic conditions in a predominantly brackish-lagoon environment. The Permian Shanxi Formation has three to seven coal seams with a thickness of up to 4.50 m (Fig. 2). The Carboniferous Taiyuang Formation has 5 to 11 coal seams. Seam 9 splits generally into several thick benches (9-1, 9-2 and 9-3, from top to bottom, Fig. 2). In the present study, six samples of Seam 9-3 (1.2 m) of the Taiyuan Group were taken from the entire seam profile in the Lincheng Mine. Eleven samples of Seam 2 (4.4 m) of the Shanxi Group were taken from the entire seam profile in the Dongpang Mine.

2. Analytical methods 2.1. Petrographic analysis The maceral composition was analyzed on polished blocks under reflected white light using a Swift point counter. The maceral groups were determined by counting 500 points per sample. In the second step, only the fluorescing liptinite macerals were measured under blue-light excitation of 450 – 490-nm wavelength. Vitrinite reflectance was measured using a Leitz MPV2 reflected light microscope that is fitted with a halogen lamp. The reflectance was measured using an oil immersion objective (32  ) using a 546nm filter. The measurement was calibrated using a Leitz glass standard. The maturation of samples from both seams was determined using vitrinite reflectance (Ro). 2.2. Organic geochemical analysis Finely ground ( < 0.2 mm) coal samples were Soxhlet-extracted for 24 h using dichloromethane as a solvent. The extracts (Extr) were separated into three

Fig. 1. Location of the study area in China.

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253

hydrocarbons with dichloromethane and the polar compounds (heterocompounds) with methanol (40 ml of each solvent). Gas chromatographic (GC) analyses were carried out on a Carlo Erba 5160 gas chromatograph equipped with a 25-m fused-silica column (0.25-mm i.d.) coated with SE-54. The oven temperature was programmed from 80 to 300 jC at 4 jC min 1 followed by an isothermal period of 15 min. Hydrogen was applied as carrier gas. The compounds were quantified by adding an internal standard (squalane) prior to GC analysis. The peak areas of standard and individual compounds in the GC traces were quantified using the Minichrom program. The identification of individual compounds was performed by gas chromatography/mass spectrometry (GC/MS) analysis using a Varian 3700 gas chromatograph coupled directly to a Finnigan MAT 8200 mass spectrometer equipped with a 25  0.25-mm (i.d.) fused-silica column coated with SE 54. The temperature program was same as that described for GC analysis. Helium was used as carrier gas. Mass spectra were recorded in the cyclic scan mode (1.1-s total cycle time). Conditions for mass spectrometry were: EI mode, electron energy 70 eV, emission current 1 mA and scan range 50 – 700 Da. Data were processed using an INCOS data system. Peak identification was based on comparison with standard spectra in the NBS library and, when necessary, confirmed by gas chromatographic coelution with authentic compounds.

3. Results and discussion 3.1. Organic petrography

Fig. 2. Stratigraphic column of the coal-bearing strata in the Xingtai Coalfield showing predominant lithologies and stratigraphic position of coal Seams 2 and 9-3.

fractions by column chromatography over pre-washed silica gel (70 – 230 mesh, 50  1 cm). The saturated hydrocarbons were eluted with n-hexane, the aromatic

In samples from the Carboniferous Seam 9-3, the vitrinite reflectance was determined to be 0.85%, and in samples from the Permian coal Seam 2, to be 0.71% on average. The coals in both seams are of high volatile bituminous rank. In samples from Seam 9-3, the amount of vitrinite reaches up to 83%, with the vitrinite group predominantly represented by telocollinite and desmocollinite (Table 1). In samples from Seam 2, vitrinites contribute only 44% to the total maceral content. Desmocollinite is the dominant vitrinite maceral. The contents of telocollinite and corpocollinite are lower (Table 2).

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Table 1 Maceral composition (vol.%, mineral matter-free) of Carboniferous Seam 9-3 from the Lincheng mine Sample number

Analysis number

Vit (%)

Tel (%)

Telo (%)

Des (%)

Vitro (%)

Ine (%)

Fus (%)

*93-6 *93-5 *93-4 *93-3 *93-2 *93-1 Base Total

8 7 5 3 2 1

71 73 89 93 78 92

0 0 0 1 1 1

41 40 65 68 28 52

30 30 24 21 38 40

0 1 0 2 9 0

26 22 9 5 16 6

10 8 4 1 4 2

83

1

49

35

2

14

5

(8) (7) (5) (3) (2) (1)

Sample number

Analysis number

Semif (%)

Mac (%)

Inert (%)

Lip (%)

Spo (%)

Cut (%)

Thickness (cm)

*93-6 *93-5 *93-4 *93-3 *93-2 *93-1 Base Total

8 7 5 3 2 1

9 7 3 2 3 2

3 3 0 1 0 1

4 4 1 1 6 2

3 5 2 3 5 3

2 4 1 2 3 2

1 1 1 1 2 1

20 20 20 20 20 20

4

3

3

1

Pyrite (%)

Car (%)

Clay (%)

Min total (%)

7 11 5

1 2 7 7 11

1 2 14 18 16 6

(8) (7) (5) (3) (2) (1)

Sample number

Analysis number

*93-6 *93-5 *93-4 *93-3 *93-2 *93-1 Base

8 7 5 3 2 1

(8) (7) (5) (3) (2) (1)

0.8

Carbonate in fracture, maybe formed in diagenesis. Vit = vitrinite; Tel = telinite; Telo = telocollinite; Des = desmocollinite;Vitro = vitrodetrinite; Ine = inertinite; Fus = fusinite; Semif = semifusinite; Mac = macrinite; Inert = inertodetrinite; Lip = liptinite; Spo = sporinite; Cut = cutinite; Car = carbonate; Py = pyrite; Min = mineral.

In Carboniferous coal from Seam 9-3, the liptinite content reaches only 3%, whereas in Permian coals from the Seam 2, the liptinite content is 12%. Sporinite dominates in liptinite group. Cutinite and resinite are lower than 1% in both seams. ‘‘Barkinite’’ is a particular type of liptinite and has been described as a maceral in the Chinese National Standard (1991). It consists of strongly fluorescing peridermal cells. In Chinese coal petrographic nomenclature, this component is called ‘‘barkinite’’ on the basis of its morphological features and because it is believed to originate from bark tissues. ‘‘Barkinite’’ has previously been reported to be present in Late Permian Chinese coals (Guo, 1987; Zhong and Smyth,

1997). Zhong and Smyth (1997) have described its petrographical properties in detail. According to the latter authors, ‘‘barkinite’’ is never transitional to vitrinite in the Late Permian coal from south China. However, transition macerals between ‘‘barkinite’’ and vitrinite are frequently found in the samples from this study and the Mowo mine (Sun, 1992). ‘‘Barkinite’’ reaches 1% in several samples of the Early Permian seam from the Dongpang Mine (Fig. 3). Three possible origins of ‘‘barkinite’’-rich coal have been suggested. Yan and Li (1958), Zhu and Zhu (1979), Luo (1980), and Han et al. (1983) proposed that the presence of ‘‘barkinite’’ was due to the unusual paleodepositional environments of marine-flooded or

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Table 2 Maceral composition (vol.%, mineral matter-free) of Permian Seam 2 from the Dongpang mine Sample number

Analysis number

Telo (%)

Corp (%)

Des (%)

Vitro (%)

V-total

Semif (%)

Fus (%)

Inert (%)

Mac (%)

Mic (%)

Inert-total

94714 94713 94712 94711 94710 94709 94708 94707 94706 94705 94704

11 10 9 8 7 6 5 4 3 2 1 average

21 16 20 6 15 19 14 9 25 29 13 17.0

7 3 3 1 3 5 2 2 7 5 2 3.6

20 19 27 12 27 27 15 22 29 22 19 21.7

2 1 1 1 2 1 1 1 3 1 1.3

51 38 52 19 46 52 33 35 61 58 35 43.6

9 10 8 11 14 12 19 16 10 6 20 12.3

10 6 9 5 6 12 10 5 9 11 6 8.1

18 23 15 31 16 14 26 30 8 11 22 19.5

2 4 2 1 0 1 4 2 1 0 4 1.9

4 4 5 1 6 2 3 2 4 3 2 3.3

43 47 39 49 43 41 61 55 32 32 53 45.0

Analysis number

Spo (%)

Cut (%)

Res (%)

Bark (%)

Alg (%)

Lipt (%)

L-total

Qtz

Clay

Carb

Other

Min-Tot

11 10 9 8 7 6 5 4 3 2 1 average

5 12 6 25 9 6 5 9 5 6 9 8.8

1 1 1 2 1 0 0

1

1

2

6 15 9 32 11 7 6 10 7 10 12 11.4

1

1 1 1

4 2 1 1

1 1 0 0.7

0 2 1 1 1 0 1 0 1 2 0.8

0 0.2 1.6 1 1.2 0.8 1 0.6 1 0 0 0.7

1

2 0.4

1 0.5

1 1 1 1 1 3 1 1

1 2 2 5

1 2 2 1

2 3 5 5 9 2

Vit = vitrinite; Tel = telinite; Telo = telocollinite; Des = desmocollinite;Vitro = vitrodetrinite; Ine = inertinite; Fus = fusinite; Semif = semifusinite; Mac = macrinite; Inert = inertodetrinite; Lip = liptinite; Spo = sporinite; Cut = cutinite; Lipt = liptodetrinite; Res = resinite; Bark = barkinite; Alg = alginite; Min = micrinite; Car = carbonate; Py = pyrite; Min = mineral.

marine-influenced peat swamps. They believed that ‘‘barkinite’’ formed in a relatively reduced environment. This suggestion is not in accordance with the observations in the Xingtai Coalfield. Seam 9-3 was formed in a marine-influenced swamp, but no ‘‘barkinite’’ is detected. However, in Seam 2 from Dongpang Mine, ‘‘barkinite’’ is present despite this seam being formed in a delta environment. Guo (1987) and Ma (1988) argued that ‘‘barkinite’’ originates from a particular vegetation. Guo (1987) stated that Lepidodendron and the tree fern Psaronius are the precursor biomass of ‘‘barkinite’’. Ma (1988) believes that ‘‘barkinite’’ formed from the root periderm of the tree fern Psaronius. However, these plants have also been found in Europe and America (Phillips and Peppers, 1974, 1984) with no ‘‘barkinite’’-like maceral known. Zhong and Smyth (1997) suggested that the preserva-

tion of ‘‘barkinite’’ is due to a combination of unique floral types and frequent marine transgressions. However, according to the regional geology, there is no evidence of marine transgressions during the formation of Seam 2. ‘‘Barkinite’’ is preferentially associated with inertinite, including inertodetrinite and semifusinite in the Early Permian coal and was described as ‘‘resinite in situ’’ (Sun, 1992). This phenomenon indicates that Seam 2 was deposited under relatively oxidizing condition. This allows one to conclude that the presence of a unique type of flora and relatively oxidizing condition during sediment deposition might be the preferential environment for the formation of ‘‘barkinite’’ in coals. In Seam 2 from the Dongpang mine, the ‘‘barkinite’’ contents are lower than 2% of the total macerals, while they reach up to 60% in the Late Permian coal

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Fig. 3. Microphotographs of sample 9 from the Dongpang mine.

(Zhong and Smyth, 1997). In a sample of Early Permian Seam 2 from the Mowo mine, ‘‘barkinite’’ content reaches 26% (Sun, 1992). This phenomenon may indicate that the precursors of ‘‘barkinite’’ were

beginning to develop in the Early Permian and became more abundant in the Late Permian. In Seam 9-3, the inertinite content is 14%, whereas it reaches 45% in Seam 2. In Seam 9-3, the inertinite

Y. Sun et al. / International Journal of Coal Geology 49 (2002) 251–262

Fig. 4. GC traces of two selected samples from Seams 2 and 9-3. For abbreviations, see Tables 3 and 4, ST = standard.

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Y. Sun et al. / International Journal of Coal Geology 49 (2002) 251–262 Table 3 (continued )

Table 3 Concentration of the aromatic compounds of the selected samples from the Lincheng mine (see Fig. 4) Compound number

0.46 1.77 2.96 1.72 1.83 6.24 7.43 4.86 8.59 1.66 2.47 2.11 3.18 1.82 3.89 1.30 3.35 4.24

20.11 70.71 50.04 8.61 5.34 31.99 38.06 28.18 36.82 5.86 9.98 10.07 3.51 8.38 11.70 3.60 4.13 8.19

0.41 0.50 2.62 1.62 2.02 10.30 11.48 5.77 13.86 2.24 3.73 3.23 1.63 6.04 2.27 3.48 6.81 6.24

9.49 4.42

2.28 7.70

5.96 14.80

6.81 4.66 3.83 2.76 0.83 6.77 6.78

9.81 17.63 13.64 16.58 6.16 12.34 12.08

6.22 13.87 6.04 3.10 1.28 11.51 8.72

5.13 7.08 5.43 4.99 0.42 7.95 5.70 6.67 5.57 4.51 1.31 2.68 2.24 0.62 5.99

11.51 24.32 7.02 5.03 1.82 11.25 10.24 12.82 9.46 3.80 1.86 2.02 1.67 1.72 8.20

7.26 10.15 7.46 5.07 2.88 9.08 7.55 10.61 7.65 3.88 2.62 3.03 1.88 3.42 8.11

1.88

4.10

3.77

1.44

2.10

3.02

Sample number 2 (mg/kg 3 (mg/kg 7 (mg/kg coal) coal) coal)

Sample number 2 (mg/kg 3 (mg/kg 7 (mg/kg coal) coal) coal)

1 = naphthalene 2 = 2-methylnaphthalene 3 = 1-methylnaphthalene 4 = 2-ethylnaphthalene 5 = 1-ethylnaphthalene 6 = 2,6- + 2,7-dimethylnaphthalene 7 = 1,3- + 1,7-dimethylnaphthalene 8 = 1,6-dimethylnaphthalene 9 = 2,3- + 1,4-dimethylnaphthalene 10 = 1,5-dimethylnaphthalene 11 = 1,2-dimethylnaphthalene 12 = 3-methylbiphenyl 13 = 4-methylbiphenyl 14 = methylethylnaphthalene 15 = dibenzofuran 16 = 1,3,7-trimethylnaphthalene 17 = 1,3,6-trimethylnaphthalene 18 = 1,3,5 + 1,4,6trimethylnaphthalene 19 = 2,3,6-trimethylnaphthalene 20 = 1,2,7 + 1,6,7 + 1,2,6trimethylnaphthalene 21 = fluorene 22 = 1,2,5-trimethylnaphthalene 23 = 4-methyldibenzofuran 24 = 2 + 3-methyldibenzofuran 25 = 1-methyldibenzofuran 26 = 2-methylfluorene 27 = 1,2,5,6tetramethylnaphthalene 28 = dibenzothiophene 29 = phenanthrene 30 = 4-methyldibenzothiophene 31 = 2 + 3-methyldibenzothiophene 32 = 1-methyldibenzothiophene 33 = 3-methylphenanthrene 34 = 2-methylphenanthrene 35 = 9-methylphenanthrene 36 = 1-methylphenanthrene 37 = dimethyldibenzothiophene 38 = dimethyldibenzothiophene 39 = 3,6-dimethylphenanthrene 40 = 2,6-dimethylphenanthrene 41 = 2,7-dimethylphenanthrene 42 = 1,3 + 2,10 + 3,9 + 3,10demethylphnan 43 = 1,6 + 2,9dimethylphenanthrene 44 = 1,7-dimethylphenanthrene

Compound number

45 = 2,3-dimethylphenanthrene 46 = fluoranthene 47 = 4,9 + 1,9dimethylphenanthrene 48 = 1,8-dimethylphenanthrene 49 = pyrene 50 = methylpyrene 51 = trimethylphenanthrene 52 = trimethylphenanthrene 53 = benzonaphtho(2,1-d)thiophene 54 = benzonaphtho(1,2-d)thiophene 55 = benzonaphtho(3,2-d)thiophene 56 = chryse 57 = methylbenzonaphthothiophene 58 = methylbenzonaphthothiophene 59 = methylbenzonaphthothiophene Extr (%) Total PAH (mg/kg coal) Total PASH (mg/kg coal)

0.70 2.38 2.58

1.80 2.30 1.62

1.82 2.94 1.86

3.42 1.52 7.84 1.87 4.27 1.97 1.24 1.56 0.37 1.58 1.74 0.57

1.60 1.56 8.10 2.52 2.41 2.88 1.62 0.88 2.20 1.60 1.18 0.84

1.77 1.71 7.45 2.08 1.89 1.86 1.22 0.67 1.74 0.87 0.62 0.41

1.30 209 30

1.10 606 40

1.10 282 35

Seam 9-3.

consists mainly of fusinite and semifusinite, whereas in Seam 2, it consists mainly of semifusinite and inertodetrinite. The morphology of fusinite shows that the plant anatomy in both seams is different. In Seam 9-3, the fusinites (5%) are composed of thin cell walls, whereas in Seam 2, the fusinites (6%) show thick plant cell walls. In Seam 9-3, fusinites occur as lenses or as layers, and these show well-preserved cellular structures. In Seam 2, fusinite macerals are present as discrete bodies (6%). In Seam 9-3, macrinite macerals are discrete detrital, angular to rounded bodies (1%). In Seam 2, macrinite occurs as two types, groundmass macrinite and discrete macrinite, the former having a concentration of 2%. Groundmass macrinites are believed to be formed in weakly oxidizing environments (Diessel, 1992). 3.2. Geochemical results Sixty-four different aromatic compounds in solvent extracts of the samples from both coal seams were identified by GC/MS analysis. The results indicate that the aromatic compounds are preferentially com-

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Table 4 Concentration of the aromatic compounds of the selected samples from the Dongpang mine (see Fig. 4) Compound number

Sample number 1 2 3 4 5 (mg/kg (mg/kg (mg/kg (mg/kg (mg/kg coal) coal) coal) coal) coal)

1 = naphthalene 2 = 2-methylnaphthalene 3 = 1-methylnaphthalene 6 = 2, 6- + 2, 7-dimethylnaphthalene 7 = 1, 3- + 1, 7-dimethylnaphthalene 8 = 1, 6-dimethylnaphthalene 9 = 2, 3- + 1, 4-dimethylnaphthalene 10 = 1, 5-dimethylnaphthalene 11 = 1, 2-dimethylnaphthalene 12 = 3-methylbiphenyl 13 = 4-methylbiphenyl 14 = 2- < 1-methyl-ethylnaphthalene 15 = dibenzofuran 16 = 1, 3, 7-trimethylnaphthalene 17 = 1, 3, 6-trimethylnaphthalene 18 = 1, 3, 5-/1, 4, 5-trimethylnaphthalene 19 = 2, 3, 6-trimethylnaphthalene 20 = 1, 2, 7-/1, 6, 7-/1, 2, 6-trimethylnaphthalene 21 = fluorene 22 = 1, 2, 5-trimethylnaphthalene 23 = 4-methyldibenzofuran 24 = 2/3-methyldibenzofuran 25 = 1-methyldibenzofuran a = cadalene 26 = 2-methylfluorene 27 = 1, 2, 5, 6-tetramethylnaphthalene 28 = dibenzothiophene 29 = phenanthrene 33 = 3-methylphenanthrene 34 = 2-methylphenanthrene b = 2-methylantracene 35 = 9-methylphenanthrene 36 = 1-methylphenanthrene 40 = demethylphenanthrene 41 = dimethylphenanthrene 49 = pyrene 50 = 4-methylpyrene 51 = trimethylphenanthrene 52 = trimethylphenanthrene 59 = chryse 60 = benzofluoranthene 61 = benzo(e)pyrene 62 = benzo(a)pyrene Extr (%) Total PAH (mg/kg coal) PASH (mg/kg coal) Seam 2.

6 7 8 9 (mg/kg (mg/kg (mg/kg (mg/kg coal) coal) coal) coal)

10 11 (mg/kg (mg/kg coal) coal)

15.25 57.64 49.65 39.54 60.15 63.36 33.76 14.37 17.47 6.87 5.33 11.86 5.13 14.80 37.80 24.31 19.60 25.00

7.63 5.71 6.94 9.87 17.76 12.02 10.91 4.64 8.95 4.02 2.38 4.52 2.07 10.18 15.20 12.51 10.27 32.04

15.11 53.71 47.06 39.19 60.60 63.99 32.10 12.34 18.34 4.53 5.21 15.57 5.06 18.80 38.27 26.25 19.20 26.25

4.89 26.91 27.56 26.60 36.07 51.74 20.59 8.31 10.81 5.30 3.60 8.99 2.91 9.20 29.40 17.52 10.70 17.52

22.61 68.04 53.68 42.38 62.56 104.69 32.07 13.27 19.37 7.74 5.68 11.89 6.35 15.20 46.80 31.90 19.80 31.50

12.43 47.91 34.98 34.54 42.44 74.66 23.01 9.08 12.61 4.65 3.73 10.95 4.60 12.11 31.02 21.96 13.40 21.96

6.80 19.19 23.03 22.11 37.90 61.71 19.33 11.22 11.37 4.47 4.39 9.92 2.10 12.40 34.00 28.46 12.80 28.46

22.70 61.34 45.36 36.55 45.23 94.65 27.59 13.70 13.99 6.35 4.80 10.15 4.40 12.70 35.92 26.01 13.90 27.98

31.91 111.64 85.40 81.07 112.77 176.87 58.81 26.31 33.99 9.22 8.78 28.27 10.10 26.10 89.40 65.55 27.20 65.55

10.55 35.96 29.97 27.28 38.45 56.73 21.26 9.48 12.86 3.76 3.26 9.57 4.10 10.40 27.57 21.08 11.70 21.08

8.23 21.21 24.93 21.01 39.45 35.11 23.46 9.29 13.66 9.12 4.94 10.10 3.35 14.80 31.75 21.40 13.20 21.40

11.21 78.84 21.54 20.52 12.86 7.93 6.84 37.67 1.41 30.97 11.83 12.75 8.60 22.30 13.11 11.98 6.15 8.85 11.01 4.27 8.09 7.38 9.04 11.58 2.07

7.60 36.89 12.58 12.37 8.20 1.81 6.89 36.62 2.91 28.27 14.54 15.10 5.60 24.85 18.46 15.74 7.12 7.44 13.54 5.30 9.20 5.02 7.26 4.26 1.36

12.70 66.36 22.79 22.72 10.77 21.64 12.79 38.25 1.62 34.12 13.91 15.28 9.80 30.60 16.75 14.53 8.10 11.59 13.99 3.96 10.35 10.32 9.97 14.18 8.6

8.30 38.26 14.67 15.16 11.20 24.30 9.20 23.26 2.88 22.48 8.99 9.72 6.71 19.10 10.96 11.11 4.11 5.03 9.00 4.20 6.28 4.61 5.10 5.30 1.29

10.60 76.39 25.70 25.22 17.80 44.34 17.10 48.28 6.80 41.79 18.05 20.61 16.60 38.21 21.36 22.09 8.80 9.08 21.76 7.10 14.94 11.90 12.82 13.25 4.1

9.10 45.74 16.83 16.58 8.80 36.43 11.70 26.39 1.20 27.83 10.20 11.80 8.90 21.14 13.56 12.50 10.20 7.15 12.38 11.40 8.09 6.93 9.01 6.11 2.02

11.60 68.54 18.79 16.16 13.80 79.91 21.90 41.96 3.80 34.74 15.22 16.51 13.40 33.28 16.79 20.82 14.40 12.52 20.59 9.20 12.15 8.25 9.59 6.50 1.6

11.20 83.56 16.79 15.69 12.20 51.78 13.70 43.39 2.20 31.86 11.26 11.80 9.80 23.23 13.95 12.49 3.42 4.08 15.22 6.30 9.68 12.46 7.07 12.44 3.8

21.20 179.17 42.24 41.50 31.40 93.54 19.60 92.96 7.50 58.24 21.38 23.07 19.60 43.89 23.34 28.67 20.10 9.00 21.25 10.40 14.67 8.22 10.78 6.11 2.02

9.60 62.83 15.53 11.73 7.10 23.01 8.20 30.70 4.10 24.90 9.92 10.69 8.20 20.05 12.15 11.68 11.40 11.23 7.12 5.10 6.90 4.88 6.13 5.53 1.6

10.20 47.15 18.00 17.87 9.20 8.74 15.40 32.50 4.10 35.15 14.40 14.02 13.20 33.07 15.89 13.84 9.20 13.25 11.35 3.10 10.99 10.10 11.97 13.68 3.9

3.05 2.94 2.98 2.71 2.43 2.52 2.53 4.11 4.59 3.55 2.71 881 487 937 600 1150 768 872 943 1899 685 717 1.41 2.91 1.62 2.88 6.80 1.20 3.80 2.20 7.50 4.10 4.10

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posed of alkylated naphthalenes and phenanthrenes (Fig. 4). Methylfluorene, 4-methyldibenzothiophene, 1-methyldibenzothiophene benzonaphthothiophenes, and methylbenzonaphthothiophenes occur only in the Carboniferous coal samples (Table 3 and Fig. 4), whereas methyldibenzofuran, methylanthracene, cadalene, retene benzo(k)fluoranthene and benzopyrenes are present only in the Permian coal samples (Table 4 and Fig. 4). 1,2,5-Trimethylnaphthalene and 1,2,5,6tetramethylnaphthalene contents are much higher in the Permian coal from Seam 2, while 2-methylfluorene contents are higher in Seam 9-3. According to Gransch and Posthuma (1973), highsulfur kerogen is primarily formed in marine environments, while low-sulfur kerogen is formed in freshwater environments. In Seam 9-3, 10 polyaromatic sulfur hydrocarbons (PASH) were detected (Table 3 and Fig. 4). The summarized quantity of these compounds is higher than 30 mg/kg coal. In contrast, their quantities in Seam 2 are lower than 8 mg/kg coal. This result is in accordance with the deposition of Seam 2 under more oxidizing conditions. 1,2,5-Trimethylnaphthalene and 1,2,5,6-tetramethylnaphthalene originate from pentacyclic triterpenoids in higher plants and are generated in sediments upon diagenesis. Additionally, the compounds might originate from hopanoids preferentially present in aerobic bacteria (Pu¨ttmann and Villar, 1987). The average contents of 1,2,5-trimethylnaphthalene and 1,2,5,6-tetramethylnaphthalene in Seam 2 reach 71 and 41 mg/kg coal, respectively, while they reach only 12 and 9 mg/kg coal, respectively, in Seam 9-3. Their different concentration in both seams may be caused by different maturity. According to Pu¨ttmann and Villar (1987), they are generated in a narrow rank range, from 0.6 to 0.8% Ro, and dissappear again at higher rank. In coal samples from Seam 9-3, the vitrinite reflectance reaches 0.85% Ro, higher compared with the vitrinite reflectance of coals from Seam 2 (0.71%). This might explain the lower contents of 1,2,5-trimethylnaphthalene and 1,2,5,6-tetramethylnaphthalene in coal samples from Seam 9-3. Considering an origin of the compounds from aerobic bacteria, the increased contents of both compounds in Seam 2 can also be explained by the more oxidizing conditions during deposition of this seam. Benzo(k)fluoranthene and benzopyrenes are detectable only in Seam 2 with average values of 9 and 12

mg/kg coal, respectively. The occurrence of benzo(k)fluoranthene and benzopyrenes in Seam 2 could be caused by different maturities. Methylfluorene are measured in both seams. It reaches 13 mg/kg coal in Seam 2, and 10 mg/kg coal in Seam 9-3. Methylfluorene is a biomarker for spores in Carboniferous coal. Methylanthracene reaches 11 mg/g coal in Seam 2. The occurrence of methylanthracene could be due to the different coal plants or depositional environment. Cadalene is a typical biomarker for conifers (Simoneit and Mazurek, 1982), and has as yet not been reported to be present in the Early Permian coals from

Fig. 5. Distribution of barkinite and cadalene from the samples of Seam 2.

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China. A high content of cadalene has been determined in the samples of Seam 2 from the Dongpang seam. The average content is 36 mg/kg coal, and the highest cadalene content reaches 94 mg/kg coal in sample 9. This may indicate that conifers were relative abundant in the Early Permian in this area. Comparing the cadalene content and maceral composition, one can find that cadalene has a positive relation to ‘‘barkinite’’ in most samples. The samples with higher ‘‘barkinite’’ have also higher cadalene contents (Fig. 5). Previous studies have shown that the Carboniferous coal and Permian flora is mainly composed of ferns (Han and Yang, 1980). The occurrences of cadalene and ‘‘barkinite exclusively in the Lower Permian coal seams argue for a major floral change at the Upper Westphalian/Lower Permian boundary in that area comparable with the floral changes known from North American coal basins (Phillips and Peppers, 1984).

4. Conclusions The Carboniferous coal Seam 9-3 and the Early Permian coal Seam 2 have different maceral compositions and organic biomarkers. These differences are associated with the formation environments of the coal peats. The higher contents of vitrinite macerals and PASH in coal Seam 9-3 indicate that this seam might be formed in a relatively reduced peat environment. The higher contents of inertinite macerals and methyldibenzofuran in the Early Permian Seam 2 indicate that this seam might have been formed in relatively oxidized peat conditions. ‘‘Barkinite’’ in Seam 2 may have formed due to the unique floral types and relative oxidized conditions. Cadalene could be the biomarker for the precursors of ‘‘barkinite’’ in this area.

Acknowledgements The authors would like to acknowledge engineers Li Caihui and Zhong Yuzeng for their help provided during sampling. The authors are very grateful to Drs. Zhang Min and John Hower for their helpful comments to improve the manuscript. This study was financially supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Educa-

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tion Ministry (No. 1998-679) and Deutscher Akademischer Austauschdienst (DAAD).

References Chinese National Standard, 1991. GB 12937-91. State Bureau of Technical Supervision of the Republic of China. Diessel, C.F.K., 1992. Coal-Bearing Depositional Systems. Springer-Verlag, Berlin, pp. 87 – 261. Gransch, J.A., Posthuma, J., 1973. On the origin of sulfur in crudes. In: Tissot, B., Bienner, F. (Eds.), Advances in Organic Geochemistry. Technip, Paris, pp. 727 – 739. Guo, Y., 1987. Study of Plagiozamites oblonggifolius, Compsopterris and Gigantoteris and the paleoecology of coal-forming vegetations of the Late Permian in the west of Guizhou. Doctoral Thesis, China Univ. Min. Technol. Han, D.X., Yang, Q., 1980. Coal Geology, vol. 2. Coal Industry Publishing, Peking, p. 350 (in Chinese). Han, D.X., Ren, D.Y., Guo, M.T., 1983. Origin of bark liptobiolite and its depositional environment of Changguang Coalfield, Zhejiang Province. Acta Sedimentol. Sin. 1 (4), 469 – 485. Lin, M.Y., Li, C.H., Sun, Y.Z., 1996. Differences of coal floral, petrological and geochemical compositions of Carboniferous coal and Permian coal from Xingtai Coalfield, north China. Neues Jahrb. Geol. Palaeontol., Abh. 202, 217 – 226, Stuttgart. Luo, S., 1980. A preliminary approach on marine coals of the C seam in Changguang Coalfield. J. China Coal Soc. 3, 26 – 37. Ma, X.X., 1988. Petrographic study of the main mineable seams (C605, C409) of Late Permian Age in the Shuicheng Basin of Guizhong: coal facies and evolution of the ancient peatland. Doctoral Thesis, China Univ. Min. Technol., Beijing. Phillips, T.L., Peppers, R.A., 1974. Fossil plants and coal: patterns of change in Pennsylvanian coal swamps of the Illinois Basin. Science 184, 1367 – 1369. Phillips, T.L., Peppers, R.A., 1984. Changing patterns of Pennsylvanian coal-swamps vegetation and implications of climatic control on coal occurrences. Int. J. Coal Geol. 3, 205 – 255. Pu¨ttmann, W., Villar, H., 1987. Occurrence and geochemical significance of 1,2,5,6-tetramethylnaphthalene. Geochim. Cosmochim. Acta 51, 3023 – 3029. Simoneit, B.R.T., Mazurek, M.A., 1982. Organic matter of the troposphere: II. Natural background of biogenic lipid matter in aerosols over the rural western United States. Atmos. Environ. 16, 2139 – 2159. Sun, Y.Z., 1992. Kohlepetrographie, Kohlefazies und ihre Beziehungen zur Kohlequalita¨t und den technologischen Eigenschaften der Kohlen von Permflo¨z 2 und Karbonflo¨z 9 im Kohlebecken Xingbei im Norden von China. Diplomarbeit an der Universita¨t zu Ko¨ln (unpublished). Sun, Y.Z., Kalkreuth, W., 2000. Explanation for peat-forming environments of Seams 2 and 9(2) in Xingtai Coalfield, China. J. China Univ. Min. Technol. 10 (1), 17 – 21. Yan, J., Li, G., 1958. Coal geology near to Leping and Lopinite. Bull. Geol. Soc. China 38 (3), 384 – 386. Yang, Q., Pan, Z.G., Wang, Z.P., 1988. Metamorphic Characteristic

262

Y. Sun et al. / International Journal of Coal Geology 49 (2002) 251–262

and Geological Causes of Perm-Carboniferous Coal in North China. Geological Publishing House Beijing, Beijing, p. 94. Zhong, N.N., Smyth, M., 1997. Striking liptinitic bark remains peculiar to some Late Permian Chinese coals. Int. J. Coal Geol. 33, 333 – 349.

Zhu, S., Zhu, D., 1979. Characteristics of the main mineable seam (No. C2) in the north of Zhejiang and the origin of periderminite coal. Contribution to the 1st National Symposium on Coal Geology, Zhejiang Coalfield Geology and Exploration Company, Zhejiang, China.