Petrological and organic geochemical characteristics of coal samples from Florina, Lava, Moschopotamos and Kalavryta coal fields, Greece

International Journal of Coal Geology 44 Ž2000. 267–292 www.elsevier.nlrlocaterijcoalgeo

Petrological and organic geochemical characteristics of coal samples from Florina, Lava, Moschopotamos and Kalavryta coal fields, Greece Cassiani Papanicolaou a,) , Janet Dehmer b, Martin Fowler c a

Institute of Geology and Mineral Exploration, Messoghion Str. 70, Athens 115 27, Greece Earth Sciences Department, UniÕersity of Cardiff, P.O. Box 914, Cardiff, CF1 3YE, Wales, UK Institute of Sedimentary and Petroleum Geology, Geological SurÕey of Canada, 3303 33rd Street N.W., Calgary, Alberta, Canada T2L 2A7 b

c

Received 5 May 1999; accepted 26 April 2000

Abstract Coal samples from Florina ŽVevi., Lava, Moschopotamos and Kalavryta basins, Greece, have been subjected to petrographic and organic geochemical analysis. The reflectance of the samples ranged from 0.26% to 0.42%, which ranks them as soft brown coals and sub-bituminous C coals. Lower reflectance values were encountered in the Florina and Kalavryta coals, whereas higher values were obtained for Lava and Moschopotamos samples. Maceral composition of the samples from the Florina area shows a high concentration of textinite A and texto-ulminite A. The samples from the Lava and Moschopotamos area are comparatively rich in humodetrinite. Samples from Florina are rich in resinite, whereas samples from Lava are rich in liptodetrinite. Rock–Eval pyrolysis data show that the samples from Florina and Kalavryta have generally high HI, SI and S2 and low Tmax values. The coal samples from Moschopotamos and Lava show the opposite, having low HI, S1 and S2 values. These distinct differences are related to the maceral composition Žtissue rich in resinitic material. and rank of the coals. Gas chromatography of the saturate fraction indicates that the samples from the Lava and Moschopotamos are rich in n-alkanes from n-C 23 to n-C 33. In contrast, the samples from Florina are rich in diterpanes, whereas those from Kalavryta are rich in sesquiterpenoids. Gas-chromatography-mass spectrometry of the saturate fraction reveals that the diterpenoids present in the

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Corresponding author. Department of Mineral Resources Engineering, Technical University of Greece, cro Dr. A.E. Foscolos, 73100 Chania, Greece. Tel.: q30-821-37455; fax: q30-821-64802. 0166-5162r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 6 - 5 1 6 2 Ž 0 0 . 0 0 0 1 4 - 8

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lignites from Kalavryta are derivatives of abietanic acid and pimaric acid, which are found in Pinaceae. The lignites from Florina mainly contain the diterpane, phyllocladane, which implies an input from Cupressaceae andror Taxodiacaea. The difference in the composition of these xylitic lignites may be attributed to differences in gymnosperm input as a response to climatic change, as the Kalavryta coals are of Pliocene age, whereas the Florina coals are of Miocene age. The study suggests that the petrology and organic geochemistry of these coals are related to the different peat-forming plant communities that were present in the Florina, Kalavryta, Lava and Moschopotamos basins. A mainly non-woody, angiosperm-dominated vegetation made up the peat that went to form the coal deposits of Lava and Moschopotamos, while the Florina and Kalavryta lignites were formed by peats derived mainly from gymnosperms. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Greece; coal petrology; organic geochemistry

1. Introduction Greece relies heavily on the use of lignite to meet its energy demands since it is the only abundant fossil fuel in the country. Out of the 6.7 billion tons of proven reserves, 3.85 billion tons are mineable with today’s technology and economic situation. Of this 3.85 billion tons of coal, 1.6 billion tons are estimated as indicated reserves, whereas 2.3 billion tons are inferred reserves. In addition, Greece possesses large reserves of peat, of which the largest and most significant is the Philippi Deposit of Eastern Macedonia, which contains 4.3 billion cubic metres of peat ŽKoukouzas et al., 1997.. Among the 43 coal basins of Greece, 75% are of Neogene age ŽFlorina, Ptolemais, Elassona and others., 16% are of Quatenary age ŽMegalopolis, Drama peat of Philippi and others. and 9% are of Eocene–Oligocene age ŽOrestiada, Alexandroupoli and others.. Most of the readily exploitable lignite deposits were formed in intermontane basinal settings in graben-like structures, although some were deposited in near coastal settings, such as deltas and alluvial plains ŽKoukouzas and Koukouzas, 1995.. While Greece is producing 57.4 million tons of lignite per year, production at the beginning of the 21st century is expected to reach over 62 million tons ŽKavouridis, 1995.. This makes Greece one of the largest producers of lignite in the world. Despite the fact that these coal deposits have been mapped and are being exploited, coal petrographical research and chemical characterisation of these deposits have been limited to a few studies ŽTeichmuller, 1968; Christanis, 1983; Cameron et al., 1984; Kaouras, 1989; ¨ Blickwede, 1991; Kaouras et al., 1991; Gentzis et al., 1990; Goodarzi et al., 1990; Kalkreuth et al., 1991; Antoniadis et al., 1992; Papanicolaou, 1992; Valceva and Georgakopoulos, 1993.. There have also been extremely few publications on the organic geochemistry of Greek coals Žvon der Dick et al., 1989; Fowler et al., 1991; Papanicolaou, 1994.. The aim of this present research is to use the conventional methods of coal analysis along with organic petrology and organic geochemistry to characterise Greek lignites from the Florina, Lava, Moschopotamos and Kalavryta coal fields to obtain an integral view of their depositional environment.

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2. Samples Fifteen lignite samples from four coal basins were selected for organic geochemical and coal petrological investigation. The selected basins are the Florina, Lava and Moschopotamos basins in northern Greece and the Kalavryta basin in southern Greece. The location of the basins are shown in Fig. 1. The age of the lignites in the basins range from Lower Miocene ŽLava basin., Upper Miocene ŽFlorina and Moschopotamos basins., and Lower Pliocene ŽKalavryta basin.. The coal samples from Florina ŽFlorina B. and Kalavryta were collected from boreholes while the others ŽLava, Moschopotamos and Florina BR. were channel samples.

3. Methods The 15 coal samples were analysed using a wide variety of coal characterisation methods and organic geochemical techniques. For proximate, ultimate and calorific values, the samples were ground to - 100 mesh Ž150 mm. and analysed following the procedures outlined by ASTM Ž1977, 1978.. Sulphur was determined by LECO apparatus, as outlined by Foscolos and Barefoot Ž1970.. For rank determinations and petrographic composition, the coals were crushed to a maximum particle size of 850 mm Ž20 mesh., mounted in epoxy resin and then ground and polished. Rank was determined by measuring the random reflectance on eu-ulminite B, using a Leitz MPVII microscope following the procedures outlined by Bustin et al. Ž1983.. Maceral analysis based on 500 points was performed using a Leitz microscope coupled to a Swift automatic point counter attached to a mechanical stage. The terminology and descriptions for the identification of the macerals used in this paper is that recommended by the International Committee for Coal Petrology Ž1971, 1975. ŽICCP. in its Handbook of Coal Petrology. Finally, the lignites were classified and described according to the optical properties recommended by Cameron et al. Ž1984.. For Rock–Eval analysis, the samples were pulverised to - 200 mesh and the measurements were made as outlined by Espitalie et al. Ž1985.. A sample size of about 5 mg was used in this study, to allow possible comparisons with other studies on the hydrocarbon potential of coal ŽTeichmuller and Durand, 1983; Durand and Paratte, ¨ 1983; Littke et al., 1989.. All the samples were run at least in duplicate. For the organic geochemical analyses, the finely milled coal samples were Soxhlet extracted for 24 h using dichloromethane as a solvent. Copper foil was placed in the flasks to bind any sulphur present. After the extraction was completed, the extract yields were weighed, then deasphalted and separated by column chromatography using 40 ml n-hexane, dichloro-methane, and methanol to elute the aliphatic, aromatic and resin fractions. The aliphatic fraction was analysed by gas chromatography ŽGC. using a Carlo Erba HRGC 5160 with a fused silica SE 54 column. The temperature program used was 100–3008C at 48Crmin with a 15-min isothermal period at 3008C. The aliphatic composition and carbon preference index ŽCPI. values were calculated from the resulting gas chromatograms.

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Fig. 1. Coal basins of Greece ŽKoukouzas and Koukouzas, 1995. and sampling locations. Ž1. Florina intermontane basin Žxylitic.; Ž2. Lava intermontane basin Žlignitic.; Ž3. Moschopotamos paralic basin Žlignitic.; 4. Kalavryta intermontane basin Žxylitic..

As the aliphatic fraction of some of the coals contained various tricyclic and pentacyclic terpenoids, which could not be identified simply by their retention times,

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samples were sent to the Geological Survey of Canada for further investigation using full-scan gas chromatography-mass spectrometry ŽGC-MS.. Here, extraction was carried out using an azeotropic mixture of chloroform and methanol in the ratio 87:13. The lignite extracts were treated with approximately 40 volumes of n-pentane to precipitate the asphaltenes before fractionation. The deasphalted extracts were fractionated using open column chromatography Ž3r4 activated alumina and 1r4 activated silica gel with an absorbant:sample ratio of 100:1.. The aliphatic fraction was recovered by eluting with 3.5 m of pentanerg of absorbant. The aromatics were recovered by eluting with 4 ml of 50:50 pentane-dichloromethanerg of absorbant, whereas the heterocomponents were recovered with 4 ml of methanolrg of absorbant. Gas chromatograms of the aliphatic fraction were acquired on a Varian 3700 FID gas chromatograph using a 30 m DB-1 column with a temperature program of 60–3008C at 68Crmin. GC-MS data were collected using a VG 70 SQ hybrid MS–MS under the control of a VG-11-250 data system. Data were collected using a 100-mA trap current and 70 eV ionization voltage. The gas chromatograph was fitted with a 25-m DB-5 column that was coupled directly to the ion source and programmed from 508C to 3108C at 48Crmin. Full-scan data for peak identification by comparison of mass spectra were obtained by scanning from mrz 650 to 50 and 1 srdecade. 4. Results and discussion 4.1. Proximate and ultimate analysis Table 1 shows the data obtained by the proximate and ultimate analysis together with the calorific and reflectance values. The proximate analysis shows that the lignites from Moschopotamos have lower volatile and higher fixed carbon values than the lignites from Lava and xylitic coals from the Florina and Kalavryta basins. Correspondingly, the ultimate analysis of the Moschopotamos basin samples have the highest organic carbon contents, ranging from 74.7% to 75.8% and calorific values Ž6811–7003 kcalrkg..1 These parameters classify these coals as sub-bituminous BrA, ŽASTM, 1982., while the reflectance values rank them at the end of the lignite stage to sub-bituminous C ŽInternational Committee for Coal Petrology, 1971.. The Moschopotamos basin coals are further characterised by low oxygen and nitrogen, and relatively high sulphur contentsŽ1.4–2.0%.. Correlating the results of carbon content, reflectance and calorific values, the two samples from the Lava basin can be ranked somewhere between the end of the lignite stage and the beginning of the sub-bituminous stage. The total nitrogen content is high, ranging from 1.8% to 1.9% ŽTable 1.. The xylitic coals from Florina have lower organic carbon contents than the coals from Moschopotamos and are also characterised by higher total hydrogen Ž5.8–7.2%. and variable total sulphur values Ž0.8–3.8%.. The calorific values are generally the lowest for the studied sample suite and range from 3973 to 5929 kcalrkg, which classifies them 1

kcalrkg=4.1855s kJrkg.

272

Location

Sample

Ash on asreceived basis Ž%.

Proximate analysis Žd.a.f.. Percentage Volatile matter

Fixed carbon

Ultimate analysis Žd.a.f.. Percentage C

H

O

S

N

Calorific value Žd.a.f.. Žkcalrkg a .

R r Ž%.

Age

Upper Miocene

Florina

b B101q102

14.2

71.6

28.4

60.1

7.2

31.4

0.8

0.5

5520

0.30

Lava

B117q118 B120 BRc4 BR 19 BR 28 BR 33 BR 35 LK 6A

11.6 12.4 14.6 8.3 17.6 32.8 12.1 35.1

66.3 68.7 59.3 63.8 61.0 60.8 60.5 57.1

33.7 31.3 40.7 36.2 39.0 39.2 39.5 42.9

61.4 64.4 64.6 64.3 68.1 67.6 64.5 61.8

6.1 5.8 4.3 6.2 6.5 6.6 6.1 6.4

31.1 28.3 27.9 26.2 20.9 21.2 26.6 28.1

0.8 1.1 2.5 2.9 3.6 3.8 2.1 2.0

0.6 0.4 0.7 0.4 0.9 0.8 0.7 1.8

5686 5929 4275 3973 4775 4472 5279 5341

0.28 0.26 0.28 0.26 0.30 0.29 0.31 0.32

Moschopotamos

LA 5 MM 1

14.2 9.6

57.7 54.5

42.3 45.5

79.3 74.7

3.7 5.7

13.6 17.5

1.4 2.0

1.9 0.1

7336 6811

0.39 0.36

Kalavryta

MM 2 MM 3 Kr7

19.7 22.6 21.7

49.3 59.1 76.4

50.7 40.9 23.6

75.8 74.7 65.3

4.9 5.7 5.2

17.1 17.5 27.7

1.4 2.0 1.0

0.9 0.1 0.9

6886 7003 5789

0.42 0.40 0.31

Kr9

45.6

72.7

27.3

66.8

5.2

25.6

1.4

1.0

5974

0.29

a

kcalrkg=4.1855s kJrkg. Bs Borehole samples. c BR s Mine face samples. b

Lower Miocene Upper Mioccene

Lower Pliocene

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Table 1 Proximate, ultimate and calorific values on dry ash free Žd.a.f.. basis, reflectance values and age of Greek coal samples from Florina, Lava Moschopotamos and Kalavryta coal basins

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as lignite. The xylitic coals from Kalavryta have carbon contents of 65.3% and 66.8% with a total hydrogen content of 5.2%. Total nitrogen is around 1%, which makes them relatively rich in this element. Rank determinations classify these coals as sub-bituminous B. Plotting the results of the ultimate analysis on a van Krevelen diagram ŽFig. 2., it is observed that the samples from Florina, Kalavryta and Lava fall into the lignite field and those from Moschopotamos into the sub-bituminous coal field. A sample from Lava basin ŽLA 5 . has the lowest OrC ratio Žsee Fig. 2., which is a attributed to its high carbon content and higher degree of aromatization. The latter explains also the high calorific value Žsee Table 1.. A substantial number of samples plot above the trend for humic coals. This is attributed to the high resinite content of the Florina coals as resinite is rich in hydrogen. Overall, the coals are ranked between soft brown coal and sub-bituminous C, ŽASTM, 1977, 1978.. They have a broad range of ash contents, from relatively low ash yields of under 10% for some samples from the Florina and Moschopotamos areas, to others with well over 20% ash ŽKalavryta samples.. The ranges of ash contents within the different basins suggest either a temporary high rate of intermittent subsidence locally Že.g. Moschopotamos Basin; Kalkreuth et al., 1991; Kotis, 1997., or, the

Fig. 2. Van Krevelen diagram showing position of analysed samples in relation to atomic HrC and OrC ratios.

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Table 2 Maceral composition Žpercentage volume. of Greek coal samples from Florina, Lava, Moschopotamos and Kalavryta on mineral matter free basis Macerals

Kalavryta Florina

Lava

Moschopotamos

Kr7 Kr9 BR 4 BR 19 BR 28 BR 33 BR 35 B101r102 B117r118 B120 LA 5 L 6A MM 1 MM 2 MM 3 Textinite A Textinite B Textoulminite A Textoulminite B Eulminite A Eulminite B Attrinite Densinite Corpohuminite Porigelinite Gelinite Levigelinite Total huminite Sporinite Cutinite Resinite Suberinite Alginite Chlorophyllinite Fluorinite Bituminite Liptodetrinite Total liptinite Semifusinite Fusinite Macrinite Micrinite Inertodetrinite Sclerotinite Total Intertinite Total organic matter

22

20

10

25

19

12

23

30

38

3

2

9

7

3

13

11

10

11

6 5 9 16 5

13 8 13 5 6

5

2 5

3 21 13 1

8 13 15 5

12 12 26 5

71

74

57

74

68

4 4 4 3 3

3 5 5 2 3

9 3 10

1 5 9 2 1

6 5 8 2

5

4 11 13 11 7

3 74

3 3 9 3 1

7 11 13 10

75

2 5 6 4

13 8 4 5

70

2 13 7 1

23 11

1 5

1

3

3

5 21 7 2

10 11 24 8 11

5 3 18 23 4

4 25 1 47 4

28 4 41 3

1

5

1 1

2

2

2

75

70

73

63

84

78

76

1 2 15 6

9 15 1

5 5 3 2 2

3 4 9 2 6

1 2 1

4 1 3

2 1

3

6

4

4 11 5 6

1 1 27 5 48

1 3 1 5

3 3

1

1

12

6

4

4

4

1

27

24

39

24

26

23

21

25

1

1

2

5

2

4

3

4

2

1

1

13

18

12

2

1 1

1 2

1 3

2 4

1 4

100 100 100 100

100

100

2

4

5 5

24

28

23

34

2

1

1

2

1 1 1

1 2

3

1

1

2

2 6

1 3

1 4

5

1

100 100 100 100

100

100

100

100

100

2

2 2

3 4

2

1 4

2 3

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presence of areas of physiographic relief in or near the basin of accumulation Že.g. Florina Basin; Papanicolaou, 1994.. 4.2. Maceral analysis The results of maceral analysis, by volume, are presented in Table 2. These values are weighted averages. Generally, the coals are characterised by high huminite Ž57–84%., moderate liptinite Ž12–39%., and low inertinite Ž1–6%. contents. The samples can be differentiated by their huminite and liptinite sub-group distributions, which are illustrated in Figs. 3 and 4, respectively. The histograms are obtained by averaging the values of the studied samples. In the xylitic coals from Florina and Kalavryta, humotelinite is abundant Ž57–75%.. These humotelinites are characterised by intense fluorescence ŽFig. 5c and d.. Further evidence for the presence of woody-derived material and cork tissues occurs in the form of corpohuminite and suberinite ŽFig. 6a and b.. In contrast, the coals from Moschopotamos are composed mainly of humodetrinite in the form of densinite, with partly gelified plant tissues Žtexto-ulminite. and abundant clay minerals. The coal shows microlayering of clay-rich and humic-rich intervals indicating that water level fluctuations took place that periodically brought inorganic material into the paleomire. Furthermore, the presence of framboidal pyrite in clay-rich as well as in humic-rich layers ŽFig. 5f., suggests anaerobic conditions coupled with sulphur-reducing bacteria activity.

Fig. 3. Average huminite composition of Greek coal samples from Florina, Lava, Moschopotamos and Kalavryta basins.

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Fig. 4. Average liptinite composition of Greek coal samples from Florina, Lava, Moschopotamos and Kalavryta basins.

Under UV light, the coal samples show a wide range of liptinite macerals; however, resinite is the most common and prevalent maceral. Samples from the Florina basin are particularly rich in resinite that occurs as oval-to-round bodies filling cell lumens ŽFig. 5g.. Also in the same samples, suberinite is common ŽFig. 6a and b.. Of note, is the occurrence of alginite in the Lava, Kalavryta and Moschopotamos coal samples, which implies the presence of water ŽDiessel, 1992. and sub-aquatic conditions during peat formation. The impregnation of humodetrinite with bituminite Žmineral–bituminous groundmass. in the Lava ŽFig. 6e and f. and, to a certain extent, in the Moschopotamos Ž1989. suggests that bituminite may be derived samples is also of interest. Teichmuller ¨ from the decomposition products of bacteria, algae and faunal plankton, which suggests Fig. 5. Photomicrographs of macerals in the studied coals. Ža. Thick-walled sclerenchymatic tissues Žsclereids. in xylitic coals from Florina ŽB101r102 ., under normal reflected light, 500=. Žb. Woody Žw. and cork Žc. tissues in xylitic coals from Kalavryta ŽKr7., under normal reflected light, 320=. Žc. Non-gelified huminitic tissue ŽHT. in xylites from Florina ŽBR 33 ., under normal reflected light, 500=. Žd. Intense fluorescence of non-gelified huminitic tissue under blue-light irradiation Žsame photo as 1c.. Že. Alternate microlayering of clay and humic rich bands in coal samples from Moschopotamos ŽMM 1 ., under normal reflected light, 320=. Žf. Framboidal pyrite Žp. in Moschopotamos ŽMM 1 ., under normal reflected light, 320=. Žg. Intense fluorescence of woody tissues showing resinitic substances within the cell lumens in Florina ŽB117r118 ., under blue-light irradiation, 500=. Žh. Fluorinite in coal sample of Moschopotamos ŽMM 3 ., under blue-light irradiation, 320=.

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that the Moschopotamos Žand Lava. coals have sub-aquatic origins. Previous investigations of the Moschopotamos samples ŽPapanicolaou, 1992. have shown that the bulk of

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the liptinite macerals occur within an intimate matrix of humodetrinite and clay minerals, the latter exhibiting a brownish fluorescence. Furthermore, microstratification

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between bands of huminite and mineral matter is a common petrological feature of these coals ŽFig. 6g and f.. Inertinite macerals account for less than 5% by volume in these samples. These are mainly restricted to sclerotinite Žnow called funginite; International Committee for Coal Petrology, 1998. and inertodetrinite, with some fusinite macerals occurring in the Florina coals. 4.3. Rock–EÕal pyrolysis Rock–Eval pyrolysis was undertaken on the coal samples as it has been shown by other workers ŽTeichmuller and Durand, 1983; Durand and Paratte, 1983; von der Dick ¨ et al., 1989; Fowler et al., 1991. to be useful in complementing organic petrological observations. Parameter S1 measures the amount of hydrocarbons liberated at 3008C and represents the volatile portion of the geologically generated bitumen from the samples. Peak S2 is the amount of hydrocarbons released during temperature-programmed pyrolysis Ž350–6008C. and represents the bitumen that would be generated if maturation would continue to completion. S1 and S2 are expressed in milligrams of hydrocarbon per gram Žmg HCrg. of sample. S3 is the quantity of CO 2 formed by the pyrolysis of the organic matter and it is expressed in milligrams Žmg CO 2rg. of rock. Tmax in degrees Celsius is the temperature of the maximum of the S2 peak and can be used to estimate thermal maturity although it is also affected by other factors such as organic matter type. Form these values, several derived parameters can be calculated. Hydrogen index ŽHI. is S2rtotal organic carbon ŽTOC., expressed in mg HCrg of TOC, and oxygen index ŽOI. is S3rTOC expressed in mg CO 2rg of TOC. HI and OI are related to the atomic HrC and OrC ratios ŽEspitalie et al., 1985; Peters, 1986.. Correlations of S1 q S2 values with the concentration of liptinites and fluorescent tissues were demonstrated by Papanicolaou Ž1994.. Therefore, the method quantifies the substances that can be gasified andror liquefied in a given coal sample and the results can be depicted on a pseudo-van Krevelen diagram of OI versus HI. The Tmax values of the xylitic coals from the Florina and Kalavryta basins are anomalously low Ž359–3808C. ŽTable 3. and are in the range expected for samples containing diterpenoid resins Žvon der Dick et al., 1989; Fowler et al., 1991.. Samples from the Lava and Moschopotamos basins have Tmax values between 401–4358C, with the Lava samples being slightly lower due to their lower maturity. The S1 q S2 values of the Florina xylites fluctuate widely between 54.39 and 149.38 mg HCrg of sample, while the lignites from the Lava and Moschopotamos are characterised by lower S1 q S2 values in the region of 50 mg HCrg of sample. The Fig. 6. Photomicrographs of macerals in the studied coals. Ža. Suberinite associated with corpohuminite ŽCh. in xylites from Florina ŽBR 35 ., under normal reflected light, 500=. Žb. Suberinite exhibiting intense fluorescence under blue-light irradiation Žsame as 2a.. Žc. Resinitic bodies ŽR. in coal samples from Lava ŽLA 5 ., under normal reflected light, 500=. Žd. Intense fluorescent resinite ŽR. in coal samples from Lava. Same photo as 1c under blue-light irradiation. Že. Humodetrinite impregnated with bituminite ŽB. and clay minerals with sclerotinite ŽSc.. Coal sample from Lava ŽL 6A ., under normal reflected light, 500=. Žf. Mineral–bituminous ground mass same sample as 2e under blue-light irradiation, 500=. Žg. Humodetriniteqmineral matrix with liptinitic macerals and framboidal pyrite Žp. in sample from Moschopotamos ŽMM 3 . under normal reflected light, 320=. Žh. Same sample as 2g exhibiting dull fluorescent colours under blue-light irradiation.

280

Location

Florina

Lava Moschopotamos

Kalavryta

Samples

B101q102 B117q118 B120 BR 4 BR 19 BR 28 BR 33 BR 35 LK6A LA5 MM 1 MM 2 MM 3 Kr7 Kr9

Rock–Eval data Tma x Ž8C.

S1 Žmgrg of sample.

S2 Žmgrg of sample.

S3 Žmgrg of sample.

TOC Ž%.

HI mg ŽHCrTOC.

OI Žmg of CO 2 rTOC.

363 361 359 365 368 380 363 358 401 419 435 433 432 364 359

8.57 14.74 10.097 7.83 42.83 7.11 10.96 13.30 5.20 4.42 0.96 0.85 1.05 5.05 9.91

120.28 134.64 100.79 73.91 92.20 47.28 46.03 69.12 53.20 48.26 42.04 49.32 51.71 99.69 102.12

23.61 22.42 18.16 37.29 30.07 46.10 25.70 36.69 40.40 45.76 34.77 23.96 23.94 27.83 20.40

48.42 44.76 40.97 49.40 59.68 45.93 44.50 56.90 43.00 53.17 57.61 50.66 67.32 43.02 45.52

248 300 246 150 154 102 103 121 123 90 72 97 76 231 224

48 50 44 75 50 100 57 64 93 86 60 47 35 64 44

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Table 3 Rock–Eval pyrolysis data on Greek coal samples from Florina, Lava, Moschopotamos and Kalavryta coal fields

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xylitic coal samples from the Kalavryta basin have higher yields of around 100 mg HCrg of sample. On a pseudo-van Krevelen diagram ŽFig. 7., most of the samples fall near the Type III curve. A few samples, from the Kalavryta and Florina basins fall closer to the Type II curve, suggesting that they may have better potential to generate liquid or gaseous hydrocarbons than the other samples.

Fig. 7. Classification of lignites on a pseudo-van Krevelen diagram based on Rock–Eval pyrolysis data ŽHydrogen Index, HI, and Oxygen Index, OI..

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4.4. Organic geochemistry Table 4 depicts the extract yields and their composition obtained after solvent extraction of the coal samples. The extract yields range from 4873 to 70 450 ppm. High yields of over 19 000 ppm were obtained from most of the Florina coals. All the extracts are comprised mainly of heterocompounds Žresinsrasphaltenes.. Percentages of aliphatic and aromatic hydrocarbons are low Žless than 12%., which is common for coals of this rank ŽHollerbach, 1980.. Despite their generally lower extract yields, the coals from Moschopotamos and Lava have the highest proportion of aliphatics and aromatics of the samples suite Žabout 11%.. To examine and assess the biomarkers present in the aliphatic fraction, GC and GC-MS analyses were performed. Based on the data in Fig. 8 and Table 5, the coals can be divided into two characteristic groups, which are also clearly evident from the gas chromatograms shown in Figs. 9 and 10. The aliphatic fractions obtained from the Florina and Kalavryta coals are composed of over 60% sesqui- and diterpenoids, whereas those obtained from the Moschopotamos and Lava coal samples contain abundant long-chained n-alkanes Žgreater than 50%.. CPI values ŽTable 5. vary widely from 3.7 to 7.9. This is believed to be due to the influence of different plant input types Žangiosperms versus gymnosperms., preservational conditions and metabolization by peat microbes ŽMeyers and Ishiwatari, 1993.. The low concentration of n-alkanes in some of the Florina and Kalavryta coals may have influenced the calculations of CPI. Despite this, the CPI values indicate that both groups of coals are immature ŽHollerbach, 1980.. 4.4.1. Group 1: Florina and KalaÕryta coals The saturate fraction of these coals is composed mainly of diterpenoids and sesquiterpenoids. The petrographical results have shown that these coals are rich in resinite, textinite and texto-ulminite, which implies a contribution of gymnosperm plant material.

Table 4 Extract yield Žin parts per million. and percentage Žby weight. of alkanes, aromatics, resins and asphaltenes of coal samples from Florina, Lava, Moschopotamos and Kalavryta coal fields Location

Extract yield in ppm

Alkanes

Aromatics

Resins

Asphaltenes

B101q102 B117q118 B120 BR 4 BR 19 BR 28 BR 33 BR 35 LAVA LK 6A LAVA LA 5 MOS MM 3 KALAV K7

43 321 27 564 20 289 27 456 70 450 27 595 8969 19 658 8927 13 667 4873 9839

1.73 2.66 2.03 0.75 0.24 3.35 1.13 1.34 1.65 0.34 3.94 3.79

4.70 3.10 2.36 2.26 1.43 3.75 5.25 5.47 2.63 1.53 6.66 8.23

23.85 38.78 27.13 38.70 27.68 51.60 49.50 25.68 32.50 11.85 28.26 29.70

69.72 55.45 68.48 58.28 70.65 41.30 44.13 67.51 63.02 86.27 61.77 58.28

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Fig. 8. Composition of saturate hydrocarbons in the extracts of coals from Florina, Lava and Moschopotamos basins.

283

284

Location

n-Alkanes

Sesquiterpens

Diterps

Degr. triterps

Squalane

Hopanoids

C-29 steroids

Monoar. anthrast.a

Isoprenes

C-29 monocyc.

C-35 monocyc.

CPI b

CPI c

FLB101q102 FLB117q118 FLB120 FL BR 4 FL BR 19 FL BR 28 FL BR 33 FL BR 35 LAVA LK 6A LAVA LA 5 MOS MM 3 KALAV K7

1.0 2.7 8.6 22.0 2.6 3.3 30.7 31.7 89.1 58.1 70.0 3.5

0.7 4.7 3.4 8.9 15.5 8.8 11.6 6.9 0.0 0.0 2.6 72.6

97.6 91.7 83.8 56.8 76.9 87.8 54.1 54.4 0.0 0.0 0.7 21.8

0.0 0.0 0.0 2.4 0.0 0.0 0.6 5.0 1.3 25.9 9.9 0.0

0.0 0.0 0.0 0.4 1.6 0.0 0.0 0.0 0.0 0.9 1.5 0.6

0.7 0.8 2.5 5.5 2.1 0.1 3.0 2.0 8.2 8.8 9.2 0.4

0.0 0.1 1.7 3.3 0.0 0.0 0.0 0.0 1.4 0.0 2.2 0.4

0.0 0.0 0.0 0.0 1.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.3 0.0

0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 1.8 1.6 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.5 0.0 0.7

4.7 4.9 5.5 5.2 – 8.9 6.9 9.9 7.3 7.0 8.0 5.4

4.3 4.3 5.4 3.4 – 6.1 4.8 6.1 7.9 4.7 4.8 3.7

a

Monoaromatics anthrasteroids.

b

CPIX s

c

CPIY s

2C 29 C 28 qC 30

ŽPhillipi, 1965..

1 C 25 qC 27 qC 29 qC 31 qC 33 2 C 24 qC 26 qC 28 qC 30 qC 32

q

C 25 qC 27 qC 29 qC 31 qC 33 C 26 qC 28 qC 30 qC 32 qC 34

ŽBray and Evans, 1961..

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Table 5 Percentage composition of saturates and carbon preference index ŽCPI. of coal samples from Florina, Lava, Moschopotamos and Kalavryta coal fields

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285

Fig. 9. Distribution of sesquiterpenoids and diterpenoids in Ža. Kalavryta xylites and Žb. Florina xylites. For peak identification, see Table 6.

Although sesquiterpenoids are rarely found in sediments because of their volatile nature ŽGrantham and Douglas, 1980., they have been found in substantial quantities in low rank coals mainly of Tertiary age ŽDehmer, 1988; Wang and Simoneit, 1990.. Paleobotanical evidence has shown that Glyptostrobus swamps dominated the coal-forming mires during the Tertiary period in Greece ŽVelitzelos and Gregor, 1990.. Glyptostrobus is a taxodiaceous gymnosperm, and is accustomed to high water-table levels. It

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Fig. 10. Distribution of n-alkanes in Ža. Moschopotamos MM 3 sample and Žb. Lava LK 6A samples Žcarbon numbers on top of each n-alkane peak, pr-pristane, ph-phytane..

co-existed with very few other vegetation types, mainly laurophyllous shrubs ŽSchneider, 1990.. The GC and GC-MS data show that over 70% of the aliphatic fraction of the Kalavryta coal consists of sesquiterpenoids. They comprise a complex suite of unknown C 14 - or C 15-saturated and mainly unsaturated bicyclic sesquiterpenoids. There are four main sesquiterpene peaks in the saturate fraction gas chromatograms of the Kalavryta coals ŽFig. 9 and Table 6.. One peak has a molecular weight of mrz 194 and major

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287

Table 6 Identification of peaks for Fig. 9 Sesquiterpenoids

Compound

Mol. wt.

Base peak

a b c d e

C15–A nordimane C15–unknown C15–unknown 4b-Ž H .-Eudesmane C15–unknown

194 210 206

81 69 191

208

109

Diterpenoids f g h i j k l m n o p

unknown D8,9 sandarcopimardiene unknown norpimarane iso-phyllocladane iso-pimara-7-15-diene pimaranersandarcopimarane a-phyllocladane coelution of abietane and phyllocladane dehydroabietane simonellite

260 272 274 262 272 272 276 274 – 270 252

123 257 259 163 – 109 – 123 – 255 237

fragment ions of mrz 81, 57 and 179 and is tentatively identified as a nordrimane, similar to that found by Weston et al. Ž1989. in crude oils from the Taranaki Basin, New Zealand. The most abundant sesquiterpenoid in the Kalavryta coal sample is 4b-Ž H .eudesmane. Eudesmane has been detected in Australia crude oils ŽAlexander et al., 1983. and in Tertiary coals and carbonaceous shales from Argentina ŽVillar et al., 1988. and is a biomarker for higher plant material. The Florina coals are dominated by an unknown C 15 H 26 unsaturated sesquiterpene with a molecular weight of mrz 206 and a base peak of mrz 191, similar to that found by Dehmer Ž1988. in Rhenish brown coals. Florina coals generally have saturate fraction gas chromatograms dominated by diterpenoids. It is estimated that up to 97% of the aliphatic fraction consists of diterpenoid compounds. The main diterpenoid present is a-phyllocladane, which has also been found to be the most dominant diterpenoid in extracts from middle Miocene brown coals from the Oberpfalz region in Germany ŽDehmer, 1989., in Hungarian brown coals from the Nograd Basin ŽAlexander et al., 1987., and Bulgarian lignite lithotypes of Miocene age ŽStefanova et al., 1995.. Other diterpenoids include D8,9 sandarcopimardiene, iso-phyllocladane, iso-primara-7-15-ene, dehydroabietane, simonellite, and an unknown diterpenoid ŽMW mrz 274, base peak mrz 259.. In contrast, the diterpenoids found in the Kalavryta coal are saturated derivatives of abietic and pimaric acid Žabietane and pimarane and their nor-derivatives. with traces of phyllocladanerkaurane-type diterpenoids. Phyllocladanerkaurane-type diterpenoids are often cited in the literature as being derived from resins in Podocarpaceae, Araucariaceae and Cupessaceae Že.g. Thomas, 1970; Noble et al., 1985.. Increasing evidence from the isolation and identification of a-phyllocladane in peats ŽDehmer, 1995., brown coal ŽDehmer, 1988. and Oligocene clay sediments ŽOtto, 1996; Otto et al., 1994., which all contain gymnosperm plant material from Taxodiaceae Že.g. Taxodium, Glyp-

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tostrobus., indicate that these tetracyclic diterpenoids may be biological markers for this group of gymnosperm plants as well. The aromatic diterpenoids, dehydroabietane and simonellite present in these coals have also been found in Taxodium peats ŽDehmer, 1995. and Oligocene Taxodium cone scales ŽOtto et al., 1997.. The presence of aromatic diterpenoids suggests oxidative dehydrogenation reactions, perhaps mediated by microbial transformation ŽBarnes and Barnes, 1981.. From the petrological data and the biomarker fingerprint of these two coal samples, it is clear that both coals are derived from woody peats dominated by gymnosperm plants. However, it is thought that different species of gymnosperm plants, in response to climatic change may have influenced the coal facies and consequently the biological markers present. The difference in the sesqui- and diterpenoid composition of the two coals may be explained by the Kalavryta coals being of Pliocene age, while those from Florina are of Miocene age. During these times, climatic conditions in this area changed from a wet, warm–temperatersubtropical climate in the Miocene to a drier, cool–temperate climate towards the end of the Pliocene. Palynological investigations of Upper Miocene and Pliocene formations in Greece Žvan de Weerd, 1983. have shown that the number of Pinus types increased during the Late Pliocene. The Pinaceae and especially Pinus, are known to normally give resins with a high content of abietic acid and its isomers ŽThomas, 1970., which has been corroborated by Gotz ¨ and Pickel Ž1995.. Their work on a resin from P. sylÕestrus, shows that it also contains some phyllocladane. Other compounds in low abundance include long-chain n-alkanes from n-C 23 –n-C 33 , with n-C 29 and n-C 31 in highest abundance and sitestene ŽC 29 higher plant sterene.. The long-chain n-alkanes are present in higher abundance in samples BR 4 , BR 35 , and BR 33 , which may be related to the higher proportion of degraded humic material present in these coal samples. Traces of degraded triterpenoids, hopanoids Žmainly hop-17Ž21.ene., squalane, and a monoaromatic anthrasteroid Žsample B 19 . in the saturate fraction point to the presence of microbial activity in the swamp. 4.4.2. Group 2: LaÕa and Moschopotamos These coals have similar biomarker fingerprints ŽFig. 10. and petrographical characteristics. They are rich in humodetrinite and appear to be derived from herbaceous material, as sesquiterpenoids and diterpenoids are not present. Their saturate fraction is dominated by odd numbered n-alkanes from n-C 23 to n-C 33 , with n-C 27 , n-C 29 and n-C 31 being the most abundant. It is well known that long-chained n-alkanes are derived from the diagenetic transformation of even-numbered carboxylic acids and alcohols present in leaf and cuticular waxes ŽTissot and Welte, 1984.. Some long-chain n-alkyl monocyclic alkanes ŽC 29 –C 35 ., with odd carbon number preference, were also detected in these samples. These compounds may be derived via cyclisation from the same precursors as the n-alkanes ŽDong et al., 1993.. Shorter-chain n-alkanes are present in the Moschopotamos coal sample, which may be evidence of bacterialrmicrobial reworking or different plant species. In comparison to the other samples investigated, the coal from Moschopotamos has a significant n-C 17 peak, which may be related to the presence of alginite in the coal. Work undertaken by Kalkreuth et al. Ž1991. using TPI and GI facies analysis on the Meliadi lignites from the Moschopotamos basin, suggest a reed marsh to wet forest-type environment in a lower delta plain setting.

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Evidence for greater microbial activity in this group of coals than in the Florina and Kalavryta coals is suggested by the higher abundance of degraded triterpenoids, especially in sample LA 5 ŽTable 5.. Degraded triterpenoids are thought to be the products of microbial photomimetic decomposition of pentacyclic triterpenoids ŽPhilp, 1981.. Compounds identified include de-A triterpenoids, although their spectrum does not resemble any previously published in the literature. They comprise two pairs of possibly related compounds, each being represented by an unsaturated and saturated member. C 30 triterpenoids are rare in this group of coals and are only represented by traces of squalane. Squalane is present in plant and animal tissues and is used as a biomarker for archaebacteria, including methanogenic bacteria ŽPeters and Moldowan, 1993.. Other biomarkers indicative of bacterial activity or input include a wide range of hopanoids, including 22,29,30-trisnorhop-17Ž21.-ene, 17b-Ž H .-trisnorhopane, hop-17Ž21.-ene, 17bŽ H .-trisnorhopane and 17b-Ž H .-homohopane. 5. Conclusions Based on the results of this investigation, the coals from the Moschopotamos basin have the highest rank of the studied coals. Following the guidelines stipulated by the ASTM Ž1982., results of the proximate, ultimate, calorific values and reflectance measurements indicate that the coals from the Moschopotamos basin can be classified as highly volatile sub-bituminous coals. The coals from the Lava, Kalavryta and Florina basins are slightly lower in rank. Although the Kalavryta and Florina coals are of a lower maturity, their hydrocarbon-generating potential is greater. The low Tmax values of these coals suggest this could possibly occur at lower-than-usual temperatures, probably as a function of their diterpenoid resin content. In terms of kerogen typing, some of the coals from the Florina and Kalavryta basin can be classified as mixed oil and gas-prone kerogens, which may produce oils of a waxy nature, rich in aromatic components, similar to oils predominately derived from terrigenous source rocks found in countries such as Australia, New Zealand, Indonesia and Taiwan ŽPhilp, 1994.. The Florina and Kalavryta coals predominately consist of woody material Žhumotelinites. with resinous matter either as resinite bodies or finely commuted liptinitic matter, dispersed in a mineral matrix. Their biomarker distributions suggest a large contribution from gymnosperm plants. The Moschopotamos and Lava coals show a more detritic nature Žhighly gelified humodetrinite and humocollinites.. Coals from both basins are characterised by high mineral matter contents, mainly clay minerals. The biomarker fingerprints indicate that gymnosperms were not an important vegetation component of the mire, which suggests a predominately angiosperm rich-herbaceous-type flora during peat formation. Acknowledgements We thank Drs. W. Kalkreuth and M. Mastalerz for their constructive comments during the review of this paper.

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