Stable carbon isotope ratios of aliphatic biomarkers in Late Palaeozoic coals

International Journal of Coal Geology 107 (2013) 127–140

Contents lists available at SciVerse ScienceDirect

International Journal of Coal Geology journal homepage: www.elsevier.com/locate/ijcoalgeo

Stable carbon isotope ratios of aliphatic biomarkers in Late Palaeozoic coals Jan Schwarzbauer a,⁎, Ralf Littke a, Ralf Meier a, Harald Strauss b a b

Institute of Geology and Geochemistry of Petroleum and Coal, Energy and Mineral Resources Group, Lochnerstr. 4-20, RWTH Aachen University, 52056 Aachen, Germany Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Corrensstr. 24, 48149 Münster, Germany

a r t i c l e

i n f o

Article history: Received 24 May 2012 Received in revised form 2 October 2012 Accepted 3 October 2012 Available online 17 October 2012 Keywords: Coal Compound specific isotope analysis (CSIA) Late Palaeozoic Biomarker Carbon isotopes

a b s t r a c t Stable carbon isotope ratios for aliphatic biomarkers were measured on 34 Late Palaeozoic coals. Compound specific isotope analysis allowed the determination of δ 13C values of individual organic compounds such as chlorophyll side-chain derived substances (pristane and phytane), leaf wax constituents (n-alkanes), or bacteria related compounds (hopanoids). Pristane and phytane can be regarded as excellent isotopic tracer molecules to ascertain isotope fractionation during primary production of organic matter by land plants in the Late Palaeozoic. Compared to the organic carbon isotope values for total terrestrial organic carbon, partly different isotope shifts and temporal trends are discernible for these isoprenoids. Such differences in carbon isotope ratios of total terrestrial organic matter and isoprenoids indicate that both isotope data sets record different bio-geochemical information. Since phytolderived isoprenoids are directly linked to the primary production of organic matter, their carbon isotopic properties seem to be most appropriate for the reconstruction of ecological systems and climate in the Palaeozoic. Interestingly, isotopic values of isoprenoids and hopanoids were not significantly affected by maturity and maceral composition of the coals. However, differences between the isotopic composition of total organic matter and of phytane (Δδ 13C values) and differences between the isotopic composition of total organic matter and of hopane seem to correlate with provenance of the samples, i.e. samples from different basins show different values. Hence, variations in different types of organic biomass might be successfully traced by the isotopic properties of characteristic molecular fossils in Palaeozoic coals. This might become an appropriate approach for future palaeoenvironmental, palaeoclimatic and palaeogeographical studies. In conclusion, the present study clearly demonstrates that molecular and carbon isotopic analyses of terrestrial organic matter, range in resolution from bulk to compound specific analyses, and it allows for the reconstruction of ecological and climatic conditions in the Late Palaeozoic. © 2012 Elsevier B.V. All rights reserved.

1. Introduction In recent years the stable isotope composition (mainly 13C but also N, 18O, 34S, and 2H) of sedimentary organic matter has been determined in order to assess its origin as well as palaeoenvironmental and palaeoclimatic conditions during biosynthesis. Carbon isotope values of carbonates and total organic carbon are believed to reflect changes in the global CO2 budget and coupled climatic changes as well as climatic parameters like humidity or temperature (Anderson and Arthur, 1983; Arens et al., 2000; Bechtel et al., 2008; Hayes et al., 1999; Lücke et al., 1999; Veizer et al., 1999). Furthermore, different photosynthetic pathways (C3, C4 or CAM) can be distinguished by their characteristic carbon isotopic fractionations (e.g. Deines, 1980; Farquhar et al., 1989; O'Leary, 1981). During photosynthesis, there is a large kinetic fractionation effect favoring 12C over 13C (Farquhar et al., 1982, 1989; O'Leary, 1981; Schleser, 1995). Consequently, isotope 15

⁎ Corresponding author. E-mail address: [email protected] (J. Schwarzbauer). 0166-5162/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.coal.2012.10.001

signatures of organic matter, including coals, have been used to identify metabolic pathways and deduce the climatic evolution during the geologic past (e.g. Lücke et al., 1999). One of the most important evolutionary trends in Earth's history was the development of land plants in the Late Palaeozoic leading to the rapid colonization of the continents (Gensel and Andrews, 1987; Gray and Shear, 1992; Kenrick and Crane, 1997). Early plants evolved during the Devonian and Carboniferous into a variety of species, including large trees. Relics of these plants are preserved in the geological record, e.g. as plant fossils, allowing for a detailed morphological and geochemical characterization of this ancient sedimentary organic matter. Many (but not all) of the morphologically well-preserved plant fossils are chemically degraded due to weathering or thermal alteration during burial. In contrast, chemically well-preserved organic matter is found in coals, which is indicated by much higher hydrogen index (HI) values as compared to kerogen from directly adjacent clastic sediments (Jasper et al., 2009; Ramanampisoa et al., 1990). Therefore, coals can be regarded as an important fossil archive of terrestrial organic matter reflecting changes in palaeoclimatic and palaeoenvironmental conditions over geological times.

128

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

The composition and properties of Palaeozoic and younger coals and coaly deposits have been frequently used in order to investigate variations in palaeoenvironmental conditions. Most of the organicgeochemical investigations focused mainly on biomarker compounds reflecting the different biogenic sources, the depositional conditions, and the diagenesis and catagenesis processes of the host sediment and its organic content after deposition. Gas chromatography–mass spectrometry (GC–MS) analysis of lipids derived from terrestrial organic matter is used to identify a great number of biomarkers that are specific to higher land plants (Alexander et al., 1987; Bechtel et al., 2007; Izart et al., 2012; Murray et al., 1997; Noble et al., 1985; Schulze and Michaelis, 1989; van Aarssen et al., 1992, 1994). With respect to the evolution of the global carbon cycle during the Palaeozoic, stable carbon isotopic composition (δ 13C) of marine carbonates was primarily used to record the evolution of the global CO2 budget and associated climatic changes. For example, Veizer et al. (1999) reported significant variations in δ 13C of marine carbonates over the Late Palaeozoic, with supporting organic carbon isotopic results reported by Hayes et al. (1999). Strong deviations from large secular variations in δ 13C were observed in the Tournaisian and Viséan (Veizer et al., 1999). The general trend in the marine environment has been parallelized for the terrestrial depositional environment (Strauss and Peters-Kottig, 2003). These authors also documented strong variations in δ 13C values of terrestrial organic carbon for several time periods during the Late Palaeozoic. Recently, δD-values of n-alkanes in coals and terrestrial sediments have been used to investigate palaeoclimatic changes during the Late Palaeozoic (Izart et al., 2012), representing a time in Earth's history when much of the continental area was situated at a low latitudinal position (Fig. 1). Despite yielding important clues on the general evolution of the global carbon budget during the Late Palaeozoic, neither Strauss and Peters-Kottig (2003) nor Izart et al. (2012) resolved changes in the plant communities and plant composition. It has been shown, however, that respective variations can be reflected in the total organic carbon isotope composition (Peters-Kottig et al., 2006; van Bergen and Poole, 2002). Basically, the δ 13C value of bulk organic matter integrates individual isotope values of different types and compound classes of that organic matter. Further information on individual compounds can be obtained by applying compound specific isotope analysis (CSIA) in particular on biomarker compounds (e.g. Freeman et al., 1990; Hayes et al., 1990). With this method, the δ 13C values of individual organic compounds (e.g. n-alkanes, pristane and phytane, hopanoids, and n-fatty acids) can be compared to one another, and in turn, these compounds have specific sources (e.g. chlorophyll, cuticular waxes, and bacteria). However, up to now little data is available for Late Palaeozoic carbon isotopes of individual organic biomarkers reflecting the contribution of specific plant remains. To fill this gap, the present study focused on CSIA of aliphatic biomarkers in Late Palaeozoic coals covering a large time span. Furthermore, it was our intention to test whether the temporal evolution of carbon isotopes as measured on TOC for a large number of samples (Strauss and Peters-Kottig, 2003) is paralleled by that of individual organic compounds related to specific plants, plant parts or bacteria. The biomarkers studied include n-alkanes, acyclic isoprenoids and hopanoids.

The majority of the investigated samples (23) are of Upper Carboniferous age. Most of them are derived from several underground coal mines in the Ruhr Basin, Western Germany. The other Upper Carboniferous samples stem from borehole sites in the Silesian Basin (Poland), Bouxhannout (Belgium) and Wemmetsweiler-North (Saar– Nahe Basin, Germany, Fig. 1). The Lower Carboniferous (Tournaisian and Viséan) is represented by four samples from four localities in Scotland and northern England. Seven samples were ascribed as Permian. Two of them are from the Sydney Basin (Australia, Upper Permian) and another two are from the Rio Bonito Formation, Candiota, Brazil. To enlarge the Permian sample set, three black shales from the Saar–Nahe Basin were also investigated. These black shales also reflect a continental depositional environment as they were deposited in a lacustrine setting. 2.2. Elemental analyses Prior to organic-geochemical analyses the samples were dried and crushed using a rotating disk mill. Total carbon (TC) and total organic carbon (TOC) contents were determined using a LECO carbonanalyser RC-412. Rock-Eval analyses were performed in duplicate using a Vinci Rock-Eval II+ instrument according to the standard technique established by Espitalié et al. (1977). Total organic carbon isotope measurements are discussed in other publications in detail (Müller et al., 2006; Peters-Kottig et al., 2006; Strauss and Peters-Kottig, 2003). 2.3. Petrology Microscopic investigations were performed on polished sections cut perpendicular to bedding using a Zeiss Axioplan microscope. Details of the analytical procedure are described in Amijaya and Littke (2006) and Littke et al. (2012). 2.4. Extraction and fractionation Coal samples (amounts between 9 and 12 g) were extracted with an azeotropic mixture of chloroform (47 wt,%), acetone (30 wt,%) and methanol (23 wt,%) for 24 h by using a Soxhlet-Extractor. Activated copper was added in order to remove elemental sulfur during the extraction process. After extraction the raw extracts were filtrated and reduced to a volume of approx. 1 mL by rotary evaporation. Subsequently, the extracts were dried over anhydrous sodium sulfate and separated by liquid chromatography (2 g of silica gel, Baker) into six fractions with increasing polarity (fraction 1: pentane; fraction 2: pentane/CH2Cl2 v:v 95:5; fraction 3: pentane/CH2Cl2 v:v 90:10; fraction 4: pentane/CH2Cl2 v:v 40:60; fraction 5: CH2Cl2; and fraction 6: methanol) according to Schwarzbauer et al. (2000). As a preliminary study the aliphatic fraction (fraction 1) of a minor set of samples was subjected directly to gas chromatography, gas chromatography– mass spectrometry and to compound specific isotope analyses after volume reduction to approx. 100 μL. The majority of the samples were subjected to a urea adduction procedure to isolate the n-alkanes from branched and cyclic compounds prior to analysis (see Table 1). 2.5. Urea adduction

2. Samples and methods 2.1. Samples Thirty-four samples were investigated (Table 1), including thirtyone coals and three lacustrine black shales (samples 5 to 7 in Table 1). Their stratigraphic age extends from the Lower Carboniferous (Tournaisian) to the Upper Permian. Absolute ages have been determined by calculating moving averages according to ages given in the Stratigraphic Timescale of Germany — STD 2002 (German Stratigraphic Commission, 2002).

The saturated fractions dissolved in n-pentane were first evaporated to dryness. Then a solution of urea in methanol (200 μL), hexane (200 μL) and acetone (200 μL) was added, and the resulting solution was cooled down to − 0.4 °C for at least 1 h. Thereafter the fractions were again evaporated to dryness and 500 μL of hexane was added to dissolve the branched and cyclic compounds. The addition of hexane was repeated three times, and the separated extracts (non-adduct fraction) were combined. The n-alkanes were recovered from the residue by resolving the urea complexes with acetone (500 μL), hexane (1 mL) and pre-extracted water (500 μL). The hexane fraction

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

Early Carboniferous

129

356 Ma

Siberia Ural Mts.

PANTHALASSIC OCEAN

Kazakstania

South China

PALEOTETHYS OCEAN

EURAMERICA

Malaya

Appalachian Mts.

Moscow Basin, Scotland

North China

Variscan Mts. Arabia

Africa

RHEIC OCEAN

Australia India

South America

Antarctica

GONDWANA

Late Carboniferous

306 Ma

Siberia

PANTHALASSIC OCEAN

Kazakstania Ural Mts. North China

PANGEA

Appalachian Mts.

Silesian Basin, Ruhr Basin, Bouxhannout, North England

Meseta

Mauretanide Mts.

Africa

South America

PALEO-TETHYS SEA South China

Arabia Australia

GONDWANA

India Antarctica

Madagascar

Late Permian

255 Ma

Saar-Nahe Basin

Siberia

Alaska

PANTHALASSIC OCEAN North China

PANGEA

California

Candiota

PALEO-TETHYS OCEAN South America

Sydney Basin, Bowen Basin

South China Indochina

Africa Turkey Iran

South Africa

Malaya Tibet

GONDWANA

TETHYS OCEAN

India Australia

Ancient Landmass

Antarctica

Modern Landmass Subduction Zone (triangles point in the direction of subduction) Sample Location

Fig. 1. Palaeo-plate reconstruction of Early and Late Carboniferous and Late Permian Period. Sample locations are inserted at time of deposition. Maps after Scotese (1997); Early Permian locations are inserted in the Late Permian map.

130

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

Table 1 General organic-geochemical characteristics of the samples investigated. Nr.

Sample

Age

Age [Ma]

TOC [%]

VRr [%]

Tmax [°C]

HI

CPI 1

1 2 3

Upper Wynn, Sydney Basin, Australia Bulli Seam, Sydney Basin, Australia Candiota, Brazil Rio Bonito-Formation, Seam BS Candiota, Brazil Rio Bonito-Formation, Seam BI Gehrweiler I Humberg Lake; Saar Basin, Germany Gehrweiler I; Rehborn or Odernheim Lake; Shale, Saar Basin, Germany Gehrweiler I; Rehborn or Odernheim Lake; Shale, Saar Basin, Germany Wemmetsweiler-North, Saar Basin, Germany Berwick upon Tweed, Northern-England Berwick upon Tweed, Northern-England Wemmetsweiler-North, Saar Basin, Germany Silesian Basin, 315 LW 155, Poland Silesian Basin, Brzeszcze 510 LW 405, Poland Prosper-Haniel, Seam Chriemhild, Ruhr Basin, Germany Prosper-Haniel, Seam O/N, Ruhr Basin, Germany Prosper-Haniel, Seam N, Ruhr Basin, Germany Polsum, Ruhr Basin, Germany

Upper Permian Upper Permian Artinskian (Lower Permian) Artinskian (Lower Permian) Rotliegendes

255 255 282.5

72.6 76.8 31.6

0.71 0.64 0.44

435 463 424

174 145 120

282.5

32.5

0.43

429

136

295

1.6

Rotliegendes

295

0.9

Rotliegendes

295

0.3

Stephanian

302.5

62.7

429

Stephanian Stephanian Westphalian D

302.5 302.5 306.5

15.1 52.9 80.2

Pennsylvanian Pennsylvanian

308 308

60.7 68.8

lower Westphalian upper Westphalian upper Westphalian Lower Westphalian Upper Westphalian lower Westphalian lower Westphalian upper Westphalian upper Westphalian upper Westphalian upper Westphalian Westphalian

309.5

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

Polsum, Ruhr Basin, Germany Well Im Felde 2A3, Seam S, Ruhr Basin, Germany Im Felde 2 A3, Seam S, Ruhr Basin, Germany Prosper-Haniel, Seam I, Ruhr Basin, Germany Prosper-Haniel, Seam H, Ruhr Basin, Germany Auguste/Victoria Flöz D/C, Ruhr Basin, Germany Auguste/Victoria, Seam H, Ruhr Basin, Germany Teutoburgia, Katharina Member, Coal-ball, Ruhr Basin, Germany Teutoburgia, Katharina Member, Coal-ball, Ruhr Basin, Germany Vollmond, Katharina Member, Coal-ball, Ruhr Basin, Germany Vollmond, Katharina Member, Coal-ball, Ruhr Basin, Germany Bouxhannout, Katharina Member, Coal-ball, Belgium Bouxhannout, Katharina Member, Coal-ball, Belgium Catcraig, Scotland Burnmouth Bay, Scotland Burnmouth Bay, Scotland Burnmouth Bay, Scotland

CPI 3

LHCPI

n-Alkane range

n-Alkane max.

Pr/Ph

Pr/ n-C17

Ph/ n-C18

1.82 1.14 2.8

1.29 0.89 1.7

1.72 3.20 2.2

15–29 14–30 13–29

23 23 25

9.7 12.1 5.1

3.8 1.7 2.4

0.3 0.1 0.4

2.6

2.2

0.4

14–30

25

5.1

3.4

0.4

1.06

0.98

6.80

11–35

13

1.1

0.2

b0.1

0.88

1.07

1.00

5.25

10–33

16

1.1

0.2

0.1

0.40

1.06

0.96

11.40

12–29

18

1.1

0.1

0.1

132

1.09

0.80

13.04

11–28

15

11.4

5.3

0.5

431 429 442

164 196 158

1.5 1.14 0.92

nc 1.23 0.93

3.35 7.06

12–29 11–29 10–30

17 19 12

4.8 10.3 4.5

2.0 8.7 0.6

0.5 0. 0.2

0.68 0.75

429 431

166 213

1.3 1.0

nc 1.0

12–27 13–31

21 19/21

6.8 7.9

4.3 3.5

0.6 0.4

73.2

0.81

434

272

1.06

1.31

0.21

13–35

17/27

10.8

8.3

0.6

312.5

71.6

0.99

437

239

1.02

1.12

0.28

12–34

27

9.9

9.2

0.8

312.5

29.6

0.88

440

209

1.04

1.08

1.79

11–34

15

8.2

1.9

0.3

312.5

75.3

0.79

441

225

1.00

0.59

1.65

13–30

19

1.3

1.4

0.9

312.5

74.2

1.05

438

253

1.05

1.07

2.41

13–31

19

5.0

3.9

0.7

312.5

19.2

0.89

437

203

1.0

1.1

0.9

13–33

15/27

6.9

2.8

0.4

312.5

53.3

0.85

436

239

0.99

1.11

0.27

12–34

29

7.0

3.3

0.4

312.5

74.8

1.02

451

219

0.97

0.99

2.93

12–33

16/18

4.7

1.0

0.2

312.5

77.8

1.02

450

221

0.96

1.04

0.55

13–34

25

5.5

10.9

1.7

312.5

78.9

0.97

449

199

0.99

1.04

0.74

12–33

24

6.0

8.8

1.3

nc 1.4

C1 B2 B2 B2 B2 B2 B2 B1 B1 B1 312.5

79.1

0.90

448

204

0.95

1.06

0.74

13–34

29

7.8

15.8

2.0

B1 A/B

313.5

14.0

0.96

439

78

0.90

0.99

1.82

12–35

16

2.0

0.6

1.6

Westphalian A/B

313.5

10.5

1.02

438

29

1.05

1.04

1.47

14–35

20

3.5

1.6

0.4

Westphalian A/B

313.5

6.7

0.92

435

40

1.03

0.95

2.18

14–32

19

4.6

2.4

0.4

Westphalian A/B

313.5

6.6

0.98

430

22

1.09

0.96

0.27

14–33

25

6.9

3.5

0.4

Westphalian A/B

313.5

5.6

2.06

525

18

1.02

1.11

2.98

13–32

20

3.5

0.2

0.1

Westphalian A/B

313.5

6.4

2.09

519

21

1.1

1.4

1.7

15–31

16

3.5

0.3

0.1

Viséan Tournaisian Tournaisian Tournaisian

335.5 351.75 351.75 351.75

62.4 53.2 48.6 44.9

0.42 0.41 0.42 0.43

426 423 425 429

330 285 109 132

1.16 1.09 1.13 1.15

1.20 1.14 1.06 1.14

1.34 0.71 2.95 1.11

12–32 12–34 12–34 12–34

21 27 23 23

5.5 5.4 6.5 5.6

7.6 6.2 1.6 3.3

1.2 1.3 0.4 0.7

was separated. In order to obtain a complete separation, the total procedure was repeated two times on the adduct fraction. Finally, both fractions, adducts and non-adducts, were subjected to gas chromatographic and gas chromatographic–mass spectrometric analyses. This procedure was adapted from Ellis and Fincannon (1998).

on a Supreme 5 fused silica capillary column (25 m length, 0.25 mm inner diameter and 0.25 μm film thickness). Chromatographic conditions were: 1 μL splitless injection at starting oven temperature of 60 °C, splitless time 60 s, 3 min hold, and then programmed at 3°/min to 300 °C, 20 min hold. Hydrogen was used as carrier gas with a velocity of approx. 40 cm/s.

2.6. Gas chromatography (GC) 2.7. Gas chromatography–mass spectrometry (GC–MS) A gas chromatograph (Fisons Instruments GC 8000 Series), equipped with a split/splitless injector (injector temperature 270 °C) and a flame ionization detector (FID), was used to analyse the separated saturated fractions. Gas chromatographic separation was performed

GC/MS analyses were performed on a Finnigan MAT 8222 mass spectrometer linked to a HP5890 gas chromatograph, which was equipped with a 30 m × 0.22 mm i.d. × 0.25 μm film BPX5 fused silica

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

2.8. Compound specific stable carbon isotope analyses (CSIA) Compound specific stable carbon isotope analyses were carried out by gas chromatography–isotope ratio monitoring-mass spectrometry (GC–irmMS) using a Finnigan Delta Plus XL mass spectrometer equipped with a GCC III combustion interface and linked to a gas chromatograph 6980A (Fisons Instruments). Gas chromatographic separation was performed on a ZB5 fused silica capillary column (60 m × 0.25 mm i.d. × 0.25 μm film). Chromatographic conditions were: 1 μL splitless injection (injector temperature 270 °C) at an oven temperature of 60 °C, splitless time 60 s, 3 min hold, and then programmed at 2°/min to 300 °C, helium carrier gas velocity was set to 35 cm/s. The oxidation of the eluting substances was carried out at 940 °C facilitated by a CuO/NiO/Pt-catalyst. Each isotope ratio determination was run in triplicate. The carbon isotope ratio of the reference gas (carbon dioxide) was calibrated with a certified reference standard purchased from Chiron (Trondheim, NO) containing n-C11 (−26.11‰ vs. VPDB), n-C15 (− 30.22‰ vs. VPDB) and n-C20 (− 33.06‰ vs. VPDB). All data presented are expressed relative to the VPDB standard. The internal precision of measurements was characterized by standard deviation between 0.1 and 0.4‰ with maximum values of 0.7–0.8‰. 3. Results and discussion 3.1. General geochemical characteristics The samples exhibit a wide range of total organic carbon contents (TOC; Table 1) with values varying between 5.6 and 80.2%. The lowest values are represented by the coal-balls (5.6–14.0%) from three different locations in the Ruhr area (Germany) and Bouxhannout (Belgium). Most of the other samples from the Ruhr Basin have a much higher TOC content (exceeding 70%) and are classified as bituminous humic coals (Taylor et al., 1998). Typical coals with high TOC content are also represented by the samples from the Polish Silesian Basin (60.7 and 68.8%), the Australian Bowen and the Sydney Basin (65.6–76.8%) and from the well Wemmetsweiler-Nord (Saar–Nahe Basin, Germany). The sample set from Scotland and northern England has a lower TOC content in the range from 39.0 to 62.4%. Important parameters providing information on the thermal maturity of the samples are vitrinite reflectance (VRr) and Tmax values derived from Rock-Eval pyrolysis. It was important to assess organic maturity for biomarker characterization so that those samples, which have little biomarker information preserved due to their high thermal stress, can be identified. For example, Ten Haven et al. (1989) showed that for a set of Carboniferous coals in the rather narrow maturity interval between 0.70 and 0.81% VRr, about 90% of hopanoid biomarkers were lost due to thermal stress. The subbituminous coals of the Brazilian Rio Bonito Formation display the lowest maturity (0.43 and 0.44% VRr), as do nearly all of the Scottish and English samples (0.41–0.61% VRr, Table 1). Most of the other samples are high volatile bituminous coals (0.6–1.0% VRr), having experienced a more severe degradation of their biomarkers. Only in a few samples does vitrinite reflectance exceed 1% VRr, indicating slightly higher maturity. These are classified as medium volatile bituminous coals. The highest maturities are represented by the two coal-balls from Bouxhannout (2.06 and 2.09% VRr).

In relation to their vitrinite reflectance values, the Tmax values for the samples appear mostly quite low (see Fig. 2). However, this agrees with earlier observations on coals (e.g. Jasper et al., 2009; Littke et al., 1989). Biomarker distributions of isoprenoids helped to further characterize the samples. Since pristane in coals mainly represents a diagenetic product resulting from oxidation and decarboxylation of phytol, high pristane/phytane ratios (Pr/Ph) indicate more oxidizing depositional environments, such as peat swamps (Powell and McKirdy, 1973a,b). For example, Püttmann et al. (1986) noted that humic vitrinitic coals from the Ruhr Basin, Germany, show Pr/Ph ratios around 9.5. The calculated Pr/Ph ratios of most of our Palaeozoic samples range from 4 to 11, as typical for humic coals (Table 1). In contrast, the Pr/Ph values of the lacustrine black shales (samples 5 to 7) display values around 1. This is regarded as indicative of more reducing conditions during deposition (Shanmungam, 1985). A cross-plot of Pr/n-C17 versus Ph/n-C18 (Fig. 3) classifies extracts into different groups, clearly separating the two black shales and their lacustrine environment (in the lower part of the diagram). Based on this data set, an oxidizing depositional environment can be assumed at the sediment surface for nearly all coal samples. However, it should be noted that anoxic conditions occur in peats within a few decimeters of the surface; therefore, Pr/Ph ratios seem to reflect only the conditions at the sediment surface. 3.2. Carbon isotopes of n-alkanes n-Alkanes from terrestrial sources, in particular higher plants, are characterized by significant contributions of long chain compounds. These indicative aliphatics generally range from n-C21 to n-C35 with odd/even predominance and are dominated by n-C27, n-C29 and n-C31. They originate from epicuticular waxes and are either synthesized directly by higher plants or are defunctionalized even-numbered acids, alcohols or esters (Peters et al., 2005). In contrast aquatic organic matter has little or no odd/even predominance in the range of n-C24–n-C35 alkanes, or in some cases of hypersaline environments, a slight preference in even numbered n-alkanes (Peters et al., 2005). Our samples showed different n-alkane distributions, often with maxima between n-C23 and n-C27 (see Table 1), which are typical of aquatic macrophyta material (Ficken et al., 1998). Only a limited number of samples showed the predominance of long-chain odd numbered n-alkanes typical of immature coaly organic matter (as expressed by the Light Hydrocarbon Preference Index LHCPI b 1.0). In contrast, several samples exhibit a predominance of short-chain homologues with no odd–over–even predominance. This fact is evident from LHCPI values distinctly higher than 1 with maxima of up to 13 (Table 1) and indicates an advanced maturity level. Preliminary stable carbon isotope analyses of n-alkanes were performed on a small sample set of English coals from Potato Pot and Destington (Westphalian age). No further purification or additional fractionation steps were carried out prior to these analyses of

400

Hydrogenindex [mg HC/g TOC]

capillary column. Chromatographic conditions were: 1 μL splitless injection (injector temperature 270 °C) at an oven temperature of 60 °C, splitless time 60 s, 3 min hold, and then programmed at 3°/min to 300 °C. Helium carrier gas velocity was approx. 35 cm/s. The mass spectrometer was operated in a low resolution electron impact ionization mode (EI +, 70 eV) with a source temperature of 200 °C scanning from 35 to 700 amu at a rate of 1 s/decade with an inter-scan time of 0.1 s.

131

0.5%VRr

1.0%VRr

350 300 1.3%VRr

250 200 150 100 50 0 400

420

440

460

480

500

520

540

Tmax [°C] Fig. 2. Crossplot of hydrogen index vs. Tmax values derived from Rock-Eval pyrolysis.

132

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

pristane / n-C17

100

analysis, the urea adduction. This analytical procedure completely separates the branched and cyclic aliphatic compounds from the n-alkanes. An alternative approach using 5 Å molecular sieves provides the same separation, but does not allow an easy access to the incorporated n-alkanes (e.g. Tolosa and Ogrinc, 2007), in particular due to the dissolving process of silicate sieves by hydrofluoric acid (HF). Therefore, this approach is more appropriate for the exclusive analysis of branched and cyclic compounds. Using the urea adduction approach, the coal sample set was analyzed with respect to stable carbon isotope ratios of the n-alkanes and no further shift in δ 13C as described above was observed (Table 2). Hence, a superimposition of branched aliphatic compounds with a significantly lighter carbon isotope signature (in particular hopanoids, see Section 3.3) appears to be the major reason for the observed shift in Fig. 4. This fact should be taken into consideration in future isotopic studies on long-chain n-alkanes to avoid misinterpretation. Generally, the stable carbon isotope ratios determined for coalderived n-alkanes range from − 32‰ to − 22‰. Based on the respective gas chromatograms of their aliphatic adduct fraction, three examples display distinct differences in the isotopic composition of the individual n-alkanes (Fig. 5). Noteworthy, the overall alkane distribution has not been alterated by the urea adduction process. The three coal samples are characterized by increasing maturity from A to C and are derived from different locations. The low maturity of the coal sample from the Rio Bonito Formation, Candiota, Brazil (0.43% VRr, sample nr. 4) is clearly indicated by the strong odd–even predominance in the n-alkane distribution (CPI of 2.6, see Fig. 5A). This distribution shows a distinct maximum at n-C23 and n-C25, indicating a major input of macrophytes (Ficken et al., 1998). The corresponding isotope values range from − 29 to − 25‰. Obviously, the C23 and C25 n-alkanes attributed to macrophyta are isotopically heavier (~ 25‰) than the C27 and C29 n-alkanes (~ 28‰) attributed to cuticular waxes of higher land plants. The n-alkane distribution of the second coal sample, from Polsum mine in the Ruhr area (Fig. 5B, sample nr. 17), shows a very uniform and monomodal distribution, without an odd–even predominance, as indicated by a CPI value of 1.0. This n-alkane pattern corresponds very well to the higher maturity, as characterized by a vitrinite reflectance of 0.79% VRr. In addition to the uniform n-alkane distribution, there is a low variability in the isotopic values, which is quite typical for most of the investigated samples (Table 2) although the range in δ 13C is often around 2‰ rather than 1‰. Consequently, a significant contribution of thermally generated n-alkanes can be assumed for this

10

1

0.1 0.1

1

10

phytane / n-C18 Fig. 3. Crossplot of pristane/n-heptadecane (pr/n-C17) vs phytane/n-octadecane (ph/ n-C18), indicating depositional redox conditions. Modified after Shanmungam (1985).

the aliphatic fractions derived from the liquid chromatography. In Fig. 4, the obtained organic carbon isotope results for n-alkanes, in the range of n-C14 to n-C31, are illustrated. The isotope values range between −32‰ and − 27‰ vs. VPDB for the individual compounds. The δ 13C-values agree very well with the typical isotope values of C3 plants (− 20‰ to − 34‰ VPDB — Deines, 1980; O'Leary, 1981) and of petrogenic compounds (− 21‰ to − 35‰, Meier-Augstein, 1999). However, a significant shift to lighter stable isotope values was obvious for the long chain n-alkanes from n-C26 to n-C33 (Fig. 4). Decreasing δ 13C values with increasing chain length have previously been reported (i.e. Collister et al., 1994; Huang et al., 1995; Lichtfouse et al., 1994; Nguyen Tu et al., 2004; Rieley et al., 1993) for n-alkanes of C3 and CAM plants of both modern and fossil origin. Collister et al. (1994) assumed that this decrease in δ 13C values depends on environmental conditions (e.g. Farquhar et al., 1982; O´Leary, 1981). For recent plants, Lockheart et al. (1997) attributed this effect to seasonal variations during the growing phase. Also, oxic degradation of terrestrial organic matter can lead to this systematic shift. However, to our knowledge a comprehensive and fundamental explanation for these 13C-depleted carbon isotope ratios of plant derived long chain n-alkanes (>n-C27) is still lacking. On the contrary, several authors attributed the observed isotope shifts to incomplete gas chromatographic separation of n-alkanes and branched isomers, e.g. isoprenoids (e.g. Tolosa and Ogrinc, 2007). It is well known that the saturated hydrocarbon fraction may contain significant amounts of branched and cyclic compounds. Consequently, we used a further purification step for samples subjected to isotope

-26

δ13C-values (‰ vs VPDB)

-28

-30

-32

-34

Potato Pot (England), Westfal B Destington I (England), Westfal / Namur Potato Pot (England), Westfal A Potato Pot (England), Westfal A

-36 n-C15

n-C20

n-C25

n-C30

n-Alkanes Fig. 4. δ13C-values of n-alkanes in extracts of Westphalian coals without prior urea adduction treatment (data are not summarized in Table 1.)

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

sample (Hunt, 1997). Therefore, a biogenic signal can neither be deduced from the n-alkane distribution pattern nor from the isotopic values with certainty. The gas chromatogram for the third sample with the highest maturity of 0.92% VRr (Fig. 5C) represents the aliphatic adduct fraction of a coal from Ruhr area (sample nr. 27). It exhibits a bimodal n-alkane distribution with two maxima at n-C19 and n-C25. The corresponding δ 13C values range between − 31.2‰ and − 27.5‰. A slight odd–even-predominance between n-C20 to n-C26 is associated with a significant variation in the isotopic values of approx. 2‰ indicating that a minor signal of unbranched aliphatic molecular fossils is superimposed by the significant contribution of thermally generated n-alkanes. The observed differences in n-alkane distribution and in the isotopic composition of individual compounds are a consequence of different alkane sources. Such sources are the initial biogenic precursors and secondary thermally generated products. However, a systematic variation in the isotopic composition of individual n-alkanes as the result of enhanced contributions of thermally cracked n-alkanes and a corresponding increase in maturity is not discernible from this data set The relative isotopic composition of short and long chain n-alkanes did not differ significantly enough. It can only be summarized that most of the samples are characterized by either a generally ‘heavy’ isotope pattern or a ‘light’ isotope pattern. This lack in correlation of carbon isotope values from thermal maturity is illustrated in Fig. 7. Carbon isotope values of five samples with vitrinite reflectance values ranging between 0.8 and 2.1 do not show any systematic shift towards higher or lower isotopic values with varying maturity, although the overall variation of δ 13C values exceeded 6‰ for individual n-alkanes. Also, deviation of isotope values of individual n-alkanes within one sample did not correlate systematically with thermal maturity. Finally, as indicated in Fig. 6 the isotopic trend of individual n-alkane homologues does not correlate very well with the temporal evolution exhibited by the δ 13C of the bulk organic matter through geologic time. Albeit, there are some similarities, such as the positive excursion for the oldest samples (left part of Fig. 6). In summary, the applicability of stable carbon isotope ratios of n-alkanes for assessing the origin of the coal material or palaeoclimatic or palaeoenvironmental conditions is restricted by significant or even dominating contributions of thermally generated compounds. In addition, interferences of gas chromatographically coeluting compounds can influence stable carbon isotope values in particular of long chain n-alkanes. A meaningful biogenic isotope signature can be derived only for samples of low maturity and after application of purification steps like urea adduction. Since low rank coals of Palaeozoic age are rare, this approach is limited to only a few fossil archives. 3.3. Isoprenoids A close linkage of photosynthesizing organisms and chemical fossils in coals can be assumed for the phytol-derived isoprenoids phytane and pristane. The most abundant source of pristane and phytane is the phytyl side chain of chlorophyll a in phototrophic organisms and bacteriochlorophyll a and b in purple sulfur bacteria (e.g. Brooks et al., 1969; Powell and McKirdy, 1973b). Hence, the carbon isotope signature of these fossil substances might be strongly related to photosynthesis under the respective palaeoenvironmental conditions. In addition to chlorophyll, other biogeochemical sources for pristane and phytane, such as Archea-derived biomolecules, have been described by several authors (e.g. Chappe et al., 1982; Goosens et al., 1984; Illich, 1983; Rowland, 1990). Chappe et al. (1982), e.g., suggested dihydrophytol, a component in archael cell membranes, as a relevant source. Goosens et al. (1984) suggested that tocopherols can be a major source of pristane. However, these compounds are minor constituents in plants and algal lipid membranes and are formed along the same biochemical

133

pathway as chlorophyll. Hence, for pristane derived from tocopherols, similar δ13C values to the phytol side chain derived compounds, can be assumed. The urea adduction applied to the aliphatic fraction of the coal extracts allowed the analysis of the branched isoprenoids in the non-adduct fraction (see Fig. 8). In addition to phytane and pristine, shorter chain acyclic isoprenoids (i-C16 and norpristane (i-C18)) were also included into the analyses. These isoprenoids originate from multiple sources and not solely from chlorophyll (Illich, 1983). However, they appeared only in low concentrations, which were frequently under the detection limit. The δ 13C-values of the isoprenoids analyzed range between − 25‰ and − 34‰ (see Table 2). A small shift of 0.5 to 0.7‰ was observed between pristane and phytane for most of the samples (Fig. 9). A slight 13 C-depletetion in phytane compared to pristane was also observed by Grice et al. (1997). They analyzed the Permian Kupferschiefer and attributed this shift to different biogenic sources. Freeman et al. (1990) suggested that the 0.5‰ lower isotopic value of phytane versus pristane in the Messel Shale was due to a derivation of some of the phytane from lipids of methanogenetic bacteria. This is also observed in the lacustrine samples from the Saar–Nahe Basin (−0.2 to − 0.4‰, Table 2, samples 5–7). In comparison, a larger 13C-depletion in phytane versus pristane exists in most of the coal samples (maximum − 3.5‰). This observation contrasts with the expectation of a lower depletion, because of a much larger input of terrestrial material versus bacterial matter in the coals. The similar trend of pristane and phytane does, however, indicate the dominance of a terrestrial input and phytol as the major source for both isoprenoids. Thus, the isotopic differences might also be the result of the distinct diagenetic pathways for both isoprenoids and corresponding variations in isotope fractionation. Interestingly, a similar shift was not observed for the shorter isoprenoids (i-C16, norpristane). They exhibit either lower or higher δ13C-values compared to phytane and pristane. Therefore, phytol cannot be presumed as the unique biogenic precursor for these isoprenoids and other sources with different isotopic signatures may have contributed. Consequently, the stable carbon isotope ratios of the shorter isoprenoids do not reflect necessarily the isotopic fractionation during the primary production of land plants. Comparing the isotope data of pristane and phytane with δ 13C-values of the total organic carbon (see Fig. 9) might reveal a distinction between the isotopic fractionation associated with photosynthesis and the sum of all metabolic and catabolic processes, which also affects the isotopic composition of organic matter. Strauss and Peters-Kottig (2003) and Peters-Kottig et al. (2006) published an organic carbon isotope record for Palaeozoic terrestrial organic matter, based on the analyses of plant fossils, coals and total organic carbon. Additionally, the δ 13C-values of the total organic carbon of all samples presented in this study are included in Fig. 10. A calculated moving average displays an increase in δ13C from the Silurian (−26‰) to a Permo-Carboniferous maximum of −23‰ (Strauss and Peters-Kottig, 2003). However, the authors acknowledge substantial isotopic variation for many time windows. The maximum difference observed amounted to 15‰ (between −31.4‰ and −16.5‰). The δ 13CTOC values measured here plot within the range of values documented for the Late Palaeozoic (Strauss and Peters-Kottig, 2003). Comparing the δ 13C values for the individual isoprenoids and for total organic carbon, a significant shift to 13C-depleted carbon isotope values (up to 10‰) is discernible for the phytol-derived isoprenoids. Furthermore, both stable carbon isotope records exhibit partially different deviations and do not present the same temporal evolution for all Palaeozoic intervals studied (Fig. 9). In summary, our data on carbon isotope ratios of pristane and phytane do not follow exactly the general temporal evolution of δ 13CTOC in the Late Palaeozoic. Furthermore, the overall deviation of isotope values with age was higher in the isoprenoid record than in the

134

Nr. Sample

δ13C bulk

1

−27.3 −32.3 −34.5 −30.7 −33.0

2 3 4 5 6

7

8 9 10 11 12 13 14

15

Upper Wynn, Sydney Basin, Australia Bulli Seam, Sydney Basin, Australia Candiota, Brazil Rio Bonito-Formation, Seam BS Candiota, Brazil Rio Bonito-Formation, Seam BI Gehrweiler I Humberg Lake; Saar Basin, Germany Gehrweiler I; Rehborn or Odernheim Lake; Shale, Saar Basin, Germany Gehrweiler I; Rehborn or Odernheim Lake; Shale, Saar Basin, Germany Wemmetsweiler-North, Saar Basin, Germany Berwick upon Tweed, Northern-England Berwick upon Tweed, Northern-England Wemmetsweiler-North, Saar Basin, Germany Silesian Basin, 315 LW 155, Poland Silesian Basin, Brzeszcze 510 LW 405, Poland Prosper-Haniel, Seam Chriemhild, Ruhr Basin, Germany Prosper-Haniel, Seam O/N, Ruhr Basin, Germany

−24.8

C16 isopr

Norpr

−23.3

Pr

Ph

25.4

n-C14

n-C15

n-C16

n-C17

n-C18

n-C19

n-C20

n-C21

n-C22

n-C23

n-C24

n-C25

n-C26

n-C27

n-C28

n-C29

n-C30

n-C31

−30.8 −29.0 −28.2 −27.8 −27.5 −27.6 −29.3 −31.0 −30.3 −29.3 −28.5 −29.7

35.1 −25.8 −26.3 −25.2 −24.6 −23.0 −22.5 −23.2 −23.7 −24.2 −25.6 −26.7 −25.7 −27.1 −27.3 −25.8 −26.5

−19.9

−25.1 −26.9

−22.1

−23.9 −25.4

−23.7 −27.3 −25.2 −27.0 −25.7 −25.3 −25.1 −24.3 −26.2 −25.1 −28.0 −26.0 −27.6 −26.4 −26.9 −26.4 −26.3 −26.6 −26.1 −25.2 −26.0 −25.1 −28.6 −28.1 −28.8 −28.7

−26.8 −28.3 −28.4 −29.1 −28.7 −29.5 −29.6 −29.3 −28.3 −29.5 −29.4 −29.3 −28.7 −29.3 −29.8 −29.6 −29.8 −29.3 −29.2 −28.9 −29.4 −29.9 −23.9 −28.2 −28.3 −29.4 −30.0 −23.7 −23.6 −23.8 −24.0 −24.3 −24.7 −24.9 −25.3 −25.7 −26.3 −26.6 −25.6 −25.9 −25.7 −25.0 −26.0 −26.2 −25.8

−24.0 −27.5 −28.1 −29.2 −29.4 −23.3 −23.3 −22.8 −23.1 −23.5 −23.8 −23.7 −24.5 −24.6 −24.9 −24.6 −25.4

−24.1

−32.2 −34.2 −27.7 −28.6 −29.0 −29.3 −30.1 −29.8 −31.2 −30.7 −30.9 −30.0 −29.5 −29.9 −29.2 −30.5 −29.6 −31.2

−24.7 −32.1 −33.1 −34.0 −36.1 −27.9 −28.2 −29.6 −30.0 −30.4 −30.7 −30.9 −31.5 −31.1 −30.7 −29.6 −30.4 −29.9 −30.6 −30.1 −30.8 −25.3 −31.1 −31.4 −30.1 −30.2 −29.9 −29.4 −30.2 −30.8 −30.6 −31.2 −30.3 −31.6 −30.6 −30.8 −29.4 −30.7 −30.1 −30.0 −30.3 −29.8 −24.2

−25.9 −27.1 −25.8 −25.7 −27.2 −27.4 −27.4 −27.5 −27.2 −27.8 −28.3 −28.1 −27.8 −28.0 −29.8 −30.4

−24.4

−28.2 −29.6 −28.5 −29.3 −28.6 −28.9 −29.4 −29.3 −28.4 −29.3 −27.9 −28.0 −28.3 −29.4 −30.6 −30.9

−23.1

−27.5 −28.0 −26.2 −26.7 −27.3 −27.6 −27.3 −27.8 −27.4 −27.8 −26.9 −27.0 −27.3 −27.7 −28.1 −28.2 −29.6 −30.2

−25.1

−26.7 −28.6

−23.6

−28.6 −29.6 −30.1 −30.5 −29.6 −32.0 −31.1 −30.4 −31.6 −30.0 −30.1 −31.8 −30.8 −32.2 −31.1

−23.8 −28.8 −27.2 −28.8 −28.8 −28.2 −28.9 −29.0 −29.2 −29.2 −29.4 −28.5 −28.5 −27.5 −27.6 −27.3 −28.8 −29.0 −28.3 −29.3 −29.5

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

Table 2 Compound specific stable carbon isotope data of n-alkanes and isoprenoids.

16 17 18 19 20 21 22 23 24

26

27

28

29 30 31 32 33 34

−22.9 −30.2 −33.1 −31.1 −30.8 −26.5 −26.4 −27.4 −27.1 −27.9 −27.5 −27.8 −27.3 −27.3 −27.0 −26.8 −26.6 −27.6 −26.5 −26.5 −27.6 −25.6 −25.7 −23.4 −26.5 −26.4 −25.7 −26.3 −24.7 −25.6 −25.6 −25.8 −25.8 −26.0 −25.8 −25.7 −25.7 −25.7 −25.7 −25.8 −25.6 −26.0 −26.0 −26.5 −26.3 −27.9 −22.9 −24.9 −24.9 −25.5 −26.2 −24.6 −25.5 −25.6 −25.8 −25.8 −25.8 −25.8 −25.8 −25.7 −25.7 −25.6 −25.6 −25.5 −25.9 −25.9 −26.3 −26.3 −27.3 −24.5 −29.7 −30.6 −28.2 −29.2 −28.4 −27.8 −28.1 −28.3 −27.4 −27.1 −27.9 −28.6 −27.8 −27.5 −27.4 −27.1 −27.3 −28.1 −28.0 −27.4 −27.5 −23.8 −30.4 −29.5 −28.9 −26.3 −24.3 −26.6 −28.1 −28.7 −27.8 −28.4 −27.4 −27.5 −28.3 −29.2 −30.0 −30.0 −27.6 −29.2 −28.5 −27.2 −29.6 −29.7 −23.2

−28.6 −26.9 −27.6

−26.5 −27.2 −27.3 −27.1 −27.2 −25.6 −24.8 −22.9 −24.5 −25.2 −29.5 −28.5 −27.3 −29.6

−23.8

−23.9 −23.3 −25.9 −27.1 −27.1 −28.0 −28.7 −26.1 −27.4 −26.4 −26.3 −26.4 −26.0 −26.6 −25.8 −27.2 −25.5 −25.6 −26.3 −25.8 −27.2

−23.5 −22.6 −28.1 −26.3 −26.6 −24.1 −24.5 −25.4 −26.1 −25.5 −25.3 −24.8 −25.7 −25.9 −26.6 −26.7 −25.6 −25.1 −25.4 −23.7 −22.4 −22.5 −23.1 −24.4 −28.1 −27.3 −27.8

−25.8 −26.3 −26.3 −26.6 −25.1 −25.5 −25.2 −25.2 −24.6 −26.7 −27.3 −26.4 −26.4 −28.0 −25.3 −27.8

−23.5 −28.9 −27.2 −27.2 −27.7 −22.3 −22.8 −22.6 −23.4 −23.3 −22.9 −23.7 −22.6 −23.6 −24.3 −24.1 −24.2 −24.5 −23.0 −21.4 −23.7 −23.4 −24.3

−23.4 −27.9 −27.2 −27.1 −27.9

−28.8 −29.0 −28.0 −28.9 −29.7 −29.0 −29.1 −29.0 −29.2 −28.9 −29.0 −29.1 −28.9 −29.3 −29.2 −30.0 −30.7

−24.0

−26.9 −26.1 −27.3

−28.4 −28.0 −28.0 −28.0 −28.1 −27.8 −31.4 −29.5 −27.5 −31.2 −27.7 −30.5 −27.9 −27.6 −28.1 −27.7 −28.9

−24.1

−26.9 −26.3 −26.9

−25.9 −26.7 −26.4 −26.1 −26.5 −26.4 −26.6 −26.5 −26.3 −26.6 −26.6 −26.3 −26.6 −26.7

−24.2

−29.2 −28.9 −29.3 −29.7 −30.1 −29.8 −29.5 −30.2 −29.1 −30.7 −29.0 −27.1 −29.4 −28.8 −30.0

−24.4

−27.9 −29.0 −29.0 −29.0 −29.3 −29.2 −29.1 −28.9 −28.9 −29.0 −29.4 −28.3 −29.2 −28.3

−24.4 −30.7 −22.4 −28.5 −23.8 −28.3 −28.7 −22.0 −28.4 −27.7

−28.9 −29.5 −29.4 −30.4

−31.1 −26.2 −27.1 −30.4 −27.6 −27.6 −27.2 −30.9 −28.0 −28.5 −28.3 −30.0 −26.9 −28.3 −27.2

−27.0 −26.3 −29.1 −28.2

−25.5 −27.5 −29.4 −27.8

−27.2 −27.8 −29.4 −28.2

−25.5 −26.8 −30.4 −29.4

−25.4 −27.1 −29.2 −30.1

−26.0 −27.1 −30.2 −30.1

−25.0 −26.5 −29.8 −30.0

−26.2 −26.7 −28.6 −30.0

−27.8 −28.0 −29.2 −30.0

−28.3 −27.0 −27.7 −28.0 −27.0 −27.5 −29.3 −29.2 −28.5 −28.5 −27.5 −28.6 −28.6 −28.6 −27.8 −26.9 −27.1

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

25

Prosper-Haniel, Seam N, Ruhr Basin, Germany Polsum, Ruhr Basin, Germany Polsum, Ruhr Basin, Germany Well Im Felde 2A3, Seam S, Ruhr Basin, Germany Im Felde 2 A3, Seam S, Ruhr Basin, Germany Prosper-Haniel, Seam I, Ruhr Basin, Germany Prosper-Haniel, Seam H, Ruhr Basin, Germany Auguste/Victoria Flöz D/C, Ruhr Basin, Germany Auguste/Victoria, Seam H, Ruhr Basin, Germany Teutoburgia, Katharina Member, Coal-ball, Ruhr Basin, Germany Teutoburgia, Katharina Member, Coal-ball, Ruhr Basin, Germany Vollmond, Katharina Member, Coal-ball, Ruhr Basin, Germany Vollmond, Katharina Member, Coal-ball, Ruhr Basin, Germany Bouxhannout, Katharina Member, Coal-ball, Belgium Bouxhannout, Katharina Member, Coal-ball, Belgium Catcraig, Scotland Burnmouth Bay, Scotland Burnmouth Bay, Scotland Burnmouth Bay, Scotland

135

136

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

Intensity

A) Candiota (Brazil); VRr 0.43%; CPI 2.6

n-C 25 -25.1

-25.2 -28.1

-26.0 -26.1

n-C20

-27.0 -28.6

-26.3

-26.4

-28.8

-26.4

n-C 30

-28.8

-26.9

Retention time

Intensity

B) Polsum (Ruhr, Germany); VRr 0.79%; CPI 1.0 n-C 20 -25.8

-25.7

-25.7

n-C 25

25.7 -25.7

-26.0

-25.8

-25.8

-25.6 -26.0

-25.8

-26.0

n-C 15

n-C 30

-25.6

-26.6 -26.3

-25.5

Retention time

Intensity

C) Vollmond (Ruhr, Germany); VRr 0.92%; CPI 1.0 -28.1 -28.0

n-C20 -27.8 -31.4

-28.0

n-C 25

-29.5

-27.5 -31.2 -27.7 -30.5

-27.9 -27.6 -28.1

-28.0

n-C30

n-C15

-27.7

-28.4

Retention time Fig. 5. A–C Gas chromatograms of aliphatic fractions after urea adduction treatment derived from three coals of different thermal maturity.

δ13CTOC. No systematic change in δ 13C due to either maturation, maceral composition or floral provinces, was observed. Therefore, it is likely that differences in environmental conditions during primary production of

organic matter primarily caused these deviations. Obviously, these processes did not affect the isotope composition of the total organic matter to the same extent.

δ13C-values ( ‰ vs VPDB)

bulk -20 -22

….

-24

n-C16 to n-C28

-26 -28

moving average of δ13C n-alkanes

-30 -32

Age (sample numbers) Fig. 6. δ13C-values of n-hexadecane to n-octacosane (after urea adduction), including the overall moving average compared to with the δ13C-values of the total organic matter (bulk). Note that sample numbers and age of samples correspond.

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

137

δ13C-values ( ‰ vs VPDB)

22 24 26

Sample 12 Sample 15

VR r 0.8 VR r 0.8

Sample 20

VR r 1.0

28

Sample 24

VR r 1.0

Sample 27

VR r 2.1

30 32 34 15

30

Carbon chain length Fig. 7. Variability of δ13C-values of n-alkanes from coals with different thermal maturity.

Consequently, isotopic properties of total organic carbon in coals and, therefore, of land plant derived organic matter were not influenced solely by differences in isotope fractionation directly linked to photosynthesis. However, there are several processes and parameters significantly affecting the isotopic fractionation during primary production. Substantial variations due to different CO2 fixation mechanisms (C3-, C4- and CAM-plants) can be excluded for the time period

of the Late Palaeozoic, because likely only C3 plants existed. However, particular environmental conditions like temperature, humidity, availability of nutrients and water, growth rate, and the concentration of atmospheric CO2 play important roles in determining the magnitude of isotopic fractionation. The variations of palaeoenvironmental and palaeogeographical conditions likely account for the observed deviations in δ 13C with an dominant influence of atmospheric O2/CO2

Zeche Vollmond, coal-ball Vr 0.92% -28.1 -28.0

n-C20 -27.8 -31.4

-28.0

n-C25

-29.5 -27.5

-31.2

-27.7 -30.5

-27.9

n-C30

-27.6 -28.1

-28.0

n-C15

-27.7

-28.4

Pristane

Hopanes

Norhopane Hopane

Norpristane Phytane

Ts

C16-Isoprenoid

retention time Fig. 8. Gas chromatogram of an aliphatic adduct and corresponding non-adduct fraction from a coal ball sample. Analyzed n-alkanes, isoprenoids and geohopanoids are marked.

138

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

total organic matter

pristane

phytane

δ13C-values ( ‰ vs VPDB)

-15 -20 -25 -30 -35 -40

Permian

Carboniferous Age (sample numbers)

Fig. 9. δ13C values of total organic carbon and compound specific isotope values of pristane and phytane in the coal samples investigated. Note that sample numbers and age of samples correspond.

ratio and its effect on the biogenic carbon isotopic fractionation as proposed by Strauss and Peters-Kottig (2003). Thus, a direct correlation of O2/CO2 ratios and δ 13C values of pristane/phytane is to be expected. In summary, phytol-derived isoprenoids are very useful molecular indicators in coals directly linked to the primary production of organic matter and provide a more precise insight into changes of environmental parameters linked with photosynthesis. Therefore, their carbon isotopic properties are most suitable for the reconstruction of ecological systems and climate in the Palaeozoic. 3.4. Hopanoids

13 δ C[

] vs. VPDB

In order to compare the isotopic signature of substances synthesized by autotrophs with those of heterotrophs, geohopanes were also analyzed. However, the samples analyzed were restricted to those twelve samples that exhibited hopane concentrations elevated enough to be measured successfully by GC/irmMS. Hopanes are pentacyclic triterpanes containing 27–35 carbon atoms in a polycyclic structure composed of four six-member rings and one five-member ring (Van Dorsselaer et al., 1977). The hopanoids are commonly believed to represent a bacterial contribution to the total organic

matter pool. They are related to specific bacteriohopanepolyols, mainly bacteriahopanetetrol, and undergo side chain shortening during diagenesis, forming C27- to C34-homologous series. The lower pseudohomologous (C30 or less) may also be related to C30 precursors, like diploptene or diplopterol (Rohmer, 1987). Noteworthy, only 18α(H)-22,29,30-trisnorneohopane and 17α(H), 21β(H)-hopane were analyzed in this study, because only these hopanoids were completely separated in gas chromatographic measurements. The δ13C values range from −30‰ to −48‰ (Table 3). Thus, the hopanes were significantly lighter with respect to carbon isotopes than the n-alkanes and isoprenoids. Depletion of 13C in non-marine sediments is also described by Freeman et al. (1990) with approx. −65‰ in the Eocene Messel Shale and by Spooner et al. (1994), with ca. −50‰ in recent lakes. This shift is the result of a secondary transformation of the organic matter by bacteria and was used, e.g., by Collister et al. (1994) to differentiate bacterial input versus primary organic matter. Interestingly, the variation of isotope values correlates partially with trends observed for the acyclic isoprenoids. In particular, trisnorhopane data exhibit the same trend over time or sample number as the phytane and pristane data (see Fig. 11), whereas δ 13C-values of hopane show some clear deviations. Hence, the isotopic signal from primary production is only partially reflected by secondary transformation products such as hopanoids. To differentiate the isotopic impact of isoprenoids and hopanoids on the composition of the total organic matter, the individual shifts of norhopane as well as phytane in comparison to bulk data have been correlated using simply the differences of the measured δ13C-values (see Fig. 12). No significant correlation was visible, neither directly nor with respect to age. However, the plot perfectly groups the individual sample sets indicating that the facies influences primarily the different contributions of chlorophyll and microbial biomass. This leads to the divergence of phytane or trisnorhopane data from total organic matter. As an approximation, higher Δδ 13C values for bulk organic matterpristane indicate a lower contribution of chlorophyll (or other pristane precursors), whereas higher Δδ 13C values for bulk organic matter-hopane would suggest a lower contribution of bacterial biomass. Hence, the type of organic matter or in turn the provenance has the highest influence on the compound specific isotopic signature of organic matter in the Palaeozoic coals investigated. These observations cannot be made when investigating bulk organic matter.

Age [Ma, STD 2002] Fig. 10. Temporal evolution in δ13C of total terrestrial organic carbon for the Palaeozoic (STD 2002) after Strauss and Peters-Kottig (2003). Samples investigated in this study are inserted as black filled circles.

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

139

Table 3 Compound specific stable carbon isotope data of geohopanoids. Nr.

Sample

18α(H)-22,29,30-trisnorneohopane

17α(H),21β(H)-hopane

1 4 8 9 19 25 26 27 28 31 33 34

Sydney Basin (Australia) Candiota (Brazil) Wemmetsweiler-North (Saar–Nahe Basin, Germany) Wemmetsweiler-North (Saar–Nahe Basin, Germany) Im Felde 2 A3 (Ruhr Basin, Germany) Teutoburgia (Ruhr Basin, Germany) Teutoburgia (Ruhr Basin, Germany) Vollmond (Ruhr Basin, Germany) Vollmond (Ruhr Basin, Germany) Catcraig (Scotland) Burnmouth Bay (Scotland) Burnmouth Bay (Scotland)

−35.7 −27.0 −40.0 −42.1 −34.3 −32.5 −31.3 −30.3 −31.4 −34.7 −42.3 −44.2

−32.6 −33.2 −31.8 −33.0 −39.9 −34.4 −33.2 −35.8 −34.3 −33.9 −46.7 −47.9

4. Conclusions Compound specific stable carbon isotope analyses applied to Palaeozoic coal samples identified pristane and phytane as suitable molecular and isotopic tracers. These tracers reflect and partially quantify the isotopic fractionation during primary production of organic matter by land plants. Analytical restrictions (especially the gas chromatographic separation) and the superimposition of thermally cracked compounds hindered the usage of further higher plant markers. In particular, the δ 13C-values of n-alkanes as well as C16and C18-isoprenoids in the samples investigated were not solely influenced by the primary production processes. Identical temporal trends in δ 13C were not observed for pristane, phytane and for total organic matter in the Late Palaeozoic coals

phytane

pristane

trisnorhopane

hopane

δ13C-values ( ‰ vs VPDB)

-20 -25 -30 -35 -40 -45

investigated in this study. Although some trends appeared to be similar, significant deviations were observed in other samples. Hence, secular carbon isotopic variations related to photosynthesis are not reflected in the δ 13C-values of bulk terrestrial organic matter. Most direct information about temporal variations in δ 13C associated with carbon cycling during primary productivity can be derived from phytol-derived isoprenoids. Furthermore, carbon isotope values for isoprenoids and hopanoids were not affected by maturity or maceral composition. However, isotopic differences between total organic matter and phytane (Δδ 13C values) correlated with the differences between total organic matter and hopane. As a result, coal samples could be distinguished by their provenance. Using these Δδ 13C values as a proxy for estimating the relative contribution of microbial or chlorophyll related biomass, a significant influence of the type of organic matter on the compound specific isotope signature is evident. Hence, individual isotopic variations in different types of biomass might be successfully traced by the isotopic properties of characteristic molecular fossils in Palaeozoic coals. A further exploration of this approach specifically with respect to palaeoenvironmental and palaeogeographical conditions seems promising. The present study has clearly demonstrated that molecular and carbon isotopic analyses of terrestrial organic matter, ranging in resolution from bulk to compound specific analyses, allow the reconstruction of ecological and climate conditions in the Palaeozoic. This approach is not without restrictions, in particular by organic matter properties (e.g. the prerequisite of organic matter with low maturity) and analytical limitations (e.g. gas chromatographic resolution).

-50

Permian

Carboniferous

References Age (sample numbers)

Fig. 11. δ13C values of pristane and phytane as well as geohopanoids from selected coal samples. Note that sample numbers and age of samples correspond.

Δ δ13C (bulk - hopane)

30 25 20 15 10 5 0 0

2

4

6

8

10

12

Δ δ13C (bulk - phytane) Fig. 12. Correlation of Δδ13C (bulk — hopane) with Δδ13C (bulk — phytane) data. All values are given as ‰ vs VPDB.

Alexander, R., Noble, R.A., Kagi, R.I., 1987. Fossil resin biomarkers and their application in oil to source rock correlation, Gippsland Basin, Australia. Australian Petroleum Exploration Association Journal 27, 63–71. Amijaya, H., Littke, R., 2006. Properties of thermally metamorphosed coal from Tanjung Enim Area, South Sumatra Basin, Indonesia with special reference to the coalification path of macerals. International Journal of Coal Geology 66, 271–295. Anderson, T.F., Arthur, M.A., 1983. Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenvironmental problems. In: Arthur, M.A., et al. (Ed.), Stable isotopes in sedimentary geology: SEPM Short Course Notes, 10, pp. 111–151. Arens, N.C., Jahren, A.H., Amunson, R., 2000. Can C3 plants faithfully record the carbon isotopic composition of the atmospheric carbon dioxide? Paleobiology 26, 137–164. Bechtel, A., Reischenbacher, D., Sachsenhofer, R.F., Gratzer, R., Lücke, A., 2007. Paleogeography and paleoecology of the upper Miocene Zillingdorf lignite deposit (Austria). International Journal of Coal Geology 69, 119–143. Bechtel, A., Gratzer, R., Sachsenhofer, R.F., Gusterhuber, J., Lücke, A., Püttmann, W., 2008. Biomarker and carbon isotope variation in coal and fossil wood of Central Europe through the Cenozoic. Palaeogeography, Palaeoclimatology, Palaeoecology 262, 166–175. Brooks, J.D., Gould, K., Smith, J.W., 1969. Isoprenoid hydrocarbons in coal and petroleum. Nature 222, 257–259. Chappe, B., Albrecht, P., Michaellis, W., 1982. Polar lipids of archaebacteria in sediments and petroleums. Science 217, 65–66. Collister, J.W., Rieley, G., Stern, B., Eglington, G., Fry, B., 1994. Compound-specific deltaC-13 analyses of leaf lipids from plants with differing carbon-dioxide metabolisms. Organic Geochemistry 21 (6–7), 619–627.

140

J. Schwarzbauer et al. / International Journal of Coal Geology 107 (2013) 127–140

Deines, P., 1980. The isotopic composition of reduced organic carbon. In: Fritz, P., Fontes, J.-C. (Eds.), Handbook of Environmental Isotope Geochemistry: Vol. 1: The Terrestrial Environment. Elsevier, New York, pp. 329–406. Ellis, L., Fincannon, A.L., 1998. Analytical improvements in irm-GC/MS analyses: advanced techniques in tube furnace design and sample preparation. Organic Geochemistry 29, 1101–1117. Espitalié, J., Laporte, J.L., Madec, M., Maquis, F., Leplat, P., Paulet, J., Boutefeu, A., 1977. Méthode rapide de caractérisation des roches mères, de leur potential pétrolier et de leur degré d'évolution. Revue de l'Institut Francais du Pétrole 32, 23–42. Farquhar, G.D., O'Leary, M.H., Berry, J.A., 1982. On the relationship between carbon isotope discrimination and the intercellular carbon dioxide concentration in leaves. Australian Journal of Plant Physiology 9, 121–137. Farquhar, G.D., Ehleringer, J.R., Hubick, K.T., 1989. Carbon isotope discrimination and photosynthesis. Annual Reviews of Plant Physiology and Plant Molecular Biology 40, 503–537. Ficken, K.J., Barber, K.E., Eglington, G., 1998. Lipid biomarker, δ13C and plant macrofossil stratigraphy of a Scottish montane peat bog over the last two millennia. Organic Geochemistry 28, 217–237. Freeman, K.H., Hayes, J.M., Trendel, J.M., Albrecht, P., 1990. Evidence from carbon isotope measurement for diverse origins of sedimentary hydrocarbons. Nature 343, 254–256. Gensel, P.G., Andrews, H.N., 1987. The evolution of early land plants. American Scientist 75, 478–489. German Stratigraphic Commission (ed.) 2002. Stratigraphic Table of Germany 2002. Goosens, H., de Leeuw, J.W., Schenck, P.A., Brassell, S.C., 1984. Tocopherols as likely precursor of pristane in ancient sediments and crude oils. Nature 312, 440–442. Gray, J., Shear, W., 1992. Early life on land. American Scientist 80, 444–456. Grice, K., Schaeffer, P., Schwark, L., Maxwell, J.R., 1997. Changes in palaeoenvironmental conditions during deposition of the Permian Kupferschiefer (Lower Rhine Basin, northwest Germany) inferred from molecular and isotopic compositions of biomarker components. Organic Geochemistry 26, 677–690. Hayes, J.M., Freeman, K.H., Popp, B.N., Hoham, C.H., 1990. Compound-specific isotopic analyses: a novel tool for reconstruction of ancient biogeochemical processes. Organic Geochemistry 16, 1115–1128. Hayes, J.M., Strauss, H., Kaufman, A.J., 1999. The abundance of 13C in marine organic matter and isotopic fractionation in the global biochemical cycle of carbon during the past 800 Ma. Chemical Geology 161, 103–125. Huang, Y., Lockheart, M.J., Collister, J.W., Eglington, G., 1995. Molecular and isotope biogeochemistry of the Miocene Clarkia Formation: hydrocarbons and alcohols. Organic Geochemistry 23, 785–801. Hunt, J.M., 1997. Petroleum Geochemistry and Geology. Freeman, New York. Illich, H.A., 1983. Pristane, phytane, and lower molecular weight isoprenoid distributions in oils. AAPG Bulletin 67, 386–393. Izart, A., Palhol, F., Gleixner, G., Elie, M., Blaise, T., Suarez-Ruiz, I., Sachsenhofer, R.F., Privalov, V.A., Panova, E.A., 2012. Palaeoclimate reconstruction from biomarker geochemistry and stable isotopes of n-alkanes from Carboniferous and Early Permian humic coals and limnic sediments in western and eastern Europe. Organic Geochemistry 43, 125–149. Jasper, K., Krooss, B.M., Flajs, G., Hartkopf-Fröder, C., Littke, R., 2009. Characteristics of type III kerogen in coal-bearing strata from the Pennsylvanian (Upper Carboniferous) in the Ruhr Basin, Western Germany: comparison of coals, dispersed organic matter, kerogen concentrates and coal-mineral mixtures. International Journal of Coal Geology 80, 1–19. Kenrick, P., Crane, P.R., 1997. The origin and early evolution of plants on land. Nature 389, 33–39. Lichtfouse, E., Derenne, S., Mariotti, A., Largeau, C., 1994. Possible algae origin of long chain odd n-alkanes in immature sediments as revealed by distribution and carbon isotope ratios. Organic Geochemistry 22, 1023–1027. Littke, R., Horsfield, B., Leythaeuser, D., 1989. Hydrocarbon distribution in coals and in dispersed organic matter of different maceral compositions and maturities. Geologische Rundschau 78, 391–410. Littke, R., Urai, J.L., Uffmann, A.K., Risvanis, F., 2012. Reflectance of dispersed vitrinite in Palaeozoic rocks with and without cleavage: implications for burial and thermal history modeling in the Devonian of Rursee area, northern Rhenish Massif, Germany. International Journal of Coal Geology 89, 41–50. Lockheart, M.J., van Bergen, P.F., Evershed, R.P., 1997. Variations in the stable carbon isotope composition of individual lipids from the leaves of modern angiosperms: implications for the study of higher plant-derived sedimentary organic matter. Organic Geochemistry 26, 137–153. Lücke, A., Helle, G., Schleser, G.H., Figueiral, I., Mosbrugger, V., Jones, T.P., Rowe, N.P., 1999. Environmental history of the German Lower Rhine Embayment during the Middle Miocene as reflected by carbon isotopes in brown coal. Palaeogeography, Palaeoclimatology, Palaeoecology 15, 339–352. Meier-Augstein, W., 1999. Applied gas chromatography coupled to isotope ratio mass spectrometry. Journal of Chromatography. A 842, 351–371. Müller, A.B., Strauss, H., Hartkopf-Froeder, C., Littke, R., 2006. Reconstructing the evolution of the latest Pennsylvanian–earliest Permian Lake Odernheim based on stable isotope geochemistry and palynofacies: a case study from the Saar–Nahe Basin, Germany. Palaeogeography, Palaeoclimatology, Palaeoecology 240, 204–224.

Murray, A.P., Sosrowidjojo, I.B., Alexander, R., Kagi, R.I., Norgate, C.M., Summons, R.E., 1997. Oleananes in oils and sediments: evidence of marine influence during early diagenesis? Geochimica et Cosmochimica Acta 61, 1261–1276. Nguyen Tu, T.T., Derenne, S., Largeau, C., Bardoux, G., Mariotti, A., 2004. Diagenesis effects on specific carbon isotope composition of plant n-alkanes. Organic Geochemistry 35, 317–329. Noble, R.A., Knox, J., Alexander, R., Kagi, R.I., 1985. Identification of tertacyclic diterpane hydrocarbons in Australian crude oils and sediments. Journal of the Chemical Society, Chemical Communications 32–33. O'Leary, M.H., 1981. Carbon isotope fractionation in plants. Phytochemistry 20, 553–567. Peters, K.E., Walters, C.C., Moldowan, J.M., 2005. The biomarker guide. Biomarkers and Isotopes in Petroleum Exploration and Earth History, vol. 2. Cambridge University Press, pp. 475–1155. Peters-Kottig, W., Strauss, H., Kerp, H., 2006. The land plant delta(13)C record and plant evolution in the Late Palaeozoic. Palaeogeography, Palaeoclimatology, Palaeoecology 240, 237–252. Powell, T.G., McKirdy, D.M., 1973a. The effect of source material, rock type and diagenesis on the n-alkane content of sediments. Geochimica et Cosmochimica Acta 37, 523–633. Powell, T.G., McKirdy, D.M., 1973b. Relationship between ratio of pristane to phytane, crude oil composition and geological environment in Australia. Nature 243, 37–39. Püttmann, W., Wolf, M., Wolff-Fischer, E., 1986. Chemical characteristics of liptinite macerals in humic and sapropelic coals. Organic Geochemistry 10, 625–632. Ramanampisoa, L., Radke, M., Schaefer, R.G., Littke, R., Rullkötter, J., Horsfield, B., 1990. Organic-geochemical characterization of sediments from the Sakoa coalfield, Madagascar. Organic Geochemistry 16, 235–246. Rieley, G., Collister, J.W., Stern, B., Eglinton, G., 1993. Gas chromatographic / isotope ratio mass spectrometry of leave n-alkanes from plants of differing carbon dioxide metabolisms. Rapid Communications in Mass Spectrometry 7, 488–491. Rohmer, M., 1987. The hopanoids, prokaryotic triterpenoids and sterol surrogates. In: Schriner, E., et al. (Ed.), Surface Structures of Microorganisms and Their Interactions the Mammalian Host. VCH Publishing, pp. 227–242. Rowland, S.J., 1990. Production of acyclic isoprenoids hydrocarbons by laboratory maturation of methanogenic bacteria. Organic Geochemistry 15, 9–16. Schleser, G.H., 1995. Parameters determining carbon isotope ratios in plants. In: Frenzel, B. (Ed.), Problems of stable isotopes in tree-rings, lake sediments and peat-bogs as climatic evidence for the Holocene: ESF Spec. Iss., 15, pp. 71–96. Schulze, T., Michaelis, W., 1989. Structure and origin of terpenoid hydrocarbons in some German coals. Organic Geochemistry 16, 1051–1058. Schwarzbauer, J., Littke, R., Weigelt, V., 2000. Identification of specific organic contaminants for estimating the contribution of the Elbe river to the pollution of the German Bight. Organic Geochemistry 31, 1713–1731. Scotese, C.R., 1997. Paleographic Atlas, PALEOMAP Progress Report 90-0497. Department of Geology, University of Texas at Arlington. Shanmungam, G., 1985. Significance of coniferous rain forests and related organic matter in generating commercial quantities of oil, Gippsland Basin, Australia. American Association of Petroleum Geologists Bulletin 69, 1241–1254. Spooner, N., Rieley, G., Collister, J.W., Lander, M., Cranwell, P.A., Maxwell, J.R., 1994. Stable carbon isotopic correlation of individual biolipids in aquatic organisms and a lake bottom sediment. Organic Geochemistry 21, 823–827. Strauss, H., Peters-Kottig, W., 2003. The Paleozoic to Mesozoic carbon cycle revisited: the carbon isotopic composition of terrestrial organic matter. Geochemistry, Geophysics, Geosystems 4 15 pp. Taylor, G.H., Teichmüller, M., Davis, A., Diessel, C.F.K., Littke, R., Robert, P., 1998. Organic Petrology. Gebrüder Borntraeger, Berlin. Ten Haven, H.L., Littke, R., Rullkötter, J., 1989. Hydrocarbon biological markers in Carboniferous coals of different maturities. Preprints — American Chemical Society, Division of Petroleum Chemistry 34 (1), 149–153. Tolosa, I., Ogrinc, N., 2007. Utility of 5 Å molecular sieves to measure carbon isotope ratios in lipid biomarkers. Journal of Chromatography A 1165, 172–181. Van Aarssen, B.G.K., Hessels, J.K.C., Abbink, O.A., de Leeuw, J.W., 1992. The occurrence of polycyclic sesqui-, tri-, and oligoterpenoids derived from a resinous polymeric cadinene in crude oils from southeast Asia. Geochimica et Cosmochimica Acta 56, 1231–1246. Van Aarssen, B.G.K., de Leeuw, J.W., Collinson, M., Boon, J.J., Goth, K., 1994. Occurrence of polycadinene in fossil and recent resins. Geochimica et Cosmochimica Acta 58, 223–229. Van Bergen, P.F., Poole, I., 2002. Stable carbon isotopes of wood: a clue to palaeoclimate? Palaeogeography, Palaeoclimatology, Palaeoecology 182, 31–45. Van Dorsselaer, A., Albrecht, P., Ourisson, G., 1977. Identification of novel 17α(H)hopanes in shales, coals, lignites, sediments and petroleum. Bulletin de la Sociétè Chimique de France 1–2, 165–170. Veizer, J., Ala, D., Azmy, K., Bruckschen, P., Bihl, D., Bruhn, F., Carden, G.A.F., Diener, A., Ebneth, S., Godderis, Y., Jasper, T., Korte, C., Pawellek, F., Podlaha, O.G., Strauss, H., 1999. 87/86Sr, δ13C and δ18O evolution of Phanerozoic seawater. Chemical Geology 161, 59–88.