GeolCarp_Vol69_No1_51

GEOLOGICA CARPATHICA

, FEBRUARY 2018, 69, 1, 51–70

doi: 10.1515/geoca-2018-0004

www.geologicacarpathica.com

Petrographic and biomarker analysis of xylite-rich coal

from the Kolubara and Kostolac lignite basins

(Pannonian Basin, Serbia)

NATAŠA ĐOKOVIĆ

, DANICA MITROVIĆ

, DRAGANA ŽIVOTIĆ

, ACHIM BECHTEL

REINHARD F. SACHSENHOFER

and KSENIJA STOJANOVIĆ

4, 1,



University of Belgrade, Innovation Centre of the Faculty of Chemistry, Studentski trg 12-16, 11000 Belgrade, Serbia;

ndjokovicpost@gmail.com; danicamitrovic87@gmail.com

University of Belgrade, Faculty of Mining and Geology, Đušina 7, 11000 Belgrade, Serbia; dragana.zivotic@rgf.bg.ac.rs

Montanuniversität Leoben, Department of Applied Geosciences and Geophysics, Peter-Tunner-Str. 5, A-8700 Leoben, Austria;

achim.bechtel@unileoben.ac.at; reinhard.sachsenhofer@unileoben.ac.at

University of Belgrade, Faculty of Chemistry, Studentski trg 12-16, 11000 Belgrade, Serbia;



ksenija@chem.bg.ac.rs

(Manuscript received March 29, 2017; accepted in revised form December 12, 2017)

Abstract: The maceral and biomarker characteristics of 4 sublithotypes of xylite-rich coal (SXCs), pale yellow, dark

yellow, brown and black, originating from the Kolubara and Kostolac lignite basins were determined. Based on these

results, differences in sources and changes of organic matter (OM) resulting in formation of 4 SXCs were established.

Conifers (particularly Cupressaceae, Taxodiaceae and Pinacea) had a significant impact on the precursor OM of all SXCs.

The contribution of gymnosperm vs. angiosperm vegetation decreased in order pale yellow SXC > dark yellow SXC >

brown SXC > black SXC. The distribution of non-hopanoid triterpenoids indicates that change of SXC colour from

yellow to black is associated with reduced input of angiosperm plants from the Betulacea family. Differences in hopane

distribution, bitumen content, proportion of short-chain n-alkanes and degree of aromatization of di- and triterpenoids of

pale yellow SXC are controlled by microbial communities which took part in the diagenetic alteration of OM. The content

of total huminites increased from black to pale yellow SXC, whereas contents of total liptinite and inertinite macerals

showed the opposite trend. SXCs differ according to textinite/ulminite ratio, which sharply decreased from pale yellow

to black SXC, reflecting increase in gelification of woody tissue. Regarding the composition of liptinite macerals,

the SXCs mostly differ according to resinite/liptodetrinite and resinite/suberinite ratios, which are higher in yellow than

in brown and black SXC. This result along with values of TOC/N ratio and Carbon Preference Index indicate that the

contribution of well preserved woody material, including lignin tissue vs. the impact of epicuticular waxes decreased

from yellow to black SXC.

Keywords: Kolubara, Kostolac, lignite, sublithotypes of xylite-rich coal, macerals, biomarkers.

Introduction

Lignite is one of the main energy resources in central and

southeast Europe. According to Reichl et al. (2016), Poland,

Turkey, Greece, Czech Republic, Serbia, Bulgaria, Bosnia and

Herzegovina, Romania and Hungary are placed among the 15

greatest producers. Serbia produced about 30 Mt of lignite in

2014. The main lignite deposits in Serbia are located in the

Upper Miocene Kolubara and Kostolac basins (Fig. 1), and in

the Kovin deposit (Jelenković et al. 2008).

According to their macropetrographic composition, struc-

ture and texture, lignites can be classified into several litho-

types. The lithotype classification system for lignite (soft

brown coal) proposed by the International Committee for Coal

and Organic Petrology (ICCP 1993; Taylor et al. 1998) distin-

guishes: xylite-rich coal, matrix coal, charcoal-rich coal and

mineral-rich coal. Lithotype varieties (sublithotypes) can be

differentiated by their degree of gelification and colour (Jacob

1961; Ercegovac 1989; Kwiecińska & Wagner 1997).

Composition and characteristics of lignite which directly

influence its applicability depend on sources of organic matter

(OM) and the degree of transformation during peat genesis

and diagenesis. For establishing the precursors of lignite OM

and its digenetic alteration, micropetrographic (maceral)

analysis and biomarker composition are most useful.

Although numerous petrographic and biomarker studies

have been performed on whole lignite samples (e.g., Bechtel

et. al. 2007; Zdravkov et al. 2011; Životić et al. 2014; Mitrović

et al. 2016), to the best of our knowledge detailed investiga-

tion of lignite sublithotypes has not been performed. Xylite-

rich coal is widespread and can form layers, several tens of

metres thick. This lithotype is abundant in Upper Miocene

deposits of Serbia, Bulgaria and Greece. Moreover, individual

sublithotypes of xylite-rich coal (SXC) influence lignite utili-

zation. In this study, four different SXCs (pale yellow, dark

yellow, brown, black) were isolated from lignites of the

Kolubara and Kostolac, the most important basins in Serbia.

The main objective was to establish the sources and to reveal

the differences of precursor organic matter which resulted in

the formation of four different SXCs. For that purpose maceral

ĐOKOVIĆ, MITROVIĆ, ŽIVOTIĆ, BECHTEL, SACHSENHOFER and STOJANOVIĆ

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

compositions and biomarker distri-

butions were investigated in detail.

Geological setting

The most important Serbian lignite

basins belong to the Pannonian Basin

System and were formed in shallow

lacustrine, delta plain and fluvial

environments during the Miocene.

Upper Miocene (“Pontian”) coal-

bearing series from the Kolubara and

Kostolac lignite basins (Pontian–

Messinian-ICS; Fig. 2) were formed

in freshwater environments. In both

basins, the coal seams are associated

with sandy–clayey sediments.

The Kolubara Basin is located

about 60 km S-SW of Belgrade

(44°28’21” N, 20°12’18” E), and

covers an area of almost 600 km

while the Kostolac Basin is loca-

ted about 90 km E of Belgrade

(44°43’41” N, 21°14’45”

E) and

covers an area of 145 km

(Fig. 1).

Annually, the Kolubara Basin pro-

duces about 30 Mt of lignite (http://

www.rbkolubara.rs/index.php?

o p t i o n = c o m _ c o n t e n t & v i e w =

article&id=83&Itemid=189). The

Kosto lac Basin produces 9–12 Mt

(http://www.te-ko.rs).

The basement of the Kolubara

Basin consists of Devonian and

Carbo niferous schists, gneisses, slates

and sandstones, Mesozoic mica-rich

sandstones, shales, dolomitic lime-

stones, limestones and flysch, and

Tertiary phenoandesites, pheno da -

ci tes, quartz-latite, ignimbrites and

quartz- latite tuffs (Ercegovac &

Pulejković 1991; Životić et al. 2014).

The Upper Miocene (“Pontian”) coal-

bearing sediments, 250 to 320 m

thick, host three coal seams (Kezović

2011; Fig. 2): Seam III (Lower Coal

Seam), Seam II (Main Coal Seam)

and Seam I (Upper Coal Seam) with

average thicknesses of 7 m, 25 m and

11 m, respectively. The coal-bearing

sediments dip at low angles towards

the northern and central parts of

the basin. On the southern border

of the SE part of the basin, coal-

bearing sediments are characterized

Fig. 1. Main geotectonic and metallogenic units of Serbia (modified after Dimitrijević 2000;

Schmid et al. 2008).

1 — Pannonian Basin; 2 — Budva-Cukali Zone; 3 — High Karst Unit; 4 — Pre-Karst and Bosnian

Flysch Unit; 5 — East Bosnian-Durmitor Thrust Sheet; 6 — Dinaric Ophiolitic Belt; 7 — Western

Vardar Ophioliic Unit; 8 — Drina-Ivanjica Thrust Sheet; 9 — Jadar-Kopaonik Thrust Sheet;

10 — Sava Zone; 11 — Eastern Vardar Ophiolitic Unit; 12 — Serbo-Macedonian Unit; 13 — Getic

Unit; 14 — Danubian Nappes; 15 — Ceahlau-Severin Unit; 16 — Central Balkan and Prebalkan

Units; 17 — Moesian Platform; 18 — External Moesian Foredeep; 19 — Boundary of metallo-

genic units; 20 — Locations of the Kolubara (A) and Kostolac (B) basins.

PETROGRAPHIC AND BIOMARKER ANALYSIS OF XYLITE-RICH COAL (PANNONIAN BASIN, SERBIA)

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

by a syn form, due to the intense post-sedimentary faulting,

causing occasional erosion of coal in the SE part of the basin.

The basement of the Kostolac Basin consists of Devonian

crystalline rocks overlain by Neogene sediments (Stojanović

et al. 2012; Fig. 2). The Upper Miocene (“Pontian”) coal-

bearing series of the Kostolac Basin hosts five coal seams,

which are termed from bottom to top seams III, II-a, II, I-a,

and I. The average thickness of Seam III is 19.4 m, while it is

1.4 m for IIa, 4.1 m for II, 1.5 for Ia and 13.9 m for coal

seam I (Životić et al. 2014). The coal-bearing sediments

generally dip toward NW at low angles of 5 –15

Methods

Two representative feed lignite samples (mass ~ 5 kg of each)

from the Kolubara and the Kostolac basins were collected

from the pre-boiler mills of thermal power plants “Nikola

Tesla” and “Kostolac B”, respectively.

For lithotype analyses, the lignite samples were crushed to

a maximum particle size of 3 mm and dried at room tempera-

ture. Lignites were manually separated into matrix, char coal,

mineral-rich coal, dopplerite coal (a black very brittle type of

coal made of humic gel; Taylor et al. 1998; Feller et al. 2010;

Pontian

Pannonian

Sarmatian

KOST

OLAC

KOLUBARA

Badenian

Ottnangian-Karpathian

Lower

Miocene

(

)

Middle

Miocene

(

)

Late

Miocene

(

)

III

M (?)

1,2

Quaternary Q

( )

Middle Pliocene Pl

(

)

IIa

III

~
~
~
~

L E G E N D:

Clay and clayey

sediments

Sandy-clayey

sediments

Marly-clayey

sediments

Sand and sandy

sediments

Marlstone and

marl sediments

Lignite

Sandstone

Limestone

KOLUBARA

Basin

Seam mark

Lithology

200

100

400

300

500

Scale

(m)

Fig. 2. Schematic lithostratigraphic column of

the Neogene from the Kolubara and Kostolac.

ĐOKOVIĆ, MITROVIĆ, ŽIVOTIĆ, BECHTEL, SACHSENHOFER and STOJANOVIĆ

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

Suárez-Ruiz et al. 2012), four different sublithotypes of xylitic

coal (pale yellow, dark yellow, brown and black; Fig. 3) and

mineral matter under the stereo microscope. Four sublitho-

types of xylite-rich coal (SXCs; pale yellow, dark yellow,

brown and black), from each basin, in total 8 samples, were

further analysed in detail (Table 1). The macroscopic descrip-

tion of the coal lithotypes followed the nomenclature proposed

by ICCP (ICCP 1993; Taylor et al. 1998). The xylite descrip-

tion used in this study follows the terminology developed by

Jacob (1961) and modified by Ercegovac (1989).

For maceral analyses, separated SXCs were crushed to

a maximum particle size of 1 mm, mounted in epoxy resin and

polished. The maceral analyses were performed on a Leitz

DMLP microscope in monochromatic and UV light illumina-

tion on 500 points (ISO 7404-3, 2009). The maceral descrip-

tion used in this study follows the terminology developed by

the International Committee for Coal and Organic Petrology

for huminite (Sykorova et al. 2005), liptinite (Pickel et al.

2017) and inertinite (ICCP 2001) nomenclature.

Elemental analysis was performed to determine the contents

of sulphur, nitrogen and total organic carbon (TOC). TOC con-

tent was determined after removal of carbonates with diluted

hydrochloric acid (1:3, v:v). The measurements were done

using a Vario EL III, CHNS/O Elemental Analyser, Elementar

Analysensysteme GmbH.

For the determination of the molecular composition of OM

approximately 5 g of pulverized material

(<150 μm) was extracted with dichloro-

methane for 1 h at 75

C and pressure of

50 bar using a Dionex ASE 200 accelerated

solvent extractor. Solvent was evaporated and

extracts (bitumens) were concentrated by

a Zymark Turbo Vap 500 device. Extracts

were dissolved in a mixture of n-hexane:di-

chloromethane (80:1, v:v) and asphaltenes

were subsequently separated by centrifuga-

tion. The n-hexane-soluble organic compounds

(maltenes) were separated into saturated

hydrocarbons, aromatic hydrocarbons and

NSO-fraction (polar fraction, which contains

nitrogen, sulphur, and oxygen compounds)

using a Kohnen–Willsch MPLC (medium

pressure liquid chromatography) instrument

(Radke et al. 1980).

The saturated and aromatic hydrocarbon

fractions were analysed by gas chromato-

graphy-mass spectrometry (GC-MS). A gas

chromatograph equipped with a 30 m DB-5MS

fused silica capillary column (i.d. 0.25 mm;

0.25 μm film thickness) coupled to a Thermo

Scientific ISQ quadrupole mass spectrometer

was used. The oven temperature was pro-

grammed from 70 °C to 300 °C at a rate of

4 °C/min followed by an isothermal period of

15 min. Helium was used as carrier gas.

The sample was injected in the splitless mode

with the injector temperature at 275 °C. The mass spectro-

meter was operated in the electron impact (EI) mode over

a scan range from m/z 50 to m/z 650 (0.7 s total scan time).

Identification of individual compounds was accomplished

based on comparison of the mass spectra with published data

(Wakeham et al. 1980; Philp 1985; Stout 1992; Killops et al.

1995, 2003; Otto & Simoneit 2002; Peters et al. 2005). Data

were processed with an Xcalibur data system. Absolute con-

centrations of individual compounds were calculated using

peak areas in relation to those of internal standards (deuterated

n-tetracosane for saturated hydrocarbons and 1,1’-binaphthyl

for aromatic hydrocarbons). The concentrations were norma-

lized against TOC contents.

Results and discussion

Bulk organic geochemical parameters

TOC contents (Table 1) are generally similar (55–61 %)

with the exception of pale yellow SXC from the Kolubara

Basin, which shows a lower amount (48 %). Sulphur content

does not show any relationship with the SXC, but is lower

in Kolubara samples (< 0.9 %) than in Kostolac samples

(1.1–2.3 %) (Table 1). Since lignites in both basins were

formed in freshwater environments, higher sulphur content in

20 mm

10 mm

20 mm

5 mm

Fig. 3. Photomicrographs of different SXCs isolated from the Kolubara and Kostolac

lignites under the stereo microscope: a — Pale yellow SXC; b — Dark yellow SXC;

c — Brown SXC; d — Black SXC.

PETROGRAPHIC AND BIOMARKER ANALYSIS OF XYLITE-RICH COAL (PANNONIAN BASIN, SERBIA)

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

the Kostolac samples could be attributed to calcium-rich sur-

face waters derived from the surrounding calcareous country

rock, which caused increase of the pH (Markic & Sachsenhofer

1997). Therefore the obtained result suggests slightly more

alkaline conditions during peatification in the Kostolac than in

the Kolubara Basin. The TOC/N ratios exceed 60 in all sam-

ples (Table 1), which is typical for terrestrial flora (Meyers &

Ishiwatari 1993). The highest ratios in both basins were

detected in yellow (pale yellow and dark yellow) SXCs, which

may be considered as an indication of terrestrial plants with

domination of lignin tissue (Edress 2007).

The extract yield of the soluble organic matter (bitumen) is

variable and ranges from 15.31 to 273.24 mg/g TOC (Table 1).

It has been attributed to the variable proportion of biogenic

and diagenetic compounds. The content of bitumen decreases

in the following order: pale yellow SXC > dark yellow SXC >

brown SXC > black SXC in both basins suggesting certain

differences in the source material, followed by less pro-

nounced condensation into macromolecular structures and/or

more intense microbial degradation of precursor biomolecules

in yellow SXCs.

The contents of saturated and aromatic hydrocarbons are

low, while the contents of asphaltenes and polar NSO fraction

(containing nitrogen, sulphur and oxygen compounds) are

high (Table 1), as expected for immature terrestrial organic

material.

Molecular composition of the organic matter

General characteristics

All investigated samples are dominated by diterpenoids,

followed by non-hopanoid triterpenoids and n-alkanes

(Figs. 4–7; Table 2). Pale yellow and dark yellow SXCs from

both basins and black SXC from Kostolac are characterized by

higher content of non-hopanoid triterpenoids than n-alkanes,

whereas brown SXCs from both basins and Kolubara black

SXC displayed the opposite trend. Since distributions of

n-alkanes (see Section n-Alkanes and isoprenoids) showed

that these biomarkers mostly originated from epicuticular

waxes, the obtained result may indicate lower contribution of

waxes to yellow SXCs in comparison to brown and black

SXCs. Other hydrocarbon constituents of bitumen are hopa-

noids, sesquiterpenoids, steroids and isoprenoids (Figs. 4–7;

Table 2). Diterpenoids have the highest proportion in all

samples. Proportion of diterpenoids decreased in order: pale

yellow SXC > dark yellow SXC > brown SXC > black SXC,

whereas proportions of all other biomarkers increased in the

opposite trend, with the exception of sesquiterpenoids which

showed a higher proportion in brown than in black SXCs from

both basins (Table 2). Hopanoids are more abundant than

sesquiterpenoids in Kolubara samples, whereas SXCs from

Kostolac demonstrate the opposite trend, with the exception of

Kostolac black SXC, which contains slightly a higher amount

of hopanoids in comparison to sesquiterpenoids (Table 2).

This result generally indicates more intense microbial activity

during peatification in the Kolubara Basin.

Diterpenoids, non-hopanoid triterpenoids and sesqui-

terpenoids

Total diterpenoids (sum of diterepenoids in saturated and

aromatic fractions) represent the most abundant hydrocarbons

in bitumen, indicating a significant contribution of conifers

(gymnosperms) to the precursor OM. The presence of a con-

siderable amount of non-hopanoid triterpenoids implies that

SXC

Short description

(%) TOC (%)

S (%)

N (%) TOC/N* Extract yield

(mg/g TOC)

Saturated

HC (%)

Aromatic

HC (%)

NSO

(%)

Asp

(%)

Kolubara

Pale yellow Pale yellow, with well–

preserved wood tissue

5.79

48.08

0.46

0.20

280.47

110.81

4.34

1.12

33.12

61.42

Dark yellow Dark yellow, with well–

preserved wood tissue

7.82

57.72

0.39

172.67

62.49

3.43

0.91

49.00

46.66

Brown

Light to dark brown,

with preserved wood

tissue

8.20

56.88

0.53

0.52

127.62

49.88

1.83

0.75

71.20

26.22

Black

Black, with visible

wood structure

9.10

56.03

0.89

0.68

96.13

22.12

3.71

1.84

48.17

46.28

Kostolac

Pale yellow Pale yellow, with well–

preserved wood tissue

7.66

60.85

2.30

0.57

124.55

273.24

3.43

0.50

73.84

22.23

Dark yellow Dark yellow, with well–

preserved wood tissue

8.35

59.78

1.09

0.52

134.12

46.57

6.71

1.23

45.63

46.43

Brown

Light to dark brown,

with preserved wood

tissue

9.22

55.14

1.36

0.78

82.47

30.26

4.53

1.71

55.95

37.81

Black

Black, with visible

wood structure

10.29

59.82

1.65

0.96

72.70

15.31

5.12

2.13

50.00

42.75

— Analytical moisture content; TOC — Total organic carbon content, dry basis; S — Total sulphur content, dry basis; N — Total nitrogen content, dry basis;

* — Molar ratio; HC — Hydrocarbons; NSO — polar fraction, which contains nitrogen, sulphur and oxygen compounds; Asp — Asphaltenes.

Table 1: Short description of SXCs and values of bulk organic geochemical parameters.

ĐOKOVIĆ, MITROVIĆ, ŽIVOTIĆ, BECHTEL, SACHSENHOFER and STOJANOVIĆ

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

angiosperms also contributed to coal formation (Figs. 4–7;

Table 2). The ratio of total diterpenoids to total non-hopanoid

terpenoids, Di/(Di+Tri) (Bechtel et al. 2002, 2003a), which is

indicative for the contribution of gymnosperm vs. angiosperm

vegetation decreased in the order pale yellow SXC > dark

yellow SXC > brown SXC > black SXC (Table 2). In all

samples sesquiterpenoids were present in lower amounts than

di- and triterpenoids (Figs. 4–7; Table 2).

Distributions of individual diterpenoids in saturated frac-

tions are similar. The 16α(H)-phyllocladane and pimarane

are dominant by far. Other diterpenoid type constituents of

saturated fraction are isopimaradiene, isonorpimarane,

norpimarane, dihydrorimuene, isophyllocladene and 16β(H)-

phyllocladane (Figs. 4, 5). A high amount of 16α(H)-

phyllocladane indicates a peat-forming vegetation built up by

Taxodiaceae, Podocarpaceae, Cupressaceae, Araucariaceae

and/or Phyllocladaceae, while high abundance of pimarane

suggests Pinaceae, Taxodiaceae and/or Cupressaceae (Otto et

al. 1997; Otto & Wilde 2001; Stefanova et al. 2005a).

Distributions of individual diterpenoids in the aromatic

fractions of all samples are relatively similar (Figs. 6, 7).

The aromatic diterpenoids consist of norabieta-6,8,11,

13-tetraenes, norabieta-8,11,13-trienes, dehydroabietane,

simonellite, retene, sempervirane, totarane, hibaene and

2-methylretene. Simonellite and dehydroabietane are predo-

minant compounds in Kolubara samples, while simonellite

prevailed in all samples from Kostolac (Figs. 6, 7). Almost all

of the aromatic diterpenoids are non-specific conifer markers,

because they are diagenetic products of a great variety of

abietane-type precursors that are common constituents of all

conifers except Phyllocladaceae (Otto et al. 1997; Otto &

Wilde 2001; Stefanova et al. 2005a). However, the presence of

totarane and hibaene in the aromatic fraction of all samples

(Figs. 6, 7) clearly indicates the contribution of Cupressaceae,

Taxodiaceae, Podocarpaceae and/or Araucariaceae to the pre-

cursor biomass (Otto & Wilde 2001). This is consistent with

the implications obtained by the analysis of saturated

biomarkers.

The ratio of saturated to aromatic diterpenoids is higher than

1 in all samples (Table 2) suggesting a low degree of aromati-

zation of these biomarkers. The ratio generally decreased from

yellow to brown and black SXCs, suggesting more intense

diagenetic aromatization of ditepenoids in later.

Yellow SXCs from the Kolubara Basin have higher absolute

content of non-hopanoid triterpenoids than brown and black

SXCx, whereas the opposite trend is observed for the Kostolac

samples (Table 2). However, the proportion of non-hopanoid

triterpenoids in both basins clearly increased in the order pale

yellow SXC < dark yellow SXC < brown SXC < black SXC

(Table 2).

Although, non-hopanoid triterpenoid biomarkers are indi-

cative for angiosperm input, they are not useful for a precise

determination of the precursor plant family, with the exception

of lupane derivatives which are generally more abundant

in the Betulacea family (Hayek et al. 1989; Regnery et al.

2013).

The non-hopanoid triterpenoids are present in low amounts

in the saturated fractions of all SXCs and consist exclusively

of des-A degraded compounds (des-A-olean-13(18)-ene,

des-A-olean-12-ene and des-A-lupane; Figs. 4, 5).

On the other hand, non-hopanoid triterpenoids predominate

in the aromatic fraction of all SXCs from the Kolubara Basin

and after diterpenoids represent the most abundant aromatic

biomarkers in Kostolac samples (Figs. 6, 7; Table 2).

Considerably higher abundance of aromatized in comparison

to saturated angiosperm triterpenoids, resulting in the ratio of

saturated to aromatic non-hopanoid triteprenoids notably < 1

in all samples (Table 2), which indicates intense aromatization

of triterpenoids during diagenesis. The same observation was

also reported by Kalkreuth et al. (1998) and Nakamura et al.

(2010), which showed that aliphatic angiosperm-derived

triterpenoids are more easily altered to aromatic derivatives

than gymnosperm-derived diterpenoids, resulting in the selec-

tive loss of analogous aliphatic compounds.

The distributions of individual non-hopanoid terpenoids in

the aromatic fractions of all samples are relatively similar

(Figs. 6, 7). The following tetra- and pentacyclic aromatic

triterpenoids occur in the aromatic fractions: ring-A-monoaro-

matic triterpenoids (24,25-dinoroleana-1,3,5(10),12-tetraene,

24,25-dinorursa-1,3,5(10),12-tetraene, 24,25-dinorlupa-

1,3,5(10)- triene, 24,25-dinorlupapentaene, trisnorlupatriene,

trisno r oleanatetraene, trisnorlupapentaene), tetramethyl octa-

hydrochrysenes, trimethyltetrahydrochrysenes, tetramethyl-

octahydropicenes and trimethyltetrahydropicenes. 24,25- Dino -

roleana-1,3,5(10),12-tetraene and 24,25-dinorlupa-1,3,5(10)-

triene are predominant compounds in all SXCs (Figs. 6, 7).

Pentacyclic triterpenoids are more abundant than tetracyclic

chrysene derivatives in all samples. This result indicates that

the main pathway of aromatization was progressive aromati-

zation (Stout 1992).

Oleanane and lupane derivatives predominated over non-

hopanoid triterpenoids with ursane skeleton in all SXCs

(Table 2). The ratio of olenane- vs. lupane derivatives increased

from yellow to brown and black SXCs (Table 2). Since lupane

derivatives mostly originated from Betulacea family (Hayek et

al. 1989; Regnery et al. 2013), the obtained result could sug-

gest a higher contribution of this family to yellow SXCs.

In contrast to the ratio of saturated to aromatic diterpenoids

which decreased from yellow to brown and black SXCs,

the corresponding ratio based on non-hopanoid triterpenoids

showed the opposite trend (Table 2). The obtained results

suggest that brown and black SXCs are enriched in aromatic

diterpenoids in comparison to yellow SXCs, whereas aromati-

zation of non-hopanoid triterpenoids was more intense in

yellow sublithotypes of xylite-rich coal. This observation may

be attributed to differences in precursor OM and activity of

different microbial communities. Moreover, degree of aroma-

tization of non-hopanoid triterpenoids is higher in Kolubara

than in Kostolac samples consistent with the already assumed

more intense microbial activity in this basin.

In all the studied samples, sesquiterpenoids occur in rela-

tively low quantities (Figs. 4–7). The absolute contents of ses-

PETROGRAPHIC AND BIOMARKER ANALYSIS OF XYLITE-RICH COAL (PANNONIAN BASIN, SERBIA)

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

Time (min)

16 ( )-

l o ladan

a H Phy l c

Norpimarane

Isonorpimarane

Std.

C 17 21 (R)

Pimarane

16 ( )-

l o ladan

a H Phy l c

Norpimarane

Std.

C 17 21 (R)

C 17 21

Pimarane

16 ( )-

l o ladan

a H Phy l c

Isonorpimarane

Norpimarane

Dihydrorimuene

Isophyllocladene

Std.

C 17 21 (R)

C 17 21

Pimarane

16 ( )-

l o ladan

a H Phy l c

16 ( )-

l o ladan

b H Phy l c

Norpimarane

Isopimaradiene

Std.

C Hop-17(21)-ene

C 17 21 (R)

C 17 21

Pimarane

a) Pale yellow SXC

b) Dark yellow SXC

c) Brown SXC

d) Black SXC

100

Relative

Abundance (%)

100

Relative

Abundance (%)

100

Relative

Abundance (%)

100

Relative

Abundance (%)

Fig. 4. TIC (Total Ion Chromatogram) of the saturated fraction of SXCs from the Kolubara Basin. • — n-Alkanes are labelled according to their

carbon number; Pr — Pristane; Ph — Phytane; Std. — Standard (deuterated n-tetracosane); 17α21β and 17β21β designate configurations at

C-17 and C-21 in hopanes, (R) designates configuration at C-22 in hopanes.

ĐOKOVIĆ, MITROVIĆ, ŽIVOTIĆ, BECHTEL, SACHSENHOFER and STOJANOVIĆ

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

100

Dihydrovalencene

16 ( )-

l o ladan

a H Phy l c

Norpimarane

Std.

Pimarane

16 ( )-

l o ladan

a H Phy l c

Std.

C 17 21 (R)

16 ( )-

l o ladan

a H Phy l c

Std.

C 17 21 (R)

C 17 21

16 ( )-

l o ladan

a H Phy l c

Norpimarane

Isonorpimarane

Dihydrorimuene

Std.

Des-A-Olean-13(18)-ene

Des-A-Olean-12-ene

Des-A-Lupane

C 17 21 (R)

C 17 21

Pimarane

Cubebane

Eudesmane

a) Pale yellow SXC

b) Dark yellow SXC

c) Brown SXC

d) Black SXC

Relative

Abundance (%)

Relative

Abundance (%)

Relative

Abundance (%)

Relative

Abundance (%)

Time (min)

C Hop-17(21)-ene

Fig. 5. TIC of the saturated fraction of SXCs from the Kostolac Basin. • — n-Alkanes are labelled according to their carbon number;

Pr — Pristane; Ph — Phytane; Std. — Standard (deuterated n-tetracosane); 17α21β and 17β21β designate configurations at C-17 and C-21 in

hopanes, (R) designates configuration at C-22 in hopanes.

PETROGRAPHIC AND BIOMARKER ANALYSIS OF XYLITE-RICH COAL (PANNONIAN BASIN, SERBIA)

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

Time (min)

a) Pale yellow SXC

b) Dark yellow SXC

c) Brown SXC

d) Black SXC

100

Relative

Abundance (%)

Relative

Abundance (%)

Relative

Abundance (%)

Relative

Abundance (%)

Pyrene

Calamenene

Cuparene

Curcumene

Dihydro-ar- curcumene

Cadalene Isocadalene

Phenanthrene

Hibaene

18-Norabieta-6,8,11,13-tetraene

18-Norabieta-8,11,13-triene

Dehydroabietane

Simonellite

Retene

otarane

Std.

Perylene

24,25-Dinorlupa-1,3,5(10),12-triene

19-Norabieta-6,8,11,13-tetraene

24,25-Dinoroleana-1,3,5(10),12-tetraene

Calamenene

Cuparene

Curcumene

Cadalene

Isocadalene

Phenanthrene

Hibaene

18-Norabieta-6,8,11,13-tetraene

18-Norabieta-8,11,13-triene

Dehydroabietane

Simonellite

Retene

otarane

Std.

Perylene

24,25-Dinorlupa-1,3,5(10),12-triene

19-Norabieta-6,8,11,13-tetraene

24,25-Dinoroleana-1,3,5(10),12-tetraene

Calamenene

Cuparene

Curcumene

Cadalene

Isocadalene

Phenanthrene

Hibaene

18-Norabieta-6,8,11,13-tetraene

Dehydroabietane

Simonellite

Retene

otarane

Std.

3,4,7,12a-T

etramethyl-1,2,3,4,4a,

1,12,12a-octahydrochrysene

3,4,7,12a-T

etramethyl-1,2,3,4,4a,

1,12,12a-octahydrochrysene

3,3,7-T

rimethyl-1,2,3,4-tetra-

hydrochrysene

3,3,7-T

rimethyl-1,2,3,4-tetra-

hydrochrysene

3,4,7-

rimethyl-1,2,3,4-tetra-

hydrochrysene

3,4,7-

rimethyl-1,2,3,4-tetra-

hydrochrysene

Perylene

24,25-Dinorursa-1,3,5(1

0),12-

tetraene

24,25-Dinorursa-1,3,5(10),1

tetraene

24,25-Dinorursa-1,3,5(

10),12-

tetraene

24,25-Dinorursa-

1,3,5(10),12-tetraene

24,25-Dinorlupa-1,3,5(10),12-triene

19-Norabieta-6,8,11,13-tetraene

1,2,4a,9-Tetramethyl-1,2,3,4,4a,5,6,14b-

octahydropicene

1,2,4a,9-Tetramethyl-1,2,3,4,4a,5,6,14b-

octahydropicene

1,2,4a,9-Tetramethyl-1,2,3,4,4a,5,6,14b-

octahydropicene

1,2,4a,9-Tetramethyl-1,2,3,4,4a,5,6,14b-

octahydropicene

4-Methyl, 24-ethyl, 19-norcholesta-

1,3,5(10)-triene

4-Methyl, 24-ethyl, 19-norcholesta-

1,3,5(10)-triene

4-Methyl, 24-ethyl, 19-norcholesta-

1,3,5(10)-triene

4-Methyl, 24-ethyl, 19-norcholesta-

1,3,5(10)-triene

7-Methyl, 3’-ethyl, 1,2-cyclo-

pentanochrysene

7-Methyl, 3’-ethyl, 1,2-cyclo-

pentanochrysene

7-Methyl, 3’-ethyl, 1,2-cyclo-

pentanochrysene

7-Methyl, 3’-ethyl, 1,2-cyclo-

pentanochrysene

1,2,9-Trimethyl-1,2,3,4-tetra-

hydropicene

1,2,9-Trimethyl-1,2,3,4-tetra-

hydropicene

1,2,9-Trimethyl-1,2,3,4-tetra-

hydropicene

1,2,9-Trimethyl-1,2,3,4-tetra-

hydropicene

2,2,9-Trimethyl-1,2,3,4-tetra-

hydropicene

2,2,9-Trimethyl-1,2,3,4-tetra-

hydropicene

2,2,9-Trimethyl-1,2,3,4-tetra-

hydropicene

2,2,9-Trimethyl-1,2,3,4-tetra-

hydropicene

24,25-Dinoroleana-1,3,5(10),12-tetraene

3,4,7,12a-T

etramethyl-1,2,3,4,4a,

1,12,12a-octahydrochrysene

3,3,7-T

rimethyl-1,2,3,4-tetra-

hydrochrysene

3,4,7-

rimethyl-1,2,3,4-tetra-

hydrochrysene

3,4,7,12a-T

etramethyl-1,2,3,4,4a,

1,12,12a-octahydrochrysene

3,3,7-T

rimethyl-1,2,3,4-tetra-

hydrochrysene

3,4,7-

rimethyl-1,2,3,4-tetra-

hydrochrysene

Calamenene

Cuparene

Curcumene

Cadalene

Isocadalene

Phenanthrene

Simonellite

Retene

otarane

Std.

Perylene

24,25-Dinorlupa-1,3,5(10),12-triene

24,25-Dinoroleana-1,3,5(10),12-tetraene

Fig. 6. TIC of the aromatic fraction of SXCs from the Kolubara Basin. Std. – Standard (1,1′ binaphthyl); H – D-ring monoaromatic hopane.

ĐOKOVIĆ, MITROVIĆ, ŽIVOTIĆ, BECHTEL, SACHSENHOFER and STOJANOVIĆ

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

a) Pale yellow SXC

b) Dark yellow SXC

c) Brown SXC

d) Black SXC

100

Relative

Abundance (%)

Relative

Abundance (%)

Relative

Abundance (%)

Relative

Abundance (%)

Time (min)

Calamenene

Cuparene

Curcumene

Cadalene Isocadalene

Fenantren

Hibaene

19-Norabieta-8,11,13-triene

18-Norabieta-8,11,13-triene

Dehydroabietane

Simonellite

Retene

otarane

Std.

Perylene

24,25-Dinorlupa-1,3,5(10),12-triene

19-Norabieta-6,8,11,13-tetraene

1,2,4a,9-Tetramethyl-1,2,3,4,4a,5,6,14b-

octahydropicene

1,2,4a,9-Tetramethyl-1,2,3,4,4a,5,6,14b-

octahydropicene

4-Methyl, 24-ethyl, 19-norcholesta-

1,3,5(10)-triene

4-Methyl, 24-ethyl, 19-norcholesta-

1,3,5(10)-triene

7-Methyl, 3’-ethyl, 1,2-cyclopentano-

chrysene

7-Methyl, 3’-ethyl, 1,2-cyclopentano-

chrysene

1,2,9-Trimethyl-1,2,3,4-tetrahydro-

picene

1,2,9-Trimethyl-1,2,3,4-tetrahydro-

picene

2,2,9-Trimethyl-1,2,3,4-tetrahydro-

picene

2,2,9-Trimethyl-1,2,3,4-tetrahydro-

picene

24,25-Dinoroleana-1,3,5(10),12-tetraene

Calamenene

Cuparene

Curcumene

Cadalene Isocadalene

Hibaene

Simonellite

Retene

otarane

Std.

Perylene

Calamenene

Cuparene

Curcumene

Cadalene

Isocadalene

Hibaene

Simonellite

Retene

otarane

Std.

Perylene

Calamenene

Cuparene

Curcumene

Cadalene

Isocadalene

Hibaene

Simonellite

Retene

Sempervirane

2-Methylretene

otarane

Std.

Perylene

Pyrene

24,25-Dinorursa-1,3,5(1

0),12-

tetraene

24,25-Dinorursa-1,3,5(10),12

tetraene

3,4,7,12a-T

etramethyl-1,2,3,4,4a,

1,12,12a-octahydrochrysene

3,4,7,12a-T

etramethyl-1,2,3,4,4a,

1,12,12a-octahydrochrysene

3,3,7-T

rimethyl-1,2,3,4-tetra-

hydrochrysene

3,3,7-T

rimethyl-1,2,3,4-tetra-

hydrochrysene

19-Norabieta-8,11,13-triene

18-Norabieta-8,11,13-triene

Dehydroabietane

24,25-Dinorlupa-1,3,5(10),12-triene

19-Norabieta-6,8,11,13-tetraene

1,2,4a,9-Tetramethyl-1,2,3,4,4a,5,6,14b-

octahydropicene

4-Methyl, 24-ethyl, 19-norcholesta-

1,3,5(10)-triene

7-Methyl, 3’-ethyl, 1,2-cyclopentano-

chrysene

1,2,9-Trimethyl-1,2,3,4-tetrahydro-

picene

2,2,9-Trimethyl-1,2,3,4-tetrahydro-

picene

24,25-Dinoroleana-1,3,5(10),12-tetraene

24,25-Dinorursa-1,3,5(1

0),12-

tetraene

3,4,7,12a-T

etramethyl-1,2,3,4,4a,

1,12,12a-octahydrochryse

3,3,7-T

rimethyl-1,2,3,4-tetra-

hydrochrysene

19-Norabieta-8,11,13-triene

18-Norabieta-8,11,13-triene

Dehydroabietane

24,25-Dinorlupa-1,3,5(10),12-triene

19-Norabieta-6,8,11,13-tetraene

1,2,4a,9-Tetramethyl-1,2,3,4,4a,5,6,14b-

octahydropicene

4-Methyl, 24-ethyl, 19-norcholesta-

1,3,5(10)-triene

7-Methyl, 3’-ethyl, 1,2-cyclopentano-

chrysene

1,2,9-Trimethyl-1,2,3,4-tetrahydro-

picene

2,2,9-Trimethyl-1,2,3,4-tetrahydro-

picene

24,25-Dinoroleana-1,3,5(10),12-tetraene

24,25-Dinorursa-1,3,5(10),1

tetraene

3,4,7,12a-T

etramethyl-1,2,3,4,4a,

1,12,12a-octahydrochryse

3,3,7-T

rimethyl-1,2,3,4-tetra-

hydrochrysene

Fig. 7. TIC of the aromatic fraction of SXCs from the Kostolac Basin. Std — Standard (1,1′ binaphthyl); H — D-ring monoaromatic hopane.

PETROGRAPHIC AND BIOMARKER ANALYSIS OF XYLITE-RICH COAL (PANNONIAN BASIN, SERBIA)

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

quiterpenoids decreased in the following order: black

SXC > brown SXC > dark yellow SXC > pale yellow SXC.

However, the proportion of these biomarkers was slightly

higher in brown than in black SXC from both basins

(Table 2).

The saturated fractions of all samples contain cubebane,

dihydrovalencene and eudesmane, whereas sesquiterpenoid

type constituents of aromatic fractions are calamenene,

cuparene, curcumene, cadalene and isocadalene. Eudesmane

predominates in distribution of saturated sesquiterpenoids,

whereas cadalene is the most abundant aromatic sesquiter-

penoid in all samples (Figs. 4–7). Sesquiterpenoid biomarkers

are often not useful for a precise determination of the

precursor plant community (van Aarssen et al. 1990; Otto et al.

1997; Otto & Simoneit 2002), with the exception of cuparene.

The presence of cuparene in all SXCs (Figs. 6, 7) clearly indi-

cates a contribution of the conifer family Cupressaceae as

a precursor of OM (Otto & Wilde 2001; Haberer et al. 2006).

Diterpenoids and sesquiterpenoids are more abundant in the

saturated than in the aromatic fraction (Table 2), indicating

a relatively low degree of aromatization. Since almost all iden-

tified sesquiterpenoids (Figs. 4 –7), as diterpenoids, originated

from conifers, the similar behaviour of these classes of bio-

markers regarding aromatization is understandable (Table 2).

The highest degree of sesquiterpenoids aromatization is

observed for dark yellow SXC and the lowest for brown SXC.

Basin

Kolubara

Kostolac

SXC

Pale yellow Dark yellow

Brown

Black Pale yellow Dark yellow

Brown

Black

Sat Di (μg/g TOC)

3153.69

2237.88

322.09

113.31

8487.60

1733.02

866.87

350.28

Arom Di (μg/g TOC)

133.40

95.48

22.77

18.60

212.57

181.37

71.03

75.11

Total Di (μg/g TOC)

3287.09

2333.36

344.86

131.91

8700.17

1914.39

937.90

425.39

Sat Tri (μg/g TOC)

0.15

2.04

1.44

1.33

2.17

2.06

10.30

12.68

Arom Tri (μg/g TOC)

126.93

123.39

41.65

49.00

50.86

54.82

50.10

62.98

Total Tri (μg/g TOC)

127.08

125.43

43.09

50.33

53.03

56.88

60.40

75.66

Sat Sesq (μg/g TOC)

37.91

17.27

22.26

10.02

46.33

20.96

59.18

20.68

Arom Sesq (μg/g TOC)

12.42

15.45

5.14

2.77

7.17

15.59

7.10

8.02

Total Sesq (μg/g TOC)

50.33

32.72

27.40

12.79

53.50

36.55

66.28

28.70

Sat hopanoids (μg/g TOC)

3.52

67.67

48.56

79.29

9.58

5.69

15.91

11.00

Arom hopanoids (μg/g TOC)

8.11

7.44

2.79

3.59

11.15

8.78

10.57

13.13

Total hopanoids (μg/g TOC)

11.63

75.11

51.35

82.88

20.73

14.47

26.48

24.13

Sat steroids (μg/g TOC)

1.11

1.14

2.84

3.03

2.84

0.62

7.40

6.88

Arom steroids (μg/g TOC)

1.51

2.57

1.29

1.05

1.66

0.40

1.43

0.51

Total steroids (μg/g TOC)

2.62

3.71

4.13

4.08

4.50

1.02

8.83

7.39

Total n-alkanes (μg/g TOC)

80.15

86.78

78.20

93.54

43.20

19.60

75.05

51.07

Total isoprenoids (μg/g TOC)

8.47

6.48

2.38

2.22

8.47

2.68

0.82

1.96

Proportion of total Di (%)

92.14

87.60

62.54

34.92

98.00

93.67

79.69

69.37

Proportion of total Tri (%)

3.56

4.71

7.81

13.32

0.60

2.78

5.13

12.34

Proportion of total Sesq (%)

1.41

1.23

4.97

3.39

0.60

1.79

5.63

4.68

Proportion of total hopanoids (%)

0.33

2.82

9.31

21.94

0.23

0.71

2.25

3.93

Proportion of total steroids (%)

0.07

0.14

0.75

1.08

0.05

0.75

1.20

Proportion of total n-alkanes (%)

2.25

3.26

14.18

24.76

0.49

0.96

6.38

8.33

Proportion of total isoprenoids (%)

0.24

0.44

0.59

0.03

0.04

0.17

0.15

Di / (Di + Tri)

0.96

0.95

0.89

0.72

0.99

0.97

0.94

0.85

Sat Di/Arom Di

23.64

23.44

14.15

6.09

39.93

9.56

12.20

4.66

Sat Tri/Arom Tri

0.001

0.02

0.03

0.04

0.21

0.20

Sat Sesq/Arom Sesq

3.05

1.12

4.33

3.62

6.46

1.34

8.34

2.58

Sat hopanoids/Arom hopanoids

0.43

9.10

17.44

22.08

0.86

0.65

1.51

0.84

Sat steroids/Arom steroids

0.73

0.45

2.20

2.89

1.71

1.55

5.19

13.50

Proportion of Ol in total Tri (%)

38.44

52.25

53.79

65.55

48.50

51.97

60.94

62.00

Proportion of Urs in total Tri (%)

16.88

10.44

11.71

8.67

15.66

19.48

8.15

10.52

Proportion of Lup in total Tri (%)

44.68

37.31

34.50

25.78

35.84

28.55

30.91

27.48

Ol/Lup

0.86

1.40

1.56

2.54

1.35

1.82

1.97

2.26

Proportion of n-C

− n-C

in total n-alkanes (%)

39.30

23.16

13.83

7.51

26.88

19.00

9.71

5.33

Proportion of n-C

− n-C

in total n-alkanes (%)

19.45

17.70

15.68

19.12

23.67

14.09

15.46

13.64

Proportion of n-C

− n-C

in total n-alkanes (%)

41.25

59.14

70.49

73.37

49.45

66.91

74.83

81.03

CPI

1.26

4.62

2.64

2.41

2.13

2.30

3.91

2.80

Pr/Ph

1.13

1.10

1.17

1.05

1.03

1.31

1.04

1.39

Sat — Saturated; Arom — Aromatic; Di — Diterpenoids; Tri — Non-hopanoid triterpenoids; Sesq — Sesquiterpenoids; Ol — Oleanane derivatives; Urs — Ursane

derivatives; Lup — Lupane derivatives; CPI — Carbon Preference Index determined for distribution of n-alkanes C

– C

, CPI = 1/2 [Σ odd (n-C

− n-C

Σ even (n-C

− n-C

) + Σ odd (n-C

− n-C

) /Σ even (n-C

− n-C

)] (Bray & Evans 1961); Pr – Pristane; Ph – Phytane.

Table 2: Absolute contents of biomarker classes, relative proportions of biomarker classes and values of biomarker parameters.

ĐOKOVIĆ, MITROVIĆ, ŽIVOTIĆ, BECHTEL, SACHSENHOFER and STOJANOVIĆ

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

n-Alkanes and isoprenoids

n-Alkanes are relatively abundant in the total ion current

(TIC) of the saturated fraction in both basins (Figs. 4, 5;

Table 2). n-Alkanes are identified in the range from C

or C

to C

or C

. Absolute contents of n-alkanes do not show

a clear relationship with SXCs. However, the proportion of

n-alkanes in both basins clearly increased from pale and dark

yellow to brown and black SXCs (Table 2).

The n-alkane patterns of all samples are dominated by odd

long-chain homologues (C

– C

) with a maximum at n-C

(Figs. 4, 5), indicating a significant contribution of epicuti-

cular waxes. Although samples showed generally similar dis-

tributions of n-alkanes, some differences in n-alkane patterns

could be observed. The proportion of short-chain n-alkanes

– C

) in both basins decreased in the order: pale yellow

SXC > dark yellow SXC > brown SXC > black SXC, associated

with an increase in the proportion of long-chain homologues

– C

) (Table 2). Since yellow SXCs contain a lower

amount of liptinite macerals (see later Table 4), elevated con-

tent of short chain n-alkanes can be attributed to microbial

degradation of long chain n-alkanes resulting in increasing

content of lower n-alkane homologues (Faure et al. 1999;

Marynowski & Wyszomirski 2008; Marynowski et al. 2011).

On the other hand, a higher proportion of short-chain

n-alkanes in yellow SXCs could be related to direct impact of

certain microbial communities since most of them are capable

of synthesizing short-chain n-alkanes (Peters et al. 2005).

The influence of different bacteria has already been supposed

based on observed differences in the aromatization degree of

di- and triterpenoids in different SXCs (Table 2). The propor-

tion of middle chain n-alkanes (C

– C

) which have nume-

rous precursors such as vascular plants, microalgae,

cyano bacteria, sphagnum and aquatic macrophytes (Ficken et

al. 2000; Nott et al. 2000) was generally similar in all SXCs,

showing slightly elevated value in pale yellow SXC from

Kostolac (Table 2).

The values of the CPI (Carbon Preference Index; Bray &

Evans 1961), ranging from 1.26 to 4.62 (Table 2), are in accor-

dance with terrestrial immature OM (Bechtel et al. 2002,

2007; Zdravkov et al. 2011, 2015). The lowest CPI in both

basins is observed for pale yellow SXC (Table 2). This result

could be attributed to the lower input of fatty acids from cuti-

cular waxes, because these acids predominantly contain even

numbers of carbon atoms in a molecule and after decarboxy-

lation they produce odd-carbon-atom n-alkanes. The obtained

result is consistent with the observation of Fabiańska &

Kurkiewicz (2013) who also reported lower CPI values in

xylites with well preserved wood structure. However, the

CPI does not show any relationship with other studied

sublithotypes.

Isoprenoids, pristane and phytane are identified in all sam-

ples in low amounts (Table 2). It is consistent with the obser-

vation that terrestrial immature OM usually contains very low

concentrations of isoprenoids (Dzou et al. 1995; Hughes et al.

1995; Vu et al. 2009). Content of isoprenoids was the highest

in yellow SXCs from Kolubara and pale yellow SXC from

Kostolac (Table 2) in accordance with higher content of

extractable OM (bitumen) in these samples (Table 1).

However, the proportion of isoprenoids increased from yellow

to brown and black SXCs (Table 2).

Taking into account the low abundance of pristane and

phytane in the studied samples and possible differences in the

precursors for acyclic isoprenoids (Goossens et al. 1984;

Volkman & Maxwell 1986; ten Haven et al. 1987), the

pristane/ phytane (Pr/Ph) ratio must be interpreted with care

and it is usually omitted from interpretation of lignites.

The investigated SXCs have generally similar values of Pr/Ph

ratio (1.03 –1.39; Table 2), which are in the range reported for

Middle and Upper Miocene lignites in Austria (Bechtel et al.

2007), Bulgaria (Zdravkov et al. 2011), Poland (Fabiańska &

Kurkiewicz 2013) and Turkey (Bechtel et al. 2014).

Steroids and hopanoids

Steroids were identified in the analysed samples in low

amounts. The low content of steroids (Table 2) could be

explained by the fact that the steroids mostly originate from

higher plants, which contain very low amount of these bio-

markers. The absolute content of steroids is higher in brown

and black than in yellow SXCs and the relative proportions of

these biomarkers follow the same trend (Table 2). Steroid bio-

markers in the saturated fraction consist predominantly of

-, Δ

- and Δ

-sterenes, consistent with peat formation

from terrigenous plants, whereas C

and C

-, Δ

- and

-sterenes are identified in trace amounts in all samples.

The single steroid compound detected in the aromatic fraction

was 4-methyl, 24-ethyl, 19-norcholesta-1,3,5(10)-triene.

The ratio of saturated to aromatic steroids was > 1 in all

samples, with the exception of Kolubara pale and dark yellow

SXCs, and showed the increasing trend from yellow to brown

and black SXCs as it was observed for aromatization of

non-hopanoid triterpenoids (Table 2).

All the samples from the Kolubara Basin, with exception of

pale yellow SXC, have higher contents of hopanoids than

samples from the Kostolac Basin (Table 2) indicating more

intense microbial activity and peatification in a slightly more

oxic environment, which is consistent with a lower amount of

sulphur (Table 1). The content of hopanoids is similar in SXCs

from the Kostolac Basin, whereas dark yellow and black SXCs

from the Kolubara Basin are enriched in these biomarkers in

comparison to pale yellow and brown SXCs. However, the

proportion of hopanoids generally increased from pale yellow

to black SXC (Table 2).

The hopane composition in the saturated fraction of all

samples is characterized by the presence of 17α(H)21β(H),

17β(H)21α(H) and 17β(H)21β(H) compounds with 27–31

carbon atoms, with the exception of C

homologues. In all

samples unsaturated C

hop-17(21)-ene and C

hop-17(21)-ene

are also identified (Table 3). The aromatic hopanoids are

represented by series of orphan aromatic hopanoids bearing

an ethyl group at C-21.

PETROGRAPHIC AND BIOMARKER ANALYSIS OF XYLITE-RICH COAL (PANNONIAN BASIN, SERBIA)

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

The main precursors of hopanoids are prokaryotes, which

were detected in much lower amounts in ferns, lichens, mosses

and fungi. C

17α(H)21β(H)22(R)-Hopane is the most abun-

dant hopanoid in the saturated fraction of all studied samples,

except the pale yellow SXC from Kostolac and Kolubara where

17β(H)-22,29,30-trisnorhopane and C

hop-17(21)-ene,

respectively predominates hopane distribution (Table 3).

Regarding hopane distribution, pale yellow SXC from both

basins differs mostly from other samples by having the lowest

proportion of C

17α(H)21β(H)22(R)-hopane and elevated

proportions of C

hop-17(21)-ene, C

17β(H)-22,29,30-trisnor-

hopane, C

17β(H)21β(H)-30-norhopane; C

hop-17(21)-ene,

17α(H)21β(H)-hopane and C

17β(H)21β(H)-hopane

(Table 3). This result suggests a distinguished microbial com-

munity taking part in peatification of this SXC. The observed

differences for pale yellow SXC, which were reflected through

the highest content of bitumen (Table 1), highest proportion of

short-chain n-alkanes and differences in aromatization degree

of di- and triterpenoids (Table 2), can be partly related to

differences in microbial communities.

Prominent C

17α(H)21β(H)22(R)-hopane is often reported

in low rank coals (Stefanova et al. 2005b; Vu et al. 2009)

and numerous precursors were proposed for this hopanoid

biomarker (van Dorselaer et al. 1975; Killops et al. 1998;

Thiel et al. 2003; Pancost et al. 2007). C

17β(H)- and

17β(H)21β(H)-hopanes could originate from heterotrophic

bacteria, chemoautotrophic bacteria and methanotrophic

bacteria (Neunlist & Rohmer 1985; Duan et al. 2004; Bechtel

et al. 2014; Mitrović et al. 2016). In addition to chemoauto-

trophic bacteria and methanotrophic bacteria, cyanobacteria

(Rohmer et al. 1984; Yamada et al. 1997), anaerobic, sul-

phate-reducing (Wolff et al. 1992) and ammonium oxidizing

bacteria (Sinninghe Damsté et al. 2004), as well as some

eukaryotic phyla (e.g., ferns, mosses; Bottari et al. 1972;

Wakeham 1990) were proposed as possible sources of

hop-17(21)-ene. Therefore, the absence of a clear relation-

ship between abundance of individual hopanoids and investi-

gated SXCs (with the exception of pale yellow SXC) can be

related to the mutual origin of individual hopanoids from

different prokaryotes.

The ratio of saturated to aromatic hopanoids sharply

increases from yellow to brown and black Kolubara SXCs,

being > 1 in all sublithotypes with the exception of pale yellow.

On the other hand, in all Kostolac SXCs except brown SXC,

aromatic hopanoids were somewhat more abundant than their

saturated counterparts, resulting in a relatively uniform ratio

of saturated to aromatic hopanoids in the range 0.65 – 0.86

(Table 2). This result can be attributed to a higher content of

saturated hopanoids in the Kolubara than in the Kostolac Basin.

Maceral composition of SXCs

The observed differences in biomarker distributions of SXCs,

related to difference in sources and diagenetic alteration of

OM, are also reflected in petrographic characteristics.

Maceral composition of SXCs from the Kolubara Basin

Huminite macerals predominate in all SXCs from the

Kolubara Basin (Fig. 8; Table 4). The content of total huminite

macerals increased in order: black SXC < brown SXC < dark

yellow SXC < pale yellow SXC, whereas lipitinite contents

showed the opposite tend. Dark yellow, brown and black

SXCs from the Kolubara Basin have relatively similar amounts

of total inertinites, while pale yellow Kolubara SXC contained

less of this maceral group. The content of total mineral matter

showed the following trend: pale yellow SXC < dark yellow

SXC < brown SXC < black SXC. Pronounced differences were

observed in the composition of huminite group macerals

(Table 4). In yellow SXCs notable predominance of texitinite

was observed, however this maceral was more abundant in

pale yellow SXC. On the other hand ulminite prevailed among

the huminite group macerals in brown and black SXC. As

expected, densinite and attrinite were present in xylite-rich

sublithotypes in a low amount. The contents of both macerals

increased from yellow to brown and black SXC (Table 4).

The content of gelinite was also very low, showing the

increased trend from pale yellow to black SXC. Content of

corpohuminite was the highest in dark yellow SXC and the

lowest in brown SXC (Table 4).

Basin

Kolubara

Kostolac

SXC

Pale yellow Dark yellow

Brown

Black

Pale yellow Dark yellow

Brown

Black

Hop-17(21)-ene

15.29

1.37

0.53

0.93

18.38

32.78

10.49

6.44

17α(H)-Hopane

0.00

0.18

0.03

0.17

6.66

1.09

0.25

1.20

17β(H)-Hopane

9.21

5.51

4.43

3.95

21.42

5.84

14.03

8.49

17α(H)21β(H)-Hopane

7.71

1.41

1.82

1.81

13.08

2.44

7.40

3.21

Hop-17(21)-ene

12.04

2.00

2.99

3.15

6.56

2.33

1.59

4.61

17β(H)21α(H)-Hopane

12.05

3.19

3.35

4.54

1.74

6.12

13.77

9.55

17α(H)21β(H)-Hopane

4.68

1.15

0.69

0.82

5.13

1.76

0.50

0.82

17β(H)21β(H)-Hopane

2.29

0.30

0.71

0.86

0.41

0.47

5.64

0.36

17β(H)21α(H)-Hopane

10.08

1.68

0.59

1.59

0.76

0.91

4.65

0.35

17α(H)21β(H)22(R)-Hopane

6.81

74.56

77.02

73.63

17.45

35.68

24.66

51.32

17β(H)21β(H)-Hopane

7.74

2.15

1.40

1.20

7.02

3.45

2.45

3.20

17β(H)21α(H)-Hopane

7.87

6.32

6.36

7.31

0.06

6.67

13.91

10.18

17β(H)21β(H)-Hopane

4.23

0.18

0.08

0.04

1.33

0.46

0.66

0.27

Table 3: Relative proportions (%) of individual hopanoids calculated from mass chromatograms m/z 191.

PETROGRAPHIC AND BIOMARKER ANALYSIS OF XYLITE-RICH COAL (PANNONIAN BASIN, SERBIA)

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

Brown and black SXCs are characterized by predominance

of suberinite among the liptinite maceral group (Table 4).

In yellow SXCs resinite prevailed over liptodetrinite, while

brown and black SXCs showed the opposite trend.

Black SXC is characterized by predominance of inerto-

detrinite and funginite among the inertinite group macerals

(Table 4). In brown SXC the prevalence of funginite, followed

by fusinite was observed. In pale yellow SXC, which gene-

rally contained a very low content of inertinites, inertodetrinite

was the most abundant inertinite maceral.

Maceral composition of SXCs from the Kostolac Basin

Huminite macerals predominate in SXCs from the Kostolac

Basin (Fig. 8; Table 4). The content of total huminite macerals

increased in order: black SXC < brown SXC < dark yellow SXC

< pale yellow SXC. Xylite sublithotypes from the Kostolac

Basin have uniform lipitinite contents, whereas inertinite

content increased in order: pale yellow < dark yellow < brown

< black. The content of total mineral matter enlarged in the

same order as inertines indicating partly allochthonous origin

of inertinite macerals. Texitinite was predominant huminite

maceral in yellow SXCs, whereas ulminite prevailed among

the huminite group macerals in brown and particularly black

SXC. The contents of densinite, attrinite and gelinite increased

from yellow to brown and black SXC (Table 4). The content of

corpohuminite is comparable in all SXCs from the Kostolac

Basin with the exception of brown SXC, which has obviously

a lower amount of this maceral (Table 4).

Resinite is the most abundant liptinite group maceral in

yellow SXCs, while suberinite prevailed in brown and black

SXCs. Inertodetrinite is the predominant inertinite maceral

group in yellow SXCs, whereas brown and black SXCs are

characterized by prevalence of funginite.

Comparison of maceral compositions of SXCs from the

Kolubara and Kostolac Basin and their relationship with

biomarker assemblages

Based on the data given in previous two chapters we can

conclude that same individual SXCs (pale yellow, dark yellow,

brown and black) from both basins generally have similar

maceral composition among itself (Table 4).

The content of total huminites increased in the order:

black SXC < brown SXC < dark yellow SXC < pale yellow SXC,

whereas inertinite content showed the opposite trend in both

basins. The content of total mineral matter increased in the

following order: pale yellow SXC < dark yellow SXC < brown

SXC < black SXC in both basins, and amount of mineral mat-

ter was almost equal in the same individual SXCs (Table 4).

Basin

Kolubara

Kostolac

SXC

Pale yellow

Dark yellow

Brown

Black

Pale yellow

Dark yellow

Brown

Black

Textinite

91.2

76.1

41.4

23.4

81.8

65.7

49.2

9.5

Ulminite

0.8

6.8

42.0

48.5

5.4

19.3

33.3

64.4

Attrinite

0.8

1.8

3.4

4.0

0.8

1.0

2.4

2.8

Densinite

0.3

1.8

2.8

5.4

2.4

2.2

4.2

7.5

Gelinite

0.3

0.8

1.8

3.4

0.8

1.0

1.2

Corpohuminite

5.1

7.8

3.8

5.5

5.2

5.6

3.4

5.4

Total huminite

98.6

95.1

90.2

96.4

94.9

93.6

90.7

Sporinite

0.3

0.4

0.2

2.0

0.2

0.4

0.6

Cutinite

0.0

0.2

0.4

0.0

Resinite

0.3

0.4

0.2

0.4

2.4

1.6

0.4

Suberinite

0.0

0.4

0.8

2.4

0.4

0.0

1.1

1.4

Liptodetrinite

0.0

0.2

0.6

0.7

0.0

0.4

0.6

0.8

Total liptinite

0.6

1.5

2.1

5.9

3.0

2.4

2.5

3.2

Fusinite

0.0

0.6

1.0

0.4

0.0

0.2

0.8

0.4

Semifusinite

0.3

1.1

0.4

0.0

0.6

0.8

0.4

Macrinite

0.0

0.2

0.0

0.2

0.0

Funginite

0.0

0.4

1.2

1.4

0.2

0.8

1.2

2.8

Inertodetrinite

0.5

1.0

0.2

1.6

0.4

1.0

0.8

2.4

Total inertinite

0.8

3.4

2.8

3.9

0.6

2.7

3.9

6.0

Mineral matter

3.2

4.3

4.5

8.0

3.1

4.2

4.8

7.4

Textinite/Ulminite

110.38

11.20

0.99

0.48

15.25

3.40

1.48

0.15

Resinite/Liptodetrinite

N.D.

2.00

0.33

0.67

N.D.

3.75

0.67

0.57

Resinite/Suberinite

N.D.

1.00

0.25

0.18

5.75

N.D.

0.40

0.31

TPI

49.47

16.81

10.79

5.38

20.81

17.06

10.06

5.77

0.07

0.21

1.06

2.01

0.16

0.41

0.76

4.27

ΣG (vol. %)

6.13

14.41

35.58

45.03

11.17

21.09

29.64

54.70

TPI — Tissue Preservation Index = (Textinite + Ulminite + Corpohuminite + Fusinite) / (Attrinite + Densinite + Gelinite + Inertodetrinite) (Diessel 1986, adopted by Kalkreuth et

al. 1991 and Bechtel et al. 2003b); GI — Gelification Index = (Ulminite + Corpohuminite + Densinite + Gelinite) / (Textinite + Attrinite + Total inertinite) (Diessel 1986, adopted

by Kalkreuth et al. 1991 and Bechtel et al. 2003b); ΣG = Gelinite + Corpohuminite + 0.67 (Ulminite + Densinite), mineral matter-free basis (Bielowicz 2013);

N.D. — Not determined, due to the absence of liptodetrinite or sporinite.

Table 4: The maceral composition of SXCs based on mineral matter-free (vol. %) and values of petrographic indices.

ĐOKOVIĆ, MITROVIĆ, ŽIVOTIĆ, BECHTEL, SACHSENHOFER and STOJANOVIĆ

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

This result suggests that clastic material is rather associated

with black and brown than with yellow SXCs.

Regarding the composition of huminite group macerals, in

accordance with the published data, SXCs differ by the

textinite/ulminite ratio which sharply decreased in the order:

pale yellow SXC > dark yellow SXC > brown SXC > black SXC

(Table 4). Textinite showed moderate positive correlation

with content of total diterpenoids and triterpenoids with ursane

and lupane skeleton, whereas ulminite negatively correlated

with mentioned biomarkers (Table 5). The contents of densi-

nite, attrinite and gelinite increased from yellow to brown

and black SXC in both basins. Attrinite and gelinite showed

negative correlation with the content of total diterpenoids,

sesquiterpenoids and triterpenoids having ursane and lupane

skeleton, whereas positive correlations were observed between

these macerals and contents of n-alkanes (particularly,

– C

long-chain homologues) and hopanoids. The obtained

result suggests a higher contribution of epicutilar waxes to

brown and black SXCs and more intense gelification

induced by microorganisms. The content of corpohuminite

showed the same increasing trend in both basins: brown

SXC < pale yellow SXC < black SXC < dark yellow SXC.

Corpohuminite positively correlated with triterpenoids, parti-

cularly those with oleanane skeleton, indicating a more

pronounced contribution of certain angiosperm families to

dark yellow SXC.

Although the content of total liptinites did not show a clear

relationship with individual SXCs, probably due to the low

content of this maceral group in all samples, some differences

are observed in abundance of particular liptinite macerals.

Brown and black SXCs are characterized by predominance of

suberinite among the liptinite maceral group (Table 4). A typi-

cal feature of yellow SXCs is the prevalence of resinite over

liptodetrinite, while brown and black SXCs showed the oppo-

site trend in both basins. Consequently, regarding the compo-

sition of liptinite macerals, SXCs mostly differ according to

resinite/liptodetrinite and resinite/suberinite ratios, which are

higher in yellow than in brown and black SXCs (Table 4).

Resinite showed significant positive correlation with content

of diterpenoids and negative correlation with content of

n-alkanes, particularly long-chain n-alkanes (C

-C

), whereas

liptodetrinite and suberinite showed the opposite correlations

(Table 5). Therefore, it can be supposed that decrease of

resinite/liptodetrinite and resinite/suberinite ratios reflect

that change in colour from pale- and dark yellow to brown

and black of SXC is followed by reduced contribution of

conifer resinous material and increased impact of epicuticular

waxes. A low contribution of epicuticular waxes to pale yellow

SXC has already been assumed based on lower CPI values

(Table 2).

No clear relationship between contents of individual inerti-

nite macerals and sublithotypes was observed, with the excep-

tion of funginite the content of which increased in the order:

pale yellow SXC < dark yellow SXC < brown SXC < black SXC

in both basins (Table 4). The absence of relationships between

contents of individual inertinite macerals and xylite sublitho-

type could be attributed to heterogeneity (Borrego et al. 1997,

2000) and possible allochthonous origin of inertinite macerals

(O’Keefe et al. 2013).

The change in colour of SXC from pale- and dark yellow to

brown and black is followed by variations in the values of

maceral indices, Tissue Preservation Index (TPI) and

Gelification Index (GI) (Diessel 1986, adopted by Kalkreuth

et al. 1991 and Bechtel et al. 2003b) (Table 4). TPI decreased

in order pale yellow SXC > dark yellow SXC > brown SXC

> black SXC, while GI, as expected, showed the opposite trend

in both basins (Table 4). Negative correlation between TPI and

content of oleanane derivatives, accompanied by positive

correlation between TPI and content of non-hopanoid triter-

penoids with lupane skeleton (Table 5), indicates that greater

tissue preservation in yellow than in brown and black SCXs,

in part can be attributed to elevated content of Betulacea tissue

which is characterized by relatively high tree density, being

therefore resistant to degradation.

r – Correlation coefficient

Tex.

Ulm.

Attr.

Gel. Corpohum.

Res.

Sub.

Liptodetr.

TPI

Total diterpenoids

0.68

− 0.69

− 0.72

− 0.50

0.15

0.81

− 0.50

− 0.81

0.44

Total non-hopanoid triterpenoids

0.50

− 0.52

− 0.44

− 0.57

0.59

− 0.33

− 0.43

− 0.52

0.65

Total sesquiterpenoids

0.56

− 0.51

− 0.63

− 0.68

− 0.39

0.30

− 0.52

− 0.48

0.43

Total steroids

− 0.51

0.53

0.40

0.09

− 0.44

− 0.29

0.49

0.50

− 0.47

Total hopanoids

− 0.32

0.24

0.67

0.69

0.40

− 0.41

0.58

0.30

− 0.53

Total n-alkanes

− 0.11

0.08

0.53

0.39

0.03

− 0.74

0.45

0.11

− 0.05

Total oleanane derivatives

0.18

− 0.23

− 0.16

− 0.37

0.68

− 0.44

− 0.13

− 0.20

− 0.79

Total ursane derivatives

0.70

− 0.69

− 0.71

− 0.69

0.40

− 0.03

− 0.69

− 0.72

0.48

Total lupane derivatives

0.63

− 0.64

− 0.51

− 0.61

0.46

− 0.28

− 0.52

− 0.65

0.79

– C

n-alkanes

0.71

− 0.71

− 0.41

− 0.45

0.35

− 0.25

− 0.46

− 0.73

0.94

– C

n-alkanes

0.11

− 0.15

0.33

0.34

0.15

− 0.49

0.35

− 0.17

0.36

– C

n-alkanes

− 0.53

0.49

0.85

0.67

− 0.10

− 0.75

0.75

0.54

− 0.89

Tex. — Textinite; Ulm. — Ulminite; Attr. — Attrinite; Gel. — Gelinite; Corpohum. — Corpohuminite; Res — Resinite; Sub. — Suberinite; Liptodetr. — Liptodetrinite;

TPI — Tissue Preservation Index = (Textinite + Ulminite + Corpohuminite + Fusinite) / (Attrinite + Densinite + Gelinite + Inertodetrinite) (Diessel 1986, adopted by Kalkreuth et

al. 1991 and Bechtel et al. 2003b). The limiting value of r for significance level (p) of 95 % is 0.70 (Davis 2002).

Table 5: Correlations between contents of selected macerals (based on mineral matter-free, vol. %) and contents of biomarkers (μg/g TOC)

according to Pearson test.

PETROGRAPHIC AND BIOMARKER ANALYSIS OF XYLITE-RICH COAL (PANNONIAN BASIN, SERBIA)

GEOLOGICA CARPATHICA

, 2018, 69, 1, 51–70

Conclusions

The petrographic composition and biomarker assemblages

of four SXCs (pale yellow, dark yellow, brown and black)

originating from the most important lignite basins in Serbia

were studied.

All the samples are dominated by diterpenoids, followed by

non-hopanoid triterpenoids and n-alkanes. Other hydrocarbon

constituents of bitumen are hopanoids, sesquiterpenoids,

steroids and isoprenoids. The proportions of diterpenoids

decrease in the following order: pale yellow SXC > dark

yellow SXC > brown SXC > black SXC, whereas proportions

of all other biomarkers increase in the opposite trend, with the

exception of sesquiterpenoids which showed slightly higher

proportions in brown than in black SXC from both basins.

Distributions of biomarkers indicate that the contribution of

arboreal vegetation vs. impact of herbaceous peat-forming

plants decreased in the order: pale yellow SXC > dark yellow

SXC > brown SXC > black SXC, which resulted in reduction of

tissue preservation. Conifers contributed significantly to the

organic matter of all samples and predominated over angio-

sperms. Input of gymnosperm vs. angiosperm vegetation

decreased from yellow to brown and black SXC. From the

identified sesqui- and diterpenoids, a predominant role of the

conifer families Cupressaceae, Taxodiaceae and Pinacea is

concluded in all samples. Distribution of non-hopanoid tri-

terpenoids indicates that the input of plants from the Betulacea

family decreased from yellow to brown and black SXCs.

The ratio of short-chain (C

– C

) to long-chain (C

– C

)

n-alkanes decreased in the order: pale yellow SXC > dark

yellow SXC > brown SXC > black SXC. In addition, pale

yellow SXC from both basins showed the lowest Carbon

Preference Index (CPI) values. These results imply the lower

input of fatty acids from epicuticular waxes, since these acids

predominantly contain even numbers of carbon atoms in

a molecule and by decarboxylation produce odd-carbon-atom

n-alkanes. The lower contribution of epicuticular waxes to

pale yellow SXC is also confirmed by the lowest content of

liptinite macerals and total n-alkanes in this sublithotype.

Regarding hopanoid distribution, pale yellow SXC differs

mostly from other SXCs having the lowest proportion of

17α(H)21β(H)22(R)-hopane. Differences in hopane distri-

bution, bitumen content, proportion of short-chain n-alkanes

and degree of aromatization of di- and triterpenoids indicate

that pale yellow SXC differs from other studied samples,

mostly because of strong OM alteration caused by microbial

communities.

The observed differences in precursor OM and diagenetic

transformations are also reflected in petrographic characteris-

tics. The content of total huminite macerals increases in the

order: black SXC < brown SXC < dark yellow SXC < pale

yellow SXC, whereas contents of total liptinite and inertinite

macerals showed the opposite trend. The predominant humi-

nite macerals in all SXCs are textinite or ulminite. SXCs differ

according to the textinite/ulminite ratio which notably decrea-

sed in the order: pale yellow > dark yellow > brown > black.

Regarding the composition of liptinite macerals, the SXCs

mostly differ according to resinite/liptodetrinite and resinite/

suberinite ratios, reflecting the contribution of well preserved

woody material, including lignin tissue vs. the impact of

epicuticular waxes. These ratios are higher in yellow than in

brown and black SXC.

Acknowledgements: The study was financed by the Ministry

of Education, Science and Technological Development of the

Republic of Serbia (Projects 176006 and 451-03-01039/2015-

09/05) and Österreichischer Austauschdienst (OeAD) (Project

No. SRB 18/2016) which are gratefully acknowledged. We are

also grateful to the anonymous reviewers.

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Table I: The list of compounds identified in the saturated and aromatic fractions of the analysed SXCs (Figs. 4–7).

Appendix

Compound

Molecular mass

Base peak(s) in the mass spectrum

Saturated fraction
Cubebane

206

163

Dihydrovalencene

206

Eudesmane

208

109

Isopimaradiene

272

257

Isonorpimarane

262

123, 109

Norpimarane

262

233

Dihydrorimuene

274

259, 149

Isophyllocladene

272

120

Pimarane

276

247, 163, 123, 191

16β(H)-Phyllocladane

274

123

16α(H)-Phyllocladane

274

123

Des-A-olean-13(18)-ene

328

189, 204, 313,

Des-A-olean-12-ene

328

203, 218, 189,

Des-A-lupane

330

163,149,191,

Hop-17(21)-ene

410

367, 231

17α(H)21β(H)-hopane

426

191

17β(H)21β(H)-hopane

426

205, 191

Aromatic fraction
Dihydro-ar-curcumene

204

119

Cuparene

202

132

Calamenene

202

159

Curcumene

204

119

Cadalene

198

183

Isocadalene

198

183

Phenanthrene

178

19-Norabieta-6,8,11,13-tetraene

254

239

Hibaene

272

134

18-Norabieta-6,8,11,13-tetraene

254

239

18-Norabieta-8,11,13-triene

256

241, 159

Dehydroabietane

270

255

Pyrene

202

Simonellite

252

237

Totarane

252

237, 195, 179

Sempervirane

252

237, 193, 179, 207

Retene

234

219

2-Methylretene

248

234

3,4,7,12a-Tetramethyl-1,2,3,4,4a,11,12,12a-octahydrochrysene

292

207

3,4,7-Trimethyl-1,2,3,4-tetrahydrochrysene

274

259

Perylene

252

24,25-Dinoroleana-1,3,5(10),12-tetraene

376

145, 158

24,25-Dinorursa-1,3,5(10),12-tetraene

376

145

24,25-Dinorlupa-1,3,5(10)-triene

378

145

D-ring monoaromatic hopane

364

211

1,2,4a,9-Tetramethyl-1,2,3,4,4a,5,6,14b-octahydropicene

342

257

4-Methyl, 24-ethyl, 19-norcholesta-1,3,5(10)-triene

394

211

7-Methyl, 3’-ethyl, 1,2-cyclopentanochrysene

310

281

1,2,9-Trimethyl-1,2,3,4-tetrahydropicene

324

324, 309

2,2,9-Trimethyl-1,2,3,4-tetrahydropicene

324

324, 268