Comparative study of Serbian Miocene coals — Insights from biomarker composition

International Journal of Coal Geology 107 (2013) 3–23

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International Journal of Coal Geology

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Comparative study of Serbian Miocene coals — Insights from biomarker composition

Ksenija Stojanović a,⁎, Dragana Životić b

a University of Belgrade, Faculty of Chemistry, Studentski trg 12-16, 11000 Belgrade, Serbiab University of Belgrade, Faculty of Mining and Geology, Djušina 7, 11000 Belgrade, Serbia

⁎ Corresponding author. Tel.: +381 11 3336776; fax:E-mail addresses: [email protected], ksenija@che

0166-5162/$ – see front matter © 2012 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.coal.2012.09.009

a b s t r a c t
a r t i c l e i n f o
Article history:Received 29 May 2012Received in revised form 18 September 2012Accepted 18 September 2012Available online 28 September 2012

Keywords:Brown coalsSerbiaMioceneOrganic matterBiomarkersPaleoenvironment

The origin of the organic matter (OM) and the characteristics of the paleoenvironment of Serbian brown coalscovering a time-span from the Lower to the Upper Miocene were evaluated and compared based on comprehen-sive petrological and biomarker analyses. Investigated coals are typical humic coals. Peat-forming vegetation ischaracterized by abundant decay resistant gymnosperm (coniferous) plants, followed by variable amount of an-giosperms. Coal forming plants belonged to the gymnosperm families Taxodiaceae, Podocarpaceae, Cupressaceae,Araucariaceae, Phyllocladaceae and Pinaceae. Peatification proceeded in fresh water environment under variableEh settings, from anoxic to slightly oxic condition. UpperMiocene lignites were formed in neutral to slightly acidicenvironment, whereas Lower and Middle Miocene coals were deposited under neutral to slightly alkaline, andmore reductive conditions,which is the result of calcium-rich surfacewaters derived from the surrounding Jurassicto Cretaceous calcareous country rock and higher water column level. Diagenetic changes of the OM weregoverned by bacterial activity, rather than thermal alteration. Biomarker pattern does not significantly differ in Ser-bian coals of different ages. The main differences between Upper, Middle and Lower Miocene coals are expressedby higher Gelification Index (GI), proxy ratio (Paq), n-C23/(n-C27+n-C31) and pimarane/16α(H)-phyllocladaneratio, as well as lower relative abundance of C31αβ(R)-hopane of the latter one. OM of Lower Miocene coals ismore mature, corresponding to immature/early mature stage (huminite/vitrinite reflectance ~0.45), whereasOM of Upper Miocene lignites is in immature diagenetic phase (huminite reflectance ~0.3). Consequently, highergelification of Lower Miocene coals is probably an effect of higher rank, however high humidity/wet climate andlow acidity within the mire could not be excluded. A good correlation between biomarker parameters andpaleoclimate data is observed, indicating that biomarker patterns represent a valuable tool that reflect even slightpaleoclimate changes in Serbia during Miocene.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

In the past fewdecades organic geochemical analysis of soluble organ-ic matter (SOM) extracted from coal has been proved as a promising toolfor reconstruction of vegetation assemblage and paleoenvironmentalconditions in peatlands during the formation of coal-bearing strata(Bechtel et al., 2002, 2003, 2004; Dehmer, 1995; Otto and Wilde, 2001).Analysis of SOM extracted from coal involves biomarker identification —

complex organic compounds with strong resemblance in structure oftheir parent organic molecules in living organisms. However, a greatnumber of organic geochemical parameters are influenced by morethan one natural factor (Peters et al., 2005; Philp, 1985). Therefore, onlycomprehensive investigation, which includes analysis of numerous bio-marker compounds combined with petrological data, provides an oppor-tunity for estimation of sedimentary environment, type of vegetation andits transformation during diagenesis.

Concerning the significance of various fossil fuel resources ofSerbia, the brown coals, particularly the lignites, are of great economic

+381 11 2636061.m.bg.ac.rs (K. Stojanović).

rights reserved.

importance as they represent the main source for the production ofelectric energy. A significant number of coal bearing basins with hugecoal reserves were formed during theMiocene in the territory of Serbia,as a result of favorable peat-forming conditions. Recent paleoclimate in-vestigations based on analysis of different fossil taxa from 12 locationsindicate relatively uniform, warm and humid climate at the territoryof Serbia during the whole Miocene (Ivanov et al., 2011; Utescher etal., 2007).

The economically most important Upper Miocene coal basins —

Kolubara, Kostolac and Kovin deposit (Fig. 1; Table 1) were formedwith-in the Pannonian Basin System in shallow lacustrine, delta plain and flu-vial environments. During early Late Miocene Pannonian Basin evolvedinto the Lake Pannon (e.g. Magyar et al., 1999). Coal deposits have largereserves and resources, and relatively simple exploitation conditions.

The economic importance of coal in the Lower (Senje–Resavica,Soko Banja, Bogovina) and Middle Miocene (Krepoljin) basins in easternSerbia decreased since the 1990s (Fig. 1; Table 1). Those coal basins have,in fact, relatively large geological resources, but with very complicatedtectonic settings and exploitation conditions. Coal was formed in limnicintermontane depressions within the “Balkan Land” (Ercegovac et al.,2006).

http://dx.doi.org/10.1016/j.coal.2012.09.009

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Fig. 1. Locations of the studied coal basins in Serbia.

4 K. Stojanović, D. Životić / International Journal of Coal Geology 107 (2013) 3–23

With the exception of lignites from Drmno field (Kostolac basin) and“D” field (Kolubara basin), in which the chemical composition of the or-ganicmatter has recently been studied (Stojanović et al., 2012; Životić etal., 2011), biomarker data are either scarce or completelymissing. In thispaper,we present the investigations of the biomarker assemblages of lig-nites of the Middle and Upper Miocene age from the Krepoljin, Kolubaraand Kostolac basins, and the Kovin deposit and subbituminous coals of

Lower Miocene age (Senje–Resavica, Bogovina and Soko Banja basins)(Ercegovac et al., 2006; Životić et al., 2008, 2010) (Fig. 1; Table 1).Based on comprehensive petrological and biomarker analyses, the originof the organicmatter and the characteristics of the depositional environ-ment of SerbianMiocene coalswere evaluated and compared.Moreover,those biomarker ratios, which show the highest variability in coals ofdifferent ages, have been correlated with paleoclimate data.

Table 1Basic geological parameters of coal in the studied coal basins.

Basin/deposit Coal field/mine Age Coal-bearingsediments

Coalification degree,average huminitereflectance

Sample no. Relative depth ofstudied samples (m)

Thickness (m) Lithotype

Senje–Resavicabasin

Senje Mine Lower Miocene around20 Ma

Marly–clayey Subbituminous0.44±0.04

1 281.00–281.30 0.30 Matrix coalJelovac 2 273.50–273.80 0.30 Matrix coalStrmosten 3 274.00–274.85 0.85 Matrix coal

4 149.40–149.9 0.50 Matrix coal5 151.32–152.02 0.70 Matrix coal6 152.15–151.27 0.12 Xylite-rich coal7 418.72–419.06 0.34 Xylite rich coal8 421.62–421.72 0.10 Xylite-rich coal

Soko Banja basin Soko Lower Miocene around17 Maa

Marly–clayey Subbituminous0.40±0.05b

9 462.30–463.16 0.86 Xylite-rich coal10 465.10–466.30 1.20 Matrix coal11 455.27–456.02 0.75 Matrix coal12 473.90–474.40 0.50 Xylite-rich coal

Bogovina basin East field Lower Miocene around19 Maa

Marly–clayey Subbituminous0.41±0.04c

13 237.14–237.37 0.23 Matrix coal14 238.38–237.42 0.04 Matrix coal15 239.68–239.71 0.03 Matrix coal16 240.28–241.48 1.20 Matrix coal

Krepoljin basin Central field Middle Miocene around12 Maa

Marly–clayey Lignite 0.32±0.03 17 175.10–175.68 0.58 Xylite-rich coal18 177.58–177.88 0.30 Xylite-rich coal19 178.38–179.58 1.20 Xylite-rich coal20 201.39–202.50 1.11 Matrix coal

Kolubara basin D field Upper Miocene (Pontian)around 6 Ma

Sandy–clayey Lignite 0.30±0.03d 21 115.60–115.90 0.30 Mineral-rich coal22 116.52–116.90 0.38 Matrix coal23 119.50–120.75 1.25 Xylite-rich coal24 121.00–121.90 0.90 Xylite-rich coal25 123.16–123.70 0.54 Matrix coal26 123.70–127.00 3.30 Xylite-rich coal27 130.30–133.10 2.80 Xylite-rich coal28 133.10–133.70 0.60 Xylite-rich coal29 133.70–136.00 2.30 Matrix coal30 143.80–146.40 2.60 Xylite-rich coal31 146.40–147.00 0.60 Matrix coal32 148.90–149.90 1.00 Xylite-rich coal33 153.20–154.40 0.70 Matrix coal34 153.90–154.40 0.50 Xylite-rich coal

Kostolac basin Drmno field Upper Miocene (Pontian)around 6 Ma

Sandy–clayey Lignite 0.30±0.03d 35 23.20–23.40 0.20 Matrix coal36 24.00–24.50 0.50 Matrix coal37 24.50–24.53 0.03 Xylite-rich coal38 24.80–24.90 0.10 Matrix coal39 100.60–101.00 0.40 Matrix coal40 102.10–102.20 0.10 Matrix coal41 103.40–104.20 0.80 Matrix coal42 104.80–104.90 0.10 Xylite-rich coal43 112.00–112.60 0.60 Xylite-rich coal44 121.40–123.70 2.30 Mineral-rich coal

Kovin deposit A field Upper Miocene (Pontian)around 6 Ma

Sandy–clayey Lignite 0.29±0.03d 45 39.00–39.30 0.30 Xylite-rich coal46 65.15–65.35 0.20 Xylite-rich coal47 65.60–65.70 0.10 Xylite-rich coal48 65.70–66.20 0.50 Matrix coal49 88.00–88.12 0.12 Xylite-rich coal50 88.40–88.60 0.20 Matrix coal51 88.60–88.80 0.20 Matrix coal

a The age of coal-bearing sediments is not precisely determined.b Životić et al. (2008).c Životić et al. (2010).d Ercegovac et al. (2006).

5K. Stojanović, D. Životić / International Journal of Coal Geology 107 (2013) 3–23

2. Geological setting

The most important brown coal basins in Serbia were formed inthe period from the Lower to the Upper Miocene as a result of strongtectonic movements (faulting) during the formation of the PannonianBasin and favorable peat-forming conditions. Two characteristic typesof the Miocene brown coal basins have been distinguished (Ercegovacet al., 2006): (1) coal basins in intermontane depressions with terrige-nous limnic facies (Senje–Resavica, Bogovina, Soko Banja and Krepoljin);and (2) coal basins along the border of the Pannonian Basin in shallowlacustrine, delta plain and fluvial environments (Kolubara, Kostolac,Kovin; Fig. 1; Table 1).

Limnic intermontane basins were formed on the “Balkan Land”contemporary to the evolution of the Pannonian Basin and compose

of marly–clayey series with one coal seam in most of the studied ba-sins, except the Bogovina East field (Fig. 2), where two coal seams(Upper and Lower) were formed with bentonitic clay in the basementof the Lower coal seam. The Lower Miocene basins (Senje–Resavica,Soko Banja and Bogovina) include subbituminous coal, while theMiddleMiocene basin (Krepoljin) includes lignite.

Brown coal basins and deposits along the border of the PannonianBasin are characterized by siliciclastic sediments. During the UpperMiocene (Pontian; Rögl, 1996) extensive marsh lands were formed innear-shore plains. Their abundant peat vegetation resulted in the forma-tion of the most important lignite basins in Serbia such as Kolubara,Kostolac and Kovin deposit (Fig. 1). Coal-bearing strata inmentioned ba-sins and deposit consist of sandy–clayey sedimentswith three (Kolubarabasin and Kovin deposit) to five coal seams (Kostolac basin) (Fig. 2).

Fig. 2. Correlation of synthesized geological columns of studied Serbian coal basins.After Ercegovac et al. (2006), modified.


2.1. Paleoclimate and paleoflora characteristics

Lower Miocene climate was warm and humid with mean annualtemperatures ~16 °C and annual rainfalls over 1000 mm (Ivanov et al.,2011; Utescher et al., 2007). The Lower to Middle Miocene flora wasrich anddiverse in thermophilous elements,which formedpolydominantmesophytic to hygromesophytic forests. Floras of the Lower Miocene ofSerbia have always included both the evergreen broadleaved and thedeciduous components, with a very common addition of xerophilouselements. The dominant conifers were Sequoia and Pinus, while the typ-ical swamp conifers Taxodium and Glyptostrobus are rare. Deciduous ele-ments such as Alnus, Salix, Populus, and some species ofMyrica, were alsopresent to various extents (Djordjević-Milutinović and Ćulafić, 2008;Ivanov et al., 2011; Pantić and Dulić, 1992; Utescher et al., 2007).

TheMiddle Miocene was the warmest period of the whole Miocene,with annual temperatures ranging from 16 °C to 19 °C and winter tem-peratures from 6 °C to 12.5 °C (Utescher et al., 2007). The warm climatephase in the Badenian corresponds to a globally observedwarm time in-terval, the Mid-Miocene Climate Optimum (Zachos et al., 2001). During

theMiddleMiocene, precipitation in thewettestmonth (MPwet) showsa decreasing trend while precipitation in the driest month (MPdry) al-most stays at the same level. The mean annual precipitation (MAP)and precipitation in thewarmestmonth (MPwarm) records, in contrast,are heterogeneous (Utescher et al., 2007).MiddleMioceneflorawas richin numerous laurophyllous elements and deciduous taxa (Salix, Alnus,Carpinus, Populus). The swamp forests with dominant Glyptostrobusand Taxodium had large extent in flood plains. The presence of Sequoia,Cupressaceae and Pinus suggests the existence of mixed conifer–laurelforest (Djordjević-Milutinović and Ćulafić, 2008; Pantić and Dulić, 1992).

According to Ivanov et al. (2011) slight cooling, followed by pro-nounced increase in seasonality of temperature and some drying isrecorded for the beginning of the Upper Miocene. Until the Pontian,mean annual temperature (MAT) has decreased by about 2.5 °C andcold month mean temperature (CMM) by 3–5 °C (Utescher et al.,2007), consistent with global Late Miocene cooling. Warm monthmean temperature (WMM) was not very much affected by this overallcooling trend staying at the high level of about 26 °C. Stronger coolingin winter temperatures as compared to summer temperatures, during

image of Fig.�2


Upper Miocene caused an increase in seasonality (Bruch et al., 2007;Utescher et al., 2007). During the Upper Miocene, a decreasing trendis observed for MAP (Ivanov et al., 2011; Utescher et al., 2007). Climaticchanges caused transformation in floristic composition and vegetationstructure. The vegetation shows a decreasing trend in abundance ofpaleotropic and thermophilous elements, reduction of macrothermicelements, and disappearance of evergreen laurel forests. In the Pontianage, coastal peatland vegetation around the southern margin of thePannonian Lakewaswell developedwith swamp forests (Glyptostrobus,Nyssa, Cyrilla, and Myrica), riparian forests (Alnus, Salix, Populus,Platanus, and Acer), and herbaceous vegetation (Juncus, Carex, Phragmi-tes, and Typha) (Pantić and Dulić, 1993).

3. Samples and analytical methods

Thirty one core samples were collected from three boreholes: theDrmno field (Kostolac basin), the “D” field (Kolubara basin) and “A”field (Kovin deposit). The thickness of each sample interval was de-termined according to the changes of coal lithotypes (Table 1). Twen-ty channel samples were collected from fresh, working faces in sixunderground mines: Senje, Jelovac and Strmosten mines (Senje–Resavica basin), Soko (Soko Banja basin), Bogovina East field(Bogovina basin), and Central field (Krepoljin basin), in East Serbia.In total, 51 samples from seven brown coal basins in Serbia were in-vestigated. Organic geochemical and coal petrology study wasperformed on the following samples: 8 samples from the Senje–Resavica basin, 4 samples from the Soko Banja basin, 4 samplesfrom the Bogovina basin, 4 samples from the Krepoljin basin, 14 sam-ples from the Kolubara basin, 10 samples from the Kostolac basin and7 samples from the Kovin deposit (Table 1).

For rank determination and maceral analysis, the coal sampleswere crushed to a maximum particle size of 1 mm, mounted inepoxy resin and polished. The maceral analyses were performed ona Leitz DMLP microscope in monochromatic and UV light on 500points. The maceral description used in this article follows the termi-nology developed by the International Committee for Coal Petrologyfor low-rank coal (Sykorova et al., 2005).

The reflectance measurements for coal from the Senje–Resavica,Soko Banja, Bogovina and Krepoljin basins were performed under amonochromatic light of 546 nm using a Leitz MPVII microscope andan optical standard having a reflectance of 0.589% in oil, followingthe procedures outlined by Taylor et al. (1998). The rank was deter-mined by measuring the random reflectance on ulminite B. Huminitereflectance data for coal from the Kolubara and Kostolac basins aswell as Kovin deposit were taken from literature (Ercegovac et al.,2006).

Elemental analysis was performed to determine the contents of sul-fur and organic carbon (Corg). Organic carbon content was determinedafter removal of carbonates with diluted hydrochloric acid (1:3, v:v).The measurements were done using a Vario EL III, CHNS/O ElementalAnalyzer, Elementar Analysensysteme GmbH.

Soluble organic matter (bitumen) was extracted from pulverizedlignites (b150 μm) using a Dionex ASE apparatus with a mixture ofisohexane and acetone (1:1, v:v) at a temperature of 80 °C and a pres-sure of 8 MPa. The asphaltenes were precipitated with petroleum–

ether and the remainder (maltenes) was separated into three frac-tions using column chromatography over silica gel and aluminumoxide. The saturated hydrocarbon fraction was eluted with isohexane,the aromatic hydrocarbons with dichloromethane and the NSO frac-tions (polar fraction, which contains nitrogen, sulfur, and oxygencompounds) with mixture of dichloromethane and methanol (1:1,v:v) (Životić et al., 2008).

Saturated and aromatic fractions isolated from the bitumen were an-alyzed by gas chromatography–mass spectrometry (GC–MS). A gas chro-matograph Agilent 7890A GC (H5-MS capillary column, 30 m×0.25 mm,He carrier gas 1.5 cm3/min, FID) coupled to a Agilent 5975C mass

selective detector (70 eV) was used. The column was heated from 80 to310 °C, at a rate of 2 °C/min, and the final temperature of 310 °C wasmaintained for an additional 25 min. The individual peakswere identifiedby comparison with the literature data (Killops et al., 1995, 2003; Ottoand Simoneit, 2002; Peters et al., 2005; Philp, 1985; Stout, 1992; Tuoand Li, 2005; Wakeham et al., 1980) and on the basis of the total massspectra (library: NIST5a). Biomarker parameters were calculated fromGC–MS chromatogram peak areas (software GCMS Data Analysis).

4. Results and discussion

4.1. Micropetrography and sulfur content

The Miocene brown coals from the studied basins are typicalhumic coals with huminite, liptinite and inertinite concentrations ofup to 92.6 vol.%, 17.4 vol.% and 15.5 vol.%, respectively (Table 2). Asexpected, huminite/vitrinite reflectance (Table 1) of Lower Miocenesubbituminous coals (Senje–Resavica, Bogovina, Soko Banja basins)is higher (0.40–0.45%Rr) than that of Middle/Upper Miocene lignites(~0.30; Krepoljin, Kolubara, and Kostolac basins and Kovin deposit).

However, huminite/vitrinite reflectance measurements (Table 1)and biomarker distributions (Figs. 3 and 4) indicate immature to earlymature stage of the OM of subbituminous Lower Miocene coals. There-fore, in order to provide comparative study of SerbianMiocene coals weused the same coal petrological terminology (Sykorova et al., 2005) forall investigated samples (Table 2).

Telohuminite and/or detrohuminite dominate by far in all Upperand Middle Miocene samples, as well as in the greatest number ofLower Miocene coals. Slight predominance of gelohuminite was ob-served in three samples (2, 4 and 5) from Senje–Resavica basin. TheLower Miocene coals are generally characterized by higher amountof gelinite than Upper Miocene lignites (Table 2).

Lignites from the Kolubara, Kostolac and Kovin are characterized byhigh amount of telohuminite with variable amount of detrohuminite,and low amount of gelohuminite. The telohuminite, especially textinite,is strongly impregnated by resinous-like substances, while thedetrohuminite occurs as groundmass surrounding liptinite or inertiniteparticles. In some cases, they are interbedded with clay minerals. Coalfrom the Senje–Resavica basin consists of variable amount oftelohuminite and detrohuminite with a high content of gelohuminite.The most abundant macerals are ulminite and densinite. High amountsof gelinite and phlobaphinite are determined in the few samples fromthe Jelovac and Senje mines. Coal from the Soko Banja basin consistsof telohuminite with ulminite as the most abundant maceral (Životićet al., 2008) and variable amount of gelohuminite and detrohuminitewith gelinite and densinite as prevailing macerals. Coal from theKrepoljin basin is composed of telohuminite with a high amountof detrohuminite. The content of gelohuminite is relatively low. Incomparison with the mentioned basins, coal from the East Field ofthe Bogovina basin consists of detrohuminite with densinite as themost abundant maceral (Životić et al., 2010), while ulminite andgelinite are less abundant (Table 2).

The liptinite content in all studied basins is generallymoderately low,with variations between the basins and even in the same basin (Table 2).Liptodetrinite and sporinite are the most abundant macerals in lignitefrom the Kolubara (Životić et al., 2011) and Kostolac basins (Stojanovićet al., 2012) and Kovin deposit while suberinite, cutinite and resiniteoccur in variable amounts. In comparison with other basins, theBogovina East Field and Senje–Resavica have higher liptinite content.Suberinite is the most abundant maceral of the liptinite group in theSenje–Resavica and Krepoljin basins, while sporinite is the most abun-dant in coal from the Bogovina and Soko Banja basins. Liptodetrinite,cutinite and alginite are present in coal from Bogovina East field in vari-able amount. A secondary maceral, exsudatinite, detected exclusively insome samples from the Bogovina East field, indicates generation of im-mature hydrocarbons.

Table 2Maceral composition (vol.%) and petrographic indices of the Serbian Miocene coals.

Basin/deposit Coal field/mine No. Textinite Ulminite Telohuminite Attrinite Densinite Detrohuminite Gelinite Corpohuminite Gelohuminite Huminite

Senje–Resavica basin Senje Mine 1 22.3 22.3 33.8 33.8 13.8 5.0 18.8 74.92 15.0 15.0 22.6 22.6 29.4 8.1 37.5 75.13 27.6 27.6 30.7 30.7 16.7 10.5 27.2 85.5

Jelovac 4 0.3 15.6 15.9 1.6 26.3 27.9 18.1 10.7 28.8 72.65 21.4 21.4 29.8 29.8 29.3 12.4 31.7 82.96 62.6 62.6 8.6 8.6 6.5 7.5 14.0 85.2

Strmosten 7 1.2 45.7 46.9 20.5 20.5 4.3 3.8 8.1 75.58 0.9 77.6 78.5 4.7 4.7 4.4 5.0 9.4 92.6

Soko Banja basind Soko 9 1.0 41.8 42.8 12.7 12.7 14.6 10.2 24.8 80.310 0.8 35.8 36.6 2.9 5.9 8.8 16.8 10.7 26.5 71.911 1.9 23.1 25.0 0.8 33.9 34.7 15.4 7.1 22.5 82.212 2.7 38.6 41.3 20.7 20.7 16.5 2.0 18.5 80.5

Bogovina basine East field 13 10.1 10.1 39.2 39.2 17.7 3.7 21.4 70.714 5.5 5.5 39.9 39.9 24.5 1.5 25.7 71.115 28.0 28.0 1.0 38.7 39.7 4.1 2.9 7.0 74.716 9.7 9.7 1.2 42.3 43.5 9.7 1.8 11.5 64.7

Krepoljin basin Central field 17 14.3 28.9 43.2 4.2 8.3 12.5 3.8 3.6 7.4 63.118 19.3 29.4 48.7 0.8 4.9 5.7 3.1 2.9 6.0 60.419 34.5 23.7 58.2 4.6 16.2 20.8 0.9 4.9 5.8 84.820 4.3 29.1 33.4 37.9 37.9 3.8 7.0 10.8 82.1

Kolubara basinf D field 21 15.3 8.2 23.5 19.0 10.6 29.6 0.1 1.4 1.5 54.622 12.7 13.8 26.5 14.7 9.7 24.4 0.7 0.3 1.0 51.923 37.0 12.7 49.7 11.0 13.5 24.5 0.9 1.6 2.5 76.724 57.0 12.6 69.6 4.9 6.1 11.0 0.4 2.7 3.1 83.725 19.0 12.0 31.0 24.4 15.5 39.9 1.1 2.3 3.4 74.326 34.2 20.8 55.0 4.2 15.5 19.7 0.3 2.2 2.5 77.227 20.7 35.2 55.9 5.8 11.2 17.0 0.9 2.2 3.1 76.028 26.2 36.1 62.3 6.5 11.5 18.0 1.3 1.7 3.0 83.329 14.3 32.4 46.7 8.1 24.0 32.1 1.0 1.7 2.7 81.530 17.7 45.8 63.5 5.2 8.8 14.0 2.0 3.5 5.5 83.031 8.7 22.2 30.9 5.6 33.7 39.3 1.2 3.3 4.5 74.732 10.7 38.1 48.8 1.5 14.8 16.3 3.7 4.4 8.1 73.233 13.9 18.8 32.7 8.5 30.4 38.9 1.9 3.8 5.7 77.334 5.7 42.6 48.3 1.8 19.1 20.9 1.0 2.5 3.5 72.7

Kostolac basing Drmno field 35 17.1 10.6 27.7 3.0 30.0 33.0 4.0 1.5 5.5 66.236 19.7 5.4 25.1 13.6 25.8 39.4 2.3 1.8 4.1 68.637 48.3 15.8 64.1 3.9 9.4 13.3 3.1 2.0 5.1 82.538 16.1 11.8 27.9 14.5 31.0 45.5 3.0 5.0 8.0 81.439 17.3 15.5 32.8 7.9 31.5 39.4 3.2 5.4 8.6 80.840 14.3 26.7 41.0 6.6 32.3 38.9 3.0 6.4 9.4 89.341 15.7 13.1 28.8 3.5 39.1 42.6 0.5 0.9 1.4 72.842 15.8 32.8 48.6 2.4 19.7 22.1 4.0 6.3 10.3 81.043 11.4 38.9 50.3 0.6 17.1 17.7 7.2 4.7 11.9 79.944 3.7 15.3 19.0 2.7 22.6 25.3 5.5 1.0 6.5 50.8

Kovin deposit A field 45 12.6 42.7 55.3 0.4 16.0 16.4 7.1 4.1 11.2 82.946 19.1 43.6 62.7 0.2 17.0 17.2 2.5 3.3 5.8 85.747 12.3 44.8 57.1 0.2 21.3 21.5 7.1 1.8 8.9 87.548 4.3 30.0 34.3 1.7 27.8 29.5 3.1 2.7 5.8 69.649 20.9 40.8 61.7 0.2 18.6 18.8 1.4 2.8 4.2 84.750 13.0 26.3 39.3 1.1 30.9 32.0 1.1 1.1 2.2 73.551 4.7 26.0 30.7 2.7 29.1 31.8 3.1 3.4 6.5 69.0

Minimum value 0.3 5.4 5.5 0.2 4.7 4.7 0.1 0.3 1.0 50.8Maximum value 57.0 77.6 78.5 24.4 42.3 45.5 29.4 12.4 37.5 92.6

Liptinite Inertinite Clay Carbonates Pyrite MBGa Other minerals Total mineral TPIb GIca MBG — mineral-bituminous groundmass (Teichmüller, 1989).b TPI=(textinite+ulminite+corpohuminite+fusinite+semifusinite)/(gelinite+macrinite+detrohuminite), by Diessel (1986) and modified by Ercegovac and Pulejković (1991).c GI=(ulminite+densinite+gelinite+corpohuminite)/(textinite+attrinite+inertinite), by Diessel (1986) and modified by Ercegovac and Pulejković (1991).d Životić et al. (2008).e Životić et al. (2010).f Životić et al. (2011).g Stojanović et al. (2012).


The inertinite content in Miocene brown coals is relatively low.Lower and Middle Miocene coals from Eastern Serbia have lower con-tent than Upper Miocene lignites (Table 2). The most abundantmaceral in all studied basins is inertodetrinite, while fusinite andfunginite are less abundant. Semifusinite and macrinite occur in lowamounts. Funginite is especially abundant in coal from the Kolubarabasin (3.7 vol.%; Životić et al., 2011), Senje Mine (Senje–Resavicabasin) and Bogovina East field (Životić et al., 2010).

Content of mineral matter in Upper Miocene and Middle Miocenelignites shows a comparatively wide range 4.3%–35.7% and 8.8–35.2,respectively (Table 2). Content of mineral matter in Lower Miocenecoals is in the range of 4.4%–21.0% (Table 2). Content of sulfur in

Upper Miocene lignites does not exceed 1.8%, with the exception ofone sample (Table 3). The same observation is related to Lower Mio-cene coals from Senje Mine and Jelovac (Senje–Resavica basin). Thetotal sulfur content in the Lower Miocene Bogovina basin is highand ranges from 3.68% to 5.35% (Table 3). Domination of clays andvery low carbonate content observed in all Upper Miocene samples(Table 2) suggest a neutral to slightly acidic environment, whereaslow sulfur content implies relatively low sulfate content of waters with-in the peat (peatification in fresh water environment) (Bechtel et al.,2004; Casagrande, 1987). The high content of mineral-bituminousground mass with increased carbonate and pyrite contents in MiddleMiocene coal from the Krepoljin, indicates peatification in reducing,

Table 2 (continued)

Liptinite Inertinite Clay Carbonates Pyrite MBGa Other minerals Total mineral TPIb GIc

5.2 1.7 10.2 0.3 4.4 2.2 1.1 18.2 0.5 44.117.4 2.4 2.4 1.1 1.6 5.1 0.3 31.35.5 2.8 3.1 0.2 1.1 0.7 1.1 6.2 0.6 30.58.9 1.0 12.1 1.3 1.6 0.3 2.2 17.5 0.6 24.47.3 0.6 6.9 2.1 0.2 9.2 0.4 138.29.4 0.8 4.0 0.6 4.6 4.0 106.5

15.8 0.9 1.6 6.2 7.8 1.8 35.41.2 1.8 0.9 1.6 1.9 4.4 8.2 34.07.9 5.9 2.3 3.6 5.9 2.0 11.54.8 2.3 9.2 0.2 3.2 8.0 0.4 21.0 1.5 11.47.6 2.7 3.6 1.1 2.4 0.4 7.5 0.5 14.76.2 7.6 1.9 1.7 1.9 0.2 5.7 1.2 7.6

14.9 4.0 7.1 1.2 1.2 0.9 10.4 0.2 17.712.0 4.3 8.7 0.3 1.2 1.8 0.6 12.6 0.1 16.59.8 2.5 9.5 1.6 0.3 1.0 0.6 13.0 0.6 21.1

16.1 6.7 11.3 0.9 0.3 12.5 0.2 8.06.5 0.2 10.9 2.4 1.2 15.7 30.2 2.8 2.43.9 0.5 7.7 0.5 3.1 21.6 2.3 35.2 5.5 2.04.9 1.5 4.3 0.8 2.1 1.2 0.3 8.8 2.6 1.16.5 0.8 2.7 2.7 5.2 10.6 0.8 15.38.7 2.6 30.5 0.5 1.8 1.3 34.1 0.8 0.6

17.2 4.6 21.1 0.1 2.1 2.2 0.8 26.3 1.1 0.88.3 3.7 5.0 0.9 0.7 3.6 1.1 11.3 2.0 0.63.8 8.1 2.1 0.2 0.4 1.3 0.4 4.4 6.3 0.3

10.4 3.5 3.7 0.5 2.6 4.6 0.4 11.8 0.8 0.74.8 1.5 13.2 0.8 0.3 1.0 1.2 16.5 2.8 1.07.3 10.1 3.4 0.4 0.7 1.7 0.4 6.6 3.2 1.47.2 2.4 4.3 0.7 1.2 0.2 0.7 7.1 3.3 1.49.3 4.4 3.4 0.2 0.6 0.4 0.2 4.8 1.4 2.27.1 3.4 4.7 0.4 0.7 0.5 0.2 6.5 4.1 2.36.3 6.5 7.9 1.0 1.2 2.2 0.2 12.5 0.9 2.94.3 15.5 2.7 0.5 3.0 0.4 0.4 7.0 2.8 2.24.2 5.4 7.8 0.9 1.0 3.4 13.1 0.9 2.04.2 6.3 9.2 0.5 2.0 5.1 16.8 2.3 4.74.3 4.0 21.8 0.7 2.3 0.7 25.5 0.8 1.95.7 7.7 11.1 0.8 2.2 0.7 3.3 18.0 0.7 0.93.3 5.9 1.4 0.9 1.8 2.4 1.8 8.3 4.2 0.56.8 4.1 5.3 0.4 0.9 1.1 7.7 0.7 1.54.3 5.0 8.3 0.4 0.5 0.7 9.9 0.9 1.82.8 1.9 3.5 1.9 0.4 0.2 6.0 1.1 3.03.4 12.2 6.1 1.6 3.2 0.7 11.6 0.7 1.73.0 4.0 9.7 1.8 0.5 12.0 2.1 2.82.5 12.5 4.3 0.8 5.1 2.5 2.83.1 10.4 31.6 0.9 1.9 1.3 35.7 0.7 2.63.4 9.2 2.8 0.2 0.6 1.0 4.6 2.7 3.24.6 5.4 2.9 0.4 0.4 0.6 4.3 3.4 2.73.2 3.8 3.0 1.0 1.5 5.5 2.1 4.65.7 5.4 12.3 3.4 1.7 1.9 19.3 1.1 5.65.4 2.1 3.4 0.6 1.8 0.9 1.1 7.8 3.2 2.74.9 3.8 11.0 4.0 1.7 0.2 0.9 17.8 1.2 3.35.9 5.9 13.7 3.5 2.0 19.2 1.0 4.61.2 0.2 0.9 0.1 0.3 0.2 0.2 4.3 0.1 0.3

17.4 15.5 31.6 4.0 6.2 21.6 5.1 35.7 8.2 138.2


neutral to slightly alkaline environment. Themost abundantminerals inSenje–Resavica and Soko Banja coals are clays and pyrite (Table 2). Thepresence of pyrite in the clay-rich and humic-rich layers impliesanaerobic conditions coupled with sulfur reducing bacterial activity.Mineral matter of coals from Bogovina basin is dominated by clays,followed by moderate amount of carbonates, suggesting peatificationin neutral to slightly alkaline environment. The relatively high sulfurcontent in Lower and Middle Miocene coals from the Bogovina, SokoBanja, Senje–Resavica and Krepoljin basin (Table 3) formed in limnicdeposition environments could be a result of calcium-rich surface wa-ters derived from the surrounding Jurassic and Cretaceous calcareouscountry rock. These waters caused neutral or even slightly alkaline

environment (Markic and Sachsenhofer, 1997), which was also as-sumed based onmineral matter composition. The fact that tuff underly-ing the coal seam in the East field of Bogovina basin was altered tobentonite also supports a near neutral or weakly alkaline environment.Also, the relatively high amounts of coal-bed methane released duringcoal mining (Životić et al., 2008) may suggest a high activity of anaero-bic bacteria in a slightly acidic to neutral methanogenic environmentrich in sulfates.

The Tissue Preservation Index (TPI; Diessel, 1986, modified byErcegovac and Pulejković, 1991), taken as the ratio between structuredand unstructuredmacerals of the huminite and inertinite group, rangesfrom 0.7 to 6.3; 0.8 to 5.5 and 0.1 to 8.2 for the Upper, Middle and Lower

Fig. 3. TIC (total ion current) of saturated fraction of Upper Miocene (a) and Lower Miocene (b) coal. Peak assignments: n-alkanes are labeled according to their carbon number;Pr — pristane; Ph — phytane; D1 — norisopimarane; D2 — norabietane; D3 — norpimarane; D4 — beyerane; D5 — isophyllocladene; D6 — isopimarane; D7 — pimarane; D8 —

16α(H)-phyllocladane; D9 — 16α(H)-kaurane; T1 — des-A-olean-13(18)-ene; T2 — des-A-olean-12-ene; T3 — des-A-olean-18-ene; T4 — des-A-urs-13(18)-ene; T5 —

des-A-urs-12-ene; T6 — des-A-lupane; T7 — 24-norolean-13(18)-ene; T8 — 24-norolean-12-ene; T9 — 24-norurs-12-ene; T10 — oleanadiene; T11 — oleanene; T12 —

olean-13(18)-ene; T13— olean-12-ene; T14— olean-18-ene; T15— urs-12-ene; ββ, βα and αβ designate configurations at C17 and C21 in hopanes, (R) designates configurationat C22 in hopanes.


Miocene coals, respectively (Table 2). Variations of TPI with depth ob-served in all studied coal fields could reflect at least to some extentthe differences in the type of peat formingplant communities. The dom-ination of structured macerals in almost all Upper and Middle Miocenesamples, as well as in several Lower Miocene coals (TPI>1; Table 2)could imply significant contribution of gymnosperm species, whichare more resistant to degradation in comparison to angiosperms(Bechtel et al., 2004, 2007; Zdravkov et al., 2011). On the other hand,relatively low TPI values for Lower Miocene coals (Bogovina, SenjeMine and Jelovac; Table 2) could indicate slightly alkaline environmentwith degradation of gymnosperm, consistentwith the results ofmineralmatter composition, or oxic and dry condition with predominance ofangiosperms. However, it was also suggested that tissue preservationdepends mostly from the relative height of the water level, pH and cli-matic settings, rather than from the botanical properties of the vegeta-tion (Dehmer, 1995). Namely, decrease in water level within the basins

during the dry seasons, contribute to establishment of more oxic condi-tions results in more extensive tissue degradation.

The Gelification Index (GI; Diessel, 1986, modified by Ercegovacand Pulejković, 1991), expressed as the ratio of gelified (ulminite,densinite, gelinite and corpohuminite) to non-gelified (textinite andattrinite) macerals, is used as an indirect measure for the height ofthe water level, due to the fact that gelification of the tissues requiressustained water presence. GI is in the range of 0.3 and 5.6 for UpperMiocene lignites. Middle Miocene Krepoljin coals are characterizedby GI values in the range of 1.1–15.3, whereas Lower Miocene sam-ples have notably higher GI values ranging between 8.0 and 138.2(Table 2). This result indicates higher maturity of OM, but highhumidity/wet climate and low acidity within the mire could not beruled out.

Vertical variations in the petrographic composition of coal in thebrown coal deposits of Serbia (Table 2) indicate the water level

image of Fig.�3

Fig. 4. TIC (total ion current) of aromatic fraction of Upper Miocene (a) and Lower Miocene (b) coal. Peak assignments: 1 — dihydro-ar-curcumene; 2 — cuparene; 3 — calamenene;4 — cadina-1(10),6,8-triene; 5 — 5,6,7,8-tetrahydrocadalene; 6 — cadalene; 7 — isocadalene, 8 — phenanthrene, 9 — norabietadiene; 10 — 19-norabieta-8,11,13-triene; 11 —

6,10,14-trimethylpentadecan-2-one; 12 — isopimaradiene; 13 — norabietatetraene; 14 — 16,17-bisnordehydroabietane; 15 — hibane; 16 — 16,17-bisnorsimonellite; 17 —

18-norabieta-6,8,11,13-tetraene; 18— 18-norabieta-8,11,13-triene; 19— dehydroabietane; 20— 1,2,3,4-tetrahydroretene; 21— 2-methyl, 1-(4′-methylpentyl), 6-i-propyl-naphthalene;22 — simonellite; 23 — totarane; 24 — sempervirane; 25 — retene; 26 — ferruginol; 27 — pentamethyloctahydrochrysene; 28 — 2-methylretene; 29 —

3,4,7,12a-tetramethyl-1,2,3,4,4a,11,12,12a-octahydrochrysene; 30 — 3,3,7,12a-tetramethyl-1,2,3,4,4a,11,12,12a-octahydrochrysene; 31 — 3,4,7-trimethyl-1,2,3,4-tetrahydrochrysene;32 — 3,3,7-trimethyl-1,2,3,4-tetrahydrochrysene; 33 — perylene; 34 — triaromatic C ring cleaved hydrocarbon; 35 — 24,25-dinoroleana-1,3,5(10),12,14-pentaene; 36 —

24,25-dinoroleana-1,3,5(10),12-tetraene; 37 — D-ring monoaromatic hopane; 38 — 24,25-dinorursa-1,3,5(10),12-tetraene; 39 — 24,25-dinorlupa-1,3,5(10)-triene; 40 —

1,2,4a,9-tetramethyl-1,2,3,4,4a, 5,6,14b-octahydropicene; 41 — 2,2,4a,9-tetramethyl-1,2,3,4,4a,5,6,14b-octahydropicene; 42 — lanosta(eupha)hexaene; 43 — 4-methyl, 24-ethyl,19-norcholesta-1,3,5(10)-triene; 44 — 7-methyl, 3′-ethyl, 1,2-cyclopentanochrysene; 45 — C31 alkan-2-one; 46 — 1,2,9-trimethyl-1,2,3,4-tetrahydropicene; 47 —

2,2,9-trimethyl-1,2,3,4-tetrahydropicene; 48— C31 benzohopane; 49— C32 benzohopane; 50 — C33 alkan-2-one; 51 — C33 benzohopane.


fluctuation in the mire (i.e. changes of redox potential and pH),which, along with suitable climatic conditions, controlled the devel-opment of characteristic phytofacies in the swamp. Higher gelinitecontent in the Lower Miocene coals could be the result of higher mat-uration of the OM formed in calcium-rich depositional environment.

4.2. Bulk organic geochemical parameters

Organic carbon contents (Corg) vary in comparable ranges:30.72%–60.00%; 45.87–62.61 and 39.40%–60.70% for the Upper, Mid-dle and Lower Miocene samples respectively (Table 3). Significantnegative linear correlation between Corg and mineral matter content(r=0.72) observed for Upper Miocene lignites indicates that the differ-ences in Corg contents of the lignites are mainly controlled by varying

amounts of mineral matter. In difference to the Upper Miocene lignitesthere is no significant negative correlation between Corg and mineralmatter content for Middle and Lower Miocene coals. This result couldbe related to the possibility that part of the organic carbon is capturedby mineral-bituminous groundmass (MBG), which is observed in highcontent in samples 10, 17 and 18 (Table 2).

The yield of the soluble organicmatter (bitumen) for UpperMiocenelignites is relatively high and varies in a broad range from 3326 to98,666 ppm, in accordance with variation in Corg (Table 3). High bitu-men content has been related to the high proportion of biogenic anddiagenetic compounds. The yields of bitumen for Middle and LowerMiocene coals are relatively uniform, with the exception of one samplefrom Jelovac field (6; 61,794 ppm), and vary in range from 9162 to17,941 ppm. The soluble organic matter of all investigated samples is

image of Fig.�4

Table 3Values of bulk organic geochemical parameters.

Basin/deposit Coal field/mine No. Corgdb a (wt.%) Stotdbb (wt.%) Bitumen (ppm) Saturated HCc (wt.%) Aromatic HC (wt.%) Asphaltenes+NSO-compounds (wt.%)

Senje–Resavica basin Senje Mine 1 49.90 1.58 17,219 9.70 11.85 78.452 60.60 1.03 17,941 5.60 8.00 86.403 59.60 0.89 13,667 8.75 8.53 82.72

Jelovac 4 50.80 0.96 16,334 7.51 7.97 84.525 39.40 0.66 10,231 11.77 8.64 79.596 53.60 0.60 61,794 5.30 2.73 91.98

Strmosten 7 56.40 4.29 14,238 4.83 6.57 88.608 60.70 2.39 14,333 10.56 4.18 85.25

Soko Banja basin Soko 9 57.84 2.70 10,922 14.98 7.83 77.1910 45.87 1.64 9162 20.56 14.53 64.9111 49.32 1.55 12,587 4.87 5.86 89.2712 53.37 1.20 14,197 1.99 1.98 96.03

Bogovina basin East field 13 51.75 4.42 13,749 3.12 3.98 92.9014 50.73 3.68 13,097 3.27 4.53 92.2015 54.52 4.92 13,347 1.89 3.97 94.1416 53.05 5.35 12,297 4.99 5.96 89.05

Krepoljin basin Central field 17 51.73 1.16 13,086 2.98 3.99 93.0318 62.61 2.09 12,146 10.97 4.06 84.9719 49.81 1.98 11,507 18.89 5.13 75.9820 45.78 3.06 12,109 12.98 4.89 82.13

Kolubara basin D field 21 36.50 0.91 13,000 4.94 6.12 88.9522 39.80 1.18 28,904 1.76 4.30 93.9423 48.90 0.26 26,578 5.97 5.23 88.8024 55.70 0.28 21,918 3.11 3.98 92.9125 55.10 0.86 71,134 5.19 3.40 91.4126 47.20 0.47 27,645 5.18 4.66 90.1627 56.40 0.00 30,961 2.36 4.52 93.1228 56.00 0.43 31,316 2.48 4.42 93.1029 60.00 0.36 37,755 2.15 3.75 94.1030 55.60 0.73 33,333 2.42 4.82 92.7531 48.70 1.01 19,557 2.66 4.57 92.7832 54.70 1.58 21,979 4.11 3.67 92.2233 44.60 0.60 19,666 3.15 5.11 91.7434 40.20 0.66 18,273 2.46 4.75 92.79

Kostolac basin Drmno field 35 38.41 0.85 15,333 2.56 2.67 94.7636 49.13 3.42 12,292 5.71 3.60 90.6937 58.09 1.80 98,666 2.33 3.79 93.8738 55.12 1.58 11,628 2.63 3.58 93.7939 54.58 0.63 10,631 3.90 4.51 91.5940 N.D.d N.D. 79,400 13.22 2.17 84.6241 51.32 1.03 6645 3.25 4.20 92.5542 51.04 1.32 40,000 6.50 3.71 89.7943 56.67 0.90 18,272 6.90 3.40 89.7044 30.72 1.23 14,950 2.23 5.50 92.27

Kovin deposit A field 45 53.76 1.67 28,145 1.18 2.35 96.4746 60.89 0.82 21,385 1.24 2.17 96.5947 60.80 1.68 16,311 1.42 1.98 96.6048 29.19 1.63 20,490 1.75 2.05 96.2049 59.85 1.67 N.D. 1.42 2.49 96.0950 17.95 1.07 9075 2.92 2.50 94.5851 8.89 0.22 3326 5.24 2.80 91.96

a Corgdb — organic carbon content, dry basis.

b Stotdb — total sulfur content, dry basis.c HC — hydrocarbons.d N.D. — not determined.


mainly represented by asphaltenes and polar, NSO compounds (64.91–96.60%). The relative contents of saturated and aromatic hydrocarbonsin SOM are low (Table 3).

4.3. Molecular composition of the organic matter

4.3.1. General characteristicsThe main constituents of saturated fraction of the Upper Miocene

samples are diterpenoids, hopanoids and n-alkanes. Non-hopanoidtriterpenoids and steroids were identified in low amounts (Fig. 3a).The main components in aromatic fractions of Upper Miocene lignitesare diterpenoids and non-hopanoid triterpenoids. Other constituentsof aromatic fractions are aromatized hopanoids, long-chain acyclicalkan-2-ones, monoaromatic steroids, sesquiterpenoids and perylene(Fig. 4a). Saturated fraction of the Lower and Middle Miocene coals is

dominated by diterpenoids and n-alkanes. Hopanoids, triterpenoids(with the exception of few samples from Senje–Resavica and onesample from Soko Banja basin) and particularly steroids were identi-fied in lower amounts (Fig. 3b). The main components in aromaticfractions of Lower and Middle Miocene coals are diterpenoids andnon-hopanoid triterpenoids. Other constituents of aromatic fractionsare aromatized hopanoids, sesquiterpenoids and monoaromaticsteroids (Fig. 4b). High content of diterpenoids in both, saturatedand aromatic fraction of all investigated samples shows that themain sources of OM were gymnosperms (conifers). The presence ofnon-hopanoid triterpenoids particularly in the aromatic fraction impliescontribution of angiosperms to the coal organic matter (Fig. 4). Highamount of hopanoids and the presence of alkan-2-ones (Ortiz et al.,2011; Tuo and Li, 2005) in Upper Miocene lignite extracts imply pro-nounced microbial activity (Figs. 3a and 4a).


4.3.2. n-Alkanes and isoprenoidsConsidering low OM maturity, n-alkanes are abundant in the total

ion current (TIC) of Upper Miocene lignites saturated fraction(Fig. 3a), with the exception of 3 samples (39, 42 and 43). On thebasis of mass chromatogram, m/z 71 of saturated fraction (Fig. 5a),n-alkanes are identified in the range of C16–C33 or C18–C33, C16–C31or C16–C33 and C15–C33 for Kolubara, Kostolac and Kovin coals, respec-tively (Table 4). The n-alkane patterns of the Upper Miocene lignitesare dominated by long-chain homologues (C27–C31; Pwax notablyhigher than Paq; Table 4) maximizing at n-C27 or n-C29, and expressedodd over even predominance, indicating a significant contribution ofepicuticular waxes. The values of the CPI (carbon preference index)and OEP 2 (odd-even predominance) higher than 3 (Table 4) are inaccordance with the low rank of the lignites. Mid-chain n-alkanes(n-C21–C25) originate from vascular plants, microalgae, cyanobacteria,sphagnum and submerged aquatic macrophytes (Andersson et al.,2011; Ficken et al., 2000; Matsumoto et al., 1990; Nott et al., 2000)are present in lower amounts in comparison with long-chain odd ho-mologues. The slight to moderate predominance of odd over evencarbon-numbered n-alkanes in the mid-range n-alkanes (parameter,OEP 1; Table 4) suggests a microbial input, consistent with abundanthopanoids (Fig. 3a). Moreover, dominance of C23 and C25 n-alkane

Fig. 5. GC–MS mass chromatograms of n-alkanes, m/z 71 of Upper Miocene (

homologues in mid-chain range implies input of submerged aquaticmacrophytes, which contribution to the OM cannot be excluded.Their presence in lower concentrations was confirmed by previouspalynological investigation (Pantić and Dulić, 1993).

n-Alkanes are abundant in the total ion current (TIC) of saturatedfraction of Lower and Middle Miocene samples. They are the domi-nant compounds in saturated fraction of Bogovina East field coals.The high content of n-alkanes in the Bogovina samples is probablyclosely related to catalytic effects enhanced by montmorilloniteunder humid conditions (Huizinga et al., 1987; Tannenbaum et al.,1986). Based on mass chromatogram, m/z 71 of saturated fraction(Fig. 5b), n-alkanes are identified in the range of C15–C33, C13–C33,and C13–C31 for Bogovina, Soko Banja and Krepoljin coals, and C16–C31or C16–C33 for Senje–Resavica samples (Table 4). The n-alkane patternsof theMiddle and LowerMiocene coals are characterized by slight dom-inance of odd long-chain homologues C27–C31 (Pwax>Paq; n-C23/(n-C27+n-C31)b0.5), or by slight dominance of mid-chain homologuesC23 and C25 (PwaxbPaq; n-C23/(n-C27+n-C31)>0.5) (Table 4). Odd overeven predominance is obvious for all samples (parameters CPI, OEP 1and OEP 2; Table 4). High amount of odd n-C27–n-C31 alkanes indicatesa significant contribution of epicuticular waxes. As mentioned abovemid-chain n-alkanes (n-C21–C25) have various sources. Prevalence of

a) and Lower Miocene (b) coal. For peak assignments, see Fig. 3 legend.

image of Fig.�5

Table 4Values of parameters calculated from distributions and abundances of n-alkanes and isoprenoids.

Basin/deposit Coal field/mine No. n-Alkane range, C no. n-Alkane max. CPI23–33a CPI25–31b OEP 1c OEP 2d Paqe Pwaxf n-C23/(n-C27+n-C31)g Pr/Phh

Senje–Resavica basin Senje Mine 1 16–31 n-C25 2.01 2.27 1.40 2.00 0.52 0.48 0.64 1.192 16–31 n-C25 1.15 1.21 1.03 1.36 0.68 0.32 0.94 0.813 16–31 n-C27 1.65 1.88 1.27 2.23 0.60 0.40 0.59 0.91

Jelovac 4 16–31 n-C27 2.56 2.73 1.71 2.22 0.41 0.59 0.39 1.175 16–33 n-C25 2.72 2.68 2.18 2.41 0.44 0.56 0.56 1.176 16–31 n-C25 2.94 2.45 4.47 2.35 0.69 0.31 1.23 1.18

Strmosten 7 16–33 n-C29 2.49 2.87 1.53 2.36 0.22 0.78 0.24 0.818 16–31 n-C27 2.84 2.81 3.48 2.72 0.50 0.50 0.62 1.14

Soko Banja basin Soko 9 13–33 n-C25 2.04 2.15 1.54 1.72 0.52 0.48 1.06 1.0610 13–33 n-C23 2.94 3.03 2.41 2.38 0.59 0.41 1.52 1.3611 13–33 n-C29 3.23 3.92 1.50 3.63 0.26 0.74 0.26 1.0412 13–33 n-C31 2.68 4.77 1.05 5.08 0.43 0.57 0.38 0.50

Bogovina basin East field 13 15–33 n-C31 3.39 3.49 1.27 2.97 0.30 0.70 0.18 0.8214 15–33 n-C23 4.32 6.58 1.91 5.11 0.45 0.55 0.61 1.6115 15–33 n-C27 3.38 4.04 1.51 4.27 0.31 0.69 0.26 1.0316 15–33 n-C27 3.24 3.77 1.65 3.67 0.35 0.65 0.31 0.83

Krepoljin basin Central field 17 13–33 n-C25 1.45 1.43 1.56 1.26 0.48 0.52 1.16 1.7818 13–31 n-C17 1.84 1.34 2.15 1.12 0.81 0.19 6.03 1.9319 13–31 n-C25 1.88 2.11 1.42 1.92 0.52 0.48 0.81 0.6320 13–31 n-C25 1.63 1.61 1.39 1.41 0.59 0.41 0.98 1.39

Kolubara basin D field 21 16–33 n-C29 3.87 3.71 2.01 2.93 0.29 0.76 0.18 N.D.22 18–33 n-C29 5.45 4.88 2.16 3.24 0.14 0.88 0.07 N.D.23 16–33 n-C29 6.02 5.50 2.09 3.67 0.13 0.89 0.08 N.D.24 18–33 n-C29 9.68 8.85 2.27 5.96 0.07 0.94 0.03 N.D.25 18–33 n-C29 6.79 6.35 2.06 3.74 0.06 0.95 0.03 N.D.26 18–33 n-C29 6.15 6.36 1.82 4.52 0.10 0.92 0.06 N.D.27 18–33 n-C29 9.31 10.22 2.21 6.45 0.04 0.97 0.02 N.D.28 18–33 n-C29 7.14 6.63 1.89 4.47 0.07 0.94 0.03 N.D.29 18–33 n-C29 7.47 6.70 2.09 4.59 0.05 0.95 0.02 N.D.30 18–33 n-C29 5.09 4.37 1.50 3.31 0.08 0.93 0.02 N.D.31 18–33 n-C29 5.17 5.31 1.57 4.85 0.18 0.87 0.04 N.D.32 18–33 n-C29 4.62 4.82 1.71 4.42 0.22 0.85 0.07 N.D.33 16–33 n-C29 3.33 3.40 1.91 2.45 0.16 0.88 0.10 N.D.34 16–33 n-C29 3.36 3.49 1.78 3.47 0.32 0.78 0.16 N.D.

Kostolac basin Drmno field 35 16–33 n-C29 3.23 4.10 0.89 3.58 0.28 0.80 0.14 0.2736 16–31 n-C29 5.24 5.00 1.65 4.57 0.23 0.83 0.10 0.3837 16–33 n-C29 4.37 4.55 0.94 3.36 0.22 0.83 0.14 1.2038 16–33 n-C29 5.08 5.61 0.92 5.13 0.17 0.88 0.06 1.2639 16–33 n-C29 4.36 4.51 1.65 4.39 0.18 0.86 0.08 0.4140 N.D.i N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D.41 16–31 n-C29 4.97 5.39 1.40 6.30 0.15 0.90 0.05 0.0842 16–33 n-C29 3.21 3.73 1.25 3.75 0.30 0.78 0.12 N.D.43 16–33 n-C29 3.92 4.17 1.89 3.24 0.22 0.82 0.19 N.D.44 16–31 n-C29 5.61 5.04 5.50 4.52 0.51 0.59 0.39 0.62

Kovin deposit A field 45 15–33 n-C27 1.66 1.85 1.17 2.14 0.50 0.50 0.38 0.9846 15–33 n-C27 1.26 1.34 1.16 1.68 0.36 0.64 0.19 0.7447 15–33 n-C29 3.71 4.48 1.70 3.54 0.27 0.73 0.26 1.9248 15–33 n-C29 3.37 3.36 1.80 3.02 0.17 0.83 0.10 1.1149 15–33 n-C29 4.85 4.11 1.74 3.62 0.17 0.83 0.10 N.D.50 15–33 n-C29 4.67 5.33 1.14 5.14 0.14 0.86 0.07 1.0451 15–33 n-C29 2.87 2.87 1.40 2.61 0.17 0.83 0.11 1.16

Standard deviation / / 1.94 1.89 0.81 1.33 0.19 0.20 0.89 0.44

a CPI23–33 — carbon preference index determined for full distribution of n-alkanes C23–C33, CPI23–33=1/2 [Σodd(n-C23−n-C33)/Σeven(n-C22−n-C32)+Σodd(n-C23−n-C33)/Σeven(n-C24−n-C34)] (Bray and Evans, 1961).

b CPI25–31=1/2 [(n-C25+2 n-C27+2 n-C29+n-C31)/(n-C26+n-C28+n-C30)] (Marynowski and Zatoń, 2010).c OEP 1=1/4 [(n-C21+6 n-C23+n-C25)/(n-C22+n-C24)] (Scalan and Smith, 1970).d OEP 2=1/4 [(n-C25+6 n-C27+n-C29)/(n-C26+n-C28)] (Scalan and Smith, 1970).e Paq=(n-C23+n-C25)/(n-C23+n-C25+n-C29+n-C31) (Ficken et al., 2000).f Pwax=(n-C27+n-C29+n-C31)/(n-C23+n-C25+n-C27+n-C29+n-C31) (Zheng et al., 2007).g Andersson et al. (2011).h Pr/Ph=Pristane/Phytane.i N.D. — not determined.


C23 and C25 homologues in n-alkane distribution of significant numberof Lower and Middle Miocene coals (Table 4) implies contribution ofsubmerged aquatic plants.

In all investigated samples short chain n-alkanes (≤ C20) are presentin low quantities (Fig. 5). The uniform distribution of low molecularweights n-alkanes in several Lower Miocene coals, at high CPI values(Table 4), may be explained by maturation changes rather than algalinput.

Isoprenoids pristane (Pr) and phytane (Ph) are present in lowamounts in extracts of Upper Miocene lignites (Kostolac and Kovin)

or completely absent (Kolubara basin) (Figs. 3a and 5a; Table 4).Low concentration of pristane and phytane is often reported in imma-ture organic matter (Dzou et al., 1995; Hughes et al., 1995; Vu et al.,2009). The Pr/Ph ratio is widely used as indicator for Eh settings of thedepositional environment (Didyk et al., 1978). However, this parameteris also known to be affected by maturation (Peters et al., 2005) and bydifferences in the precursors for acyclic isoprenoids, i.e. bacterial origin(tenHaven et al., 1987; VolkmanandMaxwell, 1986), and the formationof pristane from tocopherols or chromanes (Goossens et al., 1984). Forthis lignite sample set, the influence ofmaturity on the pristane/phytane


ratio can be ruled out. In addition to that, the lowmaturity of the ligniteprobably argues against the formation of the pristane from tocopherols(Goossens et al., 1984). Therefore, the Pr/Ph ratio varying between0.08–1.26 (Kostolac) and 0.74–1.92 (Kovin) (Table 4) may be consid-ered as an indicator of changing of Eh settings from anoxic to slightlyoxic during peat deposition. This result is consistent with variations inTPI and GI parameters (Table 2).

Lower and Middle Miocene coals contain higher amounts of pris-tane and phytane, than Upper Miocene lignites, in accordance withhigher maturity of OM. Pr/Ph ratio ranges between 0.50 and 1.61and shows variable trend with depth in all coal fields (Table 4).Based on the maceral composition (Table 2), it could be concludedthat pristane and phytane most probably originated from chlorophyllin land plant-dominated organic matter. Therefore, it could be sup-posed that values of Pr/Ph ratio imply changing of Eh settings fromanoxic to slightly oxic during sedimentation.

The increase in Eh of the environment is often associated with adecrease in water level and in some cases drainage of peat bogs. Thiscould cause an increase in the amount of inertinite macerals due tothe intensification of thermal oxidation processes and hence positivecorrelation with pristane/phytane ratio. In the coal petrological litera-ture, there is an extensive discussion whether inertinite macerals canbe used as indicators of dry and oxidizing conditions (Scott, 1989,2000). This can be explained by the fact that a lot of the thermallyaltered macerals in the peat and coal can be imported into the peatbogs throughwater or air transport. In our case, negative linear correla-tion between pristane/phytane and the quantity of inertinite macerals(r=0.51 for Upper Miocene lignites and r=0.49 for Lower and MiddleMiocene coals) is observed, whichmay suggest a predominantly alloch-thonous origin of the latter.

4.3.3. Sesquiterpenoids, diterpenoids and triterpenoids with non-hopanoidskeleton

In all investigated samples, aromatic sesquiterpenoids areobserved in low quantities (Fig. 4). Cadalene predominatesover isocadalene, calamenene and 5,6,7,8-tetrahydrocadalene.Other sesquiterpenoid constituents of coal extracts are cupareneand cadina-1(10),6,8-triene, whereas dihydro-ar-curcumene,1-methyl, 7-isopropyltetrahydronaphthalene and 1-methyl,7-isopropylnaphthalene (eudalene) were identified only in severalsamples, independent of age. However, due to their occurrence in theresins of conifers (Otto and Simoneit, 2002; Otto et al., 1997) as wellas in dammar resin (van Aarssen et al., 1990), which originates fromDipterocarpaceae and Cornaceae (angiosperms), sesquiterpenoids arenot often used for an unambiguous determination of the precursorplant community. Considering that during previous investigation resi-dues of dammar resinswere not identified in coals and surrounded sed-iments, it may be assumed that aromatic sesquiterpenoids in SerbianMiocene coals originated fromgymnosperms. The presence of cuparenein aromatic fractions of all investigated samples clearly indicates contri-bution of Cupressaceae, a family of gymnosperms to precursor OM(Haberer et al., 2006; Otto and Wilde, 2001). This result is consistentwith palynological data.

Diterpenoids are main constituents of both, saturated and aromat-ic fractions, indicating significant contribution of gymnosperms toprecursor OM. Pimarane and particularly 16α(H)-phyllocladane aredominant by far in the saturated fractions of all investigated samples.Other diterpenoid type constituents of saturated fraction, present innotably lower amount than 16α(H)-phyllocladane and pimarane are:isopimarane, norpimarane, norisopimarane, norabietane, beyerane,16α(H)-kaurane, 16β(H)-phyllocladane, isophyllocladene, and abietane(Fig. 3) and in the case of Kolubara lignites abieta-8,11,13-trien-7-one.Beyerane and 16α(H)-kaurane were identified only in Upper Mio-cene lignites. Several Lower and Middle Miocene coal extracts(Soko Banja and Krepoljin basins) have elevated contents of abietaneand norpimarane. A high amount of 16α(H)-phyllocladane indicates

that the SerbianMiocene coal forming plants could be related to the co-nifer families Taxodiaceae, Podocarpaceae, Cupressaceae, Araucariaceaeand Phyllocladaceae, while the high abundance of pimarane suggestsPinaceae, Taxodiaceae and Cupressaceae (Otto and Wilde, 2001; Ottoet al., 1997; Stefanova et al., 2002, 2005). Lower and Middle Miocenecoals show higher values of pimarane/16α(H)-phyllocladane ratiothan Upper Miocene lignites (Table 5). This result could imply higherimpact of Pinaceae to precursor biomass, consistent with floral assem-blage and palynological data.

The aromatic diterpenoids of Upper Miocene lignites comprisenorabieta-6,8,11,13-tetraene, norabieta-8,11,13-trienes, 2-methyl, 1-(4′-methylpentyl), 6-isopropylnaphthalene, 16,17-bisnordehydroabietane,dehydroabietane, simonellite, retene, sempervirane, totarane,hibaene, ferruginol, 6,7-dehydroferruginol, 16,17-bisnorsimonelliteand 2-methylretene, whereas 12-hydroxysimonellite was identified inseveral samples from Kostolac basin and Kovin deposit. Simonellite isa predominant aromatic diterpenoid, with the exception of somesamples from Kolubara and Kostolac where the most prominent isdehydroabietane (Fig. 4a). Lower andMiddle Miocene coals express al-most identical composition of aromatic diterpenoids as Upper Miocenelignites, with domination of simonellite or retene (Fig. 4b). The main dif-ferences are manifested by the presence of 1,7-dimethylphenanthrene(pimanthrene) in almost all Lower and Middle Miocene coals, and bythe absence of hibaene in samples from Bogovina and Soko Banja basins.Higher amount of triaromatic diterpenoids (retene and pimanthrene) inLower Miocene samples could be attributed to thermal alteration of OM.

Almost all of aromatic diterpenoids are nonspecific conifer markers,because they are the diagenetic products of a great variety of abietane-type precursors that are common constituents of all conifers exceptPhyllocladaceae (Otto and Simoneit, 2001; Otto et al., 1997; Stefanovaet al., 2005). In contrast, the presence of totarane, hibaene, ferruginoland 6,7-dehydroferruginol in the aromatic fraction clearly indicatesthe contribution of Cupressaceae, Taxodiaceae, Podocarpaceae andAraucariaceae to precursor biomass (Otto and Wilde, 2001), consistentwith observation derived from analysis of saturated diterpenoids.

The non-hopanoid triterpenoids are present in relatively lowamount in saturated fraction of Upper Miocene lignites and consistof des-A-olean-enes, des-A-urs-enes and des-A-lupane, whereasnon-degraded oleanenes (olean-12-ene and olean-13,18-ene) areidentified in only 6 samples from Kolubara and Kostolac basins(Fig. 3a). Predominance of des-A-degraded triterpenoids impliesmicro-bial activity, consistent with relatively abundant hopanoids (Figs. 3aand 8a). Abundance of non-hopanoid triterpenoids is also very low insaturated fraction of Middle Miocene lignites and Lower Miocenecoals, with the exception of 3 samples from Senje–Resavica basin and1 sample from Soko field (samples 1, 2, 4 and 11; Table 5). However,composition of non-hopanoid triterpenoids in extracts of Middle andLower Miocene coals notably differs from those observed for UpperMiocene lignites.Whereas saturated fractions of UpperMiocene lignitesalmost exclusively contain des-A-degraded triterpenoids, compositionof these biomarkers in extracts of Middle and Lower Miocene samplesis dominated by non-degraded triterpenoids. Oleanenes (olean-12-ene,olean-13,18-ene and olean-18-ene) were identified in relatively highamount in coal extracts from Senje–Resavica basin. Moreover, thesesamples are characterized by the presence of urs-12-ene, 24-nor-12-,24-nor-13,18- and 24-nor-18-oleanenes, oleana-diene, as well asdes-A-degraded triterpenoids (Fig. 3b). Other Lower, and MiddleMiocene samples, shownotably scarcer composition of these biomarkerswhich consist of only three compounds: olean-12-ene, urs-12-ene(absent in Bogovina coals) and des-A-lupane.

Although the non-hopanoid triterpenoids represent aminor portionof saturated fraction, these compounds are more abundant in aromaticfraction of almost all coals (exceptions are samples 5, 6, Senje–Resavicabasin; 9, 10, 12, Soko Banja basin; and 37–42, Kostolac basin) (Fig. 4;Table 5). This result shows that angiosperms also contributed to the or-ganic matter. Higher abundance of aromatized in comparison to

Table 5Values of parameters calculated from distributions and abundances of diterpenoids and non-hopanoid triterpenoids.

Basin/deposit Coal field/mine No. Pimarane/16α(H)-phyllocladane T2/T1 a Di/(Di+Tri)sat b Di/(Di+Tri)arom c 1-Ar ring/(1-+2-+3-Ar rings)diterpenoids d

Senje–Resavica basin Senje Mine 1 1.10 0.12 0.857 0.59 0.212 1.16 0.07 0.691 0.25 0.263 1.83 0.12 0.912 0.56 0.28

Jelovac 4 0.88 0.09 0.852 0.53 0.465 0.37 0.21 0.975 0.95 0.356 1.56 0.21 0.996 0.95 0.36

Strmosten 7 0.58 0.18 0.960 0.70 0.238 0.85 0.42 0.999 0.75 0.38

Soko Banja basin Soko 9 0.80 0.26 0.994 0.97 0.1910 0.09 0.28 0.989 0.99 0.1511 0.02 0.25 0.652 0.26 0.1412 0.67 0.23 0.983 0.92 0.13

Bogovina basin East field 13 1.01 N.D.e 0.940 N.D. N.D.14 0.96 0.12 0.981 0.51 0.1215 0.92 0.15 0.960 0.64 0.1716 0.99 0.19 0.978 0.72 0.14

Krepoljin basin Central field 17 0.93 0.16 0.979 0.58 0.3518 0.90 0.14 1.000 0.80 0.3219 0.88 0.10 0.946 0.59 0.3320 0.95 0.11 0.991 0.69 0.35

Kolubara basin D field 21 1.51 0.12 0.959 0.34 0.4122 0.13 0.37 0.974 0.45 0.3423 0.14 0.05 0.998 0.47 0.3824 4.44 0.09 1.000 0.41 0.3625 0.03 0.05 1.000 0.83 0.2726 2.67 0.10 1.000 0.68 0.3227 0.44 N.D. 1.000 N.D. N.D.28 1.05 0.04 1.000 0.55 0.4329 0.78 0.05 0.998 0.67 0.3130 1.05 0.02 0.976 0.52 0.3131 0.08 0.05 0.969 0.65 0.4632 0.03 0.06 0.997 0.52 0.3833 1.23 0.00 1.000 0.76 0.6634 0.14 0.11 0.975 0.70 0.26

Kostolac basin Drmno field 35 0.03 0.20 0.991 0.66 0.3936 0.33 0.78 0.995 0.84 0.3837 0.03 N.D. 1.000 0.99 0.2838 0.47 N.D. 0.978 0.95 0.6839 0.11 N.D. 1.000 0.97 0.3440 2.20 N.D. 1.000 0.99 0.6041 0.55 N.D. 0.990 0.96 0.5142 3.22 N.D. 0.999 0.99 0.4843 0.46 0.27 0.998 0.88 0.2844 0.13 0.08 0.809 0.62 0.14

Kovin deposit A field 45 0.21 0.40 0.985 0.61 0.3246 0.69 0.34 0.965 0.76 0.6347 0.12 1.09 0.966 0.81 0.4448 0.06 3.66 0.980 0.43 0.4349 0.40 1.04 1.000 0.83 0.3950 0.13 0.30 0.986 0.55 0.4351 0.23 0.94 0.944 0.66 0.49

Standard deviation 0.86 0.58 0.071 0.20 0.14

a T2/T1=(pentamethyloctahydrochrysene+3,4,7,12a-tetramethyl-1,2,3,4,4a,11,12,12a-octahydrochrysene+3,3,7,12a-tetramethyl-1,2,3,4,4a,11,12,12a-octahydrochrysene+3,4,7-trimethyl-1,2,3,4-tetrahydrochrysene+3,3,7-trimethyl-1,2,3,4-tetrahydrochrysene)/(24,25-dinoroleana-1,3,5(10),12,14-pentaene+24,25-dinoroleana-1,3,5(10),12-tetraene+24,25-dinorursa-1,3,5(10),12-tetraene+39-24,25-dinorlupa-1,3,5(10)-triene; + 1,2,4a,9-tetramethyl-1,2,3,4,4a, 5,6,14b-octahydropicene+2,2,4a,9-tetramethyl-1,2,3,4,4a,5,6,14b-octahydropicene+1,2,9-trimethyl-1,2,3,4-tetrahydropicene+2,2,9-trimethyl-1,2,3,4-tetrahydropicene), calculated from the TIC of aromatic fraction.

b Di/(Di+Tri)sat=Σditerpenoids/(Σditerpenoids+Σtriterpenoids), calculated from the TIC of saturated fraction (Bechtel et al., 2002, 2003), Σditerpenoids=(16α(H)-phyllocladane+pimarane+beyerane+isopimarane+norpimarane+norisopimarane+16α(H)-kaurane+16β(H)-phyllocladane+isophyllocladene+norabietane+abietane), Σtriterpenoids=(olean-12-ene+olean-13(18)-ene+olean-18-ene+urs-12-ene+24-norolean-13(18)-ene+24-norolean-12-ene+24-norurs-12-ene+oleanadiene+oleanene+des-A-olean-12-ene+des--A-olean-13(18)-ene+des-A-olean-18-ene+des-A-urs-13(18)-ene+des-A-urs-12-ene+des-A-lupane).

c Di/(Di+Tri)arom=Σaromatic diterpenoids/(Σaromatic diterpenoids+Σaromatic triterpenoids), calculated from the TIC of aromatic fraction (Haberer et al., 2006; Nakamura et al.,2010), Σaromatic diterpenoids=(norabietadiene+isopimaradiene+18-norabieta-6,8,11,13-tetraene+19-norabieta-8,11,13-triene+18-norabieta-8,11,13-triene+2-methyl, 1-(4′-methylpentyl), 6-isopropylnaphthalene+dehydroabietane+simonellite+retene+sempervirane+totarane+Hibaene+ferruginol+6,7-dehydroferruginol+2-methylretene+1,2,3,4-tetrahydroretene+16,17-bisnordehydroabietane+16,17-bisnorsimonellite), Σaromatic triterpenoids=(24,25-dinoroleana-1,3,5(10),12-tetraene+24,25-dinoroleana-1,3,5(10),12,14-pentaene+24,25-dinorursa-1,3,5(10),12-tetraene+24,25-dinorlupa-1,3,5(10)-triene+pentamethyloctahydrochrysene+3,4,7,12a-tetramethyl-1,2,3,4,4a,11,12,12a-octahydrochrysene+3,3,7,12a-tetramethyl-1,2,3,4,4a,11,12,12a-octahydrochrysene+3,4,7-trimethyl-1,2,3,4-tetrahydrochrysene+3,3,7-trimethyl-1,2,3,4-tetrahydrochrysene+1,2,4a,9-tetramethyl-1,2,3,4,4a,5,6,14b-octahydropicene+2,2,4a,9-tetramethyl-1,2,3,4,4a,5,6,14b-octahydropicene+1,2,9-trimethyl-1,2,3,4-tetrahydropicene+2,2,9-trimethyl-1,2,3,4-tetrahydropicene).

d 1-Ar ring diterpenoids=(18-norabieta-6,8,11,13-tetraene+19-norabieta-8,11,13-triene+18-norabieta-8,11,13-triene+dehydroabietane), 2-Ar ring diterpenoids=(2-methyl, 1-(4′-methylpentyl), 6-isopropylnaphthalene+simonellite+tetrahydroretene), 3-Ar ring diterpenoids=(retene+2-methylretene), calculated from the TIC of aromatic fraction (Habereret al., 2006).

e N.D. — not determined.



non-aromatized angiosperm triterpenoids indicates significant aro-matization of triterpenoids during diagenesis. The same result thataliphatic angiosperm-derived triterpenoids are more easily alteredto aromatic derivatives, in comparison with gymnosperm-derivedditerpenoids, resulting in the selective loss of such aliphatic com-pounds was also reported by Kalkreuth et al. (1998) and Nakamuraet al. (2010).

The following aromatic triterpenoids occur in the aromatic hydrocar-bon fractions: ring-A-monoaromatic 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), pentamethyl-octahydrochrysene, tetra-methyloctahydrochrysenes, trimethyltetrahydrochrysenes, tetra-methyloctahydropicenes and trimethyltetrahydropicenes (Fig. 4).Pentacyclic triterpenoids are notably more abundant than tetracyclicchrysene derivatives in all samples (Parameter T2/T1; Table 5). Excep-tion are samples 37–42 fromKostolac basin, which contain low amountof aromatic triterpenoids represented exclusively by des-A-degradedaromatic compounds, consistent with distribution of these biomarkersin saturated fraction (Table 5).

Due to enhanced aromatization of angiosperm derived triterpenoids,the ratio of diterpenoids to sum of di- and terpenoids in saturated frac-tion, Di/(Di+Tri)sat (Bechtel et al., 2002, 2003) shows extremely highand uniform values (above 0.95, with the exception of few samples 1,2, 4, 11 and 44) indicating that conifers almost exclusively contributeto coal formation (Table 5). Therefore, in order to estimate the contribu-tion of gymnosperm and angiosperm vegetation in the ancient peatbogs we have used the ratio of diterpenoid and angiosperm-derivedtriterpenoid aromatic biomarkers (Di/(Di+Tri)arom; Haberer et al.,2006; Nakamura et al., 2010; Table 5). Lower andMiddle Miocene sam-ples show statistically significant positive exponential correlation be-tween Di/(Di+Tri)sat and Di/(Di+Tri)arom (Fig. 6a), whereas forUpper Miocene lignites no correlation is observed, most probably dueto pronounced aromatization of triterpenoids. Moreover, a positive log-arithmic relationship exists between the Tissue Preservation Index(TPI) and Di/(Di+Tri)arom ratios of the Lower and Middle Miocenecoals (Fig. 6b), suggesting that TPI is partly controlled by the input ofresin-rich, decay-resistant conifers. On the other hand, the absence ofcorrelation between TPI and Di/(Di+Tri)arom for Upper Miocenecoals implies that tissue preservation is also dependent from the Eh,pH and climatic settings. Values of Di/(Di+Tri)arom ratio indicate thesignificant contribution of angiosperms to OM of the samples 2 and 11from Senje and Soko mines and almost all Kolubara lignites. Moderate

Fig. 6. Correlations Di/(Di+Tri)arom vs. Di/(Di+Tri)sat (a) and Di/(Di+Tri)arom vs.TPI (b) for Lower and Middle Miocene coals.

contribution of angiosperms to OM is observed in Strmosten, Bogovina,Krepoljin, Kovin and 4 Kostolac samples, whereas analysis of aromaticterpenoids reveals negligible angiosperms input to OM of coals fromSoko and Jelovac, as well as in 6 samples from Kostolac basin (Table 5).Variations in Di/(Di+Tri)arom with depth (Table 5) imply changes inpaleoenvironment (water level, i.e. Eh settings) in the mire during coalformation, consistent with conclusions derived from TPI, GI and Pr/Phratio (Tables 2 and 4).

The 1-Ar ring/(1-+2-+3-Ar rings) diterpenoid ratio is used foran assessment of the degree of aromatization (Haberer et al., 2006).Upper Miocene lignites show relatively uniform values of this param-eter, with the exception of few samples. The same observation is re-lated to Middle and Lower Miocene samples within the coal fields(Table 5). Generally lower values of 1-Ar ring/(1-+2-+3-Ar rings)diterpenoid ratio, indicating more pronounced aromatization of OMof Lower Miocene coals than Upper Miocene lignites could partly beattributed to thermal alteration of organic matter.

4.3.4. Steroids and hopanoidsThe analysis of the aliphatic fraction reveals low contents of steroids

in all investigated coals (Fig. 3). Steroid biomarkers of Upper Miocenelignites (based on mass chromatogram, m/z 215 of saturated fraction;Fig. 7a) consist predominantly of C29 Δ4-, Δ2- and Δ5-Sterenes. C28-Sterenes (Δ4-,Δ2- andΔ5) are identified in low amounts, whereas corre-sponding C27 homologues are presented in Kovin and several samplesfrom Kostolac basin. The marked predominance of C29 sterenes

Fig. 7. GC–MS mass chromatogram of sterenes, m/z 215 of Upper Miocene coal (a) andGC–MS mass chromatogram of steranes, m/z 217 of Lower Miocene coal (b). Δ desig-nates position of double bond in sterenes; αα designate configurations at C14 andC17 in steranes; (R) designates configuration at C20 in steranes.

image of Fig.�6

image of Fig.�7


(Fig. 7a; Table 6) clearly indicates peat formation from terrigenousplants.

Steroid distribution of immature Upper Miocene lignites is represent-ed by unsaturated sterenes, while in extracts of Lower and Middle Mio-cene coals saturated steranes are identified (Fig. 7b). On the one hand,this result can be attributed to higher OM maturity. However, influenceof more reductive environment, particularly in the case of less matureMiddle Miocene lignites cannot be excluded. Based on mass chromato-gram,m/z217of saturated fraction, the composition of steroid biomarkersin allMiddle and LowerMiocene samples is characterized by the presenceof C27–C29 14α(H)17α(H)20(R)-steranes and C29 diaster-13(17)-ene(24-ethyldiacholest-13(17)-ene) (Fig. 7b), whereas C29 14α(H)17α(H)20(S)-sterane is identified in several Lower Miocene samples (Bogovinabasin). Coals from Senje–Resavica basin represent exception, containingextremely low content of C27–C2914α(H)17α(H)20(R)-steranes. Distri-bution of regular C27–C29 14α(H)17α(H)20(R)-steranes shows strongpredominance of C29 homologue, indicating a terrigenous contribution.Relatively high amount of C28 and presence of C27 regular sterane(Table 6) particularly in SOM of Middle Miocene Krepoljin coals clearlyimply contribution of aquatic organisms, consistent with the abovediscussed Paq parameter (Table 4). The presence of rearranged sterene,C29 diaster-13(17)-ene ismost probably a result of diagenetic transforma-tion, catalyzed by clay minerals (Wang and Simoneit, 1990), which arepresent in high amounts in mineral matter of all samples.

Hopanoids are more abundant than steroid biomarkers in coal ex-tracts (Ster/Hop ratiob0.25 andb0.90 for Upper, andMiddle/LowerMio-cene coals, respectively; Table 6). Moreover, hopanoid biomarkersrepresent the most abundant compounds in TIC of saturated fraction ofseveral Kolubara samples. These results indicate a bacteria-influenced fa-cies and argue for the role of microorganisms in degradation of planttissue.

Based on mass chromatogram, m/z 191 of saturated fraction, thehopane composition is characterized by the presence of 17α(H)21β(H),17β(H)21α(H) and 17β(H)21β(H) compounds with 27 and 29–31 car-bon atoms (Fig. 8). Other hopanoid type constituents of saturated fractionare C27 hop-13(18)-ene, C27 hop-17(21)-ene, C30 neohop-13(18)-ene,C30 hop-17(21)-ene and C32 17α(H)21β(H)22(R)-hopane. Typical char-acteristic of Kolubara and Kostolac lignites is the presence of C27hopan-21-one (Fig. 8a). Moreover several Kolubara samples also containhopanoid ketone, C30 hop-17(21)-en-20-one.

C31 17α(H)21β(H)22(R)-hopane dominates by far in hopane dis-tribution of Kolubara lignites. This compound is also the most prom-inent in hopane distribution of several coals from Senje–Resavicabasin (particularly Senje Mine), 4 samples from Kovin deposit and 3samples from Kostolac basin (Table 7), suggesting that these sampleswere most probably deposited under relatively acidic and oxic condi-tions (van Dorselaer et al., 1975; Vu et al., 2009). The result is in agree-ment with low sulfur content (Table 3) and values of Di/(Di+Tri)aromratio (Table 5), considering that higher contribution of angiosperms ob-served in Kolubara and Senje extracts is often related to peatification indryer andmore oxic environment. The dominant hopane in all the otherLower and Middle Miocene coals, almost all Kostolac lignites and therest of Kovin samples is C2717β(H)-hopane (Table 7).

The presence of unsaturated hopenes and domination ofββ-isomersin the range of C27, and C29–C30 overαβ-hopanes in UpperMiocene lig-nites confirm an immature stage of the organic matter (Fig. 8a). On theother hand, very similar hopanoid distributions and comparable valuesof C30ββ-hopane/C30(ββ+αβ)-hopanes ratio in more mature LowerMiocene coals, comparing to Upper Miocene lignites (Fig. 8b; Table 7),indicate sedimentation in more reductive environment (Marynowskiand Zatoń, 2010). Generally higher values of C30 hop-17(21)-ene/C30αβ-hopane ratio (Table 7) for Lower and Middle Miocene samples(Bogovina, Soko, Jelovac, Krepoljin) support this assumption.

The C2717β(H)-hopane and the C2917β(H)21β(H) hopane domi-nate the distribution of C27–C31 ββ-homologues in almost all samples(Fig. 8; Table 7). Predominance of the short-chain homologues can

be interpreted as indicative of rather oxidizing paleoconditions.However, it may also signify that the precursor hopanoid lipidswere functionalized at position 29 such as aminobacteriohopanepentolabundant in methanotrophic bacteria (e.g.,Methylococcus capsulatus orMethylomonas methanica) (Neunlist and Rohmer, 1985). Assumption isconsistent with detection of coal-bed methane released during coalmining in Soko and Strmostenfields. This particular hopanoid, function-alized at position 29, cannot, however, be taken as exclusive precursorof C29 hopanes, considering the high sensitivity of side chains from bio-logic hopanoids (Burhan et al., 2002).

The identification of D-ringmonoaromatic hopane, 7-methyl, 3′-ethyl,1,2-cyclopentanochrysene and 4-methyl, 24-ethyl, 19-norcholesta-1,3,5(10)-triene in aromatic fraction of almost all investigated samples(Fig. 4) suggests partial aromatization of hopanoids and steroidsduring diagenesis, in accordance with aromatization of diterpenoidsand particularly triterpenoids.

4.4. Comparison of biomarker composition in Serbian Miocene coals andrelation to paleoclimate

Presented results suggest relatively uniform/similar biomarkerpatterns in Serbian coals from the Lower to the Upper Miocene age.The main coal extracts' constituents are diterpenoids, n-alkanes,triterpenoids and hopanoids, while contents of steroids and aromaticsesquiterpenoids are low. Despite differences in OM maturity be-tween Lower and Upper Miocene coals, all mentioned biomarkerclasses have relatively similar compositions. Sharp predominanceof 16α(H)-phyllocladane and pimarane in saturated fraction is ob-served, whereas in the majority of the samples simonellite is themost abundant diterpenoid in aromatic fraction. Typical feature ofn-alkane distribution is high amount of odd n-C27–n-C31 homo-logues. Composition of hopanoid biomarkers is represented by thesame compounds and characterized by abundant ββ-isomers in therange of C27, C29–C31 and C31αβ(R)-hopane. Pronounced aromatizationof non-hopanoid triterpenoids in comparison to diterpenoids is ob-served in all samples in which triterpenoids are present in enhancedamounts. Cadalene is most abundant aromatic sesquiterpenoid in allcoal extracts, whereas distributions of steroid biomarkers show strongdominance of C29 homologues. These results do not surprise, consider-ing that recent paleoclimate investigations indicate relatively uniform,warm and humid climate at the territory of Serbia during whole Mio-cene (Ivanov et al., 2011; Utescher et al., 2007).

The main differences between Upper Miocene coals on one hand,and Lower and Middle Miocene coals on the other, are expressed bylower relative abundance of C31αβ(R)-hopane (with the exceptionof several samples from Senje–Resavica basin) and higher sulfur content,GI, Paq, n-C23/(n-C27+n-C31), as well as pimarane/16α(H)-phyllocladaneratio of the latter. Moreover, these differences in composition of OM aresupported by differences in mineral matter composition, which arereflected by higher content of carbonates and pyrite in Lower/MiddleMiocene coals. These results indicate that Lower and Middle Miocenecoalswere formed, in comparison toUpperMiocene lignites, under slight-ly alkaline and more reducing conditions, which resulted from higherwater level.

As mentioned above, the Oligocene to late Miocene paleoclimate inSerbia has recently been reconstructed (Ivanov et al., 2011; Utescheret al., 2007). In order to check the influence of these slight paleoclimatechanges on biomarker composition, mean values of biomarker parame-terswith the greatest variability between coals of different ages are corre-lated with values of mean annual temperature (MAT), cold month meantemperature (CMM), warm month mean temperature (WMM) andmean annual precipitation (MAP) for Lower, Middle and Upper Miocene(Fig. 9). Fig. 9 shows good correlation betweenmean values of biomarkerand paleoclimate parameters. Therefore it could be assumed that varia-tions in pimarane/16α(H)-phyllocladane, Paq, n-C23/(n-C27+n-C31) andrelative content of C31αβ(R)-hopane at least to some extent, reflect

Table 6Values of parameters calculated from distributions and abundances of steroids.

Basin/deposit Coal field/mine No. % ΔC27a % ΔC28

b % ΔC29c % C27

d % C28e % C29

f Ster/Hopg

Senje–Resavica basin Senje Mine 1 N.D.h N.D. N.D. 0.062 N.D. N.D. N.D. 0.023 N.D. N.D. N.D. 0.00

Jelovac 4 N.D. N.D. N.D. 0.145 N.D. N.D. N.D. 0.076 N.D. N.D. N.D. 0.00

Strmosten 7 0.90 7.31 91.79 0.908 N.D. N.D. N.D. 0.00

Soko Banja basin Soko 9 0.59 15.88 83.53 0.6810 15.58 24.68 59.74 0.5811 18.56 8.24 73.20 0.5712 12.57 11.51 75.92 0.49

Bogovina basin East field 13 7.32 18.53 74.15 0.3414 18.55 11.31 70.14 0.2115 5.45 20.29 74.26 0.6316 5.26 15.79 78.95 0.22

Krepoljin basin Central field 17 11.59 33.20 55.21 0.2518 23.95 26.95 49.10 0.4119 30.01 24.97 45.02 0.5520 23.81 28.57 47.62 0.35

Kolubara basin D field 21 0.00 9.19 90.81 0.225422 0.00 0.00 100.00 0.003223 0.00 12.41 87.59 0.005224 N.D. N.D. N.D. 0.000025 0.00 0.00 100.00 0.006726 0.00 0.00 100.00 0.002927 N.D. N.D. N.D. N.D.28 N.D. N.D. N.D. N.D.29 0.00 0.00 100.00 0.000830 0.00 5.22 94.78 0.003131 0.00 0.00 100.00 0.002832 0.00 4.51 95.49 0.004433 0.00 0.00 100.00 0.000234 0.00 8.04 91.96 0.0081

Kostolac basin Drmno field 35 2.30 6.44 91.25 0.0736 2.43 5.28 92.29 0.0837 0.00 0.00 100.00 0.1738 4.55 3.00 92.45 0.1139 1.45 5.93 92.62 0.2440 N.D. N.D. N.D. N.D.41 1.07 3.59 95.34 0.2542 0.00 15.94 84.06 0.2243 0.26 6.00 93.74 0.1844 0.00 3.04 96.96 0.09

Kovin deposit A field 45 1.20 8.31 90.48 0.1246 1.63 7.93 90.44 0.1347 1.72 2.88 95.40 0.1248 2.55 10.28 87.17 0.1149 1.61 10.64 87.75 0.1850 3.70 9.36 86.95 0.2051 4.16 8.56 87.28 0.04

Standard deviation 1.41 4.39 4.94 9.33 8.24 14.80 0.22

Δ designates position of double bond in sterenes; αα designate configurations at C14 and C17 in steranes; (R) designates configuration at C20 in steranes; ββ, βα and αβ designateconfigurations at C17 and C21 in hopanes; Sterenes were quantified frommass chromatogramm/z 215, steranes frommass chromatogramm/z 217, C29diaster-13(17)-ene frommasschromatogram m/z 257, and hopenes and hopanes were quantified from mass chromatogram m/z 191.

a % Δ C27=100×C27(Δ2+Δ4+Δ5)-sterenes/Σ(C27–C29)(Δ2+Δ4+Δ5)-sterenes.b % ΔC28=100×C28(Δ2+Δ4+Δ5)-sterenes/Σ(C27–C29)(Δ2+Δ4+Δ5)-sterenes.c % ΔC29=100×C29(Δ2+Δ4+Δ5)-sterenes/Σ(C27–C29)(Δ2+Δ4+Δ5)-sterenes.d % C27=100×C2714α(H)17α(H)20(R)-sterane/Σ(C27–C29)14α(H)17α(H)20(R)-steranes.e % C28=100×C2814α(H)17α(H)20(R)-sterane/Σ(C27–C29)14α(H)17α(H)20(R)-steranes.f % C29=100×C2914α(H)17α(H)20(R)-sterane/Σ(C27–C29)14α(H)17α(H)20(R)-steranes.g Ster/Hop=[Σ(C27–C29)(Δ2+Δ4+Δ5)-sterenes]/[Σ(C29–C32)17α(H)21β(H)-+Σ(C29–C31)17β(H)21α(H)-+Σ(C29–C32)17β(H)21β(H)-+C2717α(H)-+C2717-

β(H)-hopanes+C30Hop-17(21)-ene+C27Hop-17(21)-ene+C27Hop-13(18)-ene] for Upper Miocene lignites; Ster/Hop=[C29diaster-13(17)-ene+Σ(C27–C29)14α(H)17α(H)20(R)-steranes] /[Σ(C29–C32)17α(H)21β(H)-+Σ(C29–C31)17β(H)21α(H)-+Σ(C29–C32)17β(H)21β(H)-+C2717α(H)-+C2717β(H)-hopanes+C30Hop-17(21)-ene+C27-

Hop-17(21)-ene+C27Hop-13(18)-ene] for Middle and Lower Miocene coals (Peters et al., 2005).h N.D. — not determined.


changes in paleoclimate duringMiocene. Namely, the highermean valuesof pimarane/16α(H)-phyllocladane, Paq and n-C23/(n-C27+n-C31), andlower relative abundance of C31αβ(R)-hopane forMiddle and LowerMio-cene coals are most probably related to increasedMAT andMAP, i.e. con-ditions favorable to extensive lauraceous forests with abundant Pinaceaeand aquatic macrophytes (due to the higher water level).

Values of biomarker parameters presented in Tables 4–7 indicatemore pronounced variations within the coal seam for Upper than forMiddle and Lower Miocene coals, consistent with increase in seasonalityduring Upper Miocene. It is caused by stronger variations in wintertemperatures as compared to summer ones, and cycling change ofhumid/dryer and warmer/cooler conditions. Biomarker composition

Fig. 8. GC–MS mass chromatograms of hopanoids, m/z 191 of Upper Miocene (a) and Lower Miocene (b) coal. For peak assignments, see Fig. 3 legend.


also indicates certain differences in paleoenvironment in which UpperMiocene lignites were formed. Based on distribution of hopanoids,ratio of Di/(Di+Tri)arom, Paq and sulfur content it could be assumedthat Kolubara lignites were formed in themost oxidative/dry and acidicconditions, whereas Kovin and particularly Kostolac coalswere deposit-ed under higher water level, which resulted in slightly lower Eh andhigher pH of the mire.

Finally, on the basis of biomarker patterns some differences inpaleoenvironment of Lower Miocene coals could be depicted aswell. Namely, relative abundance of C31αβ(R)-hopane, values ofDi/(Di+Tri)sat and Di/(Di+Tri)arom imply that samples fromSenje Mine were deposited in slightly more acidic and oxidative en-vironment than other Lower and Middle Miocene samples.

5. Conclusions

SerbianMiocene brown coals under consideration are typical humiccoals with huminite, liptinite and inertinite concentrations of up to92.6 vol.%, 17.4 vol.% and 15.5 vol.%, respectively. Telohuminite and/ordetrohuminite dominate by far in all Upper and Middle Miocene sam-ples, as well as in the greatest number of Lower Miocene coals. LowerMiocene coals are generally characterized by higher amount of gelinitethan Upper Miocene lignites, in accordance with higher rank.

Main precursors of organic matter were gymnosperms (coni-fers), followed by variable amount of angiosperms and microbialbiomass. Composition of saturated and aromatic diterpenoids ar-gues that coal forming vegetation could be attributed to the gymnospermfamilies Taxodiaceae, Podocarpaceae, Cupressaceae, Araucariaceae,Phyllocladaceae and Pinaceae. Lower and Middle Miocene coals arecharacterized by higher impact of Pinaceae to precursor biomassthan Upper Miocene lignites consistent with floral assemblage andpalynological data. The highest contribution of angiosperms to OM is ob-served in Senje Mine coals and Kolubara lignites. Moderate input of an-giosperms to OM is observed in Strmosten, Bogovina, Krepoljin, Kovinand 4 Kostolac coals, whereas, OM of coals from Soko and Jelovac, aswell as 6 samples from Kostolac basin is characterized by negligible an-giosperms input.

Coals were deposited in slightly alkaline to slightly acidic freshwater environment under variable Eh settings, from anoxic to slight-ly oxic. Bulk organic geochemical and biomarker data indicate thatLower and Middle Miocene coals were formed, in comparison toUpper Miocene lignites, under slightly alkaline and more reductiveconditions, which is the result of calcium-rich depositional environ-ment and higher water column level.

Diagenetic changes of the OM were governed by bacterial activi-ty, rather than thermal alteration. Peatification under variable Ehsettings with increasedmicrobial activity caused intense progressive

image of Fig.�8

Table 7Values of parameters calculated from distributions and abundances of hopanoid biomarkers.

Basin/deposit

Coal field/mine

No. Hopanemax.a

C30ββ-hopane/C30(ββ+αβ)-hopanes

C30Hop-17(21)-ene/C30αβ-hopane

C27β-hopane×100/(C27+ΣC29-C31)-ββ-hopanes

C29ββ-hopane×100/(C27+ΣC29-C31)-ββ-hopanes



C27α-hopane×100/(C27+ΣC29-C31)-αβ-hopanes

C29αβ-hopane×100/(C27+ΣC29-C31)-αβ-hopanes

C30αβ-hopane×100/(C27+ΣC29-C31)-αβ-hopanes

C31αβ(R)-hopane×100/(C27+ΣC29-C31)-αβ-hopanes

Senje–Resavicabasin

SenjeMine

1 C31αβ(R) 0.85 0.00 27.23 16.75 27.95 28.06 0.00 0.00 1.58 98.422 C31αβ(R) 0.78 0.10 29.25 21.42 27.70 21.64 0.00 0.00 4.33 95.673 C31αβ(R) 0.73 0.10 31.00 23.22 25.97 19.81 0.00 0.00 7.77 92.23

Jelovac 4 C27β 0.84 1.49 34.37 16.87 26.15 22.60 0.00 0.00 25.89 74.115 C27β 0.81 2.50 29.74 30.87 22.38 17.01 20.34 0.00 31.07 48.596 C31αβ(R) 0.00 2.86 33.20 23.81 0.00 42.99 0.00 0.00 5.42 94.58

Strmosten 7 C27β 0.50 0.09 33.97 26.80 23.17 16.07 8.38 0.00 33.93 57.698 C31αβ(R) 0.62 0.73 46.95 13.99 22.85 16.20 2.95 17.28 6.91 72.86

Soko Banjabasin

Soko 9 C27β 0.41 1.27 63.91 25.22 6.96 3.91 49.57 2.99 9.83 37.6110 C27β 1.00 N.D.b 71.04 14.75 3.28 10.93 74.85 8.98 0.00 16.1711 C27β 0.62 0.83 49.00 30.00 16.33 4.67 12.00 9.33 40.00 38.6712 C27β 0.53 1.11 43.48 39.13 5.80 11.59 6.45 11.29 29.03 53.23

Bogovinabasin

East field 13 C27β 0.77 1.18 50.51 24.08 19.06 6.35 2.78 8.33 47.22 41.6714 C27β 0.64 2.13 56.23 22.64 11.32 9.81 42.11 3.51 29.82 24.5615 C27β 0.63 0.68 47.47 26.58 16.46 9.49 9.52 9.52 49.21 31.7516 C27β 0.61 1.00 49.67 28.81 15.23 6.29 9.09 5.45 54.55 30.91

Krepoljinbasin

Centralfield

17 C27β 0.24 0.60 63.72 20.80 7.96 7.52 7.14 4.29 41.43 47.1418 C27β 0.51 0.89 63.14 11.98 13.36 11.52 34.44 31.13 18.54 15.8919 C27β 0.47 1.69 67.50 21.67 7.50 3.33 29.17 10.42 20.83 39.5820 C27β 0.50 1.08 70.78 16.88 9.09 3.25 46.84 11.39 17.72 24.05

Kolubarabasin

D field 21 C31αβ(R) 0.66 9.68 37.21 28.92 10.30 23.57 0.00 0.00 21.18 78.8222 C31αβ(R) 0.81 0.41 36.75 12.86 15.89 34.49 0.15 0.37 0.28 99.1923 C31αβ(R) 0.74 0.00 30.08 18.75 12.53 38.64 0.21 0.33 0.34 99.1224 C31αβ(R) 0.65 0.00 44.33 14.95 8.84 31.88 0.10 0.15 0.14 99.6125 C31αβ(R) 0.77 0.30 32.11 17.59 14.48 35.82 0.33 0.50 0.58 98.5926 C31αβ(R) 0.74 0.16 28.85 18.20 11.48 41.47 0.13 0.23 0.23 99.4227 C31αβ(R) 0.72 0.00 39.76 27.66 7.37 25.22 0.10 0.14 0.12 99.6428 C31αβ(R) 0.67 0.00 36.41 14.59 7.18 41.82 0.07 0.07 0.08 99.7829 C31αβ(R) 0.76 0.00 40.37 13.41 10.87 35.35 0.13 0.17 0.17 99.5230 C31αβ(R) 0.84 0.65 31.85 15.63 12.11 40.41 0.11 0.17 0.13 99.5931 C31αβ(R) 0.77 0.14 36.93 16.06 10.77 36.23 0.14 0.05 0.18 99.6332 C31αβ(R) 0.78 0.20 29.48 18.33 14.61 37.58 0.18 0.17 0.26 99.4033 C31αβ(R) 0.67 0.00 44.06 15.09 12.29 28.56 0.27 0.30 0.38 99.0534 C31αβ(R) 0.80 0.24 30.45 17.17 14.85 37.53 0.17 0.27 0.23 99.33

Kostolacbasin

Drmnofield

35 C27β 0.80 0.39 45.46 27.61 18.55 8.38 8.15 21.15 14.49 56.2036 C27β 0.72 0.00 44.59 29.29 17.71 8.42 10.47 18.01 22.36 49.1637 C27β 0.53 0.00 40.53 36.29 11.52 11.66 0.00 30.91 18.98 50.1138 C27β 0.90 0.00 26.93 24.47 31.17 17.43 10.93 22.84 19.62 46.6239 C31αβ(R) 0.70 0.22 35.52 23.98 28.59 11.90 5.29 12.34 16.25 66.1240 N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D.41 C27β 0.87 0.00 38.22 30.15 21.76 9.87 11.55 34.71 11.80 41.9442 C31αβ(R) 0.84 10.44 27.84 36.78 21.44 13.93 0.00 22.37 4.29 73.3443 C31αβ(R) 0.77 0.00 40.79 25.51 19.84 13.86 6.48 14.39 7.94 71.1944 C27β 0.78 0.00 50.24 23.83 16.38 9.55 8.61 16.69 12.42 62.27

Kovindeposit

A field 45 C31αβ(R) 0.74 1.96 28.81 23.38 16.88 30.94 0.55 1.46 0.96 97.0346 C31αβ(R) 0.68 0.00 24.93 39.11 16.39 19.57 1.26 0.00 3.25 95.5047 C27β 0.82 6.30 38.62 25.11 23.93 12.34 34.40 0.00 34.94 30.6648 C27β 0.67 7.61 39.87 33.62 16.54 9.97 14.92 0.00 34.53 50.5549 C31αβ(R) 0.82 9.35 29.39 25.16 20.09 25.35 1.83 0.00 1.87 96.3150 C27β 0.56 2.17 43.33 31.83 15.92 8.91 13.76 18.05 32.29 35.9051 C31αβ(R) 0.52 0.16 46.13 29.38 15.16 9.33 5.84 0.00 12.78 81.38

Standarddeviation

/ 0.17 2.62 12.08 7.13 6.97 12.31 15.87 9.59 15.51 28.44

ββ and αβ designate configurations at C17 and C21 in hopanes, (R) designates configuration at C22 in hopanes.Hopanes and hopenes were quantified from mass chromatogram m/z 191.

a Hopane max — the most abundant hopanoid in mass chromatogram m/z 191.b N.D. — not determined. 21

K.Stojanović,D

.Životić/InternationalJournalofCoalG

eology107

(2013)3–23

Fig. 9. Variations of mean values of biomarker and paleoclimate parameters during Mio-cene. MAT — mean annual temperature (°C) (Utescher et al., 2007); CMM — cold monthmean temperature (°C) (Utescher et al., 2007);WMM—warmmonthmean temperature(°C) (Utescher et al., 2007); MAP — mean annual precipitation (mm) (Utescher et al.,2007); Paq=(n-C23+n-C25)/(n-C23+n-C25+n-C29+n-C31) (Ficken et al., 2000); % C31αβ(R) Hopane=C31αβ(R)-hopane×100/(C27+ΣC29–C31)-αβ-Hopanes.


aromatization of biomarkers, particularly angiosperm derivedtriterpenoids during diagenesis.

OM of Lower Miocene coals is more mature, corresponding toimmature/early mature stage, whereas OM of Upper Miocene lignitesis in immature diagenetic phase.

Biomarker patterns show relatively similar compositions in Ser-bian Miocene brown coals. Upper Miocene lignites are characterizedby more pronounced variations of biomarker parameters within thecoal field than Middle and Lower Miocene coals, explained by in-creased seasonality during Upper Miocene. The main differences be-tween Upper and Lower Miocene coals are expressed by higher proxyratio (Paq), n-C23/(n-C27+n-C31) and pimarane/16α(H)-phyllocladaneratio, as well as lower relative abundance of C31αβ(R)-hopane of the lat-ter one. A good correlation between these biomarker parameters andpaleoclimate data is registered, indicating that biomarker patterns offervaluable information that reflect even slight paleoclimate variations inSerbia during Miocene.

Acknowledgments

The study was financed by the Ministry of Education and Scienceof the Republic of Serbia (project number 176006). Authors gratefullyacknowledge the Bundesanstalt für Geowissenschaften und Rohstoffe(BGR) Laboratories in Hannover (Germany) for technical support.Danica Mitrović, Msc in Chemistry is acknowledged for linguistic cor-rections. We are also grateful to the anonymous reviewers.

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Comparative study of Serbian Miocene coals — Insights from biomarker composition

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