Polycyclic aromatic hydrocarbons (PAHs) in late Eocene to early Pleistocene mudstones of the Sylhet...

(This is a sample cover image for this issue. The actual cover is not yet available at this time.)

This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institution

and sharing with colleagues.

Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third party

websites are prohibited.

In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further information

regarding Elsevier’s archiving and manuscript policies areencouraged to visit:

http://www.elsevier.com/copyright

http://www.elsevier.com/copyright

Author's personal copy

Polycyclic aromatic hydrocarbons (PAHs) in late Eocene to early Pleistocenemudstones of the Sylhet succession, NE Bengal Basin, Bangladesh: Implicationsfor source and paleoclimate conditions during Himalayan uplift

H.M. Zakir Hossain a,b, Yoshikazu Sampei b,⇑, Barry P. Roser b

a Department of Petroleum and Mining Engineering, Jessore Science and Technology University, Jessore 7408, Bangladeshb Department of Geoscience, Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan

a r t i c l e i n f o

Article history:Received 19 July 2012Received in revised form 21 November 2012Accepted 5 December 2012Available online 13 December 2012

a b s t r a c t

Distribution and possible sources of polycyclic aromatic hydrocarbons (PAHs) have been investigated in23 late Eocene to early Pleistocene mudstones from the Sylhet succession of the northeastern BengalBasin, Bangladesh. Paleoclimatic conditions in the southern Himalaya region throughout the Himalayanuplift were reconstructed, based on combustion derived PAHs and aromatic land plant derived biomark-ers. Phenanthrene, fluoranthene (Fla), pyrene (Py), benz[a]anthracene (BaAn), chrysene/triphenylene(Chry + Tpn), benzofluoranthenes (Bflas), benzo[e]pyrene (BePy), benzo[a]pyrene (BaPy), perylene (Pery),indeno[1,2,3-cd]pyrene (InPy), benzo[ghi]perylene (BghiP), coronene (Cor) and retene (Ret) were theidentified PAHs. Fla/(Fla + Py) ratios > 0.5 and InPy/(InPy + BghiP) > 0.2 from almost all Sylhet samplessuggest occurrence of natural wildfires. Low contents of BaAn and BaPy indicate decomposition by longexposure to sunlight before sedimentation, or early diagenetic weathering. Increased Cor, InPy and BghiPcontents suggest occurrence of larger, high temperature wildfires. Correlation coefficients of the PAHsand p-values for statistical hypothesis testing showed that the positive and negative correlations withinthe PAHs may be indicative of high or low temperatures in wildfires. Fungi derived Pery showed negativecorrelations with Py (r = �0.67, p = 4.6 � 10�4) and Fla (r = �0.56, p = 5.0 � 10�3), but not with Cor, Bflas,InPy and BghiP. Based on the correlation coefficients for all PAHs and their p-values, five statistical groups([Py, Fla], [Cor, Bflas, InPy, BghiP], [BaAn, Chry + Tpn, BaPy], [Pery] and [Ret]) were recognized. Thesegroups are probably correlated with origins and depositional processes. According to the results, the Syl-het succession was deposited in three differing paleoclimatic regimes: (1) First phase (late Eocene toearly Miocene, early to middle stage of Himalayan uplift): High contents of combustion derived PAHs(Fla, Py and BePy), significant gymnosperm derived Ret, and low Pery abundances in the Jaintia and Barailgroups indicate arid climatic conditions. Although wildfires could often occur, 5- or 6-ring combustionPAHs (Cor, InPy and BghiP) contents are low, suggesting that the wildfires were relatively low tempera-ture. (2) Second phase (middle to late Miocene: middle to late stage of Himalayan uplift): Combustionderived PAHs and fungi derived Pery were dominant in the Surma Group. The climate was arid to humidand seasonal, with a dry season giving conditions suitable for combustion. Abundant Fla, Bflas, BePy, Cor,InPy and BghiP imply high temperatures in large wildfires. However, frequency of the wildfires decreasedbecause of wet climate. (3) Third phase (late Miocene to Pleistocene: late stage of Himalayan uplift):Moderate to high Pery contents and low Fla, Py and BePy abundances in the Tipam and Dupitila groupsindicate establishment of more humid climate. InPy, BghiP, Cor, Bflas and BaPy were predominant. Inten-sified humid and seasonal climate arising from the Himalayan monsoon decreased the incidence and fre-quency of general wildfires, but increased the ratio of large to small wildfires.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Polycyclic aromatic hydrocarbons (PAHs) are a class of com-pounds consisting of two or more benzene rings fused togetherin a linear, angular, or clustered arrangement (Chefetz et al.,

2000). PAHs are widely distributed in both sediments and sedi-mentary rocks (Laflamme and Hites, 1978; Wakeham et al., 1979,1980a,b; Prahl and Carpenter, 1983; Jiang et al., 1998; Hasegawa,2001; Yunker and Macdonald, 2003; Grimalt et al., 2004; Luoet al., 2006; Grice et al., 2007). PAHs originate from varioussources, including combustion of organic matter (OM) from eitherbiomass and diagenetic alteration of natural biolipids, andemissions of non-combustion derived diagenetic processes (Hites

0146-6380/$ - see front matter � 2012 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.orggeochem.2012.12.001

⇑ Corresponding author. Tel.: +81 852 32 6453; fax: +81 852 32 6469.E-mail address: [email protected] (Y. Sampei).

Organic Geochemistry 56 (2013) 25–39

Contents lists available at SciVerse ScienceDirect

Organic Geochemistry

journal homepage: www.elsevier .com/locate /orggeochem


et al., 1977; Harvey, 1996; Chefetz et al., 2000; Luo et al., 2006;Grice et al., 2007; Yunker et al., 2011b). Parent and alkyl-substi-tuted PAHs have both natural and anthropogenic sources. Naturalsources include bitumens, coals, plant debris, forest fires andpost-depositional transformation of biogenic precursors (Venkate-san and Dahl, 1989; Killops and Massoud, 1992; Budzinski et al.,1997; Yunker et al., 2002, 2011b; Luo et al., 2006; Oros et al.,2006), whereas anthropogenic combustion sources include emis-sions from use of fossil fuels (Benner et al., 1989, 1990; Yunkeret al., 2002, 2011a,b). The combustion derived and/or pyrolyticPAHs are mainly fluoranthene (Fla), pyrene (Py), benz[a]anthra-cene (BaAn), chrysene/triphenylene (Chry + Tpn, hereafter referredto as Chry in the text), benzofluoranthenes (Bflas), benzo[e]pyrene(BePy), benzo[a]pyrene (BaPy), indeno[1,2,3-cd]pyrene (InPy),benzo[ghi]perylene (BghiP) and coronene (Cor) (Hites et al.,1977; Laflamme and Hites, 1978; Wakeham et al., 1979, 1980a;Prahl and Carpenter, 1983; Kawamura et al., 1987; Venkatesanand Dahl, 1989; Killops and Massoud, 1992; Harvey, 1996; Jianget al., 1998; Grimalt et al., 2004; Grice et al., 2007). Influx of PAHsis largely controlled by availability of biological productivity andOM particle size, and also OM stability during oxidative weather-ing, rock alteration, biodegradation and bioaccumulation, and pro-longed transport to sedimentary basins (Yunker et al., 2002,2011a,b; Haberstroh et al., 2006; Marynowski and Wyszomirski,2008; Marynowski et al., 2011a). Bflas, BePy and Cor are least sus-ceptible to transportation, alteration and biodegradation (Prahland Carpenter, 1983; Jiang et al., 1998), whereas BaAn and BaPyare degraded more easily during those processes (Sicre et al.,1987; Yunker et al., 2002, 2011a,b; Stout and Emsbo-Mattingly,2008). Retene (Ret) and perylene (Pery) are abundant in sediments,derived from biological precursors during diagenesis (Aizenshtat,1973; Laflamme and Hites, 1978; Wakeham et al., 1979, 1980b;Tan and Heit, 1981; Jiang et al., 1998, 2000). Ret can also form asa diagenetic product of abietic acid in conifer resins (Laflammeand Hites, 1978; Tan and Heit, 1981), and Pery from wood-degrad-ing fungi in humid climates (Grice et al., 2009; Suzuki et al., 2010).Both Ret and Pery may also originate from combustion of OM(Ramdahl, 1983; Simoneit, 2002; Fan et al., 2011), with the formerbeing derived from combustion of woody materials (Ramdahl,1983; Simoneit, 2002) and the latter from biomass combustionproducts (Oros and Simoneit, 2001a; Oros et al., 2006; Yunkeret al., 2011a, 2012). Ret and Pery are unique and useful aromaticbiomarkers. Phenanthrene (P) and Chry may also originate fromboth pyrolytic and diagenetic processes (Jiang et al., 1998).

The Sylhet succession of the northeastern Bengal Basin in Ban-gladesh comprises a voluminous pile of Tertiary clastic sediments,typically sandstones and mudstones. The composition of the ali-phatic biomarkers in the Sylhet succession is dominantly con-trolled by source variations which are related to Himalayan uplift(Hossain et al., 2009a). Higher plant OM is characteristic of the lateEocene to early Miocene Jaintia and Barail groups, whereasplanktonic OM is a feature of the middle to late Miocene SurmaGroup (Hossain et al., 2009a). The late Miocene to Pleistocene Ti-pam and Dupitila groups are characterized by both planktonicand higher plant OM. Hossain et al. (2009a) also showed thatmaturity of this OM was only moderate, with vitrinite reflectance(Ro) of about 0.51–0.66%, in the early stage of petroleum genera-tion. Furthermore, there was no contamination by reworking ofhighly matured OM in this region. Consequently, PAHs in theSylhet succession provide a reliable dataset to examine terrige-nous/land environments, paleoclimate and the occurrence of natu-ral wildfires.

Systematic organic geochemical data from the late Eocene toearly Pleistocene sedimentary rocks in the Sylhet succession andsurrounding areas are limited (Alam and Pearson, 1990, 1993;Ahmed et al., 1991; Hossain et al., 2009a,b). We examined the

PAHs in 23 mudstone samples spread throughout the stratigraphicsuccession. The aim of this study is to identify the distribution andpotential sources of PAHs (either diagenetic or combustion/pyro-genic) in mudstones from the Sylhet succession and to discussthe relationship with changes in the terrigenous environment aris-ing from uplift of the Himalaya.

2. Geological setting

The Bengal Basin is located in the easternmost part of the Indiansub-continent (Fig. 1a), occupying all of Bangladesh, West Bengal,Assam, Tripura and part of the Bay of Bengal. The basin originatedfrom the collision of India with Eurasia and Myanmar (also knownas Burma), forming the regionally extensive Himalayan Mountainsand Indo-Burman Ranges. The Indo-Burman collision boundaryproduced an uplifted fold belt in the eastern part; the western partof the basin is bounded by the Rajmahal Hills (Goodbred andKuehl, 2000). The sediments were derived from the rapidly risingHimalaya and were transported by the Ganges and Brahmaputrarivers and their ancestral drainage systems (Lindsay et al., 1991).The basin fill contains the thickest (ca. 22 km) sedimentary se-quence in the world (Alam et al., 2003), consisting mainly of Ceno-zoic shallow-marine and fluvio-deltaic siliciclastic sediments(Imam and Hussain, 2002).

The Sylhet Basin is a rapidly subsiding sub-basin in the north-eastern part of the Bengal Basin. The sedimentary succession com-prises roughly sub-equal proportions of alternating sandstones,siltstones and mudstones. Total organic carbon (TOC) content inthe Sylhet succession is low generally <0.5 wt% (Hossain et al.,2009a). The low TOC contents are due to high sedimentation ratescaused by rapid uplift and erosion of the Himalaya (Hossain et al.,2009a). Stratigraphically, the Sylhet succession is subdivided intothe Jaintia, Barail, Surma, Tipam and Dupitila groups, in ascendingorder from oldest to youngest (Table 1). Our present study exam-ines the late Eocene to early Pleistocene sequence from the KopiliShale Formation through to the Dupitila Formation (Table 1).Lithology of the formations has been described in detail by Rei-mann (1993), and summarized by Hossain et al. (2009a, 2010).

3. Materials and methods

3.1. Sample collection

Twenty-three unweathered, indurated mudrock samples werecollected from petroleum exploration drill core (9 samples fromthe Barail and Surma groups) and surface outcrops (14 samplesfrom the Jaintia, Barail, Surma, Tipam and Dupitila groups) in theSylhet succession. Sample locations and drill core positions areshown in Fig. 1b. The samples were chipped and subsequentlywashed with deionized distilled water to remove any loose surfacematerial, and dried in an oven at 110 �C for 24 h. The oven driedsamples were then pulverized in a tungsten carbide ring mill for25–45 s.

3.2. Solvent extraction and separation

About 35 g of each powdered sample were extracted in a Soxh-let apparatus for 72 h, using dichloromethane:methanol (9:1). Ele-mental sulfur was removed using Cu granules and the solvent wasremoved using a rotary evaporator. The soluble OM was separatedinto saturated and aromatic hydrocarbon fractions using activatedsilica gel (Kiselgel 60 PF254, Merck) thin layer chromatography byeluting with n-hexane. Hydrocarbons in the saturated fractionhave been reported by Hossain et al. (2009a).

26 H.M. Zakir Hossain et al. / Organic Geochemistry 56 (2013) 25–39


3.3. Gas chromatography-mass spectrometry (GC–MS)

The n-hexane solutions of aromatic hydrocarbon fractions wereanalyzed by gas chromatography–mass spectrometry (GC–MS)using a Shimadzu QP2010 instrument equipped with an automaticprogrammable-temperature system and a capillary column(30 m � 0.25 mm i.d.) coated with (5% phenyl) methylpolysiloxane(DB-5MS: Agilent Technologies). Oven temperature wasprogrammed isothermally at 50 �C for 5 min, from 50 to 300 �Cat 8 �C/min, and held at 300 �C isothermally for 30 min. Helium

was used as the carrier gas for the analyses. GC–MS analyses werecarried out using electron impact ionization (70 eV). Full scan spec-tra were recorded over a range of 50–850 m/z at a scan rate of 2Hz.Identification of PAHs was performed by comparison of GC reten-tion times, mass spectra with published data and standard PAHSolution Mix (Accu Standard Inc., Z-013-17). In this study, 14 indi-vidual PAHs were quantified, including P, Fla, Py, BaAn, Chry, Bflas,BePy, BaPy, Pery, InPy, BghiP, Cor and Ret. Selected PAHs weremonitored at m/z = 178 (P, An), m/z = 202 (Fla, Py), m/z = 291(Ret), m/z = 228 (BaAn, Chry), m/z = 252 (Bflas, BePy, BaPy, Pery),

Trans-Himalaya

Ophiolitic Suture

Tethys Himalaya

Higher Himalaya

Lesser Himalaya

Sub-Himalaya

Indo-Burmanturbidites &molasse

Scale

0 1000 Km

65oE 90oE

30oN

10oN

TIBET

BENGAL FAN

Indus

RSiwaliks

INDO - GANGETIC PLAINGanges R

Brahmaputra R

BENGAL BASIN

segnaR

namruB-odnI

ShillongMassif

NEPAL

N

65oE 90oEAndamanArc

INDIAN SHIELD

Studyarea

(Assam)INDIACHATTAK

DAUKI FAULT

SYLHET

4. ATGRAM

KAILAS TILA

2. FENCHUGANJ

1. RASIDPUR

HABIGANJ

SYLHET BASIN

25 N

O O O

BEANI BAZAR3. PATHARIA

92 E

Mainly Pliocene-Holocene Mainly Miocene Mainly Oligocene Mainly Eocene

Cretaceous sediments Precambrian basement Normal faults

International border

Thrust faults

Hydrocarbon exploration well

0 25 km

N

Scale

Surface sample location

INDIA

INDIASHILLONG MASSIF

(Meghalaya)

(Tripura)

a

b

Meghn

a R

Fig. 1. (a) Map showing major geographic features in the Bengal Basin and adjoining areas and location of the study area (modified from Uddin and Lundberg (1998) andHossain et al. (2009a)). (b) Geological map (modified from Hossain et al. (2009a)) of the Sylhet succession and surrounding areas, showing location of the surface outcropssampled. Drill core samples were taken from the Rasidpur, Fenchuganj, Patharia and Atgram wells.

H.M. Zakir Hossain et al. / Organic Geochemistry 56 (2013) 25–39 27


m/z = 276 (InPy, BghiP), and m/z = 300 (Cor). Relative abundance(%) and concentration (lg/g TOC) were calculated by comparingthe TIC (total ion current) chromatogram area to the standard area.

3.4. Vitrinite and inertinite reflectance

Vitrinite and inertinite reflectance (Ro) measurements weremade on selected samples (samples Z-02, 20, 28, 35, 43, 55, 57,70 and 74). Manually crushed samples (ca. 5 mm diameter) weretreated with 6 M HCl and HF (46%) for 5 days. Microscopic observa-tions and Ro measurements were carried out using a Lambda Vi-sion-OLYMPUS microscope equipped with a TFCAM7000F-LA100USW spectrograph system by means of 546 nm reflectedlight, using oil immersion objectives. The calibration standardsused were glasses with Ro of 0.299%, 0.506%, 0.940%, 1.025%,1.381% and 1.672%.

4. Results and discussion

4.1. PAHs distribution in mudstones and their origin

The concentrations and distributions of PAHs in sedimentarybasins depend on their source and diagenesis, as well as the rateof sedimentation, with variable sediment dilution effects amongriver/lacustrine and marine environments (Fernández et al.,1999; Marynowski and Wyszomirski, 2008; Marynowski andSimoneit, 2009). Hossain et al. (2009a) showed that low TOC con-tents of the mudstones in Sylhet Basin were primarily controlledby high sedimentation rate. However, the relative proportions ofPAHs derived from land areas are generally independent of sedi-mentation rate. Consequently, the relative composition of the PAHs(Table 2) could record information of terrigenous/land environ-ment in the Sylhet succession. Representative TIC chromatograms

Table 1Stratigraphy of the Sylhet succession, NE Bengal Basin, Bangladesh (after Hossain et al., 2009a).

Age Group Formation Lithology Depositional environments

Recent Alluvium Alluvium Sand, silt, clay FluvialLate Pleistocene Dihing Dihing Sandstone, mudstone Fluviala

Pliocene–Pleistocene Dupitila Dupitila Sandstone, mudstone Fluvialb,f

Late Miocene–Pliocene Tipam Girujan Clay Clay, sandstone Fluvialc, lacustrinec

Tipam Sandstone Sandstone, mudstone Fluvialb,f

Middle–late Miocene Surma Bokabil Sandstone, mudstone Marinec,d, deltaicb,c,f

Bhuban Sandstone, mudstoneLate Eocene–early Miocene Barail Renji Sandstone, mudstone Shallow marinec, deltaicf

Jenam Mudstone, sandstoneLate Eocene Jaintia Kopili Shale Mudstone, minor lst. Shallow marinec, deltaice

Early–middle Eocene Sylhet Limestone Limestone Shallow marinec,d

Paleocene–early Eocene Tura Sandstone Quartz arenites Shallow marinea,b,f

a Khan (1991).b Johnson and Alam (1991).c Reimann (1993).d Shamsuddin and Abdullah (1997).e Alam et al. (2003).f Najman et al. (2008).

Table 2Relative abundance (%) and ratios of polycyclic aromatic hydrocarbons (PAHs) in late Eocene to early Pleistocene mudstones, Sylhet succession, NE Bengal Basin, Bangladesh.Abbreviations are: P, phenanthrene; Fla, fluoranthene; Py, pyrene; BaAn, benzo[a]anthracene; Chry + Tpn, chrysene/triphenylene; Bflas, benzofluoranthenes; BePy,benzo[e]pyrene; BaPy, benzo[a]pyrene; Pery, perylene; InPy, indeno[1,2,3-cd]pyrene; BghiP, benzo[ghi]perylene; Cor, coronene; Ret, retene.

Sample No Group Formation P Fla Py BaAn Chry+Tpn Bflas BePy BaPy Pery InPy BghiP Cor Ret Fla/Py Fla/(Fla+Py) BaAn/228 InPy/(InPy+BghiP)

Z-02 Dupitila Dupitila 0.52 2.91 2.00 1.74 4.40 10.5 5.24 7.01 12.9 3.34 42.9 0.82 5.83 1.46 0.59 0.28 0.07Z-03 Dupitila Dupitila 4.00 6.49 1.99 4.54 6.87 6.77 3.64 4.93 9.05 12.2 23.0 2.47 14.1 3.26 0.77 0.40 0.35Z-14 Tipam Girujan 0.43 1.85 0.72 0.35 1.80 3.20 3.13 0.15 84.5 0.76 1.62 0.32 1.15 2.57 0.72 0.16 0.32Z-15 Tipam Girujan 2.84 9.40 8.98 4.58 17.9 7.55 4.71 3.05 27.1 2.39 –a – 11.5 1.05 0.51 0.20 –Z-20 Tipam Tipam 1.41 5.21 9.73 0.60 4.40 5.58 6.36 0.52 56.9 1.57 3.55 0.97 3.24 0.54 0.35 0.12 0.31Z-28 Tipam Tipam 1.41 2.96 3.44 0.80 5.16 6.44 10.8 1.19 53.6 1.77 7.77 1.71 3.00 0.86 0.46 0.13 0.19ZH-122 Surma Bokabil 18.3 45.4 23.7 0.33 2.26 1.94 2.30 0.35 1.07 0.62 0.62 0.18 2.95 1.92 0.66 0.13 0.50ZH-126 Surma Bokabil 5.01 53.1 24.6 0.68 3.64 2.85 3.22 0.18 1.89 0.57 1.19 0.26 2.75 2.16 0.68 0.16 0.32ZH-128 Surma Bokabil 2.37 34.0 16.6 0.79 6.57 5.03 11.0 0.52 12.3 1.14 4.88 0.81 4.02 2.04 0.67 0.11 0.19ZH-55 Surma Bokabil 43.4 17.3 10.3 0.91 3.09 3.40 5.05 0.62 8.55 0.76 2.63 0.34 3.65 1.68 0.63 0.23 0.22Z-31 Surma Bokabil 1.08 1.71 2.78 0.77 3.53 8.22 9.39 1.89 58.2 1.90 6.76 1.13 2.69 0.62 0.38 0.18 0.22Z-35 Surma Bokabil 1.69 2.21 3.22 0.77 4.74 6.78 10.9 1.42 55.8 1.59 5.91 1.30 3.69 0.69 0.41 0.14 0.21ZH-59 Surma Bhuban 0.73 11.3 7.41 1.22 9.65 11.5 18.5 0.74 21.7 2.06 8.40 1.53 5.31 1.53 0.60 0.11 0.20ZH-88 Surma Bhuban 3.18 8.39 6.41 1.71 4.96 5.14 8.45 1.99 41.2 1.19 6.48 1.62 9.27 1.31 0.57 0.26 0.16Z-43 Surma Bhuban 2.80 9.64 9.64 2.88 6.91 6.84 8.65 0.83 31.0 1.71 5.51 0.60 13.0 1.00 0.50 0.29 0.24ZH-14 Surma Bhuban 5.01 20.0 12.7 0.67 5.91 5.85 11.5 2.12 22.7 2.66 4.78 1.38 4.67 1.57 0.61 0.10 0.36Z-55 Barail Renji 33.5 10.9 17.6 5.36 7.72 1.00 4.43 1.86 2.55 0.70 1.52 0.04 12.9 0.62 0.38 0.41 0.32Z-57 Barail Renji 32.8 14.8 19.0 6.39 10.7 1.40 4.52 2.94 4.25 – 0.35 – 2.82 0.78 0.44 0.37 –ZH-11 Barail Jenam 38.5 14.4 15.7 6.93 9.19 1.20 4.34 1.67 0.89 – 0.97 – 6.18 0.91 0.48 0.43 –ZH-12 Barail Jenam 39.6 17.7 13.4 4.98 9.33 2.36 5.66 0.96 1.70 – 0.75 – 3.55 1.32 0.57 0.35 –Z-70 Jaintia Kopili 14.2 21.0 10.6 11.6 16.4 4.02 3.12 3.64 6.35 – 0.70 – 8.39 1.98 0.66 0.41 –Z-72 Jaintia Kopili 20.4 16.3 9.95 7.71 15.3 4.69 3.22 3.21 6.55 – 2.16 – 10.6 1.64 0.62 0.34 –Z-74 Jaintia Kopili 18.0 9.07 13.6 10.4 10.3 9.71 11.3 5.84 3.90 – – – 7.94 0.67 0.40 0.50 –

a Below detection limit.



(Fig. 2) and average relative proportions of PAHs for each strati-graphic group (Fig. 3) indicate that the lower part of the Sylhet suc-cession (Jaintia and Barail groups: late Eocene-early Miocene) isrich in P, Fla and Py (Figs. 2 and 3). The middle to upper Sylhet suc-cession (Surma and Tipam groups: middle-late Miocene) is domi-nated by Pery, other PAHs (Fla, Py and BePy) are relativelyabundant and minor peaks of BaAn, Bflas, BaPy, Chry, InPy, BghiP,and Cor occur (Figs. 2 and 3, Table 2). BghiP, Pery and Ret are abun-dant in the upper part of the Sylhet succession (Dupitila Group:late Miocene–Pliocene, Fig. 3 and Table 2).

Fla, Py, BaAn, Bflas, BePy, BaPy, InPy, BghiP and Cor are com-monly considered to be primarily of combustion origin (Young-blood and Blumer, 1975; Hites et al., 1977; Laflamme and Hites,1978; Wakeham et al., 1980a; Prahl and Carpenter, 1983; Killopsand Massoud, 1992; Bence et al., 1996; Jiang et al., 1998; Grimaltet al., 2004; Grice et al., 2007; Yunker et al., 2002, 2011a). Amongthem, however, Fla, Py, BaAn, InPy and BghiP are often produced bycatagenetic modification of the same PAHs from petroleum andmatured kerogen (Yunker et al., 2002). Therefore, it is necessaryto determine the degree of influence of diagenetic/catageneticPAHs relative to those produced by combustion, based on specific

indicators (Wakeham et al., 1980b; Hites et al., 1980; Prahl andCarpenter, 1983; Venkatesan, 1988; Garrigues et al., 1995; Budzin-ski et al., 1997; Baumard et al., 1998; Yunker et al., 2002). In orderto precisely identify the combustion derived PAHs, the abundancesand ratios of PAHs in the studied section are listed in Table 2 andFigs. 4–6. PAHs isomer ratios such as methylphenanthrenes/phen-anthrene (MP/P), Fla/Py, Fla/(Fla + Py), BaAn/228, InPy/(InPy + B-ghiP) are widely used to distinguish between PAH compounds ofdiagenetic and combustion/pyrogenic origin (Wakeham et al.,1980b; Hites et al., 1980; Prahl and Carpenter, 1983; Venkatesan,1988; Garrigues et al., 1995; Budzinski et al., 1997; Baumardet al., 1998; Yunker et al., 2002). Sources consisting of combus-tion/pyrogenic products derived from wood fires contain highabundances of four-, five- and six-ring PAHs because of their highformation temperature (Leeming and Maher, 1992; Oros andSimoneit, 2001a,b; Oros et al., 2006; Denis et al., 2012). The MP/Pratio has been used to differentiate diagenetically derived PAHsfrom combustion/pyrogenic derived PAHs (Prahl and Carpenter,1983; Yunker et al., 2002), and also to distinguish between hydro-thermally or diagenetically oxidized and non-oxidized OM (Clay-ton and King, 1987; Püttmann et al., 1989; Bechtel et al., 2001;

PFla

Py

Ret

BaAn

Chry+Tpn

Bflas

BaPy

InPy

Pery

BghiP

Cor

BePy

TICZ-20 (Tipam Group)Late Miocene-Pliocene

TICZH-59 (Surma Group)Middle-late Miocene

Fla

Py

Ret

BaAn

Chry+TpnBflas

BePy

InPy

Pery

BghiP

Rel

ativ

e In

tens

ity

20 25 30 35 40 45 50

P

Fla

Py

Ret BaAnChry+Tpn

Bflas

BePy

BaPy

InPy

Pery

BghiP

Cor

Retention time (min)

TICZ-55 (Barail Group)Late Eocene-early Miocene

P

Ret

BaAn

BaPyCorR

elat

ive

Inte

nsity

Fig. 2. Representative total ion current (TIC) chromatograms showing distribution of PAHs for late Eocene to early Pleistocene mudstones from the Sylhet succession in theNE Bengal Basin. Abbreviations are defined in Table 2.



Marynowski and Wyszomirski, 2008; Marynowski et al., 2011a,b).PAHs of combustion/pyrogenic origin are distinguished by highabundances of unsubstituted compounds, whereas diagenetic

PAHs are largely dominated by alkyl-substituted PAHs with twoto four rings (Liu et al., 2005). Prahl and Carpenter (1983) reportedthat MP/P values of <1 indicate combustion or pyrolytic processes.MP/P values >2 are indicative of fossil fuel or petroleum sources,i.e. diagenesis/catagenesis (Garrigues et al., 1995; Budzinskiet al., 1997). MP/P ratios in the Sylhet succession are mostly >2(Hossain et al., 2009b), suggesting diagenetic/catagenetic origin.The P and MP in the Sylhet Basin are thus considered to be mostlyof diagenetic origin, rather than of natural wildfire origin. Naturalwildfire generally means forest fires, grass fires and/or peat fires(Youngblood and Blumer, 1975; Rollins et al., 1993; Oros et al.,2006).

Sicre et al. (1987) and Baumard et al. (1998) proposed that Fla/Py ratios could also be used as a combustion parameter, with Fla/Py ratios >1 being characteristic of pyrolytic origins and values<1 implying petroleum sourced PAHs (Sicre et al., 1987; Baumardet al., 1998). Most Fla/Py ratios in the Sylhet succession are P1 (Ta-ble 2), indicating a predominance of combustion/pyrogenic input.According to Yunker et al. (2002, 2011a,b), Fla/(Fla + Py) ratios of>0.5 imply combustion of biomass/solid fossil fuel (grass orwood/coal), whereas values <0.4 are indicative of fossil fuel originand intermediate ratios of 0.4–0.5 indicate liquid fossil fuel com-bustion/mixed sources. The Fla/(Fla + Py) ratios in the Jaintia toSurma Group samples range between �0.40 and 0.67 (Table 2and Fig. 5). Relatively high Fla/(Fla + Py) ratios of up to 0.77 occurin the Tipam and Dupitila groups, although a few samples in thatpart of the succession also have relatively low Fla/(Fla + Py) ratios(<0.4). Overall, most of the Sylhet samples have Fla/(Fla + Py) ratiosof > 0.5, suggesting biomass/solid fossil fuel combustion sourcesfor Fla and Py.

Yunker et al. (2002, 2011a,b, 2012) also reported that InPy/(In-Py + BghiP) ratios of >0.5 imply combustion of biomass (grass,wood or coal), whereas ratios of 0.2–0.5 imply liquid fossil fuelcombustion/mixed sources and those <0.2 are typical of petro-leum/fossil fuel petrogenic origin. Many of the InPy/(InPy + BghiP)ratios in the Sylhet mudstones are close to or greater than 0.2(Fig. 5g and Table 2), suggesting the InPy and BghiP could be ofcombustion origin. However, Tipam and Dupitila groups (L. Mio-cene to Pleistocene) contain the low values <0.2 that are typicalof petrogenic sources. Additionally, a plot of Fla/(Fla + Py) versusBaAn/228 and InPy/(InPy + BghiP) (Fig. 6) was used to identify po-tential sources of PAHs (Yunker et al., 2002, 2011a,b). The BaAn/228 ratios are, however, not consistent with Fla/(Fla + Py) andInPy/(InPy + BghiP), showing lower values (Figs. 5 and 6). The pro-files of BaAn/228 (Fig. 5f) and contents of BaAn in the sedimentarycolumn (Fig. 4c and Table 2) are comparatively lower (0.10–0.29 inratio, and 0.35–2.96%, respectively) in the Surma and Tipam Groupsamples than the ratios of Fla/(Fla + Py) and InPy/(InPy + BghiP).BaAn is more labile to photo-oxidation (Quiroz et al., 2011; Yunkeret al., 2002, 2011a), and the low BaAn/228 ratios and low BaAncontents thus suggest that the BaAn was strongly exposed to sun-light, probably due to lengthy exposure to the air at the land sur-face and/or during prolonged transportation. Another labile PAH,BaPy, also disappears in severe weathering conditions, whereasBePy and benzo[b]fluoranthene are highly resistant to oxidationprocesses (Marynowski et al., 2011a). Yunker et al. (2002, 2011a)suggested that low amounts of BaAn and BaPy could be also dueto solubilization or biodegradation in an oxic water column, or toprolonged exposure in an oxic bottom environmental condition.Therefore, the low abundances of BaAn and BaPy in the Surmaand Tipam groups (Fig. 4) indicate strong weathering in the airand on land before sedimentation and/or in oxic water withinthe basin. Weathering processes also play a significant role indepletion of low molecular weight PAHs such as the methylnaph-thalenes (Gieskes et al., 1990; Marynowski and Simoneit, 2009;Marynowski et al., 2011a). Abundances of methylnaphthalenes in

0

10

20

30

40

50

60

a Dupitila(Pliocene-Pleistocene)

0

10

20

30

40

50

60

b Tipam(late Miocene-Pliocene)

0

10

20

30

40

50

60c Surma

(middle-late Miocene)

0

10

20

30

40

50

60

d Barail (late Eocene-early Miocene)

0

10

20

30

40

50

60

P

Fla Py

BaAn

Chr

y+Tp

n

Bfla

s

BePy

BaPy

Pery

InPy

Bghi

P

Cor Ret

e Jaintia(middle-late Eocene)

Fig. 3. Average relative abundances of PAHs in each group in the Sylhet succession.Abbreviations are defined in Table 2.



the Sylhet succession are very low or below detection limits. Thisalso suggests intensive chemical weathering in the source region,which is consistent with high chemical index of alteration (CIA)values (80–86) recorded in Sylhet mudrocks (Hossain et al., 2010).

BghiP (5-ring) and Cor (6-ring) generally have their origins incombustion (Killops and Massoud, 1992; Leeming and Maher,

1992; Jiang et al., 1998), and have been reported from high inten-sity paleovegetation fires (Finkelstein et al., 2005; Denis et al.,2012). When fuel sources are uniform, hotter fires commonly pro-duce elevated concentrations of 5- and 6-ring PAHs (Killops andMassoud, 1992; O’Malley et al., 1997; Finkelstein et al., 2005;Denis et al., 2012). BePy/InPy/BghiP (5-ring) and Cor (6-ring)

a

Plio

cene

-Pl

eist

ocen

eL.

Mio

cene

-Plio

cene

M .

- L .

Mio

cene

L.Pl

eis-

toce

neL

. Eoc

ene

-E

. Mio

cene

.L-.

E Eoce

ne

Gro

up

Lith

Aeg

Sandstone MudstoneSiltstoneGravelLegend : Lith: Lithology

0

1 km

2 km

3 km

4 km

5 km

6 km

b c fd eDihing

Fla Py BaAnD

upiti

laTi

pam

Sur

ma

Bar

a il

Jain

tiaBflasBePy

0 20 40 60 0 10 20 30 0 5 10 15 0 4 8 120 5 10 15 200 2 4 6 8

BaPy

GirujanClay

TipamSandstone

Bhuban

Bokabil

Renji

JenamKopiliShale

Dupitila

Formation

Fig. 4. Vertical distribution of PAHs in late Eocene to early Pleistocene mudstones in the Sylhet succession, NE Bengal Basin. Lithostratigraphic thicknesses provided here andin Fig. 5 are modified after Hossain et al. (2009a). Abbreviations are defined in Table 2.

Gro

up

Lith

Age

Sandstone Mudstone Siltstone Gravel

0

1 km

2 km

3 km

4 km

5 km

6 km

a c d

Pery Ret

alitipuD

mapiTa

mruS

l iaraB

aitniaJ

Chry + Tpn InPy/(InPy+BghiP) BaAn/228

e f g

Girujan Clay Tipam Sandstone

Bhuban

Bokabil

Renji

Jenam Kopili Shale

Dupitila

Formation

Dihing

Cor

b 9060300 0 3 6 9 12 1520151050 0 0.2 0.4 0.60 0.2 0.4 0.6 0 1 2 3 0.2 0.4 0.6 0.8

Fla/(Fla+Py)

Lith: Lithology

.L-.

E Eoce

neL

. Eoc

ene

-E

. Mio

cene

M .

- L .

Mio

cene

L. M

ioce

ne-P

lioce

nePl

ioce

ne-

Plei

stoc

ene

L.Pl

eis-

toce

ne

Fig. 5. Vertical distribution of selected PAHs and aromatic marker ratios in late Eocene to early Pleistocene mudstones in the Sylhet succession, NE Bengal Basin.Abbreviations are defined in Table 2. The heavy dashed lines in panels e, f and g for PAH ratios based on Fla/(Fla + Py), BaAn/228 and InPy/(InPy + BghiP), respectively, refer tothe source boundaries of Yunker et al. (2002, 2011a,b), and horizontal solid and dashed lines are boundaries between groups and formations, respectively.



therefore suggest more intense wildfires than PAH assemblagesdominated by Py, BaAn, Chry and Bflas (4-ring) in adjacent strata.Fire temperature may further depend on vegetation type and fuelload (Rundel, 1981; Scott, 2000). Low temperature fire (<350 �C)occurs in surface fires where living shrubby and herbaceous plantsor soil humus and peat burn (Albini, 1993; Scott, 2000), whereascrown fires (fires reaching into the crowns of living trees) tend tobe hotter (800–900 �C, Pyne et al., 1996; Scott, 2000). High inten-sity fires occur in environments where natural fuel sources areabundant (mainly living higher plants) and combustion of theseplants produces peak temperatures (Pyne et al., 1996; Scott,2000). In addition, highly pericondensed compounds such as Bflas,BePy and Cor are minimally susceptible to alteration and biodegra-dation (Prahl and Carpenter, 1983; Jiang et al., 1998). Accordingly,increased Cor, InPy and BghiP in the Surma, Tipam and Dupitilagroups suggest an increase in larger, higher temperature wildfires.In contrast, InPy and Cor were below detection limits in most sam-ples from the Jaintia and Barail groups (Table 2 and Fig. 3), imply-ing low to medium temperature wildfires at the time of depositionof these units. Inertinite reflectances >2% are common between2000 m and 4000 m depth (Surma–Tipam groups; Fig. 8), support-ing this interpretation. However, relatively higher concentrationsof PAHs (lg/g TOC) in the Jaintia and Barail groups (Table 4 and5) imply that frequency of the wildfires was also high.

Correlation coefficients of the PAHs and p-values (probability ofno correlation) for statistical hypothesis testing are shown in Ta-ble 3, to more precisely characterize the PAHs. Fla shows a strongpositive correlation with Py (r = 0.83, p = 8.9 � 10�7; Table 3 andFig. 7a). Fla and Py are major PAHs in the Sylhet succession, withabundances of up to 55.9% and 29.0%, respectively (Table 2 andFig. 4). Therefore, Fla and Py are easily formed in the Sylhet succes-sion, suggesting they are representative indicators for all types ofwildfires. Cor is positively correlated with InPy (r = 0.71,

p = 1.3 � 10�4; Fig. 7b), and InPy with BghiP (r = 0.60,p = 2.6 � 10�3; Table 3), and in turn, BghiP is positively correlatedwith Bflas (r = 0.53, p = 9.7 � 10�3; Table 3). Consequently, Cor,InPy, BghiP and Bflas were possibly produced from the same typeof wildfire, probably larger fires, based on their nature as highlypericondensed compounds. On the other hand, Cor is negativelycorrelated with Py (r = �0.57, p = 4.4 � 10�3; Fig. 7c) and P(r = �0.60, p = 2.5 � 10�3; Table 3). Production of Py and P is great-er than Cor in small wildfires due to their lower temperatures.These negative correlations imply that contents of PAHs producedin large wildfires vary antipathetically with PAHs produced insmall wildfires. Large wildfires generally have high temperatures,and organic materials are therefore combusted in air with low oxy-gen content. Therefore, these positive and negative correlationsamong these PAHs may be indicators for the estimation of highor low temperatures in wildfires, based on incomplete combustionof terrigenous plant materials.

BaAn shows marked positive correlations with Chry (r = 0.78,p = 1.2 � 10�5; Table 3) and BaPy (r = 0.55, p = 6.5 � 10�3). Con-tents of BaAn, Chry and BaPy are relatively low in the Surma andTipam groups (Figs. 4 and 5), whereas the other combustion de-rived PAHs such as Fla, Py, Bflas, BePy, InPy, BghiP and Cor are rel-atively enriched. BePy is one of the most stable PAHs (Jiang et al.,1998). In Table 3, BePy is positively correlated with both Cor(r = 0.50, p = 1.6 � 10�2) and Bflas (r = 0.65, p = 7.1 � 10�4). Conse-quently, the differing trends of BaAn, Chry and BaPy from those ofFla, Py, Bflas, BePy, InPy, BghiP and Cor in the sedimentary column(Figs. 4 and 5) suggests different factors controlled the abundancesof these two groups. Susceptibility to decomposition of PAHs couldbe responsible. This susceptibility could possibly be related toweathering processes before sedimentation of the PAHs, e.g. suc-cessive degradation by oxidation to BaAn, BaPy and Chry.

Pery shows a negative correlation with Py (r = �0.67,p = 4.6 � 10�4; Fig. 7d) and Fla (r = �0.56, p = 5.0 � 10�3). Pery alsoshows a marginal positive correlation with Cor (r = 0.41,p = 5.4 � 10�2), whereas Bflas, InPy and BghiP do not correlate withPery. These differences between the groups Pery-Py/Fla and Pery-Cor/Bflas/InPy/BghiP suggest that Cor, Bflas, InPy and BghiP (hightemperature wildfire indicators) do not decrease regularly withincreasing Pery. In fact, Cor increases somewhat with increasingPery. This complex relationship may depend on climate changein the southern Himalaya. As discussed in the next section, Peryis mainly derived from fungi, and hence is a humid climate indica-tor. Consequently, wet climate could decrease frequency of allwildfires, as suggested by the negative correlation of Pery-Py/Fla,while simultaneously production of land plants as fuel for largewildfires increased. The latter situation arises in a humid and sea-sonal climate, with dry season suitable for combustion of abundantdead plant material.

According to the above interpretations of correlation coeffi-cients for the PAHs and their p-values for statistical hypothesistesting, the five statistical groups of [Py, Fla], [Cor, Bflas, InPy,BghiP], [BaAn, Chry, BaPy], [Pery] and [Ret] were probably causedby ‘‘common normal wildfires’’, ‘‘larger high temperature wild-fires’’, ‘‘decomposition processes’’, ‘‘humid climate’’ and ‘‘vegeta-tion’’, respectively.

4.2. PAHs from land biomarkers

Pery and Ret are aromatic land plant biomarkers present in bothsediments and sedimentary rocks (Tan and Heit, 1981; Jiang et al.,1998; Stout and Emsbo-Mattingly, 2008; Suzuki et al., 2010). Peryis extensively distributed in freshwater sediments (Wakehamet al., 1980b; Tan and Heit, 1981) as well as in marine environments(Aizenshtat, 1973; Wakeham et al., 1979; Venkatesan, 1988). Perymay originate from both continental and aquatic OM under the

0.0

0.1

0.2

0.3

0.4

0.5

0.6

BaAn

/228

a

0.3

0.4

0.5

0.6

0.7

0.8

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

0 0.1 0.2 0.3 0.4 0.5 0.6

Fla/

(Fla

+ P

y)

InPy/ (InPy + BghiP)

b

Fla/ (Fla + Py)

Fossil fuel Liquid fossil fuel combustion

Biomass/solid fuel combustion

Fossil fuel

Liquid fossil fuel combustion



Liquid fossil fuel combustion

Fossil fuel

Mixed Sources

Combustion

Fossil fuel

Fig. 6. PAHs cross plots for source identification (after Yunker et al., 2002, 2011a,b)in late Eocene to early Pleistocene mudstones in the Sylhet succession, NE BengalBasin: (a) BaAn/228 vs. Fla/(Fla + Py) and (b) Fla/(Fla + Py) vs. InPy/(InPy + BghiP).



influence of reducing environmental conditions (Aizenshtat, 1973;Wakeham et al., 1979; Silliman et al., 2000; Suzuki et al., 2010),with deposition of perylenequinone structures/pigments from fun-gi (Jiang et al., 1998; Suzuki et al., 2010). Pery is the less stable PAHand is rapidly degraded by oxidative weathering processes (Mary-nowski et al., 2011b). Contents of Pery increase in the Surma and Ti-pam groups (Tables 2, 4 and 5), reaching peak levels in thestratigraphic succession (Figs. 3 and 5). Though a small Pery fluxmay be recognized in pyrolytic PAHs mixtures (Fernández et al.,2000), the Pery depth trend (Fig. 5) and concentration (Table 5) dif-fers from that of representative combustion PAHs such as Fla, Pyand BePy, as discussed above. Therefore, the Pery in the Sylhet Basinis considered to be mainly of fungal origin.

Ret concentrations are generally consistent with in situ diage-netic production from sedimentary precursors, most likely derivedfrom abietic acid or diterpenoid acid in higher plant residues suchas conifer resins (Thomas, 1970; Laflamme and Hites, 1978; Wake-ham et al., 1980b; Tan and Heit, 1981; Simoneit et al., 1986; Jianget al., 1998; Fernández et al., 2000; Otto and Simoneit, 2001; Ottoet al., 2003, 2005; Grimalt et al., 2004). Ret may be produced fromdehydrogenation of abietic acid during early diagenesis (Laflammeand Hites, 1978; Wakeham et al., 1980b; Wen et al., 2000). Villaret al. (1988) considered Ret in Cenozoic carbonaceous shales fromArgentina was derived from conifers resins. Ret is also derivedfrom multiple sources (Laflamme and Hites, 1978; Wakehamet al., 1980b; Ramdahl, 1983; Wen et al., 2000; Nabbefeld et al.,

2010). Ramdahl (1983) reported this compound also originatesfrom thermal degradation of conifer resin compounds and/or lowtemperature combustion of coniferous wood (Ramdahl, 1983; Ottoand Simoneit, 2001; Simoneit, 2002; Yunker et al., 2011b). Micro-bial sources have also been suggested for Ret (Jiang et al., 1998).High relative contents of Ret are sporadically observed in samplesfrom the lower Jaintia, Barail, Surma, Tipam and Dupitila groups(Figs. 3 and 5), showing difference from Pery and the other PAHs.Vitrinite reflectance values in the Sylhet Basin show diagenesis–catagenesis (Ro 0.24–0.70%; Fig. 8), with higher inertinite reflec-tances (Ro 0.8–4.7%; Fig. 8). Di-aromatic simonellite is one of thepossible precursors of tri-aromatic retene during diagenesis of vas-cular plant materials (Wakeham et al., 1980b; Yunker and Macdon-ald, 2003) and combustion of woody materials (Otto and Simoneit,2001; Simoneit, 2002; Yunker et al., 2011b). However, simonellitewas not identified in our study. Concentration of Ret (lg/g TOC inTable 5) is higher in the Jaintia and Barail groups. These featurestherefore imply that Ret abundances in this basin were controlledby conifer resin sources with wildfire. Wen et al. (2000) suggestedthat if conifer resin is a source of Ret, then the OM in the sedimentsis relatively rich in terrigenous higher plant material. Hossain et al.(2009a,b) reported that higher plant OM predominates in the low-er part of the Sylhet succession. This is consistent with the study ofsporopollen assemblages by Wu et al. (2008) and Wang et al.(2011), who found that coniferous trees were abundant in the Ti-betan Himalayas during the Miocene.

y = 1.6387x - 2.7884 r = 0.83

0

10

20

30

40

50

60

0 10 20 30

Fla

Py

y = 2.4753x - 0.0621 r = 0.71

0

2

4

6

8

10

12

14

0 1 2 3

InPy

Cor

(a) (b)

(c) (d) y = - 0.0605x + 1.3148 r = - 0.57

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30

Cor

Py

y = - 0.1893x + 14.932 r = - 0.67

0

5

10

15

20

25

30

0 20 40 60 80 100

Py

Pery

Fig. 7. Selected PAHs cross plots with correlation coefficients for Tertiary mudstones in the Sylhet succession, NE Bengal Basin.



4.3. PAHs for paleoclimate reconstruction

Based on the abundances of combustion PAHs markers and aro-matic biomarkers, the Sylhet succession is interpreted to have beendeposited in three differing paleoclimatic regimes.

In the first phase (middle Eocene to early Miocene Jaintia andBarail Group: early to middle stage of Himalayan uplift; Fig. 9a),combustion derived PAHs are abundant, along with significant aro-matic plant marker Ret contents (Figs. 3 and 5) from gymnosperm,

but with very low Pery abundances, indicating arid climatic condi-tions. This inference is supported by high CIA (�85) and plagioclaseindex of alteration (PIA, �98) values in Jaintia and Barail Groupmudstones (Hossain et al., 2010). The arid climatic conditions pro-posed are compatible with Wang et al. (2011), who showed thatpaleoclimate in the central Tibetan Plateau became dry after theEocene–Oligocene boundary. Furthermore, Wu et al. (2008)showed fossilized vegetation grew in a dry climate in the OligoceneYaxicuo Group of the Tibetan Plateau. Oligocene Lunpori oil shalein the Tibetan Plateau was deposited in a highly saline lacustrineenvironment (Wang et al., 2011), also suggesting arid climate. Oxy-gen and carbon isotope values in Oligocene carbonates in the Nimaarea of the Tibetan Plateau also suggest an arid climate at that time(DeCelles et al., 2007). The relatively low abundances of the humidclimate marker Pery in our study are consistent with relatively lowsedimentation rates (20–40 m/Ma in the Jaintia and Barail groups;Hossain et al., 2009a). Sediments in the Sylhet Basin were derivedfrom the Himalaya (Hossain et al., 2010). Organic matter in theJaintia and Barail groups (early Eocene to early Miocene) weredeposited entirely in seawater-dominated conditions, with rela-tively high contents of terrigenous higher plants including angio-sperms (Hossain et al., 2009a). Accordingly, both gymnosperms(Ret) and angiosperms were abundant in the lower Sylhet succes-sion. The predominant combustion PAHs (Fla, Py and BePy) in theJaintia and Barail groups (Fig. 4 and Table 5) indicate that wildfireoften occurred in the watersheds of the ancestral Ganges and Brah-maputra rivers during the early Eocene and early Miocene. How-ever, abundances of the 5- or 6-ring combustion PAHs (Cor, InPyand BghiP) are low and Fla, Py and BePy are high (Fig. 4 and Ta-ble 5), suggesting that the wildfires were relatively small scale,but with higher frequency. The arid and hotter climate at the timemay have supported herbaceous forests and/or savanna with onlyshort or medium height plants, hence limiting fuel for larger wild-fires. Uplift of the Himalaya and Tibetan Plateau began from theEocene at about 50 Ma. Chemical weathering then accelerated overa large area and global cooling was induced in the late Cenozoic(Raymo et al., 1988; Wang et al., 2008).

In the second climatic phase (middle to late Miocene SurmaGroup: middle to late stage of Himalayan uplift; Prell and Kutz-bach, 1992; Rea, 1992; Song et al., 2010; Fig. 9b), both combustionderived PAHs and fungi derived Pery are dominant, suggesting aridto humid and seasonal climatic conditions (Jiang et al., 1998).Abundances of combustion derived PAH high temperature markers

Fig. 8. Vertical distribution of vitrinite (filled circles) and inertinite (open circles)reflectances in mudstones in the Sylhet succession. Open squares are averagevitrinite reflectances.

Table 3Correlation coefficient (bold values, upper right) and p-value (probability of no correlation) for the statistical hypothesis testing (lower left).

P Fla Py BaAn Chry+Tpn Bflas BePy BaPy Pery InPy BghiP Cor Ret PAIa Fla/(Fla+Py)

InPy/(InPy+BghiP)

BaAn/228 TOCb

P – 0.18 0.49 0.45 0.20 �0.64 �0.39 0.04 �0.61 �0.37 �0.37 �0.60 0.01 �0.52 �0.12 �0.32 0.56 0.37Fla 0.400 – 0.83 �0.07 �0.06 �0.44 �0.26 �0.34 �0.56 �0.25 �0.32 �0.34 �0.21 �0.43 0.46 0.27 �0.18 0.08Py 0.019 0.000 – 0.17 0.17 �0.59 �0.26 �0.28 �0.67 �0.44 �0.51 �0.57 �0.11 �0.48 0.02 0.09 0.11 0.41BaAn 0.031 0.761 0.425 – 0.78 �0.13 �0.27 0.55 �0.52 �0.15 �0.21 �0.49 0.48 �0.06 �0.11 �0.69 0.87 0.63Chry+Tpn 0.360 0.792 0.425 0.000 – 0.06 �0.08 0.38 �0.40 �0.12 �0.24 �0.39 0.51 0.08 �0.05 �0.72 0.49 0.35Bflas 0.001 0.034 0.003 0.565 0.786 – 0.65 0.44 0.27 0.36 0.53 0.50 0.14 0.93 �0.10 �0.11 �0.19 �0.24BePy 0.067 0.234 0.238 0.213 0.710 0.001 – �0.10 0.26 0.00 0.05 0.50 �0.14 0.84 �0.26 0.00 �0.37 �0.16BaPy 0.848 0.111 0.199 0.007 0.071 0.036 0.634 – �0.31 0.36 0.59 0.03 0.44 0.40 �0.02 �0.46 0.60 0.33Pery 0.002 0.005 0.000 0.011 0.061 0.216 0.237 0.153 – 0.04 0.01 0.41 �0.31 0.18 �0.23 0.26 �0.53 �0.41InPy 0.079 0.246 0.033 0.482 0.584 0.096 0.996 0.089 0.852 – 0.60 0.71 0.41 0.25 0.33 0.32 0.02 �0.38BghiP 0.084 0.137 0.014 0.326 0.261 0.010 0.824 0.003 0.964 0.003 – 0.49 0.14 0.42 0.20 0.04 0.00 �0.21Cor 0.002 0.113 0.004 0.017 0.065 0.016 0.016 0.875 0.054 0.000 0.017 – 0.05 0.51 0.12 0.41 �0.39 �0.46Ret 0.977 0.333 0.629 0.019 0.013 0.511 0.537 0.034 0.150 0.053 0.509 0.804 – 0.10 0.03 �0.16 0.55 0.24PAI 0.012 0.038 0.021 0.772 0.710 0.000 0.000 0.060 0.404 0.246 0.049 0.012 0.640 – �0.20 �0.17 �0.13 �0.11Fla/(Fla+Py) 0.593 0.029 0.937 0.631 0.821 0.651 0.222 0.912 0.300 0.124 0.355 0.587 0.905 0.350 – 0.23 �0.13 �0.35InPy/(InPy+BghiP) 0.143 0.209 0.692 0.000 0.000 0.606 0.989 0.026 0.230 0.132 0.856 0.053 0.459 0.433 0.286 – �0.56 �0.24BaAn/228 0.005 0.410 0.623 0.000 0.018 0.383 0.086 0.003 0.009 0.937 0.984 0.068 0.006 0.539 0.553 0.006 – 0.55TOC 0.083 0.725 0.050 0.001 0.097 0.263 0.475 0.124 0.049 0.076 0.343 0.028 0.261 0.625 0.105 0.278 0.006 –

a PAI is the total of the pentacyclic m/z 252 aromatic hydrocarbon isomers Bflas, BePy and BaPy.b TOC data are from Hossain et al. (2009a).



Table 4Concentrations (lg/g TOC) of PAHs in Sylhet mudstones, NE Bengal Basin, Bangladesh. Abbreviations are defined in Table 2.

Sample No Group Formation Depth (m) P Fla Py BaAn Chry+Tpn Bflas BePy BaPy Pery InPy BghiP Cor Ret

Z-02-surface Dupitila Dupitila 400 0.057 0.261 0.154 0.146 0.586 1.04 0.412 0.689 1.40 0.462 5.20 0.182 0.611Z-03-surface Dupitila Dupitila 600 0.045 0.065 0.010 0.047 0.055 0.064 0.019 0.028 0.127 0.194 0.579 0.012 0.160Z-14-surface Tipam Girujan 1595 0.175 0.496 0.230 0.095 0.673 0.802 0.821 0.012 28.9 0.282 0.544 0.183 0.465Z-15-surface Tipam Girujan 1740 0.071 0.208 0.248 0.054 0.308 0.118 0.067 0.051 0.397 0.017 –a – 0.219Z-20-surface Tipam Tipam 1870 0.447 1.84 4.15 0.187 2.37 2.10 2.71 0.304 30.6 0.878 2.05 0.977 1.41Z-28-surface Tipam Tipam 2400 0.464 0.838 1.81 0.182 2.34 1.99 3.46 0.384 22.6 0.777 3.85 1.41 1.30ZH-122, 1085.4m Surma Bokabil 2820 7.26 20.7 12.6 0.105 1.72 0.711 0.892 0.046 0.532 0.355 0.429 0.224 1.34ZH-126, 1249.7m Surma Bokabil 2880 1.69 18.8 10.6 0.241 1.79 0.883 1.12 0.026 0.764 0.222 0.628 0.193 1.11ZH-128, 1827.9m Surma Bokabil 3110 0.771 11.7 7.57 0.161 3.11 1.74 3.93 0.182 4.61 0.492 2.65 0.739 2.87ZH-55, 2198.0m Surma Bokabil 3200 48.8 15.5 16.5 0.624 4.70 3.29 5.30 0.548 8.33 1.04 3.73 0.857 5.18Z-31-surface Surma Bokabil 2790 0.415 0.745 1.81 0.203 2.08 3.21 3.90 0.875 31.8 0.993 4.03 1.38 2.23Z-35-surface Surma Bokabil 2900 0.849 1.35 2.78 0.310 3.60 3.56 6.33 0.793 46.4 1.18 5.19 2.19 4.95ZH-59, 2459.0m Surma Bhuban 3750 0.215 4.25 1.85 0.265 2.95 2.56 5.17 0.241 6.00 0.806 3.38 1.32 2.77ZH-88, 3770.0m Surma Bhuban 3770 0.946 2.65 2.61 0.382 2.39 1.64 3.85 0.670 17.9 0.482 3.58 1.66 5.37Z-43-surface Surma Bhuban 3800 0.602 1.99 4.36 0.461 2.15 1.94 2.18 0.121 8.19 0.509 2.32 0.353 7.53ZH-14, 961.1m Surma Bhuban 3817 1.63 6.13 5.01 0.136 2.96 1.96 5.07 0.813 8.70 1.24 2.62 1.53 1.51Z-55-surface Barail Renji 5350 233 40.3 94.3 21.2 32.5 2.67 25.1 8.17 12.3 2.37 3.37 0.076 84.5Z-57-surface Barail Renji 5600 133 40.3 75.1 19.6 32.3 3.54 21.2 10.1 14.9 – 0.488 – 3.63ZH-11, 4733.0m Barail Jenam 6040 20.0 7.01 8.45 3.52 7.36 0.484 3.16 0.800 0.622 – 0.670 – 4.19ZH-12, 4735.0m Barail Jenam 6100 198 51.1 34.9 15.3 34.4 5.53 19.5 2.65 6.32 – 2.48 – 10.2Z-70-surface Jaintia Kopili 6300 21.8 37.4 15.7 21.2 31.0 7.00 6.69 8.61 13.0 – 1.56 – 20.0Z-72-surface Jaintia Kopili 6310 38.1 29.6 16.5 13.8 26.5 7.74 7.64 6.07 15.6 – 3.15 – 26.6Z-74-surface Jaintia Kopili 6320 22.4 9.76 19.8 15.8 20.5 26.7 23.0 9.86 6.32 – – – 15.3


H.M

.ZakirH

ossainet

al./Organic

Geochem

istry56

(2013)25–

3935


(Fla, Bflas, BePy, Cor, InPy and BghiP; Figs. 4 and 5) increase in Sur-ma Group mudstones, suggesting occurrence of periodic large for-est fires and/or peat fires (Jiang et al., 1998), although frequency ofthe wildfires decreased (Table 5). Relatively abundant Pery origi-nated from fungi flourishing in moist/humid climate (Grice et al.,2009; Suzuki et al., 2010), and were subsequently deposited in an-oxic conditions (Aizenshtat, 1973). Relative contents of Ret fromland plant gymnosperm source are moderate to high (Fig. 5). Hoss-ain et al. (2009a) reported that OM with low angiosperm contentsin the group was deposited in freshwater anoxic conditions, alongwith a small seawater influence. Low CIA ratios (�75) and TOCcontents (�0.5%) in the Surma Group mudstones suggested weakerchemical weathering even in humid climate, coinciding with rapiduplift of the Himalaya (Hossain et al., 2009a, 2010) and dilution ofOM by high sedimentation rates (40–65 m/Ma in the Surma Group;Hossain et al., 2009a). Climatic conditions around southern slopesof the Himalaya in the early Miocene were probably humid, with aforest dominated by coniferous trees. This interpretation is consis-tent with carbon and oxygen isotope evidence (Wu et al., 2009;Wang et al., 2011; Zhuang et al., 2011). These reconstructions alsosupport the suggestion of Clift et al. (2008) that strengthening ofthe Himalayan summer monsoon began during the middle Mio-cene. With the establishment of seasonal climatic conditions, dry

periods would favor combustion (Jiang et al., 1998). The Hima-laya–Tibetan Plateau had reached sufficient elevation by the lateMiocene (�10 Ma) to produce the Indian summer and winter mon-soons (Prell and Kutzbach, 1992; Rea, 1992; Song et al., 2010). Thishigh elevation may have contributed to global climate changes andsevere erosion and corresponds to a period of pronounced globalcooling (Fort, 1996; Wang et al., 2008). Rollins et al. (1993) re-ported that swamps and peat bogs are developed in fluvio-deltaicdepositional environments; these bogs would be susceptible towildfire during dry climatic seasons. Deltaic and marine deposi-tional environments existed in the Sylhet Basin (Johnson and Alam,1991; Reimann, 1993; Najman et al., 2008). Consequently, bothforest trees and peats could be possible fuels for wildfires. Thecauses of ignition of the arid plants could be due to lightningstrikes and/or volcanic activity from subduction of the oceanicplate (Tapponnier et al., 2001; Ding et al., 2003). In the earliest Ter-tiary (around 65–45 Ma) voluminous volcanic eruptions were trig-gered in the Himalaya and Tibet by the initial subduction of theIndian continental shelf (Yin and Harrison, 2000; Ding et al.,2003). The youngest volcanic eruption in the southern Lhasa ter-rane in Tibet occurred around 16–8 Ma (Ding et al., 2003).

In the third climatic phase (late Miocene to Pleistocene Tipamand Dupitila groups: late stage of Himalayan uplift; Fig. 9c),

Table 5Average PAH concentrations (lg/g TOC) in the Jaintia, Barail, Surma, Tipam and Dupitila groups of the Sylhet succession, NE Bengal Basin, Bangladesh. Abbreviations are defined inTable 2.

Group P Fla Py BaAn Chry+Tpn Bflas BePy BaPy Pery InPy BghiP Cor Ret

Dupitila 0.051 0.163 0.082 0.097 0.321 0.554 0.215 0.359 0.762 0.328 2.89 0.097 0.386Tipam 0.289 0.845 1.61 0.130 1.42 1.25 1.77 0.187 20.6 0.488 1.61 0.642 0.847Surma 6.32 8.39 6.57 0.289 2.75 2.15 3.77 0.432 13.3 0.731 2.86 1.04 3.49Barail 146 34.7 53.2 14.9 26.6 3.06 17.3 5.42 8.53 0.592 1.75 0.019 25.6Jaintia 27.4 25.6 17.4 16.9 26.0 13.8 12.4 8.18 11.6 –a 1.57 –a 20.6


Uplift

Uplift

Bay of Bengal

Continental crust Oceanic crust

Dauki fault

Bay of Bengal


Dauki fault

Sedimentsupply

Bay of Bengal


Indian Craton

(a)

(b)

(c)

SylhetBasin

SylhetBasin

SylhetBasin

Arid climate

Arid/Humidseasonalclimate

I - First Phase

II - Second Phase

III - Third Phase

(M. Eocene - E. MioceneJaintia - Barail groups)

(M. - L. MioceneSurma Group)

(L. Miocene - PleistoceneTipam - Dupitila groups)

Forest fire

Sedimentsupply

Sedimentsupply

Lowsedimentation

Highsedimentation

Highsedimentation

Arid/Humidseasonalclimate

(Himalayan monsoon)

(Himalayan monsoon)

Fig. 9. Schematic cross-sections for paleoclimatic changes in the Sylhet succession in Bangladesh during Himalayan uplift.



medium to high Pery and low contents of the general combustionderived PAHs marker (Fla, Py and BePy) indicate more humid cli-mate prevailed and frequency of the wildfires decreased succes-sively (Table 5), although intense-combustion markers (InPy,BghiP, Cor, Bflas and BaPy) remain predominant (Fig. 4). Fort(1996) reported that tropical and subtropical climates prevailedduring the Mio-Pliocene, suggesting rather warm and humid cli-matic conditions south of the Himalaya. Pollen studies in thesouthern Himalaya indicate subtropical, seasonally dry and morehumid climates during the Mio-Pliocene phases (Fort, 1996). Oxy-gen and carbon isotopic data from the late Miocene to Pliocenelacustrine–fluvial Woma Formation in the central Himalaya(southern edge of the Tethyan Himalayan thrust belt) indicatealternating wet and dry climates (Wang et al., 2012). The relativelyhigh contents of the aromatic plant marker Ret in the Dupitila sed-iments indicate that coniferous plant sources increased and botharid to humid climatic condition prevailed. Sedimentation rateswere also high at this time (30–90 m/Ma in the Tipam and Dupitilagroups; Hossain et al., 2009a). Increased humid climate arisingfrom the Himalayan monsoon could decrease general wildfires,and increase large wildfires.

5. Conclusions

The PAHs P, Fla, Py, BaAn, Chry, Bflas, BePy, BaPy, Pery, InPy,BghiP, Cor and Ret were identified in late Eocene to early Pleisto-cene mudstones from the Sylhet succession in the NE Bengal Basinin Bangladesh. Fla/(Fla + Py) ratios > 0.5 and InPy/(InPy + B-ghiP) > 0.2 from almost all Sylhet samples suggest occurrence ofwildfires of grass, wood and/or peat/coal origins. BaAn/228 ratiosand BaAn and BaPy contents were comparatively lower (0.10–0.29 ratios, 0.35–3.0% and 0.15–3.1% contents, respectively) inthe Surma and Tipam groups. This suggests that the BaAn and BaPywere exposed to strong sunlight or exposed for a long time before/after sedimentation. Increased Cor, InPy and BghiP contents in Sur-ma, Tipam and Dupitila groups suggest an increase in larger, hightemperature wildfires. Correlation coefficients of the PAHs andtheir p-values show strong correlations for Fla-Py (r = 0.83,p = 8.9 � 10�7) and Cor-InPy (r = 0.71, p = 1.3 � 10�4). The Fla andPy are major PAHs in the Sylhet succession, comprising up to55.9% and 29.0%, respectively, and are thought to be easily formedin all wildfires. Cor, InPy, BghiP and Bflas are also well correlatedwith each other, possibly indicating origin from same type of wild-fires, due to their highly pericondensed chemical structures. Fur-thermore, Cor is negatively correlated with Py (r = �0.57,p = 4.4 � 10�3). These positive and negative correlations withinthe combustion PAHs may be indicators for high and low temper-atures in wildfires. Fungi derived Pery is negatively correlated withPy (r = �0.67, p = 4.6 � 10�4) and Fla (r = �0.56, p = 5.0 � 10�3).However, Pery is not negatively correlated with Cor, Bflas, InPyand BghiP. This may be due to decreased frequency of wildfiresduring humid climate, although the ratio of large to small wildfiresincreased simultaneously, due to increased production of landplants as fuel. Based on correlation coefficients for all PAHs andtheir p-values in the Sylhet succession, five statistical groups [Py,Fla], [Cor, Bflas, InPy, BghiP], [BaAn, Chry, BaPy], [Pery] and [Ret]are recognized. These probably correlate to ‘‘common normal wild-fires’’, ‘‘larger high temperature wildfires’’, ‘‘decomposition pro-cesses’’, ‘‘humid climate’’, and ‘‘vegetation’’, respectively.

The Sylhet succession is interpreted to have been deposited un-der three differing paleoclimatic regimes, based on the patterns ofcombustion derived PAHs and aromatic land plant biomarkers.

(1) First phase (late Eocene to early Miocene: early to middlestage of Himalayan uplift): Combustion derived PAHs (Fla,Py and BePy) were abundant, combined with amounts of

the significant gymnosperm marker Ret, but with very lowPery abundances. This association indicates arid climaticconditions. Wildfires could have often occurred in the water-sheds of the Ganges and Brahmaputra rivers. However,abundances of the combustion 5- or 6-ring PAHs (Cor, InPyand BghiP) are low, suggesting the wildfires were relativelysmall.

(2) Second phase (middle to late Miocene: middle to late stageof Himalayan uplift): Both combustion derived PAHs andfungi derived Pery were dominant, suggesting arid to humidand seasonal climate with a dry season, hence suitable forcombustion. High temperature markers (Fla, Bflas, BePy,Cor, InPy and BghiP) were abundant, indicating periodiclarge forest fires and/or peat fires. Simultaneously, wet cli-mate decreased the frequency of wildfire. Ret contents aremoderate to high, suggesting a forest dominated by conifer-ous trees on the south slope of the Himalaya. These featuresmay be due to accelerated Asian monsoon caused by uplift ofthe Himalaya.

(3) Third phase (late Miocene to Pleistocene: late stage of Hima-layan uplift): Medium to high Pery and low contents of gen-eral combustion derived PAHs markers (Fla, Py and BePy)indicate more humid climate prevailed. Strong-combustionmarkers (InPy, BghiP, Cor, Bflas and BaPy) predominate.Intensified humid and seasonal climate arising from theHimalayan monsoon could have decreased incidence andfrequency of general wildfires, but increased the ratio oflarge to small wildfires.

Acknowledgements

We thank BAPEX (Bangladesh Petroleum Exploration and Pro-duction Company) and PETROBANGLA (Bangladesh Oil, Gas andMineral Corporation) for supply of core samples and printed mate-rials, and M. S.-U.-Islam, M.K. Roy, I. Hossain and A.K.M.M. Kabir fortheir enthusiasm in collecting samples during fieldwork. Reviewsby associate editor Drs. M.B. Yunker, L. Marynowski and an anon-ymous referee substantially improved this manuscript. Financialsupport from Monbukagakusho (MEXT), the Heiwa NakajimaFoundation, and Honors scholarships (to HMZH) are gratefullyacknowledged.

Associate Editor – Mark Yunker

References

Ahmed, M., Khan, S.I., Sattar, M.A., 1991. Geochemical characterization of oils andcondensates in the Bengal Foredeep, Bangladesh. Journal of Southeast AsianEarth Sciences 5, 391–399.

Aizenshtat, Z., 1973. Perylene and its geochemical significance. Geochimica etCosmochimica Acta 37, 559–567.

Alam, M., Pearson, M.J., 1990. Bicadinanes in oils from the Surma Basin, Bangladesh.Organic Geochemistry 15, 461–464.

Alam, M., Pearson, M.J., 1993. Bicadinanes and other terrestrial terpenoids inimmature Oligocene sedimentary rocks and a related oil from the Surma Basin,NE Bangladesh. Organic Geochemistry 20, 539–554.

Alam, M., Alam, M.M., Curray, J.R., Chowdhury, M.L.R., Gani, M.R., 2003. An overviewof the sedimentary geology of the Bengal Basin in relation to the regionaltectonic framework and basin-fill history. Sedimentary Geology 155, 179–208.

Albini, F.A., 1993. Dynamics and modelling vegetation fires: observations. In:Crutzen, P.J., Goldammer, J.G. (Eds.), Fire in the Environment: The Ecological,Atmospheric and Climatic Importance of Vegetation Fires. Wiley, Chichester, pp.39–52.

Baumard, P., Budzinski, H., Garrigues, P., 1998. Polycyclic aromatic hydrocarbons insediments and mussels of the western Mediterranean Sea. EnvironmentalToxicology and Chemistry 17, 765–776.

Bechtel, A., Gratzer, R., Püttmann, W., Oszczepalski, S., 2001. Variable alteration oforganic matter in relation to metal zoning at the Rote Faule front (Lubin-Sieroszowice mining district, SW Poland). Organic Geochemistry 32, 377–395.



Bence, A.E., Kvenvolden, K.A., Kennicutt, M.C., 1996. Organic geochemistry appliedto environmental assessments of Prince William Sound, Alaska, after the ExxonValdez oil spill – a review. Organic Geochemistry 24, 7–42.

Benner, B.A., Gordon, G.E., Wise, S.A., 1989. Mobile sources of atmosphericpolycyclic aromatic hydrocarbons: a roadway tunnel study. EnvironmentalScience and Technology 23, 1269–1278.

Benner, B.A., Bryner, N.P., Wise, S.A., Mulholland, G.H., Lao, R.C., Fingas, M.F., 1990.Polycyclic aromatic hydrocarbon emissions from combustion of crude oil onwater. Environmental Science and Technology 24, 1418–1427.

Budzinski, H., Jones, I., Bellocq, J., Piérard, C., Garrigues, P., 1997. Evaluation ofsediment contamination by polycyclic aromatic hydrocarbons in the Girondeestuary. Marine Chemistry 58, 85–97.

Chefetz, B., Deshmukh, A.P., Hatcher, P.G., Guthrie, E.A., 2000. Pyrene sorption bynatural organic matter. Environmental Science and Technology 34, 2925–2930.

Clayton, J.L., King, J.D., 1987. Effects of weathering on biological marker andaromatic hydrocarbon composition of organic matter in Phosphoria shaleoutcrop. Geochimica et Cosmochimica Acta 51, 2153–2157.

Clift, P.D., Hodges, K.V., Heslop, D., Hannigan, R., Van Long, H., Calves, G., 2008.Correlation of Himalayan exhumation rates and Asian monsoon intensity.Nature Geoscience 1, 875–880.

DeCelles, P., Quade, J., Kapp, P., Fan, M., Dettman, D., Ding, L., 2007. High and dry incentral Tibet during the Late Oligocene. Earth and Planetary Science Letters 253,389–401.

Denis, E.H., Toney, J.L., Tarozo, R., Anderson, R.S., Roach, L.D., Huang, H., 2012.Polycyclic aromatic hydrocarbons (PAHs) in lake sediments record historic fireevents: validation using HPLC-fluorescence detection. Organic Geochemistry45, 7–17.

Ding, L., Kapp, P., Zhong, D.L., Deng, W.M., 2003. Cenozoic volcanism in Tibet:evidence for a transition from oceanic to continental subduction. Journal ofPetrology 44, 1833–1865.

Fan, C.-W., Shiue, J., Wu, C.-Y., Wu, C.-Y., 2011. Perylene dominance in sedimentsfrom a subtropical high mountain lake. Organic Geochemistry 42, 116–119.

Fernández, P., Vilanova, R.M., Grimalt, J.O., 1999. Sediment fluxes of polycyclicaromatic hydrocarbons in European high altitude mountain lakes.Environmental Science and Technology 33, 3716–3722.

Fernández, P., Vilanova, R.M., Martínez, C.A., Appleby, P., Grimalt, J.O., 2000. Thehistorical record of atmospheric pyrolytic pollution over Europe registered inthe sedimentary PAH from remote mountain lakes. Environmental Science andTechnology 34, 1906–1913.

Finkelstein, D.B., Pratt, L.M., Curtin, T.M., Brassell, S.C., 2005. Wildfires and seasonalaridity recorded in Late Cretaceous strata from south-eastern Arizona, USA.Sedimentology 52, 587–599.

Fort, M., 1996. Late Cenozoic environmental changes and uplift on the northern sideof the central Himalaya: a reappraisal from field data. Palaeogeography,Palaeoclimatology, Palaeoecology 120, 123–145.

Garrigues, P., Budzinski, H., Mantiz, M.P., Wise, S.A., 1995. Pyrolytic and petrogenicinputs in recent sediments: a definitive signature through phenanthrene andchrysene compound distribution. Polycyclic Aromatic Compounds 7, 275–284.

Gieskes, J.M., Simoneit, B.R.T., Magenheim, A.J., Leif, R.N., 1990. Retrogradeoxidation of hydrothermal precipitates and petroleum in Escanaba Troughsediments. Applied Geochemistry 5, 93–101.

Goodbred Jr., S.L., Kuehl, S.A., 2000. The significance of large sediment supply, activetectonism, and eustasy on margin sequence development: Late Quaternarystratigraphy and evolution of the Ganges – Brahmaputra delta. SedimentaryGeology 133, 227–248.

Grice, K., Nabbefeld, B., Maslen, E., 2007. Source and significance of selectedpolycyclic aromatic hydrocarbons in sediments (Hovea-3 well, Perth Basin,Western Australia) spanning the Permian–Triassic boundary. OrganicGeochemistry 38, 1795–1803.

Grice, K., Lu, H., Atahan, P., Asif, M., Hallmann, C., Greenwood, P., Maslen, E.,Tulipani, S., Williford, K., Dodson, J., 2009. New insights into the origin ofperylene in geological samples. Geochimica et Cosmochimica Acta 73, 6531–6543.

Grimalt, J.O., Drooge, B.L.V., Ribes, A., Fernández, P., Appleby, P., 2004. Polycyclicaromatic hydrocarbon composition in soils and sediments of high altitude lakes.Environmental Pollution 131, 13–24.

Haberstroh, P.R., Brandes, J.A., Gélinas, Y., Dickens, A.F., Wirick, S., Cody, G., 2006.Chemical composition of the graphitic black carbon fraction in riverine andmarine sediments at sub-micron scales using carbon X-ray spectromicroscopy.Geochimica et Cosmochimica Acta 70, 1483–1494.

Harvey, R.G., 1996. Polycyclic Aromatic Hydrocarbons. Wiley, New York, pp. 8–11.Hasegawa, T., 2001. Predominance of terrigenous organic matter in Cretaceous

marine fore-arc sediments, Japan and Far East Russia. International Journal ofCoal Geology 47, 207–221.

Hites, R.A., Laflamme, R.E., Farrington, J.W., 1977. Sedimentary polycyclic aromatichydrocarbons: the historical records. Science 198, 829–831.

Hites, R.A., Laflamme, R.E., Windsor Jr., J.G., Farrington, J.W., Werner, G.D., 1980.Polycyclic aromatic hydrocarbons in an anoxic sediment core from thePettaquamscutt River (Rhode Island, USA). Geochimica et Cosmochimica Acta44, 873–878.

Hossain, H.M.Z., Sampei, Y., Roser, B.P., 2009a. Characterization of organic matterand depositional environment of Tertiary mudstones from the Sylhet Basin,Bangladesh. Organic Geochemistry 40, 743–754.

Hossain, H.M.Z., Sampei, Y., Roser, B.P., 2009b. Influence of organic matter type onthe distribution of tri-aromatic hydrocarbons in Tertiary mudstones in theSylhet Basin, Bangladesh. Researches in Organic Geochemistry 25, 39–52.

Hossain, H.M.Z., Roser, B.P., Kimura, J.-I., 2010. Petrography and whole-rockgeochemistry of the Tertiary Sylhet succession, northeastern Bengal Basin,Bangladesh: provenance and source area weathering. Sedimentary Geology228, 171–183.

Imam, M.B., Hussain, M., 2002. A review of hydrocarbon habitats in Bangladesh.Journal of Petroleum Geology 25, 31–52.

Jiang, C., Alexander, R., Kagi, R.I., Murray, A.P., 1998. Polycyclic aromatichydrocarbons in ancient sediments and their relationships to palaeoclimate.Organic Geochemistry 29, 1721–1735.

Jiang, C., Alexander, R., Kagi, R.I., Murray, A.P., 2000. Origin of perylene in ancientsediments and its geological significance. Organic Geochemistry 31, 1545–1559.

Johnson, S.Y., Alam, A.M.N., 1991. Sedimentation and tectonics of the Sylhet trough,Bangladesh. Geological Society of America Bulletin 103, 1513–1527.

Kawamura, K., Ishiwatari, R., Ogura, K., 1987. Early diagenesis of organic matter inthe water column and sediments: microbial degradation and resynthesis oflipids in Lake Haruna. Organic Geochemistry 4, 251–264.

Khan, F.H., 1991. Geology of Bangladesh. The University Press Limited, Dhaka,Bangladesh.

Killops, S.D., Massoud, M.S., 1992. Polycyclic aromatic hydrocarbons of pyrolyticorigin in ancient sediments: evidence for Jurassic vegetation fires. OrganicGeochemistry 18, 1–7.

Laflamme, R.E., Hites, R.A., 1978. The global distribution of polycyclic aromatichydrocarbons in recent sediments. Geochimica et Cosmochimica Acta 42, 289–303.

Leeming, R., Maher, W., 1992. Sources of polycyclic aromatic hydrocarbons in LakeBurley Griffin, Australia. Organic Geochemistry 18, 647–655.

Lindsay, J.F., Holliday, D.W., Hulbert, A.G., 1991. Sequence stratigraphy and theevolution of the Ganges – Brahmaputra Delta complex. American Association ofPetroleum Geologists Bulletin 75, 1233–1254.

Liu, G.Q., Zhang, G., Li, X.D., Li, J., Peng, X.Z., Qi, S.H., 2005. Sedimentary record ofpolycyclic aromatic hydrocarbons in a sediment core from the Pearl RiverEstuary, South China. Marine Pollution Bulletin 51, 912–921.

Luo, X.J., Chen, S.J., Mai, B.X., Yang, Q.S., Sheng, G.Y., Fu, J.M., 2006. Polycyclicaromatic hydrocarbons in suspended particulate matter and sediments fromthe Pearl River Estuary and adjacent coastal areas, China. EnvironmentalPollution 139, 9–20.

Marynowski, L., Simoneit, B.R.T., 2009. Widespread Late Triassic to Early Jurassicwildfire records from Poland: evidence from charcoal and pyrolytic polycyclicaromatic hydrocarbons. Palaios 24, 785–798.

Marynowski, L., Wyszomirski, P., 2008. Organic geochemical evidences of earlydiagenetic oxidation of the terrestrial organic matter during the Triassic aridand semi arid climatic conditions. Applied Geochemistry 23, 2612–2618.

Marynowski, L., Kurkiewicz, S., Rakocinski, M., Simoneit, B.R.T., 2011a. Effects ofweathering on organic matter: I. Changes in molecular composition ofextractable organic compounds caused by paleoweathering of a LowerCarboniferous (Tournaisian) marine black shale. Chemical Geology 285, 144–156.

Marynowski, L., Szeleg, E., Jedrysek, M.O., Simoneit, B.R.T., 2011b. Effects ofweathering on organic matter Part II: fossil wood weathering andimplications for organic geochemical and petrographic studies. OrganicGeochemistry 42, 1076–1088.

Nabbefeld, B., Grice, K., Summons, R.E., Hays, L.E., Cao, C., 2010. Significance ofpolycyclic aromatic hydrocarbons (PAHs) in Permian/Triassic boundarysections. Applied Geochemistry 25, 1374–1382.

Najman, Y., Bickle, M., BouDagher-Fadel, M., Carter, A., Garzanti, E., Paul, M.,Wijbrans, J., Willett, E., Oliver, G., Parrish, R., Akhter, S.H., Allen, R., Ando, S.,Chisty, E., Reisberg, L., Vezzoli, G., 2008. The Paleogene record of Himalayanerosion: Bengal Basin, Bangladesh. Earth and Planetary Science Letters 273, 1–14.

O’Malley, V.P., Burke, R.A., Schlotzhauer, W.S., 1997. Using GC-MS/combustion/IRMS to determine the 13C/12C ratios of individual hydrocarbons produced fromthe combustion of biomass materials – application to biomass burning. OrganicGeochemistry 27, 567–581.

Oros, D.R., Simoneit, B.R.T., 2001a. Identification and emission factors of moleculartracers in organic aerosols from biomass burning Part 1. Temperate climateconifers. Applied Geochemistry 16, 1513–1544.

Oros, D.R., Simoneit, B.R.T., 2001b. Identification and emission factors of moleculartracers in organic aerosols from biomass burning Part 2. Deciduous trees.Applied Geochemistry 16, 1545–1565.

Oros, D.R., Radzi Bin Abas, M., Omar, N.Y., Rahman, N.A., Simoneit, B.R., 2006.Identification and emission factors of molecular tracers in organic aerosols frombiomass burning: Part 3. Grasses. Applied Geochemistry 21, 919–940.

Otto, A., Simoneit, B.R.T., 2001. Chemosystematics and diagenesis of terpenoids infossil conifer species and sediment from the Eocene Zeitz formation, Saxony,Germany. Geochimica et Cosmochimica Acta 65, 3505–3527.

Otto, A., Simoneit, B.R.T., Rember, W.C., 2003. Resin compounds from the seed conesof three fossil conifer species from the Miocene Clarkia flora, Emerald Creek,Idaho, USA, and from related extant species. Review of Palaeobotany andPalynology 126, 225–241.

Otto, A., Simoneit, B.R.T., Rember, W.C., 2005. Conifer and angiosperm biomarkers inclay sediments and fossil plants from the Miocene Clarkia Formation, Idaho,USA. Organic Geochemistry 36, 907–922.

Prahl, F.G., Carpenter, R., 1983. Polycyclic aromatic hydrocarbon (PAH)-phaseassociations in Washington coastal sediment. Geochimica et CosmochimicaActa 47, 1013–1023.



Prell, W.L., Kutzbach, J.E., 1992. Sensitivity of the Indian monsoon to forcingparameters and implication for its evolution. Nature 360, 647–652.

Püttmann, W., Merz, C., Speczik, S., 1989. The secondary oxidation of organicmaterial and its influence on Kupferschiefer mineralization of southwestPoland. Applied Geochemistry 4, 151–161.

Pyne, S.J., Andrews, P.L., Laven, R.D., 1996. Introduction to Wildland Fire. Wiley,New York.

Quiroz, R., Grimalt, J.O., Fernandez, P., Camarero, L., Catalan, J., Stuchlik, E., Thies, H.,Nickus, U., 2011. Polycyclic aromatic hydrocarbons in soils from European highmountain areas. Water, Air & Soil Pollution 215, 655–666.

Ramdahl, T., 1983. Retene – a molecular marker of wood combustion in ambient air.Nature 306, 580–582.

Raymo, M.E., Ruddiman, W.F., Froelich, P.N., 1988. Influence of late Cenozoicmountain building on ocean geochemical cycles. Geology 16, 649–653.

Rea, D.K., 1992. Delivery of Himalayan sediment to the northern Indian Ocean andits relation to global climate, sea level, uplift, and seawater strontium. In:Duncan, et al. (Eds.), Synthesis of Results from Scientific Drilling in the IndianOcean. Geophysical Monograph Series 70. AGU, Washington, DC, pp. 387–402.

Reimann, K.-U., 1993. Geology of Bangladesh. Gebrüder Borntraeger, Berlin, p. 160.Rollins, M.S., Cohen, A.D., Durig, J.R., 1993. Effects of fires on the chemical and

petrographic composition of peat in the Snuggedy Swamp, South Carolina.International Journal of Coal Geology 22, 101–117.

Rundel, P.W., 1981. Fire as an ecological factor. In: Lange, O.L., Nobel, P.S., Osmond,C.B., Ziegler, H. (Eds.), Physiological Plant Ecology I, Response to the PhysicalEnvironment. Springer, Berlin, pp. 501–538.

Scott, A.C., 2000. The Pre-Quaternary history of fire. Palaeogeography,Palaeoclimatology, Palaeoecology 164, 297–345.

Shamsuddin, A.H.M., Abdullah, S.K.M., 1997. Geologic evolution of the Bengal Basinand its implication in hydrocarbon exploration in Bangladesh. Indian Journal ofGeology 69, 93–121.

Sicre, M.A., Marty, J.C., Saliot, A., 1987. Aliphatic and aromatic hydrocarbons indifferent sized aerosols over the Mediterranean Sea: occurrence and origin.Atmospheric Environment 21, 2247–2259.

Silliman, J.E., Meyers, P.A., Ostrom, P.H., Ostrom, N.E., Eadie, B.J., 2000. Insights intothe origin of perylene from isotopic analyses of sediments from Saanich Inlet,British Columbia. Organic Geochemistry 31, 1133–1142.

Simoneit, B.R.T., 2002. Biomass burning – review of organic tracers for smoke fromincomplete combustion. Applied Geochemistry 17, 129–162.

Simoneit, B.R.T., Grimalt, J.O., Wang, T.G., Cox, R.E., Hatcher, P.G., Nissenbaum, A.,1986. Cyclic terpenoids of contemporary resinous plant detritus and of fossilwoods, ambers and coal. Organic Geochemistry 10, 877–889.

Song, X., Spicer, R.A., Yang, J., Yao, Y., Li, C., 2010. Pollen evidence for an Eocene toMiocene elevation of central southern Tibet predating the rise of the HighHimalaya. Palaeogeography, Palaeoclimatology, Palaeoecology 297, 159–168.

Stout, S.A., Emsbo-Mattingly, S.D., 2008. Concentration and character of PAHs andother hydrocarbons in coals of varying rank – implications for environmentalstudies of soils and sediments containing particulate coal. OrganicGeochemistry 39, 801–819.

Suzuki, N., Yessalina, S., Kikuchi, T., 2010. Probable fungal origin of perylene in LateCretaceous to Paleogene terrestrial sedimentary rocks of northeastern Japan asindicated from stable carbon isotopes. Organic Geochemistry 41, 234–241.

Tan, Y.L., Heit, M., 1981. Biogenic and abiogenic polynuclear aromatic hydrocarbonsin sediments from two remote Adirondack lakes. Geochimica et CosmochimicaActa 45, 2267–2279.

Tapponnier, P., Xu, Z.Q., Roger, F., Meyer, B., Arnaud, N., Wittlinger, G., Yang, J.S.,2001. Oblique stepwise rise and growth of the Tibet Plateau. Science 294, 1671–1677.

Thomas, B.R., 1970. Modern and fossil plant resins. In: Harborne, J.B. (Ed.),Phytochemical Phylogeny. Academic Press, London, pp. 59–79.

Uddin, A., Lundberg, N., 1998. Cenozoic history of the Himalayan–Bengal system:sand composition in the Bengal basin, Bangladesh. Geological Society ofAmerica Bulletin 110, 497–511.

Venkatesan, M.I., 1988. Occurrence and possible sources of perylene in marinesediments – a review. Marine Chemistry 25, 1–27.

Venkatesan, M.I., Dahl, J., 1989. Organic geochemical evidence for global fires at theCretaceous/Tertiary boundary. Nature 338, 57–60.

Villar, H.J., Püttmann, W., Wolf, M., 1988. Organic geochemistry and petrography ofTertiary coals and carbonaceous shales from Argentina. Organic Geochemistry13, 1011–1021.

Wakeham, S.G., Schaffner, C., Giger, W., Boon, J.J., Leeuw, J.W.D., 1979. Perylene insediments from the Namibian Shelf. Geochimica et Cosmochimica Acta 43,1141–1144.

Wakeham, S.G., Schaffner, C., Giger, W., 1980a. Polycyclic aromatic hydrocarbons inrecent lake sediments: I. Compounds having anthropogenic origins. Geochimicaet Cosmochimica Acta 44, 403–413.

Wakeham, S., Schaffner, C., Giger, G., 1980b. Polycyclic aromatic hydrocarbons inrecent lake sediments: II. Compounds derived from biogenic precursors duringearly diagenesis. Geochimica et Cosmochimica Acta 44, 415–429.

Wang, C., Zhao, X., Liu, Z., Lippert, P.C., Graham, S.A., Coe, R.S., Yi, H., Zhu, L., Liu, S., Li,Y., 2008. Constraints on the early uplift history of the Tibetan Plateau.Proceedings of the National Academy of Sciences 105, 4987–4992.

Wang, L., Wang, C., Li, Y., Zhu, L., Wei, Y., 2011. Sedimentary and organicgeochemical investigation of tertiary lacustrine oil shale in the centralTibetan plateau: palaeolimnological and palaeoclimatic significances.International Journal of Coal Geology 86, 254–265.

Wang, Y., Deng, T., Flynn, L., Wang, X., Yin, A., Xu, Y., Parker, W., Lochner, E., Zhang,C., Biasatti, D., 2012. Late Neogene environmental changes in the centralHimalaya related to tectonic uplift and orbital forcing. Journal of Asian EarthSciences 44, 62–76.

Wen, Z., Ruiyong, W., Radke, M., Qingyu, W., Guoying, S., Zhili, L., 2000. Retene inpyrolysates of algal and bacterial organic matter. Organic Geochemistry 31,757–762.

Wu, Z., Barosh, P.J., Wu, Z., Hu, D., Zhao, X., Ye, P., 2008. Vast early Miocene lakes ofthe central Tibetan Plateau. Geological Society of America Bulletin 120, 1326–1337.

Wu, Z.H., Wu, Z.H., Hu, D.G., Peng, H., Zhang, Y.L., 2009. Carbon and oxygen isotopechanges and palaeoclimate cycles recorded by lacustrine deposits of MioceneWudaoliang Group in northern Tibetan Plateau. Geology in China 36, 966–975(in Chinese with English abstract).

Yin, A., Harrison, T.M., 2000. Geologic evolution of the Himalayan–Tibetan orogen.Annual Review of Earth and Planetary Sciences 28, 211–280.

Youngblood, W.W., Blumer, M., 1975. Polycyclic aromatic hydrocarbons in theenvironment: homologous series in soils and recent sediments. Geochimica etCosmochimica Acta 39, 1303–1314.

Yunker, M.B., Macdonald, R.W., 2003. Alkane and PAH depositional history, sourcesand fluxes in sediments from the Fraser River Basin and Strait of Georgia,Canada. Organic Geochemistry 34, 1429–1454.

Yunker, M.B., Macdonald, R.W., Vingarzan, R., Mitchell, R.H., Goyette, D., Sylvestre,S., 2002. PAHs in the Fraser River basin: a critical appraisal of PAH ratios asindicators of PAH source and composition. Organic Geochemistry 33, 489–515.

Yunker, M.B., Macdonald, R.W., Snowdon, L.R., Fowler, B.R., 2011a. Alkane and PAHbiomarkers as tracers of terrigenous organic carbon in Arctic Ocean sediments.Organic Geochemistry 42, 1109–1146.

Yunker, M.B., Lachmuth, C.L., Cretney, W.J., Fowler, B.R., Dangerfield, N., White, L.,Ross, P.S., 2011b. Biota–sediment partitioning of aluminium smelter relatedPAHs and pulp mill related diterpenes by intertidal clams at Kitimat, BritishColumbia. Marine Environmental Research 72, 105–126.

Yunker, M.B., Perreault, A., Lowe, C.J., 2012. Source apportionment of elevated PAHconcentrations in sediments near deep marine outfalls in Esquimalt andVictoria, BC, Canada: is coal from an 1891 shipwreck the source? OrganicGeochemistry 46, 12–37.

Zhuang, G., Hourigan, J.K., Koch, P.L., Ritts, B.D., Kent-Corson, M.L., 2011. Isotopicconstraints on intensified aridity in Central Asia around 12 Ma. Earth andPlanetary Science Letters 312, 152–163.


Polycyclic aromatic hydrocarbons (PAHs) in late Eocene to early Pleistocene mudstones of the Sylhet...

Documents

Transcript of Polycyclic aromatic hydrocarbons (PAHs) in late Eocene to early Pleistocene mudstones of the Sylhet...