preservation of hydrocarbons and bio markers in oil trapped

Available online at www.sciencedirect.com

www.elsevier.com/locate/gca

Geochimica et Cosmochimica Acta 72 (2008) 844–870

Preservation of hydrocarbons and biomarkers in oil trappedinside fluid inclusions for >2 billion years

Simon C. George a,*, Herbert Volk b, Adriana Dutkiewicz c,John Ridley d, Roger Buick e

a Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australiab CSIRO Petroleum, P.O. Box 136, North Ryde, NSW 1670, Australia

c School of Geosciences, University of Sydney, Sydney, NSW 2006, Australiad Department of Geosciences, Colorado State University, Fort Collins, CO 80523-1482, USA

e Department of Earth and Space Sciences & Astrobiology Program, University of Washington, Seattle, WA 98195-1310, USA

Received 15 March 2007; accepted in revised form 14 November 2007

Abstract

Oil-bearing fluid inclusions occur in a ca. 2.45 Ga fluvial metaconglomerate of the Matinenda Formation at Elliot Lake,Canada. The oil, most likely derived from the conformably overlying deltaic McKim Formation, was trapped in quartz andfeldspar during diagenesis and early metamorphism of the host rock, probably before ca. 2.2 Ga. Molecular geochemical anal-yses of the oil reveal a wide range of compounds, including CH4, CO2, n-alkanes, isoprenoids, monomethylalkanes, aromatichydrocarbons, low molecular weight cyclic hydrocarbons, and trace amounts of complex multi-ring biomarkers. Maturityratios show that the oil was generated in the oil window, with no evidence of extensive thermal cracking. This is remarkable,given that the oils were exposed to upper prehnite–pumpellyite facies metamorphism (280–350 �C) either during migration orafter entrapment. The fluid inclusions are closed systems, with high fluid pressures, and contain no clays or other minerals ormetals that might catalyse oil-to-gas cracking. These three attributes may all contribute to the thermal stability of the includedoil and enable survival of biomarkers and molecular ratios over billions of years. The biomarker geochemistry of the oil in theMatinenda Formation fluid inclusions enables inferences about the organisms that contributed to the organic matter depos-ited in the Palaeoproterozoic source rocks from which the analysed oil was generated and expelled. The presence of biomark-ers produced by cyanobacteria and eukaryotes that are derived from and trapped in rocks deposited before ca. 2.2 Ga isconsistent with an earlier evolution of oxygenic photosynthesis and suggests that some aquatic settings had become sufficientlyoxygenated for sterol biosynthesis by this time. The extraction of biomarker molecules from Palaeoproterozoic oil-bearingfluid inclusions thus establishes a new method, using low detection limits and system blank levels, to trace evolution throughEarth’s early history that avoids the potential contamination problems affecting shale-hosted hydrocarbons.� 2007 Elsevier Ltd. All rights reserved.

1. INTRODUCTION

The nature of biological evolution and its intimate rela-tionship with the rise in atmospheric oxygen during Earth’s

0016-7037/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.gca.2007.11.021

* Corresponding author. Fax: +61 (0)2 9850 8248.E-mail addresses: [email protected] (S.C. George),

[email protected] (H. Volk), [email protected](A. Dutkiewicz), [email protected] (J. Ridley), [email protected] (R. Buick).

early history continues to be the subject of intense interestand debate (e.g., Lepland et al., 2005; Brasier et al., 2006;Goldblatt et al., 2006; Ohmoto et al., 2006). Stromatolitesof undisputed biogenicity are common back to 2.8 Ga,and a strong case has been made that they extend to 3.4–3.5 Ga (e.g., Walter et al., 1980; Buick et al., 1981; Hof-mann et al., 1999; Allwood et al., 2006a). However, giventhe scarcity of well-preserved microfossils before ca.2.1 Ga (Buick, 2001), evidence for life on the early Earthis most often indirectly gleaned from carbon and sulphur

mailto:[email protected]




mailto:buick@ess. washington.edu

mailto:buick@ess. washington.edu

Preservation of biomarkers in oil inclusions for >2 billion years 845

isotopic compositions of sedimentary organic matter (e.g.,Schidlowski, 2001; Shen et al., 2001; Hayes and Waldbauer,2006), microbial traces and replacements (e.g., Rasmussen,2000; Furnes et al., 2004; Allwood et al., 2006a) and vibra-tional spectroscopy of kerogen (e.g., Schopf et al., 2002;Allwood et al., 2006b). An additional powerful approachthat has benefited from substantial technical advances in re-cent years is the use of biomarkers preserved in ancient or-ganic matter to provide constraints on life’s development.Biomarkers are complex hydrocarbons derived from bio-logical compounds in once living organisms that have beenpredictably altered during diagenesis (Peters et al., 2005).Their preservation in sediments, relatively unmetamor-phosed rocks and crude oils thus allows the evolution ofparticular classes of organisms, their metabolisms and envi-ronmental niches to be followed through Earth’s history(Peters et al., 2005).

Metamorphism causes breakdown of hydrocarbons andthus the number of old rocks suitable for study is limitedand the record of biomarker evolution very early in timeis distinctly incomplete (Hayes et al., 1983; Summonset al., 1988a,b; Summons and Walter, 1990; McKirdy andImbus, 1992). To date, only trace amounts of biomarkershave been analysed from a small number of organic-richpre-Mesoproterozoic shales (Summons et al., 1988b;Brocks et al., 1999, 2003a,d, 2005; Brocks and Summons,2005; Ventura et al., 2007; Sherman et al., 2007; Eigenb-rode, in press). Problems of contamination and syngeneityin the interpretation of biomarkers from Archaean shaleswere considered in detail by Brocks et al. (2003a), who dis-covered a suite of biomarkers in 2.7 Ga shales collectedfrom drill core from the Pilbara Craton (Brocks et al.,1999, 2003a,b,c) and from which it was inferred thateukaryotes evolved 500 million to 1 billion years beforethe evidence in the fossil record. However, a small but note-worthy degree of uncertainty exists about the age of thesebiomarkers, which have been interpreted as only ‘‘probablysyngenetic with their Archean host rock’’ (Brocks et al.,2003a). These doubts arise from the possibility that organicstaining occurred during coring, as higher heavy hydrocar-bon concentrations were recorded on the outside of thecores (Brocks et al., 2003a). Palaeoproterozoic rocks havealso been analysed for their biomarker content; some ofthem contain steranes (Summons et al., 1988b) but othersdo not (Brocks et al., 2005), a difference that could be inter-preted to indicate that the steranes are contaminants(Brocks, 2005). Regardless of the contamination issue, whatthis emphasises is the small number of reliable biomarkerstudies spanning such a very long period of geological his-tory (3.8–1.6 Ga).

An exciting development in the use of molecular evi-dence for life’s early evolution is the ability to extract oil,including its constituent biomarkers, by using ultra-sensi-tive methods from the oil-bearing fluid inclusions (FIs) thatoccur in many sedimentary rocks (George et al., 2007). Therelative age of entrapment of FIs can be determined usingtextural relationships and known diagenetic, metamorphicand deformational histories. These tiny vessels are closedsystems after entrapment and are shielded not only fromcontamination, but also from much of the alteration that

usually affects hydrocarbons over time (Dutkiewicz et al.,1998, 2003b; Volk et al., 2005). Oil-bearing FIs have beenshown to have been trapped during the Proterozoic andthe Archaean (e.g., Kelly and Nishioka, 1985; Dutkiewiczet al., 1998), and as such prove the contention that therewas sufficient biogenic kerogen produced by the primitivebiosphere to form oil during thermal maturation (Buicket al., 1998; Rasmussen, 2005). One of the first attemptsto use gas chromatography (GC)–mass spectrometry(MS) to analyse inclusion oil extracted by crushing wason FIs hosted in quartz crystals in calcite veins of unknownage from Precambrian metasediments in South-West Africa(Kvenvolden and Roedder, 1971). This pioneering studydemonstrated the presence of hydrocarbon gases, n-alkanesand isoprenoids. The technology of GC analysis of FI ex-tracts was developed by Burruss (1987) and has subse-quently been applied in a wide range of petroleumsystems studies (e.g., Karlsen et al., 1993; Nedkvitneet al., 1993; George et al., 1997; Scotchman et al., 1998;Karlsen et al., 2004). It has been applied to Proterozoicinclusion oils (e.g., Newell et al., 1993; George and Jardine,1994; Mauk and Burruss, 2002), although none of thesestudies attempted to analyse biomarkers. Recently, oilinclusions from sandstones and a dolerite sill in the RoperSuperbasin in the Northern Territory (Mesoproterozoic)and from the 2.1 Ga sandstone in Gabon that hosts theOklo natural fission reactors have been chemically analysed(Dutkiewicz et al., 2003b; Volk et al., 2003; Dutkiewiczet al., 2004; Volk et al., 2005; Dutkiewicz et al., 2006b;George et al., 2006; Dutkiewicz et al., 2007). These studiesdemonstrate the presence of abundant n-alkanes, mono-methylalkanes, isoprenoids, alkylcyclohexanes, alkylcyclo-pentanes, aromatic hydrocarbons, bicyclic sesquiterpanesand hopanes. Tricyclic and tetracyclic terpanes, 2a-meth-ylhopanes and steranes were detected in some of the oils.

Here we report the molecular geochemistry of oil inclu-sions in a ca. 2.45 Ga uraniferous conglomerate, showingthe reproducible detection of an extensive range of synge-netic hydrocarbons in the trapped FI oil, carefully con-trolled using a series of blanks. We demonstrate here thatmaturity-sensitive molecular ratios and structurally-com-plex biomarkers can survive for >2 billion years, despiteheating to >280 �C and burial to pressures of 200 MPa.The biomarker data are used to make inferences aboutthe organisms that contributed to the organic matter depos-ited in the Palaeoproterozoic source rocks from which theanalysed oil was generated and expelled. Finally, the rela-tive merits of using oil inclusions as stable palaeobiologicaltime capsules of early life on Earth are considered.

2. SAMPLE CHARACTERISTICS AND GEOLOGICAL

SETTING

The analysed sample is a uraniferous bitumen-bearingfeldspathic quartz-pebble conglomerate from the Matinen-da Formation of the lower Huronian Supergroup at ElliotLake in Canada (Fig. 1). The host Huronian Supergroupis composed of up to 10 km of fluvial, shallow marine,and possibly lacustrine, mainly siliciclastic sedimentaryrocks deposited between 2.45 and 2.2 Ga in a rift basin

Cob

altG

roup

Qui

rke

Lake

Gro

upH

ough

Lake

Gro

upE

lliot

Lake

Gro

up

Livingstone Creek Fm

Thessalon Fm (~2.45 Ga)

Matinenda Fm (fluvial-deltaic)

McKim Fm (fluvial-deltaic)

amsay Lake Fm (glaciomarine)

Fm (fluvial deltaic)

ssissagi Fm (fluvial deltaic)

Bruce Fm (glaciomarine)

Espanola Fm (marginal marine)

Serpent Fm (fluvial deltaic)

Gowganda Fm (glaciomarine)

orrain Fm (fluvial deltaic)

n Lake Fm (shallow marine)

Bar River Fm (shallow marine)

Basement (>2.48 Ga)

Palaeozoic

Nipissing Diabase (2.21 ga)

X

1 km

ElliotLake

Sault Ste.Marie

BlindRiver

Espanola

Lake Huron90 km

Xsample site

Sudbury

Gowganda

N

83oE

XHuronianSupergroup

Lake Huron

48oS

a

b

Argillite Arenite Volcanics

Carbonate Diamictite Granitoids and metamorphics

Detrital uraninite and/or pyrite

Red-beds X Sample site

Fig. 1. (a) Sample location map and geographic extent of the Huronian Supergroup, modified after Mossman (1987). (b) Stratigraphy of theHuronian Supergoup, showing that deposition of the sequence is constrained between 2.45 and 2.21 Ga (Young et al., 2001).

846 S.C. George et al. / Geochimica et Cosmochimica Acta 72 (2008) 844–870


(Fralick and Miall, 1989; Young et al., 2001). The sequenceincludes rocks deposited during three glacial periods (theHuronian diamictities), the middle of which includes acap carbonate unit. These have been interpreted to repre-sent low-latitude ‘‘Snowball Earth’’ glaciations (Williamsand Schmidt, 1997; Schmidt and Williams, 1999), thoughthis has been disputed (Hilburn et al., 2005; Kopp et al.,2005). Sulphur isotope stratigraphy shows that authigenicpyrites in the McKim and Pecors formations in the lowerhalf of the sequence preserve small magnitude mass-inde-pendent isotope fractionation (MIF) whereas this signatureis absent higher in the succession (Papineau et al., 2007).This has been interpreted as showing that the ‘‘Great Oxi-dation Event’’, the first major and permanent rise in atmo-spheric oxygen levels, occurred during this interval(Papineau et al., 2007).

In the Elliot Lake area the Matinenda Formation wasmetamorphosed to a maximum metamorphic grade oflow-pressure, low temperature upper prehnite–pumpellyite

Fig. 2. (a–f) Photomicrographs showing predominant setting in micepifluorescence; (b,d,f) transmitted light. (a,b) Trails of oil-bearing fluidH2O-dominated fluid inclusion comprising a non-fluorescing bubble ofluorescing H2O liquid. (e,f) CO2-dominated fluid inclusion with a fluoresand an outer non-fluorescing rim of H2O liquid.

facies (�280–350 �C at 50–200 MPa), as indicated by themineral assemblage illite–montmorillonite, stilpnomelane,chlorite, muscovite, and pyrophyllite (Easton, 2000). Peakmetamorphism may have been reached during the Penok-ean orogeny (Card, 1978) at 1.89–1.8 Ga (Young et al.,2001) or more likely during the earlier (�2.2 Ga) intrusionof the Nipissing Diabase suite (Mossman et al., 1993). Ba-sin modelling suggests that a maximum thickness of only�200 m of Phanerozoic sedimentary cover was subse-quently deposited over the Palaeoproterozoic rocks (Quin-lan and Beaumont, 1984).

The outcrop sample was taken directly above a U-min-eralised conglomerate and consists of a moderately-sortedmedium-grained feldspathic sandstone. It contains 5% byvolume of 1 cm-diameter rounded quartz pebbles and sev-eral 1 mm-thick heavy mineral partings containing0.5 mm sub-rounded pyrite and rounded 10 lm to 0.5 mmbitumen nodules, which based on their morphologyand composition are interpreted to be pyrobitumen. The

rofractures and the two types of oil-bearing FIs. (a,c,e) UV-inclusions in intragranular microfractures in detrital quartz. (c,d)

f water vapour surrounded by a fluorescing rim of oil and non-cing rim of oil surrounding a double bubble of CO2 gas and liquid,


petrography and microthermometry of oil-bearing inclu-sions in this conglomerate have already been discussed(Dutkiewicz et al., 2003a), and initial geochemical datahave been presented (Dutkiewicz et al., 2006a). Oil in theMatinenda Formation is hosted in four populations of fluidinclusions, although only two populations are abundantand these appear to represent two episodes of oil migration(Fig. 2). The earlier of these FI populations is located inintragranular microfractures in quartz and K-feldspar orrarely within syntaxial quartz overgrowths, indicatingentrapment early in the burial history. These inclusionsare irregular, water-dominated (liquid and vapour), andcontain 2–5% oil as fluorescing film on the vapour bubble(Fig. 2 a and b). Laser Raman spectroscopy indicated someCH4 but no CO2 in the vapour phase of these FIs, occasion-ally a solid calcite phase, and rarely a globule of bitumen.Based on gas–liquid homogenisation temperatures, this FIpopulation was interpreted to have been trapped duringdiagenesis at temperatures of 80–220 �C and at pressuresof �50–200 MPa (Dutkiewicz et al., 2003a). This FI popu-lation was subsequently heated to �280–350 �C duringmetamorphism, which caused a small proportion of theinclusions to stretch. The second FI population is highlycarbonic, consisting of 30–90 vol% CO2-bearing vapourphase, usually some water, and 2–3 vol% fluorescing oilas a meniscus to the CO2 (Fig. 2e and f). Laser Raman spec-troscopy showed that the vapour phase of these FIs con-tained up to 50% CH4, with 2–8 mol% C2H6 and 1–5mol% C3H8. This FI population was interpreted to havebeen trapped during metamorphism at temperatures of280–350 �C and pressures of �100–150 MPa (Dutkiewiczet al., 2003a). Petrographic evidence shows that both popu-lations of FI were entrapped during diagenesis or during thepro-grade metamorphic history of the host rock. In view ofthe likely age of metamorphism, it can be inferred that allMatinenda Formation FI oils were trapped prior to 2.2 Ga.The reported geochemical data thus provide a window intothe composition of early Palaeoproterozoic oils and the nat-ure of the organic matter from which they were generated.’

3. ANALYTICAL METHODS

3.1. Sample preparation and cleaning

The conglomerate was fragmented into 2 mm pieces andthoroughly cleaned with excess amounts of hydrogen per-oxide, Aqua Regia and hot chromic acid (George et al.,2007). After washing with distilled water, the rock frag-ments (21.83 g) were ultrasonicated (10 min) sequentiallywith triplicate 30 mL aliquots of methanol, dichlorometh-ane (DCM)/methanol (93:7) and DCM. These washingswere discarded, and then the rock fragments were ultraso-nicated (10 min) with three batches of DCM (30 mL),which were combined to form the first outside-rinse blank.This was purified on a micro-column composing a Pasteurpipette filled with glass wool and silica gel (C60: 60–210 lm), which was flushed with DCM. The first outside-rinse blank was spiked with �0.6 lg of an internal standard(squalane), and analysed for cleanliness by gas chromatog-raphy–mass spectrometry (GC–MS) on a Hewlett Packard

5890 gas chromatograph (DB5MS, 60 m · 0.25 mm i.d.0.25 lm film thickness) interfaced to a VG AutospecQ Ul-tima mass spectrometer [for GC programmes and typicalMS parameters used, see George et al. (2007)].

The first outside-rinse blank was found to still containtraces of hydrocarbons, so the above procedure was re-peated to produce a second outside-rinse blank. This toocontained traces of hydrocarbons, so the above procedurewas repeated a third time to produce the final outside-rinseblank, which was deemed to be sufficiently clean. Resultsfrom this final outside-rinse blank are presented in this pa-per for comparison with the off-line crushing data from theoil inclusions.

3.2. Off-line crushing

An off-line crushing method was used for the analysis oftraces of high molecular-weight C12+ hydrocarbons such asbiomarkers (George et al., 1998, 2007). The entire procedurewas carried out in replicate, including acquisition and pro-cessing of data from the system blanks. Before the inclusionfluids were extracted, procedural system blank experimentsusing the same experimental conditions and glassware(including the same amount of solvent) were carried out inorder to determine the extent of any hydrocarbon contribu-tion from the crushing cylinder and any carry-over frompreviously analysed samples or from the general laboratorybackground. The system blanks were spiked with�0.6 lg ofan internal standard (squalane), and analysed for cleanlinessby GC–MS as described above. System blanks that weredeemed to be sufficiently clean were acquired prior to crush-ing of the rock fragments, and the sample was subsequentlycrushed using exactly the same glassware.

Cleaned rock fragments (15.18 g and 12.31 g aliquotsfrom the same sample) were crushed under DCM in a stain-less steel crushing cylinder with a 55 mL capacity (Georgeet al., 2007). Two stainless steel balls were placed in the cyl-inder above the sample aliquot and 25 mL of DCM wasadded before closure of the cylinder in air at atmosphericpressure. The cylinder was vigorously shaken for2 · 10 min in a vertical motion with a throw of about40 mm, using a modified piston pump. In between thetwo crushing phases, the crusher was allowed to cool forat least 10 min in order to minimise evaporative loss ofthe leached FI oil. The resultant suspension of finelycrushed mineral in DCM was poured into a beaker, andthe crushing cylinder was rinsed with an additional 25 mLof DCM. The solution in the beaker was then ultrasonicat-ed for 10 min, allowed to settle for a few minutes and thenthe supernatant solvent layer, containing the FI extract andsuspended mineral fines, was transferred to a round bottomflask. The residual mineral powder was ultrasonicated twicewith fresh DCM (25 mL), and the supernatant was trans-ferred into the same round bottom flask. The solvent con-taining the oil extracted from the FIs (total = 100 mL)was reduced in a rotary evaporator and by blowing downwith purified nitrogen. Suspended rock powder was re-moved by passing the extract reduced to �2 mL througha short Pasteur pipette plugged with glass wool and packedwith silica gel (C60: 60–210 lm).


The amount of oil obtained from each FI oil sample wasdetermined by adding small amounts (�0.6 lg) of an inter-nal standard (squalane), since the yields were too small forgravimetric determination. Single-ion monitoring (SIM)and metastable-reaction monitoring (MRM) modes ofdetection were used. Particular care was taken to avoidevaporating the extracted FI oil to dryness, so as to pre-serve the low molecular weight hydrocarbons (see Ahmedand George, 2004). Generally, compounds down to �C8

were recovered using the off-line crushing technique, withthose from C12 to C36 recovered quantitatively.

3.3. On-line crushing

Whereas the off-line crushing method was advantageousfor the analysis of traces of C12+ hydrocarbons such as bio-markers, low molecular weight compounds (C12�) wereonly partially retained during sample work-up using theoff-line crushing method. Therefore, the molecular compo-

n-Nonaneortho-Xylene

1-cis-4-Ethylmethylcyclohexane1-trans-4-Ethylmethylcyclohexane

meta- + para-Xylene3-Methyloctane2-Methyloctane4-Methyloctane

EthylbenzeneEthylcyclohexane

1-trans-3- + 1-cis-4-Dimethylcyclohexanen-Octane

1-trans-2-Dimethylcyclohexane1,1-Dimethylcyclohexane

1-trans-4-Dimethylcyclohexane1-cis-3-Dimethylcyclohexane

3-MethylheptaneToluene

4-Methylheptane2-Methylheptane

2,3-Dimethylhexane + 2-Methyl-3-ethylpentane1,2,3-Trimethylcyclopentane1,2,4-Trimethylcyclopentane

Ethylcyclopentane2,4-Dimethylhexane2,5-DimethylhexaneMethylcyclohexane

n-Heptanetrans-1,2-Dimethylcyclopentanetrans-1,3-Dimethylcyclopentane

cis-1,3-Dimethylcyclopentane3-Methylhexane

1,1-Dimethylcyclopentane2,3-Dimethylpentane

2-MethylhexaneBenzene

Cyclohexane3,3-Dimethylpentane

2,2,3-Trimethylbutane2,4-DimethylpentaneMethylcyclopentane

2,2-Dimethylpentane2-Methylfuran3-Methylfuran

n-Hexane3-Methylpentane2-Methylpentane

2,3-DimethylbutaneCyclopentane

2,2-DimethylbutaneFuran

n-Pentanei-Pentane

0 50Normalised abundance to iso-pentane (FID-equi

Benzene off-scale

Toluene off-scale (

Fig. 3. (a) Relative abundance (FID-equivalent data) of gasoline range hMatinenda Formation fluid inclusion oil, normalised to iso-pentane. NotPrevious and superseded data (Dutkiewicz et al., 2006a) on the relativeanalysed by on-line crushing (MSSV-1) of the Matinenda Formation FIabundance calculated from m/z 57 mass chromatograms for three on-lineeach normalised to n-C14. Run A is the main data shown in (a), acquired uC is a later magnet-scan run.

sition of gasoline range hydrocarbons (C5 to C9) in the FIswas assessed in replicate using a direct on-line crushingmethod (Ruble et al., 1998; Volk et al., 2002; Dutkiewiczet al., 2004). Small amounts of the cleaned rock fragments(�50 mg) were hand crushed in the glass-lined metal insertof a Quantum MicroScale Sealed Vessel (MSSV)-2 ThermalAnalysis System (Hall Analytical Laboratories, Manches-ter) using a metal plunger. Liberated compounds were ther-mally extracted in a helium flow at 300 �C, and focussed ina cryogenic trap prior to GC separation (George et al.,1998, 2007). Chromatography was performed using aBPX5 column (5% phenyl 95% methyl silicone, 0.50 lmfilm thickness, SGE), with the oven programmed from aninitial temperature of �20 �C at the start of the crushing(7 min hold), followed by heating at 4 �C min�1 to 30 �C,with a 8 min hold, followed by heating at 4 �C min�1 to300 �C, with a 15 min hold. The cryogenic trap was re-moved after 5 min and ballistically heated to 300 �C. Com-pounds liberated from the inclusions were analysed by the

100

(a)

valent)

(419)

249)

ortho-Xylenemeta- + para-Xylene

EthylbenzeneToluene

n-Heptane3-Methylhexane

2,3-Dimethylpentane2-Methylhexane

Benzene3,3-Dimethylpentane

2-Methylfuran3-Methylfuran

n-Hexane3-Methylpentane2-Methylpentane

2,3-DimethylbutaneFuran

n-Pentanei-Pentane

0 50 100

(b)

Normalised abundance to toluene (FID-equivalent)

nC21nC20

nC19nC18

nC17nC16

nC15nC14

nC13nC12

nC11nC10

nC9

nC8nC7

nC6nC5

0 50 100

Run A

Run B

Run C

(c)

Normalised abundance to n-C14

140

ydrocarbons analysed by on-line crushing (MSSV-2; Run A) of thee that benzene and toluene are very abundant and plot off-scale. (b)abundance (FID-equivalent data) of gasoline range hydrocarbonsoil, normalised to toluene. (c) Comparison of n-alkane (C4 to C21)

crushing experiments (MSSV-2) of the Matinenda Formation FI oil,sing SIM; Run B is an earlier SIM run on the same sample; and Run

Table 1Low molecular weight parameters for the Matinenda FI oil,derived from on-line crushing

C1:C2:CO2:C3:RC4�5 hydrocarbons 40.7:2.0:55.3:0.7:1.3 –

i-C5/n-C5 1.5Benzene/n-C6 9.0Toluene/n-C7 6.1Furan/n-C6 0.44(n-C6 + n-C7)

/(cyclohexane + methylcyclohexane)2.5

Heptane value 33Isoheptane value 2.2n-C7/methylcyclohexane 2.0Cyclohexane/methylcyclopentane 0.83n-C7/2-methylhexane 2.7n-C7/methylcyclopentane 2.2Methylcyclohexane/toluene 0.13-Methylpentane/n-C6 0.30Benzene/toluene 1.7Methylcyclopentane/methylcyclohexane 0.90Toluene/o-xylene 6.9m- + p-xylene/n-C8 3.3K1: (2-MH + 2,3-DMP)/(3-MH

+ 2,4-DMP)2.1

2-MH/3-MH 1.82,4-DMP/2,3-DMP 0.22Ctemp (�C) 118K2:P3/(P2 + N2) 0.25N2/P3 1.41n-C7 (% of total C7 hydrocarbons) 11.33 Ring preference % (DMP + MH) 105 Ring preference % (DMCP + ECP) 66 Ring preference %

(methylcyclohexane + toluene)84

All data are expressed as FID-equivalent and are derived fromcorrected SIM runs, except for – (mol%).The heptane value (H; Thompson, 1979) is 100 · n-C7/R cyclo-hexane through to methylcyclohexane. The isoheptane value(Thompson, 1983) is (2-MH + 3-MH)/(c-1,3- + t-1,3- + t-1,2-DMCP). Ctemp (�C) (Bement et al., 1995; Mango, 1997) is140 + (15 · (ln [2,4-DMP/2,3-DMP])). P2 = 2-MH + 3-MH;P3 = 3,3-DMP + 2,3-DMP + 2,4-DMP + 2,2-DMP; N2 = 1,1-DMCP + c-1,3-DMCP + t-1,3-DMCP. MH, methylhexane; DMP,dimethylpentane; DMCP, dimethylcyclopentane; ECP,ethylcyclopentane.


AutoSpec GC–MS using two function SIM and magnetscan programmes. Areas of peaks in mass chromatogramswere converted to flame ionisation detector (FID)-equiva-lent data using response factors before data manipulation(e.g., George et al., 2004c), enabling comparison of thesetypes of data with conventional whole oil GC-FID analy-ses. Initial on-line crushing data reported by Dutkiewiczet al. (2006a) were acquired using an MSSV-1 system, usingsimilar conditions as above; these data are also presentedand discussed here (Fig. 3b) .

The molar distribution of gaseous compounds (C1 to C5,including CO2) in the FIs was investigated using a MSSV-1on-line crushing system with a GS-GASPRO capillary col-umn (30 m · 0.32 mm i.d.). Another aliquot of cleaned rockfragments (�50 mg) was used. The oven was programmedfrom an initial temperature of �20 �C at the start of thecrushing (4 min hold), followed by heating at 4 �C min�1

to 260 �C, with a 15 min hold. The liquid nitrogen trapwas removed after 2 min. Gases liberated from the FIs wereanalysed by the AutoSpec GC–MS using magnet scanningfrom m/z 10–75 with data for each analyte extracted frommass chromatograms (C1: m/z 15; C2: m/z 27; C3 and C4:m/z 43; C5: m/z 57; CO2: m/z 44). The analysis systemwas calibrated using injections of a natural gas standard(BOC) under the same detection conditions, from which re-sponse factors were calculated and applied to correct the FIgas data to molar composition.

3.4. Constraints on the methodology

The main constrain on the methodology is that it isimpossible to physically separate the two FI populations,so the geochemical analyses reported in this paper pertainto mixtures of both FI populations. The geochemical anal-yses reported herein may also include a contribution frompyrobitumens in the sample, as these may have been presentin the small rock fragments crushed. However, the very lowhydrocarbon levels in the final outside rinses constrain thiscontribution to trace amounts only. Very rare bitumen alsooccurs with oil in a few of the older, syn-diagenetic FIs(Dutkiewicz et al., 2003a), so would also have contributedto the geochemical analyses, but only in a very minor waybased on their low abundance. The petrographic data showthat no FI oils or bitumens were trapped subsequent tometamorphism. Therefore, the reported geochemical datapertain to Palaeoproterozoic FI oil, with a possible minorcontribution from solid bitumens of similar age but less reli-ably shielded from contamination and degradation.

4. RESULTS

4.1. Geochemical data from on-line crushing method

4.1.1. C1 to C5 gases

On-line crushing to release the FI oil from both popula-tions revealed that gaseous compounds are dominated byCH4 and CO2, with lesser amounts of C2, C3 and RC4�5

(Table 1). The CH4:CO2 ratio is intermediate between thatof the two FI types (aqueous and CO2-rich) determined byLaser Raman spectroscopy, and shows that the analysed oil

is derived from both FI populations (aqueous and CO2-rich), as would be expected from the ubiquitous distributionof both FI populations in the sample (Dutkiewicz et al.,2003a, 2006a) and the crushing technique.

4.1.2. Gasoline range C5 to C9 compounds and higher

n-alkanes

Most theoretically possible C5 to C7 hydrocarbon iso-mers and several C8 to C9 hydrocarbons were detected inthe FIs using SIM (Fig. 3a). Abundances of these com-pounds are reported as FID-equivalent data, and derivedratios are given in Table 1. Benzene and toluene were themost abundant compounds detected in this mass range,with significant amounts of iso-pentane, C5 to C9 n-alkanes,xylenes, ethylbenzene and 3-methylfuran also present. Fur-an, 3-methylfuran and 2-methylfuran are oxygenated com-

(b)17

Pr6+7+8+9

54

32

18 19 20Ph6+7+8+9

54 32

6+75

43

2

8+9+10(a)

Retention time

Res

pons

eFI oil: 88.3 ngC12–C32 n-alkanes

Squalane

8

9

?

11

12

10

13 1415

16

17

18

PhPr

1920

2122

2324

252627

2829

3031

3233 34

UCM

Blank: 9.6 ngC12–C32 n-alkanes

Rinse: 19.8 ngC12–C32 n-alkanes

(c)

-

n-Alkanes

Fig. 4. m/z 85 Mass chromatograms of the Matinenda Formation FI oil, system blank and final outside rinse blank drawn to the same scale,showing (a) the distribution of n-alkanes (n-C8 to n-C34) and isoprenoids (Pr, pristane; Ph, phytane; UCM, unresolved complex mixture; and(b) detailed monomethylalkane distribution between n-C17 and n-C20 (MHeD, methylheptadecanes; MOD, methyloctadecanes; MND,methylnonadecanes). Data were obtained by off-line crushing, with squalane added as an internal standard. Quantitative amounts of C12–C32

n-alkanes recovered in each fraction are also given in (a). The line chart (c) summarises the n-alkane recovery for the three fractions.


pounds not normally detected in crude oils. They are highlywater soluble, and their presence in FIs, together with highabundances of the most water-soluble hydrocarbons(benzene, toluene and xylenes), has been attributed to theco-analysis of aqueous inclusions during on-line crushing(Ruble et al., 1998). The dominance of these compoundsin the Matinenda FIs is consistent with the co-entrapmentof limited amounts of oil with oil-equilibrated waters inthe three-phase FIs (Dutkiewicz et al., 2006a). Most C6 toC9 parameters reflect this excess of aromatic hydrocarbonsand the relatively low amounts of branched alkanes, alkyl-cyclopentanes and alkylcyclohexanes (Fig. 3 and Table 1).

Ratios from a SIM run using the MSSV-1 equipmentwere reported as ratios in Dutkiewicz et al. (2006a) andare plotted in Fig. 3b, but should be considered supersededby the data acquired using an upgraded on-line extractionunit (MSSV-2) in Table 1. The MSSV-1 analytical run isstrongly dominated by the water-soluble compounds, withonly very low relative abundances of n-alkanes andbranched alkanes reliably detected. The inter-analysis het-erogeneity in analytical data from the on-line crushingmethod is a consequence of the small sample size used

(�50 mg). However, two SIM runs and a third magnet scanrun (Run C) on the MSSV-2 give a reproducible n-alkanemaximum at C14, with tail off above �C17 and more vari-able <C10 relative abundances (Fig. 3c). The difference inthe apparent n-alkane maxima between the on-line (C14)and the off-line crushing methods (C18; Fig. 4) is a com-bined consequence of (1) adsorption processes in the MSSVinlet, leading to reduction in the amount of high molecularweight compounds recovered during on-line crushing(George et al., 1996), and (2) partial evaporation duringsample work-up after off-line crushing, which may reducethe amount of recovered <C15 compounds (e.g., Karlsenet al., 1993; Ahmed and George, 2004).

4.2. Geochemical data from off-line crushing method

4.2.1. Linear and branched alkanes

The distribution of n-alkanes and branched alkanes inthe Matinenda Formation FI oil and associated systemand final outside-rinse blanks is shown in m/z 85 mass chro-matograms, scaled using the squalane standard so that rel-ative amounts in the three fractions can be visualised


(Fig. 4). The FI oil contains 9.2 times more C12–C32 n-al-kanes relative to the system blank and 4.5 times more rela-tive to the final outside-rinse blank. Furthermore, the intra-n-alkane peaks are considerably more evident and morenumerous in the FI oil, with a series of prominent peaks be-tween each n-alkane from C19 to C29, including a distinctunresolved complex mixture (UCM) hump. Some of thesepeaks are monomethylalkanes, as identified in Fig. 4b.The second and duplicate analysis of Matinenda FormationFI oil was unsatisfactory for detailed interpretation, (1) be-cause lower amounts of C12–C32 n-alkanes were recoveredrelative to the duplicate system blank (·3.0) and final out-side-rinse blank (·1.3), and (2) because lower abundancesand a more limited range of compounds was reliably de-tected in the duplicate run. Generally, the compounds thatcould be reliably detected in the duplicate analysis of Mat-inenda Formation FI oil have a similar distribution to thosein the original analysis reported in full here. The inter-ali-quot heterogeneity in analytical data from the off-linecrushing method reflects the extremely low amounts ofcompounds recovered from the Matinenda Formation FIoil: only 5.8 ng C12–C32 n-alkanes/g rock fragments crushedwere obtained (first aliquot), compared to typical FI oils

Table 2Alkane and aromatic hydrocarbon parameters for the Matinenda FI oil

Carbon preference index (CPI22�32)Pr/Ph (Pristane/phytane)Pr/n-C17

Ph/n-C18

RMethylheptadecanes/n-C18

3-Methylheptadecane/4-methylheptadecane2-Methylheptadecane/5-methylheptadecaneRMethylheneicosane/n-C22

3-Methylheneicosane/4-methylheneicosane2-Methylheneicosane/5-methylheneicosaneRMethyltricosanes/n-C24

3-Methyltricosane/4-methyltricosane2-Methyltricosane/5-methyltricosaneMethylnaphthalene ratio (MNR: 2-MN/1-MN)Ethylnaphthalene ratio (ENR: 2-EN/1-EN)Dimethylnaphthalene ratio-1 (DNR-1: [2,6- + 2,7-DMN]/1,5-DMN)Trimethylnaphthalene ratio-1 (TNR-1: 2,3,6-TMN/[1,4,6- + 1,3,5-TMN]Trimethylnaphthalene ratio-2 (TNR-2: [2,3,6- + 1,3,7-TMN]/[1,4,6- + 1,3Tetramethylnaphthalene ratio-1 (TeMNR-1: 2,3,6,7-TeMN/1,2,3,6-TeMNTrimethylnaphthalene ratio (TMNr: 1,3,7-TMN/[1,3,7- + 1,2,5-TMN])Tetramethylnaphthalene ratio (TeMNr: 1,3,6,7-TeMN/[1,3,6,7- + 1,2,5,6Methylbiphenyl ratio (MBpR: 3-MBp/2-MBp)Dimethylbiphenyl ratio-x (DMBpR-x: 3,5-DMBp/2,5-DMBp)Dimethylbiphenyl ratio-y (DMBpR-y: 3,30-DMBp/2,30-DMBp)Methylphenanthrene index (MPI-1: 1.5 · [3-MP + 2-MP]/[P + 9-MP + 1Methylphenanthrene ratio (MPR: 2-MP/1-MP)Methylphenanthrene distribution fraction (MPDF: [3-MP + 2-MP]/RMPDimethylphenanthrene ratio (DMPR: [3,5- + 2,6- + 2,7-DMP]/[1,3- + 3,9Dibenzothiophene/phenanthreneRMethyldibenzothiophenes/RMethylphenanthrenesRDimethyldibenzothiophenes + ethyldibenzothiophenes/RDimethylphenaMethyldibenzothiophene ratio (MDR; 4-MDBT/1-MDBT)Dimethyldibenzothiophene ratio (DMDR: 4,6-DMDBT/3,6- + 2,6-DMD

All data were derived from SIM runs: alkanes, m/z 85; for aromatic hyfactors were used in the calculation of Pr/Ph, Pr/n-C17, Ph/n-C18 and M

from Phanerozoic oil columns where yields of 80–3000 ng/g are common (George et al., 2001). Although thissample has among the lowest yields of the samples success-fully analysed at the CSIRO labs, by careful comparison ofresponses for the FI oil, the system blank and the final out-side-rinse blank, a wide range of hydrocarbons could beshown to be unambiguously present in the FI oil.

The low molecular weight (C8–C12) n-alkanes as deter-mined from the off-line crushing data in the MatinendaFormation FI oil are mainly from a system blank contribu-tion (Fig. 4c) and so are not interpretable. The n-alkanesmaximise at C18, and could be detected to C34, and in theC17–C32 region are substantially more abundant than inthe system blank and the final outside-rinse blank(Fig. 4c). There is a predominance in high molecular weightodd n-alkanes, especially at C27 and C29 (Table 2), and thisis also apparent in the final outside-rinse blank, albeit atlower concentrations (Fig. 4). Most Precambrian samples,although not all (Li et al., 2003), have low amounts of highmolecular weight n-alkanes without any odd or even num-ber predominance (Summons et al., 1988b; Brocks et al.,2003a). One interpretation of this observation is contami-nation of the Palaeoproterozoic FI oil sample by low matu-

(off-line data)

1.131.080.420.330.301.031.021.371.330.851.441.180.982.31.65.7

) 0.79,5- + 1,3,6-TMN]) 0.90) 0.63

0.70-TeMN]) 0.54

3.06.38.8

-MP]) 0.531.7

s) 0.59- + 2,10- + 3,10- + 1,6- + 2,9- + 2,5-DMP]) 0.48

0.120.31

nthrenes + ethylphenanthrenes 0.512.1

BT) 0.75

drocarbons, see Figs. 5–8 for identity of SIM run used. ResponsePI-1.


rity lipids from a post-Devonian land plant source (e.g.,Eglinton and Hamilton, 1967). However, no other evidencein the geochemical composition of the FI oil suggests eitherlow maturity or land plant contamination. Another possi-bility is that the n-alkanes were formed by dissolution insolvent and recrystallisation as waxes in remaining fracturesduring disaggregation and cleaning of the original sample(Karlsen and Skeie, 2006). The difficulty of removingstrongly adsorbed components of oils from cracks and fis-sures in mineral grains has previously been discussed (Jonesand Macleod, 2000; Karlsen et al., 2004). Blank levels inother compound groups are generally lower than for then-alkanes, providing greater confidence that they are pres-ent in the FIs.

3-Methyltetracosane2-Methyltetracosane4-Methyltetracosane5-Methyltetracosane

6-+7-+8-+9-+10-+11-+12-Methyltetracosane3-Methyltricosane2-Methyltricosane4-Methyltricosane5-Methyltricosane

6-+7-+8-+9-+10-+11-+12-Methyltricosane3-Methyldocosane2-Methyldocosane4-Methyldocosane5-Methyldocosane

6-+7-+8-+9-+10-+11-Methyldocosane3-Methylheneicosane2-Methylheneicosane4-Methylheneicosane5-Methylheneicosane

6-+7-+8-+9-+10-+11-Methylheneicosane3-Methyleicosane2-Methyleicosane4-Methyleicosane5-Methyleicosane

6-+7-+8-+9-+10-Methyleicosane3-Methylnonadecane2-Methylnonadecane4-Methylnonadecane5-Methylnonadecane

6-+7-+8-+9-+10-Methylnonadecane3-Methyloctadecane2-Methyloctadecane4-Methyloctadecane5-Methyloctadecane

6-+7-+8-+9-MethyloctadecanePh

3-Methylheptadecane2-Methylheptadecane4-Methylheptadecane5-Methylheptadecane

6-+7-+8-+9-MethylheptadecanePr

3-Methylhexadecane2-Methylhexadecane4-Methylhexadecane5-Methylhexadecane

6-+7-+8-Methylhexadecane + iC183-Methylpentadecane2-Methylpentadecane4-Methylpentadecane5-Methylpentadecane

6-+7-+8-Methylpentadecane3-Methyltetradecane2-Methyltetradecane

iC164-Methyltetradecane5-Methyltetradecane

6-+7-MethyltetradecaneiC15

3-Methyltridecane2-Methyltridecane4-Methyltridecane5-Methyltridecane

6-+7-Methyltridecane3-Methyldodecane + iC14

2-Methyldodecane4-Methyldodecane

5-+6-MethyldodecaneiC13

3-Methylundecane2-Methylundecane4-Methylundecane

5+6-Methylundecane3-Methyldecane2-Methyldecane4-Methyldecane5-Methyldecane

0 1

0 0.1 0.2 0

ng recov

ng recovered (5

Fig. 5. Semi-quantitative abundance (ng recovered) of branched alkanesrinse blank. iCxx refers to the carbon number of isoprenoids, Pr = pristato the upper axis, hydrocarbons with retention times > Pr report to the lowwere used to correct for response variation in m/z 85 between the squala

The amount (ng recovered) of branched alkanes, includ-ing C11–C25 monomethylalkanes, in the FI oil is signifi-cantly greater than for the system blank or the finaloutside-rinse blank, and the distribution is also quite differ-ent, especially for >C19 (Fig. 5). There is a greater outside-rinse blank contribution at lower molecular weights, espe-cially at C11, C12, C16 and C17, so these data are interpretedmore cautiously. The FI oil C20–C25 monomethylalkanesare strongly dominated by the co-eluting peak due to themid-chain isomers, and the 4- and 5-methylalkanes have asimilar abundance as the 3- and 2- (terminal) methylalkanes(Table 2). The proportion of total monomethylalkanes rel-ative to the n-alkane with the same carbon number in-creases with increasing molecular weight (Fig. 4a and

2 3 4 5 6

.3 0.4 0.5 0.6 0.7 0.8

FI oil

System blank

Final outside-rinse blank

ered (Pr to 3-methyltetracosane)

-methyldecane to 3-methylhexadecane)

in the Matinenda Formation FI oil, system blank and final outside-ne, Ph = phytane. The lower molecular weight hydrocarbons report

er axis. The data are semi-quantitative because no response factorsne standard and the analytes.


Table 2). C13 to C20 isoprenoids were detected in the FI oil,but only pristane (Pr) and phytane (Ph) have a significantabundance relative to adjacent n-alkanes (Figs. 4a and 5).

4.2.2. Aromatic hydrocarbons

C2–C4 alkylbenzenes were detected in the MatinendaFormation FI oil, but are also present in significant quanti-ties in the system blank and final outside-rinse blank andhence are not interpretable. Naphthalene is also affectedby a high blank (Fig. 6). The high background of C8–C10

aromatic hydrocarbons in the blanks corresponds to themolecular weight range of high n-alkane blanks and indi-cates a consistent external source of contamination, possi-bly related to the greater water solubility of C8–C10

aromatic hydrocarbons than those of higher molecularweight. Fortunately, higher molecular weight aromatichydrocarbons in the Matinenda Formation FI oil are moreabundant relative to the blanks, and thus can be interpretedmore readily. Alkylnaphthalenes detected include isomerswith one to four methyl side-chains, the scaled mass chro-matograms for which demonstrate higher abundance inthe Matinenda Formation FI oil relative to the blanks

Retentio

m/z 142m/z 156

m/z 184.1

m/z 128

m/z 170

Res

pons

e

1-MN

2-MNNaphthalene

2-EN

1-EN

1,3-+1,7-DMN1,6-DM

2,6-DMN

2,7-DMN

1,4-+DM

1

m/z 142m/z 156

m/z 184.1

m/z 128

m/z 170

m/z 142m/z 156

m/z 184.1

m/z 128

m/z 170

Fig. 6. Partial m/z 128, 142, 156, 170 and 184.1 mass chromatograms ooutside-rinse blank, all drawn to the same scale, showing the distribution odimethylnaphthalenes (DMN), trimethylnaphthalenes (TMN) and tetram

(Fig. 6). Biphenyl, diphenylmethane, dibenzofuran, meth-ylbiphenyls, methyldiphenylmethanes, ethylbiphenyls anddimethylbiphenyls are present in the Matinenda FormationFI oil (Fig. 7). These compounds are present in the systemblank and the final outside-rinse blank, but except forbiphenyl, occur are at much reduced levels. Significantlymore phenanthrene, methylphenanthrenes and dimethylph-enanthrenes were detected in the Matinenda Formation FIoil compared to the system blank and the final outside-rinseblank (Fig. 8). Thus, the alkylphenanthrene distributionsare interpreted to represent a genuine record from the fluidinclusions. Alkyldibenzothiophenes were also detected inthe Matinenda Formation FI oil, and are much less abun-dant in the blanks (Fig. 9). These sulphur-containing com-pounds in the FI oil are less abundant than phenanthreneand the alkylphenanthrenes, although this difference re-duces with increasing methylation (Table 2).

4.2.3. Terpanes

The bicyclic sesquiterpanes drimane and homodrimane,together with other rearranged C15 and C16 isomers, arepresent in the Matinenda Formation FI oil (Fig. 10). The

(a: FI oil)

n time

?

(c : Rinse)

N

2,3-N

,2-DMN

1,5-DMN1,2,4-

1,3,7-

1,3,6-

1,3,5-+1,4,6-2,3,6-

1,2,5-

1,2,6-1,6,7-

1,2,7-

?

1,3,6,7-

1,2,5,7-2,3,6,7-

1,2,5,6-+1,2,3,5-

1,2,3,6-

1,2,6,7-

1,2,4,6- + 1,2,4,7- + 1,4,6,7-

1,2,3,7-

(b: Blank)

TMNs

TeMNs

f Matinenda Formation (a) FI oil, (b) system blank, and (c) finalf naphthalene, methylnaphthalenes (MN), ethylnaphthalenes (EN),ethylnaphthalenes (TeMN).

Retention time

m/z 154

m/z 182

(c : Rinse)

m/z 168

Res

pons

e3-MBp

2-MBp

4-MBp

DPM

DBF

2,3'-DMBp2,4- + 2,4'-

DMBp

2,5-DMBp

3,3'-DMBp

3,4'-DMBp

4,4'-DMBp

4-EBp

3,5-DMBp

3-EBp2-MDPM

4-MDPM

2,3-DMBp +3-MDPM

Biphenyl (a: FI oil)

(b: Blank)

m/z 154

m/z 182

m/z 168

m/z 154

m/z 182

m/z 168

Fig. 7. Partial m/z 154, 168 and 182 mass chromatograms of Matinenda Formation (a) FI oil, (b) system blank, and (c) final outside-rinseblank, all drawn to the same scale, showing the distribution of biphenyl, diphenylmethane (DPM), methylbiphenyls (MBp), dibenzofuran(DBF), methyldiphenylmethanes (MDPM), ethylbiphenyls (EBp) and dimethylbiphenyls (DMBp).

Retention time

Res

pons

e m/z 178

9-MP

3-MP

2-MP

1-MP

1,3- + 3,9- + 3,10- + 2,10-DMP

2,7-DMP3,5- + 2,6-DMP

3-EP

1,6- + 2,9- + 2,5-DMP

1,7-DMP

2,3- + 1,9- +4,9- + 4,10-DMP

1,8-DMP

1,2-DMP

m/z 192

m/z 206

m/z 178 m/z 192

m/z 206

m/z 178m/z 192

m/z 206

Phenanthrene

9- + 2- +1-EP+ 3,6-DMP

(a: FI oil )

(b: Blank)

(c : Rinse)

Fig. 8. Partial m/z 178, 192 and 206 mass chromatograms of Matinenda Formation (a) FI oil, (b) system blank, and (c) final outside-rinseblank, all drawn to the same scale, showing the distribution of phenanthrene, methylphenanthrenes (MP), ethylphenanthrenes (EP) anddimethylphenanthrenes (DMP).


Retention time

Res

pons

e m/z 184.0m/z 198.0

m/z 212

Dibenzothiophene4-MDBT

2+3-MDBT

1-MDBT

4-EDBT

4,6-DMDBT

2,6-DMDBT

2,4-DMDBT

3,6-DMDBT

3,7- + 1,4- + 1,6- +1,8-DMDBT

1,3- + 1,9- +1,2-DMDBT

(a: FI oil)

(b: Blank)

(c : Rinse)

Fig. 9. Partial m/z 184.0, 198.0 and 212 mass chromatograms of Matinenda Formation (a) FI oil, (b) system blank, and (c) final outside-rinseblank, all drawn to the same scale, showing the distribution of dibenzothiophene, methyldibenzothiophenes (MDBT), ethyldibenzothiophenes(EDBT) and dimethyldibenzothiophenes (DMDBT).

Retention time

Res

pons

e

Drimane

Homodrimane

C16C15

C15

??

?

(a: FI oil )

(b: Blank)

(c : Rinse)

Fig. 10. Partial m/z 123 mass chromatograms of MatinendaFormation (a) FI oil, (b) system blank, and (c) final outside-rinseblank, all drawn to the same scale, showing the distribution ofbicyclic sesquiterpanes, including drimane and other C15 isomers,and homodrimane and another C16 isomer.


much lower abundance and different distribution of bicyclicsesquiterpanes in the system blank and the final outside-rinse blank is evidence that the FI oil signal is indigenous.Homodrimane is more abundant than drimane or the C15

isomers (Table 3).Fig. 11 shows the original (a) and duplicate (b) analyses

of tricyclic terpanes, tetracyclic terpanes and hopanes in theMatinenda Formation FI oil, compared to the respectivesystem and final outside-rinse blanks. Several features showthat these biomarkers are dominantly from the FI oil. First,the amount of tricyclic terpanes, tetracyclic terpanes andhopanes is considerably greater in the FI oil than in the sys-

tem blank and final outside-rinse blank, for both the origi-nal and the duplicate analyses. Secondly, the distribution ofterpanes and other peaks in the m/z 191 mass chromato-grams are different in the system blank and the final out-side-rinse blank compared to the FI oil. Thirdly, anunusual baseline hump around the position of the C28 tricy-clic terpanes is present in both analyses of the FI oil, but isnot present in any of the blanks. Fourthly, the distributionof terpanes in the duplicate run is generally quite similar tothat in the original run, albeit with a lower response andsome additional and undesignated peaks in the duplicaterun. The duplicate analysis of the terpanes is not used fur-ther for interpretation, because of the poorer data quality,but it is sufficiently similar to the original run for it to beconcluded that interpretations based on terpane distribu-tions in the duplicate would be the same as those basedon the original analysis.

The tricyclic terpanes in the Matinenda Formation FIoil are dominated by the C23 isomer, with significantamounts of the C21 and C24 isomers (Fig. 11). The hopanedistribution in the Matinenda Formation FI oil is domi-nated by C29 ab hopane, with lesser amounts of C30 ab ho-pane, the C27 isomers Ts and Tm and extended hopanes(Fig. 11). The distribution of some of the lower abundancehopanes is more clearly shown by the MRM data (Fig. 12),which was used to derive many of the hopane ratios (Table3). The m/z 205 mass chromatogram (Fig. 11c) shows thatlarge amounts of 2a-methylhopanes relative to hopanes arepresent in the Matinenda Formation FI oil, whilst they areabsent from the system blank and final outside-rinse blank.No 3b-methylhopanes could be detected. C28–C31 25-norhopanes are present in the m/z 177 mass chromatogram(not shown) of the Matinenda Formation FI oil. C28 25,30-bisnorhopane is approximately 50% of the abundance of

Table 3Biomarker ratios for the Matinenda FI oil (off-line data)

Drimane/homodrimane 0.52 §Rearranged C15 bicyclic sesquiterpanes/drimane + homodrimane

0.67 §

C23 tricyclic terpane/C30 ab hopane 0.63 $C24 tetracyclic terpane/C30 ab hopane 0.36 $C24 tetracyclic terpane/(C24 tetracyclic

terpane + C23 tricyclic terpane)0.36 $

C19/(C19 + C23) tricyclic terpanes 0.08 $(C19 + C20)/C23 tricyclic terpanes 0.34 $C26/C25 tricyclic terpanes 0.82 $C23/C21 tricyclic terpanes 2.7 $C24/C23 tricyclic terpanes 0.44 $C22/C21 tricyclic terpanes 0.49 $C29 tricyclic terpanes/C30 ab hopane 0.23 $Extended tricyclic terpane ratio

(ETR: [C28 + C29tricyclic terpanes]/Ts)0.68 $

Ts/(Ts + Tm) 0.59Tm/C27b 13.7C29Ts/(C29Ts + C29 ab hopane) 0.20C�30=C30 ab hopane 0.07C29 25-norhopane/C29 ab hopane 0.12C29 ab/(ab + ba) hopanes 0.96C30 ab/(ab + ba) hopanes 0.95C31 ab 22S/(22S + 22R) hopanes 0.58C31:32:33:34:35 ab homohopanes 41:29:13:11:6 $C29 ab hopane/C30 ab hopane 1.3 $Ts + Tm/C30 ab hopane 1.05 $C31 ab 22R hopane/C30 ab hopane 0.2629,30-BNH/C30 ab hopane 0.1628,30-BNH/C30 ab hopane 0.08C30 30-norhopane/C30 ab hopane 0.11Gammacerane/C30 ab hopane 0.06C31 2a Me/(C31 2a Me + C30 ab hopane) 0.60 �C32 2a Me/(C32 2a Me + C31 ab hopanes) 0.40 �C29 steranes/C29 ab hopane 0.48*C21 sterane/C29 aaa 20R sterane 2.1 ·C27:28:29 abb steranes 41:26:33 ¥C27:28:29 ba diasteranes 48:29:23C30/(C27 + C28 + C29 + C30)

aaa 20 R steranes (%)2.0

(C28/C29) aaa 20 R steranes 0.68C29 ba diasteranes/(aaa + abb steranes) 0.67C28 aaa steranes 20S/(20S + 20R) 0.48C29 aaa steranes 20S/(20S + 20R) 0.44C28 steranes abb/(abb + aaa) 0.54C29 steranes abb/(abb + aaa) 0.53C27 ba diasteranes 20S/(20S + 20R) 0.63C29 ba diasteranes 20S/(20S + 20R) 0.65Norcholestane ratio (24-nor/(24-nor + 27-nor) <0.35Nordiacholestane ratio (24-nor/(24-nor + 27-nor) 0.27C26 steranes: 21-nor/(21-nor + 27-nor aaa 20R) 0.66

Ratios were calculated from MRM data, (m/z) M+ fi 191, 217 forhopanes, and steranes and diasteranes, respectively), except for §(m/z 123), $ (m/z 191), � (m/z 205), · (m/z 217), ¥ (m/z 218), * (m/z217 and m/z 191).


C29 ab hopane in the m/z 177 mass chromatogram, and co-elutes with the second C30 tricyclic terpane isomers in them/z 191 mass chromatogram (Fig. 11a and b). C29 25-norhopane is 12% of the abundance of C29 ab hopane, asmeasured in the m/z 398 fi 191 MRM chromatogram

(Fig. 12). The co-occurrence of the C28–C31 25-norhopaneswith a UCM hump and n-alkanes is evidence that part butnot all of the FI oil experienced heavy biodegradation priorto trapping (e.g., Volkman et al., 1983).

4.2.4. Steranes and diasteranes

Fig. 13 shows the original (a) and duplicate (b) analysesof steranes and diasteranes in the Matinenda Formation FIoil, compared to the respective system and final outside-rinse blanks. There are significant contributions from C27

20S + 20R aaa steranes and a peak eluting just beforeC27 20S aaa sterane in both the system blank and the finaloutside-rinse blank of both analyses, so these particularmolecules are regarded as contaminants in the FI oil. TheMRM chromatograms (Fig. 14) support this conclusion,as they show anomalously high abundances of C27 aaa ster-anes relative to C27 abb steranes and ba diasteranes in them/z 372 fi 217 MRM chromatogram, whereas the C28–C30

aaa steranes have similar or lower relative abundances asthe C28–C30 abb steranes and ba diasteranes (m/z 386,400 and 414 fi 217). C27 20S + 20R aaa steranes have beenrepeatedly recorded in system blanks in the CSIRO labs tothe level of the lowest abundances of fluid inclusion oils(George et al., 2004a), and hence the occurrence of thesecompounds is not interpreted as indigenous in lean FI oilssuch as those in the Matinenda Formation. Traces of preg-nane and homopregnane are also present in both the systemblank and the final outside-rinse blank of both analyses,and C29 ba 20S diasterane and the C27 abb steranes (andpossibly a co-eluting C29 diasterane; Fig. 13) are presentin the final outside-rinse blank of the primary analysis.However, these extraneous components are in sufficientlylow relative abundance not to have influenced the dataquality of the FI oil. The C28 and C29 steranes and theC28 diasteranes are unambiguously indigenous to the oilinclusions based on both the primary and duplicate analy-ses (Fig. 13). There is an unusual UCM hump around theretention time of the C28 ba diasteranes in the m/z 217 masschromatograms that is (1) reproducible (both analyses), (2)absent from any of the blanks and (3) corresponds to thehump noted near C28 tricyclic terpanes in the m/z 191 masschromatograms. These unresolved peaks are not present inthe MRM chromatograms, and their significance is un-known. It is noteworthy that a hump due to unidentifiedcompounds at a similar retention time was also present ina bitumen extract and a fluid inclusion oil from the Palae-oproterozoic sandstone associated with the Oklo nuclearreactors (Dutkiewicz et al., 2007).

C30 24-n-propylcholestanes and 24-n-propyldiacholes-tanes were detected in the Matinenda Formation FI oilusing the m/z 400 fi 217 MRM chromatogram (Fig. 14),albeit in low proportions relative to C27–C29 steranes (Table3), but no isopropylcholestanes could be detected. Traces ofC30 methylsteranes are present in the FI oil, and include the4a-methyl-24-ethylcholestanes and 3b-methyl-24-ethylcho-lestanes (Fig. 14); no 2a-methylsteranes or dinosteraneswere detected. A doublet peak labelled Ta and Tb in them/z 217 mass chromatograms of both analyses (Fig. 13) isalso present in the m/z 218 and 259 mass chromatograms(not shown), and is not present in the blanks. Although

(a)

Retention time

Res

pons

e

(c)

Ts

C29αβ C29Ts

C29βα

C30βαC31αβ

SR

C32αβS

R C33αβS

RC34αβS R

C35αβS R

Tm

C30αβ

19/320/3

21/3

23/3

24/3

25/326/3

24/4

29/3

30/3

Squalane28/3

29,30-BNH

G

C3030-nor

C31

αβR

SC

30αβ

C32

2α(Me)

C31

2α(Me)

FI oil

Blank

Rinse

FI oil

Blank

Rinse25-nor

?

(b)

Retention time

Res

pons

e

Ts

C29αβ

C29TsC30βα

C31αβ

SRC32αβ

S

R C33αβS

R

Tm

C30αβ

19/3

20/3 + ? 21/3

23/3

24/3

25/326/3

24/4

29/3

30/3

Squalane

C3030-nor

25-nor

?

?

?

?FI oil

Blank

Rinse

22/3

22/3

25,30-BNH

29,30-BNH

25,30-BNH

G

Fig. 11. Partial m/z 191 mass chromatograms showing tricyclic and tetracyclic terpanes and pentacyclic triterpanes (hopanes) in (a)Matinenda Formation FI oil, system blank and final outside-rinse blank and (b) duplicate analysis of Matinenda Formation FI oil, systemblank and final outside-rinse blank. (c) Partial m/z 205 mass chromatograms showing methylhopanes in Matinenda Formation FI oil, systemblank and final outside-rinse blank. Peak assignments define stereochemistry at C-22 (S and R); ab and ba denote 17a(H)-hopanes and17b(H)-moretanes, respectively. 19/3 to 30/3 = C19–C30 tricyclic terpanes, 24/4 = C24 tetracyclic terpane, Ts = C27 18a(H), 22, 29, 30-trisnorneohopane, Tm = C27 17a(H), 22, 29, 30-trisnorhopane, C29Ts = 18a-(H)-30-norneohopane, BNH = bisnorhopane, 25-nor = C29 25-norhopane, C30 30-nor = C30 30-norhopane, 2a(Me) = 2a-methylhopanes (ab).


not confirmed by MRM and not quantified, these peaks aretentatively identified as tetracyclic polyprenoids. C26 ster-anes and diasteranes detected in the FI oil by the m/z358 fi 217 MRM chromatogram include 21-norcholes-tanes, possibly 24-norcholestanes, 24-nordiacholestanes,27-norcholestanes and 27-nordiacholestanes (Fig. 14).

5. DISCUSSION AND SYNTHESIS

5.1. Thermal maturity of the trapped oil

The C6 to C9 hydrocarbons in the Matinenda FormationFI oil as determined from the on-line crushing data, exclud-ing the anomalously abundant soluble aromatic hydrocar-bons discussed above, are strongly dominated by

n-alkanes (Fig. 3a), consistent with the trapped oil havinga high maturity. The heptane and isoheptane values andthe parameter n-C7/MCH (Table 1) are indicative of a‘‘supermature’’ oil (i.e., one from the peak to late oil win-dow), based on published crude oil calibrations (Thomp-son, 1983, 1987). However, other maturity-related C7

parameters, including the 2,4-/2,3-dimethylpentane ratioand the derived Ctemp in �C (Bement et al., 1995; Mango,1997), indicate a mid-oil window maturity for the Matinen-da Formation FI oil (Table 1).

Most maturity-dependent hopane ratios (e.g., ab/(ab + ba); 22S/(22S + 22R)) are at equilibrium, indicatinga mid-oil window maturity or greater. The moderate Ts/(Ts+Tm) ratio is evidence against any extensive thermalcracking of the included oil. The significant amount of tri-

m/z 370 191

Retention time

Res

pons

eTs

C29αβ

C29Ts

C30βα

C31αβR

S

Tm

C30αβ

29,30-BNH

GC3030-nor

25-nor

?

C27β

C29Ts

C29αβ

28,30-BNH

C29βαC29∗

C30∗

25-nor

C31βα

m/z 384 191

m/z 398 191

m/z 412 191

m/z 426 191

Fig. 12. Partial MRM chromatograms of Matinenda FormationFI oil showing the distribution of C27 (m/z 370 fi 191), C28 (m/z384 fi 191), C29 (m/z 398 fi 191), C30 (m/z 412 fi 191) and C31

(m/z 426 fi 191) hopanes. Peak assignments as Fig. 11, C27b = C27

17b(H), 22, 29, 30-trisnorhopane, C�29 and C�30 ¼ diahopanes.


cyclic terpanes relative to the hopanes in the MatinendaFormation FI oil (Fig. 11 and Table 3) is consistent withpeak-oil window maturity. The steranes indigenous to theoil inclusions are dominated by the C21 molecule pregnaneand lesser amounts of C22 homopregnane (Fig. 13), alsoconsistent with a peak oil window maturity. The 20S/(20S + 20R) ba diasterane ratios of the Matinenda Forma-tion FI oil have reached equilibrium (�0.6), but the 20S/(20S + 20R) aaa sterane ratios have not, with values of0.48 (C28) and 0.44 (C29). The latter value indicates amid-oil window thermal maturity of about 0.75% vitrinitereflectance equivalent [VRE], based on the calibration bySofer et al. (1993). The abb/(abb + aaa) sterane ratiosare also some way from their thermal endpoints (Table3), also consistent with a mid oil window thermal maturityfor the FI oil. For the C26 steranes, the 21-norcholestanepeak contains co-eluting isomers which are cumulativelymore abundant than the individual 24-norcholestanes and27-norcholestane isomers, consistent with a normally ma-ture oil, but inconsistent with extensive thermal cracking(Moldowan et al., 1991b).

The aromatic hydrocarbons in the Matinenda Forma-tion FI oil have a simple equilibrium-controlled distribu-tion, with no specific biogenic inputs of any particularisomer. Maturity-dependent alkylnaphthalene ratios aremostly consistent with a peak oil window maturity for theMatinenda Formation FI oil (Table 2). For example, simi-lar DNR-1 and TNR-2 values are reached in Mesoprotero-

zoic sediments at the peak of the oil window in a calibrationstudy on the McArthur Basin (George and Ahmed, 2002),and a Java Sea calibration of TNR-2 indicates a VRE of�0.94% (Radke et al., 1994). The MNR-1 is suggestive ofa late oil window maturity, based on the McArthur Basincalibration (George and Ahmed, 2002) and a coal calibra-tion (Radke et al., 1984). A different trimethylnaphthaleneratio (TMNr) and the tetramethylnaphthalene ratios(TeMNr and TeMNR-1) indicate early to peak oil windowmaturities (van Aarssen et al., 1999; George and Ahmed,2002). The methylbiphenyl ratio and the two dimethylbi-phenyl ratios (Table 2) are consistent with an early to peakoil window maturity, based on published calibrations(Cumbers et al., 1987; George and Ahmed, 2002).

Alkylphenanthrene distributions are commonly used asmaturity indicators (e.g., Radke et al., 1982b). The meth-ylphenanthrene index (MPI-1) of the Matinenda Forma-tion FI oil is low (0.53) due to the dominance ofphenanthrene over methylphenanthrenes, but otheralkylphenanthrene ratios (MPR, MPDF, DMPR; Table2) are high. For example, the MPR is suggestive of aVRE of �1.2%, based on a coal calibration (Radke et al.,1984), and a peak to late oil window is also suggested bythe calibration of MPR in the Mesoproterozoic McArthurBasin (George and Ahmed, 2002). The MPDF and theDMPR values in the Matinenda Formation FI oil are onlyreached in indigenous organic matter in more mature Mes-oproterozoic sedimentary rocks, also indicating a peak tolate oil window maturity (George and Ahmed, 2002).Accordingly, the low MPI-1 value is interpreted to be dueto demethylation of methylphenanthrenes to phenanthrene,and thus the MPI-1 is on the reversed high maturity sectionof the MPI-1 versus thermal maturity graph (Radke et al.,1982a; Boreham et al., 1988). Both the methyldibenzothi-ophene and the dimethyldibenzothiophene ratios are low,consistent with maturities in the early to peak oil window(Radke, 1988; George and Ahmed, 2002).

In general, the higher molecular weight biomarker matu-rity parameters indicate lower maturities (mid oil window)than the lower molecular weight parameters such as thosebased on alkylnaphthalenes (peak oil window), althoughthere is not a simple relationship. In part this might bedue to poor calibrations of many of these ratios into extre-mely old sequences and towards high maturities. Anothercontributory factor is that the FI oil represents a co-analy-sis of oil from two FI populations in the Matinenda Forma-tion, which are likely to have different maturities andchemical compositions. There is no reliable method withcurrent technology of separating the detailed moleculargeochemical signal from each population, although theability to obtain some geochemical data from individualFIs using laser micropyrolysis (Greenwood et al., 1998) orlaser decrepitation (Hode et al., 2006) holds promise forthe future. It is likely that the oil included in the secondhighly carbonic FI population has a higher maturity, andwould likely have contributed a greater proportion of lowmolecular weight compounds, but this remains unproven.Despite the uncertainties of the ratio calibrations and thepossibility of a mixed maturity signal, what is clear is thatthe thermal maturity of the included oil is not unusually

(a)

Retention time

Res

pons

e

FI oil

Blank

Rinse

?

(b)

Retention time

Res

pons

e

FI oil

Blank

Rinse

C27 20S βαC27 20S ααα

C27 20R αββ + C29 20S βα

C27 20Rβα

C27 20R ααα

Squalane

Squalane

Ta+Tb

C29 20R βα

C27 20R αααC27 20S ααα

?

C27 20R ααα

C27 20S αααSqualane

Pregnane (C21)

Homopregnane (C22)

C29 20S ααα

C29 20R αααC29 20S αββ

C29 20R αββ

C28 20R αααC28 20S αββC28 20R

αββC2820Sααα

C27 20S αββ+ C28 20R αβ

C28 20S βαC28 20R βα

C27 20S βα

C27 20S ααα

C27 20R αββ + C29 20S βα

C27 20Rβα

C27 20R ααα

SqualaneTa+Tb

C29 20R βα

Pregnane (C21)

Homopregnane (C22)

C29 20S ααα

C29 20Rααα

C29 20S αββC29 20R αββ

C28 20R ααα

C28 20S αββC28 20R

αββC2820Sααα

C27 20S αββ+ C28 20R αβ

C28 20S βα C28 20R βα

?

C27 20R ααα

C27 20S ααα

Squalane

Pregnane (C21)

?

Pregnane (C21)

Pregnane (C21)Homopregnane (C22)

Homopregnane (C22)

C27 20R αββ + C29 20S βα

C27 20S βα

Fig. 13. Partial m/z 217 mass chromatograms showing pregnane (C21), homopregnane (C22) and C27–C29 steranes and diasteranes in (a)Matinenda Formation FI oil, system blank and final outside-rinse blank and (b) duplicate analysis of Matinenda Formation FI oil, systemblank and final outside-rinse blank. Peak assignments define stereochemistry at C-20 (S and R); ba, aaa and abb denote 13bH),17a(H)-diasteranes, 5a(H),14a(H),17a(H)-steranes and 5a(H),14b(H),17b(H)-steranes, respectively. Ta and Tb are C30 18a(H) tetracyclicpolyprenoids (21R and 21S, respectively).


high. This is irrefutable evidence against any significantthermal cracking either prior to or subsequent to trapping.

5.2. Hydrocarbon survival at high temperatures and pressures

A wide range of hydrocarbons is present in the fluidinclusions in the Matinenda Formation sample. The com-pounds include (1) the simplest single carbon molecules(CH4 and CO2), (2) relatively abundant fundamental or-ganic compounds of simple structure, including n-alkanes,monomethylalkanes, aromatic hydrocarbons, low molecu-

lar weight cyclic hydrocarbons, and (3) trace amounts ofcomplex multi-ring biomarkers. All the commonly abun-dant hydrocarbons in Phanerozoic crude oils were found.This is not a surprise because very old FI oils are knownto have fluorescence and other physical properties like thoseof Phanerozoic equivalents (Dutkiewicz et al., 1998). More-over, although no macroscopic life existed until the late Pal-aeoproterozoic (Han and Runnegar, 1992; Hedges et al.,2004), in other respects the dominant microbial and micro-scopic life forms for a billion years before then were quitesimilar to current ones (Buick, 2001), as were many of the

m/z 358 217

Retention time

Res

pons

e

217C27

m/z 386 217C28

m/z 400 217C29

m/z 414 217C30

20S βα20S ααα

20 β

20R βα 20R ααα

Squalane

m/z 414 231

Squalane

Squalane

Squalane

20R αβ20S αβ

20S βα20S ααα 20R αββ

20R βα

20R ααα

20S αββ

20R αβ20S αβ

20S βα20S ααα

20R αββ20R βα

20R ααα20S αββ

20R αβ20S αβ

20S βα

20S ααα20R αββ20R βα

20R ααα20S αββ

Squalane

12

34

8

910

1112

135-7

7 = 24n 20S αββ

9 = 21n ααα +αββ10 = 27n 20S ααα11= 27n 20R αββ

12 = 27n20S αββ13 = 27n20R ααα

4α 20R ααα

4α 20S αββ +3β 20R ααα

4α 20R αββ4α 20S ααα+ 3β 20S αββ

3β 20S ααα3β 20R αββ

* **

*

1 = 24dn 20S βα2 = 24dn 20R βα3 = 27dn 20S βα4 = 27dn 20R βα5 = 24n 20S ααα6 = 24n 20R αββ

7 = 24n 20S αββ8 = 24n 20R ααα

m/z

R αββ20S αββ m/z 372

Fig. 14. Partial MRM chromatograms of Matinenda FormationFI oil showing the distribution of C26 (m/z 358 fi 217), C27 (m/z372 fi 217), C28 (m/z 386 fi 217), C29 (m/z 400 fi 217) and C30

(m/z 414 fi 217) steranes and diasteranes, and C30 methylsteranes(m/z 414 fi 231). Peak assignments as Fig. 13. For the C26 steranes,24n = 24-norcholestanes, 24dn = 24-nordiacholestanes, 27n = 27-norcholestanes, 27dn = 27-nordiacholestanes, and 21-nor = 21-norcholestanes. For the C30 steranes and diasteranes, the dominantseries labelled are the 24-n-propylcholestanes. 24-Isopropylcholes-tanes are below detection limit, but if there were any 24-isopropylcholestanes they would be in the locations marked by *,and would be less than 30% of the abundance of the 24-n-propylcholestanes. For the C30 methylsteranes, 3b = 3b-methyl-24-ethylcholestanes, and 4a = 4a-methyl-24-ethylcholestanes.


prevalent geological processes. Organic matter was buried,oil was generated and expelled from source rocks, and oilmigrated to reservoirs where it accumulated and in somecases was preserved (Buick et al., 1998) in much the sameway as in younger rocks. Thus, it is not unreasonable thatPalaeoproterozoic oil should have a similar chemical signa-ture, in many respects, to modern crude oils, which aredominantly formed from algal and bacterial organic matter.

What is more surprising is that this range of complexhydrocarbons has survived temperatures possibly as highas 350 �C at pressures of 50–200 MPa to which the Matin-enda Formation was exposed after diagenesis. Despiteuncertainties with respect to calibrations against othermaturity indicators or temperature, all the maturity param-eters indicate that the FI oil is mature and was generated inthe oil window. There is no evidence of extensive thermal

cracking from the molecular geochemistry data, despitethe heating of the rocks to uppermost prehnite–pumpellyiteafter entrapment of the aqueous oil-bearing inclusions andduring migration and entrapment of the oil in the carbonicinclusions. Some of the early population of oil inclusionswith high homogenisation temperatures (>200 �C) have or-ange flourescence colours and may have been stretched dur-ing metamorphism, a process that may also have led tosolid bitumen formation in a few of the oil inclusions (Dut-kiewicz et al., 2003a). These processes did not have any dis-cernible effect on the molecular geochemistry data reportedhere, which is the average composition of all included oil.The preservation of molecular maturity signatures throughheating has also been recorded in K-feldspar hosted oilinclusions in the Ula oilfield (Karlsen et al., 1993), whichhave been heated from 90 �C at trapping to 143 �C atpresent.

The previously prevailing paradigm of oil destruction attemperatures as low as 120–150 �C (e.g., Evans et al., 1971;Ungerer et al., 1987; Barker, 1990; Braun and Burnham,1992) has now been superseded by a recognition that crudeoil in open reservoirs is much more thermally stable, basedon observational data (e.g., Price, 1993; McNeil and Be-ment, 1996; Vandenbroucke et al., 1999; Sajgo, 2000), halflives of model compounds (Mango, 1991; Domine et al.,1998) and pyrolysis models (e.g., Horsfield et al., 1992; Pep-per and Dodd, 1995; Planche, 1996; Schenk et al., 1997;Domine et al., 1998; Vandenbroucke et al., 1999; Wanget al., 2006). Oil is present in some very high temperaturereservoirs, including the Elgin field in the North Sea(190 �C) (Vandenbroucke et al., 1999) and the Sweethomecondensate in Texas well TX-O-119A (200 �C) (McNeiland Bement, 1996). Traces of hydrocarbons are present ateven higher temperatures, for example in Californian wellApex-1 (223 �C) (Price et al., 1999), Hungarian well Hod-1 (233 �C) (Sajgo et al., 1988) and prograde metamor-phosed black shales (250–550 �C) (Schwab et al., 2005).These examples provide strong circumstantial evidence ofoil stability to higher temperatures, at least on the orderof 10s of million of years time scale. A consensus view fromthe above papers is that oil-to-gas cracking starts around160–215 �C, depending on heating rate, oil type, presenceof catalysts and whether it is an open or closed system.The upper temperature of crude oil stability is less well con-strained, but may be of the order of 245–275 �C (Wanget al., 2006), although stabilities for C11+ hydrocarbons atup to 250–350 �C have been proposed (Price, 1993; Priceand DeWitt, 2001). The generally recognised crude oil sta-bility temperatures are thus still below the temperatures towhich the oil inclusions in the Matinenda Formation havebeen exposed (280–350 �C). Accordingly, additional expla-nations for survival of included oil in high temperaturerocks must be sought, particularly given the very long timethat has elapsed since trapping of the oil. Three propertiesof FI oils that differentiate them from crude oil in the porespace of a petroleum reservoir are pertinent to the questionof thermal stability: (1) closed systems, (2) high fluid pres-sures, and (3) lack of clay or other mineral or metal cata-lysts, as discussed previously (Karlsen et al., 1993;Karlsen and Skeie, 2006).


(1) Fluid inclusions are generally closed systems, andexceptions of leakage or stretching can generally be easilyrecognized by petrographic work (Dutkiewicz et al.,2003a). Bulk oil-to-gas cracking and individual componentreactions such as demethylation of alkylated aromatichydrocarbons will proceed faster in an open system inwhich products are removed from the site of the reaction(Price and Wenger, 1992; Price, 1993). In closed systems,there is no opportunity for product removal away fromthe reactants, so the concentration of products builds up,thereby inhibiting the reaction according to Le Chatelier’sPrinciple. Furthermore, in closed systems where there is alack of significant interaction between hydrocarbons androck or pore waters, hydrocarbons generate their own re-dox environment and will remain stable to much highertemperatures than in an open system (Giggenbach, 1997).Water in contact with the oil within the closed system inclu-sions may also help retard oil destruction reactions by sup-pressing the formation of free radicals, as has beendemonstrated by laboratory pyrolysis experiments (Hespand Rigby, 1973; Price and Wenger, 1992).

(2) Dutkiewicz et al. (2003a) have shown that the car-bonic-rich Matinenda Formation FIs were trapped at highfluid pressures (50–250 MPa), considerably higher thanpressures in conventional oil reservoirs which are oftenaround 10–40 MPa (e.g., Losh et al., 2002; Bailey et al.,2006). It is known from many laboratory experiments thathigh fluid pressures retard petroleum maturation and crack-ing reactions (Hesp and Rigby, 1973; Horsfield et al., 1992;Price and Wenger, 1992; Price, 1993; Hill et al., 1996; Le-wan, 1997; Sajgo, 2000), and this is also seen in naturally-overpressured basins (e.g., Zou and Peng, 2001; Li et al.,2004). Therefore it is plausible that the high fluid pressuresin the Matinenda Formation FIs during migration furtherretarded oil cracking reactions.

(3) Matinenda Formation oil inclusions are trapped inquartz and K-feldspar grains, and do not have any visibleclays or other potential mineral catalysts associated withthem. Clay minerals are known to catalyse oil generationreactions in natural environments (Espitalie et al., 1980;Tannenbaum et al., 1986) and in laboratory pyrolysisexperiments (e.g., Bastow et al., 2000). Petroleum reservoirscommonly contain large amounts of detrital and diageneticclays, and so the presence of these would be expected to en-hance the cracking of crude oil in reservoirs. Transitionmetals in carbonaceous sedimentary rocks may also en-hance oil-to-gas cracking reactions and lead to the decom-position of oil (Mango and Hightower, 1997; Mango andElrod, 1998). Thus, the lack of clays or other potential min-eral or metal catalysts in contact with the oil trapped in FIsshould also contribute to the lack of thermal cracking reac-tions (Karlsen and Skeie, 2006) and thus to the survival ofincluded oil for >2 billion years.

The observation that none of the molecular maturityparameters for the oil trapped in the Matinenda FormationFIs have been significantly reset at the high temperaturesexperienced subsequent to trapping also has relevance tothe long debate about the mechanisms for changing matu-rity markers. Originally it was believed that many isomericbiomarker ratios changed due to conventional product-

reactant relationships (Mackenzie and McKenzie, 1983).Natural and laboratory studies have indicated that differen-tial rates of generation and the relative thermal stabilities ofthe isomers control maturity parameters in many instances(e.g., Peters et al., 1990; Abbott et al., 1990; Bishop and Ab-bott, 1993). Isomerisation reactions should continue withincreasing maturation in closed systems such as fluid inclu-sions, because there is no volume change so the reactionsare unimpeded. The fact that all observed maturity param-eters appear to be impeded suggest that they are all influ-enced by the selective thermal stability of the isomers, ashas been concluded previously (Karlsen et al., 1993; Karl-sen and Skeie, 2006).

5.3. Biomarker geochemistry of the Matinenda Formation FI

oil

The Pr/Ph ratio of near unity (Table 2) is suggestive of amildly reducing depositional environment. The low diben-zothiophene/phenanthrene ratio of 0.12 indicates that thetrapped oil contains low amounts of organic sulphur, andin conjunction with the low Pr/Ph ratio suggests that itwas generated from a marine shale (zone 3 of Hugheset al., 1995). The abundant monomethylalkanes are charac-teristic of Proterozoic oils and sedimentary rocks (Hoering,1967; Summons et al., 1988b) and are likely due to cyano-bacterial input (Summons and Walter, 1990; Kenig et al.,1995).

Bicyclic sesquiterpanes are ubiquitous in sediments andoils of all ages, and are thought to be the degradation prod-ucts of bacteriohopanes (Alexander et al., 1984). The tricy-clic terpanes are ubiquitous in oils and are most likelyderived from bacteria (Ourisson et al., 1982), althoughother algal sources are possible (Simoneit et al., 1993).Their isomeric distribution enables inferences to be madeabout the characteristics of the source rock that generatedthe oil, provided that inferences derived from the globalPhanerozoic database are applicable to interpreting Palaeo-proterozoic oils. The C19 and C20 tricyclic terpanes are inlow abundance relative to other tricyclic terpanes (Table3), consistent with a marine source rock containing no high-er plant organic matter (Preston and Edwards, 2000;George et al., 2004b). The low C26/C25 tricyclic terpane ra-tio shows that the Matinenda Formation FI oil was not de-rived from a lacustrine source rock (Schiefelbein et al.,1999). Extended tricyclic terpanes from C28 to C30 were de-tected (Fig. 11), but are in low relative abundance (Table 3).Therefore, the extended tricyclic terpane ratio (Holba et al.,2001) does not indicate a source rock influenced by marineupwelling (Holba et al., 2003b).

Rearranged hopanes in the Matinenda Formation FI oilinclude Ts, C29Ts and the C29 and C30 diahopanes, butthese are in low abundance and therefore suggest that thesource rock was not clay-rich (Moldowan et al., 1991a),especially in view of the relatively high thermal maturityof the FI oil. The distribution of extended hopanes, withlow amounts of the C35 isomers, and the low abundanceof 28,30-bisnorhopane relative to other hopanes (Fig. 12)supports a mildly reducing source rock depositional envi-ronment. A trace of gammacerane was identified in the


m/z 412 fi 191 MRM chromatogram (Fig. 12), but ininsufficient quantities to infer water column stratification(cf. Sinninghe Damste et al., 1995).

The C24/C23 and C22/C21 tricyclic terpane ratios of oilscan be used to predict their source-rock depositional envi-ronment, based on a calibration set of 500 crude oils (Peterset al., 2005). These ratios (Table 3) suggest that the Matin-enda Formation FI oil may have been derived from a car-bonate or marl, and this might be supported by themoderately high abundance of C24 tetracyclic terpane.The possibility of a calcareous source rock is further indi-cated by the high C29/C30 ab hopane ratio of 1.3 and theabundant 29,30-bisnorhopane and C30 30-norhopane(Moldowan et al., 1992) but not by the rather low amountsof C31 hopanes relative to C30 ab hopane or by the propor-tion of C34 and C35 homohopanes (Table 3). The high 2a-methylhopane ratios (Table 3) suggest that the source rockof the FI oil contained cyanobacteria (Summons et al.,1999). 2a-Methylhopanes are common biomarkers foundin Precambrian oils and rocks (Summons et al., 1988b;Brocks et al., 2003b; Dutkiewicz et al., 2004), although theyare also abundant in Phanerozoic carbonate-sourced oils(Moldowan et al., 1992; Summons and Jahnke, 1992). Inthis and another Palaeoproterozoic FI oil sample (Dutkie-wicz et al., 2007) it has been argued that a high C29/C30

ab hopane ratio, abundant 29,30-bisnorhopane, C30 30-norhopane and C24 tetracyclic terpane, and low amountsof diasteranes and rearranged hopanes indicate a carbonateor marly source rock with low clay content, followingPhanerozoic biomarker interpretational guidelines (Peterset al., 2005). In view of the very minor carbonate in themost likely source succession, it is proposed that insteadof the direct lithological interpretation, these biomarkerdistributions are reflecting a strong cyanobacterial contri-bution to all marine organic matter in the Proterozoic,whereas in Phanerozoic rocks such signatures are largely re-stricted to petroleum generated from carbonates.

Sterane biomarkers in the Matinenda Formation FI oilare diverse, though less abundant than hopanes (Table 3).The sterane C27:C28:C29 ratios favour the C27 isomers,based on abb steranes and ba diasteranes, and the C28/C29 aaa sterane ratio is 0.68 (Table 3). The latter is incon-sistent with this ratio decreasing with increasing geologicalage through the Phanerozoic, as suggested by Granthamand Wakefield (1988), although other Precambrian sampleshave similarly high ratios (Brocks et al., 2003a; Dutkiewiczet al., 2007). The presence of the steranes and diasteranes isevidence for eukaryotic input to the source rock that gener-ated the FI oil (cf. Summons et al., 2006). The 4a-methyl-24-ethylcholestanes in the FI oil also suggest a eukaryoticinput to either marine or lacustrine source rocks, and to-gether with 3b and 2a-methyl-24-ethylcholestanes havebeen detected in older Archaean rocks (Brocks et al.,2003a; Brocks et al., 2003b). The presence of 24-n-propyl-cholestanes is indicative of marine algal input to the sourcerock of the FI oil (Moldowan et al., 1990). The tentativelyidentified tetracyclic polyprenoids in the Matinenda For-mation FI oil are common in fresh to brackish sedimentaryenvironments and may be related to green algae (Holbaet al., 2000, 2003a). Many Neoproterozoic and early Cam-

brian oils and source rocks contain high amounts of 24-iso-propylcholestanes (McCaffrey et al., 1994; Peters et al.,1995) which are biomarkers for marine demosponges (Loveet al., 2005), but these are absent from the Matinenda For-mation FI oil (Fig. 14).

Individual ba diasterane isomers are of similar abun-dance to individual sterane isomers (Fig. 14), so theC29 ba diasteranes/(aaa + abb steranes) ratio is low (Ta-ble 3) for an oil interpreted to have been generated inthe peak oil window using other parameters. This obser-vation is consistent with the low content of rearrangedhopanes in the Matinenda Formation FI oil. As acidicsites on clays catalyse the early diagenetic reactions thatlead to diasterane formation (Sieskind et al., 1979), thisimplies that the source rock of the FI oil was not clay-rich.

Based on an empirically-observed increasing proportionof 24-norcholestanes and 24-nordiacholestanes withdecreasing age, Holba et al. (1998) has proposed twoparameters, the norcholestane and the nordiacholestane ra-tios, for constraining the age of oil source rocks. The nor-cholestane ratio of the Matinenda Formation FI oil is<0.35 (Table 3), although based on barely detectable 24-norcholestane peaks (Fig. 14), typical of Triassic and olderoils. The more reliable nordiacholestane ratio (0.27) is high-er than most Triassic and older oils (<0.2) (Holba et al.,1998), although this is based on noisy and poorly resolved24-nordiacholestane peaks (Fig. 14). These parameters in-crease due to an increasing proportion of dinoflagellateand diatom-derived 24-norsterols (Rampen et al., 2007).The presence of 24-nordiacholestanes in the MatinendaFI oil suggests that there may be a low-level, presentlyunidentified non-diatom/dinoflagellate source of these inthe Proterozoic.

Although the majority of biomarker attributes are con-sistent with a Palaeoproterozoic sources, some aspects ofthe Matinenda Formation FI oil could be argued to bedue to overprinting with Cenozoic oil or recent contamina-tion. These attributes are the high molecular weight odd n-alkanes and the higher than expected C28/C29 aaa steraneand nordiacholestane ratios. The petrographic evidencerules out the trapping of FIs post metamorphism, and thusthe possibility that oils generated from Palaeozoic sourcerocks in the Michigan Basin, for instance, could have mi-grated laterally into weathered or fractured MatinendaFormation. The methodology used with the blanks suggeststhat recent contamination has not affected the biomarkers,although the relatively high contribution of n-alkanes in theblanks may explain the unexpected distribution ofn-alkanes in the FI oil.

5.4. Source of the inclusion oil: implications for life in the

Palaeoproterozoic

The biomarker geochemistry of the Matinenda Forma-tion FI oil enables inferences about the organisms that con-tributed to the organic matter deposited in thePalaeoproterozoic source rocks from which the analysedoil was generated and expelled. Further, inferences aboutthe depositional environment can also be made.


According to Young (2001), all Huronian units belowthe Gowganda Formation were dominated by non-marinedeposition in a largely rift-controlled environment,although Fralick and Miall (1989) have described theMcKim Formation as deltaic in origin, deposited in anmarginal marine setting. The inclusion oil is probably de-rived either from the immediately overlying organic-richdeltaic McKim Formation (McKirdy and Imbus, 1992) orfrom kerogen within the Matinenda Formation (Fig. 1)(Mossman et al., 1993), as there are no known source rocksdeeper in the section. A deltaic source rock is supported bythe presence of n-propylcholestanes, indicating a contribu-tion from marine source rocks (Moldowan et al., 1990).The source rock was likely deposited in a mildly reducingenvironment, as indicated by the Pr/Ph ratio and the pres-ence of 28,30-bisnorhopane. It is not possible to perform adetailed oil-source correlation between the FI oil and its po-tential source rocks, because the latter have been exposed toupper prehnite–pumpellyite facies metamorphism in anopen system and have thus likely been rendered inert withrespect to extractable organics.

Biomarkers for bacteria in the Matinenda Formation FIoil include bicyclic sesquiterpanes, tricyclic terpanes andhopanes. Bacterial biomarkers are commonly detected inPrecambrian rocks and oils (e.g., Summons et al., 1988a;Summons et al., 1988b; Brocks et al., 1999; Brocks et al.,2003b; Dutkiewicz et al., 2003b; Dutkiewicz et al., 2004;Brocks et al., 2005). There is no evidence in the MatinendaFormation FI oil for biomarkers such as arylisoprenoids,okenane, chlorobactane or isorenieratane that might be re-lated to specific bacterial inputs of photosynthetic purple orgreen sulphur bacteria (Summons and Powell, 1986; Brockset al., 2005).

The presence of abundant monomethylalkanes andespecially the C31+ 2a-methylhopanes in the MatinendaFormation FI oil provide strong evidence for cyanobacte-rial input to the source rock of the oil (Summons and Wal-ter, 1990; Summons and Jahnke, 1992; Kenig et al., 1995).These biomarkers have been detected previously in abun-dance in Proterozoic and older oils and rocks (e.g., Sum-mons et al., 1988b; Brocks et al., 1999; Summons et al.,1999; Brocks et al., 2003b; Dutkiewicz et al., 2004), forwhich the time of deposition of the rocks, and the likelysource rocks for the oils, postdates the time of detectableoxygenation of the shallow oceans (Holland, 2006). Thoughthese molecules are not directly associated with metabo-lism, by association they imply the existence of oxygenicphotosynthesis (Summons et al., 1999), because all cyano-bacteria are capable of performing such autotrophy(Castenholz, 2001). Moreover, the production of abundantC31+ 2a-methylhopanes is widespread, while not ubiqui-tous, throughout the Phylum Cyanobacteria, including inthe basally-branching Gloeobacter violaceus (Castenholz,2001). Thus, it seems to be a reasonable inference that bio-genic oxygen was being generated during deposition of thesource rocks for the Matinenda FI oils (Dutkiewicz et al.,2006a).

A significant biomarker observation in the MatinendaFormation FI oil is the presence of diverse steranes anddiasteranes, which are evidence for eukaryotic input to

the source rock that generated the FI oil (cf. Summonset al., 2006). Despite recent speculations to the contrary(Raymond and Blankenship, 2004; Kopp et al., 2005), theonly confirmed biosynthetic pathway of precursor sterolsinvolves the epoxidation of squalene where the additionof 1

2O2 is catalysed by the enzyme squalene monooxygenase

(Jahnke and Klein, 1983). The extended biosynthetic path-way to modified sterols such as cholesterol and ergosterolinvolving cyclization and subsequent oxidative demethyla-tion requires up to twelve O2 molecules (Summons et al.,2006). Although some sterane precursors occur in otherorganisms (Volkman, 2005), high concentrations of the reg-ular steranes are apparently exclusive biomarkers fororganisms of the domain Eukarya (Brocks et al., 2003b;Summons et al., 2006). Steranes and diasteranes have beendetected in older shale extracts, such as the 2.7 Ga rocksfrom the Pilbara Craton (Brocks et al., 1999, 2003a,b),but with the caveat of ‘‘probably syngenetic’’, promptingconcerns that the ancient steranes are contaminants (Koppet al., 2005). The steranes and diasteranes reported here arefrom an oil of normal thermal maturity which was trappedin fluid inclusions early in the burial history of the Matin-enda Formation. Oil inclusions in quartz, unlike shale ex-tracts (Brocks et al., 2003a), cannot be contaminated bylater migrating hydrocarbons, and the petrographic infor-mation rules out the trapping of FIs post metamorphism.The entrapped biomarkers may be from both FI popula-tions, but comparison with the outside rinse and systemblanks shows that the bulk of the analysed biomarkersare clearly not contaminants from bitumen in the porespace, younger hydrocarbons or from anthropogenic input.Thus, the presence of steranes and diasteranes in the Mat-inenda Formation FI oil which was trapped before2.2 Ga, as well as in the Oklo FI oil which was trapped be-tween 2.0 and 2.1 Ga (Dutkiewicz et al., 2006b; Dutkiewiczet al., 2007), provide supporting, but not confirming, evi-dence in favour of the indigenous origin of the oldershale-hosted occurrences. Clearly, however, the molecularfossil record of eukaryotes substantially pre-dates that oftheir body or trace fossils, an observation concordant withcontemporary evolution models.

5.5. Proterozoic and Archean oil inclusions: biogeochemical

time capsules

Oil inclusions are found in a wide variety of rocks andminerals of all ages (Karlsen et al., 1993; Munz, 2001;and references therein). The ability to analyse the oiltrapped in FIs from early Precambrian sequences opensup a new way to obtain biogeochemical information thatcan be reliably identified as being indigenous to the hostrock. The great advantage of using FI oils is that they trapoils in an unaltered state, allowing survival of biologicallyand environmentally informative biomarkers for billionsof years, even through significant thermal events. One dis-advantage is that this is a bulk analysis technique, poten-tially resulting in the co-analysis of oil inclusions andsolid bitumens from different generations, a problem whichcan be overcome with careful petrography and sampleselection. Laser micropyrolysis or laser decrepitation GC–


MS of single oil inclusions offers a potential solution to thisdrawback (Greenwood et al., 1998; Hode et al., 2006),although with current technology it is unlikely that the de-tailed biomarker composition presented in this paper willever be able to be reproduced for single oil inclusions. An-other difficulty is relating the inclusion oil to a potentialsource rock, as the two will have necessarily undergone dif-fering maturation pathways. However, by sampling inclu-sion-bearing rocks in stratigraphic successions with alimited range of potential source rocks, reasonable sourceidentification can be achieved. Despite these two issues, thismethodology can clearly provide otherwise unattainable in-sights into biological evolution and palaeoenvironmentsduring critical stages of Earth’s early history.

6. CONCLUSIONS

(1) FI oil trapped prior to low grade metamorphism at2.2 Ga in the Palaeoproterozoic Matinenda Formationcontains CH4, CO2, n-alkanes, isoprenoids, mono-methylalkanes, aromatic hydrocarbons, low molecularweight cyclic hydrocarbons, and trace amounts of complexmulti-ring biomarkers.

(2) Maturity ratios show that the FI oil was generatedwithin the oil window, with no evidence of extensive ther-mal cracking, despite the oil inclusions having been eithertrapped at uppermost prehnite-pumpellyite facies metamor-phic grade (280–350 �C), or having been heated to thesetemperatures after entrapment.

(3) Three properties of FI oils that differentiate themfrom crude oil in the free pore space of a petroleum reser-voir may contribute to the thermal stability of the includedhydrocarbons: (a) closed systems, (b) high fluid pressures,and (c) lack of clays or other potential mineral or metalcatalysts.

(4) Biomarker geochemistry indicates that the FI oil wasderived from a marine source rock deposited in a reducingdepositional environment. Candidates include the immedi-ately overlying organic-rich deltaic McKim Formation orkerogen from within the Matinenda Formation.

(5) Biomarkers specific for bacteria in the MatinendaFormation FI oil include bicyclic sesquiterpanes andhopanes.

(6) The presence of abundant monomethylalkanes andespecially the >C31 2a-methylhopanes in the MatinendaFormation FI oil are strong evidence for a significantcyanobacterial input to the source rock of the oil.

(7) Biomarker signatures that indicate a calcareous rockwith a low clay content, based on Phanerozoic biomarkerinterpretational guidelines, may instead reflect high cyano-bacterial organic inputs that were prevalent in all Protero-zoic environments, but were later largely restricted tonon-clastic settings.

(8) Diverse steranes and diasteranes are present in the FIoil, and are evidence for eukaryotic input to the source rockthat generated the FI oil.

(9) The presence of abundant biomarkers for cyanobac-teria and eukaryotes derived from and trapped in rockswhich are interpreted to have been some of the youngestrocks deposited while the atmosphere remained largely

anoxic (Papineau et al., 2007) are consistent with an earlierevolution of oxygenic photosynthesis and suggests thatsome aquatic settings had become sufficiently oxygenatedfor sterol biosynthesis by this time.

(10) The extraction of biomarker molecules from Palae-oproterozoic oil-bearing fluid inclusions thus establishes anew method, using low detection limits and system blanklevels, to trace evolution through Earth’s early history thatavoids the potential contamination problems that can affectshale-hosted hydrocarbons.

ACKNOWLEDGMENTS

We would like to thank Robinson A. Quezada and ManzurAhmed for analytical assistance. We thank Malcolm Walter for re-view of an earlier version of this paper. The paper benefited signif-icantly from the detailed comments of journal reviewer DagKarlsen, an anonymous reviewer and Associate Editor Bob Bur-russ. This work was supported by an ARC Discovery Grant whichincludes a QEII Fellowship to A.D. and by the National Aeronau-tics and Space Administration Astrobiology Institute (R.B.).

REFERENCES

Abbott G. D., Wang G. Y., Eglinton T. I., Home A. K. and PetchG. S. (1990) The kinetics of sterane biological marker releaseand degradation processes during the hydrous pyrolysis ofvitrinite kerogen. Geochim. Cosmochim. Acta 54, 2451–2461.

Ahmed M. and George S. C. (2004) Changes in the molecularcomposition of crude oils during their preparation for GC andGC–MS analyses. Org. Geochem. 35, 137–155.

Alexander R., Kagi R. I., Noble R. and Volkman J. K. (1984)Identification of some bicyclic alkanes in petroleum. Org.

Geochem. 6, 63–70.

Allwood A. C., Walter M. R., Kamber B. S., Marshall C. P. andBurch I. W. (2006a) Stromatolite reef from the Early Archaeanera of Australia. Nature 441, 714–718.

Allwood A. C., Walter M. R. and Marshall C. P. (2006b) Ramanspectroscopy reveals thermal palaeoenvironments of c.3.5billion-year-old organic matter. Vibrat. Spect. 41, 190–197.

Bailey W. R., Underschultz J., Dewhurst D. N., Kovack G.,Mildren S. and Raven M. (2006) Multi-disciplinary approach tofault and top seal appraisal; Pyrenees-Macedon oil and gasfields, Exmouth Sub-basin, Australian Northwest Shelf. Mar.

Pet. Geol. 23, 241–259.

Barker C. (1990) Calculated volume and pressure changes duringthermal cracking of oil to gas in reservoirs. Am. Assoc. Petrol.

Geol. Bull. 74, 1254–1261.

Bastow T. P., Alexander R., Fisher S. J., Singh R. K., van AarssenB. G. K. and Kagi R. I. (2000) Geosynthesis of organiccompounds. Part V—methylation of alkylnaphthalenes. Org.

Geochem. 31, 523–534.

Bement W. O., Levey R. A. and Mango F. D. (1995) Thetemperature of oil generation as defined with C7 chemistrymaturity parameter (2,4-DMP/2,3-DMP ratio). In Organic

Geochemistry: Developments and Applications to Energy, Cli-

mate, Environment and Human History (eds. J. O. Grimalt andC. Dorronsoro). A.I.G.O.A., pp. 505–507.

Bishop A. N. and Abbott G. D. (1993) The interrelationship ofbiological marker maturity parameters and molecular yieldsduring contact metamorphism. Geochim. Cosmochim. Acta 57,

3661–3668.

Boreham C. J., Crick I. H. and Powell T. G. (1988) Alternativecalibration of the Methylphenanthrene Index against vitrinite


reflectance: application to maturity measurements on oils andsediments. Org. Geochem. 12, 289–294.

Brasier M., McLoughlin N., Green O. and Wacey D. (2006) Afresh look at the fossil evidence for early Archaean cellular life.Philos. Trans. R. Soc. Lond., B 361, 887–902.

Braun R. L. and Burnham A. K. (1992) PMOD – A flexible modelof oil and gas generation, cracking, and expulsion. Org.

Geochem. 19, 161–172.

Brocks J. J., Logan G. A., Buick R. and Summons R. E. (1999)Archean molecular fossils and the early rise of eukaryotes.Science 285, 1033–1036.

Brocks J. J., Buick R., Logan G. A. and Summons R. E. (2003a)Composition and syngeneity of molecular fossils from the 2.78to 2.45 billion-year-old Mount Bruce Supergroup, PilbaraCraton, Western Australia. Geochim. Cosmochim. Acta 67,

4289–4319.

Brocks J. J., Buick R., Summons R. E. and Logan G. A. (2003b) Areconstruction of Archean biological diversity based on molec-ular fossils from the 2.78 to 2.45 billion-year-old Mount BruceSupergroup, Hamersley Basin, Western Australia. Geochim.

Cosmochim. Acta 67, 4321–4335.

Brocks J. J., Love G. D., Snape C. E., Logan G. A., Summons R.E. and Buick R. (2003c) Release of bound aromatic hydrocar-bons from late Archean and Mesoproterozoic kerogens viahydropyrolysis. Geochim. Cosmochim. Acta 67, 1521–1530.

Brocks J. J., Summons R. E., Buick R. and Logan G. A. (2003d)Origin and significance of aromatic hydrocarbons in giant ironore deposits of the late Archean Hamersley Basin, WesternAustralia. Org. Geochem. 34, 1161–1175.

Brocks J. J. (2005) The evolution of steroids and eukaryotes in theProterozoic. EOS Transactions, AGU Fall Meeting Supplement,vol. 86 (52), Abstract B12A-05.

Brocks J. J., Love G. D., Summons R. E., Knoll A. H., Logan G.A. and Bowden S. A. (2005) Biomarker evidence for green andpurple sulphur bacteria in a stratified Palaeoproterozoic sea.Nature 437, 866–870.

Brocks J. J. and Summons R. E. (2005) Sedimentary hydrocarbons,biomarkers for early life. In Treatise on Geochemistry, Vol. 8:

Biogeochemistry, pp. 63–115.Buick R., Dunlop J. S. R. and Groves D. I. (1981) Stromatolite

recognition in ancient rocks: an appraisal of irregularlylaminated structures in an early Archean chert-barite unit fromNorth Pole, Western Australia. Alcheringa 5, 161–179.

Buick R., Rasmussen B. and Krapez B. (1998) Archean oil:evidence for extensive hydrocarbon generation and migration2.5–3.5 Ga. AAPG Bull. 82, 50–69.

Buick R. (2001) Life in the Archaean. In Palaeobiology II (eds. D.E. G. Briggs and P. R. Crowther). Blackwell Science, pp. 13–21.

Burruss R. C. (1987) Crushing-cell, capillary gas chromatographyof petroleum fluid inclusions: method and application topetroleum source rocks, reservoirs, and low temperaturehydrothermal ores (abstract). In Fluid Inclusion Research, vol.20 (eds. E. Roedder and A. Kozlowski ), p. 59.

Card K. D. (1978) Metamorphism of the middle Precambrian(Aphebian) rocks of the eastern Southern Province. In Meta-

morphism in the Canadian Shield, vol. 78-10 (eds. J. A. Fraserand W. W. Heywood). Geological Survey of Canada Paper, pp.269–282.

Castenholz R. W. (2001) Phylum BX. Cyanobacteria, oxygenicphotosynthetic bacteria. In Bergey’s Manual of Systematic

Bacteriology, vol. 1, 2nd Ed (eds. D. R. Boon and R. W.Castenholz). Springer, pp. 473–597.

Cumbers K. M., Alexander R. and Kagi R. I. (1987) Methylbi-phenyl, ethylbiphenyl and dimethylbiphenyl isomer distribu-tions in some sediments and crude oils. Geochim. Cosmochim.

Acta 51, 3105–3111.

Domine F., Dessort D. and Brevart O. (1998) Towards a newmethod of geochemical kinetic modeling: implications for thestability of crude oils. Org. Geochem. 28, 597–612.

Dutkiewicz A., Rasmussen B. and Buick R. (1998) Oil preserved influid inclusions in Archaean sandstones. Nature 395, 885–888.

Dutkiewicz A., Ridley J. and Buick R. (2003a) Oil-bearing CO2–CH4–H2O fluid inclusions: oil survival since the Palaeoprote-rozoic after high temperature entrapment. Chem. Geol. 194, 51–

79.

Dutkiewicz A., Volk H., Ridley J. and George S. (2003b)Biomarkers, brines, and oil in the Mesoproterozoic, RoperSuperbasin, Australia. Geology 31, 981–984.

Dutkiewicz A., Volk H., Ridley J. and George S. C. (2004)Geochemistry of oil in fluid inclusions in a Middle Proterozoicigneous intrusion: Implications for the source of hydrocarbonsin crystalline rocks. Org. Geochem. 35, 937–957.

Dutkiewicz A., Volk H., George S. C., Ridley J. and Buick R.(2006a) Biomarkers from Huronian oil-bearing fluid inclusions:an uncontaminated record of life before the Great OxidationEvent. Geology 34, 437–440.

Dutkiewicz A., Volk H., George S. C., Ridley J., Mossman D. andBuick R. (2006b) Oil and its biomarkers trapped inside fluidinclusions ca. 2.45–2.0 Ga. Geochim. Cosmochim. Acta 70,

A153.

Dutkiewicz A., George S. C., Mossman D., Ridley J. and Volk H.(2007) Oil and its biomarkers associated with the Palaeopro-terozoic Oklo natural fission reactors, Gabon. Chem. Geol. 244,

130–154.

Easton R. M. (2000) Metamorphism of the Canadian Shield,Ontario, Canada: II. Proterozoic metamorphic history. Can.

Mineral. 38, 319–344.

Eglinton G. and Hamilton R. J. (1967) Leaf epicuticular waxes.Science 156, 1322–1335.

Eigenbrode J. (in press) Fossil Lipids for Life-Detection: A casestudy from the early earth record. Space Sci. Rev., doi:10.1007/s11214-007-9252-9.

Espitalie J., Madec M. and Tissot B. (1980) Role of mineral matrixin kerogen pyrolysis: influence on petroleum generation andmigration. AAPG Bull. 64, 59–66.

Evans C. R., Rogers M. A. and Bailey N. J. L. (1971) Evolutionand alteration of petroleum in western Canada. Chem. Geol. 8,

147–170.

Fralick P. W. and Miall A. D. (1989) Sedimentology and the LowerHuronian Supergroup (Early Proterozoic), Elliot Lake area,Ontario, Canada. Sed. Geol. 63, 127–153.

Furnes H., Banerjee N. R., Muehlenbachs K., Staudigel H. and deWit M. (2004) Early life recorded in Archean pillow lavas.Science 304, 578–581.

George S. C. and Jardine D. R. (1994) Ketones in a Proterozoicdolerite sill. Org. Geochem. 21, 829–839.

George S. C., Lisk M., Eadington P. J., Quezada R. A., Krieger F.W., Greenwood P. F. and Wilson M. A. (1996) Comparison ofpalaeo oil charges with currently reservoired hydrocarbonsusing the geochemistry of oil-bearing fluid inclusions. Society of

Petroleum Engineers, Asia Pacific Oil and Gas Conference, SPE

paper 36980, pp. 159–171.George S. C., Krieger F. W., Eadington P. J., Quezada R. A.,

Greenwood P. F., Eisenberg L. I., Hamilton P. J. and WilsonM. A. (1997) Geochemical comparison of oil-bearing fluidinclusions and produced oil from the Toro Sandstone, PapuaNew Guinea. Org. Geochem. 26, 155–173.

George S. C., Lisk M., Eadington P. J. and Quezada R. A. (1998)Geochemistry of a palaeo-oil column: Octavius 2, Vulcan Sub-basin. In Proceedings of Petroleum Exploration Society of

Australia Symposium, The Sedimentary Basins of Western

Australia 2 (eds. P. G. Purcell and R. R. Purcell), pp. 195–210.

http://dx.doi.org/10.1007/s11214-007-9252-9

http://dx.doi.org/10.1007/s11214-007-9252-9


George S. C., Volk H., Ruble T., Lisk M., Manzur A., Liu K.,Quezada R., Dutkiewicz A., Brincat M., Middleton H., SmartS. and Horsfield B. (2001) Extracting oil from fluid inclusionsfor geochemical analyses: size matters! Abstracts of the 20th

International Meeting on Organic Geochemistry, P/TUE1/37,pp. 467–468.

George S. C. and Ahmed M. (2002) Use of aromatic compounddistributions to evaluate organic maturity of the Proterozoicmiddle Velkerri Formation, McArthur Basin, Australia. West

Australian Basins Symposium, pp. 252–270.George S. C., Ahmed M., Liu K. Y. and Volk H. (2004a) The

analysis of oil trapped during secondary migration. Org.

Geochem. 35, 1489–1511.

George S. C., Lisk M. and Eadington P. J. (2004b) Fluid inclusionevidence for an early, marine-sourced oil charge prior to gas-condensate migration, Bayu-1, Timor Sea, Australia. Mar. Pet.

Geol. 21, 1107–1128.

George S. C., Ruble T. E., Volk H., Lisk M., Brincat M. P.,Dutkiewicz A. and Ahmed M. (2004c) Comparing the geo-chemical composition of fluid inclusion and crude oils fromwells on the Laminaria High, Timor Sea. In Timor Sea

Petroleum Geoscience, Proceedings Of The Timor Sea Sympo-

sium (eds. G. K. Ellis, P. W. Baillie and T. J. Munson).Northern Territory Geological Survey, pp. 203–230.

George S. C., Volk H., Dutkiewicz A., Ridley J. and Mossman D.(2006) Oil-bearing fluid inclusions: Biogeochemical time-cap-sules for >2.0 billion years. Geochim. Cosmochim. Acta 70,

A198.

George S. C., Volk H. and Ahmed M. (2007) Geochemical analysistechniques and geological applications of oil-bearing fluidinclusions, with some Australian case studies. J. Petrol. Sci.

Eng. 57, 119–138.

Giggenbach W. F. (1997) Relative importance of thermodynamicand kinetic processes in governing the chemical and isotopiccomposition of carbon gases in high-heatflow sedimentarybasins. Geochim. Cosmochim. Acta 61, 3763–3785.

Goldblatt C., Lenton T. M. and Watson A. J. (2006) Bistability ofatmospheric oxygen and the Great Oxidation. Nature 443, 683–

686.

Grantham P. J. and Wakefield L. L. (1988) Variations in thesterane carbon number distributions of marine source rockderived crude oils through geological time. Org. Geochem. 12,

61–73.

Greenwood P. F., George S. C. and Hall K. (1998) Applications oflaser micropyrolysis gas chromatography mass spectrometry.Org. Geochem. 29, 1075–1089.

Han T.-M. and Runnegar B. (1992) Megascopic eukaryotic algaefrom the 2.1-billion-year-old Negaunee Iron-Formation, Mich-igan. Science 257, 232–235.

Hayes J. and Waldbauer J. (2006) The carbon cycle and associatedredox processes through time. Philos. Trans. R. Soc. Lond., B

361, 931–950.

Hayes J. M., Kaplan I. R. and Wedeking K. W. (1983)Precambrian organic geochemistry, preservation of the record.In Earth’s Earliest Biosphere, Its Origin and Evolution (ed. J. W.Schopf). Princeton University Press, pp. 93–134.

Hedges S. B., Blair J. E., Venturi M. L. and Shoe J. L. (2004) Amolecular timescale of eukaryote evolution and the rise ofcomplex multicellular life. BMC Evol. Biol. 4:2. doi:10.1186/

1471-2148-4-2.

Hesp W. and Rigby D. (1973) The geochemical alteration ofhydrocarbons in the presence of water. Erdol und Kohle-Erdgas

26, 70–76.

Hilburn I. A., Kirschvink J. L., Tajika E., Tada R., Hamano Y.and Yamamoto S. (2005) A negative fold test on the LorrainFormation of the Huronian Supergroup: Uncertainty on the

paleolatitude of the Paleoproterozoic Gowganda glaciation andimplications for the great oxygenation event. Earth Planet. Sci.

Lett. 232, 315–332.

Hill R. J., Tang Y. C., Kaplan I. R. and Jenden P. D. (1996) Theinfluence of pressure on the thermal cracking of oil. Energy

Fuels 10, 873–882.

Hode T., Zebuhr Y. and Broman C. (2006) Towards biomarkeranalysis of hydrocarbons trapped in individual fluid inclusions:First extraction by ErYAG laser. Planet. Space Sci. 54, 1575–

1583.

Hoering T. C. (1967) Molecular fossils from the PrecambrianNonesuch Shale. Carnegie Inst. Wash., Yearbook 75, 806–813.

Hofmann H. J., Grey K., Hickman A. H. and Thorpe R. I. (1999)Origin of 3.45 Ga coniform stromatolites in WarrawoonaGroup, Western Australia. Geol. Soc. Am. Bull. 111, 1256–1262.

Holba A. G., Dzou L. I. P., Masterson W. E., Hughes W. B.,Huizinga B. J., Singletary M. S., Moldowan J. M., Mello M. R.and Tegelaar E. (1998) Application of 24-norcholestanes forconstraining source age of petroleum. Org. Geochem. 29, 1269–

1283.

Holba A. G., Tegelaar E., Ellis L., Singletary M. S. and Albrecht P.(2000) Tetracyclic polyprenoids: Indicators of freshwater(lacustrine) algal input. Geology 28, 251–254.

Holba A. G., Ellis L., Dzou L. I. P., Hallam A., Masterson W. E.,Francu J. and Fincannon A. L. (2001) Extended tricyclicterpanes as age discriminators between Triassic, Early Jurassicand Middle-Late Jurassic oils. Abstracts of the 20th Interna-

tional Meeting on Organic Geochemistry, P/TUE1/35, p. 464.Holba A. G., Dzou L. I., Wood G. D., Ellis L., Adam P., Schaeffer

P., Albrecht P., Greene T. and Hughes W. B. (2003a)Application of tetracyclic polyprenoids as indicators of inputfrom fresh-brackish water environments. Org. Geochem. 34,

441–469.

Holba A. G., Zumberge J., Huizinga B. J., Rosenstein H. and DzouL. I. P. (2003b) Extended tricyclic terpanes as indicators ofmarine upwelling. 21st International Meeting on Organic

Geochemistry, Book of Abstracts Part I, p. 131.Holland H. D. (2006) The oxygenation of the atmosphere and

oceans. Philos. Trans. R. Soc. B 361, 903–915.

Horsfield B., Schenk H. J., Mills N. and Welte D. H. (1992) Aninvestigation of the in-reservoir conversion of oil to gas:compositional and kinetic findings from closed-system pro-grammed-temperature pyrolysis. Org. Geochem. 19, 191–204.

Hughes W. B., Holba A. G. and Dzou L. I. P. (1995) The ratios ofdibenzothiophene to phenanthrene and pristane to phytane asindicators of depositional environment and lithology of petro-leum source rocks. Geochim. Cosmochim. Acta 59, 3581–3598.

Jahnke L. L. and Klein H. P. (1983) Oxygen requirements forformation and activity of the squalene epoxidase in Saccharo-

myces cerevisiae. J. Bacteriol. 155, 488–492.

Jones D. M. and Macleod G. (2000) Molecular analysis ofpetroleum in fluid inclusions: a practical methodology. Org.

Geochem. 31, 1163–1173.

Karlsen D. A., Nedkvitne T., Larter S. R. and Bjorlykke K. (1993)Hydrocarbon composition of authigenic inclusions—applica-tions to elucidation of petroleum reservoir filling history.Geochim. Cosmochim. Acta 57, 3641–3659.

Karlsen D. A., Skeie J. E., Backer-Owe K., Bjorlykke K., OlstadR., Berge K., Cecchi M., Vik E. and Schaefer R. G. (2004)Petroleum migration, faults and overpressure. Part II. Casehistory: the Haltenbanken Petroleum Province, offshore Nor-way. In Understanding Petroleum Reservoirs: Towards an

Integrated Reservoir Engineering and Geochemical Approach

(eds. J. M. Cubitt, W. A. England and S. R. Larter). GeologicalSociety Publishing House, Geological Society Special Publica-tion 237, pp. 305–372.

http://dx.doi.org/10.1186/1471-2148-4-2

http://dx.doi.org/10.1186/1471-2148-4-2


Karlsen D. A. and Skeie J. E. (2006) Petroleum migration, faultsand overpressure, part I: calibrating basin modelling usingpetroleum in traps—a review. J. Petrol. Geol. 29, 227–255.

Kelly W. C. and Nishioka G. K. (1985) Precambrian oil inclusionsin late veins and the role of hydrocarbons in copper mineral-ization at White Pine, Michigan. Geology 13, 334–337.

Kenig F., Damste J. S. S., Kock-van Dalen A. C., Rijpstra W. I. C.,Huc A. Y. and de Leeuw J. W. (1995) Occurrence and origin ofmono-, di- and trimethylalkanes in modern and Holocenecyanobacterial mats from Abu Dhabi, United Arab Emirates.Geochim. Cosmochim. Acta 59, 2999–3015.

Kopp R. E., Kirschvink J. L., Hilburn I. A. and Nash C. Z. (2005)The Paleoproterozoic snowball Earth: a climate disaster trig-gered by the evolution of oxygenic photosynthesis. In Proceed-

ings of the National Academy of Sciences USA, vol. 102, pp.11131–11136.

Kvenvolden K. A. and Roedder E. (1971) Fluid inclusions inquartz crystals from South-West Africa. Geochim. Cosmochim.

Acta 35, 1209–1229.

Lepland A., van Zuilen M. A., Arrhenius G., Whitehouse M. J.and Fedo C. M. (2005) Questioning the evidence for Earth’searliest life–Akilia revisited. Geology 33, 77–79.

Lewan M. D. (1997) Experiments on the role of water in petroleumformation. Geochim. Cosmochim. Acta 61, 3691–3723.

Li C., Peng P., Sheng G. Y., Fu J. M. and Yan Y. Z. (2003) Amolecular and isotopic geochemical study of Meso- to Neo-proterozoic (1.73–0.85 Ga) sediments from the Jixian section,Yanshan Basin, North China. Precambrian Res. 125, 337–356.

Li H. J., Wu T. R., Ma Z. J. and Zhang W. C. (2004) Pressureretardation of organic maturation in clastic reservoirs: a casestudy from the Banqiao Sag, eastern China. Mar. Pet. Geol. 21,

1083–1093.

Losh S., Walter L., Meulbroek P., Martini A., Cathles L. andWhelan J. (2002) Reservoir fluids and their migration into theSouth Eugene Island Block 330 reservoirs, offshore Louisiana.AAPG Bull. 86, 1463–1488.

Love G. D., Grosjean E., Fike D. A., Grotzinger J. P., Bowring S.A., Lewis A. N., Stalvies C., Snape C. E. and Summons R. E.(2005) A >90 million year record of Neoproterozoic sponges(Porifera) in the South Oman Salt basin. Organic Geochemistry:

Challenges for the 21st Century, vol. 1. 22nd IMOG, Seville,Spain, pp. 123–124.

Mackenzie A. S. and McKenzie D. (1983) Isomerization andaromatization of hydrocarbons in sedimentary basins formedby extension. Geol. Mag. 120, 417–470.

Mango F. and Elrod L. W. (1998) The carbon isotopic compositionof catalytic gas: a comparative analysis with natural gas.Geochim. Cosmochim. Acta 63, 1097–1106.

Mango F. D. (1991) The stability of hydrocarbons under the time–temperature conditions of petroleum genesis. Nature 352,

146–148.

Mango F. D. (1997) The light hydrocarbons in petroleum—acritical review. Org. Geochem. 26, 417–440.

Mango F. D. and Hightower J. (1997) The catalytic decompositionof petroleum into natural gas. Geochim. Cosmochim. Acta 61,

5347–5350.

Mauk J. L. and Burruss R. C. (2002) Water washing of Proterozoicoil in the midcontinent rift system. AAPG Bull. 86, 1113–1127.

McCaffrey M. A., Moldowan J. M., Lipton P. A., Summons R. E.,Peters K. E., Jeganathan A. and Watt D. S. (1994) Paleoen-vironmental implications of novel C30 steranes in Precambrianto Cenozoic age petroleum and bitumen. Geochim. Cosmochim.

Acta 58, 529–532.

McKirdy D. M. and Imbus S. W. (1992) Precambrian petroleum: adecade of changing perceptions. In Early Organic Evolution:

Implications for Mineral and Energy Resources (eds. M.

Schidlowski, S. Golubic, M. M. Kimberley, D. M. McKirdyand P. A. Trudinger), pp. 177–192. Early Organic Evolution:

Implications for Mineral and Energy Resources. Springer.

McNeil R. I. and Bement W. O. (1996) Thermal stability ofhydrocarbons—laboratory criteria and field examples. Energy

Fuels 10, 60–67.

Moldowan J. M., Fago F. J., Lee C. Y., Jacobson S. R., Watt D.S., Slougui N. E., Jeganathan A. and Young D. C. (1990)Sedimentary 24-n-propylcholestanes, molecular fossils diagnos-tic for marine algae. Science 247, 309–312.

Moldowan J. M., Fago F. J., Carlson R. M. K., Young D. C., VanDuyne G., Clardy J., Schoell M., Pillinger C. T. and Watt D. S.(1991a) Rearranged hopanes in sediments and petroleum.Geochim. Cosmochim. Acta 55, 3333–3353.

Moldowan J. M., Lee C. Y., Watt D. S., Jeganathan A., Slougui N.E. and Gallegos E. J. (1991b) Analysis and occurrence of C26-steranes in petroleum and source rocks. Geochim. Cosmochim.

Acta 55, 1065–1081.

Moldowan J. M., Lee C. Y., Sundararaman P., Salvatori T.,Alajbeg A., Gjukic B., Demaison G. J., Slougui N. E., Watt D.S., Moldowan J. M., Albrecht P. and Philp R. P. (1992) Sourcecorrelation and maturity assessment of selected oils and rocksfrom the central Adriatic Basin (Italy and Yugoslavia). InBiological Markers in Sediments and Petroleum (eds. J. M.Moldowan, P. Albrecht and R. P. Philp). Prentice Hall, pp.

370–401.

Mossman D. J. (1987) Stratiform gold occurrences of the Witwa-tersrand type in the Huronian Supergroup, Ontario, Canada.Trans. Geol. Soc. South Africa 90, 168–178.

Mossman D. J., Nagy B. and Davis D. W. (1993) Hydrothermalalteration of organic matter in uranium ores, Elliot Lake,Canada: implications for selected organic-rich deposits. Geo-

chim. Cosmochim. Acta 57, 3251–3259.

Munz I. A. (2001) Petroleum inclusions in sedimentary basins:systematics, analytical methods and applications. Lithos 55,

195–212.

Nedkvitne T., Karlsen D. A., Bjorlykke K. and Larter S. R. (1993)Relationship between reservoir diagenetic evolution and petro-leum emplacement in the Ula Field, North Sea. Mar. Pet. Geol.

10, 255–270.

Newell K. D., Burruss R. C. and Palacas J. G. (1993) Thermalmaturation and organic richness of potential petroleum sourcerocks in Proterozoic Rice Formation, North American Mid-Continent Rift System, Northeastern Kansas. AAPG Bull. 77,

1922–1941.

Ohmoto H., Watanabe Y., Ikemi H., Poulson S. R. and Taylor B.E. (2006) Sulphur isotope evidence for an oxic Archaeanatmosphere. Nature 442, 908–911.

Ourisson G., Albrecht P. and Rohmer M. (1982) Predictivemicrobial biochemistry, a forensic approach to procaryoticmembrane constituents. Trends Biochem. Sci. 7, 236–239.

Papineau D., Mojzsis S. J. and Schmitt A. K. (2007) Multiplesulfur isotopes from Paleoproterozoic Huronian interglacialsediments and the rise of atmospheric oxygen. Earth Planet. Sci.

Lett. 255, 188–212.

Pepper A. S. and Dodd T. A. (1995) Simple kinetic models ofpetroleum formation, Part II. Oil–gas cracking. Mar. Pet. Geol.

12, 321–340.

Peters K. E., Moldowan J. M. and Sundararaman P. (1990) Effectsof hydrous pyrolysis on biomarker thermal maturity parame-ters: Monterey Phosphatic and Siliceous members. Org. Geo-

chem. 15, 249–265.

Peters K. E., Clark M. E., Dasgupta U., McCaffrey M. A. and LeeC. Y. (1995) Recognition of an Infracambrian source rockbased on biomarkers in the Bahewala-1 oil, India. AAPG Bull.

79, 1481–1494.


Peters K. E., Walters C. C. and Moldowan J. M. (2005) The

Biomarker Guide. Cambridge University Press.Planche H. (1996) Finite time thermodynamics and the quasi-

stability of closed-systems of natural hydrocarbon mixtures.Geochim. Cosmochim. Acta 60, 4447–4465.

Preston J. C. and Edwards D. S. (2000) The petroleum geochem-istry of oils and source rocks from the northern BonaparteBasin, offshore northern Australia. Aust. Petrol. Prod. Explor.

Assoc. J. 40(1), 257–282.

Price L. C. and Wenger L. M. (1992) The influence of pressure onpetroleum generation and maturation as suggested by aqueouspyrolysis. Org. Geochem. 19, 141–159.

Price L. C. (1993) Thermal stability of hydrocarbons in nature:limits, evidence, characteristics, and possible controls. Geochim.


Price L. C., Pawlewicz M. J. and Daws T. A. (1999) Organicmetamorphism in the California petroleum basins; Chapter A,Rock-Eval and vitrinite reflectance. U.S. Geological Survey

Bulletin, 2174–A, 38.Price L. C. and DeWitt E. (2001) Evidence and characteristics of

hydrolytic disproportionation of organic matter during meta-somatic processes. Geochim. Cosmochim. Acta 65, 3791–3826.

Quinlan G. M. and Beaumont C. (1984) Appalachian thrusting,lithospheric flexure and the Paleozoic stratigraphy of the EasternInterior of North America. Can. J. Earth Sci. 21, 973–986.

Radke M., Welte D. H. and Willsch H. (1982a) Geochemical studyon a well in the Western Canada Basin: relation of the aromaticdistribution pattern to maturity of organic matter. Geochim.


Radke M., Willsch H., Leythaeuser D. and Teichmuller M. (1982b)Aromatic compounds of coal; relation of distribution pattern torank. Geochim. Cosmochim. Acta 46, 1831–1848.

Radke M., Leythaeuser D. and Teichmuller M. (1984) Relationshipbetween rank and composition of aromatic hydrocarbons forcoals of different origins. Org. Geochem. 6, 423–430.

Radke M. (1988) Application of aromatic compounds as maturityindicators in source rocks and crude oils. Mar. Pet. Geol. 5,

224–236.

Radke M., Rullkotter J. and Vriend S. P. (1994) Distribution ofnaphthalenes in crude oils from the Java Sea: source andmaturation effects. Geochim. Cosmochim. Acta 58, 3675–3689.

Rampen S. W., Schouten S., Abbas B., Panoto F. E., Muyzer G.,Campbell C. N., Fehling J. and Sinninghe Damste J. S. (2007)On the origin of 24-norcholestanes and their use as age-diagnostic biomarkers. Geology 35, 419–422.

Rasmussen B. (2000) Filamentous microfossils in a 3,235-million-year-old volcanogenic massive sulphide deposit. Nature 405,

676–679.

Rasmussen B. (2005) Evidence for pervasive petroleum generationand migration in 3.2 and 2.63 Ga shales. Geology 33, 497–500.

Raymond J. and Blankenship R. E. (2004) Biosynthetic pathways,gene replacement and the antiquity of life. Geobiology 2, 199–

203.

Ruble T. E., George S. C., Lisk M. and Quezada R. A. (1998)Organic compounds trapped in aqueous fluid inclusions. Org.

Geochem. 29, 195–205.

Sajgo C., Horvath Z. A. and Lefler J. (1988) An organicmaturation study of the Hod-I borehole (Pannonian Basin).In The Pannonian Basin: A Study in Basin Evolution, vol.Memoir 45 (eds. L. Royden and Z. A. Horvath). AmericanAssociation of Petroleum Geologists, Tulsa, and the HungarianGeological Society, Budapest, pp. 297–310.

Sajgo C. (2000) Assessment of generation temperatures of crudeoils. Org. Geochem. 31, 1301–1323.

Schenk H. J., Di Primio R. and Horsfield B. (1997) The conversion ofoil into gas in petroleum reservoirs. Part 1: comparative kinetic

investigation of gas generation from crude oils of lacustrine,marine and fluviodeltaic origin by programmed-temperatureclosed-system pyrolysis. Org. Geochem. 26, 467–481.

Schidlowski M. (2001) Carbon isotopes as biogeochemical record-ers of life over 3.8 Ga of Earth history: evolution of a concept.Precambrian Res. 106, 117–134.

Schiefelbein C. F., Zumberge J. E., Cameron N. R. and Brown S.W. (1999) Petroleum systems in the South Atlantic margins. InThe Oil and Gas Habitats of the South Atlantic (eds. N. R.Cameron, R. H. Bate and V. S. Clure). Geological Society ofLondon Special Publication 153, pp. 169–179.

Schmidt P. W. and Williams G. E. (1999) Paleomagnetism of thePaleoproterozoic hematitic breccia and paleosol at Ville-Marie,Quebec: further evidence for the low paleolatitude of Huronianglaciation. Earth Planet. Sci. Lett. 172, 273–285.

Schopf J. W., Kudrayavtsev A. B., Agresti D. G., Wdowiak T. J.and Czaja A. D. (2002) Laser-Raman imagery of Earth’searliest fossils. Nature 416, 73–76.

Schwab V., Spangenberg J. E. and Grimalt J. O. (2005) Chemicaland carbon isotopic evolution of hydrocarbons during progrademetamorphism from 100 �C to 550 �C: Case study in the Liassicblack shale formation of Central Swiss Alps. Geochim. Cosmo-

chim. Acta 69, 1825–1840.

Scotchman I. C., Griffith C. E., Holmes A. J. and Jones D. M.(1998) The Jurassic petroleum system north and west of Britain:a geochemical oil-source correlation study. Org. Geochem. 29,

671–700.

Shen Y., Buick R. and Canfield D. E. (2001) Isotopic evidence formicrobial sulphate reduction in the early Archaean era. Nature

410, 77–81.

Sherman L. S., Waldbauer J. R. and Summons R. E. (2007)Improved methods for isolating and validating indigenousbiomarkers in Precambrian rocks. Org. Geochem. 38, 1987–

2000.

Sieskind O., Joly G. and Albrecht P. (1979) Simulation of thegeochemical transformation of sterols: superacid effects of clayminerals. Geochim. Cosmochim. Acta 43, 1675–1679.

Simoneit B. R. T., Schoell M., Dias R. F. and Neto F. R. D. (1993)Unusual carbon isotope compositions of biomarker hydrocar-bons in a Permian tasmanite. Geochim. Cosmochim. Acta 57,

4205–4211.

Sinninghe Damste J. S., Kenig F., Koopmans M. P., Koster J.,Schouten S., Hates J. M. and de Leeuw J. W. (1995) Evidencefor gammacerane as an indicator of water column stratification.Geochim. Cosmochim. Acta, 59.

Sofer Z., Regan D. R. and Muller D. S. (1993) Sterane isomer-ization ratios of oils as maturity indicators and their use as anexploration tool, Neuquen basin, Argentina. XII Congreso de

Geologico Argentino y II Congreso de Exploracion de Hidrocar-

buros Actas, vol. 1, pp. 407–411.Summons R., Bradley A., Jahnke L. and Waldbauer J. (2006)

Steroids, triterpenoids and molecular oxygen. Philos. Trans. R.

Soc. Lond., B 361, 951–968.

Summons R. E. and Powell T. G. (1986) Chlorobiaceae inPalaeozoic seas revealed by biological markers, isotopes andgeology. Nature 319, 763–765.

Summons R. E., Brassell S. C., Eglinton G., Evans E., HorodyskiR. J., Robinson N. and Ward D. M. (1988a) Distinctivehydrocarbon biomarkers from fossiliferous sediments of theLate Proterozoic Walcott Member, Chuar Group, GrandCanyon, Arizona. Geochim. Cosmochim. Acta 52, 2625–2637.

Summons R. E., Powell T. G. and Boreham C. J. (1988b)Petroleum geology and geochemistry of the Middle ProterozoicMcArthur Basin, Northern Australia: III. Composition ofextractable hydrocarbons. Geochim. Cosmochim. Acta 52, 1747–

1763.


Summons R. E. and Walter M. R. (1990) Molecular fossils andmicrofossils of prokaryotes and protists from Proterozoicsediments. Am. J. Sci. 290-A, 212–244.

Summons R. E. and Jahnke L. L. (1992) Hopenes and hopanesmethylated in ring A: correlation of the hopanoids from extantmethylotrophic bacteria with their fossil analogues. In Biolog-

ical Markers in Sediments and Petroleum (eds. J. M. Moldowan,P. Albrecht and R. P. Philp). Prentice Hall, pp. 182–200.

Summons R. E., Jahnke L. L., Hope J. M. and Logan G. A. (1999)2-Methylhopanoids as biomarkers for cyanobacterial oxygenicphotosynthesis. Nature 400, 554–557.

Tannenbaum E., Ruth E. and Kaplan I. R. (1986) Steranes andtriterpanes generated from kerogen pyrolysis in the absence andpresence of minerals. Geochim. Cosmochim. Acta 50, 805–812.

Thompson K. F. M. (1983) Classification and thermal history ofpetroleum based on light hydrocarbons. Geochim. Cosmochim.

Acta 47, 303–316.

Thompson K. F. M. (1987) Fractionated aromatic petroleums andthe generation of gas-condensates. Org. Geochem. 11, 573–590.

Ungerer P. F., Behar M., Villalba M., Audibert A. and Heum O.R. (1987) Kinetic modeling of oil cracking. Org. Geochem. 13,

857–868.

van Aarssen B. G. K., Bastow T. P., Alexander R. and Kagi R. I.(1999) Distributions of methylated naphthalenes in crude oils:indicators of maturity, biodegradation and mixing. Org. Geo-

chem. 30, 1213–1227.

Vandenbroucke M., Behar F. and Rudkiewicz J. L. (1999) Kineticmodelling of petroleum formation and cracking: implicationsfrom the high pressure/high temperature Elgin Field (UK,North Sea). Org. Geochem. 30, 1105–1125.

Ventura G. T., Kenig F., Reddy C. M., Schieber J., Frysinger G.S., Nelson R. K., Dinel E., Gaines R. B. and Schaeffer P. (2007)Molecular evidence of Late Archean archaea and the presenceof a subsurface hydrothermal biosphere. In Proceedings of the

National Academy of Sciences of the United States of America,vol. 104, pp. 14260–14265.

Volk H., Horsfield B., Mann U. and Suchy V. (2002) Variability ofpetroleum inclusions in vein, fossil and vug cements: geochem-

ical study in the Barrandian Basin (Lower Palaeozoic, CzechRepublic). Org. Geochem. 33, 1319–1341.

Volk H., Dutkiewicz A., George S. and Ridley J. (2003) Oilmigration in the Middle Proterozoic Roper Superbasin, Aus-tralia: evidence from oil inclusions and their geochemistries. J.

Geochem. Expl. 78–79, 437–441.

Volk H., George S. C., Dutkiewicz A. and Ridley J. (2005)Characterisation of fluid inclusion oil in a Mid-Proterozoicsandstone and dolerite (Roper Superbasin, Australia). Chem.

Geol. 223, 109–135.

Volkman J. K., Alexander R., Kagi R. I. and Woodhouse G. W.(1983) Demethylated hopanes in crude oils and their applica-tions in petroleum geochemistry. Geochim. Cosmochim. Acta 47,

785–794.

Volkman J. K. (2005) Sterols and other triterpenoids: sourcespecificity and evolution of biosynthetic pathways. Org. Geo-

chem. 36, 139–159.

Walter M. R., Buick R. and Dunlop J. S. R. (1980) Stromatolites3400–3500 Myr old from the North Pole area, WesternAustralia. Nature 284, 443–445.

Wang Y., Zhang S., Wang F., Wang Z., Zhao C., Wang H., Liu J.,Lu J., Geng A. and Liu D. (2006) Thermal cracking history bylaboratory kinetic simulation of Paleozoic oil in eastern TarimBasin, NW China, implications for the occurrence of residualoil reservoirs. Org. Geochem. 37, 1803–1815.

Williams G. E. and Schmidt P. W. (1997) Paleomagnetism of thePaleoproterozoic Gowganda and Lorrain formations, Ontario:low paleolatitude for Huronian glaciation. Earth Planet. Sci.

Lett. 153, 157–169.

Young G. M., Long D. G. F., Fedo C. M. and Nesbitt H. W.(2001) Paleoproterozoic Huronian basin: product of a Wilsoncycle punctuated by glaciations and meteorite impact. Sed.

Geol. 141–142, 233–254.

Zou Y. R. and Peng P. (2001) Overpressure retardation of organic-matter maturation: a kinetic model and its application. Mar.

Pet. Geol. 18, 707–713.

Associate editor: Robert C. Burruss

preservation of hydrocarbons and bio markers in oil trapped

Documents

20th international

great oxidation

mount bruce

ab ba

elliot lake

c30 ab hopane

bearing uid

c24 tetracyclic