Biomarkers from Huronian oil-bearing fluid inclusions: An
uncontaminated record of life before the Great Oxidation Event
Adriana Dutkiewicz School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia
Herbert Volk
⎤ Commonwealth Scientific and Industrial Organisation (CSIRO) Petroleum, P.O. Box 136, North Ryde,
⎥
Simon C. George ⎦ NSW 1670, Australia
John Ridley Department of Geosciences, Colorado State University, Fort Collins, Colorado 80523-1482, USA
Roger Buick Department of Earth and Space Sciences & Astrobiology Program, University of Washington, Seattle,
Washington 98195-1310, USA
ABSTRACT
We report detailed molecular geochemistry of oil-bearing fluid inclusions from a ca.
2.45 Ga fluvial metaconglomerate of the Matinenda Formation at Elliot Lake, Canada.
The oil, most likely derived from the conformably overlying McKim Formation, was
trapped in quartz and feldspar during diagenesis and early metamorphism of the host
rock, probably before ca. 2.2 Ga. The presence of abundant biomarkers for cyanobacteria
and eukaryotes derived from and trapped in rocks deposited before the Great Oxidation
Event is consistent with an earlier evolution of oxygenic photosynthesis than previously
thought and suggests that some aquatic settings had become sufficiently oxygenated for
sterol biosynthesis by this time. It also implies that eukaryotes survived several extreme
climatic events, including the Paleoproterozoic ‘‘snowball Earth’’ glaciations. The extraction of biomarker molecules from Paleoproterozoic oil-bearing fluid inclusions thus establishes a new method, using low detection limits and system blank levels, to trace evolution
of life through Earth’s early history that avoids the potential contamination problems
affecting shale-hosted hydrocarbons.
Keywords: oil inclusions, hydrocarbon biomarkers, Paleoproterozoic, Huronian glaciations,
Great Oxidation Event, snowball Earth.
INTRODUCTION
Biomarkers, distinctive hydrocarbons derived from biological molecules preserved in
rocks, allow the evolution of organisms and
their metabolisms to be traced through Earth’s
history (Peters et al., 2005). However, the record of biomolecular evolution very early in
time is markedly incomplete because, to date,
biomarkers have been found only in relatively
unmetamorphosed organic-rich shales (e.g.,
Brocks et al., 1999, 2005). Because hydrocarbon destruction occurs with increasing metamorphism (Hunt, 1996), the number of old
rocks suitable for study is limited, and great
age heightens the possibility of later contamination. Thus, careful assessment is required
to demonstrate that such biomarkers are syngenetic and not later geological contaminants,
a criticism recently leveled at reports of Archean shale-hosted hydrocarbon biomarkers
(Kopp et al., 2005). The new technique of ultrasensitive biomarker extraction from oilbearing fluid inclusions avoids these difficulties because such inclusions are rapidly sealed
systems (Dutkiewicz et al., 2003a), can be relatively dated using petrography, and occur in
many sedimentary rocks. These tiny vessels
are not only shielded from contamination, but
also from much of the alteration that usually
affects hydrocarbons over time (Dutkiewicz et
al., 2003a; Volk et al., 2005). Here, we describe molecular geochemistry of oil inclu-
sions in a ca. 2.45 Ga uraniferous conglomerate, showing that indigenous biomarkers
undoubtedly exist in rocks deposited before
the great environmental perturbations of the
early Paleoproterozoic.
Geological Setting
We focused our study on the fluvial-deltaic
to marine Paleoproterozoic Huronian Supergroup, Canada (Fig. 1). Its oldest rocks record
the loss of mass-independent sulfur isotope
fractionation (MIF) from the geological record
(Tachibana et al., 2004), it spans the Great Oxidation Event, and it includes evidence for
three major glaciations (Young et al., 2001).
The first oxidized red beds occur above the
glaciogenic Gowganda Formation, the third
glacial unit in the succession (Young et al.,
2001). We sampled the ca. 2.45 Ga Matinenda
Formation, which unconformably overlies Archean basement and locally covers mafic volcanics and coarse clastic sediments (Young et
al., 2001) (Fig. 1). It conformably underlies
the deltaic McKim Formation (Young et al.,
2001), which is the most likely external source
for the Matinenda hydrocarbons (McKirdy
and Imbus, 1992), and the Ramsay Lake Formation, which was deposited during the first
major Paleoproterozoic glaciation (Fig. 1).
The Penokean orogeny, which occurred at
1.89 Ga to 1.8 Ga, only weakly deformed the
Huronian Supergroup in the Elliot Lake area
(Young et al., 2001). The maximum metamorphic grade in the region never exceeded
lower greenschist facies (⬃350 ⬚C) and occurred either during the orogeny (Card, 1978)
or, more likely, with intrusion of the Nipissing
Diabase Suite ca. 2.2 Ga (Mossman et al.,
1993). The area lies north of the Michigan Basin, and models of basin evolution show a
Phanerozoic sedimentary cover of only ⬃200
m (Quinlan and Beaumont, 1984). Our biomarker data from the Matinenda Formation
oil-bearing fluid inclusions thus constrain evolution before the Great Oxidation Event ca.
2.2 Ga (Holland and Beukes, 1990) and the
first snowball Earth glaciation (Hoffmann and
Schrag, 2002).
Materials and Methods
The sample is a coarse-grained, wellcemented uraniferous feldspathic quartzpebble conglomerate obtained from an out-
Figure 1. Stratigraphy of Huronian Supergroup and constraints on deposition between 2.45 and 2.21 Ga. Modified after
Young et al. (2001).
䉷 2006 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected].
Geology; June 2006; v. 34; no. 6; p. 437–440; doi: 10.1130/G22360.1; 3 figures; Data Repository item 2006086.
437
crop in the western part of the Elliot Lake
township. Several core samples were found to
contain insufficient oil inclusions for detailed
analysis (Dutkiewicz et al., 2003b). The outcrop sample was fragmented into 2 mm pieces
and thoroughly cleaned with hydrogen peroxide, hot chromic acid, Aqua Regia, and a
range of solvents of different polarity (Volk et
al., 2005). Fragments were checked repeatedly
for cleanliness by gas chromatography–mass
spectrometry analyses of outside rinse blanks.
Online and offline crushing (Volk et al., 2005)
was used to release the fluid inclusion oil from
the rock fragments. Both experiments were
replicated, yielding similar results. A system
blank using exactly the same offline experimental conditions as the actual crushings was
obtained one day earlier. For details of analytical settings and microthermometry, see
GSA Data Repository material.1
RESULTS
Oil-Bearing Fluid Inclusions
The sample of the Matinenda Formation
contains abundant oil-bearing fluid inclusions
identified by their bright fluorescence under
ultraviolet excitation (Dutkiewicz et al.,
2003b). Most oil is hosted within two fluidinclusion assemblages. The first is composed
of irregular inclusions, 6–10 ␮m long, containing 80–85 vol% H2O, 12–16 vol% water
vapor, and 2–5 vol% oil, usually as a thin film
around the gas bubble (Fig. 2). These inclusions are located mainly in intragranular microfractures in quartz and K-feldspar or rarely
within syntaxial quartz overgrowths (Fig. 2),
indicating entrapment early in the burial history (Dutkiewicz et al., 2003b). Homogenization temperatures of the various phases
show that these inclusions were entrapped between 80 ⬚C and 220 ⬚C at pressures of
⬃50,000–200,000 kPa during diagenesis, and
were subsequently heated to ⬃300–350 ⬚C
during metamorphism (Dutkiewicz et al.,
2003b). The second assemblage has inclusions
up to 25 ␮m long; some display spherical and
negative crystal shapes consistent with hightemperature entrapment. They are generally
dominated by a carbonic phase, with 30–90
vol% CO2, 0–70 vol% H2O, and 2–3 vol%
oil, which usually shows up as a fluorescing
rim to the CO2. Raman spectroscopy and microthermometry indicate the presence of up to
50 mol% CH4, 2–8 mol% C2H6, and 1–5
mol% C3H8 in the gaseous phase (Dutkiewicz
et al., 2003b). Carbonic-phase and totalhomogenization temperatures indicate entrapment between 260 and 380 ⬚C at pressures of
100,000–150,000 kPa which is within the
1GSA Data Repository item 2006086, table of
molecular parameters and methods, is available online at www.geosociety.org/pubs/ft2006.htm, or on
request from [email protected] or Documents
Secretary, GSA, P.O. Box 9140, Boulder, CO
80301, USA.
438
Figure 2. Photomicrographs of fluorescing (under ultraviolet [UV] excitation) oil-bearing
fluid inclusions, using UV-epifluorescence (A, C), transmitted light (B), and transmitted light,
crossed nicols (D). A–B: Abundant yellow-, orange-, and blue-fluorescing oil-bearing fluid
inclusions in a detrital quartz grain surrounded by oil inclusion–free quartz overgrowth (qo)
(modified after Dutkiewicz et al., 2003b). C–D: H2O-dominated fluid inclusions comprising a
nonfluorescing bubble of water vapor surrounded by a blue-fluorescing rim of oil and nonfluorescing H2O liquid.
range of peak metamorphism at Elliot Lake
(Dutkiewicz et al., 2003b). The age of entrapment of the oil-bearing fluid inclusions is thus
constrained by deposition and metamorphism
of the Matinenda Formation to between ca.
2.45 and 2.2 Ga.
Molecular Composition of the Inclusion
Oil
Molecular parameters for the Matinenda
fluid-inclusion oil, including biomarker ratios,
are described in detail in the GSA Data Repository (see footnote one). C5-C8 hydrocarbons are dominated by benzene and alkylbenzenes. Furan is also abundant and is inferred
to have been derived from aqueous inclusions
(Ruble et al., 1998). C8⫹ hydrocarbons occur
in very low abundance compared to lower molecular weight hydrocarbons. C12-C36 compound distributions were obtained using offline crushing (Volk et al., 2005). The
distribution of n-alkanes has a maximum at nC18 and a secondary mode at ⬃n-C27 (Fig.
3A). Some n-alkanes are also present in the
blanks and the outside rinse, but have a different distribution, are in much lower abundance, and contain fewer peaks eluting between n-alkanes. A hump of unresolved
complex mixture and the presence of C29 25norhopane (Figs. 3A and 3C) indicate that at
least part of the inclusion oil was biodegraded
prior to entrapment.
The inclusion oil contains isoprenoids, hopanes, tri- and tetracyclic terpanes, and sterane
biomarkers at levels well above outside rinse
and system blank levels (Fig. 3C–E). Hopanes
are dominated by C29 17␣(H),21␤(H)-30norhopane, with 29,30-bisnorhopane and C30
30-nor 17␣(H)-hopane also relatively abundant (Fig. 3c, see also footnote one). Monomethylalkanes (Fig. 3B) and 2␣-methylhopanes
(Fig. 3D) are relatively abundant compared to
Phanerozoic oils (Summons and Jahnke,
1990). Tricyclic terpanes maximize at C23 and
also include a series of extended tricyclic terpanes to at least C31, which is typical of generation from algal and/or bacterial organic
matter. Low relative abundances of diasteranes
and rearranged hopanes are consistent with a
source rock lean in clay. Sterane biomarkers
are diverse, though less abundant than hopanes (see footnote one). The steranes indigenous to the oil inclusions are dominated by
the C21 molecule pregnane and lesser amounts
of C22 homopregnane (Fig. 3E), which is consistent with high maturity, a large contribution
from bacterial or algal organic matter, or both.
There are significant contributions from C27
20S⫹R ␣␣␣ and co-eluting C27 20S ␤␤ and
C29 20S ␤␣ steranes in both the system blank
and the final outside rinse, so these particular
molecules should be regarded as potential
contaminants. Other steranes, including the
four C28 and C29 isomers and the C27 and C28
GEOLOGY, June 2006
rich deltaic McKim Formation (McKirdy
and Imbus, 1992) or from kerogen within
the Matinenda Formation (Mossman et al.,
1993). This is supported by the presence of npropylcholestanes, which indicate a contribution from marine source rocks (Moldowan et
al., 1990). Land plant biomarkers such as
oleanane are absent, supporting syngeneity of
the inclusion oil with its early Precambrian
host rock.
Biomarker Survival
Thermal maturity–dependent molecular ratios based on alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, and biomarkers are consistent with a middle to peak
thermal maturity window for oil (see footnote
one), typical of most oils (Hunt, 1996). However, the inclusions have been heated to temperatures up to 350 ⬚C, well beyond the thermal limit previously accepted for survival of
complex hydrocarbons (Hunt, 1996). Factors
that may facilitate the preservation of biomarker molecules inside fluid inclusions are
increased fluid pressure (Lewan, 1997), a
closed system (Giggenbach, 1997), and the
absence of organometallic complexes and clay
minerals that provide catalytic sites for the
secondary cracking of petroleum (Mango,
1990).
Figure 3. Offline mass chromatograms of fluid-inclusion oil (FI), system blank, and final
outside rinse to the same scale. Squalane was added as an internal standard. A: Partial m/
z 85 mass chromatograms showing distribution of n-alkanes (n-C8 to n-C32) and isoprenoids
(Pr—pristane, Ph—phytane). B: Detailed monomethylalkane distribution from n-C17 to n-C20
(MHeD—methylheptadecanes, MOD—methyloctadecanes, MND—methylnonadecanes). C:
Partial m/z 191 mass chromatograms showing tricyclic and tetracyclic terpanes and pentacyclic triterpanes (hopanes). Peak assignments define stereochemistry at C22 (S and R);
␣␤ and ␤␣ denote 17␣(H)-hopanes and 17␤(H)-moretanes, respectively. 19/3–30/3—C19–C30
tricyclic terpanes, 24/4—C24 tetracyclic terpane, Ts—C27 18␣(H),22,29,30-trisnorneohopane,
Tm—C27 17␣(H),22,29,30-trisnorhopane, C29Ts—18␣-(H)-30-norneohopane, 25-nor—C29 25norhopane, C30 30-nor—C30 30-norhopane (BNH-bisnorhopane). D: Partial m/z 205 mass
chromatograms showing methylhopanes. 2␣(Me) refers to 2␣-methylhopanes (␣␤). E: Partial m/z 217 chromatograms showing C21-C29 steranes and diasteranes, and C30 tetracyclic
polyprenoids Ta and Tb (C30 tetracyclic polyprenoids 18␣[H], 21R and 21S, respectively).
Peak assignments define stereochemistry at C-20 (S and R); ␤␣, ␣␣␣, and ␣␤␤ denote
13␤(H),17␣(H)-diasteranes, 5␣(H),14␣(H),17␣(H)-steranes, and 5␣(H),14␤(H),17␤(H)steranes, respectively. For further details on geochemical parameters, including biomarker
ratios, see text footnote one.
diasteranes are unambiguously indigenous to
the oil inclusions (Fig. 3E). C27 diasteranes
are more abundant than C28 and C29
diasteranes.
GEOLOGY, June 2006
DISCUSSION
Source of the Inclusion Oil
The inclusion oil is probably derived either
from the immediately overlying organic-
Biogenic Oxygen Production
The Matinenda sample contains 2␣methylhopane biomarkers in quantities indicating derivation from cyanobacteria (Fig.
3D), which is in common with many, but not
all (e.g., Brocks et al., 2005), organic-rich Precambrian sedimentary rocks (Summons and
Jahnke, 1990; Summons et al., 1999). It also
contains C32 2␣-methylhopanes (Fig. 3D),
which are only known from cyanobacteria
(Brocks et al., 2003a; Summons et al., 1999).
Though not all extant cyanobacteria synthesize 2␣-methylhopanoids, the capability is distributed widely through the phylum including
Gloeobacter violaceus (Summons et al.,
1999), the basal organism on cyanobacterial
phylogenetic trees (Castenholz, 2001). As
modern cyanobacteria are all capable of oxygenic photosynthesis, including even the most
primitive thylakoid-lacking form Gloeobacter
violaceus (Castenholz, 2001), it is reasonable
to infer oxygenic photosynthesis from exclusively cyanobacterial C32 2␣-methylhopanes.
Thus, the plentiful cyanobacterial biomarkers
in the inclusion oil indicate that biogenic oxygen was being abundantly generated during
deposition of the source rocks. As the Great
Oxidation Event was recently argued to have
occurred after the Gowganda glaciation (Hilburn et al., 2005), higher in the Huronian stratigraphy (Fig. 1) than the apparent source
rocks for the Matinenda oil, this implies that
biogenic oxygen production began earlier,
at least as early as the loss of the massindependent sulfur isotope fractionation signal
439
from the geological record (Tachibana et al.,
2004).
Implications for the Domain Eukarya
Diverse and abundant steranes in a fluidinclusion oil of Paleoproterozoic age constrain
the evolution of eukaryotes. Steranes are derived from sterols, for which the only confirmed biosynthetic pathway, despite recent
speculations to the contrary (Raymond and
Blankenship, 2004; Kopp et al., 2005), involves the epoxidation of squalene, where the
addition of ½O2 is catalyzed by the enzyme
squalene monooxygenase (Jahnke and Klein,
1983). Although some sterane precursors occur in other organisms (Volkman, 2005), high
concentrations of the regular steranes ergostane (C28) and stigmastane (C29) are apparently exclusive biomarkers for organisms of
the domain Eukarya (Brocks et al., 2003a).
Although sterane biomarkers have been reported previously from Archean shale extracts
(Brocks et al., 1999) with the caveat of ‘‘probably syngenetic’’ (Brocks et al., 2003a,
2003b), some younger successions contain
very low amounts of steranes (Brocks et al.,
2005), prompting concerns that the ancient
steranes are contaminants (Kopp et al., 2005).
The steranes reported here are from an oil of
normal thermal maturity that was trapped in
fluid inclusions early in the burial history of
the Matinenda Formation. Oil inclusions cannot be contaminated by later migrating hydrocarbons, unlike shale extracts, which can potentially be adulterated by nonsyngenetic
biomarkers (Brocks et al., 2003b). The entrapped biomarkers may be from both fluidinclusion assemblages, but comparison with
the outside rinse and system blanks shows that
most are not contaminants from later hydrocarbons or from anthropogenic input. Hence,
not only do our data suggest that biogenic oxygen production began before significant atmospheric accumulation, but also that some
aquatic settings became oxygenated enough
for sterol synthesis. The abundance of diverse
steranes in the inclusions indicates a eukaryote input. Evidently, eukaryotic organisms
survived not only the Neoproterozoic snowball Earth events but also their equivalents in
the Paleoproterozoic. As oil inclusions are
found in a wide variety of rocks and minerals
of all ages, they may thus provide new and
otherwise unattainable insights into biological
evolution and paleoenvironments during critical stages of Earth’s history.
ACKNOWLEDGMENTS
We thank Mike Hailstone, Ontario Geological Survey at Sault Ste. Marie, for providing drill core access
and advice on sampling localities, Robinson Quezada
for help with organic geochemical analysis, and the
Electron Microscopy Unit at the University of Sydney
for assistance with imaging. We are also grateful to
Roger Summons, Kai-Uwe Hinrichs, and an anonymous reviewer for their thoughtful comments. This
work was supported by an Australian Research Council
discovery grant, which includes a QEII Fellowship to
440
Dutkiewicz, the J.G. Russell Award from the Australian
Academy of Science (Dutkiewicz), and the National
Aeronautics and Space Administration Astrobiology Institute (Buick).
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