Earth and Planetary Science Letters 277 (2009) 490–500
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Earth and Planetary Science Letters
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / e p s l
Siberian gas venting and the end-Permian environmental crisis
Henrik Svensen a,⁎, Sverre Planke a,b, Alexander G. Polozov a,c, Norbert Schmidbauer d, Fernando Corfu e,
Yuri Y. Podladchikov a, Bjørn Jamtveit a
a
Physics of Geological Processes (PGP), University of Oslo, PO Box 1048 Blindern, 0316 Oslo, Norway
Volcanic Basin Petroleum Research (VBPR), Oslo Research Park, 0349 Oslo, Norway
Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, 119017 Moscow, Russia
d
Norwegian Institute for Air Research, Kjeller, Norway
e
Dept. of Geosciences, University of Oslo, PO Box 1047 Blindern, 0316 Oslo, Norway
b
c
a r t i c l e
i n f o
Article history:
Received 8 July 2008
Received in revised form 7 November 2008
Accepted 14 November 2008
Editor: Dr. R.W. Carlson
Keywords:
end-Permian
Siberian Traps
Tunguska Basin
gas venting
a b s t r a c t
The end of the Permian period is marked by global warming and the biggest known mass extinction on Earth. The
crisis is commonly attributed to the formation of the Siberian Traps Large Igneous Province although the causal
mechanisms remain disputed. We show that heating of Tunguska Basin sediments by the ascending magma
played a key role in triggering the crisis. Our conclusions are based on extensive field work in Siberia in 2004 and
2006. Heating of organic-rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas
and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion. Basin
scale gas production potential estimates show that metamorphism of organic matter and petroleum could have
generated N 100,000 Gt CO2. The gases were released to the end-Permian atmosphere partly through spectacular
pipe structures with kilometre-sized craters. Dating of a sill intrusion by the U–Pb method shows that the gas
release occurred at 252.0 ± 0.4 million years ago, overlapping in time with the end-Permian global warming and
mass extinction. Heating experiments to 275 °C on petroleum-bearing rock salt from Siberia suggests that methyl
chloride and methyl bromide were significant components of the erupted gases. The results indicate that global
warming and ozone depletion were the two main drivers for the end-Permian environmental crisis. We
demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important
factor in controlling whether a Large Igneous Provinces causes an environmental crisis or not. We propose that a
similar mechanism could have been responsible for the Triassic-Jurassic (~200 Ma) global warming and mass
extinction, based on the presence of thick sill intrusions in the evaporite deposits of the Amazon Basin in Brazil.
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
The end-Permian crisis is the biggest known marine and terrestrial
extinction event (Wignall, 2001; Erwin et al., 2002). The main stage of the
extinction occurred during a relatively short time span of about
200,000 years contemporaneous with the Siberian Traps volcanism
(Bowring et al., 1998; Mundil et al., 2004; Kamo et al., 2006). A global
carbon cycle perturbation is recorded in marine and terrestrial strata (i.e.,
Retallack and Krull, 2006) with global warming extending 4–5 m.y. into to
the Triassic (Payne et al., 2004; Payne and Kump, 2007). It has recently
been shown that the main carbon isotope excursion occur before the
extinction, showing that the changes in the global carbon cycle were not a
side effect or consequence of the extinction (e.g., Retallack and Krull, 2006;
Xie et al., 2007). This link provides an important constraint of the type of
geological processes potentially causing the extinction. Amongst the
hypotheses for the end-Permian event are H2S degassing from a stratified
ocean followed by ozone layer collapse (Grice et al., 2005; Kump et al.,
2005; Meyer and Kump, 2008), degassing of CO2 from the Siberian Traps
⁎ Corresponding author.
E-mail address: hensven@fys.uio.no (H. Svensen).
0012-821X/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.epsl.2008.11.015
Large Igneous Province (LIP) (e.g., Wignall, 2001; Reichow et al., 2002;
Grard et al., 2005; Xie et al., 2007) possibly also releasing methane from
gas hydrates (Wignall, 2001; Berner, 2002), and contact metamorphism of
coal and other carbonaceous sediments in the Tunguska Basin in Eastern
Siberia generating carbon gases and possibly halocarbons (Svensen et al.,
2004; Visscher et al., 2004; Retallack and Krull, 2006; Beerling et al., 2007;
Payne and Kump, 2007; Retallack and Jahren, 2008). Siberian Traps sill
intrusions were emplaced into the vast evaporite deposits of the Tunguska
Basin, but so far the effects of contact metamorphism of salt and sulphate
sequences on the end-Permian environment have not been fully
addressed. The aim of this study is to develop a new geological mechanism
to explain the end-Permian global warming and mass extinction, by using
a combination of field work in the Tunguska Basin (followed by core
studies, petrography, U–Pb dating), and laboratory gas generation experiments on salt samples collected during a 2004 field campaign.
2. The Tunguska Basin
The vast Tunguska Basin in Eastern Siberia contains the oldest petroleum system in the world, formed during maturation of 1–8 km thick
deposits of Neo-Proterozioc shale and carbonate (e.g., Meyerhoff, 1980;
H. Svensen et al. / Earth and Planetary Science Letters 277 (2009) 490–500
Surkov et al., 1991; Sokolov et al., 1992). The Tunguska basin (Fig. 1) is
petroleum-bearing, with numerous reservoirs of oil and gas (Fig. 2).
Carbonates and minor sandstone and shale horizons dominate the
Cryogenian and Tonian (formerly Riphean) source rock sequences which
are overlain by the carbonate and evaporate facies of the Ediacaran
(formerly Vendian). Furthermore, enormous volumes of Cambrian
evaporites are present in the basin, with up to 2.5 km thick sequences
of halite-rich strata, anhydrite, and carbonates (Fig. 2) (Zharkov, 1984;
Petrychenko et al., 2005). Five major phases of salt deposition occurred
in the Cambrian, the most extensive being the 2 million km2 Early
Cambrian Usolye salt basin with an average of 200 m of halite (Zharkov,
1984). Note that the “Tunguska Basin” in the literature is frequently
included in the terms “Siberian Platform” and “Siberian Craton”, and that
the Tunguska Basin is often considered as one of many basins situated on
the platform/craton. We use the term to encompass all the post NeoProterozoic sedimentary rocks on the platform/craton.
The total thickness of the basin stratigraphy commonly varies
between 3 km and 12.5 km (Meyerhoff, 1980; Kontorovich et al., 1997),
however the Neo-Proterozoic rocks are locally present as 7–10 km
thick rift segment deposits (Sokolov et al., 1992; Kuznetsov, 1997;
Drobot et al., 2004). Post-Cambrian rocks comprise carbonates, marls,
491
sandstones, and coal (Fig. 2), and the sedimentation terminated in the
latest Permian with the onset of Siberian Traps volcanism.
The Tunguska Basin sediments were intruded by the sub-volcanic
part of the Siberian Traps. Sills and dykes are abundant throughout the
basin, and form sheets up to 350 m thick, locally comprising up to 65% of
the stratigraphy (Meyerhoff, 1980; Fedorenko and Czamanske, 1997;
Ulmishek, 2001). The maximum accumulated sill thickness in the
Cambrian to Permian strata is 1200 m (Kontorovich et al., 1997). The
thickness of sill intrusions in the Neo-Proterozoic rocks is uncertain due
to a limited number of deep boreholes in the bulk part of the basin
(Fig. 2). However, thick sills are commonly present at the base of the
Cambrian evaporate sequence (Kontorovich et al., 1997; Ulmishek,
2001). The present day area with outcropping sill intrusions is at least
1.6 million km2 (Fig. 1). The sill emplacement led to widespread contact
metamorphism of the host sediments (e.g., Kontorovich et al., 1997) and
to enhanced maturation of organic matter and the formation of
methane-rich petroleum accumulations (Sokolov et al., 1992). The
most profound results of the magma-sediment interaction are spectacular magnetite-rich breccia pipes rooted in the Cambrian evaporites or
possibly deeper. These pipes are numerous in the southern parts of the
basin, where they are filled with up to 700 m deep and 1.6 km wide
Fig. 1. Geological map of the Tunguska Basin in Eastern Siberia, Russia. Note the high abundance of phreatomagmatic pipes with magnetite south of latitude 64, and the numerous basaltfilled pipes north of 68°. Our main study area during a 2004 field campaign is indicated by the star symbol. The aerial extent of evaporite is from Zharkov (1984). The geological map is
modified from Malich et al (1974), and the positions of the pipes were compiled from various sources (Malich et al., 1974; Nikulin and Von-der-Flaass, 1985; Pukhnarevich, 1986; Von der
Flaass and Naumov, 1995; Ryabov et al., 2005; Ryabov, 2006). The outline of the Cambrian evaporite is from Petrychenko et al. (2005), comprising a total area of 2 million km2.
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H. Svensen et al. / Earth and Planetary Science Letters 277 (2009) 490–500
and Czamanske,1997; Kamo et al., 2006). Lava flows are not outcropping
south of ~60°, and the absence of lava within the crater-lake deposits
suggests that lava flows never formed an extensive cover in the southern
parts of the basin. However, pyroclastic rocks are abundant in interval of
68 to 62° (Fig. 1) (e.g., Federenko and Czamanske, 1997; Kamo et al.,
2006), but their formation and source remains poorly understood.
The Cambrian evaporite strata in the Nepa area contain sills, contact
aureoles, and volcanic breccia pipes of Siberian Traps age (Fig. 3). A 2004
field campaign to Nepa (N 59° and E 107°; Fig. 1) was targeted at cores
drilled at Nepa in the 1970's and 80's for potassium salt prospecting. The
site is unique as the drilled salt is preserved, the cores are largely intact,
and it was possible to identify core tray labels during field work. The onsite work included mapping, borehole logging, and sampling of endPermian pipe structures. A 200 m thick mafic sill is located in the upper
Cambrian strata, and a second level of sills was discovered in the section.
The upper sill has a maximum thickness of 326 m in the Nepa area
(Zamaraev et al., 1985). The sills and pipes are associated with extensive
hydrothermal alteration zones and contact aureoles. The northernmost
pipe structure at the Nepa locality, the Scholokhovskoie pipe, is
characterized by five main breccia lithologies with varying degrees of
magmatic and sedimentary fragments (Fig. 4).
3. Methods
3.1. Heating experiments
Fig. 2. Schematic stratigraphy with compiled information about the occurrences of
petroleum reservoirs in the Tunguska Basin (Meyerhoff, 1980). The stratigraphy is
considered representative for the basin segment with pipes. The thicknesses of the preCambrian strata vary considerably (1–10 km) but has not been drilled in the central
parts of the basin. Sill intrusions are present throughout the basin stratigraphy
(Kontorovich et al., 1997). The pipes are rooted in the Cambrian evaporite or possibly
deeper, but have only been drilled to Upper Cambrian levels, as at Nepa (see Fig. 3). The
inferred source region of the pipes, where intense magma-sediment interactions took
place, is likely within the lower Cambrian strata. Craters are filled with up to 750 m of
crater-lake sediments (Von der Flaass and Naumov, 1995; Von der Flaass, 1997).
Gas extraction and heating experiments were conducted at the
Norwegian Institute for Air Research on natural rock salt samples from
the 194 borehole at Nepa (Fig. 3). Eight samples were analysed, all
containing petroleum-bearing fluid inclusions. Salt from the interior of
the cores were selected for analyses to minimize possible contamination
during drilling, storage, and sampling. Contamination is accordingly
regarded as minimal, also considering that compounds formed from
heating of wood fragments or plastic bags would easily be identified
during the heating runs. Between 2 and 4 g of sample were gently
crushed to 3–10 mm pieces and split in two fractions. Gas was flushed
through Perkin Elmer stainless steel adsorption tubes prior to desorption
at 250 °C for 7.5 min, followed by GC-MS analyses on a Hewlett Packard
1800A with a detector temperature of 225 °C, and a 1 µm DB-1701 32 m
separation column. The analyses are semi-quantitative and measured
relative to a toluene standard. The degree of adsorption in the tubes is
10–50% for light gases, thus significantly underestimating the actual
concentrations. Furthermore, CO2 and CH4 are not adsorbed in the tubes.
However, the analytical setup is efficient in terms of analyzing
halocarbons, which are the targeted gas compounds in this study.
The first set of samples was crushed in a 20 ml sealed steel
chamber in an argon atmosphere at room temperature, and a known
volume of gas was sucked through the absorption tubes by a pump.
The second set of samples was used in heating experiment to
investigate the potential for gas synthesis. The crushed samples were
placed directly in the adsorption tubes and heated to 275 °C within the
thermodesorption oven in a helium atmosphere. The released gases
were continuously trapped at −60 °C before transfer to the GC-MS.
3.2. Gas production potential
crater lake deposits (Von der Flaass and Naumov, 1995; Von der Flaass,
1997). About 250 mineralized pipes with magnetite matrix are identified
in the basin based on aero-magnetic surveys. Several of these are
currently mined for magnetite. Many more pipes, especially without
magnetite, are likely present due to the poor rock exposures on the
Siberian taiga. For instance, pipes without magnetite mineralization
have been discovered by coincidence during mining. In addition, more
than 500 basaltic diatreme-like pipes are known in the northern parts of
the Tunguska Basin (Fig. 1).
Siberian Traps lava flows are covering parts of the Tunguska Basin,
and comprise up to 6500 composite meters in the north (e.g., Federenko
We have applied the following relationship to calculate the gas
production potential Wc =V ⁎ ρ ⁎S during contact metamorphism of
organic carbon, where V is the aureole volume (sill area times aureole
thickness), ρ is the rock density, and S is the aureole shape parameter
defined as the TOC profile through the aureole (Svensen et al., 2007). We
assume a linear relationship in carbon loss profiles away from the sillsediment contacts (S = 0.5), implying that half of the organic matter in
the aureole was converted to carbon gas during metamorphism.
Generally, contact aureoles have the same thicknesses as their respective
sills, both below and above intrusions in low permeability sediments
H. Svensen et al. / Earth and Planetary Science Letters 277 (2009) 490–500
493
Fig. 3. Composite cross section from the Nepa locality. The location map shows four of the Nepa boreholes that we have studied in detail and three breccia pipes. The Cambrian
evaporite strata are overlain by Ordovician clastic sediments. Core data from the 6G hole in the Scholokhovskoie pipe and from the 194 hole in the lower sill intrusion are presented
here. The topmost stratigraphic unit is Ordovician (O), and the rest of the drilled sequences are from the Late Cambrian (Verkholensk Suite), Middle Cambrian (Litvintsev Suite,
abbreviated L-S), and the Lower Cambrian (Angara Suite and Bulay Suite, abbreviated B-S). The Upper sill is sometimes referred to as the Usol'e sill (Zamaraev et al., 1985).
(e.g., Raymond and Murchison, 1989, 1991; Galushkin, 1997; Fjeldskaar
et al., 2008). This implies that the total volume of sediments affected by
contact metamorphism is equal to twice the sill volume. Note that the
gas will be produced in the aureole independent of the specific type of
organic material undergoing metamorphism (dispersed organic matter,
coal beds, or petroleum). The mass conversion factors for calculating gas
equivalents from carbon are 1.34 and 3.66 for methane and carbon
dioxide, respectively.
3.3. Dating
U–Pb analyses on two dolerite samples from the 194 borehole
(sampled at 860.8 m and 868.7 m) (Fig. 2) were carried out using ID–
TIMS (isotope dilution thermal ionization) and a Finnigan MAT262
instrument at the Department of Geosciences in Oslo. The 20 to 30
zircon grains found in each of the two samples occurred largely as
fragments, locally with some preserved euhedral faces. Most grains
showed some local turbidity, fractures or inclusions of other minerals.
Baddeleyite was only observed as an inclusion in one zircon. Abrasion
generally removed most of the turbid parts of the fragments. The best
grains were selected for analysis, some were perfectly clear but others
still contained some imperfections. Zircon grains were abraded before
analysis, then dissolved and transferred directly to the mass spectrometer for measurement, except for one larger fraction processed
through anion exchange resin. A mixed 235U–205Pb–202Pb spike was
used for internal normalization of the fractionation of Pb. See Corfu
(2004) for analytical procedures. The data were calculated using decay
constants from Jaffey et al. (1971). The uncertainties are 2σ.
4. Results
4.1. The breccia
The magmatic fragments of the Scholokhovskoie pipe are rich in
glass (Fig. 4), demonstrating rapid melt quenching in the pipe, and the
pipe formation was accordingly contemporaneous with the sill emplacement. Hydrothermal minerals include calcite, dolomite, halite,
garnet, epidote, and chlorite, either as pore filling minerals or alteration products from igneous fragments.
4.2. Gas generation experiments
Heating experiments on evaporite samples from the 194 borehole
were done to determine the type of gas generated during contact
metamorphism in the Tunguska Basin. We use natural rock samples
equivalent to those that were heated by sills during the endPermian. The samples were collected at depths between 807 and
949 m, including two reference samples from the contact aureole of
the lower sill (Table 1). The samples consist of coarse grained halite
with minor sylvine, anhydrite, and pyrite. Trails of liquid and gas
inclusions are abundant in the salt (Grishina et al., 1998), releasing
aromatic and sulphurous gases when crushed. Table 1 show that
butane, benzene, and sulphur-bearing gases are the most abundant
of the analysed petroleum compounds at room temperature.
Sulphur dioxide is identified in most samples, whereas only two
samples contain dimethyl sulphide. Note that no halocarbons were
detected.
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H. Svensen et al. / Earth and Planetary Science Letters 277 (2009) 490–500
Fig. 4. Fieldwork and sampling in eastern Siberia. A) The 3000 m wide Zheleznogorsk pit is located 350 km south-west of Nepa. The pipe is mined for magnetite. This
phreatomagmatic pipe is of similar type as the one studied at Nepa. The pipe itself is outlined on the figure (stippled) and cuts the surrounding Ordovician sediments (carbonates and
sandstones). It is one of 5–6 magnetite-bearing pipes that are currently mined in the Tunguska Basin. B) Parts of the remaining core storage at Nepa, now exposed to weather. Core
logging and sampling was conducted on site in 2004. C) Altered volcanic breccia from the 6G borehole. The matrix minerals include chlorite, epidote, magnetite, and halite. D)
Phreatomagmatic breccia with altered sedimentary fragments (red) in a fine grained volcanic matrix (black and grey). Halite is identified as cement in the breccia. E) Dolerite
fragment dominated by glass (black) and plagioclase phenocrysts (grey).
When the samples were heated to 275 °C for 7.5 min in an inert
atmosphere the concentrations of sulphur dioxide increased significantly (up to 130 times), and the concentration of other sulphur gases
and hydrocarbons decreased (up to 30 times less butane). It is
important that halocarbons like methyl chloride and methyl bromide
were identified in all heating runs, as these compounds were not
present at room temperature. Maximum concentrations of methyl
chloride was 161 ng/g rock for sample 194/4. The mass ratio of methyl
chloride to methyl bromide is between 6.6 and 58.6 with an average of
17.3 for the 8 experiments. We use the highest value (i.e., 60) to
calculate the methyl bromide generation during contact metamorphism, as bromide is present in significantly lesser amounts in the
sedimentary rocks compared to chloride. Halogenated butane,
especially 1-chloro-butane, is present in considerable amounts (up
to 51 ng/g rock) in all runs except one (sample 194/3). When
extrapolated, only 1–350 mg of methyl chloride was generated per m3
H. Svensen et al. / Earth and Planetary Science Letters 277 (2009) 490–500
495
Table 1
Gas extraction and generation from hole 194 halite
Sample
Depth
194/5
830.2
194/2
807.2
194/3
819.4
194/4
824.4
Method
Room temperature, ng gas/g rock
Sulfur dioxide
Methyl tioetane
Thiobis ethane
Dimethyl sulfide
Butane
Benzene
Methyl chloride
Methyl bromide
1-chloro-butane
1-bromo-butane
Ch3Cl/CH3Br
0.1
0.03
8.1
4.4
0.3
1.3
115.7
6.1
20.6
13.3
194/9⁎
840.9
194/21⁎
890.1
194/30
937.9
0
157.0
35.7
114.2
2.0
1.1
0.2
2.0
0
194/32
949.3
194/5
830.2
194/2
807.2
194/3
819.4
194/4
824.4
194/9⁎
840.9
194/21⁎
890.1
194/30
937.9
194/32
949.3
Heating and extraction at 275 °C, ng gas/g rock
1.4
2.5
3.9
3.9
36.2
2.3
3.0
5.8
0.9
8.1
0
6.6
17.7
2.1
7.3
7.4
8.4
0.2
11.0
0.2
7.0
0.5
0.01
0
0.03
58.6
4.6
97.2
13.4
6.5
109.9
11.5
7.0
4.8
1.7
10.6
3.7
161
15.6
19.3
6.7
10.3
5.9
0.7
29.8
0
8.4
12.1
1.3
50.9
12.6
9.3
9.1
1.0
24.1
5.5
9.4
1.5
3.7
3.5
0.13
11.1
0
27.2
⁎Sample affected by contact metamorphism.
heated evaporite. This is due to the small volume of fluid inclusions
present, and that the fluid inclusions are the only hosts of reactive
hydrocarbons in the samples. Thus, we cannot use the experiments
directly for calculating the mass of halocarbons generated during
contact metamorphism.
4.3. Gas production potential
The gas production potential (Svensen et al., 2004) during metamorphism of the Tunguska Basin sediments has been estimated based
on basin scale metamorphism of organic carbon. We have used two
approaches to estimate the carbon gas production potential during
contact metamorphism of the Tunguska basin sediments during sill
emplacement and pipe formation. 1) Pipe source region. Assumes a
5 km3 pipe source region, a 2–5 wt.% conversion of organic matter to gas,
and a rock density of 2300 kg/m3. The pipe source region size is
corroborated by geophysical data (Von der Flaass, 1997) and alteration
zones from core data. 2) Basin scale gas generation in contact aureoles
(Svensen et al., 2004). Here we assume the emplacement of one sill of
200 m thickness (e.g., Vasil'ev, 1999) in an area of 2 million km2 with
pipes, shale, evaporite, and petroleum (Fig. 1), leading to a sill volume of
400,000 km3 and hence an aureole volume of 800,000 km3. Finally, we
assume that between 0.5 and 1.5 wt.% of organic matter reacted to gas,
and that this comprised half of the bulk rock TOC in the aureole with a
density of 2.3 g/cm3. Note that this approach underestimates the gas
production because there are multiple sill emplacement levels in the
basin (cf. Kontorovich et al., 1997), and the metamorphism may locally
have affected layers with higher TOC contents higher than 3 wt.% (cf.
Kuznetsov, 1997). Furthermore, CO2 generation from metamorphism of
dolostone is not included in the estimates, but represents a potentially
significant source of isotopically heavy carbon (δ13C ~ −4 to +2‰ VPDB).
We assume a CH3Cl/TOC of 0.49 (Beerling et al., 2007), and a CH3Cl/
CH3Br of 60 (this study).
The resulting basin scale carbon gas production potential is between
9200 and 27,600 Gt C (Table 2). The results from the calculations based
on the pipes show that the production potential per pipe is 0.23–0.58 Gt
C. Mapping of pipes has been most extensive in the Bratsk region where
about 200 pipes are known in a 250 × 250 km (62,500 km2) large area
(i.e., one pipe per 312 km2). We can extend this coverage to the poorly
exposed 2,000,000 km2 large basin with evaporites, resulting in a total of
6400 pipes in the basin. The results in a potential for generating 1500–
3700 Gt C in the pipe source regions (Table 2).
4.4. Age of sill emplacement
The analytical data for zircon in the lower dolerite sill of hole 194
define a slightly elongated cluster along the Concordia curve with
206
Pb/238U dates ranging from 248.0 to 252.4 Ma (Fig. 5 and Table 3). A
check for a potential bias from disequilibrium-related excess 206Pb
shows that the effect is insignificant. The analyzed zircon grains are
very rich in U (N700 ppm–21,800 ppm) and also have high Th/U ratios
(1.5–3.5). The spread in ages is therefore most likely a result of partial
Pb loss. The uppermost analyses, however, appear to have escaped disturbances because the weighted average of their 206Pb/238U age of
252.0 ± 0.4 Ma. This is corroborated by the upper intercept age of 252.4 ±
1.2 Ma of the regression line through all 11 data points. The age of 252.0 ±
0.4 Ma is thus considered the best estimate for crystallization of the sill
intrusion.
5. Discussion
5.1. Volatile generation
The source rocks of the Tunguska Basin reached peak maturity
during the Carboniferous (Meyerhoff, 1980; Ulmishek, 2001), but
petroleum generation started as early as in the Neo-Proterozoic (Sokolov
et al., 1992). This means that the basin was petroleum-bearing prior to
the end-Permian sill emplacement. The TOC values in rocks affected by
contact metamorphism, which form the basis for estimating the carbon
gas production potential, are uncertain due to few boreholes penetrating
the source rocks in the deep central parts of the basin. However,
assuming that the available data from the basin margins are representative, a 1–3 wt.% TOC is supported (Sokolov et al., 1992; Kuznetsov,
1997; Bartley et al.,1998; Ulmishek, 2001). Organic carbon values as high
as 8–22 wt.% are present locally in source rocks (Sokolov et al., 1992;
Kuznetsov, 1997; Drobot et al., 2004). In addition, sills have intruded
petroleum-bearing Ediacaran and Cambrian levels, where 8–10 vol.%
petroleum fill is present in carbonate reservoirs (e.g., Meyerhoff, 1980;
Kuznetsov, 1997). The metamorphism also led to enhanced petroleum
migration (e.g., Polyanskii and Reverdatto, 2002).
From the composition of the sediments undergoing contact metamorphism, gases like CH4 and CO2 (from carbonates, organic matter,
and petroleum), SO2 (from evaporites) were released, in addition to
Table 2
Gas production potential in the Tunguska Basin (rounded numbers)
Method
Volume
km3
Organic carbon C
wt.%
Gt
CO2
Gt
CH4
Gt
CH3Cla CH3Brb
Gt
Gt
Pipes (1)
Pipes (1)
Pipes (6400)
Pipes (6400)
Aureoles
Aureoles
Total prod. pot.
Total prod. pot.
Lava degassing
5
5
32,000
32,000
800,000
800,000
(Low)
(High)
2
5
2
5
0.5
1.5
1.13
2.10
5400
13,500
33,700
101,000
39,000
114,000
~ 20,000
0.31
0.77
2000
4900
12,300
37,000
14,300
41,900
0.11
0.28
720
1800
4500
13,500
5200
15,300
a
b
0.23
0.58
1500
3700
9200
27,600
10,700
31,200
5400
CH3Cl/TOC = 0.49 (Beerling et al., 2007).
CH3Cl/CH3Br = 60 (this study).
0.0019
0.0047
12
30
75
225
87
255
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H. Svensen et al. / Earth and Planetary Science Letters 277 (2009) 490–500
large basin segment (i.e., one pipe per 34 km2). Assuming that each pipe
in the Tunguska Basin has a source region of 5 km3, the resulting volume
of high temperature sediment metamorphism for the 6400 pipes is
32,000 km3. This leads to an aureole-volume to pipe-volume ratio of 25.
The pipes likely formed in regions with a higher gas production potential
at the base of the Cambrian evaporite sequence, thus we use a
conversion of 2–5 wt.% organic matter to gas.
5.2. Gas experiment
Fig. 5. Concordia diagram showing the results of the zircon dating of the lower sill in the
194 Nepa borehole and the weighted average 206Pb/238U age of 252.0 ± 0.4 Ma.
minor volumes of magmatic volatiles (CO2, HCl, SO2). This is supported
by gas geochemistry from the Tunguska Basin, and methane-generation during contact metamorphism is considered the final phase of
petroleum formation in the basin (Sokolov et al., 1992). Moreover, high
concentrations of organic sulphur-compounds (mercaptans) have been
identified in oil and condensates, attributed to the contact metamorphism (Kontorovich et al., 1997). Note that the same compounds were
identified during gas extraction from the contact aureole salt samples
(Table 1).
The basin scale gas production potential estimates shows that
contact aureoles in the Southern Tunguska Basin could have generated
between 9200 and 27,600 Gt C (equivalent to 33,700–101,000 Gt CO2). In
addition, the pipes released 1500–3700 Gt C (equivalent to 5400–
13,500 Gt CO2). This estimated number of pipes is high (6400), but is still
considered realistic as it is within the same order of magnitude as the
number of hydrothermal vent complexes in the Karoo Basin in South
Africa (Svensen et al., 2006, 2007) and in the Vøring Basin offshore
Norway (Svensen et al., 2004; Planke et al., 2005). In the Vøring Basin,
there are about 2500 hydrothermal vent complexes in an 85,000 km2
The heating-experiments, although being semi-quantitative, suggest
that a series of sulphur gases and halocarbons were generated during
metamorphism in addition to the carbon gases. To our knowledge, this is
the first experimental demonstration that natural rock samples generate
halocarbons during heating. We attribute the halocarbon generation to
reactions between the petroleum bearing fluid inclusions and the host
salt on the prograde temperature path to 275 °C. A requirement for
methyl chloride generation from organic matter is the presence of
chloride ions and methyl groups (Conesa et al., 1997; Keppler et al.,
2000; Hamilton et al., 2003). In the salt samples, the chloride is present
in the inclusion fluid water, and methyl groups are produced from the
petroleum during heating. An equivalent process is likely responsible for
the formation of 1-chloro-butane, methyl bromide and 1-bromobutane. Assuming that the gas speciation is not too pressure sensitive,
the experiments show that halocarbons are natural products of contact
metamorphism of the Tunguska Basin evaporites.
5.3. Pipe processes
The pipes in the Tunguska Basin were formed as a consequence of the
pressure build-up during heating of the Precambrian and Cambrian sequences (Von der Flaass and Naumov, 1995; Von der Flaass, 1997).
Pressure build-up mechanisms contributing to pipe formation include
heating of pore fluids and metamorphic devolatilization of carbonate,
shale, liquid hydrocarbon and brine reservoirs, and halite-anhydrite
rocks, generating gases like CH4, CO2, and SO2 (cf. Jamtveit et al., 2004;
Svensen et al., 2007). Cracking of liquid petroleum to gas could have been
of major importance for pipe formation, as cracking at atmospheric
conditions results in a 700 fold volume increase (Barker, 1990). Even at
higher pressures, this conversion would lead to accelerated hydrofracturing and vertical fluid expulsion. In the Tunguska Basin, reactions with the
evaporites likely generated sulphurous gases and halocarbons, as shown
Table 3
U–Pb data for zircon
Characteristicsa
Weightb
Ub
Th/Uc
Pbcd
206
204
[g]
194/15–868.7 m, mafic sill
Z fr [1]
b1
Z f rim [1]
b1
Z fr [1]
b1
Z fr [1]
b1
Z fr im [1]
b1
[ppm]
Pb/
Pbe
207
235
Pb/
Uf
[pg]
±2
206
238
Pb/
Ud
[abs]
±2
Rho
207
Pb/
Pbf
±2
206
[abs]
206
238
Pb/
Uf
±2
207
Pb/
Uf
±2
235
[abs]
207
Pb/
Pbf
±2
206
[age in Ma]
N920
N2890
N2670
N930
N740
1.98
2.03
2.29
2.21
1.72
1.6
1.2
0.6
0.5
1.6
1487
5897
11435
4335
1146
0.2821
0.2814
0.27996
0.2793
0.2775
0.0018
0.0011
0.00078
0.0011
0.0020
0.03984
0.03981
0.03965
0.03951
0.03923
0.00014
0.00014
0.00011
0.00013
0.00012
0.60
0.85
0.85
0.78
0.53
0.05134
0.05125
0.05121
0.05126
0.05131
0.00026
0.00011
0.00008
0.00013
0.00032
251.9
251.7
250.7
249.8
248.0
0.8
0.9
0.7
0.8
0.7
252.3
251.7
250.6
250.1
248.7
1.4
0.9
0.6
0.9
1.6
256
252.2
250.3
252.7
255
12
4.9
3.4
5.6
14
194/35 – 860.8 m, mafic sill
Z fr [1]
2
5095
Z fr [1]
b1
N 2830
Z fr im [1]
1
21800
Z fr im [1]
b1
N3440
Z fr eu im [6]
2
3131
Z fr eu im [5]
7
4232
Z fr [1]
b1
N 280
2.25
1.54
3.45
1.73
2.00
1.66
2.63
1.4
0.5
1.2
0.5
1.9
2.2
0.9
13357
14651
46947
16733
6141
33506
1747
0.28202
0.28129
0.28102
0.28081
0.28001
0.27882
0.7063
0.00096
0.00077
0.00090
0.00078
0.00090
0.00064
0.0055
0.03993
0.03987
0.03975
0.03972
0.03964
0.03943
0.08726
0.00013
0.00010
0.00012
0.00010
0.00011
0.00008
0.00060
0.95
0.89
0.97
0.92
0.88
0.96
0.82
0.05123
0.05117
0.05127
0.05127
0.05124
0.05129
0.05871
0.00005
0.00006
0.00004
0.00005
0.00008
0.00003
0.00026
252.4
252.0
251.3
251.1
250.6
249.3
539.3
0.8
0.6
0.7
0.6
0.7
0.5
3.5
252.3
251.7
251.5
251.3
250.7
249.7
542.6
0.8
0.6
0.7
0.6
0.7
0.5
3.2
251.0
248.6
253.2
253.1
251.4
253.9
556.3
2.4
2.9
1.8
2.4
3.5
1.5
9.6
a
b
c
d
e
f
Z = zircon; fr = broken pieces of crystals, locally with euhedral faces (=eu); im = slight imperfections (local turbidity, rust or inclusions) [N] = number of grains in fraction.
Weight and concentrations are known to better than 10%, except for those near the ca. 1 g limit of resolution of the balance.
Th/U model ratio inferred from 208/206 ratio and age of sample.
Pbc = total common Pb in sample (initial + blank).
Raw data corrected for fractionation.
Corrected for fractionation, spike, blank and initial common Pb; error calculated by propagating the main source of uncertainty.
H. Svensen et al. / Earth and Planetary Science Letters 277 (2009) 490–500
497
Fig. 6. Schematic evolution of the Tunguska Basin pipes and the venting of carbon gases and halocarbons to the atmosphere. The pipe evolution is partly based Von der Flaass and
Naumov (1995) and Von der Flaass (1997). 1) Emplacement of sills into organic rich sediments and evaporites with petroleum accumulations (P). 2) Contact metamorphism of shale,
evaporite, and petroleum, leading to gas generation and overpressure (shown as stippled lines). Melt is accumulating within evaporite sequences in the source region of the pipe. 3)
Pipe formation and eruption. Glass in the breccias show that the magma was disrupted and fragmented in the source region before vertical transport and phreatomagmatism.
Powerful eruptions led to wide craters and subsidence. Gases generated in contact aureoles are now released to the atmosphere. 4) Continued degassing from both magma and
sediments through the pipe and the crater-lake. Contact metamorphism of shallow organic-rich sequences (coal) along dikes, and appearance of the first lava flows further to the
north in the basin. The inferred gas composition is shown in the frame, alongside the estimated carbon gas and halocarbon production potential for the pipe degassing alone.
by our experiments. Gas generation from sediment metamorphism is
known both from the Karoo Basin in South Africa and offshore Norway,
resulting in vertical piercement structures (Jamtveit et al., 2004; Svensen
et al., 2004; Svensen et al., 2007). The main differences in the pipe
forming mechanisms between these two settings and the one in Siberia,
is the presence of evaporites and petroleum in the source region, and
extensive magma-sediment interactions within the pipes. The pipes are
rooted at 2–4 km depth in magma-sediment mixing zones, probably
close to the base of the evaporite stratigraphy although the precise nature
of the roots remains unknown. Fig. 6 shows the schematic evolution of
the pipe structures. The sizes of the pipe craters in the Tunguska Basin
suggest powerful eruptions, with gases and ash likely reaching high
atmospheric levels. The presence of glass in the Scholokhovskoie breccia
pipe suggests that the pipe was formed as a phreatomagmatic event,
where the partly molten magma cooled rapidly in the pipe during
eruption. Parts of the wall-rock collapsed into the pipe, mixing with the
Fig. 7. Compilation of zircon U–Pb ages of key end-Permian events. The ages of the P–T boundary are from (Gradstein et al., 2004) deduced from Bowring et al. (1998) (stippled,
labelled “B”), and from a revised age by Mundil et al. (2001) (in grey, labelled “M”). The age of the sill emplacement at Nepa (this study) is synchronous with pipe formation and
release of carbon gases and halocarbons to the atmosphere. The main phase of the extinction is dated to have occurred between 252.3 ± 0.3 and 251.4 ± 0.3 Ma by Bowring et al. (1998)
(labelled “B”) and 252.6 ± 0.2 Ma by Mundil et al. (2004) (labelled “M”).
498
H. Svensen et al. / Earth and Planetary Science Letters 277 (2009) 490–500
brecciated sediments from the root zone and the magmatic material.
Degassing of metamorphic volatiles continued along with circulation of
brines and metamorphic reactions between fluids and breccia, as
suggested by the hydrothermal mineralogy. The world-class magnetite
reserves of the Tunguska Basin pipes likely originated from hydrothermal
leaching of iron by hypersaline brines from the source region followed by
precipitation in the breccia (e.g., Mazurov et al., 2007).
5.4. Timing, timescales, and fluxes
The sill dating demonstrates that sill emplacement at Nepa occurred 252.0 ± 0.4 Ma, overlapping the U–Pb age of lavas in the
northern parts of the basin, and the U–Pb age of 252.6 ± 0.2 Ma for the
main phase of the end-Permian extinction (Fig. 7) (Mundil et al.,
2004). This supports a causal link between the pipe degassing and the
end-Permian environmental crisis.
If the contact metamorphic carbon gas wholly or partially vented to
the atmosphere, the result would be global warming even for a 100 ky
degassing scenario (c.f., Berner, 2002; Retallack and Jahren, 2008). The
released gas would have a δ13C isotopic composition close to that of bulk
oil and organic matter (~−30 to −25‰) (Hunt, 1979). The widely used
δ13C composition of volcanic CO2 is about −6‰, and would in that case be
too isotopically heavy to have caused the end-Permian negative carbon
isotope excursion (c.f. Berner, 2002). The isotopic composition of the
released CO2 from the Siberian Traps flood basalts is not known, but is
assumed to be close to −6‰. Sill emplacement and pipe formation is
considered a rapid process (Jamtveit et al., 2004; Svensen et al., 2004),
and we assume that one pipe formed per year in the Tunguska Basin. We
stress that this is a hypothetical assumption in order to evaluate the
carbon gas fluxes. The assumption is nevertheless realistic, as only a
limited volume of melt is required to form even the most widespread sill
intrusions, and contact metamorphism and venting occurs on timescales of 10–100 years (cf. Jamtveit et al., 2004). Still, we cannot exclude
that the pipe eruptions could have been clustered in time or formed
during a period of a few tens of thousands of years. The chosen model
scenario implies a total duration for the pipe degassing of 6400 years,
and an integrated CO2 equivalent flux of 0.8–2.1 Gt CO2/y. Seepage from
contact aureoles started after the pipe degassing, releasing 0.7–2.0 Gt
CO2/y over a 50 ky period. Note that this is less than the 2000–2005
average anthropogenic emissions of about 25–28 Gt CO2/y (IPCC, 2007).
The CO2 flux from the lavas is based upon the Siberian Traps lava volume
estimate by Reichow et al. (2002), a 1 million year emplacement period,
and the CO2 basaltic lava degassing estimate by McCartney et al. (1990)
and Self et al. (2005) (giving 0.024 and 0.017 Gt C/y, respectively). Note
that a few thick lava flows or sill intrusions would have led to
perturbations in the carbon degassing, with major consequences for
the atmospheric composition.
5.5. Implications for the end-Permian ozone layer
Generation and venting of chlorinated and brominated halocarbons,
both of which are synthesized in the evaporites, could have environmental consequences due to the involvement of halocarbons in
stratospheric ozone depletion (Beerling et al., 2007). Based on mass
balance calculations, between 4500 and 13,500 Gt methyl chloride could
have been produced during the basin-scale metamorphism (Table 2),
and additional 720–1800 Gt during pipe degassing. The fluxes of methyl
chloride according to the model scenario are 0.11–0.28 Gt/y for the pipe
stage and 0.09–0.27 Gt/y for the seep stage. Recent atmospheric modelling shows that N1000 Gt of methyl chloride are required to cause significant stratospheric ozone depletion over a 100,000 year time scale,
with a resulting flux of ~0.1 Gt/y (Beerling et al., 2007). Methyl bromide
will escalate this process, and our results show that 2–5 Tg methyl
bromide could have been released during the pipe degassing stage per
year. Even if the halocarbon degassing plume was restricted to lower
atmospheric levels, coeval emissions of methane would enable the
halocarbons to pass the troposphere without reacting with OH (see
Beerling et al., 2007).
To conclude, the metamorphism and venting in the Tunguska Basin
can successfully be applied as a mechanism to explain several of the endPermian extinction hypotheses: a) extinction from global warming and
hypercapnia (e.g., Knoll et al., 2007), b) extinction from ozone layer
collapse and high levels of surface radiation (e.g., Visscher et al., 2004;
Foster and Afonin, 2005; Kump et al., 2005; Beerling et al., 2007; Lamarque et al., 2007).
5.6. The relevance for the Triassic–Jurassic mass extinction
Carbon isotope excursions and global warming were consequences
of contact metamorphism and venting during the initial stages of the
formation of the North Atlantic Volcanic Province and the Karoo LIP (e.g.,
Svensen et al., 2004, 2007). The main mechanism was contact
metamorphism of carbon-rich sediments and release of carbon gases
to the atmosphere. Even though LIPs and mass extinction are statistically
correlated (e.g., Stothers, 1993), these LIPs are not associated with major
extinctions. The key question becomes why some LIPs are associated
with extinctions, whereas others had apparently minor effects on the
biosphere. If the sediment composition around sill intrusions is the most
important parameter in causing environmental changes as suggested by
Svensen et al. (2004, 2007), we would now predict that extinctions occur
when sedimentary basins with major evaporite and organic matter
deposits are intruded by thick sill intrusions.
The second biggest known extinction occurred at the Triassic–Jurassic
boundary at about 200 Ma, contemporaneous with the formation of the
Central Atlantic Magmatic Province in the eastern US, South America, and
western Africa (e.g., Palfy and Smith, 2000; Wignall, 2001; Hesselbo et al.,
2007). Thick sills are common in this province, emplaced in thick Permian
evaporite deposits in the Amazon Basin in Brazil (e.g., Szatmari et al.,
1979). We propose that evaporite metamorphism caused generation and
venting of carbon gases and halocarbons to the atmosphere, leading to
global warming and atmospheric ozone depletion. Although the Amazon
Basin needs to be investigated in detail to lend support to this hypothesis,
the fact that the two biggest mass extinctions the last 252 Ma occurred at
the same time as two major sill emplacement events into evaporite
basins, seems to be too much of a coincidence.
6. Conclusions
We conclude that the pipe structures in the Tunguska Basin provide
direct evidence for end-Permian carbon gas and halocarbon release to
the atmosphere synchronous with sill emplacement. The end-Permian
crisis can be attributed to element mobilization from the evaporites
(producing halocarbons) and organic-rich deposits (producing greenhouse gases like CH4 and CO2) in Siberia. For the first time, we show that
halocarbons are generated when natural evaporite samples are heated to
275 °C, simulating the conditions during contact metamorphism. Basin
scale gas production potential during metamorphism shows that carbon
gases were generated in sufficient quantities to explain the end-Permian
negative carbon isotope excursion and global warming. Moreover, our
results explain how the Siberian Traps intrusions led to a mass extinction
whereas the formation of many other Large Igneous Provinces did not:
two kilometres of intruded evaporite made the difference.
Acknowledgments
This study was supported by a Centre of Excellence grant from the
Norwegian Research Council to PGP, by a Young Outstanding Researcher
grant and a PetroMaks grant to H. Svensen. We thank Morten Schjoldager for zircon separation, and Paul Meakin, Claus Nielsen, Frode
Stordal, Stephane Polteau, and Grigorii G. Akhmanov for comments to
the manuscript. Constructive reviews by Andrew D. Saunders and an
anonymous referee further improved the manuscript.
H. Svensen et al. / Earth and Planetary Science Letters 277 (2009) 490–500
References
Barker, C., 1990. Calculated volume and pressure changes during the thermal-cracking
of oil to gas in reservoirs. Aapg Bull.-Am. Assoc. Pet. Geol. 74, 1254–1261.
Bartley, J.K., Pope, M., Knoll, A.H., Semikhatov, M.A., Petrov, P.Y.U., 1998. A Vendian–
Cambrian boundary succession from the northwestern margin of the Siberian
Platform: stratigraphy, palaeontology, chemostratigraphy and correlation. Geol. Mag.
135, 473–494.
Beerling, D.J., Harfoot, M., Lomax, B., Pyle, J.A., 2007. The stability of the stratospheric
ozone layer during the end-Permain eruption of the Siberian Traps. Philos. Trans.Royal Soc., Math. Phys. Eng. Sci. 365, 1843–1866.
Berner, R.A., 2002. Examination of hypotheses for the Permo-Triassic boundary extinction by carbon cycle modeling. Proc. Natl. Acad. Sci. U. S. A. 99, 4172–4177.
Bowring, S.A., Erwin, D.H., Jin, Y.G., Martin, M.W., Davidek, K., Wang, W., 1998. U/Pb
zircon geochronology and tempo of the end-Permian mass extinction. Science 280,
1039–1045.
Conesa, J.A., Marcilla, A., Caballero, J.A., 1997. Evolution of gases from the pyrolysis of modified almond shells: effect of impregnation with CoCl2. J. Anal. Appl. Pyrolysis 43, 59–69.
Corfu, F., 2004. U–Pb age, setting and tectonic significance of the anorthosite–mangerite–
charnockite–granite suite, Lofoten–Vesteralen, Norway. J. Petrol. 45, 1799–1819.
Drobot, D.I., Pak, V.A., Devyatilov, N.M., Khokhlov, G.A., Karpyshev, A.V., Berdnikov, I.N.,
2004. Petroleum potential of Precambrian deposits of the Siberian platform and
prospects for studying their hydrocarbon content. Russ. Geol. Geophys. 45, 110–120.
Erwin, D.H., Bowring, S.A., Yugan, J., 2002. End-Permian mass extinction: a review. In:
Koeberl, C., MacLeod, K.G. (Eds.), Catastrophic events and mass extinctions: Impacts
and beyond. Geological Society of America. Special Paper 356, Boulder, Colorado.
Federenko, V., Czamanske, G.K., 1997. Results of new field and geochemical studies of
the volcanic and intrusive rocks of the Maymecha–Kotuy area, Siberian FloodBasalt Province, Russia. Int. Geol. Rev. 39, 479–531.
Fjeldskaar, W., Helset, H.M., Johansen, H., Grunnaleiten, I., Horstad, I., 2008. Thermal
modelling of magmatic intrusions in the Gjallar Ridge, Norwegian Sea: implications
for vitrinite reflectance and hydrocarbon maturation. Basin Res. 20, 143–159.
Foster, C.B., Afonin, S.A., 2005. Abnormal pollen grains: an outcome of deteriorating atmospheric conditions around the Permian–Triassic boundary. J. Geol. Soc.162, 653–659.
Galushkin, Y.I., 1997. Thermal effects of igneous intrusions on maturity of organic
matter: a possible mechanism of intrusion. Org. Geochem. 26, 645–658.
Gradstein, F.M., Ogg, J.G., Smith, A.G., Bleeker, W., Lourens, L.J., 2004. A new geologic time
scale, with special reference to Precambrian and Neogene. Episodes 27, 83–100.
Grard, A., Francois, L.M., Dessert, C., Dupre, B., Godderis, Y., 2005. Basaltic volcanism and
mass extinction at the Permo-Triassic boundary: environmental impact and modeling of the global carbon cycle. Earth Planet. Sci. Lett. 234, 207–221.
Grice, K., Cao, C.Q., Love, G.D., Bottcher, M.E., Twitchett, R.J., Grosjean, E., et al., 2005. Photic
zone euxinia during the Permian–Triassic superanoxic event. Science 307, 706–709.
Grishina, S., Pironon, J., Mazurov, M., Goryainov, S., Pustilnikov, A., Fon-Der-Flaas, G., et al.,
1998. Organic inclusions in salt. Part 3. Oil and gas inclusions in Cambrian evaporite
deposit from East Siberia. A contribution to the understanding of nitrogen generation
in evaporites. Org. Geochem. 28, 297–310.
Hamilton, J.T.G., McRoberts, W.C., Keppler, F., Kalin, R.M., Harper, D.B., 2003. Chloride
methylation by plant pectin: an efficient environmentally significant process. Science
301, 206–209.
Hesselbo, S.P., McRoberts, C.A., Palfy, J., 2007. Triassic–Jurassic boundary events: problems,
progress, possibilities. Palaeogeogr. Palaeoclimatol. Palaeoecol. 244, 1–10.
Hunt, J.M., 1979. Petroleum geochemistry and geology, San Francisco, California.
IPCC, 2007. Climate change 2007. Fourth Assessment Report (AR4). Intergovernmental
Panel on Climate Change, Geneva, 2007.
Jaffey, A.H., Flynn, K.F., Glendeni.Le, Bentley, W.C., Essling, A.M., 1971. Precision measurements of half-lives and specific activities of U-235 and U-238. Physical Review C 4,
1889–1906.
Jamtveit, B., Svensen, H., Podladchikov, Y., Planke, S., 2004. Hydrothermal vent complexes
associated with sill intrusions in sedimentary Basins. Physical geology of high-level
magmatic systems. Geological Society Special Publication, London.
Kamo, S.L., Crowley, J., Bowring, S.A., 2006. The Permian–Triassic boundary event and
eruption of the Siberian flood basalts: an inter-laboratory U–Pb dating study.
Geochim. Cosmochim. Acta 70, A303-A303.
Keppler, F., Eiden, R., Niedan, V., Pracht, J., Scholer, H.F., 2000. Halocarbons produced by
natural oxidation processes during degradation of organic matter. Nature 403,
298–301.
Knoll, A.H., Bambach, R.K., Payne, J.L., Pruss, S., Fischer, W.W., 2007. Paleophysiology and
end-Permian mass extinction. Earth Planet. Sci. Lett. 256, 295–313.
Kontorovich, A.E., Khomenko, A.V., Burshtein, L.M., Likhanov, Pavlov, A.L., Staroseltsev,
V.S., et al., 1997. Intense basic magmatism in the Tunguska petroleum basin, eastern
Siberia, Russia. Petrol. Geosci. 3, 359–369.
Kump, L.R., Pavlov, A., Arthur, M.A., 2005. Massive release of hydrogen sulfide to the surface
ocean and atmosphere during intervals of oceanic anoxia. Geology 33, 397–400.
Kuznetsov, V.G., 1997. Riphean hydrocarbon reservoirs of the Yurubchen–Tokhom Zone,
Lena-Tunguska Province, NE Russia. J. Petrol. Geol. 20, 459–474.
Lamarque, J.F., Kiehl, J.T., Orlando, J.J., 2007. Role of hydrogen sulfide in a Permian–
Triassic boundary ozone collapse. Geophys. Res. Lett. 34.
Malich, N.S., Tazihin, N.N., Tuganova, E.V., Bunzen, E.A., Kulikova, N.G., Safonova, I. V. a.
p. o. A., V.B., et al., 1974. Map of geological formations of the Siberian platform cover
(1:1 500 000). In: Malich, N.S. (Ed.), All-Union Research Geologic Institute (VSEGEI).
Leningrad.
Mazurov, M.P., Grishina, S.N., Istomin, V.E., Titov, A.T., 2007. Metasomatism and ore
formation at contacts of dolerite with saliferous rocks in the sedimentary cover of
the southern Siberian platform. Geol. Ore Depos. 49, 271–284.
499
McCartney, K., Huffman, A.R., Tredoux, M., 1990. A paradigm for endogenous causation
of mass extinctions. In: Sharpton, V.L., Ward, P.D. (Eds.), Global Catastrophes in
Earth History, 247. Geological Society of America, pp. 125–138. Special Paper.
Meyer, K.M., Kump, L.R., 2008. Biogeochemical controls on photic-zone euxinia during
the end-Permain mass extinction. Geology 36, 747–750.
Meyerhoff, A.A., 1980. Geology and petroleum fields in Proterozoic and Lower Cambrian
Strata, Lena-Tunguska Petroleum Province, Easter Siberia, USSR. In: Halbouty, M.T.
(Ed.), Giant Oil and Gas Fields of the Decade 1968–1978. American Association of
Petroleum Geologists.
Mundil, R., Metcalfe, I., Ludwig, K.R., Renne, P.R., Oberli, F., Nicoll, R.S., 2001. Timing of
the Permian–Triassic biotic crisis: implications from new zircon U/Pb age data (and
their limitations). Earth. Planet. Sci. Lett. 187, 131–145.
Mundil, R., Ludwig, K.R., Metcalfe, I., Renne, P.R., 2004. Age and timing of the Permian
mass extinctions: U/Pb dating of closed-system zircons. Science 305, 1760–1763.
Nikulin, V. I. and Von-der-Flaass, G. S., 1985. Prognosis map of Baikal-Amur Railway area
on iron ores (1:500 000). Explanation Note. Irkutsk, East-Siberian Research Institute of Geology, Geophysics and Mineral Resources (VostSibNIIGGiMS).
Palfy, J., Smith, P.L., 2000. Synchrony between Early Jurassic extinction, oceanic anoxic
event, and the Karoo-Ferrar flood basalt volcanism. Geology 28, 747–750.
Payne, J.L., Kump, L.R., 2007. Evidence for recurrent Early Triassic massive volcanism
from quantitative interpretation of carbon isotope fluctuations. Earth. Planet. Sci.
Lett. 256, 264–277.
Payne, J.L., Lehrmann, D.J., Wei, J.Y., Orchard, M.J., Schrag, D.P., Knoll, A.H., 2004. Large
perturbations of the carbon cycle during recovery from the end-Permian extinction.
Science 305, 506–509.
Petrychenko, O.Y., Peryt, T.M., Chechel, E.I., 2005. Early Cambrian seawater chemistry
from fluid inclusions in halite from Siberian evaporites. Chem. Geol. 219, 149–161.
Planke, S., Rassmussen, T., Rey, S.S., Myklebust, R., 2005. Seismic characteristics and
distribution of volcanic intrusions and hydrothermal vent complexes in the Vøring and
Møre basins. In: Dore, T., Vining, B. (Eds.), Petroleum Geology: North-West Europe and
Global Perspectives - Proceedings of the 6th Petroleum Geology Conference. Geological Society Publishing House, London.
Polyanskii, O.P., Reverdatto, V.V., 2002. Fluid convection in sediment-hosted reservoirs
due to thermal action of dikes and sills. Geol. Geofiz. 43, 27–41.
Pukhnarevich, M.M., 1986. Conditions and formation peculiarities of endogenous iron ore
deposits of the Siberian platform South. Irlutsk, Irkutsk State University Publishing.
Raymond, A.C., Murchison, D.G., 1989. Organic maturation and its timing in a carboniferous
sequence in the Central Midland Valley of Scotland: comparisons with Northern
England. Fuel 68, 328–334.
Raymond, A.C., Murchison, D.G., 1991. The relationship between organic maturation, the
widths of thermal aureoles and the thicknesses of sills in the Midland Valley of
Scotland and Northern England. J. Geol. Soc. 148, 215–218.
Reichow, M.K., Saunders, A.D., White, R.V., Pringle, M.S., Al'Mukhamedov, A.I., Medvedev, A.I.,
et al., 2002. Ar-40/Ar-39 dates from the West Siberian Basin: Siberian flood basalt
province doubled. Science 296, 1846–1849.
Retallack, G., Jahren, A.H., 2008. Methane release from igneous intrusion of coal during
Late Permian extinction events. J. Geol. 116, 1–20.
Retallack, G.J., Krull, E.S., 2006. Carbon isotopic evidence for terminal-Permian methane
outbursts and their role in extinctions of animals, plants, coral reefs, and peat
swamps. In: Greb, S.F., DiMichele, W.A. (Eds.), Wetlands through time. Geological
Society of America. Special Paper 399.
Ryabov, V.V., 2006. Petrologic features of paleovolcanic apparatus at tuffs and lavas unit of
the Siberian craton. Proceedings of 3d All-Russian Symposium on Volcanology and
Palaeovolcanology. Buryat Science Center of Siberian Branch of Russian Academy of
Scencies, Ulan-Ude, Buryat Republic, Russia.
Ryabov, V.V., Shevko, A.Y., Zateeva, S.N., 2005. Abnormal formations” in the Siberian
platform traps — indicators of geodynamic conditions of plateau basalts forming.
Lithospheres 4, 165–177.
Self, S., Thordarson, T., Widdowson, M., 2005. Gas fluxes from flood basalt eruptions.
Elements 1, 283–287.
Sokolov, B.A., Egorov, V.A., Nakaryakov, V.D., Bitner, A.K., Zkukovin, Y.A., Kuznetzov, L.L.,
et al., 1992. Geological and geophysical conditions of formation of oil and gas bearing
deposits in the ancient rocks of Eastern Siberia. Petroconsultants Australasia, Sydney, Australia.
Stothers, R.B. (Ed.), 1993. Flood basalts and extinction events. Geophysical Research
Letters, vol. 20, pp. 1399–1402.
Surkov, V.S., Grishin, M.P., Larichev, A.I., Lotyshev, V.I., Melnikov, N.V., Kontorovich, A.E.,
et al., 1991. The Riphean sedimentary basins of the Eastern Siberia Province and
their petroleum potential. Precambrian Res. 54, 37–44.
Svensen, H., Planke, S., Malthe-Sorenssen, A., Jamtveit, B., Myklebust, R., Rasmussen
Eidem, T., et al., 2004. Release of methane from a volcanic basin as a mechanism for
initial Eocene global warming. Nature 429, 542–545.
Svensen, H., Jamtveit, B., Planke, S., Chevallier, L., 2006. Structure and evolution of hydrothermal vent complexes in the Karoo Basin, South Africa. J. Geol. Soc. 163, 671–682.
Svensen, H., Planke, S., Chevallier, L., Malthe-Sorenssen, A., Corfu, F., Jamtveit, B., 2007.
Hydrothermal venting of greenhouse gases triggering Early Jurassic global warming.
Earth Planet. Sci. Lett. 256, 554–566.
Szatmari, P., Carvalho, R.S., Simoes, I.A., 1979. Comparison of evaporite facies in the Late Paleozoic Amazon and the Middle Cretaceous South-Atlantic salt basins. Econ. Geol. 74, 432-&.
Ulmishek, G.F., 2001. Petroleum Geology and Resources of the Baykit High Province, East
Siberia, Russia. U.S. Geological Survey Bulletin. 2201-F.
Vasil'ev, Y.R., 1999. A quantitative estimation of large-volume occurrences of Permian–
Triassic trap magmatism, Siberian Platform. Dokl. Earth Sci. 367, 754–757.
Visscher, H., Looy, C.V., Collinson, M.E., Brinkhuis, H., Cittert, J., Kurschner, W.M., et al.,
2004. Environmental mutagenesis during the end-Permian ecological crisis. Proc.
Natl. Acad. Sci. U. S. A. 101, 12952–12956.
500
H. Svensen et al. / Earth and Planetary Science Letters 277 (2009) 490–500
Von der Flaass, G.S., 1997. Structural and genetic model of an ore field of the Angaro-Ilim
type (Siberian Platform). Geol. Ore Depos. 39, 461–473.
Von der Flaass, G.S., Naumov, V.A., 1995. Cup-shaped structures of iron ore deposits in
the South of the Siberian Platform (Russia). Geol. Ore Depos. 37, 340–350.
Wignall, P.B., 2001. Large igneous provinces and mass extinctions. Earth-Sci. Rev. 53,
1–33.
Xie, S.C., Pancost, R.D., Huang, J.H., Wignall, P.B., Yu, J.X., Tang, X.Y., et al., 2007. Changes
in the global carbon cycle occurred as two episodes during the Permian–Triassic
crisis. Geology 35, 1083–1086.
Zamaraev, S.M., Geletii, N.K., Malykh, A.V., 1985. Temperature effects of traps on
potassium salts. Sov. Geol. Geophys. 26, 37–42.
Zharkov, M.A., 1984. Paleozoic Salt Bearing Formations of the World. Springer-Verlag,
Berlin, Heidelberg, New York & Tokyo.