print out lit report

C a n d i d a t e n u m b e r : 1 5 0 4 0 6 5 P a g e | 1

Department of Earth Sciences, Royal Holloway University of London

THE ROLE OF THE SIBERIAN TRAPS

IN THE PERMIAN TRIASSIC EXTINCTION

Candidate number: 1504065

2 nd Year

GL 2210 Literature report

Word Count:

Figure 1:Figure 1 shows a map of what is estimated to be the entire area of the Siberian Traps. This shows the outcropping of volcanic material and a lot of the boreholes which have been drilled for research and hydrocarbon exploration.

Figure Source: Saunders and Reichow 2009


Abstract

The Siberian traps are thought to be the cause of the Permian Triassic extinction event with significant evidence to prove many different factors resulting from its formation and eruption. Products from the Siberian traps caused significant change to both the atmosphere and the hydrosphere releasing significant amounts gaseous material into the environment causing extensive damage globally. Large amounts of methane released into the oceans and carbon dioxide absorbed by the oceans left them relatively inhabitable with oxygen contents at a record low and a record high pH. The atmosphere was severely damaged by the release of halogen bearing compounds from metamorphism of country rock causing a depletion in the concentration of ozone leaving life exposed to high frequency UV radiation. Acid rain is a leading theory which contributed to the destruction of life. All these processes are a result of the formation of the Siberian traps before the end of the Permian.

Introduction

The extinction event at the K-T boundary is by far the most well-known extinction event on record due to the vanishing of the Dinosaurs around 65Ma. However the extinction at the Permian Triassic boundary was by far the largest of them all. The P-T boundary occurred 250Ma (Saunders and Reichow, 2009) where it was believed that about 90% of marine species became extinct (Bambach et al., 2007) and around 70% of all terrestrial special dying out just before the end of the P-T boundary (Sahney and Benton 2008). There has been much debate to what has been the cause of what is known as “The Great Dying”. Theories over the last few decades have arisen such as the bolide impact theory (Alvarez et al., 1980) which suggests there could have been a large meteor or comet with size in the factor of kilometers which struck the earth, similar to that of the K-T boundary. Furthermore, other theories suggest that it was related to the rapid change in sea level (Wignall and Hallam, 1990), the large anoxic event in the oceans (Wignall and Twitchett, 1996) which triggered the change in the atmosphere as well as the hydrosphere and finally flood volcanism (Campbell et al., 1992). The flood volcanism of interest is the eruption of the Siberian Traps which erupted 251Ma (Black et al., 2013) just before the extinction event was recorded around 250Ma. In this report the main focus will be around the theory of the volcanism of the Siberian flood basalts which will be argued to be the primary cause of the mass extinction and highlight the main environmental factors which could have been the cause of both the terrestrial and marine collapse of biodiversity.

Mantle Plume Theory


The cause of the Permian Triassic extinction event has been in much debate over the last few decades. Between the major theories, two different theories are strongly argued in literature; the eruption of the Siberian traps and the bolide impact. The eruption of the Siberian traps are thought to be the cause of this event as little physical evidence such as shocked quartz, microtektites and Tsunami deposits have been found around the time of the extinction to support the bolide impact theory apart from the possibility of Ar/Ar ratios (Heydari and Hassanzadeh, 2003) which are not comparable to other recordings around the globe. However other scientists have struggled to recreate the results. On the other hand, there is significant evidence which supports the theory of the eruptions and at the time they occurred although much debate is still around to what may have caused this expanse of volcanic material.

There has been significant debate over the formation of the Siberian traps and their contribution to the extinction event at the end of the Permian. Researches are still unsure about how the Siberian traps formed in a region of little tectonic activity at this time period. Many different theories have been debated about the different possibilities of formations over the last 20 years. There are many theories which are based around the idea of a plume which was formed deep in the earth. Several models have been suggested such as a large mantle plume from the core-mantle boundary (Campbell and Griffiths, 1990), a theory that the traps could have formed from a process of lithospheric delamination (Elkins and Tanton, 2005) which instead of a plume suggested by Campbell and Griffiths (1990), a weaker shallower plume could have been present. Furthermore, theories included that sustained subduction beneath the continent could have resulted in saturation of the upper mantle from the partial melting of the subducting slab (Ivanov and Balyshev, 2005). The most accepted theory was from Campbell and Griffiths which suggested a large deep mantle plume from unstable behaviour deep within earth at the core mantle boundary. This is suggested to be the result of unexpectedly large amounts of radioactive decay in the core disrupting the convectional processes that occur within the mantle. This theory was the only plume theory which would have caused vast amounts of magma to erupt in Siberia in the time it did. Such significant amounts of basaltic lavas was suggested that the plume could have had a long wide head and a thin tail (Campbell and Griffiths 1990). However the debate comes in that if the plume theory was correct and that there was a tail and a head present, there should be some evidence of a continuous chain of volcanism (Campbell, 2005) similar to that of Hawaii. Nevertheless there have been suggestions that the mantle plume which formed these traps could be related with Iceland and that the evidence of volcanism is hidden beneath the Northern Oceans of the Artic. (Burke and Torsvik, 2004; Chernysheva et al., 2005).

Ozone Depletion The Eruption of the Siberian traps towards the end of the Permian caused significant alterations to the atmosphere. Every organism on the planet both terrestrial and marine had a considerable dependency on the atmosphere both directly and indirectly. When the traps erupted towards the end of the Permian, huge amounts of volatiles and other gaseous material was released into the atmosphere. The eruptions from the Traps resulted in substantial gas release both from the newly formed basaltic lavas at the surface and the high temperature low pressure metamorphism of the surrounding country rock (Black et al., 2013). In the Tunguska basin situated in the center of Siberia as we see it today, it was thought that Proterozoic hydrocarbons coexisted alongside halites in the volcanic basin (Svensen et al., 2009). The huge amounts of volatiles released from these rocks were suggested to have caused moderate reduction of ozone in the stratosphere to the total global collapse (Black et al., 2013). Chlorofluorocarbons would have been the main ozone depleting volatiles released from the salt rocks. These compounds typically contain particles of carbon, chlorine and fluorine. The presence of chlorine, fluorine and other halogens such as bromine are extremely dangerous in the atmosphere acting as catalysts for breakdown of ozone molecules (Black et al.,


2013). The most abundant compounds which could have significantly affected the ozone layer released from metamorphism and eruptions would have been chloromethane, CH3Cl, (metamorphically produced) and hydrochloric acid, HCl, (Volcanically produced). The following equations show how these halogens act as catalysts in the atmosphere destroying ozone. Chlorine is used as the example.

These equations represent the breakdown of ozone in the atmosphere with the presence of a homogeneous catalyst such as chlorine. In equation 2, you can see that chlorine is a product unlike in reaction 1 where it is a reactant. This means that it catalysis the reaction of ozone breakdown as the definition of a catalyst to some degree is that the substance is preserved and chemically unaltered in a reaction process.

Extensive modelling of global ozone depletion has taken place over the last 20 years to recreate the atmospheric conditions of the late Permian. From these models, the biggest cause is suggested to be the presence of CH3Cl which can spread in the atmosphere at alarming speeds. The modelling carried out by Black et al (2013) suggests that the ozone layer could have depleted by as much as 85% of which between 55%-67% was a result of CH3Cl release and the majority of the remainder coming from volcanic HCl (Black et al., 2013).From this, it has been suggested that an 85% reduction of stratospheric ozone could have resulted in as much as a 4900% increase in all ultraviolet (UV) radiation reaching earth’s surface (Black et al., 2013).

Scientists today categorize UV radiation into three categories, UV-A, UV-B and UV-C. These belong at the high end of the frequency range of the electromagnetic spectrum. The three categories

Figure 2:This figure shows the catalytic breakdown of ozone due to the presence of chlorine.

Figure 3: This figure shows the predicted increase of ultraviolet radiation levels towards the end of the Permian when ozone levels were at the lowest concentration in the stratosphere. This model was based on the release of CH3Cl from different sources, but mainly the metamorphism of halite based country rock in the Siberian Craton.Figure source: (Black et al., 2013)

Figure 4:This figure shows the predicted depletion in ozone concentration towards the end of the Permian. These models are based around the release of CH3Cl into the atmosphere from different sources, but mainly the metamorphism of halite based country rock in the Siberian Craton.Figure source: (black et al., 2013)

Equation 1: Cl + O3 ClO + O2

Equation 2: O + ClO Cl + O2

Net Equation: O + O3 2O2


of UV radiation are composed of different wave lengths, UV-A – 315-400 nm, UV-B 280-315 nm and UV-C 100-280 nm (Autier et al., 2005). From this, it is evident that UV-A is the more dangerous category of radiation which can cause surface damage to skin tissue to destruction and mutations of cells. From this drastic increase in UV radiation levels, the terrestrial fauna and flora would have suffered greatly with huge amounts of cellular destruction and mutation. The dying out of plants and animals over the long period of time from when the traps first erupted before the end of the P-T boundary would have meant organisms which were dependent on them would have died out too. Examples include bacteria, fungi and insects. It was suggested that the extinction event was the only event which majorly affected insects (Labandeira and Sepkoski, 1993). In the oceans, the effects could be quite profound. As UV radiation will not penetrate water to considerable depths, it could be assumed that only living organisms in shallow water could be affected directly. However, the Bleaching of Corals (brown, 1997), the destruction of planktonic phytoplankton and zooplanktons and other marine flora that dwells in the photic zone would be affected. As a result, this would cause significant disrupt to food chains, oxygenation of water and habitats affecting almost every living marine organism.

Gas Hydrate Release

There is a large misconception with what caused the inferno period at the end of the Permian which resulted in the extinction of most global species. For long periods of time it was thought that the gas release directly from the eruptions would have caused significant release of carbon dioxide into the atmosphere accelerating global warming of this period. However, it has been suggested that the gas release from the eruptions wouldn’t have been great enough to cause the extreme temperature rise which was predicted towards the end of the Permian. Another theory scientists came up with which could have caused the extreme warm period and which correlates well with the mass extinction with the oceans is the dissociation of methane gas from gas hydrates from deep ocean sediments. Gas hydrates are formed in deep waters where the temperature is very low and the pressure is high, also where there is a high abundance of methane. The methane would most likely originated from dissociation of marine gas hydrates, maturation of carbon rich sediments to produce methane aspects and finally the fracturing of deep marine petroleum reservoirs releasing huge amounts of natural gas and other petroleum products into the oceans (Heydari, Arzani and Hassanzadeh, 2009). In the case of methane, the gas hydrate is where the methane is frozen in a box like figure of water molecules trapping the CH4. As the volcanic events occur in ocean basins, there is a significant change in the conditions which keep these gas hydrates stable. These condition changes could have been temperature increase or change in pressure. The change in pressure is very hard to predict because it involves many different parameters. Pressure change could be related to change in sea level, submarine slumping or global warming (Nisbet, 1990; Kvenvolden, 1993; Dickens et al., 1995; Dickens, 2000). Research suggests that the most likely out of all of these prediction would be the change in temperature from the mantle plume situated beneath the ocean floor. From the mantle plume it was thought that a huge amount of dyke like intrusions would be present which would have been injected at high temperatures into surrounding sediments resulting in the dissociation of methane. The temperature would have changed causing the bonds between the water to weaken releasing the methane. This methane would have caused significant issues to hydrosphere and the atmosphere.

Some of this methane that is released undergoes a reaction in the water column where the methane is oxidised to producing carbon dioxide and water. This is thought to be one of the strongest theories to


the anoxic event which occurred in the oceans. The depletion of oxygen and the production of CO2 would result in the oceans becoming more acidic depending on how much buffering the oceans could with stand from the change in ion concentration. The oceans will become more acidic by the increase in concentration of hydrogen ions.

Equation 1: CH4 (g) + 2O2 (g) CO2 (aq) + 2H2O (aq)

Equation 2: CO2 (aq) + H20 (aq) H2CO3 (aq)

Equation 3: H2CO3 (aq) HCO3- + H+ CO3

2- + H+

As equation 2 is an equilibrium balance, as more and more CO2 is produced from the release of methane in the water, the equilibrium is shifted in the direction of carbonic acid which is a weak acid with a pH around 5. This law of equilibrium was introduced by Le Chatelier where he stated that an increase in entropy will drive the equilibrium to the side with the lowest entropy. This means that more carbonic acid, H2CO3, is formed when there is an increase in carbon dioxide. However carbonic acid is a weak acid which means that not all H+ ions will dissociate and only a few will meaning that acidification of the oceans will be over a long period of time. However the methane release can also react with sulphur in the water column to form hydrogen sulphide, H2S which is extremely toxic to the majority of living organisms. The rest of the methane is released into the atmosphere. This would have accelerated global warming as methane is up to 20 times more effective at trapping heat than CO2 (Archer, 2007; Archer et al.,2008). All these different reactions due to the release of methane will have a drastic effect on the diversity of the oceans and the land where fauna and flora will struggle to cope with increasing acidic conditions, especially fish and corals who are extremely sensitive to environmental change and calcite baring fauna which won’t be able to secrete their shells would have struggled to cope with the changing conditions throughout the Permian.

Acid Rain

Figure 5:This figure shows how the gas hydrates form in the ocean. This shows how water molecules bond around a methane molecule trapping it. For this methane to be released, these water molecules must break their bonds. This is normally due to the alteration of environmental conditions such as pressure and temperature.Figure Source: http://www.eu-midas.net/science/gas-hydrates


During the eruption of the Siberian traps another threat to global species was about to take its toll. Acid rain was thought to have been another serious problem to ecosystems on the planet. Acid Rain was thought to have been a result of many different contributing factors at this time. Direct products from the Siberian Traps eruptions which would have been the biggest contributor of pollutants such as SO2 and Nitrogen oxides, NOx, and large amounts of CO2 ejected from the ocean due to the imbalance of equilibrium with the atmosphere.

There is a lot of dependency on the physiology of fauna and flora and how strongly systems are buffered against the change in acidity levels (Black et al., 2013). Over the period of the eruption, the changes to the atmosphere and oceans would have significantly increased the amount of CO2 in the atmosphere resulting in prolonged acidification of rain (Black et al., 2013). This would have caused possible leaching of soils stunting the growth or plants and other microorganisms from sulphur rich rain (Howells, 1990). Furthermore marine systems especially those which are shallow and are poorly buffered against the change in hydrogen ion concentration (Black et al., 2013) would have been affected, causing pH sensitive organisms to suffer such as fish and corals. However, acid rain was more localised as you can see from figure 6 where the majority of strong acid rain fell over the northern hemisphere. The terrestrial flora and fauna would have suffered significantly in the areas where it was suggested that the pH reached as low as 2. This kind of rain is enough to stunt the growth of plants and potentially cause cellular breakdown. However, fauna thought to be a lot more sensitive in the change of rain acidity where Black (2013) suggested that fish, insects and amphibians where most likely to killed off around the pH of 3. Knowing that acid rain got to a higher pH than this suggested that the acid rain caused from the release of gaseous volatiles from the traps was a good theory in suggesting that the extinction event and acid rain were closely related. Furthermore, the evidence provided by pollen from places in South Africa, China and other areas of the globe record abnormally high sulphur readings (Maruoka et al., 2003). These have been used a significant indicators for acid rain connecting it to the mass extinction event.

Figure 6:This figure shows a reconstruction of the globe in the late Permian – early Triassic. It shows the predicted pH of acid rain across the globe. This reconstruction is based on pollen found in Greenland, Sulphur particles found in South Africa which has altered pollen and other terrestrial fossilised flora which was present at the end of the Palaeozoic.Figure Source: Black et al.,2013


Conclusion

The change in environmental conditions throughout the late Permian into the early stages of the Triassic was very drastic. The rapidly changing conditions caused by the formation of the Siberian Traps meant that plants and animals couldn’t evolve rapidly enough to adapt to the conditions entailing there survival. Even though the Siberian Traps erupted over a long period of time and not a sustained period (Pavlov et al., 2011), the atmosphere and oceans would have had some time to recover before the next Siberian pulse. This suggested that acid rain would disappear a short time after the pause in the release of sulphur bearing compounds and then reappear during eruption periods. Some extinction events throughout the Phanerozoic have been in concordance with the eruption of other flood basalts (Wignall., 2001) like the Siberian traps at the P-T boundary. For example the Deccan traps between the Cretaceous and Cenozoic, the Central Atlantic Magmatic Province between the Triassic and Jurassic and the Colombia River basalts for a smaller extinction event in the Cenozoic. Overall, the theory that the Siberian traps caused the extinction towards the end of the Permian is backed up by some strong theories as to what may have caused it and evidence supporting these theories is widely accepted. However other theories submitted by researches still create the controversy over what was the actual cause of the late Permian early Triassic Extinction.


Bibliography


Alvarez, L.W., Alvarez, W., Asaro, F., Michel, H.V., 1980. Extraterrestrial cause for the Cretaceous Tertiary extinction. Science 208, 1095–1108.

Archer, D., Buffett, B., Brovkin, V., 2008. Ocean methane hydrates as a slow tipping point in the global carbon cycle.Proc.Natl.Acad.Sci.

Black, B., Lamarque, J., Shields, C., Elkins-Tanton, L. and Kiehl, J. (2013). Acid rain and ozone depletion from pulsed Siberian Traps magmatism. Geology, 42(1), pp.67-70.

Brown, B., 1997. A Coral bleaching: Causes and consequences, in Proceedings of the 8th International Coral Reef Symposium: 65-74.

Burke, K., and Torsvik, T.H., 2004, Derivation of large igneous provinces of the past 200 million years from long-term heterogeneities in the deep mantle: Earth and Planetary Science Letters, v. 227, p. 531-538.

Campbell, I.H., 2005, large igneous provinces and the mantle plume hypothesis: Elements, v. 1, p. 265-270.

Campbell, I.H., and Griffiths, R.W., 1990, Implications of mantle plume structure for the evolution of flood basalts: Earth and Planetary Science Letters, v. 99, p. 79-93.

Campbell, I.H., Czamanske, G.K., Fedorenko, V.A., Hill, R.I., Stepanov, V. (1992) Synchronism of the Siberian Traps and the Permian-Triassic boundary, Science 258 1760-1763.

Chernysheva, E.A., Kharin, G.S., and Stolbov, N.M. 2005, Basaltic magmatism in Arctic seas related to the Mesozoic activity of the Iceland plume: Petrology, v. 13, p. 289-304.

Dickens, G.R., 2000. Methane oxidation during the Late Palaeocene thermal maximum. Bulletin de la Société Géologique de France 171, 37–49.

Dickens, G.R., O'Neil, J.R., Rea, D.K., Owen, R.M., 1995. Dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of Paleocene. Paleoceanography 10, 965–971.

Heydari, E., Arzani, N. and Hassanzadeh, J. (2009). Reply to comment on “Mantle plume: the invisible serial killer — Application to the Permian–Triassic boundary mass extinction”, 283(1-2), pp.102-105.

Heydari, E., Hassanzadeh, J., 2003. Deev jahi model of the Permian-Triassic boundary mass extinction: a case for gas hydrates as the main cause of biological crisis on Earth. Sedimentary Geology 163, 147-163

Howells, G.P., 1990, Acid rain and acid waters: Chichester, UK, Ellis Horwood, 215 p.

Ivanov, A.V., and Balyshev, S.V., 2005, Mass flux across the lower-upper mantle boundary: vigorous, absent, or limited? in Foulger, G.R., Natland, J.H., Presnall, D.C., and Anderson, D.L., Plates, plumes and paradigms: Geological Society of America Special Paper 388, p. 327-346. Knoll, A. H., Bambach, R. K., Payne, J. L., Pruss, S. & Fischer, W. W. Paleophysiology and the end-Permian mass extinction. Earth Planet. Sci. Lett. 256, 295–313 (2007).


Kvenvolden, K., 1993. Gas hydrates— geological perspective and global change. Reviews of Geophysics 31, 173–187

Labandeira, C.C., Sepkoski, J.J., (1993). "Insect diversity in the fossil record". Science 261 (5119): 310–315.

Archer , D.,2007.Methane hydrate stability and anthropogenic climate change.Bio-geosciences4,521–544.

Maruoka, T., Koeberl, C., Hancox, P., and Reimold, W., 2003, Sulfur geochemistry across a terrestrial Permian-Triassic boundary section in the Karoo Basin, South Africa: Earth and Planetary Science Letters, v. 206, p. 101–117

Morse, J.W., MacKenzie, F.T., 1990. Geochemistry of Sedimentary Carbonates. Elsevier,New York. 707 pp.

Nisbet, E.G., 1990. The end of the ice age. Canadian Journal of Earth Science 27, 148–157.

Pavlov, V.E., Fluteau, F., Veselovskiy, R.V., Fetisova, A.M., and Latyshev, A.V., 2011, Secular geomagnetic variations and volcanic pulses in the Permian-Triassic traps of the Norilsk and Maimecha-Kotui provinces: Izvestiya, Physics of the Solid Earth, v. 47, p. 402–417

Autier, P., Boniol, M., Boyle, P., Daniel, J., Doré J.F., Gandini, S., Green, A.,Newton-Bishop, J., Weinstock, M.A., Westerdahl. J., Secretan. M.B., Walter, S., (2005) Exposure to Artificial UV Radiation and Skin Cancer, World Health Organisation, International Agency for Research on Cancer. pp 14.

Sahney. S., Benton, M.J., (2008). "Recovery from the most profound mass extinction of all time". Proceedings of the Royal Society B 275 (1636): 759–765.

Saunders, A., Reichow, M., (2009). The Siberian Traps and the End-Permian mass extinction: a critical review. Chin. Sci. Bull., 54(1), pp.20-37.

Svensen, H., Planke, S., Polozov, A.G., Schmidbauer, N., Corfu, F., Podladchikov, Y.Y., and Jamtveit, B., 2009, Siberian gas venting and the end-Permian environmental crisis: Earth and Planetary Science Letters, v. 277, p. 490–500.

Wignall, P., 2001. Large igneous provinces and mass extinctions. Earth-Science Reviews 53, 1–33.

Wignall, P., Hallam, A., Anoxia as a cause of the Permian- Triassic extinction - Facies evidence from northern Italy and the western United States, Palaeogeogr. Palaeoclimatol. Palaeoecol. 93 (1992) 21-46.

Wignall, P., Twitchett, R., (1996) Oceanic anoxia and the end Permian mass extinction, Science 272 1155-1158.

http://rspb.royalsocietypublishing.org/content/275/1636/759.full

print out lit report

Documents

Transcript of print out lit report