ps418

I've written a review essay on the Permian-Triassic extinction. I basically wrote it from notes for my own future reference, but I'll probably post it on my web site, so criticisms are appreciated. Its not quite finished, but I got tired of focusing on it and want to move on to something else.

<a href="http://www.geocities.com/earthhistory/permo.htm" target="_blank">The Permian-Triassic Mass Extinction</a>

I know we dont have many (any?) young-earthers on the forum right now, but I'd love to see an attempt to explain this data within a young earth, flood geology framework.

Patrick

[ January 12, 2002: Message edited by: ps418 ]</p>

CodeMason

Marvellous! Keep up the exceptional work!

faded_Glory

Patrick,

Your review is a good concise overview of the data, and I just keep being surprised that as a non-professional you manage to lay your hands on all of those references.

Whay I feel is missing, though, is a synopsis of the various explanations offered for the observations. As it is now, it hangs a bit in the air... like a murder mystery with the last page missing

Apart from that, a handy summary and I will save the link to your page!

fG

PS: YouBetcha has emailed me that he will post as soon as he can, but mainly during weekdays and not in the weekends.

ps418

Possible solutions to the Permian murder mystery are something that I will add. From what I've seen so far, I think that a chain of events initiated by volcanic processes is the most likely candidate. Whatever the solution, it must account for the evidence for oceanic anoxia, the preferential devestation of benthic marine organisms, and the carbon isotope anomoly.

Some evidence has offerred for bolide impact, but its all equivocal, and nothing like the abundant evidence for impact at the K-T boundary.

Regarding sources, over the past couple of months, I've been getting to know the UofL library very well. I can get just about everything I need there. Although I cant check out books, since Im not a student, I can photocopy what I need, or print out papers from online journals. I love it. I wish I had started using it sooner.

theyeti

I remember reading something not long ago about evidence of changing ocean currents causing a massive release of CO2 from the ocean bottom being the likely culprit. Does this idea carry any good weight? Or do I have the wrong mass extinction?

theyeti

ps418

Yes, very much so. Only it wasnt CO2 released directly, it was methane gas hydrate, which was oxidized to CO2 in the atmosphere. And it was probably released as a result of the warming of the late Permian oceans due to CO2 input from mass volcanism. I'll give you a fuller explanation of how all this fits together in a couple of days.

Release of gas hydrates has been pretty well established as occuring at the end-Paleocene. Gas hydrates is, as far as I know, the only resevoir of isotopically light carbon that could cause the major carbon isotope shift at the P-Tr.

Patrick

theyeti

Thanks for the clarification Patrick. Now as I remember it, what I read was about a pre-existing warming trend that caused the shift in oceanic currents -- it was framed as an important lesson to learn for our own times. I can't remember exactly where I read it; I think it was a pseudo-layman mag like Discover. Anyway, I very much look forward to your elaboration.

theyeti

ps418

I haven't forgot about solving the murder mystery just yet! I decided to compate the P-Tr extinction to other extinction events, and I'm finding that the Early Jurassic (Toarcian) and the Late Paleocene extinctions seem to be good, small-scale analogues for the P-Tr. As I said above, Whatever the solution, it must account for the evidence for oceanic anoxia, the preferential devestation of benthic marine organisms, and the carbon isotope anomaly.

I have several more papers I want to read before I post something on the web page, but in the meantime, I want to make a preliminary comparison between the P-Tr and the late Paleocene extinction. The late Paleocene events show how each of these three features can be explained as consequences of massive methane release. Methane release causes warming, which causes anoxia, which preferentially kills off benthic organisms.

The Late Paleocene Thermal Maximum as a Possible Analogue for the P-Tr

The LPTM can in many ways be seen as a smaller-scale version of the P-Tr extinction.

1. The LPTM, like the P-Tr, is marked by a rapid, major negative carbon isotope excursion (CIE) in oceanic carbonates. The illustration below shows carbon isotope curves from three widely spaced ODP cores spanning the LPTM. Dickens (2001) writes:

This latest Paleocene thermal maximum, or LPTM, coincided with profound global environmental change, including an extraordinary negative carbon isotope ( del 13C ) excursion (e.g., Thomas and Shackleton, 1996).  At least 25 different Paleogene stable isotope records, including those constructed from bulk and foraminiferal carbonate of all oceans, and terrestrial carbonate and organic matter from multiple continents, now show part of a –2.5 to –3 ‰ anomaly in del 13C across the LPTM (Gas hydrates and methane blasts in the sedimentary record, presented at SEPM Diamond Jubilee). 

The LPTM, like the P-Tr (MaCleod et al., 2000), is also marked in terrestrial sections by a major negative CIE. The P-Tr curve from the Karoo basin, for instance, was constructed using the tusks of the mammal-like reptiles Dicynodon and Lystrosaurus, and using paleosol carbonate nodules.

As demonstrated by Koch et al. (1992), the same phenomena occurs at the LPTM. Here the negative CIE on land is documented in paleosol carbonates and tooth enamal apatite of the herbivorous mammal Phenacodus from the Bighorn Basin, Wyoming. Pretty cool!

The LPTM, like the P-Tr, is characterized by major warming. In the case of the P-Tr, this is inferred on the basis of oxygen isotopes (shift to lower 18O/16O, Holser et al. 1991), fossil evidence (extinction of polar floras, uniform vertebrate communities in high and low latitudes, Hallam and Wignall, 1997), and petrologic evidence (for instance, intensely leached paleosols at the P-Tr boundary in Antarctica, Retallack 1999). It is estimated that equatorial environments warmed by ~6C, and the poles may have warmed even more.

In the case of of the LPTM, warming is inferred on the basis of oxygen isotopes, which are well-documented from many sections. The latest Paleocene Thermal Maximum (LPTM) saw the most abrupt warming event ever documented. It occured as a rapid warming spike about 55My, lasting &gt;10k years, superimposed on a gradual warming trend which began in the mid Paleocene and continued into the Eocene. Katz et al (1999) notes that "over a 10,000- to 20,000-year interval about 55.5 million years ago, Earth's climate and oceans warmed as deep-ocean and high-latitude surface water temperatures soared by 4° to 8°C." Warming is also inferred on the basis of a peculiar shift in vertebrate size. Many of the mammalian species known before and after the LPTM are represented at the LPTM by unusually small representatives with wide distribution, which can easily be explained as a result of transient temperature spike (Clyde and Gingerich, 1998). However, there is not a major extinction of vertebrates at this time -- in fact, there is a major diversification.

The LPTM, like the P-Tr, is characterized by preferential extinction of benthic marine organisms. About 40-50% of benthic forams become extinction at the LPTM, coincident with the del13C shift. Few planktonic forms become extinction however. Major faunal shifts seen in other marine fauna as well (e.g. Steineck et al, 2000; Crouch, 2001).

The LPTM, like the P-Tr, is associated with the development of low-oxygen conditions (Spiejer et al., 1997), although in the case of the LPTM these conditions are shorter-lasting and much less severe than the P-Tr 'superanoxic' event.

Oceanic anoxia is promoted by warming in two ways. First, the solubility of O2 in water decreases with increasing water temperature. Second, warming can promote anoxia if the equator-to-pole temperature gradient is weaked, since this would weaken oceanic circulation (Hallam and Wignall, 1997, p. 141). As Hallam and Wignall (1997) note, most researchers implicate low-oxygen as the kill mechanism for the benthic forams:

"Taxa tolerant of stagnant environments, such as Praeglobobulima, Pleurostomella, Bulimina, lagenids, and agglutinated forms, become the main faunal component immediately after the extinction event in New Zealand and Hokkiado, suggesting that oxygen deficiency was the cause of the extinction, a view concurred with by Thomas (1990) and Kennett and Stott (1991), on the grounds that the proportion of infaunal species increased. This is a view shared by Speijer (1994), who studied the extinction and recovery patterns in benthic formainiferal paleocommunities on the northern margins of Africa and in Israel."(p. 225).

The LPTM has been explained as a result of methane release. Massive amounts of methane hydrates (1x10^19 - 2x10^19g) exist in continental slope sediments today, at depths greater than ~400m. Methane release can explain the rapid warming, as both methane and CO2 are greenhouse gasses - (once methane begins to dissociate, the ocean-atmosphere system warms even more, releasing even more methane, and a positive feedback is initiated), the preferential benthic extinction (due to anoxia in lower waters), and the rapid, worldwide shift in carbon istope ratios (methane is very 'light' and quickly diffusible). Katz et al. (1999) writes:

The "LPTM hydrate dissociation hypothesis" can be summarized as follows: Similar to the present day, vast quantities of CH4 greatly enriched in 12C (13C ~ 60 per mil) were stored as gas hydrate in the upper few hundred meters of continental slope sediments before the LPTM. Long-term global warming during the late Paleocene pushed the ocean-atmosphere system past a critical threshold, causing warm surface waters to sink and intermediate to deep ocean temperatures to rise by ~4° to 8°C. This warming propagated into the sediments, converting once solid CH4 hydrates into free gas bubbles.

The gaseous CH4 reacted with dissolved O2 [likely via bacterial activity ] to produce 12C- enriched CO2, adding carbon to all reservoirs of the global exogenic carbon cycle and substantially shoaling the depth of carbonate dissolution in the ocean. Higher bottom water temperature, lower dissolved O2, changes in surface water productivity, and more corrosive waters killed many of the deep-sea species. On land, higher partial pressure of CO2 and elevated temperatures quickly opened high-latitude migration routes for the widespread dispersal of mammals.

Major decreases in 13C records of planktonic foraminifera or bulk sediment carbonate (dominated by tests of surface-dwelling organisms) at Site 1051 and other marine locations indicate a large decrease in the 13C of surface water CO2. A decrease of 4 per mil in the 13C of terrestrial carbonate and organic carbon also has been documented. Thus, the prominent CIE across the LPTM occurred in shallow marine, deep marine, and terrestrial reservoirs, indicating massive carbon addition to the global exogenic carbon cycle, as opposed to carbon redistribution within this system.

Methane addition is probably the only way to account for the rapid and major carbon isotope excursion. CO2 from volcanic gasses (about -5) would not produce such a large shift. The oxidation of buried sedimentary organic matter (-20 to -25) could produce the shift, but not only the relatively short timescale involved with the LPTM. Calcuations show that 6500-8400 gigatons of such matter would have to be oxidized and returned to the ocean-atmosphere system within less than a few hundred thousand years or less to produce a global carbon isotopic shift of ~(-3) (Erwin, 1994, pp. 200-204).
Methane carbon, on the other hand, is isotopically very 'light,' meaning that has a very low carbon C13/12 ratio. It has a delta 13C value of -60. The other explanatory advantage is that, unlike the buried organic carbon resevoir, the methane resevoir can be thought of as a 'capacitor; that can be rapidly discharged into the ocean-atmosphere system. Converted to the gaseous state, the methane rapidly diffuses into the ocean and the atmosphere, is oxidized by methanotropic bacteria to form light CO2 and water [CH4+2O2-&gt;2H20+CO2]. The light CO2 is mixed with the oceans and atmosphere and incorporated into carbonates and organic matter, thus producing the observed carbon isotopic shift.



Behl, R.J., and Kennett, J.P., 1996, Brief interstadial events in the Santa Barbara Basin, NE Pacific, during the last 60 kyr, Nature, 379, 243-246.
Clyde, W. C. and Gingerich, P. D. 1998. Mammalian community response to the latest Paleocene thermal maximum: An isotaphonomic study in the northern Bighorn Basin, Wyoming. Geology 26:1011-1014.
Crouch, E.M. 2001. Global dinoflagellate event associated with the late Paleocene thermal maximum. Geology: Vol. 29, No. 4, pp. 315–318.
Katz et al., 1999. The Source and Fate of Massive Carbon Input During the Latest Paleocene Thermal Maximum. Science 286, pp. 1531 - 1533.
Koch, P.L., Zachos, J.C., and Gingerich, P.D., 1992. Correlation between isotope records in marine and continental carbon reservoirs near the Palaeocene/Eocene boundary. Nature, 358:319-322.
MacLeod, K G. Smith, R M H. Koch, P L. Ward, P D., 2000. Timing of mammal-like reptile extinctions across the Permian-Triassic boundary in South Africa. Geology 28, p227-230.
Speijer, R.P., Schmitz, B. & van der Zwaan, G.J. (1997): Benthic foraminiferal extinction and repopulation in response to latest Paleocene Tethyan anoxia. Geology 25, 683-686
Steineck, P.L., and Thomas, E. 1996. The latest Paleocene crisis in the deep sea: Ostracode succession at Maud Rise, Southern Ocean. Geology: Vol. 24, No. 7, pp. 583–586.

More later!

Patrick

[ January 19, 2002: Message edited by: ps418 ]</p>

faded_Glory

Farting cows?

fG

ps418

I resisted the urge to refer to farting oceans.

BTW, methane release from the oceans is occurring today, at fairly low levels. See <a href="http://www.science-frontiers.com/sf100/sf100g09.htm" target="_blank">this,</a> <a href="http://www.state.me.us/doc/nrimc/mgs/sites-1997/november.htm" target="_blank">this</a>and <a href="http://news.bbc.co.uk/hi/english/sci/tech/newsid_1047000/1047249.stm" target="_blank">this.</a>