Re: The P-Tr meteorite

[Mickey Rowe <rowe@psych.ucsb.edu>]

An unusual glitch I don't quite understand held this back.  Sorry it
took me a few days to catch it, Emma...

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Date: Mon, 24 Sep 2001 18:36:14 -0400
To: dinosaur@usc.edu
From: "Emma C. Rainforth" <emmar@ldeo.columbia.edu>
Subject: Re: The P-Tr meteorite
Cc: jeff.hecht@sff.net, david.marjanovic@gmx.at

>At 11:06 PM +0200 9/24/01, David Marjanovic wrote:
>>
>>"Kunio Kaiho of Tohoku University, Japan, and his colleagues have found
>>evidence in southern China that a massive impact converted huge amounts of
>>solid sulphur into sulphur-rich gases.
>>         The released sulphur could have consumed 20-40 per cent of the
>>atmosphere's oxygen, and generated enough acid rain to raise the acidity of
>>the ocean's surface waters temporarily to that of lemon juice. Ocean life
>>would have been pickled."
>>
>Very incredible. I wrote a short for New Scientist about it, but I 
>never could get a good explanation of how the proposed mechanism 
>worked or how they deduced such a tremendous release of sulfur from 
>the anomalous concentration of sulfur isotopes they saw. Thus I'm 
>skeptical they have "the" answer. -- Jeff Hecht

Initial comments off the top of my head (emma playing devil's advocate!):

1. It has also been proposed (hmmm, don't have the citations offhand) 
that the PT extinction was volcanism-induced: it's contemporaneous 
with the Siberian Traps (continental flood basalt province) which 
formed during an abortive continental rifting event. Interestingly 
the bedrock thru which the volcanics/intruseives passed are basically 
a huge thick evaporite sequence. Thus, volcanism+evaps = massive 
release of light-S and other nasties. The CFB was extruded RAPIDLY 
and thus the critters would not have had time to do anything (like 
evolve...) in order to counter the environmental effects...which 
might include a pickle-juice ocean, I suppose. Granted, I haven't 
checked the orig. refs for this to see their estimate of how much 
light-S could have been released as a consequence of 
volcanism-thru-evaps.....

2. Kaiho et al say that the bolide struck oceanic crust; the light-S 
probably comes from mantle rocks; youch, the bolide punched right 
thru the crust. IMHO it may have fortuitously (for science, not the 
critters) have hit the continental rift basins instead (where the 
evaps were...)

3. They state that due to a lack of other sections, the S excursion 
may be local. Which could rule out a bolide - as the CFB/evap section 
is reasonably "local" to the Meishan section.....so these evaps 
melting as a result of volcanism (okay, or impact-induced!) could 
also cause the excursion.

4. Sampling: they sample the event-PTB rather than the 
biostrat-PTB......you'd think they would have done both, and 
everything inbetween, at the same high-resolution.....

Anyhow, it comes down to: is the light-S excursion a result of 
volcanism, or impact (or both!!!!). If volcanism, one may expect the 
excursion to last longer (eg closer to the entire duration of the 
volcanism, appx. 600 ky); however the sediment layer containing the 
anomalies is only 2 cm thick and probably doesn't represent 600 ky; 
therefore the seds deposited during volcanism are not homogeneous, 
making comparisons of isotope compositions difficult (as S, and Sr, 
will be taken up differently by different lithologies). Could be hard 
to test this....

Alternatively, need some alternative physical correlation technique 
to get relative ages of: onset of volcanism; the isotopic-excursion 
layer; the PTB; magstrat may be possible but there are no ocean-floor 
reference sections and very few sections on present-day continents. 
If volcanism began after the excursion layer obviously it can not 
have caused the excursion.

Problems with a volcanic-only hypothesis: would volcanism have caused 
Ni-enrichment? Can they explain the metamorphosed grains in this 
layer? (And what about these grains anyway......are they actually 
shock-metamorphosed, impact-origin types, or 
volcanic-metamorphosed....and are there any tektites anywhere? I 
suppose if it WAS an oceanic impact, the impact site has long been 
subducted, and possibly the tektites may have not gotten as far as 
falling-out on land, and also been subducted.....if Kaiho et al are 
lucky...:-)

Okay, they were my random thoughts for the day :-)
emma

- -- 

Emma C. Rainforth
Geosciences Rm. 206E
Lamont-Doherty Earth Observatory
Rt. 9W
Palisades
NY 10964-8000
ph. (845) 365-8621
fax (801) 838-4126
emmar@ldeo.columbia.edu
http://www.ldeo.columbia.edu/~emmar/research/indexr.html
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