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Re: Chicxulub impact effects



Tommy,
Could you re-confirm that page number for me?  Is their paper only one
page long (abstract)?

Thanks,

<pb>
--

On Mon, 20 Sep 2004 21:33:57 +0200 Tommy Tyrberg
<tommy.tyrberg@norrkoping.mail.telia.com> writes:
> An interesting paper I don't think have been mentioned on the DML 
> before:
> 
> Durda, D. D. &  Kring, D. A. 2004. Ignition threshold for 
> impact-generated 
> fires. Journal of Geophysical Research 109 E08004.
> 
> They study three energy levels 51 kWm-2 for 2 minutes (ignites wood 
> under 
> any circumstances), 20 kWm-2 for 20 minutes (ignites wood in the 
> presence 
> of an ignition source) and 28 kWm-2 for 1 minute (ignites foliage, 
> rotten 
> wood and dry litter, which would provide an ignition source). 
> Calculates 
> that the threshold for continent-wide and world-wide ignition of 
> woody 
> material equates to c. 10^15 and 10^16 kilograms of ejecta 
> respectively, 
> which implies crater diameters of c. 85 and 135 km respectively.
> 
> This  means that Chicxulub is the only Phanerozoic crater certainly 
> in the 
> "worldwide" category, though the Bedout Structure would probably 
> also 
> qualify if it is really an impact crater. Definitely 
> "continent-wide" 
> impacts would include at least Manicougan, Popigai and Chesapeake 
> Bay.
> 
> An interesting feature is that in most cases the effects in the 
> antipodal 
> area are worse than near the impact (the ejecta landing there have 
> much 
> more energy). Anybody know where the antipodal points of Popigai and 
> 
> Chesapeake Bay were in the Eocene?
> 
> India and environs must have been very badly hit by Chicxulub. Might 
> 
> explain why there are no land vertebrates with definitely Mesozoic 
> antecedents on Madagascar, while New Zealand which was almost 
> completely 
> flooded in the Oligocene still has two (Sphenodon and Leiopelma).
> 
> They do not address the direct effect on animals, but even the 
> lowest 
> studied energy level would generate temperatures close to 500 
> degrees 
> centigrade on an exposed surface and certainly kill any unprotected 
> animal 
> quite quickly. Incidentally this implies that there is probably a 
> rather 
> wide range of irradiation that would kill unprotected animals but 
> not 
> ignite tree trunks, so treeholes might work as protection for small 
> animals.
> Neither is there any discussion of the effect of heavy cloud or snow 
> which 
> would certainly give some protection (in the case of snow probably a 
> lot 
> because of its very high albedo and thermal inertia).
> 
> Tommy Tyrberg
> 
> 
> 



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