Chicxulub impact effects

[Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>]

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