Re: Dino/Birds? was Mesozoic snow?

[Aidan Karley <aidan_karley@yahoo.co.uk>]

In article <007601c572b0$15055a10$a83cb23e@IPC>, David Marjanovic wrote:
> The age of that crater is very poorly resolved. However, there are _several_ 
> craters that could fit the Triassic-Jurassic boundary. For example, there's 
> a twin crater in France (one of them called Rochechouart, I forgot the 
> other), and a single one in Ukraine (aw... how to transcribe it... let's try 
> Obolon'), and one in the USA (Red... Red... something... I'll have to find 
> the paper again... Nature 1997, I think).
>
       See Nature v392 p0131 PLANETARY-SCIENCE Crater row ; Nature v392 p0171 
Evidence for a late Triassic multiple impact event on Earth. Abstract:

Evidence for the collision of fragmented comets or asteroids with some of the 
larger (jovian) planets and their moons is now well established following the 
dramatic impact of the disrupted comet Shoemaker?Levy 9 with Jupiter in 1994 
(ref. 1). Collisions by fragmented objects result in multiple impacts that can 
lead to the formation of linear crater chains, or catenae, on planetary 
surfaces2. 
Here we present evidence for a multiple impact event that occurred on Earth. 
Five terrestrial impact structures have been found to possess comparable ages 
(,214Myr), coincident with the Norian stage of the Triassic period. These 
craters are Rochechouart (France),Manicouagan and Saint Martin (Canada), 
Obolon? (Ukraine) and Red Wing (USA). When these impact structures are 
plotted on a tectonic reconstruction of the North American and Eurasian 
plates for 214Myr before present, the three largest structures (Rochechouart, 
Manicouagan and Saint Martin) are co-latitudinal at 22.88 (within 1.28, ,110 
km), and span 43.58 of palaeolongitude. These structures may thus represent 
the remains of a crater chain at least 4,462 km long. The Obolon? and Red Wing 
craters, on the other hand, lie on great circles of identical declination with 
Rochechouart and Saint Martin, respectively. We therefore suggest that the five 
impact structures were formed at the same time (within hours) during a multiple 
impact event caused by a fragmented comet or asteroid colliding with Earth. 
cRATERS (BLOODY cAPS lOCK KEY!)
Crater name            Present         Reconstructed
                       Lat.    Long.   Lat.    Long.
Rochechouart (R)       45.83   0.93    23.5    16.6
Manicouagan  (M)       51.38   -68.70  22.1    -7.0
Saint Martin (SM)      51.78   -98.53  22.7    -26.9
Obolon'      (O)       49.50   32.92   38.6    34.9
Red Wing     (RW)      47.60   -103.55 19.1    -31.1

       Interestingly, the next paper in my collection from then is 
Nature v392 p0173 Fission track ages of stone tools and fossils on the east 
Indonesian island of Flores. Another candidate for catastrophic extinction.

-- 
 Aidan Karley,
 Aberdeen, Scotland,
 Location: 57°10' N,  02°09'  W (sub-tropical Aberdeen), 0.021233
 Written at Thu, 16 Jun 2005 22:44 +0100



        
        
                
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