[meteorite-list] YD impacts: Something happened, but what and when?

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Tue, 15 Dec 2009 12:03:27 -0800 (PST)
Message-ID: <212911.86623.qm_at_web36908.mail.mud.yahoo.com>

Hi Paul, Darren, all -

A couple of points are in order here. To show you how underfunded impact research is, for several decades Chichxulub was thought to be the only impact associated with the KT boundary, and now we have Shiva.

AS regards the hypothesized YD impactors, we are not talking about KT sized impactors. Traces are in the range of parts per million to parts per billion, and then in a very very thing layer. (Consider the searches at Tunguska.)

Further, the 14C dates from this period are known to be "funky", often by several thousand years, making the search harder, and making sediment core sample dating very very difficult.

And since the impacts were not KT sized, you can expect wide regional variations. We know mammoth survived on Wrangel Island until very late.

There's anothef factor here, which is that a small impact in the right place can trigger extreme effects, say one around glacial Lake Agassiz.

Aside from passing on some of the peoples' memories of these impacts:
http://forum.palanth.com/index.php/topic,1093.0.html
and noting the quarry abandonment, there's not much more I can add o this one. (But if any list member wants a copy of the Trempealeau petroglyph, email me.)

Tomorrow's AGU session promises to be interesting and "lively".

E.P. Grondine
Man and Impact in the Americas




      
Received on Tue 15 Dec 2009 03:03:27 PM PST