Re: "Meteor theory gets rocky ride from dinosaur expert"

[Phil Bigelow <bigelowp@juno.com>]

On Thu, 26 May 2005 11:33:47 -0400 (EDT) John Bois <jbois@umd5.umd.edu>
writes:
> 
> 
> On Wed, 25 May 2005, Tommy Tyrberg wrote:
> > The "Event bed" is presumably
> > tsunami deposits, probably deposited in a few hours rather than 
> 300,000
> > (presumably extremely stormy) years.
> 
> Would a tsunami wave _transport_ materials?  How far could a 
> tsunami
> transport sediments?


That is a *characteristic* sedimentological feature of tsunami deposits. 
The trough of the tsunami wave form literally rips up the sea floor as
soon as the wave reaches shallow water.  The detached seafloor then gets
entrained in the top of the waveform and carried ashore.  Then the "back
slosh" occurs.  All of the water flows back out to sea with great
velocity, the current being tens of times more forceful than the most
powerful river current on earth.  Anything in the water gets redeposited
on the sea floor.

If you watch the videos of the water from the Indian Ocean tsunami, you
will notice how muddy the water that reached inland was.  That mud was
mostly sea floor mud.  A smaller portion of the mud in the water came
from inland sources.

Onshore, the Indian Ocean tsunami reached a maximum height of 30-40 feet.
 The primary wave from the Chicxulub tsunami is estimated to have been
anywhere from 1/2 kilometer high to one kilometer high.  Assuming that
the wave strikes perpendicular to the shore, then along the coastline of
the Western Interior Seaway (WIS), the primary wave from Chicxulub could
have penetrated 20+ kilometers inland before flowing back to the sea at
high velocity.  But if you look at a paleogeographic map of the WIS, you
will note that the wave would strike most of the Interior coastline at a
small (glancing) angle.  This geographic alignment may have moderated the
horrific effects of the tsunami within the seaway.

I'm aware of the Brazos River tsunami sections and other sections in
Texas (and have actually visited them in person), but I am interested in
any Western Interior Seaway K-T boundary sections further north, such as
in North Dakota or South Dakota.  If there are recognized sections, is
there any evidence in the seafloor mud for a tsunami?

<pb>
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