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Re: Asteroid impact finally confirmed?

From: Robert.J.Meyerson@uwrf.edu (Rob Meyerson)
 > Under continuous sedimentation models, this is certainly the case. 
 > However, during unusual events (i.e. storms), a great deal of
 > sediment can be deposited in a relatively short amount of time.

True enough.  However that is even *worse* for time resolution, as it
means fossils will tend to be concentrated in a few temporally short
clusters, with gaps between major sedimentation events.

 >  My sed/strat professor once said,
 > "Estimating deposition in sedimentary rocks is dicey at best; a river can
 > deposit an inch of sediment in one century, while a hurricane can deposit
 > several feet of material in one day."

But even in the case of the river, this sedimentation is rather
discontinuous, happening mainly during floods.

 > What needs to be determined is whether the z-coal layer
 > shows evidence of slow deposition or fast deposition.

Even if it were a fast deposition layer, what is the nature and rate
of the surrounding sedimentation?  If there is a hiatus before and/or
after, then we still have low net resolution, since any "event" that
appears to occur across the Z-coal could occur during the surrounding

 >  Does such evidence exist?
Actually, in a sense it does.  The Z-coal is not a single uniform layer.
It is not even clear that it is the *same* layer everywhere it is found.
In some places it splits into two (or more) layers.

Also, coal is derived from peat, which accumulates slowly.

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.