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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.
The peace of God be with you.