Re: Geological periods

["Mike Styzen Shelf Expl, 588-4308" <mstyzen@shellus.com>]

Steve Jackson asks:

>Is there that much dispute, or has there been a systematic reorganization
>of the periods, or what?
As the guru (by default) of geologic time for Shell in the U.S. I feel
I am somewhat qualified to answer this.
No, there isn't much debate really there are just periodic updates and
different schools of thought.  There are actually folks who make a
career of tweaking geologic ages. 
A new calibration for the geologic time scale is about to be released
(I'm anxiously awaiting my copy) it is:
Geochronology, Time Scales and Global Stratigraphic Correlation, By
Berggren et.al. 1995.  It is a special publication of SEPM.
Another popular one is by Harland et. al. 1990 called A Geologic time
Scale.  That one was published by the Cambridge University Press.
Major revisions come out every few years.  Polite authors refer to the
published time scale they are using.  Those who don't are really kind
of waving useless numbers in front of you.
Hope this helps
Mike
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