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Kevin,
Thank
you very much; that confirms my impression that a lot has been learned since
1987. It recalls to me a course in structural geology, taught in the deep
geologic past: Plate tectonics was still being debated, and one of the
professors used wonderfully sharp photos on glass plates that
were projected by a Magic Lantern. The other professor was
mathematically inclined, and, after covering the blackboard with equations
for an hour, would then tell us, "But none of these models work in practice." I
would hit the mental "erase" button, not appreciating that these imperfect
models were still the best available at the time -- and would be on the exam,
but that's another story and I caught up later.
So the
Haq curve is imperfect and we have to use it anyway while working to adjust it
locally. I can live with that.
Cheers,
Andy
Andrew
K. Rindsberg
Geological Survey of Alabama
Andy,
Only very few portions of the Haq et al sea level
curve may be considered accurate. Many lines of evidence released over
the past 15 years confidently point out the numerous flaws in the development
of the Haq curve. The reality is, teasing out a global eustatic curve
from the plethora of basins around the world at any time increment requires
tremendous data support that is lacking for most portions of the Haq
curve. Eustasy is often overprinted by tectonic or climatic signals (or
combinations thereof). Further, the biostratigraphic dating of many of
the eustatic cycles is not sufficiently refined to correlate events globally
at the time scales that Haq et al claim.
Those who still employ the Haq curve may cite the
few portions that are backed by excellent biostratigraphic control as well as
comprehensive regional geologic data from each basin contributing a particular
cycle. But be warned, most cycles lack a global comprehensive data set
to back a eustatic mechanism for sea level changes within a particular
basin.
Finally, to answer your question. A sea
level curve of the approximate frequency of the Haq curve (1 to 10 Ma) doesn't
exist.
Hope that helps.
Kevin Gostlin
University of Toronto
----- Original Message -----
Sent: Tuesday, March 23, 2004 12:20
PM
Subject: paleonet Global sea-level
curve
PaleoFolks,
Which global
sea-level curve is now considered to be standard? A web search yields a
welter of information that seems to cluster around brief and local
modifications to the sea-level curve of Haq (1987), but it's hard to believe
that anything could last so long without being superseded. After all, in
1987, I lived in another city working at another job before I was
superseded. But maybe the Haq curve is more
lasting.
Andrew K.
Rindsberg
Geological
Survey of Alabama
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