The following comments on sea level curves derive from my participation
in Exxon's effort to build a new sequence stratigraphic standard (see
SEPM Special Publication 60, Sequence Stratigraphy of European
Basins):
1) the Haq, et al. curve is a model and some parts of it were better than
others.
2) the Haq timescale is definitely out-of-date, so that the curve itself
would have to be squeezed or stretched like an accordion to a new
timescale, even assuming the sequence strat model underlying it is
unchanged. (see below)
3) a sea level curve derived from a sequence model is several levels of
abstraction removed from real data. First, you take a sequence strat
model (at a minimum, the position of sequence boundaries and maximum
flooding surfaces). You then create a coastal onlap model to capture
relative rises and falls. This coastal onlap model is averaged over
several sites. Then you can fit an estimate of sea level to the coastal
onlap model assuming some external controls on the limits to the sea
level fluctuations (for example, maximum level of the bathtub ring in the
Cretaceous highstand). This shows the uncertainty inherent in sea
level curves. It also implies the enormous work required to build
curves with a reasonable precision.
4) Algeo and Seslavinsky (1995) is an interesting (and different)
approach, but doesn't begin to have the resolution of the Haq, et al.
curve. For the upper Paleozoic at least, Charlie and June Ross have
been following a sequence approach of course.
The outcome of SEPM 60 is a sequence stratigraphic standard (i.e.,
sequence boundaries and maximum flooding surfaces in places where ages
are highly constrained, so the Haq sequence model is out-of-date
too. SEPM 60's sequences are a standard, but not a globally
documented sequence model.
Obviously, Haq, et al. and SEPM 60 were financed in large part by
industry. To make a revision of the sea level curve would require a lot
of careful age control (i.e., biostratigraphy), among other things.
Industry interest in supporting this has disappeared. So no matter
how interesting and useful a eustatic curve would be, progress seems
stymied.
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without being superseded.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
Truly yours,
Martin Farley
Geology, Old Main 213
Univ. of North Carolina at Pembroke
Pembroke, NC 28372
(910) 521-6478
mbfarley@sigmaxi.org