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N. MacLeod wrote:

        "In order to accurately estimate the confidence interval using
either the Sadler and Strauss, or the Marshall methods one needs an
accurate method of inferring
the gap size distribution.  Since sediment accumulation rates vary,
lithostratigraphic thickness cannot be used for this purpose.  It may be
that in particular sections or cores sediment accumulation rates are indeed
constant enough to allow distance to be used as a proxy for time, but this
must be demonstrated, not assumed. "

        GOOD POINT.  This very problem has kept Shaw's graphic correlation
method from being the practical tool it should be.  But, don't lose hope
yet.  If we were to pay more close attention to those pesky bentonites,
Milankovitch-type bandings / bedding, and laterally-persistive shell lags
in out sections and cores (not that some of us already have been; but just
more close scrutiny and documentation thereof), then confidence intervals
(over relatively vast distances) can be reduced to 'believable' size.  This
is not always true, but there's probably a lot of potentially useful data
out there which has heretofore simply been overlooked.

        Does anyone out there have good examples of this type of thing? 
For meself, I was able to correlate surface exposures of the Upper
Cretaceous (Coniacian) Fort Hays Limestone Member of the Niobrara Formation
in Colorado & New Mexico during my Master's thesis study over distances
greater than 100 km.  I shad thee not.  The cyclicity of the
limestone-shale bedding and the persistent bentonites (within the shales)
of the Fort Hays Mbr. facilitated this kind of "high resolution"
correlation.  Therefore, when I applied these section to graphic
correlation, the confidence intervals were quite good.  But someone working
out in the middle of a 400 metre thick package of dark shale with almost no
marker beds (as I am with the slightly younger Coniacian-Santonian Wapiabi
Formation for my Ph.D. here in Alberta), there may be no light at the end
of the tunnel!

        Does any of this ring familiar? . . .

        Speak Up!


Regards,

  TOPHER