David Tyler wrote:
"I used to use this bentonite as evidence for correlation.
However, a paper in _Geology_ (I think it was last year) provided
geochemical evidence against the US / Europe link. I can't
supply a reference now, but I'll look it up."
GM replied:
"I would be interested in any refutation of this connection that
I missed."
The reference is:
Hayes, J.T., Melson, W.G., and Kunk, M.J. 1995, "Composition of
biotite phenocrysts in Ordovician tephras cast doubt on the
proposed trans-Atlantic correlation of the Millbrig K-bentonite
(United States) and the Kinnekulle K-bentonite (Sweden)",
Geology, 23(9), 847-850.
The abstract commences: "Biotite phenocryst compositions in three
thick, widespread Ordovician K-bentonites, the Deicke and
Millbrig from Big Ridge, Alabama, and the Kinnekulle from Mossen,
Vestergotland, Sweden, fall into three distinct groups, and so
the proposed intercontinental correlation of the Millbrig and the
Kinnekulle is suspect..."
GM continued:
"But let's start with something of a less grand scale. Below
you state that bentonites can be used to correlate across wide
areas. Would you agree that the Deicke bentonite can serve as a
regional time correlation point throughout the eastern US?"
Yes I would, in principle.
GM:
"In this way we have a marker which acts as a chronomarker
connecting up several basins on a regional scale. If you accept
that, then here are the continent wide implications. By means
of this and other, overlapping bentonites I can construct a
relative chronological chart through the basis of North America.
It would look like this:
[snipped illustration]
Would you agree with this on an isolated continent? That
chronostratigraphy can be established across a continent?"
Yes, in principle. It is still necessary to document the
correlation and to publish, so that others can examine it
critically.
GM:
"... Tertiary rocks have several traits besides fossils which
mark them as different. ...."
[snip]
Sure. In many ways, this parallels the point I am making. Your
comments identify ways in which correlations can be established.
The main reason why I am taking the position that I have in this
thread is that I'm sensing that the Geological Column concept
needs to be defended/explained in a more rigorous and systematic
way.
Best wishes,
*** From David J. Tyler, CDT Department, Hollings Faculty,
Manchester Metropolitan University, UK.
Telephone: 0161-247-2636 ***