vital effect and genetics

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	I'm doing a little paper in my geochem class and I'm looking for
resources.
	My topic is the vital effect and it's possible use in determining
paleospecies.  The basic premise is that the vital effect is a biological
influence on the isotopic composition of shells and tests.  Suppose you had a
bunch of forams (or something) and you wanted to know how many species are
represented.  They all look about the same, so physical characteristics won't
help much.  So, you turn to isotopes.  Given that these forams were living in
the same region at the same time, then any isotopic differences must be genetic.
You can eliminate such other factors that can influence the isotopic composition
as diet (they look the same, they probably lived that same), temperature, water,
and climate.  That leaves the vital effect.  Since the vital effect is
biological, it must have genetic roots.  Therefore, different but closely
related species ought to have subtle differences in their vital effect.  The
question is, is this difference detectable?
	I've found five references, but I'd like more.  I'll provide a list of
what I've got if you want.
	Thanks for your help.

Eric SImpson
Dept. of Geosciences
Texas Tech University
Box 1053
Lubbock, TX  79409-1053
(806)-742-3132
76653,1410@compuserve.com