Re: conodont apatite

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Hi Cindy and Clive-

  For sometime now, our group at Wisconsin has been concerned with
radiogenic isotopes in phosphate and while our interest hasn't led to many
results yet, we are making progress.

  For example, this year we completed a study of "pristine" fish material
from the Cretaceous and Eocene of the Arctic Ocean with Sr isotopes.
Unfortunately, our results indicate that even "pristine" fish material is
too receptive to even mild diagenesis to give us the results we thought that
we should get.  We do get good Sr and Nd in younger forams, but this is well
established by many others.

  Our conodont work has been more productive and we are in the process of
Sr studies that will probably result in better stuff.  I didn't realize that
Chris Barnes was interested.  I could have talked with him at GSA about you
(Cindy) and your work.  We also have a gradiose idea on checking on Ian
Dalizel's proposed Antarctic to northern hemisphere plate movement based on
Nd in conodonts, but we are having a hard time getting the right conodonts
for this.

  I would definitely like to stay in touch with the isotopes in phosphate
sub-section of paleonet.

D. L. Clark
In message Tue, 15 Nov 1994 12:52:19 -0700,
  cwright@sol.UVic.CA (Cindy Wright)  writes:

> Hello Clive:
> I am familiar with the work that Elderfield has done, along with
> the studies with Aldridge. My understanding of the differences between
> fish and conodont apatite has to do with the degree of "porousity" (not
> the right word but good enough) and how "opened" and "closed" the systems
> are.  Conodont apatite is a relatively closed system and crystal packing
> is tight.  Once the REE (and for my purposes the Nd) gets incorporated
> into the lattice (in the Ca sites) it becomes stable against further
> diagenesis.  That last statement should be taken with a grain of
> salt....perhaps mild degrees of diagenesis is better said.  Fish bits
> (mostly scales) are relatively open and porous and interact/exchange with
> their surroundings and are more prone to changes due to diagenic affects.
> However, in defense of fish, I still think there is excellent potential
> for their use in geochemical studies.  I believe that if samples of
> ichthyloliths were prestine and showed no signs of contamination, they
> would still give excellent proxy signatures.  As for conodonts, for this
> study we have a range of CAI values and have gone as high as CAI 5 to
> test how far you can push diagenesis before it disrupts the values and
> signatures.  We are still waiting for the results to come in.  We do the
> work at Harvard University at with Stein Jacobsen.  I spent quite a few
> months there but I had to leave before all the samples were through the
> mass spec.  Hopefully, the data will not be too much longer and I can
> find out what the real story is.
> I'm interested in your work as well....let me know what is going on with
> you.
>
>
> Ciao
> Cindy
>
>
> ----------------------------------
> Cindy Wright
> School of Earth and Ocean Sciences
> University of Victoria
>