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Oxygen Isotopes



->
-> Today's New York Times has a story on research by William Showers and
-> Barrick of North Carolina State University. They say that isotope rat
-> oxygen from phosphate in tyrannosaur bones indicates that the critter
-> warm-blooded.

I have conducted several stable isotope studies (S, O, H) in cooperation
with isotope geochemists in as diverse matrices as granitoids and sour
gas - every study gave a scatter diagram.  Stable Isotope geochemists
(the isotopes are stable - not necessarily the geochemists!) can read
wonderful things into scatter data.  I've given up trying to make
sense out of their binary scatter plots and two point correlations.
When the results show a uniform isotopic signature, could the answer be
that the chemistry homogenized over geologic time?  Or is the analytical
data such that the sampling/analytical errors wipe out any correlations?

My own work on rare earths and trace elements in bituminous coals and
underclays (Int. Jour. of Coal Geology, v.19, 1991, pp219-251)
concluded that:
"Individual seams have diverse REE distribution patterns that reflect
 the depositional and diagenetic mineralogy, or reveal enrichment at
seam margins by organic complexing or fossil apatite uptake."
.."Rare earth element partitioning between organic and mineral phases
or between coals and associated strata differs over the coalfield,
reflecting the combined effects of sedimentation, water chemistry,
ion exchange and chelation."

Specifically the study of fossils such as fish teeth in coal strata
indicates chemical interaction dependent on the oxic or anoxic
environment.  For example, rare earths (REE) tend to concentrate
to an order of magnitude in the fossil bone, absorbed from the
surrounding water. Uptake is by apatite recrystallization during
organic decay. Why would the oxygen isotope signature not be affected
if other chemistry shows considerable exchange reactions? To
extrapolate from fossil chemistry to paleobiology is too big a stretch
for me.

I know it is the sign of a poor critique that I didn't bother to go
to the original source and check its validity - but life is too short
to spend it on "stable isotopes".  Just because they use fancy machinery
to pop out high-tech numbers on some samples doesn't mean it is good
science.  Do they really understand the geologic setting of their
samples, i.e. the geochemical facies of deposition and diagenesis over
time?  Sorry....but count me skeptical in Oakville, Ontario!

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    (^)              Dr. Dieter Birk, P.Geol., Oakville, Ontario, Canada
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