Dear Isotopers,

T.C. Onstott mentions an interesting subject.  The question of isotopic
exchange between organic H and ambient water has been visited in many studies.
There is an article in the latest issue of Geochimica et Cosmochimica Acta that
gives a fairly comprehensive digest in terms of a Figure and cites many
relevant papers:

Schimmelmann, A., Michael D. Lewan, and Robert P. Wintsch (1999) D/H isotope
ratios of kerogen, bitumen, oil, and water in hydrous pyrolysis of source rocks
containing kerogen types I, II, IIS, and III. Geochimica et Cosmochimica Acta
63, 3751-3766.

In a nutshell, I think it is safe to conclude that at low temperature in
absence of chemical reactions there is very little exchange between organic
carbon-bound hydrogen in lipidic material and ambient water, probably even over
geologic time. Exceptions may be certain aromatic C-H sites and C-H next to
enol-groups.  And of course almost all organic hydrogen linked to O, N, S, etc.
exchanges rapidly.

          Have a Merry Christmas and a Successful New Year,          Arndt
--
Arndt Schimmelmann, Ph.D.
Department of Geological Sciences
Geology 129, Indiana University
1005 East 10th Street
Bloomington, IN 47405-1405
Ph   (812) 855-7645
home (812) 339-3708
FAX  (812) 855-7961
e-mail  [log in to unmask]