Jens:

A few comments on aragonite-water fractionation.

*  The Grossman and Ku (1986) study includes data for mollusks (gastropods
and scaphopods) as well as benthic foraminifera.

* The combined data set (equation 1, p. 66) intersect the Tarutani et al.
(1969) datum for 25°C.

* The use of biotic carbonate to determine a CaCO3 paleotemperature scale
(Epstein et al., 1953) has been confirmed (within reasonable error) by
abiotic precipitation experiments (O'Neil et al., 1969).

We all feel more comfortable when calibrations based on biotic
mineralization are confirmed by laboratory synthesis of minerals. But don't
forget, minerals grown in the laboratory at low temperature are not
necessarily precipitated in equilibrium with their solution.  Kinetic
effects and lack of equilibrium between dissolved carbonate species and
water can play a role.  Thus, agreement between the two experimental
approaches provides mutual support.

Good luck with your work.

Regards,

Ethan


Department of Geology & Geophysics                  (409) 845-0637
Texas A&M University                            fax (409) 845-6162
College Station, TX 77843