dating

[James Rubenstone]

julia_webb27 at hotmail.com wrote:

>Could anyone give me any ideas for age dating corals other than by 
>radiocarbon (C14) dating.


U-series disequilibrium dating, using 234U-230Th and (less 
extensively) 235U-231Pa, gives excellent results for corals up to 
several hundred thousands years old. Measuring the isotopes by mass 
spectometry can give very precise ages (0.5% or better). One 
advantage over radiocarbon is that U-series gives an absolute 
(calendar) age, without the uncertainties inherent in radiocarbon 
(reservoir corrections, variable production rate, variable surface 
ocean inventory). The main problem is possible open-system behavior 
of U and Th in fossil corals, particularly those that have seen 
subaerial exposure. There are many examples of high quality coral 
dates in the literature, from labs at Caltech, Minnesota, ANU, 
Marseilles and Lamont-Doherty (and several others as well).
Jim Rubenstone
-- 
Dr. James Rubenstone                   email:  jimr at ldeo.columbia.edu
Lamont-Doherty Earth Observatory          voice:  845-365-8579
Columbia University                       fax:  845-365-8154
Palisades, NY  10964                      
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