Abstract
Fanale and Schaeffer (1965) determined He U ages of corals and other aragonitic fossils and found that the results generally agreed with independent age estimates. As a more extensive and rigorous test of the reliability of He U ages of fossil corals, I have determined He U ages on forty-five independently dated Cenozoic corals. Uranium and thorium isotope compositions and Rn 222 retentivities were also determined as consistency checks. The results indicate that reliable ages are obtained when the following consistency tests are met and the following corrections are made: 1. (1) corals are unrecrystallized aragonite. 2. (2) Th 232 is absent, indicating that the samples are free of contaminating detritus. 3. (3) U 234 U 238 and Th 230 U 234 ratios are concordant with the He/U age. 4. (4) Rn 223 leakage is less than 5 per cent. 5. (5) a correction is made for inherited helium. 6. (6) a correction is made for alpha particles ‘shot out’ from the coral walls during U and U daughter decay.
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