Age determinations of fossil corals using ²³⁰Th/²³⁴Th and ²³⁰Th/²²⁷Th

Abstract

The growth toward radioactive equilibrium of ²³⁰Th with ²³⁸U and of ²³¹Pa with ²³⁵U has successfully been used to determine the ages of fossil corals. The chemical procedures employed in these measurements can be simplified dramatically if only thorium isotopes need be measured. Our method uses ²³⁴Th as a measure of ²³⁸U and uses ²²⁷Th as a measure of ²³¹Pa to calculate the age of the coral. In addition to reducing the length of time required for an analysis by more than one half, our method does not rely on spikes but on a calibration standard that is counted to determine relative alpha and beta counting efficiencies. Ages of fossil corals from Jamaica correlate with the 120,000- to 135,000-yr-high sea stand reported by other workers.