Th230/U234age of the Pleistocene corals and oolites of Florida

Determination of the activity ratio Th230/U234 in corals from the Pleistocene Key Largo limestone, a fossil coral reef, leads to the conclusion that the reef-forming corals lived about 130,000 years ago in a sea that stood about 10 meters higher than today. Similar ages for the Pleistocene Miami oolite suggest that this formation represents oolitic sand deposited contemporaneously with the coral reef. The age calculation is based on the assumption that living corals extract no thorium from sea water and thus any Th230 found in fossils results from the decay of U234. Measurements made on Recent corals from the same area generally confirm this assumption.