Uranium-series dating of molluscs from uplifted Holocene beaches in the Persian Gulf

The study of coastal deformation and sea-level history calls for radiometric ages on shorelines older than the past 20,000 yr, the period for which reliable 14C ages can be obtained. Uranium-series disequilibrium methods have yielded the requisite ages for reef coral ranging from 5,000 to 300,000 yr but previously have proved unreliable for most molluscs, the major source of uncertainty being postmortem migration of uranium and its daughter radionuclides into and out of the shells. In the present study the 230Th/234U dating method1was applied to molluscs from Holocene beaches in the Persian Gulf which had been removed from marine influence by seismic uplift. Two specimens selected for comparative dating with the electron spin resonance (ESR) method yielded ages of the correct order of magnitude. Excellent agreement was obtained between 14C and 230Th/234U ages after detrital effects were corrected for by reference to modern comparative material for both calcitic and aragonitic specimens, which suggests that uranium-series dating of pre-Holocene molluscs may give reliable results provided the depositional history of the shoreline is well documented.