Uranium-Series Ages of Corals and Coexisting Phosphate Deposits on Pelsaert Reef Complex, Houtman-Abrolhos Islands, Western Australia

Abstract

An unusually well-defined association between guano-derived phosphate rock (apatite) and coral carbonates on Pelsaert Island has provided an opportunity to test uranium-series dating methods as applied to insular phosphorites. The phosphate deposit, which is bracketed by late Pleistocene and Holocene corals with ²³⁰Th/²³⁴U ages of 120,000 and 4700 yr B.P., respectively, has ²³⁰Th/²³⁴U ages ranging from 85,000 to 112,000 yr B.P. The mutually consistent results suggest that phosphate deposition commenced soon after the peak of the last interglaciation and has been largely controlled by sea-level fluctuations and probably other factors associated with late Quaternary climate in this area.