Oxygen-Isotope Ratios in Phosphate from Fossil Marine Organisms

Well-preserved fossil marine organisms generally yield very positive δ 18 (PO 4 3- ) values which are considered to result from relatively good preservation of the original oxygen-isotope composition of phosphatic material deposited under isotopic equilibrium conditions in oceanic water whose O 18 :O 16 ratio was more positive than that of modern oceans.