DETERMINATION OF OXYGEN-ISOTOPE FRACTIONATION BETWEEN WATER AND PHOSPHATE FROM LIVING LINGULIDS - POTENTIAL APPLICATION TO PALEOENVIRONMENTAL STUDIES

Lingulids are inarticulate brachiopods, with phosphatic shells, which live exclusively in marine waters. Their distribution is generally res tricted to the continental shelf, within the 40 degrees belt from temp erate to equatorial areas. They show a range of morphological, physiol ogical, and behavioral features that have remained remarkably constant since the Cambrian. The oxygen isotope fractionation between water an d phosphate from living lingulids was determined as a tool to investig ate the temperature and/or salinity of past coastal seawater. Oxygen i sotope measurements were performed according to the silver phosphate m ethod on a collection of lingulids coming from well-known and varied m arine environments. A global delta(18)O variation of 3.5 parts per tho usand was found for these lingulids which proves their good sensitivit y to environmental factors namely the oxygen isotope composition and t he temperature of seawater. Oceanographic data provided average temper ature and salinity values in the living sites of the studied specimens . Least squares treatment of the data gave the following fractionation equation: T(degrees 15.3-4.20+/-0.71[delta(18)O(PO4)-delta(18)O(H2O)] ; which is similar to the equations determined by Longinelli and Nuti (1973a) and Kolodny et al. (1983) for other phosphate-bearing inverteb rates and fishes. All these results suggest that a unique equation des cribes the phosphate-water fractionation of many marine organisms exce pt for mammals.