The proposed program of research is designed to improve our understanding of the chemical evolution of seawater during the last 600 m.y. of Earth history. To accomplish this, we plan to extend our analytical data base for the chemical composition of brines in fluid inclusions trapped in halite (NaCl) in marine evaporites. Many of these brines are samples of the solutions from which the salt precipitated. In marine evaporites these brines are largely or entirely derived from seawater; their composition therefore reflects the composition of seawater at the time of salt precipitation. In many instances the evolution of these brines from seawater has been so complicated, that little information regarding the composition of the parent seawater can be gained from the composition of the inclusion fluids. Fortunately, the evolution of the brines in some marine evaporites has been sufficiently simple, so that much of the chemistry of the starting seawater can be reconstructed. The data accumulated to date indicate that the composition of seawater has been surprisingly conservative during the past 600 m.y. At present these data are still fragmentary. We propose to extend them considerably, and to construct a reasonably complete record of the composition of seawater during the Phanerozoic Eon.
