Seawater Chemistry Measured From Cryogenian NeoProterozoic Australia

Analyses of fluid inclusions in Neoproterozoic marine halite provide oldest measurement of seawater chemistry

Authors:

Spear et al

Abstract:

We analyzed primary fluid inclusions in halite from marine evaporites in the ca. 830 Ma Browne Formation of the Officer Basin in Western Australia using the cryogenic scanning electron microscopy– energy dispersive X-ray spectrometry analysis technique. The concentrations of the major ions, except K+ and possibly SO42–, fall within the range of Phanerozoic seawater. This is the first direct measurement of the composition of mid-Neoproterozoic seawater, and extends present-day knowledge of seawater chemistry by ∼300 m.y. Our estimates suggest that mid-Neoproterozoic marine sulfate concentrations were lower (∼90%) than modern values. By the terminal Neoproterozoic, fluid inclusions in halite and evaporite mineralogy indicate seawater sulfate levels rose significantly, to 50%–80% of modern concentrations, which parallels increases in atmospheric and oceanic oxygen.