Ordovician Seawater Composition: Evidence from Fluid Inclusions in Halite

composition of seawater, however Ordovician halite is very rare. Ordovician is a key time during the evolution history. However there are no Ordovician seawater data reported except from the data from the halite from the boundary of Ordovician and Silurian. Ca and Mg concentration were determined in brines from large secondary inclusions, located on periphery of the chevron. In brine from the first inclusion the Са content was 87.9 and 75.8 g/l (81.9 g/l in average). In this study, we report the major compositions from middle Ordovician halite in China. Ordovician fluid inclusions give the direct evidence that the Ordovician seawater is Ca-rich seawater of calcite sea, with the Na–K–Mg–Ca–Cl type seawater composition (Kovalevich et al., 1998; Lowenstein et al., 2001), while late-stage potash salts in marine evaporates is the KCl types (Hardie, 1996).