RAPID CHANGES IN MAJOR ION CHEMISTRY OF SEAWATER AND THE END-PERMIAN MASS EXTINCTION (Invited Presentation)
Permian seawater, determined from the chemical compositions of fluid inclusions in marine halites from the North American Permian Basin (Kansas, Texas and New Mexico) and the Southern Permian Basin (Central Europe) shares chemical characteristics with modern seawater, including SO4 > Ca at the point of gypsum precipitation and evolution into a Mg-Na-K-SO4-Cl brine. An abrupt shift to Ca-rich fluid inclusions occurs in the Changhsingian Rustler Formation of New Mexico over 1.5 meter of stratigraphic section and in the Changhsingian Zechstein Cycle Na2 and basal Na3 Cycle of Poland. Such an abrupt shift in the major ion chemistry of seawater in two basins at about the same time is unusual because the residence times of SO4 and Ca in seawater are 10 m.y. and 1 m.y., respectively. Changes in the major ion chemistry of seawater are well known to occur over periods of 106 to 107 years, so the end-Permian seawater chemistry shift indicates some catastrophic process. The shift from sulfate-rich to calcium-rich brines coincides with a marked drop in δ34S in Zechstein and Rustler anhydrite, which suggests a link between changes in the major ion chemistry of seawater and perturbations in the sulfur cycle. These changes are interpreted to have been caused by overturn of anoxic sulfidic deep-waters from the Panthalassan superocean during the Changhsingian stage which may have coincided with the end-Permian mass extinction.