RAPID CHANGES IN MAJOR ION CHEMISTRY OF SEAWATER AND THE END-PERMIAN MASS EXTINCTION (Invited Presentation)

The end-Permian mass extinction is interpreted to have involved elevated global temperatures, ocean anoxia, ocean acidification, a disturbed sulfur cycle, and ocean euxinia. The same period also contains one of the largest accumulations of evaporites in the geologic record, including saline giants in the US, England, the Netherlands, Germany, Poland, Ukraine, and Russia. Here we show from fluid inclusions in marine halites that there was a major shift in seawater chemistry involving SO₄and Ca which coincides with other global perturbations in seawater chemistry at the end-Permian and perhaps the mass extinction.

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.