RATE AND MAGNITUDE OF OXYGEN STRESS LEADING INTO AND OUT OF THE KELLWASSER EVENT IN NEW YORK STATE

The Kellwasser event is associated with a major biotic turnover at the Frasnian Famennian Boundary. This event is one of several extinction pulses that in combination result in not only massive losses in marine diversity, but perhaps more significantly, major ecological restructuring. The ultimate causal mechanism of this event is still debated, however oxygen stress in the bottom waters likely had a significant role. This study evaluates bottom water conditions leading into and out of this event using trace fossils to infer relative rate and magnitude of oxygen stress. Three localities in western New York are examined. Abundant, vertical pyritized burrows are preserved up to a thin black shale interval overlain by bioturbated gray shales just below the base of the Kellwasser event. The relative amount, size, ichno-generic classification and preservation type (pyrite infilling) of burrows through this interval support a rapid decrease in bottom water oxygen conditions and then a shift to dysoxic conditions with a more gradual decrease in bottom water oxygen levels leading into the Kellwasser Event. Large (~1 cm burrow width) Thalassinoides type burrows piping into the top of the Kellwasser black shale support a rapid shift back to fully oxygenated conditions. Interpretations of inchnofabrics associated with this event support dynamic bottom water oxygen conditions through this interval.