TRACE FOSSIL ANALYSIS OF FRASNIAN STRATA EXPOSED AT IRISH GULF, BOSTON, NY

The End Devonian (Frasnian/Famennian) mass extinction is one of five major mass extinctions. The specific cause of this extinction is not well constrained, but it is commonly associated with low oxygen conditions. In order to explore the dynamics of bottom water oxygen conditions leading up to the extinction event, trace fossils are used to estimate oxygen levels at Irish Gulf in North Boston, New York where the Hanover Formation (Frasnian) is well exposed. Trace fossils were described in detail through nearly 35 meters of inter-bedded siltstones and shales. Trace fossils at this locality are identified as Plantolites and Paleophycus are common through the succession, but decrease in abundance approaching the Frasnian/Famennian boundary. Ichnofabric index as a way to quantify relative amount of bioturbation and trace fossil width recorded for more than 800 individual burrows are used to infer relative bottom water oxygen levels. Through this section, variations in trace fossil assemblages support that bottom water oxygen levels fluctuate and ultimately decrease to zero below the Frasnian/Famennian boundary.