MICROSTRATIGRAPHIC INTERPRETATIONS OF RELATIVE OXYGEN LEVELS FROM DEVONIAN BLACK SHALES OF NEW YORK STATE

High-resolution variation in relative bottom water oxygen levels is recognized from body and trace fossil data preserved in Devonian aged black shales of central and western New York. The ichnological signal is described based on burrow size, relative amount of bioturbation (ichnofabric index), and ichnogeneric diversity. Devonian dysaerobic trace fossils are consistently very small in size with approximately 90% of burrows disrupting the sediment less than 0.5 cm in depth and 94% of burrows less than 0.5 cm in width. The small size of burrows obscures cross cutting relationships typically used in post-Paleozoic strata to interpret relative oxygen levels; however variation in burrow size is correlative with inferred relative oxygen levels. Maximum burrow diameter, based on fundamental physiological oxygen demands of infaunal organisms, combined with relative amount of bioturbation, and body fossil data provide high resolution through the dysaerobic zone. Relative oxygen curves derived from the combined trace fossil and body fossil signal allow the recognition of variation in relative bottom water oxygen levels on a cm scale through multiple units representing a range of dysaerobic conditions. The scale of resolution determined using biological signals is at a finer scale of resolution that produced through several geochemical proxies including several iron proxies, sulfur isotope data and a range of trace metals including Mo and Mn.