APPLICATION OF TRACE FOSSILS, TRACE METALS, AND LIPID BIOMARKERS TOWARD AN UNDERSTANDING OF UPPER KELLWASSER BLACK SHALE DEPOSITION, NEW YORK STATE

Understanding the depositional processes leading to black shales is central to many paleoenvironmental studies because these sedimentary horizons, commonly interpreted to represent anoxic environments, are sites of exceptional fossil preservation, oil and gas production, and are commonly correlated with extinction events. The pervasiveness of black shale preservation in association with the Late Devonian biocrises has widely implicated marine anoxia in the permanent ecological turnover that occurred in the Famennian, but neither the extinction mechanisms nor the mechanisms of black shale deposition at this time are well-understood. It is clear, however, that depositional conditions were not homogeneously anoxic. Multidisciplinary research, joining ichnology, sedimentology, inorganic and organic geochemistry, is the best course for resolving the complexity of black shale deposition in the Late Devonian.

In this study, bottom water oxygen conditions are interpreted from four Upper Kellwasser (UK) black shale localities in western New York State, using inorganic and organic geochemical proxies and trace fossils at high resolution (mm-cm scale) to constrain relative oxygen levels and identify signals of anoxia and euxinia in the Devonian Appalachian Basin. Mo concentrations are suggestive of suboxic conditions and perhaps intermittent euxinia, indicating that the UK black shale preserves reduced oxygen bottom water conditions. These levels of enrichment are muted, however, especially as compared to other Phanerozoic euxinic black shale intervals. Lipid biomarker patterns are typical for Paleozoic marine rocks, indicating that the biomarker molecules in the extracted bitumens are syndepositional and not significantly affected by contamination. Significantly, no appreciable amount of aromatic carotenoid biomarkers diagnostic for green sulfur bacteria has been detected as yet at any of the Appalachian localities. These data are consistent with a local paleoredox model without a persistently shallow sulfidic zone. The trace fossil record through the UK black shale interval complements the geochemical proxies; the presence of horizons with abundant bioturbation between well-laminated intervals provides biological support for intermittently oxygenated bottom waters.