Testing the Utility of Geochemical Proxies for Interpretation of Reduced Oxygen Sediments Using Body and Trace Fossil Data from Devonian Black Shales

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Geochemical proxies, widely used in Precambrian sedimentary units to infer paleo-oxygen levels, have been well studied and well constrained in modern low oxygen environments. However in modern dysoxic settings, bioturbation, or the reworking of the sediment by infauna, is pervasive with even the slightest amounts of oxygen. Bioturbation has a profound effect on the geochemistry of the sediments, and importantly for widely used redox proxies, results in an increased rate of decomposition of organic matter and oxidation of HB2BS. As a result modern reduced oxygen settings are not an appropriate analog for Precambrian reduced oxygen settings that are devoid of bioturbation. However, Devonian aged sedimentary rocks provide a unique biogeochemical window in which trace and body fossils are widespread and abundant across reduced oxygen depositional settings, allowing for the interpretation of relative paleo-oxygen levels at very high resolution. At the same time, the burrows are shallow and small enough to minimize the dominating infaunal overprints that characterize the geochemical properties of younger sedimentary rocks. This research will test the hypothesis that DOP, TOC, trace metal compositions including Mo, Mn, and Fe, and sulfur isotope data (deltaP34PSBsulfideB) vary in a systematic and predictable manner along a gradient, as identified by the trace and body fossil record in Devonian black shales. The goal of this research is to determine the utility of these proxies as paleo-oxygen indicators in anoxic through dysoxic settings, and thus their applicability for interpretation of paleo-oxygen in the absence of a biological record.