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

地球化学指标在前寒武纪沉积单元中被广泛用于推断古氧水平，在现代低氧环境中得到了很好的研究和很好的约束。然而，在现代缺氧环境中，生物扰动，或由动物对沉积物的重新加工，即使是最少量的氧气也是无处不在的。生物扰动对沉积物的地球化学有深远的影响，对于广泛使用的氧化还原代用品来说，生物扰动导致有机质分解和HB2BS氧化的速度加快。因此，现代还原氧环境并不适合于没有生物扰动的前寒武纪还原氧环境。然而，泥盆纪古老的沉积岩提供了一个独特的生物地球化学窗口，在这个窗口中，遗迹和遗体化石在还原的氧气沉积环境中广泛而丰富，从而能够以非常高的分辨率解释相对古氧水平。与此同时，洞穴很浅，足够小，可以最大限度地减少主要的动物群叠加，这些叠加是年轻沉积岩的地球化学性质的特征。这项研究将检验这样的假设，即DOP、TOC、痕量金属组成(包括Mo、Mn和Fe)和硫同位素数据(DeltaP34PSBsulfideB)沿梯度以系统和可预测的方式变化，正如泥盆纪黑色页岩中的遗迹和遗体化石记录所证实的那样。这项研究的目的是确定这些代用品在缺氧环境中作为古氧指示剂的实用性，从而确定它们在没有生物记录的情况下解释古氧的适用性。

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.