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约束。然而，在现代缺氧环境中，生物扰动或动物对沉积物的改造，即使是最少量的氧气也很普遍。生物扰动对沉积物的地球化学具有深远的影响，对广泛使用的氧化还原指标至关重要，它会导致有机物分解和HB2BS氧化速率的增加。因此，现代的还原氧环境不能作为缺乏生物扰动的前寒武纪还原氧环境的适当类比。然而，泥盆纪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，痕迹和体化石在低氧沉积环境中广泛而丰富，可以以非常高的分辨率解释相对的古氧水平。与此同时，这些洞穴又浅又小，可以最大限度地减少表征较年轻沉积岩地球化学特性的主要动物叠印。本研究将通过泥盆纪黑色页岩的痕量和体化石记录，验证DOP、TOC、微量金属组成（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的假设。本研究的目的是确定这些代用物在缺氧或缺氧环境下作为古氧指标的效用，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.