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Refining Geochemical Proxies

In fine-grained sedimentary rocks, the most complete understanding of a rock’s history is accessed through a combined sedimentological and geochemical approach. In this endeavor, geologists know that ‘the present is the key to the past.’ Unfortunately for the development of geochemical proxies useful in deep-water shale systems, most geochemists have not had access to much of the ‘present.’ This is mainly due to the simple fact that geologists and oceanographers inhabit different academic worlds and different departments. Thus a ‘dirty secret’ is that many geochemical proxies in common use throughout industry and academia were often calibrated decades ago on a relatively small number of samples, sometimes with incomplete environmental data. Many proxies also rely on a single threshold value rather than more appropriate confidence intervals. Through links to many oceanographic institutions—including SPODDS long-standing association with MBARI—we are fortunate to have access to a large library of modern sediment samples that are directly associated with high-quality in-situ oceanographic data. Many of these samples are from modern upwelling margins (Oxygen Minimum Zones) or other hypoxic/anoxic areas—modern analogues of the sediments that form source rocks and unconventional targets. We are currently analyzing this sediment library using a variety of methods to better refine interpretations from existing proxies and to develop new proxies. By analyzing these data with machine learning algorithms we expect this project to provide the new standard in geochemical proxies and ultimately a richer understanding of ancient deep-water systems.