218-5 Characterizing Local Marine Redox Conditions Through The Great Ordovician Biodiversification Event From A Deep Water Facies Of Western Laurentia

Abstract:

The Ordovician Period (487–443Ma) marks a significant interval in Earth history that was characterized by great ecological, environmental, and climatic changes. The Great Ordovician Biodiversification Event (GOBE) represents a series of global shifts within marine ecosystems, including significant increases in biodiversity and ecosystem complexity. Coeval changes in the climate and marine ecosystem imply that changing paleo-environmental conditions likely played a role in driving the biodiversification event. An increase in atmospheric and oceanic oxygen levels is hypothesized to be one of the main drivers of these changes. Therefore, gaining a better understanding of changing Ordovician marine water column conditions, particularly during the GOBE interval, can potentially provide new insights into how environmental factors may have facilitated this major shift in the marine biosphere.

To further understand the role oxygenation played in the GOBE, detailed studies that characterize marine bottom water conditions at different paleogeographic localities that exhibit various lithologies are needed. Notably, little work has focused on characterizing marine redox conditions in deeper water environments during this interval. In this study, multiple paleoredox proxies are used to investigate local, and potentially global, marine redox conditions in the Early through Late Ordovician (Floain–Sandbian stages) from organic-rich shales of the Phi Kappa Formation at the Little Fall Creek and Trail Creek Road sections in central Idaho, USA. Specifically, we utilize the iron speciation proxy to identify anoxic and euxinic bottom water conditions. Additionally, a suite of trace metal concentrations (Mn, U, V, and Mo) will be used to assess the local redox conditions, particularly early anoxic to sulfidic conditions. These geochemical data will help provide new insights into the marine redox conditions from continental slope/basinal settings of the western Laurentian margin in the Panthalassic ocean during this important interval of Earth history.

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