SPATIAL REDOX PROXY VARIABILITY IN UPPER EDIACARAN CARBONATE STRATA FROM THE ZAVKHAN TERRANE, SOUTHWEST MONGOLIA

The terminal Ediacaran was an important interval in the evolutionary history of animals. The role of marine oxygenation in driving biotic change over this interval is debated. Constraining the redox conditions of shallow marine settings can improve our understanding of the environmental circumstances under which early animals evolved. Local redox conditions from a single basin are often interpreted as representative of regional or global redox conditions; however, geochemical redox proxy records may more strongly reflect facies variations, depositional settings, or diagenetic alteration. Despite a limited understanding of how local controls can impact redox proxy values, few studies have focused on proxy variability within a basin. In this study, we use the cerium anomaly (Ce/Ce*) to study carbonate rocks from the Zuun-Arts Formation across a depth gradient in the Zavkhan terrane, southwest Mongolia. The depth gradient is used to better understand the spatial heterogeneity of this geochemical proxy and marine oxygenation levels in this basin. The Zavkhan terrane is an ideal site to study lateral variability in local redox conditions because of its thick, well-exposed, carbonate-rich strata, which preserves continuous lateral facies changes within the basin. Carbonates from the upper Ediacaran Zuun-Arts Formation, collected from three sections, were deposited proximally to distally from the shoreline and can be generally correlated using lithostratigraphy, sequence stratigraphy, and carbon isotope chemostratigraphy. In this study, we use differences in Ce/Ce* values between localities to determine if these records track regional or site-specific influences. Our work sheds light on how local redox conditions may relate to depositional environments, as well as assesses the robustness of the Ce/Ce* proxy laterally across a carbonate platform. These results allow us to develop a more nuanced view of ocean redox spatial patterns, which ultimately is relevant to understanding conditions prior to the animal radiation in the Cambrian Period.