Paper No. 68-2
Presentation Time: 8:20 AM
MULTI-PROXY REDOX RECONSTRUCTIONS OF EDIACARAN–CAMBRIAN CARBONATE SUCCESSIONS
CHANCHAI, Watsawan, Department of Geosciences, Pennsylvania State University, Deike Building, University Park, PA 16802, SMITH, Emmy, Johns Hopkins UniversityEarth & Planetary Sciences, 3400 N Charles St, Baltimore, MD 21218-2625; Department of Earth and Planetary Sciences, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, NELSON, Lyle, Department of Earth and Planetary Sciences, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, LONSDALE, Mary C., Department of Earth and Planetary Sciences, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, HARDISTY, Dalton, Earth and Environmental Sciences, Michigan State University, East Lansing, MI 48824, BURKE, Janet, Michigan State UniversityEarth and Environmental Sciences, 288 Farm Ln, East Lansing, MI 48824-5600; Earth and Environmental Sciences, Michigan State University, East Lansing, MI 48824 and LAU, Kimberly, Department of Geosciences, Pennsylvania State University, Deike Building, University Park, PA 16801
The Ediacaran–Cambrian (EC) boundary (ca. 541–537 Ma) marks one of the most significant biotic diversifications in Earth’s history. Environmental changes—specifically redox conditions and Earth’s oxygenation—across the EC transition are poorly constrained. Redox change/instability could impact marine ecosystems and the development of animal habitability. We utilize local and global redox proxies (i.e., cerium anomalies (Ce/Ce*), iodine-to-calcium-magnesium ratios (I/(Ca+Mg)), and uranium isotopes (δ
238U)) to investigate marine oxygenation patterns in relation to the BACE (the BAsal Cambrian carbon isotope Excursion) along with other EC correlative markers. We present redox reconstructions from three carbonate successions (southwestern USA: DSF, northern Mexico: SNR, and northern South Africa: OR). A multi-site approach with synchronous local and global redox changes would support interpretations of global environmental perturbations, while spatial variability between study sites may indicate local redox fluctuations or diagenesis.
Carbonate-associated δ238U values in OR are consistently low, supporting globally extensive anoxia in the late Ediacaran. However, local redox conditions vary across study sites. The Ce/Ce* in OR records consistently ambiguous/anoxic seawater, whereas in SNR it is more variable, displaying a shift from locally anoxic to more oxic seawater by the end of the BACE interval. The I/(Ca+Mg) is dominantly low or zero at OR and DSF, suggesting anoxic shallow seawaters and/or diagenetic alteration. Positive Eu anomalies are broadly associated with the BACE, which can reflect several potential controls, including hydrothermal alteration or different ancient seawater composition. The rare earth element (REY) patterns in DSF deviate from modern seawater, indicating that redox proxies in DSF may not reliably track global seawater.
The local redox constraints from this study suggest the paleoenvironment may have experienced local fluctuations. Combined with the global U isotope data, our dataset overall support primarily anoxic seawater during the late Ediacaran. The presence of this anoxic redox state may have influenced biotic turnover during the EC transition and may have played a role in early animal evolution.
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