Geological Society of America

68 D21. Laying the Foundation for the Modern Earth System at the Neoproterozoic-Paleozoic Transition

Monday, 10 October 2022
8:00 AM - 12:00 PM
Mile High Ballroom 4C

MULTI-PROXY REDOX RECONSTRUCTIONS OF EDIACARAN–CAMBRIAN CARBONATE SUCCESSIONS

Paper number: 68-3
Program: Technical Sessions
Time: 8:20 AM – 8:35 AM

Authors

Watsawan Chanchai Presenting Author
Pennsylvania State University, University Park, PA
Emmy Smith
Johns Hopkins UniversityEarth & Planetary Sciences, Baltimore, MD
Emmy Smith
Johns Hopkins University, Baltimore, MD
Lyle Nelson
Johns Hopkins University, Baltimore, MD
Mary C. Lonsdale
Johns Hopkins University, Baltimore, MD
Dalton Hardisty
Michigan State University, East Lansing, MI
Janet Burke
Michigan State UniversityEarth and Environmental Sciences, East Lansing, MI
Janet Burke
Michigan State University, East Lansing, MI
Kimberly Lau
Pennsylvania State University, University Park, PA

Abstract

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 (δ²³⁸U)) 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.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-378570

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