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<p>Submillimeter-scale redox archives in organic-rich mudrocks elucidate dynamic environmental stress shaping early marine animal ecosystems. During the late Cambrian, benthic animals, including trilobites, thrived in intermittently&#xa0;oxygen-deficient (predominantly euxinic) outer shelf environment where the astronomically-tuned Scandinavian Alum Shale was deposited. We present ultrahigh-resolution (0.25 mm) molybdenum and uranium isotope (δ<sup>98</sup>Mo-δ<sup>238</sup>U) and concentration profiles, revealing millennial-scale redox fluctuations that intermittently disrupted bottom-water euxinia. Varying ocean circulation, redox buffer supplies, and/or reduced productivity likely created short-lived aerobic niches for opportunistic benthic animals. Distinct δ<sup>98</sup>Mo-δ<sup>238</sup>U patterns indicate recurrent chemocline shoaling with toxic hydrogen sulfide incursions into surface waters, resembling metal drawdown in modern restricted basins. These fluctuations punctuated a million-year-long global oceanic anoxic event linked to the Steptoean Positive Carbon Isotope Excursion. Following this excursion, local redox conditions oscillated around a globally more oxygenated baseline, coinciding with animal diversifications in Baltica and worldwide. These millennial-scale redox changes underscore the need for higher-resolution geochemical approaches in paleoenvironmental reconstructions.</p>

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Sub-millimeter molybdenum and uranium isotopes track millennial redox events in the Cambrian ocean

  • 期刊论文

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  • 发表日期：

    2025年9月26日

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  • Zhengfu Zhao,
  • Iben W. Hougård,
  • Caineng Zou,
  • Alexander J. Dickson,
  • Shifeng Dai,
  • Zhenhua Jing,
  • Arne T. Nielsen,
  • Pengcheng Ju,
  • Zhaojie Guo,
  • Anirban Basu,
  • Niels H. Schovsbo,
  • Tais W. Dahl

摘要

Submillimeter-scale redox archives in organic-rich mudrocks elucidate dynamic environmental stress shaping early marine animal ecosystems. During the late Cambrian, benthic animals, including trilobites, thrived in intermittently oxygen-deficient (predominantly euxinic) outer shelf environment where the astronomically-tuned Scandinavian Alum Shale was deposited. We present ultrahigh-resolution (0.25 mm) molybdenum and uranium isotope (δ98Mo-δ238U) and concentration profiles, revealing millennial-scale redox fluctuations that intermittently disrupted bottom-water euxinia. Varying ocean circulation, redox buffer supplies, and/or reduced productivity likely created short-lived aerobic niches for opportunistic benthic animals. Distinct δ98Mo-δ238U patterns indicate recurrent chemocline shoaling with toxic hydrogen sulfide incursions into surface waters, resembling metal drawdown in modern restricted basins. These fluctuations punctuated a million-year-long global oceanic anoxic event linked to the Steptoean Positive Carbon Isotope Excursion. Following this excursion, local redox conditions oscillated around a globally more oxygenated baseline, coinciding with animal diversifications in Baltica and worldwide. These millennial-scale redox changes underscore the need for higher-resolution geochemical approaches in paleoenvironmental reconstructions.