Thallium Isotopes Suggest the Global Deep Ocean Did Not Approach Modern Oxygenation During Cambrian Age 3 Metazoan Radiation

IF 3.4 2区 地球科学 Q2 BIOLOGY
Geobiology Pub Date : 2025-08-06 DOI:10.1111/gbi.70028
Jean N. R. Clemente, Haifeng Fan, Chadlin M. Ostrander, Hongjie Zhang, Hanjie Wen, Erik A. Sperling, Sune G. Nielsen
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引用次数: 0

Abstract

The geologically rapid appearance of most extant animal groups in the Cambrian fossil record is often linked to enhanced ocean oxygenation. However, conflicting reconstructions of the Cambrian redox landscape make it difficult to determine the extent of ocean oxygenation during this significant biotic event, particularly regarding the redox state of the global deep ocean. In this study, we present authigenic thallium isotope compositions (ε205Tlauth) for two shale sequences from South China (Qingjiang and Weng'an) that span the Cambrian Stage 2–3 boundary to the appearance of the Qingjiang biota, approximately 521–518 million years ago (Ma), a timeframe that chronicles a particularly rapid interval of metazoan diversification and radiation in the broader Cambrian explosion. If this event occurred amid modern-like extents of global ocean oxygenation, we would expect a significant increase in the global extent of seafloor Mn-oxide burial to drive lower ε205Tlauth values near the modern open-ocean composition of −6‱. Instead, we observe broadly stable ε205Tlauth values of around −3 to −4‱ in both studied sections. The lack of any significant Tl isotope shifts in our dataset argues against a short-term global ocean oxygenation event and suggests the global deep ocean was not characterized by modern extents of oxygenation 521–518 Ma. We reinterpret contemporaneous near-modern Mo and U isotope compositions to signal a relatively minor increase in marine oxygenation, likely limited to the continental shelves. However, ε205Tlauth lower than the average isotopic composition of approximately −2‱ in Ediacaran shales suggests a shift to comparatively better-oxygenated conditions sometime between ~555 Ma and 521 Ma. If diversification at this time was linked to increased ocean oxygen levels, these changes were likely more dominant in the relatively shallow-water settings of continental shelves most densely populated by Cambrian animals and were incapable of dramatically altering seawater Tl isotope mass balance through seafloor Mn-oxide burial.

铊同位素表明全球深海在寒武纪第三次后生动物辐射期间没有接近现代氧合
寒武纪化石记录中大多数现存动物群的地质快速出现通常与海洋氧合增强有关。然而,寒武纪氧化还原景观的相互矛盾的重建使得确定这一重大生物事件期间海洋氧化的程度变得困难,特别是关于全球深海的氧化还原状态。在本研究中,我们获得了中国南方(清江和旺安)两个页岩序列的自生钍同位素组成(ε205Tlauth),它们跨越了寒武纪2-3阶段的边界,直到清江生物群的出现,大约在5.21 - 5.18亿年前(Ma),这个时间范围记录了寒武纪大爆发中一个特别快速的后生动物多样化和辐射间隔。如果这一事件发生在类似现代的全球海洋氧化作用范围内,我们预计海底锰氧化物埋藏的全球范围将显著增加,从而推动−6‰现代公海组成附近的ε205Tlauth值降低。相反,我们在两个研究剖面中观察到大致稳定的ε205Tlauth值在−3至−4‰左右。我们的数据集中缺乏任何显著的Tl同位素变化,这表明全球海洋氧合事件不是短期的,并表明全球深海不具有521-518 Ma现代氧合程度的特征。我们重新解释了同时期近现代Mo和U同位素组成,表明海洋氧合作用相对较小的增加,可能仅限于大陆架。然而,ε205Tlauth低于埃迪卡拉系页岩中约−2‰的平均同位素组成,表明在~555 ~ 521 Ma之间的某个时间向相对较好的氧合条件转变。如果这一时期的多样化与海洋氧含量的增加有关,那么这些变化可能在寒武纪动物最密集的大陆架相对浅水环境中更为明显,并且无法通过海底mn -氧化物埋藏显著改变海水Tl同位素的质量平衡。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Geobiology
Geobiology 生物-地球科学综合
CiteScore
6.80
自引率
5.40%
发文量
56
审稿时长
3 months
期刊介绍: The field of geobiology explores the relationship between life and the Earth''s physical and chemical environment. Geobiology, launched in 2003, aims to provide a natural home for geobiological research, allowing the cross-fertilization of critical ideas, and promoting cooperation and advancement in this emerging field. We also aim to provide you with a forum for the rapid publication of your results in an international journal of high standing. We are particularly interested in papers crossing disciplines and containing both geological and biological elements, emphasizing the co-evolutionary interactions between life and its physical environment over geological time. Geobiology invites submission of high-quality articles in the following areas: Origins and evolution of life Co-evolution of the atmosphere, hydrosphere and biosphere The sedimentary rock record and geobiology of critical intervals Paleobiology and evolutionary ecology Biogeochemistry and global elemental cycles Microbe-mineral interactions Biomarkers Molecular ecology and phylogenetics.
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