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Palaeoceanographic controls on spatial redox distribution over the Yangtze Platform during the Ediacaran-Cambrian transition

Och, LM; Cremonese, L; Shields-Zhou, GA; Poulton, SW; Struck, U; Ling, H; Li, D; ... Zhu, M; + view all (2016) Palaeoceanographic controls on spatial redox distribution over the Yangtze Platform during the Ediacaran-Cambrian transition. Sedimentology , 63 (2) pp. 378-410. 10.1111/sed.12220. Green open access

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Abstract

The Ediacaran–Cambrian interval was an eventful transitional period, when dynamic interactions between the biosphere and its physical environment allowed the Earth System to cross into a new state, characterized by the presence of metazoans, more equable climates and more expansive oxygenation of the oceans. Due to the retreat of widespread sulphidic conditions, redox-sensitive trace-metals could accumulate to a greater extent in ‘black shales’ deposited in localized anoxic/euxinic environments, such as highly productive ocean margins. This study investigates the concentrations of the redox-sensitive trace-metals molybdenum and vanadium in organic-rich sedimentary rocks from seven sections of the Yangtze Platform, slope and basin. Iron speciation analyses were carried out in order to distinguish oxic, anoxic-ferruginous and anoxic-sulphidic settings, while sulphur and nitrogen isotope ratios were measured to gain insight into sulphate and nitrate availability, respectively, in the context of changing redox conditions. The data herein demonstrate an overall increase in redox-sensitive trace-metal contents in black shales across the Ediacaran–Cambrian transition, but with marked temporal and spatial variability. Euxinia is evident in South China before 551 Ma in the Ediacaran, and again in the early Cambrian. However, some time-equivalent sections are not enriched in redox-sensitive trace-metals, and also exhibit contrasting S-isotope and N-isotope systematics. A more complex configuration of the Yangtze Platform, for example with vast intra-shelf basins, together with changing (generally rising) eustatic sea-level may account for this variability. In this regard, it is proposed that a mid-depth sulphidic wedge, caused by nutrient upwelling over the south-east platform margins, migrated over time (but generally landward), leading to spatially variable redox conditions determined by sea-level, currents and bathymetric constraints. The changing extents of anoxia and euxinia appear to have limited the distribution of emerging Ediacaran and Cambrian ecosystems.

Type: Article
Title: Palaeoceanographic controls on spatial redox distribution over the Yangtze Platform during the Ediacaran-Cambrian transition
Open access status: An open access version is available from UCL Discovery
DOI: 10.1111/sed.12220
Publisher version: http://dx.doi.org/10.1111/sed.12220
Language: English
Additional information: © 2015 The Authors. Sedimentology © 2015 International Association of Sedimentologists. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Keywords: Cambrian; Ediacaran; iron speciation; Neoproterozoic; nitrogen isotopes; redox-sensitive trace-metals; sulphide isotopes
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1472612
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