Redox condition of the late Neoproterozoic pelagic deep ocean: 57Fe Mössbauer analyses of pelagic mudstones in the Ediacaran accretionary complex, Wales, UK

Tomohiko Sato, Yusuke Sawaki, Hisashi Asanuma, Wataru Fujisaki, Yoshihiro Okada, Shigenori Maruyama, Yukio Isozaki, Katsumi Shozugawa, Motoyuki Matsuo, Brian F. Windley

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    9 Citations (Scopus)

    Abstract

    We report geological and geochemical analysis of Neoproterozoic pelagic deep-sea mudstones in an accretionary complex in Lleyn, Wales, UK. Ocean plate stratigraphy at Porth Felen, NW Lleyn, consists of mid-ocean ridge basalt (>4 m), bedded dolostone (2 m), black mudstone (5 m), hemipelagic siliceous mudstone (1 m,) and turbiditic sandstone (15 m), in ascending order. The absence of terrigenous clastics confirms that the black and siliceous mudstone was deposited in a pelagic deep-sea. Based on the youngest U-Pb age (564 Ma) of detrital zircons separated from overlying sandstone, the deep-sea black mudstone was deposited in the late Ediacaran. The 5 m-thick black mudstone contains the following distinctive lithologies: (i) black mudstone with thin pyritic layers (0.8 m), (ii) alternation of black mudstone and gray/dark gray siliceous mudstone (2.4 m), (iii) thinly-laminated dark gray shale (1 m), and (iv) black mudstone with thin pyritic layers (1 m). 57Fe Mössbauer spectroscopy confirms that these black mudstones contain pyrite without hematite. In contrast, red bedded claystones (no younger than 542 Ma) in the neighboring Braich section contain hematite as their main iron mineral. These deep-sea mudstones in the Lleyn Peninsula record a change of redox condition on the pelagic deep-sea floor during the Ediacaran. The black mudstone at Porth Felen shows that deep-sea anoxia existed in the late Ediacaran. The eventual change from a reducing to an oxidizing deep-sea environment likely occurred in the late Ediacaran (ca. 564-542 Ma).

    Original languageEnglish
    Pages (from-to)472-480
    Number of pages9
    JournalTectonophysics
    Volume662
    DOIs
    Publication statusPublished - Dec 5 2014

    Keywords

    • Accretionary complex
    • Anoxia
    • Deep-sea
    • Ediacaran
    • Fe

    ASJC Scopus subject areas

    • Geophysics
    • Earth-Surface Processes

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    Sato, T., Sawaki, Y., Asanuma, H., Fujisaki, W., Okada, Y., Maruyama, S., Isozaki, Y., Shozugawa, K., Matsuo, M., & Windley, B. F. (2014). Redox condition of the late Neoproterozoic pelagic deep ocean: 57Fe Mössbauer analyses of pelagic mudstones in the Ediacaran accretionary complex, Wales, UK. Tectonophysics, 662, 472-480. https://doi.org/10.1016/j.tecto.2015.08.002