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Developing proxies to constrain redox gradients in terminal Ediacaran oceans

Tostevin, R; (2015) Developing proxies to constrain redox gradients in terminal Ediacaran oceans. Doctoral thesis , UCL (University College London). Green open access

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Abstract

There is a long-standing interest in the relationship between the rise of early Metazoans and changes in the redox structure of the oceans. As such, there is a need for reliable geochemical proxy archives that record palaeo-redox. Before we can use proxies in deep time we must understand their application in modern environments, and ensure pristine seawater signals can be extracted effectively. We investigate the sulfur cycle in the modern ocean, using new data from minor sulfur isotopes to constrain the proportional pyrite burial flux - a key control on atmospheric oxygen regulation through time - to between 20 and 35%. Ce anomalies in rare earth element patterns record redox information, and we develop the leaching methods for extracting pristine signals from carbonates. We suggest that a partial leach in nitric acid reduces the risk of contamination. We apply multiple redox proxies (Fe-speciation, TOC, carbon isotopes, CAS-pyrpaired sulfur isotopes and Ce anomalies) to terminal Ediacaran carbonates from the Nama Group, Namibia, to reconstruct the redox structure of the Nama Group and its relationship to the distribution of biomineralising Metazoans. We generate a holistic redox model that distinguishes between anoxic, intermediate and fully oxygenated waters, including identification of manganous conditions using novel observations of positive Ce anomalies. We distinguish between spatial and temporal variability in redox using nine sections from variable relative water depths. Dynamic redox conditions are associated with small, monospecific communities of Metazoans in short-lived horizons. Metazoans are largely absent from low oxygen manganous waters, whereas fully oxic waters host large, complex Metazoan communities. We suggest that redox exerted an important control on the ecological structure of terminal Ediacaran Metazoan communities.

Type: Thesis (Doctoral)
Title: Developing proxies to constrain redox gradients in terminal Ediacaran oceans
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Third party copyright material has been removed from ethesis.
UCL classification: UCL > Provost and Vice Provost Offices
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/1471013
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