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Title: Developing proxies to constrain redox gradients in terminal Ediacaran oceans
Author: Tostevin, R.
ISNI:       0000 0004 8502 2910
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2015
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available