This project compares palaeo-oxygenation related features of lower Cretaceous rocks from the shallow sea muds of the Gault Clay (south east England) and Niveau Pacquier and Briestroffer sequences (south east France), and the Tarfaya Basin upwelling-zone Amma Fatma sediments (Morocco). The palaeo-oxygenation indicators investigated include: sedimentological proxies, including ichnology, sedimentology, taphonomy and pyrite framboid size distribution; faunal proxies including macrofaunal properties, and biofacies models; and geochemical proxies, including trace-element abundances [Mo, V, Ni, Mn], element ratios and parameters [U/Th, authigenic U (Ua), V/Cr, Ni/Co, Ni/V, (Cu+Mo)/Zn, V/Sc and V/(V+Ni)] and Fe-S-C systematics [Total Organic Carbon (TOC), Total Sulphur/TOC ratio, Degree of Pyritisation and the Indicator of Anoxia]. The presence of lamination is a key sedimentological indicator of restricted bottom water oxygenation conditions. New descriptive categories of pyrite morphology are proposed. Interpretation of faunal proxies can be limited by poor preservation, but taphonomy-related indicators correlate well with proposed palaeo-oxygenation conditions. Molybdenum is the most reliable of the trace-metal enrichment proxies studied and altered numerical boundaries are proposed for Ua, U/Th, V/Cr and Ni/Co. Of the Fe-S-C systematics indicators, Total Organic Carbon and the Indicator of Anoxia to provide the greatest definition between palaeo-oxygenation data sets. Combinations of trace metal and Fe-S-C indicators such as [Molybdenum Enrichment Factor x Indicator of Anoxia], and plots of Ua against TOC provide the strongest palaeo-oxygenation proxies and distinguish between oxic/dysoxic, anoxic and euxinic conditions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:516860 |
| Date | January 2010 |
| Creators | Weavers, Ellen Louise |
| Publisher | University of Greenwich |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://gala.gre.ac.uk/8114/ |
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