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Sedimentology and Palaeontology of the Withycombe Farm Borehole, Oxfordshire, UK

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Sedimentology and Palaeontology of the Withycombe Farm Borehole, Oxfordshire, UK Sedimentology and Palaeontology of the Withycombe Farm Borehole, Oxfordshire, England By © Kendra Morgan Power, B.Sc. (Hons.) A thesis submitted to the School of Graduate Studies in partial fulfillment of the requirements for the degree of Master of Science Department of Earth Sciences Memorial University of Newfoundland May 2020 St. John’s Newfoundland Abstract The pre-trilobitic lower Cambrian of the Withycombe Formation is a 194 m thick siliciclastic succession dominated by interbedded offshore red to purple and green pyritic mudstone with minor sandstone. The mudstone contains a hyolith-dominated small shelly fauna including: orthothecid hyoliths, hyolithid hyoliths, the rostroconch Watsonella crosbyi, early brachiopods, the foraminiferan Platysolenites antiquissimus, the coiled gastropod-like Aldanella attleborensis, halkieriids, gastropods and a low diversity ichnofauna including evidence of predation by a vagile infaunal predator. The assemblage contains a number of important index fossils (Watsonella, Platysolenites, Aldanella and the trace fossil Teichichnus) that enable correlation of strata around the base of Cambrian Stage 2 from Avalonia to Baltica, as well as the assessment of the stratigraphy within the context of the lower Cambrian stratigraphic standards of southeastern Newfoundland. The pyritized nature of the assemblage has enabled the study of some of the biota using micro-CT, augmented with petrographic studies, revealing pyritized microbial filaments of probable giant sulfur bacteria. We aim to produce the first complete description of the core and the abundant small pyritized fossils preserved in it, and develop a taphonomic model for the pyritization of the “small” shelly fossils. i Acknowledgements It is important to acknowledge and thank the many people who supported me and contributed to the successful completion of this thesis. Firstly, a tremendous thank you to my supervisor Dr. Duncan McIlroy. I am beyond grateful for your guidance, experience, expert knowledge, mentorship, and your personal support during the course of this degree. Without your supervision and encouragement, this thesis would not have been possible. Thank you to my Co-supervisor Dr. Liam Herringshaw for your assistance in the UK, for the making of my thin sections, and for your constructive critique. I would also like to thank Dr. Suzanne Dufour, my supervisory committee member, for your contribution. This research was financially supported by an NSERC Discovery Grant and a Discovery Accelerator Supplement awarded to Dr. McIlroy, a Fellowship of the School or Graduate Studies and the Buchans Scholarship of ASARCO awarded to myself. Funding from the Department of Earth Sciences, School of Graduate Studies, Faculty of Science, and the Graduate Students’ Union also allowed me to travel to the United Kingdom for fieldwork and to present parts of my thesis. Many other people made this research possible and helped with the collection and analyses of the required material. I would like to express my gratitude to the folks at the British Geological Survey for hosting me, in particular Ms. Tracy Gallagher. Thank you to those at the University of Bristol (Dr. Alex Liu, Frankie Dunn, and Tom Davies) for your assistance in the CT scanning of my specimens. Thank you to Dr. David Wacey at the University of Western Australia for your collaboration and the analyses you provided. I ii am also grateful to Duncan’s former graduate students Katie Power and Chris Boyd for helping teach me to process and understand some of this data. Thank you to Dylan Goudie and David Grant at the MUN CREAIT lab for your help with the SEM. I also cannot forget to thank my many officemates: Melissa Cook, Roddy Campbell, Jessica Hawco, and Chris McKean. Thank you guys, for putting up with my foolishness and for drinking far too many coffees with me. Your friendship, collaboration, and support meant so much to me during the entirety of this project. Lastly, a huge you to all of my family and friends, particularly my mom, dad, Keegan and Steve for their phenomenal emotional support throughout the last few years, I honestly could not have done this without you. iii Table of Contents Abstract. ................................................................................................................. ii Acknowledgements. .............................................................................................. iii Table of Contents. ................................................................................................ iv List of Figures. ..................................................................................................... vii List of Appendices. ................................................................................................ x Co-authorship Statement. .................................................................................... xi Chapter 1 – Introduction and Overview ............................................................. 1 1.1 Introduction. .......................................................................................... 2 1.2 Analytical Methods ............................................................................... 3 1.3 Literature Review… .............................................................................. 5 1.3.1 Geological History ................................................................. 5 1.3.2 Small Shelly Fossils… ........................................................... 8 1.4 Relevance of the Study… .................................................................... 11 1.5 References… ....................................................................................... 14 Chapter 2 - Palaeontology of the lower Cambrian Withycombe Formation of Oxfordshire, UK… .............................................................................................. 19 2.1 Introduction… ..................................................................................... 21 2.2 Sedimentology of the Withycombe Formation… ............................... 22 2.3 Materials and Methods… .................................................................... 25 2.4 Systematic Palaeontology… ................................................................ 25 2.5 Trace fossils from the Withycombe Formation… ............................... 57 2.6 Palynology of the Withycombe Formation………………………….. 59 2.7 Possible pyritized giant sulfur bacterial sheaths… .............................. 60 2.8 Significance of the macroscopic nature of the assemblage ..................66 2.9 Stratigraphic and ecological distribution of the macrofossils… ......... 67 iv 2.10 Biostratigraphic implications of the fauna ........................................ 69 2.11 Conclusion… ..................................................................................... 72 2.12 References… ..................................................................................... 74 Chapter 3 - Taphonomy of the lower Cambrian, Withycombe Farm Borehole, Oxfordshire, England ........................................................................ 86 3.1 Introduction… ..................................................................................... 88 3.2 Sedimentology… ................................................................................. 89 3.3 Taphonomy… ...................................................................................... 91 3.3.1 Biostratinomy… ................................................................... 91 3.3.2 Diagenetic Re-mineralization… ........................................... 94 3.3.3 Biogeochemistry of pyrite formation… ............................... 98 3.4 Full Taphonomic Model…................................................................. ..99 3.5 Discussion… ..................................................................................... .100 3.6 Conclusion… ..................................................................................... .105 3.7 References… ..................................................................................... ..107 Chapter 4 - Pyritized microbial filaments from the Cambrian Stage 2 Withycombe Formation, Oxfordshire, UK… ................................................. 116 4.1 Introduction… ................................................................................... .117 4.2 Materials and Methods… .................................................................. .120 4.3 Filamentous Structures of the Withycombe Assemblage .................. .121 4.4 Discussion… ..................................................................................... ..122 4.4.1 Fossil microbes and the Genera Beggiatoa & Thioploca…..122 4.4.2 Discriminating between fossil microbes and trace fossils .. .125 4.4.3 Questioning the biogenicity of iron-mineralized filaments and tubes… ......................................................................................... ..127 4.5 Conclusion… ..................................................................................... ...129 4.6 References…………………………………………………………….131 Chapter 5 - Summary ........................................................................................ 135 5.1 Introduction… ................................................................................... 136 v 5.2 Outcomes of Chapter 2… .................................................................. 137 5.3 Outcomes of Chapter 3… .................................................................
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