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Antecedent Fluvial Systems on an Uplifted Continental Margin: Constraining Cretaceous to Present-Day Drainage Basin Development in Southern South Africa

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Antecedent Fluvial Systems on an Uplifted Continental Margin: Constraining Cretaceous to Present-Day Drainage Basin Development in Southern South Africa I Antecedent fluvial systems on an uplifted continental margin: constraining Cretaceous to present-day drainage basin development in southern South Africa Janet Cristine Richardson Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Earth and Environment May 2016 The candidate confirms that the work submitted is her own, except where work which has formed part of jointly-authored publications has been included. The contribution of the candidate and the other authors to this work has been explicitly indicated below. The candidate confirms that appropriate credit has been given within the thesis where reference has been made to the work of others. Chapter 7: Richardson, J.C., Hodgson, D.M., Wilson, A., Carrivick J.L. and Lang, A. Testing the applicability of morphometric characterisation in discordant catchments to ancient landscapes: a case study from southern Africa. Geomorphology, 201, 162- 176. DOI - doi:10.1016/j.geomorph.2016.02.026 Author contributions: Richardson, J.C – Main author. Responsible for data collection, collation and interpretation, and for writing the manuscript. Hodgson, D.M, Wilson, A., and Lang, A – Data discussion, and detailed manuscript review. Carrivick, J.L – Manuscript review. Submitted: 26th September 2015 Available online: 23rd February 2016 This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. The right of Janet C. Richardson to be identified as Author of this work has been asserted by her in accordance with the Copyright, Designs and Patents Act 1988. © 2016 The University of Leeds and Janet C. Richardson Acknowledgments I would like to thank my supervisors Dave Hodgson, Andreas Lang, Andrew Wilson and Jonathan Carrivick for their guidance and help throughout my project. I would especially like to thank Dave for the opportunity to do this PhD, for always being enthusiastic with my work (even if it meant turning into a geomorphologist!) and for ‘helping’ me to find wine! I would like to thank the British Sedimentological Research Group and British Geomorphology Society for providing postgraduate funding for the cosmogenic dating and conference attendance. I would like to thank the Council of Geoscience, South Africa for providing geological tiles for the use in ArcGIS. Midland Valley Exploration Ltd. are thanked for providing the license for their proprietary software, Move. I would like to thank the farm owners of the Western Cape for allowing me onto their land to collect samples. I would also like to thank Veerle Vanacker for her help during laboratory work for cosmogenics and for guidance in interpreting the results. Thank you to Jérôme Schoonejans and Marco Brevin for their help in the laboratory. I would like to thank Robert Duller, John Kavanagh and Barabara Mauz for the interesting talks when I spent time at Liverpool University at the start of my PhD. I would like to thank STRAT group, for all the adventures, discussions and nights out. For their support and always helping me out when I came to visit (special thanks to Michelle, Hannah and Sarah for looking after me when I didn’t live in Leeds and came to visit!). I would especially like to thank Claire Mellett for helping me start my PhD in Liverpool and to Yvonne Spychala for supporting me during the final months! Finally I would like to thank my friends and family, for listening to my research and for providing support towards the final write up period. Thank you to Garry Power and the Geography department at St Michaels Catholic High school for inspiring me about Earth sciences from a young age. I would especially like to thank my aunt Daphne and uncle Richard for their continued support during my project and previous studies. Special thanks to Stephen McCann and family for their continued support and encouragement during my PhD. Papers Several chapters within this thesis (Chapters 4 – 8) were written as papers which were submitted to various geoscience journals for publications. The status of these papers are below. In print: Richardson, J.C., Hodgson, D.M., Wilson, A., Carrivick, J.L. and Lang, A., 2016. Testing the applicability of morphometric characterisation in discordant catchments to ancient landscapes: A case study from southern Africa.Geomorphology, 261, pp.162-176. Under review: Chapter 5: Richardson, J.C, Hodgson, D.M, Paton, D., Rawcliffe, A., Lang, A. Reconstruction of the erosional landscape development of southwestern Africa since the late Jurassic: implications for offshore sediment budgets, drainage basin evolution and the Mesozoic exhumation of southern Africa: where is all the sediment? Gondwana Research, in review. Author contributions: Richardson, J.C – Main author. Responsible for data collection, collation and interpretation, and for writing the manuscript. Repeating Rawcliffe’s 3DMove work and applying further constraints. Hodgson, D.M – Data discussion, and detailed manuscript review. Lang, A, Paton, D – Data discussion and manuscript review. Rawcliffe, A. – Manuscript review and initial 3DMove work as part of M.Geol project (Appendix 1). Chapter 6: Richardson, J.C., Vanacker, V., Lang, A., and Hodgson, D.M. Constraining landscape evolution using cosmogenic nuclide dating in an ancient setting: the pediments of the Western Cape, South Africa. ESPL, in review. Author contributions: Richardson, J.C – Main author. Responsible for data collection, collation and interpretation, and for writing the manuscript. Vanacker, V – guidance in the laboratory with data processing and interpretation, manuscript review. Hodgson, D.M and Lang, A – Data discussion, and detailed manuscript review. ‘Rivers are the gutters, down which flow the ruins of continents’ Leopold et al., 1964 Abstract Reconstructing drainage evolution has important implications for constraining long- term source-to-sink configurations. Furthermore, the analysis of ancient landscapes can support research in geomorphological concepts such as steady state and landscape evolution modelling. Techniques such as cosmogenic dating and morphometric analysis have rarely been applied to investigate the long-term drainage evolution of systems draining southern South Africa. This study focusses on the large-scale antecedent Gouritz catchment, Western Cape. Integrating provenance, cosmogenic and geomorphological (planform / morphometric indices) evidence indicates the trunk rivers are Cretaceous or older in age (i.e. principal topography of Mesozoic age). The trunk rivers fed huge volumes of sediment offshore during large-scale Mesozoic exhumation of southern South Africa with remnant coeval deposits in onshore extensional basins. However, there is a mismatch of onshore exhumation and offshore deposition and material is now found on the Falkland Plateau; separating source-to-sink by 6000 km. During exhumation, large scale pediments formed that grade to individual base levels and should be taken as individual features, not ‘surfaces’ correlated across the continent. A second phase of pediment evolution occurred in the mid-Cenozoic, dissecting the pediments and eroding small catchments into the Cape Fold Belt. These smaller order streams are strongly affected by the tectonic grain of the fold belt, whereas the trunk rivers are not, which is shown by variation in morphometric indices. The lack of correlation between catchment properties and denudation rates indicate the system has decoupled and that allogenic factors are now dominant. Due to the low rates of denundation, weathering is currently the rate limiting factor. However, during the early evolution of the catchment, tectonic activity was more dominant than the present day. The ancient catchment is in geomorphic steady-state, and highlights the need for further research into long-term landscape evolution, and linkage to offshore depositional records. Table of Contents Abstract ................................................................................................................................ vi Table of Contents .............................................................................................................. vii List of Figure ...................................................................................................................... xii List of Tables ................................................................................................................... xviii Chapter 1 Introduction ....................................................................................................... 1 1.1 Project rationale ........................................................................................................ 1 1.2 Thesis aims ................................................................................................................ 2 1.3. Thesis structure ....................................................................................................... 4 Chapter 2 Literature review .............................................................................................. 6 2.1 Long-term landscape evolution ............................................................................ 6 2.1.1 Classical geomorphology; theories of landscape evolution .......................... 7 2.1.2 Controlling factors ............................................................................................. 10 2.1.3 Drainage development ....................................................................................
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