THE SEDIMENTOLOGY OF THE ASHDOWN FORMATION AND THE WADHURST CLAY FORMATION, SOUTHEAST ENGLAND Oladapo Odunayo Akinlotan A thesis submitted in partial fulfilment of the requirements of the University of Brighton, for the degree of Doctor of Philosophy October 2015 The University of Brighton Abstract Detailed sedimentological studies, using coastal and inland exposures, were carried out at formation and bed levels on the Ashdown and Wadhurst Clay formations (Late Berriasian-Valanginian) in the Weald, southeast England. Field descriptions of outcrops were conducted at seven sites and supplemented by borehole and 2D seismic data. Field samples were studied in detail using hand specimen analysis. The sandstones were described in hand specimen and via optical microscopy. Clay mineral and geochemical analyses on mudstones, shales, and ironstones were conducted using XRD, XRF, and SGR methods while SEM analyses were conducted on selected sandstones and ironstones. Porosity and permeability of selected sandstones were measured using pycnometry and gas permeametry respectively. The dominance of quartz arenites and kaolinite and the presence of thorium and Zr in the sediments suggest that they were sourced mainly from granitic and/or gneissic rocks. Materials from metamorphic sources appear to be secondary in abundance. The mineralogical and textural maturity of the sediments coupled with relatively short travel distance (~300km) suggests reworking from secondary or matured sources. The two formations received sediments from at least two sources. The clay mineral assemblage, sandstone composition, and gamma-ray data confirm that the main source of the sediments is the London Massif in the north and north east while sediments were also sourced from Armorica in the south based on the presence of detrital zircon. The palaeoclimatic conditions at the source area as revealed by the dominance of quartz arenites and kaolinite and the presence of thorium were warm and humid which led to intensive weathering. The mineralogy and geochemistry of the sediments suggest that they may have been directly or indirectly sourced from a stable craton. The lithology (sandstones, siltstones, mudstones, shales and ironstones); facies (channel and floodplain/overbank); sedimentary structures (channels, cross stratification, flaser bedding, ripples and planar laminations); sedimentary architecture (repeated cycles and vertically stacked multi-storey successions), and gamma ray data (more radioactive sandstone facies) confirm that the sediments within the two formations were deposited in predominantly fresh water environments although tidal and lagoonal conditions were clearly evident in the Ashdown Formation and Wadhurst Clay Formation respectively. The lithology and sedimentary facies show that deposition occurred in both braided and i meandering river systems although meandering facies are more prominent in the lower Ashdown Formation. The presence of abundant load and slump structures and fresh green glauconite in the sandstones provide evidence that deposition was rapid while the water depth was shallow and not beyond 2 metres based on the widespread occurrence of colour mottling and frequent exposure of the sediments to the air. Early diagenesis was confirmed by the precipitation of sideritic ironstones while diagenetic alteration is minimal based on the clay mineral assemblage. Evidence from the shallow burial nature of sideritic ironstone, the proportion of illite- smectite and the nature of diagenesis confirm that the sediments have experienced shallow burial not beyond 2km. Enrichments in redox sensitive trace elements such as Mo, U, V and Co suggest anoxic conditions in the sediments. The highest levels of anoxia were in the lower sections of the formations. Palaeosalinity as indicated by sideritic ironstone indicates a pH between 6 and 10. Porosity ranges from 6.8% to 13. 2% with an average of 9.9% while permeability ranges from 0.4mD to 11.9mD with an average of 3.1mD. The main controls on porosity and permeability are grain sizes, grain shapes, and sorting and the porosity is mainly primary. The main control on sedimentation is the local tectonics at the source areas while palaeoclimatic conditions, sea level, river dynamics, and subsidence are secondary. The proximal part of the modern Niger Delta is proposed as an analogue for the palaeoenvironments of the Ashdown and Wadhurst Clay formations. More generally, the results presented in this thesis highlight the usefulness of integrating field, petrographic, mineralogical, and geochemical data, and the use of modern analogue to fully assess the depositional environments, stratigraphic variability, post depositional changes and controls on deposition within sedimentary basins. ii Acknowledgements I sincerely appreciate my supervisors: Prof Andy Cundy, Dr Stewart Ullyott, and Dr Martin Smith for their guidance, support, and most importantly technical support. I want to express my gratitude to Pete Lyons for driving me to the field, accompanying me on the field and for carrying rock samples with me. Thank you very much for personally running the Benchtop XRF analysis and providing important support for other laboratory analyses. Thanks to Chris English for helping with the XRD analysis. I am also grateful to Christine Sinclair and Pierluigi Stroppa for accompanying me during fieldwork. Thanks to Steve Baker for proving technical support and helping with the installation of important software packages. I want to acknowledge the University of Brighton for giving me the International Research Scholarship that funded half of my tuition. Many thanks to the School of Environment and Technology for providing additional funding and to the Doctoral College for providing effective administration throughout the research. I also appreciate Dr Richard Williams and Dr Magda Groove who provided guidance in my early days at the research students’ office at the Cockcroft building. I want to thank Mr Shaun Skinner of Ibstock Brick Hudsons Ltd, for giving permission to conduct fieldwork at their quarry in East Grinstead, West Sussex. Many thanks to Amy Francis, Janet Whitman and Jane Robertson from the Sussex Land Management Team at Natural England for giving me permission to carry out fieldwork in the Sites of Special Scientific Interest (SSSI) and Geological Conservation Review (GCR) sites. I duly acknowledge Peter Anderton at the Sussex Biodiversity Record Centre for providing local geological site maps and reports, which helped to locate inland outcrops. I appreciate Glen Steffey at the UK Geophysical Library/ Lynx Information Systems Ltd for providing 2D seismic data. I sincerely appreciate my wife Abimbola and my daughters Praise and Peace for making huge sacrifices as I spent most time away from home during the research. I thank my parents: Mr and Mrs Benjamin and Esther Akinlotan, my siblings: Folarin, Mayowa, Tomi, and Timileyin for their prayer and support. I cannot but express my sincere heart of gratitude to the Almighty God who gave me the vision, insights, wisdom, and resources that ensured the successful and timely completion of this research. iii Declaration I declare that the research contained in this thesis, unless otherwise formally indicated within the text, is the original work of the author. The thesis has not been previously submitted to this or any other university for a degree and does not incorporate any material already submitted for a degree. Signed………………………. Oladapo Odunayo Akinlotan Date……………………… iv Table of Contents Abstract .............................................................................................................................. i Acknowledgements .......................................................................................................... iii Declaration ....................................................................................................................... iv Table of Contents .............................................................................................................. v List of Figures .................................................................................................................. xi List of Tables.................................................................................................................. xxi Chapter 1: Introduction ..................................................................................................... 1 1.1 Context .................................................................................................................... 1 1.2 Rationale for focusing on the Ashdown and Wadhurst Clay formations ................ 3 1.3 Wealden Research History ...................................................................................... 4 1.4 Knowledge Gaps ..................................................................................................... 5 1.5 Aim and Objectives ................................................................................................. 7 1.6 Research Questions ................................................................................................. 8 1.7 Thesis layout ............................................................................................................ 9 Chapter 2: Review of Literature ...................................................................................... 10 2.1 Tectonic Framework .............................................................................................