The Petrology and History of the Holocene Sediments of Dungeness, Kent
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THE PETROLOGY AND HISTORY OF THE HOLOCENE SEDIMENTS OF DUNGENESS, KENT TILOTTAMA BASA Thesis submitted for the degree of Ph D at the Department of Geological Sciences, University College London, University of London. March 1992 ProQuest Number: 10609844 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10609844 Published by ProQuest LLC(2017). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 In memory of my Father ABSTRACT The drilling of several deep boreholes through the 40 m thick marine Holocene succession of the Dungeness foreland on the site of the proposed Dungeness "C" Nuclear Power Station provides an opportunity to examine the nature and composition of its sediments. Selected unaltered mollusc shells were used to date the sediment succession at -34.3 m, -32.9 m, -32.4 m and -20.5 m OD to supplement the existing 14C determinations on both wood and shells. The 14C dates obtained showed that the sediments at these depths were deposited between 560±95 and 2755±175 cal. yr BP. Study of borehole cores and logs showed that these deposits consist of three distinct divisions: Basal Gravels, Middle Sands and Top Gravels. Grain size analyses indicated that the bulk of the Middle Sands succession (99% - 76%) below the Top Gravels comprised fine sand and silt, the rest being medium sand, clay and a sprinkling of fine to medium gravel. The silt fraction has a predominant peak at 5 to 6 § typical of loess. The detrital mineralogy as a whole consists of 90% quartz, the remainder being feldspar, chert, glauconite and heavy minerals, mainly zircon, tourmaline, garnet, rutile with a variable amount of staurolite, kyanite, amphibole and the epidote group of minerals. The garnets are predominantly Fe-rich with variable amounts of Mn, Ca and Mg. The clay minerals include illite, kaolinite and mixed-clay minerals with a little chlorite and smectite, similar to that reported from brickearths in Kent. The surface of the sand grains have characteristic subaqueous, aeolian and subaerial microtextures and in a few grains there is evidence of high energy glacial features. Most of the pebbles in the Basal Gravels are subangular to subrounded and consist predominantly of flint from the local Cretaceous rocks, with some sandstones, siltstones and limestones. A few exotic pebbles such as granitic angular rock fragments are also present in the Basal Gravels. The sediment constituents are of mixed provenance. The local Cretaceous bedrocks supplied the more resistant heavy minerals and the bulk of the quartz, feldspar, chert and glauconite whereas the less stable heavy minerals along with some quartz and other light minerals were derived from relatively younger Quaternary sources. The surface texture, the size distribution of the silts, the presence of unstable heavy minerals and the clay mineral types indicate an admixture of Pleistocene aeolian loessic sediments which may have been reworked a number of times before they were finally deposited at Dungeness. 3 The Quaternary sediments of the southern North Sea, which contain a large proportion of semistable to unstable heavy minerals, may have supplied sediment to the offshore area near Dungeness at a time when, as the molluscan fauna suggests, Dungeness was evolving under the influence of heavy storms. 4 TABLE OF CONTENTS PAGE Title page 1 Dedication 2 Abstract 3 Table of Contents 5 List of Tables 8 List of Figures 9 List of Plates 12 Acknowledgements 18 CHAPTER 1: INTRODUCTION 19 Introduction A review of pre-existing information on Dungeness Holocene deposits Pleistocene deposits in southeast England Sea level CHAPTER 2: THE SEDIMENTS OF DUNGENESS 38 Introduction Sampling and analytical methods Results of the detailed sedimentological analyses CHAPTER 3: MOLLUSC STUDIES 111 Introduction Mollusc shells found in Dungeness Results and Interpretation CHAPTER 4: RADIOCARBON DATING 120 Introduction Holocene deposits at Dungeness First-Order 14C dating 14C dates in the Romney Marsh area Dating of the barrier beaches Implication of the recent dates at Dungeness 5 CHAPTER 5: PROVENANCE 136 Introduction Texture Detrital mineralogy Provenance Summary CHAPTER 6: ENVIRONMENTS OF DEPOSITION 167 Introduction Barrier beach environments Reconstruction of the depositional environments at Dungeness Evolution of a barrier under the influence of storms at Dungeness Evidence of probable storm activities in the surrounding areas Evolution of Dungeness CHAPTER 7: WIDER IMPLICATIONS 194 Introduction Coastal sedimentation Holocene sea-level changes Holocene crustal movements and sea-level changes CHAPTER 8: SUMMARY OF FINDINGS 206 AND FUTURE WORK REFERENCES CITED 209 APPENDICES 231 APPENDIX 1 Borehole logs APPENDIX 2 Grain size frequency distributions APPENDIX 3 Grain-size distributions: cumulative curves APPENDIX 4 SEM surface microfeatures on quartz grains APPENDIX 5 Detrital mineralogy in thin section APPENDIX 6 Heavy mineralogy of Midley Sand and Modern Sand sediments APPENDIX 7 Heavy mineralogy of sea bed sediments near Dungeness APPENDIX 8 Distribution of tourmaline varieties 6 APPENDIX 9 Electron microprobe analysis of detrital garnets APPENDIX 10 Electron microprobe analysis of selected heavy minerals APPENDIX 11 Glauconite analyses APPENDIX 12 Semiquantitative clay determination 7 LIST OF TABLES 2.1 % of sand and silt+clay 2.2 % of silt and clay in < 4 <}> fraction of Dungeness sediments 2.3 Grain-size parameters of Dungeness sediments, Midley Sand and Modern Sand from Lydd-on-Sea 2.4 SEM surface microtextures of quartz grains 2.5 Representative electron microprobe analysis of detrital garnets 2.6 Garnet analysis according to 24 Oxygens 2.7 Mole % of different types of garnet 2.8 Representative electron microprobe analysis of glauconite from Dungeness 2.9 XRD analysis of clay 3.1 Shells from Dungeness 4.1 First-Order 14C dates from Dungeness 4.2 14C dates from Dungeness 4.3 Radiocarbon dates from Romney Marsh 5.1 Detrital mineral suites characteristic of source rock types 5.2 Comparison of grain-size parameters of Holocene sediments and of local lower Cretaceous bedrocks 5.3 Comparison of heavy mineralogy of Dungeness sediments and of lower Cretaceous bedrocks 5.4 Comparison of heavy mineralogy of coarse silt fraction of Dungeness sediments and of the Rother Valley fill sediments 5.5 Comparison of glauconite analysis of Dungeness sediments with McRae and Lambert’s (1968) glauconite analysis of Cretaceous and Tertiary sediments of southeast England. 8 LIST OF FIGURES Fig. 1.1 Location map of Dungeness Fig. 1.2 Evolution of shorelines at Dungeness Fig. 1.3 Surface deposits at and near Dungeness Fig. 2.1.1.a Borehole and sample location sites Fig. 2.l.l.b Representative lithological logs of Holocene sequence at Dungeness Fig. 2.1.1 Representative grain size frequency curves of Dungeness sediments Fig. 2.1.2 Grain size frequency curves of Midley Sand sediments Fig. 2.1.3 Grain size frequency curves of Modem Sand sediments from Lydd-on-Sea Fig. 2.2.1 Grain size distribution of representative Dungeness samples Fig. 2.2.2 Grain size distribution of Midley Sand samples Fig. 2.2.2 Grain size distribution of Modem Sand samples Fig. 2.3.a Grain size frequency distribution curves of silt and clay fraction of Dungeness sediments Fig. 2.3.b Grain size frequency distribution curves of silt and clay fraction of Dungeness sediments Fig. 2.4 Surface texture of quartz grains observed under SEM Fig. 2.5 Detrital mineralogy of Dungeness sediments in thin sections Fig. 2.6.1.a Heavy mineralogy of fine sand (2-3 <j>) fraction of Dungeness sediments Fig. 2.6.l.b Heavy mineralogy of fine sand (2-3 <J>) fractions of Dungeness sediments Fig. 2.6.2.a Heavy mineralogy of very fine sand (3-4 $) fraction of Dungeness sediments Fig. 2.6.2.b Heavy mineralogy of very fine sand (3-4 <)>) fraction of Dungeness sediments Fig. 2.6.3 Heavy mineralogy of coarse silt (<4 <J>) fraction of Dungeness sediments Fig. 2.6.4 Heavy mineralogy of Midley Sand Fig. 2.6.5 Heavy mineralogy of Modem Sand from Lydd-on-Sea Fig. 2.6.5.a Heavy mineralogy of coarse silt (<4 $) fraction of Modem Sand sediments Fig. 2.7 Distribution of tourmaline varieties Fig. 2.8 Garnet composition of sand from Dungeness Fig. 2.9 Garnet composition of sand from Midley Sand and Modem Sand at Lydd-on-Sea 9 Fig. 2.10 X-ray diffractograms of glauconite from Dungeness sediments Fig. 2.11 X-ray diffractogram of typical clay sample from Dungeness sediment Fig. 2.12 Diffractometer traces of a typical clay sample from Dungeness sediments and component clay minerals Fig. 4.1 X-ray diffractograms of aragonitic shells from Dungeness Fig. 4.2 First-Order 14C dating rig at UCL Fig. 5.1 Simplified map of solid geology of the English Channel Fig. 5.2 Typical relative frequency distribution of valley fill and floodplain sediments of the southern England rivers Fig. 5.3 Deeps and infilled channels of the English Channel Fig. 5.4 Outline map of mean spring near-surface tidal current strength on the continental shelf around the British Isles. Fig. 5.5 Net sand transport direction on the continental shelf around the British Isles Fig. 5.6 Distribution of sediment types off the southern coast of England Fig. 5.7 Generalised palaeogeography of Dungeness c.3000 yr BP and direction of sediment transport Fig.