The Physical Evolution of the North Avon Levels a Review and Summary of the Archaeological Implications By Michael J. Allen and Robert G. Scaife The Physical Evolution of the North Avon Levels: a Review and Summary of the Archaeological Implications by Michael J. Allen and Robert G. Scaife with contributions from J.R.L. Allen, Nigel G. Cameron, Alan J. Clapham, Rowena Gale, and Mark Robinson with an introduction by Julie Gardiner Wessex Archaeology Internet Reports Published 2010 by Wessex Archaeology Ltd Portway House, Old Sarum Park, Salisbury, SP4 6EB http://www.wessexarch.co.uk/ Copyright © Wessex Archaeology Ltd 2010 all rights reserved Wessex Archaeology Limited is a Registered Charity No. 287786 Contents List of Figures List of Plates List of Tables Editor’s Introduction, by Julie Gardiner .......................................................................................... 1 INTRODUCTION The Severn Levels ............................................................................................................................ 5 The Wentlooge Formation ............................................................................................................... 5 The Avon Levels .............................................................................................................................. 6 Background ...................................................................................................................................... 7 THE INVESTIGATIONS The research/fieldwork: methods of investigation ........................................................................... 10 The Sites ........................................................................................................................................... 11 1. Awkley Lane ................................................................................................................................ 11 The sequence ........................................................................................................................ 11 Chronology .......................................................................................................................... 12 Sampling the sequence ......................................................................................................... 16 Textural features of the minerogenic sequence, by J.R.L. Allen .......................................... 18 Pollen analysis, by Robert G. Scaife ..................................................................................... 18 Diatom analysis, by Nigel G. Cameron ................................................................................ 30 Molluscs, by Michael J. Allen .............................................................................................. 32 Insect remains, by Mark Robinson ....................................................................................... 32 Waterlogged plant macrofossils, by Alan J. Clapham ......................................................... 34 2. Vimpenny’s Lane ......................................................................................................................... 37 The sequence ........................................................................................................................ 37 Chronology .......................................................................................................................... 40 Sampling the sequence ......................................................................................................... 40 Textural features of the minerogenic sequence, by J.R.L. Allen .......................................... 40 Pollen analysis, by Robert G. Scaife .................................................................................... 42 Diatom analysis, by Nigel G. Cameron ............................................................................... 49 Molluscs, by Michael J. Allen .............................................................................................. 52 Insect remains, by Mark Robinson ....................................................................................... 52 Waterlogged plant macrofossils, by Alan J. Clapham ......................................................... 53 3. Hallen Marsh ................................................................................................................................ 54 The sequence ........................................................................................................................ 54 Sampling the sequence ......................................................................................................... 56 Textural features, by J.R.L. Allen ......................................................................................... 60 Pollen analysis, by Robert G. Scaife ..................................................................................... 60 Diatom analysis, by Nigel G. Cameron ............................................................................... 67 Molluscs, by Michael J. Allen .............................................................................................. 67 Charcoals, by Rowena Gale ................................................................................................. 68 4. Northwick .................................................................................................................................... 69 The sequence ........................................................................................................................ 69 Molluscs, by Michael J. Allen .............................................................................................. 72 5. Awkley Interface .......................................................................................................................... 74 The sequence ........................................................................................................................ 74 3 Molluscs, by Michael J. Allen .............................................................................................. 78 Comment .............................................................................................................................. 78 DISCUSSION AND REVIEW. The Physical and Vegetational Evolution of the Avon Levels Stratigraphic Overview .................................................................................................................... 79 The Wentlooge Formation .................................................................................................... 79 Sea-level change and palaeo-geographic reconstruction...................................................... 80 Patterns of consistency: the mapped sediments ................................................................... 82 Environmental change in the Avon Levels ...................................................................................... 85 Pollen taphonomy and interpretation ................................................................................... 85 The late prehistoric vegetation of the Avon Levels ......................................................................... 87 The regional pollen database ............................................................................................... 87 Avon Levels sites ................................................................................................................. 88 The changing wetland/floodplain/estuarine habitat ............................................................. 94 Summary .............................................................................................................................. 96 The mineral, estuarine and freshwater sediments ................................................................ 97 Archaeology and environment: marsh landscape and archaeology……………………………….. 98 Some archaeological implications ..................................................................................... ..98 History of human exploitation patterns and behaviour ...................................................... 99 Why does settlement occur? .............................................................................................. 103 What caused Iron Age abandonment? ............................................................................... 103 A change of use .................................................................................................................. 105 Land claim .......................................................................................................................... 105 Archaeological significance ............................................................................................... 106 Conclusions .................................................................................................................................... 106 Acknowledgements ........................................................................................................................ 106 Appendix: analytical techniques .................................................................................................... 108 Bibliography .................................................................................................................................. 111 4 List of Figures Figure 1. The Inner Bristol Channel and Severn Estuary showing the distribution of post-glacial alluvium comprising