GEOCHEMICAL and PALYNOLOGICAL SIGNALS for PALAEOENVIRONMENTAL CHANGE in SOUTH WEST ENGLAND by STEVEN WEST a Thesis Submitted To
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University of Plymouth PEARL https://pearl.plymouth.ac.uk 04 University of Plymouth Research Theses 01 Research Theses Main Collection 1997 Geochemical and palynological signals for palaeoenvironmental change in south west England West, Steven http://hdl.handle.net/10026.1/2156 University of Plymouth All content in PEARL is protected by copyright law. Author manuscripts are made available in accordance with publisher policies. Please cite only the published version using the details provided on the item record or document. In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be sought from the publisher or author. GEOCHEMICAL AND PALYNOLOGICAL SIGNALS FOR PALAEOENVIRONMENTAL CHANGE IN SOUTH WEST ENGLAND by STEVEN WEST A thesis submitted to the University of Plymouth in partial fulfilment for the degree of DOCTOR OF PHILOSOPHY Department of Geographical Sciences Faculty of Science July 1997. ni 90 0342204 X ik^m ov pu Item No. 9oo342204/X: Date H NOV mi ClassNd. UJ€& ContlNe, L if^Aavii^vicgS LIBRARY STORE Steven West GEOCHEMICAL AND PALYNOLOGICAL SIGNALS FOR PALAEOENVIRONMENTAL CHANGE IN SOUTH WEST ENGLAND. ABSTRACT This thesis evaluates the utility of a geochemical technique for the investigation of paiaeoenvironmental change in south west England. The method, EDMA (Energy Dispersive X-ray Micro Analysis), is a rapid, non-destructive analysis tool, capable of detecting a large range of geochemical elements. This research examines the most appropriate method of sample preparation for organic soils and peats, and investigates the reliability of results gained from EDMA with respect to conventional bulk geochemical techniques. A detailed study focused on a range of different sedimentary sites in south west England where a variety of palaeoenvironmental changes were thought to occur. Pollen analysis was undertaken on the same sedimentary material, and provided complementary information on the nature and scale of vegetation change through time. Sediments from a coastal valley mire near North Sands, Salcombe, revealed information relating to the processes of sea-level change in this part of south Devon and the subsequent autogenic processes as the sediment accumulated through time. A range of sites were located on the granitic upland of Dartmoor. A raised bog, Tor Royal, provided data relating to the changing nature of the central upland landscape from late Mesolithic times to the present day. Two soligenous sites. Upper Merrivale and Piles Copse, sought to investigate the activities of postulated anthropogenic activity at a much smaller spatial scale, with particular interest placed upon the evidence for deforestation activity and the utilisation of the local mineral resources. The last site, Crift Down, a lowland spring fed valley mire utilised geochemical and palynological fluxes within the peat to investigate processes and activities associated with archaeological evidence for Medieval tinworking in this area of Cornwall. The results from the EDMA investigations, and comparable studies using other geochemical methods including EMMA, AAS and flame photometry, suggest the technique to have greatest applicability as a first stage tool in the analysis of general activities of past environmental change. The technique was found to yield reliable results for the major elements (Si, Al, S, Fe, Ca, K, Na and Mg), but is generally incapable of providing useful data on heavy metal elements. The data from south west England suggest the method to reflect activity at a range of different scales, and as part of a structured programme of analysis may contribute information to allow a more holistic environmental reconstruction to be made. IV List of contents Page Chapter 1. Introduction 1.0 Introduction 1 1.1 Research aims 1 1.2 EDMA: a technique for palaeoenvironmental reconstruction 2 1.2.1 History and development 2 1.2.2 Uses 3 1.2.3 The physics of the system 3 1.2.4 Correction procedures 9 1.2.5 Accuracy 12 1.3 Alternatives to EDMA 14 1.4 Uses of EDMA in palaeoenvironmental reconstruction 17 1.5 Interpretation of individual elements for EDMA 18 1.5.1 Major elements 19 1.5.2 Nutrient elements 26 1.5.3 Mobile elements 27 1.5.4 Trace/heavy metal elements 29 1.5.5 Summary 35 1.6 Interpretation of multi element spectra 36 1.6.1 Behavioural trends 36 1.7 Philosophical basis for interpretation 38 1.8 Summary 41 Chapter 2. Methodology 2.0 Introduction 42 2.1 South west England and Dartmoor 42 2.1.1 Geological history 42 2.1.2 Palaeoenvironments of south west England 44 2.1.3 Archaeology of the south west 51 2.2 Field sites 58 2.2.1 North Sands, near Salcombe, south Devon 60 2.2.2 Tor Royal, central Dartmoor 60 2.2.3 Upper Merrivale, River Walkham, west Dartmoor 61 2.2.4 Piles Copse, River Erme, south Dartmoor 61 2.2.5 Crift Down, near Lanlivery, Cornwall 62 2.3 Data collection and analysis 62 2.3.1 Field sampling strategy 62 2.3.2 Laboratory sampling strategy and analytical techniques 63 2.3.3 Radiocarbon dating procedures 65 2.4 Data analysis 66 2.4.1 Profile zonation 66 2.4.2 Standard error bars 67 2.4.3 Multi-variate statistical methods 67 2.5 Summary 68 Chapter 3. Experimental procedures 3.0 Introduction 69 3.1 Investigation of EDMA sample preparation methods 69 3.1.1 Discussion of the preparation techniques 72 3.1.2 Results 74 3.1.3 Discussion 83 3.2 Comparison of EDMA and bulk chemical analysis 84 3.2.1 Results 84 3.2.2 Discussion 90 3.3 Conclusions 91 Chapter 4. North Sands pilot study 4.0 Introduction 92 4.1 North Sands and the Salcombe area 92 4.1.1 Geology and Geomorphology 92 4.1.2 Land use and modem vegetation groups 95 4.2 Sampling regime 96 4.3 Palaeoenvironmental reconstruction of the North Sands area 96 4.4 Stratigraphical description of the North Sands sediment 96 4.5 EDMA geochemical study 99 4.5.1 Multi-variate analysis of the geochemical results 100 4.5.2 Interpretation of the geochemical signals for North Sands 106 4.6 Pollen analysis of the North Sands sediment 109 4.6.1 Multi-variate analysis of the North Sands pollen data 109 4.6.2 Interpretation of the pollen evidence 109 4.7 Discussion of the palaeoenvironmental development of the North 115 Sands area 4.8 Discussion 118 4.9 Conclusions 119 Chapter 5. Palaeoenvironmental investigations at Tor Royal, central Dartmoor 5.0 Introduction 120 5.1 Site location, morphology and age 120 5.2 Sampling regime 124 5.3 Palaeoenvironmental reconstruction of the Tor Royal sediment 127 5.3.1 Stratigraphical description 127 5.3.2 EDMA investigation 127 5.3.3 Multi-variate analysis of the Tor Royal EDMA data 128 5.3.4 Interpretation of the geochemical signals from Tor Royal 128 5.4.5 Pollen analysis of the Tor Royal sediment 137 5.4.6 Multi-variate analysis of the Tor Royal pollen data 137 5.4.7 Interpretation of the Tor Royal pollen data 143 5.5 Discussion of the palaeoenvironmental development of the Tor Royal 148 area 5.6 Discussion 150 Chapter 6. Upper Merrivale, western Dartmoor 6.0 Introduction 152 6.1 Site location, morphology and modem vegetation communities 152 6.2 Archaeology of the Upper Walkham catchment 155 6.3 Sampling regime 156 6.4 Palaeoenvironmental reconstruction of Upper Merrivale, western 156 Dartmoor 6.4.1 Stratigraphic description of the sediment 158 6.4.2 Radiocarbon dating procedures and results 158 6.4.3 EDMA investigation 159 6.4.4 Multi-variate analysis of the Upper Merrivale EDMA data 165 6.4.5 Interpretation of the geochemical signals from Upper Merrivale 165 6.4.6 Pollen analysis of the sediments from Upper Merrivale 168 6.4.7 Multi-variate analysis of the Upper Merrivale pollen data 168 6.4.8 Interpretation of the Upper Merrivale pollen data 174 6.5 Discussion of the palaeoenvironmental development of the Upper 179 Merrivale area 6.6 Discussion 183 VI Chapter 7. Piles Copse: investigation of an 'ancient' woodland and its environment 7.0 Introduction 184 7.1 The status of the relict high level oak woodlands in the British Isles 187 7.2 Sampling regime 188 7.3 Radiocarbon dating of the Piles Copse profiles 188 7.4 Palaeoenvironmental reconstruction of the Piles Copse area 189 7.4.1 Stratigraphical description 189 7.4.2 EDMA investigation of the Piles Copse sediment 192 7.4.3 Multi-variate analysis of the Piles Copse EDMA data 192 7.4.4 Interpretation of the geochemical signals from Piles Copse 203 7.4.5 Pollen analysis of the Piles Copse sediment 208 7.4.6 Multi-variate analysis of the Piles Copse pollen data 208 7.4.7 Interpretation of the Piles Copse pollen data 217 7.5 Discussion of the palaeoenvironmental development of the Piles Copse 221 area Chapter 8. Investigation of a lowland Cornish site: Crift Down 8.0 Introduction 225 8.1 Site location and morphology 225 8.2 Sampling regime 228 8.3 Radiocarbon dating 228 8.4 Palaeoenvironmental reconstruction of the Crift Down sediment 229 8.4.1 Stratigraphical description 229 8.4.2 EDMA investigation of the Crift Down sediment 231 8.4.3 Multi-variate analysis of the Crift Down EDMA data 231 8.4.4 Interpretation of the geochemical signals from Crift Down 237 8.4.5 Pollen analysis of the Crift Down sediment 240 8.4.6 Multi-variate analysis of the Crift Down pollen data 240 8.4.7 Interpretation of the Crift Down pollen data 246 8.5 Discussion of the palaeoenvironmental development of the Crift Down 250 area Chapter 9.