A THE entitled

REGIONAL GEOCHEMICAL STUDIES OF BLACK SHALE FACIES WITH PARTICULAR REFERENCE TO TRACE ET,EMENT DISORDERS IN ANIMALS

Submitted for the degree of DOCTOR OF PHILOSOPHY in the FACULTY OF SCIENCE IN THE UNIVERSITY OF LONDON by IAN THOMSON

Royal School of Mines, February, 1971 Imperial College. ABSTRACT

The results of multi—element stream sediment reconnaissance in nine areas of England and Wales totalling; 1150 square miles are described. Black shale outcrops are present in each survey area. Regional patterns of molybdeniferous stream sediments are recordedlrelated to the outcrop of marine black shales ranging in age from Ordovician to Cretaceous, and transported overburden derived from these rocks. Observations are made on the relationship between geochemical patterns displayed by Mo, Cu, Co, Mn, Pb, Se and Zn and trace element disorders in animals. Detailed studies in five selected areas demonstrate that patterns of stream sediment containing raised values of Mo relate to districts with molybdeniferous soils derived from rocks of marine black shale facies syngenetically enriched in Mo. Where the black shales are mantled by barren overburden and in areas of other parent materials background values of Mo are recorded in soils and stream sediments. In all the areas studied the Mo content of pasture herbage on molybdeniferous soils is significantly greater than that on background soils and a broad relationship between the Mo content of stream sediment, bedrock, soil and herbage is demonstrated. However, although primarily related to the total Mo content of topsoils the Mo status of pasture herbage is shown to be influenced by soil drainage conditions and the pH, organic carbon and total iron content of topsoils. The Mo:Cu status of pasture herbage growing on molybdenum anomalous soils in the areas investigated is within the range associated with molybdenum induced copper deficiency in cattle. The results obtained indicate the probable presence of an agricultural problem in grazing cattle within the molybdenum anomaly areas. The present investigation demonstrates the extensive occurrence of molybdeniferous black shale formations and confirms the probability that molybdenum induced bovine hypocuprosis is correspondingly widespread. ii

CONTENTS

VOLUME I 22E2 ABSTRACT

LIST OF TABLES xi LIST OF FIGURES xvi CHAPTER 1 INTRODUCTION 1 1. Regional Geochemistry 2 2. Regional Geochemistry and Agriculture 4 3. Presentation of Thesis 10 4. Acknowledgements 11 CHAPTER 2 BLACK SHALES 12 1. Definition and Occurrence 12 2. Geochemistry 14 3. Black Shales and Agriculture 17 4. Black Shales in England and Wales 19 5. Selection of Reconnaissance Survey Areas 25 PART A

CHAPTER 3 REGIONAL GEOCHEMICAL RECONNAISSANCE WEST CARMARTHENSHIRE SURVEY AREA 30 1. Description of the Area 30 Location 30 K Geology and Mineralisation 30 Topography and Drainage 32 rD Climate 33 Soils 33 B Land Use 34 2. The Regional Geochemical Patterns 34 (A) Patterns related to bedrock and mineralisation 36 (B) Patterns related to the secondary environment 37 3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals 38 (A) Molybdenum and Copper 38 (B) Cobalt 39 CHAPTER 4 REGIONAL GEOCHEMICAL RECONNAISSANCE RHAYADER SURVEY AREA 40 1. Description of the Area 40 A Location 40 B Geology 40 C Topography and Drainage 42 iii

page. D Climate 42 Soils 42 Land Use 43 2. Theg Regional Geochemical Patterns 43 (A) Patterns related to bedrock and glacial drift 43 (B) Patterns related to the secondary environment 45 3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals 47 (A) Molybdenum and Copper 47 (B) Cobalt 48 CHAPTER 5 REGIONAL GEOCHEMICAL RECONNAISSANCE SHELVE SURVEY AREA 49 1. Description of the Area 49 Location 49 B Geology and Mineralisation 49 C Topography and Drainage 51 D Climate 52 E Soils 52 F) Land Use 53 2. The Regional Geochemical Patterns 53 (A) Patterns related to bedrock 55 (B) Patterns related to mineralisation 55 (C) Patterns related to the secondary environment 56 3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals 57 (A) Molybdenum and Copper 57 (B) Other Metals 57 CHAPTER 6 REGIONAL GEOCHEMICAL RECONNAISSANCE MACHYNLLETH SURVEY AREA 58 1. Description of the Area 58 A Location 58 B Geology and Mineralisation 58 C Topography and Drainage 60 (D Climate 61 B Soils 61 Land Use 62 2. The Regional Geochemical Patterns 62 ) Patterns related to bedrock 62 k) Patterns related to mineralisation 65 (C) Patterns related to the secondary environment 66 3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals 68

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(A Molybdenum and Copper 68 (B Cobalt 69 (C Other Metals 69 CHAPTER 7 REGIONAL GEOCHEMICAL RECONNAISSANCE KENDAL SURVEY AREA 70 1. Description of the Area 70 A Location 70 B Geology and Mineralisation 70 C Topography and Drainage 72 D Climate 72 (E) Soils 73 (F) Land Use 73 2. The Regional Geochemical Patterns 73 Patterns related to bedrock 74 Patterns related to mineralisation 76 (C) Patterns related to the secondary environment 76 3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals 77 (A) Molybdenum and Copper 77 (B) Cobalt 77 CHAPTER 8 REGIONAL GEOCHEMICAL RECONNAISSANCE BOWLAND FOREST SURVEY AREA 78 1. Description of the Area 78 A Location 78 B Geology and Mineralisation 78 C Topography and Drainage 80 D Climate 81 E Soils 81 F Land Use 82 2. The Regional Geochemical Patterns 82 (A) Patterns related to bedrock 84 (B) Patterns related to mineralisation 85 (C) Patterns related to the secondary environment 85 3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals 86 (A Molybdenum and Copper 86 (B Selenium 87 (C Manganese 87 CHAPTER 9 REGIONAL GEOCHEMICAL RECONNAISSANCE SHAFTESBURY SURVEY AREA 88 1. Description of the Area 88 .L1) Location 88 B) Geology 88 page (C Topography and Drainage 90 Climate 90 E Soils 91 Land Use 91 2. TherF Regional Geochemical Patterns 92 3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals 95 (A) Molybdenum and Copper 95 B) Selenium 96 0) Cobalt 96 D) Manganese 96

CHAPTER 10 REGIONAL GEOCHEMICAL RECONNAISSANCE THAME SURVEY AREA 97

1. Description of the Area 97 A Location 97 B Geology 97 C Topography and Drainage 99 D Climate 100 E Soils 100 F Land Use 101 2. The Regional Geochemical Patterns 101 A Patterns related to bedrock 103 Patterns related to pollution 104 C Patterns related to the secondary environment 105 3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals 105 Molybdenum and Copper 106 B Cobalt 106 C Other Metals 107 CHAPTER 11 REGIONAL GEOCHEMICAL RECONNAISSANCE MARKET RASEN SURVEY AREA 108 1. Description of the Area 108 (A Location 108 " Geology • 108 C Topography and Drainage 110 Climate 111 (Er Soils 111 (F)1 Land Use 112 2. The Regional Geochemical Patterns 112 3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals 116 CHAPTER 12 GENERAL DISCUSSEION : STREAM SEDIMENT RECONNAISSANCE IN AREAS OF BLACK SHALE FACiES 117 1. The Geochemical Patterns 117 vi

page (IL) Geochemical patterns related to the bedrock 117 (B) Geochemical patterns related to mineralisation and pollution 121 (C) Geochemical patterns related to the secondary environment 121 2. Agricultural Application of the Stream Sediment Reconnaissance Data 122 A Molybdenum and Copper 122 B Selenium 124 C Cobalt and Manganese 125 D Other Metals 125 3. Selection of Areas for Detailed Geochemical Investigations 126 PART B CHAPTER 13 DETAITRD GEOCHEMICAL INVESTIGATIONS WEST CARMARTHENSHIRE AREA 129 1. Introduction 129 2. Description of the.Area 129 A Geology 129 B Soils 130 C Land Use 131 3. Distribution of Metals in the Bedrock 131 4. Distribution of Metals in the Overburden 135 (A) Lateral distribution 135 (i) Metal distribution patterns related to the bedrock 135 (ii)Metal distribution patterns related to the secondary environment 138 (B) Vertical distribution 139 5. Relationship between the Metal Content of the Bedrock, Overburden and Stream Sediment 143 6. Metal Content of Herbage and Factors Influencing the Uptake of Molybdenum and Copper by Herbage 148

CHAPTER 14 DETAITRD GEOCHEMICAL INVESTIGATIONS :OWLAND FOREST AREA 152 1. Introduction 152 2. Description of the Area 152 Geology 152 B Soils 154 C Land Use 156 3. Distribution of Metals in the Bedrock 156 4. Distribution of Metals in the Overburden 163 vii

page (A) Lateral distribution 163 (i) Metal distribution patterns related to the parent materials 165 (a) Residual soils on the Millstone Grit 165 (b) Residual soils on on the Bowland Shale Group 165 (c) Soils developed on transported overburden 166 (ii) Metal distribution patterns related to the secondary environment 168 (B) Vertical distribution 171 5. Relationship between the Metal Content of the Bedrock, Overburden and Stream Sediment 174 6. Metal Content of Herbage and Factors Influencing the Uptake of Molybdenum and Copper by Herbage 179 CHAPTER 15 DETAIT,ED GEOCHEMICAL INVESTIGATIONS SHAFTESBURY AREA 185 1. Introduction 185 2. Description of the Area 185 Geology 185 B Soils 186 rCi Land Use 187 3. Distribution of Metals in the Bedrock 188 4. Distribution of Metals in the Overburden 188 (A) Overburden derived from the Oxford Clay and adjacent deposits 190 (i) Lateral distribution 190 (ii)Vertical distribution 193 (B) Overburden derived from the Kimmeridge Clay and adjacent deposits 195 (i) Lateral distribution 195 (a) Metal distribution patterns related to the bedrock 195 (b) Metal distribution patterns related to the secondary environment 196 (ii) Vertical distribution 197 5. Relationship between the Metal Content of the Bedrock, Overburden and Stream Sediment 200 6. Metal Content of Herbage and Factors Influencing the Uptake of Molybdenum and Copper by Herbage 204 viii

CHAPTER 16 DETAILED GEOCHEMICAL INVESTIGATIONS THANE AREA 209 1. Introduction 209 2. Description of the Area 209 A Geology 209 B Soils 212 C Land Use 213 3. Distribution of Metals in the Bedrock 213 4. Distribution of Metals in the Overburden 218 (A) Lateral distribution 218 (i) Metal distribution patterns related to the parent materials 218 (ii)Metal distribution patterns related to the secondary environment 223 (B) Vertical distribution 224 5. Relationship between the Metal Content of the Bedrock, Overburden and Stream Sediment 228 6. Metal Content of Herbage and Factors Influencing the Uptake of Molybdenum and Copper by Herbage 233 WAFTER 17 DETAILED GEOCHEMICAL INVESTIGATIONS MARKET RASEN AREA 237 1. Introduction 237 2. Description of the Detailed Study Areas 237 (A) Geology 237 (B) Soils 238 (C) Land Use 239 3. Distribution of Metals in the Bedrock 239 4. Distribution of Metals in the Overburden and the Relationship between the Metal Content of Rock, Soils and Stream Sediment 241 (A) Cold Hanworth district 241 (B) South Will itgham district 246 5. Metal Content of the Herbage 252 CHAPTER 18 METAL DISPERSION IN AREAS OF BLACK 253 SHALE FACTES I PRIMARY DISPERSION Distribution of Metals in the Bedrock 253 1. Introduction 253 2. The Metal Content of the Bedrock 254 3. Metal Associations in the Bedrock 258 II SECONDARY DISPERSION 263 1. Distribution of Metals in the Overburden 263 ix

page (A) The lateral distribution of metals in the overburden 263 (i) Metal distribution patterns related to parent materials 263 (ii)Metal distribution patterns related to the secondary environment 264 (B) The vertical distribution of metals within soils 265 2. The Relationship between the Metal Content of the Bedrock, Overburden and Stream Sediment and the Dispersion of Metals from Rocks of Black Shale Facies 270 (A) The dispersion of molybdenum and associated metals 270 (B) The influence of the secondary environment on metal dispersion 275 (C) Other factors influencing the relationship between the metal content of the overburden and stream sediments 277 3. The Metal Content of Herbage and Factors Influencing the Uptake of Molybdenum and Copper by Pasture Herbage 277 (A) Factors affecting the metal content of .herbage 278 (i) The influence of pasture species 278 (ii) Seasonal variation in the metal content of herbage 279 (iii)The influence of climate on the molybdenum content of herbage 280 (B) Factors influencing the molybdenum and copper status of herbage on molybdenum anomalous soils 280 (i) The molybdenum and copper content of the topsoils 280 (ii)The soil environment 281 CHLPTER 19 AGRICULTURAL SIGNIFICANCE OF DATA FROM THE DETAILED STUDY AREAS 286 1. Molybdenum and Copper 286 /133 West Caluarthenshire 290 Bowland Forest 291 C Shaftesbury 292 D Thame 294 E Market Rasen 295 2. Selenium 297 3. Cobalt 297 4. Manganese 298 x

PUP CHAPTER 20 EXTRAPOLATIONS BEYOND THE SURVEY AREAS 300 1. The Black Dicranograptus Shales 300 2. The Bowland Shale Group 301 3. The Lower Oxford Clay 302 4. The Kimmeridge Clay 304 5. Conclusions 306 CHAPTER 21 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER RESEARCH 307 1. Summary and Conclusions 307 (A) Initial statements 307 (B) Stream sediment regional geochemical reconnaissance surveys 307 (0) Distribution of metals in the bedrock 310 (D) Distribution of metals in the overburden 311 (E) Relationship between the metal content of bedrock, overburden and stream sediment 313 (F) Metal content of pasture herbage 314 (G) Agricultural significance of data from detailed study areas 316 (H) Extrapolations 316 2. Recommendations for Further Research 317 REFERENCES 320 APPENDIX 333 1. Sampling and Sample Preparation 333 A Stream sediment samples 333 B Rock samples 336 C Soil samples 336 D Herbage samples 339 2. Analysis of Samples 339 A Spectrographic method 340 B Atomic absorption methods 346 C Wet chemical methods 348 D Comparison of analytical results 350 3. Data Handling 351 (A) Statistical processing 351 Presentation of data 353 VOLUME II Part 1 Maps depicting the results of the nine geochemical stream sediment surveys Part 2 Figures illustrating the distribution of metals in the bedrock Part 3 Figures illustrating the relationship between the metal content of the overburden and geology along soil traverse lines in the five detailed study areas xi

LIST OF TABLES

No. Title page. 1 Essential trace elements for higher plants and mammals including man 5 2 Stratigraphy of the West Carmarthenshire survey area 31 3 Range and mean metal content of the minus 80—mesh fraction of stream sediments from the principal geological units of the West Carmarthenshire survey area 35 4 Stratigraphy of the Rhayader survey area 41 5 Range and mean metal content of the minus 80—mesh fraction of stream sediment from the principal geological units of the Rhayader survey area 44 6 Range and mean metal content of the minus 80—mesh fraction of stream sediments, and pH of stream waters, from areas of open moorland and agricultural land in the Rhayader survey area 46

7 Stratigraphy of the Shelve survey area 50 8 Range and mean metal content of the minus 80—mesh fraction of stream sediments from the principal geological units of the Shelve survey area 54 9 Stratigraphy of the Machynlleth survey area 59 10 Range and mean metal content of the minus 80—mesh fraction of stream sediments from the principal geological units of the Machynlleth survey area 63 11 Range and mean metal content of the minus 80—mesh fraction of stream sediments, and pH of stream waters, from the upland and coastal plateau districts of the Machynlleth survey area 67

12 Stratigraphy of the Kendal survey area 71 13 Range and mean metal content of the minus 80—mesh fraction of stream sediments from the principal geological units of the Kendal survey area 75 14 Stratigraphy of the Bowland Forest survey area 79 15 Range and mean metal content of the minus 80—mesh fraction of stream sediments from the principal geological units of the Bowland Forest survey area 83 16 Stratigraphy of the Shaftesbury survey area 89 xii No page 17 Range and mean metal content of the minus 80—mesh fraction of stream sediments from the principal geological units of the Shaftesbury survey area 93 18 Stratigraphy of the Thane survey area 98 19 Range and mean metal content of the minus 80—mesh fraction of stream sediments from the principal geological units of the Theme survey area 102 20 Stratigraphy of the Market Rasen survey area 109 21 Range and mean metal content of the minus 80—mesh fraction of stream sediments from the principal geological units of the Market Rasen survey area 113 22 Range and mean metal content of the Ordovician rock units in the area of detailed studies, West Carmarthenshire area 133 23 Range and mean metal content of overburden developed on the principal parent materials, West Carmarthenshire area 136 24 Range and mean metal content of residual overburden on the Hendre Shales at Meidrim and Llanboidy 137 25 Range and mean metal content of soils,sampled at two depths, developed on the principal parent materials, West Carmarthenshire 140 26 Metal content of selected residual soils of varying drainage status developed on the Dicranograptus shale s 142 27 Range and mean metal content of rocks and associated residual soils around Meidrim, West Carmarthenshire 144 28 Mean metal content of soils and stream sediments on the principal bedrock units in the West Carmarthenshire area 145 29 Range and mean molybdenum and copper content of topsoils and associated herbage on soils derived from the principal parent materials in the West Carmarthenshire area 149 30 Range and mean metal content of the principal Carboniferous rock units, Bowland Forest area 157 31 Range and mean metal content of the principal lithologies of the Bowland Shale Group and the Worston Shale Group 158 32 Mean metal content of samples from Upper Visean/ Lower Namurian marine black shales at three localities in England and Eire 160

xiii No . psea

33 Range and mean metal content of overburden developed on the principal parent materials, Bowland Forest area 164 34 Range and mean metal content of soils from shedding sites and receiving sites on fell slopes and normal sites on low angled slopes away from the fells 170 35 Range and mean metal content of soils, sampled at two depths, developed on the principal parent materials, Bowland Forest area 172 36 Metal content of selected molybdenum anomalous soils of varying drainage status, Bowland Forest area 173 37 Mean metal content of rocks, soils and stream sediments in the Easington Brook catchment, Bowland Forest area 175 38 Mean metal content of soils and adjacent stream sediments at normal and receiving sites in the Chipping district, Bowland Forest area 178 39 Range and mean molybdenum and copper content of topsoils and associated herbage on soils derived from the principal parent materials in the Bowland Forest area 180 40 Range and mean molybdenum and copper content of herbage on molybdenum anomalous soils of contrasting drainage status, Bowland Forest area 182 41 Metal content of bedrock samples from the Shaftesbury survey area 189 42 Range and mean metal content of overburden developed on the principal parent materials, Shaftesbury area 191 43 Range and mean metal content of soils, sampled at two depths, developed on the principal parent materials, Shaftesbury area 194 44 Metal content of selected residual soils developed on the Kinneridge Clay 198 45 Mean metal content of soils and stream sediments on the principal bedrock units in the Shaftesbury area 202 46 Range and mean molybdenum and copper content of topsoils and associated herbage on soils derived from the principal parent materials in the Shaftesbury area 205 xiv

No. page

47 Range and mean metal content of the principal bedrock units in the Thame area 215 48 Range and mean metal content of samples from clay and shale members of the Oxford Clay formation, Thane area 216 49 Range and mean metal content of overburden developed on the principal parent materials, Thane area 219 50 Range and mean metal content of soils, sampled at two depths, developed on the principal parent materials, Thame area 225 51 Metal content of selected soils developed on the principal parent materials in the Oxford Clay Vale, Thame area 226 52 Range and mean metal content of rocks and associated residual soils, Thame area 229 53 Range and mean metal content of soils and stream sediments on the principal i.arent materials in the Thane area 231

54 Range and mean molybdenum and copper content of topsoils and associated herbage on soils derived from the principal parent materials in the Thane area 234 55 Range and mean metal content of overburden developed on the principal parent materials in the Cold Hanworth district 242 56 Mean metal content of soils and associated stream sediments on the principal parent materials in the Cold Hanworth district, Market Rasen area 245 57 Range and mean metal content of overburden developed on the principal parent materials in the South Willingham district 247 58 Mean metal content of rocks, soils and associated stream sediments in the South Willingham district, Market Rasen area 249 59 Range and mean molybdenum and copper content of topsoils and associated herbage on soils derived from the principal parent materials, Market Rasen area 251 60 Essential features of the four black shale formations sampled in the programme of detailed studies 255 XV

No. 61 Mean metal content of the four black shale formations sampled compared with average values for sedimentary rocks 256 62 Geometric mean values for the ratio metal content of topsoil (0-6 inches)/metal content of subsoil (12-18 inches), calculated from 154 Mo—rich soils 267 63 The molybdenum and copper status of mixed pasture herbage from molybdenum anomalous and background districts in five areas of detailed studies 289 64 Regional stream sediment reconnaissance survey sampling logistics 334 65 Distribution of rock, soil and herbage samples from the fire follow up areas 337 66 Spectrographic equipment and conditions 342 67 Wavelengths and effective concentration ranges 343 68 Analytical precision of the spectrographic method, based on replicate analyses of randomly selected samples of stream sediment, rock and soil 344 69 Accuracy of the spectrographic method as shown by ten replicate analyses of G.1 and W.1 345 70 Instrument settings for the determination of copper using the Perkin—Elmer 303 spectrophotometer 347 ::vi

LIST OF FIGURES

Figure Title ZIES 1 Outcrop of the Principal Marine Black Shales in England and Wales 20 2 The Incidence of Bovine Copper Deficiency in Relation to the Outcrop of the Principal Marine Black Shales in England and Wales 25 3 Location of Stream Sediment Reconnaissance 27 Survey Areas 4 Location and Topography of the West Carmarthenshire Survey Area 30 5 Geology of the West Carmarthenshire Survey Area 31 6 Map Illustrating the Glaciation of South and Central Wales and the Welsh Borderlands 31 7 The Incidence of Trace Element Induced Agricultural Disorders in the West Carmarthenshire Survey Area 38 8 Location and Topography of the Rhayader Survey Area 40 9 Geology of the Rhayader Survey Area 41 10 Location and Topography of the Shelve Survey Area 49 11 Geology of the Shelve Survey Area 50 12 The Incidence of Trace Element Induced Agricultural Disorders in the Shelve Survey Area 56 13 Location and Topography of the Machynlleth Survey Area 58 14 Geology of the Machynlleth Survey Area 59 15 The Incidence of Trace Element Induced Agricultural Disorders in the Machynlleth Survey Area 68 16 Location and Topography of the Kendal Survey Area 70 17 Geology of the Kendal Survey Area 71 18 Map Illustrating the Glaciation of Nbrth West England 71 19 Location and Topography of the Bowland Forest Survey Area 78 xvii Following; Figure maa 20 Geology of the Bowland Forest Survey Area 79 21 The Incidence of Trace Element Induced Agricultural Disorders in the Bowland Forest Survey Area 86 22 Location and Topography of the Shaftesbury Survey Area 88 23 Geology of the Shaftesbury Survey Area 89 24 The Incidence of Trace Element Induced Agricultural Disorders in the Shaftesbury Survey Area 95 25 Location and Topography of the Thame Survey Area 97 26 Geology of the Thame Survey Area 98 27 The Incidence of Bovine Copper Deficiency and Infertility in the Thame Survey Area 105 28 Location and Topography of the Market Rasen Survey Area 108 29 Geology of the Market Rasen Survey Area 109 30 Map Illustrating the Glaciation of Mid Lincolnshire and the Distribution of Certain Superficial Deposits 109 31 Location, Geology and Distribution of Molybdenum in Stream Sediment South West of Bedford 120 32 Location of Soil Traverse Lines and Rock Sampling Points in Relation to the Molybdenum Stream Sediment Anomalies in the West Carmarthenshire Survey Area 129 33 Variation of Iron with Manganese and Cobalt, Molybdenum with Organic Carbon, Iron and Vanadium, and of Vanadium with Organic Carbon in the Dicranograptus Shales 134 34 Molybdenum Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil 150 35 Copper Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil 150 36 Location of Soil Traverse Lines and Rock Sampling Points in Relation to the Molybdenum Stream Sediment Anomalies in the Bowland Forest Survey Area 156 xviii

Following, Figure Page 37 Variation of Organic Carbon and Iron with Molybdenum, Selenium, Copper, Vanadium, Chromium and Nickel and of Organic Carbon with Iron in the Bowland Shales 160 38 Molybdenum Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil 182 39 Copper Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil 183 40 Location of Soil Traverse Lines and Rock Sampling Points in Relation to the Molybdenum Stream Sediment Anomalies in the Shaftesbury Survey Area 189 41 Molybdenum Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil 206 42 Copper Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil 207 43 Location of Soil Traverse Lines and Rock Sampling Points in Relation to the Molybdenum Stream Sediment Anomalies in the Thane Survey Area 209 44 Molybdenum Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoils 235 45 Copper Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil 235 46 Location of Soil Traverse Lines and Rock Sampling Points in the Market Rasen Survey Area 237 47 Metal Content of Bedrock Samples from the South Willingham District, Market Rasen Survey Area 239 48 Relationship between the Molybdenum Content of Topsoils and Pasture Herbage 280 49 Relationship between the Copper Content of Topsoils and Pasture Herbage 281 50 Outcrop of the Black Dicranograptus Shales in South and South West Wales 300 xi::

Foilowin Figure pa e 51 Outcrop of the Bowland Shale Group and Associated Rocks in Lancashire and Yorkshire 301 52 Outcrop of the Oxford Clay Formation in England 302 53 Vertical Sections Illustrating the Variation in Facies and Thickness of the Oxford Clay Formation 302 54 Outcrop of the Kimmeridge Clay Formation in England 304 55 Vertical Sections Illustrating the Variation in Facies and Thickness of the Kimmeridge Clay Formation 304 56 Relationship between Spectrographic and Colorimetric Determination of Molybdenum and Spectrographic and Atomic Absorbtion Determination of Copper. Data from 220 Samples of Stream Sediment and Soil 350 1

CHAPTER 1: INTRODUCTION

In view of the rapidly expanding human population it is essential that maximum levels of food production are achieved and any factor relevant to this objective is worthy of consideration. Extensive scientific investigation has led to a better understanding of those features affecting fertility and production. The complex relationship between the plant and its environment is being revealed, and the importance of minor elements present in trace quantities is now known. Work in many countries has shown that these elements may be present in varying quantities in the soil and that these variations, although small, can lead to nutritional disorders in both plants and grazing animals. Developed for use in mineral exploration, regional geochemical surveys are yielding considerable data on the distribution of trace elements in rocks, soils, herbage, stream sediment and drainage water. Webb (1964) proposed that these surveys could, with a little modification, be used to provide information of agricultural and medical value. Previous work in the British Isles has related nutritional disorders in grazing cattle, due to a high dietary intake of Mo and Se, to syngenetic enrichment of these metals in rocks of black shale facies underlying the pastures. Geological considerations indicate widespread areas of England and Wales underlain by black shales where similar metal enrichment and associated nutritional disorders might be expected. 2

In this thesis the results of regional geochemical stream sediment surveys in nine areas are presented together with soil, herbage and rock sampling in selected districts. The relationship between patterns of raised levels of Mo in stream sediments and the occurrence of Mo—rich soils and herbage associated with black shales enriched in Mo is discussed, together with the agricultural significance of the data obtained. It is shown that in several previously unrecorded areas the raised levels of Mo in herbage are sufficient to be detrimental to animal health and affect fertility and production.

1. Regional Geochemistry Original work by Goldschmidt in Scandinavia and by Vernadsky and Fersman in the U.S.S.R. during the 1930s demonstrated that anomalously high concentrations of trace elements in rocks were reflected by similar anomalies in the soil and herbage above. Systematic sampling of soils or herbage could thus be used to delineate concealed mineral deposits. Since then applied geochemical techniques have been widely used in the search for minerals. This work is encouraged by the demands of our hilly developed society and growing population for further metal reserves. Techniques of rock, soil, herbage, stream sediment and water sampling have been developed (Hawkes and Webb, 1962). As a means of rapid and inexpensive reconnaissance, stream sediment sampling has been proved most effective and is now a standard exploration technique in the mining industry. Stream sediment is composed of clastic material together with soluble matter, incorporated by precipitation 3 or by adsorption and absorbtion on elastic or organic material. The technique is based on the premise that these materials are all weathering products derived from the catchment area and that the sediment is thus a composite sample of the rocks and soils of the catchment area upstream from the sample point. Systematic sampling and analysis reveals catchments containing gross geochemical anomalies suggesting the presence of mineralisation. Stream sediment reconnaissance surveying on a regional scale in eastern Canada (Hawkes et al, 1956) revealed not only gross anomalies due to mineralisation but also broad background variation in the distribution of trace elements correlated with the principal bedrock units. Subsequent multi—element regional geochemical surveys in Zambia (Webb et al, 1964), Sierra Leone (Nichol et al, 1966) and in England and Wales (Khaleelee, 1969) confirmed that the composition of the bedrock is the dominant influence on geochemical patterns revealed by stream sediment surveys. Nevertheless the relationship between bedrock, soil and stream sediment geochemistry is not simple. The dispersion of elements from the bedrock to the soil and drainage network is influenced by physical and chemical factors related to local environment. These principally affect the relative mobility of elements through the media. The more soluble elements may be preferentially leached from the soil; conversely, metal accumulation may occur due to the formation of soil concretions. In stream sediments precipitation and co—precipitation phenomena may enhance the levels of trace elements in local situations. The relationship between unweathered bedrock, soil and 4

stream sediment may therefore be complex and topography, hydrography, vegetation, climate and soils are amongst the environmental features that must be considered when interpreting geochemical data. Despite the complexities referred to above, in drift free areas the composition of the bedrock remains the principal influence on geochemical patterns revealed by stream sediment surveys.

2. Regional Geochemistry and Agriculture Over the last sixty years research in various branches of the biological sciences has demonstrated that in addition to the more widely recognised nutritional requirements very small quantities of certain elements are necessary for healthy plant and animal life. These are the micro nutrients or essential trace elements (Table 1) and are generally available to the plant via the soil. Other trace elements, including As, Hg and Pb, though not essential to life, are known to be toxic when present in quantities above a tolerance level (Underwood, 1962). Disorders in plants and animals resulting from an imbalance amongst the essential trace elements are recognised and have been reviewed (Underwood, 1962, Schutte, 1964). The trace element status of the plant is the product of complex environmental circumstances. These include the composition of the soil parent material, together with the nature of the weathering process and the chemistry of the soil produced which influences the mobility, distribution and occurrence of trace elements and hence their availability to plants. Plants themselves exhibit selective rates of trace element uptake between species and seasonal variations

5

Table 1 Essential trace elements for higher plants and mammals including man (Modified from Schutte (1964), Underwood (1962) and Voisin (1959))

Higher Plants Mammals

Iron Iron Boron Chlorine Chlorine Copper Copper. Cobalt Manganese Iodine Molybdenum Manganese Zinc Molybdenum Selenium Zinc within species (Fleming, 1965). By the application of fertilisers man may alter the trace element status of a soil. Lime and other soil dressings may drastically affect soil chemistry and the availability of trace elements to plants (Mitchell, 1955). In turn the grazing animal is dependent on plant material for the greater part of its trace element requirements. The animal may spend much of its life in the confined area of one farm where, for the six to eight months of the grazing season, it is dependent on local pasture for its nutrition. Some animals, particularly dairy cattle, receive a food supplementation of artificial concentrates with added vitamins and trace elements to aid milk yield or weight gain. In winter many animals receive food stuffs produced outside the local area. These additional foods will probably correct trace element imbalances and modify the animals! response to the local environment. The suggestion that geology influences human health is more controversial. Many peoples are dependent on locally grown food for their diet. In rural areas of Great Britain milk and vegetables are frequently obtained from producer retailers. Furthermore supplies of drinking water may be obtained from restricted catchments or particular underground sources. However, it is argued that in modern society the nutritional status of any one person is dependent on foods gained from a host of sources widely dispersed geographically. The link between local geology, trace elements and health is, therefore, largely obscured or destroyed. Nevertheless, the importance of trace elements in nutrition is recognised and there is a growing awareness of 7 the importance of geology as a controlling influence. With the accumulation of information on trace element content of rocks, soils and herbage, workers in the U.S.S.R. have been able to observe regional variations. Pioneer studies by Vinogradov and other Soviet scientists established the concept of 'biogeochemical provinces' defined by Vinogradov (1963) as:— II regions on the earth's surface that differ from adjacent regions in their contents of certain elements or compounds and thus impress specific biological characteristics on the local flora and fauna. In extreme cases, as a result of deficiency or excess of an element (or elements) certain endemic diseases may exist within a biogeochemical province which affects plants, animals and man." Extensive studies in the U.S.S.R. are reviewed by Glazovskaya (1967). Similar studies by western scientists include work in the British Isles by Ferguson et al (1943) on molybdenum induced copper deficiency in Somerset, Bromehead (1943) on the occurrence of fluorosis, Fleming (1962) on the distribution of seleniferous vegetation and the incidence of selenosis in Ireland and Pizer et al (1966) on copper deficiency on Penland soils. The use of stream sediment surveys to delineate areas characterised by trace element distributions of consequence to agriculture or epidemology was suggested by Webb (1964) who described exploratory studies which proved encouraging. It was found that in Eire low levels of Co in stream sedithent in Co. Wicklow and Co. Carlow outlined a granite outcrop and enclosed an area with a high incidence of cobalt pine in sheep. In Co. Limerick anomalously high concentrations of Se and Mo in stream sediments were found in areas underlain by Namurian black shales, associated with farmland on which selenium toxicity and molybdenum induced copper deficiency were known. In addition a reconnaissance survey in Devon revealed a previously unknown zone of Mo—rich stream sediments, soils and rocks. The incidence of copper deficiency in livestock in the area is probably related to the high Mo concentrations. Subsequently research was extended by multi—element regional geochemical surveys in North Wales, North Devon and Derbyshire. From these surveys further information of agricultural significance was gained in relation to the incidence of cobalt pine in sheep, manganese deficiency and infertility in cattle and molybdenum induced bovine hypocuprosis (Webb, Thornton and Nichol, 1966, Fletcher, 1968, Thornton, 1968). The survey of Derbyshire revealed raised levels of No in stream sediments, soils and herbage in areas underlain by Visean/Namurian marine black shales. Although clinical copper deficiency had been recognised in the area, he known area of incidence occupied less than 10% of the total area of the Mo anomaly. Subsequent blood testing of stock within the Mo. anomalous area and in nearby control areas demonstrated the strength of the correlation between the extended Mo anomaly area revealed by the survey and the incidence of bovine hypocupraemia. The disorder occurred for the most part at a subclinical level. Although animals lacked the usual symptoms of copper deficiency an improvement of up to 50% in live weight gain was observed on copper supplementation trials in anomalous areas 9

(Thornton, 1968). The results obtained in Derbyshire thus fully justified the claim made earlier (Thornton et al, 1966) that:— "Under conditions where visual symptoms of a deficiency or toxicity are not always apparent and ,There the problem may be largely at a sub— clinical level, geochemical reconnaissance techniques are seen to present a useful additional aid to the agricultural specialist and advisor." Latterly a geochemical stream sediment reconnaissance survey of the entire outcrop of the bias in England and Wales has shown that the occurrence of raised levels of Mo related to marine black shales in the formation is very much more extensive than had been previously recognised by agriculturalists (Thornton, Moon and Webb, 1969). The enrichment of Mo and Se to levels potentially toxic to livestock has been /16-bed in a number of black shale facies during regional geochemical reconnaissance surveys in the British Isles (Webb and Atkinson, 1965, Webb, Thornton and Fletcher, 1966, 1968, Thornton, 1968, Thorilton, Moon and Webb, 1969). Enrichment of trace elements in rocks of this type is a feature often recorded in the geological literature (Goldschmidt, 1954, Krauskopf, 1955, Dunham, 1961, Vine, 1966, 1969). In view of this feature the present study was initiated in 1967 to investigate a number of black shales in England and Wales and to assess the potential extent of further areas in which molybdenum induced bovine copper deficiency might be expected. The work forms part of the continuing studies by the Applied Geochemistry Research Group under the direction of Professor J.S. Webb. 10

3. Presentation of Thesis In this thesis the writer presents a review of black shale geochemistry, paying particular regard to the agricultural implications of Mo enrichment in these rocks. The occurrence of black shales in England and Wales is described and the selection of areas for investigation is made on geological grounds. Part A contains the results of multi—element stream sediment surveys in nine reconnaissance areas. The data is displayed in map form (Volume II) with a short interpretive description of principal patterns in the text. An appraisal is made of the geochemical and agricultural significance of the results. In Part B detailed geochemical investigations in five selected areas characterised by Mo—rich stream sediments are recorded. Soils, herbage and rocks were sampled and the results of multi—element analysis are described. The dispersion of Mo and associated metals in bedrock of marine black shale facies and soils and stream sediments derived from these rocks is examined. In addition the Mo and Cu status of mixed pasture herbage on Mo anomalous and background soils is investigated with regard to the possible incidence of molybdenum induced bovine copper deficiency. The geochemical and agricultural implications of the detailed surveys are discussed and possible extrapolations demonstrated. Suggestions are then made for further work. A description of the sampling and analytical techniques used and the methods of data handling employed are found in the Appendix. 4. Acknowledgements The writer is indebted to all members of the Applied Geochemistry Research Group for their comradeship and is most grateful to his supervisors, Professor J.S. Webb and Dr. I. Thornton,for their constant advice, encouragement and criticism. The support of M. Clements and E. Bannejee on analytical matters is appreciated. Advice and assistance from Dr. R. Howarth and members of the Imperial College Computer Unit and the University of London Computer Centre is acknowledged. The co—operation and assistance of the Institute of Geological Sciences, the National Agricultural Advisory Service, the Soil Survey of England and Wales and the Veterinary Investigation Service is acknowledged. Messrs. B. Clayden, D. Carrol and D. Findlay, officers of the Soil Survey, are thanked for their assistance in providing information in the field. The co—operation of local veterinary practitioners is appreciated, together with the understanding of farmers and landowners in the areas investigated, without whose permission field sampling would have been impossible. The London Brick Company are thanked for making available samples of Oxford Clay from their Calvert Brickworks. For unfailing support and encouragement and her considerable assistance in the typing of this thesis the writer is indebted to his wife. The writer received financial support from the Natural Environment Research Council during the three years of research work. 12

CHAPTER 2: BLACK SHALES

1. Definition and Occurrence It is not possible to apply a precise definition to black shales because of the frequent casual use of the term in the past. Essentially understood as describing a dark coloured, fine grained, sedimentary rock, the term 'black shale' has been applied in a variety of circumstances. Shale has a precise definition in terms of coiiposition. In the context of 'black shale', the term has been used to describe rocks more precisely defined as siltstone (Payton and Thomas, 1959, Conant and Swanson, 1961, Vine, 1969), marlstone (Wedepohl, 1964) and also to intermediate deposits of claystone and coal (Zangerl, Rainer and Richardson, 1963) and of phosphorite and siltstone (Vine, 1969). Shale also has a connotation of fracture habit implying fisility. Black shales have been recorded with a variety of fracture habits (Swanson, 1961), including massive, conchoidal, slaty,. plastic, nodular and the normal shale fisility. Pew black shales are truly 'black' in colour; most are dark hues of brown and olive (Swanson, 1961). The dark colour is usually,imparted by disseminated carbonaceous material of organic origin, whilst in recent black muds the colour is often due to the presence of dark sulphides. Alternatively the dark colour may be due to the presence of manganese oxide or a concentration of dark detrital minerals (Swanson, 1961) Usually grouped with black shales are a host of other rocks, including oil shale, bituminous shale, graphitic shale, alum shale, jet rock, euxinic shale, sapropelite, 13

gyttja, black clay and black mud (Krauskopf, 1955). In an attempt to explain the application of the term black shale Vine (1966, 1969) adopted the following classification: "A classification for black shale could be constructed on a triangular diagram the corners could be thought of as (1) Fine grained detrital minerals, (2) Chemically or biogenetically precipitated mineral natter and (3) Carbonaceous organic matter potential end members include claystone, siltstone, limestone, dolomite, annhydrite, chert, phosphorite and coal. this allows a wide range of rock types to be included in the general term black shale. By this definition black shale includes all rock types of intermediate character but not the pure end member this wide range of rock types includes examples from many geological environments If The term black shale lacks any full genetic significance apart from implying a reducing environment at deposition, with poor water circulation, thus permitting the accumulation of organic matter, sulphides and fine grained detrital material. Black shales and recent black muds (the presumed precursor of black shales) are recognised as accumulating in a variety of ancient and modern environments (Dunham, 1961, Twenhofel, 1939) including: (i) Ill drained terrestrial swamps (ii) Eutrophic lakes (iii) River estuaries — tidal lagoons and delta tops (iv) Land locked sea basins and arms of the sea with silled straits or entrances (v) Deposits in sea basins or in open seas of varying depth lacking any circulation of bottom waters. A broad twofold division of ancient deposits into marine and non—marine black shales is possible based on the 14 character of black shale, associated sediments, fauna and flora. Marine black shales are characterised by a uniformity of thickness and lithology over wide areas whilst non—marine shales tend to be erratic in thickness and lithologically variable, grading rapidly into normal shale, sandstone or coal. In marine black shales, in addition to the presence of organic matter and sulphides, the restricted environment of deposition is demonstrated by the fauna. Fossil organisms encountered are consistently representative of a planktonic, pseudo—planktonic or neretic habitat, having entered the black mud from a favoured environment in oxygenated surface waters. Indiginous benthonic forms are almost unknown indicating a hostile, fetid sea bottom, rich in decaying organic matter and sulphides, lacking the free oxygen necessary for normal life (Mari., 1925).

2. Geochemista In addition to the more widely encountered processes affecting metal distributions in fine grained detrital sediments, the presence of organic matter and sulphides play important roles in the accumulation of trace elements in black shales. Krauskopf (1955) notes the occurrence of significant accumulations of trace elements in organic deposits, including black shales, and records Ag, As, Mo, V, Ni, Pb, Ge, Cr, Zn and El in concentrations from x10 to x10,000 greater than the average for sedimentary rocks. Many other workers have studied the role of organic matter in the accumulation of trace elements in sedimentary deposits. Much of the 15

information gained has been reviewed by Manskaya and Drozdova (1968) who recognise a number of processes facilitating trace element concentration including: (i) the accumulation of trace elements during the life processes of plants and animals (ii) the formation of strong organo-metal complexes that persist during putrefaction (iii) the sorbtion of elements onto dispersed organic matter in aqueous media. In stagnant water conditions of black shale deposition hydrogen sulphide may accumulate in solution to the point where sulphides are precipitated (Twenhofel, 1939). Further sulphides are formed by bacterial activity and during the putrefaction of organic matter (Dunham, 1961). These sulphides, dominantly pyrite, are able to incorporate trace elements by absorption and adsorption either directly from solution in water or by redistribution of elements from decomposing organic matter. A feature of many marine black shales is the formation of an intimate mixture of organic matter and sulphides termed gyttja or sapropelite (Goldschmidt et al, 1948, Krauskopf, 1955). In general sulphides are more abundant in marine organic deposits than in those of non-marine origin. Pertinent to the present investigation is the emphasis that Korolev (1958) has placed on the role of iron sulphides in the accumulation of Mo, Ni, Co and V in sedimentary rocks of black shale facies. It may be concluded that black shales are rocks of mixed composition in which the content of trace elements is the result of a variety of processes which may be 16 summarised as: (i) trace elements in detrital minerals (ii) trace elements incorporated with clay minerals by adsorption and absorption (iii) trace elements incorporated with organic matter (iv) trace elements incorporated in sulphides (pyrite etc.) Geochemical differences between marine and non—marine black shales are recorded in the literature (Krauskopf, 1955, Degens, Williams and Keith, 1957, Dunham, 1961, Swanson, 1961, Tourtelot, 1964). The distinction can be largely explained by the differing role. of organic matter in trace element accumulations in the two environments. Krauskopf (1955) and Goldschmidt (1954) recognise a tendency for coal (terrestrial organic matter) to be enriched in Di, Cd, Ni, Ge, As whilst U, V, Ni, Mo, Cu, Pb, Zn, Co, W and Ag tend to be enriched in petroleum (marine organic matter) and form the assemblage typical of oil, asphalt and marine black shales. Manskaya and Drozdova (1968), noting observed and experimental work, explain the above distribution as due to differences in the physical and chemical composition of terrestrial/non—marine and marine organic matter together with the influence of contrasting environments of deposition in fresh and saline waters. Manskaya and Drozdova (1968) stress the role of organic matter in controlling the accumulation of U, V, and Mo in marine sedimentary rocks. The total trace element content of a black shale is thus dependent not only on the factors noted earlier but also on the quantity and composition of the organic matter present. Additional factors controlling trace element 17 accumulation are a continuing supply of metals and the maintenance of reducing conditions. The accumulation of trace elements may be so considerable that the resulting concentrations are of economic value as ores. The Cu deposits of the Kupferschiefer (Wedepohl, 1964) and Rammelsberg (Kraume, 1955) in Germany, Mt. Isa Queensland (Fisher, 1960), the Zambian Copper Belt (Garlick, 1961) are all associated with or included in marine black shales and their origin attributed to sedimentary processes.

3. Black Shales and Agriculture By the processes of weathering a black shale will give rise to a soil. In cool temperate climates, two features of consequence to agriculture will be imparted to the soil so produced: (±) Physical characters. Black shales tend to offer little resistance to weathering processes, forming vales between ridges supported by more resistant rocks. Soils on black shales are typically heavy textured and poorly drained due to the high content of fine grained material inherited from the bedrock, and the impervious nature of the underlying solid geology. (ii) Chemical characters. Reference here is restricted to the trace elements. The general trace elememt character of the bedrock is usually preserved in the soil produced. Soils derived from organic rich or pyritous marine black shales will thus tend to contain higher levels of V, Mo, Ni, 18

Cr, Pb and Cu than those on surrounding rocks. Molybdenum is an essential element in the nutrition of plants and higher animals (Underwood, 1962). However, if Mo is present in the diet of bovines above a tolerance level it will interfere with the normal metabolic processes of the animal, producing a conditioned copper deficiency (Underwood, 1962). The disorder can be corrected by providing a supplementary supply of Cu or by removing the animal to an area where the level of Mo is normal. Raised levels of Mo in black shales are made available to animals via the soil and plants although the relationship between Mo in rock, soil and plants is not always straightforward. Extensive studies have been made on the mode of occurrence, distribution and availability to plants of soil Mo. Various authors have concluded that under field conditions the uptake of Mo by herbage is influenced by environmental conditions including soil reaction (Lewis, 1943, Piper and Beckwith, 1949, Davies, 1956, Jones, 1957), drainage conditions (Lewis, 1943, Mitchell et al, 1957, Kubota et al, 1961, 1963), and the fixation of Mo by ferric oxides (Robinson and Edgington, 1954, Wells, 1956, Reisenaur et al, 1962) whilst topsoil organic matter may also be of importance (Barshad, 1951a, Grigg, 1953, Walsh et al, 1953, Davies, 1956, Ng and Bloomfield, 1961, 1962, Bloomfield, 1963, Mitchell, 1966). Further studies have been made of Mo in plants (Barshad, 1948, 1951a, 1951b, Piper and Beckwith, 1949, Stout et al, 1951, Kretschmer and Allen, 1956, Mitchell, 1957, Field, 1957, Fleming, 1965) and on the role of Mo in bovine nutrition (Ferguson et al, 1943, Allcroft, 1946, 1952, Allcroft and Lewis, 1956, 1957). Selenium is also essential for higher mammals and 19 similarly is toxic in quantities above a tolerance level (Underwood, 1962). Selenium is an element occasionally concentrated in marine black shales. In Co. Limerick, Ireland, raised levels of Se in Namurian black shales are known to be the cause of selenosis in livestock (Webb and Atkinson, 1965). The conditions for Se uptake by plants and hence availability to animals are, however, specific even if large quantities of Se are present in the soil. Selenium rich vegetation is restricted to organic rich (peaty) alkaline soils (Webb and Atkinson, 1965). A number of studies in the British Isles have identified marine black shales as the source of raised levels of Mo and Se responsible for nutritional disorders in livestock (Ferguson et al, 1943, Le Riche, 1959a, 1959b, Webb, 1964, Webb and Atkinson, 1965, Webb, Thornton and Nichol, 1966, Webb, Thornton and Fletcher, 1966, Thornton, Atkinson, Webb and Poole, 1966, Thornton, 1968).

4. Black Shales in England and Wales Marine black shales are recorded throughout England and Wales from all the geological systems. A limited number of geochemical studies have been made, both of the rocks alone and with application to agricultural problems, and are referred to below. An investigation of the geological literature reveals further marine black shales likely to be enriched in Mo and Se. A sound prediction of trace element enrichment is not possible due to the uncertainty of correctly recognising the distinctive lithological and faunal features of metal rich deposits from published descriptions of black shales. This is due to (i) the lack 20 of a precise definition for the term black shale and its subsequent casual use, often to describe what is merely the darkest rock of an area and (ii) the stress placed on palaeontology by many workers in England and Wales, frequently to the exclusion of a full description of the rocks under consideration. Nevertheless, a number of distinctive marine black shales can be recognised as displaying, to a greater or lesser extent, the characters of metal rich black shales and are noted below, together with those already known to be enriched in trace elements. The principal occurrences are summarised stratigraphically and their outcrop shown in Fig. 1. A. Cambrian (Al)* The mid Cambrian Clogau Shales (Menevian) pf the Harlech Dome have been studied by Price (1963) and identified as a source of Mo by Thornton (1968). Additional black shale developments are the Upper Cambrian Dolgellau Beds (A2)(Cox and Wells, 1927). In the Welsh Borderlands the Upper Cambrian Shineton Shales of Shropshire (A3) contain thin black shale horizons (Whittard, 1952) whilst the Whiteleaved Oak Shales of Malvern (A4) are knom to be enriched in some trace elements (pers. comm. J. Dawson). B. Ordovician Marine black shales are developed at a number of horizons throughout the Welsh geosyncline as part of the graptolitic

* The outcrop of black shales mentioned in the text is displayed in Fig. 1 where the formations are identified by the symbols Al, A2 etc. -H1 Fig.1. Outcrop of the Principal Marine "Black Shales" in England and Wales. Ft (for explanation and key see text)

E3

Ft "Black Shale" Outcrop.

AZ (H1 Al B4 83 B B3

ci 83

Southern Luna of Quaternary Ice Sheet. --

H4

2p 4p 6p El? Igo Scale In Miles 21 shale facies (0.T. Jones, 1938). (B1) Arenig — Black graptolitic shales occur in Pembrokeshire (O.T. Jones, 1938, 1956). (B2) Llanvirn — Graptolitic black shales are encountered in Pembrokeshire interbedded with volcanics extending into Western Carmarthenshire at a few horizons (O.T. Jones, 1938, 1956). Thin black shales of Llanvirn age are found in the volcanic sequences of Cader Idris (Cox, 1925) and Arenig (Fearnsides, 1905). (B3) Caradocian — The Caradocian includes an extensive black shale facies, the Dicranograptus shales (0.T. Jones, 1938, 1956) occurring in Pembrokeshire, Carmarthenshire, Radnorshire, Shropshire, Montgomery, Denbigh, Carnarvonshire, and Anglesey. In Central Wales the Nod Glas, a phosphatic black shale, occurs at this horizon (Jones and Pugh, 1935) from which Cave (1965) records slightly raised levels of Mo. Horsnail (1968) records raised levels of Mo from pyritous black shales interbedded with volcanic rocks in the Snowdon area. (B4) Ashgillian — Graptolitic black shales are developed in Central Wales as the Red Vein (Jones and Pugh, 1935). C. Silurian Within the Welsh geosyncline extensive black shales are developed at the base of the Silurian. (C1) Llandovery — Black shales are developed in the Lower Llandovery of North Cardigan and Montgomery (Jones and Pugh, 1935). Davies (1932) records thin black shales in the Llandovery of South Cardigan and North Carmarthenshire. In the English Lake District, Howgill Fells and the Cross Fell Inlier, the Llandoverian Stockdale Shales contain 22 well developed black graptolitic shales (Marr, 1925, Rickards, 1964). The geochemistry of some Mid Llandovery Shales has been studied by Spencer (1966), revealing considerable enrichment in Mo and Cu. (C2) Wenlock — Black shales persist into the Lower Wenlock of the Howgill Fells (Rickards, 1964). D. Devonian (Dl) Marine black shales are encountered in the Upper Devonian of North Cornwall and South Devon (Dewey, 1948). E. Carboniferous Marine black shales are extensively developed in the Visean and Namurian in South West and Central England (George, 1958). The thin black shales found in Northern England as part of the Yoredale Series and the thin marine black shale horizons of the Coal Measures are not included in the present study. (El) The Lower Culm of Devon includes black shales containing raised levels of Mo and Se (Webb, Thornton and Fletcher, 1966). (E2) The Edale Shales of Derbyshire have been identified as an extensive source of raised levels of Mo responsible for copper deficiency in livestock (Webb, Thornton and Fletcher, 1968) and also contain enhanced levels of Se. (E3) The Bowland Shales include sandstones and limestones within a thick sequence of marine black shales (Rayner, 1953). Raised levels of Mo are recorded in soils derived from Bowland Shale and Bowland Shale drift around Chipping, Lancashire (Morgan and Clegg, 1958, pers. coml. N.H. Brooksbank). F. Permian (Fl) Hirst and Dunham (1963) note a considerable enrichment in trace elements in the Marl Slate, a thin marginal development of the Kupferschiefer. 23

G. Trias (G1) Black shales are locally developed at the base of the Rhaetic. Khan (1964) reports raised levels of Mo from the Westbury Beds of South West England. The Rhaetic is included in the geochemical survey of the Lias outcrop reported by Thornton, Moon and Webb (1969). H. Jurassic Extensive deposits of organic rich and pyritic dark marine clays (black shales) were laid down during the Jurassic. (H1) hias — The dark Lower Lias clays of Dorset, Somerset and Gloucestershire are recognised as the source of Mo in the fteart pastures (Ferguson et al, 1943). Extensive studies have been made on the distribution of Mo in the Lias in South West England (Le Riche, 1959a, 1959b). North of Market Weighton the black shale facies is restricted to the lowest part of the Lower Lias (Arkell, 1933). Thornton, Moon and Webb (1969) record raised levels of Mo at a number of areas along the Lower Lias outcrop. The Upper Lias of Yorkshire contains bituminous shales, jet rock and alum shales from which Gad, Catt and Le Riche (1969) record raised levels of several trace elements including Mo. (H2) Oxford Clay — A dark organic rich shaley clay forms the Lower Oxford Clay of Buckinghamshire, Bedfordshire and Lincolnshire where locally it is exploited for brickmaking (Arkell, 1933). Bituminous clays are also developed in the Lower Oxford Clay of Dorset (Arkell, 1947b). Thornton (1968) records raised levels of Mo in soils derived from the Lower Oxford Clay near Bicester. (H3) Ampthill Clay — Between Oxford and the Humber the Oxford and Kimmeridge Clay formations are separated by an intensely 24

black marine clay (Arkell, 1933) the Ampthill Clay. However, Chatwin (1961) reports that a well developed benthonic fauna is found in the clay, a feature inconsistent with metal rich black shales. (H4) Kimmeridge Clay — Bituminous shales and oil shales occur in the Kimmeridge Clay of Dorset, Wiltshire, Buckinghamshire, Lincolnshire and Yorkshire (Arkell, 1933). The organic content is occasionally so great that some of the shale members will readily ignite (Arkell, 1933). J. Cretaceous Within the Cretaceous only the Lower Gault Clay is of note. (J1) In Kent, Surrey, Sussex, Hampshire, Oxfordshire, Buckinghamshire and Bedfordshire the Lower Gault Clay is a dark marine clay containing some pyrite and phosphate. Elsewhere it passes laterally into sandy or calcareous developments (Edmunds, 1954, Chatwin, 1960,1961, Sherlock, 1960). K. Tertiary. Marine black shales are largely unrepresented in the Tertiary of England. Nevertheless raised levels of Mo are believed to occur in some parts of the London Clay (pers. comm. G. Lewit3). L. Recent Recent black marine muds are probably the source of raised levels of Mo in some areas of reclaimed land in England and Wales (Thornton, 1968). The further consideration of this mode of occurrence is, however, beyond the scope of this discussion. The southern limit of glaciation is indicated in Fig. 1. North of this line the bedrock is often concealed by drift, modifying the relationship between bedrock and soil, by masking or smearing the parent material. The extensive recent deposits of the Pens also conceal the underlying geology. 25

5. Selection of Reconnaissance Survey Areas Although far from complete, the above summary and accompanying map give some impression of the known and potentially molybdeniferous marine black shales, as of January 1968. Observations may be made on the relationship between the outcrop of marine black shales and the incidence of copper deficiency in livestock (Fig. 2). Information on bovine hypocuprosis was made available by the Veterinary Investigation Service and local veterinary practitioners, and is complete to January 1970. The data on copper deficiency are far from comprehensive. Hypocuprosis is often treated on the farm and not systematically recorded and thus a bias, imparted by veterinary practitioners who do record this information may have produced a fortuitous distribution. However, examination of the data obtained reveals that some 65% of the cases of bovine copper deficiency in England and Wales, confirmed by blood copper analysis, occur at localities underlain by the black shales mentioned above or, in some coastal areas, recent black muds. A high frequency of hypocuprosis occurs on the Lower bias in the tteart pastures' of Somerset and also in Glamorgan and Warwickshire, with further groupings associated with the Low/Mid Carboniferous black shales in the South Pennines and North Lancashire. In all these areas molybdenum induced copper deficiency has been confirmed. Diffuse patterns of hypocuprosis are also formed over the Oxford Clay and Kimmeridge Clay formations in Wiltshire, Berkshire, Oxfordshire and Buckinghamshire, with sporadic occurrences on black shales elsewhere in England Site of Bovine Copper Deficiency . Fig.2. The Incidence of Bovine Copper Confirmed by Blood Copper Analysis. Deficiency' in Relation to the

Areas of Bovine Copper Deficiency Outcrop of the Principal Marine Attributed to Industrial Pollution "Black Shales" in England around Bedford, Peterborough, Sheffield and Stoke-on-Trent. and Wales.

Outcrop of Marine "BlackShales"

'(Information made available by the Veterinary investigation Service.)

Southern Limit of Quaternary Ice 5.h7e

Ro 6° tp t To Scale in Miles. 26 and Wales. In view of the possible presence of raised levels of Mo in the bedrock at these sites such cases of bovine copper deficiency may possibly be Mo induced. Copper deficiency also occurs as one of a number of disorders due to industrial pollution in the areas indicated in Pig. 2. Many of the remaining occurrences of copper deficiency are in areas underlain by sands, sandstone or limestone, rocks typically low in Cu (Turekian and Wedepohl, 1961) where an absolute deficiency may be inferred. A total of 6000 square miles of England and Wales is thought to be underlain by rocks of black shale facies (Pigs. 1 and 2) although the presence of glacial drift or recent deposits, as in the Pens, modifies the relationship between bedrock and soil. In view of the large extent of possibly molybdeniferous bedrock, it appears likely that production on a considerable number of farms may be depressed by the conditioning effect on cattle of a high dietary intake of Mo. Of great significance is the possibility of molybdenum induced copper deficiency occurring at the subclinical level. This would affect production but would probably remain unnoticed by the farmer or veterinary practitioner. Cattle production, however, is most important in the western counties of South and Central England, in South West Wales and the Welsh Borderlands and on the flanks of the Pennines (Coppock, 1964). Black shales outcropping in these areas are thus likely to be of greatest consequence to livestock farming. To illustrate the further occurrence of Mo enrichment in rocks of black shale facies and assess the agricultural 27 significance of the raised levels of Mo, regional geochemical survey areas were selected on the basis of the following criteria: (i) to contain marine black shales thought likely to be enriched in Mo (ii) to contain, as a control, areas of contrasting rock types (iii) supplementary information on geology, soils, land use etc. to be available (iv) areas to be of from 75 to 200 square miles in area, these being the limits of easily managed stream sediment reconnaissance surveys (v) to take account of possible lateral or vertical facies within the black shales (vi) to be sited largely in areas of livestock and/or dairy farming. The areas selected are described in full in the following pages with their location shown in Fig. 3. The West Carmarthenshire, Rhayader and Shelve survey areas examine Ordovician black shales, particularly the black Dicranograptus shales. The Machynlleth and Kendal areas include Silurian black shales whilst the Bowland Forest area encloses a sequence of Lower/Mid Carbonaceous black shales. The Shaftesbury, Thane and Market Rasen survey areas cover the Oxford and Kimmeridge Clay formations at three points on their outcrop. Geochemical reconnaissance surveys employing stream sediment sampling at a density of one sample per square mile were undertaken during the period March to May 1968 in the nine areas selected for study.

0 50 100 Kendal. Scale in Miles.

--q • - - ,•"" Bowland Forest,

•," ..-., r1' Market ,-1. S. .. I. I,.. — ti t • 1 Rasen. st.....e 'Y'' s is I :0'1 I s...' • •.. ., .• ^\ is rc:. -.....N,, , I 1. Shelve. 61, • ) " s \ , ."., 0, ,... 4. e • ( ,..,. \,,-- .1- -'-', "4-•-. .. 1)..• , f) S r'---1, , • Ma chynll eth. q ,_ i i .— •sv„.., ••• • ,e )...... '''I../ ..... 1 ,.....,,,• ) .. , j""•• L., • N.— • , r 1 —.. s‘,..... C. t e••• r•r• I 1 •,e, ) Cr/ ,a ,= Rhayader. 1 , r-- r e ....„?... ; l...,,•,. - .. i T.—_i-'- I• t 1 t r *.r.• i r '1 ..%%0•••••J ) .' 5, c‘.1-'. IIC: I...C:: • ;:,,_,_, ( ---, ter- ‘..., , \ 7 • ...... ss.I r r ,,,.- ,)

.1..• • J e ... I t. r•-• % ...... L... I i West c •.•".• %,„ Carmarthenshir e. ?,...... • ....- ---4

•••••••:-.•„,

Th am e.

Shaftesbury.

Fig.3 Location of Stream Sediment Reconnaissance Survey Areas. 28

Sediment samples were collected following the procedures outlined by Hawkes and Webb (1962) and analysed spectrographically for Co, Cr, Cu, Gal Mn, Mo, NI, Pb, Ti, V, Zn and Fe (expressed as ferric oxide). Selected samples were also analysed colorimetriaally for Mo and Se, and for Cu by atomic absorption. A full account of the methods of sampling, analysis and data handling employed is given in the }appendix.. In the following pages the results of multi—element reconnaissance surveys in the nine areas are presented. The accounts are in an order fcllowing the stratigraphy of the survey areas with the results of surveys over black shales of similar age arranged consecutively. This section is not intended as a definitive account of the geochemical patterns revealed; only the principal patterns are examined. Regional geochemical maps of the nine areas, to accompnay this section, are to be found in Volume II. In the following descriptions emphasis is placed on the agricultural application of the surveys, particularly the occurrence of enhanced levels of Mo in areas underlain by rocks of black shale facies. Experience in previous geochemical surveys carried out by the A.G.R.G. has shown that where patterns of greater than 3 p.p.m. Mo in stream sediment occur, it is possible that within the catchment areas soils and herbage are sufficiently enriched in Mo to give rise to a conditioned copper deficiency in livestock (Thornton, 1968). Where patterns of greater than 7 p.p.m. Mo in stream sediment occur there is a greater possibility of an associated pattern of Mo induced copper deficiency in livestock. In the surveys described here patterns of 29 of 3 p.p.m. Mo and greater in stream sediment are regarded as being significant and worthy of further investigation. In view of the association Of Mo and Se noted in Ireland (Webb and Atkinson, 1965) and in Derbyshire, Devon and North Wales (Webb, Thornton and Fletcher, 1966) and the possible influence of raised levels of Se on the health of grazing animals, selected Mo—rich and background sediments were analysed for Se. 30

CHAPTER 3: REGIONAL GEOCHEMICAL RECONNAISSANCE WEST CARMARTHENSHIRE SURVEY AREA

1. Description of the Area (A) Location The area, shown in Fig. 4, is rectangular, occupying some 155 square miles of Carmarthenshire immediately west of Carmarthen, the county town.

(B) Geology and Mineralisation The geology has been examined by Evans (1905) and surveyed for the Geological Survey by Strahan et al (1909, 1914). The stratigraphy is summarised in Table 2 and the geology in Fig. 5. The sedimentary rocks comprise Ordovician and Silurian ashes, shales, flagstones and grits Dverlain by Old Red Sandstone, gritty flags and marls. The Ordovician and Silurian are folded into an east—west trending anticline, the axis of which delineates two sedimentary environments in the Lower Palaeozoic (Pringle and Neville George, 1948). On the southern limb of the fold littoral deposits are found, whilst the northern limb contains sediments of geosynclinal aspect. Black shales occur at a number of horizons in the Ordovician with a full development in the'black Dicranograptus shales. In this area the Meidrim Shales (Caradocian) are largely dark grey to sooty black pyritous shales (Strahan et al, 1909). The underlying Hendre Shales (Llandeilo), grouped within the Dicranograptus shale facies by Evans (1905) are brown weathering, calcareous black shales. 0 J Scale in miles

1000 ft. contour 600 ft. contour 200 ft. contour •Towns

Key to Towns B.P. Bury Port C.E. Conwyl Elfed K. Kidwelly N. Narbeth P. Pendine S.C. St. Clears S. Saundersfoot T. Trelech W. Whitland

Key to Rivers 1. Eastern Cleddau 2. Afon Cynin 3. Afon Cywyn 4. Afon Duad 5. Afon Taf 6. Afon Tywi

Fig. 4. Location and Topography of the West Carmarthenshire Survey Area 31

Table 2 StratiLzany211222122121rmarthenshire- survez area (From Evans, 1905 and Strahan et al, 1909, 1914)

GEOLOGICAL FORMATION LITHOLOGY

Recent Alluvium Gravel, sand and silt

Pleistocene Glacial Drift Stiff boulder clay, sand and gravel

Red and green marls, flaggy micaceous Old Red Sandstone sandstones, cornstones and conglomerates

Silurian Lower Llandovery Conglomerates, sandstone, blue mudstone and flags

North limb South limb of anticline of anticline Ashgill Dark grey flaggy Grey mudstones and mudstones sandstones over thin limestones Caradoc Coal black Sandy black shales pyritous shales with rotten with black limestones Ordovician limestone Llandeilo Buff weathering Black limestone black shales, ash with dark and flagstones calcareous shales Llanvirn Shales, mudstones, Black shales and grits, black mudstones with Shales and ashes ash bands Arenig Blue, grey and black shales and mudstones, grits, conglomerates and ashes

Igneous Rocks Rhyolite, andesite, porphyry and diabase nwyl Elted. en imit A ir41 t11111101 1 :111111 11111114

10111111011111

Old Red Sandstone. Abernan 11 _ --- _ _ f 011.1 Silurian.

...

Ashgill.

Dicranograptus Shales.

Llanvirn & Lower Llandeila

.1-langynog Arenig.

• ...... + + + . . + + Igneous Rocks. Llanddowr r...... • • • • • • •• • • • • • • • . • .1 • • • • • • • . . . • • ..... lllllli ;I • ...... • • • • • • • • • • . • • • • . . • • • • • • • • . . . . ; . . • • • • • • • • • • • • • • • • • • • • • • • • • • • • ...... • • ...... • . • • • • • • • • • 0 1 2. .. • • • • . . • • • • • • • • • • • • • • • . • . • • • • Scale in Miles . • . ' •A -. • • • . •

Fig. 5. Geology of the West Carmarthenshire Survey Area (Based on I.G.S. maps and Evans, 1905.)

Direction of Flow of Welsh Ice. 1 West Carmarthenshire Area.

.11...... Direction of Flow of Irish Sea Ice. 2 Rhayader Area. .mM•mm.m...... 11MM Extent of Welsh Ice Sheet. 3 Machynlleth Area. 4 Shelve Area.

Key to Towns.

A. Aberystwyth, Ca. Carmarthen, Cd. Cardiff, H. Hereford,

LI.Llandrindod Wells, S. Swansea, Sh. Shrewsbury.

Fig.6. Map Illustrating the Glaciation of South and Central Wales and the Welsh Borderlands (Based on Pringle and Neville George, 1948 and Pockock and Whitehead, 1948.) 32 Igneous rocks are restricted to interbedded ashes in the Arenig, Llanvirn and Llandeilo and a small area of acid extrusives and intrusives south of Llangynog. Mineralisation is unrecorded from the survey area. However, immediately east of Carmarthen lead and silver were raised from veins in the Arenig Grits and to the north of the area, around Trelech and Llanfrynach, lead was gained from a number of veins in Ashgillian shales and grits. During the Quaternary glaciation the bulk of the area was covered by Irish Sea Ice with the eastern portion of the area invaded by ice from Central Wales (Fig. 6). Small areas of boulder clay occur sporadically throughout the area becoming more extensive to the north west. Around Whitland, St. Clears and north of Llangynog there are thick patches of boulder clay, glacial sands and gravel. Extensive areas of recent fluvial and marine alluvium have accumulated in the lower reaches of the river valleys and in the estuaries of the Taf and Towy.

(C) Topography and Drainage A broad east—west valley runs through the survey area, occupied by the lower reaches of the Rivers Taf and Towy (Fig. 4). To the south the land rises steeply up a scarp before falling gently towards sea cliffs. North of the Taf—Towy valley the land rises rapidly to a rolling plateau which stretches north towards the Prescelly Mountains. Austin Miller (1937) recognises a series of erosion surfaces from which the discordant drainage north of the Taf—Towy valley has been superimposed. Rivers are deeply incised into the rolling plateau where local relief can be severe and steep valley sides are typical. The tributary 33 drainage is well developed, actively eroding, flowing in colluvial banks or rock walls. However roads tend to follow the interfluves, avoiding steep slopes and the stream sediment samples are not uniformly distributed.

(D) Climate Mean annual precipitation exceeds 40 inches per annuri throughout the area rising to more than 60 inches around the Prescelly Mountains. The Old Red Sandstone ridge south of the Taf—Towy valley receives some 50 inches of rain per annum. Seasonal climatic changes are tempered by the strong maritime influence experienced in South West Wales. Even so, the higher land to the north of the area is wetter, cooler, more exposed and is consequently poorer agriculturally.

(E) Soils Although soil series are unmapped in this area, the soils developed on the Lower Palaeozoic sediments are recognised as being broadly comparable with those described by Rudeforth (1966, 1970) in Mid Wales (pers. comm. B. Clayden). Soils are dominantly residual and can be grouped according to the parent material. Thus on the Old Red Sandstone deep, freely drained, red brown looms and sandy loams with local areas of impeded drainage are found. The soils developed on the Lower Palaeozoic sediments are characterised by having some degree of impeded drainage and comprise variable depths (usually thin) of brown earths, gleyed brown earths and non calcareous surface—water gleys. The steep slopes of incised stream valleys have iumature soils with active creep discernable at most sites. Valley floors carry alluvial soils with waterlogging a common feature. 34

Two small areas of peat occur east and north east of Llangynog.

(F) Land Use West Carmarthenshire is one of the principal dairying areas of Wales. Grassland is dominant and farms are generally small family units, well managed and intensively worked (Daley, 1963). To the north dairy farming declines due to increasing elevation, exposure and severity of climate, and mixed dairy, beef and sheep farming is typical. On the Old Red Sandstone the better drained sandy loans are often cultivated with root crops or cereals. Elsewhere occasional fields are ploughed up for roots or kale for winter feed. The steep slopes are almost entirely wooded, some of this being managed commercially, but the majority is waste land.

2. The Regional Geochemical Patterns The most striking feature of the West Carmarthenshire area is that, despite the variation in parent materials, geochemical patterns related to bedrock are apparent only for Mo and V. The metal content of stream sediment over the principal geological units is summarised in Table 3. It can be seen that range and mean values for most metals are similar for all geological units. However, patterns related to bedrock, mineralisation and secondary environment are recognised. Table 3 Range and mean* metal content of the minus 80-mesh fraction of stream sediment from the principal geological units of the West Carmarthenshire survey area

Metal content (p.p.m.) MADA Cu V Pb Ga Zn Til- Ni Co Mn+ Cr Fe203% Old Red Sandstone. <2 41 75 13 12 105 5576 35 12 586 101 7.6 <2 20- 60- 8- 8- 50- 4000- 20- 10- 400- 60- 5.2- (27 samples) -2 60 160 20 30 160 8500 50 16 1300 130 11.0 Ashgill (North limb <2 38 146 14 15 126 5582 30 15 554 99 9.6 of anticline) (2 20- 100- 8- 10- 60- 5000- 20- 10- 300- 60- 6.6- (28 samples) 85 300 100 20 300 8500 40 30 1000 130 15.0 Dicranograptus shales <2 40 137 19 16 116 4984 30 13 442 99 10.6 North anticlThe)20-85-TO6- 23 E 5— 100— 85— samples) -30 400 40 400)1% 60400 k0-, Llanvirn and Lower <2 42 120 15 16 132 5313 35 19 700 102 8.8 Llandeilo (North limb 2 ' 16- 60- 5- 8- 60- 3000- 10- 10- 300- 60- 5.0- of anticline) >1% 60 60 5000 (53 samples) -2 85 200 40 50 300 160 15.0 Ordovician and Silurian (2 37 91 12 12 120 5489 31 16 792 86 7.9 (South limb. of anticlinel 2... ,40- 7c). .;,(7, 2000- 16- 400- 60- (27 samples) r,',—) o 6(, .c();,— 160- .e.O. Arenig (2 48 103 16 14 138 5755 38 23 1521 100 10.4 <2 20- 60- 8- 8- 85- 5000- 20- 13- 400- 60- 6.2- (27 samples) 85 160 30 20 200 8500 85 60 flio 160 17.0

* Geometric mean A Meals calculated with <2 p.p.m. = 1 p.p.m. Mean calculated with >1% = 2% 36

(A) Patterns related to 1edrock and mineralisation Chromium, titanium, gallium, lead and zinc are evenly distributed through the area whilst Co, Cu and Ni show some evidence of a decrease in value from west to east. Levels of V are characteristically lower over the Old Red Sandstone than elsewhere in the area. The most conspicuous geochemical pattern is that shown by the distribution of Mo which is largely undetected 2 p.p.m.) over the area. Anomalous levels of Mo (3-30 p.p.m.) occur in the sediment of streams draining some 5 square miles of the black Dicranograptus shale outcrop on the north limb of tha anticline between Meidrim and Llanglydwen. Follow up work (Ch. 13) has confirmed the presence of enhanced levels of Mo in the Dicranograptus shales and the occurrence of Mo—rich soils derived from these rocks. The Mo anomaly is depressed or completely suppressed in sediments from streams having complex catchment areas in which the Dicranograptus shales form only a part of the catchment area. In these circumstances it is thought that Mo—rich Dicranograptus shale material in the stream sediment is diluted by material containing background levels of Mo. Anomalous levels of Mo are undetected in the sediment of streams draining the Dicranograptus shales on the southern limb of the anticline where the parent rocks are of a littoral facies with limestones and arenaceous shales. The detectable concentrations of Mo are accompanied by higher values of V (up to 400 p.p.m.) with these two metals displaying a similar distribution (correlation statistically significant with P =-:0.01*) in stream sediments

* See Appendix for account of statistical methods 37

derived from the Dicranograptus shale outcrop. Selenium is detected in selected stream sediment samples carrying raised levels of Mo (Se< 0.2-0.9 p.p.m., mean 0.4 p.p.m.) and is undetected (< 0.2 p.p.m.) elsewhere in the area of investigation. A single sediment sample containing anomalous levels of Pb (100 p.p.m.), Cu (85 p.p.m.) and Zn (300 p.p.m.) occurs two miles north east of Meidrim. These slightly raised levels may indicate the presence of mineralisation. Debris weathered from a quartz vein is abundant in the stream and adjacent fields, but no visible evidence of mineralisation could be found. No follow up work was undertaken.

(B) Patterns related to the secondary environment High levels of Mn () 1000 p.p.m.) are frequently recorded in streams draining the Arenig outcrop. However these occurrences are thought to reflect local soil conditions rather than an enrichment of Mn in the Arenig sediments. Very high levels of Mn (2000 p.p.m. >1%) occur in a zone east and west of St. Clears in the sediment of streams draining areas of very low relief and boulder clay cover where soils are very poorly drained non calcareous surface—water gleys. It is thought that Mn is leached from the acid waterlogged soils and precipitated from groundwater on entering the stream environment in a manner similar to that observed by Horsnail (1968). Thick crusts of black Mn02 are observed coating pebbles in streams within this zone. Elsewhere in the survey area levels of 1000 p.p.m. Mn and above occur in the sediment of streams recorded as flowing in colluvial or alluvial banks with very poorly 38 drained water meadows adjacent to the stream. Here again it is thought that Mn is leached from the adjacent poorly drained soils and precipitated in the stream sediment. The scavenging of Co by Mn oxides precipitated in the streams as reported by Horsnail (1968) and Hawkes and Webb (1962), cannot be dismissed in view of the coincidence of higher levels of Co () 30 p.p.m.) in the west central part of the survey area with an area of high Mn in stream sediment. However, this same coincidence is not seen in the zone of very high Mn around St. Clears. Iron is present in large quantities () 12% Fe203) in a number of stream sediments throughout the area. These are almost all at sites where Fe seepages were noted. The highest levels of Fe (>18% Fe203)occur in streams draining the Dicranograptus shales of the north limb of the anticline. Iron seepages are very common in this zone and it is thought that the Fe comes from the weathering of Meidrim Shales which are rich in pyrite. There is no evidence of the scavenging of metals with the precipitation of these high concentrations of Fe.

3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals The incidence of known trace element disorders is shown in Fig. 7.

(A) Molybdenum and Copper Bovine copper deficiency, confirmed by blood copper analysis, has been recorded on three farms in the area. There are no geochemical features common to these occurrences. Conwyl Elted.

Abernant /7 , Molybdenum A stream sediment anomaly.

Bovine Copper Deficiency. Whitland. 0 . •Llangynog St Clears. Area in which Cobalt Pine occurs. Llanddowror.

0 1 2 I i Scale in Miles.

Fig. 7. The Incidence of Trace Element Induced Agricultural Disorders in the West Carmarthenshire Survey Area 39

Infertility in dairy cows responding to copper and manganese therapy is a frequent occurrence in herds grazing areas underlain by the Old Red Sandstone. The stream sediment survey reveals no evidence of low Cu or Mn in soils on the Old Red Sandstone. Stream sediment reconnaissance reveals no areas of low Cu likely to be of agricultural significance. The zone of anomalous levels of Mo between Meidrim and lilanglydwen is previously unrecorded and apart from a single farm on which copper deficiency has been confirmed at Meidrim, there is no record of any incidence of disorders attributable to trace elements in this district.

(B) Cobalt Veterinary practitioners report an area of Carmarthenshire extending into the north of the study area as one in which cobalt pine (cobalt deficiency) in sheep occurs. However, stream sediment reconnaissance reveals no pattern of low Co in stream sediment in the north of the area nor any clear evidence of Co enrichment in stream sediments. Levels of Co in stream sediment are lower (10-13 p.p.m.) in the south and east of the study area but at no time fall to the low levels ( 5 p.p.m.) encountered in areas of cobalt pine in Devon (Fletcher, 1968, Thornton, 1968) and Ireland (Webb, 1964). 40

CHAPTER 4: REGIONAL GEOCHEMICAL RECONNAISSANCE RHAYADER SURVEY AREA

1. Description of the Area (A) Location The area, shown in Fig. 8, occupies some 65 square miles of north west Radnorshire immediately east of Rhayader and north of Llandrindod Wells.

(B) Geology The geology is described by Lapworth (1900) and Roberts (1929). The generalised stratigraphy is shown in Table 4 and the geology in Fig. 9. The rocks are sediments of Ordovician and Silurian age deposited near the eastern margin of the Welsh geosyncline (0.T. Jones, 1938). These sediments comprise shales, mudstones and sandy mudstones with considerable thicknesses of grits and conglomerates within the Upper Ordovician and Llandovery. East of Nantmell a small dolerite sill intrudes the Ordovician. Black shales of Caradocian age occur in the Carmel Group. These are coal black graptolitic shales, of Dicranograptus shale facies, laterally equivalent to the middle part of the Meidrim Shale of Carmarthenshire (Roberts, 1929). The area, which was close to the centre of the Welsh Ice Sheet (Fig. 6), is thickly covered with lc-Lally derived drift with most river valleys, including those of the tributary streams, partially filled with boulder clay. Typically only the steeper slopes are drift free (Roberts, 1929). 0. 4 8 Scale in miles

Land above 1400 ft. • Towns ---.---- 1000 ft. contour --,...---- 600 ft. contour

Key to Towns C. Crosgates L. Llandrindod Wells N. Nantmel Ne. Newbridge-on-Wye R. Rhayader

Key to Rivers 1. River Aran 2. Clywedog Brook 3. Elan River 4. River Ithon 5. River Marteg 6. River Wye

Fig. 8. Location and Topography of the Rhayader Survey Area 41

Table 4 Stratigraphy of the Rhayader survey area (From Roberts, 1929)

GEOLOGICAL FORMATION LITHOLOGY

Recent Alluvium Gravel, sand and silt

Pleistocene Glacial Drifts Boulder clay and morainic gravels

Wenlock Dark blue calcareous mudstones and shales Silurian Upper Llandovery Grey blue soft mudstones and pale green shales Lower Llandovery Dark blue rusty weathering shales with grits

Ashgill Blue sandy mudstones, (Camlo Hill Group) grits and conglomerates with dark blue shales Ordovician Caradoc/Llandeilo Coal black graptolitic (Carmel Group) Shales, mudstones and grit bands — gt.Harm n -----

ity

# • ayader: " ' • ' •

2 9 1 Scale in Miles. Wenlock.

Upper Llandovery.

— Middle Llandovery

_4009 Dolerite. Lower Llandovery

Ashgill.(Camlo Hill Group)

Llandeilo/Caradoc (Carmel Group)

Fig.9. Geology of the Rhayader Survey Area (Based on Roberts, 1929.) 42

(C) Topography and Drainage The area lies at the edge of a rolling upland plateau and is deeply dissected by tributary streams of the Rivers Wye and Ithon, principally the Clywedog Brook. Local relief is severe and whilst the upper slopes are rounded, lower slopes tend to be steep and pronounced due to the incision of the drainage network.

The tributary drainage is well developed with streams actively eroding and the majority flowing in colluvial banks.

(D) Climate

A distinct reduction in the amount of rainfall is observed from west to east across the survey area. West of Rhayader more than 70 inches of rain per annum is recorded whilst to the east Crossgates receives only 35-40 inches per annum.

Temperatures reflect the altitude and mountainous aspect with cool wet summers and cold winters. West facing slopes are more exposed.

(E) Soils

Soils developed over the drift, shales and grits all show some degree of impeded drainage with a variable depth of brown earth or gleyed brown earth dominating below 1,000 feet. Above 1,000 feet peaty gleyed podzols with local areas of blanket peat are found. Valley floors have alluvial soils whilst steeper slopes carry skeletal soils with soil creep active at many sites. 43 (F) Land Use Land above 1,000 feet, and at lower levels in the west and north, is open moorland with unimproved rough land used for sheep grazing. The lower hills carry marginal grassland used for beef cattle and sheep rearing while the lowest slopes and valley floors support mixed dairy/beef farming. Some of the steep valley slopes and areas of marginal upland are being afforested by the Forestry Commission.

2. The Regional Geochemical Patterns The Rhayader area is one of low geochemical relief with the two most obvious patterns being a small Mo anomaly around Nantmell and the high levels of Fe, Mn and Co in the north west of the area. These two patterns are related to the bedrock and secondary environment respectively. The range and geometric mean values of metals in stream sediments are summarised in Table 5.

(A) Patterns related to bedrock and glacial drift Stream sediment levels of Ti, Ga, Cr, Ni, Pb and Zn show little regional variation and no discernable patterns related to geology. The low geochemical relief and lack of patterns related to geology may possibly be due to the homogenising effect of the extensive drift cover in the area which destroys the contrast that may be present between some of the rock types. Molybdenum is present below the detection limit with the exception of a small anomaly (3-6 p.p.m.) around Nantmell in the sediment of streams draining the Llandeilo/Caradoc Carmel Group. Within stream sediment from the Carmel group the anomalous levels of Mo are associated with slightly raised levels of V and Cu (Table 5 ). The source of the enhanced levels of Mo is regarded as being Caradocian

Table 5 Range and mean* metal content of the minus 80-mesh fraction of stream sediment from the principal Eeological units of the Rhayader survey area

Metal content (p.p.m.) lioA Cu V Pb Ga Zn Ti Ni Co Mn Cr Pe203% Upper LlandoNaly <2 43 128 15 13 144 5542 33 16 888 95 11.9 and Wenlock <2 30- 100- 6- 8- 100- 4000- 20- 13- 600- 60- 3.2- (15 samples) 60 160 40 16 200 8500 50 20 1600 130 30.0 Middle Llandovery <2 37 170 16 20 153 6571 38 21 1195 109 15.2 :2 20- 85- 8- 8- 100 - 4000- 20- 13- 400- 60- 5.0- (21 samples) -2 60 200 85 30 200 8500 60 50 6000 130 30.0 Lower Llandovery (2 38 172 15 20 153 6625 43 16 888 119 7.8 <2 20- 130- 8- 13- 130- 6000- 20- 13- 850- 85- 6.3- (4 samples) 50 200 30 30 160 8500 60 20 1000 130 9.4 kshgill <2 30 154 11 15 145 6140 35 17 649 110 6.4 (Camlo Hill Group) <2 16- 85- 8- 8- 100- 4000- 20- 10- 300- 60- 1.7 (32 samples) -3 40 200 30 30 300 8500 60 50 1300 130 16.0 Llandeilo ayld 3 48 195 12 16 170 6000 33 16 725 100 6.9 Caradocian <2 40- 160 - 10 - 13 - 160- 6000 30- 10- 600- 85- 4.1- (4 samples) -6 60 300 16 20 200 40 20 850 130 10.0

* Geometric mean A Mean calculated with <2 p.p.m. = 1 p.p.m. 45 graptolitic shales within the Carmel Group. The Meidrim Shales of West Carmarthenshire (50 miles to the south west) are sediments of the same age and facies (Dicranograptus shale facies) enriched in Mo (page 36 ) displaying a similar association of Mo with V in stream sediments. No follow up work was undertaken in the area.

(B) Patterns related to the secondary environment The north west part of the Rhayader area, east of St. Harmon, is characterised by high levels of Mn (>1000 p.p.m. and Fe (10-30% Fe203) in stream sediments with an associated enrichment in Co (up to 50 p.p.m.). The anomalous zone transgresses the various Llandovery sediments but is contained by a distinct environment. The zone, lying above 1,000 feet, is one of open moorland and very poor permanent pasture where soils are dominantly poorly drained peaty gleys and podzols. The zone may be contrasted with an area of similar geology, to the west of Crossgotes, with moderate to poorly drained brown earths under fair to good permanent pasture. Table 6 , showing the metal content of stream sediments, reveals a mean enrichment of x4 for Fe, x3 for Mn and x2 for Co in the St. Harmon area as opposed to the Crossgates area_ The enhanced levels of Fe, Mn and Co are regarded as being due to environmental circumstances comparable to those reported by Nichol et al (1967) in North Wales. The following features are common to both the Rhayader and North Wales areas: 1. High levels of Fe, Mn and Co in stream sediment occur in areas of very poorly drained upland soils. 2. The patterns of high Fe, Mn and Co transgress the underlying geology. Table 6 Range and mean* metal content of the minus 80-mesh fraction of stream sediments and pH of stream waters from areas of open moorland and agricultural land in the Rna;arler survey area siml••••••...11rataIN•mit

pH of Number Fe203(%) Mn(p.p.m.) Co(p.p.m.) stream waters of samples

Moorland east of Pt. Harmon Poorly drained peaty ,;ley 24.1 1720 ,)0- 6.7 13 and podzol soils 13.0-30.0 600-1600 16-40 6.0-7.0

Agricultural land wowt of Crossgates Moderate to poorly drained 6.8 674 14 6.8 18 brown eart1, 1.7-14.0 300-850 10-20 6.5-7.0

* Geometric mem_ 47

3. Levels of Ti, Ga, Cr and V are similar in areas of both high and low Fe, Mn and Co stream sediment patterns. 4. Thick black precipitates of Mn oxides are observed coating pebbles in the stream draining the upland areas. 5. The levels of Fe, Mn and Co in the stream sediment from the upland have significantly higher range and mean values than those from the lowland areas. Detailed studies by Nichol et al (1967) led the authors to conclude that stream sediment patterns of high Fe, Mn and Co in areas of very poorly drained upland soils may be explained as follows. Under the low pH and Eh conditions present in the waterlogged soils, Mn and Fe are mobile and present in solution in groundwaters. On entering the streams, Fe. and Mn precipitate from the groundwaters following a rise in pH and Eh. It is believed that the Mn is first precipitated as colloidal hydrated 1_2 which ages to the inert Mn02. The Mn oxide precipitated readily adsorbs and scavenges any available Co thereby effecting the common distribution of these metals.

3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals

(A) Molybdenum and Copper Swayback (a copper deficiency affecting now born lambs) is common throughout the area. There is, however, no relationship between the occurrence of swayback and the distribution of Cu, Mo or any other element in this area. 48

There are no records of confirmed copper deficiency in bovines within this area, nor have any disorders been attributed to copper deficiency. The occurrence of Mo in the Rhayader area has not been previously recorded. The small Mo anomaly in stream sediment around Nantmell is probably associated with areas of anomalous soils but in view of the unknown influence of drift cover no estimate of the extent of anomalous soils can be made.

(B) Cobalt Cobalt pine has been recorded in the area. Levels of Co in stream sediment are occasionally lower than average, falling to 10 p.p.m. on occasions, but are not of the levels (-4. 5 p.p.m.) encountered in areas of cobalt pine in North Wales and Devon (Fletcher, 1968, Thornton, 1968). In view of the possible enrichment of Co in stream sediments in the north east of the Rhayader area, no estimate can be made of the Co status of soils in this zone. 49

CHAPTER 5: REGIONAL GEOCHEMICAL RECONNAISSANCE SHELVE SURVEY AREA

1. Description of the Area (A) Location The Shelve area, shown in Fig. 10, covers 100 square miles of south west Shropshire and adjacent parts of Montgomeryshire. The area is centred on a knot of hills known as the Shelve Upland (after the village of Shelve) and includes part of the north flank of Clun Forest.

(B) Geology and Mineralisation A review of the geology is given by Whittard (1952) and of the mineral deposits by Dines (1958). The generalised stratigraphy is shown in Table 7 and the geology in Fig. 11. The sedimentary rocks of the area range in age from Precambrian to Old Red Sandstone and include shales, flagstones, limestones, grits, conglomerates and pyroclastics. Intrusive igneous bodies of picrite, dolerite and andesite occur in the Cambrian and Ordovician sediments. The Ordovician rocks of the Shelve district were deposited close to the eastern margin of the Welsh geosyncline (0.T. Jones, 1938, 1956) with black shales developed at a number of horizons. (a) Llanvirn. The Hope Shales and Stapley Shales are both rusty weathering blue black shales interbedded with tuffs and ashes. However, though both are very dark coloured, fine grained rocks, they contain a well developed benthonic fauna, a feature atypical of metal rich black shales.

4 Scale in miles Land over 1400 ft. 1000 ft. contour 600 ft. contour • Towns

Key. to Towns B.S. Bishops Castle C. Clun C.A. Craven Arms C.H. Church Stretton M. Montgomery P. Pontesbury W. Welshpool

Key to Rivers 1. Byne Brook 2. Camlad 3. River Clun 4. Cound Brook 5. River Onny 6. Rea Brook 7. River' Severn

Fig. 10. Location and Topography of the Shelve Survey Area 50

Table 7 Stratigraphy of the Shelve survey area (Based on Whittard, 1952) GEOLOGICAL FORMATION LITHOLOGY.

Recent Alluvium Sands, fine sands and silts

Pleistocene Glacial Drifts Boulder clay, fluvioglacial sands and lacustrine clays

Old Red Red and green marls, shales Sandstone sandstones, grits and cornstones

Silurian CM.careous shales, grits and conglomerates

Intrusive igneous Picrite, dolerite and rocks andesite

Ashgill Blue grey shales and ashes Caradoc Black shales, grey shales grits and tuffs Ordovician Llandeilo Shales, mudstones, tuffs and ashes Llanvirn Black shales with flags, shales, tuffs and ashes Arenig Quartzite overlain by dark gritty flags

Cambrian Arenaceous grey shales, flags and mudstones

Precambrian Longmyndian Green and purple shales, flags, grits and conglomerates • . 6 4

• • • 0 1 2 • • • • • • . Old Red Sandstone. Scale in Miles.

Silurian.

Caradoc & Ashgill.

Llandeilo. I

Llanvirn.

Igneous Rocks. Arenig.

Cambrian. + Mims. 0 0 0 0 0 Precambrian.

Fig. 11. Geology of the Shelve Survey Area (Based on I.G.S. maps) 51

(b) Caradocian. (i) The Rorrington Shales are 500 feet of very soft sooty blue black mudstones and flags, zraptolitic with some pyrite having"a close lithological similarity to the Dicranograptus shales of Wales" (Whittard, 1952). (ii) The Aldress, Hagley and Whittery Shales, separated by grits and volcanic horizons, are rusty weathering; soft blue black shales. However these sediments do not show the marked lithological similarity with the Dicranograptus shales exhibited by the Rorrington Shales. Further, in addition to graptolites, the shales contain a benthonic fauna that includes forms unknown in the black shale environment in which metal enrichment takes place. Mineralisation occurs within the Precambrian, Cambrian and Ordovician. The deposits are fissure veins carrying barytes with Pb, Zn and occasionally copper sulphides in a gangue of quartz, calcite, crushed countryrock, fluorite and pyrites. Sulphide bearing veins are almost restricted to the Mytton Flags (Arenig) whilst barytes veins occur more extensively where the countryrock is a grit or pyroclastic. The numerous mines (Fig. 11) are now all disused. Land up to 1,300 feet was invaded by the Welsh Ice Sheet (Fig. 6) and boulder clay occurs on valley floors below this level. Slopes and hill tops are usually free of glacial drift. For some time a lake occupied the valley between Church Stoke and Plowden where lacustrine clays were deposited. Periglacial solifluction deposits and post glacial head occur extensively on slopes.

(0) Topography and Drainage The area may be conveniently divided into three 52

topographic units, the Shelve Upland, the north flank of Clun Forest and the remaining lowland. The Shelve Upland comprises NNE—SSW trendilag -ridges separated by flat floored valleys. Slopes are steep and local relief often severe. The topography here is controlled by the geology with hard rocks, grits and volcanics, supporting the ridges. Clun Forest, a rolling upland of flat topped hills separated by wide, deep valleys with long convex slopes, rises steeply to the west of Bishops Castle. A broad vale extends from Chirbury through Church Stoke to Lydham and Flowden. The drift cover here gives rise to a gently rolling topography of low relief. The drainage of the area is dominated by tributaries of the Rivers Camlad and Onny. The tributary drainage is well developed, flowing in colluvial banks in the uplands and alluvial banks in the lowlands where many streams are meandering.

(D) Climate In the Shelve area climate is dependent on altitude with the upland districts colder and wetter than lowland areas. Thus the lowland between Chirbury, Church Stoke and Lydham receives some 30 inches of rain per annum whilst the Shelve Upland and Clun Forest receive in excess of 40 inches.

(E) Soils The soils of Shropshire are described by Burnham and Mackney (1964) who recognise certain major associations in the Shelve district. Acid brown soils and podzols of variable texture are 53

extensive in the Shelve Upland and Clun Forest. Hilltops and local hollows carry iron podzols and/or peaty gleyed podzols whilst valley floors have non—calcareous surface—water gley soils. The extensive areas of drift in the Chirbury—Church Stoke— Plowden lowland and other valleys are covered by non—calcareous surface—water gleys. Alluvial soils, groundwater gleys of variable texture, occur beside the Rivers Camlad and Onny and in the valley east of Bishops Castle.

(F) Land Use The area is dominantly grassland with stock rearing the prime occupation (Burnham and Mackney, 1964). The Shelve Uplands are largely poor grassland used for cattle and sheep rearing with unimproved moorland on the higher hills. Clun Forest is similarly an area of livestock rearing with better quality grassland and local areas under arable cultivation. The lowland areas support the best . grassland and mixed fatstock and dairy farming predominates.

2. The Regional Geochemical Patterns

Despite the variety of parent materials present in the Shelve area regional variations in the distribution of Cr, Ti, V, Ga and Ni are not observed. Patterns related to bedrock, mineralisation and the secondary environment are, however, recognised among the remaining metals. The metal content of stream sediments on the principal bedrock units is summarised in Table 8. Table 8 Range and. near„ metal content of the minus 80-mech fraction of stream sediment from the DTincipal_Peological units of the Shelve survey area

Metal content (p.p.m.) TioA Cu V Pb+ Ga Zn+ Ti Ni Co Mn Cr Fe203% Old Red Sandstore <2 49 140 28 17 100 5988 53 16 640 122 7.3 <2 40- 100- 16- 16- 85- 5000- 40- 16- 500- 100- 6.2- (8 samples) 60 200 50 20 160 8500 60 20 850 130 9.0 Silurian e2 46 145 40 15 125 5709 34 15 595 97 8.1 (Drift covered) <2 30- 100- 16- 8- 60- 4000- 16- 13- 400- 50- 6.6- (32 samples) 85 200 400 20 600 8500 50 30 1000 130 12.0 Llandeilo, Caradocian <2 36 178 48 21 163 5958 33 23 1117 97 9.9 and Ashgill (Drift <2 16- 100- 30- 13- 100- 4000- 16- 13- 300- 60- 6.7- covered inpart) -4 50 300 160 30 400 6000 40 30 1600 130 12.0 (15 samples) (1600) (600) Llanvirn <2 34 153 115 19 458 6115 27 22 907 90 8.7 <2 16- 85- 30- 13- 100- 3000- 16- 13- 400- 50- 6.6- (30 samples) 50 200 300 30 600 8500 50 50 6000 130 12.0 (400) - (>1%) (`>10) Arenig • <2 34 125 31 12 - .225 4996 24 20 1066 89 6.6 <2 13- 85- 30- 6- 100- 3000- 16- 16- 300-. 60- 2.9- (6 samples) 60 160 60 16 500 6000 50 50 6000- 100 8.4 (p1%) (>1%)

Cambrian <2 39 148 87 15 281 5449 28 22 943 83 9.6 (Drift covered) <2 20- 130- 50- 13- 200- 4000- 20- 16- 600- 60- 6.6- (8 samples) 50 200 300 16 400 6000 40 30 1300 100 13.0 Precambrian <2 53 185 40 16 136 5428 17 18 807 70 10.2 2 40- 130- 20- 13- 60- 4000- 13- 13- 500- 50- 6.2- (19 samples) 85 200 85 20 300 6000 30 30 1600 130 17.0

* Geometric mean A Mean calculated with <2 p.p.m. = 1 p.p.m. + Anomalously high metal ralues due to contamination (auoted in parenthesis) excluded from the calculation 55

(A) Patterns related to bedrock Molybdenum is undetected (C2 p.p.m.) over the greater part of the Shelve area. Weakly anomalous levels of Mo (3-4 p.p.m.) occur in three streams draining the basal Caradocian. The source of the Mo is believed to be the black shales (Dicranograptus shale facies) developed in the Rorrington Shale group. The raised levels of Mo occur only in those streams which have cut through the drift cover into the Rorrington Shale. The slightly raised levels of sediment Mo may reflect similar values in the bedrock but may well be suppressed due to dilution of the stream sediment by barren drift or material derived from adjacent non black shale horizons. The Rorrington Shale has a long but very narrow outcrop (maximum width 400 yards at Rorrington) frequently covered by exotic drift, in a valley bounded by slopes of grit and grey shales. No follow up work was undertaken in the Shelve area. The Silurian and much of the Caradocian and Cambrian is covered by a variable thickness of superficial deposits, principally glacial drift, which is probably modifying the geochemistry of these areas by masking or smearing material from the underlying rocks.

(B) Patterns related to mineralisation Very high levels of Pb (300 p.p.m. - 1%) and Zn (600 p.p.m. - 1%) in stream sediment from the Shelve Upland occur in streams draining mineralised areas and most can be attributed to contamination from disused mine workings, dressing areas, tip heaps and drainage adits. Anomalous levels of Cu (85-400 p.p.m.) near Shelve and Hope occur in 56 stream sediments collected downstream from disused mine workings and are similarly attributed to contamination. The limited extent of the Cu anomalies reflects the restricted occurrence of Cu in the mineral veins of the area. Raised levels of Zn (400-600 p.p.m.) and Pb (85-300 p.p.m. north of Hope, occur in an area with no record of mining and may be due to as yet unrecognised mineralisation associated with grits and volcanic horizons in the Llanvirn. However, mineral veins carrying workable quantities of lead and zinc sulphides are almost restricted to the Arenig Mytton Flags (Dines, 1958) and the anomalies noted here, if due to mineralisation, most probably originate from fissure vein deposits in which sulphides will be subordinate to barytes.

(C) Patterns related to the secondary environment High levels of Mn in stream sediment (1600-6900 p.p.m.) occur in the Shelve Uplands in areas of poorly drained peaty gley soils. It is thought that the high levels of Mn reflect increased leaching from these reduced soils followed by precipitation from groundwater entering the stream. The common occurrence of enhanced values of Co (30-50 p.p.m.) in these sediments with raised levels of Mn suggests that Co may be scavenged by the precipitating manganese oxides. The high levels of Fe (16.0% Fe203) in stream sediments north of Wentnor occur at sites where large Fe seepages were noted, arising from marshy areas beside the streams. Fig. 12. The Incidence of Trace Element Induced Agricultural Disorders in the Shelve Survey Area 57

3. Correlations between Regional Geochemical Patterns and The Incidence of Trace Element Disorders in Animals Pig. 12 shows the incidence of trace element disorders in animals.

(A) Copper and Molybdenum Bovine copper deficiency has been confirmed on a number of farms in the area. Veterinary practitioners suspect that hypocuprosis may be widespread in cattle grazing areas underlain by Old Red Sandstone west of Bishops Castle (pers. comm. D.J.C. Jones to I. Thornton). The present survey reveals no evidence of low Cu or raised Mo levels in any of the areas in which bovine hypocuprosis has been confirmed or is suspected. The raised levels of Mo recorded between Rorrington and Church Stoke may be related to Mo—rich soils. However the occurrence of Mo here is thought to have little agricultural significance due to: 1. The very limited extent of the narrow Rorrington Shale outcrop (3/4 square mile). 2. The presence of exotic drift and head derived from adjacent grit and grey shale horizons masking the Rorrington Shale.

(B) Other Metals Lead poisoning has affected sheep and cattle grazing contaminated pastures over old mine tips at Whitegrit, west of Shelve (pers. comm. S. Gillette). The derelict nine areas and tip heaps are usually fenced to keep animals out. 58

CHAPTER 6: REGIONAL GEOCHEMICAL RECONNAISSANCE MACHYNLLETH SURVEY AREA

1. Description of the Area (A) Location The survey area, of 100 square miles, is located north of Aberystwyth (Fig. 13). The area is bounded on the west by Cardigan Bay and extends inland to enclose parts of the Plynlimon range and the town of Machynlieth.

(B) Geology and Mineralisation The geology has been described by Jones and Pugh (1935) and is presently being resurveyed by the I.G.S. The geology of the area is shown in Fig. 14 and the stratigraphic succession summarised in Table 9. The geological succession is of mixed geosynclinal sediments deposited near the axis of the Welsh geosyncline (0.T. Jones, 1938, 1956) and comprises shales, flags, grits and greywackes. Black shales occur at two principal horizons. (a) North of the River Dovey the Nod Gins, of Caradocian age, is a soft, black, pyritous and phosphatic graptolitic shale, some 70 feet thick, having a sinuous outcrop in a rough upland area. Cave (1965) records raised levels of Mo (up to 15 p.p.m.) in the Nod Glas west of Welshpool. (b) The Lower Llandovery formation comprises 550 feet of soft, black rusty weathering pyritic shales (Jones and Pugh, 1935). There are two lesser occurrences of black shale facies. (i) North of Dovey the Red Vein (Ashgillian) is 350 feet of soft, dark blue, graptolitic mudstones, weathering rusty, "often resembling the Lower Llandovery Shales" (Jones and Pugh, 1935). Scale in miles

Land over 2000 ft. ,— 1000 ft. contour • Towns 600 ft. contour A' Plynlimon 200 ft. contour

Key to Towns A. Aberystwyth Ab. Aberdovey B. Borth M. Machynlleth P. Ponterwyd T. Towyn

Key to Rivers 1. River Dovey 2. Afon Dulas 3. Afon Dysynni 4. Afon Rheidol 5. River Wye

Fig. 13. Location and Topography of the Machynlleth Survey Area• 59

Table 9 Stratigraphy of the Machynlleth survey area (From Jones and Pugh, 1935)

GEOLOGICAL FORMATION LITHOLOGY Alluvium Gravel, sand and silt

Recent Peat Peat

Pleistocene Glacial Drift Boulder clay, morainic gravels and sand

Upper Llandovery Grey shales with interbedded grits

Silurian Middle Llandovery Pale mudstone and grits with graptolitic black shale bands Lower Llandovery Rusty weathering dark blue and black pyritous shales

North of North of Dovey Davey Ashgill Blue mudstones Massive blue with grits and mudstones, flaggy conglomerates, mudstones and grits Ordovician soft rusty weathering dark blue mudstones Caradoc Blue mudstones Not exposed and grits with soft black pyritous shales No• Alluvium, etc.

Middle & Upper Llandovery. Silurian. 0 1 2 1 Lower Llandovery. Scale in Miles

Ashgillian Ordovician. Caradocian.

Mineral Veins.

x Mines.

Fig. 14. Geology of the Machynlleth Survey Area (Based on Jones and Pugh, 1935.) 60

(ii) Within the Middle Llandovery are found five black shale bands (Jones and Pugh, 1935), thin beds of from one inch to three feet in thickness. Spencer (1966) records considerable enrichment of Mo (3-175 p.p.m.), Cu (32-302 p.p.m.) and several other trace elements in the Monograptus leptotheca band. However, these black shale bands have a very small outcrop. The area is extensively mineralised (Fig. 14) and mining was formerly widespread (Jones, 1922). Mineralisation occurs as near vertical veins and lodes associated with faults and minor dislocations trending NE—SW and ENE—WSW. Lead, zinc and copper sulphides occur with a gangue of quartz where the wall rock is a grit; in areas of shale wall rock only the gangue occurs (0.T. Jones, 1922). The Plynlimon area formed a distribution contre of the Welsh Ice Sheet (Fig. 6) and a major glacier occupied the Davey Valley (Jones and Pugh, 1935). However, glacial deposits are restricted to valley bottoms, lower slopes near the coast and to local areas of drift in upland hollows. Alluvium occurs in the larger river valleys. Extensive areas of alluvial silts and marine warp overlain by peat occur in the Dovey estuary (Borth Bog) and around Towyn.

(C) Topography and Drainage From the low coastal plain the ground rises abruptly to a dissected, rolling coastal plateau from which the land again rises to uplands around Plynlimon (Fig. 13) Rivers and streams are deeply incised into the upland and coastal plateau where local relief may exceed 300 feet and steep valley slopes with bare rocks are typical. Inland 61 the tributary drainage is actively eroding and streams flow within colluvial banks or rock walls, whilst in coastal areas many streams flow in alluvial banks in their lower courses. Access by roads and Forestry Commission tracks is generally fair, although some areas proved inaccessible and were unsampled.

(D) Climate The climate reflects the wide topographic range with a strong maritime influence causing high humidity, modifying the temperature regime and providing strong rain bearing onshore winds. The average annual rainfall ranges from 35 inches on the coast to 100 inches in the uplands around Plynlimon, rainfall being at a minimum in late spring and early summer. On the coast mean daily temperatures in January and July average about 40°F and 60°F respectively; in the uplands the values fall off to about 35°F and 53°F.

(E) Soils The soils of the area have been described by Rudeforth (1966, 1970) who recognises a number of major associations. Alluvial soils, gleys and peaty gleys, occur in the Dovey estuary and along river valleys. At elevations between 200 and 600 feet (the coastal plateau) soils are dominantly deep, acid, brown earths (Denbigh Series), cultivated, with some gleying. Gleys and peaty gleys occur over drift areas. Over higher ground and more exposed slopes soils become podzolised and have an increasing development of peat (Manod and Hiraethog Series); gleying occurs locally and areas of bare rock are found. 62

Upland ridges, spurs and the high plateau (above 1000 feet) are covered with a variable thickness of peat between areas of bare rock.

(F) Land Use Alluvial areas along the coast and beside the larger rivers support a small dairy farming industry. Inland on the coastal plateau grassland farming is practised with beef cattle, sheep and some milk production. The uplands are largely unenclosed and unimproved moorland with poor sheep grazing. Large areas of valley sides and upland slopes have been systematically afforested with conifers.

2. The Regional Geochemical Patterns Within the Machynlleth area regional geochemical patterns are recognised and interpreted as reflecting: (i) variations in the bedrock (ii) extensive mineralisation in the area (iii) features of the secondary environment. The metal content of stream sediments on the principal geological units is summarised in Table 10. Data from stream sediments on the Ordovician rocks are divided into two groups, north and south of the Dovey, to take account of the differing rock types found in the two areas. The Mid and Upper Llandovery areas are grouped together for simplicity, the geology of both groups being essentially similar.

(A) Patterns related to bedrock In spite of the considerable variation in rock types present in the area the regional distribution of Ti, Ga, Cr, Table 10 Range and mean* netal content of the minus 80-mesh fraction of stream sediment from the principal geclogical units of the Machynlleth survey area

Metal content (p.p.m.

AoA Ou+ V Pb+ Ga Zn+ TiY Ni Co MnY Cr Fe2 03 cf' Borth Bog 4 74 83 434 14 445 8962 50 45 950 50 7.2 <2 30- 50- 60- 5- 50- 850- 40- 30- 600- 30- 3.7- (4 samples) -8 130 200 850 20 850 )1% 60 60 1600 60 11.0 Middle and Upper <2 44 160 58 27 540 >1% 47 81 2164 83 6.8 Llandovery <2 30- 85- 20- 13- 300- 8500 40- 30- 600- 40- 3.5- (44 samples) -8 85 300 130 30 850 ->5,% 300 1000 >1% 130 14.0 (>1%) (>1%) (>1%) Lower Llandovery (2 65 145 49 23 568 >1% 52 138 3318 76 7.6 :2 30- 100- 20- 16- 300- 8500 30- 40- 600- 40- 3.5- (29 samples) -5 200 200 160 30 850 -`).1% 85 600 >1% 100 16.0 (1600) (>1%) (6000) Ordovician <2 34 123 42 23 472 >1% 42 61 1384 60 4.2 (North of Davey) <2 30- 100- 16- 20- 300- 6000 30- 40- 850- 40- 2.9- (13 samples) -2 60 160 500 30 850 -)1% 60 100 5000 85 5.0 (1000) Orovician <2 41 118 44 24 292 >1% 36 152 3031 66 4.2 (South of Dovey) <2 30- 85- 20- 20- 160- 6000 30- 50- 1000 50- 3.1- -2 60 200 50 30 300 ->1% 40 400 -1% 100 5.8 (850) * Geometric mean A Mean calculated with <2 p.p.m. = 1 p.p.m. Y Mean calculated with - Anomalously high meta.1 values due to nortn?tion (cuctec in pal.eubilesis) excluded from cP10-1Pton 64

V and Ni show no discernable patterns related to geology. Indeed the observed variation in values for these elements is only a little greater than the expected deviation due to analytical precision (see Appendix). Anomalous concentrations of Mo (3-8 p.p.m.) are recorded in a number of stream sediments from areas underlain by the Lower Llandovery shales, with further occurrences in streams with both Lower and Mid Llandovery in their catchment areas. The source of the anomalous levels of Mo is thought to be the Lower Llandovery black shales with possibly some contribution from Mid Llandovery black shale bands. The mineralisation of the area is thought unlikely to be a source of Mo in stream sediment since Mo is undetected in ore minerals from veins in North Cardiganshie (Shazly et al, 1957). The occurrence of Mo—rich sediments in streams draining the Lower Llandovery black shales is restricted to streams having catchments developed wholly on these shales whilst there are no Mo anonalies associated with the Ordovician north of the Davey. (Black shales in the Ordovician succession might be expected to contain raised levels of Mo (see page 58)). It is thought that this is probably a reflection of the low sample density obtained away from the coast where it was frequently possible to sample only the larger streams with catchments containing a variety of rock types. In these situations the black shale outcrops usually form a minor portion of the catchment and consequently Mo—rich material from them is completely masked by non black shale material in the stream sediment. Anomalous levels of Mo (5-8 p.p.m.) occur in two streams draining Borth Bog west of Tre'r—ddol. (The values are 65

confirmed by colorimetric determination and are thought to be significant.) The samples were of mineral material (loss on ignition (5%) despite the peaty nature of the catchments. The Mo may be derived from black shale material brought into the area by streams draining the nearby Lower Llandovery, or nay come from dark marine silts underlying the peat. The presence of raised levels of Pb (850 p.p.m.) and Zn (850 p.p.m.) in the same samples suggests mine contamination and the introduction of detrital material by streams draining from the adjacent hills. Iron shows a twofold distribution. There are a number of high levels of Fe in upland areas that are probably due to the influence of the secondary environment (see following paragraphe). High levels of Fe ( >7.5% Fe203) also occur in a number of streams draining the Lower Llandovery in both upland and lowland areas. At these sites Fe seepages were noted. The source of Fe in these circumstances is regarded as being the weathering of pyrite which is abundant in the Lower Llandovery shales

(B) Patterns related to mineralisation Massive stream sediment anomalies in Pb (100 p.p.m. — >1%) and Zn (600 p.p.m. — >1%) and to a lesser extent Cu (85 p.p.m. — >1%) occur in areas of previous mining activity and are considered to be due to contamination. Further small anomalies are recognised that may be due to as yet unknown mineralisation. Copper anomalies are less frequent and have a lower contrast than those of Pb and Zn. Copper is usually a minor constituent of the mineral veins (0.T. Jones, 1922). Two groups of anomalies are recognised: those 66

associated with known mineralisation and those ocnurring away from known mineralisation. (1) Anomalies due to contamination from previous mining activity. Mining was previously so extensive that it is practically impossible to avoid contamination in the areas of known mineralisation. (a) Happy Valley (Pb and Zn anomaly). Streams draining Happy Valley, to the north of Aberdovey, carry anomalous levels of Pb and Zn in sediments. All the anomalous samples were taken downstream of mine workings (Fig. 14). (b) Trelr—ddol — Talybont. (Pb, Zn and Cu anomaly). The anomaly area extends from the Bryno valley along the coast to Tre!r—ddol and Talybont and thence inland along the Clettewr, Ceulan and Leri valleys. All the catchments contain disused mines, smelters or dressing areas (Fig. 14). (2) Anomalies outside areas of known mineralisation. Raised levels of Pb, Cu and Zn (Pb 20-600 p.p.m., Cu 30-100 p.p.m., Zn 590-1000 p.p.m.) occur north of the Dovey estuary between Pennal and the north east corner of the survey area. There is no record of mineralisation in the area north of Machynlleth. However, the structural trends (ENE WSWfaulting) and sedimentary rocks (Mid and Upper Llandovery grits and shales) appear favourable for mineralisation.

(C) Patterns related to the secondary environment Patterns of high levels of Mn (7) 1600 p.p.m.) and Co (>100 p.p.m.) are observed in the sediment of streams

Table 11 TDII.E .pd mean* metal content of the minus 80—mesh fraction of stream sediments and pH of stream raters from the upland and coastal plateau districts of the Machynlleth survey area

pH of Number Fe203(%) Mn(p.p.m.)A Co(p.p.m.) stream waters of samples

Upland Poorly drained peaty ;;ley 7.5 >1% 356 6.1 22 and podzolised soils 4.3-14.0 850-51% 40-1000 5.0-6.5

Coastal plateau Moderately d-rainec:, acid 5.9 1409 54 6.6 17 brown earths 3.5-7.8 850-4000 40-85 6.0-7.0

* Geometric mean A Mean calculatel with > 1% = 2% 68

draining upland areas, contrasting with lower levels of Mn and Co in the coastal plateau area (Table 11). The high Mn and Co patterns are discordant with geology but follow closely the distribution of poorly drained peaty gley and peaty podzol soils (Hiraethog Series) characteristic of moorland areas in the uplands. In contrast the lower levels of Mn and Co in the coastal plateau occur in areas of moderately drained brown earth soils (Denbigh Series). The circumstances of the high Mn and Co patterns are thus similar to those observed in the Rhayader survey area (page 45) and in North Wales by Nichol et al (1967). Iron shows only slightly higher range and mean values in the Machynlleth upland area (Table 11) unlike the Rhayader and North Wales situations, where the upland has significantly higher levels of Fe than the lowland. The distribution of Fe in the Machynlleth area however is modified by the occurrence of high levels in the sediments of streams draining the Lower Llandovery in both upland and lowland areas (see page 65).

3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals The occurrence of known trace element disorders is shown in Fig. 15.

(A) Molybdenum and Copper Swayback occurs over large parts of the Machynlleth area. There is no pattern of low Cu in stream sediment coincident with the swayback areas. No other elements show patterns coincident with the swayback areas. + Lead and Zinc Toxicity. .%""v Molybdenum j stream sediment anomaly. 0 Bovine Copper Deficiency. 0 2 Areas in which Scale in Miles. Swayback occurs.

Fig. 15. The Incidence of Trace Eleftlent Induced Agricultural Disorders in the Machynlleth Survey Area 69

Copper deficiency in bovines has been recognised on farms near Towyn and confirmed by blood copper analysis. Although levels of Cu in stream sediment are lower in this area than elsewhere they do not fall to significantly low levels. The presence of Mo is confirmed over some 8 square miles of the Machynlleth area and probably occurs over further areas underlain by Lower Llandovery black shales. Although the outcrop of Lower Ilandovery is narrow it extends for some 14 square miles, part of this being in the area of the coastal plateau where dairy cattle are reared and the presence of raised levels of Mo may be a hazard to the health of grazing cattle.

(B) Cobalt Cobalt deficiency in sheep occurs occasionally in the area. The stream sediment survey reveals no areas of very low Co. However in view of the probable enrichment of Co in stream sediments in the upland areas, due to environmental circumstances, no estimate can be made of the Co status of soils in this zone.

(C) Other Metals Lead and zinc toxicity in cattle have been reported from Furnace. The contaminated pastures occur over a former slag area where waste from ore smelting was dumped. Lead and zinc poisoning occurs occasionally elsewhere in the mining area. 70

CHAPTER 7: REGIONAL GEOCHEMICAL RECONNAISSANCE KENDAL SURVEY AREA

1. Description of the Area (A) Location The reconnaissance area, enclosing 75 square miles of the south flank of the Lake District Dome, is situated east of Lake Windermere and north of Kendal (Fig. 16).

(B) Geology and Mineralisation The geology is reviewed by Eastwood (1963) and described in greater detail by Aveline, Hughes and Strahan (1888) and Marr (1925, 1927). The stratigraphic succession is summarised in Table 12 and the geology shown in Fig. 17. The rocks of the area are of Ordovician and Silurian age with Devonian and Carboniferous outliers near Kendal. The lithologies present include acid volcanics and pyroclastics, greywackes, grits, flagstones and shales. Graptolitic black shales are developed in the Stockdale Shales (Llandovery) and persist into the base of the Brathay Flags (Wenlock). Sedimentary characters of the black shales have been described by Marr (1925) and Rickards (1964) whilst Spencer (1966) has examined the geochemistry of the Mid Llandovory Monograptus leptotheca horizon from which he records levels of 3-12 p.p.m. Mo and 199-289 p.p.m. Cu. Two small veins carrying Pb are recorded in the Silurian Slates of the area (Fig. 17). Elsewhere in the southern Lake District important Cu bearing veins have been worked in the Borrowdale Volcanics (Dewey and Eastwood, 1925). The Central Fells, north of the survey area, formed an Land above 1400 ft. ,— _-- 1000 ft. contour Towns ------600 ft. contour ,------200 ft. contour

Key to Towns

A. Ambleside, • K. Kentmere, S. Staveley, Te. Tebay, Tr. Troutbeck, W. Windermere

Key to Rivers and Lakes

1. River Brathay, 2. River Kent, 3. River Lune, 4. River Mint, 5. Lake Windermere

Fig.16. Location and Topography of the Kendal Survey Area 71

Table 12 Stratigraphy of the Kendal survey area (From Eastwood, 1963)

GEOLOGICAL FORMATION LITHOLOGY Alluvium Gravel, sand, silts and clay Recent Peat Peat Diatomite Silaceous earths (at Kentmere)

Pleistocene Glacial Drift Boulder clay, stony boulder clay, fluvioglacial gravels and sands

Old Red Sandstone Sandstone, sandy shales and Carboniferous and conglomerate

Bannisdale Slates Thin bedded dark gritty silts, mudstones and grit - Coniston Grits Coarse, grey green greywacke grits Silurian Caldwell Beds Grits and dark laminated siltstones Brathay Flags Black graptolitic shales and dark laminated siltstones Stockdale Shales Black graptolitic shales with grey and green shales

Ashgill Series Calcareous shales, ashes and limestones Ordovician Coniston Limestone Calcareous shales and ashes with limestone and conglomerate Borrowdale Volcanics Andesites,rhyolites, ashes and tuffs 0 1 2 0 0 0 Scale in Miles. 0 0 Carboniferous.

Banhisdale Slates.

Coniston Grits. ....,' Mineral Veins. Caldwell Beds & Brathay Flags.

Coniston Lstn, Ashy:II Series and Stockdale Shales. x

Bcrrowdale Volcanics.

Fig.17. Geology of the Kendal Survey Area (Based on I.G.S. maps.) 5 10 scale in miles

•

Movement of Lake District and Irish Sea Ice.

Movement of Pennine (Carboniferous) Ice.

1 Kendal Area. 2 Bowland Forest Area.

Fig. 18. Map Illustrating the Glaciation of North West England (Based on Eastwood, 1963 and Earp et al, 1961.) 72 ice distribution centre during the Quaternary (Fig. 18). Locally derived glacial drift is found in the valleys and on the flanks of hills. The drift is of diverse character being locally stiff stony clay, sand or morainic gravels.

Ice deepened valleys are now occupied by lakes (Windermere) 9 former lake deposits (including diatomite at Kentmere) or by rivers and their associated alluvium.

(C) Topography and Drainage The principal physical features are shown in Fig. 16. North of Kentmere and Troutbeck summit levels are about 2000 feet with valley floors at 400-500 feet. To the south summit levels fall off to 800 feet between Kendal and Lake Windermere whilst valley floors drop to 200 feet. Local relief can be severe with long, steep slopes. The drainage of the area is almost entirely within the catchment of the River Kent. The larger valley floors carry alluvium whilst the tributary drainage is actively eroding and flows in colluvial banks or rock walls. A number of valleys in the north east portion of the area are without road access and were unsampled

(D) Cliiw to Climate follows topography in this upland area, with rainfall ranging from 50 inches per annum around Kendal and 60 inches in the fells between Kendal and Lake Windermere to 100 inches per annum in the fells north of Kentmere and Troutbeck. 73

(E) Soils The soils of the Lake District are briefly outlined by Bainbridge (1939) and preliminary mapping by the Soil Survey south and west of Lake Windermere is applicable here (Hall, 1969). Soils derived from the volcanic rocks are thin and coarse textured between areas of peat and bare rock. On the sedimentary rocks, drift and alluvium, Hall (1969) recognises a number of soil associations. At low levels and in river valleys, brown earths, gleyed brown earths, groundwater gleys and organic soils derived from stony drift and alluvium together with local areas of peat are found. Above these are found bare rocks and rankers with brown earths and gleys replaced by podzols, peaty grey podzols and blanket peat above 1000 feet; gleys occur in flush sites.

(1) Land Use Rough fell grazing occurs above 900 feet and on steep slopes at lower altitudes. Between 600-900 feet, and on moderate slopes, are farms of mixed beef and sheep rearing on difficult land that needs constant attention to maintain productivity. The lower slopes and valley floors, when drained, support fine grasslands (particularly around Kendal) where successful dairy and dairy/beef farming is practised. Large areas of marginal land, particularly steep hillsides are being afforested by the Forestry Commission.

2. The Regional Geochemical Patterns The stream sediment survey of the Kendal area reveals 74 little overall geochemical relief. However, patterns related to the bedrock, mineralisation and secondary environment are discernable. The metal content of stream sediments over the principal bedrock units is summarised in Table 13. Data from the Coniston Limestone, Ashgill Series, Stockdale Shales and Brathay Flags are grouped together. This group occupies a hollow between the Borrowdale Volcanics and the Coniston Grits within which the local drainage covers all four formations.

(a) Patterns related to bedrock In general the area displays relatively uniform metal distributions despite the wide variety of parent materials. However, range and mean levels of Ni and Cr are lower in the sediments of streams draining the Borrowdale Volcanics than other groups in Table 13. Molybdenum is below the detection limit throughout the area except for two unrelated samples in Long Sleddale (3 p.p.m. Mo) regarded, in the present study, as being insignificant. The absence of the anticipated Mo anomaly in the sediment of streams draining the Stockdale Shales may be explained as follows. The black shale facies of the Stockdale Shales is thin (a total of 30 feet) giving rise to a very narrow outcrop. Streams draining this portion of the succession have only a very small area of black shale within their catchments. It is thus thought that the Mo anomaly recorded in the bedrock (Spencer, 1966) is completely masked by the dominance of barren material in the stream sediments.

Table 13 Lan ;e and me ma* metal content of the minus 80-mesh fraction of stream sediment from as...=• •••••• the princLpal geological units of the Kendal survey area

Metal content ( p. p .ra. ) A Pb Ga Zn Ti+ Ni Co Mn+ Cr Mc Cu V Fe 203%

Bannisdale 31E. te s <- 2 39 92 53 19 530 7948 67 39 1354 102 3.4 <2 16- 40- 20- 13- 300- 6000- 40- 20- 600- 60- 1.9— (47 samples) -2 60 130 300 30 1300 > 1% 100 85 ;: I% 200 5. 2 Coniston Grits <2 33 110 49 18 510 8649 57 37 1092 103 3.4 <2 20- 100- 40- 13- 300- 6000- 40- 20- 600- 85- 2.8- (8 samples) -2 40 130 60 20 850 1% 100 60 6000 160 4.1 Coniston Limestone, (..2 61 128 49 21 704 'T i% 51 41 2306 82 3.8 Ashgill Series, <2 50- 100- 40- 16- 600- 8500- 30- 20- 600- 50- 2. 8- Sto ckdale Shales and -3 100 160 60 30 1300 > 1% 130 85 > 1% 130 5.4 Bra thay Flags ( 7 samples ) Borrowdale lolcanic s (2 32 123 46 20 624 ) 1% 23 33 2392 58 3.9 <2 20- 85- 30- 16- 500- 1%- 10- 20- 850- 30- 3.2— (10 samples) -3 50 200 160 20 1300 ':"1% 60 50 >1% 100 5.4

* Geometric me an A Mean calculated with <2 p.p.m. = 1 p.p.m. + Mean calculated with )l% = 2% 76

(B) Patterns related to mineralisation A lead and zinc anomaly (Pb 85-160 p.p.m., Zn 1300- 3000 p.p.m.) occurs in an east bank tributary of the River Kent north of Stavely. Within the catchment area of this stream Pb mineralisation is known from trials in 1865 which proved mineralisation of insufficient size to be worked economically (Aveline et al, 1888). A further anomaly in a west bank tributary of the River Kent (Pb 300 p.p.m., Zn 1000 p.p.m.) may indicate mineralisation on both sides of the Kent valley in this area and that the mineral veins are thus much more extensive than previously recognised. ILt the head of Long Sleddale east bank tributaries contain anomalous levels of Zn (1300 p.p.m.) and raised levels of Cu (50-100 p.p.m.) in stream sediments. These may indicate the occurrence of mineralisation in the Borrowdale Volcanics and adjacent sedimentary rocks.

(C) Patterns related to the secondary cavirohment Throughout the study area high levels of Mn (3000 p.p.m.— > 1%) are found in the sediment of streams draining areas of poorly drained peaty gleys and peaty podzols. In all cases a conspicuous black precipitate of Mn02 is observed coating pebbles in the stream bed. Such levels of Mn and precipitate in streams are not the occurrence of black Mn02 recorded from streams draining steep fell slopes and the moderately drained pastures of the south and east of the area. The high levels of Mn are thus thought to be due to leaching from acid, waterlogged soils followed by precipitation in the stream environment (see page 47). There is no clear evidence that Mn precipitates are 77 scavenging any other metals on deposition. However, the limited data from streams draining the Borrowdale Volcanics suggests that Co is scavenged where high levels of Co (85 p.p.m.) are coincident with the massive enrichment (>1%) of Mn. Iron has a small range of values within the study area and shows no significant enrichment in areas of high Mn or elsewhere.

3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals (A) Molybdenum and Copper Swayback occurs sporadically in this area. There is no pattern of low Cu in stream sediment coincident with the swayback occurrences. No other metal displays a pattern coincident with the swayback areas. Although high levels of Mo are recorded in the Stockdale Shales (Spencer, 1966) the anomaly does not show in the stream sediment. Furthermore, the narrow outcrop is restricted to areas of unenclosed rough fell grazing and may be regarded as of no real significance to agriculture.

(B) Cobalt Cobalt deficiency occurs occasionally in sheep grazing the open fells. In view of the apparent common enrichment of Co with Mn in the sediment of streams draining the Borrowdale Volcanics, the Co levels in some of the soils on the Borrowdale Volcanics may be lower than the stream sediment values. 78

CHAPTER 8: REGIONAL GEOCHEMICAL RECONNAISSANCE BOWLAND FOREST SURVEY AREA

1. Description of the Area (A) Location The area, shown in Fig. 19 and covering 195 square miles of Lancashire and West Yorkshire, is one of broken ground drained by the Rivers Hodder and Ribble in the upland district known as Bowland Forest.

(B) Geology Comprehensive accounts of the geology are given by Parkinson (1936),Moseley (1954) and Earp et al (1961). The succession is summarised in Table 14 and the geology shown in Fig. 20. The Lower Carboniferous sediments, shallow water marine limestones, calcareous shales-with reef limestones and black shales, were deposited near the northern margin of the Central England Basin (George, 1958). Overlying the marine sequence is a considerable thickness of rythmically bedded non—marine sandstones and shales of Millstone Grit facies (Moseley, 1954). Black shale facies are represented by the Bowland Shale Group. This sequence of Upper Visean/Lower Namurian age usually outcrops on slopes below the Millstone Grit. The Bowland Shales comprise dark grey to black shaley mudstones and paper shales and include interbedded limestones and sandstones. Pyrite is generally present in the shales and oil occasionally found in 'solid' goniatites (Dunham, 1961). Molybdenum induced copper deficiency reported around Chipping by Morgan and Clegg (1958) has been related to GI

6

0 4 8 Scale in miles Land over 1400 ft. 1000 ft. contour 600 ft. contour •Towns 200 ft. contour Key to Towns B. Bentham B.B. Bolton-by-Bowland C. Chipping

Ga. Garstang Gi. Gisburn L. Longridge N. Newton

P. Padiham Se. Settle - Sl. Slaidburn W. Whalley

Key to Rivers

1. River Calder 2. River Hodder 3. River Lune 4. River Ribble 5. River Wenning 6. River Wyre

Fig. 19. Location and Topography of the Bowland Forest Survey Area 79

Table 14 Stratigraphy of the Bowland Forest survey area (Based on Earp et al, 1961)

GEOLOGICAL FORMATION LITHOLOGY Alluvium and Gravel, sand, silt Recent colluvium and clay Peat Peat

Pleistocene Glacial Drifts Locally derived silty or sandy boulder clay, fluvioglacial gravel and sands

Permo—Triassic Red sandstone and marl

Millstone Grit Series Rhythmically bedded non marine sandstones Upper and sandy shales with Carboniferous marine shale bands (Namurian) Bowland Shale Group Marine black shales, mudstones and cementstones with sandstones and limestones

Worston Shale Group Calcareous mudstones Lower and shales with Carnoniferous limestones. Knoll (Visean and reef limestones at base Tournaisian) Chatburn Limestone Dark grey crystalline Group limestones with calcareous shales ...... ------...... • . . • • • . .... • " . 4111111 11111 • • •• • • • • • • • • ,i. 11.A III . 10111• . . . . ••••••••.•...... •. IF 1 .. • . • . • ioil . . • : • . ' • . • • • • e • Cr;9.;d.9 ;. •. 1111(''it1il 41111111 evil h eiiiiiii,11111111100 IIIllIbliw.**i II 'i .I 1 411 ill 110111 .....•1.. - • rel. • •• • • .11411111 ...... , i' *op* . : .: . .. . 0110 . 40111 . . 11111f . 111110, AV • 401 II' ..• filliard,'". / ,i rilifi 4r i

. . : 311114 II ill IIIL IAW.111111Slaidbursp . II 11144r. 111111°i •• ...... III III 11;41' 1 :::.:41111111111111111°1 111 f 1.111 IIIIIP III giMr 1 il1 ,,il, Ir od 0 - 11 111,4e. v". Ill Mill, II . ..- .1 I • • Permoi Triassic. 4 /•• • - • • • .,I,rJaw *. 4111 :. to b •• • • • AI II) ...... • ...... v if 1.1 •: : . •:•:,,„:: . 'r4.1 0owlani1A . ' .: Bleasdefe Moors. ' 1:fare.en Fell .. '. ill r ,::. • 17 • . .. . , SPA .. • Millstone• Grit• Series. Pia •• -iiiro" :: .. ;1 la 6./..: ,- -.: . :.:...... ;.. Iiiiii Ai Rowland Shale Group. 11,1• .4iiimpliitinvi I ::. I 11 ..:: Iwo Gr'rlidie c;r1.4e tcw•-- 7 440 / / Worston Shale Group. Jill NOP aw &Mei I OWPF 1 li • 410 wa an _..b.atburn. --"-IIIIII . . Chatburn Lstn Group. , Atie. -- • v . A4woo 411 Ch:pping. rClitheroe. Ar...... - Mineral eins. woiff Hoolla.ii .III.111111 I . 0, ' , ie 11 1111 0 1 2 fr AY, ...... 1 Or • Olry I Longridge fell : . II • Scale in Miles. i All •• . • ..1.- f. . • !I i ar" .41

Fig. 20. Geology of the Rowland Forest Survey Area. (Based on I.C.S. maps and Parkinson, 1936.). 80

enhanced levels of Mo in soils derived from the Bowland Shale and Bowland Shale drift (pers. coven. N.H. Brooksbank). Mineralisation is recorded at a number of localities (Fig. 21) where galena, with a gangue of barytes and withertte, occurs in veins or as replacement bodies in reef limestones (Earp et al, 1961). Valley floors and slopes up to 1200-1500 feet are invariably mantled by glacial drift (Earp et al, 1961). Boulder clay predominates with local morainic gravels. The drift is of local origin with the composition of the boulder clay largely reflecting the underlying rocks. Ice movement was from NE—SW through the area (Fig. 18) skirting the fells which are usually drift free.

(C) Topography and Drainage Tha main physical features are shown in Fig. 19. The fells, part of a dissected, rolling upland, underlain by Millstone Grit, terminate at a scarp above long concave slopes of Bowland Shale which descend to the Hodder, Ribble and Chipping valleys. Away from the steep slopes the lower areas have a huirmocky topography produced by the mantle of glacial drift. The drainage of the area is dominated by the Rivers Hodder and Ribble. Fells to the north of Chipping and the vale west of the town are drained by the River Wyre. The principal rivers of the area are deeply entrenched into the landscape with their tributary streams actively eroding and flowing in colluvial banks or rock walls. Areas of alluvium are small, and virtually restricted to the larger river valleys. 81 The drainage network is well developed and road access generally good. However, 35 square miles in the north of the area proved inaccessible and were unsampled.

(D) Climate The climate reflects topography with annual rainfall ranging from 40-45 inches per annum at Chipping and in the lower parts of the Ribble and Hodder valleys to more than 70 inches on the fells north of Chipping and Slaidburn. Newton Fell receives more than 60 inches of rain. Rainfall is spread evenly throughout the year. At Chipping mean daily temperatures in January and July average 41°F and 60°F respectively; on the fells values fall off to about 39°F and 55°F.

(E) Soils Soils developed on upper slopes and on the fells are briefly described by Pepper (1963) and by Hall (1961, 1962). Elsewhere in the area soils described by Crompton (1966) can be recognised. In the valleys and on valley sides the boulder clay and Carboniferous shale parent witerials give rise to fine grained soils which, in this area of high rainfall, suffer from impeded drainage, with gleying a frequent occurrence. Major soil associations follow the topography. The fells have extensive areas of hill peat, with peaty iron podzols and skeletal soils. Along the scarps where erosion and creep is active, screes and skeletal soils are found. Steep upper slopes, where there is some free drainage, carry thin peaty podzols, becoming gleyed down—slope when drainage 82 deteriorates. Peaty gleys are developed on less steep mid—slopes where the high rainfall is supplemented by run—off from the higher slopes. Similar soils are found in receiving sites at lower altitudes. Throughout the remainder of the area non—calcareous surface—water gleys of variable texture are typical, with alluvial soils adjacent to some streams and rivers and peat developed in local hollows.

(IP) Land Use The area is devoted to permanent grassland with farms typically small family units, raising cattle and sheep. Open moorland used for sheep grazing is found above 1000 feet and extends to lower altitudes on steep slopes below the Millstone Grit scarp. Below the moorland is a zone of marginal land, grassland infested with rushes, corresponding to peaty gley soils, used for beef cattle and sheep grazing. Large areas of good permanent pasture occur below 600 feet, supporting mixed dairy and beef farming.

2. The Regional Geochemical Patterns The principal geochemical patterns are related to: (a) the syngenetic enrichment of Mo and associated metals in the Bowland Shale Group and their redistribution by glacial action (b) localised base metal anomalies reflecting mineralisation (c) patterns of raised Mn levels in areas of very poorly drained agricultural soils. Trace element levels on the major geological units are suowarised in Table 15. The extensive and diverse drift Table 15 F.ange End mean* metal content of the minus 80-mesh fraction of stream sediments from the principal geological units of the Bowland Forest survey area

Metal content (p.p.m.)

MoA Cu V Pb Ga Zn+ TiY Ni Co MnY Cr Fe203%

Millstone Ccrit (,rith <2 24 73 27 15 378 8543 55 43 124E3 60 3.4 local drift cove-2) <2 8- 40- 3- 6- (50- 3000- 10-. 20- 60- 16- 1.3- (23 sampls) -5 60 200 60 30 1000 >1% 200 85 1% 130 7.2 BowiaLl Shale 7 46 97 46 13 859 6925 65 48 2131 61 3.9 (with drift cover) <2 10- 20- 13- 5-. 200- 2000- 16- 16- 500- 13- 1.1- (60 samples) -60 300 200 300 30 5000 >1% 300 400 >1% 130 18.0 Worston Jhale and 2 30 77 44 11 540 5977 58 36 1734 54 3.2 Chatburn Lii.estme <2 10- 40- 13. 4- 50- 1000- 20- 20- 400- 20- 1.3- (with drift cover) -8 60 130 850 20 1600 >1% 160 100 >1% 100 18.0

* Gecmetric mean A Meen calculated with ,‘2 p.p.m. = 1 p.p.m. + Mean calculated with (50 p.p.m. = 40 p.p.m. •Mean calculc ted with >1% = 2% 84 cover and complex geology preclude the breakdown of the stream sediment data into smaller units.

(A) Patterns related to bedrock Sediments characterised by containing enhanced levels of Mo (3-60 p.p.m.) delineate broad areas around Chipping and to the north and east of Newton Fell. Similar patterns are clearly seen in the distribution of Cu and V and appear to be present for Cr, Ni and Fe. The distribution of Mo anomalous sediments indicates that the source of Mo lies in the Bowland Shale Group and this has been confirmed in follow up studies (Ch. 14). Enhanced levels of Pb and Zn are also often associated with Mo-rich sediments but although in part this reflects syngenetic enrichment in the Bowland Shale Group the patterns are also related to mineralisation (page 85). In the Chipping district and to the west of Newton Fell are found a number of Mo-rich sediments (3-8 p.p.m.) in streams draining drift covered areas underlain by the Worston Shale Group. The Mo anomalous sediments occur in areas south and west of Bowland Shale outcrops and are thought to reflect the redistribution of Mo-rich bedrock in the boulder clay. Follow up work (Ch. 14) has demonstrated the smearing of Mo-rich bedrock at a number of sites in the area. Levels of <0.2-17.0 p.p.m. Se (mean 1.8 p.p.m.) are recorded in selected Mo-rich stream sediment samples compared with values of <0.2 p.p.m. Se in background areas. The levels of No and Se observed are comparable to those encountered by Fletcher (1968) in streams draining Visean/Namurian black shales in the South Pennines. 85

In the north east of the study area there are a limited number of Mo—rich sediments in streams draining areas underlain by Bowland Shales. Exotic drift, with Lake District erratics, entering this part of the survey area appears to have almost completely masked the Bowland Shales with barren, sandy boulder clay suppressing the Mo stream sediment anomaly originating in the black shales. No distinctive geochemical patterns are recognised on the Millstone Grit.

(B) Patterns related to mineralisation The zone of very high Zn values (850-3000 p.p.m.) with some raised levels of Pb (50-100 p.p.m.) in stream sediment which occurs between Slaidburn and Bolton—by—Bowland may be due to the mineralisation known in this area. Elsewhere coincident high levels of Pb and Zn may be indicative of mineralisation similar to that already recognised in the area. However, follow up studies (Ch. 14) have shown that syngenetic enrichment of Pb and Zn occurs in the Bowland Shales and thus some of the stream sediment anomalies may owe their origin to Bowland Shale material rather than mineral veins.

(0 Patterns related to the secondary environment High levels of Mn in stream sediments ( 3000 p.p.m.) are a frequent occurrence in the following localities: (i) along the foot of Longridge Fell and Pendle Fell (ii) on the north and east flanks of Newton Fell (iii) in the north east of the study area. In all three districts there are large areas of very poorly drained soils. At the first two localities extensive areas 86 of waterlogged peaty gley soils occur in receiving sites below long fell slopes. The north east of the study area has a thick drift cover giving rise to a hummocky topography of low relief on long, shallow slopes where very extensive development of peaty gleys and gleyed brown earths are found. It is believed that the high sediment Mn levels reflect increased leaching from the acid, waterlogged soils. Thick encrustation of black Mn oxides occur in streams in the high Mn districts.

3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals The recorded incidence of trace element disorders in animals is shown in Fig. 21.

(A) Molybdenum and Copper Bovine copper deficiency has been confirmed on a number of farms within the Bowland Forest area. The recorded occurrences show a close coincidence with the Mo anomalies delineated by the stream sediment survey. Molybdenum induced copper deficiency has been confirmed in the Chipping district (Morgan and Clegg, 1958). However, the area delineated by Mo—rich stream sediments (35 square miles) is considerably more extensive than that within which bovine hypocuprosis has been confirmed. In the light of previous work in an area of similar geology, topography and farming in the South Pennines (Fletcher, 1968, Thornton, 1968), it is possible that molybdenum induced bovine copper deficiency may occur in many more herds than is at present recognised. Swayback in sheep is recorded from many flocks. Although

/ . 0 0,4 Croasdale , Fel 4 10)01„ / , . a Iinbeystea. 0 0 Slaidbur' / CI . 07 O 4 If - New n.• C;olof / /7 • Newton olton by 0 Fell.. 4 wlan. Bleasdale Moors. Har den F I. .0 1/,1 0 Bovine Copper Deficiency. / • e , 4,0 ______fAir )1/ 'WO/ 4. .0• ri;dtet0% _ . Areas in which el _, ------Swayback occurs. / 0 ,,

Fig. 21. The Incidence of Trace Element Induced Agricultural Disorders in the Bowland Forest Survey Area 87

the reported incidence is in part coincident with the distribution of Mo—rich stream sediments, Mo is not normally recognised as a factor causing ovine hypocuprosis under field conditions. No patterns of very low Cu were detected by the stream sediment survey.

(B) Selenium Although raised levels of Se are recorded from the Bowland Forest area it is unlikely that selenium toxicity is affecting animals. The environmental conditions required for Se to be taken up by plants, an alkaline organic (peat) soil, are not recognised in the study area.

(C) Manganese A number of cases of bovine infertility in the area have been attributed, in part, to manganese deficiency. The distribution of Mn as shown in the stream sediment survey reveals that, whilst Mn may be depleted from soils in certain environments, there is no clear evidence of low Mn in the agricultural soils of the btudy area. The overliming of soils to above pH 6.5 will frequently reduce the availability of Mn to plants and this may have occurred locally. 88

CHAPTER 9: REGIONAL GEOCHEMICAL RECONNAISSANCE SHAFTESBURY SURVEY AREA

1. Description of the Area (A) Location The area encloses some 120 square miles of the north end of the Vale of Blackmoor within the counties of Wiltshire, Dorset and Somerset and includes the towns Shaftesbury, Mere, Gillingham and Wincanton (Fig. 22).

(B) Geology A full description of the geology, which comprises Jurassic and Cretaceous shelf sediments, is given by Osborne White (1923) and Mottram (1961). The succession is summarised in Table 16 and the geology shown in Fig. 23. The clays, shales, limestones and sandstones exposed in the area include two formations that contain sediments of black shale facies: (a) The Oxford Clay. The formation is only very rarely exposed and has been described by Osborne White (1923) as "blue—grey pyritous clays, marly clays and shales with layers of septarian concretions". The area lies between well documented sections at Weymouth (Arkell, 1947b) and Melksham (Whitaker and Edmunds, 1925) where bituminous shale is recorded in the Lower Oxford Clay whilst data from a borehole at Gillingham (Whitaker and Edwards, 1926) reveals 140 feet of brown leathery (bituminous?) shales with stone bands forming the lower part of the Oxford Clay formation. .(b) The Kimmeridge Clay. Osborne White (1923) describes

/ .. --\ .p..... ,/ ‘,, • 1-7. 7 rl ,—: ...._ . ) ------...,) • ir\\...... ) t .---‘ i \,:,

r• — — --, ../) ., , ) ) / ( r, ...... ri 1 U 1\2-7 , I ra 11- s .5 h. ----% f ... S ...., r r* - - . i... . 1... t I I...., 1.-1, ...... ) ,...... 1 ..... r----___r. ". I-,,...... , • n 1 V1 5j--..-- 2---' .2 •-• -V \i "-r-* rut — .)?` < r 0 ...... " (c.,-) ., -... , , 1( (- ,1 r.f '''' \-- . —1 —,.. i (..,,,, ) ( ..--r C1). , C....Y*1f '- I e If i

Scale in miles 600 ft. contour ------400 ft. contour • Towns ----- . 200 ft. contour

Key to Towns B. Bruton C.C. Castle Cary G. Gillingham M. Mere Sb. Sherbourne S.N. Sturminster Newton Sh. Shaftesbury W. Wincanton

Key to Rivers 1. R. Alham 2. R. Brue 3. R. Cale 4. R. Nadder 5. R. Stour 6. R. Wylye

Fig. 22. Location and Topography of the Shaftesbury Survey Area 89

Table 16 Stratigraphy of the Shaftesbury survey area (Based on Osborne White, 1923 and Mottram, 1961) GEOLOGICAL FORMATION LITHOLOGY

Recent Alluvium and Sands, silts and clays colluvium

Pleistocene Head Unconsolidated sands and loams

Upper Cretaceous Chalk White limestone with flints

Upper Greensand Micaceous and glauconitic sands and sandstones with chert beds Lower Gault Blue grey micaceous clay and Cretaceous sandy clays Lower Greensand Fine ferruginous and glauconitic sands

Purbeck Shelly limestones with calcareous clays and shales Portland Compact limestones with chert overlying grey sands and clays Kimmeridge Clay Dark bituminous shaley clays Upper with cementstone bands Jurassic Corallian Oolitic limestones, ragstones, marls and calcareous clays Oxford Olay Blue grey pyritous clays, dark shales and cementstones Kelloways Beds Calcareous sands and sandy clay

Cornbrash Rubbly limestone, marlstone marl and clay Mid Forest Marble Flaggy shell limestones, grey Jurassic clays and shales Fullers Earth Grey marls and clays with Argillaceous limestone

Mere., 0 • ••• if- 0 0 0 •Jeals.„.• 0 0 0 . • /0 0 • 0 0 • 0

0 0 0 0 • • 0 0 0 0 0

0 0 0 O 0 0 0

O 0 0 0 O 0 0 • 0

o 0 0 : 0 0 O 0 • 0 0 ip Gilli gham. o o •0 0 0 5 I

0 0 0 ••••••••• o •o 0 Buckhorn O 0 0 0 0 Weston.' 0 • 0 0 0 0 ••••••••• •••••ro, . . 0 0 0 0 • • • . .. • • • • • • • 0 • • • • • • • •••••••• • 0 Shaftesbury .• 0 .... .

0 0 0 1 2 0 0 Portland Oxford Clay. o 0 Kimmeridge Qay. & Purbeck. Chalk. Scale in Niles. . . I I 1 -•-••••• I I . • • ••••..r.• • • Gault I 1 Middle Jurassic. Corallian LiMestone. . ' , ' & Upper Greensand.

Fig. 23. Geology of the Shaftesbury Survey Area (Based on I.G.S. maps and Mottram, 1961.) 90 the Kimmeridge Clay as "dark grey to black bituminous shaley clay with bands of septarian cementstone and disseminated selenite". The formation here is similar to that of the Dorset coast (Arkell, 1947b) where bituminous shales and oil shales contain from 3-70% organic matter (Downie and Wilson, 1968). The area lies beyond the southern limit of the Quaternary Ice Sheets and drift is therefore absent. However, head and coombe rock together with landslipping and colluvial downwash are found on many of the scarp slopes.

(C) Topography and Drainage The topography (Fig. 22) is controlled by geology. The alternation of lithologies gives rise to west and south facing scarps supported by limestones and sandstones separated by broad vales underlain by the Oxford Clay and Kinmeridge Clay formations. Streams, rising from springs on the limestones and sandstones, flow sluggishly across the clay vales between alluvial and colluvial banks, then rapidly unite to form slow flowing rivers liable to flooding. The tributary drainage is well developed only at the margins of the vales and this, together with a road network that avoids the vales, results in an uneven distribution of stream sediment samples. Streams draining the Mid Jurassic are distinguuihed by containing a considerable precipitate of CaCO3, with tufa encrustation of pebbles and twigs a common feature.

(D) CUT-nate Mean annual precipitation in the area ranges from 91 30-32 inches per annum in the vales to 35 inches on the ridges and rises to more than 40 inches on the chalk hills north of Mere. Rainfall occurs evenly throughout the year with a winter surplus over evaporation and run—off leading to waterlogging and flooding in the vales.

(E) Soils The soils of Dorset are described by Robinson (1948). Soils are residual except where a mixing of materials occurs due to downwash or solifluction on steep slopes. The Oxford and Kimmeridge Clays carry very heavy non—calcareous surface—water gleys (Denchworth Series) which suffer seasonal waterlogging and occasional flooding. The ridges of Jurassic Limestone usually support a variable depth of moderate to freely drained grey brown loam over rubbly limestone. Heavy clay loans occur over marl and clay horizons. The Greensand ridges carry acid, light or medium sandy loans with free drainage, becoming podzolised where drainage is excessive. Chalk areas have very thin grey brown clay learns over weathered chalk. Alluvial soils, waterlogged clay loans, occur beside some streams on the vales.

Land Use The clay vales carry permanent pastures used for dairy farming. Some beef cattle are raised. Small uncultivated areas on the clay vales are covered by dense 92

hawthorn thickets. The better drained soils of the limestone ridges support mixed dairy and arable farming including some cereals. The Greensand ridges are largely afforested with mixed stands of beech and conifers. Elsewhere on the Greensand mixed farming with dairying and cereal production is practised.

2. The Regional Geochemical Patterns The regional geochemical patterns revealed in the Shaftesbury area are, in general, coincident with the outcrop of the geological units and can be related to the parent rocks. The patterns, shown in map form in Volume II, are reflected in Table 17 which groups the stream sediment data according to the geF:llogy of the catchment areas. The sediment of streams draining the Oxford Clay and Kimmeridge Clay contain higher levels of Cu, Cr, Ga, Fe, Pb, Mo, Ti, V and Zn than those from the adjacent limestone and sandstone areas (Table 17); Co, Mn and Ni show a similar but less pronounced distribution. Follow up work has confirmed that metal values in stream sediment derived from the clay and sandstone outcrops are generally similar to those in associated soils ( Ch: 15 ). However, the presence of large amounts of CaCO in streams draining the Mid Jurassic 3 and Corallian outcrops, precipitated from groundwaters entering the drainage channel, has depressed metal values in stream sediments (' Ch. 15 ) due to a process of dilution similar to that recorded by Thornton (1968) thereby exaggerating the contrast between clay and limestone areas. The most conspicuous geochemical patterns are those Table 17 Range and mean* metal content of the minus 80-mesh fraction of stream sediment from the nrinciDal geological units of the Shaftesbury survey area

Metal content (p.p.m.) MoL Cu V Pb Ga Zn+ Ti Ni Co Mn Cr Pe203% Cretaceous <2 14 36 15 7 126 2400 25 21 154 55 2.4 (Greensand and OhaTh) <2 6- 16- 10- 4- 60- 1300- 16- 13- 60- 20- 1.4- (12 samples) -2 "30 85 40 13 300 3000 40 40 300 300 4.8 Kimmeridge Clay 2 35 105 24 15 244 4300 44 32 319 91 5.6 < 2 10- 40- 13- 4- 85- 1300- 10- 16- 85- 40- 2.1- (60 samples) -13 100 200 60 30 500 850 85 60 1600 200 12.0 Corallian • <2 14 59 13 7 148 2400 32 28 442 53 3.5 <2 10- 20- 8- 4- 85- 1300- 20- 20- 100- 30- 1.4- (11 samples) 30 130 20 16 500 4000 60 40 1300 85 8.8 Oxford Clay <2 28 73 20 13 228 3520 42 34 521 73 5.8 <2 10- 30- 10- 5- 100- 1600- 20- 20- 85- 30- 1.7 (34 samples) -6 100 200 40 30 850 6000 60 60 4000 130 28.0 Middle Jurassio <2 18 49 16 9 114 2340 35 26 641 49 3.1 2.3- <2 13- 30- 13- 6- <50- 1300- 16- 16- 300- 30- (22 samples) 40 100 40 13 500 4000 50 40 1000 300 6.4

* Geometric mean 46' Mean Jalculatau with (2 p.p.m. = 1 p.p.m. Mean calculated with <50 p.p.m. = 40 p.p.m. 94 shown by Mo which occurs below the detection limit (<2 p.p.m.) over much of the area providing a strong contrast with anomalous zones (Mo > 3 p.p.m.) over the Kimmeridge Clay and Oxford Clay. An extensive Mo anomaly (M6 3-13 p.p.m., mean 4 p.p.m.) with associated patterns of high V (130-200 p.p.m.) and Cu (40-85 p.p.m.) occurs in the sediment of streams draining some 22 square miles underlain by Kimmeridge Clay. Follow up work (Ch. 15 ) has confirmed anomalous levels of Mo in residual soils developed on the Kimmeridge Clay within the area of the stream sediment anomaly. Anomalous levels of Mo (3-6 p.p.m.) are found in the sediment of streams draining two small areas of the Oxford Clay to the north and south of Wincanton. Follow up studies (Ch. 15) have shown that raised levels of Mo occur in residual soils over the Lower Oxford Clay. The Mo is thought to be derived from a bituminous shale facies of the Lower Oxford Clay. Selected stream sediment samples from Mo anomalous and background areas were analysed for Se. Sediments from the Kimmeridge Clay anomaly contain from (0.2-1.5 p.p.m-. Se (mean 0.9 p.p.m.) whilst levels of < 0.2-0.9 p.p.m. Se (mean 0.2 p.p.m.) are recorded from the Oxford Clay anomalies. These values contrast with background areas where Se is undetected (<0.2 p.p.m.). Follow up work revealed 1.5 p.p.m. Se in the Kimneridge Clay (Ch..15).. Manganese has an irregular distribution through the area with the highest values in the sediment of streams draining the Mid Jurassic limestones and Oxford Clay. Sporadic high values (700-4000 p.p.m.) throughout the area 95 probably reflects increased. leaching from poorly drained soils developed over marls or clays and subsequent Mn precipitation in the streams. The geochemical relief of the area is apparently modified by the process of dilution affecting sediment samples from streams which rise on the limestone and sandstone ridges and flow onto the clay vales. In these streams the presence of material with a low metal content, derived from limestone or sandstone, dilutes material rich in metals derived from the clays giving rise to a zone of intermediate sediment values around the margins of the clay vales (see Ch. 15).

3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals The incidence of confirmed trace element disorders is shown in Fig. 24.

(A) Molybdenum and Copper Three occurrences of bovine copper deficiency have been confirmed in the area by blood-;copper analysis (Fig. 24). Copper levels fall in the Greensand areas and are lower in areas of limestone where availability may be reduced by a high soil pH. There is no confirmed record of copper deficiency in cattle on farms within the areas of Mo anomalous stream sediments. However, veterinary practitioners are aware of a high incidence of infertility and poor growth in stock in the Kimmeridge Clay vale (pers. comm. J. Cripps). This has been attributed to the poorer waterlogged pastures of .East Knoyle. -

O

Shaftesbury.

0 1 2 Molybdenum Areas in which stream sediment anomaly. Cobalt Pine occurs. 0 Bovine Copper Deficiency. Scale in Miles

Fig. 24. The Incidence of Trace Element Induced Agricultural Disorders in the Shaftesbury Survey Area 96 the vale and a high prevalence of fluke infestation. However, the occurrence of raised levels of Mo in stream sediment indicates the presence of a factor that may be contributing to the lower standard of animal production.

(B) Selenium Environmental conditions favouring the uptake of Se (see page 19) are unrecorded in this area. It is therefore thought that the occurrence of raised levels of Se is unlikely to be of significance to agriculture.

(C) Cobalt Cobalt pine in sheep occurs sporadically in flocks grazing the hills of the west and north of the area. However, the stream sediment data does not indicate any patterns of significantly low Co.

(D) Manganese An absolute deficiency of Mn in cattle has not been confirmed anywhere in the area. However, cases of bovine infertility responding to manganese injections occur occasionally and are usually attributed to the overlim.ing of pastures. 97

CHAPTER 10: REGIONAL GEOCHEMICAL RECONNAISSANCE THAME SURVEY AREA

1. Description of the Area (A) Location The rectangular survey area of 230 square miles covers a large area of Buckinghamshire, north of the Chilterns, together with adjacent parts of Oxfordshire, around the towns of Bicester, Aylesbury, Theme and Princes Risborough (Fig. 23).

(B) Geology_ The area has been described by Arkell (1947a) and Sylvester—Bradley and Ford (1968). The succession is summarised in Table 18 and the geology shown in Fig. 26. The sedimentary rocks are regarded as shallow water marine deposits (Arkell, 1947a) and include impure limestones, clays and sandstones. Black shales are developed at a number of horizons. (a) The Lower Oxford Clay comprises some 70 feet of dark brown, grey brown and khaki coloured bituminous shales containing up to 5% of free carbon (Calloman, 1968). Thornton (1968) records 2-10 p.p.m. Mo in residual soils derived from the Lower Oxford Clay near Bicester. (b) The Ampthill Clay. North of Brill the Corallian Limestones pass into a clay formation that extends northwards into Lincolnshire. The clay is very dark, almost black, and selenitic, with subordinate thin limestones. However, the fauna of the clay contains an active benthos, including worm tubes (Chatwin, 1961), a feature atypical of metal

0 4 8 Scale in miles

Land over 800 ft. 600 ft. contour

.% I 400 ft. contour • Towns 200 ft. contour Key to Towns B. Brill C. Chinnor G.M. Great Missenden H. Haddenham L.C. Long Crendon M.G. Marsh Gibbon P.B. Preston Bissett P.R. Princes Risborough Q. Quainton S.A. Stratton Audley S.C. Steeple Claydon S. Stokenchurch Wa. Waddesdon We. Wendover Wg. Wing Wh. Wheatley Wn. Winslow Wt. Whitchurch Key to Rivers 1. River Ouse 2. River Ousel 3. River Ray 4. River Thame 5. River Thames Fig. 25. Location and Topography of the Thame Survey Area 98

Table 18 Stratigraphy of the Thame survey area (Modified from Arkell, 1947a)

GEOLOGICAL FORMATION LITHOLOGY Recent Alluvium Gravel, sand, silt and clay

Glacial Drift Sand and loamy pebble drift, clay loam and Pleistocene gravel Head Unconsolidated sandy clay loam

Chalk White limestone with flints Upper Greensand Glauconitic and calcareous sandstone Cretaceous Gault Clay Dark silty clays with phosphatic horizons Lower Greensand Green and grey sands, clays and ferruginous sands

Purbeck Green clays and marls, white limestone and ferruginous sands Portland Massive limestones, marlo and glauconitic sands Kimmeridge Clay Grey shales and clays, limestone bands, Upper glauconitic loams Jurassic Corallian/ Rubbly limestone and Ampthill Clay grit passing north into dark selenitic clays Oxford Clay Bituminous shales, blue grey plastic clays and cementstones Kelloways Loans, clays and sands

Lower Cornbrash Rubbly, shelly limestone Jurassic Forest Marble Flaggy and rubbly limestones, marls, clays and sands .Ludgershall

0 0 C 0 C • 0 —.-0 0 0 0 0 0 0 0

0 -' 0 0 1 2 0 Scale in Miles. Oxford Clay. 0 0 Kirnmeridge Clay. Lower Greensand Upper Greensand. Glacial Drift.

I 1 ••••• Corallian Limestone Portland Middle Jurassic. & Ampthill Clay. & Purbeck. Gault Clay. Chalk.

Fig. 26. Geology of the Thame Survey Area (Based on I.G.S. maps.) 99 rich black shales (see page 14). (c) The Kimmeridge Clay. The succession is attenuated over the Oxford Shallows (Arkell, 1947a). The lower part of the Kimmeridge Clay includes sediments of black shale facies with black selenitic shaley clay and grey shales with jet (A.M. Davies, 1907). However, the succession as a whole is regarded as being a sandy and calcareous development of the Kinmeridge Clay, lacking the typical bituminous shales developed elsewhere in England (Arkell, 1933, 1947a, Downie and Wilson, 1968). (d) The Gault Clay. This is a dark blue, or dark grey micaceous clay, calcareous with phosphatic horizons (Arkell, 1947a). A thin covering of glacial drift occupies higher ground - in the north east of the area. The drift is exotic, of northern origin,comprising roughly rounded pebbles set in a matrix of sand, clay and silty loam. Periglacial solifluction deposits, coombe rock and head, occur on the scarp of the Chilterns and in dry valleys on the Chalk.

(C) Topography and Drainage The topography, controlled by the underlying geology, exhibits a series of scarps and vales trending NE—GW. Two main vales occur developed on the Oxford Clay and the Kimmeridge—Gault Clay respectively and occupied by drainage systems of the Rivers Ray, Ouse and Thame. A broken line of hills separates the two clay vales whilst to the south east the chalk scarp of the Chiltern Hills rises to overlook the whole area. 100

The tributary drainage tends to originate in low hills, or on the scarps, and then meanders sluggishly across the vales. The streams have a very low gradient, flow in mixed alluvial and colluvial banks and are frequently choked by weeds.

(D) Climate Mean annual precipitation is around 25 inches per annum rising to over 30 inches on the Chilterns. Rainfall is at a minimum in early spring. Mean monthly temperatures for January and July are 39°F and 63°F respectively at Oxford, falling to 37°F and 62°F on the Chilterns.

(E) Soils Soils are dominantly residual. Around Aylesbury the soils have been described in detail by Avery (1964); elsewhere they are similar to those described by Kay (1934) and Robinson (1948) in the Vale of the White Horse and Dorset respectively. The most extensive soils are non—calcareous surface— water gleys (Denchworth Series) developed on the Oxford and Kimneridge Clays. The Gault Clay gives rise to a calcareous surface—water gley, becoming very calcareous where chalk downwash is present. The Jurassic limestones support well drained sandy clay loans of variable depth with local heavy clay loads. The Cretaceous ironsands give rise to well drained highly ferruginous sandy loans. The Chiltern Hills generally have a thin cover of brown earths and rendzinas. 101

Soils on the glacial drift are moderately to poorly drained sandy clay loams, locally gleyed.

(F) Land Use The clay vales support dairy farming, with some beef and sheep production on poorly drained permanent pastures (Usher, 1963). Where drainage has been possible some land goes under the plough for root crops. The limestone districts of the north and around Thame, together with the hills capped by glacial drift, have better drained soils locally cultivated for cereals. Similar cropping is found on the slopes at the foot of the Chiltern scarp. The scarp face of the Chilterns _is grasl,land whilst on top of the hills extensive beech woods occur between areas of mixed arable and grassland farming. Areas of sandy drift, east of Marsh Gibbon, are covered by deciduous woodland.

2. The Regional Geochemical Patterns The regional geochemical patterns observed in the Thame area can be related to variations in the parent materials, pollution and the secondary environment. Table 19 summariseQ the metal content of stream sediments on the principal geological units. Streams draining the Upper Jurassic commonly have areas of Kimmeridge Clay, Corallian, Portland and Purbeck material within their catchment areas; these divisions are thus grouped together in Table 19. Thornton (1968) presents the results of a limited stream sediment survey in the Bicester district. The results Table 19 Range and mean* metal content of the minus 80-mesh fraction of stream sediment from the principal _geological units of the Thame survey area

Metal content (p.p.m.) TiDA Cu V Pb Ga Zn+ Ti Ni CoY Mn Cr Fe003% Glacial Drift .'.2 37 116 20 7 94 4430 22 15 564 84 5.4 <2 13- 60- 10- 4- (50- 1600- 8- 5- 160- 40- 1.4- (31 samples) -3 200 200 60 16 400 8500 40 30 1600 200 14.0 Upper Greensand !2 9 46 12 4 <50 2739 15 15 280 33 1.3 and Chalk 6- 30- 8- 2- 1300- 8- 5- 100- 16- 1.1- (10 samples) :2 13 60 20 8 <50 6000 20 40 600 40 1.6 Gault Clay <2 21 75 13 6 53 3492 24 17 380 70 2.7 <2 10- 40- 4- 2- <50- 1300- 10- <5- 85- 30- 1.5- (42 samples) -2 60 160 50 10 200 1% 60 40 1300 160 5.4 Corallian, Kimmeridge K2 22 78 13 6 66 2197 18 12 474 66 3.5 Clay, Portland, Purbcck <2 8- 30- 6- 3- c50- 1300- 8- 45- 100- 16- 1.7- and Lower Greensand 50 60 5000 130 13.0 (53 samples) -2 85 130 40 16 400 5000 Oxford Clay 2 48 136 22 11 127 4915 36 20 613 97 6.8 :2 13- 50- 8- 5- <50- 1600- 13- 13- 200- 30- 1.9- (62 samples) -9 200 600 85 30 400 8500 85 40 2000 200 19.0 Middle Jurassic <2 25 105 19 6 <50 3800 18 12 398 73 3.6 < 5 <50- 1003 - 6- < 5- (22 samples) - 2 85 160 60 10 300 5000 40 20 1000 160 9.2 * Geometric mean Mean calculated with <50 p.p.m. = 40 p.p.m. A Mean calculated with (2 p.p.m. = 1 p.p.m. Y Mean calculated with .<5 p.p.m, = 3 p.p.m. 103 of the present ouvey and those of Thornton reveal the same geochemical patterns with similar trace element concentrations from comparable sample sites.

(A) Patterns related to bedrock The distribution of metals in stream sediment, suumarised in Table 19, is broadly related to the parent material of the stream catchment areas. Sediments from streams draining the Oxford Clay outcrop have the highest mean levels of Co, Cu, Ga, Fe, Mo, Ni, V, Zn and, with reduced contrast, Cr, Pb, Mn and Ti. Maximum values for Ga, Pb, Mo, Ni and V in this area occur in stream sediments on the Oxford Clay. Stream sediments derived from the remaining groups identified in Table 19 tend to have lower range and mean metal values than the Oxford Clay although, apart from the very. aow values of Cu, Cr, Fe, Mn and V associated with the Upper Greensand and Chalk, there are no clear patterns related to individual geological units. Molybdenum is undetected (<2 p.p.m.) over much of the area, contrasting with two zones of Mo—rich sediment in streams draining some 7-1-- square miles of the Oxford Clay around Marsh Gibbon (Mo 3-5 p.p.m.) and Steeple Claydon (Mo 3-8 p.p.m.). Follow up studies (Ch. 16) have revealed anomalous levels of Mo in residual soils developed over the Lower Oxford Clay whilst rock samples collected in the district have shown that anomalous levels of Mo (3-14 p.p.m.) are restricted to the bituminous shales of the Lower Oxford Clay. Selenium is detected in selected stream sediment samples from the north west half of the Thame area. Stream sediments with anomalous levels of Mo contain .3.3-1.7 p.p.m. 104

(mean 0.9 p.p.m.) whilst streams with no detectable Mo from areas of limestone, drift and Upper Oxford Clay contain 0.2-0.7 p.p.m. Se (mean 0.5 p.p.m.). The source of the Se is unknown since it is detected only in /trace? amounts (0.1-0.2 p.p.m.) in rock samples collected in the area. It is noted that the higher levels of Se occur in those streams with greater amounts of organic matter in the stream sediment and thus the Se may be accumulating with organic matter in the stream sediment, a feature observed by Atkinson (1967) in Eire. Background levels of Mo (( 2-3 p.p.m.) are found in the sediment of streams draining the Ampthill Clay, Kimmeridge Clay and Gault Clay. This'is regarded as reflecting the absence of significant quantities of Mo in these rocks. All three clays display faunal and lithological characteristics atypical of metal rich black shales (see Ch. 2).

(B) Patterns related to pollution Anomalously high levels of Cu 70 p.p.m.), Pb (s; 50 p.p.m.) and Zn (:.? 300 p.p.m.) occur at a number of sites throughout the area, with a greater frequency on the Oxford Clay vale. These levels are considerably higher than soil and rock values recorded later (Ch. 16). However, a common ecology was observed in the field with anomalous levels occurring in: (±) very slow flowing streams in which clay size particles (< 200 mesh) dominate in the sediment and where organic matter is accumulating (ii) streams in which pollution by sewage can be 105

identified either visually or by a characteristic odour. Whilst the high metal values could result from the concentration of naturally occurring background levels by sorbtion onto organic matter or clay minerals in the stream sediment, the gross enrichment of metals is thought to be largely due to pollution from untreated or part treated effluent entering the streams. Swaine (1962) reports that untreated and part treated sewage effluent contains up to 3200 p.p.m. Cu, 900-1900 Pb and >1% Zn. The Thame area has a high rural population that has grown rapidly in recent years and continues to expand. Many village sewage treatment works are now overloaded, as at Gawcott, permitting untreated sewage to reach the streams.

(C) Patterns related to the secondary' environment Manganese has an erratic distribution with a greater frequency of high values in the clay vales. High levels of Mn (7 1000 p.p.m.) are thought to reflect increased leaching from waterlogged soils followed by precipitation from groundwater on entering the streams. The distribution of Mn, as shown by the mean values in Table 19, is thus a reflection of bedrock only to the extent that waterlogged soils occur more frequently on the clay vales.

3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals The incidence of disorders is shown in Fig. 27. Aylesbury.

,Tingews k. .Steeple Cla •on.

,Stone.

Princes isborough. 0.Edgcott.

.Grendon Underwood.

att n Ludger shall Haddenham.

0 i:hinnor Piddington. 0 .81 •kthorn. Thome,

Bicesten 0

0, 1 2 o Infertility. Molybdenum Copper Deficiency. Scaly in Miles. UI stream sediment anomaly.

Fig.27. The Incidence of Bovine Copper Defidiency and..Infertil#T-An'the Thame Survey Area 106

(A) Molybdenum and Copper Cases of bovine copper deficiency confirmed by blood copper analysis are known in two districts within the Thane area: (a) around Brill (b) on the Oxford Clay vale, centred around Marsh Gibbon. In addition, a number of cases of infertility in the Marsh Gibbon district have responded to copper therapy. The distribution of Cu, as shown by the stream sediment survey, is seen to be unrelated to the observed incidence of bovine copper deficiency. The Oxford Clay area is characterised by very high levels of Cu and the Brill district has adequate levels of Cu (15-30 p.p.m.). Low levels of Cu (< 10 p.p.m.) occur to the north of Thame in an area of Portland and Purbeck sands, and in a zone along the foot of the Chiltern Hills. In neither of the low Cu areas have any nutritional disorders in cattle been reported. The distribution of Mo shows an encouraging correlation with the incidence of bovine copper deficiency. The area of anomalous levels of Mo encloses most of the copper deficient farms in the Marsh Gibbon district, an association suggestive of the presence of molybdenum induced copper deficiency. Molybdenum is not detected in stream sediment in the Brill district.

(B) Cobalt Low levels of Co (<5-7 P.P.m-) occur in stream sediments in three areas: 107

(a) west of Bicester in an area of Cornbrash Limestone (b) north of Thame in an area of Portland and Purbeck sands (c) south of Aylesbury in an area of Upper Greensand and Chalk. Over the remainder of the study area Co levels are within the normal range (10-49 p.p.m.). The low levels of Co are comparable to values recorded elsewhere in England and Wales in areas having a severe incidence of pine in sheep (Fletcher, 1968, Thornton, 1968). However sheep are only very rarely found in this district.

(C) Other metals Lead, copper and zinc appear to be accumulating in some streams due to pollution by sewage. Although the greater hazard to health is from organic pollutants in effluent, metallic pollution is of concern in view of its persistence and possible cumulative effect. 108

CHAPTER 11: REGIONAL GEOCHEMICAL RECONNAISSANCE MARKET RASEN SURVEY AREA

1. Description of the Area (A) Location The reconnaissance area is situated north east of Lincoln (Fig. 28) and comprises 110 square miles of the drift covered clay vale between Lincoln Edge and the Lincolnshire Wolds.

(B) Geology Descriptions of the geology are given by Usher, Jukes—Brown and Strahan (1888) and Swinnerton and Kent (1949), whilst features of the drift cover are recorded by Straw (1957, 1968). The stratigraphic succession is shown in Table 20, the solid geology in Fig. 29 and the drift cover in Fig. 30. The sedimentary rocks, Mesozoic shelf sediments which include clays, limestones and sandstones, are frequently concealed by thick spreads of glacial drift. Black shale facies are developed at a number of horizons underlying the clay vale. (a) The Lower Oxford Clay, which is very rarely exposed, is described as "dark, bituminous shale" by Swinnerton and Kent (1949). (b) The Ampthill Clay, largely masked by drift, is described by Roberts (1889) as a "black clay with selenite". However, Chatwin (1961) records a well developed benthonic fauna from the clay, a feature inconsistent with metal rich black shales. 0 Scale in miles

400 ft. contour •Towns ------200 ft. contour

Key to Towns D. Donnington-on-Bain F. Faldingworth K. Kirton-in-Lindsey M.R. Market Rasen T. Tealby W. Wragby

Key to Rivers 1. R. Witham 2. R. Bain 3. R. Ancholm 4. R. Langworth

Fig. 28. Location and Topography of the Market Rasen Survey Area 109

Table 20 Stratigraphy of the Market Rasen survey area (Based on Swinnerton and Kent, 1949)

GEOLOGICAL FORMATION LITHOLOGY Alluvium Gravel, sand and silt Recent Aeolian Sand Quartzose sand, occasionally ferruginous

Pleistocene Glacial Drifts Boulder clay, sands, clays and gravel

Upper Cretaceous Chalk White limestone with flints

Langton Series Dark clays and sands Fulletby Beds Dark clay, oolitic iron ore Lower and sands Cretaceous Tealby Series Clays, shales and sands, limestones Spilsby Series Sandstone, dark clay and iorn ore

Kimmeridge Clay Dark clay, bituminous shales and oil shales Upper Ampthill Clay Black selenitic clays Jurassic Oxford Clay Blue grey shales and bituminous shales Kelloways Sandstone with clay bands

Cornbrash Shelly limestone and ferruginous sands Blisworth Clay Blue green clay Middle Gt. Oolite lstn. Hard, fissile limestone Jurassic Upper Esturine Dark green silts and clays Series with limestones Lincolnshire Hard, oolitic and siliceous lstn. limestone

‘Xtes 0 • 0 asen. ----- Market • 0 0 0 I ....". 1.--- —..... '--.'.. Rasry. • 0 0 0 0 1 2 0 0 0 0 . WI ft: a: .7----E-- • 0 0 0 0 0 0 Scale in Miles. wmb % -...... ,...... • ••••.-..• ,-.....• • _ ." .....,/ ..._::.. 0 0 0 0 0 11 r....., ,...... , -.....• C.• rt , 0 0 0 0 ..... ,,L• "...J...... 1 , o 0 0 0 r 0 mem. ••••...• ••••••• mismo:wwfp s ••••..r. ....-... ‘ 5 0 0 0 0 ...... , --... --. ,,,, 0 0 0 0 0 0 0 0 .Spridlingto ,Fat1din• • • I' h. • o o .... ti O CI Hain • • 11101111W—maLIESk • 0 • • . . . 0 0 0 • 0 o • . . . .111WM, ngton. Sau •••••.•• 0 0 0 0 I n ham. • • • 3 Do 1.54A ▪ ••••••••• •••••••,..• 0...4.- 0 • 0 0 • )0 0 0 meallrall4 o T T 0 0 •••••••• ••••••-... • 0 0 0 0 ••••.-.• • O 0 0 NMI 1111•1:1111. 1.•• 0 0 0 0 r•—• sEast. o o 0 --11_arkw1 a •

O 0 0 0 Chalk. o 0 Kimmerldge Clay. Cretaceous.

Lower Cretaceous. Ampthill Clay. Jurassic.

Oxford Clay.

Mid Jurassic & Cornbrash

Fig. 29. Geology of the Market Rasen Survey Area (Based on I.G.S. Maps.) 9 4 c Scale in Miles.

Direction of Ice Movement.

Limit of Intensly Chalky Boulder Clay.

Aeolian Sand.

MI Chalk.

Fig.30. Map Illustrating the Glaciation of Mid Lincolnshire and the Distribution of Certain Superficial Deposits (Based on Straw, 1957, 1958.) 110

(c) The Kimmeridge Clay comprises black shales and clays with cementstones of a facies comparable with the bituminous ,hale- group of the Kimmeridge Clay in Dorset (Arkell, 1933, Downie and Wilson, 1968). The area was invaded by the Quaternary Ice Sheets (Fig. 30) which left extensive glacial deposits. Whilst Lincoln Edge is drift free, up to 40 feet of drift covers the clay vale (Straw, 1958). The drift is very variable, being dominantly a stiff decalcified stony clay but also includes irregular areas of gravel, sand, marl and lacustrine clgys. Locally the clay matrix includes material derived from the underlying Oxford and Kimmeridge Clay (Straw, 1957, 1958). Chalk and flints are present in the drift throughout the vale, but adjacent to the Wolds the drift becomes intensely chalky (Fig. 30). In many places the drift extends up the escarpment onto the Wolds. To the east and south east of Market Rasen areas of fine, white or locally ferruginous aeolian sands are found.

(C) Topography and Drainage Topography is controlled by geology, with very subdued local relief except where the Cretaceous scarp of the Wolds rises above the clay vale. Almost all streams rise at springs along the foot of the Wolds or on Lincoln Edge and flow across the clay vale before entering the Ancholm or Langworth Rivers. In crossing the vale several of the streams have cut through the drift into the Jurassic clays beneath,which'are occasionally exposed in the valley sides during excavations. The streams themselves flow in alluvial and colluvial banks. 111

The River Bain is entrenched into the Wolds occupying a valley initiated during the glacial period (Straw, 1958). Road access is excellent but the poorly developed tributary drainage of the vale made it necessary to sample streams at close intervals to obtain a final sample density of 1.0 samples per square mile.

(D) Climate Rainfall in the area ranges from 22-25 inches per annum on the vale, rising to 25 inches on Lincoln Edge Whilst to the east it exceeds 30 inches on the Wolds. Rainfall is at a minimum in early spring.

(E) Soils The area is one of intensive arable cultivation where drainage and ploughing have greatly modified soil conditions. In the vale soils are typically heavy clay foams and sandy clay foams. The low relief, impervious substrate and high water—table give rise to conditions of impeded drainage; waterlogging is common after prolonged rain. Soils on Lincoln Edge are better drained with a variable depth of stony and sandy clay loam developed over the rubbly Jurassic limestones. Over the Wolds and adjacent areas of chalky boulder clay heavy calcareous clay foams are found with local areas of light acid sandy foams developed on Cretaceous sandstones. The aeolian sands around Market Rasen display a variety of drainage status but are usually freely drained podzols. 112

Land Use Almost all the land is under arable cultivation; crops include sugar beet, brassicas and legumes in addition to a considerable acreage of cereals. Dairy farming is now limited to a number of farms at the webtern margin of the vale and along the foot of the Wolds scarp. Large areas of the aeolian sands carry forests of conifers managed by the Forestry Commission.

2. The Regional Geochemical Patterns The geochemical patterns identifiable in the Market Rasen area lack definition due, most probably, to two factors:

(i) the smearing, mixing and masking of material by glacial activity, particularly in the vale area where the drift is thick and quite variable in character (ii) the type of stream sediment samples obtained. It was necessary to sample streams at close intervals due to the very poor development of the tributary drainage. The samples obtained were thus composite in character and cannot be related to discreet catchment areas. The metal content of stream sediments over the principal geological units is; suillniarised in Table 21. The drift covered clay vale is regarded as a single unit due to the overall similarity of materials within the vale and the difficulty in identifying stream sediment samples with a distinct catchment or parent material. No readily observed patterns are noted for Ti and Pb. Table 21 'Lan.ve and mean*. metal content of the minus 80-mesh fraction of stream sediment from the principal geological units of the Market Rasen survey area

Metal content (p.p.m.) MoA Cu V Pb Ga Zia+ Ti Ni Co Mn Cr Fe200

Cretaceous (2 13 154 29 9 229 3700 48 36 679 133 5.9 <2 10- 40- 13- 8- 100- 2000- 30- 13- 400- 60- 1 (2- (10 samples) -3 20 400 60 13 400 5000 85 60 1000 850 25.0 Drift covered Upper <2 17 97 20 11 176 3847 39 27 426 86 2.9 Jurassic Clay "Vale <2 4- 30- 8- 4- (50- 1300 10- 5- 60- 13- 1.0- (92 samples) -5 60 300 160 30 850 -1% 100 60 5000 300 11.0 Middle Jurassic (2 12 66 18 8 84 3163 23 20 452 64 2.3 <2 5— 20— 8— 4— <'50— 1300— 10— 5— 200— 10— 1.1— (8 samples) —3 30 100 30 16 200 4000 50 40 600 850 5.0

* Geometric mean H A Mean calculated with <2 1.p.m. = 1 p.p.m. + Mean calculated <50 p.p.m. = 40 p.p.m. 114

However, patterns related to drift or bedrock can be identified amongst the remaining elements shown in the maps in Volume II. The occurrence of detectable concentrations of Mo appears, at first, to be sporadic. In the west of the vale Mo is detected in a number of stream sediments (3-5 p.p.m.) but forms no pattern. Follow up work (Ch. 17) has shown that the occasional detectable concentrations of Mo reflect localised areas of Mo-rich soils derived from the lower part of the Oxford Clay formation. Selenium is not detected in any stream sediment samples from the west of the vale. In the east of the vale anomalous levels of Mo (3-4 p.p.m.) occur in a number of samples from near the foot of the Wolds scarp. The anomalies are, however, restricted to those streams which have cut through the drift cover into the Upper Kimmeridge Clay beneath. Follow up work has confirmed the presence of Mo-rich residual soils on the Kimweridge Clay at South Willingham whilst soils derived from the overlying boulder clay contain background levels of Mo. Samples of Kimmeridge Clay collected in the area contain 7-30 p.p.m. Mo. Selenium is recorded in trace quantities only ( < 0.2-0.2 p.p.m., mean <0.2 p.p.m.) in streams carrying anomalous levels of Mo and is undetected ( <" 0.2 p.p.m.) elsewhere in the east of the vale. Anomalous levels of Mo (3 p.p.m.) in the sediment of two streams draining the Lower Cretaceous in the Bain valley may be derived from thin Mo-rich black marine clays in the Lower Cretaceous. 115

The sediment of streams draining areas of aeolian sand east and south east of Market Rasen have lower values of Cu, Cr, Ga, Mn and V and, with reduced contrast, Ni and Fe than adjacent areas of boulder clay. Lower levels of these elements persist down—drainage indicating the presence of the white sands, with a low metal content, in the stream sediments. The spread of sand for up to four miles downstream was noted in the field. The metals Cu, Cr, Ga and V occur in lower concentrations in the sediments of streams draining the Mid Jurassic limestones and calcareous clays in the west of the area than on the adjacent clay vale. Follow up work (Ch. 17) has shown that metal values in stream sediments over the Mid Jurassic are depressed due to dilution with CaCO3 precipitate,which is consipicuous in the drainage channels, in a manner similar to that encountered in the Shaftesbury area (see page 92). Table 21 shows that the sediments of streams draining the Cretaceous contain higher mean levels of Co, Fe, Pb, Mn, Ni, V and V than sediments derived from adjacent marine clays and shales. Sedimentary ironstones in the Lower Cretaceous may contain similarly enhanced metal values and contribute to the high mean values that characterise this group of stream sediments. There is little consistent variation in levels of Fe over most of the area. Samples taken from streams draining the lower part of the Lower Cretaceous in the east of the area are found to contain large amounts of Fe (9.6-25.0% Fe203). The source of these large amounts of Fe, the Claxby Ironstones, is evidenced by the presence of hematite ooliths derived from the Ironstone in the stream sediment samples. 116

3. Correlations between Regional Geochemical Patterns and the Incidence of Trace Element Disorders in Animals Trace element disorders are not recorded in the area, although it is pertinent to note that the livestock population is small and restricted to areas along the margins of the vale and in the Bain valley. However, farmers at South Willingham, where anomalous levels of Mo occur, report that infertility is a problem in dairy cows. It may be that the presence of Mo is a contributary factor in the infertility observed. 117

CHAPTER 12: GENERAL DISCUSSION : STREAM SEDIMENT RECONNAISSANCE IN AREAS OF BLACK SHALE PWIES

1. The Geochemical Patterns As is typical of multi—element regional geochemical surveys, information on a wide variety of subjects ancillary to the main objective is obtained by examining the stream sediment data. Thus the full interpretation of the regional geochemical data has involved recognition of patterns related to: (A) the bedrock geology and glacial drift (B) the secondary environment (C) mineralisation, contamination from mining activity and pollution by domestic effluent.

(A) Geochemical •atterns related to bedrock In eight of the nine reconnaissance areas stream sediment surveys reveal patterns of raised levels of Mo related to the outcrop of rocks of black shale facies. A total of 86 square miles is outlined, based on catchment areas in which stream sediment levels of greater than 3 p.p.m. Mo are recorded. These results support the original supposition that raised levels of Mo may be found in rocks of black shale facies, and that anomalous levels of Mo (> 3 p.p.m. in stream sediment) are more extensively distributed than was previously recognised. The patterns of enhanced levels of Mo are often accompanied by similar patterns of V and Cu, and occasionally Cr, Ni, Pb and Zn which probably reflect the syngenetic enrichment of these metals in the black shale bedrock. 118

The association of these metals is taken to indicate the preservation of bedrock characters in stream sediment. The absence of a close association of No with Fe is noteworthy, although levels of Fe are often higher in streams draining black shales than elsewhere in an area, reflecting a large source of Fe in the weathering of pyrite from the shales. The scavenging of Mo by ferric oxides in stream sediments has been reported elsewhere (Atkinson, 1967) and were this to occur frequently the anomaly patterns produced would be a feature localised in the stream sediment thus making an agricultural assessment,of the data difficult. Interpretation of the present data suggests that the Mo patterns are dominantly detrital and, very probably, related to Mo—rich soils of possible agricultural significance. Stream sediment reconnaissance sampling at a density of one sample per square mile fails to reveal the raised levels of Mo known to occur in the Llandovery of the Kendal and Machynlleth areas. This may be explained by a factor of dilution occurring where the outcrop of a metal rich source forms only a small part of the total area of a stream catchment. The stream sediment contains so much barren material that the anomaly arising from the metal rich source is diluted or completely masked. This factor is a serious limitation to the effectiveness of stream sediment surveys, but can be overcome by adopting a closer sampling interval. The limitation is greatest in upland areas of highly deformed Lower Palaeozoic rocks in Wales and the Lake District where the outcrops of black shale are narrow and contorted, and stream catchment areas are large due to 119 the restriction on sampling resulting from poor road access. There are large outcrops of rocks of black shale appearance in drift free areas without coincident No sediment anomalies or apparent enrichment of other metals. Typical of these are the Ampthill, Kimmeridge and Gault Clays of the Thame area and veiny of the Ordovician shales of West Carmarthenshire and Shelve. All are dark coloured, fine grained rocks,often containing some pyrite. However, these sediments are reported to contain a well developed benthonic fauna, a feature inconsistent with metal rich black shales (Dunham, 1961). Furthermore, these rocks are often sandy or calcareous exhibiting features of a turbulent aerated environment far removed from the stagnant conditions under wiri,ch metal accumulation occurs. The reconnaissance surveys demonstrate that in areas affected by the Quaternary Glaciation the composition of drift (boulder clay, gravel and sand) strongly influences the geochemical patterns. Stream sediment reconnaissance in the Market Rasen area indicates that the drift cover to the clay vale contains background levels of No. Anomalous levels of Mo in the east of the vale are restricted to areas where streams have cut through the drift into the Mo—rich Kimmeridge Clay. A contrasting situation exists in the Bowland Forest area where metal rich material is apparently smeared in local drift giving rise to sediment anomalies in zones to the south and west of the outcrop of the molybdeniferous Bowland Shales. The distribution of Se is erratic, occurring with Mo in some situations and being absent in others. Substantial quantities of Se are found in sediment derived from the 120

Bowland Shale where the values recorded are comparable to those detected by Fletcher (1968) in an area of Visean/ Namurian marine black shale in Derbyshire, although lower than levels recorded from a similar source in South West Ireland by Atkinson (1967). The erratic distribution of Se accords with the observations of Goldschmidt (1954) and is most readily explained as due to variation in the availability of Se at the time of deposition of the parent rocks. The black shales over which sediment Mo anomalies are recorded are typical of the metal rich marine black shales described by Dunham (1961) in having a well developed neretic fauna, a restricted or absent benthos and in displaying a limited vertical thickness and wide lateral extent. Patterns of molybdeniferous stream sediments are related to the outcrop of extensive black shale formations at widely spaced localities, viz the Dicranograptus shales in the West Carmarthenshire, Rhayader and Shelve survey areas, Visean/Namurian black shales in Derbyshire (Fletcher, 1968), South West Ireland (Atkinson, 1967) and the Bowland Forest survey area, the Lower Oxford Clay in the Shaftesbury, Market Rasen and Thame survey areas, the Kimmeridge Clay in the Shaftesbury and Market Rasen survey areas. Furthermore, a stream sediment survey of the Bedford area (Fig. 32) made at the same time as the main reconnaissance survey, reveals a pattern of Mo—anomalous stream sediments from an area underlain by bituminous Lower Oxford Clay. In adjacent areas of glacial drift (derived from older rocks to the north) and overlying Lower Greensand Mo is undetected. It is suggested that zones between the survey areas,

Bedford

e... •,. •-• r "7 % . ... l •-- ../s1s,-----_...... „, .;- ...... , ...... • . 11 •t. 7 "...'t - r• ": . . • I.„„.....r S •. . "'N. . I.. e • . 1--.4,,,,- -z.i e . 1 • • • • • • • • • • • • • • • • • •••• • . . • . 4 . . • ••• •••• ••• .•• • •• • . •••

• ••• •• • ••• ••• • /••• .•• •• • • • • • ••• ••• •• "•• •• •• /•• • 411111• 0 ,. .".. .A •, • • •• • •• • • •• • - , . • • •• • ••••• 0 • • ••• • 10 t„ • • ...... , • • • • 0 • • • 1. • • • Sar....••••• •• 7.%.....,• . • . • • • . • • • • • . • • • i 0 0 . 1.,11.0••'•••••• a...ft...a ••••••• • • • • • • • ...... 1 .IN. ••••••+. 0 13 ''.. 0 _.. 4 .1. .1:4, •' • •41 0 0 0 0 0 -..! * • ? ,. . • ".."' "-, .:...... -•• • ••• 1 • • • • • • 8 -,-;,..y.y o o o • o o c

0 0 0 0 0

el 1:0

Molybdenum p:p.m. Alluvium. I Mile 0 <3 Boulder Qay. ® 3 - 7 • Lower -Greensand. 7 -15

Kimmerldge Clay. Fig.31 Location, geology and distribution Ampthill Clay.

Oxford Clay. of molybdenum in stream sediment

Cornbrash Limestone. south west of Bedford. 121

underlain by contemporary sediments of essentially similar facies, may also be Mo—rich. This possibility is examined in Chapter 20.

(B) Geochemical patterns related to mineralisation and pollution Massive Pb, Zn and Cu anomalies occur in the Shelve and Machynlleth mining areas with less extensive anomalies attributed to mineralisation in the Kendal, Bowland Forest and West Camarthenshire areas. Most of the anomaly patterns may be related to known mineralisation and contabination from mining activity, spoil tips, dressing areas, smelters or slag heaps. Further sediment anomalies occur in areas where mining has not taken place and may be indicative of a metal rich source in mineralised ground within the stream catchment area. Successful geochemical prospecting in those areas where contamination is extensive would require a carefully planned stream sediment survey avoiding sources of contamination, backed up by detailed soil sampling. The probable introduction of metals into streams with domestic effluent is indicated by the distribution of anomalous levels of Cu, Pb and Zn in the Thame area. The pollution, evidenced initially by the presence of offensive matter in the streams, is apparently peculiar to this area although may be a more extensive feature of districts having a rapidly expanding village population with inadequate sewage treatment systems.

(C) Geochemical atterns related to the secondar environment The secondary concentration of Fe, Mn and Co in stream 122

sediments, due to environmental circumstances, is recognised following the criteria established by Horsnail (1968). The occurrence of very high sediment levels of Fe, Mn and Co is frequently similar to that described by Nichol et al (1967) with patterns discordant with geology in areas of very poorly drained moorland soils. Iron and Mn are leached from the soils to be precipitated as hydroxides in the stream environment following a rise in pH and Eh; these secondary oxides scavenge available Co. Elsewhere high sediment Mn levels probably reflect increased leaching from poorly drained agricultural soils. A further modification to geochemical patterns is anticipated in limestone districts where large CaCO3 precipitates (tufa) are found in streams, as in the Shaftesbury area. In such districts metal values are likely to be depressed by dilution of the sediment with barren CaCO as described by Thornton (1968). 3'

2. Agricultural Application of the Stream Sediment Reconnaissance Data (A) Molybdenum and Copper Copper levels in stream sediment are generally in the range of 20-60 p.p.m. with anomalously high levels due to mineralisation, contamination and pollution. Copper levels fall to (15 p.p.m. in areas underlain by limestone and sandstone in the Shaftesbury, Thame and Market Rasen areas where a similar fall in soil levels may be anticipated although the suppression of metal values in stream sediment due to dilution with CaCO must be considered in the 3 Shaftesbury and Market Rasen areas. Patterns of :7 p.p.m. Cu 123

found by Thornton (1968) to be indicative of districts where an absolute deficiency of Cu affects cereals and conifers, are not recorded in the areas surveyed. The results of the present survey indicate that the occurrence of raised levels of Mo >3 p.p.m. in stream sediment) is far more extensive than agriculturalists had previously recognised. Molybdenum-rich soils have been reported in the Thame area (Thornton, 1968) and in the Chipping district of the Bowland Forest area Mo-rich soils and herbage have been confirmed and copper deficiency in cattle recognised for some time (Morgan and Clegg, 1958). However, in these areas the full extent of the Mo anomaly as shown by stream sediment reconnaissance had not been realised. Elsewhere the disclosure of raised levels of sediment Mb over extensive areas provide entirely new information for the agriculturalists. As has been described in the account for each reconnaissance area, some cases of bovine hypocuprosis have been recognised within the area delineated by high sediment Mo. Elsewhere veterinary opinion is that the Mo sediment anomaly areas are often coincident with areas of poor animal health and low productivity that have previously been attributed to a variety of causes including poor grassland and fluke infestation. The present data suggest that within the catchment areas from which anomalous (> 3 p.p.m.) Mo sediments are obtained, areas of Mo-rich soils exist, with the possibility of Mo-rich herbage. Thus the stream sediment reconnaissance surveys delineate some 86 square miles within which raised levels of Mo (si 3 p.p.m.) in stream sediments indicate the presence of a toxic metal in concentrations potentially hazardous to the health of 124

cattle grazing pastures therein. The above conclusion is of considerable importance when considering the type of agriculture practised in the reconnaissance areas. The West Carmarthenshire and Shaftesbury areas, where extensive sediment Mo anomalies are disclosed, are premier dairying areas wherein animal health and productivity are of the utmost economic importance. Similarly the Thame area is important for dairying and otockrearing, whilst in the Bowland Forest area stockrearing; is the most widespread occupation. The present data on the distribution of Mo are perhaps of greater significance in the stockrearing areas where animals are almost entirely dependent on local forage. In the Machynlleth area the Mo sediment anomaly is largely in the upland sheep grazing areas with only a restricted occurrence in lowland districts Where dairying and stockrearing are of local importance. In the remaining areas (Rhayader, Market Rasen and Shelve) the area of the Mo sediment anomalies is small and would seem to indicate a restricted occurrence of potentially Mo—rich pastures.

(B) Selenium Selenium is recorded in stream sediment in a number of the reconnaissance areas at levels (0.2-17.0 p.p.m.)

considerably greater than the normal background (<0.2 p.p.m. ) • The agricultural significance of the anomalously high levels of Se is negligible since in none of the areas are the necessary environmental conditions (Webb and Atkinson, 1965) found for the uptake of Se by plants. 125

(C) Cobalt and Manganese Thornton (1968) regards patterns of <10 p.p.m. Co in stream sediments as likely to delineate areas in which cobalt deficiency occurs in sheep. Such patterns are recognised only in localised situations in the present survey. However, there is evidence to suppose that Mn and Co distributions are frequently influenced by the secondary environment. Thus in upland districts of the Rhayader and Machynlleth areas it is anticipated that stream sediment values of Mn and Co are considerably higher than soil values. It is thought possible that the soils of these districts are impoverished in Co and Mn to a point where nutritional disorders may arise. In the other areas the Mn and Co values observed generally fall within the normal range for stream sediments (Mn 200-850 p.p.m., Co 20-50 p.p.m.) although the local occurrence of coincident high levels of Mn and Co (or Mn alone) suggest that leaching from soils may be occuiTing. Thornton (1968) concludes that stream sediment reconnaissance surveys may give an indication of the Mn and Co status of pastures providing the modified soil—stream sediment relationship, due to environmental circumstances, is recognised. Thus ancillary information on the soil conditions are needed to aid the interpretation of stream sediment data.

(D) Other Metals The massive metal anomalies in the mining areas are noteworthy in view of the possible contamination of agricultural land with toxic quantities of Pb, Zn and Cu. Spoil tips and slag .heaps are an overt indication of 726

possible contamination and are usually fenced to protect stock from hazard. The transport of mine waste downstream in stream sediment and the dispersal of this material onto adjacent pastures at times of flood is worthy of consideration. Alloway (1969) has investigated this process in the Aberystwyth district and has demonstrated the spread of metal rich waste over pastures on the alluvial flood plains of rivers draining from the mining districts.

3. Selection of Areas for Detailed Geochemical Investigations Following a careful appraisal of the reconnaissance data, areas were selected for detailed study on the following basis: (a) the presence of patterns of Mo—rich stream sediments (b) the occurrence of such anomalies in areas of dairying and/or cattle rearing where the presence of raised levels of Mo in pastures might influence the health of grazing animals. Thus the West Carmarthenshire, Bowland Forest, Shaftesbury and Theme areas were selected for follow up studies. Although the Market Rasen area is dominated by arable farming it was decided to undertake detailed studies here to complement investigations on the Oxford and Kinmeridge Clay formations in the Shaftesbury and Theme areas. Preliminary studies in the five areas, taking the form of soil sampling along traverse lines, made between March and May 1969, were followed by a programme of rock, soils and herbage sampling undertaken during July and August 1969. Samples were collected from the areas delineated by Mo—rich sediments and also from adjoining non—anomalous (background) areas. 127

The procedures employed in sample collection and analysis are summarised in the Appendix as are the methods of data handling employed. In all, some 1400 samples were collected, most of which were analysed spectrographically for 12 elements including Mo and Cu. Molybdenum topsoil and herbage levels were determined colorimetrically and Cu in topsoils and herbage by atomic absorption. Detailed studies in the selected areas sought to: (i) define the source of Mo in the bedrock (ii) delineate the extent of Mo—rich overburden (iii) identify features of the distribution of Mo in rock and soil and establish the relationship between the Mo content of rock, soil and stream sediment (iv) determine the Mo and Cu content of herbage on Mo—anomalous and background soils and examine features influencing the uptake of Mo by herbage on anomalous soils (v) assess the agricultural significance of the raised levels of Mo found in soils and herbage. However, since multi—element spectrographic analysis was widely employed, features of the distribution of metals other than Mo were revealed and are mentioned in the following pages. Particular attention is paid to metals having a common distribution with Mo and metals strongly influenced by the secondary environment. In the following pages (Part B) an account of metal distributions in each of the five detailed areas is presented. Features of the metal distributions are discussed and the agricultural significance of the data obtained is assessed 128 and discussed. Figures to accompany the text (identified by the prefix R or T), in which the distribution of metals in the bedrock and ove.cburden are illustrated, are to be found in Volume II. 129

CHAPTER 13: DETAIIIRD GEOCHEMICAL INVESTIGATIONS WEST CARMARTHENSHIRE AREA

1. Introduction Stream sediment reconnaissance in the West Carmarthenshire area, reported in Chapter 3, reveals raised levels of Mo (3-30 p.p.m.) in the sediment of streams draining 5 square miles of the Dicranograptus shale sequence between Meidrim and Llanglydwen.

2. Description of the Area Detailed investigations were undertaken around Meidrim and Llanboidy over the outcrop of the Dicranograptus shales and adjacent rocks (Fig. 32). Essential features of the wider reconnaissance area are summarised in Chapter 3.

(A) Geoloay The Dicranograptus shale sequence is described in detail by Evans (1905) and Strahan et al (1909). Some 500 feet of black shales, weathering brown, buff and yellow, form the Hendre Shale formation. The overlying Meidrim Shales commence with several feet of thin bedded dark grey impure limestone with soft black shale partings (the Meidrim Limestone) which are succeeded by 500-600 feet of evenly bedded dark grey to sooty black soft pyritous shales. The depositional environment of the Dicranograptus shales has been the subject of considerable discussion (0.T. Jones, 1938). However, authorities are agreed that -deposition took place in quiet water. Both faunal and lithological features provide a further indication of the conditions of deposition. • Conwyl lfed

yp.verse 3

Llanboid Abernant

Rock Sampling Point

• Key to Rock Samples. Lion gym 1 Llanvirn & Lower Llandeilo. 2 Hendre Shale. 3 Meidrim Lstn & Shale. 4 Redhill Beds.

Whitland •Llangynog

Molybdenum Stream Sediment anomaly. • Llanddowror

1 2 Scale in Miles.

Fig. 32. Location of Soil Traverse Lines and Rock Sampling Points in Relation to the Molybdenum Stream Sediment Anomalies in the West Carmarthenshire Survey Area 130

The Hendre Shales, sandy and at some time calcareous, contain an abundant graptolitic fauna and also a number of benthonic forms. The depositional environment appears to have been restricted, resulting in a poor benthos, but nevertheless there was some bottom turbulence evidenced by the sandy nature of the shales. The succeeding Meidrim Limestone and Meidrim Shales mark a period of more typical black shale deposition. The fauna of both limestone and shale is restricted to graptolites, and there is no evidence of any benthos. This, together with the dark colour of the sediments and the abundant pyrite, are taken as indicating an anaerobic bottom environment inimical to life. The fine grained shales were deposited in quiet waters following a period of limited sediment supply during which the Meidrim Limestone was deposited. The formations above and below the Dicranograptus shales are of more normal facies. The underlying rocks, of Llanvirn and Lower Llandeilo age, include occasional thin black shale horizons, but are, for the most part, shales with ash bands deposited in aerobic conditions near the southern margin of the Welsh geosyncline. The overlying Redhill Beds (Ashgillian) are dark grey mudstones, shales and grits deposited under 'normal' geosynclinal conditions (0.T. Jones, 1938, Pringle and Neville George, 1948).

(B) Soils Soil sampling along traverse lines (Fig. 32) revealed certain pedological characters peculiar to the area of detailed studies. The distribution of soils is governed closely by parent material and topography, with the two variables 131 interdependent in the detailed study area. The area is virtually free of drift (Evans, 1905) and soils E-1::e thus either residual or colluvial with alluvium beside some streams. The Dicranograptus shales are soft, easily weathered sediments outcropping typically in low ground between ridges supported by more resistent rocks (note sections in Fig. Tl). These fine grained shales give rise to heavy textured soils, all of which show signs of impeded drainage. Gleyed soils are found in receiving sites at the foot of slopes and in areas of low relief where there is little water run—off. In contrast the adjacent sedimentary rocks weather to give coarser textured soils which, since they occupy rising ground, tend to be better drained. In general, the latter soils are moderately to imperfectly drained brown earths. Long steep valley slopes carry thin soils on which soil creep is active. Alluvium is restricted to narrow areas beside the larger streams where coarse and fine textured groundwater gleys are found.

Land Use Within the area of detailed studies grassland predominates, supporting an intensive dairy farming industry. The heavier soils of the Dicranograptus shale outcrop are entirely under pasture whilst the better drained soils elsewhere are occasionally ploughed to supply winter feed for stock. Soils are typically acid and liming is widely practised.

3. Distribution of Metals in the Bedrock Bedrock material was obtained by chip sampling from 132

sections at Meidrim recorded by Evans (1905) and Strahan et al (1909), supplemented by material obtained from exposures at Llanboidy and Cwmfelin Mynach recorded by Evans (1905). The location of sample sites is indicated in Fig. 32. Exposures of bedrock are restricted to badly weathered stream and road sections with occasional quarry faces from which relatively fresh material can be obtained. Analytical data obtained from the bedrock samples are displayed stratigraphically in Fig. R1 and are summarised in Table 22. The results clearly indicate that, where sampled, the Meidrim Shale formation is the source of anomalous levels of Mo. Molybdenum values of 2-7 p.p.m. (mean 5 p.p.m.) in the Meidrim Shale contrast with levels of <2-3 p.p.m. (mean 2 p.p.m.) in the Hendre Shales whilst Mo is below the limit of detection ( <2 p.p.m.) in the remaining rock samples. The presence of 3 p.p.m. Mo in a dark grey shale horizon of the Hendre Shaleo,sampled at Meidrim, probably indicates the eastern limit of a molybdeniferous phase in the Hendre Shales (see page 139). The raised levels of Mo in the Meidrim Shales are accompanied by a higher mean content of organic carbon (x4), V (x3) and Pb (x2) than adjacent shales whilst levels of greater than 30 p.p.m. Cu are restricted to the Meidrim Shales. The comparison of metal values with those obtained from the Redhill Beds is open to doubt because of the few samples of the latter and the singularly fresh condition of the Redhill Beds material. Selenium is largely undetected ( <0.1 p.p.m.) in the bedrock samples obtained. The role of organic matter in the accumulation of Mo Table 22 Range and meat* metal content of the Ordovician rock units in the area of detailed studies, West CarmerthenF;hire area

Metal content (p.p.m.) f, Org. Mod Cu V Se+ Pbt\ Ga ZnY Ti NiP CoP % C Mn Cr As Fe203 %a .... 2,edhill Bedsk <2 25 125 <0.1 6 30 150 3500 35 15 575 55 <5 6.1 0.3 - (4 samples) < 2 15- 10C <0.1 3- 30 100- 3000- 30- 13- 200- 50- :5 5.4- 0.2- 34 130 10 200 4000 40 16 1300 GO r-5 7.2 0.4 Neidrim Shale and 5 25 141 <0.1 22 21 <50 2675 18 6 67 46 <5 2.4 1.3 limestone <0.1- - 5- (16 2- 9- 50- <2 <50- 600- <5- <5- 13- 10- <5 1.3- 0.5- samples) 7 70 30C. 0.1 60 30 100 4000 40 13 160 60 -5 3.8 1.9 flendre Shale 2 21 75 <0.1 14 18 64 3143 23 <5 53 43 <5 2.9 0.4 (7 samples) <2 13- 40- <0.1- 8- 16- 50- 2000- 13- <5 30- 30- r 2.1- 0.1- -3 27 100 0.1 16 20 100 4000 30 -5 85 50 ') 3.6 0.7 Tlanvirn and :2 18 60 <0.1 13 23 73 2467 16 <5 135 34 <5 3.2 0.3 I,ower Llandeilo 9 samples) 2 8- 16- 0.1 3- 10- <50- 600- 6- <5 40- 5- <5 1.2- <0.1- 31 100 20 30 200 4000 20 -5 600 50 -5 5.8 0.6

Geometric mean except k arithmetic mean Y Mean calculated with <50 p.p.m. = 40 p.p.m.

Mean calculated with 42 p.o.m. = 1 p.p.m. 1 Mean calculated with <5 p.p.m. = 3 p.p.m. Mean calculated with <0.1 p.p.m.= 0,0 p.p.m. a Mean calculated with <0.10 = 0.0% 134

and V in the Meidrim Shale is evidenced by the strong positive correlation between the metals and organic carbon displayed in Fig. 33. Although Pb and Cu show no relationship with organic carbon, the greater concentration of these metals in the Meidrim Shale may be due to accumulation with organic matter or sulphides brought about in a "black shale" environment. Molybdenum, V, Pb and organic carbon show no correlation with total Fe in the Meidrim Shale; however, although total Fe is probably present largely as pyrite in unweathered Meidrim Shale, the appearance of the samples obtained, with streaks of rusty iron oxides on shale partings, indicate the substantial redistribution of Fe during weathering. An examination of the data in Fig. 33 reveals that the distribution of Fe in the samples of Dicranograptus shale is similar to that of Mn and Co. A similar association is found in the soils of the West Carmarthenshire area where it reflects the common response of these elements to the secondary environment (page 139). The similarity of the bedrock and soil association suggests that Mn, Co and Fe are being mobilised during the weathering of the bedrock and are probably being leached, in a manner encountered in soils, by groundwater circulating in the: degraded bedrock. It would be wrong to place too much reliance on the data from these badly weathered rocks. However, the presence of raised levels of Mo in association with V and organic carbon in a rock of black shale facies has been established and the source of the Mo anomaly in the West Carmarthenshire area defined. 4-

3 3-

••••••••

072

Lt. + +

1

16 20 50 100 200 5 5 10 20 Manganese (Rpm) Cobalt (p.pm)

10- 300-

+ + ++ 200- + + + + +44. - + + +

§ 100 a, ++ .o C O M 2- • 50 <2-

2.0 0.1 02 05 1.0 2.0 04 02 0.5 1.0 Organic Carbon (v.) Organic Carbon (%)

10- 10-

+ ++ + +

0.ct5 - 45_ + ++ Meidrim Shales. E C C C V V .CI Hendre Shales. ›.• O E X 2 X2- 1-f • •• • +

<2 <2-

50 100 200 500 2 3 4 Vanadium (ppirt) Fe2 03 (7.)

Fig.33. Variation of Iron with Manganese and Cobalt., Molybdenum with Organic Carbon, Iron and Vanadium,and of Vanadium with Organic Carbon, in the Dicranograptus Shales. 135

4. Distribution of Metals in the Overburden (A) Lateral distribution Soil samples were taken at 200 foot intervals along traverse lines at Meidrim and Llanboidy (Figs. 32, Tl) orientated perpendicular to the strike of the rocks and crossing the Mo anomaly delineated by stream sediment reconnaissance. Samples were of residual and colluvial soils together with alluvial soils sampled away from the traverse lines.

(i) Metal distribution patterns related to the bedrock The data in Fig. Ti and Table 23 indicate that the distribution of anomalous quantities of Mo in soils, although principally localised to overburden derived from the Dicranograptus shales, is more extensive than one would have suspected on examination of the rock data alone. Maximum values (30 p.p.m. Mo) and the highest mean content of Mo (9 p.p.m.) occur in residual soils on the Meidrim Shales with further raised levels of Mo (up to 16 p.p.m., mean 4 p.p.m.) in soils developed on the Hendre Shales. Molybdenum is detected in residual and colluvial soils derived from the Hendre Shales with values of up to 5 p.p.m. (mean 2 p.p.m.) at Meidrim contrasting with levels of up to 16 p.p.m. (mean 8 p.p.m.) at Llanboidy (Table 24). The Mo content of soils developed on the Meidrim Shale, in contrast, is similar at Meidrim (< 2-30 p.p.m.) and Llanboidy ( K2-20 p.p.m.), Soils on the Hendre Shale at Llanboidy are dominantly residual and there is no evidence to suggest that the enhanced levels of Mo result from the introduction of Meidrim Shale material. The presence of raised levels of Mo Table 23 RIrIge and mean* metal content of overburden developed on the principal parent materials Uest C3Eme,?thenshire area (sample depth 12-18 inches) Metal content (p.p.m.) Parent material MoA Cu V Pb Ga Zn+ Ti Ili CoY Mn Cr Fe203%

Residual soils Redhill Beds <2 29 253 34 27 89 6295 30 14 998 124 9.9 <2 16- 100- 20- 20- 50- 4000- 20- 8- 400- 85- 7.8— (31 samples) -3 40 300 100 40 160 8500 40 30 2000 160 13.2 Meidrim Shales and J 26 266 31 25 56 5749 16 5 261 114 7.4 Limestone ?- 6- 85- 5- 16- (50- 4000- 5- <5- 50- 85- 4.4— (33 samples) 7,0 50 400 40 40 160 8500 40 20 1300 300 10.0 Hendre Shales 4 28 226 31 22 103 5688 33 8 295 99 7.7 <2- 13- 100- 16- 13- <50- 4000- 10- 45- 130- 60- 4.0- (28 samples) 16 40 400 60 30 400 8500 100 40 1300 160 12.8 Llanvirn and <2 29 177 34 27 67 5963 22 6 409 114 7.4 Lower Llandeilo 2 13- 130- 20- 20- (50- 3000- 5- <5- 200- 60- 5.2— (26 samples) -5 50 300 85 40 200 8500 40 16 1000 200 12.8 Alluvial soils Dicranograptus shales 4- 37 218 42 24 118 6400 32 8 247 107 6.1 2— 16— 130— 30— 20— <50— 4000— 13— <5-- 50— 60— 3.1— (26 samples) 13 50 300 50 30 300 8500 60 20 400 160 10.0 Milled parentage :2 30 129 28 30 166 5000 33 13 . 593 97 7.4 <2 16— 85— 16— 20— 100— 4000— 13— <5— 160— 85— 5.3— (6 samples) -2 50 200 40 40 200 6000 85 30 1000 130 10.5 *'Geometric mean A Mean calculated with (2 p.p.m. = 1 p.p.m. + Mean calculated with (50 p.p.m. = 40 p.p.m. H Y Mean calculated with (5 p.p.m. = 3 p.p.m. CT1 Table 24 Ilange any: mean* metal content of residual overburden on the Hendre Shales at Meidrim and Ilanboidy (sample depth 12-18 inches)

Metal content (p.p.m.) MoL Cu V Pb Ga Zia+ Ti Ni Mn Cr Fe203 % 0••••• ....111••••••••••....• Meidrim 2 25 198 31 25 98 4750 22 5 360 83 6.8 <2 13- 160- 16- 20- (50- 4000- 10- <5- 160- 60- 4.0- (12 samples) -5 40 200 40 30 200 6000 50 10 1300 130 8.4 Llanboidy 8 32 269 35 20 169 6781 52 14 306 117 8.7 2- 16- 100- 16- 13- (50- 4000- 30- <5- 130- 85- 6. - (16 samples) 16 40 400 60 30 400 859P 100 40 400 160 12.8

Geometric mean A Mean calculated with <2 p.p.m. = 1 p.p.m. Mean calculated with (50 p.p.m. = 40 p.p.m. Y Mean calculated -rith <5 p.p.m. = 3 p.p.m. 138 in residual soils on the Hendre Shales at Llanboidy is thus thought to reflect syngenetic enrichment in the black shale bedrock unrepresented by the rock samples collected at Meidrim. The presence of higher mean levels for other metals at Llanboidy (Table 24) further suggests the presence of a metal rich parent material. Levels of Mo in soils on the Meidrim and Hendre Shales at Llanboidy are similar suggesting, in view of the continuity of the secondary environment over both outcrops, that the distribution of Mo in bedrock and soil is subject to similar controls throughout. Anomalous levels of Mo (3-10 p.p.m.) are recorded in alluvial soils situated down—drainage of the Dicranograptus shale outcrop. These soils contain fragments of metal rich bedrock, thereby illustrating the mechanical dispersion of molybdeniferous material as detritus in the streams (page 148). The occasional raised levels of Mo in soila on the Llanvirn and Lower Llandeilo (3-5 p.p.m.) occur in drift free areas and probably relate to thin black shale horizons in the succession reported by Strahan et al (1909). Amongst the remaining metals there is little overall variation in the range and mean content of tho various groups identified in Table 22 although soils developed on the Redhill Beds have a high mean content of Mn (x2—x4). ThiB is. regarded as largely a reflection of the secondary environment prevailing in the typically moderately drained soils on the Redhill ' Beds although rock sampling identified the highest concentrations of Mn and Co in the Redhill Beds.

(ii) Metal distribution patterns related to the secondary. environment Manganese, Co, Zn and to a lesser extent Fe are strongly 139

influenced by the secondary environment and their erratic distribution reflects changes in the drainage status of soils and as such shows no consistent relationship with parent material. Thus on Traverse 3 the high ground at each end of the traverse lines, carrying moderately drained soils, tends to have a high content of Mn, Co, Zn and possibly Fe. Towards the north end of Traverse 3 the small level area west of Cwmfelin Mynach with very poorly drained gleyed soils contains very much lower values of Mn, Co, Zn and, with reduced contrast, Fe. Between these areas values of the above metals show an erratic distribution with rapid fluctuations in total metal content irrespective of parent material, with the lowest values encountered in poorly drained residual soils and in alluvial groundwater gleys near streams. The lateral distribution of Mo and the remaining metals appears to be unaffected by the secondary environment. There is no sign of Mo accumulating in the receiving sites at the foot of slopes, nor is there any evidence of a common distribution with Fe; indeed Mo and Fe assume an inverse relationship on Traverse 2 (Fig. Tl). The distribution of Mo is thus closely related to the geology and Mo most probably occurs with weathered bedrock material in the soils.

(B) Vertical distribution The metal content of soils sampled at 0-6 inches and 12-18 inches depth is summarised in Table 25; all soils support permanent pasture. The data reveal certain general relationships; values of Mo, Cr, Cu, Ni and V tend to be lower in topsoils than associated subsoils. In contrast, Table 25 Range and mean* metal content of soils, sampled at two depth:., developed on the principal anent materials, West Carmarthenshire Sample deptn Parent (ins) Metal content (p.p.m.) materials (No. of samples) Mo Cu V Pb Ga Zn+ Ti Ni CoY Mn Cr Fe203/0 pH 0-6 (2 24 130 37 23 78 4800 12 7 1500 66 5.2 5.6 <2 21- 100- 30- 20- <50- 4000- 8- 5- 1300- 40- 4.4- 5.4- (6) -3 300 50 30. 200 6000 16 10 2000 85 6.4 6.8 Redhill Beds 27 12-18 :2 33 300 35 25 78 6417 33 19 1083 125 9.3 5.3 2- 3)- 300 20- 20- 50- 6000- 20- 16- 600- 100- 6.8- 5.2- (6) 3 43 50 30 100 8500 50 20 1300 130 10.5 5.6 0-6 8 26 150 57 27 98 5260 10 :5 460 97 4.6 5.4 2- 19- 85- 20- 16- <50- 3000- 5- ::5- 160- 50- 3.0- 4.2- (17) . 1:, 37 200 200 40 200 6000 20 -5 1600 100 6.2 6.8 Meid rim ;Jhales 12-18 1,1- 29 327 43 23 59 6500 20 5 355 114 7.8 4.9 2- 13- 200- 20- 16- <50- 5000- 5- ?5- 85.- 100- 4.4- 4.2- (17) ..30 5.) 400 85 30 130 8500 40 20 1300 160 12.8 6.1 0-6 <2 Li 125 58 21 300 5100 21 7 530 83 5.1 5.4 c2 17- 100- 40- 16- 50- 4000- 13- (5- 300- 60- 4.0- 4.4- (12) -4 30 160 40 500 6000 40 16 1000 100 6.2 6.6 Hendre 85 :hales 12-18 8 32 -242 38 20 169 6708 49 14 313 123 8.5 4.7 2- 15- 100- 30- 13- 50- 4000- 20- <5- 160- 85- 6.2- 4.2- (12) 16 40 400 85 30 400 85)0 100 40 400 160 11.0 5.1 0-6 .7 21 93 52 25 120 4750 12 5 370 58 4.8 6.0 (2 15- 60- 30- 20- <50- 4000- 8- <5- 200- 40- 3.3- 5.0- Llanvirn and (10) 26 160 :100 30 400 6000 20 13 1300 85 6.9 7.1 Lower 12-18 3 32 159 30 27 103 6000 36 11 406 105 8.2 5.0 Mandell° <2 16- 100- 20- 20- c50- 4000- 20- 5- 160- 85- 6.8- 4.7- (10) -5 50 200 40 50 200 8500 85 30 1000 160 12.3 5.4 * Geometric mean + Mean calculated with <50 p.p.m. = 40 p.p.m. A Mean calculated with (2 p.p.m. = 1 p.p.m. Y Mean calculated with <5 p.p.m. = 3 p.p.m. H 0 141

Pb, Mn and Zn are frequently enriched in topsoils Whilst such variation as is observed between topsoil and subsoil levels of Co, Ga and Ti is insignificant when considered with respect to the analytical precision of the spectrographic method (see Appendix). The fall in metal values between subsoils and topsoils is attributed to the leaching and redistribution of metals from the topsoils into the lower horizons of soil profiles. The greatest contrast between topsoil and subsoil values of Mo tends to occur where topsoils are more neutral, as at site 3193 (Table 26). The apparent greater leaching of Mo with a rise in topsoil pH is consistent with the generally stated belief that the mobility of Mo in soils is increased under neutral to alkaline conditions (Davies, 1956). Thus in the less acid topsoils Mo is more mobile and suffers a greater degree of leaching into lower soil horizons. Moreover, Mo uptake by herbage on these soils is also increased (page 151), further contributing to the depletion of topsoil Mo. The low contrast in Mo values seen at sites 3176 and 3183 (Table 26) can be accounted for by the inhibiting effects on Mo mobility of the low topsoil pH, with Mo retained in topsoils by sorbtion onto clay minerals, ferric oxides or in combination with organic matter. Site 3183 has very poor profile drainage in which the downward movement of water, and hence leaching potential, is small, which may further contribute to the very low contrast in Mo values between topsoil and subsoil. Table 26 Metel content of selected residual soils of varying drainage status developed on the Dicianogreptus shales

Sample Site Profile depth Metal content (p.p.m.) No. drainage (ins) Mo Cu V Pb Ga Zn Ti Ni Co Mn Cr Fe203% pH

3193 Moderatley draiD.e6. 0-6 2 25 160 60 20 200 5000 16 (5 400 60 4.0 6.3 (Upper valley slope) 12-18 13 40 300 30 30 50 5000 30 5 160 100 7.0 5.1 3176 Moderately drained 0-6 4 26 130 60 20 400 6000 20 10 600 85 5.6 5.5 (Crest of hill) 12-18 10 40 300 50 20 200 8500 60 13 300 130 10.0 4.6 3183 Very poorly drained 0-6 10 21 160 60 30 100 5000 8 <5 200 60 4.3 5.0 (Valley floor) 12-18 13 20 300 30 20 50 6000 10 <5 130 100 7.6 4.6 143

5. Relationships between the Metal Content of the Bedrock, Overburden and Stream Sediment The data in Table 27 are from rocks and soils collected in the immediate vicinity of Meidrim. A marked discrepancy between mean values of Mo, Cr, Ga, Mn, Pb, Ti, V, MI and Fe in the bedrock and residual soils is noted. Whilst the rise in both range and mean levels of Mn and Fe (x3 and x6 respectively) between bedrock and soils can be accounted for in terms of redistribution of these metals in the overburden, the contrast amongst the remaining metals cannot be so readily explained. The differences may be due to the homogenising effects of soil forming processes for, as can be seen in Table 27, the range of metal values is broadly similar in both rocks and soils except for Mo, Cr and Ti. Furthermore, it is suggested that the limited programme of rock sampling is possibly not truly representative since it includes a number of relttively metal poor samples. Nevertheless the occurrence of anomalously high levels of Mo in the overburden is localised to soils derived from Mb—rich black shales and as such clearly indicates the close control of bedrock on the distribution of Mo in the soils of West Carmarthen shire. The relationship between the metal content of soils and stream sediment is summarised in Table 28. In general there is a poor correlation between soils and associated stream sediments, athough it is noteworthy that detectable quantities of Mo are restricted to the sediments of streams draining outcrops of the Dicranograptus shales. It .must be remembered, however, that, due to the discordancy of the drainage network in West Carmarthenshire, most stream Table 27 Ranf4e and :sear* metal content of rocks and associated residual soils (sample depth 12-18 inches) around Meidrim, West Carmarthenshire Metal content (p.p.m.) Mot Cu V Pb Ga Zia+ Ti Ni Coy Mn Cr ,,,CFe203%

Meidrim Shale and Lime stJne Residual soils 9 35 238 32 30 78 4867 24 7 373 115 7.5 2- 16— 85— 20— 20— 50— 4000— 8.4. <5— 130— 85—" 5.6— (15 samples) 30 50 400 40 40 160 6000 40 20 1300 130 10.1 Rock samples 5 30 155 25 24 50 2700 21 6 59 51 2.4 2— 10— 85— 13— 13— :50— 1300 8— (5- 16- 30- 1.4- (8 samples) 7 70 300 60 30 —50 4000 50 13 160 60 3.8 Hendre Shales Residual soils 2 25 198 30 25 97 4750 22 5 360 83 6.8 (2 13— 160— 16— 20— <50— 4000— 13- <5- 160— 60— 6.2- (12 samples) -5 40 300 50 30 200 6000 40 10 1300 130 8.4 Rock samples 2 21 75 14 18 64 3143 23 5 53 43 2.9 <2 22— 50— 10— '16— 50— 2000— 20 <5 30— 40— 2.5- (7 samples) --3 27 100 16 30 100 4000 30 -5 85 50 3.6

* Geometric mean A Mean calculated with .<2 T.p.m. p.p.m. Mean c-)lculated with (50 p.p.m. = 40 p.p.m. Y Mean calculated with :5 p.p.m. = 3 p.p.m. Table 28 Mean* metal content of soilsA and stream sediments+ alltincippl bedrock units in the West Carmarthenshire area

Media Metal content (p.p.m.) Parent (No. of material samples) Mo Cu V Pb Ga Zn Ti Ni Co Mn Cr Fe203%

Ashgill bcils <2 29 253 34 27 89 6295 30 14 988 124 9.9 (31) (Redhill Beds) Stream <2 38 146 14 15 126 5582 30 15 554 99 9.6 sediments (28)

Dicranograptus Saila 7 27 248 31 24 78 5421 24 6 277 107 7.5 shales (61) Stream 2 40 137 19 16 116 4984 30 13 442 99 10.6 sediments (28)

Llanvirn and soils 2 29 177 34 27 67 5963 22 6 409 114 7.5 (26) Lower Llandeilo stream <2 42 120 15 16 132 5313 35 19 700 102 8.8 sediments (53)

* Geometric mean Sample d)pth 12-18 inches + Data from minus 80—mesh fraction l4ti catchment areas contain a variety of rock types. Thus in Table 28, whilst the soils are entirely residual on the Dicranograptus .shales, the stream sediment data include samples from catchments that contain only a small area of Dicranograptus shale outcrop. This situation is particularly true of the area west of Llanboidy where the geology is disrupted by faulting and rocks outcrop as narrow east—west belts. Nevertheless, detailed examination reveals that there is a close correlation between the Mo and V content of soils and associated sediments from streams with catchments developed wholly on the Dicranograptus shale outcrop. This is clearly shown in data from localities at Llanboidy and Meidrim respectively: Catchment A (grid reference 22282251) Llanboidy Stream sediment: 20 p.p.m. Mo, 300 p.p.m.V. Soils (12-18 inches depth) mean of 7 samples: 15 p.p.m. Mo (range 8-20 p.p.m.), 328 p.p.m. V (range 300-400 p.p.m.)

Catchment B (grid reference 22682211) Meidrim Stream sediment: 13 p.p.m. No, 300 p.p.m. V. Soils (12-18 inches depth) mean of 8 samples: 12 p.p.m. Mo (range 2-30 p.p.m.), 312 p.p.m. V (range 200-400 p.p.m.) The similar values for .Mo and V in soils and stream sediment noted above indicate that the dominant process whereby these metals are dispersed from soil to stream sediment is the mechanical distribution of fine grained detrital material derived from the metal rich black shale bedrock. The mechanical dispersion of these 147 metals is further indicated by the presence of Mo anomalous detritus in alluvial soils and by the fact that the strong positive correlation between Mo and V noted in the bedrock (page 135) is also present in the sediments of streams draining the Dicranograptus shale outcrop (page 36). The fall in mean Mo values between soils and stream sediment illustrated in Table 28 may be explained by the dilution of Mc—rich detritus in stream sediment with material derived from background areas within catchments of complex geology. Hence the suppression of the Mo anomaly in stream sediments west of Llanboidy where the Dicranograptus shale outcrop is disrupted by faulting. The fall in mean levels of Pb, Ga, Ti and Cr between soils and stream sediment in all the groups illustrated in Table 28 may be explained by the presence of metal poor detritus derived from areas unrepresented in the limited soil sampling programme. In contrast mean levels of Mn, Fe, Co and Zn are higher in stream sediments derived from the Dicranograptus shales than in associated soils. It was noted (page 140) that total values of these metals are low in poorly drained soils wherein these metals are mobile. It is suggested than Mn, Fe, Co and Zn are leached from poorly drained soils and transported by circulating groundwaters into the drainage network as described by Horsnail (1968) where a rise in pH and Eh (soils (12-18 inches depth) mean pH 4.8 : Drainage waters mean pH 7.0) results in the precipitation of Mn and Fe hydroxides in the drainage network onto which Co and Zn are scavenged. Nichol et al (1967) have suggested that Mn is first precipitated in drainage channels as colloidal hydrated Mn01_2 and that this then ages to inert Mh02. 148

Mean levels of Cu and Ni are also higher in stream sediment than soils although there is no evidence of these metals being mobilised in soils. Copper and Ni are recorded as being incorporated with Mn and Fe hydroxides (Goldschmidt, 1954, Rankama and Sahama, 1950) and thus may be scavenged by oxides in streams, thereby bringing about the metal accumulation noted here. Furthermore, Horsnail (1968) reports the mobilisation of Ni and Cu in poorly drained soils followed by their deposition with secondary Fe and Mn oxides in drainage channels in Devon. Raised levels of Mn and Co in stream sediment in the West Carmarthenshire reconnaissance area have already been related to areas of poorly drained soils where leaching conditions are locally intensified(Ch.3) whilst the peculiar high levels of Fe in stream sediments over the Dicranograptus shale outcrop occur in a zone of frequent stream bank iron seepages.

6. Metal Content of Herbage and Factors Influencing the Uptake of Molybdenum and Copper by Herbage Analytical data from grab samples of mixed herbage and associated topsoils taken from permanent pasture are sumnarised in Table 29. Pasture herbage throughout the area is dominantly mixed grasses, clover being rare on all but the least acid soils. Rushes occur at more poorly drained sites and were included where present in the herbage samples The data in Table 29 reveal that the Mo anomaly present in soils is reflected in the herbage and a broad correlation exists between the Mo content of topsoils and herbage with maximum values on anomalous soils derived from the Table 29 Range and mean* molybdenum and copper content of topsoils and associated herbage+ on soils derived from the principal parent materials in the West Carrnartnenshire area

Mo status as defined ay Mo(p.p.m.)Y Cu(p.p.m.) stream sedimeLt and Parent soil sampling material Herbage Topsoil Herbage Topsoil Licranograptus shales 1.6 6 7.7 24 (28 samples) 0.1-3.8 -1-14 5.0-17.5 17-37 Anomalous Alluvial soils largely Oerived from the 1.8 5 7.8 27 Iicranograptus shales (5 samples) 1.0-3.8 2-10 6.0-10.8 23-33 Redhill Beds 0.9 2 8.3 25 (6 samples) 0.5-2.0 '1-3 6.3-10.3 21-27 Backcrroun.'b - Llanvirn and Lower Llandeilo 0.9 (.1 8.7 21 (9 samples) 0.3-2.6 (1-2 7.3-9.8 17-26

* Arithmetic mean + Mixed pasture herbage, oven dry weight 1-1 6' Sample depth 0-6 inches Y Mean calculated with<1 p.p.m. = 0 p.p.m. LLD 150

Dicranograptus shales. However, the contrast between the mean Mo content of herbage on background and anomalous sites (x1.7) is less than the contrast in total topsoil Mo (x3). Thus, although the Mo content of topsoils is apparently the principal factor determining the Mo status of herbage, a relatively large proportion of the total Mo in anomalous topsoils appears to be in a form unavailable to herbage. In the West Carmarthenshire area there is no relationship between the uptake of Mo by herbage and the limited variations in soil drainage status observed at anomalous and background sites. The uptake of Mo by herbage (expressed as the ratio herbage Mo : topsoil Mo) is plotted in Fig. 34 as a function of topsoil pH, organic carbon and total Fe (expressed as Fe203). Although no relationship can be seen between Mo uptake and organic carbon or total Fe, a broad trend is revealed between Mo uptake and pH, with the uptake of Mo increasing with a rise in topsoil pH over the range 4.0-6.8. This relationship agrees with the observations of Davies (1956) and is considered to indicate the occurrence of conditionally available Mo present in the topsoil, most probably as anionic No adsorped onto clay minerals or ferric oxides. The relatively depressed uptake of Mo by herbage on the Mo anomalous soils is thus due, at least in part, to the irmobilisation of Mo under the low pH conditions that are typical of soils derived from the Dicranograptus shales (Table 25). Walsh et al (1953) have suggested that at a low pH the availability of Mo to herbage is increased in poorly drained soils with a high organic matter content. However, in this areas topsoil organic matter has no influence

8.

7 - + + + 6- • t + + • • 1+ pH + 5- $ 4 • + + + * + 4- +

3-

0:1 0:2 0:5 1.0 2:0 Herbage Mo! Topsoil Mo

8- + 7.

•

+ + + + + + +4' + + + + ++ * • 8 3_ + • • AP • ill • + 2-

oi 0.2 01 1.0 2.0 Herbage Mo/ Topsoil Mo

7. +

+ 6-

0., + + +• • 1* + U. 4- + + + +

3-

1 I I 0.1 0.2 0•5 1.0 2:0 Herbage Mo! Topsoil Mo

+ Molybdenum anomalous soils. • Background soils.

Fig.34. Molybdenum Content of Pasture Herbage in Relation to the pH,Iron and Organic Carbon Content of the Topsoil. (Topsoil 0-6ins depth. Herbage-Oven dry weight.)

West Carmarthenshire area. + Molybdenum anomalous soils. • Background soils. 8-

8-

6- 7- 7- c 0 + + • a 5- 6- _FS 6- U + •+ pH + •+ • cr. 5- a4- 5- 4.• + 0 En + • 0 + 4* * u_ 3- 000 4- 4- • • • 2- 3- 3-

. 0.2 0.5 1.0 0.2 0.5 1.0 0.2 0.5 1.0 Herbage Cu/ Topsoil Cu Herbage Cu/ Topsoil Cu Herbage Cu/ Topsoil Cu

Fig.35. Copper Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil. (Topsoil 0 -6ins depth. Herbage-Oven dry weight.)

West Carmarthenshire area. 151 on Mo uptake by herbage. The data in Fig. 34 reveal that in soils of a similar pH Mo uptake by herbage at background sites is frequently greater than at anomalous sites; a simple pH effect is thus not the only control. However, it is suggested that in anomalous soils a relatively large amount of total Mo is retained, in an immobile form, with fine detrital fragments of bedrock material. In contrast, the Cu status of both topsoil and herbage is similar at Mo anomalous and background sites (Table 29). The drainage status of soils has no influence on Cu uptake by herbage. However, topsoil pH seems to be a significant control, at least at background sites (Fig. 35) where Cu uptake appears to increase with a rise in topsoil pH over the range 5.0-7.0. This is, however, inconsistent with the generally stated beliefs on the mobility of Cu in soils and the availability of Cu to herbage (Whitehead, 1966). The relationship may thus be fortuitous or reflect an unrecognised or unmeasured factor. 152

CHAPTER 14: DETAILTM GEOCHEMICAL INVESTIGATIONS BOWLAND FOREST AREA

1. Introduction The stream sediment reconnaissance survey of the Bowland Forest area, reported in Chapter 8, reveals levels of up to 60 p.p.m. Mo in sediment from streams draining outcrops of the Bowland Shale Group, a Low/Mid Carboniferous marine black shale formation. An appraisal of the distribution of anomalous quantities of Mo in stream sediment (' 3 p.p.m.) suggests a primary source in the Bowland Shale Group with Bowland Shale material smeared to the south and west by glacial action giving rise to Mo sediment anomalies down—drift of the source rock.

2. Description of the Area A general account of the area is presented in Chapter 8. Particular attention is now given to the geology of the Bowland Shale Group, identified as the source of anomalous levels of Mo, together with the drift and soils associated with these rocks.

(A) Geology. The Geological Survey Memoir for Clitheroe and Nelson (Earp et al, 1961) provides a comprehensive account of the area and forms the basis of the following descriptions. The Worston Shale Group, Bowland Shale Group and Millstone Grit foriattion underlie the greater part of the area (Fig. 20, Table 14). The Worston Shale Group (Upper Visean, S2, D1) outcrop 153 over wide areas beneath drift cover. The succession is of grey calcareous shales with thin interbedded impure limestones and cementstones. The sediments are very uniform, apart from the local development of limestone knolls at Clitheroe and Newton, and contain a rich benthonic fauna. The overlying Bowland Shale Group (Upper Visean/Lower Namurian, Pi, P2 and El) are dominantly a marine black shale sequence with interbedded sandstones and limestones. The shales, which include both calcareous and non calcareous developments, are persistent throughout the outcrop of the formation with little lateral variation in facies or thickness. The sandstones, lenticular and almost restricted to the Lower Bowland Shales are of Millstone Grit facies. Limestones of varying thicknesses, well bedded, light grey to black, crinoidal and shelly, occur in the Lower Bowland Shales. The depositional environment of the Bowland Shale Group has been the subject of a number of studies including those of Bisat (1924) and Trotter (1952). The black shales which dominate the succession are the result of deposition in up to 100 fathoms of quiet water (Black, 1957). The shales contain a rich neretic fauna, with a restricted benthonic fauna at some horizons. Anaerobic bottom conditions are evidenced by the severely restricted benthonic fauna and the accumulation of organic matter and pyrite in the shales. Pyrite, which is conspicuous only in the Upper Bowland Shales, is found throughout the shale sequence dispersed in the sediments, often in intimate association with organic matter (Black, 1959). Oil is occasionally . found in the chambers of solid goniatites 154

(Dunham, 1961). The succeeding Millstone Grit formation (Namurian) comprises a thick sequence of massive non—marine sandstones with non—marine shales and mudstones. The solid geology is mantled by extensive spreads of glacial drift deposited by ice moving from north east to south west through the area (Fig. 18). The drift is dominantly of local origin and it is possible to identify trains of boulder clay smeared down—drift from outcrops of distinctive bedrock (Earp et al, 1961). Material from the Bowland Shales is readily identified and for the purpose of the following discussion the drift is classified by the amount of Bowland Shale debris present. A threefold division is adopted: (a) Bowland Shale Drift — Fragments of Bowland Shale dominate over other material in this drift which is typically a greasy grey black clay, weathering brown. (b) Mixed Drift — This is the result of the mixing of Bowland Shale debris with other material and grades from Bowland Shale Drift into Barren Drift with an increasing content of non Bowland Shale material. (c) Barre:a Drift — This contains no Bowland Shale material and is often sandy or comprises material derived from the Worston Shale Group.

(B) Soils Although there is no soil series map available for the whole area, local studies by Hall (1961, 1962), Pepper (1963) and Crompton (1966) together with the provisional county map for Lancashire by the Soil Survey provide essential 155

information. For the purpose of describing metal distributions a broad twofold division is adopted wherein residual and transported soils are distinguished, with both topography and drainage important qualifying characters. In the present investigation residual soils were found developed only on the Millstone Grit and Bowland Shales. Transported Boils are derived from glacial drift, colluvial head and allulium. Soils on the Millstone Grit are sandy and well drained but under the climatic conditions of the area (high altitude, high rainfall, low evaporation and con temperatures) become intensely leached peaty podzols and peaty gley podzols. Residual soils on the Bowland Shale Group occur typically on long slopes below the sandstone scarp of the fells. The soils are of a variable depth and occupy moderate to free draining shedding sites (Pepper, 1963). However, they are subject to a constant lateral movement of water downslope from the fells above and are thus gleyed in the lower part of the profile. At the break in slope below the fells groundwater accumulates in receiving sites which carry very poorly drained gleys and peaty gleys sited either on the Bowland Shales or drift. Few of the residual soils on the Bowland Shales are in situ or uncontaminated. Slopes are subject to continual soil creep and sandy material, brought down from the sandstone scarps, is present in many of the profiles examined. The colluvial downwash of Bowland Shale material onto the drift or over the Worston Shale series occurs where there is no break in slope at the foot of the Bowland Shale outcrop. 156 Soils developed on the drift invariably show signs of impeded drainage (Hall, 1961) and gleying is a frequent ocurrence. Drainage improves in shedding sites and locally where the drift has a sandy matrix. Alluvial soils are of a restricted occurrence for many streams are incised and actively eroding. Such soils are found only beside the larger streams, and the Rivers Hodder and Ribble, occurring as coarse or fine textured groundwater gleys.

(C) Land Use The patterns of land use are related in Chapter 8.

3. Distribution of Metals in the Bedrock Chip samples of Worston Shale, Bowland Shale and Warley Wise Grit were obtained from stream sections east of Slaidburn (Fig. 36) recorded by Parkinson (1936) and Earp et al (1961). Stratigraphic sampling (Fig. R2, Table 30) reveals that enhanced levels of Mo ( > 3 p.p.m.) occur in all three zones of the Bowland Shale with peak values of up to 40 p.p.m. Mo. In contrast, Mo values are consistently below 3 p.p.m. in the Worston Shale Group samples and Mo is undetected in the Warley Wise Grit. The three zones of the Bowland Shale Group are also enriched, with respect to the underlying Worston Shale Group, in Zn (x5—x16), V (x3—x7), Cu (x2—x3), organic carbon (x2—x3), Ti (x2—x3), Se (x1.5—x2.4), Pb (xl—x5), As, Cr, Ga and Fe (x2). Of the elements determined, only Mn and Co do not show this conspicuous enrichment in the Bowland Shale Group. Table 31 illustrates that the greatest metal concentrations occur in the black shales of the Bowland Shale Group. The sandstone and sandy shales of the P1 and Erollon by Rock Sampling Point owlan

Key to Rock Samples 1 Worstcn Shale Group 2 Bowland Shale Group. 3 Millstone Grit.

Molybdenum stream sediment anomaly.

0 1 2 Longridge Scale in Miles.

Fig. 36. Location of Soil Traverse Lines and Rock Sampling Points in Relation to the Molybdenum Stream Sediment Anomalies in the Bowland Forest Survey Area

Table 30 Range and inean* metal content of the principal Carboniferous rock units, Bowland Forest area Metal content (p.p.m.) Org. Mob Cu V Se+ pbA GaA Zn? Ti NiP Cop Mn Cr Asp Fe203% C%a Ei Warley <2 6 5(1 <0.1 15 8 150 2000 16 <5 170 23 ;5 1.4 <0.1 Wise Gritk <2 5- 30 <0.1- 10- 8 100- 2000 13- <5 40- 16:- <5 1.3 - <0.1 (2 samples) 7 0.2 20 150 20 300 30 1.5 El Upper 15 55 345 4.6 90 16 628 1840 94 17 322 104 15 4.6 2.1 Bowland <2- 11- 4C- <0.1- 16- 6- 50- 850- 30- -f'5- 16- 50- <5- 2.1- 0.9 - Shale 300 40 1300 160 80 7.5 (9 samples) 32 100 60) 17.0 500 40 4000 3000 3.5

P2 Lower 21 10? 412 S• .5 26 12 950 1760 117 20 57 119 8 4.4 3.1 Bowland 8- 71- 160- 3.5- 16- <2- 50- 600- 50- 13- 20- 60- <5- 1.9- 2.3- Shale 160 40 100 160 20 6.1 3.8 (5 samples) 34 184 600 16.0 60 16 2000 3000 P1 Lower 8 72 165 6.1 34 9 333 1213 93 16 215 85 14 3.3 2.1 Bowland 2- 3- 13- <0.1- <2- <50- 50- <5- 16- 3- (5- 0.8- 0.1- Shale 300 40 500 160 90 6.6 4.4 (12 samples) 4u 160 400 35.0 100 16 1600 2000 B2 Worston <2 35 56 0.4 21 7 60 712 53 10 319 49 7 1.8 1.2 Shale and (2 10- 2J- <0.1- :2- <2- <50- 50- <5- <5- 130- 8- 5- 1.0- 0.3 - Pendleside -2 48 130 1.5 30 16 100 1600 130 30 1000 85 20 2.7 2.0 Limestone (8 samples)

* Geometric mean except k arithmetic mean y Mean calculated with <50 p.p.m. = 40 p.p.m. A Mean calctlated with (2 p.p.m. = 1 p.p.m. p dean calculated with <5 p.p.m. = 3 p.p.m. Mean calaLlated with (0.1 p.p.m. = 0.0 p.p.m. m Mean calculated with (0.1% = 0.0.%

Table 31 Ran,;;e and marl* metal content of the principal lithologies of the Bowland Shale Group and and the Wo,:ston Shale Group

Metal content (p.p.m.) Or %• M06' Cu V Se+ Pb GaA ZnY Ti N±P CoP Mn Cr AsP FP-2 0 3 ° C

1. Bowland Shale Group Calcareous 13 107 337 9.3 38 13 813 1623 140 26 151 133 17 4.5 3.1 black shales 2- 57- 130- (0.1- 16- 8- (50- 600- 60- 5- 20- 85- <5- 2.6- 1.3- and black 40 181 600 35.0 100 16 2000 3000 300 40 300 160 90 6.6 cementstones 4.4 (10 samples) Non-calcareous 22 61 354 5.0 117 18 707 1821 93 14 292 94 17 4.9 2.6 black shales <2- 27- 160- <0.1- 16- 6- 50- 850- 30- <5- 16- 60- <5- 2.1- 1.3- (7 samples) 34 1C3 600 17.0 500 40 4000 3000 300 40 1300 160 80 7.5 3.5 ___ 21 sandstones <2 17 45 0.7 11 13 70 1975 36 10 216 56 <5 2.7 0.6 d El sandy <2 3- 13- <0.1- 5- 4- <50- 1300- 10- <5- 16- 16- <5 0.8- 0.1- shales :-.2 411. 130 2.0 20 30 100 3000 85 30 500 130 4.9 1.5 (4 samples) Limestones 8 49 183 5.2 18 <2 .58 363 53 7 296 53 <5 2.1 2.0 (5 samples) 4- 13- 40- <0.1- 2- <2 1,50- 50- <5- <5- 85- 5- <5 1.7- 0.8- 1? 72. 500 16.0 40 -3 100 600 130 16 500 160 -5 2.4 3.1

Worston Shale Group (Trey calcarecus :2 39 53 0.7 25 8 56 730 51 8 218 53 7 1.7 1.6 shales <2 29- 30- <0.1- 16- 2- <50- 300- 30- 5- 130- 40- <5- 1.3- 0.3- (5 samples) -2 48 85 1.5 30 10 100 1300 85 16 300 85 20 2.7 2.0 Iimestonesa <2 27 60 <0.1 14 8 67 683 58 12 487 41 5 2.0 0.5 (3 samples) 30_ ;2 10- 20- <0.1 <2- <2- 50- 50- <5- <5- 160- 8- <5- 1.0- 0.3- 43 130 30 16 100 1600 130 1000 85 10 2.6 0.7

* Geometric mean except a arithmetic mean Y Mean calculated with <50 p.p.m. = 40 p.p.m.

A Mean calculated with <2 p.p.m. = 1 p.p.m. (3 Mean calculated with <5 p.p.m. = 3 p.p.m. ‘11 Mean calculated with <0.1 p.p.m. = 0.0 p.p.m. CO 1159

upper B1 divisions of the Bowland Shale formation are conspicuously lower in Me, Cu, Se, V and organic carbon than the black shales. The limestones, on the other hand, although low in many metals, contain high values of Mo, Se and organic carbon. The role of organic matter in the accumulation of Mo and Se is discussed below. The metal enrichment recorded in the Bowland Shales is similar to that encountered by Atkinson (1967) and Fletcher (1968) in Visean/Namurian marine black shales in Co. Limerick, South West Ireland, and the South Pennines respectively (Table 32). The present investigation complements the previous studies in demonstrating metal rich marine black shales of Upper Visean/Lower Namurian age at localities up to 300 miles apart, and confirms the presence of Mo—rich deposits on the northern margin of the Lower Carboniferous central province as suggested by Fletcher (1968). Peculiar to the Bowland Shale Group is a higher mean content of Se, Pb, Ni and Cr whilst values of Ti and Mn are low. The remaining metals display mean values similar to or intermediate between values recorded in Limerick and the South Pennines. These differences presumably reflect local variation in the supply of metals and/or changes in the depositional environment influencing metal concentrations. The mineralogy of the Bowland Shale is also thought to influence metal concentrations (see below). Metal relationships within samples from the Bowland Shale Group are shown graphically in Fig. 37, in which data from the various lithologies are distinguished. Data from samples of Pendleside Sandstone are conspicuously apart in many of the plots, reflecting the very different depositional Table 32 Mean* metal content of samples from Upper Visean/Lower Namurian marine black shales at three localities in England and Eire

Metal content (p.p.m.) Ho Cu Se V Pb Ga Ti Ni Co Mn Cr As Fe203%

Bowland Shale 17 89 7.6 '344 69 15 1700 122 21 206 118 17 4.7 Group

Edale Shales 11 110 4.4 265 25 19 4500 100 30 905 100 17 2.9 South West Pennines (Fletcher, 1968)

Clare Shales 27 79 2.9 365 22 15 2420 54 13— 340 87 4— 4.5 Co. Limerick, Lire 20 11 (Atkinson, 1967)

* Geometric mean A Samples of panct,stcme and limestone excluded

10.0- 10.0- 10-0- 10 0- 10 0- 10-0- 50- 5-0- 5-0- 5-0- .1. 5.0— • + + + • + •• cf 0 0+ • • I+ • +0- • • + at 0+ : + alt ++ ++ %) + + A. + + 4v 4..•+ ;_--- +1. • t • 4, .+ • • 0 ( 0 0 O 0 0 + o ++ • + + • + 0 bon + . ZT, 1-0 r ,.. 10_ 8 1-o- 0 tO 0 0 Ca 0 0 0 8 08 0

1.1 U ic 0.5 - 'E M- 'E0-5- c c0'5- C a an 0 Cl an CP rn .02 0 Org 8 C

0 0 0.1- S 0 o e 01- 0 0.1- 0.1-

I I 1s I I 1 I 50 100 500 2 10 100 10 5 100 500 <2 2 ; 10 50 <01 01 0.5 1.0 5.0 10.0 5 10 50 100 Copper (ppm.) Vanadium (p.p.m.) Chromium (ppm.) Nickel (p.p.m.) Molybdenum (P-PIT1.) Selenium (p.p.m.)

10- 10- 10- 10- • • ++• ++ • ++ 4k* .+ ++ +. • • • 0 ++ 81? 5- o o • + ++ ,•-•T 5- o + + + . o • +. f • + 0+ 0 • • + + + o ;1' ++ 0 +• + + ocn 0 + + o 0 0 + 4. 0 o + . o . 0 cg, 0 0 • N • • 0 0 0 s) 0 0 0 0 0 0 0 s.... 0 U- 0 0 1^ 1- - 1- 0 0 0 0 I I I I I 500 I I 50100' 500 2 10 100 10 50 100 ; 10 50 <01 01 0 5 1-0 5.0 10.0 5 10 50 100 Vanadium (p.p.m.) Chromium (pp.m.) Nickel (p.p.m.) Molybdenum (pp.m.) Selenium (p.p.m) Copper (p.p.m.)

10-0-

5.0- • Non-Calcareous Shales. Fig.37. Variation of Organic Carbon and Iron -with Molybdenum, Selenium, Copper, Vanadium, + Calcareous Shales. Chromium and Nickel.,and of Organic Carbon with Iron, in the Bowland Shales.

E 1.0- 0 0 Limestones. 8 0'5- 0 Sandy Shales and Sandstones. rn 0

0.1- 8

I a 05 - 1-0 5-0 160 Fe203 (%) 161 environment of the sandstones (Millstone Grit facies) from that of the remaining lithologies. Among samples of shale and limestone, Mo, Se, Cu, V, Cr and Ni show a strong positive correlation with organic carbon. Organic carbon and total Fe (as Fe203) also display a close positive correlation. Copper, V, Ni and less distinctly Mo are correlated with Fe although Se shows no relationship with Fe. The positive correlation between organic carbon and Fe is regarded as reflecting the intimate association of organic matter with pyrite reported by Black (1959). The data in Fig. 37 suggest that both organic matter and pyrite influence the distribution of metals although it is not possible to establish the definitive role of these factors except in the case of Se for which organic matter is clearly the control. That several metals show a positive relationship with both Fe and organic carbon may be a reflection of the common distribution of pyrite and organic matter with the metals associated with one of these factors, or the metals may themselves by incorporated with both pyrite and organic matter. However, the closer correlation of Mo, Cu and V with organic carbon suggests that the accumulation of these metals is more dependent. on the presence of organic matter than pyrite. Although Mo and Se are both enriched in the Bowland Shale they do not have a close common distribution. A similar situation is observed by Fletcher (1968) in the Visean/Namurian of the South Pennines and is probably due to slight variation in the supply of metals and/or local environment affecting the concentration of these two metals. Lead, As and Zn are also enriched in the Bowland Shale although these metals display no relationship with organic carbon or Fe. Coincident high levels of Pb and As occur 162

at the base of the P 1 and E1 sequences, whilst Zn has an erratic distribution with occasional very high levels (1300-4000 p.p.m.). The high values of these metals may be due to the presence of detrital minerals containing Pb, Asand Zn or, alternatively, may be the result of the temporary introduction of these metals into the area and their incorporation with organic matter or pyrite. The present data are insufficient to determine either the position of Pb, As and Zn in the rock or the processes leading to their accumulation. However, since the high levels are restricted to black shale horizons the environment of black shale deposition is apparently an important controlling feature. Levels of Ti in the Bowland Shale, although higher than in the adjacent Worston Shales (Tables 30 and 31), are lower than in the comparable deposits of Limerick and the South West Pennines (Table 32). This is probably a reflection of the mineralogy of the Bowland Shales which are dominantly quartz rich siltstones (Purton and Youell, 1969). Titanium is usually associated with clay minerals (Goldschmidt, 1954) which form a lesser portion of the rock than in the Limerick and South West Pennine successions. The data portrayed in Fig. R2 and Table 30are from samples taken near Slaidburn (Fig. 36). Parkinson (1936), Rayner (1953), Earp et al (1961)and Walker (1967) have all stated that the black shale facies of the Bowland Shale Group is remarkably constant throughout its outcrop in the reconnaissance area (Fig. 20). Such variation as does exist in the Bowland Shale Group is restricted to the incoming of limestones at the base of the sequence in some 163 areas (Parkinson, 1936) and the presence of lenticular sandstones. It is thus anticipated that metal values are similar throughout the outcrop area, a feature indicated by the stream sediment survey and substantiated in the soil sampling programme reported in the following pages.

4. Distribution of Metals in the Overburden (A) Lateral distribution Soil samples were collected at intervals of 200-500 feet along regional traverse lines (Figs. 36, T2, T3 and T4). The traverse lines are so orientated as to cross the strike of the bedrock and the direction of ice movement and thus examine the role of both bedrock and drift in controlling the distribution of Mo anomalous soils. In addition, the traverses cover a variety of soil conditions and topographic situations revealing the role of secondary environment in influencing metal distributions. An examination of the data in Table 33 reveals that the main control on the distribution of Mo in the Bowland Forest area is parent material. The highest mean content of Mo, V, Cr and Ga is in residual soils on the Bowland Shale. High mean values of No, V, Cr, Ga and Ti are revealed for sails on the Bowland Shale Drift with values falling successively in soils developed on Mixed Drift and again on Barren Drift. High values of Me, V and Cr are also characteristic of alluvium containing Bowland Shale material. In contrast, Mn, Co, Zn, Ni and Fe are erratically distributed due to mobilisation and redistribution of these metals in the overburden. Attention is given first to those features characteristic Table 33 Range and aear* metal content of overburden developed on the principal parent materials Bowland Forest area (sample depth 12-18 inches) Metal content (p.p.m.) Parent material Mo,6 Cu V Pb Ga Zn+ Ti Ni Co? Mn Or Fe203% Residual Soils Bowland Shale (Troul, 12 27 177 52 18 79 4883 23 7 219 103 4.9 <2- 8- 40- 20- 10- <50- 3000- 5- 5- 13- 40- 1.5- (62 samples) 85 85 100 850 40 400 8500 160 40 6000 200 10.5 Millstone Grit <2 11 50 49 10 :50 3857 11 5 39 53 2.1 <2 2- 16- 20- 3- :50- 2000- 5- <5- 13- 20- 1.2- (15 samples) -4 40 130 100 20 1.30 6000 30 5 200 100 5.8 • Transported Soils Bowland Shale Drift 7 24 141 48 16 121 4974 31 9 356 94 5.2 <2- 5- 50- 16- 13- <50- 4000- 10- 16- 60- 1.8- (87 samples) 40 160 300 200 30 600 8500 85 40 8500 160 11.0 Mixed Drift 4 25 112 48 16 190 4626 42 14 536 89 5.6 (2 8- 60- 20- 13- <50- 3000- 10- <5. 30- 40- 2.5- (34 samples) -10 60 200 100 20 400 6000 85 30 6000 160 8.5

Barren Drift <2 11 83 27 14 84 4122 26 7 . 139 --, 69 3.7 2 -- 2- 40- 13- 3- <50- 2000- 10- <5- 16- 40- , 1.4- (71 samples) -4 30 200 160 20 400 6000 60 30 4000 160 9.8 _...... , - Alluvial Soils Alluvium containing 9 40 154 68 17 309 4714 71 19 2236. 124 6.4 Bowland Shale debris 4- 8- 60- 30- 8- 160- 3000- 20- 8- 300- 60- 4.6- (7 samples) 20 60 200 100 30 400 6000 130 30 5000 200 8.3 Barren Alluvium <2 33 115 47 16 197 6167 43 9 883 92 6.5 42 30- 85- 40- 13- 160- 4000- 40- 8- 500- 60- 4.3- (3 samples) -3 40 160 60 20 300 8500 50 10 1300 130 9.5

* Geometric mean except p arithmetic mean L\ Mean calculated, with <2 p.I.m. = 1 p.p.m. + Mean calculated ':rith :50 p.p.m. = 40 p.p.m. rn Y Mean calculated with <5 p.p.m. = 3 p.p.m. 165

of soils developed on the various parent materials, particularly the distribution of Mo; consideration is then given to those metal distributions influenced by secondary environment. (i) Metal distribution patterns related to the parent materials (a) Residual soils on the Millstone Grit These soils are found supporting rough moorland on the Fells at heights of 1000-1500 feet. Where sampled, these soils are freely or excessively drained peaty podzols with bleached grey or grey brown coarse textured sands below peat. The metal content of the bedrock is low (Table 30) and most metal values in the soils are similarly low when compared with soils developed from other patent materials. The excessive drainage may have led to the leaching of some metals, further lowering metal values in these soils. (b) Residual soils on the Bowland Shale Groin Residual soils derived from the Bowland Shale Group contain the highest mean content of Mo, V and Cr, and also high levels of Pb and Cu, features consistent with the distribution of metals observed in the bedrock samples obtained. Low levels of Mo 2-4 p.p.m.) are encountered in residual soils on the sandstones interbedded -with the Bowland Shale on Traverse 7. Sampling of the bedrock demonstrates that the sandstones are low in Mo in the few samples obtained. Anomalous levels of Mo (3-85 p.p.m.) are found wherever soils are developed on the Bowland Shales although values fall (3-10 p.p.m.) in the upper• parts of the steep fell slopes where colluvial downwash of the overlying barren Namurian sandstone probably suppresses metal values in the soils. 166

(c) Soils developed on transported overburden Ice movement from north east to south west through the area has smeared bedrock materials for variable distances down—drift from outcrop (Tarp et al, 1961), thus greatly modifying geochemical patterns due to the contrasting metal content of the various bedrocks. The smearing of metal—rich Bowland Shale material, causing the extension of Mo anomalous soils can be demonstrated by examining the data obtained from the soil traverses. In all cases where raised levels of Mo (> 3 p.p.m.) were encountered in soil samples (12-18 inches depth) on the various drifts and alluvium,black shale debris, derived from the Bowland Shales, could be found in the sample or was observed in the immediate vicinity. Thus on Traverse 2 and 3 anomalous levels of Mo (4-13 p.p.m.) are found in soils developed on Bowland Shale Drift overlying barren Worston Shale at sites up to 12 miles down—drift of the large Bowland Shale Group outcrops at Bolton—by—Bowland and Grindleton respectively. A similar situation is seen on Traverse 5 on the north side of Newton Fells. On Traverse 6 anomalous levels of Mo (4-10 p.p.m.) are encountered in soils derived from drift overlying Worston Shale at two zones one mile down—drift of the Bowland Shale Group outcrop. In the south west of the area on Traverse 7 and 8 anomalous levels of Mo (4-40 p.p.m.) are encountered in drift derived soils over large areas of the broad vale west of Chipping. By way of contrast at the north end of Traverse 1 the introduction of Barren Drift, from the north, onto the Bowland Shale outcrop is seen to suppress the Mo anomaly, although the transport of molybdeniferous black shale 167 several hundred yards south, up slope, onto the barren Pendleside Sandstone illustrates the very local origin of the drift. Again, towards the south east end of Traverse 1, up to 10 p.p.m. Mo is encountered where sandy drift containing black shale debris is smeared onto the Pendleside Sandstone from the narrow shale outcrop to the north east. The spread of molybdeniferous black shale by colluvial downwash on slopes is btrongly suspected as contributing to the anomalous soils of Traverse 2. There 4-8 p.p.m. Mo is recorded from soils on drift overlying Worston Shale on very steep slopes below an area of Bowland Shale outcrop on equally steep slopes. Ample evidence of soil creep is seen by the development of terracettes. Colluvial downwash may also contribute black shales material to the Mo anomalous soils in the mid part of Traverse 5. The distribution of molybdeniferous black shale material by fluvial action is indicated by the results of the stream sediment reconnaissance. Areas of alluvium carrying Mo anomalous soils are found beside streams with catchments draining outcrops of the Bowland Shale Group or drift containing Bowland Shale material. Thus on Traverse 8 the alluvial soils contain 16 p.p.m. Mo, beside a stream draining an area of residual soils on the Lower Bowland Shales, whilst adjacent soils derived from Mixed and Barren Drift contain <2-13 p.p.m. Mo (mean 5 p.p.m.). In both the residual soils derived from the Bowland Shale and the soils derived from the drift the distribution of No is significantly correlated with that of V, Cr and Cu (P = 0.01), an association similar to that in the Bowland Shale bedrock. The association, and the common fall in 168 levels of these metals (although less distinctly for Cu) with an increase in the non Bowland Shale content of the drift indicates that the dispersion of these metals is dominantly elastic with the physical transport of weathered and unweathered black shale material the main process by which anomalous levels of Mo, and associated metals, are spread in the Bowland Forest area. Similarly mean levels of Se fall from 1.8 p.p.m. (<0.2-17.0 p.p.m.) on the Bowland Shale Drift to <0.2 p.p.m. (all samples <0.2 p.p.m.) in Barren Drift. Stream sediment data (see page 85 ) reveal occasional low levels of Mo (2-3 p.p.m.) in the north east of the survey area suggesting that the molybdeniferous Bowland Shale Group is being masked by barren drift; indeed sandy drift derived from the Millstone Grit outcrop to the north and north east is very extensive hereabouts. However, the exact extent of the various types of drift is not known and it is possible that areas of residual soils together with Mo anomalous areas of sandy drift similar to those encountered on Traverse 1 occur. Similarly it is a lack of follow up data which precludes any assessment of the distribution of Mo anomalous soils in the south east and far south west of the reconnaissance area.

(ii) Metal distribution patterns related to the secondaa environment In contrast to the metals mentioned above the distribution of Mn, Co, Ni, Zn and to a lesser extent Fe, is erratic and largely independent of parent material. In general low levels of these metals are encountered in the 169 intensely leached sandy moorland soils on the Millstone Grit and poor and very poorly drained soils elsewhere. High values for this group of metals tend to occur in better drained soils, alluvium and in sites at the base of slopes. A critical examination of data from Traverses 6 and 7 reveals that Mn, Co, Ni, Zn and Fe are all enriched (x2—x50) in receiving sites (page 155) at the foot of long fell slopes (Table 34) with respect to shedding sites on the fell slopes and 'normal' sites on the floor of the broad valley south and east of Chipping, whilst levels of Ga, a metal little affected by the secondary environment, remain unchanged. Soils at the receiving sites are very poorly drained gleys and peaty gleys that receive an excess of water due to run—off from the long slopes above. It would appear that the constant lateral passage of water through the gleyed lower profile of soils at shedding sites on steep slopes is leaching Mn, Co, Zn, Ni and Fe and removing these metals to receiving sites at the fell foot. The data in Table 34 are from soils developed exclusively on the Bowland Shales and Bowland Shale Drift in order to provide some continuity. It is expected, however, that metals removed from the intensely leached sandy soils on the Namurian scarp contribute to the accumulation in receiving sites. The soils of !normal' sites have a lower content of Mn, Co, Zn, Ni and Fe than the receiving sites although levels tend not to fall to those encountered in the shedding sites. The lowest Mn, Co and Zn values in the area of 'normal' sites tend to occur in gleyed soils on slopes where these metals are probably mobilised and leached into the drainage network by circulating groundwaters (see also Table 34 Range and meml* metEl content of soils from shedding sites and receiving sites on fell slopes and normal s7:tes on low angled slopes away from the fells _(,sample depth 12-18 inches)

Ni Ga pH Number of -Pee 2()3 Mn CoA Zn+ (o) (P.P.m.) (P.P-m.) (P.P.m.) (P.P.m.) (P.P.m.) samples

Shedding sites 3.8 88 45 56 15 15 5.1 12 (Upper fell slopes) 1.8-7.8 13-600 <5-10 <50-160 5-20 10-20 4.2-5.7

Receiving sites 5.6 3524 22 222 56 16 5.0 12 (Base of fell 4.4-10.5 2300-6000 6-40 50-500 20-160 13-30 4.3-5.8 slopes)

Normal sites 3.3 436 6 <50 22 16 4.9 22 (Low angle slopes) 1.6-5.4 30-4000 <5-40 <50-160 10-40 10-20 4.1-5.2

* Geometric mean A Mean calculated with <5 p.p.m. = 3 p.p.m. + Mean calculated with (50 = 40 p.p.m. 0 171 page 147). Horsnail (1968) working in North Wales and Devon reports a similar translocation of mobile metals (Mn, Co and Ni) on slopes into receiving sites. However, the contrast in metal values observed by Horsnail is not as large as those noted here although it must be considered that the angle of slope, severity of relief and rainfall in the areas studied by Horsnail are not as great as those of Bowland Forest. Despite the considerable influence of the secondary environment on the lateral distribution of the above metals there is no indication that Mo is involved in such processes.

(B) Vertical distribution Analytical data from soils under permanent pastures, sampled at depths of 0-6 inches and 12-18 inches, are summarised in Table 35. The generalised metal relationships may be summarised as follows. Levels of Mo, Cu, Ni and Fe tend to fall in topsoils (average x2), whilst values of Pb and Zn rise (up to x10). The distribution of Mn is erratic whilst for the remaining metals (Co, Cr, Ga, Ti and V) any variation observed is small and generally insignificant. The fall in levels of Mo, Cu, Ni and Fe between subsoils and topsoils is thought to be due to leaching. The greatest contrast tends to occur in better drained soils, as at site 3409, where the downward movement of water is most pronounced and conditions favour leaching. The moderately high pH of some topsoils (up to 6.8) favours the leaching of Mo Whilst the lower pH of subsoils is likely to lead to the immobilisation of Mo, leached from above, by sorbtion onto clay minerals or secondary oxides. Table 35 Range and mean* metal content of soils, sampled at two depths, developed on the •rincipal parent materials, Bcwland Forest area Sample depth Parent (ins) Metal content (p.p.m.) material (No. of MO Cu V Pb Ga Zn+ Ti Ni CoY Mn Cr Fe 0 % pH samples) 2 3 0-6 10 22 280 115 20 90 4200 28 6 380 107 4.1 5.9 6- 11- 130- 85- 16- <50- 3000- 16- <5- 60- 85- 1.9- 5.4- Bowland (8) 14 35 500 160 30 400 5000 40 20 850 130 7.8 6.4 Shale 12-18 34 41 288 44 20 76 5500 34 6 129 123 5.7 4.6 10- 20- 200- 20- 16- <50- 4000- 10- <5- 30- 100- 2.9- 3.9- (8) 85 83 300 160 30 300 6000 85 30 1000 130 9.8 5.4 0-6 8 22 150 160 12 340 4000 29 9 990 82 6.1 5.6 Bowland 2- 14- 85- 60- 13- <50- 3000- 20- <5- 50- 60- 2.6- 3.8- (12) 20 34 390 400 30 850 6000 100 30 4000 130 19.0 6.8 Shale Drift 12-18 13 25 170 47 15 176 4778 28 7 406 92 5.1 4.8 5- 13- 100- 30- 13- <50- 2000- 13- 5- 40- - 50- 2.2- 4.4- (12) 20 60 300 60 20 400 6000 85 20 1000 160 6.6 5.6 0-6 4 25 125 140 16 350 3900 46 12 1400 90 4.0 5.6 2- 13- 100- 100- 13- 200- 3000- 40- <5- 400- 60- 2.2- 5.0- Mixed (10) 5 35 160 160 20 500 4000 60 16 3000 130 4.8 6.4 Drift 12-18 5 44 116 72 16 340 4800 61 19 3100 102 6.4 5.0 2- 4.)- 85- 50- 13- 300- 4000- 30- 10- 500- 85- 4.7- 4.2- (10)• 8 50 200: 100 20 400 6000 85 -.:30- 6000 130 8.3 5.7 0-6 <2 11 140 88 17 100 4000 26 7 345 65 2.6 5.6 <'4 )- 130- 85- 13- 50- 3000- 20- <5- 130- 60- 2.5- 5.2- Barren (5) -2 14 160 100 20 200 5000 30 10 400 85 2.8 6.0 Sandy 0-6 . <2 7 70 29 18 145 /M OO 33 10 199 73 4.7 4.7 Drift <2 I.- 60- 13- 13- 50- 4000- .30- 6- 50- 50- 3.3- 4.4- (5) -3 12 85 50 20 300 5000 40 16 400 85 5.8 4.8

* Geometric mean + Mean calculated with <50 p.p.m. = 40 p.p.m. .6, Mean calculated with <2 p.p.m. = 1 p.p.m. Y Mean calculated with <5 p.p.m. = 3 p.p.m. Table 36 Metal content of selected molybdenum anomalous soils of varying rainage status, Bowland Forest ar.3a

Site no. and Sample parent Profile depth Metal content (p.p.m.) material drainage (ins) Mo Cu V Pb Ga Zn Ti Ni Co Mn Cr Fe203% pH

3409 Moderately df.ained C-6 10 35 160 130 16 400 4000 40 20 850 130 7.8 6.0 Bowland Shale (Mid slope) 12-18 20 85 300 30 16 300 4000 85 30 1000 130 9.8 5.0 3392 Moderately drained 0-6 2 13 130 100 16 200 4000 40 <5 400 100 2.2 6.4 Bowland Shale (Top of hill) 12-18 4 40 100 60 20 300 4000 50 10 500 100 6.2 5.4 Drift 3403 Poorly drained 0-6 12 28 160 160 30 100 4000 30 <5 160 130 3.2 5.4 Bowland Shale (Va1lcy floor) 12-18 13 40 200 50 16 60 5000 16 <5 50 130 4.3 4.4 Drift 174

Herbage/topsoil relationships (page 183) indicate that part of the No in topsoils is immobilised onto ferric oxides.

5. Relationships between the Metal Content of the Bedrock, Overburden and Stream Sediment The complex solid geology and extensive drift cover prevent a general appraisal of the rock, soil and stream sediment relationships in the Bowland Forest area. However, an examination of a single catchment area is instructive and, for the present discussion, Easington Brook, an east bank tributary of the River Hodder east of Slaidburn, is taken as the example. The mean metal content of the various media within the Easington Brook catchment is presented in Table 37, in which the soil data are subdivided according to parent naterial. The relationship between bedrock and soil is illustrated for the Bowland Shale Group in Table 37. However, the limited extent of residual soils in the Easington Brook catchment, developed principally over the P2 and lower El divisions of the Bowland Shale Group, mean that any interpretation based on the data in Table 37 cannot be wholly objective and is therefore not attempted. Nevertheless, the data gained from all the soil traverses, reported in Section 4,have shown that the bedrock is the major influence on the distribution of Mo, V, Cr, Cu and also Se in soils, with the highest levels of these metals occurring in soils developed on the metal—rich Bowland Shales and glacial drift, colluvium and alluvium derived from these shales. Furthermore, in soils derived from mixed parent materials, the Mo status appears to be roughly Table 37 Mean* metal content of rocks, soilsA and stream sediments+ in the Easington Brook qatchment. Bowland Forest area

Metal content (p.p.m.) Ab Cu V Pb Ga Zn Ti Ni Co Mn Cr Fe203%

Rocks Bowland Shale Group 13 72 275 52 12 554 1535 98 17 222 98 3.9 (26 samples) Worston Shale Group <2 35 56 21 7 60 712 53 10 319 49 1.8 (8 samples) Soils Residual on Millstone <2 13 30 55 6 :50 3500 12 <5 14 45 1.4 Grit (4 samples) Residual on'Dowland _31 36 255 42 19 94 5166 31 10 378 116 5.3 Shale Group (12 samples)

Drift Derived 11 30 172 48 16 125 5000 28 ,<5 380 96 4.4 (26 samples) All soils 16 30 182 47 16 108 4905 27 5 345 97 4.4 (42 samples) Stream sediments 6 samples) 6 42 117 27 14 942 4000 64 50 1283 75 5.1 * Geometric mean A Sample depth 12-18 inches + Data from minus 80—mesh fraction 176 proportional to the amount of Bowland Shale debris present. Table 37 shows that levels of Mo, Cr, Ga, Pb, Ti and V are lower in stream sediments than in associated soils. It is considered that these metals are, for the most part, distributed into the drainage network mechanically in fine grained detrital material with the fall in metal values being due to a dilution by metal—poor sandy material derived from the Millstone Grit and Fendleside Sandstone outcrops. The stream sediment reconnaissance survey (Ch. 8) reveals that the highest levels of Mo occur in streams with catchments developed solely on the Bowland Shale Group. Many of the sedimentain the Easington Brook streams contain appreciable amounts of sandy material, whilst the catchment includes large areas of Millstone Grit not fully represented by the limited number of soil samples taken in the area. In contrast, levels of Mn, Co, Ni and Zn are conspicuously enriched in stream sediments (x2—x10) with levels of Fe and Cu also higher in stream sediments than associated soils. The mobility of Mn, Co, Ni, Zn and Fe in soils has been demonstrated (page 169). It is considered that these metals are leached from the poorly drained soils which dominate the catchment areas,passing into the drainage network with circulating groundwaters (see also page 147). There is no evidence of Cu being mobilised in soils in the same manner as the above metals although the enrichment of Cu in stream sediments may be due to such leaching from soils with subsequent sorbtion onto secondary oxides in the drainage network. The mobility of Cu would be favoured by the modest pH (4.3_5.2) of soils and the sorbtion of Cu onto secondary Mn and Fe hydroxides in streams is noted by Goldschmidt (1954). Furthermore, 177

Horsnail (1968) notes the local mobilisation of Cu in poorly drained and gleyed soils developed on Culm shales in Devon followed by its deposition with secondary Mn and Fe oxides in drainage channels. The extensive mobilisation of Mn, Co, Ni, Zn and Fe in soils on long fell slopes and accumulation in sites at the foot of these slopes has been demonstrated. The relationship between soils and stream sedimentsat fell foot receiving sites and 'normal' sites is shown in Table 38 in which data from the Chipping district are presented. The relationship between soils and stream sediments is similar in both groups for the metals Mn, Ni and Fe althOugh Co and Zn levels are enhanced to a greater degree in stream sediment adjacent to 'normal! sites with values of Zn similar in both groups of stream sediments. It thus appears that in both 'normal' and receiving sites a similar pl-Dportion of the soil Mn, Ni and Fe makes its way into the stream sediment, although more Co and Zn is leached from !normal' soils. The very high levels of Mn in stream sediments noted earlier (Ch. 8) as occurring near the foot of the fells are thus :indicative of proximity to receiving site soils, whilst high levels in areas of 'normal' soils are due to increased leaching from very poorly drained soils. It is noteworthy that, in contrast to the data in Table 37, mean levels of Fe in the Chipping district are lower in stream sediments than adjacent soils. Goldschmidt (1954) and more recently Handa•(1970) report that Fe precipitates from solution in natural waters before Mn. Rankama and Sahama (1950) observe that Mn usually remains in solution until the bulk of Fe has precipitated, bringing about a separation of these metals. Streams in the Chipping district are invariably incised, contrasting with the Easington Brook catchment in Table 38 Mean* metal content of soil& and adjacent stream sediments+ at ?normal! and 'receiving' sites in the Chipping district, Bowland Forest area

Media Mn Fe203 Co Ni Zn Ga pH (No. of samples) p.p.m. % p.p.m. p.p.m. p.p.m. p.p.m.

Scils 112 3.3 <5 22 (50 16 4.9 (22) Normal sites Stream sediments 1093 2.3 31 46 522 9 7.4 (20)

Soils 3252 6.6 22 56 222 16 5.0 (1a) Receiving sites Stream sediments 8073 5.2 48 85 515 11 7.3 (10) * Geometric mean A Sample depth 12-18 inches + Data from minus 80-mesh fraction 179

which streams are only occasionally incised. It is considered that in both areas Mn and Fe are mobilised in poorly drained soils and translocated with groundwaters towards the drainage network. In the absence of further data it is suggested that in the Chipping district Fe precipitates close to the stream bank or in the better drained alluvial or colluvial soils adjacent to streams. Manganese remains with groundwaters to precipitate in the stream channel, becoming incorporated with active stream sediment. The rise in Fe levels between soil and stream sediment seen in the Easington Brook catchment is thus thought to reflect the increased redistribution of Fe in this area where waterlogged soils and associated Fe seepages are common alongside the streams.

6. Metal Content of Herbage and Factors Influencing the Uptake of Molybdenum and Copper by Herbae Analytical data from samples of topsoil and herbage, collected from areas defined as Mo anomalous and background by soil and stream sediment sampling, are summarised in Table 39. .:111 samples were taken in permanent pastures in which mixed grasses dominate, with clover occurring locally where the soil is least acid. Rushes are a common feature of the more poorly drained pastures and were included where present in the herbage samples. No samples were taken from moorland areas or on the open fells. The Mo and Cu status of herbage in the Chipping district has already been investigated (Morgan and Clegg, 1958). The present sampling programme thus concentrated on the north east portion of the Bowland Forest reconnaissance area and material was obtained from around Easington, Harrop and Table 39 Ilan-:e and mean* molybdenum and copper content of topsoiloA and associated herbage+ on soils derived from the principal parent materials in the BowlEnd Forest area

Mo status as defined -ay Mo(p.p.m.)Y Cu(p.p.m.) stream sediment End Parent soil sampling material Herbage Topsoil Herbage Topsoil

Bowland Shale 3.8 10 10.5 22 (8 samples) 1.0-5.6 7-14 7.5-18.5 11-26 Anomalous Bowland Shale Drift 3.3 8 12.0 22 (15 samples) 0.2-7.2 2-20 7.5-19.0 14-34 Mixed Drift 1.5 4 11.0 25 (10 samples) 0.8-2.6 2-5 5.5-22.5 13-35 b.... Barren Sandy Drift 0.9 1 10.7 11 Background (5 samples) 0.7-1.0 <1-2 8.0-13.5 9-14

* Arithmetic mean Mixed pasture herbage, oven dry weight

A Sample depth 0-6 inches '( Mean calculated with <1 p.p.m. = 0 p.p.m. 181

Bolton—by—Bowland (Fig. 36). Examination of Table 39 reveals that the Mo content of soils is reflected by the Mo status of herbage growing at the same sites, indicating that the increased quantities of Mo in anomalous soils are available to herbage. However, the contrast between the mean Co content of herbage on background and anomalous soils (x2—x4) is less than the contrast between topsoil values (x4—x100. Furthermore, the Mo content of herbage growing on anomalous soils is very variable. Thus, although the greater quantities of Mo present in the anomalous soils are reflected by increased levels of Mo in herbage, the uptake of Mo by herbage on No anomalous soils is limited to a varying degree. An increased uptake of Mo is seen in herbage growing on very poorly drained soils (Table 40) compared with moderately and poorly drained soils and herbage Ho exceeds total topsoil Mo in some cases. An increased uptake of Mo on very poorly drained soils has been reported by Lewis (1943), Mitchell et al (1957) and Kubota et al (1961, 1963). Examination of the data in Fig. 38 shows that, whilst no meaningful relationships are observed in..the plots for Ph and organic carbon, a broad inverse relationship exists between total Fe (expressed as Fe203) and Mo uptake by herbage. Two parallel trends are observed, dependent on the drainage status of the soil, with Mo uptake consistently greater from very poorly drained soils. The retention of Mo by ferric oxides in soils, in a form unavailable to herbage, has been reported by Ifells (1956) and Robinson and Edgington (1954). The limiting effect of Table 40 .d.anve and mean* molybdenum and copper content of herloceA on molybdenum anomalous soils+ of contrastinp drainal e status, Bowland Forest area

Mo(p.p.m.) Cu(p.p.m.) Drainage conditions Herbage Topsoil Herbage Topsoil

Moderate to poorly drained 3.5 10 10.3 22 samples;) 1.0-7.2 4-18 5.0-18.0 11-35

Very poorly drained 4.1 7 11.6 21 (7 samplec) 2.4-7.2 2-20 9.0-19.0 15-25

* met-1n A Mixed pasture herbage, oven dry weight Hample deptn 0-6 inches

12- 0

11- 0 + Molybdenum anomalous soils. 10- + 10 0 DI ii II very poorly drained. 9- Background soils. a- 0 a4 + 0 7- a + 0 .0 0 + 'a G- + 7- U 0 U + + + _ + + 0 + + + + 0 6- +4+ 0 + ti. al + + + (3'4- * + O + + + + + + + pH + • + + 5- + + 4' + + it + 0 0 + + + + + 0 o + + 3- • ++ . • + 4- +•;I- + . + + + • + + o + • 4. + + 0 + + . . + 2- + 1- 3-

I I i 1 I I 1 0.2 0.5 1.0 2.0 0.2 0.5 1.0 2.0 0.2 0.5 1.0 20 Herbage Mo/ Topsoil Mo Herbage Mo/ Topsoil Mo Herbage Mo! Topsoil Mo

Fig.38. Molybdenum Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil. (Topsoil,-0-6ins depth. Herbage-Oven dry weight)

Bowland Forest area. 183

increasing soil Fe on the uptake of Mo by herbage is thus considered to reflect the sorbtion of Mo onto secondary ferric oxides in topsoils. Jones (1957) and Reisenauer et al (1962) have shown that the amount of Mo sorbed onto ferric oxides decreases as the soil pH is raised. No such trend is observed in the present data and Mo thus appears to be relatively firmly bound in secondary ferric oxides. Molybdenum uptake is considerably increased on very poorly drained soils. It is possible that, due to waterlogging, reducing conditions prevail in these soils and that Mo, although still attracted by iron oxides, is only loosely bound with ferrous oxides. However, it is probable that ferric oxides are formed in these topsoils during periods When the groundwater table falls. Bloomfield (1963) has suggested that, once formed, a zone of hydrous ferric oxides would be able to convert ferrous ions to the ferric oxides on which Mo is very readily adsorbed (Wells, 1956, Jones, 1957). In the present circumstances it is probable that the formation of 'aged' ferric oxides in which Mo is firmly (Wells, 1956) is prevented due to the frequent waterlogging of these soils. The increased uptake appears to be due simply to the absence of a fixing agent for the trend in Fig. 38 is unrelated to organic matter and pH has no modifying influence over the range pH 3.8-6.8. Fletcher (1968) working in the South Pennines on very similar soils also found that the uptake of Mo by herbage is limited by the immobilisation of Mo onto secondary iron oxides in topsoils. However, he did not find any clear evidence of increased Mo uptake by herbage on very poorly drained soils. 12- 0

11- 11- 0 + Molybdenum anomalous soils. 10- 10- 0 48 01 very poorly drained. 9- 9- Background soils.

8- 8- 0 si —7^ 7-

0 0 7- '61 6- 0 OC') 6 + + + + 4.0 + + 5 5- ++ 6- ++4j. +++430 0+ + + 4- + 0 4- 5- + 0 0 + + + 0 + • + 3- • • 3- + 4- + * • .4. • 0 ++ 0 -v" 2- 2- 3-

I 1 1 0.2 0.5 1.0 2.0 0.2 0.5 1.0 2.0 0.2 0.5 1.0 2.0 Herbage Cu/ Topsoil Cu Herbage Cu! Topsoil Cu Herbage Cu/ Topsoil Cu

Fig.39. Copper Content of Pasture Herbage in Relation to the . pH, Iron and Organic Carbon Content of the Topsoil. (Topsoil 0-6 ins depth. Herbage -Oven dry weight.)

Bowland Forest area. 184

In Co. Limerick, South West Ireland, Webb and Atkinson (1965) and Atkinson (1967) record values of herbage Mo equal to or in excess of total soil Mo levels. Fletcher (1968) attributes this high rate of uptake to the conditions produced in soils developed on drift in which molybdeniferous black shale and limestone debris are intermixed. In the Bowland Forest area Earp et al (1961) recognise trains of drift containing a mixture of material derived from the Bowland Shales and the calcareous Worston Shales. There is, however, no evidence from the present study of increased Mo uptake by herbage on soils developed from this type of drift. This lack of increased uptake, as in the South Pennines (Fletcher, 1968) is most probably a result of the decalcification of soils, particularly the B horizon, due to leaching. Unlike the soils of Co. Limerick which are both calcareous and alkaline (Atkinson, 1967), the lower horizons of soils in the Bowland Forest area are uniformly acid or slightly acid (pH 3.8-6.8). The mean Cu status of herbage is similar on both background and anomalous soils despite a x2 increase in the Cu content of soils with anomalous levels of Mo. An examination of environmental factors likely to affect the uptake of Cu by herbage reveals no conclusive evidence that the drainage status, pH, organic carbon or total Fe content of topsoils have any influence (Fig. 39). 185

CHAPTER 15: DETAITRD GEOCHEMICAL INVESTIGATIONS SHAFTESBURY AREA

1. Introduction Stream sediment reconnaissance in the area (Ch. 9) reveals anomalous lovels of Mo (3-13p.p.m.) throughout the outcrop of the Kimmeridge Clay. The zone delineated is extensive, covering some 22 square miles. Further localised sediment anomalies (3-6 p.p.m. Mo) occur north and south of Wincanton in streams draining the Oxford Clay formation.

2. Description of the Area The main features of the reconnaissance area are outlined in Chapter 9. More detailed information on the geology of the Kimmeridge Clay and the soils of the area is now given to aid the interpretation of the geochemical data.

(A) Geology The geological succession, summarised in Table 16, includes Mesozoic limestones, impure limestones, clays, shales and sandstones. Bituminous shales are probably present in the Lower Oxford Clay (page 88 ). A more considerable development of clays and shales of black shale facies occurs in the Kimmeridge Clay. Due to the very few exposures of the Kimmeridge Clay formation in the Shaftesbury area, it has not been' possible to construct the detailed succession in this district. However, Downie and Wilson (1968) suggest that the Kimmeridge Clay succession, although thinner than on the Dorset coast, is essentially similar to that of Kimmeridge Bay (Arkell, 1947b). 186

Thus, above a thin transition series of calcareous clays which succeeds the Corallian limestones, there is a thick sequence of carbonaceous clays and bituminous shales, with oil shales in the middle of the formation. This is followed by further bituminous shales with calcareous clays beneath an extended upper transition sequence of calcareous silts and clays underlying the Portland. Dunn (pers. comm.) reports that on the Dorset coast raised levels of Mo (> 3 p.p.m.) characterise the organic rich horizons of the Kimmeridge Clay with up to 50 p.p.m. Mo in oil shales. In contrast, No values fall to background (< 2 p.p.m.) in calcareous clays and silts low in organic matter. Deposition of the Kinneridge Clay is thought to have taken place in a depth of 40-100 feet of quiet water on an extensive shallow shelf in which wave energy was dissipated offshore, thus allowing anaerobic conditions to develop (Downie and Wilson, 1968). Anaerobism is evidenced by an impoverished benthonic fauna and the accumulation of both organic matter and pyrite in the sediments. Considerable quantities of organic matter are present (up to 70% in the oil shales) and pyrite is common, both occurring finely dispersed in the clays and shales. The organic matter is largely of terrigenous origin, resembling lignite in composition, although microplankton debris is also found (Downie and Wilson, 1968).

(B) Soils The dominant soils on both the Oxford and Kimmeridge Clay outcrops are slightly acid surface—water gleys of the Denchworth Series (Robinson, 1948). Soils are typically 187 residual and, except on steep slopes, there has been little mechanical redistribution of weathering products (Robinson, 1946). On both the Oxford and Kimmeridge Clay, samples at 12-18 inches depth showed the soils to be typically weakly calcareous. However, liberal use of lime as a topsoil dressing has elevated the pH of many topsoils to anomalously high levels (pH +6.5). Soils on the clay vales are uniformly poorly drained and many sites have seasonal waterlogging. Soils on the Mid Jurassic, Corallian, Portland and Purbeck are light to heavy loans, usually alkaline, derived from mixed limestones, with local areas of clay loam over marls and clays. Over the Mid Jurassic soils tend to be well drained, whilst the Corallian supports soils that are typically deep, free draining sandy clay loans. Where sampled, the Portland and Purbeck formations carry free draining sandy clay loans, with drainage becoming excessive on the upper part of scarp slopes. Narrow zones of mixed soils are found at the margins of the clay vales. These arise from the mixing of locally derived clay with exotic material washed down from the limestone and sandstone scarps. Beside some of the larger streams and small rivers are alluvial areas with silty or clay silt groundwater gleys.

(C) Land Use The patterns of land use are described in Chapter 9. 188

3. Distribution of Metals in the Bedrock The area is noteworthy for its lack of bedrock exposures. The Oxford and Kimmeridge Clay formations are usually revealed only in temporary excavations, whilst the limestones and sandstones are seen in badly weathered sections in disused quarries and overgrown roadsides. Chip samples were obtained from the principal bedrock units, with the exception of the Oxford Clay. The location of the sample sites is shown in Fig. 40 and the analytical data in Table 41. It can be seen that the Kimmeridge Clay sample obtained, in a badly weathered condition from near the mid part of the succession, contains raised levels of Mo (12 p.p.m.) and Se (1.5 p.p.m.) and also appreciable amounts of organic carbon. In contrast the other rocks sampled contain very small amounts of organic carbon and both Mo and Se are undetected. Furthermore, the overall metal content of the clay is very much greater than that of the nearby limestones and sandstones, with the exception of Mn and possibly Co. It is not possible to draw extensive conclusions as to the distribution of metals in the bedrock from these few samples. Nevertheless the presence of raised levels of Mo and Se in the Kimmeridge Clay, a formation of black shale facies, is established. In addition, the contrast in metal content between the Kimmeridge Clay and the limestones and sandstones is in accordance with the distribution of metals amongst sedimentary rocks noted by Turekian and Wedepohl (1961).

4. Distribution of Metals in the Overburden Soils samples were taken at 200 to 1000 foot intervals Table 41 Metal content of bedrock samples from the Shaftesbury survey area

Formation and Metal content (p.p.m.) Samiae lithology No. Ho Cu Se V Pb Ga Zn Ti Ni Co Mn Cr As Org.C.% Fe203%

Upper Greensand 3260 <2 4 <0.2 40 3 5 <50 300 16 13 30 30 <5 <0.1 3.1 Glauconitic sandstcne 3264 .Z2- 8 <0.2 40 13 3 (50 600 8 C5 160 16 :5 0.1 2.0 Portland limestone 3'c65 <2 6 <0.2 30 2 ('.2 (50 50 <5 <5 160 3 :5 <0.1 1.3 Fine grained shell 3266 <2 5 (0.2 40 6 <2 :50 130 <5 (5 200 4 (5 0.3 1.2 limestone ---- Kimmeride Clay Blue black shaley '239 12 43 1.5 130 30 16 50 3000 50 10 160 100 <5 3.8 4.0 clay Corallian Limestone :)263 <2 5 <0.2 50 3 <2 <50 60 10 :5 500 10 5 0.1 1.3 Shelly oolitic .26. c.2 6 ;.0.2 50 2 <2 <50 85 10 5 600 13 <5 <0.1 1.4 limestone 3L,51 :2 6 <0.2 50 3 <2 50 100 5 <5 400 6 5 <0.1 1.8 Forest Marble 3263 <2 8 :0.2 40 2 <2 :50 50 "-r.5 5 300 (2 <5 <0.1 1.3 Very coarse, flaggy ,_677 <2 9 :0.2 30 10 <2 <50 60 :5 <5 400 (2 <5 (0.1 1.4 shelly limestone hattesbury.

Key to Rock Samples. td L Forest Marble. 0 1 2 Molybdenum 2. CoraUlan. 4 Portland Lstn. stream sediment anomaly. + Rock Sampling Point. 3. Kimmeridge Clay. 5. Upper Greensand. Scale in Miles.

Fig.40. Location of Soil Traverse Lines and Rock Sampling Points in Relation to the Molybdenum Stream Sediment Anomalies in the Shaftesbury Survey Area 190 along traverse lines crossing the outcrops of the Oxford Clay and Kimmeridge Clay and adjacent formations. The traverses, shown in Figs. 40, T5 and T6, are orientated perpendicular to the strike of the geology in order to reveal any stratigraphic control on the distribution of No in the area. To simplify discussion on metal distributions the data from traverses crossing the Oxford Clay (Fig. T5) and the Kimmeridge Clay (Fig. T6)are considered separately. Jnalytical data from soils developed on the principal parent materials are summarised in Table 42.

(A) Overburden derived from the Oxford Clay and adjacent deposits (i) Lateral distribution Anomalous levels of Mo 3 p.p.m.) are found in soils derived from the Mid Jurassic rocks on Traverse 1 and the Lower Oxford Clay on Traverses 1 and 2 (Fig. T5); elsewhere background levels of Mo ((2 p.p.m.) are encountered. From 3-5 p.p.m. Mo is recorded in soils derived from the Cornbrash on Traverse 1; however, to the south Mo is undetected 2 p.p.m.) in soils over the same horizons on Traverse 2. The source of these anomalous concentrations of Mo is considered to be dark clays in the Cornbrash, reported in this area by Woodward (1895). On the Oxford Clay anomalous levels of Mo (3-16 p.p.m. are accompanied by slightly raised levels of Cu, V and Cr. The No anomaly occupies a narrow zone over the lower part of the Oxford Clay. From the width of the zone it is estimated that some 120 feet of Mo—rich bedrock is present. Table 42 Range an(1. moar*. _metal content of overburden developed on the dncipal parent materials Shaftesbury area (sample depth 12-18 inches)

Metal content (p.p.m.) Parent material MoA Cu V Pb Ga Zn+ Ti Nil' Cer Mn Cyr Pe 203e Residual soils Greensana <2 . 9 40 40 8 <50 3000 5 <5 225 40 3.0 8- 30- 30- 5- <50 (5 50- <2 3000 5 30- 2.9- (2 samples) 10 50 50 10 -50 -5 400 50 3.1 Portland and Purbeck <2 10 68 20 9 54 2213 17 5 220 65 6.1 <2 4- 50- 10- 5- <50- 2000- 8- <5- 60- 50- 3.2- (8 samples) -2 20 100 40 13 200 3000 40 10 500 85 7.4 Kimmeridge Clay 4 20 139 27 19 58 5231 27 7 152 107 5.6 <2- 5- 60- 13- 13- <50- 3000- 10- <5- 40- 60- 2.7- (71 samples) 20 60 300 50 40 300 1% 85 50 500 200 17.0 Corallian Limestonc3 .:2, 20 134 28 9 84 2212 34 15 593 66 5.5 (2 13- 50- 13- 6- <50- 1300- 10- <5- 100- 40- 3.3- (14 samples) -3 85 300 85 13 300 4000 60 30 3000 100 14.6 Oxford Clay 2 18 116 26 17 106 3477 32 12 292 98 5.6 <2- 8- 60- 13- 10- <50- 1600 <5- <5- 85- 50- 3.4- (15 samples) 16 40 300 130 30 200 5000 60 100 2000 300 9.8 _ Cornbrash Limestoneq <2 22 138 36 15 121 3593 31 17 1424 119 6.9 <2 16- 60- 13- 13- 50- 3000- 10- 8- '3000- 60- 3.8- (14 samples) -5 40 300 60 20 300 5000 40' 30 5000 200 9.2 Mixed and Alluvial soils Mixed soils on 2 14 83 23 15 56 4042 21 6 193 87 5.4 Kimmeridge Clay <2 8- 60- 13- 8- <50- 2000- 13- <5- 50- 60- 2.8- (14 samples) -5 20 130 40 20 100 6000 40 20 850 130 7.5 Mixed Oxford Clay and <2 5 53 19 10 53 3641 8 5 96 66 3.2 Greensand <2 2- 20- 13- 4- <50- 2000- <5— <5- 30- 40- 1.2- (5 samples) 8 100 40 16 160 5000 20 20 400 100 7.8 Alluvium on KiLAierid -re 6 19 166 24 18 104 6020 38 12 258 149 6.8 Clay <2- 16- 130- 20- 16- K50- 4000- 30- 6- 60- 60- 5.2- (5 samples) 13 60 200 30 30 200 8500 40 30 500 200 10.2

Geometric mean except P arithmetic mean • A Mean calculatea. with CL p.p.m. = 1 p.p.m.

Mean calculated with <5) p.p.m. = 40 p.p.m. H Y Mean calculated with :5 p.p.m. = 3 p.p.m. 192

This figure compares well with the thickness of 140 feet of bituminous shales in the Lower Oxford Clay of this district based on data from published sections (page 88 ). The coincidence of the anomaly with the probable outcrop of bituminous shales and the absence of any environmental control on the distribution of Mo suggests in situ elastic dispersion of Mo brought about by weathering of Mo—rich bLack shale parent material. Although anomalous levels of Mo are of restricted occurrence, relatively high levels of V ( )160 p.p.m.) are found elsewhere on the outcrop of the Oxford Clay suggesting further V—rich horizons in the bedrock. The zone of Mo anomalous soils, although narrow, appears to be persistent along the strike of the Lower Oxford Clay attaining a width of one mile on Traverse 2. Within the reconnaissance area a total of Ti square miles of Mo anomalous soils derived from bituminous shales of the Lower Oxford Clay are envisaged. The fall in values of Cu, Cr, Ni, V and also Ga and Ti at the east and of Traverse 1 occurs in broken ground below the Upper Greensand scarp where considerable colluvial downwash of metal poor sands has mixed with Oxford Clay material in soils, thereby suppressing metal values. Manganese, Co, Fe and Zn display a similar distribution with high values in soils derived from limestones and erratic levels in soils on the Oxford Clay (Fig. T5 and Table 42). On Traverse 1 the rise in levels of Mn, Co and Zn in hollows below the Greensand scarp is thought to be due to the accumulation of these metals, leached from poorly drained soils on the slopes above in a manner similar to that observed in the Bowland Forest area (page 169). On Traverse 2 Mn, Co, Fe and Zn levels 193 are high in soils on the limestones, falling to low values in very poorly drained clay soils at the margins of the vale, then rising to high values again in similar soils on the lowlying ground in the middle of the vale.

(ii) Vertical distribution Data from soils on the Oxford Clay and Cornbrash sampled at depths of 0-6 inches and 12-18 inches are summarised in Table 43. In soils derived from the Cornbrash such contrast in metal values between topsoils and subsoils as is seen is of doubtful significance in view of the low precision of the analytical techniques. Copper is depleted from a number of topsoils, presumably due to leaching. Molybdenum is usually very suseptible to leaching from topsoils (page 266) It is suggested that the similarity of topsoil and subsoil values is due, at least in part, to the immobilisation of Mo in free drained topsoils by sorbtion onto secondary ferric oxides. Soils on the Oxford Clay display a general tendency for levels of No, Cu and Fe to fall in topsoils, although in several cases this is of doubtful significance. The contrast between topsoils and subsoils displayed by the remaining metals is usually insignificant although Pb levels are enhanced (up to x2) in some topsoils. Such depletion of topsoil values as is observed is attributable to leaching with the impervious clay soil and high groundwater table inhibiting the downward movement of metals,although Mo may be ±etained with ferric oxides or organic matter in topsoils (see following section).

Table 43 Range and mean* metal content of soils sampled at two depths, developed on the principal :rent materials Shaftesbury area Sample depth Parent (ins) Metal content (p.p.m.) material (No. of sampleL) Mod Ou . V Pb Ga Zn+ Ti Ni Coy Mn Cr Fe2 03 ' pH 0-6 3 18 138 57 20 84 5500 25 6 230 71 3.9 6.4 (2- 11- 85- 30- 13- (50- 3000- 13- t5- 100- 50- 2.9- 5.3- Kimmeridge (30) 10) 40 200 100 30 200 8500 '40 13 850 130 5.8 7.8 Clay 12-18 6 22 152 30 22 77 5914 28 6 168 133 6.7 5.8 (2- 10- 85- 13- 13- (50- 3000- 10- :5- 40- 50- 3.2- 4.8- (30) le 60 300 60 40 300 8500 50 10 400 200 18.4 6.3 0-6 17 145 62 11 125 3500 34 12 820 57 5.2 6.6 2 11- 100 - 50- 8- (50- 3000- 16- <5- 85- 40- 5.2- 5.1- (11) -2 26 300 130 16 300 5000 85 30 5000 85 9.9 7.4 Corallian 12-18 <2 25 141 29 10 97 2409 28 16 841 72 5.7 6.6 <2 13- 60- 16- 6- (50- 1300- 20- (5- 100- 50- 3.4- 5.8- (11) -3 85 300 85 13 300 4000 60 30 3000 100 14.6 7.9 0-6 3 18 115 54 17 175 4700 23 8 320 88 4.3 6.3 ,..52 10- 100- 40- 10- 30 - 4000, 16- <5- 130- 60- 2.9- 5.4- (10) Oxford - 25 160 85 30 300 - 6000 30 13 600 160 5.4 7.8 Clay 12-18 4 23 113 33 25 157 45 00 34 21 405 133 6.7- 5.9 (2- 8- 85- 16- 16- 60- 3000- 13- 5- 85- 60- 3.4- 5.2- (10) 13 50 200 40 _ 40 200 5000 60 30 1000 300 9.2 7.4

0-6 3 17 140 50 14 150 4700 28 12 1190 100 7.4 5.8 2- 15- 130- 40- 13 - 100 - 4000- 20- 5- 160- 100 4.4 - 5.4 - (4) 4 20 160 60 16 200 5000 30 16 3000 9.8 6.6 CornbrashP 12-18 3 ?4 190 28 16 110 4250 40 17 2150 157 7.1 6.3 2 16- 100- 13- 13 - 50- 4000- 10- 8-- 300- 100 - 3.8 - 6.0- (4) -5 40 300 50 20 160 5000 50 20 4000 200 9.2 6.6

Geometric mean except p arihmetic mean + Mean calculated with (50 p.p.m. = 40 p.p.m. A Mean calculated with <2 11.7).2. = 1 p.p.m. Y Mean calculated with <5 p.p.m. = 3 p.p.m. 195

(B) Overburden derived from the Kimmeridge Clay and adjacent deposits (i) Lateral distribution (a) Metal distribution patterns related to the bedrock Anomalous levels of Mo (3-30 p.p.m.) occur in residual and mixed soils developed on the Kimmeridge Clay and also in alluvium derived from the outcrop of the formation (Table 42 and Fig. T6). Anomalous levels of Mo occur right across the outcrop of the Kimmeridge Clay indicating that the bulk of the bedrock succession is Mo—rich. The raised levels of Mo are accompanied by enhanced values of Cr, V and Fe in soils derived from the Clay. In contrast, soils developed on the Corallian and on the Portland and Purbeck formations contain background levels of Mo (< 2-3 p.p.m.) and lower ralues of Cr, although mean values for V and Fe are similar in all three groups (Table 42). A soil traverse from west to east across the Kimmeridge Clay outcrop mimics a traverse up the stratigraphic succession whereupon the distribution of Mo is found to follow closely the suggested lithological succession in the area (see page 185). Over the far western outcrop of the Kimmeridge Clay is a zone of soils containing background levels of Mo (<3 p.p.m.) which would correspond to the lower transition zone. Moving east the broad zone of consistently Mo anomalous soils (up to 20 p.p.m. Mo) on both Traverses 3 and 4 is thought to be derived from the outcrop of the thick bituminous shale and oil shale sequence. To the east of this the zone of discontinuous No anomalous soils would correspond to the upper mixed sequence of bituminous shales and barren calcareous clays. Finally in 196 the far east of the vale Mo values fall to background over the outcrop of the upper transition series beneath the Portland formation. The distribution of Mo appears to follow the anticipated occurrence of major black shale units in the bedrock and parent material is thus emphasised as the dominant control on the distribution of No in the Shaftesbury area. Furthermore, the common distribution of Cr, V and less distinctly Fe with Mo in residual soils derived from the Kimmeridge Clay (Fig. T6) is thought to reflect the metal associations present in the bedrock. Not only does the stratigraphic succession appear to be similar to that on the Dorset coast but Mo levels in soils in the Shaftesbury area are similar to those in bedrock samples from the Kimmeridge Bay section (pers. comm. C. Dunn). The Kimmeridge Clay formation thus probably displays similar lithological and geochemical characters in North and South Devon. The distribution of the remaining metals in soils derived from the Corallian, Kimmeridge Clay, Portland and Purbeck formations is summarised in Table 42. The low metal values in mixed Kimmeridge Clay soils are partly the result of naturally low metal values inherited from the bedrock in the far east of the Kimmeridge Clay outcrop. However, metal values are further suppressed by the considerable colluvial downwash of metal poor limestone debris from the Portland and Purbeck escarpment (FIg. T6). (b) Metal distribution patterns related to the second environment The distribution of Mn and Co along Traverses 3 and 4 (Fig. T6) is largely coincident with both metals showing 197 a common response to environmental circumstances. Values of Mn and Co are high in the free drained soils derived from the Corallian. Here Mn is probably immobilised as an oxide onto which Co is scavenged. On the Portland and Purbeck scarp, however, excessive drainage appears to have resulted in the leaching of Mn and Co from some sites (Fig. T6). Over the Clay vale, values of Mn and Co fluctuate rapidly in response to local environmental conditions. Manganese and Co levels are high in soils on slight eminences and slopes, falling off in very poorly drained soils in hollows, on level ground and in alluvial sites. In many of the sites where Mn and Co values are low, Zn values also fall. It is suggested that on slopes and eminences the impervious nature of the clay soils results in most of the rainfall passing away in overland flow and, although the soils are invariably gleyed with Mn and Co mobile, there is little circulation of groundwaters to translocate these metals.

(ii) Vertical distribution Data in Tables 43 and 44 reveal that in soils developed on the Kimmeridge Clay levels of Mo, Cu, Cr and Fe tend to be lower in topsoils than subsoils, whilst levels of Pb, Zn and Mn tend to be higher in topsoils. The contrast observed between topsoil and subsoil levels of the remaining metals is always insignificant. The lower topsoil levels of Mo, Cu, Cr and Fe are thought to be due to leaching of metals into lower horizons of the soil. Molybdenum usually displays the greatest contrast between topsoil and subsoil (up to x6) and this is

Table 44 Metal content of selected residual soils developed on the Kimmeridge Claz

2ample Site Profile depth Metal content (p.p.m.) No. drainaga (ins) Mo Cu V Pb Ga Zn Ti Ni Co Mn Cr Fe203% pH

3207 Very poorly drained 0-6 3 16 200 85 20 50 6000 30 5 100 85 3.7 7.1 (Top of low rise on 12-18 8 20 200 50 30 130 6000 30 5 85 200 12.4 6.4 floor of vale) 3209 Very poorly drained 0-6 5 20 200 50 30 100 6000 30 10 200 100 4.8 6.6 (Mid slope) 12-18 16 30 300 40 30 50 6000 40 6 60 200 10.9 5.4 3243 Very poorly drained 0-6 2 11 130 50 13 50 4000 13 6 160 60 3.2 6.9 (Top of steep slope) 12-18 6 16 130 20 16 50 5000 30 10 160 130 5.8 6.0 3216 Very poorly drained 0-6 3 16 130 85 20 50 5000 30 8 130 60 2.9 5.7 (Hollow on hilltop) 12-18 2 16 100 40 20 60 6000 20 .C5 100 130 5.1 5.2 3214 Very poorly drained 0-6 4 16 160 50 20 50 5000 30 <5 200 85 3.6 5.9 (Levelground near 12-18 6 30 200 50 30 400 8500 30 5 300 130 7.0 5.6 stream) 3235 Very poorly drained 0-6 10 20 130 50 20 60 5000 20 10 300 85 4.3 6.0 (Waterlogged) (Hollow on floor of 12-18 8 16 130 20 16 <50 4000 20 8 100 100 4.1 4.9 vale) 199 thought to reflect increased leaching from topsoils, favoured by the relatively neutral pFrof tapsoils.(mean pH 6.6). At a number of sites, despite a moderately high topsoil pH,the contrast between topsoil and subsoil levels of Mo, Cu, Cr and Fe is often insignificant. Both profile and site drainage at these sites tends to be poor and the potential for leaching much reduced. Herbage/topsoil relationships (page 207) suggest that in topsoils part of the labile Mo and Cu is associated with organic matter and it is possible that these metals are retained in topsoils in this combination. Molybdenum is possibly also retained in topsoils by fixation with ferric oxides and the low contrast at very poorly drained sites is perhaps due in part to the retention of Mo by active ferric oxides in soils suffering periodic waterlogging, as described by Robinson and Edgington (1954). Data from residual soils on the Corallian, summarised in Table 43, reveal relatively small variation between topsoil and subsoil levels of all metals except Pb and Cu. Samples of topsoil and subsoil were found to be texturally very similar, apart from the presence of organic matter in the topsoils. It is suspected, however, that a marked rise in levels of many metals will be encountered at a depth of 18-30 inches. The upper 18 inches of the majority of soils sampled are eluviated and a perceptible textural change begins between 15-18 inches with clay increasing as the illuvial portion of these deep free drained soils is approached. 200

5. Relationships between the Metal Content of the Bedrock, Overburden and Stream Sediment The few rock samples, and hence the limited amount of analytical data, preclude a full assessment of the relationship between the metal content of rocks and soils. However, one feature is apparent from an examination of the data in Tables 41 and 42. The strong contrast in metal values between limestone and Kimmeridge Clay displayed by rock samples is much reduced in soils derived from these parent materials. This is considered to be the result of soil forming processes operative on the limestones. Calcium carbonate, which forms the major part of the bedrock, is removed in solution during weathering to leave the insoluble clay and detrital mineral content of the parent material with which the bulk of the trace elements are associated. The solution of CaCO thus brings about a concentration 3 of metal rich insoluble detritus, thereby reducing the contrast in metal values between soils derived from the limestone and Kimmeridge Clay formations. The preferential removal of CaCO3 from the free drained limestone derived soils also leads to the accumulation of Mn and Fe which are immobilised in the oxidising environment and retained probably as hydrous oxides. In the Shaftesbury area Mo anomalous soils are restricted to overburden derived from black shale bedrock. In addition the common distribution of Mo with Cr, V and Fe in residual soils derived from the clay is regarded as reflecting the metal association of the bedrock. Furthermore, the distribution of these metals is independent of environmental circumstances. The dispersion of Mo and 201 associated metals in the overburden is thus considered to be dominantly elastic brought about by the weathering of Mo—rich black shale bedrock and it is probable that Mo, Cu and V values are similar in bedrock and residual overburden. The relationship between the metal content of soils and stream sediments is summarised in Table 45. It is noted in Chapter 9 that a strong contrast exists between the metal content of stream sediment derived from the outcrops of the Mid Jurassic and Corallian limestones and the Oxford and Kimmeridge Clays, with the limestone derived sediments relatively low in Cr, Cu, Ga, Ti, V, Zn and Fe. However, as noted above, although such a contrast exists in the bedrock, it is present in the soils at a much reduced level. There is thus•.a fall in metal values between soils and stream sediment derived from the Mid Jurassic limestones and, to a lesser extent,' the Corallian. This is attributed to the dilution of stream sediment by

CaCO3, barren of trace elements, precipitated from solution in groundwater s on entering the drainage network, a phenomenon previously encountered by Thornton (1968) in areas underlain by similar Mid and Upper Jurassic limestone s. The precipitation of CaCO3 as tufa is a conspicuous feature of many streams on the lime stone outcrops in the Shaftesbury area (page 90 ) . The spread of this metal poor stream sediment down—drainage onto the out crop of the Oxford Clay, and parts of the western margin of the Kinneridge Clay results in stream sediment values being lower than adjacent soil values. Thus the Mo anomaly present in soils south of Wincanton is suppressed in adjacent stream sediments. To the north of Wincanton the MO anomaly found in soils over Table 45 Mean* metal content of soilsA and stream sediments+ on the princlpal bedrock units in the Shaftesbury area ,Parent Media Metal content (p.p.m.) (No. of Material Mo Cu V Pb Ga Zn Ti Ni Co Mn Cr Pe203%

Soils 4 19 132 26 18 60 5090 27 7 164 106 5.1 (90) Kimmeridze Stream 2 35 105 24 15 244 4300 44 52 319 91 5.6 Clay sediments (6G) Soils <2 20 134 28 9 84 2221 34 15 539 66 5.5 (14) Corallian Stream <2 14 59 13 7 148 2400 32 28 442 53 3.5 sediments (11) Soils <2 17 108 25 17 101 3943 29 11 272 95 5.4 (50) Oxford Clay Stream '2 28 73 20 13 228 3520 42 34 571 73 5.8 sediments (3A) Soils (2 22 138 36 15 121 3593 31 17 1424 119 6.9 (14) Middle Jurassic Stream <2 18 49 16 9 114 2340 35 26 64.1 - 49 3.1 sediments (22) * Geometric mean A Sample depth 12-18 inches 4 Data from minus BO—mesh fraction 203 the Lower Oxford Clay is present only in streams with catchments wholly on the Oxford Clay, with the stream sediment Mo anomaly apparently displaced some 1-2 miles east of its position in soils. With respect to the Kimmeridge Clay, there is a fall in levels of Mo, V, Cr, Ga and Ti between soils and stream sediments. This is attributed, again, to the dilution of stream sediment by detritus of a low metal content derived in this case from the Chalk and Greensand whereon the majority of streams traversing the Kipifieridge Clay originate. Thus, although the Mo anomaly confirmed in soils is clearly displayed in stream sediments, values in sediments, with the exception of streams originating wholly on the Clay as around Knoyle (Fig.40 ) are typically lower than in adjacent soils. The above features, together with the absence of any evidence of the distribution of Mo in stream sediment being influenced by the secondary environment, indicate that the mechanical transport of Mo—rich detrital material derived from a Mo—rich black shale parent material is the mechanism whereby Mo is dispersed from rock to soil and into the drainage network in the Shaftesbury area. Similarly, it is concluded that in both limestone and cray districts V, Cr, Ga and Ti are dispersed mechanically from soil to stream sediment with detrital material. In areas underlain by the Oxford and Kimmeridge Clay formations levels of Co, Cu, Fe, Mn, Ni and Zn are higher (x2—x5) in stream sediments than associated soils. Manganese, together with Co, Zn and Fe are probably mobilised in the gleyed soils on the clay vales and leached with circulating groundwatsrs into the drainage network 204 (see page 147). However, although the soil traverses reveal some evidence of the mobilisation of Mn, Co, Zn and locally Fe in subsoils, no similar patterns were found for Cu and Ni, despite the fact that the present relationship suggests that the latter metals may be so mobilised. Nevertheless, Horsnail (1968) reports the local mobilisation of Cu and Ni in very poorly drained soils and their translocation into the drainage network. This process may be operative here with the wide spaced soil sampling unable to identify the local redistribution of Cu within the overburden.

6. Metal Content of Herbage and Factors Influencing the Uptake of Molybdenum and Copper by Herbage The Mo and Cu content of herbage and associated topsoils at Mo anomalous and background sites on the various parent materials is suHliarised in Table 46. The herbage samples were all taken in permanent pastures and consist of mixed pasture grasses and clover, which is locally abundant. The data reveal that, with the exception of sites on the Cornbrash, soils with raised levels of Mo support herbage containing enhanced levels of Mo. Thus the increased amounts of Mo in the anomalous soils are generally available to the herbage. In contrast, mean levels of soil and herbage Cu are similar in all groups identified in Table 46. The relatively few samples taken on the Cornbrash and Oxford Clay prevent a full assessment of factors influencing the uptake of Mo and Cu. However, it is thought that the low levels of Mo in herbage on the Corallian (low when compared to other anomalous sites in the Shaftesbury area) Table 45. Range Pni_mean* molybdenum and copper content of to soils' and associated harbage+ on soils derived from the principal parent mate:2islc in the Shafteaur area

Mo status as defiacd by Mo(p.p.m.)Y Cu(P.1"m°) stream sediment and Parent soil sampling material Herbage Topsoil Herbage Topsoil Kimmeridge Clay 2.4 3 9.9 18 (30 samples) 0.6-6.4 <1-10 6.5-16.0 11-40 Lower Oxford Clay 2.5 4 7.6 19 Anomalous (5 samples) 2.1-2.8 2-6 6.5-9.0 15-25 Cornbrash 0.7 3 7.5 17 (4 samples) 0.5-1.4 2-4 5.5-9.0 15-25 Corallian 0.8 <1 7.6 17 (11 samples) 0.2-2.4 <1-3 4.0-13.5 11-26 Background Upper Oxford Clay 0.5 <1 7.0 14 (5 samples) 0.2-0.9 <1-2 4.0-9.0 10-21

* Geometric man + Mixed pasture herbage, oven dry weight Sample depth 0-6 inch3s Y Mean calculated with (1 p.p.m. = 0 p.p.m. (\)

\.71 206 are the result of immobilisation of Mo onto secondary ferric oxides in the surface layers of these free drained soils. On the Oxford Clay it is suspected that Mo uptake on anomalous soils increases with a rise in soil pH. The greater amount of data obtained from sites on the Corallian and Kimmeridge Clay permits a fuller investigation of factors influencing the uptake of Mo and Cu by herbage. Soil drainage is broadly similar over the Kimffleridge Clay and Corallian respectively, thereby preventing any assessment of the role of soil drainage status in influencing metal uptake. With respect to the uptake of Mo by herbage (Fig. 41), sites on the Kimmeridge Clay display a general trend for No uptake to increase with a rise in topsoil pH, over the range pH 5.3-7.8 due, it is assumed, to the increasing mobility of anionic Mo in more alkaline soils. Molybdenum uptake is particularly enhanced on soils with a pH greater than 7.0 where herbage Mo levels are consistently in excess of total soil values. Lewis (1943) notes that on soils in the Iteart pastures? of Somerset, similar in many ways to the Denchworth soils, Mo uptake reaches a maximum in soils of pH +7.0. However, the relationship between topsoil pH and Mo uptake in Fig. 41 is diffuse, suggesting that further factors are influencing the Mo status of herbage at sites on the Kimmeridge Clay. There is no recognisable relationship between total Fe and Mo uptake. There is, however, a broad trend for Mo uptake on the Kimmeridge Clay to increase with a rise in the organic content of topsoils, over the range 2.3-6.7% organic carbon. This trend is independent of soil pH and total Fe. Both Barshad (1951a) and Grigg (1953) have

8-

+

+ + 7- + . + + ++ pH + + + + 6- + + + ++ + + + +* + +

5

. . . 0.2 0.5 1.0 2.0 Herbage Mo! Topsoil Mo

10-

9-

8 -

7-

+

• • + + + + + + 4- + + + +4. + + + + + + 44- .1. • • + + + 1- 3- + +

0'2 0.5 1.0 2.0 Herbage Mo! Topsoil Mo

7- +

+ + + + • • + + + + + + + + + + + + + + + + + 2-

5 .0 0.2 0. 5 FO 2.0 Herbage Mo! Topsoil Mo

+ Soils on Kimmeridge Clay. • Soils on Corallian Beds. Fig.41. Molybdenum Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil. (Topsoil0-6ins depth. Herbage-Oven dry weight.) 207 related part of the readily extractable topsoil Mo to the organic ratter content of soils whilst Ng and Bloomfield (1961, 1962) found that rotting plant debris mobilises Mo from co—precipitation with Mn and Fe hydroxides and from soil Mo. In the present situation it is thought that part of the Mo available to plants is present in plant debris within topsoils. Davies (1956) and Vinogradov (1959) record the role of plants as Mo accumulators. It is suggested that on the Kimmeridge Clay vale plants growing on anomalous soils concentrate Mo during their life 'daich is returned to the soil when the plant dies. l'avies (1956) regards the No content of organic matter as being in a continual state of circulation due to microbial breakdown. However, it is probable that in the poorly drained surface—water gley soils of the Kimmeridge Clay vale organic matter decays relatively slowly and there is a large reserve of organically combined Mo in decomposing plant litter. It is also probable that the decomposition of the plant litter in the more waterlogged soils brings about the release of further No from combination with mineral debris in the soil (Ng and Bloomfield, 1961, 1962). The uptake of this organically combined Mo, and Mo released by rotting plant debris, is likely to be encouraged by moderately high pH of topsoils (mean pH 6.4) even though the observed trend (Fig. 41) is apparently independent of soil pH. Data from sites on the Corallian reveal a weak inverse relationship between the uptake of Cu by herbage and soil pH and,less distinctly, total Te (Pig. 42).. Copper • mobility in soil media is generally thought to fall with a rise in soil pH (Whitehead, 1966) and the trend observed

8 + +

• + • 7 • + + ++ + pH + • • + + + ++ • 6- + • + + + ++ 4+ +Fr + + + +

5-

0.2 0.5 1.0 i0 Herbage Cu! Topsoil Cu

10

9

8

7-

+ + ++ .+ + • • + + 4- + ++ + 4+ + ++++•++ 4++ ' +' + + +4; ++

3- + +

0.2 0.5 1.0 210 Herbage Cu/ Topsoil Cu

7 ++ + + 6- 5' + + + + + 5 5- + a + 6" • + + U + • + + + u 4- + + c ++ + + + + d 4- + CT . + 1- + + • 4+ • cIs 3 + . + 2-

0.2 0.5 1.0 2.0 Herbage Cu! Topsoil Cu

+ Soils on Kimmeridge Clay. • Soils on Corallian Beds.

Fig.42. Copper Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil. (Topsoil 0-6 ins depth. Hebage-Oven dry weight.) 208 is probably a reflection of this relationship. The immobilisation of Cu onto secondary Fe oxides in topsoils on the Corallian may be responsible for the second trend observed. The uptake of Cu at sites on the Kimmeridge Clay is largely independent of variables measured. However, a broad inverse relationship between Cu uptake and organic carbon may be present due, it is suggested, to the iuiiobilisation of Cu as organic—Cu complexes in topsoils. 209

CHAPTER 16: DETAILED GEOCHEMICAL INVESTIGATION THAME AREA

1. Introduction Stream sediment reconnaissance in the Thame area, reported in Chapter 10, reveals anomalous concentrations of Mo (3-8 p.p.m.) in streams draining the outcrop of the Oxford Clay around Marsh Gibbon and Steeple Claydon. Molybdeniferous soils in this district have been reported by Thornton (1968) who provisionally ascribed the source of the anomalous concentration of Mo to bituminous shales in the Lower Oxford Clay.

2. Description of the Area Essential features of the reconnaissance area are described in Chapter 10. Detailed investigations were undertaken over the Oxford Clay Vale around Stratton Audley, Marsh Gibbon, Piddington, Ludgershall and Brill (Pig. 43)

(A) Geology The Oxford Clay outcrops beneath the broad vale east of Bicester. The detailed succession has been described by Calloman (1968) and a broad two part division is possible, made on lithological considerations, which overlap the palaeontological zonation. Thus a lower ishaleyr and an upper !olay? division are recognised.

(i) The Lower Oxford Clay, occurring in the zones of K. jasoni, E. coronatum and lower P. athleta (Calloman, 1968), is some 70 feet of dark grey and grey brown bituminous shales Aylesbury.

•Tingew .Quainton. •Stedp1 :CI. don.

.Stone. .Wadd sdon. • 1 7:1 + Calvert ( Princes co Twyf d brickpit. 2 Risborough. .Edgcott. +w odham ckpit. .Grendon Underwood.

Stratton qv

Audley. e V .Ludgershall Haddertam.

.fhinnor. Piddington Long .Bla kthorn. Cjendon. &MC.

BiceMer.

. Key to Rock Samples. 0 1 1 Lower Oxford Clay. 3 Cornbrash & Forest Marble. + Rock Sampling Point. Molybdenum Scale in Miles. 2 Upper Oxford Clay. 4 Portland Lstn. stream sediment anomaly.

Fig. 43. Location of Soil Traverse Lines and Rock Sampling Points in Relation to the Molybdenum Stream Sediment Anomalies in the Thame Survey Area 210 and carbonaceous clays with thin interbedded shell bands and cementstone horizons. The bituminous shales succeed the sandyKolloways Beds abruptly and grade rapidly up into the overlying Upper Oxford Clay. The Lower Oxford Clay is rich in organic matter (up to 4% free carbon), with the greatest quantities found in the shale horizons, and is low in both lime and sulphur (Calloman, 1968). Anaerobic bottom conditions, evidenced by the rich neretic and sparce benthonic fauna, prevailed during the deposition of the Lower Oxford Clay, permitting the accumulation of organic matter in the sediments. Typically the organic matter is dispersed throughout the clay although its full composition is not known (Freeman, 1956, 1964). Pyrite is virtually restricted to the shell bands where it occurs replacing skeletal material in ammonite shells (Hudson and Palframan, 1969) although some pyrite is also found dispersed in the clay.

(ii) The Upper Oxford Clay is separated from the Lower division by a series of intermediate horizons, in the Lower—Middle P. athleta zone, in which the organic matter content of the clay falls to almost nil and the amount of lime increases (Freeman, 1956). It has not been possible to map this boundary in the field because of the complete absence of natural exposures. The Upper Oxford Clay is some 150 feet thick comprising grey, blue grey and brown plastic or nodular clays with thin cementstone and limestone horizons. The change from the Lower Oxford Clay appears to be the result of increased 211 bottom aeration during sedimentation precluding the retention of organic matter and favouring the accumulation of CaCO3 and the development of a rich and varied benthonic fauna (Hudson and Palframan, 1969). Despite the subtle variation in bottom environment permitting the accumulation of organic matter in the Lower Oxford Clay, conditions of sedimentation remained broadly similar throughout the deposition of the Oxford Clay. A shallow shelf sea with relatively quiet water is envisaged (Arkell, 1933), to which only clay size detritus was supplied. A reduction in the supply of detritus permitted the formation of limestone horizons whilst the shell beds accumulated by the winnowing action of moving water removing the clay material (Arkell, 1933). The remainder of the stratigraphy is summarised in Table 18. Sediments are of a shelf sea clay, carbonate and sand facies, the product of deposition in an aerobic shallow sea shelf environment. It is pertinent to repeat that the Kimmeridge Clay of this district consists largely of dark calcareous clays and sands, contrasting with the bituminous shales encountered in Dorset and Lincolnshire (see also Ch. 20). Transported overburden forms an extensive cover to the solid geology in the area of detailed studies where, in addition to alluvium, three main types are recognised: (a) Glacial drift occupies hill tops in the north east of the area, overlying both the Mid Jurassic limestones and the Oxford Clay. The drift is of northern origin and comprises sand and pebbles set in a clay loam matrix. The distribution of the drift has been mapped and is shown in Fig. 26. 212

(b) Recent work by the Soil Survey (pers. comm. D. Mackney) has revealed the presence of Clay Head deposits mantling the Oxford Clay on low ground around Marsh Gibbon, extending southwards towards Piddington and Ludgershall and westwards to Bicester. The distribution of the Head is, as yet, imperfectly known. It has been suggested (pers. comm. D. Mackney) that the Clay Head is reworked Oxford Clay and glacial drift of local origin similar to the deposits of Otmoor which are thought to have formed under periglacial conditions (Cooper and Marker, 1961). (c) The slopes of Brill Hill and Muswell Hill are mantled by colluvium and solifluction deposits which conceal much of the Corallian with a mixture of Kimmeridge, Portland and Purbeck material. The programme of detailed studies sought to minimise the effects of downwash by sampling along ridges and spurs.

(B) Soils The main features of the soils of the district are outlined in Chapter 10. Knowledge of soil series in the area of detailed investigation is confined to single catchment studies (pers. comm. D. Mackney). However the principal soil associations of the whole area have been provisionally mapped by the Soil Survey. Over the Clay Vale poorly drained non calcareous (occasionally calcareous) surface—water gleys of Denchworth aspect are found both as residual soils on the Oxford Clay and on the Clay Head. Surface—water gleys extend up the slopes of Brill Hill and Muswell Hill where impervious Kimmeridge material spreads over the Corallian. The summits 213 of these two hills, capped by limestone and sands, carry well drained brown earths of sandy loam texture. A poorly drained phase is found on slopes where a mixing of limestone and sandstone debris with impervious Kimmeridge Clay takes place. Soils on the Cornbrash around Bicester are well drained sandy clay loams developed on the brashy limestone whilst on the glacial drift moderate to poorly drained stony and sandy clay loams overlie the clay loam parent material.

(C) Land Use Land use in the area of detailed studies falls broadly into two parts following the drainage status of the soils. Thus the better drained soils of the Cornbrash and drift support mixed dairy and arable farming. The poorly drained soils developed on the drift, Clay Head and Oxford Clay are all under permanent pasture. Here dairying is the principal source of income with stock rearing becoming important on very poorly drained land.

3. Distribution of Metals in the Bedrock There are very few exposures of the bedrock in the area of detailed studies. The Oxford Clay formation is normally seen only in rare and badly weathered ditch sections, although the large brickpits at Calvert and Woodham provided fresh samples from some 70 feet of Lower Oxford Clay and 40 feet of Upper Oxford Clay respectively (Fig. 43). Samples of Cornbrash were obtained from the Blackthorn Hill railway cutting whilst a roadside exposure 214 on Muswell Hill yielded a sample of Portland Limestones (Fig. 43). Analytical data obtained from the samples of bedrock are portrayed stratigraphically in Fig. R3 and summarised in Tables 47 and 48. Detectable quantities of Mo occur only in the bitaminous shale facies of the Lower Oxford Clay exposed at Calvert, where from 2-14 p.p.m. Mo (mean 5 p.p.m.) are recorded. The enrichment of Mo in the Lower Oxford Clay is accompanied by very much higher range and mean levels of organic carbon and Zn than the other rock groups sampled, and by higher mean levels of all other metals except Mn and As. Trace quantities of Se (‹:0.1 p.p.m.) are found in a few samples of Lower Oxford Clay. An effective comparison of the metal content of the clays and that of the limestones is not possible because of the few samples of limestone obtained. Howevor, the overall metal - ontent of the limestones, except for Mn and As, is clear:1.y less than that of the clays. A comparison of metal values from clays and shales in the Upper and Lower divisions of the Oxford Clay, as shown in Table 48- emphasises the increased metal content of the Lower Oxford Clay. That the Lower Oxford Clay should contain higher levels of so many of the metals is a little surprising since Freeman (1956, 1964) reports that the only mineralogical difference between the Calvert and Woodham sections is the amount of organic matter and lime in the clay. Gallium and Ti are usually associated with clay minerals (Goldschmidt, 1954), the content of which remains constant throughout the Oxford Clay (Freeman, 1956, 1964). :?able 47 Range and mean* metal content of the principal bedrock units in the Thame area

Metal content (p.p.m.) Org. Mod Cu V Se+ Pb Ga'6 ZnY Ti NiP Co(3 Mn Cr As Fe203% C % a

Portland Limestone <2 11 50 <0.1 20 <2 (50 130 <5 <5 130 6 <5 1.2 0.7 (1 sample) Upper Oxford Clay <2 a. 70 !.0.1 13 9 (50 1904 28 10 150 51 45 3.0 0.6 (9 samples) <0 13- 50- <0.1 10- 3- (50 850- 13, <5- 130- 30- <5- 1.6- 0.3- 37, 130 16 16 -50 3000 40 16 160 60 10 4.5 1.0 Lower Oxford Clay 5 31 93 <0.1 15 16 220 3020 41 12 163 68 <5 4.6 3.6 (15 samples) 2- 14- 2- <0.1- 2- 2- <50- 300- 13- <5- 60- 16- <5 1.5- 2.2- 14 42 130 0.1 40 20 600 4000 60 16 1000 100 -8 8.0 4.9 Cornbrashk < 7 10 40 <0.1 4 2 (50 337 5 <5 187 7 <5 1.3 0.2 <2 60- <5 <5 160- 2- 1.1- <0.1- (3 samples) <2 7- 40 <0.1 3- <50 :5 15 5 -4 850 -8 -5 200 20 1.5 0.3

Geometric mean except k arithmetic mean Y Mean calculated with <50 p.p.m. = 40 p.p.m. i Mean calculated with <2 p.p.m. = 1 p.p..m. P Mean calculated with <5 p.p.m. = 3 p.p.m. Mean calculated witn

Metal content (p.p.m. Org. MoA Uu V Se+ Pb Ga ZnY Ti Ni Co Mn Cr AO Fe203% C % Upper Oxford Clay 42 20 76 (.0.1 13 11 <50 2260 31 12 147 56 <5 3.3 0.8 (7 samples) 15- 50- 10- 8- <50- 1600- 30- 6- 130- 40- <5- 2.6- 0.5- <2 21. 13C <0.1 16 16 50 3000 40 16 160 60 10 4.2 1.0 Lower Oxford Clay 5 54 101;- <0.1 16 18 250 3550 46 13 104 75 ef5 4.4 3.9 (11 samples) 2- 20- 60- <0.1- 10- 13- 50- 3000, 30- 10- 60- 60- <5 3.7- 2.8- 14 42 13C 0.1 40 20 600 4000 60 16 160 100 5.0 4.9

* Geometric mean Y Mean calculated with <50 p.p.m. = 40 p.p.m.

A Mean calculated with <2 p.p.m. = 1 p.p.m. 13 Mean calculated with <5 p.p.m. = 3 p.p.m. + Mean calculated vith <0.1 p.p.m. = 0.0 p.p.m. 217

The small enrichment of these metals in the Lower Oxford Clay may be due to increased sorbtion onto clays in the anaerobic depositional environment. Organic matter and/or features of the environment in which organic matter accumulates are regarded as responsible for the particularly enhanced levels of Mo and Zn in the Lower Oxford Clay and to influence the distribution of Cr, V and Cu. However, none of these metals has a common distribution with organic carbon, neither do they display any inter—relationships. Nevertheless, in the shell beds, cementstones and limestones of the Lower Oxford Clay, both Mo and organic carbon remain enhanced although levels of most metals are much reduced. This relationship indicates the role of organic matter in facilitating the accumulation of Mo. Freeman (1956) has suggested that there is more than one type of organic matter in the bituminous Lower Oxford Clay at Calvert, although.only lignite (presumed to be of terrestrial origin) is positively identified. Analysis of a single sample of lignite from the E. coronatum zone reveals no detectable quantities of Mo (4.1 p.p.m.) and no enrichment in Zn (<50 p.p.m.) or Cu (17 p.p.m.). However the lignf.te contains 200 p.p.m. Cr and 400 p.p.m. V (corrected for loss on ignition) — levels x2 to x4 those of adjacent clays. Association with pyrite is not considered to be a control on the distribution of Mo, Cu and Zn in the Lower Oxford Clay. Jackson (pers. comm.) observes that almost all the iron in the Lower Oxford Clay occurs with pyrite; however there is no relationship between the distribution of Mo, Cu or Zn and Fe amongst the samples obtained. 218

Thus in the Lower Oxford Clay it is concluded that whilst Cr and V are concentrated in the lignite the enhanced levels of Mo, Zn and Cu are due to accumulation with other, unidentified, forms of organic matter. Values of Mn are higher in the calcareous Upper Oxford Clay and the Jurassic limestones and are elevated in all the shell beds, cementstones and limestones interbedded with the Lower and Upper Oxford Clay reaching a maximum of 1000 p.p.m. in the Acuti striatum stone band. The observed distribution is in accordance with the observations of Goldschmidt (1954) and Rankama and Sahama (1950) that Mn occurs in greater concentrations in limestones and other calcareous sediments than in bituminous deposits.

4. Distribution of Metals in the Overburden (A) Lateral Distribution Soil samples were taken at intervals of 200-1000 feet along traverse lines crossing the Mo anomaly zone defined

'37 st-ceam sediment reconnaissance, the remainder of the 0:

(±) Metal distribution patterns related to -p.5.2parent materials The distribution of Mo along traverse lines (Figs. T7,T8) and the data in Table 49 indicate that residual soils derived from the Lower Oxford Clay are characteristically molybdeniferous with values of up to 8 p.p.m. and a mean of 3 p.p.m. In contrast mean values of less than 2 p.p.m. Mo are associated with soils developed on the remaining parent Table 49 Range and mean* metal content of overburden developed on the principal parent materials Thame area. (sample depth 12-18 inches) Metal content (p.p.m.) Parent material MbA Cu V Pb Ga Zia+ Ti Ni CoY Mn Cr Fe207%J Residual soils Lower GreensandP <2 22 225 64 9 350 2900 136 53 4000 105 30.6 <2 16- 200- 50- 5- 300- 1600- 85- 50- 3000- 60- 18.4- (4 samples) -2 30 300 85 10 400 4000 200 60 5000 130 40.0 Portland and Purbech <2 6 51 ' 11 6 60 1475 28 10 475 43 5.2 e2 57. 50- 8- 3- 0 1000- ?0- 6- 300- 30- 4.1- (4 samples) 6- 60 16 10 6 2000 30 13 600 60 6.6 Kimmeridse Clay <2 18 98 48 11 66 3250 33 11 684 58 4.6 <2 15- 60- 10- 4- (50- 2000- 10- 5- 50- 10- 2.8- (16 samples) -5 30 200 200 16 130 5000 50 20 2000 85 7.0 Corallian <2 15 169 16 18 89 4125 38 19 368 94 5.7 <2 10- 130- 10- 13- <50- 3000- 20- 8- 130- 85- 5.2- (8 samples) -2 30 200 30 40 300 5000 60 30 850 100 6.6 Upper Oxford (flay <2 15 143 17 14 99 4813 43 18 288 87 5.9 --<2 8- 85- 10- 10- 50- 4000- 30- 8- 200- 60- 4.7-; (16 samples) 20 200 30 20 160 6000 60 30 400 100 7.5 Lower Oxford OlE7 3. 24 - 121 20 16 132 4750 43 16 244 98 5.5 - :2 ',-10:=. 50- .10..: 6- e50_ 3000- 20- 8- 100- 50- 3.1- (33 sample s) -8 85 200 - 4q, 20 600 600p, 60 30 850 200 7.8

Cornbrash <2 21 94 25 11 75 3025 36 14 874 60 5.7 <2 10- 60- 10- 5- <50- 1600- 20- 5- 130- 50- 3.1- (26 samples) -2 30 200 100 16 200 5000 85 30 2000 85 11.2 • ...Transported I-32±16 Glacial Drift <2 23 136 21 17 160 4855 50 18 479 83 7.1 <2 13- 85- 5- 10- 50- 4000- 30- 8- 160- 8- 3.8- (26 samples) -2 30 300 40 30 500 6000 130 40 1300 200 13.0 Clay Head and Alluvival <2 16 81 14 13 67 3661 32 10 155 68 4.1 <2 10- 40- 5- 5- :50- 2000- 16- 5, 50- 40- _ 2.4- (58 samples) -4 50 200 85 30 300 8500 60 20 400 130 7.3 * Geometric mean except ¢ arithmetic mean A Mean calculated with 2 = 1 p.p.m. + Mean calculated with <50 p.p.m. = 40 p.p.m. Y Mean calculated with 45 p.p.m. = 3 p.p.m. 220 materials although detectable concentrations of Mo are encountered locally with significant quantities (>3 p.p.m. Mo) in soils developed on the Clay Head, alluvium and Kimmeridge Clay. The localisation of molybdeniferous soils to sites developed on the Lower Oxford Clay confirms the supposition made earlier as to the distribution of Mo in this area (Thornton, 1968) and indicates that the bedrock is the dominant control on the distribution of Mo. In addition, soils developed on the Lower Oxford Clay have a higher mean content of Cu and Zn than residual soils on the Upper Oxford Clay, a feature also displayed in the bedrock (Table 49). The values of Mo in residual soils are, however, often lower than those encountered in the bedrock with Mo undetected at a number of sites. Whilst the absence of detectable quantities of Mo may reflect local variatim in the metal content of the bedrock it is probable that many of the low values of Mo are due to the presence in soils of material barren of Mo. Residual soils in the area of the traverse lines locally contain material derived from the pre—existing cover of glacial drift (pers. comm. D. Mackney) which is typically barren of Mo (Table 49). The presence of this material in residual soils could suppress Mo values to the modest levels observed. Nevertheless, maximum levels of soil Mo are similar to values recorded by Thornton (1968) in residual soils on the Lower Oxford Clay south west of Bicester and thus demonstrate a continuity for the Mo anomaly associated with the Lower Oxford Clay in Oxfordshire and Buckinghamshire. 221

It is anticipated that all residual soils developed on the Lower Oxford Clay will contain levels of Mo similar to those recorded in Table 49. However, the extent of such soils within the reconnaissance survey area is uncertain since: (a) the outcrop of the bituminous facies of the Lower Oxford Clay has not been mapped and (b) the extent of residual soils and transported overburden (Clay Head and glacial drift) is, as yet, imperfectly known. Nevertheless, some 12 square miles of Mo anomalous residual soils on the Lower Oxford Clay are anticipated in the area north of Marsh Gibbon between Stratton Audley, Steeple Claydon and Winslow (Figs. 26 and 43). Detectable quantities of Mo occur sporadically in soils on the Clay Head where this material overlies the Lower Oxford Clay, with maximum values (3-4 p.p.m. Mo) found near the margins of the Clay Head along the northern leg of Traverse 1 (Fig. T7). It would appear that locally the Clay Head, otherwise barren of Mo, includes some Mo—rich material derived from the Lower Oxford Clay. The full extent of Mo—bearing Clay Head cannot be ascertained by the present survey for the occurrence of Mo in significant quantities in samples from 12-18 inches depth is seen to be erratic and will be defined only by detailed sampling. Furthermore an examination of topsoils (page 224) developed on the Clay Head and Upper Oxford Clay has revealed the accumulation of Mo in surface horizons at some sites with values comparable to those of Mo—rich soils on the Lower Oxford Clay. Molybdenum is found in the alluvium of streams draining 222 areas of residual soils developed on the Lower Oxford Clay. This occurrence indicates the mechanical dispersion of Mo—rich detritus into the stream and subsequent deposition in alluvium during the development of the drainage network. Indeed similar levels of Mo in stream sediment (5 p.p.m.) and adjacent alluvium (4 p.p.m.) on Traverse 1 suggest a common origin. Raised levels of Mo (3-5 p.p.m.) occur in a narrow zone on both Traverses 1 and 2 (Fig. T7) at sites occupying a position near the base of the Kimmeridge Clay. Although it is fairly certain that there has been some downslope movement of weathered material at these points it is considered that the source of Mo lies in black shale horizons near the base of the Kimmeridge Clay succession. Davies (1907) and Arkell (1947a) record thin bands of bituminous shale, over some 20 feet in the Aulacostephanus zone, commencing 12 feet above the base of the Clay. The Mo—rich soils occupy a small area on Traverses 1 and 2; however, it is probable that to the south and east, where relief is lees severe,the thin bituminous shales will have a more extensive outcrop with a correspondingly greater area of Mo—rich soils. The distribution of the remaining metals is summarised in Table 49. There is little overall variation in the range and mean metal content of soils developed on the principal parent materials in the Clay Vale, except for Mn. Soils on the Portland/Purbeck limestones are, however, lower in Cr, Cu Ga, Ni, Pb, Ti and V than other soil groups. In contrast, soils derived from the Lower Greensand are conspicuously rich in Co, Cr, Mn, Ni, Pb, V, Zn and Fe. The latter are residual soils developed from a sedimentary ironstone, and the high metal values in the overburden may reflect syngenetic enrichment in the parent material. Similar high metal values associated with Mesozoic sedimentary ironstones have previously been encountered by Thornton (1968) and are found in the Market Rasen reconnaissance area in streams draining areas underlain by Lower Cretaceous iron ores (Ch. 11). There are no geochemical characteristics that positively indicate the origin of the Clay Head. Mackney (pers. comm.) has suggested that the Clay Head is locally derived. However whilst sporadic occurrences of Mo at the margin of the Head indicate the local incorporation of Lower Oxford Clay material the Head is typically barren when overlying molybdeniferous bedrock. Thus, although confirming the exotic nature of the Head, the present data reveal no distinctive geochemical features to associate the Clay Head with other clay deposits in the survey area.

(ii) Metal distribution patterns related to the secondary. environment Manganese and Co display a broadly similar distribution along the traverse lines (Figs. T7, T8) with levels of Mn in particular reflecting the local drainage status of each sample point. High levels of Mn and Co tend to occur in better drained soils developed over limestones. In contrast low levels of Mn and Co characterise the poorly drained surface—water gleys of the Oxford Clay Vale, with the lowest Mn values occurring in waterlogged alluvial soils adjacent to drainage channels. 224

(B) Vertical distribution Analytical data from soils sampled at two depths are summarised in Table 50. All the soils examined support permanent pastures and are thus relatively undisturbed. Certain general trends are revealed in Table 50; at almost all sites topsoils are conspicuously richer than subsoils in Pb (x4—x10) and Zn (x2—x5) whilst Mn levels are often significantly greater in topsoils than associated subsoils. Within the limits of analytical precision, the observed variation between topsoil and subsoil levels of Co, Cr, Ga, Ni, Ti and V are generally insignificant. Data in Table 50 show that in soils on the Clay Vale (Clay Head and Oxford Clay) there is a weak tendency for levels of Mo, Cu, Ni, Co and Fe to be lower in topsoils than subsoils, as seen at site 3276 (Table 51), a feature attributed to the leaching of these metals from the surface horizons. However, these soils frequently show a very low contrast between topsoil and subsoil levels of these metals as seen at sites 3303 and 3299. This situation is similar to that observed in the Shaftesbury area and is thought to reflect a low rate of leaching in very poorly drained soils composed of relatively impervious material. Molybdenum is probably also retained with secondary ferric oxides or organic matter in the oxidised surface horizons of these gleyed soils. In a number of soils on the Clay Head and Upper Oxford Clay a conspicuous surface enrichment of Mo (more than x4) and Cu (up to x2) is seen as at site 3301 (Table 51). The sites at which the accumulation is observed occupy topographic and geographic situations where the introduction Table-2Q ~~an&e and me:.~£:'~EQ- content of soils, sampled at two deEt~? developed on the principal 'p"aren~ materials? Thame area ------Sample depth Parent (ins) Metal content (p.p.m.) material (No. uf Mob Cu V Pb Ga Zn+ Ti Ni sample L) 0-6 1 18 125 83 21 500 3667 35 16 950 68 6.1 5.9 13- 100- 60- 16- 400- 3000- 30- 13- 850- 60- 5.4- 5.2- UL'per (6) 25 130 100 30 600 4000 40 70 1300 85 606 6.8 Oxford 12-18 <1 13 t6~ l~ 15 102 5~61 38 19 3!1 87 6.2 6:4 Clay , .. '..L. 8- 85- 10- 10- 60- 4000- 30- 8- 200- 85- 5.6- 6.2- (6) -j. 20 200 30 20 160 6000 50 30 400 100 7.5 7.0 0-6 3 1) 136 44 18 294 4333 30 10 367 89 3.8 6 .. 6 2- r 12- 60- '30" ~'.'. 50- 4000- 20- <5- 200- 50- 303- 6.2- Lower (8) \) 24 200 85 20 600 5000 40 16 60J 130 4.5 608 Oxford 12-18 4 24 117 18 17 122 4443 40 10 147 81 5.1 6.4 Clay 1- 13- 50- 10- 13- <50- 3000- 20- 8- 100- 50- 3.1.- 5.7- (8) 8 40 200 30 20 200 6000 60 20 300 100 7.1 7.0 ·0 .... 6 1 ~3 115 83 16 130 3400 36 19 1680 54 701 '~1 - 20- 85- 60- 13- 50- 3000- 30- 10- 1600~ 50- 6.8- (5) -2 . 3q;\~ .. 130 100 20 200 4000 40 . ·so '. 2000 '. 60 . 7.4 Cornbrash 12-18' <. 1 .' .::: ~.J.: 6· '., , :8 3 ··:18""'10':::: ·.63:':,.'"3200 32·· ,12 870 56 5.7·. 6.9 .. <]. .·~0~ 60~ 13-' '5- 50"';, 2000-.. 20~ ."10... ,.. 600-· 50- 4.8- 6.6- . '~1 . . (5). '26".100 20 13 85··4000 "40 16 1300 60 6'. 8""~':: 7.1 . ".' __~ ______~_;..;._~_ ...... ~ _____ • __• ... ______x~ ____...... __._ ... --.'> 0-6 2 18 89 50 20 212 3917 28 11 392 80 4.1 ' 5.8 12- 60- 30- 13- 50- 3000- 16- 5- '160- 50- 3.2- 4.8- (13) 4 28 130 60 40 600 5000 40 16 850 100 6.1 6.6 Clay Head 12-18 2 18 96 19 15 83 4000 36 10 182 73 4.5 6.2 1- 1)- 60- 10- ·13- <50- 3000- 20- 6- 85- 50- 3.2- 504- (13) 3 30 160 20 30 200 5000 50 20 300 130 6.6 7.0 I------~~--~------0-6 17 138 60 16 480 4200 38 14 720 76 4.5 6.1 {I 15- 100- 30- 13- 300- 3000- 30- 10- 300- 50- 402- 5.6- Glacial (5) -2 19 200 85 20 600 5000 50 16 1300 100 5.0 7.0 Drift 12-18 1 22 109 16 15 152 4800 44 22 820 83 6.9 5.8 (1 20- 85- 13- 10- 100- 4000- 40- 20- 600- 60- 506- 4.7- (5) -2 ~o 160 20 20 300 5000 50 30 1000 100 800 7.0 ------.------* Geometric mean + Mean calcu18 te ('1 'Va th < 50 p. p. mo ::: 40 p. p. m. IJ. Mean '-calculated 'With <1 p.p.m. ::: 0 p.p.m. "( Mean calciilatec1 "lith < 5 p.p.mo 3 pop.m. I\) = I\) \Jl Table 51 Metal content of selected soils developed on the principal parent materials in the Oxford Clay Vale Thame area

Site no. and Sample parent Profile depth Metal content (p.p.m.) material drainage (ins) Mo Cu V Pb Ga Zn Ti Ni Co Mn Cr Fe203% pH

3299 Very pooily drained 0-6 2 20 160 40 20 600 4000 40 13 400 130 5.0 6.4 Clay Head (Level, middls of 12-18 2 20 160 20 20 200 5000 50 10 160 100 4.6 5.1 vale) 3301 Very pooily drained 0-6 4 23 130 85 30 500 4000 40 20 850 85 6.6 6.2 Uppe.. Oxford (Level) 12L18 (1 20 200 30 20 160 5000 50 16 400 850 6.8 5.8 Clay 3303 Very poorly d7.:.ainea 0-6 <1 17 130 85 20 600 4000 40 16 1000 60 6.4 5.2 Upper Oxford (Base of slight 12-18 <1 13 200 16 16 130 6000 40 20 200 100 7.5 6.0 Clay slope, near margin of vale) 3276 Poorly drained 0-6 2 20 160 40 20 600 4000 40 13 400 130 4.5 6.4 Lower Oxford (On mid part of 12-18 5 30 160 20 20 200 5000 50 10 160 100 7.1 5.1 Clay sliGht slope) 3274 Vertu poorly drained 0-6 3 16 130 30 13 200 4000 30 16 600 85 3.7 6.8 Lower Oxford (Lerel, at base of 12-18 3 20 130 20 20 2C) 5000 50 10 200 85 5.2 5.7 Clay slight slope) _ 227

of Mo—rich material to the topsoils from nearby Mo—rich sources is not possible. The feature is, however, of particular importance for up to 4 p.p.m. Mo is recorded in topsoils from sites where Mo is undetected (= 1 p.p.m.) at a depth of 12-18 inches. Thus topsoil levels similar to those ass:-oiated with the Mo—rich Lower Oxford Clay are Encountered in background areas on the Clay Head and Upper Oxford Clay. There is no direct evidence as to the foam of Mo in these topsoils. It is suggested that the levels of Mo and Cu observed are the result of concentration by organic processes (Davies, 1956, Vinogradov, 1959) and fixation onto ferric oxides in the surface horizon of soils suffering periodic waterlogging (Robinson and Edgington, 1954). However the surface accumulation of Mo is not a •consistent feature and is apparently unrelated to parent material, topographic -situation, drainage conditions, pasture species present in the sward, topsoil pH or the amount of organic matter and Fe in the topsoil. It is possible that the accumulation reflects slightly increased amounts of Mo in the parent material (although still below the detection limit of 1 p.p.m. Mo) coupled with favourable conditions for plant uptake and the retention of metals in the soil, although the present investigation is unable to illuminate such processes. It is therefore not-possible to suggest the extent of the areas in which topsoil accumulations of Mo are likely to be present. Soils sampled on the Cornbrash are uniformly shallow, well drained sandy clay looms. The data in Table 50 reveal a weak tendency for the 12-18 inches sample to have a lower metal content than the 0-6 inches sample. The 12-18 inches 228 depth sample occasionally penetrates the upper C horizon Which is lower in metal bearing clays and secondary oxides than the 0-6 inches sample. Topsoils (0-6 inches) are dark brown clay looms rich in metal bearing clays and also containing secondary Fe and Mn oxides, often seen as fibrous concretions on root channels. Manganese and Fe are likely to be iplmobilised throughout the profile of these well drained soils with the apparent accumulation of Mn (x2) in topsoils possibly encouraged by the maintenance of oxidising conditions in the surface layers. Soils sampled on the glacial drift are typically moderately drained sandy clay loans in which topsoils are relatively depleted in Cu, Ni, Co, Mn and Fe (xl—x3), a situation attributed to leaching, whilst differences in levels of Ga, V, Ti and Cr between topsoils and subsoils are insignificant.

5. Relationships between the Metal Content of the Bedrock, Overburden and Stream Sediment The data in Table 52 reveal a broadly similar metal content for residual soils on the Lower Oxford Clay and the bedrock, although there are lower mean values for metals other than Mo, Cu and Zn in the bedrock than the soils. The low mean values are thought - to be due solely to the presence of a number of limestone samples with a low metal content in the bedrock data. Molybdenum values tend to fall between bedrock and soil due, it is suggested, to the presence in residual soils of colluvium barren of Mo (page 220). The good correlation between metal values in the Lower Oxford Clay bedrock and overburden is regarded as indicative of a Table 52 Range and mean* metal content of rocks and associated residual soilsA, Tbame area Metal content (p.p.m.) Ao-i- Cu V Pb Ga Zn? Ni Cod Mn Cr Fe203%

1222.2S91121121EX Residual soils <2 15 143 17 14 99 4813 43 18 288 87 5.9 <2 8— 85— 10— 10— 50— 4000— 30— 8— 200— 60— 4.7— (16 samples) 20 200 30 20 160 6000 60 30 400 100 7.5 Rock samples <2 20 70 13 9 <50 1904 28 10 150 51 3.6 <2 13- 50- 10- 3- %50 850- 13- <5- 130- 30 1.6- (9 samples) 33 130 16 16 -50 3000 40 16 160 60 4.2 Lower Oxford Clay Residual soils 3 24 121 20 16 132 4750 43 16 244 98 5.5 <2 10— 50— 10— 6— <50— 3000— 20— 8— 100— 50— 3.1- (33 samples) -8 85 200 40 20 600 6000 60 30 850 200 7.8 Rock samples 5 31 93 15 16 220 3020 41 12 163 68 4.6 2- 14- 2- 2- 2- ;50- 500- 13- :5- 60- 16- 1.5 (15 samples) 14 42 130 40 20 600 4000 60 16 1000 100 8.0

Geometric mean A Sample depth 12-18 inches + Mean calculate0. with (2 p.p.m. = 1 p.p.m. Y Mean calculated with i'50. = 40 p.p.m. P Mean calculated wit]. 5 = 3 p.p.m. 230

dominantly elastic dispersion, with metals in the overburden largely associated with weathered bedrock material. However, the distribution of Mo is modified by the local secondary accumulation of Mo in topsoils on the Clay Head and the Upper Oxford Clay with values similar to those encountered in Mo anomalous Oxford Clay soils. The data for the Upper Oxford Clay reveal higher range and mean values in soils than bedrock for all metals except Cu. The poor relationship between bedrock and overburden cannot be immediately explained. However it is likely that the soils are derived from higher zones of the Oxford Clay than are represented in the bedrock samples and it is thus, perhaps, unwise to make a direct comparison of the metal values in Table 52. The large area of Clay Head between Marsh Gibbon and Piddington appears to cover the upper P. athleta, Q. lamberti and lower Q. marine zones sampled at Woodham. Examination of Tables 47 and 49 reveals that the marked contrast in metal values between samplbs of Oxford Clay and Cornbrash is not preserved in residual soils derived from these formations. It is suggested that this is a result of a concentration of metals in soils over the Cornbrash, brought about by weathering of the limestone, similar to that observed in the Shaftesbury area (see page 200). The relationship between the metal content of soils and associated stream sediment is summarised in Table 53. The data reveal a generally good correlation between metal values in soils and stream sediments with a broadly similar relationship displayed in all groups by Mo, Cr, Go, Ni, Pb Ti and V suggesting that these metals are dispersed mechanically with weathered bedrock material and soil debris. Mechanical Table 53 Range_ and mean* metal content of soilsA and stream sediments+ on the principal paar2t. materials in the Thame area Parent Aedia Metal content (p.p.m.) Cgo, of material samples) Mo? Cu V Pb Ga ZnP Ti Ni Co Mn Cr Fe203% Soils <2 23 136 21 17 160 4855 50 18 479 84 7.1 :2 13- 85- 5- 10- 50- 4000- 30- 8.-; 160- 8- 3.8- Glacial (26) -2 30 300 40 30 500 6000 130 40 1300 200 13.0 Drift :2 43 122 18 9 138 4667 28 18 758 97 6.5 sediments <2 30- 60- 13- 6- 85- 2000- 16- 13- 400- 40- 3.7- (5) -2 60 160 20 19 300 6000 40 30 1600 130 7.9 <2 24 131 17 17 133 45 00 45 12 232 92 5.8 Clay Head and <2 16- 85- 10 - 13 - 50 3000- 40- 5- 85- 60- 4.4 - Upper Oxford (15) 50 200 30 30 300 8500 50 20 300 130 7.3 Clay Stream <2 59 142 23 14 82 5200 38 18 740 112 6.9 sediments, 40- 130- 10- 8- <50- 4000- 30- 13- 400- 100- 5.4- (5) < 100 160 40 20 130 6000 60 30 1600 130 8.0 So:LIE 3 24 121 20 16 132 4750 43 16 244 98 5.5 <2 10- 50- 10- 6- C50- 3000- 20- 8- 100- 50- 3.1- Lower Oxford (33) - -8 85 200 40 20 600 6000 60 30 850 200 7.8 Clay Stream 3 64 140 27 13 204 5300 43 24 716 119 8.0 sediments <'2 16- 85- 10- 6- 60- 4000- 13- 13- 300- 85- 1.9- (15) -8 . 200 600 60 20 ,400 8500 85 40 16 00 200 11.0 Soi13 <2 21 94 25 11 75 3025 36 14 874 60 5.7 <2 10- 60- 10- 5- <50- 1600- 20- 5- 130- 50- 3.1- (26) -2 30 200 100 16 200 5000 85 30 2000 85 11.0 Cornbrash Stream <2 30 118 25 6 <50 4300 22 15 450 83 3.9 sediments <2 20- 85- 13- 4- <50- 3000- 13- 8- 300 50- 2.3- (10) -2 60 160 60 10 130 5000 40 20 1000 100 9.2

*A Geometric mean Y Mean calculated with <2 p.p.m. = 1 p.p.m. Sample depth 12-18 inches 13 Mean calculated with (50 p.p.m. = 40 p.p.m. + Data from minus 80-mesh fraction 232 dispersion of Mo into the drainage network is further indicated by the localisation of Mo anomalous stream sediments to streams draining areas of residual soils on the Lower Oxford Clay. Molybdenum anomalous stream sediments are not encountered in areas of Clay Head and Upper Oxford Clay where secondary accumulations of Mo were observed in topsoils. The absence of sediment anomalies in these districts strongly suggests that the quantities of Mo in the catchment areas are small and the area of soils in which the secondary Mo concentrations occur probably limited. The soils with secondary Mo concentrations are found to be quite irregularly placed and apparently unrelated geographically. In contrast levels of Mn, Fe and less distinctly Co are higher in stream sediment than in associated soils on the Oxfn:d Clay Vale, with a similar relationship seen for Mn on the glacial drift. The rise in metal values in stream sediments is considered to result from the leaching of Mn, Fe and Co from gleyed soils into the drainage network as described by Horsnail (1968). On the Cornbrash Mn and Fe levels are higher in the soils than associated stream sediments. This relationship is thought to result from the immobilisation and retention of Mn and Fe as =,.ccondary oxides in the freely drained limestone soils. High levels on Mn () 1600 p.p.m.) in stream sediment occur locally over the Cornbrash adjacent to small areas of very poorly drained soils, as at Stratton Audley, where it is probable that increased leaching of Mn from these soils is followed by precipitation in the stream. Stream sediments on the clay vale contain higher mean Cu values than associated soils and include anomalously high 233 values (up to 200 p.p.m. Cu). The high values are thought to be due to the introduction of Cu into the drainage network with part treated or untreated sewage from inefficient treatment works. The high mean values of Zn in stream sediment on the Lower Oxford Clay and the sporadic occurrence of high values of Pb and Zn in stream sediment elsewhere in the survey area are also attributed to this type of contamination(see also page 104).

6. Metal Content of Herbage and Factors Influencing the Uptake of Molybdenum and Copper by Herbage, Samples of horbage and topsoil (0-6 inches) were collected from sites on the principal parent materials in the area of detailed study and included material from districts defined as Mo anomalous and background by the stream sediment and soil sampling. All samples of herbage were taken in permanent pastures and comprised mixed grasses with clover included where present. The data in Table 54 reveal that the mean Mo content of herbage is roughly proportional to the mean total Mo content of associated topsoils, with maximum mean levels of herbage and topsoil Mo associated with the Lower Oxford Clay, earlier noted as being characteristically molybdeniferous. Thus the increased amounts of Mo present in topsoils developed on the Kimmeridge Clay, Clay Head and Upper and Lower Oxford Clay are available to herbage at these sites. Furthermore, the modifications to the distribution of Mo on the clay vale, brought about by the secondary concentration of Mo in topsoils at localities with background levels of Mo in the subsoil (12-18 inches depth) and bedrock, are maintained in the

Table 54 .Sage and mean* molybdenum and copper content of topsoii3A and asscciated herbage+ on soils derived from the_Erincipal parent materials in the Thame area

Mo(p.p.m.)Y Cu(p.p.m.) Parent materials Herbage Topsoil Herbage Topsoil

Cornbrash and Portland limestones 0.4 1 5.5 21 (8 samples) 0.2-0.5 <1-2 5.0-7.5 17-24 Kimmeridge Clay 0.9 2 6.8 13 (5 samples) 0.3-2.0 2-3 5.5-7.0 10-19 Upper Oxford Clay 1.2 1 7.8 18 (6 samples) 0.5-2.4 <1-4 4.5-9.5 13-25 Lower Oxford Clay 1.7 3 6.8 19 (8 sample3) 1.0-2.4 2-6 4.5-11.0 12-24 Clay liaaa 1.3 2 7.3 18 (13 saLl.dles) 0.5-2.4 2-4 5.0-10.0 12-28 GlaciaJ Drift 0,5 1 9.1 17 (5 samlfies) 0.3-0.8 :1-2 7.5-11.0 15-19

* Arithmetic moen + Mixed pasture herbage, oven dry weight 6' Sample depth 0-6 inches Y Mean (alculated with (.1 p.p.m. = 0 p.p.m. herbage. However, whilst levels of herbage Ho are generally lower than total topsoil levels, the reverse situation is seen for the Upper Oxford Clay. Thus the uptake of Mo by herbage from Mo—rich topsoils is clearly not a constant feature. In contrast the range and mean levels of topsoil Cu show a small variation between sites on the main parent materials suggesting a fairly uniform rate of Cu uptake by herbage in this area. An examination of the features likely to influence the uptake of Mo by herbage on soils in the Clay Vale fails to reveal any evidence of environmental control (Fig. 44). The plots in Fig 44 clearly indicate that the relationship between Mo levels in herbage and topsoil are very variable, but also reveal that the relationship is independent of topsoil pH, organic carbon and total Fe. It is thus not possible to determine the features which influence the uptake of Mo by herbage with the data available, and it is not known why Mo uptake is particularly increased on certain soils developed on the Upper Oxford Clay. It was noted earlier that the occasional presence of detectable amounts of Mo in topsoils developed on the Upper Oxford Clay and Clay Head is a result of secondary concentration, in marked contrast to topsoils on the Lower Oxford Clay and locally on the Clay Head and Kimmeridge Clay where Mo is probably present largely in fine grained detritus derived from a Mo—rich parent material. Thus it is possible that in these two contrasting situations the Mo available to herbage is present in different forms although the present limited investigation cannot identify these forms of Mo. 1 8-

7- 0+ + + . 4 t

0 • I. + + • 0 6- 0 o pH o 5-

4-

3-

• 0.2 0.5 1.0 Z•0 Herbage Mo! Topsoil Mo

7- O 0 0 6- 0 0 ..., 0 at 5- m 0 + CV LE 4- + + + + +

• • + • 3-

1 0.2 0.5 1.0 A Herbage Mo! Topsoil Mo

7- 0 6- 0 0 0 0 0 . •

+ + + + +

2- . t

0.2 0.5 1.0 2.0 Herbage Mo/ Topsoil Mo O Soils on Upper Oxford Clay. • Soils on Clay Head. + Soils on Lower Oxford Clay.

Fig.44. Molybdenum Content of Pasture Herbage in Relation to the pH, Iron and Organic Carbon Content of the Topsoil. (Topsoil 0-6ins depth. Herbage-Oven dry weight.)

Thame area. 8_

7 + +0 + + 1+ • • + . 0 %I.o • 6 0 . • ' pH 0 0 5

4-

3-

02 0.5 1!() Herbage Cu! Topsoil Cu

7- 0 0 0 6- . 0 0 0 •I

+

+ 04 + +. + • ..0 + • • • 3

i 0•2 0.5 1.0 Herbage Cu/ Topsoil Cu

7- 0 6- 0 0

a...a 0 at o 5- 0 o .o :61 4. + + • u + c + •+. o ..c? 3' + + o 2 + . ..

0.2 0.5 1.0 Herbage Cu! Topsoil Cu o Soils on Upper Oxford Clay. • Soils on Clay Head. + Soils on Lower Oxford Clay.

Fig.45. Copper Content of Pasture Herbage in Relation to the pH,Iron and Organic Carbon Content of the Topsoil. (Topsoil 0-6ins depth. Herbage-Oven dry weight.)

Thame area 236

The data in Table 54 suggest that the uptake of Cu by herbage is fairly constant although the ratio between mean levels of herbage and topsoil Cu at sites on the Cornbrash and Portland limestones (ratio 1 : 3.8) suggests that Cu uptake is least on limestone derived soils. On the Clay Vale, however, range and mean Cu values for herbage and topsoil on the three parent materials are very similar. Nevertheless Fig. 45 reveals an imperfect trend for Cu uptake to fall with a rise in topsoil pH over the range pH 4.8-6.8 whilst Cu uptake is independent of the total Fe and organic carbon content of topsoils. 237

CHAPTER 17: DETAILED GEOCHEMICAL INVESTIGATIONS MARKET RASEN AREA

1. Introduction Stream sediment reconnaissance, reported in Chapter 11, reveals diffuse patterns of weakly anomalous levels of Mo (3-5 p.p.m.) along the eastern and western margins of the drift covered clay vale. Although the anomaly area is small, the Mo levels low and the area dominantly of arable farming, follow up work was carried out around Cold Hanworth and South Willingham (Fig. 46) to complement the studies made over the Oxford Clay and Kimmeridge Clay outcrops in Dorset and Buckinghamshire.

2. Description of the Detailed Study Areas A general account of the geology, topography, climate, soils and land use in the Market Rasen area is given in Chapter 11. The distribution of Mo anomalous stream sediments suggest that the primary source of Mo lies in bituminous shales in the Lower Oxford Clay and the Kimmeridge Clay and this is confirmed by the follow up work.

(A) Geology The lower part of the Oxford Clay in the Market Rasen area includes bituminous shales (Swinnerton and Kent, 1949) which, at Spridlington north of Cold Hanworth, are described as "dark grey shaley clay with pyritised ammonites and nucula" (Usher et al, 1888). Usher et al (1888) record that at South Willingham

Wes asen. Market Rosen. 0 1 2 •rth Willingham. Scale in Miles Owmb

•Spridlingto Xddin •• orth. „Hainton.

Cold •Li ngton. Sout illin• am.. Hanworth. Do iv non raverse 1. o raverse 2. Hain. Traverse 1.

Travers East. Barkwi

A. Cold Hanworth District. + Rock Sampling Point. Key to Rock Samples B. South Willingham District. 1 Kimmeridge Clay. 2 Spilsby Sandstone.

Fig. 46. Location of Soil Traverse Lines and Rock Sampling Points in the Market Rasen Survey Area G38

the Kimmeridge Clay contains "bands of hard inflammable oil shale separated by blue clay and stonebands", and the authors further observe that oil shale bands are present throughout the district from Donnington—on—Bain to Tealby. Almost the entire 300 feet of Kimmeridge Clay in Lincolnshire is of black shale facies with dark carbonaceous clays and bituminous shales (Pringle, 1919, Arkell, 1933, Swinnerton and Kent, 1949). Both Arkell (1933) and Downie and Wilson (1968) regard the Kimmeridge Clay sequence and the lithologies as closely similar to those of Dorset. The drift cover west of Cold Hanworth is discontinuous and of a very variable character (Straw, 1958), including stony boulder clay and small areas of lacustrine clay and aeolian sand. Usher et al (1888) record erratics of Pennine and Scandinavian origin; however, Straw (1958) regards the matrix of the boulder clay to be largely reworked Oxford Clay of local origin. Around South Willingham the Chalky Boulder Clay (Pig. 30) forms an extensive cover to the solid geology, although the larger streams have cut through the drift into the bedrock. On valley slopes some colluvial downwash of boulder clay over the Kimmeridge Clay is detected and many residual soils on the Clay contain debris derived from the drift.

(B) Soils Soils in both districts are broadly similar. Residual soils on the Oxford and Kimideridge Clays are very poorly drained clays whilst drift derived soils, although more variable in texture, are usually poorly drained stony clay 239 loams, locally calcareous Where chalk fragments are present. Residual soils on the Mid Jurassic near Cold Hanworth are naturally moderate to freely drained sandy clay loans, becoming poorly drained over clay and marl horizons. Alluvial areas are characteristically silty clay loams, locally stony, with drainage impeded by a high groundwater table. Almost all land on the Jurassic clays and glacial drift has tile drainage and the fields are regularly ploughed. Both processes improve profile drainage although gleying sets in below plough depth (10-15 inches) in the heavier textured soils.

(0) Land Use Arable farming dominates with both cereal and root production important. The heavy, poorly drained residual soils on the Jurassic clays are difficult to work and locally carry grassland used for dairy farming.

3. Distribution of Metals in the Bedrock There are no exposures of unweathered bedrock in or near the Cold Hanworth district. Temporary sections are opened from time to time in deep excavations, but none were present to permit sampling of the bedrock. The Kimmeridge Clay is exposed north of Hainton (Figs. 46, 47) where interbedded black paper shales and clays with black cementstone bands are found. Some of the shale partings are crowded with crushed pyritised ammonites. The section is similar to that at South Willingham (Usher et al, 1888) and to large parts of the Donnington borehole Colluvium. Mo Se Cu Pb V In Ti Hi Co Mn Cr As Ga Fe203% Org C %

Massive,Gritty, SPILS BY Ferruginous <2 <01 6 . 10 30 <50 200 20 16 130 10 <5 2 8.2 <0.1 SANDSTONE. Sandstone.

Yellow/Grey Unconsolidated <2 <0.1 6 5 40 <50 300 8 <5 16 20 <5 4 5.4 <01 Sandstone.

Colluvium.

Colluvium. Black Bituminous Paper Shale. 16 1.5 51 13 130 50 3000 85 13 130 100 <5 13 4.4 5.8 KIMMERIDGE CLAY. Black Stone Band.(calcareous) 16 3.8 45 20 130 <50 3000 85 10 130 100 <5 16 5.4 4-8

Black Bituminous 30 6.5 70 40 130 200 3000 100 10 100 100 5 16 10.5 Paper Shale. 6.8

4

Stiff Black Clay. 7 0.4 27 13 130 50 4000 Scale 50 13 85 100 <5 16 6.8 2.8 •2 in Feet. Hard Black Shale. 14 15 41 30 130 <50 4000 85 10 100 85 <5 16 5.0 58 0 Colluvium.

Fig.47. Metal Content' of Bedrock Samples from the South Willingham District,Market Rasen Area. * values in p.p.m. except where indicated. (Pringle, 1919) and is thus thought to be typical of most of the Kimmeridge Clay in Lincolnshire. Samples of Spilsby Sandstone (basal Lower Cretaceous) were obtained from a section east of South Willingham (Fig. 46). The rock is massive or poorly consolidated coarse yellow sandstone, generally ferruginous with localised carstone developments. The metal content of the bedrock samples obtained is displayed in Fig. 47. In the few samples examined, the Kimmeridgo Clay contains from 7-30 p.p.m. Mo (mean 17.0 p.p.m.) together with 0.4-6.5 p.p.m. Se (mean 2.7 p.p.m.) contrasting with the sandstone in which these metals are undetected. In addition levels of Cr, Cu, Ga, Ni, Pb, Ti, V and organic carbon in the Kimmeridge Clay are consistently greater than those recorded from the sandstone. Amongst the Kimmeridge Clay samples Mo, Se, Cu and less markedly Ni and Pb appear to display a common distribution together with Fe and organic carbon. The possible presence of such metal associations suggests that organic matter and/or pyrite (represented by total Fe) have some influence on the distribution of metals and incorporation with these compounds may have brought about the observed enrichment of Mo and Se. Levels of Cr, Ga, Ti and V show little variation between Kimmeridge Clay samples. These metals are probably associated with the clay minerals, the content of which is apparently fairly uniform despite lithological variation. Downie and Wilson (1968) record that in Dorset lithological variation in the Kimmeridge Clay arises from variations in the organic matter and carbonate content whilst the amount of clay in the 241 rocks remains fairly constant. By way of contrast, the sandstone, with little or no clay content, has low values of Cr, Ga, Ti and V. The occurrence of Mo and Se in the Kimmeridge Clay confirms the original supposition on the distribution of Mo in the bedrock based on the results of the stream sediment reconnaissance (Ch. 11). Furthermore, if the small section at Hainton is representative of the Kimmeridge Clay in mid Lincolnshire then the full sequence is probably enriched in both Mo and Se.

4. Distribution of Metals in the Overburden and the Relationship between the Metal Content of Rocks, Soils and Stream Sediments Soil samples were collected at 200-500 foot intervals along traverse lines crossing the principal geological units in each district and including both residual and drift derived soils within the zones of Mo anomalous stream sediments (Figs. 46, R9, R10). The metal content of the soils developed on the principal parent materials is summarised in Tables 55 and 57. Results from the two areas of detailed studies are discussed separately below.

(A) Cold Hanworth District An examination of the data in Table 55 reveals that the distribution of Mo is closely controlled by parent material. Raised levels of Mo (<2-16 p.p.m., mean 4 p.p.m.) occur in residual soils derived from the Lower Oxford Clay where peak values are accompanied by high values of Cr, Cu and V. Further detectable concentrations of Mo (2-3 p.p.m.) occur Table 55 lance and mean* metal content of overburden. develo ed on the rihcipal parent materials in the Cold Hanworth dittriA (sample -aepth 12-i8 inches)

• Metal content (p.p.m.) MoA Cu V Pb Ga Zn+ • Ti Ni CoY Mn Cr Fe203% Transported overburden Alluvium <2 19 127 18 16 110' 2883 40 11 375 94 6.7 <2 10- 60- 10- 10- <50- 1600- 30- 5- 200- 50- 4.5- -3 30 300 30 30 (12 samples) 200 4000 50 20 1000 130 11.1... Drift: Boulder clay <2 23 132 19 17 112 3307 43 12 444 100 5.9 and sands <2 8- 30- 5- 5- -:0- 850- 8- =5- 85- 50- 1.8- (21 samples) -3 40 200 30 30 160 5000 60 30 1600 160 8.9

Residual soils Oxford Clay 4 26 177 18 19 107 3869 62 8 190 446 6.1 2- 16- 85- 13- 13- 50- 1300- 50- c5 40- 85- 2.0- (13 samples) 16 40 300 30 30 200 6000 85 13 500 200 15.0 Mid Jurassic limestone and <2 24 131 27 16 94 2899 42 14 989 85 8.2 clays (includinL Kelloways• <2 10- 60- 13- 13- :50- 1600- 20- 8- 300- 50- 5.2- Beds) -2 40 300 30 30 200 4000 60 50 2000 130 11.5 (14 samples) * Geometric mean • A Mean calculateU with -=2 = 1 p.p.m. N.) Mean calculated p.y.m. = 40 p.p.m. Y Mean calculated vitk :5 p.p.m. = 3 p.p.m. 243

in some of the drift and alluvial soils, whilst Mo is undetected (<2 p.p.m.) in soils derived from the Mid Jurassic sediments. The distribution of Mo suggests a primary origin in the bituminous shales of the Lower Oxford Clay. Low Mo values in drift derived soils are probably due to the mixing of molybdeniferous Lower Oxford Clay with normally barren material. The further occurrence of detectable concentrations of Mo in alluvial soils suggests the mechanical distribution of Mo—rich material into the drainage network with a similar dilution depressing No values. Although Straw (1958) regards the matrix of the boulder clay in the western half of the vale to be dominantly reworked Oxford Clay of local origin, the Mo anomaly is much reduced in drift derived soils. However, the apparently molybdeniferous bituminous shales of Lower Oxford Clay form only a small proportion of the whole formation and can have contributed only a small amount of material to the drift. The Mo—rich material was thus probably rapidly diluted by large amounts of barren Oxford Clay debris as the drift was homogenised at the base of the Ice Sheet. Residual soils on the Lower Oxford Clay have a higher mean content of Cr, Ni and V than the other soil groups, whilst peak values of Mo are accompanied by high values of Cr, Cu and V. These metals may be enriched together with Mo in the bituminous shales, an association of metals similar to that found in the Lower Oxford Clay at Thame (page 217). The distribution of the remaining metals is summarised in Table 55. Mean values of Mn and Cr: are lowest in the 244

Oxford Clay soils, rising in drift and alluvial soils and are highest in soils derived from the Mid Jurassic limestones; the latter group also contain the highest range and mean content of Fe. Critical examination of the data reveals that, regardless of parent material, levels of Mn and Co are lowest in the most poorly drained soils, wherein they are most mobile, with highest values of Mn and Co in moderately and freely drained soils. The mean metal content of soils and stream sediment in the Cold Hanworth district, derived from both the Mid Jurassic limestones and their drift cover and also the Oxford Clay and its drift cover, is shown in Table 56. Mean values of all metals, except Mn, Co, Zn and Fe, in stream sediments derived from the drift and the Oxford Clay are close to those of the combined data from residual soils on the Oxford Clay and soils on the drift. This relationship suggests that anomalous levels of Mo are suppressed in stream sediment by dilution with barren material. Furthermore, the relationship is thought to indicate that mechanical dispersion is operative in the transport of metals from soils into the drainage network. In contrast the enrichment (x2—x3) of Mn and Co in stream sediments together with the rise in Zn values may be explained by the mobilisation of these metals in very poorly drained soils and their removal to the drainage network with circulating groundwater (see page 147) Stream sediments derived from the Mid Jurassic limestones and their drift cover tend to have a lower metal content than associated soils. Since large amounts of CaCO precipitate, coating pebbles and twigs in streams, 3 Table 56 heap( metal content of soilsA and associated stream sediments+ on the principal parent mfiterials in the Cold Hanworth district, Market Rasen area

Media Metal content (p.p.m.) Parent material (No. of samples) Mo Cu V Pb Ga Zn Ti Ni Co Mn Cr Fe203%

Soils 2 22 147 19 18 109 3379 48 10 324 114 6.0 Oxford Clay, drift (43) cover and alluvium Stream sediments 42 24 126 20 13 159 4400 47 29 780 102 3.2 (15)

Mid Jurassic Soils 2 24 124 29 16 101 2917 42 14 967 83 8.3 limestones and (17) clays with Stream sediments <2 12 66 18 8 84 3136 23 20 456 64 2.3 drift cover (8) * Geometric wean A Sample depth 12-18 itches + Data on mi-auL 8C—mesh fraction 246 were noted during the stream sediment reconnaissance survey, it is concluded that the dilution of stream sediments by 0300 3 precipitated from groundwater entering the streams (see page 201) is responsible for much of the contrast in metal values noted in Table 56. The formation of imiaobile Mn and Fe oxides in the freely drained soils on the limestone is possibly responsible for some of the contrast between soils and sediment values.

The occurrence of detectable concentrations of Mo in some sediments derived from the Mid Jurassic rocks and their sparse drift cover is probably due to the presence of Mo in drift derived from the Lower Oxford Clay low down on the limestone outcrop.

(B) South Willingham District The data in Table 57 show that the distribution of Mo in soils is closely related to parent material. Residual soils on the Kimmeridge Clay contain up to 16 p.p.m. Mo

(mean 4 p.p.m.), contrasting with soils on the Chalky Boulder Clay in which Mo is only occasionally detected

(< 2-2 p.p.m.). The Kihicteridge Clay soils also contain higher mean levels of Co, Cr, Ga, Pb, Ti, V and Fe.

The situation revealed is one of a metal rich black shale overlain by a drift barren of Mo and lower in most other metals.

Range and mean values of Mo and Cu are lower in residual soils on the Kimmeridge Clay than in the bedrock samples obtained (Table 58). However, levels of Mo and Cu fall off in soils on slopes below the Chalky Boulder Clay cover where values are probably suppressed by the presence Table 57 Range and rean* metal content of overburderLdeveloped on the principal parent materialb. in the South Willingham diiArict (sample-de th 12-18 inches)

Metal content (pp.m.) Mc6' Cu V Pb Ga Zn+ Ti Ni COY Mn Cr Pe203% Transported ove2burden Alluviums 5 21 150 27 16 104 3250 40 11 707 84 9.5 <2— 13— 100— 20— 13— 85— 2000— 20— 10— 130— 50— 4.8- (4 samples) 10 30 200 40 20 130 6000 50 13 1000 100 20.0 Chalky boulde2 clay 2 17 80 23 10 79 2098 34 11 511 56 4.0 5— 40— 5— 3— (50— 600— 13— <5— 30— 30— 1.8- (27 samples) 30 200 50 20 200 4000 85 30 1600 130 8.6

Tlesidual soils

Kimmeridge Clay 4 24 120 31 16 95 3079 41 14 432 82 6.7

* Geometric mean except fcr a arithmetic mean Mean calculated with <2 2.p.m. = 1 p.p.m. Mean calculated ir.:_th <50 p.p.m. = 40 p.p.m. IN) Y Mean calculated with <5 2.P.m. = 3 p.p.m. 248 of barren material introduced by colluvial downwash. It is probable that Mo values in residual soils are somewhat depressed by the presence of barren material derived from the pre—existing drift cover and that this is at least partly responsible for the contrast between bedrock and soil values. The presence of raised levels of Mo in alluvium is considered to be due to the incorporation of metal rich detritus derived from the Kimmeridge Clay. alluvium beside a stream draining areas of Chalky Boulder Clay and Spilsby Sandstone contains no detectable quantities of Mo. A broadly similar range of values for Mn, Co and Zn is encountered in both the drift derived and the Kimmeridge Clay soils. However, low levels of these metals characterise the gleyed clay soils and more poorly drained drift soils where these metals are mobile, whilst the better drained soils, more typical of the drift, contain higher levels of these metals. The mean metal values for sediment from streams draining areas of Chalky Boulder Clay and of soils derived from this parent material are shown in Table 58 together with the mean metal values of sediments from streams draining areas of boulder clay, Lower Cretaceous and Kimmeridge Clay and the mean metal contents of all the soils sampled in Sotuh Willingham district. The latter grouping is adopted because of the composite nature of streams with catchments on the Kimweridge Clay. The mean metal content of stream sediment and soils derived from the Chalky Boulder Clay is broadly similar except for Zn with is enriched in the sediment and Fe which is apparently retained in soils. The reason for the observed distribution of Zn and Fe cannot be explained with the data available. However, the similar content of other Table 58 Mean* metal ccntent of rocks, soilsA and associated stream sediments+ in the South Uillinham district, Market Rasen area

Media Metal content (p.p.m.) Parent material (No. of samples) Mo Cu V Pb Ga Zn Ti Ni Co Mn Cr Fe203%

Rocks? 17 47 130 25 15 76 3400 81 11 109 97 6.6 (5) Kimmeridge Clay L.3sidual soils 4 24 120 31 16 95 3079 41 14 432 82 6.7 (20 d Soils <2 17 80 23 10 79 2098 34 72 511 56 4.0 (27) Chalky Boulder Strevm sediments <2 15 81 23 11 238 3556 28 21 594 57 2.3 Clay (15) ;-oils 2 21 99 27 13 87 2560 37 12 474 68 5.3 Kimmeridge Olay, (15) Chalky Boulder Ltream sediments 2 21 148 25 15 317 4000 48 37 767 117 5.1 Clay and Allmiuill (8) * Geometric mean except ? arithmetic mean A Sample depth 12-18 luches + Data on minus 80—mesh fraction 250

metals strongly suggests that the mechanical distribution of metals, in weathered material, into the drainage network is the dominant process of metal dispersion on the Chalky Boulder Clay. For the remaining soils and stream sediments a less perfect relationship exists due, most probably, to the composite nature of the stream catchments and the unrepresentative soil data which do not include any samples from the Lower Cretaceous. However, the similar mean No and Cu levels in soil and sediment, contrasting with the levels in residual Kimmeridge Clay soils only (Table 57), indicates that sediment levels are probably depressed by dilution with material barren of Mo and low in Cu. Thus the dispersion of Mo in this district appears to be dominantly mechanical with the high levels present in the bedrock suppressed first in the soils by barren colluvium and secondly in the stream sediments by large quantities of. barren material derived within stream catchments of composite geology and overburden. The increase in levels of Mn, Co and Zn between soils and sediment is probably due to the introduction of metals leached from poorly drained and waterlogged soils which are common on the Kimmeridge Clay beside watercourses. Levels of V and Cr are raised in the sediment in apparent contradiction of the observations made above concerning Mo and Cu. However the sediments contain some debris derived from the Lower Cretaceous which, the stream sediment reconnaissance demonstrated, contain large quantities of V and Cr, sufficient to be responsible for the values observed here. Table 57 Range and mean molybdenum and copper content of topsoils and associated he-rloage+ on soils derived from the principal parent materials Narket Kasen area

Mo(p.p.m.)Y Cu(p.p.m.) Mo status and parent Locality material Herbage Topsoil Herbage Topsoil Anomalous :1.9 3 10.5 13 Oxford Clay 0.6-4.8 <1-5 7.5-14.0 11-14 (4 samples) Cold Hanworth district Background 0.7 1 9.4 15 Boulder Clay 0.5-0.8 <1-1 7.5-11.5 12-18 (4 samples) Anomalous 1.9 3 11.0 18 Kimmeridge Clay 1.7-2.0 2-4 7.0-15.0 11-25 (4 samples) South Uillintl,ham district Background 0.7 -(1 7.5 14 Chalky Boulder Clay 0.6-0.9 •=l-2 6.5-8.5 12-15 (3 samples)

* Arithmetic mean Mixed pasture herbage, oven dry weight

A Sample depth 0-6 inchas Y Mean calculated with '.1 p.p.m. = 0 p.p.m. H 252

5. The Metal Content of Herbage Grab samples of herbage containing mixed grasses and clover were obtained from permanent pastures and leys at Mo anomalous and background sites in the two districts. The data in Table 59 show that the Mo anomaly in soils is reflected in the herbage growing at such sites. The Mo content of herbage is broadly related to the Mo status of topsoil and the increased quantities of Mo in anomalous soils appear to be largely available to plants. However with the limited data it is not possible to ascertain whether the Mo and Cu status of herbage on anomalous soils is influenced by environmental factors. 253

CHAPTER 18: METAL DISPERSION IN AREAS OF BLACK SHALE FACIES

Geochemical investigations in five areas, reported in Chapters 13-18 have, by means of multi—element analysis, examined the distribution of Co, Cr, Cu, Fe, Ga, Mn, Mo, Ni, Pb, Ti, V and Zn in rocks, soils and stream sediment, of Mo and Cu in pasture herbage and some aspects of the distribution of As and Se. For the purpose of discussing metal dispersion in the areas of black shale facies examined in detail a twofold division is adopted following the practice of Howtes and Webb (1962).

I PRIMARY DISPERSION — the distribution of metals in the bedrock II SECONDARY DISPERSION — the distribution of metals in soils and stream sediment. The relationship between the metal content of rocks, soils and stream sediments and the uptake of metals by herbage

In this chapter, as elsewhere, emphasis is placed on the distribution of Mo.

I PRIMARY DISPERSION Distribution of Metals in the Bedrock

1. Introduction The regional geochemical surveys reported in the 254

preceeding pages have identified and delineated areas characterised by anomalously high levels of Mo, with the source of raised levels of Mo (> 3 p.p.m.) restricted to bedrock of black shale facies. Essential features of the four molybdeniferous formations studied in detail are summarised in Table 60; all the rocks have characteristics that classify them as "black shales" as defined in Chapter 2. They display.a large variety of lithologies, a range of colours (but are never black), are representative of several tectonic environments and range in age from Upper Ordovician to Upper Jurassic. Nevertheless, all display features of quiet water deposition in an anaerobic environment, and all are enriched in organic matter with respect to adjacent "normal shales".

2. The Metal Content of the Bedrock Goldschmidt (1954) has stated thut an enrichment in Mo, V, Ni and Cu is typical of marine black shales. An examination of Table 61 reveals that whilst all four black shales are enriched in Mo (x2—x7) the enrichment of other metals with respect to the "average shale" values of Turekian and Wedepohl (1961) is a variable phenomenum. Thus in the Bowland Shale Cu, ni, Pb, Se, V and Zn are enriched (x2—x12) with respect to the average shale values. In contrast the Kimmeridge Clay samples are significantly enriched only in Se (x4) and the Lower Oxford Clay only in Zn (x3) whilst the Meidrim Shale, rather than being enriched in metals is depleted in all except V. Cave (1965) has suggested that only those shales displaying an enrichment in Mo, V, Ni and Cu can be Table 6C Essential features of the fcur black shale formations sampled in the programme of detailed studies

Metals enriched with Metals respect associated to with Tectonic Colour Benthonic average organic Formation Age Environment Lithology (Munsell notation) Fauna* shale+ matter. Kimmeridge Upper • Clu.df Clay, carbonaceous 2.5Y.N3/2., 5Y.N4/1., Rare to Mo, Se Yo, Se, Cu Clay Jurassic clay, bituminous 5Y.N4/2., 5Y.N5/1. occasional. (Ni, Pb, Fe) shale, cementstone Abundant forms but few species. No infauna

Lower Upper Snelf Clay, carbonaceous 2.5Y.N8/0., 5Y.N5/1., pare to absent Mo, Zn (HO, Cr, Cu Cxford Jurassic clay, bituminous 5Y.N5/2., 5Y.N6/1., in clays. V, Zn) Clay shale , 5Y.N6/2., 5Y.N7/1., Abundant forms 5Y.N7/2., 10YR.N2/2. but few species in limestones and shell beds. No infauna

Bowland Low/Mid Ba.ciri Calcareous shale, 2.5Y.N3/2., 2.5Y.N4/2., Very rare or Mo, Cu" Mo, Cr, Cu, Shale Carboniferous, fissile siltstone, 2.5Y.N5/2., 2.5Y.N6/2., absent in Ni, Pb, Ni, Se,-,V; Group siltstone, shale, 2.5Y.N7/1., 2.5Y.N7/2., shales. Se, V, Fe • paper shale, 2.5Y.N7/4":5Y.N3/1., Occasional to Zn cementstone, . 5Y.N3/2., 5Y.N4/l., common in • ... b • argillaceous 5Y.N4/2., 6Y.N5/1., limestones. limestone, 5Y.N6/1., 10YR.N2/2., No infauna , sandstone 10YR.N4/2., 10YR.N8/4. _ — Meidrim Upper Geosyncline Shale, c,.6.1careous 2.5Y.N3/0., 2.EY.N4/0 Absent Mb Mo, V Shale Ordovician shale, 2.5Y.N5/0., 5Y.N4/1., argillaceous 5Y.N5/0., 5Y.N5/l., limestone 5Y.N5/2., 7.5YR.N3/0.

* For source of information see 2(A) Geology in Chapters 13, 14, 15, 16 and 17. + Average shale values of Tvrekisn and v.cdepohl, 1861 Table 61 Mean* metF1 content of the four black shale formationsA sampled, compared with average value for sedimentary rocks

Metal content (p.p.m.) rg. Flo Cu V Se Pb Ga Zn Ti Ni Co Mn Cr As Pe203% CO % Kimmerdige Clay 16 46 130 2.5 24 16 72 3330 76 11 118 98 .!5 6.1 5.0 (6 samples)

Lower Oxford Clay 5 34 103 <0.1 16 18 250 3550 46 13 104 75 45 4.4' 3.9 (11 samples) Bowland Shale 17 18 344 7.6 69 15 772 1700 122 21 206 118 17 2.9 4.7 (17 samples) Meidrim Shale 5 23 160 <0.1 20 25 50 3250 15 6 54 50 45 2.4 1.5 (14 samples)

Average Shale+ c,.6 45 130 0.6 20 19 95 4600 68 19 850 90 13 611P

Average Black ShaleY 10- 20- 50- 20- - 100-. - 20- 5- - 10- 75- • •••• 300 300 200 400 1000 300 50 500 225 * Geometric mean + Turekian and Wedepohl, 1961 A Clay and shale Samples only Y Krauskopf, 1955 257

classified as true black shales. By this criteria only the Bowland Shale displays the necessary features. This would, however, seem to be an over—application of Goldschmidt's • conclusions and disregards other important features. The four black shales sampled are enriched in a number of metals with respect to adjacent "normal shales" in the study areas. Furthermore Mo and various other metals are associated with the increased amounts of organic matter present only in the black shales. Krauskopf (1955) recognises that the metal content of black shales is variable, as shown in his "average black shale" values (Table 61) and that the accumulation of organic matter is the most typical feature of black shales. The metal content of the shales sampled (Table 61) generally falls within the ranges given by Krauskopf for "average black shales" although the levels are for the most part at the low end, particularly for Mo. Vine (1966, 1969) and Vine, Tourtelot and Keith (1969) studying a number of American black shales also note variety in both the metals enriched in these deposits and the degree of enrichment. This lack of consistency may be attributed to variations in the supply of metals and changes in the depositional environment resulting in differences in both the total metal content and the metal associations in the rocks (Vine, 1969). It is beyond the scope of the present study to determine the supply of metals to the areas of deposition. However, since the enhanced metal values in any area occur only where the organic matter content of the bedrock is increased, the role of organic matter, or the environment in which organic matter accumulates, is thought to be more important than any changes in metal supply. 258

3. Metal Associations in the Bedrock Although only a few rock samples were obtained, often in a weathered condition, it has been possible to suggest factors controlling the occurrence of metals in the bedrock by identifying suites of metals with similar distributions. By far the most important control is organic matter, for this appears to be responsible for the accumulation of anomalously high levels of Mo in the four black shales sampled. Thus in cementstones, limestones and shell beds interbedded with the black shales there is a fall in levels of metals associated with clay minerals and detrital fraction, Ga and Ti and variously Cr, Cu, Ni, Pb, V and Zn but where the organic matter is still present those metals associated with the organic fraction retain their enhanced values. Goldschmidt (1954) regards Mo, V, Ni and Cu as the suite of metals typically associated with organic matter in oil, asphalt and marine black shales. However, in Chapter 2 it was noted that the trace element content of black shales is strongly influenced by the quantity and composition of the organic matter present in the rock and also the depositional environment. The data from the present investigation show that, in the Meidrim Shale, Mo and V are associated with organic matter whilst in the Bowland Shale the association is of Mo, Se, Cu, V, Cr, Ni and total Fe with organic matter. There is very little data from the Kipmeridge Clay but it would appear that Mo, Se and Cu are associated with organic matter, whilst total Fe, Pb and Ni may also be part of the assemblage. Metal distributions in the Lower Oxford Clay are difficult to interpret with the small amount of data available. For, whilst 259

there is evidence that Cr and V are concentrated in lignite, Mo, Cu, Zn and organic matter are enriched in the Lower Oxford Clay but show no common distribution. Vine (1966, 1969), Vine and Tourtelot (1969, 1970) and Vine, Tourtelot and Keith (1969) record considerable variations in the metals associated with the organic matter fraction in black shales. Changes in the metal associations may be attributed to variations in both the supply of metals and the depositional environment which affects the availability of elements and the degree of metal enrichment. The Bowland Shale displays a considerable enrichment in a number of metals, with Mo, Se; V, Cu, Cr, Ni and total Fe associated with organic carbon. The close correlation of total Fe, present as pyrite, with organic carbon reflects the intimate association of pyrite and organic matter in the bedrock. This association in a rock containing little or no benthonic fauna is typical of sapropelite (Goldschmidt et al, 1948). Sapropelite is formed under extremely reducing conditions with the stagnant bottom waters and sediments charged with H2S. These deposits are particularly enriched

in Mo, V, Ni and Cu (Goldschmidt et al, 1948) — as is the Bowland Shale with respect to the other shales examined in the present survey. The environment of sapropelite is favourable for the accumulation of metals with both organic matter and sulphides (Krauskopf, 1955). The enhanced levels of Pb, Zn and As in the Bowland Shale are probably due to precipitation as sulphides and incorporation with pyrite (Goldschmidt, 1954, Rankama and Sahamal 1950) although these metals may accumulate with organic matter (Krauskopf, 1955). Korolev (1958) has demonstrated that, following the 260

co—precipitation of Mo with PeS2, Mo ray occur with pyrite in sedimentary rocks of black shale facies. Using the present data it is impossible to identify the definitive role of organic matter and pyrite in the accumulation of Mo although it is considered that the Mo is probably associated with the organic matter in view of the close correlation of Mo and organic carbon (Fig. 37 ). Similarly it is suggested that Se, Cu and V are associated with organic matter in the Bowland Shales. A modern counterpart to the Bowland Shale environment may be found in the metal rich organic muds now accumulating in troughs in the Baltic (Manheim, 1960). Loyola of 2,.g, Cu, No, V and Zn all show a sharp increase on passing from near shore oxygenated sands into the reduced muds of the stagnant trough. Considerable metal concentrations are noted where both sediments and bottom waters are stagnant and charged with H2S; up to 80 p.p.m. Mo is recorded. In the case of the Baltic, as with the Bowland Shale environment, although bottom conditions are hostile to life, the surface waters are oxygenated and support a full neretic and planktonic fauna. In contrast to the Bowland Shale the Lower Oxford Clay is only marginally enriched in Mo and Zn, despite the relatively large amounts of organic matter present (up to 4.8% organic carbon). The total metal content and the metal associations observed in the Lower Oxford Clay suggest two important controls: (a) environment and (b) the composition of organic matter. (a) Environment — The Lower Oxford Clay contains some pyrite, large quantities of organic matter and also a sparce benthonic 261 fauna, an association closely similar to that encountered in gyttja (Goldschmidt et al, 1948). Gyttja is produced in very much less intense reducing conditions than sapropelite and contains lesser concentrations of Mo, V, Ni and Cu although Cr may be enriched (Goldschmidt et al, 1948). Thus, to a large extent, the difference in metal content for Mo, V, Ni and Cu in the Bowland Shale and Lower Oxford Clay can be accounted for in terms of the intensity of the reducing conditions set up in the depositional environment. (b) The composition of the organic matter. Manskaya and Drozdova (1968) quote extensive studies that illustrate the comparative role of both environment and different types of organic natter in the accumulation of Mo, Cr, Cu and V in rocks of marine black shale facies. The Lower and Upper Oxford Clay differ mineralogically only in their content of organic matter and lime (Freeman, 1956, 1964). With the increase in organic matter in the Lower Oxford Clay values of Mo, Cr, Cu, V and Zn also rise. From the data available Cr and V appear to be enriched with lignite whilst Mo, Zn and Cu are probably associated with the unidentified forms of organic matter dispersed in the clay. Manskaya and Drozdova (1968), Goldschmidt (1954) and Krauskopf (1955) observe that in black shales Mo is more frequently associated with organic matter of marine origin rather than terrigenous matter such as lignite. Thus the unidentified forms of organic matter in the Lower Oxford Clay may well be of marine origin. The above results indicate that the probable factors controlling metal distribution in the Lower Oxford Clay are far more complex than can be ascertained in the present limited investigation. 262

For the remaining sets of black shale samples the metal associations provide little insight into the depositional environment due, in the case of the Kimmeridge Clay to the small amount of data available and in the case of the Meidrim Shale to the badly weathered nature of the samples and probable redistribution of iron. However, certain coyirients can be made. The Kimmeridge Clay samples reveal a considerable enrichment in Mo, Se and organic carbon which would seem to indicate the suitability of the organic matter for metal enrichment and a moderately intense reducing environment during deposition. Vanadium does not appear to be enriched and shows no common distribution with organic matter, features also noted in rock samples from the Dorset coast (pers. comm. C. Dunn). It is possible that the type of organic matter present was not that with which V is readily concentrated; alternatively the supply of V to the depositional areas was small during Kimmeridge Clay deposition. It is noteworthy that the mean metal content of Mo is the same for both the Meidrim Shale and the Lower Oxford Clay, despite the Lower Oxford Clay having the larger (x2) content of organic carbon. Furthermore the Meidrim Shale has a higher mean content of V. However, the close association of Mo and V with organic carbon is unlike the metal relationships observed in the Lower Oxford Clay suggesting that the type of organic matter present in the Meidrim Shale favours the accumulation of the two metals. 263

The enrichment of Mo in all four rocks, despite apparent contrasts in environment and organic matter, is significant • since it confirms the conclusion made by Krauskopf (1955) that Mo is the metal most consistently concentrated in marine black shales.

II SECONDARY DISPERSION 1. Distribution of Metals in the Overburden The detailed geochemical studies reported in Chapters 13-18 examine metal distributions in the overburden from two aspects: (A) the lateral distribution of metals as revealed by sampling along traverse lines and (B) the vertical distribution of metals within soils as shown by sampling at two depths.

(A) The lateral distribution of metals in the overburOen Systematic sampling at a depth of 12-18 inches along regional soil traverse lines has demonstrated that metal distributions are broadly related to either (i) the parent material of the soils or (ii) the secondary environment.

(i) Metal distribution patterns related to parent material In the areas studied No anomalous soils are restricted to residual overburden developed on Mo—rich black shales and alluvium, colluvium or glacial drift derived from these rocks. Similarly the distributions of Cr, Cu, Ga, Ni, Pb, Se, Ti and V have been related to the outcrops of distinctive parent materials in the areas investigated, although locally,as in the Bowland Forest area, the distribution of Ni is influenced by the secondary environment. 264

In areas of residual soils the distribution of Mo is essentially simple and directly related to the outcrop of Mo—rich black shale horizons as in the Shaftesbury and West Carmarthenshire areas. However, the presence of transported overburden greatly modifies distribution patterns with two principal relationships noted in the present study. The incorporation of Mo—rich black shale debris in transported overburden gives rise to Mo anomalous soils beyond the outcrop of black shale formations and !smear patterns! are observed as in the Bowland Forest and Market Rasen areas. Atkinson (1967) working in Ireland notes a similar extension of Ho anomalous overburden, related to the Mo—rich Clare Shales, due to the incorporation of Clare Shale debris in locally derived boulder clay. In contrast the presence of exotic overburden containing background levels of Mo in the Thame and Market Rasen areas masks Mo—rich black shales and limits the extent of Mo anomalous soils to areas of residual soils and associated alluvium. Fletcher (1968) notes a similar mantling of Mo—rich black shales by barren drift in the South Pennines and consequent restricted area of Mo anomalous soils.

(ii) Metal distribution patterns related to the secondary environment In general, levels of Mn, Co and Fe reflect the local drainage status of the overburden rather than the composition of the parental material,. Occasionally the distribution of Ni and Zn follows that of Mn, Co and Fe, Characteristically, poorly drained soils contain low levels of this group of metals contrasting with adjacent 265 better drained soils containing higher metal concentrations. Horsnail (1968) observes a similar distribution in some parts of Devon and North Wales and notes that the mobility of this group of metals is greatly increased in poorly drained soils where reducing conditions prevail. In the present survey it is suspected that in all the areas Mn, Co and Fe are transported laterally in the overburden from poorly drained and waterlogged soils, moving with groundwaters towards the drainage network. Indeed the considerable mobilisation of Mn, Co, Ni, Fe and Zn on long steep slopes carrying poorly drained soils is observed in the Bowland Forest area with lateral redistribution of these metals to sites where their accumulation results in localised anomalies of some magnitude (page 169).

(B) The vertical distribution of metals within soils In the present study it has not been possible to examine systematically the distribution of metals within soil profiles. Nevertheless samples taken at two depths (0-6 inches and 12-18 inches) provide data illustrating the generalised relationship between the metal content of topsoils and subsoils. Typically soils developed on Mo—rich black shale parent material suffer impeded drainage with the 0-6 inches sample in moderate to poorly drained topsoils and•the 12-18 inches sample in gleyed subsoil. However, the soils examined range from freely drained brown earths in parts of the Bowland Forest area to waterlogged surface— and groundwater gleys on the Oxford and Kimmeridge Clay vales. The relationship between the metal content of 154 topsoils and subsoils developed on 266

Mo—rich parent material is summarised in Table 62. The data indicate a clear tendency for levels of Mo, Fe, Ni, Cu, Cr, V and Co to fall in topsoils whilst Pb, Zn and Mn are enriched. In contrast Ga and Ti show no significant variations between topsoil and subsoil. Goldschmidt (1954) regards Ti and Ga as those elements most usually associated with clay minerals in sediments and soils. The similar values for these metals thus reflect limited redistribution of clay minerals and as such emphasise field observations that textural variations within the soils examined are generally small. In view of the limited redistributions of clays the fall in values of Mo, Fe, Ni, Cu, Cr, V and Co in topsoils is largely attributed to leaching. Other workers have reported similar trace element distributions in soils developed on a variety of parent materials of sedimentary origin in England. Butler (1954) found that maximum concentrations of Fe, Ga, Cr, V, Li, Ni, Co, Zn, Yt, Sr, Ba and Rb occur in the lowest horizons of brown earths and gleyed soils derived from glacial drift and Carboniferous shales in Lancashire. Similarly Le Riche and Weir (1963) found that the Co, Ni, Cr and Ga content of brown.earths, developed on chalk head and loess in Southern England, increased with depth, a feature attributed to the leaching of elements associated with secondary ferric oxides and metal rich clays. Examination of Table 62 suggests that, taken overall, the susceptibility of metals to leaching from the topsoil is Mo >Fe> Ni> Cu> Cr> V> Co. Unlike the majority of trace elements the mobility of Mo is increased with a rise in soil pH (Davies, 1956). That- Mo should be the element most suseptible

Table 62 Geolnetric mean values for the ratio metal content of tcnsoil 0-6 inches) metal content of subsoil (12.-18 inches) calculated from 154 Mo—rich soils

Mo Cu Pb Ga Zn Ti Ni Co Mn Cr Pe203%

0.62 0.75 0.84 2.17 0.97 1.78 1.01 0.74 0.87 1.57 0.77 0.72 268 to leaching is considered to reflect the pH of topsoils, maintained for the most part near pH 6.0 by agricultural practice. Soils with a lower topsoil pH in West Carmarthenshire were found to display a reduced contrast in Mo content between topsoils and subsoils. A reduced contrast is also encountered where Mo is probably retained in topsoils in combination with organic matter and secondary ferric oxides. Indeed in the Thane area accumulation with organic matter and ferric oxides is thought to be responsible for the conspicuous enrichment of Mo seen in a number of topsoils. Similar values for the metals suseptible to leaching are found at both sample depths at waterlogged sites and in very poorly drained soils developed on the Oxford and Kimmeridge Clay. This is thought to largely reflect the limited downward movement of water, due to waterlogging and/or an impervious parent material. In addition secondary concentration by sorbtion onto active Fe and Mn oxides found in surface horizons with periodic flooding must be considered. In contrast to the metals discussed above, Pb, Zn and Mn show an overall trend towards accumulation in topsoils. The surface accumulation of Pb is one of the most consistent features observed during the present investigation. Swaine and Mitchell (1960) attribute a similar topsoil enrichment in Scottish soils to accumulation by plants, with Pb held in the surface horizon in an insoluble complex formed on the decay of the plant material. In contrast Butler (1954) attributes the source of high Pb levels in Lancashire topsoils to Pb—rich baryte concretions. Since the present study reveals the greatest enrichment in Pb (up to x10 subsoil values) in uncultivated organic rich topsoils, at sites typically removed 269

from sources of pollution, the accumulation of Pb due to plant activity is considered the most satisfactory explanation. Hibbard (1940) found that topsoils in California contain large amounts of Zn where grass growth had long been undisturbed. He concludes that the accumulation of Zn was caused by the action of plants drawing metals from the subsoils followed by immobilisation of Zn in topsoils on the death of plants. Similarly, in the present investigation, the accumulation of Zn is apparent in organic rich topsoils where it may be attributed largely to plant activity. However, it is possible that Zn may be immobilised in topsoils by sorbtion onto secondary Fe and Mn oxides. Furthermore, the contrast between topsoil and subsoil values in gleyed soils may be enhanced by the leaching of Zn from the lower part of the soil profile (page 275). The distribution of Mn between the topsoils and subsoils examined is irregular although the data in Table 62 reveal a strong tendency for Mn levels to be greatest in the 0-6 inches sample.. Butler (1954) observes an irregialar distribution for Mn in the profiles of very poorly drained soils from Lancashire and concludes that the formation of Mn02 renders Mn relatively immobile and not easily redistributed by leaching and gleying processes. It is suggested that in soils derived from the Mo—rich black shales, although the pH relationships of topsoils and subsoils in the present investigation are variable, the Eh of topsoils is commonly higher than subsoils, due to improved drainage of surface horizons, thereby fa7auring the formation of Mn02. Thus Mn is probably retained in the surface horizons due to its immobility whilst it is leached from the poorly drained 270

subsoils (see page 275) thereby contributing to the contrast between topsoil and subsoil values, However, such a mechanism does not provide a compre.t2 explanation when the Mn—rich topsoils of moderate and freely drained soils are considered, for here Mn is unlikely to be very mobile in the subsoils. However, plants are recognised as accumulators of Mn (Goldschmidt, 1954) and the high levels of topsoil Mn may well be due to processes similar to those operative for Pb and Zn. Manganese oxides readily scavenge other metals, notably Co and Zn (Goldschmidt, 1954) and the low contrast between topsoil and subsoil levels of Co may be due to the frequent retention of this metal in topsoil by sorbtion onto secondary oxides.

2. The Relationship between the Metal Content of the Bedrock, Overburden and Stream Sediment and the Diszorsion of Metals from Sedimentary Rocks of Black Shale Facies The relationship between the Mo content of rock, soil and stream sediment is simple and direct. Similarly the metals Cr, Ga, Pb, Se, Ti and V generally have simple relationships between the three media contrasting with Mn, Fe, Co and Zn which often display a variety of values reflecting substantial redistribution of these metals due to the influence of the secondary environment.

(A) 21.t lisersionofmoll bed raetais In areas of residual overburden the Mo content of rocks and associated soils is broadly similar. Furthermore in such areas streams with catchments developed wholly on the outcrops of the Mo—rich formations contain sediment with Mo 271

values similar to adjacent soils. The distribution of No in these areas, as exemplified by the West Carmat.thenshire survey area and the Kimmeridge Clay vale in the Shaftesbury survey area, is thus quite simple and relationships between the three media direct. In the course of the present investigation factors have been observed that complicate the rock, soil, stream sediment relationship. These factors are (i) the presence of transported overburden and the.composition of this material, (ii) the character of the drainage network and its relationship with areas of Mo—rich soils, (iii) the presence of secondary precipitates in the drainage network. It is noted in a previous section (page 263) that the lateral distribution of Mo in soils is related to the composition of the overburden. Thus exotic material containing background levels of Mo masks Mo—rich bedrock in the Thame and Market Rasen areas contrasting with the situation observed in the Bowland Forest area where the incorporation of Ho—rich black shale debris in boulder clay of local origin gives rise to transported anomalies in soils and adjacent stream sediments. In the Bowland Forest area the Mo status of sails is roughly proportional to the amount of Bowland Shale debris in the drift. Similarly, Cu, Cr, Se and V syngentically enriched with Mo in the Bowland Shales are incorporated in the boulder clay and the content of these metals in soils is roughly proportional to the amount of Bowland Shale debris in the drift. Soil—stream sediment relationships in areas of transported overburden are similarly related to the composition of the overburden. Thus in the Bowland Forest area 272

Mo anomalous stream sediments are found related to Mb-rich soils developed on drift containing Bowland Shale debris. In the Thame and Market Rasen areas, in contrast, background levels of Mo prevail in areas of exotic overburden with Mo anomalous stream sediment restricted to areas of residual soils developed on Mb-rich black shale horizons. In several areas Mo anomalous soils form only a minor part of stream catchments, as in West Carmarthenshire due to the discordancy of the drainage network and the restricted outcrop of black shales, in Bowland Forest due to the complex geology and drift cover, in the Market Rasen area due to the extensive cover of exotic glacial drift. In these situations the Mo levels in stream sediments are lower than Mo levels in adjacent anomalous soils. This is thought to reoult from the suppression of Mo values by the dilution of stream sediment containing Mb-rich debris with material containing background levels of Mo. It is suspected that detailed examination of such relationships will show that the No status of stream sediments in these areas is roughly proportional to the amount of Mo-rich debris in the sediment. In West Carmarthenshire the complete suppression of Mo sediment anomalies related to the black Dicranograptus shales occurs in streams with catchments containing only very limited outcrops of black shale. Both Fletcher (1968) and Thornton (1968) note a similar suppression of Mo values in the sediment of streams having catchment areas of complex geology and attribute this to the dilution of sediment by material containing background levels of Mo. The further suppression of Mo levels in stream sediments adjacent to Mo anomalous soils occurs in limestone districts 273

barren of trace as in the Shaftesbury area, where CaCO3 elements precipitates in stream sediments from groundwaters entering the drainage network. Thornton (1968) reports a similar occurrence in areas of Mid Jurassic limestone. Nevertheless in all the areas investigated Mo anomalous stream sediments are related to Mo-rich soils derived from Mo-rich rocks of marine black shale facies. This is consistent with the findings of Fletcher (1968), Horsnail (1968) and Thornton (1968) who observe a direct relationship between Mo anomalous stream sediment and Mo-rich soils and rocks. Such a direct and simple relationship is indicative of mechanical dispersion and it is thought that apart from some redistribution in topsoils, Mo is largely associated with weathered bedrock material which is transported with detritus from soil to stream sediment. Hansauld (1966) observes that the behaviour of Mo during secondary dispersion is often complex although Mo is generally stable in acid environments, becoming increasingly mobile above pH 6.0. However, it is unlikely that conditions in any of the detailed study areas are appropriate for Mo to become extensively mobile except in topsoils where pH values are maintained at a hiGh level by agricultural practices. The persistence of certain metal associations in bedrock, soil and stream sediment is regarded as further indication of mechanical dispersion of metals associated with fine grained detrital material derived from the weathering of the bedrock. Thus the association of Mo with V is noted in both the black Dicranograptus shale bedrock and associated stream sediment in West Carmarthenshire. Similarly the association of No with Cu, Cr and V observed in the Bowland Shales is also found in 274

overburden derived from the Shales whilst Me, Cu, V and less distinctly Cr display a similar distribution in stream sediments in the Bowland Forest survey area. The mechanical dispersion of Mo with detrital material is further evidenced by the presence of raised levels of Mo in alluvium containing debris derived from the Mo—rich black shale formations, with Mo values in the alluvium similar to that of adjacent stream sediments. It is thus possible to conclude that in the British Isles stream sediment reconnaissance surveys revealing patterns of Mo anomalous sediments related to the outcrop of rocks of marine black shale facies may, with some confidence, be assumed to be associated with areas of Mb—rich soils and bedrock. Molybdenum values in associated soils can be expected to be similar to or less than those observed in stream sediment. Limitations in the stream sediment reconnaissance method are revealed by the complete suppression of Mo sediment anomalies in areas of complex geology and in limestone areas where CaCO 3 precipitates occur in streams. However these are perhaps of little concern since the areas of Mb anomalous soils involved are generally small and the more significant regional patterns associated with extensive areas of Mo—rich soils are readily identified. Stream sediment sampling at a closer density than one sample per square mile may reveal these small areas of Mo anomalous soils but this may increase the cost of the reconnaissance survey to a point where it is no longer a viable procedure. A direct and simple relationship between the Ga, Pb and Ti content of bedrock, soil and stream sediment is observed for 275 most of the black shales investigated and the dispersion of these metals similarly regarded as dominantly mechanical.

(B) The influence of secondary environment on metal dispersion In contrast to the above metals the relationship between the rock, soil and stream sediment content of Mn, Fe, Co, Ni and Zn is complex. The small amount of data prevents detailed assessment of the rock—soil relationship. Nevertheless the rapid fluctuation in Mn, Co, Fe and Zn values in the overburden related to drainage status or topographic situation rather than parent material indicate a very poor relationship between bedrock and soil in areas underlain by marine black shales. Within the overburden the substantial lateral redistribution of Mn, Co, Fe, Ni and Zn is observed in the Bowland Forest area where these metals are mobilised in very poorly drained soils. The lateral redistribution of Mn, Co and Zn in very poorly drained soils on scarp slopes is also noted in the area. Horsnail (1968) totes a similar lateral redistribution of these metals on slopes carrying gleyed soils and records that Mn, Fe, Co, Ni and Zn all show increased mobility under reducing conditions at a low pH. Soil—stream sediment relationships in the areas of residual and transported overburden associated with the black shale facies examined are fairly uniform. Levels of Mn, Fe, Co, Ni and Zn are quite consistently higher in stream sediments than associated soils with the contrast varying from x2 to x10. Fletcher (1968), Horsnail (1968) and Thornton (1968) note a similar relationship in areas of poorly drained 276

agricultural soils developed on black shales in England and Wales. This relationship is readily explained (Nichol et al, 1967, Horsnail, 1968); Mn, Fe, Co, Ni and Zn are mobile under the reducing conditions and low pH that prevail in the poorly drained soils that characterise black shale outcrops. These metals are transported with circulating groundwaters to the drainage network. On entering the drainage network Mn and Fe precipitate as hydroxides following a rise in both pH and Eh. The remaining metals are readily scavenged by the oxides precipitated. The present investigation includes data that suggest Cu may be similarly mobilised for in the West Carmarthenshire, Bowland Forest and Shaftesbury areas Cu levels are higher in stream sediments than in adjacent poorly drained soils. In general Cu is mobile under acid oxidising conditions. In the areas where the above relationship is observed soils are neutral or acid (pH 3.8-7.4); however these soils are poorly drained and frequently gleyed. Nevertheless, Horsnail (1968) notes that under conditions of low pH and Eh Cu may pass into ionic solution and migrate for varying distances with groundwater and be deposited with secondary Fe and Mn oxides in drainage channels. The present survey reveals no evidence of the mobilisation of Cu in the overburden; however, it is considered that the rise in Cu levels between soils and associated stream sediments noted in several areas may be attributed to the processes described by Horsnail (1968). Molybdenum is singularly unaffected by the secondary environment apart from limited redistribution in topsoils. Wells (1956) and Jones (1957) record the outstanding ability 277

of iron oxides to scavenge Mo. Atkinson (1967) notes a limited amount of Mo scavenging by Fe in stream sediments in Ireland and Fletcher (1968) reports that in the South West Pennines the mobility of Mo in the overburden is limited by retention on secondary ferric oxides. However it would appear that environmental conditions prevailing in the areas studied are unsuitable for the mobilisation of significant amounts of Mo within the overburden and that the dispersion of Mo is dominantly mechanical.

(C) Other factors influencin the relationshi• between the metal content of the overburden and stream sediments The introduction of large quantities of Cu, Pb and Zn with untreated and part treated sewage is thought to be responsible for the Cu, Pb and Zn sediment anomalies and high contrast between soil and stream sediment in the Thame survey area. Such contamination resulting from pollution by sewage may occur elsewhere. It is thus suggested that careful evaluation of stream sediment data in areas of high rural populttion is necessary to distinguish metal anomalies resulting from pollution from those related to syngenetic metal enrichment in bedrock of marine black shale facies.

3. The Metal Content of Herbage and Factors Influencing the Uptake of Molybdenum and Copper Detailed follow up studies, reported in previous pages, have shown that the Mo anomaly areas delineated by stream sediments are related to soils containing similarly anomalous levels of Mo. Furthermore herbage _growing on these soils contains greater concentrations 278

of Mo than herbage on nearby background soils. Investigations revealed, however, that although the Mo status of herbage is roughly proportional to the total Mo content of topsoils, Mo uptake is influenced by various environmental features. In contrast, the Cu status of herbage in any one area is relatively uniform despite wide variations in the total Cu content of the topsoils. An examination of the literature reveals that the Mo and • Cu content of pasture herbage in July/August, the time when grab samples were obtained, is dependent on a number of factors in addition to the total metal status of topsoils and features of the soil environment observed in the present investigation.

Factors affecting the metal content of herbage The influence of pasture species The Mo content of herbage is dependent on both the plant species (Fleming, 1965, Mitchell, 1957) and the part of the plant (Barshad, 1948, Fleming, 1965) with the highest levels in leaves and growing points. Since the herbage samples collected comprise a bulk of the pasture species growing at a given sitc,the role of individual species in affecting particular No concentrations cannot be discerned. However, it is important to note that the Mo content of clovers is consistently greater than that of grasses (Mitchell, 1957). Clover did not foLm more than a minor part of any sample collected, and is rare in the Mo anomalous pastures of West Carmarthenshire and Bowland Forest where sail pH is frequently below the optimum (pH 6.0-6.5) for establishment. 279

The situation for Cu is similar with clover usually containing more Cu than grasses (Mitchell, 1957, Fleming, 1965). As with Mo the highest levels of Cu are found in leaves and growing points (Fleming, 1965).

(ii) Seasonal variation in the metal content of herbage In the literature, herbage Mo values are usually reported as increasing slightly through the growing season to give maximum values in late summer and autumn (Ferguson et al, 1943, Field, 1957, Havre and Dynna, 1961, Fleming, 1965). However, Piper and Beckwith (1949), examining subterranean clover in Australia, report a rapid initial rise in Mo levels followed by a steady decrease in values through the growing season. Nevertheless Kretschmer and Allen (1956) note an increase in the Mo content of mixed grasses in early autumn and draw attention to the possibly unfavourable Mo:Cu ratio in plants at this time, which might have serious consequences for grazing stock. Despite the reports of relatively large fluctuations in the Mo content of herbage at the beginning and end of the growing season, the Mo content of herbage in late July and early August is probably representative of the greater part of the growing season. Contrasting accounts have also been published concerning seasonal variation in the Cu content of pasture species. Piper and Beckwith (1949) report that the Cu content of subterranean clover increases steadily through the growing season. Fleming (1965), on the other hand, reports a fall in the Cu content of mixed grasses through the growing season, as does Field (1957) and Kretschmer and Allen (1956). 280

However, as with Mo, the July/August levels of herbage Cu are probably representative of much of the growing season.

(iii) The influence of climate.on the molybdenum content of herbage Lewis (1943), examining the status of the teart pastures in Somerset, found that the Mo content of herbage was highest in mild, wet growing seasons, and that Mo levels fell in periods of drought and dropped rapidly to near normal after frosts. Herbage sampling in the present survey took place near the mid point of an extended dry period affecting the whole of England and Wales. Spring was late in 1969 and although the weather in the early part of the growing season was dull, cold and wet, rainfall during the period June 1st to August 31st was abnormally low whilst temperatures remained above the seasonal average. It is thus probable that the Mo content of herbage sampled is less than is achieved in a more moist growing season.

(B) Factors influencing the molybdenum and copper status of herbage on molybdenum anomalous soils (i) The molybdenum and copper content of the topsoils In the widely spaced areas in England and Wales where detailed studies were undertaken, districts defined as Mo anomalous by stream sediment and soil sampling were found to carry herbage containing greater amounts of Mo than on background sites. Fig. 48 shows that, taken overall, there is a broad, although fairly clearly defined, trend for the Mo content of herbage (mixed pasture species) to rice

100

• • • •.• • 0.•.• • . • : :" • • •• • ••••:: . `:• •• . ••• • ...nu e • • •••• • -•• • • • • *4 • • • • • • • •• • •+ • • • . • •• • * •• •• * • • • • • • • • • • • • • •

•

10 100 Herbage Cu pp.m.

Fig.49. Relationship Between Copper Content of Topsoils and Pasture Herbage.

(Topsoil 0-6ins depth. Herbage-oven dry weight.) 281

with increasing topsoil values. In contrast the Cu content of the herbage samples obtained is fairly constant despite the often large range of values for total Cu in the corresponding topsoils. There is no overall relationship between herbage Cu levels and the total Cu content of topsoils (Fig.49). Thus, irrespective of parent material and the total Cu content of the topsoils, uptake by the mixed herbage sampled appears to be fairly uniform.

(ii) The soil environment Examination of the data gained in the detailed study areas has shown that the contrast between the mean Mo content of herbage on anomalous and background soils is usually less than between the corresponding topsoils. Thus, although the Mo content of the topsoil is the principal factor determining the Mo status of herbage, a relatively large proportion of the total Mo in anomalous topsoils appears to be in a form unavailable to herbage. The reduced contrast between herbage values, compared to that between anomalous and background topooils, is consistent with the findings of Fletcher (1968) in the South Pennines, but is in contrast with the results of Webb and Atkinson (1965) and Atkinson (1967). These authors found that on molybdeniferous in Co.'Ilineriek, South West Ireland, Mo levels in herbage are similar to, or in excess of, topsoil values. A relatively depressed uptake of Mo by herbage has been reported by Robinson and Edgington (1954) and attributed by them to the immobilisation of available Mo due to fixation by active ferric oxides. Davies (1956) has pointed. 100

• • • 44

*••• •f • : :** # #* •••::. r• • • • • • • •4 t • • ••• • • • • • • • • • • • •• • •• 4 • • • 4 • ••• • •• • • • • • • • 4 • •• 44 • • • • • + • • • •

• • • • •

•

•

10 100

Herbage Cu pp.m. 4

Fig.49. Relationship Between Copper Content of Topsoils and Pasture Herbage.

(Topsoil 0-6ins depth. Herbage-oven dry weight.) 282

to the role of soil reaction in limiting Mo uptake by herbage whilst other authors (Lewis, 1943, Mitchell et al, 1957, Kubota et al, 1961, 1963) have illustrated that soil drainage status can influence the Mo content of herbage. Unlike most trace elements the availability of Mo to plants increases when the pH of the soil is raised (Davies, 1956). Jones (1957) and Davies (1956) have indicated that this is due to the increased sorbtion of molybdate anions on ferric oxides and clay minerals under conditions of increasing acidity. Occasionally, however, abnormally high Mo uptake is reported from acid, organic rich soils (Walsh et al, 1953, Mitchell, 1963) and abnormally low uptake on neutral soils (Robinson and Edgington, 1954). A simple pH effect is, therefore, not always involved. Drainage conditions can influence the mobility and availability of Mo by many interrelated processes. Thus drainage directly influences the leaching of soluble forms of Mo from topsoils and, by modifying the pH and Eh status of the soil, partly determines the forms of Mo present and its sorbtion onto Fe oxides and clay minerals. Furthermore, changes in pH and Eh brought about by drainage conditions may modify the major constituents of the soil, particularly the Fe OXitS, and thereby influence the sites available for Mo retention. Examination of environmental features likely to influence the uptake of Mo by herbage has shown that soil reaction, drainage status, secondary Fe oxides in soils and organic matter are all features of consequence in one or more of the areas studied. Davies (1956) has classified the forms of soil Mo uAder 283 the following headings: (a) Unavailable — held within the crystal lattice of primary and secondary minerals (b) Conditionally available — retained as the Mo0 anion by clay minerals and 4 available to a greater or lesser degree depending on the pH and probably the phosphate status

(0) In organic matter (d) Water soluble The low contrast between herbage Mo values from anomalous and background sites in all areas, compared with that between the corresponding topsoils indicates that the levels of available Mo are relatively low in the anomalous topsoils. There is no direct evidence as to the form of available Mo in any of the areas investigated. However, it is likely that levels of both water soluble and conditionally available Mo are limited by fixation onto secondary ferric oxides and sorbtion onto clay minerals, particularly in the more acid soils. Furthermore, the absence of fully oxidising conditions in anomalous soils, except in Bowland Forest, precludes the development of 'aged' ferric oxides onto which Mo is most firmly immobilised (Wells, 1956, Jones, 1957). Thus in most areas the sorbtion of Mo onto clay minerals and association with organic matter is considered to be as important, or more important, than scavenging by Fe oxides. This is evidenced by the clear relationship between topsoil pH and organic matter and the uptake of Mo by herbage in the West Carmarthenshire and Shaftesbury areas. 284

The clear relationship between Mo uptake and the Fe content of topsoils in the Bowland Forest area indicates that the relatively low levels of available Mo in the better drained soils are due, at least partly, to retention with ferric oxides. The immobilisation of Mo with ferric oxides is further favoured by the slightly acid reaction of the soils. Moreover, the increased uptake on very poorly drained soils where ferric oxides are probably only poorly developed emphasises the efficiency of secondary ferric oxides in immobilising Mo as noted by Jones (1957) and Wells (1956). Molybdenum associated with organic matter is probably in a state of continual circulation due to microbial breakdown (Davies, 1956). Thus if microbial breakdown is effective the Mo associated with rotting plant litter could well be an important source in all areas. Certainly the increased Mo uptake with increasing topsoil organic matter, irrespective of pH, on the Kimmeridge Clay of the Ohaftesbury area suggests this role although here the larger amounts of decomposing plant debris may aid the release of Mo from combination in the soil. The various controls observed as limiting the uptake of Mo by herbage are related to the secondary environment formed on black shales in different parts of the country. In soils developed on the Dicranograptus shale;.: of West Carmarthenshire and the Jurassic clays, low relief, moderate rainfall and poor drainage give rise to conditions in which Mo fixation by secondary ferric oxides is of le;Jser importance than the release of anionic Mo, controlled by pH, and the recirculation of Mo in organic matter. The soils 285

of Bowland Forest, in contrast, form in an area of greater relief and variety of drainage conditions amongst soils. Here, in better drained soils, Mo is firmly immobilised by sorbtion onto secondary ferric oxides. The situations observed are comparable to those encountered by Lewis (1943) on the iteart pastures' of Somerset and by Fletcher (1968) in the uplands of the South Pennines. However, it is anticipated that only a portion of the total topsoil Mo is controlled by the above factors. The greater part of Mo in topsoils is probably retained in the primary silt and clay fraction of the weathered parent material which constitutes the bulk of soils. As such this forms a reservoir of Mo from which pedological processes steadily release small amounts of Mo in a mobile form available to plants. With respect to Cu, the environmental factors observed in the present investigation do not have any substantial influence on the metal status of herbage. Diffuse trends were observed locally in which the uptake of Cu by herbage appears to be related to soil pH, total Fe and organic matter. However, the influences seem to be slight and are insignificant in terms of affecting the nutritional status of the herbage to grazing animals (see page 288). 286

CHAPTER 19: AGRICULTURAL SIGNIFICANCE OF DATA FROM THE DETAITRD STUDY AREAS

1. Molybdenum and Copper Stream sediment reconnaissance surveys have delineated zones characterised by anomalous levels of Ho. Detailed follow up studies in selected areas have revealed Mo—rich soils in the anomalous stream catchments with the source of Mo in all cases in bedrock of marine black shale facies. Examination of herbage on both molybdenum anomalous and background sills has demonstrated that the Ho status is related to the total Mo content of the soils. Thus, although plant uptake is dependent to some extent on environmental factors in all the areas studied Mo—rich soils carry Mo—rich herbage. In contrast, the Cu content of herbage remains similar throughout any area despite variation in both the total Cu content of the soils and environmental factors. Since the original work of Ferguson et al (1943) in recognising that an excessive dietary intake of Mo was the cause of molybdenosis on the 'teart' pastures of Somerset, considerable evidence has been amassed demonstrating how molybdenum interferes with copper metabolism in bovines (Underwood, 1962). Essentially two types of copper deficiency are recognised, either 'simple' in which the Cu content of the herbage is abnormally low or 'conditioned! (or 'induced') where the Cu levels are normal but the Mo content of herbage is raised. Thus in the 'tear-0 pastures of Somerset Allcroft and Lewis (1956) record clinical cases of molybdenum induced copper deficiency where herbage contains 3.6-26 p.p.m. Mo 287

(mean 12 p.p.m.) and 7.5-13 p.p.m. Cu (mean 10 p.p.m.). In Ireland, herbage levels of 5-25 p.p.m. Mo and 7 p.p.m. Cu have been related to conditional copper deficiency (Walsh et al, 1952). In the U.S.A. Dye and O'Hara (1959) relate a forage content of more than 5 p.p.m. Mo with conditioned copper deficiency, whilst in New Zealand Cunningham (1954) notes that 10 p.p.m. Mo in pastures is toxic if Cu intake is normal and 3-10 p.p.m. harmful if Cu intake is below normal. More recently Farmer (pers. comm. to I. Thornton) has found conditioned copper deficiency in cattle from Somerset and Gloucestershire where herbage Mo is 2-4 p.p.m. and Cu levels low. Cunningham (1950) and Dick (1953) demonstrate that the full limiting effect of Mo on copper metabolism is much reduced when there is a low dietary intake of inorganic sulphate. However the work of Allcroft and Lewis (1956) and the data of Morgan and Clegg (1958) indicate that low inorganic sulphate is most unlikely to be a limiting factor under British conditions. Although the Mo and Cu status of herbage associated with clearly healthy cattle and those displaying clinical symptoms of simple and induced copper deficiency have been described, it is not yet possible to define precise limits, particularly for the sub—clinical condition. At the sub—clinical level the animal appears generally healthy but may display infertility, poor conformation, slow growth or low milk yield. Although at no time appearing sick, the animal is inefficient and unable to realise the full economic potential possible were the conditioning effects of Mo not operating. Furthermore, the degree of response to raised levels of No varies with species and age. In 288 general, beef cattle are more resistant than dairy cattle and young animals less able to cope with raised levels of Mo in the diet than mature stock (Underwood, 1962). Nevertheless, it has been generally accepted that with pasture herbage containing < 4 p.p.m. copper deficiency will occur even if Mo levels are normal (Whitehead, 1966). In England and Wales the Agricultural Research Council (1966) has tentatively placed the Cu requirements of cattle at 10 p.p.m. Cu in herbage (D.M.). With regard to Mo, the normal dry matter content in herbage is probably close to the figure of 0.85 p.p.m. quoted by Alderman (1968) as the average for South East England. Indeed, the mean background level from the present investigation is 0.85 p.p.m. Mo. Data from Mo anomalous sites (Table 63) reveals that herbage Mo values are typically at the low and of the range associated with molybdenum induced copper deficiency. The mean Mo content of herbage on anomalous soils is significantly different from that of background areas (x2—x3) whilst Cu levels are invariably low (Table 63) and often less than 10 p.p.m. In fact, in the data obtained from the present survey no herbage sample contains. less than the 4 p.p.m. Cu at which Isimplef copper deficiency is suspected. Nevertheless 76.4% of the samples contain less than 10 p.p.m. Cu, 21.2% contain from 10-15 p.p.m. and only 2.4% contain in excess of 15 p.p.m. Cu. (Total number of samples, 212) This is in samples obtained from widely spaced localities in England and Wales and bears comparison with the data of Alderman (1968) who found 88.3% of herbage samplesfrdm South East England contained less than 10 p.p.m. Cu. Two principal methods of correcting molybdenum induced Table 63 The molybdenum and copper status of mixed pasture herbage* from molybdenum anomalous and background districts in the five areas of detailed studies Background Molybdenum anomalous districtsA districts Lower Oxford Kimmeridge Clay Clay 4 samples 4 samples 7 samples No 1.9+ 1.9 0.7 (p.p.m.) 0.6-4.8 1.7-2.0 0.5-0.9 Market Rasen Cu 10.5 11.0 8.6 (n.p.m.) 7.5-14.0 7.0-15.0 6.5-11.5 Mean Mo:Cu ratio 1:5.5 1:5.8 1:12.3 Lower Upper Oxford Oxford Clay Kimmeridge Clay Clay Head Clay 8 samples 6 samples 13 samples 5 samples 13 samples Mo 1.7 ' 1.2 1.3 0.9 0.4 (p.p.m.) 1.0-2.4 0.5-2.4 0.5-2.0 0.3-2.0 0.2-0.8 Thane Cu 6.8 7.8 7.5 6.8 5.9 (1).13.m.) 4.5-11.0 4.5-9.0 5.0-10.0 5.5-7.0 5.0-11.0 Mean Mo:Cu ratio 1:4.0 1:6.3 1:5.6 1:7.5 1:14.7 Lower Oxford Kiwmeridge Clay Clay 5 samples 30 samples 20 samples Mo 2.5 2.4 0.7 (p.p.m.) 2.1-2.8 0.6-6.4 0.2-2.4 Shaftesbury Cu 7.6 9.9 7.6 6.5-9.0 6.5-16.0 4.0-13.5 Mean Mb:Cu ratio 1:3.3 1:4.1 1:10.8 Bowland Shale and drifts 33 samples 5 samples Ho 2.9 0.9 (p.p.n.) 0.8-7.2 0.7-1.0 Bowland Forest Cu 11.3 10.7 (13.12-m.) 5.5-22.5 8.0-13.5 Mean Mr:Cu ratio 1:3.9 1:11.9 Dicranograptus shales 32 samples 15 samples 1.5 0.9 (p.p.n.) 0.1-3.8 0.3-2.6 West 1.5u 7.2 8.5 Carmarthenshi:oe (p.o.m.) 5.0-17.5 6.3-10.3 Mean Mc:Cu ratio 1:4.8 1:9.4

* Oven dry wei,.;ht 6. Grouped by parent material Arithmetic mean 290 copper deficiency are employed: (i) methods of grassland management may be adopted which minimise the influence of raised levels of Mo on animals and top dressings applied to reduce the uptake of Mo by pasture herbage (Lewis, 1943, Barshad, 1951b, Stout et al, 1951) (ii) the conditioned copper deficiency can be corrected by the direct administration of copper supplement to the animal either in the form of copper sulphate mineral as in 'teart cake' or by injection as copper glyciue (ialcroft and Uvarov, 1959).

(Al.) West Carmarthenshire Herbage growing on Mo anomalous soils(derived directly or indirectly as alluvium from the Dicranograptus Shales) contains up to 3.8 p.p.m. Mo although the mean value is only 1.5 p.p.m. However, the Cu content of the herbage is low, mean 7.2 p.p.m., and it therefore appears probable that the Mo and Cu status of the herbage is such that a conditioned copper deficiency is affecting grazing livestock within the anomaly area at a sub—clinical level. Copper deficiency has been reported from only one farm in the anomaly area (Fig. 7); however, veterinary practitioners suspect that animals within the anomaly area are possibly poorer in terms of conformation and fertility than those outside. In this district soil reaction is the main factor limiting the uptake of Mo by herbage. Levels of herbage No recorded in Table 63 occur on soils having a mean pH of 5.3 with values falling to 4.2 and only rarely exceeding 6.0, levels well below the optimum for Mo uptake. Farmers in the area believe that liming would improve pastures by X91

enhancing the quality of the grass and promoting the establishment of clover. If the soil pH is increased the Mo status of grasses will certainly rise as more No is made available whilst the establishment of clovers, with their greater content of Mo, will further increase the hazard of the conditioned copper deficiency. The total area of Mo anomalous soils is probably some 8 square miles and occurs in the heart of an area of intensive dairy farming. Farm units are small but stocking rates are high and a large number of holdings are sited entirely within the anomaly, particularly between Meidrim and Llanglydwen.

(B) Bowland Forest The metal content of herbage from Mo anomalous sites on the Bowland Shale and associated drifts, obtained between Slaidburn and Bolton—by—Bowland, is comparable with the data of Morgan and Clegg (1958) from the Chipping district. These authors record herbage with 3.4-6.7 p.p.m. Mo and 7.2-11.5 p.p.m. Cu from farms with animals displaying clinical symptoms of copper deficiency. In the present data herbage Mo values of up to 7.2 p.p.m. are recorded (mean 2.9 p.p.m. Mo) with the mean Cu content of herbage 11.3 p.p.m. (Table 63). The reported incidence of bovine copper deficiency in the Bowland Forest area (Fig. 21) is less frequent than might be expected in view of the moderately high levels of Mo involved. Moreover, the Mo stream sediment anomaly extends well beyond the localities where copper deficiency has been recognised. It is thus likely that many farmers 292 within the 35 square miles of the Mo stream sediment anomaly are experiencing poor stock performance due to conditioned copper deficiency, probably at a sub—clinical level. On many farms animals are protected from the worst effects of raised Mo levels by traditional farming practices. Cattle, particularly young animals, are not put out to grass in 'red water' areas; here sheep are grazed. Such areas are zones of poor and very poorly drained soils developed on the Bowland Shales and associated drifts, characterised by rusty coloured iron seepages. Long experience has taught farmers that stock are particularly distressed when grazing these localities. The present investigation shows that not only are soils in these areas Mo—rich but that the uptake of Mo by herbage is greater at such very poorly drained sites. Improving soil drainage could possibly reduce Mo uptake by herbage in some places. However, herbage levels of 4-6 p.p.m. Mo are frequently encountered on moderately drained soils. Lime and basic slag are used liberally in this area to improve pastures. Both result in a rise in soil pH and an increase in the clover content of pastures which could raise the Mo status of herbage and intensify the problem of conditioned copper deficiency.

(C) Shaftesbua The two large Mo anomalies identified, associated with the Lower Oxford Clay and the Kinrieridge Clay, are considered separately: (i) Lower Oxford Clay. Herbage sampling within the soil anomaly north of Wincanton reveals values consistently in 293 excess of 2 p.p.m. Mo, whilst Cu levels are less than 10 p.p.m. The Mo and Cu status of herbage appears most unfavourable for grazing animals with levels similar to those associated with conditioned copper deficiency in Gloucestershire (pers. comm. P. Farmer to I. Thornton). The anomaly is, however, restricted, forming a belt up to one mile wide, probably extending to some 72 square miles in the reconnaissance area. .As yet no cases of bovine copper deficiency have been reported from within the anomaly area. The attention of veterinary practitioners has now been drawn to this district and a full investigation of animal health is being made. Anomalous levels of Mo are encountered in soils over the Cornbrash north of Wincanton (page 190). However the restricted area of anomalous soils (they are not found south of Wincanton) and the low Mo status of herbage (0.5-1.4 p.p.m. indicate that this soil anomaly is of little agricultural significance. Nevertheless, the levels of soil Mo are such that they are of potential significance if the uptake of Mo by herbage is increased by management practices.

(ii) Kimmeridge Clay. Herbage values for Mo and Cu obtained from sites on the molybdeniferous Kimmeridge Clay (Table 63) are broadly similar to those encountered in Bowland Forest where bovine copper deficiency has been recognised. There has been no record of bovine copper deficiency on the clay vale; however, it appears likely that this has been overlooked. Animals grazing in the vale have a lower standard of health than might reasonably be expected, attributed in the past to a variety of causes including poor 294 quality forage and parasite infestation. The attention of veterinary practitioners has now been drawn to the probability of a conditioned copper deficiency and a further investigation has been initiated. On the clay vale Mo uptake by herbage is related to soil reaction but since topsoils are almost neutral in reaction (mean pH 6.4) it is unlikely that there will be any rise in soil pH due to liming. However, many farmers wish to improve pastures by increasing the amount of clover in the sward. Were this to occur the Mo status of pastures would almost certainly rise. Part of the Mo available to herbage appears to be held with organic matter in topsoils (page 207) and it is possible that the Mo status of herbage on the more humose topsoils might be reduced by cultivating the soils to disperse the organic matter. The area of the Mo anomaly as delineated by soil and stream sediment sampling is some 22 square miles. The soil anomaly is more consistent and has higher No values in the western half of the vale. Nevertheless the whole of the Kimmeridge Clay outcrop must be regarded as suspect from an agricultural viewpoint.

(D) Thame Characteristically molybdeniferous soils are restricted to the Lower Oxford Clay and carry herbage containing up to 2.4 p.p.m. Mo. However, secondary accumulations of Mo are encountered on the Clay Head and Upper Oxford Clay with herbage containing up to 2.4 p.p.m. Mo on these soils. Further molybdeniferous soils are found on the Kinuneridge Clay supporting herbage containing up to 2.0 p.p.m. Mo. Thus, 295

throughout the clay vale pastures containing more than 2.0 p.p.m. Mo in herbage are to be found, although the distribution of molybdeniferous soils and associated herbage can only be predicted with confidence for the Lower Oxford Clay with some 12 square miles envisaged north and east of Marsh Gibbon. The raised levels of Mo in herbage on the clay vale are accompanied by consistently low Cu values (Table 63). The combined features of marginally raised herbage Mo and low Cu appear potentially hazardous for grazing livestock. Bovine copper deficiency and infertility responding to copper therapy is widely recorded on the clay vale (Fig. 27). It is thus tentatively suggested that the copper disorders in grazing cattle within the Mo anomaly area are due to a high dietary intake of Mo. The raised levels of Mo in soils and herbage on the Kimmeridge Clay (page 222) may be a local expression of more extensive No anomalous soils and pastures in the Brill district where bovine hypocuprosis is reported from several farms. Joint studies by the National Agricultural Advisory Service and the Veterinary Investigation Service were initiated in 1970 to follow up the work described in this thesis and to provide more complete information on. the distribution of Mo anomalous soils and herbage and the copper status of animals on the vale and adjacent areas.

(E) Market Rasen Soils with anomalous levels of Mo and carrying molybdeniferous herbage are associated with the Lower Oxford Clay and the Kimmeridge Clay. The two occurrences are 296

considered separately. (i) Lower Oxford Clay. A maximum of 4.8 p.p.m. Mo is found in herbage growing on Mo anomalous soils in the Cold Hanworth district, putting the pastures into the range associated with conditioned copper deficiency. However, the Mo anomalies are very localised due to the cover of barren drift, and molybdeniferous residual soils on the Lower Oxford Clay occupy little more than single fields extending to a maximum of 3 square miles around Cold Hanworth, Spridlington and Owmby, with no farm sited wholly on anomalous soils.

(ii) Kimmeridge Clay. Molybdenum anomalous soils derived from the Kimmeridge Clay support herbage containing up to 2.0 p.p.m. Mo. However, the high values of Mo in soils (up to 16 p.p.m.) and the bedrock (up to 30 p.p.m.) indicate a considerable hazard and a rise in soil pH and an increase in the clover content of pastures (at present clover is uncomidon on anomalous soils) might raise the total Mo content of herbage to more significant levels. The extent of anomalous soils is not large, dueto the extensive cover of barren drift, and some 4 sauare miles are anticipated around North Willingham, East Barkwith and in the valley of the River Bain. Almost all the grassland in the east of the vale is found on these heavy clay soils; therefore, cattle in the area are dependent largely on molybdeniferous pastures for their forage. Although there is no record of bovine copper deficieny in the Market Rasen area-farmers at South Willingham report illthrift and infertility in grazing animals attributed, at least in part, 297

to 'nutritional problems'.

2. Selenium Experience in Ireland (Webb and Atkinson, 1965) and in England (Fletcher, 1968) has demonstrated that the uptake of toxic quantities of Se by herbage occurs only under restricted environmental conditions. Thus Webb and Atkinson (1965) report that seleniferous vegetation ('"1.5 p.p.m. Se D.M.) is restricted to alkaline organic rich soils ' (pH 6.6-7.5) and that on topsoils that are similar except for their acidity (pH 4.6-4.8) Se herbage values are <0.3 p.p.m. Fletcher (1968) also concludes that a low pH is a limiting factor on the uptake of Se by herbage from organic soils. In the present study, localised areas of organic rich topsoils are encountered only in Bowland Forest. However, although up to 17.0 p.p.m. Se is present in soils, topsoil pH is found to vary between 4.1 and 6.2,values consistently more acid than those associated with toxic herbage in Ireland. Furthermore, no Se accumulator plants are found in the areas of seleniferous soils. It is thus concluded that although anomalously high levels of Se (0.2-35.0 p.p.m.) are encountered in the Bowland Forest, Shaftesbury and Market Rasen areas environmental factors are unfavourable for seleniferous herbage and no hazard to grazing animals exists.

3. Cobalt Patterson (1946) reports a mean total Co content of 4 p.p.m. in soils in areas of cobalt pine, compared with 100 p.p.m. elsewhere. The data for soils in the five areas 298 of detailed studies disclose values of more than 30 p.p.m. Co only in rare and exceptional circumstances, due usually to environmental factors. Large areas of soils containing less .than 5 p.p.m. total Co are revealed and the mean total Co content of all the soils sampled is only 11 p.p.m. Cobalt pine in sheep is largely unknown in the detailed study areas and cobalt deficiency in other animals and crops unrecorded. In the absence of any data on 'available' Co in soils or the Co status of herbage in the follow up areas it can only be assumed that although total soil Co is low over large areas, sufficient is usually taken up by herbage to supply grazing animals with an adequate dietary intake of Co. An absolute deficiency of Co may be suspected on the intensely leached sandy soils found in the moorland areas of Bowland Forest. Here conditions are so severe that all available Co may be leached, leaving a small amount of Co in the soil innobile and unavailable to plants.

4. Mano.anese Manganese has been shown to be very mobile (page 275) with the total Mn content of soils fluctuating; rapidly in response to environmental conditions, and only to a lesser extent parent material. Values of up to 8500 p.p.m. total Mn are encountered in some soils; many, however, contain less than 300 p.p.m. total Mn. However, no data was obtained on lavailablel soil Mn or the herbage content of Mn. Disorders in grazing cattle responding to manganese therapy are reported from a number of areas (pages 87 and 96). As with cobalt, in the absence of complete data, it can only 299 be assumed that the uptake of Mn by herbage is, in general, sufficient to provide grazing animals with an adequate dietary intake of Mn, or that deficiencies are sub.-clinical and at present unrecognised. 300

CHAPTER 20: EXTRAPOLATIONS BEYOND THE SURVEY AREAS

The reconnaissance surveys and detailed follow up work have demonstrated the occurrence of anomalous levels of Mo related to bedrock of black shale facies in widely spaced localities. The black shales persist for long distances beyond the survey areas and it is thus probable that the extent of Mo—rich rocks, and associated soils, is very much greater than has yet been defined.

1. The Black Dicranograptus Shales In South and South West Wales the most characteristic Caradocian lithology is that of the black Dicranograptus shales (0.T. Jones, 1956) which are recorded from the Shelve Inlier and also in Radnorshire, Carmarthenshire and Pembrokeshire (Fig. 50) passing laterally into grits, flags and slates near Crymmych_ in South Cardiganshire (Evans, 1940). In West Carmarthenshire and Pembrokeshire black Dicranograptus shale deposition began earlier in the Upper Llandeilo and is represented by the Hendre Shales. The black Dicranograptus shales have a remarkably consistent lithology along the strike shown in Fig. 50 and the facies persists, largely unchanged, into North Wales (0.T. Jones, 1956). The total area underlain by these rocks in Fig. 50 is, however, only some 50 square miles and the outcrop is always narrow and often disrupted by faulting; furthermore, large areas are drift covered. Studies in West Carmarthenshire reveal anomalous levels of Mo in residual soils on the Dicranograptus shales with herbage uptake sufficient to present a hazard to Montgomery•

a

2.

Rhayade Ci

•Llanwertyd Wells.

.Crymmych .Llandovery. Arms. •Llangadog

Metdrim. Llandeila '71 °Carmarthen Outcrop of Shale. Lr 1. 1. West Carmarthenshire Area, Z Rhayader Area. 3. Shelve Area. Denby. 0 5 10 Scale in Miles.

Fig. 50. Outcrop of the - Black Dicranograptus Shales in South and South West Wales (Modified from Jones, 1938, 1956.) 301

grazing livestock. Molybdenum stream sediment anomalies related to the outcrop of the black Dicranograptus shales are also observed in the Rhayader and Shelve survey areas. It thus appears probable that the black Dicranograptus shales are molybdeniferous throughout the outcrop shown in Fig. 50. Residual soils predominate in West Carmarthenshire, Pembrokeshire and South Cardiganshire where the distribution of Mo is anticipated as being essentially similar to that found in the detailed study area (Ch. 13). Between Carmarthen and Liangadog the Dicranograptus shale outcrop is thin and much faulted with large areas covered by glacial drift and alluvium which most probably masks the Mo—rich whales with barren material. The outcrops at Llanwrtyd, Rhayader and Shelve are also mantled by glacial drift.

2. The Bowland Shale Group The results of detailed studies in the Bowland Forest area complement the work of Atkinson (1967) in Ireland and Fletcher (1968) in Derbyshire in confirming that the deposition of molybdeniferous black shales was widespread during the

Upper Visean/Lower Namurian periods of the Carboniferous. The Bowland Shale Group, identified as molybdeniferous in the detailed study area, outcrop over some 96 square miles from north of Preston to Grassington (Fig. 51). The group retain the black shale facies throughout their outcrop, passing laterally into the'littota1 Yoredale facies along the line of the Mid Craven Fault (Rayner, 1953). There is every reason to believe that the black shales are molybdeniferous throughout their outcrop.

0 2 4 Scale in Miles.

Bowland Forest Survey Area.

•, .1) •:A, A Skipton. ::**•,/ •;/...... ,..e-„,,r• / • • /••••• .,., •. • . v.:, c , t • • / Barnoldswick. •\) /.. / ...,-r. ,...,.,.., ,...,. N`, ) J • -....4 c‘ J:,,, *N.; /• . -..._..- :J.: ..; '7 1.. • . •••• i,." •-• 1 . 1 .: :::t;.1- V,__ VV.,:.:.*....:1 .Chipping. ‘.:t .21 `c.:.,...1.•1 v.r.....:..-..rS •, .1 \ ..... Clitheroe s.• • 7-/••••-• t. Post-Carboniferous. (Trios) • • 1. A o".'d 14 /.',' /'• • 1.1 ., ...0 Caine. • • . 1 .1..., Carboniferous. I . • /. , • 1.1 ,..../ Post- Bowland Shales. % 1. 1f.1 ., ,.*:•;" Nelson. I. A /:•:•..1 f.., Bowland Shale Group.

Pre-Bowland Shales. ' Pcrston. • • \\ • Solid Geology. Blackburn.

Fig. 51. Outcrop of the Bowlanda Shale Group and Associated Rocks in Lancashire and Yorkshire (Based on I.G.S. maps.) 302

West of the survey area results from stream sediment reconnaissance over the Lancashire Plain indicate the smearing of molybdeniferous Bowland Shale drift onto the Trias north of Preston (pers. comm. W.C. Davies). East and north east of the survey area glacial drift of various types forms an extensive cover to land below 1000 feet (Earp et al, 1961) and it is probable that both the masking and smearing phenomena seen around Slaidburn, Clitheroe and Chipping occur here.

3. The Lower Oxford Clay Enhanced levels of Mo are recorded from the bituminous shales and carbonaceous clays of the Lower Oxford Clay in the Thame area where residual soils are similarly enriched in Mo and support molybdeniferous herbage. Molybdeniferous soils are also reported from the Shaftesbury and Market Rasen areas where they are thought to be derived from bituminous shales in the Lower Oxford Clay. Arkell (1933) regards shales as the typical lithology of the Lower Oxford Clay in England with a bituminous facies widely represented along the outcrop. In contrast, the Upper Oxford Clay is invariably blue grey and brown calcareous and plastic clays with little or no organic matter. As yet the outcrops of the various divisions of the Oxford Clay formation are unmapped. Bituminous shales are recorded in the Lower Oxford Clay at Weymouth (Arke11,1947b) and Melksham (Whittaker and Edmunds,, 1925) and are probably present in the Shaftesbury area (page 88 ). It is suggested that since residual soils dominate in this part of the country \Scarborough.

•

ti ket Rasen. •

Chippenham

Outcrop of Oxford Clay Formation. rerrrton. •Gilliqgham. Southern Limit of Quaternary Ice Sheet. \-0.0"

1. Shaftesbury Area.

2. Thame Area

3. Market Rasen Area

0 20 40 Scale in Miles.

Fig. 52. Outcrop of the Oxford Clay Formation in England

Top of Formation.

Base of Formation. Weymouth. Melksharn. Swindon Oxford Lincolnshire. N.Yorkshire. borehole. Peterborough.

200 Bituminous Shales. Vertical Scale. Calcareous and 100 (In feet) Sandy Clays .

Sandstone. 0

Fig.53. Vertical Sections Illustrating the Variation in Facies and Thickness of the Oxford Clay Formation (For sources of information see text.) 303

(Robinson, 1948) raised levels of soil Mo will characterise an estimated 45-50 square miles of Lower Oxford Clay outcrop from the coast to Chippenham with Mo levels in soils and herbage probably similar to those recorded at Wincanton North of Chippenham the Lower Oxford Clay passes into a sandy facies that persists past Swindon (Woodward, 1886) to Cricklade (Arkell, 1933) although at Oxford there has been a return to bituminous shales (Arke11,19478). Between Oxford and Peterborough the Lower Oxford Clay displays a full development of bituminous shales which are almost certainly molybdeniferous throughout (Fig. 53). However, data from the Thame survey area and stream sediment reconnaissance near Bedford (page 120) indicate that the occurrence of Mo anomalous soils is restricted due to the extensive cover of barren drift and head on the No—rich bedrock. North of Peterborough the drift cover is thick and extensive and bedrock exposures few. In the Lincoln area bituminous shales in the Lower Oxford Clay (Swinnerton and Kent, 1949) are believed to be the source of Mo in soils in the Cold Hanworth district (page 243). In this area the data indicate that the drift is largely masking the anomaly. An Oxford Clay drift is recognised in many parts of the East Midlands (Sylvester—Bradley and Ford, 1968) in which the anomaly could be smeared. However, the outcrop of the bituminous shale is probably always less extensive than the Upper Oxford Clay which has been found to contain background levels of Mo (Table 47, page 190). It is thus suggested that in the drift the weakly molybdeniferous 304

Lower Oxford Clay is rapidly diluted to insignificance by the larger quantities of Upper Oxford Clay material. North of the Humber the Lower Oxford Clay passes laterally into sandstone and calcareous clays (Arkell, 1933). Due to the unknown extent to which the drift may influence the distribution of molybdeniferous soils in the area between Oxford and the Humber it is not possible to suggest their extent.

4. The Kimmeridge Clay The levels of Mo recorded from samples of bedrock and residual soils at Shaftesbury and Market Rasen are moderately high and the values of herbage Mo at Shaftesbury within the range associated with conditioned bovine hypocuprosis. The black shale facies of carbonaceous clays, bituminous shales and oil shales shown to be molybdeniferous at Shaftesbury (page 188) forms almost the entire Kimmeridge Clay succession from the Dorset coast to Devizes (Downie and Wilson, 1968). Dunn (pers. comm.) records up to 50 p.p.m. Mo in bituminous shales at Kimmeridge Bay, with bedrock Mo values generally similar to those found in residual soils in the Shaftesbury area. Since re-sillual- soils occur on the greater part of the outcrop of the Kimmeridge Clay in this area (Robinson, 1948) the formation probably carries some 75 square milqs of molybdeniferous soils and herbage containing Mo levels similar to those recorded at Shaftesbury (Tables 42 oaad 46). West of Swindon the Kimmeridge Clay formation passes laterally into a thin succession of calcareous clays, \Scarborough,

Boston

ngs Lynn.

Great Yarmouth

Ipswich.

gi-;t on 'Buzzard. \

win do n.

Outcrop of Kimmendge Clay Formation.

Southen Limit of --- Quaternary Ice Sheet.

. aftesbury. Approximate Limit of "Kimmendgian Drift."

1, Shaftesbury Area.

2. Thame Area. We mouth 3. Market Rasen Area. Kimmeridge Bay. 0 20 40 Scale in Mlles.

Fig.54. Outcrop of the Kimmeridge Clay Formation in England (Limit of "Kimmeridgian Drift" from Harmer, 1928.) Top of Formation "Black Shales" Calcareous Clays, Silts and Sandy Clays...

Sands

2001

Vertical Scale. (in feet) 100

0

Transgressive Lower Cretaceous Unconformable on Kimmeridge Clay.

Base of Formation. Dorset Swindon. Oxford. Lincolnshire. Yorkshire. Coast.

Fig. 55. Vertical Sections Illustrating the Variation in Facies and Thickness of the Kimmeridge Clay Formation (For sources of information see text.) 305 sandy clays and sands (Fig, 55) although bituminous shales remain at one horizon (Arkell, 1933). This sequence continues east with little change to near Leighton Buzzard. Data from soil samples taken at Brill Hill (page 222). in the Thame area suggest- that there a thin bituminous shale sequence nay be molybdeniferous and it is probable that the thin bituminous shales of Swindon are also molybdeniferous. It thus appears likely that between Swindon and Leighton Buzzard large areas are underlain by thin bands of molybdeniferous bituminous shale. When the Kimmeridge Clay reappears again, 10 miles west of Cambridge, the lithology has returned to carbonaceouE.: clays and bituminous shales (Figs. 54 and 55) and continues in this facies throughout Lincolnshire and Yorkshire (Arkell, 1933). The succession is entirely of black shale facies similar to that found to be molybdeniferous at Market Rosen and underlies approximately 575 square miles of East Anglia. However, the outcrop from Cambridge to the Humber and again in Yorkshire is almost completely covered by drift of various types, including peat and alluvium in the Fens.. The effect of much of this exotic overburden will probably be to mask the molybdenum anomaly. In contrast, large areas of Icimfteridgian Drift" (Harmer, 1928) occur in South Lincolnshire and underlie some 185 square miles of Cambridgeshire and Suffolk (Fig. 54). The bulk of this drift is composed of Kimmeridge Clay material and is thus probably molybdeniferous and may support Mo anomalous soils in these districts. 306

5. Conclusion From the available information it appears highly probable that Mo anomalous rocks and soils associated with the four horizons studied in detail are more extensive than now defined. However, the effects of facies change and overburden on the geochemical patterns can only be speculated on, li geochemical survey of the entire outcrop of each of these formations would be most instructive and of considerable value to agriculture, 507

CHAPTER 21: SUMMARY, CONCLUSIONS AND RECO umTDATIONS FOR FURTHER RESEARCH

1. Summary and Conclusions (A) Initial statements (1) Previous studies in the British Isles have related the occurrence of molybdenum induced hypocuprosis in grazing cattle to the syngenetic enrichment of Mo in rocks of marine black shale facies underlying the pastures. (ii) Examination of the literature reveals that some 6000 square miles of England and Wales are underlain by black shales that display, to a greater or lesser extent, characters comparable with known metal—rich black shales. It is possible that Mo enrichment occurs in these sediments and that molybdenum induced bovine hypocuprosis may be associated with the raised levels of Mo. (iii) Nine areas in England and Wales containing outcrops of black shales thought likely to be enriched in Mo were selected for multi—element regional geochemical reconnaissance employing stream sediment sampling at a density of one sample per square mile: (a) West Carmarthenshire (b) Rhayader (c) Shelve (d) Machynlleth (e) Kendal (f) Bowland Forest (g) Shaftesbury (h) Thame (i) Market Rasen (Fig. 3).

(B) Stream sediment regional geochemical reconnaissance surveys (i) Reconnaissance sampling over a total of 1150 square miles reveals districts, extending to some 86 square 308

miles, characterised by anomalously high values of Mo (3-60 p.p.m. Mo) in stream sediments. The distribution of molybdenum anomalous sediments is related to the outcrop of marine black shales, ranging in age from Ordovician to Cretaceous, and transported overburden derived from these rocks. Background values of Mo (< 2 p.p.m. ) are found in areas of other shales, clay, sandstone, limestone and transported overburden derived from these deposits. Molybdenum anomaly patterns are depressed or suppressed in streams with complex catchment geology and those with conspicuous precipitates of CaCO3, a situation attributed to the dilution of stream sediment by barren material. (ii) Selected sediment samples from anomalous and background areas have been analysed for Se. In the West Caruiarthenshire, Bowland Forest and Shaftesbury areas, anomalous levels of Mo are accompanied by raised levels of Se (0.2-17.0 ) contrasting with background areas where Se is undetected ( < 0.2 p.p.m. ). However, in the Thame area Se levels (0.2-1.7 p.p.m.) are similar in both molybdeniferous and background areas. (iii) Patterns of high Co, Fe and Mn are observed associated with poorly drained moorland and agricultural soils. The patterns are attributed to the leaching of these metals from the poorly drained soils and precipitation in the drainage network as described by Nichol et al (1967)and Horsnail (1968). 309

(iv) Anomalously high levels of Cu, Pb and Zn related to mineralisation or contamination from previous mining activity are recognised in the West Carmarthenshire, Shelve,Machynlleth, Kendal and Bowland Forest areas. (v) Anomalously high levels of Cu, Pb and Zn in the Thame area are considered to be due to pollution by untreated and part—treated sewage. (vi) Prior to the present investigation raised levels of Mo had been reported from localised districts in the Machynlleth (Spencer, 1966), Kendal (Spencer, 1966), Bowland Forest (Morgan and Clegg, 1958) and Thame (Thornton, 1968) areas and related to conditioned copper deficiency in livestock only in the Bowland Forest area (Morgan and Clegg, 1958). Elsewhere the surveys have delineated new suspect areas wherein molybdenum induced bovine hypocuprosis may occur. (vii) Patterns of Se—rich stream sediments (0.2-17.0 p.p.m.) are recorded in the West Carmarthenshire, Bowland Forest, Shaftesbury and Thame survey areas. However, the environmental conditions necessary for the establishment of seleniferous vegetation (Webb and Atkinson, 1965) are not recorded in the areas of Se—rich stream sediments. It is thus concluded that there is no hazard to grazing cattle. (viii) Five areas were selected for detailed geochemical studies employing rock, soil and herbage sampling: (a) West Carmarthenshire (b) Bowland Forest 310

(c) Shaftesbury (d) Thame (e) Market Rasen.

(C) Distribution of metals in the bedrock

(i) Sampling of the bedrock demonstrates that raised levels of Mo (> 3 p.p.m.) are restricted to formations of marine black shale facies. Background levels of Mo (< 2 p.p.m.) prevail in all other rocks examined. The Mo—rich formations, the Meidrim Shales (Ordovician), the Bowland Shale (Carboniferous), the Lower Oxford Clay and Kimmeridge Clay (Jurassic) all display features of quiet water deposition in an anaerobic environment and all are enriched in organic matter with respect to adjacent normal shales. (ii) Although the four black shales are enriched in Mo (2-7 times average shale values) ,enrichment in other metals is variable. In the Bowland. Shale Cu, Ni, Pb, Se, V and Zn are enriched (x2—x12), in the Kimmeridge Clay only Se (x4), in the Lower Oxford Clay Zn (x3) and in the Meidrim Shales no other metals are enriched. (iii) In the black shales studied the distribution of the following metals is related to organic natter; Mo and V in the Meidrim Shale, Mo, Cr, Cu, Fe, Ni Se and V in the Bowland Shale and No, Cu, Se and possibly Fe, Ni and Pb in the Kimmeridge Clay. Metal relationships in the Lower Oxford Clay are obscure but it is thought that Mo, Cr, Cu, V and Zn are associated with organic matter. (iv) The accumulation of Mo and the other metals 311

associated with organic matter in the black shales is considered to result largely from the sorbtion of metals on organic matter in the anaerobic environment of black shale deposition. The enrichment of Pb and Zn in the Bowland Shale was most probably brought about by sorbtion onto organic matter or by sorbtion and co-precipitation with iron sulphides. (v) Prom the results obtained it appears that the character of the metal enrichment and metal associations observed in the Mo-rich black shales are related to: (a) variations in the supply of metals to the site of deposition (b) the intensity of the reducing conditions set up at the time of deposition (c) the composition of the organic matter present in the sediment.

(D) Distribution of metals in the overburden (±) The Mo content of overburden is closely related to parent material. In all areas examined anomalous soils are restricted to residual and/or transported overburden derived from the Mo-rich black shale formations. Background levels of Mo are associated with overburden derived from other parent materials. Thus the incorporation of Mo-rich debris in locally derived drift gives rise to "smear patterns" in the Bowland Forest area in which extensive areas of molybdeniferous soils are found at sites removed from the outcrop of 312

the Mo—rich black shale source rock. Conversely exotic overburden containing background levels of Mo masks Mo—rich bedrock in the Market Rasen and Thane areas. (ii) The distribution in overburden of Cr, Cu, Ga, Pb, Se, Ti, V and frequently Ni can also be related to the principal parent materials of the areas studied. (iii) In contrast the distribution of Co, Fe, Mn, Ni and Zn in the overburden is often erratic and largely unrelated to geology. In general, levels of these metals are low in poorly drained soils with maximum values in well drained soils on limestones, sandstones and shales. There is extensive redistribution of Co, Fe, Mn, Ni and Zn in gleyed soils on slopes in the Bowland Forest area, and of Co, Mn and Zn under similar circumstances in the Shaftesbury area. The translocation of these metals is attributed to mobilisation in poorly drained soils and transport with groundwater as described by Horsnail (1968). (iv) Within molybdenum anomalous areas, total Mo values in topsoils tend to be lower than in associated subsoils, a relationship arising largely from the leaching of Mo from topsoils. Reduced contrast is observed in soils with poor profile drainage and/or where topsoil pH values are low and consequently the mobility of Mo is inhibited. A reduced contrast and local topsoil accumulation is noted at further sites where it is probable that Mo is retained in topsoils with organic 313

matter and/or secondary iron oxides. (v) Generalised metal relationships shown by soil samples taken at two depths (0-6 inches and 12-18 inches) indicate that the susceptibility of metZls to leaching from topsoils is Mo > Fe > Ni > Cu Cr. V) Co whilst Mn, Zn and Pb show increasing tendencies towards accumulation in topsoils

(E) Relationship between the metal content of bedrock, overburden and stream sediment (±) The relationship between the Mo content of rock, soil and stream sediment in all the areao examined is simple and direct. The fall in Mo values between rock and soil or soil and stream sediment noted in many localities is due to the physical suppression of Mo levels resulting from dilution of the media by material containing background levels of Mo arising from (a) mixing of parent materials in overburden or stream sediment and (b) the precipitation of CaCO in stream sediment. Thus, 3 apart from limited redistribution in topsoils, the dispersion of No from the black shales examined is dominantly mechanical. (ii) In areas of black shale, other shales, clays and sandstones a simple and largely direct relationship is observed between the Cr, Cu, Ga, Pb, Ti and V contents of rock, soil and stream sediment. The dispersion of these metals is thus dominantly mechanical (iii) In districts underlain by Jurassic limestones in the 314

Shaftesbury and Market Rasen areas, metal values in stream sediments are often lower than in adjacent soils due to the precipitation of CaCO3 from groundwater entering streams and consequent dilution of stream sediment as described by Thornton (1968). (iv) Levels of Mn, Co, Fe, Ni and Zn are often appreciably higher in stream sediment than associated soils. This trend is observed in all areas of poorly drained agricultural soils and is attributed to the mobilisation and redistribution of these metals in the overburden followed by precipitation in the drainage network as described by Nichol et al (1967) and Horsnail (1968). (v) In the West Carmarthenshire, Bowland Forest and Shaftesbury areas Cu values are higher in stream sediments than adjacent poorly drained soils. This relationship is attributed to the leaching of Cu from soils into the drainage network and incorporation with Fe and/or Mn oxides in stream sediments as described by Horsnail (1968).

(p) Metal content of pasture herbage (±) The Mo status of mixed pasture herbage is broadly related to the total Mo content of topsoils. Thus the molybdenum anomalies delineated in soils are also present, though with reduced contrast, in herbage. (ii) Although the Mo status of herbage is principally related to the total Mo content of topsoils, Mo uptake is influenced by soil reaction and the total 315

Fe, organic matter and drainage status of topsoils. Thus in West Carmarthenshire and on the Kimmeridge Clay in the Shaftesbury area Mo uptake by herbage increases with a rise in soil pH suggesting that part of the soil Mo is held in an exchange position with clay minerals or'secondary ferric oxides. In the Shaftesbury area herbage uptake also appears to be broadly related to the organic content of topsoils. In Bowland Forest Mo uptake is greatest on very poorly drained soils whilst herbage/topsoil relationships suggest that much of the labile Mo is innobilised with secondary ferric oxides. Molybdenum uptake by herbage in the Thane area is unrelated to the soil characters measured. (iii) From the results obtained it is concluded that the Mo available to plants growing on molybdenum anomalous soils may be (a) in solution with soil water, (b) held in an anionic exchange position with clay minerals or secondary ferric oxides, (c) associated with organic matter. .(iv) The Cu status of herbage in any one of the areas examined is relatively uniform despite wide variations in the total Cu content of topsoils. Moreover, apart from imperfect relationships observed in the West Carmarthenshire and Shaftesbury areas Cu uptake by herbage is unrelated to soil reaction, organic matter, total iron or soil drainage conditions. 316

(G) Agricultural significance of data from detailed stua areas (i) Critical examination of the herbage data reveals that the Mo status of herbage on molybdenum anomalous soils is at the low end of the range associated with molybdenum induced bovine copper deficiency. Moreover, the Cu status of herbage is generally low and frequently less than 10 p.p.m. Cu,regarded as the minimum dietary requirement for livestock by the Agricultural Research Council (1966). In view of the stream sediment—soil—herbage relationships established and the extensive molybdenum stream sediment anomalies it is considered that large numbers of cattle within the anomaly areas are affected by a conditioned copper deficiency most probably at a sub—clinical level. (ii) The present investigation demonstrates that, as proposed by Webb (1964), geochemical reconnaissance surveys can be used to identify and delineate new areas of consequence to agriculture.

(H) Extrapolations (i) The present regional geochemical surveys identify molybdenum anomalous soils and stream sediments related to the outcrop of certain black shales:— (a) The black Dicranograptus shales in the West Carmarthenshire, Rhayader and Shelve areas (b) Visean/Namurian black shales in the Bowland Forest area (c) The Lower Oxford Clay in the Shaftesbury, 317

Thame and Market Rasen areas and also near Bedford (d) The Kimmeridge Clay in the Shaftesbury, Theme and Market Rasen areas. (ii) Examination of the literature reveals that the above formations retain the black shale facies identified as Mo—rich for long distances beyond the reconnaissance areas. There is every reason to believe that the black shale facies are Mo—rich throughout their extensive outcrop and thus the source of raised levels of Mo over large areas of England and Wales. (iii) The broad relationship between the Mo content of stream sediment, rock, soil and herbage observed in the present survey is consistent with results from previous investigations (Webb, 1964, Atkinson, 1967, Fletcher, 1968, Horsnail, 1968, Thornton, 1968) and together indicate that the dispersion of Mo from rocks of marine black shale facies in the British Isles is dominantly mechanical and Mo soil—herbage relationships are relatively simple. Thus it is anticipated that in future reconnaissance surveys, patterns of Mo anomalous stream sediments related to outcrops of marine black shales will be associated with areas of Mo—rich bedrock, soil and herbage.

2. Recommendations for Further Research (i) Selenium enrichment in the black shales examined in the present survey is found to be a variable feature. Nevertheless, it is probable that further large areas are 318 underlain by seleniferous bedrock and that critical examination of soil series information will lead to identification of sites where the environment is suitable for the establishment of seleniferous herbage. In view of the tendency towards a common enrichment of Mo and Se in black shales it is reasonable to use Mo as an indicator for the possible presence of Se. However, it is hoped that techniques will soon be available for the determination of Se as part of the semi—automatic multi—element analysis of stream sediment, soil and rock.

(ii) The present investigation has shown that in some districts Cu values are higher in stream sediments than in adjacent poorly drained soils. Further work is recommended to establish the conditions under which the modified Cu soil—stream sediment relationship is encountered and thus enable more accurate interpretation of future stream sediment reconnaissance surveys.

(iii) The secondary precipitation of CaCO3 in areas underlain by limestones has a marked effect on metal relationships between soil and stream sediment. The secondary precipitation is readily identified in the field and consideration can be given to possible metal relationships. However, the development of techniques that can establish direct metal relationships between soil and stream sediment under these conditions is recommended as an aid to the interpretation of stream sediment data for agriculturalists. 319 (iv) In view of the current awareness of the delicate balance of the environment and to aid the interpretation of geochemical patterns in populous areas it is recommended that further investigation is made of pollution from sewage and similar sources and of the dispersion of metal pollutants in stream sediments, soils, water and air. 320

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1. Sampling and Sample Preparation During the course of the present investigation a total of 2621 samples of stream sediment, rock, soil and herbage were collected (Tables 64 and 65). Care was taken at all times to avoid contamination, to ensure correct sample identification and for the accuracy of observations made at sample points. Implements used in sample collection, trowel, spade, soil auger and shears for herbage collection, were cleaned regularly to reduce metal contamination and avoid the cross contamination of samples. Samples were sieved using nylon bolting cloth in perspex sieve frames or Endecot alloy sieves. All samples were placed in kraft paper bags carrying a sample identification number. Records of sample number, sample location and relevant observations on the sample and site were made in duplicate. Copies of the field notes were despatched regularly to Imperial College for safekeeping.

(A ) Stream sediment samples Stream sediment sampling followed the procedures described by Hawkes and Webb (1962). Sediment samples were collected along road traverses from tributary streams with catchment areas of less than 10 square miles, to achieve a final density of approximately one sample per square mile. Duplicate samples of active stream sediment were taken at each sample site from

Table 64 Regional st/eam sediment reconnaissance survey sampling logistics rara.•• Sample Area in Number of density Number of Sample rate Study area Eq. miles samples per sq. mile days in field samples per day West Carmarthenshire 155 190 1.20 6.0 25.83 Rhayader 65 76 1.17 2.0 38.00 Shelve 100 118 1.18 3.5 33.71 Machynlleth 100 99 0.99 3.0 33.00 Kendal 75 75 1.00 3.0 25.00 Bowland Forest 195 170 1.04* 6.0 28.33 (0.87+) Shaftesbury 120 139 1.16 5.0 27.80 Thame 230 220 0.95 8.0 27.50 Market Rasen 110 110 1.00 3.5 31.43

TOTAL 1150 1197 1.04 40.0 29.93

* Sample density excluding unsampled area ' Sample density over whole area 335

mid channel, upstream from the road crossing, to avoid collapsed bank material and road contamination. Samples were stored in kraft paper bags holding some 100-150 grammes of sediment. This usually produced sufficient minus 80-mesh material for analysis. Sample number and location (Ordnance- Survey grid reference) were recorded on field sheets, together with observations on the bank material, size and velocity of the stream, the physical and chemical characters of the sediment and the presence of any precipitates. The geology and possible sources of contamination were also noted. A rapid determination of the pH of the stream water was made using B.D.H. liquid universal indicator. Ordnance Survey one inch to the mile maps were used during the stream sediment reconnaissance survey. Samples were dried overnight at 8000 in an electrically heated drying cabinet. Samples were then gently disaggregated in a porcelain mortar and the minus 80-mesh (less than 204 microns) fraction sieved off and retained. This fraction is suitable for spectrographic, colorimetric and atomic absorption analysis without further preparation and its use is standard practice in A.G.R.G. routine reconnaissance surveys. A five-hundredweight van was used for the stream sediment survey and was found to be ideal for both sample collection and transporting field equipment. Singlehanded it was possible to collect some 30 samples per day (Table 64) dependent on the density of the stream and/or road network and the accessibility of the watercourses. Parts of the Machynlleth, Bowland Forest and Kendal survey areas are 7-15E

without road access and were unsampled. Sample sieving took place during the evenings. Stream sediment sampling took place during the period March to May 1968 when agricultural data from N.A.A.S. and V.I.S. officers, local veterinary practitioners and farmers were also collected and a brief visual examination made of the soils in the reconnaissance areas. In addition, a further 637 stream sediment samples were collected in a programme incidental to the present study.

(B) Rock Sampling Grab samples of 150-300 grammes were collected by chip sampling from sections described in the literature. The sampling programme attempted to be representative of the lithologies present and stratigraphically distributed. The samples collected were of the least weathered material obtainable. The rock samples were crushed in a small jaw crusher to minus 10—mesh, coned and quartered to give a 10-15 gramme sample. This was ground to minus 80—mesh, in a Tema agate mill, for analysis. The Tema mill was cleared with white sand and washed with hydrochloric acid between runs to prevent salting.

(C) Soil Samples Soil samples were collected initially along traverse lines at intervals of from 200 to 1000 feet. Samples were taken at a depth of 12-18 inches using a 1 inch screw auger Each sample comprised a bulk of five samples taken from an area five yards square. 337

Table 65 Distribution of rock, soil and herbage samples from the five follow up areas

Soils 12-18" 0-6" Rocks Herbage

West Carmarthenshire 125 49 36 49

Bowland Forest 279 38 36 38

Shaftesbury 178 62 10 62

Thame 191 48 29 48

Market Rasen 111 15 5 15

Total no. of samples 884 212 116 212 338

After examining the initial data, sites were selected where topsoil samples (0-6 inches depth) comprising a bulk of five samples taken in an area five yards square were taken and the subsoils (12-18 inches depth) resampled to give information on the vertical distribution of metals in the soils. Ordnance Survey two and a half inch to the mile maps were used to locate sample sites. Sites and soil samples were described briefly following the recommendations of Clarke (1957). Attention was given to the drainage conditions and the presence of secondary iron oxides in the soils. The pH of topsoils was determined in the field using a portable meter, with glass—calomel electrode, previously calibrated at 4.0 and 9.3 units using buffer solutions. Two determinations were made at each site and the mean value taken. The soil samples, some 300 grammes, were placed in kraft paper bags and dried at 60-800C in an electric drying cabinet. Following agricultural practice, the minus 10— mesh (minus 2 mm.) fraction of the soils was analysed. Soils were disaggregated in a porcelain mortar and sieved to minus 10—mesh to remove stones and coarse concretions. The minus 10—mesh fraction was coned and quartered and a 10-15 gramme sample then ground in a porcelain mortar to minus 80—mesh for analysis. Samples of peat are difficult to disaggregate and are unsuitable for spectrographic analysis; these samples were sieved to minus 20—mesh and analysed by wet chemistry and atomic absorbtion. 7.5:39

(D) Herbage Samples Herbage samples were collected at those sites where topsoil samples were obtained. Only agricultural land under grass was sampled, thus herbage was dominatly of mixed pasture grasses and some clover. Grab samples of herbage were collected in 1969 during the last week of July and the first week of August. Each sample is a bulk cut from an area five yards square. Herbage was cut a few inches above the ground to reduce contamination by soil. No attempt was made to separate grasses from clover and rushes were included in poorly drained sites. It was attempted to make the samples typical of the herbage ingested by grazing animals. A close inspection of the pasture quickly revealed those grasses not eaten by cattle. Herbage samples were placed in kraft paper bags and dried at 6000 in an electric drying cabinet. Samples were not washed before drying and milling and, therefore, although cut a few inches above the ground, probably include very small increments of trace elements resulting from soil contamination. The work of Mitchell (1960) indicates that, in the present survey, soil contamination is unlikely to affect the herbage results. Dried herbage samples were prepared for analysis by grinding in a Christy Norris mill. The mill was cleaned carefully between runs to prevent cross contamination.

2. Analysis of Samples All stream sediment, rock and snil samples (except organic rich and peat samples) were analysed spectrographically for Co, Cr, Cu, Ga, Mn, Mo, Ni, Pb, Ti, -540

V, Zn and Fe (expressed as Fe203). Further analyses, employing wet chemical methods were undertaken to yield data on Mo, Se, As and organic carbon, whilst Cu was determined by atomic absorbtion. Analytical precision, quoted at the 95 per cent confidence level, was calculated from replicate• anclypos of randomly selected samples employing the equation:

6 = (2 — x)2 n — 1 . 26 x 100

where n = no. of determinations, x = individual values, mean, with a minimum of five replicate analyses used in the calculation. The accuracy of the analyses was confirmed by determinations made of the international rock standards G.1 and W.1 (Table 69).

(A) Spectrographic method The rapid semi—quantitative multi—element method of Nichol and Henderson—Hamilton (19'65) is in routine use by A.G.R.G. Metal values in parts per million and Fe203 as a percentage are all determined in this way. Samples are ignited at 450-50000 for three hours to remove combustible material and water. A weighed sample is mixed in a 1 : 1 ratio with a lithium carbonate—carbon buffer containing 400 p.p.m. Ge as an internal standard. Sample and buffer are homogenised by shaking for 30 seconds in a Wig—L—Bug and then packed in a graphite anode. The 341

Spectrographic equipment, wavelengths and detection limits are summarised in Tables 66 and 67. Trace element concentrations in parts per million are determined by the visual comparison of spectra against artificially produced standards which increase in concentration semilogarithmically. Greater precision is obtained by comparing the spectral densities using a microphotometer. Fe203 is determined by comparing the spectral density reading given by the microphotometer with a graph produced from readings obtained from various rock standards including G.1 and W.1. Analytical precision for the spectrographic method has a variation in mean levels of between ±36 and ±76 per cent with an overall observed variation of from ±0 to ±125 per cent (Table 68). Precision becomes unacceptably poor (). 1--75 per cent) in samples close to the lower detection limits (notably Mo). This is of particular importance with respect to the low levels of Mo examined in the present study and is discussed later. The accuracy of the spectrographic method was checked by the determination of G.1 and W.1, employing the routine procedure, at irregular intervals throughout the analytical programme. Table 69 compares the results obtained with those published by Stevens (1950). A satisfactory degree of accuracy is indicated. Productivity for the spectrographic method, employing visual determination of metal values, is 30 samples per man day for 11 elements and Fe203%. Nichol and Henderson—Hamilton (1965) report that extreme matrices of ferruginous or silica—alumina composition bias the spectrographic determination of trace elements. In general Co, Cu and Ni are enhanced in a 342

Table 66 Spectrographic equipment and conditions (Modified from Nichol and Henderson—Hamilton, 1965)

Source Unit Hilger and Watts FS 131 Spectrograph Hilger and Watts Large Quartz E492 Arc Stand Hilger and Watts FS 55 Comparator—Microphotometer Hilger and Watts L90 0 Wavelength Range 2800 — 4950 A Emulsion Ilford N30 Anode Ringsdorf R.W. 403 6.15mm. Graphite Tapered crater 3.18mm. deep 2.13mm. tapering to 0.64mm. Cathode Ringsdorf R.W. 403 Flat ended Gap 3mm. Slit 15 m Arc Current 12.5 A Collimator Internal Step Sector 1 : 1 : 1 4 7 Exposure 20 sec.

Processing 5 min. Kodak D.19b developer at 1800, 10 sec. stop, 10 min. fix, wash 343

Table 67 Wavelengths and effective concentration ranges (Modified from Nichol and Henderson—Hamilton, 1965)

0 Wavelength A Range of concentration p.p.m.

Co ' 3453.5 5 1% Cr 4254.3 2 500 2843.3 500 1% Cu 3274.0 2 200 2961.2 200 1% Ga 2943.6 2 1% Mn 4035.5 5 500 2933.1 500 1% Mo 3170.3 2 1% Ni 3414.8 5 200 3050.8 200 1% Pb 2833.1 2 .... 100 2873.3 50 1% V 3185.4 2 1% Zn 3345.0 50 1%

344

Table 68 Analytical precision* of the spectrographic method, based on replicate analyses of randomly selected samples of stream sediment rock and soil

Stream sediments Rocks and Soils (15 samples) (27 samples) Range of Meant and Range of Mbant and values range of value range of recorded precision recorded precision Pb 3-400 p.p.m. 53 13-130 p.p.m. 47 (11-74) (9-71) Ga 6-40 p.p.m. 36 8-40 p.p.m. 43 (16-41) (11-68) V 40-400 p.p.m. 53 50-400 p.p.m. 38 (20-66) (25-42) Mo <2-100 p.p.m. 76 42-60 p.p.m. 35 (15-125) (22-56) ) Cu 5-160 p.p.m. 51 5-100 p.p.m. 34 (17-71) (22-60) Zn <50•-500 p.p.m. 46 <50-400 p.p.m. 52 (22-98) (35-100) Ti 2023 p.p,m.-1% 40 1000 p.p.m.-1% 39 (8-51) (10-55) f Ni 10-130 p.p.m. 35 5-100 p.p.m. 33 (22-48) (10-42) Co 13-100 p.p.m. 34 <5-60 p.p.m. 53 (23-46) (0-69) _ . 7.-n 35-1300 p.p.m. 50 16-4000 p.p.m. 35 (33-67) (16-62) 30-500 p.p.m. 53 40-400 p.p.m. 46 (25-71) (25-65) Fe203% 1.3-19.0% 47 2.3-17.2% 39 (12-66) (15-61)

* At the 95 per cent confidence level A Geometric mean

Table 69 the spectrographic method as shown by ten replicate analyses of G1 and W1 Metal content (p.p.m.) Pb Ga V Mo Cu Zn Ti Ni Cc Mn Cr

Stevens-* 50 18 21 7 13 N.D. 1400 1.2 2.2 210 22 Mean+ 44 23 20 8 16 :50 1720 (5 (5 140 17 G1 Range 30-50 16-30 16-30 5-10 11-20 <50 1600- <5 (5 100- 13-20 3000 160 Analytical PrecisionA 41 74 57 45 41 - 101 - - 60 33

Stevens 7 16 240 <2 110 N.D.: 7400 82 51 1300 120 Mean+ 5 17 260 <2 118 136 8167 73 50 1100 140 W1 Range 5-6 13-20 160- <2 100- 85- 6000 60-85 40-60 850- 130- 300 130 200 -1% 1600 160 Analytical Precisic3A 29 35 60 - 25 76 44 38 36 54 22

* Stevens 1960 (Bull. U.S. Geol. Surv. 1113) + Geometric mean

A At the 95 per cent co3fidence level N.D. No data 346 siliceous matrix and Mo and V in a ferruginous matrix. Variation in the silica—alumina composition of the samples is unknown. Variation in the ferruginous composition of the samples is all compared with those quoted by Nichol and Henderson—Hamilton as producing significant variations in the apparent trace element composition. Samples containing very large amounts of calcium carbonate were encountered in areas of impure limestones. The calcium carbonate gave rise to strong interference patterns in sample spectra. The Zn line was masked by dark bands whilst elsewhere on the spectrum interference produced a more intense background which could be compensated for in both visual and microphotomter determinations. Samples giving Ge (internal standard) values of (300 p.p.m. and 7 600 p.p.m. were re—analysed.

(B) Atomic absorbtion methods All rock, topsoil and herbage samples were analysed for Cu by atomic absorbtion. The instrument employed was a Perkin Elmer 303 spectrophotometer with a hollow cathode copper lamp. The instrument settings are summarised in Table 70. The solutions were aspirated and the absorbtion measured. The values recorded were converted to parts per million by comparison with a graph prepared from absorbtion values obtained by spraying artificially prepared standards. Selected samples of stream sediment and subsoils were analysed for Cu by this method for comparison with spectrographic determinations. The procedures employed were as follows: (a) Sediment, rock and soil samples: the sample is 347

Table 70 Instrument setting for the determination of copper using the Perkin—Elmer 303 Spectrophotometer

0 Wavelength 3247.5 A Lamp Hollow Cathode Current 10 milliamperes Slit 4 (= 1 m.m. slit opening) Burner Single Slot Fuel Flow 9 divs. Air Flow 8 divs. 348 attacked using a 4 : 1 nitric and perchloric acid mixture which is slowly evaporated to dryness. The residue is taken up in 0.5N hydrochloric acid. Standards are also prepared in 0.5N hydrochloric acid. The solutions are sprayed and compared with the standards as described above. Analytical precision is better than ±10 per cent with productivity of 100 samples per man day. (b) Herbage: a 5 gramme sample of herbage is digested in 4 : 1 nitric and perchloric acid mixture which is slowly evaporated to dryness. The residue is taken up in 0.5N hydrochloric acid and sprayed as above. The analytical precision observed was better than ±5 per cent with a productivity of about 40 samples per man day.

(c) Wet chemical methods Molybdenum, selenium and arsenic were determined calorimetrically. Organic carbon determinations were made by a titrimetric procedure. The analytical procedures outlined below follow methods in routine use at A.G.R.G. Molybdenum was determined by the procedure, modified from that of Stanton and Hardwick, outlined in A.G.R.G. Tech. Com. No. 56 (1967). Sediment, rock and soil samples are attacked by a bisulphate fusion followed by a leach in 6M hydrochloric acid. A suitable aliquot is reacted with dithiol to give a green Mo—dithiol complex. The complex is extracted with light petroleum and compared with artificially produced standards. A lower detection limit of 0.8 p.p.m. is possible. Analytical precisions of ±5 to ±15 per cent were obtained. Productivity is about 75 samples 349 per man day. Herbage samples, organic rich soils and peats were analysed for Mo by the above procedure following an attack by a 4 : 1 nitric and perchloric acid mixture slowly evaporated to dryness. Analytical precision is of a similar level whilst productivity falls to 25 samples per man day.

Selenium determination followed the procedures of Stanton and McDonald as outlined in A.G.R.G. Tech. Com. No. 51 (1965). Samples were digested in a 4 : 1 nitric and perchloric acid mixture. A yellow coloured complex is then formed between selenium and 3,3 diamenobenzidine which is extracted in benzene after adjusting the pH of the solution. The intensity of the colour of the sample is compared with artificially produced standards. Values down to 0.2 p.p.m. Se can be determined with an analytical precision of better than +10 per cent. An average of 20 samples can be analysed per man day.

Arsenic was determined using the procedure of Stanton (1964) outlined in A.G.R.G. Tech. Com. No. 49 (1965). Following a bisulphate fusion arsenic is converted to arsine which is swept from the test tube by hydrogen to react with mercuric chloride papers, giving a yellow to dark brown spot depending on the concentration of the arsenic. A range of 5-250 p.p.m. is covered in routine analysis with a precision of better than ±25 per cent. Productivity is about 100 samples per man day. 550

Organic carbon The method used is a modification of that of Schollenberger described in A.G.R.G. Tech. Com. No. 32 (1967). Potassium dichromate is added to the sample which is then oxidised with sulphuric acid and organic carbon estimated by titration with ferrous ammonium sulphate using diphenylamine solution as an indicator. Results are lower than those obtained by combustion methods. Productivity is 50 samples per man day over the range 0.1-3.9% extended to 39.0% by altering the sample weight, with analytical precision of better than ±10 per cent.

(D) Comparison of analytical results It was necessary to be confident of the accuracy and precision of the results for Mo and Cu obtained during the reconnaissance survey and subsequent follow up. Thus selected samples were analysed colorimetrically and by atomic absorbtion to check the spectrographic data. In view of the poor precision of the spectrographic method at low levels and the significance of levels of Mo as low as 3 p.p.m. in agriculture, all low levels of Mo (<5 p.p.m. were confiLmed by colorimetric analysis. In addition sediment samples in which Mo might have been expected to be present, yet was undetected in the spectrographic determination, were analysed calorimetrically. Fig. 56 shows the relationship between the spectrographic determination of Mo and Cu and the results of colorimetric and atomic absorbtion analyses of the same samples. A good correlation between the methods of analysis is demonstrated for both Mo and Cu, most of the variation observed being explained by the greater imprecision

Molybdenum. Copper.

50- ++ 100

++ + ++++ 50 ++ + +++ + +++++++ +

6 ++ +14 4++ ++ + + . _ Li ...,=

cl_ lc E "10- + + + + + ci m. ci_ Q. + +1-1+ -H. +1+

C3 cn p. i_ + + + ++ c) cr) E L p + + + ++ +I++ 1+ + + er I-- -0 + 4++ + + ++++ + + + +++ ++++ + + Copp a.) cc) 10' + +++ + + ++1+ + + + + + + ++

+ + 5 2- -f + + + 44-4+

. <2

■ 5$ 5 10 50 100 Molybdenum p p m Copper p. p m Colorimetric (dithiol). Atomic Absorption.

Fig.56. Relationship between Spectrographic and Calorimetric determination of Molybdenum, and Spectrographic and Atomic Absorption determination of Copper. Data from 220 samples of Stream Sediment and Soil. (minus 80-mesh fraction) 351

of the spectrographic data and the arbitary divisions adopted for visual estimation of spectral densities. As might be expected, the deviation is greatest near the spectrographic detection limit of Mo. Since the colorimetric method of Mo determination has a much better precision at low levels (< 5 p.p.m. Mo) than the spectrographic method, the data were corrected to the values obtained colorimetrically.

3. Data Handling A total of 2621 samples of stream sediment, rock, soil and herbage yielded 30674 items of analytical data. In addition further data were obtained from replicate analyses and the supplementary determinations made to verify the spectrographic results. To cope with the large volume of data routine methods of data checking, storage and sorting with automatic data processing employing an electrical digital computer were adopted. The corrected data were placed on computer punch cards. The data for each sample occupy a single 80 column punch card carrying the sample number, grid co-ordinates (for stream sediment samples) and the analytical information in parts per million and per cent. The cards are conveniently stored in boxers and readily sorted (e.g. by -the geology of the sample parent material) for visual examination, data plotting or automatic processing.

(A) Statistical processing Simple statistical evaluation of the data was undertaken as routine. The programme GSTAT (Garrett, 1967a) was used, operating on the Imperial College I.B.M. 7090/94 352 and the University of London C.D.C. 6600 electrical digital computers. The programme is written in Fortran IV. The programme handles up to 20 variables on each of a maximum of 500 cases and computes with or without an optional logarithmic transference. Experience at A.G.R.G. has shown that geochemical data usually approximates to a lognormal distribution. Statistical parrmeters (geometric mean etc.) based on log transformed data are therefore employed. The following options are available and operate, for the variables specified, in response to instructions punched on programme control cards. 1. The mean, variance, standard deviations (1-3 limits about the mean) skewness and kurtosity are computed. 2. Histograms may be plotted to display population distributions. 3. A chi—square test for the normality of the population. 4. A correlation matrix may be computed, in order to gain insight on the interrelation between the variables, and a students t test to assess the statistical significance of the correlation co—effic ient s. The significance of the correlation is established by references to tables of r and t. Attempts to emply R—mode factor analysis to the data a further interpretive technique, using the programme RSCORE (Garrett, 1967b),were unsuccessful. It was found that the data from the present survey areunsuitable for this type of statistical treatment. In general, sample populations are small and many of the variables (metal 353

values) display only a limited amount of variation. Thus with so many similar distributions the programme RSCORE is frequently unable to discriminate meaningful associations.

(B) Presentation of data In order to make the vast arrays of data readily understandable the presentation of data is standardised to three forms: (i) tables (ii) maps (i41) graphs. (i) Tables: the range and geometric mean values of sample populations are quoted. These values are computed using the GSTAT programme, after the raw data have been sorted into the chosen groupings (e.g. geology of sample parent material). (ii)Maps: in order to facilitate the interpretation of the geochemical patterns revealed by stream sediment reconnaissance, the information is presented in a simplified form. The stream sediment data are split into groups of semilogarithmic dimensions covering the range observed in a given area. Group boundaries are established with respect to the standards used in the spectrographic determination following the practice established by Viewing (1963). Thus group boundaries of 1.5, 3.0, 7.0, 15.0 etc. have been used throughout. Stream sediment data were plotted manually on transparent overlays, with a base map showing the drainage network and geology, at a scale of 1 : 126,720. Maps showing single element distributions, for each of 11 trace elements and Fe203 in the nine reconnaissance areas, are found in Volume II. These maps show the metal content of stream sediments plotted as symbols over the sample sites, 354

the symbol indicating the concentration group into which the data fall. (iii) Graphs: the distribution and concentration of metals along traverse lines, and in rock samples, is portrayed graphically. Data are plotted on a logarithmic scale with the topography, geology and overburden present along the traverse lines displayed below the metal values.