THE UNIVERSITY of HULL Conodonts, Correlation
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THE UNIVERSITY OF HULL Conodonts, correlation and stratigraphy of the Plymouth Limestones being a Thesis submitted for the Degree of Doctor of Philosophy in the University of Hull by Michael James Orchard, B. Sc. July 1975 PAGE NUMBERINGAS ORIGINAL CONTENTS Summary Acknowledgements Part I : INTRODUCTION . General Introduction 1 Historical Introduction 2 Previous Work ' 5 British Devonian Conodonts 7 Part II : THE CONODONTS Introduction and techniques 9 DEVONIAN C0N0D0NT ZONATION • The Conodont Zonation of the European Middle Devonian Foreword 12 The Nonlatericrescid Icriodus Fauna of the ‘Upper Emsian’ 13 The Icriodus corniger Zone 15 The Spathognathodus bidentatus Zone ' 1 7 The Polygnathus kockelianus Zone - 2 0 The Conodont Zonation of the North American Middle Devonian 22 The Icriodus obliquimarginatus Zone 25 The Polygnathus varcus Zone 28 The transversus Zone 32 Middle Devonian conodont successions in Australia 33 The hermanni-cristatus Zone ' 35 The Spathognathodus insitus Fauna 39 The Middle#Upper Devonian Boundary 40 The Ccnodont Zonation about the Middle#Upper Devonian Boundary History of work 41 Discussion 43 The Conodont Zonation of the Upper Devonian 45 THE PLYMOUTH CONODONT FAUNAS 48 SYSTEMATIC PALAEONTOLOGY ’ Foreword 55 The Ancyro group 58 - 1 Ancyrodella: A. curvata 59 A. gigas 61 A. nodosa 62 A.‘rotundiloba 63 A.r. alata 64 A.r. rotundiloba 65 A. rugosa s.l. 66 Ancyrognathus: 67 A. triangularis 68 A. cryptus 69 Icriodus: 69 I. corniger 72 I. expansus s.l. 76 I. nodosus s.l. 77 The Icriodus expansus - I. nodosus plexus 78 I. expansus - I. nodosus qroup 80 morphotype 1 81 morphotype 2 82 morphotype 3 83 I. fusiformis 84 I. obliquimarqinatus 85 I. regularicrescens 86 1. retrodepressus 87 K n.sp.a 88 I_. n.sp.b 91 I_. n.sp.c 89 1* sp.a 90 I. n.sp. a sensu BULTYNCK 90 Upper Devonian Icriodus from Plymouth 91 K aff. K alternatus 92 i* brevis 95 K expansus - I_. nodosus group 98 I_. symmetric!)?, group 99 m _I. symmetricus 1-00 morphotype 1 101 morphotype 2 102 _I. n. sp. aff. _I. alternatus 102 Palmatolepis: 103 Pa« aff. £ a . fransi tans 104 Pa. n. sp. a 105 Pa. durnfordi n. sp. 105 Polygnathus : 107 Po. aff. Po. aspera 107 The Po. asymmetricus group 109 Po. £. asymmetricus 111 Po. a_. oval is 112 Po. dengleri 114 Po. ni smi n. sp. 115 The Po. costatus group 118 Po. £. costatus 118 Po. pseudofoliatus 119 Po. cristatus 121 The '1inguiformid'group Po. cattedowni n. sp. 123 Po. linqui form's 124 Po. 1inguiformis group 127 Po. 1_. cooperi 131 Po.JL. 1 inguiformis 132 $ morphotype 133 Po. forma nova 1 136 Po. 1. forma nova 2 137 Po. mucronatus 138 Po. serratus n. sp. 140 Po. transversus 142 Po. latus 143 Po. aff. Po. 1atus * 144 Po. n. sp. aff. Po. porci 11 us 145 The Po. robusticostatus- oroun 146 Po. anqustipennatus s. 1. 147 Po. tuberculatus 150 The Po. varcus group ' 152 Po. biconvexus n. sp. 155 Po. rhenanus 156 Po. aff. Po. rhenanus 157 Po. timorensis 158 Po. varcus 161 Po. xylu$ 162 Po. aff. Po. xylus 164 Spathognathodus: 164 §.* bidentatus 164 S. bipennatus 165 IS. brevis 167 S. planus 169 PART III: FACIES AND ENVIRONMENTS Introduction 170 The Carbonate environment 170 Regional and structural context 174 Local context 176 The Plymouth situation 178 Environmental synopsis 192 Conodont distributions and biofacies Introduction 195 Previous Work 195 Plymouth distributions: discussion 197 Simple cones 197 Icriodus and Polygnathus 199 Ancyrodella and Palmatolepis 202 Summary 203 BIBLIOGRAPHY 204 - V - APPENDIX Statigraphical detail; Foreword 231 Rum Bay - Dunstone Point 232 Batten Bay - Mount Batten (West) 233 Hooelake Quarry - Turnchapel 236 Clovelly Bay : Turnchapel - Mount Batten 238 Hexton Quarry 239 Langshi11 Quarry, Oreston 239 Radford Quarry 240 Breakwater - Bedford Quarry 242 Pomphlett Mill Quarry, Billacombe 243 Sal tram Quarry 244 Laira Bridge Cutting 245 Cattewater Road 246 Princerock Quarry (Plymouth Power Station) 248 Faraday Road 250 Cattedown Quarry 251 Gasworks (Esso) Quarry 253 Fisons Quarry, Cattedown (South) 255 Teat's Hill Quarry, Coxside 258 Sutton Pool, Coxside 261 Dead Man's Bay (Quarry), Coxside 261 Drakes Island 262 West Hoe - Hoe - Citadel 264 Richmond Walk (Devonport Hi 11- Ordnance Quarries - Cole's Timber Yard) 266 Mount Wise - Mutton Cove - Dock Yard - Devonport 269 Devils Point - Western King (Point) 271 Eastern King 276 Durnford Street 277 Barn Pool - Cremyl 279 Botus Fleming 282 Neal (Nail) Point 283 -285 - vi - Figures: 1. Conodont zonal schemes - Middle/Upper Devonian 2. Hypothetical relationships of conodont faunas about the Middle/Upper Devonian boundary and Lower Upper Devonian. 3. The Geological context of the Plymouth Limestones 4. Key to figures 5-16, 18-21 5. Mount Batten — Locality and section detail — 6. Langshi11 Quarry, Hooelake Quarry. 7. ’Radford Quarry, Oreston 8. Pomphlett Mill Quarry, Sal tram Quarry, Bedford Quarry. 9. Princerock 10. Cattedown - North 11. Cattedown - South 12. Coxside, East Hoe. 13. Richmond Walk, Mount Wise 14. Durnford Street, Western King, Eastern King 15. Cremyl, Barn Pool 16. Neal Point, Botus Fleming, Drakes Island. 17. Correlation of Plymouth (& Tamar) Limestones 18a Plymouth localities 18b Lower/ltiddle Eifelian distributions/conodont ratios 19a Upper/Eifelian distributions/conodont ratios 19b Lower Middle Givetian distributions/conodont ratios 20a varcus Zone distributions/condont ratios 20b Lower-Middle asymmetricus zone distributions/conodont ratios 21a Middle-Upper asymmetricus zone distributions/conodont ratios 21b Mid Frasnian (-Lower Famennian) distributions/conodont ratios 22. Sketch map of the Plymouth limestone - boundaries and structure; sketch sections Plates: 1-6 Middle Devonian Icriodus 7 Middle Devonian Spathognathodus et al_. 8-9 Middle Devonian Polygnathus 10-16 The Polygnathus varcus group 17 Polygnathus cattedowni n.sp. 18-23 Polygnathus linguiform's group 24 Polygnathus linguiform's group ; Po. tuberculatus 25-27 The Anc.yro group 28-29 The Polygnathus asymmetricus group £t al_. 30-32 . Palmatolepis 33-34 Upper Devonian Icriodus 35 Bars and blades (Velements) et al. 36 Bars and blades (B elements) et al_. r V1U Summary This work embraces the study of the conodonts and the environments of the Plymouth Limestones (Devonian, South Devon). Widespread sampling of calcareous strata in the Plymouth area has produced conodonts indicative of high Emsian to mid - Famennian levels. The European Conodont Standard is reviewed and comparisons are made with North American and Australian successions; the South Devon faunas are examined and discussed in their light. The results indicate that, on the whole, the Upper Devonian faunas are comparable but Middle Devonian successions differ in some respects. Most of the diagnostic conodonts are treated systematically and several new form-species are introduced. Correlation based on the conodont faunas are presented for most of the disjunct sections. The Plymouth Limestones are discussed in the context of the Variscan geosyncline and Cornubian palaeogeography. A review of the Devonian carbonate buildups, and the facial differentation therein, is followed by an assessment of the local situation in terms of possible European counterparts. It is suggested that the carbonate complex developed in anarea of shallowing within the geosvncline and was unrelated to a northern shelf. ' ’Rather, a restricted environment 1s indicated to the east and southeast in which direction a Plymouth Schwelle may have had its maximum relief. Conodont biofacies are . discussed and assessed in relation to the Plymouth distributions and the inferred environmental picture. An appendix includes biostrati graphical detail, and diagrammatic presentation of sample location and composition and distribution of the conodont faunas in space and time. The conodonts are illustrated on thirty-six plates of stereoscan photographs. Acknowledgements This study and report were made possible by a N.E.R.C. grant and the patience and encouragement of colleagues, friends and family. In particular the guidance and supervision of Professor ,M.R. House is gratefully acknowledged. The work was undertaken at the Geology Department of the University of Hull and latterly at the Sedgwick Museum, University of Cambridge, and thanks go to the assistant staff of these institutions for their help and advice. Thanks also go to Professor P. Bultynck of the Royal Academy, Brussels and Dr. N. Mouravieff, University of Louvain, Belgium for some useful discussion and access to their collections. Acknowledgements also to Dr. R. Aldridge of the University of Nottingham who also made his conodont collections available for reference. ‘ Sincere thanks go to my wife and mother who patiently typed the manuscript. PART I INTRODUCTION - 1 - General Introduction The Plymouth Limestone of South-west Devonshire consists of a carbonate complex some six miles long (east - west) and, at its maximum, approximately one mile in breadth (see Fig. 3). The city of Plymouth and its docklands have been built on, and excavated in, the limestones, especially in the west, and consequently correlation across the area is hampered. Furthermore, the Variscan Orogeny was responsible for the upheaval and tearing of the limestone to such a degree that its present disposition and orientation .bears no necessary relationship to the original. The complexity of the structure, the lack of continuous strike and dip sections, subsequent metamorphism and dolomitization, and last, but not least, the common, often subtle, facies changes, both lateral and vertical, contribute to the difficulties confronting one in any attempt to elucidate the stratigraphy and thereby gain an insight as to the nature of these limiting factors. Such an attempt has been made by the use of conodonts. The study has mainly concentrated on the immediate area of Plymouth (see fig. 18) westward to the limestone's edge around Mutton Cove and Cremyl and eastward to the area of Plymstock; the limestones appear to be most variable within and across this area. The study has also embraced goegraphically isolated limestone developments outside the main area, in East Cornwall and (not included in this report) in central South Devon.