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The systematics and paleobiology of Hettangian ammonites from the allochthonous terranes of British Columbia Longridge, Louise M. 2007

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T H E SYSTEMATICS AND P A L E O B I O L O G Y OF H E T T A N G I A N A M M O N I T E S F R O M THE ALLOGHTHONOUS TERRANES OF BRITISH C O L U M B I A  by  LOUISE M. LONGRIDGE B.Sc, The University of British Columbia, 1998  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  DOCTOR OF PHILOSOPHY in  THE FACULTY OF GRADUATE STUDIES  (Geological Sciences)  THE UNIVERSITY OF BRITISH COLUMBIA September 2007  © Louise M. Longridge, 2007  ABSTRACT The Hettangian is a poorly understood 3 million year time interval following the TriassicJurassic mass extinction during which the biosphere struggled to rebuild its diversity. Hettangian ammonite faunas are examined from the two key areas of the terranes of British Columbia, Taseko Lakes and the Queen Charlotte Islands (QCI). In total, 90 different species or taxonomic groups are described representing 32 genera. Thirteen new species are recognized. Stratigraphic ranges are identified for each taxon and the North American Zonation is updated so that it is more representative of Canadian sequences. Except for the definitive occurrence of the Spelae Zone, all Hettangian zones of the North American Zonation are present in the BC terranes. A section on Kunga Island in the QCI demonstrates a spectacular radiolarian turnover across the Triassic-Jurassic transition interval (T-J boundary), provides a radiometric date to constrain the boundary, contains ammonites which permit correlations with other areas and can be correlated with a carbon curve which shows a distinct negative excursion just below the radiolarian turnover. This section is proposed as a potential Global Stratotype Section and Point for the basal Jurassic if radiolarians are selected as the primary standard for defining the T-J boundary or as a parastratotype section to assist with characterizing the interval if radiolarians are not selected. Detailed correlations are suggested between the Hettangian and lower Sinemurian of the terranes and other areas of North America, South America, New Zealand, western and eastern Tethys, and northwest Europe.  1  The lateral distribution of ammonite faunas suggest there may have been some longitudinal separation between the craton and the Cadwallader, Wrangellia and Peninsular terranes during  the Hettangian. They also support a significant northward displacement for Wrangellia relative to the craton since Early Jurassic time and suggest that the Hispanic Corridor connecting the Panthalassa and Tethys oceans may have been open during the Hettangian. Sexual dimorphism is recognized in several Hettangian genera including  Kammerkarites,  Eolytoceras, Sunrisites and Badouxia. Asymmetries in the vertical position of the internal elements of the phragmocone of B. columbiae were assessed for a potential counterbalance mechanism using computer modeling. No counterbalance mechanism was recognized.  TABLE OF CONTENTS ABSTRACT  «  T A B L E OF CONTENTS  iv  LIST OF TABLES  •  xii  LIST OF FIGURES  xiii  LIST OF PLATES  xvii  ACKNOWLEDGEMENTS  xviii  DEDICATION  xix  CO-AUTHORSHIP STATEMENT  xx  CHAPTER 1: INTRODUCTION 1.1 Introductory statement 1.2 P r e v i o u s w o r k 1.2.1 S y s t e m a t i c s  1 •  1 3 3  1.2.1.1 F a u n a s f r o m the a l l o c h t h o n o u s terranes o f B C  3  1.2.1.2 Faunas f r o m other areas o f N o r t h A m e r i c a  5  1.2.1.3 Faunas f r o m other areas o f the w o r l d  5  1.2.2 N o r t h A m e r i c a n Z o n a t i o n  6  1.2.3 C o r r e l a t i o n s b e t w e e n C a n a d i a n successions a n d other areas  6  1.2.4 T r i a s s i c - J u r a s s i c b o u n d a r y d e f i n i t i o n  7  1.2.4.1 D a t e o f T - J b o u n d a r y  7  1.2.4.2 E n d - T r i a s s i c mass e x t i n c t i o n  7  1.2.4.3 T r i a s s i c - J u r a s s i c b o u n d a r y d e f i n i t i o n 1.2.5 P a l e o b i o g e o g r a p h y  10 13  iv  1.2.5.1 Hispanic Corridor  13  1.2.5.2 Terranes  13  1.2.6 Paleobiology  1  4  1.2.6.1 Sexual dimorphism  14  1.2.6.2 Hydrostatic implications of asymmetries of the ammonite phragmocone  15  1.3 Summary of Objectives  15  1.4 Methods  16  1.4.1 Literature review  16  1.4.2 Field work  16  1.4.3 Collections from other areas in the BC terranes  17  1.4.4 Laboratory work  18  1.5 Presentation  18  1.6 References  23  C H A P T E R 2: E A R L Y H E T T A N G I A N T H E  QUEEN  A M M O N I T E S  C H A R L O T T E ISLANDS A N D THEIR  A N DR A D I O L A R I A N S B E A R I N G O NT H E  O F T H ET R I A S S I C - J U R A S S I C B O U N D A R Y  F R O M  DEFINITION 40  2.1 Introduction  40  2.2 Geological Setting  42  2.3 Biostratigraphy  43  2.3.1 Kennecott Point - section 1  44  2.3.2 Kennecott Point - section II  46  2.3.3 Kunga Island - section III  47  2.3.4 T-J boundary radiolarian faunas  48  2.3.4.1 Rhaetian radiolarian faunas and the end-Triassic extinction  49  2.3.4.2 The lower Hettangian radiolarian fauna  50  2.3.4.3 Surviving radiolarian genera  52  2.4 Discussion  53  2.4.1 Strengths and weaknesses of North American T-J boundary sections  54  2.4.1.1 New York Canyon, Ferguson Hill, Nevada  54  2.4.1.2 Kunga Island (Section III), British Columbia  55  2.4.1.3 Kennecott Point (Sections I and II), British Columbia  56  2.4.2 Joint North American Proposal  57  2.5 Conclusions  58  2.5.1 Ammonites  58  2.5.2 Radiolarians  59  2.5.3 Joint North American GSSP proposal  60  2.6 Palaeontology  60  2.6.1 Ammonites  60  2.6.2 Radiolarians (E. S. Carter)  72  2.7 References C H A P T E R 3: T H E T R I A S S I C - J U R A S S I C T R A N S I T I O N Q U E E N C H A R L O T T E ISLANDS  95 A TK U N G A  ISLAND, 106  3.1 Introduction  106  3.2 Location and Access  107  3.3. Paleogeographical Context  107  3.4 Tectonic History and Structural Setting  108  3.5 Lithostratigraphy and Depositional Paleoenvironment  108  3.6 Paleontology  109  111  3.6.1 Biostratigraphy 3.6.1.1 Radiolarian biology and extinction  112  3.6.1.2 Worldwide correlation using radiolarians  114  3.7 Radioisotopic Dating  115  3.8 Magnetostratigraphy and Carbon Isotope Stratigraphy  115  3.9 The Base of the Jurassic System at Kunga Island  116  3.10 References  130  3.11 Update on proposed definition of T-J boundary, September, 2007  137  C H A P T E R 4: M I D D L E A N D L A T E H E T T A N G I A N A M M O N I T E S  ( E A R L Y  JURASSIC)  F R O M T H EQ U E E N C H A R L O T T E I S L A N D S  140  4.1 Introduction  140  4.2 Geological Setting  141  4.2.1 Stratigraphic sections  142  4.3 Systematic Paleontology  143  4.4 North American Middle and Upper Hettangian Ammonite Zones  207  4.5 Correlation with Other Areas  208  4.5.1 North America  208  4.5.1.1 Canada  208  4.5.1.2 Alaska  210  4.5.1.3 Oregon, Nevada and Mexico  210  4.5.2 South Pacific  213  4.5.2.1 South America  213  4.5.2.2 New Zealand  214  4.5.3 Europe  214  vii  4.5.3.1 Western Tethys (circum-Mediterranean)  214  4.5.3.2 Eastern Tethys  215  4.5.3.3 Northwest Europe  216  4.6 Paleobiogeography  217  4.7 Conclusions  218  4.8 References  253  C H A P T E R 5: T H E E A R L Y J U R A S S I C A M M O N I T E  BADOUXIA  F R O M  C O L U M B I A  BRITISH »264  5.1 Introduction  264  5.2 Revisions to the North American Zonation  266  5.2.1 Mineralense Zone  267  5.2.2 Rursicostatum Zone  268  5.2.3 Columbiae Zone  269  5.3 Geological Setting  270  5.3.1 Stratigraphic sections  270  5.3.2 Isolated localities  271  5.4 Systematic Paleontology  271  5.5 Summary and Conclusions  283  5.6 References  313  C H A P T E R 6: T H R E E N E W A M M O N I T E  SUNRISITES  SPECIES O FT H E H E T T A N G I A N F R O M BRITISH C O L U M B I A  ( E A R L Y  JURASSIC) 318  6.1 Introduction  318  6.2 Geological Setting  319  6.2.1 Stratigraphic sections  319  6.2.2 Isolated localities  320  6.3 Systematic Paleontology  320  6.4 Discussion  330  6.5 References  346  C H A P T E R 7: L A T E H E T T A N G I A N  ( E A R L Y JURASSIC) A M M O N I T E S  T A S E K O L A K E S , BRITISH C O L U M B I A  F R O M 354  7.1 Introduction  354  7.2 Geological Setting  356  7.2.1 Stratigraphic sections  356  7.2.2 Isolated localities  357  7.3 Systematic Paleontology  357  7.4 North American Upper Hettangian Ammonite Zones  403  7.5 Correlation with Other Areas  403  7.5.1 North America  403  7.5.1.1 Canada  403  7.5.1.2 Alaska  405  7.5.1.3 Oregon and Nevada  406  7.5.1.4 Mexico  408  7.5.2 South Pacific  408  7.5.2.1 South America  408  7.5.2.2 New Zealand  409  7.5.3 Europe  409  7.5.3.1 Western Tethys (circum-Mediterranean)  409  7.5.3.2 Eastern Tethys  410  7.5.3.3 Northwest Europe  4  7.6 Summary and Conclusions  4  7.7 References  1  12  43^  C H A P T E R 8: T H E I M P A C T P H R A G M O C O N E  1  O FA S Y M M E T R I E S  I N T H EE L E M E N T S O F T H E  O FE A R L Y JURASSIC A M M O N I T E S  446  8.1 Introduction  4  4  6  8.2 Methods  4  4  7  8.2.1 Model 1 - Components within a single phragmocone chamber  448  8.2.1.1 Scanned fragment  448  8.2.1.2 Single septal face  448  8.2.1.3 Single chamber length of siphuncle  450  8.2.1.4 Cameral sheets  451  8.2.1.5 Complete model  452  8.2.2 Model 2 - Entire ammonite animal at 30 mm shell diameter  452  8.2.2.1 Whorl dimensions  452  8.2.2.2 Septal face surface area, thickness and number  453  8.2.2.3 Siphuncle diameter  454  8.2.2.4 Shell thickness  454  8.2.2.5 Cameral sheets  455  8.2.2.6 Body chamber length  ,  455  8.2.2.7 Model assembly  456  8.2.2.8 Component masses and positions  456  8.2.3 Model 3 - Entire ammonite animal at 54 mm maximum shell diameter 8.3 Results and Discussion  457 457  8.4 Summary and Conclusions  460  8.5 References  479  C H A P T E R 9: C O N C L U S I O N S  9.1 Summary of Results 9.2 Significance of Research 9.2.1 Hettangian ammonites in time - vertical distribution  481  •  481 483 483  9.2.1.1 Models of recovery from mass extinction  483  9.2.1.2 Phylogeny methodology  484  9.2.1.3 Hettangian ammonite radiation  485  9.2.2 Hettangian ammonites in space - lateral distribution  493  9.2.3 Paleobiology  493  9.2.3.1 Siphuncle and septal face asymmetries  493  9.2.3.2 Sexual dimorphism  496  9.3 Future Research  496  9.4 References  506  APPENDIX A : C H A P T E R 2 LOCALITIES  515  APPENDIX B: C H A P T E R 3 LOCALITIES  518  APPENDIX C: C H A P T E R 4LOCALITIES  521  APPENDIX D:C H A P T E R 4M E A S U R E M E N T S  524  APPENDIX E: C H A P T E R 5LOCALITIES  533  APPENDIX F:C H A P T E R 5M E A S U R E M E N T S  539  APPENDIX G : C H A P T E R 6 LOCALITIES  549  APPENDIX H :C H A P T E R 7LOCALITIES  551  A P P E N D I X I: C H A P T E R 7 M E A S U R E M E N T S  554  LIST O F T A B L E S Table 2.1. Measurements of Tipperella kennecottensis  83  Table 6.1. Locality information and measurements for Sunrisites from Taseko Lakes  335  Table 8.1. Measurements from the Badouxia columbiae cross-sections  461  Table 8.2. Data for the morphological components of model 1  462  Table 8.3. Data for each morphological component in model 2  463  Table 8.4. Masses and positions of coordinates for model 2  464  Table 8.5. Data for each morphological component in model 3  465  Table 8.6. Masses and positions of coordinates for model 3  466  xii  LIST OF FIGURES F i g u r e 1.1.  Map of Hettangian ammonite occurrences and terranes in British Columbia  F i g u r e 1 . 2 . Zonation for  western Cordillera of North America  20 21  F i g u r e 1.3.  Map showing the location of the Hispanic Corridor  22  Figure 2.1.  Locations of latest Triassic and early Hettangian faunas in the QCI  84  F i g u r e 2.2.  Rhaetian and lower Hettangian zones in the QCI  85  F i g u r e 2.3.  Early Hettangian ammonites in the QCI  86  Figure 2.4. Latest Rhaetian and early Hettangian radiolarians in the QCI  87  F i g u r e 2.5.  Sections showing radiolarian and ammonoid fossil localities in the QCI  88  F i g u r e 2.6.  Range chart of occurrence of Rhaetian - Hettangian genera in the QCI  89  F i g u r e 3.1.  Sections showing radiolarian and ammonoid fossil localities in the QCI  118  F i g u r e 3.2.  Photo of proposed stratotype section on Kunga Island  119  F i g u r e 3.3.  Proposed Kunga Island section showing faunal localities  120  F i g u r e 3.4.  Radiolarians from the proposed section at Kunga Island  121  F i g u r e 3.5.  Latest Rhaetian conodonts from the proposed section at Kunga Island  124  F i g u r e 3.6.  Early Hettangian ammonites from the proposed section at Kunga Island  125  F i g u r e 3.7. 8 Corg 13  record for Rhaetian to Lower Hettangian at Kennecott Point  126  Figure 4.1.  Localities of middle and late Hettangian ammonites in the QCI  219  F i g u r e 4.2.  Zonation for Hettangian and lower Sinemurian  220  F i g u r e 4.3.  Section A, QCI  221  F i g u r e 4.4.  Section B, QCI  222  F i g u r e 4.5.  Section C, QCI  223  F i g u r e 4.6.  Sections D-F, QCI  224  F i g u r e 4.7.  Sections G-I, QCI  m  F i g u r e 4.8.  Correlation of stratigraphic sections from the QCI  226  F i g u r e 4.9.  Ranges of middle and late Hettangian ammonites in the QCI  227  F i g u r e 4.10.  Septal suture and whorl cross-sections for ammonites from the QCI  228  F i g u r e 4.11.  Plots of measurements of Phylloceratina and Psiloceratina  229  F i g u r e 4 . 1 2 . Plots  of measurements of Psiloceratina  230  F i g u r e 4.13.  Plots of measurements of Psiloceratina  231  F i g u r e 4.14.  Plots of measurements of Psiloceratina  232  F i g u r e 4 . 1 5 . Plots  of measurements of Psiloceratina  233  F i g u r e 5.1.  Revised Zonation for Hettangian/Sinemurian boundary in North America  287  F i g u r e 5.2.  Localities bearing Badouxia in Taseko Lakes  288  F i g u r e 5.3.  Section A, Taseko Lakes  289  F i g u r e 5.4.  Section B, Taseko Lakes  290  F i g u r e 5.5.  Section C, Taseko Lakes  291  F i g u r e 5.6.  Section D, Taseko Lakes  292  F i g u r e 5.7.  Section E, Taseko Lakes  293  F i g u r e 5.8.  Section F , Taseko Lakes  294  F i g u r e 5.9.  Section G, Taseko Lakes  295  F i g u r e 5.10.  Whorl shape cross-sections for species of Badouxia  296  F i g u r e 5.11.  Traces of septal suture for species of Badouxia  297  F i g u r e 5.12.  Measurements of Badouxia canadensis  298  F i g u r e 5.13.  Measurements of Badouxia canadensis transient A  299  F i g u r e 5.14.  Measurements of Badouxia canadensistransient B  300  F i g u r e 5.15.  Measurements of Badouxia castlensis sp. nov  301 xiv  F i g u r e 5.16.  Plots of measurements of Badouxia forticostata sp. nov  302  F i g u r e 5.17.  Plots of measurements of Badouxia columbiae  303  F i g u r e 5.18.  Correlation of stratigraphic sections from Taseko Lakes  304  F i g u r e 6.1.  Standard zonation for the Hettangian  336  F i g u r e 6.2.  Localities of yielding Sunrisites in Taseko Lakes  337  F i g u r e 6.3.  Sections A - D , Taseko Lakes  338  F i g u r e 6.4.  Correlation of stratigraphic sections from Taseko Lakes  339  F i g u r e 6.5.  Map of terranes that were allochthonous during the Hettangian  340  F i g u r e 6.6.  Traces of septal suture and whorl shape cross-sections for Sunrisites  341  F i g u r e 7.1.  Localities bearing late Hettangian ammonites in Taseko Lakes  413  F i g u r e 7.2.  Zonation for Hettangian  414  F i g u r e 7.3.  Section A, Taseko Lakes  415  F i g u r e 7.4.  Section B, Taseko Lakes  416  F i g u r e 7.5.  Section C, Taseko Lakes  417  F i g u r e 7.6.  Section  418  F i g u r e 7.7.  Correlation of stratigraphic sections from Taseko Lakes  419  F i g u r e 7.8.  Ranges of late Hettangian ammonites from Taseko Lake  420  F i g u r e 7.9.  Whorl shape cross-sections for late Hettangian ammonites  421  D,  Taseko Lakes  F i g u r e 7.10.  Traces of septal suture for late Hettangian ammonites  422  F i g u r e 7.11.  Measurements of Phylloceratina and Psiloceratina  423  F i g u r e 7.12.  Measurements of Psiloceratina  424  F i g u r e 7.13.  Measurements of Psiloceratina  425  F i g u r e 7.14.  Measurements of Psiloceratina  426  F i g u r e 7.15.  Hettangian ammonites from Taseko Lakes as established in other regions  428  xv  F i g u r e 8.1.  Scanned fragment and suture line of Badouxia columbiae  467  F i g u r e 8.2.  A, Computer model of scanned fragment and septal face  468  F i g u r e 8.3.  A, Thin section of siphuncle and septal face  469  F i g u r e 8.4.  Plot of measurements of model components  470  F i g u r e 8.5.  Model of single septal face including one chamber length of siphuncle  471  F i g u r e 8.6.  Direction notation for models 2 and 3  472  F i g u r e 8.7.  Specimens and fragments of Badouxia columbiae  473  F i g u r e 8.8.  A, Angle convention for model assembly. B, Model assembly  474  F i g u r e 8.9.  Plot of measurements of model components  475  F i g u r e 8.10.  Specimen used for shell thickness measurements  476  F i g u r e 8.11.  Model showing centres of mass for each element of animal  477  F i g u r e 8.12.  Model showing centres of buoyancy and mass for animal  478  F i g u r e 9.1.  Hettangian ammonite genera present in the QCI and Taseko Lakes  499  F i g u r e 9.2.  Model of adaptive radiation following mass extinction  500  F i g u r e 9.3.  Phylogeny of Hettangian ammonites  501  F i g u r e 9.4.  Hettangian ammonite superfamilies in the Jurassic  502  F i g u r e 9.5.  Hettangian ammonite phylogeny based on systematic studies in the US  503  F i g u r e 9.6.  Hettangian ammonite phylogeny based on South American faunas  504  F i g u r e 9.7.  Species with affinities to forms from Canadian terranes  505  xvi  LIST O F P L A T E S Plate 2.1. Early Hettangian ammonites from the QCI  91  Plate 2.2. Hettangian radiolarians from the QCI  94  Plate 3.1. Diagnostic Radiolaria from the QCI  129  Plate 4.1. Middle and late Hettangian ammonites from the QCI  236  Plate 4.2. Middle and late Hettangian ammonites from the QCI  239  Plate 4.3. Middle and late Hettangian ammonites from the QCI  241  Plate 4.4. Middle and late Hettangian ammonites from the QCI  243  Plate 4.5. Middle and late Hettangian ammonites from the QCI  245  Plate 4.6. Middle and late Hettangian ammonites from the QCI  247  Plate 4.7. Middle and late Hettangian ammonites from the QCI  249  Plate 4.8. Middle and late Hettangian ammonites from the QCI  252  Plate 5.1. Badouxia species from Taseko Lakes  306  Plate 5.2. Badouxia species from Taseko Lakes  308  Plate 5.3. Badouxia species from Taseko Lakes  310  Plate 5.4. Badouxia species from Taseko Lakes  312  Plate 6.1. Sunrisites species from Taseko Lakes  343  Plate 6.2. Sunrisites species from Taseko Lakes  345  Plate 7.1. Late Hettangian ammonites from Taseko Lakes  431  Plate 7.2. Late Hettangian ammonites from Taseko Lakes  433  Plate 7.3. Late Hettangian ammonites from Taseko Lakes  435  Plate 7.4. Late Hettangian ammonites from Taseko Lakes  437  xvii  ACKNOWLEDGEMENTS I express my special appreciation to my advisor, Paul Smith, for providing the laboratory facilities, generous funding, ample advice and endless patience, enthusiasm and support throughout my project. Also a very special thank you to Howard Tipper who passed away before the completion of my thesis. His knowledge of geology and biostratigraphy in British Columbia was extremely helpful and I am very grateful for his interest and encouragement at the beginning of my project. My appreciation goes to Jozsef Palfy for his help in the Queen Charlotte Islands, his input on several manuscripts from my thesis and for helpful discussions of other areas of science including geochronometry and geochemistry. Thanks to Beth Carter for many discussions on Triassic-Jurassic boundary issues. Kurt Grimm is thanked for his advice and suggestions as a member of my supervisory committee. Thanks also to Stuart Sutherland for his input as a member of my supervisory committee. His endless good humor and support have bolstered me in difficult times. I would like to thank my colleagues from the laboratory at the University of British Columbia. Jin Zhang, Melissa Grey, Farshad Shirmohammad, Emily Hopkin and Andrew Caruthers have been the source of many fruitful discussions and much support over the years. I am indebted to the Geological Survey of Canada for the use of their collections, laboratory space and fossil preparation equipment. I wish to thank other faculty members, technicians and graduate students at the University of British Columbia for their input with computer problems and other analyses that I required. Allison Perrigo is thanked for her photography of some of the middle Hettangian ammonite faunas from the Queen Charlotte Islands. Financial support was provided by a Graduate Fellowship from NSERC and a University Graduate Fellowship from the University of British Columbia. Thanks to Hilvi Garrow for helpful discussions around the construction of the ammonite computer models. Thanks to the referees who reviewed various chapters of the thesis as submitted manuscripts including K. Page, A. von Hillebrandt, J. Cope, J. Callomon, P. Niege, J. Guex, R. Hori and J. Palfy. I would like to thank my parents, husband and siblings for their help in thefieldand general encouragement and support.  DEDICATION Torayhusband Oliver, who endured several blizzards, giant horse flies, wading up waist deep rivers and frightening off grizzly bears while helping me on variousfieldexcursions. I will always appreciate his unwavering support throughout my project.  xix  CO-AUTHORSHIP STATEMENT This thesis results from the work and leadership of Louise Longridge. Louise is principally responsible for performing the research and data analyses including the majority of the ammonite systematics. Apart from the exceptions discussed below, Louise is responsible for virtually all manuscript content. This research produced papers co-authored with 7 other scientists. The extent and scope of this collaboration was as follows: 1. The work was carried out under the supervision of Paul Smith as part of his research program dealing with Jurassic extinction, radiation and biogeography, funded by NSERC. Smith initiated the project and provided scientific guidance in the field and in the laboratory, as well as editorial input. 2. The late Howard Tipper of the Geological Survey of Canada provided fossil collections, stratigraphic information and scientific guidance regarding ammonite biostratigraphy. 3. Elizabeth Carter is completely responsible for all aspects of the radiolarian studies which form part of Chapters 2 and 3 and had editorial input in other portions of these chapters. 4. Jozsef Palfy performed the original systematic work on the latest Hettangian faunas from the Queen Charlotte Islands. This data was updated by Louise and is included in Chapter 4. He also completed the initial systematics on one of the Sunrisites species included in Chapter 6 and provided editorial input on Chapters 4 and 6. 5. James Haggart of the Geological Survey of Canada contributed content and had editorial input on Chapter 3. 6. Bill Rawlings and Voytek Klaptocz worked in close consultation with Louise to construct the computer ammonite models and perform the analyses in Chapter 8.  xx  1 INTRODUCTION 1.1 Introductory Statement This thesis research addresses 4 broad questions: 1. How does the Canadian succession of Hettangian ammonites contribute to our understanding of the recovery of this group directly following their near demise during the Triassic-Jurassic extinction? The recovery of the ammonites in the Hettangian Stage represents the beginning of one of the most spectacular adaptive radiations in the fossil record. This study provides insight into how this major group recovered and flowered to become a dominant force throughout the following hundred and thirty-five million years. Hettangian ammonites occur in several of the tectonostratigraphic terranes that make up western Canada (Fig. 1.1). The two most important areas are the Queen Charlotte Islands (QCI), which contain a virtually complete Hettangian succession, and Taseko Lakes, which contains a diverse and well preserved late Hettangian fauna. 2. How does the Canadian succession potentially contribute to a) the definition of the Triassic-Jurassic boundary, b) recognition of the Triassic-Jurassic transition elsewhere in the world, and c) time scale calibration? The mass extinction at the end of the Triassic is one of the "big five" mass extinctions in the Phanerozoic. Despite its importance, this extinction is relatively poorly understood due in part to the small number of continuous sections spanning the Triassic-Jurassic boundary (T-J boundary) as a result of eustatically low sea level at the time. This problem has also led to difficulties in choosing a global stratotype section and point (GSSP) to define the boundary. Ammonites are usually chosen as index fossils in the Jurassic, but the low diversity and rare occurrence of earliest Jurassic ammonites make 1  them imperfect for use as the primary standard. The QCI have the potential to assist with boundary definition primarily because two sections from the area contain a diverse and complete radiolarian record which shows a spectacular turnover across the T-J boundary. Although ammonites were widespread in Early Jurassic seas, significant endemism and provincialism existed within the faunas. This led to Taylor et al. (2001) establishing a regional zonation for the Hettangian and Sinemurian of western North America (Fig. 1.2). However, this zonation is incomplete and inaccurate with respect to the fauna from the Canadian terranes. The unusual biogeographic setting of the terranes means the Canadian fauna maximizes correlation potential with other regions because it contains east-Pacific, Tethyan and rare Boreal forms. These correlations are of added importance, because fossiliferous strata are often interbedded with ash beds in North America, permitting the calibration of biochronologic and geochronologic time scales. 3. What was the relationship between paleobiogeography and plate tectonics during and subsequent to the Hettangian? Fossils are essential to understanding the tectonically complex history of western North America. Ammonites from British Columbia (BC) provide useful data for testing previous hypotheses of terrane movements and the possible existence during the Hettangian of the Hispanic Corridor, a trans continental seaway linking the Panthalassa and Tethyan oceans (Smith 1983; Fig. 1.3). 4. What insights can be gained concerning the paleobiology of the ammonites during this critical phase of their evolution? Sexual dimorphism is relatively poorly documented in Hettangian forms yet is common in several genera from the BC terranes. Furthermore, it is common for Hettangian ammonites to have asymmetries in the elements of their phragmocone. This  2  raises the question as to whether a counterbalance mechanism was in effect, allowing the animal to remain upright in the water column.  1.2 Previous Work 1.2.1 Systematics  Work on Hettangian ammonite systematics has been underway in numerous parts of the world for many years. Previous studies have revealed that Hettangian ammonites are not cosmopolitan but are restricted to two faunal provinces. The Boreal Province occupies the northern part of the Northern Hemisphere, while the Tethyan Province occupies the rest of the world (sensu Westermann 2000). The two faunal realms were separated by a gradational boundary which fluctuated in position through time (Smith and Tipper 1986; Smith 1999; Cecca and Westermann 2003). 1.2.1.1 Faunas from the allochthonous terranes of BC (Fig. 1.1). Although no comprehensive taxonomic studies exist, preliminary studies of some Hettangian ammonites from the allochthonous terranes of BC have been published. Frebold (1951, 1967) completed the first systematic studies of the upper Hettangian ammonite succession of the Taseko Lakes area. These works documented important genera such as Paracaloceras  and Eolytoceras and identified the first Psiloceras canadense (now  Badouxia  canadensis). A taxonomic study of the Schlothemiid fauna was completed by Smith and Tipper (2000). In the Queen Charlotte Islands (QCI), preliminary lists of the main taxa were given by Tipper and Carter (1990), Tipper and Guex (1994), Tipper et al. (1994) and Carter et al. (1998). Palfy (1991) studied the latest Hettangian faunas as part of his unpublished Master's thesis but only a biostratigraphic summary is in print (Palfy et al. 1994).  3  Frebold and Tipper (1970) and Frebold and Poulton (1977) listed taxa from Morehead Creek in the Quesnel Lake area under the names Psiloceras canadense Frebold and Paracaloceras sp. Frebold and Tipper (1970) and Frebold and Poulton (1977) listed Schlotheimia cf. S. montana (Wahner) from the Mount Waddington Area. Frebold and Tipper (1970) listed the occurrence of Eolytoceras cf. E. tasekoi Frebold from the Babine Lake area, although this claim was not supported in Frebold and Poulton (1977). A fossiliferous section occurs in Holberg Inlet on northern Vancouver Island; however, fossils are rare and specimens poorly preserved. Identification is often difficult even at the generic level, although possible Discamphiceras,  Saxoceras, Franziceras and Pleuroacanthites  may be present in the middle Hettangian while Badouxia and Schlotheimia may occur in upper Hettangian strata. Three specimens that may be of Hettangian age were described from the Salmo area of southeast BC under the names ammonite gen. et sp. indet. 1, ammonite gen. et sp. indet. 2 and Gyrophioceras (?) sp. indet (Frebold and Little 1962). Poor preservation makes confident identification impossible even at the generic level (Frebold and Little 1962; Frebold and Tipper 1970; Taylor etal. 1984). In the Iskut River map area, Frebold and Tipper (1970) listed Psiloceras canadense from the Unuk River. Nadaraju (1993) included descriptions of taxa under the names Badouxia cf. canadensis (Frebold), Alsatites (?) cf.proaries Paracaloceras  (?) (Neumayr), Canavarites sp. indet.,  cf. rursicostatum Frebold, P. cf. multicostatum Frebold, P. cf. coregonense?  (Sowerby) and P. sp. indet from several different localities as part of her unpublished Master's thesis. Jakobs and Palfy (1994) listed taxa from the area under the names Metophioceras cf. rursicostatum, Paracaloceras  sp., P. cf. cordieri, Eolytoceras sp. Badouxia  canadensis,  Sulciferites cf. marmoreus and S. cf. trapezoidalis.  4  Frebold (1958, 19646) described a collection from the Telegraph Creek area under the name Psiloceras canadense Frebold.  1.2.1.2 Faunas from other areas of North America Imlay (1981) documented Hettangian faunas across Alaska, whereas Palfy et al. (1999) published a more local study of the ammonites from Puale Bay in southern Alaska. The Yukon has yielded isolated specimens of generally poorly preserved material that is probably of Hettangian age (Lees 1934; Frebold 1964a; Frebold and Tipper 1970; Frebold and Poulton 1977; Poulton 1991), although the majority of the material is too poor for species level identification. A fauna of early to late Hettangian age was described from the BC craton in the Williston Lake area (Fig. 1.1; Tozer 1982; Hall and Pitaru 2004). A single specimen of Discamphiceras  was found in Alberta (Hall et al. 2000).  In Nevada and Oregon, several areas yield well preserved sequences of Hettangian ammonites (Guex and Taylor 1976; Guex 1980, 1982, 1995; Taylor 1988, 1990, 1998, 2000; Guex et al. 1998, 2002; Taylor and Guex 2002). Gonzalez-Leon et al. (1996, 2000) and Taylor et al. (2001) documented late Hettangian ammonites from Sonora in northern Mexico. 1.2.1.3 Faunas from other areas of the world In South America, Hettangian ammonites are present in Peru, Chile and Argentina (e.g., Tilmann 1917; Cecioni and Westermann 1968; Geyer 1979; Hillebrandt 1981a, 1988, 1990, 1994, 2000a, b; Corvalan 1982; Prinz 1985; Quinzio Sinn 1987; Riccardi etal. 1988, 1991). Many detailed taxonomic studies have been published on the Boreal faunas of northwest Europe (e.g., Sowerby 1812-1846; Wright 1879; Reynes 1879; Spath 1922, 1924; Elmi and Mouterde 1965; Bloos 1979, 1981, 1983, 1988, 1994, 1999; Lange 1941, 1951; Donovan 1952; Schlegelmilch 1976; Hodges 1986; Guerin-Franiatte 1990; Kment 2000; Bloos and Page 2000).  5  Extensive taxonomic studies have also been completed on the Tethyan successions of the Mediterranean area (e.g., Gumbel 1861; Neumayr 1879; Wahner 1882-1898; Canavari 1888; Lange 1952; Blind 1963; Rakus 1975, 1993a, b, 1999; Rakus and Lobitzer 1993; Bloos 1979, 1983, 1988, 1994; Braga etal. 1984; Venturi 1985; Donovan 1958; Dommergues etal. 1995; Bohm et al. 1999; Palfy and Dosztaly 2000; Kment 2000; Bertinelli et al. 2004). Hettangian faunas also occur in several other areas of the world including New Caledonia, Timor and New Zealand (Spath 1923; Krumbeck 1923; Avias 1953; Stevens 2004), China (Yin et al. 1999, 2007; Yin and Enay 2000), and the Russian Federation (e.g., Repin 1977, 1984; Dagys 1996).  1.2.2 North American Zonation Northwest European ammonite successions (e.g., Dean et al. 1961; Mouterde and Corna 1997; Page 2003) are considered the primary standard for Early Jurassic biochronology (Callomon 1984). In 1961, Dean et al. erected the Planorbis, Liasicus and Angulata zones for the region (Fig. 1.2). Correlation of these three classic zones with North America has been difficult because key European index genera and species are missing. Early Jurassic ammonites in North America have more in common with Tethyan successions from Mediterranean countries than the Boreal successions found in northwest Europe. In addition, a high number of endemic forms in the eastern Pacific further complicates this issue. For these reasons, a separate zonation for the Hettangian and Sinemurian of the Western Cordillera of North America was established by Taylor et al. (2001) (Fig. 1.2). Unfortunately, this zonation is inaccurate and incomplete with respect to the Canadian forms.  1.2.3 Correlations between Canadian successions and other areas Similar to the situation with northwest Europe, endemism and provincialism make correlations difficult between North American successions and those of South America, New Zealand, and western and eastern Tethys. Correlations with other areas are of particular 6  significance because interbedded volcanic and fossiliferous marine rocks in Canada and Alaska permit the calibration of geochronological and biochronological time scales (Palfy et al. 1999, 2000a, b). 1.2.4 Triassic-Jurassic boundary 1.2.4.1 Date of T-J boundary Until recently, a date of 199.6 /D.3 was used to constrain the T-J boundary (Palfy et al. +  2000a, b). This date, obtained using multi-grain zircon analysis from an ash bed on Kunga Island, is now considered too young, and further work is underway to refine its accuracy (Palfy and Mundil 2006). A date of 201.27±0.27 Ma was obtained for the T-J boundary from a Central Atlantic Magmatic Province (CAMP) flow in Nova Scotia, Canada using single-crystal zircon analysis (Schoene et al. 2006). 1.2.4.2 End-Triassic mass extinction The Hettangian is the first stage in the Jurassic. Thus, it falls directly after the mass extinction which defines the T-J boundary. This extinction is commonly cited as one of the five most severe mass extinctions in the Phanerozoic. Approximately 22% of marine families, 53% of genera and 80% of species became extinct (Sepkoski 1996; Palfy 2003), and there was also a significant extinction in the terrestrial realm at this time (e.g. Visscher and Brugman 1981; Fowell et al. 1994; Hallam and Wignall 1997). Despite significant progress (Hesselbo et al. 2007), the end-Triassic event is one of the most poorly understood and least researched in the Phanerozoic (Twitchett 2006). A large volume of literature exists on the groups affected by high extinction rates in the latest Triassic, and only a brief summary is provided here. Brachiopods, bivalves, reef organisms, ammonoids, nanofossils, palynomorphs, ostracodes, foraminifera, radiolarians, conodonts, plants and vertebrates are all affected (e.g., Hallam 1996, 2002; Hallam and Wignall 1997; Palfy 2003; Tomasovych and Siblik 2007; Hillebrandt et al. in press; and references therein). Some 7  taxa show a marked turnover at the boundary. The radiolarians demonstrate a distinct change where rich and diverse Triassic forms were mostly replaced by a low diversity basal Hettangian fauna composed of very simple forms (Carter 1994, 1998; Carter et al. 1998; Carter and Hori 2005; Longridge et al. 2007). Although not evident in all cases, a clear extinction is also recognized in palynomorph assemblages (e.g., Visscher and Brugman 1981; Fowell et al. 1994; Hallam and Wignall 1997; Gomez et al. 2007; Kuerschner et al. 2007; Whiteside et al. 2007). In addition, extinction rates were probably high in bivalves, brachiopods, reef biota and possibly plants at the boundary (Laws 1982; McRoberts and Newton 1995; Hallam 2002; Palfy 2003; McRoberts 2004; and references therein). Other groups exhibit more gradual extinction in the Late Triassic including ammonites, conodonts and land vertebrate taxa (Benton 1991; Taylor et al. 2000; Hallam 2002; Palfy 2003; Tanner et al. 2004; and references therein). Kiessling et al. (2007) analyzed the abundance and diversity patterns of marine benthic organisms such as sponges, corals, bivalves, gastropods and brachiopods across the T-J boundary using data from the Paleobiology Database. Despite the gradual extinction pattern of some groups, they found these groups have elevated extinction rates and reduced origination rates in the Rhaetian and suggest that the end-Triassic does qualify as a true mass extinction when considered against Middle Triassic or Middle Jurassic background levels. Environmental changes recognized over the T-J boundary interval include global warming, a widespread regression/transgression couplet, oceanic anoxia and widespread aridification (e.g., Tucker and Benton 1982; Hallam and Wignall 1997, 2000; McElwain et al. 1999; Hallam 1997, 2001; Hesselbo et al. 2004; Tanner et al. 2004; and references therein). There was also a significant perturbation to the global carbon cycle across the boundary interval. Negative isotope anomalies have been identified in marine strata in BC, Nevada, England, Austria, Italy, China and Hungary (McRoberts et al. 1997; Palfy et al. 2001; Ward et al. 2001, 2004, 2007; Hesselbo et al. 2002; Guex et al. 2003, 2004, 2007; Galli et al. 2005; Hillebrandt 2006; Yin et 8  al. 2006; Williford et al. 2007; Kuerschner et al. 2007; Lucas et al. 2007) and in terrestrial strata in Greenland and China (Hesselbo et al. 2002, 2006). Tanner et al. (2004) suggest that the biotic turnover in the latest Triassic may be caused by a combination of gradualistic and catastrophic mechanisms of environmental change such as long term ecological degradation from sea-level fluctuation or climate change in addition to more abrupt events like flood basalt volcanism or bolide impact. Flood basalt volcanism of the CAMP is currently the most favored trigger for the environmental perturbations and biotic crisis at the end-Triassic (e.g., Marzoli et al. 1999, 2004; Palfy et al. 2002; Hesselbo-er al. 2002, 2007; Palfy 2003; Knight et al. 2004; Golonka 2007). The flood basalt, brought about by the beginning of the rifting of Pangea in the latest Triassic, extends over 7 x 10 km (Marzoli et al. 1999). This event may have been responsible for 6  2  environmental change via volcanic outgassing of C O 2 or S O 2 or possibly by indirectly triggering the release of methane hydrates from the sea floor (Palfy et al. 2001; Hesselbo et al. 2002). Although recent work by Verati et al. (2007) reveals intrusive magmatism commenced about 201 Ma ago, peak activity is restricted to between 199 and 197.5 Ma, and currently the temporal feasibility of CAMP as the main trigger for end-Triassic events is controversial. For example, Marzoli et al. (2004) and Knight et al. (2004) believe the beginning of CAMP pre-dates the Triassic-Jurassic palynological turnover event in the terrestrial realm, whereas Whiteside et al. (2007) suggest it post-dates the turnover. Bolide impact has also been suggested as a possible cause for the end-Triassic event based principally on a modest iridium anomaly and a fern spore spike in eastern Canada (Olsen et al. 1987, 2002 a, b; Fowell and Olsen 1993; Fowell et al. 1994). Shocked quartz was reported from T-J boundary sections in Austria and Italy (Badjukov et al. 1987; Bice et al. 1992), but these reports have been discounted (Hallam and Wignall 1997). At this stage, an impact cannot be excluded although no impact crater has been found that conclusively coincides with the end-  Triassic event (Palfy 2004; Hesselbo et al. 2007). Furthermore, a low rate of origination in the Rhaetian as well as the dependency of extinction intensity on the habitat of taxa make an impact scenario less likely (Kiessling et al. 2007). As discussed by Hesselbo et al. (2007), one of the biggest problems in resolving the causes and events surrounding the end-Triassic mass extinction is lack of sufficiently high temporal resolution. Many of the published Ar/ Ar and U-Pb dates may be too young due to an 40  39  uncertainty in the decay constant of K and slight Pb loss in multi-grain U-Pb analyses. Recent 4 0  advances mean these problems may be overcome and will lead to greater confidence in comparing the timing of different events in the future. 1.2.4.3 Triassic-Jurassic boundary definition Attempts to select a global stratotype section and point (GSSP) to define the basal Jurassic have been ongoing for over 20 years. Due to low sea level across the T-J boundary interval there are relatively few continuous sections worldwide (Hallam and Wignall 1997; Hesselbo et al. 2007). This issue is further complicated by the low diversity and low abundance of faunas, especially in the basal Jurassic. Six GSSP candidates from five areas are currently under consideration by the Jurassic Subcommission, and a report is in preparation which will provide details of each proposal. A very brief outline of each candidate is included here. 1) St. Audrie's Bay, England (e.g. Warrington et al. 1994; Hesselbo et al. 2004; and references therein) The boundary level would probably be at the lowest occurrence of Psiloceras  planorbis.  This level has historic precedence because it has been used to define the base of the Hettangian Stage in the United Kingdom for many years (e.g. Cope et al. 1980). The section provides a carbon isotope curve that shows a marked negative anomaly across the boundary interval and also provides magnetostratigraphy (Hesselbo et al. 2002; Hounslow et al. 2004). Unfortunately, a stratigraphic gap of about 10 m exists between the highest 10  Triassic bivalve and lowest P.planorbis  (e.g., Warrington et al. 1994; Hounslow et al.  2004), although a Triassic conodont closes this gap to about 6 m. The section also includes a major facies change over the T-J boundary interval and lacks Triassic type ammonoids. This proposal would place the T-J boundary above the incoming of the first Psiloceras in St. Audrie's Bay (e.g. Bloos and Page 2000) and other areas (e.g., Lucas et al. in press; Hillebrandt et al. in press; and references therein). 2) Larne section, Waterloo Bay, Northern Ireland (Simms and Jeram 2006, in press) The boundary level would be at the lowest occurrence of Psiloceras planorbis.  The Larne  section can be readily correlated with the St. Audrie's Bay section. Although the latter section is much better studied, the Larne section is an expanded section and has better ammonite preservation, diversity and abundance. It also has the potential for a useful carbon isotope curve and provides cyclostratigraphy and sequence stratigraphy. However, no Triassic type ammonites are present, and the Triassic fossil record is generally poor. At present, it lacks detailed data on the bivalve fauna and the presence of useful magnetostratigraphy. 3) Karwendel syncline, Austria (Hillebrandt et al. 2006, in press) The boundary would be placed at the incoming of the first psiloceratid ammonite, Psiloceras cf. spelae. This section contains well preserved latest Triassic and earliest Hettangian type ammonites, other macrofossils and diverse microfossils. A palynological marker species permits correlation with coeval terrestrial sections. A carbon isotope curve is available showing a negative anomaly below the incoming of Jurassic type ammonites (Hillebrandt in press; Ruhl et al. in prep). The section may be remagnetized. 4) Ferguson Hill, Nevada - negative carbon isotope excursion (McRoberts et al. in press) The boundary would be placed at the first negative peak in the carbon isotope excursion that spans the T-J boundary interval (Guex et al. 2003, 2004, 2007; Ward et al. 2007; 11  McRoberts et al. in press). This proposal has the advantage of widespread correlation between marine and terrestrial sections which also contain carbon curves with a marked negative excursion across the T-J boundary (e.g. Hesselbo et al. 2002, 2006; McRoberts 2004; Guex et al. 2004; Galli et al. 2005). The excursion would have to be correlated with a biostratigraphic datum (Remane et al. 1996; McRoberts 2004; Lucas et al. 2005). Both bivalves and ammonites are present in the section and could be used although they occur 1.6 and 2.5 m above the negative peak. 5) Ferguson Hill, Nevada - lowest occurrence of Psiloceras tilmanni Lange (Taylor et al. 1983; Guex et al. 1997. 2006; Lucas et al. 2005, 2007. in press; and references therein) The boundary would be placed at the incoming of ammonites of the Psiloceras  tilmanni  group (first occurrence of P. spelae). This section has moderately abundant Triassic and Jurassic type ammonites across the T-J boundary interval although a stratigraphic gap of about 7 m exists between the highest Triassic and lowest Jurassic ammonite. Several microfossil groups including conodonts and radiolarians have been collected from the T-J boundary interval (Orchard et al. 2007). As discussed above in proposal 4, this section also provides a useful carbon isotope curve. In this proposal, the negative excursion would fall in the latest Triassic. 6) Kunga Island, QCI (Carter and Tipper 1999; Longridge et al. 2007, in press; and references therein) The boundary would be placed at the dramatic turnover of radiolarian fauna that constrains the boundary to 0.8 m (Carter 1994, 1998; Carter et al. 1998; Longridge et al. 2007). This section has provided a date to constrain the T-J boundary (Palfy et al. 2000a, b) and can be correlated with a useful carbon isotope curve from a section at Kennecott Point (Fig. 1.1) that shows a negative peak just below the radiolarian turnover. The Kunga Island section contains Jurassic ammonites from the Minutum to Polymorphum zones  (Fig. 1.2), which permit correlation with other areas. However, the section is difficult to access, lacks Triassic ammonites and lacks definitive ammonites from the Spelae Zone (Fig. 1.2). Thus it may be more suitable as a parastratotype section to assist with characterizing the boundary rather than as the holostratotype which defines it. 1.2.5 Paleobiogeography  1.2.5.1Hispanic Corridor The western Tethys was linked to the eastern Pacific Ocean during Jurassic time via the Hispanic Corridor (Smith 1983; Fig. 1.3). The precise time of the initial opening of this seaway is still uncertain and has been the subject of much debate. Although sedimentological or geophysical evidence supporting this connection suggests an age no older than the late Middle Jurassic (Smith and Tipper 1986; Smith et al. 1990; Aberhan 2001; Rueda-Gaxiola 2006), paleontological data suggest a significantly earlier marine connection across rifting continental crust (e.g., Damborenea and Mancefiido 1979; Hillebrandt 19816, 2002; Smith and Tipper 1986; Sandy and Stanley 1993; Damborenea 2000; Aberhan 2001; Smith et al. 2001; Moyne et al. 2004). 1.2.5.2 Terranes Western North America is a tectonically complex area that is made up of many 'suspect terranes' (e.g., Coney et al. 1980; Monger and Nokleberg 1996). The terranes were transported by subduction of the Pacific Plate beneath the North American Plate and then accreted to the stable craton of North America. The term suspect refers to the terranes uncertain paleogeographic affinities. By the end of the Early Jurassic, the terranes were approximately in their current latitudinal position with respect to the craton (Aberhan 1998; Smith 2006). However, faunal evidence suggests many of the terranes underwent significant northward displacement during the Early Jurassic (Taylor et al. 1984; Smith and Tipper 1986; Aberhan and Muster 1997; Aberhan 1998, 1999; Smith etal. 2001; Smith 2006). Faunal evidence also 13  suggests significant longitudinal displacement since Permian time (Belasky 1994), although by the Early Jurassic the terranes were positioned within the eastern Pacific (Taylor et al. 1984; Aberhan 1998; Smith 2006). Hettangian ammonites are found in four different terranes that make up BC (Fig. 1.1). Holberg Inlet and the QCI are part of Wrangellia; Iskut River, Telegraph Creek and Babine Lake are part of Stikinia; Quesnel Lake and Salmo are part of Quesnellia; and Mt. Waddington and Taseko Lakes are part of the Cadwallader terrane (Fig. 1.1). 1.2.6 Paleobiology  1.2.6.1 Sexual dimorphism Sexual dimorphism is recognized within a species by the presence of two different adult morphologies. Expected differences between the two groups include characteristics like bimodal size distribution, variocostation (when ribbing style on the outer whorls differs markedly from that on the inner), differences in the number of whorls and the presence of lappets or long rostra on the peristome (e.g. Callomon 1963). The larger form is the 'macroconch' and is believed to have been the female. The smaller form is the 'microconch' and is believed to have been the male (Callomon 1955, 1963; Davis et al. 1996). In order to be identified as dimorphs, the two groups must have the same stratigraphic range, there must be no mature intermediate forms, they should have identical early ontogenies, the ratio between dimorphs should be consistent across the stratigraphic and geographic range of the taxon and they should have identical phylogenies (Makowski 1963; Callomon 1963; Davis et al. 1996 and references therein). In 1963, Callomon stated that the lowest point in the Jurassic where dimorphism became clearly recognizable was the late Toarcian, although it was probably present before that. Although dimorphism remains relatively poorly documented in the Hettangian, more recent work has led to the identification of dimorphism in numerous Hettangian groups (e.g., Rakiis 1975, 1993a; Donovans al. 1981; Guex 1981, 1995). 14  1.2.6.2 Hydrostatic implications of asymmetries of the ammonite phragmocone In most ammonites the siphuncle runs ventrally down the centre of the shell; however, in many Hettangian taxa, the siphuncle is displaced to one side (e.g., Guex 1995; Hillebrandt 2000a). This character is accompanied by an asymmetric septal suture line where the ventral lobe is shifted to one side of the whorl. The elements of the suture line are expanded on the nonsiphuncle side, suggesting that septae may have had a greater surface area on this side. In contrast, on the siphuncle side, the elements of the suture line are simplified and compressed suggesting that septae may have had a reduced surface area. It is possible that the displacement of the tissue and blood filled siphuncle may have affected the position of the shell's centre of mass. If the septal faces were expanded on the non-siphuncle side, this may have offset the mass of the displaced siphuncle and acted as a counterbalance mechanism that allowed the ammonite to remain upright in the water column. This hypothesis is tested in this thesis. 1.3 Summary of Objectives 1) To provide a complete and detailed taxonomic analysis of the Hettangian ammonites from the two primary areas on the terranes of BC; the QCI and Taseko Lakes. 2) To provide a complete and detailed taxonomic analysis of the Badouxia fauna from Taseko Lakes including the earliest Sinemurian forms. 3) To use measured sections from the QCI and Taseko Lakes to delimit the stratigraphic ranges of each taxa. 4) To provide detailed information about the T-J boundary sections in the QCI.  5) To propose the Kunga Island section as a type section for the basal Jurassic.  15  6) To update the Hettangian and lowest Sinemurian portion of the North American Zonation of Taylor et al. (2001) based on the ammonite faunas from the QCI and Taseko Lakes. 7) To improve correlations between the.terranes of BC and other areas of North America, South America, New Zealand, western and eastern Tethys, and northwest Europe during the Hettangian. 8) To consider whether the Hispanic Corridor was an effective influence on paleobiogeography during the Hettangian. 9) To use paleobiogeography to test the postulated positions of the Peninsular, Wrangellia and Cadwallader terranes during Hettangian time. 10) To more thoroughly document and improve understanding of sexual dimorphism in Hettangian ammonites. 11) To examine the hydrostatic implications of the asymmetric position of the siphuncle in B. columbiae.  1.4 Methods 1.4.1 L i t e r a t u r e r e v i e w  An extensive literature review was carried out to summarize the state of affairs in Hettangian and earliest Sinemurian ammonite systematics, Early Jurassic biogeography in the eastern Pacific and relevant aspects of ammonite paleobiology. 1.4.2 F i e l d w o r k  Extensive fossil collections were made in Taseko Lakes during the summers of 2001,2002 and 2003. Previous collections made by officers of the Geological Survey of Canada (GSC) 16  provided a large amount of supplementary material. In the field, sections were measured using the Brunton compass and tape technique. True stratigraphic thickness was calculated using Microsoft Excel. Small Hettangian collections were made in the QCI during the summer of 2005; however, the majority of the fossil material was collected by officers of the GSC (primarily H. W. Tipper) as well as by previous graduate students of the University of British Columbia (UBC) (primarily G. Jakobs and J. Palfy). Stratigraphic sections were measured by H. W. Tipper and E. S. Carter using the pogo stick method. Preliminary collections from Holberg Inlet made by J. Palfy were supplemented in the summer of 2004. Although identifying middle and upper Hettangian strata was possible, poor exposure made measuring a section impractical. Collections from the Quesnel Lake area, made by officers of the GSC, are currently misplaced. An attempt was made tofindthe locality in the summer of 2004; however, instructions on its location were incomplete and despite an extended search, it could not be found. 1.4.3 C o l l e c t i o n s f r o m o t h e r a r e a s i n t h e B C t e r r a n e s  Other areas in the BC terranes with minor occurrences of Hettangian ammonites were not revisited, although in some cases this information was included in the body of the thesis. The data of Jakobs and Palfy (1994) from Iskut River and the data of Frebold (1964/3) from Telegraph Creek were included in the relevant synonymy lists and discussions in the body of the thesis. Due to journal restrictions on unpublished work, the data of Nadaraju (1993) from Iskut River was not considered. Due to the poor preservation, the Holberg Inlet faunas were not considered in the body of the thesis. Similarly, due to poor preservation and uncertain age allocation, the collections from the Salmo area were not included. The presence of Hettangian  17  taxa from Quesnel River could not be verified and it was not included. The single specimen collections from Babine Lake and Mount Waddington were not considered. 1.4.4 Laboratory work Fossils were prepared for systematic study using rock saws, pneumatic drills and sandblasters. Where necessary, casts and molds were constructed. To facilitate data entry, the qualitative and quantitative measurements conform to the AMMON database developed at UBC (Smith 1986; Liang and Smith 1997). Taxonomic open nomenclature follows Bengston (1988). 1.5 Presentation The body of this dissertation is made up of seven chapters (Chapters 2-8). The chapters are roughly ordered to follow geological time beginning with the T-J boundary and earliest Hettangian faunas and finishing with studies of late Hettangian and earliest Sinemurian faunas. Each chapter is a self-contained research article; chapters 2 and 5 are published, chapters 3, 6 and 7 are accepted for publication and chapters 4 and 8 are to be submitted for publication in various science journals and reports. This approach rather than a standard thesis format is useful to rapidly communicate results to the scientific community but it does result in some repetition. Although an effort was made to minimize redundancy, it was often unavoidable in the introduction to each paper and, to a lesser extent, in the discussion sections. Chapter 2 is a study of the lower Hettangian sections in the QCI and includes the proposal of a section from Kunga Island as a parastratotype to assist with characterization and recognition of the T-J boundary. A detailed taxonomic study of the early Hettangian ammonite faunas from the QCI is included here. Chapter 3 is a comprehensive study of the T-J boundary section at Kunga Island. The section is proposed as a potential GSSP for the basal Hettangian if radiolarians are designated as the primary marker fossil or as a parastratotype section if radiolarians are not chosen. 18  Chapter 4 consists of a comprehensive taxonomic study of the middle and late Hettangian faunas from the QCI. Based on these data, changes are made to the middle and upper Hettangian portion of the North American Zonation of Taylor et al. (2001). The data is also used to suggest correlations with other areas of North America, South America, New Zealand, western and eastern Tethys, and northwest Europe as well as to constrain the position of the Wrangellia terrane during the Hettangian. Chapter 5 includes a taxonomic study of the Badouxia fauna from the late Hettangian and early Sinemurian in Taseko Lakes. Based on this data, changes are made to the upper Hettangian and lower Sinemurian portion of the North American Zonation of Taylor et al. (2001). Sexual dimorphism is noted in several species of Badouxia and discussed. Chapter 6 consists of a taxonomic study of the late Hettangian Sunrisites fauna from Taseko Lakes. Paleobiogeographic issues are considered including a possible opening of the Hispanic Corridor as well as implications for the position of several terranes in the Hettangian. Sexual dimorphism is noted and discussed within the faunas. Chapter 7 is a comprehensive taxonomic study of the late Hettangian fauna from Taseko Lakes [excluding the Badouxia and Sunrisites faunas and also the Angulaticeras  fauna which  was studied by Smith and Tipper (2000)]. Based on the data, changes are made to the upper Hettangian portion of the North American Zonation of Taylor et al. (2001) and correlations are suggested with other areas of North America, South America, New Zealand, western and eastern Tethys, and northwest Europe during the Hettangian. Chapter 8 is a computer based study of the hydrostatic effects of asymmetries within the phragmocone of the earliest Sinemurian ammonite, B. columbiae.  19  Figure 1.1. Map showing approximate locations of Hettangian ammonite occurrences in British Columbia (excluding Vancouver which is indicated only to assist with orientation); approximate positions of relevant terranes are also indicated. Terrane locations modified from Taylor et al. (1984) and Aberhan (1999).  20  NORTH AMERICA  MIDDLE HETTANG IAN  (Tayloretal. 2001)  Columbiae Subzone  CO  "to £  (Donovan in Dean etal. 1961; Page 2003)  WESTERN TETHYS (Wanner 1886; Page 2003)  Bucklandi Zone  9>  Canadi Zor  UPPE R HETTANGIAN  LOWER SINEMURIAN  AGE  NORTHWEST EUROPE  Rursicostatum Subzone  Oregonensis Zone  Angulata Zone  Marmoreum Zone  Morganense Zone Sunrisense Zone Pleuroacanthitoides Zone Coronoides Zone  Liasicus Zone  Megastoma Zone  Occidentalis Zone  LOWER HETTANGIAN  Mulleri Zone Polymorphum Zone Pacificum Zone  Planorbis Zone  Calliphyllum Zone  Minutum Zone Spelae Zone  Figure 1.2. Zonation for western Cordillera of North America as proposed by Taylor et al. (2001). Correlations with zones from northwest Europe and western Tethys are also shown. Only approximate correlations are implied.  21  Figure 1.3. Map showing the location of the Hispanic Corridor. Modified from Cecca (2002).  22  1.6 References ABERHAN, M. 1998. 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