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Triassic-Jurassic stratigraphy and paleontology of the Takwahoni and Sinwa Formations at Lisadele Lake,… Shirmohammad, Farshad 2006

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TRIASSIC-JURASSIC STRATIGRAPHY AND P A L E O N T O L O G Y OF T H E TAKWAHONI AND SINWAlFORMATIONS A T LISADELE^LAKE, .TULSEQUAH MAP-AREA, NORTHWESTERN BRITISH COLUMBIA L  by FARSHAD  SHIRMOHAMMAD  B. Sc., The University of Shahid Bahonar, 1992 M . S c , The University of Shahid Beheshti, 1997  A THESIS S U B M I T T E D IN P A R T I A L F U L F I L L M E N T OF T H E R E Q U I R E M E N T S F O R T H E D E G R E E OF M A S T E R OF S C I E N C E  in T H E F A C U L T Y OF G R A D U A T E STUDIES Geological Sciences  T H E U N I V E R S I T Y OF BRITISH C O L U M B I A M a y 2006  © Farshad Shirmohammad, 2006  Abstract A southwestern outlier of the Whitehorse Trough basin strata in the central Tulsequah map area includes interbedded fossiliferous conglomerate, sandstone, siltstone, and mudstone of the Lower to Middle Jurassic Takwahoni Formation (Laberge Group) which unconformably overlies Upper Triassic limestone of the Sinwa Formation. Ammonite collections record all stages from Pliensbachian to the Bajocian except for the Aalenian. Middle Toarcian ammonite faunas include the first record of the Tethyan genus Leukadiella in the Tulsequah map-area. The refined age and provenance of several episodes of coarse clastic input into the basin show that the character of the dominant clasts in the conglomerates changes up-section. Immediately above the unconformity, breccias and conglomerate contain sedimentary clasts derived from the Sinwa Formation. Clast dominance changes to volcanic near the base o f the section, plutonic (in Pliensbachian-Toarcian strata), metamorphic (in uppermost Toarcian rocks), and finally, after an interval of fine-grained sedimentation, to chert in the Middle Jurassic strata of Early Bajocian age. The uppermost chert pebble conglomerates are tentatively placed in the Bowser Lake Group. The relative proportions of lithic fragments, feldspar, and quartz in the Lisadele Lake sandstones, plotted on the ternary tectonic discrimination diagram, indicate a complex arc-basin evolution. The biochronological age control of three recognized sandstone petrofacies illustrates strong temporal trends and rapid tectonic and magmatic events. The trends indicate a very rapid change from transitional to dissected arc and finally a recycled orogen during the evolution of the northern Stikinia in Early and Middle Jurassic time.  Geochronological studies of samples of detrital zircons and plutonic clasts from Lower Jurassic strata in the Lisadele Lake area indicate a very rapid uplift, exhumation, and deposition. Comparison o f the isotopic ages o f the zircons and granite clast ages with the biochronologically constrained ages of the enclosing strata suggests that Early Jurassic intrusion, uplift, unroofing, and deposition probably occurred within five m i l l i o n years.  T A B L E OF CONTENTS  Abstract  1 1  Table of Contents  .  List of Tables  iv viii  List of Figures  >  x  List of Appendices  xiii  Acknowledgements  xiv  CHAPTER I INTRODUCTION  1  1.1  Location of the Study Area  2  1.2  Previous Studies...  3  1.3  Objectives  4  CHAPTER II REGIONAL GEOLOGICAL SETTING 2.1  2.2  2.3  9  Tectonic Setting  9  2.1.1  9  Intermontane Superterrane  Stratigraphy  13  2.2.1  Stuhini Group  13  2.2.2  Laberge Group  18  2.2.3  Bowser Lake Group  20  The Whitehorse Trough and Depositional Setting of the Laberge Group  >22  CHAPTER III BIOCHRONOLOGY AND BIOSTRATIGRAPGY  25  3.1  Introduction  25  3.2  Upper Triassic Sinwa Formation  32  3.3  Lower and Middle Jurassic Takwahoni Formation  32  3.3.1  Pliensbachian Stage  32  3.3.2  Toarcian Stage  44  3.3.3  Aalenian Stage  46  3.3.4  Bajocian Stage  46  CHAPTER IV T H E GEOCHRONOLOGY OF CLASTIC COMPONENTS....48 4.1  Introduction  48  4.2  Methods  48  4.3  Sandstone Detrital Zircons  51  4.4  Granitic Clasts  59  4.5  Metamorphic Clasts  63  4.5.1  Methods  63  4.5.2  Results  64  4.6  Summary  CHAPTER V C O N G L O M E R A T E ANALYSES  68  72  5.1  Introduction  72  5.2  Conglomeratic Units  72  5.2.1  74  Conglomerate Unit 1  v  5.2.2  Conglomerate Unit 2  75  5.2.3  Conglomerate Unit 3  76  5.2.4  Conglomerate Unit 4  78  5.2.5  Conglomerate Unit 5  82  5.3  Temporal Trends  83  5.4  Provenance  87  5.4.1  Limestone Clasts  87  5.4.2  Volcanic Clasts  87  5.4.3  Plutonic Clasts  5.4.4  Metamorphic Clasts  88  5.4.5  Chert Clasts  88  CHAPTER VI SANDSTONE PETROGRAPHY  •  87  89  6.1  Introduction  89  6.2  Methods  90  6.3  Analyses  92  6.4  Tectonic Setting  95  6.4.1  Petrofacies A  95  6.4.2  Petrofacies B  95  6.4.3  Petrofacies C  95  CHAPTER VII 7.1  SUMMARY AND CONCLUSIONS  Biochronology and Biostratigraphy.  97 97  vi  7.2  Correlation  100  7.3  Geochronology  104  7.4  Depositional and Tectonic Setting  105  REFERENCES APPENDICES PLATES  110 •  119 154  vii  Page  List of Tables T a b l e s 1. E s t i m a t e d t h i c k n e s s o f t h e L a b e r g e G r o u p i n B r i t i s h C o l u m b i a a n d t h e Y u k o n . M o d i f i e d a f t e r M i h a l y n u k et a l . , 1 9 9 9 . L o c a t i o n s g i v e n i n F i g u r e 9. T a b l e 2. N a t u r e o f t h e b a s a l c o n t a c t o f the L a b e r g e G r o u p i n B r i t i s h C o l u m b i a a n d t h e Y u k o n . M o d i f i e d a f t e r M i h a l y n u k et a l . , 1 9 9 9 . L o c a t i o n s g i v e n i n F i g u r e 9. T a b l e 3. U / P b S H R I M P a n a l y t i c a l d a t a .  56-58  T a b l e 4. U / P b T I M S a n a l y t i c a l d a t a .  62  T a b l e 5. A r / A r a n a l y t i c a l d a t a f o r c l a s t s a m p l e C 3  66  T a b l e 6. A r / A r a n a l y t i c a l d a t a f o r c l a s t s a m p l e C 4  67  T a b l e 7. A s u m m a r y o f t h e r e s u l t s a n d t h e c a l c u l a t e d d i f f e r e n c e b e t w e e n the a g e o f b i o c h r o n o l o g i c a l z o n e s , a n d the g e o c h r o n o l o g i c a l age o f c r y s t a l l i z a t i o n . N o t e s m a l l d i f f e r e n c e s in m i l l i o n s o f years, i n d i c a t i n g very rapid sequence o f arc d e v e l o p m e n t , uplift, d i s s e c t i o n , and d e p o s i t i o n into the adjacent b a s i n ( W h i t e h o r s e T r o u g h ) , d u r i n g E a r l y a n d e a r l y M i d d l e Jurassic.  69  T a b l e 8. G e o c h r o n o l o g i c a l a n d b i o c h r o n o l o g i c a l r e s u l t s p l o t t e d o n t h e J u r a s s i c t i m e s c a l e . T h e J u r a s s i c t i m e s c a l e is f r o m P a l f y et a l . , ( 2 0 0 0 ) . N u m b e r s i n b l u e a n d r e d are f r o m t h e present study.  71  T a b l e 9. C o n g l o m e r a t e c l a s t c o u n t d a t a o f L o w e r to M i d d l e J u r a s s i c c o n g l o m e r a t e u n i t s i n t h e L i s a d e l e L a k e area.  84  T a b l e 10. P o i n t c o u n t d a t a f r o m L i s a d e l e L a k e s a n d s t o n e s . A g e a s s i g n m e n t s : P l i e n s . = P l i e n s b a c h i a n ; Toar. = T o a r c i a n .  91  viii  List of Figures  Page  Figure 1. Map showing the location of the study area in the northwestern British Columbia.  7  Figure 2. Map showing the location of the study area with regard to the Cordilleran terranes. Modified after Wheeler and McFeely, 1991.  8  Figure 3. Photograph of flat lying Eocene volcanic rocks of the Sloko Group (ES) overlying Lower Jurassic Takwahoni Formation (JT). View to the west across Lisadele Lake.  10  Figure 4. Terrane map, indicating the major belts in northern Cordillera (after Wheeler and McFeely, 1991).  11  Figure 5. A n interpretation showing the possible relationship between allochthonous terranes and depositional basins in the northern Cordillera during late Triassic time. The separation between Wrangellia and Stikinia is not to scale. Modified after Souther (1991). 12 Figure 6. Lower Jurassic conglomerates and breccias (conglomerate unit 1) resting unconformably on Upper Triassic limestone of the Sinwa Formation. The dashed-line indicates the approximate position of the erosional unconformity. View is to the northwest. 16 Figures 7a and 7b. Photomicrographs of limestone from the Upper Triassic Sinwa Formation, Tulsequah map-area: a) packed biomicrite with algal and crinoidal biochems in a cement locally rich in iron oxide; b) packed biomicrite with bivalves shell fragments; scale bar s 0.1 mm.  17  Figure 8. Corals in the Upper Triassic Sinwa Formation are aligned and indicate a local northeastdirected paleocurrent direction (the arrow). View is to the south. 17 Figure 9. Location of the measured Laberge Group outcrops mentioned in tables 1 and 2.  21  Figure 10. Schematic cross-section illustrating the tectonic evolution of the Whitehorse Trough. Modified after Dickie and Hein, 1995. 23 Figure 11. North American Early and Middle Jurassic ammonite biochronological units. Modified after Palfy et al., 2000.  26  Figure 12. Panoramic picture of the Lower and Middle Jurassic succession in the Lisadele area. View is to the southeast. 28 Figure 13. Fauna chart showing taxa presented in the Lisadele Lake area. See figure 14 for the stratigraphic section and appendix 1 for the localities guide. 29 Figure 14. Lithostratigraphy and fossil localities of Lisadele Lake section. See figure 16 for legends and figure 13 for the fauna present. The locality numbers and their correlative G S C localities are listed in appendix 1.  30  Figure 15. Geologic map showing distribution of the five Takwahoni Formation conglomeratic units and location of fossil and geochronology samples. 31  IX  List of Figures  Page  Figure 16. Detailed stratigraphic section. Lisadele Lake area, Tulsequah map sheet.  34  Figure 17. Detailed stratigraphic section. Lisadele Lake area, Tulsequah map sheet.  35  Figure 18. Detailed stratigraphic section. Lisadele Lake area, Tulsequah map sheet.  36  Figure 19. Detailed stratigraphic section. Lisadele Lake area, Tulsequah map sheet.  37  Figure 20. Detailed stratigraphic section. Lisadele Lake area, Tulsequah map sheet.  38  Figure 21. Detailed stratigraphic section. Lisadele Lake area, Tulsequah map sheet.  39  Figure 22. Detailed stratigraphic section. Lisadele Lake area, Tulsequah map sheet.  40  Figure 23. Detailed stratigraphic section. Lisadele Lake area, Tulsequah map sheet.  41  Figure 24. Detailed stratigraphic section. Lisadele Lake area, Tulsequah map sheet.  42  Figure 25. Detailed stratigraphic section. Lisadele Lake area, Tulsequah map sheet.  43  Figure 26. Lisadele Lake stratigraphic section showing the fossil localities, geochronology samples and conglomerate units.  50  Figure 27. Detrital zircons from sample SI (S.Cgl-f) on the S H R I M P mount.  51  Figure 28. The age of detrital population of the sample SI (S.Cgl-f).  52  Figure 29. Detrital zircons from sample S2 (S.b.Cgl-1) on the S H R I M P mount.  53  Figure 30. The age of detrital population of the sample S2 (S.b.Cgl-1).  53  Figure 31. Detrital zircons from sample S3 on the S H R I M P mount.  54  Figures 32a (above), and 32b (below) show the age of detrital population of the sample S3.  55  Figure. 33. U-Pb Concordia diagram for granitoid clast sample C I .  61  Figure. 34. U-Pb Concordia diagram for granitoid clast sample C2.  61  Figure 35. Inverse isochron calculation for the sample C3.  64  Figure 36. Spectrum graph for the sample C3. The plateau does not have a set of stages with the same age indicating a wide age range. 65 Figure 37. Spectrum graph for the sample C4 shows no plateau and indicate a minimum age of 160.1+/- 1.3 M a . 65  x  List of Figures  Page  Figure 38. Lithostratigraphy, fossil localities and conglomerate units of Lisadele Lake section. See figure 16 for legends and figure 13 for the fauna present. The locality numbers and their correlative G S C localities are listed in Appendix 1. 73 Figure 39. Unit 1: Lower Jurassic poorly sorted sub-angular to angular limestone breccia.  74  Figure 40. Channelized Lower Jurassic (Sinemurian/Pliensbachian?) conglomerate of Unit 2, dominated by volcanic rock clasts.  75  Figure 41. Yellow weathering, highly oxidized clasts in the conglomerate unit 2.  76  Figure 42. Unit 3: Pliensbachian-Toarcian well-rounded cobble-boulder conglomerates, rich in plutonic clasts. 77 Figure 43. Thin-bedded sandstone layers locally abundant in fragmented plant fossils.  78  Figure 44. Upper Toarcian metamorphic-rich clasts conglomerate of unit 4 with orange to brown-orange matrix.  80  Figure 45. Well-sorted pebble to cobble conglomerates of unit 4, interbedded with brown to light grey coarse-grained sandstone.  80  Figures 46a and 46b. Augen texture in a metamorphic clast sample from Upper Toarcian conglomerate (C4).  81  Figure 47. Garnet mineral in a metamorphic clast sample from Upper Toarcian conglomerate M.Cgl-4.  82  Figure 48. Early Bajocian well-sorted chert-pebble conglomerate of unit 5.  83  Figure 49. Variation of clast type with stratigraphic level in the Takwahoni Formation conglomerates, Lisadele Lake area. The dominant sedimentary components of the conglomerates are differentiated in this chart. Note strong provenance shifts during Early and Middle Jurassic time. 85 Figure 50. Ternary diagram of Takwahoni Formation conglomerate. Poles represent clast modes for plutonic (P), volcanic (V), and combined sedimentary (S) clasts.  86  Figure 51. The Quartz, Feldspar, Lithic components of sedimentary rocks in various tectonic settings. Modified after dickinson and suczek (1979), by courtesy of Fichter (2006).  89  Figure 52. Sandstone classification scheme modified after Folk (1974).  93  Figure 53. Petrographic names assigned to the sandstone samples. The sample numbers are circled (e.g.(ij|= sample number FS-06-SS-1).  93  Figure 54. Ternary diagrams of Takwahoni Formation sandstones. Poles represent total detrital modes for quartz (Q), feldspar (F), and lithic fragments (L). Tectonic discrimination fields indicate sandstone provenance (from Dickinson et al., 1983).  94  xi  List of Figures  P A  8  E  i  Figure 55. Panoramic picture of the Lower and Middle Jurassic succession and the conglomerate units in the Lisadele area.View is to the southeast.  98  Figure 56. Stratigraphy of Laberge and Bowser Lake groups within the Whitehorse Trough. B L G = Bowser Lake Group. Atlin area: Johannson et al., 1997; Yukon area: Hart et al., 1995; Tulsequah area: Present study.  99  Figure 57. Estimated geographic location of the sections in figure 57.  102  Figure 58. Correlation of Jurassic rocks of the Tulsequah map area with Spatsizi and Cry Lake areas. 103 Figure 59. Model for deposition of fan deltas associated with uplift and regional subsidence of the arc margin. Modified after Dickie and Hein, 1995. 106 Figure 60a. Cross-section and plan-map views of the dominant geographical processes interpreted for deposition of the Laberge Group. R S L = Relative Sea-Level. Modified after Dickie and Hein, 1995.  108  Figure 60b. Cross-section and plan-map views of the dominant geographical processes interpreted for deposition of the Laberge Group. R S L = Relative Sea-Level. Modified after Dickie and Hein, 1995.  109  xii  List of Appendices  Page  Appendix 1. Guide for locality and sample numbers, geographic locations, rock type, age and the type of analyses.  119  Appendix 2. Taxonomy.  120  Appendix 3. Analytical techniques used in the U/Pb geochronology.  152  xiii  ACKNOWLEDGEMENTS This study benefited from support, assistance, and interest of many people. In fact, I consider myself a very lucky person, in having had great people i n my life. First, m y sincerest gratitude goes to m y supervisor Professor Paul L. Smith. This project was suggested, shaped, directed, and conducted under his supervision and guidance. H i s endless supply of patience, excellent humor, and extensive knowledge helped me develop both personally and academically. I would like to thank Dr. Bob Anderson ( G S C Vancouver) for sharing his invaluable knowledge of the Canadian Cordillera, as well as his field knowledge and support i n summer 2004. Dr. Anderson's critical review o f this manuscript is also greatly appreciated. I owe a great deal to Dr. Stuart Sutherland for his inexhaustible resource o f assistance, great sense o f humor, and valuable guidance i n completion of this thesis project. Dr. Sutherland's critical review of this manuscript is gratefully acknowledged. In addition, I wish to thank him as m y wrestling coach here at U B C . Special thanks to V i c k i J. M c N i c o l l , isotope geoscientist from Geological Survey o f Canada (Ottawa), for conducting geochronology analyses and providing very helpful diagrams, interpretations, and comments. I would like to thank Dr. James K . Mortensen who contributed greatly with his expertise concerning Canadian Cordilleran tectonics and geochronology. I wish to thank Dr. Kurt G r i m m for interesting and instructive discussions on the sedimentology and sedimentary environments of the Canadian Cordilleran basins.  xiv  I am indebted to Drs. James Scoates, Mary L o u Bevier ( U B C ) and Huawei C a i (Nanjing Institute of Geology and Paleontology, China), for sharing their knowledge and their generosity with their time and expertise. I wish to express my respect and gratitude to the late Dr. Howard W. Tipper (Tip), a pioneer in the Jurassic of the Canadian Cordillera ( G S C , Vancouver) who made great deal o f impression on me with his extensive knowledge, enthusiasm and encouragement about the Lisadele Lake project. Unfortunately, he passed away in 2005 but his field notes, maps and samples from the Lidasele Lake area helped me a lot in the completion of my thesis. Special thanks are due to the faculty and staff of the Department of Earth and Ocean Sciences: A l e x A l l e n , Deborah Varley, Teresa Woodely, Mandy Wu, Sukhi Hundal, David Jones, K a r i m Damani, Thomas U l l r i c h (especially for great discussions about the isotopic dating techniques), Arne Toma and Hai L i n (Hailin) for their generous assistance and excellent technical support. I also wish to thank Peter Krauss ( G S C , Vancouver) for microfossils processing. I am very indebted to my previous professors, Drs. Mohammad Reza Chahida, Iraj Moemeni and Mohammad Ghavidel-Syooki for all their instructions, support and encouragements during the last ten years of my academic studies. I owe a great deal (as I always say: until the next Jurassic, at least!) to my friend Reza Tafti, an outstanding graduate student here at the U B C . Sharing his expertise in the isotope geology, geochronology and computer knowledge, especially when I started my course of study as a newcomer is greatly appreciated.  I would like to thank my colleagues in the Paleontology Lab at the University of British Columbia, Louise Longridge, Melissa Grey, and E m i l y Hopkin for providing such a friendly and constructive environment in the lab. They are especially thanked for their support and patient in answering my endless questions about computer and English language! I would like to thank Jason Loxton for his great assistance in the field season of 2004. His willingness to help plus excellent fossil finding capabilities was so helpful and is much appreciated. I wish to thank my fellow graduate students in the E O S department who helped me with their interest, friendly support and for sharing their knowledge and experience: Daniel Ross, Gareth Chalmers, Goran Markovic, Tilman Roschinski and Luke Beranek. I would like to express my sincere gratitude to Kate Gordanier-Smith (Paul's wife) who made my wife and I feel at home in a new country. She kindly helped L e i l i (my wife) to get through the hard times, when she was a newcomer and I had to leave her during the field season o f 2004. I would like to extend a special note of appreciation to Diana and Jeff Jewell, my first friends, host and teachers in Canada. I could not have had such a quick start without their generous support and valuable guidance. Special thanks to my friend Farid Mostafavi for his support and encouragement during the days of our hard work and study. Most importantly, I would like to give a heart-felt thank to my parents and my wife, for their unfailing encouragement and support during the preparation of this thesis. For the  xvi  last two years, L e i l i provided excellent companionship with her endless love and patience and made the completion of this research possible.  I dedicate this research to my parents and my wife  CHAPTER I INTRODUCTION Stikinia is the largest accreted terrane in the Canadian Cordillera. Its interaction with adjacent terranes, as recorded in its sedimentary basins, is critical to understanding the tectonic evolution of western Canada. Terrane interactions and tectonic setting o f the Jurassic sedimentary basins in the northern Cordillera are rather complex and diverse interpretations and models have been suggested for the tectonics of this part of the world (e.g., Mihalynuk et al., 1994). The present study is an attempt to contribute more data into the geology of the northwestern British Columbia. In northwestern British Columbia, Jurassic deposits of the Laberge Group represent an overlap assemblage that links Stikinia and the Cache Creek terrane (e.g., Wheeler et al., 1988). The Whitehorse Trough formed by the convergence of Stikinia and the pericratonic terranes and includes Jurassic fine- to coarse-grained clastic rocks o f the Laberge Group, that extend from north-central British Columbia west and northwest to southwestern Yukon. Although the Trough is faulted along most of its margins, with the oceanic Cache Creek terrane to the northeast and volcanic arc-related Stikine terrane to the'southwest, its depositional history is related to the evolution of these important terranes and consequently it has been well-studied throughout its extent (e.g., Souther, 1971; Bultman, 1979; Thorstad and Gabrielse, 1986; Gordey et al., 1991; Hart et al., 1995; Mihalynuk et al., 1995a, b, 1999, 2004; Johannson et al., 1997; English et al., 2003 and references therein). The Laberge Group also occurs in scattered outliers southwest of the main extent of the Whitehorse Trough. One of the best-exposed and most complete stratigraphic sections o f  1  the Takwahoni Formation of the Laberge Group occurs in the vicinity of Lisadele Lake in the central part o f the Tulsequah map area (Mihalynuk et al, 1995a, b). A t this locality, the sequence rests with angular unconformity on the Sinwa Formation and includes five conglomerate units whose biochronology, constrained by over 40 ammonite collections, is the subject of this thesis. Establishing the qualitative and quantitative nature of these units and their relations are important for understanding the tectono stratigraphic characteristics of the evolving arc-basinal complex during Early and M i d d l e Jurassic time. In addition, age constraints o f detrital zircons in sandstone matrices and o f some granitoid clasts in conglomerate units whose ages are well-constrained biochronologically, help define the basin evolution, provenance, terrane interaction and the nature and timing of their amalgamation. B y providing new data on the geological history of northern Canadian Cordillera during a significant period of mineralization, this study could also assist with exploration for mineral deposits in this part of the world.  1.1 Location of the study area: The Tulsequah map-area in the northwestern British Columbia which contains the study area comprises approximately 12,800 square kilometers of mountainous country, bounded by latitudes 58° and 59° N ; longitude 132° on the east; and the A l a s k a boundary on the west (Fig. 1). The study area lies within the 1:50,000 Stuhini Creek (NTS 104 K / l 1) map area which covers about 800 square kilometers of the Coast Mountains, centered about 100 kilometers south of Atlin. There are no roads or established trails within the map area. Helicopter from Dease Lake or A t l i n is the most effective means of access as the lakes near the study area are too  2  small for floatplanes. K i n g Salmon Lake, the nearest large enough for floatplane landing, is about 10 kilometers to the north of the Lisadele Lake area (Figs. 1, 2), which makes it impractical except for the ferrying of equipment and supplies. The targeted section is situated within the following quadrangle area:  U T M coordination:  [ Northing: 6501000 m - 6508000 m  N A D = 27  [ E a s t i n g : 610000 m - 6 1 5 0 0 0 m  Latitude: 58° 38' N - 58° 42' N . Longitude: 133° 00' W - 133° 06' W.  1.2 Previous studies: Lower to Middle Jurassic strata in northern B . C . (Takwahoni and Inklin formations) and their depositional basin, the Whitehorse Trough, have undergone numerous geological studies during last decades. Many of these studies involved regional mapping of Whitehorse Trough strata and other volcanic and plutonic rocks in the adjacent regions resulting in the publication of a number of 1:50,000 open file maps and field reports (e.g., Mihalynuk and Rouse, 1988b; Anderson, 1989, 1993; Mihalynuk et al. 1989, 1990, 1992, 1994a, 1994b, 1995, 1999, 2004; Johansson, 1994, 1997). The Klondike G o l d Rush of 1896 and a major gold discovery in the A t l i n area resulted in the first geological maps of the northwestern British Columbia, including the Whitehorse Trough, and more geological investigations in the adjacent areas. Mineral exploration in the Tulsequah area dates back to the discovery of the Tulsequah Chief deposit in 1923 (about 30 k m west of the Lisadele Lake). One of the earliest systematic geological studies  3  in the area was made by Cockfield and Kerr (1926) when they mapped parts of the Tulsequah area east of the Sheslay River. Kerr (1930) provided a geological study of the area between Stikine and Taku Rivers (Kerr, 1931), and later mapped the Taku River area (Kerr, 1948). Souther (1971) completed l:250,000-scale mapping of the Tulsequah map area and reported on its geology and mineral deposits. Monger (1980), with a focus on the Upper Triassic strata, mapped parts of the northern Stuhini Creek map-area (NTS 104 K / l 1). Mihalynuk et al. (1995) extended the previous 1: 50 000-scale mapping of the Tulsequah mapsheet (104 K / 1 2 ; Mihalynuk et al. 1994a, b) eastward into the Stuhini Creek map area (NTS 104 K / l 1). They reported the geology and mineral prospects of the Lisadele Lake area. Mihalynuk et al. (1999) reported age constraints for emplacement of the northern Cache Creek terrane and provided a simplified regional geology map and stratigraphic column of the Laberge Group strata near Lisadele Lake in the central parts of the Stuhini Creek map-area ( N T S 104 K / l 1). Mihalynuk et al. (2004) studied stratigraphy and geochronology of the oceanic strata in French Range (near Dease Lake, northwestern British Columbia) of the exotic Cache Creek terrane and reported that subduction to exhumation happened in less than 2.5 m.y. Canil et al. (2005) carried out heavy mineral sampling and provenance studies in northwestern British Columbia and provided a report on the potentially diamond-bearing rocks in the Jurassic Laberge Group. They showed that the potential source for the garnet in the Laberge Group could be the erosion of peridotite and eclogite as xenoliths in rocks such as kimberlite.  4  1.3 Objectives: This study intends to resolve fundamental questions about the age, provenance, depositional history, and tectonic setting of the Takwahoni Formation (Laberge Group). The Lower to Middle Jurassic Takwahoni Formation forms part of the Laberge Group in northwestern British Columbia and straddles the Stikine and Cache Creek terranes along much of the length of the Whitehorse Trough. The deposition of the Laberge Group records a critical time in the evolution of the Whitehorse Trough during Early and Middle Jurassic. The Laberge Group strata are an ideal subject of provenance studies. In the Stuhini Creek map area, the Takwahoni Formation conglomerates are interbedded with fossiliferous fine-grained sediments. The majority of the Takwahoni Formation sandstones contain a high percentage of unstable components that preclude much transport or chemical weathering. Ammonites provide good biostratigraphic age control for interpreting temporal trends in basin-fill history. This research w i l l address the following issues that have important implications for understanding the geology of the Lisadele Lake area.  1. Stratigraphy and age constraints The main goal is to provide a biochronological/geochronological framework by using ammonite studies and isotopic dating, and to compare it with the adjacent areas. Questions to be addressed: a.  What is the age range of the Takwahoni succession in the Tulsequah map-area and what is the nature of its contact with older and younger rock units?  b.  H o w does the Lisadele Lake succession correlate with other Jurassic sequences in the Whitehorse Trough?  5  c.  What is the time difference between the age of the crystallization of zircons and the age of sediments i n which the zircons or granites are now included as clastic particles?  2. Sedimentological interpretations Petrographic and petrologic data are important in determining provenance and for gaining insight into regional tectonic regimes. Questions to be addressed: a.  What are the sources of clastic materials and have sources changed during the course o f sedimentation?  b.  Is there any change in the rate of sedimentation and how does uplift and subsidence relate to tectonics?  3.  Tectonic setting and terrane interactions  The main purpose of this chapter is to understand the tectono-stratigraphic settings of the Takwahoni Formation in the context of interactions between the Stikine and Cache creek terranes. a.  What was the nature and timing of the arc-basin evolution in the southern Whitehorse Trough?  b.  What are the tectonic implications of provenance shifts?  c.  What is the timing of basin closure?  d.  What do detailed correlations of Jurassic strata across the Whitehorse Trough tell us about the tectonic evolution of the area?  6  0  500  250 kilometres 130°  led S t a t e s o f Arrterica  I 115'  Figure 1. M a p showing the location of the study area in the northwestern British Columbia.  7  Figure 2. Study area with regard to the Cordilleran Terranes. M o d i f i e d after Wheeler and McFeely, 1991. 8  CHAPTER II REGIONAL GEOLOGICAL SETTING 2.1 Tectonic Setting Four major building blocks form the terrane superstructure o f northwestern British Columbia: 1. A western block of polydeformed, metamorphosed Proterozoic to middle Paleozoic pericontinental rocks (Nisling assemblage o f Y u k o n Tanana Terrane as used by Mortensen, 1992); 2. A n eastern block o f oceanic crust and low-latitude marine strata (Cache Creek Terrane o f Coney et al., 1980); 3. Central blocks including Paleozoic Stikine assemblage (Monger, 1977; B r o w n et al., 1991); and, 4. Triassic arc-volcanic and flanking sedimentary rocks o f Stikine Terrane, and overlying Lower to M i d d l e Jurassic arc-derived strata o f the Whitehorse Trough basin. These latter strata include parts of the Upper Triassic Sinwa Formation, Lower to Middle Jurassic Takwahoni Formation, and Middle Jurassic Bowser Lake Group. The sedimentary record o f the succession marks the uplift and erosion o f crust during the Early and Middle Jurassic and the deposition and burial o f detritus in a marine fore-arc basin (Monger et al., 1991). Flat lying Eocene continental arc volcanic rocks of the Sloko Group overlie Takwahoni Formation indicating no widespread deformation after the Early Eocene (e.g. Mihalynuk etal., 1994) (Fig. 3).  2.1.1 Intermontane Superterrane: Three terranes (Quesnel, Cache Creek and Stikine terranes) comprise the Intermontane Superterrane which is now juxtaposed alongside the pericratonic terranes (Fig.4). Derived eastward-flanking Jurassic deposits of the Laberge Group, composed of the Inklin  9  Figure 3. Flat lying Eocene volcanic rocks of the Sloko Group (ES) overlying Lower Jurassic Takwahoni Formation (JT). V i e w to the west across Lisadele Lake.  and Takwahoni formations in British Columbia (Souther, 1971), are widely interpreted to represent an overlap assemblage that links the Stikine and Cache Creek terranes (e.g., Wheeler et al., 1988). Stikinia is remarkably similar to Quesnellia in terms of tectonic setting, age, and metallogeny, and they may be closely related but the two are separated by the Cache Creek Terrane which contains exotic (Tethyan) fossils (Fig. 5). The Stikine terrane is the largest of the accreted terranes in the Canadian Cordillera, comprising Lower Devonian to Upper Jurassic sedimentary, volcanic and comagmatic plutonic rocks. It extends through much of western British Columbia into southern Yukon. This allochthonous terrane is a key element of the Mesozoic  10  From Wheeler and McFeefy (1991) Geological Survey of Canada Map 1712a  5  Study z  ~] North American craton North American margin • (ancestral North America) | | MO (Monashoe; craton fragment) Terranes I  I mixed, TU (Taku)  I  I ST(Stikinia)  H  ON (Quesnellia)  I  I  HA (Harrison)  I  I  CD (Cadwallader)  H  CK (Chiliwack)  I  | MT(Hethow)  |  | AX (Alexander)  Baa I  CC (Cache Creek) undivided metamorphic and plutonic rocks | CA(Cassiar)  |  Hi DY(Dorsey) I I NS(Nisling) •  YT (Yukon-Tanana)  |  | KO(Kootenay)  |  1 PG (Pel V Gneiss)  |  1 WR(Wrangellia)  |  1 SM (Side Mountain)  Jurassic Sedimentary Basins  I Bowser Basin • |  Whitehorse Trough (Takwahoni facias) \ Whlehorse Trough (Inklin facias)  Figure 4. Terrane map, indicating the major belts i n northern Cordillera (after Wheeler and McFeely, 1991). 11  Figure 5. A n interpretation showing the possible relationship between allochthonous terranes and depositional basins in the northern Cordillera during Late Triassic time. The separation between Wrangellia and Stikinia is not to scale. Modified after Souther (1991).  geological and tectonic history of the Canadian Cordillera and has been the subject of considerable research concerning its age, basinal and structural history, lithological characters and the nature and timing of its amalgamation. The Cache Creek terrane is a belt of oceanic rocks, extending the length of the Cordillera in British Columbia. Cache Creek fossils are exotic with respect to the rest of the Canadian Cordillera, as they are of Tethyan affinity, contrasting with coeval faunas in adjacent terranes that show closer linkages with ancestral North America (English et al., 2002).  12  Rocks of the Cache Creek Terrane are dominated by basic volcanics and carbonate but include slivers of ultramafic, chert and argillite of ophiolitic origin (Monger, 1975; A s h and Arksey, 1990b) and coarse clastic rocks of arc affinity (See Figure 2). Microfossil biostratigraphic studies by Cordey et al. (1991) and Cordey (1990) showed that the radiolarian-bearing strata range in age from Permian to Early Jurassic. Radiolarians have been recorded, but are commonly recrystallized (Cordey, 1990). Orchard et al. (2001), based on the micro and macro fossil studies, constrained the age range of the Cache Creek Terrane from Late Carboniferous to Early Jurassic (Toarcian) in central British Columbia. Stikinia and Cache Creek terranes are characterized by distinct Permian and older stratigraphies and geological histories. There is a general agreement that these two terranes were juxtaposed by the Middle Jurassic (Ricketts et al., 1992), although their relationship during Triassic and Early Jurassic interval is unclear (Mihalynuk et al., 1999).  2.2 Stratigraphy 2.2.1 Stuhini Group: Stuhini Group strata in the Tulsequah area were named by Kerr (1948) although much of the Tulsequah area originally mapped as Stuhini Group is now recognized to be Paleozoic in age (Mihalynuk et al., 1994a, b). To the north, strata correlative with the Stuhini Group are named the Lewes River Group (e.g., Wheeler, 1961; Hart et al., 1989a).  13  The Norian Sinwa Formation of the Stuhini Group consists of light to dark grey massive to thick-bedded limestone. The fossiliferous limestone is poorly bedded and generally marks the contact between rocks of the Upper Triassic Stuhini and Lower Jurassic Laberge groups. It can be traced for over 320 kilometres from the Tulsequah area to near Whitehorse (Mihalynuk et al., 1999). This carbonate unit in B C and Y u k o n is carried over coarse-grained strata of the Lower Jurassic Takwahoni Formation in the hanging w a l l of the K i n g Salmon thrust (Thorstad and Gabrielse, 1986). Bultman (1979) mapped the Sinwa limestone in the Tagish area as Upper Triassic, based on lithologic similarity and along strike continuity with rocks mapped at the type locality in the Tulsequah map area (Souther, 1971). It yielded a latest Norian conodont fauna but only at localities sampled north of the Tulsequah map area (104K). Two samples collected from Sinwa Formation in our study did not yield conodonts, just non-diagnostic ichthyolith microfossils. It is noteworthy that Mihalynuk et al. (1999) indicated that conodonts become less frequent in the Sinwa Limestone from the Y u k o n southward into British Columbia. Probably, the southern part of the Sinwa carbonate was deposited in an environment in which the conodont animal did not thrive and/or the southern and northern limestone units are not correlative (Mihalynuk et al., 1999). Other fauna from Sinwa Formation include the finely ribbed bivalve Halobia of Carnian age and the Norian bivalves Monotis and Halorites (Souther, 1971). In the southwestern A t l i n map area (104N), much of the Stuhini Group was originally thought to be Pennsylvanian and/or Permian in age based on poorly preserved fossils, mainly corals and bryozoa from a ferruginous limestone bed (Harker in Aitken, 1959). However, in the Bennett Lake map area (104M), in correlative rocks to the immediate  14  west of the A t l i n area, Christie (1957) recognized that much of the Stuhini Group is Triassic. Reexamination of the poorly preserved fossils by Harker and Tozer (in: Souther, 1971, p. 23) indicated a probable Late Triassic age. The Sinwa Formation is one of the most distinctive lithological units in northwestern British Columbia (Souther, 1971). It consists of carbonate-rich rocks, including major reef buildups, extending from the Tulsequah map area in the south (the type locality; Souther, 1971) northwards to the Tagish Lake area and into the Y u k o n where patch reefs occur (Reid and Tempelman-Kluit, 1987). In the study area, the limestone forms the base of the sequence and is about 30 metres thick. The contact between the Sinwa Formation and the Lower Jurassic conglomerate and sandstone of the Laberge Group is an erosional unconformity (fig. 6).  15  Figure 6. Lower Jurassic conglomerates and breccias (conglomerate unit 1) resting unconformably on Upper Triassic limestone of the Sinwa Formation. The dashed line indicates the approximate position of the erosional unconformity. V i e w is to the northwest.  The Sinwa Formation is a fossiliferous, thick-bedded, massive, light grey limestone, with a distinctive light pink weathering color. Iron oxide cement is present in most samples and locally it is abundant. Microscopic study of the limestone indicates that it is a packed biomicrite (classification of Folk, 1959) with allochems that are mainly bivalve, gastropod and brachiopod shell fragments. Crinoids, corals, and algae are also present (Figs. 7a and 7b). These sediments were probably deposited in a generally low energy environment, below wave base and close to a source of reef detritus. Coral alignment indicates local paleocurrents were directed to the northeast (Fig. 8).  16  Figure 7a and 7b. Photomicrographs of limestone from the Upper Triassic Sinwa Formation, Tulsequah map-area: a) packed biomicrite with algal and crinoidal biochems in a cement locally rich in iron oxide; b) packed biomicrite with bivalves shell fragments; scale bar is 0.1 mm.  Figure 8. Corals in the Upper Triassic Sinwa Formation are aligned and indicate a local northeast-directed paleocurrent direction (the arrow). V i e w is to the south.  17  2.2.2 Laberge Group: Cairns (1911) used "Laberge series" to include conglomerates, greywackes and argillites along the shores o f Lake Laberge that were thought to be of Jurassic-Cretaceous age. Wheeler (1961) applied the lithostratigraphic name "Laberge Group" to correlative strata in the Whitehorse area and recognized them as part of a regional northwest-trending belt of basinal rocks (Whitehorse Trough) that are restricted to the Early and early Middle Jurassic. Wheeler divided the trough into three facies belts: a western, proximal coarse conglomerate belt fringing the dissected arc; a central, fine-grained distal argillite belt in the medial Whitehorse Trough; and an eastern conglomerate belt of uncertain provenance. To the south, i n the Tulsequah area, Souther (1971) divided the Laberge Group into the proximal, fossiliferous, shallow water Takwahoni, and deep-water, fossilpoor Inklin formations. More recently, researchers have used Takwahoni and Inklin formation names to distinguish strata of different provenance. For example, Wheeler and M c F e e l y (1991) use Takwahoni to distinguish elastics derived from Stikinia, and Inklin for those with Cache Creek and Quesnel Terrane provenance. In developing sedimentation models for the Whitehorse Trough, the total thickness and the nature of the basal contact of the Laberge Group across the basin is important. Tables 1, 2 and figure 9 indicate the estimated Laberge Group thicknesses by different workers and i n different areas. In the Lisadele Lake area, the Sinwa Formation is unconformably overlain by about 3000 meters o f coarse clastic Lower and M i d d l e Jurassic sediments.  18  Author  Thickness in metres  Area  Cairns, 1912 Cockfield and Bell, 1926 Bostock, 1936 Wheeler, 1961  1500 >3050 2750 2425  Wheaton River Whitehorse Carmacks Whitehorse  Souther,  3100 I n k l i n ; 3350 T a k w a h o n i  Tulsequah  5000-7000 >3000 3500-4000m total Inklin  Bennett-Atl in Whitehorse southern Atlin  1971  Bultman, 1979 Dickie, 1989 Johannson, 1994 M i h a l y n u k et al.,  1999  This study, 2006  4000 -3000  Tulsequah Tulsequah  Table 1. Estimated thickness of the Laberge Group in British Columbia and the Yukon. Locations given in figure 9. Modified after Mihalynuk et al., (1999).  Laberge area, Bostock and Lees, 1938: Conformably overlies Lewes River (Stuhini) Group; may be disconformable Whitehorse area, Wheeler, 1961: A t least two locations display a disconformable contact with underlying Lewes River (Stuhini) Group. Bennett-Atlin, Bultman, 1979: M a i n l y in fault contact with older rocks, may conformably overly Peninsula Mountain suite  Tulsequah, Souther, 1971: Inklin: structurally conformable (disconformity) with underlying Sinwa Formation Takwahoni: disconformably or unconformably overlies Stuhini; Sinwa has been removed by erosion at most localities. Tulsequah, this study, 2006: Takwahoni Formation conglomerate and breccia unconformably overlies Sinwa Formation. Clasts of the Sinwa Formation limestone dominates the coarse clastic materials. Table 2. Nature of the basal contact of the Laberge Group in British Columbia and the Yukon. Locations given in Figure 9. Modified after Mihalynuk et al., (1999).  19  2.2.3 Bowser Lake Group: The Bowser Lake Group is a thick sequence of marine and nonmarine shale, siltstone, sandstone, and conglomerate which is considered to range from Bajocian to m i d Cretaceous (Evenchick and Thorkelson, 2005). The basal contact is commonly characterized by a chert-pebble conglomerate which is time-transgressive and could range from Upper Bajocian to Upper Bathonian (Tipper and Richards, 1976). Presence o f rounded chert clasts and paucity of detrital mica have been used to distinguish these basinal strata whose chert clasts were derived from the Cache Creek Terrane (Evenchick and Thorkelson, 2005).  20  0 i  250  500  i  •  kilometres 1  States of America  130°  l 115°  Figure 9. Areas where the Laberge Group outcrops, as mentioned in Tables 1 and 2.  21  2.3 The Whitehorse Trough and depositional setting of the Laberge Group: The Whitehorse Trough is an elongate arc-marginal marine sedimentary basin. It represents submarine-fan deposition in a fore arc basin that received detritus from the Upper Triassic Stuhini and Lower Jurassic Hazelton magmatic arcs to the west and southwest during Late Triassic to Middle Jurassic time (e.g., Tempelman-Kluit, 1979; Dickie and Hein, 1995; Hart et al., 1995; Johannson et al., 1997). The Whitehorse Trough contains volcaniclastic and carbonate strata of the Upper Triassic Stuhini Group and siliciclastic strata of the Lower to Middle Jurassic Laberge Group. It is believed that the Whitehorse Trough evolved as a basin between two converging and rising tectonic assemblages, Stikinia and Quesnellia terranes (see Fig. 5), interpreted to have resulted in the mechanical flexure of thin oceanic-to-transitional crust (Cache Creek-Nisling assemblages) flooring the basin (Fig. 10). The Whitehorse Trough was tectonically shortened during the Middle Jurassic because o f a collisional event that involved the west-directed emplacement of the Cache Creek terrane over the Whitehorse Trough and Stikine terrane (Mihalynuk, 1999). Stikinia accreted to the composite western edge of the North American plate (Cache Creek, Quesnellia, Slide Mountain, Kootany and North America) in early Middle Jurassic (Ricketts et al., 1992) (Fig. 10). Paleoflow direction studies indicate that the clastic sediments were mainly derived from a source in the west and southwest of the basin during Early Jurassic (e.g., Johannson et al., 1997; Wight et al., 2004), but questions concerning the paleoflow directions during Middle Jurassic (Early Bajocian) remain to be answered.  22  East  West  Stikinia  Stikinia  Early Jurassic  Stuhini arc volcanics Cache Creek N i s l i n g assemblage Composite western edge of the North American plate  Laberge Group Sinwa Limestone Volcanic sandstones? Triassic and Jurassic plutons  Figure 10. Schematic cross-section illustrating the tectonic evolution of the Whitehorse Trough. Modified after Dickie and Hein (1995).  23  Dominantly arc-derived clastic strata of the Whitehorse Trough mainly show no sedimentological indication of its proximity (Johannson, 1994), except in the Tulsequah area (Mihalynuk et al., 2004). Whitehorse Trough strata in the Tulsequah map-area are dominated by the conglomerate facies of the Takwahoni Formation. Ammonite collections from fine-grained interbeds indicate an age range of late Early Pliensbachian to Early Bajocian (Mihalynuk et al., 1999). Sedimentological observations (e.g., Dickie and Hein, 1995; Mihalynuk et al., 1995) suggest a prograding fan delta setting with distal equivalents. In the Tulsequah map-area proximal conglomeratic strata onlap onto Upper Triassic carbonate rocks of the Sinwa Formation of the Stuhini Group (e.g., Souther, 1971; Monger et al., 1991). Sedimentological studies by Bultman (1979) and Dickie (1989) concluded that Laberge Group strata are subaqueous fans. According to M c G o w a n (1970), a fan delta is an alluvial fan that has prograded into a sea or a lake. Stow (1986) considered a fan delta to be " a type of submarine fan", that is in fact the sub aqueous part of the alluvial fan which progrades from highlands directly into a standing body of water. Not all Whitehorse Trough depositional settings were of deep water. The Skolithos trace fossil ichnofacies identified locally in the Whitehorse Trough sedimentary rocks is apparently restricted to littoral and sublittoral marine environments (Frey and Pemberton, 1984).  24  CHAPTER III BIOCHRONOLOGY AND BIOSTRATIGRAPHY 3.1 Introduction: Macrofossils collected in this study represent many faunal groups including poorly to moderately well preserved ammonites, bivalves, gastropods, and corals. Microscopic studies of the thin sections from Upper Triassic Sinwa Formation limestone indicate the presence o f ichthyoliths and fragments o f crinoids, corals, algae, and brachiopods. Ammonites, which form the base of the biochronology in this research, are one of the most important index fossils for biochronological dating because of their rapid evolution and pelagic habit. Because of biogeographic differences and the commonly large number o f endemic species, it is difficult to apply the standard northwest European zonal scheme o f Dean et al. (1961) in western North America. Endemism can be marked, especially in the Early Jurassic Pliensbachian stage when many European taxa are absent or rare in North America (Smith and Tipper, 1986). A s a result, North American standard zonations for the Pliensbachian (Smith et al., 1988) and the Toarcian (Jakobs et al., 1994; Jakobs, 1997) have been established. A standard zonation for the Aalenian of North America has not yet been established. The regional zonation for Western Canada, documented by Poulton and Tipper (1991) is used in this paper. Similarly, a standard North American zonation for the Bajocian stage has not been developed but several regional zonations have been proposed and are adopted i n this study (Hall and Westermann, 1980; Taylor, 1988).  25  Geochronologic time scales express the estimated numerical ages o f chronostratigraphic units i n millions o f years. Palfy et al. (2000) defined Jurassic chrono stratigraphic units based on the North American ammonite biochronologic standard (Fig. 11).  SI AGL  NORTH AMERICAN AMMONITE CHRONS  MASAI. DAM". - - ERROR  Epizigzagiceras  BAJOCIAN  I.  Rotundum Oblatum Kirschneri  I.  Crassicostatus Widebayense  • 174 0 79 +  Howell i  <  » 177 6 ! i +  Scissum  7  Westermanni  <  h 178 0 i ? +  Yakounensis  TO\R( 1 W  1.  M  1.  £0 V. Z w  b 181 4 l? +  Planulata Kanense  b 1 Jtt fi !T +  Carlottense Kunae  <  » 184 1^6 h 185 7"ni  Freboldi h  1-  180 1 "lo  Hillebrandti Crass icosta  I:  <  h  186 7 \i +  Whiteavesi Imlayi — • 191.5-J:? +  Figure 11. North American Early and Middle Jurassic ammonite biochronological units. Modified after Palfy et al. (2000).  Ammonite biochronology is used to date the stratigraphic range of the Upper Triassic to Lower and early Middle Jurassic succession at Lisadele Lake area and to establish a temporal framework for the provenance studies. Collections obtained from the study area contain more than 34 species of ammonites, representing 32 genera. Their collective stratigraphic ranges span Late Triassic, Pliensbachian, Toarcian, probable Aalenian, and Early Bajocian ammonite zones (Figs. 12-15).  27  Figure 12. Panoramic picture of the Lower and Middle Jurassic succession in the Lisadele area. The red circle indicates the location of camp. View is to the southeast.  to  GO  TAXA  Omojw'cn'ites sp. Eclolcites sp.  1  • •  El F.2 E3 E4 2 2.1 3  0  Fuciniceras sp.  Arieticeras sp. Fanninoceras (Fanninoceras) sp. Fuciniceras cf. intumescens Amallheus slokesi Amallheus margaritalus Arieticeras cf. algovianum Pmtogrammoceras cf. pectinatum Leptaleoceras accuratum Fanninoceras (Charlotticeras) cf. maudense Reynenoceras cf. italicum Fonlanelliceras sp Pmlogrammoceras (Pwlogrammoceraj) cf. pallum Lioceratoides (Pacificeras) angioma Tillonicerus antiquum Lioceratoides (Pacificeras) propinquum Fieldingiceras sp. Dactylioceras sp. Dactylioceras cf kanense Fonlanelliceras ex grfonlaiiellense Harpoceras sp. Cleviceras sp. Taffertia cf laffertensis Harpoceras cf. svbplanatum Leukadiella wmiratica Peronoceras sp. Hiklaites mjirleyi? Hildailes sp. Dactylioceras cf. commune leukadiella sp. Fseudolioceras sp. Fseudolioceras cf. lythense Pliylloceras sp. Phymalocerus hillebrandli Podagrosites sp. Phymatuceras sp. Pianammaloceras sp. Fonlannesia sp. Sonninia spp. Sonninia cf. adicra Dorsetensia spp.  Stephanoceras spp. S. (Skirmceras) cf. kirschneri Normanniles sp. Chondmceras cf. allani Chondmceras defontii  ^  0 0  0  8  9 10 11 12 13 E9 14 IS  16 17 18 E10 TAXA  Omojuvavites sp. Ectolcites sp. Fuciniceras sp.  0  o  o o  •  0  LOCALITIES 5 6 7  Metaderoceras sp.  • • •0 • • •  o o  0  4 E5 E6 E7 E8  Arieticeras sp.  Fanninoceras (Fanninoceras) sp. Fuciniceras cf. intitmescens  0  Pmtogrammoceras Amallheus stukesi (Pmlogrammoceras) sp.  0  Amaltheu. margaritalus Arieticeras cf. algovianum Pmtogrammoceras cf. pectinatum  0  • • • •  Leptaleoceras accuralum Fanninoceras (Fanninoceras) kunae Arieticeras cf. micrasterias Reynenoceras cf. italicum  • 0• • • •0 o • 0 0  o  o Lioceialoidei (Pacificeras) angioma  o  0  •  o  0  Lioceratoides (Pacificeras) sp. Ttltoniceras antiquum Lioceratoides (Pacificeras) pmpinquum  o  • • • • • •o • • • o 0  Fieldingiceras sp. Dactylioceras Dactylioceras sp. cf. kanense  • •  Fontanelliceras ex gr fonlaiiellense Harpoceras sp. Cleviceras Taffertia cf sp. laffertensis  o  Harpoceras cf. subplanatum Leukadiella amuralica  o  • • • • •o o  Pewnoceras sp. Hildailes iinuleyi? Hildailes sp. Dactylioceras cf. commune  o  Leukadiella sp. Fseudolioceras sp. Fseudolioceras cf. lythense  o  Pliylloceras sp. hillebrandli Phymalocerus  •o  • •  Podagrosiles Podagrosiles sp. latescens  o  •  Phymalocerus sp. Pianammaloceras sp.  • • • • • •  Fonlannesia sp.  Sonninia spp. adicra Sonninia cf.  • •o  Dursetensia  spp.  Stephanoceras spp.  0 o  S. (Skirmceras) cf. kirschneri Normannites Chondmceras sp. cf. allani Chondroceras defontii  Figure 13. Fauna chart showing taxa presented in the Lisadele Lake area. See Figure 14 for the stratigraphic section and appendix 1 for the localities guide.  Figure 14. Lithostratigraphy and fossil localities o f Lisadele L a k e section. See figure 16 for legends and Figure for the fauna present. The locality numbers and their correlative G S C localities are listed in appendix 1.  6 1 1 0 0 0 m . E.  6 1 5 0 0 0 m . E. 6508000m. N .  ©  Ammonite locality  ©  Bivalve locality  ^  Gastropod locality  ©  Crinoid locality Ichthyolith locality Fault  y  Lake  Unit 5: Chert pebbles fn ?»m and granules 0<  Unit 4: Metamorphic-rich clasts conglomerate.  58° 4 0 ' N  conglomerate. Unit 2: Volcanic-rich clasts conglomerate. Unit 1: limestone-rich clasts breccia and conglomerate. Q  U/Pb age date: Sandstone. U/Pb age date: Granitoid clast. Ar/Ar age date: Metamorphic clast. Location of measured section Fossil locality  Sloko Group  Eocene  6502000m. N .  Volcanic package dominated by rhyolite flows, light to medium grey and white: Eocene. SIS  White to light grey quartz porphyry intrusive: probably genetically related to E S . Chert-pebble conglomerate: Lower Bajocian.  ni U» | pcr Stuhi Group Triassic  Formation  Takwahoni  Laberge Group  Lower & Middle Jurassic  BLG  Sinwa Formation  MJB  Argillites, thinly bedded greywacke-siltstone couplets: L o w e r Bajocian. Conglomerates, medium-to thick-beddedgreywackes, siltstones and mudstones: Toarcian.  UP  Conglomerates, greywackes, shales, siltstones and mudstones: Pliensbachian. Conglomerates, bioclastic sandstones, siltstones and mudstones: L o w e r Jurassic (Sinemurian?)  UTrS  Fossiliferous thick-bedded to massive, light grey limestone: Norian.  SIS:  S l o k o Intrusive Suite  B L G = Bowser Lake Group  F i g u r e 1 5 . G e o l o g i c m a p s h o w i n g d i s t r i b u t i o n o f t h e five L i s a d e l e L a k e s u c c e s s i o n c o n g l o m e r a t i c u n i t s and location o f fossil a n d geochronology samples. 31  3.2 Upper Triassic Sinwa Formation: The precise age o f the uppermost beds o f the Sinwa Formation is important i n assessing the duration of the hiatus between depositions of the Sinwa sediments and overlying Lower Jurassic strata. One constraint derives from the Early and Middle Norian age determined for ammonites collected from the limestone a few meters below the unconformity. The ammonite fauna include Omojuvavites sp. and Ectolcites sp., indicating a Late Triassic Norian age for the Sinwa Formation in the study area (Fig. 16). Samples collected for microfossils from the uppermost limestone in the Sinwa Formation and from conglomerate clasts within the basal Laberge Group yielded a non-diagnostic icthyolith and echinoderm fauna.  3.3 Lower and Middle Jurassic Takwahoni Formation: 3.3.1  Pliensbachian Stage:  Pliensbachian sedimentary rocks are recorded by fossil collections made to the north and northeast of Lisadele Lake. Three ammonite zones are recorded: Freboldi Zone (Early Pliensbachian), Kunae Zone (Late Pliensbachian), and Carlottense Zone (Late Pliensbachian). Compiled fossil ranges are illustrated in Figures 17 and 18. the Pliensbachian ammonite Metaderoceras sp. from locality E l is the oldest Jurassic ammonite collected from the area (Mihalynuk et al., 1999). This genus is restricted to the Early Pliensbachian (Smith et al., 1988). The oldest widespread Takwahoni Formation rocks near Lisadele Lake are Kunae Zone (Upper Pliensbachian) in age. The ammonite fauna collected from north o f Lisadele Lake  includes Fanninoceras (Fanninoceras) kunae, Fanninoceras (Charlotticeras) cf.  32  maudense, Arieticeras cf. micrasterias, Arieticeras cf. algovianum, Protogrammoceras (Protogrammoceras) sp., Protogrammoceras c f pectinatum, Reynesoceras italicum, and Fuciniceras cf. intumescens. Intergrated collections from correlative outcrops, made by Smith and Tipper (1988) and  Mihalynuk et al. (1999) include Fuciniceras intumescens, Arieticeras sp., Fuciniceras  sp., Fanninoceras sp., Leptaleoceras accuratum, Protogrammoceras pectinatum, Amaltheus stokesi, and Amaltheus margaritatus (Fig. 17). The appearance o f the widely distributed genus Fanninoceras is used as the basis for separating the lower and upper Pliensbachian in North America (Smith et al., 1988). Amaltheids were collected from the north of the Lisadele Lake are typical of the early Kunae Zone. Amaltheus margaritatus is rarely found in the Cordillera and has only been collected from Cry Lake map-area (104 I), northern parts o f the Whitehorse Trough (Fish Lake Syncline, Y u k o n Territory), and northern A l a s k a (Smith et al., 2001).  33  Figure 16 D. OO  S  to  il  El  I Clay | U I C M F | c|vc| Graval |  LEGEND P^T*J Limestone  Plutonic rich clasts  ^  j". • , j Sandstone  Volcanic rich clasts  © Crinoid  TfTl Pebbly °° ° n 1 Sandstone  Metamorphic rich clasts  £2> Brachiopod  p.'*^ Conglomerate  Chert rich clasts  ^  U/Pb age date: detrital zircon  T T q Sand and siltstone • • I interbeds  Limestone rich clasts  ^  U/Pb age date: granitoid clast  •  In situ locality  <^  Ar/Ar age date: metamorphic clast  O  Ex situ locality  -  |  .: ;| Sandy silt Siltstone  p  jg) Ammonite locality  ^| Dike & Sill  [22]  A r  g  n i i t e  ^ X ^ Covered  ©  Bivalve  D<±=>  |  Gastropod  /www Unconformity 1-14 Stratigraphic location of sandstones, see also Chapter 6, Table 9.  Ichthyolith  _J X metre removed for drafting convenience  34  FORMATION STAGE ZONATION THICKNESS  TAKWAHONI Upper Pliensbachian :  |CZ  w  200^  o 1  •'•••r.'---i-- --r l  ,-p.: ;-p.: ;-p. 0  0  #  1  1  1  1  ."••-fL-.f-L-.,-  1 •  X 1  1  1  • I.-.  LITHOLOGY  X  Kunae  .-9--Q-.-P--Q--2>  Localities Situ Samples  In Situ  WWW KJ UJ Ji.  Ex  o  Fieldingiceras  O  —  . t ||||H'|'||1'|L|I o  1  IIIMIMllMMaMMMMMMIIMMMMM  c >—0 c  •  • •  1  sp.  sp.  Arieticeras  sp.  Amaltheous  cf. stokesi cf.  margaritatus  Fanninoceras (Fanninoceras) kunae Fanninoceras (Charlotticeras) cf Maudense  •  Arieticeras  cf.  micrasterias  Arieticeras  cf.  algovianum  Reynenoceras Fuciniceras c  cf. cf.  italicum intumescens  > Lioceratoides (Pacijiceras) propinquum  () (  (Fanninoceras)  Amaltheus  >-•  c  accurafum  Fanninoceras Fuciniceras  -o  sp.  Leptaleoceras  Protogrammoceras  TT  cf.  pectinatum  i Protof^raniftioccras (P' rolo^rammoceras) sp *  Fontanelliceras Tiltoniceras  d  sp. antiquum  Lioceratoides  (Pacijiceras)  > Lioceratoides  (Pacijiceras)  1  <»  <ji  Fieldingiceras  sp. angionus  fieldigii  Protogrammoceras (Protogrammoceras) cfpaltum  L e g e n d as for Figure 16.  ©•s  ® O  O  ® n^O^  ®  O  O In Situ L o c a l i t i e s  ro  ^  Ex Situ S a m p l e s  c)  Phylloceras sp.  c  Podagrosites latescens Hildaites sp.  4 T • <  1  Dactylioceras sp.  "t 1  Dactylioceras cf. commune  •  Leukadiella sp. m  )  m  m  m  m  m  Podagrosites sp. Peronoceras sp. Cleviceras sp.  0  •  Pseudolioceras sp. Fseudolioceras cf. lythense  Figure 20  Legend as for Figure 16.  r  a rjq  CD  to  3 w  1-1  ,-o:: :-p::. 0  .•P-::-o-: 0  /« Situ L o c a l i t i e s  J cn  Ex Situ S a m p l e s  Phymatoceras sp. Phymatoceras  cf.  hillebrandli  Planammatoceras sp.  3  r  rjq'  CD  OQ  R  a  n  a  to to  JO  TAKWAHONI  FORMATION  Aalenian (?)  B A J O C I A N  o ON  1  I  L  roo o  J  I  L  I  THICKNESS (meters)  L i  .'•  -i  .'•  -i  H O  r o c  1  <<  J> 1  m  /« S/ta Localities Ex Situ Samples  Fonlannesia sp. Planammatoceras sp.  O  31 fjq' s  r o n  to  a w  ft On  1 ^  <~fi  On  -J  In Situ Localities Ex Situ Samples  • 4  Sonninia spp. Sonninia cf. adicra  •  Dorsetensia spp.  Figure 24  Legend as for Figure 16. 42  Legend as for Figure 16. 43  Hildoceratids and Amaltheids are dominant and only a single Dactylioceratid, Reynesoceras italicum, is present. Specimens of several indeterminate moulds of bivalves were also collected. In addition, a sandstone bed, almost entirely made up of gastropods was found in the Kunae Zone, below the locality 2 (Fig. 16). Tulsequah area is considered as one of the reference sections for the Kunae Zone in North America (Smith e t a l , 1988). Specimens characteristic of the Carlottense Zone include Lioceratoides (Pacificeras) cf. angionus, Lioceratoides (Pacificeras) propinquum, and Lioceratoides (Pacificeras) sp. Other ammonites present include Protogrammoceras pectinatum, Protogrammoceras (Protogrammoceras) paltum, Protogrammoceras sp., Fontanelliceras sp., Arieticeras sp., Fieldingiceras sp., and Amaltheus margaritatus (Figs. 17, 18). First occurrences of Lioceratoides and Protogrammoceras at locality 3, indicates the base o f the Carlottense Zone in the study area. Smith et al. (1988) collected Lioceratoides (Pacificeras) propinquum, from a level correlative with locality 3. There is presently no entirely suitable stratotype for the Carlottense Zone, although the Tulsequah section at Lisadele Lake has been put forward as the best candidate (Smith et al., 1988).  3.3.2  Toarcian Stage:  Toarcian rocks are found throughout the study area to the north and south of Lisadele Lake. Ammonite collections are mainly Early or early Middle Toarcian (Kanense or Planulata Zone) (Fig. 18-21). The early Late Toarcian (Hillebrandti Zone) is only recorded from south and southwest of the Lisadele Lake at localities 12 and 13 (Figs. 19 and 21).  44  The base of the Toarcian stage in the study area is marked by the appearance of Dactylioceras occurring with holdovers from the Late Pliensbachian, such as Fontanelliceras sp., Lioceratoides (Pacificeras) propinquum, which extend into the lowermost Toarcian at the locality 5 (Fig. 18). The Early Toarcian ammonite fauna collected from north, west and east of Lisadele Lake includes Dactylioceras sp., Fontanelliceras sp., Harpoceras sp., Hildaites c f murleyi, Lioceratoides (Pacificeras) propinquum, Protogrammoceras sp., Dactylioceras kanense, and Taffertia cf. taffertensis (Locality 5). About 10-15 meters above the Kanense Zone localities, the appearance of the Leukadiella cf. amuratica marks the base of the Planulata Zone (Fig. 18). Presence of the Planulata Zone in the Lisadele Lake area (Localities 6-11) is indicated by specimens o f Leukadiella amuratica, Leukadiella sp., Harpoceras cf. subplanatum, Peronoceras sp., Cleviceras sp., Dactylioceras cf. commune, Phylloceras sp., Pseudolioceras lythense and Pseudolioceras sp. (Figs. 18, 19). This is the first recorded occurrence of the Tethyan genus Leukadiella in the Tulsequah map-area; it was previously only known from the Queen Charlotte Islands (Wrangellia) and Spatsizi and Hazelton areas of Stikinia (Jakobs, 1995, 1997; Jakobs et al., 1994). The distribution of Leukadiella and Peronoceras indicates the influence of the Hispanic Corridor linking western Tethys and the eastern pacific during the Middle Toarcian. Specimens characteristic of the Hillebrandti Zone were collected from localities 12 and 13 (Figs. 19-21), and include Podagrosites sp., Phymatoceras hillebrandti, Phymatoceras sp., and Podagrosites latescens. Abundant shell pavements of the bivalve Bositra sp. are widespread south of the Lisadele Lake in Middle to Upper Toarcian strata (Fig. 19,  45  locality 12). They were also collected from Whitehorse Trough strata in the Y u k o n and A t l i n Lake areas (Aberhan, 1998). Elsewhere, Bositra forms shell pavements in rocks as old as Middle Toarcian (Damborenea, 1987; Etter, 1996; Hallam, 1995). A coarsegrained fossiliferous sandstone about 50 meters below the locality 13 yields abundant bivalves including Weyla sp. (Fig. 20).  3.3.3 Aalenian Stage: Aalenian index fossils have not been collected from the study area. A single collection (locality E9) with two small fragments of probable Planammatoceras (Poulton and Tipper, 1991) may be of Aalenian age. Three ex-situ small fragments of ammonites were also found in the Lisadele Lake area between localities 13 and 14; the specimens are not complete enough to be compared in detail with known species. A s Poulton and Tipper (1991) collected their samples somewhere near locality 13 (siltstone beds cut by Tertiary rhyolite dykes), these specimens might also be of Aalenian age as well (Figs. 21, 22).  3.3.4 Bajocian Stage: Only the Early Bajocian is present in the study area, restricted to 2-4 k m south of Lisadele Lake (localities 14-18). Occurrence of a single specimen of Fontannesia sp. at locality 14 marks the base of the Lower Bajocian stage in the Lisadele Lake area (Fig. 22). First common occurrence of Middle Jurassic ammonites is known from the localities 1517 (Fig. 23). Specimens characteristic of the Early Bajocian stage include Sonninia spp., Sonninia cf. adicra, and Dorsetensia spp. and mark the time of the latest fine-grained  46  sedimentation in the Whitehorse Trough. Influx of the chert-rich materials into the basin and final stage of the basin closure is demonstrated by the appearance of chert-pebble conglomerates above locality 18 which has yielded Stephanoceras spp., Stephanoceras (Skirroceras) kirschneri, and Normannites sp. Mihalynuk et al. (1999) reported Early Bajocian Chondroceras cf. allani and Chondroceras defontii from within the chertpebble conglomerate (locality E10) at the uppermost part of the section (Fig. 25).  47  CHAPTER IV THE GEOCHRONOLOGY OF CLASTIC COMPONENTS 4.1 Introduction: The geochronological age determination of the clastic components o f sedimentary rocks is a well-established tool for evaluating the relationship between tectonic activity and provenance o f the sediments. The age distribution o f detrital zircons provides significant data about their provenance and sheds light on the rate of tectonic uplift. A wide age range in populations o f grains indicates derivation from a variety o f sources, whereas a narrow range o f ages points to one or a few sources. A s well, U - P b isotopic dating o f granitoid clasts in the conglomerate beds indicates specific crystallization ages to provenance components. Another approach is to compare the biostratigraphy of the enclosing sedimentary beds and the geochronology o f their clastic components, utilizing a well-calibrated time scale (e.g., Palfy et al., 2000). Small age differences between the sedimentation age and the crystallization age implies rapid erosion and deposition o f the source(s) providing clastic materials to adjacent basins.  4.2 Methods Geochronological studies o f samples o f detrital zircons and plutonic clasts from Lower Jurassic strata were completed at the Geological Survey o f Canada Geochronology Laboratory i n Ottawa (see Appendix X). This includes S H R I M P (Sensitive H i g h Resolution Ion Microprobe) analyses o f detrital zircons from three sandstone samples, and U - P b I D - T I M S (isotope dilution thermal ionization mass spectrometry) zircon dating  48  of two granitoid clasts collected from biostratigraphically well-constrained Upper Pliensbachian and Toarcian strata. Radiometric A r / A r dating on biotites from two metamorphic clasts from Upper Toarcian strata, was undertaken at P C I G R (Pacific Centre for Isotopic and Geochemical Research), the U B C Geochronology Laboratory. The geochronological samples were selected from localities with a good biochronological age control and/or important facies change (e.g. shifts in clast dominance in conglomerates) to provide a crystallization-sedimentation age comparison for the Early Jurassic arc-basin system (Fig. 26).  49  THICKNESS LITBOLOCY (meters) 2900-F  ^  U / P b age d a t e : sandstone d e t r i t a l z i r c o n  ^  U / P b age d a t e : g r a n i t o i d c l a s t  ^  A r / A r a g e date: m e t a m o r p h i c c l a s t  g)  A m m o n i t e locality  B L G = Bowser Lake Group 1 2500-4  U n i t 5: C h e r t - p e b b l e c o n g l o m e r a t e  ISMS  U n i t 4: M c t a m o r p h i c - r i c h c l a s t c o n g l o m e r a t e  j§§  U n i t 3: P l u t o n i c - r i c h c l a s t c o n g l o m e r a t e U n i t 2: V o l c a n i c - r i c h c l a s t c o n g l o m e r a t e U n i t 1: L i m e s t o n e - r i c h c l a s t c o n g l o m e r a t e Mudstone  2000  Sandstone and siltstone  *3 IT w  Limestonestone  184.4 ± 1 M a : S a m p l e S 3 (S.J-1)  O  O >160.1±1.3 M a : S a m p l e C 4 ( M X g l . 4 - C 4 )  « w as •<  ^  = o  1=  1500—1 .  177 ±15 M a : S a m p l e C 3 ( M . C g l . 5 - C l )  —  •  221 M a : S a m p l e C2 ( C g l - 3 ) 1000-  .4  186 M a : S a m p l e C I  (Cgl-1)  g — • 184.4±1.2 Ma: Sample S2 (S.b.Cgl-1)  500  -©  £3  0 •  -  •.'  i l l  •  189.6±1 Ma: Sample SI (S.Cgl-f)  Figure 26. Lisadele Lake stratigraphic section showing the fossil localities, geochronology samples and conglomerate units. 50  4.3 Sandstone Detrital Zircons: 1. Analyses from sandstone sample SI (Field number: S.Cgl-f): Ammonites from several meters below the sample (locality 2) indicate a well defined Kunae Zone (Upper Pliensbachian) age constraint. The next fossil localities (2.1 and 3) are about 100 meters above the sample and indicate Upper Pliensbachian Carlottense Zone (Figs. 17 and 26) suggesting a possible age range of Kunae to Carlottense zones for the SI sedimentation, although a Kunae zone age is most likely. A n image of the detrital zircons from this sample included on the S H R I M P mount is below (Fig. 27). The detrital grains in this sample have a range of morphologies, from equant to delicate elongate grains. They range from faceted to sub-faceted; however, most of the detrital zircon in this rock is quite well faceted. A total of 31 detrital zircons were analyzed from this sample, all comprising one-age population, and therefore, most likely are derived from one source (Fig. 28, Table 3). The age of this detrital population is 189.6 ± 1.0 M a ( M S W D = 0.9).  Figure 27. Detrital zircons from sample SI (S.Cgl-f) on the S H R I M P mount (by courtesy of V i c k i J. M c N i c o l l ) . 51  0.140  S H R I M P II data  0.120  ±1.0  M a  H  0.100 =  0.080  o  0.060 •{  XI (0  189.6  Detrital z i r c o n data c o m p r i s e d of o n e age population  n=31  CL  0.040 0.020 0.000  170  "i  1  r  180  190 Age (Ma)  ™i  r  18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0  Tl CD XI c 3 CD O «<  210  Figure 28. The age of detrital population of the sample SI (S.Cgl-f) (by courtesy of V i c k i J. M c N i c o l l ) .  2. Analyses from sandstone sample S2 (Field number: S.b.Cgl-1): Middle Toarcian (Planulata Zone) index fossils stratigraphically below (localities 6-9) and above (localities 10, 11) sample S2 provides a marked Middle Toarcian age constraint for the S2 sedimentation (Figs. 18, 19 and 26). Detrital zircons retrieved from this sample range in morphology from equant to elongate, and from faceted to subfaceted, however, much of the detrital zircon is quite well faceted (Fig. 29). The majority of the detrital zircons analyzed from this rock define one population with an age of 184.4 ± 1.2 M a ( M S W D = 1.6, n=35). There are a few older detrital grains analyzed from this sample, with ages of ca. 192 M a and ca. 197 M a (Fig. 30, Table 3).  52  Sample S2 (S.b.Cgl-1) zircons for S H R I M P ^  Figure 29. Detrital zircons from sample S2 (S.b.Cgl-1) on the S H R I M P mount (by courtesy of V i c k i J . M c N i c o l l ) .  15 14 184.4 ±1.2 Ma h 13 , n=35 12 11 Age of youngest r 10 dominant population Tl 9 of detrital zircon data 8 n c  0.100  SHRIMP II data  0.090  A l l data n=38  0.080 0.070 §  0.060 H  RJ 0.050 -| jQ  7  Older detrital zircons  CL  0.030 -  /  0.020 0.000 0.010  165  6 5 4 3 r 2 1 0  r  2 0.040  -i  r  r — r  175  185  195  CD 3  o  205  Age (Ma) Figure 30. The age of detrital population of the sample S2 (S.b.Cgl-1) (by courtesy of Vicki J. McNicoll).  53  3.  Analyses from sandstone sample S3 (Field number: S.J-1):  Upper Toarcian (Hillebrandti Zone) index fossils about 400 meters stratigraphically below (locality 12) and about 100 meters above (locality 13) sample S3 provide the age constraint (Figs. 19-21, and 26). Detrital zircons from this sample display a range of sizes and morphologies, from equant to elongate. They range from well faceted to sub-rounded, although most of the detrital grains in this rock are faceted (Fig. 31).  S a m p l e S3  Figure 31. Detrital zircons from sample S3 on the S H R I M P mount (by courtesy of V i c k i J. M c N i c o l l ) .  Two cumulative probability plots are included below. The first cumulative probability plot includes all of the detrital data. There is one detrital zircon analysis with an age of ca.1420 M a (Fig. 32a). The second plot is an expanded view of the younger detrital data  54  from this sample. These data are dominated by the youngest detrital population i n the rock, which has an age o f 184.4 ± 1.0 M a ( M S W D = 1.0, n=38) (Fig. 32b, Table 3). This is the same age population as that obtained from sample S2, perhaps reflecting the same source. Other detrital zircons from this sandstone have ages o f ca.192 M a , 194 M a , 205 M a , 215 M a , and 220 M a .  32 a  0.090  SHRIMP II data All data n=47  0.080 0.070  27 24 23 20 19  0.060 =  XC> O  0.050  15  •2  0.040  11 o j o x  2  j §  8 7  1420  4 3  i iii iii ii iii iii iiiii i ii ii iiiii' i'i ii ii'i'i ir l 0 150\250 350 450 550 650 750 850 950 10501150125013501450 Age (Ma) 32b 0.100 •  184.4 ±1.0 Ma  0.090 0.080 -  Age of youngest dominant population of detrital zircon data  0.070 •  abi  0.060 -  o l.  n  rx  CD XI  c  0.050 0.040 -  n=46  0.030 •  CD 3o  ><  0.020 • 0.010 • 0.000  1 60  i i i—i~r V T / i r i—i i r i - r i r r r~i i r i ' vr i ' i '  170 180  190 200 210 220 230 240 Age (Ma)  Figures 32a (above), and 32b (below) show the age of detrital population o f the sample S3 (by courtesy of V i c k i J. M c N i c o l l ) .  55  Table 3: U/Pb S H R I M P analytical data Spot name  Th U (ppm) (ppm)  Th U  Pb Pb* (ppm) (PPb) 2M  2M  2M  Pb Pb  Sandstone sample S1 (z8463; field number S.cgl-f) 10 8 0.000963 121 0.367 341 8463-1.1 14 0.000860 20 319 0.510 647 8463-2.1 3 0.000201 21 366 0.569 665 8463-3.1 6 0.000435 16 302 0.639 489 8463-4.1 17 11 0.000780 296 0.560 546 8463-5.1 8 0.000442 22 398 0.611 672 8463-6.1 18 6 0.000411 282 0.504 579 8463-92.1 4 0.000201 24 418 0.582 742 8463-93.1 3 0.000193 17 303 0.581 538 8463-94.1 17 3 0.000200 264 0.507 538 8463-96.1 8 0.000503 20 326 0.542 622 8463-104.1 7 0.000605 15 214 0.462 478 8463-81.1 7 0.000784 10 121 0.356 351 8463-71.1 16 9 0.000665 540 207 0.397 8463-72.1 15 8 0.000642 487 204 0.433 8463-49.1 12 11 0.001091 406 144 0.365 8463-48.1 1 0.000056 20 325 0.526 638 8463-47.1 6 0.000532 13 425 182 0.443 8463-40.1 25 10 0.000525 542 0.746 750 8463-34.1 10 0.000567 21 306 0.490 646 8463-33.1 8463-32.1 8463-53.1 8463-55.1 8463-73.1 8463-74.1 8463-88.1 8463-90.1 8463-85.1 8463-86.1 8463-87.1 8463-9.1  OS.  457 720 584 547 489 506 331 367 370 429 419  184 505 289 274 183 233 133 155 143 186 164  6.417 0.724 0.510 0.516 0.387 0.475 0.414 0.437 0.398 0.447 0.405  13 23 18 17 15 16 10 11 11 13 13  12 10 7 11 8 5 3 5 4 10 8  0.000981 0.000528 0.000485 0.000754 0.000616 0.000402 0.000380 0.000533 0.000378 0.000883 0.000729  Pb Pb  206  Pb ° Pb  2M  2M  f(206)  2M  2  6  2M  Pb  2os  pb  0.000283 0.000191 0.000168 0.000301 0.000229 0.000189 0.000177 0.000125 0.000134 0.000261 0.000174 0.000249 0.002279 0.000190 0.000218  0.0167 0.0149 0.0035 0.0075 0.0135 0.0077 0.0071 0.0035 0.0033 0.0035 0.0087 0.0105 0.0136 0.0115 0.0111  0.1102 0.1469 0.1864 0.2163 0.1655 0.2021 0.1602 0.1825 0.2047 0.1645 0.1746 0.1397 0.1139 0.1231 0.1332  0.0116 0.0082 0.0075 0.0138 0.0101 0.0082 0.0098 0.0067 0.0069 0.0108 0.0078 0.0113 0.0853 0.0107 0.0092  0.000298 0.000464 0.000199 0.000158 0.000206  0.0189 0.0010 0.0092 0.0091 0.0098  0.1036 0.1763 0.1417 0.2327 0.1527  0.000248 0.000239 0.000180 0.000186 0.000262 0.000305 0.000555 0.000216 0.000317 0.000237 0.000273  0.0170 0.0092 0.0084 0.0131 0.0107 0.0070 0.0066 0.0092 0.0066 0.0153 0.0126  0.1156 0.2278 0.1561 0.1613 0.1393 0.1513 0.1552 0.1443 0.1301 0.1310 0.1305  207  Pb U  2M  207  2M  Pb U  20s  Pb U  23!  0.0120 0.0177 0.0088 0.0095 0.0089  0.2094 0.1886 0.2125 0.2269 0.1923 0.1992 0.1977 0.2128 0.2178 0.2178 0.1931 0.1978 0.2027 0.2014 0.1952 0.1893 0.2319 0.2111 0.1989 0.2039  0.0194 0.0132 0.0133 0.0212 0.0162 0.0138 0.0158 0.0097 0.0105 0.0186 0.0126 0.0170 0.1468 0.0186 0.0151 0.0205 0.0316 0.0144 0.0115 0.0148  0.0295 0.0295 0.0299 0.0306 0.0300 0.0302 0.0295 0.0304 0.0300 0.0300 0.0300 0.0297 0.0295 0.0301 0.0295 0.0296 0.0302 0.0300 0.0302 0.0308  0.0102 0.0105 0.0107 0.0082 0.0108 0.0149 0.0218 0.0136 0.0140 0.0122 0.0114  0.1873 0.1933 0.2086 0.1933 0.2171 0.2201 0.2313 0.2171 0.2148 0.1849 0.1894  0.0172 0.0161 0.0131 0.0131 0.0183 0.0209 0.0372 0.0192 0.0220 0.0204 0.0212  0.0295 0.0297 0.0300 0.0294 0.0298 0.0298 0.0301 0.0294 0.0299 0.0297 0.0301  2M  2M  Pb U  0.0004 0.0003 0.0003 0.0004 0.0004 0.0004 0.0004 0.0004 0.0004 0.0004 0.0004 0.0004 0.0012 0.0004 0.0004 0.0004 0.0005 0.0004 0.0004 0.0004 0.0004 0.0004 0.0003 0.0004 0.0005 0.0004 0.0005 0.0004 0.0004 0.0004 0.0010  Corr Coeff  0.267 0.285 0.301 0.265 0.297 0.299 0.280 0.391 0.360 0.269 0.319 0.271 0.181 0.269 0.288 0.247 0.237 0.317 0.346 0.286 0.258 0.263 0.302 0.296 0.304 0.253 0.221 0.259 0.265 0.235 0.422  207  Pb  2oe  pb  0.0516 0.0464 0.0516 0.0539 0.0465 0.0478 0.0486 0.0509 0.0526 0.0526 0.0467 0.0483 0.0498 0.0485 0.0481 0.0465 0.0557 0.0511 0.0478 0.0481 0.0461 0.0472 0.0504 0.0478 0.0529 0.0536 0.0557 0.0535 0.0521 0.0452 0.0457  Pb Pb  207  20e  0.0046 0.0031 0.0031 0.0049 0.0038 0.0032 0.0038 0.0022 0.0024 0.0044 0.0029 0.0040 0.0358 0.0044 0.0036 0.0049 0.0074 0.0033 0.0026 0.0034 0.0041 0.0038 0.0031 0.0031 0.0043 0.0050 0.0088 0.0046 0.0052 0.0049 0.0047  Ages (Ma)" Pb Pb U U 206  2,6  2M  2M  187 187 190 194 191 192 187 193 191 191 191 189 188 191 187 188 192 190 192 195 187 189 191 187 189 189 191 187 190 188 191  2 2 2 3 3 2 2 2 2 2 2 2 8 3 2 2 3 3 3 2 2 2 2 2 3 2 3 2 3 2 6  Ages (Ma) Pb Pb 6  2M  20s  ZM  U  187 188 189 193 191 192 187 192 190 190 191 189 187 192 187 188 191 190 192 196 188 189 191 187 188 188 190 186 189 189 192  2M  U  2 2 2 2 3 2 2 2 2 2 2 2 2 3 2 2 3 2 2 2 2 2 2 2 3 2 2 2 3 2 6  Table 3. Cont'd  Sandstone sample S2 (z8465; field number S.b.Cgl-1) 8465-73.1  167  116  0.719  5  13  0.003040  0.001479  0.0527  0.1833  0.0574  0.1104  0.0920  0.0276  0.0009  0.162  0.0291  0.0241  175  5  179  3  8465-80.1  244  136  0.575  7  6  0.000988  0.000360  0.0171  0.1782  0.0155  0.1682  0.0231  0.0282  0.0004  0.227  0.0432  0.0058  180  3  181  2  8465-52.1  264  140  0.547  8  4  0.000567  0.000499  0.0098  0.1947  0.0226  0.2094  0.0315  0.0283  0.0004  0.222  0.0537  0.0080  180  3  179  2  8465-55.2  484  199  0.424  14  7  0.000581  0.000587  0.0101  0.1384  0.0224  0.2071  0.0374  0.0283  0.0005  0.229  0.0531  0.0094  180  3  179  3  8465-59.1  305  203  0.686  9  8  0.001036  0.000386  0.0180  0.2154  0.0192  0.1851  0.0257  0.0283  0.0005  0.255  0.0474  0.0064  180  3  180  3  8465-5.1  301  128  0.440  9  8  0.001097  0.000368  0.0190  0.1210  0.0156  0.1766  0.0241  0.0285  0.0004  0.227  0.0450  0.0060  181  3  182  2  8465-75.1  456  259  0.588  14  6  0.000558  0.000243  0.0097  0.1864  0.0119  0.1985  0.0162  0.0285  0.0004  0.300  0.0505  0.0040  181  3  181  3  5  8  0.001905  0.000508  0.0330  0.1396  0.0208  0.1763  0.0331  0.0285  0.0005  0.214  0.0448  0.0083  181  3  182  3  8465-70.1  166  76  0.476  8465-14.1  400  292  0.754  12  10  0.000959  0.000816  0.0166  0.2199  0.0334  0.1791  0.0512  0.0286  0.0006  0.194  0.0455  0.0129  181  4  182  3  8465-6.1  400  216  0.558  12  8  0.000766  0.000283  0.0133  0.1839  0.0120  0.1880  0.0187  0.0286  0.0004  0.276  0.0477  0.0046  182  3  182  3  8465-60.1  259  121  0.483  8  5  0.000821  0.000470  0.0142  0.1604  0.0188  0.2036  0.0303  0.0286  0.0005  0.228  0.0517  0.0075  182  3  181  2  8465-10.1  214  177  0.854  7  5  0.000918  0.000710  0.0159  0.2847  0.0541  0.1726  0.0463  0.0287  0.0005  0.193  0.0437  0.0116  182  3  183  3  8465-101.1  256  155  0.626  8  2  0.000289  0.000422  0.0050  0.1990  0.0175  0.2330  0.0294  0.0288  0.0005  0.260  0.0586  0.0072  183  3  181  3  8465-58.1  382  173  0.468  12  3  0.000360  0.000282  0.0062  0.1697  0.0118  0.2165  0.0189  0.0288  0.0004  0.264  0.0545  0.0046  183  2  182  2  8465-53.1  312  133  0.440  9  5  0.000696  0.000283  0.0121  0.1391  0.0133  0.1891  0.0189  0.0289  0.0004  0.258  0.0476  0.0046  183  2  184  2  8465-11.1  254  141  0.573  8  5  0.000847  0.000406  0.0147  0.1774  0.0170  0.1977  0.0276  0.0289  0.0004  0.227  0.0496  0.0068  184  3  183  2  8465-7.2  769  468  0.628  24  4  0.000194  0.000371  0.0034  0.2096  0.0146  0.2142  0.0244  0.0289  0.0005  0.263  0.0537  0.0060  184  3  183  3  8465-18.1  289  78  0.281  8  9  0.001227  0.000391  0.0213  0.0747  0.0154  0.1863  0.0256  0.0290  0.0004  0.223  0.0467  0.0063  184  3  184  2  8465-71.1  504  263  0.540  15  9  0.000728  0.000266  0.0126  0.1616  0.0110  0.1836  0.0176  0.0290  0.0004  0.251  0.0460  0.0043  184  2  185  2  8465-69.1  719  556  0.799  24  6  0.000317  0.000173  0.0055  0.2635  0.0131  0.2066  0.0141  0.0290  0.0003  0.292  0.0517  0.0034  184  2  184  2  8465-81.1  227  77  0.351  7  5  0.000874  0.000558  0.0151  0.1247  0.0219  0.2081  0.0368  0.0291  0.0006  0.229  0.0519  0.0090  185  3  184  3  8465-56.1  331  107  0.335  9  10  0.001152  0.000338  0.0200  0.1020  0.0137  0.1735  0.0226  0.0291  0.0005  0.246  0.0432  0.0055  185  3  186  3  8465-13.1  550  312  0.587  17  7  0.000475  0.000180  0.0082  0.1818  0.0095  0.1921  0.0129  0.0292  0.0003  0.293  0.0478  0.0031  185  2  186  2  8465-15.1  339  185  0.565  11  2  0.000230  0.000229  0.0040  0.1905  0.0156  0.2146  0.0165  0.0294  0.0004  0.288  0.0530  0.0039  186  2  186  2  8465-19.1  396  275  0.718  13  5  0.000502  0.000258  0.0087  0.2308  0.0117  0.2125  0.0186  0.0294  0.0004  0.263  0.0525  0.0045  187  2  186  2  8465-1.1  579  189  0.338  17  2  0.000110  0.000263  0.0019  0.1175  0.0104  0.2176  0.0176  0.0294  0.0004  0.271  0.0537  0.0042  187  2  186  2  8465-74.1  503  373  0.765  16  9  0.000713  0.000169  0.0124  0.2255  0.0106  0.1901  0.0129  0.0294  0.0004  0.296  0.0469  0.0031  187  2  187  2  8465-9.1  572  294  0.530  17  11  0.000720  0.000233  0.0125  0.1602  0.0097  0.1899  0.0161  0.0294  0.0004  0.263  0.0468  0.0039  187  2  188  2  8465-47.1  756  354  0.484  23  9  0.000471  0.000127  0.0082  0.1572  0.0059  0.1979  0.0093  0.0294  0.0004  0.373  0.0488  0.0022  187  2  187  2  8465-94.1  772  534  0.714  25  6  0.000288  0.000140  0.0050  0.2282  0.0067  0.2093  0.0101  0.0295  0.0003  0.349  0.0516  0.0023  187  2  187  2  8465-20.1  537  351  0.674  17  5  0.000401  0.000162  0.0070  0.2097  0.0087  0.2026  0.0115  0.0295  0.0003  0.319  0.0499  0.0027  187  2  187  2  8465-92.1  475  174  0.378  14  4  0.000353  0.000147  0.0061  0.1188  0.0098  0.2095  0.0109  0.0296  0.0004  0.348  0.0514  0.0025  188  2  187  2  8465-12.1  698  255  0.377  21  3  0.000144  0.000115  0.0025  0.1226  0.0054  0.2134  0.0097  0.0296  0.0004  0.406  0.0522  0.0022  188  2  188  2  8465-44.1  952  766  0.832  33  7  0.000271  0.000147  0.0047  0.2732  0.0088  0.2185  0.0106  0.0299  0.0004  0.357  0.0530  0.0024  190  2  189  2  8465-17.1  559  328  0.605  18  5  0.000319  0.000159  0.0055  0.2080  0.0077  0.2099  0.0115  0.0300  0.0004  0.332  0.0508  0.0027  190  2  190  2  8465-82.1  752  409  0.561  24  7  0.000371  0.000275  0.0064  0.1772  0.0119  0.2003  0.0196  0.0302  0.0004  0.244  0.0482  0.0046  192  2  192  2  8465-55.1  1101  682  0.640  36  3  0.000120  0.000088  0.0021  0.2070  0.0050  0.2188  0.0083  0.0303  0.0004  0.454  0.0524  0.0018  192  2  192  2  8465-7.1  903  284  0.325  28  9  0.000358  0.000131  0.0062  0.0962  0.0062  0.2084  0.0100  0.0311  0.0004  0.369  0.0487  0.0022  197  2  197  2  Table 3. Cont'd  Sandstone sample S3(Z8464; fieldnumber S.J-1) 8464-28.1 8464-24.1  167 131  8464-100.1  257  8464-88.1  154  149  0.600  8464-42.1  108  68 63  0.459 0.606  3  8464-27.1  256  180  0.726  8  8464-90.1  238  108  0.471  7  8464-5.1  253  91  0.370  7  8464-29.1  217  99  0.470  6  8464-34.1  241  148  0.634  7  8464-40.1  196  112  0.587  6  8464-85.1  213  131  0.633  7  8464-84.1  211  122  0.598  7  8464-35.1  175  99  0.582  5  8464-31.1  351  233  0.686  11  8464-79.1  272  170  0.643  8  8464-8.1  536  391  0.754  17  . 8464-3.1  354  218  0.635  11  8464-70.1  377  186  0.509  11  8464-25.1  410  328  0.826  13  8464-78.1  408  218  0.553  12  8464-33.1  239  145  0.625  8  8464-37.1  459  338  0.761  15  8464-89.1  183  0.540  6  8464-26.1  196  0.520  6  8464-14.1  201  0.354  6  8464-21.1  281  178  0.654  9  8464-76.1  424  332  0.809  14  8464-13.1  495  547  1.141  18  8464-10.1  532  380  0.737  17  8464-55.1  191  102  0.551  6  8464-4.1 8464-77.1 8464-22.1 8464-23.1 8464-75.1 8464-36.1 8464-39.1 8464-30.1 8464-32.1 8464-101.1 8464-86.1 8464-38.1 8464-12.1  486  85  0.529  70  0.554  289  508  185  130  64  504  436  371  212  500  377  541  206  653  624  636  299  383  197  463  244  447  207  162  63  0.615 0.377 0.509 0.894 0.590 0.778 0.393 0.988 0.486 0.533 0.545 0.478 0.403  5  5  16 15 4 17 12 17 17 23 20 12 15 15 6  8464-41.1  417  70  0.172  14  8464-81.1  215  96  0.459  8  8464-67.1  191  68  0.369  49  8  0.0348  0.1376  0.0250  0.1392  0.0438  0.0282  0.0008  0.208  0.0358  0.0111  179  5  182  0.000726  0.0395  0.1493  0.0292  0.1744  0.0464  0.0283  0.0006  0.201  0.0447  0.0118  180  4  180  3  0.002279  0.000604  0.0318  0.1763  0.0255  0.1577  0.0382  0.0283  0.0005  0.192  0.0404  0.0097  180  3  182  2  0.001834  0.000566  0.0259  0.1521  0.0234  0.1881  0.0374  0.0284  0.0005  0.216  0.0481  0.0094  180  3  180  3  0.001492  0.000979  0.0442  0.1736  0.0391  0.1830  0.0628  0.0284  0.0008  0.205  0.0468  0.0158  180  5  181  4  0.002550  0.000441  0.0325  0.2249  0.0191  0.1632  0.0285  0.0285  0.0004  0.209  0.0416  0.0072  181  3  183  2  0.001876  0.000459  0.0191  0.1558  0.0205  0.1931  0.0299  0.0285  0.0005  0.236  0.0491  0.0075  181  3  181  3  0.001102  0.000484  0.0246  0.1100  0.0209  0.1947  0.0318  0.0286  0.0004  0.218  0.0494  0.0079  182  3  182  0.001419  0.000584  0.0252  0.1493  0.0231  0.1995  0.0378  0.0288  0.0005  0.211  0.0503  0.0094  183  3  182  0.001455  0.000395  0.0287  0.1786  0.0167  0.1632  0.0261  0.0288  0.0005  0.229  0.0412  0.0064  183  3  184  3  0.001658  0.000751  0.0246  0.1831  0.0293  0.1766  0.0480  0.0288  0.0006  0.199  0.0445  0.0119  183  4  184  3  0.001418  0.000469  0.0244  0.2081  0.0197  0.2044  0.0312  0.0288  0.0005  0.237  0.0515  0.0077  183  3  182  3  0.001406  0.000468  0.0146  0.2140  0.0226  0.2400  0.0325  0.0288  0.0004  0.233  0.0604  0.0080  183  3  181  2  0.000842  0.000602  0.0267  0.1812  0.0273  0.1890  0.0393  0.0288  0.0005  0.206  0.0476  0.0098  183  3  183  3  0.001541  0.000341  0.0167  0.1998  0.0160  0.1970  0.0236  0.0289  0.0004  0.238  0.0495  0.0058  183  3  183  2  0.000966  0.000419  0.0275  0.1742  0.0192  0.1640  0.0274  0.0289  0.0004  0.215  0.0412  0.0068  184  3  185  2  0.001588  0.000173  0.0084  0.2489  0.0158  0.2206  0.0123  0.0289  0.0004  0.357  0.0553  0.0029  184  2  182  2  0.000486  0.000289  0.0069  0.2165  0.0152  0.2299  0.0199  0.0289  0.0004  0.274  0.0576  0.0048  184  2  182  2  0.000398  0.000344  0.0158  0.1453  0.0177  0.1777  0.0226  0.0290  0.0004  0.238  0.0445  0.0055  184  3  185  2  0.000914  0.000355  0.0121  0.2666  0.0148  0.1923  0.0235  0.0290  0.0005  0.248  0.0480  0.0057  185  3  185  3  0.000698  0.000487  0.0178  0.1576  0.0190  0.1769  0.0315  0.0291  0.0004  0.204  0.0441  0.0077  185  3  186  2  0.001029  0.000307  0.0128  0.2072  0.0143  0.2221  0.0210  0.0291  0.0005  0.286  0.0553  0.0051  185  3  184  3  0.000736  0.000249  0.0061  0.2493  0.0108  0.2101  0.0167  0.0292  0.0004  0.284  0.0523  0.0040  185  2  185  2  0.000349  0.000470  0.0204  0.1781  0.0195  0.2198  0.0313  0.0292  0.0005  0.232  0.0546  0.0076  185  3  184  2  0.001178  0.000480  0.0225  0.1705  0.0198  0.2177  0.0324  0.0292  0.0006  0.263  0.0541  0.0078  185  4  184  4  0.001297  0.000909  0.0376  0.0966  0.0351  0.1930  0.0597  0.0293  0.0007  0.198  0.0477  0.0146  4  186  3  0.002171  0.000279  0.0086  0.2100  0.0124  0.2068  0.0192  0.0293  0.0005  0.287  0.0511  0.0046  3  186  3  0.000498  0.000231  0.0077  0.2647  0.0107  0.2150  0.0159  0.0294  0.0004  0.287  0.0531  0.0038  2  186  2  0.000446  0 000165  0.0100  0.3813  0.0092  0.2101  0.0131  0.0294  0.0004  0.312  0.0518  0.0031  187  2  186  2  0.000579  0.000316  0.0101  0.2356  0.0129  0.2028  0.0209  0.0295  0.0004  0.247  0.0500  0.0050  187  2  187  2  0.000582  0.000461  0.0074  0.1966  0.0193  0.2604  0.0324  0.0295  0.0006  0.283  0.0640  0.0077  187  4  184  3  0.000428  0.000261  0.0092  0.2044  0.0110  0.2130  0.0177  0.0296  0.0004  0.277  0.0523  0.0042  188  2  187  2  0.000533  0.000235  0.0073  0.1190  0.0096  0.2119  0.0185  0.0296  0.0004  0.282  0.0519  0.0044  188  3  187  3  0.000422  0.000637  0.0116  0.2336  0.0261  0.3099  0.0436  0.0296  0.0006  0.255  0.0759  0.0104  188  3  182  3  0.000672  0.000212  0.0084  0.2858  0.0098  0.1986  0.0159  0.0297  0.0004  0.270  0.0486  0.0038  188  2  189  2  0.000482  0.000441  0.0064  0.1900  0.0229  0.2256  0.0304  0.0298  0.0006  0.267  0.0550  0.0072  189  4  188  3  0.000372  0.000180  0.0104  0.2443  0.0085  0.2059  0.0132  0.0298  0.0004  0.304  0.0502  0.0031  189  2  189  2  0.000597  0.000111  0.0011  0.1376  0.0056  0.2195  0.0123  0.0300  0.0004  0.356  0.0530  0.0028  191  3  190  3  0.000061  0.000114  0.0073  0.3131  0.0068  0.2100  0.0089  0.0301  0.0004  0.387  0.0505  0.0020  191  2  191  2  0.000419  0.000148  0.0010  0.1610  0.0071  0.2141  0.0151  0.0304  0.0004  0.283  0.0512  0.0035  193  2  193  2  0.000055  0.000237  0.0148  0.1655  0.0104  0.2114  0.0218  0.0306  0.0004  0.245  0.0501  0.0051  194  2  194  2  0.000852  0.000571  0.0028  0.1925  0.0224  0.2271  0.0386  0.0307  0.0005  0.214  0.0536  0.0090  195  3  194  2  0.000161  0.000353  0.0082  0.1550  0.0143  0.2273  0.0260  0.0323  0.0005  0.262  0.0510  0.0057  205  3  205  3  0.000472  0.000823  0.0316  0.1252  0.0323  0.2626  0.0631  0.0342  0.0007  0.212  0.0557  0.0132  217  5  215  3  0.001825  0.000205  0.0063  0.0560  0.0081  0.2507  0.0180  0.0350  0.0004  0.290  0.0520  0.0036  221  3  221  3  0.000363  0.000677  0.0074  0.1510  0.0261  0.2689  0.0524  0.0350  0.0007  0.220  0.0558  0.0107  222  220  3  0.000428  0.000093  0.0024  0.1063  0.0039  3.1313  0.0729  0.2471  0.0032  0.655  0.0919  0.0016  1423  1420  18  0.000137 Notes (see Stem. 1997V Uncertainties reported at 1 a (absolute) and are calculated by numerical propagation of all known sources of error. f206 a  2 0 4  refers to mole fraction of total  204-corrected ages;  b  3 M  5  0.000571  0.002009  P b that is due to common Pb, calculated using the ^ P b - m e t h o d ; c o m m o n Pb composition used is the surface blank  207-corrected ages (Stern 1997)  T h e sputtered area for analysis was ca. 25 urn in diameter with a b e a m current of 5 n A ( G S C Mount #350). T h e 1a external error of ^ P b / ^ U ratios reported in the table incorporate a +/- 1% e r r o r in c a l i b r a t i n g t h e s t a n d a r d z i r c o n ( s e e S t e m a n d A m e l i n , 2 0 0 3 ) .  2 .  2  4.4 Granitic Clasts: U-Pb dating o f zircons from two granitoid clasts, collected from biostratigraphically w e l l constrained M i d d l e Toarcian strata indicate two crystallization dates: •  Clast sample C I (Field number: Cgl-1): 186.6  ± 0.5  •  Clast sample C 2 (Field number: Cgl-3): 221  + 1 Ma  Ma  Clast sample C I contains abundant, high quality, euhedral zircon ranging in morphology from equant to prismatic. Five multigrain zircon analyses overlap each other and intersect concordia (Fig. 33, Table 4). A Concordia age calculated using all 5 analyses is 186.6 ± 0.5 M a ( M S W D of concordance and equivalence = 1.2), which is interpreted to be the age of the clast. Clast sample C 2 contains euhedral zircon (with minor inclusions) ranging from stubby prismatic to elongate in morphology. Three multigrain fractions and overlap each other and Concordia (Fig. 34, Table 4). A concordia age is calculated to be 221 ± 1 M a ( M S W D of concordance and equivalence^.7) using these 3 analyses. Fraction B 2 is discordant and is interpreted to have undergone Pb loss. Middle Toarcian (Planulata Zone) index fossils about 50 meters stratigraphically below (localities 6-9) and about 30 meters above (localities 10,11) the C I clast provide an age constraint for enclosing conglomerate (Figs. 18, 19 and 26). Clast sample C 2 was obtained from a conglomerate bed about 100 meters stratigraphically above C I . The bed was biostratigraphically located a few meters above the last occurrence of Middle Toarcian ammonites (locality 11) and about 250 meters below the first occurrence of the Upper Toarcian ammonites (locality 12) indicating a Middle-Upper Toarcian age range  59  (Figs. 18 and 26). The U - P b concordia diagram for the granitoid clasts C I and C 2 showing the crystallization age of their source plutons is illustrated in figures 33 and 34.  60  Granitoid Clast: S a m p l e M R B - 0 4 - c g l 1 c 3 (z8466)  0.0302  1  n  0.0286  0.201  0.199  0.197  r  0.205  0.203  0.207  207PD/235U  Fig. 33. U - P b Concordia diagram for granitoid clast sample C I .  Granitoid Clast: Sample MRB-04-Cgl.3-C9 (z8575) 0.0355  i  1  r  0.0351 h"  0.0347 Ql  CO 0.0343  0.0339 H  0.0335 0.234  0.236  0.238  0.240  0.242  0.244  0.246  207PW235U  Fig. 34. U - P b Concordia diagram for granitoid clast sample C 2 .  0.248  Table 4: U-Pb TIMS analytical data  Isotopic Ratios  5  Fract.  1  Wt. ug  U ppm  Pb  J  ppm  206Pb  Pb  4  3  204Pb  pg  208Pb  207Pb  1SE  206Pb  206Pb  235U  Abs  238U  Abs  Sample C1 (Z8466; field sample Cgl-1)  1SE  Ages (Ma)  7  Corr. Coeff. 6  207Pb  1SE  206Pb  Abs  206Pb  2SE  238U  207Pb  2SE  207Pb  2SE  %  Disc  206Pb  235U  A2(Z)  33  469  14  3678  8  0.13  0.20247  0.0003  0.02941  0.00004  0.8307  0.04993  0.00004  186.9  0.5  187.2  0.5  191.5  3.9  2.5  A3(Z)  30  473  14  10231  3  0.14  0.20174  0.00028  0.02933  0.00004  0.8043  0.04989  0.00004  186.3  0.5  186.6  0.5  190.1  3.8  2.0  Z1 (Z)  35  592  18  6794  6  0.14  0.20128  0.0003  0.02928  0.00004  0.9345  0.04986  0.00003  186.0  0.4  186.2  0.5  188.5  2.5  1.3  Z1B(Z)  44  375  11  24740  1  0.12  0.20196  0.00028  0.02937  0.00004  0.9356  0.04988  0.00002  186.6  0.4  186.8  0.5  189.4  2.3  1.5  Z3(Z)  28  270  8  12  0.15  0.20229  0.00046  0.02938  0.00004  0.8087  0.04994  0.00007  186.6  0.5  187.1  0.8  192.3  6.5  3.0  2.5  1162  Sample C2 (Z8575; field sample Cgl-3) A1(Z)  24  279  10  4968  3  0.17  0.24278  0.00038  0.03475  0.00005  0.8263  0.05067  0.00005  220.2  0.6  220.7  0.6  225.7  4.2  A2(Z)  31  231  8  3079  5  0.16  0.24336  0.00036  0.03487  0.00004  0.8028  0.05062  0.00004  220.9  0.5  221.2  0.6  223.7  4.1  1.3  B1(Z)  32  245  9  15210  1  0.16  0.24233  0.00042  0.03476  0.00006  0.8593  0.05056  0.00005  220.3  0.7  220.3  0.7  220.7  4.2  0.2  B2(Z)  34  216  8  34  0.16  0.23746  0.00101  0.03395  0.00006  0.7269  0.05074  0.00016  215.2  0.7  216.3  1.7  228.8  14.9  6.1  Notes: 1  All fractions are zircon and h a v e  475  been a b r a d e d  following the method of Krogh (1982).  2  Radiogenic P b  3  M e a s u r e d ratio, c o r r e c t e d for s p i k e a n d fractionation  " T o t a l c o m m o n P b in a n a l y s i s c o r r e c t e d f o r f r a c t i o n a t i o n a n d s p i k e 5  C o r r e c t e d f o r b l a n k P b a n d U a n d c o m m o n P b , e r r o r s q u o t e d a r e 1 s i g m a a b s o l u t e ; p r o c e d u r a l b l a n k v a l u e s for this s t u d y r a n g e d w e r e 0.1 p g f o r U a n d 1 - 2 p g f o r P b ; P b b l a n k i s o t o p i c c o m p o s i t i o n is b a s e d o n the a n a l y s i s o f p r o c e d u r a l b l a n k s ; c o r r e c t i o n s for c o m m o n P b w e r e m a d e u s i n g S t a c e y - K r a m e r s c o m p o s i t i o n s  Correlation C o e f f i c i e n t Corrected f o r b l a n k a n d  On  to  c o m m o n Pb,  errors  quoted  are 2  s i g m a in M a .  4.5 Metamorphic Clasts: Sample C 3 : Micaschist (Field number: M . C g l - 5 - C l ) : 177 ± 15 Ma Sample C4: Gneiss (Field number: M . C g l - 4 - C 4 ) : >160.1 + 1.3 Ma Upper Toarcian (Hillebrandti Zone) index fossils stratigraphically below (locality 12) and above (locality 13) the C3 and C4 enclosing conglomerate beds provide an Upper Toarcian age constraint for their sedimentation (Figs. 20 and 26). Isotopic A r / A r dating on the biotites of the metamorphic clasts were processed at the U B C Geochronology Laboratory.  4.5.1 Methods Mineral separates were hand-picked, washed in acetone, dried, wrapped in aluminum foil and stacked in an irradiation capsule with similar-aged samples and neutron flux monitors (Fish Canyon T u f f sanidine, 28.02 M a (Renne et al., 1998)). The samples were irradiated on February 15 through 17, 2006 at the M c M a s t e r Nuclear Reactor in Hamilton, Ontario, for 90 M W H , with a neutron flux of approximately 3 x 1 0  16  neutrons/cm . Analyses (n=57) o f 19 neutron flux monitor positions produced errors of <0.5% in the J value. The samples were analyzed by T o m U l l r i c h on March 5, 2006, at the Noble Gas Laboratory, Pacific Centre for Isotopic and Geochemical Research, University of British Columbia, Vancouver, B C , Canada. The mineral separates were step-heated at incrementally higher powers in the defocused beam of a 10W C O 2 laser (New Wave Research M I R 1 0 ) until fused. The gas evolved from each step was analyzed by a V G 5 4 0 0 mass spectrometer equipped with an ion-counting electron multiplier. A l l measurements were corrected for total system blank, mass spectrometer sensitivity, mass  63  discrimination, radioactive decay during and subsequent to irradiation, as well as interfering A r from atmospheric contamination and the irradiation o f C a , CI and K (Isotope production ratios: ( Ar/ Ar) =0.0302±0.00006, ( Ar/ Ar) =1416.4±0.5, 40  39  37  K  39  Ca  ( Ar/ Ar) =0.3952±0.0004, Ca/K=1.83±0.01( Ar / Ar ).). 36  39  37  Ca  Ca  39  K  4.5.2 Results The data indicate a cooling age o f 177 ± 15 M a for the sample C 3 , based on an inverse isochron calculation (Figs. 35 and 36), and a minimum age o f 160.1 ±1.3 M a for the sample C4. The C 4 spectrum graph shows no plateau (Fig. 37 and Tables 5, 6) and the age o f 160.1 + 1.3 M a is an integrated age, which is equivalent to a conventional K - A r age (J.K. Mortensen, personal communication, 2006).  Mcgl-5-C1 Biotite  data-point error ellipses are 2a  0.00036  Age 4 0  0.00032  = 177±15 M a Ar/  3 6  A r =780  M S W D = 2.0  0.00028  36 40  Ar Ar  0.00024  0.00020  0.00016 0.077  0.079  0.081  0.083 3 9  0.085  0.087  0.089  Ar/ Ar 4 0  Figure 35. Inverse isochron calculation for the sample C 3 .  64  Mcgl-5-C1 Biotite box heights are 2a  Plateau steps are filled, rejected steps are open  300  CO  200  a> < 100  20  Cumulative  80  60  40  3 9  100  A r Percent  Figure 36. Spectrum graph for the sample C 3 . The plateau does not have a set of stages with the same age indicating a wide age range.  Mgcl-4-C4  400  Plateau steps are filled, rejected steps are open  box heights are 2u  300  ns 200  ro  <  100  20  60  40  80  100  39  Cumulative  A r Percent  Figure 37. Spectrum graph for the sample C 4 shows no plateau and indicate a minimum age of 160.1 ± 1.3 M a .  65  Table 5. Mcgl-5-C1  Biotite  Laser Power(%)  Isotope Ratios 40Ar/39Ar  38Ar/39Ar  37Ar/39Ar  36Ar/39Ar  Ca/K  Cl/K  % 4 0 A r atm  f 39Ar  40Ar*/39ArK  Age  2 2.1 2.2  4 0 . 5 2 1 ±0.067 19.155 0.005 14.408 0.006  0.085±0.059 0.051 0 . 0 2 3 0.043 0.027  0 084±0.067 0 047 0.020 0 0 4 2 0.022  0.142±0.060 0.053 0.019  0 208 0 116 0 102  0.01 0.006  103.65 82.67 51.87  4.85 8.02 4.91  -1.506±3.064  -29.56±60.62 62.75 5.63 128.97 3.24  12.875 0.005  0.040 0.023 0.037 0.022 0.037 0.019  0 031 0 037 0 044 0 071  0.020 0.020 0.023 0.018  0.011 0 . 0 2 5 0.005 0.031  0.006 0.005 0.005 0.005  24.4 11.61  0.004 0.046 0 . 0 0 4 0.031  0 076 0 091 0 108 0 176  8.81 9.21  17.75 13.1 6.54 12.99  9.683 0.096 10.885 0.069 11.111 0 . 0 7 1 11.366 0.062  0.003 0.027  0 488  0.005  7.98  13.47  11.225 0.055  0 3 3 6 0.015 0 351 0.013 0 554 0.015  0.003 0.062 0.003 0.082 0.003 0.075  0 828 0 865 1 367  0.005 0.005 0.005  7.1 6.4  5.95 6.76  10.914 0.080 10.752 0.082  3.7  0.021 0.023 0.018 0.042  0 198 0.014  11.836 0.005 11.568 0.004 11.510 0.005  0.038 0.036 0.036 0.037  6.46  4.09  4  11.685 0.007  0.041 0 . 0 5 0  1 191.0.016  0.005 0.153  2 939  0.006  8.76  1.58  Total/Average  14.300±0.004  0.042±0.004  0 194±0.002  0.017±0.011  100  10.760±0.078  2.4 2.5 2.6 2.8 3 3.2 3.4  12.381 0.005 12.272 0.004 12.584 0.004 12.261 0.004  0.038 0.014  J=  0.010787±0.000016  Volume 39ArK =  835.68  Integrated D a t e =  0.025 0.023  0.006  0.006  3.281 0 . 2 9 9 6.870 0.179  179.23 200.29  1.69 1.21 1.24  204.22 208.65 206.21  1.07 0.96  10.666 0.083  200.79 197.97 196.47  1.39 1.42 1.46  10.463 0.220  192.92 3.85  173.59±2.75  Volumes are 1E-13 c m 3 N P T N e u t r o n flux m o n i t o r s : 2 8 . 0 2 M a F C s ( R e n n e et al., 1 9 9 8 ) Isotope production ratios: (40Ar/39Ar)K=0.0302, ( 3 7 A r / 3 9 A r ) C a = 1 4 1 6 . 4 3 0 6 , ( 3 6 A r / 3 9 A r ) C a = 0 . 3 9 5 2 , C a / K = 1 . 8 3 ( 3 7 A r C a / 3 9 A r K ) .  Table 6. Mcgl-4-C4  Biotite  Laser Power(%)  Isotope Ratios 40Ar/39Ar  38Ar/39Ar  1.8  37Ar/39Ar  36Ar/39Ar  Ca/K  Cl/K  % 4 0 A r atm  f 39Ar  40Ar*/39ArK  Age  148.15 100.03  0  61.664149.686  920.221580.81  0.38 0.38 6.36  -0.109 4.452 2.870 1.383 1.407 0.279  -2.13 86.77 55.02 26.11  9.81 12.05  1.898 0 . 1 7 0  27.19 36.58  4.858 0.331 7.537 0.191  92.19 6.12 141.07 3.43  9.361 0 . 1 8 0  173.60 3.19 203.14 3.19 210.96 2.50 2 1 5 . 0 2 1.64 2 3 8 . 3 4 1.64 2 3 7 . 5 7 1.49  2 7 0 . 9 3 1 ±0.355  0.686±0.625  1.107±0.548  1.23710.390  -1.071  -0.101  2 2.1  266.347 0.009 71.536 0.010  0.471 0.025  0.900 0.018 0.233 0.022  2.3 2.5 2.7  0.715 0.021 0.610 0.029 0.272 0.014  1.854 1.58 0.698  0.068 0.015 0.006  10.166 0.008 13.769 0.023  0.348  0.004 0.003  2.9 3.1 3.2 3.3  16.730 0.005  11.547 0.016 12.214 0.016 0.015 0.007 0.006 0.006 0.005  0.123 0.050 0.048 0.019 0.036 0.016 0.034 0.035 0 . 0 2 9 0.031 0.028 0.020 0.026 0.022 0.025 0.030  0.136 0.016 0.124 0.032 0.110 0.028 0.144 0.025  0.052 0.018 0.028 0.021 0.030 0.032 0.013 0.032  0.318 0.282  0.010 0.026  0.37 1.196 2.798 4.206 4.607  0.032 0.049 0.025 0.027  0.466 0.023 1.088 0 . 0 1 4 1.636 0.014 1.777 0 . 0 1 3  0.005 0.005 0.005 0.005  0.027 0.081 0.039 0.029  3.5 3.8 4.1  12.608 12.824 12.942 14.427 14.616  4.5  14.735 0.005  0.028 0.023 0.029 0.056  1.837 0 . 0 1 3 4.329 0.013  0.006 0.033 0.010 0.047  Total/Average  14.233±0.002  0.032±0.004  1.092±0.003  0.019±0.004  j=  0.01079110.000016  Volume 39ArK=  1018.17  Integrated D a t e =  0.002 0.002 0.002 0.003 0.003 0.003  64.42 34.26 22.95 11.99 9.63 9.02 9.05 10.37 16.34  0.001  9.23 14.33 12.93 3.48  11.045 0.183 11.495 0 . 1 4 4  9.63 14.02 5.29  11.730 13.088 13.043  2.11  12.243 0.157  100  13.0761 0.035  160.9111.28  V o l u m e s are 1 E - 1 3 c m 3 N P T N e u t r o n flux m o n i t o r s : 2 8 . 0 2 M a F C s ( R e n n e et a l . , 1998) Isotope production ratios: (40Ar/39Ar)K=0.0302, (37Ar/39Ar)Ca=1416.4306,  ON  4.766 11.283  0.003 0.003  95.96 91.39 80.97  (36Ar/39Ar)Ca=0.3952,  Ca/K=1.83(37ArCa/39ArK).  0.095 0.096 0.087  223.87  5.36 3.25  2.71  4.8 S u m m a r y :  Following is a summary of the isotopic dating of three sandstone and two granitic clasts and their stratigraphic position, compared to their biostratigraphic age control. Early Jurassic zonal time scale is from Palfy et al., (2000).  1. Sandstone samples SI: •  Isotopic age of the detrital Zircon: 189.6 ± 1.0 Ma  •  Sedimentation age (ammonite biochronological age): Kunae Zone: 185.7 ^  to  184.1 _H +  2. Sandstone samples S2: •  Isotopic age of the detrital Zircon: 184.4 ± 1.2 Ma  •  Sedimentation age (ammonite biochronological age): Planulata Zone: ~182 Ma (older than 184.4 ± 1.2 Ma and younger than 183.6 _\ ; Figure 11). +  7  3. Sandstone samples S3: •  Isotopic age of the detrital zircon: 184.4 ± 1.0 Ma  •  Sedimentation age (ammonite biochronological age): Hillebrandti Zone: -181 Ma (older than 181.4 ± 1.2 Ma and younger than 180.1 _° l; Figure 11). +  3  4. Plutonic clast sample CI: •  Isotopic age of the clast (crystallization date): 186.6±0.5 Ma  68  •  Sedimentation age (ammonite biochronological age): Planulata Zone: -182 Ma  5.  Plutonic clast sample C2:  •  Radiometric age of the clast (crystallization date): 221+1 Ma  •  Sedimentation age (ammonite biochronological age): Planulata Zone: -182 Ma  See table 7 for a summary o f the results. Enclosing bed age and the detrital zircon age are either small (< 5 m.y.) or not measurably different, suggesting rapid rates of pluton unroofing. This may be explained by relatively shallow angle of plate subduction resulting in shallow pluton intrusion.  '1 oa rcian  Stage  Pliensbachian  Samples  SI  S2  CI  C2  S3  A ) Age o f enclosing bed (Zone mean, Palfy et al., 2000)  Kunae  Planulata  Planulata  Planulata  185.7 S i  183.6:;  183.6:;  183.6:;  Ma  Ma  Ma  Ma  Hillebrandti 181.4+1.2 Ma  189.6±1 M a  184.4±1.2 Ma  186.6±0.5 Ma  221±1 Ma  184.4±1 Ma  186±2 M a  175±5 M a  186±0.4 Ma  220.2+0.6 Ma  179±5 M a  B) Mean age o f detrital components  C) M i n i m u m age o f detrital components  7  7  7  Table 7. A summary of the chronological results and an estimate for the hiatus between emplacement (crystallization age), uplift, unroofing and erosion o f igneous source area(s) and depositional age for enclosing sediments. Note small differences in millions of years.  69  Results from biochronological/geochronological studies are plotted on the Jurassic time scale (after Palfy et al., 2000) to illustrate the near contemporaneity between the arc uplift and/or dissection and deposition into the Whitehorse Trough (Table 8).  70  Jurassic time scale  Ma  -1.8  140 145  TTH  CD  CD  ro oo  CO  oo  150 +3.8/-3.3  155  OXF  +11  BTH  AAL TOA  -7.9 +1 2  CM OO  ro  ro  m c ro  CD 03  Ma  c 185 190  -4.'  HET'  c ro  ro ro  0J  -1.1  PLB SIN  IT) 00  180  CD  CM 00  1^  175  -1.5 + 1.0  i CD CO  c ro  170  BAJ  ro o_  CD in c CD  OO + I  184"4 Ma  186./ Ma 189 6 Ma  186.6 Ma •  •  + i  C  Q_ I  165  -5 6 -3.8  ro  ro  160  a 5  •4—1  C  +3.1/-5.1  CLV.  ro  ro  Cgl-1  | I * " . ' 1844 Ma • S.b.Cgl-1  73 C  ro CD  ro </) o  CJ CO CO  ro <% J ; S.J-1 I :  S Cg!-f  H.9  195  -5.7 1  LEGEND 185.7 M a  J jg) Biochronological age control o f the bed (number and error bars are examples)  189.6 M a  J + I  Geochronological age control of the clast/grain (number and error bars are examples) T i m e difference between geochronological (crystallization) and biochronological ( s e d i m e n t a t i o n ) age c o n t r o l s  Table 8 . Geochronological and biochronological results plotted on the Jurassic time scale. The Jurassic time scale is from Palfy et al., (2000). Numbers i n blue and red are from the present study.  71  CHAPTER V CONGLOMERATE ANALYSES  5.1 Introduction: Five conglomerate units are recognized i n about 3000-meters o f conglomerate, sandstone, siltstone, and mudstone which constitute the Laberge Group and a probable Bowser Lake Group in the study area (Figs. 26 and 38). Takwahoni Formation conglomerates and conglomeratic beds were studied i n detail to provide data on provenance relationships and temporal trends i n arc dissection. Quantitative data were collected i n the field and include clast counts, modal clast size, and maximum clast size determinations. Only basic lithologic divisions (sedimentary, volcanic, porphyry, plutonic and metamorphic) were used for the purposes o f clast counts. The high-resolution age control on these units provides an opportunity for documenting any temporal trends i n clast lithologies.  5.2 Conglomerate Units: In stratigraphically ascending order, conglomerate units in the Lisadele Lake sequence contain a predominance o f sedimentary, volcanic, plutonic, metamorphic, and chert clasts (Mihalynuk et al., 1999). Distinctive clast populations permit subdivision o f conglomerate into five map able units:  72  ExSilu  Samples  In Situ  Localities  18  JEK)  17 16 15  14 E9  13  12 11 • 10 •  9  •  8  • . • -  7 6 5 4  . -  3 2.1  .  2  lES-8  JE2-4 El  -  I  ei.Jl MIC Ivl  P  Iclvola-vil  1  • . Kanense Zone  Figure 38. Lithostratigraphy, fossil localities and conglomerate units of Lisadele Lake section. See Figure 16 for legends and Figure 13 for the fauna present. The locality numbers and their correlative G S C localities are listed in Appendix 1. ^  5.2.1 Conglomerate Unit 1: The lowermost five metres of the Takwahoni Formation consists of poorly sorted, matrixsupported limestone-pebble to cobble (5mm-205mm) breccia and conglomerate. The matrix consists of reddish-brown weathering sand and siltstone, whereas the poorly sorted sub-angular to angular clasts weather a distinctive white to light grey color (Fig. 39). They seem to be in situ intraclastics with an entirely intrabasinal origin. The age o f the lowest conglomerate is poorly constrained. It is conformably overlain by conglomerate unit 2 and unconformably overlies the Sinwa Formation. It is tentatively considered to be of probable Sinemurian age by analogy with the succession exposed in the A t l i n Lake area (Johannson et al., 1997), and correlative unit of Upper Sinemurian age in the Cry Lake map area (104 I). See chapter 7 for correlation data and charts.  Figure 39. Unit 1: Lower Jurassic poorly sorted sub-angular to angular limestone breccia.  74  5.2.2 Conglomerate Unit 2: Within the Lisadele Lake area, the thickness of this unit varies between 100-160 meters. The channelized conglomerates are pebble to cobble (10-80mm) white-grey weathering, moderately to well sorted and contain dominantly volcanic clasts which are sub-rounded to rounded (Fig. 40). Some o f the conglomeratic beds contain yellow weathering; highly oxidized clasts (Fig. 41) Bioclastic coarse-grained sandstone, greywacke, siltstone, and mudstone are the other components o f this stratigraphic unit. Clast lithologies are intermediate to felsic volcanic rocks, dominated by dark grey and green weathering feldspar porphyries. Felsic volcanic rocks may have been locally produced late in the arcbuilding process, and were among the first to have been eroded. Biochronological age control has been difficult to obtain but Mihalynuk et al. (1999), reported a Lower Pliensbachian Metaderoceras from just above the unit.  Figure 40. Channelized Lower Jurassic (Sinemurian/Pliensbachian?) conglomerate of Unit 2, dominated by volcanic rock clasts. 75  Figure 41. Y e l l o w weathering, highly oxidized clasts in the conglomerate unit 2.  5.2.3 Conglomerate Unit 3: Unit 3 is the thickest conglomerate unit (approximately 1200 m thick) and is dominated by plutonic, pebble to boulder-sized clasts (5-400 mm, up to 2 meter). The conglomerates are poorly sorted but the large clasts show high sphericity (Fig. 42); normal and locally reversed grading is evident. Common clast lithologies include leucogranite, diorite, monzonite and quartz monzonite. Intermediate to felsic volcanic rocks are minor components and carbonate sedimentary clasts, possibly derived from the Sinwa  76  Formation, are rare. Thin-bedded sandstone layers contain locally abundant, fragmented plant fossils. Plant fossils are also locally abundant in sandstone interbeds indicating shallow water deposition and periodic rapid sedimentation rates, which locally exceeded subsidence rates (e.g. Dickie and Hein, 1995) (Fig. 43). The age of unit 3 is constrained by 12 ammonite collections, distributed fairly evenly from 250 to 1350 metres above the base of the section, ranging from Upper Pliensbachian to Middle Toarcian. The lowest locality is a few metres below the base o f the unit 3. The 5 localities interbedded with the lower part of conglomerate unit 3 yield typical Upper Pliensbachian ammonites belonging to the genera Fanninoceras, Arieticeras, Fuciniceras, Reynesoceras and Fontanelliceras. The upper seven localities within unit 3 yield Lower and Middle Toarcian species of the genera Cleviceras, Harpoceras, Dactylioceras, Leukadiella, Hildaites, and Phymatoceras.  Figure 42. Unit 3: Pliensbachian-Toarcian well-rounded cobble-boulder conglomerates, rich in plutonic clasts. 77  Figure 43. Thin-bedded sandstone layers locally abundant in fragmented plant fossils.  5.2.4 Conglomerate Unit 4: Conglomerate in unit 4 is about 200 metres thick and contains abundant metamorphic rock clasts. The conglomerate beds within unit 4 are less dominant than in unit 3 but locally reach thicknesses of about 30 metres. They contain pebble to cobble sized (10100mm) clasts that are white or light to dark grey in colour and set in a dark matrix that is locally orange to brown-orange (Fig. 44). Clasts are dominated by metamorphic, and to a lesser extent, plutonic rocks. The clasts are poorly sorted and well rounded with local current-generated imbrications, suggesting northeast-directed paleocurrents. The upper parts of unit 4 display well-sorted pebble to cobble (mainly 10-15mm, maximum size up to 70mm) conglomerates interbedded with brown to light grey coarse-  78  grained sandstone (Fig. 45). Quartz-rich schist and gneiss clasts are the most common lithologies. For example, microscopic study of sample C4 ( M . C g l - 4 - C 4 ) indicate that it is a foliated gneiss, containing about 60-65% quartz, 20-25% feldspar, 15-20% biotite, and about 5 % muscovite with common presence of epidote as the accessory mineral. Augen texture is also common in the quartz grains, indicating strong deformation during metamorphism (Figs. 46a and 46b). Some of the clasts yield garnet crystals (Fig. 47). Possible provenance affinities include the potential Early Jurassic linkage with the Nisling Assemblage, which was supported by similar observations in the Tagish Lake (Currie and Parrish, 1993) and Y u k o n areas (Hart and Pelletier, 1989). Previous isotopic studies on the metamorphic clasts indicate that the presence of metamorphic clasts and elevated initial Sr values in Whitehorse Trough clastic sedimentary rocks are associated with a continental source, probably Nisling or Yukon-Tanana Terrane (Hart et al., 1995). Two ammonite localities bracket conglomerate unit 4; the lower locality is approximately 200 meters below the base of the unit, and the upper one immediately overlies the upper contact. Both localities yield Upper Toarcian species of the genera Phymatoceras and  Podagrosites. In contrast to the Lisadele Lake area, the youngest Early Jurassic conglomerates in the A t l i n Lake area about 100 kilometres to the north, are of Pliensbachian age; no Toarcian rocks are present (Johannson et al., 1997). Farther to the north in the Y u k o n , Toarcian conglomerates have been recognized but metamorphic clasts are rare and granitic clasts predominate (Dickie and Hein, 1995; Hart et al., 1995).  79  Figure 4 4 . Upper Toarcian metamorphic-rich clasts conglomerate of unit 4 with orange to brown-orange matrix.  Figure 4 5 . Well-sorted pebble to cobble conglomerates of unit 4 , interbedded with brown to light grey coarse-grained sandstone. V i e w is to the northwest.  80  Figures 46a and 46b. Augen texture in a metamorphic clast sample from Upper Toarcian conglomerate (C4).  81  Figure 47. Garnet mineral in a metamorphic clast sample from Upper Toarcian conglomerate M . C g l - 4 .  5.2.5 Conglomerate Unit 5: The upper approximately 1000 metres o f the Jurassic succession at Lisadele Lake is characterized by siltstone and mudstone but the uppermost 5-10 metres of the section consists o f angular to sub-angular and well-sorted, chert-granule to pebble conglomerate. Ammonite collections from this interval include species of the genera Sonninia, Dorsetensia and Stephanoceras, indicating an Early Bajocian age. Stephanoceratids from about 20 metres below conglomerate unit 5 indicate an Early Bajocian age and Mihalynuk et al. (1999) reported Early Bajocian ammonites from within the conglomerate. Variegated chert clasts include black, dark green, white, red, and light to medium yellow varieties (Fig. 48). Mihalynuk et al. (1999) report that some clasts within this unit contain radiolarians, ranging in age from Early Permian through Early Jurassic.  82  Figure 48. Early Bajocian well-sorted chert-pebble conglomerate of unit 5.  5.3. Temporal Trends: Conglomerate pebble count data show significant compositional changes through time and indicate a strong temporal trend that represents provenance shifts (table 9). Variations of clast type with stratigraphic level (time) are illustrated in figure 49.  T A B L E 8: CLAST COUNT DATA  Plutonic  % Metamorphic  % Sedimentan  Sample No.  5  4  0  68  62  30  4  0  4  Tr.l.s.l Tr.cgl.3  Early Pliens. Late Pliensbachian. Pliensbachian - Toarcian Early Toarcian Middle Toarcian Middle Toarcian Middle Toarcian Middle Toarcian Late Toarcian  55  36  5  0  5  Tr.cgl.4  12  51  33  0  5  Cgl.d  22  32  44  0  2  Cgl.c  32  11  52  0  5  Cgl.b  32  16  47  0  5  Cgl.a  9  13  76  0  2  Cgl.l  11  22  65  0  2  Cgl.2  9 4  26 25  61 68  0 0  4 4  Cgl.3 Cgl.4  Late Toarcian  2  7  77  0  14  Cgl.5  Late Toarcian Late Toarcian Late Toarcian Early Bajocian  7 3 2  2 15 10  45 37 33  39 40 54  7 5 2  5  5  0  2  88  M.cgl.5 M.cgl.4 M.cgl.3 S.ch.5cgl  Age of I'nit  % Volcanic  Porphyry  Sinemurian?  23  Sine.-Pliens.  (v)  Table 9. Conglomerate clast count data o f Lower to Middle Jurassic conglomerate units in the Lisadele Lake area.  84  I Sedimentary (undifferentiated) i 1 1 Sedimentary (limestone-rich) 1  1  Figure 49. Graphic depiction of temporal clast trends in the Takwahoni Formation conglomerates, Lisadele Lake area. The dominant sedimentary components of the conglomerates are differentiated in this chart. Note strong provenance shifts during Early and M i d d l e Jurassic time.  Ternary plots of clast composition (Fig. 50) show the predominant clast composition within the Takwahoni Formation conglomerates. It reflects significant trend shifts, which are consistent with uplift and unroofing o f sedimentary coastal and shelf deposits, volcanic arc cover, deep batholiths within the volcanic arc complex, and finally a deeper metamorphic source in the lower crust (arc), and/or in the affinity of the subduction zone.  85  Sedimentary clasts  Volcanic clasts  Plutonic clasts Early Jurassic (Sinemurian?) ilv Jurassic (Sinem./Pliens.*. arly Jurassic (Early Plieus.? Late Pliensbachian (Carlottense Z.) ,ate Pliensbachian (Carlottense Z.)  iddle Toarcian (Planulata M i d d l e Toarcian (Planulata Z.) M i d d l e / Late Toarcian Late Toarcian (Hillebrandti Z.) Late Toarcian (Hillebrandti Z.) Figure 50. S P V ternary diagram of Takwahoni Formation conglomerate. Poles represent clast modes for plutonic (P), volcanic (V), and combined sedimentary (S) clasts.  86  5.4 P r o v e n a n c e :  5.4.1 Limestone Clasts: The limestone sedimentary clasts in the base of the Takwahoni Formation were produced probably during the development of the erosional unconformity on the carbonate shelf and margins of the Whitehorse Trough (recorded in the Sinwa Formation) during earliest Jurassic (Sinemurian?) time.  5.4.2 Volcanic Clasts: The volcanic rocks, which may have been produced in the arc-building processes, were the next source to have been eroded. The volcanic rich clast conglomerates indicate a gradual increase in the percentage of the porphyry volcanics, probably due to deeper exhumation of the arc. It could be considered as a transitional stage from a volcanogenic provenance to a dissected (plutonic roots) arc provenance.  5.4.3 Plutonic Clasts: The large volume of granitic clasts in the Lower Jurassic Laberge Group strata infers the extensive exposure o f the comagmatic plutons as the source. Accelerated uplift, accompanied with intra-arc strike-slip faults probably were important factors in this distinct depositional episode. The effect of the intra-arc strike-slip faulting has also been documented in A t l i n Lake area to the north (Johannson, 1994; Johannson et al., 1997).  87  5.4.4 Metamorphic Clasts: The presence and abundance of metamorphic clasts in Lower Jurassic conglomerates of Takwahoni Formation is unique to the Lisadele Lake area. They made up to 5 0 % of the clasts in the Upper Toarcian conglomerates, whereas they rarely exceed 1-2% in the Y u k o n area (Hart et al., 1995). Hart et al. (1995) showed that in the Y u k o n area, elevated initial Sr values in Whitehorse Trough elastics indicate a continental source, probably N i s l i n g or Yukon-Tanana Terane.  5.4.5 Chert Clasts: The obduction of the Cache Creek Terrane, in the final stages of basin closure, caused the erosion and influx chert-rich materials into the Whitehorse Trough. The obducted Cache Creek Terrane was the main source of coarse clastic siliceous materials, supplying the adjacent basin(s) in Middle Jurassic time. This important unit, and probably parts of the underlying Bajocian thick shale and argillite beds are tentatively placed in the Bowser Lake Group.  88  CHAPTER VI SANDSTONE PETROGRAPHY 6.1 Introduction: Petrographical analysis o f clastic sedimentary rocks are important because it provides a record o f the source regions uplifted and eroded during orogeny (Dickinson et al., 1983). The sedimentary fill o f arc-marginal basin may record tectonic evolution and phases o f arc growth and erosion in island arc systems. A detailed petrographic study o f the sedimentary rocks, and here particularly the sandstones, is a fundamental tool for unraveling complex arc-basin history and paleotectonic reconstruction. In addition, it is critical to have a good biostratigraphic control on the depositional episodes and sedimentary regimes (Fig. 51).  The QFL Distribution Of Sedimentary Rocks In Various Tectonic Regimes  Figure 51. The Quartz, Feldspar, Lithic components of sedimentary rocks i n various tectonic settings. Modified after Dickinson and Suczek (1979), by courtesy o f Fichter (2006).  89  Ammonite collections from the study area provide the age control necessary for the definition of temporal petrofacies. More than 40 ammonite collections representing Late Triassic to Middle Jurassic time were obtained across the section and many of them were determined to zonal stratigraphic resolutions as detailed in Chapter 3.  6.2 Methods: Petrographic analysis of Late Triassic to Middle Jurassic sandstones was conducted to delineate the depositional episodes in the context of Early and Middle Jurassic arc evolution in northwestern British Columbia and to refine trends of clast type with time noted in the study of conglomerate units. Samples were collected across the succession in the Lisadele Lake area from all stratigraphic levels (Table 10). The Gazzi-Dickinson method of point counting was followed, where sand-sized crystals included in lithic fragments are counted as the mineral component to overcome the effect of grain size (Ingersoll et al., 1984). Point counting was conducted to calculate the percentage of quartz, feldspar, and lithic fragments in the sandstones. When a modal analysis of a thin section is made, there is obviously a relationship between the number of points counted and the accuracy of the result (Van Der Plas and Tobi, 1965). To obtain statistically reliable results a total of between 200-250 points were randomly counted for each thin section. However, due to the infrequency of sandstones in the dominantly conglomeratic Takwahoni Formation, it was difficult to always obtain samples that had an ideal, w e l l sorted grain size distribution. Sandstones with medium to coarse grain sizes were selected  90  for point counting and although the results are consistent with the conglomerate analyses, a more detailed microscopic study remains to be done.  Recalculated parameters in percentage Figure Label  Sample No.  Age  1  1  Sandstone name  Q%  F%  1,%  1  FS-06-SS-1  Late Triassic, Norian  Lithic arkose  4  52  44  2  FS-06-SS-2  Sine./Plien.?  Arkose  10  70  20  3  FS-06-SS-3  Early Plien.?  Arkose  48  40  12  4  FS-06-SS-4  Arkose  43  58  9  5  FS-06-SS-5  25  35  FS-06-SS-6  Feldspathic litharenite Lithic arkose  40  6  43  35  22  7  FS-06-SS-7  Lithic arkose  40  33  27  8  FS-06-SS-8  Arkose  52  40  8  9  FS-06-SS-9  Late Plien.- Carlottense Zone Late Plien.- Carlottense Zone Middle Toar.- Planulata Zone Middle Toar.- Planulata Zone Late Toar.- Hillebrandti Zone Late Toar./ Aalenian?  51  19  30  10  FS-06-SS-10  Late Toar./ Aalenian?  60  12  28  11  FS-06-SS-11  Early Bajocian  59  21  20  12  FS-06-SS-12  Early Bajocian  Feldspathic litharenite Feldspathic litharenite Feldspathic litharenite Lithic arkose  60  25  15  13  FS-06-SS-13  Early Bajocian  Lithic arkose  61  30  9  14  FS-06-SS-14  Early Bajocian  Litharenite  37  5  58  Q = Quartz F = Feldspar L = Lithics Table 10. Point count data from Lisadele Lake sandstones. A g e assignments: Sine. = Sinemurian; Pliens. = Pliensbachian; Toar. = Toarcian. See figures 16-25 for the stratigraphic location of the sandstones (shown by figure label).  91  6.3 A n a l y s e s : Sandstones i n the study area were classified using the widely-used scheme o f F o l k (1974). Fig. 52 shows Folk classification (1974) of the clastic rocks containing less than 15% fine-grained matrix. Thin-sections cut from 14 sandstone samples whose biostratigraphic position is w e l l known represent the Upper Triassic, Lower Jurassic, and lower Middle Jurassic strata in the study area. One sample is collected from Upper Triassic strata (sample number F S 0 6 - S S - l ) ; two samples are interpreted to be of Early Jurassic, possibly Sinemurian/Pliensbachian age (samples number FS-06-SS-2,3); two samples of Late Pliensbachian age (samples number FS-06-SS-4,5); two samples of Middle Toarcian age (samples number FS-06-SS-6,7); three samples of Late Toarcian age (samples number FS-06-SS-8-10); and four samples of Middle Jurassic (Early Bajocian) age (samples number F S - 0 6 - S S - 11-14). Proportions of quartz, feldspar, and lithic fragment components of the sandstones are shown in figure 53. See figure 54 for the inferred stratigraphic setting of modally analyzed samples. Takwahoni Formation sandstones are both texturally and compositionally immature. The textural immaturity is shown by the moderate to poor sorting, angular to sub-rounded grains, and the common presence of matrix (although less than 15%). The sandstones are compositionally dominated by feldspar and quartz, with variable amounts o f lithic fragments.  92  Q  3:1  1:1  1:3  Figure 52 (above). Sandstone classification scheme modified after Folk (1974). Q=Quartz, F=Feldspar, L=Lithic fragments. Figure 53 (below). Petrographic names assigned to the sandstone samples. The sample numbers are circled (e.g.,(H= sample number FS-06-SS-1). 93  Q Recycled Orogen  SAM1M i  :  AGE  L a t e Triassic  PETROFACIES  SAMPI.K  ©  AGE  Late Toarc.  PETROFACIES  B  Late Toarc/Aalen.?  Sine./Pliens.?  %  Early Pliens.  ®  Late Toarc/Aalen.?  O  Late Pliens.  CD  Early Bajocian  0  Late Pliens.  0  Middle Toarc.  ©  Middle Toarc.  C  Early Bajocian  ®  Early Bajocian Early Bajocian  Figure 54. Q F L ternary diagrams o f Takwahoni Formation sandstones. Poles represent total detrital modes for quartz (Q), feldspar (F), and lithic fragments (L). Tectonic discrimination fields indicate sandstone provenance (from Dickinson et al., 1983).  94  6.4 Tectonic setting: The relative proportions of lithic fragments, feldspar, and quartz in clastic sediments have been used to deduce the tectonic setting of deposition and provenance in other basinal strata (Dickinson et al., 1983; Marsaglia and Ingersoll, 1992). Ternary diagram of the succession's detrital modes graphically illustrates strong temporal trends. It indicates a complex arc-basin evolution and reveals significant tectonic and magmatic events in the evolution o f northern Stikinia during the Early and Middle Jurassic. Results were plotted on the ternary tectonic discrimination diagram (Dickinson et al., 1983), showing fields for three sandstone petrofacies (A, B, and C, fig. 54).  6.4.1 Petrofacies A: Upper Triassic and Lower Jurassic (Sinemurian/ Pliensbachian) sandstones (samples F S 0 6 - S S - l , 2) show a l o w proportion o f quartz grains, while feldspars are dominant. This petrofacies fits into "Transitional A r c " field.  6.4.2 Petrofacies B: Upper Pliensbachian and Toarcian sandstones (samples FS-06-SS-3-8): indicates a gradual increase in the percentage of quartz grains, moving from a "Transitional A r c " field to a "Dissected A r c " field.  6.4.3 Petrofacies C: Upper Toarcian and Lower Bajocian sandstones (samples FS-06-SS-9-14): rocks contain mainly feldspar and quartz fragments, although, the percentage of lithic fragments is  95  slightly increased. Sample number FS-06-SS-14 shows the highest percentage of lithic fragments in the Lower Bajocian sandstones of the Lisadele Lake succession. This petrofacies falls within the "Recycled Orogen" field, suggesting the latest stages of terrane collision and basin closure (Fig. 54). Detrital components of the sandstones and conglomerates suggest they were derived by unroofing and dissection of an arc/ basin system related to collisional events.  96  CHAPTER VII SUMMARY AND CONCLUSIONS 7.1 Biochronology and Biostratigraphy: Ammonite biochronology constrains Takwahoni Formation and probable Bowser Lake Group strata i n the Lisadele Lake area to an age range between Pliensbachian and Early Bajocian i n age, with all stages except for the Aalenian definitely represented (Fig. 55). Chert-pebble conglomerate deposited i n the Early Bajocian yields a minimum age for the obduction of the Cache Creek Terrane (Mihalynuk et a l , 1999). This age control has significant implications on terrane interaction, basin closure and collisional events i n northwestern British Columbia during Early and Middle Jurassic. In addition, correlation o f depositional and tectonic events between the Lisadele Lake area and other parts of the Whitehorse Trough indicate: 1) a similar age range for the Laberge Group in the Y u k o n and 2) a shorter age range o f Sinemurian to Early Pliensbachian (but with the top of the Group is probably not exposed) in the A t l i n Lake area between Lisadele Lake and Y u k o n (Fig. 56). In this study, we found the first record of the Middle Jurassic Tethyan ammonite Leukadiella in the Lisadele Lake area. This contradicts the observation o f Mihalynuk et al. (1999; 2004) that the Whitehorse Trough was isolated except to the north, the source of Boreal (cooler water) ammonites during the Toarcian.  97  Unit 5  Figure 5 5 . Panoramic picture of the L o w e r and Middle Jurassic succession and the conglomerate units in the Lisadele area. The indicates the location of camp. V i e w is to the southeast.  Atlin  Tulsequah  Yukon  Chert-Pebble conglomerate Metamorphic-rich clast conglomerate Plutonic-rich clast conglomerate Volcanic-rich clast conglomerate Limestone conglomerate and breccia Pebbly sandstone Mudstone Siltstone, mudstone, sandstone Conglomerate  ]  Sandstone N o sedimentation  I ' l l  Limestone  Figure 56. Stratigraphy of Laberge and Bowser Lake groups within the Whitehorse Trough. B L G = Bowser L a k e Group. A t l i n area: Johannson et al., 1997; Yukon area: Hart et al., 1995; Tulsequah area: Present study. 99  7.2 Correlation: The inception of the Bowser Basin in the Spatsizi area is marked by a shale-dominated phase, namely the A b o u Formation (Aalenian) overlain by the fine-grained Quock Formation (Lower Bajocian) both of the Spatsizi Group (Ricketts et al., 1992). This succession is separated from the overlying Bowser Lake Group (the Ashman Formation) of Bathonian age by a slight angular unconformity (Thomson et al., 1986). The Ashman Formation is a characteristically thick (more than 300 meters) sequence that passes from shale at the base, upwards into sandstone and chert-pebble conglomerate (Tipper and Richards, 1976). The Ashman Formation is at least 500 meters in the Spatsizi area (Evenchick and Thorkelson, 2005) and at least 300 meters in the Smithers and Hazelton areas (Tipper and Richards, 1976). Another exposure o f the Bowser Lake Group occurs in the footwall o f the K i n g Salmon Fault in the Cry Lake map area where there is a similar lithological package: shaledominated strata of the Early Bajocian age overlain by thick chert-pebble conglomerate (Gabrielse, 1998; Evenchick and Thorkelson, 2005). Gabrielse (1998) suggested an age range of Bajocian-Callovian for the Bowser Lake Group in the Cry Lake map area. In the Lisadele Lake area chert-pebble conglomerate (conglomerate unit 5) and the underlying shale/siltstone in the upper part of the succession is lithologically similar to the Ashman Formation whose locus of sedimentation is to the south in central Stikinia (Bowser Basin). Significantly, the Early Bajocian age of this unit in the Lisadele Lake area is older than its correlatives to the south in the Spatsizi, Smithers and Hazelton areas where they are only as old as Bathonian (Tipper and Richards, 1976; Gabrielse and Tipper, 1984).  100  Chert-pebble conglomerate of the Bowser Lake Group is an important unit that marks the beginning of the Stikinia and Cache Creek amalgamation. It reflects the influx of chert into the basin in response to the collisional events and the subaerial exposure o f Cache Creek rocks in the upper plate. The diachronism with younging to the south suggests that the obduction of the Cache Creek terrane (resulting in deposition of chert-pebble conglomerates) started in the Tulsequah and Y u k o n (?) areas to the north in the Early Bajocian. It continued toward south and constituted the lower parts of the Bowser Lake Group strata (Ashman Formation) during the Bathonian-Callovian.  101  Estimated geographic location of the sections Spatsi/i m a p area  (B)  C r y L a k e m a p area Tulsequah m a p area  Terranes m  ST (Stikinia) | QN (Quesnellia) | CC (Cache Creek)  Jurassic Sedimentary Basins Bowser Basin ] Whitehorse Trough (Takwahoni facies) | Whitehorse Trough (Inklin facies) F i g u r e 57. E s t i m a t e d g e o g r a p h i c l o c a t i o n o f the sections i n F i g u r e 58.  Limestone conglomerate Stuhini volcanics Sinwa Limestone  Rhyolite, breccia Sandstone, siltstone Conglomerate  Dark shale and mudstone Shale, calcareous concretions Resistant grey sandstone  Chert-pebble conglomerate 'VS/WVSA  1-5  200 m vertical ^ • • ^ scale  Unconformity Conglomeratic units  F i g u r e 5 8 . C o r r e l a t i o n o f J u r a s s i c r o c k s o f the T u l s e q u a h m a p area w i t h S p a t s i z i a n d C r y L a k e areas.  103  7.3 Geochronology: The Laberge Group and its correlatives within the Whitehorse Trough provide many lines of evidence that indicate rapid uplift, exhumation, and deposition of the arc during the Early and early Middle Jurassic. The U - P b age o f the granitic clasts in two conglomeratic beds and the biostratigraphically identified depositional age of fine-grained sedimentary rocks interlayered with these conglomerates suggests intrusion in the arc, rapid uplift, exhumation and deposition in as little as five million years. The mid-Pliensbachian age (186.6 ± 0.5 Ma) of a granitic clast collected from a Planulata Zone age (Middle Toarcian) conglomerate is significant. A s well, the SinemurianPliensbachian age (189.6 ± 1 Ma) of detrital zircons collected from a Kunae Zone age sandstone, and the Late Pliensbachian age (184.4 ±1.2 Ma) of detrital zircons collected from a Planulata Zone age sandstone suggest a single main source and very rapid uplift and erosion. The smallest time difference between the age of crystallization, and the age of the sedimentation (< 2.5 million years), was seen in Planulata Zone. However, more geochronological data are needed to provide information about relative rates of unroofing within the Early Jurassic. These data contradict the suggestion of Hart et al. (1995) that plutons dated 192 M a or younger could not have been sources for Pliensbachian sediments. There is also evidence of provenance from Late Triassic (221 ± 1 Ma) plutons in Middle Toarcian conglomerates of the Takwahoni Formation.  104  7.4 Depositional and tectonic setting: The Whitehorse Trough saw a change in depositional setting from shallow marine carbonate facies in the Late Triassic to coarse-grained clastic facies in the Early Jurassic. The uplift probably began during the latest Triassic-earliest Jurassic (Fig. 59). It affected the frontal arc and resulted in extensive erosion and deep incision of the shelf deposits. Very rapid uplift produced a Lower Jurassic erosional disconformity into Late Triassic arc and arc-flanking shelf deposits recorded by accumulation of basal Takwahoni Formation coarse clastic rocks dominated by intra-basinal clasts that are angular and commonly composed of Upper Triassic Sinwa Limestone. The next phase of fore-arc evolution is reflected in the coarse-clastic sedimentation that indicates fore-arc subsidence from the Sinemurian/Pliensbachian to the Bajocian. It required rapid initiation o f a high-energy transport system associated with steep topographic gradients that suggests tectonic controls. Uplift of the arc and volcanism in the Early Jurassic led to the production of volcanic clast-dominated conglomerates (conglomerate unit 2), followed by plutonic clast rich conglomerates (conglomerate unit 3). Lower Jurassic plutonic boulder conglomerates required significant paleotopographic gradients to exhume the plutonic roots of the arc and to prograde the influx of coarse-grained clastic sediments into the basin. To the north, in the Y u k o n area, N i s l i n g Terrane has been considered as the source o f the metamorphic clasts (conglomerate unit 4) in the Laberge Group conglomerates (Hart et al., 1995). It is presumed that it was the source of the metamorphic clasts in the Tulsequah area as well, although, a solid reason for their much higher percentage in the study area relative to the Y u k o n remains to be answered.  105  Uplift  However, most of the Laberge Group conglomerates were deposited within deep-water settings, suggesting that the basin subsided rapidly, increasing gradients between the arc crestline and the margin of the basin. The slope enabled coarse clastic materials to bypass the drowned shelf and be deposited on the base of the slope, within deep water. This theory was first suggested for the northern part o f the Whitehorse Trough (Yukon area) by Dickie and Hein (1995) (Figs. 60a and 60b). The Middle Jurassic strata indicate a markedly different depositional environment compared to the Lower Jurassic strata. Overall lithology changes from a coarse-grained sedimentary regime to fine-grained sedimentation. Strata vary from sandstone, siltstone, and shale to argillite near the top of the section, indicating basin deepening associated with crustal flexure and/or eustatic sea-level changes (Dickie and Hein, 1995). The crustal flexure might reflect final stages of the basin closure in the Whitehorse Trough. The appearance of chert-granule to pebble conglomerate (conglomerate unit 5) at the highest stratigraphic level near the top of the succession reflects the new importance of oceanic sedimentary rocks from the Cache Creek Terrane as a source area. The uppermost chert pebble conglomerates are tentatively placed in the Bowser Lake Group. In summary, in the Lisadele Lake area, the fan-delta conglomerates and successions o f the Lower and Middle Jurassic conglomerates overlie the uppermost Triassic (Norian) carbonates of the Sinwa Formation. The large-scale trends in the facies changes indicate that the Whitehorse Trough experienced pulses of rapid uplift stages, followed by basin subsidence, and relative sea-level change during the Early and early Middle Jurassic.  107  ARC UPLIFT  Phase 1: Schematic cross-section Figure 60a: Phase 1 Cross-section and plan-map views of the dominant geographical processes interpreted for deposition of the Laberge Group. R S L = Relative Sea-Level. Modified after Dickie and Hein (1995). 108  Phase 2: Schematic plan view  RSL  Phase 2: Schematic cross-section Figure 60b: Phase 2 Cross-section and plan-map views of the dominant geographical processes interpreted for deposition of the Laberge Group. R S L = Relative Sea-Level. 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Northward displacement of north-central British Columbia; Nature, V o l . 285, pp. 289-294. Monger, J.W.H., Wheeler, J.O., Tipper, H.W., Gabrielse, H., Harms, T., Struik, L.C., Campbell, R.B., Dodds, C . J . Gehrels, G.E., and O'Brien, J . , 1991. Part B. Cordilleran terranes; in Upper Devonian to Middle Jurassic assemblages, Chapter 8 of Geology of Cordilleran Orogen in Canada, Gabrielse H., and Yorath C . J . , (eds.); Geological Survey of Canada, Geology of Canada, N o . 4, pp. 281-327 (also Geological Society of America, The Geology of North America, V o l . G-2). Mortensen, J . K . 1992. Pre-mid-Mesozoic tectonic evolution of the terrane, Y u k o n and Alaska; Tectonics, V o l . 11, pp. 836-853.  Yukon-Tanana  Neumayr, M . 1875. Die ammoniten der Kreide und die Systematik der Ammonitiden. Zeitschrift der Deutsche geologische Gesellschaft, 27, 854-892. Orchard, M . J . , Cordey, F., R u i , L., Bamber, W., Struik, L.C., and Sano, H. 2001. 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N e w U - P b zircon ages integrated with ammonite biochronology from the Canadian Cordillera. Canadian Journal of Earth Sciences, 37: 549- 67. Parrish, R.R., Roddick, J.C., Loveridge, W.D., Sullivan, R.W., 1987. Uranium-lead analytical techniques at the Geochronology Laboratory, Geological Survey of Canada. Radiogenic age and isotope studies, Report 1, Geol. Surv. Can. Paper 87-2, 3-7.  116  Poulton, T.P., and Tipper, H.W. 1991. Aalenian ammonites and strata o f Western Canada. Geological Survey o f Canada, Bulletin 411,71 pages. Renne, P.R., C.Swisher, C.C., III, Deino, A . L . , Karner, D.B., Owens, T. and DePaolo, D.J., 1998. Intercalibration of standards, absolute ages and uncertainties in 4 0 A r / 3 9 A r dating. Chemical Geolology, 145(1-2): 117-152. Reid, P.R. and Templeman-Kluit, D.J. 1987. Upper Triassic Tethyan-type reefs i n the Yukon. Bulletin of Canadian Petroleum Geology, v. 35, no. 3, p. 316-332. Ricketts, B.D., Evenchick, C.A., Anderson, R.G., and Murphy, D.C. 1992. 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Assessment of errors in S I M S zircon U - P b geochronology using a natural zircon standard and N I S T S R M 610 glass; Chemical Geology, v. 197, p. 111-146. Suess, E. 1865. Uber Ammoniten: Sitzungsberichte der Mathematisch Naturwissenschaftlichen. Klasse der Kaiserlichen Akademie der Wissenschaften, 52, 71 89. Thomson, R.C., and Smith, P.L. 1992. Pliensbachian biostratigraphy and ammonite fauna from the Spatsizi area, north-central British Columbia. Geological Survey of Canada, Bulletin 437. Thorstad, L . E . and Gabrielse, H. 1986. The Upper Triassic Kutcho Formation, Cassiar Mountains, north-central British Columbia; Geological Survey of Canada, Paper 86-16, 53 p. Tipper, H. W., and Richards, T.A. 1976. Jurassic stratigraphy and history of north central British Columbia; Geological Survey of Canada, Bulletin 270, 73 pages. Taylor, D.G. 1988. M i d d l e Jurassic (late Aalenian and early Bajocian) ammonite biochronology of the Snowshoe Formation, Oregon. Oregon Geology, V o l . 50, pp. 123138. Wheeler, J.O. 1961. Whitehorse map-area, Y u k o n Territory, (105D); Geological Survey of Canada, Memoir 312, 156 pages. Wheeler, J.O., Brookfield, A . J . , Gabrielse, H., Monger, J . W . H . , Tipper, H.W., and Woodsworth, G.J. 1988. Terrane M a p of the Canadian Cordillera; Geological Survey of Canada, Open File 1894. Wheeler, J.O., and McFeely, P. 1991. Tectonic assemblage map of the Canadian Cordillera and adjacent parts of the United States of America; Geological Survey of Canada, M a p 1712A, scale 1:2 000 000. Zittel, K. A . V o n . 1884. Mollusca und Arthropoda, 329-522. Handbuch der Palaeontologie. Cephalopoda, 1(2). Miinchen und Leipzig, 893 pp.  118  Appendix 1: U T M easting U T M northing  Handsample/ locality  (NAD 27)  rock type  fossil  collection,  collection hie  age  age  n situ  number  Lab s a m p l e number  G S C C-number  N T S map area ( N A D 27)  Tr.LS-1  Tr.L.S-1  C-307225  104K/11  612663  6507312 limestone  U. Triassic  U. Triassic  X  ex situ  U B C loc. FS-1  1  104K/11  612663  6507312 limestone  U. Triassic  U. Triassic  X  U B C loc. F S - 2  2  104K/11  613724  6506462 sandstone  K u n a e Z.  Carlottense Z.  X  2.1  104K/11  613491  6506297 sandstone  K u n a e Z.  Carlottense Z.  X  U B C loc. F S - 3  3  104K/11  613491  6506292 siltstone  Carlottense Z. Carlottense Z.  X  U B C loc. FS-4  4  104K/11  613399  6506193 siltstone  Carlottense Z. Carlottense Z.  X  U B C loc. FS-5  5  104K/11  613357  6506133 siltstone  K a n e n s e Z.  K a n e n s e Z.  X  U B C loc. F S - 6  6  104 K/11  613428  6506058 sandstone  Planulata Z.  Planulata Z.  X  U B C loc. FS-7  7  104K/11  613440  6506027 sandstone  Planulata Z.  Planulata Z.  X  U B C loc. FS-8  8  104 K/11  613654  6505778 sandstone  Planulata Z.  Planulata Z.  X  U B C loc. F S - 9  9  104K/11  613483  6505596 siltstone  Planulata Z.  Planulata Z.  X  U B C loc. F S - 1 0  10  104 K/11  613689  6505430 siltstone  Planulata Z.  Planulata Z.  X  U B C loc. FS-11  11  104 K/11  613380  6505410 sandstone  Planulata Z.  Planulata Z.  X  U B C loc. F S - 1 2  12  104 K/11  613102  6505511 sandstone  Hillebrandti Z.  Hillebrandti Z.  X  U B C loc. FS-13  13  104 K/11  613571  6504558 siltstone  Hillebrandti Z.  Hillebrandti Z.  X  U B C loc. FS-14  14  104 K/11  613459  6503915 siltstone  Bajocian  Bajocian  X  U B C loc. F S - 1 5  15  104 K/11  siltstone  Bajocian  Bajocian  X  FS-16  16  104 K/11  612690  6503697 siltstone  Bajocian  Bajocian  X  U B C loc. F S - 1 7  17  104 K/11  612690  6503697 siltstone  Bajocian  Bajocian  X  U B C loc. FS-18  18  104 K/11  612203 *  6502895 mudstone * *  Bajocian  Bajocian  X  Freboldi Z.  Freboldi Z.  X  U B C loc. FS-2.1  U B C loc.  missing  missing  petrograp  fossil maximum strat minimum strat  E1  E1  C-211256  104 K/11  E2  E2  C-86512  104 K/11  *  *  *  K u n a e Z.  K u n a e Z.  X  E3  E3  C-86513  104 K/11  *  *  *  K u n a e Z.  K u n a e Z.  X  E4  E4  C-86511  104 K/11  *  *  *  K u n a e Z.  K u n a e Z.  X  E5  E5  104 K/11  *  *  *  Carlottense Z. Carlottense Z.  X  E6  E6  C-86509 *  104 K/11  *  *  *  Carlottense Z. Carlottense Z.  X  E7  E7  *  104 K/11  *  *  *  Carlottense Z. Carlottense Z.  X  E8  E8  *  104 K/11  *  *  *  Carlottense Z. Carlottense Z.  X  E9  E9  C-86522  104 K/11  *  *  *  Aalenian?  Aalenian?  X  E10  E10  104 K/11  *  *  *  Bajocian  Bajocian  X  S.Cgl-f  S1  C-211248 *  S.b.CgM  S2  Cgl-1  analysis  U-Pb  Ar-Ar  analysis  analysis  104 K/11  613724  6506360 sandstone  K u n a e Z.  Carlottense Z.  X  *  104 K/11  613483  6505596 sandstone  Planulata Z.  Planulata Z.  X  C1  *  104 K/11  613317  6505638 conglomerate  Planulata Z.  Planulata Z.  X  Cgl-3  C2  *  104 K/11  613448  6505395 conglomerate  Planulata Z.  Planulata Z.  X  M.Cgl.5-C1  C3  »  104 K/11  613501  6504952 conglomerate  Hillebrandti Z.  Hillebrandti Z.  M.Cgl.4-C4  C4  *  104 K/11  613545  6504881 conglomerate  Hillebrandti Z.  Hillebrandti Z.  S.J-1  S3  104 K/11  6504712 sandstone * sandstone  Hillebrandti Z.  FS-06-SS-1  613277 *  Hillebrandti Z.  Tr.S-1  • *  Tr.S.Cgl-2  FS-06-SS-2  *  104 K/11  S.F-g  FS-06-SS-3  *  104 K/11  S.b.Cgl.d  FS-06-SS-4  *  104 K/11  S.b.Cgl.c  FS-06-SS-5  *  104 K/11  S.I.Cgl.b  FS-06-SS-6  *  104 K/11  S.I.Cgl.3  FS-06-SS-7  *  104 K/11  S.H  FS-06-SS-8  104 K/11  S.G  FS-06-SS-9  • *  S.F  FS-06-SS-10  *  104 K/11  S.E1  FS-06-SS-11  *  104 K/11  613459  S.E2  FS-06-SS-12  *  104 K/11  S.A  FS-06-SS-13  *  S.Ch.4  FS-06-SS-14  *  104 K/11  * 613747  • *  *  sandstone  6506460 sandstone * sandstone *  sandstone  613440 *  6506027 sandstone  613571 *  6504558 sandstone  *  sandstone  X X X  U. Triassic  U. Triassic  X  Sine./Pliens.?  Sine./Pliens.?  X  Freboldi Z.  Freboldi Z.  X  Carlottense Z. Carlottense Z.  X  Carlottense Z. K a n e n s e Z.  X  Planulata Z.  Planulata Z.  X  Planulata Z.  Hillebrandti Z.  X  Hillebrandti Z.  Aalenian?  X  *  sandstone  Hillebrandti Z.  Aalenian?  X  *  sandstone  Hillebrandti Z.  Aalenian?  X  6503915 sandstone  Bajocian  Bajocian  X  613459  6503915 sandstone  Bajocian  Bajocian  X  104 K/11  613300  6503545 sandstone  Bajocian  Bajocian  X  104 K/11  612298  6502859 sandstone  Bajocian  Bajocian  X  104 K/11  *  Appendix 2: TAXONOMY Introduction: Identification of ammonoid fossils are based on comparing collections with Type Specimens figured by other authors. Synonymies presented below are not complete but indicate the type specimen and other occurrences already reported from North America. Where possible, the population-variation studies, including qualitative approaches based on A M M O N , have been done to confirm the identifications. Selected morphologic measurements of the specimen were plotted on the actual graph of the candidate genus and/or species. The graphs were derived from A M M O N , a database containing data from Jurassic ammonoids and stratigraphy of western North America (Liang and Smith, 1997). A M M O N is a computer file, established and based in the Paleontology Lab of the Department of Earth and Ocean Sciences at U B C . The morphologic terminology used in the systematic measurements of ammonoids follows that of Smith (1986). A l l measurements for the ammonoids are in millimeters. Abbreviations used for the measurements are as follow:  D  = Shell Diameter  UD  = U m b i l i c a l Diameter at diameter = D  U  = ( U D / D ) x 100  WH  = Whorl Height at diameter = D  WW  = Whorl Width at diameter = D  WW/WH = (WW/WH)xl00 PRHW  = Primary Ribs per H a l f Whorl  120  For open nomenclature, we follow the conventions established by Bengston (1988). A question mark indicates uncertainty at the generic or subgeneric level and cf. (an abbreviation of confer, meaning to compare) is used to indicate a similarity to a previously described species where identification is not confident. The uncertainty is mainly due to poor preservation. The locality numbers and their corresponding G S C locality numbers are listed in Appendix 1. A l l specimen numbers are indicated by the prefix " F S - S p . "  Order AMMONOIDEA Zittel, 1884 Suborder CERATITINA Hyatt, 1884 Superfamily TROPITACEAE Mojsisovics, 1875b Family JUVAVITIDAE Tozer, 1971 Genus OMOJUVAVITES Tozer, 1994 Type species: Omojuvavites ventroplicatus Tozer, 1994 Omojuvavites sp. Plate 1, figure 1 Omojuvavites n. gen. Tozer, 1994, p.244. Material: 1 poorly preserved silicified sample in the limestone. Occurrence: Omojuvavites is known from northeastern British Columbia and this is the first occurrence of this genus in northwestern British Columbia. Locality: 1 Age: Norian (Late Triassic)  121  Measurements: Specimen l-S-Sp.l  I) (mm) 31  HI) (mm) 3  IJ % 10  Wll (mm) 15  WW  WW W H  PltHW  (mm) 10  66.6  -  Superfamily CLYDONITACEAE Mojsisovics, 1879 Family DISTICHITIDAE Diener, 1920 Genus ECTOLCITES Mojsisovics, 1893 Type species: Ammonites pseudoaries, Hauer Ectolcites sp. Plate 1, figures 2a,b Material: N o material is available. One poorly preserved silicified sample i n the limestone and pictures taken o f specimen in the field (the sample was too delicate to extract). Occurrence: Ectolcites is known from northeastern British Columbia and this is the first occurrence of this genus in northwestern British Columbia. Locality: 1 Age: Norian (Late Triassic)  Measurements: Specimen FS-Sp.2  1.) (mm) 14.3  1 I) (mm) 6.6  IJ % 46  Wll (mm) 4.5  WW (mini -  W W W 11 % -  PKIIW  ^BffillBIBIil -  122  Suborder PHYLLOCERATINATINA A r k e l l , 1950 Superfamily P H Y L L O C E R A T A C E A E Zittel, 1884 Family PHYLLOCERATIDAE Zittel, 1884 Subfamily PHYLLOCERATINAE Zittel, 1884 Genus PHYLLOCERAS Suess, 1865  Type species: Ammonites heterophyllus Sowerby, 1820 Phylloceras sp. Occurrence: Worldwide from Early Jurassic to the Cretaceous.  Locality: 12 Age: Middle Toarcian  Suborder AMMONITINA Hyatt, 1889 Superfamily E O D E R O C E R A T A C E A E Spath, 1929 Family DACTYLIOCERATIDAE Hyatt, 1867 Genus REYNESOCERAS Spath, 1936  Type species: Ammonites ragazonii Hauer, 1861. Reynesoceras italicum (Fucini, 1901) Plate 4, figure 3  Coeloceras italicum Meneghini in Fucini, 1901, p. 98, pi. 13, fig. 4. Prodactylioceras italicum italicum (Fucini). Imlay, 1968, p. 38, pi. 10, fig. 3. Reynesoceras italicum (Fucini). Smith and Tipper, 1996, p. 47, pi. 18, fig. 3.  Material: One specimen.  Occurrence: In the North Pacific it is known in Alaska (Imlay, 1981); Oregon (Smith, 1981); possibly the Y u k o n (Frebold, 1970, pi. 4, fig. 1).  Locality: 2 Age:  Freboldi and Kunae Zones (Late Pliensbachian).  Genus DACTYLIOCERAS Hyatt, 1867  Type species: Ammonites communis Sowerby, 1815 Dactylioceras cf. kanense Mclearn, 1930 Plate 4, figures 1, 2a,b  Dactylioceras kanense n. sp. McLearn, 1930, p. 4, pi. 1, fig. 2. Dactylioceras kanense McLearn. M c L e a r n , 1932, p. 59-62, , pi. 3, fig. 5, pi. 4, fig. 1-7, pi. 5, fig. 6-9.  Dactylioceras cf. kanense McLearn. Imlay, 1955, p. 88, pi. 10, fig. 14. Dactylioceras (Orthodactylites) kanense McLearn. Imlay, 1968, pi. 3, fig. 12. Dactylioceras kanense McLearn. Tipper et al., 1991, pi. 5, fig. 4. Dactylioceras kanense McLearn. Jakobs et al., 1994, pi. 1, figs. 9-14.  Dactylioceras kanense McLearn. Jakobs et al., 1995, pi. 1, fig. 1. Dactylioceras kanense McLearn. Jakobs, 1997, p. 42, pi. 1, figs. 9-12, 19, 20.  Material: Two specimens. Occurrence: This species is known from Queen Charlotte Islands, Hazelton map area, and southern A l a s k a (Jakobs, 1997).  Locality: 5 Age:  Kanense Zone (Early Toarcian).  124  Dactylioceras cf. commune (J. Sowerby, 1815) Plate 4, figures 5, 6a,b cf. Ammonites communis J. Sowerby, 1815, p. 10, pi. 107, figs. 2, 3. Dactylioceras cf. crassiusculosom (Simpson). Imlay, 1955, p. 88, pi. 10, fig. 9, pi. 11, figs. 16-18. Dactylioceras cf. commune (Simpson). Imlay, 1955, p. 88, pi. 10, figs. 10-12, pi. 11, figs. 4-6. Dactylioceras cf. directum (Buckman). Imlay, 1955, p. 88, pi. 11, figs. 7-11, 14. Dactylioceras cf. delicatum (Buckman). Imlay, 1955, p. 88, pi. 10, figs. 15, 16. Dactylioceras cf. commune (J. Sowerby). Frebold, 1957, p. 2,3, pi. 1, figs. 1-7. Dactylioceras cf. commune (J. Sowerby). Jakobs et al., 1994, pi. 2, figs. 11, 12, 15, 16. cf. Dactylioceras cf. commune (J. Sowerby). Jakobs et al., 1997, p. 42, 43, pi. 1, figs. 13, 14,21,22. Material: Two specimens. Occurrence: This species is known from Spatsizi River map area, Cry Lake map area, Taseko Lakes map area, and southern Alaska (Jakobs, 1997). Localities: 10, 11 Age:  Planulata Zone (Middle Toarcian).  Dactylioceras sp. Plate 4, figure 4 Material: T w o specimens.  125  Localities: 10, 11 Age: Planulata Zone (Middle Toarcian).  Genus PERONOCERAS Hyatt, 1867  Type species: AmmonitesfibulatusSowerby, 1823 Peronoceras sp. Localities: 6, 11 Age: Planulata Zone (Middle Toarcian).  Family EODEROCERATIDAE Spath, 1929 Genus METADEROCERAS Spath, 1925  Type species: Ammonites muticus d'Orbigny, 1844 Metaderoceras sp. Plate 1, figures 3a,b  Material: One specimen. Occurrence: This genus is known from Queen Charlotte Islands (Jakobs, 1997), and Tulsequah map area (Mihalynuk et al., 1999).  Locality: E l Age: Imlayi Zone (Early Pliensbachian)  Family AMALTHEIDAE Hyatt, 1867 Genus A M A L T H E U S de Montfort, 1808  Type species: Amaltheus margaritatus de Montfort, 1808  126  Amaltheus stokesi (J. Sowerby, 1818) Plate 7, figures 3-7a,b Ammonites stokesi Sowerby, 1818, p. 205, pi. 191. Amaltheus stokesi (J. Sowerby). Frebold, 1964, p. 9, pi. 2, figs. 2-6. Amaltheus cf. stokesi (J. Sowerby). Frebold, 1966, p. 2, pi. 2, figs. 1-4. Amaltheus stokesi (J. Sowerby). Frebold et al., 1967, p. 14, pi. 1, figs. 1-3, 5, 7. Amaltheus stokesi (J. Sowerby). Frebold, 1970, pi. 3, fig. 1. Amaltheus stokesi (J. Sowerby). Frebold, 1975, p. 10, pi. 4, figs. 3, 4. Amaltheus stokesi (J. Sowerby). Imlay, 1981, p. 37, pi. 10, figs. 23, 24, 27, 28. Amaltheus stokesi (J. Sowerby). Smith and Tipper, 1996, p. 51, pi. 19, fig. 1, p i . 20, fig. 3. Material: Seven specimens. Occurrence: Amaltheus is a common genus in northern latitude (a Boreal genus). The species A. stokesi has been collected from the north o f the Whitehorse Trough i n the Tulsequah and Telegraph Creek areas (Frebold, 1964, 1970, Smith et al., 1988), northern Wrangellia in A l a s k a (Imlay, 1981), Queen Charlotte Islands (Smith and Tipper, 1996), Cultus Lake, southwestern B C (Ham, 1997), Canadian Arctic (Frebold, 1975), central and northern Y u k o n (Frebold et al., 1967), and also on the North American craton as far south as 51°N (Frebold, 1966). Locality: E 4 Age:  Kunae Zone (Late Pliensbachian).  127  Amaltheus margaritatus (de Montfort, 1808) Plate 7, figures 1,2  Amaltheus margaritatus n. sp. de Montfort, 1808, p. 90. Amaltheus margaritatus de Montfort. Imlay, 1981, p. 37, pi. 10, figs. 25, 26.  Material: Two specimens. Occurrence: This species has been collected from Tulsequah, Cry Lake, southern Yukon, and northern A l a s k a (Smith et al., 2001).  Locality: E 4 / E 5 Age: Kunae/Carlottense Zone (Late Pliensbachian).  Superfamily H I L D O C E R A T A C E A E Hyatt, 1867 Family HILDOCERATIDAE Hyatt, 1867 Subfamily ARIETICERATINAE Howarth, 1955 Genus ARIETICERAS Seguenza, 1885  Type species: Ammonites algovianus Oppel, 1862 Arieticeras cf. algovianum (Oppel, 1862) Plate 2, figures la,b  cf. Ammonites algovianus Oppel, 1862, p. 137. Arieticeras algovianum (Oppel). Frebold, 1964, p. 13, pi. 3, figs. 3-5, pi. 4, fig. 2, pi. 5, fig. 3. Arieticeras cf. algovianum (Oppel). Imlay, 1968, p. 34, pi. 4, figs. 1-8.  Arieticeras algovianum (Oppel). Frebold, 1970, p. 443, pi. 2, fig. 1. Arieticeras cf. algovianum (Oppel). Imlay, 1981, p. 40, pi. 10, figs. 16-20.  128  Arieticeras cf. domarense (Oppel). Imlay, 1981, p. 39, pi. 10, figs. 1, 2, 9, 10. Arieticeras aff. algovianum (Oppel). Thomson and Smith, 1992, p. 36, pi. 14, figs. 1-7. cf. Arieticeras aff. algovianum (Oppel). Smith and Tipper, 1996, p. 54, pi. 20, figs. 11, 12. Material: Two specimens. Occurrence: This species is known from western United State, northern British Columbia (Frebold, 1964a, 1970; Thomson and Smith, 1992), and northwestern British Columbia (Smith et al., 1988; this study). Locality: 2 Age:  Kunae Zone (Late Pliensbachian).  Measurements: Specimen 1 s-Sp.3  1) (mm) 24  1 if) (mm) 13  % 54  Wll (mm) 7  WW  (mm) -  WW  WH  -  PRHW  21  129  UD/D for Arieticeras aglovianum/FS-Sp.3  35  f  30  25 o Arieticeras algovianum  0_  20  • FS-Sp.3  % o o O  o  0  15  0  10  20  30  40  50  60  70  80  90  Figure 61. U D / D for Arieticeras algovianum and specimen FS-sp.3 measurements. 30  25  O  o  O o  0 0 o o  o  o Arieticeras algovianum » FS-sp.3  10  10  15  20  25  30  35  40  UD  Figure 62. P R H W for Arieticeras algovianum and specimen FS-sp.3 measurements.  130  Arieticeras cf. micrasterias (Meneghini, 1874) Plate 2, figures 2a,b  Ammonites (Harpopceras) mercati Hauer var. micrasterias Meneghini, 1874, appendix, pi. 2, fig. 14 only, 1875, appendix, p. 3, cf. Hildoceras rimotum Fucini, 1905, p. 282, pi. 45, fig. 12, 1908b, p. 48, pi. 1, figs. 47, 48.  Arieticeras sp. Imlay, 1981, p. 40, pi. 10, fig 21. Arieticeras cf. micrasterias Smith and Tipper, 1996, p. 56, pi. 20, fig. 8. Material: One specimen. Occurrence: This species is known from Alaska (Imlay, 1981), and Tulsequah map area.  Locality: 2 Age: Kunae Zone (Late Pliensbachian).  Measurements: Specimen FS-Sp.9  L) (mm) 12.5  Ul) (mm) 4.5  1  I' % 36  i  \\ 11 mm i 4.8  WW (mm)  W W W II  I'KIIW  -  -  12  Arieticeras sp. Material: Six specimen.  Localities: 3, E 2 Age: Kunae Zone (Late Pliensbachian).  Genus LEPTALEOCERAS Buckman, 1918  Type species: Leptaleoceras leptum Buckman, 1918 Leptaleoceras cf. accuratum (Fucini, 1931) 131  Arieticeras (?) accuratum n. sp. Fucini, 1931, p. 117, pi. 24, fig. 10. Arieticeras cf. domarense (Meneghini). Imlay, 1981, p. 39, pi. 10, fig. 15. Leptaleoceras aff. accuratum (Fucini). Smith et al., 1988, p. 4, fig. 9. Leptaleoceras aff. accuratum (Fucini). Thomson and Smith, 1992, p. 34, pi. 13, figs. 1-6. Leptaleoceras aff. accuratum (Fucini). Smith and Tipper, 1996, p. 57, pi. 22, figs. 6, 8-9. Occurrence: This species is known from the Whitehorse and Telegraph Creek areas by Frebold (1964, 1970). It also has been collected from Spatsizi area and Queen Charlotte Islands (Smith and Thomas, 1992), and Alaska (Imlay, 1981). Locality: 2 Age: Kunae Zone (Late Pliensbachian).  Genus FONTANELLICERAS Fucini, 1931 Type species: Harpoceras fontanellense Gemmellaro, 1886 Fontanelliceras sp. Plate 3, figure 7; Plate 3, figures 4, 5 Material: T w o specimens. Locality: 3 Age: Kunae Zone (Late Pliensbachian) to Early Toarcian.  132  30  h  o Fontanelliceras sp. 20  • FS-Sp.10  15  o o .  4*  10  0  10  20  30  40  50  60  70  D  Figure 63. U D / D for Fontanelliceras sp. and specimen FS-sp.10 measurements.  Fontanelliceras ex gr. fontanellense (Gemmellaro, 1886) Plate 3, figures 9, 10 Fontanelliceras cf. fontanellense (Gemmellaro). Imlay, 1981, p. 40, pi. 11, figs. 19, 20. Fontanelliceras cf. fontanellense (Gemmellaro). Palfy and Hart, 1995, pi. 1, fig. 8. Fontanelliceras sp. Smith and Tipper, 1996, p. 58, pi. 22, figs. 1, 2. Material: Two specimens. Occurrence: This species has been collected in southern Alaska (Imlay, 1981), Southern Y u k o n (Palfy and Hart, 1995) and from the Queen Charlotte Islands by Smith and Tipper (1996).  133  Localities: 5, 6 Age: Kanense Zone (Early Toarcian).  Measurements: WW/WH  PRHW  -  % -  16  10  -  -  17  9  -  -  15  WW (mm)  50  WH (mm) 6.5  19  52  16  50  U D  U  (mm) 9  %  FS-Sp.10  D (mm) 18  FS-Sp.30  36  FS-Sp.33  32  Specimen  40  35  e Fontanelliceras sp.  g  •  20  15  FS-sp.30  A FS-sp.33  h  Q | 10  20  30  40  50  60  D  Figure 64 . U D / D for Fontanelliceras sp. and specimens FS-sp.30, 33 measurements. Subfamily BOULEICERATINAE A r k e l l , 1950 Genus LEUKADIELLA Renz, 1913  Type species: Leukadiella helenae Renz, 1913 134  Leukadiella amuratica Renz & Renz, 1947 Plate 5, figures la,b Leukadiella amuratica Renz & Renz, 1947, p. 174, pi. 12,fig.6. Leukadiella amuratica Renz & Renz. Jakobs, 1997, pi. 6. figs. 5, 6. Material: One specimen. Occurrence: This is the first record of the Tethyan genus Leukadiella in the Tulsequah map-area; it was previously only known from the Queen Charlotte Islands, Spatsizi and Hazelton areas (Jakobs, 1995, 1997; Jakobs et al., 1997). Locality: 6 Age: Planulata Zone (Middle Toarcian Leukadiella sp. Plate 5, figure 2 Material: Three specimens. Localities: 10, 11 Age: Planulata Zone (Middle Toarcian)  Subfamily HARPOCERATINAE Neumayr, 1875 Genus FUCINICERAS Haas, 1913 Type species: Harpoceras lavinianum Meneghini in Fucini, 1900 Fuciniceras cf. intumescens (Fucini, 1901) Plate 2, figure 8 Hildoceras intumescens Fucini, 1901, p. 89, p i . 13,fig.3. Fuciniceras? cf. intumescens (Fucini). Imlay, 1968, p. C42, pi. 8, figs. 1-7, 9, 10.  135  Fuciniceras aff. intumescens (Fucini). Smith et al., 1988, pi. 4, fig. 14. cf. Fuciniceras aff. intumescens (Fucini). Smith and Tipper, 1996, p. 63, pi. 22, fig. 16. Material: One specimen. Occurrence: F. aff intumescens is known from Oregon (Imlay, 1968), Tulsequah map area (Smith et al., 1988), and F. cf. intumescens is known from Tulsequah map area i n this study. Locality: 2 Age: Kunae Zone (Late Pliensbachian). Measurements: Specimen FS-Sp.5  UD (mm) 22  D (mm) 51  U % 43  W H  (mm) 17  W W  WW/WH  PRHW  (mm) -  % -  26  30  o Fuciniceras intumescens «FS-Sp.S  10  20  30  40  50  60  70  80  D  136  Figure 59. U D / D for Fuciniceras cf. intumescens and specimen FS-sp.5 measurements.  Fuciniceras sp. Localities: 2, E 2 Age:  Kunae Zone (Late Pliensbachian).  Genus FIELDINGICERAS Wiedenmayer, 1980  Type species: Ammonites fieldingii Reynes, 1868 Fieldingiceras cf. fieldingii (Reynes, 1868) Plate 2, figures 3a,b  Ammonites Fieldingii Reynes, 1868, p. 97, pi. 4, fig. 1. cf. Fieldingiceras fieldingii (Reynes). Smith and Tipper, 1996, p. 60, pi. 20, fig. 14, pi. 21, fig. 3.  Material: One specimen.  Locality: 3 Age:  Carlottense Zone (Late Pliensbachian).  Measurements: Specimen I S-Sp.15  D (mm) 9.6  !  UD (mm) 3.7  U % 38  Wll i mm i 3.7  WW (mm)  -  WW  WH %  -  PRHW 8  Fieldingiceras sp. Locality: 3 Age:  Carlottense Zone (Late Pliensbachian).  137  Genus PROTOGRAMMOCERAS Spath, 1913 Subgenus PRPTOGRAMMOCERAS Spath, 1913  Type species: Grammoceras bassanii Fucini, 1910a Protogrammoceras (Protogrammoceras) cf. paltum Buckman, 1922 Plate 3, figure 3 Paltarpitespaltus Buckman, 1922, pi. 362A. Harpoceras cf. exaratum (Young and Bird). Frebold, 1964a, p. 16, pi. 6, figs. 1, 5. Paltarpites paltus Buckman. Frebold, 1970, p. 443, pi. 4, figs. 5-7.  Protogrammoceras cf. (Protogrammoceras) paltum (Buckman). Imlay, 1981, p. 41, pi. 12, figs. 11, 12.  Protogrammoceras (Protogrammoceras) paltum Buckman. Howarth, 1992, p. 57, pi. 1, figs. 1-3, pi. 2, figs. 1,3.  cf. Protogrammoceras (Protogrammoceras) cf. paltum (Buckman). Smith and Tipper, 1996, p. 66, pi. 24, figs. 1-4.  Material: One specimen. Occurrence: In North America, this species has been known from northern British Columbia (Frebold, 1970; Thomson and smith, 1992), A l a s k a (Imlay, 1981), and Arctic Canada (Hall and Howarth, 1983).  Localities: 3-5, E7 Age: Carlottense Zone (Late Pliensbachian).  Measurements: Specimen FS-Sp.20  D i nun)  27  U D (mm) 6  U % 22  Wll (mm) 13  WW  W W W 11  PRHW  (mm) -  % -  23  138  Protogrammoceras (Protogrammoceras) kurrianum (Oppel, 1862) Locality: E4 Occurrence: In North America, it is known from Oregon (Imlay, 1968), northern British Columbia (Frebold, 1970; Thomson and smith, 1992), and A l a s k a (Imlay, 1981). Age: Carlottense Zone (Late Pliensbachian).  Protogrammoceras (Protogrammoceras) spp. Plate 3, figures 8a,b Material: Four specimens.  Localities: 2.1, 3-5 Age: Kanense Zone (Early Toarcian).  Genus LIOCERATOIDES Spath, 1919 Subgenus PACIFICERAS Repin, 1970  Type species: Schloenbachiapropinqua Whiteaves, 1884 Lioceratoides (Pacificeras) angionus (Fucini, 1931) Plate 2, figure 7  Praelioceras angionum Fucini, 1931, p. 107, pi. 12, figs. 1-5. Lioceratoides angionus (Fucini). Guex, 1973, p. 507, pi. 1, fig. 5. Lioceratoides (Pacificeras) angionus (Fucini). Smith and Tipper, 1996, p. 71, pi. 27, figs. 3-7.  139  Material: One specimen. Occurrence: In British Columbia, this species is known from Queen Charlotte Islands (Smith and Tipper, 1996), and Tulsequah map area. Locality: 3 Age:  Carlottense Zone (Late Pliensbachian).  Measurements: Specimen FS-Sp.14  1) (mm) 67  1 1) (mm) 10  V % 15  WH (mm) 28  WW (mm) -  WWW % -  PKIIW  II  -  Lioceratoides (Pacificeras) sp. Plate 2, figure 6 Material: One specimen. Locality: 3, 4, E8 Age:  Carlottense Zone (Late Pliensbachian).  Measurements: Specimen TS-Sp.19  I) (mm) 55  UD (mm) 16  U % 30  WH (mm) 20  WW (mm) -  WW Wl 1 % -  PKIIW -  Lioceratoides (Pacificeras) propinquum (Whiteaves, 1884) Plate 2, figures 4, 5 Schloenbachiapropinqua Whiteaves, 1884, p. 247, 1900, pi. 33, figs. 2 and 2a. Tiltoniceras propinquum (Whiteaves). Thomson and Smith, 1992, p. 39, pi. 15, figs. 5-7.  140  Lioceratoides (Pacificeras) propinquum (Whiteaves). Smith and Tipper, 1996, p. 71, 72, pi. 28, figs. 1-11, pi. 29, fig. 1. Material: Two specimens. Occurrence: This species is only known from the northeast Pacific and reported from Queen Charlotte Islands (Smith and Tipper, 1996), and Tulsequah map area. Localities: 3, 5, E 6 Age: Carlottense Zone (Late Pliensbachian)  Genus TILTONICERAS Buckman, 1913 Type species: Tiltoniceras costatum Buckman, 1913 Tiltoniceras antiquum (Wright, 1882) Occurrence: This species is reported from Queen Charlotte Islands (Smith and Tipper, 1996), and Tulsequah map area. Locality: 3 Age: Carlottense Zone (Late Pliensbachian) and Early Toarcian (Kanense Zone).  Genus HARPOCERAS Waagen, 1869 Type species: Ammonites falcifer Sowerby, 1820 Harpoceras cf. subplanatum (Oppel, 1856) Plate 3, figure 2 Ammonites subplanatus Oppel, 1856, p. 244. cf. Harpoceras cf. subplanatum (Oppel). Jakobs, 1997, p. 49, pi. 3, fig. 15.  141  Occurrence: This species is reported from Queen Charlotte Islands (Jakobs, 1997), and Tulsequah map area. Locality: 6 Age:  Kanense Zone (Early Toarcian).  Measurements: Specimen FS-Sp.32  D (mm) 34  CD (mm) 11  I." % 32  WII (mm) 12  WW  WW i  nun -  W'H % -  i  PR1-IW -32  Harpoceras spp. Plate 3, figure 6 Material: Five specimens. Localities: 5, 7, 9 Age:  Kanense Zone (Early Toarcian).  Measurements: Specimen FS-Sp.25  I) (mm) 27  I'D (mm) 7  1 % 26  WM (mnn 13  WW (mm) -  WW  W'H % -  PKIIW 35  Genus CLEVICERAS Howarth, 1922a Type species: Ammonites exaratus Young and Bird, 1828 Cleviceras spp. Plate 3, figures 4, 5 Material: Three specimens. Localities: 5, 8, 11 Age:  Early and Middle Toarcian. 142  Genus TAFFERTIA Guex, 1973a Type species: Taffertia taffertensis Guex, 1973 a Taffertia cf. tafferentis Guex, 1973a Plate 3, figures la,b Taffertia taffertensis Guex, 1973a, p. 503, pi. 2, fig. 6, pi. 10, fig. 7, pi. 15, fig. 13. Taffertia taffertensis Guex. Jakobs et al., 1994, pi. 1, fig. 3, 4. cf. Taffertia taffertensis Guex. Jakobs, 1997, p. 51, pi. 3, figs. 8, 9. Material: One specimen. Occurrence: This species is reported from Queen Charlotte Islands (Jakobs, 1997), and Tulsequah map area (Mihalynuk et al., 1999). Locality: 5 Age: Kanense Zone (Early Toarcian).  Genus PSEUDOLIOCERAS Buckman, 1889 Type species: Ammonites compactilis Simpson, 1855 Pseudolioceras cf. lythense (Young and B i r d , 1828) Occurrence: This species is known in British Columbia from Spatsizi River map area (Jakobs, 1997) and also from Arctic Canada (Frebold, 1975a, 1960, 1975). Locality: 11 Age: Middle Toarcian.  143  Pseudolioceras sp. Plate 3, figures 1 la,b Material: One specimen. Locality: 11, 12 Age: Middle to Late Toarcian.  Subfamily HILDOCERATINAE Hyatt, 1867 Genus HILDAITES Buckman, 1921 Type species: Hildaites subserpentinus Buckman, 1921 Hildaites cf. murleyi (Moxon, 1841) Occurrence: It is known from  Queen  Charlotte Islands, Spatsizi River and Cry Lake map  areas (Jakobs, 1997). Locality: 6 Age: Kanense Zone (Early Toarcian). Hildaites sp. Plate 5, figures 8a,b Material: One specimen. Locality: 10 Age: Planulata Zone (Middle Toarcian).  Subfamily GRAMMOCERATINAE Buckman, 1904 Genus PODAGROSITES Guex, 1973b Type species: Pseudogrammoceras podagrosum Monestier, 1921  144  Podagrosites cf. latescens (Simpson, 1843) Occurrence: This species is known from Queen Charlotte Island (Jakobs, 1997), and Tulsequah map area (Mihalynuk et al., 1999). Locality: 12 Age: Hillebrandti (Late Toarcian). Podagrosites sp. Plate 5, figure 7 Material: One specimen. Locality: 12 Age: Hillebrandti Zone (Late Toarcian).  Measurements: Specimen FS-Sp.43  D (mini 26  UD (mini 10  li % 38  ; W'H ' (mm) 9  WW (mm> -  WW  Wll  !  % -  PRI1W  16  Family H A M M A T O C E R A T I D A E Buckman, 1887 Genus PLANAMMATOCERAS Buckman, 1922 Type species: Planammatoceras planiforme Buckman, 1922 Planammatoceras? sp. Occurrence: This genus is known in western Canada in the Taseko Lakes, Spatsizi, the Laberge map areas (Poulton and Tipper, 1991), and a probable occurrence in the Tulsequah map area is also reported in this study. Locality: E 9 145  Age: Aalenian.  Family PHYMATOCERATIDAE Hyatt, 1867 Subfamily PHYMATOCERATINAE Hyatt, 1900 Genus PHYMATOCERAS Hyatt, 1867 Type species: Phymatoceras robustum Hyatt, 1867 Phymatoceras hillebrandti Jakobs, 1994 Plate 5, figures 3, 6 Phymatoceras hillebrandti n. sp. Jakobs, 1994, pi. 4, figs. 13, 14, 18-23. Phymatoceras hillebrandti Jakobs, 1997, pi. 14, figs. 1-6, pi. 15, figs. 1-12, pi. 16, figs. 7, 8. Material: Two specimens. Occurrence: This species is known from Queen Charlotte Islands, Iskut, Spatsizi, M c C o n n e l l Creek, Hazelton areas (Jakobs, 1994), and Tulsequah map area (this study). Localities: 12, 13 Age: Hillebrandti Zone (Late Toarcian).  Phymatoceras sp. Plate 5, figures 4a,b-5 Material: Two specimens. Locality: 13 Age: Hillebrandti Zone (Late Toarcian).  146  Family SONNINIIDAE Buckman, 1892 Genus SONNINIA Bayle, 1879  Sonninia cf. adicra (Waagen, 1867) Plate 6, figure 1 A  Ammonites adicrus Waagen, 1867, p. 591, pi. 25, figs, l a , b. Sonninia (Euhoploceras) adicra (Waagen). Imlay, 1973, p. 65, pi. 13, figures 5-12, pi. 14-17.  Material: One specimen.  Locality: 16 Age: Early Bajocian  Sonninia spp. Plate 6, figure 2 Material: Five specimens.  Localities: 15-17 Age: Early Bajocian  Genus DORSETENSIA Buckman, 1892  Dorsetensia spp. Plate 6, figure I B  Material: T w o specimens.  Localities: 16, 17 Age: Early Bajocian  147  Genus FONTANNESIA Buckman, 1902  Fontannesia sp. Plate 6, figure 5  Material: One specimen.  Locality: 14 Age: Late Aalenian-Early Bajocian  Superfamily STEPHANOCERATACEAE Neumayr, 1875 Family STEPHANOCERATIDAE Neumayr, 1875 Genus NORMANNITES Munier & Chalmas, 1892  Normannites sp. Plate 6, figure 6  Material: One specimen.  Locality: 18 Age: Early Bajocian  Family STEPHANOCERATIDAE Neumayr, 1875 Genus STEPHANOCERAS Waagen, 1869  Type species: Ammonites humphriensianus Sowerby, 1825 Stephanoceras (Skirroceras) kirschneri Imlay, 1973 Plate 6, figure 4  Stephanoceras (Skirroceras) kirschneri Imlay, 1964b, p. B47, pi. 18, figs. 1-4, pi. 19.  148  Stephanoceras (Skirroceras) kirschneri Imlay, 1973, p. 87, pi. 30, fig. 13, pi. 42, figs. 110.  Material: One specimen.  Locality: 18 Age: Early Bajocian  Stephanoceras spp. Plate 6, figures 3a,b  Material: 22 specimens.  Locality: 18 Age: Early Bajocian  Family SPHAEROCERATIDAE Buckman, 1920 Genus CHONDROCERAS Mascke, 1907  Chondroceras cf. allani (McLearn, 1927)  Locality: E10 Age: Early Bajocian  Chondroceras defontii (McLearn, 1927)  Locality: E10 Age: Early Bajocian  Superfamily PSILOCERATACEAE Hyatt, 1867 Family OXYNOTICERATIDAE Hyatt, 1875  149  Genus FANNINOCERAS McLearn, 1930 Subgenus FANNINOCERAS McLearn, 1930  Type species: Fanninoceras fannini McLearn, 1930 Fanninoceras (Fanninoceras) kunae McLearn, 1930 Plate 1, figure 5  Fanninoceras kunae McLearn, 1930, p. 5, pi. 2, fig. 4, 1932, p. 77, pi. 8, figs. 11,12 Fanninoceras lowrii McLearn, 1930, p. 5, pi. 1, fig. 6, 1932, p. 79, pi. 9, figs. 10, 11. Fanninoceras (Fanninoceras) kunae (McLearn). Smith and Tipper, 1996, p. 30, pi. 4, figs. 5-8, 11, 12.  Material: One specimen. Occurrence: This species is known from eastern Pacific (Smith et al., 1988).  Locality: 2 Age: Kunae Zone (Late Pliensbachian).  Measurements: Specimen l'S-Sp.4  1) (ir m i 34  I l> (mm i 12  i; % 35  Wll (mm) 19  WW (mm) -  W W W l l | PRIIW -  •  30  Fanninoceras (Fanninoceras) sp. Material: One specimen  Localities: 2, E3 Age: Carlottense Zone (Late Pliensbachian).  Subgenus CHARLOTTICERAS Smith & Tipper, 1996 150  Type species: Fanninoceras (Charlotticeras) maudense Smith & Tipper, 1996 Fanninoceras (Charlotticeras) maudense Smith & Tipper, 1996 Plate 1, figures 6a,b  Fanninoceras (Charlotticeras) maudense n. sp., Smith & Tipper, 1996, p. 32, pi. 6, figs. 6-11.  Material: One specimen. Occurrence: This species is known from the Queen Charlotte Islands (Smith and Tipper, 1996), and Tulsequah map area (this study).  Locality: 2 Age:  Kunae Zone (Late Pliensbachian).  Measurements: Specimen 1 s-Sp.6  i mm i 16  I'D (mm) 5  I' % 31  Wll i mm) 6.5  WW imim -  WW  Wll % -  PRI1W 11  151  Appendix 3: U-Pb GEOCHRONOLOGY Analytical Techniques S H R I M P II (Sensitive H i g h Resolution Ion Microprobe) analyses were conducted by V i c k i M c N i c o l l at the Geological Survey o f Canada (GSC) using analytical procedures described by Stern (1997), with standards and U - P b calibration methods following Stern and A m e l i n (2003). Zircons from the samples were cast i n 2.5 cm diameter epoxy mounts ( G S C mount #350) along with fragments of the G S C laboratory standard zircon (z6266, with  2 0 6  Pb/  2 3 8  U age = 559 Ma). The mid-sections of the zircons were exposed  using 9, 6, and 1 L i m diamond compound, and the internal features of the zircons were characterized with backscatter electrons (BSE) and cathodoluminescence ( C L ) utilizing a Cambridge Instruments scanning electron microscope ( S E M ) . Mount surfaces were evaporatively coated with 10 n m of high purity A u . Analyses were conducted using an 1 6  0 " primary beam, projected onto the zircons at 10 k V . The sputtered area used for  analysis was ca. 25 L i m i n diameter with a beam current o f ca. 5-6 nA. The count rates o f ten isotopes of Z r , U , T h , and P b in zircon were sequentially measured over 5 scans +  +  +  +  with a single electron multiplier and a pulse counting system with deadtime o f 35 ns. Off-line data processing was accomplished using customized in-house software. The l a external errors o f  P b / U ratios reported in Table 1 incorporate a ±1.0 % error i n  calibrating the standard zircon (see Stern and A m e l i n , 2003). N o fractionation correction was applied to the Pb-isotope data; common Pb correction utilized the measured 2 0 4  Pb/ Pb/  2 0 6  P b and compositions modelled after Cumming and Richards (1975). The U ages for the analyses have been corrected for common Pb using both the 204-  and 207-methods (Stern, 1997), but there is generally no significant difference in the  152  results (Table 1). The  2 0 6  Pb/  2 3 8  U ages of the detrital zircons from the sandstone samples  are represented in cumulative probability plots (Figs. 28, 30, and 32). Isoplot v. 2.49 206  (Ludwig, 2001) was used to calculate weighted means o f  z u o  238  Pbr  J O  U ages.  U-Pb I D - T I M S (isotope dilution thermal ionization mass spectrometry) analytical methods utilized in this study are outlined in Parrish et al. (1987). Heavy mineral concentrates were prepared using standard crushing, grinding, Wilfley™ table, and heavy liquid techniques. Mineral separates were sorted by magnetic susceptibility using a Frantz™ isodynamic separator. Multigrain zircon fractions analyzed were very strongly air abraded following the method of Krogh (1982). Treatment o f analytical errors follows Roddick et al. (1987) with errors on the ages reported at the 2 a level (Table 2). U - P b T I M S concordia diagrams are presented in Figures 33 and 34. A Concordia age (Ludwig, 1998) is calculated for the samples analyzed by T I M S . A Concordia age incorporates errors on the decay constants and includes both an evaluation of concordance and an evaluation of equivalence of the data. The calculated Concordia ages and errors quoted i n the text are at 2 sigma with decay constant errors included.  153  E X P L A N A T I O N OF P L A T E 1 A l l figures are natural size unless otherwise indicated  Figure 1. Omojuvavites sp. Specimen: F S - S p . l ; Locality 1; Sinwa Formation; Norian (Late Triassic). 2a, b. Ectolcites sp. Specimen: FS-Sp.2; Locality 1; Sinwa Formation; Norian (Late Triassic). 3a, b. Metaderoceras sp. Specimen: -, Locality: E l ; Takwahoni Formation; Imlayi Zone (Early Pliensbachian). 4. Aptychi (Cornaptychus?) Specimen: FS-Sp.36; Locality 9; Takwahoni Formation; Planulata Zone (Middle Toarcian). 5. Fanninoceras (Fanninoceras) kunae McLearn, 1930 Specimen: FS-Sp.4; Locality 2; Takwahoni Formation; Kunae Zone (Late Pliensbachian). 6a, b. Fanninoceras (Charlotticeras) maudense Smith & Tipper, 1996 Specimen: FS-Sp.6; Locality 2; Takwahoni Formation; Kunae Zone (Late Pliensbachian).  154  PLATE 1  E X P L A N A T I O N OF P L A T E 2 A l l figures are natural size unless otherwise indicated  Figure la, b. Arieticeras cf. algovianum (Oppel, 1862) Specimen: FS-Sp.3; Locality 2; Takwahoni Formation; Kunae Zone (Late Pliensbachian). 2a, b. Arieticeras cf. micrasterias (Meneghini, 1874) Specimen: FS-Sp.9; Locality 2; Takwahoni Formation; Kunae Zone (Late Pliensbachian). 3a, b. Fieldingiceras cf. fieldingii (Reynes, 1868) Specimen: FS-Sp.15; Locality 3; Takwahoni Formation; Carlottense Zone (Late Pliensbachian). 4. Lioceratoides (Pacificeras) propinquum (Whiteaves, 1884). Specimen: -, Locality E6; Takwahoni Formation; Carlottense Zone (Late Pliensbachian). 5. Lioceratoides (Pacificeras) propinquum (Whiteaves, 1884 ). Specimen: FS-Sp.28; Locality 5; Takwahoni Formation; Carlottense Pliensbachian).  Zone (Late  6. Lioceratoides (Pacificeras) sp. Specimen: FS-Sp.19; Locality 4; Takwahoni Formation; Carlottense Zone (Late Pliensbachian). 7. Lioceratoides (Pacificeras) angionus (Fucini, 1931) Specimen: FS-Sp.14; Locality 3; Takwahoni Formation; Carlottense Zone (Late Pliensbachian). 8. Fuciniceras cf. intumescens (Fucini, 1901) Specimen: FS-Sp.5; Locality 2; Takwahoni Formation; Kunae Zone (Late Pliensbachian).  156  E X P L A N A T I O N OF P L A T E 3 A l l figures are natural size unless otherwise indicated  Figure la, b. Taffertia cf. tafferentis Guex, 1973a Specimen: -, Locality 5, Takwahoni Formation; Kanense Zone (Early Toarcian). 2. Harpoceras cf. subplanatum (Oppel, 1856) Specimen: FS-Sp.32; Locality 6; Takwahoni Formation; Kanense Zone (Early Toarcian). 3. Protogrammoceras (Protogrammoceras) cf. paltum Buckman, 1922 Specimen: FS-Sp.20; Locality 4; Takwahoni Formation; Carlottense Zone (Late Pliensbachian) to Early Toarcian. 4. Cleviceras sp. Specimen: FS-Sp.35; Locality 8; Takwahoni Formation; Middle Toarcian. 5. Cleviceras sp. Specimens: FS-Sp.26; Locality 5; Takwahoni Formation; Kanense Zone (Early Toarcian). 6. Harpoceras sp. Specimen: FS-Sp.25; Locality 5; Kanense Zone (Early Toarcian). 7. Fontanelliceras sp. Specimen: FS-Sp.10; Locality 3; Takwahoni Formation; Carlottense Zone (Late Pliensbachian). 8a, b. Protogrammoceras (Protogrammoceras) sp. Specimen: FS-Sp.12; Locality 3; Takwahoni Formation; Kunae Zone (Late Pliensbachian). 9,10.  Fontanelliceras ex gr.fontanellense (Gemmellaro, 1886) 9. Specimen: FS-Sp.30; Locality 5; Takwahoni Formation; Kanense Zone (Early Toarcian). 10. Specimen: FS-Sp.33; Locality 6; Takwahoni Formation; Kanense Zone (Early Toarcian).  11a,  b. Pseudolioceras sp. Specimen: FS-Sp.54; Locality 12; Takwahoni Formation; Late Toarcian.  158  159  E X P L A N A T I O N OF P L A T E 4 A l l figures are natural size unless otherwise indicated  Figure 1. Dactylioceras cf. kanense Mclearn, 1930 Specimen: -, Locality 5; Takwahoni Formation; Kanense Zone (Early Toarcian). 2a, b. Dactylioceras cf. kanense Mclearn, 1930 Specimen: -; Locality 5; Takwahoni Formation; Kanense Zone (Early Toarcian). 3. Reynesoceras italicum (Fucini, 1901) Specimen: FS-Sp.8; Locality 2; Takwahoni Formation; Kunae Zone (Late Pliensbachian). 4. Dactylioceras sp. Specimen: FS-Sp.41; Locality 11; Takwahoni Formation; Middle Toarcian. 5-6a,  b. Dactylioceras cf. commune (J. Sowerby, 1815) 5. Specimen: FS-Sp.38; Locality 10; Takwahoni Formation; Middle Toarcian. 6a, b. Specimen: FS-Sp.40; Locality: U B C loc. F S - 1 1 ; Takwahoni Formation; Middle Toarcian.  160  PLATE 4  161  E X P L A N A T I O N OF P L A T E 5 A l l figures are natural size unless otherwise indicated  Figure la, b. Leukadiella amuratica Renz & Renz, 1947 Specimen: FS-Sp.34; Locality 6; Takwahoni Formation; Planulata Zone (Middle Toarcian).  2. Leukadiella sp. Specimen: FS-Sp.42; Locality 11; Takwahoni Formation; Planulata Zone (Middle Toarcian). 3, 6. Phymatoceras hillebrandti Jakobs, 1994 3. Specimen: -; Locality 13; Takwahoni Formation; Hillebrandti Zone (Late Toarcian). 6. Specimen: -; Locality 13; Takwahoni Formation; Hillebrandti Zone (Late Toarcian).  4a, b.-5. Phymatoceras sp.  4a, b. Specimen: FS-Sp.44; Locality 13; Takwahoni Formation; Hillebrandti Zone (Late Toarcian). 5. Specimen: FS-Sp.45; Locality 13; Takwahoni Formation; Hillebrandti Zone (Late Toarcian).  7. Podagrosites sp. Specimen: FS-Sp.43; Locality 12; Takwahoni Formation; Hillebrandti Zone (Late Toarcian).  8a, b. Hildaites sp. Specimen: FS-Sp.39; Locality 10; Takwahoni Formation; Planulata Zone (Middle Toarcian).  162  163  E X P L A N A T I O N OF P L A T E 6 A l l figures are natural size unless otherwise indicated  Figure I A . Sonninia cf. adicra Westermann & Riccardi, 1972 Specimen: F S - S p . 5 2 - A . B ; Locality 16; Takwahoni Formation; Early Bajocian.  I B . Dorsetensia sp.  Specimen: F S - S p . 5 2 - A . B ; Locality 16; Takwahoni Formation; Early Bajocian.  2. Sonninia sp. Specimen: FS-Sp.49; Locality 15; Takwahoni Formation; Early Bajocian.  3a, b. Stephanoceras sp.  Specimen: FS-Sp.53; Locality E10; Takwahoni Formation; Early Bajocian.  4. Stephanoceras kirschneri Arthur, 1985 Specimen: - ; Locality E10; Takwahoni Formation; Early Bajocian.  5. Fontannesia sp.  Specimen: FS-Sp.48; Locality 14; Takwahoni Formation; Late Aalenian-Early Bajocian.  6. Normannites sp.  Specimen: -; Locality E10; Takwahoni Formation; Early Bajocian.  164  PLATE 6  E X P L A N A T I O N OF P L A T E 7 A l l figures are natural size unless otherwise indicated  Figure 1, 2. Amaltheus margaritatus (de Montfort, 1808) 1. Specimen: -, Locality E 4 / E 5 ; Takwahoni Formation; Kunae/Carlottense Zones (Late Pliensbachian). 2. Specimen: -, Locality E 5 ; Takwahoni Formation; Carlottense Zone (Late Pliensbachian). 3-7a,  b. Amaltheus stokesi (J. Sowerby, 1818) 3. Specimen: -, Locality E4; Takwahoni Formation; Kunae Zone (Late Pliensbachian). 4. Specimen: -, Locality E 4 ; Takwahoni Formation; Kunae Zone (Late Pliensbachian). 5. Specimen: -, Locality E 4 ; Takwahoni Formation; Kunae Zone (Late Pliensbachian). 6. Specimen: -, Locality E4; Takwahoni Formation; Kunae Zone (Late Pliensbachian). 7a, b. Specimen: -, Locality E4; Takwahoni Formation; Kunae Zone (Late Pliensbachian).  166  PLATE 7  4  5  167  E X P L A N A T I O N OF P L A T E 8 A l l figures are natural size unless otherwise indicated  Figure 1. Weyla sp. indet. Specimen: FS-Sp.55; Locality 2; Takwahoni Formation; Late Pliensbachian. 2. Pectinid gen indet. Specimen: FS-Sp.56; Locality 2; Takwahoni Formation; Late Pliensbachian. 3a, b. Pleuromya sp. indet. Specimen: FS-Sp.57; Locality 2; Takwahoni Formation; Late Pliensbachian. 3 a: Left valve of internal mould. 3b: Top view of internal mould. 4a, b. Gastropoda gen indet. Specimen: FS-Sp.58; Locality 2; Takwahoni Formation; Late Pliensbachian.  PLATE 8  E X P L A N A T I O N OF P L A T E 9 A l l figures are natural size unless otherwise indicated  Figure la, b. Trigonia sp. indet. Specimen: FS-Sp.59; Locality 13; Takwahoni Formation; Late Toarcian.  2. Trigonia sp. indet. Specimen: FS-Sp.60; Locality 13; Takwahoni Formation; Late Toarcian.  3a, b. Pectinid gen indet. Specimen: FS-Sp.61; Locality 2; Takwahoni Formation; Late Pliensbachian.  4.  Crassitella sp. indet. (Coral) Specimen: FS-Sp.62; Locality 1; Sinwa Formation; Late Triassic.  5a, b. Bositra sp. indet. Specimen: FS-Sp.63; Locality 12; Takwahoni Formation; Late Toarcian.  PLATE 9  

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