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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 PALEONTOLOGY OF THE TAKWAHONI ANDLSINWAlFORMATIONS AT LISADELE^LAKE, .TULSEQUAH MAP-AREA, NORTHWESTERN BRITISH COLUMBIA by F A R S H A D S H I R M O H A M M A D 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 BRIT ISH C O L U M B I A May 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 of 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 of the isotopic ages of 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 mi l l ion years. TABLE OF CONTENTS Abstract 1 1 Table of Contents . iv List of Tables 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 9 2.1 Tectonic Setting 9 2.1.1 Intermontane Superterrane 9 2.2 Stratigraphy 13 2.2.1 Stuhini Group 13 2.2.2 Laberge Group 18 2.2.3 Bowser Lake Group 20 2.3 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 THE 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 68 CHAPTER V CONGLOMERATE ANALYSES 72 5.1 Introduction 72 5.2 Conglomeratic Units 72 5.2.1 Conglomerate Unit 1 74 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 • 87 5.4.4 Metamorphic Clasts 88 5.4.5 Chert Clasts 88 CHAPTER VI SANDSTONE PETROGRAPHY 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 SUMMARY AND CONCLUSIONS 97 7.1 Biochronology and Biostratigraphy. 97 vi 7.2 Correlation 100 7.3 Geochronology 104 7.4 Depositional and Tectonic Setting 105 REFERENCES 110 APPENDICES • 119 PLATES 154 vii List of Tables Page Tab les 1. E s t i m a t e d t h i c k n e s s 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 and the Y u k o n . M o d i f i e d after M i h a l y n u k et a l . , 1999 . L o c a t i o n s g i v e n i n F i g u r e 9. Tab l e 2. N a t u r e o f the basa l contac 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 the Y u k o n . M o d i f i e d after M i h a l y n u k et a l . , 1999 . L o c a t i o n s g i v e n i n F i g u r e 9. Tab l e 3. U/Pb S H R I M P a n a l y t i c a l data . Tab l e 4. U/Pb T I M S a n a l y t i c a l data . Tab l e 5. A r / A r a n a l y t i c a l data f o r c las t s amp le C 3 Tab l e 6. A r / A r a n a l y t i c a l da ta f o r c las t s amp le C 4 56-58 62 66 67 Tab l e 7. A s u m m a r y o f the resul ts a n d the c a l c u l a t e d d i f f e r ence be tween the age 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 rences i n m i l l i o n s o f years , i n d i c a t i n g v e r y r ap id sequence o f arc d e v e l o p m e n t , up l i f t , d i s s e c t i o n , a n d d e p o s i t i o n in to the ad jacent bas 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 and ea r l y M i d d l e Ju rass i c . 69 Tab l e 8. G e o c h r o n o l o g i c a l and b i o c h r o n o l o g i c a l results p lo t t ed o n the Ju rass i c t i m e sca le . T h e Ju rass i c t i m e sca le is f r o m P a l f y et a l . , ( 2000 ) . N u m b e r s i n b l ue a n d red are f r o m the present study. 71 Tab l e 9. C o n g l o m e r a t e c las t coun t data o f L o w e r to M i d d l e Ju rass i c c o n g l o m e r a t e units i n the L i s a d e l e L a k e area. 84 Tab l e 10. P o i n t coun t data f r o m L i s a d e l e L a k e sandstones . 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 v i i i 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 northeast-directed 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 GSC 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 SHRIMP 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 SHRIMP 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 SHRIMP 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 Ma. 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 GSC 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 80 Figure 44. Upper Toarcian metamorphic-rich clasts conglomerate of unit 4 with orange to brown-orange matrix. 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. Atl in 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. RSL = 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. RSL = Relative Sea-Level. Modified after Dickie and Hein, 1995. 109 x i i 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 x i i i 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 in my life. First, my sincerest gratitude goes to my supervisor Professor Paul L. Smith. This project was suggested, shaped, directed, and conducted under his supervision and guidance. His endless supply of patience, excellent humor, and extensive knowledge helped me develop both personally and academically. I would like to thank Dr. Bob Anderson (GSC Vancouver) for sharing his invaluable knowledge of the Canadian Cordillera, as well as his field knowledge and support in summer 2004. Dr. Anderson's critical review of this manuscript is also greatly appreciated. I owe a great deal to Dr. Stuart Sutherland for his inexhaustible resource of assistance, great sense of humor, and valuable guidance in completion of this thesis project. Dr. Sutherland's critical review of this manuscript is gratefully acknowledged. In addition, I wish to thank him as my wrestling coach here at U B C . Special thanks to V i c k i J . McN ico l l , isotope geoscientist from Geological Survey of 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 Gr imm 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 Lou Bevier (UBC) and Huawei Cai (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 (GSC, 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 lex Al len, Deborah Varley, Teresa Woodely, Mandy Wu, Sukhi Hundal, David Jones, Kar im Damani, Thomas Ul l r ich (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 (GSC, 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 Emi ly 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 EOS 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 Le 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 of 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 xv i last two years, Le 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 of 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 of 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 of 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 Middle Jurassic time. In addition, age constraints of detrital zircons in sandstone matrices and of 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 Alaska 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 At l in . There are no roads or established trails within the map area. Helicopter from Dease Lake or At l in 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 [East ing: 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 Gold Rush of 1896 and a major gold discovery in the At l in 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 km 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 /12 ; 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 (NTS 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-fil l 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 in 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 of 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 0 250 500 kilometres 130° led States o f Arrterica I 115' Figure 1. Map showing the location of the study area in the northwestern British Columbia. 7 Figure 2. Study area with regard to the Cordilleran Terranes. Modif ied after Wheeler and McFeely, 1991. 8 CHAPTER II REGIONAL GEOLOGICAL SETTING 2.1 Tectonic Setting Four major building blocks form the terrane superstructure of northwestern British Columbia: 1. A western block of polydeformed, metamorphosed Proterozoic to middle Paleozoic pericontinental rocks (Nisling assemblage of Yukon Tanana Terrane as used by Mortensen, 1992); 2. A n eastern block of oceanic crust and low-latitude marine strata (Cache Creek Terrane of Coney et al., 1980); 3. Central blocks including Paleozoic Stikine assemblage (Monger, 1977; Brown et al., 1991); and, 4. Triassic arc-volcanic and flanking sedimentary rocks of Stikine Terrane, and overlying Lower to Middle Jurassic arc-derived strata of 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 of the succession marks the uplift and erosion of 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). View 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) B a a CC (Cache Creek) I 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) J u r a s s i c Sed imentary B a s i n s I Bowser Basin • Whitehorse Trough (Takwahoni facias) | \ Whlehorse Trough (Inklin facias) 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. Modif ied 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; Ash 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 Yukon is carried over coarse-grained strata of the Lower Jurassic Takwahoni Formation in the hanging wal l of the K ing 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 Yukon 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 At l in 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 At l in 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 Yukon 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 iew 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 iew is to the south. 17 2.2.2 Laberge Group: Cairns (1911) used "Laberge series" to include conglomerates, greywackes and argillites along the shores of 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, in the Tulsequah area, Souther (1971) divided the Laberge Group into the proximal, fossiliferous, shallow water Takwahoni, and deep-water, fossil -poor Inklin formations. More recently, researchers have used Takwahoni and Inklin formation names to distinguish strata of different provenance. For example, Wheeler and McFeely (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 in different areas. In the Lisadele Lake area, the Sinwa Formation is unconformably overlain by about 3000 meters of coarse clastic Lower and Middle Jurassic sediments. 18 Author Thickness in metres Area Cairns, 1912 1500 Wheaton River Cockfield and Bell, 1926 >3050 Whitehorse Bostock, 1936 2750 Carmacks Wheeler, 1961 2425 Whitehorse S o u t h e r , 1971 3 1 0 0 I n k l i n ; 3 3 5 0 T a k w a h o n i Tulsequah Bultman, 1979 5000-7000 Bennett-Atl in Dickie, 1989 >3000 Whitehorse Johannson, 1994 3500-4000m total Inklin southern Atlin M i h a l y n u k et a l . , 1 9 9 9 4 0 0 0 Tulsequah T h i s s t u d y , 2 0 0 6 - 3 0 0 0 Tulsequah Table 1. Estimated thickness of the Laberge Group in British Columbia and the Yukon. Locations given in figure 9. Modif ied after Mihalynuk et al., (1999). Laberge area, Bostock and Lees, 1938: Conformably overlies Lewes River (Stuhini) Group; may be disconformable Whitehorse area, Wheeler, 1961: At least two locations display a disconformable contact with underlying Lewes River (Stuhini) Group. Bennett-Atlin, Bultman, 1979: Mainly 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. Modif ied 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 mid-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 of 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 0 250 500 i i • kilometres 1 130° States of America 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 West East Stikinia Stikinia Early Jurassic Stuhini arc volcanics Cache Creek Nisl ing 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 McGowan (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 of ichthyoliths and fragments of 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 of endemic species, it is difficult to apply the standard northwest European zonal scheme of 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). As 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 in this study (Hall and Westermann, 1980; Taylor, 1988). 25 Geochronologic time scales express the estimated numerical ages of chronostratigraphic units in millions of 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 BAJOCIAN I. Epizigzagiceras • 174 0+79 BAJOCIAN Rotundum BAJOCIAN I. Oblatum BAJOCIAN Kirschneri BAJOCIAN Crassicostatus BAJOCIAN Widebayense < 7 < Howell i » 177 6 +! i Scissum h 178 0 +i ? Westermanni TO\R( 1 W 1. Yakounensis h 180 1 "lo TO\R( 1 W Hillebrandti b 181 4+l? TO\R( 1 W M Crass icosta TO\R( 1 W Planulata b 1 Jtt fi+!T TO\R( 1 W I: Kanense < < £0 V. Z w 1. 1-Carlottense » 184 1^6 Kunae h 185 7"ni Freboldi h 186 7 +\i Whiteavesi Imlayi — • 191.5+-J:? Figure 11. North American Early and Middle Jurassic ammonite biochronological units. Modif ied 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 LOCALITIES TAXA 1 El F.2 E3 E4 2 2.1 3 4 E5 E6 E7 E8 5 6 7 8 9 10 11 12 13 E9 14 IS 16 17 18 E10 TAXA Omojw'cn'ites sp. • Omojuvavites sp. Eclolcites sp. • Ectolcites sp. 0 Metaderoceras sp. Fuciniceras sp. 0 0 Fuciniceras sp. Arieticeras sp. 0 0 Arieticeras sp. Fanninoceras (Fanninoceras) sp. o • Fanninoceras (Fanninoceras) sp. Fuciniceras cf. intumescens o • Fuciniceras cf. intitmescens 0 • • • • 0 Pmtogrammoceras (Pmlogrammoceras) sp. Amallheus slokesi o 0 Amallheus stukesi Amallheus margaritalus 0 0 Amaltheu. margaritalus Arieticeras cf. algovianum o • Arieticeras cf. algovianum Pmtogrammoceras cf. pectinatum o Pmtogrammoceras cf. pectinatum Leptaleoceras accuratum 0 Leptaleoceras accuralum • Fanninoceras (Fanninoceras) kunae Fanninoceras (Charlotticeras) cf. maudense • • Arieticeras cf. micrasterias Reynenoceras cf. italicum • Reynenoceras cf. italicum Fonlanelliceras sp • • Pmlogrammoceras (Pwlogrammoceraj) cf. pallum 0 • o o • Lioceratoides (Pacificeras) angioma • Lioceialoidei (Pacificeras) angioma 0 • o Lioceratoides (Pacificeras) sp. Tillonicerus antiquum o Ttltoniceras antiquum Lioceratoides (Pacificeras) propinquum 0 0 • Lioceratoides (Pacificeras) pmpinquum Fieldingiceras sp. 0 Fieldingiceras sp. Dactylioceras sp. o o • • Dactylioceras sp. Dactylioceras cf kanense 0 Dactylioceras cf. kanense Fonlanelliceras ex grfonlaiiellense • • Fontanelliceras ex gr fonlaiiellense Harpoceras sp. • • • Harpoceras sp. Cleviceras sp. • • o Cleviceras sp. Taffertia cf laffertensis o Taffertia cf laffertensis Harpoceras cf. svbplanatum • Harpoceras cf. subplanatum Leukadiella wmiratica • Leukadiella amuralica Peronoceras sp. o o Pewnoceras sp. Hiklaites mjirleyi? 0 Hildailes iinuleyi? Hildailes sp. • Hildailes sp. Dactylioceras cf. commune • • Dactylioceras cf. commune leukadiella sp. • • Leukadiella sp. Fseudolioceras sp. o o Fseudolioceras sp. Fseudolioceras cf. lythense o Fseudolioceras cf. lythense Pliylloceras sp. o Pliylloceras sp. Phymalocerus hillebrandli • Phymalocerus hillebrandli Podagrosites sp. • Podagrosiles sp. o Podagrosiles latescens Phymatuceras sp. • Phymalocerus sp. Pianammaloceras sp. o Pianammaloceras sp. Fonlannesia sp. • Fonlannesia sp. Sonninia spp. • • • Sonninia spp. Sonninia cf. adicra • Sonninia cf. adicra Dorsetensia spp. • • Dursetensia spp. Stephanoceras spp. • Stephanoceras spp. S. (Skirmceras) cf. kirschneri • S. (Skirmceras) cf. kirschneri Normanniles sp. o Normannites sp. Chondmceras cf. allani 0 Chondmceras cf. allani Chondmceras defontii o 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 Lake 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. 611000m. E. 615000m. E. 6508000m. N . © Ammonite locality © Bivalve locality ^ Gastropod locality © Crinoid locality Ichthyolith locality y Fault Lake Unit 5: Chert pebbles fn0<?»m and granules 58° 4 0 ' N Unit 4: Metamorphic-rich clasts conglomerate. 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 6502000m. N . Eocene Sloko Group Eocene Sloko Group SIS Lower & Middle Jurassic B L G Lower & Middle Jurassic Laberge Group Takwahoni Formation U|»pcr Triassic Stuhini Group Sinwa Formation MJB U P UTrS S I S : Volcanic package dominated by rhyolite flows, light to medium grey and white: Eocene. White to light grey quartz porphyry intrusive: probably genetically related to E S . Chert-pebble conglomerate: Lower Bajocian. Argillites, thinly bedded greywacke-siltstone couplets: Lower Bajocian. Conglomerates, medium-to thick-beddedgreywackes, siltstones and mudstones: Toarcian. Conglomerates, greywackes, shales, siltstones and mudstones: Pliensbachian. Conglomerates, bioclastic sandstones, siltstones and mudstones: Lower Jurassic (Sinemurian?) Fossiliferous thick-bedded to massive, light grey limestone: Norian. S l o k o Intrusive Suite B L G = B o w s e r Lake G r o u p F igure 15. G e o l o g i c m a p s h o w i n g d is t r ibut ion o f the five L i sade l e L a k e success ion cong lomera t i c units and locat ion o f foss i l and geochrono logy samples. 31 3.2 Upper Triassic Sinwa Formation: The precise age o f the uppermost beds of the Sinwa Formation is important in 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 of 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 of 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 of the Whitehorse Trough (Fish Lake Syncline, Yukon Territory), and northern Alaska (Smith et al., 2001). 33 Figure 16 D. OO to E l i l S I Clay | U I C M F | c|vc| Graval | LEGEND P^T*J Limestone j". • , j Sandstone TfTl Pebbly °° ° n 1 Sandstone p.'*^ Conglomerate T T - q Sand and siltstone • • I interbeds | .: ;| Sandy silt Siltstone p ^| Dike & Sill [22] A r g n i i t e ^X^ Covered Plutonic rich clasts Volcanic rich clasts Metamorphic rich clasts Chert rich clasts Limestone rich clasts • In situ locality O Ex situ locality jg) Ammonite locality © Bivalve D<±=> Ichthyolith | _J X metre removed for drafting ^ Gastropod © Crinoid £2> Brachiopod ^ U/Pb age date: detrital zircon ^ U/Pb age date: granitoid clast <^ Ar/Ar age date: metamorphic clast /www Unconformity 1-14 Stratigraphic location of sandstones, see also Chapter 6, Table 9. convenience 34 T A K W A H O N I FORMATION Upper Pliensbachian STAGE : Kunae | C Z ZONATION 200^ w o 1 1 1 1 1 1 1 1 1 THICKNESS X •'•••r.'---i-- l--r ,-p.: 0;-p.: 0;-p. # .-9--Q-.-P--Q--2> ."••-fL-.f-L-.,- • X • I.-. LITHOLOGY LITHOLOGY In Situ Localities WWW KJ UJ Ji. Ex Situ Samples o Fieldingiceras sp. O Leptaleoceras accurafum Fanninoceras (Fanninoceras) sp. . t ||||H'|'||1'|L|I 1 I I I M I M l l M M a M M M M M M I I M M M M M Fuciniceras sp. — o - o Arieticeras sp. c >—0 Amaltheous cf. stokesi c Amaltheus cf. margaritatus • 1 Fanninoceras (Fanninoceras) kunae • Fanninoceras (Charlotticeras) cf Maudense • Arieticeras cf. micrasterias c >-• Arieticeras cf. algovianum • Reynenoceras cf. italicum Fuciniceras cf. intumescens c > Lioceratoides (Pacijiceras) propinquum ( ) Protogrammoceras cf. pectinatum ( i Protof^raniftioccras (P' rolo^rammoceras) sp T T * Fontanelliceras sp. Tiltoniceras antiquum d 1 Lioceratoides (Pacijiceras) sp. > Lioceratoides (Pacijiceras) angionus < » Fieldingiceras fieldigii <j i Protogrammoceras (Protogrammoceras) cfpaltum Legend as for Figure 16. © • s ® O ® n ^ O ^ ® O O O ^ ro In Situ Loca l i t i es Ex Situ Samples c ) Phylloceras sp. c Podagrosites latescens 4 Hildaites sp. 1 Dactylioceras sp. T " 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 3 w 1-1 ,-o::0:-p::. .•P-:0:-o-: CD to J /« Situ Loca l i t i e s cn Ex Situ Samples Phymatoceras sp. Phymatoceras cf. hillebrandli Planammatoceras sp. r CD OQ a a JO o ON 1 Aalenian (?) TAKWAHONI B A J O C I A N 1 I L ro o o J I L I L i . ' • - i . ' • - i FORMATION THICKNESS (meters) H O r o c << 3 rjq' R n to to J> /« S/ta Localities 1 m Ex Situ Samples Fonlannesia sp. Planammatoceras sp. O r o n a w ft On 1^  31 fjq' s to <~fi O n - J In Situ Localities Ex Situ Samples Sonninia spp. • Sonninia cf. adicra 4 • Dorsetensia spp. Figure 24 Legend as for Figure 16. 42 Legend as for Figure 16. 4 3 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 of 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 of 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 l inking 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 Yukon and At l in Lake areas (Aberhan, 1998). Elsewhere, Bositra forms shell pavements in rocks as old as Middle Toarcian (Damborenea, 1987; Etter, 1996; Hallam, 1995). A coarse-grained 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 km 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 15-17 (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 chert-pebble 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 of sedimentary rocks is a well-established tool for evaluating the relationship between tectonic activity and provenance of the sediments. The age distribution of 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 of ages points to one or a few sources. As well , U-Pb isotopic dating of 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 of 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 of the source(s) providing clastic materials to adjacent basins. 4.2 Methods Geochronological studies of samples of detrital zircons and plutonic clasts from Lower Jurassic strata were completed at the Geological Survey of Canada Geochronology Laboratory in Ottawa (see Appendix X). This includes S H R I M P (Sensitive High Resolution Ion Microprobe) analyses of detrital zircons from three sandstone samples, and U-Pb ID -TIMS (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 w O « w as •< = o • 1= THICKNESS (meters) LITBOLOCY 2 9 0 0 - F 2500-4 2000 1500—1 . — ^ U/Pb age date: sandstone detr i ta l z i r c o n ^ U/Pb age date: g ran i to id c last ^ A r / A r age date: me tamorph i c c last g) A m m o n i t e l oca l i t y B L G = B o w s e r L a k e G r o u p 1 U n i t 5: Chert-pebble cong lomera te ISMS Un i t 4: M c t a m o r p h i c - r i c h clast cong lomera te j§§ U n i t 3: P lu ton ic-r i ch c last cong lomerate *3 I T U n i t 2: Vo l can i c- r i ch c last cong lomerate U n i t 1: L imes tone-r i ch c last cong lomerate M u d s t o n e Sandstone and si l tstone L imes tones tone 184.4 ± 1 M a : S a m p l e S3 (S.J-1) O >160.1±1.3 M a : S a m p l e C 4 ( M X g l . 4 - C 4 ) ^ 177 ±15 M a : S a m p l e C 3 ( M . C g l . 5 - C l ) 1 0 0 0 -221 M a : Sample C2 (Cgl-3) .4 186 M a : Samp le C I (Cgl-1) 5 0 0 g — • 184.4±1.2 Ma: Sample S2 (S.b.Cgl-1) -© £3 • 189.6±1 Ma: Sample SI (S.Cgl-f) 0 • -• . ' i l l 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 . McNico l l ) . 51 0.140 0.120 0.100 H = 0.080 XI (0 o 0.060 •{ CL 0.040 0.020 0.000 SHRIMP II data 1 8 9 . 6 ± 1 . 0 M a Det r i ta l z i r c o n d a t a c o m p r i s e d o f o n e a g e p o p u l a t i o n n=31 "i 1 r 170 180 190 Age (Ma) ™i r 210 18 17 16 15 14 13 12 11 Tl 10 CD XI 9 c CD 8 3 7 O «< 6 5 4 3 2 1 0 Figure 28. The age of detrital population of the sample SI (S.Cgl-f) (by courtesy of V i c k i J . McNicol 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) z i r c o n s f o r 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 . McNicol l ) . 0.100 0.090 0.080 0.070 § 0.060 H RJ 0.050 -| jQ 2 0.040 CL 0.030 -0.020 -0.010 0.000 SHRIMP II data Al l data n=38 -i r 165 175 184.4 ±1.2 Ma , n=35 Age of youngest dominant population of detrital zircon data Older detrital zircons / r — r 15 14 h 13 12 11 r 10 9 8 7 6 r 5 4 3 r 2 1 0 Tl n c CD 3 o 185 195 Age (Ma) 205 Figure 30. The age of detrital population of the sample S2 (S.b.Cgl-1) (by courtesy of V i c k i J . McNicol l ) . 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 . McNicol 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 in 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 Ma , 205 M a , 215 M a , and 220 Ma . 0 .090 0 .080 0 .070 0 .060 = 0 .050 X> CO •2 0 .040 32 a SHRIMP II data All data n=47 1420 i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i ' i ' i i i i i ' i ' i i r l 27 24 23 20 19 15 2 j § 11 o j o x 8 7 4 3 0 150\250 350 450 550 650 750 850 950 10501150125013501450 Age (Ma) 32b 0.100 • 0 .090 -0.080 -0.070 • 0.060 -abi 0.050 -n o l . 0.040 -rx 0.030 • 0.020 • 0.010 • 0 .000 184.4 ±1.0 Ma Age of youngest dominant population of detrital zircon data n=46 CD X I c CD 3 o >< 1 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 ' 60 170 180 190 200 210 220 230 240 Age (Ma) Figures 32a (above), and 32b (below) show the age of detrital population of the sample S3 (by courtesy of V i c k i J . McNicol l ) . 55 Table 3: U/Pb SHRIMP analytical data Ages (Ma)" Ages (Ma)6 Spot name U Th Th Pb* 2 MPb 2 MPb 2 MPb 2 MPb 2 MPb 207Pb 207Pb 20sPb 2 MPb Corr 207Pb 207Pb 2 , 6Pb 206Pb 20sPb 2 MPb (ppm) (ppm) U (ppm) (PPb) 2MPb 206Pb f(206)2M 2°6Pb 2ospb 2 M U 2 M U 2 3 !U 2 M U Coeff 2oepb 20ePb 2 M U 2 M U Z M U 2 M U Sandstone sample S1 (z8463; field number S.cgl-f) 8463-1.1 341 121 0.367 10 8 0.000963 0.000283 0.0167 0.1102 0.0116 0.2094 0.0194 0.0295 0.0004 0.267 0.0516 0.0046 187 2 187 2 8463-2.1 647 319 0.510 20 14 0.000860 0.000191 0.0149 0.1469 0.0082 0.1886 0.0132 0.0295 0.0003 0.285 0.0464 0.0031 187 2 188 2 8463-3.1 665 366 0.569 21 3 0.000201 0.000168 0.0035 0.1864 0.0075 0.2125 0.0133 0.0299 0.0003 0.301 0.0516 0.0031 190 2 189 2 8463-4.1 489 302 0.639 16 6 0.000435 0.000301 0.0075 0.2163 0.0138 0.2269 0.0212 0.0306 0.0004 0.265 0.0539 0.0049 194 3 193 2 8463-5.1 546 296 0.560 17 11 0.000780 0.000229 0.0135 0.1655 0.0101 0.1923 0.0162 0.0300 0.0004 0.297 0.0465 0.0038 191 3 191 3 8463-6.1 672 398 0.611 22 8 0.000442 0.000189 0.0077 0.2021 0.0082 0.1992 0.0138 0.0302 0.0004 0.299 0.0478 0.0032 192 2 192 2 8463-92.1 579 282 0.504 18 6 0.000411 0.000177 0.0071 0.1602 0.0098 0.1977 0.0158 0.0295 0.0004 0.280 0.0486 0.0038 187 2 187 2 8463-93.1 742 418 0.582 24 4 0.000201 0.000125 0.0035 0.1825 0.0067 0.2128 0.0097 0.0304 0.0004 0.391 0.0509 0.0022 193 2 192 2 8463-94.1 538 303 0.581 17 3 0.000193 0.000134 0.0033 0.2047 0.0069 0.2178 0.0105 0.0300 0.0004 0.360 0.0526 0.0024 191 2 190 2 8463-96.1 538 264 0.507 17 3 0.000200 0.000261 0.0035 0.1645 0.0108 0.2178 0.0186 0.0300 0.0004 0.269 0.0526 0.0044 191 2 190 2 8463-104.1 622 326 0.542 20 8 0.000503 0.000174 0.0087 0.1746 0.0078 0.1931 0.0126 0.0300 0.0004 0.319 0.0467 0.0029 191 2 191 2 8463-81.1 478 214 0.462 15 7 0.000605 0.000249 0.0105 0.1397 0.0113 0.1978 0.0170 0.0297 0.0004 0.271 0.0483 0.0040 189 2 189 2 8463-71.1 351 121 0.356 10 7 0.000784 0.002279 0.0136 0.1139 0.0853 0.2027 0.1468 0.0295 0.0012 0.181 0.0498 0.0358 188 8 187 2 8463-72.1 540 207 0.397 16 9 0.000665 0.000190 0.0115 0.1231 0.0107 0.2014 0.0186 0.0301 0.0004 0.269 0.0485 0.0044 191 3 192 3 8463-49.1 487 204 0.433 15 8 0.000642 0.000218 0.0111 0.1332 0.0092 0.1952 0.0151 0.0295 0.0004 0.288 0.0481 0.0036 187 2 187 2 8463-48.1 406 144 0.365 12 11 0.001091 0.000298 0.0189 0.1036 0.0120 0.1893 0.0205 0.0296 0.0004 0.247 0.0465 0.0049 188 2 188 2 8463-47.1 638 325 0.526 20 1 0.000056 0.000464 0.0010 0.1763 0.0177 0.2319 0.0316 0.0302 0.0005 0.237 0.0557 0.0074 192 3 191 3 8463-40.1 425 182 0.443 13 6 0.000532 0.000199 0.0092 0.1417 0.0088 0.2111 0.0144 0.0300 0.0004 0.317 0.0511 0.0033 190 3 190 2 8463-34.1 750 542 0.746 25 10 0.000525 0.000158 0.0091 0.2327 0.0095 0.1989 0.0115 0.0302 0.0004 0.346 0.0478 0.0026 192 3 192 2 8463-33.1 646 306 0.490 21 10 0.000567 0.000206 0.0098 0.1527 0.0089 0.2039 0.0148 0.0308 0.0004 0.286 0.0481 0.0034 195 2 196 2 8463-32.1 457 184 6.417 13 12 0.000981 0.000248 0.0170 0.1156 0.0102 0.1873 0.0172 0.0295 0.0004 0.258 0.0461 0.0041 187 2 188 2 8463-53.1 720 505 0.724 23 10 0.000528 0.000239 0.0092 0.2278 0.0105 0.1933 0.0161 0.0297 0.0004 0.263 0.0472 0.0038 189 2 189 2 8463-55.1 584 289 0.510 18 7 0.000485 0.000180 0.0084 0.1561 0.0107 0.2086 0.0131 0.0300 0.0003 0.302 0.0504 0.0031 191 2 191 2 8463-73.1 547 274 0.516 17 11 0.000754 0.000186 0.0131 0.1613 0.0082 0.1933 0.0131 0.0294 0.0004 0.296 0.0478 0.0031 187 2 187 2 8463-74.1 489 183 0.387 15 8 0.000616 0.000262 0.0107 0.1393 0.0108 0.2171 0.0183 0.0298 0.0005 0.304 0.0529 0.0043 189 3 188 3 8463-88.1 506 233 0.475 16 5 0.000402 0.000305 0.0070 0.1513 0.0149 0.2201 0.0209 0.0298 0.0004 0.253 0.0536 0.0050 189 2 188 2 8463-90.1 331 133 0.414 10 3 0.000380 0.000555 0.0066 0.1552 0.0218 0.2313 0.0372 0.0301 0.0005 0.221 0.0557 0.0088 191 3 190 2 8463-85.1 367 155 0.437 11 5 0.000533 0.000216 0.0092 0.1443 0.0136 0.2171 0.0192 0.0294 0.0004 0.259 0.0535 0.0046 187 2 186 2 8463-86.1 370 143 0.398 11 4 0.000378 0.000317 0.0066 0.1301 0.0140 0.2148 0.0220 0.0299 0.0004 0.265 0.0521 0.0052 190 3 189 3 8463-87.1 429 186 0.447 13 10 0.000883 0.000237 0.0153 0.1310 0.0122 0.1849 0.0204 0.0297 0.0004 0.235 0.0452 0.0049 188 2 189 2 8463-9.1 419 164 0.405 13 8 0.000729 0.000273 0.0126 0.1305 0.0114 0.1894 0.0212 0.0301 0.0010 0.422 0.0457 0.0047 191 6 192 6 OS. 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 8465-80.1 244 136 0.575 7 6 0.000988 8465-52.1 264 140 0.547 8 4 0.000567 8465-55.2 484 199 0.424 14 7 0.000581 8465-59.1 305 203 0.686 9 8 0.001036 8465-5.1 301 128 0.440 9 8 0.001097 8465-75.1 456 259 0.588 14 6 0.000558 8465-70.1 166 76 0.476 5 8 0.001905 8465-14.1 400 292 0.754 12 10 0.000959 8465-6.1 400 216 0.558 12 8 0.000766 8465-60.1 259 121 0.483 8 5 0.000821 8465-10.1 214 177 0.854 7 5 0.000918 8465-101.1 256 155 0.626 8 2 0.000289 8465-58.1 382 173 0.468 12 3 0.000360 8465-53.1 312 133 0.440 9 5 0.000696 8465-11.1 254 141 0.573 8 5 0.000847 8465-7.2 769 468 0.628 24 4 0.000194 8465-18.1 289 78 0.281 8 9 0.001227 8465-71.1 504 263 0.540 15 9 0.000728 8465-69.1 719 556 0.799 24 6 0.000317 8465-81.1 227 77 0.351 7 5 0.000874 8465-56.1 331 107 0.335 9 10 0.001152 8465-13.1 550 312 0.587 17 7 0.000475 8465-15.1 339 185 0.565 11 2 0.000230 8465-19.1 396 275 0.718 13 5 0.000502 8465-1.1 579 189 0.338 17 2 0.000110 8465-74.1 503 373 0.765 16 9 0.000713 8465-9.1 572 294 0.530 17 11 0.000720 8465-47.1 756 354 0.484 23 9 0.000471 8465-94.1 772 534 0.714 25 6 0.000288 8465-20.1 537 351 0.674 17 5 0.000401 8465-92.1 475 174 0.378 14 4 0.000353 8465-12.1 698 255 0.377 21 3 0.000144 8465-44.1 952 766 0.832 33 7 0.000271 8465-17.1 559 328 0.605 18 5 0.000319 8465-82.1 752 409 0.561 24 7 0.000371 8465-55.1 1101 682 0.640 36 3 0.000120 8465-7.1 903 284 0.325 28 9 0.000358 0.001479 0.0527 0.1833 0.0574 0.1104 0.0920 0.0276 0.000360 0.0171 0.1782 0.0155 0.1682 0.0231 0.0282 0.000499 0.0098 0.1947 0.0226 0.2094 0.0315 0.0283 0.000587 0.0101 0.1384 0.0224 0.2071 0.0374 0.0283 0.000386 0.0180 0.2154 0.0192 0.1851 0.0257 0.0283 0.000368 0.0190 0.1210 0.0156 0.1766 0.0241 0.0285 0.000243 0.0097 0.1864 0.0119 0.1985 0.0162 0.0285 0.000508 0.0330 0.1396 0.0208 0.1763 0.0331 0.0285 0.000816 0.0166 0.2199 0.0334 0.1791 0.0512 0.0286 0.000283 0.0133 0.1839 0.0120 0.1880 0.0187 0.0286 0.000470 0.0142 0.1604 0.0188 0.2036 0.0303 0.0286 0.000710 0.0159 0.2847 0.0541 0.1726 0.0463 0.0287 0.000422 0.0050 0.1990 0.0175 0.2330 0.0294 0.0288 0.000282 0.0062 0.1697 0.0118 0.2165 0.0189 0.0288 0.000283 0.0121 0.1391 0.0133 0.1891 0.0189 0.0289 0.000406 0.0147 0.1774 0.0170 0.1977 0.0276 0.0289 0.000371 0.0034 0.2096 0.0146 0.2142 0.0244 0.0289 0.000391 0.0213 0.0747 0.0154 0.1863 0.0256 0.0290 0.000266 0.0126 0.1616 0.0110 0.1836 0.0176 0.0290 0.000173 0.0055 0.2635 0.0131 0.2066 0.0141 0.0290 0.000558 0.0151 0.1247 0.0219 0.2081 0.0368 0.0291 0.000338 0.0200 0.1020 0.0137 0.1735 0.0226 0.0291 0.000180 0.0082 0.1818 0.0095 0.1921 0.0129 0.0292 0.000229 0.0040 0.1905 0.0156 0.2146 0.0165 0.0294 0.000258 0.0087 0.2308 0.0117 0.2125 0.0186 0.0294 0.000263 0.0019 0.1175 0.0104 0.2176 0.0176 0.0294 0.000169 0.0124 0.2255 0.0106 0.1901 0.0129 0.0294 0.000233 0.0125 0.1602 0.0097 0.1899 0.0161 0.0294 0.000127 0.0082 0.1572 0.0059 0.1979 0.0093 0.0294 0.000140 0.0050 0.2282 0.0067 0.2093 0.0101 0.0295 0.000162 0.0070 0.2097 0.0087 0.2026 0.0115 0.0295 0.000147 0.0061 0.1188 0.0098 0.2095 0.0109 0.0296 0.000115 0.0025 0.1226 0.0054 0.2134 0.0097 0.0296 0.000147 0.0047 0.2732 0.0088 0.2185 0.0106 0.0299 0.000159 0.0055 0.2080 0.0077 0.2099 0.0115 0.0300 0.000275 0.0064 0.1772 0.0119 0.2003 0.0196 0.0302 0.000088 0.0021 0.2070 0.0050 0.2188 0.0083 0.0303 0.000131 0.0062 0.0962 0.0062 0.2084 0.0100 0.0311 0.0009 0.162 0.0291 0.0241 175 5 179 3 0.0004 0.227 0.0432 0.0058 180 3 181 2 0.0004 0.222 0.0537 0.0080 180 3 179 2 0.0005 0.229 0.0531 0.0094 180 3 179 3 0.0005 0.255 0.0474 0.0064 180 3 180 3 0.0004 0.227 0.0450 0.0060 181 3 182 2 0.0004 0.300 0.0505 0.0040 181 3 181 3 0.0005 0.214 0.0448 0.0083 181 3 182 3 0.0006 0.194 0.0455 0.0129 181 4 182 3 0.0004 0.276 0.0477 0.0046 182 3 182 3 0.0005 0.228 0.0517 0.0075 182 3 181 2 0.0005 0.193 0.0437 0.0116 182 3 183 3 0.0005 0.260 0.0586 0.0072 183 3 181 3 0.0004 0.264 0.0545 0.0046 183 2 182 2 0.0004 0.258 0.0476 0.0046 183 2 184 2 0.0004 0.227 0.0496 0.0068 184 3 183 2 0.0005 0.263 0.0537 0.0060 184 3 183 3 0.0004 0.223 0.0467 0.0063 184 3 184 2 0.0004 0.251 0.0460 0.0043 184 2 185 2 0.0003 0.292 0.0517 0.0034 184 2 184 2 0.0006 0.229 0.0519 0.0090 185 3 184 3 0.0005 0.246 0.0432 0.0055 185 3 186 3 0.0003 0.293 0.0478 0.0031 185 2 186 2 0.0004 0.288 0.0530 0.0039 186 2 186 2 0.0004 0.263 0.0525 0.0045 187 2 186 2 0.0004 0.271 0.0537 0.0042 187 2 186 2 0.0004 0.296 0.0469 0.0031 187 2 187 2 0.0004 0.263 0.0468 0.0039 187 2 188 2 0.0004 0.373 0.0488 0.0022 187 2 187 2 0.0003 0.349 0.0516 0.0023 187 2 187 2 0.0003 0.319 0.0499 0.0027 187 2 187 2 0.0004 0.348 0.0514 0.0025 188 2 187 2 0.0004 0.406 0.0522 0.0022 188 2 188 2 0.0004 0.357 0.0530 0.0024 190 2 189 2 0.0004 0.332 0.0508 0.0027 190 2 190 2 0.0004 0.244 0.0482 0.0046 192 2 192 2 0.0004 0.454 0.0524 0.0018 192 2 192 2 0.0004 0.369 0.0487 0.0022 197 2 197 2 Table 3. Cont'd Sandstone sample S3 8464-28.1 167 8464-24.1 8464-100.1 8464-88.1 8464-42.1 8464-27.1 8464-90.1 8464-5.1 8464-29.1 8464-34.1 8464-40.1 8464-85.1 8464-84.1 8464-35.1 8464-31.1 8464-79.1 8464-8.1 . 8464-3.1 8464-70.1 8464-25.1 8464-78.1 8464-33.1 8464-37.1 8464-89.1 8464-26.1 8464-14.1 8464-21.1 8464-76.1 8464-13.1 8464-10.1 8464-55.1 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 8464-41.1 8464-81.1 8464-67.1 131 257 154 108 256 238 253 217 241 196 213 211 175 351 272 536 354 377 410 408 239 459 183 196 201 281 424 495 532 191 486 508 130 504 371 500 541 653 636 383 463 447 162 417 215 191 (Z8464; field 85 0.529 70 0.554 149 0.600 68 0.459 number S.J-5 8 63 180 108 91 99 148 112 131 122 99 233 170 391 218 186 328 218 145 338 178 332 547 380 102 289 185 64 436 212 377 206 624 299 197 244 207 63 70 96 68 0.606 0.726 0.471 0.370 0.470 0.634 0.587 0.633 0.598 0.582 0.686 0.643 0.754 0.635 0.509 0.826 0.553 0.625 0.761 0.540 0.520 0.354 0.654 0.809 1.141 0.737 0.551 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 0.172 0.459 0.369 5 3 8 7 7 6 7 6 7 7 5 11 8 17 11 11 13 12 8 15 6 6 6 9 14 18 17 6 16 15 4 17 12 17 17 23 20 12 15 15 6 14 8 49 1) 0.002009 0.002279 0.001834 0.001492 0.002550 0.001876 0.001102 0.001419 0.001455 0.001658 0.001418 0.001406 0.000842 0.001541 0.000966 0.001588 0.000486 0.000398 0.000914 0.000698 0.001029 0.000736 0.000349 0.001178 0.001297 0.002171 0.000498 0.000446 0.000579 0.000582 0.000428 0.000533 0.000422 0.000672 0.000482 0.000372 0.000597 0.000061 0.000419 0.000055 0.000852 0.000161 0.000472 0.001825 0.000363 0.000428 0.000137 0.000571 0.000726 0.000604 0.000566 0.000979 0.000441 0.000459 0.000484 0.000584 0.000395 0.000751 0.000469 0.000468 0.000602 0.000341 0.000419 0.000173 0.000289 0.000344 0.000355 0.000487 0.000307 0.000249 0.000470 0.000480 0.000909 0.000279 0.000231 0 000165 0.000316 0.000461 0.000261 0.000235 0.000637 0.000212 0.000441 0.000180 0.000111 0.000114 0.000148 0.000237 0.000571 0.000353 0.000823 0.000205 0.000677 0.000093 0.0348 0.0395 0.0318 0.0259 0.0442 0.0325 0.0191 0.0246 0.0252 0.0287 0.0246 0.0244 0.0146 0.0267 0.0167 0.0275 0.0084 0.0069 0.0158 0.0121 0.0178 0.0128 0.0061 0.0204 0.0225 0.0376 0.0086 0.0077 0.0100 0.0101 0.0074 0.0092 0.0073 0.0116 0.0084 0.0064 0.0104 0.0011 0.0073 0.0010 0.0148 0.0028 0.0082 0.0316 0.0063 0.0074 0.0024 0.1376 0.1493 0.1763 0.1521 0.1736 0.2249 0.1558 0.1100 0.1493 0.1786 0.1831 0.2081 0.2140 0.1812 0.1998 0.1742 0.2489 0.2165 0.1453 0.2666 0.1576 0.2072 0.2493 0.1781 0.1705 0.0966 0.2100 0.2647 0.3813 0.2356 0.1966 0.2044 0.1190 0.2336 0.2858 0.1900 0.2443 0.1376 0.3131 0.1610 0.1655 0.1925 0.1550 0.1252 0.0560 0.1510 0.1063 0.0250 0.0292 0.0255 0.0234 0.0391 0.0191 0.0205 0.0209 0.0231 0.0167 0.0293 0.0197 0.0226 0.0273 0.0160 0.0192 0.0158 0.0152 0.0177 0.0148 0.0190 0.0143 0.0108 0.0195 0.0198 0.0351 0.0124 0.0107 0.0092 0.0129 0.0193 0.0110 0.0096 0.0261 0.0098 0.0229 0.0085 0.0056 0.0068 0.0071 0.0104 0.0224 0.0143 0.0323 0.0081 0.0261 0.0039 0.1392 0.1744 0.1577 0.1881 0.1830 0.1632 0.1931 0.1947 0.1995 0.1632 0.1766 0.2044 0.2400 0.1890 0.1970 0.1640 0.2206 0.2299 0.1777 0.1923 0.1769 0.2221 0.2101 0.2198 0.2177 0.1930 0.2068 0.2150 0.2101 0.2028 0.2604 0.2130 0.2119 0.3099 0.1986 0.2256 0.2059 0.2195 0.2100 0.2141 0.2114 0.2271 0.2273 0.2626 0.2507 0.2689 3.1313 0.0438 0.0464 0.0382 0.0374 0.0628 0.0285 0.0299 0.0318 0.0378 0.0261 0.0480 0.0312 0.0325 0.0393 0.0236 0.0274 0.0123 0.0199 0.0226 0.0235 0.0315 0.0210 0.0167 0.0313 0.0324 0.0597 0.0192 0.0159 0.0131 0.0209 0.0324 0.0177 0.0185 0.0436 0.0159 0.0304 0.0132 0.0123 0.0089 0.0151 0.0218 0.0386 0.0260 0.0631 0.0180 0.0524 0.0729 0.0282 0.0283 0.0283 0.0284 0.0284 0.0285 0.0285 0.0286 0.0288 0.0288 0.0288 0.0288 0.0288 0.0288 0.0289 0.0289 0.0289 0.0289 0.0290 0.0290 0.0291 0.0291 0.0292 0.0292 0.0292 0.0293 0.0293 0.0294 0.0294 0.0295 0.0295 0.0296 0.0296 0.0296 0.0297 0.0298 0.0298 0.0300 0.0301 0.0304 0.0306 0.0307 0.0323 0.0342 0.0350 0.0350 0.2471 0.0008 0.0006 0.0005 0.0005 0.0008 0.0004 0.0005 0.0004 0.0005 0.0005 0.0006 0.0005 0.0004 0.0005 0.0004 0.0004 0.0004 0.0004 0.0004 0.0005 0.0004 0.0005 0.0004 0.0005 0.0006 0.0007 0.0005 0.0004 0.0004 0.0004 0.0006 0.0004 0.0004 0.0006 0.0004 0.0006 0.0004 0.0004 0.0004 0.0004 0.0004 0.0005 0.0005 0.0007 0.0004 0.0007 0.0032 0.208 0.201 0.192 0.216 0.205 0.209 0.236 0.218 0.211 0.229 0.199 0.237 0.233 0.206 0.238 0.215 0.357 0.274 0.238 0.248 0.204 0.286 0.284 0.232 0.263 0.198 0.287 0.287 0.312 0.247 0.283 0.277 0.282 0.255 0.270 0.267 0.304 0.356 0.387 0.283 0.245 0.214 0.262 0.212 0.290 0.220 0.655 0.0358 0.0447 0.0404 0.0481 0.0468 0.0416 0.0491 0.0494 0.0503 0.0412 0.0445 0.0515 0.0604 0.0476 0.0495 0.0412 0.0553 0.0576 0.0445 0.0480 0.0441 0.0553 0.0523 0.0546 0.0541 0.0477 0.0511 0.0531 0.0518 0.0500 0.0640 0.0523 0.0519 0.0759 0.0486 0.0550 0.0502 0.0530 0.0505 0.0512 0.0501 0.0536 0.0510 0.0557 0.0520 0.0558 0.0919 0.0111 0.0118 0.0097 0.0094 0.0158 0.0072 0.0075 0.0079 0.0094 0.0064 0.0119 0.0077 0.0080 0.0098 0.0058 0.0068 0.0029 0.0048 0.0055 0.0057 0.0077 0.0051 0.0040 0.0076 0.0078 0.0146 0.0046 0.0038 0.0031 0.0050 0.0077 0.0042 0.0044 0.0104 0.0038 0.0072 0.0031 0.0028 0.0020 0.0035 0.0051 0.0090 0.0057 0.0132 0.0036 0.0107 0.0016 179 180 180 180 180 181 181 182 183 183 183 183 183 183 183 184 184 184 184 185 185 185 185 185 185 187 187 187 188 188 188 188 189 189 191 191 193 194 195 205 217 221 222 1423 5 4 3 3 5 3 3 3 3 3 4 3 3 3 3 3 2 2 3 3 3 3 2 3 4 4 3 2 2 2 4 2 3 3 2 4 2 3 2 2 2 3 3 5 3 182 180 182 180 181 183 181 182 182 . 184 184 182 181 183 183 185 182 182 185 185 186 184 185 184 184 186 186 186 186 187 184 187 187 182 189 188 189 190 191 193 194 194 205 215 221 220 1420 5 3 2 3 4 2 3 2 2 3 3 3 2 3 2 2 2 2 2 3 2 3 2 2 4 3 3 2 2 2 3 2 3 3 2 3 2 3 2 2 2 2 3 3 3 3 18 Notes (see Stem. 1997V Uncertainties reported at 1 a (absolute) and are calculated by numerical propagation of all known sources of error. f 2 0 6 2 0 4 refers to mole fraction of total 3 M P b that is due to common Pb, calculated using the ^Pb-method; common Pb composition used is the surface blank a 204-corrected ages; b 207-corrected ages (Stern 1997) The sputtered area for analysis was ca. 25 urn in diameter with a beam current of 5 nA ( G S C Mount #350). The 1a external error of ^ P b / ^ U ratios reported in the table incorporate a +/- 1% error in cal ibrating the s tandard z ircon (see S t e m a n d A m e l i n , 2003) . 4.4 Granitic Clasts: U-Pb dating o f zircons from two granitoid clasts, collected from biostratigraphically wel l -constrained Middle Toarcian strata indicate two crystallization dates: • Clast sample CI (Field number: Cgl-1): 186.6 ± 0.5 Ma • Clast sample C2 (Field number: Cgl-3): 221 + 1 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 C2 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 B2 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 C2 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 C2 showing the crystallization age of their source plutons is illustrated in figures 33 and 34. 60 0.0302 Gran i to id C las t : S a m p l e M R B - 0 4 - c g l 1 c 3 (z8466) n 1 r 0.0286 0.197 0.199 0.201 0.203 2 0 7 P D / 2 3 5 U 0.205 0.207 Fig. 33. U - P b Concordia diagram for granitoid clast sample C I . Ql CO 0.0355 0.0351 h" 0.0347 0.0343 0.0339 H Granitoid Clast: Sample MRB-04-Cgl.3-C9 (z8575) i 1 r 0.0335 0.234 0.236 0.238 0.240 0.242 0.244 2 0 7 P W 2 3 5 U 0.246 0.248 Fig. 34. U - P b Concordia diagram for granitoid clast sample C2. Table 4: U-Pb TIMS analytical data Isotopic Ratios5 Ages (Ma)7 Fract.1 Wt. U P b J 206Pb 3 Pb4 208Pb 207Pb 1 S E 206Pb 1SE Corr.6 207Pb 1 S E 2 0 6 P b 2 S E 207Pb 2 S E 207Pb 2 S E % ug ppm ppm 204Pb pg 206Pb 235U Abs 238U A b s Coeff. 206Pb A b s 238U 235U 206Pb Disc Sample C1 (Z8466; field sample Cgl-1) A 2 ( Z ) 3 3 4 6 9 1 4 3 6 7 8 8 0 . 1 3 0 . 2 0 2 4 7 0 . 0 0 0 3 0 . 0 2 9 4 1 0 . 0 0 0 0 4 0 . 8 3 0 7 0 . 0 4 9 9 3 0 . 0 0 0 0 4 1 8 6 . 9 0 . 5 1 8 7 . 2 0 . 5 1 9 1 . 5 3 . 9 2 . 5 A 3 ( Z ) 3 0 4 7 3 1 4 1 0 2 3 1 3 0 . 1 4 0 . 2 0 1 7 4 0 . 0 0 0 2 8 0 . 0 2 9 3 3 0 . 0 0 0 0 4 0 . 8 0 4 3 0 . 0 4 9 8 9 0 . 0 0 0 0 4 1 8 6 . 3 0 . 5 1 8 6 . 6 0 . 5 1 9 0 . 1 3 . 8 2 . 0 Z 1 (Z ) 3 5 5 9 2 1 8 6 7 9 4 6 0 . 1 4 0 . 2 0 1 2 8 0 . 0 0 0 3 0 . 0 2 9 2 8 0 . 0 0 0 0 4 0 . 9 3 4 5 0 . 0 4 9 8 6 0 . 0 0 0 0 3 1 8 6 . 0 0 . 4 1 8 6 . 2 0 . 5 1 8 8 . 5 2 . 5 1.3 Z 1 B ( Z ) 4 4 3 7 5 11 2 4 7 4 0 1 0 . 1 2 0 . 2 0 1 9 6 0 . 0 0 0 2 8 0 . 0 2 9 3 7 0 . 0 0 0 0 4 0 . 9 3 5 6 0 . 0 4 9 8 8 0 . 0 0 0 0 2 1 8 6 . 6 0 . 4 1 8 6 . 8 0 . 5 1 8 9 . 4 2 . 3 1 .5 Z 3 ( Z ) 2 8 2 7 0 8 1 1 6 2 1 2 0 . 1 5 0 . 2 0 2 2 9 0 . 0 0 0 4 6 0 . 0 2 9 3 8 0 . 0 0 0 0 4 0 . 8 0 8 7 0 . 0 4 9 9 4 0 . 0 0 0 0 7 1 8 6 . 6 0 . 5 187 .1 0 . 8 1 9 2 . 3 6 . 5 3 . 0 Sample C2 (Z8575; field sample Cgl-3) A 1 ( Z ) 2 4 2 7 9 1 0 4 9 6 8 3 0 . 1 7 0 . 2 4 2 7 8 0 . 0 0 0 3 8 0 . 0 3 4 7 5 0 . 0 0 0 0 5 0 . 8 2 6 3 0 . 0 5 0 6 7 0 . 0 0 0 0 5 2 2 0 . 2 0 . 6 2 2 0 . 7 0 . 6 2 2 5 . 7 4 . 2 2 . 5 A 2 ( Z ) 31 2 3 1 8 3 0 7 9 5 0 . 1 6 0 . 2 4 3 3 6 0 . 0 0 0 3 6 0 . 0 3 4 8 7 0 . 0 0 0 0 4 0 . 8 0 2 8 0 . 0 5 0 6 2 0 . 0 0 0 0 4 2 2 0 . 9 0 . 5 2 2 1 . 2 0 . 6 2 2 3 . 7 4.1 1 .3 B 1 ( Z ) 3 2 2 4 5 9 1 5 2 1 0 1 0 . 1 6 0 . 2 4 2 3 3 0 . 0 0 0 4 2 0 . 0 3 4 7 6 0 . 0 0 0 0 6 0 . 8 5 9 3 0 . 0 5 0 5 6 0 . 0 0 0 0 5 2 2 0 . 3 0 . 7 2 2 0 . 3 0 . 7 2 2 0 . 7 4 . 2 0 . 2 B 2 ( Z ) 3 4 2 1 6 8 4 7 5 3 4 0 . 1 6 0 . 2 3 7 4 6 0 . 0 0 1 0 1 0 . 0 3 3 9 5 0 . 0 0 0 0 6 0 . 7 2 6 9 0 . 0 5 0 7 4 0 . 0 0 0 1 6 2 1 5 . 2 0 . 7 2 1 6 . 3 1.7 2 2 8 . 8 1 4 . 9 6.1 Notes: 1 A l l f r a c t i o n s a r e z i r c o n a n d h a v e been a b r a d e d f o l l o w i n g t h e m e t h o d o f K r o g h ( 1 9 8 2 ) . 2 R a d i o g e n i c P b 3 M e a s u r e d ra t io , c o r r e c t e d f o r s p i k e a n d f r a c t i o n a t i o n " 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 fo r t h i s s t u d y r a n g e d w e r e 0.1 p g fo 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 i s 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 fo r 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 c o m m o n P b , errors q u o t e d are 2 s i g m a in M a . On to 4.5 Metamorphic Clasts: Sample C3: Micaschist (Field number: M .Cg l - 5 -C l ) : 177 ± 15 Ma Sample C4: Gneiss (Field number: M .Cg l -4 -C4 ) : >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 foi l and stacked in an irradiation capsule with similar-aged samples and neutron flux monitors (Fish Canyon Tuff sanidine, 28.02 M a (Renne et al., 1998)). The samples were irradiated on February 15 through 17, 2006 at the McMaster Nuclear Reactor in Hamilton, Ontario, for 90 M W H , with a neutron flux of approximately 3x10 1 6 neutrons/cm . Analyses (n=57) of 19 neutron flux monitor positions produced errors of <0.5% in the J value. The samples were analyzed by Tom Ul l r ich 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 MIR10) until fused. The gas evolved from each step was analyzed by a VG5400 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 of Ca, CI and K (Isotope production ratios: (40Ar/39Ar)K=0.0302±0.00006, (37Ar/39Ar)Ca=1416.4±0.5, (36Ar/39Ar)Ca=0.3952±0.0004, Ca/K=1.83±0.01(37ArCa/39ArK).). 4.5.2 Results The data indicate a cooling age of 177 ± 15 M a for the sample C3, based on an inverse isochron calculation (Figs. 35 and 36), and a minimum age of 160.1 ±1.3 M a for the sample C4. The C4 spectrum graph shows no plateau (Fig. 37 and Tables 5, 6) and the age of 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 36 A r 40 A r 0.00036 0.00032 0.00028 0.00024 0.00020 0.00016 data-point error ellipses are 2a A g e = 177±15 M a 4 0 A r / 3 6 A r =780 M S W D = 2.0 0.077 0.079 0.081 0.083 0.085 0.087 0.089 3 9 A r / 4 0 A r Figure 35. Inverse isochron calculation for the sample C3. 64 Mcgl-5-C1 Biotite Plateau steps are filled, rejected steps are open box heights are 2a 300 CO 200 a> < 100 20 40 60 80 100 Cumulative 3 9 A r Percent 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. Mgcl-4-C4 400 300 Plateau steps are filled, rejected steps are open ns ro < 200 100 box heights are 2u 20 40 60 80 100 39 Cumulative Ar Percent Figure 37. Spectrum graph for the sample C4 shows no plateau and indicate a minimum age of 160.1 ± 1.3 Ma . 65 Table 5. M c g l - 5 - C 1 B io t i t e L a s e r I s o t o p e R a t i o s P o w e r ( % ) 4 0 A r / 3 9 A r 3 8 A r / 3 9 A r 3 7 A r / 3 9 A r 3 6 A r / 3 9 A r C a / K C l / K % 4 0 A r a t m f 3 9 A r 4 0 A r * / 3 9 A r K A g e 2 4 0 . 5 2 1 ±0.067 0.085±0.059 0 084±0.067 0.142±0.060 0 2 0 8 0.01 1 0 3 . 6 5 4 . 8 5 -1.506±3.064 -29.56±60.62 2.1 1 9 . 1 5 5 0 . 0 0 5 0.051 0 . 0 2 3 0 0 4 7 0 . 0 2 0 0 . 0 5 3 0 . 0 1 9 0 116 0 . 0 0 6 8 2 . 6 7 8 . 0 2 3 .281 0 . 2 9 9 6 2 . 7 5 5 . 6 3 2 .2 1 4 . 4 0 8 0 . 0 0 6 0 . 0 4 3 0 . 0 2 7 0 0 4 2 0 . 0 2 2 0 . 0 2 5 0 . 0 2 3 0 1 0 2 0 . 0 0 6 5 1 . 8 7 4 .91 6 . 8 7 0 0 . 1 7 9 1 2 8 . 9 7 3 .24 2 .4 1 2 . 8 7 5 0 . 0 0 5 0 . 0 4 0 0 . 0 2 3 0 0 3 1 0 . 0 2 0 0.011 0 . 0 2 5 0 0 7 6 0 . 0 0 6 2 4 . 4 1 7 . 7 5 9 . 6 8 3 0 . 0 9 6 1 7 9 . 2 3 1.69 2 . 5 12 .381 0 . 0 0 5 0 .037 0 . 0 2 2 0 0 3 7 0 . 0 2 0 0 . 0 0 5 0 .031 0 091 0 . 0 0 5 11.61 13.1 1 0 . 8 8 5 0 . 0 6 9 2 0 0 . 2 9 1.21 2 .6 1 2 . 2 7 2 0 . 0 0 4 0 .037 0 . 0 1 9 0 0 4 4 0 . 0 2 3 0 . 0 0 4 0 . 0 4 6 0 108 0 . 0 0 5 8.81 6 . 5 4 11.111 0 .071 2 0 4 . 2 2 1.24 2 . 8 1 2 . 5 8 4 0 . 0 0 4 0 .038 0 . 0 1 4 0 0 7 1 0 . 0 1 8 0 . 0 0 4 0.031 0 176 0 . 0 0 5 9.21 1 2 . 9 9 1 1 . 3 6 6 0 . 0 6 2 2 0 8 . 6 5 1.07 3 1 2 . 2 6 1 0 . 0 0 4 0 . 0 3 8 0.021 0 1 9 8 0 . 0 1 4 0 . 0 0 3 0 . 0 2 7 0 4 8 8 0 . 0 0 5 7 . 9 8 1 3 . 4 7 1 1 . 2 2 5 0 . 0 5 5 206 .21 0 . 9 6 3 .2 1 1 . 8 3 6 0 . 0 0 5 0 .036 0 . 0 2 3 0 3 3 6 0 . 0 1 5 0 . 0 0 3 0 . 0 6 2 0 8 2 8 0 . 0 0 5 7.1 5 . 9 5 1 0 . 9 1 4 0 . 0 8 0 2 0 0 . 7 9 1.39 3 .4 1 1 . 5 6 8 0 . 0 0 4 0 .036 0 . 0 1 8 0 351 0 . 0 1 3 0 . 0 0 3 0 . 0 8 2 0 8 6 5 0 . 0 0 5 6.4 6 . 7 6 1 0 . 7 5 2 0 . 0 8 2 1 9 7 . 9 7 1.42 3 .7 1 1 . 5 1 0 0 . 0 0 5 0 .037 0 . 0 4 2 0 5 5 4 0 . 0 1 5 0 . 0 0 3 0 . 0 7 5 1 3 6 7 0 . 0 0 5 6 . 4 6 4 . 0 9 1 0 . 6 6 6 0 . 0 8 3 1 9 6 . 4 7 1.46 4 1 1 . 6 8 5 0 . 0 0 7 0.041 0 . 0 5 0 1 1 9 1 . 0 . 0 1 6 0 . 0 0 5 0 . 1 5 3 2 9 3 9 0 . 0 0 6 8 . 7 6 1 .58 1 0 . 4 6 3 0 . 2 2 0 1 9 2 . 9 2 3 . 8 5 T o t a l / A v e r a g e 14.300±0.004 0.042±0.004 0 194±0.002 0.017±0.011 0 . 0 0 6 1 0 0 10.760±0.078 J = 0.010787±0.000016 V o l u m e 3 9 A r K = 8 3 5 . 6 8 In tegrated D a t e = 173.59±2.75 V o l u m e s a r e 1 E - 1 3 c m 3 N P T N e u t r o n f lux 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) I s o t o p e p r o d u c t i o n ra t ios : ( 4 0 A r / 3 9 A r ) K = 0 . 0 3 0 2 , ( 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. M c g l - 4 - C 4 B io t i t e L a s e r I s o t o p e R a t i o s P o w e r ( % ) 4 0 A r / 3 9 A r 3 8 A r / 3 9 A r 3 7 A r / 3 9 A r 3 6 A r / 3 9 A r 1.8 2 7 0 . 9 3 1 ±0.355 0.686±0.625 1.107±0.548 1 . 2 3 7 1 0 . 3 9 0 2 2 6 6 . 3 4 7 0 . 0 0 9 0 .471 0 . 0 2 5 0 . 7 1 5 0 .021 0 . 9 0 0 0 . 0 1 8 2.1 7 1 . 5 3 6 0 . 0 1 0 0 . 1 2 3 0 . 0 5 0 0 . 6 1 0 0 . 0 2 9 0 . 2 3 3 0 . 0 2 2 2 . 3 1 6 . 7 3 0 0 . 0 0 5 0 . 0 4 8 0 . 0 1 9 0 . 2 7 2 0 . 0 1 4 0 . 0 5 2 0 . 0 1 8 2 . 5 1 0 . 1 6 6 0 . 0 0 8 0 . 0 3 6 0 . 0 1 6 0 . 1 3 6 0 . 0 1 6 0 . 0 2 8 0.021 2 . 7 1 3 . 7 6 9 0 . 0 2 3 0 . 0 3 4 0 . 0 3 5 0 . 1 2 4 0 . 0 3 2 0 . 0 3 0 0 . 0 3 2 2 .9 1 1 . 5 4 7 0 . 0 1 6 0 . 0 2 9 0 .031 0 .110 0 . 0 2 8 0 . 0 1 3 0 . 0 3 2 3.1 1 2 . 2 1 4 0 . 0 1 6 0 . 0 2 8 0 . 0 2 0 0 . 1 4 4 0 . 0 2 5 0 . 0 1 0 0 . 0 2 6 3 . 2 1 2 . 6 0 8 0 . 0 1 5 0 . 0 2 6 0 . 0 3 2 0 . 4 6 6 0 . 0 2 3 0 . 0 0 5 0 . 0 2 7 3 . 3 1 2 . 8 2 4 0 . 0 0 7 0 . 0 2 2 0 . 0 4 9 1 .088 0 . 0 1 4 0 . 0 0 5 0.081 3 . 5 1 2 . 9 4 2 0 . 0 0 6 0 . 0 2 5 0 . 0 2 5 1 .636 0 . 0 1 4 0 . 0 0 5 0 . 0 3 9 3 . 8 1 4 . 4 2 7 0 . 0 0 6 0 . 0 3 0 0 . 0 2 7 1 .777 0 . 0 1 3 0 . 0 0 5 0 . 0 2 9 4.1 1 4 . 6 1 6 0 . 0 0 5 0 . 0 2 8 0 . 0 2 3 1 .837 0 . 0 1 3 0 . 0 0 6 0 . 0 3 3 4 . 5 1 4 . 7 3 5 0 . 0 0 5 0 . 0 2 9 0 . 0 5 6 4 . 3 2 9 0 . 0 1 3 0 . 0 1 0 0 . 0 4 7 T o t a l / A v e r a g e 14.233±0.002 0.032±0.004 1.092±0.003 0.019±0.004 C a / K C l / K % 4 0 A r a t m f 3 9 A r 4 0 A r * / 3 9 A r K A g e - 1 .071 -0 .101 1 4 8 . 1 5 0 6 1 . 6 6 4 1 4 9 . 6 8 6 9 2 0 . 2 2 1 5 8 0 . 8 1 1 .854 0 . 0 6 8 1 0 0 . 0 3 0 . 3 8 - 0 . 1 0 9 4 . 4 5 2 - 2 . 1 3 8 6 . 7 7 1.58 0 . 0 1 5 9 5 . 9 6 0 . 3 8 2 . 8 7 0 1 .383 5 5 . 0 2 26.11 0 . 6 9 8 0 . 0 0 6 9 1 . 3 9 6 . 3 6 1 .407 0 . 2 7 9 2 7 . 1 9 5 .36 0 . 3 4 8 0 . 0 0 4 8 0 . 9 7 9 .81 1 .898 0 . 1 7 0 3 6 . 5 8 3 . 2 5 0 . 3 1 8 0 . 0 0 3 6 4 . 4 2 1 2 . 0 5 4 . 8 5 8 0 .331 9 2 . 1 9 6 .12 0 . 2 8 2 0 . 0 0 3 3 4 . 2 6 9 . 2 3 7 . 5 3 7 0 .191 1 4 1 . 0 7 3 . 4 3 0 . 3 7 0 . 0 0 3 2 2 . 9 5 1 4 . 3 3 9 .361 0 . 1 8 0 1 7 3 . 6 0 3 .19 1 .196 0 . 0 0 2 11 .99 1 2 . 9 3 1 1 . 0 4 5 0 . 1 8 3 2 0 3 . 1 4 3 .19 2 . 7 9 8 0 . 0 0 2 9 . 6 3 3 . 4 8 1 1 . 4 9 5 0 . 1 4 4 2 1 0 . 9 6 2 .50 4 . 2 0 6 0 . 0 0 2 9 . 0 2 9 . 6 3 1 1 . 7 3 0 0 . 0 9 5 2 1 5 . 0 2 1.64 4 . 6 0 7 0 . 0 0 3 9 . 0 5 1 4 . 0 2 1 3 . 0 8 8 0 . 0 9 6 2 3 8 . 3 4 1.64 4 . 7 6 6 0 . 0 0 3 1 0 . 3 7 5 . 2 9 1 3 . 0 4 3 0 . 0 8 7 2 3 7 . 5 7 1.49 1 1 . 2 8 3 0 . 0 0 3 1 6 . 3 4 2.11 1 2 . 2 4 3 0 . 1 5 7 2 2 3 . 8 7 2.71 0 .001 1 0 0 1 3 . 0 7 6 1 0 . 0 3 5 j = 0 . 0 1 0 7 9 1 1 0 . 0 0 0 0 1 6 V o l u m e 3 9 A r K = 1 0 1 8 . 1 7 In tegrated D a t e = 1 6 0 . 9 1 1 1 . 2 8 V o l u m e s a r e 1 E - 1 3 c m 3 N P T N e u t r o n f lux 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) I s o t o p e p r o d u c t i o n r a t i o s : ( 4 0 A r / 3 9 A r ) K = 0 . 0 3 0 2 , ( 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 ) . ON 4.8 Summary : 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 +_\7; Figure 11) . 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 +_°3l; Figure 11) . 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. Stage Pliensbachian '1 oa rcian Samples SI S2 C I C2 S3 A ) Age of enclosing bed (Zone mean, Palfy et al., 2000) Kunae 185.7 S i M a Planulata 183.6: ; 7 M a Planulata 183.6: ; 7 M a Planulata 183.6: ; 7 M a Hillebrandti 181.4+1.2 M a B) Mean age of detrital components 189.6±1 M a 184.4±1.2 M a 186.6±0.5 M a 221±1 M a 184.4±1 M a C) Min imum age of detrital components 186±2 M a 175±5 M a 186±0.4 M a 220.2+0.6 M a 179±5 M a Table 7. A summary of the chronological results and an estimate for the hiatus between emplacement (crystallization age), uplift, unroofing and erosion of 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 -1.8 TTH +3.8/-3.3 OXF +3.1/-5.1 C L V . a 5 +11 BTH -5 6 -3.8 BAJ -7.9 AAL +1 2 -1.5 + 1.0 TOA -1.1 PLB -4.' SIN H.9 -5.7 HET ' 1 Ma 140 145 150 155 160 165 170 175 180 185 190 195 O O + I 1^  IT) 0 0 0J ro CD 03 c 186./ Ma 189 6 Ma CD ro oo ro C ro Q_ I CD in c CD c ro CM 0 0 ro ro 186.6 Ma • Cgl-1 CD CO oo ro •4—1 ro C ro o_ i CD CO CD c ro CM OO ro m c ro Ma I 184"4 Ma | * " . ' 1844 Ma J • S.b.Cgl-1 + i 73 C ro CD ro </) o CJ CO CO ro < % I ;: S.J-1 • S Cg!-f LEGEND 185.7 M a J jg) Biochronological age control of the bed (number and error bars are examples) 189.6 M a J + Geochronological age control of the clast/grain (number and error bars are examples) I T i m e di f ference between geochrono log i ca l ( c rys ta l l iza t ion) and b i o ch rono log i c a l (sedimentat ion) age contro ls Table 8 . Geochronological and biochronological results plotted on the Jurassic time scale. The Jurassic time scale is from Palfy et al., (2000). Numbers in blue and red are from the present study. 71 CHAPTER V CONGLOMERATE ANALYSES 5.1 Introduction: Five conglomerate units are recognized in about 3000-meters of 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 in detail to provide data on provenance relationships and temporal trends in arc dissection. Quantitative data were collected in 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 of clast counts. The high-resolution age control on these units provides an opportunity for documenting any temporal trends in clast lithologies. 5.2 Conglomerate Units: In stratigraphically ascending order, conglomerate units in the Lisadele Lake sequence contain a predominance of sedimentary, volcanic, plutonic, metamorphic, and chert clasts (Mihalynuk et al. , 1999). Distinctive clast populations permit subdivision of conglomerate into five map able units: 72 In Situ Localities ExSilu Samples JEK) 18 17 16 15 14 E9 13 12 11 • 10 • 9 • 8 • 7 . 6 • 5 lES-8 - 4 . 3 - 2.1 . 2 JE2-4 - 1 El I ei.Jl MIC Iv l P I c l v o l a - v i l • . 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 GSC localities are listed in Appendix 1. ^ 5.2.1 Conglomerate Unit 1: The lowermost five metres of the Takwahoni Formation consists of poorly sorted, matrix-supported 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 of 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 At l in 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 of the conglomeratic beds contain yellow weathering; highly oxidized clasts (Fig. 41) Bioclastic coarse-grained sandstone, greywacke, siltstone, and mudstone are the other components of 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 arc-building 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. Ye l low 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 of 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 (10-100mm) 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.Cgl -4-C4) 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 Nisl ing Assemblage, which was supported by similar observations in the Tagish Lake (Currie and Parrish, 1993) and Yukon 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 Nisl ing 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 At l in 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 Yukon, 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 iew 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.Cgl -4. 5.2.5 Conglomerate Unit 5: The upper approximately 1000 metres of the Jurassic succession at Lisadele Lake is characterized by siltstone and mudstone but the uppermost 5-10 metres of the section consists of 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. TABLE 8: CLAST COUNT DATA Age of I'nit % Volcanic Porphyry Plutonic % Metamorphic % Sedimentan Sample No. Sinemurian? 23 5 4 0 68 Tr. l .s. l Sine.-Pliens. 62 30 4 0 4 Tr.cgl.3 (v) Early Pliens. 55 36 5 0 5 Tr.cgl.4 Late Pliensbachian. 12 51 33 0 5 Cgl.d Pliensbachian - Toarcian 22 32 44 0 2 Cgl.c Early Toarcian 32 11 52 0 5 Cgl.b Middle Toarcian 32 16 47 0 5 Cgl.a Middle Toarcian 9 13 76 0 2 Cg l . l Middle Toarcian 11 22 65 0 2 Cgl.2 Middle Toarcian 9 26 61 0 4 Cgl.3 Late Toarcian 4 25 68 0 4 Cgl.4 Late Toarcian 2 7 77 0 14 Cgl.5 Late Toarcian 7 2 45 39 7 M.cgl.5 Late Toarcian 3 15 37 40 5 M.cgl.4 Late Toarcian 2 10 33 54 2 M.cgl.3 Early Bajocian 5 5 0 2 88 S.ch.5-cgl Table 9. Conglomerate clast count data of Lower to Middle Jurassic conglomerate units in the Lisadele Lake area. 84 I Sedimentary (undifferentiated) i 11 11 Sedimentary (limestone-rich) 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 Middle 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 of 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 Plutonic clasts Early Jurassic (Sinemurian?) ilv Jurassic (Sinem./Pliens.*. arly Jurassic (Early Plieus.? Late Pliensbachian (Carlottense Z.) ,ate Pliensbachian (Carlottense Z.) iddle Toarcian (Planulata Middle Toarcian (Planulata Z.) Middle / Late Toarcian Late Toarcian (Hillebrandti Z.) Late Toarcian (Hillebrandti Z.) Volcanic clasts 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 Provenance: 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 At l in 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 50% of the clasts in the Upper Toarcian conglomerates, whereas they rarely exceed 1-2% in the Yukon area (Hart et al. , 1995). Hart et al. (1995) showed that in the Yukon area, elevated initial Sr values in Whitehorse Trough elastics indicate a continental source, probably Nisl ing 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 of clastic sedimentary rocks are important because it provides a record of the source regions uplifted and eroded during orogeny (Dickinson et al., 1983). The sedimentary f i l l of arc-marginal basin may record tectonic evolution and phases of arc growth and erosion in island arc systems. A detailed petrographic study of 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 in various tectonic settings. Modif ied after Dickinson and Suczek (1979), by courtesy of 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, wel 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 Sample No. Label 1 Age 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 Late Plien.- Carlottense Zone Arkose 43 58 9 5 FS-06-SS-5 Late Plien.- Carlottense Zone Feldspathic litharenite 40 25 35 6 FS-06-SS-6 Middle Toar.- Planulata Zone Lithic arkose 43 35 22 7 FS-06-SS-7 Middle Toar.- Planulata Zone Lithic arkose 40 33 27 8 FS-06-SS-8 Late Toar.- Hillebrandti Zone Arkose 52 40 8 9 FS-06-SS-9 Late Toar./ Aalenian? Feldspathic litharenite 51 19 30 10 FS-06-SS-10 Late Toar./ Aalenian? Feldspathic litharenite 60 12 28 11 FS-06-SS-11 Early Bajocian Feldspathic litharenite 59 21 20 12 FS-06-SS-12 Early Bajocian 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. Age 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 Ana lyses: Sandstones in the study area were classified using the widely-used scheme of Folk (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 wel 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 -06 -SS- 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 FS-06-SS- 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 of 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 : A G E Late Triassic Sine. /Pl iens.? % Early Pliens. O Late Pliens. 0 Late Pliens. 0 Middle Toarc. © Middle Toarc. P E T R O F A C I E S SAMPI.K A G E P E T R O F A C I E S © Late Toarc. B Late Toarc/Aalen.? ® Late Toarc/Aalen.? CD Early Bajocian C Early Bajocian ® Early Bajocian Early Bajocian Figure 54. Q F L 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 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 of 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 FS -0 6 - S S - l , 2) show a low proportion of 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 in the Lisadele Lake area to an age range between Pliensbachian and Early Bajocian in age, with all stages except for the Aalenian definitely represented (Fig. 55). Chert-pebble conglomerate deposited in 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 in northwestern British Columbia during Early and Middle Jurassic. In addition, correlation of 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 Yukon and 2) a shorter age range of Sinemurian to Early Pliensbachian (but with the top of the Group is probably not exposed) in the At l in Lake area between Lisadele Lake and Yukon (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 of 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 Lower and Middle Jurassic succession and the conglomerate units in the Lisadele area. The indicates the location of camp. V iew is to the southeast. Tulsequah At l in Yukon ] I ' l l 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 Limestone Figure 56. Stratigraphy of Laberge and Bowser Lake groups within the Whitehorse Trough. B L G = Bowser Lake Group. At l in 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 Abou 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 of 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: shale-dominated 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 Yukon (?) 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 map area (B) C r y Lake map area Tulsequah map area Terranes m ST (Stikinia) | QN (Quesnellia) | CC (Cache Creek) Jurassic Sedimentary Basins Bowser Basin ] Whitehorse Trough (Takwahoni facies) | Whitehorse Trough (Inklin facies) Figure 57. Est imated geographic locat ion o f the sections in Figure 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 Unconformity 1-5 Conglomeratic units 200 m vertical ^ • • ^ scale F igu re 58. Co r r e l a t i on o f Jurass ic rocks o f the Tu lsequah map area w i t h Spa ts iz i and 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-Pb age of 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 mil l ion 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. As well , the Sinemurian-Pliensbachian 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 mil l ion 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 of 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 Yukon area, Nis l ing Terrane has been considered as the source of 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 Yukon 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 of 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. Modif ied 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. Modif ied after Dickie and Hein (1995). 109 References Aberhan, M . 1998. Early Jurassic Bivalv ia of western Canada. Part I. Subclasses Palaeotaxodonta, Pteriomorphia, and Isofi libranchia. Beringeria, V o l . 21, pp. 57-150. Anderson, R.G. 1989. 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FS-2.1 2.1 104K/11 613491 6506297 sandstone Kunae Z. Carlottense Z. X U B C loc. FS-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 Kanense Z. Kanense Z. X U B C loc. FS-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. FS-9 9 104K/11 613483 6505596 siltstone Planulata Z. Planulata Z. X U B C loc. FS-10 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. FS-12 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. FS-15 15 104 K/11 missing missing siltstone Bajocian Bajocian X U B C loc. FS -16 16 104 K/11 612690 6503697 siltstone Bajocian Bajocian X U B C loc. FS-17 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 E1 E1 C-211256 104 K/11 * * * Freboldi Z. Freboldi Z. X E2 E2 C-86512 104 K/11 * * * Kunae Z. Kunae Z. X E3 E3 C-86513 104 K/11 * * * Kunae Z. Kunae Z. X E4 E4 C-86511 104 K/11 * * * Kunae Z. Kunae Z. X E5 E5 C-86509 104 K/11 * * * Carlottense Z. Carlottense Z. X E6 E6 * 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 C-211248 104 K/11 * * * Bajocian Bajocian X S.Cgl-f S1 * 104 K/11 613724 6506360 sandstone Kunae Z. Carlottense Z. X S . b . C g M S2 * 104 K/11 613483 6505596 sandstone Planulata Z. Planulata Z. X Cgl-1 C1 * 104 K/11 613317 6505638 conglomerate Planulata Z. Planulata Z. X Cgl-3 C 2 * 104 K/11 613448 6505395 conglomerate Planulata Z. Planulata Z. X M.Cgl.5-C1 C 3 » 104 K/11 613501 6504952 conglomerate Hillebrandti Z. Hillebrandti Z. X M.Cgl.4-C4 C 4 * 104 K/11 613545 6504881 conglomerate Hillebrandti Z. Hillebrandti Z. X S.J-1 S3 • 104 K/11 613277 6504712 sandstone Hillebrandti Z. Hillebrandti Z. X Tr.S-1 FS-06-SS-1 * 104 K/11 * * sandstone U. Triassic U. Triassic X Tr.S.Cgl-2 FS-06-SS-2 * 104 K/11 * * sandstone Sine./Pliens.? Sine./Pliens.? X S.F-g FS-06-SS-3 * 104 K/11 613747 6506460 sandstone Freboldi Z. Freboldi Z. X S.b.Cgl.d FS-06-SS-4 * 104 K/11 • * sandstone Carlottense Z. Carlottense Z. X S.b.Cgl.c FS-06-SS-5 * 104 K/11 * * sandstone Carlottense Z. Kanense Z. X S.I.Cgl.b FS-06-SS-6 * 104 K/11 613440 6506027 sandstone Planulata Z. Planulata Z. X S.I.Cgl.3 FS-06-SS-7 * 104 K/11 * * sandstone Planulata Z. Hillebrandti Z. X S.H FS-06-SS-8 • 104 K/11 613571 6504558 sandstone Hillebrandti Z. Aalenian? X S.G FS-06-SS-9 * 104 K/11 * * sandstone Hillebrandti Z. Aalenian? X S.F FS-06-SS-10 * 104 K/11 * * sandstone Hillebrandti Z. Aalenian? X S.E1 FS-06-SS-11 * 104 K/11 613459 6503915 sandstone Bajocian Bajocian X S.E2 FS-06-SS-12 * 104 K/11 613459 6503915 sandstone Bajocian Bajocian X S.A FS-06-SS-13 * 104 K/11 613300 6503545 sandstone Bajocian Bajocian X S.Ch.4 FS-06-SS-14 * 104 K/11 612298 6502859 sandstone Bajocian Bajocian X 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 U D = Umbil ical Diameter at diameter = D U = ( U D / D ) x 100 W H = Whorl Height at diameter = D W W = Whorl Width at diameter = D W W / W H = ( W W / W H ) x l 0 0 P R H W = Primary Ribs per Hal 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 "FS-Sp." 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 I) HI) I J W l l W W WW W H Pl tHW (mm) (mm) % (mm) (mm) l -S-Sp. l 31 3 10 15 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 in the limestone and pictures taken of 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 1.) 1 I) IJ W l l W W W W W 11 PKIIW (mm) (mm) % (mm) (mini % ^BffillBIBIil FS-Sp.2 14.3 6.6 46 4.5 - - -122 Suborder PHYLLOCERATINATINA Arkel l , 1950 Superfamily PHYLLOCERATACEAE 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 EODEROCERATACEAE 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 Yukon (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. McLearn, 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 Alaska (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: Two specimens. 125 Localities: 10, 11 Age: Planulata Zone (Middle Toarcian). Genus PERONOCERAS Hyatt, 1867 Type species: Ammonites fibulatus Sowerby, 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 AMALTHEUS 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 of the Whitehorse Trough in the Tulsequah and Telegraph Creek areas (Frebold, 1964, 1970, Smith et al., 1988), northern Wrangellia in Alaska (Imlay, 1981), Queen Charlotte Islands (Smith and Tipper, 1996), Cultus Lake, southwestern B C (Ham, 1997), Canadian Arctic (Frebold, 1975), central and northern Yukon (Frebold et al. , 1967), and also on the North American craton as far south as 51°N (Frebold, 1966). Locality: E4 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 Alaska (Smith et al., 2001). Locality: E4 /E5 Age: Kunae/Carlottense Zone (Late Pliensbachian). Superfamily HILDOCERATACEAE 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) 1 i f ) W l l W W W W W H P R H W (mm) (mm) % (mm) (mm) 1 s - S p . 3 24 13 54 7 - - 21 129 UD/D for Arieticeras aglovianum/FS-Sp.3 35 f 30 25 20 15 0_ % o o O o 0 o Arieticeras algovianum • FS-Sp.3 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 10 O O 0 0 o o o o o 10 15 20 UD 25 30 35 o Arieticeras algovianum » FS-sp.3 40 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 L) Ul) 1 I' (mm) (mm) % \\ 11 i mm i W W (mm) W W W II I'KIIW FS-Sp.9 12.5 4.5 36 4.8 - - 12 Arieticeras sp. Material: Six specimen. Localities: 3, E2 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: Two specimens. Locality: 3 Age: Kunae Zone (Late Pliensbachian) to Early Toarcian. 132 o Fontanelliceras sp. • FS-Sp.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 Yukon (Palfy and Hart, 1995) and from the Queen Charlotte Islands by Smith and Tipper (1996). 30 h 20 15 10 4* o o . 133 Localities: 5, 6 Age: Kanense Zone (Early Toarcian). Measurements: Specimen D (mm) U D (mm) U % W H (mm) W W (mm) W W / W H % P R H W FS-Sp.10 18 9 50 6.5 - - 16 FS-Sp.30 36 19 52 10 - - 17 FS-Sp.33 32 16 50 9 - - 15 40 35 g 20 15 h Q | 10 20 30 40 D 50 60 e Fon tane l l i ce ras s p . • F S - s p . 3 0 A F S - s p . 3 3 Figure 64 . U D / D for Fontanelliceras sp. and specimens FS-sp.30, 33 measurements. Subfamily BOULEICERATINAE Arkel 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 in this study. Locality: 2 Age: Kunae Zone (Late Pliensbachian). Measurements: Specimen D U D U W H W W W W / W H P R H W (mm) (mm) % (mm) (mm) % FS-Sp.5 51 22 43 17 - - 26 30 o Fuciniceras intumescens «FS-Sp.S 10 20 30 40 D 50 60 70 80 136 Figure 59. U D / D for Fuciniceras cf. intumescens and specimen FS-sp.5 measurements. Fuciniceras sp. Localities: 2, E2 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 D ! U D U W l l W W W W W H P R H W (mm) (mm) % i mm i (mm) % I S-Sp.15 9.6 3.7 38 3.7 - - 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), Alaska (Imlay, 1981), and Arctic Canada (Hall and Howarth, 1983). Localities: 3-5, E7 Age: Carlottense Zone (Late Pliensbachian). Measurements: Specimen D U D U W l l W W W W W 11 P R H W i nun) (mm) % (mm) (mm) % FS-Sp.20 27 6 22 13 - - 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 Alaska (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 1) 1 1) V (mm) (mm) % WH (mm) W W (mm) W W W II % PKIIW FS-Sp.14 67 10 15 28 - - -Lioceratoides (Pacificeras) sp. Plate 2, figure 6 Material: One specimen. Locality: 3, 4, E8 Age: Carlottense Zone (Late Pliensbachian). Measurements: Specimen I) U D U W H W W W W Wl 1 PKIIW (mm) (mm) % (mm) (mm) % TS-Sp.19 55 16 30 20 - - -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, E6 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 D C D I." WII WW W W W'H PR1-IW (mm) (mm) % (mm) i nun i % FS-Sp.32 34 11 32 12 - - - 3 2 Harpoceras spp. Plate 3, figure 6 Material: Five specimens. Localities: 5, 7, 9 Age: Kanense Zone (Early Toarcian). Measurements: Specimen I) I'D 1 WM W W WW W'H PKIIW (mm) (mm) % (mnn (mm) % FS-Sp.25 27 7 26 13 - - 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 Bird, 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 Q u e e n 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 D (mini UD (mini li ; W'H % ' (mm) WW (mm> WW Wl l ! P R I 1 W % FS-Sp.43 26 10 38 9 - - 16 Family HAMMATOCERATIDAE 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: E9 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, McConnel 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 1A 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 IB Material: Two 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. 1-10. 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 1) (ir mi I l> (mm i i ; % W l l (mm) W W (mm) W W W l l | PRIIW l'S-Sp.4 34 12 35 19 - - • 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 I'D I' W l l W W W W W l l PRI1W i mm i (mm) % i mm) im im % 1 s - S p . 6 16 5 31 6.5 - - 11 151 Appendix 3: U-Pb GEOCHRONOLOGY Analytical Techniques S H R I M P II (Sensitive High Resolution Ion Microprobe) analyses were conducted by V i c k i M c N i c o l l at the Geological Survey of Canada (GSC) using analytical procedures described by Stern (1997), with standards and U-Pb calibration methods following Stern and Amel in (2003). Zircons from the samples were cast in 2.5 cm diameter epoxy mounts (GSC mount #350) along with fragments of the G S C laboratory standard zircon (z6266, with 2 0 6 P b / 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 (CL) utilizing a Cambridge Instruments scanning electron microscope (SEM). Mount surfaces were evaporatively coated with 10 nm of high purity Au . Analyses were conducted using an 1 6 0 " primary beam, projected onto the zircons at 10 kV . The sputtered area used for analysis was ca. 25 L i m in diameter with a beam current of ca. 5-6 nA. The count rates of 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 of 35 ns. Off-line data processing was accomplished using customized in-house software. The l a external errors of Pb/ U ratios reported in Table 1 incorporate a ±1.0 % error in calibrating the standard zircon (see Stern and Amel in, 2003). No fractionation correction was applied to the Pb-isotope data; common Pb correction utilized the measured 2 0 4 P b / 2 0 6 P b and compositions modelled after Cumming and Richards (1975). The Pb/ 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 P b / 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. 2.49 206 238 (Ludwig, 2001) was used to calculate weighted means o f z u o P b r J O U ages. U-Pb ID -TIMS (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 of analytical errors follows Roddick et al. (1987) with errors on the ages reported at the 2a level (Table 2). U-Pb T IMS concordia diagrams are presented in Figures 33 and 34. A Concordia age (Ludwig, 1998) is calculated for the samples analyzed by TIMS. 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 in 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 P L A T E 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 Zone (Late Pliensbachian). 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. FS-11; Takwahoni Formation; Middle Toarcian. 160 P L A T E 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 IA . Sonninia cf. adicra Westermann & Riccardi, 1972 Specimen: FS-Sp.52-A.B; Locality 16; Takwahoni Formation; Early Bajocian. IB . Dorsetensia sp. Specimen: FS-Sp.52-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 P L A T E 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 E4 /E5; Takwahoni Formation; Kunae/Carlottense Zones (Late Pliensbachian). 2. Specimen: -, Locality E5; 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 E4; Takwahoni Formation; Kunae Zone (Late Pliensbachian). 5. Specimen: -, Locality E4; 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). 1 6 6 P L A T E 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. P L A T E 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. P L A T E 9 

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