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Stratigraphy and structural geology of Upper Triassic and Jurassic rocks in the central Graham Island… Hesthammer, Jonny 1991

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STRATIGRAPHY AND STRUCTURAL GEOLOGY OF UPPER TRIASSIC AND JURASSIC ROCKS IN THE CENTRAL GRAHAM ISLAND AREA, QUEEN CHARLOTTE ISLANDS, BRITISH COLUMBIA By Jonny Hesthammer Cand. Mag., University of Bergen, Norway, 1988 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Geological Sciences We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April, 1991 ©Jonny Hesthammer, 1991 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of ^L^t -oOi tcv^ u The University of British Columbia Vancouver, Canada Date fVP&lU QX , [c\Q[[ DE-6 (2/88) Abstract ii ABSTRACT Upper Triassic and Jurassic rocks in the central Graham Island.area comprise shale, siltstone, sandstone, and conglomerate of the Kunga, Maude, and Yakoun Groups. Volcanic rocks are common in the Middle Jurassic Yakoun Group. The oldest unit exposed within the study area is the Lower Jurassic Sandilands Formation of the Kunga Group, a more than 250 metre thick sequence of interbedded organic-rich shale, tuff, siltstone, and sandstone. The Lower Jurassic Maude Group conformably overlies the Kunga Group and is divisible into four formations. The Ghost Creek Formation is an organic-rich black fissile shale, and is overlain by calcareous sandstone of the Fannin Formation. The Whiteaves Formation consists of fissile calcareous grey shale that grades upwards into fossil-rich medium- to coarse-grained, sandstone of the Phantom Creek Formation. The base of the Middle Jurassic Yakoun Group is marked by an angular unconformity. The unit is more than 1500 metres thick and is divided into four lithofacies. The lowermost shale and tuff lithofacies is a sequence of interbedded shale, tuff, siltstone, and sandstone, with shale dominating. The sandstone lithofacies overlies and partly interfingers with the shale and tuff lithofacies and comprises medium- to thickly-bedded lithic arenite interlayered with thinly-bedded shale. The conglomerate lithofacies exists within the sandstone lithofacies and consists mostly of thickly-bedded pebble and cobble conglomerate. The volcanic lithofacies interfingers with, and overlies the sedimentary rocks of the Yakoun Group, and includes lava flows, pyroclastic rock deposits, and lahars. Abstract iii The Kunga and Maude Groups record several relative changes in sea level. They formed in a progressively deepening basin. In Pliensbachian time, the basin shallowed and deposition, represented by the upper Fannin Formation of the Maude Group, was near-shore. Toarcian time is marked by an abrupt transgression. The upper part of the Whiteaves Formation and the Phantom Creek Formation of the Maude Group indicate a subsequent regression. The sedimentary rocks of the Yakoun Group were deposited in local shallow marine basins. Volcanic rocks are most abundant in the eastern parts of the map area, and indicate that an igneous source is located in that direction. All rock units in the map area are deformed by major northwest-trending faults and folds, reflecting at least four northeast-southwest oriented deformational events. The angular unconformity at the base of the Yakoun Group restricts one compressional phase to mid-Jurassic time. Abundant southwest-verging folds suggest development of northeast-dipping thrust faults during this compressional event. Northeast-trending normal faults cut through the thrust faults, postdating them and indicating a period of extension. Rocks of the Sandilands Formation are observed thrust on top of the Yakoun Group, thus indicating a second compressional event. Several small-scale strike-slip faults cut through all described rock units and overlying Tertiary sections, suggesting a late Tertiary deformational event. The Middle Jurassic compressional event may be a result of collision of Wrangellia with North America, or could have been caused by changes in relative plate motion between the North American and Pacific plates during the break-up of Pangaea. Abstract iv Lithologic similarities between the Jurassic and older units of Wrangellia on the Queen Charlotte Islands and coeval rocks of the Alexander terrane in southeastern Alaska suggest that there are no clear differences between the two, and that they were contiguous since Upper Paleozoic time. Table of contents v TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS v LIST OF TABLES vii LIST OF FIGURES viii ACKNOWLEDGEMENTS xii 1. INTRODUCTION 1 1.1. Objectives 1 1.2. Location, physical features, and access 2 1.3. Previous work 4 1.4. Geologic setting 5 1.5. Methods of study 8 2. STRATIGRAPHY 10 2.1. Introduction 10 2.2. Kunga Group 14 2.2.1. Sadler Limestone.. 14 2.2.2. Peril Formation 17 2.2.3. Sandilands Formation 17 2.3. Maude Group 27 2.3.1. Ghost Creek Formation 28 2.3.2. Fannin Formation 29 2.3.3. Whiteaves Formation 33 2.3.4. Phantom Creek Formation 35 2.4. Yakoun Group 39 2.4.1. Previous work 39 2.4.2. A new stratigraphic scheme for the Yakoun Group..... 40 2.4.3. Shale and tuff lithofacies 43 2.4.4. Sandstone lithofacies 45 2.4.5. Conglomerate lithofacies 47 2.4.6. Volcanic lithofacies 49 2.5. Intrusive rocks 55 2.6. Summary and discussion 57 Table of contents vi 3. STRUCTURE 62 3.1. Introduction. 62 3.2. Macroscopic structures... 64 3.2.1. Macroscopic folds 64 3.2.2. Macroscopic faults 73 3.3. Mesoscopic structures 75 3.3.1. Mesoscopic folds 75 3.3.2. Mesoscopic faults 79 3.4. Microscopic structures 82 3.4.1. Microscopic folds 82 3.4.2. Microscopic faults 83 3.4.3. Other microscopic structures 84 3.5. Summary and discussion 87 3.5.1. Macroscopic structures 87 3.5.2. Mesoscopic structures 91 3.5.3. Microscopic structures 100 4. SUMMARY AND DISCUSSION 102 5. REFERENCES 112 6. APPENDICES 122 6.1. Major and trace element analyses 122 6.1.1. Introduction 122 6.1.2. Major element geochemistry 124 6.1.3. Trace element geochemistry. 126 6.1.4. Summary and discussion ......129 6.2. X-ray diffraction (XRD) analyses of clay minerals 132 6.3. Fossil report 138 6.4. Geological maps 4-§2-List of tables vii LIST OF TABLES Table la-b) Major and trace element concentration of unknowns. Table II) 20 values for XRD-analyzed samples. List of figures vm LIST OF FIGURES Fig. 1) Map of western Canada. Fig. 2) Location map showing map area on central Graham Island. Fig. 3) Areas of additional detailed mapping by author. Fig. 4) Location map showing "map area" and "study area". Fig. 5) Stratigraphic column for the Queen Charlotte Islands. Fig. 6) Stratigraphy and lithology of Upper Triassic and Jurassic rocks. Fig. 7) Location map showing areas were the author studied lithology and structural styles of the Sadler Limestone, the Peril Formation, and the Sandilands Formation. Fig. 8) The Sadler Limestone of the Kunga Group. Fig. 9) The Peril Formation of the Kunga Group. Fig. 10) The Sandilands Formation of the Kunga Group. Fig. 11) Thick sandstone layers (more than 5 metres) in the Sandilands Formation. Fig. 12) SEM-photograph of albite in the feldspar-rich ash/tuff layers of the Sandilands Formation. Fig. 13) EDS-analysis of a feldspar grain in the Sandilands Formation. Fig. 14) EDS-analysis of a chlorite-clay in the Sandilands Formation. Fig. 15) EDS-analysis of carbonate in the Sandilands Formation. Fig. 16) Organic-rich layers of the Sandilands Formation with frequent circular or elliptical quartz grains. Fig. 17) SEM-photograph of a contact between chlorite matrix and a calcite filled fracture in the Sandilands Formation. Fig. 18) SEM-photograph of a sample from the Sandilands Formation in close proximity to an intrusive body. Fig. 19) EDS-analysis of clay from the sample seen in figure 18. Fig. 20) SEM-photograph from the Sandilands Formation showing chlorite filling in the pore spaces Fig. 21) A more than 30 metre thick sequence of interbedded sandstone and shale in the Fannin Formation. List of figures ix Fig. 22) Photo-micrograph of eroded skeleton in the Fannin Formation. Fig. 23) Photo-micrograph of organic-rich layer with frequent chert-replaced radiolarians (?) within the Fannin Formation. Fig. 24) Zoned plagioclase and euhedral plagioclase crystals in the Fannin Formation. Fig. 25) The Phantom Creek Formation. Fig. 26) Photo-micrograph of carboniferous rocks in the Phantom Creek Formation. Fig. 27) Chamosite ooids in the Phantom Creek Formation Fig. 28) Map showing the distribution of the Yakoun Group. Fig. 29) Map showing the distribution of the the different lithofacies of the Yakoun Group. Fig. 30) The shale and tuff lithofacies. Fig. 31) The lower part of the sandstone lithofacies. Fig. 32) Photo-micrograph of organic-rich shale with clay.lithic fragments within the Yakoun Group. Fig. 33) SEM-photograph (back-scattered-electron image) of Na-plagioclase (albite) and calcite in the Yakoun Group. Fig. 34) Lava flow in the Yakoun Group. Fig. 35) Coarse pyroclastic breccia of the volcanic lithofacies. Fig. 36) Ash-flow tuff of the volcanic lithofacies. Fig. 37) Oil seep in the volcanic rocks of the Yakoun Group. Fig. 38) Photo-micrograph of a euhedral clino-pyroxene phenocryst in matrix of a pyroclastic rock within the Yakoun Group. Fig. 39) Lahar of the volcanic lithofacies. Fig. 40) Plot of standardized orthogonal thickness t'-a plotted against angle of dip a and the main types of fold classes. Fig. 41) The study area divided into three domains. Fig. 42a-d) Stereonet-plot of poles to all bedding measurements within the study area. Fig. 43a-c) Stereonet-plot of poles to all bedding measurements within domain 1. Fig. 44a-d) Stereonet-plot of poles to all bedding measurements within domain 2. List of figures x Fig. 45a-d) Stereonet-plot of poles to all bedding measurements within domain 3. Fig. 46) A simplified map showing the distribution of major faults within the map area. Fig. 47) A gently dipping to sub-horizontal thrust fault placing the Sandilands Formation on the Yakoun Group. Fig. 48) Closed to isoclinal buckle fold in the Sandilands Formation. Fig. 49) Isoclinal fold in the Sandilands Formation showing curvilinear hinge line. Fig. 50) Buckle fold in the Sandilands Formation showing vergence towards the southwest. Fig. 51) Thrust fault in the lower parts of the Fannin Formation. Fig. 52) Stereonet-plot of poles to faults in the study area. Fig. 53) Folded rocks of the Sandilands Formation. Fig. 54) Decollement surface in the Sandilands Formation. Fig. 55) Photo-micrograph showing the core of an isoclinal fold in the Sandilands Formation. Fig. 56) Photo-micrograph of organic rich layers in the Sandilands Formation. Fig. 57) Photo-micrograph of folded rocks in the Sandilands Formation. Fig. 58) Photo-micrograph of microscopic imbricate thrust faults in the core of a fold in the Sandilands Formation. Fig. 59) SEM-photograph of a calcite-clay contact in the Sandilands Formation. Fig. 60) SEM-photograph (back-scattered-electron image) of a calcite vein in contact with chlorite and Na-plagioclase. Fig. 61) Simplified block-diagram showing main structures observed in the Jurassic rocks in central Graham Island. Fig. 62) Volcanic rocks of the Yakoun Group unconformably overlying rocks of the Sandilands Formation. • Fig. 63a-h) Geometry and kinematics of cover responses for back thrusting, coupling, forethrusting, and deposition. Fig. 64a-c) Mechanisms of thrust sheet motion. Fig. 65) Stylolites and veins in the Peril Formation of the Kunga Group. Fig. 66) Highly veined rocks of the Peril Formation. Fig. 67) Buckle fold and associated detachments surface in the Sandilands Formation. Fig. 68) Detachment surface in the Sandilands Formation with accompanying buckle folding. List of figures xi Fig. 69) Typical chevron fold style in the Sandilands Formation. Fig. 70) Collapsed fold hinge in the Sandilands Formation. Fig. 71) Buckle fold in the Sandilands Formation. A fault that is parallel to bedding cuts into the core of the fold where ft dies out. Fig. 72a-b) Stereo projection (crossed-eye technique) of a core of a fold in the Sandilands Formation. Fig. 73) Low-angle imbricate thrust faults in the Sandilands Formation. Fig. 74) Photo-micrograph showing microscopic thrust faults in the Sandilands Formation developed in order to relieve the stress build-up caused by a competent ash layer. Fig. 75) Geological evolution of the central Graham Island area. Fig. 76) Map of the Queen Charlotte Islands showing the major deformational zones. Fig. 77) Map showing locations were samples were collected for XRF-analysis. Fig. 78) Alkali-silica plot of volcanic rock samples from the Yakoun Group Fig. 79) Potassium-silica plot dividing andesftes into low-, medium-, and high-potassium andesites. Fig. 80) AFM plot of volcanic rock samples showing tholeiitic and calc-alkaline suites. Fig. 81) Binary plot of FeOVMgO vs. SiC>2 showing tholeiitic and calc-alkaline suites. Fig. 82) Binary discriminant diagram using Ti and Zr. Fig. 83) Discriminant diagram using Ti/100, Zr, and Y x 3. Fig. 84) Discriminant diagram using Ti/100, Zr, and Sr/2. Fig. 85) XRD reflections from an untreated sample of clay from the Sandilands Formation. Fig. 86) XRD reflections from a glycolated sample of clay from the Sandilands Formation. Fig. 87) XRD reflections from a heated sample of clay from the Sandilands Formation. Fig. 88) XRD reflections from a heated and glycolated sample of clay from the Sandilands Formation. Fig. 89) XRD reflections from a heated and glycolated sample of clay from the Sandilands Formation, compared to XRD reflections from clinochlore, montmorillonite, quartz, and albite. Acknowledgements xii ACKNOWLEDGEMENTS I thank Dr. John Ross for acting as thesis supervisor. This work benefited greatly from his technical and administrative expertise. Thanks are extended to Drs. Howard Tipper, Marc Bustin, Bill Barnes, Jim Haggart, and Bob Thompson for directions during the authors research. Stanya Horsky helped with the XRD-analysis. The work on this thesis benefited greatly from the excellent team work ' with Jarand Indrelid, Peter Lewis, Susan Taite, and Henry Lyatsky. Thanks also goes to Regan Palsgrove for being such a wonderful office mate. Charle Gamba, Giselle Jakobs, and Joszef Palfy are thanked for useful discussion in field. Field assistance was provided by Mark Hamilton, Ian Foreman, Greg Gillstrom, and Mike Neylan. The majority of this work was funded by the Geological Survey of Canada's Frontier Geoscience Program for the Queen Charlotte Islands. Logistic support from Chevron Canada Resources Ltd. and NSERC grant 82134 are kindly acknowledged. I would like to thank Hilde Larsen for her encouragement and emotional support. Without my parents financial support, I would never have been able to cross the Atlantic Ocean. Steinar Hesthammer and Erik Skogen provided useful discussions during their visits. And finally, my thanks goes to all my fellow students at UBC for keeping social activity at a respectable level and making my years in Canada so enjoyable. Introduction 1 1. INTRODUCTION 1.1. Objectives The Queen Charlotte Islands, located off the west coast of Canada, comprise a wide variety of rocks ranging in age from Late Paleozoic to recent (Sutherland Brown, 1968; Hesthammeret al., 1991a). The objectives of this thesis are to understand the stratigraphy and structural geology of Upper Triassic and Jurassic rocks in the central Graham Island area (Fig. 2), and to relate these to the regional geology of the west coast of Canada. In Jurassic time the west coast of North America was characterized by arc-related volcanism with volcanogenic marine sediments deposited in basins of varying shapes and sizes (Churkin, 1974; Coney, 1978; Jones et al., 1982; Monger, 1984). Jurassic rocks are widely exposed in the Queen Charlotte Islands, particularly in central Graham Island. Six months were spent mapping and describing the rocks in the central Graham Island area in an attempt to understand their structural history. One 1:50,000 scale map is published as a result of recent mapping carried out by the author and other workers in the central Graham Island area (Hesthammer et al., 1991 b), and this thesis will describe and discuss in detail the Upper Triassic and Jurassic geology represented on this map. Cretaceous and Tertiary rocks in central Graham Island are discussed only briefly. For a more thorough description and discussion of these rocks, the reader is referred to Jarand Indrelid's Masters thesis (1991). Introduction 2 1.2. Location, physical features, and access Fig. 1) Map of western Canada showing the location of the Queen Charlotte Islands. The Queen Charlotte Islands are about 800 kilometres north-west of Vancouver and 140 kilometres from mainland British Columbia (Fig. 1), between latitudes 51053'-54015' north and longitudes 130°54'-133o09' west. The map Introduction 3 132 131" Figure 2) Location map showing study area on central Graham Island. square kilometres, with Graham Island alone be area is on central Graham Island, which is the largest of the islands, between latitudes 53°15'-53°30' north and longitudes 132o05 ,-132o24 , west (Fig. 2). The Queen Charlotte Islands comprise 152 islands, the main ones being, from north to south, Graham, Moresby, Louise, Lyell, and Kunghit islands. The island group is roughly 300 kilometres long and 50 kilometres wide, forming a scimitar shape, and has a total land area of almost 10,000 ing 6,450 square kilometres. The northeastern part of Graham Island is the flat Queen Charlotte Lowlands. To the south and southwest is the Skidegate Plateau with a gentle landscape but also some rugged areas. The southwestern part of the islands is a rugged terrane characterized by mountain ranges. The climate is mild but stormy with high precipitation. Introduction 4 Daily air service from Vancouver to Sandspit on the north-eastern tip of Moresby Island is available, and a ferry connects the Moresby and Graham islands. A logging road (Queen Charlotte Main) gives access to the study area from Queen Charlotte City. A permit is required from the MacMillan-Bloedel logging company to drive on the logging roads and this may be obtained from their office in Queen Charlotte City. 1.3. Previous work The earliest geological work in the Queen Charlotte Islands was by Richardson (1873), Dawson (1880), and Whiteaves (1883). In the early 2 0 t h century a more intense study was started on Graham Island by Ells (1906), Clapp (1914), and MacKenzie (1916). Then followed a period of few geological studies of the islands. In 1949 and 1953 McLearn published a detailed study of Triassic and Jurassic rocks. Sutherland Brown (1968) produced the first comprehensive report on the geology of the Queen Charlotte Islands. The purpose of his study was to aid the search for iron-ore deposits, and his work resulted in the publication of 1:125 000 scale geologic maps for all the islands. McLearn (1972) and Riccardi (1981) published reports on the ammonoid and inoceramid faunas of the Queen Charlotte Group. Yorath and Chase (1981) and Yorath and Hyndman (1983) used Sutherland Brown's work as a basis to develop tectonic models for the Queen Charlotte Islands region. In 1985, Cameron and Tipper published the first detailed paleontological and lithological study of Jurassic rocks. Their study Introduction 5 areas were central Graham Island and eastern Skidegate Inlet, and the work resulted in a better understanding of the stratigraphy of the Jurassic rock units. In 1986 a remapping of the Queen Charlotte Islands started with the introduction of the Queen Charlotte Islands Frontier Geoscience Program (QCIFG.P). The project was begun in order to evaluate oil potential in the Hecate Strait, and the objectives were to: 1) understand crustal processes that controlled the Queen Charlotte basin development, 2) outline the internal geology and evolutionary history, 3) establish the character and distribution of source- and reservoir- type rocks, and 4) evaluate hazards that could affect petroleum exploration and production. The project has involved detailed onshore geological mapping and the contributors to the recent mapping are Thompson and Thorkelson (1989), Lewis (1991b), Hickson (1990), Haggart et al. (1990), Hesthammer (1990), Indrelid (1990), and Taite (1991). 1.4. Geologic setting Western Canada is divided into five tectonics belts (Fig. 1). These are, from east to west, the Foreland, Omineca, Intermontane, Coast, and Insular belts The Queen Charlotte Islands comprises the west-central part of the Insular Belt. This belt includes several possibly allochtonous terranes, and the Queen Charlotte Islands lie within Wrangellia (Jones et al., 1977; Monger, 1984; Gardner et al., 1988). Wrangellia is recognized from Alaska in the north (Smith and MacKevett, 1970) to Oregon in the south (Vallier, 1977) and is believed by several authors to have collided with North America in Jurassic time (Wernicke, 1988; van der Heyden, 1989, Thompson et al., 1991). West of Wrangellia is the Introduction 6 Alexander terrane (Jones et al., 1977). The suture between Wrangellia and the Alexander terrane was earlier believed to be represented by the Sandspit Fault on the Queen Charlotte Islands (Yorath and Chase, 1981). More recent studies question this (e.g., Woodsworth, 1988), and the author will, in the chapter concerned with tectonic interpretations (chapter 4), discuss differences between the two terranes and whether they could be a single terrane rather than two separate ones. Rocks exposed in the Queen Charlotte Islands range in age from Carboniferous (?) and Permian to present (Fig. 5), and several different assemblages are recognized: 1) The lowermost comprise an unnamed "carbonate-chert" unit consisting of interbedded limestone, chert, and dolomite, and occasional argillite, sandstone, and conglomerate. The unit was not recognized until the field season of 1990, and it defines the oldest rocks observed on the Queen Charlotte Islands (Hesthammer et al., 1991a). Unconformably overlying this is the Triassic Karmutsen Formation comprising pillow basalts and breccia, flows, and locally interbedded limestone (Sutherland Brown, 1968). Possible subaerial pyroclastic rock deposits observed in western Moresby Island may be related to the Karmutsen Formation or to an older volcanic unit (Indrelid and Hesthammer, 1991). Intercalated limestone, shale, siltstone, and sandstone of the Upper Triassic to Lower Jurassic Kunga and Maude Groups overlie the Karmutsen Formation (Sutherland Brown, 1968; Cameron and Tipper, 1985). 2) Calc alkaline volcanic rocks and volcanic derived sediments of the Middle Jurassic Yakoun Group overlie older strata with an angular unconformity. The Yakoun Group were formed in a volcanic arc setting. As a result of the detailed mapping in the central Graham Island area, the lithological description of the Introduction 7 Yakoun Group has been redefined, and will be discussed as one of the main topics in this thesis. 3) Overlying the Yakoun Group is the Queen Charlotte Group, a Lower Cretaceous sequence of sandstone and occasional conglomerate that grades into shale (Haggart, 1991; Haggart et al., 1991; Indrelid, 1991). Conformably overlying and partially interbedded with the shale are turbidites of the Skidegate Formation. The Honna conglomerate overlies the older units, but can also be found interlayered with the Skidegate Formation. Several hundred metres of volcanic rocks and minor sedimentary rocks overlie and partially interbeds the Honna Formation (Fogarassy and Barnes, 1988; Haggart et al., 1989). The Cretaceous rocks of the Queen Charlotte Group define a marine transgressive sequence that culminated in Late Cretaceous time with deposition of the coarse Honna conglomerate (Haggart, 1991). 4) Tertiary rocks on the Queen Charlotte Islands comprise Paleogene black shale and minor sandstone (White, 1990; Lewis and Ross, 1991; Haggart et al., 1990), Tertiary volcanics and undefined Tertiary sediments (Hickson, 1990; Haggart et al., 1990; Indrelid, 1991), and arkosic sandstones, shales, and conglomerates of the Skonun Formation (Shouldice, 1971; Higgs, 1991). 5) Several plutonic suites are recognized. The San Christoval and Burnaby Island plutonic suites are of Jurassic age, and the Kano plutonic suite is of Tertiary age (Anderson and Reichenbach, 1989; 1991). Introduction 8 1.5. Methods of study 132 131* Figure 3) Areas were the author did additional detailed mapping (see Indrelid et al., 1991a).  The author together with J . Indrelid spent three field seasons on the Queen Charlotte Islands from 1988 to 1990, mapping the central portion of Graham Island in detail. Some time was spent looking at the Peril Formation and Sadler Limestone at Kunga Island, in Englefield Bay, in Skidegate Inlet and in Rennell Sound (Fig. 7). Additional detailed mapping on the islands includes the areas along the west coast of Graham Island, on western Moresby Island, and in Cumshewa Inlet (Fig. 3). A four wheel drive vehicle was used in most of the study area. The author used a Zodiac inflated boat in the Yakoun Lake region and a helicopter to map the mountains south-west of Yakoun Lake. Outcrops are mainly in road cuts, quarries, and creeks, and the numerous logging roads made detailed mapping possible. Introduction 9 Thin sections were cut from selected hand samples. Forty were stained with sodium cobaltinitrite for easier determination of clay and potassium feldspar (Hughton 1980). Most of the thin sections were also vacuum impregnated with blue dyed epoxy resin for visual porosity studies following the procedures of Yangras and Paxton (1986). Chevron Canada Resources did scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses on five selected samples. A Siemens® X-ray diffractrometer (XRD) at the University of British Columbia (UBC) Department of Geological Sciences was used for studies of the clay mineralogy. The writer analyzed nine samples for major and trace element concentrations using the UBC Department of Geological Sciences X-ray fluorescence spectrometer (XRF). StratiaraDhv/lntroduction 10 Z STRATIGRAPHY 2.1. Introduction The purpose of this thesis is to outline the stratigraphy and structural geology of Upper Triassic and Jurassic rocks exposed in the central Graham Island area. Most of the total stratigraphic section of the Queen Charlotte Islands is exposed within the study area. Description and discussion of Cretaceous and Tertiary rocks are treated in Indrelid's M.Sc.-thesis (1991), and will only be briefly discussed in this thesis under the chapter concerned with tectonic evolution. The map submitted in this thesis includes some work by other geologists. Their work is not discussed in this thesis, but is included on the map in order to better achieve an understanding of the geology of southern Graham Island. For discussion purposes the map is separated into "map area" (total area mapped) and "study area" (where data have been analyzed; see Fig. 4 for explanation). Figure 4) Location map showing the difference between "map area" (totalarea mapped) and "study area" (area were data have been analyzed by writer).  Stratigraphy/Introduction 11 CHRONOSTR ATIGR APHIC UNIT O 00 D o UJ o < o 00 00 < or 3 O 00 00 < CC P L E I S T O C E N E MIOCENE E O C E N E P A L E O C E N E MAASTRICHTIAN C E N O M A N I A N H A U T E R I V I A N V A L A N Q I N I A N T I T H O N I A N KIMMER10GIAN A A L E N I A N PLIENSBACHIAN H E T T A N G I A N G R I E S B A C M I A N P E R M I A N . A G E (Ma I 1.6 5.3 23.7 366 57.8 66.4 74.5 84.0 87.5 88.5 91 97.5 113 119 124 131 138 144 152 156 163 169 176 183 187 193 198 204 208 225 230 235 240 S T R A T I G R A P H Y Un i t / l i t ho logy Th ickness M A S S E T FM basalt to rhyollts <^ ^^ > flows, pyroclaatlca. S K O N U N sanaston shale, cong., W O O O m * ^ sooom F O R M A T I O N "onit«. m / , 2 | U N N A M E D Dasatt. andesite V O L C A N I C R O C K S Hows, volcam-clastic cong. * L W A M E O black snale. S E D W E N T A R Y « O C K S sandstone 100 nr"31 d Q-< 3 X O O CL U N N A M E D S E D I M E N T A R Y R O C K S grey snale, mttw sandstone U W A M C D VOLCANIC R O C K S arKMsita-Dasalf Hows, flow Breccia 800 m<5> HONMA FORMATION conglomerate, lesser sandstone S K I D E G A T E J ™ " * - X . F O R M A T I O N ™ « i o r » _ C R E T A C E O U S S H A L E sandstone, siltstone, mudstone C R E T A C E O U S S A N D S T O N E M O R E S B Y G R O U P f . ? ^ ^ . ^ * ' " " * ' ° " * Y A K O U N G R O U P 3 O < or anoaftic flows, flow braccits, tuff, volcanic sandstono. sdtstons. cong. TTTtTrtTT PHANTOM CREEK FORMATION sandstone, l o s s * tarQua sandstone WHtTEAVES FORMATION grey shale, mudsione 100 mie! F A N N N FORMATION sdtstona, sandstone, sfiaie 120 m'Bl G H O S T C R C € K FORMATION dark gray sfiaie < a SANOILANOS FORMATION i ^ ^ s f o n V ' ^ n o r .ull PERIL FORMATION i DiacK. inimy-oeoded >ADLER LIMESTONE i massive gray K A R M U T S E N F O R M A T I O N limestone and argillite U N N A M E D C A R B O N A T E - C H E R T UNIT thinly- lo truckiy-beddad tni«rlay«fad cfien. timeatone. and dolomite minor ar guilts, sandstone, conglomerate, and schist P L U T O N I C H I S T O R Y K - A r A G E K A N O P L U T O N I C S U I T E - ^ 2 7 — So CD Q . r i - 1 5 8 --f"172 ^ is. U 5 -1 4 7 -< t-> 5 O to III Mickson I199U (21 Shouidice H971I (31 Lewis H990) 1*1 Haggan ana v-ttggs n969t (5) Haggart at al. 11989) (6) Sutherland Brown M968) (7) Haggart 11989) (8) Cameron ana TiDDer (9) JakoDs (1990) 110) Desrochers and Orchard 11991) (11) Hesthammer ai al. (1991) (121 Anderson and ReichenQtcn 1:99 il Figure 5) Stratigraphic column for the Queen Charlotte Islands (modified from Lewis, 1991b). Figure 5 shows a stratigraphic section for the different rock units exposed in the Queen Charlotte Islands. A stratigraphic column of Upper Triassic and Jurassic rocks exposed in the study area are shown in figure 6. Stratigraphy/Introduction 12 o CO (0 <D 3 O CO (0 o 176 183 187 193 198 204 208 225 Yakoun Group Q. 3 O 5 •o (0 2 a 3 O 5 (0 D5 c 3 Phantom Creek Fm. Whiteaves Formation Fannin Formation Ghost Creek Formation Sandilands Formation Peril Formation Sadler Limestone < 700 m 15 m 100 m 120 m 45 -70 m > 3 0 0 m 250 m 5 -50 m shale, si l tstone. . sandstone, conglomerate, volcanic -flows, pyroc las t ic r ocks lahars medium- to coarse-gra ined fossi l i ferous sst. f issile grey shale, ca lc concret ions, minor ' sandstone medium- to th ickly-beaded sandstone. minor intenavered shale and tuff organic-ncn dark-grey and olack fissile shale, minor sandstone and tuff thinly-bedded inter layered turDiditic snaie. si l tstone. tuff and sandstone thinly-beddeo inter layered dark grey and black l imestone, shale, si l tstone. and sandstone medium- to thickly-bedoed and massive grey styloiit ic l imestone Figure 6) Stratigraphy and lithology of Upper Triassic and Jurassic rocks within the study area. Cameron and Tipper (1985) provide an excellent general description of lithologies and detailed biostratigraphy of the Sandilands Formation, the Maude Group, and the Yakoun Group based on studies carried out mainly in Skidegate Inlet, but also in the central Graham Island area. Stratiaraph v/lntroduction . 13 Upper Triassic through Cretaceous rocks in the Queen Charlotte Islands have been through low-grade metamorphism. Only rocks in close proximity to intrusives and larger plutons have undergone higher-grade contact metamorphism. Most rocks in the vicinity of contact-aureoles appear as either amphibolites or homfels, and are described in detail by Sutherland Brown (1968). The author did not focus on studies of metamorphic rocks. Stratiaraphv/Kunaa Group 2.2. Kunga Group 14 The Kunga "Formation" was first named by Sutherland Brown and Jeffrey (1960) but was recognized as an entity as early as 1880 by Dawson. Cameron and Tipper (1985) studied the unit in the region around Maude Island and completely revised the stratigraphic nomenclature. They raised the Kunga Formation to group status and considered the members to be formations. They renamed the black argillite member of Sutherland Brown (1968) to Sandilands Formation, and Desrochers and Orchard (1991) further renamed the black and grey limestone members (Sutherland Brown, 1968) to the Peril Formation and the Sadler Limestone respectively. Sadler Limestone is a massive or thickly bedded limestone and the Peril Formation consist of dark-grey to black interbedded limestone, shale, siltstone, and sandstone in 2 to 10 centimetre thick beds. Sandilands Formation comprises thin- to medium-bedded shale, tuff, siltstone, and sandstone layers. Sadler Limestone and the Peril Formation are not exposed within the study area. However, based on structural styles observed in the central Graham Island area, it is inferred that both formations underlie most of the area. 2.2.1. Sadler Limestone The Sadler Limestone was studied on reconnaissance trips to Kunga Island, Rennell Sound, and Englefield Bay (Fig. 7) in order to understand the lithologies and structural styles of the unit. This formation is a massive or thickly-bedded light- to dark-grey stylolitic and vein-rich fossiliferous wackestone (Fig. Stratiaraohv/Kunaa Group 15 132' 131' 8). Sutherland Brown (1968) separated the unit on basis of lithologic differences from other units. Sadler Limestone is heavily bioturbated and contains frequent ooids (Desrochers, 1988). Contact with the underlying Karmutsen Formation is sharp and conformable. Lewis (1991b) suggested a thickness of the unit of about 50 metres, and Carter et al. (1989) restricted the age of the Sadler Limestone to Upper Carnian based on radiolarian microfauna. Good sorting, absence of mud, and well-formed ooids suggest accumulation on bars and shoals under relative high-energy conditions in shelf-margin positions (Desrochers, 1988). Bioturbated limestones with a diverse fossil assemblage in parts of the formation, however, suggest deposition in low-energy subtidal environments (Desrochers, 1988). Figure 7) Location map showing areas were the author studied lithology and structural styles of the Sadler Limestone, the Peril Formation, and the Sandilands Formation. Stratiaraphv/Kunaa Group 1 6 Figure 8) The Sadler Limestone of the Kunga Group. The formation is a massive or thickly-bedded light- to dark-grey stylolitic and vein-rich limestone.  Figure 9) The Peril Formation of the Kunga Group. The unit comprises 2-10 centimetre thick interbedded limestone, shale, argillite, siltstone, and sandstone layers where limestone is the major component.  Stratiaraphv/Kunaa Group 2.2.2. Peril Formation 17 Due to lack of exposure in the,map area, the Peril Formation was studied by the author on Kunga Island, in Rennell Sound, and in the Englefield Bay area (Fig. 7). The contact with the Sadler Limestone is sharp and conformable (Carter et al., 1989), and the unit is separated from Sadler Limestone based on distinct lithologic changes. Its appearance is somewhat similar to the overlying Sandilands Formation. The Peril Formation comprises 2-10 centimetre thick interbedded calcarenite, shale, siltstone, and sandstone layers where limestone is the major component (Fig. 9). Pure limestone sequences are common, and tuff and ash layers show evidence of volcanic activity. The formation can often be distinguished because of abundance of Monotis subcircularis towards the top of the section. Ammonoids, conodonts and radiolarians are common in the lower part of the formation (Carter et al., 1989). Orchard (1990) suggested a thickness of about 250 metres for the Peril Formation. Desrochers (1988) suggested the mudstone facies of the unit reflects deep-water pelagic fallout, and proposed a proximal turbidite environment for the laminated siltstone and sandstone. The age of the formation is Upper Carnian to Upper Norian, based on microfauna (Carter and Golbrun, 1990). 2.2.3. Sandilands Formation The Sandilands Formation overlies the Peril Formation with a gradational contact (Carter et al., 1989), and the author was not able to locate the contact based on lithologic differences alone. The unit is widely exposed in the map Stratiaraphv/Kunaa Group 18 area. The age is, based on ammonoid fauna, restricted to Late Norian to latest Sinemurian or earliest Pliensbachian (Tipper and Carter, 1990). Thickness is estimated to be several hundred metres, but is probably less than 500 metres as indicated by Sutherland Brown (1968). Lithologies include interbedded shale, tuff, siltstone, and sandstone (Fig. 10).  Figure 10) The Sandilands Formation of the Kunga Group is a turbiditic sequence of interbedded shale, tuff, siltstone, and sandstone. The unit is easily recognized because of its banded pattern resulting from colour differences and preferential weathering.  The rocks range in composition from a lithic arenite to lithic greywacke and commonly contain thicker sandstone layers and calcareous, often fissile, shale and black organic rich shale (argillite). Tuff layers are seen at all levels, and limestone is most common in lower parts of the unit. Thickness commonly is from 2-10 centimetres with 1-2 centimetre pyrite lenses. Lewis (1991b) recorded a 50 metre thick sandstone layer in Rennell Sound, and sandstone layers thicker than 5 metres are observed in central Graham Island (Fig. 11). Stratiaraphv/Kunaa Group 19 Thirty to one hundred centimetre thick massive sandstone layers are common in parts of the section. This abundance of sandstone was not observed by Cameron and Tipper (1985). The rocks become more shaly towards the top of the unit and characteristically have less input of volcanic material. Figure 11) Thick sandstone layers (more than 5 metres) are seen in parts of the Sandilands Formation, and are most likely restricted to lower parts of the unit. Primary structures observed within the Sandilands Formation are load casts, flame structures, and graded bedding. Cross bedding, ripple marks, and other current structures are rare. The colour varies from light grey (tuff layers) to black (argillite). Fresh surfaces generally are dark and weathered surfaces are rusty. The Sandilands Formation is often recognized because of its banded pattern resulting from colour differences and preferential weathering (see Fig. 10). The rocks vary from hard and compact to soft and fissile depending on tuff and silica content and degree of weathering. Tuff layers commonly weather to soft clay layers. Several authors use the term "tuff" to describe the light grey to Stratiaraphy/Kunga Group 20 rusty looking thin bands that occur throughout the Peril and Sandilands Formations and also in the Maude Group (e.g., Cameron and Tipper, 1985; Desrochers, 1988). To confirm their volcanic origin, one sample was collected from one of the suspected tuff layers in the Sandilands Formation for X-ray diffraction analysis (the data and interpretations are included in appendix 1). This analysis shows the sample to consist mainly of smectite (in the form of a mixed-layer clay) with a volcanic origin. 3,82KX 19UM- 20KU W0:24MM S 00000 P 00004 Sandstone layers within the Sandilands Formation are made up of 5-40 percent plagioclase crystals, less than one millimetre long, and mostly restricted to well defined ash/tuff layers. The plagioclase is albite (Fig. 12 and Fig. 13) and is commonly altered to mica or replaced by calcite, typical for volcanic-derived material. Energy dispersive spectrometry (EDS) analyses of the clay matrix, show that most is made up of chlorite (Fig. 14). Iron oxides are common in the matrix, and pyrite is most pronounced in organic-rich mud layers. The layers also have a high amount of organic residue restricted to foliation surfaces. Oil seeps are common in Figure 12) SEM-photograph of albite in the feldspar-rich ash/tuff layers in the Sandilands Formation. Stratiaraphv/Kunaa Group 21 2 B - M a y - 1 9 9 0 0 9 : 1 5 : 4 0 P I T B L P r e s e t ' 1 0 0 s e e s V e r t * 3 6 9 8 c o u n t s D i s p = 1 E l a p s e d * 1 0 0 s e e s S i ' 0 1 flu 1 ' N a ,XAJ^L__ _. 1 1 12 13 1 4 15 16 1 7 18 h i- 0 . 0 0 0 R a n g e = 2 0 . 4 6 0 k e V 1 0 . 1 0 0 I n t e g r a l 0 = 8 0 7 0 7 Figure 13) EDS-analysis of a feldspar grain in the Sandilands Formation. The analysis indicate a Na-plagioclase, most likely albite. 1 4 - M a u - 1 9 9 0 1 1 : 1 2 : 5 7 PIT HM V e r t = 1 1 4 8 c o u n t s D i s p = P r e s e t = E l a p s e d * 1 0 0 s e e s 1 0 0 s e e s St 4- 0 . 0 0 0 R a n g e - 2 0 . 4 6 0 k e V 1 0 . 1 0 0 I n t e g r a l 0 = 5 5 9 9 2 Figure 14) EDS-analysis of the clay in the Sandilands Formation shows presence of Mg, Al, Fe, and Si. The clay is likely a chlorite. XRD-analysis of the clay (see appendix A) suggest a mixed-layer clay of chlorite and montmorillonite. Stratiaraphv/Kunaa Group ; 22 fractures related to folding and carbonate is mostly restricted to fractures caused by depositional loading prior to deformation (see chapter 3). The carbonate typically lacks iron (Fig. 15). The organic-rich layers are also high in circular or elliptical quartz grains that may represent radiolarians (Fig. 16). Euhedral quartz crystals are commonly seen in 1 4 - t 1 a y - 1 9 9 8 0 9 : 2 5 3 0 P I T Hr) P r e s e t • 1 0 0 s e e s V e r t " 2 9 5 2 c o u n t s D i s p - 1 E l a p s e d " 1 0 0 s e e s Q u a n t e x > C a flu 1 0 C a L. , i flu n r 13 1 4 15 \6 1 ? 18 19 4- 0 . 0 0 0 R a n g e » 2 0 . 4 6 0 k e V 1 0 . 1 0 0 I n t e g r a l 0 • 8 0 9 3 5 Figure 15) EDS-analysis of carbonate in the Sandilands Formation. The analysis shows no presence of iron. This is typical for all the carbonates analyzed.  the chlorite matrix (Fig. 17). Minor amounts of volcanic quartz and rock fragments are found in sandstone layers brought into the environment by turbidity currents. Rocks of the Sandilands Formation commonly contain pyrite framboids (Fig. 18). EDS-analyses of the clay in these rocks, show traces of sulphur which is likely from pyrite in the clay (Fig. 19). Stratiaraphv/Kunaa Group 23 Particles in the unit vary from clay- to coarse sand-size but variations within each lamina are small. The grains show a medium sorting and sphericity with angular, grain-supported fragments. All pore-spaces are filled by carbonate or chlorite (Fig. 20). Fracture permeability can reach 20% in places, but, these are in outcrop samples, and may well represent enlargement by surficial processes. Figure 16) The organic-rich layers of the Sandilands Formation contain frequent circular or elliptical quartz grains. These may represent radiolarians, where the original quartz have been replaced by chert, macroquartz, and sometimes calcite. Parts of the Sandilands Formation contain many ammonites often deformed in the bedding planes. Bivalves are found occasionally (Cameron and Tipper, 1985). Detrital wood fragments are common in thicker sandstone layers. The parts of the Sandilands Formation containing thicker sandstone layers, can resemble the Middle Jurassic Yakoun Group. The high amount of organic material resulting from pelagic fallout makes the Sandilands Formation one of the best source rocks in the Queen Charlotte Islands Stratiaraphv/Kunaa Group ; 24 (Macauley, 1983; Cameron, 1987; Hamilton and Cameron, 1989; Vellutini, 1988; Indrelid and Hesthammer, 1990). Ammonoid fauna shows deposition in a marine environment, and presence of tuff suggest a distal volcanic source. The thin bedding and amount of pyrite probably suggest deposition in relatively deep water. Cameron and Tipper (1985) stated that only minor parts of the formation show grading. The writer disagrees and believes that most layers show normal-graded bedding. This graded bedding together with abundant bottom structures and regular sequences of shale, siltstone, and sandstone suggest deposition by turbidity currents. The sandstone layers with rock fragments were probably brought into the environment by these currents. The presence of thicker sandstone layers in the lower part of the Sandilands Formation suggests that this section was deposited in closer proximity to the source than the underlying Peril Formation. The upper part of the Sandilands Formation is characterized by distal turbidites deposited in relatively deep water.. The Early to Middle Jurassic Bonanza Group on Vancouver Island may be a possible source for the volcanic ash/tuff seen so commonly in the formation (see chapter 4). Stratiaraphv/Kunaa Group 25 Figure 17) SEM-photograph of a contact between chlorite matrix and a calcite filled fracture in the Sandilands Formation. Note the abundance of euhedral quartz crystals in the chlorite matrix.  Figure 18) SEM-photograph of a sample from the Sandilands Formation in close proximity to an intrusive body. These rocks contain frequent pyrite framboids (the bright spots).  Stratiaraphv/Kunaa Group 26 •Jun-1990 1 3 : 0 1 : 0 9 ? 5 8 c o u n t s D i s o = 1 P r e s e t = £ 1 a p s e d -100 sees 100 sees 11 12 13 14 \i 16 1 7 18 19 4- 0 . 0 0 0 R a n g e * 2 0 . 4 6 0 k e V 1 0 . 1 0 0 I n t e g r a l 0 4 8 6 6 1 Figure 19) EDS-analysis of clay from the sample seen in figure 18. Presence of sulphur probably results from pyrite within the clay.  Figure 20) SEM-photograph from the Sandilands Formation. Chlorite commonly fills the pore spaces, and very little porosity is observed. The fracture seen in the picture probably occurred during preparation of the sample. Stratiaraphv/Maude Group 2.3. Maude Group 27 The Maude "Formation" was first named by MacKenzie (1916). The definition of the formation, however, was vague and has since been shown to include rocks from the Yakoun, Longarm, and Queen Charlotte Groups. Sutherland Brown (1968) restricted the formation to Pliensbachian to Toarcian age based on fossil control. Cameron and Tipper (1985) raised the formation to group status, and based on lithologic differences, defined five formations within the Maude Group. These are the Ghost Creek, Rennell Junction, Fannin, Whiteaves, and Phantom Creek Formations. Problems in separating the Rennell Junction Formation and the Fannin Formation from lithology alone, led Tipper et al. (1991) to combine the two into one formation and keep the name as the Fannin Formation. The Ghost Creek Formation consists mainly of a dark shale. The Fannin Formation comprises 10-100 centimetre thick calcareous sandstone layers. The Whiteaves Formation is a grey or greenish-grey shale, whereas the Phantom Creek Formation is the youngest and consists mainly of a coarse sandstone with frequent ooids. The two oldest formations show upward coarsening and probably result from a decrease in relative seawater level. The two youngest formations may represent a transgression and a regression respectively. The total thickness of the group in the central Graham Island area is approximately 250 metres (Cameron and Tipper, 1985; Jakobs, 1990). Stratiaraphv/Maude Group  2.3.1. Ghost Creek Formation 28 The Ghost Creek Formation overlies the Sandilands Formation gradationally and comprises organic-rich dark-grey or black silty shale with occasional light grey or brownish limestone beds and lenses. Cameron and Tipper (1985) measured the thickness of the type section in central Graham Island to be 68.5 metres, but in Skidegate Inlet they found that the formation is less than 46 metres thick. Chapter 3 describes how lithologies of the Ghost Creek Formation affect the structural styles, and the author believes that the unit has undergone a large amount of bulk shortening. Ammonoid fauna restricts the age to Lower Pliensbachian (Cameron and Tipper, 1985). The lower part of the Ghost Creek Formation is similar to the Sandilands Formation but with far fewer tuff beds present. Most of the formation is a fissile homogeneous shale with bed thickness ranging from 1 or 2 millimetres to 10 centimetres. Rare ash beds or tuffaceous shale beds are present throughout the formation. No primary structures were seen. The rocks have a very dark grey colour on fresh surfaces, and weathered surfaces are often rusty. The formation is recessive except for harder limestone beds or lenses. Shale is the dominant rock type in most parts of the formation but grades to siltstone and fine sandstone in thicker beds (less than 20 centimetres) near the top. Cameron and Tipper (1985) recognized glauconite in the upper part of the unit. Imprints of ammonites, often deformed but clearly defined, are common on bedding planes. The Ghost Creek Formation is very organic rich, and oil stains are common throughout the unit. The formation is considered a major Stratigraphv/Maude Group ; : 29 hydrocarbon source rock in the Queen Charlotte Islands (Macauley, 1983; Cameron, 1987; Hamilton and Cameron, 1989, Vellutini, 1988). Cameron and Tipper (1985) suggested deposition of the Ghost Creek Formation in a deep sedimentary basin which became shallower to the south. The glauconite present implies slow deposition. Glauconite is an authigenic mineral formed where sedimentation rate is nil or very slow at water depths of 50-500 metres, and great quantities of glauconite usually exist at depths between 200-300 metres (Giresse and Odin, 1973; Odin and Matter, 1981). The large amount of pyrite and the dark colour suggest deposition beneath the oxygen minimum zone. The Ghost Creek Formation received far less volcanic input than the Sandilands Formation. The general upward coarsening within the upper part of the formation probably show a shallowing of the basin or more rapid deposition. 2.3.2. Fannin Formation The total thickness of the Fannin Formation is measured to be 110 metres on Maude Island but only 73 metres in central Graham Island (Cameron and Tipper, 1985). The unit is, however, faulted, and true thickness is difficult to obtain. The contact with the underlying Ghost Creek Formation is gradational and marked by increasing amounts of sandstone. The boundary between the two formations is approximately where the amount of sandstone and shale is equal. Ammonites in the Fannin Formation indicate a Early Pliensbachian to Early Toarcian age (Cameron and Tipper, 1985). Stratigraphy/Maude Group 30 The Fannin Formation consists of homogeneous sandstone beds with thinner interlayered shale. The rocks range in composition from lithic arenite to lithic greywacke. Bed thickness becomes greater towards the top and grain size increases. Bed thickness in the lower part of the unit seldom exceeds 15 centimetres where the sandstone layers are interbedded with 5-8 centimetre thick shale layers (Fig. 21). Towards the top the beds can be as much as a metre thick. Each bed shows a constant thickness over long strike distances. The sandstones are generally interbedded with lenticular limestone beds and 2-15 centimetre thick shale layers. Light grey and rusty ash and tuff layers are common throughout the unit and resemble those of the underlying units. The sandstone beds are often calcareous and massive with few primary structures except for graded bedding. Cameron and Tipper (1985) observed some low angle cross bedding. Figure 21) A more than 30 metre thick sequence of interbedded 10-20 centimetre thick sandstone layers and 5-8 centimetre thick shale layers in the Fannin Formation. Stratiaraphv/Maude Group 31 Figure 22) Photo-micrograph of eroded skeleton in the Fannin Formation. Fresh surfaces are often bluish-grey, and are mostly hard and dense. When weathered, the rocks commonly show a characteristic greenish colour, and can be soft. The formation usually has a massive appearance. Shell fragments (Fig. 22) and well preserved ammonites and belemnites are abundant. Concretions are common at all levels. Some of the concretions are made up entirely of cemented brachiopods, ammonites, and bivalves. The sandstone is heavily bioturbated. Grain size is seldom larger than 1 millimetre and mostly less than 1/4 millimetre. The rocks are medium sorted with angular grains and poor sphericity. Thin sections show primarily grain supported rocks where the pore spaces are filled with carbonate or chlorite. The rocks have large amounts of volcanic material and thin layers of ash or tuff are common. Euhedral feldspar crystals are abundant, commonly altered to mica or replaced by calcite, and seldom larger in size than 1/8 millimetre. The amount of calcite in the sandstone Stratigraphy/Maude Group 32 can in places reach 70 percent, present as shell fragments and cement. Some thin layers consist mainly of chert replaced radiolarians (?) and have a high percentage of organic matter (Fig. 23). Chlorite, glauconite, and biotite are common mica minerals. A few volcanic quartz grains and some rock fragments with a pronounced diabasic texture occur. _ Chamosite ooids are seen in parts of the Fannin Formation. An important condition for chamosite ooids to form, is a continental source where iron can be concentrated (Hallam, 1984). The lower part of the Fannin Formation, where shale is abundant, was most likely deposited in relatively deep water. The amount of highly bioturbated sandstone, and presence of chamosite ooids in the upper part of the unit suggest deposition near shore (Cameron and Tipper, 1985). Volcanic fragments and the presence of zoned plagioclase, which is common in volcanic rocks (Folk, 1974), indicate volcanic activity (Fig. 24). The source must have been fairly distal, since only ash-size (< 2 millimetres) fragments are found in these outcrops (see chapter 4). Figure 23) Photo-micrograph of organic-rich layer with frequent chert-replaced radiolarians (?) within the Fannin Formation. The fracture is filled with calcite. Stratiaraphv/Maude Group  2.3.3. Whiteaves Formation 33 The Whiteaves Formation is a grey-green, homogeneous shale. It is rarely exposed in the Queen Charlotte Islands, but a few good sections can be found on central Graham Island. Jakobs (1990) has assigned an Early to Late Toarcian based on ammonoid fauna. The type section is along the Yakoun River and measures 98 metres, whereas the thickness on northern Moresby Island is only 26 metres (Cameron and Tipper, 1985). The Whiteaves Formation has probably undergone layer parallel shortening (see chapter 3). Low-angle imbricate thrusts like those observed in the Sandilands Formation may also have played a major role in the shortening of the unit, but these are very difficult to observe in pure shale Figure 24) The sandstone of the Fannin Formation show abundance of zoned plagioclase and euhedral plagioclase crystals. This suggests that the fragments have a volcanic origin. sequences. The contact with the Fannin Formation is abrupt (Cameron and Tipper, 1985). Cameron and Tipper (1985) separated the formation into two members; the Septarian Shale Member and the Concretionary Shale Member. The author was unable to separate the Whiteaves Formation into these Stratigraphv/Maude Group 34 members based on lithologic differences alone. The lower part of the Whiteaves Formation is characterized by pale-grey septarian nodules, whereas the upper part of the unit is more sandy and contains frequent spherical or discoidal calcareous nodules. The transition from lower to upper parts of the formation is, however, very gradational, and at most outcrops it is impossible to say anything about stratigraphic levels without fossil control. The unit has a massive and homogeneous appearance, but lamination can be seen especially where ash beds become frequent. No current structures were seen. Fresh surfaces are bluish-grey, and weathered surfaces are greenish or reddish-brown. The rocks are recessive with the exception of limestone nodules which are quite hard. Rock samples "crumble" into tiny pieces as a result of bedding planar fissilities and a weakly developed cleavage. Well preserved large fragments of ammonites and belemnites can be found in parts of the unit. Most of the Whiteaves Formation is weakly calcareous, and glauconite is common at the base. Euhedral feldspar crystals in thin laminae probably represent ash-beds. Grain size is mostly less than 1/16 millimetres but can reach sand size towards the top of the unit. The abundance of shale, general lack of sandstone, and presence of glauconite in the Whiteaves Formation suggest slow deposition at water depths between 200 and 500 metres. Frequent ash beds show evidence of distal volcanic activity. Rich micro fauna and shell fragments support the theory of a slow filling of the basin. The moderately deep basin conditions of the Whiteaves Formation are in large contrast to the shallow marine conditions of the upper parts of the Fannin Formation. Stratiaraphv/Maude Group  2.3.4. Phantom Creek Formation 35 The Phantom Creek Formation is a fine- to coarse-grained, medium- to thickly-bedded lithic arenite. Jakobs (1989, 1990) found that the maximum thickness of the formation probably does not exceed 15 metres. She used ammonite fauna to confine the age of the unit to late Upper Toarcian to Early Aalenian. This formation is best exposed in central Graham Island where Cameron and Tipper (1985) divided the unit into two informal members. The lowermost is the coquinoid sandstone member and the uppermost the belemnite sandstone member. The transition between the two members is very gradational and the writer mapped the formation as one unit. Figure 25) The Phantom Creek Formation is a fine- to coarse-grained, medium- to thickly-bedded lithic arenite. Bed thickness commonly range from 10-30 centimetres. Stratigraphy/Maude Group 36 The Phantom Creek Formation conformably overlies the Whiteaves Formation. The contact is gradational over several metres in central Graham Island. Bed thickness commonly ranges from 10 to 30 centimetres (Fig. 25) but has been observed in the map area to be up to a metre thick. The basal part of the unit is shaly with irregular bedding and weathers easily. The lower part also comprises some characteristic sandy limestone lenses, whereas the upper part is more massive and uniformly bedded and typically hard and compact. Primary structures are scarce in all parts of the unit. Fresh surfaces are most commonly grey or brownish-grey, and weathered surfaces are pale-brown or "earthy". Calcareous concretions are abundant. Belemnites are the most common fossils and increase in abundance towards the top of the unit. Well preserved ammonites occur in parts of the formation. Grain size range from less than 1/16 millimetres to 4 millimetres but is mostly that of medium to coarse sand. The rocks are medium sorted and consist of angular grains with poor sphericity. They are grain-supported and ail pore spaces are filled with carbonate or chlorite. Stratigraphy/Maude Group 37 The rocks are calcareous and the amount of calcite cement can in places reach 40 percent (Fig. 26). Quartz generally do not exceed 10 percent of the overall composition. Rock fragments of volcanic origin are common. Abundant thin layers of euhedral plagioclase crystals in a clay matrix are probably related to volcanic fallout. The matrix is rich in hematite. Zoned plagioclase crystals are seen in a few thin sections. The amount of mica seldom exceeds 10 percent, and the Phantom Creek Formation is easily recognized on the amount of chamosite ooids present (maximum 30 percent; Fig. 27). Chamosite ooids are not observed in any other units on the Queen Charlotte Islands, except for the Fannin Formation, where they occur in only small amounts. The gradational transition from shales in the Whiteaves Formation to sandstone in the Phantom Creek Formation, probably indicate a shallowing of the basin. Chamosite ooids suggest deposition in a near-shore environment. Figure 27) The Phantom Creek Formation is easiest recognized on the amount of chamosite ooids (maximum 30%). The ooids commonly have a volcanic nucleus. Stratiaraphv/Maude Group \ 38 Volcanic rock fragments and tuff layers suggest distant volcanic activity. Volcanic activity is also supported by the presence of zoned plagioclase. Stratigraphy'/Yakoun Group 2.4. Yakoun Group 39 The Middle Jurassic Yakoun Group on the Queen Charlotte Islands is known for its extensive distribution and lithologic variety. Shale, siltstone, sandstone, conglomerate, lava flows, pyroclastic rock deposits, and lahars make up the unit. The time of deposition is coeval with, or post-dates one of the major compressional events recorded on the islands (Thompson et al., 1991; Lewis and Ross, 1991). The Yakoun Group rocks overlie the Maude and Kunga Groups along a moderate to sharp angular unconformity (Hesthammer et al., 1989; Thompson and Thorkelson, 1989). 2.4.1. Previous work The volcanic rocks of the Yakoun Group were first described by Dawson (1880) and were originally named Yakoun Formation by MacKenzie (1916). Sutherland Brown (1968) divided the unit into five informal members. Biostratigraphic studies by Cameron and Tipper (1985) redefined parts of the Yakoun Formation as the Yakoun Group comprising two formations and several members. At Skidegate Inlet and on central Graham Island, the Yakoun Group consists of two formations, the Graham Island Formation, and the overlying Richardson Bay Formation which together make up more than 1000 metres of strata (Cameron and Tipper, 1985). The Graham Island Formation was subdivided into four informal members. In ascending order, these are the shale-tuff member (found only on central Graham Island); the mottled siltstone member (found only around Skidegate Inlet); the volcanic sandstone member (central Graham Island); and the lapilli member (Skidegate Inlet). The lower two StratiaraphvfYakoun Group 40 members are fossil poor, and are interpreted as deep to shallow marjne deposits (Cameron and Tipper, 1985). The upper two members typically contain a greater amount of sandstone and volcanic material, and are interpreted as shallow marine and partly nonmarine (Cameron and Tipper, 1985). The Richardson Bay Formation was subdivided into two informal members, the volcanic breccia member and the dark sandstone member (Cameron and Tipper, 1985). The volcanic breccia member comprises epiclastic breccia and conglomerate, tuff, and lahars. The dark sandstone member is, typified by dark, greenish-grey, volcanic-derived sandstone containing bivalves, wood, and plant fragments, interlayered with siltstone and shale. The age of the unit is early Bajocian (Cameron and Tipper, 1985). 2.4.2. A new stratigraphic scheme for the Yakoun Group Cameron and Tipper's (1985) subdivisions cannot be mapped regionally without extensive fossil control because of the diverse lithology and abrupt facies change within the Yakoun Group. For example shale and tuff are most common in the Graham Island Formation, but are also present at several places within the Richardson Bay Formation. It is difficult to distinguish between the volcanic sandstone member of the Graham Island Formation and the dark sandstone member of the Richardson Bay Formation. The conglomerate lithofacies defined in the new stratigraphic scheme is mainly restricted to the Richardson Bay Formation, but likely interfingers with the upper part of the Graham Island Formation. The "volcanic breccia member" is not an adequate description of all volcanic lithologies now recognized in the Yakoun Group. Also, volcanic rocks of the Yakoun Group are not restricted to the Richardson Bay Formation, but Stratiaraohv/Yakoun Group 41 Figure 28) Map showing the distribution of the Yakoun Group within the study area (hatched areas). Thick lines represent faults and thin lines are stratigraphic or intrusive contacts. interfinger with the Graham Island Formation. These findings require a revision of the existing stratigraphic scheme for the Yakoun Group. Detailed mapping resulted in four lithofacies being defined: the shale and tuff lithofacies; the sandstone lithofacies; the conglomerate lithofacies; and the volcanic lithofacies.-Stratlaraphv/Yakoun Group 42 V Figure 29) Map showing the distribution of the different lithofacies of the Yakoun Group within the study area. Thick lines are faults.  These lithofacies are not mappable on 1:50,000 scale due to the lateral discontinuity of the group, and are thus not represented on the map. Figure 28 shows the distribution of the Yakoun Group in a part of the map area, and figure 29 shows the distribution of the different lithofacies. The lithofacies are defined Stratigraphy'/Yakoun Group 43 on the major lithology seen in each unit, and comprise several additional lithologies. The character of each lithofacies in central Graham Island is described below. 2.4.3. Shale and tuff lithofacies The shale and tuff lithofacies is more than 200 metres thick and occurs mostly in northern and western parts of the map area (Fig. 29). The unit is restricted to local small basins and comprises interbedded shale, tuff, siltstone, and sandstone. Lithologically it can resemble the Sandilands Formation (Kunga Figure 30) The shale and tuff lithofacies. The main components are shale and tuff, but the unit also comprises minor siltstone, sandstone, and pyrite layers. Group) or the Ghost Creek Formation (Maude Group), but can often be differentiated from these older units by its greater amount of terrestrial wood fragments. Medium- to thickly-bedded shale dominates over minor, intercalated crystal tuff, siltstone, and sandstone (Fig. 30). Bed thickness in places reaches Stratiaraphv/Yakoun Group : 44 30-40 centimetres, and rare thicker (up to 50 centimetres), internally bedded sandstone layers occur. Ovoid concretions, 2-3 centimetre large, are common in the more calcareous parts of the lithofacies. Pyritic nodules and layers (1-3 centimetre thick) are also abundant. Black or dark grey to blue and bluish-grey fresh surfaces weather to brown, rusty, or green. The rocks are soft and friable, and the shale component often has a well-developed bedding plane fissility. Quartz in the sandstone and siltstone does not exceed 20%. Some sandstone layers comprise up to 80% volcanic rock fragments and feldspar laths up to 2 millimetres. Those rock fragments are intermediate to mafic in composition. Some of the shale units are rich in organic material, and may contain up to 60% silicified radiolarians. Crystal tuff layers comprise up to 60% unbroken, euhedral feldspar crystals, which are commonly partially altered to clay. Chlorite is the most common mica seen in all rock types. Sorting is poor and the grains are angular. Well preserved terrestrial wood fragments, minor coal seams, belemnites, and ammonite imprints are common. The abundance of wood fragments may suggest near-shore environment. Angular grains probably indicate short transport distances. Deposition of the unit was coeval with nearby active volcanism, but it was distal enough so that only ash-size air-fall fragments reached the basins. Stratigraphy'/Yakoun Group  2.4.4. Sandstone lithofacies 45 Figure 31) The lower part of the sandstone lithofacies. The unit overlies the shale and tuff lithofacies with a gradational contact.  The sandstone lithofacies occurs in all parts of the study area except in the most easterly regions, and is the most abundant sedimentary facies (Fig. 29). It consists of spheroidal weathering, medium- to thickly-bedded lithic arenite, interlayered with thinly-bedded shale. Parts of the unit resemble the Fannin and the Haida Formations, and it can be difficult to distinguish between them without fossil control. The sandstone lithofacies overlies the shale and tuff lithofacies with a gradational contact (Fig. 31). Light grey or bluish-grey fresh surfaces weather green, yellowish-green, brownish-grey, or rusty. Shale, crystal tuff, and pyrite beds, 2-10 centimetre thick, are commonly interbedded with the sandstone layers. Minor granule to pebble conglomerate beds (< 1.5 metre thick) occur throughout the sequence. A coal bed in the northeastern part of the map area, near Wilson Creek, measures more than 2 metres in thickness, and Stratigraphy'/Yakoun Group 46 may belong to the overlying Moresby Group rather than the Yakoun Group. Load structures, mud drapes, crossbedding, bioturbation, and root casts are common. Grain sizes within the sandstone layers vary from clay to pebble (average = 0.5 millimetre). Sorting is poor to medium and the grains are angular with poor to medium sphericity. The sandstone layers lack porosity. Fragments of ammonites, belemnites, bivalves, as well as coal and detrital wood are common in all parts of the lithofacies. Figure 32) Photo-micrograph of organic-rich shale with clay lithic fragments within the Yakoun Group.  The sandstone matrix is chlorite and contains up to 30% glauconite which likely gives the rocks the green colour. Subhedral feldspar crystals, partially altered to clay, are also common in some of the sandstone beds, and are probably associated with volcanic fall-out of crystal tuff. The rocks contain up to 30% plutonic quartz grains with undulose extinction. Volcanic quartz occur occasionally, and may have been derived from the intercalated volcanic rocks. Stratiaraphv/Yakoun Group . 47 Less than 10% chert and polycrystalline quartz are present. Biotite, microcline, plagioclase, and potassium feldspar are minor constituents. The sandstones have abundant lithic fragments, some weathered to clay (Fig. 32). The organic-rich matrix is high in siderite. A few chamosite ooids occur in some of the coarser sandstone layers. The presence of detrital wood, bivalves, and ooids suggest a shallow marine and possible deltaic setting. The thick coal seam suggest deposition in swamps. Contemporaneous volcanism, suggested by crystal tuff members, probably was too far away to provide epiclastic fragments larger than ash-size. Angular lithic grains indicate a local source. The source for the plutonic quartz is not exposed on the Queen Charlotte Islands today but may be covered (see summary and discussion). The volcanic quartz probably results from erosion of the volcanic lithofacies which is coeval with the other lithofacies of the Yakoun Group. 2.4.5. Conglomerate lithofacies This sequence comprises thickly-layered pebble and cobble conglomerate interlayered with thinly-layered sandstone, shale, siltstone, and rare tuff. The best exposure of the unit is 60 metres thick and provides a minimum estimate of its thickness. The unit exists within the sandstone lithofacies and is probably related to the lower part of this facies (Fig. 29). Beds range in thickness from 15 centimetres to 1.5 metres and are massive. Dark fresh surfaces weather to brown or rust. Spheroidal weathering is rare and the matrix is soft and friable. The friable and brown weathering Stratiaraphv/Yakoun Group 48 appearance distinguishes the unit from the Upper Cretaceous Honna Formation conglomerate. Clasts range from large pebbles to cobbles (1-40 centimetres, average = 4 centimetres), and are of volcanic, sedimentary, and occasionally plutonic origin. Volcanic clasts and sandstone clasts are apparently mostly derived from underlying parts of the Yakoun Group. Some volcanic clasts are red. Clasts are poorly to moderately sorted and exhibit medium rounding and sphericity. The most resistant clasts are angular, and breccia is a local component. The rocks are matrix-supported with very little or no porosity. The sandstone matrix contains quartz, quartzite, and plagioclase, which is often altered to calcite (Fig. 33). Other common matrix minerals are chlorite, biotite, and amphibole. Carbonate occur as cement as well as in veins and as single crystals. Concretions contain well-preserved but rare ammonites. Abundant wood probably suggests a near-shore environment of deposition. Figure 33) SEM-photograph (back-scattered-electron image) of Na-plagioclase (albite) and calcite in the Yakoun Group. The picture shows no grain-boundary and suggest a gradational replacement of the plagioclase with calcite. Stratigraphy'/Yakoun Group  2.4.6. Volcanic lithofacies 49 Volcanic rocks of the Yakoun Group are most common in the eastern part of the map area (Fig. 29). Andesitic to basaltic lava flows, pyroclastic rocks, and lahars make up the volcanic lithofacies. Felsic rocks are rare. The unit is several hundred metres thick and overlies and interfingers with the other lithofacies of the Yakoun Group. Individual flows vary from 10 centimetres to a few metres in thickness, but pyroclastic deposits and lahars are usually several metres thick. All the volcanic rocks are highly faulted which makes the field relationships difficult to interpret. Lava flows Lava flows in the central Graham Island area are homogeneous-looking Figure 34) Lava flow in the Yakoun Group. The flows may show columnar jointing.  Stratiaraphv/Yakoun Group 50 and the boundaries between the flows are often difficult to locate. This is especially a problem in flows of andesitic composition. More mafic flows may show flattened vesicles towards the top. Red-oxidized boundaries are also commonly observed in the mafic flows, which are often columnar jointed. Fresh surface-colour of flows ranges from light-grey to black, but is generally dark grey to bluish-grey (Fig. 34). Weathered outcrops are soft and the lava flows can sometimes be mistaken for a feldspar-rich sandstone. The flows are aphanitic with feldspar and pyroxene micro phenocrysts and commonly vesicular or amygdaloidal with calcite infillings. Plagioclase can comprise up to 80% of the rock. Plagioclase phenocrysts are euhedral, 1-4 millimetre in diameter, and partially replaced by calcite. Biotite occurs as rare phenocrysts. The groundmass comprises 30% or less (but up to 70%) chlorite, and is also high in siderite. A few samples show a weak linear alignment of plagioclase laths and chlorite crystals. Figure 35) Coarse pyroclastic breccia of the volcanic lithofacies. Clasts are of cognate or accidental origin. Stratiaraphv/Yakoun Group  Pyroclastic rocks 51 Pyroclastic rocks include both pyroclastic flow deposits and air-fall deposits. Pyroclastic flow deposits in the central Graham Island area include thickly-bedded and massive, monolithic to heterolithic, matrix-supported pyroclastic breccia (Fig. 35), ash-flow tuff (Fig. 36), and lapilli tuff. Columnar jointing and flow textures are scarce in all the pyroclastic deposits. Both weathered and fresh surfaces have a dark to intermediate colour, and the rocks are commonly very hard. Figure 36) Ash-flow tuff of the volcanic lithofacies. The outcrop is very faulted, which is typical for the competent rocks of the Yakoun Group. No bedding is seen at this outcrop.  In coarse pyroclastic breccia and the lapilli-flow tuff, cognate or accidental clasts dominate over juvenile clasts. Clast colours vary, and may be black, grey, Stratiaraphv/Yakoun Group 52 blue, red, or green, ranging in composition from intermediate to felsic. Clast size is mostly less than 20 centimetres (average = 2-3 centimetres), but rare clasts are up to 50 centimetre in diameter. Sorting is poor and fragments are commonly angular and free-floating in the matrix. Large clast sizes in some of the pyroclastic breccia suggest deposition close to the volcanic sources. Sedimentary accidental clasts indicate a basement of sedimentary origin (possibly from the lower part of the Yakoun Group). Oil seeps are common in all the volcanic rocks of the Yakoun Group (Fig. 37). Ash-flow tuff and the groundmass of the pyroclastic breccia and the lapilli-flowtuff are commonly intermediate in composition, aphanitic, and may resemble the lava flows. In addition to feldspar, amphibole, orthopyroxene, and clinopyroxene (Fig. 38) also occur as phenocrysts but none are aligned. Volcanic quartz exist occasionally. Stratigraphv/Yakoun Group 53 Figure 38) Photo-micrograph of a euhedral klino-pyroxene phenocryst in matrix of a pyroclastic rock within the Yakoun Group. Air-fall deposits are generally moderate to well-sorted, graded beds of air-fall crystal-tuff of intermediate composition. Juvenile clasts are rare. Plagioclase phenocrysts are embedded in an ash-matrix. Agglomerate is rare in the central Graham Island area. The volcanic rocks are commonly interbedded with sedimentary rocks of the Yakoun Group and this helps distinguishing this unit from the Tertiary Masset Formation. Lahars Lahars are common in the map area, especially in the eastern parts. The rocks are usually highly altered and can resemble the conglomerate lithofacies. They are, however, most easily recognized due to poor sorting and abundance of feldspar crystals in the matrix. Fresh surfaces are dark and weather rusty or brown with a loose appearance. The lahars are poorly lithified and contain poorly sorted, angular, heterolithic clasts (0.5 centimetre to more than 2 metre in size: Fig. 39). Stratiaraphv/Yakoun Group 54 Figure 39) Lahar of the volcanic lithofacies. The rocks are poorly sorted with angular, heterolithic clasts. Clast sizes vary from 0.5 centimetres to more than 2 metres. A granular greywacke and mud matrix contain reworked feldspar phenocrysts, pyroxene, potassium feldspar, chlorite, biotite, calcite, siderite, and pyrite. Epiclastic fragments can make up as much as 80% of the clast-supported rocks. These fragments may contain up to 70% lithic or crystal tuff, and lesser clasts of sedimentary or plutonic origin. Fossil wood is abundant. The lithofacies is partly equivalent to Cameron and Tipper's (1985) volcanic breccia member of the Richardson Bay Formation. Stratigraphy/Intrusive rocks 2.5. Intrusive rocks 55 Intrusive rocks are common in all parts of central Graham Island. They cut all other Jurassic rocks and occur mostly as dykes but also as sills. The intrusives resemble the andesitic lava flows, and because the rocks are highly faulted, it is possible that some rocks mapped as flows could be sills. The intrusive dykes and sills are intensely veined. Calcite is the most common mineral seen in the veins The dykes are usually straight and range in thickness from a few centimetres to several tens of metres. Xenoliths or columnar jointing are seldom seen. Contacts between intrusives and wall-rocks are sharp, and the wall-rock of the thicker intrusives is usually marked by a distinct contact aureole. Igneous rocks range in composition from felsic to mafic with the most common being intermediate. Fresh surfaces are often pinkish-grey or bluish-grey and weather to a dark greenish-grey colour. White, brownish and rusty weathering are also observed. The rocks are very hard when fresh and are readily distinguished from sedimentary rocks. When weathered, the rocks become softer and can be difficult to distinguish from sandstones. Igneous rocks within the area contain feldspar phenocrysts that are seldom larger than 3 millimetres. Pyroxene and chlorite phenocrysts exist occasionally. Much of the plagioclase has weathered to mica or been replaced by calcite. Chlorite is the most common mica seen. Quartz is scarce. The texture is mostly aphanitic and feldspar-phyric, but can be fine- to medium-grained phaneritic and also aphyric. Both equigranular and Stratigraphy/Intrusive rocks 56 inequigranular rocks are observed. The phenocrysts are euhedral whereas the rest of the minerals are subhedral to anhedral. Up to 5 millimetre diameter vesicles and calcite amygdules are frequent. Quartz amygdules are observed in a few places. Fractures often contain oil seeps. The intrusive rocks are of several ages. Most seem to occur as feeders for the Middle Jurassic Yakoun Group volcanic rocks. Because the rocks are highly faulted, the author was not able to document the relationship between the intrusive rocks and volcanic rocks of the Yakoun Group. Other intrusives are most likely parts of Tertiary igneous events. Plutonic bodies that crop out within the map area are described by Indrelid (1991). Stratiaraphy/Summary and discussion 2.6. Summary and discussion 57 The massive to thickly-bedded light-grey stylolitic and vein-rich limestone of the Upper Carnian Sadler Limestone overlies the volcanic Karmutsen Formation with a gradational contact. Deposition of the unit was partly in high-energy shelf-margin positions, and partly in low-energy subtidal environments (Desrochers, 1988). The Norian Peril Formation comprises 2-10 centimetre thick interbedded limestone, shale, argillite, siltstone, and sandstone layers. Limestone dominates over the other lithologies. The unit conformably overlies the Sadler Limestone. Lithologies suggest a deeper water environment than that of the Sadler Limestone. The siltstone and sandstone probably reflect proximal turbidites, and mudstone most likely is a result of pelagic fall-out (Desrochers, 1988). The Sandilands Formation overlies the Peril Formation along a gradational contact and range in age from Late Norian to latest Sinemurian (Tipper et al., 1990). The unit consists of interbedded turbiditic shale, tuff, siltstone, and sandstone. Most of the radiolarian-rich shale in the Sandilands Formation probably results from pelagic fallout. Graded bedding, moderate sorting, and well-developed primary structures in the siltstone and sandstone of the Sandilands Formation suggest deposition by turbidity currents. Large amounts of sandstone in parts of the unit suggests deposition in closer proximity to the source than that of the Peril Formation. Stratiaraphv/Summarv and discussion 58 The Maude Group is divided into five formations. The lowermost is the Ghost Creek Formation, comprising organic-rich dark-grey or black shale with occasional sandstone beds at the bottom and top. The unit gradationally overlies the Sandilands Formation, and was deposited in a transgressional marine environment. The middle part of the unit was deposited in a relatively deep sedimentary basin with slow deposition. The top of the formation represents a regression, and the unit grades into the overlying Fannin Formation. The lower part of the Fannin Formation comprises 5-15 centimetre thick interbedded sandstone and shale. Towards the top, bed thickness becomes greater and can be as much as one metre. The sandstone is commonly calcareous. The depositional regime was characterized by regression, and the top of the unit was deposited near shore where ooids were formed. The Whiteaves Formation marks an abrupt change in the depositional environment. The formation overlies the Fannin Formation with a sharp and conformable contact, and the unit comprises mainly shale with abundant calcareous concretions and lenses. The depositional environment was relatively deep and characterized by slow sedimentation. Towards the top, the Whiteaves Formation becomes more sandy and grades into the Phantom Creek Formation. The Phantom Creek Formation comprises 10-100 centimetre thick medium- to coarse-grained sandstone beds. Chamosite ooids are common, especially in upper parts of the unit, and indicate deposition near shore. Stratigraphy/Summary and discussion 59 Sedimentation of the Kunga and Maude Groups started in shelf-margin position and the basin became gradationally deeper during deposition of the Peril Formation. The Sandilands Formation and lower parts of the Ghost Creek Formation represent a transgression of the sedimentary basin. During deposition of the upper parts of the Ghost Creek Formation and throughout the Fannin Formation, the basin became shallower and deposition of the upper part of the Fannin Formation was near-shore. The Whiteaves Formation marks an abrupt deepening of the basin. During deposition of the upper parts of the formation and throughout Phantom Creek deposition, water depth again decreased, and deposition of the upper part of the Phantom Creek Formation was near-shore. The Yakoun Group marks the end of the major Jurassic basin and development of several local basins. The group overlies the other units with a sharp and angular unconformity. Four lithofacies are recognized: The shale and tuff lithofacies is a more than 200 metre thick sequence of interbedded shale, tuff, siltstone, and sandstone, where shale is dominant. The shale layers range in thickness from a few millimetres to 40 centimetres. Deposition was coeval with nearby volcanism, but was distal enough so that only ash-size air-fall fragments reached the basin. The sandstone lithofacies overlies and partly interfingers with the shale and tuff lithofacies. The unit consists of spheroidal weathering medium- to thickly-bedded lithic arenite, interlayered with thinly-bedded shale. The depositional environment was shallow-marine and possibly partly deltaic. Stratigraphy/Summary and discussion 60 Contemporaneous volcanism was too far away to provide fragments larger than ash-size. Presence of coal beds indicate partly non-marine deposition. The conglomerate lithofacies comprises thickly-bedded pebble and cobble conglomerate interbedded with thinly-bedded sandstone, shale, siltstone, and rare tuff. The unit has a minimum thickness of 60 metres and is probably restricted to within the lower parts of the sandstone lithofacies. The depositional environment was likely near-shore. The volcanic lithofacies probably reach more than 1000 metres in thickness, and is divided into lava flows, pyroclastic rock deposits, and lahars. Lava flows consist of 10 centimetre to a few metre thick sequences of feldspar-phyric, mostly intermediate rocks. Pyroclastic rocks include pyroclastic flow deposits and air-fall deposits. The former consist of thickly-bedded and massive pyroclastic breccia, ash-flow tuff, and lapilli-tuff, Air-fall deposits comprise moderate to well-sorted, graded beds of air-fall tuff of intermediate composition. The lahars are highly altered, poorly lithified, and contain poorly sorted, angular, heterolithic clasts, with a granular greywacke and mud matrix. The volcanic rocks of the Yakoun Group increase in abundance towards the northeast, and it is likely that a igneous source is located in that direction (Sutherland Brown, 1968; Hesthammer, 1991). Volcanic rocks are, however, also quite abundant toward the west. This indicates that several volcanic sources existed during the deposition of the group. Volcanic rocks, especially tuff, overlie, but also interfinger with all other lithofacies of the Yakoun Group. This suggest that volcanism was contemporaneous with deposition of the sedimentary units, but that the intensity of volcanic activity increased during Stratigraphy/Summary and discussion : 61 deposition of the upper parts of the Yakoun Group. The general dip of all rock units in the map area is to the northeast (see figure 42a) and this together with increasing amounts of volcanic rocks upsection can partly explain the abundance of volcanic rocks to the east. The source for the plutonic quartz observed in the Yakoun Group is uncertain. No dated plutonic bodies in the Queen Charlotte Islands have yielded Bajocian or older age. The area has, however, been uplifted and eroded and the plutons may be covered today by younger units. Also, lack of exposure, especially in eastern parts of the map area where an igneous source for the Yakoun Group is postulated, may be the reason why the plutonic bodies are not observed. Intrusive rocks in the study area occur as dykes and sills of mainly intermediate composition. The intrusives are highly fractured and veined, and calcite is the most common mineral in the veins. Most of the intrusives are probably feeders for the Yakoun volcanic rocks, whereas others are related to Tertiary igneous events. Structure/Introduction 62 3, STRUCTURE 3.1. Introduction Several deformational events have affected the rocks in the Queen Charlotte Islands and have resulted in a complicated structural geology. Four major episodes of deformation are recognized in the central Graham Island area: -Middle Jurassic shortening resulting in northwest-trending folds and contractional faults. -Late Jurassic through Cretaceous southwest-northeast oriented block faulting which resulted in northwest oriented normal faults. -Late Cretaceous/early Tertiary folding and faulting resulting in deformed northwest oriented Cretaceous belts -A late Tertiary deformational event caused north, northwest, and northeast oriented normal faults and strike-slip faults (for review, see Lewis and Ross, 1991; Lewis et al., 1991). The most pronounced structural features observed in Jurassic rock units within the map area are macroscopic northwest-trending folds and faults. A minor fault set and fold set trend towards the northeast. The overall orientation of bedding is dip towards the northeast. The abundance of the folds and faults is clearly related to the lithology of the rock units and the age of the rocks. Several of the fault systems have been reactivated during later deformational events. Cleavage is seldom observed in the study area, but bedding plane fissility is common in the shale units. The fold style is dominated by parallel folds (class Structure/Introduction 63 1b after Ramsay and Huber, 1983), but pure shale sequences tend to be similar in style (class II) (Fig. 40). 30 60 90 Fig. 40) Plot of standardized orthogonal thickness t'-cc plotted against angle of dip a and the main types of fold classes (after Ramsay and Huber, 1983).  For descriptional purposes, the structures are divided into macroscopic, mesoscopic, and microscopic structures. Macroscopic structures are normally not observed in outcrop and are mostly inferred from map-pattern. Mesoscopic structures can only be seen at outcrop-scale. Microscopic structures are those observed in thin-sections or scanning electron microscopy. Structure/Macroscopic  3.2. Macroscopic structures 64 3.2.1. Macroscopic folds Macroscopic folds are defined as folds with wavelengths and amplitudes of a few tens of metres or more. The characteristics of macroscopic folds tend to vary with geographical position and structural level. In order to describe behavior of the folds, the study area is divided into three domains from southeast to northwest (Fig. 41). A general description of all three domains and all Jurassic rock units exposed in the study area will follow first, then each domain and each rock unit will be treated separately. General description Most macroscopic folds in central Graham Island trend towards the northwest. Wavelengths typically range from 10's of metres to several 100's of metres wfth amplitudes of less than a few tens of metres. The folds are mostly gentle to open but can also be close. Their axial surfaces are upright to moderately inclined towards the northeast with subhorizontal fold axes. The folds commonly show vergence towards the southwest. Folds in older rock units Figure 41) The study area is divided into three domains from north to south. generally have a tighter hinge region than folds in younger units but this also depends on rock type. A few macroscopic folds trend towards the northeast and have wavelengths that can reach one hundred metres. Amplitudes do not exceed a few tens of metres. The folds are open and upright with subhorizontal fold axes and no vergence is observed in these folds. There is no evidence suggesting that older units are tighter folded than the younger units. To obtain an understanding of the regional map patterns, all bedding measurements are plotted on stereonets. Plots are made for each domain and for the different Jurassic rock units exposed within the study area. The following section will describe the results of these plots. Stereonet-plot of poles to all beds within the study area is shown in figure 42a. The data are scattered but the most dominant dip is roughly 20-60° towards the northeast. Minor clusters show dips between 20 and 80° towards the southwest. An inferred axial plane dips towards the northeast, and suggests a southwesterly vergence that is commonly observed in outcrop (see later description). The calculated fold axis is subhorizontal. Bedding measurements from the Sandilands Formation are fairly uniformly distributed (Fig. 42b). One cluster, however, shows dip 20-60° towards the northeast, while a possible minor cluster shows beds dipping 30-70° towards the southwest. Also here an inferred axial plane dips to the northeast Structure/Macroscopic North North Maude Group Yakoun Group Figure 42a-d) Stereonet-plot of poles to all bedding measurements within the study area. Figure a) shows a plot of the measurements undivided, b) the Sandilands Formathn, c) the Maude Group, andd) the Yakoun Group. Contour method: Kamb (1959). Contour interval=3. Structure/Macroscopic and suggests a southwesterly vergence. The calculated fold axis is subhorizontal or shallowly plunging to the southeast. 67 Measurements of bedding taken from the Maude Group are widely distributed in the stereonet-plot and there are no major concentrations of data points (Fig. 42c). There may be an indication for most beds to dip towards the northeast. Bedding in the Yakoun Group dips mainly towards the east-northeast and towards the northeast (Fig. 42d). Very few beds dip towards the southwest; those that were found have dips that range from 20-90°. An inferred axial plane dips towards the northeast. Domain 1 {southeastern area) Figures 43a-c show the stereonet-plots for the rock units in domain 1. Folds are not commonly seen in this domain. The Maude Group is very poorly exposed in this area and too few data points (7) were measured to be presented in a stereonet plot. In figure 43a, poles to bedding for all the Jurassic rock units in domain 1 are represented. A "best-fit" 7r-circle strikes from 20-30° with poles to bedding distributed along this circle. One cluster shows beds dipping shallowly towards the northeast. The calculated fold axis is subhorizontal or shows a very shallow dip towards the northwest. Structure/Macroscopic 68. Domain 1: Yakoun Group Figure 43a-c) Stereonet-plot of poles to all bedding measurements within domain 1 (southeastern area). Figure a) represent measurements from all Jurassic units, b) the Sandilands Formation, andc) the Yakoun Group. Contour method: Kamb (1959). Contour interval = 3. Poles to bedding in the Sandilands Formation show an even distribution along a "best-fit" x-circle striking towards the northeast (Fig. 43b). A minor concentration of measurements shows dips towards the northeast. The calculated fold axis is plunging shallowly to the west-northwest with the axial plane dipping steeply towards the northeast. Bedding measurements in the Yakoun Group from domain 1 differ significantly from those observed in domains 2 and 3 in that most beds in this domain dip towards the east (Fig. 43c). The data is, however, scattered and difficult to interpret. Domain 2 The 550 data points collected in domain 2 are distributed along a "best-fit" x-circle striking between 20 and 40° (Fig. 44a). The calculated fold axis plunges shallowly towards the southeast. This is different from the fold axes calculated in stereonet-plot for domains 1 and 3 where the fold axis plunges to the northwest. The majority of the beds dip 20-50° towards the northeast, and minor concentrations of poles to bedding show vertical to medium dip towards the southwest. Axial planes are steep with a general dip towards the northeast. Poles to bedding for rocks of the Sandilands Formation show the majority of the beds dipping towards the northeast, whereas a few dip towards the southwest (Fig. 44b). The data points are, however, scattered and this makes interpretations difficult. A calculated fold axis in this stereonet is plunging shallowly to the southeast. Structure/Macroscopic Domain 2: Maude Group Domain 2: Yakoun Group Figure 44a-d) Stereonet-plot of poles to all bedding measurements within domain 2. Figure a) represent measurements from all Jurassic units, b) the Sandilands Formation, c) the Maude Group, andd) the Yakoun Group. Contour method: Kamb (1959). Contour interval=3. Structure/Macroscopic 71 Seventy data points were collected from the Maude Group in domain 2. The only indication that can be read from the stereonet is a general dip towards the northeast with some preference towards the east (Fig. 44c). Most beds from the Yakoun Group in this domain dip to the northeast, and poles to bedding are aligned along a Tr-circle trending to the northeast. The calculated fold axis plunges shallowly towards the southeast (Fig. 44d). Some beds dip to the southwest and to the southeast. In this domain, several bedding surfaces strike towards the northwest with a sub-vertical dip. This is not observed in domains 1 and 3. Domain 3 (northwestern area) Most beds in domain 3 strike towards the northwest and show a southwesterly vergence (Fig. 45a). The calculated fold axis is subhorizontal or shallowly dipping to the northwest. Poles to bedding in the Sandilands Formation are far less scattered than those of domain 2 (this could in part be a result of fewer data points collected; 189 versus 317 in domain 2) and a regressed ir-circle trending towards the northeast can be seen (Fig. 45b). Poles to bedding are fairly evenly distributed along this ir-circle but there seems to be a majority of beds dipping towards the northeast with a minor cluster dipping steeply to the southwest. The calculated fold axis from this stereonet-plot plunges shallowly towards the northwest. V Structure/Macroscopic 72 a North b ' North Domain 3: Maude Group Domain 3: Yakoun Group Figure 45a-d) Stereonet-plot of poles to all bedding measurements within domain 3 (northwestern area). Figure a) represent measurements from all Jurassic units, b) the Sandilands Formation, c) the Maude Group, and d) the Yakoun Group. Contour method: Kamb (1959). Contour interval = 3.  Poles to bedding for the Maude Group are widely distributed (as they are for the previous domain) and almost no preferred orientation can be seen. A weak concentration shows beds dipping towards the north-northeast (Fig. 45c). Poles to bedding in the Yakoun Group are scattered but one cluster indicates that most beds dip towards the northeast (Fig. 45d). 3.2.2. Macroscopic faults Macroscopic faults are defined here as faults showing offset of a few tens of metres to several hundred metres. Figure 46 shows the distribution of macroscopic faults within the map area. Most macroscopic faults trend towards the northwest and are mainly northeast-dipping thrust/reverse faults and subvertical normal faults. Map patterns indicate several hundred metres of offset along these faults. A subhorizontal thrust fault juxtaposing rocks of the Sandilands Formation on those of the Yakoun Group (Fig. 47) was observed at one location, the fault itself being sharply defined. Other major faults place rocks of Jurassic age next to rocks of Cretaceous age. Due to lack of exposure, macroscopic faults are seldom seen, and are therefore mostly inferred from the regional map pattern. Figure 46) A simplified map showing the distribution of major faults within the map area. Most faults strike towards the northwest, and a minor set strike towards the northeast. Figure 47) A gently dipping to sub-horizontal thrust fault placing the Sandilands Formation (SA) on the Yakoun Group (YA). A few macroscopic faults strike east-northeast and show both dip-slip and strike-slip offset. Offset along these faults ranges from a few tens of metres to several hundred metres. The faults are subvertical and sometimes occur on the lateral edges of larger thrust faults. None of these faults is observed in outcrop and they are therefore inferred from regional map pattern. Structure/Mesoscopic 3.3. Mesoscopic structures 3.3.1. Mesoscopic folds 75 Style and behavior of mesoscopic folds depend largely on lithology and age of the rocks. The following section describes the folds observed within each rock unit. Mesoscopic folds are defined as folds with amplitudes and wavelengths of a few metres or less. An important feature of a fold is the degree of tightness. This is defined by determining the interlimb angle. The following terms recommended by Fleuty (1964) are used: Gentle interlimb angle 180°-120° Open 120°-70° Close 70°-30° Tight 30°-0° Isoclinal : 0° Figure 48) Closed to isoclinal buckle fold in the Sandilands Formation. Structure/Mesoscopic 76 Sandilands Formation Most mesoscopic folds trend northwest to north-northwest but the orientation vary dramatically. Fold axes are mostly gently plunging but can be vertical. Wavelengths range from several centimetres to a few metres with amplitudes of tens of centimetres to less than 10 metres. The folds range from chevron to concentric, and vary from isoclinal to open with close being most common (Fig. 48). The hingeline can be either linear or curvilinear (Fig. 49). Axial planes are upright to moderately inclined and dip mostly towards the northeast. A vergence towards the southwest is common (Fig. 50), although some folds were observed with a northeasterly vergence. Figure 49) Isoclinal fold in the Sandilands Formation showing curvilinear hinge line. Pencil for scale is 15 centimetres long. Several samples were collected at this outcrop and analyzed in thin sections and with SEM (see later discussion). A few folds in the study area trend towards the northeast and to the east with wavelengths of 1-2 metres and amplitudes of less than 2 metres. These Structure/Mesoscopic 77 Figure 50) Buckle fold in the Sandilands Formation showing vergence towards the southwest. View looking northeast.  Figure 51) Thrust fault in the lower parts of the Fannin Formation. The fault surface dips towards the northeast. Beds are buckle folded and show vergence towards the southwest. Structure/Mesoscopjc 78 folds mostly have a concentric geometry. They range from open to close with a subhorizontal linear hingeline. Axial planes are upright and no vergence is observed. Maude Group Folds in the Maude Group show little consistency in trend. Some preferences may be seen towards the northwest and also to the northeast. Wavelengths vary from several metres to a few tens of metres and amplitudes range from more than 3 metres to less than 15 metres. The Ghost Creek Formation and the Whiteaves Formation tend to fold into similar (class II) folds while the Fannin Formation and the Phantom Greek Formation are more parallel in geometry (Fig. 51). The folds range from close to open with open being most common. The hingeline is subhorizontal to gently plunging towards the northwest, and the axial plane is upright to steeply inclined. A few northwesterly trending folds show a vergence towards the southwest (Fig. 51). Yakoun Group The volcanic rocks of the Yakoun Group show no mesoscopic folding, and the sedimentary rocks rarely show folding on outcrop scale. The few folds observed typically trend to the north-northwest or towards the northwest. Wavelengths range from several 10's of metres to a few hundred metres with amplitudes of 10 to a few 10's of metres. The folds are mostly concentric in geometry; they are open to gentle with a few close folds observed, and fold axes are subhorizontal. Axial planes are upright or steeply inclined towards the northeast, and a southwesterly vergence was seen at one outcrop. Structure/Mesoscopic 79 3.3.2. Mesoscopic faults Mesoscopic faults are defined as faults with offset of a few metres or less. These are commonly observed in outcrop but do not show up on the map. Faults are most common in the volcanic rocks of the Yakoun Group. Sedimentary rocks of the Yakoun and Maude Groups show far fewer faults on , the faults are mostly related to the fold mechanism(s) involved (see summary and discussion). Figure 52 shows a stereonet-plot for faults measured at several outcrops in the study area. Although the faults are widely distributed, some preference can be seen for faults striking to the northwest and to the northeast. Most faults are . steeply dipping. The most common faults seen in all the rock units at outcrop scale are northeast to east-northeast trending strike-slip faults. Offset along these faults is minor (less than a couple of metres). The faults dip steeply to subvertically. Most slickensides plunge less than 30° and show that the latest movement was sinistral offset. The faults are fairly planar and spaced a few centimetres to 2 metres apart. outcrop scale. Within the Sandilands Formation North Faults Figure 52) Stereonet-plot of poles to faults measured at several outcrops in the study area. Most faults are vertical or steeply dipping. Contour method: Kamb (1959). Contour interval = 3.  Structure/MesoscoDic Other mesoscopic faults strike towards the northwest and are subvertical with less than 2 metres offset. They are mostly strike-slip faults. The faults are more or less straight in plan and are spaced up to several metres apart. A few mesoscopic faults show dip-slip or thrust movement and have offsets of a few centimetres to a few metres. These faults are either curved or straight in plan and are spaced several metres apart. Figure 53) Folded rocks of the Sandilands Formation. A thrust fault parallel to bedding cuts into the core of the fold, thus solving the space problem created by buckle folding (see later discusston).  Most faults observed in the Sandilands Formation trend parallel to the axial traces of the folds. Offset seldom exceeds 1-2 metres and occurs along subhorizontal to subvertical surfaces with steeply dipping being most common. Slickensides are mostly perpendicular to fold axes and show bedding planar movement perpendicular to the fold hinge lines. Thrust faults commonly are parallel to bedding and cut into the core of the folds where they die out and shortening is accommodated by folding (Fig. 53). These faults are often curved in plan with abundant splays, and the fault surfaces commonly show slickensides oriented perpendicular to the fold axes. Several minor decollements along bedding surfaces are observed throughout the Sandilands Formation. Rocks above the decollement surface are deformed, whereas rocks below commonly are undisturbed (Fig. 54). Figure 54) Decollement surface in the Sandilands Formation. Rocks above the decollement are heavily deformed, whereas rocks below the surface appear undisturbed. Structure/Microscopic  3.4. Microscopic structures 82 Microscopic structures are best seen in the Sandilands Formation. Other units show few or no micro-structures except for fracturing. Several thin sections were cut from isoclinal folds in the Sandilands Formation. Wavelengths in these folds are typically a few tens of centimetres with amplitudes up to a couple of metres. The following describes the micro-structures seen in the thin sections cut from these rocks. Figure 55) Photo-micrograph showing the core of an isoclinal fold in the Sandilands Formation. 3.4.1. folds Microscopic The folds range from chevron to concentric depending on the radius of the folds, and the bedding thus behaves differently in different parts of the total geometry; the cores of folds commonly show chevron folding while the outer parts of the folds tend to fold concentrically. The folds are isoclinal to tight with curvilinear or linear hingeline. Axial planes are upright to gently inclined with fold axes being subhorizontal to subvertical. All folds are highly fractured and calcite fills most of these fractures (Fig. 55). 3.4.2. Microscopic faults Offset along the faults range from a couple of millimetres to a few centimetres. Slickensides appear perpendicular to the fold axes. Bedding planar shear surfaces are spaced a few millimetres to several centimetres apart (Fig. 56) and are controlled mainly by bottom structures and bioturbation which weld together the individual beds (Tanner, 1989). Spacing of movement horizons is also related to the thickness of stiff units and the tightness of the folds; smaller interlimb angles result in more closely spaced movement horizons (Tanner, 1989). The cores of folds are commonly highly fractured (Fig. 57). Microscopic thrust faults are oriented parallel to the beds and then cut into the core of the folds where shortening is taken up by folding of the core (Fig. 58). Figure 56) Photo-micrograph of organic rich layers in the Sandilands Formation. Bedding planar movement horizons are spaced a few millimetres to several centimetres apart. The veins are filled with calcite and appear mostly perpendicular to bedding. They pre-date the faults and are most likely a result of depositional loading. Structure/Microscopic 84 3.4.3. Other microscopic structures Veins are mostly perpendicular to bedding and are commonly calcite-filled (Fig. 56). Calcite also fill in some of the fractures caused by deformation related to the folding (Fig. 55). Bitumen is concentrated along seams parallel to bedding, and define a weak bedding planar foliation (Fig. 55). A bedding planar fissility intersecting a weakly developed axial planar cleavage in the Ghost Creek Formation outlines a pencil intersection lineation observed at some outcrops. Bedding planar foliation and the weakly developed cleavage are the only evidences seen for pressure solution. A weakly developed pencil intersection lineation is also seen in the Whiteaves Formation and explains the "crumbly" appearance of this unit. Radiolarians (?) sometimes show bedding planar flattening, and oil stains are seen along microscopic dip-slip and thrust faults (Fig. 57). Figure 57) Photo-micrograph of folded rocks in the Sandilands Formation. Dip-slip faults (upper part of picture) relieve stresses that build up in the core. Oil commonly fill fractures caused by compression and extension. Structure/Microscopic 85 Figure 58) Photo-micrograph of microscopic imbricate thrust faults in the core of a fold in the Sandilands Formation. Little primary or secondary porosity is seen (e.g., Fig. 59). All fractures observed are either filled with calcite or dead oil. Some fracture permeability can be seen in the calcite veins (Fig. 60), but broken edges rather than dissolved edges, however, suggest that this permeability was developed during preparation of the thin sections rather than being naturally developed. Structure/Microscopic 8 6 1,53KX 28KU W022MM S = 08099 P : 99983 28UM Figure 59) SEM-photograph of a calcite-clay contact. No porosity is seen along this contact. Several euhedral quartz crystals are observed in the chlorite-clay.  2,95KX 25KU WD 24MM S=88899 P 89887 18UM Figure 60) SEM-photograph (back-scattered-electron image) of a calcite vein (upper part of picture) in contact with chlorite (middle) and Na-plagioclase (lower part). The bright spots are pyrite framboids. A fracture appear along this contact, but broken rather than dissolved edges suggest that the fracture was developed during preparation of the sample rather than being naturally developed.  Structure/Summary and discussion 3.5. Summary and discussion 87 Jurassic rocks in central Graham Island. Thick lines are faults with apparent offset, thin lines represent bedding. The oldest features are northwest-trending thrust faults with associated southwest-verging folds. Strike-slip faults are developed on the lateral edges of the thrust faults. The thrust faults are cut by northwest-trending normal faults. The youngest structures in the diagram are east-northeast and northwest oriented strike-slip and dip-slip faults.  Figure 61 shows the main features observed in central Graham Island. These include major northwest-trending dip-slip faults, thrust faults and folds, with minor northeast-trending folds and steep dipping faults. 3.5.1. Macroscopic structures Stereonet plots of poles to bedding measurements within the map area show a fair amount of scatter as one would expect for rocks that have undergone several phases of deformation. Most measurements, however, lie Structure/Summary and discussion 88 close to ^ -circles and indicate that the rocks fold cylindrically. This is also supported by observations at outcrop-scale. The northwest-trending faults and folds indicate major northeast-southwest oriented compressional and extensional events. The abundance of southwest-verging folds suggests development of northeast-dipping thrust faults during the compressional events. Some of the minor faults striking northeast are most easily interpreted as strike-slip faults on the lateral edges of the thrust sheets. During the latest deformational event, these faults were probably reactivated and extended, and several new strike-slip and dip-slip faults were generated. -a « • ... *** 1 k<jw Figure 62) Volcanic rocks of the Yakoun Group unconformably overlying rocks of the Sandilands Formation. This angular unconformity restricts at least one deformational phase to mid-Jurassic time. The angular unconformity at the base of the Yakoun Group (Fig. 62) restricts at least one deformational phase to mid-Jurassic time. Elsewhere in the Structure/Summary and discussion 89 islands, folded rocks underlie the unconformity (Thompson and Thorkelson, 1989; Taite, 1990). Two theories are possible for this pre-Bajocian deformational event. The deformation may have taken place post-deposition of the Maude Group and pre-deposition of the Yakoun Group, or the compressional event may have been syn- or post-deposition of the Kunga Group and syn-deposition of the Maude Group. Dunne and Ferril (1988) described geometry and kinematics of blind thrust systems (Fig. 63a-h), and as can be seen from ••.••••X <2Z Figure 63a-h) Geometry and kinematics of cover responses for backthrusting (a,b), coupling (c,d), forethrusting (e,f), and deposition (g,h). From Dunne and Ferril, 1988. figure 63g-h, syn-depositional compression can explain less deformation in the Maude Group than in the Kunga Group. However, no unconformities are observed in the Maude Group, and it is more likely that thrust faulting (see below) was active in the Kunga Group while the Maude Group acted as a cover Structure/Summary and discussion ; 90 and shortening was here accommodated by layer-parallel-shortening (LPS) and coupling (where the cover deforms locally above the blind thrust system) (Fig. 63c-d). Development of a weak axial planar cleavage in the Ghost Creek Formation indicate that the unit deformed by bulk shortening. North-northeast-trending normal faults cut through the thrust faults, postdating them and defining a period of extension. Some of the normal faults in the map area also cut through the Cretaceous rock units (Indrelid, 1990), dating those as Late Cretaceous or Tertiary. Both the normal faults and the thrust faults were reactivated several times during different periods of extension and compression. Evidence for this was not found in the central Graham Island area, but is observed elsewhere in the islands (Thompson et al., 1991). During deformational events, generation of fractures tend to follow favorably-oriented pre-existing weakness zones such as older faults, and it is thus possible that the extensional vectors differed somewhat from being perpendicular to the normal faults observed. A strongly deformed Cretaceous belt in the Yakoun lake region, and a thrust fault cutting through Cretaceous strata north of Yakoun Lake, suggest a Late Cretaceous/early Tertiary compressional event (Indrelid, 1991). Within the study area, rocks of the Sandilands Formation are observed thrust on top of Yakoun Group rocks. This may be a result of reactivation of existing faults during this Late Cretaceous/early Tertiary event. Several sets of north-, northwest-, and northeast-oriented strike-slip and normal faults cut through all rock units within the map-area, and suggest a late Tertiary deformational event (Indrelid, 1991). Structure/Summary and discussion 3.5.2. Mesoscopic structures 91 IMBRICATE THRUST a DECOLLEMENT THRUST The major northwest-trending thrust faults observed in the map area were earlier interpreted as listric in geometry (Hesthammer et al., 1989; Hesthammer and Indrelid, 1990;lndrelid et al., 1991b). The abundance of detachment surfaces observed at outcrop-scale in the Peril Formation, the Sandilands Formation and possibly in the Maude Group suggests that imbricate thrusting, decollement thrusting, and LPS thrusting (Fig. 64a-c; from Geiser, 1988) all acted together during deformation, resulting in a variety of faults, and not only listric thrust faults as indicated by Hesthammer (1990). LPS thrusting often precedes the others LPS THRUST Figure 64a-c) Mechanisms of thrust sheet motion: (a) shortening of thrust sheet by doubling of stiff layer by imbrication; (b) shortening of thrust sheet by folding and development of decollement; (c) shortening of thrust sheet by differential LPS (layer-parallel-shortening) between ductile upper layer and more rigid substratum (from Geiser, 1988).  Structure/Summary and discussion 92 (Geiser, 1988). In the Sandilands Formation the most active faults are low-angle imbricate thrusts and decollement thrusts. The mesoscopic strike-slip faults observed in outcrops can have two possible origins. They can be minor structures active during Jurassic and Cretaceous thrust faulting and/or normal faulting, or they can be related to a late Tertiary deformational event. The occurrence of strike-slip faults in the Cretaceous units (Indrelid, 1990) and also in Tertiary volcanics (Haggart et al., 1990) shows that at least some of the strike-slip faults in the map area are related to a late Tertiary deformational event. The offset along the strike-slip faults is minor (less than a few metres), but the abundance of faults and the preference for sinistral movement indicates that much total displacement may have taken place in late Tertiary time. Fractures in rocks can precede folding, and subsequently these fractures can become slip-planes, veins or even pressure solution seams (Hancock. 1985). They must, however, be favorably oriented with respect to the local stress regime in order to be reactivated. It is thus possible that some of the fractures in the map area exist at oblique angles to the original stress vectors. No evidence was found for folded fractures. Mesoscopic structures within Sadler Limestone The Sadler Limestone is not observed in the map area but is believed to underlie all of central Graham Island and played an important role in the development of structural styles. Studies of the limestone unit on Kunga Island, in Skidegate Inlet, and in Moore Channel, show presence of several generations Structure/Summary and discussion 93 of veins and stylolites. The limestone is massive and bedding is not always seen. This makes observations of mesoscopic folds difficult. Stylolites, however, suggest that a large part of the shortening is taken up by pressure solution as well as folding and faulting. Mesoscopic structures within the Peril Formation Figure 65) Stylolites and veins in the Peril Formation of the Kunga Group. Arrow shown for scale is 4 centimetres long. This picture shows a classic example of joint drag (Ramsay and Huber, 1983) probably caused by physical rotation of a zone of rock lying between two pre-existing fractures or join surfaces. Calcite-filled spaces arise from rotation of the kinked sector.  The Peril Formation is mechanically similar to the Sandilands Formation and structural styles consequently are comparable in style. However, a larger abundance of calcareous veins and stylolites in the Peril Formation (Fig. 65 and Fig. 66) shows that some shortening was taken up by pressure solution rather than by folding, but not to the same extent as in the Sadler Limestone. Detachment surfaces exist throughout the Peril Formation and the Sandilands Formation, and movement has taken place along several smaller detachment surfaces rather Structure/Summary and discussion 94 than along one major decollement. This conclusion is consistent with observations made in Rennell Sound and Sialun Bay (Lewis and Ross, 1991). Figure 66) Highly veined rocks of the Peril Formation. Sigmoidal en-echelon calcite veins define brittle-ductile shear zones. Arrow shown for scale is 4 centimetres long. Mesoscopic structures within  the Sandilands Formation Variations in structural styles reflect different mechanisms by which shortening is accommodated, and is directly related to the lithology. Buckle folding forms by slip along layers. This is commonly observed in outcrop (Fig. 67 and Fig. 68). The uniform bed thickness of alternating competent sandstone and incompetent shale in the Sandilands Formation has led to buckle folds. Chevron buckle folds develop where the sandstone layers have uniform thickness (Fig. 69). Where rare thicker sandstone layers occur, concentric buckle folds are apparent. Collapsed fold hinges are found where a thicker sandstone layer is interbedded with thinner sandstone and shale layers (Fig. 70). Faults commonly are parallel to bedding and cut into the core of folds, thus solving the space problem in the cores created by buckle folding (Ramsay and Huber, 1983) (Fig. 71). The cores Structure/Summary and discussion 95 of folds are often deformed as a result of structural styles of buckle folds (Fig. 72a-b). Imbricate thrust faults cutting the layers at angles as shallow as 15° (Fig. 73). Structure/Summary and discussion Figure 67) Buckle fold and associated detachments surface in the Sandilands Formation. A detachment surface has been created in the upper part of the photograph where the fold dies out.  Figure 68) Detachment surface in the Sandilands Formation with accompanying buckle folding.  96 Structure/Summary and discussion 97 Figure 69) Typical chevron fold style in the Sandilands Formation developed where the thickness of the sandstone layers is uniform. Figure 70) Collapsed fold hinge in the Sandilands Formation caused by a thicker sandstone layer interbedded with thinner sandstone and shale layers. Structure/Summary and discussion 98 Figure 72a-b) Stereo projection (crossed-eye technique) of a core of a fold in the Sandilands Formation. The core is very fractured and deformed as a result of room problem.  Structure/Summary and discussion 99 Figure 71) Buckle fold in the Sandilands Formation. Faults commonly are parallel to bedding and cut into the core of folds, thus solving the space problem created by buckle folding.  Figure 73) Low-angle imbricate thrust faults in the Sandilands Formation. Structure/Summary and discussion Mesoscopic structures within the Maude Group 1 0 0 Only a few folds were observed in the Maude Group on outcrop scale,.. suggesting that most of the deformation was accommodated by bulk shortening and possibly by faults. A few listric thrust faults were observed within the group (Fig. 51). Shale units tend to fold into similar folds (class II) due to the incompetency of these rocks: The more competent sandstone layers tend to fold into class 1 b folds. Mesoscopic structures within the Yakoun Group Very few folds are observed at outcrop scale in the Yakoun Group. A reason for this could be that the unit has been through fewer deformational events than the underlying units. Class 1b folds were observed where the unit comprises interbedded competent sandstone layers and incompetent shale layers. Faulting and possibly layer parallel shortening (bulk shortening) account for some of the shortening observed in the Jurassic rocks of the Yakoun Group. Volcanic rocks of the Yakoun Group are very competent with little or no bedding. No folding was observed in these rocks, and shortening was accommodated by faulting. 3.5.3. Microscopic structures Small thrust faults in the Sandilands Formation commonly developed in order to relieve the stress build-up (Fig. 74). Calcite fractures are mostly perpendicular to bedding (Fig. 56), and are offset by later slip movement. This suggest that the fractures were developed due to sedimentary loading prior to Structure/Summary and discussion 101 deformation rather than being a result of the folding. Some of the calcite-fiiled fractures are clearly related to a deformational event, but these are minor and most of the fractures related to the folding are filled with dead oil. Figure 74) Photo-micrograph showing microscopic thrust faults in the Sandilands Formation developed in order to relieve the stress build-up caused by a competent ash layer.  The bitumen seen along foliation surfaces together with flattened radiolarians (?) suggest significant compaction due to sedimentary loading. This is supported by the well developed bedding planar fissility observed in the shale units. Summary and discussion 4, SUMMARY AND DISCUSSION 102 Geological history In Jurassic time the west coast of North America was characterized by arc-related volcanism with volcanogenic marine sediments deposited in basins of varying shapes and sizes. The tectonic history is complicated and involves several phases of deformation. The following section gives a summary of the geological history of the central Graham Island area, and attempts to place this local history in a much larger regional tectonic framework. The lower part of the Kunga Group is not exposed within the study area but is inferred, from a knowledge of structural styles, to underlie all of central Graham Island (see crossections in appendix). The Upper Carnian Sadler Limestone is the oldest formation of the group and comprises stylolitic and vein-rich limestone. Deposition of the unit was partly in high-energy shelf-margin positions, and partly in low-energy subtidal environments (Desrochers, 1988). In Norian time, deposition was in a deeper environment, and resulted in interbedded limestone, shale, siltstone, and sandstone of the Peril Formation. Siltstone and sandstone probably reflect proximal turbidites, and shale most likely is a result of pelagic fallout (Desrochers, 1988). During Late Norian time, the sedimentary basin received sandstone of the lower part of the Sandilands Formation. This suggests deposition in closer proximity to the source than that of the Peril Formation. The upper part of the organic-rich Sandilands Formation consists of interbedded distal, deep-water turbiditic shale, tuff, siltstone, and sandstone, with most of the shale resulting from pelagic sedimentation. The only Summary and discussion 103 nearby exposed source for the tuff layers is the Early to Middle Jurassic Bonanza Group on Vancouver Island. The group comprises 300 metres of andesitic to dacitic breccia, tuff, and lava flows, and shows evidences for explosive volcanism (Muller et al., 1974). In Sinemurian and Early Pliensbachian time deposition was influenced by a transgressive event. Rocks of the Sandilands Formation grade into black fissile shale of the Ghost Creek Formation. During deposition of the upper part of the Ghost Creek Formation, a regression resulted in a shallower basin, with deposition of the Fannin Formation of the Maude Group. The Lower Pliensbachian to Lower Toarcian Fannin Formation comprises interbedded calcareous sandstone and shale deposited in a regressional regime. Ooids observed near the top of the unit indicate deposition in shallow water. Early Toarcian time marked an abrupt change in the depositional environment following a rapid transgression with deposition of the fissile concretionary shale of the Whiteaves Formation. Towards the top (Late Toarcian time), the Whiteaves Formation becomes more sandy and grades into the Upper Toarcian and Lower Aalenian Phantom Creek Formation of the Maude Group. The unit consists of medium- to coarse-grained sandstone. Ooids are common, especially in upper parts of the unit. The regressional regime that characterized the deposition of the upper part of the Whiteaves Formation, continued throughout the Phantom Creek Formation and deposition of the upper part of the unit was most likely near-shore. In Middle Jurassic time (Late Aalenian/Early Bajocian), the West Coast was affected by major northeast-southwest oriented compression. This is reflected in strongly folded and faulted rocks of the Kunga and Maude Groups. Summary and discussion 104 C r e t a c e o u s / T e r t i a r y Y a k o u n Group Maude Group Kunga Group v v K a r m u t s e n v v« F o r m a t i o n r — -Jurassic p luton Figure 75) Schematic diagram showing the geological evolution of the central Graham Island area during Middle Jurassic time to present. Modified from Lewis et al. (1991). Summary and discussion 105 Northeast-dipping thrust faults and southwest-verging folds were developed during this compressional event (Fig. 75). The Bajocian Yakoun Group marks the end of the major Jurassic basin and development of several local basins. This volcanogenic material overlies the other units with a sharp angular unconformity and is divisible into four lithofacies. The lowermost is the shale and tuff lithofacies; a sequence of interbedded shale, tuff, siltstone, and minor sandstone. Deposition was slow and perhaps in a relatively deep environment, coeval with nearby volcanism. The sandstone lithofacies overlies and partly interfingers with the shale and tuff lithofacies. The unit comprises lithic arenite interlayered with thinly-bedded shale, and was rapidly deposited in a possibly deltaic environment. The conglomerate lithofacies exists within the sandstone lithofacies and consists mainly of thickly-bedded pebble and cobble conglomerate. The depositional environment was near-shore and possibly deltaic. The volcanic lithofacies is divided into lava flows, pyroclastic rock deposits, and lahars. Lava flows consist of feldspar-phyric rocks. Pyroclastic rocks include pyroclastic breccia, ash-flow tuff, lapilli-tuff, and air-fall tuff. The lahars contain poorly sorted, angular, heterolithic clasts in a granular greywacke and mud matrix. The lithofacies was deposited rapidly and contemporaneously with the sedimentary rocks of the Yakoun Group, and volcanism was most active during deposition of the upper parts of the unit. The volcanic rocks of the Yakoun Group increase in abundance towards the northeast, and an igneous source is likely located in that direction. Northeast-trending normal faults cut the Middle Jurassic thrust faults and rocks of the Yakoun Group, thus postdating them and demonstrating a period of Summary and discussion 106 132° 131" extension. Some of the normal faults also cut Cretaceous rock units, thus indicating a Late Cretaceous and/or Tertiary extensional event (Fig.75). A major fault system, the Sandspit Fault system (Fig. 76), is located east of the study area. The Sandspit Fault trends towards the northwest. It can be traced for more than 50 kilometres onshore and probably extends offshore into the Hecate Strait for several kilometres (Sutherland Brown, 1968). Rocks exposed west of the fault system are older than those to the east, demonstrating that the eastern block is downdropped relative to the western block. Sutherland Brown (1968) suggests the fault system was most likely active in Cretaceous time. The deformational event resulting in the development of the Sandspit Fault system may also have caused some of the normal faults observed in the map area. Figure 76) Map of the Queen Charlotte Islands showing the three major deformational zones recognized: the Sandspit Fault, the Long Inlet Deformational Zone, and Louscoone Inlet Fault System. The Queen Charlotte Fault is located just west of the islands and defines the boundary between the Pacific Plate and the North American Plate. Summary and discussion 107 Within the study area, rocks of the Sandilands Formation are observed thrust on top of the Yakoun Group, providing evidence for a second compressional event postdating deposition of the Yakoun Group. Elsewhere in the map area a thrust fault cuts Cretaceous strata and suggests Late Cretaceous and/or Tertiary compression (Fig. 75). This deformation probably postdates the extensional event. A major structural feature, the Long Inlet deformational zone (LIDZ), exists southwest of the map area (Fig. 76). The zone, studied in detail by Lewis (1991b), trends northwesterly and is 4-5 kilometres wide. The most dominant features within the zone are northwest-trending megascopic folds and faults (Lewis and Ross, 1991; Lewis, 1991b). The compressional event took place in Late Cretaceous and/or Early Tertiary time (Lewis and Ross, 1991) and may have caused the post-Bajocian compression in the map area. The latest deformational event in the map area has resulted in several sets of strike-slip faults that are easiest observed on outcrop-scale. They cut Tertiary strata (Indrelid, 1991) and demonstrate that the faulting was active in Tertiary time. A 2 kilometre wide anastomozing fault system, the Louscoone Inlet fault system (LIFS), trends north-northwesterly for 120 kilometres through . the southern Queen Charlotte Islands (Fig. 76). This system divides rocks recording a north-south-directed Tertiary extension to the east from largely undeformed rocks to the west (Lewis, 1991a). The major fault movement is dextral strike-slip (Sutherland Brown, 1968; Lewis and Ross, 1991; Lewis, 1991a), and the strike-slip faults observed within the map area are probably a result of the deformational event that caused the LIFS. Summary and discussion 108 Several dykes and sills cut the Jurassic rocks in the central Graham Island area. Most are feeders for the Yakoun Group volcanic rocks, whereas others are related to Tertiary volcanism. Tectonic setting of western Canada The oldest age at which one can with some certainty determine relative plate motions is approximately 180 Ma. Any descriptions of plate motions before Early Jurassic time will have large uncertainties (Engebretson et al., 1985). During Jurassic and Cretaceous time, western North America was characterized by major convergence where the Pacific plate was rapidly subducted under the North American plate (Riddihough, 1982; May and Butler, 1986; Debiche et al., 1986; Jurdy, 1984). During the last several million years, transform movement with a small component of convergence has typified the relative plate motion (Riddihough and Hyndman, 1989; Engebretson, 1989). Microplates in the Pacific ocean during Jurassic and Cretaceous time moved towards North America and were finally accreted to the continent. Jones et al. (1982) propose that western North America has grown by more than 25% through accretion since Early Jurassic time. The Queen Charlotte Islands are a part of the Wrangellia terrane (Jones et al., 1977). An age for a possible collision between Wrangellia and North America is poorly constrained. Wernicke (1988) proposed that the collision was ongoing from Middle Jurassic to Middle Cretaceous time. Monger et al. (1982) suggested accretion in Late Cretaceous time, and van der Heyden (1989) and Armstrong (1988) indicated a collision prior to Late Jurassic time. In the Queen Summary and discussion 109 Charlotte Islands a major unconformity exists at the base of the Middle Jurassic Yakoun Group (Sutherland Brown, 1968; Cameron and Tipper, 1985; Thompson and Thorkelson, 1989; Hesthammer et al., 1989, 1991b; Hesthammer, 1990, 1991; Taite, 1990; Indrelid et al., 1991). Rocks below the unconformity are more intensely folded than those above, and restrict a strong compressional event to pre-Bajocian time. In southwestern British Columbia, evidence for Middle Jurassic deformation is found along the western edge of the Intermontane superterrane (Rusmore et al., 1988). Also in Alaska there is evidence for a Jurassic deformational event (McClelland and Gehrels, 1990), and this further emphasizes the regional extent of the mid-Jurassic event. Two origins are possible for the Jurassic compressional event. It can be a result of collision of Wrangellia with North America, or it can be related to changes in relative plate motion during the break-up of Pangaea and the opening of the Atlantic ocean. The Jurassic event recorded within the Alexander terrane in Alaska is somewhat older than the deformation on the Queen Charlotte Islands (McClelland and Gehrels, 1990), but this may be easily explained by oblique collision of the Wrangellia/Alexander terrane with North America. X-ray fluorescence analyses of volcanic rocks from the Yakoun Group suggest calc-alkaline affinity (see appendix 1) related to a convergent margin tectonic setting with the development of a volcanic arc. This arc probably reflect creation of a new subduction zone just west of the Queen Charlotte Islands. This again could possibly, but not necessarily, be a result of the collision of Wrangellia with North America. During the break-up of Pangaea and the opening of the Atlantic ocean in Lower and Middle Jurassic time, the North American plate started to move Summary and discussion 110 westwards with respect to the Pacific plate (Coney, 1978). This resulted in a complex plate tectonic setting along the west coast of North America, and it is possible that changes in relative plate motion could have caused the Middle Jurassic deformational event (R.L. Armstrong and J.W.H. Monger, pers. comm. 1989). The oldest rocks exposed in the Queen Charlotte Islands belong to the recently discovered Carboniferous (?) and Permian "carbonate-chert" unit (Hesthammer et al., 1991a). This unit comprises mainly limestone, chert, and dolomite but also minor argillite, sandstone, conglomerate, and schist. Hesthammer et al. (1991a) correlate this unit with Paleozoic rocks of Wrangellia in Alaska, on Vancouver Island, and in Oregon. In southeastern Alaska, Upper Paleozoic and Jurassic rocks of the Alexander terrane bear remarkable similarities to time-equivalent units exposed in the Queen Charlotte Islands. Jones et al. (1972) noted presence of Upper Carboniferous chert and limestone, and Permian chert, dolomite, argillite, and greywacke within the Alexander terrane. Buddington and Chapin (1929) recognized Upper Carboniferous limestone and Permian interlayered limestone and chert as well as conglomerate, sandstone, and volcanic rocks in southeastern Alaska. Their description of Triassic and Jurassic rocks also bear similarities to the Triassic Karmutsen Formation and the Upper Triassic and Jurassic Kunga and Maude Groups. Based on these lithologic similarities, the author finds it reasonable to assume that there is no clear difference between the Jurassic and Upper Paleozoic parts of the Alexander terrane in southeastern Alaska, and Wrangellia in the Queen Charlotte Islands. 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(eds.), The Eastern Pacific Ocean and Hawaii: Boulder, Colorado, Geological Society of America, the geology of North America, volume N, p. 403-411. Ross, C.S., and Shannon, E.V. 1926: Minerals of bentonhe and related clays and their physical properties; Journal of American Ceramics Society, v.9, p. 77-96. Rusmore, M.E., Potter, C.J., and Umhoefer, P.J. 1988: Middle Jurassic terrane accretion along the western edge of the Intermontane superterrane, southwestern British Columbia; Geology, v. 16, p. 891-894. Shouldice, D.H. 1971: Geology of the western Canadian continental shelf; Bulletin of Canadian Petroleum Geology, v. 19, p. 405-436. Smith, J.G., and MacKevett, E.M., Jr. 1970: The Skolai Group in the McCarthy B-4, C-4, and C-5 quadrangels, Wrangell Mountains, Alaska; United States Geological Survey Bulletin, 1274-Q, p. Q1-Q26. References 120 Sutherland Brown, A. 1968: Geology of the Queen Charlotte Islands; British Columbia Department of Mines and Petroleum Resources, Bulletin 54, 226 p. Sutherland Brown, A., and Jeffrey, W.G. 1960: Preliminary geological map, southern Queen Charlotte Islands; British Columbia Department of Mines. Taite, S.P. 1990: Observations on structure and stratigraphy of the Sewell Inlet-Tasu Sound area, Queen Charlotte Islands, British Columbia; in Current Research, Part F, Geological Survey of Canada, Paper 90-1F, p. 19-22. Taite, S.P. 1991: Geology of the Sewell Inlet/Tasu Sound area, Queen Charlotte Islands, British Columbia; in Current Research, Part A, Geological Survey of Canada, Paper 91-1 A, p. 393-400. Tanner, P.W.G. 1989: The flexural-slip mechanism; Journal of Structural Geology, v. 11, no. 6, p. 635-655. Thompson, R.I., and Thorkelson, D. 1989: Regional mapping update, central Queen Charlotte Islands, British Columbia; in Current Research, Part H, Geological Survey of Canada, Paper 89-1H, p. 7-12. Thompson, R.I., Haggart, J.W., and Lewis, P.D. 1991: Late Triassic through early Tertiary evolution of the Queen Charlotte Basin, British Columbia, with a perspective on hydrocarbon potential; in "Evolution and Hydrocarbon Potential of the Queen Charlotte Basin, British Columbia", G.J. Woodsworth (ed.), Geological Survey of Canada, Paper 90-10, p. 3-30. Tipper, H.W., Smith, P.L., Cameron, B.E.B., Carter, E.S., Jakobs, G.K., and Johns, M.J. 1991: Biostratigraphy of the Lower Jurassic formations of the Queen Charlotte Islands, British Columbia; in "Evolution and Hydrocarbon Potential of the Queen Charlotte Basin, British Columbia", G.J. Woodsworth (ed.), Geological Survey of Canada, Paper 90-10: 203-236. Tipper, H.W., and Carter, E.S. 1990: Evidence for defining the Triassic-Jurassic boundary at Kennecott Point, Queen Charlotte Islands, British Columbia; in Current Research, Part F, Geological Survey of Canada, Paper 90-1F, p. 37-41. Vallier, T.L. 1977: The Permian and Triassic Seven Devils Group, western Idaho and northeastern Oregon; United States Geological Survey Bulletin, 1437, 58 pp. van der Heyden, P. 1989: U-Pb and K-Ar geochronology of the Coast Plutonic Complex, 53° to 54° N, British Columbia, and implications for the Insular-lntermontane superterrane boundary; unpublished Ph.D. thesis, University of British Columbia, Vancouver, B.C., 392 pp. References 121 Vellutini, D. 1988: Organic maturation and source rock potentials of Mesozoic and Tertiary strata, Queen Charlotte Islands, British Columbia; unpublished M.Sc. thesis, University of British Columbia, Vancouver, British Columbia. Weaver, C E . 1956: The distribution and identification of mixed-layer clays in sedimentary rocks; American Mineralogist, v. 41, no. 3-4, p. 202-221. Wernicke, B. 1988: Escape hypothesis for the Stikine block; Geology, v. 16, p. 461-464. White, J . 1990: Evidence of Paleogene sedimentation on Graham Island, Queen Charlotte Islands, West Coast, Canada; Canadian Journal of Earth Sciences. Whiteaves, J.F. 1883: On the Lower Cretaceous rocks of British Columbia; Royal Society of Canada, Transactions, v. 1, sec. IV, p. 81-86. Woodsworth, G.J. 1988: Karmutsen Formation and the east boundary of Wrangellia, Queen Charlotte Basin, British Columbia; in Current Research, Part E, Geological Survey of Canada, Paper 88-1E, p. 209-212. Yanguas, J.E., and Paxton, S.T. 1986 A new technique for preparation of petrographic thinsections using ultraviolet-curing adhesive; Journal of Sedimentary Petrology, v. 56, p. 539-540. Yorath, C.J., and Chase, R.L. 1981: Tectonic history of the Queen Charlotte Islands and adjacent areas-a model; Canadian Journal of Earth Sciences, v. 18, p. 1717-1739. Yorath, C.J., and Hyndman, R.D. 1983: Subsidence and thermal history of Queen Charlotte Basin; Canadian Journal of Earth Sciences, v. 20, p. 135-159. Appendices/Maior and trace element analyses , 122 6, APPENDICES 6.1. Major and trace element analyses 6.1.1. Introduction Chemical analyses were performed on nine samples of the Yakoun Group volcanic rocks. Sample locations are shown in figure 77. Analyses were done with the UBC Department of Geological Sciences X-ray fluorescence spectrometer using the sample preparation and analysis procedures The chemical composition of the Yakoun Group volcanic rocks are used to interpret the paleo-tectonic setting using chemical discrimination diagrams. It is important to emphasize that the chemical data are used solely to support petrographic- and field-data. The major and trace element (Zr, Y, and Sr) concentrations for the nine samples are shown in table la and lb. Two samples were discarded from use in // O M4° 1 ii ©«« i \V\ • , 0 8 T A. / 0 81an Ti\ Ou«*n ChulatU J Figure 77) Map showing locations were samples were collected for XRF-analysis. Numbers indicate station locations. described by Hickson and Juras (1986). Aopendices/Maior and trace element analyses 123 ******MAJOR ELEMENT CONCENTRATION OF UNKNOWNS****** Si02 Ti02 A12Q3 Fe2Q3 MnO MqQ CaO Na2Q K2Q P2Q5 SAMPLE 8091B 50. 54 0. 76 17. 00 9. 88 -0.06 9.37 4. 72 3 .96 1. 78 2. 05 SAMPLE 9272T 52. 52 0. 82 18. 34 12. 67 -0.06 7.40 2 . 66 4 .09 0. 71 0. 86 SAMPLE 9286A 53. 50 0. 78 18. 49 11. 54 -0.02 2.59 8. 20 3 .73 0. 65 0. 54 SAMPLE 9183 53. 77 0. 76 17. 84 10. 76 0.00 4.73 7. 48 3 .18 0. 68 0. 81 SAMPLE 9340 60. 81 0. 79 15. 26 8. 87 -0. 05 3.47 4. 18 4 . 12 1. 78 0. 76 SAMPLE 9193 57. 79 0. 52 16. 78 9. 07 -0.05 4.47 4. 83 3 .95 1. 80 .0. 83 SAMPLE 8249 47. 37 2. 32 16. 89 14. 29 -0.06 3.71 1. 09 3 .25 0. 36 10. 78 SAMPLE 8057 74. 13 0. 36 8. 02 6. 62 -0.05 1.54 5. 60 2 .32 1. 15 0. 32 SAMPLE 9272A 59. 73 0. 61 17. 85 7. 48 -0. 06 2.40 4 . 01 5 .64 1. 85 0. 49 Table la) Major elements concentrations from analyses of nine samples of volcanic rocks within the Yakoun Group  discrimination diagram plots. Sample 8057 has a Si02 content of 74.13%, which is too high to be represented in most published diagrams. Sample 8249 showed a P2O5 content of 10.78%. This is very high, and thin-section analysis showed that the sample is highly altered. Most discrimination diagrams are not valid for highly altered rocks, and the sample should thus be excluded from the discriminate diagram plots. Appendices/Maior and trace element analyses 124 ******TRACE ELEMENT CONCENTRATION OF UNKNOWNS* * * * * * SAMPLE NB ZR Y SR RB 8091B - 4 . 5 5 8 7 . 7 3 0 . 8 4 8 8 3 . 2 5 1 4 8 . 9 2 9272T - 4 . 5 5 9 9 . 9 3 3 0 . 8 4 4 4 2 . 9 3 1 4 8 . 9 2 9286A - 4 . 5 5 7 1 . 2 9 3 0 . 8 4 3 0 9 . 5 3 1 4 8 . 9 2 9183 0 . 7 2 1 3 7 . 2 9 3 0 . 8 4 8 9 7 . 9 8 1 4 8 . 9 2 9340 6 3 . 4 6 2 4 8 . 9 4 3 0 . 8 4 4 0 1 . 9 6 1 4 8 . 9 2 9193 - 4 . 4 7 1 1 6 . 1 6 3 0 . 8 4 8 1 6 . 4 8 1 4 8 . 9 2 8249 6 . 8 6 1 6 9 . 5 7 3 0 . 8 4 1 3 4 . 3 2 1 4 8 . 9 2 8057 - 4 . 5 1 6 4 . 9 4 3 0 . 8 4 3 5 5 . 3 1 1 4 8 . 9 2 9272A - 4 . 5 5 1 8 5 . 6 4 3 0 . 8 4 3 3 8 9 . 0 1 1 4 8 . 9 2 Table lb) Trace elements concentrations from analyses of nine samples of volcanic rocks within the Yakoun Group v There is only one previously published chemically analyzed sample from the Yakoun Group (Sutherland Brown, 1968), and nobody has investigated the chemical characteristics of the Yakoun Group or the tectonic affinity. In the following section, five major element and three trace element tectonic discrimination diagram plots are presented. 6.1.2. Major element geochemistry In order to separate between alkaline and sub-alkaline rocks, the author used a classification scheme proposed by Irvine and Baragar (1971). All samples except one plot in the sub-alkaline field (Fig. 78). Apoendices/Maior and trace element analyses 125 Irvine a Baragar 1871 (fig 3) "I r Alkaline field O O Sub-alkaline nek) J 1_ 35 40 45 50 55 60 65 70 S 0 2 (wt%) Figure 78) Alkali-silica plot of volcanic rock samples from the Yakoun Group with alkaline and sub-alkaline fields delineated. Dividing line of Irvine and Baragar (1971) is from analyses of alkaline, tholeiitic, and calc-alkaline suites. Gill 1881 (fig 1.2) I I Acidic I 1 I — - Basic High-K o O O o Medtun>K o o O _ _ -J Low-K i I SD2 (wt%) Figure 79) Potassium-silica plot dividing andesites into low-, medium-, and high-potassium andesites (after Gill, 1981).  Appendices/Maior and trace element analyses 126 In a plot by Gill (1981), the rocks were differentiated into low-, medium-, and high-potassium andesites (Fig. 79). All samples are within the medium-K field and show a trend from the low-K part to the high-K part of the field. Within the sub-alkaline field, assignment to either tholeiitic or calc-alkaline suits is based on iron-enrichment trends which can be illustrated on a ternary AFM plot (Fig. 80) (after Irvine and Baragar, 1971). Tholeiitic suites tend to display strong iron enrichment followed by late stage alkali enrichment, whereas calc-alkaline suites have continuous and moderate iron enrichment. In this plot, the analysis that fell within the alkaline field in figure 78 is not included in this diagrams, since the purpose of the diagram is to further separate the sub-alkaline rocks. All analyzed samples, except one, plot in the calc-alkaline field. In an alternative plot by Miyashiro (1974) (Fig. 81),the rocks are scattered and no assignment to either tholeiitic or calc-alkaline field can be made. The next section further differentiates between calc-alkaline and tholeiitic fields based on trace elements. 6.1.3. Trace element geochemistry Trace element abundances vary systematically with tectonic environment (Pearce and Cann, 1973; Floyd and Winchester, 1975; Pearce et al., 1984; see Erdman, 1985, for review). Binary and ternary discrimination diagrams showing this variation are constructed using trace element analyses of unaltered rocks. The mobility of trace elements vary and should be considered when interpreting trace element discrimination diagram plots. Ti, Zr, Y, and Cr have demonstrated Aopendices/Maior and trace element analyses 127 FeO* Na20 + K20 , MgO Figure 80) AFM plot of volcanic rock samples showing tholeiitic and calc-alkaline suites (after Irvine and Baragar, 1971).  Miyeahiro 1874 (fig 1a) 45 i 1 1 i i i i i i | i i i i 4 - 0 3.5 3 ? 5.5 o CO 1 Tholeiite O 0 O 0 1.5 1 .5 i Calc-Alkalin* i ' i i i i I i 1 1 1 u • 48 SO 55 60 65 S 0 2 (wt%) Figure 81) Binary plot of FeOVMgO vs. S1O2 showing tholeiitic and calc-alkaline suites. Appendices/Major and trace element analyses 128 low mobility during alteration, whereas Sr is fairly mobile and should be used with care (Pearce and Cann, 1973). Paarcft & Cann 1073 (fig 2) 1B000 15000 12000 |ooo P 6000 3000 0 0 25 50 75 100 125 150 175 200 225 250 Zr (ppm) Figure 82) Binary discriminant diagram using Ti and Zr (after Pearce and Cann, 1973). Calk-alkaline basalts (CAB) plot on fields A and C, low-potassium tholeiites (LKT) in fields A and B, and ocean floor basalts (OFB) in fields D and B.  A binary plot of Ti versus Zr (after Pearce and Cann, 1973) shows six of seven analyses plotting in the calc-alkaline field (Fig. 82). The diagram is based on tholeiite magmas showing an increase in Ti with differentiation, whereas calc-alkaline magmas do not (Hoy, 1989). The analyses also seem to follow a volcanic arc trend with enrichment of Zr. An alternative ternary plot of Ti, Zr, and Y, proposed by Pearce and Cann (1973), shows three samples plotting in the calc-alkaline field and three samples plotting outside the proposed field (Fig. 83). Also here an enrichment-trend of Zr can be observed. The purpose of this diagram is to distinguish within-plate Appendices/Major and trace element analyses 129 Ti/100 Pearce & Cann 1973 WPB = D OFB = B LKT = A,B CAB = B,C basalts (WPB) from calc-alkaline basalts (CAB), low-potassium tholeiites (LKT), and ocean-floor basalts (OFB). The latter three can effectively be distinguished by using a ternary plot of Ti, Zr, and Sr (Pearce and Cann, 1973). Convergent margin basalts have higher K and Sr, and lower Zr relative to OFB (Erdman, 1985). In figure 84, four samples plot within the CAB-field and three samples plot outside. An enrichment trend appears towards Sr. Zr Y * 3 Figure 83) Discriminant diagram using Ti/100, Zr, and Yx3. Fields for different tectonic settings are defined by Pearce and Cann (1973). Calc-alkaline basalts (CAB) plot in fields B and C, within plate basalts (WPB) in field D, ocean floor basalts (OFB) in field B, and low-potassium tholeiites (LKT) in field A and B. 6.1.4. Summary and discussion The chemical composition of the Yakoun Group volcanic rocks suggest a calc-alkaline affinity. The results based on discriminate diagram plots alone are, however, not conclusive and several limitations are recognized: -The rocks are altered to various extents, and this may have affected major and trace element abundances through fluid aided mass-transfer or diffusional Appendices/Major and trace element analyses 1 3 0 processes. K and Sr are especially mobile, and discriminate diagrams based on these elements should be used with care. -Compositional fields in discrimination diagrams are empirical and limited by available data from previous studies. -The rocks analyzed are porphyritic, and although the least porphyritic parts of the samples were analyzed, the chemistry of the phenocrysts may have affected the results somewhat. -Chemical variation between tectonic environments is gradational, and some overlapping is expected. Petrographic studies of volcanic rocks of the Yakoun Group show lithologies of mainly intermediate composition with abundant feldspar phenocrysts and lesser pyroxene phenocrysts. These findings suggest rocks of calc-alkaline affinity and support results from chemical analyses of the rocks. The diversity seen in some of the discrimination plots can be explained by the Ti /100 Figure 84) Discriminant diagram using Ti/100, Zr, and Sr/2. Fields for different tectonic settings are defined by Pearce and Cann (1973). The fields show calc-alkaline basalts (CAB), low-potassium tholeiites (LKT), and ocean-floor basalts (OFB).  Appendices/Maior and trace element analyses 131 time-span of eruption (several million years), rocks resulting from different volcanoes, proximity to the volcano, age of the rocks, and alteration. Volcanic rocks of calc-alkaline series are confined to orogenic regions, and the occurrence of these rocks or great amounts of andesitic and dacitic rocks suggests the former existence of an island arc or an active continental margin (Miyashiro, 1975). Tholeiitic magmas commonly occur together with calc-alkaline magmas in subduction zones (Hickson, 1991), which explains why some discrimination diagrams have analyses which plot in both the calc-alkaline and the tholeiitic fields. Evidence for convergent margin tectonic setting along the west coast of North America during deposition of the Yakoun Group is consistent with what is observed by several others (e.g., Debiche et al., 1986; Engebretson et al., 1985; Jones et al., 1977; May and Butler, 1986). Appendices/XRD-analvses 132 6.2. X-ray diffraction (XRO) analyses of clay minerals The clay mineralogy of one suspected tuff sample (sample 8290a) from the Sandilands Formation was determined by X-ray diffraction analysis. The sample was crushed to fine powder and immersed in distilled water. Clay minerals were separated by pipetting a fraction of the supernatant liquid onto four glass slides. One slide was then heated to 500°C, a second was glycolated, the third slide was both heated and glycolated, and the last slide was left untreated. For analysis, Cu-radiation was used with the following scan conditions: scan-angle = 5-28° 20, step size = 0.01° 20 , and step time = 1 second. Data from the XRD-analyses are shown in table II. ss: 0.0180 tm: 1.00 CuKal+2 < 5.008 27.990 d 3.1858 C 153. 27.990) Figure 85) XRD reflections from an untreated sample of clay from the Sandilands Formation. Figure 85 shows the resulting analysis of the untreated slide. Most of the peaks to the right result from quartz and albite (see Fig. 89). Heating or ADDendices/XRD-analvses 133 C N I t o O LO O J ' — C D C D C D C D C D C D CD rNf O J CNI C D C O ONI C D CNI CN. r — t o i n r o c n c o t o C — C N - WT c o c o c n CD - 3 c •— - r c n t o t o • — CNI i > C N I OO » ~ C N " — c n L O c o t o i _ " C n L P ; t o r — L C r- -C \ J C D r — t o t o C N I r — c o r o r o r o r o r o rc CD r — C N r o r o <=> C O C D C O C D f— r— — i n C D C N I G O C N I c o r o - — c n L T ) t o r — 0 0 c r . C O ' — C D t— c o WT c o L O t o CN* t o CNJ t o CN) ONI CN* ON* — »— c n cr> CNi CN» <Nj CN» CN) C O C D C O t O U 7 C D OO C D C D C D C D CNi CNI CD CNi CNI CNI C D QO O «7 o c CNI C N I C O C D C T ! <-0 CNI flj L O L O L O L O C N ; C N I c n t o C D L O e n t o r — «— O - CNi O t C D t o t o c n r o t o ( — «— t o t o — c n t O L O t O c n r o L O r o L O 0 0 t o L O r o C N I i n c o c o r o C D o c 1— t — r — t o C N I c — C D A~> « r c r — t o t — C D CNI o o «— 0 0 C D r o r o OJ c n - — c - . r o ur> 0 0 c n - L O wr 0 0 t o t — c n WT t o t o r — c o c n C D < 0 rr tO O «— t o c n t — CNI L O O O C D 0 0 r — r o «a- c o C N I c n WT t o c n t o c o C N I t o wt c — L O t o --cr c i r — C D t o t o C N I wt- c— m c o - — KT cr" «— t O C n C O c 3 CNI r — I— -— C O t o C O C D C D C O C C c n t o c n C N . L O c n c o r o c o c — i — t o c n c o L O c o •—• C D L O CNi c n C D CNi « — * — C D t o »cf r o 0 0 t ,p t p • — C D c n t o CNI c n L O t o t o r o r — t o t o r o cr> 0 0 CNI C D WT c e c r t o t O C~ '_0 C T r o C D L O - — t o CNI t o r — r o r o c-'j r»*» WT r o - ^ r - s r r — r o r o L O t o J-» C D r — r o C N I « — Qj t O CT • <r— C N J C D • — L O L O t O CNI r — c n 0 0 t o r o C D cr - — r -<u — C O r o CNI WT c n 0 0 - — L O — r — t o t o t o t o t o t o t o OC r — t o t o ^ r - t o t o r o C D 0 0 r o t o « — CNI r o C N I C D r — L O L O CO r o c o r o r o — r o L O i — c o CNI r — CNI c o r o c o c o t o CNI - — *_> L O t o t o C N I c o C D ' — m L D CNI C N I CNI C j CNI C N . c r * — CNI r o t o t o r — c o c n CD — C D t O C D C D C N I C D C D C D C D C D L O L O CNi CNI L O C D t O CNI C D C D Q J C D C O O O c o c o 0 0 r-— C N i L O L O C N I t O O O O O C D C D c n CNI c— L O - — c o WT -— WT C N I c o t o c n WT t o CNI r o C D — - — r o C D t o C D r o CNI c n t o r o r o c o r o r o c o t o j - / c n r — c n QJ c n r — t o c o C D r o t o r o L O I — 1 * — L O c o WT t o C O CNI L O w — OC. CD — CNI GO C O C**l CNI CNI CNI L O t O CNI CO L O L O C O C D Cs* CNI CNI CNI r — CNI t o c o c n ' CNi C D C D " — " "** . — r — c n C * J — t o C O CNi WT O O C D C O f — C O C N I t o *=~ c o c o C N I t o WT c n C O L O * — C D C O ~ a C C C O C M t o "*=r U D L O t — L O ' — c n r — c-7 c — CNI C D 1— t o L O r o C N I « — WT t— t o ^ r - a - ^ r r o r o r o r o r o r o c o WT C D c c C D CD CD C D L O • — CNI C D C D L O C D C O C D C D C O CNt WT C D C D t o CNI C D t o CO CN, -^r ^T C D L O C O CNI t O C D C O t O C D C O C D -cr L O CNI C O ( — C O r — C D L O ^rr CD CD C D C O C D L O ' — r — t o WT WT r o r o r o r o r o r o r o r o a3 0 " i t o c D C N i L o c o r o L O C O O G C D t « o « ^ > « J r - c - C N < ^ ^ c o t o c n ^ c D C C . - ~ ^ r t o * ^ c c c o c -—1 QJ CNI c n CNI a o a o c o t o r o C D CN? CNI L O 1— C j c n r j r — r — c o c n L o r o c o L O r — c r J^J t -o c~~> r o 0 0 C D • r o WT CN ' • CNI CNI CN) CN: r o t o t o c— C O c n C D L J - nr c -— CNI c o WT L O t o c— 0 0 c n C D <TJ IT" t O to cr. Table II) 29 values for the untreated clay sample (CLAY), the glycolated sample (CLAYG), the heated sample (CLAYH), and the heated and glycolated clay sample (CLAYHG).  Appendices/XRD-analyses 134 glycolating of the slides did not affect these peaks. The two main peaks to the left are fairly wide and probably represent one or more clay minerals. In an attempt to identify the clay minerals, a glycolated slide was examined. Montmorillonite is the only clay mineral that will change as a result of glycolation (Carroll, 1970). In figure 86, the peak farthest to the left becomes lower and wider, and seems to consist of several sub-peaks. The rest of the peaks in the figure remain unchanged. This indicates the presence of several clays, where montmorillonite may be one of them. A closer look at the (001) reflection shows that parts of the left peak moved to the left. This is a typical behavior for montmorillonite (Carroll, 1970). To further separate the clays, a slide was heated to 500° for one hour to evacuate the water. If illite existed, the peaks would become more intense. This did not happen (Fig. 87), and it is unlikely that illite is present in the sample. Nor do any of the peaks disappear completely, and this suggests that kaolinite does not occur. One heated slide was also glycolated in order to separate the leftmost peaks even further. In figure 88, the presence of several sub-peaks is obvious. Some of the peaks in the figure did not change after heating and glycolation, and suggest presence of chlorite. By matching the peaks characteristic for different minerals, the following minerals were identified: quartz, albite, clinochlore, and montmorillonite (Fig. 89). Chlorite in clay material is generally found intimately mixed with other clay minerals (Grim, 1968), and most sedimentary rocks contain some variety of mixed-layer clays (Weaver, 1956). It is therefore most likely that chlorite and montmorillonite occur together as a mixed-layer clay. ADDendices/XRD-analvses 135 Figure 86) XRD reflections from a glycolated sample of clay from the Sandilands Formation. C L A V H ' " ' ' r~ ' r ' 0 ss: 0.0100 tn: 1.00 CuKal+2 I Figure 87) XRD reflections from a heated sample of clay from the Sandilands Formation. Appendices/XRD-analvses 136 < 5.880 x : 2theta y : 149. Linear 27.990) Figure 88) XRD reflections from a heated and glycolated sample of clay from the Sandilands Formatbn. x : 2theta y : 149. Linear 29-0853 Mg5Al<Si3Al)Oi0<OH>3 C l i n o c h l o r e IT H I I h KG 33-1161 * Si02 Quartz sun 20-6554 C NaAlSi308 A l b i t e low 27.998) Figure 89) XRD reflections from a heated and glycolated sample of clay from the Sandilands Formation, compared to XRD reflections from clinochlore, montmorillonite, quartz, and albite. ADDendices/XRD-analvses 137 Thin sections made from sample 8290a, and several other thin sections from the Sandilands Formation show abundant angular albite crystals mixed in with the clay. The most likely explanation for this is that the clay is a bentonite that resulted from alteration of vitric volcanic fragments, whereas the albite crystals represent volcanic crystal tuff fragments. The albite might also be expected as a diagenetic neomorph. Bentonite refers to clays formed by alteration of volcanic ash in situ. In order for bentonite to form, it is probably necessary for the ash to fall in water (Ross and Shannon, 1926). The presence of non-clay minerals, such as feldspars, may provide evidence for the origin from ash (Ross and Shannon, 1926). Appendices/Fossil report 138 6.3. Fossil report Report J1-1990-HWT Report on Jurassic fossils collected from Graham Island, Queen Charlotte Islands by J. Hesthammer and J. Indrelid, University of Briti s h Columbia i n 1988 and 1989 and submitted for identification in 1989. "The relevant parts of any manuscript prepared for publication that paraphrase or quote from this report should be referred to H.W. Tipper for possible revision" Field No.: 8267 GSC Loc. No.: C-157574 Locality: North Yakoun Lake, Queen Charlotte Islands, British Columbia. King Creek logging area. Lat. 53°26,04", Long. 132°19,15". Identifications: Dubarlceraa freboldi Dommergues, Mouterde, and Rivas Hetadoceras sp? Oxytoma sp. rhnchonellid brachiopods Age & Comments: Early Pliensbachian, Freboldi zone. F i e l d No.: 8265A GSC Loc. No.: C-157573 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. King Creek l o g g i n g area. L a t . 53°26'00", Long. 132°19'21". I d e n t i f i c a t i o n s : Tropidoceras n. sp. sma l l pelecypods Age & Comments: E a r l y P l i e n s b a c h i a n , probably Imlayi zone. Appendices/Fossil report 139 F i e l d No.: 8274 GSC Loc. No.: C-157576 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. King Creek l o g g i n g area. L a t . 53°26'25", Long. 132°19,25". I d e n t i f i c a t i o n s : d i s t o r t e d ammonites pelecypods Age & Comments: Age not determined, Sinemurian i s p o s s i b l e . F i e l d No.: ?? GSC Loc. No.: C-156468 L o c a l i t y : Queen C h a r l o t t e I s l a n d s , Graham I s l a n d . I d e n t i f i c a t i o n s : Zemistephanus c a r l o t t e n s i s (Whiteaves) Age & Comments: Lower B a j o c i a n . F i e l d No.: 8261 GSC Loc. No.: C-157571 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. King Creek l o g g i n g area. L a t . 53°26'24", Long. 132°18,06". I d e n t i f i c a t i o n s : Aveyroniceras sp., c f . A. colujbri/orme B e t t o n i Age & Comments: E a r l y t o Late P l i e n s b a c h i a n , F r e b o l d i or Kunae zone. Spans the Upper and Lower P l i e n s b a c h i a n boundary, t h e r e f o r e mid-Pl i e n s b a c h i a n . Appendices/Fossil report 140 Field No.i 8270 GSC Loc. No.i C-157575 Locality: North Yakoun Lake, Queen Charlotte Islands, British Columbia. King Creek logging area. Lat. 53°26'12", Long. 132°19'42". Identifications: A r i e t i c e r a s n. sp.? Age & Comments: Late Pliensbachian, Kunae or ?Carlottensis zone. F i e l d No.: 8262 GSC Loc. No.: C-157S72 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. King Creek l o g g i n g area. L a t . 53°26'18", Long. 132°18,06". I d e n t i f i c a t i o n s : Fontanelliceras? sp. A r i e t i c e r a s sp. Aveyroniceras c f . A. colubriforme B e t t o n i Age & Comments: Late P l i e n s b a c h i a n , Kunae zone. F i e l d No.: 8256 GSC Loc. No.: C-157S70 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Road up from northern i n t e r s e c t i o n of C h a r l o t t e main and Ghost main. L a t . 53°25'59", Long. 132°17'38". I d e n t i f i c a t i o n s : Leptaleoceras sp. bi v a l v e B Age & Comments: Late Pliensbachian. Appendices/Fossil report 141 Field No.i 9008 GSC Loc. No.: C-1575B4 Locality: West Yakoun Lake, Queen Charlotte Islands, Bri t i s h Columbia. Near Shield's Bay. Lat. 52820,30", Long. 132°24'36". Identifications: hildoceratid ammonite Age 6 Comments: Probably Late Pliensbachian. F i e l d No.: 8313 GSC Loc. No.: C-157581 L o c a l i t y : North Yakoun Lake r e g i o n ; Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Middle King Creek area. L a t . 53 027'15", Long. 132°18'10". I d e n t i f i c a t i o n s : Dubariceras freboldi Dommergues, Mouterde and Rivas Metoderoceras n. sp. Dubariceras sp. a f f . D. s i l v i e s i Age & Comments: E a r l y P l i e n s b a c h i a n , F r e b o l d i zone. F i e l d No.: 8332 GSC Loc. No.: C-157582 L o c a l i t y : North Yakoun Lake r e g i o n , Queen C h a r l o t t e IslandB, B r i t i s h Columbia. Near C h a r l o t t e main and Ghost main. L a t . 53°25'36", Long. 132 o18'10". I d e n t i f i c a t i o n s : ammonite indeterminant - p o s s i b l y an Aveyroniceras or Reynesoceras Age & Comments: Late P l i e n s b a c h i a n i s probable. Appendices/Fossil report 1 4 2 F i e l d No.: 829SB GSC Loc. No.: C-157579 L o c a l i t y : North Yakoun Lake r e g i o n , Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. King Creek logging area. L a t . 53 026'42", Long. 132°19'11". I d e n t i f i c a t i o n s : Aveyroniceraa sp. belemnites Oxytoma sp. Age & Comments: Late o r E a r l y P l i e n s b a c h i a n , ( m i d - P l i e n s b a c h i a n ) . F i e l d No.: 8334 GSC Loc. No.: C-157583 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia -North Ghost Creek. L a t . 53°25,31", Long. 132°18 ,35". I d e n t i f i c a t i o n s : Leptaleoceras a f f . accuratum ( F u c i n i ) Age & Comments: Late P l i e n s b a c h i a n , Kunae zone. F i e l d No.: 8296 GSC Loc. No.: C-157580 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia - King Creek l o g g i n g area. L a t . 53°26'32", Long. 132°19•00". I d e n t i f i c a t i o n s : h i l d o c e r a t i d ammonite, p o s s i b l y A r i e t i c e r a s Age & Comments: Late P l i e n s b a c h i a n , probably. Appendices/Fossil report 143 Field No.: 8060 GSC Loc. No.< C-157530 Locality: North Yakoun Lake, Queen Charlotte Islands, B r i t i s h Columbia. Midway on Charlotte main. Lat. 53,24,55", Long. 132°18'00". Identifications: Geamellaroceraa sp. fragments - possibly Pseudoakirroceraa plant fragments Age & Comments: Early Pliensbachian, possibly Imlayi zone. F i e l d No.: 8036 GSC Loc. No.: C-157528 L o c a l i t y : 3 km nort h e a s t of Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. L a t . 53°22 ,13", Long. 132°15'44". I d e n t i f i c a t i o n s : Entolium balteatum Crickmay Age & Comments: Probably l a t e s t Sinemurian. F i e l d No.: 8063 GSC Loc. No.: C-157531 L o c a l i t y : ??? Queen C h a r l o t t e I s l a n d s , Graham I s l a n d , B r i t i s h Columbia. I d e n t i f i c a t i o n s : ammonite i n d e t . Age & Comments: Lower J u r a s s i c ? Appendices/Fossil report 144 Field No.i 8006 GSC Loc. No.: C-1S7524 Locality: North Yakoun Lake, Queen Charlotte Islands, British Columbia. Where Phantom Creek joins Yakoun River. Lat. S3°23'03", Long. 132o16'03-. Identifications: hildoceratid ammonite - Arieticeras sp.? Age & Comments: Late Pliensbachian. F i e l d No.: 8018 GSC Loc. No.: C-157525 L o c a l i t y : Yakoun Lake area. Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. 4 km south of Rennell J u n c t i o n towards Queen C h a r l o t t e C i t y . Lat. 53°21 ,36", Long. 132°15,18-. Ident i f i c a t i o n s : Tropidoceras actaeon (d'Orbigny) Pseudosklrroceras sp. Age & Comments: E a r l y P l i e n s b a c h i a n , I m l a y i zone. F i e l d No.: 8034 GSC Loc. No.: C-157527 L o c a l i t y : Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. 2.2 km nor t h e a s t of Yakoun Lake. L a t . S3°22,02", Long. 132 c15'18". I d e n t i f i c a t i o n s : Tropidoceras c f . s i m i l a r t o T. erythreum or t o a new species Age & Comments: E a r l y P l i e n s b a c h i a n , I m l a y i zone. Appendices/Fossil report 145 Field No.« 8072 GSC Loc. No.t C-157532 Locality: North Yakoun Lake, Queen Charlotte Islands, B r i t i s h Columbia. Just down from our camp. Lat. 53°24,55", Long. 132°15'12". Identifications: Monotis? sp. Age & Comments: Late Triassic? F i e l d No.: 8083 GSC Loc. No.: C-157535 L o c a l i t y : East Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. South Sue Lake. L a t . 53 < ,22'00", Long. 132°12'46". I d e n t i f i c a t i o n s : Dubariceras freboldi Dommergues, Mouterde and Rivas Age & Comments: E a r l y P l i e n s b a c h i a n , F r e b o l d i zone. F i e l d No.: 8080 GSC Loc. No.: C-157533 L o c a l i t y : East Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Sue Lake. L a t . 53°21'54", Long. 132 013*27". I d e n t i f i c a t i o n s : Asteroceras sp. e c h i o c e r a t i d - Paltechioceras? Age & Comments: Late Sinemurian. i Appendices/Fossil report 146 F i e l d No.: 6081 GSC Loc. No.: C-157534 L o c a l i t y : East Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. North Brent Creek. L a t . 53°21'33", Long. 132°13'00". I d e n t i f i c a t i o n s : ammonite i n d e t . - Crucilobiceras?? Entolium balteatum Crickmay Age & Comments: Late Sinemurian. F i e l d No.: 8090 GSC Loc. No.: C-157536 L o c a l i t y : Northeast Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Close t o Sue Lake (1 km west). L a t . S3°22'25", Long. 132°13'36". I d e n t i f i c a t i o n s : Tropidoceras actaeon Hetaderoceras evolutum (d'Orbigny) Age £ Comments: E a r l y P l i e n s b a c h i a n , I m l a y i or Whiteavesi zone. F i e l d No.: 8158 GSC Loc. No.: C-157543 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Midway on Queen C h a r l o t t e main. L a t . 53°24,53", Long. 132°18'22". I d e n t i f i c a t i o n s : Tropidoceras actaeon (d'Orbigny) Entolium a f f . balteatum Age & Comments: E a r l y P l i e n s b a c h i a n . Appendices/Fossil report 147 Field No.: 8181 GSC Loc. No.t C-157546 Locality: North Yakoun Lake, Queen Charlotte Islands, B r i t i s h Columbia. West Yakoun River. Lat. 53°24,16", Long. 132°17,31". Identifications: Aveyroniceras sp. small bivalves Age S Comments: Pliensbachian, probably Late. F i e l d No.: 8111 GSC Loc. No.: C-157539 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. In Yakoun R i v e r towards our camp. Lat. 53°23'24", Long. 132°15*39". I d e n t i f i c a t i o n s : r h n c h o n e l l i d brachiopods Age & Comments: Age not determined. F i e l d No.: 8100 GSC Loc. No.: C-157538 L o c a l i t y : East Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Close to Sue Lake (2 km west). Lat. 53°22,30", Long. 132°14'15". I d e n t i f i c a t i o n s : ammonites not determined Entolium sp. Age & Comments: Age not determined, could be Late Sinemurian i f the l i t h o l o g i c u n i t i s c o r r e c t . Appendices/Fossil report 148 F i e l d No.t 8125 GSC Loc. No.i C-157540 L o c a l i t y : ??? Queen C h a r l o t t e I s l a n d s , Graham I s l a n d , B r i t i s h Columbia. I d e n t i f i c a t i o n s : probably Phlyseogrammoceras sp. according t o G i B e l l e Jakobs Age & Comments: l a t e L ate T o a r c i a n . F i e l d No.: 8155 GSC Loc. No.: C-157542 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. C h a r l o t t e main. L a t . 53 025'15", Long. 132°17'50". I d e n t i f i c a t i o n s : ammonite - Tropidoceras? Age & Comments: Probably E a r l y P l i e n s b a c h i a n . F i e l d No.: 8169 GSC Loc. No.: C-157545 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. On the road east of C h a r l o t t e main. Lat. 53°24'46", Long. 132°17'06". I d e n t i f i c a t i o n s : Hummatoceras sp. Age & Comments: Late T o a r c i a n or? E a r l y Aalenian. Appendices/Fossil report 149 Field No.: 8191 GSC Loc. No.: C-157547 Locality: Queen Charlotte Islands, Graham Island, British Columbia. Identifications: ammonites belemnite Age & Comments: Probably Toarcian to Bajocian. F i e l d No.: 8212 GSC Loc. No.: C-157549 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Ghost Creek loggin g area. L a t . 53°25'16", Long. 132°19'48". I d e n t i f i c a t i o n s : Gemmellaroceras or in n e r whorls of Tropidoceras erythreum fragments of Tropidoceras Age & Comments: E a r l y P l i e n s b a c h i a n . F i e l d No.: 9057 GSC Loc. No.: C-157590 L o c a l i t y : West Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Phantom Creek. Lat. 53°20'39", Long. 132°21,18". I d e n t i f i c a t i o n s : a c o l e o i d Age & Comments: Age unknown. Appendices/Fossil report 150 F i e l d No.: 8248 GSC Loc. No.: C-157569 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Ghost Creek logging area. L a t . 53 ,25'45", Long. 132°19*33". I d e n t i f i c a t i o n s : Polymorphites a f f . confusus Pseudoakirroceras sp. Age & Comments: E a r l y P l i e n s b a c h i a n , I m l a y i zone. F i e l d No.: 8213 GSC Loc. No.: C-157550 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Ghost Creek loggin g area. L a t . 53°25'31", Long. 132°19'51". I d e n t i f i c a t i o n s : - Dubariceras freboldi Dommergues, Mouterde and Rivas Age & Comments: E a r l y P l i e n s b a c h i a n , F r e b o l d i zone. F i e l d No.: 8247 GSC Loc. No.: C-157568 L o c a l i t y : North Yakoun Lake, Queen C h a r l o t t e I s l a n d s , B r i t i s h Columbia. Ghost Creek loggin g area. L a t . 53°25'53", Long. 132 019'38". I d e n t i f i c a t i o n s : Dubariceras sp. Age 6 Comments: E a r l y P l i e n s b a c h i a n , F r e b o l d i zone. 

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