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Late cenozonic geology of the southern Rocky Mountain trench, British Columbia Clague, John Joseph 1973

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LATE CENOZOIC GEOLOGY OF THE SOUTHERN ROCKY MOUNTAIN TRENCH, BRITISH COLUMBIA by  JOHN JOSEPH CLAGUE A.B., Occidental College, 1967 M.A., University of California, Berkeley, 1969  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS OF THE DEGREE OF DOCTOR OF PHILOSOPHY  in the Department of Geological Sciences  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA November 1973  li  In presenting  t h i s thesis i n p a r t i a l fulfilment of the requirements for  an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t freely available for reference  and  study.  I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may by his representatives.  be granted by the Head of my Department or  It i s understood that copying or publication  of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department of  Geological Sciences  The University of B r i t i s h Columbia Vancouver 8, Canada  Date  November 7,  1973  iii  ABSTRACT Geologic studies which have provided information on the late Cenozoic history of the southern Rocky Mountain Trench, B r i t i s h Columbia include:  (1) the St. Eugene Formation and the o r i g i n of the southern  Rocky Mountain Trench, (2) the stratigraphy and correlation of Quaternary sediments, (3) the patterns of g l a c i e r flow and the o r i g i n of late Wisconsinan t i l l , and (4) the sedimentology and paleohydrology of late Wisconsinan outwash.  (1) The T e r t i a r y history of the southern Rocky Mountain Trench i s inferred from a study of the d i s t r i b u t i o n , stratigraphy, f a b r i c , l i t h o l o g i c composition, structure, and palynology of the Miocene S t . Eugene Formation.  This unit consists of flood-plain and fan facies  and represents the uppermost T e r t i a r y sediments f i l l i n g block-faulted basins i n the Trench.  Sediment deposition was probably contemporaneous  with f a u l t i n g , but at least 600 m of displacement along the east side of the Trench postdates deposition of the St. Eugene Formation.  The  Miocene southern Rocky Mountain Trench was similar i n morphology and p o s i t i o n to the present Trench, but the Miocene climate was more temperate than the present climate of the area.  Palynological results  indicate that during the Miocene southeastern B r i t i s h Columbia had abundant summer p r e c i p i t a t i o n and m i l d , moist winters.  (2) Exposed Pleistocene sediments correlate with deposits of the Pinedale Glaciation and the preceding i n t e r g l a c i a t i o n .  Deposits of  three stades and two interstades of the Pinedale Glaciation are recog-  iy  nized.  During the e a r l i e r interstade the f l o o r of the Trench i n south-  eastern B r i t i s h Columbia was deglaciated, whereas during the l a t e r interstade residual i c e apparently remained l o c a l l y along the center of the TrenchCS) Pinedale glacier-flow patterns and t i l l genesis i n the southern Rocky Mountain Trench were determined through a study of g l a c i a l landforms, t i l l f a b r i c , and t i l l composition.  A review of the ways i n  which directed t i l l f a b r i c s originate indicates that t i l l associated with drumlins accumulated by lodgement of p a r t i c l e s due to subglacial pressure melting.  Landforms and t i l l fabrics document one major s h i f t  in the pattern of g l a c i e r flow near the end of g l a c i a t i o n .  In mountain-  ous areas t i l l composition i s less sensitive as an indicator of such s h i f t s than t i l l f a b r i c .  T i l l composition instead r e f l e c t s the dominant  pattern of i c e flow during g l a c i a t i o n .  T i l l constituents decrease with  distance from their bedrock sources because of progressive deposition, d i l u t i o n through sediment mixing, and breakage and abrasion during transport.  Other factors which may a f f e c t the d i s t r i b u t i o n and r e l a t i v e  abundance of constituents i n Trench t i l l s include reworking at the ice-sediment interface and transport of constituents e n g l a c i a l l y and s u b g l a c i a l l y by meltwater.  (4) Late Wisconsinan channeled outwash i s coarse, poorly sorted, shows large-scale cross-bedding, and was deposited i n channel-bar complexes of high-energy  rivers.  Peak discharges calculated from channel  morphometry and maximum p a r t i c l e s i z e are larger than maximum discharges attributable to uninterrupted summer runoff. Many channels transmitted  '•VP-  peak discharges during jbkulhlaups from glacial lakes in tributary valleys.  An empirical relationship between total volume discharged  during documented jbkulhlaups and corresponding maximum instantaneous discharges is applied to one Pleistocene glacier-dammed lake in the study area to show that discharges equal to or larger than those calculated from channel morphometry were attained during jbkulhlaups. Some applications of these geologic studies include the pre<diction of flood magnitudes from self-dumping glacier-dammed lakes, the determination of the source of ore clasts or minerals in t i l l , and a preliminary assessment of the groundwater resources of the southern Rocky Mountain Trench.  vi  TABLE OF CONTENTS page  ABSTRACT  i i i  TABLE OF CONTENTS  v i  LIST OF TABLES  :x  LIST OF FIGURES  x i  LIST OF APPENDICES  xvi  ACKNOWLEDGMENTS  CHAPTER ONE:  :;xvii  INTRODUCTION  ,  1  PREVIOUS GEOLOGIC WORK  2  BEDROCK GEOLOGY  4  SURFICIAL GEOLOGY  6  Introduction  6  Deposits  7  St. Eugene Formation  8  I n t e r g l a c i a l Sediments  8  Older  Drift  Inter-drift Younger  10  Sediments  Drift  P o s t g l a c i a l Sediments LITERATURE CITED CHAPTER TWO:  16 18  42 44  THE ST. EUGENE FORMATION AND THE DEVELOPMENT  OF THE SOUTHERN ROCKY MOUNTAIN TRENCH  47  ABSTRACT  47  INTRODUCTION  48  DISTRIBUTION AND CHARACTER OF THE ST. EUGENE FORMATION  49  Colluvium and Fanglomerate  51  Stratified  53  S i l t and Sand  Coarse Gravel with Minor Sand Interbeds  53  page  PROVENANCE OF ST. EUGENE FANGLOMERATE A n a l y t i c a l Procedure  54 54  Fan-fabric Analysis  54  Method  55  Results  56  Clast Lithology Analysis  57  Method  57  Results  58  Discussion  58  DEFORMATION OF THE ST. EUGENE FORMATION  60  ST. EUGENE PALEOFLORA AND PALEOCLIMATOLOGY  61  A n a l y t i c a l Procedure  62  Method  62  Results  63  Discussion  64  Age Assigned by Comparison with Similar Floras  64  Paleoecology Inferred from E c o l o g i c a l Requirements of Extant Counterparts  76  Paleogeography Inferred from Physical Characteristics of Sediments  86  NEOGENE DEFORMATION IN SOUTHEASTERN BRITISH COLUMBIA  88  CONCLUSIONS  100  LITERATURE CITED  102  CHAPTER THREE:  GLACIER-FLOW PATTERNS AND THE ORIGIN OF  LATE WISCONSINAN  TILL  109  ABSTRACT  109  INTRODUCTION  110  DISTRIBUTION AND CHARACTER OF TILL  112  GLACIER-FLOW PATTERNS  114  A n a l y t i c a l Procedure  116  T i l l - f a b r i c Analysis Englacial  117  transport  119  Deposition Post-depositional  120  reorientation  121  viii  page Method  123  Results  124  Heavy Mineral Analysis  126  Method  129  Results  130  Clast Lithology Analysis  132  Method  132  Results  133  Discussion  .134  CONCLUSIONS  166  LITERATURE CITED  174  CHAPTER FOUR:  SEDIMENTOLOGY AND PALEOHYDROLOGY OF  LATE WISCONSINAN OUTWASH  179  ABSTRACT  179  INTRODUCTION  180  DISTRIBUTION AND CHARACTER OF OUTWASH  181  Sedimentary Textures  181  Sedimentary Structures  182  Pebble Lithologies and Provenance  183  PALEOHYDROLOGY  '. 185  Paleodischarge Determinations from Channel Morphometry  187  Paleodischarge Determinations from Discharge Records of P r o g l a c i a l Rivers  198  Discussion of Results  206  CONCLUSIONS  210  LITERATURE CITED  212  CHAPTER FIVE:  GEOMORPHIC HISTORY  LITERATURE CITED  CHAPTER SIX:  APPLICATIONS OF GEOLOGIC KNOWLEDGE  215 233  235  MAGNITUDE OF JOKULHLAUPS  235  MINERAL EXPLORATION  238  :ix  page  GROUNDWATER . .. ,  , .. ,  LITERATURE CITED CHAPTER SEVEN: SUGGESTIONS FOR FURTHER RESEARCH  240 247 249  TILL FABRICS AND TILL GENESIS  249  ORIGIN OF DRUMLINS  250  COLLECTION OF FABRIC DATA  250  DECREASE OF TILL CONSTITUENT WITH DISTANCE FROM SOURCE  251  QUATERNARY STRATIGRAPHY  252  SEDIMENT CONSOLIDATION  252  GROUNDWATER RESOURCES  253  LITERATURE CITED  254  APPENDICES  255  '.X  LIST OF TABLES  Bedrock units in and adjacent to the study area. Palynomorph assemblages from the St. Eugene Formation. Comparison of the St. Eugene microflora and Miocene microfloras from British Columbia and the northwestern United States. Relation between orientation of fabric elements in t i l l and t i l l genesis. Comparison of t i l l - f a b r i c maximum clustering axes and the trends of associated glacial lineations. Peak velocities and discharges determined from channel morphometry and maximum particle size. Relation of glacier area and meltwater discharge during periods of maximum melt. Jbkulhlaup data.  xi  LIST OF FIGURES page  Frontispiece, Figure 1.  i Index map of the Rocky Mountain Trench and the  11  study area. Figure 2.  Locality index map.  13  Figure 3.  The southern Rocky Mountain Trench, British  15  Columbia. Figure 4.  Generalized geologic map of part of southeastern  17  British Columbia. Figure 5.  Surficial geology, southern Rocky Mountain Trench,  in pocket  British Columbia. Figure 6.  Map of Bouguer gravity in the southern Rocky  21  Mountain Trench, and gravity profiles and inferred geologic sections across the Trench. Figure 7.  Thickness of Quaternary sediments.  23  Figure 8.  Composite columnar section of late Cenozoic sediments  25  exposed in the southern Rocky Mountain Trench. Figure 9.  The St. Eugene Formation.  27  Figure 10.  Interglacial sediments, Sand Creek.  29  Figure 11.  Chronology and correlation of late Pleistocene  31  events in the Pacific Northwest and the Rocky Mountains of the United States. Figure 12.  Older  drift.  Figure 13.  Attitudes of beds, faults, and fractures in deformed  33  outwash of the older Figure 14.  Inter-drift  Figure 15.  Younger  sediments. drift.  35  drift.  37 39  xii  page Figure 16.  P o s t g l a c i a l sediments and landforms.  41  Figure 17.  Index map showing outcrop areas of the S t . Eugene  69  Formation. Figure 18.  Stratigraphic sections of the S t . Eugene Formation.  71  Figure 19.  The S t . Eugene Formation.  73  Figure 20.  Fabrics of p a r a g l a c i a l a l l u v i a l fans.  75  Figure 21.  Relation between fan-fabric strength and differences  77  i n the f a b r i c results for samples of s i z e 60 and 20. Figure 22.  Fan fabrics from the S t . Eugene Formation.  79  Figure 23.  Percent of clasts of the following l i t h o l o g i e s i n  81  St. Eugene fanglomerate:  laminated greenish-gray  a r g i l l i t e (source i s largely the Roosville and Gateway Formations), red-purple a r g i l l i t e and quartz arenite (largely of the P h i l l i p s Formation), and mafic igneous rocks (Purcell v o l c a n i c s ) . Figure 24.  The f a b r i c of mudflow g r a v e l .  83  Figure 25.  Deformation of the S t . Eugene Formation.  85  Figure 26.  Plant m i c r o f o s s i l sample s i t e s from the S t . Eugene  87  Formation. Figure 27.  Selected plant m i c r o f o s s i l s from the S t . Eugene  91  Formation. Figure 28.  Location of some Miocene palynomorph assemblages i n  95  B r i t i s h Columbia and the northwestern United States. Figure 29.  Relation between age of f l o r a and percent of f o s s i l  97  genera s t i l l l i v i n g near their f o s s i l l o c a l i t i e s for mega- and microfloras from the western United States and B r i t i s h Columbia. Figure 30.  Block diagram showing the proposed model of Tertiary sedimentation controlled by block f a u l t i n g i n the southern Rocky Mountain Trench, B r i t i s h Columbia.  99  xiii  page Figure 31.  Index map showing trends of g l a c i a l lineations and  135  the d i s t r i b u t i o n of d r i f t . Figure 32.  Late Wisconsinan t i l l i n the southern Rocky  137  Mountain Trench. Figure 33.  Features which indicate the d i r e c t i o n of i c e flow  139  immediately p r i o r to deglaciation of the southern Rocky Mountain Trench. Figure 34.  Relation between t i l l - f a b r i c strength and differences  143  i n the f a b r i c results for samples of size 60 and 20.  145  Figure 35.  Selected fabrics from the younger  Figure 36.  Magnitude and d i r e c t i o n of plunge of t i l l c l a s t s .  147  Figure 37.  Comparison of t i l l - f a b r i c axes of maximum  149  till.  clustering and associated g l a c i a l l i n e a t i o n s . Figure 38.  Till-fabric  axes of maximum clustering determined at  153  v e r t i c a l intervals of 1 to 5 m through the younger  drift. Figure 39.  Relation between percent of a constituent i n t i l l  155  and distance from the bedrock source. Figure 40.  Sediment sample s i t e s .  157  Figure 41.  D i s t r i b u t i o n of selected bedrock l i t h o l o g i e s .  159  Figure 42.  Amphibole d i s t r i b u t i o n i n t i l l of the southern  161  Rocky Mountain Trench. Figure 43.  Garnet d i s t r i b u t i o n i n t i l l of the southern Rocky  163  Mountain Trench. Figure 44.  D i s t r i b u t i o n of mafic igneous pebbles i n t i l l of  165  the southern Rocky Mountain Trench. Figure 45.  D i s t r i b u t i o n of Blairmore Group c l a s t s i n d r i f t of the southern Rocky Mountain Trench.  167  xiy  page  Figure 46.  Two phases of g l a c i e r flow near the end of the  169  Pinedale G l a c i a t i o n . Figure 47.  Patterns of g l a c i e r coalescence off tributary  171  valleys i n the C o r d i l l e r a . Figure 48.  D i s t r i b u t i o n of outwash and meltwater channels,  189  Rocky Mountain Trench, southeastern B r i t i s h Columbia. Figure 49.  Cumulative size frequency curves of outwash samples.  191  Figure 50.  Sedimentary structures i n outwash at gravel p i t s .  193  Figure 51.  Percent of clasts of the following l i t h o l o g i e s i n  195  outwash and t i l l :  laminated greenish-gray  a r g i l l i t e (source i s largely the Roosville and Gateway Formations), red-purple a r g i l l i t e and quartz arenite (largely of the P h i l l i p s Formation), and mafic igneous rocks (Purcell volcanics and i n t r u s i o n s ) . Figure 52.  Fourth-order trend surface map  of percent laminated  197  greenish-gray a r g i l l i t e i n t i l l . Figure 53.  Meltwater channels.  199  Figure 54.  Topographic p r o f i l e s across a major meltwater channel.  201  Figure 55.  Relation of g l a c i e r area, A, and maximum instantaneous  205  discharge, Q. Figure 56.  Relation of t o t a l volume drained during jOkulhlaup  209  and peak water discharge. Figure 57.  Pattern of i c e flow i n southeastern B r i t i s h Columbia  219  and southwestern Alberta during the Pleistocene. Figure 58.  D i s t r i b u t i o n of existing glaciers i n southeastern B r i t i s h Columbia and southwestern  Figure 59.  Map  Alberta.  of the C o r d i l l e r a n Ice Sheet and related features  i n southeastern B r i t i s h Columbia, northwestern Montana, and northern Idaho.  221  223  page Figure 60.  Comparison of a contemporary ice sheet and the  225  Cordilleran Ice Sheet during the maximum Pinedale advance. Figure 61.  A contemporary analogue of the Pleistocene  227  glacierized Rocky Mountain Trench. Figure 62.  Comparison of contemporary and ancient landforms  229  produced by glaciers which remained active during recession rather than stagnating. Figure 63.  A contemporary analogue of Pleistocene ice-dammed  231  lakes in the southern Rocky Mountain Trench. Figure 64.  Relation of cumulative volume drained during  241  jOkulhlaups and instantaneous water discharge. Figure 65.  Meltwater channels in the vicinity of Cranbrook,  243  British Columbia. Figure 66.  Meltwater channel complex northwest of Bull River; mean water discharge records of Norbury Creek and Bull River.  245  xvi  LIST OF APPENDICES page  APPENDIX 1. Stratigraphic sections.  256  APPENDIX 2. Southern Rocky Mountain Trench radiocarbon dates.  258  APPENDIX 3.  Size frequency data for selected t i l l samples.  259  APPENDIX 4. Fan-fabric sites and results.  260  APPENDIX 5. Contoured diagrams of selected t i l l fabrics.  262  APPENDIX 6.  263  Till-fabric sites and results.  APPENDIX 7. Heavy mineral and clast lithology data.  266  APPENDIX 8. Textural parameters of outwash underlying late  274  glacial meltwater channels in the southern Rocky Mountain Trench.  xvii  ACKNOWLEDGMENTS A study of the surficial geology of the southern Rocky Mountain Trench began in 1969 with funds provided by the Water Investigations Branch of the British Columbia Department of Lands, Forests, and Water Resources.  Continued research (1970-73) was supported by the  National Research Council of Canada through Postgraduate Scholarships and Grant A-1107. Thanks are extended to W.H. Mathews for guidance, criticism, and encouragement during a l l phases of this study. My ideas were formulated, in part, through conversations and correspondence with W.C.  Barnes, M.A. Church, A. Dreimanis, R.J. Fulton, P.L. Gordy,  R.E. Kucera, L.M. Lavkulich, G.B. Leech, J.E. Reesor, G.E. Rouse, J.M. Ryder, 0. Slaymaker, and P.N. Sprout. M.A. Church suggested the method of paleodischarge determination from channel morphometry. I am grateful to P. Barnes of the British Columbia Department of Highways for drillhole and sediment texture data; to F.R. Edmunds of Cominco Ltd. for data on the thickness of semiconsolidated and unconsoli*dated sediments; to P.L. Gordy, G.W.  Graff, and G. Steward of Shell  Canada Ltd. for seismic records and d r i l l e r s ' logs; to D.M. Mark for a computer program which analyzes axial orientation data; to A. Post for some of the photos used in this thesis; and to J.A. Westgate for the identification of tephra samples. Earlier versions of the thesis were reviewed by W.C. Barnes,  xvlii  M.A. Church, R.E. Kucera, L.M. Lavkulich, W.H. Mathews, B.C. McDonald, G.E. Rouse, 0. Slaymaker, and D. Smith. A.C. Clague assisted in the field and typed the manuscript. Also gratefully acknowledged are the services and research f a c i l i t i e s provided by the Department of Geological Sciences at the University of British Columbia.  A 'A  1  CHAPTER ONE: INTRODUCTION Research on the surficial geology of the southern Rocky Mountain Trench was undertaken in order to (1) determine the origin and evolution of this remarkable valley, (2) test the applicability of certain tech^niques i n the investigation of glacial and other deposits in cordilleran regions, and (3) provide geologic knowledge applicable to man's development of the region. The organization of the report is as follows.  This chapter  describes the geologic and geographic setting of the Rocky Mountain Trench in southeastern British Columbia.  Previous geologic work in the  area is briefly reviewed and the distribution and character of bedrock, semiconsolidated and unconsolidated sediments discussed. Chapters 2, 3, and 4 each present in detail one aspect of the Cenozoic geology of the southern Rocky Mountain Trench.  Each documents a particular develop-  mental stage in the history of the Trench; together they provide a record of the evolution of the Trench and of the processes which have formed and modified i t .  Tertiary block faulting and structurally con-  trolled sedimentation are discussed in Chapter 2, Pleistocene glaciation in Chapter 3, and late Pleistocene meltwater erosion and sedimentation in Chapter 4. The geomorphic history of the area is reviewed i n Chapter 5, and applications of geologic information gained during the study which relate to man's future activities in the region and elsewhere are considered in Chapter 6. Suggestions for further research are outlined in a concluding chapter.  2  PREVIOUS GEOLOGIC WORK The Rocky Mountain Trench i s a major topographic depression, extending from northwestern Montana through British Columbia almost to the Liard River (Fig, 1), The part of the Trench occupied by the Kootenay River i s a flat—bottomed, somewhat sinuous valley 3 to 16 km wide, bounded by the Rocky Mountains to the east and the Purcell Mountains to the west (Figs, 2 and 3). Major tributaries to the Kootenay River include St. Mary, Bull, and Elk Rivers,  Most of the Trench within  the study area is between 760 and 910 m in elevation. The Rocky Mountain Trench has interested earth scientists since i t was recognized as a major physiographic form. The s u r f i c i a l geology, however, has received l i t t l e attention.  Early references to the geology  of the region occur in the writings of Bauerman (1884) and Dawson (1885, 1890).  Dawson (1885, p. 28-31 and 146-157) commented on the geomorphology  of the Trench. Daly (1912) investigated the bedrock and structure of the southern Rocky Mountain Trench during his geologic explorations through the Cordillera.  He briefly discussed glaciation of the Galton Range and  the Purcell Mountains (p. 584-588).  Shortly thereafter, Schofield (1915,  1920) mapped the geology of the Cranbrook area and commented on the genesis of the Rocky Mountain Trench. He described sediments predating the last glacial advance; these he termed the St. Eugene s i l t s and assigned to the "St. Eugene interglacial (?) epoch," Hollick (1914, 1927) assigned a Tertiary age to f o s s i l plants from the St, Eugene s i l t s , and Berry (1929) compared the St. Eugene flora to similar Miocene floras in  3  Washington and Idaho.  The Miocene age of the St. Eugene s i l t s  was  accepted by Rice (1937) i n his -memoir on the bedrock and structure of the Cranbrook-Kimberley area.  However, the S t . Eugene s t r a t a as defined  by Rice are only the lower part of the unit specified by Schofield. Unconsolidated deposits are discussed b r i e f l y (p. 24-25) and are shown on the geologic map  as undifferentiated Recent and Pleistocene s i l t , sand,  g r a v e l , and g l a c i a l d r i f t .  Rice (1936) stated that g l a c i a l erosion i n  the Cranbrook area was minor and that deglaciation was accompanied by stagnation of large parts of the g l a c i e r i n the Trench.  The geology of the Trench and adjacent areas between 49° and 50°15'N l a t i t u d e was mapped and discussed by Leech (1954, 1957, 1959a, 1959b, 1960, 1966).  1958,  Quaternary deposits are shown as undifferen-  t i a t e d t i l l , g r a v e l , sand, s i l t , and alluvium on Leech's geologic maps. P r i c e (1962) mapped the geology of Elk V a l l e y .  The B r i t i s h Columbia Department of Agriculture conducted a s o i l survey of the Upper Kootenay Valley (Kelley and Sprout, 1956),  The  s u r f i c i a l geology i s discussed i n the survey report, and s o i l maps i n d i cate the d i f f e r e n t s o i l parent materials and l a t e Quaternary  landforms.  From gravity data Garland and others (1961) and Thompson (1962) proposed the existence of basins of Cenozoic sedimentation at Fort Steele, J a f f r a y , and Waldo, containing up to 430, 1100, and 1500 m of semiconsolidated to unconsolidated sediments r e s p e c t i v e l y .  Depth estimates  based upon seismic r e f r a c t i o n data (Lamb and Smith, 1962) agreement with the gravity depth estimates.  are i n general  4  Crickmay (1964) reviewed previous work bearing on the origin of the Trench and concluded that ice was a minor agent compared to running water in excavating the valley.  He also stated, without supporting  evidence, that the St. Eugene s i l t s are Pliocene in age. Pardee (1910, 1942, 1950), Hershey (1912), Davis (1921), Alden (1953), Richmond (1965), and Richmond and others (1965) described the landforms and unconsolidated sediments of northwestern Montana and discussed the geomorphic history of the region.  Alden (1948), Pardee (1948) ,  and Johns (1970, p. 6-12) discussed the s u r f i c i a l geology of the Kootenai Valley area south of 49°N latitude. The present study i s based upon f i e l d work completed during the summers of 1970, 1971, and 1972.  Mapping was done on Department of Mines  and Technical Surveys topographic maps of the Columbia River Basin, Upper Kootenay River Area, printed i n 1951.  These maps have a 20-foot (6.1-m)  contour interval and a scale of 1:31,680. Aerial photographs supplied by the Surveys and Mapping Branch of the British Columbia Department of Lands, Forests, and Water Resources facilitated mapping. The photos were flown in 1968 and 1969 and are at a scale of 1:31,680.  BEDROCK GEOLOGY Bedrock within the study area i s composed of sedimentary rocks of Precambrian to Cretaceous age, volcanic rocks of Precambrian age, and intrusive igneous rocks of Precambrian and Early Cretaceous (?) age (Fig. 4, Table 1).  5  Stratified rocks of Precambrian age in the Canadian Cordillera have been broadly subdivided into the Purcell (older) and Windermere (younger) Groups.  The Purcell Group is informally subdivided into upper  and lower divisions, each of which consists of several formations,  Purcell  rocks crop out over large portions of the Purcell Mountains. The west front of the Rocky Mountains from near Premier Lake to Sand Creek is largely Lower Purcell rocks overlain by the Siyeh Formation,  The Galton  Range to the south is underlain mainly by Upper Purcell rocks, In general, Purcell strata on the east side of the Trench strike north to northwest parallel to the mountain front and dip east to northeast.  Strata  in the Purcell Mountains also tend to strike north to northwest, but folding and faulting complicate the geology. The Moyie intrusions are diorite and quartz gabbro s i l l s and dikes intruded dominantly into the Aldridge and Kitchener Formations of the lower division of the Purcell Group. These intrusions, especially common in St. Mary Valley, are of Precambrian age and may be related i n origin to andesitic lavas at the top of the Kitchener and Siyeh Formations. Windermere strata crop out along the west side of the Trench north of 50°N latitude and are particularly common in the Purcell Mountains northwest of the study area.  On the east side of the Trench these rocks  are limited to small fault slices near 50°15'N latitude. Rocks of Paleozoic age crop out over large areas of the Hughes and Lizard Ranges of the Rocky Mountains, but are much less common in the Purcell Mountains.  The west escarpment of the Rocky Mountains north of  Lussier River and between Sand Creek and Elko consists of Paleozoic rocks  6  underlain by Upper Purcell strata,  Cambrian rocks crop out at the north  end of the Galton Range near the crest.  Paleozoic rocks are also present  along the floor of the Rocky Mountain Trench north of Premier Lake, between Kimberley and Cranbrook, from the vicinity of Bull River to Sand Creek, and at Roosville. Rocks of Mesozoic age include sedimentary rocks which crop out in Elk Valley and granitic rocks which occur as batholiths, stocks, and dikes intruding Precambrian and Paleozoic strata.  The largest intrusion  is a batholith at the headwaters of Skookumchuck Creek.  Other intrusions  within the Trench and too small to be shown on the geologic map (Fig. 4) include those near Bull River, on Kootenay Indian Reserve, on Sheep Mountain, and near Elko.  SURFICIAL GEOLOGY Introduction Thick deposits of semiconsolidated and unconsolidated sediments are limited to the major valley bottoms and are of Tertiary and Quaternary age; the drift cover is thin or absent on the uplands (Fig. 5). Cenozoic sediments in the Trench as determined from gravity (Garland and others, 1961; Thompson, 1962) and seismic (Lamb and Smith, 1962) data are as much as 1500 m thick; in some places, however, bedrock crops out across nearly the complete width of the Trench. Three deep basins i n the Trench are separated by bedrock with only thin sediment cover (Fig. 6). The thickness of Quaternary deposits has been estimated from deep  s t r a t i g r a p h i c exposures along the major r i v e r v a l l e y s i n the Trench and from seismic records where low-velocity Quaternary sediments are d i s t i n guishable from intermediate-velocity T e r t i a r y deposits ( F i g , 7),  In  general, Quaternary deposits are about 100 m or less i n thickness along the sides of the Trench, but are l o c a l l y much thicker along the Trench axis.  Deposits  Despite the genetic complexity of many sediments, i t i s convenient to c l a s s i f y them according to transportational agency. further subdivided on the basis of depositional medium.  They may be  In the Rocky  Mountain Trench the following deposits are recognized:  Transportational agency  Depositional medium  Deposits  ice  ice  i c e and water  water  (flowing)  g l a c i o f l u v i a l sediments  ice and water  water  (standing)  g l a c i o l a c u s t r i n e sediments  water  water  (flowing)  alluvium ( 1f l u v i a l and fan deposits )  water  water(transitional from flowing to standing)  d e l t a i c sediments  water  water  lacustrine sediments  wind  air  mass movement  till,  (standing)  erratics  l o e s s , dune sand landslide d e b r i s , colluvium  L i s t e d i n order of decreasing age, the known deposits i n the  ^anglomerate i s consolidated and semiconsolidated a l l u v i a l fan sediment.  8  southern Rocky Mountain Trench include the following: Formation, i n t e r g l a c i a l sediments, older drift,  younger drift,  and p o s t g l a c i a l sediments.  presented i n Appendix 1.  the S t . Eugene  inter-drift  sediments,  Stratigraphic sections are  A generalized composite section i s shown i n  Figure 8.  St. Eugene Formation  The S t . Eugene Formation ( F i g . 9 ) , exposed beneath Quaternary sediments along S t . Mary River, E l k River, and Gold Creek, consists of the following sediment types:  (1) colluvium and fanglomerate,  (2) s t r a t i f i e d s i l t and sand, and (3) coarse gravel with minor sand interbeds.  Interglacial  Details of stratigraphy are presented i n Chapter 2.  Sediments  I n t e r g l a c i a l sediments ( F i g . 10) crop out along Sand Creek (49°21'25"N, 115°17'05"W) where they are overlain by t i l l ; the unit i s not exposed.  the base of  The sediments consist of about 7 m of i n t e r -  bedded c l a y , s i l t , sand, and gravel ranging i n color from very l i g h t gray to yellowish gray (N 8 to 5Y 8/1).  2  Fragments of wood, of which  the largest i s about 0.5 m i n length, are abundant.  The lower part (4 m) of the i n t e r g l a c i a l unit at Sand Creek i s gravel consisting of well-rounded pebbles and cobbles i n a s i l t and sand  Colors are from Rock-color Chart (Goddard and others, 1963).  9  matrix.  Most clasts are 1 to 8 cm i n maximum s i z e ; many are weathered,  i n contrast to those i n the overlying d r i f t which are f r e s h .  Both  p a r a l l e l and c r o s s - s t r a t i f i c a t i o n are present, but are inconspicuous because v a r i a t i o n i n c l a s t s i z e within the gravel i s s l i g h t and because c l a y , s i l t , and sand interbeds are uncommon.  The upper part (3 m) of the i n t e r g l a c i a l unit at Sand Creek i s c l a y , s i l t , and fine-grained sand with weak p a r a l l e l s t r a t i f i c a t i o n . Fine-grained sediment also occurs as rare interbeds and lenses within the  underlying gravel.  The gravel facies i s interpreted as a n o n g l a c i a l , high-energy channel deposit, while the fine-grained facies represents either an overbank or lacustrine deposit.  Abundant l o c a l vegetation supplied  woody detritus to the accumulating sediment.  The Sand Creek i n t e r g l a c i a l sediments are believed to correlate with Olympia I n t e r g l a c i a l deposits of the coastal P a c i f i c Northwest (Armstrong and others, 1965; Crandell, 1965) and with deposits of the B u l l Lake-Pinedale i n t e r g l a c i a t i o n of the Rocky Mountains of the United States (Richmond, 1965) (Fig.  11). Wood from sand d i r e c t l y below  till  yielded a radiocarbon date of 26,800 ± 1000 years (GX-2032; see Appendix 2 ) .  No other Rocky Mountain Trench sediments which d e f i n i t e l y correlate with the Sand Creek i n t e r g l a c i a l sediments have been found. Some s i l t , sand, and gravel exposed i n the walls of the major r i v e r valleys may be i n t e r g l a c i a l i n o r i g i n .  These sediments, however, d i f f e r  10  from those at Sand Creek in that they lack visible organic detritus and commonly contain dropstones; the gravel fraction is coarser, more poorly sorted, and consists of less weathered clasts.  Thus, i t i s thought that  these sediments were deposited in a proglacial environment after deposition of the interglacial unit at Sand Creek.  Older  Drift  Older drift  (Fig. 12) crops out along major valleys in the study  area where i t overlies either bedrock or sediments of the St. Eugene Formation.  More commonly, however, the base of the unit i s not exposed,  The glacial deposits consist of t i l l (maximum observed thickness 23 m) and outwash (maximum observed thickness 46 m).  The former i s a  massive diamicton of clay, s i l t , sand, and clasts of a range of sizes (Appendix 3).  It is light gray to very light gray (N 7 to N 8) except  where clasts of grayish-orange and light-brown St. Eugene colluvium or fanglomerate are incorporated in the lower part of the t i l l .  Clasts are  subangular to subrounded, commonly striated, and consist of a variety of rock types cropping out in the mountains flanking the study area.  older  till  3  is overlain either by coarse outwash, inter-drift  sand, or younger t i l l .  The  s i l t and  In the last case, the contact between the two  t i l l s i s generally unrecognizable because of similarities in texture and color.  Where overlain by s i l t and sand, the t i l l grades upward into  pebbly s i l t s by a decrease in number of clasts.  d  T i l l of the older drift  t i l l ; t i l l of the younger drift  is referred to as the older  or lower  i s called the younger or upper t i l l .  11  Figure 1. Index map of the Rocky Mountain Trench (darkened) and the study area (stippled). Position and extent of Rocky Mountain Trench from Holland (1964).  12  Outwash consists mainly of sandy gravel, i t s color differing with lithologic composition. Clasts are well rounded and generally lack glacial striations,  Outwash occurs as lenses in older t i l l , as horizontal  and cross-stratified beds, and as broadly folded beds locally cemented by calcium carbonate. The latter sediments are of particular interest because they are widely distributed and are thought to represent a thick supraglacial outwash mantle which deformed competently during melting of underlying stagnant ice.  Strata commonly dip 5 to 30° with  dip components perpendicular to the axis of the valley in which the unit is exposed (Fig, 13). High-angle normal and reverse faults and fractures cut the outwash and are oriented parallel to the walls of what must have been major meltwater discharge routes.  Similar faults in glaciofluvial  sediments have been shown to originate by adjustments in the sediment pile as masses of associated ice melt (McDonald and Shilts, in press). Broadly folded, cemented outwash passes downward into cross-stratified, uncemented sand and gravel; in places i t grades upward into uncemented  inter-drift  s i l t and sand or is overlain across an angular unconformity  by younger  drift.  The older drift  is considered to be Wisconsinan in age and to  correlate with early deposits of the Fraser Glaciation and with sediments of the early stade of the Pinedale Glaciation (Fig. 11).  drift  Clasts in older  are fresh in comparison to those in the Sand Creek interglacial  unit; thus, the former unit i s thought to be younger than the latter. The overlying inter-drift  sediments were probably deposited in a pro-  glacial environment during a relatively short interval between major ice advances.  Since the Olympia Interglaciation was a nonglacial interval  13  Figure 3.  The southern Rocky Mountain Trench, B r i t i s h Columbia.  A.  Floor and east wall of the Trench south of E l k River (BC 577:38).  B.  Trench f l o o r and Kootenay River flood p l a i n viewed toward the southeast from near Fort Steele (BC 898:50).  C.  Floor and west wall of the Trench north of S t . Mary River (BC 583:68).  D.  Rocky Mountain Trench viewed toward the south from near 50°N latitude (BC 896:19).  1 5  Figure 3  16  of major duration (Armstrong and others, 1965; Fulton, 1971), the  inter-drift  sediments were most l i k e l y deposited during an interstade  within the l a s t g l a c i a t i o n .  A rounded c l a s t of wood from the older  t i l l yielded a radiocarbon date of > 36,000 years (GX-2031; see Appendix 2).  The wood was probably eroded from older sediments and  redeposited i n t i l l .  Inter-drift  Sediments  Inter-drift the  sediments (Fig.  14) up to 61 m thick crop out along  valley walls of Kootenay River and i t s t r i b u t a r i e s .  They o v e r l i e  older g l a c i a l deposits and are overlain by younger t i l l and outwash. The sediments are very light-gray to white (N 8 to N 9) s i l t , sand, and minor gravel.  No organic matter has been found i n these sediments.  Individual s t r a t a range from laminae to beds more than a meter i n thickness. massive.  Rhythmic bedding i s uncommon, and many exposures appear Soft-sediment deformation, although uncommon, has l o c a l l y  produced contorted beds overlain by undisturbed s t r a t a , load casts, flame-like projections of fine-grained sediment into overlying s i l t and sand, and coherent blocks of sediment that slumped toward the center of the  depositional basin.  Also present are high-angle f a u l t s and f r a c t u r e s ,  c l a s t i c dikes intruded from below, and channel s c o u r - a n d - f i l l structures. Isolated pebbles and cobbles i n s i l t and sand are present near the base and top of the unit and were probably deposited from i c e r a f t s .  Inter-drift  s i l t and sand were deposited i n one or more lakes  which formed on the f l o o r of the Rocky Mountain Trench during a period  17  Figure 4. Generalized geologic map of part of southeastern British Columbia (compilation from Leech, 1957, 1959a, 1960; Price, 1962). The following are the formations and groups included in the composite map units: map unit (1) Fort Steele, Aldridge, and Creston Formations; (2) Kitchener and Siyeh Formations, Dutch Creek Formation (includes Roosville, Phillips, and Gateway Formations), and Mount Nelson Formation; (3) Toby Formation and Horsethief Creek Series; (4) Eager, Cranbrook, and Burton Formations; (5) Elko and Jubilee Formations; (6) McKay Group, Wonah and Glenogle Formations; (7) Beaverfoot-Brisco Formation; (8) Fairholme and Rundle Groups, Harrogate, Burnais, Alexo, Palliser, Banff, and Exshaw Formations; (9) Rocky Mountain Formation; (10) Fernie and Blairmore Groups, Spray River and Kootenay Formations. The dotted line is the boundary of the geologic map.  18  of g l a c i e r recession. lying older  The t r a n s i t i o n between these sediments and under-  outwash i s gradational, with dropstones, gravel lenses, and  sediment deformation (p. 12) increasing downward; thus, deposition of  inter-drift top  s i l t and sand began i n a p r o g l a c i a l environment.  of the inter-drift  Near the  unit there i s an upward increase i n dropstones  related to the readvance of the C o r d i l l e r a n Ice Sheet indicating that the  upper part of the unit was also deposited i n a p r o g l a c i a l environment.  Dropstones and other indicators of nearby glaciers are absent i n the middle part of the u n i t , so i t i s not known whether these sediments are g l a c i o l a c u s t r i n e or simply lacustrine i n o r i g i n .  The absence of v i s i b l e  organic matter throughout the unit may indicate that vegetation was never firmly established during this nonglacial i n t e r v a l .  Inter-drift of  sediments are tentatively correlated with deposits  the interstade separating the early and middle stades of the Pinedale  G l a c i a t i o n (Fig. 11).  Younger Drift Younger g l a c i a l deposits (Fig. of  15) crop out over large portions  the f l o o r of the Rocky Mountain Trench and i t s tributary v a l l e y s .  These sediments are l a t e Wisconsinan i n age and are correlated with deposits of middle and l a t e Pinedale age.  They include t i l l ,  glacio-  f l u v i a l sand and g r a v e l , and g l a c i o l a c u s t r i n e c l a y , s i l t , and sand.  The t i l l  (up to 44 m thick) i s massive diamicton similar i n  color and texture to t i l l of the older drift  (Appendix 3),  The younger  19  Table 1. Bedrock units in and adjacent to the study area (from Leech, 1954, 1958; Price, 1962).  MESOZOIC and (?) CENOZOIC 1  Era  System or Series  Lithologies  Croup or Formation  Lower Cretaceous and (?) l a t e r  Monzonite, quartz monzonite, granodiorite Not i n contact  Lower Cretaceous  Blairmore Group •  Shale, mudstone, sandstone, conglomerate  MESOZOIC  Unconformity Lower Cretaceous and Jurassic  Kootenay Formation  Shale, s i l t s t o n e  sandstone  conglomerate, coal  Juras i c  Fernie Group  Shale, s i l t s t o n e  sandstone  limestone  Shale, s i l t s t o n e  dolomltic s i l t s t o n e  Disconformity Trias  Spray River Formation Unconformity  Permian and Pennsylvanian  Mississippian •  Upper Devonian •  Rocky Mountain Foraatlo  S i l t s t o n e , sandstone, dolomitlc sandstone, sandy dolostone and limestone, chert  Rundle Group  Limestone, c r l n o l d a l and cherty In part  Banff Formation  Limy s i l t s t o n e , limeptone, s i l t y limestone, cherty limestone  Exshaw Formation  Shale, limestone  P a l l i s e r Formation  Upper member: limestone  argillaceous limestone; Lower (main) member:  Alexo Formation  Sandstone, sandy and argillaceous limestone  Falrholme Group  Upper part: shale, limestone; Lover part: limestone, s t r o m a t o l i t l c and c o r a l l i n e i n part; dolostone  Middle Devonian  Harrogate Formation  Shale, limestone, argillaceous limestone  Middle Devonian or e a r l i e r  Burnais Formation  Limestone, dolostone, gypsum  Middle Devonian or e a r l i e r and (?) Upper Devonian  Basal Devonian unit  Shale, sandstone, dolomltic sandstone, conglomerate, dolostone sandy dolostone  Middle(?) and Lower S i l u r i a n , Upper Ordovlclan  Beaverfoot-Brlsco Formation  Upper or Middle Ordovlclan  Wonah Formation  HiddleC?) and Lower Ordovlclan  Glenogle Formation  Shale, s i l t s t o n e , limestone  Lover Ordovlclan and Upper Cambrian  McKay Group  Shale, limestone, intraformational limestone-conglomerate  Upper and/or Middle Cambrian  Jubilee and Elko Formations  Unconformity Limestone, dolostone; thin shale near top; sandstone and conglomerate l o c a l l y at base Disconformity?  Unconformity?  Dolostone Disconformity?  Middle Cambrian  Burton Formation  Shale, sandstone, conglomerate, limestone  Middle(?) and Lover Cambrian  Eager Formation  Shale, s i l t s t o n e , sandstone, limestone  Lower Cambrian  Cranbrook Formation  Sandstone, conglomerate Unconformity  Horsethief Creek Series Windermere  A r g i l l i t e , conglomerate  Toby Formation  A r g i l l i t e , conglomerate Unconformity  Upper Purcell or ( ) later  Moyie intrusions  D i o r i t e ; quartz gabbro  Intrusive contact between Moyie intrusions and some Upper Purcell strata Mount Nelson Formation  A r g i l l i t e , sandstone, dolostone 'Roosville Formation  Upper P u r c e l l -  Dutch Creek _ Formation  P h i l l i p s Formation .Gateway Formation  Kitchener Formation* (west of Trench)  Siyeh Formation* (east of Trench)  Creston Formation  Lover P u r c e l l -  Aldridge Formation (west of Trench)  •Kitchener and Siyeh Formations are only i n part equivalent.  A r g i l l i t e , s i l t s t o n e , sandstone, limestone, dolostone A r g i l l i t e , s i l t s t o n e , sandstone A r g i l l i t e , dolomitlc a r g i l l i t e , s i l t s t o n e , dolomltic s i l t s t o n e sandstone, dolostone A r g i l l i t e , dolomltic a r g i l l i t e , sandstone, dolostone, sandy dolostone; andesitic lava and tuff at top A r g i l l i t e , sandstone, argillaceous sandstone  I 1 I L  Aldridge Formation (east of Trench) , Fort Steele FormatL (east of Trench)  A r g i l l i t e , sandstone, argillaceous sandstone A r g i l l i t e , dolomitlc a r g i l l i t e , sandstone, argillaceous sandstone, dolostone  20  t i l l i s somewhat more clayey and s i l t y near i t s base, probably due to the  incorporation of underlying fine-grained inter-drift  sediments.  Clasts are subangular to subrounded, striated, and of a variety of rock types cropping out in and near the study area. The t i l l is calcareous except where derived entirely from the Purcell Mountains.  A detailed  study of t i l l composition is presented and discussed in Chapter 3. is underlain by either advance outwash gravel or inter-drift sand.  At some localities inter-drift  without a sharp break. between the two.  Till  s i l t and  sediments grade upward into t i l l  More commonly, there is a pronounced unconformity  Some thick t i l l exposures may include both older and  younger t i l l s with no intervening stratified sediments. Glaciofluvial sediments, consisting mainly of sandy gravel, occur locally beneath the younger t i l l (advance outwash), as lenses within the t i l l (englacial and subglacial outwash), and as channel and valley train deposits overlying the t i l l sheet (recessional outwash). Thickness of glaciofluvial sediments i s highly variable, but is greatest along the margins of the Trench off tributary valleys and near the axis of the Trench along what i s now the valley of Kootenay River, These were the sites of major meltwater drainage during and immediately following glaciation.  A bedrock channel along the east side of the  Trench just south of Elko contains 40 m of outwash.  South of Sheep  Mountain, very poorly sorted subglacial outwash is as much as 52 m thick and occupies much the same stratigraphic position as t i l l in the central part of the Trench. is thin or absent.  Where younger t i l l is thickest, underlying outwash The spotty occurrence of advance outwash is due  either to restriction to meltwater channels or subsequent erosion by ice.  Figure 6. Map of Bouguer gravity in the southern Rocky Mountain Trench, and gravity profiles and inferred geologic sections across the Trench (from Thompson, 1962).  22  Figure 7. Thickness of Quaternary sediments. Areas where bedrock is at or near the surface inside the dotted line are stippled; areas of thick Quaternary sediments inside the dotted line are unpatterned. The d r i l l hole data were provided by the Water Resources Branch of the British Columbia Department of Lands, Forests, and Water Resources. Seismic records were supplied by Shell Canada Ltd.  23  24  Likewise, recessional outwash is thickest beneath meltwater channels, valley trains, and kame terraces which dissect the drumlinized  till  plain on the Trench floor. Gravel outwash, deposited in high-energy, proglacial river channels, consists largely of pebbles and cobbles and a matrix of sand. Clasts are well rounded, and sorting and stratification vary with amount of water-working prior to deposition.  The more poorly sorted and weakly  stratified glaciofluvial gravels probably represent proximal ice-contact deposits, worked by water to only a minor degree.  Other gravels are  better sorted and stratified, reflecting greater fluvial transport. Imbrication in the latter shows that meltwater drainage was in a southerly direction, much as the present  drainage.  Sand outwash, representing low-energy river or backwater deposits in meltwater channels, is most common as a thin layer over gravel outwash along the axial part of the Trench.  Some discontinuous  sand beds are associated with gravel outwash beneath and within the  younger t i l l . The sedimentology and paleohydrology  of recessional glaciofluvial  sediments are considered in detail in Chapter 4. Glaciolacustrine clay, s i l t , and sand occur along the Trench margins and i n tributary valleys at two stratigraphic levels within the  younger drift:  (1) i n t r a - t i l l glaciolacustrine sediments, and (2) supra-  t i l l glaciolacustrine sediments.  25  ENVIRONMENT OF DEPOSITION c i PROGLACIAL  •n--.&.o:<V9.-'  i  Glaciolacustrine, glaciof luvial  GLACIAL  at  I  2 PROGLACIAL • • •  a • • •  • •a  Glaciolacustrine  PROGLACIAL  Glaciof luvial  GLACIAL •  • • • • • • •  trtf  sS Ou  g| 5 £ ul Z <« • • • • • • •  i  Q.*0  O  Cf.JD  C] .0 #  • •  •  »p  • •.•fl'.p •**• q»M*.p •"  ££££  PROGLACIAL  Glaciof luvial  PROGLACIAL and (?) NONGLACIAL  Glaciolacustrine and (?) lacustrine  PROGLACIAL, SUPRAGLACIAL  Glaciof luvial  GLACIAL NONGLACIAL  Fluvial and (?) lacustrine Fluvial  NONGLACIAL  Locustrine, fluvial Mass movement and mudflow deposition  !•••••[ COLLUVIUM, FANGLOMERATE  •  RADIOCARBON DATE —  STRATIFIED GRAVEL  h/o.O-.'^UV-l TILL  CLAY, SILT, SAND  26,800 ± 1000  'GLACIOLACUSTRINE SEDIMENTS PRESENT IN TRIBUTARY VALLEYS. 2  SEDIMENTS PRESENT ALONG TRENCH MARGINS.  ^SEDIMENTS PRESENT IN ROCKY MOUNTAIN TRENCH NEAR TRIBUTARY VALLEYS.  Figure 8. Composite columnar section of late Cenozoic sediments exposed in the southern Rocky Mountain Trench. Column heights are proportional to the maximum exposed thickness of each unit.  26  Figure 9. The St. Eugene Formation. A.  Colluvium, Elk River.  B and C. Fanglomerate, Elk River. D. Laminated organic-rich s i l t , sand, and gravel, St. Mary River. E. Laminated organic-rich s i l t , St. Mary River. F.  Coarse gravel, St. Mary River.  27  Figure 9  28  Figure 10. Interglacial sediments, Sand Creek. A.  Interbedded sand and gravel overlain by s i l t and sand.  B and C.  Interbedded sand and gravel containing fragments of wood.  D.  Gravel consisting of well-rounded pebbles in a s i l t and sand matrix.  E.  Cross-bedded gravel.  F.  Contact between interglacial sediments and overlying t i l l .  29  F i g u r e 10  30  I n t r a - t i l l g l a c i o l a c u s t r i n e sediments are massive and rhythmic a l l y bedded c l a y , s i l t , and sand occurring along the margins of the Rocky Mountain Trench s t r a t i g r a p h i c a l l y above inter-drift within the younger t i l l .  sediments, but  The sediments crop out near St. Mary Valley  (up to 16 m thick) along the west side of the Trench, and near E l k Valley (up to 28 m thick) along the east s i d e , but are absent as a d i s t i n c t unit i n c e n t r a l Trench exposures.  Instead, at the same s t r a t i -  graphic l e v e l are discontinuous i n t r a - t i l l lenses of ice-contact sand and g r a v e l , and coarse channel f i l l .  Although the g l a c i o l a c u s t r i n e unit  along the Trench margins cannot be continuously traced l a t e r a l l y into the coarse outwash pockets at the center of the Trench, i t i s believed that the two are genetically r e l a t e d , the former representing deposits in water ponded behind sediment or i c e dams, and the l a t t e r deposits beneath or near remnant i c e masses i n the central part of the Trench. I n t r a - t i l l g l a c i o l a c u s t r i n e sediments were deposited i n ice-marginal lakes during an i n t e r v a l of g l a c i e r recession.  This i n t e r v a l i s  tentatively correlated with the interstade separating the middle and l a t e stades of the Pinedale Glaciation ( F i g . 11).  Trench-marginal  g l a c i o l a c u s t r i n e deposition during this i n t e r v a l contrasts with Trenchwide deposition of inter-drift  sediments during an e a r l i e r interstade  when the entire f l o o r of the Rocky Mountain Trench i n the study area was temporarily free of i c e .  S u p r a - t i l l g l a c i o l a c u s t r i n e sediments were deposited i n i c e dammed lakes i n the major tributary v a l l e y s during f i n a l deglaciation of the southern Rocky Mountain Trench.  The sediments, i n general, are  31  RADIOCARBON YEARS B.P.  SOUTHWESTERN BRITISH COLUMBIA WESTERN WASHINGTON  ROCKY MOUNTAINS  .BRIDGE RIVER ASH FALL. -ST. HELENS Y ASH FALL•MAZAMA ASH FALL-  Z  10,000—r^-,  Sumas Stade  o  20,000-  o  Everson Interstade  <  Io  . M A Z A M A ASH FALL-  Vashon Stade  Late stade Interstade -GLACIER PEAK ASH F A l l -  §  Middle stade  o  Evans Creek Stade  Ul  Interstade  Ul  Early stade  3 Z a!  INTERGLACIATION  30,000— OLYMPIA  INTERGLACIATION  'Second glacial episode  40,000—  Nonglacial interval  <  Younger glacial episode  Nonglacial  z  interval  Older glacial episode  Z O  §  Late stade  _  Nonglacial  First glacial episode  interval  Early stade  10  o  Figure 11. Chronology and correlation of late Pleistocene events in the Pacific Northwest and the Rocky Mountains of the United States (from Crandell, 1965; Richmond, 1965).  Figure 12.  Older  drift.  A.  T i l l , Elk River.  B.  Glaciofluvial gravel partially cemented by calcium carbonate, near confluence of Kootenay and Elk Rivers.  C.  Deformed glaciofluvial sand and gravel overlain by younger t i l l , Sand Creek.  D.  High-angle faults and fractures in outwash, St. Mary River (see also Fig. 13). Sand and gravel are partially cemented by calcium carbonate.  33  34  Figure 13. Attitudes of beds, faults, and fractures in deformed outwash of the older drift. Top: index map showing the location of the deformed outwash and the attitudes of beds. Bottom right: equal-area projection of poles to fault, fracture, and bedding planes. Bottom l e f t : contoured diagram of poles to fault and fracture planes (contours approximately 3-8-13% per 1% area).  35  49"36'N  40°34'N  KILOMETERS  FAULT AND FRACTURE LOCALITIES  F  FAULT OR FRACTURE  •  STRATIFICATION  Figure 13  w  "-"^. •  36  Figure 14.  Inter-drift  sediments.  A and B. Contact between inter-drift River.  sediments and younger t i l l , Elk  C.  Basal inter-drift  D.  Thick-bedded s i l t with a blocky fracture pattern, Elk River.  sand and dropstones, St. Mary River.  E and F. Interlaminated s i l t and sand, Elk River. The uppermost s i l t and sand laminae i n F were scoured and incorporated as clasts i n the overlying sand.  Figure 14  38  Figure 15. A.  Younger  drift.  Advance outwash gravel underlying younger t i l l , Elk River.  B and C.  T i l l , St. Mary River.  D.  I n t r a - t i l l sand, St. Mary River.  E.  I n t r a - t i l l g r a v e l , St. Mary River.  F.  S u p r a - t i l l rhythmically-bedded s i l t and sand, St. Mary River.  G and H. Gravel underlying late g l a c i a l meltwater channel, Kootenay River near Kikomun Creek.  39  40  Figure 16. P o s t g l a c i a l sediments and landforms. A.  E o l i a n sand overlying outwash gravel, Kootenay River near Kikomun Creek.  B.  A l l u v i a l fan, near Grasmere.  C and D. Mudflow gravel of an a l l u v i a l fan b u i l t out onto the present Kootenay flood p l a i n south of Wasa Lake. Mazama 0 tephra i s the l i g h t layer at the t i p of the shovel i n D. E.  P o s t g l a c i a l canyon of B u l l River.  F.  Kootenay River flood p l a i n and alluvium, near Kikomun Creek.  41  Figure 16  42  rhythmically laminated and contain dropstones. They exceed 50 m i n thickness i n St. Mary Valley and occur at least as high as 980 m above sea  level.  In Elk Valley, late glacial lake sediments crop out to  about 1360 m above sea level.  S i l t and fine sand were also deposited  in shallow ponds on the floor of the Trench during deglaciation. Although widespread, the sediments are thin (1 to 15 m in thickness). Deltas of coarse gravel formed where meltwater streams entered late glacial lakes and ponds.  Postglacial Sediments Postglacial deposits (Fig. 16) include loess, dune sand, colluvium, and alluvium.  Loess and eolian sand up to 1 m thick form a surface  mantle over much of the study area.  Surface sand in some meltwater  channels and drained ponds has been reworked by wind into small dunes. Talus cones, alluvial fans, and thin colluvial mantles occur along the margins of the Trench and major river valleys (Fig. 5). Degradation by rivers and streams began during or shortly after deglaciation.  The rivers have since cut down through sediments and bedrock  alike and have left multiple terraces bordering their valleys. Beneath the terraces interstratified sand and gravel are inset on older sediments.  These terrace sediments were deposited during an interval  of rapid downcutting following deglaciation and are thus very late Pleistocene or early Holocene in age.  The main evidence for this i s :  (1) the occurrence of 6600-year-old Mazama 0 tephra (glass analyses by J.A. Westgate, Department of Geology, University of Alberta) i n alluvial  43  fans graded to alluvium of the present Kootenay River flood p l a i n , and (2) the presence of kettled terraces at Wasa Lake which are only 5 to 10 m above the present flood p l a i n (Figs. 2 and 5 ) .  44  LITERATURE CITED Alden, W.C, 1948, Pleistocene glaciation, in Gibson, Russell, Geology and ore deposits of the Libby Quadrangle, Montana: U.S. Geol. Survey Bull. 956, p. 49-61. 1953, Physiography and glacial geology of western Montana and adjacent areas: U.S. Geol. Survey Prof. Paper 231, 200 p. Armstrong, J.E., Crandell, D.R., Easterbrook, D.J., and Noble, J.B., 1965, Late Pleistocene stratigraphy and chronology in southwestern British Columbia and northwestern Washington: Geol. Soc. America Bull., v. 76, p. 321-330. Bauerman, Hilary, 1884, Report on the geology of the country near the forty-ninth parallel of north latitude west of the Rocky Mountains: Canada Geol. Survey Rept. Prog. 1882-83-84, rept. B, p. 1-42. Berry, E.W., 1929, The age of the St. Eugene s i l t in the Kootenay Valley, British Columbia: Royal Soc. Canada Trans., ser. 3, sec. 4, v. 23, p. 47-48. Crandell, D.R., 1965, The glacial history of Washington and Oregon, in Wright, H.E., Jr., and Frey, D.G., eds., The Quaternary of the United States: Princeton, New Jersey, Princeton Univ. Press, p. 341-353. Crickmay, C.H., 1964, The Rocky Mountain Trench: Jour. Earth Sci., v. 1, p. 184-205.  a problem:  Canadian  Daly, R.A., 1912, Geology of the North American Cordillera at the fortyninth parallel: Canada Geol. Survey Mem. 38, 857 p. Davis, W.M., 1921, Features of glacial origin in Montana and Idaho: Assoc. Am. Geographers Annals, v. 10, p. 75-147. Dawson, G.M., 1885, Preliminary report on the physical and geological features of that portion of the Rocky Mountains between l a t i tudes 49° and 50°30': Canada Geol. Survey Ann. Rept,, v. 1, rept. B, p. 1-169. 1890, On the later physiographical geology of the Rocky Mountain region in Canada, with special reference to changes in elevation and to the history of the glacial period: Royal Soc. Canada Trans., ser. 2, sec. 4, v. 8, p. 3-74. Fulton, R.J., 1971, Radiocarbon geochronology of southern British Columbia: Canada Geol. Survey Paper 71-37, 28 p.  45  Garland, G.D., Kanasewich, E.R., and Thompson, T.L., 1961, Gravity measurements over the southern Rocky Mountain Trench area of British Columbia: Jour. Geophys. Research, v. 66, p. 24952505. Goddard, E.N., Trask, P.D., DeFord, R.K., Rove, O.N., Singewald, J.T., Jr., and Overbeck, R.M., 1963, Rock-color chart: Boulder, Colorado, Geol. Soc. America. Hershey, O.H., 1912, Some Tertiary and Quaternary geology of western Montana, northern Idaho, and eastern Washington: Geol. Soc. America Bull., v. 23, p. 517-536. Holland, S.S., 1964, Landforms of British Columbia, a physiographic outline: British Columbia Dept. Mines and Petroleum Resources Bull. 48, 138 p. Hollick, Arthur, 1914, A preliminary report by Mr. Arthur Hollick of the New York Botanical Garden, upon plants from the Pleistocene deposits: Canada Geol. Survey Summ. Rept., 1913, p. 133-135. 1927, The flora of the Saint Eugene s i l t s , Kootenay Valley, British Columbia: New York Bot. Garden Mem., v. 7, p. 389-465. Johns, W.M., 1970, Geology and mineral deposits of Lincoln and Flathead Counties, Montana: Montana Bur. Mines and Geology Bull. 79, 182 p. Kelley, C.C., and Sprout, P.N., 1956, Soil survey of the upper Kootenay and Elk River valleys in the East Kootenay district of British Columbia: British Columbia Soil Survey Rept. 5, 99 p. Lamb, A.T., and Smith, D.W., 1962, Refraction profiles over the southern Rocky Mountain Trench area of British Columbia: Alberta Soc. Petroleum Geologists Jour., v. 10, p. 428-437. Leech, G.B., 1954, Canal Flats, British Columbia: Paper 54-7, 32 p. 1957, St. Mary Lake, British Columbia: 15-1957.  Canada Geol. Survey Canada Geol. Survey Map  1958, Fernie map-area, west half, British Columbia: Geol. Survey Paper 58-10, 40 p. 1959a, Canal Flats, British Columbia: 24-1958.  Canada  Canada Geol. Survey Map  1959b, The southern part of the Rocky Mountain Trench: Canadian Mining Metall. Bull., v. 52, p. 327-333.  46  1960, Fernie, west h a l f , B r i t i s h Columbia: Map 11-1960. 1966, The Rocky Mountain Trench: 66-14, p. 307-329.  Canada Geol. Survey  Canada Geol. Survey Paper  McDonald, B.C., and S h i l t s , W.W., 1973, Interpretation of faults i n g l a c i o f l u v i a l sediments, in J o p l i n g , A.V., and McDonald, B.C., eds., G l a c i o f l u v i a l and g l a c i o l a c u s t r i n e sedimentation: Soc. Econ. Paleontologists and Mineralogists Spec. Pub. ( i n press). Pardee, J.T., 1910, The G l a c i a l Lake Missoula: p. 376-386.  Jour. Geology, v. 18,  1942, Unusual currents i n G l a c i a l Lake Missoula, Montana: Soc. America B u l l . , v. 53, p. 1569-1600.  Geol.  1948, Physiography, in Gibson, R u s s e l l , Geology and ore deposits of the Libby Quadrangle, Montana: U.S. Geol. Survey B u l l . 956, p. 61-67. 1950, Late Cenozoic block f a u l t i n g i n western Montana: Soc. America B u l l . , v. 61, p. 359-406.  Geol.  P r i c e , R.A., 1962, Fernie map-area, east h a l f , Alberta and B r i t i s h Columbia: Canada Geol. Survey Paper 61-24, 65 p. Rice, H.M.A., 1936, G l a c i a l phenomena near Cranbrook, B r i t i s h Columbia: Jour. Geology, v. 44, p. 68-73. 1937, Cranbrook map-area, B r i t i s h Columbia: Survey Mem. 207, 67 p.  Canada Geol.  Richmond, G.M., 1965, Glaciation of the Rocky Mountains, in Wright, H.E., J r . , and Frey, D.G., eds., The Quaternary of the United States: Princeton, New Jersey, Princeton Univ. Press, p. 217-230. Richmond, G.M., F r y x e l l , Roald, Neff, G.E., and Weis, P.L., 1965, The C o r d i l l e r a n Ice Sheet of the Northern Rocky Mountains, and related Quaternary history of the Columbia Plateau, in Wright, H.E., J r . , and Frey, D.G., eds., The Quaternary of the United States: Princeton, New Jersey, Princeton Univ. Press, p. 231242. Schofield, S.J., 1915, Geology of the Cranbrook map-area, B r i t i s h Columbia: Canada Geol. Survey Mem. 76, 245 p. 1920, The o r i g i n of the Rocky Mountain Trench, B.C.: Canada Trans., s e r . 3, sec. 4, v. 14, p. 61-97.  Royal Soc.  Thompson, T.L., 1962, Origin of the Rocky Mountain Trench i n southeastern B r i t i s h Columbia by Cenozoic block f a u l t i n g : Alberta Soc. Petroleum Geologists Jour., v. 10, p. 428-437.  47  CHAPTER TWO: THE ST. EUGENE FORMATION AND THE DEVELOPMENT OF THE SOUTHERN ROCKY MOUNTAIN TRENCH ABSTRACT  The Tertiary history of the southern Rocky Mountain Trench i s inferred from a study of the d i s t r i b u t i o n , stratigraphy, f a b r i c , l i t h o l o g i c composition, structure, and palynology of the Miocene St. Eugene Formation i n southeastern B r i t i s h Columbia.  The S t . Eugene Formation consists of flood-plain and fan facies and represents the upper part of up to about 1500 m of sediments which accumulated i n the proto-Rocky Mountain Trench upon cessation of Laramide deformation and after i n i t i a t i o n of extension and block f a u l t i n g i n the eastern C o r d i l l e r a during Eocene or early Oligocene time.  Deep  T e r t i a r y basins i n the southern Rocky Mountain Trench are bounded on the east and west by high-angle f a u l t s p a r a l l e l to the Trench margins and on the north and south by faults transverse to the trend of the Trench. Block f a u l t i n g of a half-graben s t y l e was probably contemporaneous with sediment deposition, but at least 600 m of displacement on the east boundary f a u l t postdates deposition of the S t . Eugene Formation. Although there i s no present seismic a c t i v i t y along the Rocky Mountain Trench north of l a t i t u d e 49°N, Holocene f a u l t scarps and earthquakes i n a zone along the Rocky Mountains of the United States attest to the continuation of block f a u l t i n g south of 49°N.  48  The St. Eugene microflora includes at least 39 genera of ferns, gymnosperms, and anthophytes.  Phytogeographic reconstruction based upon  the habitats of extant counterparts indicates floral elements growing on poorly drained lowlands, adjacent slopes, and montane uplands; thus, there was moderate to high relief in southeastern British Columbia during St. Eugene time.  The climate apparently was temperate, with warm summers,  mild winters, and abundant, uniformly distributed precipitation.  This  contrasts with the present climate of the southern Rocky Mountain Trench which i s semiarid with hot summers and cold winters, and suggests that the mountain barriers which presently restrict cool, moist, Pacific maritime air masses to the coast were lower during the Miocene, or that the polar seas were relatively warm.  INTRODUCTION The Rocky Mountain Trench i s a long, narrow, intermontane valley that extends northwest from Montana through British Columbia.  The  origin of this major topographic feature has been long debated; various theories, summarized by Eardley (1951, p. 317-318), North and Henderson (1954), and Crickmay (1964), include the formation of the Trench by erosion without faulting and by erosion along a fault zone.  Recent work  (Garland and others, 1961; Lamb and Smith, 1962; Thompson, 1962) documents the presence of deep, sediment-filled, bedrock depressions in the southern Rocky Mountain Trench.  Leech (1966) has emphasized that these basins are  tectonic i n origin, having formed by half-graben block faulting following Cretaceous to Paleocene (?) thrusting.  The present configuration of the  Trench results from sediment i n f i l l i n g of these tectonic depressions,  49  glaciation, and Holocene erosion. These conclusions are supported by evidence for Cenozoic block faulting in northwestern Montana (Pardee, 1950;  Johns and others, 1963; Johns, 1970) and Tertiary sedimentation  controlled by block faulting in the Flathead Valley parallel to and east of the southern Rocky Mountain Trench (Price and Wise, 1959; Barnes, 1963;  Price, 1966). The continuity of the Trench for over 600 km indicates that  i t i s located along a major zone of crustal weakness, perhaps an ancient continental margin (Thompson, 1962; Price and Mountjoy, 1970; Berry and others, 1971). The nature of the structural control undoubtedly differs along the length of the Trench; although block faulting characterizes the southern part, other types of deformation may have affected the region of the Trench to the north. Further information on the Cenozoic tectonics of southeastern British Columbia has been gained by a study of late Tertiary sediments in the Rocky Mountain Trench. This paper describes these sediments, termed the St. Eugene s i l t s by Schofield (1915), and discusses their implications regarding late Tertiary tectonics, paleogeography, and paleoclimatology.  DISTRIBUTION AND CHARACTER OF THE ST. EUGENE FORMATION The St. Eugene s i l t s were defined by Schofield as s i l t , sand, and gravel underlying t i l l of the last glaciation along St. Mary River between Wycliffe and St. Eugene Mission.  So defined, the St. Eugene s i l t s  occur widely i n the Rocky Mountain Trench and are exposed i n the major  50  river valleys beneath late Wisconsinan d r i f t , but the unit i s a grouping of diverse geologic-climatic subunits of different ages.  Schofield  assigned the sediments to the "St. Eugene interglacial (?) epoch," although he thought a "pre-Glacial" age possible. A collection of f o s s i l leaves from stratified s i l t near the base of Schofield's St. Eugene unit was examined by Hollick (1914, 1927), who thought the flora to be Tertiary in age. St. Eugene flora in the Miocene Epoch.  Berry (1929) placed the  Rice (1937) then redefined the  St. Eugene s i l t s as s i l t , sand, and gravel of Miocene age underlying a l l glacial and interglacial deposits. He l i s t s four l o c a l i t i e s , a l l along St. Mary River in the vicinity of Wycliffe and St. Eugene Mission, where these sediments are exposed. The unit i s here raised to formational rank in recognition of equivalent exposures along St. Mary River, Elk River, and Gold Creek (Fig. 17). Stratigraphic sections including the St. Mary River type locality sections are presented in Figure 18. The St. Eugene Formation unconformably overlies bedrock of Precambrian and Paleozoic age along the margins of fault-bounded basins, conformably (?) overlies sediments of Tertiary age near the basin centers, and i s overlain by Pleistocene sediments. The following types of sediment constitute the St. Eugene Formation:  (1) colluvium and fanglomerate, (2) stratified s i l t and sand,  and (3) coarse gravel with minor sand interbeds (Fig. 19). In general, colluvium and fanglomerate are the oldest exposed sediments, and coarse gravel the youngest. A palynomorph assemblage from stratified s i l t and sand of the St. Eugene Formation i s considered to be Miocene in age.  51  Colluvium and Fanglomerate Colluvium and fanglomerate are the lowest exposed sediments of the St. Eugene Formation. Colluvium crops out above bedrock along the valley walls of St. Mary, Kootenay, and Elk Rivers; fanglomerate i s present above bedrock and colluvium along Gold Creek and Elk River (Figs. 17 and 18).  St. Eugene colluvium is over 10 m thick i n some St. Mary  River exposures, and fanglomerate is at least 18 m thick at some Elk River sites. Colluvium consists of poorly sorted, weakly stratified, angular debris in a clay-silt matrix.  Most of the sediment comprises clasts of  one or a few lithologies which crop out nearby. For example, St. Eugene colluvium east of St. Eugene Mission consists of shale, siltstone, and sandstone derived from nearby Paleozoic bedrock. The colluvium is rock debris carried mainly by gravity to the base of h i l l s or ridges. Fanglomerate (i.e., indurated alluvial fan sediment) also i s a debris accumulation at the foot of a slope, but is deposited from mudflows or flowing water. Like the colluvium, i t is poorly sorted, consisting of clasts up to 1 m in diameter i n a clay- and s i l t - r i c h matrix.  Stratifica-  tion is defined by discontinuous s i l t and sand beds. Many of the larger clasts are well rounded, but granules and small pebbles are commonly angular to subrounded. Sorting and clast roundness increase upward i n fanglomerate exposures, presumably due to increased water-working of sediments during transportation and deposition. The only observed sedimentary structures other than discontinuous parallel stratification are  52  channels cut into, and f i l l e d with, fanglomerate. Colluvium and fanglomerate are distinguishable from other sediments in the Trench by their colors. Hues are generally brown, orange, or yellow (5YR, 10YR,  5Y), and values are above 5.  1  In contrast, glacial  deposits are light gray to very light gray (N 7 to N 8).  The coloring  of the colluvium and fanglomerate is thought to be due to the presence of iron oxide formed during weathering.  Lengthy or intense weathering  is also indicated by probable paleosols, rotten clasts, and secondary (?) clay.  About 3 km northeast of St. Eugene Mission colluvium crops out  along the north valley wall of St. Mary River and is overlain by St. Eugene s i l t and sand.  Below the contact is a probable paleosol. The uppermost  2 m of colluvium are light brown to moderate orange pink (5YR 6/4 to 5YR 8/4), whereas the underlying colluvium is yellowish gray or grayish orange (5Y 7/2 or 10YR 7/4).  This difference may be due to more intense  weathering of shale and siltstone clasts in the upper part of the unit. Soil horizons in the paleosol are not well developed; eluvial and i l l u v i a l zones and horizon structures, i f present, are indistinct.  Brownish-gray  (5YR 4/1) cemented zones (pans) up to 3 cm thick are laterally discontinuous with wavy boundaries.  Although present throughout the vertical  range of the exposure, the largest number and best developed pans are in the upper few meters of colluvium.  These s o i l characteristics are similar  to those of some soils which form in subtropical regions (for example, see Bennema, 1963).  Colors are from Rock-color Chart (Goddard and others, 1963).  53  Stratified S i l t and Sand The middle unit of the St. Eugene Formation i s stratified s i l t and sand. At Gold Creek and St. Mary River these sediments overlie colluvium and fanglomerate and are overlain by coarse St. Eugene gravel or d r i f t ; s i l t and sand are interstratified with fanglomerate along Elk River (Figs. 17 and 18). The unit i s over 18 m thick i n some St. Mary River exposures, but i s less than 4 m thick along Gold Creek and Elk River. The unit consists of gently dipping beds of very light-gray to bluish-white (N 8 to 5B 8/1) s i l t and sand with abundant plant remains i n places.  Interbeds of well-sorted, well-rounded gravel are uncommon,  although along St. Mary River the unit i s locally underlain by such gravel.  Parallel stratification i s the most common sedimentary structure;  large-scale trough cross-stratification i s rare.  The sediment probably  accumulated i n lakes or backwater ponds on flood plains, with the gravel layers representing higher energy channel deposits.  Coarse Gravel with Minor Sand Interbeds The uppermost unit of the St. Eugene Formation i s coarse gravel. It overlies fine-grained St. Eugene sediment across a sharp, unconformable (?) contact i n eastern St. Mary River exposures and at Gold Creek, but correlative gravel i s absent elsewhere (Figs. 17 and 18). However, similar but finer gravel underlies s i l t and sand both northeast and northwest of St. Eugene Mission. Also, St. Eugene fanglomerate exposed along Elk  54  River is characterized by better sorting and higher clast roundness near the stratigraphic top of the unit, where i t approaches the coarse gravel in texture.  Maximum observed thickness of the unit is about 35 m.  The unit consists of well-sorted, stratified gravel with minor sand layers. Gravel clasts, which are as large as 1 m in diameter, are well rounded and highly weathered (most are stained by iron oxide, many are rotten). A matrix of medium- to coarse-grained sand surrounds the clasts.  The sediment was deposited in river channels under high-energy  conditions.  PROVENANCE OF ST. EUGENE FANGLOMERATE Analytical Procedure Provenance of the St. Eugene Formation was determined from the fabric and lithologic composition of fanglomerate.  Fan-fabric Analysis Elongate or plate-shaped particles transported in a viscous medium can assume a preferred orientation which is a function in part of the nature of the medium, particle shape, the terrain over which the particles are transported, and other external interactions with the medium. For sedimentary particles, preferred orientations developed during transport may be altered during or after deposition. The occurrence of oriented fabrics in t i l l is well documented, although an understanding of the means by which glacier ice produces such  55  fabrics i s s t i l l incomplete. Nevertheless, t i l l fabrics have been used extensively to determine the flow directions of former glaciers (e.g., Holmes, 1941; West and Donner, 1956; Wright, 1957; Andrews and Smith, 1970; Lineback, 1971).  Clasts can also become strongly oriented by  flowing water as indicated by the common occurrence of clast imbrication in river channels. Lindsay (1968) has shown on theoretical grounds that strongly directed fabrics are also produced by mudflows. The extremely poor sorting, abundant clay and s i l t matrix, and discontinuous, weak stratification indicate that much of the St. Eugene fanglomerate was deposited by mudflows. Late glacial and early postglacial alluvial fans are prominent landforms i n the interior valleys of southern British Columbia.  paraglacial  These  fans (Ryder, 1971) formed from reworked drift deposited by  streams and mudflows during final deglaciation of the Interior.  Although  differing somewhat in origin, St. Eugene fanglomerate is texturally similar to sediment of the paraglacial alluvial fans.  Method. The fabric of a paraglacial alluvial fan in southwestern British Columbia was determined as a model for St. Eugene fanglomerate (Fig. 20). The fan was selected because of continuous exposures of mudflow gravel along an arc about the source, and because the surface morphology of the fan defined the transport direction of the sediment. At each of four fabric sites, 2 to 4 m below the surface of the fan, the trend and plunge of 60 elongate pebbles {alb > 2, b/c - 1, a > 1 cm) were  56  measured.  Data were plotted on an equal-area net and contoured according  2  to the method reviewed by Ragan (1968, p. 79-82).  A spherical probability  distribution applicable to three-dimensional data was used to determine axes of maximum and minimum clustering for each fabric (Mark, 1973). Each data set was tested for randomness by using significance tests based on this distribution (Anderson and Stephens, 1971). The fabric of St. Eugene fanglomerate at Gold Creek and Elk River was determined by this procedure. Each fabric consists of 20 or 60 individual measurements; i t was found that mean vectors of smaller samples are similar to those of larger samples from the same populations for strongly oriented fabrics, but generally not for weak fabrics (Fig. 21). Andrews and Smith (1970, p. 520-521) have shown that for their t i l l - f a b r i c samples of size 25, 50, and 100, the smaller samples exhibit the main characteristics of the larger samples, and standard deviation does not increase with decreasing sample size.  Results.  The data from the paraglacial alluvial fan are  presented in Appendix 4, and the results in Figure 20.  Mean vectors are  approximately parallel to the direction of transport and plunge up-fan. The mean vector of fabric no. 1 i s parallel to the transport direction of a small fan just east of site no. 1; the gravel was probably deposited by mudflows originating at the apex of this fan. The data from St. Eugene fanglomerate are shown in Appendix 4,  The long, intermediate, and short axes of clasts are called the a, b, and c axes respectively. z  57  and the results, including maximum clast size, are plotted in Figure 22. Mean vectors from Elk River sites trend and plunge northeast toward the north end of the Galton Range. Gold Creek fan fabrics are weaker than those along Elk River and trends of mean vectors are variable.  Clast Lithology Analysis The Purcell Mountains in the vicinity of Gold Creek and the Galton Range are underlain mainly by Precambrian sedimentary and igneous rocks (Fig. 23). areas.  Paleozoic sedimentary rocks crop out north of these  The sedimentary rocks are quartz arenite, s i l t i t e , a r g i l l i t e , i n  part dolomitic, dolostone, and minor limestone; mainly andesitic lavas.  the igneous rocks are  In the Galton Range these rocks strike north  parallel to the range front and dip moderately to the east.  Igneous rocks  crop out i n a single zone at elevations ranging from 910 to over 1500 m. Along the west margin of the Trench, near Gold Creek, sedimentary and igneous rocks are folded and offset along a series of steeply dipping, northwest-striking faults.  Method. Clast lithologies were determined from random samples of 100 pebbles (£> axis 16 to 32 mm) collected from fresh exposures of St. Eugene fanglomerate.  Similar lithologies are found in a number of  formations, and some formations occur over large areas, thus i t i s commonly impossible to determine the bedrock source for pebbles in fanglomerate.  Some lithologies, however, are useful for provenance study  because they are restricted to one or a few bedrock units which crop out over a limited area.  Rock types which crop out i n the vicinity of fan-  58  glomerate exposures and which are suitable for provenance study include andesite; grayish-red-purple quartz arenite, s i l t i t e , and a r g i l l i t e ; and laminated greenish-gray a r g i l l i t e .  The occurrence and relative abundance  of these lithologies i n relation to their present bedrock distribution indicate the probable source of the fanglomerate and provide evidence for Neogene deformation within the study area.  Results.  Percentages of laminated greenish-gray a r g i l l i t e ,  red-purple clastic sedimentary rocks, and mafic igneous rocks are presented in Figure 23. These lithologies represent the majority of fanglomerate clasts, the remainder being light-colored a r g i l l i t e probably derived from the same formations as the laminated greenish-gray a r g i l l i t e .  The litho-  logic composition of fanglomerate at Gold Creek i s similar to that of bedrock cropping out to the west and north; fanglomerate along Elk River is lithologically most similar to bedrock cropping out to the east and northeast.  Dolomitic a r g i l l i t e and dolostone which crop out on Sheep  Mountain were not found as clasts i n fanglomerate exposures to the immediate south. not found.  Clasts eroded from Paleozoic and Mesozoic rocks were  Mafic igneous clasts, although common i n fanglomerate at Gold  Creek, are absent i n Elk River exposures.  Discussion Although clast orientations parallel to flow were consistently observed i n the case of the paraglacial alluvial fan (Fig. 20, Appendix 4), there are areas where fabric maxima transverse to the flow direction are to be expected (Fig. 24). Boulton (1971, p. 52-54) has shown that, in the  59  main body of a flow, longitudinal extension and v e r t i c a l s e t t l i n g result i n alignment of p a r t i c l e s p a r a l l e l to the flow d i r e c t i o n ; the dip of the  a-b planes i s dependent on the shape of the underlying bed.  This f a b r i c  i s replaced at the nose of the flow by one resulting from longitudinal compression and characterized by transverse a-axis orientations and  a-b planes dipping up-flow.  Since sediment deposited near the nose of  most a l l u v i a l fan mudflows i s volumetrically subordinate to sediment of the main body of the flow, fabrics taken randomly i n a mudflow unit w i l l generally y i e l d maxima p a r a l l e l to flow, as was Canyon a l l u v i a l fan ( F i g . 20).  the case for the Fraser  Transverse maxima can be recognized i n a  mudflow unit of unknown source i f the s p a t i a l fabric pattern of the unit i s determined.  From the results of geophysical surveys across the southern Rocky Mountain Trench, Garland and others (1961), Lamb and Smith (1962), and Thompson (1962) have inferred the presence of several fault-bounded basins containing up to 1500 m of semiconsolidated and unconsolidated sediments.  The S t . Eugene Formation represents the uppermost exposed  T e r t i a r y sediments of this basin f i l l .  The geophysical results and  those  from f a b r i c and c l a s t lithology studies indicate that fanglomerate of the St. Eugene Formation was deposited i n these basins and adjacent to uplands from which i t s constituent clasts were eroded.  Transport was  to  the southwest and west on the east side of the Trench, and probably to the south, southeast, or east on the west side of the Trench.  These  r e s u l t s , as w e l l as the coarseness of the sediment, suggest that r e l i e f was moderate to high and that the physiography  of the area during  deposition of the St. Eugene Formation was broadly similar to that of the  60  present. The absence of mafic igneous clasts from fanglomerate along Elk River i s noteworthy, because andesite crops out on the adjacent flank of the Galton Range. This i s explained by upward displacement of the southern Rocky Mountains relative to the Rocky Mountain Trench after deposition of the St. Eugene Formation (p. 92).  DEFORMATION OF THE ST. EUGENE FORMATION The St. Eugene Formation i s only mildly deformed (Fig. 25). In fact, i t might be mistaken for a Quaternary unit were i t not for a detailed study of i t s fabric (p. 54), composition (p. 57), minor structures, and palynomorph assemblages (p. 61). Fanglomerate on the east side of the Trench strikes N50-80°E and dips gently southeast.  The dip direction i s approximately parallel  to the adjacent front of the Galton Range.  It is thought that these  attitudes are the result of deformation rather than deposition, because fan-fabric and clast lithology analyses indicate a source to the northeast of the depositional site rather than north to northwest as would be the case i f the beds were deposited with the attitudes described.  Furthermore,  Sheep Mountain, the only nearby bedrock high which could have supplied detritus in a south to southeast direction, is underlain by bedrock which differs in lithology from clasts i n the fanglomerate. Fanglomerate and interbedded s i l t and sand at Gold Creek strike about N45°E and dip gently southeast.  Here the strata are offset by faults  61  which strike northeast and dip steeply northwest (Fig, 25). The rake of slickensides i s steep indicating oblique-slip offset with the dip-slip component of movement greater than the strike-slip component. Stratified s i l t and sand, and coarse gravel along St. Mary River strike north to northeast and dip gently east to southeast.  ST. EUGENE PALEOFLORA AND PALEOCLIMATOLOGY Stratified s i l t and sand of the St. Eugene Formation include beds rich i n f o s s i l plant remains. Hollick (1927) identified 18 plants from fossil leaf and fruit impressions collected near St. Eugene Mission. His f l o r a l l i s t , modified according to LaMotte (1952) where necessary, includes the following: Alnus sp.  Betula ulmoides  Cocculus heteromorpha Fagus borineviliensis Fagus sp. Ficus canadensis Carpites interglacialis Carya egregia  Monocotyledon  Passiflora canadensis Platanus dissecta Quercus kootenayensis Quercus sp. Tilia (?) incertae Vaccinium pseudocorymbosum Vitis alia  According to Hollick, the flora indicates a warm temperate climate such as that of the southeastern United States today.  Berry (1929) concluded  that the flora was late Tertiary i n age on the basis of similarities with Miocene floras of the northwestern United States.  62  Analytical Procedure The St. Eugene Formation was analyzed for plant microfossils in order to:  (1) determine the assemblages that existed in the area  during deposition of the St. Eugene Formation; (2) compare the assemblages from the different outcrops; (3) assess the Miocene age assigned to the unit; (4) compare the St. Eugene microflora with similar floras elsewhere in British Columbia and the northwestern United States, and thus infer the late Tertiary climate and geography of the area.  Method Samples were collected from outcrops of the St. Eugene Formation along St. Mary River (four sites), Elk River (three sites), and Gold Creek (one site) (Fig. 26).  At each site the total thickness of exposed  s i l t and sand was sampled by carefully cleaning the exposure face, then trenching the sediments.  Spot samples were also collected from f o s s i l -  iferous beds at the Gold Creek and St. Mary River sites.  No organic-rich  layers are present in the relatively thin s i l t and sand beds at the three Elk River sites. Plant microfossils were recovered from sediment samples by means of standard palynological techniques (outlined in Brown, 1960; Kummel and Raup, 1965).  Briefly, this involved:  (1) elimination of  mineral matter by treatment in hydrochloric acid, then hydrofluoric acid; (2) removal of cellulose by boiling in a solution of acetic anhydride and sulfuric acid (acetolysis); (3) elimination of carbonized exteriors of  63  microfossils with n i t r i c acid.  Pollen and spore concentrates were then  alkalized, stained with safranine, and mounted on glass slides for further examination. Spores and pollen were identified to genus where possible; certain genera are represented by more than one species,  Taxa were listed  in two general categories, palynomorph present and palynomorph common.  Results ' The palynomorph assemblages from the St. Eugene Formation are summarized in Table 2.  Of the localities sampled, three St. Mary River  sites and the Gold Creek site yielded plant microfossils.  Samples from  thin sand interbeds in fanglomerate and coarse gravel contained no palynomorphs.  No major differences were found among f l o r a l  assemblages  at various sampling sites, except that the number of genera recognized is less in samples with low pollen and spore content. The most common palynomorphs are found in a l l samples; the rarer ones occur sporadically. These observations suggest that the f o s s i l pollen rain was similar at sampling sites along Gold Creek and St. Mary River, and that the strata of these two areas are of the same age. At least 39 genera of ferns, gymnosperms, and anthophytes are represented (Fig. 27).  An examination of Table 2 indicates that the  dominant palynomorphs are spores of the Polypodiaceae-Dennstaedtiaceae group, pollen of Pinaceae (Cedrus, Picea, and Pinus), and pollen of Alnus and Betula.  Less common woody elements include the Taxodiaceae (.Glypto-  strobus, Metasequoia, Sequoia, and Taxodium), other members of Pinaceae  64  (Abies, Pseudotsuga, and Tsuga), and a variety of dicotyledons (Acer, Aesculus, Carpinus, Carya, Castanea, Corylus, Fraxinus, Ilex, Liquidambar, Myrica, Nyssa, Platanus, Pterocarya,  and Ulmus-Zelkova).  Juglans,  Quercus, Salix,  Tilia,  The following families and genera are also present:  Caprifoliaceae, Chenopodiaceae, Compositae, Ephedra, Ericaceae, Gramineae,  Pachysandra-Sarcococca,  Podocarpus, and various ferns.  Discussion Fossil floras provide information as to the age of associated sedimentary strata, the climate existing during growth of the plants, and phytogeography near the depositional site.  These factors are often  interdependent, therefore, caution must be exercised in interpretation of microfloras.  For example, climate at the site of growth is in part  determined by regional topography and elevation.  Nevertheless, certain  conclusions can be drawn regarding the age and paleoecology of the St. Eugene Formation by utilizing the following approaches:  (1) the St. Eugene  assemblage can be compared with dated floras of similar composition from the same paleoprovinces;  (2) the climatic and edaphic requirements of  members of the St. Eugene flora may be deduced from the modern habitats of similar plants; (3) paleogeography may be inferred from the physical characteristics of the St. Eugene sediments.  Age Assigned by Comparison with Similar Floras Penny (1969) and Leopold (1969) have reviewed microfloras of late Mesozoic and Cenozoic age.  In middle and high latitudes of the  65  Northern Hemisphere, Paleogene floras are strikingly different from the Neogene floras which are of particular interest here.  In general, late  Tertiary floras are less rich in species and contain a higher proportion of extant taxa than those of early Tertiary age from the same region. Certain groups such as the Compositae f i r s t appear i n the f o s s i l record in the Neogene. Neogene floras are more closely related to the modern floras living near the f o s s i l locality than are Paleogene floras.  Also,  late Tertiary floras are more provincial in distribution than those of early Tertiary age.  These differences are due to the progressive  evolution and migration of floral elements in response to a gradual deterioration of climate and differentiation of topography during the Cenozoic.  Early Tertiary floras show marked similarities throughout the  Northern Hemisphere and commonly grew under tropical or subtropical climatic conditions (Penny, 1969).  In later floras, the palms and  broadleaf evergreens are replaced by warm temperate, deciduous anthophytes and conifers.  In the late Tertiary, cool temperate taxa and herbs are  important f l o r a l elements. Although many late Tertiary megafloras from the Pacific Northwest have been described (references in Chaney, 1959; Axelrod, 1964), detailed palynological studies are few.  Table 3 illustrates the similarity  between the St. Eugene and some other microfloras of Miocene age in British Columbia and the northwestern United States which are located in Figure 28. Because microfloras and megafloras from the same f o s s i l locality often differ (in part because of relative differences in pollen, leaf, and fruit productivity and the relative transportability and preservation of these materials), direct comparisons are not made with Miocene megafloras.  66  Piel (1969, 1971) has described a succession of middle to late Tertiary pollen floras in central British Columbia. The Miocene assemblage, indicative of a warm temperate climate with abundant summer rainf a l l , contains essentially the same taxa as the St. Eugene Formation. The deciduous broadleaf element which characterizes Piel's Miocene unit is subordinate to the coniferous element in the succeeding Mio-Pliocene assemblage which Piel believes to have existed under a cool temperate climate.  Also clearly different i s the subtropical to warm temperate  Oligocene flora which includes many genera not found in younger rocks of the area (e.g., Diervilla,  Sciadopitys,  and  Engelhardtia,  Psilastephanocolpites,  Sigmopollis).  Martin and Rouse (1966) have discussed a late Miocene or early Pliocene microflora from the Queen Charlotte Islands off the coast of British Columbia.  Generically, the flora is remarkably similar to that  of the St. Eugene Formation (Table 3), although gymnosperms (specifically  Cedrus, Picea, and Pinus) are relatively more abundant in the St. Eugene flora.  Fern spores, especially the Polypodiaceae-Dennstaedtiaceae complex,  are abundant in both floras.  The microfossil assemblage from the Queen  Charlotte Islands apparently grew on a coastal lowland under a relatively humid, mild temperate climate. Eocene and Miocene microfossil assemblages from the Whatcom Basin, southwestern British Columbia and northwestern Washington have been described by Hopkins (1966, 1968).  The younger assemblage includes  the following dicotyledons and gymnosperms:  Castanea, Cedrus, Engelhardtia,  Acer, Alnus, Carpinus,  Fagus, Glyptostrobus,  Ilex,  Juglans,  Carya,  67  Keteleeria,  Liquidambar, Metasequoia, Momipites, Picea, Pinus,  Quercus, Salix,  Tilia,  Taxodium, and Ulmus-Zelkova.  Pterocarya,  Again the similarity  with the St. Eugene Formation is marked. Absent are many of the characteristic Eocene palynomorphs including Anemia, Azolla,  Pistillipollenites,  and Platycarya.  Cicatricosisporites,  The Miocene flora grew on the Whatcom  Basin lowland and upland basin margins under a temperate to warm temperate climate. Microfossil assemblages from five localities in south-central British Columbia are considered by Mathews and Rouse (1963) to be late Miocene or early Pliocene in age.  Associated volcanic rocks at two  localities yielded K-Ar dates of 10 ± 2 and 12 and 13 million years. These floras are somewhat less diverse than the St. Eugene flora, contain a higher percentage of total conifer pollen and a lower percentage of spores (especially the family Polypodiaceae), and lack Betula two common constituents of the St. Eugene Formation.  and Cedrus,  These floras, then,  appear slightly younger than the St. Eugene microflora, although phytogeographic factors such as nearness to uplands may in part explain the differences. The St. Eugene flora is generally similar to Middle and Upper Miocene floras from Mascall, Blue Mountains, Stinking Water, Sucker Creek, and Trout Creek of eastern Oregon (Chaney, 1959; Graham, 1965).  Tuffs  associated with the last two have been dated at 16.7 and 13.1 million years respectively.  Differences among the floras are attributed in large  part to phytogeographic variables and, to a lesser extent, age.  68  Figure 17. Index map showing outcrop areas of the S t . Eugene Format i o n . The r e l a t i v e ages of two or more sediment types which crop out at one s i t e are indicated by diagonal lines separating the older (to the right of the line) from the younger (to the l e f t of the l i n e ) .  69  70  Gray (1964, her Table 1) has compiled Tertiary microfloral l i s t s for Washington, Oregon, Idaho, and California.  The St. Eugene  microflora i s closely related to the Miocene assemblages from these states (Table 3) and shows less similarity to both Oligocene and Pliocene floras. Somewhat more distant from southeastern British Columbia i s the Miocene Kilgore fossil locality in northern Nebraska (MacGinitie, 1962). Nevertheless, the Kilgore and St. Eugene floras are similar, the major difference between the two being the comparative rarity of gymnosperm pollen from Nebraska. In summary, the palynomorph assemblage of the St. Eugene Formation can be considered Miocene in age on the basis of similarities with other microfloras from western North America assigned to this epoch by means of vertebrate and invertebrate fossils and radiometric age dates. The correctness of this age assignment is further indicated by the degree of modernity of the flora.  Wolfe and Barghoorn (1960) have shown a close  relation between mega- and microfloral age and the proportion of f o s s i l genera s t i l l living near their fossil localities in western North America (Fig. 29). The progressive modernization of floras during the Tertiary presumably resulted from gradual cooling and topographic differentiation. The closeness of the relationship in Figure 29 based on widely separated floras is somewhat surprising and suggests that local climatic and topographic considerations were of secondary importance in comparison to age in characterizing the degree of floral modernity.  The St. Eugene assem-  blage with about 44% native genera i s determined to be of middle Miocene  Figure 18. Stratigraphic sections of the St. Eugene Formation. T i l l unconformably overlies the St. Eugene Formation at sites 1, 3, and 4, and outwash at sites 2 and 5.  72  Figure 19.  The S t . Eugene Formation.  A.  Colluvium, E l k River,  B.  Fanglomerate, Elk River.  C.  Laminated organic-rich s i l t , S t . Mary River,  D and E. F.  Coarse g r a v e l , S t . Mary River.  Organic-rich s i l t ( l i g h t layer) overlain by coarse gravel and underlain by fanglomerate, Gold Creek.  73  Figure 19  Figure 20. Fabrics of paraglacial alluvial fans. Top: location and morphometry of the studied alluvial fans. Fan-fabric sample sites and axes of maximum clustering at each site are shown. Bottom: contoured diagrams of fabric data (contours approximately 2-5-8% per 1% area; each fabric consists of 60 measurements). Photo numbers BC 4246-180 and -181. Sample statistics are presented in Appendix 4.  76  age and is grouped with such floras as the Sucker Creek (41%), Mascall (40%), and Trout Creek (47%).  Paleoecology Inferred from Ecological Requirements of Extant Counterparts The paleoecology of fossil plant assemblages traditionally has been assessed by determining the distribution and ecological requirements of the extant counterparts of f o s s i l genera.  This approach was f i r s t  used i n studies of fossil leaves by such workers as Brown (1934), Chaney (1936, 1938, 1959), Axelrod (1941), and Dorf (1959, 1963), and later was applied to palynological studies by, among others, Traverse (1955), Rouse (1962), Hills (1965), Stanley (1965), Martin and Rouse (1966), and Rouse and others (1970).  In such studies i t i s generally assumed that fossil  plants had environmental requirements similar to their extant counterparts. This assumption has certain limitations (Wolfe and Hopkins, 1967; Wolfe, 1971; Hopkins and others, 1972), but i t s application here is supported by the observation that the St. Eugene flora consists of associations of plants that today occur together in restricted climatic provinces.  Also,  although most modern genera have wide geographic and ecological ranges, plant associations are more restricted i n their distribution and ecological requirements. The St. Eugene flora resembles the modern flora of the eastern and southeastern United States, especially of those areas between the Appalachian Mountains and the Mississippi Valley where oak-hickory-walnutelm-beech forests border upland areas dominated by mixed deciduous and coniferous elements.  A similar resemblance between Miocene floras of the  50  50  -40  £  30  30  -L  10  _|_ 20  _L  30  40  10  Azimuth Plunge DIFFERENCE BETWEEN AXES OF MAXIMUM CLUSTERING FOR SAMPLES OF SIZE 60 AND 20 (in degrees) • £  one point two coincident points  Figure 21. Relation between fan-fabric strength and differences in the fabric results for samples of size 60 and 20. Theta i s the standard scattering angle around the axis of maximum clustering (in general, the greater the directional strength of the fabric, the smaller i s theta). Theta is plotted against the difference in orientation of the clustering axes of the larger and smaller samples. Differences between samples of size 60 and 20 are small where fabrics are strongly directed.  Figure 22. Fan fabrics from the St. Eugene Formation. Right: index map of sample sites. Clustering axes at each site were determined from the sum of 2 or 3 samples with maximum lateral spacings of about 100 m. Left: contoured diagrams of fabric samples (contours approximately 2-5-8% per 1% area; each fabric consists of 60 measurements). Sample statistics are presented in Appendix 4.  FAN  FABRICS  Figure 22  80  Columbia Plateau and the modern floras of the eastern and southeastern United States has been noted by Chaney (1959).  The presence of Taxodium  and other lowland genera indicate the presence of swamps or poorly drained lowlands in southeastern British Columbia.  In contrast, the  strong representation of Pinaceae suggests a nearby montane region. Mixed deciduous hardwood and conifer forest probably occupied the slopes between these two habitats. The St. Eugene flora i s also similar to the extant flora of warm temperate parts of central and southeastern China. Asian genera no longer native to North America include Cedrus, Glyptostrobus, and Pterocarya.  Metaseguoia,  Numerous other St. Eugene genera are associated with  these Asiatic trees under climatic conditions close to those existing in southeastern North America. Thus, the St. Eugene plant community consists of plants which now occur as two separate floral elements subject to the same summer-wet, temperate climate (Chaney, 1948, 1959).  Glyptostrobus  If the climatic requirements of  and Taxodium are about the same today as during the Miocene,  the lowland habitats in southeastern British Columbia during the Miocene probably had the following climate:  average annual precipitation, 100 to  150 cm, evenly distributed through the year; mild winters with temperatures seldom below freezing and warm summers (Fullard and Darby, 1967).  If  upland slopes were climatically similar to the Appalachian-Mississippi Valley region, the Miocene mixed deciduous hardwood-conifer forest received similar amounts of precipitation, with the mean temperature between 10 and 18°C.  In contrast, the present climate of the floor of  the southern Rocky Mountain Trench according to the KBppen classification  81  Figure 23. Percent of clasts of the following lithologies i n St. Eugene fanglomerate: laminated greenish-gray a r g i l l i t e (source i s largely the Roosville and Gateway Formations), red-purple a r g i l l i t e and quartz arenite (largely of the Phillips Formation), and mafic igneous rocks (Purcell volcanics). No mafic igneous clasts were found in fanglomerate exposed along the east side of the Trench. Bedrock geology from Leech (1958, 1960).  82  i s Bsk (Continental Cold Semiarid) (Krajina, 1965).  Average annual precip-  i t a t i o n at Newgate (1918-1954) and Cranbrook (1916-1954) i s 35 and 37 cm respectively and i s distributed approximately evenly through the year. Mean temperatures at Newgate and Cranbrook are 6 and 5°C respectively. The climate i s truly intemperate, with average summer temperatures above 16°C and average winter temperatures well below freezing (Kelley and Sprout, 1956).  The present climate i s controlled i n part by the  southward movement of cold continental a i r from the A r c t i c and by the northward movement i n the summer of warm, dry a i r from the i n t e r i o r of the United States.  Low p r e c i p i t a t i o n i n part results from i s o l a t i o n of  the area from the moderating influence of the P a c i f i c by a series of north- to northwest-trending mountain ranges.  Mathews and Rouse (1963)  have suggested that the humid, warm climate necessary to sustain the Miocene floras of south-central B r i t i s h Columbia might have resulted i f the Coast Mountains were much lower during the late Tertiary than at present.  Another factor responsible for the humid, temperate climate  may have been the existence of a warm polar sea during the T e r t i a r y ( P i e l , 1971, p. 1895).  Under such conditions and with atmospheric c i r c u -  l a t i o n similar to that of the present, warm, moist a i r would move south through B r i t i s h Columbia instead of the cold, dry a i r which i s a factor c o n t r o l l i n g the present d i s t r i b u t i o n of vegetation.  High p r e c i p i t a t i o n  would result as these warm, moist a i r masses were driven against mountain ranges by westerly winds from the P a c i f i c .  The presence of late Tertiary mountain ranges i n southeastern B r i t i s h Columbia i s shown by regional tectonic evidence and by the compos i t i o n of the S t . Eugene f l o r a .  The Rocky Mountains originated during  oo CO  STONES WITH a-b PLANES DIPPING IN DIRECTION OF SHORT LINE; LONG LINE SHOWS a-AXIS TREND. STONES WITH VERTICAL a-b TREND.  PLANES; LONG LINE SHOWS  a-AXIS  STONES WITH HORIZONTAL a-b PLANES; LONGEST DIMENSION Of ELLIPSE SHOWS a-AXIS TREND. DIRECTION OF TRANSPORT.  Figure 24.  The fabric of mudflow gravel.  A. Small debris flow in Elk Valley.  B. Mudflow clast orientations.  00 •p-  Figure 25. Deformation of the St. Eugene Formation. A, B, and C. Faulted St. Eugene strata, Gold Creek. Faults strike northeast and dip steeply northwest. The rake of slickensides is also steep (B and C). Overlying Quaternary sediments are not offset. D.  Gently tilted St. Eugene fanglomerate, Elk River. The fanglomerate dips gently to the south and southeast, but the source of the sediment, the precipitous east wall of the Trench, is east and northeast of the depositional site.  8 5  86  the Laramide Orogeny which probably began in the late Cretaceous and ended in the early Oligocene (Russell, 1951, 1954b; Douglas and others, 1968, p. 464).  Epeirogenic uplift continued from the Oligocene until late  Pliocene, with many areas of the Rockies uplifted 1500 m or more during this interval (Cook, 1960).  Diverse habitats for St, Eugene f l o r a l  elements also indicate moderate to high relief in southeastern British Columbia during the Neogene; for example, Glyptostrobus  and Taxodium were  probably limited to lowlands near the depositional site, whereas the strong representation of conifers such as Abies and Picea suggests the presence of montane uplands.  Paleogeography Inferred from Physical Characteristics of Sediments Moderate to high relief near the depositional site is also suggested by the physical characteristics of the St. Eugene Formation and the Eocene-Oligocene Kishenehn Formation (Price, 1962; Johns, 1970) in the Flathead Valley to the east.  Gravel and fanglomerate of the  St. Eugene Formation were deposited by rivers from high-gradient tributary valleys and by mudflows from adjacent mountain fronts (Fig. 30).  Barnes  (1963, p. 70) has concluded that the Kishenehn Formation accumulated in large part in flood-plain lakes, swamps, and river channels; deposition of coarse conglomerate marginal to the broad flood plain was by mudflows from bordering uplands.  87  PLANT SAMPLE SITE: PLANT MICROFOSSILS COMMON PLANT MICROFOSSILS RARE OR ABSENT CHANNEL SAMPLE  J  M I C R O F O S S I L S A M P L E SITES  • o  ST. EUGENE FORMATION—SEDIMENT TYPES: STRATIFIED GRAVEL SILT AND SAND COLLUVIUM OR FANGLOMERATE  1 : l : III i K-^.j-j  Figure 26. Plant microfossil sample sites from the St. Eugene Formation. Columnar sections show locations of microfossil channel samples.  88  NEOGENE DEFORMATION IN SOUTHEASTERN BRITISH COLUMBIA The St. Eugene Formation provides evidence for Tertiary tectonic activity i n the eastern Cordillera.  The restricted occurrence  of the St. Eugene Formation in the Trench and the derivation of the strata from adjacent uplands indicate that the Trench was already a major physiographic form by the Miocene.  Alden (1953) has suggested that the  Purcell and adjacent trenches developed by erosion and faulting prior to the Miocene.  This is deduced from the fact that lake beds were deposited  in the southern Purcell Trench and later covered by Columbia River basalts. Alden interpreted some bedrock benches in major valleys and basins of western Montana and Idaho as remnants of Pliocene valley bottoms produced during regional uplift prior to glaciation.  Most of the major British  Columbia drainage routes were established by the Miocene as evidenced by occurrences of Miocene sediments along the Fraser Valley and i t s tributaries near Quesnel and Prince George (Piel, 1969). The Miocene age of the St. Eugene Formation, however, represents only a minimum age for the formation of the southern Rocky Mountain Trench as a major physiographic form and sedimentation trough. The occurrence of deep structural basins with Tertiary f i l l s i n the Trench indicates that unexposed sediments overlying Precambrian and Paleozoic bedrock in these basins may be older than Miocene.  About 2000 m of late Eocene and early  Oligocene sediments crop out in the Flathead Valley to the east i n a similar stratigraphic and structural setting (Russell, 1954a; Barnes, 1963; Price, 1966).  These sediments unconformably overlie strata deformed  89  Table 2. Ralynomorph assemblages from the S t . Eugene Formation. Assemblage no. 2 includes m i c r o f o s s i l s from samples c o l l e c t e d at two adjacent l o c a l i t i e s (see F i g . 26). P = palynomorph present; C = palynomorph common.  Gold Creek* (1)  „ , u Palynomorph taxa  St. Mary River* (3) (2)  Division Lycopodophyta P P  Lycopodium Selaginella  P  Division Pterophyta  Deltoidospora Osmunda  Polypodiaceae-Dennstaedtiaceae (includes Laevigatosporites)  Triplanosporites  P P  P  c  c  P P  P  P  P  P C P P P P c c p p  P P P  P C P  P P c c  P P C c  p  p  Division Coniferophyta  Abies Cedrus  Cupressaceae-Taxaceae  Ephedra Glyptostrobus Metasequoia Pice a Pinus Podocarpus Pseudotsuga-Ijarix Sequoia Taxodium Tsuga  ?  ?  ?  p p  p p  p p  p p c p p  p  p  c c  c c  Division Anthophyta  Acer Aesculus Alnus Betula  Caprifoliaceae  Carpinus-Ostrya Carya Castanea  Gramineae  Ilex Juglans Liquidambar Hyrica Nyssa Pachysandra-Sarcococca Platanus Pterocarya Quercus Salix Tilia Ulmus-Zelkova  p  p p  p  p  p p p p p  p  p ?  Chenopodiaceae-Amaranthaceae Compositae Corylus Ericaceae  Fraxinus  ?  pp ? ?  p p  ?  p p p  ?  1  p p  p  p  ?  p  P  p p  p  P  ?  0  *Location of sample sites:  p p p p p p p  ,. 115 14'W; (2) 49°35'N, 115°49'W; (3) A9°36'N, 115°44'W (1) 49°04'N  90  Figure 27. Selected plant m i c r o f o s s i l s from the S t . Eugene Formation. A— Ly copodium', B—Osmunda; C—Polypodiaceae-Dennstaedtiaceae; D— Triplanosporites; E—Cedrus; F—Ephedra; G— Glyptostrobus; H— Picea; I—Tsuga; J— Aesculus; K and L— Alnus; M— Betula; N—Carya; 0—Compositae; P— Ilex; Q—Juglans; R—Liquidambar; S—Nyssa; T— Pterocarya; U— Pachysandra-Sarcococca; V—Ulmus-Zelkova; W and X — u n i d e n t i f i e d t r i colpate p o l l e n . Bar length represents 10 um.  91  92  during the Laramide Orogeny and, therefore, establish an upper age for this event.  Late Cretaceous and early T e r t i a r y postorogenic sediments  accumulated i n intermontane troughs along the northern Rocky Mountain and T i n t i n a Trenches (Eisbacher, 1972).  Sedimentation i n the southern Rocky Mountain Trench was probably controlled by fault-block topography.  The eastern margin of the Trench  coincides with a major normal f a u l t (Leech, 1966).  Coarse fanglomerate  derived from the east and northeast occurs on the downthrown side of the f a u l t (p. 59).  Similar occurrences of fanglomerate on the west side of  the Trench may be associated with a series of steeply dipping, north- to northwest-striking f a u l t s north of 49°N l a t i t u d e .  Thompson (1962) has  concluded that the deep (up to 1500 m) bedrock basins beneath the Trench were formed by normal f a u l t i n g .  Presumably these basins are bounded by  f a u l t s transverse to the trend of the Trench.  East-west faults s t r i k i n g  beneath the unconsolidated sediments i n the Trench have been mapped by Leech (1960).  At least some f a u l t i n g postdates deposition of the St. Eugene Formation. slip faults.  Strata along Gold Creek are offset by northeasts-striking dipThe c l a s t composition of fanglomerate adjacent to the normal  f a u l t on the east margin of the Trench indicates a minimum of 600 m of post-St. Eugene displacement.  Mafic igneous clasts are absent from this  fanglomerate (elev. 760 to 910 m) despite the bedrock occurrence along the adjacent mountain front of a mafic lava as high as 1500 m (p. 57). Rather, the fanglomerate consists of l i t h o l o g i e s present i n bedrock units s t r a t i g r a p h i c a l l y above the lava.  This suggests that units below and  93  Table 3. Comparison of the St. Eugene microflora and Miocene microfloras from B r i t i s h Columbia and the northwestern United States. The floras are located i n Figure 28.  Palynomorph t a x a , S t . Eugene F o r m a t i o n  (i)  D i v i s i o n Lycopodophyta Lycopodiura  (2)  (3)  (4)  (5)  (6)  X  X  X  X  X  D i v i s i o n Pterophyta Deltoidospora  X  Osmunda Polypodiaceae-Dennstaedtiaceae Laevigatosporites Triplanosporites  X  X X  X X X  X X  X X  X X X  X X  AA  Coniferophyta X  X  X  X  X X  Cupressaceae-Taxaceae  Ephedra Glyptostrobus Metasequoia  X X X  Picea Pinus Podocarpus  X X X  Pseudotsuga-Larix Sequoia Taxodi um Tsuga Division Acer  X X  X X X X  X X X X  X X  X  X  X X X X X  X  X X X  X X  X X X X X X  (10)*  (11)*  (12)*  (13)*  (14)  X  X X  X  X  AA  AA  **  AA  **  *A  AA  AA  X  X  X  X  X X  X X  X X X  X  X  X X  X  X X X X  X  X X X  x  X  X X X  X X  X X  X X  X X  X X  X X  X X  X X  X  X  X  X  X  X X  X X  X X  x  X  X  X  X  X  X  X X X  X X  X  X  X  X  X  X  X  X  X  X  X  X X  X X  X X  X X  X X  X X  X X  X  X X X X X X  X X X X X  X X  X  X  X X X  x  X X X  X X X  X X  X X X X X X  X X X X X X  X X X X X  X X X  X X X  X  X X X X X  X X X X X  X X X X X X  X X X X X X  X X x X X x  X X X X  11  8  12  9  5  X  Caprifoliaceae Carpinus-Ostrya Carya Castanea  X  X  X  X X  X X X  X  X X X X X  Chenopodiaceae-Amaranthaceae Compositae Corylus  X  Ericaceae Fraxinus  X  X X X  X X X X X X X  X X X  Number o f g e n e r a o r f a m i l e s from S t . Eugene  Fm.  British  X X X  X X X  X  X X  X X  X  X X  X X X X X  2  5  1  Columbia, Mio-Pliocene  X X X  (Piel,  X X X X X  5  X  X  X X X X X  X X X X X X X X  X X X X  X X X X  X  X  X X X X X X  10  6  5  6  9  (1)  South-central  (2) (3) (4)  S o u t h - c e n t r a l B r i t i s h Columbia, Miocene ( P i e l , 1969). S o u t h - c e n t r a l B r i t i s h C o l u m b i a , M i o c e n e o r e a r l y P l i o c e n e (Mathews a n d R o u s e , 1 9 6 3 ) . Queen C h a r l o t t e I s l a n d s , B r i t i s h C o l u m b i a , M i o - P l i o c e n e ( M a r t i n and R o u s e , 1 9 6 6 ) .  1969).  (5) (6) (7)  Whatcom B a s i n , B r i t i s h C o l u m b i a , M i o c e n e ( H o p k i n s , S u c k e r C r e e k , O r e g o n , M i o c e n e (Graham, 1 9 6 5 ) . M a s c a l l , Oregon, Miocene (Chaney, 1959).  1966).  S t i n k i n g Waters, Oregon, Miocene (Chaney, 1959). Blue Mountains, Oregon, Miocene (Chaney, 1959). Western Oregon, composite Miocene m i c r o f l o r a (Gray, 1964). E a s t e r n O r e g o n , c o m p o s i t e M i o c e n e m i c r o f l o r a ( G r a y , 1964).Washington, composite Miocene m i c r o f l o r a (Gray, 1964). Idaho, composite Miocene m i c r o f l o r a (Gray, 1964). K i l g o r e , Nebraska, Miocene ( M a c G i n i t l e , 1962).  * M i c r o f l o r a i n c l u d e s o n l y woody a n g i o s p e r m s a n d g y m n o s p e r m s . **Genera o f Taxodiaceae not i d e n t i f i e d . ***Gyntnosperms a n d a n g i o s p e r m s .  X X X  X  x X  X X  X x' X X X  X X X X X X  X X X X X X X X  X  X  Gramineae Ilex Juglans Liquidambar Myrica Nyssa Pachysandra-Sarcococca Piatanus Pterocarya Quercus Salix Tilia Ulmus-Zelkova  (8) (9) (10) (11) (12) (13) (14)  (9)  Anthophyta  Aesculus Alnus Be tula  absent  (8)  X  Selaginella  Division Abies Cedrus  (7)  X X  X X X X  X  X  Figure 28. Location of some Miocene palynomorph assemblages in British Columbia and the northwestern United States. (1) South-central British Columbia, Mio-Pliocene (Piel, 1969); (2) south-central British Columbia, Miocene (Piel, 1969); (3) south-central British Columbia (Mathews and Rouse, 1963) ; (4) Queen Charlotte Islands (Martin and Rouse, 1966); (5) Whatcom Basin (Hopkins, 1966); (6) Sucker Creek (Graham, 1965); (7) Mascall (Chaney, 1959); (8) Stinking Waters (Chaney, 1959); (9) Blue Mountains (Chaney, 1959); (10) western Oregon (Gray, 1964); (11) eastern Oregon (Gray, 1964); (12) Washington (Gray, 1964); (13) Idaho (Gray, 1964); (14) Kilgore (MacGinitie, 1962).  Figure 28  96  including the lava were not being eroded in this area during St. Eugene time and therefore were lower than the fan apices. Subsequently, these units were elevated relative to the fanglomerate at least 600 m along the bounding normal fault.  Strata originally dipping west to southwest off  the Galton Range scarp were mildly deformed; they now dip south to southeast.  Again there i s a similarity between these conditions and  those occurring somewhat earlier in the Flathead Valley, where conglomerate and breccia were deposited in a structural basin on the downthrown side of the Flathead fault (Price, 1966).  Displacement was simultaneous with  deposition as the sequence of lithologies that occur as clasts is opposite that of the normal stratigraphic succession of bedrock lithologies in the hanging wall of the fault. Cenozoic normal faults are widespread across the Cordillera. Pardee (1950) and Alden (1953) have described block-faulted basins in northwestern Montana which are underlain by Cenozoic sediments similar to the St. Eugene Formation.  Both fan and flood-plain facies are present,  and interbeds of ash are locally common. Much of the strata are faulted and tilted.  Alden has concluded that during deposition there was  considerable relief i n northwestern Montana resulting from block faulting superimposed on epeirogenic uplift.  Uplands and basins were in about  the same positions as they are now, and there is no evidence of widespread peneplanation in the area following deposition of the basin sediments. Faulting has persisted to the present in the Rocky Mountains of the United States (Woollard, 1958; Milne and others, 1970), but the zone of seismicity dies out near the International Boundary.  Figure 29. Relation between age of flora and percent of f o s s i l genera s t i l l living near their fossil localities for mega- and microfloras from the western United States and British Columbia (from Wolfe and Barghoorn, 1960, their Fig. 1). About 44% of the fossil genera of the St. Eugene Formation are s t i l l extant in the general area of the unit.  loor— 90 80  2 HI  Z  ui  70-  o ui >  60-  E  50-  tj  30-  5  Microflora of St. Eugene Formcition  Ul  O.  20-  8> o  10 -  oL-  EOCENE  OLIGOCENE  AGE  OF  1 FLORA  MIOCENE  PLIOCENE  98  In summary, deposition of S t . Eugene and other basin sediments i n the eastern C o r d i l l e r a postdates the major compressional of the Rocky Mountains during the Laramide Orogeny.  deformation  This deformation,  which culminated i n the development of the Columbian Foreland Thrust and Fold B e l t , may  have resulted i n part from subduction along the P a c i f i c  margin of the C o r d i l l e r a (Wheeler and others, 1972).  Except o f f southern  B r i t i s h Columbia and Washington, underthrusting ended by the Oligocene and was  replaced by l a t e r a l s h i f t i n g of plates along transform faults o f f  the coast and by i s o s t a t i c u p l i f t elsewhere. was  U p l i f t of the C o r d i l l e r a  accompanied by extension and block f a u l t i n g which produced the major  basins and trenches of the Rocky Mountains i n southern Canada and the United States.  Sediment deposition was  margins of grabens and half-grabens.  controlled by f a u l t i n g along the  In places, u p l i f t , extension, and  f a u l t i n g were accompanied by the widespread and abundant extrusion of lavas and the i n t r u s i o n of epizonal plutons (Wheeler and others, 1972). Faulting continued after deposition of the Miocene S t . Eugene Formation i n southeastern B r i t i s h Columbia and has continued to the present i n the Rockies south of 49°N.  The Rocky Mountain Trench (south of 50°N) , then, consists of tectonic depressions formed by Cenozoic half-graben block f a u l t i n g superposed on late Cretaceous thrust structures.  to early T e r t i a r y allocthonous f o l d and  These depressions have been modified by sediment  i n f i l l i n g , g l a c i a t i o n , and p o s t g l a c i a l effects (Leech, 1966).  The  remarkable continuity of the Trench from 47°N to beyond 59°N and i t s trend across structures produced during the Laramide Orogeny suggest that i t delineates a s t r u c t u r a l boundary of continental proportions.  This i s  FLOOD-PLAIN FACIES  FAN FACIES  Figure 30. Block diagram showing the proposed model of Tertiary sedimentation controlled by block faulting in the southern Rocky Mountain Trench, British Columbia (diagram modified from a lecture sketch by W.M. Davis in King, 1959, his Fig. 86).  100  supported by abundant geophysical evidence which shows the Trench to be a major crustal boundary.  Between 49° and 56°N the Trench i s the western  limit of broad, high-amplitude aeromagnetic anomalies found over the Rockies and the Plains (Haines and others, 1971).  Geomagnetic depth-  sounding results indicate that the Trench marks a transitional zone between a conductive, hydrated lower crust to the west and a resistive lower crust to the east (Caner, 1970).  Gravity data show the craton  ending at the Trench north of 50°N, although to the south the craton extends west of the Trench farther into the Cordillera.  Finally, seismic  results show that the lithosphere may thin toward the Cordillera (Wickens and Pec, 1968).  Berry and others (1971) have suggested from this geophys-  i c a l evidence that the Rocky Mountain Trench between 50° and 56°N i s the margin of the Precambrian craton.  They thus agree with Price and Mountjoy  (1970) who consider the Trench to mark a Paleozoic hinge zone along the craton margin.  CONCLUSIONS (1) The St. Eugene Formation consists of flood-plain and fan facies deposited i n a depression similar in morphology and position to the present southern Rocky Mountain Trench.  The flood-plain facies  includes both high-energy river gravels deposited off tributary valleys and shallow-lake or slack-water s i l t and sand.  The fan facies consists  of talus and fanglomerate deposited along the margins of the proto-Rocky Mountain Trench and derived from adjacent fault-bounded uplands. (2) Up to 1500 m of sediment are present in a series of  101  structural basins underlying the Trench and bordered by high-angle faults transverse to the Trench trend.  The Miocene St. Eugene Formation includes  only the uppermost strata of these basin f i l l s , and i t i s probable that deeper sediments are i n part Oligocene and perhaps Eocene in age.  Sedi-  ments of Upper Eocene and Oligocene age occur in the structurally comparable Flathead Valley to the east and provide an upper age limit for the Laramide Orogeny i n the southern Canadian Rockies.  Compressional  deformation which produced the Rocky Mountain fold and thrust belt during the late Cretaceous and early Tertiary was followed by a period of isostatic uplift and extension accompanied by block faulting in the Cordillera.  This change in tectonics may be due to the cessation of  subduction along the northern Pacific margin and i t s replacement by lateral displacement of plates along transform faults.  The southern  Rocky Mountain Trench formed by block faulting of a half-graben style. Deposition of sediment in the Trench and erosion of the uplands were probably contemporaneous with faulting, although 600 m or more of displacement along the east boundary fault occurred after deposition of the St. Eugene Formation. (3) Palynological results substantiate conclusions based on the texture, structure, and lithologic composition of the St. Eugene Formation. The microflora includes elements which grew on poorly drained lowlands and montane uplands.  The climate was humid with abundant summer precipi-  tation and mild, moist winters; i t was thus more temperate than the present climate of the area.  Factors which may have controlled the Miocene climate  include a relatively warm polar sea and lower mountain barriers between southeastern British Columbia and the Pacific Ocean.  102  LITERATURE CITED Alden, W.C, 1953, Physiography and glacial geology of western Montana and adjacent areas: U.S. Geol. Survey Prof, Paper 231, 200 p. Anderson, T.W., and Stephens, M.A., 1971, Tests for randomness of directions against equatorial and bimodal alternatives: Dept. Statistics, Stanford Univ., Tech. Rept. 5, 19 p. 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H o l l i c k , Arthur, 1914, A preliminary report by Mr. Arthur H o l l i c k of the New York Botanical Garden, upon plants from the Pleistocene deposits: Canada Geol. Survey Summ. Rept., 1913, p. 133-135. 1927, The f l o r a of the Saint Eugene s i l t s , Kootenay V a l l e y , B r i t i s h Columbia: New York Bot. Garden Mem., v. 7, p. 389-465. Holmes, CD., 1941, T i l l f a b r i c : p. 1299-1354.  Geol. Soc. America B u l l . , v. 52,  Hopkins, W.S., J r . , 1966, Palynology of Tertiary rocks of the Whatcom basin, southwestern B r i t i s h Columbia and northwestern Washington [Ph.D. t h e s i s ] : Vancouver, B r i t i s h Columbia Univ., 184 p. 1968, Subsurface Miocene rocks, B r i t i s h Columbia—Washington, a palynological investigation: Geol. Soc. America B u l l . , v. 79, p. 763-768. Hopkins, W.S., J r . , Rutter, N.W., and Rouse, G.E., 1972, Geology, paleoecology, and palynology of some Oligocene rocks i n the Rocky Mountain Trench of B r i t i s h Columbia: Canadian Jour. Earth S c i . , v. 9, p. 460-470. Johns, W.M., 1970, Geology and mineral deposits of Lincoln and Flathead Counties, Montana: Montana Bur. Mines and Geology B u l l . 79, 182 p. Johns, W.M. , Smith, A.G., Barnes, W.C, Gilmour, E.H., and Page, W.D., 1963, Geologic investigations i n the Kootenai-Flathead area, northwest Montana: No. 5, western Flathead County and part of Lincoln County: Montana Bur. Mines and Geology B u l l , 36, 68 p. K e l l e y , C C , and Sprout, P.N., 1956, S o i l survey of the upper Kootenay and E l k River valleys i n the East Kootenay d i s t r i c t of B r i t i s h Columbia: B r i t i s h Columbia S o i l Survey Rept. 5, 99 p.  105  King, P.B., 1959, The evolution of North America: Princeton Univ. Press, 189 p.  Princeton, New Jersey,  Krajina, V.J., 1965, Biogeoclimatic zones and classification of British Columbia, in Krajina, V.J., ed., Ecology of western North America: Dept. Botany, British Columbia Univ., v. 1, p. 1-17. Kummel, Bernhard, and Raup, David, eds., 1965, Handbook of paleontological techniques: San Francisco, W.H. Freeman and Co., Inc., 852 p. Lamb, A.T., and Smith, D.W., 1962, Refraction profiles over the southern Rocky Mountain Trench area of British Columbia: Alberta Soc. Petroleum Geologists Jour., v. 10, p. 428-437. LaMotte, R.S., 1952, Catalogue of the Cenozoic plants of North America through 1950: Geol. Soc. America Mem. 51, 381 p. Leech, G.B., 1958, Fernie map-area, west half, British Columbia: Geol. Survey Paper 58-10, 40 p. 1960, Fernie, west half, British Columbia: Map 11-1960. 1966, The Rocky Mountain Trench: 66-14, p. 307-329.  Canada  Canada Geol. Survey  Canada Geol. Survey Paper  Leopold, E.B., 1969, Late Cenozoic palynology, in Tschudy, R.H., and Scott, R.A., eds., Aspects of palynology, an introduction to plant microfossils in time: New York, John Wiley and Sons, Inc., p. 377-438. Lineback, J.A., 1971, Pebble orientation and ice movement in southcentral I l l i n o i s , in Goldthwait, R.P., ed., T i l l : a symposium: Columbus, Ohio State Univ. Press, p. 328-334. Lindsay, J.F., 1968, The development of clast fabric in mudflows: Jour. Sed. Petrology, v. 38, p. 1242-1253. MacGinitie, H.D., 1962, The Kilgore flora, a late Miocene flora from northern Nebraska: California Univ. Pubs. Geol. Sci., v. 35, p. 67-158. Mark, D.M., 1973, Analysis of axial orientation data, including t i l l fabrics: Geol. Soc. America Bull., v. 84, p. 1369-1374. Martin, H.A., and Rouse, G.E., 1966, Palynology of late Tertiary sediments from Queen Charlotte Islands, British Columbia: Canadian Jour. Botany, v. 44, p. 171-208. Mathews, W.H., and Rouse G.E., 1963, Late Tertiary volcanic rocks and plant-bearing deposits in British Columbia: Geol. Soc. America Bull., v. 74, p. 55-60.  106  Milne, W.G. , Smith, W.E.T., and Rogers, G.C, 1970, Canadian seismicity and microearthquake research i n Canada: Canadian Jour. Earth Sci., v. 7, p. 591-601. North, F.K. , and Henders on, G.G.L., 1954, The Rocky Mountain Trench, in Scott, J.C., and Fox, F.G., eds., Guidebook, 4th annual field conference: Alberta Soc. Petroleum Geologists, p. 82-100. Pardee, J.T., 1950, Late Cenozoic block faulting in western Montana: Geol. Soc. America Bull., v. 61, p. 359-406. Penny, J.S., 1969, Late Cretaceous and early Tertiary palynology, in Tschudy, R.H., and Scott, R.A., eds., Aspects of palynology, an introduction to plant microfossils i n time: New York, John Wiley and Sons, Inc., p. 331-376. Piel, K.M., 1969, Palynology of middle and late Tertiary sediments from the central interior of British Columbia, Canada [Ph.D. thesis]: Vancouver, British Columbia Univ., 157 p. 1971, Palynology of Oligocene sediments from central British Columbia: Canadian Jour. Botany, v. 49, p. 1885-1920. Price, R.A., 1962, Fernie map-area, east half, Alberta and British Columbia: Canada Geol. Survey Paper 61-24, 65 p. 1966, Flathead map-area, British Columbia and Alberta: Geol. Survey Mem. 336, 221 p.  Canada  Price, R.A., and Mountjoy, E.W., 1970, Geologic structure of the Canadian Rocky Mountains between Bow and Athabasca Rivers—a progress report, in wheeler, J.O., ed., Structure of the Canadian Cordillera: Geol. Assoc. Canada Spec. Paper 6, p. 7-25. Price, R.A., and Wise, D.U., 1959, Flathead, British Columbia and Alberta: Canada Geol. Survey Map 1-1959. Ragan, D.M., 1968, Structural geology, an introduction to geometrical techniques: New York, John Wiley and Sons, Inc., 166 p. Rice, H.M.A., 1937, Cranbrook map-area, British Columbia: Survey Mem. 207, 67 p.  Canada Geol.  Rouse, G.E., 1962, Plant microfossils from the Burrard Formation of western British Columbia: Micropaleontology, v. 8, p. 187-218. Rouse, G.E., Hopkins, W.S., Jr., and P i e l , K.M., 1970, Palynology of some Late Cretaceous and Early Tertiary deposits i n British Columbia and adjacent Alberta, in Kosanke, R.M., and Cross, A.T., eds., Symposium on palynology of the Late Cretaceous and Early Tertiary: Geol. Soc. America Spec. Paper 127, p. 213-246.  107  Russell, L.S., 1951, Age of the Front-Range deformation in the North American Cordillera: Royal Soc. Canada Trans., ser. 3, sec. 4, v. 45, p. 47-69. 1954a, Mammalian fauna of the Kishenehn Formation, southeastern British Columbia: Natl. Mus. Canada Bull. 132, p. 92-111. 1954b, The Eocene-Oligocene transition as a time of major orogeny in western North America: Royal Soc. Canada Trans., ser. 3, sec. 4, v. 48, p. 65-69. Ryder, J.M., 1971, The stratigraphy and morphology of para-glacial alluvial fans in south-central British Columbia: Canadian Jour. Earth Sci., v. 8, p. 279-298. Schofield, S.J., 1915, Geology of the Cranbrook map-area, British Columbia: Canada Geol. Survey Mem. 76, 245 p. Stanley, E.A., 1965, Upper Cretaceous and Paleocene plant microfossils and Paleocene dinoflagellates and hystrichosphaerids from northwestern South Dakota: Bulls. Am. Paleontology, v. 49, p. 175-384. Thompson, T.L., 1962, Origin of the Rocky Mountain Trench in southeastern British Columbia by Cenozoic block faulting: Alberta Soc. Petroleum Geologists Jour., v. 10, p. 428-437. Traverse, Alfred, 1955, Pollen analysis of the Brandon lignite of Vermont: U.S. Bur. Mines Rept. Inv. 5151, 107 p. West, R.G., and Donner, J.J., 1956, The glaciations of East Anglia and the East Midlands: a differentiation based on stone-orientation measurements of the t i l l s : Geol. Soc. London Quart. Jour., v. 112, p. 69-91. Wheeler, J.O., Aitken, J.D., Berry, M.J., Gabrielse, Hubert, Hutchison, W.W., Jacoby, W.R., Monger, J.W.H., Niblett, E.R., Norris, D.K., Price, R.A., and Stacey, R.A., 1972, The Cordilleran structural province, in Price, R.A., and Douglas, R.J.W., eds., Variations in tectonic styles in Canada: Geol. Assoc. Canada Spec. Paper 11, p. 1-81. Wickens, A.J., and Pec, K., 1968, A crust-mantle profile from Mould Bay, Canada to Tucson, Arizona: Seismol. Soc. America Bull., v. 58, p. 1821-1831. Wolfe, J.A., 1971, Tertiary climatic fluctuations and methods of analysis of Tertiary floras: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 9, p. 27-57. Wolfe, J.A., and Barghoorn, E.S., 1960, Generic change in Tertiary floras in relation to age: Am. Jour. Sci., v. 258-A, p. 388-399.  108  Wolfe, J.A., and Hopkins, D.M., 1967, Climatic changes recorded by Tertiary land floras in northwestern North America, in Hatai, Kotora, ed., Tertiary correlations and climatic changes in the Pacific: Proc. 11th Pacific Sci. Cong., Tokyo, v. 25, p. 67-76. Woollard, G.P., 1958, Areas of tectonic activity in the United States as indicated by earthquake epicenters: Am. Geophys. Union Trans., v. 39, p. 1135-1150. Wright, H.E., J r . , 1957, Stone orientation in Wadena drumlin f i e l d , Minnesota: Geog. Annaler, v. 39, p. 19-31.  109  CHAPTER THREE:  GLACIER-FLOW PATTERNS AND THE  ORIGIN OF LATE WISCONSINAN TILL  ABSTRACT Late Wisconsinan glacier-flow patterns and t i l l genesis in the southern Rocky Mountain Trench, British Columbia were determined through a study of glacial landforms, t i l l fabric, and t i l l composition. At least one major shift in the pattern of glacier flow occurred near the end of glaciation.  An earlier stage when major tribu-  tary glaciers were coalescent with the trunk glacier in the Rocky Mountain Trench was followed by recession of tributary glaciers and invasion of side valleys by the trunk glacier.  Final recession of the  trunk glacier occurred with no major halts and without major stagnation of  the terminus. A review of the ways in which strongly directed t i l l fabrics  originate indicates that t i l l associated with drumlins accumulated by lodgement of particles due to subglacial pressure melting against a planar substratum and not by the melt-out process (slow melting in at  the base or surface of stagnant ice masses) nor by post-depositional  reorientation caused by glacier overriding. lower part of the younger ice  situ  Some fabrics from the  t i l l sheet suggest either complex patterns of  flow similar to those at junctions of many modern valley glaciers,  or mass movement of supraglacial t i l l (flowtill) associated with an interstadial interval within the late Wisconsinan glaciation.  110  Compositional analyses are less sensitive as indicators of glacier-flow patterns than t i l l - f a b r i c results in the southern Rocky Mountain Trench.  This is apparently the result of two processes:  (1) t i l l may have been reworked at the ice-sediment interface; and (2) sediment may have been transported to a subglacial depositional site by a mechanism other than the flowing ice i t s e l f , specifically by meltwater via an englacial "plumbing" system, followed by lodgement through pressure melting. Nevertheless, t i l l composition reflects the dominant pattern of ice flow during glaciation. Most pebbles and fine sand in the t i l l s of the Rocky Mountain Trench are of local origin.  Local constituents decrease in relative  amounts away from the mouths of tributary valleys from whence they were derived. These decreasing gradients cannot be due entirely to breakage and abrasion during transport, but rather are likely explainable by progressive deposition and dilution through sediment mixing. Compositional differences in t i l l are pronounced off tributary valleys, but become less distinct to the south. This probably results from lateral mixing of sediment due to shifts in the zone of coalescence of trunk and tributary glaciers with changes in relative ice flux from the two.  INTRODUCTION The existence of a former glacier is indicated by t i l l , a poorly sorted sediment deposited directly from ice and characterized by a variety of mineral and rock types and, commonly, subangular clasts,  Ill  some striated sand grains, pebbles, and coarser clasts, and a pronounced directional fabric.  Lenses of sorted, water-worked sediment are common  in t i l l , and the t i l l unit itself commonly overlies or contains striated pavements. T i l l is a widespread sediment in areas glaciated during the Quaternary, but, as indicated by Goldthwait (1971), is most common and thickest i n the outer part of each glaciated area, where multiple t i l l layers record successive glacial advances.  T i l l studies to date have been  primarily concerned with the characterization and correlation of s t r a t i graphic sequences.  Common methods used in such studies include strati-  graphic position of t i l l , associated landforms, textural and lithologic analyses, color, weathering, and sometimes fabric analysis. Recently, increased emphasis has been placed on using the above methods to gain insight into the mode of origin of t i l l (review in Goldthwait, 1971). Such investigations are complemented by those of glaciologists and others concerned with how sediment is entrained, transported, and deposited by ice  (Goldthwait, 1951; McCall, 1952; Weertman, 1961; Kamb and LaChapelle,  1964; Boulton, 1970a, 1970b, 1971; Nobles and Weertman, 1971). T i l l of late Wisconsinan age in the Rocky Mountain Trench of southeastern British Columbia was studied to determine the pattern of glacier flow in the Trench and i t s major tributaries; to assess the applicability of certain methods of t i l l investigation in the Cordillera, specifically fabric and lithologic analyses; and to determine the mode of origin of the t i l l .  112  DISTRIBUTION AND  CHARACTER OF TILL  Unconsolidated and partially consolidated deposits mantle the bedrock floor of the southern Rocky Mountain Trench and consist of up to 1400 m of Tertiary sediments overlain by Quaternary sediments locally thicker than 200  m.  Deposits of three glacier advances are recognized.  These  advances are tentatively correlated with stades of the Pinedale Glaciation of the Rocky Mountains in the United States (Richmond, 1965), and with the Fraser Glaciation in the coastal Pacific Northwest (Armstrong and others, 1965;  Crandell, 1965).  Interglacial sediments which contain wood dated  at 26,800 ± 1000 years B.P.  (GX-2032) underlie drift of the early stade.  Glacier recession between the middle and late advances was of short duration and extent; glaciolacustrine sediments were deposited only along the margins of the Rocky Mountain Trench, and apparently residual ice remained in the center of the Trench.  In contrast, during the interstade  between the early and middle glacier advances, the Rocky Mountain Trench within the study area was completely deglaciated, and sediments were deposited in one or more lakes on the floor of the Trench. the early stade are informally called older drift  Deposits of  (also lower  drift);  those of the middle and late stades are referred to as younger drift  upper drift,  Wycliffe  (also  till).  T i l l of latest Wisconsinan age is the dominant surface on the floor of the Rocky Mountain Trench (Fig. 31).  deposit  Called the Wycliffe  t i l l by Schofield (1915), i t is a massive, unsorted deposit of clay, s i l t , sand, and clasts ranging widely in size (Fig. 32, Appendix 3), and is  113  l i g h t gray to very l i g h t gray (N 7 to N 8) i n c o l o r .  The clasts are  subangular to subrounded, commonly s t r i a t e d , and consist of a variety of rock types present i n the P u r c e l l and Rocky Mountains flanking the map area.  The t i l l i s calcareous except where derived e n t i r e l y from the  P u r c e l l Mountains.  In general, patches of noncalcareous t i l l i n the  Trench are limited to the lower slopes of the P u r c e l l s .  Kelley and  Sprout (1956, p. 27) have reported noncalcareous t i l l o f f S t . Mary Valley as f a r east as W y c l i f f e .  Lenses of water-worked sand and gravel are present within the t i l l sheet.  Horizontally s t r a t i f i e d lake s i l t s from 3 to 15 m thick  occur within the Wycliffe t i l l along the margins of the Trench and may record an i n t e r v a l of g l a c i e r recession between the middle and late stades of  the Pinedale G l a c i a t i o n .  Where exposed i n the walls of major p o s t g l a c i a l v a l l e y s , Wycliffe t i l l ranges i n thickness from a few meters to more than 40 m, but is most commonly 10 to 30 m t h i c k .  The surface of the t i l l sheet slopes  gradually to the south down the Trench (approximate slope = 0.7 m/km). The base also has a down-Trench slope, although there i s substantial l o c a l r e l i e f on the interface between the t i l l and underlying sediments.  Immediately p r i o r to deglaciation, Wycliffe t i l l covered the entire Trench f l o o r .  This constructional surface was modified by l a t e r a l ,  p r o g l a c i a l , and subglacial meltwater as the glaciers receded.  The  till,  thus, was reworked l o c a l l y into outwash; i t was removed completely along the major r i v e r valleys during the Holocene Epoch.  114  GLACIER-FLOW PATTERNS The Glacial Map of Canada (Prest and others, 1967) records observations of glacial striae, drumlins, other glacial lineations, and meltwater channels. In many cases, these indicate the centers of ice accumulation and regional patterns of ice movement in British Columbia during the Wisconsinan Glaciation.  Major centers in both the Columbia  and Rocky Mountains fed the glacier that was flowing southeast through the Rocky Mountain Trench into Montana. The following is my interpretation of the events that were occurring during this time. At the climax of the last major Pleistocene glaciation, the mountains bordering the southern Rocky Mountain Trench were almost completely buried by ice.  Erratics and striae along the Rocky Mountain  front just north of Bull River indicate the glacier reached an elevation of at least 2260 m there.  On the west side of the Trench, Mount Baker  (elev. 2210 m) has a rounded, streamlined crest resulting from glacier overriding.  Daly (1912) concluded that at the peak of glaciation the  average level of ice in the Galton Range and Purcell Mountains near 49°N latitude was 2230 m.  The Cordilleran Ice Sheet was thus about  1500 m thick over the Trench at the International Boundary.  In the  Rocky and Purcell Mountains only the higher peaks projected above the glacier surface.  Ice in the ranges bordering the Trench on the east  discharged . . .in a general southward direction and was largely concentrated in the Wigwam Valley and in the Rocky Mountain Trench, though some of the ice flowed eastward into the North Flathead glacier before beginning i t s southward journey. (Daly, 1912, p. 585)  115  Landforms on the Trench floor record directions of ice movement during the closing phase of the last glaciation and also provide information on the manner in which deglaciation occurred. Drumlins and modified drumlins are the dominant landforms developed on Wycliffe t i l l (Fig. 33). In general, these drumlins trend south and southeast parallel to the margins of the Rocky Mountain Trench; this indicates, as one might expect, that topography exerted primary control on the direction of glacier flow.  The dominance of drumlinized topography and the rarity of ice-  stagnation features such as eskers, hummocky ground moraine, kames, kame moraines, and kettles suggest that deglaciation occurred by uniform recession of an active terminal zone without large-scale stagnation of any part of the glacier.  Most kettles occur i n the recessional outwash  underlying outwash plains, kame terraces, and meltwater channels, rather than in Wycliffe t i l l .  Apparently, there were no major standstills or  readvances during deglaciation, as recessional and end moraines are absent on the Trench floor from at least the International Boundary to the north end of the study area, a distance of about 150 km. One possible exception is a hummocky ridge just north of Bull River that may represent part of a moraine deposited by the Bull Valley glacier. Although drumlins provide a reasonably complete picture of the pattern of last ice flow, other directional indicators must be used off major tributaries.  This is because Wycliffe t i l l at the mouths of these  tributary valleys was eroded by meltwater entering the Trench, and subsequently was removed during early Holocene valley cutting. Fortunately, near these tributary mouths there are bedrock surfaces which were subject to glacial erosion throughout glaciation.  On these surfaces,  116  the l a s t major d i r e c t i o n of g l a c i e r flow i s indicated by s t r i a t i o n s , crescentic gouges, and crescentic fractures (Figs. 31 and 33).  This  additional information shows that the g l a c i e r flowing down the Trench fanned out to occupy the lowland i n the Kimberley-Cranbrook-Fort Steele area and bulged up into Elk V a l l e y .  This implies that tributary glaciers  i n St. Mary and Elk Valleys had receded p r i o r to deglaciation of the Trench f l o o r , a conclusion corroborated by stratigraphic evidence for the existence of late g l a c i a l lakes i n these v a l l e y s .  These g l a c i a l deposits and landforms are time transgressive, being younger toward the north.  For example, the late g l a c i a l lake  impounded by Trench i c e i n St. Mary Valley i s at least i n part younger than a comparable lake i n Elk V a l l e y .  The extent to which these features  transgress time i s not known, as there i s at present only one  radiocarbon  date providing a minimum l i m i t i n g age for deglaciation of the  southern  Rocky Mountain Trench at one point (10,000 ± 140 years B.P.; 51°28'55"N, 117°13'25"W; GSC-1457; Fulton, 1971).  location—  On the basis of  other l i m i t i n g radiocarbon dates from southern B r i t i s h Columbia, i t has been speculated that the i c e margin i n the Trench was about 12,000 to 13,000 years ago  at 49°N l a t i t u d e  (Prest, 1969).  A n a l y t i c a l Procedure  Further information on the pattern and mechanics of g l a c i e r flow has been obtained from an investigation of the f a b r i c , heavy mineral composition, and clast l i t h o l o g i e s of the late Wisconsinan t i l l . The pattern of g l a c i e r flow as determined independently  from drumlins,  117  striations, and other flow indicators (p, 115) provides an internal check by which the applicability of these methods in glaciated areas of the Cordillera may be evaluated.  T i l l - f a b r i c Analysis The f i r s t major quantitative work on the fabric of t i l l was done by Richter (1932).  Since that time t i l l fabrics have been exten-  sively employed as indicators of the flow directions of former glaciers. It was found that elongate clasts preferentially trend parallel to flow and plunge up-glacier, although fabrics with transverse maxima were also recognized.  Holmes (1941) showed that clast shape in part determines  whether the fabric maximum i s parallel or transverse to the flow direction. However, the mechanisms by which clasts in t i l l become oriented remained poorly understood, even though numerous hypotheses were advanced on empirical and theoretical grounds (Richter, 1936; Holmes, 1941; Sitler and Chapman, 1955; Glen and others, 1957; Harrison, 1957; Wright, 1957). Several authors have commented on the internal variability of t i l l fabric.  West and Donner (1956) and Young (1969) concluded that horizontal  variation is small in comparison to vertical variation, thus making i t possible to differentiate major ice advances.  Harrison (1957) and  Kauranne (1960), on the other hand, found considerable variation in short lateral distances, although horizontal variation is less than vertical variation between levels.  In perhaps the most detailed study of within-  and between-site variability, Andrews and Smith (1970) concluded that within-site precision estimates are low and similar to estimates on cross-beds, whereas between-site precision estimates over short lateral  118  and vertical distances vary from low to high.  The treatment and assess-  ment of t i l l - f a b r i c data improved with the application of three-dimensional analytical techniques and statistical tests of significance (Andrews and Smith, 1970; Mark, 1973). At present, however, there is a general lack of uniformity i n t i l l - f a b r i c investigation and analysis procedures (Andrews, 1971), at least in part due to lack of consensus on the origin of the t i l l fabric.  There is an absence of standardization i n data  collection (geometry and size of clasts; limiting ratios of a, b, and c axes; axes or planes measured; aspect of sampling site; sample size), 1  sampling control (measure of within-site variability of fabrics), data portrayal (various rose diagrams, contour diagrams, and stereograms), and quantitative analysis of data (two- and three-dimensional methods with a variety of associated statistics including mean direction, dispersion about the mean, and tests of randomness). Despite the above d i f f i c u l t i e s , a better understanding of how sediment i s entrained in a glacier, transported, and deposited is being provided by glaciologists.  With regard to t i l l fabrics, the work of  Boulton (1968, 1970a, 1970b, 1971) i s particularly important.  Boulton  has studied the transport and fabric characteristics of sediment within Spitsbergen glaciers and the fabric of t i l l freshly deposited by the glaciers. "He has recognized that t i l l fabric may be due to one or a combination of the following:  (1) orientation of sediment particles  during transport, (2) acquisition of preferred orientation during  The long, intermediate, and short axes of t i l l clasts are called the a, b, and c axes respectively. 1  119  deposition, and (3) post-depositional reorientation resulting from mass movement or glacier overriding.  Each of these i s considered below and  the evidence provided by Boulton (1971) and others briefly reviewed.  Englacial  transport.  It has been shown both on theoretical  and empirical grounds that randomly oriented particles immersed i n a shearing, viscous or quasi-viscous fluid develop a preferred orientation. Jeffrey (1922) concluded that ellipsoidal particles rapidly develop a long-axis distribution with a peak parallel to the flow direction.  He  pointed out, however, that energy dissipated by an ellipsoid is minimal i f the long axis i s in the transverse position.  Thus, there may be a  reorientation from the parallel to the transverse position over a long period of time, although the exact way in which this occurs i s not understood.  These conclusions are substantiated by observations of the  englacial fabric by Boulton (1971).  He found that the a axes of rod-  shaped clasts and the a-b planes of blade-shaped clasts l i e i n the foliation plane.  The orientation of the a axes within this plane i s  dependent upon the local stress conditions i n the glacier; in the terminal zone of compressive flow, a-b planes and ice foliation dip steeply up-glacier, and a axes are transverse to flow; in zones of extending flow, on the other hand, a-b planes are sub-horizontal, and a axes of blades and rods are parallel to flow.  In zones where there is  neither marked compression nor extension, preferred orientation of a axes of blades and rods i s weak or absent.  Where shear planes dipping up-  glacier intersect the ice foliation, blades are reoriented so that their  a-b planes are parallel to the shear surface. The a axes of both rods and blades are parallel to the direction of movement along these surfaces,  120  and therefore parallel to the direction of ice flow,  Deposition.  An englacial fabric may be inherited or modified  depending on the manner of t i l l deposition.  Boulton has suggested that  there are three major processes of t i l l deposition and thus three groups of t i l l :  lodgement t i l l , melt-out t i l l , and f l o w t i l l .  Lodgement t i l l  is deposited either from active ice by melting under pressure at the t i l l - g l a c i e r interface, or from a zone of debris-laden stagnant ice separating  the active glacier from the sediment substratum.  Melt-out  t i l l is deposited subglacially or supraglacially by the in~situ out from stagnant ice of englacial debris.  melting-  Flowtill originates when  supraglacial melt-out t i l l undergoes mass movement, Boulton (1971) observed the deposition of lodgement t i l l by pressure melting of active ice against obstructions.  The orientation of  plastered-on elongate particles is dependent upon the geometry of the substratum.  Where this is non-transverse, parallel-to-flow a-axis  orientations result, but dip directions of a-b planes and plunge directions of a axes are limited by the slope direction of the surface.  Boulton  (1970a) has described a subglacial t i l l deposited by the melting of debris-rich stagnant ice overridden by active ice along a dScollement surface.  The t i l l has a fabric inherited from englacial transport, but  altered along shear planes produced after deposition by glacier overriding. Melt-out t i l l forms in the terminal zone of a glacier and is likely to eventually undergo mass movement and thus become f l o w t i l l . fabric of melt-out t i l l reflects that of the englacial debris which is  The  121  concentrated by the melting of i n t e r s t i t i a l ice.  The amount of alteration  of the englacial fabric depends on the percentage of ice eliminated during melting; where ice content is high, fabric modification is substantial. This modification mainly involves a decrease i n the angle of dip of blades which in the terminal zone are aligned in the englacial state parallel to the up-glacier-dipping  foliation.  When supraglacial t i l l moves under the influence of gravity, any pre-existent  fabric related to ice flow w i l l be replaced by one  related to mass movement forces.  Fabric elements both parallel and  transverse to the resulting sediment transport direction develop, but, since this direction is rarely related to the direction of ice movement, the resulting fabric yields l i t t l e information on the glacier-flow pattern.  Post-depositional  reorientation.  Fabric reorientation can  occur along closely spaced shear zones or by viscous flow in watersaturated t i l l as i t i s overridden by active ice. MacClintock and Dreimanis (1964) and Ramsden and Westgate (1971) have described fabrics modified by glacier overriding.  The a axes of elongate particles are  reoriented parallel to the direction of glacier movement.  Fabric  reorientation can also result from postglacial mass movement (e.g., landslides, creep). Table 4 summarizes the relationships between t i l l - f a b r i c elements and processes of glacier flow and t i l l deposition.  Considering the  intricacy of interrelationships between these factors, i t is not surpris-  122  ing is  that w i t h i n - s i t e v a r i a b i l i t y i s large and that f a b r i c interpretation fraught with d i f f i c u l t i e s .  made. is  Nevertheless, certain conclusions can be  I f the d i r e c t i o n of i c e movement responsible f o r a p a r t i c u l a r  till  independently known, i t may be possible to i n f e r the mode of o r i g i n of  the t i l l .  T i l l characterized by blades with a-b planes dipping steeply  up-glacier and rods with a axes transverse to flow indicates preservation by melt-out of an englacial compressive f a b r i c produced i n the terminal zone of a g l a c i e r .  I f a-b planes of blades are s i m i l a r l y oriented, but  the a axes of rods are p a r a l l e l to flow and dip steeply up-glacier, an englacial f a b r i c produced along shear planes i n the terminal zone and inherited during melt-out i s indicated.  A variety of interpretations may be placed on strongly directed fabrics with gently dipping elongate p a r t i c l e s .  For example, they may  a r i s e by the weakening of a steeply dipping englacial f a b r i c during melt-out, by subglacial lodgement through pressure melting, by preservat i o n of an englacial f a b r i c i n zones of extending flow, or by postdepositional reorientation along sub-horizontal shear planes under an active g l a c i e r .  In most of these cases, maxima are p a r a l l e l rather than  transverse to flow.  I n t u i t i v e l y , one might expect that most t i l l would  originate i n one or more of these ways; thus, i t i s not surprising that most f a b r i c diagrams f o r t i l l from areas of ground moraine are characterized by a gently dipping g i r d l e with either a single maximum on the g i r d l e o r , less commonly, with two maxima 90° apart (Holmes, 1941, p. 1313; Harrison, 1957, p. 283; Kauranne, 1960, p. 87; Ramsden and Westgate, 1971, p. 339).  The l a t t e r s i t u a t i o n might originate by the melt-out of a  composite englacial f a b r i c i n which rods i n the terminal area of the  123  glacier are parallel to flow in shear zones and transverse to flow along foliation planes. Strong fabrics which are neither parallel nor transverse to the direction of ice flow may indicate deposition as flowtill or alteration of a pre-existent fabric by post-depositional and postglacial mass movement.  Method. The fabric of late Wisconsinan t i l l in the southern Rocky Mountain Trench was investigated to supplement information on the pattern of ice flow and the origin of the t i l l . Fabrics were determined at 3 sites from the lower t i l l and at 26 localities as near as possible to the stratigraphic top of the upper t i l l , but below the zone of active frost disturbance and pedogenesis. At several localities i t was necessary to sample well below the stratigraphic top of the upper t i l l because of erosion of ground moraine by late glacial meltwater.  Sampling was limited to natural exposures along  major river valleys and to fresh road cuts.  At several sample sites,  where a substantial vertical section of the t i l l sheet is exposed, fabrics were measured at 1 to 5 m vertical intervals. At each sampling site an inclined or vertical exposure free of slumping and 1 m high by 2 to 10 m wide was cleared.  The trend and plunge of 20 or 60 elongate  pebbles (a/b > 2, b/c - 1, a > 1 cm) taken from the cleared exposure were recorded.  A l l clasts which met the elongation criteria were measured.  Optimum sample size was determined by comparing the mean orientations of fabrics of size 20 and 60 taken from the same sites (Fig. 34).  Mean  orientations were nearly the same for t i l l samples with strong fabrics,  124  but in general were quite different for weaker fabrics,  Andrews and  Smith (1970, p. 520-521) have shown that for t i l l - f a b r i c samples of size 25, 50, and 100,  the smaller samples yield essentially the same results  as the larger samples, and standard deviation does not increase with decreasing sample size. Internal variability in t i l l fabric was evaluated by selecting a group of control sampling sites where the direction of ice flow is known from such criteria as drumlins and bedrock striations.  Fabrics  determined at these sites were compared with the trends of the associated glacial lineations. Data were plotted on an equal-area net and contoured according to the method reviewed by Ragan (1968, p. 79-82).  A spherical  probability  distribution applicable to three-dimensional axial data was used to determine axes of maximum and minimum clustering for each fabric (Mark, 1973).  Each data set was tested for randomness by using significance  tests based on this distribution (Anderson and Stephens, 1971).  Results.  Examples of typical t i l l - f a b r i c patterns are shown  in Figure 35 and Appendix 5. Most of the t i l l fabrics show one of the following patterns recognized by Ramsden and Westgate (1971, p. 339) as common in ground moraine:  (1) sub-horizontal girdle with a single maximum  on the girdle, or (2) sub-horizontal girdle with two maxima 90° apart on the girdle.  For 3120 pebbles measured, the modal plunge angle is 5°, the  mean, 20°, and the median, 14° (Fig. 36).  Within the control group of  samples, there is a close relationship between fabric maxima and trends  125  of associated g l a c i a l lineations  ( F i g . 37, Table 5).  In a l l except two  cases, the axis of maximum clustering i s within 24° of the d i r e c t i o n of g l a c i e r flow defined by g l a c i a l l i n e a t i o n s .  One of the two exceptions  represents an a-axis maximum transverse to g l a c i e r flow (fabric no. 1); the other f a b r i c has a maximum 59° from the trend of the associated drumlin (fabric no. 15). The fabric maximum of the l a t t e r i s p a r a l l e l to and aligned with B u l l Valley  ( F i g . 37) which carried a major tributary  g l a c i e r during late Wisconsinan time.  I t i s possible that this f a b r i c ,  measured 1 to 2 m below the drumlin surface, represents a p a r a l l e l fabric produced by the B u l l Valley trend originated  tributary g l a c i e r ; i f so, the oblique drumlin  s l i g h t l y l a t e r by flow down the Trench following  recession of B u l l Valley g l a c i e r .  Evidence showing that tributary  glaciers receded before the active g l a c i e r i n the Trench i s presented on p. 116. The close correspondence between f a b r i c maxima and trends of other indicators of g l a c i e r flow shows that i n t e r n a l v a r i a b i l i t y at f a b r i c s i t e s i s low and that fabrics i n the Trench are characterized by sub-horizontal girdles with a axes generally p a r a l l e l to flow.  Although  there i s no systematic plunge d i r e c t i o n of f a b r i c maxima, 69% of p a r a l l e l to-flow fabrics have axes of maximum clustering which plunge up-glacier (43% of i n d i v i d u a l clasts plunge up-glacier, 30% down-glacier, and 27% have transverse  orientations).  Axes of clustering and associated measures of s t a t i s t i c a l significance for each t i l l f a b r i c are presented i n Appendix 6. Axes of maximum clustering f o r nonuniform samples are plotted i n Figures 37 and 38. Figure 37 presents a l l f a b r i c results from the lower the top of the upper  t i l l , including  t i l l and from near  the control group; Figure 38  126  presents results of fabrics determined vertically through the upper t i l l .  Heavy Mineral Analysis Heavy mineral concentrates from t i l l have long been used to differentiate t i l l sheets and determine the sources of the glaciers which deposited them (e.g., Dreimanis and others, 1957; Dreimanis,  1961;  Bayrock, 1962; Willman and others, 1963). Most such studies have been made in regions of low relief such as central North America.  Recently,  studies of t i l l composition, including heavy mineralogy, have yielded information on the entrainment and transport history of sediment by glaciers (Dreimanis and Vagners, 1971; Gross and Moran, 1971).  For  example, Dreimanis and Vagners (1971) have identified "terminal grades," or  limiting grain sizes produced by glacial comminution for a variety of  heavy minerals.  The proportion of a particular mineral in i t s terminal  size fraction is then a measure of the length of transport of the t i l l matrix. T i l l s in the southern Rocky Mountain Trench contain a characteristic suite of heavy minerals.  Since the provenance of certain of  these heavy minerals i s known, i t has been possible to obtain information on the pattern of glacier flow in the Trench, which complements that provided by t i l l fabrics, and on the mechanisms of entrainment, transportation, and deposition of sediment by ice. The amount of a given mineral or rock constituent in t i l l is dependent on a number of factors, the most important being: of  (1) abundance  outcrop of the mineral or rock at the base of the glacier upstream from  127  the depositional s i t e (Harrison, 1960, p. 443; F l i n t , 1971, p, 180); (2) e r o d i b i l i t y of the source rock ( F l i n t , 1971, p. 180); (3) d u r a b i l i t y of the rock or mineral i n transport (Holmes, 1952; Dreimanis and Vagners, 1971; F l i n t , 1971, p. 181); and (4) distance of transport (Gravenor, F l i n t , 1971, p. 181).  1951;  The fourth factor i s related to d u r a b i l i t y , d i l u -  t i o n , and progressive deposition away from the source area.  Since the  turbulent mixing c h a r a c t e r i s t i c of r i v e r s i s absent i n g l a c i e r s , and since d i f f u s i o n of coarse sediment i s probably n e g l i g i b l e , sediment d i l u t i o n by mixing within glaciers terminal areas.  i s probably limited to shear zones i n  However, d i l u t i o n may occur at the till-glacier  inter-  face as pressure melting releases a mix of sediment eroded from different bedrock sources.  D i l u t i o n by this mechanism would be expected at the  base of two coalescent glaciers with l i t h o l o g i c a l l y d i s t i n c t sediment loads.  As the boundary between the two glaciers shifted l a t e r a l l y due  to variations  i n r e l a t i v e i c e f l u x , sediment at the t i l l - g l a c i e r  interface  previously deposited by one g l a c i e r would be diluted with sediment released by pressure melting from the other.  Even beneath a single  u n i d i r e c t i o n a l g l a c i e r , l a t e r a l dispersion of sediment may  occur, as  shown by dispersion of indicator l i t h o l o g i e s i n fan-shaped patterns downg l a c i e r from point sources (Dreimanis, 1956; Goldthwait, 1968) and by flow divergence around basal obstructions (Carol, 1947; L l i b o u t r y , 1959). The amount of a p a r t i c u l a r constituent i n t i l l i s , of course, proportional to the amount present at the sole of the glacier during deposition.  Near  the source area, a high percentage of a p a r t i c u l a r rock type or mineral at the base of the g l a c i e r would result through the pressure-melting depositional process i n lodgement t i l l which also has a high content of  128  that constituent. at ice  As this constituent is deposited, less is available  the glacier base for deposition farther from the source.  Thus, both  and lodgement t i l l contain progressively less of a mineral or  rock type as distance from the source increases.  This assumes that the  constituent i s transported near the base of the glacier rather than in an englacial position above the zone of active deposition.  This general  relationship may be expressed mathematically:  d  «N  N  dx  Nx  (1)  *  V  is the amount of the constituent at the glacier base or in t i l l at a  distance, x, from the source.  If a constant, k, is introduced:  Eq. (2) can be integrated (at x = 0, Nx  = e  m  = N , where m is a constant  of integration): N  x  =  N e  o  kX  (3)  The constant, k, is a measure of the rate as a function of distance at which deposition occurs.  This depositional rate constant may be determined  by glacier dynamics or by size and physical properties of the transported constituent. Data collected by Gravenor (1951) and Dreimanis (1956) show the relationship between percent of various t i l l constituents and distance from source (Fig. 39).  If mathematical expressions of the form of Eq. (3)  are fitted to the data, high correlation coefficients are obtained.  129  Method. Bulk t i l l samples for heavy mineral analysis were collected at 136 sites in the southern Rocky Mountain Trench and major tributary valleys (Fig. 40).  Of these, 117 were collected from canyon  walls, road cuts, and surface excavations near the stratigraphic top of the upper t i l l .  These samples were taken below the s o i l horizon of  calcium carbonate accumulation.  An additional 16 samples were collected  vertically through the t i l l sheet at several localities.  The remaining  samples (nos. 18, 23, and 99) are from the lower t i l l exposed along St.  Mary and Elk Rivers. Each sample is a composite of 1 to 2 kg of t i l l taken from two  1 m  2  plots separated approximately 3 to 5 m laterally.  Recovery of the  heavy mineral fraction was accomplished through standard procedures (Krumbein and Pettijohn, 1938) of disaggregation, wet sieving, and gravity separation in bromoform (density = 2.89).  The fine sand (105-210 urn)  fraction was selected for quantitative analysis because i t represents the largest size fraction consisting almost entirely of monomineralic grains.  Minerals were identified optically and by magnetic separation  and x-ray diffraction methods.  Grain mounts were then prepared, and  500 grains on each of two glass slides were point-counted for each sample.  Recounts of the same sample yielded similar results.  Data were  recorded both as volume percent of total heavy minerals of fine sand size and as volume percent of the total fine sand fraction. The areal distribution of certain minerals near the top of the t i l l sheet was determined by trend-surface statistical techniques. A computer program modified from that of O'Leary and others (1966) was used  130  to process the data.  Results.  The following heavy minerals are recognized i n Rocky  Mountain Trench t i l l s :  p y r i t e , s p h a l e r i t e , galena, hematite, ilmenite,  r u t i l e , goethite (pseudomorphic after p y r i t e ) , magnetite, dolomite, a p a t i t e , garnet, z i r c o n , kyanite, s t a u r o l i t e , sphene, epidote group, tourmaline, amphibole family (hornblende, a c t i n o l i t e ) , muscovite, b i o t i t e , and c h l o r i t e . a l l samples.  2  Altered s i l i c a t e grains, mainly amphibole, are common i n Several rare minerals were not i d e n t i f i e d .  Several minerals  have r e s t r i c t e d bedrock sources and are therefore of value i n determining glacier-flow  patterns.  For example, i n the f i n e sand f r a c t i o n amphibole  i s almost e n t i r e l y r e s t r i c t e d t o , and magnetite most common i n , mafic s i l l s and dikes of Precambrian age, which are most common i n the St. Mary Valley area ( F i g . 41).  Tourmaline i s an a l t e r a t i o n mineral associated  with the S u l l i v a n ore body near Kimberley, but i t s frequency i n t i l l i s very low.  Garnet and s t a u r o l i t e are rare minerals i n southern Rocky  Mountain Trench bedrock which has only been metamorphosed to a maximum of the greenschist grade (Wheeler and others, 1972, their F i g . 16).  These  minerals are present i n the contact zones of g r a n i t i c bodies i n the P u r c e l l Mountains (J.E. Reesor, written commun., 1971).  However, t i l l s  i n t r i b u t a r i e s draining such g r a n i t i c bodies (e.g., samples 159 and 160, Appendix 7) contain very l i t t l e garnet and s t a u r o l i t e .  I t i s thought  that the source of these two minerals i s regionally metamorphosed rocks of the s t a u r o l i t e and kyanite zones which crop out extensively along the  2  bromoform.  P a r t i a l separation of muscovite, b i o t i t e , and c h l o r i t e i n  131  Trench north of Kinbasket Lake (latitude 52°N), Percentages of abundant heavy minerals and some less common ones with restricted bedrock sources are presented in Appendix 7.  Adjacent  samples at a site exhibit l i t t l e variation in heavy mineral content indicating that internal variability is slight.  Although there are some  differences i n heavy mineral percentages among vertical samples through the t i l l sheet at a station, there i s no systematic variation with depth. The heavy minerals may be placed into two groups on the basis of their source and areal distribution:  (1) local—minerals eroded from  bedrock sources within the study area and transported short distances; (2) foreign—minerals from outside the study area transported relatively long distances. The f i r s t group includes such minerals as magnetite, dolomite, and amphibole; the second, garnet and staurolite. Figure 42 shows the areal distribution and trend of amphibole from the top of the t i l l .  The local bedrock source, mafic dikes and  s i l l s in St. Mary Valley, i s readily apparent.  Of particular note are  (1) the rapid decrease of amphibole in t i l l away from the source, and (2) the presence of bands of amphibole-poor  t i l l parallel to the Trench  trend south of two major tributaries (Elk Valley and the Kootenay-Lussier Valleys).  These bands become diffuse with distance down-Trench from the  tributary mouths.  Similar results are provided by magnetite and other  opaque minerals. Figure 43 shows the areal distribution and trend of garnet. Although the fitted surface does not have as high a correlation coeffi-  132  cient as that for amphibole, some observations can be made:  (1) the  garnet content in t i l l i s highest at the north end of the study area, which is in agreement with the postulated northern source for the mineral; (2) an area of low-garnet t i l l off St. Mary Valley separates areas with higher garnet percentages to the north and south; and (3) as in the case of amphibole and other minerals of local origin, bands of garnet-poor t i l l parallel to the trend of the Trench occur south of Elko and the Kootenay-Lussier Valleys.  Clast Lithology Analysis Clast lithologic analyses of t i l l have been widely used to determine glacier-flow patterns (Milthers, 1942; Dreimanis, 1956), to differentiate t i l l s (Howard, 1956), and to infer the mechanism of sediment transport and the cause of the down-glacier decrease i n clast frequency (p. 126) (Holmes, 1952; Anderson, 1955).  Method. Clast lithologies were determined from samples of 100 pebbles (2> axis 16 to 32 mm) sieved from several kilograms of t i l l and outwash.  In addition to t i l l samples collected from near the top of the  t i l l sheet, a suite of vertical samples was taken at several sites (Fig.  40).  Most samples analyzed for heavy mineral content were also  analyzed for clast lithologies. There are few distinctive bedrock lithologies which are restricted i n distribution i n the study area.  Granitic rocks, although  distinctive, are distributed too widely to be of value as provenance  133  indicators.  Mafic igneous rocks of Precambrian age, although widespread,  are most abundant in St. Mary Valley (Fig, 41),  Precambrian laminated  greenish-gray a r g i l l i t e and red-purple a r g i l l i t e , s i l t i t e , and quartz arenite are most abundant along the east side of the Trench south of Elko,  Paleozoic carbonates crop out extensively along the east side of  the Trench near Elko and at the north end of the study area.  Finally,  distinctive chert-pebble conglomerate and chert arenite of Mesozoic age are restricted to Elk Valley.  Results.  Percentages of the above mentioned rock types (in  the pebble fraction of t i l l and outwash) are presented in Appendix 7. Adjacent t i l l and outwash samples are similar in composition; as was true for heavy mineral analyses, there is no systematic variation in lithology with depth at multiple sampling sites. The areal distribution of clasts from the top of the t i l l sheet shows that local bedrock i s the dominant component i n t i l l .  Mafic igneous  pebbles are common only near their bedrock source at the mouth of St. Mary Valley (Fig. 44), and their frequency decreases rapidly with increasing distance from this source.  The pattern for mafic igneous clasts i s  nearly identical to that for amphibole (Fig. 42).  Since both were  derived from the same source, their history of entrainment, transport, and deposition must have been similar.  Other clast lithologies also show  peaks i n frequency immediately down-glacier from their bedrock sources: laminated greenish-gray a r g i l l i t e is common only along the east side of the Trench south of Elko, dolostone is common at the north end of the study area, and limestone both at the north end of the study area and  134  near Elko. Foreign clasts are rare in Rocky Mountain Trench t i l l .  Durable  Mesozoic rocks which crop out only in Elk Valley are present, however, as conglomerate and sandstone pebbles.  The area of occurrence of Elk Valley  chert-pebble conglomerate and chert arenite in Trench t i l l is shown in Figure 45.  Their occurrence north of the mouth of Elk Valley is perhaps  due to the spillover of ice from Elk Valley into the Trench via Sand Creek or to the lateral transfer of clasts englacially by meltwater.  Discussion The dominance of drumlins as surface landforms on t i l l in the southern Rocky Mountain Trench indicates that t i l l deposition during the closing phases of glaciation occurred subglacially beneath active ice rather than by supraglacial melt-out or mass movement of supraglacial till.  Fabric characteristics establish further limits on the mode of t i l l  deposition.  Most fabrics, including those taken in control areas below  drumlin surfaces, display sub-horizontal axes of maximum clustering parallel to the direction of glacier flow (p. 124).  Such fabrics are  produced at the active g l a c i e r - t i l l interface by subglacial melt-out of overridden sediment-charged ice or by lodgement resulting from pressure melting (Table 4; Boulton, 1970a).  Alternatively, similar fabrics are  produced by shear or viscous flow following deposition of the t i l l , with the necessary force provided by glacier overriding (Ramsden and Westgate, 1971). However, post-depositional fabric reorientation has not occurred to any significant depth in the southern Rocky Mountain Trench, as  135  Figure 31. Index map showing trends of glacial lineations and the d i s t r i bution of drift (alluvium, present along major rivers, i s not differentiated from drift i n this diagram). Relatively thick t i l l is present over much of the Trench floor, but i s thin or absent on the uplands. The dotted line i s the limit of differentiation of bedrock and unconsolidated sediments. Distribution of bedrock and unconsolidated sediments from Leech (1958, 1960).  Figure 32. Late Wisconsinan t i l l in the southern Rocky Mountain Trench. A.  Younger t i l l overlying sand deposited during the early interstade of the Pinedale Glaciation, Elk River (dotted line at contact).  B and C. Younger t i l l , St. Mary River.  137  138  evidenced by sharp vertical changes in fabric orientation resulting from shifts in ice-flow direction.  Had fabric reorientation occurred, the  t i l l fabric would have been homogenized vertically at any one site.  It  is probable, then, that much of the t i l l accumulated by lodgement against a planar substratum.  The exact mechanism by which this occurs is not  known, but the following are possibilities:  (1) particles may become  individually lodged against an obstacle already present on the floor (Goldthwait, 1971, p. 16; Post and LaChapelle, 1971, their Fig. 29); (2) basal layers of debris-rich, moving ice melt when the combination of geothermal heat and heat produced by sliding exceeds that conducted away from the base of the glacier (Nobles and Weertman, 1971); calculations indicate that several centimeters of ice per year may be melted by these sources of heat (Robin, 1955; Weertman, 1963); (3) basal debris-rich ice may become immobile beneath the overriding glacier.  A l l of these  mechanisms involve basal sliding, and thus a glacier not frozen to i t s bed (Weertman, 1961). The record of glacier flow variations shown by fabrics through the t i l l sheet suggests that t i l l deposition occurred either progressively or  sporadically throughout glacial occupation of the area, and was not  limited to the terminal phase of glacier recession when large masses of englacial debris might be freed by rapid bottom melting as suggested by Goldthwait (1971, p. 17).  The presence of a drumlinized t i l l surface  further argues against the latter depositional mechanism. T i l l fabrics successfully document at least one major shift in the pattern of late Wisconsinan ice flow in the southern Rocky Mountain  Figure 33. Features which indicate the direction of ice flow immediately prior to deglaciation of the southern Rocky Mountain Trench. A and B. Drumlins. C. Bedrock striations. The direction of flow was toward the left in A and C, and toward the right in B. Aerial photo number BC 5353-101.  140  Trench (Fig. 46). Combined t i l l - f a b r i c , striation, and drumlin data show the pattern of last flow (Fig. 37) to be parallel to the Trench margins except where ice fanned out in the Kimberley-Cranbrook lowland and bulged up into St. Mary, Elk, and probably Bull Valleys.  Tributary glaciers at  this time were isolated from active ice in the Trench.  This stage was  preceded by a period when tributary glaciers were confluent with the trunk glacier, as indicated by fabrics off St. Mary, Elk, and Bull Valleys with orientations parallel to the flow directions from these tributaries. These fabrics occur below those with down-Trench orientations.  Tentative  correlations of fabrics in the upper part of the t i l l sheet at vertical sampling localities along St. Mary River have been made on the basis of fabric and stratigraphic similarities (Fig. 38). Glaciolacustrine sediments below the lowest fabric at site no. 19 correlate with i n t r a - t i l l glaciofluvial gravel (elev. 820 m) near site no. 24. Fabrics above these stratified sediments exhibit similar patterns at each station.  Thus,  correlation's made on the basis of fabric similarity are in agreement with the stratigraphic evidence.  At the three sites (nos. 23, 24, and 25) off  St. Mary Valley where fabric data could be gathered low in the t i l l sheet, correlations are more tenuous.  Some fabrics display axes of maximum  clustering either transverse to flow or at an acute angle to the overall down-Trench transport direction.  It is possible that the latter repre-  sent f l o w t i l l fabrics formed during melt-out accompanying the onset of the interstade between the middle and late stades of the Pinedale Glaciation.  If this interpretation is correct, no fabric correlation  either between sites or with respect to the glacier-flow direction would be expected.  This explanation requires glacier stagnation which should  Table 4.  Relation between orientation of fabric elements in t i l l and t i l l genesis.  ORIENTATION OF FABRIC ELEMENTS  GENESIS OF FABRIC E n g l a c i a l transport  a axes of rods and blades p a r a l l e l to flow d i r e c t i o n .  Deposition  P a r a l l e l p o s i t i o n a t t a i n e d by elongate objects i n a shearing medium ( J e f f r e y , 1922).  a axes of rods plunge upg l a c i e r ; a-b planes of blades dip u p - g l a c i e r .  Shear along planes i n terminal zone of g l a c i e r .  a axes of rods and a-b planes of blades subhorizontal.  Extending flow.  a axes of rods and blades transverse to flow d i r e c t i o n .  a axes of rods subh o r i z o n t a l ; a-b planes of blades dip up-glacier. a axes of rods and a-b planes of blades unrelated to flow.  Reorientation p o s i t i o n to where there dissipation  from p a r a l l e l transverse p o s i t i o n i s minimum energy ( J e f f r e y , 1922),  Post-depositional reorientation  Melt-out ( p r e s e r v a t i o n of e n g l a c i a l f a b r i c ; magnitude of plunge of a axes dependent on debris content of i c e p r i o r to melt-out). Lodgement by pressure melting against an o b s t r u c t i o n . * (Fabric may be produced by dragging of c l a s t s at base of g l a c i e r . )  Shear w i t h i n t i l l by overriding glacier.  Melt-out ( p r e s e r v a t i o n of e n g l a c i a l f a b r i c ; magnitude of dip of a-b planes dependent on debris content of i c e p r i o r to melt-out). Lodgement by pressure melting against an o b s t r u c t i o n . * (Fabric may be produced by r o l l i n g of c l a s t s at base of g l a c i e r . )  Compressive flow i n terminal zone of g l a c i e r .  Neither marked compressive extending flow.  nor  Melt-out ( d e s t r u c t i o n of e n g l a c i a l fabric). Mass movement of s u p r a g l a c i a l (flowtill).  till  Postglacial creep or l a n d s l i d e .  * S u b g l a c i a l f a b r i c s produced by pressure melting depend on the c o n f i g u r a t i o n of the g l a c i e r - t i l l i n t e r f a c e ; where t h i s i n t e r f a c e i s p l a n a r , p a r a l l e l f a b r i c s are dominant.  142  be indicated i n the stratigraphy at these l o c a l i t i e s .  Although there  are lenses of water-worked sand and gravel and l o c a l occurrences of crude s t r a t i f i c a t i o n i n the lower part of the t i l l sheet, their regional s i g n i f i c a n c e i s unknown. An alternative explanation i s that the pattern of i c e coalescence o f f tributary valleys preceding the interstade was geometrically complex as a result of rapid changes i n the flux of i c e out of the t r i b u t a r i e s .  T i l l f a b r i c at any one s i t e might then r e f l e c t  l o c a l anomalies of i c e flow rather than the regional down-Trench flow direction.  Examples of such distorted flow patterns are common where  t r i b u t a r i e s j o i n trunk glaciers i n the presently glaciated C o r d i l l e r a (Fig.  47).  Whatever the explanation, the fabric pattern i n the lower  part of the upper t i l l sheet i s more variable than that near the top i n r e l a t i o n to ice-flow pattern.  Heavy mineral and c l a s t lithology r e s u l t s , as w e l l as the results of t i l l - f a b r i c analyses, show the dominant pattern 'of i c e flow i n the southern Rocky Mountain Trench:  a south- to southeast-flowing  trunk g l a c i e r augmented by coalescent tributary g l a c i e r s .  Compositional  differences are most d i s t i n c t just south of the mouth of each major t r i b u tary where sediments of Trench and side-valley provenance occur as more or less d i s t i n c t e n t i t i e s .  Farther down the Trench, l a t e r a l differences  i n composition become less d i s t i n c t , probably as a r e s u l t of l a t e r a l mixing of sediment e n g l a c i a l l y or s u b g l a c i a l l y .  This mixing may be due  to l a t e r a l s h i f t s i n the position of the zone of coalescence of Trench and tributary glaciers with changes i n r e l a t i v e i c e flux between the two.  Temporal fluctuations i n the pattern of g l a c i e r flow, although  1  — I V  10  DIFFERENCE (in degrees)  20  DIFFERENCE (in degrees)  50  |  I  -|50  40  40 t  •  30  30  10  20  J.  30  -II-  ±  70  80  -I  L  10  Plunge Azimuth DIFFERENCE BETWEEN AXES OF MAXIMUM CLUSTERING FOR SAMPLES OF SIZE 60 AND 20 (in degrees) Figure 34. Relation between t i l l - f a b r i c strength and differences in the fabric results for samples of size 60 and 20. Theta i s the standard scattering angle around the axis of maximum clustering (in general, the greater the directional strength of the fabric, the smaller i s theta). Theta is plotted against the difference in orientation of the clustering axes of the larger and smaller samples. The histograms show that most of the smaller samples have clustering axes near those of the paired larger samples; trend differences (left) are mostly less than 20°, and differences in plunge magnitude (right) are mostly less than 10°. one point two coincident points  144  Figure 35. Selected fabrics from the younger t i l l . Also shown is a contoured diagram of 156 axes of maximum clustering representing a l l t i l l - f a b r i c results from the southern Rocky Mountain Trench. Contours approximately 2-5-8% per 1% area. Additional t i l l - f a b r i c contoured diagrams are shown in Appendix 5, and a l l t i l l - f a b r i c sample statistics are presented in Appendix 6.  145  TILL FABRICS TILL-FABRIC SAMPLE NUMBER A N D SITE TILL-FABRIC AXIS OF MAXIMUM CLUSTERING  1  •  146  Figure 36. Magnitude and direction of plunge of t i l l clasts. A. Curve shows the cumulative percent of clasts plunging less steeply than values listed on the abscissa; a l l t i l l - f a b r i c data are included. B. Rose diagram shows direction of plunge of t i l l clasts (the arrow points down-glacier); only t i l l - f a b r i c data for which the direction of glacier flow i s independently known are included.  147  —r— 99.5 99 98  r—  1  1  1—— T " l  —  -  -  -  95 r-  290 *  80  h  -  -  -  -  S 50  3  40 30  -  20 10  nc3120 i 10  i 20  A.  1 30  1 1 40 50 PLUNGE ( ° )  i 60  MAGNITUDE OF PLUNGE  n = 960  B.  DIRECTION OF PLUNGE Figure 36  1 70  148  Figure 37. Comparison of t i l l - f a b r i c axes of maximum clustering (shown by lines) and associated glacial lineations (shown by arrows) (see also Table 5). T i l l - f a b r i c sample statistics are presented in Appendix 6.  149  Table 5. Comparison of t i l l - f a b r i c maximum clustering axes and the trends of associated glacial lineations (see also Fig. 37).  Fabric no.  Location  Elevation* (m)  Number ofs observations  CD Till fabricazimuth of axis of maximum clustering  (2) Associated drumlins or s t r i a t i o n s — up-glacier trend*  Difference i n orientation between (1) and (2) i n degrees  1  49°06'20"N, 115°05'30"W  850  60  72  344  AA  49 10'25"N, 115°11'10"W  821  20  336  345  9  6  49°12'00"N, 115°15'25"W  820  60  10  346  24  o  86  7  49°12'35"N, 115°07'20"W  880  60  171  346  5  8A  49°12'40"N, 115°10'15"W  829  20  170  342  8  10  49°16'00"N, 115°11'50"W  820  60  345  345  0  11  49°17'25"N, 115°08'10"W  900  60  36  27  9  12  49°18'00"N, l i s ' i e ^ ' v *  820  60  145  333  8  13  49°20'35"N, 115°17'10"W  840  60  150  326  4  14  49°23'20"N, 115°15'35"W  870  60  341  327  14  15  49°24'25"N, 115°22'45"W  870  60  14  315  59  16  49°27*20"N, 115°04'10"W  1000  60  351  344  7  17  49°34'25"N, 115°40'25"W  870  60  315  311  4  19A  49°35*15"N, 115°48'40"W  919  20  32  28  23A  49°36'45"N, 115"42'35"W  864  60  334  331  24A  49°36'50"N, 115 40'05"W  840  60  328  319  9  28  49°42'25"N, 115°49'05"W  910  60  200  11  9  29  49°59'20"N, 115°45'20"W  900  60  317  339  22  <>  *Approximate.  .  4  3  o  151  shown by fabric analyses, are not recorded in t i l l composition. For example, although fabrics, glacial lineations, and stratigraphy  show a  late shift i n glacier flow resulting from recession of tributary glaciers out of the Trench (p. 116 and 140), heavy minerals and clasts near the top of the t i l l sheet off these tributaries are, in large part, of side valley rather than Trench provenance (Figs. 42 and 44). upper part of the t i l l sheet i s characterized  In detail, the  by an increase i n tributary  lithologies and a decrease in Trench lithologies toward the mouths of side valleys.  Even very near the tributary sources, however, t i l l  contains a minor component of Trench provenance.  The heavy mineral and  clast lithology results, then, suggest some local, subglacial reworking or mixing of sediment.  Localized reworking of previously deposited t i l l  would complicate an earlier flow pattern by indicating different flow directions at what appears to be the same stratigraphic level i n the t i l l ; this may explain some of the apparently anomalous fabrics of Figure 38. Mixing may also explain the apparent homogeneity of t i l l composition, particularly i f the mechanism of mixing is independent of shifts i n directions of glacier flow.  One such possibility i s the  introduction to the subglacial position of a mix of sediment via a system of englacial meltwater conduits.  Sediment transported to the glacier  base by meltwater might be deposited as lodgement t i l l ; i t s vertical distribution i n t i l l would be sensitive to availability of supply and only indirectly or not at a l l to shifts i n flow direction.  Areal d i s t r i -  bution would reflect proximity to bedrock source and direction of englacial meltwater transport.  The pattern of englacial "plumbing" would necessarily  evolve with glacier flow.  There was meltwater within or at the base of  Figure 38. Till-fabric axes of maximum clustering determined at vertical intervals of 1 to 5 m through the younger drift. Each open and closed circle represents one fabric; circles without attached lines are fabrics which are statistically uniform at the 10% level. The maximum clustering axis of each nonuniform fabric is shown by a line which ends in a circle at the elevation of the sample (north-south lines are parallel to the short edge of the page). The words gravel and silt refer to sediments which overlie and underlie the t i l l . A question mark indicates that the base of the t i l l i s unexposed. The word top indicates that the stratigraphic top of the t i l l is present. Tentatively correlated fabrics from sites 19, 23, 24, 25, and 26 are labelled the same letter (x, y, or z) . T i l l - f a b r i c sample statistics are presented in Appendix 6.  154  the active Trench glacier because lenses of water-worked sand and gravel are present within otherwise massive t i l l .  If this explanation is  correct, the distribution of lithologies in the t i l l may be, in large part, controlled by meltwater and, to a lesser extent, by active-ice transport. Two other observations, which are enigmatic i f active-ice transport is sought as their sole explanation, are explained by the above hypothesis:  (1) Garnet-staurolite distribution.  Garnet and staurolite  are thought to have been transported by ice from their source in the Trench north of about 52°N latitude (p. 130).  Both minerals decrease in  abundance southward in the area studied here.  Off St. Mary Valley there  is a pronounced garnet-staurolite low flanked to the north and south by higher frequencies.  Although one might anticipate a decrease in these  two minerals due to the supply of garnet-staurolite-poor sediment by the St.  Mary tributary glacier, their increase south of St. Mary Valley would  be unexpected unless they were transported englacially in a position or manner separate from minerals of St. Mary Valley provenance.  This would  be achieved i f much of the local sediment was transported in a short distance to the subglacial depositional position by meltwater, while the long-traveled foreign sediment was transported by the host ice. In this manner, locally derived sediment would greatly dilute garnet and staurolite southeast and east of St. Mary Valley, but the normal englacial load of garnet and staurolite would not be diluted with the short-traveled meltwater load farther south. arenite distribution.  (2) Chert-pebble conglomerate and chert  The occurrence in Trench t i l l of distinctive clastic  rocks cropping out only in Elk Valley is shown in Figure 45.  Pebbles  Figure 39. Relation between percent of a constituent in t i l l and distance from the bedrock source. A. Crystalline clasts, southwestern Ontario (data from Gravenor, 1951). B. Iron ore clasts, southern Ontario (data from Dreimanis, 1956).  156  occur i n relatively low abundance at the top of the t i l l sheet on both sides of the Trench south and west of Elk Valley, despite the fact that associated t i l l fabrics and landforms indicate a terminal phase of flow down-Trench with no contributions of ice from tributary valleys.  These  anomalous observations are reconciled i f the pebbles were transported down and across the Trench via meltwater through ice tunnels to near the base of the glacier, where they were deposited as lodgement t i l l .  The  occurrence of these pebbles at the very top of the t i l l sheet must be due to reworking of older lodgement t i l l .  Alternatively, the pebbles  might have been reworked from sediments older than late Wisconsinan t i l l , but this leaves unexplained their Trench-wide distribution and restricted northward occurrence. It is generally argued that breakage and abrasion during transport are the controlling factors in percentage decreases of minerals and clasts down-glacier from their sources (Holmes, 1960; Dreimanis and Vagners, 1971; Drake, 1972).  Certainly abrasion i s indicated by  striated and faceted clasts common in t i l l , and clast size decreases with distance from source.  But caution must be exercised in conclusions of  this sort based on lithologic studies of specific t i l l size fractions. Losses within a size fraction due to breakage would normally be compensated by additions due to breakage of larger clasts.  Indeed, at the  "terminal grade" of breakage (p. 126; Dreimanis and Vagners, 1971) for a particular mineral, the additions from larger size fractions might result in net increases of that mineral with distance of transport.  Thus,  breakage w i l l not necessarily result in the decrease in abundance of a mineral or rock type within a specific size fraction with increasing trans-  157  158  Figure 41. Distribution of selected bedrock lithologies; unpatterned areas inside the solid line represent other bedrock lithologies. Laminated greenish-gray a r g i l l i t e and red-purple a r g i l l i t e , s i l t i t e , and quartz arenite are most common on the east side of the Rocky Mountain Trench south of Elko. Mafic igneous rocks are most abundant in St. Mary Valley. Bedrock geology modified from Leech (1958, 1960)  159  160  Figure 42. Amphibole distribution in t i l l of the southern Rocky Mountain Trench. At sites where two or more samples were collected, the mean amphibole content i s shown. Contours are from the fourthdegree trend surface ( r = 0.88). Values are expressed as percent of fine sand fraction multiplied by 10 . 2  2  161  162  Figure 43. Garnet distribution i n t i l l of the southern Rocky Mountain Trench. At sites where two or more samples were collected, the mean garnet content i s shown. Contours are from the sixth-degree trend surface ( r = 0.57). Values are expressed as percent of fine sand fraction multiplied by 10 . 2  2  163  164  Figure 44. Distribution of mafic igneous southern Rocky Mountain Trench. At sites were collected, the mean content of mafic Contours are from the fourth-degree trend Values represent percent of t i l l pebbles.  pebbles in t i l l of the where two or more samples igneous pebbles is shown. surface ( r = 0.72). 2  165  166  port.  Where such decreases are observed, dilution by sediment mixing  at the g l a c i e r - t i l l interface (p. 127 and 151) or progressive deposition of sediment away from i t s source (p. 127) should be considered as controlling factors.  Both factors have been shown to strongly influence  mineral and clast lithology distributions in Rocky Mountain Trench t i l l . Although not directly evaluated, breakage and abrasion may be important as well.  CONCLUSIONS (1) Deposits of three glacial advances have been identified i n the southern Rocky Mountain Trench, and are tentatively correlated with deposits of the Pinedale Glaciation of the Rocky Mountains i n the United States. (2) T i l l fabrics, landforms, and stratigraphic evidence show at least one major shift i n the pattern of glacier flow near the end of glaciation i n the southern Rocky Mountain Trench.  An earlier period  when major tributary glaciers coalesced with the trunk glacier i n the Trench was followed by a period when tributary glaciers receded and active ice in the Trench bulged into the side valleys.  The later phase  was followed by orderly recession of the trunk glacier with neither major halts nor terminal stagnation and by drainage of ice-dammed lakes i n tributary valleys. (3) T i l l fabrics are applicable i n cordilleran areas and provide information on directions of glacier flow and t i l l genesis. Strongly oriented fabrics both transverse and parallel to flow are produced during  167  Figure 45. Distribution of Blairmore Group clasts i n drift of the southern Rocky Mountain Trench. Topographic contour interval 2000' (610 m). Outcrop area of Blairmore Group from Price (1962).  NO a BLAIRMORE « CLASTS  ELKOI  BLAIRMORE CLASTS PRESENT  BLAIRMORE GROUP  OUTCROP AREA OF BLAIRMORE GROUP. 9 BOUNDARY BETWEEN DRIFT WITH  BLAIRMORE CLASTS AND DRIFT WITHOUT BLAIRMORE CLASTS.  I N  KILOMETERS  49fyo'N  Figure 46. Two phases of "glacier flow near the end of the Pinedale Glaciation. A. During the earlier phase tributary glaciers were confluent with the trunk glacier in the southern Rocky Mountain Trench (arrows show directions of ice flow). B. During the later phase tributary glaciers were isolated from active ice in the Trench. The trunk glacier spread out across the lowland in the vicinity of Cranbrook and bulged into side valleys. Unpatterned area is lower than 1220 m (4000') in elevation.  169  M,0Q o Sll  vO  M,00 o Sll  170  Figure 47. Patterns of g l a c i e r coalescence off tributary v a l l e y s i n the C o r d i l l e r a . Top: coalescent glaciers flowing as separate i c e streams p a r a l l e l to the valley walls (Shakes G l a c i e r , Alaska; photo by Austin P o s t ) . This flow pattern was probably common i n the southern Rocky Mountain Trench during Pleistocene g l a c i a t i o n s , as indicated by the occurrence off major tributary valleys of compositionally d i s t i n c t bands of t i l l p a r a l l e l to the Trench w a l l s . Bottom: complex distortions of flow due to a surge by a tributary g l a c i e r (Susitna G l a c i e r , Alaska; photo by Austin Post).  171  172  englacial transport, during deposition, and by shear and viscous flow within already-deposited t i l l .  A consideration of the most common s i t u a -  tions i n which t i l l originates leads to the conclusion that certain f a b r i c patterns are to be more expected than others, namely, elongate elements defining a gently dipping g i r d l e with either a single maximum p a r a l l e l to flow o r , less commonly, two maxima 90° apart.  In areas of the Rocky  Mountain Trench where the d i r e c t i o n of g l a c i e r flow i s independently known, rods i n t i l l are p a r a l l e l to flow and tend to plunge gently upglacier.  These fabrics were produced by lodgement of clasts due to  subglacial pressure melting against a planar substratum, not by postdepositional reorientation nor by the melt-out process.  Some fabrics  from the lower part of the younger t i l l below i n t e r s t a d i a l sediments suggest either complex patterns of i c e flow or mass movement of supraglacial t i l l  (flowtill).  In most areas, maximum information on t i l l o r i g i n and the d i r e c t i o n of i c e flow can be obtained by measuring the a axes of both rods and blades and the a-b planes of blades.  A standardized procedure,  incorporating Andrews's (1971) suggestions, should be adopted.  (4) Heavy mineral and c l a s t l i t h o l o g y analyses are less sensit i v e as indicators of ice-flow patterns than t i l l - f a b r i c results i n the southern Rocky Mountain Trench because t i l l may have been reworked at the ice-sediment interface and because sediment may have been transported to i t s subglacial depositional s i t e by a mechanism other than the flowing ice i t s e l f .  The d i s t r i b u t i o n and r e l a t i v e abundance of pebbles and  minerals i n r e l a t i o n to their bedrock sources are compatible with (a) the  173  meltwater transport of part of the locally derived sediment to i t s subglacial position via a system of conduits in ice, followed by lodgement through pressure melting, and (b) limited reworking of t i l l at the glacier sole.  Whatever their transportational history, most of the  pebbles and fine sand In Rocky Mountain Trench t i l l are of local origin; garnet and staurolite, however, probably were transported by ice down the Trench at least 300 km from north of Kinbasket Lake.  Observed rapid  decreases in relative amounts of certain heavy minerals and pebbles away from their sources at the mouths of tributary valleys cannot be entirely due to breakage and abrasion en route, but are explained instead by progressive deposition and dilution through sediment mixing. Compositional differences in t i l l are most pronounced off tributary valleys and become less distinct in a down-glacier direction. This probably results from lateral mixing of sediment englacially or subglacially due to short-term shifts of the zone of coalescence of Trench and tributary glaciers caused by changes in relative ice flux between the two.  174  LITERATURE CITED Anderson, R.C., 1955, Pebble lithology of the Marseilles t i l l sheet i n northeastern I l l i n o i s : Jour. Geology, v. 63, p. 228-243, Anderson, T.W., and Stephens, M.A., 1971, Tests for randomness of directions against equatorial and bimodal alternatives: Dept. Statistics, Stanford Univ., Tech. Rept, 5, 19 p. Andrews, J.T., 1971, Methods i n the analysis of t i l l fabrics, in Goldthwait, R.P., ed., T i l l : a symposium: Columbus, Ohio State Univ. Press, p. 321-327. Andrews, J.T., and Smith, D.I., 1970, Statistical analysis of t i l l fabric: methodology, local and regional variability (with particular reference to the north Yorkshire t i l l c l i f f s ) : Geol. Soc. London Quart. Jour., v. 125, p. 503-542. Armstrong, J.E., Crandell, D.R., Easterbrook, D.J., and Noble, J.B,, 1965, Late Pleistocene stratigraphy and chronology in southwestern British Columbia and northwestern Washington: Geol. Soc. America Bull., v. 76, p. 321-330. Bayrock, L.A., 1962, Heavy minerals i n t i l l of central Alberta: Alberta Soc. Petroleum Geologists Jour., v. 10, p. 171-184. Boulton, G.S., 1968, Flow t i l l s and related deposits on some Vestspitsbergen glaciers: Jour. Glaciology, v. 7, p. 391-412. 1970a, On the deposition of subglacial and melt-out t i l l s at the margins of certain Svalbard glaciers: Jour, Glaciology, v. 9, p. 231-245. 1970b, On the origin and transport of englacial debris i n Svalbard glaciers: Jour. Glaciology, v. 9, p. 213-229. 1971, T i l l genesis and fabric i n Svalbard, Spitsbergen, in Goldthwait, R.P., ed., T i l l : a symposium: Columbus, Ohio State Univ. Press, p. 41-72. Carol, Hans, 1947, The formation of roch.es moutonnees: Jour. Glaciology, v. 1, p. 57-59. Crandell, D.R., 1965, The glacial history of Washington and Oregon, in Wright, H.E., Jr., and Frey, D.G., eds., The Quaternary of the United States: Princeton, New Jersey, Princeton Univ. Press, p. 341-353. Daly, R.A., 1912, Geology of the North American Cordillera at the fortyninth parallel: Canada Geol. Survey Mem. 38, 857 p.  175  Drake, L.D., 1972, Mechanisms of clast attrition in basal t i l l : Soc, America Bull., v, 83, p. 2159-2166. Dreimanis, Aleksis, 1956, Steep Rock iron ore boulder train: Canada Proc, v. 8, p. 27-70.  Geol.  Geol, Assoc,  1961, T i l l s of Southern Ontario, in Legget, R.F., ed., Soils in Canada, geological, pedological, and engineering studies: Royal Soc. Canada Spec. Pub. , 3, p. 80-96. :  Dreimanis, Aleksis, Reavely, G.H., Cook, R.J.B., Knox, K.S., and Moretti, F.J., 1957, Heavy mineral studies in t i l l s of Ontario and adjacent areas: Jour. Sed. Petrology, v. 27, p. 148-161. Dreimanis, Aleksis, and Vagners, U.J., 1971, Bimodal distribution of rock and mineral fragments in basal t i l l s , in Goldthwait, R.P., ed., T i l l : a symposium: Columbus, Ohio State Univ. Press, p. 237250. Flint, R.F., 1971, Glacial and Quaternary geology: and Sons, Inc., 892 p.  New York, John Wiley  Fulton, R.J., 1971, Radiocarbon geochronology of southern British Columbia: Canada Geol. Survey Paper 71-37, 28 p. Glen, J.W., Donner, J.J., and West, R.G., 1957, On the mechanism by which stones in t i l l become oriented: Am. Jour. Sci., v. 255, p. 194205. Goldthwait, R.P., 1951, Development of end moraines in east-central Baffin Island: Jour. Geology, v. 59, p. 567-577. 1968, Surficial geology of the Wolfeboro-Winnipesaukee area, New Hampshire: Concord, New Hampshire Dept. Resources and Econ. Development, 60 p. 1971, Introduction to t i l l , today, in Goldthwait, R.P., ed., T i l l : a symposium: Columbus, Ohio State Univ. Press, p. 3-26. Gravenor, CP., 1951, Bedrock source of t i l l s in southwestern Ontario: Am. Jour. Sci., v. 249, p. 66-71. Gross, D.L., and Moran, S.R., 1971, Grain-size and mineralogical gradations within t i l l s of the Allegheny Plateau, in Goldthwait, R,P., ed., T i l l : a symposium: Columbus, Ohio State Univ. Press, p. 251-274. Harrison, P.W., 1957, A c l a y - t i l l fabric: Jour. Geology, v. 65, p. 275-308.  i t s character and origin:  1960, Original bedrock composition of Wisconsin t i l l in central Indiana: Jour. Sed. Petrology, v. 30, p. 432-446.  176  Holmes, C D . , 1941, T i l l f a b r i c : p. 1299-1354.  Geol. Soc. America B u l l . , v. 52,  1952, D r i f t dispersion i n west-central New York: America B u l l . , v. 63, p. 993-1010.  Geol. Soc.  1960, Evolution of t i l l - s t o n e shapes, central New York: Soc. America B u l l . , v. 71, p. 1645-1660.  Geol.  Howard, A.D., 1956, T i l l - p e b b l e isopleth maps of parts of Montana and North Dakota: Geol. Soc. America B u l l . , v. 67, p. 1199-1206. J e f f r e y , G.B., 1922, The motion of e l l i p s o i d a l p a r t i c l e s immersed i n a viscous f l u i d : Royal Soc. London P r o c , s e r . A, v. 102, p. 161179. Kamb, W.B., and LaChapelle, E.R., 1964, Direct observation of the mechanism of g l a c i e r s l i d i n g over bedrock: Jour. Glaciology, v. 5, p. 159-172. Kauranne, L.K., 1960, A s t a t i s t i c a l study of stone orientation i n glacial t i l l : Finlande Comm. Geol. B u l l . 188, p. 87-97. K e l l e y , C.C., and Sprout, P.N., 1956, S o i l survey of the upper Kootenay and Elk River valleys i n the East Kootenay d i s t r i c t of B r i t i s h Columb i a : B r i t i s h Columbia S o i l Survey Rept. 5, 99 p. Krumbein, W.C., and P e t t i j o h n , F . J . , 1938, Manual of sedimentary petrography: New York, D. Appleton-Century Co., Inc., 549 p. Leech, G.B., 1958, Fernie map-area, west h a l f , B r i t i s h Columbia: Geol. Survey Paper 58-10, 40 p. 1960, Fernie, west h a l f , B r i t i s h Columbia: Map 11-1960.  Canada  Canada Geol. Survey  L l i b o u t r y , Louis, 1959, Une th£orie du frottement du g l a c i e r sur son l i t : Annales Geophys., v. 15, p. 250-265. MacClintock, Paul, and Dreimanis, A l e k s i s , 1964, Reorientation of t i l l f a b r i c by overriding g l a c i e r i n the S t . Lawrence Valley: Am. Jour. S c i . , v. 262, p. 133-142. Mark, D.M., 1973, Analysis of a x i a l orientation data, including t i l l fabrics: Geol. Soc. America B u l l . , v. 84, p. 1369-1374. McCall, J.G., 1952, The i n t e r n a l structure of a cirque g l a c i e r , report on studies of the englacial movements and temperatures: Jour. Glaciology, v. 2, p. 122-131. M i l t h e r s , Keld, 1942, Ledeblokke og Landskabsformer i Danmark: Geol. Unders., s e r . 2, no. 69, 137 p.  Danmarks  177  Nobles, L.H., and Weertman, Johannes, 1971, Influence of i r r e g u l a r i t i e s of the bed of an i c e sheet on deposition rate of t i l l , in Goldthwait, R.P., ed., T i l l : a symposium: Columbus, Ohio State Univ. Press, p. 117-126. O'Leary, Mont, L i p p e r t , R.H., and S p i t z , O.T., 1966, FORTRAN IV and MAP program for computation and p l o t t i n g of trend surfaces for degrees 1 through 6: Kansas Geol. Survey Computer Contr. 3, 48 p. Post, A u s t i n , and LaChapelle, E.R., Univ. Press, 110 p.  1971, Glacier i c e :  S e a t t l e , Washington  Prest, V.K., 1969, Retreat of Wisconsin and Recent i c e i n North America: Canada Geol. Survey Map 1257A. P r e s t , V.K., Grant, D.R., and Rampton, V.N., Canada Geol. Survey Map 1253A.  1967, G l a c i a l map  of Canada:  P r i c e , R.A., 1962, Fernie map-area, east h a l f , Alberta and B r i t i s h Columbia: Canada Geol. Survey Paper 61-24, 65 p. Ragan, D.M., 1968, Structural geology, an introduction to geometrical techniques: New York, John Wiley and Sons, Inc., 166 p. Ramsden, John, and Westgate, J.A., 1971, Evidence for reorientation of a t i l l fabric i n the Edmonton area, A l b e r t a , in Goldthwait, R.P., ed., T i l l : a symposium: Columbus, Ohio State Univ. Press, p. 335-344. Richmond, G.M., 1965, Glaciation of the Rocky Mountains, in Wright, H.E., J r . , and Frey, D.G., eds., The Quaternary of the United States: Princeton, New Jersey, Princeton Univ. Press, p. 217-230. Richter, Konrad, 1932, Die Bewegungsrichtung des Inlandeises, rekonstruiert aus den Kritzen und Langsachsen der Geschiebe: Z e i t s c h r . fur Geschiebeforsch., v. 8, p. 62-66. 1936, Gefugestudien im Engebrae, Fondalsbrae, und ihren Vorlandsedimenten: Z e i t s c h r . fur Gletscherk., v. 24, p. 22-30. Robin, G. de Q., 1955, Ice movement and temperature d i s t r i b u t i o n i n g l a c i e r s and i c e sheets: Jour. Glaciology, v. 2, p. 523-532. S c h o f i e l d , S.J., 1915, Geology of the Cranbrook map-area, B r i t i s h Columbia: Canada Geol. Survey Mem. 76, 245 p. S i t l e r , R.F., and Chapman, C A . , 1955, Microfabrics of t i l l from Ohio and Pennsylvania: Jour. Sed. Petrology, v. 25, p. 262-269. Weertman, Johannes, 1961, Mechanism for the formation of inner moraines found near the edge of cold i c e caps and i c e sheets: Jour. Glaciology, v. 3, p. 965-978.  178  1963, P r o f i l e and heat balance at the bottom surface of an i c e sheet fringed by mountain ranges: Internat. Assoc. S c i . Hydrology, Gen. Assembly of Berkeley, 1963, Pub. 61, p. 245-252 [also available as U.S. Army Cold Regions Research and Eng. Lab., Research Rept. 134 (1964), 7 p . ] . West, R.G., and Donner, J . J . , 1956, The glaciations of East Anglia and the East Midlands: a d i f f e r e n t i a t i o n based on stone-orientation measurements of the t i l l s : Geol. Soc. London Quart. Jour., v. 112, p. 69-91. Wheeler, J.O., Aitken, J.D., Berry, M.J., Gabrielse, Hubert, Hutchison, W.W., Jacoby, W.R., Monger, J.W.H., N i b l e t t , E.R., N o r r i s , D.K. , P r i c e , R.A., and Stacey, R.A., 1972, The C o r d i l l e r a n s t r u c t u r a l province, in P r i c e , R.A., and Douglas, R.J.W., eds., Variations i n tectonic styles i n Canada: Geol. Assoc. Canada Spec. Paper 11, p. 1-81. Willman, H.B., Glass, H.D., and Frye, J.C., 1963, Mineralogy of g l a c i a l t i l l s and their weathering p r o f i l e s i n I l l i n o i s . Part 1. Glacial t i l l s : I l l i n o i s Geol. Survey C i r c . 347, 55 p. Wright, H.E., J r . , 1957, Stone orientation i n Wadena drumlin f i e l d , Minnesota: Geog. Annaler, v. 39, p. 19-31. Young, J.A.T., 1969, Variations i n t i l l macrofabric over very short distances: Geol. Soc. America B u l l . , v. 80, p. 2343-2352.  179  CHAPTER FOUR:  SEDIMENTOLOGY AND PALEOHYDROLOGY OF LATE WISCONSINAN OUTWASH  ABSTRACT Late Wisconsinan ground moraine in the Rocky Mountain Trench, southeastern British Columbia, is dissected by meltwater channels which formed during the final retreat of the Cordilleran Ice Sheet,  Outwash  underlying the channels is coarse, poorly sorted, shows large-scale cross-bedding, and was deposited in channel-bar complexes of high-energy proglacial rivers. to  Length of transport of outwash gravel from t i l l source  channel depositional site i s relatively short. The coarse fraction of  t i l l is also of local derivation, as lithologies are similar to nearby bedrock lithologies. Peak discharges calculated from channel morphometry and maximum particle size were 10,000 to 20,000 m /sec, larger than estimated maximum 3  discharges of several thousand m /sec attributable to summer runoff. Many 3  channels transmitted peak discharges during jOkulhlaups from glacial lakes in tributary valleys.  An empirical relationship between total volume  discharged during documented jOkulhlaups and corresponding maximum instantaneous discharges is applied to Glacial Lake Elk to show that discharges equal to or larger than those calculated from channel morphometry were attained during jOkulhlaups. Mean discharge excluding jOkulhlaups for most of the active channels i s estimated to be less than 1000 m /sec; the ratio of maximum 3  180  instantaneous to mean discharges was about 10:1 but may have exceeded 20:1 in some channels. At low and moderate stages rivers had braided patterns within individual meltwater channels, but during peak flows channel bars were submerged.  INTRODUCTION The Rocky Mountain Trench acted as a major channel for meltwater during retreat of the Cordilleran Ice Sheet from southern British Columbia. Wasting ice in the Trench and i n the flanking Rocky and Columbia Mountains contributed meltwater which flowed south past 49°N latitude (Fig. 48), Deposits and landforms of the southern Rocky Mountain Trench record late glacial events. The flat valley floor is largely ground moraine with drumlins parallel to the Trench margins.  This t i l l plain i s  traversed by meltwater channels, many of which are underlain by outwash. Large valley trains and kame terraces occur along the margins of the Trench (Fig. 48). The purposes of this paper are:  (1) to characterize outwash  and associated landforms produced during glacial recession in one area of the Canadian Cordillera and (2) to outline the paleohydrology of certain meltwater channels from the physical characteristics of the channels and from an empirical model based upon discharge records of proglacial rivers.  181  DISTRIBUTION AND CHARACTER OF OUTWASH  The recessional outwash consists mainly of sand and gravel underlying meltwater channels or forming valley trains and kame terraces. On the east side of the Trench between Elko and Red Canyon Creek i s a large terraced and channeled outwash p l a i n .  Individual meltwater  channels trend south and southwest from this outwash surface towards the axis of the Trench.  Sedimentary Textures  The recessional outwash i s poorly to very poorly sorted (Folk, 1968, p. 46) and coarse, with l i t t l e material larger than cobble-size or smaller than sand ( F i g . 49, Appendix 8). Although lenses of sand are present i n most exposures, bulk samples of outwash consist of from over 50% to more than 90% gravel. alluvium of Kootenay River.  The sediment i s much coarser than the modern In general, size frequency d i s t r i b u t i o n s are  strongly fine-skewed to fine-skewed (Folk, 1968, p. 47) and range from very p l a t y k u r t i c to very leptokurtic (Folk, 1968, p. 48).  Plots of skewness v s . deviation and skewness v s . kurtosis show the sediments to have textural attributes similar to r i v e r sediments but unlike other sediment groups (Friedman, 1961; Moiola and Weiser, 1968).  Coarse channeled outwash near the Kootenay River i s overlain by s i l t y sand ( F i g . 48).  The f i n e sediment probably accumulated during  l a t e stages of channel flow as backwater deposits where the channels intersected the ancestral Kootenay River.  182  Sedimentary Structures Common sedimentary structures in the outwash include parallel bedding, planar and trough cross-stratification, and current ripple lamination (Fig, 50).  Small-scale cross-lamination, common in sand  layers, is i n part related to the migration of current ripple marks during deposition (Allen, 1963, p. 107-108) and in part to channel scour and f i l l .  Large-scale cross-bedding predominates in gravel layers,  Beds  dip from a few degrees up to 30° and presumably originated through deposition at the site of migrating avalanche faces of bars and by channel f i l l following scour. Pebbles and cobbles within gravel beds are commonly imbricated with individual clasts inclined upstream. Surface bed forms of channels could not be adequately evaluated because of surface modification following channel abandonment. Changes include loess deposition on outwash surfaces and pedogenesis. Nevertheless, large bars and scour channels are preserved. Bars are mainly longitudinal and are flanked by scour channels. avalanche faces.  Some terminate with steep bar-  Most outwash surfaces are terraced and marked by a  network of indistinct braided channels, or bear no visible bed forms. Probable large-scale mega-ripples with wave lengths up to about 25 m were observed on one outwash surface. These sedimentary structures and bed forms are characteristically associated with fluvial and glaciofluvial deposits (Harms and Fahnestock, 1965).  Similar structures occur in high-energy channel-bar  complexes of contemporary braided rivers such as Donjek River, Yukon Territory (Williams and Rust, 1969).  183  Pebble Lithologies and Provenance Local differences in bedrock lithology enabled a study to be made of provenance of clasts in t i l l and outwash.  Bedrock in and adjacent  to the study area i s composed of sedimentary and igneous rocks of Precambrian to Early Cretaceous (?) age (Leech, 1958, 1960).  Similar  lithologies are found in a number of formations, thus i t is commonly impossible to determine the bedrock source for pebbles and cobbles in outwash.  Some rock types, however, are useful for provenance study.  Lower Cretaceous chert-rich rudite, arenite, and s i l t i t e crop out in Elk Valley.  Clasts of these rocks are locally abundant in Elk Valley outwash,  but are only minor constituents of outwash in the Rocky Mountain Trench, Other lithologies helpful in determining outwash provenance are mafic igneous rocks, grayish-red-purple quartz arenite, s i l t i t e , and a r g i l l i t e , and laminated greenish-gray a r g i l l i t e . age.  These rocks are a l l of Precambrian  Laminated greenish-gray a r g i l l i t e crops out extensively on the east  wall of the Trench south of Elko but i s less common in the Rocky Mountains to the north (Fig. 51).  A Precambrian formation of red-purple a r g i l l i t e  crops out mainly along the mountain front south of Elko, but also is present north of the study area.  Mafic igneous rocks occur on the east  side of the Trench north of Bull River and south of Elko. Pebble lithologies were determined from samples of 100 clasts (mean diameter 16 to 32 mm) sieved from several kilograms of outwash and till.  Two clusters of sample sites on the east side of the Trench were  chosen, with adjacent bedrock lithologies differing at each cluster locality (Fig. 51); each cluster includes 5 outwash samples and 5 t i l l  184  samples.  The purpose of the sampling scheme was to answer the following  questions.  Do the cluster l o c a l i t i e s d i f f e r i n their c l a s t l i t h o l o g i c a l  make-up, and, i f so, are these differences related to differences i n bedrock l i t h o l o g i e s ?  How  f a r was the gravel f r a c t i o n of t i l l transported?  How much of the gravel was eroded from bedrock i n the immediate v i c i n i t y of  the sampling s i t e and how much was transported down the Trench from  exposures f a r to the north?  Do outwash samples d i f f e r from t i l l samples  within a c l u s t e r , and what implications might this have for the length of  transport of outwash clasts?  Percentages of laminated greenish-gray a r g i l l i t e , red-purple c l a s t i c sedimentary rocks, and mafic igneous rocks are presented i n Figure 51.  Student's t-test (at 1% l e v e l of significance) shows both  greenish-gray and red-purple a r g i l l i t e to be s i g n i f i c a n t l y more abundant in  the southern cluster than i n the northern c l u s t e r .  Mafic igneous  clasts are s i g n i f i c a n t l y more abundant at northern sample s i t e s .  The pebble component of t i l l i s thus l i t h o l o g i c a l l y similar to bedrock to the east and northeast.  Most of the clasts have been trans-  ported on the order of 10 km or l e s s , rather than hundreds of kilometers. Paleozoic limestone, a major rock type immediately east and north of Elko and an important constituent of t i l l and outwash at Elko, i s a subordinate l i t h o l o g y i n sediments at the southern sample l o c a l i t y about 17 km to the south.  The areal d i s t r i b u t i o n of green a r g i l l i t e clasts (Fig.  52), based  on 28 t i l l samples, further indicates the s i m i l a r i t y between pebble and l o c a l bedrock l i t h o l o g i e s and supports the idea of short transport distances.  Outwash on the f l o o r of the Rocky Mountain Trench formed when  185  meltwater eroded ground moraine.  The volume of t i l l gravel eroded by  meltwater i s about the same as the volume of gravel deposited by p r o g l a c i a l streams.  Selective sorting during g l a c i o f l u v i a l transport and areal  variations i n t i l l composition would result i n l i t h o l o g i c a l differences between adjacent deposits of outwash and t i l l i f transport of the gravel f r a c t i o n by meltwater was  far.  However, t i l l and outwash are not s i g n i -  f i c a n t l y d i f f e r e n t (5% level) i n lithology at either sampling c l u s t e r , The derivation of outwash from t i l l and the l i t h o l o g i c a l s i m i l a r i t y between adjacent t i l l and outwash samples thus indicate short transport of outwash g r a v e l .  PALEOHYDROLOGY  During the retreat of the C o r d i l l e r a n Ice Sheet, large amounts of meltwater were discharged from the g l a c i e r f r o n t .  The large meltwater  channels, their outwash, and underfit streams and v a l l e y s i n the Rocky Mountain Trench indicate that hydrologic conditions were d i f f e r e n t from the present.  Hydrologic conditions during deglaciation were probably  similar to those existing today i n heavily glaciated c o r d i l l e r a n areas such as parts of Alaska, Yukon T e r r i t o r y , and B r i t i s h Columbia.  Most  temperate mountain glaciers there have receded since the Neoglacial maximum. Landforms uncovered during deglaciation and  ice-marginal  g l a c i o l a c u s t r i n e features are similar to l a t e Pleistocene features i n the Trench.  Modern p r o g l a c i a l streams are commonly braided, transport  coarse debris, have r e l a t i v e l y steep gradients, and exhibit extremes of discharge.  Ice-dammed lakes may  drain rapidly during jOkulhlaups,  and  p r o g l a c i a l r i v e r s then have peak water discharges tens of times greater  186  than average (Bradley and others, 1972; Mathews, in press), Meltwater channels are conspicuous features of the present landscape i n the southern Rocky Mountain Trench.  The channels vary i n  morphology and include the following types, (1) Narrow, relatively deep channels cutting across drumlins. These channels are generally discontinuous, in many places terminating against unmodified drumlins or kettle holes. There i s generally l i t t l e or no outwash underlying their floors. features.  They are thus strictly erosional  Their anomalous morphology and association with ice-contact  features suggest these channels were carved when the surrounding landscape was at least partly mantled by stagnant ice. Closely related to these are "serpentines" (Mannerfelt, 1945, p. 95-97, 212-214), small, sinuous channels situated on the flanks and tops of topographic highs. (2) Strictly lateral, single-walled channels.  Such channels  are ice-marginal erosional features formed before the bottom of the Trench was free of ice. The floors of many are bedrock, but in places have a thin cover of glaciofluvial gravels. (3) Wide, relatively shallow, double-walled channels underlain by outwash.  Some are several hundred meters wide and many kilometers  long, but most are short segments truncated by younger channels to the north and northwest (Figs. 48 and 53).  They tend to be flat-floored  except in areas of bars and scour channels (Fig. 54),  Ice-marginal kame  terraces and remnants of older, higher proglacial meltwater channels flank some of the channels. Most of the channels are cut in t i l l and  187  contain an outwash f i l l which, is generally a few meters in thickness but in places is thicker than 15 m.  Cross-stratification and pebble imbrica-  tion show that the outwash was deposited from water flowing to the south, southwest, and southeast away from the ice front.  The distance between  the active ice front and the depositional site was probably short, as most meltwater channels are pitted with kettles. Paleodischarges in meltwater channels may be calculated from empirically derived equations involving channel morphometric parameters and outwash texture. Dury (1965), for example, formulated equations relating meander morphometry and discharge at bankfull stage, and Schumm (1968) showed that channel morphometry varies with type and amount of sediment load as well as with discharge.  Alternatively, since meltwater  discharge is related to a number of basin parameters such as glacierized area and the number and volume of self-dumping ice-dammed lakes, paleodischarges may be estimated from basin morphometry in the southern Rocky Mountain Trench.  Paleodischarge Determinations from Channel Morphometry In a non-cohesive gravel-bed river, the size of the largest moving particle may be a measure of the c r i t i c a l tractive force, x . This c  is expressed by the Shields relationship, x = 890l>, where D is grain c  diameter in m, and x  2  c  i s in newtons/m (Shields, 1936).  fully turbulent flow (i.e., generally, for D > 0.005 m).  This is valid for Church (1970,  his Pig. 11.1) shows that for some flume, canal, and river data different constants apply in the above relationship, because of the variable effects  188  Figure 48. D i s t r i b u t i o n of outwash and meltwater channels, Rocky Mountain Trench, southeastern B r i t i s h Columbia. The dotted l i n e southeast of Elko i s the l i m i t of d i f f e r e n t i a t i o n of Quaternary sediments. Areas of rock outcrop and near-surface rock from Leech (1960).  189  UNDIVIDED QUATERNARY SEDIMENTS I 6 | ALLUVIUM  ALLUVIAL  FAN DEPOSITS  OUTWASH SILT AND SAND  OUTWASH  GRAVEL  TILL  BEDROCK AT OR NEAR THE SURFACE  BLUFFS OF UNCONSOLIDATED SEDIMENTS d, k SURFACE DUNED, KETTLED  MARGIN OF MELTWATER CHANNEL OR TERRACE  DRUMLIN  STRIATIONS (DIRECTION OF ICE FLOW KNOWN, UNKNOWN)  j  ~K.CROWSNEST C PASS  MORRISSET  \  KIIOMETERS  i  CONTOUR INTERVAL 1000' (305 m)  Figure 48  i  o  k m  2  4 KILOMETERS  6  8  190  of imbrication and packing patterns of channel sediments and, to a lesser extent, suspended sediment concentration and viscosity as controlled by water temperature.  For Baffin Island sandar: T  = 1800D  c  (1)  A similar constant applies to other gravel-paved rivers (Church, 1970, his Fig. 11.1).  Outwash on Baffin Island sandar and on Rocky Mountain  Trench outwash plains i s similar in texture and structure.  In both  areas channel sediment i s characterized by pebble imbrication and other oriented clast packing patterns, resulting i n stable bed conditions under shear stresses i n excess of the c r i t i c a l value predicted from the Shields relationship.  These similarities suggest that the constant of Eq. (1) may  yield more realistic estimates of c r i t i c a l tractive force than the standard Shields constant. C r i t i c a l tractive force i s also related to the slope of the energy grade line, s, and flow depth, d, by the formula: T  = pgsd  C  (2)  Combining Eqs. (1) and (2):  d = 0.184D/s  (3)  (mks units)  (4)  (mks units)  The Manning flow resistance equation i s :  v =  i  ?  2/3 l/2 s  Substituting d from Eq. (3) for R (hydraulic radius, R, i s approximately equal to d for very wide channels) in Eq. (4) yields:  Figure 49. Cumulative size frequency curves of outwash samples. The graphs relate grain sizes and weight percent of the sediment coarser than those sizes. A. Gravel pit 1, 49°13'N, 115°16'W (Appendix 8). B. Gravel pit 4, 49°13'N, 115°09*W (Appendix 8).  192  Figure 50.  Sedimentary structures in outwash at gravel pits.  A.  Large-scale cross-bedding; exposure i s about 5 m high and is parallel to axis of meltwater channel.  B.  Dipping gravel beds of A.  C.  Lensing of sand and gravel near margin of secondary channel; exposure is about 3 m high and i s approximately normal to channel axis.  D.  Channel scour and f i l l ; trend of channel is normal to exposure  E.  Cross-laminated sand and parallel-bedded gravel; exposure is about 5 m high.  F.  Cross-laminated sand of E.  193  Figure 50  194  Figure 51. Percent of c l a s t s of the following l i t h o l o g i e s i n outwash and t i l l : laminated greenish-gray a r g i l l i t e (source i s largely the Roosville and Gateway Formations), red-purple a r g i l l i t e and quartz arenite (largely of the P h i l l i p s Formation), and mafic igneous rocks (Purcell volcanics and i n t r u s i o n s ) . Undifferentiated P u r c e l l igneous rocks crop out on the east w a l l of the Trench near the northern sample c l u s t e r . At each of the two sampling clusters are f i v e outwash and f i v e t i l l samples. Bedrock geology of the east side of the Trench from Leech (1958, 1960).  195  Figure 51  196  0.323P / 2  v =  3  C5)  The resistance coefficient, n, is estimated from the Strickler equation (Chow, 1959, p. 205-206; Church, 1970, p. 467):  n = 0.038D / 1  6  (6)  (mks units)  This equation yields resistance coefficients based upon the size of bed roughness elements, but not form resistance elements such as channel cross section and alignment. Combining Eqs. (5) and (6) yields velocity in terms of particle size and slope of the energy grade line; multiplying by Eq. (3) results in an equation for specific discharge, which when multiplied by channel width, w, leads to peak discharge, Q, during periods of flow capable of moving the largest outwash particles: Q = 1-56D3/2„  (  7  )  7/6 s  D was determined from the mean 2>-axis diameters of the 25 largest outwash clasts found at gravel pits along the meltwater channels, Very large, glacially striated clasts, thought to have been either ice rafted or incorporated in outwash as lag boulders from t i l l without glaciofluvial transport, were excluded i n the calculation of D.  Energy  gradients were calculated from topographic maps with a 20-ft (6.1 m) contour interval and by surveying. To minimize the effect of differential isostatic rebound after channel abandonment, gradients were measured where channel directions are closest to the axis of zero differential  197  Figure 52. Fourth-order trend surface map of percent laminated greenishgray a r g i l l i t e in t i l l ; r = 0.96. Contours are drawn only on the floor of the Rocky Mountain Trench. Bedrock on the east wall of the Trench at and south of Elko i s mainly gray and green a r g i l l i t e of Precambrian age. Laminated green a r g i l l i t e i s less common in bedrock northwest of Elko. 2  198  uplift.  Channel widths were measured from 1:31,680 topographic maps and  represent average values over sections of channel for which gradients were determined.  V e l o c i t i e s and discharges for several of the larger  meltwater channels are presented i n Table 6. Larger channels  carried  3  discharges of about 20,000 m /sec.  Paleodischarge Determinations  from Discharge Records of  P r o g l a c i a l Rivers  Total meltwater runoff from g l a c i e r i z e d basins i n the C o r d i l l e r a i s a function of numerous variables including climate, i c e surface area, and basin morphometry.  P r o g l a c i a l meltwater discharge may be interrupted  by storage and intermittent release of water i n self-dumping ice-dammed lakes.  On the other hand, meltwater discharge produced by melting without  storage i n self-dumping g l a c i a l lakes i s continuous.  In the l a t t e r case  average discharge for a maximum flow period i s closely related to the area of i c e upstream from a p r o g l a c i a l r i v e r .  The data i n Figure 55,  derived from topographic maps and water supply records for p r o g l a c i a l r i v e r s , indicate a power relationship between peak discharge and g l a c i e r ized area.  The equation i s of the form Q = aA^, where a and b are  constants.  S p e c i f i c equations determined for periods of maximum flow  are:  Mean of maximum year of discharge:  Q = 0.26A  0 , 9 8  c o e f f i c i e n t of determination =0.92  Mean of maximum month of discharge:  1  Q = 0.43-fl *  c o e f f i c i e n t of determination = 0.95  06  199  :  PS »^ 1P^^^-' '  3 t  , KM.  1 1  1 — z  Figure 53. Meltwater channels. A. Photo stereogram of t i l l plain cut by meltwater channels, 49°06'-09'N, 115 05'-ll'W (BC 5353-052 and -053). B. Floor and east wall of one of the large meltwater channels of A. o  200  Peak discharge:  Q = 2.!U Q  99  coefficient of determination = 0,82 As the water discharge records are of limited and variable duration, derived Q values are somewhat less than long-term maxima produced by ablation.  The small scatter of the data points of Figure 55 indicates,  however, that derived discharges are similar in magnitude to long-term maxima for individual rivers; variance attributable to divergence of the two is relatively small. This i s in part explained by observations that discharge differences between glacier runoff events with large recurrence intervals are proportionately smaller than differences between events with small recurrence intervals (Church, 1970, his Fig. 42). Maximum discharges can be determined i f the total glacier area contributing runoff to meltwater channels i s estimated.  In the  case of paleochannels in the southern Rocky Mountain Trench such an estimate i s only an approximation because the limits of ice contributing meltwater to channels south of Elko are not known. A major meltwater channel leaves the Trench at Cranbrook (approximately 49°30'N, 115°45'W) and probably discharged much of the meltwater originating north of Cranbrook.  No other channels leave the Trench between 49°30' and 49°00'N,  thus, channels on the east side of the Trench floor south of Elko were being fed by the Trench glacier at least as far north as Cranbrook.  The  estimate of glacierized area, assuming various positions of the glacier terminus between Elko and the 49th parallel, and varying degrees of tributary deglaciation, is then greater than 1000 but less than 4000 km . 2  The resulting estimates of average discharges for maximum periods of flow  Figure 54. Topographic profiles across a major meltwater channel. Flat-floored parts of the channel (profile C-D) are separated by segments with longitudinal bars and secondary scour channels (profiles A-B and E-F).  o  202  are listed in Table 7.  Normal summer melt produced discharges of several  thousand m /sec, much smaller than the maximum value of about 20,000 m /sec 3  3  determined from channel morphometry.  It is thought that the larger dis-  charges occurred during jokulhlaups, which are floods resulting from the breaching of ice-dammed lakes. (Fig.  This is supported by the distribution  48) and size of outwash in relation to former ice-dammed lakes in  Trench tributary valleys, and by the presence of large longitudinal bars and probable mega-ripples (p. 182) on the surfaces of meltwater channels. Many tributary valleys were largely deglaciated when ice s t i l l f i l l e d the Trench.  Ice-dammed lakes were present in the valleys of  Wigwam, Elk, and St. Mary Rivers, and perhaps others.  As the Trench  glacier receded additional ice-dammed lakes formed in tributary valleys to the north.  Recession of the trunk glacier probably caused progressive  lowering and weakening of each ice dam until breached during jbkulhlaups. Many historic ice-dammed lakes drain catastrophically during a c r i t i c a l period of trunk glacier recession.  For example, annual jSkulhlaups from  Vatnsdalur, Iceland occurred only after 1898 during a period of rapid recession of the impounding glacier that began in 1887 1939, p. 223-224).  (Thorarinsson,  Although glacier-dammed Summit Lake, British Columbia  has existed since at least the f i r s t decade of this century, i t has drained catastrophically only since 1961 (Mathews, in press).  Also, as  Knik Glacier, Alaska receded during the 1930's, 40's, and 50's there was a trend toward earlier annual release of the water impounded by the glacier in Lake George (Stone, 1963, p. 34-35). These observations support the idea of a close relationship between the occurrence of jbkulhlaups and the strength of the ice dam.  Table 6. Peak velocities and discharges determined from channel morphometry and maximum particle size.  Diameter L o c a t i o n  of  (b  l a r g e s t (m)  4 9 ° 0 0 ' - 0 5 ' N 1 1 5 ° 0 3 ' - 0 5 ' W  4 9 " 0 4 ' - 0 9 ' N 1 1 5 ° 0 5 ' - 0 9 ' W  4 9 ° 0 6 * - 1 0 ' N 1 1 5 ° 0 8 ' - 1 2 ' W  4 9 ° 1 3 * - 1 5 ' N 115°08'-10'W  4 9 ° 1 5 ' - 1 8 ' N 115°11'-14'W  a x i s ) c l a s t s  Channel g r a d i e n t  Average channel width  (m)  V e l o c i t y  T =890D c  Peak  (m/sec)  T =1800D c  d i s c h a r g e  ( m  3  / s e c )  T =890D c  T =1800D c  0.09  0.005  540  4  6  4.000  10,000  0.09  0.004  630  4  7  6,000  20,000  0.09  0.003  520  4  7  6,000  20,000  0.10  0.009  340  4  6  1,000  4,000  0.10  0.005  570  4  7  4,000  10,000  204  Glacial Lake Elk was representative of lakes trapped in tributary valleys by ice in the Rocky Mountain Trench,  Active ice pushed into  lower Elk Valley to maintain a dam near Morrissey.  Glacial Lake Elk  i n i t i a l l y drained eastward at Crowsnest Pass (elev. 1357 m). Later the lake discharged to the southeast at an elevation of 1204 m near Morrissey. At this stage the lake had an area of about 200 km and a volume of more 2  than 20 km . 3  After the ice south of Morrissey receded below the elevation  of the Morrissey outlet, Glacial Lake Elk drained to the southwest towards Elko, thence south along the margin of the Trench into lower Wigwam Valley. A major bedrock gorge southeast of Elko (Fig. 48) was occupied and excavated by meltwater.  Large amounts of greenish-gray  a r g i l l i t e were eroded from the walls of the gorge, transported, and deposited on a wide depositional terrace north of Wigwam River near i t s mouth. The tremendous influx of debris into Wigwam Valley forced Wigwam River against the south wall of the valley. then flowed southwest into the Trench.  The combined meltwater  The size of outwash clasts  downstream from the bedrock gorge indicates a major flood, probably produced by a jdkulhlaup from Glacial Lake Elk.  During such meltwater  floods, the terminus of the Trench glacier must have been south of Elko. Many of the channels in the southern part of the study area may have formed or been modified by jbkulhlaups from Glacial Lake Elk, An estimate of the maximum instantaneous discharge of a flood from Glacial Lake Elk may be made. Figure 56 shows the relationship between maximum instantaneous flood discharge and lake volume drained. For documented limno-glacial jbkulhlaups the equation of the regression line ( r = 0.96) is Q = 75V * , where Q is the peak discharge in m /sec 2  0  67  3  205  / /  10  1  io  2  io  3  GLACIER AREA (km ) 2  Figure 55. Relation of glacier area, A, and maximum instantaneous discharge, Q; r = 0.82. Data are from water discharge records and topographic maps. Glacier or proglacial river: 1—Ram, Alberta; 2—Sentinel, British Columbia; 3—Woolsey, British Columbia; 4— Peyto, Alberta; 5—Wolverine, Alaska; 6—Athabasca, Alberta; 7— Lemon, Alaska; 8—Gulkana, Alaska; 9—Eklutna, Alaska; 10—Berendon, British Columbia; 11—Nellie Juan, Alaska. 2  206  and V is the volume drained (x 10 m ). 6  3  If Glacial Lake Elk at the  1204-m stage drained completely, the maximum discharge of the resulting flood would be about 60,000 m /sec. 3  For only partial emptying, and for  jbkulhlaups during the later stages of the lake, maximum discharges would be less. Meltwater channels west and northwest of Elko were not formed by floods from Lake Elk.  Tributary valleys to the north, such as that  of St. Mary River and possibly those of Bull River and Sand Creek, supported ice-dammed lakes somewhat younger than Glacial Lake Elk. Jbkulhlaups from these lakes were probably important i n the formation of some meltwater channels within the study area. Flood waters probably traveled subglacially and englacially from the breach in the ice dam to the terminus of the Trench glacier. In many documented jbkulhlaups the distance between the source and the surface discharge point at the glacier terminus is many kilometers (Marcus, 1960; Mathews, 1965).  Discussion of Results Peak discharges calculated from channel morphometry and outwash size were probably 10,000 to 20,000 m /sec for several large meltwater 3  channels (Table 6).  Ablation would have been sufficient to account for  the largest discharges only i f a very large glacierized area were contributing meltwater which was then funneled into a single proglacial channel (Table 7).  The most likely value for glacier area results in peak dis-  charges from ablation of several thousand m /sec, lower than maximum 3  Table 7. Relation of g l a c i e r area and meltwater discharge during periods of maximum melt. Discharge estimates are determined from l i m i t i n g values of g l a c i e r i z e d area with the g l a c i e r terminus south of Elko.  Mean of maximum year of discharge Regression equation  Coefficient of determination  Q =  0.26A°-  3Q  Mean of. maximum month of discharge 1  Q = 0.43A '  0.92  06  Maximum instantaneous discharge 0  0 = 2.JU -  99  0.82  0.95  3  Q* (m /sec) for maximum .glacier area  3  10 low  3  10 low  10  3  high  3  Q* (m /sec) for minimum glacier area  2  10 low  10  2  high  3  10 low  •Minimum and2 maximum order-of-magnitude estimates of discharge calculated from limiting values of glacierized area, A (km ). Low = order of magnitude of Q x 1, 2, 3, or 4; high = order of magnitude of Q x 5, 6, 7, 8, or 9.  208  values determined from channel morphometry. water channel trended along what i s now  A l s o , since a major melt-  the valley of the Kootenay  River, and since this channel was active throughout deglaciation, i n contrast to channels entering i t from the east and northeast ( F i g . 48), t o t a l meltwater was divided between at least two channels at any given time during deglaciation.  Direct runoff from the g l a c i e r was p e r i o d i c a l l y augmented by large volumes of water released from ice-dammed lakes.  Jbkulhlaups with  3  peak discharges up to 60,000 m /sec swept down the Trench from G l a c i a l Lake E l k .  3  Lake Elk was probably smaller than 20 km  (the volume upon  which the peak estimate was based) when channels south of Elko formed. 3  However, a jokulhlaup of 20,000 m /sec could result from a lake of 4 much smaller than G l a c i a l Lake Elk at the 1204-m stage. 1  magnitude IO * to 10  5  3  km ,  Jbkulhlaups of  3  m /sec compare i n s i z e to many Icelandic volcano-  g l a c i a l floods (Thorarinsson, 1953; R i s t , 1955)  and floods from Lake  George, Alaska (Stone, 1963; U.S. Geological Survey, 1969; Bradley and others, 1972), but are smaller than the late Pleistocene jbkulhlaups of Lake Bonneville (Malde, 1968)  and Lake Missoula (Bretz, 1925,  1969;  Pardee, 1942; Bretz and others, 1956; Baker, 1971).  Peak discharges were many times larger than long-term mean discharges.  Mean discharge excluding jbkulhlaups for p r o g l a c i a l r i v e r s 3  i n the study area was probably less than 1000 m /sec, even for years of exceptional melt (Table 7).  The r a t i o of maximum instantaneous discharge  to mean discharge was about 10:1 and may have exceeded 20:1 i n channels affected by jbkulhlaups. Thus, during peak flows, bars on r e l a t i v e l y  209  Figure 56. Relation of 2t o t a l volume drained during jBkulhlaup and peak water discharge; r = 0.96. Dashed lines indicate 95% confidence i n t e r v a l for estimates of peak discharge (residuals are assumed to be normally d i s t r i b u t e d ) . Ice-dammed lakes: 1—Strupvatnet (Whalley, 1971); 2—Ekalugad Valley (Church, 1970); 3—Demmevatn (Strom, 1938); 4—Gjanupsvatn (Arnborg, 1955); 5—Vatnsdalur (Thorarinsson, 1939); 6—Tulsequah (Marcus, 1960); 7—Summit (Mathews, 1965 and i n press); 8—Graenalon (Thorarinsson, 1939); 9—George (Stone, 1963); 1 0 — Missoula (Bretz, 1925; Pardee, 1942).  210  flat-floored channels were submerged, whereas at low and moderate stages, rivers had braided patterns within individual meltwater channels.  CONCLUSIONS (1) Channeled outwash in the southern Rocky Mountain Trench was deposited by proglacial rivers during the final retreat of the Cordilleran Ice Sheet. (2) Large channels, coarse sediment, and sedimentary structures such as large-scale cross-stratification indicate deposition i n channelbar complexes of high-energy rivers. (3) Outwash was formed by the erosion of t i l l ; fines were removed and gravel transported a relatively short distance.  The coarse fraction  in t i l l is also of local derivation. (4) Peak discharges calculated from channel morphometry and maximum particle size were 10,000 to 20,000 m /sec, larger than estimated 3  maximum uninterrupted discharges such as would have resulted from direct summer runoff. (5) Many channels probably discharged peak volumes during jOkulhlaups from glacial lakes i n tributary valleys.  From an empirical  relationship between total volume discharged during documented meltwater floods and corresponding maximum instantaneous discharge, i t is estimated that Glacial Lake Elk at one stage drained with discharges up to 60,000 m /sec. 3  Smaller floods during lower stages of the lake and jbkulhlaups  from other lakes to the north may have formed many of the meltwater  211  channels and outwash deposits south of Elko. (6) Mean discharge for meltwater channels i n the southern 3  Rocky Mountain Trench was probably less than 1000 m /sec, and the ratio of maximum instantaneous to mean discharges was about 10:1 and may have exceeded 20:1 i n some channels.  212  LITERATURE CITED Allen, J.R.L., 1963, The classification of cross-stratified units, with notes on their origin: Sedimentology, v. 2, p. 93-114. Arnborg, Lennart, 1955, Hydrology of the glacial river Austurflj&t: Geog. Annaler, v. 37, p. 185-201. Baker, V.R., 1971, Paleohydrology and sedimentology of Lake Missoula flooding in eastern Washington [Ph.D. thesis]: Boulder, Colorado Univ., 146 p. Bradley, W.C, Fahnestock, R.K. , and Rowekamp, E.T,, 1972, Coarse sediment transport by flood flows on Knik River, Alaska: Geol. Soc. America Bull., v. 83, p. 1261-1284. Bretz, J.H., 1925, The Spokane flood beyond the channeled scablands: Jour. Geology, v. 33, p. 97-115, 236-259. 1969, The Lake Missoula floods and the channeled scabland: Jour. Geology, v. 77, p. 505-543. Bretz, J.H., Smith, H.T.U., and Neff, G.E., 1956, Channeled scabland of Washington: new data and interpretations: Geol. Soc. America Bull., v. 67, p. 957-1049. Chow, V.T., 1959, Open-channel hydraulics: Co., 680 p.  New York, McGraw-Hill Book  Church, M.A., 1970, Baffin Island sandar, a study of arctic fluvial environments [Ph.D. thesis]: Vancouver, British Columbia Univ., 1066 p. Dury, G.H., 1965, Theoretical implications of underfit streams: U.S. Geol. Survey Prof. Paper 452-C, 43 p. Folk, R.L., 1968, Petrology of sedimentary rocks: Hemphill's, 170 p.  Austin, Texas,  Friedman, G.M. , 1961, Distinction between dune, beach, and river sands from their textural characteristics: Jour. Sed. Petrology, v. 31, p. 514-529. Harms, J . C , and Fahnestock, R.K., 1965, Stratification, bed forms, and flow phenomena (with an example from the Rio Grande), in Middleton, G.V., ed., Primary sedimentary structures and their hydrodynamic interpretation: Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 12, p. 84-115. Leech, G.B., 1958, Fernie map-area, west half, British Columbia: Geol. Survey Paper 58-10, 40 p.  Canada  213  •  1960, Fernie, west h a l f , B r i t i s h Columbia: Map 11-1960.  Canada Geol. Survey  Malde, H.E., 1968, The catastrophic l a t e Pleistocene Bonneville flood i n the Snake River P l a i n , Idaho: U.S. Geol. Survey Prof. Paper 596, 52 p. Mannerfelt, CM., 1945, Nagra glaciomorfologiska formelement och deras vittnesbbrd om inlandsisens avsm^ltningsmekanik i svensk och norsk f j a l l t e r r a n g : Geog. Annaler, v. 27, p. 1-239. Marcus, M.G., 1960, Periodic drainage of glacier-dammed Tulsequah Lake, B r i t i s h Columbia: Geog. Rev., v. 50, p. 89-106. Mathews, W.H., 1965, Two self-dumping ice-dammed lakes i n B r i t i s h Columbia: Geog. Rev., v. 55, p. 46-52. 1973, The record of two jbkulhlaups: Internat. Assoc. S c i . Hydrology, Symposium on the hydrology of g l a c i e r s , Cambridge, September 1969 (in p r e s s ) . Moiola, R.J., and Weiser, D., 1968, Textural parameters: Jour. Sed. Petrology, v. 38, p. 45-53.  an evaluation:  Pardee, J.T., 1942, Unusual currents i n G l a c i a l Lake Missoula, Montana: Geol. Soc. America B u l l . , v. 53, p. 1569-1600. R i s t , Sigurjon, 1955, Skeioararhlaup 1954 (the hlaup of Skeifrara 1954): J b k u l l , v. 5, p. 30-36. Schumm, S.A., 1968, River adjustment to altered hydrologic regimen— Murrumbidgee River and paleochannels, A u s t r a l i a : U.S. Geol. Survey Prof. Paper 598, 65 p. Shields, A., 1936, Anwendung der Aehnlichkeitsmechanik und der Turbulenzforschung auf die Geschiebebewegung: Preuss. Versuchsanst. fur Wasserbau und Schiffbau M i t t . 26. Stone, K.H., 1963, The annual emptying of Lake George, Alaska: v. 16, p. 26-40.  Arctic,  Strom, K.M., 1938, The catastrophic emptying of a glacier-dammed lake i n Norway 1937: Geologie der Meere und Binnengewasser, v, 2, p. 443-444. Thorarinsson, Sigurdur, 1939, The ice-dammed lakes of Iceland with p a r t i c u l a r reference to their values as indicators of g l a c i e r o s c i l l a t i o n s : Geog. Annaler, v. 21, p. 216-242. 1953, Some new aspects of the Grimsvbtn problem: Glaciology, v. 2, p. 267-275.  Jour.  214  U.S. Geological Survey, 1969, The breakout of Lake George: Survey non-technical leaflet, 15 p.  U.S. Geol.  Whalley, W.B,, 1971, Observations of the drainage of an ice-dammed l a k e — Strupvatnet, Troms, Norway: Norsk Geog, Tidsskr., v. 25, p. 165174. Williams, P.F., and Rust, B.R., 1969, The sedimentology of a braided river: Jour. Sed, Petrology, v. 39, p, 649-679.  215  CHAPTER FIVE:  GEOMORPHIC HISTORY  Geophysical evidence (p. 100) indicates that the Rocky Mountain Trench i s a s t r u c t u r a l boundary of continental proportions, possibly marking a Paleozoic hinge zone along the margin of the Precambrian craton.  Evolution of the southern Trench as a major physio-  graphic feature began a f t e r a period of late Cretaceous and early Tertiary compressional deformation which produced the Rocky Mountain f o l d and thrust b e l t .  This was followed i n the Eocene by a period of i s o s t a t i c  u p l i f t and extension accompanied by block f a u l t i n g i n the C o r d i l l e r a , The change i n tectonics may be due to the cessation of subduction along the northern P a c i f i c margin and i t s replacement by l a t e r a l displacement of plates along transform f a u l t s .  The southern Rocky Mountain Trench  formed by block f a u l t i n g of the half-graben s t y l e .  Structural basins  along the axis of the Trench served as the depositional s i t e s for e l a s t i c s eroded from the adjacent uplands.  Although the age of the  oldest sediments i s not d i r e c t l y known, sediments of Upper Eocene and Oligocene age occur i n the s t r u c t u r a l l y comparable Flathead Valley to the east.  Sedimentation continued into the Miocene with deposition of  the St. Eugene Formation, which includes the uppermost part of as much as 1400 m of T e r t i a r y s t r a t a .  The S t . Eugene Formation consists of  flood-plain and a l l u v i a l fan f a c i e s ; the former includes both highenergy r i v e r gravel deposited off major tributary valleys and shallowlake or slack-water s i l t and sand; the l a t t e r consists of talus and fanglomerate deposited along the margins of the Rocky Mountain Trench and derived from adjacent fault-bounded uplands.  The Miocene climate  216  was more temperate than the present climate of the area; summer precipitation was abundant, and winters were moist and mild.  Deposition of  sediment in the Trench and erosion of the uplands were probably contempo-r raneous with faulting, although 600 m or more of normal dip'-slip displacement along the east margin of the Trench occurred after deposition of the St. Eugene Formation. There is a hiatus in the geologic record of the southern Rocky Mountain Trench between deposition of the St. Eugene Formation and the Wisconsinan Glaciation.  Although southeastern British Columbia i s not  now a seismically active area, block faulting may have continued with decreasing intensity perhaps into the Quaternary.  Young fault scarps in  western Montana and a belt of recent earthquakes parallel to the northern Rocky Mountains i n the United States indicate that block faulting is s t i l l occurring south of 49°N.  It i s possible, then, that additional  strata of similar character to the St. Eugene Formation accumulated in the southern Rocky Mountain Trench during late Tertiary and early Quaternary time.  If so, these strata either have been removed by  Quaternary glacial and fluvial erosion or are concealed beneath Quaternary deposits, or both.  It i s noteworthy that outcrops of St. Eugene strata  are few as a result of both these factors; strata are exposed largely on the protected down-glacier flanks of bedrock highs and along the few deep postglacial valleys where rivers have cut through the Quaternary section.  Alternatively, i t i s possible that significant sediment accumu-  lation on the floor of the Trench ceased after deposition of the St. Eugene Formation, although this is considered unlikely because of major postSt. Eugene block faulting.  However, i f the structural basins were  217  already f i l l e d , and i f there was no rise in local base level, additional sediment eroded from the surrounding uplands might have been transported out of the study area. I t is believed that the presence or absence of Pliocene or early Quaternary sediments w i l l be determined only by d r i l l i n g the sediment f i l l underlying the floor of the Rocky Mountain Trench. Whatever the extent of Pliocene and early Quaternary sedimentation, the St. Eugene Formation was gently deformed and eroded prior to the Wisconsinan Glaciation.  Tectonic deformation of Wisconsinan glacial  deposits was not observed. During each glaciation, the eastern Cordilleran Ice Sheet formed through the coalescence of large valley and piedmont glaciers i n the Rocky and Columbia Mountains and flowed south through outlet valleys such as the Rocky Mountain Trench and the Purcell Trench to the west (Fig. 57).  The source areas of the ice sheet were probably the high  alpine areas which presently support glaciers (Fig. 58). The glacier flowing through the Rocky Mountain Trench was augmented by tributary valley glaciers in southern British Columbia and Montana, and reached south of 47°30'N at the peak of glaciation (Fig. 59).  Near the maximum  of each advance, the glacier flowing south through the Purcell Trench dammed the Clark Fork River at Lake Pend Oreille to form Glacial Lake Missoula. Multiple glaciation in British Columbia during the Pleistocene Epoch i s well documented (for example, see Armstrong and Tipper, 1948; Armstrong and others, 1965; Fulton, 1972; Fulton and Halstead, 1972), but the stratigraphic record for pre-Wisconsinan glaciations is poor and i s  218  largely known from d r i l l records or by comparison with the more complete g l a c i a l record i n Washington, Idaho, and Montana.  Wisconsinan glaciers  covered nearly a l l of B r i t i s h Columbia and removed or buried most of the record of e a r l i e r g l a c i a t i o n s .  Deeply oxidized d r i f t of one pre-Bull Lake (pre^-Wisconsinan) g l a c i a t i o n has been i d e n t i f i e d i n northwestern Montana (Richmond and others, 1965, p. 234), but c o r r e l a t i v e deposits were not found i n the southern Rocky Mountain Trench i n B r i t i s h Columbia.  Three t i l l s representing stades of the B u l l Lake (early Wisconsinan) G l a c i a t i o n are separated by lacustrine deposits of G l a c i a l Lake Missoula south of Flathead Lake i n northwestern Montana (Richmond and others, 1965). (Alden, 1953).  The terminus of the l a t e stade i s the Mission moraine  In this area, g l a c i e r s advanced farther south during the  B u l l Lake G l a c i a t i o n than during the Pinedale (late Wisconsinan) Glaciation ( F i g . 59).  However, no deposits of early Wisconsinan age have been  i d e n t i f i e d i n the southern Rocky Mountain Trench.  The B u l l Lake Glaciation was followed by a major nonglacial i n t e r v a l , referred to as the Olympia I n t e r g l a c i a t i o n i n the P a c i f i c Northwest.  Fulton (1971), i n a paper on the radiocarbon geochronology  of southern B r i t i s h Columbia, has concluded that the Olympia Interglaciat i o n began more than 52,000 years ago and ended about 19,000 years ago, A nonglacial sequence i n the P u r c e l l Trench spans the i n t e r v a l from 43,800 ± 800 to 25,840 ± 320 years B.P.  Three major depositional cycles  within the Olympia I n t e r g l a c i a t i o n have been i d e n t i f i e d — e a r l y and late periods of aggradation when base l e v e l was higher than at present, and an  219  Figure 57. Pattern of ice flow in southeastern British Columbia and southwestern Alberta during the Pleistocene. The southern Rocky Mountain Trench was one of several outlet valleys of the Cordilleran Ice Sheet in southern British Columbia (from Prest and others, 1967).  220  intervening time of low base l e v e l characterized by stream erosion with continued sedimentation i n lake basins (Fulton, 1968).  During the  Olympia I n t e r g l a c i a t i o n , as at present, the major s i t e s of sedimentation were v a l l e y s located between h i l l y or mountainous upland areas.  Channel,  overbank, and a l l u v i a l fan sediments accumulated on the valley bottoms, and lacustrine and d e l t a i c sediments were deposited i n lake basins. The climate i n the I n t e r i o r during at least part of this period was s u f f i c i e n t l y warm and moist to support forests and large vertebrates (Fulton, 1971, p. 5 ) .  Olympia I n t e r g l a c i a l deposits i n the southern Rocky Mountain Trench include channel, overbank, and, probably, lacustrine  sediments.  Wood from these sediments yielded a radiocarbon age of 26,800 ± 1000 years (GX-2032).  This nonglacial i n t e r v a l terminated with the invasion of the Rocky Mountain Trench by i c e at the onset of the Pinedale or Fraser Glaciation.  As i n e a r l i e r advances, the trunk g l a c i e r was augmented by  l o c a l alpine g l a c i e r s . advancing i c e sheet.  Drainage was diverted along the margins of the Eventually, i c e covered the Trench as well as the  flanking mountains, with only the higher peaks projecting above the g l a c i e r surface ( F i g . 60).  E r r a t i c s and s t r i a e on the east side of the  Trench just north of B u l l River indicate the trunk g l a c i e r reached an elevation of at least 2260 m there.  Daly (1912) concluded that the  elevation of the i c e surface i n the Galton Range and P u r c e l l Mountains near the International Boundary was 2230 m. was  The C o r d i l l e r a n Ice Sheet  thus about 1500 m thick over the Trench near the 49th p a r a l l e l . I t  221  Figure 58. Distribution of existing glaciers in southeastern British Columbia and southwestern Alberta (from Prest and others, 1967).  222  terminated in a lobate front marginal to Glacial Lake Missoula near the present Flathead Lake (Fig. 59). Three Pinedale stades are recognized in northwestern Montana (Richmond, 1965; Richmond and others, 1965),  The Poison moraine (Alden,  1953) south of Flathead Lake i s a compound moraine consisting of drift of the early and middle stades.  Moraines at Kalispell and Coram were  deposited by late Pinedale glaciers. In the southern Rocky Mountain Trench in British Columbia, deposits of three late Wisconsinan ice advances are recognized and are tentatively correlated with the three stades of the Pinedale Glaciation. At the beginning of the early stade, ice advanced over weathered bedrock and sediments on the Trench floor; weathered clasts of various units were incorporated in the basal t i l l of this advance. At i t s maximum advance the trunk glacier reached a terminal position at the Poison moraine.  As the early stade ended, portions of the glacier in the  Trench apparently became stagnant and were buried beneath thick accumulations of glaciofluvial sand and gravel along routes of meltwater discharge and beneath glaciolacustrine s i l t and sand elsewhere.  The glaciolacustrine  sediments are in part contemporaneous with and in part younger than the coarse outwash. With melting of the underlying stagnant ice blocks, these sediments were broadly folded and faulted.  It i s not known whether the  fine-grained sediments accumulated in one or a number of lakes occupying the floor of the Trench; neither i s the cause of impoundage known, although possibilities include ice or sediment dams and differential isostatic depression of the surface of the Trench in a northerly to  223  mm*) i«  7»J . , T  114°W  5?/  f:..<  c  M  CO 4-1  OJ T J  td C cu n)  Xi +J 3  TJ  C o Q co 6 Xi C O  •rl  bilk  -H  Pi  CO OJ rl 3  g  O  rl 4 J LH Cd w  cu  M-l  TJ OJ  cu  u Tj  c  O Xi cd Tj C  *w  T5o  H  CU Xi 4J  l-l  o  CU TJ  cu d •C cd cn CD  Pe->  cd  o c  PEND OREILLE :  cd  M  cd  cu rH •rl TJ rl  CU  -GLACIAL LAKE COEUR D'ALENE  O  CJ  60 CU rl  O C rl <4-l -H O • > CU  !  4J  GLACIAL LAKE MISSOULA ::  N  Cd , G  31  2 V  U  *o  ^  -  3 io  rH  \0  • o cn  CTI U  m  20  rH  40  V  KILOMETERS  xi CU CO CO r l "H 3 4J CU 60-rl •H H *J  U  115 W 6  - J  Fu PQ O -"j>I ' tS'^'tS*' t  GLACIERS • '  PINEDALE GLACIATION (LATE, MIDDLE, EARLY STADES) BULL LAKE GLACIATION (LATE, EARLY STADES)  PLEISTOCENE GLACIAL LAKES  AREAS NOT COVERED BY CORDILLERAN ICE SHEET OR GLACIAL LAKES (LOCAL ALPINE GLACIERS NOT SHOWN) NUNATAK AREAS AREAS ABOVE CORDILLERAN ICE SHEET - MAXIMUM PINEDALE ADVANCE (IN BRITISH COLUMBIA AREA ABOVE 2440m ALTITUDE IS SHOWN)  (sooo) ft  CONTOURS ON SURFACE OF CORDILLERAN ICE SHEET PINEDALE ADVANCE  MAXIMUM  224  northwesterly direction due to the presence of an ice cover to the north.  Ice-rafted clasts were deposited with the fine sediments early  and late in the interstade,  Glaciolacustrine deposition ended when  glaciers of the middle stade advanced down the Trench.  Once again, the  maximum advance of the trunk glacier was to the Poison moraine. Recession from the Poison moraine may correlate with an interval of ice-marginal glaciolacustrine deposition along the sides of the Trench and subglacial or proglacial glaciofluvial sedimentation in the center of the Trench.  It is thought that ice locally remained in the center of  the Trench throughout the interstade between the middle and late stades. During the late stade, ice advanced as far south as Kalispell (Fig. 59). During f i n a l deglaciation of southeastern British Columbia, the glacier in the Rocky Mountain Trench became increasingly confined by the flanking mountains.  Spillover of ice from the Trench into the parallel-  trending Flathead and Bull Valleys and from Elk Valley into the Trench which occurred during glacial maxima ceased as the uplands appeared through the ice cover (Fig. 61).  As i n other areas of southern British  Columbia, ice disappeared from the mountainous uplands before the adjacent valleys were deglaciated (Dawson, 1889; Nasmith, 1962; Fulton, 1967, 1969), However, the shrinking glacier in the southern Rocky Mountain Trench remained active throughout deglaciation and did not stagnate as did the early Pinedale glacier.  The presence of drumlinized ground moraine and  the absence of end moraines and major ice stagnation features such as kettle and kame topography and eskers indicate that the trunk glacier receded by downwasting and orderly frontal retreat without major glacial standstills (Fig. 62).  Tributary glaciers retreated far into their  Figure 60. Comparison of a contemporary ice sheet and the Cordilleran Ice Sheet during the maximum Pinedale advance. A. Antarctic Ice Sheet (U.S. Geological Survey photo number TMA 892 F33). B. Maximum extent of the Cordilleran Ice Sheet over part of southeastern British Columbia. Nunatak areas are black and glacier-covered areas white.  226  Figure 61. A contemporary analogue of the Pleistocene g l a c i e r i z e d Rocky Mountain Trench. A. The g l a c i e r i s confined to a wide, l i n e a r valley by flanking mountains, much as was the Trench g l a c i e r immediately before and after maximum g l a c i e r advances (Bagley Ice F i e l d , Alaska; photo by Austin P o s t ) . B. The southern Rocky Mountain Trench and flanking mountains viewed toward the south from near 49°45'N (BC 896:106).  227  Figure 61  228  valleys prior to the disappearance of the trunk glacier.  The latter  blocked the side valleys, thus impounding lakes in which clay, s i l t , sand, and deltaic gravel accumulated (Fig. 63).  Drainage from these lakes and  from the receding trunk glacier was south beneath and along the margins of  the glacier (Glacial Lake Elk at an early stage overflowed to the  east via Crowsnest Pass).  Periodically, glacier-rdammed lakes drained  rapidly to produce jbkulhlaups, and many of the large meltwater channels on the floor of the Rocky Mountain Trench were formed or modified by these floods. As the ice surface was lowered, ice-marginal channels at lower elevations were progressively occupied and abandoned. The courses of major streams entering the Trench reflect this phase of deglaciation. Streams such as Gold Creek and Elk River swing abruptly to the southeast along the Trench margins before crossing the valley to join Kootenay River. These streams were forced southeast by ice covering the Trench floor and became entrenched i n their courses before ice disappeared from the valley bottom. courses.  Some streams, however, failed to entrench along southeast Sand Creek, for example, flowed along the Trench margin to near  Elko, but, as the trunk glacier receded, this ice-marginal route was abandoned for a more direct westerly course.  Recessional outwash on the  floor of the Rocky Mountain Trench includes kame terrace gravel, and sand and gravel underlying ice-frontal meltwater channels carved across the t i l l plain. The sequence of late glacial events occurred at different times along the length of the Trench.  For example, while glaciofluvial gravel  was being deposited near 49°N, t i l l was being lodged on the Trench floor farther north.  Limiting radiocarbon dates for deglaciation are not  Figure 62. Comparison of contemporary and ancient landforms produced by glaciers which remained active during recession rather than stagnating. A. Drumlinized ground moraine uncovered during the recent retreat of Muir Glacier in Alaska (photo by Austin Post). B. Drumlinized ground moraine left during the retreat of the late Pinedale glacier from the southern Rocky Mountain Trench in British Columbia (BC 5298-261). The flow direction i s from the labelled corner of each photo.  Figure 63. A contemporary analogue of Pleistocene ice-dammed lakes in the southern Rocky Mountain Trench. A. Lake Tulsequah, British Columbia shortly after i t emptied during a jbkulhlaup. The lake is impounded by a lobe of Tulsequah Glacier (photo by Austin Post). B. Pleistocene Glacial Lake Elk dammed by a lobe of ice flowing up Elk Valley from the Rocky Mountain Trench. The lake periodically drained during jbkulhlaups. Darkened areas are above an elevation of 1830 ra (6000').  232  available for the study area.  However, a bog-bottom date of 10,000 ± 140  years from the Rocky Mountain Trench at l a t i t u d e 51°29'N (GSC-1457; Fulton, 1971), provides a minimum deglaciation date. The oldest p o s t g l a c i a l date from southeastern B r i t i s h Columbia i s 11,000 ± 180 (GSC-9095 Fulton, 1971), which was obtained from freshwater marl i n the Columbia River Valley at l a t i t u d e 49°30'N.  During the Holocene, r i v e r s entrenched the unconsolidated sediment mantle on the Trench f l o o r , i n places carving canyons i n bedrock. Much of this downcutting occurred within a few thousand years after d e g l a c i a t i o n , as evidenced by kettles present on some lower r i v e r terraces and by Mazama 0 tephra (age 6600 years B.P.)  interstratified  with mudflow gravels deposited on the present Kootenay River flood p l a i n . Holocene deposition i s limited to (1) small talus cones and a l l u v i a l fans along the margins of the Trench and r i v e r v a l l e y s , (2) a thin mantle of loess, (3) small sand dunes, and (4) flood-plain sediments i n the major river valleys.  Most of these deposits probably formed by the reworking  of d r i f t during a short span of time immediately following deglaciation.  233  LITERATURE CITED  Alden, W.C., 1953, Physiography and g l a c i a l geology of western Montana and adjacent areas: U.S. Geol. Survey Prof. Paper 231, 200 p. Armstrong, J.E., Crandell, D.R., Easterbrook, D.J.,,and Noble, J.B., 1965, Late Pleistocene stratigraphy and chronology i n southwestern B r i t i s h Columbia and northwestern Washington: Geol. Soc. America B u l l . , v. 76, p. 321-330. Armstrong, J.E., and Tipper, H.W., 1948, Glaciation i n north-central B r i t i s h Columbia: Am. Jour. S c i . , v. 246, p. 283-310. Daly, R.A., 1912, Geology of the North American C o r d i l l e r a at the fortyninth p a r a l l e l : Canada Geol. Survey Mem. 38, 857 p. Dawson, G.M., 1889, Glaciation of high points i n the southern i n t e r i o r of B r i t i s h Columbia: Geol. Mag., decade 3, v. 6, p. 350-352. Fulton, R.J., 1967, Deglaciation studies i n Kamloops region, an area of moderate r e l i e f , B r i t i s h Columbia: Canada Geol. Survey B u l l . 154, 36 p. 1968, Olympia I n t e r g l a c i a t i o n , P u r c e l l Trench, B r i t i s h Columbia: Geol. Soc. America B u l l . , v. 79, p. 1075-1080. 1969, G l a c i a l lake h i s t o r y , southern Interior Plateau, B r i t i s h Columbia: Canada Geol. Survey Paper 69-37, 14 p. 1971, Radiocarbon geochronology of southern B r i t i s h Columbia: Canada Geol. Survey Paper 71-37, 28 p. 1972, Stratigraphy of unconsolidated f i l l and Quaternary development of North Okanagan Valley: Canada Geol. Survey Paper 72-8, pt. B, p. 9-17. Fulton, R.J., and Halstead, E.C., 1972, Quaternary geology of the southern Canadian C o r d i l l e r a : Guidebook, F i e l d Excursion A02, 24th Internat. Geol. Cong., Montreal, 49 p. Nasmith, Hugh, 1962, Late g l a c i a l history and s u r f i c i a l deposits of the Okanagan V a l l e y , B r i t i s h Columbia: B r i t i s h Columbia Dept. Mines and Petroleum Resources B u l l . 46, 46 p. P r e s t , V.K., Grant, D.R., and Rampton, V.N., 1967, G l a c i a l map of Canada: Canada Geol. Survey Map 1253A. Richmond, G.M., 1965, G l a c i a t i o n of the Rocky Mountains, in Wright, H.E., J r . , and Frey, D.G., eds., The Quaternary of the United States: Princeton, New Jersey, Princeton Univ. Press, p. 217-230.  234  Richmond, G.M., Fryxell, Roald, Neff, G.E., and Weis, P.L., 1965, The Cordilleran Ice Sheet of the Northern Rocky Mountains, and related Quaternary history of the Columbia Plateau, in Wright, H.E., Jr., and Frey, D.G., eds., The Quaternary of the United States: Princeton, New Jersey, Princeton Univ. Press, p. 231-242.  235  CHAPTER SIX: APPLICATIONS OF GEOLOGIC KNOWLEDGE S u r f i c i a l geology studies i n the southern Rocky Mountain Trench have provided information on the o r i g i n and evolution of the Trench, on the a p p l i c a b i l i t y of c e r t a i n procedures of t i l l investigation i n mountainous regions, on t i l l genesis, and on paleohydrologic determinations i n the g l a c i o f l u v i a l environment.  These s c i e n t i f i c contributions are  outlined i n Chapters 2, 3, and 4.  Additional geologic information  relevant to man's a c t i v i t i e s i n and outside the study area i s presented in  this chapter.  General applications of geologic knowledge outside the  southern Rocky Mountain Trench include the prediction of flood magnitude from self-dumping glacier-dammed lakes and the determination of the source of  ore clasts or minerals i n t i l l .  The groundwater resources of the  study area are assessed i n the f i n a l section of this chapter.  1  MAGNITUDE OF JOKULHLAUPS  Catastrophic floods from glacier-dammed lakes (jOkulhlaups) have resulted i n l i f e and property losses i n such areas as Iceland and Alaska.  As g l a c i e r i z e d areas are increasingly populated, i t becomes  ever more important to determine the hazards posed by s p e c i f i c g l a c i e r dammed lakes.  Jbkulhlaup prediction w i l l be possible only after an  understanding i s gained of the causes of these floods and the factors  ^Discussion adapted from Clague, J . J . , and Mathews, W.H., 1973, The magnitude of jSkulhlaups: Jour. Glaciology ( i n press).  236  a f f e c t i n g their magnitude.  Analyses of the hydrographs for two successive jbkulhlaups from glacier-dammed Summit Lake, B r i t i s h Columbia (Mathews, i n press) show that instantaneous water discharge, £> t , i s related not to time, t , since the s t a r t of each flood but to the volume of water, V t , released from the lake during this time.  For a l l but the i n i t i a l stages of the  f l o o d , discharge can be expressed by a formula of the form;  Qt  = K(Vt )  (in which f o r Summit Lake K - 0.72 3  m /sec and Vt  3  in m  6  x 10 ) .  b  (1)  and b = 1.5 i f Qt  i s expressed i n  Equations of this same form apply to  jbkulhlaups from f i v e other ice-dammed lakes, although the c o e f f i c i e n t and exponent d i f f e r for each lake (Table 8).  Hydrographs for these  floods, based on calculated or measured discharges plotted against cumulative volume l o s t , instead of time, are shown i n Figure 64.  Values of K and b for the s i x examples show large v a r i a t i o n s , with extreme values found at two B r i t i s h Columbia lakes, Summit and Tulsequah.  Possible factors influencing these values include:  the  head l o s s , H, between the high water mark i n the reservoir and the toe of the i c e dam where the escaping water generally emerges; the distance, L, from reservoir to point of emergence; the depth, Z>, of the reservoir at the dam;  and the capacity, V^^,  of the reservoir (Table 8),  A plot  v  °f max against the r a t i o H/L for the data of Table 8 i n d i c a t e s , as one might expect, that small reservoirs are i n general impounded by dams with large height-to-length r a t i o s .  Likewise, K displays a negative r e l a t i o n -  237  ship to V  MAX  ,  albeit a weak one.  For a small dam the passage of 10° nr  of water [for this volume, QT = K in Eq, (1)] can be expected to generate a larger leak, a higher discharge, and hence a higher value of K than is the case for larger ice dams with generally smaller values of H/L. Thus, the size of the dam may control both the available reservoir storage and the coefficient of Eq. (1); accordingly, wholly independent of one another. VMAX , K,  and H/L  K  and  VMAX  are not  However, the interrelationships of  a l l show large scatter, far beyond that of the individual  points on the rising curves of the hydrographs, and none of the other factors investigated can be clearly associated with variations in values of  K  and b. In Figure 64 the peak discharge, Qmax* occurring at the end of  each jbkulhlaup i s designated by a dot.  Curiously, a l l peak discharge  values f a l l close to a common line despite the variations in slope and position of the individual hydrographs.  Peak discharges for floods from  four additional ice-dammed lakes are presented in Table 8, and Figure 56 shows the resultant relationship between maximum flood discharge (in m /sec) and available water storage (in m 3  3  x 10 ) for the ten lakes. 6  The data points cluster about a line represented by: Qmax =  (r  2  75(T/roax)°-67  (  2  )  = 0.96)  This relationship is a remarkably good one considering that the data include peak discharges measured at varying distances from the toes of ice dams and are derived from lakes of widely differing size and other  238  characteristics.  More data from other jbkulhlaups and from other ice-dammed lakes are c l e a r l y needed to c l a r i f y and explain the r e l a t i o n s h i p s , but i n the meantime the log-log plot of Qt against Vt i s a useful tool for i n v e s t i gating i n d i v i d u a l jbkulhlaups, and Eq. (2) offers an empirical basis f o r estimating possible maximum discharges from self-dumping ice-dammed lakes.  These two expressions may thus be h e l p f u l i n evaluating hazards  to l i f e and property posed by ice-dammed lakes.  MINERAL EXPLORATION  Many ore deposits i n North America and Europe have been scoured beneath glaciers and buried by d r i f t .  An increasingly important tool i n  locating such ore deposits i s the tracing of ore clasts and minerals i n d r i f t back to their bedrock sources (e.g., Dreimanis, 1956; Lee, 1965). The down-glacier fan-shaped pattern of many boulder trains helps to locate bedrock sources.  The observed exponential decrease of t i l l  constituents with distance from point sources (p. 155) may also be of use i n mineral exploration.  In the case of a mineral or rock type  eroded from a r e s t r i c t e d bedrock source and transported near the base of a g l a c i e r , the exponential decrease with distance may be due to one or a combination of the following: abrasion, d i l u t i o n .  progressive deposition, breakage and  Where d i l u t i o n by l o c a l l y derived sediment has been  n e g l i g i b l e , the decrease of a constituent with distance can be expressed by:  Nx = N0 e~  kx  (3)  Table 8. JOkulhlaup data: K and b, coefficient and exponent of Eq. (1), p. 236; #> height of lake surface above toe of ice dam; L, distance from lake to toe of dam; D, depth of lake at ice dam; Vmax , reservoir storage; QmaX y maximum instantaneous water discharge. The jbkulhlaups are historic except from Lake Missoula which is of late Pleistocene age. Floods resulting from volcanic activity are excluded. Some of the data were compiled from topographic maps and air photographs.  Year  K  b  H (m)  S t r u p v a t n e t , Norway  1969  88  0.84  186  1  0.19  Ekalugad V a l l e y , B a f f i n I s l a n d  1967  46  0.91  120  2  0.06  120  Demmevatn  1937  —•  0.14  79  Gjanupsvatn, I c e l a n d  1951  30  0.03  20  Vatnsdalur, Iceland  1898  ~  1958  150  Lake  Tulsequah Lake, B r i t i s h Summit Lake, B r i t i s h  Columbia  Columbia  1965, 1967  +  0.72  ~  0.72+  D (•)  "max 6 3 (10 m )  29*  2.6** 4.8 11.6  tT  Qmax 3 (m /sec)  Reference  150  Whalley, 1971  200  Church, 1972 Strom, 1938  1,000  5  --  372  10  0.04  188  120  3,000  Thorarinsson,  0.49  210  8  0.03  73  229  1,556  Marcus, 1960  1.5  620  12  0.05  200  251  3,260  Mathews, 1965  535  19  0.03  230  1,500  5,000  Thorarinsson,  40  9  40  1,730  10,100  1939  24  0.77  Lake George, A l a s k a t t t  1958  — —  — —  Pleistocene  406  H/L  167  Graenalon, I c e l a n d  Lake M i s s o u l a , Montana  L (km)  640  —  0.004  —  610  20  2 x 10  Arnborg, 1955  370  6  1.87 x I O  1939  1939  Stone, 1963 65  B r e t z , 1925; Pardee,  *Depth to bedrock knob l i m i t i n g magnitude of JOkulhlaup = 13 m. 6 3 6 3 **Volume s t o r e d i n lake = 4.6 x 10 m ; water r e l e a s e d i n JOkulhlaup = 2.6 x 10 m. ***Very approximate. t C o e f f i c i e n t and exponent determined from hydrograph of JOkulhlaup o f June 1951; o t h e r data p e r t a i n to JOkulhlaup of October 1951. T+Lowering of lake s u r f a c e during J O k u l h l a u p . t t t D r a i n s at s u r f a c e along i c e margin. ^max estimated f o r f l o o d wave at W a l l u l a Gap i n s o u t h e a s t e r n Washington.  1942  240  (where N i s the amount of the constituent at the g l a c i e r base or i n t i l l at a distance, x, from the source; NQ i s the amount at x = 0; and Jc i s a constant r e f l e c t i n g the rate as a function of distance at which deposition or breakage occurs).  Thus, knowing NQ and k, and determining N at two or  more points along the glacier-flow path, one can calculate x, which serves to approximately locate the ore deposit.  The constants, NQ and ky  may be estimated from the frequency d i s t r i b u t i o n of other t i l l uents of known source.  constit-  I f breakage i s the factor c o n t r o l l i n g the d i s -  t r i b u t i o n , however, constituents of similar d u r a b i l i t y should be compared, and the "terminal grades" of minerals  ( i . e , , minimum grain size below  which breakage i s rare; Dreimanis and Vagners, 1971) taken into account. A l s o , with increasing distance of transport, sediment may be transferred from a subglacial to an e n g l a c i a l p o s i t i o n , thus becoming unavailable for  immediate deposition.  Since the above relationship i s based on the  assumption that transport occurs near the base of the g l a c i e r , Eq. (3) may not be applicable to the frequency d i s t r i b u t i o n of a constituent far from i t s source.  Nevertheless, the central part of the d i s t r i b u t i o n  should y i e l d r e l i a b l e estimates of distance to source.  GROUNDWATER  Annual p r e c i p i t a t i o n on the f l o o r of the southern Rocky Mountain Trench i s less than water losses due to evapotranspiration, but there i s a continual i n f l u x of surface water and groundwater from the adjacent water-positive mountainous areas. the area.  The water table i s high throughout  K e t t l e lakes fluctuate i n size seasonally but rarely dry up;  springs and seepage occur along the walls of the major r i v e r v a l l e y s .  VOLUME  (m ) 3  Figure 64. Relation of cumulative volume drained during jbkulhlaups and instantaneous water discharge. Equations are of the form Qt = iC(v t )^, in. which the coefficient, K, and exponent, for each flood are listed in Table 8. The peak discharge for each jbkulhlaup is indicated by dot. E—Ekalugad Valley; Gj—Gjanupsvatn; Gr—Graenalon; St—Strupvatnet; Su—Summit Lake; T—Tulsequah Lake.  242  The water requirements of the r u r a l population are s a t i s f i e d from shallow wells and by direct extraction from r i v e r s , streams, and lakes. Cranbrook, however, i s using large amounts of groundwater from unconsolidated deposits.  The large volume of semiconsolidated and unconsolidated sediments i n the Trench may represent a sizable groundwater r e s e r v o i r . Although the character of sediments beneath the St. Eugene Formation i s not known, these sediments f i l l s t r u c t u r a l basins up to 1500 m deep. Most St. Eugene sediments and Pleistocene c l a y , s i l t , and diamictdn have low permeabilities and probably form p a r t i a l b a r r i e r s to the movement of groundwater.  Sand and gravel exposed i n the v a l l e y walls  along Kootenay River may be the uppermost sediments of a permeable  fill  underlying the center of the Rocky Mountain Trench. Outside this central zone, permeable units of Pleistocene age are r e l a t i v e l y thin and discontinuous.  Older outwash, although probably not an important  aquifer, i s permeable and may thus affect groundwater movement. If there i s channel continuity beneath Wycliffe t i l l , permeable p r o g l a c i a l outwash of the younger drift  may transmit abundant groundwater.  Further information on the d i s t r i b u t i o n and s p e c i f i c y i e l d s of these p o t e n t i a l aquifers can be obtained through a limited program of d r i l l i n g and pumping t e s t s .  The most accessible source of groundwater,  however, i s late Wisconsinan outwash gravel underlying the major meltwater channel s on the Trench f l o o r (Fig.  5 ) . The gravel i s extremely  permeable and, i n general, i s underlain by r e l a t i v e l y impermeable c l a y , s i l t , and diamicton.  243  Figure 65. Meltwater channels in the vicinity of Cranbrook, British Columbia. The large south- to southwest-trending channel i s underlain in part by water-bearing glaciofluvial gravel. Two production wells (darkened circles) have a combined maximum design capacity of 1500 U.S. gpm (0.095 3 m /sec), and the channel transmits a natural flow twice as large (Brown and others, 1970).  244  Figure 66. Meltwater channel complex northwest of Bull River (top); mean water discharge records of Norbury Creek (1959-1970) and Bull River (19141970) (bottom). Norbury Creek i s fed by groundwater from the channel complex. Gauging stations on Norbury Creek and Bull River are indicated by triangles. Geology in part from Kelley and Sprout (1956) and Leech (1960).  245  Figure 66  246  The City of Cranbrook is extracting groundwater from the gravel of one large meltwater channel (Fig. 65).  Two production wells are  rated at a combined maximum design capacity of 1500 U.S.  gal/min  (0.095 m /sec), and i t has been estimated that the channel in which the 3  wells are founded carries a natural flow twice as large (Brown and others, 1970).  Permeability of the aquifer gravel is very high; from  coefficients of transmissibility reported by Brown and McNichol  (1969),  hydraulic conductivity at the two wells is determined to be about 10,000 and 100,000 gal/day/ft (0.0004 and 0.004 m /sec/m ). 2  3  2  The  groundwater contains between 400 and 500 ppm total dissolved solids of which the bulk is Ca^  and HC03~, with lesser amounts of Mg"" and 1 1  SO^ . -  Many other late glacial meltwater channels represent potential groundwater sources.  An example i s the north-south trending channel  located on the east side of the Trench north of Bull River (Figs. 5 and 66).  This channel is recharged by abundant surface flow; the safe  yield can be estimated from the mean discharge of the groundwater-fed stream draining the channel—about  1.0 m /sec. 3  A comparison of the  hydrographs of this stream (Norbury Creek) and rivers fed by surface runoff (e.g., Bull River) (Fig. 66) shows:  (1) the more uniform dis-  charge of Norbury Creek, with Bull River characterized by high late spring and summer maxima and low base flows during the remainder of the year; (2) the occurrence of the Norbury Creek peak discharge about one to two months after the Bull River peak.  This difference represents the  average transit time of groundwater through the outwash gravel of the meltwater channel.  247  LITERATURE CITED Arnborg, Lermart, 1955, Hydrology of the glacial river Austurfljot: Geog, Annaler, v. 37, p, 185-201.. Bretz, J.H., 1925, The Spokane flood beyond the channeled scablands: Jour, Geology, v. 33, p. 97-115, 236-259, Brown, W.L., and McNichol, Corporation of the Roberts, and Brown Vancouver, British  R.T., 1969, Groundwater development, the City of Cranbrook: Report by Robinson, Ltd. for Associated Engineering Services Ltd., Columbia, 11 p.  Brown, W.L., McNichol,. R.T. , and Dakin, R.A. , 1970, Production wells, the Corporation of the City of Cranbrook, B.C.: Completion report by Robinson, Roberts, and Brown Ltd. for Associated Engineering Services Ltd., Vancouver, British Columbia, 9 p. Church, M.A., 1972, Baffin Island sandurs: a study of Arctic fluvial processes: Canada Geol. Survey Bull. 216, 208 p. Dreimanis, Aleksis, 1956, Steep Rock iron ore boulder train: Canada Proc, v. 8, p. 27-70.  Geol. Assoc.  Dreimanis, Aleksis, and Vagners, U.J., 1971, Bimodal distribution of rock and mineral fragments in basal t i l l s , in Goldthwait, R.P., ed., T i l l : a symposium: Columbus, Ohio State Univ. Press, p. 237-250. Kelley, C.C., and Sprout, P.N., 1956, Soil survey of the upper Kootenay and Elk River valleys in the East Kootenay district of British Columbia: British Columbia Soil Survey Rept. 5, 99 p. Lee, H.A., 1965, Investigation of eskers for mineral exploration: Geol. Survey Paper 65-14, pt. 1, 17 p. Leech, G.B., I960, Fernie, west half, British Columbia: Survey Map 11-1960.  Canada  Canada Geol.  Marcus, M.G., 1960, Periodic drainage of glacier-dammed Tulsequah Lake, British Columbia: Geog. Rev., v. 50, p. 89-106. Mathews, W.H., 1965, Two self-dumping ice-dammed lakes in British Columbia: Geog. Rev., v. 55, p. 46-52. 1973, The record of two jokulhlaups: Internat. Assoc. Sci. Hydrology, Symposium on the hydrology of glaciers, Cambridge, September 1969 (in press) . Pardee, JIT., 1942, Unusual currents in Glacial Lake Missoula, Montana: Geol. Soc. America Bull., v. 53, p. 1569-1600.  248  Stone, K.H., 1963, The annual emptying of Lake George, Alaska; v. 16, p. 26-40.  Arctic,  StrOm, K.M., 1938, The catastrophic emptying of a glacier^dammed lake in Norway 1937: Geologie der Meere und BinnengewSsser, v, 2, p. 443444. Thorarinsson, Sigurdur, 1939, The ice-dammed lakes of Iceland with partis cular reference to their values as indicators of glacier oscillations: Geog. Annaler, v. 21, p. 216-242. Whalley, W.B., 1971, Observations of the drainage of an ice-dammed l a k e — Strupvatnet, Troms, Norway: Norsk Geog. Tidsskr., v, 25, p. 165174.  249  CHAPTER SEVEN:  SUGGESTIONS FOR FURTHER RESEARCH  Research projects often produce more questions than answers. Such questions, however, invite additional research which expands the basic body of scientific knowledge.  In effect, advances in science  result from individuals extending and modifying the conclusions of their colleagues. The following are some suggestions for further research based upon my studies in the Rocky Mountain Trench.  TILL FABRICS AND TILL GENESIS Boulton (1971) has discussed the relationships that exist between t i l l - f a b r i c elements and t i l l genesis (p. 118, Table 4).  In an  extension of Boulton's work, I have interpreted the depositional history of Pleistocene t i l l from t i l l - f a b r i c data.  This method of determining  the genesis of Pleistocene t i l l might be further tested in another mountainous area where the direction of glacier flow i s known and where there were no coalescent tributary glaciers which might have produced complex t i l l fabrics.  In such an area the orientations of blade-shaped  clasts in t i l l should yield information on the transportational and depositional history of the sediment (see Table 4).  250  ORIGINS OF DRUMLINS  Drumlins have been extensively studied, but their o r i g i n i s s t i l l debated (for a review and references, see Gravenor, 1953; and Unwin, 1968). drumlins form:  There are, however, two main hypotheses as to  how  by subglacial deposition and by subglacial erosion of  pre-existent materials.  The dynamics of drumlin formation might be  understood better i f drumlin fabrics were determined. may  Smalley  Since t i l l fabrics  provide information both on t i l l genesis and the d i r e c t i o n of i c e  movement during deposition, f a b r i c data collected at a number of s i t e s on a drumlin might indicate whether or not t i l l deposition and drumlin formation were contemporaneous.  If the drumlin formed by the erosion of  pre-existent t i l l , fabrics might be unrelated to drumlin morphometry.  COLLECTION OF FABRIC DATA  One major impediment to the use of fabric techniques i n sediment investigations i s the large amount of time required for data c o l l e c tion and analysis (for example, several hours are commonly required to measure and process a single f a b r i c sample of 50 c l a s t s ) . rapid macroscopic techniques (Dreimanis, 1959) (Dapples and Rominger, 1945)  Although more  and microscopic methods  have been devised, a l l require that the  orientations of i n d i v i d u a l grains or clasts be determined.  Because  elongate grains and clasts i n sediments with directed fabrics are nonrandomly oriented, these sediments are anisotropic i n terms of properties such as thermal conductivity, r e s i s t i v i t y , permeability, shear  251  strength, and magnetic s u s c e p t i b i l i t y .  I f any of these anisotropics are  instrumentally detectable, a rapid technique would then be available for measuring the d i r e c t i o n and strength of p a r t i c l e alignment i n sediments.  DECREASE OF TILL CONSTITUENT WITH DISTANCE FROM SOURCE  Mineral grains and clasts decrease i n abundance i n t i l l with increasing distance from their bedrock sources.  Explanations  for this  relationship include breakage and abrasion during transport, progressive deposition of sediment away from i t s source, and d i l u t i o n by sediment mixing at the g l a c i e r - t i l l interface (p. 127).  The importance of each  of these factors can best be evaluated by determining the amount of the t i l l constituent as a function of distance to source for each till  fraction.  size  The functional relationships among these three variables  (amount of constituent, distance to source, and grain size) would presumably depend upon the factors (breakage and abrasion, progressive depos i t i o n , and d i l u t i o n ) operative at the glacier base.  For example,  breakage would produce a decrease i n frequency of the largest clasts away from the source, but might result i n a net increase with distance of a constituent at i t s "terminal grade" (minimum size below which breakage rarely occurs).  Other patterns would result where the controlling factor  i s progressive deposition or d i l u t i o n . progressive deposition, and d i l u t i o n may  Obviously, breakage, abrasion, occur simultaneously  rather complex relationships between constituent abundance and to source.  Explanations  to produce distance  for such patterns require data from a l l t i l l  size fractions rather than from a single grade.  252  QUATERNARY STRATIGRAPHY  The stratigraphy of Quaternary deposits i n the Rocky Mountain Trench between latitudes 49° and 50°10'N has been determined, and correlations have been made with deposits of the Flathead Lake area i n north-western Montana.  A study of Quaternary sediments and g l a c i a l landforms  i n the Trench north of 50°10'N might provide additional information on the extent of g l a c i e r recession during each of the two Pinedale interstades, and on the pattern and timing of deglaciation.  SEDIMENT CONSOLIDATION  The thickness of sediment or i c e which once covered a clay or s i l t unit may i n some places be determined from bulk density measurements on the clay or s i l t .  The relationship between bulk density and b u r i a l  depth, however, i s not a simple one, because such factors as postdepositional sediment d e s i c c a t i o n , pore pressure during compaction, and variable clay and s i l t mineralogy must be evaluated.  Clay and s i l t  occur  at f i v e stratigraphic levels i n the southern Rocky Mountain Trench. Inasmuch as the maximum b u r i a l depths of these units are known, the a p p l i c a b i l i t y of consolidation techniques may be determined. The uppermost, or late g l a c i a l , s i l t has not been overridden by i c e ; s i l t within the younger drift  and inter-drift  s i l t have been compacted by the  weight of overlying sediments plus about 1500 m of i c e ; fine-grained sediments of the Olympia Interglaciation and the St. Eugene Formation have been buried at a minimum by the sediments presently overlying them and by about 1500 m of i c e .  253  GROUNDWATER RESOURCES Additional information on the distribution of groundwater and units of semiconsolidated and unconsolidated sediment in the Rocky Mountain Trench can be obtained from a program of d r i l l i n g and pumping tests.  254  LITERATURE CITED Boulton, G.S., 1971, T i l l genesis and fabric in Svalbard, Spitsbergen, in Goldthwait, R.P., ed., T i l l : a symposium: Columbus, Ohio State Univ. Press, p. 41-72. Dapples, E.C., and Rominger, J.F., 1945, Orientation analysis of finegrained clastic sediments: a report of progress: Jour. Geology, v. 53, p. 246-261. Dreimanis, Aleksis, 1959, Rapid macroscopic fabric studies i n d r i l l cores and hand specimens of t i l l and t i l l i t e : Jour. Sed, Petrology, v. 29, p. 459-463. Gravenor, CP., 1953, The origin of drumlins: p. 674-681.  Am. Jour. Sci,, v. 251,  Smalley, I.J., and Unwin, D.J., 1968, The formation and shape of drumlins and their distribution and orientation i n drumlin fields: Jour. Glaciology, v. 7, p. 377-390.  255  APPENDICES  APPENDIX 1 STRATIGRAPHIC SECTIONS  E52  COUUVIUM, FANGLOMERATE  Till  4 — * 3 — *  YOUNGER DRIFT** INTER-DRIFT  SEDIMENTS*  2 — * O l O £ R DRIFT* 1 —  INTERGLACIAL SEDIMENTS  5 —  ST. EUGENE FORMATION  R —  BEDROCK  10  ms  Ki  CT*  pi  E "  5  4 4 > »«?c£  12 11  lis  13 4  4  pi  .ap.K; ;  t l  w  *GX-2031 >36,000 (wood)  p0§  3  26,800±1000  (wood!  14  | •- Htfn t1j,-tft*;o . •.•tl" "dr-Jl  APPENDIX 1  (Continued)  STRATIGRAPHIC SECTIONS  APPENDIX 2. Southern Rocky Mountain Trench radiocarbon dates. A l l samples were collected by J.J. Clague and analyzed by Geochron Laboratories, Inc. Dates are based on a half l i f e for C of 5570 years and are referenced to the year A.D. 1950. 11+  Laboratory sample no.  Material  Location  GX-2031  wood  49°  GX-2032**  wood  49°21 '25"N, 115°17'05"W  GX-2033***  peat  49°23 '25"N, 115°18'20"W  GX-2034***  wood  49°27 '50"N, 115°27'50"W  09 '45"N, 115°13'25"W  Stratigraphic position of sample  Radiocarbon age (years B.P.)  older t i l l  >36,000+  Olympia Interglacial sediments channeled outwash at top of younger  drift  channeled outwash at top of younger  drift  19,100±850 14,0001750  *Sample i s part of a clast of wood i n t i l l . The wood was probably reworked from sediment older than the till. Sample pretreatment—removal of foreign organic material, immersion in hot dilute HCI and i n hot dilute NaOH. **Sample was collected about 0.5 m below contact with t i l l . Sample pretreatment—removal of foreign organic material, immersion in hot dilute HCI and i n hot dilute NaOH. ***Samples GX-2033 and GX-2034 are clasts of peat and wood from permeable glaciofluvial gravel. Many cobbles and pebbles in the gravel have rinds of precipitated CaC0 . The peat and wood possibly were reworked from sediments older than the gravel, and probably have been contaminated since outwash deposition. Sample pretreatment—concentration of organic material, removal of foreign organic material, immersion in hot dilute HCI. +Count rate of sample could not be distinguished from background rate. 3  259  3. Size frequency data for selected t i l l samples. Only that-portion of each sample f i n e r than -2<j> was analyzed. The sediment was sieved at half-<J> intervals from -2<j> to 4<f>, and pipette samples were collected at one-<j> intervals from 4<f> to 12<j). A l l t i l l samples are from the younger drift, except nos. 1 and 5 which are from the older drift. Sample nos. 6 and 7 are from the same s i t e ; no. 6 was collected from the top of the t i l l and no. 7 from the base just above inter-drift s i l t s . Sample locations: 1 — 4 9 ° 1 1 ' 5 5 " N , 115°08'00"W; APPENDIX  2—49°12'40"N,  115°10'15"W;  3 — 4 9 ° 23  1  20"N,  115°15'35"W;  115°04'10"W;  5 — 4 9 ° 3 6 ' 1 5 " N , 1 1 5 ° 4 2 ' 15"W;  6 and  115°40'05"W;  8 — 4 9 ° 3 7 '05"N,  9 — 4 9 ° 37 ' 25"N,  10—49°53'40"N,  115°41'15"W;  116°13'50"W;  1 1 — 5 0 ° 0 8 ' 10"N,  0  7—49°36  50"N , 115°56'20"W;  115°43'25"W.  GRAIN SIZE SAND  CLAY  4 — 4 9 ° 2 7 ' 20"N, 1  SILT  APPENDIX 4.  FAN  Fan-fabric sites and results.  FABRIC SITES  INDEX MAP OF FAN-FABRIC AREAS Samples from an alluvial fan of Quaternary age: Samples from fanglomerate of Miocene age (St. Eugene Formation): MAP OF FAN-FABRIC SITES IN THE SOUTHERN ROCKY MOUNTAIN TRENCH  1 ~4 5 o -  (Continued)  APPENDIX 4  Fabric no.  Location  Axis of maximum clustering** 8l \  Elevation* (m)  Number of observations  420 400 400 400  60 60 60 60  94 42 74 117  750  140 20 60 60  p  Paraglacial alluvial tan. Fraser Canyon, British Columbia 1 2 3 4  50°46'00"N, 12i°50'10"W 50°46'05"N, 121°50'2O"W 50°46'10"N, 121°50'25"W 50°46'20"N,'121°50"15"W  Axis of minimum clustering** 9 s3 ••«3 ^3 rl  2  +  +  13 1 13  33.5 39.4 41.5 39.9  0.696+ 0.597+ 0.561 0.588+  0 208 336 247  62 77 83 71  71.2 71.5 70.5 69.3  0..104 0..101+ 0,.111*t 0.,125  8 318 28 186  3 8 10 0  46.5 41,.8 45..5 45..9  0..473+ 0,.555++ f 0,.491 f 0.,485  249 75 245 279  84 74 78 82  69..0 73,.9 67..7 70.,7  0,.129+ + 0,,077 + 0,,144 0.,109  790  120 60 60  29 33 14  8 12 0  38.,0 30.,8 43.,4  0,,621+ t 0..738 0.,528+  238 169 285  80 73 79  70..1 74..1 68.,1  0,.116+ 0..075+ f 0.,139  49''11 55"N, 115°08'35"W  770  120 60 60  76 49 86  7 1 11  39.,8 41..4 35..0  0..591+ + 0..563t 0.,672  291 303 288  82 86 79  78,,4 77.,9 79. 8  0.,040 0.,044+ + 0.,031  49°12'15"N, 115°07'45"W  810  180 60 60 60  55 61 66 43  8 4 19 2  42..7 45..8 40. 5 39.,8  0.,540 0..486+ 0..578+t 0.. 590  266 307 248 217  80' 81 71 88  70.,4 68.4 71. 3 74..0  0.,113+ 0.,136+ 0.,103+ 0..076+  St. Eugene fanglomerate, Rocky Mountain Trench, British Columbia 5  s  5A 5B 5C 6§ 6A 6B5 7 7A 7B s  8 8A 8B 8C  49°04'20"N, 11S°14'20"W  C  0  49 11'55"N, 115°08'00"W ,  +  f  +  *Approximate. **Axes calculated by the "eigenvalue" method for the analysis of axial orientation data (Mark, 1973). The two vectors are orthogonal. A = azimuth; P = plunge; 6 " standard scattering angle around the associated vector; S = statistic against which the null hypothesis that the population is uniform may be tested (Anderson and Stephens, 1971). ^Population is nonuniform, 99% confidence limits. "^'Population is nonuniform, 95% confidence limits. ^Composite fabric of two or more individual fabrics taken at intervals of several meters to about 100 m laterally.  262 TILL FABRICS TILL-FABRIC SAMPLE NUMBER A N D SITE (upper till, lower till)  * D  -J "  TILL-FABRIC AXIS OF M A X I M U M CLUSTERING  APPENDIX 5, Contoured diagrams of sele cted t i l l fabrics, Contours approximately 2-5-8% per 1% area. Additional t i l l - f a brie diagrams are shown in Figure 35.  263  SOUTHERN ROCKY M O U N T A I N TRENCH CONTOUR INTERVAL 2000' (610m) 5  0  l-l I I I I  5  10  Kilometers  14 „13 12  TILL-FABRIC SITES TILL-FABRIC SAMPLE NUMBER AND SITE: UPPER TILL (single sample, multiple sample) LOWER TILL (single sample)  •  F] 2  A  45'  APPENDIX 6.  T i l l - f a b r i c sites and results.  15  20  264  APPENDIX 6 (.Continued)  „ , , Fabric n o 1  2  3§ 3A 3B  Axis of maximum , . *4 clustering** _ fl> _  . , Location  Elevation , . <m>  c Number of , , observations  ,  A9°06'20"N, 115°05'30"W A9°09'A5"N, 115°13'25"W A9°10'15"N, 115°11'15"W  850 730 790-817 817 815  60 60 419 20 20  72 27 165 302 335  9 16 2 12 17  39.2 42.0 46.3 33.7 37.9  0.599+ 0.553 f 0.476 + 0.692+ 0.623 +  ,  Axis of minimum . , ** clustering*" „ ,  257 247 47 . 139 106  81 70 86 78 65  67.5 69.8 65.6 73.8 69.0  0.146+ 0.120+ 0.171+ 0.078+ 0.128++  3C 3D 3E 3F 3G  813 8L2 810 808 807  20 59 20 20 20  148 276 301 21 185  2 27 7 10 16  31.1 47.9 38.8 43.7 39.7  0.734+ 0.449+++ o.car 0.523+++ 0.593+  238 101 207 281 298  32 63 24 46 53  71.1 67.2 65.0 67.1 64.0  0.105+ 0.150+ 0.178 0.151++ 0.193  3H 31 3J 3K 3L  805 80 A 801 800 798  20 20 20 20 20  57 164 310 309 342  6" 11 1 19 19  46.8 32.6 41.8 AA.2 41.0  0.468 0.709+ 0.555'+ 0.315n + 0.569T+  315 278 44 122 106  65 65 80 71 59  68.3 73.3 75.0 71.5 72.1  0.137++ 0.092+ 0.0671" 0.101 + 0.094+  3M 3N 30 3P  795 793 792 791 790  20 20 20 60 20  0 155 32 180 173  0 10 7 15 22  A4.4 48.8 35.1 43.7 44.5  0.511 0.433 0.670+ 0.523 f 0.509  269 301 296 329 320  73 78 43 72 65  67.8 66.1 73.9 71.0 66.3  0.142++ 0.16A++ + 0.077+ 0.106 T 0.161'++  818-821 821 819 818 790  60 20 20 20 60  167 336 165 179 355  3 1 8 4 8  35.1 32.5 40.3 28.9 43.6  0.670+ 0.711+ 0.581+ 0.766+ 0.524 r  68 67 60 76 199  70 61 62 73 81  69.7 69.0 65.4 76.6 67.2  0.121+ 0.128'+ 0.173. 0.054 T 0.150+  820 880 819-829 829 828  60 60 140 20 20  10 171 351 170 32  12 2 2 5 27  42.1 38.6 A1.8 32.3 37.A  0.551+ 0.610+ 0.556+ 0.714 T 0.631+  248 296 254 332 267  68 86 69 84 48  64.1 70.5 67.6 69.8 67.5  0.191+ 0.112 T 0.145+ 0.119+ 0.1467+  825 823 822 821 819  20 20 20 20 20  339 153 38 209 349  7 8 18 6 11  35.8 33.4 45.3 45.4 35.5  0.658+ 0.697' 0.494 0.493 0.663+  248 285 251 321 220  1 78 69 73 72  69.3 70.6 70.7 71.2 70.8  0.125++ 0.111 T 0.109+ 0.104+ 0.108+  3Q 4? 4A AB AC 5  A9°10'2S"N,  115°11'10"H  49°11'55"N,  115°08'00"W  6 7 85 8A 8B  49''12'00"N, 1 1 5 ° 1 5 ' 2 5 " W 4 9 ° 1 2 ' 3 5 " N , 115°07'20"W A9°12'40"N, 115°10'15"W  8C 8D 8E 8F 8G 9 10 11 12 13  49°15'35"N, 49°16'00"N, A9"17'25"N, A9°18'00"N, A9°20'35"N,  115°05'55"U 115°11'50"W U5 o 08'10"W 115°16'35"W 115°17'10"W  9A0 820 900 820 8A0  60 60 60 60 60  59 345 36 145 150  12 1 8 3 3  43.1 44.9 35.6 40.5 39.4  0.534+ 0.502+ 0.661+ 0.578+ 0.597+  215 253 147 241 53  77 65 67 67 64  68.9 66.9 69.9 66.4 71.9  0.130+ 0.153 T 0.118+ 0.160+ 0.096+  IA 15 16 17 18  A9°23'20"N, 49°24'25"N, A9°27'20"N, 49°34-25"N, A9'3A'A5"N,  115°15'35"W 115°22'A5"W il5°0A'10"W 115*40'25"W 115°A7'00"W  870 870 1000 870 890  60 60 60 60 60  341 14 351 315 23  2 14 3 13 12  31.0 36.1 47.1 39.0 46.2  0.734+ 0.652+ 0.463++ 0.605+ 0.480 T  225 231 249 173 229  84 .76.4 72 72.4 73 65.3 74 67.8 76 68.1  0.056+ 0.091+ 0.174+ 0.142+ 0.139+  195 19A 19B 19C 19D  49°35'15"N,  115"A8'A0"W  907-919 919 916 913 910  100 20 20 20 20  150 5 32 5 150 12 154 ' 4 133 6  42.3 36.7 30.9 38.4 35.8  0.547+ 0.642+ 0.736+ 0.614+ 0.658+  265 293 253 302 276  78 63 49 85 82  68.5 70.1 72.6 66.1 68.6  0.134+ 0.116+ 0.090+ 0.164+++ 0.133++  A9°36'00"N, A9 0 36'15"N, 49°36'15"N, 49°36'45"N,  m'siuo'^  907 870 820 870 820-86A  20 60 60 60 440  301 193 315 39 0  4 18 13 11 6  44.1 44.5 39.1,_ 36.4 45.9  0.516+++ 0.509+ 0.602'; 0.647+ 0.484 T  195 356 169 211 136  76 71 75 79 82  71.6 70.5 70.8 71.7 68.8  0.100+ 0.111+ 0.109+ 0.099+ 0.131+  23A 23B 23C 2 3D 23E  864 861 859 857 855  60 20 20 20 20  334 342 27 326 156  8 8 15 10 5  36.4 34.3 42.6 38.5 35.1  0.648+ 0.683+ 0.541++ 0.612+ 0.669 f  100 120 248 208 13  76 80 70 70 83  73.4 75.8 73.9 68.6 72.2  0.082+ 0.060+ 0.077+ 0.133++ 0.094+  23F 23G 23H 231 23J  853 851 849 8A6 843  20 20 20 20 20  349 144 352 337 217  4 1 8 8 4  37.6 42.3 41.6 38.5 36.8  0.628+ 0.546+T 0.559++ 0.612+ 0.641+  236 236 146 219 128  79 70 81 74 8  73.4 70.9 71.2 69.8 66.9  0.082+ 0.108+ 0.104+ 0.119+ 0.154+++  23K 23L 23M 23N 230  840 838 835 832 830  20 20 20 20 20  20 196 75 13  7 18 8 7 3  42.2 47.2 35.9 41.8 38.2  0.549++ 0.462 0.657+ 0.555++ 0.618+  127 21 167 117 135  66 72 6 61 78  70.3 68.3 67.9 67.8 76.0  0.113+ 0.137++ 0.141++ 0.142++ 0.058+  19E 20 21 22 235  115°A2'15"W 115*52'55"W 115"42'35"W  3;  265 APPENDIX 6  „ . , Fabric no.  231' 23<J 23R 23S 23T 245 24A 24B 24C 2 AD 24E 24F 24G 24H 241 24J 24K 24L .'24M 24N 240 24P 24Q 24R 25§ 25A 25B 25C 25D 25E 26^ 26A 26B 26C 26D 26E 27 28 29  „. Location  t  49°36'45"N, 115*/,2'35"W  49*36'50"N, 115°40'05"W  49°37'15"N, 115°37'05"W  <  49'37'25"N, 115°56'20"W  <,  49 37'S5"N, 115"57'30"W 49°42'25"N, 115°49'05"W 49°59'20"N, 115°45'20"W  Elevation ,m,) (  HZH 826 824 822 820 810-840 840 839 838 837 836 834 833 831 829 826 824 822 820 818 816 814 812 810 795-805 805 804 802 800 795 909-917 917 915 913 911 909 910 910 900  *  (Continued)  „ , , N. umber „ of. observations  20 20 20 20 20 481 60 20 20 20 20 20 20 20 60 20 20 20 20 20 20 21 20 60 180 60 20 20 20 60 100 20 20 20 20 20 60 60 60  Axis of maximum , . ** clustering A ;  P j  2 CO 5 284 59 231 345 328 317 "308 103 331 351 24 42 36 319 324 20 168 290 344 26 358 34 300 55 223 313 142 321 91 84 80 269 313 242 65 200 317  8 j  11 8 16 7 14 14 10 12 1 2" 13 21 26 30 15 19 20 3 6 2 15 23 20 22 12 1 13 23 8 20 2 6 14 2 11 7 20 26 12  Axis of minimum . . ** clustering  S j  A j  1  41. 1 0. V.')' >' 34 .3 0.682+ 39 .6 0.595+ 38 .8 0.608+ 20..2 0.880+ 45 .1 0.499+ 32 .0 0.719+ 34 .8 0.674+ 37 .9 0.622+ 36 .4 0.648+ 45 .8 0.487 44..2 0.515+++ 35 .6 0.661+ 34 .6 0.678+T 38,.0 0.621 33,.0 0.704+ 29 .9 0.752' 42 .8 0.539++ 33 .3 0.699+ 41,.7 0.558++ 35,.4 0.664+ 46,.5 0.473 43,.6 0.524+++ 42,.3 0.547+ 49,.4 0.423+ 40,.9 0.571+T 42,.4 0.546+ 44,,7 0.506 44,.9 0.501 38..4 0.613+ 40..9 0.571+ 45..6 0.489 28.,2 0.777+ 31..0 0.735+ 37.,8 0.624+ 43.,9 0.520+++ 37..0 0.638+ 38..2 0.618+ 28.,4 0.774+  P j  B j  158 172 38 174 135 209 187 74 214 358 210 218 150 237 244 154 220 282 69 196 247 263 226 219 143 324 54 115 15 213 185 180 282 0 209 114 219 69 87  50 81 56 74 24 71 77 66 78 82 66 60 49 59 73 71 32 73 55 62 19 53 60 68 77 56 76 66 76 38 66 41 75 22 48 79 68 54 73  S j  t,<).1  72 .7 67 .7 69 .5 78 .0 67 .8 72 .4 74 .1 67 .6 66 .6 71.9 66 .7 69 .5 75 .0 68 .4 72 . 5 69 .9 68 .5 71.0 66 .9 67 .5 65 .2 72 .1 66 .8 63 .6 63 .5 70 .9 66 .8 67 .2 67 .8 67 .8 68 .5 73 .1 69 .6 70 .4 72 .5 67 .9 72..0 75 .9  0. I.20+ 0.,089 + 0,.143++ 0,.123+ 0..043+ 0..142+ 0.,092+ 0.•°"L 0,.145++ 0.,158+++ 0.,096+ 0..156+++ 0.,123+ 0..067+ 0.,135+ 0.,090+ 0,.119+ 0.,134++ 0,.107+ 0.,154+++ 0.,147++ 0.,176 0.,094+ 0.,155+ 0.198+ 0.199+ 0.,107+ 0.155+++ 0.,150++ 0.143+ 0.,143+ 0..134++ 0.084+ 0.122+ 0.113+ 0.091+ 0.142+ 0.096+ 0.059+  *Approximate. **Axes calculated by the "eigenvalue" method for the analysis of axial orientation data (Mark, 1973). The two vectors afe mutually orthogonal. A ° azimuth; P = plunge; 6 » standard scattering angle around the associated vector; S = statistic against which the null hypothesis that the population is uniform may be tested (Anderson and Stephens, 1971), "fpopulatioryis nonuniform, 99% confidence limits. "^Population is nonuniform, 95% confidence limits. +++Pop ulation is nonuniform, 90% confidence limits. SComposite fabric of three or more individual fabrics taken at intervals vertically through the t i l l sheet.  266  15'  II5"00  SOUTHERN ROCKY MOUNTAIN TRENCH CONTOUR INTERVAL 2000' (610 m)  Ir-SCOO'  ,0  5  10  Kilometers  115^122  •  JO  JO  121  1,4 ' i f 0_lio  83  82  A—Pebble samples B—Heavy mineral samples C—Pebble and heavy mineral samples -15'  SEDIMENT SAMPLE SITES SAMPLE SITE AND NUMBER  UPPER TILL  •'"B'» « " * ' • multiple sample  LOWER TILL  single sample  OUTWASH  f"**, multiple sample  II6 00' 0  49-00'  /049  1  i •  A  B  •  B  a  c •  •  A  o O  45'  30'  APPENDIX 7. Heavy mineral and c l a s t lithology data.  15  20  267 APPENDIX 7 (Continued).  «  B  0 c  c  • cH o cj »0 J  0) CU  S rt  W  C o u to > at  w  * *VD.  *  «  >•  U Ct  a  w  Clast lithology data.  u  ±>  •w (fl u O•  C  <u -v  +-  i3n 0JrtO *J C 0J-I- n +• rS * > Oi0-wIa-t 0H 14-t-1 O (0 ^orao a—lt iat odrt rt u u HUH — " t— 1 c r H 3 « a C 1^1 <u c•o at oo*-l H O 0 H £. O c ^ 6 ai rt 0 rt C X O o rto rt cr 3 u O cd ro rt o rt •r*  o at c O0  V u D T3  Si Xi O  rt*H at u * J a.£j  rt -!-  CL  X.  N  U  00  •H  -H  U  U  CL -o OO 1 u  at c  sto'  at c  *j VI  CO  at —]  o ao  •H  o  E  at  percent of pebbles  1 2 3 4 5  49°00'20"N 49°00'50"N 49°02'15"N 49°02'20"N 49°02'35"N  115°03'40"W 115°07'55"W 115°03'50"W 115°12'45"W 115°07'10"W  870 800 900 770 810  T T 0 T 0  0 0 0 0 0  0 3 5 3 0  0 2 0 3 0  0 0 0 0 0  40 44 44 24 50  4 5 6 7 7  17 6 0 9 6  4 2 0 5 1  35 38 45 49 36  6 8 9 10 11  49°O4'05"N 49°04'25"N 49°05'15"N 49°06'20"N 49°07'25"N  115°10'35"W 115°14'25"W 115°06'15"W 115°05'30"W 115°08'35"W  790 780 840 850 820  T T O T 0  0 0 0 0 0  0 12 0 0 1  0 0 1 1 0  0 0 0 0 0  50 16 42 60 52  4 7 1 4 6  12 9 8 15 8  3 3 4 1 4  31 53 44 19 29  12 13 14 16 18  49°07'30"N 49°07'30"N 49°07'45"N 49°09'30"N 49°09'45"N,  115°08'35"W 115°15'45"W 115°14'30"W 115°07'40"W 115°13'25"W  820 780 760 860 730  T 0 T 0 T  0 0 0 0 0  0 1 0 0 1  0 2 2 0 0  0 0 0 0 1  42 25 28 73 16  5 6 3 1 6  11 16 18 5 12  4 2 3 2 6  38 48 46 19 58  19 20B 20C 20D 20E  49"10'00"N 49°10'15"N 49°10'15"N 49°10'15"N 49°10'15"N,  115°13'50"W 115°11'15"W 115°11'15"W 115°11'15"W 115°11'15"W  780 817 812 800 790  T T T T T  0 0 0 1 0  1 2 2 2 1  6 3 0 1 0 '  0 0 0 0 0  19 34 34 29 43  1 5 5 6 9  25 25 19 17 19  5 3 6 3 5  43 28 34 41 23  21 22 23 24 25  4 9 ° 1 0 ' 5 0 " N , 115°11'00"W 4 9 ° 1 1 ' 4 5 " N , 115°17'40"W 4 9 ° 1 1 ' 5 5 " N , 115°08'00"W 49°12'00"N, 115°15'25"W 4 9 ° 1 2 ' 2 5 " N , 115°14'40"W  810 920 790 820 780  0 T T T 0  0 0 1 0 0  2 1 0 3 1  0 3 3 2 0  1 0 0 0 1  19 24 34 17 5  3 4 4 2 3  23 18 18 23 11  ,6 5 2 3 6  46 45 48 50 73  26 27A 27B 29 30  49°12'35"N) 49°12'40"N, 49°12'40"N, 49°13'20"N, 49°13'35"N,  115°12'15"W 115"16'25"W  ii5°io'i5"w  880 829 819-821 810 810  T T T 0 T  0 0 0 1 0  0 2 4 1 1  0 6 1 6 0  0 0 0 0 0  33 15 18 16 12  6 5 3 3 1  24 29 25 27 40  2 5 4 4 7  35 38 45 42 39  31 32 33 34A 34B  49°13'40"N, 49°14'50"N, 49°15'35"N, 49°15'45"N, 49°1.5'45"N,  115°12'45"W 115"05'55"W 115"05"55"W 115°05'50"W 115°05'50"W  800 960 940 920 880  T 0 T 0 O  0 0 0 0 0  0 1 0 0 2  1 0 1 2 4  0 0 0 0 0  13 51 64 39 54  3 9 1 6 4  28 3 20 27 19  2 1 2 6 1  53 35 12 20 16  35 36 38 39 40  4 9 ° 1 6 ' 0 0 " N , 115 o lL'50"W 49°]6'no"N, 115°18'05"W 4 9 ° 1 6 ' 5 0 " N , 115°05'50"W 4 9 ° 1 6 ' 5 5 " N , 115°10'10"W 4 9 ° 1 7 ' 0 5 " N , 115°06'15"W  820 770 940 850 940  T O T 0 O  0 0 1 0 0  0 2 0 0 0  1 0 3 0 0  0 1 0 . 0 0  7 4 68 6 8  1 1 1 1 2  46 15 19 20 43  7 9 2 1 3  38 68 6 72 44  41 42 43 44 45  * 4 9 ° 1 7 ' 1 0 " N , 115°07'25"W 4 9 ° 1 7 ' 2 5 " N , 115°08'10"W 4 9 ° 1 7 ' 5 0 " N , 115°06'15"W 4 9 ° 1 7 ' 5 0 " N , 115*07'50"W 4 9 ° 1 7 ' 5 5 " N , 115°06'45"W  900 900 940 910 950  0 T 0 0 0  0 0 0 0 0  0 1 1 1 0  0 1 2 0 0  0 0 2 0 0  8 33 10 6 12  4 3 2 3 3  33 34 27 52 53  4 2 6 8 6  51 26 50 30 26  4 . 5 5 9 5  57 45 60 51 42  115°07'20"W 115°10'15"W  46 47 48 49 50  49°18'05"N, 49°18'20"N, 49°18'40"N, 49°19'35"N, 49°19'50"N,  115°07,20"W 115°14'20"W 115"10'50"W 115°17'25"W 115°01'05"W  900 820 860 810 960  0 T T 0 0  0 0 0 0 0  0 4 0 2 0  0 0 0 0 6  0 1 0 0 1  7 10 3 7 10.  1 3 1 4 5  31 32 31 27 31  51 52 54 55 56  49°20'20"N, 49°20'35"N, 49°20'45"N, 49°21'00"N, 49 < , 21'05"N,  115°17'45"W 115°00'55"W 115°00'15"W 115°20'55"W 115°12'00"W  800 970 970 830 870  0 0 0 T T  4 0 0 0 0  6 4 0 6 1  0 2 i 0 0  0 0 0 1 0  4 10 15 9 8  0 4 2 3 3  27 44 30 25 29  0 15 5 5 3  59 21 47 51 56  57 58 59 60 62  49"21'10"N, 49°21'15"N, 49'23'20"N, 49*23'25"N, 49°23,50"N,  115°00'40"W 115°59'55"W 115°15'35"W 115°18'20"W 115*23'35"H  970 950 870 840 820  0 0 T 0 T  0 0 0 0 1  0 0 0 0 2  12 29 0 0. 0  0 0', 0 2 1  0 0 4 10 7  0 0 5 0 2  44 0 28 32 35  5 0 9 5 1  39 71 54 51 51  64 65 66 67 68  49°24'15"N, 49°24'55"N, 49°25'05"N, 49°25'15"N, 49°25'40"N,  115°0'1'00"W 115°23'50"W 115°08'45"W 115°02'40"W 115 o 24'40"W  1020 810 1070 970 810  T 0 T 0 T  0 0 0 0 0  0 0 0 0 2  48 0 0 9 0  0 0 0 0 1  0 2 23 0 3  0 7 0 0 2  5 11 41 32 28  10 10 0 3 8  37 70 36 56 56  .  268 APPENDIX 7 (Continued).  Clast lithology data.  1 WCO 69  7 70 1 72 73 74 75 7 6 7 7 78 80 82 1 8 83 84 87 88 90 91 92 93 9 4A 95 9 95 5B C 97 99 1 10 00 1 102A 102B 1 10 02 2C D 1 0 2 102FE 102G 1 0 2 H1 1 0 2 10 05 3 1 106 1098A 1 10 09B 110 111 112 1 14 3 1 1 115 116 117 118 119 120 121 1 12 22 3 1 2 4 125 127 1 8 12 29 1 3 0 131  a  o  U o C O  a  o  •rt  C O >  at  w  49°25'45"N 115°16'40"W 910 4499° °2277''3250""NN 111155° 05 00 0 °0340''1500""WW 18 49°27'50"N 115°27'45"W 790 .49°28'55"N 115°25'40"W 840 49°29'10"N 115°21'30"W 900 49*29'10"N,115°33'00"W 840 4499° 3300''0500""NN 111155° 0427''4205""WW 19 05 80 0 ° ° 49°30'55"N 115*31'50"W 820 49°31'25"N,115°36'35"W 830 4499° °3312''5200""NN,,111155° °2389''2050""WW 9 80 50 0 49°32'20"N,115°44'00"W ' 920 49°33'10"N,115*33'35"W 860 49°34'05"N,115°35'55"W 870 49°34'10"N,115°19'40"W 870 49°34'45"N,115°47'00"W 890 49°34'55"N,115*47'10"W 860 49°35'00"N,115°44'35"W 890 49°35'05"N,115°47'00"W 820 4499° *34 81 39 0 °3355''1155""NN,,1 11155° 4' 8'2400" "W W 9 4 *353' 4' 8'4400" "W W 9 499° 51 '155""NN, ,111155° *48 81 73 0 49°36'00"N,115°51'40"W 870 49°36'15"N,115°42'15"W 820 4499° °1582''0505""WW 10 86 70 0 °3366''1350""NN,,111155° 49°36'50"N,115°40'05"W 840 49*36'50"N,115°40'05"W 837 4499° 3 °3366''5500""NN,,111155° °4400''0055""WW 8 83 29 °3366''5500""NN,,111155° °4400''0055""WW 8 4499° 82 24 2 49°36'50"N,115°40'05"W 820 4499° 3366''5500""NN,,111155° 4400''0055""WW 8 1 6 ° ° 8 1 0 4499° °3376''0500""NN,,111156° 4 3 ' 5 5 " W 8 5 0 *14'20"W 1020 49°37'05"N,116°13'50"W 1020 4499° 377''1255""NN,,1 155° *37 ' 0250""W 81 03 5 111 5' 6'2 W 9 49° *373' 25"N,1 5*56 0"W 90 9 49°37'50"N,115°57'20"W 920 49°37'50"N,115°59'45"W 910 49°38'00"N,115°41'25"W 850 4499° ° 8''1050""NN,,111155° 4578''0105""WW 10 81 80 0 0 3 3 8 ° 4938'55"N,115°56'30"W 1030 49°39'20"N,115*36'40"W 910 49°39'25"N,115°39'25"W 820 49*39'30"N,115°52'20"W 980 49'40'10"N,115°47'15"W 870 49*40'20"N,115°34'25"W 1040 49°40'45"N,115°38'55"W 870 49°4r20"N, 115°41'00"W . 790 49'41'20"N,115°57'40"W 1120 4499° 1'3205""NN, ,111155° 15 10 0 *414' °3443''0255""WW 18 49°41'50"N,115°52'30"W 1010 499° 2'2305""NN, ,111155° 0 4 *434' °3492''0305""WW 9 82 00 4 9 ° 4 3 ' 5 5 " N , 1 1 5 ° 5 0 ' 2 0 " W 9 7 0 49*44'00"N,115°45'40"W 870  TO tn  0 T T 0 T 0 T T T T T T T T T T T T 0 T 0 T T T T T T T T T T T T T T T T T T T T T T T T T T T 0 T T 0 T T T T 0 T T T T T 0 T T  •ti C O o  u *rt  X  0 0 0 3 0 6 0 2 12 10 0 0 0 1 0 0 0 1 6 5 1 9 1 4 5 0 1 8 1 3 0 • 0 5 1 4 0 12 0 11 0 1 0 0 15 1 0 7 1 7 0 4 0 4 1 10 2 0 1 2 0 6 2 1 . 35 1 5 0 2 0 3 1 0 0 4 0 7 4 8 2 20 .0 1 9 2 0 1 17 0 44 0 27 0 4 0 5 0 4 0 33 0 6 0 11 0 11 1 3 0 0 0 2 0 0 15 1 0 0 0 2 0' 5 6 •01 0 0 9 0 6  6  TC 30 -tiJ  CJ O •+cj cj c •rt ft i-i CU C U +l-i 4J Ji u o vt •rt U CJ u •rt CJ I cj cj *oOQ -C " p cu •rt | D W -rt ™ C *rt O. i-l O C a ct—i -o Vt O •a oo u u ca a co cr ca cj c O co ai co percent of pebbles  < u a. *J  0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0•  kj -rt  •0 rt0 *J 1 0 0 2 0 0 0 0 1 1 0 1 0 1 0 1 0 0 1 0 5 0 2 1 2 2 0 0 0 0 3 0 0 0 4_ 2 1 0 0 0 0 0 2 0 0 0 1 2 3 0 0 0 1 1 0 1 0 2 0 0 2 0 0 1 0  13 0 4 6 8 1 6 10 3 8 10 28 1 17 2 2 13 8 7 7 3 19 2 17 1 5 7 3 0 9 6 4 0 4 4 7 7 5 9 9 5 9 7 7 4 4 3 1 1 14 2 2 3 11 9 5 2 8 0 3 5 7 16 3 6  9  1 0 0 2 4 5 4 0 1 2 2 4 0 2 '2 4 0 2 3 2 3 3 0 3 2 5 3 1 0 4 1 1 0 0 4 4 1 0 1 0 0 1 1 2 0 0 3 3 2 1 2 0 4 1 0 4 0 6 0 3 1 1 1 8 2  Lone-  a  o lgnt  o  "a"  **  V  .merit t  «  0 s)  .->  33 7 19 8 20 7 54 5 0 1 5 9 9 4 3 11 10 10 3 3 6 9 13 1 4 4 1 13 30 9 6 7 1 5 25 1 12 1 9 1 15 3 8 0 0 10 0 0 0 0 13 12 2 0 12 7 0 11 0 9 10 2 10 2 4 2 9 0 17  tone'  1  Vt  •rt o  0 .82 10 5 23 9 0 1 7 5 4 3• 2 14 13 12 7 0 0 8 5 5 3 1 2 8 1 0 0 14 1 15 2 1 7 18 5 1 8 20 3 0 0 10 0 0 0 0 12 6 0 0 8 4 1 4 0 4 9 0 10 8 9 10 0 1 0 14  o  52 14 6 1 58 54 17 75 17 07 0 71 64 6 68 8 66 67 64 60 75 74 74 71 6 5 69 7 1 76 81 65 82 6 1 78 63 5 58 9 6 1 57 70 57 5 5 7 5 79 73 6 7 7 1 74 52 69 64 6 1 7 5 64 70 75 72 70 94 75 7 74 1 16 02 0 70 72 6 7 6 6 58  269  APPENDIX 7 (Continued),  Clast lithology data.  (C 0 .01 -1M T*OI cti <-t t-t « (T3percent I-i 3 ofOH-pebbles  •H M  a nj u w a^  t/J  'H  (0 t-H N I-H *J  CJ  aratr u 133 134 135 137 138  49°46'00"N, 49°47'25"N, 49°48'30"N, 49°50'35"N, 49°51'10"N,  115°42'10"W 115°39'40"W 115"47'30"W 115°40'10"W 115°42'05"W  830 970 890 860 870  T T T T T  0 0 2 0 0  0 3 4 0 1  0 0 0 0 0  0 0 1 0 • 0  3 7 9 2 5  0 1 5 0 2  26 11 9 29 22  24 14 11 22 16  47 64 59 47 54  139 140 141 142 143  49°51'40"N, 115°47'10"W 49°53'40"N, 115°41'15"W 115°47'20"W 49°54'40"N, < 49 '56'00"N, 115*41'35"W 49°56'10"N, 115°41'00"W  860 880 840 840 900  T T T 0 T  0 0 0 1 0  10 2 1 0 1  0 0 0 0 0  0 0 2 11 0  12 4 9 2 6  2 4 1 5 0  10 19 12 7 29  12 14 9 7 33  54 57 66 67 31  144 145 146 147 148  49°56'35"N, 49°57'00"N, 49°58'10"N, 49°59'20"N, 50°00'05"N,  115°45'00"W 115°47'25"W 115°42'10"W 115"45'20"W ' 115°40'05"W  860 850 910 900 970  T T T T T  0 0 0 0 0  1 0 1 1 0  0 0 0 0 0  0 11 0 0 1  1 2 1 4 0  0 3 0 0 2  20 10 18 30 19  38 7 40 16 52  40 67 40 49 26  149 150 151 152 154  50°01'30"N, 50°02'40"N, 50°05'10"N, 50°06'25"N, 50°07'45"N,  115°48'25"W 115"45'05"W 115°45'20"W 115°48'20"W 115°37*50"W  840 890 890 860 1150  T T T T T  1 0 1 1 0  2 0 1 0 0  0 0 0 0 0  8 0 1 21 0  2 4 0 16 1  7 1 0 0 0  7 40 39 11 7  20 28 25 9 73  53 27 33 42 19  155 156 157 158  50°08'00"N, 115°58'55"W 50°08'10"N, 115°43'25"W 50°08'15"N, 50°09'20"N, 115°50'55"W  1060 1060 900 920  T T T T  0 0 0 0  2 0 0 0  0 0 0 0  0 1 0 2  39 1 4 4  4 1 2 7  0 37 30 9  0 26 17 20  55 34 47 58  Approximate. **T, t i l l ; 0, outwash. ***Andesite to quartz gabbro (Purcell extrusives and intrusives)—Precambrian. ^Blairmore Group—Mesozoic. "^Toby Formation and Horsethief Creek Series, Windermere System—Precambrian. + "*""*"Mainly Upper Purcell System—Precambrian. ^Mainly Paleozoic. .^Includes shale, s i l t i t e , quartz arenite, and argillite (dolomitic in part) of Purcell System—Precambrian; shale, s i l t i t e , and sandstone—Paleozoic.  270  Heavy mineral data.  Others  Amphibole  Staurollte  Sphene  Dolomite  <3 fl  Sphene Amphibole  | Dolomite  Location  a « « c o a V c o V c. M £ k 1 a t d a o N O N CJ Ul percent of heavy mineral separate of percent of total fine sand fraction by fine sand fraction byvolume* volume (x 10)** 1 49*00'20"N 115*034 ' 0"W 870 0.8 0.6 6 47 53 3 1 T T T 12 31 3 26 29 1 1 T T T 7 22 2 49*00'50"N 115*075 ' 5"W 800 1.0 0.6 8 49 57 2 2 0.1 0.3 0.2 13 25 5 32 37 1 1 T 0.2 0.1 8 13 4 49*O2'20"N 115*124 ' 5"W 770 2.4- 1.6 13 42 55 3 2 0.1 0.4 0.5 11 28 20 66 86 5 4 0.2 0.6 0.8 18 45 6 49*04'05"N 115*10'35"U 790 1.3 0.9 3 44 47 7 4 T 0.4 0.6 11 30 3 39 42 7 •3 T 0.4 0.5 10 27 7 49*04'25"S 115*135 ' 5"W 750 7.7 4.8 69 2 1 T 0.1 0.2 7 21 330 7 4 0.5 1.0 34 103 8 49*04'25"N 115*142 ' 5"W 780 4.4 2.8 11 56 67 5 1 T 0.1 T 7 20 30 160 190 14 3 0.3 19 54 10 49*06'20"N 115*053 ' 0"W 850 0.9 0.6 52 7 1 T 0.1 0.2 6 34 31 4 1 T T 0.1 4 20 12 49*07'30"N 115*083 ' 5"W 820 0.8 0.5 46 4 2 0.2 0.8 0.2 20 27 23 2 1 0.1 0.4 0.1 10 13 14 49*07'45"N 115"143 ' 0"W 760 1.5 1.0 4 39 43 17 2 T 0.4 0.6 12 25 4 40 44 18 2 T 0.4 0.6 13 22 15 49*08'55"N 115*083 ' 0"W 840 0.2 0.1 58 T 3 0.3 0.5 1.0 12 24 7 T T T T 0.1 1 2 17 49*09'35"N 115*17'20"w 890 1.6 1.2 35 11 5 0.1 0.6 0.3 17 31 41 12 6 0.1 0.7 0.4 20 40 18 49*09'45"H 115*132 ' 5"W 730 1.5 1.0 43 8 5 T 1.0 0.6 11 31 44 8 5 T 1.0 0.6 11 30 20A 49*10'15"N 115*11'15"H t t t 1.5 1.1 34 26 3 T 0.2 0.3 10 26 39 29 3 T 0.2 0.3 11 27 20B 49*10'15"N 115*111 ' 5"W 817 1.2 0.8 6 41 47 3 5 0.2 1.0 0.5 14 30 5 34 39 3 4 0.2 0.8 0.4 12 21 20C 49*10'15"N 115*111 ' 5"W 812 1.0 0.7 3 47 50 6 3 T 0.7 0.5 13 27 2 32 34 4 2 T 0.5 0.4 9 20 20D 49*10'15"N 115°11'15"W 800 1.4 1.0 3 31 34 7 6 T 1.3 0.9 19 32 3 31 34 7 6 T 1.3 0.9 19 32 20E 49*10'15"N 115*11'15"U 790 1.1 0.8 3 29 32 5 7 0.3 0.7 0.8 15 39 2 24 26 4 6 0.3 0.6 0.7 13 29 22 49*11'45"N 115*'.7'40"U 920 1.0 0.7 4 32 36 4 5 0.1 0.5 0.5 22 32 3 22 25 3 4 T 0.4 0.4 16 21 23 49*11'55"N 115*080 ' 0"W 790 1.0 0.6 2 59 61 5 1 0.1 0.3 1.2 2 29 1 37 38 3 1 T 0.2 0.8 1 16 24 49*12'00"N, 115*152 ' 5"W 820 1.6 1.2 6 26 32 3 8 0.2 1.1 1.2 21 34 7 30 37 4. 9 0.2 1.3 1.4 25 42 26 49*12'35"N, 115*072 ' 0"W 880 1.1 0.7 4 61 65 5 1 0.3 0.1 0.3 8 20 3 41 44 3 T 0.2 T 0.2 6 17 - 27A 49*12'40"N, 115*101 ' 5"W 829 1.5 1.0 3 44 47 4 2 0.2 0.4 0.7 10 36 3 45 48 4 3 0.2 0.4 0.7 11 33 27B 49*12'40"K 115*10')5"U 819-821 1.4 1.0 3 46 49 7 3 0.1 0.5 0.2 13 27 3 44 47 7 3 0.1 0.5 0.2 13 29 28 49"12'55"N 115*11'40"U 820 0.9 0.6 67 1 2 0.2 0.3 0.7 8 21 37 1 1 0.1 0.2 0.4 4 16 30 49*13'35"H 115°16'25"w 810 1.5 1.1 4 25 29 6 7 0.2 1.6 1.3 22 33 4 28 32 7 8 0.2 1.7 1.4 24 36 33 49"15'35"N 115*055 ' 5"W 940 0.5 0.3 56 8 1 T T 0.2 4 31 19 2 T T T T 1 8 35 49*16'00"S 115*115 ' 0"W 820 1.2 0.9 3 40 43 2 4 0.1 0.3 0.2 15 35 36 1 3 T 0.3 0.2 12 37 37 49*16'40"N, 115*103 ' 5"W 860 0.4 0.2 63 1 3 0.3 0.2 0.5 9 23 15 T 1 T T 0.1 2 2 38 49*16'50"N 115*055 ' 0"W 940 0.3 0.2 60 3 1 T 0.1 0.3 2 34 13 1 T T T T 1 5 42 49°17'25"N 115*081 ' 0"W 900 0.6 0.4 3 57 60 9 1 T 0 0.1 3 27 1- 21- 22 4 T T 0 T 1 13 47 49*18'20"N 115*142 ' 0"W 820 1.0 0.7 4 45 49 1 6 0.1 0.8 1.2 13 29 2 31 33 1 4 T 0.5 0.8 9 22 48 49"18'40"N 115*105 ' 0"W 860 2.1 1.4 3 67 70 3 I 0.1 0.1 ' T 5 21 3 91 94 5 2 0.1 0.1 T 7 32 53 49°20'35"N 115*1"71 '0"W 840 1.5 1.0 43 8 6 0.2 0.5 0.9 10 31 43 8 6 0.2 0.5 0.9 10 31 55 49*21'00"N, 115°20'55"H 830 1.9 1.4 5 24 29 4 8 0.4 0.6 0.4 25 33 7 33 40 5 11 0.5 0.8 0.5 33 49 56 49*21'05"N 115*120 ' 0"W 870 2.0 1.3 2 70 72 4 1 T T 0.3 3 20 3 88 91 6 2 T T 0.4 4 27 59 49*23'20"N 115*153 ' 5"W 870 1.8 1.2 2 42 44 4 3 0.2 1.0 1.5 15 31 3 51 54 5 4 0.2 1.2 1.8 18 36 61 49*23'40"N 115*205 ' 0"W 830 1.4 1.0 30 2 8 0.5 1.0 0.6 17 41 31 2 8 0.5 1.0 0.6 17 40 62 49*23'50"N, 115"233 ' 5"W 820 1.5 1.1 4 25 29 5 9 0.1 1.1 0.9 17 38 5 27 32 5 10 0.1 1.2 1.0 19 42 63 49*24'10"H, 115*261 ' 0"W 860 1.0 0.7 31 3 10 0.3 1.8 1.1 20 33 21 2 7 0.2 1.2 0.8 13 25 64 49*24' 15'H, 115*010 ' 0"W 1020 0.7 0.5 1 73 74 T T 0.2 0 T T 26 T 34 34 T T T 0 T T 16 66 49*25'0S"N, 115*08'45"M 1070 1.9 1.1 T 82 82 7 T 0.1 0 0 T 10 T 92 92 8 T 0.1 0 0 1 9 68 49*25'40"N, 115*24'40"U 810 1.2 0.9 5 23 28 4 8 0.2 1.0 1.1 18 40 4 20 24 3 7 0.2 0.9 1.0 16 38 70 49*27'20"N, 115*041 ' 0"W 1000 0.6 0.4 48 2 T I 0 0.1 T 50 T 19 19 1 T T 0 T T 20 71 49"27'35"N, 115*305 ' 0"W 850 1.9 1.4 3 27 30 10 6 T 0.9 1.1 17 35 5 37 42 14 8 T 1.2 1.5 24 49 73 49*28'55"N, 115*254 ' 0"W 840 4.0 2.7 1 51 52 9 4 T 0.4 0.1 7 28 4 139 143 25 11 1.1 0.3 18 72 75 49*29'10"K, 115"330 ' 0"W 840 2.0 1.5 4 25 29 9 6 T 1.5 0.9 19 35 6 37 43 13 9 T 2.2 1.3 27 54 76 49*30'00"N, 115*024 ' 0"W 1080 0.3 0.2 54 0 0 T 0 0 T 46 10 0 0 T . 0 0 0 10 77 49*30'50"N, 115*472 ' 5"W 950 3.8 2.9 3 16 19 2 1 T T 0.7 41 36 9 47 56 7 4 2.0 118 103 78 49*30'55"N, 115*315 ' 0"W 820 2.1 1.6 5 27 32 6 5 T 1.1 0.6 16 39 8 41 49 10 8 1.7 0.9 24 66 79 49*31'00"N, 115*360 ' 5"W 830 2.5 1.9 24 0 4 0.1 0.4 1.1 36 34 46 0 7 0.2 0.8 2.1 67 67 SO 49*31'25"N, 115*363 ' 5"W 830 2.6 1 .9 4 21 25 4 3 0.2 0.3 0.8 33 34 8 40 48 7 6 0.4 0.6 1.5 64 62 81 49*31'50"N, U5*28'25"U 900 2.9 2.1 4 24 28 4 5 0.1 1.0 0.6 17 44 9 51 60 9 11 0.2 2.1 1.3 35 91 82 49*32'20">1, 115*390 ' 0"W 850 2.4 1.8 4 27 31 4 2 T 0.5 0.9 23 39 7 48 55 7 4 0.9 1.6 42 69 83 49*32'20"N, 115*440 ' 0"W 920 4.3 3.3 4 15 19 4 1 T 0.4 0.7 35 40 13 51 64 14 3 1.3 2.3 116 129 84 49*33'10"N, 115°33'35"W 860 2.9 2.1 8 23 31 6 5 0.1 0.7 0.9 19 37 16 49 65 13 11 0.2 1.5 1.9 40 77 85 49*33'45"N, 115*414 ' 5"W 920 4.8 3.5 28 6 3 T T 1.1 27 35 100 22 10 3.9 95 119 86 49*33'55"N, 115*303 ' 5"W 870 3.3 2.5 27 16 3 T 0.2 0.4 11 42 66 39 6 0.5 1.0 28 109 87 49*34'05"K, 115*36'55"U 870 3.1 2.3 7 15 22 4 4 0.2 0.5 1.1 32 36 17 35 52 8 8 0.5 1.2 2.6 73 65 88 49*34'10"N, 115*19'40"H 960 2.3 1.5 1 64 65 19 T 0.2 0 0 T 16 2 96 98 29 T 0.3 0 0 T 23 89 49*34'15"N, 115*48'10"U 920 6.9 5.3 23 5 1 T T 1.3 33 37 121 27 7 6.9 174 194  i  Anphlbole/garnet  Total opaques  Magnetite Non-magnetic opaques  «  Magnetite Non-magnetic opaqueB* Total opaquea  Percent by weight of heavy minerals In fine Band fractJ Lon Percent by volume of heavy minerals in fine sand fractl[on  Elevation (m)*  APPENDIX 7 (Continued).  z  13 7 5 3 9 7 7 9 5 4 3 2 4 3 5 3 2 4 2 3 16 4 5 4 3 3 4 3 2 5 2 5 2 3 3 5 2 2 2 2 4 2 3 2 3 34 3 10 11 3 10 39 4 10 4 9 24  271  lion ' heavjr minerals 1 'racl:ion  APPENDIX 7 (Continued).  Heavy mineral data.  n e  c B a V  «  o c  e  c «  1  0  svati  CJ  M  0 ~1  •£ 5a  >  C ttJ c  « 3 c r. P O  tr  TJ  o a K I V Xi B B V c c tl B  CJ Cu  CJ 3  V  o. CJ o tl  c  CJ 3 cr a.  a  o . eJ « X o o CJ  ?  H  CJ  |0 o  c  « o u 3  «J C3  CJ  «  a  CJ fi VI  V B  o  c a X tt  164 136 116 57 67  21 23 27 11 4  0 0 1.1 0.6 0.7  5.8 0.2 3.7 2.2 2.1  365 T 61 49 51  316 10 76 71 65  111 2 5 5 6  1.1 1.7 0.6 1.6 1.4  2.4 1.5 1.1 2.2 2.2  46 36 33 35 29  71 48 53 50 43  5 4 3 4 3  1.5 1.4 0.3 2.9 0.3 1.0 0.4 1.2 10.7 0  30 96 130 124 255  48 90 87 121 160  3 18 42 28 250  7.4 0.3 0.5 2.9 4.2  277 29 28 510 559  154 120 114 311 339  521 4 3 41 49  0 0 1.3 1.8  6.7 9.1 3.6 1.6 5.2  643 716 38 39 566  367 396 45 56 349  115 111 5 5 42  0.5 0.3  0.6 0.7 0 0.8  1.2 1.0 0 1.1  66 278 33 3 30  119 198 68 202 54  25 37 8 3 11  9 0 4 4 5  0.8 0 T 0.1 T  1.2 0 0.8 0.6 0.7  3.6 0 0.4 1.4 1.1  161 2 13 25 16  133 354 32 44 34  19  13 24 12 1 8  2 5 8 6 11  0.3 T 0.2  0.7 1.1 0.8 1.8  0.2 1.7 1.5 0.4 1.1  36 40 23 10 5  90 114 48 21 28  22 8 3 2 1  74 39 42 65 23  16 5 3 9 5  5 11 3 9 8  T T T T  0.4 1.3 0.2 1.1 1.0  1.7 0.1 0.2 0.3  37 39 4 7 6  78 43 18 29 17  7 4 2 1 1  38 21 40 25 36  22 3 17 4 21  12 7 7 3 12  T T T T  1.8 1.1 1.4 0.5 1.2  3.1 0.2 1.5 0.2 1.1  46 4 22 3 22  57 24 41 14 47  4 1 3 1 2  3 8 11 5 2  0.3 0.1 0.1 0.4 0.4  0.7 0.8 0.5 0.6 1.2  31 30 14 19 18  36 29 38 30 40  25  106  7  82  9  35  131 140 89 44 44  3 42 35 40 17  7 6 1 3 8  T T T 0 5 T 5 T 5 0.1  0 0 0.5 0.3 0.4  0.7 0.2 1.7 1.2 1.2  44 1 28 27 29  39 16 35 34 34  30 1 20 12 11  93 36 33 35 30  123 37 53 47 41  7 33 13 11 12  3 T 12 9 8  6 6 6 5 6  5 0.1 5 T 8 T 6 T 8 0.1  0.6 1.1 0.4 1.1 1.0  1.3 1.0 0.7 1.5 1.6  25 24 21 24 21  35 33 32 32 31  13 14 14 12 13  36 32 37 33 31  49 46 51 45 44  11 9 9 7 8  9 8 12 9 12  32 23 33 34 16  5 2 2 4 0  6 0.1 2 T 1 T 1 T T T  1.1 0.1 0.1 0.1 0  1.0 1.1 0.3 0.3 2.1  21 37 38 31 50  34 35 26 30 32  12 16  31 44  47  7 5 7 15 0  9 6 3 4 1  0.1  36  43 60 112 134 83  1 9 9 T 1  T 0.1 3 T 4 0.1 1 T 1 0  T 0.1 0.2 T T  1.4 0.1 0.2 0.3 0.4  52 12 12 53 54  29 47 45 33 33 .  27  60  6 22 25  61 107 95  87 72 67 129 120  3 21 20 4 6  1 7 10 13 12  0.5  26 11 9  16 29 29 13 11  2 4 10 4 1  7 9 24 21 9  9 13 34 25 10  T. T 5 8 T  1 0 1 T 5 T 5 0.1 1 0  0 0 0.8 1.1 T  0.6 0.7 2.2 1.0 0.5  58 55 23 24 54  31 30 30 36 34  19 56 16 7 6  77 115 40 34 99  96 171 56 41 105  1 1 9 12 1  6 7 7 8 14  0  4 8 7 3 5  1 2 6 T 2  16 13 25 41 31  17 15 31 41 33  4 1 0.2 1 . 1 0.1 6 3 T T 0.1 19 7 2 0.2  T 0.1 0.4 0 0.5  T 0.2 0.6 0 0.7  28 48 20 1 19  50 35 39 39 38  3 11 10 1 3  39 75 43 219 47  42 86 53 220 50  9 8 10 103 11  3 8 4 1 3  0.5 0.6  4 6 0 1 1  0 7 9 3 1  3 T 5  18 38 33  2 0.2 0 0 5 T 3 0.1 5 T  0.3 0 0.9 0.5 0.6  0.9 0 0.4 1.1 1.0  41 T 14 20 15  33 53 34 32 30  71 252 29  32  2 9 8 7 11  12 1 4  5  21 38 38 36 37  5  36  83 253 33 46 41  8 61 7 9 12  4 2 7 9 1  1 2 1 0 0  8 4 3 6 8  2 3 6  19 20 22  0.6 T 0.2 0.1 0.2  T 0.3 0.9 1.4 2.2  0.1 0.7 1.2 0.7 1.3  20 16 18 16 .6  50 48 37 34 35  34 47 28  27  7 10 9 2 10  4 8 8  4  21 23 28 36 31  3  22  38 55 36 21 25  970 890 850 860 870  2 9 1 9 1.0 1 8 0 9  2 1 0 1 0  1 4 7 2 6  1 12 1 2 3  33 16 61 51 33  34 28 62 53 36  8 4 5 7 8  3 T 8 T 4 T 7 T 12 0.1  0.2 0.9 0.3 0.9 1.5  T 1.2 0.2 0.2 0.5  17 28 5 5 9  38 30 23 27 33  3 16 1 2 2  71 23 41 63 21  860 880 840 900 860  2 0 1 0 1  1 0 1 0 1  8 6 3 5 4  9 4 4 4 5  12 34 27 43 22  21 38 31 47 27  12 5 13 8 15  7 T 13 0.1 5 T 6 0.1 9 T  1.0 2.0 1.1 0.9 0.9  1.7 0.3 1.2 0.3 0.8  26 31 7 35 17 32 5 33 16 .31  17 2 6 2 6  21 19 34 23 30  27 16 22 27 29  30 22 26 30 33  5 3 8 4 3  95C 96 97 98 99  49*35'15"N 49*35'20"N, 49*36'00"N 49*36'10"N 49"36'15"N  115*48'40"W 115*40'10"W 115*51'40"W U5*39'30"W 115*42'15"W  870 840 870 830 820  6 6 3 2 2  1 4 7 3 3  4 4 2 1 1  5 7 8 8 7  6  23  3  30  5  20  29 30 33 25 25  1 9 11 23 10  2 1 1 2 5  100 101 10 2A 102B 102C  49*36'15"K 49*36'30"N 49*36'50"N, 49"36'50"N, 49*36'50"N  115*52'55"W 115*18'00"W 115*40'05"W 115*40'05"W 115°40'05"W  870 1060 840 837 833  10 1 3 2 2  3 2 0 5 4  8 0 2 1 1  2 8 2 9 8  4 1 9 7 6  tl 43 15 19 17  15 44 24 26 23  1 39 6 6 7  102D 102E 102F 102G 102H  49*36'50"N 49*36'50"N 49*36'50"N 49*36'50"N 49*36'50"N,  115*40'05"W 115*40'05"W 115*40'05"W 115*40'05"W 115*40'05"W  829 824 822 820 816  2 2 2 2 2  5 1 2 1 0  1 1 1 1 1  9 5 6 5 4  7 9 9 8 9  20 21 23 22 22  27 30 32 30 31  1021 103 104A 104B 105  49*36'50"K 49*36'50"H 49*36'55"N 49*36'55"N 49*37'00"N  115*40'05"W 115*43'55"U 115*49'40"W 115*49'40"W 116*14'20"W  810 850 960 960 1020  1.9 3 5 4 7 5 4 6 5  1 2 3 4 5  4 6 4 0 1  9 6  23 17  106 107 108 109A 109B  49*37'05"N 49*37'10"N, 49*37'15"N 49*37'25"N 49*37'25"N  116*13'50"W 115*37'00"« 115*37'05"W 115'56'20"W 115*56'20"W  1020 800 805 913 909  6 3 3 12 12  8 3 2 1 9  7  9  5 2 2 9 10  3 5 4 7 4  5  11  3 2 2  110 111 112 113 115  49*37'50"N, 49*37'50"N 49*38'00"N 49*36'00"N 49*38'55"N  115*57'20"W 115*59'45"W 115"41'25"W 11S*47'00"U 115°56'30"U  920 910 850 880 1030  13 16 2 2 12  6 0 3 2 8  11 13 1 1 10  2 0 6 6 4  116 118 119 120 121  49*39'20"N 49*39'30"N, 49*40'10"N, 49*40'20"N. 49°40'45"N,  115'36'40"W 115*52'20"W 115*47'15"W 115*34'25'U U5*38'55"U  910 980 870 1040 870  3 7 2 7 2  1 3 3 3 1  2 5 1 5 1  123 124 125 126 127  49*41'20"N 49*41'25"N, 49"41'30"N, 49*41'45"N, 49*41'50"N,  115"57'40"W 115*34'05"U 115*43'25"W 115*48'55"U 115*52'30"U  1120 1110 850 910 1010  5 9 1 1 1  2 1 3 8 6  128 130 131 132 133  49*42'35"N, 49*43'55"N 49*44'00"N, 49*45'45"N, 49*46'00"N,  U5*39'00"U 115°50'20"W 115*45'40"W 115*46'40"W 115*42'10"U  920 970 870 880 830  2 3 1 0 1  134 135 136 137 138  49*47'25"N, 49*48'30"N, 49*49'50"N 49*50'35"N 49*51'10"N,  115*39'40"U 115*47'30"U 115*41'55"« 115*40'10"W 115"42'05"U  139 140 141 143 144  49*51'40"S, 49*53'40"N, 49*54'40"N. 49*56'10"N. 49*56'35 N.  115*47'10"U -115*41'15"W 115°47'20"U 115*41'0O"W 115*45'00"W  ,,  140 142 37 34 31  13 16 13 15 12  3 6 4 .3 4  4 8 8 8 8  1 T 2 0.1 7 T 1 T 1 T  1 2 6 10 14  T T 0 T 0  s  3.2 3.8 1.4 1.1 2.1  91 109 44 103 117  0 0 7 5 5  o  1.4 0.5 0.3 0.7 0.7  81 77 37 94 103  3 5 1 3 3  %  20 23 2 16 35  10 32 7 9 14  4 0 6.5 2 3 4 7 4.8  0J  137 169 75 145 143  45 34 43 42 42  890 890 830 919 913  c tt a. t/i  54 187 24 79 74  18 37 14 22 21  115*47'00"W 115*44'35"W 115*34'20"W 115*48'40 W 115"48'40"U  CJ CJ  0.9 10.5 1.9 3.2 1.1  0.3 2.1 1.1 0.9 0.3  49"34'45"N 49*35'00"N 49*35'15"N 49"35'15"N 49*35'15"N  0 3  1.3 0 0.4  0.3 T 0.8 0 0.1  90 92 94 95A 95B  «  tl B a cc  percent of total fine sane fraction by volume U 1 0 ' ) "  1  ,,  B nj 4J a S a 6 CBJ o 1 a O o O H a o N «J  tt  percent of heavymineral separate of fine sand fraction by volume"  CJ 3 er g.  ihibc  « o «  Jhlbc  V  :con  IM  0.9  0 0 0  0.2 0.2  0.1  0.2  0.3 0.5  0  0.2 0  1.1  3 6 3  272  APPENDIX 7 (Continued).  «J u a  B  a  «  B  g «  0  !  • u  O .J  > u  *  i  CS  «  |  u  >.  is «v u e UB E>M t. U T« «t 01 e. a.  *B "£  « «  o au  opaquec  oM u w *. U B 00  j* «t  opaquec  u a  '. heavy :ion  a  *  ' heavy :lon  co  Heavy mineral data.  u  s  cr a V ce o 3 i B ce OB a o |o a t* Ct X «  Ci  «  B M e u  B t* .N  S o 3 a  CO  « V JG  a.  C/l  e o  « <  X jl  1  0>  £  O  49*57'00"1» 49*58'10"N 49*59'20"H 50*00'05"N 50*01'30"H 50"02'40"N 50*05'10"N 50*06'25"N 50*07'35"N 50*07'45"N 50*08'00"H 50*08'10"N 50*08'15"N 50*09'20"N 50*50'10"N 50*51'50"N  115*47 25"W 115*42 10"W 115*45 20"U 115*40 05"W 115*48 25"U 115*45 05"M 115*45 20"W 115*48 20"W 116*01 05"W 115*37 50"U 115*58 55"W 115*43 25"W 115*46 55"W 115*50 55"U 116*39 05"W 116*34 15"W  850 910 900 970 840 890 890 860 1090 1150 1060 1060 900 920 1360 1160  2.6 1.1 2.2 0.7 2.0 1.2 1.8 3.3 4.4 0.3 4.3 1.2 2.5 2.0 2.8 2.3  1.8 0.8 1.6 0.5 1.5 0.8 1.4 2.3 3.2 0.2 3.1 0.8 1.7 1.5 2.0 1.8  5 2 5 3 4 6 6 2 4 3 6 5 12 4 4 3  30 27 26 36 27 28 24 40 36 34 28 37 33 24 42 27  35 29 31 39 31 34 30 42 40 37 34 42 45 28 46 30  15 12 11 10 14 6 10 11 30 3 9 7 14 3 25 8 2 T 11 6 17 T 14 2 10 2 27 4 7 T 50 T  Q.l T 0.2 0.3 T T T 0.2 T 0.3 0 0.3 0.1 6.1 0.2 0.3  2.4 2.1 1.3 1.1 1.2 1.3 0.4 1.3 T 1.7 T 1.0 0.4 0.3 0 0  0.8 1.0 1.6 0.7 0.6 1.2 1.0 T 0.1 0.6 0.1 0.8 1.3 0.7 T T  9 15 18 11 10 15 24 3 33 7 10 13 15 17 1 T  e 0 e o  H  .  e  uc  O Ct  « u  B u u  • o s  CO  e « JS B. CO  0  jt ji %  m ot X  o  e B » e o x X  1  percent of total fine sand fraction by volume (x 10O**  percent of heavy mineral aeparate ol fine sand fraction by volume* its 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160  « it e • 3 c J B Bc ce O & z  5cr  26 32 28 27 24 32 28 20 25 36 39 27 26 23 46 20  9 54 63 1 23 24 9 42 51 1 18 19 5 40 45 5 23 28 8 32 40 4 92 96 13 112 125 1 8 9 19 88 107 4 30 34 20 57 77 6 36 42 7 83 90 5 47 52  27 9 23 5 43 7 19 58 7 3 52 11 17 41 14 88  22 8 10 5 4 6 4 19 I 1 1 2 4 5 T T  0.2 I 0.3 0.2 T T I 0.5 T 0 0.2 0.2 0.2 0.4 0.5  4.3 1.7 2.1 0.5 1.7 1.1 0.5 3.0  1.5 0.8 2.6 0.3 0.9 1.0 1.4  0.3 0.4 0.1 0.3 0.8 0.7 0.7 2.2 0.5 1.1 0 0  17 45 13 23 29 42 5 15 15 40 12 25 33 42 8 45 105 83 2 4 31 119 11 20 26 43 26 34 1 95 1 38  ^Approximate. **Hainly goethite (pseudomorphic after pyrite) and llmenite. ***Hainly altered silicate grains, but includes minerals of low abundance such as apatite, kyanite, epidote, and tourmaline. ^Percentages calculated from point counts of 500 mineral grains on each of tvo glass slides; for zircon, staurolite, and sphene, T<0.1Z; for other minerals listed, T < 0.5Z. •*""*Tor lircon, staurolite, and sphene, T<0.001X; for other minerals listed, T < 0.005Z, ••"I"-"Sample from upper part of late Wisconsinan till sheet; elevation of sample not known.  1 2 3 1 4 2 9 1 1 50 6 7 5 5 2  273  APPENDIX 7 {Continued)• Correlation matrix for heavy mineral and clast lithology data. The upper number of each pair i s the coefficient of correlation; the lower number i s the probability that the correlation is not significant (F-test).  Longitude  0 81 0 00  T o t a l heavy mineralo  0 13 0 14  0 49 0 00  Magnetite  0 04 0 67  0 45 0 00  0 66 0 00  Non-magnetic opaques*  0 03 0 74  0 16 0 09  0 59 0 00  0 26 0 01  T o t a l opaques  0 04 0 69  0 25 0 00  0 67 0 00  0 45 0 00  0 98 0 00  Dolomite  0 43 0 00  0 31 0 00  0 13 - 0 12 0 12 0 21  0 48 0 00  Garnet  0 19 0 03  0 28 0 00  0 19 0 03  0 18 - 0 13 - 0 01 0 05 0 16 0 88  0 03 0 75  Staurolite  0 23 0 01  0 23 - 0 13 0 01 0 15  0 02 - 0 23 - 0 14 0 80 0 02 0 12  0 07 0 47  0 82 0 00  Sphene  a 09 0 30  0 48 0 00  0 67 0 00  0 80 0 00  0 11 0 25  0 29 - 0 08 0 00 0 34  0 25 0 00  Amphibole  0 07 0 45  0 43 0 00  0 92 0 00  0 66 0 00  0 30 0 00  0 38 - 0 14 0 00 0 11  0 20 - 0 13 0 02 0 14  0 71 0 00  Granitic  0 01 a 89  0 10 0 30  0 06 0 54  0 11 0 28  0 16 0 10  0 17 0 06  0 14 0 14  0 09 0 35  0 13 0 17  0 01 0 85  Mafic igneous**  0 06 0 56  0 48 0 00  0 84 0 00  0 57 0 00  0 30 0 00  0 42 - 0 15 0 00 0 10  0 19 - 0 12 0 04 0 22  0 66 0 00  0 89 0 00  Chert-pebble conglomerate and sandstone***  0 16 - 0 28 - 0 11 - 0 13 - 0 08 - 0 10 - 0 12 - 0 18 - 0 16 - 0 11 - 0 08 - 0 05 - 0 10 0 09 0 00 0 24 0 19 0 44 0 30 0 21 0 05 0 11 0 25 0 43 0 63 0 28  Dark a r g i l l i t e , argilllteand quartz-pebble 7 conglomerate  0 31 0 00  Greenish-gray a r g i l l i t e + t  0 59 - 0 53 - 0 24 - 0 14 - 0 08 - 0 18 - 0 15 - 0 36 - 0 27 - 0 25 - 0 18 - 0 06 - 0 19 0 00 0 00 0 01 0 15 0 43 0 05 0 10 0 00 0 00 0 01 0 06 0 52 0 04  Red-purple  0 34 - 0 24 - 0 19 - 0 05 - 0 10 - 0 09 - 0 04 - 0 04 0 00 0 01 0 04 0 63 0 32 0 34 0 65 0 65  argillitett  0 23 0 02  0 00 - 0 03 0 92 0 77  0 06 0 52  0 37 0 00  0 07 0 49  0 06 0 55  0 37 0 00  0 46 0 00  0 08 0 38  0 53 - 0 05 - 0 05 0 00 0 64 0 62  0 11 0 24  0 01 - 0 07 - 0 06 0 86 0 47 0 55  0 05 - 0 18 - 0 18 - 0 02 - 0 12 - 0 07 0 63 0 05 0 05 0 83 0 20 0 44  0 13 - 0 49 - 0 50 - 0 44 - 0 38 - 0 42 - 0 22 - 0 14 - 0 06 - 0 36 - 0 40 - 0 13 - 0 45 o 17 0 00 0 00 0 00 0 00 0 OO 0 02 0 14 0 58 0 00 0 00 0 17 0 00  Hrae8tone't"''+  0 55 0 00  -  Dolostone '"'"-' ,  T o t a l carbonates''"'" '  0 19 - 0 32 - 0 25 - 0 37 - 0 35 - 0 02 0 05 0 00 0 01 0 00 0 00 0 79  0 14 0 14  0 24 - 0 23 - 0 54 - 0 46 - 0 49 - 0 51 - 0 17 - 0 01 0 01 0 01 0 00 0 00 0 00 0 00 0 07 0 87  0 00 - 0 09 0 93 0 34  0 02 - 0 13 0 84 0 18  0 19 - 0 21 - 0 26 - 0 07 - 0 28 - 0 03 0 05 0 02 0 01 0 49 0 00 0 74  0 36 0 00 0 01 - 0 13 0 86 0 16  0 03 - 0 34 - 0 23 0 75 0 00 0 01  0.17 0.07  0 08 - 0 38 - 0 43 - 0 13 - 0 48 - 0 01 - 0 07 - 0 19 - 0 23 0 44 0 00 0 00 0 17 0 00 0 90 0 46 0 04 0 01  0.81 0.00  at c JS to  a. c  *Mainly goethite (pseudomorphic a f t e r pyrite) and llmenite. **Andesite to quartz gabbro (Purcell extruslves and i n t r u s i v e s ) — P r e c a m b r i a n . ***Blairmore Group—Mesozoic. + Toby Formation and Horsethief Creek S e r i e s , Windermere System—Precambrian. tlMainly Upper P u r c e l l Syatetn—Precambrian. tttMainly Paleozoic.  0 03 0 72  -  o. ti  0.72 0.00  274  APPENDIX 8. Textural parameters of outwash underlying late glacial meltwater channels i n the southern Rocky Mountain Trench.  , * Sample*  , , Location  uj Kd^  S t a t i s t i c a l parameters u „ «. « z oJ SAj .  r * c  Gravel:sand: ( s i l t +  c l a y )  -3.8 -3.4 -4.4 -4.2 -4.0 -4.2  -2.8 -2.3 -3.1 -3.4 -2.7 -3.0  2. 8* 3.2$ 3.3* 2.8* 3.2* 3.3<p  0.50 0.42 0.53 0.48 0.54 0.55  0.90 0.68 1.06 1.40 0.76 1.59  74:25:1 64:34:2 76:22:2 81:16:3 69:28:3 80:15:5  l(avc.)  -4.0  -2.9  3.1$  0.50  1.07  74:23:3  2A 2B 2C  -3.3 -4.2 -1.3  -2.5 -3.0 -1.9  2.2$ 2.6$ 2.8$  0.50 0.62 -0.20  0.72 1.10 0.65  69:29:2 81:17:2 52:46:2  - -2.2 -3.1 -4.1  _ 3  -5* 2.7$ 2.6$ 2.7$  °-19 -0.05 0.18 0.32  -2.7  2.6$  0.22  -2.7  2.4$  ~4'A -4.1 -4.0  " 3 - 8 " 4 a -3.8 -2.6  * 2 , ° * 2.2$ 3.1$  3(ave.)  -3.9  -3.4  2.2$  4A 4B 4C 4D 4E 4F 4G 4H 41 4J  -1.2 -2.3 -2.1 -1.5 -4.3 -3.3 -4.0 -3.2 -2.5 -2.9  -1.5 -2.3 -2.3 -2.0 -3.7 -3.3 -3.8 -3.2 -2.6 -2.9  2.0$ 1.8$ 2.0$ 2.2$ 2.0$ 1.7$ 1.7$ 2.0$ 2.1$ 2.2$  -0.15 0.02 -0.11 -0.25 0.48 0.10 0.32 0.08 -0.06 0.05  -2.7  -2.8  . 2.0$  -2.6 -4.5 -4.1 -4.9  -2.4 -4.1 -3.7 -4.4  -4.0  -3.7  IA IB IC ID IE IF  2D 2R 2V 2G  49°13' N 115'16' W  „ ii^Tii "  u  2(ave.)  -3.2 *<>••<;•  N  iie«i7i u  49*13' N 115*09' W  4(ave.)  5A 5B 5C 5D 5(ave.)  2  -3.1  3A 3B 3C 3D 3E  3  49° 10' N 115*08' W  "  3  -  8  - ° -2.4 -2.B -3.6  2  0.69 0.75 0.93  74:24:2 60:38:2 68:30:2 81:17:2  0.79  69:29:2  0  7  1  0.94  75:23:2  0.40 0.56  - 6 4 2 ' 0 3 1.60 0.95  94:5:1 89:9:2 89:8:3 75:24:1  0.38  1.43  84:14:2  0.83 0.95 0.79 0.93 0.94 1.06 1.32 1.03 1.01 0.82  52:46:2 77:22:1 69:30:1 59:39:2 87:12:1 90:9:1 91:8:1 86:13:1 77:22:1 79:20:1  0.05  0.97  77:22:1  1.7$ 1.7$ 1.9$ 1.6$  0.10 0.49 0.37 0.58  1.49 1.11 0.B8 1.29  83:16:1 91:8:1 88:11:1 92:7:1  1.7$  0.39  1.19  89:10:1  1  -  5  0.40  l  °0  ,  0 9 4  1  6  '  * 4 t o 10 s a m p l e s from 5 g r a v e l p i t s . G r a i n s i z e a n a l y s e s by B r i t i s h C o l u m b i a Department o f H i g h w a y s . " S t a t i s t i c a l p a r a m e t e r s a r e median (Md*), G r a p h i c Mean ( » z ) , I n c l u s i v e G r a p h i c S t a n d a r d D e v i a t i o n ( o j ) . I n c l u s i v e G r a p h i c Skewness ( S * j ) and G r a p h i c K u r t o s i s ( % ) ( F o l k , 1 9 6 8 ) . " d ^ and Mz e x p r e s s e d i n $.  A  115V  116°oo'  h50°oo'  50 oo-  Ik  49oo' 116°oo  49°oo 45  30  FIGURE 5  115W  /  

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