QUATERNARY STRATIGRAPHY AND GEOMORPHOLOGY OF LOWER BRIDGE RIVER VALLEY, BRITISH COLUMBIA by DON EDWIN HOWES B.A., University of Western Ontario, 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of Geography We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April, 1975 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver 8, Canada ii ABSTRACT Bridge River is an east-flowing tributary of Fraser River originating in the Coast Mountains of British Columbia . Its confluence with the Fraser River is near the village of Lillooet. This study encompasses the lower 15 miles (24 km) of Bridge River Valley. The purpose of the study is: (1) to describe and reconstruct the local Quaternary events and relate them to the regional chronology, (2) to produce a surficial geology map, at a scale of 1:50,000. Lacustrine, ice contact fluvio-glacial, fluvio-glacial (lacking ice contact features), glacial, alluvial fan and recent deposits occur here. From their characteristics and stratigraphic relationships, two alternative Quaternary chronologies can be reconstructed: A: Silts and clays deposited in a proglacial lake were subsequently overridden and partly deformed by ice of the last glaciation . Late- glacial aggradation of as much as 400 feet (120 m) of outwash material was succeeded by the fluvial degradation and terracing which continues at present. B: The outwash material represents two phases of proglacial deposition that were preceded by a glacial interval, and separated by the glacial lake phase and the ensuing glaciation. The latter, Chronology B, is favoured. This has been tentatively correlated with the Pleistocene chronology in the adjacent part of Fraser River Valley. iii TABLE OF CONTENTS INTRODUCTION 0.1 LOCATION 1 0.2 OBJECTIVES -1'3 0.3 GENERAL PROCEDURES 3,5 0.3.1 Mapping Procedures 3 0.3.2 Stratigraphic and Geomorphic Procedures 5 0.3.2.1 Surveying 5 0.3.2.2 Stratigraphic Studies 5 CHAPTER ONE 1.1 INTRODUCTION 6 1.2 GEOLOGY OF STUDY AREA 6-8 1.3 DESCRIPTION OF THE STUDY AREA 9-15 1.3.1 Interior Plateau 9,11 1.3.2 Coast Mountains 11 1.3.3 Central Valley Region 14 CHAPTER TWO 2.1 LATE-PLEISTOCENE CHRONOLOGY OF FRASER LOWLAND 16,17 2.2 GENERAL PLEISTOCENE CHRONOLOGY FOR INTERIOR BRITISH COLUMBIA 2.2.1 Evidence of Multiple G laciations 18 2.2.2 Olympia Interglacial 18,19 2.2.3 Fraser G laciation Advance 19,21 2.2.4 Fraser Glaciation Retreat 21 IV Page 2.2.5 Fraser Glaciation During Sumas Stade 22 2.2.6 Post-Glacial Climare and Ashfalls 22,23 2.3 RELATED PLEISTOCENE STUDIES 23-25 2.4 BRIDGE RIVER VALLEY DURING FRASER GLACIATION 25-27 CHAPTER THREE 3.1 INTRODUCTION 28 3.2 LACUSTRINE DEPOSITS 23-32 3.3 GLACIAL DEPOSITS: TILL 33 3.3.1 Description of Till 33-42 3.4 ICE CONTACT FLUVIO-GLACIAL DEPOSITS: KAME TERRACES 42-45 3.5 FLUVIO-GLACIAL DEPOSITS: AGGRADATION GRAVELS OF VALLEY TRAIN 3.5.1 Introduction _ 45*46 3.5.2 A Typical Section - The "Horseshoe Section" 46-52 3 .5 .3 Downstream Sections of Aggradation Gravels 52-56 3.5.4 Discussion 56-61 3.6 ALLUVIAL FAN DEPOSITS 62-63 3.7 RECENT DEPOSITS 64 CHAPTER FOUR 4.1 BRIDGE RIVER CHRONOLOGY 65-71 4.2 CORRELATION WITH FRASER RIVER VALLEY PLEISTOCENE CHRONOLOGY 72-76 V Page SUMMARY STATEMENT 77 BIBLIOGRAPHY 78-81 APPENDIX A Classification Used for Surficial Geology Map 82-83 APPENDIX B Procedures Conducted at Each Stratigraphic Section 84-86 vi LIST OF TABLES Page TABLE I SUB-UNITS OF FRASER GLACIATION 17 TABLE II POST-GLACIAL ASHFALLS -i 23 TABLE III TENTATIVE CHRONOLOGY FOR FRASER VALLEY BETWEEN LYTTON AND LILLOOET 25 TABLE IV DESCRIPTION OF TILL SITES 35 TABLE V DESCRIPTION OF HORSESHOE SECTION 47,48 VII LIST OF FIGURES Page FIGURE 0.1 LOCATION OF STUDY AREA .. 2 FIGURE 0.2 INDEX MAP OF BRITISH COLUMBIA SHOWING facing 3 AREAS OF OTHER QUATERNARY STUDIES FIGURE 0.3 FLOW DIAGRAM OF PROCEDURES 4 CHAPTER ONE FIGURE 1.1 REFERENCE MAP OF BRIDGE RIVER BASIN facing 6 FIGURE 1 .2 GEOLOGY OF STUDY AREA V FIGURE 1 .3 REFERENCE MAP OF STUDY AREA 10 FIGURE 1.4 SURFICIAL GEOLOGY OF STUDY AREA 12 CHAPTER TWO FIGURE 2.1 ICE MOVEMENTS DURING FRASER GLACIATION 20 FIGURE 2.2 TENTATIVE CHRONOLOGY OF FRASER RIVER 24 VALLEY BETWEEN LYTTON AND LILLOOET FIGURE 2.3 GLACIAL STRIAE INDICATING DIRECTION OF 26 ICE MOVEMENT CHAPTER THREE FIGURE 3.1 CLAY PIT SECTION facing 28 FIGURE 3.2 STEP-LIKE PATTERN OF SILT BED OBSERVED ON EASTERN FLANK OF CLAY PIT facing 29 FIGURE 3.3 OVERRIDDEN LACUSTRINE SEDIMENT 31 FIGURE 3.4 TILL SITES AND UNDERLYING BEDROCK 34 FIGURE 3.5 DEFORMATION TILL 39 FIGURE 3.6 AN EXAMPLE OF HOW DEBRIS CAN BE 41, INCORPORATED INTO AN ICE SHEET 'viii Page FIGURE 3.7 CORRELATION OF KAME DEPOSITS facing 44 FIGURE 3.8 CROSS-SECTION SHOWING STRATIGRAPHIC RELATIONSHIP OF LACUSTRINE, GLACIAL, facing 45 FLUVIO-GLACIAL, AND ICE-CONTACT • FLUVIO-GLACIAL DEPOSITS FIGURE 3.9 ILLUSTRATION OF "HORSESHOE SECTION'-' facing 47 FIGURE 3.10 CORRELATION OF OUTCROPS OF VALLEY TRAIN 53 GRAVELS CHAPTER FOUR FIGURE 4.1 POSSIBLE CHRONOLOGIES OF BRIDGE RIVER 66 VALLEY FIGURE 4.2 A POSSIBLE MECHANISM ACCOUNTING FOR SLUMPING IN LACUSTRINE SEDIMENTS 68 FIGURE 4.3 RELATIONSHIP OF DEGRADATION TERRACES 70 TO VALLEY TRAIN SURFACE AND PRESENT PROFILE OF BRIDGE RIVER FIGURE 4.4 TENTATIVE CORRELATION OF BRIDGE AND FRASER RIVER VALLEYS 73 ix LIST OF PLATES Page CHAPTER ONE PLATE 1.1 BEDROCK RIVER SCARPS OF LILLOOET facing 9 GROUP PLATE 1.2 MORPHOLOGY OF UPPER PART OF facing 9 BRIDGE RIVER VALLEY (in study area) PLATE 1.3 COLLUVIAL FAN DRAPED OVER CENTRAL 13 VALLEY FILL PLATE 1.4 FLUVIAL TERRACES (foreground) AND STEP-LIKE MORPHOLOGY OF MISSION RIDGE (background) 13 DUE TO FAULTING PLATE 1.5 POT-HOLE IN CHANNEL BED NEAR THE 15 HORSESHOE EXPOSURE CHAPTER THREE PLATE 3.1 OVERALL VIEW OF CLAY PIT SECTION 29 PLATE 3.2 FRACTURED AND FAULTED CLAY FROM 29 CLAY PIT SECTION PLATE 3.3 LODGMENT TILL (MEMBER A AT HORSESHOE 37 SECTION) PLATE 3.4 STRIATED CLAST FROM UPLAND-ZONE A: TILL 37 PLATE 3.5 DEFORMATION TILL: AN EXAMPLE (NOTICE 38 FRACTURES AND CONTORTED SILT BANDS) PLATE 3.6 LENSES OF SMALL, ANGULAR CLASTS IN 38 LODGMENT TILL (MEMBER A AT HORSESHOE SECTION) PLATE 3.7 KAME TERRACE ALONG SOUTH SIDE OF BRIDGE 43 RIVER VALLEY NEAR MOUTH OF BRIDGE RIVER PLATE 3.8 MEMBERS N, M, L, K, J, AT HORSESHOE SECTION 49 (140 FEET/ 42 METRES) PLATE 3.9 UPPER PART OF HORSESHOE SECTION 49 (NOTICE CONTINUITY OF MEMBERS) X Page PLATE 3.10 MEMBER H AT HORSESHOE SECTION 50 (NOTE: SEEPAGE STAIN) PLATE 3.11 INDURATED MEMBERS A TO E AT HORSESHOE .50 SECTION PLATE 3.12 SITE ONE OF DOWNSTREAM SECTIONS 57 PLATE 3.13 ASYMMETRICAL RIPPLES IN MEMBER H AT 57 SITE FOUR OF DOWNSTREAM SECTIONS PLATE 3.14 SCOUR AND FILL STRUCTURES AT SITE FIVE 58 OF DOWNSTREAM SECTIONS PLATE 3.15 COLLUVIAL MATERIAL INCORPORATED IN 58 AGGRADATION GRAVELS (SITE FIVE) PLATE 3.16 MUDFLOW BAND IN ALLUVIAL FAN DEPOSIT facing 62 PLATE 3.17 CLOSE-UP OF MUDFLOW BAND ILLUSTRATING facing 62 TEXTURE PLATE 3.18 VOLCANIC ASH SURROUNDED BY COLLUVIAL 63 MATERIAL CHAPTER FOUR PLATE 4.1 KAME TERRACES IN BRIDGE RIVER (FOREGROUND) 75 AND FRASER RIVER VALLEY (BACKGROUND) xi ACKNOWLEDGEMENTS The author would like to thank first Dr. June Ryder for her encouragement and advice during the preparation of this thesis, and Dr. W.H . Mathews for reviewing the final draft. I am also grateful to Mr. P.N. Sprout, Chief of the Soils Division, B.C. Department of Agriculture, for the "loan" of Mr. Andrew Holmes. Mr. Holmes was a most willing field assistant. Special thanks are due to my wife, Peggy Howes, for her assistance and patience in the preparation of this thesis. Field work was financially supported by NRC Grant #A8171 to Dr. June Ryder. 1 INTRODUCTION 0.1 LOCATION Bridge River is an east flowing, glacier-fed tributary of Fraser River originating in the Coast Mountains of British Columbia. Its confluence with Fraser River is approximately 5.2 miles (8.3 km) north of the village of Lillooet. This study encompasses the lower 15 miles (24 km) of the Bridge River Valley, between Fraser and Yalakom Rivers (FIGURE 0.1). This segment of the river is the boundary between the Interior Plateau to the east and the Coast Mountains to the west (Holland, 1964). Most of the land in the study region is in the Bridge River Indian Reserve. The dominant occupation of the inhabitants is part-time ranching. 0.2 OBJECTIVES The study has two objectives. The first is to provide a detailed description and reconstruction of the local Quaternary events and relate them to the regional chronology. The second is to produce a surficial geology map, at a scale of 1:50,000.