LATE QUATERNARY GEOLOGY of SOUTHWESTERN BRITISH COLUMBIA by John J
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Field Trip Guidebook TRIP 6 LATE QUATERNARY GEOLOGY OF SOUTHWESTERN BRITISH COLUMBIA by John J. Clague and John L luternauer University of Victoria, VIctoria, B.C. MAY 11 .. 13, 1983 GEOLOGICAL ASSOCIATION MINERAlOGICAl CANADIAN GEOPHYSICAl OF CANADA ASSOCIATION OF CANADA UNION ASSOCIATION• GEOLOGIQUE ASSOCIATION UNION GEOPHYSIQUE DU CANADA MINERALOGIQUE DU CANADIENNE CANADA VICTORIA '83 FIELD TRIP COMMITTEE VIC PRETO (Chairman) B.C. Ministry of Energy, Mines and Petroleum Resources DIRK TEMPELMAN-KLUIT Geological Survey of Canada TRYGVE H~Y B.C. Ministry of Energy, Mines and Petroleum Resources GERRY RAY B.C. Ministry of Energy, Mines and Petroleum Resources WARD KILBY B.C. Ministry of Energy, Mines and Petroleum Resources GEOLOGICAL ASSOCIATION OF CANADA MINERALOGICAL ASSOCIATION OF CANADA CANADIAN GEOPHYSICAL UNION JOINT ANNUAL MEETING VICTORIA, B.C. FIELD~RIP 6 • • LATE QUATERNARY GEOLOGY OF SOU'!'HWESTE\\t~TISH COLUMBIA by John J. Clague1 and John L. Luternauer2 May 8 - 10, 1983 ~ Copyright Geological Association of Canada~ Victoria Section 1Geological Survey of Canada, 100 West Pender Street, Vancouver, British Columbia, V6B 1R8 2Geological Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Road, Sidney, British Columbia, V8L 4B2 - ii - CONTENTS Page PREFACE . • . 1 PHYSIOGRAPHY AND GENERAL GEOLOGY 1 LATE PLEISTOCENE HISTORY AND SEDIMENTARF:ENVIRONMENTS • ~ . 3 Introduction . 3 Olympia Nonglacial Interval. 5 Sedimentary Record ·, . e 'a·· '\" • • 5 Paleoclimate 7 Fraser Glaciation 9 Advance Phase . 9 Sedimentary Record 9 Paleoclimate . 18 Fraser Glaciation Climax 19 Recessional Phase . 19 Sedimentary Record . 21 Origin of Sediments 24 Comparable Contemporary Sedimentary Environments 24 Paleoecology of Fort Langley Formation and Capilano Sediments . • . • • . 28 Paleoclimate . , . , . • 30 Sea-·Level Changes during Deglaciation 30 THE FRASER DELTA 33 Introduction . 33 Setting . .. 33 Surface Sediments and Present-Day Sedimentary Environments 33 Subsurface Sediments and Past Sedimentary Environments 39 Age of the Fraser Delta ........ 41 Evolution of the Lower Fraser River Valley and Delta Lf4 FIELD TRIP 52 Introduction ..... 52 Day 1. The Fraser Lowland and Coquitlam Valley 52 Stop 1-1, Point Grey 52 Stop 1-2 Port Moody Disposal Pit 56 Stop 1-3, Coquitlam Valley Gravel Pits I 58 Stop 1-4, Coquitlam Valley Gravel Pits II 61 Stop 1~5, 88th Avenue Gravel Pit 62 Stop 1-6, 256th Street Gravel Pit 63 Stop 1-7, Sumas Valley Gravel Pit 67 Stop 1-8, Lefeuvre Road Borrow Pits 68 Stop 1-9, Anderson Creek Sand Pit 71 Stop 1~10, King George Highway 73 Day 2. Chilliwack Valley , , ... 75 Stop 2-1, Chilliwack River Gravel Pit 75 Stop 2~2, Slesse Creek 77 Stop 2-3, Larsons Bench .. 81 Stop 2-4, Post Creek 81 Day 3. The Fraser River Delta 83 - iii - Page Stop 3-1, Burns Bog • • • • • • • • • • • • • • • • • • 83 Stop 3-2, Iona Island Sewage Treatment Plant Causeway 86 Stop 3-3, CBC Broadcasting Towers Boardwalk ••••• 91 Stop 3-4, Roberts Bank Coal Port Causeway and Tsawwassen Ferry Terminal Causeway • • • • • • • 94 ACKNOWLEDGMENTS •· 99 REFERENCES 100 - 1 - PREFACE Quaternary sediments and landforms in southwestern British Columbia will be examined on this excursion in order to document the recent geologic evo lution and the sedimentary environments of this region. The field trip and this guidebook are concerned primarily with the Fraser Lowland, an area of low to moderate relief south and east of Vancouver, and with the lower parts of bordering mountain valleys. The organization of the guidebook is as follows. The first section following this introduction summarizes the physiography, geographic setting, and general geology of the Fraser Lowland. This is followed by a section on late Pleistocene history, sediments, and sedimentary environments of south western British Columbia. The sedimentary environments and Holocene evo lution of the Fraser River delta are reviewed in the next section. Site in formation for all field trip stops (Days 1 through 3) is presented in the final section of the guidebook. PHYSIOGRAPHY AND GENERAL GEOLOGY The Fraser Lowland forms the southwestern corner of the British Columbia mainland and the adjoining northwestern corner of Washington State (Holland, 1964). It is a triangular-shaped area of about 3000 km2 bounded on the west by the Strait of Georgia and Puget Sound, on the north by the Coast Mountains, and on the south and southeast by the Cascade Mountains (Fig. 1). The Coast and Cascade Mountains are major mountain systems with many peaks in excess of 2500 m in southwestern British Columbia and northwestern Washington. In con trast, the Fraser Lowland consists of flat-topped and gently rolling hills, most of which are below 150 m in elevation and which are separated by wide valleys. The largest of the valleys in the lowland is occupied by the Fraser River which drains most of the southern and central interior of British Colum bia and which terminates in a large delta prograding westward into the Strait of Georgia. The Fraser Lowland is part of a major structural trough which has sub sided repeatedly since late Cretaceous time and into which more than 4000 m of sediments, eroded from the adjacent mountains, have been deposited (Math ews, 1972). The present physiography of the region was produced largely dur ing late Tertiary and Quaternary time when rivers and glaciers dissected the Coast and Cascade Mountains, shedding detritus into the Georgia Depression, Puget Lowland, and Pacific Ocean (Mathews, 1972; Ryder, 1981). The lithology of Quaternary sediments in the Fraser Lowland relates closely to that of rocks outcropping in adjacent montane areas from which the sediments were de rived. For example, sediments with a high content of quartz, feldspar, and granitic lithic fragments were transported south into the lowland from the southern Coast Mountains ~:.vhich are underlain dominantly by granitic rocks. In contrast, sediments rich in sedimentary, metasedimentary, volcanic, and metavolcanic material were transported west and northwest from the Cascade Mountains where these rock types are common at the surface. Figure 1. Laca ion of the Fraser Lowland (darkened cir cle) in relati to the Cordilleran Ice Sheet at its Pleis- tocene ma.ximum. CA, Cascade l'1:::Junta-Lns; CO Coast Mountains; SG, Strait of , .h;an de Fuca Strait; 0, Olympic Peninsula; Vancouver Island. Arrows indicate of cier flow" Modified from Vlin - 3 - Quaternary deposits up to 300 m thick underlie most of the Fraser Low land, with bedrock hills projecting through the Quaternary cover in only a few localities (Armstrong, 1977a, b). There is little or no relationship between the present land surface and the surface upon which the Quaternary sediments rest. Rather, the present surface is primarily a product of de positional processes operative during final Pleistocene deglaciation of the area 11,000 to 13,500 years ago and, to a lesser extent, during Holocene time. The Quaternary succession in the Fraser Lowland consists of sediments deposited during alternating glacial and nonglacial intervals. The lowland was repeatedly invaded by glaciers from the adjacent high mountains during the Pleistocene Epoch. Thick complex drift sequences deposited in associa tion with these glaciers ,,Jere eroded by overriding ice and by fluvial, marine, and mass-wasting processes operative during subsequent nonglacial intervals. As a result of these processes, the Quaternary fill in the Fraser Lowland consists of several drift packages separated by unconformities and by nonglacial deposits. Each major glaciation was accompanied by isostatic adjustments related to glacier build-up and subsequent decay. Combined with eustatic changes in sea level, these glacio-isostatic adjustments produced vertical fluctuations in shoreline positions of up to 200m in the Fraser Lowland (Mathews et al., 1970). As a consequence, low-lying land areas were repeatedly transgressed and regressed by the sea during Pleistocene time, and marine, glaciomarine, and deltaic sediments were deposited in complex associations with glacial, glaciofluvial, and ice-contact materials. Little information is available on the early Quaternary history of the Fraser Lowland, but some of che deeply buried deposits probably date back to this time. In particular, the lower parts of some of the thick marine se~ quences which underlie large parts of the lowland and which are known only from deep drill holes perhaps record the transition from the Pliocene to the Pleistocene. A more complete record of late Pleistocene events is available locally. This record is reviewed in the following section of this guidebook. Holocene sediments and associated landforms, including deltas, floodplains, bogs, and landslides, are common. The sedimentary processes that created these landforms are operative today and contrast sharply with the generally higher energy processes that prevailed in the Fraser Lowland during Pleisto cene glaciations. LATE PLEISTOCENE HISTORY AND SEDIMENTARY ENVIR01"'MENTS Introduction Pleistocene sedimen environments in British Columbia, in general, and in the Fraser Lowland, in particular, have been controlled primarily by alternat and ial. in.ter·vals,. Repeatedly dur the Pleisto cene, global of glaciers in the high mountains of Eriti,3h Colurnbia ~ At the beg of each major cooling - 4 - episode, alpine glaciers advanced do"m mountain valleys. With continued cooling and perhaps increased precipitation, these glaciers coalesced to form piedmont complexes and small mountain