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Sea-Level Change and Delta Growth, Fraser Delta, British Columbia

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Sea-Level Change and Delta Growth, Fraser Delta, British Columbia SEA-LEVEL CHANGE AND DELTA GROWTH: FRASER DELTA, BRITISH COLUMBIA Harry F. L. Williams B.Sc (HONS) Plymouth Polytechnic 1980 M.Sc University of ~ritishColumbia 1983 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Geography Harry F. L. Williams 1988 SIMON FRASER UNIVERSITY July 1988 All rights reserved. This work may not be reproduced in whole, or in part, by photocopy or other means, without permission of the author. APPROVAL Name : Harry F. L. ~illiams Degree: Ph. D Geography Title of thesis: Sea-Level Change And Delta Growth: Fraser Delta, British Columbia Examining Committee: Chairman: Dr. L. Evenden Dr. M. C. Roberts Senior Supervisor- Dr. -E. J. Hickin Dr. P~utchinson AD/[ J. L. ~uteinauer Geological Survey of Canada - -. J. D'Auria artment of Chemistjy 1,- - - y,,, D'- D'- External Examiner Department of Geography University of Calgary Date Approved: @/ PARTIAL COPYRIGHT LICENSE I hereby grant to Slmn Fraser University the right to lend my thesis, project or extended essay (the title of which is shown below) to users ot the Simon Fraser University Library, and to make partial or single copies only for such users or in response to a request from the library of any other university, or other educational institution, on its own behalf or for one of its users. I further agree that permission for multiple copying of this work for scholarly purposes may be granted by me or the Dean of Graduate Studies. It is understood that copying or publication of this work for financial gain shall not be allowed without my written permission. Title of Thesis/Project/Extended Essay British Columbia Author: (signature) Harry Frederick Leonard Williams ( name 1 (date) ABSTRACT The depositional framework of the northern part of the Fraser Delta (Lulu Island) was investigated using a series of drill cores, in order to determine the manner in which aggradation occurred on the delta in response to a mid-Holocene rise in sea-level. Selected contemporary depositional environments on Lulu Island were characterised in terms of their lithology, pollen spectra and microfossil content, in order to establish a comparative framework for the paleoenvironmental interpretation of subsurface facies. A chronology of the evolution of Lulu Island was developed, based on C dating, the identificaticn of tephra layers encountered in drill cores and stratigraphic correlation. The response of the deltaic system to the rise in sea-level w s found to have taken the form of a depositional regression, ratheri than a marine transgression. Deposition was sufficient to maintain seaward progradation, even during the period of rising sea-level. At the same time, rising base level triggered aggradation of the delta and the adjoining Fraser River floodplain. Facies incorporated into the structure of the delta during this stage of its growth are of the same internal character and vertical order as their modern analogues, but may be of considerably greater vertical extent. Former sea-levels were established within the body of the delta by a lithologic transition from organic-rich silt of tidal marsh origin, to silts and sands of intertidal origin. This method of identifying former sea-levels, combined with the chronological control provided by this study, enabled a revised sea-level curve to be developed for the Fraser Lowland. The revised curve contains a hitherto unknown stillstand occurring at 6000 yr BP and indicates that the sea did not stabilize at its present level until 2250 yr BP. Details of the Fraser Delta's Holocene progradation rates and vertical accretion rates calculated in this study, are used to estimate the Fraser River's sediment discharge rates during the last 9000 years. The estimate, although only a first approximation, suggests that the Fraser River's sediment discharge has been stable for the last 6000 years and was higher in the early Holocene, which is in accordance with the paraglacial concept. The results from the Fraser Delta serve as a model for the depositional regression style of coastal aggradation. DEDICATION This work is dedicated to my wife, Kathy, for -her moral support, limitless encouragement and divine patience. ACKNOWLEDGEMENTS I would like to thank my senior supervisor, Mike Roberts, for guidance, encouragement and for always willing to "give it our best try". John Luternauer provided valuable advice and assistance throughout the course of this study. I extend my thanks to my other committee members, Ted Hickin and Ian Hutchinson, for their helpful reviews of this thesis. The study would not have been possible without the hard work of my field assistants and drill crew volunteers - Greg Gjerdalen, Nick Kiniski, John White, Nancy Hori, Harry Jol, Bill Ophoff, Butch Morningstar, Valerie Cameron and Cliff Roberts. Bruce Cameron, Richard Hebda and Geoff Quickfall are thanked for their help with the paleontological studies. John Clague offered many useful comments as the work progressed. John DIAuria, Mike Cackett and Karen Moore provided guidance in the XES study. Bryan Kern and Bob Gerath are thanked for their assistance in obtaining Dept. of Highways materials. The study was funded by an Energy, Mines and Resources research grant awarded to Dr. M, C. Roberts and a Geological Society of America dissertation grant awarded to the author. TABLE OF CONTENTS ABSTRACT ................................................... iii DEDICATION ................................................. v ACKNOWLEDGEMENTS ........................................... vi TABLE OF CONTENTS .......................................... vii LIST OF TABLES ............................................. xiv LIST OF FIGURES ............................................ xv SECT1ON ONE : INTRODUCTORY MATERIAL '......................... 1 CHAPTER ONE: INTRODUCTION .................................. 2 1.1 INTRODUCTION ........................................... 2 1.2 DELTAS: DEPOSITIONAL RESPONSE TO RISING SEA LEVEL ...... 2 1.3 RATIONALE AND BASIS OF THE RESEARCH .................... 8 1.4 OBJECTIVES OF THE STUDY ................................ 13 1.5 METHODOLOGICAL APPROACH ................................ 14 1.6 ORGANIZATION OF THE TEXT ............................... 16 CHAPTER TWO: THE STUDY AREA ................................ 20 2.1 PHYSIOGRAPHY ........................................... 20 2.2 CONTEMPORARY DEPOSITIONAL ENVIRONMENTS ................. 24 2.2.1 FORESLOPE ........................................ 24 2.2.2 SUBAQUEOUS PLATFORM .............................. 27 2.2.3 TIDAL FLATS ...................................... 27 2.2.4 FLOODPLAIN ....................................... 29 2.2.5 PEAT BOG ........................................ 29 vi i i 2.2.6 RIVER CHANNELS ................................... 30 2.3 LATE QUATERNARY SEA-LEVEL FLUCTUATIONS IN THE FRASER LOWLAND REGION .................................. 31 2.4 PREVIOUS WORK ON THE STRUCTURE AND EVOLUTION OF THE FRASER DELTA ....................................... 33 2.4.1 STRUCTURE OF THE DELTA ............................... 33 2.4.2 AGE OF THE DELTA ..................................... 36 2.4.3 EVOLUTION OF THE DELTA ............................... 38 SECTION TWO: CONSTRUCTION OF INTERPRETIVE FRAMEWORK AND SUBSURFACE DATA COLLECTION ............................. 43 CHAPTER THREE: LITHOLOGIC CHARACTERISTICS OF CONTEMPORARY DEPOSITIONAL ENVIRONMENTS .............................. 44 3.1 INTRODUCTION ........................................... 44 3.2 FIELD PROCEDURES ....................................... 45 3.3 LABORATORY ANALYSIS .................................... 48 3.4 RESULTS ................................................ 48 3.4.1 INTERTIDAL SURFACE SAMPLES ....................... 48 3.4.2 SUBSURFACE FACIES OF THE INTERTIDAL ZONE ......... 55 3.5 DISCUSSION AND SUMMARY ................................. 58 CHAPTER FOUR: PALYNOLOGICAL CHARACTERIZATION OF CONTEMPORARY DEPOSITIONAL ENVIRONMENTS .............................. 62 4.1 INTRODUCTION ........................................... 62 4.2 CHARACTERISTIC POLLEN ASSEMBLAGES OF CONTEMPORARY DE& IT I ONAL ENVIRONMENTS ON THE FRASER DELTA ........... 62 4.2.1 PEAT BOG ......................................... 63 4.2.1.1 Wet heathland ............................ 63 4.2.1.2 Dry heathland ............................ 64 4.2.1.3 pine woodland ............................ 66 4.2.1.4 ~irchwoodland ........................... 67 4.2.1.5 Spiraea brushland ........................ 67 4.2.2 CHENOPODIACEAE SALT MARSH ........................ 67 4.2.3 COASTAL GRASSLAND ................................ 69 -_.- 1- 4.2.4 RIVER MARSH (PROXIMAL FLOODPLAIN) ................ 69 /' 4.2.5 RIVER SWAMP (DISTAL FLOODPLAIN) .................. 70 4.2.6 TIDAL MARSH ...................................... 72 4.3 POST-EUROPEAN SETTLEMENT VEGETATION CHANGES ON THE FRASER DELTA .................................... 74 4.4 THE PALYNOLOGICAL DISTINCTION OF FLOODPLAIN AND TIDAL MARSH DEPOSITS ................................... 75 4.5 SUMMARY ................................................ 77 CHAPTER FIVE: FORAMINIFERAL ZONATIONS ON THE LULU ISLAND TIDAL FLATS ............................................ 80 5.1 INTRODUCTION ........................................... 80 5.2 PREVIOUS WORK .......................................... 81 5.3 METHODS ............................................. 82 5.3.1 SAMPLING ......................................... 82 5.3.2 SAMPLE ANALYSIS .................................. 84
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