Late Pleistocene Stratigraphy and Events in the Asbestos-Valcourt Region, Southeastern Quebec
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TH 1456 LATE PLEISTOCENE STRATIGRAPHY AND EVENTS IN THE ASBESTOS-VALCOURT REGION, SOUTHEASTERN QUEBEC. LATE PLEISTOCENE STRATIGRAPHY AND EVENTS IN THE ASBESTOS -VALCOURT REGION, SOUTHEASTERN QUEBEC by Michel Parent Department of Geology Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Faculty of Graduate Studies The University of Western Ontario London, Ontario April 1987 © Michel Parent 1987 THE UNIVERSITY OF WESTERN ONTARIO FACULTY OF GRADUATE STUDIES CERTIFICATE OF EXAMINATION Chief Advisor Examining Board ~G.tgmA4 l ►7 Advisory Committee The thesis by Michel Parent entitled Late Pleistocene stratigraphy and events in the Asbestos—Valcourt region, southeastern Québec is accepted in partial fulfillment of the requirements of the degree of Doctor of Philosophy Date 162 ~ G Chairman of Examining Board ii ABSTRACT The stratigraphic record of the Asbestos-Valcourt region indicates that glacial sediments deposited during at least two regional glacial advances (drift units A and C) underlie ice-contact and glaciolacustrine sediments deposited during the last deglaciation (Late Wisconsinan); glaciolacustrine sediments of unit B which were deposited during a rather short-lived interstade underlie till deposited during the Late Wisconsinan glacial maximum (drift unit C). Till deposited in the Appalachian Uplands during the earlier gla- cial advance (drift unit A) contains only rare Precambrian (Shield-type) erratics and has a distinctive Appalachian provenance. Till geochemis- try as well as till clast lithology and fabrics indicate that drift unit A was deposited by a glacier that was advancing westward from Appala- chian outflow centers. However, the presence of some northwest-derived clasts in till of drift unit A provides evidence for an earlier phase of southeastward ice-flow. This glacial unit is believed to be a correla- tive of Chaudière Till. The upper part of drift unit A contains no record of an influx of northwest-derived debris that should be expected from a long episode of coalescence with the Laurentide Ice Sheet, such as that proposed by earlier workers. Instead, ice-flow sequences re- corded in drift unit A suggest that a shift of outflow centers within ah Appalachian-based glacier took place toward the close of glacial phase A; it is during this part of glacial phase A that a northward ice-flow episode occurred in uplands of the Asbestos region. Glaciolacustrine sediments of unit B were deposited in a glacial lake (or a series of glacial lakes) that was impounded in front of the glacier which subsequently deposited drift unit C. The age of these mainly proximal glacial-lake sediments remains poorly known; unit B is a probable correlative of the Gayhurst Formation (Middle Wisconsinan). iii Till deposited during the last regional ice advance (drift unit C) commonly contains Precambrian erratics as well as abundant northwest- derived local debris. Glacial dispersal trains, subtill glacitectonic - deformations and till clast fabrics consistently indicate that drift unit C and its equivalent, Lennoxville Till, were deposited by ice that advanced southeastward from a Laurentide outflow center and that this ice-flow pattern was maintained until final ice-retreat. During northward ice-retreat that followed glacial phase C, a series of recessional end-moraines (Cherry River / East-Angus, Mont Ham and Ulverton-Tingwick Moraines, in order of decreasing age) were depo- sited and glacial lakes were impounded south of the ice front. The Mont Ham Moraine is coeval with the maximum extent of the Sherbrooke phase of Glacial Lake Memphremagog while the Ulverton-Tingwick Moraine was built after glacial-lake level had fallen to that of the Fort Ann phase of Glacial Lake Vermont. Subsequent glacial retreat along the edge of the Appalachian uplands together with deglaciation of the Québec City nar- rows allowed marine waters to invade the isostatically depressed Central St. Lawrence Lowland, thus forming the Champlain Sea about 12 000 years BP. Patterns and gradients of marine-limit isolines closely resemble those of previous glacial-lake isobases, thus providing additional sup- port to the proposed deglacial history. Absence of Lake Vermont strandlines in valleys northeast of Warwick together with regional deglacial patterns suggest that a large mass of residual Laurentide ice may have been isolated in uplands of the Thetford-Mines area as a result of marine incursion. A late-glacial northward ice-flow reversal may have taken place in that region as a result of drawdown toward a calving bay that retrograded up. the St. Lawrence River estuary. However, this ice-flow reversal apparently did not produce the northward- and westward-trending striations recorded in the Asbestos-Valcourt region; the latter are best interpreted as resi- dual features that were formed during glacial phase A. iv ACKNOWLEDGEMENTS I wish to express my deep gratitude to Dr. Aleksis Dreimanis who supervised this investigation; his encouragement and his thoughtful comments through all phases of this study were greatly appreciated. Sincere thanks are also extended to Drs. Jean-Marie M. Dubois (Université de Sherbrooke) and William W. Shilts (Geological Survey of Canada) who contributed several discussions during the course of this investigation and critically read the near-final draft of this manus- cript. Dr. Stephen R. Hicock kindly reviewed and commented on an earlier draft of this thesis. Drs. Gordon G. Winder and William R. Church reviewed the chapter on bedrock geology and physiography. This thesis has been financially supported through NSERC grant A-4215 (Canada) to A. Dreimanis and through FCAR grant EQ-2057 (Québec) to J.M.M. Dubois. This support was essential and is strongly acknow- ledged. Several colleagues and friends discussed facts and interpretations presented in this thesis: Michel Lamothe, Robert A. Stewart, Bruce E. Broster, Guy Lortie, R. Claude Gauthier, Q. Hugh J. Gwyn, Serge Occhietti, Gilbert Prichonnet and Pierre Clément. Michel and Bob shared my office room in London and are particularly thanked for numerous memo- rable discussions on the infinitudes of glacial geology, till genesis and Quaternary stratigraphy. I also thank Manon Tétreault (U. de S.) for her competent word- processing as well as Marc Lacroix and François Charron (U. de S.) for their fine photographic work of my text-figure originals. Roger Lafontaine (U. de S.) prepared the photographic plates. Sincere thanks are also extended to Mrs. Karin Lootsma (UWO) for carrying out the gra- nulometric and carbonate analyses, to Guy Bilodeau and Mariette Lambert (U. de S.) for assisting me with microfossil extraction and identifica- v tion and with other laboratory work, to John Forth (UWU) for preparing thin sections and to Luc St-Pierre (U. de S.) for computing some of the clast fabric statistics. I also thank W.W. Shilts for defraying the cost of most of the geochemical analyses. Finally, I would like to thank my wife, Claire, for her patience and for encouragement throughout this study. To her and to my children, Daniel and Johanne, I apologize for my absences, both mental and phy- sical. vi TABLE OF CONTENTS CERTIFICATE OF EXAMINATION ii ABSTRACT iii ACKNOWLEDGEMENTS v TABLE OF CONTENTS vii LIST OF PHOTOGRAPHIC PLATES x LIST OF TABLES xi LIST OF FIGURES xii CHAPTER 1 - INTRODUCTION 1 1.1 Statement of project 1 1.2 The study area 1 1.3 Previous work 3 1.3.1 Development of a regional stratigraphic framework (the Traditional Framework) 4 1.3.2 Regional extent of the northward ice-flow episode and the need for a revision of the Traditional Framework 8 CHAPTER 2 - GEOLOGIC AND PHYSIOGRAPHIC SETTING 14 2.1 Bedrock geology 14 2.2 Physiography 19 2.2.1 St. Lawrence Lowland 22 2.2.2 Appalachian Piedmont 22 2.2.3 Green Mountains and Notre-Dame Mountains 22 2.2.4 Appalachian Uplands 23 2.2.5 Boundary Mountains 28 2.2.6 Monteregian Hills 29 CHAPTER 3 - METHODS OF INVESTIGATION 30 3.1 Field methods 30 3.1.1 Mapping glacial and deglacial landforms and deposits 30 3.1.2 Section description and surface till sampling . 31 3.1.3 Glacial soriations 31 3.1.4 Till clast fabric measurements 33 3.1.5 Paleocurrent measurements 33 3.1.6 Till clast lithology 34 3.1.7 Altimetry 34 3.2 Laboratory methods 35 3.2.1 Granulometric analysis 35 3.2.2 Carbonate analysis of the silt-clay fraction . • 36 3.2.3 Trace element analysis of the silt-clay fraction ▪ 36 3.2.4 Heavy mineral analysis 37 3.2.5 Analysis and presentation of paleocurrent data . 39 3.2.6 Analysis and presentation of till clast fabric data 39 3.2.7 Organic matter content 49 3.2.8 Extraction and identification of microfossils . • 49 vii CHAPTER 4 - LATE PLEISTOCENE GLACIAL UNITS AND INTERCALATED NON-GLACIAL SEDIMENTS 50 4.1 Introduction 50 4.2 Drift unit A 53 4.2.1 Norbestos section (MP-79-18) 53 4.2.2 Rivière des Rosiers section (MP-79-9) 67 4.2.3 Willow Brook section (MP-76-1) 74 4.2.4 Chemin des Ecossais section (MP-79-1) 78 4.2.5 Rivière Noire section (MP-82-4) 82 4.2.6 Summary of provenance interpretation and ice-flow sequences: evidence for Appalachian centers of glacial outflow 86 4.3 Unit B - Interstadial glaciolacustrine sediments 92 4.3.1 Proximal deep-water muds and diamictons 95 4.3.2 Subaquatic outwash sediments 102 4.4 Drift unit C - Surface till 106 4.4.1 Norbestos section (MP-79-18) 106 4.4.2 Rivière des Rosiers section (MP-79-9) 109 4.4.3 Willow Brook section (MP-76-1) 111 4.4.4 Chemin des Ecossais section (MP-79-1) 113 4.4.5 Rivière Noire section (MP-82-4) 113 4.4.6 Wotton section (MP-79-5) 114 4.4.7 Notre-Dame-de-Ham section (MP-79-17) 122 4.4.8 Tingwick section (MP-79-15) 125 4.4.9 Bromptonville section (MP-80-2) 130 4.4.10 Arthabasca section (MP-79-14) 132 4.4.11 The Asbestos ultramafic dispersal train 137 4.4.12 Summary of provenance interpretation and ice-flow patterns 147 CHAPTER 5 - LATE WISCONSINAN STRATIGRAPHY AND DEGLACIAL EVENTS .