June 1983 the Eastern Outlets

THE EASTERN OUTLETS OF LAKE AGASSIZ A THESTS PRESENTED TO THE FACULTY OF GRADUATE STUDIES UNTVERSITY OF MÄNITOBA IN PARTIAL FULFILMENT OF THE REQUTREMENTS FOR THE DEGREE MASTER OF SCTENCE L. HARVEY THORLETFSON JUNE 1983 THE EASTERN OUTLETS OF LAKE AGASSIZ BY LEONARD HARVEY THORLEIFSON A thesis submitted to the FacLrlty of" Graduate Studies of the University of Marlitoba in partial fulfillnle¡lt of the requirer¡e¡ts of the degree of MASTER OF SC]ENCE o 1983 Pernlission has been granted to the LIBRARY OF THE UNIVER- SITY OF MANITOBA to lend or sell copies of this thesis. to the NATIONAL LIBRARY OF CANADA to microfilnr this thesis and to lend or sell copies of the film, and UNIVERSITY MICROFILMS to publish a¡r abstract of this thesis. The author reseryes other publicatjon rights, and neittrer the thesis nor extensive extracts from it may be printed or other- wise reproduced without the author's writteu pernrission. TABLE OF CONTENTS LIST OF FIGURES I]-I LIST OF TABLES l-v ABSTRACT v INTRODUCTION I History of the Concept of the Eastern Outlets 2 Obj ectives 5 Methods 5 Terminology B Acknowledgements II GEOLOGIC SETTING L2 Precambrian L2 Archean L2 Proterozoic L2 Pal-eozoic and Mesozoic I6 Quaternary I7 THE LAKE LEVEL RECORD 24 I sobases 25 Lake Levels 25 DESCRIPTTON OF EASTERN OUTLET SYSTEMS 32 Kaiashk System 35 Kopka System 40 Pillar System 4I Armstrong System 44 Pikitigushi System 44 PAT,EOHYDROLOGY 47 CHRONOLOGY OF THE EASTWARD DRAINAGE OF LAKE AGASSIZ 53 IntroducÈion 53 Revisions to the Lake Agassiz leveI Chronology 54 Introduction ,54 Strandline gradients and age 55 Age of the Ojata strandline. 5B Summary. 6.1. Moorhead Phase 62 Initiation of the Moorhead Phase 62 Extent of iqe retreat and lake level lowering during thé Moorhead Phase 62 End of the Moorhead Phase 64 Emerson Phase 64 Southernmost advance of ice in northwestern Ontario at the beginning of the Emerson Phase 64 Events during early Emerson Phase 70 Readvance to the Lac Seul Moraine 70 Origin of the lower Campbell beach 7r Correlation of Emerson Phase lce Margins 73 I Nipigon Phase 74 Kaiashk system 74 Kopka and Pillar sYstems 76 Armstrong and Pikitigushi systems 7B Ojibway Phase.. 7B SUMMARY BO REFERENCES B3 al- LIST OF FIGURES 1 Regional Bedrock Distribution ,L4 2 Distribution of undeformed Proterozoic diabase t5 3 Moraines in the eastern outlet region TB 4 Distribution of red glaciolacustrine clay in the Lake Agassiz basin 22 5 Late glacial isobases for central North America 26 6 Lake Agassiz strandline diagram 2B 7 Lakes Superior, Nipigon, and Ojibway strandl-ine diagrams 3I B Location of glacial lake features in the eastern outlet region 33 9 Geographical features in the area of the Kaiashk system 37 10. The Kaiashk system 3B 11. Geographical features in the area of the Kopka and Pillar systems 42 12. The Kopka and Pillar sYstems 43 13. Geographicat features in the area of the Armstrong and Pikitigushi systems 45 14. The Armstrong and Pikitigushi systems 46 15. Two model-s for isostatic rebound 51 16. Rebound of the eastern outlet 52 J.7. Two models for the relationship of the Herman strandlines to the highest Norcross strandline 57 18. Two possible paleogeographic reconstructions of northwestern Ontario at the beginning of the E¡nerson Phase 66 19. Beginning of the Emerson Phase 69 20. Readvance to the Lac Seul moraine 69 2r. Readvance to the Sioux Lookout and Nipigon I morarnes 72 22. Opening of the Kaiashk sYstem 72 23. Ice margin ât the Whitewater, Nipigon II, and Onaman moraines 77 24. Ice margin at the Agutua and Crescent moraines 77 l- l_ l_ LÏST OF TABLES 1. Composite Stratigraphic Section 13 2. The Nipigon Phase Outlets of Lake Agassiz 36 l-v ABSTRACT Lake Agassíz was the largest of several glacial lakes which formed along the southern margin of the retreating late I'trisconsínan ice sheet' Its evolutíon, which spanned the period between 11r500 and 8,000 B'P" was controlled by boÈh its southern outlet, fromwhich Lake Agassiz was draÍned Lo Èhe Gulf of Mexíco vía the llissíssippí River' and its eastern outlets r^rhich crossed the contínental drainage divide in Ontario and drained into the Great l,akes/St. Lawrence system. Lake Agassiz üras drained by the southern outlet during íts early period of development, the Cass and Lockhart Phases, between 11,500 and 10,goo B.P. The southern outleË was then temporarily abandoned as lovrer outlets whích drained into Lakes Superior and Nípigon and' possíbly' an outlet in Saskatcher¿an were actíve for the duration of the Moorhead Phase, between 10,900 and 9900 B.P. A major glacial readvance at 9900 B.p. blocked the Moorhead Phase eastern outleÈs and reached the Hartman, Dog Lake, and Marks moraínes in norËhwestern Ontario. Lake Agassíz rose to íts Norcross leve1, which was confluent \^títh Lake Kaminístikwía ín the Thunder Bay, Ontario area. The southern ouÈlet \'Ías reactivated' initiat.ing the Emerson Phase. The second períod of eastward outflor^¡ followed the Emerson Phase and ís referred to as the Nipigon Phase' This períod was initiated as íce retreated from the Sioux Lookout moraine around 9200 B.P. series of seventeen outlets drained Lake Agassiz into .A Lake Nipigon. I{hen ¡he lowest of these outlets was abandoned' before 8200 B.P., Lake Agassíz outflow was transferred into Lake Cjibway, a large glacial lake r¡hích extended across northern Qntario and into Quebec' Lake Agassíz was finally drained around 8000 B.P. when the contínental v íce sheet split and drainage through Hudson Bay to the North Atlantic began. The Nipigon Phase eastern outlets, which drained Lake Agassiz into Lake Nípi-gon, are well preserved. Huge floods formed grouPs of large channels as these outlets were opened. Cataracts \^¡ith 100 m vertical r^ralls were eroded, large rounded boulders were left in channels, and deltas or subaqueous fans were deposíted where the channels reached Lake Nipigon. opening of the eastern ouÈlets of Lake Agassiz substantially increased the rate of flow through the Great Lakes' vl_ INTRODUCTION Lake Agassiz was a huge lake r¡hich filled large lo¡^rland areas ín central North Arnerica beËween the retreating ice margín and the continental dívide. Lake Agassiz initially formed as the margin of the continental ice sheet retreated from the southernmost part of the Red Ríver valley. The lake filled the valley to a level determined by an outlet at the lowest deglaciated col on the continental divide. The ÍnÍtial spillover point, known as Èhe southern outlet' carríed outflow to Èhe Mínnesota River valley, the Mississippi River and, ultimately, the Gulf of Mexico. The level of the lake did not fall below a 1evel determined by this outlet untíl íce retreat exposed lower cols on the drainage divide. Except for one possible outlet at the Clearwater River valley ín northwesËern Saskatchewan (Elson, Lg67), al1 Lake Agassiz outlets which were lo\¡Ier than the southern outlet and which preceded Ëhe final drainage of the lake into Hudson Bay were tteastern ouLletstr. The eastern outlets crossed the continental divide in Ontario and carried outflow ínto the Great Lakes/ St. Lawrence system. The history of Lake Agassíz can be divided ínto two major phases of southward outflow into the Mississippí River, each followed by abandonment of the southern outleÈ and a period of eastward outflow (Fenton et. al. , 1983) . Abandonment of the southern ouÈlet first occurred about 10,900 B.P. (clayton and Moran, L982). This event rnarked the transítíon from the high-water Cass and Lockhart Phases, during which I 2 the southern outlet r^las active, to the low-water Moorhead Phase' Eastern outlets r¿ere active throughouÈ the Moorhead Phase, assuming outflow through Èhe Clearwater Valley did not occur. The morphology of these eastern out.lets has been obscured l-n some cases by readvancing ice and ín others by lnundatíon under later hígh levels of Lake Agassfz. Their locaÈion is here límited to speculation on the basis of the elevation of cols on the continental divide. The Moorhead Phase outlets were re-dammed by readvancing ice about 9900 B.P. (Clayton and Moran , ilg82) and the southern ouÈlet was re-occupied, initiating the high-water Emerson Phase. The second period of eastward outflow, the Nipigon and Ojibway Phases (Teller and Thorleifson, 1983),was iniriated about 9200 B.P. (Clayton and Moran , IgB2), when ice retreat opened a series of eastern outlets causing the abandonmenË of the southern outlet and the end of the Emerson Phase. As successive outlets \^7ere opened, Lake Agassiz was drained in a seríes of steps. The channels which vrere formed by outflor¿ from Lake Agassíz into Ëhe Lake Nipigon basin' north of ThundeT Bay' OnÈario, duríng this period are well preserved and are the focus of this study. History of the ConcepÈ of the Eastern Outlets Upham (1890,1895) was first to recognize the existence of the eastern outlets, referred to as rnortheastward outletsr by him. Although he acknowledged that Èhe courses of the outlets \,rere unexpl-oredrhe described abandonment of the souÈhern outlet due to northeastward outflow along the the margln of the recedíng íce into Lake Superlor. He proposed that outflow was flrst tributary to the Mississippi by way of Lakes Superior J and Míchigan, then east through the Great Lakes basín, and, finally, vía the lowest outlet across the dlvide, through Lakes Abitibi, Des Qulnze, and Temlscamíng to the Ottawa arm of the Gulf of St. Lawrence (upharu, 1895, p. 233). The l-atter course, in the vicinity of the boundary between Ontario and Quebec, south of James Bay, ís now known to have been occupted by gI-aclal Lakes Barlow and Ojibway' The locaÈion of outlet channels ís today and v¡as, fn the past' determined by exfrapolating uplifted Lake Agassiz water planes to their intersection with the drainage dívide, wíth confirmation that a partícul-ar col qras an outlet comíng from erosional and depositíonal features downstream from the possible outlet.

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