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Ministry of Northern Development and Mines Ontario

ONTARIO GEOLOGICAL SURVEY

Open File Report 5799

Quaternary Geology of the Mackinac Basin, Lake Huron

By

A. Zilans

1991

Parts of this publication may be quoted if credit is given. It is recommended that reference to this publication be made in the following form: Zilans, A. 1991. Quaternary Geology of the Mackinac Basin, Lake Huron; Ontario Geological Survey, Open File Report 5799, 108p.

Queen©s Printer for Ontario, 1991

Ontario Geological Survey

OPEN FILE REPORT

Open File Reports are made available to the public subject to the following conditions:

This report is unedited. Discrepancies may occur for which the Ontario Geological Survey does not assume liability. Recommendations and statements of opinions expressed are those of the author.or authors and are not to be construed as statements of govern ment policy. This Open File Report is available for viewing at the following locations:

(1) Mines Library Ministry of Northern Development and Mines 8th floor, 77 Grenville Street Toronto, Ontario (2) The office of the Regional or Resident Geologist in whose district the area covered by this report is located.

Copies of this report may be obtained at the user©s expense from a commercial printing house. For the address and instructions to order, contact the appropriate Regional or Resident Geologist©s office(s) or tile Mines Library. Microfiche copies (42x reduction) of this report are available for S2.00 each plus provincial sales tax at the Mines Library or the Public Information Centre, Ministry of Natural Resources, W-1640, 99 Wellesley Street West, Toronto. Handwritten notes and sketches may be made from this report. Check with the Mines Library or Regional/Resident Geologist©s office whether there is a copy of this report that may be borrowed. A copy of this report is available for Inter-Library Loan.

This report is available for viewing at the following Regional or Resident Geologists© offices: Cobalt-Box 230,Presley St.,Cobalt POJ ICO London-Box 5463,659 Exeter Rd,London N6A 4L6 Porcpine-60 Wilson Ave.,Timmins P4N 2S7 Sault Ste.Marie-Box 130 875 Queen St. E.,Sault Ste. Marie P6A 5L5 . Sudbury-2 n Floor,159 Cedar St.,Sudbury P3E 6A5

The right to reproduce this report is reserved by the Ontario Ministry of Northern Development and Mines. Permission for other reproductions must be obtained in writing from the Director, Ontario Geological Survey.

V.G. Milne, Director Ontario Geological Survey

CONTENTS Page

ABSTRACT ...... ix QUATERNARY GEOLOGY OF NORTHWESTERN LAKE HURON ...... l INTRODUCTION ...... l Present Geological Survey ...... l Location of Report Area ...... l Acknowledgements ...... 5 Previous work ...... 5 REGIONAL GEOLOGY ...... ©...... 7 Bedrock Geology ...... 7 Quaternary Geology and History...... 8 METHODOLOGY ...... 14 Sources and Description of Data ...... 14 Analytical Methods ...... 17 BASIN MORPHOLOGY ...... 18 Bedrock Topography ...... 18 Bathymetry ...... 23 Glacial Morphology ...... 26 QUATERNARY GEOLOGY ...... 29 Introduction ...... 29 Surficial Sediment Thickness ...... 39 Till ...... 42 Glaciolacustrine Clay ...... 44 Postglacial Sediments ...... 55 EVIDENCE FOR A LOW WATER STAGE ...... 58 DATING OF SEDIMENTS ...... 62 Palynologic Chronology ...... 62 Paleomagnetic Chronology ...... 65 Radiocarbon dates ...... 65 Chronology of Sedimentation ...... 67 SUMMARY ...... 74 CONCLUSIONS ...... 80 REFERENCES ...... 86 APPENDIX A Great Duck Island Gas Well Log ...... 95 APPENDIX B Stratigraphy of the Sediment Cores ...... 95 APPENDIX C Results of Grain Size and Carbonate Analyses ...... 102 APPENDIX D Results of Grain Size Analyses on Samples from M-core ...... 105 APPENDIX E Results of Carbonate Analyses on Samples from M-Core ...... 106 APPENDIX F Pebble Lithology of Tills ...... 107 APPENDIX G Results of Organic Carbon Analyses on Samples from M-core ...... 107 CONVERSION TABLE ...... , ...... 108

LIST OF FIGURES Page Figure 1. Report area ...... 3 Figure 2. Physiography of Lake Huron ...... 4 Figure 3. Bedrock Geology ...... 9 Figure 4. Time-distance diagram showing glacial advances and lake .phases...... 11 Figure 5. Location of reflection seismic and echo sounding lines ...... 15 Figure 6. Location of sediment samples...... 16 Figure 7. Elevation of bedrock surface...... in Back Pocket Figure 8. Morphology of the bedrock surface...... 22 Figure 9. Bedrock morphology in the region of the Duck Islands...... 24 Figure 10. Summary of grain size and carbonate analyses in cote. 18 ...... 30 Figure 11. Summary of grainsize and carbonate analyses in core 19b...... 31 Figure 12. Summary of grain size and carbonate analyses in core 21 ...... 32 Figure 13. Summary of grain size and core analyses in core 22...... 33 Figure 14. Summary of grain size and carbonate analyses in core PC-2 ...... 34 Figure 15. Summary of grain size and carbonate analyses in M-core ...... 35 Figure 16. Summary of grain size and cabonate analyses in core 19...... 36 Figure 17. Echograms of sediment types ...... 37 Figure 18. Echograms of sediment types...... 38 Figure 19. Distribution of surficial sediments ...... 40 Figure 20. Thickness of surficial sediments...... 41 Figure 21. Thickness of glaciolacustrine sediments ...... 46 Figure 22. Echograms of surficial sediment sequences ...... 48 Figure 23. Erosional unconformity between the glaciolacustrine clay and the postglacial sill...... 61 Figure 24. Mackinac basin, M-core, pollen percentage diagram .. in Back Pocket Figure 25. Paleomagnetic logs and time scale ...... in Back Pocket Figure 26. Comparison of palynologic and paleomagnetic chronologies...... 68 Figure 27. Age versus depth diagram and average sedimentation rates for sediment intervals in M-core . 70 Figure 28. Mackinac basin, M-core, pollen concentration diagram . . . i n Back Pocket Figure 29. Position of the ice margin during the two Rivers - Onaway ice advance about 11 500 years B.P...... 75 Figure 30. Retreat of the Two Rivers - Onaway ice from the Mackinac basin about 11 000 years B.P. . 76 Figure 31. Lake Stanley low-water phase in the Lake Huron basin about 9500 years B.P...... 79 Figure 32. The Nipissing phase (three outlet phase) about 5500 years B.P...... 81

LIST OF TABLES

Page Table 1. Summary of Quaternary deposits and events in the mackinac basin area ...... 10 Table 2. Comparisons of red and grey laminae in the glaciolacustrine day of M-core ...... 53 Table 3. Dated pollen diagrams used to interpret the pollen profile from the mackinac basin ...... 64

vii

ABSTRACT

The glacial and postglacial geology of the Mackinac basin in northwestern Lake Huron was investigated

using air gun seismic reflection profiles, echograms, sediment cores and grab samples, and bathymetric maps. The

geophysical techniques provided good acoustic penetration and resolution in fine-grained lacustrine sediments.

However, in dense, highly reflective sediment such as till, the acoustic response was poor. Consequently, it was not

possible to identify confidently and to determine the distribution of all glacial sediments and landforms.

The morphology of the basin is largely a reflection of the underlying bedrock. The Thunder-Duck Sill

topographic high along the eastern edge of the basin is partly bedrock-controlled. The Duck Islands, forming the

emergent northern part of the Sill, consist entirely of surficial sediment.

The southeasterly trending topographic highs, offshore of the Les Cheneaux Islands, are thought to be

submerged drumlins of the Les Cheneaux drumlin field. The Les Cheneaux drumlins are believed to have been

formed by the Two Rivers - Onaway advance. The south-southwest trending shoals off the south shore of Drummond

Island may be drumlins formed by the Algoma ice lobe, which is thought to have readvanced after the Two Rivers

- Onaway advance. The shoals offshore of Cockburn Island may be composed of glacial sediment deposited during

the same glacial event The position of the Algoma ice margin in the Mackinac basin was not established.

Four lithologic units were mapped: undifferentiated till or bedrock, glaciolacustrine clay, postglacial clay,

and postglacial silt. Till was cored at three sites. The undulating surface of the till or bedrock is exposed around the periphery of the basin, but toward the centre of the basin is conformably overlain by glaciolacustrine clay, which

in turn is discontinuously covered by postglacial clay. The postglacial silt is the shallow-water equivalent of the postglacial clay.

Sedimentation has been concentrated in the topographic lows of the irregular surface of the bedrock, particulary along the west-northwest to east-southeast mid-line of the basin, where surficial sediment thicknesses average 40 m and in places exceed 100 m. The thickness of glaciolacustrine clay frequently exceeds 35 m; postglacial clay and postglacial silt have a maximum thickness of 13 m and 15 m respectively.

ix

In the glaciolacustrine clay and postglacial sediment, the carbonate content varies directly with texture, whereas the calcite/dolomite ratio displays an inverse relationship with texture. The carbonate content is higher in the glaciolacustrine clay than in the postglacial clay, whereas the organic carbon content is low in the glaciolacustrine clay, but increases upward in the postglacial clay. The mineralogy of the clay-size fraction is similar in both sediments and consists of quartz, feldspar, carbonate, amphibole, and clay minerals.

The glaciolacustrine clay accumulated in Main Lake Algonquin and the post-Main Lake Algonquin lakes.

The sedimentary characteristics of the glaciolacustrine clay document the retreat of the glacier from the basin and may reflect late-glacial events in the Lake Superior basin and the lowering of the water to the Lake Stanley low- water phase.

An erosional unconformity between the glaciolacustrine clay and the postglacial sediment, indicated by shallow-water sediments and sometimes mollusc shells, is interpreted as evidence for the lowering of water levels during the Lake Stanley low-water stage. The unconformity is present to a water depth of about 75 m (101 m above sea level), whereas shallow-water sediments of Lake Stanley occur to a water depth of 107 m (69 m above sea level).

The Mackinac basin has been isostatically uplifted approximately 47 m since Lake Stanley time, therefore the original elevation of Lake Stanley was 54 m.

Pollen and paleomagnetic stratigraphies were compiled for the sediment in a core from the deep-water part of the basin and correlated with radiocarbon-dated profiles. The palynologic chronology is believed to be more accurate and has been used to date the sediment in the basin. The age of the glaciolacustrine-postglacial sediment contact was inferred to be about 10,200 years B.P.

A glaciolacustrine clay sample was radiocarbon-dated at 11,810 i 520 years B.P., whereas a radiocarbon age of 3,440 ± 390 years B.P. was obtained from a sample in the postglacial clay. Sedimentation rates were high during the deposition of the glaciolacustrine clay, averaging about 2 to 2.3 cm per year, but decreased sharply during postglacial time to between 0.59 and 0.32 mm per year.

xi Quaternary Geology, of the Mackinac Basin, Lake Huron

By A. Zilans 1

Marshall Macklin Monaghan Limited Manuscript approved for publication by C. Baker, Acting Section Chief, Engineering and Terrain Geology Section, Ontario Geological Survey, April 30, 1991. This report is published with the permission of V.G. Milne, Director, Ontario Geological Survey. QUATERNARY GEOLOGY

OF

NORTHWESTERN LAKE HURON

by

A. Zilans

INTRODUCTION

Present Geological Survey

The Quaternary geology of the Great Lakes region has been studied by systematic geological and geomorphological mapping and site specific studies. Most of the investigations have been carried out on land since these Quaternary deposits are most amenable to study. Relatively little research has been done on the geology and geomorphology of the sediments in the Great Lake basins. However, considering the large area covered by the Great

Lakes, a substantial portion of the Quaternary geology of the region, particularly the record of postglacial sedimentation, is preserved within the Great Lakes basins. The Great Lakes basins contain the largest sediment volume and most extensive sedimentary record of postglacial time.

The purpose of this report is to present information on the nature and distribution of the glacial and postglacial sediments which occur beneath the northwestern part of Lake Huron. Insights into the glacial and postglacial history of the area are also presented. This report compiles the results of many different investigations that were carried out by several individuals and organisations. Results from air gun seismic reflection profiles, echograms, sediment cores, grab samples and bathymetric maps have been incorporated into this compilation report.

Location of Report Area

The report area is located in the northwestern part of Lake Huron which has a surface elevation of 176.8 m above sea level. It has an east-west length of approximately 140 km and a north-south breadth of 30 to 80 km

l (Figure 1). It is bounded in the north by Manitoulin, Cockburn, and Drummond Islands and the Upper Peninsula of

Michigan.

The report area includes the Mackinac basin and surrounding nearshore zones and topographic highs (Figure

1). The Mackinac basin was defined by Thomas et al. (1973) as the depositional basin in the northwest portion of

Lake Huron. At its western end, the Mackinac basin terminates in the Straits of Mackinac, to the south it is bordered by Lower Michigan. In the east, it is separated from the Manitoulin basin of Lake Huron by the Thunder-Duck Sill, a discontinuous underwater ridge extending south from the Duck Islands to the vicinity of Presque Isle, Michigan

(Figure 2).

The Mackinac basin is connected to the North Channel of Lake Huron by three narrow waterways; 1)

Mississagi Strait between Manitoulin Island and Cockburn Island, 2) False Detour Channel between Cockburn Island and Drummond Island, and 3) De Tour Passage between Drummond Island and the Upper Peninsula of Michigan

(Figure 1). Drainage from Lake Superior enters the Mackinac basin mainly through De Tour Passage via the St.

Mary©s River (Beeton and Chandler 1963). The Mackinac basin is connected to and receives outflow from Lake Michigan through the Straits of Mackinac.

The Mackinac basin is situated in the United States and Canada. The International Boundary crosses the

Thunder-Duck Sill trending northwestward approximately along the mid-line of Lake Huron and then veers northward to pass through False Detour Channel between Cockburn and Drummond Islands (Figure 1).

The Mackinac basin is covered by Canadian and United States topographic maps Alpena (41 G), Sault Ste.

Marie (41 K) and Cheboygan (NL L6-9) at a scale of 1:250 000. Hydrographic coverage is provided by the Canadian nautical chart 2297 (Duck Islands to De Tour Passage) at a scale of 1:91 085 and the United States nautical charts

14881 (De Tour Passage to Waugoshance Point) and 14864 (Harrisville to Forty Mile Point) at scales of 1:80 000 and 1:120 000 respectively. UPPER PENINSULA OF MICHIGAN

-4SV

Bay

Figure 1. Report Area. Kilometres

Figure 2. Physiography of Lake Huron (from Thomas et al. 1973).

4 Acknowledgements

The author acknowledges the many people whose assistance facilitated the completion of this report. Dr.

C.F.M. Lewis and Dr. T.W. Anderson of the Geological Survey of Canada provided the geophysical records and sediment samples. Dr. J.S. Mothersill of Royal Roads Military College supplied a piston core and paleomagnetic curves. Discussions concerning paleomagnetic stratigraphy with him were also helpful. Dr. T.C. Johnson of the

University of Minnesota provided a 3.5 kHz seismic reflection profile and the Canada Centre for Inland Waters for provided hydrographic field maps.

Palynology: Dr. B.G. Warner, University of Waterloo, Dr. J.H. McAndrews, of the Royal Ontario Museum and Dr. T.W. Anderson for interpreting the pollen diagrams. Mollusc identification: Leslie Kerr-Lawson and Anita

Godwin. Sedigraph analysis: G.A. Duncan, Sedimentology laboratory, Canada Centre for Inland Waters. Clay-size mineral analysis: Ray Laakso of the Ontario Geological Survey. Bathymetric maps: Walter Kresovic for his invaluable assistance with digitizing and programming. Radiocarbon dates: University of Waterloo radiocarbon laboratory. Photography: Peter Fisher, Department of Earth Sciences, University of Waterloo. Drafting: Teika Zilans and Cathy Moddle. Word Processing: Linda Churchman, Nason St. Associates. Helpful suggestions were also provided through discussions with Dr. P.P. Karrow, Dr. D. E. Lawson, D.A.V. Morgan, University of waterloo, Dr.

O.L. White, Ontario Geological Survey, Dr. J.P. Coakely of the Canada Centre for Inland Waters and various colleagues at Department of Earth Sciences, University of Waterloo.

Previous work

The first investigations of the surficial geology in the northwest Lake Huron region were carried out during the last century. Logan (1863; 1865), Bell (1866), and Bell (1870) documented evidence of glacial and postglacial erosion and deposition along the North Shore of Lake Huron and on St. Joseph, Drummond, Cockburn, and Manitoulin Islands.

Russell (1905) carried out a geological reconnaissance along the north shore of Lake Huron and Lake

Michigan. Several episodes of glacial advance were identified on the basis of the discordant directions of striae. The sediments and strandlines of Main Lake Algonquin and the Nipissing lake phase were also mapped. Leverett (1914)

5 identified the Main Lake Algonquin and post-Main Lake Algonquin shorelines on St. Joseph, Cockburn, Manitoulin, and Mackinac Islands and on the eastern pan of the Upper Peninsula of Michigan.

Leverett and Taylor (1915) were the first researchers to present a comprehensive interpretation of the glacial geology and late-glacial and postglacial lake history in the northwestern Lake Huron region. They recognized that the late-glacial ice flow patterns in the Straits of Mackinac region were complex, as did Leverett (1929), Bergquist

(1943), and Stanley (1945).

The work of Bretz (1951), Zumberge and Potzger (1956), and Hough (1958) established that the ice front retreated to at least the area of the Straits of Mackinac, before the ice readvanced southward to deposit the youngest till in the region, the Two Rivers Till of Wisconsin (formerly Valders Till), now classed as Greatlakean age, which overlies the Two Creeks forest bed. Melhorn (1956), Burgis (1977), and Burgis and Eschman (1981) mapped the extent of the Greatlakean advance across the northern part of Lower Michigan. The position of the ice margin in the

Straits of Mackinac region during the Mackinac and Two Creeks Interstadial was discussed by Farrand et al. (1969).

Boissonneau (1968), on the basis of regional reconnaissance, interpreted the glacial history of the North

Shore of Lake Huron. Karrow (1982, 1983) mapped glacial deposits and documented ice advance directions along the North Shore of Lake Huron and on the eastern part of the Upper Peninsula of Michigan. Drexler et al. (1983) documented a late-glacial readvance of the Superior ice lobe on the eastern part of the Upper Peninsula of Michigan which built the Grand Marais moraine. Chapman and Putnam (1966, 1984) and Prest (1970) summarized the glacial and postglacial history of the northern part of the Lake Huron basin.

A number of investigations have been carried out on specific aspects of the glacial and postglacial lake history. As a continuation of his investigation of the Main Lake Algonquin and post-Main Lake Algonquin lake events in the Lake Huron basin, Stanley (1938) documented the presence of a deeply incised bedrock valley through the Straits of Mackinac. This valley was interpreted as having been deepened during a period of low lake levels in the Lake Huron and Michigan basins following the drainage of Main Lake Algonquin. Hough (1955), Moore (1961), and Buckley (1974) documented the existence of a postglacial low lake phase

in the Lake Michigan basin, whereas Rodgers (1957) and Hough (1962) identified a comparable lake phase in the

Lake Huron basin. Lewis (1969) on Manitoulin Island and Karrow et al. (1975) in southwestern Ontario refined the

chronology of the glacial and postglacial lake events in the Lake Huron basin. Harrison (1972) identified outlets east

of Georgian Bay in the Algonquin highland, through which some of the post-Main lake Algonquin lakes drained.

Hough (1958), Prest (1970), and Sly and Lewis (1972) have summarized the history of water level changes in the

Lake Huron basin.

The lithologic characteristics of the sediments in the Mackinac basin have been examined by Lauff et al.

(1961) and Thomas et al. (1973). The latter utilized seismic reflection techniques in their investigation.

A limited number of polynological studies (Anderson and Terasmae 1966; Tovell et al. 1972; Anderson

1978; McAtee 1977) and paleomagnetic investigations (Mothersill 1981; Mothersill and Brown 1982) have been

carried out in the Lake Huron basin, but none have been initiated in the Mackinac basin.

REGIONAL GEOLOGY

Bedrock Geology

The report area is underlain by Paleozoic limestones, dolostones, shales, and evaporites which generally dip

south-southwestward into the Michigan Basin at 3.75 to 9.5 m per kilometre (Liberty 1957). Differences in the

susceptibility to erosion of the bedrock units account for the regional orientation of the lake basin and major

topographic features on the lake bottom (Thomas et al. 1973).

The bedrock north of the Mackinac basin on Manitoulin, Cockburn, and Drummond Islands and along the

eastern end of the Upper Peninsula of Michigan is mainly dolostone of Middle and Late Silurian age (Liberty 1957;

Winder and Sanford 1972). The Paleozoic rocks along the north shore of Lower Michigan and in the Straits of

Mackinac area are of Early and Middle Devonian age and consist of limestones, dolostones, and cherts (Dorr and

Eschman 1970). Based on regional dips, borehole data, and the morphology of the Mackinac basin, the distribution of bedrock under the basin has been inferred by Cvancara and Melik (1961) (Figure 3). The strike of the bedrock contacts is to the southeast. The units underlying the basin, from north to south, are the Silurian Amabel Formation,

Guelph Formation, and Salina-Bass Island Formations and the Devonian Bois Blanc Formation, Detroit River Group,

Rogers City Formation, and Dundee Formation. The relatively soft Salina-Bass Island Formations, consisting of dolostone, shale, halite, and anhydrite form the bedrock along the main axis of the Mackinac basin. The Six Fathom escarpment, which extends to the southeastern part of the Mackinac basin (Figure 2), is believed to be capped by limestone of the Rogers City and Dundee Formations. Other bedrock-controlled topographic features in the Mackinac basin will be discussed subsequently.

Quaternary Geology and History

The Mackinac basin was likely glaciated prior to the Late Wisconsinan, but no evidence of these glaciations has been recognized. During most of Late Wisconsinan time, the Mackinac basin was filled with ice. When the climate ameliorated, the ice front retreated generally to the north and became concentrated in the topographic lows of the Great Lakes basins. The subsequent glacial history is characterized by the retreat of the ice front along the axes of the basins, interrupted by periodic readvances. Glacial lakes that formed in the lake basins underwent a complex history of water level changes due to the oscillating nature of the retreating ice lobes which opened and closed outlets. Downcutting of outlets and isostatic readjustment of the land surface contributed to the complexity

of the glacial and postglacial lake events. The Late Wisconsinan and Holocene sequence of ice advances, lake phases,

and deposits in the Mackinac basin and the surrounding region is summarized in Table l and Figure 4.

The ice front retreated to, and may have uncovered a portion of, the Mackinac basin for the first time during

the Mackinaw Interstadial. The most convincing evidence for this event is the Cheboygan County bryophyte bed,

located 15 km south of the Straits of Mackinac, in the northern part of Lower Michigan. The bryophyte bed is dated

at about 13,300 years B.P. (Farrand et al. 1969). The presence of a low-water event in the Lake Huron and Erie

basins during the Mackinac Interstadial has been documented by Dreimanis and Goldthwait (1973). A

contemporaneous reduction of water levels is also recorded in the Lake Michigan basin (Hough 1958). This implies DEVONIAN SILURIAN Drc-d Rogers City-Dundee Ss-bi Salina-Bass Island Ddr Detroit River Sa-g Amabel-Guelph Dbb Bois Blanc Se Cataract Ou ORDOVICIAN

Figure 3. Bedrock Geology (from Cvancara and Melik 1961). Table 1. Summary of Quaternary deposits and events in the Mackinac basin area.

Age Time Stratigraphic Rock Stratigraphic Deposit or Event Sediments Unit Unit

Recent Lake H iron massive to faintly Algoma lake phase laminated grey clay Nipissing lake phase clay

Lake Stanley low-water shallow-water sand phase

post-Main Lake laminated and mottled

Algonquin levels reddish-brown to

Main Lake Algonquin greyish-brown clay

Greatlakean Stadial Algoma advance till reddish-brown, sandy Onaway advance till silt to silty sand till

Two Creeks Interstadial

Late Wisconsian Port Huron Stadial Port Huron Drift (?) Port Huron Till (?) reddish brown, sandy silt to silty sand till

Mackinaw Interstadial Port Bruce Stadial Port Bruce Drift (?) Port Bruce Till (?) greyish-brown sandy silt to silty sand till that a drainage route was opened in the Straits of Mackinac area, but the exact position of the ice margin is not known.

During the subsequent Port Huron Stadial, the ice readvanced southward and filled the entire Lake Huron basin. The ice retreated from the Port Huron maximum after 13 000 years B.P. and glacial lakes Whittlesey, Warren,

Grassmere, and Lundy expanded in front of the northward-receding ice margin and drained through various outlets.

Low-level lakes were created in both the Lake Michigan and Huron basins when the Kirkfield outlet, in

Ontario, was opened by the northward retreating ice. This low-lake period occurred during the Two Creeks

Interstadial which is dated 11 850 B.P. at Two Creeks, Wisconsin (Broecker and Farrand 1963). A comparable low- lake stage in the Lake Huron basin is dated at 11 500-11 200 years B.P. (Karrow et al. 1975). The occurrence of simultaneous low lake levels in the Lake Huron and Michigan basins indicates that a connection existed between the two basins across or around the northern part of Lower Michigan. It is speculative as to how far north the ice retreated.

10 1000©s LAKE SUPERIOR LAKE HURON BASIN BASIN Years TIME

B. P. Z

water levels falling m north rising in south

Algoma phase

levels 4 - falling water LU Z LU O Nipissing phase g o - 6

nsmc watei levels

8 - Houghton low-water phase nsmg water levels

post-Mmong phase

Lake Stanley low-water phase Lake M mono Marquette advance 10 - CO Mam Lake Aigonqum levels i Greatlakean Q Algoma ice aa vance ~~^a* Mam Lake Aigonqum f/) l Z CO Two Rivers-On; way advance O O "f - 12 - Two Creeks

Port Huron

LU Mackinaw en

- 14 - i Q < Por© Bruce advance Port Bruce K (f)

Figure 4. Time-distance diagram showing glacial advances and lake phases. Time stratigraphic divisions are listed in the right hand column. Sources: Broecker and Farrand 1963; Farrand et al. 1969; Prest 1970; Dreimanis 1977;

Drexler et al 1983; and Karrow 1984.

11 Based on evidence at the Cheboygan bryophyte site, Farrand et al. (1969) concluded that the area was not deglaciated during the Two Creeks Interstadial. Burgis (1977) reinterpreted the Cheboygan bryophyte site and concluded that the ice had retreated from the area, but could not provide further insight concerning the extent of the

retreat. Both Farrand et al. (1969) and Burgis (1977) recognized that the Indian River lowland could have carried

discharge from the Two Creeks low-water stage in the Lake Michigan basin to the Lake Huron basin.

Non-glacial sediment underlying till, interpreted as Greatlakean in age, on St. Joseph Island, may indicate

that the Island was deglaciated during the Two Creeks Interstadial.

The last ice advance that affected the Mackinac basin occurred during Greatlakean time. This advance is

believed to be equivalent to the late-glacial advance documented at Two Creeks, Wisconsin, in the Lake Michigan

basin, where the Two Rivers (Valders) Till overlies the Two Creeks forest bed, dated at 11 850 years B.P. (Broecker

and Farrand 1963). In Lower Michigan, the Greatlakean ice advanced generally to the southeast, depositing a

lithologically distinct red clayey till (Burgis 1977). The thick deposits of glacial till on Cockburn and Great Duck

Islands may have been deposited during Greatlakean time. The drumlins on the Les Cheneaux Islands and striae on

the adjacent mainland show a distinct southeastward orientation and thus are believed to have been formed by the

Greatlakean-age Onaway ice advance documented in northeastern Lower Michigan.

On the eastern part of the Upper Peninsula of Michigan, the Newberry and Munising moraines, with a

northeast to southwest orientation, are believed to mark the trend of the Superior ice lobe following the Two Rivers

advance, when it was separating from the Algoma ice to the northeast

Along the North Shore of Lake Huron and on Manitoulin, Cockburn, Drummond, and St. Joseph Islands,

the last ice advance was to the south-southwest. The Kinross moraine, on the Upper Peninsula of Michigan,

approximates the western margin of the advance. This advance of the Algoma ice is believed to be younger than the

advance that formed the southeasterly trends in Upper and Lower Michigan, but older than the Marquette advance

of the Superior ice lobe that built the Grand Marais moraine shortly after 10 000 years B.P. (Karrow 1983; Drexler

et al. 1983).

12 At about the time of the Greatlakean age Two Rivers - Onaway advance in northern Lake Huron, the

Kirkfield outlet was closed either by isostatic uplift or by an ice advance. The water in the Lake Huron basin rose to the Main Lake Algonquin level of 184 m and drainage was transferred to the Port Huron outlet. Main Lake

Algonquin continued to exist as the ice front retreated north and out of the Lake Huron basin. Main Lake Algonquin shorelines are found in Lower Michigan (Burgis 1977), along the North Shore of Lake Huron (Boissonneau 1968), on St Joseph (Karrow 1982) and Cockburn Islands (Chapman and Putnam 1984), and along the eastern pan of the

Upper Peninsula of Michigan (Futyma 1982; Drexler et al. 1983).

As the ice retreated northward, lower outlets were uncovered east of Georgian Bay (Harrison 1972) and the water in the Lake Huron basin was lowered through a series of post-Main Lake Algonquin levels. The termination of the Main Lake Algonquin stage has been dated at between 10 500 and 10 000 years B.P. (Karrow et al. 1975).

When the ice uncovered the isostatically depressed North Bay outlet, water in the Lake Huron basin fell to the Lake

Stanley low-water level, at 58 m above sea level (Hough 1962). Lake Stanley was confined to the Mackinac and

Manitoulin basins in the northern part of the Lake Huron basin. Lake Stanley received drainage from Lake Chippewa,

the contemporaneous low-water stage in the Lake Michigan basin, through the Straits of Mackinac. Lake Stanley drained via Mississagi Strait into the North Channel, then eastward over the La Cloche lowland to Lake Hough, the

low-level equivalent in Georgian Bay. Lake Hough drained through the North Bay outlet into the Mattawa - Ottawa

River Valleys. Outflow from the Lake Superior basin did not enter Lake Stanley, but instead flowed across the North

Channel directly into Lake Hough (Sly and Lewis 1972).

Subsequent isostatic uplift of the North Bay outlet raised the water in the Lake Huron basin and initiated the Nipissing phase at an elevation of 184 m. The Nipissing waters drained through the North Bay, Port Huron, and

Chicago outlets and has been dated at about 5500 years BP. (Lewis 1969). As uplift in the northeast continued, the

North Bay outlet was abandoned and drainage was completely transferred to the two southern outlets. Downcutting of the Port Huron outlet, which was floored in glacial drift, resulted in the abandonment of the Chicago outlet. As a consequence, water levels fell and finally stabilized at 181 m, the Algoma phase. This occurred between 3200 and

2500 years B.P. (Thomas et al. 1973). Continued downcutting of the Port Huron outlet has lowered the water in Lake

Huron to its present level of 176.8 m.

13 METHODOLOGY

Sources and Description of Data

The data used in this study were provided by researchers and government agencies who had carried out earlier studies in the Mackinac basin. The primary data base was obtained from the Geological Survey of Canada.

It consisted of low frequency air gun seismic reflection profiles, high frequency echo sounding records, sediment cores, and descriptions of surface sediment samples. The information was gathered by the Canada Centre for Inland

Waters during geology cruises in 1969 and 1971.

The seismic reflection profiles were run along a north-south grid having a line spacing of 10 km (Figure

5). A total of approximately 1000 km of air gun seismics were run in the Mackinac basin. The acoustic pulse was generated with a 5 cubic inch chamber air gun. The profiles were produced using a 500 millisecond sweep and recorded at frequencies ranging from 100 - 700 Hz to 500 - 15,000 Hz. The acoustic reflections were received with a MP35 single hydrophone and processed and recorded with a Huntec 2B hydrosonde. The reflection trace was plotted on an Alden 19-inch wet paper recorder (Lake Huron Limnogeology Cruise 69-2-01 log book).

The high frequency reflection profiles were produced with a Kelvin Hughes MS26 echo sounder. The acoustic pulses were emitted from a magnetostrictive transducer at a frequency of 14.25 kHz 200 times per minute.

Reflected signals were received by a similar transducer, amplified, and converted to direct current The current flowed through a rotating stylus which burned a trace on dry recording paper (Lewis 1966). The echograms were collected along the same lines as the air gun seismic reflection profiles and along southwest trending grid lines have a spacing of 14.5 km (Figure 5). Approximately 1500 km of echogram lines were run in the Mackinac basin.

The sediment samples obtained from the Geological Survey of Canada were collected using several sampling techniques. The surface sediment samples were retrieved with a Shipek bucket sampler, while subbottom sediments were obtained with Alpine and Benthos gravity corers and an Alpine piston corer. The gravity cores had a maximum length of 2 m, whilst the piston cores were up to 17 m long. A total of seven gravity and eight piston cores were obtained from the Geological survey of Canada (Figure 6). Cores 21, P-30, 305, 314, 316, and 317 are located on the eastern slope of the Thunder-Duck Sill, just east of the Mackinac basin. However, they provided much needed

14 ___ Air Gun Seismtes and Echo Sounding —— - Echo Sounding ——... 3.5 kHz Selsmics

Figure 5. Location of reflection seismic and echo sounding lines.

15 Q 21 3 ' 6 Piston Cores g] ©314 Gravity Cores Q Shipek Grab Samples - ©305

Figure 6. Location of sediment samples.

16 control for the stratigraphy and the distribution of sediments on Thunder-Duck Sill and a means of comparing the sediments in the Mackinac basin with those in the adjacent part of Lake Huron.

Additional data were acquired from other sources. An 18 m long piston core, collected by the Canada Centre for Inland Waters in 1983, was obtained from Dr. J.S. Mothersill, of Royal Roads Military College, Dr. Mothersill also provided paleomagnetic inclination and declination curves he had complied for the sediments in this core. A

3.5 kHz seismic reflection profile, trending southeastward across the Mackinac basin from De Tour Passage (Figure

5), was obtained from the University of Minnesota. Detailed hydrographic field map coverage for the Mackinac basin was provided by the Canada Centre for Inland Waters.

Analytical Methods

The distribution and stratigraphy of lacustrine sediments in the Mackinac basin were interpreted from the characteristics of bottom and subbottom reflection traces on the echograms. The air gun seismic reflection profiles largely provided information concerning the total thickness of surficial sediments and the depth to bedrock. The interpretation of geophysical records has been discussed by Silver and Lineback (1972) and Lewis (1966).

The sediment retrieved with the piston and gravity corers was used to determine the distribution, stratigraphy, and physical properties of the sedimentary units in the Mackinac basin. The sediment cores were in various states of preservation when received by the author. Some had undergone considerable drying and shrinkage, whereas others had been disturbed. The piston cores from the Geological Survey of Canada had been logged in considerable detail shortly after retrieval. Since these cores were dried out and many of the original sedimentary structures were obscured, they were not re-logged. The core obtained from Dr. Mothersill (M-core) was in a relatively good state of preservation and was re-logged.

Several types of analyses were carried out on the sediment cores. These included grain size analysis, the determination of carbonate and organic carbon content, and clay mineral identification. The procedures followed in the analyses are those detailed by the American Society for Testing and Materials - Standard D422-63 (1972), Welch et al. (1979), Duncan and La Haie (1979), Dreimanis (1962), Dean (1974) and Whittig (1965). References by Brown

17 (1961), Whittig (1965), Mitchell (1976) and Brindley and Brown (1980) were used as guides for the interpretation

of the X-ray diffraction traces.

A pollen analysis was carried out on the sediment in M-core. The core was sampled at 20 cm intervals to

a depth of 580 cm. The first sample was taken 20 cm from the top of the core. Below 580 cm, the sampling interval

was 40 cm. The pollen analysis procedure used was a modified version of the method presented by Faegri and

Iverson (1975) and Benninghoff (1962). Palynomorphs were identified by comparison with the University of

Waterloo, Earth Science reference collection, the Royal Ontario Museum reference collection with the help of Dr.

J.H. McAndrews, of the Royal Ontario Museum, and with the aid of publications by Wodehouse (1935), Kapp (1969)

and McAndrews et al. (1973).

Paleoinclination and paleodeclination curves were complied for the sediment in M-core by Dr. J.S.

Mothersill. The procedure used was that described by Mothersill (1985). The paleomagnetic curves were also

interpreted by Dr. Mothersill.

Detailed bathymetry of the Mackinac basin is contained on 27 hydrographic field sheets. The hydrographic

sheets are at scales ranging from 1:10 000 to 1:50 000.

BASIN MORPHOLOGY

Bedrock Topography

The topography of the bedrock surface was determined from the air gun seismic reflection profiles. The

lowest reflection on the profiles was assumed to correspond to the surface of the bedrock. In most cases this

assumption is valid, but it appears that sometimes the lowest reflection recorded is the till surface. In such instances,

inaccuracies are introduced to the determination of the bedrock elevation. However, on a basin-wide scale these errors are probably small.

The topography of the bedrock surface is displayed in Figure 7. The contour interval is 30 m and elevations are relative to sea level. The map illustrates only the major features of the bedrock surface. Due to the wide spacing

18 Figure 7. Elevation of bedrock surface. In back pocket.

19 of the seismic lines and the large number of local bedrock irregularities, it was necessary to generalize the contouring.

The extremely irregular bathymetry of the Mackinac basin is to a large extent controlled by the configuration of the bedrock. The bedrock basin and the topography in it were formed by the differential erosion of rocks having various degrees of competency. Depressions on the bedrock surface may result from post-Silurian solution weathering and collapse of Salina Formation gypsum and salt beds, which overlie the Guelph dolostones. Isolated bedrock highs may be controlled by patch and pinnacle reefs which developed in the Middle Silurian Guelph Formation (Thomas et al. 1973).

Faulting may also have affected the topography of the bedrock in the Mackinac basin. Major faults in the northern part of the Lake Huron basin are orientated northwest to southeast and are believed to represent reactivation of Precambrian basement faults (Sanford and McFall 1984). Landsat images (flight line 21, frame 28, 1974) show distinct lineations on Manitoulin Island which are believed to be fault controlled. Great Duck Island may be underlain by one of these faults, based on magnetic anomaly data (Ontario Department of Mines 1963) and work by Churcher

(personal communication). Seismic reflection data from immediately east of Great Duck Island indicates the presence of a possible bedrock scarp with considerable relief.

The effect of glaciation on the bedrock topography is uncertain. Most likely, glacial erosion served to emphasize the features on the pre-glacial bedrock surface. The fact that several locations on the bedrock surface lie well below sea level suggests that the effect of glacial erosion was substantial. Glaciere may also have smoothed some of the bedrock irregularities in the basin.

The total bedrock relief in the Mackinac basin is considerable. At the west end of the basin, Mackinac

Island, which is almost entirely composed of bedrock, has a maximum elevation of 275 m. The total relief from this bedrock high to the lowest point on the bedrock surface in the adjacent basin is 264 m. In the eastern part of the basin, the bedrock relief from the highest point on the bedrock surface, about 2 km south of Great Duck Island, to the lowest point in the basin is approximately 270 m. During the later stages of the Wisconsinan glaciation, when

20 the ice was retreating northward and thinning, the bedrock basin with its striking relief must have exerted considerable control on the configuration and movement of the ice margin.

The bedrock surface lies at or close to the surface of the lake along the shoreline. From the shore, the bedrock surface slopes rapidly into the centre of the basin, at a rate of 5 to 10 m per kilometre. The slope of the bedrock is not smooth, but is marked by numerous irregularities with considerable relief. Local relief of 5 to 30 m is not uncommon. Figure 8 shows the bedrock morphology on the southward-sloping floor of the basin south of the eastern end of the Upper Peninsula of Michigan. Figure 7 does not depict all of these local features since the data are much too sparse.

Along the east-southeast to west-northwest mid-line of the basin, the bedrock elevation is approximately

55 m, although in the western end of the basin the bedrock is at a slightly higher elevation. There are numerous bedrock depressions that extend to depths much below this general elevation. In the western portion of the basin, north and northeast of the eastern end of the Bois Blanc Island, the bedrock surface at some locations lies 30 m deeper. The minimum elevation of the bedrock surface in this part of the basin is 10 m. Further to the east, in the middle of the basin, at the longitude of Cockburn Island, the bedrock surface was identified at an elevation of 95 m below sea level. This is the lowest point on the bedrock surface encountered in the Mackinac basin. The extremely low points may be part of an interconnecting channel system or simply isolated depressions.

The mid-basin bedrock low extends westward to the vicinity of Mackinac Island where it narrows and forms the Mackinac bedrock valley (Stanley 1938). The Mackinac bedrock valley begins in the Lake Michigan basin, north- northwest of Beaver Island, trends eastward to pass through the Straits of Mackinac, and then swings northward along the west side of Mackinac Island. The valley has a relief of 30 to 45 m, an average bottom elevation of 100 m, and a width of l to 3 km between the 115 m bedrock contour lines (Figure 7). The precise elevation of the bottom of the reflection data are poor quality. Other investigations (Rosenau 1956, 1958) have revealed that the deepest point in the bedrock valley, in the Straits of Mackinac, is in excess of 106 m below lake level or less than70 m above sea level. A smaller bedrock valley, with a bottom elevation of 104 m, is located 2.4 km south of the main valley or about l km from the south shore of the Straits of Mackinac (Rosenau 1958).

21 E jt —l (O

V)

lto c c CQ

o o C/] o .C

d o

•ag o X) o

to j2 "lo o

o- 00 / > 4* l o 3

I.I.I l . l . l l . i o o o O O O O O co o J! V (O ut In the eastern part of the basin, between Presque Isle, Michigan and the Duck Islands, two bedrock highs, together with subsequently deposited glacial and postglacial sediment, form the cross-lake bathymetric high known as Thunder-Duck Sill (Thomas et al. 1973). The southern part of the bedrock ridge is a broad bedrock high that trends northeastward from Presque Isle. Along the shore, the bedrock surface has an elevation of 145 m, but it slopes into the basin, maintaining an elevation of greater than 55 m. The northern limb of the bedrock ridge is a more pronounced feature. It is situated at the southern tip of Great Duck Island, where it rises to within 10 m of the lake surface. To the east and west, the bedrock slopes rapidly into the Manitoulin and Mackinac basins respectively.

Southward, the bedrock slopes more gently and maintains an elevation of greater than 55 m. The lowest point on the bedrock surface between the southern and northern limbs of the bedrock high is approximately 25 to 55 m. To the north of the northern limb of the bedrock ridge, the bedrock surface descends about 70 m into a bedrock saddle, with a bottom elevation of 86 m, before rising up toward the shore of Manitoulin Island (Figure 9). The southern slope of this bedrock depression has a steep gradient, forming a scarp-like feature. Well data from Great Duck Island also suggest the presence of a bedrock scarp (Davidson 1976). Reactivation of Precambrian basement faults may be partly responsible for the relief on the Paleozoic bedrock in the region of the Duck islands (Sanford and McFall

1984; Churcher personal communication, 1985).

Bathymetry

The bathymetry of the Mackinac basin is largely a reflection of the underlying bedrock surface. The main effect of glaciation and post-glacial sedimentation has been to subdue the relief in the basin by infilling the bedrock depressions. The deepest points in the lake are found in the areas where the bedrock surface is lowest. Topographic highs, with a few exceptions, are areas underlain by bedrock highs.

The basin is characterized by west-northwest to east-southeast trough that extends from Mackinac Island in the west to the Thunder-Duck Sill in the east. This topographic low is a broad area in the eastern portion of the basin, but northwestward, it becomes a narrow channel only a few kilometres in width. North of Bois Blanc Island, in the deepest portion of the trough, the lake is about 60 m deep. Further to the east, water depths reach a maximum of 155 m. The lake bottom along the trough is predominately level. The slope into the trough is characterized by minor topographic irregularities, but the contour lines generally parallel the shoreline.

23 r--

l 60 E

Q 6 g o S

o S S/5 O

•o ea

o Q o

VM O

W) fi O •S c

60 "oO e- o E

g T3 O ffi Os o* u 3 fif L" The Thunder-Duck Sill is the most distinctive bathymetric feature in the eastern part of the basin (Figure

2). As was already mentioned, the sill is in part bedrock controlled and partly composed of surficial sediments.

Glacial and postglacial sediments have infilled the bedrock lows between the bedrock high segments of the sill and thus created a better defined feature. The lowest point on the sill, between Great Duck Island and Presque Isle, is

110 to 120 m below lake level. Surficial sediments have contributed 20 to 50 m of elevation to this lowest portion of the sill. The Thunder-Duck Sill, between the northern limb of the bedrock high and Manitoulin Island, is a topographic high created by a thick accumulation of glacial sediments. The Duck Islands are aerial portions of this feature.

In the western part of the Mackinac basin, the bathymetry reflects the presence of the Mackinac valley

(Stanley 1938). The depth of the bedrock valley has been reduced as a result of infilling by glacial and postglacial sediments, but it can nevertheless be traced from the Lake Michigan basin, northwest of Beaver Island, to the Straits of Mackinac and northward to the northern tip of Mackinac Island. Southeastward, along the northeast side of

Mackinac Island, the valley broadens into the central part of the basin. The valley has a depth greater than 50 m along its entire course, with depths exceeding 70 m in many places. A maximum depth of 90 m is recorded 4 km northeast of Mackinaw City. The valleys© width at 30 m depth varies from about 1.5 to 3 km.

Along the shore of Lower Michigan, the topography is relatively uniform except for two small shoals east of Bois Blanc Island, Raynolds and Spectacle reefs, which are believed to be bedrock controlled (Lauff et al. 1961).

The north shore of the basin, along the Upper Peninsula of Michigan, Drummond Island and Cockburn Island, has irregular topography that is caused either by relief on the bedrock surface or by glacial deposits.

The topography offshore of the Les Cheneaux Island has a preferred orientation, from the northwest to the southeast, which appears to be related to the glacial landforms on the adjacent islands and mainland. The Les

Cheneaux Islands are the lakeward extension of the drumlin Held that occurs along the south shore of the eastern part of the Upper Peninsula of Michigan. The bathymetry south and southeast of the Les Cheneaux Islands suggests that these drumlins extend into the lake for at least 10 km. A series of shoals, St Martin Reef being the largest, have

25 the same orientation as the Les Cheneaux drumlins. In many places, the water depth over these shoals is less than

10m.

Offshore of Drummond Island, there are numerous shoals that extend southward into the lake. These topographic highs are not as well defined as those at the Les Cheneaux Islands and usually only project 3 to S km lakeward. The relief over these features is 10 to 15 m. These features are either bedrock controlled or are of glacial origin.

South of the southern tip of Cockburn Island, the bathymetric contours bulge prominently into the basin.

The topographic high, Magnetic Reef, extends lakeward for 10 km and maintains an elevation of usually less than

20 m below lake level.

Glacial Morphology

The bathymetry of the Mackinac basin is predominantly controlled by the bedrock surface, as the previous discussion has indicated. However several features in the basin are incongruent with the morphology of the bedrock which suggests that they are formed of glacial drift. Glacial landforms have been positively identified only where they can be traced into the lake from adjacent land areas using the bathymetry maps or where they are exposed above the surface of the lake. The air gun seismic reflection profiles and the echograms were of little use in identifying glacial landforms lying below the post glacial sediment cover or even where they were exposed at the lake bottom.

The pulse emitted from the echo sounder did not penetrate highly reflective surficial sediments such as till. The air gun provided better acoustic penetration, but still was unsatisfactory in penetrating and resolving glacial sediments.

It appears that at locations where glacial deposits having a particulary high reflectivity overlay the bedrock surface, the impedance contrast between these sediments and the bedrock was not sufficiently large to create a distinct reflection on the seismic profile. Instead, the lowest strong reflection often occurred at the upper surface of the glacial sediment It was not always possible to determine whether the lowest reflection was from the surface of the glacial sediment or from the bedrock surface.

26 Glacial landforms identified around the periphery of the basin on the bathymetric map can be traced into the centre of the basin only as far as they appear as distinct morphologic forms on the lake bottom. Since thick units of glaciolacustrine and postglacial sediments cover the entire central part of the lake, no glacial landforms could be traced across the basin. The seismic lines usually did not extend into the shore zone where glacial landforms are exposed at the lake bottom. Thus, the correlation of morphologic features on the bathymetric maps with reflectors present on the seismic profiles was largely not possible.

The most distinctive glacial feature recognized in the Mackinac basin is the thick accumulation of glacial deposits lying between Manitoulin Island and the northern limb of the Thunder-Duck Sill bedrock high. The Duck

Islands are the emergent part of this glacial feature which has a north-south length of 15 km and a width of about

7km.

Great Duck Island, the largest of the Duck Island group, is 6.45 km long and 1.3 km wide. Its greatest elevation is slightly greater than 244 m or 67 m above lake Huron. The other Duck Islands are smaller in size and lower in elevation. Western Duck Island has an elevation of between 198 and 213 m. (22 and 37 m above lake level), whereas the remaining Islands have elevations of 183 to 198 m (7 to 22 m above lake level).

Based on the seismic data and a well log, it is believed that the Duck Islands are underlain by a bedrock depression which has been infilled with glacial sediments. Along the seismic line east of the Duck Islands, the surficial sediments have a maximum thickness of only 15 m (Figure 9). Westward, toward the Duck Islands, the surficial sediments thicken considerably. A gas well drilled on the east side of Great Duck Island, at an elevation of 8 m above lake level, penetrated 73 m of surficial sediments without reaching bedrock (Appendix A). The seismic line along the west side of the Duck Islands does not indicate the presence of a bedrock depression or a thick accumulation of surficial sediments. It appears that the bedrock depression and the thick glacial sediments are local phenomena.

Great Duck Island is underlain by 132 m of surficial sediments, 67 m lying above the lake and at least 65 m below lake level. The gas well log is very generalized (Appendix A), but a large portion of the sediment on Great

27 Duck Island appears to be sand, gravel, and boulders, possibly of glaciofluvial origin. A buff-brown, sandy-silt till has been recognized from between 229 and 236 m (53 to 60 m above lake level). The fabric of the till indicates ice movement from the north-northwest to the south-southeast (Davidson 1976). The distribution and thickness of the till is not known. The Duck Islands were completely submerged by Main Lake Algonquin and again partly submerged during the postglacial Nipissing phase. As a result, the islands have been considerably wave-washed and are mostly covered by sand, gravel and boulders.

Since the subsurface stratigraphy of the Duck Islands sediment complex is unknown, it is not possible to interpret its origin. These sediments may represent deposition during one or more glacial periods. The presence of a great thickness of sediment, a large portion of which, according to the gas well log, is sand and gravel, suggests a still-stand of the ice margin in the area adjacent to the Duck Islands. It appears that the bedrock depression underlying the Duck Islands sediment complex was a centre of sediment accumulation. Perhaps the northern limb of the Thunder-Duck Sill bedrock high to the south of the Duck Islands exerted some control on the position of the ice margin during late-glacial time.

The drumlins of the Les Cheneaux drumlin field, along the south shore of the Upper Peninsula of Michigan, continue lakeward to form the Les Cheneaux Islands. These drumlins are 1.6 to 3.2 km long, 150 to 244 m wide, and have a height of 12 to 15 m. Their average trend is to the southeast at a bearing of 1280. They are predominantly composed of compact reddish sandy till (P.F. Karrow personal communication, 1985) and contain many large boulders (Russell 1905). Southeast from the Les Cheneaux Islands, the bathymetry indicates that the drumlins continue offshore for a distance of 10 km. Further into the basin, the drumlins are obscured by glaciolacustrine and postglacial sediments, and thus are not evident on the bathymetric maps. The lowest distinct reflector on the seismic air gun profiles south and southeast of St. Martin Reef has an undulating surface. The undulations have relief of 12 to 33 m and a width of 450 to 1000 m. The swales between these morphologic features are infilled with glaciolacustrine clay and postglacial silt and clay. Throughout this area, the location of the lowest reflector, which should be the bedrock surface, is ambiguous. It seems likely that these subbottom morphologic features are drumlins, but since a strong reflector corresponding to the bedrock surface is not present beneath them, the identity of these undulations cannot be positively established.

28 The nature of the topographic highs aligned north-south off the south shore of Drummond Island is uncertain. Seismic lines which might provide additional information about the composition of these features are not available. South-southwest trending dmmlins are present on Drummond Island (Karrow 1983), suggesting that the shoals (Holdhdge Shoal and Big Shoal) may be submerged drumlins.

The Magnetic Reef topographic high, off the south shore of Cockburn Island, can be traced 10 km into the basin. The seismic profiles that intersect it, do not provide the resolution necessary to determine whether it is bedrock controlled or composed of glacial sediments. Water well records indicate the presence of a thick sequence of glacial drift on Cockburn Island. It is possible therefore, that Magnetic Reef is also of glacial origin.

QUATERNARY GEOLOGY

Introduction

The characteristics, distribution and stratigraphy of the Quaternary sediments of the Mackinac basin were determined through the analysis of sediment samples obtained from cores and the interpretation of echograms and air gun seismic reflection profiles. A detailed sedimentological analysis of the sediment cores was not attempted.

Instead, only the salient characteristics of each of the major sediment types were determined in order that changes in sedimentation could be documented. The stratigraphy of the sediment cores is described in Appendix B. Analytical results are presented in Appendices C, D, E, F and G. The analytical data for cores 18, 19B, 21, 22, PC-2, M-core and 19 are summarized in Figures 10 to 16 respectively.

The main geologic units recognized from the geophysical records and verified by the sediment samples are bedrock (Figure 17A), till (Figure 17B), glaciolacustrine clay (Figure 18B), sand and gravel (Figure 18Q, and silty sand (Figure 18D). Together these units represent nearly the full range of sediment types found in the Mackinac basin. However, because of the wide spacing of the echo sounding lines and the sediment samples, the comparatively limited areal extent of some of the sediment units, and the local variability in sediment texture, it was not possible to determine the distribution of all of these sedimentary units. Consequently, the discussion of the distribution of the surficial sediments is essentially generalized.

29 Core 18 Water Depth: 68 metres

o i—

POSTGLACIAL

SEDIMENT

SILT

sandy silt with shells

THINLY

LAMINATED

CLAY

GLACIOLACUSTRINE

CLAY

10 THICKLY LAMINATED

12

TILL SAND

16 SEDIMENT

TYPE O 20 40 60 80 100 10 20 30 40 5O 60

PERCENT

CLAY SILT SAND PERCENT CARBONATE

Figure 10. Summary of grain size and carbonate analyses in core 18.

30 Core 19B

Water Depth;.30 5 metres

o i-

POSTGLACIAL

SANDY

SILT

TOTAL

CARBONATES cr 1-tO -*3

POSTGLACIAL SILT CLAYEY

SILT

sand with shells GLACIOLACUSTRINE ? SEDIMENT

TILL

O 20 40 60 80 100 K) 20 30 40 SO 60 70 SEDIMENT PERCENT TYPE CLAY SILT SAND PERCENT CARBONATE

Figure 11. Summary of grain size and carbonate analyses in core 19b.

31 Core 21

Water Depth: 122 metres

POSTGLACIAL

SEDIMENT

THINLY

LAMINATED CLAY

GLACIOLACUSTRINE

-TOTAL

CLAY CARBONATES

4

5 —

CO

6 —

TILL

7 ^ SEDIMENT O 20 40 60 80 100 20 30 40 50

TYPE PERCENT

CLAY SILT SAND PERCENT CARBONATE Figure 12. Summary of grain size and carbonate analyses in core 21.

32 Core 22

Water Depth: 107 metres

o i-

POSTGLACIAL

SEDIMENT

plant detritus

CALCITE

HOMOGENEOUS

TO CLAY

LU 6 FAINTLY CC O o LAMINATED GLACIOLACUSTRINE

CLAY SILT

SAND

10 THINLY

LAMINATED

GLACIOLACUSTRINE

CLAY

12

SEDIMENT

TYPE O 20 40 60 80 100 10 15 20 25 30

PERCENT

CLAY SILT SAND PERCENT CARBONATE

Figure 13. Summary of grain size and carbonate analyses in core 22.

33 Core PC-2

Water Depttv 122 metres

o i—

POSTGLACIAL

SEDIMENT

THICKLY

LAMINATED

GLACIOLACUSTRINE

CLAY

CLAY UJ g 8 O THINLY

LAMINATED •SAND

Q. HI GLACIOLACUSTRINE o 10 CLAY

12

14

16 -. SEDIMENT l

TYPE O 20 40 60 80 100 10 15 20 25 30

PERCENT

CLAY SILT SAND PERCENT CARBONATE

Figure 14. Summary of grain size and carbonate analyses in core PC-2.

34 Water Depth: 134 metres

o r HOMOGENEOUS

POSTGLACIAL

CLAY

2 . 'SILT

\ FAINTLY SAND LAMINATED l POSTGLACIAL

CLAY

CLAY

~ 8

10 THINLY LAMINATED

GLACIOLACUSTRINE

CLAY

12

MOTTLED

GLACIOLACUSTRINE

CLAY

16

18 L SEDIMENT

TYPE 10 15 20 25

Figure 15. Summary of grain size and carbonate analyses in M-core.

35 Core 19

Water Depth- 30-5 metres

1 1

CLAY S.

POSTGLACIAL l UJ SEDIMENT SILT oc o f o dO AND Q -TOTAL

LU CARBONATES

7 L. SEDIMENT j i i i i i

TYPF O 20 40 60 80 100 10 15 20 25

PERCENT

CLAY SILT SAND PERCENT CARBONATE

Figure 16. Summary of grain size and carbonate analyses in core 19.

36 \

^^^"WtCNk/

B

Figure 17. Echograms of sediment types. A-bedrock; B-till; C-glaciolacustrine clay.

37 ^^'^^^^^K!^

D Figure 18. Echograms of sediment types. Legend: A, postglacial clay; B, postglacial silt; C-sand and gravel; D-silty sand.

38 Four geologic units were mapped in the Mackinac basin: undifferentiated till or bedrock, glaciolacustrine clay, postglacial clay and postglacial silt. The distribution of these sediments is shown in Figure 19. The textural terms applied to the lacustrine units are those defined by Folk (1954). The sediment in these three units is not homogeneous, but contains both lateral and vertical variations in texture. The textural terms describe the predominant texture of the sediment.

Surficial Sediment Thickness

The total thickness of the surficial sediments in the Mackinac basin was determined largely from the air gun seismic reflection profiles, the air gun provided penetration through the entire surficial sediment sequence, to the underlying bedrock. In some instances however, the air gun seismic reflection profiles did not resolve the contact between the surficial sediments and the bedrock, thus perhaps resulting in an accurate determination of the thickness of the surficial sediment. However, such errors would be relatively minor and should not significantly affect the overall interpretation.

Figure 20 displays the regional distribution of surficial sediment thicknesses. Numerous local variations have been omitted for the sake of clarity. The thickness of surficial sediments in the western part of the basin was not determined because of insufficient data. The extreme inshore areas also lacked data and thus the thickness of the surficial sediments is unknown.

Sedimentation in the basin during late-glacial and postglacial time has been strongly influenced by the morphology of the bedrock surface. Thick deposits of surficial sediments are found along the mid-line of the lake, where in excess of 40 m of sediment have accumulated. The thickest accumulations are found north of Bois Blanc

Island and in the middle of the lake, at the longitude of Presque Isle. The former location has 100 m of sediment whereas the latter location records 118 m.

The surficial sediments thin up the slope of the basin toward the shore. Data from areas immediately adjacent to the shore are lacking, but judging from the shoreward thinning trend, sediment thicknesses are interpreted

39 i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i'i 1 ci!i!i!i!i!i!i!i!i!i!i!i!i!i!i!i!i!i!i!i !!i!!B!i!S!i!i!i!i!i!i!!!i!!!!!!W

.I ' , 'I'l'i'i'i'i'i'i'i'iiiii1 1 1 1 1 1 1 1 1 1 1 1 1 1 ii ii i 'l'lM'l'l'lMM'IMMMMMM'l'I'l'i ••HIl l l l l l l l l l l l l 1

"o2 'c

40 o E l

e

o ri v O 3

41 to be less than 10 m. The surficial sediments also thin along the Thunder-Duck Sill, particularly on the northern limbof the bedrock high, south of Great Duck Island, where the bedrock is exposed at the lake bottom.

The thickest deposit of surficial sediments in the Mackinac basin occurs in the Duck Islands glacial complex, but it could not be contoured because of a lack of data. Great Duck Island is underlain by greater that 132 m of surficial sediments.

Till

The oldest surficial sediment unit encountered in the basin is till. On the echograms, till produces a distinct irregular reflection from its upper surface, allows little or no penetration of acoustic pulse, and has hummocky regional relief (Figure 17B). Since till and bedrock produce similar reflections, it is difficult to differentiate the two.

Till was mapped along the inshore zone around the periphery of the basin, in the region east of Bois Blanc

Island, and in the area surrounding the Duck Islands (Figure 19). Much of this zone is in fact mantled by sand and gravel, sand and silty sand, which has likely been winnowed from the till by current and wave action. However, the seismic reflection profiles indicate that till or bedrock is near the surface of the lake bottom throughout this zone.

Since sand and gravel allow little or no penetration of the acoustic signal generated by the echo sounder, and the air gun seismics provide minimal resolution within the surficial sediments in general, it is likely that portions of the inshore zone contain sediment units other than till or bedrock. However, these would be of limited extent and thickness.

The thickness of glacial sediment is largely unknown due to the inability of the echo sounder and the air gun seismic profiler to penetrate and resolve dense, highly reflective sediments, certainly, thick deposits of glacial sediment must be present in the basin, but simply have not been recognized.

Glacial sediments of considerable thickness have been identified and mapped on the surrounding land. The drumlins in the Les Cheneaux drumlin field have a height of 15 m (Russell 1905) and are composed of compact

42 sandy till. Since the drumlins can be traced into the lake from the Les Cheneaux Islands, thicknesses of till comparable to those found in the drumlins on land can be expected to be present in the lake basin.

The region surrounding the Duck Islands has a thick accumulation of glacial and glaciofluvial sediments

(up to 132 m). A road cut on Great Duck Island exposes 4.2 m of buff-brown, sandy silt till (Davidson 1976), but its total thickness and distribution is unknown.

Till was penetrated by cores 18, 19B and 21. The total thickness of the till at each of the coring sites is unknown since the corers attained only limited penetration in the dense sediment. A maximum of 3 m of till was cored at sampling site 18. Till is believed to underlie the cored sediments of the other sites.

The tills at coring sites 18 and 21 are greyish-brown (2.5 Y 5/2), whereas at site 19B the till is reddish- brown (5 YR 4/4). No significant textural differences exist between the tills (Figures 10, 11, 12). Each till has a sandy silt to silty sand texture and contains abundant granules and pebbles (sufficiently numerous to do a pebble count). Analyses of nine samples indicated that the sand content averages 429fc (27 to 659fc), whereas silt averages

(29 to 629fc). Clay is a minor component of the tills, averaging 107o (3 to

Carbonate analyses were carried out on five, three and one till sample(s) in cores 18, 19B and 21 respectively (Figures 10, 11, 12). The abundance of matrix carbonate varies only slightly between tills. The till in core 18 has 619& (59 to 64*8?) matrix carbonate, whereas the tills in cores 19B and 21 have 559fc (51 to 589fc) and

42*8? respectively. Dolomite is the most abundant carbonate mineral in all the tills. The calcite/dolomite rations in cores 18, 19B and 21 are 0.2 (0.1 to 0.3). 0.1 (0.0 to 0.1) and 0.1 respectively.

One sample from each of the tills was analyzed for pebble lithology. The lithologies of the clasts in the tills indicate a predominantly local provenance (Appendix F). A minimum of 80*fo of the clasts are derived from the

Paleozoic bedrock that underlies the basin, with carbonates being the major component. Limestone is the dominant carbonate clast in till 18 (489fc limestone, 36*8? dolostone) and 19B (73*26 limestone, 169fc dolostone), whereas

43 dolostone is the more abundant carbonate mineral in till 21 (12*8? limestone, 6S9& dolostone). Shale and chert are the other Paleozoic rock types, whereas quartz and igneous rock types comprise the remainder of the clasts.

Although similarities exist between the tills, the small number of samples does not allow conclusions to be drawn concerning their correlation and distribution. However, based on the colour of the till in core 19B and the tills cored by Lauff et al. (1961) and Hough (1962), red till appears to underlie the western part of the Mackinac basin.

Red till is also found on St Joseph Island (Karrow 1982), in the Les Cheneaux drumlins (Russell 1905) and in north eastern Lower Michigan (Burgis 1977). The red colour of the till is believed to be primarily derived from the red

Keweenawan age shales, sandstones and volcanic rocks in the Lake Superior basin. The red colour is produced by a hematite stain on mineral grains or by clay size grains on hematite (Murray 1953). It is likely that only a small amount of the red component is needed to impart a noticeable reddish colour to a sediment

The age of the red till in core 19B is unknown. It could be of Port Huron or Greatlakean age, since in northeastern Lower Michigan, tills deposited during both of these stages are red (Burgis 1977). Grain size characteristics do not assist correlation of the red tills. The till in the Les Cheneaux drumlins is sandy (P.F. Karrow personal communication 1984) whereas in northeastern Lower Michigan, adjacent to the Mackinac basin, the Port

Huron age till is sandy and the Greatlakean age till is more clayey in texture (Burgis 1977).

The age relationship between the grey brown tills in cores 18 and 21 is uncertain. The grey brown till in northeastern Lower Michigan is believed to be of port Bruce age (Burgis 1977), whereas the age of the buff-brown till of Great Duck Island is not known. The grey colour in these tills may be derived from the Paleozoic bedrock that underlies the Mackinac basin or the predominantly grey brown Precambrian rock north of the Lake Huron basin.

Glaciolacustrine Clay

Glaciolacustrine clay overlies the till along the slope and in the central part of the basin. On echograms

(Figure 17C) it is characterized by a well-defined upper reflection, good acoustic penetration, numerous closely spaced continuous internal reflections, and hummocky regional relief, as a consequence of the sediment mirroring the underlying topography, the internal reflections are also conformable with the underlying topography.

44 Glaciolacustrine clay forms the surface sediment between the inshore undifferentiated till or bedrock zone and the deep-water offshore zone (Figure 19). Lakeward from its area of outcrop, the glaciolacustrine clay is concealed underneath the postglacial sediments. The area south and immediately to the west and northwest of Bois

Blanc Island is also mapped as glaciolacustrine clay. The glaciolacustrine clay in this region is in fact mantled by a wide variety of near shore sediment types ranging in texture from sand and gravel to silty mud. Since the echogram and sediment sample surface sediments is locally quite variable, it was not possible to delineate the distribution of

the uppermost sediments. Instead the underlying sediment, the glaciolacustrine clay, was mapped as the regional surficial unit. This interpretation is a generalization because acoustic penetration at locations covered by highly reflective sediments, such as sand and gravel, is severely limited. Thus, in many locations, the true identity of the underlying sediment is unknown. However, enough soundings, penetrated glaciolacustrine clay to justify mapping the area as such. Glaciolacustrine clay also is the surface sediment on bathymetric highs, particulary over a large portion of the Thunder-Duck Sill.

The glaciolacustrine clay unit constitutes the thickest surficial sediment unit in most of the Mackinac basin.

The thickness of the glaciolacustrine clay frequently exceeded the maximum thickness of sediment that can be recorded on the echograms. The air gun seismic reflection profiles did not provide the resolution necessary to identify consistently the glaciolacustrine clay and to define its thickness. Consequently, the maximum thickness of glaciolacustrine clay that could be determined was limited by the maximum thickness of sediment that can be recorded on the echograms, about 35 m. Glaciolacustrine clay in most of the Mackinac basin is less than 35 m, thus variations in its thickness could be delineated for most of the basin (Figure 21). Areas enclosed by the 35 m contour likely have thicknesses of glaciolacustrine clay far in excess of 35 m. As with the other surficial sediments, the thickness of the glaciolacustrine clay is a function of the topography of the basin. The thickness of the glaciola custrine clay was not contoured in the western part of the basin because of insufficient data.

Cores retrieved from water depths of less than 75 m contain an erosional unconformity between the glaciolacustrine clay and the overlying postglacial sediment indicating that part of the glaciolacustrine sediment has been eroded. Similarly, on the echograms, glaciolacustrine clay exposed at water depths less than 75 m, shows evidence of erosion at its upper surface. Reflectors within the glaciolacustrine clay, that can be traced shoreward from

45 o l 3 O

e

46 the centre of the basin, gradually rise up toward the surface of the unit and are truncated at the lake bottom.

Shoreward from its area of outcrop, the glaciolacustrine clay thins and becomes obscured by a strong reflector, likely consisting of sand (Figure 22A). Along the inshore zone, only isolated remnants occur in depressions on the till or bedrock surface. The glaciolacustrine clay is discontinuously overlain by postglacial clay. The contact between the two units is usually quite well-defined on the echograms (Figure 22B).

Since no single core contains the entire glaciolacustrine clay unit, the sequence of sedimentation and the properties of the sediment were determined by combining the partial sedimentation and the properties of the sediment were determined by combining the partial sediment records contained in each core. Using the underlying till and overlying partial sediment as reference points, and assuming that the whole basin underwent a similar sedimentation history, it is possible to document the significant changes that occurred in glaciolacustrine sedimentation during late- glacial time.

The contact between the till and the glaciolacustrine clay is variable. Sometimes the contact is sharp, possibly an unconformity, whereas other times it is gradational. The contact between the till and the glaciolacustrine clay in cores 21 and 18 is sharp. In core 21, it is marked by a 9 cm thick band of grey sand which is immediately overlain by glaciolacustrine clay. The till does not grade into the sand layer, but based on the similarity in colour, it appears that the sand was deposited shortly after the till was deposited, the rapid transition from the grey sand to the grey varved glaciolacustrine clay suggests that a deep proglacial lake existed in front of the retreating ice margin.

In core 18, the contact between the till and the glaciolacustrine clay is sharp, and a colour difference exists between

the sediment units. The till is greyish-brown, whereas the glaciolacustrine clay is reddish-brown, these sedimentary

features suggest that the till may have been deposited during an earlier glacial episode, not immediately preceding the deposition of the glaciolacustrine clay. If so, the contact is an unconformity.

The sediment at the bottom of core P-30 consists of pebbles and granules imbedded in a sandy silt matrix

(Appendix B). It is till-like in texture but it is apparent that water has played a significant role in its deposition. This sediment grades upward into glaciolacustrine clay over a distance of 0.5 m. It is likely that till underlies the till-like sediment. If so, at this site there is a complete gradation from till to glaciolacustrine sediment.

47 97.5

107.5

± 1 1 7.5

127.5

A

U6.5

156.5

CD

176.5

186.5 Km

B Figure 22. Echograms of surficial sediment sequences. A) Shallow-water surficial sediment sequence. Note that

towards the shore, the glaciolacustrine clay thins and becomes obscured by a strong reflector. B) Deep-water surficial

sediment sequence. Note the strong, continuous reflections from the upper part of the glaciolacustrine clay unit and

the weak, discontinuous reflections from the lower portion of the post glacial clay. The upper part of the postglacial

clay is transparent. Legend: Gl, glaciolacustrine; Pg, postglacial.

48 The oldest glaciolacustrine sediment lying directly over till is generally coarse grained in relation to younger glaciolacustrine sediment It consists predominantly of clay and silt size sediment, but sand can comprise a significant proportion of the unit (up to 289fc in core 18). Lenses of sand and silt and isolated pebbles, possibly ice-rafted, occur in this portion of the glaciolacustrine sediment. The sediment is abundantly laminated, consisting of two or three alternating colour bands. The predominant colours of the laminae are reddish-brown, greyish-brown and grey. The laminae range in thickness from 2 to 25 cm. In other sections of the sediment, the laminations are absent and the sediment is a homogeneous greyish-brown to reddish-brown sediment. The lowest part of the glaciolacustrine clay sequence contains an abundance of carbonate minerals relative to the glaciolacustrine clay higher in the sequence.

The carbonate content ranges from 3 to 4096. The calcite/dolomite ratio ranges from 0.1 to 2.0 but is generally low, averaging 0.3 in core 18 and 0.9 in core 21.

Higher in the glaciolacustrine sequence, the sediments become finer, and laminae of silt and sand and ice- rafted clasts are absent. The sediment is predominantly clay size in texture. The clay content ranges from 63 to 100*8; and averages 75*?fc, 86*^, 89*8? and 959fc in cores 18,22, PC-2 and M-core respectively. The sediment is mainly thinly laminated, with the laminae varying in thickness from l mm to 3 cm. The laminae are usually reddish-brown, greyish-brown, brown and grey in colour and are arranged in pairs and triplets. In places the laminations fade and the clay is mottled with irregular patches of reddish-brown, greyish-brown, brown and grey sediment The lower 5 m of M-core consist entirely of reddish-brown and grey molded clay. The carbonate values are generally lower than in the underlying glaciolacustrine sediment. They range from 8 to 29*fo and average 2l^o in core 18, 149& in cores

22 and PC-2, and 139& in M-core. The calcite/dolomite ratio is higher in this portion of the glaciolacustrine sediment than in the lower part of the unit. The ratio ranges from 0.3 to 3.7 and averages 0.6, 1.2, 2.3 and 1.3 in cores 18,

22, PC-2 and M-core respectively.

The upper part of the glaciolacustrine clay sequence differs markedly from the underlying thinly laminated clay. The sediment is more massively-bedded, with beds ranging in thickness from 2 cm to l m. The colour of the sediment is variable, but it is usually a shade of reddish-brown, brown, or greyish-brown. Some of the reddish-brown clay is brighter than the typical reddish-brown clay found in the remainder of the glaciolacustrine sediment Hough

49 (1962) found similar bright red beds in the upper part of the glaciolacustrine clay he retrieved in cores from the

western pan of the Mackinac basin. The significance of this bright reddish-brown sediment remains to be established.

The youngest glaciolacustrine sediment in core 22 differs from the typical upper glaciolacustrine sequence

in that it is homogeneous to faintly laminated. However, common to all of the upper glaciolacustrine sediment in

the cores is the presence of silt laminae with thicknesses of 3 to 20 cm. Core PC-2 has five silt bands, whereas M-

core and core 22 have l and 2 bands respectively. In addition to the laminae of silt, the upper unit of glaciolacustrine

sediment in these cores has other common properties that differentiate it from the underlying thinly-laminated

glaciolacustrine clay. The sediment is generally coarser, contains more carbonate and has greater variability in

carbonate values. In core 22 (Figure 13), the clay and silt content averages 729k (45 to 909&) and 279o (10 to

respectively. The sediment in core PC-2 (Figure 14) averages 809o clay (72 to 999o) and 209o silt (l to

whereas in M-core (Figure 18) the clay size fraction averages 939fc (85 to 999fc) and the silt 89fc (l to 1496). The total

carbonate values average 259o (18 to 299o), 219& (13 to 299fc) and 169& (12 to 239fc) in cores 22, PC-2 and M-core

respectively. The corresponding calcite/dolomite ratios are 8.0 (0.4 to 1.2), 0.9 (0.5 to 1.2) and 1.8 (0.6 to 3.5) lower

than in the underlying thinly laminated glaciolacustrine sequence.

The textural variations in the glaciolacustrine sediment are believed to document the retreat of the glacier

from the basin. The lowest portion of the retreating ice margin. The coarse-grained component of this sequence may represent a turbidite deposit, whereas the fine-grained sediment likely settled out of suspension. The middle fine grained thinly laminated part of the sediment was probably deposited when the ice margin had largely retreated out of the Mackinac basin. The coarse-grained, thickly laminated upper portion of the glaciolacustrine sequence may reflect a readvance of the glacier, an increase in glacial meltwater discharge, an increase in the discharge from the upper Great Lakes, or documents the draw down of water to the lake Stanley low-water level. The latter two explanations are the most plausible. The middle and upper portions of the glaciolacustrine sequence were mostly deposited from suspension.

The sediment texture and the carbonate content display a correlation which is consistent with the origin of the sediment from a glacial source. In sediment derived by glacial abrasion and crushing, each mineral has a unique

50 fine-grade terminal mode (Dreimanis and Vagners 1971). Further abrasion will not significantly decrease the grain size of the minerals. The carbonate minerals, calcite and dolomite have a terminal mode of 4 to 9 phi, whereas for clay minerals, the terminal mode is greater than 9 phi. A glacially derived sediment containing predominately clay- size grains will have a smaller percentage of carbonate minerals than a sediment composed of silt size particles. This relationship is true for glaciolacustrine sediment in the Mackinac basin.

An inverse relationship exists between sediment texture and the calcite/dolomite ratio that can partly be explained by the different terminal mode for dolomite and calcite. The terminal mode for dolomite is coarse to medium silt (4 to 6 phi), whereas for calcite it is fine silt 6 to 9 phi). A coarse grained sediment would therefore tend to have more dolomite than calcite. Another factor that is likely to affect the distribution of dolomite and calcite in sediment derived from suspension, is the density difference between dolomite and calcite. In water, dolomite has an 8*fo higher density that calcite (Kennedy and Smith 1977). Thus, density sorting would also concentrate dolomite in a coarser grain-size fraction than calcite.

One of the most diagnostic characteristics of the glaciolacustrine clay in the Mackinac basin is its reddish colour. The reddish-brown colour dominates the glaciolacustrine sequence in all of the cores from within the basin.

The glaciolacustrine clay in core 21, located on the eastern side of the Thunder-Duck Sill and, to a lesser degree, the glaciolacustrine clay in the other cores on the Thunder-Duck Sill, contain predominantly grey and greyish-brown sediment. Only minor amounts of reddish sediment are present, the contrast in colour between the glaciolacustrine clay in the Mackinac basin and in the area immediately to the east is probably derived from the late-glacial ice that advanced from the Lake Superior basin and deposited red till, whereas the grey glaciolacustrine sediment originated from the ice that flowed from a more northerly direction and deposited grey till. The Thunder-Duck Sill may have acted as a barrier to the movement of red glaciolacustrine sediment to the eastern part of Lake Huron.

The glaciolacustrine clay from the Thunder-Duck Sill contains less carbonate than the glaciolacustrine clay further to the west in the mackinac basin. This again suggests a different source for the glaciolacustrine sediments deposited on and to the east of the Thunder-Duck Sill.

51 As discussed previously, the laminae in the glaciolacustrine clay occur in pairs or triplets, each lamina being of a different colour. The colours of the laminae range from grey to reddish-brown, in most cases the lower lamina(e) in a pair or triplet is grey or grey brown, whereas the upper lamina is brown or reddish-brown. The grey lamina in the alternating grey and red sequence in M-core is sometimes underlain by a thin (l mm) lamina of grey brown silt.

This silt may be equivalent to the lowest lamina in the triplets which is usually thinner than the middle and upper laminae. The contacts between adjacent laminae in the pairs and triplets are in some places distinct, but at other places they are gradational. The contact between the red upper lamination in a pair or triplet and the grey lamination in the next pair or triplet is usually distinct

The alternating arrangement of the red and grey laminae suggests a cyclicity to the process creating them.

Three pairs of laminae in M-core were examined in detail to determine if any difference exists between the red and grey sediment (Table 2). The red laminae have a slightly finer texture, but the difference is small, just outside the limits of analytical error. The red laminae have slightly more carbonate than the grey laminae, whereas the calcite/dolomite ratio is higher in the red laminae.

Since the differences in the properties of the red and grey laminae are minor, one possibility is that the alternating colours merely reflect the oxidized and reduced state of the same sediment, however, if reducing conditions occurred in the lake during part of the year, they would have been confined to the deep-water areas. The laminations are found in all the glaciolacustrine clay, regardless of water depth, thus oxidation and reduction of the iron minerals is not a viable explanation.

An alternative mechanism for the formation of the laminations is differential settling of the sediment from suspension. Both red and grey sediment were introduced into the lake as suspended sediment during the summer, but since the grey sediment was slightly coarser it settled out of suspension first Any red sediment that settled out during the summer would have been obscured by the predominantly grey sediment The silt lamina that sometimes underlies the grey clay lamina may represent coarse sediment transported into the lake at the beginning of summer

52 Table 2. Comparison of red and grey laminae in the glaciolacustrine clay of M-core

Texture * Carbonate* **

Sample (cm) Colour Mn Sand Silt Clay Calcite Dolomite Total C/D

1006-1007.5 red(5YR573) 11.07 0 2 98 9.5 4.13 13.63 2.30

1007.5-1009.5 greydOYRS/l) 10.77 0 5 95 6 6 12 1 1045-1046.75 red(5YR573) 11.49 0 3.5 96.5 8.5 4.5 13 1.89

1046.75-1048.75 grey(10YR5A) 11.04 0 4 96 4.75 5.75 10.5 0.83 1127-1128.75 grcy(10YR5/!) 10.83 0 4.5 95.5 5.25 6 11.5 0.88

1128.75-1130.5 ied(5YR573) 11.25 0 3 97 9.63 4.8 14.43 2.01

Abbreviations: Mn, mean grain size (phi units); C/D, calcite/dolomite ratio. meltwater discharge. The sharp contacts between laminae in a pair, and the second and third laminae in a triplet, can be explained if the water column was stratified during the period sediment was introduced to the lake. Only the coarsest sediment would settle out during the period of water stratification, whereas the fine clay would be trapped in the epilimnion. The fine clay would settle out only after overturn and would form a distinct, non-gradational lamina on top of the summer layer (Sturm 1979). In cases where the contact is gradational, the water column may have been unstratified, causing a graded sequence to be deposited. The mottled glaciolacustrine clay may represent sediment in which laminations have been destroyed by post-depositional disturbance.

Several other parameters of the glaciolacustrine clay were examined. Organic carbon content was determined for the glaciolacustrine clay in M-core. Values are low throughout the sequence, ranging from l to 29fc. The low organic carbon concentrations reflect both low biological productivity in and adjacent to the lake and high rates of sedimentation. The glaciolacustrine clay in core PC-1, in the extreme northwestern part of the Mackinac basin, is unusual in that it contains plant debris scattered within the clay and concentrated in a 2 cm wide lens. This suggests that the surrounding land was vegetated at the time of glaciolacustrine sedimentation.

Mineralogical analyses on the glaciolacustrine clay in M-core indicate that the clay-size fraction consists of quartz, feldspar, carbonate, amphibole, and clay minerals. Illite, chlorite, and kaolinite are the most abundant clay minerals, although montmorillonite and mixed-layer minerals occur in smaller quantities. No difference in the clay

53 mineral assemblage exists between the red and grey laminae, or between the bright red clay and the "normal" red clay.

On the echograms, the glaciolacustrine clay contains numerous variably spaced reflections that trend sub- parallel to the surface on which the sediment unit rests (Figures 17C and 22B). Many of the reflections are traceable only l or 2 km before they fade, bifurcate, or combine with other reflections. Some reflections are more continuous and can be traced over distances of 15 km before they fade or alter in appearance. The glaciolacustrine clay retrieved from the cores lacked any obvious sedimentary structures that could account for particular reflections on the echograms. It is believed that the laminated structure of the sediment and textural variations between the laminae are responsible for generating the internal reflections. A reflection may be caused by a single reflector or by a series of closely spaced reflectors.

Even over short lateral distances, the reflections in the glaciolacustrine clay display variations in the depth at which they occur in the glaciolacustrine sequence. It appears that the vertical position of a particular sediment unit in the glaciolacustrine clay is strongly influenced by the topography upon which it was deposited. Glaciolacustrine clay accumulated more rapidly in bathymetric lows than on highs. Consequently, a lamina in the glaciolacustrine clay is thicker in bathymetric depressions than on bathymetric highs. In addition, the reflections show lateral changes in thickness and intensity. These changes are perhaps indicative of changes in the impedance contrast between the sediment units responsible for the generation of the reflections. This would imply a change in the physical properties of the sediment and would further complicate correlation of reflections with sediment structures. Since the sediment cores in this study were not retrieved directly on the echo sounding tracks and logged sediment thicknesses were not adjusted for the effects of compression during coring, it was not possible to correlate reflections with specific sediment structures. Furthermore, the piston coring technique usually fails to sample a portion of the surface sediments.

A feature common to much of the glaciolacustrine clay is the concentration of particulary distinct reflections in its upper part (Figure 22B). The reflections begin immediately below the top of the sequence and extend down

54 for 2 to 7 m. The number of distinct reflections varies from 2 to 5. The glaciolacustrine clay in M-core indicates that these reflections may be caused by a zone of thickly laminated (0.5 to 10 cm thick) clay containing silt laminae.

Postglacial Sediments

The surface sediment in the offshore deep-water zone is postglacial clay (Figure 19). Postglacial clay is seldom found at water depths less than 75 m. Since the Mackinac basin has a complex, undulating bathymetry, and sedimentation rates have been low during postglacial time (Kemp et al. 1974), the deep-water zone is covered by a discontinuous cover of postglacial clay. The area mapped as postglacial clay includes outcrops of glaciolacustrine clay, but postglacial clay covers greater than 50 percent of the lake bottom.

The thickness of the postglacial clay can readily be determined because it is thin enough to be displayed

in its entirety on the echograms and can usually be recognized on the air gun seismic reflection profiles. The

postglacial clay is a discontinuous sediment unit whose thickness varies according to the topography of the

underlying surface. It is thickest in the bathymetric lows, and thins or pinches out completely along the slope of the basin and on bathymetric highs, where the glaciolacustrine clay becomes the surface unit It was not possible to plot

an isopach map of the postglacial clay due to the extreme local variations in its thickness. Along the mid-line of the

basin, the postglacial clay averages about 7 m in thickness, but toward the shore it thins rapidly. The postglacial clay

reaches a maximum thickness of 13 m in the deepest part of the lake.

On the echograms (Figure ISA), the postglacial clay has an indistinct upper reflection and is acoustically

nearly transparent, with faint, discontinuous internal reflections usually restricted to the lower portion of the

postglacial clay. Its surface reflection darkens and it becomes acoustically less transparent toward shallow-water

areas, probably due to the increase in the texture of the sediment.

Several areas of postglacial silt are delineated (Figure 19). The postglacial silt is usually found between the

inshore undifferentiated till or bedrock zone and the area of glaciolacustrine clay outcrop. However, in the western

part of the basin, southeast of the Les Cheneaux Islands, the postglacial silt and postglacial clay are laterally

55 gradational. Postglacial silt was recognized in other areas besides those delineated on the surficial sediment distribution map, but the areas were too limited in extent to be mapped.

Postglacial silt has a more uniform thickness than the postglacial clay. The postglacial silt north of Rogers

City has a thickness of about 5 m, whereas east of Bois Blanc Island, it averages 7.5 m. North of Bois Blanc Island, postglacial silt thicknesses of 15 m are common, but in shallower water the unit thins considerably.

On the echograms, the postglacial silt is characterized by a moderately distinct reflection from its upper surface, good acoustic penetration, and faint, discontinuous to distinct and continuous internal reflections (Figure

18B). The internal reflections and the upper surface of the unit do not conform to the underlying topography. The upper surface is regionally smooth to very gently undulating.

In areas with water depths less than 75 m, postglacial sediments unconformably overlie till or glaciolacustrine clay. The unconformity is frequently marked by a thin layer of sand, sometimes containing mollusc shells. On the echograms in water shallower than about 75 m, the glaciolacustrine clay is frequently overlain by a strong reflector which does not mirror the undulating internal reflectors of the glaciolacustrine unit (Figure 23A,B).

Further toward the shore, the reflectivity of this reflector increases and the underlying glaciolacustrine clay becomes obscured. This strong reflector is believed to correspond to the layer of sand found at the unconformity between the glaciolacustrine clay and the postglacial sediment in the cores.

At water depths greater than 75 m, the glaciolacustrine clay grades into postglacial sediment. The transition from glaciolacustrine clay to postglacial sediment is characterized by a change in sediment colour from red to grey.

Where the glaciolacustrine clay - postglacial sediment contact is erosional, the boundary between the red and grey colours is sharp, whereas in the deep-water areas, a gradation exists between the red and grey sediments.

At all locations in the basin, the texture of the postglacial sediment is coarser than the glaciolacustrine clay that underlies it. There are several reasons for this. As the glacier retreated away from the Mackinac basin, the influx of fine-grained rock flour ceased. Sediment deposited in the basin during postglacial time has been derived from two

56 sources: the erosion of glacial and glaciolacustrine sediment in the basin, and from the weathering and erosion of rock and sediment on the adjacent land. Furthermore, during postglacial time, the depth of water in the Mackinac basin has been less than when Main Lake Algonquin flooded the basin. Water depths have decreased due to the downcutting of the Port Huron outlet and as a result of isostatic uplift, which has differentially uplifted the northern pan of the Lake Huron basin. Energy levels in the basin have consequently increased, causing coarser sediment to be deposited where previously finer sediment accumulated. Fine sediment, which under deeper water conditions was deposited, is transported out of the basin.

The postglacial sediment is exclusively grey and greyish-brown in colour. It is generally massive and non- laminated, although the lower part of the sequence, as in M-core, is faintly laminated with thin bands (0.5 to 1.0 cm) of light and dark grey sediment.

The sediment sequence in core 19B (Figure 11; Appendix B) is more complex than in the other cores.

Below the upper 2.84 m of sandy silt sediment, there are two units of laminated, grey and greyish-brown clayey silt, the upper of which contains shell fragments. The contacts between the two units and with the overlying and underlying sediments are sharp, likely erosional. The lower unit is underlain by a 7 cm thick lens of sand containing mollusc shells which in turn is underlain by a 14 cm thick layer of clayey silt. The clayey silt overlies till. This sequence of sediments documents several episodes of deposition and erosion which likely occurred during the post-

Main Lake Algonquin drop in water level.

Grain size analysis indicates that the texture of the postglacial sediment varies with depth, with finer sediment being found at greater water depths. Only weak trends are present in the vertical distribution of grain size in the cores. The postglacial sediment adjacent to the contact with the glaciolacustrine clay is generally coarser than the sediment in the middle part of the postglacial sequence. Toward the top of the unit, the texture of the sediment again increases. However, some of the cores, particularly those from the deep-water part of the basin that do not bear evidence of water drawdown during the Lake Stanley low-water stage, show a continuous coarsening upward trend from the glaciolacustrine clay.

57 The postglacial sediment generally has a lower carbonate content than the glaciolacustrine clay. Since the postglacial sediment largely consists of reworked glacial and glaciolacustrine sediment (Thomas et al. 1973), the carbonate content is likely diminished through weathering on land and solution with slower sedimentation. The low calcite/dolomite ratios in the postglacial sediment may be a reflection of this process since calcite is more soluble than dolomite (Chilingar 1956). Carbonate values show considerable variability, but are correlated with sediment texture. The calcite/dolomite ratios are inversely correlated with sediment texture.

The grey colour of the postglacial sediment is likely due to the reduction of iron minerals by decomposing organic matter. The concentration of organic matter in the sediment increased during postglacial time as a result of greater biological productivity in and adjacent to the lake and as a result of lower sedimentation rates. Stratification of the water during part of the year may also contribute to the creation of reducing conditions. Organic carbon analyses of the postglacial sediment in M-core (Figure 15) show an increase in organic carbon from 1.59fc at the glaciolacustrine contact, to over 5*^ in the youngest sediment. The postglacial sediment in all of the other cores contains organic matter, either as wood, peat, or disseminated plant debris. The iron sulphide stains and bands present in most of the postglacial sediment represent reduced iron and hematite (Hough 1958).

Mineralogical analyses of the postglacial sediment in M-core indicate the presence of quartz, feldspar, carbonate, amphibole, and clay minerals. Illite and chlorite are the most abundant clay minerals, whereas kaolinite, montmorillonite, and mixed-layer minerals occur in smaller quantities. The postglacial sediment contains the same clay mineral assemblage as the glaciolacustrine clay except that kaolinite is less abundant This may reflect dilution of the reworked glaciolacustrine sediment by sediment from other sources.

EVIDENCE FOR A LOW WATER STAGE

The echograms and the sediments in the cores indicate that during late-glacial or early postglacial time, the water in the Mackinac basin was drained to a low level, much below the level occupied by Main Lake Algonquin and present-day Lake Huron. The decrease in water levels resulted from the opening of isostatically depressed outlets east of Georgian Bay as the glacier retreated northward during Late Wisconsinan deglaciation (Harrison 1972). The lowest lake level established in the Mackinac basin is known as Lake Stanley (Hough 1955).

58 Cores taken from a water depth greater than 107 m contain a gradational contact between the predominantly red glaciolacustrine clay and the grey postglacial sediment. No evidence of an increase in the grain size of the sediment corresponding to low-water levels is present in the transitional zone between the glaciolacustrine clay and the postglacial sediment

In core 22, from a water depth of 107 m, the contact between the glaciolacustrine clay and the postglacial sediment is marked by a 15 cm thick band of silt containing minor amounts of disseminated plant detritus. The contacts with the underlying glaciolacustrine clay and the overlying postglacial sediments are gradational. These silts likely represent deposition during the Lake Stanley low-water stage.

Cores 19B and 18, from a water depth of 30.5 m and 68 m respectively, contain an erosional contact between the glaciolacustrine clay and the overlying postglacial sediment. The contact zone contains a band of sand with mollusc shells. The majority of the gastropods in the sand are Valvata tricarinata (Say), Valvata sincera (Say), and Valvata sincera helicoidea (Dall). Several Gyraulus parvus (Say), Amnicola limosa Say), and Probythinella lacustris (Baker) were identified. The pelecypods include Pisidiwn spp., Sphaeriwn spp., and Unionid clam. Although these molluscs inhabit a range of water depths, they are predominantly shallow-water dwellers found at depths of less than 15 m (Clarke 1981; La Rocque 1967, 1968). The molluscs, the coarse-grained sediments, and the unconformable contact provide definitive evidence of low-water conditions.

Since no cores were retrieved from water depths between 68 m and 107 m, the water depths at coring sites

18 and 22 respectively, the limit of the erosional unconformity cannot be determined. From the cores, the minimum depth to which erosion is known to have occurred is 73 m below present lake level. This value is based on the depth below lake level for the erosional unconformity in core 18.

The echograms allow a more precise limit to be placed on the erosional unconformity in the sediments. At many locations in the basin, a strong reflector overlies and truncates the hummocky surface of the glaciolacustrine clay, and is overlain by postglacial sediment. The strong reflector is either the surface of the glaciolacustrine clay

59 that was exposed subaerially during the low-water stage or shallow-water sands deposited during the same event.

Toward the shore, the truncation of the glaciolacustrine clay becomes more pronounced and the intensity of the reflection from the unconformity increases. Eventually, the entire acoustic pulse is reflected from the unconformity and the underlying glaciolacustrine clay is completely obscured. In deeper water, erosion of the glaciolacustrine clay is less evident and the intensity of the reflection from the zone between the glaciolacustrine clay and the postglacial sediment decreases. Figure 23 illustrates the erosional unconformity and shows the relationship between water depth and the development of the unconformity. In Figure 23A, truncation of the glaciolacustrine clay occurs at a depth of 65 m, whereas in Figure 23B, it occurs at 75 m. The two sites are located in the western part of the Mackinac basin where wave-base would have been shallower during the Lake Stanley low-water stage, due to a limited fetch

(assuming prevailing westerly winds). Consequently, the depth to which the glaciolacustrine clay is eroded approximates the lowest water level reached by Lake Stanley.

In other parts of the basin, at water depths between 107 m and 75 m, the glaciolacustrine clay exposed at the lake bottom shows evidence of erosion. It is possible that some of the erosion is of recent origin, but based on the great depth to which the erosion is present, it likely occurred during the Lake Stanley low-water stage. Variations in the depth to which the glaciolacustrine clay is eroded are a function of wave-base. Areas exposed to a long fetch are eroded to a greater depth, due to the generation of larger waves. This may explain why the glaciolacustrine clay is generally eroded to a greater depth in the eastern part of the basin.

Along the inshore zone, at water depths of usually less than about 75 m, but sometimes as deep as 107 m, the glaciolacustrine clay is extensively eroded and becomes completely obscured by a strong reflector consisting of silty sand, sand, and sand and gravel. Sand and gravel are presently being transported and deposited in the shallow parts of the inshore zone, but where the coarse-grained sediments are found offshore, at water depths greater than about 33 m (a value based on data presented by Sly (1978) on the potential influence of wind waves on bottom sediments), they were likely deposited during the Lake Stanley low-water stage. Thus, the effects of the low-water event are still evident in the distribution of the surface sediments in the Mackinac basin.

60 sisr*. 49

59

CD 69

79

Km 0 1 2 3 1 1 i i A

CD "CDk—

69

79 ^l?^gg^^ Gl

Km

B Figure 23. Erosional unconformity between the glaciolacustrine clay and the postglacial silt. Erosion of the glaciolacustrine clay increases towards the shore (to the right). The strength of the reflection from the unconformity also increases shoreward, causing the glaciolacustrine clay to be obscured. Legend:- Gl, glaciolacustrine; Pg, postglacial.

61 From the echograms, it is estimated that the level of Lake Stanley was 75 m below present lake level or at an elevation of 101 m. This is the uplifted level. The post-Main Lake Algonquin uplift on Mackinac Island is 63 m (Landes et al. 1945). Along the isobase that passes through Mackinac Island and the middle of the Mackinac basin, it was determined that 25*^ of the post-Main Lake Algonquin uplift occurred by the time of Lake Stanley (Hough

1962). The Lake Stanley shoreline has thus been uplifted approximately 47 m. Therefore, the original level of Lake

Stanley was 54 m. This value compares favourably with the estimate of 58 m provided by Hough (1962).

DATING OF SEDIMENTS

The late-glacial and postglacial chronology of sedimentation was determined by palynologic and paleomagnetic analyses. The two techniques are independent of one another, although both rely on radiocarbon datingfor their absolute chronologies. Both analyses were carried out on the sediments of M-core, and thus the correlativity of the two techniques can be evaluated. In addition, two radiocarbon dates were obtained on disseminated microscope size organic material in the glaciolacustrine and postglacial clay.

The site of M-core is located in the deep part of the Mackinac basin where sedimentation has been continuous since late-glacial time. The chronology of sedimentation derived from the palynologic and paleomagnetic analyses is applicable to all deep-water parts of the Mackinac basin.

The assumptions of and problems inherent to radiocarbon dating have been discussed by Godwin (1969),

Turner et al. (1983) and McAndrews (1984). The possible sources of error present in pollen diagrams compiled from pollen deposited in large lakes have been considered by McAndrews and Power (1973), Maher (1977), Davis and

Brubaker (1973), McAtee (1977), McAndrews (1972) and Davis (1969). The principles and shortcomings of the paleomagnetic dating technique are discussed by Greer and Tucholka (1982), Banerjee et al. (1979), Mothersill (1979,

1981, 1985), and Johnson and Fields (1984).

Palynologic Chronology

Five horizons on the pollen percentage diagram (Figure 24) were assigned dates based on correlations with dated profiles. Table 3 lists the pollen diagrams used to interpret the pollen profile for the Mackinac basin. The

62 Figure 24. Mackinac basin, M-core, pollen percentage diagram. In back pocket.

63 Table 3. Dated pollen diagrams used to interpret the pollen profile from the Mackinac basin

Marker Horizon Location Age (years B.P.) Source

Spruce Peak Kincardine, Ontario 11 200+170 Anderson 1971 Minesing Basin, Ontario 10 280 i 100 Fitzgerald 1982 Sault Ste. Marie, Ontario 9500 Saamisto 1974 Manitoulin Island, Ontario 11 000-10 500 A 11 000-8000 Warner et aL 1984 Eastern Upper Michigan 9880 i 135 Futyma 1982 Spruce-Pine Transition An average for six sites in southwestern 10600 Anderson 1971 Ontario Edward Lake, Ontario 10550 McAndrews 1981 Georgian Bay, Ontario 9500 Tovell et al. 1972 Manitoulin Island, Ontario 10500 Warner et al. 1984 Eastern Upper Michigan 9500 Futyma 1982

Vesuburg Bog, Lower Michigan 10 328 i 436 GUliam et al. 1967

Abbies Peak Kincardine, Ontario 10600+150 Anderson 1971

Edward Lake, Ontario 10550 McAndrews 1981

Vesuburg Bog, Lower Michigan 10 328 i 436 GUliam et al. 1967

Pine Peak Edward Lake, Ontario 9000 McAndrews 1981

Kincardine, Ontario 9000 Anderson 1971

Manitoulin Island, Ontario 10000-8000 Warner et al. 1984

Eastern Upper Michigan 9000 Futyma 1982 First Hemlock Rise Edward Lake, Ontario 7670 McAndrews 1981

Vesuburg Bog, Lower Michigan 7982 Gilliam et al. 1967

Minesing Basin, OnUrio 6170 i 100 Fitzgerald 1982

Beaver Island 7200 Kapp et al. 1969

Eastern Upper Michigan 5000 Futyma 1982

Second Hemlock Rise Eastern North America 3000 Davis 1981

Southwestern OnUrio 3500 Anderson 1971

pollen horizons identified on the pollen diagram from the Mackinac basin and the dates assigned to them are as

follows: the spruce-pine transition, 10 500 years B.P.; the pine maximum, 9000 years B.P.; the hemlock rise, 7600

years B.P.; the hemlock decline, 4800 years B.P.; and the resurgence of hemlock, 3500 years B.P.

64 Paleomagnetic Chronology

The paleodeclination and paleoinclination curves (Figure 25) were compiled and interpreted by J.S.

Mothersill. The marker horizons were identified and the dates assigned according to the type curves compiled by

Greer and Tucholka (1982). The interpretations above three metres in the core are considered more reliable than those lower in the sediment sequence (J.S. Mothersill, personal communication, 1985). However, all correlations should be considered tentative since an unknown thickness of sediment was not retrieved with the piston corer. A gravity core, collected simultaneously with the piston core, should contain the youngest sediment, but was not analyzed for paleomagnetics. The chronology inferred from paleomagnetics is generally younger than that determined by palynological analysis.

Radiocarbon Dates

The organic carbon content in the sediments in M-core is low, averaging t.5% in the glaciolacustrine clay and rising to 5^o in the postglacial clay at the top of the core (Figure 15). In order to obtain sufficient organic carbon for dating, it was necessary to use a considerable length of sediment core. The time span represented by the sampled interval is dependent on the sedimentation rate. In the postglacial clay, the sediment sample may encompass many years of sediment deposition, since sedimentation rates were low. In the glaciolacustrine clay, however, the sampled interval may represent only a few years, due to high sedimentation rates. The obtained date is the average age for the accumulation of the sediment and is assigned to the mid-point of the dated section.

The dated sample from the postglacial clay includes sediment from O to 2 cm, 4 to 10 cm, and 12 to 13 cm in the core. These three sediment intervals were combined to make one sample. The second date was obtained on glaciolacustrine sediment from the 1266 to 1300 cm level.

The organics in the postglacial clay yielded an age of 3,440 ± 390 years B.P. (WAT-1177). This confirms the findings of the pollen and paleomagnetic analyses, that a portion of the most recent postglacial clay was not sampled by the piston corer. The radiocarbon date is closer to the dates assigned to the upper part of the core using pollen stratigraphy, and since the "hard-water effect" is likely negligible in the carbonate-impoverished postglacial clay, it is thought to be reasonably valid.

65 Figure 25. Paleomagnetic logs and time scale. in back pocket.

66 A date of 11,810 ± 520 years B.P. (WAT-1179) was obtained on the glaciolacustrine clay sample. The accuracy of the radiocarbon date could not be evaluated against the pollen and paleomagnetic chronologies, since it was not possible to assign dates to the lower portion of the core using these two dating techniques. However, in the context of the regional late-glacial chronology, the date appears to be too old. Contamination by "old" carbon or by "hard-water" is likely responsible for the apparent old age of the sample. The "hard-water effect" would be more pronounced in the glaciolacustrine clay since the carbonate content is greater than in the postglacial clay.

Chronology of Sedimentation

The palynologic and paleomagnetic chronologies differ substantially (Figure 26). Although both rely on radiocarbon dating, the identified pollen horizons have been dated at many locations using different types of organics,

whereas the paleomagnetic type curves for the Great Lakes region are based entirely on a group of radiocarbon dates

obtained on sediments from two Minnesota lakes (Banerjee et al. 1979). Due to the form of the paleomagnetic curve

and the spread of points along the curve, there is considerable subjectivity involved in identifying specific marker

horizons, particularly when sediment recovery is incomplete. Changes in the abundance of palynomorphs on a pollen

diagram are usually well defined and unidirectional, and thus the identification of pollen horizons is less subjective.

The lower part of the palynologic chronology correlates better with the sediment stratigraphy in the core

and the regional deglaciation history than does the paleomagnetic chronology. On the basis of sedimentary properties

and reflection characteristics on the echograms, it was determined that the red laminated sediment is glaciolacustrine

in origin, whereas the overlying greyish sediment was deposited during postglacial time. In M-core, the contact

between the glaciolacustrine clay and the postglacial sediment occurs at 6.88 m. The date for this contact, based on

the palynologic chronology, is 10 200 years B.P., a date of about 9000 years B.P. was determined by paleomagnetic

correlation. The date derived by palynologic analysis is believed to be accurate, whereas the paleomagnetic date

appears to be too young.

Over the entire late-glacial and postglacial sediment sequence, the paleomagnetic chronology is younger than

the palynologic chronology. The palynologic chronology is thought to be more accurate because it correlates better

with the sequence of regional late-glacial events. Consequently, it is used to date the sediment sequence in M-core.

67 M -core Stratigraphy Palynologic Paleomagnetic Chrorlology (Yrs BP) Chror lOlogy(YrsBP)

0 — Homogeneous 2,000 1 Postglacial 3,500 5,000 Clay "~ 3,000 — 6,000 t 4,000 7,000 — 5,000 3 MM* 8,000 — 6,000 9^)00 4 — Faintly Laminated

Postglacial 7gOOO MM* 5 — Clay

8.0OO •MM* —w 6 0) l— 10,000 QJ 9,000? J. 7 CD Thickly b Laminated 10,500 0 8 c Glaciolacustrine Clay Q. Q MM* OB 8 Thinly 10 Laminated

11 Glaciolacustrine Clay

12

13

14 Mottled Glaciolacustrine 15 Clay

16

17

18

Figure 26. Comparison of palynologic and paleomagnetic chronologies.

68 Although not confirming the absolute accuracy of the palynologic chronology, the radiocarbon date from the top of the core provides support for its reliability.

The chronology of sedimentation and sedimentation rates can only be determined for the upper part of M- core because dating control is absent in the older sediment. In total, five dates were assigned to the sediment sequence. The age versus depth diagram in Figure 27 was used to interpolate dates between the dated pollen horizons. The ages of the five dated horizons are connected with lines whose slopes are equal to the average rate of sedimentation for each stratigraphic interval. Sedimentation rates for each interval are plotted on the right hand column in Figure 27. Sedimentation rates in the Mackinac basin are very much depth dependent as was discussed in a previous section. Thus, the sedimentation rates determined for the sediments in M-core can only be considered representative of the deep-water areas.

Although the palynologic chronology does not extend into the glaciolacustrine sediment, it is possible to estimate glaciolacustrine sedimentation rates. The echograms indicate that approximately 30 m of glaciolacustrine clay are present at the site of M-core. Since the Two Rivers - Onaway ice advance occurred after 11 850 years B.P.

(Broecker and Farrand 1963), and most probably covered the entire Mackinac basin, the site of M-core could not have become ice free until about 11 000 to 11 500 years B.P. Based on a date of about 10 200 years B.P. for the termination of glaciolacustrine sedimentation (Figure 26), the glaciolacustrine sediments accumulated over a span of 1,000 to 1,300 years. The average sedimentation rate would have been 2 to 2.3 cm per year. The distinctly laminated portion of M-core, form 902.5 to 1231 cm, contains 157 pairs of red and grey laminae. If these pairs are interpreted as annual deposits, then the average rate of sedimentation was approximately 2 cm per year. Thus, the estimated average rate of sedimentation for the entire glaciolacustrine clay sequence appears reasonable.

The sediment interval from 8.0 to 3.62 m, dated between 10 500 and 9000 years B.P., has an average sedimentation rate of 2.79 mm per year (Figure 27). This value is not very representative of the sedimentation rate during this time, since the rate was probably very variable. The lower part of this interval consists of glaciolacustrine clay which accumulated rapidly, whereas during the deposition of the upper part of the unit, sedimentation rates were much lower than the average rate. The pollen concentration diagram (Figure 28) shows uniformly low pollen

69 1000's of Years B.P Sedimentation Rate(mmvyr) Logarithmic Scale Stratigraphy 10 11 12 01 05 10 5 10 30 5 l r r 0•32mm/yr 0-56mmfyr r Hemlock Rise O SQmm/yr Pine Peak

279 418cm in 150Oyr mm/yr r

Spruce-Pine Transition-

10 Thinly Laminated Glaciolacustrine Clay

12 23 cm/yr 13

Mottled GlacioJacustrine

15 Clay

16 17 r 18

Figure 27. Age versus depth diagram and average sedimentation rates for sediment intervals in M-core. Left, age

versus depth diagram. Right, average sedimentation rates.

70 Figure 28. Mackinac basin, M-core, pollen concentration diagram. In back pocket.

71 concentrations in the glaciolacustrine clay, but upward from the glaciolacustrine-postglacial clay contact, pollen concentrations rise steadily to approximately the 3.62 m level in the core. If the changes in pollen concentrations largely reflect changes in sedimentation rates, not pollen influx, then it can be concluded that sedimentation rates were high during the deposition of the glaciolacustrine sediment, but decreased steadily during the early postglacial period.

According to the chronology, glaciolacustrine clay deposition ceased about 10 200 years B.P., after which, greyish, faintly-laminated postglacial sediment began to accumulate. The transition from glaciolacustrine to lacustrine sedimentation occurred as the water levels in the Mackinac basin were being lowered to the Lake Stanley low-water stage. The rate of the drawdown and the time the lowest water level was reached is uncertain. Organics that accumulated during the Lake Stanley low-water stage have been dated 9260 ± 290 to 8310 ± 130 years B.P.

(Anderson 1978) and 9370 ± 180 to 8460 ± 180 years B.P. (Anderson and Lewis 1974). However, dates as old as

9930 i 250 and 9940 ± 160 years B.P. have been obtained on organics related to the low-water event (Tovell 1978).

An indication of the timing of post-Main Lake Algonquin drawdown of water can be obtained from the late- glacial events in the Lake Superior basin. The Au Train-Whitefish outlet, which drained the post-Duluth lakes, was graded to a water level in the Michigan basin 10 m below that of the Sheguiandah level (Drexler 1981). The Au

Train-Whitefish outlet was abandoned when the Marquette ice retreated from the Grand Marais moraine and allowed the post-Duluth lakes to discharge into Lake Minong in the eastern part of the Lake Superior basin. The retreat from the Grand Marais moraine occurred about 9800 years B.P. (Drexler et al. 1983). Thus, by 9800 years B.P., the water level was well on its way to the Lake Stanley low-water stage.

Clayton (1983) and Teller and Thorleifson (1983) have documented two periods of catastrophic outflow from

Lake Agassiz to the Lake Superior basin which would have discharged into the Lake Huron basin. The first drainage event occurred during the Moorehead Phase of Lake Agassiz, about 10 800 to 9900 years B.P. (Teller and

Thorleifson 1983), when Main Lake Algonquin and the post-Main Lake Algonquin lakes occupied the Lake Huron basin. The second period of discharge occurred around 9500 years B.P. (Teller and Thorleifson 1983), during the

Nipigon Phase of Lake Agassiz, when the water in the Lake Huron basin was at the Lake Stanley low-water level.

72 Considering the magnitude of the Lake Agassiz discharge events, their effects might be expected to be felt in the

Lake Huron basin and recorded as a change in sedimentation. Assuming that the chronology determined for the sediment in M-core is correct, evidence for the Moorehead Phase drainage event may be present in the sediment record of the Mackinac basin. The thickly-laminated upper part of the glaciolacustrine clay unit in M-core, containing a lamina of silt, may represent an increase in the influx of sediment as a result of increased outflow from the Lake

Superior basin. Similarly, the upper portion of the glaciolacustrine clay sequence in cores PC-2 and 22 may have been deposited during the same event. Sediments associated with discharge from the Nipigon Phase of Lake Agassiz were not identified. Perhaps this discharge event entirely by-passed the Mackinac basin through the North Channel, since during the Lake Stanley low-water event, it is believed that outflow from the Lake Superior basin did not enter

the main part of the Lake Huron basin (Sly and Lewis 1972).

The sediment interval from 3.62 to 2.8 m is dated at 9000 to 7600 years BP. During this time, the average sedimentation rate was 0.59 mm per year (Figure 27), about five times lower than in the underlying sediment unit.

The pollen concentration diagram (Figure 28) shows that the influx of pollen levelled off during this interval and did not change substantially during the remaining postglacial period. This suggests that sedimentation rates stabilized, a fact that is supported by the sedimentation rate calculations (Figure 28). Faintly-laminated postglacial clay continued to be deposited as the water level rose in response to the isostatic uplift of the North Bay outlet.

From 2.8 to 1.22 m, sedimentation rates decreased only slightly to 0.56 mm per year (Figure 27). The interval is dated at 7600 to 4800 years B.P., during which time water levels continued to rise, until drainage began through the Port Huron and Chicago outlets, and the Nipissing phase was initiated. The faintly-laminated grey clay accumulated about 5800 years B.P., after which, predominantly homogeneous grey clay was deposited.

Between 1.22 and 0.8 m, the sedimentation rate decreased to 0.32 mm per year (Figure 27). This interval, bracketed by dates of 4800 and 3500 years B.P., encompasses the period from the Nipissing to the Algoma phase, when downcutting of the Port Huron outlet lowered the water level and caused the abandonment of the Chicago outlet The sedimentation rate in the upper part of the core could not be determined, but it is expected that the rate

73 did not change substantially. A sedimentation rate of 2.2 mm per year has been calculated for the deposition of recent

sediments in the Mackinac basin (Kemp and Harper 1977).

SUMMARY

The Mackinac basin may have been deglaciated during the Two Creeks Interstadial as suggested by the

presence of sub-till sediments of St. Joseph (Karrow 1982), Cockburn (Chapman and Putnam 1984), and Great Duck

Islands (Davidson 1976). However, the sediments may have accumulated during an earlier or later deglaciation since

their age is unknown.

Following the Two Creeks Interstadial, the ice readvanced over previously deglaciated terrain (Figure 29).

In the Lake Michigan basin, the Two Rivers ice advance overrode the Two Creeks forest bed about 11 600 years

B.P. (Broecker and Farrand 1963), while northeastern Lower Michigan was synchronously affected by the

southeasterly advancing Onaway ice. The orientation of the Les Cheneaux drumlins, along the south coast of the

eastern part of the Upper Peninsula of Michigan, indicates they were also formed by an ice advance to the southeast.

These drumlins can be traced into the Mackinac basin for 10 km until they become obscured by glaciolacustrine and postglacial sediments. They are believed to continue for an unknown distance further into the basin. The similarity

in the orientation of the Les Cheneaux drumlins and the direction of Greatlakean ice flow in northeastern Lower

Michigan suggests that the same ice advance was involved. Since the southeastern margin of the Onaway advance

in northeastern Lower Michigan is placed between Alpena and Tawas City (Burgis 1977), it appears that the entire

Mackinac basin was glaciated during this period.

Following the Two Rivers-Onaway advance, the ice in the Lake Huron basin retreated northward and the

Mackinac basin was inundated by Main Lake Algonquin or water rising up to the Main Lake Algonquin level.

Deglaciation of the Mackinac basin could have begun between 11 500 and 11 000 years ago. During this retreat, the

Superior ice lobe was separating from the Algoma ice to the northeast and a reentrant in the ice front developed south of Sault Ste. Marie (Karrow 1983) (Figure 30). The Algoma ice is believed to have readvanced a short distance to the south-southwest, depositing the youngest till and forming the south-trending drumlins on St. Joseph and

Drummond Islands (Karrow 1983). The glacial deposits on Cockburn and Great Duck Islands may have also been

74 Figure 29. Position of the ice margin during the Two Rivers-Onaway ice advance about 11 500 years B.P. Sources:

Hough 1958; Prest 1970; Black 1976; Chapman and Putnam 1984.

75 Figure 30. Retreat of the Two Rivers-Onaway ice from the Mackinac basin about 11 000 years B.P. Sources: Hough

1958; Prest 1970; Chapman and Putnam 1984.

76 deposited during this readvance of the Algoma ice. The southward extent of this ice advance into the Mackinac basin has not been defined. The topography south of Drummond and Cockburn Islands the readvance of the Algoma ice.

As the Mackinac basin was uncovered following the Greatlakean ice advances, glaciolacustrine sediment

was deposited conformably over the irregular surface of the bedrock and glacial deposits. Sedimentation was rapid,

since more than 35 m of glaciolacustrine sediment accumulated in the central part of the basin. The oldest

glaciolacustrine sediment was likely deposited proximally to the ice margin to account for its coarse-grained texture

and the ice-rafted debris. As the ice retreated from the basin, predominately very fine-grained sediment accumulated,

the laminated structure of portions of the glaciolacustrine clay may represent the fine-grained equivalent of classical

varves.

The upper portion of the glaciolacustrine sequence in some of the cores consists of thickly laminated clay.

Laminae of silt and bright red clay are characteristically present in this unit. The reason for the change in

sedimentation is uncertain. One possibility is that the change in sedimentation was caused by a glacial advance. The possibility is that the change in ice could not be the cause, since its effects would have been recorded early in the glaciolacustrine sequence. The marquette advance in the Lake Superior basin, dated at about 10 000 years B.P.

(Drexler et al. 1983) terminated on the Upper Peninsula of Michigan. Glacial meltwater discharge from this advance could be the sediment source for the upper part of the glaciolacustrine sequence. Another possibility is that theupward part of the sequence documents the drawdown of water from the Main Lake Algonquin level to the Lake Stanley

low-water stage. A third, more plausible explanation, is that the upward coarsening sequence was caused by the

catastrophic draining of water from the Moorehead Phase of Lake Agassiz between 10 800 and 9900 years B.P.

(Teller and Thorleifson 1983), when the water in the Lake Huron basin at the Main Lake Algonquin and the post-

Main Lake Algonquin levels. A combination of the latter two explanations is also a possibility.

The Mackinac basin was deglaciated rapidly. The Algoma ice stood at the Whiskey Lake Moraine during

the Main Lake Algonquin stage and had retreated to at least the Cartier HI Moraine during the Post-Main Lake

Algonquin lake stages (Boissonneau 1968). The Superior ice lobe front retreated an unknown distance into the Lake

Superior basin, beginning about 11 500 years B.P. (Drexler et al. 1983), although the quantity of glaciolacustrine

77 sediment carried into the Mackinac basin would have already diminished during the earlier retreat of the Algoma ice. The glacioiacustrine-postglaciaJ sediment contact is dated at 10 200 years B.P. using the palynologic chronology, which is only slightly too old according to the regional late-glacial chronology.

During the transition from glaciolacustrine to post glacial sedimentation, the water in the Mackinac basin was dropping toward the Lake Stanley level. As water levels fell, discharge from the Lake Superior basin, draining through the outlet at Sault Ste. Marie, by-passed the Mackinac basin via the North Channel (Sly and Lewis

1972)(Figure 31). Water in the lake Michigan and Huron basins became separated through the straits of Mackinac.

Outflow from the Lake Michigan basin was carried by a river which may have re-excavated the bedrock valley in the Straits of Mackinac and discharged into the Mackinac basin northeast of Bois Blanc Island, the Mackinac basin was connected to Manitoulin basin by a constricted body of water across the Thunder-Duck Sill. The elevation of the Thunder-Duck Sill, between the Duck Islands and Lower Michigan, is sufficiently low that the water in the

Mackinac and Manitoulin basins would have been at the same level during the Lake Stanley low-water stage.

Outflow from the Mackinac basin passed through Mississagi Strait, to the North Channel, and eastward into Lake

Hough, the low-water equivalent in Georgian Bay (Sly and Lewis 1972).

Lake Stanley had a pre-uplift elevation of approximately 54 m. Isostatic uplift has raised its shoreline about

47 m, to an elevation of 101 m. During the Lake Stanley low-water stage, all areas in the basin situated at presentwater depths of less than about 75 m were dewatered, whereas shallow-water sediments were deposited to a water depth of at least 107 m. Deeper portions of the basin do not contain a record of low-water conditions.

The water level in the Mackinac basin was dropping while glaciolacustrine sediments were still being deposited. Regression of the water must have caused some of the previously deposited glacial and glaciolacustrine sediment to be eroded. This sediment would have been deposited in the upper part of the glaciolacustrine sequence in the deep-water areas. Erosion of the glacial and glaciolacustrine sediment and the deposition of the shallow-water sediment in areas where fine grained sediment is presently accumulating, continued during the extended period of

Lake Stanley (9500 to 5500 years B.P.) when water was slowly transgressing over perviously exposed areas. In the deep water areas, it is difficult to define precisely which sediment unit was deposited during the Lake Stanley low-

78 Figure 31. Lake Stanley low-water phase in the Lake Huron basin about 9500 years B.P. Sources: Hough 1955,1958; Prest 1970; Sly and Lewis 1972.

79 water phase. According to the dates assigned to the sediment sequence in M-core, most of the faintly laminated postglacial clay accumulated during this period, on the echograms, this sediment corresponds to the portion of the postglacial unit containing faint, closely spaced, discontinuous reflections.

During early postglacial time, sedimentation rates declined, and by 9500 to 9000 years B.P., they had stabilized at a rate that decreased only slightly to the present Sedimentation has been most rapid in the bathymetric lows where a maximum of 13 m of postglacial sediment has accumulated. The sediment deposited in the Mackinac basin during postglacial time has been derived from the erosion of glacial and glaciolacustrine deposits in the basin and from the surrounding land (Thomas et al. 1973). Increased biological productivity in and adjacent to the basin and slower sedimentation rates have increased the concentration of the organic matter has caused the reduction of iron minerals, imparting the grey colour to the postglacial sediment.

By about 5500 years B.P., the North Bay outlet was uplifted to the elevation of the Port Huron and Chicago outlets and the Nipissing phase was initiated (Figure 32). Continued uplift of the North Bay outlet led ti its abandonment, and by 4700 years B P., Nipissing drainage was completely transferred to the southern outlets (Lewis

1969). As the Fort Huron outlet was downcut and water levels fell, the bedrock-floored Chicago outlet was abandoned. During the downcutting of the Fort Huron outlet, at about 3000 years B.P. (Karrow 1982), the Algoma beach was formed in the Lake Huron, Michigan and Superior basins. Continued downcutting of the Port Huron outletlowered the water in the Mackinac basin to its present level. Since the Nipissing phase, grey, homogeneous postglacial clay has been accumulating in the topographic lows of the Mackinac basin. The postglacial sediment presently forms a discontinuous cover over the irregular surface of glacial and glaciolacustrine deposits.

CONCLUSIONS

1. Four lithologic units were mapped: undifferentiated till or bedrock, glaciolacustrine clay, postglacial clay

and postglacial silt. Till or bedrock is exposed around the periphery of the basin and adjacent to the Duck

Islands. Toward the centre of the basin, glaciolacustrine clay conformably overlies the till or bedrock and

is discontinuously covered by postglacial clay, usually overlying glaciolacustrine clay.

80 Figure 32. The Nipissing phase (three outlet phase) about 5500 years B.P. Sources: Hough 1958; Prest 1970; Karrow

1984.

81 2. Based on a similarity in colour with tills in northeastern Lower Michigan, the till in core 18 may be of Port

Bruce age, whereas the till in core 19B may be of Port Huron of Greatlakean age. The age of the till in core

21 is unknown.

3. The reddish-brown colour of the till in core 19B and the predominately red colour of the glaciolacustrine

clay likely reflects a sediment source in the Lake Superior basin.

4. The average grain size of the glaciolacustrine clay decreases with an increase in water depth. Total

carbonates vary directly with texture, whereas the calcite/dolomite ratio varies inversely with texture, the

organic carbon content is low, averaging about 1.596. The laminated structure of the glaciolacustrine clay

may represent the fine-grained equivalent of classical varves. the grey laminae may be the summer layers,

and the red laminae the winter layers. The former have a coarser texture and a lower calcite/dolomite ratio

than the latter.

5. The texture of the postglacial sediment varies directly with water depth. Pronounced trends in the vertical

distribution of the grain size are lacking, although in cores taken from water depths of less than 107 m, the

sediment adjacent to the contract with the glaciolacustrine clay is coarser grained than in the remainder of

the unit This sediment was likely deposited during the Lake Stanley lo w-water phase. The carbonate content

in the postglacial sediment generally varies directly with sediment texture, whereas the calcite/dolomite ratio

shows an inverse relationship with texture. The grey colour of the postglacial sediment is believed to be

imparted by iron minerals which have been reduced through the decomposition of organic matter. The

organic carbon content in the postglacial clay ranges from 1.5 92? at the glaciolacustrine-postglacial clay

contact, to about 59fc near the top of the sediment sequence.

6. The mineralogy of the clay fraction in the glaciolacustrine clay and post glacial clay is similar. Quartz,

feldspar, carbonate, amphibole and clay minerals are present in both units. Illite, chlorite and kaolinite are

the most abundant clay minerals in the glaciolacustrine clay, whereas illite and chlorite dominate in the

82 postglacial clay, with kaolinite being less abundant Minor amounts of montmorillonite and the mixed-layer

minerals are present in both sediments.

7. The chronology of glaciolacustrine and postglacial sedimentation was determined by palynologic and

paleomagnetic stratigraphic correlation, the palynologic chronology is believed to be more accurate because

the marker horizons are better formed and have been more reliably radiocarbon dated. The palynologic

chronology also correlates better with the regional late-glacial chronology and thus has been used to date

the sediment in the Mackinac basin. A date of 10 000 years BP. was determined for the glaciolacustrine-

postglacial sediment contact, which is slightly too old according to ages determined for other regional late-

glacial events. Grey, faintly laminated postglacial sediment accumulated until about 5800 years B.P., after

which predominantly grey homogeneous postglacial sediment was deposited.

8. The radiocarbon date of 11 810 i 520 years BP. obtained on the glaciolacustrine clay sample appears to

be too old based on the regional late-glacial chronology. Contamination by "hard-water" or "old" carbon

may account for the apparent old age.

9. The youngest postglacial sediment in M-core was radiocarbon dated at 3,440 ± 390 years BP. This date

correlates well with the date determined for the same sediment interval by palynologic stratigraphic

correlation and thus is believed to be valid.

10. Sedimentation rates were high during the deposition of the glaciolacustrine sediment, averaging about 2 to

3 cm per year. The rate of sediment accumulation decreased sharply following the retreat of the glacier from

the drainage basin. The sediment interval encompassing the transition from glaciolacustrine to postglacial

sedimentation has an average sedimentation rate of 2.79 mm per year, whereas during the remainder of post

glacial time, the sedimentation rate changed from 0.59 to 0.32 mm per year.

11. Glacial and postglacial sedimentation has been concentrated in the bathymetric lows, especially along the

west-northwest to east-southeast mid-line of the basin, where the surficial sediment thickness averages 40

83 m and in places exceeds 100 m. The maximum thickness of the glaciolacustrine clay is greater than 35 m,

whereas the postglacial clay and postglacial silt have a maximum thickness of 13 m and 15m respectively.

12. The glaciolacustrine clay was deposited in Main Lake Algonquin and the post-Main Lake Algonquin lakes.

The thickly laminated, coarse textured glaciolacustrine clay, in the lower part of the glaciolacustrine

sequence, was likely deposited close to the ice margin, whereas the fine-textured, thinly laminated

glaciolacustrine clay higher in the unit, likely accumulated as the ice retreated from the Mackinac basin. The

upper pan of the glaciolacustrine clay contains lenses of silt and generally has thicker laminae and a coarser

grain size than the middle portion of the glaciolacustrine sequence, the change in sedimentation is believed

to be the result of the catastrophic draining of water from the Moorehead Phase of Lake Agassiz between

10 800 and 9900 years BP.

13. The Lake Stanley low-water phase reached its minimum level about 10 000 to 9500 years B J*, during or

shortly after the Marquette ice advance on the Upper Peninsula of Michigan. Lake Stanley had an elevation

of about 54 m. Isostatic uplift has raised its shoreline about 47 m, to an elevation of 101 m All areas in the

Mackinac basin with present water depths of less than 75 m were uncovered and thus contain an erosional

unconformity between the glaciolacustrine clay and the postglacial sediment. Shallow-water sediments were

deposited to present water depths of at least 107 m. Deeper parts of the basin do not contain a record of

low-water conditions.

14. The Thunder-Duck Sill is formed by a discontinuous bedrock high and subsequently deposited glacial and

lacustrine sediment, the Duck Islands are the emergent pan of the surficial deposits forming the northern

pan of the sill and are underlain by a bedrock depression.

15. The sub-till sediments on St Joseph Island (Karrow 1982), Cockburn Island (Chapman and Putnam 1984)

and Great Duck Island (Davidson 1976) suggest that the Mackinac basin may have been deglaciated during

the Two Creeks Interstade, but the sediment could also date from an earlier or later deglaciation.

84 16. The Two Rivers - Onaway advance is believed to have covered the entire Mackinac basin. The

southeastward trending Les Cheneaux dnunlins in the eastern pan of the Upper Peninsula of Michigan are

believed to have been formed by this advance. The drumlins can be traced 10 km lake ward from Les

Cheneaux Islands and likely extend further into the Mackinac basin, but are obscured by glaciolacustrine

and postglacial sediment

17. A south-southwesterly readvance of the Algoma ice lobe, which is thought to post-date the Two Rivers -

Onaway advance (Karrow 1983), is believed to have deposited the youngest till and formed the drumlins

on St Joseph and Drummond Islands. The glacial deposits on Cockburn Island and Great Duck Island may

also have been deposited during this readjustment in the Algoma ice margin. The north-south trending shoals

off the south shore of Drummond Island may represent submerged drumlins formed by the Algoma ice.

Similarly, the topographic highs south of Cockburn Island may be glacial landforms deposited during this

advance. The southward extent of the Algoma ice advance into the Mackinac basin could not be established

from core stratigraphy and geophysical records.

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94 APPENDIX A Great Duck Island Gas Well Log

County: Manitoulin Location: 400 metres north of Little Harbour, near Gravel Point Well Name: Great Duck Island. Driller F. and E. Randall Total Depth: 240 feet (73 metres) Year Completed: 1935 Elevation: 606 feet (185 metres)

Geological Formation Top Elevation Thickness feet (m) feet (m) feet (m)

Sand and Gravel 0(0) 606(185) 152(46.3) Boulders 152(46.3) 454(138.4) 10(3.1) Gravel and Sand 162(49.4) 444(135.4) 28(8.5) Hard day 190(57.9) 416(126.8) 40(12.2) Gravel 230(70.1) 376(14.6) 10(3.1) Loose White Sand (?) 240(73.1) 366(111.6) ?

APPENDIX B Stratigraphy of the Sediment Cores

Notes on terminology: Calcareous (calc.) - effervesces with addition of HO. Non-Calcareous (non-calc.) - does not effervesce with the addition of HCl. Hydrogen Sulphide - hydrogen sulphide gas given off with the addition of HCL No Hydrogen Sulphide - no hydrogen sulphide gas given off with the addition of HCl.

Note: The descriptions of cores PC-1, PC-2, 18, 19, 19B, 21, and 22 were obtained from core logs on files at the Geological Survey of Canada, in Ottawa. Cores H-32, P-30, 251, 305, 314, 317, and M-core were described by the author.

Core: PC-1

Sampled with: Alpine piston corer Year collected: 1969 Collected by: Canada Centre for Inland Waters Location: 45*59*48" N 84*35*30" W Described by: M. Simpson Water Depth: 30.5 metres

Depth (centimetres)

O clay; glaciolacustrine, stiff, varved, dry and crinkly 1) reddish brown (5 YR 5/3) 2) brown (7.5 YR 5/2), 5-7 mm 3) light brown (7.5 YR 6/4), sandy, 3-4 mm; calc., no hydrogen sulphide; empty cavity at 33 to 35 cm with plant debris on either side; plant debris at 64cm. 93 clay as above with varves of light grey sand (10 YR 7/2) 1-2 nun wide; very calc. at 93, 94 and 96 cm, l mm sand veins; at 103 cm plant debris, lacy root-like appearance; below 110 cm sand veins relatively sparse; at 155-163 cm, vertical band 3 mm wide of grey clay. 196 homogeneous red brown clay (5 YR 5/3); at 230 cm, 2 mm wide sand vein; sand vein at 232 cm; 3 mm sand vein at 235 cm. 248 end of core.

Core: PC-2

Sampled with: Alpine piston corer Year collected: 1969 Collected by: Canada Centre for Inland Waters Location: 45*39*05" N 83*34*01" W Described by: M. Simpson Water Depth: 122 metres

Depth (centimetres)

O fine silt, soft, wet with vague sulphide-rich veins and mottling; dark grey (4 Y 4/1); sulphide is black (5 Y 2.5/1); silt is non-calcareous, sulphide-rich; sulphide veins are slightly calcareous and give off abundant hydrogen sulphide. 48 grey silt (5 YR 5/1); calc., some hydrogen sulphide. 112 silt; with sulphide mottling; greyish-brown (10 YR 5/2); calc., hydrogen sulphide. 132 glaciolacustrine; clayey silt; reddish-brown (5 YR 5/3); calc., no hydrogen sulphide. 149 clayey silt; banded reddish-brown and greyish-brown (10 YR 5/2); no sulphides. 180.5 soft silt; brown (7.5 YR 5/2); calc. 194 clayey silt; reddish-brown (5 YR 5/3); calc

95 204 sQl; brown (7.5 YR 6/2 - 5/2); calc. 210 clayey silt; reddish-brown (S YR 5/3) with laminations of grey brown (10 YR 5/2); calc. 242 clayey silt; brown (7.5 YR 5/2). 252 clayey silt; reddish-brown (5 YR 5/3). 271 clay; very soft, wet, sticky, reddish-brown (5 YR 5/3), homogeneous; calc., no sulphide. 361 silt; homogeneous; clayey, brown (7.5 YR 5/2); calc. 374 clay; soft, wet, varved, brown (7.5 YR 5/2) and reddish-brown (5 YR 5/3); calc. 396 clay; homogeneous, brown; blebs and stringers of stiffer beige clay from 407 -410 cm. 428 soft mud; semi-fluid, silty, brown (7.5 YR 5/4); calc. 457 clay, soft, wet, sticky, reddish-brown (5 YR 5/3); calc. 541 clay; slightly silty, wet, very soft, sticky, brown (7.5 YR 5/2); calc. 593 clay; very slightly silty, faintly laminated, with varves of slightly lighter and darker reddish-brown (5 YR 5/3); at 619 cm, a 2-3 mm band of pinkish-grey clay (5 YR 6/2); calc. 626 sharp contact; glaciolacustrine clay; varved, sticky, semifirm, with horizontal varving 1) reddish-brown (5 YR 5/3), 5-30 mm wide, slightly calc. 2) brown (7.5 YR 5/2), 3-8 mm wide, slightly calc., changing slowly to grey-brown (10 YR 5/2); calc. 774 clay; as above, sticky, semifirm, varved 1) reddish-brown, 2 - 5 cm wide, calc. 2) greyish brown (10 YR 5/2), 5-20 mm wide, calc., a slip at 878 - 894 cm. 954 varved clay as above; now tricolour 1) reddish-brown (5 YR 5/3) 2) brown (7.5 YR 5/2) 3) greyish-brown (10 YR 5/2); slightly calc. 1013 tricolour clay; colour change, narrower bands and more numerous grey-brown ones. 1) reddish-brown (5 YR 5/3), 3-5 mm wide, calc. 2) greyish-brown (10 YR 5/2), 7 - 12 mm wide, non calc. 3) very thin grey (5 Y 5/1), l - 2 mm wide, calc. 1050 varved clay as above; relatively wider grey-brown bands (l cm) and reddish-brown bands (1-2 cm); brown (10 YR 5/3), calc., silty clay at 1104 - 1106 cm; bands in tricolour clay become narrower towards bottom, averaging 5 mm wide. 1127 wide bands of the tricolour clay. 1135 clay; semifirm, sticky, varved, tricolour 1) reddish-brown (5 YR 5/3), 3 - 8 cm wide, calc. 2) brown (7.5 YR 5/2), 5 - 10 mm wide, calc. 3) lighter reddish-brown (5 YR 5/3) - (5 YR 6/3), thin bands l - 3 mm, calc. 1297 clay; tricolour varved 1) reddish-brown (5 YR 5/3), 3 cm, calc. 2) greyish-brown (10 YR 5/2), l cm thick, calc. 3) slightly lighter grey- brown below greyish-brown varve, 5-8 mm, vague contacts. 1440 tricolour clay; 1) reddish-brown gradually darkens to brown (7.5 YR 5/2), calc. 2) greyish-brown (10 YR 5/2), l cm, calc. 3) lighter grey-brown bands, vague, below greyish-brown, 3-8 mm, calc. 1478 clay; varved 1) reddish-brown (5 YR 5/3) 2) brown (7.5 YR 5/2). 1504 clay as above but varves contorted. 1522 end of core.

Core: 18

Sampled with: Alpine piston corer Year Collected: 1971 Collected by: Canada Centre for Inland Waters Location: 45*30*00" N 83*23*16" W Described by: M. Simpson Water Depth: 68 metres

Depth (centimetres)

O muddy water and fluid mud; very dark greyish-brown (2.5 Y 3/2) with patches of very soft mud, very dark greyish-brown (10 YR 3/2); non-calc., slight hydrogen sulphide. 71 silty mud; soft, wet, very dark greyish-brown (2.5 Y 3/2), slight FeO-staining in cracks, slightly sticky; calc., slight hydrogen sulphide. 161 silt; soft, dark olive grey ( 5 Y 3/2), with occasional black sulphide-rich blebs and lenses (l - 2 mm); non-calc., hydrogen sulphide given off; tiny bleb of plant debris, l mm x 7 mm, at 227 cm; hard sulphide blebs at 275 and 286 cm. 304 fluid mud (muddy water), dark olive-grey (5 Y 3/2); non-calc., hydrogen sulphide. 342 sill; dive-grey (5 Y 4/2), numerous sulphide laminae, l - 7 mm wide, black (5 Y 2.5/2); tiny pebble at 354 cm (3 x 3 mm) and 374 (2x5 mm); non-calc., hydrogen sulphide. 400 silt; dark greyish-brown (2.5 Y 4/2), with few sulphide veins; sandy silt vein at 417 cm; non-calc., slight hydrogen sulphide. 432 silt; grey (5 Y 5/1) to dark grey (5 Y 4/1), semi-soft, slightly sticky, some polygonal fracturing; non-calc., slight hydrogen sulphide. 497 sandy silt with shell fragments and shells (gastropods); greyish-brown (2.5 Y 5/2); calc., no hydrogen sulphide. 513 contact; glaciolacustrine; clay, varved, tricolour 1) brown (7.5 YR 4/4), 5 - 10 mm, calc., no hydrogen sulphide 2) brown (10 YR 5/3), 3-10 mm, calc., no hydrogen sulphide 3) greyish-brown (10 YR 5/3), 5-10 mm, calc., no hydrogen sulphide; colours gradually change to brown, pinkish-grey, and reddish-brown. 590 glacial clay; colour change to 1) brown (7.5 YR 5/2) 2) slightly greyer tone; calc 613 clay; relatively homogeneous greyish-brown (10 YR 5/2); calc. 642 clay; mottled, reddish-brown (7.5 YR 5/2); cala 662 clay; clearer varving than above 1) reddish-brown (5 YR 5/3), 6 mm, calc. 2) greyish-brown (10 YR 5/2), 3 mm, calc. 670 colour change from above to tricolour 1) brown (7.5 YR 5/2), 8 mm, calc. 2) greyish-brown (10 YR 5/2), 3 mm, calc. 3) greyish-brown (2.5 Y 5/2), l - 2 mm, calc. 703 varved as above, predominantly 1) red-brown, 0.7 - 2 cm 2) grey, 3-7 mm 3) grey, 1-3 mm. 771 reddish-brown clay band, homogeneous (5 YR 5/3); calc. 780 varved clay as previously 1) brown (7.5 YR 5/2) 2) greyish-brown (10 YR 5/2) 3) greyish-brown (2.5 YR 5/2); calc. 812 same as above but colour change in brown lamination to 7.5 Y 5/2; other two colours the same; calc.

96 883 tricolour varved clay, semifirm, sticky 1) brown (7.5 YR 5/2), 5 - 20 mm 2) greyish-brown (10 YR 5/2), 3 - 5 mm 3) brown (10 YR 5/3), l - 2 mm; sand vein at 932 cm; calc. 940 clay, homogeneous, reddish-brown 5 YR 5/3 with occasional streaks of light grey (7/2); stiff clay vein, light grey 5 Y 7/2; calc. 1008 silt; grey 5 Y 5/1 - 5 Y 4/1; non-calc., slight hydrogen sulphide. 1013 fluid mud and water, greyish-brown 10 YR 5/2; calc., hydrogen sulphide. 1042 sandy silt; brown (10 YR 5/3). soft, with pebbles; starting at 1052 cm, clay content increases and colour changes to reddish-brown (5 YR 5/3); calc. 1062 clay; varved 1) reddish-brown (5 YR 5/3) 2) slightly darker reddish-brown, slightly firmer 3) slightly lighter of the same tone; calc. 1086 silt; brown (10 YR 5/3), sandy, wet, semifirm; grades into varved clay about 1100 cm. 1110 varved clay; very thin even varves 1) greyish-brown (10 YR 5/2) 2) brown (7.5 YR 5/2); semifirm, sticky; calc. 1126 clay; homogeneous, reddish-brown (5 YR 5/2); calc. 1143 varved clay, very thin varves, 3 - 5 mm average thickness 1) greyish-brown (10 YR 5/2) 2) brown (7.5 YR 5/2); at 1170 -1175 varves 1-2 mm wide; at 1175 cm varved with sandy veins; at 1186 cm, stone 18x15 mm, rounded, orange quartz and biotite; pebbles at 1200cm. 1218 contact; till; silty clay with occasional stone and pebble, greyish-brown (2.5 YR 5/2); pebbles abundant from 1218 - 1236 cm, limestone, chert, felsic igneous rock, sand present; 1280 - 1285 cm, limestone rock 5x4x5 cm, fossiliferous; many fossiliferous limestone rocks in till. 1522 end of core.

Core: H-32

Sampled with: Benthos gravity corer Year Collected: 1969 Collected by: Canada Centre for Inland Waters Location: 45*50*24" N 83*49*48" W Described by: A. Zilans Water Water Depth: 85 metres

Depth (centimetres)

1 very dark greyish-brown (10 YR 3/2) sandy silt 2 dark brown (7.5 YR 3/2) silty clay. 10 dark brown (7.5 YR 3/2) silty clay with increasing amount of brown (7.5 YR 5/4) silty clay towards bottom, giving a mottled appearance (grading into glaciolacustrine sediment). 21 brown (7.5 YR 5/4) silty clay, with lens of sand. 31 end of core.

Core P-30

Sampled with: Benthos gravity corer Year Collected: 1969 Collected by: Canada Centre for Inland Waters Location: 45*40*54" N 82*47*48" W Described by: A. Zilans Water Depth: 73 metres

Depth (centimetres)

O very dark greyish-brown (2.5 Y 3/2) sandy silt mud. 2 yellowish-brown (10 YR 5/4) sandy silt; a few pebbles; small pelecypod shells. 36 reddish-brown (5 YR 5/3) silty clay; sand streaks in upper part. 80 glaciolacustrine; laminated reddish-brown (5 YR 5/3) and greyish-brown (2.5 Y 5/2) sandy silt; few granules towards bottom and grey colour becoming dominant; bottom part is gradational from underlying till-like unit 97 silty sand with granules and pebbles, greyish-brown (2.5 Y 5/2); coarser at bottom of section, more granules and pebbles; till or till- like. 134 end of core.

Sample: 19

Sampled with: Alpine piston corer Year Collected: 1971 Collected by: Canada Centre for Inland Waters Location: 45*49*36" N 84*31*00" W Described by: M. Simpson Water Depth: 30.5 metres

Depth (centimetres)

O sandy mud; fine-grained sand, very soft, dark greyish-brown (2.5 Y 4/2), sulphide laminae at 50 cm; very slightly calc., hydrogen sulphide.

97 61.5 sandy silt; dark greyish-brown (2.5 Y 4/2), with tiny pebbles and shell fragments (?), soft, cracked, FeO staining; very slightly cala, strong hydrogen sulphide; white chalk blebs at 178 cm; patch of organic matter at 211 - 214 cm; patch of plant debris 4 mm long at 222 cm; oxidation layer at 247 cm; chalk blebs, beige white at 250 cm. 250 silt; very dark greyish-brown (2.5 Y 3/2); non-calc., hydrogen sulphide; evidence of polygonal fractures and a dark sulphide-rich patch at 300 cm. 325 sandy silt; very dark greyish-brown (2.5 Y 3/2), soft with scattered plant debris; plant debris, seedpod (?) at 352 cm, rough outer surface, black, semi-spherical 6-7 mm in diameter, vague darker-coloured band along core length: at 380 cm oxidized band along core edge; at 417 - 420 cm wood, barkless, 3.5 cm long by 5 mm wide, twig, brown-green colour, soft, wet 439 silt; oxidized to dark greyish-brown (2.5 Y 4/2), tiny pebbles throughout, sandy in spots; non-calc., very slight hydrogen sulphide; limestone pebble 1x1 cm, pale grey, friable, at 513 cm; limestone pebble at 533 cm; at 533 cm numerous FeO stained cracks; polygonal fracturing below 540 cm. 679.5 end of core (the entire core consists of postglacial sediment).

Core: 19B

Sampled with: Alpine piston corer Year Collected: 1971 Collected by: Canada Centre for Inland Waters Location: 45^50-00" N 84*32*38" W Described by: M. Simpson Water Depth: 30.5 metres

Depth (centimetres)

O sandy silt mud; very soft, very wet, dark, greyish-brown (10 YR 4/2), with wood fragments and plant debris and possibly some tiny sulphide blebs; wood fragment, 6x3 mm at 65 cm; non-calc., no hydrogen sulphide. 85 sandy silt; soft, dark greyish-brown (2.5 Y 4/2) with disseminated plant debris; l mm band of organics at 99 cm; plant debris at 110 cm; l mm band of black organic material at 113 cm; wood, 14 x 5 mm, water-logged, barkless, at 117 cm; non-calc., no hydrogen sulphide. 125 same as above but colour change to very dark greyish-brown (2.5 Y 3/2), with vague darker banding; disseminated plant debris; wood with bark, 6x7 mm, (poplar stem ? section ?) at 150 cm; wood particle 5x2 mm at 153 cm; wood particle 6x2 mm at 167 cm; non-calc., hydrogen sulphide. 175 sandy silt; with sulphide blebs and plant detritus; one side of core oxidized; unoxidized shows bands of darker silt; oxidized, dark greyish-brown (2.5 Y 4/2), non-calc., no hydrogen sulphide; unoxidized, dark greyish-brown, non-calc., strong hydrogen sulphide; wood fragment at 197 cm, peat bleb at 221 cm, wood 15x5 mm at 248 cm, peat bleb 2 mm wide at 263 cm, sulphide patch at 284 cm. 285 sharp, diagonal contact; silty clay, oxidized, greenish-grey (5 GY 5/1), sticky, semifirm; calc., no hydrogen sulphide; shell fragment at 315 cm. 318 same as above but gradual colour change to grey (5 Y 5/1); calc., no hydrogen sulphide; shell fragment at 321 cm; from 320 cm, mottled with beige and grey laminae, visible on x-ray, sand bleb at 338 cm. 338 clay, greenish-grey (5 GY 5/1), calc. 343 clay; greyish-brown (10 YR 5/2); mottling of beige and grey, calc., very slight hydrogen sulphide. 354 contact; colour change marked by sand vein 2 mm wide with sandstone fragment; clay; brown (10 YR 5/3) with mottled laminae, calc., no hydrogen sulphide; 1) greyish-brown (10 YR 5/2) 2) beige - light greenish-grey (5 GY 7/1), drier, thin 3) dark grey (5 Y 4/1), sparse and thin, 1-3 mm. 408 colour change from above - clay, greenish-grey (5 GY 6/1) with blebs of beige sand and firmer clay, grey (5 Y 6/1), dark grey (5 Y 4/1) veins, sandy, cala, no hydrogen sulphide; none at 428 cm, limestone, 4.5 x 2.5 cm, flat angular, laminated. 449 contact; low water, sandy shell layer, bivalves (l cm wide), gastropods, fragments and complete shells; grey (5 Y 6/1); limestone pebble at 450 - 452 cm., 2.5 x 2.5 x 2.0 cm, angular, calc. 456 contact; clayey silt; brown, stiff, with stiff grey clay (5 Y 6/1) blebs throughout; calc. 470 muddy water. 476 contact; silt till, many rocks and pebbles, silt matrix, brown (7.5 YR 5/4); pebble at 480 cm, soft, calc., friable, angular, laminated grey mudstone, 4x3x3 cm; at 497 cm, angular pebble, beige limestone, 2.5 x 2.5 cm. 533 end of core.

Core: 21

Sampled with: Alpine piston corer Year Collected: 1971 Collected by: Canada Centre for Inland Waters Location: 45"27 W N 82'50'06" W Described by: M. Simpson Water Depth: 121 metres

Depth (centimetres)

O silty clay, brown (10 YR 5/3), soft, wet with brown (reddish) mottling (7.5 YR 5.4); calc., no hydrogen sulphide. 40 contact, glaciolacustrine clay, brown (7.5 YR 5/2), soft, wet; evidence of very faint laminations, slightly darker and slightly lighter bands; 92 - 104 cm increasing red colour, very slightly calc., slight hydrogen sulphide. 104 clay; dark grey-brown (10 YR 5/2); calc. 120 clay; reddish-brown (5 YR 5/3); calc., no hydrogen sulphide; 138 - 141 cm, gradational colour transition.

98 141 clay; greenish-grey (S GY 5/1). faintly laminated; non-calc., very slight hydrogen sulphide. 175 interbanded grey-green and brown day, vague boundaries. 208 - gradual fade out of grey. 220 clay; 1) brown (10 YR 5/3) 2) greyish-brown (10 YR 5/2); banding very faint, sticky, semifum; fades out almost completely towards bottom; non-calc. 292 gradual colour change to brown (7.5 YR 5/2), sernifirm, sticky; very faint laminations at 350 cm; non-calc., no hydrogen sulphide. 402 - day; brown (7-5 YR 5/4) laminated pattern, 1-2 mm wide non-calc. 439 - clay; colour change to brown (7-5 YR 5/2); two tiny pebbles at 475 cm, largest is 3 x 3 mm; pebble at 484 cm; igneous, quartz, biotite, hornblende or tourmaline, 7x6 mm. 491 clay; alternating banding in two tones of brown, (7.5 YR 5/2) and (7.5 YR 5/4); semifiim, sticky; darkening from 531 cm to greyish- brown (10 YR 5/2), with occasional brown bands 2 cm wide and grey band 3-5 mm wide; non-calc. 581 varved clay; tricolour 1) olive-grey (5 Y 5/2), 3-7 mm, no calc., no hydrogen sulphide 2) greyish-brown (2.5 Y 5/2), 3-5 mm wide, non-calc., no hydrogen sulphide 3) grey (5 Y 5/1), 1-2 mm wide, slightly calc., two sand bands l mm wide at 622 cm. 623 grey sand lens. 632 contact; till; greyish-brown (2.5 Y 5/2), sandy clay matrix with angular and subangular pebbles scattered throughout, 1.5 x l cm and smaller, limestone; calc. 648 end of core.

Core: 22

Sampled with: Alpine piston corer Year Collected: 1971 Collected by: Canada Centre for Inland Waters Location: 45*46*16" N 83*55*18" W Described by: J.R.H. Water Depth: 107 metres

Depth (centimetres)

O very soft gritty clay, speckled with dark brown (10 YR 3/3); non-calc., no hydrogen sulphide. 4 gritty clay; brown (7.5 YR 5/2), less specks; non-calc., no hydrogen sulphide. 25 gradual colour change to grey (10 YR 5/1); partially oxidized down sides; dark grey-black sulphide streaks (10 YR 4/1); non-calc., faint hydrogen sulphide. 200 silty clay; soft, subtle colour change to 10 YR 5/1; slightly calc., mild hydrogen sulphide; towards bottom, gradual colour change to brown (7.5 YR 5/2), becoming sticky, no hydrogen sulphide. 310 - contact; glaciolacustrine; sandy clayey with plant detritus and root like fibres; becomes silty day at 325 cm; calc., no hydrogen sulphide; after 325 cm, faintly laminated reddish and greyish silty days; dominant colour reddish-brown (5 YR 5/3); fairly firm; has mottled appearance especially around 405 cm. 433 firm, very silty band, dark greyish-brown; calc, no hydrogen sulphide. 442 same as above but becomes less silty and more sticky with depth; very firm homogeneous sticky clay, reddish-brown (5 YR 5/3); calc., no hydrogen sulphide; gradual colour change to brown (7.5 YR 5/2), very faint laminations. 928 contact; colour change to reddish-brown (5 YR 5/3) clay with distinct grey (5 YR 5/1) silty clay laminations; very mildly calc. 996 same as above but dominant colour is grey (5 YR 5/1). 1038 laminated clay as above but reddish-brown (5 YR 5/3) clay dominates. 1048 - distinct laminations again; reddish-brown (5 YR 5/3) clay and grey (5 YR 5/1) silty clay. 1085 laminations fade again and colour changes gradually to brown (7.5 YR 5/2); very firm, very sticky clay; becomes faintly laminated brown (7.5 YR 5/2) very firm, very sticky clay; mildly calc., no hydrogen sulphide produced. 1190 end of core.

Core: 251

Sampled with: Benthos gravity corer Year Collected: 1971 Collected by: Canada Centre for Inland Waters Location: 45*48*46" N 83*15*35" W Described by: A. Zilans Water Depth: 46 metres

Depth (centimetres)

O grey-brown to black silty sand with many black streaks and bands (sulphide). 5 rust-brown to beige-brown silt zone. 7.5 beige, grey-brown silty clay; black streaks (sulphide). 10 - dark greyish-brown (2.5 Y 4/2) silty clay with abundant streaks and bands of black (sulphide); at 46 cm blue igneous pebble, 1.5 cm diameter. 109 greenish-brown sand layer. Ill grey-brown silty clay becoming brown downward. 115 end of core (entire core in postglacial sediment).

99 Core 305

Sampled with: Benthos gravity corer Year Collected: 1971 Collected by: Canada Centre for Inland Waters Location: 45*21*00" N 82*52*48" W Described by: A. Zilans Water Depth: 122 - 137 metres

Depth (centimetres)

O greyish-brown (10 YR 5/2) sticky clay. 5 reddish-brown (5 YR 5/3) to brown (10 YR 5/3) sticky clay. 12 - greenish-grey-brown clay. 20 alternating indistinct red-brown and grey-brown bands; almost a mottled appearance; bands are 3 - 5 cm thick. 34 greyish-brown (10 YR 5/2) sticky homogeneous clay. 66 greyish-brown (10 YR 5/2) sticky clay; very faint grey and brown laminations. 102 clay; sticky, same as above but becoming greyish due to increase in number of faint grey laminations. 127 clay, reddish-brown (5 YR 5/3) with faint laminations of greyish clay. 139 end of core (entire core in glaciolacustrine sediment).

Core: 314

Sampled with: Benthos gravity corer Year Collected: 1971 Collected by: Canada Centre for Inland Waters Location: 45*23*00" N 82*56*48" W Described by: A. Zilans Water Depth: 122 metres

Depth (centimetres)

O black, organic-rich, sandy silt. l glaciolacustrine sediment; (10 YR 5/3) sticky clay; faintly laminated. 19 light reddish-brown (5 YR 6/3) to reddish-brown (5 YR 5/3); faint grey laminations. 124 end of core.

Sample: 316

Sampled with: Benthos gravity corer Year Collected: 1971 Collected by: Canada Centre for Inland Waters Location: 45*25*55" N 82*56*48" W Described by: M. Simpson Water Depth: 106 - 122 metres

Depth (centimetres)

O black sulphide-stained silty clay. 2 dark greyish-brown (2.5 Y 4/2) silty clay with dark black stains and bands (sulphide); fining towards bottom; brown silty clay ball at 53 cm. 70 brown silty clay layer. 73 dark greyish-brown (2.5 Y 4/2) silty clay; abundant black sulphide streaks, bands; colour less grey downward. 127 greyish-brown (2.5 Y 5/2) silt with sand lenses. 129 greyish-brown (2.5 Y 5/2) to dark greyish-brown (2.5 Y 4/2), faintly mottled silty clay. 138 brown clay, homogeneous (grading into glaciolacustrine sediment). 140 - end of core.

Core: 317

Sampled with: Benthos gravity corer Year Collected: 1971 Collected by: Canada Centre for Inland Waters Location: 45*28*12" N 82*56*42" W Described by: A. Zilans Water Depth: 106 metres

Depth (centimetres)

O greyish-beige clay; homogeneous with occasional lamination of brown silt 30 glaciolacustrine; reddish-brown (5 YR 5/3) clay; massive. 48 - reddish-brown (5 YR 5/3) clay, sticky, homogeneous. 113 end of core.

100 Core: M-core

Sampled with: Alpine piston corer Year Collected: 1983 Collected by: Canada Centre for Inland Waters Location: 45"36'52" N 83"23f 16" W Described by: A. Zilans Water Depth: 134 metres

Depth (centimetres)

O dark grey (5 Y 4/1) homogeneous clay; no laminations. 174 faintly laminated dark grey (S Y 4/1) and olive-grey (S Y 4/2) clay, laminations are 0.5 - 1.0 cm thick; thin (0.1 cm) sand streaks present at 196.5, 198, 204, 208 and 232 cm. 265 dark grey (5 Y 4/1) and olive-grey (5 Y 5/2) faintly laminated clay; no distinct boundaries between the laminations; black sulphide streaks present; rock granule (0.3 cm) present at 295 cm. 330 three-colour very faintly laminated clay, dark grey (5 Y 4/1), olive-grey (5 Y 5/2) and dusky-red (2.5 YR 3/2, not an exact match); boundaries between the laminations are indistinct, one colour grades into the next colour. 356 non-laminated clay; grey (5 Y 5/1) to olive-grey (5 Y 5/2). 370 non-laminated day; dark grey (5 Y 4/1), with slight greenish tinge; much disturbance present in the sediment between 443.5 to 530 cm; one sulphide band at 512 cm. 530 very faintly-laminated clay, laminations are 0.5 to 1.0 cm thick; grey (5 Y 5/1) or dark grey (5 Y 4/1) and olive-grey (5 Y 5/2); much disturbance of the sediment between 563 and 652 cm. 652 faintly-laminated clay; dark bands are dark grey (5 Y 4/1) and the light bands are grey (5 Y 5/1) or olive-grey (5 Y 5/2); the laminations are 0.5 to 1.0 cm thick; a pinkish tinge starts appearing in the clay at 680 cm. 688 glaciolacustrine; beginning of distinctly reddish clay and thick distinct laminations; dominantly homogeneous, light reddish-brown clay (2.5 Y 6/2); very faint bands (0.1 - 0.3 cm) of greyish-brown clay (2.5 Y 5/2). 691 faintly-laminated clay; laminations are variable in thickness (1.0 - 4.0 cm) and tend to be gradational; no distinct boundaries; laminations are grey (5 Y 5/1), to olive-grey (5 Y 5/2) and light, reddish-brown (2.5 YR 6/4); the grey-coloured laminations are dominant in this section. 709 light (bright) reddish-brown (2.5 YR 6/4) and grey-brown (5 Y 6/1), laminated clay; reddish colour is dominant with the grey clay forming the more minor component; the grey laminations are 0.5 cm wide. 722 homogeneous greyish-brown clay (2.5 Y 5/2). 731 homogeneous light reddish-brown clay (2.5 YR 6/4). 733.5 homogeneous greyish-brown (2.5 Y 5/2) clay. 738 homogeneous light (bright) reddish-brown clay (2.5 YR 6/4). 748 - greyish-brown (10 YR 5/2) clay; light grey streaks of silt at 748.5 and 750 cm, the silt streaks are 0.1 to 0.2 cm thick. 753.5 - faintly laminated (bright) light reddish-brown (2.5 YR 6/4) and grey (5 Y 6/1) clay; laminations are 0.25 to 0.75 cm thick; four pairs of laminations. 766 section missing. 744 faintly laminated clay; (bright) light reddish-brown (5 YR 6/3) laminations l cm thick and grey (5 Y 6/1) laminations 0.5 cm thick; 10 pain of laminations. 794.5 homogeneous (bright) light reddish-brown clay (2.5 YR 6/4). 803.5 - faintly-laminated clay; (bright) light reddish-brown (5 YR 6/3) laminations l cm thick and grey (5 Y 6/1) laminations 0.5 cm thick; 2 pairs of laminations. 807 homogeneous brown clay (7.5 YR 5/2). 815 homogeneous reddish-brown clay (5 YR 5/3); a few silt streaks present. 867 brown (7.5 YR 5/2) very fine sand or silt; one lamination (0.2 cm) of light brownish-grey silt. 870.5 faintly laminated clay, reddish-brown (5 YR 5/3) laminations l cm thick and greyish-brown clay (10 Y 5/2) laminations 0.5 cm thick; laminations run together so they are not possible to count; light grey (5 YR 7/1) silt streaks 0.1 - 0.2 cm thick at 885 and 886 cm; a few bright reddish-brown laminations present near the top of this section. 902.5 thin, distinct reddish and greyish clay laminations begin; reddish-brown (5 YR 5/3) laminations 0.5 - 7 cm thick with an average thickness of 2 - 3 cm; grey laminations (10 YR 5/1) are 0.5 cm thick; some bright reddish-brown clay present in the upper pan of this section; the colour changes in the red laminations to reddish-brown (2.5 YR 5/4) towards the bottom of the section; red and grey laminations attain a uniform thickness downward and eventually the grey laminations become thicker than the red; light brownish-grey (2.5 Y 6/2) silt streaks (0.1 - 0.2 cm) at 1001.5, 1049.5, 1058.5 and 1176 cm; the silt streaks are found at the top of the red laminations or at the base of the grey laminations; 157 pairs of red and grey laminations present in this section. 1231 start of reddish-brown (2.5 YR 5/4) and grey (10 YR 5/1) mottled day with no distinct laminations; very pale brown (10 YR 7/3) silt streaks (0.1 - 0.2 cm) at 1361.5 and 1362.5 cm. 1446 a more homogeneous clay than in the above section; light reddish-brown (2.5 YR 6.4) or reddish-brown (5 YR 5/4) clay with mottles or zones of grey (10 YR 5/1) day; very pale brown (10 YR 7/3) silt stringers found at 1470, 1475 -1477, 1490 -1493, 1500 and 1510 cm; a distinct grey clay (10 YR 5/1) mottle at 1518 - 1524 cm; section missing at 1464.5 - 1465.5 cm and 1573 - 1577 cm. 1614 - mottled reddish-grey (5 YR 5/3) and grey (10 YR 5/1) clay; towards the bottom the colour changes to reddish-brown (2.5 YR 5/4) and grey (10 YR 6/1) and the grey colour becomes dominant giving a grey-brown tone to the sediment at 1630 - 1631.5 cm. 1776.5 end of core.

101 APPENDIX C Results of Grain Size and Carbonate Analyses

Abbreviations used in the following table:

Sample No. - Sample number Int. Sampled - Interval sampled in centimetres Sed. Type - Sediment type Pg - Postglacial sediment Glu - Undifferentiated glaciolacustrine sediment Git - Thinly laminated glaciolacustrine sediment Glth - Thickly laminated glaciolacustrine sediment Glhf - Homogeneous to faintly laminated glaciolacustrine sediment Glm - Mottled glaciolacustrine sediment T-T01 snd - Percent sand sit - Percent silt dy - Percent clay md - Median diameter in millimetres T - Percent total carbonate C - Percent calcite D - Percent dolomite C/D - Calcite to dolomite ratio

Texture Sample No bit Sampled Sed. Type snd sit cly md T C D C/D Core PC-1 1 19 -39 Glu 1 39 60 .0014 20 7 13 0.5 2 119 - 139 Glu 1 22 .77 20 11.5 8.5 1.3 3 196 -216 Glu 1 19 80 19 11.5 7.5 1.5

CorePC-2 1 90 - 110 Pg 0 21 79 14 4.5 9.5 1.5 2 194 -204 Glc 0 32 68 29 11 18 0.6 3 230.5 -240.5 Glc 0 1 99 - 4 271 -291 Glc 0 28 72 13 7 6 1.2 5 361 -374 Glc 0 57 43 .0029 14 6 8 0.8 6 386 -406 Glc 0 27 73 27 12 15 0.8 7 457 -477 Glc 1 27 72 24 11.5 12.5 0.9 g 573 -593 Glc 2 16 82 18 9 9 1.0 9 643 -663 Git 2 7 91 18 10 8 1.3 10 708.5 - 728.5 Git 2 10 88 14 10.5 3.5 3.0 11 814 -834 Git 2 7 91 13 9 4 2.3 12 904 - 924.5 Git 2 13 85 14 9.5 4.5 2.1 13 984.5 - 1004.5 Git 2 13 85 11 7.5 3.5 2.1 14 1045 - 1065 Git 2 8 90 12 8 4 2.0 15 1135 -1155 Git 2 11 87 15 11 4 2.8 16 1207 - 1227 Git 3 5 92 14 9.5 4.5 2.1 17 1297 - 1317 Git 2 4 94 15 9.5 5.5 1.7 18 1388 - 1408 Git 2 H 87 14 11 3 3.7 19 1478 - 1498 Git 3 9 88 12 8 4 2.0

Core H-32 1 6- 10 Pg 24 40 36 .0055 2 2 0 - 2 24 -28 Pg 5 54 41 .0031 2 2 0 -

Core P-30 1 20 -28 Pg 3 74 23 .0075 26 5.5 20.5 0.3 2 65 -70 Glu 0 20 80 3 3 0 - 3 89 -94 Glu 4 55 41 .003 11 3.5 7.5 0.5 4 121 - 125 Glu 21 61 18 .014 21 4 17 0.2

102 Sample No Int Sampled Sed. Type snd sit cly md T C D C/B Core 19 1 56-66 Pg 33 63 4 .054 12 2 10 0.2 2 80-90 Pg 32 64 4 .050 15 1 14 0.1

3 145 - 155 Pg 35 60 5 .052 17 3 14 0.2 4 200 -210 Pg 47 49 4 .059 14 2 12 0.1 5 255 -265 Pg 25 69 6 .048 17 1.5 15.5 0.1 6 315 -325 Pg 25 70 5 .050 16 2 14 0.1 7 355 -365 Pg 35 60 5 .053 14 1 13 0.1 8 409 -419 Pg 34 61 5 .050 15 2 13 0.2 9 464 -474 Pg 34 61 5 .050 14 1 13 0.1 10 554 -564 Pg 24 71 5 .049 16 2 14 0.1 11 643 -653 Pg 34 62 4 .052 14 2 12 0.2

Core 19B 1 65 -85 Pg 14 79 7 .031 12 2 10 0.2 2 113 - 130 Pg - - - - 15 1 14 0.1 3 175 - 186 Pg 25 70 5 .045 16 1 15 0.1 4 245 -256.6 Pg 24 67 9 .033 19 1 18 0.1 5 284 -297 Pg 3 62 35 .007 54 4 50 0.1 6 356 -373 Pg 0 56 44 .0029 50 6.5 43.5 0.2 7 429.5 -446.5 Pg 0 62 38 .0036 65 3 62 0.1 g 456.5 - 459.5 Glu? 7 76 17 .013 46 1 45 0.0 9 486 -498 T 27 58 15 .018 55 5 50 0.1 10 526.5 - 533.5 T 30 53 17 .015 50 1 49 0.0 11 516.5 -526.5 T 30 55 15 .0195 58 4 54 0.1

Core 18 21 101 -115 Pg 23 53 24 .012 6 3 3 1 20 190 -205 Pg - - - - 8 1 7 . 0.1 19 271 -291 Pg 17 45 28 .007 12 2 10 0.2 18 371 -391 Pg 15 60 25 .007 22 1 21 0.1 17 432 -452 Pg 15 59 26 .011 38 1 37 0.0 16 503 -513 Pg 25 61 14 .045 46 2 44 0.1 15 518 -533 Git 7 21 72 - 29 7 22 0.3 14 543 -563 Git - - - - 18 7 11 0.6 13 613.5 -633 Git 7 30 63 - 20 4 16 0.3 12 723 -743 Git - - - - 23 8 15 0.5 11 793 -806 Git - - - - 19 9 10 0.9 10 823 -838 Git - - - - 19 6 13 0.5 9 893 -908 Git 5 15 80 - 25 6 19 0.3 8 939 -955 Git 5 12 83 - 15 9 6 1.5 7 979 -989 Git - - - - 21 10 11 0.9 6 1035 - 1047 Glc 28 65 7 .044 36 4 32 0.1 5 1067 - 1079 Glc 7 23 70 - 26 7 19 0.4 4 1107 - 1118 Glc 8 47 45 .003 37 5 32 0.2 3 1132 - 1144 Glc 7 45 48 .0022 40 13.5 26.5 0.5 2b 1161 - 1170 Glc 5 37 58 .0012 28 5 23 0.2 2a 1202 - 1217 Glc 11 32 57 .0012 32 3.5 28.5 0.1 le 1280 - 1292 T 65 29 6 .140 59 11.5 47.5 0.2 Id 1324 - 1338 T 58 39 3 .155 63 14.5 48.5 0.3 le 1382 - 1398 T 35 62 3 .17 60 10.5 49.5 0.2 Ib 1480 - 1498 T 56 38 6 .09 59 10 49 0.2 la 1518 - 1521 T 37 52 11 .031 64 7 57 0.1 Core 21 1 42 -62 Git 0 8 92 - 10 5 5 1.0 2 154 - 174 Git 0 13 87 - 4 2 2 1.0 3 221.5 - 241.5 Git 0 3 97 - 4 2 2 1.0 4 297 -312 Git 0 10 90 - 3 2 1 2.0 5 352 -372 Git 0 10 90 - 6 2 4 0.5 6 437 -457 Git 0 10 90 - 7 3 4 0.8 7 531.5 - 551.5 Git 0 17 83 - 9 3 6 0.5 8 603.5 - 621.5 Git 0 14 86 - 11 3 8 0.4

103 Texture Sample No. Int Sampled Sed. Type snd alt cly md T C D C/D 9 634 -648 T 40 45 15 .033 42 5 37 0.1

Core 22 - 1 0-20 Pg 1 57 42 .032 3 3 0 0.21 2 92.5 - 112.5 Pg 0 45 55 .0016 14 2 12 3 183 -203 Pg 0 33 67 25 7 18 0.4 4 252.5 -272.5 Pg 0 32 68 20 6 14 0.4 5 328 -348 Glhf 0 46 54 .0016 26 8 18 0.4 6 413 -433 Glhf 0 10 90 18 10 8 1.2 7 483 -503 Glhf 1 18 81 18 9 9 1.0 8 572.5 -592.5 Glhf 0 20 80 26 12 14 0.9 9 662.5 -68Z5 Glhf 2 27 71 26 11 15 0.7 10 753 -773 Glhf 2 32 66 29 11 18 0.6 11 843 -863 Glhf 2 31 67 28 11 17 0.7 12 903 -923 Glhf 2 33 65 29 12 17 0.7 13 933.5 - 953.5 Git 1 10 89 15 9 6 1.5 14 1003.5- 1023.5 Git 2 11 87 11 4 7 0.6 15 1085 - 1105 Gil 2 13 85 13 7 6 1.2 16 1161 - 1181 Git 2 15 83 17 10 7 1.4

Core 251 1 20 -27 Pg 7 70 23 .012 23 1 22 0.1 2 67 -74 Pg 6 75 19 .013 23 1 22 0.1

Core 305 - 5- 10 Glu 0 8 92 1 1 0 1 - 2 60 -66 Glu 0 12 88 1 1 0 - 3 95 -102 Glu 0 11 89 2 2 0 4 133 - 139 Glu 0 7 93 3 2 1 2.0

Core 314 1 5- 12 Pg 0 14 86 3 1.5 1.5 1.0 2 61 -68 Glu 0 8 92 4 2 2 1.0 3 118 - 124 Glu 0 8 92 5 2 3 0.7

Core 316 - 1 30 -36 Pg 5 59 36 .0041 2 2 0 2 80 -86 Pg 2 43 55 .0015 4 2 2 1.0 3 131 -137 Glu 2 46 52 .0014 9 1 8 0.1

Core 317 1 16 -26 Pg 3 70 27 .0075 20 2 18 0.1 2 58 -64 Glu 0 H 89 4 2 2 1.0

104 APPENDIX D Results of Grain Size Analyses on Samples from M-core

Abbreviations used in the following table:

Sample No. - Sample number Int Sampled - Interval sampled in centimetres Sed. Type - Sediment type Pgh - Homogeneous postglacial sediment Pgf - Faintly laminated postglacial sediment Glth - Thickly laminated glaciolacustrine sediment Git - Thinly laminated glaciolacustrine sediment Glm - Mottled glaciolacustrine sediment snd - Percent sand sit - Percent silt dy - Percent clay Mn - Graphic mean (phi units) ScD. - Inclusive graphic standard deviation (phi units) Sk - Inclusive graphic skewness K - Graphic kurtosis * - 95th percentile extrapolated ** - 84th and 95th percentiles extrapolated *** - 75th, 84th and 95th percentiles extrapolated

Sample No. Int Sampled Sed. Type Texture cly Mn St.D. Sk K 1 0- 1 Pgh 0 58 8.63 2.04 0.06 0.88 2 30-32 Pgh 0 65 8.93 3.21 0.07 1.07 * 3 60-62 Pgh 1 60 8.63 2.34 0.01 1.00 * 4 90-92 Pgh 0 71 9.10 1.85 0.02 0.96 * 5 120 - 122 Pgh 0 65 8.95 2.11 -0.02 0.86 6 150 - 152 Pgh 0 69 9.00 2.02 0.03 1.00 * 7 180- 182 Pgf 0 66 8.90 2.05 0.13 1.02 * 8 210-212 Pgf 0 63 8.87 2.26 0.09 0.96 * 9 240 - 242 Pgf 2 60 8.61 2.43 -0.02 0.92 * 10 270 - 272 Pgf 0 68 9.26 2.31 -0.16 0.93 * 11 300-302 Pgf 3 68 9.24 2.43 0.12 1.03 * 12 330 - 332 Pgf 0 90 10.79 1.92 -0.2 1.22 ** 13 360 - 362 Pgf 0 69 9.20 2.08 0.05 0.73 * 14 390 - 392 Pgf 2 84 10.74 2.47 -0.28 0.96 15 420 - 422 Pgf 0 84 10.24 2.14 -0.02 0.88 ** 16 450 - 453 Pgf 0 74 9.96 2.44 -0.04 0.79 ** 17 480 - 483 Pgf 0 85 10.71 2.32 -0.19 0.85 *** 18 510-513 Pgf 0 87 10.53 2.01 -0.16 1.04 ** 19 540 - 542 Pgf 0 91 10.80 1.85 -0.14 1.20 ** 20 570 - 573 Pgf 0 81 9.77 2.06 -0.04 1.17 * 21 609-612 Pgf 0 83 10.13 2.2 0.01 0.94 ** 22 638 - 641 Pgf 0 88 10.35 1.79 -0.20 1.08 * 23 670 - 672 Pgf 0 84 10.07 2.0 -0.004 1.01 ** 24 710-713 Glth 0 95 11.11 1.7 0.08 0.91 *** 25 734 - 736 Glth 0 89 10.75 2.06 -0.04 0.96 *** 26 780 - 782 Glth 0 99 11.35 1.58 0.04 0.74 ** 27 799 - 802 Glth 0 98 11.32 1.25 0.18 1.09 ** 28 809 - 812 Glth 0 88 10.56 2.02 -0.09 1.13 ** 29 860 - 862 Glth 0 66 9.2 2.07 0.27 0.84 * 30 900-902 Glth 0 85 10.38 2.16 0.02 0.93 ** 31 952 - 954 Git 0 98 11.41 1.63 0.01 0.79 ** 32 1006 - 1007.5 Git 0 98 11.07 1.34 0.13 1.08 ** 33 1007.5 - 1009.5 Git 0 95 10.77 1.43 -0.19 1.44 * 34 1045 - 1046.75 Git 0 96 11.49 1.63 -0.005 0.81 *** 35 1046.75 - 1048.75 Git 0 96 11.04 1.61 0.03 1.16 ** 36 1127 - 1128.75 Git 0 95 10.38 1.40 -0.16 1.29 * 37 1128.75- 1130.5 Git 0 97 11.25 1.31 0.17 1.11 ** 38 1195 - 1197 Git 0 95 10.94 1.64 0.07 1.17 ** 39 1245 - 1247 Glm 0 100 11.36 1.27 0.16 1.06 **

105 Sample No. Int Sampled Sed. Type Texture snd sit cly Mn St.D. Sk K 40 1295- 1297 Glm 0 5 95 10.60 1.23 -0.28 0.94 41 1345- 1347 Glm 0 7 93 10.48 1.18 -0.30 1.21 42 1395- 1397 Glm 0 4 96 10.67 1.23 -0.07 1.07 43 1440- 1442 Glm 0 2 98 10.85 1.24 -0.02 1.00 44 1495- 1497 Glm 0 9 91 10.07 1.69 0.07 0.88 45 1545- 1547 Glm 0 4 96 11.09 1.64 0.03 0.94 46 1595- 1597 Glm 0 4 96 10.65 1.21 -026 1.27 47 1645- 1647 Glm 0 4 96 10.71 1.06 -0.29 1.07 48 1695- 1696 Glm 0 5 95 11.01 1.45 -0.08 1.07 49 1745- 1747 Glm 1 5 94 10.65 1.40 -0.14 1.35

APPENDIX E Results of Carbonate Analyses on Samples from M-Core

Abbreviations used in the following table: T - Percent total carbonate C - Percent calcite D - Percent dolomite C/D - Calcite to dolomite ration Sample No. - Sample number Int. Sampled - Interval sampled (centimetres) Sed. Type - Sediment type Pgh - Homogeneous postglacial sediment Pgf - Faintly laminated postglacial sediment Glth - Thickly laminated glaciolacustrine sediment Git - Thinly laminated glaciolacustrine sediment Glm - Mottled glaciolacustrine sediment

Sample No. Int. Sampled Sed. Type Carbonates t D C/D 1 0-1 Pgh 2 30-32 l l 0 . 3 60-62 l l 0 - 4 90-92 l l 0 - 5 120-122 1 l 0 - 6 150-152 2 l 1 1.0 7 180-182 5 l 4 0.3 8 210-212 3 O 3 - 9 240-242 7 O 7 - 10 270-272 8 l 7 0.1 11 300-302 6 O 6 - 12 330-332 O O 0 - 13 360-362 9 I 8 0.1 14 390-392 O O 0 - 15 420-422 2 O 2 - 16 450-453 4 O 4 - 17 480-483 3 O 3 - 18 510-513 4 1 3 0.3 19 540-542 5 2 3 0.7 20 570-573 17 6 11 0.6 21 609-612 15 4 11 0.4 22 638-641 7 2 5 0.4 23 670-672 15 5 10 0.5 24 710-713 15 II 4 2.8 25 734-736 14 7 7 1.0 26 780-782 18 14 4 3.5 27 799-802 12 9 3 3.0 28 809-812 13 7 6 1.2 29 860-862 14 6 8 0.8 30 900-902 23 9 14 0.6 31 952-954 16 11 5 2.2 32 1006-1007.5 14 10 4 2.5 33 1007.5-1009.5 12 6 6 1.0 34 1045-1046.75 13 8 4 2.0

106 Sample No. Ink Sampled Sed. Type Carbonates T C D C/D 35 1046.75-1048.75 Git 11 5 6 0.8 36 1127-1128.75 Git 11 5 6 0.8 37 1128.75-1130.5 Git 15 10 5 2.0 38 1195-1197 Git 10 4 6 0.7 39 1245-1247 Glm 11 6 5 1.2 40 1295-1297 Glm 12 7 5 1.4 41 1345-1347 Glm 13 8 5 1.6 42 1395-1397 Glm 13 8 5 1.6 43 1440-1442 Glm 17 11 6 1.8 44 1495-1497 Glm 19 11 8 1.4 45 1545-1547 Glm 14 10 4 2.5 46 1595-1597 Glm 8 4 4 1.0 47 1645-1647 Glm 8 4 4 1.0 48 1695-1696 Glm 13 8 5 1.6 49 1745-1747 Glm 14 8 6 1.3

APPENDIX F Pebble Lithology of Tills

Values are in percent.

Core Colour Limestone Dolostone Shale Chert Igneous Quartz 18 2.5Y5/2 73 16 7-31 19B 5YR4/4 48 36 4 10 2 21 2.5Y5/2 12 68 18 2

APPENDIX G Results of Organic Carbon Analyses on Samples from M-core

Abbreviations used in table: Pgh - homogeneous postglacial sediment Pgf - faintly laminated postglacial sediment Glth - thickly laminated glaciolacustrine sediment Git - thinly laminated glaciolacustrine sediment Glm - mottled glaciolacustrine sediment

Sample No. Interval Sampled (cm) Sediment Type *k Organic Carbon 1 2-4 Pgh 5.1 2 10-12 Pgh 4.5 3 41-43 Pgh 5.3 4 70-72 Pgh 6.0 5 78-80 Pgh 5.2 6 101 - 103 Pgh 4.8 7 148 - 150 Pgh 8 161 - 163 Pgh 3.8 9 198-200 Pgf 3.1 10 268 - 270 Pgf 2.6 H 338-340 Pgf 2.5 12 410-412 Pgf 2.6 13 483 - 486 Pgf 1.9 14 550-552 Pgf 1.5 15 622-625 Pgf 2.0 16 691 - 693 Glth 1.6 17 760-762 Glth 1.4 18 835 - 837 Glth 1.2 19 897-899 Git 1.6 20 990-992 Git 1.6 21 1098-1100 Git 1.9 22 1301 - 1303 Glm 1.8 23 1501 - 1503 Glm 1.4 24 1701 - 1703 Glm 1.9

107 CONVERSION FACTORS FOR MEASUREMENTS IN ONTARIO GEOLOGICAL SURVEY PUBLICATIONS Conversion from SI to Imperial Conversion from Imperial to SI 57 Unit Multiplied by Gives Imperial Unit Multiplied by Gives LENGTH 1 mm 0.039 37 inches 1 inch 25.4 mm 1 cm 0.393 70 inches 1 inch 254 cm 1m 3.28084 feet Ifoot 03048 m 1m 0.049 709 7 chains 1 chain 20.116 8 m 1km 0.621 371 miles (statute) 1 mile (statute) 1.609344 km AREA 1 cm2 0.155 0 square inches 1 square inch 6.451 6 cm2 1m2 10.763 9 square feet 1 square foot 0.092 903 04 m2 Ikm2 0.386 10 square miles 1 square mile 2.589 988 km2 lha 2.471 054 acres 1 acre 0.404 685 6 ha VOLUME 1 cm3 0.061 02 cubic inches 1 cubic inch 16387 064 cm3 1m3 35.314 7 cubic feet 1 cubic foot 0.028 316 85 m3 1m3 1.308 0 cubic yards 1 cubic yard 0.764 555 m3 CAPACITY 1L 1.759 755 pints 1 pint 0.568 261 L 1L 0.879 877 quarts 1 quart 1.136 522 L 1L 0.219 969 gallons 1 gallon 4.546 090 L MASS lg 0:035 273 96 ounces (avdp) 1 ounce (avdp) 28.349 523 g lg 0.032 150 75 ounces (troy) 1 ounce (troy) 31.103 476 8 g 1kg 2.20462 pounds (avdp) 1 pound (avdp) 0.453 592 37 kg 1kg 0.001 102 3 tons (short) 1 ton (short) 907.184 74 kg It 1.102311 tons (short) 1 ton (short) 0.907 184 74 t 1kg 0.000 984 21 tons (long) 1 ton (long) 1016.046 908 8 kg 1 t 0.984 206 5 tons (long) 1 ton (long) 1.016 046 908 8 t CONCENTRATION l g/t 0.029 166 6 ounce (troy)/ l ounce (troy)/ 34.285 714 2 ton (short) ton (short) l g/t 0.583 333 33 pennyweights/ l pennyweight/ 1.714 285 7 ton (short) ton (short) OTHER USEFUL CONVERSION FACTORS Multiplied by l ounce (troy) per ton (short) 20.0 pennyweights per ton (short) l pennyweight per ton (short) 0.05 ounces (troy) per ton (shorl)

Note: Conversion factors which are in bold type are exact. The conversion factors have been taken from or have been derived from factors given in the Metric Practice Guide for the Canadian Mining and Metallurgical Indus tries, published by the Mining Association of Canada in co-operation with llie Coal Association of Canada.

108 ELEVATION OF THE BEDROCK SURFACE

Contour interval equals 30 metres —- --© Contour interred Elevations are relative to sea level Elevation of the surface of Lake Huron is 176.8m

10 15 2O 25 Km

Figure 7 Mackinac Basin, M-Core, Pollen Percentage Diagram

Arboreal Pollen Herb Pollen

CO 0 3 CO mc 3 CO CO o c Q) CD Q) 3 O J 2 O 03 ID O Homogeneous Postglacial 4800-5obo- Clay 6OOO

Cy. 7OOO S. Cy. le. 00- ^^^^•^•^^ S. 8OOO S. Cy. l c. O/C •T. A. S. ^9000 Cy. le. Faintly .S. le. S. Laminated A. S. le. Postglacial Clay

10000

Thickly Laminated '1O5OO- Glaciolacustrine Clay CD O Thinly } T. Ca. S. Co. Cy. le. O/C. O 10 ! Dates determined T. S. O/C. T l. Laminated 4by palynologic C stratigraphic 11 Glaciolacustrine correlation a Clay T. Cy. lc.II. 0 Q 12 Ca. S. le. O/C includes: Equisetum, Selagijiella, Pteridium, Sphagnum, 13 \ Lycopodium, Polypodium, Dryopteris , Gjystopteris

14 Mottled Glaciolacustrine Abbreviations 15 Clay A-Alnus Ca-Carya iDates 16 Co-Corylus determined Cy-Cyperacea by Ic-Iva ciliata palynological 17 J-Juglans stratigraphic O/C-Ostrya/Carpinus correlation S-Salix 18 T-Tilia i Tl-Typha latifolra

O 20 40 60 80 10O O 2O 40 6O" 8O 10O O 2O O 20 40 O 2O 40 Q 5 O 5 10 15 20 O 5 1O O 5 10 O 5 O 5 10 O 5 10 O 5 10 O 5 10 O 5 1O O 5 10 O 5 10 15 2O 25 Percentage of Total Arboreal, Shrub, and Herb Pollen

Figure 24 Stratigraphy Paleomagnetic DECLINATION INCLINATION Time Scale (Yrs BP) .go0 0( +900 -600 -30C O0 +30' +600 +900 O O i i j___i 2000 ' ':,' D? Homogeneous f ••- Postglacial Clay 1 - 1 - 3000 * * V. • 4000 2 - 2-

5000 3- 3-

6000

4- 4- Faintly -.'

Laminated 7000 5- Postglacial 5- y. Clay H ^ 8000 6- 6-

9000?h 7- 7- Thickly Laminated M? •-; Glaciolacustrine 8 8 8- * * Clay CD

I 9 9- O •f Thinly 10- 10- h.4- Laminated 8 Glaciolacustrine Clay 11- 11- l?

12- 12-

13- 13-

Mottled 14- 14- Glaciolacustrine Clay • 15- 15-

16- 16-

17- 17-

18 J.S. Mothers!11 Figure 25 Mackinac Basin, M-core, Pollen Concentration Diagram

Arboreal Pollen Herb Pollen

o Homogeneous Postglacial Clay 6000

7OOO

76OO-^^^^^^^M 8OOO

*90OO Faintly Laminated Postglacial Clay

1OOOO

Thickly

Laminated 10500 CD Glaciolacustrine O Q Clay O 9

C •~ 10 Thinly Laminated Q. 0) 11 Glaciolacustrine D Clay 12

13

14 Mottled Glaciolacustrine 15 Clay

16 *Dates determined by 17 palynological stratigraphic correlation

O 20 40 60 80 100 120 140 O 1 O 20 40 60 80 100 120 140 O 1 401 3 5 7 0123 01230 101 7 O 1 201234Q1 20 1 20 1 20

Grains/cm^ sediment(x1O includes: Equisetum, Selaginella, Pteridium, Sphagnum, Lycopodium, Polypodium, Figure 28 Dryopteris , Cystopteris