The Deep Time Geological Story of Georgian Bay and the North Channel
Why Georgian Bay and the North Channel as a Global Geopark?
Georgian Bay is the fifth largest (15,000 km2) Great Lake and its shoreline exposes some of the most diverse geology anywhere in North America, recording in total more than 2.5 billion years of Earth history, or close to half of our planet’s entire lifetime. Few areas of the planet contain such a long geologic record. The region has a long history of groundbreaking geological research of international significance, that is ongoing. It has significant opportunities for geotourism and public education, and is moreover, highly accessible, close to the major population centre in Canada the Greater Toronto Area, and for international visitors.
Its landscapes and culture are unique in Canada and helped shape a distinct national identity as the country slowly learned to embrace its harsh uncompromising heartland; the Canadian Shield which defines the eastern, and northern shores of the Georgian Bay Geopark. To the west and south, much younger sedimentary rocks create very different landscapes typical of Southern Ontario, such as limestone plaisn and escarpments.
Globally, the Canadian Shield of Georgian Bay is a major character in the story of Earth’s long history. Its highly deformed Shield rocks, called gneisses, formed 30 km deep at the base of tectonic plates and now exposed at surface by erosion. These beautifully banded rocks, loved by artists, inspired the Canadian father of plate tectonics, Jock Tuzo Wilson who had a cottage on Go Home Bay, to propose that continents drift, collide and break apart, with oceans opening and closing in a never-ending cycle, now called the Wilson Cycle. The Shield records key phases in the growth of the North American continent by the additions of small crustal blocks called ‘terranes’ during successive Wilson Cycles. Proposed by a Canadian geologist, it explains how all continents have grown through time, and the geology of Georgian Bay is an excellent laboratory to showcase the tectonic processes of continent building, and the achievements of Wilson.
Georgian Bay: The Home of Geological Discoveries including Plate Tectonics
In earlier tectonic collisions, South America and Africa were once former neighbors, locked together in the area that we now call Georgian Bay, imprisoned in giant supercontinents that broke apart leaving parts of these landmasses behind as terranes. The Shield rocks now at surface, are the roots of high mountains thrown up by plate collisions affording geologists a unique window into the base of tectonic plates as they glide across hotter softer rocks of the mantle below. The formation and erosion of ancient mountains, vestiges of ancient ice ages and giant rivers, the nature of Earth’s early atmospheres, and the crash of giant meteorites, are too, recorded in the rocks that surround the Aspiring Georgian Bay UNESCO Geopark.
Emerging technologies and the need for mineral resources played their role in telling the story of Georgian Bay rocks. In the 1890s, Arthur P. Coleman pioneered the use of new high precision German-made microscopes, the best in the world, to unravel the intricacies of mineral formation in gneisses deforming at great depths and under enormous pressures. He is credited with the first detailed mapping of the rich nickel and copper ores at Sudbury. Between 1910 and 1920, W. H. Collins identified that these rocks are inherited from much older rocks, now known to have been caught between colliding plates. His pioneering use of float planes and air photographs in mapping the north shores of Georgian Bay and around Blind Bay, ultimately led to the discovery and mining of rich uranium ores at Elliot Lake. The ability to date rocks as old as the planet (4.56 billion years), owes much to Tom Krogh’s investigations of lead produced by the decay of unstable uranium isotopes trapped inside zircon crystals, a dating technique now used worldwide. His dating of Georgian Bay’s ancient Precambrian rocks in the 1970s validated Tuzo Wilson’s grand ideas of supercontinents, revealing the areas surrounding the Bay retained a record of four supercontinents (Superia at 2.5 billion years, Nuna at 1.8 billion, Rodinia at 1.1 billion and Pangea some 350 million years ago) unlike anywhere else on the planet. The tradition of innovative geological research around Georgian Bay, continues today with the work of Mike Easton, Nick Culshaw, Rebecca Jamieson and Toby Rivers, and their many colleagues.
A key event occurred about 600 million years ago, when ancestral North America broke away from the grip of Rodinia and drifted free across the equator where warm inland seas flooded across the Shield now denuded of mountains. These seas left a legacy of fossil-rich limestones and ancient tropical reefs seen today on the western side of the Bay on the limestone plains of the Bruce Peninsula and its extension on Manitoulin Island. Several sites are internationally well known for the diversity and quality of their fossils; Alexander Murray made the first collections in 1843 and these became the basis for subdividing Paleozoic rocks that rest on the Shield, in central Canada. Ancient earthquakes are also recorded in these rocks and provide clues to the origins of modern earthquakes. Until 1872, shale rock was burned at Meaford on the southern coast of Georgian Bay, to produce oil.
The Waters of Georgian Bay and the North Channel
The Bay is an arm of Lake Huron and like all the other Great Lake basins, is geologically recent in age, less than 2.5 million years old, having been carved out by giant ice sheets, much like that of Antarctica today, grinding their way south from kilometre-thick snowfields in Quebec-Labrador. Unlike Antarctica, the beds of the ancient ice sheets are well exposed around Georgian Bay, allowing geologists insights into glacial processes at work under ice sheets. The deep basins of Parry Sound, and Owen Sound, which would later prove key to Great Lakes transportation, owe their origins to glacial erosion.
As the sixth Great Lake, Georgian Bay contains some 5% of the planet’s freshwater that are among its most pristine. Glacial scouring of the Shield produced more than 30,000 Islands along its eastern shore, the largest freshwater archipelago anywhere in the world, and a unique North American ecosystem composed of a mixture of boreal species with southern temperate species; what ecologists refer to as an ‘ecotone’ that collectively, is more diverse than either.
Human Settlement
The stark contrast between the rugged Precambrian Shield to the east and north, and the softer landscapes of the south, has dictated the story of human settlement around Georgian Bay. Hardy Paleo-Indians occupied tundra landscapes just as the last ice sheet finally disappeared from the Bay, following caribou herds along the shores of an enlarged and much deeper lake called glacial Lake Algonquin, infested with icebergs. These people mined copper along the north shore of Georgian Bay, and hard chert along the base of the Niagara Escarpment near Meaford and quartzite on Manitoulin Island to make arrow heads and tools. Their camp sites are preserved around the now high and dry shores of Lake Algonquin. Sand and mud accumulating on the floor of Lake Algonquin created opportunities for farming in the nineteenth century, dictating the success or failure of settlements across the otherwise rock-strewn Shield.
Later, indigenous migratory Ojibwe-Ottawa hunter-gatherers on the Shield traded furs for maize with densely-populated settled Huron (Wendat) communities on the rich farmland to the south. Wyandot legends speak of the god Kitchikewana guarding the Bay’s water, throwing clods of earth into its waters to form the 30,000 islands of its eastern shore. Early French explorers such as Samuel Champlain (1615-16) travelled through the area and overwintered, leaving detailed accounts of natural landscapes, wildlife, indigenous culture and customs, naming the body of water now known as Georgian Bay, ‘La Mer douce’; the sweetwater sea. The first European settlement in what is now Ontario and what was then New France, was established at Sainte-Marie among the Hurons near present-day Midland, from 1639-1649 by Jesuit priests. Georgian Bay was the frontier between opposing American and British forces in the War of 1812, with a naval base built by the British at Penetanguishene which later became a stepping off point for Arctic explorers such as Franklin (1825).
Thereafter, with accelerated European settlement after 1840, the Bay became a major transportation crossroads when voyageurs and the Hudson Bay Company used its myriad waterways as a marine highway extending westward from Ottawa along the Ottawa and French rivers, to explore the continental interior and develop northern trade routes, and the Fur Trade. This has given rise to a rich Metis culture in southern Georgian Bay.
Georgian Bay was the first district anywhere in Canada to be studied for its mineral resources by the newly-formed Geological Survey of Canada after 1842. The Survey quickly established the lack of coal in Southern Ontario and was the impetus for Confederation in 1867 to integrate Ontario’s manufacturing industry with Nova Scotia’s coal. The Director of the Survey, the Montreal-born Sir William Edmond Logan, promoted settlement of the Shield around Georgian Bay, and the construction of colonization roads to increase the population of Southern Ontario, but the difficulty of ‘farming rocks’ prompted many to leave for Western Canada.
Lakeside communities along the south shore of the Bay flourished as the Bay became a major entrepot for new settlers coming to Canada and moving westward. The loss of the steamship Asia in 1882 just off the Limestone Islands near the entrance to Parry Sound, was Canada’s worst maritime disaster. It inspired the charting of the waters of Georgian Bay by Commander John Boulton of the Royal Navy (1883-1894) which, in 1904, resulted in the establishment of the Canadian Hydrographic Survey, a national first. Surveying was completed under very difficult conditions especially in springtime with drifting ice still on the Bay. Boulton wrote of the 30,000 Island district, that ‘this shore possesses all the characteristics unfavourable to the hydrographical surveyor. In the first place, the coast has by some mighty agency been broken into countless low islets and rocks. A more broken-up coastline it is impossible to conceive.’ The need to complete the survey was hastened by a growing tourist industry and the beginning of the tradition of cottage living in the summer, supplied by steamers working out of the southern ports. By this time, marked seasonal and longer term changes in lake level had been noticed, and the first systematic measurement of seasonal lake level fluctuations began in 1913. Indigenous Ojibwe legends tell of the Great Drying of the Spirit Lake when much of the floor of the Bay was exposed as climate warmed, now known to have been about 7000 years ago, during the span of lakes Hough and Stanley. The same legends speak of the waters of these lakes ‘being like tears’ a reference to their brackish waters. It may be a foretaste of things to come in a warming world and is driving further research on the history of the Bay over the last 10,000 years.
Today, Georgian Bay is a nexus of Metis, English, and Indigenous First Nation communities; a meeting place for different perspectives and stories of its varied and inspiring landscapes, and what it means to live on the edge of the rugged Shield. Georgian Bay Geopark aspires to use research, public outreach, and education about the history of our planet to promote reconciliation with First Nations. We all share common bonds of conservation and respect for the landscapes around us that have shaped Canadian history and which reconciles our futures in a shared space.
The communities surrounding Georgian Bay are moving away from a dependence on finite natural resources, primarily fishing and lumber, and welcomes millions of domestic and international visitors each year, many from Canada’s largest city (and airport) just two hours to the south drawn to the Bay’s unique land- and waterscapes and habitats. However, the unique environments of the Bay face many challenges, especially from urban development, unbridled mass tourism, and the impacts of quarrying along the Niagara Escarpment and on the Shield.
Acknowledgments
We acknowledge financial and logistical assistance in developing Geosites and producing educational modules from the Learning and Educational Advancement Fund (LEAF) at the University of Toronto, the Province of Ontario, the Department of Physical and Environmental Sciences at the University of Toronto, Scarborough, the Ontario Geological Survey and the Geological Survey of Canada. For additional geosites, a glossary of terms, index of minerals and rocks and other resources see:
https://planetearth.utsc.utoronto.ca/
https://www.ontario.ca/page/geology-and-geoscience
Further Geological Reading
Armstrong, D.K. and Carter, T.R., 2010. The subsurface Paleozoic stratigraphy of Southern Ontario. Ontario Geological Survey, Special Volume 7, 301 pp.
Barnett, P.J. 1992. Quaternary Geology of Ontario. In: Geology of Ontario. Edited by P.C. Thurston, H.R. Williams, R.H. Sutcliffe, and G.M. Stott. Ministry of Northern Development and Mines Ontario Geological Survey, Special Volume, 4, Part 2: pp. 1011–1088.
Bukhari, S., Eyles, N., Kennedy, K., Paulen, R., Ross, M. Mulligan, R. 2023. Laurentide Ice Sheet configuration during the last glacial cycle from deep stratigraphic drilling and LIDAR mapping in Southern Ontario. Canadian Journal of Earth Sciences 61, 1073-1106.
Barnett, P.J., Cowan, W.R., and Henry, A.P., 1991. Quaternary Geology of Ontario, southern sheet; Ontario Geological Survey, Map 2556, scale 1:1 000 000.
Culshaw, N., Corrigan, D., Ketchum, D.W.F., Wallace, P., Wodicka, N and Easton, R.M. 2004. Georgian Bay Geological Synthesis, Grenville Province: Explanatory Notes for Preliminary Maps P.3548 to P. 3552. Ontario Geological Survey Open File Report 6143.
Culshaw, N.G., Jamieson, R.A., Ketchum, J.W.F., Wodicka, W., Corrigan, D. and Reynolds, P.H. 1997. Transect across the northwestern Grenville Orogen, Georgian Bay, Ontario: Polystage convergence and extension in the lower orogenic crust. Tectonics, 16, 966-982.
Dickin, A, Hynes, E, Strong, J and Wisborg, M. 2016. Testing a back-arc ‘aulacogen’ model for the Central Metasedimentary Belt of the Grenville Province. Geological Magazine 153, 681–95.
Dickin, A and North, R. 2015. Nd isotope mapping of the Allochthon Boundary Thrust on the shores of Georgian Bay, Ontario: significance for Grenvillian crustal structure and evolution. Geological Magazine 152, 993–1008
Dineva, S., Eaton, D.M., Ma, S., and Mereu, R. 2007. The October 2005 Georgian Bay, Canada, earthquake sequence: Mafic dykes and their role in the mechanical heterogeneity of Precambrian crust. Bulletin of the Seismological Society of America 97, 457-473.
Doughty, M., Eyles, N., Wallace, K.W., Boyce, J.I., and Eyles, C. 2014. Lake sediments as natural seismographs: earthquake-related deformations (seismites) in central Canadian (Ontario and Quebec) lakes produced by reactivation of Precambrian structures. Sedimentary Geology 313, 45-67.
Dyke, A.S., 2004. An outline of North American deglaciation with emphasis on central and northern Canada. In: Quaternary Glaciations – Extent and Chronology, Part II, (eds.) 424. Ehlers and P.L. Gibbard; Elsevier, Amsterdam, p. 373-424.
Eyles, N. 2017. Editor. Georgian Bay: Discovering a Unique North American Ecosystem. Fitzhenry and Whiteside, Markham ON., 260 pp.
Eyles, N. and Miall, A.D. 2018. Canada Rocks: A Geologic Journey. Fitzhenry and Whiteside, Toronto. 2nd edition, 529 pp.
Eyles, N. 2013. Road Rocks Ontario: More than 250 Geologic Wonders to Discover. Fitzhenry and Whiteside, Toronto, 580 pp.
Eyles, N. 2011. Canadian Shield: The Rocks that Made Canada. Fitzhenry and Whiteside, Toronto, 128 pp.
Eyles, N., 2012. Glacially-cut rock drumlins and megagrooves of the Niagara Escarpment Ontario, Canada cut below the Saginaw-Huron Ice Stream. Quaternary Science Reviews, 55, 34-49.
Eyles, N., 2013. Road Rocks Ontario: Over 250 Geological Wonders to Discover.
Fitzhenry and Whiteside, Markham, Ontario, 570 p.
Eyles, N., Zajc, A. and Doughty, M. 2015 High-resolution seismic sub-bottom reflection record of low Hypsithermal levels in Ontario lakes. Journal of Great Lakes Research 41, 41-52.
Jamieson, R.A., Beaumont, C., Warren, C.J. and Nguyen, M.H. 2010. The Grenville Orogen explained. Canadian Journal of Earth Sciences 47, 517-539.
Jamieson, R.A., Culshaw, N.G., Corrigan, D. 1995. Northwest propagation of the Grenville orogeny near Key Harbour, Georgian Bay. Journal of Metamorphic Petrology 13, 185-207.
Ketchum, J.W.F., and Davidson, A. 2000. Crustal architecture and tectonic assembly of the Central Gneiss Belt, Georgian Bay. Canadian Journal of Earth Sciences 37, 217-236.
Krogh, T.E. 1994. Precise U-Pb ages for Grenvillian and pre-Grenvillian thrusting within the Grenville Front Tectonic Zone. Tectonics 13, 963-82.
Marsh, JH, Culshaw, NG and Gerbi, CC. 2013. Timing and conditions of poly-phase metamorphism within the Twelve Mile Bay shear zone: implications for the evolution of mid-crustal decollement zones and western Grenville tectonics. International Geology Review 55, 525-47.
Marsh, J.H, Gerbi, C.C, Culshaw, N.G, Johnson, S.E, Wooden, J.L and Clark, C. 2012. Using zircon U-Pb ages and trace element chemistry to constrain the timing of metamorphic events, pegmatite dike emplacement, and shearing in the southern Parry Sound domain, Grenville Province, Canada. Precambrian Research 192, 142–65.
McCarthy, F.M.G. and McAndrews, J.H. 2012. Early Holocene drought in the Great Lakes basin caused hydrologic closure of Georgian Bay. Journal of Paleolimnology 47, 411-428.
McCarthy, F.M.G., Tiffin, S.H., Sarvis, A.P., McAndrews J.H., Blasco, S.M. 2012. Early Holocene brackish closed basin conditions in Georgian Bay: microfossil evidence. Journal of Paleolimnology 47, 429–445.
McCarthy, F.M.G., Mertens, K.N., Ellegaard, M., Sherman, K., Pospelova, V., Ribeiro, S., Blasco, S., Vercauteren, D. 2011. Resting cysts of freshwater dinoflagellates in southeastern Georgian Bay (Lake Huron) as proxies of cultural eutrophication. Review of Palaeobotany and Palynology 166, 46-62,
Mulligan, R.P.M., Eyles, C., and Bajc, A.F. 2018b. Stratigraphic analysis of Late Wisconsin and Holocene glaciolacustrine deposits exposed along the Nottawasaga River, southern Ontario, Canada. Canadian Journal of Earth Sciences 55, p. 863-885.
Rivers, T. and Corrigan D. 2000. Convergent margin on southeast Laurentia during the Mesoproterozoic. Canadian Journal of Earth Sciences 37, 359-383.
Hynes, A. and Rivers, T. 2010. Protracted continental collision: Evidence from the Grenville Orogen. Canadian Journal of Earth Sciences 47, 591-620.
Robertson, J.A. and Card, K.D. 1974. Geology and Scenery: North Shore of Like Huron Region. Ontario Division of Mines Geological Guidebook 4, 224 pp.
Slawson, C.B. 1933. The jasper conglomerate, an Index of drift dispersion. The Journal of Geology 41, 546-552.
Thurston, P.C., Williams, H.R., Sutcliffe, R.H., and F.G. Scott. 1992. Geology of Ontario. Ontario Geological Survey, Special volume 4, Part 1 and 2. 1451pp.
Wallace, K. and Eyles, N. 2015. Seismites in Lower Paleozoic carbonates and siliciclastics: Southern Ontario. Sedimentary Geology 316, 80-95.
Discover the DEEP TIME geology of the Georgian Bay Geopark
DEEP TIME’ is the themed expression of how exploring and understanding the past helps create a better future. The unique DEEP TIME story and its eight geological chapters encourages both visitors and residents to know the past, celebrate the present and help create a more resilient future for the Bay and its many communities.
DEEP TIME Zone 1
The Huronian
Ocean
2.7 billion years
Sault Ste Marie to Serpent River
The ancient mineral-rich rocks of the North Channel record the breakup of the planet’s oldest supercontinent – and the birth of the Huronian Ocean.
DEEP TIME Zone 2
Continents
Collide
1.8 billion years
Serpent River to Killarney
The Group of Seven’s white rolling quartzite hills are the stumps of mountains formed when landmasses collided to form supercontinent Nuna
DEEP TIME Zone 3
The Ancient
Himalayas
1.3 billion years
Killarney to Honey Harbour
The waterscape of the 30,000 Islands exposes the deep crustal roots of the immense Grenville Mountains formed when North and South America collided.
DEEP TIME Zone 4
Tropical
Seas
500 million years
Manitoulin Island
Much of North America was covered by warm shallow seas, teeming with early marine life that left fossil-rich limestones on Manitoulin Island.
DEEP TIME Zone 5
The Limestone
Coast
350 million years
Tobermory to Wiarton
Within the last 2 million years, the Bruce/Saugeen peninsula was scoured by Ice Age ice sheets that cut deep valleys into the face of the Niagara Escarpment such as at Owen Sound.
DEEP TIME Zone 6
Ice Ages &
Early
Cultures
13,000 years
Collingwood to Wiarton
The raised beaches of glacial Lake Algonquin surround the coast of southern Georgian Bay like staircases and hosted the camps of caribou-hunting Paleo-Indians 11,000 years ago.
DEEP TIME Zone 7
The Meeting
Place
Last 10,000 years
Collingwood to Honey Harbour
The ancient hard rocks of the Canadian Shield meet the softer limestones of the ancient seas creating a stark contrast in landscapes, ecosystems, and a diverse cultural history unique in North America.
DEEP TIME Zone 8
Mindo Gami Great
Spirit Lake
4,000 years to today
Waters of Georgian Bay
In 1615 Samuel de Champlain called Georgian Bay ‘La Mer Douce’ (the sweet water sea). An early map also portrays it as Karegnondi, derived from ‘lake’ in the language of the Petun First Nation.