A map of Canada's earth materials |
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Geoscape Canada A map of Canada's earth materials Earth Materials - Ice Age sediment
Ice Age sediment is common throughout most of Canada except in northern Yukon Territory and the western Arctic Islands. It forms a widespread, discontinuous blanket overlying rock. Most Ice Age sediment was deposited between about 20 000 and 10 000 years ago when ice sheets, similar to those in Greenland and Antarctica today, covered large areas of Canada.
Silt and clay (or mud)
Silt and clay were deposited in lakes dammed by decaying glaciers at the end of the ice ages. They were also deposited on coastal lowlands that were inundated by the sea due to depression of the land by the weight of ice sheets (e.g. lower Ottawa and St. Lawrence river valleys). Silt and clay form rich agricultural soils. Leda Clay in the St. Lawrence Valley is susceptible to landslides ('quick clay' failures).
Figure 9. Sandy silt, Niagara Peninsula, Ontario (R.J.W Turner).
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Figure 10. The Red River flows across a flat plain of ancient glacial lake silt (G.R. Brooks).
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Sand and gravel
Sand and gravel were deposited by streams flowing from retreating glaciers at the end of the ice ages. They are important sources of aggregate used in road construction and in the production of asphalt and concrete. Groundwater aquifers in shallowly buried sand and gravel bodies provide important water supplies to communities across Canada.
Figure 11. Coarse gravel, Coast Mountains, British Columbia (J.J. Clague).
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Figure 12. Gravel pit, southern Ontario (A.V. Morgan).
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Till
Till, the most common surface material in Canada, is debris deposited by glaciers. It consists of a mix of clay, silt, sand, and gravel. The composition of till is closely related to that of the rock from which it is derived. Typically, calcareous till overlies carbonate terrane, clay-rich till overlies shale and volcanic terranes, and sand-rich till overlies granitic terrane.
Figure 13. Till, southern Vancouver Island, British Columbia (J.J. Clague).
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Figure 14. Hummocky till terrain, southern Alberta (J.J. Clague).
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