1. 10. The Glaciation of Canada
Quaternary periods – time scales
The older glacial period
Pre-Sangamon
Sangamon interglacial
Early and middle Wisconsin events
The late Wisconsin
Glacial lakes
Depositional and erosional zones

2. (a) Quaternary periods (geological time scales)
Quaternary period: last 1.65 million years
Quaternary:
Holocene (last 10,000 years)
Pleistocene
. Wisconsin glacial (from 75 ka)
. Sangamon (interglacial); from 130 ka
. Early Pleistocene
(ka: thousands of years)

3. (b) The older glacial period
Pre-Sangamon:
Some evidence of glacial and nonglacial stages dating back to early Pleistocene
Evidence of pre-Wisconsin glaciations in several areas (sometimes as many as three)
e.g. presence of till beneath deposits considered to be of Sangamon age

4. Sangamon Interglacial and early Wisconsin events
Late Pleistocene stratigraphy of Toronto area (e.g. exposed along Scarborough Bluffs):
Why lacustrine sediments: elevation above lake Ontario suggests that water level was as much as 20 m higher than today
Early and middle Wisconsin events: from 75,000 to 23,000 years ago: no consensus on the extent of glacial ice in Middle Wisconsin (Non-glacial conditions in western Canada and major part of Ontario probably).

5. (c) The late Wisconsin
Continental ice sheet in late Wisconsin (from 23,000 to about 10,000 years ago)
General agreement on at least three ice centers (centers of ice accumulation and dispersal)
These centers controlled independent flow patterns and ice “divides”

6. Laurentide Ice sheet Three ice caps:
High arctic glacial complex
Cordilleran glacial complex
Ice flowing radially outwards from a central dome located over Hudson Bay
Extent of Laurentide ice sheet and retreat:

7. Maximum dimensions approximately 18,000 years ago
Slight changes in position from 18,000 to 14,000 years ago
Significant retreat after about 13,000 years
About 11,000 years ago, formation of the Champlain sea in St-Lawrence valley

8. Extent – retreat of Laurentide ice sheet (cont.)
8000 years ago: Tyrell sea in Hudson Bay; regional ice masses predominant
Final retreat only about 6000 years ago (Labrador – New Quebec ice)

10. (d) Glacial Lakes and seas
Isostasy (glacial isostasy): Involved the depression of the land owing to the weight of a large body of ice, and uplift or rebound as a result of disintegration or retreat of the ice
Ice retreated, sea flooded depressed coastal regions

11. Proglacial lakes and seas
Champlain sea
Goldthwait sea; Gulf of St-Lawrence, east of Quebec city
Tyrell sea; around Hudson Bay
Largest lakes formed around the margins of the Laurentide ice sheet.

12. Formation of glacial lakes
Glacial meltwater confined between ice margin (as glacier retreats) and higher land (deglaciated)
Retreating ice prevents drainage towards Hudson bay
Tow main reasons:
Isostatic uplift
Fluctuations in position of ice margins

13. Proglacial lakes
More than 50% of the area occupied by Laurentide ice sheet was, following the deglaciation, covered by water
Largest proglacial lakes: Agassiz and Barlow-Ojibway
Agassiz: Biggest of all proglacial lakes. Disappeared about years ago.

14. Lake Aggassiz
Covered, at it maximum extent, almost 106 km2 in Northern USA, as well as major parts of Ontario, Manitoba and Sask.
Began its formation 11,700 years ago while Laurentide ice sheet was retreating

15. (e) Depositional and erosional zones in Canada
Conflicting opinions about amount of erosion associated with continental ice sheets of north America
Unconfined glacial flow does not accomplish large amounts of erosion (as opposed to confined, valley glaciers, fro instance).
e.g.: tills deposited near margins of continental ice sheets do not contain large amounts of shield material

16. Last glaciation: average depth of erosion of the order of 1-2 m??
Most research workers believe that total amount of glacial erosion on the shield during the whole Pleistocene was less than 20 m.

17. Tills…
Tills: poorly sorted (i.e. wide range of particle sizes), glacially deposited sediment.
Characteristics of a till in a given area determined by:
Type of bedrock
Way debris are carried by ice
Distance of travel
Glacial erratics: rock fragments carried by the ice from their place of origin and left in an area where there is a different type of bedrock.

18. Tills and moraines
Most tills in Canada formed in the Wisconsin glacial stage (23,000 to 10,000 years B.P.)
Tend to have a rather coarse matrix; thickness often of the order of a few meters (although highly variable locally)

19. Glacial erratics…
Current view of glacial flow patterns associated, in part, with presence of erratics and tills
Erratics distributed in long, narrow dispersal trains, extending back to their source areas

22. Moraines
Ridges or mounds of glacial material deposited at, or close to, the ice margins
Terminal moraine: observed close to the former margin of the ice sheet; not common in central zones where ice retreated and melted
When mapped, terminal moraines provide valuable indications of the position(s) of the ice margin.

23. Terminal moraines in Canada

24. Note on Oak Ridges Moraine
Formed about 13,000 years ago, at the margin of an advancing ice lobe.
Part of the deposit was overridden and covered by the advancing ice.

25. Deglaciation – the “Ontario island”

26. Moraines of southern Ontario

27. Drumlins
Drumlins: a mound of glacial debris with the longitudinal axis parallel to the direction of ice movement
Origin still a matter of debate.
Differential erosion of bedrock
Hollows at the base of glaciers (due to subglacial meltwater), subsequently filled with sediment
Length-to-width ratios: 1:3
Height: meters common.

28. Drumlin formation and morphology

29. Eskers Sinuous ridges of glaciofluvial material.
Long eskers constructed in stages as ice margins retreated
Two major formation processes:
Streams contained within tunnels running through the ice or along its floor
In open, ice-walled trenches
Stagnant ice provides sufficient meltwater for the formation of eskers.

30. Eskers (cont.)
During final deglaciation stages, down-wasting and ice stagnation. Esker formation in tunnels at the ice base (more eskers on the shield than surrounding areas)

32. Orientation of streamlined features

33. Sequence of depositional landforms
A simple model to account for the distribution of glacial depositional landforms from an ice dispersal centre
Erosion dominates in the vicinity of the ice dispersal centre. Deposition becomes progressively more important as we move towards outer zone
Basal debris “streamlined”
Deposition and glaciofluvial deposits by meltwater dominates the outer area.