Late Wisconsin Ice Sheets in North America

106

margin, the coastal mountains of Labrador-Un-
gava and Baffin Island are the dissected edges of 
plateau blocks that have been uplifted and tilted. 
Of two early views of Wisconsin ice extent, the 
first proposed limited Wisconsin ice extent. Fol-
lowing the work by Lieber (1861), Daly (1902) 
suggested that the Torngat Mountains in Labra-
dor were not overtopped by Labradorean (Lau-
rentide) ice that streamed through deep troughs 
toward the Atlantic. This conclusion was based 
largely on the observed upper limit of glacier 
deposits, as well as on the presence of wide-
spread felsenmeer at high levels. Coleman (1920, 
1921) later agreed with these conclusions and 
even argued that Laurentide ice did not reach 
the Atlantic. Coleman (1921, 1926) further pos-
tulated that Wisconsin Laurentide ice did not 
overrun the southeast coast of Labrador and that 
the widespread presence of high-lying felsen-
meer suggests that much of Newfoundland re-
mained free of ice throughout Wisconsin time. 
The second early theory, which supported more-
extensive Wisconsin ice, was put forward by 
Odell (1933) and accepted by Tanner (1944). The 
main evidence cited for this viewpoint was the 
presence of high-level erratics and poorly pre-
served striations; the felsenmeer was assigned a 
postglacial age. Flint and others (1942) postu-
lated, on the basis of high erratics and striated 
surfaces, that the Shickshock Mountains in the 
Gaspe Peninsula were overrun by Wisconsin ice; 
felsenmeer on the summits was again thought to 
have originated in postglacial time. Subse-
quently, Flint (1971, p. 484-485) inferred that the 
Laurentide Ice Sheet overran all coastal high-
lands between New York and Labrador at some 
time during the Wisconsin glaciation. 

The modern view of Wisconsin ice extent has 
its roots in field work carried out in the past two 
decades (reviewed by Ives, 1978). The major re-
sult has been the development of the weathering 
zone concept. The weathering zones envisioned 
are not to be confused with the geologic terms 
"weathering zone" or "zone of weathering," 
which refer to a weathered zone in bedrock or 
regolith that is nearly parallel with the surface 
(Flint, 1971, p. 287). Rather, it refers to "units of 
the land surface which are distinguishable from 
each other on the basis of the distinct weathering 
features that record different lengths of time 
through which they have formed" (Dyke, 1977, 
p. 40). Three broad weathering zones, as well as 
possible subdivisions, have been recognized 
along the entire northeastern margin of the Lau-

rine limit (Fig. 2-2) show a distinct pattern of 
calving-bay propagation into northern Lauren-
tide ice. This pattern in itself is a strong indicator 
that the maximum reconstruction in Figure 2-2 
is more nearly correct than the minimum. The 
sea penetrated northwestern ice-stream channels 
in M'Clure Strait and Amundsen Gulf by 12,600 
BP, at least 3000 yr prior to penetration of the 
eastern ice-stream channel in Lancaster Sound. 
In fact, the Amundsen Gulf ice stream had re-
ceded by 10,215 BP to Coronation Gulf, where 
a bottleneck checked calving-bay propagation; 
also, the M'Clure Strait ice stream lay against the 
Winter Harbor moraine between about 11,000 
and 10,000 BP, without concurrent recession of 
the Lancaster Sound ice stream in the east. Rapid 
breakup of northern Laurentide ice commenced 
after 10,000 BP with the withdrawal of ice from 
the Winter Harbor moraine. A calving bay had 
propagated eastward into Viscount Melville 
Sound by 9800 BP and into Barrow Strait north 
of Prince of Wales and Somerset Islands by 9380 
BP. Westward propagation of a calving bay into 
Lancaster Sound was underway by 9280 BP. Sub-
sequently, coastal Somerset and Prince of Wales 
Islands, as well as northern Boothia Peninsula, 
were largely cleared of ice by 9200 BP, and the 
southern Gulf of Boothia was cleared by 8870 
BP. Thus, the northern sector of the Laurentide 
Ice Sheet was dissected by calving bays that 
propagated inland to the upper marine limit. By 
8160 BP, the northern ice-sheet margin, no 
longer being dissected by calving bays, lay 
against the MacAlpine moraine system (Blake, 
1966), which partly outlines the residual Kee-
watin dome, and against moraines on Melville 
Peninsula (Craig, 1965a), which may possibly 
mark the western margin of a residual dome in 
Foxe Basin. Recession from these moraine sys-
tems and final ice-sheet disintegration are dis-
cussed with the history of the interior of the Lau-
rentide Ice Sheet.

Northeastern Sector

Late Wisconsin Maximum. The northeastern 
margin of the Laurentide Ice Sheet, particularly 
in Labrador and Baffin Island, is discussed in 
detail here, because the concepts derived from 
studies of this margin have greatly influenced 
development of the model of a restricted Arctic 
ice cover during the late Wisconsin glaciation. At 
its maximum, the northeastern margin of the Lau-
rentide Ice Sheet extended from the Maritime 
Provinces to northern Baffin Island. Along this