Abstract:
Sediment relationships observed during geological mapping
in southeastern Ontario indicate a relatively simple deglaciation
history for the area during late Wisconsin time. The
ice from the north (part of the Lake Simcoe lobe) and the
Lake Ontario ice lobe, which were coalesced during most of late
Wisconsin time, initially separated along the crest of the
Oak Ridges Moraine. Available data indicate that the Oak
Ridges Moraine is composed primarily of sediments pre-late
Wisconsin in age capped by late Wisconsin till and interlobate
deposits.
Retreat of the northern ice was relatively steady and
resulted in the deposition of the Dummer Moraines, a facies
of the drumlinized till to the south. Retreat of the Lake
Ontario ice lobe into the Lake Ontario basin was interrupted
by a re-advance which covered the southeastern half of the map
area. The northern ice had already retreated from the area
by this time. The Lake Ontario lobe was fed through the
St. Lawrence Valley, indicating that the Ottawa Valley was
ice filled at this time.
High level glacial lakes fronted the ice during deglaciation.
These waters quickly fell to low levels as the ice
retreated from the St. Lawrence Valley, opening lower outlets.
