Some problems of late Wisconsin history and geochronology in southeastern Ontario

Palynological studies and radiocarbon dating of sediments from about 20 lakes and bogs in southeastern Ontario have been used to establish a palynostratigraphic sequence of six pollen zones extending to approximately 12 000 years BP and indicating that deglaciation occurred between 12 500 and 11 500 years BP, probably during the Two Creeks interstadial interval.The glacial Lake Iroquois existed in the Lake Ontario basin from about 12 500 – 11 800 years BP while the Lake Ontario ice lobe was retreating northeastward, and the Kirkfield – Fenelon Falls outlet from glacial Lake Algonquin (in the Georgian Bay – Lake Huron basin) to Lake Iroquois opened about 12 000 years ago when the Dummer Moraine was deposited as a stagnant ice disintegration feature south of the Algonquin and Haliburton Highlands.Most radiocarbon dates (about 25) on marine shells, whale bone, and algae from Champlain Sea beach deposits are in the range of 10 000 – 11 800 years BP, indicating that the Champlain Sea episode is younger than glacial Lake Iroquois. However, a few Champlain Sea dates are older than 12 000 years BP and present an unresolved problem in geochronological correlation because they conflict with proposed deglaciation histories for southeastern Ontario.Late Wisconsin ice marginal positions are poorly known in southeastern Ontario and comprise another problem for further study.The end of glacial Lake Algonquin phase (the main drainage event in the North Bay area) probably occurred between 10 800 and 10 500 years BP, after the Champlain Sea had reached its maximum western limit in the Pembroke area (upper Ottawa River valley) as indicated by stratigraphic relationships of surficial deposits.