Deglaciation of The Central St. Lawrence Lowland and The Champlain Sea


Correlation of paleowater levels along the southern margin of the Champlain Sea and in the Lake Ontario basin show that a proglacial lake covered part of the lowland before the Champlain Sea inundated the area. The Candona subtriangulata ostracod assemblage in rhythmically-laminated or varve like sediments below Champlain Sea deposits is evidence for a pre-Champlain Sea proglacial lake. (Rodrigues, 1992) pointed out that rhythmites characterized by the ostracod Candona subtriangulata and the absence of forminifers were deposited in a pre-Champlain Sea proglacial lake, glacial Lake St. Lawrence, and those characterized by foraminifers and/or the ostracod Cytheropteron pseudomontrosiense and the absence of Candona subtriangulata were deposited in a glaciomarine envirnoment.

The Candona subtriangulata assemblage also is present in rhythmically-laminated sediments stratigraphically above the maximum extent of the Champlain Sea south of the St. Lawrence River in New York and west of th Champlain Sea in the Lake Ontario Basin. The assembledges west of the maximum extent of the Champlain Sea are related to glacial Lake Iroquois and post-Lake Iroquois levels in the Lake Ontario basin. Glacial Lake Iroquois expanded into the central St. Lawrence Lowland after ice retreated from the eastern end of the basin, providing a corridor for the migration of Candona subtriangulata into the lowland. Main Lake Iroquois ended with drainage through the Covey Hill gap into glacial Lake Vermont in the Lake Champlain basin. During the retreat of the ice from the Covey Hill area, glacial Lake Iroquois and glacial Lake Vermont merged to form glacial Lake St. Lawrence. This lake includes the Belleville phase of post Lake Iroquois levels in the Lake Ontario basin and the lowermost Fort Anne phase of glacial Lake Vermont in the Champlain Valley.