Deglaciation and Differential Postglacial Rebound in the Appalachian Region of Southeastern Quebec

Deglaciation of southeastern Quebec occurred between 12,000 and 13,000 B.P. by northwestward retreat of an active ice-front. Moraines, including the Stoke Mountain Interlobate Moraine and the Cherry River and Highland Front end moraines, which are associated with evidence of readvance, were formed during this general retreat. The Highland Front Moraine probably formed about 12,600 B.P. A complex series of glacial lakes was ponded southeast of the retreating ice-front. Isobases indicate that the water-plane of the Sherbrooke phase of Glacial Lake Memphremagog is tilted up to the northwest at 3.8 feet/mile (72 cm/ kilometer). A lower glacial-lake system may have been confluent with late-glacial water bodies in the St. Lawrence Lowland and Lake Champlain Basin. The marine limit of the Champlain Sea is at an altitude of 540 feet (165 m.); shells of the Champlain Sea have been dated at 12,000 ± 230 and 11,500 ± 160 B.P. The Champlain Sea episode may be partly correlative with Glacial Lake Iroquois and with the Two Creeks Interstadial.