LATE PLEISTOCENE DEGLACIATION OF THE LAURENTIDE ICE SHEET, ACROSS AND NORTH OF THE USA-CANADA INTERNATIONAL BORDER

Complex sequences of ice marginal and frontal deposits have been mapped and documented in the Saint-François and Chaudière river valleys, north of the international border. In most cases, these sediments and landforms as well as other geomorphological features, are valuable indicators of the extent of former ice-dammed lakes, as their elevation is strongly constrained by well-documented outlets. In the case of the Lake Memphrémagog and of some of its earlier unnamed phases, the outlets are located on both sides of the USA-Canada border. The routing of surface water drainage and its link to glacial lakes documented in the Connecticut and Hudson river valleys have been revisited. As their chronological framework has been recently synchronized using 14C ages-controlled paleomagnetic signatures, the evolution of the Glacial Lake Memphrémagog phases can now be drawn into a new time-space correlation scheme across the Saint-François River and the Lake Champlain valleys. In the Chaudière River drainage basin, glaciolacustrine conditions prevailed as well during deglaciation, the ice-dammed lake outlet routing the meltwaters through the Chain Lakes in West-Central Maine. Therein, most of the surface drainage is sub-aerial, mostly on the lee-side of the major drainage divide between the Atlantic Maine coastal waters and the nascent Chaudière River system and hence, chronological control is poor. As ice retreated from the Famine-Daquaam outlet, meltwater drainage was open to the unglaciated parts of the Saint-John River Valley, and hence to the Bay of Fundy marine basin. New field and geochronological data are being acquired in the Chaudière Basin, in the course of a groundwater/Quaternary geology mapping project that was initiated in late Fall of 2006, some of which will be presented at the meeting.