LATE-WISCONSINAN DEGLACIATION AND DEVELOPMENT OF PROGLACIAL LAKES IN THE CHARLEVOIX REGION, SOUTHEASTERN QUÉBEC

The Charlevoix region, in southeastern Québec, is characterized by a dramatic landscape formed by the junction of the Laurentian Highlands, the Charlevoix Astrobleme and the St. Lawrence Estuary. This study, based on two extensive field campaigns and the interpretation of high-resolution 3D digital air photos and LiDAR data, documents a glacial landsystem dominated by the development of proglacial lakes during deglaciation due to a very irregular topography and the presence of major moraine systems. Our results provide a relative chronology for the development and drainage of series of proglacial lakes formed during each successive stage of deglaciation. In the region, the Laurentian Highlands are characterized by a high plateau (700-1174 m) and deeply incised river valleys (Malbaie, Saint-Anne, à Mars). The Charlevoix Astrobleme is characterized by a circular graben (Malbaie and du Gouffre river valleys) and a central uplift (Mount of Éboulements and Saint-Hilarion hills). Four moraine systems are observed in the region: the Rochette and Brûlée-Sainte-Anne systems, probably developed during the Older Dryas (~ 14 cal. ka BP), and the Saint-Narcisse and Mars-Batiscan systems dating from the Younger Dryas (12.9 to 11.7 cal. ka BP). Deltas, varves, coastal deposits, lacustrine terraces, breaches and drainage deposits were used to identify 91 proglacial lakes. Five types of proglacial lakes were identified based on their location, orientation, type of dams, associated moraine complex and stratigraphy: 1- Jean-Noël and du Seigneur valley lakes, constrained by glacial ice in the St. Lawrence Estuary or by the Rochette moraine, and draining later into the Goldthwait Sea; 2- Astrobleme side valley lakes, constrained by du Gouffre and Malbaie glacial tongues and draining into the graben of the astrobleme; 3- Sainte-Aimée-des-Lacs lakes, constrained by moraine ridges associated with Saint-Narcisse moraine systems; 4- Sainte-Anne Sector lakes, constrained by Brûlé-Sainte-Anne moraines or by valley glaciers lakes and draining through the Sainte-Anne and Montmorency river valleys; 5- Northern Laurentian lakes: constrained first by the Laurentide Ice Sheet and then by the moraines of the Saint-Narcisse and Mars-Batiscan moraine systems, and draining northward towards Lake St-Jean and Saguenay River.