Deglaciation of the Rimouski area, Lower St. Lawrence (Quebec): stratigraphical evidences of a glacial readvance into the Goldthwait Sea between 12,400 and 12,000 yr BP.

The spatial distribution of landforms associated with the deglaciation of t he Rimouski area (outwash deltas, eskers, kames, and ice disintegration fea tures) was analysed in relation to the morphostructural framework. The main physiographic elements are NE-SW ridges and depressions parallel to the St . Lawrence Valley. To regional scale, the St. Lawrence Valley played a majo r role in the pattern of deglaciation. The fast penetration of the Goldthwa it Sea along the St. Lawrence Valley from the Gulf to Quebec City between 1 4 000 and 12 400 yr BP isolated a regional ice cap on the Appalachian Mount ains. After the passage of the calving bay through the study area, slightly before 13 360 yr BP, the Appalachian ice margin stabilized along the first prominant Appalachian ridge (> 140 m) behind the present shore line. This suggest that this ridge helped to anchor the ice cap margin along the south ern shore of the Goldthwail Sea. When ice margin retreated behind the first major Appalachian ridge between 13 360 and 12 700 yr BP, large dead ice bo dies were abandonned in the Neigette fault-line valley and in the valleys n ear Saint-Fabien. Between ca. 12 400 and 12 000 yr BP, the Appalachian ice front stood along the margin of the Sainte-Blandine plateau, only 13 km beh ind the present shore line. Stratigraphical data indicate that Appalachian ice readvanced into Goldthwait sea during this stage (Older Dryas?). The pa ttern and chronology of deglaciation beyond the marine limit are still unkn own.