La déglaciation de la région de Rimouski, Bas-Saint-Laurent (Québec) : indices d’une récurrence glaciaire dans la Mer de Goldthwait entre 12 400 et 12 000 BP

• Published in: Géographie physique et Quaternaire
• Main Author: Hétu, Bernard
• Format: Text
• Language: French
• Published: Les Presses de l'Université de Montréal 1998
• Subjects: Barres; Goldthwait; Ice cap
• Online Access: http://id.erudit.org/iderudit/004832ar; https://doi.org/10.7202/004832ar

The spatial distribution of land- forms associated with the deglaciation of the Rimouski area (outwash deltas, eskers, kames, and ice disintegration features) 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 major role in the pattern of deglaciation. The fast penetration of the Goldthwait Sea along the St. Lawrence Valley from the Gulf to Québec City between 14 000 and 12 400 yr BP isolated a regional ice cap on the Appalachian Mountains. 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 southern shore of the Goldth- wait Sea. When ice margin retreated behind the first major Appalachian ridge between 13 360 and 12 700 yr BP, large dead ice bodies were abandonned in the Neigette fault-line valley and in the valleys near 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 behind the present shore line. Stratigraphical data indicate that Appalachian ice readvanced into Goldthwait sea during this stage (Older Dryas?). The pattern and chronology of deglaciation beyond the marine limit are still unknown. La distribution des dépôts de marge glaciaire de la région de Rimouski a été analysée en fonction du cadre morphostructural préglaciaire, caractérisé par un relief appalachien typique dont les barres et les sillons, orientés NE-SO, sont subparallèles à la vallée du Saint-Laurent. Cette étude met en lumière l'influence déterminante du contexte morphostructural sur le mode de déglaciation, tant à l'échelle régionale que locale. L'invasion de la Mer de Goldthwait le long du Saint-Laurent, à partir de 14 000 BP, isole ...