La batture de l’anse au Sable à Rimouski : un estran typique de la rive sud de l’estuaire maritime du Saint-Laurent, Québec

• Published in: Géographie physique et Quaternaire
• Main Author: Dionne, Jean-Claude
• Format: Text
• Language: French
• Published: Les Presses de l'Université de Montréal 2007
• Subjects: geo; envir; Goldthwait; Gravier; Sandy Cove; The Handle; Ice Sheet
• Online Access: https://doi.org/10.7202/038992ar; http://id.erudit.org/iderudit/038992ar

Among the various cold region shorelines, those of the Lower St. Lawrence estuary have particular characteristics that need to be better known. The shore at Anse au Sable (Sandy Cove), near Rimouski, is of special interest. Located at the foot of an Appalachian rock ridge oriented SW-NE, the shoreline includes a narrow sandy gravel beach at the high tide level, a relatively wide rock platform in the upper half of the strand, and, in the lower half, a clayey substrate which is covered by boulders, 65 % being Precambrian erratics from the Laurentidian Shield located 30 km north of the St. Lawrence valley. Precambrian and Appalachian far-travelled erratics were first moved toward the estuary by Wisconsinian glaciers. Most erratics were then transported and dropped on the sea floor of the Goldthwait Sea by icebergs during deglaciation between 13 and 10 ka. An unknown percentage of Precambrian erratics, first displaced by the Laurentide Ice Sheet and dropped in the Appalachian region, were removed and displaced northward and northeastward at the Late Glacial maximum. The sedimentary errratics at Anse au Sable have two origins. Most are from local bedrock outcrops near the present shoreline, whereas a low percentage are from the Ordovician and Silurian formations of the Appalachians south of the coastal area submerged by the postglacial sea. Erosion by waves and currents during the Holocene of shore and marine clay deposits containing ice rafted coarse debris resulted in a boulder lag from which boulders were removed by shore ice and concentrated on the lower clayey tidal flat. Parmi les rivages des régions froides, ceux de la rive sud de l’estuaire maritime offrent des particularités qui méritent d’être mieux connues. Celui de l’anse au Sable, près de Rimouski, appartient à cette catégorie. Situé le long d’une crête rocheuse appalachienne orientée SO-NE, il comprend dans la partie supérieure un étroit cordon littoral composé de sable et gravier, une ancienne plate-forme rocheuse qui occupe la moitié supérieure du ...