AN OUTLINE OF THE QUATERNARY OF THE SAGUENAY AT ITS ENTRY

The outlet of the Saguenay fiord, near the head of the Laurentian Chan nel, is characterised by a sequence of original morpho-sedimentary uni ts including a raised (120-125 m) delta at Tadoussac, a thick fluvio-m arine valley fill in Riviere du Moulin a Baude, a 60-m high marine ter race at Pointe aux Vaches, a complex terrace at Pointe aux Alouettes, wide silty-clayey (rhythmites) terraces at Pointe Hubert and Pointe au Bouleau, a large tidal flat at Pointe aux Alouettes, and three submer ged half-moon shaped ridges. According to C-14 dates and aminochronolo gy on shell fragments from a relict sand deposit at Pointe aux Alouett es, 35 ka or older, the area was ice-free during a Wisconsinan interst adial. This marine event was followed by a period of sand and gravel d eposition, a period of marginal ice shelf deposition, and by one or se veral glacial episodes. During Late Wisconsinan, partial deglaciation and marine submergence occurred before 11.1 ka. Diamicts interstratifi ed with marine clay and a till deposit occurring to the S of the fjord outlet, the outwash raised delta at Tadoussac built between II and 10 .6 ka are correlated with the St. Narcisse event. Subsequently, the Go ldthwait Sea at least by 10.4 ka submerged the ice-free topographic de pressions of the Laurentidian Shield to a relative level 140-150 m. Th en the Laurentide Ice Sheet retreated to the NW progressively thinning on the highlands while an ice tongue remained in the fjord. This isos tatic recovery has been rapid, the 20-m level being emerged by 8 ka. A round 6 ka, the relative sea-level was approximately that of today. It rose subsequently, building the 6-m Mitis terrace dated between 1.2 a nd 1.6 ka.