THE MITIS TERRACE AT POINTE AUX ALOUETTES, NORTH SHORE OF THE MIDDLE ST-LAWRENCE ESTUARY, QUEBEC

There is a remnant of the Micmac shoreline at Pointe aux Alouettes, at the entry of the Saguenay fjord. This shoreline is composed of the Go ldthwait's Micmac cliff and of the Dionne's Mitis terrace. The low ter race is a polygenic feature built in two stages. During the first epis ode erosional shore processes cut a platform and a cliff into the loca l silty-clayey 20-m terrace. During the second episode, fine-grained i ntertidal deposits and coarse-grained shore deposits accumulated on th e platform and isolated the former cliff. Whence emerged, about a thou sand years ago, alluvial cones (mud flows) were built at the outlet of small ravines cut into the Micmac cliff. Locally and away from the ba se of cliff, thin sheets of rainwash colluvium progressively accumulat ed over the former terrace surface. The mean radiocarbon age of the in tertidal and shore deposits is respectively 1.4 and 1.3 ka. At Points aux Alouettes, the Mitis terrace is about 600 years younger than elsew here along the St. Lawrence estuary. Despite a recent mean rate of lan d emergence 5.7 mm/yr during the last three decades, the mean annual e rosion rate of the Mitis terrace has been approximately 100 cm.