DISCOVERY OF A MIDDLE HOLOCENE FOSSILIZED LANDSLIDE, AT MONTMAGNY, SOUTH SHORE OF THE ST.-LAWRENCE ESTUARY, QUEBEC

Discovery of a middle Holocene fossilized landslide, at Montmagny, sou th shore of the St. Lawrence estuary, Quebec. A small middle Holocene rotational slump has been discovered at Montmagny, south shore of the St. Lawrence estuary. Portions of the apron (foot) and of the bowl (am phitheater) have been exposed by recent erosion of the upper tidal mar sh and of the former cliff in front of the 8-m terrace in which the la ndslide occurred. This slope failure in a silty-clay deposit happened after 5.8 ka, but most likely around 5 ka. The ruptured zone was refil led by an intertidal stratified deposit during the Laurentian Transgre ssion. As a consequence, there is no evidence in the present day topog raphy of this former landslide. This is one of the rare known examples of a fossilized landslide.