A catastrophic flood event layer in Champlain Sea sediments recorded at the 2010 St. Jude landslide (Québec, Canada): regional stratigraphic insights from piezocone data

As part of the 2010 St. Jude landslide study, a detailed investigation of a distinctive high strength piezocone signature within the lower Champlain Sea sediment sequence revealed a mass transport deposit containing red beds. Base on geotechnical and sedimentological properties, this deposit is interpreted as an event layer that records an abrupt change in sedimentation conditions in the western Champlain Sea. Similar high strength signatures have been identified at multiple sites in the St. Lawrence Valley where they appear to influence the location of failure surfaces in some retrogressive landslides. The widespread occurrence of this layer suggests deposition during a single sedimentological event across the western Champlain Sea basin approximately 11,500 years ago, likely associated with a catastrophic outburst flood event of cold and oxygen-rich water from glacial Lake Algonquin through the Ottawa River Valley. The timing of this event could be related to the Preboreal Oscillation cooling event (~11,500 cal yr BP). Drawing on numerous piezocone profiles from the western Champlain Sea region, a schematic stratigraphic model, including the event layer, is proposed to support subsurface investigations and improve the risk assessment of large retrogressive landslides in this area.