Virginia Brake

Partly-filled U-shaped morphology of the Laurentian Channel, St Lawrence Estuary, Canada

The geomorphology of the St Lawrence Estuary seafloor is dominated by post-glacial landforms and processes. However, some segments of the estuary are still characterized by a U-shaped morphology, inherited from one or more glacial episodes, that is only partially modified by postglacial sedimentation. Marine-geophysical data on the morphology and stratigraphy of the estuary are used to describe and interpret this partly sediment-filled submarine environment. The Laurentian Channel is a long and continuous trough >300 m deep that extends 1500 km from the mouth of the Saguenay River in the St Lawrence Estuary to the edge of the continental shelf in the Atlantic Ocean (Fig. 1). It is a clear physiographic feature, whose U-shaped morphology in cross-section, including steep bounding escarpments, is particularly well developed at its upstream (western) extent (Fig. 1a). Fig. 1. Multibeam bathymetry, high-resolution seismic and schematic geometry of the U-shaped segment of the Laurentian Channel in the St Lawrence Estuary. ( a ) Sun-illuminated multibeam-bathymetric image showing the U-shaped portion of the Laurentian Channel (LC). Acquisition system Kongsberg EM1000 (before 2005) and Kongsberg EM1002 (2005 and 2006 surveys). Frequency 95 kHz. Grid-cell size 10 m. ( b ) Perspective view from the NE. VE ×15. ( c ) Perspective view from the east …