Morphodynamics in Sediment-Starved Inner-Shelf Submarine Canyons (Pointe-des-Monts, Eastern Canada)

English Abstract:

The activity and sedimentary processes in a series of inner-shelf submarine canyons located in the Lower St. Lawrence Estuary was examined using high-resolution multibeam bathymetry, backscatter and seismic data as well as by analyzing a ~9 m-long sediment core. The presence of crescentic bedforms, probably representing cyclic steps that were displaced upslope at the bottom of the canyons between 2007 and 2012 indicates that they are currently active through the remobilization of sediment by gravity flows. However, the shelf and shores of the region are characterized by the absence of sediment. Our results indicate that gravity flows currently eroding the canyon floors do not transport new material downslope coming from the shelf but rather remobilize in-situ deglacial sediments within the canyon thalweg. End-member modeling analysis performed on grain-size distributions reveals the presence of quasi-continuous flows within the canyons and the presence of only one turbidite. Based on these results, we suggest that frequent hydrodynamic processes and infrequent slope failures are responsible for sediment remobilization in these canyons, although their role in the upslope migrating crescentic bedforms is still unclear. This presentation provides further evidence that sediment supply is not a prerequisite for the origin and activity of inner-shelf submarine canyons.