Deltaic Complexes of the Québec North Shore

Abstract

One of the most particular morphological features of the Québec North Shore (North Shore of the Estuary and Gulf of the St. Lawrence, eastern Canada) is the occurrence of deltaic complexes that form thick and extensive sediment bodies (gravel, sand and mud) along the modern coastline. The deltaic complexes were emplaced during the retreat of the Laurentide Ice Sheet from the region that commenced about 11 ka in the context of falling relative sea level. Deltaic complexes are made up of three distinct, superimposed depositional systems, consisting of: (1) ice-contact subaqueous fans and deltas, (2) ice-distal glacifluvial deltas, and (3) coastal suites and meandering channel belts. Ice-contact systems were emplaced immediately after deglaciation of the region at the front of the ice-margins. Subsequent ice retreat fed glacifluvial deltas in meltwater and glacigenic sediments until the complete retreat of the ice-margin from the drainage basin a few thousand years ago. The resulting shutdown in sediment supply led to the reworking of the now-inactive glacifluvial deltas by shore-related and fluvial processes that resulted in the deposition of coastal suites and meander channel belts. Submarine sediment accumulations and related morphologies revealed by high-resolution swath bathymetric and seismostratigraphic data collected off these deltaic complexes are the subaqueous counterparts of these deltas. The modern evolution of these deltaic complexes is controlled by the reworking, transport, and deposition of sediments by shore-related processes along the coast, on the shallow shelf, and through submarine channels and canyons.