Role of the bedrock topography in the Quaternary filling of a giant estuarine basin: the Lower St. Lawrence Estuary, Eastern Canada

Abstract

The geometry of estuarine and/or incised‐valley basins and their protected character compared with open sea basins are favourable for the preservation of sedimentary successions. The Lower St. Lawrence Estuary Basin (LSLEB, eastern Canada) is characterized by a thick (>400 m in certain areas) Quaternary succession. High‐ and very high‐resolution seismic reflection data, multibeam bathymetry coverage completed by core and chronostratigraphic data as well as a 3‐D seismic stratigraphic model are used to document the geometrical relationships between the bedrock and the Quaternary units of the LSLEB. The bedrock geometry of LSLEB is characterized by two large troughs that are interpreted as resulting mainly from repeated (?) periods of glacial overdeepening of a pre‐Quaternary drainage system. However, other mechanisms with complex feedback effects such as differential glacio‐isostatic uplift, erosion, sedimentary supply, and subsidence may have contributed to the formation of bedrock troughs. The two large bedrock troughs are mostly filled by ∼200 m thick Wisconsinan (Marine Isotopic Stages 2–4) and possibly older sediments. Overlying units recorded the retreat of the Laurentian Ice Sheet during the Late Wisconsinan (Marine Isotopic Stage 2) and estuarine conditions during the Holocene. The strong correlation existing between the bedrock topography and the thickness of the Quaternary succession is indicative of the effectiveness of the LSLEB as a sediment trap.

Holocene Refreshening and Reoxygenation of a Bothnian Sea Estuary Led to Enhanced Phosphorus Burial

“…The central Bothnian Bay was also likely more saline and productive in the early Holocene than today (Ingri et al 2014). Other brackish basins have also been subject to Holocene isostatic uplift, such as the Lower St. Lawrence Estuary and Norwegian Fjords (Skei 1988;Duchesne et al 2010). These basins may also have become more vulnerable to hypoxia since deglaciation, as proposed recently by Jilbert et al (2015).…”

LiDAR Validation of a Video-Derived Beachface Topography on a Tidal Flat

“…Despite previous Quaternary [52][53][54], coastal erosion [51], and sea ice [55,56] studies in the area, little is known on the morphodynamics of the Manicouagan beaches. Coastal citizens are facing constant erosion and one of the hotspots is located on the beach of Pointe-Lebel ( Figure 1c).…”

“…Beaches of the Manicouagan Peninsula can be exposed to strong ENE winds blowing on a 350 km long fetch [53]. Being oriented ESE, this is especially the case of the Pointe-Lebel beach where the video camera system is located.…”

Origin and provenance of spherules and magnetic grains at the Younger Dryas boundary

“…The extent to which pre-YDB sediment was present in the St. Lawrence estuary around Sept Iles is not known. A recent study combines seismic reflection data, multibeam bathymetry, and core and chronostratigraphic data to infer that ∼26-93 m of pre-Holocene till was deposited in the Lower St. Lawrence estuary farther to the west of Sept Iles (61). If Quebecia-derived till blanketed the Ordovician limestone around Sept Iles at the time of the Corossol impact, it could be the source of Melrose (and Newtonville) spherules.…”