Late Quaternary Evolution of Fjord-Lakes Pentecôte, Walker and Pasteur (Québec North-Shore, Eastern Canada)

English Abstract:

High-resolution bathymetric data acquired using a multibeam echosounder and an interferometric side-scan sonar in 2011 and 2014 allowed mapping the sublacustrine geomorphology of three fjord-lakes of the Québec-North Shore region (eastern Canada) for the first time. Detailed bathymetric maps with a 1 to 3 m resolution produced during these surveys allowed the observation of deep V-shaped bedrock valleys, morainal banks, deep and circular depressions (kettles?), disintegration moraines, slide scars, mass movement deposits and crescent-shaped bedforms. These lakes, located near Younger Dryas morainic systems, were flooded during the Goldthwait Sea postglacial marine transgression and contain sedimentary archives that recorded paleo-environmental changes that have occurred since the last glaciation. Acoustic sub-bottom profiles acquired using a bi-frequency Chirp echosounder (3.5. & 12 kHz), together with sediment core data, reveal the presence of six sedimentary units: bedrock and/or ice-contact sediments (U1), glaciomarine silts and clays (U2), rhythmically laminated silts and clays, possibly varves (U3), mass movement deposits (U4), fluvial deposits (U5) and organic-rich postglacial sediments that contain series of rapidly deposited layers (U6). This poster unveils the results of these underwater mapping surveys and demonstrates their significant contribution to the understanding of Quaternary geological evolution and sedimentary records of deep formerly glaciated lacustrine basins.