Valley morphology and Quaternary seismic stratigraphy of the Manicouagan impact crater lake (Eastern Canada)

Lakes in formerly glaciated regions can provide valuable paleoclimate archives. Lake Manicouagan (Manikuakan, according to Innu toponymy), formed in the basin of the similar to 214-Ma Manicouagan impact crater of eastern Quebec, is a key area for reconstructing long-term environmental change, as it was directly affected by the Pleistocene glaciations and the waxing and waning of the Laurentide Ice Sheet. Here, we present high-resolution seismic data revealing an overdeepened bedrock valley filled with a sedimentary sequence. We assess its potential to serve as a paleoclimate archive. The varying shape of the overdeepened valley indicates complex erosional processes. A lower narrow V-shaped gorge is indicative of either pressurized subglacial meltwater or pre-Quaternary fluvial erosion, or a combination of both. Three scenarios are discussed regarding deposition of the sedimentary sequence: (i) deposition only during and after retreat of the last glacial episode; (ii) deposition during multiple glacial-interglacial cycles; and (iii) deposition mainly during a subglacial lake stage. We suggest subglacial followed by proglacial sedimentation as the most probable scenario for deposition of the sedimentary succession. We recommend considering the sediments of Lake Manicouagan as a paleoclimate archive reaching back at least to 7.5 ka, but the lake also probably contains sediments deposited before the last deglacial period.