|
|||||
|
|
Morphological signatures of deglaciation and postglacial sedimentary processes in a deep fjord-lake (Grand Lake,Labrador) |
|
| Authors: | Annie-Pier Trottier Patrick Lajeunesse Antoine Gagnon-Poiré Pierre Francus |
| Institution: | 1. Département de Géographie, Université Laval, Québec, QC, Canada;2. Département de Géographie, Université Laval, Québec, QC, Canada
Centre d'Études Nordiques (CEN), Université Laval, Québec, QC, Canada;3. Centre d'Études Nordiques (CEN), Université Laval, Québec, QC, Canada Institut National de Recherche Scientifique (INRS), Centre Eau Terre et Environnement, Québec, QC, Canada |
| Abstract: | High-resolution multibeam bathymetric data and acoustic sub-bottom profiles were recently collected in Grand Lake (Labrador), one of the deepest lake basins in eastern North America, to reconstruct: (1) the retreat of the Laurentide Ice Sheet (LIS) west of Lake Melville and (2) the history of sedimentation since deglaciation in this 54 km-long, 3 km-wide fjord-lake. Our results provide a morphostratigraphical framework that brings new insights to the style and pattern of retreat of the LIS in the region, as well as deglacial and postglacial sedimentary dynamics. Terrestrial glacial lineations observed on a digital elevation model (DEM) provide evidence of a previously undocumented ice stream in the Grand Lake area. This newly mapped ice stream suggests that the calving bay formed in Lake Melville triggered a reorganization of the regional drainage pattern of the LIS. The sedimentary infill of Grand Lake consists of a sequence of deglacial to postglacial sediments that contain deposits related to a series of mass movements. The 8.2 cal ka BP cold event is recorded in Grand Lake by a series of closely spaced moraines deposited at the outlet of the fjord-lake to form a morainic complex similar to the Cockburn morainic complex on Baffin Island. During deglaciation, a dense dendritic network of proglacial gullies incised into the steep sidewalls of the lake. Since deglaciation, paraglacial and postglacial sedimentation has led to the deposition of large prograding deltas at the fjord head, where density currents remain active today and have formed a series of sediment waves on the frontal slopes and a prodeltaic environment. © 2019 John Wiley & Sons, Ltd. |
| Keywords: | geomorphology deglacial landforms fjord-lake ice-stream bathymetry |