| Popis: |
Lakes in formerly glaciated areas are prone to provide valuable paleoclimate archives, which contain information about the glacial processes influencing the region in which the lakes formed. The eastern Canadian provinces Québec, Newfoundland and Labrador are key areas to understand climate changes since the Cenozoic. Lake Manicouagan is a 214 Myr old impact crater lake located in the province of Québec, 220 km north of the Saint Lawrence River. This area was directly affected by the waxing and waning of the Laurentide Ice Sheet at least during the last glaciation. Here, we present high-resolution seismic data imaging the glacially excavated thalweg of Lake Manicouagan and a sedimentary sequence filling it. On that basis, we assess the potential of this sedimentary sequence as a paleoclimate archive. Our high-resolution seismic data reveal a varying shape of the valley throughout the lake. A U-shape of the valley suggests that grounded glacial erosion excavated the thalweg, whereas a narrow V-shape in some areas is indicative of pressurized subglacial meltwater erosion. We discuss three different scenarios regarding the deposition of sediment and the evolution of Lake Manicouagan during the Upper Pleistocene and Holocene: (1) the entire sedimentary sequence was deposited during and after the final retreat of the Laurentide Ice Sheet or (2) the deposits are the result of multiple glacial-interglacial cycles or (3) Lake Manicouagan was a subglacial lake during the last glaciation. We favor the third scenario because it explains missing interglacial units and erosional ice contact surfaces in the sedimentary sequence. Lake Manicouagan holds a valuable paleoclimate archive regardless of the scenario. Either the lake is a high-resolution paleoclimate record of the last 7.5 kyr, or the lake sediments contain pre-deglacial information, located in an area which was directly affected by advance and retreat of the Laurentide Ice Sheet during the Wisconsin glaciation. |
