St. Lawrence Ice Stream overflow on the northern edge of the middle Estuary during the Bølling-Allerød and response of the Laurentide Ice Sheet margin to the Intra-Allerød Cold Period in southern Québec, Canada

• Published in: Quaternaire
• Main Authors: Occhietti, Serge, Bhiry, Najat, Dubois, Jean-Marie, Govare, Étienne, Richard, Pierre J.H., Robert, Francine
• Format: Article in Journal/Newspaper
• Language: English
• Published: Association française pour l’étude du quaternaire 2022
• Subjects: courant glaciaire du Saint-Laurent; Bølling-Allerød; IACP; flux glaciaires; St. Lawrence Ice stream; IACP moraines; ice flows; geo; envir; Beaupré; Canada; Lawrence River; Ice Sheet
• Online Access: http://journals.openedition.org/quaternaire/16779

The middle and upper Estuary regions of the St. Lawrence River include the Laurentian highlands to the north and the Appalachian piedmont and uplands to the south. From a synthesis of the literature, the glacial dynamics of these regions are the result of: 1) the changing position of an ice dispersion centre in the Québec-Labrador Dome; 2) the upstream retreat of a calving bay from the Gulf of St. Lawrence to the middle Estuary at the origin of the rapid inland extension of the St. Lawrence Ice Stream (StLIS) of the Laurentide Ice Sheet (LIS); 3) the progressive separation of Appalachian ices from the LIS; and 4) an increasing topographic control on ice flows. The LIS ice flowed southeastward over the area independently of structural topography during the Glacial Maximum or closely thereafter. From published and original data, the StLIS eventually reached the lower part of the middle estuary as a moving-inland head of ice flow convergence. The ice diversion accelerated the regional-scale ablation on both sides of the estuary likely under the warmer Bølling climate. A generalized thinning in the middle estuary is inferred to cause the northward ice-flow reversal of the Appalachian ice divide to expand into the studied region, consequently initiating the Northward Ice Overflow (NIO) on the Laurentian margin, up to elevations of 750 to 950 m in the Beaupré Basin. This likely took place between the end of the Bølling and the early Allerød. Based on this study, the northern part of the region records a detailed Late Glacial sequence of ice flows and retreat events. After the initiation of the NIO, the overflow ice in the Beaupré Basin thinned by at least 100 m during part of the Allerød. The Beaupré Group of Moraines and the Savane Moraine in the Laurentians provide evidence of a significant subsequent slowdown in the glacial retreat. These moraines are attributed to the Intra-Allerød Cold Period (IACP) between approximately 13.250 and 13.050 cal ka BP, based on their older age position relative to: 1) the ...