Dominique Harmand

Late Winconsinan glacial dynamics, deglaciation, and marine invasion in southern Quebec

Deglaciation patterns of the Laurentide ice sheet in southern Québec were related to climatic and nonclimatic factors. Thinning of the ice sheet and thermolatitudinal ice retreat are directly linked to the global warming at the end of late Wisconsinan time, between 17 ka and 11 ka. However, correlations between regional deglacial events and global climatic oscillations during that period have yet to be established, except for the St. Narcisse Moraine event, which has been assigned to the Dryas III, and perhaps for the reactivation of Laurentide ice in the middle Chaudiere Valley area during an older cold event. Nonclimatic factors also played a major role on the deglaciation of the region. After the last glacial maximum, the Laurentide ice sheet began to decrease, and the St. Lawrence corridor channelized a major ice stream, the St. Lawrence ice stream, which became a major feature of the southeast sector of the ice sheet. The St. Lawrence ice stream is a flow convergence zone caused by a combination of ice dynamics and topographic factors and rapid ablation at its terminus. The head of the flow convergence migrated deeply into the Laurentide ice sheet and caused thinning of adjacent ice masses. As a consequence of this accelerated ablation, an Appalachian sector became differentiated from the main ice sheet. Regionally, the terminus of the ice stream was a calving bay that retreated along the Laurentian channel to the mouth of the Saguenay fjord. The ice stream and the deglaciated estuary generated the well-known flow reversal along much of the northern margin of the Appalachian sector. In addition to these generalized deglaciation processes, local and regional topographic features influenced the ice dynamics and the final deglaciation patterns. Occhietti, S., Parent, M., Shilts, W.W., Dionne, J.-C., Govare, É., and Harmand, D., 2001, Late Wisconsinan glacial dynamics, deglaciation, and marine invasion in southern Québec, in Weddle, T.K., and Retelle, M.J., eds., Deglacial History and Relative Sea-Level Changes, Northern New England and Adjacent Canada: Boulder, Colorado, Geological Society of America Special Paper 351, p. 243–270. E-mails: Occhietti, ochietti.serge@uqam.ca; Parent, parent@gsc.nrcan.gc.ca; Shilts, shilts@geoserv.isgs.uiuc.edu; Dionne, ggr@ggr.ulaval.ca; Govare, e.govare@sympatico.ca; Harmand, harmand@clsh.univ-nancy2.fr on February 28, 2015 specialpapers.gsapubs.org Downloaded from

Contrôle morphostructural de l'histoire d'un réseau hydrographique: le site de capture de la Moselle

Abstract By comparing the topographic contour map, the Bajocian limestone structural contour map and alluvial terraces in the Toul and Nancy area, it is possible to reconstitute the changes in the drainage pattern and the Moselle and Meuse cuestas (cotes de Moselle et de Meuse) retreat that have taken place since the late Tertiary. The highest reworked alluvial deposits of the palaeo-rivers (‘Haute-Moselle’ and ‘Paleo-Meurthe’), are now situated on the inverted relief top of the Moselle cuesta. They suggest that the course of these rivers drifted and that the relief in the late Tertiary was subdued. The clearing of the back slope surfaces only started at the beginning of the Pleistocene (at 350 m) as a result of a climatic deterioration. Since this time, downcutting erosion and the correlative removal of clays have strongly emphasized cuesta relief although there has been a certain retreat which varies about 6 to 21 km, depending on the basement dip. The main rivers are almost entirely superimposed on the palaeo structural frame-work. On the contrary the tributaries of the left bank originally extended and changed on the Callovo-Oxfordian clays before penetrating into the Bajocian limestones, according to the cuestas retreat during the Plio-Pleistocene. Only small strike rivers were in accordance with structural features; sinking into the underlaying Bajocian limestones these entrenched rivers quickly dried up. On the opposite, the flow of the eastward rivers, independent of the structure, grew upstream to downstream, because these rivers first drained the Callovo-Oxfordian clays, before cutting across the Bajocian limestones groundwater. It is the same nowadays. The piracy of the Moselle can be explained by the evolution of the ‘Paleo-Terrouin’, a major eastward palaeo tributary of the ‘Paleo-Meurthe’, and by the retreat of the Meuse cuesta. The significant retreat of this cuesta in the ‘Toul syncline’, changing from an inverted relief to a structural relief in the Dieulouard structural basin, led to a widening of the Callovo-Oxfordian clay plain and a broadening of the ‘Paleo-Terrouin’ s hydrographic basin. As a result, the ‘Paleo-Terrouin’ captured the ‘Riviere de la Haie Plaisante’, a small strike tributary of the Upper Moselle, and then eastward, the Upper Moselle. In the future, it will probably also capture the Upper Meuse.