Buried preglacial fluvial gorges and valleys preserved through Quaternary glaciations beneath the eastern Laurentide Ice Sheet

摘要: The geomorphology, geometry, and sedimentary infill of buried gorges V-shaped valleys observed at the base major river in formerly glaciated southeastern Canadian Shield region have been revealed from excavation drilling data acquired during construction hydro-electric dams seismic collected on lakes offshore. Compilation these previously published unpublished provided an exceptional opportunity to examine morphology spatial distribution bedrock mechanical processes responsible for their erosion. In some valleys, detailed observations deep allowed by exhumation over large areas. Archive photographs show potholes, natural pillars, furrows, flutes, scallops well-polished walls gorges. They also reveal that a sharp-ending V shape very narrow are superimposed U-shaped valley, forming valley-within-valley topography. cross-profile gorges, slopes, type bedforms within them typical features fluvial channels. Drilling operations many sites topography nature infill. different lines evidence presented this paper indicate were not eroded Laurentide Ice Sheet Quaternary glaciations but relics preserved preglacial system lower level. This paleofluvial is interpreted be linked fluvially cut channels seafloor Estuary Gulf St. Lawrence.