LiDAR-based mapping of paleo-ice streams in the eastern Great Lakes sector of the Laurentide Ice Sheet and a model for the evolution of drumlins and MSGLs

摘要

Analysis of newly available, high resolution DEM and LiDAR imagery permits detailed geomorphological mapping of glacially streamlined subglacial bedforms (drumlins and megascale glacial lineations; MSGLs) in unprecedented detail over a very large (170,500km(2)) area of eastern North America extending from the western end of Lake Erie east through the Lake Ontario basin to the Hudson Valley east of the Adirondack Mountains, and south to the Finger Lakes. Digital imagery and field work identify the beds of eight paleo-ice streams that record a major region-wide ice streaming event within the Laurentide Ice Sheet (LIS) which appears to have commenced after c. 14,400 ybp. A large southwestward-flowing ice stream (the Ontario-Erie Ice Stream; OEIS) sourced from the southern Quebec sector of LIS was initiated along the axis of the Ontario basin coeval with its counterpart to the east, the long-recognized St. Lawrence Ice Stream flowing from the same Quebec source to Gulf of St. Lawrence. Deep ice-frontal lakes at the margin of the retreating ice sheet may have played a role in the onset of fast flow similar to its easternmost marine-terminating margin. It is hypothesized that drumlin bedforms formed under steady state flow regimes are reshaped and dissected into MSGLs by deforming subglacial debris as fast flow propagates upglacier from the ice margin or grounding line. Ice is pulled out of ice sheets by headward-propagating ice streams; the formation of MSGLs from drumlins reflects accompanying subglacial erosion by deforming subglacial sediment to reduce bed relief and basal drag.