LiDAR-based quantitative assessment of drumlin to mega-scale glacial lineation continuums and flow of the paleo Seneca-Cayuga paleo-ice stream

Abstract

Shortly after 14,500 ybp during the deglaciation of the Laurentide Ice Sheet in eastern North America, the 80 km wide Seneca-Cayuga paleo ice stream occupied the overdeepened New York State Finger Lake basins. The topography of the former ice stream bed can be evaluated from high-resolution LiDAR DEM data, allowing mapping of almost four thousand subglacially streamlined bedforms such as drumlins and mega-scale glacial lineations using Curvature-based Relief Separation. Qualitative and quantitative techniques were then applied to the statistical analysis of bedform elongation ratio and orientation using Natural Neighbor Interpolation and unsupervised machine learning-based data clustering. Analysis reveals a geomorphic continuum of as many as seven morphotypes of streamlined bedforms from drumlins to mega-scale glacial lineations with intermediate ‘channeled drumlins’ possibly recording erosion of parent drumlins. Spatial analysis using orientation Grouping Analysis identifies several flow-parallel sets of bedforms reflecting the presence of multiple ice flow units in the ice stream up to 10 km wide that were topographically controlled by glacially-overdeepened basins of lakes Canandaigua, Seneca, and Cayuga (−151, −306, −242 below mean sea level respectively). Longitudinal variation in bedform elongation along as much as 60 km length of flow lines is provisionally interpreted as a proxy for ice flow velocities which ranged from steady state flow (drumlins), intermediate velocities (channeled drumlins) to fast flow (mega-scale glacial lineations). Evolution in bedforms occurred rapidly likely over a time frame of several hundred years. Quantitative data also identifies faster axial flow and slower flow along the margins of each ice flow unit. Fast flow was triggered at the grounding lines of flow units terminating in deep (as much as 600 m) proglacial lakes at the southern end of each overdeepened Finger Lake basin and propagated northwards along each flow unit at different rates reflecting the size and depth of frontal waterbodies. Petrographic data from tills derived from distinctive Paleozoic quartzites outcropping in a narrow west-east belt perpendicular to flow of each ice stream identifies extended longitudinal subglacial advection during fast flow consistent with very rapid bedform evolution.