On the origin of tunnel valleys of the Saginaw Lobe of the Laurentide Ice Sheet; Michigan, USA

摘要: Tunnel valleys are common throughout the terrain of Saginaw Lobe Laurentide Ice Sheet in southern Michigan. The set described this paper is regularly spaced a radial pattern behind Kalamazoo Moraine, an ice-marginal position formed during retreat from Last Glacial Maximum. These divided into proximal and distal groups lying north south, respectively, major river valley that cross-cuts tunnel at right angles. Based on series rotasonic borings core analysis, shallow, contain minimal sediment fill, overlie fine-grained diamicton glaciolacustrine sediment, whereas deeply incised substrate partially filled with coarse sediment. terminate within broad zone high-relief, hummocky topography representing stagnation collapse ice margin. occur more subdued landscape located farther Although some elements existing genetic models consistent these valleys, none appears to be completely compatible their stratigraphy morphology. Initial incision could have involved short-lived moderate- high-discharge flows, followed by deposition or after events. deep thick, stagnant marginal probably supraglacial meltwater draining bed as margin downwasted. Fining-upward eskers inset were flows declining energy small late-stage conduits.