Pleistocene sediment sources, debris transport mechanisms, and depositional environments: a Bering Glacier model applied to northeastern Appalachian Plateau deglaciation, central New York

A modified ice-tongue model suggests that subglacial, saturated, fine sediment derived from local bedrock sources reduced basal shear strength and lowered the ice surface gradient sufficiently to produce ice tongues 20 km long in all major north-south oriented valleys on the northeastern Appalachian Plateau, while adjacent uplands were virtually ice-free. Associated environments of deposition produced two different landform assemblages, one representative of active ice retreat in through valleys and another that depicts widespread stagnation in non-through valleys.Pebble count data indicate that sediment transport by glacial flow was important to the moraine-building process, but the occurrence of isolated kame fields suggests an origin linked to inwash from major upland tributaries.All coarse valley fill (sand and gravel) is derived from two basic sources: (1) re-worked upland drift, and (2) resedimented debris from upvalley sources, including the glacier. Processes common to through valleys favor upvalley sources and active ice landforms, whereas inwash and stagnant ice sedimentation are typical of non-through valleys. Although extensive ice-free uplands served as a source of some fine sediment, a comparison of sediment volume to upland area indicates that inwash processes could not have yielded sufficient fines to account for the volume of fine sand and silt found within the valley fill. Meltwater flow via subglacial tunnels discharged saturated, fine sediment directly into proglacial lakes and served as the major source and transport mechanism for most sand and silt.The Laurentide deglacial environment throughout the upper Susquehanna region was characterized by proglacial lakes, detached remnant ice masses, dead-ice sedimentation and collapsed ice tongues. Stagnation and downwasting in ice-contact lakes peripheral to the eastern Bering Piedmont Glacier, Alaska, serve to depict analog conditions for retreat in central New York.