Abstract

Glacier retreat from areas of moderate to high relief typically occurs along a lobate ice margin controlled by underlying topography, as was the situation on the Appalachian Plateau of central New York. Stagnation of entire valley ice lobes is attributed to restricted glacier flow across headward divides. Detachment of stagnant ice blocks is also related to limited flow through deeply incised valley meanders.

Melting of a detached ice block, several thousand metres across and hundreds of metres thick, within a valley train creates a depression referred to as a dead-ice sink. Ice-lobe stagnation involving several closely spaced sinks results in a chain of depressions called a dead-ice moat.

Topographic evidence of the dead-ice sink environment is an anomalously broad flood plain that spans most of the valley width and is bounded upvalley and downvalley by dissected valley-train outwash. Dead-ice sink sedimentation results in a stratigraphic sequence typical of an ice-contact environment and includes interstratified silt, sand, and gravel hundreds of metres thick. Juxtaposed water-well logs reveal stratigraphic units of highly variable texture and thickness that defy lateral correlation.

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