Subglacial imprints associated with the isolation and decay of an ice mass in the Lower Lough Erne basin, Co. Fermanagh, NW Ireland

摘要

High-resolution Chirp sub-bottom profiler and side-scan sonar data record the final phases of ice margin activity in the Lower Lough Erne basin at the end of the last cycle of Quaternary glaciations in Ireland. Relative to the terrestrial glacial landforms the features in the Lough are smaller in scale and are considered to represent local ice mass dynamics that followed regional-scale events. Four phases are identified. (1) After the last ice sheet-wide readvance associated with the Killard Point Stadial (between 15.0 and 14.1 C-14 ka bp), stagnation zone retreat resulted in isolation of a residual ice block in the Lower Lough Erne basin. (2) Proglacial waters developed coeval with retreat of the western margin of the ice block. Drawdown induced localized surging and the generation of push features and lineations. (3) Squeeze-up features, reflecting a heavily crevassed ice margin, mark the quiescent phase of the local surge cycle. (4) Iceberg grounding pits and keel marks record calving and rapid disintegration of the Lough Erne ice margin. The well-preserved glacigenic features observed in the lake basin suggest formation by a succession of mechanisms that were too short lived to obliterate the underlying evidence of ice margin dynamics.