Timing and position of Late Wisconsinan ice-margins on the upper slope seaward of Laurentian Channel

摘要: At the last glacial maximum, major ice outlet through Laurentian Channel terminated on upper continental slope. A 10 km square area of slope has been investigated in detail, using airgun and boomer seismic reflection profiles piston cores. Sediment failure during 1929 Grand Banks earthquake resulted exposure at seabed Last Glacial Maximum sediments that are normally buried beneath tens metres younger strata. Ice-margin acoustic lithofacies interpreted criteria developed shelf chronology is provided by AMS radiocarbon dates situ mollusc shells. Seismic data show a morainal ridge 500 mbsl (mbsl = below (present) sea level) corresponding to grounding line. change thermal regime or subglacial meltwater outburst, 16.5 ± 0.15 ka (radiocarbon years, -0.4 marine reservoir correction applied), release sediment-laden eroded gullies This erosion surface immediately overlain prominent stony diamict extends about 700 may represent till deposition from surge. The margin then retreated upslope 16.3 ka, probably moraine 380 lip Channel. Evidence mud turbidites Fan suggests this marginal position have persisted until 14.2 ka. Ice rapidly northwards up Channel, synchronous with Heinrich Event 1 14 Younger proglacial sediment slumped 12 as result loading late-ice advance across St. Pierre Bank.