ICE-SHEET SOURCED JUXTAPOSED TURBIDITE SYSTEMS IN LABRADOR-SEA

Ice-sheet sourced Pleistocene turbidite systems of the Labrador Sea ar e different from non-glacially influenced systems in their facies dist ribution and depositional processes. Two large-scale sediment dispersa l systems are juxtaposed, one mud-dominated and associated with the No rthwest Atlantic Mid-Ocean Channel (NAMOC), the other sand-dominated a nd forming a huge submarine braided sandplain. Go-existence of the two systems reflects grain-size separation of the coarse and fine fractio ns on an enormous scale, caused by sediment winnowing at the entrance points of meltwater from the Laurentide Ice Sheet (LIS) to the sea (Hu dson Strait, fiords) and involves a complex interplay of depositional and redepositional processes. The mud-rich NAMOC system is multi-sourc ed and represents a basinwide converging system of tributary canyons a nd channels. It focusses its sand load to the central trunk channel in basin centre, in the fashion of a ''reverse'' deep-sea fan. The sand plain received its sediment from the Hudson Strait by turbidity curren ts that were generated either by failure of glacial prodelta slopes at the ice margin, or by direct meltwater discharges with high bedload c oncentration. We speculate that the latter might have been related to subglacial-lake outburst flooding through the Hudson Strait, possibly associated with ice-rafting (Heinrich) events.