DEPOSITIONAL FACIES OF LATE PLEISTOCENE HEINRICH EVENTS IN THE LABRADOR SEA

Late Pleistocene Heinrich ice-rafting events produced layers rich in i ce-rafted debris in major parts of the North Atlantic north of 40 degr ees N. A high detrital carbonate content points to the Hudson Strait o utlet of the Laurentide ice sheet as a dominant source of the icebergs , Heinrich events were coupled with short-term climate fluctuations du ring the last and penultimate glaciations and provide evidence for cry osphere-hydrosphere-atmosphere interaction in Pleistocene climate chan ge. An unsolved problem with Heinrich layers has been their high conce ntration of fine-grained detrital carbonate (>80% of the total detrita l carbonate), which cannot have been delivered by icebergs alone, We p ropose combinations of different processes that deposited four sedimen tologically different types of Heinrich layers: ice rafting alone for the coarser, sand-to gravel-sized fractions and the fine fractions in distal regions (type TV Heinrich layers), whereas nepheloid flows depo sited the bulk of the fine sediment in regions proximal to the Hudson Strait (type I Heinrich layers). On the Labrador slope, turbidity curr ents spilling over from canyons were also involved in transporting the fine-grained carbonate-rich material, causing an alternation of mud-t urbidites and thin laminae of ice-rafted debris in type II Heinrich la yers. On the levees of the Northwest Atlantic Mid-Ocean Channel, the t hickness relationship is reversed: mud-turbidites deposited by occasio nal spillover of currents from the channel are thin and alternate with thicker laminae of ice-rafted debris (type III Heinrich layers).