THE MAGNETIC SIGNATURE OF RAPIDLY DEPOSITED DETRITAL LAYERS FROM THE DEEP LABRADOR SEA - RELATIONSHIP TO NORTH-ATLANTIC HEINRICH LAYERS

Rock magnetic parameters from deep Labrador Sea piston core (P-094) ar e useful for recognizing rapidly deposited detrital layers, some of wh ich correlate with North Atlantic Heinrich layers. Variations in magne tic properties and lithology distinguish two classes of rapidly deposi ted detrital layers during the last ice age: (1) seven detrital carbon ate (DC) layers have high carbonate content and mean magnetite grain d iameters about 4 times greater than the background sediments; (2) six low detrital carbonate (LDC) layers have very similar magnetic propert ies to DC layers but low carbonate content (similar to the background sediments). The magnetite associated with DC and LDC layers is well so rted and relatively uniform within and between layers. Ice-rafted detr itus (IRD), recognized by increased percentage of the >125 micron grai n-size fraction and by high magnetic susceptibility, is associated wit h most DC and LDC layers but is not the dominant detrital constituent. The correspondence of DC and LDC layers with increased grain size of well-sorted magnetite, but not with coarse fraction content, precludes ice rafting as the primary depositional mechanism. DC and LDC layers may have been deposited from suspended sediment derived from turbidite activity in the nearby Northwest Atlantic Mid-Ocean Channel (NAMOC). This interpretation is supported by a piston core (P-013) from a Green land Rise site largely, but not completely, outside the influence of t he NAMOC. The association of DC layers with IRD and the apparent age c orrelation of DC layers to North Atlantic Heinrich layers suggest that the ice advances which produced the IRD in P-094 and in correlative N orth Atlantic Heinrich layers also triggered turbiditic flows down the NAMOC. Several DC and LDC layers, however, do not correlate with reco gnized Heinrich layers but appear to be coeval with recently discovere d high-frequency IRD-rich layers in the North Atlantic.