ICE EXTENT OF THE LATE PLEISTOCENE LAURENTIDE ICE-SHEET IN HUDSON STRAIT DURING HEINRICH EVENTS H1 TO H3

High resolution airgun seismic reflection profiles from the wide continental shelf seaward of the Hudson Strait show a regional erosion surface 10-200 m subbottom that is locally channelled and truncates Tertiary strata on the inner shelf and prograded diamict wedges on the outer shelf. This unconformity is overlain on the outer shelf by an acoustically incoherent diamict unit at least 30 m thick. Above this unit, at least two distinct diamict sheets terminate on the inner continental shelf. The outer shelf diamict unit can be traced down the continental slope seaward of Hudson Strait as an acoustically incoherent unit corresponding to a flow till or debris-flow deposit. At lateral pinchouts, this deposit can be correlated into a carbonate-rich turbidite unit in piston cores dated as corresponding to Heinrich event H3. The stratigraphic equivalent position of Heinrich layer 3 in some cores of the northwest Labrador Sea is occupied by parallel-laminated, thick fine-grained, carbonate-rich mud turbidites, as opposed to the typical nepheloid-layer deposits observed in Heinrich layers (Rashid et al., 2003). These data imply that grounded surging Laurentide ice crossed the continental shelf during H3, delivering diamict to the continental slope, but during the younger Heinrich events H1 and H2, grounded ice probably only reached the inner shelf. These findings can account for the contrasts in the source mechanism for observed differences between H3 and younger Heinrich events in the Labrador Sea.

Rashid, H., Hesse, R., and Piper, D.J.W., 2003, Origin of the unusually thick Heinrich layers HL-1 to HL-3 in the northwest Labrador Sea, Earth Planet. Sci. Lett., 208, 319-336.