Abstract

North Atlantic Heinrich events, which dispersed widespread sediment plumes and icebergs, originated principally from Hudson Strait ice streams of the Laurentide Ice Sheet. The dynamics and extent of these ice streams across the wide continental shelf seaward of Hudson Strait are not well understood. High-resolution airgun seismic reflection profiles from the outer shelf and slope show an acoustically incoherent, prograded unit at least 30 m thick. This unit has been sampled by piston cores and corresponds to a carbonate-rich diamicton unit interpreted as a glacigenic debris flow, locally overlain by carbonate-rich mud turbidites, dated as corresponding to Heinrich event 3 (H3). Younger glacigenic debris flow deposits are lacking. These data are compared with the seismic-stratigraphic record on the continental shelf, where a regional erosion surface at 10–200 m depth below the sea floor truncates Tertiary strata and is overlain by a 50 m thick diamicton (?subglacial till) sheet and is correlated with the H3 glacigenic debris flows. Above this unit, at least two distinct diamicton sheets terminate on the inner continental shelf. These data imply that grounded Laurentide ice crossed the continental shelf during H3, delivering large amounts of diamicton to the continental slope, but during the younger Heinrich events H1 and H2, no detectable record of diamicton was left on the outer shelf or slope. These findings account for observed differences between H3 and younger Heinrich events in the Labrador Sea.

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