Abstract

Huntec deep-tow records, 3.5 and 12 kHz echo-sounder profiles backed by airgun reflection, cores, and 14C dates delineate 10 mappable acoustic/morphologic units between 57°N and 61°N on the northern Labrador Shelf. These include: I—section composed of numerous horizontal reflectors with minimal scattering and smooth microrelief; II—acoustically transparent section with numerous subparallel, draped reflectors at its base—it underlies unit I in basin centers; III—section marked by intense scattering, point reflectors, and a rough microrelief; IV—section exhibiting strong scattering as in III, but with smooth microrelief and obvious terraces; V(a,b)—outcropping portions of II-type sediments variably dissected; VI—outcrops of II exhibiting warping, acutely intersecting reflectors and undulating mesorelief; VII(a,b)—areas of strong macrorelief with ridges and wedge- or lens-shaped reflectors and strong scattering; VII—section exhibiting strong macrorelief as in VII(a,b) but with somewhat rougher microrelief.A thin (<1 m) ubiquitous surface-sediment veneer that is not clearly identifiable on acoustic profiles is 14C dated at graphic. Unit II dates between 9770 and 8380 BP and unit III at 10 260 BP. These dates are based on shells. Unit I is inferred to span the interval <8380 to >6050 BP. Total organic carbon dates from units I and II are deemed too old by as much as 17 000 years because of the introduction of reworked older carbon.The data suggest the following sequence of glaciation and deposition: (1) ice grounds on the shelf and upper slope during the glacial maximum; (2) shelf-basinal and bank portions of the ice sheet begin basal melting before 9770 and ca. 10 260 BP, respectively; (3) degrounding of the ice in shelf basins and admission of sea water by 9770 BP, perhaps at first beneath ice shelves; (4) deposition of fine-grained glacial muds in basins as runoff from actively ablating valley glaciers on Labrador finds its way into fjord-like embayments in the ice sheet (ca. 9770–8380 BP); and (5) deformation of sediments on shallower portions of the shelf and upper slope possibly by Hudson Bay, Foxe Basin, or Ungava Bay surge ice exiting outer Hudson Strait, ca. 8380–7500 BP.

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