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Paper No. 3
Presentation Time: 8:30 AM


ANDREWS, John T., INSTAAR and Dept. of Geological Sciences, Univ of Colorado, 450 UCB, Boulder, CO 80309-0450, BARBER, Donald C., Geology, Bryn Mawr College, 101 N. Merion Ave, Bryn Mawr, PA 19010, EBERL, Dennis D., 2. U.S. Geological Survey, 3215 Marine St., Suite E-127, Boulder, CO 80303, JENNINGS, Anne E., INSTAAR and Dept. of Geological Sciences, University of Colorado, Box 450, Boulder, CO 80309-0450, KIRBY, Matthew E., Geological Sciences, California State University, Fullerton, 800 N. State College Blvd, Fullerton, CA 92834, MACLEAN, Brian, Geological Survey of Canada Atlantic, BBedford Institute of Oceanography, Dartmouth, NS B2Y 4A2, Canada and STONER, Joseph S., College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Admin BLDG, Corvallis, OR 97330,

Core HU97048-007PC (1220 cm) was taken from the upper slope of the NW Labrador Sea in 945 m water depth (62.673°N, 60.573°W) and ~500 m shallower than the well-studied core HU87033-009. These sites lie seaward of Cumberland Sound (CS), a 1200 m deep trough that was a possible ice-flow conduit for the Foxe sector of the Laurentide Ice Sheet (LIS). The deep landward basin (a graben) is floored by Cretaceous mudstones, which are flanked to the south by Paleozoic carbonates that extend out onto the shelf. The surrounding bedrock is Precambrian (~1.9 Ga) granite and gneiss of the Cumberland batholith. The core site is 200 km NE of Hudson Strait (HS), the source for Heinrich (H) events. Visual core logging revealed detrital carbonate-rich (DC-) layers, a black-colored facies, and hemipelagic sediments. To investigate the provenance of the different facies we undertook quantitative X-ray diffraction (qXRD) analysis of potential source rocks and bulk (< 2mm fraction) down-core samples every 10 cm, as well as u-channel paleomagnetic measurements at 1-cm intervals. The chronology of 007PC is constrained by 6 AMS radiocarbon dates and relative paleointensity, which indicate that the core spans 10-58 cal ka BP. Eight of 9 bedrock carbonate samples from HS and on the shelf are calcite-rich with one dolomitic outcrop. The Cretaceous mudstone is characterized by kaolinite (20 wt%) and vermiculite (6%); thus, down-core variations in kaolinite wt% provide a proxy for the activity of ice in CS. In the upper 7 m, 007PC consist of 7 DC units with carbonate contents of 30-50 wt%. These DC events have calcite:dolomite ratios of ~5:1 for H-events 1-4, but dolomite is dominant in H-0. Kaolinite wt% in the cores reach maximum values of 4% and qXRD indicates positive correlations between the black facies, kaolinite peaks, and peaks in total organic carbon—another signature of the Cretaceous mudstone. A compositional unmixing algorithm was applied to the 007PC data with end members from 1) CS—late Holocene sediments, 2) CS—kaolinite-rich, 3) Hudson Strait deglacial, and 4) Baffin Bay deglacial. Results indicate that on average, Cumberland Sound sources constituted 67 wt% of the composition. CS-kaolinite facies constituted 60-80% of the sediment immediately prior to H-2 and H-1 (~24 and 16 cal ka BP), with prolonged CS activity between 30-27 and 15-13 cal ka BP.
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