HR: 0800h
AN: PP41C-0679    [Abstracts]
TI: Drawdown Episodes of the Labrador-Quebec Ice Dome Through Ungava Bay During Heinrich Events? Insights From the Sediment Sources of Ice Streams
AU: * Roy, M
EM: roy.martin@uqam.ca
AF: Département des Sciences de la Terre, Université du Québec à Montréal, C.P. 8888, Succ. Centre-Ville, Montréal, QC H3C 3P8, Canada
AU: Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, PO Box 1000, 61 Route 9W, Palisades, NY 10964,
AU: Parent, M
EM: miparent@nrcan.gc.ca
AF: Geological Survey of Canada, 490 rue de la Couronne, Quebec City, QC G1K 9A9, Canada
AU: Machlus, M
EM: machlus@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, PO Box 1000, 61 Route 9W, Palisades, NY 10964,
AB: Glacial terrains surrounding the Ungava Bay region are characterized by abundant drumlins, crag-and-tails, and other lineations indicating convergent ice flow towards the bay. These geomorphologic features have been interpreted to represent a complex network of fast-flowing ice (ice streams), which drained the eastern sector (Labrador-Quebec ice dome) of the Laurentide ice sheet at some time during the last glacial cycle. It was recently proposed that the Ungava Bay ice streams may be responsible for the massive iceberg discharges in the North Atlantic that are at the origin of Heinrich events (e.g. Jansson et al., Boreas, v. 32, p. 256, 2003). Several other provenance studies have attributed the characteristic high detrital carbonate content of these anomalously thick layers of ice rafted deposits (IRD) to a calving ice margin that overrode the carbonate-floored Hudson Bay/Strait, while lead isotopes and ⁴⁰Ar/³⁹Ar ages measured on feldspar and hornblende grains have identified the rock-source area of Heinrich layers as being the Paleoproterozoic Churchill province of the Canadian Shield. Although the Laurentide ice sheet was unequivocally the main contributor of detrital material to Heinrich layers, the exact sector of the Laurentide ice sheet that collapsed and drained through Hudson Strait has yet to be identified, and is currently ascribed to the broader Hudson Bay/Strait region. Here we evaluate the possible contribution of the Labrador-Quebec ice dome to these iceberg discharges by documenting the provenance of glacial sediments (tills) representing the catchment (source) area of the Ungava Bay ice streams. Specifically, we used the ⁴⁰Ar/³⁹Ar fusion method to date about 10 individual hornblende grains in 13 samples distributed along a latitudinal transect (lat. 58°) extending east and west of Ungava Bay. We also date hornblende grains from IRD and bounding sediments in a North Atlantic deep-sea core (Orphan Knoll) to evaluate whether the provenance signature of Ungava Bay glacial deposits can be recognized in sediments spanning the time interval comprised between H4 to H0. The results show that most tills located east of Ungava Bay are characterized by grains with early Paleoproterozoic ages (2.0 to 1.8 Ga), with a few till samples containing a small population of grains with Archean ages (>2.6 Ga). Tills west of Ungava Bay are largely dominated by Archean-age grains. These results contrast with the predominant late Paleoproterozoic ⁴⁰Ar/³⁹Ar ages (1.8 to 1.6 Ga) that characterize hornblende grains in typical Heinrich layers, thereby indicating that drawdown episodes of the Labrador-Quebec ice dome through Ungava Bay during Heinrich events are unlikely. Hornblende grains from marine deposits are currently being analyzed and the results should provide information on when these ice streams were active during the last glaciation.
DE: 0726 Ice sheets
DE: 1040 Radiogenic isotope geochemistry
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4914 Continental climate records
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting